AEROSPACE REPORT NO
                                                TOR-0059(6769-01)-2. VOL.
                    Final Report
Hybrid  Heat Engine  /  Electric Systems Study
           Volume I: Sections 1  through 13
                        71 JUN
        Prepared for DIVISION OF ADVANCED AUTOMOTIVE
               POWER SYSTEMS DEVELOPMENT
          U. S. ENVIRONMENTAL PROTECTION AGENCY
                    Ann Arbor, Michigan
                  Contract No. F04701-70-C-0059
                                               Office of Corporate Planning
                                         THE AEROSPACE CORPORATION
                                                   El Segundo, California

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                                              Report No.
                                              TOR-0059(6769-01)-2,
                                              Vol.  1
                     FINAL REPORT

   HYBRID HEAT ENGINE/ELECTRIC  SYSTEMS STUDY

             Volume I:  Sections 1 through 13
                        71 JUN 01
               Office of Corporate  Planning
             THE AEROSPACE CORPORATION
                  El Segundo, California
                       Prepared for

Division of Advanced Automotive Power Systems Development
      U.S.  ENVIRONMENTAL PROTECTION AGENCY
                   Ann Arbor, Michigan
              Contract No.  F04701 -70-C-0059

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                               FOREWORD
Basic to analyzing the performance of the hybrid vehicle was the importance
of understanding the  characteristics of each major component since each
would be operating in a nonstandard mode required by the hybrid arrange-
ment.   In addition, the potential for improvement had to be  understood to
predict the performance of advanced designs.  This report, therefore, con-
tains two types  of information: (a) hybrid system analysis and results; and
'(b) major component state-of-the-art discussions, characteristics used in
this study, and  advanced technology assessments.  Heat engine  operating
characteristics, mechanical parameters, and exhaust emissions are covered
extensively because of both their  primary importance and the difficulty
involved in collecting a reliable comprehensive set of data;  this should relieve
future  investigators making studies of nonconventional propulsion systems of
the necessity of repeating the  burdensome task of assembling a  data bank.

It should be recognized that calculated results  are based on data compiled in
this study.  The magnitude and trends were established on the basis <>l <-i
comprehensive  survey and evaluation of the best data from both the open
literature and current available unpublished data sources.   These cliita eire
considered suitable for use in the  feasibility study conducted under this ron-
tract.   However,  for further  detailed design a  substantial refinement of the
data base would be necessary.

  he report is organized to give a logical build-up of  information starting with
study specification, analytical techniques, and component character is tics and
concluding with system performance results and recommendations for develop-
ment.   However,  selective reading of major systems performance results is
possible and to  assist those so interested, the following brief guide is pre-
sented:

      Section 1                        Summary of study results and recom-
                                      mentations

      Sections 2,  3,  10, and 11        Presentation of study objectives,
                                      design specifications, and results
     Sections 3 and 4                 Description of computational techniques
                                      and performance requirements

     Sections 6 through 9             Review of contemporary and projected
                                      technology of major components
     Section 12                      Cost  estimates for high-volume pro-
                                      duction of hybrid cars
     Section 13                      Presentation of a technological  plan for
                                      component and system development
                                   -m-

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This report is published in two volumes for convenience; however, separation
of the material is made with due regard to organization.  Volume I consists of
Sections 1 through 13 and presents the essential study information, while
Volume II consists of Appendices A through F and presents supplementary
data.

The period of performance for  this  study was June 1970 through June  1971.
                                    -IV-

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                         ACKNOWLEDGMENTS
The extensive diversity in technological capabilities  necessary for a  thorough
evaluation of the hybrid electric vehicle has required the reliance for support
and expertise on select members of The Aerospace Corporation technical
staff as well as  members of the national technical  community.  Recognition
of this effort is  expressed herewith:
The Aerospace Corporation

      Mr.  Dan Bernstein
      Mr.  Lester Forrest
      Mr.  Gerald Harju

      Mr.  Merrill Hinton


      Dr.  Toru lura
      Mr.  Dennis Kelly
      Mr.  Jack Kettler


      Mr.  Harry Killian


      Mr.  Robert La France

      Mrs.  Roberta Nichols
      Mr.  Wolfgang Roessler


      Dr. Henry Sampson



      Mr.  Raymond Schult


University of California,  Berkeley

      Dr. Robert Sawyer

University of California,  Irvine

      Dr. Robert M. Saunders
Electrical System-Control System
Heat Engines (Internal Combustion)
Programming for Computations

Vehicle Specifications/Conceptual Design
and Sizing Studies
Heat Engines (Internal Combustion')
Heat Engine Exhaust Emissions
Vehicle Exhaust Emissions  Test Program
Electrical System - Motor and Generator
Electrical System - Batteries
Heat Engines (External Combustion)

Computational Techniques
Electrical System - Batteries

Electrical System - Motor,  Generator,
Control Systems

Vehicle Exhaust Emission Test Program
Heat Engine Exhaust Emissions
Vehicle Exhaust Emission Test Program

Vehicle Specifications
Computational Techniques
Vehicle Power Requirements

Electrical System - Motor,  Generator,
Control Systems
Heat Engine Exhaust Emissions
Electrical System - Motor  Generator,
Control Systems
                                    -v-

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It is to be noted that considerable data of great value to this study were

kindly provided by individuals in industry, universities, and government

agencies.  Acknowledgment of these data sources is given in Appendix F

to this report.
                                      Donald E. Lapedes
                                      Manager,  Hybrid VehiqAe Program
                                      Joseph Meltzer        A
                                      )irex:tor,  Pollution and Resources
                                      XPro grams
                                      Office of Corporate Planning
                                   -VI-

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                               CONTENTS

The major sections and appendices of Volumes I and II are listed below.  For
detailed tables of contents and lists of illustrations see the individual sections
and appendices.

                                Volume I
Section                                                              Page
1.    Summary	    1-1
2.    Introduction	    2-1
3.    Vehicle Specifications and Study  Methodology	    3-1
4.    Computational Techniques	    4-1
5.    Vehicle Power Requirements	    5-1
6.    Electrical System - Motor, Generator, and Control
      Systems  	    6-1
7.    Electrical System - Battery Characteristics and
      Operation	    7-1
8.    Heat Engine Performance  Characteristics and Operation.  . .    8-1
9.    Heat Engine Exhaust Emissions	    9-1
10.   Conceptual Design and Sizing Studies   	   10-1
11.   Summary of Results	   11-1
12.   Vehicle Production Cost Comparison	   12-1
13.   Technology Development Program Plan	   13-1

                                Volume II

Appendix
A.    Hybrid Vehicle Performance Evaluation Computer
      Program	    A-l
B.    Heat Engine Exhaust Emissions Collation and Analysis ....    B-l
C.    Vehicle Exhaust Emissions Test Program	    C-l
D.    Vehicle Characteristics Over  Emission Driving Cycle  ....    D-l
E.    Heat Engine Data Compilation	    E-l
F.    Acknowledgments to Sources of Subsystems/Component
      Data  	    F-l
                                  -vii-

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SECTION 1






SUMMARY

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                               CONTENTS
1.    SUMMARY	     1-1
     1. 1   Introduction  	     1-1
     1.2   Study Ground Rules and Procedures	     1-1
     1. 3   Summary of Results	     1-3
           1.3. 1    Family Car and Commuter Car	     1-4
           1.3.2    Buses and Vans	     1-11
     1.4   Summary of Recommendations  	     1-12
           1.4. 1    Phase I - Detailed Hybrid System Analysis
                    and Expanded Data Base	     1-13
           1.4.2    Phase II - Component Advanced Technology .  .     1-16
           1.4.3    Phase III - Test Bed and Prototype Vehicle
                    Development	     1-17
                    1. 4. 3. 1    Recommended System
                              Development	     1-18
                    1.4.3.2    Recommended Hybrid  Vehicle
                              System Design	     1-18
                    1.4.3.3    Recommended Component
                              Development	     1-19

                                FIGURES
 1-1.   Vehicle Emission Comparison, Conventional
        Operation Versus Hybrid Operation	     1-5
 1-2.   Comparative Emission Levels  of the  Family
        and Commuter Cars	     1-6
 1-3.   Installed Battery Requirements and Projected
        Battery Capabilities	     1-9
 1-4.   Hybrid Electric Recommended Development Schedule  ...     1-13

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                               SECTION 1
                               SUMMARY
1. 1       INTRODUCTION
This report contains the results of a comprehensive study aimed at deter-
mining the feasibility of using a hybrid heat engine /electr ic propulsion
system as a means of reducing exhaust emissions from street-operated
vehicles. In this hybrid concept, the source of power is a combination of
heat engine and batteries (in essence, the heat engine supplies steady state
power  and the batteries supply transient power demands).  The study
examined --  for several classes of vehicles -- many types  of heat engines,
batteries, and other  major components,  as well as several design configura-
tions.  Following a review of the associated technologies, hybrid perfor-
mance, exhaust emissions, and major component requirements were deter-
mined.   Based on these results, recommendations are formulated to ensure
the development of critical powertrain components for an early demonstration
of prototype vehicles.
1. 2       STUDY GROUND RULES AND PROCEDURES
In the propulsion of the hybrid heat engine/electr ic vehicle,  the ultimate
source of all energy  to be expended is the heat engine.   The key to success
in reducing exhaust emissions is good part-load and full load efficiency of
powertrain components,  and the ability  to restrict operational requirements
for the heat engine to those of supplying road load power and  (in conjunction
with a generator) recharging  advanced high power/high energy density
batteries  that supply acceleration power.  With this idea in mind, the study
was tailored to examine  six classes of vehicles:  the  4000-lb  family  car,
1700-lb commuter car, low-  and high-speed postal/delivery van, and lo\v-
and high-speed intracity bus.   For each class of vehicle, five engines were
included in the powertrain: spark ignition, compression ignition, gas turbine,
Rankine cycle, and Stirling cycle.   Lead-acid, nickel-cadmium,  and
                                    1-1

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nickel-zinc batteries were studied for adequacy in supplying acceleration

power to each vehicle.  Also,  a wide range of AC and DC motors, generators,
and power  conditioning and control  systems were evaluated for performance,

efficiency, weight, simplicity, and cost.


Throughout the study, the following ground rules prevailed:

      1.     Conventional automotive vehicles are to be matched in
            acceleration,  speed, gradeability,  curb weight,  range,
            and powertrain weight.

      2.     The battery is not to require external recharge.  Therefore,
            the range of the vehicle is not  dependent on the installed
            battery capacity.  This requirement  was simulated in
            computations by requiring that the heat engine-driven
            generator recharge  the battery to the original state-of-charge
            prior  to the end of the emission driving cycle.

      3.     The battery is to discharge only when the vehicle is undergoing
            acceleration,  not on a smooth  grade  or at cruise  conditions.

      4.     The heat engine is to supply steady road load power and is
            not required to undergo rapid acceleration.

      5.     Only design concepts compatible with near term (1972-1975)
            prototype vehicle development are to be considered.

With the establishment of the ground rules, the study was executed in the

following manner:

      1.     Formulate quantitative  specifications based on current
            conventional vehicle performance and design  data.  These
            values were coordinated with  the Air Pollution Control Office
            (APCO),  Environmental Protection Agency (EPA).
      2.     Review contemporary and projected technology for  powertrain
            components and determine performance, design,  and cost
            characteristics.

      3.     Evaluate conceptual designs and select a series and a parallel
            powertrain configuration for further  analysis.  The series
  Reference is made throughout this report to the DHEW (Department of
  Health, Education and Welfare) Driving Cycle.  The sponsoring  research
  and development office was formerly the Air Pollution Control Office and
  a part of the DHEW.
                                    1-2

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            configuration is  characterized by the principle that all power is
            transmitted to the rear wheels by an electric drive motor.
            The parallel configuration is characterized by the principle
            that the heat engine is mechanically linked to the drive wheels
            to supply a portion of the  power required, while the electrical
            system  supplies the remainder.

      4.     Calculate component and vehicle power and energy require-
            ments for acceleration and steady road load.

      5.     Determine  battery power  density and energy density require-
            ments based on realistic component weights and powertrain
            weight allocations.

      6.     Calculate vehicle fuel consumption and exhaust emissions,
            based on the energy expended by the heat engine for the vehicle
            operating over the emissions  driving cycle.  For the family
            and commuter car, the 1972 DHEW emission driving cycle
            was used.

      7.     Determine  the trade-off between vehicle exhaust emissions
            and such factors as engine and battery type, battery recharge
            efficiency,  electric motor efficiency,  regenerative braking
            efficiency,  vehicle weight, and parallel and series powertrain
            configurations.

      8.     Recommend viable configurations for further study and propose
            a program  designed  to ensure component  development for early
            demonstration of a hybrid heat engine/electric vehicle; in this
            regard, estimate both development and high rate production
            costs.

1. 3       SUMMARY OF RESULTS

So many different types of vehicle/configuration/heat  engine combinations
were studied that it is difficult to highlight every result shown in the body

of the report; therefore, only the most important are  enumerated in the

following paragraphs.


It should be recognized that  the calculated vehicle exhaust emission  results

are based on measured engine exhaust emission data compiled during the

course of this study. Engine exhaust emission magnitudes and trends were

established on the basis of a comprehensive survey and evaluation of the

best data from both the open literature and current available unpublished
engine data sources. However,  it was found that very little emission data
                                    1-3

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were available for the hybrid type of operation and especially for part-load

engine operating conditions and for the cold start requirement consistent

with the  1 972 Federal Test Procedure.  The resulting data are considered

suitable  for use in an initial feasibility study as conducted under this

contract.  However, in further detailed design studies, a substantial

increase in the data base will be  necessary for powertrain optimization.

The  current study data base is  fully discussed in Appendix B.


In addition to reflecting the engine emissions  data base,  the study results

also reflect the use of selected battery models.  The  charge-discharge

characteristics for lead-acid, nickel-cadmium, and nickel-zinc batteries

were based on available data but  modified on the basis of projections for

future near-term capability.  These battery models are  discussed in

Section 7. 3 of the report.

1.3.1    Family Car and  Commuter Car

The  following observations can be made about these classes of vehicles:

      1.     For the available powertrain weight and volume and vehicle
            performance specified for this study, only the spark ignition
            internal combustion engine (both reciprocating and rotary)
            and the gas turbine engines can be practically packaged  into
            the hybrid heat engine/electric vehicle.  These  engines
            impose realistically achievable goals  on the  battery
            specifications for power and  energy density.

      2.     All hybrids examined showed marked calculated emission
            reductions over current conventional vehicles.  This is
            illustrated by the results shown in Figure 1-1. In this figure,
            measured cold start emission data available for a 1970
            conventional spark ignition engine automobile is compared
            with calculated hot start emission levels for several develop-
            ment stages of a spark ignition engine in a hybrid powertrain
            automobile.  In the first emissions comparison,  a small
            conventional engine is used in the hybrid vehicle;  the second
            comparison is  for the same engine but operating over the
            restricted air/fuel ratio range noted and with exhaust
            recirculation; the third comparison is for an advanced
            technology engine operating at very high air/fuel ratio with
            exhaust gas recirculation and incorporating catalytic converters.
                                     1-4

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   50
O)
'E
1  40
o

g  30
UJ
—I

o  20


   10


   0
   CO
   CO
               8
                      CONVENTIONAL
                       S.I. ENGINE
                     (VARIABLE A/F

                            o
   CONVENTIONAL
    S.I. ENGINE
(A/F = I5-I6) + RECIRC.
                     ADVANCED
                    TECHNOLOGY
                       PLUS
           CONVENTIONAL
             VEHICLE
           (COLD START)
   HYBRID VEHICLE
(4000-lb FAMILY CAR)
     (HOT START)
Figure 1-1.  Vehicle Emission Comparison,  Conventional Operation
            Versus Hybrid Operation (Spark-Ignition Engine,
            DHEW Driving Cycle)
        Based on analysis,  if currently available engine technology
        is used, no version of the family car could meet 1975/76
        emission standards.  No catalytic converters or thermal
        reactors were added to the powertrain for this case.
        Calculations based on hot start with advanced engine technology
        indicates that all versions could meet 1975/76 standards except
        for the NOo excess  for  the spark ignition family car version
        (discussed in item 6) and the NOŁ excess for the diesel.
        Potential diesel  engine  improvements that might reduce the
             emission level are discussed in Appendix B.
        Commuter car emissions are less than one-half of those for
        the family car and with advanced technology easily meet the
        1975/76 standards as shown in Figure  1-2.  (The commuter car
        weighs only 1700 Ib and has reduced acceleration and maximum
        cruise  speed  capabilities. )
                                 1-5

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co


O
2:

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7.    Emissions are sensitive to:  (a) heat engine class and assumed
      engine emission part-load, characteristics; (b)  driving cycle
      characteristics selected for evaluation; (c) the engine operating
      mode used over the cycle; (d) the battery discharge and charge
      characteristics assumed for the analysis; and (e) electric drive
      motor efficiency and  part load characteristics.

8.    Only spark ignition and gas turbine engine versions warrant
      intensive near term effort when availability, weight,  emissions,
      and cost are considered.
9.    Emissions are approximately 10 and 1 5 percent lower for the
      parallel powertrain configuration as compared to the series
      configuration in the family and commuter cars, respectively.
      However,  the parallel powertrain is more complex.
      Descriptions of the powertrains analyzed can be found in
      Section 1 0. 1.

1  0.   As noted earlier,  study results are based primarily on hot
      start data.  Incorporation of cold start effects, based on the
      limited amount of  cold start data available,  would still allow
      the advanced technology engine  (very lean with exhaust treatment)
      versions of  the hybrid vehicle to meet 1 975 HC and CO standards.
      The NO? emission values are reduced when cold start effects
      are incorporated.  Cold start effects are discussed in Section 9.

11.    An improved lead-acid battery is needed which provides
      increased power density capabilities under shallow discharge
      operation  to be used in near term hybrid applications.  The
      near term application will not quite meet vehicle specifications
      for vehicle performance due to an exceeding of the powertrain
      weight allocation or due  to insufficient battery lifetime.   In
      order to meet all  specifications, the nickel-zinc battery looks
      promising for the  post-1975 period.  Production costs for both
      types of batteries  must be carefully considered in selection of a
      suitable battery design.

12.   Based on the powertrain and battery models assumed and the
      two driving  cycles used in analysis of the family car
      (Section 3. 3), lead-acid battery development goals were generated.
      The analysis results  in the  goal of a 38  amp-hr battery which
      operates at less than  4 percent depth-of-discharge.  Normal
      vehicle operation over the DHEW Driving Cycle requires up to
      260 peak amperes  for acceleration with an average discharge
      current of about 50 amperes and a maximum energy drain of
      0. 3 kw-hr (which is replenished by the generator before the end
      of the cycle).  During occasional maximum vehicle acceleration
      to 80 mph, about 460  peak amperes and 0. 5 kw-hr are withdrawn
      from  the battery.  For a design life of 5000 hr of operation or
                               1-7

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      about 1 00, 000 vehicle miles of city driving, between 900, 000
      and 1, 000, 000 charge/discharge cycles occur (Section 7. 6).
13.   In Figure 1-3, battery power density and energy density
      capabilities are compared with installed battery requirements
      for a spark  ignition,  series  powertrain version of a family car.
      The  installed requirements for energy density are based on the
      battery charge/discharge characteristics assumed for this study
      and may vary somewhat depending on actual test data from a
      particular advanced battery  design.  The intersection of the
      battery capability and vehicle-required installed densities gives
      the power and energy density compatible with vehicle weight
      (and battery weight) allocation.   For the lead-acid case  shown,
      the maximum power  density requirement ranges from 11 8 to
      1 50 watt/lb  and  the installed energy density ranges from 11 to
      14 watt-hr/lb.   The vehicle  weight ranges from 4200  to 4400 Ib,
      which represents  600 to 800 Ib of batteries; this vehicle would
      have reduced road performance.  With the  nickel-zinc battery,
      a 4000-lb car could be built  which meets the performance
      specifications of this study.  Nickel-zinc power density and
      energy density values would be approximately 230 and 20,
      respectively.
14.   Battery charge acceptance characteristics  play an extremely
      important role  in  determining resultant vehicle exhaust
      emissions (Section 7).
15.   Regenerative braking has essentially no effect on emissions for
      the hybrid heat engine/electric vehicle due to battery charge
      acceptance limitations that preclude  the ability to  store  the
      braking energy.  Hence, the expected advantage in reduced
      generator output for  recharging batteries (and therefore
      reduced engine power and  emissions) did not materialize.

      Charge acceptance improvement goals should be at least 40
      amperes at  over 95 percent  state-of-charge without
      regenerative braking and as high as 400 amperes at over
      95 percent state-of-charge with regenerative braking to
      minimize emissions.

1 6.   Battery lifetime and  charge  acceptance are  important areas
      for battery improvements.
17.   Vehicle weight increases of  several hundred pounds to
      accommodate additional battery or engine weight have a
      minor effect on exhaust  emissions, but the heavier vehicles
      would have  reduced road performance.

18.   Realistically varying the battery recharge efficiency (to
      account for  resistive losses and incomplete chemical
      reactions) has little effect on emissions.
                               1-8

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    320
    280
    240
    200

 o
 Q-
    160
    120
     80
     40
      0
        4600 Ib
                               VEHICLE
                               WEIGHT = 4000 Ib
                               NICKEL ZINC
                               BATTERY
                                INSTALLED
                                BATTERY  REQUIREMENTS-
  FAMILY CAR
  S.I. ENGINE
  SERIES CONFIGURATION
                I
I
I
       0        10        20        30       40
          MAXIMUM INSTALLED ENERGY DENSITY, W-hr/lb
                          50
Figure 1-3.   Installed Battery Requirements and
              Projected Battery Capabilities
                           1-9

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19.   Fuel consumption values for the spark ignition engine are
      summarized in the following table for all vehicles operating
      over their emission driving cycles (the 1972 DREW  Driving
      Cycle for the commuter car and the family car).   The levels
      shown for the family and commuter cars are competitive with
      equivalent 1970 conventional vehicles.

                         Series  Configuration    Parallel Configuration
         Vehicle         	(mi/gal)	    	(mi/gal)	

      Commuter Car           26                       30. 5
      Family Car              11                        12. 5

      Low-speed Van            3.75                    	
      High-speed  Van           4                        5

      Low-speed Bus            1.25                    	
      High-speed  Bus            1.5                      2

      These results were developed using specific fuel consumption
      characteristics based on the minimum SFC/rated horsepower
      correlation  presented in Section 8.  The data here are
      representative of  current carbureted spark ignition engines
      operating at air/fuel ratios of from 14 to 1 6.  No adjustment
      in SFC was  made  for the lean air/fuel  ratio regimes adopted
      for hybrid operation because  there is  every reason to expect
      that appropriate modifications in the design of advanced engine
      systems  (viz. stratified charge) will permit  operation at high
      air/fuel ratios without serious degradation in fuel consumption.
      If no improvement were made,  the miles per gallon at the
      very lean air/fuel ratios would be approximately 20 percent
      lower than those  shown.

20.   Estimates of consumer costs for the major subsystems  of
      an advanced hybrid vehicle in large volume production were
      prepared by judging system complexity and performance
      requirements using current hardware cost data wherever
      available.  The powertrain and vehicle component cost
      estimates were then used to construct  a total-vehicle-cost
      comparison between hybrid system  designs for the family car
      and current (1 970) conventional family cars. As shown  in
      the following table,  the hybrid costs range from 1 . 4 to 2.25
      times higher than conventional cars.  However, it is expected
      that the conventional car meeting the 1975  emission standards
      will be more expensive than today's version.  It should also
      be noted  that the hybrid using the Diesel,  Rankine, and
      Stirling engines  would not meet the  powertrain weight
      allocations or the performance  specifications.
                               1-10

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            The tabulation results  should be approached with caution, giving
            due regard to the preciseness of the assumptions made in the
            cost analysis.   The hazard of assigning significance to the
            relative magnitudes of the cost ratio  is apparent when it  is
            recognized that to arrive at production costs it has  been
            necessary to estimate  figures for a number of critical com-
            ponents which at present may be barely classified as being in
            a conceptual design phase.   The basis of these estimates arc
            presented in Section 12.

                    Vehicle                 Relative Costs

            Current Conventional Car             1

            Hybrid Car

               Spark Ignition                 1.4 - 1.6
               Diesel                        1.5-1.7
               Gas Turbine                      1 . 6
               Rankine                           2 +

               Stirling                           2. 25+

1.3.2     Bussesand Vans

Extensive investigation was also conducted on busses and vans in this si.udy.

This included analysis of component requirements, vehicle performance

and exhaust emission levels.  The  information generated on busses and vans

can be found throughout this report.

The following limited observations can be made about these classes of
vehicles:

     1.     Relative evaluations were not possible since emission
            standardsj vehicle emissions test data, and realistic driving
            cycle data were not available.

     2.     Emission data  to be used in future hybrid evaluations were
            generated over a representative driving cycle.
     3.     For the bus, battery power density and energy density
            requirements are such that batteries  could be readily made
            with current technology.
                                   1-11

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1.4       SUMMARY OF RECOMMENDATIONS
The intent of the recommended programs presented in this report is to
provide the EPA with a planning document for ensuring the early availability
of a low emission, viable alternative to the conventional automotive passenger
car.   In this regard, a development effort has been formulated in three
phases.  In brief, the first phase should be aimed at a finer definition of
important hybrid parameters through both expanded analysis and data
collection.  A study should be performed to define  in greater detail the
hybrid vehicle production and operating costs since costs are an important
parameter in determining if the hybrid is a viable competitor to the con-
ventionally powered automobile.  In addition to the cost analysis,  a
performance analysis should be performed to a  level of depth greater  than
was performed in this feasibility study.  Acquisition of component test data
is needed to support this analysis.  A  very important area  for expanded
data collection is in the engine emission area.   Here,  data on engines
operating in the hybrid mode are needed to strengthen the data base used
for analysis.  Comparative analysis between cars using hybrid heat
engine-electric powertrains and those using advanced engines should be
made to determine the advantages or disadvantages of the hybrid concept
as n means of reducing auto pollution.  Recommendations for additional
work effort in Phases II and III are of course highly dependent  on the
results of  studies conducted in Phase I.

The second phase should consist of an intensive effort to develop critical
powertrain components destined for a  prototype vehicle.  This would
incb de advanced technology work on engines, batteries,  motors/generators
  id control systems designed to operate in the hybrid mode.

The third phase encompasses the hardware definition and development
necessary for an early test bed vehicle as well as for a later prototype
vehicle.  The details of each phase of the recommended work effort, are
summarized in the subsequent discussion.
                                    1-12

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 Figure 1-4  shows a schedule of activity for the  three phases of recommended
 hybrid heat engine/electric system efforts.  More information on these
 recommendations  can be  found in Section 13 and also in Sections 6 through 9
 for individual components
        PHASE I - ANALYSIS 8 DATA
                ACQUISITION
          PERFORMANCE ANALYSIS
          DATA ACQUISITION
          COST ANALYSIS
          POWERTRAIN COMPARISONS
          DECISION WHETHER  TO
          PROCEED WITH TEST BED
        PHASE H-ADVANCED TECHNOLOGY
          RESEARCH
          DEVELOPMENT
        PHASE ffl-SYSTEM HARDWARE
          TEST BED
          PROTOTYPE
                                                YEARS
                                      12345
1.4.1
         Figure 1-4.  Hybrid Electric Recommended Development
                      Schedule
Phase I  - Detailed Hybrid System Analysis and
Expanded Data Base
A logical progression from the current feasibility study would be a study
directed at an in-depth analysis of the  hybrid vehicle powertrain in a
passenger car application.  Thus,  in a study narrowed in scope, the  more
intricate details  of component operation and installation in the vehicle can
be examined. The analysis is fundamental to establishing a firmer basis
for objective evaluation of the hybrid electric vehicle in terms of exhaust
emissions and costs when compared to present and projected versions of
the engine-driven passenger car.
                                    1-13

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A major effort in the study program should be the establishment of an
expanded data base for the powertrain components.   This could be
accomplished in two ways: (1) through planning and conducting of tests on
specific component hardware to define performance maps over the entire
operating range, and (2) through consultation with component manufacturers
and reliance on their existing and projected data.  These discussions with
manufacturers should also provide a means of assessing the cost factors
associated with variations in component operation.

Three major subsystems appear to need markedly increased scrutiny before
a major funding  effort for hybrid vehicle hardware can be initiated.  These
are:  (1) heat engines (advanced internal combustion engines and gas
turbines), (2) motor/generator  control systems, and (3) batteries.  The
variation in heat engine emissions at part-load conditions can be very
critical in ultimately  determining vehicle exhaust emissions.   Hence, these
data are needed for the  following engines operating in the hybrid mode:
      1.    Advanced internal combustion engines operating in the  lean
             regime
            a.    Spark ignition engines
                        modified conventional engine
                        stratified charge engine
                        pre-chamber engine
                        modified rotary (Wankel) engine
             b.    Compression ignition engine (cursory examination)
                        modified diesel engine (low NO  ,  lightweight)
       2.    Gas Turbine
                        single and dual shaft
                        recuperated and non-recuperated
 The complete operating maps for these engines  should be compared with the
 operating maps  of the electrical components  in order to define the interface
 relationships of power and rpm that are crucial for maintaining low
 emissions  and high overall efficiency resulting in low fuel consumption.

 Through discussions  with hardware manufacturers and  the further
                                     1-14

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clarification of electrical component operation in the hybrid car that will be
accomplished in the Phase I effort, the electrical and electronic elements of
the subsystems in the overall vehicle control system can be defined.  This
step is necessary in order to confidently predict the production costs
associated with the entire electrical system.  The control system  circuit
design should also be examined from the viewpoint of reliability and main-
tainability as well as first costs,  and the complexity should be evaluated in
terms of heat engine  operating modes and the  degree of manual control that
could be realized.

As part of the Phase  I effort to  improve the data base,  performance of the
latest lead-acid batteries should be documented.  Test  data should include
charge/discharge characteristics, temperature effects, and in particular
cycle lifetime at  shallow discharge.  These data should be  supplemented
with test results  for high power density cells that are under laboratory
development. If  control system operation induces transient currents at the
battery  terminals, the resultant effects on battery lifetime  should  be
ascertained.

To provide an expanded  critique of the hybrid  electric system  one  further
evaluation merits inclusion in Phase I studies.  This relates to comparing
the advanced version of  the hybrid electric passenger car with advanced
versions of engine-driven passenger cars.  Because of near-term potential
for use  in cars, only the spark  ignition and gas  turbine engines are recom-
mended for powerplants  to be included in each vehicle's powertrain.  For
equivalent performance  in terms  of acceleration,  cruise  speed,  and grade-
ability,  the respective systems should be  compared on  the  basis of
production cost,  exhaust emissions, and fuel consumption.

Finally,  in addition to establishing a solid basis for  estimating comparative
hybrid passenger vehicle emission levels and  production  and operating costs,
the proposed work effort should also provide a definitive  package of
information that is required prior to implementation of hardware assembly
                                    1-15

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for a test bed vehicle and prior to implementation of fully funded development
programs for a prototype vehicle.  This information package should consider

such items as:

      1.     Recommended powertrain design and vehicle weight and
            powertrain weight allocations

      2.     Performance specifications for each major component in the
            powertrain for the test bed and prototype vehicles based on
            vehicle specifications to be defined for acceleration, cruise
            speed,  and gradeability

      3.     Rationale for powertrain design and component selection
            including trade-offs between cost, exhaust emissions, fuel
            consumption, and reliability
      4.     Vehicle performance  capabilities including the effect of various
            driving cycles and cold-start on exhaust emissions

1. 4.Z    Phase II  -  Component Advanced Technology

A research  and development program is recommended to provide  powertrain

components with performance markedly improved over  contemporary  hard-
ware.  The  effort should lie  predominantly in the areas of heat engine

emissions and battery lifetimes.  Initially, the program emphasis should be
on research with limited funding until the Phase I  study results in the  form

of comparative vehicle  performance and cost as well as component specifi-
cations are available for review.  Should these Phase I  results still favor

the development of a hybrid electric automobile,  then the Phase II effort

should be expanded rapidly with increased funding and eventual initiation of

the hardware development portion of the program.  The required work effort
is summarized as follows:

      1.    Internal Combustion Engine

           Design for low specific mass emissions at part-load engine
           operation.  Lean air/fuel ratio engines should be evaluated to
            select the best approach towards  achieving low emission goals
            consistent with fuel economy.  Approaches to be  evaluated
            should include the stratified charge engine,  pre-chamber
           engine, and engines with optimized induction system design.
           The rotary  combustion (Wankel) engine, because  of its low
           weight and volume and its potential for operating  in the lean
                                   1-16

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            air/fuel ratio regime, should also be investigated.   Diesel
            engine technology should be investigated to assess its potential
            for reducing NO  emissions and engine weight.  A two-year
            engine research and development  program should be conducted
            with efforts also directed towards incorporating efficient
            catalytic converters, thermal reactors, and exhaust gas
            recirculation.

      2.     Advanced Gas  Turbine Engine

            Design a burner to minimize the NO? emissions of  the gas turbine.
            Studies should be conducted to select an optimized gas turbine
            and to plan its development to meet the requirements of the
            prototype vehicle.   The gas turbine should be  developed with the
            hybrid vehicle in mind and have good part-load emission
            characteristics and provide optimum matching of the heat engine
            with the electrical drive system.

      3.     Batteries

            The battery research and development program should  consist
            of parallel  laboratory studies of a lead-acid battery and a nickel-
            zinc battery optimized to the hybrid vehicle requirements in
            terms of power density,  energy density, lifetime, and charge
            acceptance. It is anticipated that nickel-zinc  batteries  will
            demonstrate superior performance characteristics  than lead-
            acid but  will be more expensive.  It is also anticipated that
            selection of an  optimum battery for the prototype vehicle will
            be made at the  end of two years.

Design concepts generated  in this Phase II program should eventually be

introduced into the hybrid vehicle test  bed program  for evaluation,  and field

test results should be used to tailor the later  development work effort.  The
test bed program is discussed next in Phase III of the overall development
effort.

1.4.3     Phase III  -  Test Bed and Prototype Vehicle Development

The following recommendations are based on  results of the completed
feasibility study on hybrid electric vehicles, and should be considered

solely as  generalized planning information at  this time. If results  from

the Phase I program are favorable for continued development of the hybrid

electric automobile,  then the available detailed design information  from the

expanded  analysis and data base can be used to refine  the  plans formulated

in the subsequent discussion.  Detailed plans  for the prototype  vehicle
                                    1-17

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should also be dependent on the  success in improving component performance
demonstrated in the Phase II research effort.
1. 4. 3. 1  Recommended System Development
A 2-1/2 yr program is recommended for development of two mobile test beds
for the hybrid electric vehicle.  The intent of developing these instrumented
test vehicles is to permit early  evaluation of system integration in the auto-
motive environment presented by actual urban driving situations not readily
simulated in the laboratory.

The test vehicle is expected to demonstrate marked improvements in exhaust
emissions,  but  will likely not meet the 1975 emission standards.   That goal
is  expected to be fulfilled by a prototype hybrid electric vehicle planned for
completion in the 1 974-1 975 time period -- a vehicle which will largely
benefit from the experience and component development accrued within the
test bed vehicle and advanced component technology programs.  It is
expected that specifications can be released for component development
bids nine  months after Phase I initiation, and completely assembled vehicles
will be available for a  road test program within 21 months after Phase III
initiation.
1 . 4. 3. 2   Recommended Hybrid Vehicle System Design
Only two heat engines offer the combination of near term availability with
low emissions and also provide  acceptable vehicle performance without
requiring unreasonable battery power/energy density goals.  These are the
spark ignition engine (with exhaust catalytic converters and/or thermal
reactors) and the gas  turbine.  The rpm range for a  spark ignition engine
is  compatible with transmission/wheel rpm and this  engine should be
considered for use in  the parallel mode configuration.  The gas turbine,
however,  is  more suitable for the series configuration because it  can
operate at the normally high rpm without requiring a gear reduction system.
Hence,  for the test bed vehicle development program,  two system designs
(incorporating the two  configurations previously outlined) are recommended
                                    1-18

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at this time in order to most effectively utilize each of these heat engines.
It is expected that both configurations will have  received sufficient evaluation
in the test bed program  to permit the choice to be narrowed to just one
configuration for the prototype vehicle program.

Both  configurations  should use DC traction motor(s) for acceleration because
of past experience with this  equipment in  vehicular applications and because
the torque characteristics are well matched to vehicle needs over a  wide
speed range.

An SCR-augmented control system  designed for varying motor voltage and
use of separately excited field power is recommended.   This system offers
considerable flexibility in design which is  essential to solution of design
problems that may arise once all powertrain elements are integrated on the
test bed vehicle.

Alternators are generally recommended for providing battery recharge
power, but, because of the rpm  range  of the spark ignition engine and  the
restricted electric generator power output range required in the single motor
parallel configuration, a DC generator may prove to be  acceptable.

Lead-acid batteries are suggested for  both configurations since they have
the greatest experience  factor,  are not costly, and appear to have the
best near-term potential for marked increases in performance.  Nickel-zinc
batteries,  because of their current underdevelopment but future potential
for even greater increases in performance, might eventually replace
lead-acid batteries.
1. 4. 3. 3   Recommended Component Development
A well-planned and executed component development program is essential
for ensuring  the vehicle  performance intended for the hybri   electric
prototype vehicle.  Because of the infuence on vehicle performance, all
components and subsystems are  to be designed for low weight and volume
with due  regard for effects on part-load to full load efficiency.  They are
                                   1-19

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also to be designed to operate acceptably under the environmental

conditions  expected during final evaluation in the test bed vehicle and

prior to introduction into the prototype vehicle.


The following brief comments serve to highlight those essential design goals

that are peculiar to the hybrid electric vehicle.

      1.     Motor/Generator

            Design for low cooling requirements,  for non-steady operation,
            and for an optimized balance between weight,  part-load
            efficiency and efficiency achievable at  full load.

      2.     Control System

            Design for simplicity, reliability, and low audible noise and
            vibration.
      3.     Batteries

            Design for lead-acid batteries with high power density, long
            life, high charge acceptance, minimum (or zero) maintenance,
            and low production costs.  For charge/discharge characteristics
            similar to those assumed for this study, high energy density is
            also a  design requirement.

      4.     Heat Engine

            Design for low emissions at full load and part-load consistent
            with good fuel economy.   Application of catalytic converters
            and/or thermal reactors,  as well as exhaust gas recirculation
            should be considered for the internal combustion engine  case.
                                     1-20

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  SECTION 2






INTRODUCTION

-------
                               CONTENTS
2.    INTRODUCTION	   2-1
      2. 1   Purpose of Study	   2-1
      2.2   The Hybrid Vehicle Concept	   2-1
      2. 3   Organization of Study	   2-2
      2.4   Scope of Study	   2-2
Figure 2-1  Major Study Tasks	   2-3
                                   2-i

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                                SECTION 2

                             INTRODUCTION
2. 1      PURPOSE OF STUDY
In search of alternative vehicular power sources that are expected to offer
substantial  reductions in exhaust pollution of the atmosphere over that pro-
duced by the internal combustion engine,  the Air Pollution Control Office
(APCO), Environmental Protection Agency (EPA),  has ranked the hybrid heat
engine/electric system high on the  list of candidates.  However,  before it
could commit funds for promoting  early development of this power source,
APCO required detailed substantiation of its design feasibility and potential
for major reductions in exhaust emissions.  Hence,  the present study was
directed at  providing an analysis of the hybrid heat engine/electric system
by examination of the performance  and exhaust emissions resulting from
computer simulation of vehicles operating over select driving cycles.
Establishment of general design goals for  components and subsystems in the
vehicle powertrain was also included.   In addition,  a technical development
plan was formulated for defining the schedule and allocation of  resources
by APCO to accelerate the development of critical  components  so that
viable  production vehicles could be expected by 1975.
2. 2      THE HYBRID VEHICLE CONCEPT
There are numerous types of hybrid power plants which conceivably could
be considered in a search for  low-pollution systems, e.g. , flywheel/heat
engine hybrid or battery-battery hybrid.  This study was limited solely  to
the hybrid heat engine/electric vehicle concept in which the power for vehicle
propulsion is  supplied by two specific sources: a heat engine and a set of
batteries.   The heat engine is  designed to  supply cruise power  while the
batteries are  designed to supply power for acceleration.  In this  combination
the heat engine can be reduced markedly in size  compared to a conventional
                                     2-1

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propulsion system and,  by restricting the rpm range and permitting only
slow acceleration of the engine, its design and operation can be optimized to
substantially reduce exhaust emissions and enhance longevity.   (Detailed
discussion of engine operating modes and power distribution between engine
and batteries can be found  in Section  10. )  Moreover,  the benefits accruing
from restricted operation of the engine may also carry over to ancillary
equipment such as catalytic converters.  Furthermore,  since the heat engine
can be linked to an electric generator,  the batteries can be  recharged in tran-
sit and the complexities associated with providing area-wide electric power
sub-stations are avoided.   Thus, the  hybrid vehicle represents an inter-
mediate  step between  current internal combustion engine-powered vehicles
and the practical all-electric vehicle  of 1985-1990.
2. 3    ORGANIZATION OF STUDY
To fulfill the objectives  of  this  study, the work effort was divided into four
major interrelated study tasks  (Fig.  2-1).  The first task -- Systems Synthesis
and Preliminary Sizing  --  was  designed to establish at an early date the power -
train configurations to be  investigated and the general range of power require-
ments for each component  and subsystem in the powertrain.  The second
task -- Subsystem/Component Data Acquisition and Technology Assessment--
involved the polling of acknowledged experts in industry, universities, and
government on the state of the art in  specific technical areas and the merits
or deficiencies of proposed methods of operation for each component or  sub-
system.   The third task -- Systems Evaluation and Comparison -- consisted
of collation of  empirical data, formulation of computational procedures,
selection of the most promising combinations of powertrain components and
subsystems, and detailed  evaluation of the resulting vehicle exhaust emis-
sions and design requirements.  The  fourth task -- Technology  Development
Program Plan  -- covered the required planning and funding for research and
development efforts necessary  to upgrade the performance of critical com-
ponents .
2. 4    SCOPE OF STUDY
This study did  not encompass a detail design effort.  Rather, its scope was
limited to an evaluation  of  contemporary technological capabilities as well as

                                   2-2

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      TASK I
       TASK 2
SYSTEMS  SYNTHESIS
       AND
 PRELIMINARY SIZING
      TASK 3
SYSTEMS EVALUATION
       AND
   COMPARISON
 SUBSYSTEM/COMPONENT
 DATA ACQUISITION AND
 TECHNOLOGY ASSESSMENT
       TASK 4
TECHNOLOGY DEVELOPMENT
    PROGRAM  PLAN
             Figure 2-1. Major Study Tasks
                         2-3

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near term advancements in technology for powertrain component development,
illumination of potential problem areas, and establishment of some  exemplary
powertrain systems for hybrid vehicles with potential for low exhaust emissions.

Although major emphasis in the study was placed on evaluation of the hybrid
concept for the full-size family car,  three other classes of vehicles were
considered:  the  two-passenger commuter car, delivery/postal van, and
intra-city  bus.  Within each class, several different types of heat engine
(ranging from spark-ignition to Stirling cycle) were considered.  In addition,
a large variety of batteries, motors, generators,  etc. , were studied for
incorporation into the vehicle powertrain.

The performance of a baseline configuration for each class of vehicle was
established for each type of heat engine.  Since a specific detail design was
not a  goal  in this study (rather design feasibility),  the effect  on vehicle
exhaust emissions  and battery design goals of such diverse factors as com-
ponent efficiencies, regenerative braking, vehicle weight,  powertrain weight,
types of driving cycle, and  types of battery was also covered.  Hence,  the
relative importance of these factors  in establishment of vehicle design goals
can be readily assessed.

It should be noted that because of the multiplicity of vehicle classes and engines
considered in this study, it was considered prudent to constrain the investi-
gation to vehicles of fixed curb •weight and powertrain weight. However, for
the detailed design of a specific vehicle class, the vehicle and powertrain
weights should be allowed to vary in  order to diminish the severity of battery
design requirements without compromising the goal of maintaining low vehicle
exhaust emissions .
                                    2-4

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                      SECTION 3






VEHICLE SPECIFICATIONS AND STUDY METHODOLOGY

-------
                              CONTENTS
3.     VEHICLE SPECIFICATIONS AND STUDY METHODOLOGY  . .     3-1
      3. I    Vehicle Specifications	     3-1
      3.2    Vehicle Accessory Power Requirements	     3-4
      3.3    Driving Cycle Specifications	     3-4
            3. 3. 1    Emission Comparison Driving Cycles	     3-4
            3.3.2    Design Driving Cycles	     3-6
      3.4    Study Methodology	     3-10
            3.4.1    Preliminary System Synthes is	     3-10
            3.4. 2    Development of Computational
                    Techniques	     3-14
            3.4.3    Subsystem Technology Evaluation	     3-14
            3.4.4    Conceptual Design and Sizing  Studies	     3-15
            3.4.5    Performance and Tradeoff Studies	     3-15
            3.4.6    Technology Development Program Plan	     3-15
      3. 5    References	     3-16
                                   3-i

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                                TAB LES



3-1.     APCO Hybrid Vehicle Specifications	   3-2

3-2.     Engine-Driven Accessory Power Requirements	   3-5

3-3.     Vehicle  Component Array	   3-13




                                FIGURES



3-1.     Driving  Cycles  for  Emission Comparisons,
         Family and Commuter Cars	   3-7

3-2.     Driving  Cycles  for  Emission Comparisons	  3-8

3-3.     Design Driving  Cycle,  4000-lb Family Car	   3-9

3-4.     Schematic of Hybrid-Electric  Powerplant Concepts	   3-11
                                    3-ii

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                                SECTION 3
         VEHICLE SPECIFICATIONS AND STUDY  METHODOLOGY


3. 1      VEHICLE SPECIFICATIONS
The APCO specifications for the four vehicles to be examined for potential
applicability of the heat engine/electric hybrid powerplant concept are shown
in Table 3-1.  Significant vehicle design point conditions most likely to
affect powerplant sizing and operational capability include vehicle top speed,
gradeability (in terms of percent grade, velocity on the grade,  and grade
length),  vehicle weight, and aerodynamic drag area and drag coefficient.
The only limitations  imposed upon the power  train were the assigned power
train weights and volumes.  A final requirement was that the acceleration
capability of each vehicle with a hybrid powerplant installed was  to be equal.
to that of a  contemporary automotive vehicle.  Therefore, as stipulated by
the APCO specifications  of Table 3-1, any resulting hybrid vehicle must
match the acceleration, speed,  and gradeability characteristics of conven-
tional, contemporary vehicles.  The rationale for  this requirement  is that
such performance will  enhance public  acceptance  of the hybrid  vehicle and
will also avoid the prospect of poor traffic safety.
In addition to the above constraints,  certain criteria in the areas  of (a) bat-
tery state-of-charge condition and (b)  vehicle characteristics were adopted
by Aerospace.  Since a prime objective of a hybrid-electric powerplant  is
an inherent capability to  recharge the  batteries used with the incorporated
heat engine (i.e., no external source require' to recharge batteries for
operational readiness),  it was further defined that: (a) when the vehicle  is
operated at cruise conditions under the gradeability requirements of Table 3-1,
the installed heat engine power output  shall  be sufficient  to prevent the bat-
tery from discharging; and (b) when  the vehicle is  operated over  a represen-
tative driving cycle for emission calculations, the  hybrid-electric powerplant
                                    3-1

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                                   Table 3-1.  APCO Hybrid Vehicle Specifications
I
ro
Vehicle Characteristics
Maximum cruise velocity (mi/hr)
Cruise velocity for maximum
range (mi/hr)
Velocity on grade at grade
(mi/hr at percent)
Grade length (mi)
Range (mi)
Curb weight (Ib)
Loaded weight (Ib)
Assigned power train weight (Ib)
Assigned power train volume (ft-*)
Aerodynamic drag area (ft^)
Drag coefficient, C^
Acceleration
Family Commuter
Car Car

80
66.5
40 at 12
8
200
3,500
4,000
1,500
28
25
0. 5

70
59.4
33 at 12
4
50
1,400
1,700
600
16
18
0.35
Intracity Bus
Low Speed Highspeed"1
40
40
6 at 20
0.5
200
20,000
30,000
6,000
175
80
0.85
60
60
10 at 10
0. 5
200
20,000
30,000
6,000
175
80
0.85
Delivery/Postal Van
Low Speed Highspeed''
40
40
8 at 20
0.5
60
4,500
7,000
1,700
42
42
0. 85
65
65
8 at 20
0.5
60
4,500
7,000
1,700
42
42
0.85
Equal to contemporary automotive vehicle
             Recommended Aerospace values


             See Section 5.4.3 and Figs.  5-1 and 5-2 for values used.

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shall have the batteries fully recharged at the end of the driving cycle.
Consideration was also given to operation of the battery at shallow dis-
charge with the anticipated goal of improved battery  lifetime as soci;il:ec!
with shallow discharge.   Under these conditions, the vehicle range is not
dependent on installed battery capacity.
It was recognized that the requirement for the battery full  state-of-charge
at the end of the driving cycle might be  extreme for such vehicles as delivery
vans and buses which are  garaged in facilities which could be readily modi-
fied to provide recharging capability at  the end of a prescribed work cycle
or day.   However,  personal transit vehicles (i.e.,  family cars,  commuter
cars, etc. ) present a more stringent requirement in that rechar-ging
facilities are not readily  available to them, at least at the  present time.
Therefore,  it was felt more reasonable to adopt the "fully-recharged at
end of driving cycle" design criterion for all vehicles as  a baseline  require-
ment; appropriate tradeoffs for the delivery van and  bus might: be made in
subsequent studies to assess the importance of this requirement.
It was further felt appropriate to  add two more vehicle classes to be
examined,  in addition to the four  classes specified by APCO.  As can be
noted in Table 3-1,  both the delivery/postal van and  the intracity bus have
very low (40 mph) top speeds and severe (ZO percent) grade requirements.
While these characteristics may be very adequate for many municipalities
(e. g., San  Francisco),  they would not appear to be most appropriate for
urban areas with large freeway networks on which these vehicles are
required to operate  (e.g.,  Los Angeles).  Therefore, a high-speed version
of the delivery van and bus was added to the basic group of vehicles  listed
in Table  3-1.  The top speeds of the delivery van and the bus were selected
as 65 mph and 60 mph, respectively. No gradeability requirement was set
for these two additional vehicles; the resulting gradeability was  determined
from sizing for maximum velocity.  Aside from top speed  and gradeability,
the other specifications of Table 3-1 apply to the two additional  vehicles.
                                    3-3

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3. 2      VEHICLE ACCESSORY POWER REQUIREMENTS
Conventional vehicles normally are provided with accessory features such
as air conditioning, lights,  instrumentation power, and power steering by
engine-driven accessory units.  When the vehicle is driven by conventional
internal combustion engines, the maximum accessory power load varies  as
a function of engine rpm,  which in turn is a function of vehicle velocity and
transmission gear ratio.
As the hybrid heat engine/electric powerplant is currently conceptual in
nature, the variation of heat engine rpm and power output capability versus
vehicle velocity is not definitized.  Therefore, the accessory power require-
ments for the various vehicle classes were stipulated by  APCO to be of
constant value over the operational speed range of each vehicle,  as shown
in Table 3-2.  It is recognized that this approach will likely result in exhaust
emission calculations being based upon a greater heat engine  power output
at low vehicle speeds than would be required if variable accessory power
requirements were used  (See Section  8).  However, this leaves some margin
available for electronic and electrical cooling power  requirements which
will  rise in the low-speed range where  free convection air flow rates are
low.
3. 3      DRIVING CYCLE SPECIFICATIONS
3.3.1    Emission Comparison Driving Cycles
A number of driving cycles have been used/proposed  by various  municipal,
state,  and  federal agencies.  The current test procedures utilized by the
Federal Government (and California)  to enforce existing automotive emis-
sion standards  are conducted with the "seven-mode driving cycle. "  The
seven-mode cycle is an abbreviated test cycle intended to simulate urban
driving requirements as  exemplified by the ~22-min. LA-4 traffic  route
pattern. For this purpose,  the seven-mode test results are modified by
weighting factors, as set forth in the  test procedures published in the
Federal Register  (Ref. 3-1).
                                    3-4

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     Table 3-2.  Engine-Driven Accessory Power Requirements
                                              Power Requirement, hp
                                                 Air  Conditioning
       Vehicle                                With            Without
Family Car                                   12. 6               6. 7

Commuter Car                                 5.7               1.7

Delivery/Postal Van                           ----               2.3

Intracity Bus                                  39. 3              12. 3
Note:  Includes cooling fan, air conditioning, lights,  instrumentation
       power, etc.  Power steering also included on Family Car and
       Intracity Bus.

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It is currently proposed to modify the federal test procedures to require
emission testing over the complete ~22-min. urban traffic  route (LA-4).
This new test cycle is called the DREW urban dynamometer driving
schedule and hereafter will be  referred to as the  DHEW urban driving
cycle (Ref. 3-2).   Figure 3-1 illustrates the salient features of  the seven-
mode and DHEW urban driving cycle  in terms of vehicle speed versus time.
For comparison purposes, an urban driving cycle characteristic of
New York City is  also shown (Ref.  3-3).
For the present study, the proposed DHEW urban driving  cycle  was selected
as the baseline driving cycle for emission calculations and battery  compari-
sons for the family car and the commuter car.  For the family car, selected
comparisons with the New York City driving cycle were also made.
Similar driving cycles for such vehicles as delivery vans  and buses do not
currently exist.   Therefore, based upon available nominal work or duty
cycle data, emission driving cycles •were postulated for these vehicles.
These cycles are  shown in Fig. 3-2,  along  with the  DHEW urban driving
cycle for comparative purposes.
3.3.2    Design Driving Cycles
The vehicle specifications of Table 3-1 and the emissions-related driving
cycles do not in themselves afford a basis  for completely  comparing the
performance of a  vehicle with a conventional powerplant against a similar
vehicle with a hybrid-electric powerplant.   Therefore, design driving cycles
were  postulated for each vehicle which contain the criteria of Table 3-1 and
which afford a definitive basis  for comparison.  The design  driving cycle for
the family car is  shown  in Fig.  3-3, and includes the performance  phases of
maximum acceleration,  maximum high-speed cruise, high-speed cruise for
range, and the gradeability requirement.

Tin; design  driving cycles for the other vehicles tire presented In l.abular
lorm.il.  in Appendix D.
                                    3-6

-------
OJ
I
               CX
               E
               Q_
               CO
               o.
               E
               Q_
               CO
               Q
               UJ
               UJ
                      0
                    60 i-
                   30  -
 0



60

40

20

 0



60

40


20

 0
                      0
                 DHEW URBAN DRIVING CYCLE
            400       600       800
                         TIME, sec

           NEW YORK CITY DRIVING CYCLE
                                  1000
1200
                                                              1400
25
50
                      0      25     50      75 '    100
                                        TIME, sec
                              125
                75     100    125     150     175
                    TIME, sec

7-MODE DRIVING CYCLE
200
                              150
                          Figure 3-1.  Driving Cycles  for Emission Comparisons
                                       Family and Commuter Cars

-------
           FAMILY AND
           COMMUTER
           CAR
           INTRA-CITY
           BUS
00
DELIVERY
VAN
                          O.
                          E
                         CL
                         CO
                          a.
                          E
                         O.
                         CO
                          e
                         a.
                         CO
                              0
                             60
                  30
                              0
                             60
                                                              7.5  miles
                                                   400
                                                  600       800

                                                    TIME, sec
                                     1000
1200
1400
O.I miles
                                                I
                                          I     I
                                0    10   20   30   40   50

                                          TIME, sec
                                                   02 miles
/ ,
3
|
20
l \ 1
40
,
60
i l ,
80 l(
                              0
                                                      TIME,  sec

                           Figure 3-2.  Driving Cycles for Emission Comparisons

-------
O
UJ
Q_
CO
CJ
                     MAXIMUM ACCELERATION

                                 HIGH SPEED  CRUISE
                  25
475 480
                                                HIGH  SPEED  CRUISE
                                                FOR RANGE
                                               12%  GRADE
                                                                              •I/-
      10,330  10,340

TIME, sec
1,061    11,075
                                Figure 3 - 3.
               Design Driving  Cycle,
               4000-lb Family Car

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3. 4      STUDY METHODOLOGY
The methodology selected for the conduct of the study consisted of the fol-
lowing essential steps:
      1.     Preliminary system  synthesis
      2.     Development of computational techniques
      3.     Subsystem technology evaluation
      4.     Power train conceptual design synthesis and sizing
      5.     Performance and  tradeoff studies
      6.     Technology development program plan
3.4.1    Preliminary System  Synthesis
A preliminary system synthesis was performed to (a) identify reasonable
hybrid-electric powerplant concepts and (b) identify reasonable subsystem
performance and technology requirements.   In this effort, material readily
available in the literature was reviewed to ascertain the type and depth of
information pertaining to hybrid vehicles and powerplants.  Specific materials
used in this task are listed in Refs.  3-4 through 3-11.
Hybrid-electric powerplant concepts can be grouped into two broad classes
as shown in Fig.  3-4.   The  first  class, series configuration,  is charac-
terized by the principle that all power is transmitted to the  rear wheels via
an electric drive motor which receives electrical energy either  from a
generator, a battery, or both, depending upon the electric motor power
demand and the generator output  at the time of demand.   The heat
engine drives the generator mechanically; however, all other  elements of
the powerplant system are electrical in nature.  In  the series configuration,
the heat  engine  is decoupled from the drive wheels.  The fact  of decoupling
enables a wide variety of heat engine/generator operational  modes to be
envisioned as possible.  Several  of these operational modes and their
attendant ramifications  are discussed  in more detail in Section 10.
                                    3-10

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            SERIES CONFIGURATION
u>
HEAT
ENGINE
i
i


GENERATOR


I
C



MOTOR
t
ONTROL
SYSTEM
L

>
i
BATTERIES
K wurn 9


            PARALLEL CONFIGURATION
                      HEAT
                     ENGINE
                          I
 CONTROL
 SYSTEM
                   GENERATOR
                                       I
                  GEARING
BATTERIES
MOTOR
                WHEELS
                  Figure 3-4.  Schematic of Hybrid - Electric Po\verplant Concepts

-------
The second class,  parallel configuration, is characterized by the principle
that the heat engine is mechanically linked to the drive wheels to supply
all  or a portion of the power  required there.  The mechanical link can be
one of several gearbox/transmission arrangements.  It is a further principle
of the parallel configuration that the power mechanically transmitted  from
the  heat engine to the drive wheels be sufficient only to maintain vehicle
cruise speeds, and that power required for acceleration of the vehicle be
supplied by an electric drive motor which derives its energy source from a
battery and/or a generator, also driven by the heat engine.  There are
many specific  parallel  arrangements which can be  envisioned; some of these
will be more thoroughly discussed in Sections 6 and  10.
Various subsystems/components considered for use  in the hybrid-electric
powerplant, whether of  series or  parallel configuration,  are shown in
Table 3-3.  In the heat engine area, an investigation of conventional
spark-ignition engines,  diesels, gas  turbines, Raiikine cycles, and the
Stirling cycle was conducted.  In the  battery area,  recent assessments of
capability indicated that-for near-term application  (circa 1975),  the
lead-acid,  nickel-cadmium,  and nickel-zinc  were of prime importance;
advanced batteries with better power density and energy  density charac-
teristics would enhance the capability of a hybrid-electric powerplant,
but  would require extensive development funding and would not be available
for  production by 1975.  Electric  drive motors of specific types (i.e. , AC
induction,  DC  shunt-wound, DC brushless) have been shown to have
specific advantages in specific  installations.  Both DC and AC generators/
alternators had been shown to be promising,  depending upon the specific
vehicle/powerplant configuration.   In the  power conditioning and control
area, a wide range  of types from  silicon-controlled rectifiers (SCRs)
to relays/switches had been shown to be reasonable/attractive,  depending
again upon the application and method of control selected.
                                    3-12

-------
                   Table 3-3.   Vehicle Component Array
Engines                                Generators
     1C Spark                               DC
     Diesel                                  AC (Alternator)
     Gas Turbine                              _   ,     .
                                       Power Conditioning and Control
     Rankine Cycle
     ,,,.  ,.    ,-.  ,                            Silicon Controlled Rectifiers
     Stirling Cycle
                                            Inverters
Batteries                                   ..,  ... _            ,.,,-•
	                                   Solid State Integrated Circuits
     Lead-Acid                              Cycloconverter
     Nickel-Cadmium                       Relays /Switches
     Nickel-Zinc                            Resistors/Inductors
Motors
     AC Induction
     DC Shunt Wound - Externally Excited
     DC Series Wound
     DC Compound Wound
     DC Brushless
                                     3-13

-------
In addition to the components  outlined in  Table 3-3,  mechanical gearboxes,
differential drive units, and transmissions (of several varieties) are also
required to complete the basic elements  of the hybrid-electric powerplant.
3.4.2    Development of Computational Techniques
An essential step in  the evaluation and capability assessment of the various
heat engine/electric hybrid powerplant concepts  is the development of
computational techniques adequate to:
      1.    Accommodate the various heat engine/electric  hybrid  concepts
      2.    Determine the characteristics of various vehicle classes and the
            subsystem/component requirements for  vehicle operation over
            a.    Design driving cycles
            b.    Emission  driving cycles
      3.    Determine heat  engine exhaust emission levels
      4.    Determine battery charge/discharge  characteristics over various
            driving cycles
      5.    Determine distribution of useful and dissipated energy  throughout
            the system
The specific details  of the computer program developed for these purposes
and  its  use in subsequent analyses  are described in Section 4.  The use of
other existing computer programs to determine the various vehicle power
requirements (i.e., acceleration, torque, power,  etc. ) over the different
driving cycles is described  in Section 5.
3.4.3    Subsystem Technology Evaluation
The efforts devoted to determining subsystem performance,  weight,  and
design characteristics are presented in Sections  6 through 9,  for both cur-
rent state-of-the-art and future projections of technology.   The data presented
have been carefully constituted to provide practical,  contemporary informa-
tion as  confirmed by an intensive in-depth survey of acknowledged  experts in
specific technical areas.  (Sources of data may be found in Appendix F. )
                                     3-14

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3.4.4    Conceptual Design and Sizing Studies
Those  conceptual design studies made to select heat engine/electric power
train combinations for detailed analysis are treated in Section 10,  together
with the  resultant subsystem/component sizing necessary to meet  vehicle
performance specifications.  This section also develops battery weight
allocations as a function of powerplant installed weight for the various
vehicles and various heat engines within a vehicle class.
3.4.5    Performance and Tradeoff Studies
Section 11 presents the results of the study, in terms of vehicle exhaust
emissions levels and battery  design goals for  the various vehicle/powerplant
combinations discussed in Section 10.  Also presented are the results  of
various tradeoff studies  to assess emission/vehicle performance sensitivity
and battery  design  goals sensitivity to:
     1.    Effect of regenerative braking
     2.    Effect of battery recharging efficiency
     3.    Effect of vehicle weight (other than  baseline)
     4.    Effect of drive motor efficiency
     5.    Effect of type  of battery
     6.    Effect of emission  driving cycle (DHEW cycle versus  New York
          driving cycle)
     7.    Series versus parallel mode of operation
3.4.6    Technology Development Program Plan
Section 1 delineates a recommended technology development program plan,
based on the results given in  Section 11 and the technology capability pro-
jections  of Sections 6 through 9.  The program plan is directed toward
defining  a technology development program for the most promising systems
and is designed to enhance the probability of viable prototype hardware in
the near  future and production hardware  in the 1975-1980 time period.
                                   3-15

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3. 5      REFERENCES

3-1.     Federal Register,  vol. 33, no. 108, 4 June 1968.

3-2.     Federal Register,  vol. 35, no. 136, 15 July 1970. *

3-3.     J. T. Higgins, New York City  Traffic,  Driver Habit and Vehicle
         Emissions Study,  Bureau of Air Resource  Development,  New York
         State Department of Health,  1  June 1969 (a condensation of final
         report submitted by Scott Research Laboratories).

3-4.     Prospects  for Electric Vehicles --A Study of Low-Pollution-
         Potential Vehicles--Electric,  National Air Pollution Control
         Administration Publication No. APTD 69-52,  Prepared by
         Arthur D.  Little,  Inc., October  1969.

3-5.     Frontiers of Technology Study, North American Rockwell Corpora-
         tion^5 January  1968.

3-6.     G. A.  Hoffman,  Hybrid Power  Systems for  Vehicles, University of
         California  at Los Angeles.

3-7.     N. A.  Richardson,  G. H. Gelb, T. C. Wang, and J. A. Lecari,
         System Design Implications of Electric  and Hybrid  Vehicles,
         TRW Systems, Inc., Redondo Beach,  California, IECEC  Paper
         No. 689109.

3-8.     G. H.  Gelb, N. A.  Richardson, T. C. Wang, andR.S. DeWolf,
         Design and Performance Characteristics of a Hybrid Vehicle
         Power Train, TRW Systems, Inc.,  Redondo Beach,  California,
         SAE Paper No.  690169.

3-9-     Selected descriptive material provided by Minicars,  Inc., Goleta,
         California.

3-10.    R. K.  Lay and W. E. Fraize, Propulsion Systems for Low Emission
         Urban  Vehicles, MITRE Corporation, Washington,  D. C.,  Report
         WP-1200,  vols. land  II, 23  January 1970.

3-11.    Study  of Unconventional Thermal,  Mechanical, and Nuclear Low-
         Pollution Potential Power Sources for Urban Vehicles,  Battelle
         Memorial Institute, Columbus, Ohio, 15 March,  1968.
  Revised per Federal Register,  vol. 35, no. 219, 10 November 1970
                                    3-16

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          SECTION 4






COMPUTATIONAL TECHNIQUES

-------
                              CONTENTS


4.    COMPUTATIONAL TECHNIQUES   	   4-1
      4. 1   Introduction	   4-1
      4. 2   Analytical Model of Hybrid Vehicle
           Power-train  	   4-1
      4.3   Description of Computer Program	   4-2
           4.3. 1    Program Logic Elements 	   4-2
           4.3.2    Program Input Data Requirements	   4-4
           4.3.3    The Handling of Output Data  	   4-4
      4.4   Application of Performance Evaluation
           Computer Program	   4-5


                                FIGURES


4-1.  Simplified Flow Chart of HEVPEC Program   	   4-3
                                   4-i

-------
                               SECTION 4
                     COMPUTATIONAL TECHNIQUES
4. 1       INTRODUCTION
The evaluation of the performance of the various hybrid vehicle power train
concepts considered in this study is performed with the aid of a digital
computer program.   This  program, entitled Hybrid Electric Vehicle
Performance Evaluation Computer Program (HEVPEC), was developed
specifically for this study.  A computer simulation technique is used to
determine the performance of hybrid vehicles over a specified driving cycle.
The overall objective of these calculations is to identify those design
approaches  which  give low exhaust emission, to determine the sensitivity
of emission levels to changes in the operating characteristics of various
power train components, and to determine the resulting battery requirements.
This section contains a discussion of the analytical model,  a brief description
of the computer program,  followed by an explanation of how the program was
used to achieve the desired results.
4. 2       ANALYTICAL MODEL OF HYBRID VEHICLE
          POWER TRAIN
An analytical model of a hybrid vehicle power train was derived and pro-
grammed for the Aerospace CDC 6600 digital computer.  The basic
equations for the rectilinear motion of a  rigid body were combined with
Newton's Second Law of Motion to establish the basic link between the
velocity  of the vehicle as specified by the driving cycle and the  net driving
force at  the wheels.  Detailed models of  several of the  major components of
the power train  were incorporated in the computer program to determine
the response of  power train elements  to instantaneous power demands
associated with  vehicle operation on a given driving cycle.   The major
components of the hybrid power trains were considered to be the heat
                                    4-1

-------
engine, a generator, a secondary battery, an electric traction motor,  an
electrical control package, and,  in the parallel configuration, a power
transmission.   Models of two different power train configurations  designated
as "series" and "parallel" were derived.  In both configurations the heat
engine provides all energy expended for  vehicle operation,  and the secondary
battery provides most of the  power required for vehicle acceleration.
4.3       DESCRIPTION OF COMPUTER PROGRAM
4. 3. 1     Program Logic Elements
The  computer program includes not only the basic mathematical expressions
associated with the analytical model discussed above,  but also the logic f
required to regulate the power and  energy flow from each component during
vehicle operation over the driving cycle. A simplified version of the basic
program is presented in Fig.  4-1.
There are  sets  of logic elements built into the program that warrant special
mention.  The first controls  battery charge and discharge.   If the  power
demanded by the motor exceeds generator output power level, an amount of
power equal to the deficiency is directed from the battery to the electric
motor.  Another logic element tracks the state-of-charge and voltage of the
battery and terminates the calculation procedure if the latter falls below
some specified value.  Power for battery charging is available if the power
demand by the motor is less  than the output of the generator.  The maximum
charging power the battery can accept is constrained by the battery charge
characteristics and by a specified maximum allowable  voltage level  of the
battery.  Excess power that the battery  cannot accept is assumed to be
dissipated  in resistive load.  The cumulative  amount of energy so  dissipated
is calculated and included in  the output data.
 Refer to Appendix A for a detailed description of the computer program
 logical  structure.
                                    4-2

-------
(TM
r
T ELECTRIC
OR CURRENT
^
t SPEED OF
RIVE MOTOR
>
E ElfCTRIC
OR OUTPUT
QUE
t
NET FORCE
KEELS
f
E VEHICLE
TION AND
EED
ESPEED\
ROFIIf




-------
The second special set of logic elements controls the mode of operation of
the heat engine. '    A simulation can be run with the heat engine operating
at constant power output; i. e. ,  independent of vehicle speed or power
demand at the wheels. This  mode of operation is applicable only to a
series-configured power train.  In an alternate mode of operation applicable
to both the series and parallel configurations, the heat engine power output
varies with total road load horsepower  down to a minimum specified value
below which the engine output is constant.
4. 3. 2      Program Input Data Requirements
The input data  required for a simulation run on the computer are presented
in detail in Appendix A and include tables of battery charge and discharge
data, heat engine emission characteristics, driving cycle data (velocity,
time, road grade),  vehicle characteristics  (weight,  frontal area,  rolling
resistance coefficients, aerodynamics drag coefficients, gear ratio, tire
radius, etc. ).
4.3.3      The  Handling of Output Data*
Output from a typical run for each version of the program includes the
folio-wing:
      1.     Vehicle Status
            a.    Profile time
            b.    Speed
            c.    Acceleration
            d.    Wheel horsepower
            e.    Total road  resistance
#*
  Refer to Section 10 for a full discussion of heat engine operating modes.
  Sample printouts from typical simulation runs are .presented in
  Appendix A.
                                    4-4

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      2.     Heat Engine-Generator Status
            a.     Power output
            b.     Generator Current
            c.     Emissions (CO,  HC, NO2)
      3.     Electric Motor Status
            a.     Speed
            b.     Input current
            c.     Output torque
      4.     Battery Status
            a.     State of charge
            b.     Discharge current
            c.     Maximum discharge current available
            d.     Total charge current available
            e.     Maximum acceptable charge current
            f.     Cell voltage
The user has the option of obtaining the above information at each time
point  of the driving cycle or at only the last time point.  In addition to the
digital output, a graph plotting routing was added to the program and
allows the  user  to obtain the results printed out in  graphical form.  Samples
of both the digital printout and plotted output are included in Appendix A.
4.4     APPLICATION OF PERFORMANCE  EVALUATION
        COMPUTER PROGRAM
Two types  of simulations were required to obtain a complete evaluation of a
particular  hybrid power train.  The first type involved simulated operation
of a vehicle over a design driving  cycle and was  performed  to verify sizing
of the heat engine and battery.  The electric drive  motor was  sized using
the results of the  analysis presented in Section 5 of this report.  The design
driving cycle was synthesized from APCO  specifications defining the
                                    4-5

-------
required vehicle maximum performance.  Although a different design
cycle was required for each vehicle considered in this study,  they were
similar in organization because they each contained maximum acceleration
to maximum cruise  speed,  cruise at constant speed,  and operation on a
grade at constant speed.
Having verified adequate  sizing for the hybrid power train,  the emissions
(HC, CO, and NCO were then determined by simulating vehicle operation
over an emission driving cycle.   A more detailed discussion of the
emission  driving cycles used in this study is presented in Section 5,
and speed-time plots of each cycle are presented in Appendix D.
                                   4-6

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           SECTION 5






VEHICLE POWER REQUIREMENTS

-------
                             CONTENTS
5.    VEHICLE POWER REQUIREMENTS	    5-1
5. 1
5.2
5. 3


5.4









5. 5





5.6






5. 7
Introduction 	
Summary of Vehicle Specification 	
Emission Driving Cycle Analysis 	
5.3. 1 Objectives of Driving Cycle Analysis 	
5.3.2 Results of Driving Cycle Analysis 	
Hybrid Drive-Train Power and Torque Requirements
for the Family and Commuter .Cars 	
5. 4. 1 Computational Procedure 	
5.4.2 Vehicle Speed-Time Characteristics 	
5.4.3 Acceleration Performance 	
5.4.4 Horsepower Requirements of Hybrid
Drive Train 	
5.4.5 Gradeability Performance Requirements 	
5.4.6 Torque Requirements for the Electric
Drive Motor 	
Hybrid Drive- Train Power and Torque Requirements
for the Delivery Van 	
5. 5. 1 Computational Procedure 	
5. 5. 2 Acceleration and Gradeability Performance . . .
5.5.3 Hybrid Drive-Train Power and Torque
Requirements 	
Hybrid Drive-Train Power and Torque Requirements
for Intracity Bus 	
5. 6. 1 Computation Procedure 	
5. 6. 2 Acceleration and Gradeability Performance . . .
5. 6. 3 Hybrid Drive- Train Power and Torque
Requirements 	
5.6.4 Emission Driving Cycle for High-speed Bus . . .
References 	
5-1
5-2
5-2
5-2
5-4

5-4
5-4
5-6
5-6

5-6
5-10

5-13

5-15
5-15
5-15

5-23

5-23
5-23
5-23

5-31
5-31
5-36
                                 5-i

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                                 TABLES
5-1.   Vehicle/Driving Cycle Combinations	   5-3

5-2.   Summary of Vehicle Performance Requirements
       Derived From Emission Driving  Cycle  Analysis	   5-5

5-3.   Summary of Body and Chassis Characteristics for  a
       Delivery Van	   5-18

5-4.   Comparison of Low- and High-speed Van Acceleration
       Performance and Emission Driving Cycle Acceleration
       Requirements   	•	   5-19

5-5.   Comparison of Intracity Bus Acceleration Capability with
       Emission Driving Cycle Acceleration Requirements  ....   5-27

5-6.   Specifications for High-speed Bus	   5-30

5-7.   Comparison of Intracity Bus Emission Cycles	   5-35
                                   5-ii

-------
FIGURES
5-1.
5-2.
5-3.
5-4.
5-5.
5-6.
5-7.
5-8.
5-9.
5-10.

5-11.
5-12.
5-13.
5-14.
5-15.

5-16.
5-17.
5-18.

5-19.

Speed Versus Time Curves for Family Cars 	
Speed Versus Time Curves for Commuter Cars 	
Comparison of Vehicle Velocity-Acceleration
Characteristics to DHEW Driving Cycle Requirements ....
Power Requirements for Family Car 	
Power Requirements for Commuter Car 	 ; 	
Gradeability of Family and Commuter Cars 	
Required Motor Torque for Family Car 	
Required Motor Torque for Commuter Car 	
Speed Versus Time Curves for Delivery Van 	
Acceleration Performance Requirements for
Delivery Van 	
Maximum Gradeability Performance of Delivery Van ....
Power Requirements for Delivery Van 	
Electric Motor Torque Requirements for Delivery Van ....
Speed Versus Time Curves for Intracity Bus 	
Acceleration Performance Requirements for
Intracity Bus 	
Maximum Gradeability Performance of Intracity Bus 	
Power Requirements for Intracity Bus 	
Electric Motor Torque Requirements for Low-speed
Intracity Bus 	
Electric Motor Torque Requirements for High-speed

5
5
5
5
5
5
5
5
5

5
5
5
5
5

5-
5
5

5

5
-7
-8
-9
-11
-12
-14
-16
-17
-20

-21
-22
-24
-25
-26

-28
-29
-32

-33

-34
    5-iii

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                            NOMENCLATURE









A        frontal area of vehicle,  ft




a        acceleration of vehicle,  mph/sec




C ,       aerodynamic drag coefficient




HP      wheel horsepower, hp




F,       road resistance force,  Ib




F        propulsive force (at wheels), Ib




C        gear ratio




m       actual vehicle mass, Ib-sec/mph




mv      effective vehicle mass = 1. 1 m




n        electric motor speed, rpm




P        tire pressure,  psi




Rr       tire radius, ft




TE      tractive effort  (force),  Ib




Tm      electric motor output torque, ft-lb




V        vehicle speed,  mph




W        loaded vehicle weight, Ib




 H        driveline  efficiency,  percent




 0        grade angle
                                    5-iv

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                               SECTION 5
                   VEHICLE POWER REQUIREMENTS
5. 1      INTRODUCTION
This section presents a discussion of the development of power and torque
requirements for the drive train of the hybrid engine.  These requirements
were developed for each class of vehicles studied.   The following criteria
were used as the principal guidelines in  establishing the  vehicle performance
requirements upon which the power and torque requirements are based:
      1.    Vehicle performance must meet all specifications of the Air
            Pollution Control Office  (APCO), Environmental Protection
            Agency*
      2.    Vehicle performance must be adequate to meet the acceleration
            requirements  of emission driving cycles
      3.    Vehicle performance must be comparable to  that of present-day
            vehicles of the same class.
The  third criterion appears reasonable for at least first-generation hybrid
vehicles since they would  share  the roads with present vehicles.  Incorpora-
ting  hybrid vehicles having a significantly less performance capability than
conventional vehicles into  metropolitan traffic would probably not only
increase congestion but might also promote unsafe driving  conditions.  As
discussed  in Sections 5. 5  and 5. 6, the incorporation of high speed versions
of the intracity bus and delivery van is justified on the basis of  this criterion.
The  procedure used to  establish baseline vehicle performance requirements/
capabilities and to develop hybrid drive-train power  and  torque requirements
was  not the same  for each vehicle class.  Published  road test data were
used to  define the basic acceleration characteristics for  the family and
commuter  cars.   The unavailability of similar test data for the van and bus
made it necessary to use either manufacturer acceleration performance
  This agency was formerly designated as the National Air Pollution Control
  Administration.
                                   5-1

-------
calculations or to derive vehicle acceleration performance using vehicle
specification and engine performance data.  Hybrid drive-train power and
torque requirements were derived from the acceleration curves for each
vehicle.
Analysis of each emission driving cycle was performed to determine the
peak acceleration, peak power, and total energy requirements for vehicle
operation.   The results of these analyses were used as minimum  design
constraints for hybrid drive-train components.  Additional use  of emission
driving cycles and design driving cycles is discussed in Section 4.4 of this
report.
5. 2      SUMMARY OF VEHICLE SPECIFICATION
Section 3. 1 summarizes  the basic specifications that were used in establish-
ing power requirements for each  class  of vehicle.
5. 3      EMISSION DRIVING CYCLE  ANALYSIS
5. 3. 1    Objectives of Driving Cycle Analysis
The primary objective  of this work was to compute drive-train  output
requirements for vehicle emission driving  cycle combinations listed in
Table 5-1.
The low-speed delivery van and low-speed  bus emission cycles  were
developed using the basic velocity mode characteristics presented in Sec-
tion 3.  The development of an  emission cycle for the high-speed  bus  is
discussed in Section 5. 6. 4.  It  was not  necessary to derive separate cycles
for the high- and low-speed van (See Section 5. 5. 2).
A revised version of the  Department of Health,  Education,  and  Welfare
(DHEW)  cycle has recently been published (Ref. 5-3).  This new cycle
has peak acceleration requirements which are significantly lower than the
previous DHEW version.  The potential impact of the revised cycle on
vehicle performance requirements could not be  assessed due to the time
limitations on this study.
                                    5-2

-------
             Table 5-1.  Vehicle/Driving Cycle Combinations
       Vehicle Type          Weight, Ib







Family Car                    4,000




Family Car                    4,000




Commuter Car                 1,700




Delivery Van  (Low Speed)      7,000




Delivery Van  (High Speed)      7,000




High-speed Intracity Bus      30,000




Low-speed Intracity Bus       30,000
         Driving Cycle






DREW* (Ref.  5-1)




New York (Ref. 5-2)




DHEW




Van Emission Cycle




Van Emission Cycle




High-speed Bus Emission Cycle




Low-speed Bus Emission  Cycle
 DHEW - Department of Health, Education, and "Welfare
                                   5-3

-------
5. 3. 2    Results of Driving Cycle Analysis
A driving cycle analysis computer program was used to determine power,
energy,  and torque requirements for each vehicle.  Output from the program
included plots of:
      1.     Vehicle speed versus time
      2.     Vehicle acceleration versus time
      3.     Cumulative distance traveled versus time
      4.     Wheel horsepower versus time
      5.     Cumulative energy delivered to wheels versus time
      6.     Wheel torque versus time
      7.     Vehicle acceleration versus vehicle speed
      8.     Wheel horsepower versus vehicle speed
A set of  these plots for each vehicle/driving cycle combination is presented
in Appendix D.  A summary of the principal results is presented Ln
Table 5-2.
5. 4      HYBRID DRIVE-TRAIN POWER AND TORQUE REQUIRE-
         MENTS FOR THE FAMILY AND COMMUTER  CARS
5. 4. 1    Computational Procedure
The  following procedure was used to establish baseline vehicle performance
and to define drive train torque and power output requirements:
      1.    Acquire  speed-time  (maximum acceleration) curves and physical
            characteristics for  each class of conventional vehicles from
           published road test  results
      2.    Select reference speed-time curves from these data which define
            the required performance for each  class of hybrid vehicle
      3.     Use the reference acceleration curves to compute (a) accelera-
           tion versus speed, (b) power output (at the wheels) versus speed,
            (c) gradeability versus speed, and (d) required motor torque
           versus motor speed
     4.     Verify that the selected (reference) performance for  each hybrid
           vehicle is  adequate  to meet the performance specifications and
           the requirements of the DHEW driving cycle which was used for
           subsequent emission calculations
                                    5-4

-------
                     Table 5-2.  Summary of Vehicle Performance Requirements Derived
                                From Emission Driving Cycle Analysis
Ul
        Vehicle Type
        Commuter
        Family
        (Low and High
        Speed)


        Intracity Bus
Cycle
        Peak             Peak      Average      Total Energy at
Acceleration, mph/sec  Power, hp   Power, hp   Wheels, hp-hr/Cycle
DREW
DHEW
APCO
APCO
Aerospace
5
5
4
4
2.5
26
61
98
265
105
2.7
6.2
6.56
39
27
1.
2.
0.
0.
0.
03
34
17
39
28
                        Corporation

-------
 5. 4. 2   Vehicle Speed-Time Characteristics
 Figures 5-1 and 5-2 show speed-time curves for several makes of conven-
 tional cars  in the 4000-lb and  1700-lb classes, respectively.   The baseline
 curve for the family car •was selected to represent a performance inter-
 mediate between high and low  performance vehicles.
 The baseline speed-time curve shown in Fig. 5-2 for the commuter car was
 selected primarily to satisfy requirements of the DHEW driving cycle as
 discussed in the following section.
 5.4.3   Acceleration Performance
 An acceleration-speed relationship was obtained for each vehicle by
 graphically differentiating the results shown in Figs. 5-1 and 5-2.  The
 results  are plotted in Fig.  5-3.  Acceleration-time points computed from
 DHEW driving cycle data are also plotted in  Fig. 5-3.  These  results show
 that hybrid  powerplants sized on the basis of the reference performance
 curves will satisfy all points and are therefore capable of operating over
 the DHEW driving cycle.  Figure 5-3 also shows that the reference com-
 muter car curve has adequate  performance  for the DHEW cycle.
 5. 4. 4   Horsepower Requirements of Hybrid Drive Train
 The required wheel horsepower  that must be supplied by a hybrid drive
 train as  a function of vehicle speed,  weight,  and drag characteristics was
 derived from the reference plots  shown in Fig. 5-3.  The  instantaneous
 propulsive force required to accelerate a vehicle can be expressed as

      Fp(V)  = m*a(V) + 0. 002558 Cd AV2 + ^ (lO. 0 + *°° +  0-070V2 \
                                                                     (5-1)
where the acceleration, a, is expressed as a function of vehicle speed, and
 the first, second, and third terms on the right of the equation  represent
 the inertia, aerodynamic drag, and rolling resistance forces,  respectively.
 The rolling  resistance  is given in Ref.  5-4.
                                   5-6

-------
   120
100
80
Q_
CO
60
40
                                     o
                                o
                           o
                      o
20
    0
                                                ,BASELINE
                                                 (AEROSPACE)
                                                ROAD TEST DATA
                                                 4000 Ib CLASS
                                             O ASTON  MARTIN
                                             A FORD  FAIRMOUNT
                                             D RAMBLER, REBEL-6
                                                 3200 ib  CLASS
                                             • OPEL COMMODOR
                                             A TOYOTA CROWN
                                             • BMW-2000
                                                               I
     0
                  10
                           15
   20
TIME, sec
25
30
35
40
            Figure 5-1.  Speed Versus Time Curves for Family Cars

-------
          100
I
00
           80
         Q.
         E
        LU
        O_
        CO
           60
= 40
           20
           0
             0
                    BASELINE (AEROSPACE)
                                          D
            10
                              A
                              A
                                         O
                                D
                 ROAD TEST DATA
                MINI I275GT
                NSU SUPER PRINZ
                RELIANT REBEL 700 ESTATE
                VW 1500 (BUG)
                MORRIS  MINI
                HONDA 600
                                                         1
20      30      40      50
                TIME, sec
60
70
                                                                        -O
80
90
                     Figure 5-2.  Speed Versus Time Curves for Commuter Car

-------
o
h-
or
     -8
                                           jji[|jj|l|j{tffi{y|l!j[{jj|-j{| ijl|tj([jjji[!;i
                                           REFERENCE FAMILY CAR]
                                            AEROSPACE)
                                                           PREFERENCE COMMUTER CAR!;
                                                             (AEROSPACE)
                                                       DHEW ACCELERATION EVENT
       0
       Figure  5-3.
   16
32      40      48

 VELOCITY,  mph
Comparison of Vehicle Velocity - Acceleration Characteristics to
DHEW  Driving Cycle Requirements
                                               5-9

-------
The instantaneous horsepower during maximum acceleration can be
expressed by

                         HP(V) =  0.00267 F (V)V                     (5-2)

With the exception of the tire pressure, P, values of the parameters used to
numerically  evaluate Eqs.  (5-1) and (5-2) are presented in the vehicle
specifications.
The resulting equations  for each vehicle are
         Family Car:

              HP(V) = 0. 534 a(V) + 0. 106 V + 9. 88 x 10"5 V3          (5-3)

         Commuter  Car:

             HP(V)  =  0. 227 a(V) V + 0. 0455 V + 4.  83 x 10"5 V3        (5-4)

Cruise and maximum acceleration power requirements  at the wheels are
depicted in Figs. 5-4 and 5-5.
5. 4. 5    Gradeability Performance Requirements
The basic  specifications give a gradeability requirement for  each vehicle.
Gradeability is defined as the maximum grade on which a specific velocity
can be maintained.   Mathematically, it can be expressed by

                              F (V) - Fd(V)     m»
                      sme=^—w	=   w                   <5-5>
                                    5-10

-------
cr
o
o_
                                                     MAXIMUM
                                                     POSSIBLE
                                                     SPEED
         TOTAL  POWER
        (AT MAX. ACCELERATION)
                                    /—POWER TO ACHIEVE
                                       GRADEABILITY
                                   |   REQUIREMENT
                                                             80mph
                                                             CRUISE
                    CRUISE POWER
                    (ROLLING  RESISTANCE
                    PLUS AERODYNAMIC
                    DRAG )
20 —
     0
                                  40     50     60

                                    SPEED, mph
                Figure 5-4. Power Requirements for Family Car

-------
o:
                                                     MAXIMUM
                                                     POSSIBLE
                                                     SPEED
        TOTAL POWER
           (AT MAX. ACCELERATION)
                                POWER TO ACHIEVE
                                GRADEABILITY
                                REQUIREMENT
                                                             70 mph
                                                             CRUISE
            CRUISE POWER
               (ROLLING RESISTANCE
               PLUS AERODYNAMIC
               DRAG)
20 —
10 —
     0
                                 40     50     60
                                     SPEED,mph
              Figure 5-5.  Power Requirements for Commuter Car

-------
So that Lf a(V) is the maximum acceleration capability at any velocity, then 0
is  the gradeability at that velocity.  Substituting for mv and adjusting units
gives
                   sin6  =
Percent grade  is equal to 100 x tan 6.  The data in Fig. 5-3 were used to
obtain tan 0 as  a function of vehicle speed and the results for each vehicle
are shown  in Fig. 5-6.  It can be seen that both vehicles have a maximum
gradeability performarv.ce which  exceeds  the specification requirement.
Maximum gradeability is that which could be achieved with full power train
output.  It  is more than could be achieved using,  for example, only the
power output of the heat engine.  Output horsepower at  the wheels required to
achieve a certain gradeability  performance can be expressed as

                    HP =  0. 00267 [W sin 6 + F,(V)] V                (5-7)

The APCO gradeability specifications require output horsepowers of 61  hp
                                              i
and 21 hp for the family car and the commuter car, respectively.  Each of
these specifications is well below the maximum power  required for accelera-
tion performance.
5. 4. 6    Torque Requirements for the Electric Drive Motor
Torque requirements  for an electric drive motor  (assuming that the motor
is the only source of drive  torque) were obtained using the  relation

                        F  (V) R     R
                  Tm  = ~    -  =
                                    5-13

-------
  60
   50
  40
S30

-------
A driveline efficiency of 90 percent and a tire radius of 1. 1 ft was assumed
for the family and commuter  car.  Calculations were performed for gear
ratios of 1. 0, 2. 5, 5. 0, and  10.  In order to express torque as a function of
motor speed, n,  the  following expression was used:

                        " =              =  1Z.75VG                 ^-9)
The results are plotted in Figs.  5-7 and 5-8.
5. 5      HYBRID DRIVE -TRAIN POWER AND TORQUE REQUIRE-
         MENTS FOR THE DELIVERY VAN
5. 5. 1    Computational Procedure
The following procedure was  used to compute hybrid drive-train power and
torque requirements for the delivery van:
      1.     Compute tractive effort-speed relationship for a typical
            van using manufacturers' engine  performance and body data
      2.     Simulate vehicle acceleration and calculate wheel power,  wheel
            torque,  and gradeability performance
      3.     Compare calculated performance with APCO  specifications and
            emission cycle acceleration requirements
5. 5. 2    Acceleration and Gradeability Performance
Tractive effort versus speed  was computed using engine torque and trans-
mission data supplied by the manufacturer (Ref.  5-5).  It was found that the
following expression gives a good approximation of van tractive effort (i.e.,
propulsive force)

                      TE  =  2511. 8 - 46. IV + 0. 26 V2                  (5-10)

The coefficients  in  Eq. (5-10) were used as inputs for a vehicle performance
computer program  (Ref. 5-6) which was developed to determine  vehicle
speed, acceleration, drag force,  gradeability, and total output horsepower at
the  wheels  as a function  of time.
                                    5-15

-------
                  I   I   I
o
or
o
cc
o
i—
o
                        T
IT
                                   AT MAXIMUM ACCELERATION
            GEAR RATIO (DIRECT DRIVE)

             1.0
                 VEHICLE  WEIGHT-4000 Ib

                 ROLLING  RADIUS- 1.1 ft

                 DRIVELINE EFFICIENCY =90%
                                                V=80mph
                           V-75 mph>
    10
                  j	I
      10
I02                 I03

 MOTOR SPEED, rpm
   I04
          Figure 5-7.  Required Motor Torque for Family Car
                               5-16

-------
                  I   I   I
                       VEHICLE  WEIGHT--1700 Ib

                       ROLLING  RADIUS = Lift

                       ORIVELINE  EFFICIENCY = 90%
    I03
GEAR RATIO

  1.0
o
o:
o
or
o
             AT MAXIMUM  ACCELERATION
    10
                                    j	I
      10
             102
                           MOTOR SPEED, rpm
                                         V=70mph
I04
         Figure 5-8.  Required Motor Torque for Commuter Car
                               5-17

-------
 Table 5-3.   Summary of Body and Chassis Characteristics for a
             Delivery Van
I
h—•
00
Body
    Type
    Wheel Base
    Load  Length
    Body  Weight
    Frontal Area*
Chassis
    Manufacturer
    Engine Type
    Engine Displacement
    Rated Horsepower
    Transmission Type
    Gear  Ratios
    Axle Ratio
    Chassis Weight
Maximum Payload Weight
Maximum Loaded Vehicle Weight'
Approximate Maximum Speed
Forward Control
137 in.
12 ft
1675 Ib
46 ft2
Ford Motor Co.
6 Cylinder
240 in.3
150 at 4000 rpm
Three-speed Manual
3. 77,  1. 87, 1.0
4. 58
2900 Ib
3240 Ib
7815 Ib
70 mph
 *                                                      2
  Performance requirements based on frontal area of 42 ft
  A loaded weight of 7000 Ib was assumed for performance
  requirements calculations

-------
Acceleration performance of the delivery van is shown  in Fig.  5-9 and is
comparable to performance  of vans which have been in  use since 1965
(Refs. 5-7 and 5-8).  Basic  body and engine data for a typical van are sum-
marized in Table 5-3.  Results from Fig. 5-9 were used to obtain accelera-
tion and  gradeability versus  vehicle speed as shown in Figs.  5-10 and 5-11.
Figure 5-11 shows that van performance is more than adequate to meet the
APCO gradeability specification.  Also,  Table 5-4  shows that the accelera-
tion capability for both the low- and high-speed versions of the delivery van
is sufficient to meet the acceleration requirements  of a proposed delivery
van emissions driving cycle  presented in Appendix  D.   Therefore,  the  same
emission cycle could be used for both versions of the van.

           Table 5-4.  Comparison of Low-  and High-speed Van
                      Acceleration Performance and Emission
                      Driving Cycle Acceleration Requirements

         Velocity Mode, mph              Time, sec
                                 Proposed  Cycle     Calculated
                                   Requirement     Performance

                0-16                  4               3. 5
               16-32                  4               3. 5

The performance of the low- and high-speed vans is based on the same
vehicle-engine combination.   It is assumed that,  for a conventional vehicle,
a governor would be used to  limit the rpm of the  engine in the low-speed
vehicle to a value consistent with a maximum vehicle speed of 40 mph.   The
maximum attainable velocity of the high-speed van was  found to be approxi-
mately 75 mph and was determined by plotting tractive effort versus  speed
and the sum of the  road resistance forces versus speed on the same graph.
Maximum vehicle speed is the point at which the curves cross.   The  75-mph
calculated maximum theoretical speed is consistent with a maximum speed
estimate of 70 mph for existing vans of similar size and weight.
                                   5-19

-------
ro
o
           100
            80
         E  60
         LU
         UJ
            40
            20
                                 MAXIMUM PERFORMANCE
                                (HIGHSPEED VAN)
                                 GOVERNED PERFORMANCE
                                (LOW SPEED VAN)
            0
                       I
                       I
              0
10
20
30
40     50
 TIME, sec
60
70
80
90
                     Figure 5-9. Speed Versus Time Curves for Delivery Van

-------
   8
CO
2 4

   0
                             DELIVERY VAN
             GOVERNOR LIMITED
           PERFORMANCE OF LOW
            SPEED DELIVERY VAN
                I
    0
10
20
30      40
 SPEED,  mph
50
60
70
       Figure 5-10.  Acceleration Performance Requirements for
                   Delivery Van
                               5-21

-------
   32
   28
   24
   20
§ 16
ct:
   12
    8
    0
     0
                              DELIVERY VAN
                              (HIGH SPEED)
APCO SPECIFICATION
FOR DELIVERY VAN
( LOW SPEED)
                                 \
        DELIVERY VAN -
   (GOVERNOR LIMITED-
          LOW SPEED)
                                    I
                  1
  10
20      30     40
        SPEED, mph
50
60
      Figure 5-11.
        Maximum Gradeability Performance of
        Delivery Van
                           5-22

-------
5. 5. 3    Hybrid Drive-Train Power and  Torque Requirements
The power that must be delivered to  the wheels in order to achieve the
acceleration performance presented  in Fig. 5-9 is shown in  Fig. 5-12.
The total power requirement is approximately the same for the low-  and
high-speed versions in the speed range  between 0 and 40 mph.
Electric motor torque requirements  are shown in Fig.  5-13.
5. 6      HYBRID DRIVE-TRAIN POWER AND TORQUE REQUIRE -
         MENTS FOR  INTRACITY BUS
5. 6. 1    Computation Procedure
The following procedures were used  to compute hybrid  drive-train power
and torque requirements  for the low- and high-speed versions  of the  intra-
city bus:
      1.     Computation Procedure for  Low-speed Bus
            a.    Use  APCO gradeability and maximum speed  specifications
                 and emission cycle accelerations to calculate tractive
                 effort/speed relationship
            b.    Using the tractive-effort/speed relationship as input to the
                 computer program, calculate acceleration, wheel horse-
                 power,  wheel torque,  and gradeability as a function of
                 vehicle speed
      2.     Computation Procedure for  High-speed Bus
            a.    Use  manufacturers' published speed-time data to calculate
                 vehicle acceleration as a function of speed
            b.    Using the results of the preceding  calculations,  calculate
                 wheel horsepower,  torque, and gradeability as a function of
                 speed,  and synthesize the exhaust-emission cycle
5. 6. 2    Acceleration  and Gradeability Performance
The  acceleration curves for  the low- and high-speed versions of an intracity
bus are shown in Fig.  5-14.  Only guidelines (1) and (2) discussed  in Section
5. 1 were used to estimate the  required performance for the  low speed bus
                                   5-23

-------
   120
  100
   80
CC.
UJ
^
o
Q_
60
   40
   20
    0
     0
           TOTAL POWER
           (AT MAXIMUM
          ACCELERATION)
                                 • GOVERNER
                                 I LIMITED POWER
                               (LOW SPEED VAN)
         — POWER REQUIRED TO
            OVERCOME GRADE
            (20%AT8mph)
                                                       MAXIMUM SPEED
                                                   65 mph CRUISE
                                           CRUISE POWER
                                           (ROLLING RESISTANCE
                                           PLUS AERODYNAMIC DRAG)
               40 mph CRUISE
         10
20
30     40      50
        SPEED, mph
60
70
80
90
              Figure 5-12. Power Requirements for Delivery Van

-------
            i      i    r
         GEAR RATIO (G)
           1.0
                                                        I   I   I
                                    V=40mph
                                          = 70mph
-Q
 i
o
cr
cc
o
       _   5.0
           10.0
                                                 V=
    10'
    10
      10
           20.0
               VEHICLE WEIGHT--7000Ib
               ROLLING RADIUS = 1.68ft
               DRIVE TRAIN EFFICIENCY =90%
                                                  '=40mph


                                            V=70mDfiVV--40mph
              GOVERNOR LIMITED MOTOR
              SPEED LIMIT FOR  G=I.O
                 J   i  I
                                   i
5.0   10.0   20.0  -\

  t     1     \
  f i    T i   ifi
                                                               10
                            MOTOR SPEED, rpm
         Figure 5-13.
                      Electric Motor Torque Requirements for
                      Delivery Van
                               5-25

-------
ro
                                                        LOW SPEED BUS
HIGH SPEED BUS
                                             60        80
                                               TIME, sec
                       Figure 5-14.  Speed Versus Time Curves for Intracity Bus

-------
because data obtained from transportation agencies  indicate that the vast
majority of vehicles in use today have a maximum speed capability in excess
of 40 mph (Refs. 5-9  and 5-10).  The acceleration  curve for the low-speed
bus was derived by first estimating the tractive force required to  (a) satisfy
the APCO gradeability specification (20 percent grade at 6 mph),  (b) provide
the acceleration required by a proposed low-speed bus driving cycle in the
speed ranges 0-19. 2 mph and 19. 2-25. 6 mph, and (c) cruise at a constant
speed of 40 mph.  The lower boundary envelope of these tractive effort-
speed points was then fitted to a quadratic function using the least-square
fitting technique.  The expression  that resulted  is
                         TE  =  7234 -  85V -1.2V
(5-11
The above  coefficients -were used as input to a computer program (Ref.  5-6)
and velocity, acceleration, gradeability, wheel power, wheel torque, and
load resistance forces were computed as a function of time.  Acceleration
and gradeability performance for the  low-speed bus are shown in Figs.  5-15
and 5-16, respectively.  A comparison  of the acceleration  rates in
Table 5-5 verifies that the proposed low-speed bus has an acceleration
capability sufficient to meet emission driving cycle requirements.

     Table 5-5.  Comparison of Intracity Bus Acceleration Capability
                 with Emission Driving Cycle Acceleration
                 Requirements
Driving Cycle Requirement
Velocity Mode,
mph
0 - 19. 2
19. 2-25.6
Time,
sec
6
2
Maximum Performance Capability
Low-speed Bus
Velocity Mode,
mph
0 - 19.3
19. 3 - 25. 5
Time,
sec
5
2
High-speed Bus
Velocity Mode,
mph
0 - 12
12 - 15
Time,
sec
5
2
                                   5-27

-------
I
ro
oo
               5
                                                    	EXTRAPOLATED
        LOW SPEED
           BUS
                        10
20
30
40      50
 SPEED, mph
60
70
80
90
                 Figure 5-15.  Acceleration Performance Requirements for Intracity Bus

-------
  24
  20
   16
cr 19
CD IC
O

-------
The acceleration curve for the high-speed bus shown  in Fig.  5-14 is typical
of the performance of buses currently in operation in Los Angeles  and
Chicago (Refs. 5-9  and 5-10).   Technical specifications supplied by the
manufacturers are listed in Table 5-6.

               Table 5-6.   Specifications for High-speed Bus

    Engine Type                       Diesel
        Manufacturer and Model No.     Cummins,  V8-265 (special)
        Displacement                   785 in.
        Rated Horsepower               210 hp
    Torque Converter                 Spicer 184-A
    Axle Ratio                         4. 625
    Rolling Radius                     1.68ft
    Curb Weight                       22,600 Ib
    51  Passenger + Driver             7,800 Ib
    Maximum Loaded Weight*          30,400 Ib
      30,000-lb loaded weight was used in the performance calculations.

Table 5-5 also shows that a typical high-speed bus does not have the accelera-
tion capability to meet bus  driving cycle  requirements.  Therefore, it was
necessary  to synthesize a new cycle for the high-speed bus  (See Section  5. 6. 4]
A graphical procedure was used to determine the variation  of acceleration
with speed using the data from Fig. 5-14 for the high-speed bus and the
results  are shown in Fig.  5-15.  Since the data shown in Fig. 5-14 do not
show  a limiting  speed,  it was necessary  to extrapolate the acceleration-
speed curve to zero slope to obtain an estimate of the  maximum speed.
The zero acceleration point,  i. e.,  maximum speed point, is approximately
67 mph.  The gradeability-speed relationship for the high-speed bus  is
shown in Fig. 5-16.
                                   5-30

-------
5. 6. 3    Hybrid Drive-Train Power and Torque Requirements
Hybrid engine drive-train power requirements for the low- and high-speed
versions of the intracity bus are presented in Fig. 5-17.  The total power
curve of the low-speed bus peaks at approximately 295 hp and this peak
stems directly from the acceleration requirements imposed by the bus
driving cycle (See Table 5-5).  For the high-speed bus,  the following rela-
tionship was derived to express instantaneous wheel horsepower as a func-
tion of vehicle speed

               HP(V) = 4. 01a(V)V + 0.8V + 5. 58xlO"4V3          (5-12)

A plot of the above expression is also shown in Fig.  5-17.  The maximum
practical speed was considered to be 60 mph for this study so that the peak
power output of a hybrid drive train for  the high-speed bus is approximately
230 hp.   The power requirement for steady cruise, however, is only 170 hp.
Torque curves  for  the low-speed bus are presented in Fig. 5-18 and similar
data for the high-speed bus  are presented in Fig.  5-19.   Torque-motor speed
relationship was computed using Eqs. (5-8) and (5-9) for a rolling radius of
1.68 ft, drive line  efficiency of 90  percent,  and gear ratios of 1,  5,  10, and
20.
5.6.4    Emission  Driving Cycle for High-speed Bus
Because  of  reasons discussed  in Section 5. 6. 2, an emission  driving cycle
was  developed for the high-speed bus. This cycle was used for subsequent
exhaust emission calculations.  The cycle •was designed on the basis of the
following criteria:
      1.     Cycle acceleration requirements must be compatible  with bus
            performance
     2.     Distance traveled in each velocity mode  must be  approximately
            equal to the respective distances in the low-speed bus cycle
     3.     Rest time must be the same as  that for low-speed bus cycle
                                    5-31

-------
OJ
tSJ
         CCL
            350
           300
            250
           200
            150
            100
             50
              0
               0
                     TOTAL POWER LOW SPEED BUS
                     (AT MAX. ACCELERATION)
    TOTAL POWER
    HIGH SPEED BUS
    (AT MAX. ACCEL)
                          40 mph CRUISE
                                   I       I       I      I

                                 GRADEABILITY REQUIREMENT
                                 FOR LOW SPEED BUS
                                 GRADEABILITY  REQUIREMENT
                                 FOR'HIGH SPEED  BUS
   MAX. SPEED
   HIGH SPEED BUS
                                                             60 mph CRUISE
                                   CRUISE POWER
                                   ( ROLLING RESISTANCE
                                    PLUS AERODYNAMIC DRAG)
                            MAX. SPEED
                            LOW SPEED BUS
                                                 I
              1
10      20     30     40     50     60
                       SPEED, mph
70
80     90
100
                       Figure 5-17.  Power Requirements for Intracity Bus

-------
    10"
          GEAR RATIO

            1.0
    10
.0

 I
O
cr
o
cc
o
      10
                  I    I  1
                                 VEHICLE WEIGHT--30,000Ib

                                 DRIVE LINE EFFICIENCY = 90%

                                 ROLLING RADIUS = 1.68 ft
                                      = 40mph
                                                        = 40mph
                          2
  I0
                         MOTOR SPEED, rpm
10'
         Figure 5-18.
Electric Motor Torque Requirements for

Low-speed Intracity Bus
                                5-33

-------
                      \  I
    10'
           GEAR RATIO
              1.0
o
cc
o

or
o
o
                            VEHICLE  WEIGHT - 30,000 Ib
                            ROLLING  RADIUS = 1.68ft
                            DRIVE  LINE EFFICIENCY =90%
    10'
       10
                  i    i  i
V=60mph
                                                   V=60mph   _
                                                         -GOmph
                         MOTOR SPEED, rpm
         Figure 5-19.  Electric Motor Torque Requirements  i'or
                      High-speed Intracity Bus
                                5-34

-------
Adoption of the second criterion means that both buses can be compared
over the same route, I.e.,  distance between stops is the same for both
cycles.  The two driving cycles are compared in Table 5-7.

         Table 5-7.   Comparison of Intracity Bus  Emission Cycles
Low-speed Bus
Velocity Mode,
mph
0 - 19. 2
19.2
19. 2 - 25. 6
25. 6
25. 6 - 0
0
Total
Time,
sec
6. 0
4. 0'
2. 0
3. 0
8. 0
13. 0
36
Distance,
ft
99
112
71
112
132
0
526
High-speed Bus
Velocity Mode,
mph
0 - 16.2
16. 2
16. 2-20
20
20-0
0
Time,
sec
8.0
4. 7
3. 0
3.8
9.0
13. 0
41. 5
Distance,
ft
99
112
71
112
132
0
526
Effective Speed = 10 mph
Distance Between Stops  = 0. 1 mile
Effective Speed  = 8. 6 mph
Distance Between Stops  =  0. 1 mile
Braking time for the high-speed bus cycle is based on a constant braking
rate of 2.2 mph/sec.
                                   5-35

-------
5.7    REFERENCES
5-1.   "DHEW Urban Dynamometer  Driving Schedule, " Federal Register,
       vol. 35,  no.  136,  pp.  11357-11359, 15 July 1970.

5-2.   J. T.  Higgins,  New York City Traffic,  Driver Habit and Vehicle
       Emissions Study,  Scott Research Laboratories, 1  June 1969.

5-3.   Federal Register, vol. 35, no.  219, pp.  17311-17312, 10 November
       1970.

5-4.   S. F.  Hoerner, Aerodynamic  Drag,  Otterbein Press,  Dayton,  Ohio,
       Chapter  12, p. 7, 1965.

5-5.   D.  Maiolfi, Ira Escobar Ford,  Inc., Los Angeles, California,
       Personal Communication, June 1970.

5-6.   H. T.  Sampson, Development of a Computer Program for  Vehicle
       Performance  Prediction (To be Published as an Aerospace Report).

5-7.   R.  Ewbank, J. B. E. Olson Company,  Personal Communication,
       June  1970.

5-8.   D.  Helland, United Parcel Service, Personal Communication,
       June  1970.

5-9.   G. W. Heinle, Southern California Rapid  Transit District (SCRTD),
       Personal Communication, February 1970.

5-10.  J. Burgeson,  Chicago Trans it Author ity  (CTA), Personal Com-
       munication, June  1970.
                                  5-36

-------
                  SECTION 6

ELECTRICAL SYSTEM - MOTOR, GENERATOR,
           AND CONTROL SYSTEM

-------
                               CONTENTS
6.     ELECTRICAL SYSTEM - MOTOR, GENERATOR,
      AND CONTROL SYSTEM	    6-1

      6. 1   Introduction	    6-1

      6. 2   Systems Synthesis   	    6-1

      6. 3   Subsystem Technology	    6-6

           6. 3. 1    Motor Characteristics and Control	    6-6

                    6. 3. 1. 1    Near Term Motor Application -
                               1972 to 1975  	    6-11

                    6. 3. 1.2    Long Term Motor Application -
                               Beyond 1975	    6-22

           6.3.2    Generator Characteristics and Control	    6-22

      6.4   Subsystem Evaluation and Comparison	    6-24

           6.4.1    Electric Drive Motor Systems	    6-24

                    6.4. 1. 1    Operating Characteristics
                               Compared	    6-29

                    6.4. 1.2    Control System Complexity
                               and Cost	    6-30

                    6.4. 1.3    Motor Size and Comparison of
                               Operating Limits	    6-32

           6.4.2    Method of Sizing of Motor and Generator ....    6-36

      6.5   Design Goals	    6-39

      6.6   Recommended Subsystem Development	    6-41

      6. 7   References	    6-42

      6.8   Bibliography	    6-44
                                   6-i

-------
                                TABLES
6-1.  Comparison of Motor  Controllers	     6-9

6-2.  Standard Ventilation for DC Motors and Manufacturers
      Data Points	     6-35

6-3.  DC Electric Motor Weights  (Including Forced Air
      Cooling)	     6-39
                                   6-ii

-------
                                FIGURES



6-1.     Electrical Control Schematic, Series Configuration  ....    6-2

6-2.     Single Motor  Parallel Configuration	    6-2

6-3.     Single Motor  Parallel Configuration Concept - Variable
         Velocity Heat Engine with In-Line Augmenting Electric
         Motor/Generator  	    6-3

6-4.     Dual-Motor Parallel Configuration Concept	    6-3

6-5.     Separately Excited DC Motor with Step Voltage Control . .    6-8

6-6.     Series Motor Controller  	    6-12

6-7.     Cost of High Current Rating SCRs
         1970 Catalogue Prices in Quantities of  1000	    6-13

6-8.     Separately Excited Field Motor  Controller	    6-15

6-9.     Typical DC Motor Efficiency	    6-16

6-10.    Separately Excited Motor  Controlled by Field
         Control and Chopper	    6-17

6-11.    Torque and Efficiency Characteristics  of Separately
         Excited DC Motor	    6-18

6-12.    Performance Characteristics  -  Separately Excited  DC
         Motor (I) and Series  DC Motor (II)	    6-21

6-13.    Weight Comparison for  Electric  Motors with
         Overload Capability	    6-23

6-14.    Generator Efficiency	    6-25

6-15.    Generator Efficiency, AC (Calculated  Data)	    6-26

6-16.    Weight Comparison for  Electric  Generators Not
         Designed for  Overload	    6-27

6-17.    Generator Controller	    6-28

6-18.    Typical Power Density  vs Maximum Efficiency,  DC
         Motors - Family and Commuter  Cars	    6-38

6-19.    Typical Density  vs Horsepower,  DC Motors Including
         Forced Air Cooling - Family and Commuter Cars	    6-38


                                   6- iii

-------
                               SECTION 6
            ELECTRICAL SYSTEM -  MOTOR,  GENERATOR,
                         AND CONTROL SYSTEM
6. 1          INTRODUCTION
The  electrical system is composed of the electric traction motor, generator,
control system, and batteries.   Batteries are discussed in Section 7,  but the
remainder of the items will be  treated here.  First, the electrical system
parameters or characteristics  that have the greatest impact on the total
system are considered.   Next,  details of the advantages and disadvantages
of various approaches are summarized, and, finally,  development efforts
are recommended.
6.2          SYSTEMS SYNTHESIS
There are many different design approaches to the development of an elec-
trical system for the hybrid vehicle.  The series  versus the parallel power-
train configuration is a major division of the concepts.  One form of the
series configuration is shown in Fig.  6-1, in which all of the energy of the
heat engine flows through the generator and the motor to the wheels.  Part of
the energy used for peak power requirements flows through the battery.
The battery is then recharged during  cruise  and its energy utilized for
starting and acceleration.  In Figs. 6-2,  6-3,  and 6-4,  three different
design approaches  are shown for the parallel configuration.  The first two
have been built and tested with varying degrees of success.  In addition,  the
electric motor, battery,  and control system portions of the third approach
have been built and tested in a prototype wheelchair propulsion system.
Figure 6-2  is  a block diagram similar to the TRW parallel configuration.
The power from the heat engine is transferred to  a planetary differential
gearing arrangement,  which transmits a portion of the energy directly to the
wheels.  The remainder, not required for propulsion,  is converted  to elec-
trical energy  in the generator and  stored in the battery.  During periods of
                                   6-1

-------


HEAT
ENGINE


f]
J
FIELD
CONTROL
i"
ALTERNATOR
RECTIFIER
*'-' *
(.
<.
c
(_
(.
(v (v r\ r\ r\ r

^
7
•>
J
fo

BATTERY

POWER
CONDITIONER


Lr\o^
NJ \J X


MOTDD
n\\J 1 \jn






vA/urn
WnLtL
             MECHANICAL POWER
            -ELECTRICAL POWER
             SENSING OR CONTROL
              Figure 6-1.
Electrical Control Schematic,
Series Configuration
r~
r—
L

HEAT
ENGINE

FIELD
CONTROL

'• .


PLANETARY
DIFFERENTIAL
•^
_^>
ALTERNATOR/
RECTIFIER
t Iq <



1

MOTOR/
GENERATOR
; '
POWER
CONDITIONER*
L

?
POWER
CONDITIONER
L-^/O^^xi^x,^^
>

n
g^
=



•



A
i! WIILLL


— MECHANICAL POWER
                               BATTERY
                        	SENSING OR CONTROL
rMAY BE OMITTED IF ALTERNATOR FIELD CONTROL  COVERS  VELOCITY  RANGE
            Figure 6-2.  Single Motor Parallel Configuration
                                   6-2

-------
HEAT
ENGINE

! r
FIELD
CONTROL



• — •
i
MOTOR/
GENERATOR
j $
"4
BATTERY
t TRAN^MI^ION

. MFPHAIMIP/!
S\ f\ f* r TC>IA»A
• -V V V C.LLI 1 mv,M
	 ccMCiMr. n


WHEELS
iL POWER
L POWER
a rnMTDni
                                   MOTOR/GENERATOR OVERLOAD RATED FOR
                                   DEMAND LESS HEAT ENGINE POWER
         Figure  6-3.
Single Motor Parallel Configuration Concept -
Variable Velocity Heat Engine with In-Line
Augmenting Electric Motor/Generator
FIELD
CONTROL

HEAT
ENGINE

- — i
•li
! u-
i


BATTERY
--•$
MOTOR/
GENERATOR
No. 1




REDUCING
PLANETARY
DIFFERENTIAL
1:1 4il 1!1
1


Ł«--
MOTOR/
GENERATOR
No. 2
OUTPUT
SHAFT
i
WHEELS

	MECHANICAL POWER
J\AP ELECTRICAL  POWER
	 SENSING OR CONTROL
      EACH MOTOR/GENERATOR OVERLOAD RATED FOR
      1/2 DEMAND LESS HEAT ENGINE POWER
                                                                     FIELD
                                                                    CONTROL

           Figure 6-4.  Dual-Motor Parallel Configuration Concept
                                     6-3

-------
start and acceleration,  power is drawn from the battery for the motor/
generator to help the heat engine drive the wheels.   During deceleration,
the motor/generator becomes a generator and feeds energy back into the
battery.  At low vehicle speeds,  the heat engine operates at very nearly
constant power  and speed.   For more details, see Ref. 6-3.
In Fig.  6-3 (Refs.  6-1 and 6-2),  the Minicar approach to a parallel system
design is shown.  It also has a direct drive to the wheels but not through a
differential.  The motor/generator is mounted on the same shaft as the
heat engine, with its rotor a part of the drive  shaft.   During periods of
start and acceleration,  the motor/generator acts as a motor and assists
the heat engine  in driving the wheels.  During cruising and deceleration,
the motor/generator operates as a generator and feeds energy back into
the battery.  Gear shifting is required and the heat engine must operate at
variable speed and power output.
Figure  6-4  is a dual motor concept that has  interesting possibilities.   One
form of this system was developed by Electric Motion Control Corporation
as a completely electrical drive  for wheelchairs, fork lift trucks,  golf carts,
etc.  Portions of the system are proprietary pending patent agreements, so
it cannot be discussed in complete detail.  However,  suffice to say that each
motor/generator can and does help drive the wheels under heavy loading
situations,  such as  start and acceleration.   Electric  Motion Control Corpo-
ration states that the control system complexity is considerably reduced
when compared to other parallel configurations.
In summary,  it can be said  that the electric motors  can  be smaller in  the
parallel configuration than in the series configuration, due to the fact that
they are used only during peak loading situations.  The parallel arrangement
appears  to have the potential of greater efficiency because a large  portion
of the energy does not flow through the lossy electrical system but is
channeled directly to the wheels.  The principal loss is friction in  the
mechanical system, and the  electrical loss is reduced below the series
configuration of Fig. 6-1.
                                    6-4

-------
Another major division in design concepts  is the AC versus  DC motor approach.
The AC motors are smaller, lighter, and easier to cool, but they require a
variable-frequency power supply that must be derived from  DC power if a
storage battery is to be used in the system.  If an AC generator is used in
the system, regardless of the type of motor used,  rectification of this power
source is necessary for recharging the battery.
The AC power can  be made available by passing battery power through an
inverter.   Either induction or synchronous motors can be used,  and being
considerably smaller than equal-power-output DC machines, they are more
easily adaptable to mounting as a part of the wheel assembly.
If  DC motors  are utilized, a decision must be made relative to the field con-
figurations, that is, the manner of separately exciting the main field current
and the relative benefits derived from compensating and  interpole windings.
The operating characteristics must be analyzed to determine specific design
details affecting overall efficiency, weight, size,  complexity, cost, develop-
ment-status,  etc.  Low-weight components are  important,  since  the  power
required to propel  the vehicle depends on its weight.
The selection of system voltage  is primarily based on the weights of  the
electrical components.  Higher voltages result in lower weights for distri-
bution wir ing,  motors, generators,  and controls.  For the commuter and
family cars, a 220-V system was  selected to limit currents so that they do
not exceed 500 amp.  For the bus  and van, a 440-V system  was recommended
to  supply higher power requirements and still not exceed 500 amp.  The
voltages  and currents  are based on the  case of the series powertrain configu-
ration where the motor provides total power to the wheels.  The motor under
consideration has active independent field control for meeting power  require-
ments over the entire  vehicle speed  range.  In the parallel powertrain con-
figuration, requirements are somewhat lower since this  motor will deliver
only acceleration power.
                                   6-5

-------
6. 3           SUBSYSTEM TECHNOLOGY
6. 3. 1         Motor Characteristics and Control
Designs for electric motor drive systems should have the following goals
for performance characteristics:
      a.    High starting torque
      b.    Sufficient accelerating torques over the  specified speed range
      c.    High overall operating efficiency
      d.    Simple,  inexpensive speed control
      e.    Simple,  inexpensive,  efficient regenerative braking
The  most common approach  to the design of electrically propelled vehicles
in the United  States has been to use DC series motors utilizing chopper
circuits for their control,  either pulse frequency or pulse duration.
Although this approach appears reasonable for  some classes of vehicles
and driving cycles, it is not  optimum for all types.  Hence,  this section
will  be  devoted to an analysis of the motor characteristics for a number of
different design approaches  that could be used for the hybrid vehicle electric
propulsion system.
The  motor-induced voltage varies with speed; it is very low  at zero speed  and
increases as  the motor  speed increases.  Exceeding this voltage results in
high currents leading to  overheating  of the motor.  The armature applied
voltage must  be varied to match the induced voltage of the motor at all  speeds.
This can be achieved in several ways:
      1.    Chopper circuit
      2.    Variable resistance in armature circuit
      3.    Step voltage  change and field control
The  chopper circuit provides an efficient means for transforming a fixed
battery voltage to a smoothly variable effective voltage matching the require-
ment of the motor  at all  speeds of operation and providing a  smoothly
variable speed.  Also, while the chopper sees a varying impedance: from tlie-
motor  (depending on motor speed), it presents  a relatively constant high
                                   6-6

-------
impedance to the battery when used with proper filtering elements.  This
allows the reduction of high current pulses  in the  battery.  The main dis-
advantage of the chopper is the high cost of the power switching components
and the associated control circuitry.  Also,  compared to pure DC control,
the chopper introduces losses due to high frequency operation.   This can be
partially reduced  by special motor design and adequate  filtering.
The use of variable resistance in the  armature circuit introduces high losses
associated with the voltage drop in the resistance, and is an  inefficient
method of voltage  control for a vehicle required to operate over a wide speed
range.
Motor voltage control can also be  achieved by step voltage  switching of the
battery cell groups from parallel to series as the vehicle speed is increased.
However, to provide  adequate voltage matching over a wide speed range
several stages of  voltage switching are required to obtain reasonable motor
efficiency and avoid excessive loading of the battery.  The  number of
switching steps may be reduced by combining field control  with voltage
switching.   This method  is schematically illustrated in  Fig.  6-5 showing
how voltage switching is  accomplished by speed sensing and relays (Ref.  6-10).
A comparison of operational characteristics utilizing the three types of con-
trollers are given in  Table 6-1.  Additional comparisons can be found in
Ref. 6-11 which discusses actual field testing of electric cars.
The general motor equation used  for the transformation of  electrical to
mechanical power in  the  computer study is

                                K =  IV/rN
                                   6-7

-------
c»
                                                                     RPM SENSOR
                                                                        AND
                                                                      ACTUATOR
                                                                   220/IIOV
                                                             TRICKLE
                                                             CHARGE
                                                               _=-SLI
                                                               -=-BATTERY
                                                                   24V
                                                                1
   DC
  'MOTOR  '
'ARMATURE
 ^  DC
 3 MOTOR
   FIELD
I
                              Figure 6-5.  Separately Excited DC Motor with Step
                                          Voltage Control

-------
                        Table  6-1.  Comparison of Motor Controllers
     Item
   DC Chopper
Variable Resistance
      Step Voltage
    with Field Control
Types  of Motor
Controlled
Velocity Range

Smoothness of
Velocity Change
Controller Protection
Controller Cost (1975)

Controller Efficiency


Special Sensors and
Control Logic

External Smoothing
Filter

Starting Torque


Velocity Stability
Torque at High Speed
All DC brush motors
Zero to maximum
speed

Very smooth


Solid state only -
circuit breakers
and fuses too slow

High

Medium


Complex


Heavy filter required


High but inefficient


Stable with shunt
motor, decreasing
with load on series
motor

High
All DC brush motors



Start only


Jumpy


Circuit breakers
and fuses sufficient


Low

Very low


Simple


Not required


Medium  and very
inefficient

Somewhat unstable
varying with load



Low.
Only separately excited,
stabilized or compound
wound

Wide  with three steps or
more

Initial jump 0-5 mph
then smooth

Circuit breakers and
fuses
Medium

High with controller logic


Complex


Not required


High with inefficient over -
excitation

Stable up to torque limit
Medium-limited by field
weakening ratio

-------
                 Table 6-1.   Comparison of Motor Controllers (Continued)
     Item
                                      DC Chopper
Variable Resistance
    Step  Voltage
 with Field Control
Power Conditioning
Character istics
                                   Modulation of full
                                   power used by motor
High switching currents
with much dissipation
With small signal field
control,  high  contactor
currents at switch closing
but zero contactor cur-
rents on switch opening'1"
I
>—'
o
 Before a change of armature voltage takes place,  the field is momentarily increased to the
 point where armature current reaches zero.   The feedback from the current sensor then
 allows the armature relay to open.  The  usual problem of interrupting DC current is thus
 avoided.

-------
where
         K  =  constant s 0. 142
         I   =  amperes
         V  =  volts
         T  =  torque in Ib-ft
         N  =  rpm
This equation is applicable to all types of motors, both AC and DC, but
does not include the efficiency of transformation of electrical into mechanical
power.  Efficiency was included in the computer program as a separate item.
6.3.1.1      Near  Term Motor Application -  1972 to 1975
6.3.1.1.1    DC Series Motor
For this application,  the DC series field motor  with chopper control is the
most  highly developed approach  (Fig. 6-6) attained in this country (Refs.  6-3
through 6-9).   It has  the advantage of a high starting torque and smooth
power control.
The main disadvantage of the chopper control is the present high cost of SCR's,
These costs have been coming down  in recent years, however,  and  can be
expected to continue to do  so.  A cost-versus-current rating for 300, 600,
and 1000 V SCR's,  given in 1970 catalogues for  quantities up to 1000 is
shown in Fig. 6-7.
Since starting current surges can be several times larger than the normal
cruising power, rather large current SCR ratings are  required.  The current
and voltage ratings of SCR's (allowing for safety factors) are  on the order of
1000 amp at 1000 V for the bus,  and 500  amp at 500 V for the family car
vehicles.   Thus, the  present catalogue cost of the power  SCR's is approxi-
mately $50 per SCR for the smaller  vehicles, and in the neighborhood of
$200 each for  the larger vehicles in  quantities of 1000.
                                   6-11

-------
ISOLATION  SWITCH
	o o	
                           CURRENT
                            SENSE
                         SCRi V
                                                ACCELERATOR
                                                                   SCR
                                                                A~ SCR;
                Figure 6-6.  Series Motor Controller

-------
   120
   100
   80
or
   60
   40
   20
    0
      0
200
  400        600
CONTINUOUS AMPERES
800
1000
            Figure 6-7.
        Cost of High Current Rating SCRs
        1970 Catalogue Prices in Quantities
        of 1000
                               6-13

-------
6.3.1.1.2   Separately Excited DC Motors
Separately excited field control (sometimes  called shunt field control)
combined with voltage  switching for DC motors was  investigated and appears
to have considerable advantage from the standpoint of cost.  Figure 6-8 is a
diagram of this approach.  The starting current can be  limited to safe  values
by the application of low voltage steps for  starting.
As normally used, a shunt field DC motor also has a few shortcomings, the
principal ones being low starting torque and limited  speed  control range.
It has many advantages, however,  such as good accelerating torque at  high
speed and high operating efficiency  (see Fig. 6-9).
A scheme where the advantages of both the series  and shunt motor can  be
realized is shown in Fig.  6-10.  In this scheme the armature is energized
from a  chopper and the field  is separately excited  through  a field controller.
The  armature and field current are  independent, thus, by proper control of
the field current, the high torque  characteristics of  the series motor at low
speeds  can be combined with the high efficiency of the shunt motor at high
speeds.   This scheme  offers the  following advantages and disadvantages:
      1.    During the  generating mode the induced voltage can be varied
            to match the battery voltage (except at very low speeds) so  as
            to improve the efficiency of charging the battery  and increase
            the effectiveness of electr ical  braking.
      2.    Compared  to the  series  motor, the field  current  is low thus
            minimizing the switching problems involved  in reversing the
            direction of motor  torque.
      3.    It has a more  complex and  costly control system when compared
            to the chopper -controlled DC series motor or when compared to
            step  voltage with field control  of the separately excited motor.
      4.    A larger size  external series choke is  required compared to
            other methods  of control.
Figure 6-11  illustrates the relationship of torque to speed for various values
of field excitation p, which is  defined as the ratio of armature current 1  to
                                                                      cL
field current I, (Ref. 6-10).  There  is an optimum value of |3 that will produce
                                    6-14

-------
                           t
                           •-
i
(—•
U1
ACCELERATOR
                     r
                   osc
                                             RDM
                               jrT
                                                 CURRENT

                                                  SENSE
        Figure 6-8.  Separately Excited Field Motor Controller

-------
                    0-7mph (START)
             SERIES CONFIGURATION
               WHEEL RADIUS   =  I ft
               GEAR RATIO     =10=1
               CONTINUOUS HP  =  60
             SEPARATELY  EXCITED VOLTAGE
             STEP AT 20mph
                                  NOTE: CHANGE IN SCALE
10
0
 0
                50     75     100    150

                RATED LOAD OUTPUT,  %


     Figure 6-9.  Typical DC Motor Efficiency
200    300
                     6-16

-------
I
t—1
-o
           CHOPPER a
            CONTROL
             CIRCUIT
  FIELD
CONTROL
j
Figure 6-10.  Separately Excited Motor Controlled by
             Field Control and Chopper

-------
00
              cx
              O
                          EFFICIENCY, %

                          TORQUE
j8  = IQ /If  =  VRf/R(
                                               SPEED, N
                       Figure 6-11. Torque and Efficiency Characteristics of Separately
                                   Excited DC Motor  (from Ref. 6-10).

-------
the maximum electrical efficiency of a separately excited machine at


any speed.  This optimum value P0 can be expressed as
Also, one finds that
                        T = (K/2ir)I If = (K/2nB)I
                                   a i         r  a
where
             T = torque


             K = constant
R   = armature resistance
 a

R,  = field resistance
and
where
                          E = KNIf = KNIa/p
      E  =  induced armature voltage


      N  =  rpm



Now it is seen that
                             V   - E = I R
                              D        a a
and
              2         2
       T  =  (V-P)/(2-rrKN )    (this is an approximation where the

                              I R  product is neglected)
where
                           V_  = applied voltage
                                   6-19

-------
From the above equation, it is evident that torque and speed can be
controlled by varying (3 (field excitation) and/or V_.  The curves in
Fig. 6-11 and the above equations neglect  the effect of friction, windage,
and core losses, which could be similar for series and separately excited
machines.  Figure 6-11 also shows efficiency versus speed for various
values of (3.   Over excitation reduces efficiency primarily due to the
increased field losses; however,  the increased excitation is required only
for starting and low-speed operation.  As  speed increases, the excitation
is reduced until, at rated speed,  normal excitation is applied and normal P_
efficiency is obtained.   Figure 6-12 presents test data taken from a series
motor  and a separately excited motor.  It  shows that for (3  = 1 the machines
are comparable.  Hence,  (3 can be increased to obtain better high-speed
performance  for the  separately excited motor.
6.3.1.1.3    AC Induction Motor /Inverter
Recently, a great deal of development work has been done in the area of AC
induction motors for the propulsion of vehicles by General Motors Research
Laboratories  and the U.S.  Army Equipment Research and Development
Center at Fort Belvoir, Virginia (Refs.  6-12,  6-13,  and 6-17).  The concept
involves an alternator driven by a gas turbine or other engine, and a
cycloconver ter  (variable -frequency ) driving induction motors  on the individual
wheels.   This concept was  developed primarily for high-traction vehicles
utilizing electric motors on each wheel.   One General Motors passenger car
concept uses an AC generator, a rectifier, a battery, and a var iable- frequency
inverter driving an AC induction motor.   For larger vehicles,  this approach
has merit, primarily due to the small lightweight motor.  The var iable -
frequency inverter is heavy,  relatively large,  and would be extremely complex
and expensive, however.  Induction motor weights on the order of 1. 1 Ib/hp
have been achieved with oil-cooled motors, and variable frequency inverters
have been built that weigh about 1. 7 Ib/peak hp using oil cooling (Ref. 6-17).
This could be reduced with more effective cooling.  Peak efficiency of the
motor and the inverter system is approximately 85 percent.  This corresponds
                                    6-20

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CO
cc.
o
Q±
o
   8
   0
                       TEST DATA FOR THESE CURVES WERE
                       TAKEN FROM TWO  l-hp 30-V
                       DC MOTORS, ONE SERIES WOUND AND
                       THE OTHER SEPARATELY  EXCITED
                                                n
       	TORQUE/SPEED CHARACTERISTICS
       	EFFICIENCY/SPEED CHARACTERISTICS
                                   80
                                   60
                                                             40 y
                                                             20
     0
1000
SPEED, rpm
2000
                                   0
    Figure 6-12. Performance Characteristics —Separately Excited DC
               Motor (I) and Series DC Motor (II) (see Ref. 6-10).
                                6-21

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to an efficiency of 91 percent for the  same motor driven by a sine wave
(Ref. 6-18).  If the weight of the oil-cooling system is added to  it,  the
motor and inverter system still weighs less than a DC motor and control
and is particularly advantageous for larger power requirements as shown
in Fig. 6-13.
At present this method is more  costly than previously mentioned approaches;
however, it may be  feasible for larger vehicles.
6.3. 1.2      Long Term Motor  Application - Beyond  1975
6. 3. 1. Z. 1   Synchronous Motors
Great advances have been made in the use of ceramic magnets for motor
applications in recent years.  Barium ferrite is used  in place of Alnico as a
permanent magnet material for  DC as well as AC synchronous motors.  This
material  is very cheap and economically magnetized,  and the new types  are
not easily demagnetized.  Permanent ceramic magnet synchronous AC motors
are feasible for electric  drives  for vehicles, although they are expected to
be heavier and more costly than induction  motors of the same size.  A
var iable-frequency inverter is  also required as the basic power controller.
This approach appears attractive for  large high-traction vehicles.
6.3.1.2.2   Brushless DC Motors
Brushless DC motors have been built in small sizes at great cost for limited
applications.  They  have been developed primarily for space vehicles where
brush-type motors •would not be suitable due to  the limited  life of the brushes
in the  vacuum environment.  Additional development and cost reduction could
make this type competitive with existing motors and provide the advantage
of longer  life (Ref. 6-14).
6.3.2        Generator Characteristics and Control
Both AC and DC generators have been highly developed for automotive and
aircraft applications, and considerable data exist on expected performance
except for those that operate at very high speeds, i. e.,  50,000 rpm and
                                    6-22

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  1400
  1200
  1000
~  800
   600
   400
   200
DC MOTOR + SCR CONTROLLER
t  COOLING SYSTEM
DC MOTOR t COOLING
SYSTEM
                          AC MOTOR + INVERTER
                          + COOLING SYSTEM
                      FAMILY CAR
                          REFS. 6-12,6-13,6-17,6-18
     0
      0
      50          100          150        200
            CONTINUOUS RATED POWER, hp
250
            Figure 6-13. Weight Comparison for Electric Motors
                       with Overload Capability

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above  (Refs. 6-15 and 6-16).  The efficiency of DC generators for  aircraft
runs on the order of 80 percent at full load and rated rpm ,  and about 90
percent for AC generators of equal weight.  For equal efficiency, the DC
generator  is heavier due to the added weight of commutation and, in  some
cases, interpole compensation.  Figure 6-14 gives efficiency curves for
AC and DC machines.  The numbers are nominal values and increased
efficiencies can be obtained by adding weight (iron and copper) to reduce
the losses.  Power  rectifiers  are required if AC  generators are used; how-
ever, the peak efficiency of these rectifiers is very high, exceeding  99
percent, and their weight and  size are very small.
Of great interest for the automotive application is the variation of efficiency
with the load and speed of the  machine.  Since the generator on a hybrid
vehicle operates at  part-load for a  large part of the time, part-load  efficiency
is very important.   The results of calculations of efficiency are  presented  in
Fig. 6-15.
Lastly, a weight comparison of AC and DC generators is shown in  Fig. 6-16.
Overall, it is clear  that the AC generator  has  distinct advantages over the
DC from the standpoint of efficiency and weight (and volume).  The use of AC
generators is recommended for all classes of  vehicles.
The problem of controlling the generator was analyzed and  it was found that
field excitation controlled by a switching transistor circuit would be  the least
costly,  simplest,  and most efficient method available today.  Efficiencies
of 99 percent or better can be achieved when controller losses are compared
to generator output  power.  The reason  is that in controlling the field,  only
a small portion of the generator output  power goes  through the regulator
circuitry.   Figure 6-17 is  a block diagram of a controller that could be used
for all sizes of vehicles.
6.4          SUBSYSTEM EVALUATION AND COMPARISON
6.4.1        Electric Drive Motor  Systems
A comparison of electric motor systems must include:
      a.      Operating character istics and suitability to demand requirements
      b.      Control system complexity and cost

                                   6-24

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   95
   85
>-"75
o
   65
   55
   45
            DC GENERATOR
     0
25
                         DATA SHOWN ARE FOR AIRCRAFT

                         APPLICATIONS WITH AC  AND DC

                         GENERATORS OF EQUAL WEIGHTS
                                     REFS. 6-19,6-20
 50        75

FULL LOAD, %
100
25
            Figure 6-14..  Generator Efficiency
                            6-25

-------
   100
    90
    80
    70
 -  60
>-
    50
    40
    30
    20
      0
                               RATED rpm
25       50      75
        FULL LOAD, %
100
       Figure 6-15. Generator Efficiency, AC
                   (Calculated Data)
                       6-26

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               10'
                                      I   I
                                           I     I   I
I
tVJ
            2 I0
10
                                                       DC
                                                                                   AC  -
                                                                  REFS. 6-15,6-16,6-19,6-20
                                                        FAMILY CAR
                                                           I T I    I
                                           10                        I02
                                        CONTINUOUS RATED POWER,  kW
                       Figure 6-16.  Weight Comparison for Electric Generators
                                    Not Designed for Overload

-------
                   CURRENT
                     SENSE
Figure 6-17.  Generator Controller
              6-28

-------
      c.    Operating limits  including:
            1.     Surge currents
            2.     Commutating current limit
            3.     Temperature rise limit
            4.     Velocity limit set by centripetal strength and commu-
                  tation speed
      d.    Power density (Ib/hp) and efficiency
      e.    Motor cost and availability
      f.     System weight
      g.    Reliability and maintainability
Series, separately excited,  compound and brushless DC motors as well as
AC induction types were evaluated on  the basis of the above mentioned
parameters.  Detailed explanations follow.
6.4.1.1     Operating Characteristics  Compared
The series-wound DC motor  is basically a torque demand system with
velocity as  a function of both applied voltage and  load (torque applied).  At a
given voltage,  a change in velocity will occur with a change of load.  At a
constant load,  the velocity will vary approximately in proportion to the
applied voltage.   Its  use is principally in applications requiring high starting
torque.
The separately excited DC motor  (shunt-wound but not necessarily shunt-
connected) is basically a velocity  demand  system.  With constant field exci-
tation,  torque demanded at a given velocity will automatically be met up to
the commutation limit.  It is used extensively in  industry where starting
loads are not high, but where relatively high constant speed is  required under
varying loads  (or at constant load).  Velocity can be widely varied, however,
by changing the applied voltage and/or by  changing the field excitation.
Velocity variation through "field weakening" in a standard motor is limited
to about 3:1; but in conjunction with changing the  applied voltage to the arma-
ture, this variation can be extended to a wider  speed range.
                                    6-29

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The  compound motor has both the series and shunt field windings to provide
the automatic high starting torque of the  series motor and high-speed
constant velocity with variable load that is characteristic of the  shunt motor.
A  small penalty of increased weight and increased complexity of the  control
system results from use of this motor.
The  torque motor is listed as a candidate where low-speed,  precise  velocity
control is important.   The large number of commutation segments and large
diameter yield a weight penalty that makes  it non-competitive at this time.
The  brushless DC motor is listed as a candidate but it is presently constrained
by cost and further  development required in the power ranges of the hybrid
vehicles.  To date,  it is known to have been built by Aeroflex Corporation
up to only 20 kW, but  present technology in SCR's makes this motor practical
for any size of vehicle. It is created essentially  from the  redesign of a
shunt motor by providing brushless commutation  with armature position
sensors driving SCR switches.  Its operation is thus  similar to that of the AC
synchronous motor  controlled with a variable-frequency feedback system.
The  AC  induction motor operating at a fixed frequency is not practical for
variable speed applications.  However, when driven by a variable frequency
inverter or  cycloconverter, torque-speed characteristics similar to  DC
motors can be obtained.  Controlled  slip mode of operation is described  in
Ref. 6-21.  The  induction motor has the  advantage in specific power  com-
pared to DC motors at the vehicle horsepower levels.  Its  overwhelming
utilization in industry and its simple construction make  it a strong contender
for future vehicles.
6.4.1.2     Control System Complexity and Cost
In  a  comparison trade-off of  the drive train,  it is very  important to also
include the costs and weight of the  control system.   In terms of performance
and versatility, the selection of an adequate control  system is as significant
as the selection of the  motor.  All of the contending  electric motors need
variable voltage applied.  Step voltage has been used by which multiple-pole
                                   6-30

-------
relays switch batteries from parallel to series  in steps.  This is undesirable
because:  velocity increments may prevent a vehicle from following another
vehicle at the same  velocity; the relays are constantly working under load,
thereby shortening their lives and producing some ozone from the arcs; and
the generator must  feed constantly changing voltage levels,  which complicates
its  control logic.
A step-voltage system augmented  by field control can be made more desirable
by using armature current sensing to provide feedback information for con-
trolling the field.  This would control current surges and the  corresponding
jerks.
A much improved variable-voltage system is being used more generally for
low-speed vehicles  whereby smoothly varying effective voltage may be applied
to the motor.  This  DC chopper system provides pulse frequency, pulse
width, or a combined pulse width and frequency modulation.   The result   is
smooth control of power supplied to the motor.  At present, the cost is high.
However, if industry has the incentive for high production levels, it is
estimated that at some period beyond 1975 the price  of the high-current,
high-voltage SCR should be reduced sufficiently to make it economically
viable.  But,  the SCR protection circuit and the current smoothing filters
will still remain as  significant cost factors.
Since the  forward voltage  drop of the high-current SCR is about 1 V, it can
be seen that at 500 amp,  0. 5 kW would  be lost in the SCR which represents
a heat dissipation problem.   The higher the maximum voltage of the system,
the lower the proportionate loss of the SCR controller  system at a given
motor power.
There is one other problem with the SCR effective voltage controller when
it is used with a series field winding.  The field magnetic material must be
laminated with higher permeance steels to prevent relatively high core
losses at the chopper  frequency.   An attempt to reduce motor losses by
decreasing the chopper frequency  can cause motor noise and vibration if
the size of the current smoothing filters is not allowed to increase.
                                   6-31

-------
A fully compensated motor has very low inductance in  the armature.   There-
fore, an external inductor filter is needed to smooth the motor current at
the chopper frequency.
Of greater complexity are the controllers  for the brushless DC and the AC
induction motors  since they must provide not only variable voltage but also
variable-frequency to the motor.  At present, three-phase, variable-
frequency and var iable-voltage inverters at  power levels associated with the
hybrid vehicles are very expensive, since they are complex (12 SCR's or
more are needed  with at  least six having high current ratings).  The voltage
control may be  incorporated into the  inverter or a separate chopper may be
used.
The  more complex and expensive controllers have not  yet been fully developed;
therefore, an engineering risk still appears  at this time.   Following is the
estimated order of increasing complexity and cost.
      a.    Step voltage, relay-operated controller
      b.    Step voltage augmented with field control and armature
            current sensing
      c.    Pulse-width modulation SCR chopper
      d.    Chopper with both frequency and pulse width modulation
      e.    SCR controller with position sensor for DC brushless  motor
      f.     Multiphase inverter with  variable frequency and voltage control.
6.4.  1. 3      Motor Size  and Comparison of  Operating  Limits
The  frame size of a motor  is determined by  several factors such as torque
and speed, thermal characteristics,  the type of motor, and the efficiency
required.  The  duty cycle of operation for which the motor is  designed is
also  an important factor  in determining the motor  size.  This provides the
weighting factor necessary to determine the  instantaneous and average loss
in the motor during the duty cycle for which  the motor  is used.  These data
combined with the thermal  characteristics of the motor can be used to
determine the motor temperature  under  various ambient conditions.
                                   6-32

-------
Generally speaking, the higher speed motors are lighter in weight, and less
expensive than low speed motors.   The implication  is that, other things
being equal,  higher speed motor should be chosen.  However, besides the
mechanical limitations there are other factors limiting the increased speed
such as poor commutation.
To prevent excessive  losses and brush wear, as well as flashover at weak
field, some form of compensation for armature reaction must be built into
the DC motor.   Variable pole-face air gaps and pole-face windings are
possible.   Interpoles, commutation segment resistance,  or  diodes have also
been used to reduce circulating currents and arcing.  For given operational
characteristics a fully compensated motor need weigh no more than its
uncompensated counterpart (Ref. 6-8), however,  it is more expensive.
For standard applications such as fan drive, pump drive,  etc., the horse-
power rating and size of the motors have been established over the years
and can be obtained from manufacturers.   The requirements imposed on
motors  suitable for electric drive are  new and different.  Considerable
research and manufacturing efforts are needed for developing and designing
motors  optimized for  such applications.  It is hoped that this report provides a
basis for further investigation.
6.4. 1.3. 1    Surge Current  Limit
Some small motors (under 2 hp) can tolerate the sudden application of full
voltage  if the motors are completely unloaded, since  the current surge is
for a short duration; but most DC motors would suffer catastrophic failure
under full load without an  armature current limiter.  In the  series power-
train configuration, the  electric motor is gear-linked directly to the wheels
and is thus required to start under  possibly heavy loads (up  to the traction
limit of the tires).   The current must therefore be limited to a value required
to provide the maximum low speed torque.   Due  to absence of brushes, the
AC induction motor is not as  susceptible to immediate damage under heavy
surge conditions.
                                   6-33

-------
All motors will need a device to disconnect them from the power source  in
the event of overload.  Remotely reset current cut-out relays, magnetic
trip circuit breakers,  magnetic blow-out arc extinguishers,  and redundant
fuses will have to be investigated further to determine the best means of
protection.
6.4.1.3.2    Commutating Current Limit
Once a DC motor starts turning, the  overload current is limited by the maxi-
mum amount  that the brushes can commutate to the bar segments.   A com-
pensated motor is  superior in this respect.
6.4.1.3.3    Thermal  Temperature Rise Limit
The type and  quality of insulating material constrains the temperature rise
capability.  The continuous duty rated current is established by the thermal
limit.   Overloads may be tolerated for short  durations at spaced intervals.
For example,  compensated DC motors are  usually capable of the following
at low speeds (Ref. 6-22):
      Rated Current,  %      Duration      Repeated Less Than
           800               0. 5 sec          1 per min
           550               5. 0 sec          1 per 5 min
           350               1. 0 min          1 per 20 min

These overload capabilities gradually decrease with increased velocity.  It is
significant that these overload torque values  (approximately proportional to
current) are not absolute  limits.  Therefore, acceleration frequently
repeated and  lasting less  than 1 min  allows 300 percent or more  overload
capability,  compared to the continuous rating.  In this study,  overload cur-
rent for acceleration was allowed to  reach three times the continuous current.
A cooling system increases the  load  ratings for  a motor  of given size,  since
considerable  heat losses can be transferred out,  with the monitor remaining
within the thermal rise limit.  If the  appropriate surfaces are coated black,
heat transfer  through radiation is  improved somewhat.  Conduction of heat to
                                    6-34

-------
the vehicle  frame is  desirable, but vibration-suppressing rubber  shock
mounts may impede conduction.  Convection transfer of heat remains the
method that can be well controlled and is very effective.
Future large motors for the buses may justify the use of cryogenic cooling,
such as liquid nitrogen, to provide higher power density.   The Fort Belvoir
Research Center is investigating this cooling system for large trucks and
off-the-road vehicles that use electric drive systems.
Currently,  it is practical to cool brush-type DC motors with forced-air
systems only.  Self-cooling is not effective at low speeds where considerable
loading occurs, and the windage loss becomes excessive at very high speeds.
Air vanes should be limited,  therefore,  to self-ventilated motors that operate
at only one  velocity.   Hence, for automotive vehicle applications, a forced-
air system, capable  of supplying sufficient cubic feet per minute at the
proper pressure,  is  a definite requirement.  Table 6-2 gives some current
data points  for the forced-air cooling systems of typical DC motors.
           Table 6-2.  Standard Ventilation for DC Motors and
                       Manufacturers Data Points
Efficiency Range,
%
90 up


75 to 80

Continuous Range,
hp
5 to 20
25 to 60
75 to 150
10
20
Forced Air ,
ft3/min
150
350
800
350
350
Static Pressure Drop,
in. HZO
1. 00
1. 25
1. 90
1. 00
6. 00
A recycling oil-cooled system can be used for large AC induction motors.
Since the  squirrel cage, or solid rotor,  can withstand extremely high temp-
eratures, the oil cooling is constrained to the wire-wound stator.  Such a
system allows a continuous power density capability to 1 Ib/hp.
                                   6-35

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6.4.1.3.4    Velocity Limit
Most motors  show a marked improvement of power density with higher
velocities.  Three factors constrain the application of very high rpm to DC
motors: the safe velocity beyond which there is danger of centrifugal forces
causing catastrophic failure,  such as pulling armature wires  out of their
slots; commutation speed; and the increase of power losses.  Core  losses
increase with motor speed.  This limits the highest speed for a given
efficiency of the motor.   Wind and friction  losses can be minimized by a
smooth armature surface and quality bearings.
The  AC motor can achieve much higher velocities since the solid or squirrel
cage  rotor can be built with greater centripetal strength,  and brush friction
is eliminated.
6. 4. 2        Method of Sizing of Motor and Generator
A trade-off can be made  between size and weight,  or between a motor that
meets a certain torque and  power requirement, and its efficiency.   The
weight of the  mounting frame  must be minimized  without compromising
structural rigidity.  Next, the weight of core material can be reduced by
using core stock that is more expensive but of higher  permeability.   If the
same core stock is used  but reduced in size, then there will be more core
losses for obtaining the same magnetic flux magnitude.  Another way to
save  weight is to reduce  the copper  cross section, which results in  more
copper  loss (I R).   Since  all this increased loss is in the form of heat, more
energy  is  required to operate the cooling system,  and  this results in still
less overall efficiency.
Power densities as low as 1 Ib/hp can be obtained with DC motors but with
such  low efficiency that it is impractical for continuous duty.   Figure 6-18
shows the relationship between efficiency and power density for DC  motors
currently available in the speed range of 4000 to 8000 rpm.
                                   6-36

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For  a given duty cycle,  a given speed/range,  and a given type of motor,
the weight in pounds per horsepower decreases with increase in horsepower
(Fig. 6-19).  Hence, at a given efficiency, a large motor will have better
power density.  The usual large motor thus provides greater efficiency as
well as  improved power density.  Unfortunately,  this advantage  is offset by
the part-load penalty in efficiency.  For  example,  the peak efficiency of a
certain  DC motor,  rated at 60 hp continuous duty,  is approximately 92 per-
cent (see Fig.  6-9).  However, when the part-load and high-speed efficiency
penalties were included and efficiency, velocity,  and load were integrated
throughout the  DHEW Driving Cycle, it was determined that the  average
efficiency is 80 percent.
In this study,  the weight and efficiency of the  DC motor for a given speed
range was determined from Figs. 6-18 and 6-19.   For example,  for the
series power train configuration for the family car,  the continuous power
rating is  61 hp..  This  corresponds to a power density of 6.4 Ib/hp deter-
mined from Fig. 6-19 and a corresponding motor weight of 390 Ib.  The
corresponding  efficiency determined from Fig. 6-18 is 92 percent.  These
data are applicable to  standard DC motors currently available in the range
of 4000  to 8000 rpm.  It is anticipated  that by improving motor  design  and
raising  the speed of operation that the  weight  can be reduced.
Based on the data of Fig. 6-16, the weight of  a 12,000 rpm alternator pro-
viding 51 kw is about 70 Ib.  Allowing a derating  factor of 15 percent for
possible variation in heat engine speed, the size  of the alternator required  is
80 Ib.   For the hybrid mode of operation, the  generator is released from
providing the acceleration power and no derating factor is necessary for
overload capability.
Figure  6-16 also presented data on high speed, low •weight generators that
have been developed for space vehicles.   These types of generators have
not been produced in large quantities.  If  a 20,000 rpm generator of this type
were used for the family car, the generator would  weight about 48 Ib.  High
speed generators are readily adaptable to turbine drive systems.  For spark
ignition engines, gearing would be required to match the engine to the gene-
rator.
                                   6-37

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     95
     90
     85
    80
    75
            BASED ON CONTINUOUS
            RATED POWER
SPEED RANGE
4000-8000 rpm
                           567
                       POWER DENSITY, Ib/hp
Figure 6-18.  Typical  Power Density vs Maximum Efficiency,
               DC Motors - Family and Commuter  Cars
   >-• 7
   h—
   l/>
   z
   UJ
   a
   en c
   o
   O-
                               SPEED RANGE
                               4000-8000 rpm
              20      40      60      80      100
                       CONTINUOUS RATED POWER, hp
                   120
140
   Figure 6-19.   Typical  Density vs Horsepower,  DC Motors
                   Including Forced Air  Cooling- Family and
                   Commuter  Cars
                                 6-38

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6.5
DESIGN GOALS
As  indicated,  AC and DC generators have been developed to a fairly high
degree for aircraft and automotive applications, and it is apparent that
little development work is required in this area.  The AC generator (with
rectifiers) is  preferred for the hybrid vehicle  because of higher efficiency,
lighter weight, and low cost.  Some effort should be expended, however,
to improve the part-load efficiency.
Electric motors,  on  the other hand, particularly DC motors,  have not been
developed to optimize efficiency, weight, size, and cost for vehicle propul-
sion.  It is believed that DC electric motors can be designed with higher
efficiencies and lighter weights than those on the market today, and with
equal reliability  and  lifetimes.  Reasonable weight and efficiency  goals,
which it  is expected can be achieved for the various classes of vehicles,
are tabulated  in Table 6-3 for the  series  configuration.   Efficiency can  be
traded off against motor weight as has been indicated in  Fig.  6-18.
                 Table 6-3.  DC Electric  Motor Weights
                             (Including Forced Air Cooling)
Vehicle,
hp
Commuter, Zl
Family, 61
Van
Low Speed, 30
High Speed, 80
Bus
Low Speed, 100
High Speed, 175
Weight,
Ib
160
390

180
430

870
1050
Power Density,
Ib/hp
7.6
6.4

6.0
5.4

8.7
6. 0
Maximum Efficiency,
%
92
92

92
94

94
94
                                  6-39

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For  a given design power level, the weight per unit horsepower can be
decreased if the efficiency is allowed to decrease.  Power densities of
from 5. 5 to 8 Ib/hp should be achievable at reasonable cost by merely
optimizing the design for the particular  application and utilizing lightweight
materials -whenever possible.  The efficiencies of these devices would range
between 90 and 94 percent at design load depending on the size of  the motor.
The  weight per unit of horsepower may be further reduced by the  use  of AC
motors, inverters,  and liquid cooling.   Part-load efficiency is also very
important because during a typical driving cycle, the motor operates  at
part-load most of the time.
It is further estimated that the efficiencies  of the controllers and  the motor
in the regenerative mode (with the motor acting as a generator when the
vehicle is decelerating) can be improved quite markedly,  thus  increasing
the  overall efficiency of  the vehicle.  The field power of the separately
excited motor  is typically 5 percent of full load power of the motor.  Since
the  controller  directly changes only the  field current,  its efficiency is thus
high when compared  to the total motor power being altered.  It appears
reasonable to believe that regenerative efficiencies on the order of between
25 and 40 percent should be achievable.   These values represent the com-
bined efficiencies of:  the drive motor acting as a generator, the battery
charge,  mechanical friction, and the effect of the driving cycle on battery
charge  acceptance.
Overall system efficiencies of the different parallel power train approaches
for  various  vehicles  and  driving cycles should be investigated to determine
which one will have the greatest possibilities for  high efficiency and low
pollution levels.  One such system,  not  analyzed in depth nor tested,  is the
one shown in Fig. 6-4.   It is recommended that this system be analyzed
and tested,  and then  compared with  the other two parallel systems as well
as with the series approach.  The parallel system is  most likely to achieve
higher efficiencies since a considerable portion of the energy does not pass
through the  generator, motor,  and battery,  thus  eliminating the attendant
1 o s s e s .
                                    6-40

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6. 6          RECOMMENDED SUBSYSTEM DEVELOPMENT

As already discussed in detail in this section,  certain areas require

further development effort in the electrical system (exclusive  of batteries;

which are covered in Section 7).  These efforts consist of the  following:

      a.    Develop lightweight, efficient DC motors optimized for
            efficiency and weight for the automotive application.
            Both shunt and series types are required.

      b.    Develop lightweight, efficient controllers for shunt motors.
            Very little development appears necessary in the area of
            series choppers.

      c.    Develop small and compact,  vehicle-borne logic and control
            circuits to optimize  electrical/heat engine performance.
            Inputs to the logic circuit would be generator current,
            battery charge current, motor armature  current,  engine
            speed, battery voltage, and accelerator pedal position.  Based
            on these inputs  the logic circuit would determine the desired
            optimum heat engine power setting.  Under these conditions,
            maximum utilization of energy available from regenerative
            braking could be achieved.

      d.    Investigate  the various parallel system approaches to the
            design of hybrid cars.  Two parallel concepts have been
            evaluated, the TRW  and Minicar types; however,  the  efficiency
            of a third type (Fig.  6-4) using  two motors requires further
            evaluation.   Two versions  of this configuration need to be
            investigated,  one using armature voltage and/or external
            excitation as a speed control mechanism,  and the  other using
            a proprietary scheme proposed by  Electric Motion Control
            Corporation of Pasadena,  California.

      e.    Determine and compare the efficiencies and heat rejection
            systems of DC and AC motors and  associated control systems,
            particularly for the large vehicles.

      f.     Compare in more detail the cost of various approaches.
                                   6-41

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6. 7       REFERENCES
6-1.      I. R. Barpal,  "Investigation of Feasibility of Hybrid and Advanced
          Power Trains, "  Minicars, Inc., report to  UMTA Contract
          PA-MTD-8,  30 September 1969.

6-2.      D.  Friedman,  "Hybrid Power Plant - Transition to  the Future,"
          Minicars,  Inc., International Electric Vehicle Symposium,
          5-7 November 1969,  Phoenix, Arizona.
                                              /
6-3.      G. H.  Gelb, N. A. Richardson, T. C. Wang, and B.  Herman,
          "An Electromechanical Transmission for Hybrid Vehicle Power
          Trains, " TRW Systems Group Paper No. 710235 presented SAE
          Automotive Engineering Congress,  Detroit,  Michigan,  11-15
          January 1971.

6-4.      B.  Berman,  "Battery Powered Regenerative SCR Drive, " Paper
          presented IEEE/IGA Conference, Detroit,  Michigan, 12-14
          October 1970.

6-5.      V.  Wouk, "Electronic Circuits for Speed Control and Braking, "
          Gulton Industries,  Inc.,  Paper presented Power Systems for
          Electric Vehicle Symposium, Columbia University,  New  York,
          N. Y.,  6-8  April  1967.

6-6.      V.  Wouk, "High  Efficiency, High Power, Load Insensitive DC
          Chopper for Electronic Automobile  Speed Control, "  Paper
          presented IEEE/IGA Conference, Detroit,  Michigan,  12-14
          October 1969.

6-7.      L.  Miller, POLYSPEDE  Traction Motor Controls,  Polyspede
          Electronics Corporation.

6-8.      K. M. Chirgwin and G. P.  Kalman, Electric Propulsion for  Short
          Haul Commercial Vehicles and City  Buses, The Garrett Corpora-
          tion, AiResearch Manufacturing  Company Division,  Los Angeles,
          Calif,  (undated).

6-9.      W. H. Koch and D. B. Frames, "Exper imental Electr ic Vehicles,"
          Ford Motor Company paper presented at International Electric
          Vehicle Symposium,  Electric Vehicle Council,  Phoenix,  Arizona,
          5-7 November 1969.

6-10.     S. M.  Bird and R. M. Harlen, "Variable Characteristic DC
          Machines," Proceedings  of the IEEE,  vol.  113, no.  11, 1966.
                                   6-42

-------
6-11.     Sir  Jon  M. G.  Samuel, "Enfield '465' - City Electric Car,"  Paper
          presented at International Electric Vehicle Symposium, Electric
          Vehicle Council,  Phoenix,  Arizona, 5-7 November 1969.

6-12.     D. J. Roesler and A. L. Jokl, "A Rationale for Electric Drive
          Trains for Heavy Duty Vehicles, " U.S. Army Mobility Equipment
          Research and Development  Center,  Fort  Belvoir,  Va.,  Paper
          No. 700732  presented SAE Conference, Milwaukee, Wisconsin,
          14-17 September  1970.

6-13.     D. J. Roesler,  Study of an Electrically Propelled,  High-Speed Air
          Cushion Amphibian, U.S. Army Mobility Equipment Research and
          Development Center,  Fort Belvoir,  Va.,  Report No.  1949
          (May 1969).

6-14.     R. D.  Thornton, Motors for Electric Vehicles,  Present and Future,
          The Massachusetts Institute of Technology,  Cambridge,  Mass.
          (undated).

6-15.     Space Power Systems, North Atlantic Treaty Organization Advisory
          Group for Aerospace  Research and Development (November 1969).

6-16.     A Study of Advanced Auxiliary Power Unit (APU) Systems, The
          Garrett Corporation,  AiResearch Manufacturing Company Division,
          Los Angeles,  Calif.,  Report No. WADDR-TR-60-626 (1 June I960)
          (ASTIA AD247200).

6-17.     P. D. Agarwal and I. M. Levy, "A High Performance  Electric Drive
          System," SAE Paper  670178, Automotive Engineering Congress,"
          9-13 January 1967, Detroit, Michigan.

6-18.     P. D. Agarwal, "The  GM High Performance AC Electric Drive
          System," IEEE Transactions on Power Apparatus  and Systems,
          Vol. PAS-88, No. 2,  February 1969.

6-19.     "Aircraft Electrical Power  Equipment, "  Bendix Aviation Corp.,
          Eatontown,  New Jersey.

6-20.     "Product Data,"  Lear Siegler, Inc.,  Power  Equipment Division,
          Cleveland, Ohio.

6-21.     J. T. Salihi,  "Simulation of Controlled Slip,  Variable  Speed
          Induction Motor Drive Systems," IEEE Transactions  on Industry
          and General Applications, Vol.  IGA-5, No.  21, March/April 1969.

6-22.     A.  Kusko,  "Solid State DC Motor Drives," MIT Press, 1969,
          Cambridge, Mass.
                                   6-43

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6.8       BIBLIOGRAPHY
Agarwal, P. D.,  "The CM High-Performance  Induction Motor Drive System,"
          IEEE Transactions  on Power Apparatus and Systems, vol.  PAS-88,
          no. 2, February 1968.

Agarwal, P.O., R.  Mooney,  and R. Toepel, "STIR-LEC 1,  a Stirling Elec-
          tric Hybrid Car," General Motors Research Laboratories Paper
          No.  690074 presented SAE Conference, 13-17 January 1969.

Electric Control and Transmission Systems from the  Automobile and Air
          Pollution, Part II (Clearinghouse for Federal and Scientific Infor-
          mation,  Department of Commerce, Springfield, Va.,  December
          1967).

Friedman, Donald,  "An Electric Automobile Power Plant Survey, " General
          Motors Corporation paper presented IEEE Conference,  18-22
          March 1968.

Gelb, G.H.,  N. A.  Richardson, T. C. Wang,  andR.S.  DeWolf,  Design and
          Performance Characteristics of a Hybrid Vehicle Power  Train,
          TRW Systems Group, Redondo  Beach, California.

George, J.H.B.,  L. J. Stratton, and R. G. Acton, Prospects  for Electric
          Vehicles, Arthur D. Little, Inc., Cambridge,  Mass., Report No.
          C-69260 (15 Mah 1968).

Greenblatt,  S.,  and J.  Wawzonek,  Study and Development of High Efficiency
          Induction Motor Amplifier System,  Bose Corporation,  Natick,
          Mass.,  Report No.  NAS 12-588 (March 1968),

Hoffman, George A.,  "Energy Requirements for Electric Automobiles,"
          University of California,  Los Angeles,  paper  presented AIAA
          Intersociety Energy Conversion Engineering Conference, 26-28
          September 1966.

Hoffman, George A.,  "Future Electric Cars," University of California,
          Los Angeles, California,  Paper No. 690073 presented SAE
          Conference, 13-17 January 1969.

Johnson, R. W., "Modulating Inverter System for Variable Speed Induction
          Motor Drive (CM Electrovair II),"  Paper presented IEEE Winter
          Power Meeting,  28  January - 2 February 1968.

Koch,  W. H.,  "The Route to Control:  Electronics," Applied Electronics
          Department, Ford Motor Company,  Electro-Technology article
          (May 1968).
                                   6-44

-------
Kusko,  Alexander, Solid State DC Motor  Drives (The Massachusetts
          Institute of Technology Press,  Cambridge, Mass.,  1969).

Marks,  C.,  E. A.  Rishavy,  and F. A. Wyczalek, "Electrovan - a Fuel Cell
          Powered Vehicle, " General Motors  Corporation Paper No.
          670-76 presented SAE Automotive Congress and Exposition,
          Detroit,  Michigan, 9-13 January 1967.

Rishavy, E.A.,  W. D.  Bond, and T. A.  Zechin, "Electrovair - a Fuel
          Cell Powered Vehicle, " General Motors Corporation Paper No.
          670175 presented SAE Automotive Congress and Exposition,
          Detroit,  Michigan, 9-13 January 1967.

Salihi, J. T., P. D. Agarwal,  and G. J.  Spix, "Induction Motor  Control
          Scheme for  Battery Powered Electric Car (GM Electrovair I), "
          IEEE  Transactions on Industry and General Applications, vol.
          IGA-3,  no.  5, September -October 1967.

Sandes,  Launcelot R., Electric Automobile Initial  Cost,  thesis for  M.S.  in
          Engineering, University of California at Los Angeles, California
          (1970).

Slabiak,  W., An A-C Individual Wheel Drive System for  Land Vehicles,
          U.S. Army  Tank-Automotive Center, Fort Belvoir,  Va.

Thornton, R.O.,  "Design Considerations for an Electric Car," Massachu-
          setts Institute of  Technology Paper No.  700020 presented SAE
          Automotive  Engineering Congress, Detroit, Michigan, 12-16
          January 1970.
                                  6-45

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                              SECTION 7






ELECTRICAL SYSTEM - BATTERY CHARACTERISTICS AND OPERATION

-------
                                CONTENTS
7.     ELECTRICAL SYSTEM - BATTERY CHARACTERISTICS
      AND OPERATION    	   7-1
   7. 1   Introduction    	   7-1
   7.2   Battery Selection Criteria    	   7-1
   7.3   Models of Battery Characteristics  	   7-3
   7.4   Battery Sizing and Operation Over Driving Cycles	   7-9
   7. 5   Review of Battery State of the Art  	   7-16
      7. 5. 1    The Lead-Acid  Battery    	   7-19
         7.5. 1. 1   Present Battery Characteristics   	   7-19
         7.5. 1.2   Battery Failure Modes   	   7-19
         7. 5. 1. 3   Battery Advancements    	   7-24
      7.5.2    The Nickel-Cadmium Battery    	   7-27
         7. 5. 2. 1   Present Battery Characteristics   	   7-27
         7.5.2.2   Advanced Battery Characteristics    	   7-28
         7. 5. 2. 3   Industrial Capability   	   7-28
         7. 5. 2. 4   Availability  	   7-35
      7. 5. 3    The Nickel-Zinc Cell   	   7-36
         7.5.3. 1   Performance Characteristics   	   7-37
         7.5.3.2   Industrial Capability   	   7-42
      7. 5. 4    Summary of Battery State of the  Art   	   7-45
   7. 6   Design and Development Goals   	   7-47
      7.6. 1    Vehicle Battery Requirements   	   7-47
      7. 6. 2    Battery Development   	   7-50
         7.6.2. 1   Cell  Capacity   	   7-50
         7.6.2.2   Power and  Energy Density   	   7-52
         7.6.2.3   Hybrid Battery Life   	   7-52
         7.6.2.4   Charge  Acceptance    	   7-53
         7. 6. 2. 5   Thermal Control   	   7-53
      7. 6. 3    Summary of Development Goals  	   7-55
                                   7-i

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                          CONTENTS (cont. )
7.7   Recommended Battery Development Program  . .	    7-55
   7.7. 1    General Battery Development (Phase I)   	    7-55
      7.7. 1. 1   Development of Lead-Acid Battery
                for Hybrid Electric Vehicle     	    7-55
      7.7. 1.2   Hybrid Electric Vehicle Battery
                Simulation and Analysis  	    7-58
   7.7.2    Advanced Battery Development (Phase II)    	    7-58
      7.7.2. 1   Lead-Acid Battery Development   	    7-58
      7.7.2.2   Nickel-Zinc Battery Development	    7-59
      7. 7. 2. 3   Pre-Production Phase of Advanced
                Hybrid Electric Vehicle Battery   	    7-61
   7.7.3    Battery Applied Research (Phase III)   	    7-61
7. 8   References	    7-62
7. 9   Bibliography	    7-63
                                 7-ii

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                                 TABLES
7-1.   Cell Model Characteristics	   7-7

7-2.   Baseline Design Energy Expenditures Over Emission
       Driving Cycles (Advanced Lead-Acid
       Battery)	   7-10

7-3.   Advanced Lead-Acid Battery Energy Utilization Over
       Emission Driving Cycles (Recharge  Efficiency = 70%) ....   7-17

7-4.   Characteristics of Batteries	   7-18

7-5.   Characteristics of Secondary Batteries Selected
       for Investigation	   7-46

7-6.   Battery Development Goals, Family Car
       (Lead-Acid Battery)	   7-49

7-7.   Summary of Battery System Design and Operating
       Characteristics, Series Configuration	   7-51

7-8.   Summary of Battery Design Specifications,  Series
       Configuration	   7-56
                                   7-iii

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                                 FIGURES
7-1.   Computer Program Model of Advanced Lead-Acid Battery  .  . .   7-4

7-2.   Computer Program Model of Advanced Nickel-Cadmium
       Battery  	   7-5

7-3.   Computer Program Model of Nickel-Zinc Battery   	   7-6

7-4.   Battery Discharge Characteristics, Design Driving Cycle,
       Family Car  	   7-11

7-5.   Battery Discharge Characteristics, Design Driving Cycle,
       Commuter Car  	   7-11

7-6.   Battery Discharge Characteristics, Design Driving Cycle,
       Low Speed Van  	   7-11

7-7.   Battery Discharge Characteristics, Design Driving Cycle,
       High Speed Van	   7-11

7-8.   Battery Discharge Characteristics, Design Driving Cycle,
       Low Speed Bus  	   7-11

7-9.   Battery Discharge Characteristics, Design Driving Cycle,
       High Speed Bus	   7-11

7-10.  Duration Distribution of Battery Discharge  	   7-12

7-11.  Battery Discharge Current Distribution   	   7-12

7-12.  Amp-hr Distribution During Battery Discharge	   7-12

7-13.  Battery Discharge Characteristics   	   7-13

7-14.  Battery Peak Discharge Currents   	   7-13

7-15.  SLI Lead-Acid Battery Charge/Discharge Characteristics  .  . .   7-20

7-16.  Discharge-Voltage Curves and Number of Ampere-Hours
       Available at  Various Rates of Discharge   	   7-21

7-17.  Tempe rature Correction Curve for  Stationary Batteries   ....   7-Z2

7-18.  Effect of Temperature  on Cycling Life  	   7-23
                                   7-iv

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                             FIGURES (cont. )
7-19.  High Power Density Battery Compared to SLI Battery  	  7-25

7-20.  Cell Voltage vs  AH Capacity at Various Discharge Rates
       for Nickel-Cadmium Cell  	  7-29

7-21.  Typical Voltage Characteristics at C/6 Charge and Discharge
       Rates for Sealed Nickel-Cadmium Cells	  7-30

7-22.  Estimated Cycle Life of Sealed Nickel-Cadmium Cells  as a
       Function of Temperature for Various Depths of Discharge  ...  7-31

7-23.  Estimated Cycle Life of Sealed Nickel-Cadmium Cells  as a
       Function of Depth of Discharge for Various  Temperatures  ...  7-32

7-24.  Construction of  a Bipolar Battery   	  7-33
                                                2
7-25.  Voltage-Current Relationship for a  100 in.  Electrode  Area
       Nickel-Cadmium Bipolar Battery   	  7-34

7-26.  Comparison of Energy/Power  Density Characteristics  of High
       Power Density Lead-Acid and  Nickel-Zinc Batteries	  7-38

7-27.  Nominal Discharge Characteristics of 5 AH Nickel-Zinc Cell
       at 75°F  	  7-39

7-28.  Nominal Discharge Characteristics of 5 AH Nickel-Zinc Cell
       at Various Temperatures  	  7-40

7-29.  Representative Charge-Discharge Characteristics of 2- 2.5 AH
       Nickel-Zinc Cells	  7-41

7-30.  Nominal Discharge Characteristics of 5 AH Nickel-Zinc Cell
       at 75 °F After Cycling Tests to 75%  DOD at C/2.5 Rate   	  7-43

7-31.  Capacity vs Cycles for Nickel-Zinc Cells	  7-44

7-32.  Cycle Life of Lead-Acid Batteries   	  7-48

7-33.  Battery Development Program Schedule    	  7-57
                                    7-v

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                                 SECTION 7

 ELECTRICAL, SYSTEM  - BATTERY CHARACTERISTICS AND OPERATION

7. 1         INTRODUCTION
Next to the heat engine and its associated emission characteristics, the battery
is the most important element in the hybrid electric vehicle powertrain since
it has a marked effect on vehicle exhaust emissions.  It is the intent of this
section to elaborate on this point by showing the rationale  for battery  selection,
the assumed battery characteristics, how the battery operates in the hybrid
vehicle, the resulting battery design goals,  and,  finally,  a recommended pro-
gram for battery development.   In addition to hybrid electric vehicle-oriented
battery considerations, an assessment is made of the state of the art  for gen-
eral battery technology to enhance evaluation of expected progress in  developing
high-performance batteries.
7. 2         BATTERY SELECTION CRITERIA
Because of the large battery  capacity required  in the hybrid electric
vehicle, battery cost will represent a  significant fraction of overall vehicle
cost.   Hence, only reasonably priced batteries  could be considered for personal
transportation vehicles, leaving the more expensive batteries for commercial
vehicles where first costs are more readily depreciated.  Besides the initial
costs, the  cost of battery replacement  over the vehicle lifetime must  be  con-
sidered (even for commercial vehicles).   Therefore, battery lifetime becomes
a major evaluation factor in battery selection and in permissible  cyclic opera-
tion in the  hybrid vehicle.

Battery maintenance can also be viewed as a cost factor.  Inspection and/or
test of a large complex of individual cells would be time consuming for the user
of personal transportation vehicles and would possibly be a major cost factor
for  commercial vehicle operators in view of the added labor and time out of
service.  Therefore, battery selection should consider low maintenance  or
(preferably)  no maintenance batteries.
                                     7-1

-------
To achieve superior battery lifetime by avoiding deep discharge, the battery
energy capacity must be reasonably large relative to the maximum energy
demand.  At the same time, to supply the large currents required by the
electric motor  for producing maximum vehicle acceleration, the battery
must be capable of delivering high power for short periods.  For fixed
battery weight, these are conflicting requirements since energy capacity is
usually traded to enhance power capability and vice versa.   Thus, there is
no perfect battery system and  a compromise must be reached between
acceptable vehicle acceleration and acceptable battery lifetime.
One other  major factor not  to be overlooked is availability.   There are some
very advanced battery concepts being examined and tested in both research
and  early development programs.  However, with the possible  advent of a
prototype hybrid electric vehicle within a few years and with a  need to ensure
production of a viable hybrid electric vehicle  in the 1975 to  1980  period,
attention must be focused on those systems that are readily available or have
short term development potential.
With the recognized  importance of the battery system to the feasibility  and
success of the hybrid electric  vehicle, the Air Pollution Control  Agency
(APCO) (at the  time,  NAPCA)  and  The Aerospace Corporation convened a
meeting at Argonne National Laboratories, Argonne, Illinois, of government
and  university battery experts  to decide which batteries should receive
primary emphasis in this study.  The discussion included a review of pre-
liminary study  results depicting the type of battery operation to be  expected
in the hybrid electric vehicle.   After  evaluating performance, cost, iind
availability (with availability the dominant factor),  the final consensus of
both the invited attendees and members of The Aerospace Corporation was
that only two types of batteries were suitable for application to a  hybrid
electric vehicle at this time: lead-acid and nickel-/.inc.  A third battery,
nickel -cadnii urn,  was added because of its high  state of development, high
power  density,  and ability to accept rapid charge; however, the rost. and
limited availability ol cadmium restricts the consideration of this battery
                                    7-2

-------
primarily to commercial hybrid electric vehicles of low levels  of produc-
tion and to test bed hybrid vehicles for prototype evaluation programs.
7. 3          MODELS OF BATTERY  CHARACTERISTICS
Battery characteristics in terms of voltage, current, and state of charge
were simulated in  the Hybrid Electric Vehicle Performance  Computer
Program by linearized approximations for  each  of the three batteries.
The charge-discharge models shown  in Figs. 7-1,  7-2,  and  7-3 for lead-
acid, nickel-cadmium, and nickel-zinc batteries,  respectively,  were
entered in tabulated form into the  computer program and used for all analy-
ses documented in this report.   These characteristics were based on avail-
able data and projections of future  capability.  They have a marked  effect on
selection of heat engine/generator  operating mode and power  output level as •
well as on battery  design goals for energy density and lifetime.  Hence,
final selection  of hybrid vehicle design specifications and operation  will be
influenced by the test data emanating from  battery development programs.
The characteristics of the advanced lead-acid battery shown in  Fig.  7-1  are
generally beyond any which have now been demonstrated, but they are based
on extensions of the data of Ref. 7-1 and follow the extrapolations indicated
in Ref.  7-2.  The nickel-cadmium battery model in Fig.  7-2 represents
advanced characteristics of a sintered plate prismatic design.  For the
nickel-zinc battery model (Fig.  7-3),  characteristics of all the batteries
described in Refs. 7-3 through 7-8 were examined  to determine if any simi-
larities existed, but no consistent form was shown.   Therefore, the  charac-
teristics  of the cells  described in Ref. 7-6  were generally used  in establish-
ing  the model.
The characteristics of the battery cell models are summarized in Table  7-1.
These  characteristics are based upon  specific batteries,  but within  any
battery type  any number of variations  can exist.   The maximum and  minimum
allowable voltage  for each battery model was established to limit outgassing
during charge  and  to  limit energy drain during discharge; in  both cases the
objective  of imposing these constraints is to prolong battery  life. On a
                                   7-3

-------
.2.8


2.6


2.4
2.0


1.8


1.6


1.4
       50% CHARGE
       25% CHARGE
          CHARGE
                                    FULL CHARGE
                                    95%
                                    90%
                                    85%
                                    75%
0     8     64      2          -2     -4    -6    -8
              NORMALIZED  RATE, CURRENT (Amp)/CAPACITY (AH)
                                                                 -10    -12
  Figure 7-1.  Computer Program Model of Advanced Lead-Acid Battery

-------
                                     FULL CHARGE
                                     95%
                                     75%
                                     50%
                                     25%
                                      0%
10
8
6420-2-4-6

NORMALIZED RATE, CURRENT(Amp)/CAPACITY(AH)
-8    -10
 Figure 7-2.  Computer Program Model of Advanced Nickel-Cadmium Battery

-------
UJ
o
O
                                          FULL CHARGE
                                          75%
                                          50%
                                          25%
                                           0%
            8
64      2      0-2-4-6-8

NORMALIZED RATE, CURRENT(Amp)/CAPAClTY(AH)
-10   -12
            Figure 7-3.  Computer Program Model of Nickel-Zinc Battery

-------
 normalized basis, the ratio between the minimum and maximum voltages is
 about the same for all of the cells.   This ratio is important in establishing
 the operating range of the generator and drive motors and might indicate
 that batteries of different types could be used interchangeably in a hybrid
 vehicle.
                 Table 7-1.  Cell Model Characteristics
CHARACTERISTICS
Open Circuit Voltage
Minimum Allowable Discharge
Voltage
Maximum Allowable Charge
Voltage
Maximum I/ C Rates
Discharge, 90% DOD**
Charge, 100% Charge
CELL MODEL
Lead-Acid
2. 1
1. 50
2.40
11.7
1.0
Nickel- Cadmium
1.35
1. 10
1. 55
12. 1
1. 1
Nickel -Zinc
1. 8
1. 30
2. 10
17. 8
1. 35
*I/C = Current/Rated Capacity
**DOD = Depth of Discharge
The cell models  indicate a definite advantage for  the nickel-zinc battery in
terms of high current capability.  Whether this model can be achieved in a
high-cycle life cell or whether the other cells would be improved is another
factor which must be determined.
In the computer program, at the  start of each emission driving cycle,  the
battery is set to  full charge.   As explained further  in Section 4 and Appendix
A,  the voltage, current,  and state of charge are calculated at each one  second
time step throughout the  cycle; during discharge,  the state of charge is deter-
mined by the equation
                             = S.  -
                                           R
              (discharge current efficiency assumed = 100%)
                                   7-7

-------
and during charge by the equation
                                       LB  (ti+l  - V100
                                          CR
where
      S     =  battery state of charge,  percent
      i     =  battery charge or discharge current, amp
      t     =  time, hr
      C     =  battery rated  capacity, amp-hr
      ^D ia  =  battery recharge current efficiency
       t\ tj
The recharge efficiency is used to account for both internal and external
resistive losses as  well as for deviations  from complete theoretical chemical
conversion between electrodes and electrolyte.
All calculations were conducted for the battery initial and  final states -of-
charge of 100 percent; somewhat different results may  have resulted by
using a lesser value for the state-of-charge.  This would improve charge
acceptance but diminish discharge capacity.  The overall effect on vehicle
operation may show improvement and warrants further study.
With the magnitude  of current drained given by the difference between electric
traction motor demand and generator current,  and following calculation of the
state  of charge,  the battery voltage is then uniquely determined from tabular
reproductions of Figs. 7-1,  7-2,  and 7-3.   If at any time during the emission
cycle the lower voltage limit  is passed, computation is halted.  With regard
to the  upper  voltage limit, it  can be seen by reference  to the aforementioned
figures that the maximum allowable charge  current is established by the bat-
tery capacity and the state of charge.  Since the available  charge current can
readily exceed the allowable value, the excess  current is shunted to a load
resistor and accounted for in the computer program.
                                    7-8

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7. 4         BATTERY SIZING AND OPERATION OVER DRIVING CYCLES
Fundamental sizing of the battery is established by the ability to furnish  power
and energy as required by the vehicle  during operation over design and emis-
sion driving cycles.  In establishing battery capacity, a minimal value was
selected to fulfill the more restrictive of two requirements by:
      a.     Ensuring that the voltage does not  fall below minimum allowable
            voltage  for maximum power demand during acceleration  on the
            design driving cycle.
      b.     Ensuring that required  generator power output for emission
            driving  cycles is established at low levels.  (It has been  deter-
            mined that as battery capacity was decreased the  required gen-
            erator output remained at  low levels until a critical  point was
            reached where the required  output rose sharply.  Since a higher
            generator output power level is reflected directly in  higher
            exhaust emissions, this operating  region is to be  avoided. )
Table 7-2 shows the required lead-acid  battery capacity for each class of
vehicle along with system voltage and  minimum  generator current.   With these •
capacities,  battery  discharge current  during vehicle operation over the design
driving cycle is shown for several representative  cases in Figs. 7-4 through
7-9.  Peak currents range from  a high of ~500 amp for the low-speed bus to  a
low of ~150  amp for the commuter car;  the family car required  ~460 atrip.

With battery capacity established, the operating characteristics  can  next be
established  for the emission driving cycles.  Typical battery  operation is
illustrated for the family car using a lead-acid battery in Figs.  7-10 through
7- 14.   A total of 73 battery discharge cycles was noted during the driving
cycle as shown in Fig. 7-10.  Total duration of discharge  operation was
406 sec, leaving 964 sec available for recharge.

Peak discharge  currents for each of the discharge cycles are described in
Fig. 7-11.  The  peak current was 261  amp,  and the next highest 145 amp.
Average of all peak currents for  all of the cycles is about  49 amp with a  median
current of under 40  amp.  These high  power discharge cycles are also the
*
 to return battery to original state of charge
                                     7-9

-------
               Table 7-2.  Baseline Design Energy Expenditures  Over Emission Driving Cycles
                                                 (Advanced Lead-Acid Battery)
Configuration
Series
Series
Seri es
Series
Series
Series
Parallel
Parallel
Parallel
Parallel
Notes: (1 ).
I
Vehicle
Family Car
Commuter Car
Low -Speed Van
High-Speed Van
Low -Speed Bus
High-Speed Bus
Family Car
Commuter Car
High-Speed Van
High-Speed Bus
Time To
Traverse Cycle
(sec)
1370
1370
96
96
36
42
1370
1370
96
42
W"
(amp)
38
17
53
54.5
100
79
34
14.5
43
73
System
Voltage, V
(volt)
220
220
220
220
440
440
220
220
220
440
Minimum
Heat Engine
Power Output
(hp)
20.7
7.97
22.4
22.4
86
70.6
19.2
7. 1
18. 1
66.2
Rated
Heat Engine
Power Output
(hp)
92
33
42.3
107
168
257
84.2
30.3
102
236
Installed Battery
Capacity
(amp- hr)
38
20
40
40
90
79
30
20
40
70
Heat Engine
Energy Output
(hp-hr)
8.37
3. 19
0.602
0.602
0.885
0.843
7. 32
2.7
0.481
0.751
Cvera,,(3'_
Efficiency, H
28. 6
32
29.2
29.2
44
32. 8
31.9
38
36.6
36. 8
Heat Engine
Energy Per Mile
(hp-hr/mi)
1. 12
0. 425
3. 05
3. 05
8.95
8. 10
0. 975
0. 36
2.43
7. 22
X V - electrical equivalent of sum of mechanical and electrical power delivered by heat engine.
For parallel configuration, generator current decreases as vehicle speed (road load) increases
(see Section 10).
' With accessories but no A. C.
T
- energy required at vehicle wheels
energy output from heat engine

-vj
I

-------
 .  -100
   inn
 6  400
1 1
A.
1 \ SERIES CONHGURAIION
I GtMHATOH OUTPUT 38 Amp ICONS!)
\ 38 AH LI AD- ACID BATTERY
\\
1 i i
FIG 7-4. FAMILY CAR
1 i (o)~
ill 1
   ?no
   MX)
   400
v?  200
                       SERIES CONFIGURATION
                       GENERATOR OUTPUT 53 Amp (CONST)
                       40 AH LEAD-ACID BATTERY
                      FIG  7-6  LOW-SPEED VAN
                                                  Ic)
SERII-j CONFIGURATION
GLNEHAIOH OUTPUT 100 Amp (CONST)
90 AH LEAD-ACID BATTERY
                      FIG 7-8.  LOW-SPEED BUS
                                                  (e)
                                                                        "T
                                                                         SERIE'J (-ONIIGUHAIION
                                                                         GFNEHAIOR OUlPUt I/Amp (C.ONS
                                                                         20 AH LEAD-ACID BATTERY
                                                                         FIG 7-5. COMMUTER  CAR
                                                                                                       (b)
                     50              100
                       ELAPSED TIME, sec
                               150  0
                                                     PARALLEL CONFIGURATION
                                                     GENERATOR OUTPUT 43 Amp (CONST)
                                                     40 AH LEAD-ACID BATTERY
                                                    FIG 7-7  HIGH-SPEED VAN
                                                                                (d)
 PARAIIEI  CONFIGURATION
 Gf.NERAIOK OUlf'DT  73 Amp I'.O'i'.D
 IQ AH LIAD-ACIU
                                                    FIG 7-9.  HIGH-SPEED BUS
50              100
  ELAPSED TIME, sec
           Figs.   7-4 through 7-9.
                      Battery Discharge Characteristics,
                      Design Driving  Cycle
                                                  7-11

-------
    20
                               4000 Ib FAMILY CAP
                               DHEW EMISSION DRIVING CYCLE
                               GENERATOR OUTPUT = 38 Amp
                               38AH LEAD-ACID BATTERY
                                                     _TL
                4        8         12         16        20

                       DURATION  OF DISCHARGE CYCLES, sec

             KiK»irc V-1U.  Duration  Dinlribiilion i>< Battery DiacM«rgc
                              4000 Ib FAMILY CAR
                              DHEW  EMISSION DRIVING CYCLE
                              GENERATOR OUTPUT =  38 Amp
                              38 AH LEAD-ACID BATTERY
5   4
    40
                                             I
                                                     J_
               40        80       120       160       200

                         BATTERY DISCHARGE CURRENT, Amp

               I-'iKurc 7-11.  Battery Discharge- Current Dmt nbutiu
                                                                    JIL
                                   240
                                            280
    32
4000 Ib FAMILY CAR
OHfW EMISSION DRIVING CYCLE
GENERATOR OUTPUT = 38 Amp
38 AH LEAD-ACID BftlHRY
 o  16
      '0      Olffl
   024     O.V     O-'O      O'lH
Amo-hr PER DISCHARGE CYCl f
                                                                      ClJ
            h"i(.'iire 7-li.  Atnp-hr Distribution Dunni; Bditury Discharge
                                      7-12

-------
   100
o^ 99

UJ

cc




f 98
o
 J
UJ
I—
-
CD
     0
                                                          I
                                              4000 Ih FAMILY CAR

                                              DHEW EMISSION DRIVING CYCLE

                                              GENERATOR OUTPUT = 38 Amp

                                              38 AH LEAD-ACID BATTERY
       0
                       5                10               15


                               ELAPSED TIME, sec



                Figure 7-14.  Battery Peak Discharge Currents
         20
                                      7-13

-------
 highest amp-hr discharge cycle and are 17 and 18 sec Ln duration with an average
 current during the two discharges of 129.2 and 76.0 amp,  respectively.

 The amp-hr contained in each discharge cycle is shown in Fig.  7-12.  The total
 energy is 4.76 amp-hr with the maximum during any discharge  of 0. 6 1 amp-hr;
 the average is 0.065 amp-hr.  Median discharge is about  0.02 amp -hr.

 The state of discharged battery capacity for the family car during the DREW
 Emission Driving Cycle  is given in Fig. 7-13.  In this case, the battery reached
 a minimum charge level of 96.47 percent  state of charge which  corresponds to
 1. 34 amp-hr.  This form of  shallow discharge was demonstrated by all batteries
 and  is considered to be characteristic of how batteries will operate when con-
 tinually recharged by a generator/alternator on all classes of hybrid electric
 vehicles.

 The current traces for the two maximum power (also maximum energy)  cycles
 are  shown  in  Fig.  7-14.   It is to be noted  that the high currents  exist  for only
 about a second.

 The emphasis to this  point has been upon the family passenger car and its
 requirements.  For the commuter  car and vans which were operated over their
 respective  emission driving  cycles, the results were almost identical in terms
 of number  of cycles and duration of cycles,  but the power requirements  were
 different.   In all cases,  the maximum power demand occurred during the
 design driving cycle - nearly twice that  resulting from the emission driving
 cycle.

 Some general  comments should be  made concerning how changes in operating
 parameters affect the characteristics shown in Figs. 7-10 through 7-14.  The
 first change which might be considered is an increase in generator output.
 This will restore the  battery to full charge more rapidly,  will reduce the
 average battery  current,  and may change  the number of discharge cycles.
.Raising the generator current, however, has the disadvantage of increasing
 vehicle exhaust emissions since  the average engine output is increased.   By
                                     7-14

-------
operating the battery more fully charged battery life could increase,  but the
amount of energy dissipated through  the external resistor circuit or in the
battery is also increased and  this could have the opposite effect of decreasing
battery life.  Nonetheless, in this study, the objective was to decrease
emissions and for that reason increasing generator  output is not an attractive
alternative.
Another  method of decreasing the number of discharge cycles  might be to
increase battery capacity.   This  is accomplished with a proportional increase
in battery weight.  An  increase in battery capacity will cause improved charge
acceptance  and will lower the maximum depth of discharge. The larger bat-
teries would provide a smaller depth of discharge which  is ordinarily benefi-
cial to battery life.
The emission driving  cycles  utilized in this study are considered to  be typical
of driving conditions expected for each vehicle.   However, based upon  the
approach of maintaining the battery state of charge after  each  driving cyc.le,
an  important factor affecting design of the battery system may  be the type of
driving cycle employed.  Hence,  for prototype vehicles operated in various
cities, a more sophisticated battery  control system may  be necessary; e.g.,
one which senses  battery voltage and possibly other parameters continuously,
and regulates charge current  levels according to need rather than in  a  pre-
determined manner.
One other important factor describing battery performance is  the percentage
of recharge energy shunted to the load resistor  because available recharge
current exceeded  allowable recharge current.  Since this  represents wasted
energy (i.e.,  generator output must be increased to overcome this loss and
still ensure a fully charged battery at the end of the emission driving cycle),
the resultant effect is   increased vehicle exhaust emissions for  batteries with
poor charge acceptance.
The charge  acceptance characteristics also have a marked effect on the utili-
zation of energy from regenerative braking.  This utilization was shown to be
negligible for all batteries  in this  study  since  the regenerative  braking charging
                                    7-15

-------
currents generally exceeded the  allowable charging current by up to an order
of magnitude.  Some improvement might be possible by starting the battery on
emission driving  cycles at less than  100 percent state-of-charge and likewise
the goal would be to return to the original state-of-charge by resetting gener-
ator output at a lower value.  This technique would be evaluated in a prototype
vehicle.  If this condition were carried  over  to the design driving cycle, how-
ever, a greater battery capacity might be needed to maintain battery voltage
above the minimum allowable level.
The battery models employed in  the analysis generally had acceptable  charge
acceptance as  shown typically by the charge energy utilization factors  for the
advanced lead-acid battery given in Table 7-3.  Here it can be seen that for
the family car only 1.4 percent of available charge energy was  shunted to the
load resistor.  Similarly  low values  are apparent for the  commuter car, the
van, and the bus.  Although not shown,  far worse per for mam:c  was given by
contemporary  lead-acid batteries; they  require that the generator current
level be about  twice that  needed for the  advanced lead-acid battery.  The
result  is a significant increase in vehicle exhaust emissions (See Section 11).
Hence,  battery development  programs should be  directed toward achieving at
least the charge  acceptance capabilities of the battery models used  in this
study.   To utilize energy  from regenerative braking,  however,  charge accep-
tance would have  to be improved  significantly further.  This is  considered to
be a very important aspect in assuring a viable hybrid electric  vehicle.
7. 5          REVIEW OF BATTERY STATE OF  THE ART
The characteristics of a  large number of batteries are presented in Table 7-4.
While these are of interest in establishing the state of the art for the general.
battery field,  the succeeding discussions will be  limited to those batteries
considered for near term use with the hybrid electric vehicle:  the lead-acid,
n ickel -cadmium,  and nickel-x.inc batteries.
                                     7-16

-------
Table 7-3.  Advanced Lead-Acid Battery Energy Utilization Over
     Emission Driving Cycles (Recharge Efficiency =  70%)
CONFIGURATION
Series
Series
Series
Series
Series
Series
Parallel
Parallel
Parallel
Parallel
Notes:
(1) BU.
VEHICLE
Family Car
Commuter Car
Low-Speed Van
High-Speed Van
Low-Speed Bus
High-Speed Bus
Family Car
Commuter Car
High-Speed Van
High-Speed Bus
BUF*1'
0. 582
0. 597
0. 541
0. 541
0. 700
0. 611
0. 628
0.638
0.689
0. 696
E (Z)
^S
0..127
0. 0033
0. 0246
0. 0246
0. 0001
0. 034
0.243
0. 0001
0. 022
0. 023
BLF(3)
0. 014
0. 008
0. 0261
0. 0261
0. 0002
0. 057
0. 029
0. 00003
0. 030
0. 0435
^ _ amp-hr delivered by battery
amp-hr available for charging battery
(2) E = amp-hr shunted to load resistor
(3) BLJ
_ amp-hr shunted to load resistor
amp-hr available for charging battery
                             7-17

-------
                                   Table 7-4.  Characteristics of Batteries
CELL
LEAD-ACID
NICKEL -CADMIUM
NICKEL-IRON (EDISON)
MCKEL-ZINC
SILVER -CADMIUM
SILVER-ZINC
MERCURY-CADMIUM
LALANDE
LE CLANCHE (DRY CELL)
ALKALINE
EDISON AIR CELL
MERCURY (RUBEN)
MAGNESIUM DRY CELL
MAGNESIUM -CHLORINE
SODIUM -CHLORINE
SODIUM -SULFUR
ALUMINUM -FLUORINE
LITHIUM-CHLORINE
LITHIUM-FLUORIDE
LITHIUM -CHLORIDE
LITHIUM-SELENIUM
LITHIUM -SULFUR
A LL'MINUM -CH LOR INE
H.,-0, FUEL CELL
ANODE
Pb
Cd
Fe
Zn
Col
Zn
Cd
Zn
Zn
Zn
Zn
Zn
Mg
Mg
Na
Na
Al
Li
Li
Li
Li
Li
Al
H2
CATHODE
PbO2
NiOOH
NiOOH
NiOOH
Ag20/AgO
Ag20/AgO
HgO
CUO
MnO2
Mn02
°2
HgO
Mn02
C12
ci2
S
F2
C12
NiF.,
C-TeCl4
Se
S
ci2
°2
ELECTROLYTE
H.SO,
KOH
KOH
KOH
KOH
KOH
KOH
NaOH
NH4C1
NaOH
KOH
KOH
MgBr
MgCl2
NaCl
Na2O.HAl203
Na,AlF,
J O
LiCl
PC
KCl/LiCl
-
Lil/LiCl/KI
AlClj
KOH
THEORETICAL
Cell Voltage
2. 04
1. 30
1. 58
1. 74
142/1. 15
1. 85/1. 59
0. 907
-
-
-
1.65
1. 34
-
-
3. 98
-
-
-
-
3. 25
2. 2
2. 25
3. 02
1. 23
Energy Density
(W-hr/lb)
74
96
142
170
122/82
220/130
67
109
153
149
671
116
247
954
849
346
1. 940
990
626
-
-
-700
828
17,875
REPORTED
Energy Density
(W-hr/lb)
20-30
12-20
10-13
15-30
20-30
25-1 10
18-35
20
25-30
30-45
50-55
45-52
45-50
-
-
148
-
125-250
100
60
130
70
-
45
Energy per Unit Volume
(W-hr/in. 3)
2. 0
1.1
1. 2
2.0
2.9
4. 5
6
0.9
2. 5
2. 2
2. 5
8
2. 5
-
-
8. 1
-
-
-
5
-
6. 7
-
2.8
co

-------
7.S.I       The Lead-Acid Dattory
The  lead-acid battery is of primary interest because of its low cost,
reliability,  and availability.  The battery can be mass produced easily with
inexpensive tooling, and the formation procedure is simple.  In 1967, there
were 233 companies producing lead-acid batteries (Ref. 7-9) and, of these,
1ZO had more than 20 employees.  These  companies did 580 million dollars
worth of business, with 260 million dollars of this being value added by manu-
facture and the rest being cost of materials.  In 1967, the average  cost of
lead was  14 cents/lb whereas the current cost is 16.5 cents/lb.  Retail cost
of starting-lighting-ignition (SLI) batteries is 40 to 80 cents/lb, and at open
circuit voltage, from 2.2 to 4.0 cents/watt-hr .   Industrial lead-acid batteries
cost about twice as much.
7.5.1.1     Present Battery Characteristics
Characteristics under discharge and charge for SU batteries are given in
Fig. 7-15 and at various  rates in Fig. 7-16.  The tendency for capacity to
decrease with discharge rate is indicated by this curve.  It is interesting to
note, as shown in  Fig. 7-17,  that the capacity of a lead-acid battery increases
with temperature.  In Fig.  7-18 is shown the trend of cycle  life with
temperature.
7.5.1.2     Battery Failure Modes
Three modes of battery failure  are generally  considered.  The first type
involves the gradual dissolution of the positive grid.  Under charge, a small
layer of the grid may become oxidized, and this  layer is then stripped off
during discharge.   Eventually,  as  the grid is  eaten away,  the conductive path
is broken and the  active  material may lose contact with grid.   Industrial bat-
teries and,  to a certain extent,  golf cart batteries avoid or delay onset of this
problem by using  thicker grids.

A second type of failure,  not  entirely dissociated from the first,  is the
sloughing off of material  from the  plates and the accumulation of this material
                                     7-19

-------
-o
i
M
O
                                                    O   FULL CHARGE

                                                    D   75%

                                                    A   50%

                                                    O   25%
                                                                -200
                           0        -100

                            Amp

Figure 7-15.  SLI Lead-Acid Battery Charge/Discharge Characteristics
-300

-------
2.2
2.0
 1.8
 1.6
 1.4
   0
                        minutes
                                                hours
                                       DISCHARGE RATE
                                                           CURRENT, Amp
20
40         60          80
    CAPACITY, Amp-hr
100
120
    Figure 7-16.  Discharge-Voltage Curves and Number of Ampere-Hours
                 Available at Various Rates of Discharge

-------
   140
   120
   100
O

    80
oo
u_
o

o  60
QC
LU
Q_
    40
    20
     0
    -20
0
20        40        60

    TEMPERATURE,°F
80        100
   Figure 7-17.  Temperature Correction Curve for Stationary Batteries
                                  7-22

-------
OO
         CO
         >-
           700
           600
            500
           400
         o
         
-------
in the bottom of the battery.  With time the materials can build up to the point
where the plates become shorted across the bottom edges.

The third type of failure mode involves separator failure.  This failure mode
is normally associated with service where considerable shock and vibration
are present.

The venting of hydrogen with the carryover of sulfuric acid,  while not truly a
failure mode, presents an operational  problem. Sulfuric acid produces cor-
rosion of wiring and metal parts located in the vicinity of the battery. Hydro-
gen represents an explosive hazard which must be considered in large capacity
or enclosed installations, and,  as a further problem, represents a loss of
water from the electrolyte.
7.5.1.3     Battery Advancements
7.5.1.3.1   Low Maintenance
Recently, there has been progress in overcoming the shortcomings of the SLI
battery and in producing a maintenance-free or low-maintenance battery in
which water addition will no longer be  necessary and there is no longer any
acid carryover.  Several approaches have been followed in achieving the low-
maintenance battery.  Generally, the new batteries use grids of calcium or
pure lead instead of antimony and this  reduces the tendency to gas.  By having
the voltage regulator maintain charge voltage  below  2.3 volt, gassing is
reduced  or eliminated.
7. 5.1. 3.Z   Battery Design Changes
Adoption of calcium grids,  while causing the lead-acid battery to be more
expensive, does allow for thinner plates so that more surface area can be
packed into the same volume. It has been estimated that surface area can be
increased by a factor of three.  Fig. 7-19 shows the effect of increasing sur-
face area upon both the power and energy density of  a battery with comparison
to an SLI battery.
                                    7-24

-------
   500
   400
                                                      REF. 7-22
   300
CO


LU
o
Q_
HIGH POWER  DENSITY
   200
    100
                                               SLI
     0
       0
   2345

      ENERGY  DENSITY, Watt-hr/lb
        Figure 7-19.  High Power Density Battery Compared to SLI Battery

-------
The dead short circuit current of a common SLI battery is above 1000 amp
with the  instantaneous power  density approximately 200 to 250 watt/lb.  The
limitation to higher currents  is the resistance of the terminals and posts
which eventually melt.  It is also probably true that much of the heating in
the lead-acid battery is caused by the resistance of the posts and terminals,
so it would be recommended that the battery be redesigned to provide a lower
resistance current path. At the  same time, redesign  of the  case to use
plastics  rather than hard rubber should provide a savings in weight and volume
which can be reflected as higher power  or  energy density. Several companies
have designed semi-transparent  plastic cases which can be used to indicate
electrolyte level.

As is  well known, the active lead oxide  paste is retained  within an inactive
lead grid which accounts for about 30 percent of the positive plate weight.
Several new developments indicate that  the grid weight might be decreased
substantially and provide other beneficial effects. Dr. Samuel Ruben of
Ruben Laboratories has recently patented (Ref.  7-10)  a titanium nitride grid
which provides a stronger grid with good conduction,  thermal,  and electrical
characteristics.  Besides reducing weight, thinner plates (to 20 mils  thick)
have been fabricated using this new grid material. To make the grids,  tita-
nium  sheet is nitrided and then expanded to form the grid which is then pasted.
Dr. Ruben has indicated (Ref. 7-11) that although he is having problems in
retaining the paste at high temperatures (140°F)  development prospects
remain encouraging.

Another  development by L.D.  Babusic and others at Bell Telephone Labora-
tories (BTL) (Ref.  7-1) uses  a pure lead grid which is shaped to maximize
strength, and electrical and thermal conductivity.  The BTL battery,  which
uses cone-shaped grids with a concentric and radial spike pattern, is claimed
to increase  battery life to over 30 years.
                                    7-26

-------
The lead industry is continuously investigating new types and forms of lead
oxide, some of which show promise in increasing the specific power and
energy density of the lead-acid battery.
7.5.1.3.3   Battery Control
Successful long term battery operation depends upon adequate voltage control.
Generally, battery charge voltage must be maintained below 2.3 to 2.5 volt
in order to prevent gassing  and the consumption of water.  However, these
low voltages will reduce the rate at which the battery can be recharged.

Recently, it has been announced that  rapid recharge of lead-acid batteries
is possible; reports  are made that  batteries can be fully recharged at high
voltage  in under  15 min with low  temperature rise and no water consumption.
This procedure initially causes electrolysis of the electrolyte and the forma-
tion of oxygen and hydrogen bubbles on the  cathode.   Then,  current reversal
causes the bubbles to be driven off the electrode into  the electrolyte where
they rise to the volume maintained above the cell.  At this location, a small
tungsten electrode causes the gases to recombine and form water  (Ref.  7-12).
High-rate recharge would be a des Lrable feature for the hybrid vehicle battery s ince
this might allow recovery of the energy produced by regenerative  braking  and
improved use of energy produced by the  heat engine/generator.

Thermal control  of the batteries  should be considered in any battery system.
Because of the high current drain and recharge rates, it may be necessary
to examine the use of active coolant systems.
7.5.2      The Nickel-Cadmium Battery
7.5.2.1    Present  Battery Characteristics
A curve showing  the discharge characteristics of a nickel-cadmium cell is
shown in Fig. 7-20.   Temperature  effects upon the nickel-cadmium cell are
shown in Fig. 7-21 for both charge and discharge.  The effect of temperature
                                   7-27

-------
and depth of discharge on cycle life are shown in Fig. 7-22 while Fig. 7-23
shows the trend in cycle  life with depth of discharge at constant temperature.
7.5.2.2    Advanced Battery Characteristics
For high-rate applications the bipolar battery, illustrated in Fig.  7-24,  is of
interest.  In this battery, the nickel of one cell and the cadmium of the next
cell are plated onto the two  sides of a conducting thin sheet  or substrate.
These cell elements  are  stacked together,  with a suitable separator and
electrolyte in between to  form a pile or stack. The current enters the bat-
tery at one end and exits  at the other,  and because of the direct current path
the internal impedance is low (accounting for the high-rate capability).  With
adequate voltage control,  cell gassing can be minimized so that sealed con-
struction can be used.

Power densities as high as 1000 watt/lb on a microsecond basis and
300 watt/lb for minutes have been described for bipolar cells.  Voltage-
current characteristics for a 100 in.   cell are given in Fig 7-25.

It has been estimated that a  battery capable of 450  amps at 70 volt
(31, 500 watt) with  10 amp-hr capacity would weigh 125 Ib and would occupy a
volume of 24 x 12x8 in.   Since the energy density of this battery at low  rate
is  only about 7 watt-hr/lb, the  rating appears conservative.
7.5.2.3    Industrial Capability
The following concerns are, or have been, involved in the fabrication and
manufacture of nickel- cadmium batteries.

      Bright Star  Industries, Clifton, New Jersey
      Catalyst Research  Corp. , Baltimore, Maryland
      Eagle Picher Corp. , Joplin, Missouri
      ESB/Ray-O-Vac, Madison, Wisconsin
      General Electric, Gainesville,  Florida
                                    7-28

-------
                   ROOM TEMPERATURE
                                     22 AH CELL
I
[\J
sD
                  0
9       12       15       18
   CAPACITY,  OUTPUT,  AH
21       24      27
                  Figure 7-20.  Cell Voltage vs AH Capacity at Various Discharge Rates
                              for Nickel-Cadmium Cell

-------
00
O
          LU
          O
              1.7
              1.6
              1.5
              1.4
               .3
              1.2
                                                        -IO°F\  +IO°F\   A+75°F
                                                              l\
                0
4        5
 TIME, hr
7        8
                  Figure 7-21.  Typical Voltage Characteristics at C/6 Charge and Discharge Rates
                                for Sealed Nickel-Cadmium Cells

-------
   I04
o
CJ>
Q
CO
   I03
                       I
I	I
                                                   9%
      0       20      40       60      80       100      120      140
                         CELL TEMPERATURE, °F
   Figure 7-22.  Estimated Cycle Life of Sealed Nickel-Cadmium Cells as a
                Function of Temperature for Various Depths of Discharge
                                   7-31

-------
o
LU
h-

-------
1


j
\
1
:•:•:•':
Ijivi
I



4 i
TT^
5
 I. SUBSTRATE FOR END PLATE
 2. SINTERED MATRIX - NiOXIDE POS. PLATES
 3. SEPARATOR
 4. SUBSTRATE FOR INTERIOR PLATE
 5. END TERMINAL
 6. SINTERED MATRIX-CADMIUM  NEG. PLATES


Figure 7-24. Construction of a Bipolar Battery
                 7-33

-------
^j
OJ
             1.2
             1.0
             0.8
             0.6
             0.4
             0.2
              0
                0
400
800           1200
LOAD CURRENT, Amp
1600
2000
                   Figure 7-25.  Voltage-Current Relationship for a 100 in.  Electrode Area
                                Nickel-Cadmium Bipolar Battery

-------
      Gould-National, St. Paul,  Minnesota (Ni-Cd Division)
      Gulton Industries, Metuchen, New Jersey
      NIFE,  Copiague, New York
      Marathon (Sonotone Corp.),  Elmsford, New York
      Sprague Electric, North Adams, Massachusetts
      Sylvania  Electric Products,  New York
      Union Carbide/Eveready, New York

7.5.2.4    Availability
The availability of cadmium is the principal problem affecting use of nickel-
cadmium batteries in the hybrid vehicle.  Some thought has been given to the
possibility of overcoming the scarcity of cadmium by recycling nickel-
cadmium batteries.   The nickel electrode is little affected during battery
usage so that it can be  reused simply by washing and rewrapping with new
separators.  It thus  is  possible to  rebuild a nickel-cadmium battery by
replacing the cadmium electrode,  the separators, and the electrolyte and,
since the remainder of the battery is  reusable and the cadmium replaced is
recoverable, the cost might not be prohibitive.  This would imply that once
a stable relation  between new batteries  being sold and old batteries being
turned in or  scrapped was reached there would be only a  limited demand upon
the primary  sources  of cadmium metal.

This argument has several  weaknesses.  If it is assumed that roughly
fifty million hybrid vehicles are on the road, each containing 200 Ib of bat-
teries, the total cadmium supply requirement would be about one billion pounds
or about  30 times the annual world production of cadmium.   Also,  the cost of
nickel-cadmium batteries for a vehicle  will be  prohibitive.   Based upon mate-
rial costs, a nickel-cadmium battery will be about 10 to 15 times more  expen-
sive than a comparable lead-acid battery or about $10 to  $15/lb; therefore,
batteries for a hybrid car would cost between $2000  and $3000.
                                    7-35

-------
It is therefore judged that nickel-cadmium batteries, while attractive in an
engineering sense,  should not be considered further for widespread use in the
personal family or commuter car versions of the hybrid vehicle so long as
suitable alternate battery systems exist or can be developed.  However, the
nickel-cadmium battery may be considered for special situations where cost
and availability are not of concern.  Such applications may be found with the
limited production levels associated with intracity buses and  delivery/postal
vans.
7.5.3       The Nickel-Zinc  Cell
The nickel-zinc cell was first described as early as 1898, appeared briefly
as an experimental railway battery (Drumm Cell) in the 1930's,  and,  in the
early 1950's,  the  Russians became active in  its development.  About  1966,
the U.S. Army Electronic Components  Laboratory began an investigation of
the battery as  a replacement for the nickel-cadmium battery  in field radio
equipment. At the same time, industry had become interested in the  battery
because of success with zinc electrodes in orbiting spacecraft batteries and
the fact that this battery, among  the batteries composed of silver and nickel,
cadmium and  zinc, was the least developed and should exhibit many desirable
characteristics as listed below:
      a.   High Energy Density— The  theoretical energy density of the
           nickel-zinc cell is 50 percent greater than the cells for either
           nickel-cadmium or lead-acid.  As high as 30 watt-hr/lb might
           be anticipated.
      b.   Discharge Voltage — The 1.71 discharge voltage of the nickel-
           zinc battery is high compared to the 1. 30 voltage  of the nickel-
           cadmium cell.  The lower voltage compared to  the lead-acid
           cell reduces the tendency towards gassing and makes hermetic
           sealing feasible.
      c.   Stable Voltage — Voltage is  stable with depth of  discharge  since
           the electrolyte is not  involved in the reaction.
      d.   Temperature — Electrode characteristics are favorable under
           high rate  and low temperature conditions.
      e.   Deep Discharge — Fairly good cycle  life has been  demonstrated
           under  complete or high-discharge cycling.  Complete discharge
           is not  injurious to further operation.
                                    7-36

-------
      Ł.    Cost — The cost is expected to be about twice that of lead-acid
            and considerably  lower than nickel-cadmium batteries.
      g.    Availability — No  materials are used which are,  or  are likely to
            be,  in critical supply.
      h.    Safety — The materials used in the battery are relatively
            nonhazardous.
7.5.3.1    Performance Characteristics
The theoretical energy density of the nickel-zinc cell is 146 watt-hr/lb com-
pared to 95.3 for the nickel-cadmium battery.  Some difference of opinion
exists in the literature over the voltage of the zinc half-cell reaction so that
the theoretical energy density for the nickel-zinc cell can be as high as
148 watt-hr/lb. Since the practical density for a vented battery is about
20 percent of theoretical, it would be expected that 30 watt-hr/lb is a
realistic goal.

In Fig.  7-26, test results for a nickel-zinc battery are shown in comparison
to those of a high power density lead-acid battery.  At  150 watt/lb, the energy
density is 17 watt-hr/lb rather than the 2.5  watt-hr/lb of the lead-acid bat-
tery which indicates that the nickel-zinc  battery might be designed for  even
higher power densities or that improved  cycle life might be  expected because
of a lower depth of discharge.

Figure  7-27  shows the characteristics of a five amp-hr  cell at 75° F and
Fig. 7-28 shows the effect of ambient temperature upon performance.  Data
are lacking  on the characteristics of the  battery at high ambient temperatures.
Tests have been conducted where a  battery was soaked at 300° F followed by
recharge and discharge.  After 149 hr at 300° F,  battery capacity after recharge
was only 40 percent  lower than its initial capacity, indicating low permanent
damage.

Charge  characteristics for the nickel-zinc battery are plotted in Fig.  7-29-
Below 1 . 88  to 1.92 charge voltage,  there is no evidence of gassing.  At higher
charge voltages, the characteristics are nearly the same as those of the
                                    7-37

-------
       300
       200
	  \
    CO
    ct:
    o
    Q_
       100
_    I
                          REFS. 7-5, 7-22
         0
          0
     I

      I  LEAD-ACID

      I
                                      NICKEL-ZINC
                     10

              ENERGY DENSITY, Watt-hr/lb
20
Figure 7-26.
  Comparison of Energy/Power Density Characteristics of High

  Power Density Lead-Acid and Nickel-Zinc Batteries
                                 7-38

-------
 0
2
  3          4
CELL CAPACITY, hr
Figure 7-27. Nominal Discharge Characteristics of 5 AH Nickel-Zinc-Cell at 75 °F

-------
                              3           4
                            CELLCAPACITY.hr
Figure 7-28. Nominal Discharge Characteristics of 5 AH Nickel-Zinc
             Cell at Various Temperatures

-------
  2.5
CD
   1.5
                  	   I    Amp RATE(~C/2.5)4mA/cm2
                  	10  Amp RATE(~ 4C)40mA/cm2
                 1.72 OPER.  CURR. VOLT.
                     AFTER 24 hr STAND
             I
                                                         REF. 7-6
0      20      40     60      80      100  0      40     80
                         DISCHARGE CAPACITY, %
                                                                     120
         Figure 7-29. Representative Charge-Discharge Characteristics of
                     2- 2.5 AH Nickel-Zinc Cells

-------
nickel-cadmium cell in that an equilibrium of generation and recombination
is achieved so that pressure rise is limited and hermetic sealing is possible.

At present, the nickel-zinc cell characteristically degrades with number of
operating cycles as indicated in Figs.  7-30 and 7-31.  Tendency of the zinc to
move around and loss of electronic contact are given as reasons for the loss
of capacity.  Dendritic shorting has not been a problem with the nickel-zinc
cell.

A repeatable life of 150 complete discharges is currently possible. This is
comparable to the capability of the lead-acid cell and is perhaps one-fifth that
of the nickel-cadmium cell. Atomics International (Ref. 7-13)  and
Professor Edwin Gilliland of the Chemical Engineering Department at MIT,
(Refs. 7-3 and 7-14) report a deep depth cycle life  of greater than 500.  Little
is known of the cycle life under float operation and  at low depths of discharge.
7.5.3.2     Industrial Capability
Government support of nickel-zinc battery development has been confined to
the U.S. Army Electronic Components Laboratory,  Fort Monmouth,  New
Jersey, with Mr.  Martin Sulkes the cognizant project officer.   Since the
success of the nickel-zinc battery is associated with development of reliable
zinc electrodes and separators, the directed effort of the NASA Lewis
Research Center and the Air Force Aero Propulsion Laboratory in these areas
should also be considered.   Principal  industrial efforts have been centered
among the following organizations:
      Eagle Picher, Joplin, Missouri
      Energy Research, Bethel, Connecticut
      E.S.B., Raleigh,  North Carolina
      General  Electric,  Gainesville, Florida
      General  Telephone and Electronics, Bayside,  New York
      Gould Battery Company,  Minneapolis, Minnesota
                                    7-42

-------
1.6
1.4
1.0
 0
                                             100
                                                                   INITIAL   _
                           60   30
                          CYCLES
  0
     3          4
CELL CAPACITY, Amp-hr
    Figure 7-30.  Nominal Discharge Characteristics of 5 AH Nickel-Zinc Cell
                 at 75-F After Cycling Tests to 75% DOD at C/2. 5 Rate

-------
   8


   7
2
4



3


2

 <

0
                CHARGE AT 2 Amp WITH 15% OVERCHARGE
                DISCHARGE AT 4 Amp  TO 1.0 V CUTOFF
                REF. 7-4
    0
                50
100
 CYCLES
150
200
       Figure 7-31.  Capacity vs Cycles for Nickel-Zinc Cells

-------
      Gulton Industries, Inc. ,  Metuchen, New Jersey
      NAR-Atomics International,  Canoga Park,  California
      Whittaker Corporation, Denver,  Colorado
      Yardney Electric, Pawcatuck, Connecticut
Other organizations such as Delco-Remy and Leesona-Moos might be involved
in any long range development program due to their experience with zinc
electrodes.
7.5.4      Summary of Battery State of the Art
Characteristics of the three candidate batteries are summarized in Table 7-5.
Based on the theoretical voltages,  it is  apparent that the lead-acid battery
would have one advantage over the  others in that the number of cells  would be
lower to achieve a given voltage.   This  is particularly important for  the hybrid
vehicle in that the assigned voltages are on the order of 200 volt for the pas-
senger  cars and vans and 400 volt  for the buses.  (The  checking of fewer cells
should reduce the maintenance time for the battery system.)

In terms of theoretical energy density,  it appears that the  nickel-zinc battery
has a definite potential advantage compared to the other two.

Relative costs as indicated  on the chart are based upon raw material costs of
the electrodes.  Construction of a  lead-acid battery is relatively simple com-
pared to the other two battery types so the differences could be even  more
pronounced.  It is expected that construction of the nickel-zinc battery will
follow  closely the configuration of  the nickel-cadmium battery.

Demonstrated power density of the three battery types is perhaps inconclusive
because of the limited test time at  these values.  They  are  shown only to
indicate that  some rather high power densities  have been obtained.  Those
listed have been achieved for times of only seconds; even higher power densities
have been demonstrated on  a microsecond basis.   The nickel-zinc  battery
seems to demonstrate an encouraging combination of both high energy and
                                    7-45

-------
        Table 7-5.   Characteristics  of Secondary Batteries Selected for Investigation
CHARACTERISTICS
Voltage, Theoretical
Theoretical Amp-hr, AH/lb
Theoretical Energy Density, W-hr/lb
Relative Cost'''
Demonstrated Capability
Power Density, W/lb
Bipolar
Prismatic
Energy Density, W-hr/lb
Bipolar
Prismatic
Volumetric Power Density, W/in.
Bipolar
Pr ismatic
Cycle Life at Depth of Discharge
Bipolar

Pr ismatic
BATTERY TYPE
Lead-Acid
2. 041
37. 8
77. 1
1. 0


226
328

23. 3

22. 5
1. 82
200,000 at
2. 0% at 14C
rate*:':
19,000 at
<5%t
Nickel -Cadmium
1.299
73. 3
95.3
11. 1


450
100
8.3
18

33
1. 5



34,000 at 25%
at C/10 ratett
Nickel-Zinc
1. 735
85.4
148. 1
2. 5


	
180

22

	
1.6



2,300 at 30%^
Based on Active Material Cost
Ref. 7-15
tt
Ref. 7-16
Ref. 7-17
                                   "?Ref. 7-18

-------
power density.  (Except for the bipolar nickel-cadmium and the nickel-zinc
batteries,  the power and energy densities were measured under different
conditions  and,  hence, are not consistent with one another.)

Volumetric power density indicates a very strong advantage to bipolar type
construction. No strong advantage is indicated for any  battery type.

There are  few test results which would indicate the potential cycle life of the
candidate batteries at low depths of discharge.  Since high-cycle life has been
achieved with what might be considered a highly experimental lead-acid
bipolar cell, the more highly developed prismatic  cell could prove to perform
even better. Figure 7-32 is an attempt based on rather limited data to define
the relationship between cycle life and depth of discharge.  While a straight
line on this chart may not represent a true situation,  it  is generally accepted
in predicting cycle characteristics of nickel-cadmium batteries.   Other
observers, however,  feel that a line of constant energy  may be more signifi-
cant and one is shown plotted in this figure.  It is obvious that  such a result,
if true, would indicate reduced cycle life  characteristics for a hybrid electric
vehicle.
7.6         DESIGN AND DEVELOPMENT GOALS
Because of the problem  of cost and availability associated with nickel-cadmium
batteries,  they have been  excluded from consideration in the remainder  of the
discussion in Section 7.
7.6.1       Vehicle  Battery Requirements
For each class of hybrid vehicle, battery requirements  are influenced by
numerous factors.   Furthermore, once battery power and energy require-
ments are  defined,  the power and energy density  requirements will be estab-
lished by available powertrain weight less the weight of  all other powertrain
components and subsystems.  Since  component and subsystem weights will
increase with the severity of imposed vehicle specifications (e.g., accelera-
tion, peak  cruise speed), the resulting reduction in allocated battery weight
will correspondingly increase the severity of battery design requirements.
                                    7-47

-------
   I06
      h \
   10*
UJ
DC
O
I—
CO
UJ
	I


O
                 GOULD-NATIONAL
             \   BIPOLAR (1968)
                 (REF. 7-15)
              EAGLE-PICHER
              MILK TRUCK
              SIMULATION
              (REF 7-16)

               \   ^-STATE-OF-ART

                   \
                                            HYBRID
                                            GOALS
   10'
     0
                     \
             •CONSTANT
              ENERGY       \

             fc:,       ESB     \
                       PROJECTION N
                       (REF 7-19)--  N
                SLI     "m
            REQUIREMENT  "
         (SAE TEST, REF 7-11)
                     PRESENT
                     CAPABILITY ESB
20        40        60

     DEPTH OF DISCHARGE, %
                                            80
100
            Figure 7-32.  Cycle Life of Lead-Acid Batteries
                               7-48

-------
As indicated in Section 7.4,  the hybrid vehicle battery must be capable of

a large number  of cycles and of sustaining high currents for a period of

up to 20 sec.  As an additional constraint the battery should be capable of

accepting all the charge current delivered by the generator.  An indication of

requirements for the family car is given by the results  of analyses using the
DREW Emission Driving Cycle and Design Driving Cycle (Table 7-6).


The development goals of 500-hr design life or 100, 000 mi of service are
arbitrary but in  keeping with a requirement that the hybrid vehicle be econom-

ical and not present any major impact upon vehicle operation.  This develop-

ment goal would correspond  roughly to the design life of the engine.
           Table 7-6.  Battery Development Goals, Family Car
                           (Lead-Acid Battery)
          DHEW Emission
           Driving Cycle
       38 AH battery operating
       for 1370 sec
       7.5 vehicle miles with
       73 battery charge/
       discharge cycles and
       1 . 34 AH depth of
       discharge
       Design driving cycle
       38 AH battery delivered
       462 amp
Hybrid Vehicle-Family
Car Development Goals
38 AH battery at less than
5% depth of discharge to
deliver up to 500 amp

5000 hr of operation
and 100, 000 vehicle
miles with 975, 000
charge/discharge cycles
                                   7-49

-------
The life of 975,000 cycles is well beyond any demonstrated performance
and thus becomes a critical development goal.   If the DHEW Driving Cycle
is representative of average driving requirements (a conservative assump-
tion),  then each  event in the cycle would occur over  13,000 times during the
life of the batteries.

The data in Table 7-6 can also be used to provide additional information on
battery operation. With the battery capacity established to provide low
emission levels and the maximum current established from the Design
Driving Cycle, an assumed power density for the lead-acid battery of
150 watt/lb would result in a requirement for 680  Ib of batteries. In a.
similar fashion for the nickel-zinc  battery, with a power density of
250 watt/lb and  30 AH of capacity  needed,  the battery weight would  be  410 Ib.
At these weights  and capacities the energy density of the lead-acid and nickel-
zinc batteries would be  16.5 and 22.5 watt-hr/lb,  respectively.

In a similar fashion the weights of batteries and their requirements for the
other vehicles  can be obtained and these  are indicated in Table 7-7.   Use of
the parallel configuration will reduce the battery capacities shown by about
ten percent.

7.6.2       Battery Development

7.6.2.1     Cell  Capacity

Required battery capacities as determined in this study are preliminary and
further battery testing  and  design analysis are needed before the  final
battery capacities can be specified. These capacities have been based upon
cell models which must be  verified; furthermore, information is  needed on
such considerations as degradation with  time.  Changes to the system as
well as differences between actual and design efficiencies will also have
a bearing upon the final battery capacity  which might be established.
                                    7-50

-------
Table 7-7.  Summary of Battery System Design and
 Operating Characteristics, Series Configuration
CHARACTERISTICS
Generator Current, amp
Maximum Charge Voltage
Battery Capacity. AH
No. of Cells
Majtimum Discharge Current, amp
Minimum Battery Voltage
Battery Weight. Ib
Battery Volume, ft
Battery Power Density
W/lb
W/in. 3
Battery Energy Density
W-hr/lb
W-hr/in. 3
PASSENGER CAR
Commuter
Lead-
Acid
17
340
20
147
148
220
300
2.. 3

109
8.3

20
1. 5
Nickel -
Zinc
17
340
16
170
148
220
170
1.5

192
13.3

29
2.0
Family
Lead-
Acid
38
340
38
147
462
220
680
4.3

ISO
15.0

16.5
1.5
Nickel -
Zinc
38
340
30
170
462
220
410
2. 7

250
24. 4

22. 4
2.0
VAN
Low -Speed
Lead-
Acid
53
340
40
147
402
220
720
4.6

127
11.3

16.4
1. 5
Nickel-
Zinc
53
340
32
170
402
220
440
2.9

211
18. 1

22.3
2.0
High-Speed
Lead-
Acid
54. 5
340
40
147
402
220
720
4.6

127
1 1.3

16.4
1.5
Nickel -
Zinc
54.5
340
32
170
402
220
440
2.9

211
18. I

22.3
2.0
BUS
Low -Speed
Lead-
Acid
100
680
90
294 .
506
440
2700
20.4

83
6. 3

20
1. 5
Nickel -
Zinc
100
680
70
340
506
440
1500
12.5

149
10.4

29
2.0
High-Speed
Lead-
Acid
79
680
79
294
142
440
2400
18.0

27
2.0

20
1. 5
Nic kel -
Zinc
"79
680
65
340
142
440
1400
11. 6

45
3. 1

29
Z. 0

-------
Battery capacity is established by the required charge acceptance to
produce low emission levels and the current discharge capability to achieve
designated vehicle accelerations.  A reduction in the acceleration require-
ments would have an extremely pronounced effect upon battery capacity.
For the family car the installed battery capacity could be  reduced by one
third if the  DHEW Emission Driving Cycle acceleration levels formed the
specifications.

7 . 6. 2 . Z     Power and Energy Density

Based on  the previous .discussions, it appears that power densities of
150 and 250 watt/lb are reasonable objectives for the lead-acid and nickel-
zinc batteries,  respectively.   It has been determined that on the hybrid
vehicle the battery depth of discharge is 5  percent or less; therefore,
these power densities need only be achieved for shallow discharge.   To
the power density requirements must be added the other constraints  of
energy density, cycle life, and degradation.  The power and energy densities
as determined by available battery weight in the powertrain for each class
of vehicle can be higher or lower than these values depending on the  lieat
engine used and the allowable  powertrain  weight (see Section 11).

7.6.2.3     Hybrid Battery Life

As indicated for the family car about one million charge/discharge cycles
would be  expected for each 100, 000  mi of  operation.   Even if the design
life were  to be decreased to 50,000  mi, the resulting number of cycles
would be well beyond any existing demonstrated capability.  It is there-
fore important that this criterion be  prominent in any development pro-
gram . Furthermore,  the battery should be exposed to a reproduction of
the current  levels and charge/discharge periods resulting  from operation
over the emission driving cycle in a  hybrid vehicle, rather than to the
                                    7-52

-------
normally accepted procedure of repetitive  cycles having constant magnitude
and duration.

7.6.2.4    Charge Acceptance

An important finding in the computer studies to determine minimum emis-
sion designs has been the importance of charge acceptance characteristics
indicated by the cell model.   Charge acceptance is not ordinarily treated
with enough importance in any battery  development program and care
should be taken that the charge characteristics are fully explored  and
acceptance rates maximized; charge acceptance will be particularly impor-
tant if regenerative braking is utilized.   Laboratory  studies might be  con-
ducted to determine whether the maximum  allowable voltage limits can be
raised in order to improve charge acceptance.

7.6.2.5    Thermal Control
A desirable characteristic of any  cell or battery is  that the dominant
reaction proceed reversibly.  Also, the current efficiency of the bat-
tery should be as near  100 percent as possible.   In the absence of any
side reactions,  efficiency of a reversible battery may be described in
terms of voltages.   Therefore, charge efficiency,  n   ,  of a battery is
given by
                                    7-53

-------
where Ep  is the charge voltage and ER is the reversible or theoretical cell
voltage and the discharge efficiency,  T| n, is given by
                                       ED
where E~ is the discharge voltage.  Overall battery efficiency, r|   can be
expressed as the product of the two efficiencies using the average values
                                       F    F     F
                                        R     D     D
In the analyses of this study the battery current efficiency will be near.ly 100%
since the limiting charge voltage has been established low enough to avoid
the normal side reaction,  the  electrolysis of water.  There will  be  some
thermal  flux created in the battery due to discharge inefficiency, but this
should not be too much of a problem since the battery will normally be oper-
ating in a range close to the reversible voltage.

A more critical thermal problem associated with the battery will be that due
to overcharge.  The charge control system should include provisions to pre-
vent the  continued charging of a fully charged battery.  To accomplish this,
the battery will  need a control system based upon sensors which measure
battery voltage and possibly temperature.  While a sensor which could mea-
sure battery state -of-charge would be ideal for this purpose,  such  sensors
are not yet sufficiently accurate to serve  as a control input.

It is quite important that battery thermal  control be an integral part of any
battery development program.  Adequate thermal control may be as impor-
tant to the successful  performance of a hybrid vehicle battery as any other
factor.
                                    7-54

-------
7.6.3       Summary of Development Goals
A preliminary listing of the development goals for the hybrid batteries is
given in Table 7-8.  Battery weights shown result from  stipulating that for
lead-acid and nickel-zinc batteries, respectively,  the power densities not
exceed  150 watt/lb and 250 watt/lb and that energy densities not exceed
16.  5 watt-hr/lb and 22. 5 watt-hr/lb; similarly the volumes shown were dic-
                                         3
tated by limits of 1. 5 and 2. 0 watt-hr/in.  .

It should be emphasized that these specifications are preliminary since  a
more detailed  system analysis  of a specific vehicle might indicate that cer-
tain requirements should be relaxed such as that of acceleration  since this
factor has dominated battery sizing for the family car.  Another factor which
has influenced the battery sizing has been  the cell modeling. It might be
possible to develop better batteries or perhaps the combination of life and
cycle requirements may not cause a relaxation in requirements.  It might
also be  (hat the combination of  energy and power density along with the life
and cycle requirements may not be achieved which could also reflect on these
development goals.
7. 7         RECOMMENDED BATTERY DEVELOPMENT PROGRAM
With battery design and development goals tempered by current and projected
technology,  a development  program oriented toward the hybrid electric
vehicle  can  be evolved.  A suggested program  is schematically described in
Fig. 7-33.
7. 7. 1       General Battery Development (Phase I)
7. 7. 1. 1     Development of  Lead-Acid Battery for Hybrid Electric  Vehicle
First,  it is  apparent that lead-acid battery technology exists which could
provide an acceptable interim battery for the hybrid electric vehicle  by 1973.
While the technology exists, the hardware does not, so  it will be  necessary
in a Phase I Program to redesign and repackage the battery into  a form more
suited for the hybrid vehicle and to make  such  minor improvements which
                                    7-55

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                 Table 7-8.  Summary of Battery Design Specifications,  Series Configuration
i
01
CHARACTERISTICS
Battery Capacity, AH:
Lead -Acid
Nickel-Zinc
Maximum Battery Weight, Ib:
Lead -Acid
Nickel-Zinc
Maximum Battery Volume, ft :
Lead-Acid
Nickel-Zinc
Minimum Battery Voltage, v
Maximum Charge Voltage, v
Life, yr
Charge/Discharge Cycles
Cycle Distribution
Maximum Rate
Temperature, °F:
Normal
Capability
Maximum Charge Rate
Maintenance
PASSENGER CAR
Commuter
20
16
300
170
2. 3
1. 5
220
340
5
500,000
Family
38
30
680
410
4. 3
2.7
220
340
5
1, 000, 000
VAN
Low -Speed
40
32
720
440
4.6
2.9
220
340
5
1, 000, 000
High-Speed
40
32
720
440
4.6
2.9
220
340
5
1, 000, 000
1% OF CYCLES, 5% DOD. 12C* (5 sec) & 5C
2% OF CYCLES. 2% DOD, 6C (5 sec) & 3C
7% OF CYCLES, 1% DOD, 2C (2 sec) & C
10% OF CYCLES, 0. 5% DOD. C (2 sec) & C/2
80% OF CYCLES. 0. 25% DOD, C/2
C/10* (60 min) + 12C (5 sec)
BUS
Low -Speed
90
70
2700
1500
20. 4
12. 5
440
680
5
1, 000, 000
High-Speed
79
65
2400
1400
18. 0
11.6
440
680
5
500,000
3% OF CYCLES, 5%
DOD. 6C (5 sec) & 3C
7% OF CYCLES, 1%
DOD. 2C (2 sec) & C
10% OF CYCLES, 0. 5%
DOD, C (2 sec) & C/2
80% OF CYCLES, 0. 25%
DOD, C/2
C/10 (60 min) f 6C
(5 sec)
30-120
0-160
>C (lead acid) >1 . 3C (nickel -zinc)
2 yr minimum
P/KT - Capacity Ampere Hours _ ,
'•' Time to 100% Discharge Hours -im,jL
DOD - Depth of discharge
res

-------
             1971
1972
1973
    CALENDAR YEAR
1974   •    1975   •   1976
1977
1978
PHASE I
PHASE H
           DEVELOPMENT OF LEAD-ACID
           BATTERY BASED ON 1970
           TECHNOLOGY
          DETAILED BATTERY SYSTEM
          DESIGN OE HYBRID VEHICLE WITH
          EXPERIMENTAL STUDIES OF
          BATTERY INTEGRATION PROBLEMS
                 TEST OF  I
                 ADVANCED I
                 LEAD-ACID1
                 BATTERYJ

                       REQ'TS
          APPLIED RESEARCH OF ADVANCED
          LEAD-ACID BATTERY
          ADVANCED RESEARCH OF NICKEL-
          ZINC BATTERY
                            DEVELOPMENT AND PREPRODUCT.
                            OF ADVANCED HYBRID VEHICLE
                            BATTERY
PHASE
          APPLIED RESEARCH OF ADVANCED BATTERY TYPES
          FOR HYBRID AND ALL ELECTRIC VEHICLES
                    Figure 7-33.  Battery Development Program Schedule

-------
will not add undue  risk or expense.  An objective of this program would be to
provide battery performance equivalent to or better than that characterized
in Fig.  7 - 1.
7.7. 1.2    Hybrid Electric Vehicle Battery Simulation and Analysis
At the same time it would be worthwhile to conduct additional studies of the
hybrid electric  vehicle using more accurate battery simulations, and driving
profiles more representative of the wide variety of vehicle usage throughout
its  lifetime.  This would allow a better evaluation of charge  acceptance,
thermal effects, charge control,  cycle life,  and other  potential problems.
As  the more advanced cells and batteries become available, these could then
be tested and compared with the results obtained in these more detailed
studies.
7. 7. 2       Advanced Battery Development (Phase II)
As  the second phase of the battery  development program, advanced studies
should be undertaken for both the lead-acid and nickel-zinc batteries.  Fol-
lowing is a list  of possible and  suggested  tasks which might  be included in
the Phase II effort.
7. 7. 2. 1     Lead-Acid Battery  Development
From available data and through discussions with lead-acid  battery manu-
facturers and cognizant government personnel it is apparent that there  is a
possibility for  much improvement of the lead-acid battery and optimization
for the hybrid electric vehicle.  Some  of these areas where development
could be productive are listed below.
           a.    Increase electrode area  per  unit volume
                 1.     Use thinner plates
                 2.     Use corrugated plates
           b.    Decrease internal resistance
                 1.     Redesign posts and internal collectors
                 2.     Optimize grids for current collection
                                    7-58

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                  3.    Use bipolar design
                  4.    Decrease electrode spacing
                  5.    Develop new grid alloys
                  6.    Consider stirred electrolyte
            c.     Investigate new concepts
                  1.    Lightweight grids
                  2.    Plastic cases
                  3.    Low maintenance design
                  4.    Improved lead oxide
                  5.    Stirred electrolyte
                  6.    Cylindrical packaging
            d.     Improve charge control
                  1.    Use rapid charge systems
                  2.    Increase charge acceptance
7. 7. 2. 2     Nickel-Zinc Battery Development
Most development work accomplished  so far with the nickel-zinc battery has
been directed towards utilization of its good energy density characteristics
and so there has been relatively little  effort devoted to determination or
development of nickel-zinc battery characteristics for low-energy discharge
under controlled float operation.  Studies of this nature should be  pursued
along with the development and determination of optimum charge control
methods.

The U. S.  Army, which has been developing nickel-zinc batteries, is pri-
marily interested in low-rate,  high-depth-of-discharge batteries  to replace
nickel-cadmium batteries.  In battlefield situations, the long cycle life of the
nickel-cadmium cell is not needed so the good energy density, limited  cycle
life, and relatively low cost of the nickel-zinc battery  are attractive.  As a
result, present  cell designs may not be  configured towards hybrid vehicle
characteristics.  In  like manner, the Army is  not interested in systems
                                    7-59

-------
employing such innovations as a stirred electrolyte battery,  even though the
performance of the  electrolyte is significant, since this kind of battery must
sacrifice some  energy density.  However,  the zinc electrode is especially
sensitive to concentration polarization effects,  so some experimental work
with stirred electrolyte systems should be conducted.

The  zinc  electrode and its  separator system are the keys  to successful
development of  the nickel-zinc battery.  While some  performance improve-
ment can be made in the  nickel electrode,  the major development emphasis
should be on the zinc electrode.

Funding of nickel-zinc batteries may have important consequences elsewhere.
Whether the nickel-zinc cell may directly  replace nickel-cadmium or
LeClanche cells is questionable because of the different voltage range.   But
the energy and power density capabilities of  the nickel-zinc battery are, as a
minimum, about 50 percent greater (with possibly reduced cycle life, how-
ever) than either nickel-cadmium or lead-acid systems,  and this along with
attractive cost would provide a significant market incentive.

The  two major shortcomings of the nickel-zinc  battery are its  cost, perhaps
two to three times  that of a lead-acid battery,  and a questionable cycle life.
A feature of the nickel electrode is that it  is relatively unaffected during life
of the battery,  and in nickel-cadmium or zinc batteries it is  the cadmium or
zinc electrodes  which degrade.  Provided that reasonable  development objec-
tives can be met during early development phases, the final nickel-zinc bat-
tery design might consider periodic maintenance of the battery.  The design
should probably allow replacement  of the zinc electrode, the separator
system,  and the electrolyte. Since the major and expensive components of
the battery are  reusable, the cost of a nickel-zinc battery could possibly be
competitive with the lead-acid battery.
                                    7-60

-------
Development, funding of nickel-zinc batteries should be directed as described
above to the following areas in the approximate order of priority shown:
            a.     Zinc electrode
            b.     Zinc separator  system
            c.     Stirred electrolyte systems
            d.     Float characteristics
            e.     Charge control
            f.      Low maintenance, salvageable design
7. 7. 2. 3    Pre-Production Phase of Advanced Hybrid Electric  Vehicle
            Battery
After completion of Phase I and Phase II Programs,  a better indication of
battery requirements will be available and it should be possible to make a
decision as to which battery type  merited further effort.  Development of the
selected battery would then proceed into pre-production.
7. 7. 3       Battery Applied Research (Phase III)
As a concurrent task to Phases I  and II,  it would be desirable to maintain an
applied research program for advanced types of batteries.  This effort  should
be broad in scope and should be directed to develop batteries which might be
useful to either the hybrid electric  or all-electric vehicle systems.
                                    7-61

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7. 8        REFERENCES


7-1.     D. O. Koontz,  et al,  "Reserve Batteries for Bell System Use:
         Design of the New  Cell," Bell System Tech.  J., Vol. 1, no. 7,
         pp.  1253-1278 (1970).

7-2.     G. H. Gelb, et al,  "Design and Performance Characteristics of a
         Hybrid Vehicle Power  Trans," SAE Paper 690169, January 1969.

7-3.     S. Goldin, Development of Zinc  Electrodes,  Massachusetts Institute
         of Technology,  Master of Science  Thesis,  June 1970 .

7-4.     M. J. Sulkes, "Nickel-Zinc Secondary Batteries," Proc. 23 Annual
         Power  Sources Conference, May 1969.

7-5.     A.  Charkey,  "Performance Characteristics of Nickel-Z Lnc Cells,"
         Proc. 23rd Annual Power Sources Conference,  May  1969.

7-6.     P.  Goldberg, "Nickel Zinc Cells - Part I," Proc. 21st Annual Power
         Sources Conference, May 1967.

7-7.     E.P. Broglio,  "Nickel-Zinc Cells - Part 2, " Proc. 21st Annual
         Power  Sources Conference, May 1967.

7-8.     P. V. Popat,  E.J.  Rubin, and R. B.  Flanders, "Nickel-Zinc Cells -
         Part 3," Proc. 21st Annual Power Sources Conference, May  1967.

7-9.     Storage Batteries, U.S.  Department of Commerce,  1967 Census of
         Manufacturers, Preliminary Report MC 67 (P)-36E-1 (October 1969).

7-10.    S. Ruben,  U.S. Patent 3, 486, 940, 1969.

7-11.    S. Ruben,  Personal  Communication, 25 August 1970.

7-12.    J. H. Bigbee, Per sonal Communication, McCulloch  Corporation,
         Los Angeles, California.

7-13.    L.  Heredy,  Personal Communication, Atomics International,
         11 November 1970.

7-14.    Professor Gilliland, Personal Communication,  Massachusetts
         Institute of Technology,  19 November 1970.

7-15.    R. D. Nelson, " Des ign and Fabr ication  of 300 Volt,  3. 6 KW Pulse
         Type Bipolar Lead-Acid  Battery for Pulse Duty," Gould National
         Report 68D-116, 20  December 1968.

7-16.    F.  Dittman,  Personal  Communication,  Eagle-Picher,  7 July  1970.
                                   7-62

-------
7-17.    D. E.  Mains, "Evaluation Program for Secondary Spacecraft Ce 1 Is ,"
         Seventh Annual Report of Cycle Life  Test,  Crane Ammunition
         Depot Report QE/C 71-, March 1971.

7-18.    R. Kruger  and  J. W. Barrick,  "Battery Ratings," SAE Paper 660029,
         10-14 January  1966.

7-19.    J. R. Smyth,  Power Systems for Electric  Vehicles,  Battery Council
         International, 8 May 1970.

7-20.    B. Agrus,  "Testing Batteries for Vehicular Applications," J^
         Electrochem. Soc.  117 (9), pp. 1204-1210,  1970.

7-21.    M. Barak,  "Development in Electro-Chemical Energy Conversion
         Devices - Batteries and Fuel  Cells," Institute of Electrical
         Engineering, May 1965.

7-22.    J.  Macres,  Personal Communication,  C&D Batteries,  6 July 1970.

7-23.    C. L.  Rosen, Personal  Communication, Gulton Industries,
         29 October 1970.

7-24.    S.  Char lip,  et al,  "Parallel Operation of Two Battery Systems for
         Vehicular Propulsion, " IEEE Automotive  Conference, September
         1967.


7.9        BIBLIOGRAPHY
Caprioglio,  Giovanni, "Review of Battery Systems for Electric Vehicles,"
         SAE Paper 690129.

Cohn,  E. M., "Electrochemical Space Power Sources, " Space Power Systems
         AGARD (November 1969),  pp.  443-501.

Dalin,  G. A., and Kober,  F.B., "A Hybrid Battery System for Electric
         Vehicle Propulsion," SAE Paper 690203.

Eisenberg,  M.,  "The New Mercuric Oxide-Cadmium Battery System for
         Medical and Implantation  Applications, "  1ECEC  Conference,
         Washington, D. C.,  22-26 September 1969.

General  Service Manual -  Motive  Power Batteries, C&D  Batteries,
         Section .7-610, 1966.

Giner, J., and Holleck, G. L., Aluminum Chlorine Battery,  Tyco Labora-
         tories Report NAS1-2-688 (26 August  1969).
                                 7-63

-------
Haring,  H. E., and Thomajs, U. B.,  "The Electrochemical Behavior of Lead,
         Lead-Antimony and Lead-Calcium Alloys in Storage Cells," Trans.
         Electrochem.  Soc.,  68,  293-307 (1935).

Jasinski, R., High Energy Batteries (Plenum Press, 1967).

Kettler,  J. R., Meeting on Hybrid Vehicle Batteries, Argonne National
         Laboratories, 9 September 1970,  The Aerospace Corporation
         ATM-71(6769)-8  (6 October 1970). *

Kummer, J. T., and Weber, N.,  "A Sodium-Sulfur Secondary Battery, "
         SAE Paper 670179, 9-13 January  1967.

Longer Life for Lead-Acid Stationary Batteries, C&D Batteries,  Section
         12-400, 1 November  1964.

Moulds,  D. E.,  "Cadmium, " Minerals  Yearbook, Department of Interior
         (1968).

Price, A. C., "A Proposed New Rating Standard for  Automatic Batteries, "
         SAE Paper 680392, 20-24  May 1968.

Ragone,  D. V.,  "Review of Battery  Systems for  Electrically Powered
         Vehicles, " SAE Paper 680453.

Roberts,  W.H., "Batteries,"  Machine Design, pp.  26-29 (21 June 1968).

Ruben, S.,  "Sealed Mercurial Cathode Cells," CITCE Lecture, Tokyo,
         Japan, September 1966.

Seiger, H. N.,  et a.l,  "Organic Electrolyte  Batteries," 21st Power Sources
         Conference, 1 6-1 8 May  1 967.

Shimotake,  H.,  et al,  Lithium/Sulfur Cells and  Their Potential for Vehicle
         Pr opuls ion,  International Electric Vehicle  Symposium, Phoenix,
         Arizona,  5-7 November  1969.

Shimotake,  H.,  Fischer, A. K., and Cairns, E. J., Proc. 4th Intersociety
         Energy Conversion Conference, AIChE, New York,  p. 538 (1969).

Vinal, G. W., Storage Batteries (John Wiley and Sons, Inc.,  New  York,  1955]
         4th ed.

Yao,  N.P., Heredy,  L. A., andSanduers,  R.C., "Secondary Lithium-Sulfur
         Battery, " Electrochem.  Soc.  Paper  60, Atlantic,  New Jersey,
         4-8 October 1970.
 Not available outside The Aerospace Corporation
                                    7-64

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            SECTION 8

   HEAT ENGINE PERFORMANCE
CHARACTERISTICS AND OPERATION

-------
                              CONTENTS
8.     HEAT ENGINE PERFORMANCE CHARACTERISTICS
      AND OPERATION	     8-1
      8. 1  Introduction	     8-1
      8.2  Otto Cycle (Spark Ignition) Engine	     8-1
           8.2.1    General Description   	     8-1
           8.2.2    Hybrid Operation	     8-5
           8.2.3    Engine Characteristics	     8-13
                    8.2.3.1   Specific Fuel  Consumption	     8-13
                    8.2.3.2   Specific Weight  	     8-16
                    8.2.3.3   Specific Volume	     8-19
      8.3  Diesel Cycle (Compression Ignition) Engine   	     8-23
           8. 3. 1    General Description	     8-23
           8.3.2    Hybrid Operation	     8-26
           8.3.3    Engine Characteristics	     8-30
                    8. 3. 3. 1   Specific Fuel  Consumption	     8-30
                    8.3.3.2   Specific Weight  	     8-35
                    8.3.3.3   Specific Volume	     8-37
      8.4  Brayton Cycle  (Gas Turbine Engine)   	     8-39
           8.4. 1    Thermodynamic Processes   	     8-39
           8.4.2    Vehicular Design Considerations	     8-42
           8.4.3    Engine Characteristics	     8-48
                    8.4.3.1   Specific Fuel  Consumption	     8-54
                    8.4.3.2   Specific Weight	     8-54
                    8.4.3.3   Specific Volume	     8-55
      8.5  Rankine Cycle	     8-55
           8. 5. 1    Thermodynamic Processes   	     8-55
           8.5.2    Vehicular Design Considerations	     8-57
                                   8-i

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CONTENTS (Continued)









8. 6







8. 7
8. 8





8.9
8.5.2.1 Expander 	
8.5.2.2 Burner 	
8. 5. 2. 3 Boiler 	
8. 5. 2. 4 Condenser 	
8. 5. 2. 5 Regenerator Economizer . . . .
8. 5. 3 Engine Characteristics 	
8. 5. 3. 1 Specific Fuel Consumption . . . .
8.5.3.2 Specific Weight 	
8.5.3.3 Specific Volume 	
Stirling Cycle 	
8. 6. 1 Thermodynamic Processes 	
8. 6. 2 Cycle Characteristics 	
8. 6. 3 Operating Considerations 	
8. 6. 4 Engine Characteristics 	
8.6.4. 1 Specific Fuel Consumption. . . .
8.6.4.2 Specific Weight 	
8.6.4.3 Specific Volume 	
Comparison and Evaluation of Heat Engines . . . .
Technology Goals 	
8. 8. 1 Spark- Ignition Engines 	
8.8.2 Compres s ion- Ignition Engines 	
8. 8. 3 Gas -Turbine Engines 	
8. 8. 4 Rankine Engines 	
8. 8. 5 Stirling Engines 	
References 	
. . 8-62
. . 8-62
. . 8-63
. . . 8-63
. . 8-64
. . 8-64
. . 8-64
. . 8-64
. . 8-68
. . 8-68
. . 8-68
. . 8-68
. . 8-73
. . 8-76
. . 8-76
8-80
. . 8-80
. . 8-80
8-87
. . 8-87
. . 8-91
. . 8-93
. . 8-94
. . 8-95
. . 8-96
          8-ii

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                                 TABLES
8-1.     Gas Turbine Characteristics Assumed in Cycle

8-2.
8-3.
8-4.
8-5.
8-6.
8-7.
8-8.
8-9.
8-10.
8-11.
8-12.
Analysis 	
Gas Turbine Cycle Analysis Results 	
Gas Turbine Engine Characteristics 	
Rankine Engine Characteristics 	
Performance of Rankine Heat Engines 	
Characteristics of Stirling Engines 	
Family Car Heat Engine Characteristics 	
Commuter Car Heat Engine Characteristics ....
Low-speed Van Heat Engine Characteristics ....
High-speed Van Heat Engine Characteristics ....
Low-speed Bus Heat Engine Characteristics ....
High-speed Bus Heat Engine Characteristics ....
8-45
8-46
8-49
8-60
8-70
8-77
8-83
8-83
8-83
8-84
8-84
. . . 8-84
                                   8-iii

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FIGURES
8-1.
8-2.

8-3.

8-4.
8-5.

8-6.

8-7.

8-8.

8-9.

8-10.

8-11.
8-12.
8-13.
8-14.
8-15.
8-16.

8-17.
The Otto Cycle 	
Spark Ignition Engine Performance Characteristics
(258-CID American Motors Ambassador) 	
Auxiliary Power Requirements (232-CID American
Motors Hornet) 	
S. I. Engine SFC Map (Normalized) 	
S.I. Engine Specific Fuel Consumption - Air/Fuel
Characteristics at Constant RPM 	
S. I. Engine Part Throttle Specific Fuel Consumption
(RPM Constant at 80-Percent Rated Horsepower) 	
S. 1. Engine Part Throttle Specific Fuel Consumption
(Optimum Throttle Setting) 	
S.I. Engine SFC Cruise Profile (Parallel Hybrid-
Vehicle Operation) 	
Minimum Specific Fuel Consumption -
Reciprocating Piston S. I. Engine 	
Minimum Specific Fuel Consumption -
Rotary Piston S. I. Engine 	
Specific Weight - Reciprocating Piston S.I. Engine . . .
Specific Weight - Rotary Piston S. I. Engine 	
Specific Volume - Reciprocating Piston S.I. Engine . . .
Specific Volume - Rotary Piston S. I. Engine 	
The Diesel Cycle 	
Compression Ignition Engine Performance
Characteristics (154-CID Daihatsu) 	
CI Engine SFC Map (Normalized) 	
8-3

8-4

8-6
8-7

8-9

8-10

8-12

8-14

8-15

8-17
8-18
8-20
8-21
8-22
8-24

8-25
8-27
   8-iv

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                         FIGURES (Continued)
8-18.   Cl Engine Part-Load Specific Fuel Consumption

8-19.

8-20.

8-21.
8-22.
8-23.
8-24.
8-25.

8-26.
8-27.
8-28.

8-29.
8-30.
8-31.

8-32.


8-33.
8-34.
8-35.

(RPM Constant at 80-Percent Rated Horsepower) 	
CI Engine Part- Load Specific Fuel Consumption
(Optimum Throttle Setting) 	 ' 	
CI Engine SFC Cruise Profile (Parallel Hybrid-
Vehicle Operation) 	
Minimum Specific Fuel Consumption - CI Engine 	
Specific Weight - CI Engine 	
Specific Volume - CI Engine 	
Gas Turbine Cycle and Schematic Arrangement 	
Effect of Recuperator Effectiveness on Recuperated
Brayton Cycle Performance 	
Cycle Diagram of Ford 704 Gas Turbine Engine 	
Design SFC of Automotive Gas Turbines 	
Part- Load BSFC Characteristics of Automotive Gas
Turbine Engines 	
Specific Weight of Automotive Gas Turbines 	
Specific Volume of Automotive Gas Turbines 	
Schematic Diagram of Rankine Engine Using Type B
Working Fluid 	
Efficiency of Steam Turbine and Reciprocating
Expanders as a Function of Power Output
(1200°F, 1200 psia) 	 	 	
Carnot Efficiency of Various Engine Types 	
Design SFC of Automotive Rankine Engines 	
Part-Load BSFC Characteristics of Automotive Rankine
Engine 	
8-29

8-31

8-32
8-33
8-36
8-38
8-40

8-41
8-43
8-50

8-51
8-52
8-53

8-56


8-58
8-59
8-65

8-66
                                  8-v

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                           FIGURES (Continued)



8-36.    Specific Weight of Automotive RankLne Engines	  8-67

8-37.    Specific Volume of Automotive Rankine Engines	  8-69

8-38.    Pressure-Volume and Temperature-Entropy Diagrams
         for Carnot  and Stirling Cycles	  8-71

8-39.    Stirling Part-Load Characteristics	  8-72

8-40.    Estimate of Response Characteristics for Stirling
         Engine  	  8-75

8-41.    Design SFC of Automotive Stirling Engines	  8-78

8-42.    Part-Load  BSFC Characteristics  of Automotive
         Stirling Engines	  8-79

8-43.    Specific Weight of Automotive Stirling Engines	  8-81

8-44.    Specific Volume of Automotive Stirling Engines	  8-82

8-45.    Heat Engine SFC Comparison	  8-86

8-46.    Heat Engine Weight Comparison	  8-86

8-47.    Heat Engine Volume Comparison	  8-86
                                    8-vi

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                               SECTION 8
   HEAT  ENGINE PERFORMANCE CHARACTERISTICS AND OPERATION


8. 1       INTRODUCTION
The hybrid propulsion concept treated in this  study comprises a heat engine/
generator power set, electric drive motor(s),  and batteries. The basic
function of the heat engine is to provide rotational power to the generator.
In the parallel configuration, which incorporates a direct mechanical
link to the drive wheels,  the heat engine may  simultaneously provide
power  to  the vehicle drive shaft.
The five candidate thermal engine systems which were examined for possible
use  in  the hybrid concept are:
      1.    Otto Cycle  (Spark Ignition Engine)
      2.    Diesel Cycle (Compression Ignition Engine)
      3.    Brayton Cycle (Gas Turbine  Engine)
      4.    Rankine Cycle ("Steam" Engine)
      5.    Stirling Cycle
Sections 8. 2 through  8. 6 of this report provide  a general description of each
system and  its design options  (where applicable), a discussion of considera-
tions pertaining to heat engine operation in the hybrid mode, and a charac-
terization of engine fuel consumption, weight,  and volume properties.
Section 8.7  compares and evaluates the relative merits of the alternative
engine types.   Guidelines for future engine development efforts are discussed
in Section 8. 8.
8. 2       OTTO CYCLE (SPARK IGNITION) ENGINE
8. 2. 1     General Description
Most spark-ignition engines operate on a reciprocating piston principle in
which a piston sliding back and forth in a cylinder transmits power through a
connecting rod and crank mechanism to the drive shaft.  The Wankel engine
                                     8-1

-------
substitutes a rotary member for the reciprocating piston, resulting in
definite engine weight and volume advantages  (See Section 8.2.3).  The
following  remarks on engine operation will be addressed to the four-stroke
reciprocating system which is typical of automotive designs worldwide.
The engine thermodynamic cycle is illustrated in  Fig.  8-1.  The familiar
four-stroke sequence of engine operations consists of an intake stroke
(terminating at Point  1),  a compression stroke (Point 1 to Point 2) followed
by ignition and combustion of the charge (Point 2 to Point 3), an expansion
or power  stroke  (Point 3  to Point 4), and an exhaust stroke (Point 4 to
Point 1).  The fuel charge  enters and the exhaust products leave the  cylinder
through poppet valves operated by a cam mechanism driven  by the crank-
shaft.  The charge is ignited by an  electric  spark, which is  timed in relation
to the top dead center piston position by speed and manifold  pressure con-
trols to ensure maximum performance  at different engine rpm and load
conditions.
The charge mixture is controlled in conventional engines by a  carburetor
consisting basically of a  venturi, fuel nozzle, and throttle valve. The
nominal air/fuel ratio is  about 15,  but values from 12 to 16  are  developed
over the normal  operating  range of the  engine.  Speed and load control is
achieved by altering  the position of the  throttle valve to restrict the flow of
air through the carburetor.  A number  of foreign manufacturers, including
Volkswagen, Opel, Mercedes,  Porsche,  Volvo, and  Triumph, have recent.ly
converted to port-type fuel injection systems  in their production engines,
primarily to avoid characteristically high HC emissions produced by
conventional carburetor systems during periods of acceleration  and
deceleration.
Representative performance curves for an automotive S. I.  engine are
shown  in Fig.  8-2  (Ref. 8-1).  Typically, the power output peaks at about
65 percent of maximum rpm and the rated performance of the  engine is
quoted at  this point.   Also,  the torque  curve peaks at about half  the speed of
the horsepower peak, while the lowest value of specific fuel consumption  (SFC)
occurs near  the midrange of speed.

                                   8-2

-------
oo
i
OJ
cr.
n>
CO
CO
LU
ai
Q_
                     S
                              CONST
                      CONST
                           VOLUME,  V
                                                      QC
                                                      LU
                                                      Q_
                                                                    CONST
                                                           ENTROPY,  S
                                      Figure 8-1.  The Otto Cycle

-------
   160
   140
   120
   100
§  80
CO
ct:
o
    60
   40
   20
     0
      0
                              SFC
                         I
                    I
1000    2000     3000
          ENGINE RPM
4000
                                       240
                                       200-
                                       160
                                                         o
                                       120
                                       0.6
                                       0.5
                                                          CO
                                       0.4
        Figure 8-2.  Spark Ignition Engine Performance

                    Characteristics (258-CID American

                    Motors  Ambassador)
                            8-4

-------
It should be noted that the power curve shown in Fig. 8-2 is based on
dynamometer test results obtained with an engine  stripped  of normal running
equipment and accessories,  including fan, pump,  generator, air  cleaner,
and conventional exhaust system.  When these as well as convenience acces-
sories such as power steering and air conditioning are  added to the engine,
the peak power output at the flywheel may be reduced by 25 to 30  percent.
Auxiliary power  requirements for a  135 hp, 232-CID engine are shown in
Fig. 8-3 (Ref. 8-2).  The air cleaner/exhaust system curve is an estimate
based on data from Ref. 8-3.  At a vehicle cruise speed of 80 mph, which  in
this system occurs at an engine rpm of  3450,  the loss due to accessories
and running equipment  is 26 hp.  At  rated conditions, the loss is  33 hp, or
25 percent of peak rated power.
8. 2. 2     Hybrid Operation
The curves shown in  Fig.  8-2 are typical of the limited performance data
normally supplied by the engine manufacturer.  They represent S.I.  engine
performance solely under the conditions where the throttle  is fixed in its
wide open position and  rpm is varied by an adjustment of external load.
Normally,  the automotive engine operates to accommodate  load and speed
changes by varying the  throttle setting;  therefore, a knowledge of engine
characteristics over  the complete spectrum of throttle  settings is essential
to the present investigation of hybrid vehicle potentialities.
A complete performance map for  a small automotive engine such as  might
be used in  the hybrid family car  is presented  in Fig.  8-4 (Ref. 8-4).  The
SFC is plotted versus engine gross horsepower output at constant rpm.   The
term "gross horsepower" refers to the  sum of the flywheel and accessory
power quantities.  The  near-closed throttle position appears at the upper left
hand corner of the plot.   This region is  characterized by high specific  fuel
consumption,  due partly to pumping losses created by throttling the incoming
air charge.   As the throttle plate  is opened at constant  rpm, the pressure  in
the intake manifold increases,  the pumping loss decreases,  the net engine
power output increases, and the SFC declines accordingly.
                                   8-5

-------
00
I
                          A - A/C COMPRESSOR
                          B - AIR CLEANER ft EXHAUST SYSTEM
                          C-FAN
                          D-POWER STEERING
                          E-ALTERNATOR (55A)
                          F - WATER PUMP
                                                                                       oc
                                                                                       ID
                                                                                       o
                                                                                       LU
                                                                                       or
                                                                                       en
o
Q.
                                                                                       cc.
                                                                                       o
                                           500   2000    2500    3000    3500    4000
                                               ENGINE RPM
                  Figure 8-3.  Auxiliary Power Requirements (232-CID American Motors Hornet)

-------
00
I
~J
          CO
                   ~~ OO  O O O
                   H: ro ir>  r- co
                                              WOT =WIDE OPEN THROTTLE
             100
                            20     30     40     50     60     70     80

                               GROSS  HORSEPOWER OUTPUT, % OF RATED

                ^MINIMUM SFC
                          Figure 8-4. S. !. Engine SFC Map (Normalized]

-------
During the above process the air/fuel ratio remains essentially constant.
At near full-throttle opening, a mixture enrichment device in the carburetor
goes into operation  to permit maximum power to be obtained from the engine.
Thus, the SFC passes through a minimum and begins  to increase with
enrichment of the charge as the throttle further moves toward the wide open
position.  Additional information on air/fuel effects related to throttle
position  is provided in Fig.  8-5.
A number of different engine operating modes may be postulated for the
hybrid vehicle  application.  For the series propulsion configuration,  in which
the coupling between engine and drive wheels is purely electrical, the engine
may operate at fixed speed and fixed power output, at fixed rpm and variable
power output, and at variable rpm and variable power output.  Studies  show
that the fixed power output mode does not match a number of vehicle duty
cycle energy requirements and/or may severely limit the maximum top
speed of the vehicle (See Section  10).  Therefore, this mode, which is
represented simply as a single point on the Fig. 8-4 operating map, will
not be discussed further at this time.
The fixed rpm  and variable power output mode is frequently used in engine/
generator power units and may also be applied to the hybrid vehicle.  Here
the engine rpm is held constant by the action of a governor (mechanical or
otherwise) which operates to adjust  the engine throttle setting to accommodate
changes  in loads imposed by the generator.  Current industrial practice
suggests  that 80 percent of rated rpm may be taken as a limiting speed level
for operation in this mode.  Then,  based on  the 80 percent rpm  charac-
teristic given in Fig.  8-4 and on engine SFC data developed in Section 8. 3,
the SFC/power output relationship for hybrid vehicle engines would appear as
shown in  Fig. 8-6.  The dashed portion of the SFC characteristic represents
the region of power output that  is not presently  attainable with conventionally
carbureted  engines  except through rich mixtures.  If one elects  not to operate
in  this Kone (in consideration of its impact on emissions), a 15  percent loss
of  potentially available power at 80 percent rpm is incurred.
                                     8-8

-------
oo
i
                     oo  o o o
                     ro 10  r- oo O>
                                               WOT = WIDE OPEN THROTTLE
             100
                             20     30    40     50     60     70     80

                               GROSS HORSEPOWER OUTPUT, % OF RATED


                           SFC
                          Figure 8-4.  S. !.  Engine SFC Map (Normalized)

-------
During the above process the air/fuel ratio remains  essentially constant.
At near full-throttle opening,  a mixture enrichment device in  the carburetor
goes  into operation to permit maximum power to be obtained from the engine.
Thus, the SFC passes through  a minimum and begins to increase with
enrichment of the charge as the throttle further moves toward the wide open
position.  Additional information on air/fuel effects related to throttle
position is provided in Fig.  8-5.
A number of different engine operating modes may be postulated for the
hybrid  vehicle application.  For the series propulsion configuration,  in which
the coupling between engine and drive wheels is purely electrical, the engine
may operate at fixed speed and fixed power output, at fixed rpm and variable
power output, and  at variable  rpm and  variable power output.  Studies  show
that the fixed  power output mode does not match a number of vehicle duty
cycle energy  requirements and/or may severely limit the maximum top
speed of the vehicle (See Section 10).  Therefore, this mode, which is
represented simply as a single point on the Fig. 8-4 operating map, will
not be discussed further at this time.
The fixed rpm and variable power output mode is frequently used in engine/
generator power units and may also be applied to the hybrid vehicle.  Here
the engine rpm is held constant by the action of a governor (mechanical or
otherwise) which operates to adjust  the engine throttle setting  to accommodate
changes in loads imposed by the generator.  Current  industrial practice
suggests  that  80 percent of rated rpm may be taken as a limiting speed level
for operation  in this mode.  Then, based on  the 80 percent rpm  charac-
teristic given in Fig.  8-4 and on engine SFC data developed in Section 8. 3,
the SFC/power output relationship for hybrid vehicle engines would appear as
shown in  Fig. 8-6.  The dashed portion of  the SFC characteristic represents
the region of  power output that is not presently attainable with conventionally
carbureted  engines  except through rich mixtures.  If one elects  not to operate
in this zone (in consideration of its impact on emissions), a 15 percent loss
of potentially  available power at 80 percent rpm is  incurred.
                                     8-8

-------
oo
i
vO
              200
               180
               160
gj  140
               20
              100
                  10
                    20% rpm |
                          ^360

                           \
                            I
                            \
                            I
                             1:300

                              \
                                \
                                                              80% rpm
                                                                 360C
                                                   MANIFOLD
                                                   VACUUM, mm Hg-J,
                                WOT
                                            \
                  II
12         13
   AIR/FUEL RATIO
14
15
16
                    Figure 8-5.  S. I. Engine Specific Fuel Consumption - Air/Fuel
                                Characteristics at Constant RPM

-------
00
i
              1.4
              1.2
               .0
              0.8
           CO
              0.6
              0.4,
10        20
                                              RATED HORSEPOWER


                                             10  20  30 50   100  200
                                  30       40       50       60       70

                                  GROSS  HORSEPOWER OUTPUT, % OF RATED
80       90
                   Figure 8-6.  S. I.  Engine Part Throttle Specific Fuel Consumption

                              (RPM Constant at 80-Percent Rated Horsepower)

-------
For the variable rpm and variable power output mode,  operation  at optimum
throttle setting  (optimum SFC) suggests itself as an interesting possibility.
The air/fuel characteristic for  this mode is indicated in Fig. 8-4 by the
numbers spotted along  the rpm  envelope curve.   Operation along  this curve
can be approximated by removing the carburetor power enrichment device
and holding the  throttle at a fixed position at or  near the wide open setting.
The deletion of  carburetor  enrichment results in a 7 percent loss of available
power at 100 percent of rpm.  However, some form of speed governing may
actually be desirable to limit rpm at minimum load conditions.   In this
mode, the  SFC/power output  relationship for hybrid vehicle engines would
appear as shown in Fig. 8-7.
In general,  low  SFCs favorably influence vehicle exhaust emissions.   By
comparing the two postulated series-configuration operating modes on this
basis, it is evident from Fig. 8-4 that the optimum throttle mode is prefer-
able since  it provides  significantly lower SFCs over a substantial portion of
the power range.  The  performance advantage is particularly apparent in
the low range of power output where the heat engine will frequently  operate.
It seems possible that the elimination of throttle travel may facilitate  car-
buretor design improvements which could further enhance the SFC charac-
teristic for operation in this mode.
The parallel-propulsion hybrid  vehicle configuration features a direct
mechanical link from heat engine to drive wheels.   The heat engine operates
in a quasi-steady-state manner  to provide sustaining power for cruise
at any given vehicle speed, while power demands  for acceleration are met
by the electric drive motors using battery and/or generator current.   In the
TRW Systems design,  the heat engine is operated at constant speed and
power output over the  speed range up to 40 mph and at variable speed and
power output over 40 mph.  Other transition speeds and other direct drive
systems are possible and are currently being studied.  Lacking definite
design details at this time, it may be adequate to describe  the fuel consump-
tion characteristic for  this mode of operation by simply defining the
                                    8-11

-------
             0.8
00
I
             0.7
             0.6
          CO
0.5
             0.4,
               10
           20
                                       RATED  HORSEPOWER
                                                10
30       40       50       60       70
GROSS  HORSEPOWER OUTPUT, % OF RATED
80       90
                      Figure 8-7. S.I.  Engine Part Throttle Specific Fuel Consumption
                                 (Optimum Throttle Setting)

-------
requirements for  cruise over the complete range of vehicle operating speeds.
This may be done for a given vehicle (car, van or bus) by the use of the
engine performance map together with relationships linking wheel  speed
and road power with engine rpm and gross power output.  For example,
Fig. 8-8 shows the cruise SFC  profile for the 4000-lb hybrid family
car superimposed on the S. I. engine SFC map (Fig. 8-4).  The cruise
profile for other vehicles will vary depending upon road load and auxiliary
power requirements.
It should be noted that the cruise curve depicted  in Fig. 8-8 for  the family
car was constructed using the auxiliary power characteristics shown in
Fig. 8-3 (excluding alternator). Based on these data,  an engine rated at
4000 rpm, which is typically in the speed range of most U.S. designs,  would
require 98 hp in order to meet  the 80-mph cruise speed requirement for
the hybrid family  car (A value of 92 hp was  obtained in Section 5 using
accessory power data supplied  by the APCO. ).
8. 2. 3      Engine  Characteristics
8.2.3.1   Specific Fuel  Consumption
The lowest value fuel consumption in the engine operating map was identified
earlier as "minimum SFC. "  In addition to its utility as an index of optimum
performance, this parameter also serves to identify characteristic perfor-
mance trends related to heat engine size or rated horsepower.
A correlation of minimum SFC  data for various industrial and automotive
reciprocating spark ignition engines (identified in Appendix E) is shown in
Fig. 8-9.   The horizontal scale, Rated Horsepower, refers to the bare
engine peak power output at the engine flywheel.  A negative trend of
minimum SFC with rated horsepower is  indicated,  with SFCs ranging from
0. 58 to 0. 47 over  the rated horsepower band from 20 to 200.  This correla-
tion was used in conjunction with the Fig. 8-4 performance map to develop
the spark ignition  engine SFC/power output  characteristics shown in
Figs.  8-6 and 8-7.
                                    8-13

-------
oo
i
   200





^  180

ID



1  160

Ll_
O


^  140
          CO
               20
              100
                     oo o
    >  o oo
    )  r^- cocr>
    \ \  \ \
\\\\\\  \  \  \


!  \\\\  \ \ \
                                         •CRUISE PROFILE
                                                     80 mph

                                         RPM,% OF RATED

                                           60    70    80   90
                       ,  y \\VA  \   \   \
                       \ I.  \ lv\ \  \.   \
                 0      10     20     30     40     50    60     70     80

                                GROSS HORSEPOWER  OUTPUT,  % OF RATED
                                                         90    100
                            Figure 8-8. S. I. Engine SFC Cruise Profile

                                      (Parallel Hybrid-Vehicle Operation)

-------
                          o
                                                                             22)
oo

»—*
tn
CJ>
Ll_
co
•  AUTOMOTIVE

O  INDUSTRIAL
             10"
                10
                                                  I02

                                RATED HORSEPOWER,  hp
                     Figure 8-9.  Minimum Specific Fuel Consumption

                                 Reciprocating Piston   SI Engine

-------
For comparison,  minimum SFC data for Wankel-type rotary piston spark
ignition engines (Ref. 8-5) are displayed with the SFC correlation for
reciprocating engines in Fig.  8-10.   The Wankel data are derived from
production engines manufactured by Curtiss Wright.   The industrial engines
are air-cooled; the automotive engines are water-cooled.   The 20-hp,  air-
cooled engine is currently  in use in two U.S. manufactured snowmobiles
(Arctic Cat and Polaris).   Two automotive engines  are shown.  One of these,
the RC 2-30 (128. 5 hp at 5500 rpm),  is used in the German NSU RO-80 and
the Japanese Mazda  110 S automobiles.  The other automotive engine,  the
RC 2-30-10A (110 hp at 7000 rpm), is used in the Japanese Mazda R-100
automobile.
it may be concluded  from Fig.  8-10 that the minimum SFC characteristic
for the Wankel engine is very similar to the reciprocating engine.  We note
that the data shown represent all versions of the Wankel engine currently  in
production.  Engines currently under development  include a Mercedes-Benz.
three-rotor, 110-CID,  335-hp engine and NSU engines ranging from 3  to
800 hp.  No additional information on these models is available.
8.2.3.2   Specific Weight
Although much information on industrial engines was acquired, sufficient
data for automotive-type spark ignition engines  were accumulated to permit
an accurate weight correlation to be made without the necessity of using the
industrial data.  This arrangement is preferred primarily because the
auxiliary equipment on industrial engines  may differ  somewhat from auto-
motive engines (e. g., fan,  flywheel) and also because the peak power ratings
of industrial engines  vary,  depending on service or application.   Thus, the
data points plotted in Fig.  8-11 exclusively represent automotive engine
designs and equipment.   The weight indicated is based on a complete engine,
including starter, alternator and flywheel, but excluding radiator, oil,  and
water.  Twenty-five  data points are shown (See  Appendix E for identification)
of which 23 are cast-iron block engines and two are aluminum block (Vega)
engines.  A least-squares  fit has been drawn through the cast-iron data set
                                    8-16

-------
                                      I      I
I   I  I  IT
                                                                      I     I
          I
          Q-
_Q
                                     o
                                              •RECIPROCATING  S.I. ENGINE
                                                O    O
c»
          CO
                                 O INDUSTRIAL
                                 • AUTOMOTIVE
             10'
                                                                      I	I
                           10
                                                     10
                                                                2
                                          RATED HORSEPOWER,  hp
                      Figure 8-10.  Minimum Specific Fuel Consumption
                                   Rotary Piston   SI Engine

-------
            10'
         O.


         -Q
         O
         Ł  10
00
I
00
o
UJ
Q_
CO
                                                          • CAST IRON  BLOCK

                                                          O ALUMINUM  BLOCK
                                       RATED HORSEPOWER, hp
                     Figure 8-11. Specific Weight - Reciprocating Piston  SI Engine

-------
and this line may be  interpreted as representing the mean for current
state-of-the-art automotive engine designs.  The line labelled "projected"
has been drawn through the lighter of the two aluminum block engines and
is proposed to represent a mean characteristic for the year 1975.
For  comparison,  weight data for the Wankel engines  discussed under
Section 8.2.3. 1, Specific Fuel  Consumption, are displayed with the current
weight correlation for reciprocating engines in  Fig. 8-12.  The automotive
Wankel engines average about 35 percent lighter than  the reciprocating
engines.
8.2.3.3  Specific Volume
Specific volume data (ft /hp) for current automotive and industrial recipro-
cating spark ignition engines are correlated with rated horsepower  in
Fig.  8-13.  Wherever necessary,  the industrial data were adjusted to reflect
a bare-engine  peak horsepower rating equivalent to the  rating for an auto-
motive  engine.  The  volume represented in the plot is the engine  envelope
from fan to flywheel  and from air  cleaner to crankcase pan.  Representative
dimensions for the volume envelope are characterized by the following
ratios:
          Length/Length     1.0
          Width/Length      0.8
          Height/Length     0.9
The least-squares data fit shown in Fig.  8-13 is reproduced in Fig.  8-14
for comparison with  the Wankel data.  Note that a significantly steeper trend
with engine rated horsepower is indicated for the Wankel engines. At the
115-hp  rating,  the Wankel volume  is indicated to be 6. 5 ft  compared with
       3
14.6 ft   for the reciprocating piston design, or less than 50 percent the  size.
Representative dimensions for the  Wankel engine volume envelope are charac-
terized  by the following  ratios:
          Length/Length     1.0
          Width/Length      1.5
          Height/Length     1. 1

                                    8-19

-------
  I02
                                                                 1    TT
ex
-C
    10
                                                   O INDUSTRIAL
                                                   • AUTOMOTIVE
                               RECIPROCATING S.I. ENGINE (CURRENT)
00



O
UJ
a.
CO
O
  O
                                   O
                  O
                                             O
                             10
                              RATED  HORSEPOWER,  hp
                                                  10'
              Figure 8-12. Specific Weight - Rotary Piston   SI Engine

-------
              10
                               1    I
          ro
              10'
                                        •O
                                                     O
                                                 O
                                                      o
                                                         .o      o
                                               o
oo
i
           Q_

           CO
              10'
r2
                         • AUTOMOTIVE

                         o INDUSTRIAL
I	     I
                                        10
I    I
I	I
                                                 10
                                                                 2
                                          RATED HORSEPOWER, hp
                                10'
                            Figure 8-13.  Specific Volume - Reciprocating Piston  SI Engine

-------
00
               10
           Q.
          -C

          rO
          ID

          O
LU
Q_
CO
             10'
             10
    -2
                                               O
                                O  INDUSTRIAL
                                •  AUTOMOTIVE
                                           RECIPROCATING S.I. ENGINE
                                            O  O
                                        10                     I02
                                           RATED HORSEPOWER,  hp
                                                                             I03
                       Figure 8-14.  Specific Volume - Rotary Piston   SI Engine

-------
 8. 3       DIESEL CYCLE (COMPRESSION IGNITION) ENGINE
 8. 3. 1     General Description
 The thermodynamic cycle for this  reciprocating piston  engine is shown in
 Fig. 8-15.  The four-stroke sequence of engine operations consists of an
 air-only intake stroke (terminating at Point 1), a compression stroke which
 raises the temperature of the air above the auto-ignition point of the fuel
 (Point 1  to Point 2) followed by combustion of the injected  fuel charge
 (Point 2  to Point 3), an expansion or power stroke  (Point 3 to Point 4),  and
 an exhaust stroke (Point 4 to Point 1).  The classical constant pressure
 combustion  process illustrated in  Fig. 8-15 is achieved by metering fuel
 into the cylinder during the expansion stroke.   In fact,  however, combustion
 in most modern compression ignition (CI) engines proceeds first at constant
 volume (the S. I.  engine combustion process) and late burning occurs at
 constant pressure.
 Fuel under high pressure  (2000 to  20,000 psia) is delivered to the cylinder
 through individual-cylinder nozzle injection valves  by an injection pump
 operated by the camshaft.  Air enters and  exhaust products leave the  cylinder
 through intake and exhaust poppet valves also  operated  by  the camshaft.
 Unlike the spark ignition  engine, the charge mixture is not regulated and
 air/fuel  ratios ranging from 20 to  75 or higher may be  encountered over
 the normal operating range of the engine.   Load and speed control is achieved
 by adjusting the amount of fuel injected during the combustion cycle.  Maxi-
 mum fuel delivery is fixed by control stops  on the injection pump to limit
 the power output over  the speed range to conform with specified  smoke
 standards for operation on the  road.  A governing mechanism is  also  included
 to limit engine speed at predetermined minimum and maximum values.
 Representative performance curves for an  automotive  CI engine  (Ref.  8-6)
are shown in Fig.  8-16.   Typically,  the power curve does  not display  a
peak point because this region  of CI engine operation usually  is accompanied
by heavy smoke  which, if sustained, will cause the engine  to foul.  The rated
                                   8-23

-------
00
I
ro
         Q_
         CC
         =D
         CO
         CO
         LU
                            s
                             CONST
                 'CONST
                        VOLUME,  V

-------
   80
   70
   60
    50
§ 40
CO
oc
o
    30
   20
    10
     0
                                      TORQUE
                            HORSEPOWER
      SFC
      0
                                      160
                                      140  Ł?
                                            I


                                           u_T

                                      120  g
                                      100
                                       0.60
0.50
                                                         i
                                                         o.
                                                         -O
                                                          _
                                                         CO
                                      0.40
1000    2000    3000    4000    5000

           ENGINE RPM
      Figure 8-16.  Compression Ignition Engine Performance

                  Characteristics  (154-CID Daihatsu)
                           8-25

-------
power of the engine, therefore,  is not sharply defined by an intrinsic upper
bound on energy output [as the wide-open throttle (WOT) peak for spark
ignition engines], but is based instead on some limiting condition of exhaust
smoke, either defined by the manufacturer or  stipulated by legislation
prohibiting excessive smoke on  the road.  Typically, the torque curve peaks
and the SFC curve bottoms at a  somewhat lower  percentage  of rated rpm
than the spark ignition engine.   However,  variations in injection system
and combustion chamber design may alter this relationship significantly.
8. 3. 2     Hybrid Operation
Investigations discussed in Section 9,  Heat Engine Exhaust Emissions,
indicate that diesel engines with indirect injection  (i.e., divided) combustion
chamber designs [turbulence chambers (TC) or precombustion chambers
(PC)] have emission characteristics that are superior to those for direct
injection combustion chamber designs.  For this reason, the divided chamber
engine has been selected as the  preferred diesel configuration for  the hybrid
vehicle application.  A complete SFC performance map (normalized) for an
engine of this type (Refs.  8-7 and 8-8) is presented in Fig. 8-17.  The
characteristics shown,  though based specifically on a turbulence chamber
design, are believed to  be more or less  typical of  divided chamber (TC or
PC) engines with rated speeds in the neighborhood of 3500 rpm.
In general, the map displays trends that are similar to those shown for the
spark ignition engine.  One difference that may be observed is that the SFC
characteristic is relatively flat  over a broad range of power output.  This
feature is  frequently claimed to be typical of all  diesel engines;  actually, it
is not readily distinguishable in some  designs.  Values for SFC  at the left
of the map approach infinity as a limit as the net engine power output
diminishes.
The air/fuel ratio  varies significantly with load as shown by the numbers
spotted on  the 80 percent rpm curve.   This is  because  (ho Cl engine takes
in a lull charge of  air at each induction stroke  and adjusts the amount of fuel
injected to control power output. The SFC declines along with air/fuel  ratio as
                                    8-26

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oo

-j
                                                   RPM, % OF RATED
            100
               0      10     20    30     40     50     60     70    80
                              GROSS  HORSEPOWER OUTPUT, % OF RATED
               ^MINIMUM SFC
                          Figure 8-17.  Cl Engine SFC Map (Normalized;

-------
brake mean effective pressure  (BMEP) increases with increase of the fuel
charge.  Minimum SFC at fixed rpm is achieved at about 75 percent of load
and with air/fuel ratio in the range from 24 to 22.  At or near this point a
haze appears  in the engine exhaust because of failure of the  fuel to find  air.
With further increase in load the haze  darkens and the SFC begins to
increase.
The Fig. 8-17 rpm curves,  which  are  shown to  terminate at a smoke rating
of Bosch 3, have been extended beyond the normal operating limits  of the
engine to illustrate the relationship between exhaust smoke, fuel consump-
tion, and power output at rich mixture conditions.  The true load  limit
envelope  is shaped by the setting of the fuel delivery stop and may  cut
across several smoke lines,  depending on  the speed characteristics of the
injection system.   Bosch 3 represents a slight discoloration of the exhaust
equivalent  to a U.S. smoke obscurity rating of about 4 percent in  engines
up to 100 hp (Ref.   8-9); Bosch 1. 5 and lower is  nearly invisible.
Following the procedure employed for  spark ignition engines, the normalized
SFC map for the diesel  engine may be  used to develop characteristic curves
of fuel consumption for  the hybrid  vehicle.  For the series-propuls ion con-
figuration we  may again postulate the constant speed (80 percent rated rpm)
mode of  operation as one of several alternatives.  Then,  based on the 80
percent characteristic of Fig. 8-17 and on SFC  data for  divided chamber
diesel engines developed in Section 8.3,  the SFC/power  output relationship
for hybrid  vehicle diesel engines would appear as shown in  Fig. 8-18.   The
dashed portion of each curve identifies a zone of progressively darkening
exhaust haze which, though innocuous, should perhaps be avoided for the
hybrid application.
A variable  rpm and variable power output mode  which conforms to the
optimum SFC envelope in Fig. 8-17 is  another series-configuration operating
mode which might be considered.  Operation along the optimum curve can be;
approximated by fixing the control rod or rack at an appropriate  nuiximum
stop position or, more accurately, by  speed governing the injection system to
                                    8-28

-------
oo
i
          CO
                                            RATED HORSEPOWER


                                              10    100   300
                                  30       40      50       60       70

                                 GROSS  HORSEPOWER  OUTPUT,  % OF RATED
80
90
                         Figure 8-18.  CI Engine Part-Load Specific Fuel Consumption

                                     (RPM Constant at 80-Percent Rated Horsepower)

-------
an optimum fuel delivery profile.  In this case, the SFC/power output
characteristic for hybrid vehicle engines appears as shown in Fig. 8-19.
With regard to the parallel-propulsion hybrid configuration, the remarks
under spark ignition engines concerning operation  in this mode apply also to
diesel engines.   An SFC profile which matches  engine rpm and flywheel
brake horsepower output to vehicle cruise speed and road power require-
ments can be  constructed  for a vehicle  of given weight,  frontal area, and
wheel diameter.  This has been done for the 4000-lb hybrid vehicle family
car using the  engine auxiliary power data presented in Fig. 8-3.   The
resulting SFC characteristic is shown superimposed on  the diesel SFC  map
reproduced in Fig.  8-20.
8. 3. 3      Fngine Characteristics
8. 3. 3. 1    Specific Fuel Consumption
A correlation of minimum SFC versus rated horsepower for compression
ignition engines is  shown in Fig.  8-21.   The horizontal scale,  Maximum
Rated Bare Engine Horsepower, refers  to a no-accessory power  output
equivalent to the automotive rating for a spark ignition engine.  All of the
data shown conform to this rating  basis  (See Appendix E for identification of
data).
Figure 8-21 distinguishes  the characteristics of divided chamber diescls
from open chamber (direct injection) diese.ls, the former being preferred for
the  hybrid application because of lower emissions.  Two major types of
divided chamber designs which have been identified are  (a) turbulence
chamber  (TC) designs as exemplified by Continental, Waukesha,  Daihatsu,
Peugot,  and Ricardo diesels,  and  (b) precombustion chamber (PC) designs
as exemplified by Caterpillar,  Perkins, Onan,  Mercedez-Benz, and Leyland
d'iesels.   Both systems operate on basically the same principle; that is, both
develop swirl and initiate  combustion in an antechamber  separated from the
main chamber by a  restricted passageway.   The TC antechamber  is larger
(50  percent of the clearance volume) than the PC chamber (20 to 30 percent
of the clearance volume).   Its principal distinction appears to be  that it
                                    8-30

-------
              0.7
oo
i
              0.6
           i
           o_
              0.5
0.4
                             RATED  HORSEPOWER
                             10       100      300
              0.3
                 10       20
                    30       40       50       60       70
                    GROSS  HORSEPOWER OUTPUT,  % OF RATED
80       90
                      Figure 8-19.  CI Engine Part-Load Specific Fuel Consumption
                                   (Optimum Throttle Setting)

-------
oo

ro
             200
              80
              60
O

^°
           -  140
         CO
              20
             100
  o o o
  ^ to GO
 o o  o  o
 ŁO to  Is-  CD
  in \  \ \ \
  111 \ \  \  \
  M M \ \ \
 -M \  \ \ \ \
  MM \ \  \
   M \ \  \  \  \
   \\\\\\ \
 - \ \ \ \ \  \ \

    \\\\\\   N
L  \\\ \\ \  A
                                      -CRUISE PROFILE
                                                            80 mph'
                                         RPM.% OF RATED
       0     10     20     30    40     50    60     70     80

                     GROSS HORSEPOWER OUTPUT, % OF RATED
                                                                          90
                                                                100
                           Figure 8-20.  CI Engine SFC Cruise Profile
                                      (Parallel Hybrid-Vehicle Operation)

-------
                       DIVIDED CHAMBER ENGINE

                            O
                            ^^^•B

                       	00 — ^Q-

                       DIRECT INJECTION ENGINE
oo
i
LO
10
CO

PRECOMBUSTION CHAMBER
TURBULENCE CHAMBER
DIRECT INJECTION
AUTO
•
A
•
IND
O
A
D
             10'
                10
                                                I02
                       MAXIMUM RATED BARE ENGINE HORSEPOWER
                    Figure 8-21.  Minimum Specific Fuel Consumption - CI Engine

-------
develops a higher degree of swirl than the PC type.   For the purpose of this
analysis (though not necessarily from the standpoint of emissions),  it was
assumed that PC and TC diesels could be lumped together and correlated
under the single category of "divided chamber"  engines.  Figure 8-21
symbolically distinguishes  the individual chamber types for information
purposes only.
Fifty-two data points are plotted in Fig.  8-21; 32 for direct injection (DI)
engines and 20 for divided chamber (DC) engines.   The correlation approach
first isolated the DI data, producing the least squares fit shown by the lower
of the two lines.  The correlation for DC  engines  (upper line) was then
obtained by translating the  DI slope to  the mean level of the DC data  set.
This procedure was preferred to fitting a new slope to relatively few DC
data points  embracing a much smaller horsepower range.   The upper line,
or DC correlation, was  used in conjunction with the Fig.  8-17 performance
map to develop the diesel engine SFC/power output characteristics shown in
Figs. 8-18  and 8-19.
Figure 8-21 indicates that the SFC for DC engines is higher (by about 10
percent) than the SFC for DI engines.  This result is supported by the  fol-
lowing considerations:
      1.     The DC engine  has a greater heat loss due to (a) the higher
            surface-to-volume ratio of the divided chamber and (b) higher
            secondary turbulence.   It also has a greater throttling loss due
            to  the flow restriction  created by the antechamber throat.
      2.     The DI engine has a higher maximum pressure and a higher
            pressure rate than the DC  engine.   Therefore,  it should  have a
            correspondingly higher indicated thermal efficiency.
It .should be cautioned that Fig. 8-21 may not be freely translated as a
statement on engine fuel economy.  Duty cycle may have a significant dif-
ferential effect on the overall performance of the two engine types.
                                    8-34

-------
The effects of turbocharging on minimum SFC were examined and were
found t:o be negligible.  P"or a moderate degree of turbocharging (e.g., 40
percent),  the minimum SFC is reduced about 5 percent from the values
shown in Fig.  8-21.  If the degree of turbocharging involves a reduction
in compression  ratio to avoid excessive peak cylinder pressures, the
improvement in SFC is smaller (or non-existent) and dep.ends in part on
the net change in compression ratio.
8.3.3.2  Specific  Weight
Specific weight data for compression ignition engines are correlated with
rated horsepower in Fig. 8-22.  The correlation attempts to distinguish the
weight characteristics of DC engines (PC and  TC types) from DI engines.
The theoretical  justification for doing this is that DI engines develop higher
peak combustion pressures and therefore it is reasonable to expect that
certain engine components such as the  cylinder head, connecting rods,
crankshaft, and bearings will tend to be heavier than similar components
in the  DC engine.
Seventy-two data points are shown of which 45 represent DI  engines.
Because of their number  and range of horsepower, the  DI data were used
exclusively to establish the trend of  specific weight with rated horsepower.
The correlation for DC engines was  obtained by translating this slope to
the mean level of the DC  data set.   The data shows that  DC engines  generally
run 25 percent lighter than DI engines.  Even  so,  a 100-hp DC diesel is
80 percent heavier than a spark-ignition engine with the  same power rating.
The use of turbocharging as a means of increasing power output and there-
fore improving the specific weight characteristic for diesel  engines was
examined.   The available turbocharged engine data, however, proved not
to be useful since the data indicated  a specific weight characteristic that
falls on or above the naturally aspirated line.  This may be related  to the
fact that turbocharging usually is  accompanied by higher mechanical loads,
and consequently, engines that are structurally overdesigned are most
suitable for conversion.
                                    8-35

-------
               50
oo
                            fi
PRECOMBUSTION CHAMBER
TURBULENCE CHAMBER
DIRECT INJECTION
AUTO.
•
A
•
IND.
0
A
             o.



            JQ


            I—"


            O
               10
o
LU
Q_
CO
                     A  DIRECT INJECTION

                     B  DIVIDED CHAMBER (DC)

                     C  DC TURBOCHARGED(TBC)

                     D  PROJECTED TBC
                                        10                     10*
                                MAXIMUM RATED BARE ENGINE HORSEPOWER
                                   Figure 8-22.  Specific Weight - CI Engine

-------
The turbocharged characteristic shown in Fig. 8-22 was obtained by
assuming that light automotive DC-type engines might be turbocharged
to 40 percent above  their rated power level (naturally aspirated) and that
turbocharging components might add 4 percent to the engine weight.   The
power assumption is an extrapolation (down) of current commercial practice
which limits turbocharging to give 50 to 75 percent power increase.   How-
ever,  the available data indicate that these levels  are not attainable (from
the standpoint of limiting peak pressures) with engine specific weights
below about  10 Ib/hp.  With 40 percent turbocharging, the indicated weight
of a 100-hp diesel engine is 520 Ib, compared to 350 Ib for the  spark-
ignition engine.  The weight discrepancy tends to get larger at  higher rated
power.
The projected  1975 weight characteristic was obtained by assuming that new
materials combined with higher operating piston speeds might bring the
turbocharged engine  specific weight to a level corresponding to 75-percent
turbocharging of current DC engines.
8. 3. 3. 3   Specific Volume
Specific volume data for automotive and industrial compression ignition
engines are correlated with rated horsepower in Fig.  8-23.   The volume
represented  is the engine envelope  from fan  to flywheel  and  from air  cleaner
to oil pan.   There is no reason to expect biases between  engines of different
combustion chamber design, and no attempt  has been  made to isolate and
correlate the data on this basis.   While there is considerable scatter in
the plot, the least-squares fit represented by the drawn line indicates a
relatively high degree of correlation.  The turbocharged characteristic
shown in the figure was obtained on the basis of turbocharging to a power
output 40 percent above rated horsepower.  No additional volume allowance
was made for turbocharging components,  since these may easily be fitted
within the naturally-aspirated engine envelope.  Representative dimensions
for the Dl volume envelope are characterized by the same ratios given  in
Section 8.2.3 for spark-ignition engines.
                                    8-37

-------
oo
i
OJ
oo
        10
                                       0
                                           o
      Q-
      -C=

     ro
               TURBOCHARGED
      o
      >
      O
      Q_
      CO
        10'
• AUTOMOTIVE
O INDUSTRIAL
        10
          -2
    I    I   I
                                 10                    \tf
                       MAXIMUM  RATED BARE ENGINE HORSEPOWER, hp
                                                        10*
                                Figure 8-23.  Specific Volume - CI Engine

-------
8.4       BRAYTQN CYCLE (GAS TURBINE ENGINE)
8. 4. 1     Thermodynamic Processes
The gas turbine (Brayton or Joule) cycle is illustrated in Fig.  8-24.   In the
basic cycle the inlet air is compressed (Point 1 to Point 2),  heated at
constant pressure (Point 2 to Point 4), expanded through a power turbine
(Point 4 to Point 5), and discharged to the atmosphere (Point 5) where it
eventually reaches equilibrium with the environment (Point 1).  As will
be shown,  it is advantageous  to use a regenerator in this cycle to recover
some of the rejected heat (Point 5 to Point 6) and reintroduce it into the
cycle (Point 2 to Point  3) to conserve input energy.
Gas turbine performance can be improved by increasing the  maximum cycle
temperature and by improving component efficiencies.  Other  methods which
might be used involve the incorporation of additional components.  In
particular,  intercooling can be added to multistage compressors and reheat
can be added to  multistage turbines.   However,  in many applications,
including  the hybrid vehicle,  the complication of the additional ducting and
components required by intercooling and reheating cannot be justified for
the small performance  gains  realized.  Improvement in efficiency is best
obtained by improving component efficiencies and/or by raising temperature
limits  of the cycle as permitted by material advances.   In Fig. 8-25,  it is
noted that the optimum  value  of the parameter  AT /T decreases with
increasing recuperator effectiveness, but is not affected, to any degree, by
independent changes in  turbine or compressor efficiency (AT  is the actual
temperature rise across  the compressor and T is the compressor inlet
absolute temperature).   However, lower AT  /T  values require fewer
compressor stages or lower stage pressure ratios,  implying potentially
higher compressor performance.  Hence, in practice, high recuperator
effectiveness is  doubly  desirable.
                                    8-39

-------
          
-------
p-
>-

-------
8. 4. 2     Vehicular  Design Considerations
Vehicular gas turbines under development as prime power sources all
employ regeneration.  As indicated in Fig.  8-26,  the cycle arrangements
can be complicated,  even without such special  features as variable turbine
nozzles.
Because of the possibility of extended idle operation in the hybrid applica-
tion,  it is important  to consider cycle arrangements which would provide
lower  idle fuel consumption than that normally encountered with constant
speed  gas turbines.  In constant speed gas turbines, no load fuel consump-
tion  may be as high as 60 percent of the  full load consumption.   A major
design consideration  of vehicular gas turbines  which has  actually dictated
the final design is the response to load change.  Because of the differences
between normal vehicular operation  and  hybrid operation it was  considered
advantageous to do some preliminary studies to determine possible configu-
rations for the hybrid vehicle.
The  gas turbine configurations  investigated are as follows:
      1.   Simple
      2.   Simple with free turbine
      3.   Simple with regeneration
      4.   Simple with free turbine and reheat
      5.   Twin spool
      6.   Twin spool with regeneration
      7.   Twin spool with intercooling
      8.   Twin spool with reheat
      9.   Twin spool with regeneration and intercooling
      10.   Twin spool with regeneration and reheat
      11.   Twin spool with intercooling and reheat
      12.   Twin spool with regeneration,  intercooling, and reheat
                                    8-42

-------
      4-
          1203° F
          14.8 psia
                      RECUPERATOR
625° F
224 psia
          272° F
          56.0 psia
          INTERCOOLER

          436° F
          57.3 psia
SILENCER
100° F
14.7 psia
              _L
                           966° F  COMBUSTOR
                           221 psia
                                               1700° F
                                               212.1 psia
                                             •
                           HIGH PRESSURE
                               SPOOL
                                      REHEAT
                                  COMBUSTOR
                                              1335° F
                                              84.6 psia
                                    POWER
                                   TURBINE
                                              I700°F
                                              81.4 psia
                          1404° F
                          39.9 psia
                                            T
                           LOW PRESSURE
                               SPOOL
                                              1079°F
                                              15.9 psia
Figure 8-26.  Cycle Diagram of Ford 704 Gas Turbine Engine
                         8-43

-------
Configurations 1, 2,  and 3  represent those in common use for vehicular
applications.  The other arrangements were examined to determine if their
characteristics  might be better suited to hybrid application.  The interest
in the free turbine and twin spool configurations stems  from their good idle
and acceleration characteristics.  Interceding and reheat are chiefly
valued for their effect upon increasing the power density of the gas turbine.
Regeneration is the most effective method of decreasing fuel consumption
by increasing thermal efficiency.
The assumptions used in the analysis are given  in Table 8-1.   The stage
pressure ratio was established at 2. 8 to represent what a moderate per-
formance centrifugal compressor might do.  The other efficiencies  and the
turbine inlet temperature would be considered advanced over what might be
considered for industrial purposes.   They would not, however, be as  high  as
those being achieved  in aircraft gas  turbines.  The assumption of constant
specific  heat, while technically not exact, will lead to results  which will be
accurate within  10 percent  and therefore usable for comparative purposes.
In this study, a  low-speed, no-load condition of 45-percent rated speed
was assumed.  This assumption,  based on a priori judgment,  is well  above
the self-sustaining speed to assure stability and fast  acceleration to rated
speed, and yet it is low enough to cause a substantial air flow  reduction in
the machine  in comparison to  the rated  speed air flow.   Air flow reduction
pays off  directly in lower power losses  in the cycle at no-load and,  there-
fore,  in  lower fuel consumption at no-load.   The results indicate that the
no-load fuel  consumption can be reduced from as high as 60 percent of rated
fuel consumption at full-speed idle to under 20 percent of the  rated full-load
consumption by  using a low-speed idle.   Another method, not  investigated,
\vhich would  produce  similar and possibly even lower idle fuel consumption
would be to use  variable turbine nozzle  vanes.  Results  of the  study are
presented  in Table 8-2.
                                   8-44

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                    Table 8-1.  Gas Turbine Characteristics Assumed in  Cycle Analysis
oo
i
Compressor  Inlet Pressure
    Inlet Temperature
    Pressure Ratio/Stage
    Stage Efficiency
Turbine Inlet Temperature
    Stage Efficiency
Mechanical Efficiency
Combustor Efficiency
    Pressure Drop
Regenerator  Effectiveness
    Pressure Drop
Intercooler Effectiveness
    Pressure Drop
                                                             14. 7 psia
                                                             80°F
                                                             2.8
                                                             0. 80
                                                             1600°F
0. 83
0.95
0. 98
5 Percent of Inlet Absolute Pressure
0.95
2.5 Percent Inlet Absolute Pressure/Leg
  o.
                                                             10 F Above Ambient
                                                             2. 5 Percent Inlet Absolute Pressure
             Turbine Weight Flow =  Compressor Weight Flow
             Specific Heat                                    1. 395
             Fuel Lower  Heating  Value                        18,700 Btu/lb

-------
                             Table  8-2.  Gas  Turbine Cycle Analysis Results
Cycle
1 . Simple Cycle
itfa
2. Free Turbine
.^tf-A
°C?r-S3 SJ
3. Single Shaft + Regeneration
»
4. Free Turbine -r Reheat
CC CC i
rfAfrt
°c?-^i U
5. Simple Twin Spool
cc
o P i^~^ U
1 t I 1
6. Twin Spool - Regeneration
R
" 	 1 i 	 ; !~^~^~t i 	 1 i
^r^KvPr^]
0 LJ c? — ^ U
Thermal
Efficiency
0. 11
0. 11
0.33
0. 10
0. 15
0. 16
BSFC,
Ib/bhp-hr
1.24
1.24
0.42
1.43
0. 93
0. 84
Specific
Output,
hp/lb (air ) min
0. 94
0.94
0. 84
0. 97
0. 97
0. 89
Exhaust
Volume
Flow,
ft /hp (rated)
44. 2
44. 2
24. 5
48.6
34. 2
30. 6
Low Speed Idle
Turb. Inlet
Temp.,°F
703
703
1035
703
703
1035
Fuel
Consumption,
Percent
of Maximum
18.2
18.2
11.9
15.8
22.0
6. 0
00

-------
                              Table 8-2.  Gas Turbine  Cycle Analysis  Results  (Continued)
Cycle
7. Twin Spool + Intercooling
8. Twin Spool + Reheat
C C t T
9. Twin Spool -f Regeneration +
1 1C | ^ R Intercooling
rTfOT^^
10. Twin Spool + Regenerator +
olT^^^^Vl
C ^ I*" T
1 1. Twin Spool + Intercooling + Reheat
CwJ CC CC i
C C T I
12. Twin Spool + Regen. * Intercooling
IJ&J Ł* * Rcheat
pjM^'^Vi^l
C C ^ '
Thermal
Fffic iency
0. 18
0. 15
0. 31

0.21


0. 17


0.29


BSFC,
Ib/bhp-hr
0. 74
0.88
0.44

0.64


0. 80


0. 47


Specific
Output,
hp/lb lair) ; .in
1. 59
1. 37
1. 52

1.23


1.74


1. 65


Exhaust
Volume
Flow,
ft?/hp (rated)
21.0
28.9
18.8

23.0


21.7


12.6


Low Speed Idle
Turb. Inlet
Temp.,°F
703
703
1035

1035


703


1035


Fuel
Consumption,
Percent
of Maximum
30.4
25.6
1 1.4

7.8


28. 1


10. 7


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           Key    (~) Generator            T  Turbine
                   C Compressor          R  Regenerator
                  CC Combustion Chamber  1C  Intercooler

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As  expected,  the systems using regenerators had appreciably higher thermal
efficiencies and therefore lower SFC than did the  systems without regenera-
tors.  As is generally true, the regenerator is more effective at lower
compressor discharge  temperatures so that the single-stage compressor
or the two-stage compressor with intercooling will have a higher thermal
efficiency.
The use of intercooling and reheat increases the horsepower available from
a given air flow rate.   This implies  that the compressor  inlet area would
be lower with reheat and intercooling and therefore the size of an inlet air
or noise filter would be lower.   On the other hand, regeneration increases
air flow requirements slightly.  This can be explained by the pressure loss
in the regenerator which leaves less head available across the turbine and
necessitates  a higher air flow to compensate.
Somewhat the opposite  trend is noticed in the  exhaust volume flow of the
regenerated engines since the temperature drop (density  increase) of the gas
through the regenerator reduces the si/.e of the exhaust ducting needed.
A review of all these factors indicates that the simple cycle with regenera-
tion (i. e.,  recuperation) would  be preferred for use with  the hybrid vehicle
in comparison to the other  cycles examined.  The regenerated gas turbine
could use either a single shaft or a free  turbine, however,  the use of multiple
shafts  do not offer any  advantages in this application.  An advantage,  indicated
by the  results  of the study, is that the simple regenerated cycle would
operate at  a lower speed than the other arrangements  (because  of higher air
flow rates  which would entail larger rotating machinery)  and would there-
fore be more  suited for a generator/alternator drive.  As a further result
of this study,  it does not appear that intercooling  or reheat would be advisable
for a low-power gas turbine.
8.4.3     Engine Characteristics
Performance  characteristics for gas turbine engines are presented in Table  8-3.
Based on these figures, specific fuel consumption, specific weight and specific
volume are presented in Figures 8-27 through 8-30.
                                    8-48

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                                    Table 8-3.   Gas Turbine Engine Characteristics
Gas Turbine
1. AiResearch
2. AiResearch
3, Chrysler
4. Chrysler
5. Ford
6. General Motors
7. General Motors
8. Rover
9. Volvo
0. Williams
1. Williams
Model
331
331
120
CR2A
704
305
--
2S/140
--
--
--
Rated
HP
300
400
120
140
300
225
175
150
250
80
180
Weight
(Ib)
--
--
199
445
651
596
825
470
805
290
550
Volume
(r«3)


17.2
20. 0
18.3
13.7
--
18.3
23.2
3. 5
6.05
Rated
SFC
(Ib/hp-hr)
0.465
0.465
0.602
0.515
0.544
0.535
0. 586
0.549
0.401
0. 590
0.470
Comp.
Pressure
Ratio
8. 0
8.0
4.25
4.0
4.0
3. 5
--
3.92
3.01
4. 0
4. 0
Turbine Inlet
Temperature
OF
--
--
1507
1702
1697
1597
--
1538
1562
--
--
oo

-------
oo
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1
i Le
o
1 —
Q_
^j-
i 12
co ' •t-
o
o
_J
UJ
H>
o °'8
\H
1 a 1
V ^ I
0.
CO
§ 0.4
CO
UJ
o
n
1 1 1 1 1 1 III
• REGENERATED G.T. -BSFC < 0.6
0 OTHERS
00


~ O
r RECOMMENDED Q %° o
/ EXTRAPOLATION O
- J 0 O
^^ — — — - J°* 3. 8°.7°6° °°
* REFER TO DATA FIT FOR 9
TABLE 8-3 FOR REGENERATED G.T. WITH
IDENTIFICATION BSFC < 0.6
i i i i 1 i lit
                   10
        I02

HORSEPOWER  OUTPUT, hp
I03
                         Figure 8-27.  Design SFC of Automotive Gas Turbines

-------
oo
      O
      Ll-
      CO
      CD
         1.2
1.0
      Ł0.8
      LU
      O
         0.6
      CO
      CD
o 0.4
      CE
      O

      fe  0.2
      CD
          0
          FREE TURBINE CONFIGURATION

          VARIABLE NOZZLE Tt IN CONST

          VARIABLE NOZZLE Tt OUT CONST-

          FIXED NOZZLE
                                                                               DESIGN
                                                            SIMPLE CYCLE PLUS
                                                            MODERATE REGENERATION
                                                            CONSTANT SPEED
           0              0.2             0.4              0.6              0.8              1.0
                                              LOAD RATIO

             Figure 8-28.  Part-Load BSFC Characteristics of Automotive Gas Turbine Engines

-------
                                                                  1  i  i  i
oo

ro
 "  3
L^   r\
—   c.
Q_
CO
                 RECOMMENDED
                 EXTRAPOLATION
                                                  O
                                         O  rDATA FIT FOR  REGENERATED
                                              G.T. WITH BSFC <0.6
                                      10    /           o
• REGENERATED  G.T. ~  BSFC
  <0.6
O OTHERS
                                                                  O
                                                                  O
                                                                  O
         * REFER TO
          TABLE 8-3 FOR
          IDENTIFICATION
                        O
                                                               O
                                                                            O
    0
                                                                   i	i
                  10
                                       I0
                                         2
                               HORSEPOWER OUTPUT,  hp

           Figure 8-29.  Specific Weight of Automotive Gas Turbines
                                                             10'

-------
00
I

Ul
              0.20
              0.16
ro
              0.12

o
LU
Q_
CO
    0.08
              0.04
                 0
                              i     i     i
                                                      O
                            RECOMMENDED
                            EXTRAPOLATION
                                 7

                                -f
             • REGENERATED  G.T.  -BSFC < 0.6

             0 OTHERS
Q
                                         '°
                      * REFER TO
                        TABLE 8-3 FOR
                        IDENTIFICATION
                                      8
                                   ll
                                                          i     i     i   i  i
                                                         DATA FIT FOR

                                                         REGENERATED G.T.
                                                         WITH BSFC < 0.6
                                                                          0
                                                                 O
                                                       °
                                                                         ill
                   10
                                            HORSEPOWER OUTPUT, hp
                    Figure 8-30.  Specific Volume of Automotive Gas Turbines

-------
8. 4. 3. 1   Specific Fuel Consumption
Specific fuel consumption characteristics for a number  of gas turbines have
been plotted in Fig. 8-27.  Since the gas turbines represented on the curve
vary widely in arrangement and application, the characteristic performance
has been based upon only those whose SFC is 0.6 Ib/hp-hr or lower.   The
gas turbines in this set include all of the normal vehicular types.  Those not
included are, for the most part,  aircraft and stationary auxiliary power units
which are  designed for characteristics other than fuel consumption.   It is
also to  be  noted that all of these contain regenerators which should provide
a good basis for  weight and volume characteristics.
Part-load  characteristics for the gas turbine are shown in Fig.  8-28.  Here
the ratio of design SFC and part-load SFC is plotted.  This,  in effect, then
shows the  variation in  efficiency with part-load.  The upper curves are for
a vehicular gas turbine with and without a variable nozzle turbine while the
bottom  curve is for a constant speed gas turbine with a fixed nozzle.   In the
upper curves,  temperature of the turbine inlet is held constant in one case,
while in the other, the  turbine discharge temperature is held constant.  For
the design case used in this study the variable nozzle arrangement with a
fixed turbine discharge temperature has been selected.  This arrangement
gives good part-load characteristics and is "easier" on  the turbine  since
gas temperatures will  be lower at part-load.  In the  case  of a constant turbine
inlet temperature, turbine discharge temperature would increase at part-load.
8.4.3.2   Specific Weight
Specific weights  of the  selected gas turbines have been plotted in Fig. 8-29
as a function of output  horsepower.  A characteristic curve for these  data
has been established and has been extrapolated  into the lower horsepower
region of interest.  It is to be noted  that the  gas turbine, at least from
these data, does  not show as low a specific weight as might be expected.
Instead  of  one pound per horsepower,  the specific weight is closer to three
pounds  per horsepower.  The difference is due  to the inlet silencers,
rcjjonerntors and heat  exchangers, and the gearing needed  in the  vehicular
design as compared to  aircraft-type gas turbines.
                                    8-54

-------
8.4.3.3  Specific Volume
Specific volume characteristics for the gas turbine are  shown in  Fig.  8-30.
A wide scatter of data is shown which reflects the type of regenerator used,
whether rotary or stationary,  and the amount of inlet silencing.  Again, the
volume is higher  than anticipated.  The energy conversion section of the gas
turbine is usually small but, because of the high volume of gas flow,  the
inlet and exhaust  gas handling sections are large.
8. 5       RANKINE CYCLE
8. 5. 1     Thermodynamic Processes
A cycle  diagram and schematic of the Rankine cycle  engine is shown in
Fig. 8-31.  It is difficult to explicitly relate Rankine efficiency to Carnot
efficiency because the Rankine cycle  working fluid undergoes phase changes,
and substantial .real-gas effects accompany vapor expansion processes.  It
is known that cycle efficiency  is closely related to the shape of the T-S dia-
gram and,  thus,  will vary considerably from fluid to fluid.  In general, it
has been found that the Rankine cycle efficiency, 7yR  , can be expressed in
terms  of the Carnot efficiency, T]  , as

                                     T  -T
                               =  "^  =     "
                                  e                   c
                             i          m
where
      T)   = engine efficiency (constant for a given system design and  set
            of operating conditions)
      T   = the maximum cycle temperature
      T   = the minimum cycle  temperature
The term TJ approaches 0. 9 for an ideal Rankine cycle.
           G
In the actual cycle the expander  will have an efficiency, «  ,  of generally
                                                        * G X
0. 7 to 0. 85 times that of an ideal isentropic engine.  The reciprocating
expander will usually have an efficiency of about 0.8.   A single turbine
                                    8-55

-------
oo
i
01
            VAPOR DOME FOR
            WORKING FLUIDS, eg.:
                FREONS
                BIPHENYL
                SULFUR
                ALUMINUM BROMIDE
                MANY HYDROCARBONS J
            cc
            ^>
            
-------
stage cannot generally utilize effectively the pressure head available and
will tend towards lower  efficiencies as shown in Fig. 8-32.
In the Rankine cycle,  the temperature rise of the working fluid is low
compared to other heat engines.  Due to incomplete combustion and because
it is not practical to exhaust the burner gases at the minimum cycle temperature,
the burner efficiency, T]~, will be approximately 0.8.
The Rankine cycle employs or needs considerable auxiliary equipment. In
order to keep condenser size low, the condenser fans will use considerable
power.  The pumps for working fluid  and  lubricant and the  blower fans for
the combustor.will also  require considerable shaft power so the efficiency in
the utilization  of shaft power,  TJ ,  will be about 0. 7.  Mechanical efficiency
                               s
of the expander, 77  ,  due to friction losses in bearings and seals will be
about 0. 95.  If all of  these efficiencies are combined, then
                                          T  -T
                 *i                         m  o
                                            m
                                                     T  -T
                      = 0. 9 x 0. 8 x  0. 8  x 0. 7 x 0. 95 —^	
                                                        m
                                T  -T
                      = 0.383   m   °
                                 T
                                  m
Figure 8-33 illustrates a plot of Carnot efficiency as a function of. the
maximum and minimum cycle temperatures.  Spotted on the curve are the
Carnot efficiencies for different engine cycles,  including three Rankine
engines.
8.5.2     Vehicular Design Considerations
Characteristics of a number of proposed and actual Rankine cycle systems
are presented in Table 8-4. In all of the reciprocating engines, except for
the Kinetics and the Thermo Electron engines,  steam is used.  Since none
                                    8-57

-------
oo

oo
                           RECIPROCATING
                           EXPANDER
                                                                      TURBINE
                                                                      EXPANDER
                                               POWER OUTPUT, hp
                       Figure 8-32.  Efficiency of Steam Turbine and Reciprocating Expanders as a
                                    Function of Power Output (1200°F, 1200 psia)

-------
oo
i
             100
              80
           >-
                   GAS TURBINE


                  STIRLING
              60
cc

-------
Table 8-4.   Rankine Engine Characteristics
Posi;: ve Displacement
Expanders
1. Frnplr:cal Eng. Co.
Miduav City. Calif.
2. Energy Systems
Cambridge, Mass.
3. General Motors
Warren, Mich.
4. Gibbs &.- Hostck
Greensboro. N. C.
5. Kinetics, Inc. (Mintol
Sarasota, Fla.
00
' 6. McCulloch Corp.
(—, Los Angeles. Calif.
7. Pritchard Steam Power
Melbourne. Australia
8. Thermal Kinetics
Hoc/heater, N. Y.
9. Thermo Electron Fng. Co.
Wakham. Mass.
10. Williams Eng. Co.
Ambler. Pa.

Power.
hp
250

200

160

1000

350


120

50-75

80

103

125
300
400
Working
Fluid
Steam

Steam

Steam

Steam

F 113
CC1F-CC1F2

Steam

Steam

Steam

Thiophene
SCH:CHCH:CH
Steam
Steam
Stram
Weight,
Ib
100

	

1 140

300

340


953

450

800

"57

500
650
800
Temperature.
°F
700

1000

700

1000

390


900

870

850

550

1000
1000
1000
Pressure, Efficiency.
psia Percent
1000 28

1000 26

800

2000

500 17


2000 23

1000

1200

500 13.7

1000 26
1000
1000

References
8-10

8-11

8-12, 8-13

8-11, 8-14

8- 15, 8-16. 8-17


8-18

8-11

8-11

8-19

8-11.8-20.8-21



-------
Table 8-4.  Rankine Engine  Characteristics  (Continued)
Rotary l)ispla< <-nu-nt
Expanders
1 1 . Af roii'i NIK lea r
.A/iisa. California
\1. Fairchilri-Hiller
Bay Shore, N. Y.
13. General Dvnamics/
Convai r
San Diego. Calif.
Sarasoia, Fla.
00
^ 13. NAR/Rocketdyne
,_ Canoga Park, Calif.
10. Pa.we
Costa Me.sa, Calif.
Working Working Thermal
Power. \\'ork:ng Weight. Temperature. Pressure. Efficiency.
hp Fluid Ib °F psia percent References
8.05 Dowthc-rm A --- 700 145 17.7 8-22,8-23,8-24
2°-^C12H10
2.0 Perfluoro-2- 145 428 206 14.6 - 8-25
Butyltet rahydro-
foran
500 Steam --- 1000 1200 22 8-26
. ... R i|3 	 325 220 	 8-15.8-16,8-17
CCIF-CC1F2
2.0 Monoisopropy! 74 750 	 7.2 8-27
Biphenyl
C15H16
160 Carbon Terra- 647 --- --- 17.9 8-28
chloride
CCL,

-------
of the efficiencies projected have been substantiated (except for that quoted
for the Thermo Electron engine), it is believed that burner efficiency and
allowances for auxiliary horsepower have not been considered.
Of the rotary expander systems listed,  only the Kinetics and Paxve designs
are specifically designed for vehicle application.  The other systems have
been designed for use in powering generator sets and, in one case, a battle
tank.
8. 5. 2. 1   Expander
A variety of expanders have been proposed for use in Rankine engines.  Partly
because  of engineering evolution and also because of specific speed considera-
tions, the majority of Rankine automotive engines have used reciprocating
expanders.   Generally,  a Rankine expander will develop several times the
power per unit volume that a corresponding spark ignition or diesel engine
can.  This is due to the  use of a higher average BMEP and the use  of a
two-stroke rather than a four-stroke design.
Another  advantage of the Rankine engine compared to the gasoline  engine is
its high-stall torque.  Because of the torque characteristics, it is possible
to eliminate  the need for a  gear box.
Due to the inherently small size of  the reciprocating expander, as well as
its relatively high efficiency and simple throttle control, a strong  argument
for turbomachine expanders does not exist.  In  central station powerplants,
thermal  efficiency now approaches  45 percent, but this is accomplished with
considerably more complexity than is possible for a small automotive engine.
The heat exchanger  size, especially that of the  condenser,  is critical to
vehicle installation and  since size is directly related to  thermal efficiency,
it is advisable to use the most efficient expander.
8. 5. 2. 2   Burner
Two types of burners  have  been used in Rankine cycle engines.  Most
commonly used is the vortex burner which was used in the Doble steam car
and has been adapted to  many of the new systems.  Because of their relatively
                                    8-62

-------
long flame path and high volume,  these burners provide  sufficient time for
near complete  oxidation of hydrocarbons and carbon monoxide.  These
                                                /          «
burners are capable of heat release rates up to  10  Btu/hr-ft -atm.
A more compact burner design results from the gas-turbine-type annular
burner in which the fuel is injected into a linearly flowing air stream.  At
Rankine cycle conditions, burner heat release rates of up to 4 x  10  Btu/hr-
  3
ft  -atm can be obtained.  Since the flame is quenched more rapidly, these
burners will produce more hydrocarbons and carbon monoxide than the
vortex burners.
The Rankine burner operates  at essentially  atmospheric pressure and
therefore it is  relatively easy to introduce recirculation for control of nitro-
gen oxides.  The vortex burner can provide  such natural recirculation so
that this capability along with the  normally low flame temperature results
in low nitrogen oxide formation.
8. 5. 2. 3   Boiler
Most  Rankine cycle systems have used monotube boiler designs even though
more compact  systems could  be obtained if  flash evaporators were used.
Safety and ease of control are prime considerations in selecting the mono-
tube design.  It would be possible, with the  hybrid vehicle,  to consider use
of an  electric heater to assist the initial warmup of the  engine.  Currently,
                                           3
it is possible to obtain about 1 million Btu/ft  in boiler  designs.
8.5.2.4   Condenser
There were no major problems with condenser frontal area because most
of the early steam  cars used engines having less than 75 horsepower and
steam venting was  allowed.  However,  if higher horsepower  and complete
condensing is needed (when working fluids other than water are  used),
there  can be problems in obtaining sufficient condenser area.
Specific output for  condensers is about 150,000 to 175, 000 Btu/hr-ft   of
                                      •3
frontal area, 350, 000 to 700,  000 Btu/ft  of  core volume, and one horsepower
per each 70, 000 to  100, 000 Btu of condensing capacity.
                                   8-63

-------
8.5.2.5  Regenerator Economizer
In the  steam cycle with expansion into the wet region, it is not possible to
use regeneration.  Regeneration should be used, however, when using a work-
ing fluid which allows expansion into a superheated region.  An economizer
can be used which preheats the water by using the boiler flow gases; where
even higher efficiency  is desired, an air preheater may be used to preheat
the combustor inlet air also using flue gases.
8. 5. 3     Engine Characteristics
8. 5. 3. 1  Specific Fuel Consumption
Specific fuel consumption for Rankine engines as a function of horsepower is
given in Fig.  8-34 with a characteristic line estimated.  As with specific
weight, the estimate is based largely upon the data of the General Motors
Corporation SE101 and the Thermo Electron 184-CID engines.  The other
values appear overly optimistic or have failed to include proper allowances
for burner efficiency and auxiliary equipment.
Part-load fuel consumption characteristics for a reciprocating  and a rotary
expansion Rankine cycle  system are presented in Fig. 8-35.
8.5.3.2  Specific Weight
The specific weight characteristics of the Rankine engines listed in Table 8-4
have been plotted in Fig. 8-36.  An estimate of engine specific weight as  a
function of horsepower is also provided.  The estimate is  mostly based upon
the characteristics of the Thermo Electron 184-CID engine and the General
Motors SE101 engine,  both of  which are fully documented.  Allowance has
been made for some improvement to these and a scale factor equivalent to a
5-percent decrease in specific weight for each doubling of  power level has
also been included.
Documentation of most other Rankine engine systems is too inaccurate to
be used in establishing their characteristics. In the cases where very low
specific weights  are indicated,the weights are based upon only the weight  of
the bare expansion engine and do not include provisions for heat exchangers
or auxiliary equipment.

                                    8-64

-------
CO
          i
         O.
             1.2
             1.0
             0.8
         CO

         O
         0  0.6
            0.4
         Q_
         CO
            0.2
              0
                                           i    i
•  COMPLETE HARDWARE
O  INCOMPLETE  HARDWARE
 * REFER TO TABLE 8-4
   FOR IDENTIFICATION
                                    10
                                                            O   O2
                                                                       5
                                     10             50     100
                                     RATED HORSEPOWER,hp
                                                  500   1000
                      Figure 8-34.  Design SFC of Automotive Rankine Engines

-------
oo
i
     CO
     CO
         1.2
         1.0
     Q

     3 0.8
0.6
     CO
     CO

     o 0.4
     or
        0.2
     CO
          0
           0
                                               RECIPROCATING  EXPANDER
                   0.2
                                     TURBINE EXPANDER
0.4              0.6
     LOAD RATIO
                                                                          DESIGN
0.8
1.0
             Figure 8-35.  Part-Load BSFC Characteristics of Automotive Rankine Engines

-------
00
i
                 12
                 10
                  8
              o
              CO
                  0
                      72lb/hp
•  COMPLETE  HARDWARE

O  INCOMPLETE HARDWARE
                          *REFER TO TABLE 8-4
                            FOR IDENTIFICATION
 I.I  I  I I  I I I
                                                         7*
                                                         'o
                                                             I000
                                                                 16
                                                                    I0
ll  I  1  I I I iQ
                   I                    10                  100

                                        RATED HORSEPOWER, hp


                    Figure 8-36.  Specific Weight of Automotive Rankine Engines
                                                      1000

-------
8.5.3.3  Specific Volume
Specific volumes for Rankine cycle systems are presented in Fig.  8-37 with
an estimated design trend again with high reliance upon the SE101 and 184-
CID systems.
In Table 8-5 the volumes for the Thermo Electron 184-CID and the General
Motors SE101 systems are presented in detail.
8. 6       STIRLING CYCLE
8. 6. 1     Thermodynamic  Processes
The pressure-volume and temperature-entropy diagrams for the Stirling
cycle are shown in Fig. 8-38.  The ideal Stirling cycle may be described
as a constant volume-regenerative cycle consisting of two constant volume
processes and two isothermal processes.  It differs from the Carnot cycle
in that it employs two constant volume processes in place of the Carnot's
two isentropic processes.  The practical cycle employs a reciprocating
engine that functions with a fluid having a low molecular weight (e.g., helium).
Torque, efficiency,  and power characteristics of a Stirling engine are
presented in Fig.  8-39.
8. 6. 2     Cycle Characteristics
The basic cycle efficiency equations are  independent of working fluid.
However, the design of the engine  tends to be limited by heat transfer, and
therefore, it is advisable to use low molecular weight gases such as  hydrogen
and helium.  While in some cases  hydrogen has been used,  safety considera-
tions have more often prompted the use of helium.  It is also believed that the
use of hydrogen at high temperatures should be avoided because of possible
leakage.  Loss of efficiency using  helium rather than hydrogen is on  the
order of three percent.
Aluminum chloride has been  suggested as a working fluid because of  its
apparently jjood heat transfer characteristics; however,  no known work
has been done with this gas.  Since the boiling point of aluminum chloride
is 361  F, such a system could be used only in special situations.
                                    8-68

-------
00
I
          0.5
          0.4
       Q.


      \
      ro
          0.3
0.2
       o
       LU
       Q_
       CO
          0.
            0
                 * REFER TO
                  TABLE 8-4 FOR
                  IDENTIFICATION

                     i     I   I  I  I  I i  i
                                    1     T
                                      10                50     100

                                       RATED HORSEPOWER, hp
                                                                       500    1000
                       Figure 8-37.  Specific Volume of Automotive Rankine Engines

-------
             Table 8-5.  Performance of Rankine Heat Engines
             System
Thermo Electron
     184-CID
General  Motors
   SE-101
Working Fluid
Net Shaft Horsepower
Engine
   Dimensions, in.
   Volume, ft
   Specific Horsepower, hp/ft
Burner
   Dimensions, in.
   Volume, ft
   Btu Output,  Btu/hr
   Combustion Intensity
     Btu/hr-ft3-atm
Boiler
   D imen s ion s , in.
   Volume, ft3
   Btu Output,  Btu/hr
   Specific Output, Btu/ft
Condenser
   Dimensions, in.
   Volume, ft
   Frontal Area,  ft '
   Capacity, Btu/hr
   Specific Frontal Area,  Btu/ft''
   Specific Capacity, Btu/ft
Regenerator
   D imen s io n s , in.
   Volume, ft
   Capacity, Btu/hr
   Specific Capacity, Btu/ft
Thiophene
103. 2

19. 7 x 19 x 27. 2
5.91
17. 5

20.2 x 21.3 x 8. 5
2. 02
2. 06 x IO6
2.8 x IO6
18.2 x 21.3 x 14.5
2. 68
1. 7 x IO6
0. 64 x IO6
50 x 19. 9 x 3
1.73
6.91
1. 2 x IO6
1. 7 x IO5
7. 0 x IO5

28. 6 x 7. 7 x 6. 8
0. 87
2. 5 x IO5
2. 8 x IO6
Water
113
10 dia x 7. 5 (two)
0.68
4.2 x IO6
3. 75 x IO6
32 x 15 x  11. 5
3.34
3.4 x IO6
1.02 x IO6
19 x 42. 2 x 5
2. 33
5.56
8. 2 x IO5
1.5 x IO5
3.5 x IO5
None
                                    8-70

-------
         CARNOT CYCLE
00
          oc
          ID
          CO
          CO
          LU
                   VOLUME
          STIRLING CYCLE
          QC
          ZD
          CO
          CO
          LU
          CC
          Q_
oc
LU
D_
cc
LU
Q_
         ENTROPY
                                                    • 2
EFFICIENCY


   '••^

MEAN EFFECTIVE PRESSURE
                                                                 m
                                  (T|-T3)wRln(V2/V,)

                                        (v,-v3)
                   VOLUME
         ENTROPY
                 Figure 8-38.  Pressure-Volume and Temperature-Entropy Diagrams for
                             Carnot and Stirling Cycles

-------
   140
   120
   100
X

-------
8.6.3    Operating Considerations
The major factor creating interest in the Stirling cycle is its high thermal
efficiency achieved  with a relatively low working fluid temperature.  The
specific fuel consumption of the Stirling engine is approximately that of the
diesel engine.  Thermal  efficiencies between 30  and 40 percent have been
demonstrated.  Also, since effectiveness of the  regenerators and heat
exchangers increases at low loads, part-load efficiency of the engine is good.
The operating temperature of the Stirling engine is  on the order of 1200°F
with a maximum burner temperature  of about 1400°F.  This can be con-
trasted to temperatures above 3000°F for diesel and Otto  cycle engines. As
a result the nitrous  oxide emission is projected as being drastically reduced
for the Stirling engine.
A Stirling engine without  any acoustic treatment,  tested in comparison to a
standard military engine  of the same  size,  indicated a sound level  21 db
quieter than diesel and Otto cycle  engines at 100 ft.  The sound level  was
40 db.
Since the engine uses an  external burner  system, any type of fuel  can  be
used.  It is likely that the engine could  run  interchangeably with several
types of fuels. Use of non-leaded fuels allows the use of exhaust reactors
to eliminate unburned hydrocarbons or  nitrogen oxide emissions.
The prototype versions of high-performance Stirling cycle engines have not
demonstrated good life capability with something less than 1000 hr being the
best life period recorded in the literature.  The high efficiencies which have
been  reported have  been  obtained with well-tuned, new engines operating at
conditions which  would not promote long life. One of the main problems
with the Stirling engine is the fact that the working fluid does not contain any
lubricating qualities so the life of  seals and piston rings has been  low.  How-
ever,  Philips reports rolling seals having been tested for 11,250 hr which
may provide  a longer life engine.
                                    8-73

-------
The Stirling engine has a sizeable thermal inertia due to the mass of the
burner, the heat exchangers, the regenerator, and the engine itself.  The
engine is therefore sluggish to load changes.  Figure 8-40 shows response
times to full load from 0 and 50 percent initial loads by changing system
pressure and by increasing temperature.  Use of a working fluid accumu-
lator has been  suggested as  perhaps the best method of achieving good
response.  However, such an approach would affect efficiency and would
add additional bulk to the engine.
The engine is best  suited as a constant-speed,  constant-load device because
of its poor response to load  change  due to the thermal inertia of the regen-
erator, heat exchangers, and the engine itself, and is thus best suited for
the hybrid vehicle rather than as a primary powerplant.  The control system
would be elaborate to permit higher reaction rates and quite probably would
reduce the engine's efficiency.
No one has proposed a multicylinder engine in which the  critical functions
could be combined.  For example, in  present designs each cylinder will
have its own burner,  heat exchangers, and regenerator.   The number of
elements in the crankshaft and drive mechanism would increase materially
if  a multicylinder engine were used since  each cylinder would have to be
controlled individually.
Starting may be a problem with the  engine, especially in cold weather.  The
engine would have to be  motored for a considerable period before it could
sustain itself.   The large number of bearings add to the problem.  Also,
the engine would tend to motor after the burner has shut  down.
The  Stirling engine has approximately the same thermal  efficiency as an Otto
or diesel cycle  engine, but in the Otto and diesel engines, about one-third of
the energy contained in the fuel goes out the exhaust with only about 17 percent
                                   8-74

-------
oo
I
-J
01
           100
           80
         Q
         
-------
of the energy being rejected into the cooling water.  In the  closed-cycle
Stirling engine, about 60 percent of the fuel's energy will be rejected into
the cooling system provided an efficient burner system is used.   The
Stirling engine will therefore need a radiator  area three to four times
larger than those used in comparable present-day vehicles, and power
for the cooling fan will be appreciably higher.
Modern development of the Stirling engine has practically been restricted
to Philips  in the Netherlands and to General Motors (licensed by Philips)
in the United States.   This  has produced a limited amount of actual test
information, and the number of specialists in Stirling engine technology
is likewise limited.  This lack of experience would increase the cost and
time needed to bring the engine to vehicle  readiness.   Also, the licensing
agreement could hinder any industry-wide program for development of
the engine.
8.6.4      Engine Characteristics
8. 6. 4. 1    Specific  Fuel Consumption
A number  of Stirling engines of both conceptual and prototype designs are
listed in Table 8-6.  Specific fuel consumption is plotted in Fig. 8-41. It
should be noted that the data for conceptual engines indicate lower fuel
consumption than that of the prototype engines. However,  the difference
is not large and may be achieved through growth and design refinements.
A curve  showing anticipated part-load fuel consumption is given in Fig. 8-42,
The curve is characteristic of regenerated engines with a  slight improve-
ment  in efficiency  at high part-loads with increased consumption at low
part-loads as parasitic loads become prominent.
                                    8-76

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                                     Table 8-6.   Characteristics of Stirling  Engines
oo
i
-j
Engine Model
1
2
3
4
5
6
7
8
9
10
11
12
13
14
CM
CM
Research GPU-2
Research GPU-3
Philips 3015
CM
Electromotive 8015
Philips Marine
CM
CM
CM
KB
KB
KB
KB
KB
KB
Allison PD-67
Research
Research
United Stirling
United Stirling
United Stirling
United Stirling
United Stirling
United Stirling
hŁ
7.5
10
40
380
120
7
8.63
40
27
20
80
175
200
300
Volume,
ft3
3.
4.
6.
130
23.
3.

3.
2.
5.
30.
30.
41.
04
89
4

20
5

25
53
06
6
6
3
ft3/hp
0.40
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
49
16
34
19
50
121
127
064
175
153
138
Weight,
Ib
90
188
550
5000
725
186
127
450
240
150
440
2200
2200
2900
Ib/hp

12.0
18.8
13.8
13.2
 6.0
26.6
14.7
11.0
 8.9
 7.5
 5.5
12.6
11.0
 9.7
                                                                                                BSFC
                                                                                               Ib/bhp-hr
0. 595
0. 508
0.351
0.457
0.343
0.457
0.470
0.358
0.410
0.395
0.410
0.365
0.375
0. 375
Reference

    1
    1
    1
    1
    1
    1
    2
    2
    3
    3
    3
    3
    3
    3
          References:
          1.  Battelle Memorial Institute,  "Study of Unconventional Power Sources for Urban Vehicles, " 15 March 1968.
          2.  Flynn, G.,  Jr., W. Percival, F. R. Heffner,  "GMR Stirling Thermal Engine> " SAE Trans. Vol. 68, 1960.
          3.  KB United Stirling, Brochure,  1970.

-------
              1.0
             0.8
         o
         h-
         Q_

         Z5
         CO

         O
0.6
00
I
00
        UJ
        Q.
        CO
        CO
        UJ
        O
0.4
             0.2
      * REFER TO
        TABLE 8-6 FOR
        IDENTIFICATION
              0
                       10
                                  50         100
                                RATED HORSEPOWER, hp
500
1000
                     Figure 8-41. Design SFC of Automotive Stirling Engines

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CO
I
                                               0.4            0.6
                                                    LOAD RATIO
                            Figure 8-42,
Part-Load BSFC Characteristics of
Automotive Stirling Engines

-------
8.6.4.2  Specific Weight
Specific weight characteristics are described in Fig.  8-43.  From the raw
data it is difficult to judge what the true potential of the Stirling engine
might be.  The list includes heavy laboratory-type engines and some opti-
mistic conceptual designs, along with some marine systems which reduce
the cooling  system weight.  However, it is quite probable that a detailed
engineering design utilizing such advanced techniques as heat pipes and
lightweight  materials could reduce the weight of the Stirling system signi-
ficantly.  It does not appear realistic when considering the comparative
thermal efficiencies that the Stirling engine should be larger and heavier
than a Rankine engine.
8.6.4.3  Specific Volume
Specific volume characteristics  for the Stirling engine are shown in
Fig.  8-44.

8. 7       COMPARISON AND EVALUATION OF HEAT ENGINES
Heat  engine horsepower requirements for the various classes  of hybrid
vehicles are delineated in Section 10.  The requirements for series and
parallel operation are not significantly different. For simplicity in the
discussion that follows, it will be assumed that the series configuration
power requirement represents  the  engine  size needed in each vehicle
class.  With this assumption,  the heat engines for each of the  hybrid
vehicle classes maybe  described in single-valued terms of  weight,
volume, and  specific fuel consumption as shown in  Tables 8-7
through 8-12.
                                   8-80

-------
           25
           20
        o.

       ^v
       -O
oo
i
oo
           15
o
       Q.
       CO
           10
                                '10
                * REFER TO
                  TABLE 8-6  FOR
                  IDENTIFICATION
            0
                              I    i
                    10
                                     50        100

                                   RATED HORSEPOWER, hp
500
1000
                    Figure 8-43.  Specific Weight of Automotive Stirling Engines

-------
oo
i
oo
   0.5
            0.4
         o.

        \
        ro
          - 0.3
y  0.2
         o
         LU
         Q_
         C/5
             O.
                  * REFER  TO
                    TABLE  8-6 FOR
                    IDENTIFICATION
              0
                      10
                                           3
                                                                    1      I    I       I  i  i  i
                                                         12
                                                          13'
                                                                         14
                                                                     i      i    i
                                      50        100

                                     RATED  HORSEPOWER, hp
500        1000
                    Figure 8-44.-  Specific Volume of Automotive Stirling Engines

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  Table 8-7.  Family Car Heat Engine Characteristics
Heat Engine
S. I. Engine -
Piston
S. I. Engine -
C! Engine
Brayton Cycle
Rankine Cycle
Stirling Cycle
Reciprocating
Rotary Piston

Engine
Engine
Engine
SFC, Ib/hp-hr
0.
0.
0.
0.
0.
0.
50
50
43
57
87
42
Weight, Ib
335
216
493
310
846
1153
Volume, ft3
11.
5.
15.
10.
13.
22.
8
8
1
4
5
8
Table 8-8.  Commuter Car Heat Engine Characteristics
Heat Engine SFC, Ib/hp-hr
S. I. Engine -
Piston
S. I. Engine -
CI Engine
Brayton Cycle
Kankine Cycle
Stirling Cycle
Reciprocating 0. 56
Rotary Piston 0. 56
0.45
Engine 0. 65
Engine 0. 93
Engine 0. 43
Weight, Ib Volume, ft3
180 6.
116 4.
228 8
125 3.
322 5.
432 8.
1
0
9
9
5
6
Table 8-9.   Low-speed Van Heat Engine Characteristics
Heat Engine SFC, Ib/hp-hr
S. 1. Engine -
Piston
S. I. Engine -
CI Engine
Brayton Cycle
Rankine Cycle
Stirling Cycle
Reciprocating 0. 54
Rotary Piston 0. 54
0.46
Engine 0. 63
Engine 0.92
Engine 0.43
Weight, Ib Volume, ft3
205 7.2
134 4.2
273 10. 1
155 4.8
403 6. 8
546 10.9
                          8-83

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Table 8-10.  High-speed Van Heat Engine Characteristics
Heat Engine
S. I. Engine - Reciprocating
Piston
S. I. Engine - Rotary Piston
Cl Engine
Brayton Cycle Engine
Rankine Cycle Engine
Stirling Cycle Engine
SFC, Ib/hp-hr Weight, Ib Volume, ft3
0.50 357 12.8
0.50 236 6.1
0.43 545 16. 1
0. 56 350 11.8
0.86 963 15.3
0.42 1305 25.7
Table 8-11.  Low-speed Bus Heat Engine Characteristics
Heat Engine
S. I. Engine - Reciprocating
Piston
S. I. Engine - Rotary Piston
CJ ! Engine
Brayton Clyde Engine
Rankine Cycle Engine
Stirling Cycle Engine
SFC, Ib/hp-hr Weight, Ib Volume, ft3
0. 48 478 17. 3
0.48 311 7.2
0. 42 755 20. 3
0.52 521 15.0
0.83 1462 22.7
0.41 1949 38. 1
Table 8-12.  High-speed Bus Heat Engine Characteristics
Heat Engine
S. I. Engine -
Piston
S. I. Engine -
Cl Engine
Hrayton Cycle
Hankine Cycle
Stirling Cycle
Reciprocating
Rotary Piston

Engine
Engine
Engine
SFC, Ib/hp-hr Weight, Ib Volume, ft3
0.46 626 22.4
0.46 405 8.6
0.41 1050 2S. 3
0. 50 744 19. 8
0.81 2218 13.9
0.40 2793 53.0
                               8-84

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The tabular data were developed fromheat engine characteristics given in the
preceding sections. The weights represent current technology for each engine
type.  Values shown for the rotary piston S. I. engine were estimated from
the Curtiss Wright data, appropriately adjusted to reflect a consistent set
of automotive accessories for  all engines.   Weights  and SFCs for the CI
engine are based on turbocharged, divided-chamber designs.   The SFCs
for spark and compression ignition engines  represent the minimum point in
the engine operating map;  the SFCs for the Brayton,  Rankine,  and Stirling
engines represent the design or full-load point in the engine operating map.
Nevertheless, no great error  is incurred by comparing these values on an
equal basis,  since  the SFC characteristic for all (design-optimized) systems
under consideration is  relatively  flat over a wide range of load.
A broader view  of the tabulated results may be obtained by referring  to the
plots of Figs. 8-45, 8-46  and  8-47, where  the data are grouped by heat
engine characteristic and  are plotted over the range of vehicle-class  horse-
powers.   The SFC  plot, Fig.  8-45, shows that the Stirling and compression-
ignition engines provide the lowest fuel consumption for all hybrid vehicles.
The  spark-ignition engine  ranks second on  this basis, with SFCs ranging 25
to 12 percent higher for low to high horsepower applications.
The  weight plot,  Fig.  8-46, shows that the rotary-piston spark-ignition
engine is  the lightest of the heat engine candidates for all hybrid vehicles.
The  Brayton  cycle  is second best in this  category for the commuter car and
low speed van (i.e., the lower horsepower  applications).  The reciprocating-
piston  spark-ignition engine is (a) competitive with the Brayton cycle for the
family car and high-speed van and (b) superior to the Brayton cycle for the
two buses.  The Stirling and Rankine cycles run significantly heavier than
other heat engine types and, in view of the  criticality of weight in relation
to battery power density requirements,  these systems  appear not to be useful
in their present form.
                                   8-85

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        Figure 8-45.
        Heat Engine
     SFC Comparison
                                                      00   150   200
                                                    CNCINt R4TEO HOfiSl POWER
2bOO
1000
            100    150    200    ?50
            INGIN! R»TED HORSEPOWER
    Figure  8-46.
    Heat Engine
Weight Comparison
       Figure 8-47.
       Heat Engine
   Volume Comparison
                                                          I bo   ?1M]

                                                         HflM tl >({1H',t POwf H
                                    8-86

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In addition, the latter two engine types make a generally poor showing in
volume,  as indicated by Fig.  8-47 (The volume improvement in the Rankine
system at low rated horsepower levels is noted. ).  Volume, it may be
observed,  has  a secondary impact on engine-assignable weight,  since a
bigger structure  is required to support and enclose a larger engine envelope.
The rotary-piston spark-ignition engine  is best in the volume  category for
all vehicles, while the Brayton cycle  is second best for all vehicles.
The practice of using  numerical weighting factors to  evaluate  the relative
merits of alternative systems  frequently produces  specious results which
depend heavily on the  influence assigned to the individual criteria of evalua-
tion.  For this reason, and because exhaust emissions are a  primary con-
cern of this study,  a ranking of the alternative heat engine systems based on
SFC,  weight,  and volume considerations will not be attempted.  It is
apparent, however, that (a) the rotary-piston engine  is a  prime candidate
for further examination and evaluation in relation to the full spectrum of
hybrid vehicle  applications, (b) the Brayton cycle constitutes a promising
alternative for applications involving  low horsepower requirements,  and (c)
the reciprocating spark-ignition engine must be included for consideration
as an alternative to the rotary-piston engine for applications  involving
intermediate to high horsepower requirements.
8. 8       TECHNOLOGY GOALS
8. 8. 1     Spark-Ignition  Engines
The impact of engine weight on battery power density requirements is dis-
cussed in Section 11.  In  general,  a reduction of engine weight is desirable
from  the standpoint of relieving design constraints on other propulsion sys-
tem components; in particular, a  reduction of engine weight is an absolute
necessity for the application of certain heat engines to  specific hybrid
vehicle classes.
                                   8-87

-------
Weight has never had a strong influence on automotive engine design practice
except as it indirectly impacts production cost through raw material pur-
chase expense.  In this sense, the present specific weight status of auto-
motive spark-ignition engines is largely artificial and can be significantly
improved if requirements demand.  There are a number of general
approaches which can be  taken to bring this about.  One of these,  not related
to weight per se, is to increase engine power  output by  increasing engine
speed, by increasing compression ratio, or by supercharging.  The first
technique results in reduced mechanical and volumetric efficiency with
concomitant loss in engine fuel economy.  Neither of the latter two techniques
is recommended since they both raise combustion temperature and pressure,
require higher octane fuels to prevent detonation,  and may therefore add to,
rather than improve, engine exhaust emissions.
Another  approach is to reduce engine weight through the use of materials
having maximum strength-to-weight ratios such as high tensile  alloy steels
and aluminum and magnesium alloys.  This route  is assuredly expensive,
yet it is  doubtful that significant advances can be  made in this area without
economic repercussions of some  magnitude.  The Vega aluminum block
engine is an elementary example  of what might be accomplished by this
approach (the 105-hp Vega engine specific weight is 2.6 Ib/hp, or 24 percent
lower than the mean characteristic for cast iron block engines).
Design modifications in the direction of large  bores and minimum number of
cylinders offer the best hope  for substantial gains and should be pursued.
High-displacement, short-stroke, air-cooled  designs with opposed cylinder
arrangements (such as used by Volkswagen and Porsche)  to effectively
treat the reciprocating-mass  balance problem appear attractive from the
standpoint of both weight  and  volume.
New principles of operation,  as embodied by the rotary-piston engine,
clearly  provide  breakthroughs to  uniquely low levels of  weight and volume.
These systems are attractive, provided that they do not introduce more
problems than they solve.
                                    8-88

-------
The major emphasis  in rotary-engine systems has been placed on the Wankel
engine, which has been under development for barely over 10 years and is
under limited production by NSU in Germany,  Toyo Kogyo (Mazda) in Japan,
and  Citroen in France.  In addition to its weight and volume  features, the
Wankel engine provides smoother operation (no reciprocating parts to
contribute to unbalanced inertia forces), has fewer components,  and
(probably) can be mass-produced cheaper than the conventional S. I.  engine.
Attendant with these advantages are a number of problems and disadvantages
which need resolution before the system can be regarded  as  being truly on  a
competitive developmental par with the  reciprocating type.   These problems
include high HC and CO emission levels, difficulties in rotor lubrication, and
poor durability of the rotor apex seals.
The emissions problem stems from wall quenching effects associated with
the high surface-to-volume ratio of the  combustion chamber, combined with
the action of the trailing apex seal which scrapes off the quench layer into
the exhaust port (Ref. 8-30).   The use of a thermal reactor with  air  injec-
tion has enabled NSU and Mazda to meet current U. S.  emission standards.
However,  it appears  likely that drastic  changes in engine design  might be
required in order to meet U.S. standards proposed for 1975.
Citroen has approa.ched the lubrication problem by adding about one percent
oil to the  incoming gasoline.  This has further complicated the problem of
emission  control, requiring the addition of an afterburner.   The  efforts of
NSU to  reduce seal wear has led to the development of a secondary combus-
tion chamber  in which tip seal blow-by is contained.  The chamber retards
further passage of combustion gases,  preventing the intermingling of oil
with blown-through volatile combustion  residue.  Seal life is thus claimed
to be extended and the previously  recommended 12,000-mi engine oil change
has been eliminated (Ref. 8-31).
Other rotary-engine systems  are  under  development and  should be investi-
gated as possible Wankel alternates for  application to the hybrid  vehicle
family.   One of these, the  Walker  engine (New Zealand) utilizes an elliptical
                                    8-89

-------
rotor.  A two-rotor version, now possibly in production,  develops  60 to
100 hp and has only seven moving parts (Ref. 8-32).   Production costs have
been estimated at about $200.  Unlike the Wankel,  the seals on the  Walker
engine are mounted on the engine casing rather than on the rotor, permitting
simpler adjustment or replacement (Ref.  8-33).  The 90-hp, 135-lb English
"Tri-Dyne" (Ref. 8-34) might also be mentioned, as well as the U.S.
Tschudi, a torroidal rotary engine rated 88-hp at 1600 rpm.  The latter
engine employs  conventional compression rings on the torroidal pistons,
thereby avoiding the seal problems associated with the Wankel  design
(Refs. 8-31 and 8-34).
Aside from the general desirability of seeking means  to reduce engine weight
and volume (properties which appear not to be critical for spark-ignition
engine application to the hybrid vehicle), every effort should be made to
investigate, encourage, and/or support the development  of techniques which
may lead to the  attainment of satisfactory engine operation at high air/fuel
ratios.  As shown in Section 11,  an estimated air/fuel ratio of  about 22
would permit  the hybrid commuter car and  family vehicle, equipped with
appropriate controls, to meet or  approach the emission goals set for 1975/
1976.      Current technology limits lean operation for conventional vehicles
to an air/fuel ratio  of about 17  and for hybrid vehicles to an estimated air/
fuel  ratio of about 19.
The  general challenge  in achieving extremely lean operation is to maintain
normal vehicle driveability  functions.  Lack of throttle response, stalls,
and unsteady vehicle forward progress are  always encountered at the extreme
limits indicated above,  primarily as a result of deterioration in combustion.
The  driveability  problem is more severe in conventional vehicles because
the heat engine is the sole source of power  needed for rapid response to
acceleration demands; the problem is considered to be significantly more
l.ractable in the  hybrid vehicle  since the heat  engine is required only to  provide
.sl.eiidy or  quasi-steady power output.   High idle speeds in some of the pro-
posed configurations may  also  serve to minimise the hybrid driveability
problem.
                                   8-90

-------
The means to achieve satisfactory lean operation may lie in improvements or
innovations  in the engine induction and/or combustion systems.  As a first
step,  improvements which lead to more uniform distribution of the air /fuel
ratio  among individual cylinders should be pursued in order to prevent local
fuel starvation with a mixture which would otherwise be satisfactory if homo-
geneously dispersed.  Changes in  inlet manifold ducting or carburetor design
would thereby be indicated.   The  use of liquid fuels which are inducted as a
gas;  Propane,  for example,  should be considered (Propane also provides
the additional advantage of reduced exhaust HC  reactivity).
The distribution problem might also be solved by the use of fuel injection
systems,  either port-type such as recently adopted by foreign engine manu-
facturers (e.g., Volkswagen,  Opel) or, preferably, direct-cylinder-injection
type.   In this  connection,  the stratified charge concept, as exemplified by the
Ford  Combustion  Process, might  be  mentioned as an injection technique
which simultaneously treats the distribution problem and additionally promotes
and improves combustion  at lean  mixtures by providing a localized-r ich
charge mixture in the vicinity of the spark electrodes (Ref.  8-35).   Precom-
bustion chamber designs which implement the same process by isolating  the
rich  mixture zone in  an  external pre-chamber should also be  investigated.
In each innovative, lean-operating design examined, consideration must be
given to the possible  degradation  of maximum power output for current engine
designs.  Satisfactory methods of  treating this problem must  be found in
order to limit the growth in engine size required to offset the  power loss.  It
is anticipated that in  the future such methods can be achieved  (viz., strati-
fied charge  engines) and,  hence,  the  power loss effects were  not included in
the analysis.
8. 8. 2     Compression-Ignition Engines
Unlike the spark-ignition engine,  the weight of the diesel engine is critical and,
for the baseline propulsion system allocation, the battery requirements are exces-
s ive for certain hybr id vehicle applications such as the commuter and family car s .
                                   8-91

-------
The remarks made under spark-ignition engines with regard to engine design
practice apply also to diesel practice but with considerably more emphasis.
While  it is unrealistic from the  standpoint of the fundamental compression-
Ignition process to expect that the automotive diesel  engine could rapidly
overtake the spark-ignition  engine weight advantage,  it is nevertheless
evident that the industry has in the past been guided by application require-
ments  dictating durability and long life,  and that significant improvements
in weight and volume are achievable.  As an example of what might be
accomplished, the specific weight for  a conceptual design intended for light
aircraft application may be  cited:  1. 8 Ib/hp at  180 hp (Ref.  8-36).   This
compares with 4. 5 Ib/hp indicated by the state-of-the-art characteristic
for divided-chamber  turbocharged engines shown in Section  8. 3. 3.
Diesel HC  and CO emission characteristics look relatively good compared
with S. I. engines, -while NO? emissions,  which are generally higher than
S. I. engines, might be effectively treated by recirculation.   The NO2 prob-
lem is compounded, however, by the necessity  of resorting  to turbocharging
in order to achieve reasonable values  for engine specific weight.  There-
fore, the possibilities for weight improvement in naturally-aspirated designs
should be pursued.  New swirl and prechamber configurations which act to
reduce peak  cylinder pressures, thereby minimizing static and dynamic loads
on the  engine system, might be  investigated for this  purpose.
In further connection with innovative designs, the weight and volume proper-
ties of rotary-piston diesel-process machines look attractive and these
should be examined in light  of their  potential for hybrid vehicle use.  For
example, the Rolls-Royce model 2-R6, a two-stage, two-bank diesel
Wankel which is now  being built for  testing  in early 1971, develops 350 hp
at a weight of 929 lb and a volume of 19. 3 ft3  (2. 7 Ib/hp, 0. 055 ft3/hp). Diesel
Wankels are currently being developed for Great  Britain's Military Vehicle
Engineering  Establishment (Ref. 8-37).
                                    8-92

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8. 8. 3     Gas-Turbine Engines
As noted previously,  the gas turbine engine for the hybrid vehicle can be
simpler than an engine designed for prime power.  Ordinarily, a regenerated
gas turbine is sluggish in response to load or speed change due to the
thermal inertia of the regenerator and thus additional complexity is needed
to improve the engine's response  capability.  As  a result,  it has been
estimated that  in high production the automotive gas-turbine  engine will
cost more  than a spark-ignition engine.  This additional cost is estimated
at anywhere from 10  to 50 percent more.  However, the hybrid gas turbine
will  operate at a nearly constant speed for long periods and there is no need
to provide  for rapid response to speed or  load change.  Hence, added
cost factors may be minimized.
The  areas  where effort is needed  in the development of the hybrid gas turbine
are described in the following paragraphs.
In order to improve response of the gas turbine,  it has been  necessary to
decrease the inertia of the rotating assembly which necessitates  increasing
the specific output.  Higher pressure ratios, reheat,  intercooling, and
other techniques are  used to provide the high specific output. The hybrid
engine does not need  a high specific output.  As a matter of fact, just the
opposite might be true, for if a direct generator  drive is used, lower
specific output will provide greater  compatibility between the gas turbine
speed and the desired speed range for a generator.
In the previous section where gas turbine  design  arrangements were  investi-
gated,  a moderate pressure ratio was assumed.  This pressure ratio was
selected because it is more compatible with that  of gas turbines currently
in production.
A turbocharger  is a gas turbine which uses the  diesel engine it serves as a
source of energy to power the turbine.  A turbocharger equivalent  in air
flow  to a 40-hp gas turbine will cost under $50 [Original Equipment Manu-
facturer (OEM)  Price] and run for 4000 hr under  off-highway conditions with
                                   8-93

-------
full warranty.   To make a hybrid gas turbine from a turbocharger it is
necessary to add all of the auxiliaries.  Although it appears that the rota-
ting assembly will not be too expensive, the  regenerator,  controls, and
combustor will  be the main sources of cost.
Therefore, a major  study of  the hybrid gas turbine should be undertaken.
This study should concentrate on cost aspects and determine what the true
high production costs of the  gas turbine will  be.  An important output of
this study will be the weight, volume, and configuration specifications for
the hybrid gas turbine.
The hybrid engine could have as few as  two operating points, full speed
(design output) and idle speed (no output condition).  This latter condition
will be especially important to the commuter car, and the low-speed van
and bus.  Some  additional thought should be given to the reduction of fuel
consumption at  idle.  As mentioned earlier,  the reduction of speed  and the
use of variable  turbine nozzles would decrease fuel consumption at  idle.
While the gas turbine has low emission  characteristics, it should be
possible to make some further significant reductions.   The main  considera-
tions used in the design of present combustor systems have been low volume
and high combustion  efficiency with little or  no thought given to emissions.
It would appear  that vaporizing injectors and recirculation could be inte-
grated into the combustor to  reduce emissions.   Development studies of
gas turbines should be performed to reduce emissions.
8.8.4     Rankine  Engines
A wide number  of concerns have examined the Rankine engine for application
as a  prime powerplant for vehicles. Considerable  support to Rankine cycle
development has been and is  being provided by the Atomic Energy Commis-
sion  and by the  U.S.  Army.   Rankine cycle engines, by virtue of  their
external burner system, have better emission characteristics than  any of
the internal combustion engines and for this  reason their use has been
advocated in spite of their rather poor weight,  volume,  and  specific fuel
                                    8-94

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consumption characteristics.  Unfortunately,  the basic problem relative
to any significant improvement in these items is the second law of thermo-
dynamics.  Due to the characteristics of working fluids there does not
appear to be any room for revolutionary improvements to the present sys-
tems.  However, because of the low emission characteristics,  it might be
advisable (although low in priority for hybrid application) to continue some
work on Rankine engines with a view to refining the design of the  components.
8.8.5     Stirling Engines
Available data on the Stirling engine indicate that it has, or should have,
very good specific fuel consumption and low emission characteristics.  The
principal problems of concern are weight,  volume, and life.  Since none of
the existing engines appears suited to hybrid vehicle  application,  a design
study and analysis of the Stirling engine powerplant would  have  to be con-
ducted with the objective of decreasing its  weight and volume before it could
be considered for use in the hybrid engine.  With acceleration modes  removed
for hybrid operation, potential performance improvements should be examined.
The characteristics of all auxiliary equipment such as radiator, fans,  pumps,
and burners should also be investigated. Consideration should  be given to
variations  (e. g. , the use of heat pipes) in the cycle which  would permit con-
solidation of some of the engine processes  so that the coolers and burners
might be shared by the individual cylinders.  The  problem of increasing the
life of seals and bearings as well as improving accessibility and maintenance
should also be studied.
                                    8-95

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8. 9      REFERENCES


8-1.     "American Motors and Jeep Engines," Data Transmittal and Price
         Quotation from American Motors Corporation,  Detroit, Michigan,
         18 August 1970.

8-2.     "V-Belt Application and Power Curves," Engineering Specifications
         for 6-Cylinder  American  Motor Engines, American Motors
         Corporation, Detroit, Michigan, May 1968.

8-3.     Compilation of  Power Curve  Data for Ford and American Motors
         Automotive Engines.

8-4.     Data Transmittal from Toyota  Motor Co., Ltd.,  Lyndhurst, New
         Jersey, 6 August 1970.

8-5.     Specification Data for Rotary Power Systems,  Curtiss-Wright
         Corporation, Wood-Ridge, New Jersey.

8-6.     Wilcap Diesel D-154 Specifications, Wilcap Company,  Torrance,
         California.

8-7.     E. F. Obert,  "Internal Combustion  Engines," International Text-
         book Company, Scranton, Pennsylvania,  December 1968.

8-8.     A. W.  Judge, "High Speed Diesel Engines, " Chapman and Hall,
         Ltd., London,  1968.

8-9.     Personal Communication, White Motors Corporation, Torrance,
         California, 1 December 1970.

8-10.    "Steam Powered Automobiles May Solve Pollution Problems, "
         Product Engineering, 10 April 1967.

8-11.    C.E. Wise,  "Steam is Back,"  Machine Design, 29 August  1968.

8-12.    P. T. Vickers,  et al,  "General Motors' Steam Powered Passenger
         Cars -  Emissions,  Fuel Economy and Performance, " SAE Paper
         700670, 24 August 1970.

8-13.    P. T. Vickers,  et al,  " The Des ign Features of the  CM SE- 101 -
         A Vapor-Cycle  Powerplant, " SAE Paper  700163, 12  January 1970.

8-14.    "New Revolver  - Like Steam Engine," Popular Science, February 1966.

8-15.    W. L.  Minto, "  Low Entropy Engine, " U.S.  Patent 3, 479, 817,
         25 November 1969.
                                   8-96

-------
8-16.   N. L.  Chironis,  "Organic Fluids  Vie  for Chance to Supply Power
         for Steam Cars," Product Engineering, 12 October 1970.

8-17.    E. F. Lindsley,  "New: Minto's Unique Steamless Steam Car,"
         Popular  Science, October  1970.

8-18.    J. L.  Dooley and A. F. Bell, "Description of a Modern Automotive
         Steam Powerplant, " SAE Paper S338, 22 January 1962.

8-19.    D. T. Morgan and R. J. Raymond,  "Rankine Cycle  Power System
         with Organic Working Fluid and Reciprocating Engine for Passenger
         Vehicles,"  Thermoelectron Corporation, Report No.  TE 4121-133-
         70, June 1970.

8-20.    "Study of Unconventional Thermal, Mechanical and Nuclear Low-
         Pollution -  Potential  Power Sources  for Urban Vehicles,"
         Battelle  Memorial  Institute, 15 March 1968.

8-21.    "Those Bloomin1 Steamers,"  Car Life,  April  1967.

8-22.    J. J.  Marick and W. T.  MacCauley, "Oracle-Technical Assessment
         of an Organic Rankine Power  Conversion System Operated as a
         Breadboard Engine," IECEC  Conference,  1968.

8-23.    R. W. Barret, et al,  "Organic Rankine Power  Unit  Testing,"
         IECEC Conference, 1970.

8-24.    "Advanced Rankine Generator  Could  Keep Auto Engines Clean, "
         Product  Engineering,  6  July 1970.

8-25.    E.  Kaplan and E.  Lodwig,  "An Organic Rankine Cycle Power
         System for  Waste Heat Reclamation in the Tipi Total Environment
         Facility," Proc. 23rd Annual Power Sources Conference,  May
         1969.

8-26.    V.  Millman, "Advanced Technology Applied to the Steam Powered
         Vehicle," SAE Paper 931A, 1964.

8-27.    J. A.  Hagel  and  W. W. Velie,  "Self Contained Organic Rankine
         Silent Engine,"  Proc. 23rd Annual Power Sources Conference,
         May 1969.

8-28.    E. B. Zwick,  "The 'Smog Free1 Engine of Tomorrow - Today,"
         IECEC Conference, September 1970.

8-29.    "Advanced Stirling Engines for Space Vehicle  Power, " Allison
         Division of  General Motors Corporation, Engineering Department
         Report No.  2929,  30  July 1962.
                                  8-97

-------
8-30.    D. E. Cole and C, Jones, "Reductions of Emissions from the
         Curtiss-Wright Rotating Combustion Engine with an Exhaust
         Reactor, " SAE  Paper No.  700074, January 1970.

8-31.    Product Engineering, p. 80-81,  13 April 1970.

8-32.    "Rotary Engines," Scientific American, February 1969.

8-33.    Product Engineering, 7 April 1969.

8-34.    Product Engineering, 10 March 1969.

8-35.    Bishop and Simko, "A New Concept  of Stratified Charge Combustion
         the Ford Combustion Process (FCP), " SAE Paper No. 680041,
         January 1968.

8-36.    Preliminary Description,  TRAD-4180, McCulloch Diesel Aircraft
         Engines,  McCulloch  Corporation, Los Angeles, California.

8-37.    Machine Design, 7 January 1971.
                                 8-98

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            SECTION 9






HEAT ENGINE EXHAUST EMISSIONS

-------
                               CONTENTS
9.     HEAT ENGINE EXHAUST EMISSIONS	    9-1
      9. 1  General	    9-1
           9. 1. 1   Introduction	    9-1
           9. 1.2   Exhaust Emission  Data  Format	    9-2
           9.1.3   Cold Start Emissions	    9-3
      9.2  Spark Ignition  Engine Emissions	    9-4
           9. 2. 1   Design Load Emissions	    9-4
                    9.2.1.1   State-of-the-Art Technology	    9-4
                    9.2.1.2   Projected Technology	    9.-4
           9.2.2   Part-Load Emissions	    9-6
           9.2.3   Cold Start Emissions	    9-8
           9.2.4   Other  Pollutants	    9-9
      9. 3  Diesel Engine  Emissions	    9-9
           9. 3. 1   Design Load Emissions	    9-9
                    9.3.1.1   State-of-the-Art Technology	    9-9
                    9.3.1.2   Projected Technology	    9-11
           9.3.2   Part-Load Emissions	    9-12
           9.3.3   Cold Start Emissions	    9-14
           9.3.4   Other  Pollutants	    9-14
      9. 4  Gas Turbine Emissions	    9-15
           9.4. 1   Design Load Emissions	    9-15
                    9.4.1.1  State-of-the-Art Technology	    9-15
                    9.4.1.2   Projected Technology	    9-15
           9.4.2   Part-Load Emissions	    9-17
           9.4.3   Cold Start Emissions	    9-19
           9.4.4   Other  Pollutants	    9-19
                                    9-i

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                   CONTENTS (Continued)
9. 5   Rankine Engine Emissions	     9-20
      9. 5. 1   Design  Load Emissions	     9-20
              9.5.1.1  State-of-the-Art Technology.  . . .     9-20
              9.5.1.2  Projected Technology	     9-20
      9.5.2   Part-Load Emiss ions	     9-22
      9.5.3   Cold Start Emissions	     9-22
      9.5.4   Other Pollutants  	     9-22
9.6   Stirling Engine Emissions	     9-24
      9.6. 1   Design  Load Emissions	     9-24
              9.6.1.1  State-of-the-Art Technology.  . . .     9-24
              9.6.1.2  Projected Technology	     9-24
      9.6.2   Part-Load Emissions	     9-26
      9.6.3   Cold Start Emissions	     9-26
      9.6.4   Other Pollutants  	     9-26
9. 7   Summary	     9-26
                             9-ii

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                                FIGURES
9-1.   Spark Ignition Engine (Gasoline) Emissions, Steady State
       Design Load:  (a) Hydrocarbon, (b) Carbon Monoxide,
       (c) Nitric Oxide	    9-5

9-2.   Spark Ignition Engines - HC,  CO, NO,  Emissions,
       Steady State Part-Load,  Air/Fuel = 15-16   	    9-7

9-3.   Four Cycle Diesel Engine Emissions, Steady State
       Design Load:  (a) Hydrocarbon, (b) Carbon Monoxide,
       (c) Nitric Oxide	    9-10

9-4.   Four Cycle Diesel Engine Emissions, Steady State
       Part-Load,  Constant Speed:   (a) Hydrocarbon, (b) Carbon
       Monoxide, (c) Nitric Oxide	    9-13

9-5.   Gas Turbine Emissions, Steady State Design Load:
       (a) Hydrocarbon, (b) Carbon Monoxide,  (c) Nitric Oxide  .  .    9-16

9-6.   Gas Turbines  - HC,  CO, NO, Emissions, Steady
       State Part-Load	    9-18

9-7.   Rankine Engine Emissions, Steady State Design  Load:
       (a) Hydrocarbon, (b) Carbon Monoxide,  (c) Nitric Oxide. .  .    9-21

9-8.   Rankine Engines - HC,  CO, NO,  Emissions, Steady
       State Part-Load	    9-23

9-9.   Stirling Engine Emissions,  Steady State Design Load:
       (a) Hydrocarbon, (b) Carbon Monoxide,  (c) Nitric Oxide. .  .    9-25

9-10.  Stirling Engines - HC, CO, NO,  Emissions,  Steady
       State Part-Load	    9-27

9-H.  Heat Engine Exhaust Emissions,  Large Engines  (>  50 hp)
       Steady State Design Load:  (a) Hydrocarbon,  (b)  Carbon
       Monoxide, (c) Nitric Oxide	    9-28
                                    9-iii

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                               SECTION 9
                  HEAT ENGINE EXHAUST EMISSIONS
9. 1       GENERAL
9. 1. 1     Introduction
Five heat engine concepts were investigated for the hybrid heat engine/
electric vehicle systems considered in this study.   They are the  following:
          Spark Ignition Engine (Otto Cycle)
          Compression  Ignition Engine  (Diesel Cycle)
          Gas Turbine Engine (Brayton Cycle)
          Rankine  Engine ("Steam")
          Stirling Engine
This section discusses the heat engine exhaust emission characteristics
utilized in the calculation  of vehicle exhaust emissions.  These characteris-
tics were derived as a result of evaluating all available information in the
open Literature as well as much unpublished data obtained from various
engine mjinufacturers.   Discussion of the data and the various  options of
engine operation are contained in Appendix B.  This section is  devoted
primarily to describing  the engine exhaust emission characteristics that
were selected as representative of state-of-the-art technology and projected
technology,  and were used in the  vehicle emission calculations.
The major pollutants emitted from heat engines are hydrocarbons (HC),
carbon monoxide (CO), oxides of  nitrogen  (NO ),  oxides of sulfur,  aldehydes,
and particulates.  This study was limited to the HC, CO,  and NO emis-
                                                                X
sions since  these are the pollutants of primary concern with respect to
vehicle emission standards.  Because of the lack of quantitative  information,
other pollutants will be discussed qualitatively in connection with the emis-
sions of each type of engine.
                                   9-1

-------
Engine exhaust specific mass emissions for NO  are reported on a nitric
oxide (NO) basis.  Nitric Oxide was used as a matter of convenience since
the NO   in the engine exhaust gases is predominantly NO (on the order of
95 percent or more).  However, since Federal regulatory requirements
will stipulate the vehicle NO  emissions to be reported as NO,,  the vehicle
                           X                                Ł
emission data presented in this study have been calculated on the basis of
NO?-  The factor for converting NO mass emission to NO-,  is 1.  533, which
is  the ratio of the molecular weights.
9.1.2     Exhaust Emission Data Format
Inasmuch as the vehicle exhaust emissions are to be expressed on a mass
basis in  terms of grams per mile, it  was found most convenient, especially
for the hybrid mode of  heat engine operation,  to express  emissions in terms
of specific mass  emissions having the units of grams per bhp-hr.  Mass
emission correlations were established for the five heat engines and curves
were generated describing the exhaust emission characteristics  of heat
engines, at both design load (or full load) and part-load conditions. Thus,
for each pollutant there will be two basic curves:
      1.     Design load specific mass emissions (grams /bhp-hr) as a func-
            tion of engine design horsepower
      2.     Part-load emission factors (ratio of part-load specific mass
            emission to design  load specific mass emission at rated speed)
            as a function of percent design load
The variation of the emissions  with part-load conditions can be very
critical  in determining the exhaust emission characteristics of a hybrid
vehicle.   In conducting the data correlation,  it was discovered that a severe
shortage of steady-state mass emission data, particularly at part load,
existed in the open literature.  Considerable information is available on
concentrations of pollutants,  but usually without the information  necessary
for conversion to mass numbers.  Although the curves presented here  have
been established from  the best  data available  today, considerable  effort is
warranted to develop a more comprehensive and  reliable data base for emis-
sions.   In particular,  part-load emission data are inadquate for  several  types
of engines.

                                   9-2

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9.1.3     Cold  Start Emissions
For light-duty vehicles  (under 6000-lb gross weight), the Federal test
procedures  specify that the vehicle be kept at ambient temperature for
12 hr prior  to the test.  The  HC and CO emissions are generally higher
when  the engine is cold; thus, it is necessary to account for the emissions
during this  cold start period, which can be considerable, depending on
engine operating conditions.  In an engine equipped with  a catalytic converter,
there is an  additional degradation  of emission during the engine and catalyst
warmup period.
The engine  exhaust emission characteristics presented  in this section are
based on steady-state,  hot engine  data and the vehicle emission levels
computed for the various options and configurations  presented in this  study
are therefore hot t^lart emission levels.  The effects of engine cold starts
on emissions are not included in the recommended correlations at this time
because of the following factors:
      1.     Cold start data arc; not available for all the heat engines.
      2.     Inclusion of cold  start effects  are required at present only for
            the  Lightweight vehicles tested over the DHEW cycle  (passenger
            car  and  commuter car).
To incorporate  cold start effects,  a cold start emission  factor (ratio of
cold start cycle emission to hot start cycle emission) can be applied to the
vehicle emission levels computed  from the hot engine data. Some cold
start  emission characteristics  are available for conventionally powered
automobiles.  Additional data were generated during  the  period of this study
that pertain to spark ignition engine cold starts in the hybrid mode of  opera-
tion as well as in diesel engines.  These cold start factors are summarized
in Section 9. 2. 3.
For low-pollution engines, the  effect of  cold start can be very critical,  since
the emissions generated in the  first minutes of  warmup can overshadow the
emissions generated during the rest of the driving cycle  when  the engine is
hot.   Much work remains  to be done in this area on evaluation of data and
investigation of  techniques to minimize cold start effects.

                                    9-3

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9.2       SPARK IGNITION ENGINE EMISSIONS
9. 2. 1     Design Load Emissions
9.2.1.1   State-of-the-Art Technology
The design load specific mass emissions are presented in Figure
9-1.  Selected air/fuel ratios are presented in this curve to represent
regimes of operation with spark ignition engines.   Other  cases were covered
and are described in Appendix B.  The data for operation at air/fuel ratios
between  15-16 were based on evaluation of characteristics from  two basic
engines and were used to represent emission levels from current engines
operating at theit particular air/fuel  ratio.   Since Jean operation  (high air/
fuel ratio) appears to be attractive from the standpoint of minimizing CO
and NO emissions, an air/fuel  ratio of approximately 19 was selected to
represent the present state-of-the-art technology.   It would be difficult,  of
course,  to operate such an engine in a normal automotive vehicle; however,
the "driveability" problems normally associated with lean engine operation
should be minimized in the hybrid because the engine can be designed for
essentially steady-state operation over  a restricted range of operating
conditions.  The assumed increase in HC specific mass  emissions at an air/
fuel ratio of 19 compared to an air/fuel ratio of 15  to 16 is due to the combined
effects of power  loss and increasing quench effects.  The specific  mass
emissions are assumed to be constant for engine design power levels above
approximately 50 hp.   Below that point, the emissions were assumed to
increase, reflecting  the trend of decreasing engine efficiency with decreasing
s ize.
9.2. 1.2   Projected  Technology
Many approaches are possible toward decreasing engine emissions.  These
are discussed in Appendix B  and include variation of spark timing,  chamber
design, mixture  preparation, manifold pressure, exhaust gas recirculation,
water injection,  and  catalytic converters.   For the projected technology
spark ignition engine, an ultra-lean  air/fuel ratio of approximately 22 was
                                   9-4

-------
                       1—r
                      	1	1—r-]	1	r

                       PROJECTED TECHNOLOGY
                      ___    ULTRA LEAN   A/F=22



                                       A/F = I9

                      _               A/F--I5-I6
                                   PROJECTED TECHNOLOGY

                                   A/F = 22, CATALYST, RECIRCULATION
 E
 o
(a)
    m1
    10
 E
 o
o"   I
    10
o.
-Ł=

,O
E
o
    I    I   I
                          I   I   I
                                               i    i  i
               (b)
               (c)
                                             A/F =  15-16
                                        PROJECTED TECHNOLOGY
                                             ULTRA LEAN

                                             A/F = 22
                                             A/F =  19
                                  ~-^.___   PROJECTED TECHNOLOGY

                                   A/F--22, CATALYST, RECIRCULATION
                                   i      i    i  i  I       i	i	i   i
                          1  I
                                                              i    i   i
                                             A/F = 15-16
                               • —	A/F = 19
                        PROJECTED TECHNOLOGY
                             ULTRA LEAN

                              A/F = 22
                                       PROJECTED  TECHNOLOGY
                                 ,___	A/F = 22, RECIRCULATION
                   i    i   i
                           10                     I02
                           DESIGN BRAKE HORSEPOWER
    Figure 9-1.
  Spark Ignition Engine  (Gasoline) Emissions, Steady

  State Design  Load: (a) Hydrocarbon,  (b) Carbon

  Monoxide,  (c) Nitric Oxide


                    9-5

-------
selected to indicate the potential offered by the spark ignition engine.   The
data base for  such an operating point are the single-cylinder data obtained
informally from the Bureau of Mines and the dual-chamber engine work of
Newhall at the University of Wisconsin.  Other lean-engine approaches which
could potentially achieve the same results  are the stratified charge com-
bustion chamber,  and utilization of improved carburetor/intake manifold
configurations, and pre-heated or pre-mixed air/fuel charges.  Further
studies are required to determine the optimum lean air/fuel ratio by con-
sidering emissions as well as  engine performance aspects. The lower
projected technology curve is based on an air/fuel ratio of 22 and utilization ofa
catalytic converter for  HC  and CO reduction, and exhaust gas recirculation
for further NO control.  A  catalyst conversion efficiency of 70 percent and an
exhaust gas recirculation effectiveness  of 50 percent were used to construct
the projected  technology curve.
9.2.2     Part-Load Emissions
The part-load emission characteristics of  spark ignition  engines operating
at air/fuel ratios  of 15-16 are presented in Fig.  9-2 in terms of the ratio of
specific mass emissions at part-load to  specific mass emissions at design
load versus percent design load.  These curves  were derived for constant
engine speed from the very limited data  sample  provided by Toyota Motor
Company and another manufacturer.     The two engines showed somewhat
different part-load emission characteristics, and the curves presented in
Fig. 9-2 are the average from the two engines.  Part-load emission data for
CX) and NO recently received from General Motors and TRW Systems indi-
<-.;itrj similar trends.
R  is realized that  engine exhaust  emissions are  also a function of engine
speed.  As a result,  lower part-load emission factors might be obtained by
varying speed as load is varied.  The optimum speed versus load schedule
must be determined for each hybrid system application by considering heat
engine emissions  as well as the performance characteristics of other
components such as the generator,  motor,  controls, etc.  Presently, there
                                   9-6

-------
   2.5
CO
•2L
O

CO
CO
O

-------
is  a serious lack of applicable engine data,  and thus speed could not be used
as an emission correlation parameter.  More work is required in this
area before these questions can be adequately answered.
For the purpose of this study, HC,  CO, and NO specific emissions  were
assumed to be constant for all load conditions for the lean air/fuel ratios
of 19  and 22.  This  choice was made primarily because of the lack of
applicable  test data. Also,  it appears that  change in spark timing and
engine design modifications,  together with the addition of catalytic con-
verters and exhaust gas recirculation, can  result in considerably different
part-load emission  characteristics,  and these changes cannot be anticipated
at this time.   It is most important that additional work be conducted to
acquire data  to resolve these questions.
9. 2. 3
Cold Start Emissions
Some cold start emission data for conventionally powered automobiles are
available,  and during the course of this study,  additional data were made
available  by  TRW Systems which are applicable to state-of-the-art lean
engines operating in the hybrid mode.  Cold start vehicle emission data
•were also obtained from General Motors.  These are discussed in Appendix B.
Based on  these data, the following numbers were selected to be indicative
of the cold start correction factors to be used for the spark ignition engines
considered in this study.

Pollutant
HC
CO
NO
Cold Start Correction Factor
State-of-the-Art
Technology
1. 30
1. 30
0. 95
Projected Technology
1. 20
1. 20
0. 95
The above factors apply only to the vehicle emissions computed over the
DHEW driving cycle.
                                    9-8

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9.2.4     Other Pollutants
No quantitative data on other pollutants are available for spark ignition
engines.  Sulfur and lead oxides can be controlled by limiting the sulfur
and lead content in the fuel.   Smoke is generally not a problem in spark
ignition engines except in poorly maintained engines.
9. 3       DIESEL ENGINE EMISSIONS
9. 3. 1     Design  Load Emissions
9.3.1.1   State-of-the-Art Technology
The design load specific mass emissions are presented in Figure 9-3.
State-of-the-art technology emission characteristics are shown
for three types of four-cycle diesel engines:  (1) naturally aspirated, direct
injection, (2) turbocharged,  direct injection,  and (3) turbocharged pre-
chamber.  These  curves were based on emission test data obtained  from the
literature as well as directly from the manufacturer.  Insufficient data
were available to  classify the two-cycle  diesels.  As shown,  constant speci-
fic  mass emissions were assumed for each engine type for design power
levels above 50 HP.  Below  that point, the emissions are assumed to
increase, primarily to reflect the lower engine efficiency and the higher
wall quenching effects, resulting from less favorable cylinder  surface area-
Lo-volume ratios.  The NO increases at  a lower rate than HC and CO.
As  indicated in Fig. 9-3a,  the HC specific mass emissions of the four-cycle
turbocharged,  direct injection engine are the highest of the three engine
types, although theoretically the  HC emissions of turbocharged diesels
should be lower than those of naturally aspirated engines.  Additional emis-
sion data are needed for turbocharged,  direct injection diesels to clarify
this issue.  The four-cycle turbocharged, prechamber diesel indicates the
Lowest HC emission level.
The design load emission  characteristics of the  turbocharged,  direct injec-
tion and  prechamber diesels were derived from a very limited data  sample,
and as a result the effects of manufacturing tolerances may not be adequately
accounted for.   This should  be considered when  using these curves.

                                    9-9

-------
                            X    ---	  STATE OF THE ART TECHNOLOGY
                               "^ ^         TURBOCHARGED, DIRECT INJECT.
                                             STATE OF THE ART TECHNOLOGY"
                                             NAT. ASPIRATED, DIRECT INJECT.
   ID'1
                                             STATE OF THE ART TECHNOLOGY
                                       	   TURBOCHARGED. PRECHAMBEft
              (a)                            PROJECTED TECHNOLOGY
                            \                TURBOCHARGED, PRECHAMBER
                              ^ ^           W/CAT 8 EGR
I         I      I    I   I
  \
                                         STATE OF THE ART  TECHNOLOGY
                                         NAT. ASPIRATED, DIRECT INJECTION
                                         STATE OF THE ART TECHNOLOGY
                                         TURBOCHARGED, DIRECT INJECTION
                                          STATE OF THE ART TECHNOLOGY
                              ^   _ ^    TURBOCHARGED,  PRECHAMBER
              (b)
                                          PROJECTED TECHNOLOGY
                            \             TURBOCHARGED, PRECHAMBER
                              ^ -^       W/CAT 8 EGR
            r      i    i   \  |      i       i    i   i        i       i    r
    101	                                   STATE OF THE ART TECHNOLOGY
                            ^--	TURBQCHARGED, DIRECT INJECTION
                            ---.>	STATE OF THE ART TECHNOLOGY
                                           NAT. ASP, DIRECT INJECTION
|                                           STATE OF THE ART TECHNOLOGY
CT    i_                                     TURBOCHARGED, PRECHAMBER

              (C)
                                             PROJECTED TECHNOLDGY
                            """-—	TURBO PRECHAMBER 8 F.GR
            I	I    III	|	I    III      i       i	I   I
                                                                        J
     I                      10                     I0                     IO
                          DESIGN BRAKE HORSEPOWER


Figure 9-3.  Four   Cycle  Diesel Engine Emissions, Steady
                State  Design  Load: (a) Hydrocarbon, (b) Carbon
                Monoxide,  (c ) Nitric Oxide

                                 9-10

-------
The CO specific mass emission data from various  engines  used to construe).
the curves of Fig. 9-3b showed considerably smaller variation than that
shown by the HC data.  This trend was expected, since CO concentration is
determined primarily by  air/fuel ratio and the design point air/fuel  ratios
of the diesels are  quite comparable.  In accordance with expectations,  the
highest  CO emissions are obtained with the naturally  aspirated, direct
injection diesels and the lowest emissions with the turbocharged prechamber
engines.
Nitric oxide represents the major emission problem in diesel engines.   As
indicated  in Fig. 9-3c, the turbocharged, direct injection diesel has  (.he
highest  NO emissions, and these  values are comparable  to the NO emitted
from present spark ignition engines.  The naturally aspirated, direct injec-
tion diesels show  somewhat lower NO emissions.   The NO emissions of
turbocharged prechamber engines are even lower.   As will be  shown in
Section  11, the NO emission levels of present diesels have to be reduced
significantly before future emission goals  can be met.
Because of its low specific mass  emissions,  the turbocharged,  prechamber
diesel curves were used to represent state-of-the-art technology diesel
engines  for the vehicle emission comparisons.  Notice,  however,  that  the
specific fuel consumption of prechamber diesel engines  is  slightly higher
than that of direct injection engines (see Section 8).
9.3. 1. Z    Projected  Technology
The projected technology design load emission curves shown in Figure
9-3 are  based on improvements to the turbocharged, prechamber diesel
engine.  An arbitrary reduction by a factor of 4 was applied to the state-of-
the-art  technology emission levels for all  pollutants (HC, CO,  and NO).
The improvements in HC and CO  reduction are considered reasonable goals,
achievable with modified  injection systems, combustion chambers,  injection
timing,  and catalytic converters.  The effects of catalytic  converters on
diesel engine emissions have been investigated by Springer at Southwest
Research  Institute and more recently by Aerospace (Appendix C) and some
                                   9-11

-------
reduction  in HC and CO emission was achieved.  In addition to reducing
HC and CO, the odor level of the diesel exhaust was reduced.  Further tests
are needed to evaluate the catalyst performance as affected by operating
time.
The projected NO emissions shown in Fig. 9-3c reflect the effects of exhaust
gas recirculation, as well as chamber and injection system modifications,
and possibly a  catalyst.   Since no data are available on diesel engine exhaust
recirculation and its effect on NO emission,  the selected reduction factor
of 4 is approximate  at best.   Research work should be conducted, particu-
larly  in exhaust recirculation, to provide the parametric data required for a
complete assessment of this concept, including the effects on engine per-
formance and "driveability. " At present,  the prospects for NO catalysts are
not bright, but such a device might become feasible in the future.
9. 3. 2     Part-Load Emissions
The part-load emission  characteristics for the three types of diesel  engines
operating at rated speed are shown in Figure 9-4  in terms of the
ratio  of part-load specific mass emissions to the full load emissions at
rated speed versus percent full load.  The HC  emissions increase with
decreasing load for  all engines.   For the direct injection engines, the CO
emissions decrease initially as a result  of increasing air/fuel ratio, and
then increase again  as load is further reduced.  This increase is  the result
of lower engine efficiency and some increase of CO concentration.  The CO
emissions of  the turbocharged prechamber  engine increase steadily with
decreasing load.
The part-load NO emission characteristics showed rather distinct and dif-
fering trends for the three types  of engines.  The  naturally aspirated, direct
injection engine has a flat characteristic, whereas the turbocharged  pre-
chamber engine showed  an increase and  the turbocharged, direct  injection
engine a decrease in emissions with decreasing load.
                                   9-12

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The part-load curves shown here are based on constant speed operation
and were used for the state-of-the-art vehicle emission calculations.   For
the projected technology, because of the lack of data on catalytic devices
and exhaust gas recirculation effects with load,  a flat  (invariant with load)
characteristic was assumed for all pollutants.
A second set of part-load curves  based on varying engine speed with load
was constructed and is presented in Appendix B.  In general, it is  more
desirable from  an emission and SFC point of view to vary engine speed with
load.   However, in a hybrid vehicle, the operating characteristics (primarily
efficiency) of the other system components must be considered  in selecting
the optimum engine speed schedule.
Owing to the lack of data,  no attempt was made  to establish part-load
emission factors for  two-cycle engines.
9. 3. 3     Cold  Start  Emissions
The only cold start emission data available  for diesel  engines are  from the
tests  conducted  by  The Aerospace Corporation as a part of this  study.  The
details of this program are contained in Appendix C of this report.  Multiple
bag vehicular tests indicate that  there  is no change in  CO emissions from
cold to hot start conditions. The HC emissions also appear  to be the same for
both cold and hot conditions, based on  comparison of seven-mode data
calculated from hot FID concentration  data.  The NO emissions, as expected,
showed a decrease under cold  start conditions.
9.3.4     Other Pollutants
The diesel engine can emit other pollutants, primarily odor and  smoke.
Much work has been conducted in the past to study the odor characteristics
of diesels, and it is generally concluded that a relationship exists between
odor and aldehydes.  However, further  study  is required before  this problem
is completely understood.  There are indications that the odor/aldehyde
emissions from prechamber diesels are lower than those from naturally
aspirated engines. Odor from diesel  engines  can be  reduced  by  fuel
                                   9-14

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injection system modification and by using a catalytic converter in the
exhaust.  This is discussed in Appendices B and C.
Smoke is largely dependent upon engine air/fuel ratio and load,  but is also
affected by combustion chamber and injection system design,  type  of fuel
used, and engine maintenance.  Formation of smoke has been reduced by
using barium additives in the fuel.
9. 4       GAS TURBINE EMISSIONS
9.4.1     Design Load Emissions
9.4.1.1  State-of-the-Art Technology
The  design load specific mass emissions are presented in Figure  9-5.
While these  characteristics were based  on evaluation of eight
different engines, the curves representing the state-of-the-art technology
were drawn through the data points from the General  Motors GT-309 gas
turbine. The HC and CO curves were derived from the basic GT-309 with
the so-called standard burner,  and the NO curve more nearly matches  that
indicated by  the GT-309 with the modified  burner designed for minimum NO.
The  design load emission correlations are flat for  engine  design loads above-
50 ill'.  Be-low that point,  the specific mass  emissions are assumed to
increase as a result  of lower turbomachinery efficiencies.  In addition,  wall
quench  effects may become increasingly important, resulting in higher
HC and  CO concentrations.  The HC and CO specific mass emissions are
assumed to  increase similarly, while NO increases less.
9.4.1.2  Projected  Technology
The  projected technology emissions are  also presented in Figure 9-5.
Examination of current specific mass emission data indicates that
nitric oxide poses the most serious emission problem in gas turbines,  and
significant improvements must be  made  before  the future  emission goals
can be met.
                                    9-15

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                                              PROJECTED TECHNOLOGY
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                                                 PROJECTED TECHNOLOGY
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         Figure 9-5.   Gas Turbine Emissions, Steady State Design
                      Load: (a) Hydrocarbon, (b) Carbon Monoxide,
                      (c) Nitric Oxide

                                  9-16
                                                      I    I   I
                                                                      I03

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Since the formation of NO is kinetically controlled and is rather slow by
comparison to other chemical reactions in the burner,  it can be controlled
by quenching the NO formation reactions immediately downstream of the
primary zone of the burner.  The addition of secondary  air further upstream
of the burner can accomplish this by reducing the residence time of the
combustion gases in the primary zones.  Experimental work indicates that
the nitric oxide  emissions are affected by primary zone air/fuel ratio.
Reduction in NO by a factor of approximately 2 has been demonstrated
experimentally without adversely affecting engine and burner operation and
the emissions of hydrocarbon and carbon monoxide.  Further improvements
are believed to be possible through additional work on the burner, including
optimization of primary and secondary zones, inlet air  temperature, mix-
ture and mass flow distribution, and addition of exhaust gas recirculation.
Also, the feasibility of an exhaust  gas reactor should be investigated,
especially  if significantly higher HC and CO emissions  would be obtained
as a result of the modifications required for  control  of nitric oxide emis-
s ions.
Based on these considerations, a reduction of the NO emissions by a factor
of 5, compared  to the present state-of-the-art values,  appears to be feasible.
The projected HC and CO emissions are reduced by a factor of Z.
9.4. Z     Part- Load .Em is s ions
The recommended part-load  emission characteristics are presented  in
Fig. 9-6.   Since the  General Motors GT-309 gas turbine was designed for
automotive use with exhaust emissions a design consideration,  its part-load
emission data were used as the basis for the part-load  curves of Fig.  9-6.
The HC and CO  specific mass emissions of all engines  increased with
decreasing load.  This is largely due to a reduction of turbomachinery and
cycle efficiencies with decreasing  load.
Single spool  gas turbines show an increase in NO specific mass emissions
with decreasing load,  which is a direct  result of lower  thermodynamic cycle
efficiency at part load.  However,  as shown in Fig.  9-6,  the part-load NO
                                   9-17

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CO
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emissions  of the General Motors automotive gas turbine  increase initially
with decreasing load as a result of increasing burner air inlet temperature.
As the degree of power transfer is reduced, both burner and turbine  inlet
temperature decrease rapidly,  resulting in lower specific mass emissions
of NO.  At very low part loads,  the NO emissions increase again as a result
of rapidly decreasing turbomachinery efficiencies.
The  part-load emission characteristics for the  projected technology are
assumed to be  identical to the present state-of-the-art characteristics.   Thus
the curves presented in Fig.  9-6  are considered applicable  to both present
and projected technologies.
9. 4. 3      Cold Start Emissions
Some cold  start dal.a are available for gas  turbine automobiles.   These indi-
cate that the ratios of cold start versus hot start emissions  for HC, CO,  and
NO are J.Z1,  1.17,  and 0.89, respectively.  These ratios are  in reasonable
agreement with those determined for spark ignition engines.  Additional
experimental work is required before the question of cold start versus hot start
emissions  from gas turbines  can be: adequately  answered.
9. 4. 4     Other  Pollutants
As previously mentioned,  this study is only concerned with the emission of
HC,  CO,  and NO.  However, a few comments on the other pollutants emitted
from gas  turbines are in order.   Often smoke can be observed in the exhaust
of gas turbines, primarily at high loads.  This  is the  result of locally fuel-
rich zones in the combustor.  Aldehydes are believed to be related to lean
combustion and to the temperature-time history of the combustion products.
Sulfur dioxide emission  is directly related to the sulfur content in the fuel
and control is achieved by limiting the allowable sulfur content.  Control of
smoke and sulfur dioxide appears  to be well  in hand.  However, additional
work is required to characterize the emissions  of aldehydes  from gas tur-
bines and to develop methods which will  effectively  reduce these products.
                                   9-19

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9. 5       RANKINE ENGINE EMISSIONS
9. 5. 1     Design Load Emissions
9.5.1.1   State-of-the-Art Technology
The design load specific mass emissions are presented in Fig. 9-7.
Data used to characterize the state-of-the-art  curve were based primarily
on information from the General  Motors Research SE-101 and SE-124
steam engines,  the Doble  automobile tested by General  Motors,  and the
Williams Steamer, as well as burner data  from the  Marquardt Corporation,
Thermo  Electron Corporation,  and the  University of California at Berkeley.
There was a very large scatter in the HC data  used  to arrive at the HC curve,
but much better agreement is achieved  in NO primarily, and in CO.
Inadequate HC measuring  techniques and differences in burner specific heat
release rates (residence time) may partially explain the data scatter.  In
view of these uncertainties, it was decided to use the Stirling engine HC
data (which was based on the more reliable hot FID  instrumentation) dis-
cussed in Section 9. 2. 5 as a guideline to establish the design load emission
characteristics  of Rankine engines.  This  can be done because of the  simi-
larity  in burners for  these two engine types.   The specific mass emission
data are based upon the assumption of a constant engine efficiency of  15
percent.  Changes in this  parameter affect the calculated emissions.
The design load emission  correlations are flat for engine design loads
above  50 hp.  Below that point, the specific mass emissions are assumed to
increase because of lower engine efficiency.
9.5.1.2   Projected Technology
The projected technology emissions  are also presented  in Fig. 9-7.
The most critical emission  specie of the Rankine  cycle  is NO.  Reduc-
tion of NO is believed to be  possible by  means  of optimizing the primary
and secondary zones  of the burner.  In  addition,  exhaust gas recirculation
may be feasible.  This technique  has been  used successfully on the Philips
Stirling engine.   Based on these considerations,  the projected NO emission
                                   9-20

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      Figure 9-7.  Rankine Engine Emissions,  Steady State Design
                   Load: (a)  Hydrocarbon,  (b) Carbon Monoxide,
                   (c) Nitric Oxide

                                  9-21

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is estimated to be 40 percent of the present state-of-the-art technology
value.  The projected reduction in HC and CO is somewhat lower,  reflecting
the general tendency of obtaining higher HC and CO concentrations with the
burner design modifications required for  NO control.
9. 5. 2     Part-Load Emissions
There is little agreement in the part-load emission characteristics of the
engines and burners tested.  Some data indicated a reduction in the concen-
tration of CO and HC with decreasing load,  and other data showed  little
change over  a wide range of part-load conditions.  For NO, there  is
reasonable agreement and very little change in NO concentration with load
is observed.
Considering  the lack of a  sufficiently large data sample and the contradictory
trends observed  in the data,  it was  decided to use engine efficiency as a
measure of the part-load  emissions  for both present and  projected technolo-
gies.  The part-load factors presented in Fig.  9-8  reflect the variation of
efficiency with load.   Obviously,  this is a crude  assumption and points out
the need of reliable  Rankine engine  part-load emission data.
9. 5. 3     Cold Start Emissions
The only cold start emission information  available is the data  published by
Go:neral  Motors for  the G. M. SE-101, SE-124,  and Doble steam cars.
These are discussed in Appendix B.   The warmup emissions have  only a
small effect  on the total emissions of the  SE-101 automobile, resulting
from the fact that only a 2. 8-min warmup period was required to achieve
adequate steam pressure.  In the SE-124  and the Doble,  the warmup emis-
sions represent a significant portion of the total  emissions, primarily
because a much longer warmup time was  required.
9.5.4     Other  Pollutants
In addition to measuring the emissions of HC, CO, and NO, General Motors
has made attempts to determine the  odor  and smoke characteristics  of their
engine.  No offensive odor was detected so long as air/fuel ratio was below
40:1.  Smoke was never observed at air/fuel ratios of 25:1 or higher.

                                   9-22

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CO
                           40        60
                    PERCENT OF DESIGN LOAD
        Figure 9-8.   Rankine Engines  - HC, CO,  NO,  Emissions,
                     Steady State Part-Load
                                9-23

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9. 6       STIRLING ENGINE EMISSIONS
9. 6. 1     Design Load Emissions
9.6.1.1  State-of-the-Art Technology
Characteristics of the exhaust emissions of Stirling engines are based upon
emission data from two engines  built and tested by General Motors Research
Laboratories and by Philips Research Laboratories of the Netherlands.
The  design load specific mass emission characteristics are shown in Fig.
9-9-  The upper  curves in these figures are considered a reasonable
representation of the state-of-the-art technology.  As in the other heat
engines the  specific mass emissions  are considered constant for design
power  levels above  50 hp.  Below that point the specific mass emissions
are assumed to increase to reflect  the deterioration of engine efficiency.
It should  be pointed out that in arriving at the state-of-the-art curve,
several HC  and CO  data points actually fell below the  selected curve.  How-
ever, the corresponding NO emissions for these points were  excessive.
This points  out the importance of selecting the proper combination of engine
operating parameters to minimize all emissions.   Since HC and CO are
inherently low,  attention must be primarily focused on NO.  The curves
reflect  this  approach.
9.6. 1.2  Projected Technology
Nitric  oxide  is the principal emission problem in Stirling engines.  A number
of approaches were  considered to reduce the emissions, including burner
modifications,  exhaust gas recirculation, lower burner air inlet temperature
and reduction of residence time  of the gases  in the primary zone of the
burner.
With these considerations in mind the projected technology-specific mass
emission curves were drawn in  Figure 9-9.  The projected NO emissions
are lower than the corresponding present state-of-the-art values by
a factor of three.   Since the  various approaches aimed at reducing NO
have a tendency to increase  the other emission species,  it is assumed
that  the projected HC and CO emissions are reduced by only a factor of 1. 5

                                   9-24

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        Figure  9-9.  Stirling Engine Emissions, Steady State Design
                    Load: (a) Hydrocarbon, (b) Carbon Monoxide,
                    (c) Nitric Oxide

                                  9-25
                                                                       10'

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9. 6. 2     Part-Load Emissions
Lacking sufficient test data, a meaningful part-load emission study could
not be conducted for the Stirling engine.   To account for at least some of
the part-load effects it was decided to use the cycle efficiency versus per-
cent of design load correlation as the basis for estimating the emissions at
part load.   The same  approach was used to characterize the part-load
emissions of Rankine  engines.  The  recommended part-load emissions are
presented in Fig. 9-10 in terms of the ratio of part-load emission to design
load emission versus percent of design load.  These factors are applicable
to HC,  CO and NO,  for both present state-of-the-art and projected tech-
nologies.  This approach  is  approximate, at best, and points out the need of
a comprehensive Stirling  engine emission test program.
9. 6. 3     Cold Start Emissions
There is no  information available to characterize cold start emissions of
Stirling engines.  Obviously these factors have to be resolved before a
complete assessment  can be made of the emissions  from a Stirling engine.
9.6.4     Other  Pollutants
Little  information is available on smoke and odor of the Stirling engine
exhaust.  The General Motors engine was reported to be smoke free at all
operating conditions,  including cold  start.  Also no  odor was detected.
The Philips  engine shows some smoke during warmup.  However,  it appears
that this problem might be alleviated by means of burner modification
and/or variation of the air/fuel ratio during warmup.
9. 7       SUMMARY
The design  load specific  mass emissions  for each of the five heat engines
are summarized in bar-chart format in Fig. 9-11 for  engines greater than
50 hp.   These charts allow a relative comparison of the  specific mass
emissions for each engine category for both state-of-the-art and projected
technologies.  It is emphasized that the values indicated do not give a direct
                                   9-26

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TURBINE  CYCLE    CYCLE
        ENGINE    ENGINE
Figure 9-11.  Heat Engine Exhaust Emissions, Large
                Engines  (> 50 hp) Steady State Design
                Load: (a) Hydrocarbon,  (b) Carbon
                Monoxide,  (c) Nitric Oxide

                            9-28

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correlation to vehicle emissions since the latter will be based on the
part-load operating point and its attendant emission level.
Figure 9-1 la compares the HC emissions for the five engines.  The spark
ignition engine is  considerably higher than the other four engines,  and even
with a catalyst, the HC level of the projected technology engine  is still a
problem insofar as  spark ignition  engines are concerned.   Figure 9-lib
concerns  the CO emissions for the five engines.  Notice that the level indi-
cated for  the state-of-the-art technology  spark ignition engine corresponds
to operation at an air/fuel ratio of 19:1.  The conventional spark ignition
engines operating in a rich air/fuel ratio regime would more  typically have
       /
CO specific mass emissions of 40 grams /bhp-hr or greater.  Even for  an
air/fuel ratio of 15-16 the CO specific mass emission  level is 5. 5  grams/
bhp-hr.  Figure 9-1 lc compares the NO emissions, and it can be  seen that
for state-of-the-art technology, spark ignition engines, diesel engines,  and
the gas turbine all exhibit relatively high NO  emissions.  With projected
improvements, these  levels can be reduced considerably.  As discussed
in Appendix B, the possibility exists for lower NO emissions  than indicated
for the diesel engines; however, no supporting data were available during
the course of the study.
Again, from the standpoint of the impact of the specific mass  emissions on
hybrid vehicle  emissions, the part-load characteristics for each engine are
critical,  and more data are required to substantiate the projections made.
References for this discussion of heat engine exhaust emissions are provided
in Appendix B, together with a collation of pertinent data.
                                    9-29

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                SECTION 10






CONCEPTUAL DESIGN AND SIZING STUDIES

-------
                              CONTENTS


10.    CONCEPTUAL DESIGN AND SIZING STUDIES	     10-1
      10. 1    Conceptual Designs	     10-1
             10.1.1    Introduction  	     10-1
             10. 1.2    Series Configuration   	     10-3
                       10. 1.2. 1   Basic Subsystems/
                                  Components	     10-3
                                                                    v
                       10.1.2.2   Operational Modes  	     10-3
             10.1.3    Parallel Configuration	     10-11
                       10. 1. 3. 1   Basic Subsystems/
                                  Components	     10-11
                       10.1.3.2   Operational Modes  	     10-J 3
      10.2    Sizing Studies	     10-16
             10. 2. 1    Subsystem Siz ing	     10-16
                       10.2. 1. 1   Series Configuration	     10-17
                       10.2.1.2   Parallel Configuration	     10-20
             10.2.2    Sizing Criteria	     10-20
                       10.2.2.1   Series Configuration	     10-20
                       10.2.2.2   Parallel Configuration   ....     10-22
             10.2.3    Powerplant Weight Analyses	     10-24
                       10.2.3.1   Powerplant Elements	     10-24
                       10. 2. 3. 2   Scaling  Assumptions	     10-27
                       10.2.3.3   Results	     10-29
      10.3    Summary   	     10-43
      10.4    References  	     10-45
                                  10-i

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                                TABLES
10-1.     Baseline Series Configuration Characteristics of
          Selected Electrical Subsystems	      10-18

10-2.     Baseline Parallel Configuration Characteristics of
          Selected Electrical Subsystems	      10-19

10-3.     Baseline Series Configuration Subsystem Sizing
          Criteria	      10-21

10-4.     Baseline Parallel Configuration Subsystem Sizing
          Criteria	      10-23

10-5.     Weight Apportionment in Conventional and Hybrid
          Vehicles	      10-25

10-6.     Weight Scaling/Computational Techniques	      10-28

10-7.     Preliminary Weight and Volume Summary of Power
          Train - Family Car Series  Mode	      10-30

10-8.     Preliminary Weight and Volume Summary of Power
          Train - Commuter Car Series Mode	      10-31

10-9.     Preliminary Weight and Volume Summary of Power
          Train - Low-speed Delivery Van Series Mode	      10-32

10-10.    Preliminary Weight and Volume Summary of Power
          Train - High-speed  Delivery Van  Series Mode	      10-33

10-11.    Preliminary Weight and Volume Summary of Power
          Train - Low-speed Intracity Bus Series Mode	      10-34

10-12.    Preliminary Weight and Volume Summary of Power
          Train - High-speed  Intracity Bus  Series Mode	      10-35

10-13.    Preliminary Weight and Volume Summary of Power
          Train - Family Car Parallel Mode	      10-36

10-14.    Preliminary Weight and Volume Summary of Power
          Train - Commuter Car Parallel Mode	      10-37
                                   10-ii

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                          TABLES (Continued)
10-15.    Preliminary Weight and Volume Summary of Power
          Train -  Low-speed Delivery Van Parallel Mode   ....     10-38

10-16.    Preliminary Weight and Volume Summary of Power
          Train -  High-speed Delivery Van Parallel Mode   ....     10-39

10-17.    Preliminary Weight and Volume Summary of Power
          Train -  Low-speed Intracity Bus Parallel Mode	     10-40

10-18.    Preliminary Weight and Volume Summary of Power
          Train -  High-speed Intracity Bus Parallel Mode	     10-41

10-19.    Summary of Powerplant Weights and Effects	     10-42
                                  10-iii

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                                FIGURES
10-1.    Effect of Heat Engine Power Profile on Required
         Maximum Battery Power	     10-2

10-2.    Selected Baseline Series Configuration	     10-4

10-3.    Various Heat Engine Operational Modes
         Series  Configuration	     10-5

10-4.    Heat Engine Variable Power Output Mode
         "Biased" Throttle Setting Feature	     10-9

10-5.    Heat Engine Variable Power Output Mode
         Step-Mode	     10-10

10-6.    Series  Configuration - Variation of Heat Engine
         Power  with Vehicle Speed	     10-12

10-7.    Selected Baseline Parallel Configuration Concept	     10-14

10-8.    Parallel Configuration - Variation of Heat Engine
         Power  with Vehicle Speed	     10-15
                                  10-iv

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                               SECTION 10
               CONCEPTUAL DESIGN AND SIZING STUDIES
10. 1            CONCEPTUAL DESIGNS
10. 1. 1          Introduction
Heat engine/electric hybrid powerplant concepts  can be grouped into two
broad classes: series  and parallel configurations, as previously defined in
Section 3 and further discussed in Section 6.
In all cases, the difference between power required for vehicle propulsion
and power  supplied by the heat engine must be supplied by the batteries.
Hence,  at the outset, it should be recognized that once the vehicle maximum
power requirements have been established, the battery design goals  can be
markedly influenced by the heat engine power output profile.  This effect is
shown in Fig. 10-1 where vehicle maximum power (for maximum acceleration)
and cruise power requirements are illustrated,  along  with three different
vehicle-velocity  varying power profiles delivered by the heat engine.  Pro-
file #2 is defined as that power output profile which will result in the batteries
being fully recharged at the end of the  driving cycle.
It is clear  that profile #1 imposes far less severe requirements on the battery
(in terms of power demand) than profiles #2 and #3, but it also  requires a
higher level of sustained heat engine power output at lower vehicle speeds, and
is  in excess of that heat engine power level required to maintain the  battery
state-of-charge, thus  resulting in higher heat engine exhaust emissions and
increased fuel consumption.
An  alternative type of power profile to those shown in Fig. 10-1 can be  en-
visioned wherein the heat engine is required to accelerate (change power output)
rapidly,  as in conventional SI engine-powered vehicles.   The heat engine could
have a power output profile similar to  profile #3  for constant velocity operation,
and accelerate to a maximum power level (similar to the level of profile #1)
                                   10-1

-------
during periods of vehicle acceleration, thus reducing battery peak demand
requirements.  However, for purposes of this study,  it was  assumed that
this form of engine performance might not be attainable with low-pollution
engines with possible "driveability" (i.e., smooth power-output profiles
under instantaneous load changes) constraints.
Therefore,  all subsequent discussion is directed toward conceptual approaches
in which heat engines are not subjected to large  instantaneous changes in power
output.   In the following illustrative cases which depict power output varying
with time, vehicle velocity, or step changes, it  is assumed that these power
changes  take place  over finite time intervals commensurate  with the acceler-
ation capability of the engine under load.
o
a.
                MAXIMUM
                POWER SUPPLIED
                BY BATTERIES
                                   MAXIMUM POWER REQUIRED
                                   (MAXIMUM VEHICLE ACCELERATION)
                            HEAT ENGINE POWER PROFILE
                                                               REQUIRED
                                                       CRUISE  SPEED
                                          CRUISE POWER REQUIRED
           Figure  10-1.
    SPEED
Effect of Heat Engine Power Profile on
Required Maximum Battery Power
                                    10-2

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10.1.2          Series Configuration
10. 1. 2. 1        Basic Subsystems /Components
A heat engine/electric hybrid powerplant configured for the series mode, as
defined above,  requires certain basic subsystems /components which can
vary as to type and/or number according to designer's choice.
For example, a single electric drive motor can be utilized with a central
differential drive to the  driving wheels, or multiple drive motors could be
used with a drive motor at each wheel,  negating the need for  the differential
drive.  However, aside  from this configurational  design option,  the  remaining
options  in the series configuration primarily center around selection of the
specific type of subsystem/component to be used,  and the control system to
be used for the preferred mode of operation.
The selected series configuration used  as a baseline in the present study for
all  vehicles is as shown in Fig. 10-2.   A single electric drive motor is used
to  supply power to  the rear wheels through a central differential drive unit.
Where appropriate, the  differential drive unit is envisioned to contain an
overdrive unit to provide a  step change  in electric drive motor rpm  to allow
high-speed cruising at near-maximum drive motor efficiency levels.
The generator is mechanically-driven by the heat engine through a gearbox
(speeder/reducer)  which allows the generator (or  alternator  as the case may
be) and the heat engine to operate at different rpm levels.  The other two
major subsystems  (i.e., battery,  control  system) are then electrically-
connected to the generator and drive motor  as schematically  represented in
Fig. 6-1.
10.1.2.2        Operational Modes
With the foregoing  series configuration  arrangement,  a number of modes of
operation  are conceivable.  Several of the more significant modes are shown
in  Fig.  10-3 and discussed  in the  following paragraphs in terms  of the mode
of  operation of the  heat engine.  The heat  engine mode of operation was
                                    10-3

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                                                 WHEEL   )
   BREEDER/REDUCER
   A.C
GENERATOR
«—>
  POWER
CONDITIONING
 & CONTROL
  SYSTEM
4	*
D.C. ELECTRIC
DRIVE MOTOR
                 BATTERY
                                 DIFFERENTIAL
                                 DRIVE UNIT
 Figure 10-2. Selected Baseline Series Configuration

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                   CONSTANT POWER OUTPUT
               o
               o_
               Q_
               I—

               o
                   I
CONTINUOUS OPERATION
OF HEAT ENGINE
                         TIME-
o
I
U1
                                                  o
                                                  a.
                            Q_
                            t—
               cc.
               o
               Q_
               Q_
               I—
               •^>
               O
                        ON-OFF OPERATION
                        OF HEAT ENGINE
                                   VARIABLE POWER OUTPUT
                                   OUTPUT POWER --
                                      f  (VELOCITY)

                                      VEHICLE VELOCITY
                          TIME
                         Figure 10-3.  Various Heat Engine Operational Modes

                                     Series Configuration

-------
selected as the descriptor  in that heat engine exhaust emission determination,
a principal objective of this study,  is more directly-relatable to this descrip-
tor.
10.1.2.2.1     Constant Speed (rpm) and Power Output
10.1.2.2.1.1   Heat Engine Operated Continuously
In this mode of operation,  a  severe problem arises in relation to sizing the
heat engine.  If the heat engine is  sized only to produce a total energy required
in the time duration of the  emission driving cycle (including inefficiencies of
the powerplant system), then the heat engine may not provide  the proper
continuous high-speed power demand  for highway operation.  This results  in
discharge  of the batteries at high speeds  (if the heat engine size is  too
small).  Conversely,  if the heat engine is sized for the maximum continuous
power  demand for  highway operation,  excessive energy loss to a heat-dump
can occur  (if heat engine size is too large).
This mode of heat  engine operation is of course attractive from the stand-
point of heat engine exhaust emissions per se,  in that it should be possible
to select an operating point (i. e.,  rpm, air/fuel ratio, etc. ) most amenable
to reduced emissions.   However,  its apparent inflexibility with regard to
heat engine sizing  and meeting both design driving  cycle  as well as emission
driving cycle vehicle performance  led to  its  discard as a  viable series mode
of operation for the particular  classes of vehicles under  consideration.
However,  this mode may still be suitable for vehicles with reduced top
speeds and/or revised specification requirements.
10.1.2.2.1.2   On-Off Operation of Heat Engine
As an alternative to continuous operation, it is possible to operate  a  constant
power  output heat engine in an  "on-off" mode.   Here, the heat engine would
be sized to meet the continuous high-speed power demand for  highway opera-
tion, and would operate intermittently during urban driving conditions.  The
heat engine could be turned on  or off in response to (a) a battery voltage and/
or state-of-charge signal,  (b) a power demand from the electric drive motor,
or (c) a combination of both.

                                    10-6

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In this manner, various total energy requirements can be matched by the
"pulse" mode operation of the heat engine, which would allow the engine  to
be off more in low-energy portions of urban driving cycles.
Preliminary calculations, however,  indicated that this mode of operation
resulted in very high energy losses during those time periods when drive
motor demand is low due to battery charge rate limitations, i.e., a good
portion of heat engine power output must be dumped because the battery
simply cannot accept the power at the rate being supplied.  This same
limitation applies to the continuous heat engine operation mode  previously
discussed.
There is one  further  disadvantage of intermittent or on-off operation.  When
operating continuously,  power from the heat engine/generator can go directly
to the drive motor during periods of power demand and bypass the battery
loop entirely.  When  operating in the on-off mode,  it would only be  fortuitous
if drive motor power demand occurred at the same time the engine  was on.
Therefore, more  of the heat engine power output flows through  the battery
circuit in the  "on-off" mode than in the continuous operation mode.   Even if
battery recharge efficiency is high, the on-off mode of operation would be
less efficient  than the continuous mode of operation.   It was concluded that
while on-off operation of the heat engine at constant power output was more
flexible than  continuous operation at  constant power output,  it was not
adequate for  the wide range of vehicle driving requirements under considera-
tion.
10.1.2.2.2      Variable Power Output
10. 1.2.2.2. 1    Heat Engine Operated Continuously
Many of the deficiencies of. the constant-power  output  mode of operation  can
be avoided by allowing  the power output of the heat engine to vary.  In this
case, the heat engine can be sized for the maximum continuous  power
requirement and allowed to operate  at lower power levels for those periods of
                                   10-7

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vehicle driving cycles which require less power.  If heat engine rpm is also
allowed to vary to produce this variation in power output (as in conventional
internal combustion engines),  it is  envisioned that the control  system can
effectively vary throttle setting response  time constants so that engine rpm
and power changes take place  at a controlled rate in such a manner that no
true vehicle acceleration demands are imposed  on the heat engine  in the
conventional sense.
Such a mode of operation •would allow the  energy requirements of a variety
of urban driving cycles to be more  closely matched (than with  constant power
output mode), although the matching of all duty cycle energy requirements
may not be  possible.  To overcome this difficulty, it has been suggested
that the heat engine power output be scheduled as  a function of vehicle
velocity (heat engine produces more power as road load increases) with a
throttle "bias" feature  in the heat engine fuel control system to increase or
lower the baseline  heat engine power output schedule in accordance with an
input  signal related to battery voltage and/or state-of-charge as illustrated
in Fig.  10-4.
With these features,  the continuous operation of the heat engine on a variable
power output basis appears to be a  highly versatile and accommodating mode
of operation for the series configuration of a heat engine/electric hybrid
powerplant.
10. 1.2. 2. 2. Z   "Step-Mode" Operation
Another technique for varying heat  engine power output is  to schedule power
output in discrete steps.   Figure 10-5  illustrates  one such  approach, wherein
three levels of power output are used.   A "low"  level would be scheduled
for a  low-velocity range (e.g., 0-30 mph), an "intermediate" level for
velocities between  the low-velocity range and vehicle top speed, and a  "peak"
level  for cruising at maximum continuous power conditions.
Again, battery voltage and/or state-of-charge signals could be used to over-
ride the nominal schedule of power output versus  velocity.
                                    10-8

-------
o
I
sO
*
cc
UJ
o
Q_
I—
ZD
Q_
»—
ZD
O
         BATTERY VOLTAGE AND/OR
         STATE-OF-CHARGE SIGNAL
         CAN BE USED TO DEPART
         FROM  NOMINAL SCHEDULE -
       (WITHIN  UPPER 8  LOWER LIMITS)
                       	/
                                                                /UPPER  LIMIT
                                                                 NOMINAL SCHEDULE
                                                                 LOWER LIMIT
                                          VEHICLE VELOCITY
                        Figure 10-4.  Heat Engine Variable Power Output Mode
                                    "Biased" Throttle Setting Feature

-------
O

K—

O
                                            "INTERMEDIATE" UEVEL
or
LU
5S
O
Q_
"LOW" LEVEL
                                                                    "PEAK" LEVEL
                                             •TOP VEHICLE
                                              SPEED
                                          VEHICLE VELOCITY
                        Figure 10-5.  Heat Engine Variable Power Output Mode
                                     Step-Mode

-------
10.1.2.2.3    Selected Baseline Operational Mode
On the basis of the discussion of characteristics, advantages, and disad-
vantages,  the variable power output mode with the heat engine operating
continuously throughout  the driving cyc.le was selected for  the series con-
figuration.  More specifically, the heat engine power output was tailored in
accordance with  vehicle velocity as  shown in Fig.  10-6. The specific heat
engine power  output profile for each vehicle is a function of the  power
required for steady road load above a  certain vehicle velocity.  Below this
velocity, the power output is at a constant value.   This value is determined
uniquely for each vehicle as the value  required to result in the battery being
returned to its initial state-of-charge  at the end of the vehicle driving cycle.
The more  sophisticated  approach of having  battery voltage and/or state-of-
charge override  this value as depicted in Fig.  10-4,  while offering greater
system flexibility, falls outside the  scope of the current study.
10.1.3         Parallel Configuration
10. 1. 3. 1       Basic Subsystems/Components
A heat engine/electr ic hybrid powerplant configured  for the parallel mode
requires the same basic  subsystems/components as  the series  mode plus
the additional need for a  transmission or gearbox for the mechanical drive
from  the heat engine to the differential drive and/or  wheels.  However, the
sizing criteria for some  subsystems are very  different from those in  the
series mode.   For example,  the drive motor in the series case must  be
sized to provide  all power required  at the wheels.  In the parallel case,  the
drive motor is supplementary to the mechanical power  supplied by the heat
engine, and is sized to provide acceleration torques  on an  intermittent basis,
not continuous duty.  The generator in the series case is sized  to accommo-
date  full power output of  the heat  engine, while in the parallel case the
generator  is sized on  the basis of heat engine minimum operating power  level.
The size of the heat engine required can differ between the two  concepts,
depending  upon the particular subsystem efficiencies assumed.   The particular
choice of mechanical arrangement of the heat engine, generator,  transmission/
gearbox, and  drive motor can also result in the requirement for more than one
drive motor,  or  for the drive motor to have the dual function of motor and
generator  (motor /generator).

                                   10-11

-------
                                          LEVEL ROAD
o
I
           O
           CL
VEHICLE UNDER
ACCELERATION:
  EXCESS TO MOTOR

VEHICLE AT CRUISE:
  EXCESS TO BATTERY
  AND/OR ENERGY
  DUMP CIRCUIT-,


  MINIMUM
  ALLOWABLE
  POWER-
                                                    POWER
                                                  DELIVERED
                                                            POWER REQUIRED FOR
                                                            STEADY ROAD LOAD
                                    VEHICLE SPEED,   mph
                   Figure 10-6.
               Series Configuration - Variation of Heat Engine
               Power with Vehicle Speed

-------
Because of the wide variation in mechanical approaches possible for the
parallel configuration,  a simple concept was selected for the baseline parallel
configuration in the present study which more readily allowed for a direct
comparison of the inherent features of the parallel versus series approach in
terms of heat engine power/energy requirements and resultant exhaust
emissions over the emission driving cycles.   A discussion of various parallel
configurations  can  be found in  Section 6.
As shown in  Fig. 10-7,  the baseline parallel concept utilizes an automatic
transmission to provide the mechanical drive connection from the  heat  engine
to a differential drive unit powering the drive wheels.  The electric drive
motor,  used for vehicle acceleration torque demands, is geared to the  output
shaft  of the transmission. The generator is similarly geared to the output
shaft  of the heat engine.  The control system is postulated to have the capa-
bility to synchronize the input  and output rpm's of the automatic transmission
(by  controlling heat engine  rpm, generator load, and drive motor rpm)  to the
extent they are essentially  equal and that fluid coupling losses are minimal
(i. e. ,  no torque amplification  used).
In this concept, the generator  can supply power to the batteries  when heat
engine power is in  excess of wheel demand, and the drive  motor can also
function as a generator during periods of deceleration, if desired (regenera-
tive braking).  Additionally, the drive motor could also function as a
generator during vehicle cruise periods if the heat engine  power output  was
prescheduled or "biased" via the  throttle schedule in the control system to
provide more power at any given  speed than required by the vehicle for road
load power.  Conceptually,  the  baseline parallel system provides all of  the
operational attributes postulated for the various single motor parallel concepts,
10.1.3.2       Operational Modes
With the parallel configuration  arrangement, a  single mode of operation was
selected as most compatible with the hardware  arrangement and as providing
an equitable  comparison with the  operational mode selected for  the baseline
series configuration. .As shown in Fig.  10-8, the total power output of  the
heat engine is scheduled as a function of vehicle velocity,  with that portion
above a certain velocity equal  to the steady road load power.  Below this
velocity, a minimum power level, constant with velocity,  is  selected.  The
                                    10-13

-------
                                                                 WHEEL
 HEAT
ENGINE
V
/
 AUTOMATIC
TRANSMISSION
                         A.C.
                      GENERATOR
                  D.C.
                MOTOR
                                  POWER
                               CONDITIONING
                               8  CONTROL
                                 SYSTEM
                        1
                                                 BATTERY
                                  DIFFERENTIAL'
                                  DRIVE UNIT
        Figure 10- 7.  Selected Baseline Parallel Configuration Concept

-------
                                         LEVEL  ROAD
           QL

          of
          O
          Q_
O
I
               ALLOWABLE
               POWER
VEHICLE UNDER ACCELERATION
 EXCESS TO WHEELS'

VEHICLE AT CRUISE:
 EXCESS TO GENERATOR
 (TO BATTERY AND/OR
 ENERGY DUMP CIRCUIT)
     TOTAL POWER
     DELIVERED
                                                      POWER TRANSMITTED
                                                      MECHANICALLY TO REAR
                                                      WHEELS (EQUAL TO POWER
                                                      REQUIRED FOR STEADY
                                                      ROAD LOAD)
                                      VEHICLE SPEED,  mph
                   Figure 10- 8.  Parallel Configuration - Variation of Heat Engine
                               Power with Vehicle Speed

-------
portion of heat engine power transmitted mechanically to the rear wheels is
shown by the  dashed line and is just equal to that power required for  constant
velocity road load demand.  The difference, then,  between the selected mini-
mum power level and road-load demand is available to the generator, and is
either used to charge the battery, go to the drive motor during acceleration,
or to an energy dump circuit as appropriate to the  particular driving
schedule/cycle.   During periods of vehicle deceleration, the mechanical
power is reduced to zero and the heat engine power output  is reduced to
the minimum level.  The motor (as a generator) and/or the generator can
then utilize the heat engine power output during vehicle deceleration for
battery recharging.
10. 2           SIZING STUDIES
10.2. 1         Subsystem Sizing
In order to conduct the desired performance and tradeoff studies, it was
necessary to  select subsystems, define vehicle characteristics and establish
a baseline for comparing various vehicle classes.   It should be stressed
that, due  to the complexity of factors and problems  involved in analyzing
various hybrid systems  during the short duration of this study, it was only
possible to make limited,  general investigations of the wide range of sub-
systems and alternative schemes possible.  This report should therefore
be considered in this context and as establishing the basis for more refined
inves tig at ions .
Component characteristics for  the electrical subsystem are merely  initial
selections, based on the limited scope of technology review of Section 6,  and
do not at this  time represent either optimized systems or  preferred
approaches.   Rather they are considered to be preliminary selections serving
as a baseline  for comparison of various vehicles.
In the case of the  family car for example,  to establish a baseline two types  of
motor voltage control were considered,  namely:
           A solid state chopper control
           Voltage step switching combined with field control of  the motor
                                  10-16

-------
Since step voltage  switching combined with field control of the motor has
not been extensively demonstrated for automotive  application, this scheme
would require thorough investigation to determine the feasibility of use in
hybrid powertrains.   If such a scheme  is proven to be feasible,  it offers the
advantages of higher efficiency, lighter weight,  and possibly lower cost.
A  comparison of component we ights for electrical subsystems in series and
parallel powertrain configurations is shown in Tables 10-1  and 10-2 for
each vehicle class.  All data shown are based on a control scheme using
step voltage switching combined with field control of the motor except for
the first column in each table which is  based on a  chopper scheme for
controlling motor voltage.  The two types of electrical control systems
have been presented here in the case of the  family car  solely for relative
comparison of weight, volume, and efficiency.  This shows  that the dif-
ference  in the total weight of electrical components in the two approaches
is  quite  small compared to the overall  family car  weight.
The step voltage/field control scheme was  chosen for the final analysis
of component weights, power  requirements,  and costs, and  was used as
the basis for comparing the performance of various classes of vehicles.  It
is  felt that the  performance data  obtained with this scheme  applies approxi-
mately to the chopper approach.
10.2. 1. 1     Series  Configuration
Table 10-1 denotes the  characteristics of the electrical subsystems  (drive
motor,  motor controller, generator, generator controller,  AC rectifier)
selected for the baseline series configuration for  each of the six vehicle
classes.  Included in  the table are such features as subsystem type, rating
(where appropriate),  volume, weight, and efficiency at rated load conditions.
As mentioned previously, the final drive for the series configuration  is
defined  as a conventional  differential drive unit, adapted  to contain an over-
drive mechanism for a  step-change in gear  ratio during high-speed cruise
operation for increased drive motor efficiency.  The heat engine,  of course,
                                   10-17

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                         Table 10-1.
Baseline Series Configuration  Characteristics of
  Selected Electrical Subsystems
~~~— ---^____^ Vehicle
5'jb system ' 	
Electric Drive Motor
Type
Rated Voltage, volts
Rated HP. hp
Volume, ft
Weight, Ib (5)
Efficiency @ Rated Load. %
Motor Controller
| Volume . ft
| '•'•'eight, Ib
Efficiency's Rated Load, %
Generator ( 1 )
Type
Maximum-RPM
Rated Output, kw
Volume, ft
Weight, Ib (4)
Efficiency @ Rated Load, %
AC Rectifier
Volume, ft3
Weight, Ib
Efficiency 
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                        Table 10-2.
Baseline Parallel Configuration Characteristics of

   Selected Electrical Subsystems
o
i
i—'
NO
~~~ 	 Vehicle
Subsystem """"""- — *_^_^
Electric Drive Motor
Type
Haled Voltage, volts
Rated HP. hp
Volume, ft3
Weight. Ib (5)
Efficiency (? Rated Load, %
Motor Controller
Volume. ft3
Weight, Ib
Efficiency @ Rated Load, %
Generator (1)
Type
Maximum RPM
Rated Output, kw
Volume, ft3
Weight. Ib (4)
Efficiency (Ł> Rated Load, %
AC Rectifier
Volume, ft3
Weight. Ib
Efficiency ©Rated Load, %
Generator Controller
Volume, ft3
Weight, Ib
Cables, Low Level Electronics,
Accessories, Cooling System &
Miscellaneous
Weight, Ib (2)
Family Car
DC Chopper

DC Series
220
38
3.0
232
90

1.5
100
95

AC
12,000
B. 1
0.08
19
90

0. 1
9
99 f

0.009
2



55
Step Voltage L-
Field Control (3)

DC Shunt-Wound
220
38
3.4
250
92

0.023
12.5
99 +

AC
12,000
7.5
0.07
18
90

0.1
9
99 +

0.009
2



50

i Commuter Car

DC Shunt-Wound
220
12
1.2
83
92

0.023
9.5
99 +

AC
12,000
4.5
0.06
12
90

0.05
5
99 +

0.009
2



38
Delive ry/ Postal Van
Low Speed

DC Series
220
30
2.95
170
92

1.4
64
97.4

AC
12,000
13
0.08
27
90

0.1
9
99.6

0.009
'



45
High Speed

DC Series
220
30
2.95
170
94

1.4
64
97.4

AC
12,000
13
0.08
27
90

0. 1
9
99.6

0.009
1



80
City Bus
Low Speed

DC Series
440
100
14.66
831
94

3.0
135
97.7

AC
12,000
63
0. 19
95
90

0. 1
9
99.6

0.009
1



120
High Speed

DC Compound
440'
30
2.95
170
94

1 .4
64
97.4

AC
12.000
38
0. 14
65
90

0. 1
9
99.6

0.009
1



150
(1) Gear weight accounted for in Tables 10-13 through 10-18.
(2) This weight accounted for as part of vehicle body weight.
(3) This column used for final analysis results (Sections 10 and 11).
(4) Allowing a derating factor of 1 STo for possible variation in heat engii'.e speed.
(5) Without forced air cooling system.

-------
can be any one of the five  classes under examination in the present study
(i.e., S.I. engine, diesel,  gas turbine, Rankine, Stirling).  A small gearbox
(speeder or reducer) is utilized between the heat engine and generator to
produce the desired speed ratio between these subsystems.
The required batteries, in terms of power density and energy density, were
not treated in this portion of the study effort except  on the basis of power-
plant weight  available for  battery use.  Rather, the  battery requirements
were determined with the  use  of the computer program and the various driving
cycles for each vehicle  (See Section 11).
10.2.1.2       Parallel  Configuration
Electrical subsystems  with characteristics similar  to those of Table  10-1
were also considered to be applicable to the parallel configuration, except
for rated  size, weight,  and volume changes necessitated by the sizing require-
ments  of the parallel mode of  operation.  Table 10-2 denotes the electrical
subsystem characteristics selected for the baseline parallel configuration.
The same comments as to batteries,  control system, generator, heat engine,
speeder/reducer, and final drive that were made for the series configuration
apply to the parallel configuration.  In addition, a conventional automatic
transmission was assumed in  the driveline between  the heat engine and the
final drive unit.
10.2.2         Sizing Criteria
10.2.2.1       Series Configuration
The essential sizing criteria and significant operational efficiencies assumed
for the baseline series configuration are shown in Table 10-3.
With regard  to electric  drive motor sizing, the family car, commuter car,
low-speed van, and low-speed city  bus were all sized for the continuous rated
or 100 percent load condition to occur at the grade power and velocity con-
ditions.  The high-speed van and high-speed bus were conversely sixed at
the maximum cruise velocity power level.
                                  10-20

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                      Table 10-3.  Baseline Series Configuration Subsystem Sizing Criteria
— — -^^^ Vehicle
Sizing Criteria ~~~~— _^___^
Vehicle Specification
Requirement 5
Maximum Cruise Speed
. ™Ph
Velocity on Grade, mph @ %
Road HP@Vmax, hp
ao.dHP@Vgr.de. hp
Selected Baseline Subsystem
Efficiencies for Design-Point
Sizing
Final Drive (Differential), %
Electric Drive Motor, %
Control System, %
Generator, %
Accessory Power Requirements
All Accessories, hp
No Air Conditioning, hp
Maximum Heat Engine Power
Output Required, hp
Selected Baseline Subsystem
Efficiencies for Part-Load
Operation iJuring Emission
Driving Cycles
Final Drive (Differential), %
Electric Drive Motor, %
Control System, %
Generator, %
Family Car
DC Chopper

80
40 § 12
58
61

95
90
95
90

12.6
6.7
100


95
80
95
80
"Step Voltage Si
Field Control

80
40® 12
58
61

95
90
99.5
90

12.6
6.7
93


95
80
99.5
80
Commuter Car

70
33@ 12
20
21

95
90
99.5
90

5.7
1.7
33


95
80
99.5
80
Delivery/Postal Van
Low Speed

40
8
-------
The various  subsystem efficiencies used in determining the power output
required from the heat engine (at the aforementioned design sizing points)
are as shown in the table.
The accessory power  requirements (previously given in Section 3) are
repeated for clarity.
Thus the maximum heat engine power output shown in the  table for each
vehicle is the power required at the output of the heat engine to enable the
drive motor  to perform at the rated condition shown (grade or  maximum
velocity point) with the intervening subsystem efficiencies indicated,  and to
provide the maximum accessory power load.
Also shown in the table are those subsystem efficiencies assumed for the
part-load operation of the series configuration under the various emission
dr iving cycles.
10.2.2.2       Parallel Configuration
Table  10-4 contains similar assumptions for the baseline  parallel configura-
tion defined previously.
While  the design points (grade or maximum velocity condition) are the same
for  each vehicle as in the series configuration,  here it is  the automatic
transmission and final drive  unit (and their efficiencies) which combine with
accessory power requirements to  define the  maximum power output  required
of the  heat engine.   In either case, grade or maximum velocity sizing point,
the  heat engine is providing all required road power to the wheels mechani-
cally.  As no acceleration is involved,  the motor is not under load,  and
battery and power  conditioning control system are inactive.
For purposes of powerplant  weight determination,  the electric drive motor
was assumed to have a continuous duty rated power level equal to one-third
of the  maximum power required from the motor during  vehicle maximum
acceleration.  This was based on the criteria of Section 6 which indicated
the  drive  motor was capable  of 300 percent overload for short  periods of
time,  such as those which occur during  vehicle accelerations.  The  generator
                                   10-22

-------
Table  10-4.  Baseline  Parallel Configuration Subsystem Sizing Criteria
--^^^ Vehicle
Sizing Criteria ~~ — -^____^
Vehicle Specification
Requi rements
Maximum Cruise Speed
Velocity on Grade, mph Ł TJ
Road HP <Ł. Vmax. hp
RoadHPi Vgrade. hp
Selected Baseline Subsystem
Efficiencies for Design-Point
Sizing
Final Drive (Differential), To
Automatic Transmission, %
Electric Drive Motor
(Torquer), %
Control System. rc
Generator, %
Accessory Power Requirements
All Accessories, hp
No Air Conditioning, hp
Maximum Heat Engine Power
Output Required, hp
Selected Baseline Subsystem
Efficiencies for Part-Load
Operation During Emission
Driving Cycles
Final Drive (Differential
Automatic Transmission
Electric Drive NUuor
(Torque r)
Control System
Ge ne rruo r
Family Car
DC Chopper


80
•10 Ł 12
Sri
61



95
90
90

97
90

12.6
6.7
84





95
90
SO

97
80
-Step Voltage i*
Field Control


80
40 Ł 12
58
61



95
90
90

99.5
90

12.6
6.7
84





95
90
80

99.5
80
*' This column uSi'H Inr lin.il analysis results (Sections 10 and 11)

Corn mule r Car


70
33 'Ł. 12
20
21



95
90
90

99.5
90

5.7
1.7
31





95
90
80

99.5
60

Delive ry .' Postal Van
Low Speed


40
S Ł20
2-1
30



93
90
90

99.5
90

2.3
2.3
38





95
90
80

99.5
50
High Speed


65
_
so
-



95
90
90

99.5
90

2.3
2. 3
96





95
90
80

99.5
80
City Bus
Low Speed


40
6 @20
70
100



95
90
90

99.5
90

39.3
12.3
156





95
90
80

99.5
80
High Speed


60
-
170
-



95
90
90

99.5
90

39.3
12.3
240





'95
90
60

99.5
80


-------
was assumed to have a continuous duty power rating equal to the minimum
power level of the heat engine, as defined in Section 10. 1. 3. 2.
As  can be noted by comparing Tables 10-3 and 10-4, the power train drive-
line efficiency (from heat engine  to drive •wheels) at maximum continuous
power demand conditions is higher for the parallel configuration than for
the series  configuration.  Consequently,  the heat engine  size (HP) for the
parallel  configuration is  smaller  than for the series  configuration in the
order  of 6  to  10 percent.
10.2.3        Powerplant Weight Analyses
10.2.3.1      Powerplant Elements
The APCO has defined (under their Advanced Automotive Power Systems
Program) the powerplant or propulsion system weight (W ) to include the
energy storage unit (including containment),  power converter (including both
functional components and controls), and power transmission to the  driven
wheels.  It also includes the exhaust system, pumps, motors, and fans
necessary  for operation of the propulsion system, as well as any propulsion
system heating or cooling devices.
Based upon this definition, and adopting elements of nomenclature and weight
apportionment after Hoffman (Refs.  10-1 and 10-2),  the weight apportionment
for conventional and hybrid  vehicles of the personal transit type are shown
in Table  10-5.
As  can be seen, the vehicle weight without propulsion (W ) includes  tires,
wheels,  and brakes and equals 67.3 percent  of the vehicle curb weight (W  ),
where
                              W   = W   + W
                               cop

Also, the powerplant or propulsion system weight (W  ) is then  42. 7 percent
of the curb weight for the  roriventionnl vehicle.
                                  10-24

-------
                            Table 10-5.  Weight Apportionment in Conventional and

                                         Hybrid Vehicles
Component
Vehicle Weight (No Propulsion).
Body
Trim
Class
Suspens ion
Steering
Tires
Wheels
Brakes
W
o








W / W
Vehicle Weight/Component Weight. o' c
Power Train. W
P
Heat Engine
Fluid Systems
Radiator (Full)
Fuel Tank (Full)
Exhaust
Electrical
Battery
Generator and Controls
Starter
Transmission
Drive Line
Rear Axle Drive
Electric Drive Motor
Motor Controller
AC Rectifier
Gearing (H. E. to Generator
Power Train Weight/ Component


















)
Weight. VWc

Conventional Vehicle
Component Weight/
Curb Weight

0. 330
0. 140
0. 032
0. 060
0. 016
0. 032
0. 025
0. 038
0. 673


0. 150

0. 014
0. 044
0. 014

0. 012
0. 005
0. 005
0. 040
0. 020
0. 023
0
0
0
0
0. 327

Hybrid Vehicle
Component Weight/
Curb Weight

0. 330
0. 140
0. 032
0. 060
0. 016
0. 032
0. 025
0. 038
0. 673


A*

B
0. 044
C

D
E
F
G
H
0. 023
1
J
K
L
0. 067
Plus A-L
•xSt'i' Table 10-6 for d.'.ia applicable to "A'1 through " L" .
O
I

-------
The APCO has further defined a vehicle test weight (W ) as

                          yr  = W  + W + 300 Ib
                           top

The term W is the vehicle weight at which all accelerative maneuvers,  fuel
economy, and emissions are to be calculated by participants in their
Advanced Automotive Power  Systems Program.
Based upon these definitions  and using  the 4000-lb family  car  of the present
study as an example,  the 4000-lb weight corresponds to W .  Subtracting
the 300-lb allowance for passengers and/or baggage  implies a 3700-lb curb
weight and a 1210-lb weight allowance for the powerplant  (W  ), based on
the 32. 7 percent allowance of curb weight.
Referring to the vehicle specifications  previously outlined in Section 3,
which were given as  study guidelines prior to the current  powerplant weight
guidelines stated above, it can be  seen that a 500-lb  weight allowance was
made for passengers and/or  baggage (3500-lb curb weight) and that a 1500-lb
allowance is stipulated for the powerplant.  Therefore,  it is apparent that
the power plant weight allocations given as guidelines for the present study
are at variance with  current APCO powerplant weight criteria.  The recog-
nition of this deviation between initial study guidelines and current APCO
criteria came too late  in the  program to adjust the study guidelines.  Conse-
quently, the powerplant weights  (less batteries) developed in the remainder
of this section have been compared to the 1500-lb weight allowance required
by t.he original vehicle specifications as stated in Section  3.  This compari-
son was made to determine the amount of weight available for batteries  (in
any given vehicle and powerplant combination) and to initially assess the
impact of such allowable battery weight on battery power  density and energy
density requirements.
                                    10-26

-------
However, in Section  11, parametric displays of the effect of power plant
weight allocation on battery power density are presented which afford the
opportunity  to observe  the effect of changing the  1500-lb powerplant weight
allocation of the family car  (as an example) to the  1210-lb value mentioned
previously,  or any other  reasonable value.
10.2.3.Z     Scaling Assumptions
Again, referring to Table 10-5, the  weight allocations for the various power
train subsystems/components of the hybrid vehicle are represented by letters
(A through L) except for the fuel tank and rear axle drive.   It should be
noted that the total power train system includes elements not often specifi-
cally considered (full fuel tank, full  radiator,  exhaust system, etc.  ).
Even though departing from the current APCO criteria that  power train
weight is constrained to 32. 7 percent of the vehicle curb weight, it was
found extremely useful to adhere  to  various conventional-vehicle component
weight characteristics  developed  by  Hoffman  (as shown in Table 10-5) for
some components and also  to use these characteristics as a basis of weight-
scaling for other components.
In the present study, fuel tank (full)  weights  were maintained at 0.44 W for
the family car,  commuter car, and  van.  In  the case  of the  bus, a 95-gallon
tank was provided per current intracity buses.
The  rear axle drive weight was calculated as 0. 023 W  for  the family car
and commuter car.   For  the van and bus,  the fami.ly car rear axle drive
weights were increased by  the ratio  of  vehicle maximum acceleration power
demand divided by family car maximum acceleration  power demand.
The  remaining powerplant subsystem/component weights were either the
result of calculations performed for the hybrid study  or were based upon
conventional family car weight allocations modified by suitable power ratios,
as above.  The specific scaling/computational techniques are illustrated in
Table 10-6.
                                  10-27

-------
          Table 10-6.  Weight Scaling/Computational Techniques
                       (See Table 10-4)
A
B
D
E
F
H


I
J
K
L
=  Calculated heat engine weight/curb weight
=  0 for gas turbine, Rankine,  Stirling systems (engine weight
   includes radiators)
     =  0.014X
              hybrid vehicle heat engine rated hp
           conventional vehicle heat engine rated hp •'
   (for S. I. engine and diesel)
_  „ „, .      hybrid vehicle heat engine rated hp
           conventional vehicle heat engine rated hp
   (for all heat engines)
=  Calculated battery weight/curb weight
=  Calculated generator and control weight/curb weight
=  0 (if generator can also be used to start heat engine)
   n OO'i*    hybrid vehicle heat engine rated hp
           conventional vehicle heat engine rated hp
=  0 (in series mode)
   n n~  ,     hybrid vehicle heat engine rated hp    ..      „  .     ,  .
=  0. 02 X 	*—:	:	rr—;—r	r—°—:	-• ,*>—  (in parallel mode)
          conventional  vehicle heat engine rated  hp      r
=  0 (in series mode)
   n rt-s ^     hybrid vehicle heat engine  rated hp     ..      ..  .     ,  .
=  0. 02 X 	*——.	;	r-^:—r	r~^	:	'  ,r,—  (in parallel mode)
          conventional  vehicle heat engine rated  hp      r
=  Calculated drive  motor weight/curb weight
=  Calculated controller weight/curb  weight
=  Calculated AC rectifier weight/curb weight
=  Calculated gearing weight/curb weight
 Conventional vehicle heat engine rated hp  =  vehicle peak hp demand/0. 75
                                   10-28

-------
10.Z.3.3      Results
Using  the powerplant element weight scaling techniques  delineated above
(Section 10.2.3.2 and Table  10-6) and the subsystem s izing cr iter ia
previously defined (Section 10.2. 1  and Tables 10-1, 10-2,  10-3,  and 10-4),
the powerplant weight estimations for the various vehicle classes are
shown in Tables  10-7 through 10-12 for the  series  configuration, and
Tables I 0-1 i through 10-18 for the  parallel configuration.   It should be
noted that the diesel system  weights are based on the  use of a divided
chamber turbocharged engine as described in Section  8.
These .results  are  summarized  in Table  10-19 in terms  of powerplant  we ights
and volumes (less  batteries) and weight and volume allowances for batteries
under  the vehicle specification criteria  of Section 3.
10.2.3.3.1     Family  Car
Only the S. I.  engine and the  gas turbine heat engines result in meaningful
weight allocations  for batteries. For these cases, the parallel configuration
is lighter in  weight than the series and allows 62 to 73 more pounds  for
batter ies.
10.2.3.3.2     Commuter Car
Again,  on.ly the S. 1.  engine and gas turbine  result  in meaningful -weight allo-
cations for batteries (101 to  211 Ib) with the parallel configuration allowing
the highest battery weights.
10.2.3.3.3     Low-speed Van
The extremely low continuous power requirements of  the low-speed  van
enable all heat engine classes to result  in meaningful  battery weight alloca-
tions.   However,  in this case, the  electric drive motor  and heat  engine
weights are nearly the same  in  the parallel  configuration as in the series
configuration.  Therefore, the additional driveline and transmission weights
of the parallel configuration make it the heaviest, thus being more restric-
tive in battery weight allocation.
                                   10-29

-------
                         Table 10-7.  Preliminary Weight and Volume Summary of

                                     Power Train  - Family Car Series Mode
" ~~ — ^^^^ Heat-Engine
Power Train^~~~^-^__^^^ Cla8S
Subsystems ~~ • 	
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Sub -Total
Assigned Value
Available for Batteries
S. I. Engine
wt.(1>
337. 0
12. 5
80. 0
18. 0
3.0
154.0
80. 5
335.0
11.5
29. 7
29.7
10.7
1101.6
1300.0
398.4
Vol.<2>
4.80
0.02
0. 16
0. 15
0.02
3. 08
0.48
11.80
0.09
0. 39
0.48
0.09
21.56
28.0
6.44
Diesel
Wt.


1

J













493.0
11.5
29.7
29.7
10.7
1259. 6
1500.0
240.4
Vol.






15. 10
0.09
0.39
0.48
0.09
24.86
28.0
3. 14
Gas Turbine
Wt.






310.0
11. 5
0
29.7
10. 7
1046.9
1500.0
453. 1
Vol.






10-4
0.09
0
0.48
0.09
19. 77
28.0
8. 23
Rankine
Wt.






846.0
11. 5
0
29.7
0
1572.2
1500.0
0
Vol.






13.50
0.09
0
0.48
0
22. 78
28.0

Stirling
Wt.






11 53.0
11.5
0
29.7
0
1879.2
1500.0
0
Vol.






22. 80
0.09
0
0.48
0
32.08
28.0

I'jWeight in Ib
1 'Volume in ft3
o
I
OO
O

-------
                       Table  10-8.  Preliminary Weight and Volume Summary of Power
                                    Train - Commuter Car Series Mode
" — -»^^^ Heat-Engine
Po«/er Train~~~~~~~~----_^____^ Class
Subsystems ~— ~-______^
Electrical Drive Motor
Controller (.Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Sub-Total
Assigned Value
Available (or Batteries
S. I. Engine
Wt.<"
133. 0
9. 5
37. 0
9. 0
1.0
61.6
32. 2
180.0
4. 1
13. 3
13. 3
4.8
498.8
600.0
101.2
Vol.<2>
2. 24
0. 02
0.09
0. 05
0.01
1.24
0. 15
6.03
0. 03
0. 15
0. 19
0. 04
10. 24
16. 0
5.76
Diesel
Wt.
\

(
(

;
228. 0
4. 1
13. 3
13. 3
4.8
546. 8
600.0
53.2
Vol.






8. 90
0. 03
0. 15
0. 19
0.04
13. 1 1
16. 0
2. 89
Gas Turbine
Wt.






125. 0
4. 1
0
13. 3
4.8
430. 5
600.0
169. 5
Vol.






3.90
0. 03
0
0. 19
0.04
7.96
16.0
8.04
Rankine
Wt.






322. 0
4. 1
0
13. 3
0
622. 7
600.0
0
Vol.






5. 50
0. 03
0
0. 19
0.04
9. 56
16.0

Stirling
We.






432. 0
4. 1
0
13. 3
0
732. 7
600. 0
0
Vol.






S. 60
0. 03
0
0. 19
0.04
12. 66
16. 0

ijjwcinhi in Ib
'"'Volume in ft3
o
UJ

-------
Table 10-9.  Preliminary Weight and Volume Summary of Power
            Train - Low-speed Delivery Van Series Mode
' — -_____^ Heat-Engine
Power Train^~~~~~~— — ~^_____^ Class
Subsystems ^____^
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Sub -Total
Assigned Value
Available for Batteries
S. I. Engine
Wt.<"
156. 0
64.0
52. 0
9.0
3.0
198. 0
80. 5
205. 0
5.0
13.6
13.6
4.85
804.6
1700.0
895.4
Vol.(2>
2. 94
1.40
0. 12
0. 10
0.02
3.98
0.48
7. 15
0.04
0. 18
0. 22
0.04
16.67
42.0
25. 33
Diesel
Wt.
V
j
(
(

/
273. 0
5.0
13.6
13.6
4.85
872. 6
1700.0
827. 4
Vol.






10. 1
0.04
0. 18
0.22
0.04
19.62
42.00
22. 38
Gas Turbine
Wt.






155.0
5.0
0
13.6
4.85
741. 0
1700.0
959
Vol.






4. 75
0.04
0
0.22
0.04
14.09
42.0
27.91
Rankine
Wt.






403. 0
5.0
0
13.6
0
984. 1
1700.0
715.9
Vol.






6. 80
0.04
0
0.22
0
16. 10
42.0
25.90
Stirling
Wt.






546. 0
5.0
0
13.6
0
1127. 1
1700.0
572.9
Vol.






10.90
0.04
0
0.22
0
20.20
42.0
21.80
''{Weight in Ib
1 'Volume in ft3

-------
Table 10-10.  Preliminary Weight and Volume Summary of Power
             Train -.High-speed Delivery Van Series Mode
	 ___^^ Heat-Engine
r> T • ~~~ — — ^. Class
Power Train ^_^^
Subsystems • — --^^^^^^^
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Sub-Total
Assigned Value
Available for Batteries
{''weight in Ib
'Volume in ftj
S. I. Engine
Wt.(1)
462. 0
84.0
103.0
9.0
3.0
19S. 0
80. 5
357.0
27.0
35.0
35.0
12. 5
1406.0
1700.0
294

Vol.<2'
6.75
1. 30
0. 25
0. 10
0.02
3.98
0.48
12. 30
0. 22
0.45
0. 56
0. 10
27. 51
42. 0
14.49

Diesel
Wt.
\


(

/
545.0
27.0
35.0
35.0
12. 5
1594. 0
1700. 0
!06

Vol.






16.1
0.22
0.45
0. 56
0. 10
30.81
42. 0
11.19

Gas Turbine
Wt.






350.0
27.0
0
35.0
12.5
1364.0
1700. 0
336

Vol.






11.8
0.22
0
0. 56
0. 10
26. 06
42.0
15. 94

Rankine
Wt.






963.0
27.0
0
35.0
0
1964. 5
1700.0
0

Vol.






15.3
0. 22
0
0. 56
0
29. 46
42.0


Stirling
Wt.






1305.0
27.0
0
35. 0
0
2306. 5
1700. 0
0 '

Vol.






25. Y
0.22
0
0. 56
0
39.86
42.0



-------
                       Table 10-11.  Preliminary Weight and Volume Summary of Power

                                     Train - Low-speed Intracity  Bus Series  Mode
"-•—-. __^^ Heat-Engine
D - ^"--- •— ^_ Class
Po'A'er ; ra:n — -^___^^
Subsysterr.s ~~"~— —-^____^
Electrical Drive Motor
Cor.t.-olle.- (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Sub-Total
Assigned Value
Available for Batteries
S. I. Engine
wt.<"
816. 0
135.0
1Z6. 0
9.0
3. 0
763.0
212.0
478. 0
42.5
55.0
55.0
19. 7
2714. 2
6000. 0
3285.8
Vol.<21
14.60
3.00
0. 30
0. 10
0. 02
15. 30
1.26
17. 30
0. 34
0. 71
0. 88
0. 17
53. 98
175. 0
121. 02
Diesel
Wt.
\

(
I

/
755. 0
42. 5
55.0
55.0
19. 7
2991. 2
6000. 0
3008. 8
Vol.






20. 3
0. 34
0.71
0.88
0. 17
56.98
175.0
118. 02
Gas Turbine
Wt.






521. 0
42.5
0
55.0
19. 7
2702. 2
6000.0
3297. 8
Vol.






15. 0
0.34
0
0. 88
0. 17
50. 97
175.0
124. 03
Rankine
Wt.






1462. 0
42.5
0
55.0
0
3623. 5
6000. 0
2376. 5
Vol.






22. 7
0. 34
0
0. 88
0
58. 5
175. 0
1 16. 50
Stirling
Wt.






1949. 0
42. 5
0
55. 0
0
41 10. 5
6000. 0
1889. 5
Vol.






38. 1
0. 34
0
0. 88
0
73. 90
175.0
101. 1
{iS'eight in Ib
'"'Volume in ft
- -
o
I
OJ

-------
                     Table 10-12.  Preliminary Weight and Volume Summary of Power

                                   Train - High-speed Intracity Bus Series Mode
~"~"~ — -_____^ Heat-Engine
T-> T* • ""-— --^ Class
Power Train 	 	
Subsystems " - — ^____^
Electrical Drive Motor
Controller (Motor)
Gene rator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Sub-Total
Assigned Value
Available for Batteries
S. I. Engine
Wt.("
968.0
112. 0
195.0
18.0
3.0
763.0
141.0
626.0
67.0
87.0
87.0
31.0
3098.0
6000. 0
2902
Vol.'21
14. 33
2. 50
0. 50
0. 20
0. 02
15. 30
0. 84
22.40
0. 54
1. 13
1.43
0.27
59.66
175.0
1 13. 34
Diesel
Wt.











1050.0




67.0
87.0
87.0
31.0
3522.0
6000.0
2478
Vol.






25.3
0. 54
1. 13
1.43
0.27
62. 56
175.0
1 12.44
Gas Turbine
Wt.






744.0
67.0
0
87.0
31.0
3129.0
6000. 0
2871
Vol.

Rankine
Wt.


1



19.8
0. 54
0
1.43
0.27
35.93
175. 0
1 19. 07



2218.0
67.0
0
87.0
0
4572.0
6000.0
1428
Vol.






33.9
0. 54
0
1.43
0
69. 76
175.0
105.24
Stirling
Wt.






2793.0
67.0
0
87.0
0
5147.0
6000.0
853
Vol.






53.0
0. 54
0
1.43
0
88.86
175.0
86. 14
{'{weight in Ib
1 'Volume in ft3
o
I

-------
                     Table  10-13.  Preliminary Weight and Volume Summary of Power

                                  Train - Family Car Parallel Mode
"— — -_^__^^ Heat-Engine
T-> T • ' • 	 Class
Power Train —• -~____^^
Subsystems ' • — -.^^^^
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Transmission
Drive Line
Sub-Total
Assigned Value
Available for Batteries
S. I. Engine
wtu>
250.0
12. 5
18.0
9.0
2.0
154.0
80. 5
319.0
2.0
27. 1
27. 1
10.0
59.0
70.0
1040. 2
1500.0
459.8
Vol.<2>
3.40
0.02
0.07
0. 10
0.01
3.08
0.48
10.90
0.02
0.36
0.44
0.08
0.42
0. 15
19.53
28.0
8.47
Diesel
Wt.











445.0






2.0
27. 1
27. 1
10.0
59.0
70.0
1166. 2
1500.0
333. 8
Vol.






14.30
0.02
0.36
0.44
0. 08
0.42
0. 15
22.93
28.0
5.07
Gas Turbine
Wt.






280.0
2.0
0
27. 1
10.0
59.0
70.0
974. 1
1500.0
525.9
Vol.






8.65
0.02
0
0.44
0.08
0.42
0. 15
16.92
28.0
11.08
Rankine
Wt.






755.0
2.0
0
27. 1
0
59.0
70.0
1439. 1
1500.0
60.9
Vol.






12.20
0.02
0
0.44
0
0.42
0. 15
20.39
28.0
7.61
Stirling
Wt.






1025.0
2.0
0
27. 1
0
59.0
70.0
1709. 1
1500.0
0
Vol.






21.00
0.02
0
0.44
0
0.42
0. 15
29. 19
28.0

j'|\Veight in Ib ..
1 'Volume in ft
o
I
UJ

-------
                       Table 10-14.   Preliminary Weight and Volume Summary of Power

                                     Train - Commuter Car Parallel Mode
" 	 ^____^ Heat-Engir.e
Power TrairT" — _^^ Cla53
Subsystems — -~_^^
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Transmission
Drive Line
Sub-Total
Assigned Value
Available for Batteries

S. I. Engine
Wt.(1) ! Vol. (2)
i
83.0 1.20
9. :> . 0.02
12.0 0.06
5.0 0.05
2.0 0.01
61.6 1. 24
32. 2 0. 15
171. 0 ' 5. 70
!
1.3 0.01
12. 1 0. 14
12. 1 0. 17
4.3 0.04
21.0 j 0. 15
28.0 0.05
433.3 8.99
600.0 lo.O
144.7 7.01
1
Diesel
Wt.











217. 0






1. 5
12. 1
12. 1
4. 3
21.0
28.0
501. 3
600. 0
98. 7
Vol.






8.70
0. 01
0. 14
0. 17
0.04
0. 15
0. 05
11.99
16.0
4.01

Gas Turbine
Wt.






1 17.0
1. 5
0
12. 1
4. 3
21.0
23. 0
389. 2
600.0
210.8

Vol.






3.60
0.01
0
0. 17
0.04
0. 13
0.05
6. 75
16. 0
9. 25
Rankirie
wt.






300.0
1. 5
0
12. 1
0
21.0
28. 0
567.9
600.0
32. 1
I
Vol.






5. 30
0. 01
0
0. 17
0
0. 15
0. 05
8.41
16.0
7.59

Stirling
Wt.






390.0
1 . 5
0
12. 1
0
21.0
28.0
675.9
600. 0
0

Vol.






7. 80
0. 01
0
0. 17
0
0. 15
0. 05
10.91
16. 0


{'jWeiRht in Ib
1 'Volume in ftj
o
I

-------
                     Table 10-15.  Preliminary Weight and Volume Summary of Power

                                   Train -  Low-speed Delivery Van Parallel Mode
- — -^____^ Heat-Engine
_ 	 __^^ Class
Subsystems -~— .^^^
Eiec'.rieal Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
T ransmission
Drive Line
Sub-Total

Assigned Value
Available ior Batteries
S. I. Engine
Wt.("
170.0
64.0
27.0
9.0
1.0
198.0
80. 5
198. 0
3.0
12. 3
12. 3
4.4
26.6
70. 0
876.4

1700. 0
823.6
Vol.(2)
2.95
1.40
0.03
'
0. 10
0.01
3.98
0.48
6.65
0.03
0. 16
0. 20
0.04
0. 20
0.07
16. 35

42.0
25. 65
Diesel
Wt.



1

J




f
\
(
f
253. 0








1
3. 3
12. 3
12. 3
4.4
26.6
70.0
^33 4
Vol.







9. 50
0.03
0. 16
0.20
0.04
0.20
0.07
19.2
i
1
700.0 42.0
I
76b. o
22.80
Gas Turbine
Wt.







143. 0
3. 3
0
12. 3
4.4
26.6
70. 0
809. 1

1700.0
890.9
Vol.







4. 40
0.03
0
0. 20
0.04
0. 20
0.07
13.94

42. 0
28.06
Rankine
Wt.







360.0
3. 3
0
12. 3
0
26.6
70. 0
1021.7

1700. 0
678. 3
Vol.







6. 1
0.03
0
0. 20
0
0. 20
0. 07
15.60

42.0
26.40
Stirling
Wt.







494. 0
3. 3
0
12. 3
0
26.6
70.0
1 155. 7

1700.0
544. 3
Vol.







10. 00
0. 03
0
0. 20
0
0.20
0. 07
19. 50

42. 0
22. 50
}l|weight in Ib3
'"'Volume in ft
O
I
oo

-------
                      Table  10-16.  Preliminary Weight and Volume Summary of Power

                                   Train - High-speed Delivery  Van  Parallel Mode
• — -~^___^ Heat-Engine
^~~~~-----^___^^ Class
Power Train — 	
Subsystems "" *^^^^
Electrical Drive Motor
Controller (Motor)
Gene rator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear .Axle Drive
Heat Engine •
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
T r ansmi ssion
Drive Line
Sub-Total
Assigned Value
Available for Batteries
S. I. Engine
Wt.">
170.0
64.0
27. 0
9.0
1.0
198.0
80. 5
345.0
3. 3
31. 1
31. 1
11.1
67.0
70. 0
1 103. 1
1700.0
591.9
Vol.'21
2.95
1.40
0.08
0. 10
0.01
3.98
0.48
12.00
0.03
0.40
0. 50
0.09
0.48
0. 17
22.67
42.0
19. 33
Diesel
Wt.



(

)
500.0
3. 3
31. 1
31. 1
11.1
67. 0
70.0
1263 1
1700.0
436 9
Vol.






15. 50
0.03
0.40
0. 50
0.09
0. 48
0. 17
26. 17
42.0
15.83
Gas Turbine
Wt.






315. 0
3. 3
0
31. 1
11.1
67. 0
70.0
1047.0
1700.0
653.0
Vol.






9.60
0.03
0
0. 50
0.09
0. 48
0. 17
19. 87
42. 0
22 13
Rarikine
Wt.






855.0
3. 3
0
31. 1
0
67.0
70.0
1575.9
1700.0
124. 1
Vol.






14. 40
0.03
0
0. 50
0
0. 48
0. 17
24. 58
42. 0
17. 42
Stirling
Wt.






1150.0
3. 3
0
31. 1
0
67. 0
70. 0
1870.9
1700.0
0
Vo!.






23.70
0. 03
0
0. 50
0
0.48
0. 17
33. 88
42.0
8 12
J2J Weight in Ib 3
V o 1 u in o in ft
O
I
to

-------
                      Table 10-17.   Preliminary Weight and Volume Summary of Power

                                    Train - Low-speed Intracity Bus Parallel Mode
^^-^^^ Heat -Engine
n -r • 	 • 	 Class
Power Train — •— __^_^^
Subsystems ~~~~- 	
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Fulll
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Transmission
Drive Line
Sub -Total
Assigned Value
Available for Batteries
S.I. Engine
wt.1"
831.0
135.0
95.0
9.0
1 .0
763.0
212.0
468.0
15.7
50. 5
50. 5
18. 1
1 10.0
184.0
2942.8
6000.0
3057.2
Vol.(2'
14.66
3.00
0. 19
0. 10
0.01
15. 30
1.26
16.40
0. 13
0. 65
0. 81
0. 16
0.78
0.28
53.73
175.0
121.27
Diesel
Wt.


|
'
)






716.0
15.7
50. 5
50. 5
18. 1
1 10.0
184.0
3190. 8
6000.0
2809.2
Vol.






19. 50
0. 13
0.65
0. 81
0. 16
0.78
0.28
56.83
175.0
118.17
Gas Turbine
Wt.






485.0
15.7
0
50.5
18. 1
110.0
184.0
2909. 3
6000.0
3090.7
Vol.






14.00
0. 13
0
0. 81
0. 16
0.78
0.28
50.68
175.0
124. 32
Rankine
Wt.






1350.0
15.7
0
50. 5
-
110.0
184.0
3756.2
6000.0
2243.8
Vol.






21.00
0. 13
0
0.81

0.78
0.28
57.52
175.0
1 17.48
Stirling
Wt.






2025. 0
15. 7
0
50. 5
-
110. 0
184. 0
4431. 2
6000. 0
1568. 8
Vol.






36. 00
0. 13
0
0. 81

0. 78
0. 28
72. 52
175.0
102. 48
'"'weight in Ib
'Volume in ft
o
I

-------
Table 10-18.  Preliminary Weight and Volume Summary of Power
              Train - High-speed Intracity  Bus Parallel Mode
~~~ 	 __^_^ Heat-Engine
... T — -^^ C ia 5 3
Power Train — _____^^
Subsystems -^^___^^
Electrical Drive Motor
Controller (Motor)
Generator
AC Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
Gearing (Heat Engine to Generator)
Radiator (Full)
Exhaust
Starter
Transmtss ion
Drive Line
Sub-Total
Assigned Value
Available for Batteries
S. I . Engi ne
Wt.">
170.0
o4.0
bi.O
0.0
1 .0
750.0
208.0
t>14.0
9. '-i
79. J
79. 5
28.4
172.0
184.0
2433.9
6000.0
3566. 1
Vol.'2'
2.95
1.40
0. 14
0. 10
0. 01
15. 30
0.84
21.80
0.08
1 .03
1.31
0.25
1.23
0.45
46. 79
175.0
128.21
Diesel
Wt.



(

/
985. 0
9. 5
79. 5
79. 5
28. 4
172. 0
184. 0
2804. 9
6000. 0
3195. 1
Vol.






24.0
0.08
1.03
1.31
0.25
1.23
0.45
49.09
175.0
125.91
Gas Turbine
Wt.






710.0
9. 5
0
79.5
28.4
172.0
184.0
2450. 4
6000.0
3549.6
Vol.






18. 30
0.08
0
1.31
0.25
1.23
0.45
42. 36
175.0
132.64
Rankine
Wt.






2000.0
9. 5
0
79.5
0
172.0
184. 0
3712.0
6000.0
2288.0
Vol.






30.00
0.08
0
1.31
0
1.23
0.45
53.81
175.0
121. 19
Stirling
Wt.






2700.0
9.5
0
79.5
0
172.0
184. 0
4412.0
6000.0
1588.0
Vol.






51.50
0.08
0
1.31
0
1.23
0. 45
75. 31
175.0
99-69
J2JWoisht in Ib ,
V ol ume in l"t "

-------
                        Table 10-19.  Summary of Powerplant Weights and Effects
o
i
•Jk
ro
	 -~__ 	 Heat Engine
• 	 	 	 Class/Mode
Vehicle/Characteristic ~~ 	 — ^^^
Family Car
Powerplant Weight (Less BatteVies), Ib
Powerplant Volume (Less Batteries), ft^
Weight Available for Batteries, Ib
Volume Available for Batteries, ft-*
Commuter Car
Powerplant Weight (Less Batteries). Ib
Powerplant Volume (Less Batteries), ft-'
Weight Available for Batteries, Ib
Volume Available for Batteries, ft
Low -Speed Van
Powerplant Weight (Less Batteries), Ib
Powerplant Volume (Less Batteries), ft
Weight Available for Batteries. Ib
Volume Available for Batteries, ft^
High-Speed Van
Powerplant Weight (Less Batteries), Ib
Powerplant Volume (Less Batteries), ft
Weight Available for Batteries, Ib
Volume Available for Batteries, ft
Low-Speed Bus
Powerplant Weight (Less Batteries), Ib
Powerplant Volume (Less Batteries), ft
Weight Available for Batteries, Ib
Volume Available for Batteries, ft
High-Speed Bus
Powerplant Weight (Less Batteries), Ib
Powerplant Volume (-Less Batteries), ft
Weight Available for Batteries, Ib
Volume Available for Batteries, ft
S. I. Engine
S
1102
21.6
398
6.4

499
10. 2
101
5. 8
805
16.7
895
25. 3
1406
27. 1
294
14.9
2714
53.9
3286
121.0
3098
59.7
2902
115.3
P
1040
19.5
460
8. 5

455
9.0
145
7. 0
876
16. 4
824
25.6
1108
22. 7
592
19. 3.
2943
53. 7
3057
121. 3
2434
46.8
3566
128. 2
Diesel
S
1260
24.9
240
3. 1

547
13. 1
53
2.9
873
19.6
827
22.4
1594
30.4
106
11.6
2991
57.0
3009
118
3522
62.6
2478
112.4
P
1 166
22.9
334
5. 1

501
12.0
99
4.0
933
19.2
767
22.8
1263
26.7
437
15.8
3191
56.8
2809
118.2
2805
49.1
3195
125.9
Gas Turbine
S
1047
19.8
453
8.2

430
8. 0
170
8. 0
74 J
14. 0
959
27.9
1364
25. 6
336
16.4
2702
51.0
3298
124.0
3129
55.9
2871
119.1
P
974
16.9
526
11.1

389
6.8
211
9. 2
809
13. 9
891
28. 1
1047
19. 9
653
22. 1
2909
50. 7
3091
124. 3
2450
42.4
3550
132.6
Rankine
S
1572
22. 8
0

623
9.6
0
984
16.1
716
25.0
1965
29.0
0
3624
53. 7
2648
121. 3
3964
62.9
2036
112. 1
P
1439
20. 4
61
7. 6

568
8.4
32
7.6
1022
15.6
678
26.4
1576
24. 6
124
17. 4
3756
57.5
2244
117.5
3712
53.8
2288
121.2
Stirling
S
1879
32. 1
0
0

733
12. 6
0
1127
20.2
573
21.8
2307
39.4
0
4111
74. 0
1888
101. 0
5147
89.9
853
86.1
P
1709
29.2
0

658
10. 9
0
1 156
19. 5
544
22. 5
1871
33.9
0
4431
72. 5
1569
102. 5
4412
75. 3
1588
99.7

-------
10.2.3.3.4    High-speed  Van
The higher continuous power requirements of the high-speed van again
indicate  that only the S. I. engine and the gas turbine systems afford meaning-
ful battery weight allocations.  The parallel configuration again  is the
lightest and allows more battery weight.  Although the parallel configuration
of the diesel and Rankine systems shows some battery weight allowance,
they are definitely inferior to the S. I. engine and gas turbine  in this respect.
10.2.3.3.5    Low-speed Bus
All heat  engine classes  result in substantial weight allocations for batteries,
although the Stirling engine system  is definitely  inferior to  the other classes.
As in the case of the low-speed van, the parallel configuration is heavier
in weight than its series counterpart,  with a lower battery weight allocation.
10.2.3.3.6    High-speed  City Bus
Again, all heat engine classes  indicate meaningful battery weight allocations.
The parallel configuration  results in lighter powerplant weights (less
batteries) in all cases.
The foregoing remarks  are,  of course,  made with reference to the baseline
powerplant weight and volume allocations for each vehicle as  specified  in
Section 3 (and indicated on  Tables 10-7 through  10-18).  The effect of the
resulting battery weight and volume allocations of Table 10-19 will be
discussed further in Section  11 with regard to battery power-dens ity and
energy-density requirements.
10.3          SUMMARY
The conceptual design analyses and vehicle powerplant weight determinations
have resulted in baseline series and parallel powerplant configurations for
further analysis as to their relative value in terms of (a) vehicle emissions
characteristics and (b) battery design goals and characteristics.
                                   10-43

-------
In the process of configuration selection, several important differences
between the series and parallel configurational approaches were noted which
will be  further elaborated on in Section 11.
The first such difference is that the parallel configuration has  superior
high-speed cruise efficiency due to the direct mechanical transmission of
power from the heat engine to the drive wheels at this operating condition.
As  previously noted, this reduces the heat engine size in the order of 6 to
10 percent.  This higher high-speed cruise efficiency should also result in
better fuel economy.
A second difference  is that,  in most cases, the parallel  configuration results
in a lighter powerplant weight (less batteries)  which allows  more battery
weight for the same  total powerplant (including batteries) installation weight.
This lighter weight  system results from the 6  to 10 percent smaller heat
engine size,  a reduction in electric drive motor weight,  reduced generator
and generator gearbox weights, and ancillary system weight reductions
afforded by the above (i.e., radiator,  etc. ).  These weight reductions offset
the weight additions  of the  transmission and main driveline  (heat engine to
transmission  to differential).
As  noted previously, however, the specific vehicle  classes  of low-speed van
and low-speed city bus show a higher powerplant •weight  (less batteries) for
the parallel configuration than the series configuration.  This is  brought
about by the fact that, regardless of whether series or parallel configuration
is used, the low-speed design conditions result in very similar weights for
the drive motor and  heat engine.  Thus, the weight  of the additional trans-
mission and driveline in the  parallel configuration makes it a. heavier  instal-
lation for these two vehicle classes.
As  opposed to the advantages described above  for the parallel configuration,
it should be mentioned that the series mode offers  greater simplicity and
flexibility  in powerplant/vehicle design, and is more amenable to conversion
to an all-electric powerplant system  at a future date.
                                   10-44

-------
10.4           REFERENCES


10-1.           G. A.  Hoffman, Hybrid Power Systems for Vehicles,
               University of California at Los Angeles.

10-2.           G. A.  Hoffman, Automobiles  - Today and  Tomorrow,
               RAND Corporation, Report RM-2922-FF,  November  1962.
                                  10-45

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      SECTION 11






SUMMARY OF RESULTS

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                            CONTENTS









11   SUMMARY OF RESULTS	   11-1




     11. 1
     11.2
     11. 3
General !
11.1.1
11. 1.2
Baseline
11. 2. 1


11. 2.2








11. 2. 3


11. 2.4
Tradeoff
11. 3. 1








Study Results 	
Family Car and Commuter Car 	
Buses and Vans 	
Conceptual Designs 	
Heat Engine Minimum Operating Power
Levels for Baseline Emission

Resultant Vehicle Exhaust Emissions . . .
11.2.2.1 Family Car 	
11.2.2.2 Commuter Car 	
11.2.2.3 Low Speed Delivery/
Postal Van 	
11.2.2.4 High Speed Delivery/
Postal Van 	
11. 2. 2. 5 Low Speed Intra-City Bus . . .
11.2.2.6 High Speed Intra-City Bus . . .
Resultant Battery Requirements 	
11.2.3.1 Series Configuration 	
11.2.3.2 Parallel Configuration 	
Vehicle Fuel Economy 	
Studies 	
Effect on Vehicle Emission Levels 	
11. 3. 1. 1 Regenerative Braking 	
11.3.1.2 Battery Recharge
Efficiency 	
11.3.1.3 Vehicle Weight Effect 	
11.3. 1.4 Battery Capacity and Type . . .
11.3.1.5 Drive Motor Efficiency ....
1 1. 3. 1. 6 Type of Emission Driving
Cycle 	
11-1
11-2
11-5
11-6


11-8
11-8
11-16
11-18

11-19

11-20
1 1-20
11-21
11-21
11-23
11-24
1.1-25
11-26
11-27
11-27

11-27
11-31
11-36
11-37

11-42

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                    CONTENTS  (Continued)
       11.3.2    Effect on Battery Requirements	   11-44

                  11.3.2. 1   Effect of Available Power train
                             Weight on Required Battery
                             Power  Density	   11-44

                  11.3.2.2   Comparison of Ser ies Versus
                             Parallel Configuration Effects
                             on Battery Power Density
                             Requirements	   11-57

                  11. 3. 2. 3   Effect of Drive Motor and  Heat
                             Engine Weights on Required
                             Battery Power Density for the
                             Family  Car	   11-59

                  11.3.2.4   Effect of Des ign  Point Sizing on
                             Battery Power Density Require-
                             ments for the Family Car  .  .  .   11-61

                  11.3.2.5   Effect of Electric Drive Motor
                             Efficiency on Battery Power
                             Density  Requirements for the
                             Family  Car	   11-63

                  11.3.2.6   Effect of Spark Ignition Engine
                             Air/Fuel Ratio	   11-63

11.4   Cold Start Effects	   11-66

11.5   References	   11-71

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                                TAB LES
I 1-1.   Summary of Baseline and Trade-off Areas Investigated
        for. Vehicle Emission Effects   	       11-7

11-2.   Heat  Engine Minimum Operating Power  Levels for
        Baseline Emission Driving Cycles	       11-9

11-3.   Resultant Battery Requirements  (Baseline Cases)	       1 1 -22

11-4.   Battery Requirements - Series Versus Parallel
        Configuration, S.I.  Engine   	       11-58

11-5.   Cold  Start Emiss ion Correction Factors	       11-70

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FIGURES
11-1.

11-2.

11-3.

11-4.

11-5.

11-6.

11-7.

11-8.

11-9.

11-10.

11-11.

11-12.

11-13.

11-14.

11-15.

Family Car /DREW Cycle - Series Configuration -
HC Emissions 	
Family Car /DREW Cycle - Series Configuration -
CO Emissions 	 	
Family Car /DREW Cycle - Series Configuration -
NO_ Emissions 	
Family Car /DREW Cycle - Parallel Configuration -
RC Emissions 	 	 . . . .
Family Car /DREW Cycle - Parallel Configuration -
CO Emissions 	
Family Car /DREW Cycle - Parallel Configuration -
NO? Emissions 	
Commuter Car/DHEW Cycle - Series Configuration -
HC Emissions 	
Commuter Car/DHEW Cycle - Series Configuration -
CO Emissions 	
Commuter Car/DHEW Cycle - Series Configuration -
NO- Emissions 	
L*
Commuter Car/DHEW Cycle - Parallel Configuration -
HC Emissions 	
Commuter Car/DHEW Cycle - Parallel Configuration -
CO Emissions 	
Commuter Car/DHEW Cycle - Parallel Configuration -
NO-> Emissions 	
Low-Speed Van - Series Configuration -
HC Emissions 	
Low-Speed Van - Series Configuration -
CO Emissions 	
Low-Speed Van - Series Configuration -
NO-, Emissions 	

11

11

11

11

11

11

11

11

11

11

11

11

11

11

11

-10

-10

-10

-10

-10

-10

-11

-11

-11

-11

-11

-11

-12

-J2

-12
   11-iv

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                         FIGURES (Continued;
11-16.  High-Speed Van - Series Configuration -
        HC Emissions   	      11-13

11-17.  High-Speed Van - Series Configuration -
        CO Emissions   	•	      11-13

11-18.  High-Speed Van - Series Configuration -
        NO? Emissions	•    11-13

11-19.  High-Speed Van - Parallel Configuration -
        HC Emissions   	•	      11-13

11-20.  High-Speed Van - Parallel Configuration -
        CO Emissions   	      11-13

11-21.  High-Speed Van - Parallel Configuration -
        NO? Emissions	     . 11-13

11-22.  Low-Speed Bus - Series Configuration -
        HC Emissions	      11-14

11-23.  Low-Speed Bus - Series Configuration -
        CO Emissions   	      11-14

11-24.  Low-Speed Bus - Series Configuration -
        NO2 Emissions	      11-14

11-25.  High-Speed Bus - Series Configuration -
        HC Emissions   	      11-15

11-26.  High-Speed Bus - Series Configuration -
        CO Emissions   	      11-15

11-27.  High-Speed Bus - Series Configuration -
        NO9 Emissions	      11-15
           C*

11-28.  High-Speed Bus - Parallel Configuration -
        HC Emissions   	      11-15

11-29.  High-Speed Bus - Parallel Configuration -
        CO Emissions   	    .  11-15

11-30.  High-Speed Bus - Parallel Configuration -
        NO- Emissions	      11-15
                                  11-v

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                          FIGURES (Continued)
11-31.   Effect of Battery Recharge Efficiency on HC Emissions -
         Family Car  - Series Configuration - Current
         Technology  ..........................    11-29

11-32.   Effect of Battery Recharge Efficiency on CO Emissions -
         Family Car  - Series Configuration - Current
         Technology  ..........................    11-29
11-33.   Effect of Battery Recharge Efficiency on NC^ Emissions -
         Family Car  - Series Configuration - Current
         Technology  ..........................     11-29

11-34.   Effect of Battery Recharge Efficiency on HC Emissions -
         Family Car  - Series Configuration - Projected
         Technology  ..........................     11-29

11-35.   Effect of Battery Recharge Efficiency on CO Emissions -
         Family Car  - Series Configuration - Projected
         Technology  ..........................     11-29

11-36.   Effect of Battery Recharge Efficiency on NO2 Emissions -
         Family Car  - Series Configuration - Projected
         Technology  ..........................     11-29

11-37.   Effect of Battery Recharge Efficiency on HC Emissions -
         Family Car  - Parallel Configuration - Current
         Technology  ..........................     11-30

1 1-38.   Effect of Battery Recharge Efficiency on CO Emissions -
         Family Car  - Parallel Configuration - Current
         Technology  ..........................     11-30
11-39.   Effect of Battery Recharge Efficiency on NOŁ Emissions -
         Family Car - Parallel Configuration - Current
         Technology ..........................     11-30

11-40.   Effect of Battery Recharge Efficiency on HC Emissions -
         Commuter Car - Series  Configuration - Current
         Technology ..........................     11-30

11-41.   Effect of Battery Recharge Efficiency on CO Emissions -
         Commuter Car - Series  Configuration - Current
         Technology ..........................     11-30
                                   11-vi

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                          FIGURES (Continued)
11-42.   Effect of Battery Recharge Efficiency on NC>2 Emissions -
         Commuter Car - Series Configuration - Current
         Technology	     11-30

11-43.   Effect of Vehicle Weight on  HC Emissions - Family Car/
         DHEW Cycle - Series Configuration - Current
         Technology	     11-32

11-44.   Effect of Vehicle Weight on  CO Emissions - Family Car/
         DHEW Cycle - Series Configuration - Current
         Technology	     11-32

11-45.   Effect of Vehicle Weight on  NC>2 Emissions - Family Car/
         DHEW Cycle - Series Configuration -  Current
         Technology	     11-32

11-46.   Effect of Vehicle Weight on  HC Emissions - Family Car/
         DHEW Cycle - Series Configuration - Projected
         Technology	     11-32

11-47.   Effect of Vehicle Weight on  CO Emissions - Family Car/
         DHEW Cycle - Series Configuration - Projected
         Technology	     11-32

11-48.   Effect of Vehicle Weight on  NO2 Emissions - Family
         Car/DHEW Cycle - Series Configuration - Projected
         Technology	     11-32

11-49.   Effect of Vehicle Weight on  HC Emissions - Family
         Car/DHEW Cycle - Parallel Configuration - Current
         Technology	     11-33

11-50.   Effect of Vehicle Weight on  CO Emissions - Family
         Car/DHEW Cycle - Parallel Configuration - Current
         Technology	     11-33

11-51.   Effect of Vehicle Weight on  NO2 Emissions - Family
         Car/DHEW Cycle - Parallel Configuration - Current
         Technology	     1U33

11-52.   Effect of Vehicle Weight on  HC Emissions - Family
         Car/DHEW Cycle - Parallel Configuration - Projected
         Technology	     11-33
                                  11-vii

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                          FIGURES (Continued)
11-53.   Effect of Vehicle Weight on CO Emissions - Family Car/
         DHEW Cycle -  Parallel Configuration -  Projected
         Technology	       11-33

11-54.   Effect of Vehicle Weight on NC>2 Emissions - Family
         Car/DHEW Cycle  - Parallel Configuration  - Projected
         Technology	       11-33

11-55.   Effect of Vehicle Weight on HC Emissions - Commuter
         Car/DHEW Cycle  - Series Configuration -  Current
         Technology	       11-34

11-56.   Effect of Vehicle Weight on CO Emissions - Commuter
         Car/DHEW Cycle  - Series Configuration -  Current
         Technology	•  .       11-34

11-57.   Effect of Vehicle Weight on NO^ Emissions - Commuter
         Car/DHEW Cycle  - Series Configuration -  Current
         Technology	       11-34

11-58.   Effect of Vehicle Weight on HC Emissions - Commuter
         Car/DHEW Cycle  - Series Configuration -  Projected
         Technology	       11-34

11-59.   Effect of Vehicle Weight on CO Emissions - Commuter
         Car/DHEW Cycle  - Series Configuration -  Projected
         Technology	       11-34

11-60.   Effect of Vehicle Weight on NOŁ Emissions - Commuter
         Car/DHEW Cycle  - Series Configuration -  Projected
         Technology	       11-34

11-61.   Effect of Battery Capacity and Type on HC,  CO, and
         NO2 Emissions  - Family Car/DHEW Cycle - Series
         Configuration	       11-38
11-62.   Effect of Battery Capacity on HC, CO,  and NO2
         Emissions  - High-speed Bus	       11-38
11-63.   Effect of Drive Motor Efficiency on HC Emissions -
         Family Car/DHEW Cycle - Series  Configuration -
         Current Technology	       11-40
                                   11 -viii

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                          FIGURES (Continued)
11-64.   Effect of Drive Motor Efficiency on CO Emissions  -
         Family Car/DHEW Cycle - Series Configuration -
         Current Technology	      11-40

11-65.   Effect of Drive Motor Efficiency on NC»2 Emissions -
         Family Car/DHEW Cycle - Series Configuration -
         Current Technology	      11-40

11-66.   Effect of Drive Motor Efficiency on HC Emissions  -
         Family Car/DHEW Cycle - Series Configuration -
         Projected Technology	      11-40

11-67.   Effect of Drive Motor Efficiency on CO Emissions  -
         Family Car/DHEW Cycle - Series Configuration -
         Projected Technology	      11-40

11-68.   Effect of Drive Motor Efficiency on NO2 Emissions -
         Family Car/DHEW Cycle - Series Configuration -
         Projected Technology	      11-40

11-69.   Effect of Drive Motor Efficiency on HC Emissions  -
         Family Car/DHEW Cycle - Parallel Configuration  -
         Current Technology	      11-41

11-70.   Effect of Drive Motor Efficiency on CO Emissions  -
         Family Car/DHEW Cycle - Parallel Configuration  -
         Current Technology	      11-41

11-71.   Effect of Drive Motor Efficiency on NO? Emissions -
         Family Car/DHEW Cycle - Parallel Configuration  -
         Current Technology	      11-41

11-72.   Effect of Drive Motor Efficiency on HC Emissions  -
         Family Car/DHEW Cycle - Parallel Configuration  -
         Projected Technology   	      11-41

11-73.   Effect of Drive Motor Efficiency on CO Emissions  -
         Family Car/DHEW Cycle - Parallel Configuration  -
         Projected Technology   	      11-41

11-74.   Effect of Drive Motor Efficiency on NO-> Emissions -
         Family Car/DHEW Cycle - Parallel Configuration  -
         Projected Technology   	      11-41
                                   11-ix

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                          FIGURES (Continued)
11-75.   Effect of New York Cycle on HC Emissions - Family
         Car/DREW Cycle - Current Technology	    11-43

11-76.   Effect of New York Cycle on CO Emissions - Family
         Car/DHEW Cycle - Current Technology	    11-43

11-77.   Effect of New York Cycle on NC>2 Emissions - Family
         Car/DHEW Cycle - Current Technology	    11-43

11-78.   Effect of New York Cycle on HC Emissions - Family
         Car/DHEW Cycle - Projected Technology	    11-43

11-79.   Effect of New York Cycle on CO Emissions - Family
         Car/DHEW Cycle - Projected Technology	    11-43

11-80.   Effect of New York Cycle on NO2 Emissions - Family
         Car/DHEW Cycle - Projected Technology	    11-43

11-81.  Effect of Powertrain Weight on Battery Requirements
         Family  Car - Series Configuration	    11-45

11-82.   Effect of Power train Weight on Battery Requirements
         Commuter Car  - Series  Configuration	    11-46

11-83.   Effect of Powertrain Weight on Battery Requirements
         Low-speed Van - Series  Configuration	    11-47

11-84.   Effect of Powertrain Weight on Battery Requirements
         High-speed Van - Series Configuration	    11-48

11-85.   Effect of Powertrain Weight on Battery Requirements
         Low-speed Bus - Series  Configuration	    11-49

11-86.   Effect of Powertrain Weight on Battery Requirements
         High-speed Bus - Series Configuration	    11-50

11-87.   Effect of Powertrain Weight on Battery Requirements
         Family  Car - Parallel Configuration	    11-51

11-88.   Effect of Powertrain Weight on Battery Requirements
         Commuter Car  -  Parallel Configuration	    11-52

11-89.   Effect of Powertrain Weight on Battery Requirements
         Low-speed Van - Parallel Configuration	    11-53
                                  11-x

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                         FIGURES (Concluded)
11-90.  Effect of Power-train Weight on Battery Requirements
        High-speed Van - Parallel Configuration	     11-54

11-91.  Effect of Powertrain Weight on Battery Requirements
        Low-speed Bus  - Parallel Configuration	     11-55

11-92.  Effect of Powertrain Weight on Battery Requirements
        High-speed Bus - Parallel Configuration	     11-56

11-93.  Effect of Drive  Motor and Heat Engine Weights on
        Battery Power Density - Family Car -  Series
        Configuration	     11-60

11-94.  Effect of Design Point Sizing on Battery Power Density
        Requirements - Family Car - Series Configuration	     11 -62

11-95.  Power Density vs. Maximum Efficiency -  DC  Motors -    ?
        Family and Commuter  Cars	     11-64

11-96.  Effect of Drive  Motor Efficiency on  Battery Power
        Density Requirements - Family Car - Series
        Configuration	     11-65

11-97.  Effect of Catalyst Cold Time on Effective Catalyst
        Efficiency DHEW  Cycle	     11-67

11-98.  Effect of Equivalent Cold Start Time on Cold Start
        Emission Correction Factor  - HC and CO  Emissions,
        DHEW Cycle  .  .	     11-69
                                   11-xi

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                        SUMMARY OF RESULTS
 11.1         GENERAL STUDY RESULTS
This section is designed to summarize  all of the computational results con-
ducted under this study  and to offer an  interpretation of those results which
can be used to help direct future APCO research and development programs
associated with hybrid heat engine/electric vehicles.  With so many different
types of vehicle/configuration/heat engine combinations, it is difficult to
highlight every result shown  in the body of the report; however, the most
important results for  each vehicle class are delineated  in the following sub-
sections.
It should be recognized  that the calculated vehicle exhaust  emission results
are based on measured  engine exhaust emission data compiled in this  study.
The engine exhaust emission  magnitudes and trends were established on the
basis of a comprehensive  survey and evaluation of the best data from both the
open literature and current available unpublished  engine data sources.  How-
ever, it was found that very little emission data were available  for the hybrid
type of operation and especially for part-load engine operating conditions and
for  the cold start requirement consistent with the 1972 Federal  Test Procedure.
The resulting data are considered  suitable for use in an  initial feasibility study
as conducted under this  contract.  However, in further  detailed design studies,
a substantial increase in the  data base would be necessary  for powertrain
optimization.  The current study data base  is fully discussed in Appendix B.
In addition to reflecting  the engine emissions  data base,  the  study results also
reflect the use of selected battery  models.  The charge-discharge  charac-
teristics for lead-acid,  nickel-cadmium, and nickel-zinc batter ies were
based on available data but modified on the basis of projections  for future
near-term capability.   These battery models  are  discussed in Section 7. 3
of the report.
                                   11-1

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11.1.1
    Family Car and Commuter Car
The following observations can be made  about these classes of vehicles:

             a.     For the available power train weight and volume and
                    vehicle performance  specified for this study, only the
                    spark ignition internal  combustion engine (both recipro-
                    cating and rotary) and the gas turbine engines can be
                    practically packaged  into the hybrid heat engine/electr ic
                    vehicle.  These engines impose realistically achievable
                    goals on the battery specifications for power and  energy
                    dens ity.

             b.    All hybrids examined showed marked calculated emission
                   reductions over  current conventional vehicles.  This  is
                   illustrated by the results  below,  where  measured cold
                    start emission data available for  a  1970 conventional
                    spark ignition engine automobile is compared with calcu-
                    lated hot start emission levels for several development
                    stages  of a spark ignition engine Ln a hybrid power -
                   train automobile.
          50
         40
          30
20
       CO
       CO
                 CONVENTIONAL
                  S.I. ENGINE
               .(VARIABLE A/F),
                                8
CONVENTIONAL
 S.I. ENGINE        ADVANCED
 --I5-I6I + RECIRC.  TECHNOLOGY
 	'    PLUS
               CONVENTIONAL
                  VEHICLE
                (COLD START)
                               HYBRID VEHICLE
                            (4000-lb FAMILY  CAR)
                                 (HOT START)
                                    11-2

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      In the first emissions comparison, a small conventional
      engine is used in the hybrid vehicle; the second compari-
      son is for the same engine but operating over  the restricted
      air/fuel ratio range noted and with exhaust recirculation;
      the  third comparison  is for an advanced technology engine
      operating at very high air/fuel ratio with exhaust gas recir-
      culation and incorporating catalytic converters.

c.    Based on analysis, if currently available engine technology
      is used, no version of the family car could meet  1975/76
      emission standards.  No  catalytic converters  or  thermal
      reactors were added to the powertrain for this case.

d.    Calculations based on hot start with advanced  engine tech-
      nology indicate that all versions could meet 1975/76
      standards except for the NC>2 excess for the spark ignition
      family car version (discussed in item f) and the NC>2 for the
      diesel.  Potential  dlesel engine improvements that might
      reduce the NC>2 emission  level are discussed in Appendix B.

e.    Commuter car emissions  are less than one-half of those
      for  the family car and with advanced technology easily meet
      the  1975/76  standards.  (The commuter car weighs only
      1700 Ib and has reduced acceleration and maximum cruise
      speed capabilities. )

f.     Calculated hot start emissions for family and commuter
      cars using advanced spark ignition and gas turbine engines
      with the parallel powertrain  configuration meet the numeri-
      cal  values of the 1975/76  standards (cold start),  except for
      NO2 in the spark ignition  family car, and even this value
      is very close.   This  standard could be  met if vehicle speci-
      fications were revised to  permit a slight reduction in
      vehicle performance and  approximately a  10 percent reduc-
      tion in family car  weight  specifications.

g.    Emissions are sensitive to:  (1) heat engine class and
      assumed engine emission part-load characteristics; (2)
      driving cycle characteristics selected for evaluation;
      (3) the engine operating mode used over the cycle; (4) the
      battery discharge  and charge characteristics assumed for
      the  analysis; and  (5) electric drive motor efficiency and
      part-load  characteristics.
                      11-3

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h.    Emissions are approximately 10 and 15 percent lower for
      the parallel powertrain configuration as compared to the
      series configuration in the  family and commuter cars,
      respectively.   However,  the parallel powertrain is more
      complex.   Descriptions of the powertrains analyzed can
      be found in Section 10. 1.

i.     As noted earlier,  study results  are based primarily on hot
      start data.  Incorporation of cold start effects,  based on
      the limited amount of cold start data available,  would still
      allow the advanced technology engine (very lean with
      exhaust treatment) versions of  the hybrid vehicle to meet
      1975 HC and CO standards.  The NO2 emission
      values are reduced when  cold start effects are incorporated.
      Cold start  effects are  discussed in  Section 9.

j.     Regenerative braking has essentially no effect on emissions
      for the hybrid heat engine/electric  vehicle due to battery
      charge acceptance limitations that preclude the ability  to
      store the braking  energy.   Hence,  the expected advantiige
      in reduced generator output for recharging batteries (and
      therefore reduced engine power and emissions) did not
      mater ialize.

k.    Vehicle weight increases of several hundred pounds to
      accommodate additional battery or  engine weight have a
      minor effect on exhaust emissions, but the heavier vehicles
      would have reduced road  performance.

1.     Battery power density requirement  for a series powertrain
      family car with a  spark ignition engine is 232 w/lb; the
      installed energy density is  20 w-hr/lb.  The requirements
      for energy density are based on the battery charge/
      discharge characteristics assumed for this study and may
      vary somewhat depending on actual test data from a.
      particular  advanced battery design.

m.   Realistically varying the  battery recharge efficiency (to
      account for resistive losses and incomplete chemical
      reactions) has little effect on emissions.

n.    Fuel consumption  values for the spark ignition engine are
      summarized in the following table  for all vehicles operating
      over their  emission driving cycles  (the 1972 DHEW Driving
      Cycle for the  commuter car and the family car).  The
      levels shown for  the family and commuter cars are com-
      petitive with equivalent 1970 conventional vehicles.
                      11-4

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                        Series Configuration     Parallel Configuration
          Vehicle       	(mi/gal)	     	(mi /gal)	

      Commuter Car            26                     30.5
      Family Car               11                     12. 5
      Low-speed Van            3.75                  	
      High-speed Van            4                      5
      Low-speed Bus            1.25                  	
      High-speed Bus            1.5                    2
                 These results were developed using specific fuel consump-
                 tion characteristics based on the minimum SFC/rated
                 horsepower correlation presented in Section 8. 0.  The
                 data here are representative of current carbureted spark
                 ignition engines operating at air/fuel ratios from 14-16.
                 No adjustment in SFC was made for the lean A/F regimes
                 adopted for hybrid operation because there is every reason
                 to expect that appropriate modifications in the design of
                .advanced engine systems  (viz.  stratified charge) will per-
                 mit operation at high air/fuel ratios without serious
                 degradation in fuel consumption.  If no improvement wer e
                 made,  the miles per gallon would be approximately 20
                 percent lower  than shown above.

11. 1.2     Buses and Vans

           a.    Little comment can be  offered regarding emissions for
                 the other classes of vehicles (low and high-speed postal/
                 delivery van  and low and high-speed intracity bus)
                 because there are no emission standards currently available
                 to provide a reference comparison,  nor are there measured
                 emissions available from conventional versions  of these
                 vehicles driven over a representative driving cycle.

           b.    A comparison of hybrid versions of passenger  cars with
                 current conventional cars driven over the same  cycle
                 showed  the hybrid to have significantly less emission.
                 If similar comparisons of buses and vans  could be made,
                 commensurate reductions for the hybrid are anticipated.
                                  11-5

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            c.     In the case of the bus (with its generous weight allocation
                  for the propulsion system), battery power and energy density
                  requirements are quite low.  These values are available
                  today.  For this case, battery life would be an area of con-
                  centration for future improvements.
            d.     A hybrid bus design could be formulated in the near future.
                  The work in this study could be expanded in the bus to try
                  and arrive at  a firm conceptual design.
The following sections present the significant results of the present study for
each reference  vehicle class in terms of:
            1.     Driving cycle emission levels.
            2.     Battery power density and energy density requirements.
            3.     An assessment of the interactions  and effects of significant
                  variations from adopted baseline study assumptions via
                  appropriate trade-off analyses.
Vehicle emission level determinations are summarized in Table  11-1 for those
combinations of vehicle class,  operational mode, and subsystem character-
istic variations investigated in the present study.
For convenience of presentation and discussion, the various  study results
have been grouped as they pertain to  either:  (a) the baseline conceptual
designs and operational conditions, or  (b) a variation in subsystem
characteristic/capability or operational mode (from the baseline case
assumption).
Recommendations based on  the  study results are presented in Section 13.
11.2       BASELINE  CONCEPTUAL DESIGNS
In this section,  all results pertain to the baseline vehicles with powerplants
as conceptually defined in Section 10  (series and parallel configurations), and
as operated over  the pertinent emission driving  cycle (e. g. ,  DHEW cycle) as
set forth in Section 3.  Similarly,  all baseline battery characteristics are for
the Pb-Acid batteries,  as defined in Section 7.
                                    11-6

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Table 11-1  Summary of Baseline and Trade-off Areas Investigated
                  for Vehicle Emission Effects
~~~ • 	 _______^ VEHICLE CLASS/MODE
AREA ' 	 >^_^^^
BASELINE VEHICLE EMISSION DATA
Baseline Emission Driving Cycle
All Heat Engine Classes (Current and
Advanced Technology)
Pb-Acid Batteries
EFFECT OF REGENERATIVE BRAKING
Pb-Acid Batteries
EFFECT OF BATTERY RECHARGE EFFICIENCY
Pb-Acid Batteries
EFFECT OF VEHICLE WEIGHT
Pb-Acid Batteries
EFFECT OF BATTERY TYPE
Ni - Cd
Ni - Zn
EFFECT OF EMISSION DRIVING CYCLE
New York City vs. DHEW
EFFECT OF DRIVE MOTOR EFFICIENCY LEVEL
Pb-Acid Battery
FAMILY CAR
Series
V




^
V
V

^
J
V
I/
Parallel
^




W
V
V



^
V
COMMUTER CAR
Series
V




^
V
V





Parallel
J




^







DELIVERY/POSTAL VAN
Low Speed
Series
V












Parallel













High Speed
Series
V












Parallel
V












INTRA-CITY BUS
Low Speed
Series
V












Parallel













High Speed
Series
v












Parallel
V













-------
11.2. 1      Heat Engine Minimum Operating Power Levels for Baseline
            Emission Driving Cycles
As defined in Section 10, the heat engines for all vehicle classes were
constrained to operate with output power as a discrete function of vehicle
velocity (See Fig. 10-6 for series configuration and Fig. 10-8 for parallel
configuration).  In all cases the output power was constant in the low-velocity
(0 to 30, and 40 mph) region,  at a "minimum operating  power level" which
was just sufficient to result in the batteries being fully charged at the end of
the  emission driving cycle.
These values  were determined with the use of the computer  program, as
described in Section 4, and are listed in Table 11-Z for  each vehicle class
and powerplant configuration.
11. 2. 2      Resultant Vehicle Exhaust Emissions
Figures 11-1  through 11-30 summarize, for all vehicle  classes  and heat
engines considered,  the vehicle exhaust emissions which result  from the use
of a given powerplant over the baseline emission driving cycle using the  part-
load exhaust emission characteristics described in Section 9.  It should be
pointed  out that these calculations are based on the baseline vehicle weights
and therefore assume that the required battery weight (to fulfill  the design
driving  cycle  requirements of battery power and energy density) can be
installed in any given powerplant within the baseline powerplant  weight
allocation.  The implications arising from not  having  sufficient weight avail-
able for batteries are discussed separately in Section 11.3.  1.3.
It should also be  emphasized that the emission values shown do not  include
cold-start effects, as they are not known or defined for  certain heat engine
classes.  The effect of cold starts on these baseline emission values were
discussed in Section 9 based  on existing data on spark-ignition,  diesel,  and
gas turbine  engines.  Cold-start data are presented in Appendices B and C.
A brief  discussion of cold-start effects can also be found in  Section 11.4.
                                    11-8

-------
        Table  11-2.  Heat Engine  Minimum Operating Power Levels
                    for Baseline Emission Driving Cycles
       Vehicle Class
 Heat Engine Minimum
Operating Power Level", hp
       Family Car
           Series Configuration
           Parallel Configuration
       Commuter Car
           Series Configuration
           Parallel Configuration
       Low-speed Van
           Series Configuration
       High-speed Van
           Series Configuration
           Parallel Configuration
       Low-speed Bus
           Series Configuration
       High-speed Bus
           Series Configuration
           Parallel Configuration
         20. 70
         19.20

          7.97
          7. 10

         22.40

         22.40
         18. 10

         86. 00

         70. 60
         66. 20
        Does not include air conditioning power requirements.

The values for 1975/76 emission standards used Ln this section are found on
each of the curves in grams/mile;  they are for HC = 0. 46,  CO = 4. 7,  and
NO2  =  0.4.   In the case of NO2 standards, the value of 0.4  grams/mile is
not firm.  Values ranging from 0. 4 to 0. 8 grams/mile have been discussed
as possible  standards.  The use of the lowest estimated value for comparative
purposes should be considered in evaluating the results.
                                   11-9

-------
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                                                                      11-15

-------
11.2.2.1   Family Car
Figures  11-1,  11-2,  and 11-3 denote the resultant family car exhaust
emissions in terms of hydrocarbons (HC),  carbon monoxide (CO),  and oxides
of nitrogen (NO-,), respectively, for all five classes of heat engines examined
incorporated in a series powerplant configuration.  Figures  11-4,  11-5, and
11-6 contain similar  results for the parallel powerplant  configuration.
In the case of the series powerplant configuration, all heat  engine classes,
except for the spark  ignition and diesel,  meet the 1975 HC standards with
current technology engine capability (Fig.  11-1). With projected technology
all heat engines exceed the 1975 standard by considerable margins. The
spark ignition engine HC emissions are 78. 5 percent of the 1975 standard;
the gas turbine HC emissions are 20. 5 percent, while the diesel,  Rankine,
and Stirling engines are considerably lower,  as shown.
With regard to CO emissions,  all heat engine  classes measurably exceed the
1975 standard with current technology capability (Fig. 11-2), while projected
technology greatly reduces CO  emissions (to 10. 5 percent of the 1975 standard
for the spark ignition engine and 19. 8 percent for the gas turbine).
The estimated  1976 NO2 emission standards are not met by any of the 5 heatengine
classes with current  technology capability  (Fig. 11-3). The Rankine and
Stirling engines come closest to the standard at approximately two times the
required value.  However,  even with projected technology,  only the Stirling
engine is below  the 1976 standard (78. 5 percent). The spark ignition,  gas
turbine,  and Rankine engines do not greatly exceed the standard (126 percent,
104 percent,  and 104 percent,  respectively), but they still do not meet the
1976 standards.
In the case of the parallel powerplant configuration,  all heat engine classes
except the spark ignition engine meet the 1975 HC standard with current
technology (Fig.  11-4).  With projected technology, the spark ignition engine
is below  the standard (70 percent),  while all other heat engines are consid-
erably lower (from 3 percent for the Stirling to  19 percent for the gas turbine).
                                   11-16

-------
The 1975 CO emission standards are met by all heat engines with current
technology (Fig.  11-5).  With projected technology, the CO emissions are
reduced to 4. 6 percent of the standard for the diesel and to 9. 4 percent of
the standard for the spark ignition engine.
Again,  the 1976 NO^ standards are not met by any heat engine class with
current technology (Fig.  11-6). (The Rankine and Stirling engines are the
lowest at approximately 2 times the standard  value).  With projected technol-
ogy, the gas turbine, Rankine,  and Stirling engines are below the 1976 stan-
dard (88. 5 percent, 93 percent, and 70 percent,  respectively).  The spark
ignition engine is  113 percent of the 1976  standard.
With reference to the spark ignition engine and gas turbine (those baseline
powerplants resulting in a meaningful weight allocation for batteries in the
family car),  it can be seen that the spark ignition engine requires projected
technology advancements to meet  1975 HC standards and does not quite meet
1975 NO., standards even with projected technology (113 to  126 percent). The
CO standard is easily met with current technology.
The gas turbine,  on the other hand, only requires projected technology capa-
bility to meet the  1976 NO-, standard,  and even then it slightly exceeds the
1976 value in the series configuration (104 percent).
The parallel configuration results  in lower exhaust emissions in any heat
engine class.  The ratio of parallel configuration emissions divided by series
configuration emissions (with projected technology) for spark ignition and
gas turbine engines are:
                          Spark Ignition           Gas Turbine
           HC                0.895                   0.913
           CO                0.895                   0.925
           NO2               0. 895                   0. 858
Therefore, in general,  the use of the parallel configuration results in an
approximately  10 percent reduction in  exhaust emissions  for  the family car
operated over the DHEW driving cycle (over the series configuration).
                                    11-17

-------
11.2.2.2   Commuter  Car
Figures  11-7,  11-8,  and 11-9 illustrate the emission characteristics (HC,
CO,  NO-,,  respectively) of the commuter car operated over the DHEW  cycle
with a series powerplant configuration.  Figures  11-10,  11-11,  and 11-12
contain similar results for the parallel powerplant configuration.
For the series configuration, all heat engine classes are below 1975 HC
standards with current technology engine capability (Fig. 11-7). With pro-
jected technology, the HC emissions are greatly  reduced. In this case the
spark ignition engine HC emissions are 30. 6 percent of the standard,  while
gas turbine emissions are only 7. 4 percent.  Diesel,  Rankine, and Stirling
HC emissions became miniscule.
The  same situation is present with regard to CO  emissions (Fig.  11-8).
Current  technology capability is below the  1975 standard (e. g. , 12 percent
for the spark ignition engine  and 9 percent for  the gas turbine) while pro-
jected technology further reduces these already low values (e. g. , 4. 1 per-
cent for  the spark ignition engine and 6. 8 percent for the gas turbine).
The  1976 NO? emission standard is met only by the Stirling (90 percent)  and
Rankine  (99 percent) engines with current technology capability. The  spark
ignition engine and gas turbine values are 576 percent and 226 percent,
respectively (Fig.  11-9).  However, with projected technology capability, all
engines except the Diesel (123 percent) are below the standard (e. g. ,  49 per-
cent for  the spark ignition engine and 45 percent  for the gas  turbine).
In the case of the parallel powerplant configuration, again all heat engine
classes are below the 1975 HC standard with current technology (Fig.   ] 1-10).
With  projected technology, these emission values are greatly reduced (e. g. ,
26 percent for  the spark ignition engine and 6. 8 percent for the gas turbine).
The  CO emission standard is also met by all heat engine classes with current
technology (Fig.  11-11).  With projected technology,  CO emissions  arc: further
reduced  (e. g. , 3.5 percent for the spark ignition engine and 6.  5 percent for
the gas turbine).
                                   11-18

-------
The  1976 NO, standard is met by only the Rankine (85 percent) and Stirling
(77. 5 percent) engines with current technology (Fig.  11-12).  With projected
technology,  all heat engines except the Diesel (104 percent) are lower than
the 1976 standard.  The spark ignition engine and gas turbine levels are
41. 5 percent and 33. 6 percent, respectively,  of the  1976 standard.
With reference to the spark ignition engine and gas turbine (those baseline
powerplants resulting in a meaningful weight allocation for batteries in the
commuter car), it can be seen that both require projected technology only to
meet 1976 NO2 standards, the HC and CO standards being met with current
technology.
The parallel configuration results in lower exhaust emissions in any heat
engine class.  The ratio of parallel configuration emissions divided by  series
configuration emissions (with projected technology) for spark ignition and
gas turbine  engines are:
                           Spark Ignition           Gas Turbine
            HC                0.85                    0.915
            CO                0.85                    0.960
            NO2               0.83                    0.745
Therefore,  in general,  the  use of the parallel configuration results in an
approximately  10 to 15 percent reduction in exhaust  emissions for the com-
muter car operated over the DREW driving  cycle (over the series
configuration).
As expected, the commuter  car, with its lower weight and top cruise speed,
has significantly lower emissions than  the family car.

11.2.2.3    Low Speed Delivery/Postal Van
Figures 11-13,  11-14,  and  11-15 illustrate  the emission characteristics
(HC,  CO,  and NO?,  respectively) of the low speed delivery/postal van  oper-
ated over the selected driving cycle with a series  powerplant configuration.
                                  11-19

-------
No applicable standards presently exist for this vehicle class and therefore
no comparisons can be made in this regard.
The figures do serve to illustrate the variation of emission level with heat
engine class and do indicate the  reductions in emissions possible with pro-
jected technology capability.  These analyses will become valuable when
standards are established or can be used to help formulate feasible
standards.
11.2.2.4   High Speed Delivery/Postal Van
Figures  11-16,  11-17,  and 1 1 - 18 illustrate the emission  characteristics
(IIC,  CO, and NO2> respectively) of the  high speed delivery/postal van
operated over the selected driving cycle with a series powerplant configuration.
Again, as no applicable standards for this  vehicle class presently exist, no
comparisons in this regard can be made.
The relative emission levels of the various heat  engine classes are as shown,
and the reductions in emissions  possible with projected technology as
delineated.  Figures 11-19 through 11-21 give results for the parallel configuration.
Comparison of the series and parallel configurations indicates that the paral-
lel configuration results  in lower exhaust emissions in all heat engine
classes except the gas  turbine.  The ratio of parallel configuration emissions
divided by series configuration emissions (with projected technology) for
spark ignition, gas turbine, and diesel engines are:
                   Spark Ignition        Gas Turbine        Diesel
       HC             0.80                  1.02            0.80
       CO             0. 80                  1. 30            0. 80
       NO2            0.80                  0.76            0.80
11. 2.  2. 5   Low  Speed  Intra-City Bus
Figures  11-22,  11-23,  and 11-24 depict the emission  characteristics (HC,
CO, and NO^,  respectively) of the low speed intra-city bus over the  selected
driving cycle with a series powerplant configuration.
                                    11-20

-------
As no applicable standards presently exist for this vehicle class,  no
comparisons can be made in this regard.
Again, the variation of emission level with heat engine class and reductions
in emissions possible with projected technology are evident from  inspection
of the figures.
11.2.2.6   High Speed Intra-City Bus
Figures  11-25,  11-26,  and 11-27 show the emission characteristics (HC,
CO,  and NO7,  respectively) of the high-speed intra-city bus operated over
            c*
the selected driving cycle with a series powerplant configuration.  Fig-
ures 11-28, 11-29, and 11-30 depict similar results with a parallel power-
plant configuration.
No comparisons with standards are shown since no standards presently exist
for this vehicle class.
The  relative emission levels  of the various heat engine classes and the
reductions in emissions possible with projected technology are evident from
the figures.
Comparison of the series and parallel configurations indicates that the par-
allel configuration results in  lower exhaust emissions in all heat engine
classes.   The  ratio of parallel configuration emissions divided by series
configuration emissions (with projected technology) for spark ignition, gas
turbine and diesel engines are:
                   Spark Ignition         Gas Turbine        Diesel
                                                             0. 89
                                                             0. 89
                                                             0. 89
Table 11-3 summarizes,  for all vehicle classes and powerplant combinations,
the power density and energy density requirements which result from either
the design driving cycle or emission driving cycles applicable to each
                                   11-21
HC
CO
NO2
1 1. 2. 3 Resultant
0. 89
0. 89
0. 89
Battery
Requirements
0.
0.
0.
895
905
885

-------
                         Table  11-3.   Resultant Battery Requirements  (Baseline Cases
	 VEHICLE CLASS/MODE
AREA — 	 _____^__^
PEAK POWER DEMAND (kw)
(From Design Driving Cycle)
INSTALLED ENERGY CAPACITY (kw-hr)
(From Design and/or Emission Driving Cycle)
WEIGHT AVAILABLE FOR BATTERIES (Ib)
(From Baseline Weight Statements - Section 10)
- 51 Engine
- Diesel
- Gas Turbine
- Rankine
- Stirling
POWER DENSITY REQUIRED (w/lb)
- SI Engine
- Diesel
- Gas Turbine
- Rankine
- Stirling
ENERGY DENSITY REQUIRED4 (w-hr/lb)
- SI Engine
- Diesel
- Gas Turbine
- Rankine
- Stirling
FAMILY CAR
Series
92. 5

8. 36



398
Z40
453
0
0

Z3Z
385
Z04
-
-

20
35
18.4
-
-
Parallel
9Z. 5

8. 36



460
334
526
61
0

Z01
277
176
1520


18. 1
Z5
15.9
137
-
COMMUTER CAR
Series
28

4.40



101
53
170
0
0

Z79
527
165
-
-

43.8
83
Z5. 9
-
-
Parallel
28

4. 40



145
99
211
32
0

193
284
133
875


30. 3
44.5
20.9
137
-
DELIVERY/POSTAL VAN
Low Speed
Series
90

8.80



895
827
959
716
573

101
109
94
125
157

9.9
10. 6
9. 2
12. 3
15. Z
Parallel
90

8.80



824
767
891
678
544

109
117
101
133
165

10.7
11.5
9.9
13
16. 1
High Speed
Series
90

8.80



294
106
336
0
0

306
850
268
-
-

30
83
26. 4
-
-
Parallel
90

8.80



592
437
653
124
0

152
Z06
138
725
-

14.9
20. 1
13.5
71
-
INTRA-CITY BUS
Low Speed
Series
210

39.6



3286
3009
3298
2377
1890

64
70
64
88
1 1 1

12. 1
13. Z
12.0
16.7
Zi
Parallel
210

39.6



3057
2809
3091
2244
1569

69
75
68
93
134

13
14. 1
13
17.6
25. 3
High Speed
Series
136

30.8



2902
2478
2871
1428
853

47
55
47
95
160

10.6
IZ. 4
10.7
21.6
36. 1
Parallel
136

30.8



3566
3195
3550
2288
1588

38
42
38
59
86

8.6
9. 6
8.6
13. 5
19. 4
tSJ
ro
          See Section ~. 4.

-------
vehicle (see Section 3) and the weight available for batteries  in each

powerplant type, as delineated in Tables 10-7 through  10-18  of Section 10.

As can be seen  in Table 11-3 (and discussed earlier  in Section 10), certain

power plants are not applicable under the baseline powerplant weight alloca-

tion constraints as defined in Section 3  in that they simply do not allow

enough (or any) weight for batteries.

Therefore the vehicle emission data presented for these vehicle powerplant

combinations  (Section 11.2.2) do not apply, and must be modified to reflect

increased vehicle weights which do incorporate the required  battery weights.

Such increased  vehicle weight effects are discussed later for the family car.

Brief comments pertaining to the more significant aspects of the data in

Table  11-3 are  summarized in the following sections.  Energy density figures

are based on the battery model characteristics assumed in this study.

11.2.3.1   Series  Configuration

           1.    Family Car  - Only the spark ignition engine and the gas
                 turbine result in powerplant we ights  sufficiently less than
                 the 1500-lb allocation to result in meaningful battery power
                 density requirements (204 to 232 watts/lb). For the same
                 battery, the energy density is 18 to 20 w-hr/lb.

           2.    Commuter  Car  - Again,  only the spark ignition engine and
                 the gas turbine afford any weight allowance for batteries,
                 resulting in power density requirements of 165 to 279
                 watts/lb and energy density is 26 to 44 w-hr/lb.

           3.    Low-speed Delivery/Postal Van  - The extremely low con-
                 tinuous power requirements of this vehicle enable all
                 examined heat engines to result in  powerplant weights
                 allowing battery weights  which indicate meaningful  power
                 density requirements of  94 to 157 watts/lb  and  energy den-
                 sity is 9 to 15 w-hr/lb.

           4.    High-speed Delivery/Postal Van  - The much higher  contin-
                 uous power requirements of this vehicle again limit the
                 heat engines to spark ignition engine  and gas turbine,  inso-
                 far as affording battery weight allowances  (power density
                 requirements of 268 to 306 watts/lb and energy density is
                 26 to 30 w-hr/lb).
                                   11-23

-------
            5.     Low-speed Intracity Bus - The generous weight allowance
                  for the power plant (6000 Ib) allows all heat engine classes
                  to indicate reasonable battery weight allowances resulting
                  in lower easily achievable  battery power density require-
                  ments (64 to 111 watts/Ib)  and energy density  (12 to 2 1
                  w-hr/lb).

            6.    High-speed Intracity Bus - As in the case of the low-speed
                  bus,  all heat engine classes indicate  reasonable battery
                  weight allowances  (power density requirements of 47 to
                  160 watts/lb and energy density is  10 to 36 w-hr/lb).
11.2.3.2    Parallel Configuration
            1.    Family Car - Four of the five heat engine classes  (exclud-
                 ing Stirling) provide for some battery weight allowance;
                 however, the Rankine value is so low  it results in extremely
                 high battery power density requirements  (1520 watts/lb).
                 Therefore only the spark ignition engine and gas turbine
                 are regarded as realistic  contenders, resulting in battery
                 power density requirements of 176  to  201 watts/lb and
                 energy density  is 16 to 18 w-hr/lb.  The  diesel engine
                 requires  277 watts/lb and  25 w-hv/lb; further engine weight
                 reductions are required in order to make this engine a
                 firm  contender.

            2.    Commuter Car - Again, only the spark ignition engine and
                 the gas turbine afford any weight allowance for batteries,
                 resulting in power density  requirements of 133 to  193
                 watts/lb and energy density is 21 to 30 w-hr/lb.

            3.    Low-speed Delivery/Postal Van - The extremely low
                 continuous power requirements  of this vehicle enable all
                 examined heat engines to result in powerplant weights
                 allowing battery weights which indicate power density
                 requirements of 101 to 165 watts/lb and energy density  is
                 10 to 16 w-hr/lb.

            4.    High-speed Delivery/Postal Van - The higher continuous
                 power requirements of this vehicle limit  the heal engine
                 applicability to four classes (excludes Stirling); however,
                 only the spark ignition engine and the  gas turbine  afford
                 reasonable power density  requirements (I'i8 to  152 watts/lb)
                 and energy density (13 to 15 w-hr/lb).

            5.    Low-speed Intracity Bus -  Again the generous weight
                 allowance  for the powerplant (6000  Ib) indicates all heat
                 engine classes are feasible,  from the standpoint of
                                   11-24

-------
                 battery power density requirement of 68 to  134 watts/lb
                 and energy density is 13  to 25 w-hr/lb.
            6.    High-speed Intracity Bus - As in the case of the low-speed
                 bus,  all heat engine classes indicate reasonable battery
                 weight allowances  (power density requirements  of 38 to
                 86 watts/lb and energy density is 8 to  20 w-hr/lb).
 11.2.4 '    Vehicle Fuel Economy
 The results of an analysis of fuel economy for hybrid vehicles equipped with
 gasoline-powered reciprocating spark ignition engines are shown  in the
 table below.  The levels shown for the family and commuter cars may be
 seen to be competitive  with equivalent 1970 conventional vehicles.

                            Series Configuration     Parallel  Configuration
            Vehicle         	(mi/gal)	     	(mi/gal)	
        Commuter Car             26                      30. 5
        Family Car                11                      12.5
        Low-speed  Van              3.75                   	
        High-speed Van             4                        5
        Low-speed  Bus              1.25                   	
        High-speed Bus              1.5                      2

 These results were developed using  specific fuel consumption characteristics
based on the minimum  SFC/rated horsepower correlation presented in
Section 8. 0, Fig. 8-9.   The data here are  representative of current (car-
bureted) SI engines operating at air/fuel ratios from 14  to 16.  No adjust-
ment in SFC was made for the lean A/F regimes adopted as goals for hybrid
operation (19 for current technology  and 22 for projected technology) because
there is every reason to expect that  appropriate modifications in the design
of advanced engine  systems  will permit operation at high air/fuel ratios
without serious degradation  in fuel consumption.
According to Refs.  1, 2, and 3,  the  current technology goal of 19 A/F ratio
 is attainable with minimal design modifications  to the conventional engine.
 Hansel (Ref. 1) shows a fuel economy characteristics for a conventional engine
                                   11-25

-------
with standard spark timing that is essentially flat at an optimum level out to
an air/fuel ratio of 19.  The same general trend was achieved by Toyota
(Ref. 2) with spark timing adjusted for best  torque.  Additionally, Ref.  3
provides substantial evidence indicating that the current lean  limit for auto-
motive  engines  can be extended significantly with modifications  to the ignition
system and control of mixture  distribution.
With regard to the projected technology A/F goal of 22, a limited amount of
data (e.g.,  Ref.  1) suggests that conventional engines with minor modifications
to spark timing may suffer fuel economy losses of 25 percent or more at lean
mixtures approaching 21 A/F.   It is therefore anticipated that alterations  in
the design  of the engine may be required in order to achieve far-lean opera-
tion with satisfactory fuel consumption.  There is encouraging evidence that
the 22 A/F goal might be achieved by use of the stratified charge concept or
by a precombustion chamber design.   Both of these approaches  indicate the
potential of low SFC  at the lean operating condition.  Reference 4 indicates
that a 20 percent SFC improvement over  the carbureted gasoline engine can
be achieved with the  stratified  charge  approach.  Emission data  from the
s ingle-cylinder prechamber concept of Newhall (Ref. 5) also looks promising
with regard to satisfactory lean operating performance.  Data obtained from
Newhall's work shows that ISFC  (indicated SFC) decreases as A/F ratio is
increased.  This trend suggests  that the increase in BSFC at  high air/fuel
ratios may be minimal.
11.3        TRADEOFF STUDIES
A number of selected tradeoff studies  were made to  determine the sensitivity
of vehicle emissions to a number of potential subsystem variables and opera-
tional variables (as shown in Table 11-1) as  well as  the effect of powerplant
weight on battery requirements,  as mentioned previously and discussed in
Section 10.
'rhe.se results are discussed in the following suctions,  with regard to the ef-
fect of the  variable on vehicle emission levels and/or battery requirements.
                                    11-26

-------
 11. 3. 1     Effect on Vehicle Emission Levels
 11.3.1.1   Regenerative Braking
 Computations for the family car and the commuter car indicated that varying
 regenerative braking efficiency from zero percent (as used  in all baseline
 vehicle cases) to 100 percent had no effect on vehicle exhaust emissions.
 While  contrary to expectations,  analysis of the  computer data indicates  that
 this is the unique result of the heat engine power output schedule used as a
 baseline in the present study,  coupled with charge-rate limitations of the
 batteries.
 More specifically,  as explained in Section 10, when the vehicle  decelerates,
 the heat engine power automatically drops to the "minimum operating power
 level"  during the entire deceleration time  interval.   Using the family car as
 an example (series configuration),  the generator output current at this con-
 dition  is ~38 amps.  The maximum charge-rate of the battery,  due to its
 relatively high state-of-charge throughout the DREW cycle,  is also  -38 amps.
 Therefore the  battery is being supplied by the generator up  to its full capacity
 and current generated by the regenerative-braking process  simply  cannot  be
 accepted by the battery under these conditions.
 These  results  clearly indicate that  if regenerative braking is to be  useful, the
 heat-engine power output schedule should be such that power output  is reduced
 to a minimal value (idle power) during vehicle deceleration  periods.
 11.3. 1.2   Battery Recharge Efficiency
 A series of computer runs  was made with the family car and the commuter
 car to  determine the  effect of battery recharge  efficiency  on vehicle exhaust
 emissions.  Figures  11-31, 11-32,  and 11-33 present the results for the
 various emissions (HC, CO, and NO?, respectively) with  all five classes of
heat engines having current technology capability installed in the family car in
a series configuration.  Similar results are presented in Figs.  11-34,  11-35,
and 11-36 wherein the heat engines  incorporate  projected  technology.  Figures
 11-37,  11-38,  and 11-39 contain similar information for the family  car with
 current heat engine technology in a  parallel configuration, while Figs.  11-40,
                                   11-27

-------
11-41, and  11-42 show similar results for the commuter car with current
heat engine  technology in a series configuration.
With the exception of the gas turbine and diesel engines,  the remaining heat
engines indicate  a nearly linear relationship between battery recharge effi-
ciency and exhaust emissions.   Using  the family car and the spark ignition
engine as an example,  the significant values are listed in the following  table,
where change in  emissions is expressed as a percentage increase or decrease
from that existing for the baseline recharge efficiency of 70 percent.
Compared to 70 Percent
Recharge Efficiencies
Recharge Efficiency,
Percent
Change in Emissions,
. Pe rcent:
HC
CO
N02
Current Heat Engine
Technology
Series
50

+8
+8
+8
100

-12. 5
-12. 5
-12. 5
Parallel
50

+ 12. 5
f 13. 0
+ 13. 0
100

-12. 5
-12. 5
-12. 5
Projected
Heat Engine
Technology
Series
50

+8. 0
+7. 5
+ 7. 0
100

-12. 5
-13. 0
-12. 5
Thus it can be seen that the parallel configuration  is slightly more sensitive
to reduced recharge efficiencies  than the series configuration.
The  diesel and gas turbine engines exhibit characteristics associated implicitly
with the particular emission constituent,  as a result of the assumed part-load
emission  characteristics as delineated in Section 9.  Most noticeable is the
increase of CO occasioned by increasing recharge  efficiency (Figs.  11-32,
1  1-35,  11-38) with the gas turbine engine.  In addition, the gas turbine exhibits
more marked sensitivity of NO., emissions  to recharge efficiency than the
other heat engines (Figs.  11-33,  11-36, 11-39).
In the case of the commuter car (Figs. 11-40,   11-41,  and 11-42), similar
results are obtained except for the fact that the emission sensitivity to
recharge  efficiency is  slightly greater than in the case of the family car.
                                   11-28

-------
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                                                                    11-29

-------
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-------
11.3.1.3    Vehicle Weight Effect
As mentioned previously,  the baseline powerplant weight computations of
Section 10 indicated that for several vehicle classes  only the spark ignition and
gas turbine engines afforded meaningful weight allocations for batteries,  and
that even  in these  cases  the resultant battery power density and energy density
requirements were very high (See Table 11-3).
Therefore computations  were made for the family car and  commuter car to
determine the effect on exhaust emissions of increasing vehicle weight to
allow more weight for batteries, thereby reducing their power density and
energy density requirements.
These results are illustrated in Figs.  11-43 through 11-60 in the following
sequence:
                             Current Heat Engine
                                  Technology
                 Projected Heat Engine
                     Technology
  Family Car
  (Series Configuration)
       HC
       CO
       N02
Fig. 11-43
     11-44
     11-45
Fig. 11-46
     11-47
     11-48
  Family Car
  (Parallel Configuration)
       HC
       CO
     11-49
     11-50
     11-51
     11-52
     11-53
     11-54
  Commuter Car
  (Series Configuration)
       HC
       CO
     11-55
     11-56
     11-57
     11-58
     11-59
     11-60
                                    11-31

-------
s*
                            4JOO    4400    4XXJ
                               VEHICLE HEIGHT.Ib
       4400    4»o
       C wEKXI.lb
  11
      „„!	1	1	
       1"    4 MO
  VIHILIT «{IO41. Ib
II
   ••
                                 j.	J	L	I	
                                   4400    4100
                                 CMiai  *IICNI. ib
                                                                    11-32

-------
4000     4 ICO    4?(JO
                      «WO     "00    4500

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                                                                                4000    «iriO     vnu
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4000     4100    4K»    4JOQ     44QO    4MO
                                                                                        
-------
1700    1750
1900     IS50     1900    1950     2000    2050    1000
         VEHICLE  *ŁiCMT. It
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                                                                                                                       2000     20X1
                                                                     s j"
                                                                11-34

-------
The family car results were obtained for vehicle weights up to 4600 Ib
(a 600-lb increase over the baseline  vehicle weight) and the commuter car
results for vehicle weights up to 2040 Ib (a 340-lb increase over the baseline
vehicle weight).
In the case of the family car, all heat engines except the diesel and gas tur-
bine exhibited a fairly uniform rise in all  species of emissions with increasing
vehicle weight.  Using the  spark ignition engine as a representative example,
the percentage increase in exhaust emissions at the 4600-lb weight level
(over the emission levels at 4000 Ib) are:
Percent of Change
in Emissions
HC
CO
NO2
Current Technology
Series
+6
+9. 5
+9.5
Parallel
+7. 5
+7. 5
-1-7. 5
Projected Technology
Series
+9.5
+9. 5
+9. 0
Parallel
+7. 5
+7. 5
+7. 5
Thus, for a 15-percent increase in family car weight (to 4600 Ib) the emis-
sions were increased ~9. 5 percent for the series configuration and ~7. 5 per-
cent for the parallel configuration.
Again, using the spark ignition engine as a representative example, the per-
centage increase in exhaust emissions for the commuter car (series configu-
ration) at the 2040-lb weight level  (over the emission levels at 1700 Ib)  are:
Percent of Change
in Emissions
HC
CO
NO2
Current Technology
+9
+9
+9
Projected Technology
+9
+9
+9
Thus, for the 12-percent increase in commuter car weight (to 2040 Ib), the
emissions were increased ~9 percent with a series configuration.
                                    11-35

-------
The  variation of emissions for diesels and gas turbines is again a unique
function of the particular emission constituent,  whether family car or com-
muter car,  due to the part-load emission characteristics delineated in Sec-
tion  9.   In the case of the gas turbine, CO emissions decrease ( ~3. 5 percent
for the family car and  ~7 percent for the commuter car) at the maximum
vehicle weights examined,  while NO-, emissions  increase with vehicle weight
at a  greater  rate than other heat engine classes  (~20  percent for the family
car and  ~22 percent for the commuter  car).
Aside  from these unique variabilities of the gas turbine,  it appears that
vehicle weights could be increased ~15 percent to afford more weight for bat-
teries (and thus  reduce power density and energy density requirements) at a
minimal (~10 percent) sacrifice in increased vehicle  emissions.
Jt should be noted that these results were generated using the baseline pro-
pulsion system  sized for a  1700-lb commuter car or a 4000-lb family  car
driven over the DHEW  driving cycle.  Although these  vehicles with increased
weight variations were not  driven over  the design driving cycle,  it is most
probable that the peak cruise  speed and maximum acceleration capabilities
were reduced.
11.3.1.4   Battery Capacity and Type
All baseline  vehicle emissions shown in Section  11.2.2 were calculated with
the baseline  installed battery  capacities delineated in  Table 11-3.  In the case
of the  family car, the installed battery  had a capacity of 38  amp-hr, which
was  required to  meet the design driving cycle requirements.  At this installed
capacity, all three battery  types investigated (Pb-acid, Ni-Zn, and Ni-Cd)
resulted in the same family car emissions over the DHEW  cycle.
To investigate the effect of changing battery  installed  capacity and type, com-
puter runs were made with the family car having  Pb-acid batteries ranging
from 20 to 70 amp-hr in capacity, and Ni-Zn batteries having capacities
from 18 to 70 amp-hr.   The results of these calculations are shown in Fig.
11-61, where the emissions (HC,  CO, NO-,)  are  normalized by dividing the
calculated results by the 1975/76 standards. As  can be seen,  the installed bat-
tery capacity of  the family  car can indeed be reduced  for the DHEW cycle
                                    11-36

-------
(at some sacrifice in maximum vehicle design acceleration capability) at the
expense of increased exhaust emissions.
For example, if the 38-amp-hr capacity was reduced to 20 amp-hr, the Pb-
acid battery  results indicate a 36-percent increase  in NO?,  a 33-percent
increase in HC, and a 35-percent increase in CO.   For the same reduction in
capacity (to 20 amp-hr),  the Ni-Zn battery results indicate a  15-percent
increase in NO?,  a 21-percent increase in HC, and a 15-percent increase in CO.
Conversely,  however,  increasing battery capacity above the baseline require-
ment does  not lead to decreased exhaust emissions.
Similar results  pertaining to battery capacity effects on emission  levels are
shown in Fig. 11-62 for the  high-speed Lntracity bus (spark ignition engine,
projected technology,  series configuration) with Pb-acid batteries. Reducing
installed battery capacity in half  (from 70 amp-hr to 35 amp-hr) increases
HC, CO, and NO^ by   51 percent each.
Another very significant  effect was shown by using present day battery charge/
discharge characteristics for a lead-acid battery rather than the advanced
design characteristics  presented  in Section 7.   Because of the reduced charge
acceptance capabilities of the present  battery, the generator power output
level in the family car  nearly doubled  in order to return the battery state-of-
charge  to its initial value at the end of the DHEW cycle.  Consequently,  the
emission levels increased over the baseline series powertrain configuration by
the following factors for  the current heat engine technology:  HC,  1. 35;  CO,
1. 33; NO2,  1. 28.
11.3. 1.5   Or ive Motor  Efficiency
The baseline drive motor average operational efficiency in all vehicle classes
was shown to be 80 percent (see Table 10-3).   To assess the importance of
this important subsystem efficiency on the baseline emissions,  a number of
computer runs of the family car on the DHEW cycle (series  and parallel con-
figurations) were made in which the drive motor average efficiency was varied
from 50 to 100 percent.  The results of these computer simulations are shown
in Figs. 11-63 through 11-74 in the following order.
                                   11-37

-------
        2.0
      or

      2
   cz  t
         1.6 -
   to
   to
      \ 0.8 -
     §• 0.4 -
'
~
—
_

—


—
1
	 1 	

\
>~>\>
x^-..

.
x\
1975 / 1976
STANDARDS
HC -0.46gm/mile
CO -4.7 gm/mile
N02~0.4 gm/mile
1
i

^_
,
1 , 1 1 1
S.I. ENGINE/PROJECTED TECHNOLOGY
1 /—BASELINE BATTERY CAPACITY USED
Lr^ FOR FAMILY CAR EMISSION
. ____ r CALCULATIONS
1
i
i




j HC
	 Pb- ACID BATTERY
	 Ni-Zn BATTERY
O Ni-Cd BATTERY ~

» r*/\

10      20      30      40      50


             BATTERY CAPACITY. Amp-hr
                                                         60
                                                    70
               80
       Figure  11-61.  Effect of Battery  Capacity and Type;  on HC,

                        CO, and NO2 Emissions  -  Family Car/DHEW

                        Cycle - Series Configuration
  10
P  6
E
en


CO


i  4
co
CO
   0
                                                  I
                                     S.I. ENGINE/PROJECTED TECHNOLOGY
                           BASELINE BATTERY CAPACITY USED

                           FOR HIGH-SPEED BUS EMISSION

                           CALCULATIONS
                                   _N02

                                    "CO
     0
20       40       60       80       100



            BATTERY CAPACITY, Amp-hr
120
                                                140
160
       Figure 11-62.  Effect of Battery  Capac ity on HC,  CO,

                        and NOo  Emissions- High-speed Bus
                                    11-38

-------

HC
CO
NO2
Series
Current
Technology
Fig. 11-63
11-64
11-65
Projected
Technology
Fig. 11-66
11-67
11-68
Parallel
Current
Technology
Fig. 11-69
11-70
11-71
Projected
Technology
Fig. 11-72
11-73
11-74
In the case of the series configuration •with current technology (Figs.  11-63
to 11-65), all heat engines except the gas turbine and diesel indicate a fairly
uniform relationship between drive motor average efficiency and emission
level.  Using the spark ignition engine for illustration purposes,  increasing
the drive motor efficiency from 80 to 100 percent reduced all emissions
(HC, CO,  and NO-,)  by  14 percent. Decreasing drive motor efficiency from the
80-percent baseline to  50 percent increased all emissions by  44 percent.
The gas turbine and diesel reflect emission-specie-dependent relationships
between drive motor efficiency and emission level because of their unique
part-load  emission characteristics,  as defined in Section 9.  As can be seen
in Fig.  11-64,  gas  turbine CO emissions actually increase with increasing
drive motor efficiency. The NO2 emiss ions, for gas turbines (Fig. 11-65) are
much more sensitive to drive motor  efficiency than the other heat engine classes.
Using projected technology heat engine capability (Figs.  11-66 to  11-68), the
results are very similar to the current technology case just discussed.
When the parallel configuration is considered (Figs. 11-69 to 11-71 for
current technology;  Figs.  11-72 to 11-74 for projected technology),  the
results are the same except for absolute values.  Again using the  spark igni-
tion engine for illustrative purposes  (current technology),  increasing the
drive motor efficiency  to 100 percent reduced all emissions 10 percent
(as opposed to  14 percent in the series case),  while decreasing the efficiency
to 50 percent increased emissions 22. 5 to 25 percent (as  opposed to 44 per-
cent for the series  case).  Therefore, the parallel configuration is less
                                    11-39

-------
40     50     60    '0     80     90     100
             MO'OR IFFICIENCT (1((l. %
                                                                     I!,,
                                                                                                                   C«S TURBINE
                                                                                                                 ~>S.I EMGINI
                                                                           «0     50     60    /O    80     90     100
                                                                                      WJTOR EFIiClfNO I, I. •/.
                                         S I  tNCINf
             60     70     10    00
             MnrOR LMIOIM.I  I, I. V.
                                                                            40    511     60     /o     no    90    mo
                                                                                      MOIOH(mmNf.T i., i. •/.
       -,(1    60     '0     80    90
            unidR IfMtlFNCt (,.!.%
40     50     60    '0    80    90    100
          MOIOntfFlCrtNCI l
                                                                  11-40

-------
                                                                                   I JO
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                                                                             §  |

                                                                             el  no
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     HO     Ml     fO     70    BO    90     100
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    •10    X    60    70    60     90     100

             UOrOR  EFFICIENCY (i,,!. X
                                                                                            •>0    60     70     80     90    10

                                                                                                MOTOR EFFICIENCY I,„!.•/.


                                                                                                  l.m.tr C../DHT* C,,1. .  pYr'.lf.Y'r,'
                                                                   11-41

-------
sensitive to drive motor efficiency effects.  This is because only acceleration
power is affected by motor efficiency in the parallel configuration whereas
ail power to the wheels is affected in the series configuration.
11.3.1.6   Type of Emission Driving Cycle
All of the baseline emission calculations for the family car and commuter car
were made with computer runs simulating the DREW driving cycle (See
Section 3). While this is the  proposed Federal test cycle requirement, it is
known that some urban areas exhibit markedly different "average" or
"typical" driving cycle profiles.  One such different cycle is the New York
City cycle (profile shown in Fig.  3-1).  To assess the effects of such driving
cycle profile variations,  computer sirrulations were made with the family
car driven over the New York cycle. As for the DHEW driving cycle,  the
heat engine power output was adjusted to assure that the battery final state-
of-charge matched the initial state-of-charge.  Figures  11-75 through  11-80
illustrate the  results of these calculations in a comparative  fashion, wherein
the ordinate 'scale (normalized emissions) is the ratio of New York cycle
emissions divided by DHEW cycle emissions.  Figures 11-75, 11-76, and
11-77 present emission results (HC, CO, and NO2* respectively)  for current
technology, while Figs. 11-78, ll-79i  and  11-80 present similar  values for
the projected  technology case.
Examination of the figures shows that driving profile of the New York cycle
results in a 45- to 55-percent increase in vehicle emissions over  those ocur-
ring during the DHEW driving cycle. Although the  various heat engine classes
show minor deviations from one another (the gas turbine being the most
singular in deviation),  the series configuration (exclusive of the gas turbine)
results in 45- to 54-percent increases, while the parallel configuration
(exclusive of the gas turbine) results in 49- to 55-percent increases. In
general, the parallel configuration,  for any given heat engine,  results in a
greater sensitivity to the  New York driving cycle.  However, the differences
are not sufficiently high to alter the fact that the absolute emission values for
                                    11-42

-------
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                                                                           11-43

-------
the parallel configuration are lower than  for the series  configuration on the
New York cycle.
The increased emissions of the New York cycle apparently are the result of
more accelerations,  more decelerations,  and more time stopped  (than in the
case of the DREW cycle) which poses a greater energy demand per mile from
the power plant.
11. 3. 2      Effect on Battery Requirements
A number of battery requirement tradeoff analyses were made,  utilizing the
baseline series and parallel  configurations and  powertrain weights deter-
mined in Section 10.   In terms of weight effects, two of the most meaningful
parameters are the relationship between  powertrain weight and required
battery power  density and energy density for  a given vehicle.  As  shown in
Section 10,  baseline powertrain weights were determined for all subsystems/
components except battery weights. For  any given vehicle class and allowable
weight for the  powertrain,  the weight available  for batteries  is uniquely
established and the power density requirement determined by the  peak  power
demand in the  battery during vehicle maximum  acceleration, and  the energy-
density requirement determined by the necessary  installed capacity.
Utilizing this approach, the following tradeoffs  were made.
11.3.2.1    Effect of Available Powertrain Weight  on Required
            Battery Power Density
The baseline tabular  data developed in  Tables 10-7 through 10-18  for the
powerplant weights of the various vehicle  classes and heat engines (series
and parallel  configurations) were utilized  to  develop parametric displays of
the effect of available powertrain weight on the  battery power density required
for each vehicle.  These parametric results are shown  in Figs.  11-81  through
11-86 for the series configurations and in Figs.  11-87 through 11-92 for the
parallel configurations.  In each case,  the Hludy baseline for allowable
powertrain weight is  indicated.  Battery power  den.yily ;ind energy density
requirements for any  of the five classes of heat engines at any other allowable
powertrain total weight can be determined by inspection.
                                    11-44

-------
  1000
   800
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   400
CO

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                                                    STIRLING
                                                            92.5 kW PEAK
                                                            POWER DEMAND
            S.I.
         ENGINE
           GAS TURBINE
     1000      1200     1400      1600      1800     2000      2200
                             AVAILABLE POWERTRAIN WEIGHT,  Ib
                                                                    2400
        2600
     1000      1200
      Figure 11-81.
                       1400      1600      1800     2000     2200

                            AVAILABLE POWERTRAIN WEIGHT, Ib
2400
2600
                       Effect of Powertrain Weight on Battery  Requirements
                       Family Car - Series Configuration
                                     11-45

-------
UJ

O
CC.
O
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cc
UJ

-------
1000
                     STIRLING

                     RANKINE

                     DIESEL
                                          |90 KW PEAK POWER DEMAND)
     S.I. ENGINE .
     GAS TURBINE
cc
   1000      1200      1400      1600      1800      2000     2200      2400     2600
                        AVAILABLE POWERTRAIN WEIGHT, Ib
                                         8.8kW-hr INSTALLED CAPACITY
     S.I. ENGINE
     GAS TURBINE
   1000     1200     1400     1600     1800     2000     2200
                        AVAILABLE  POWERTRAIN WEIGHT, Ib
                                                                    2400
2600
Figure 11-83.  Effect of Powertrain Weight on Battery Requirements
                 Low-Speed Van - Series  Configuration
                                   11-47

-------
   1000
   800
CO


8 600

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   400
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                S.I. ENGINE
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    100
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-------
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   1000
   800
   600
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   200
     0
     S.I. ENGINE
 "~    DIESEL
           GAS TURBINE
                                            STIRLING

                                            RANKINE
                                              210 kW PEAK POWER DEMAND
CO
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   1000
   800
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cr
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   400
   200
     0
            GAS TURBINE
                                                                136 kW  PEAK
                                                                POWER DEMAND
               S.I. ENGINE
>-
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      1000     2000     3000     4000      5000      6000     7000

                              AVAILABLE POWERTRAIN WEIGHT, Ib
                                                                     8000
     1000     2000     3000     4000     5000     6000      7000      8000      9000

                              AVAILABLE POWERTRAIN WEIGHT, Ib
               GAS TURBINE



                 S.I. ENGINE
9000
    Figure 11-86.   Effect of Powertrain Weight on Battery Requirements
                     High-Speed Bus  -  Series  Configuration
                                      11-50

-------
  1000
                                                  92.5 kW PEAK POWER  DEMAND
    1000     1200     1400      1600      1800      2000      2200     2400     2600
                             AVAILABLE POWERTRAIN WEIGHT,  Ib
   100
>-
t_-

s
s
cc
   80
   60
   40
   20
                                                  8.36 kW- hr INSTALLED CAPACITY
S.I. ENGINE

     GAS TURBINE
    1000     1200      1400     1600      1800      2000      2200
                             AVAILABLE POWERTRAIN WEIGHT,  Ib
                                                                    2400
                                                                      2600
 Figure 11-87.  Effect of Powertrain Weight on Battery Requirements
                  Family Car  - Parallel Configuration
                                    11-51

-------
   1000
   800  -
UJ
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   600  -
O
UJ
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                                                    28 kW PEAK  POWER  DEMAND
   400 —
    200 -
      400
600      700      800      900


   AVAILABLE  POWERTRAIN WEIGHT, Ib
                  1200
 a:
 oc.
 CD


 Ct
                                          S.I. ENGINE

                                          DIESEL

                                          RANKINE
                                                   4.4 kW-hr INSTALLED CAPACITY
     40 -
     20
      400
600      700      800      900

   AVAILABLE POWERTRAIN WEIGHT. Ib
1000
1100
1200
    Figure  11-88.  Effect of Powertrain Weight on Battery Requirements

                     Commuter Car - Parallel Configuration
                                        11-52

-------
1000
                                              90 kW PEAK POWER DEMAND
                    STIRLING
                    DIESEL
                    RANKINE
            1200
            1400     1600      1800     2000     2200
                   AVAILABLE  POWERTRAIN  WEIGHT, Ib
2400
2600
                                              8.8 kW-hr INSTALLED CAPACITY
   1000


Figure
    1200      1400      1600      1800     2000     2200
                   AVAILABLE  POWERTRAIN WEIGHT, Ib
2400
 2600
11-89.  Effect of Power-train Weight on Battery Requirements
        Low-Speed Van  -  Parallel Configuration
                                  11-53

-------
   1000
   800
   600
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o
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   400
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                                                        90 kW PEAK POWER  DEMAND
                                                            STIRLING
               S.I.
            ENGINE
       GAS TURBINE
                                                     I
                                                                     I
     1000      1200      1400       1600      1800      2000      2200     2400     2600

                              AVAILABLE POWERTRAIN WEIGHT, Ib
.
CC
_ J
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-------
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S  600
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   400
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              S.I. ENGINE

                 DIESEL




           GAS TURBINE
F                                                STIRLING


                                               (ANKINE
                                                    2lOkW PEAK POWER DEMAND
     1000     2000     3000     4000     5000      6000      7000

                           AVAILABLE  POWERTRAIN WEIGHT, Ib
                                                                     8000
                                                                              9000
    100
 i  80
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    60
    40
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            S.I. ENGINE


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                 DIESEL
                                                STIRLING

                                               RANKINE
                                                 39.6kW-hr INSTALLED CAPACITY
     0

     1000



   Figure
              2000
                                                            7000
8000
             3000      4000     5000     6000

                AVAILABLE POWERTRAIN WEIGHT,  Ib

11-91.   Effect of Powertrain Weight on  Battery Requirements

         Low-Speed Bus - Parallel Configuration
9000
                                     11-55

-------
  1000
   800 -
CO
Q

CC
o
Q_
>-
CC
QD

O
UJ
CC
O
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600 -
      S.I. ENGINE

     GAS TURBINE
                                              I36KW PEAK POWER DEMAND
   400 -
   200 -
      1000
           2000     3000     4000     5000     6000

                        AVAILABLE POWERTRAIN  WEIGHT, Ib
                                                     7000
8000
9000
                                                30.8kW-hr INSTALLED CAPACITY
1000      2000     3000     4000     5000     6000     7000
                      AVAILABLE POWERTRAIN WEIGHT, Ib
                                                                    8000
                                                                         9000
   Figure 11-92.  Effect of Powertrain Weight on Battery Requirements
                    High-Speed  Bus - Parallel  Configuration
                                      11-56

-------
 Alternatively, the  curves can also be used to assess the impact on required
 battery power density and energy density of reducing powertrain subsystem
 weights below those baseline values presented in Tables 10-7 through 10-18.
 For example, in Fig. 11-81  (family car, series mode) the study baseline
 was 1500-lb allowable total powertrain weight.   At that value,  the battery
 power density requirement,  if the spark ignition engine is assumed,  is
 232 watts/lb.  Assuming a 200-lb weight reduction in the  spark ignition
 engine weight itself (e. g., through use  of the  Wankel engine), this would be
 equivalent,  as far  as the battery is concerned,  of having an additional 200 lb
 available for batteries.   The effect of this 200-lb battery  weight increase
 can be observed by entering  the figure  at 1700-lb available powertrain  weight
 instead of 1500  lb,  with a resultant power density requirement of 155 watts/lb.
 Conversely, powerplant weight: increase effects  are determinable by entering
 the figure at an available powertrain weight commensurately less than  the
 baseline value.
 11.3.2.2   Comparison of Series Versus Parallel Configuration
            Effects on Battery Power Density Requirements
 Because of  the many variables involved in the cases  discussed above (series
 mode, parallel  mode, five heat engines, six vehicle  classes),  it is worth-
 while to briefly compare the  significant differences occasioned by the choice
 of .series versus parallel configuration for the vehicle  classes.  For this pur-
 pose, the conventional spark ignition engine  powerplant was  selected as
 illustrative  of the trends.  Table 11-4 summarizes,  from Tables 10-7  through
 10-18,  the baseline powertrain weight (less batteries),  the allowable battery
weight (baseline case), and the resulting required battery power density and
energy  density to meet the vehicle peak acceleration power demands and
 installed energy capacity requirements.
As  can be seen,  for all vehicles except the low-speed van and the low-speed
bus, the use of  the parallel configuration results in a reduction of power
density requirement ranging  from 13 to 52 percent, depending  upon the
specific vehicle class.   Conversely, use of the  parallel configuration in the
                                   11-57

-------
                          Table  11-4.  Battery Requirements - Series  Versus  Parallel

                                        Configuration,  S. I.  Engine
' — • — -^____^^ VEHICLE CLASS 'MODE
AREA ' • 	 _^__
BASELINE POWERTRAIN WEIGHT fib)
(Less Batteries)
NET WEIGHT ADVANTAGE lib!

ALLOWABLE BATTERY WEIGHT lib)
(Baseline Case)
REQUIRED BATTERY POWER DENSITY !» Ib)
REQUIRED BATTERY ENERGY DENSITY (»-hr/lb)
ELECTRIC DRIVE MOTOR WEIGHT !lb)
SI ENGINE WEIGHT (lb>
FAMILY CAR
Series
1102



398

232
20
337
335
Parallel
1040

62

460

201
18. 1
350
319
COMMUTER CAR
Series
499



101

279
43.8
133
180
Parallel
455

44

145

193
30. 3
83
171
DELIVERY/ POSTAL VAN
Lo
-------
low-speed van and bus results in increases in battery power density require-
ments of 9 and 8 percent, respectively.
In all vehicle classes,  the same basic weight tradeoff phenomena are  involved,
as far as  series  mode versus parallel mode is concerned.  Use of the parallel
configuration has two very s ignificant weight-advantageous  characteristics
(as opposed to the  series configuration):
      1.     The electric  drive motor is sized  (100-percent  rating or design
            point) at one-third the peak acceleration power  demand of the
            vehicle (in the case  of the series  configuration,  the drive  motor
            is sized at maximum continuous power demand  of vehicle).
      2.     The heat engine size is reduced (as mentioned in Section 10) due
            to the efficiency advantage assumed for the mechanical power
            transmission feature of the parallel configuration at maximum
            continuous vehicle power demands.
Table  11-4 also lists the drive motor  and heat engine weights (from Tables
10-7 through  10-18 for the spark ignition engine examples shown.  As can
be seen in all cases except the low-speed van and low-speed bus, the  parallel
configuration does have reduced drive motor  and heat engine weights.
However,  in the  case of the low-speed van  and bus, the electric drive motor
sized for  maximum continuous operation in the series  configuration is
essentially the same motor size required for the parallel configuration,
when  sized for one-third maximum acceleration power demand (300-percent
overload rating of electric drive motor).   Therefore, in these two cases,
use of the  parallel configurations affords only slight heat engine weight
reductions which are more than  offset by drive line and transmission  weights
of the parallel configuration (not used in series) and result  in a net increase
in powerplant weight and battery power and energy density.
11.3.2.3    Effect  of Drive Motor and Heat Engine Weights  on Required
            Battery Power  Density  for the Family Car
To further illustrate the various  interactions  between battery power density
sensitivity and powertrain subsystem weights, Fig. 11-93 is included to show
parametr ically the effects of electric drive motor and heat  engine weights on
                                   11-59

-------
   1400
    200
^ 1000
800
    600
CO
^
UJ
o

en
o
Q_
en
OQ
Ł  400

:z>
o
LU
cc
    200
      0
         FAMILY CAR -SERIES MODE

         VMAX=80mph

         PEAK POWER DEMAND = 92.5kW

         1500 Ib POWER PLANT WEIGHT ALLOCATION

         BASELINE CONFIGURATION
                                   S.I. ENGINE,

                                   BASELINE CASE
       0
200       400       600

      HEAT  ENGINE WEIGHT, Ib
                                          800
000
         Figure 11-93.  Effect of Drive Motor and Heat Engine Weights

                      on Battery Power Density - Family Car  -

                      Series Configuration
                               U-60

-------
power density requirements for the family car.  The powertrain configura-
tion Is series and the  figure is  commensurate with the 1500-lb baseline
powerplant weight allocation.  All other subsystems are constant at the
weight values given in Table  10-7.
The drive motor and heat engine (at the spark ignition engine baseline case
point shown) represent two-thirds of the powerplant weight.  Reducing both
the drive motor and heat engine weights over the assumed baseline values
by 50 percent results  in decreasing the required battery power density by
48 percent.
I 1. 3. Z. 4   Effect of besign Pou.t Sizing on  Battery Power Density
            Requirements for the Family Car
It has been recogni^ed that the  requirement, in the case of the family car,
to meet the  40 mph/ 12-percent grade and 80-mph maximum cruise speed
requirements is a most  severe one and that  substantial  reductions  in battery
requirements would result  from lowering the maximum speed requirements
due to weight savings  made by sizing the various subsystems at lower power
ratings.
To  illustrate such effects,  Fig.  11-94 was prepared  for  the family car, with
a series configuration incorporating a spark ignition heat engine.  Figure
11-94  indicates that as  the V    condition is lowered from 80 to 60 mph,  the
                             max
total powertrain weight  (less  batteries) is reduced from 1102 Ib to  806  Ib
(with air conditioner)  and the battery power  density requirement reduced
from 232 watts/lb to 133 watts/lb.   These decreases are occasioned by a
98-lb decrease in spark ignition engine weight, a 177-lb decrease  in electric
drive motor weight, and a 21-lb decrease in generator weight, for the  total
weight decrease of 296 Ib.  All other subsystems/components remain
invariant, as  shown in Table  10-7.
                                   11-61

-------
                500
                400
ro
            CO
            cr
            LU
            ^
            O
            Q_

            >-
            cr
            QD

            o
            UJ
            cr
            ID
            O
            LU
            cr
                300
                200
00
                  0
        I             I             I           ~T

       FAMILY CAR - SERIES MODE - S.I. HEAT ENGINE

       POWERPLANT WEIGHT ALLOCATION = 1500 Ib

       PEAK POWER DEMAND FROM BATTERIES = 92.5kW
                                               NO AIR
                                               CONDITIONING
            NO AIR
            CONDITIONING
                                                                                    100
                                                                                        CO
                                                                                        UJ

                                                                                        CT
                                                                                   looo
                                                                                        CO
                                                                  900
                                                                  800
                                                                       
-------
It should be mentioned that no specific gradeability requirement was stipulated
for any V     condition on Fig. 11-94 except at the 80-mph condition;  i.e., a
         msLx
reduced sustained gradeability must be accepted along with the reduced size of
heat engine.  As long as  the rated power output of the electric drive motor
remains greater than one-third of the peak power output established for the
baseline configuration, the acceleration capability of the vehicle will not have  to
be reduced.
11.3.2.5    Effect of Electric Drive Motor Efficiency on Battery Power
            Density Requirements for the  Family Car
It was further recognized that significant electric drive motor weight savings
could be made through use of motors incorporating advanced design techniques.
However, for the same 100-percent or design point sizing  condition,  a reduced
motor maximum efficiency is  realized.  This relationship  is shown in Fig. 11-95
where motor efficiency is related to motor weight in terms of Ib/hp.
Again, the family car with a series configuration incorporating the spark ignition
heat engine was selected  to illustrate the resulting vehicle  characteristics, as
shown in Fig. 11-96.  Here the effect of reducing the drive motor maximum
efficiency from  90 to 80 percent i.s  shown.   The total powertrain weight (less
batteries) is  reduced from 1102 Ib to 983 Ib (a 119-lb savings) with a decrease
in battery power density from 232 to  179 watt/lb.
Here,  the drive motor weight  was reduced from 337 to 188  Ib (a 149-lb savings).
However,  to  overcome the reduced motor  efficiency, more engine/generator
power is required and the heat engine weight was increased from 335 Ib to
359 Ib (a 24-lb increase),  and the generator weight also increased  6 Ib.  All
other subsystem/components remained invariant, as in Table 10-7.
11.3.2.6    Effect of Spark Ignition Engine Air/Fuel Ratio
The baseline spark ignition engine weights used in all cases were consistent with
the normalized variation  of spark ignition  engine weight with rated horsepower,
depicted in Section 8,  regardless of air/fuel ratio.  It was  recognized that for
spark ignition engines lean air/fuel ratios  such as selected for the purposes
                                    11-63

-------
   100
    95
    90
>-
C_J>
    85
    80
    75
                                 5            6

                         POWER DENSITY, Ib/hp
7
      Figure 11-95.  Power Density vs. Maximum Efficiency -

                    DC Motors - Family and Commuter Cars
                             11-64

-------
   500
=e  400
CO
   300
O
Q_

>-
ca
200
CO

a 100

o
     0
              FAMILY CAR - SERIES MODE- S.I.HEAT ENGINE

              POWERPLANT WEIGHT ALLOCATION ~- 150015

              PEAK POWER DEMAND FROM BATTERIES ~- 9?..5kW

              BASELINE CASE;VMAX  =80mph
                                                                    MOO Ł
                                                                     CO
                                                                     LU

                                                                     or
                                                                    10005

                                                                         CO
                                                                         CO
                                                                    900
                                                                 800
                                                                     or
                                                                     o
                                                                     Q_
                                                                    700
           80   81    82   83   84   85   86   87

                            MOTOR  EFFICIENCY, %
                                                     89   90
Figure 11-96.  Effect of Drive Motor Efficiency on Battery Power Density Requirements

             Family Car - Series Configuration

-------
of this study (a ratio of 19 for current technology and 22 for projected
technology) would most likely result in a power loss (at the same displace-
ment) over  spark ignition engines having more conventional air/fuel ratios of
15 to 17.  However,  there was insufficient data to establish discrete  variation
from the "band" of spark ignition engine weight versus horsepower character-
istics displayed in Section 8.
Assuming,  for purposes of discussion, that the normalized variation of spark
ignition engine weight versus rated horsepower used as a study baseline was
strictly applicable to only nominal air/fuel ratios, and further assuming an
~15 percent loss in rated power output to occur at an air/fuel ratio of ~19,
the increase in engine weight for the family car would be approximately 30 Ib.
Assuming an ~ 30-percent loss  in rated power output to occur at an air/fuel
ratio of ~22,  the increase in engine weight for  the family car would be
approximately 59 Ib.  As noted  previously,  these weight increases are not
expected in future engine designs and, hence, were not included in the
powertrain  weight tables.
11.4       COLD START EFFECTS
The  vehicle emission levels computed for the various options and configura-
tions presented previously in this section represent hot start  cycle emissions
since they are based on steady-state, hot engine exhaust emission  data.  For
light-duty vehicles, the Federal test procedures specify that the vehicles
be "cold-soaked" for 12  hours prior to the test.   The HC and  CO emissions
are generally higher when the engine is  cold; thus it is necessary to account
for the emissions during this cold start period.  In an engine  equipped with a
catalytic converter,  there is an additional degradation of emission during  the
engine and catalyst warmup period.  Figure  11-97 illustrates the effect of
equivalent cold catalyst time (i.e., period during which the catalyst is inef-
fective) on effective catalyst efficiency over  the DHEW cycle.  For example,
with a hot catalyst efficiency of 0. 7, if the equivalent time period during
which the catalyst is cold is 2 min (zero efficiency assumed) a hot  catalyst
efficiency of 78 percent is  required to give the equivalent emission over the
DHEW cycle.   Conversely,  the  same cold catalyst time will result in a
degraded  value of catalyst efficiency over the DHEW cycle to  a value of 0. 63.
                                   11-66

-------
    i.O
    0.9
    0.8
 UJ
o

5  0.7
    0.6

-------
In order to incorporate cold start effects, a cold start emission factor
(ratio of cold start cycle emission to hot start cycle emission) can be
applied to the vehicle HC and CO emissions computed from the hot engine data.
Figure 11-98 illustrates the effect of equivalent cold start time on the
emission correction factor  for various values of catalyst efficiency and
ratio of cold period to hot period engine emission level,  XQ/X^J,  where
XQ is the representative engine emission level during the cold transient
period and Xj_j is the steady-state hot emission level.  It  should be noted
that the correction factors increase with increasing values of Xp/XH and
are lower with lesser values of catalyst efficiency.  It should also be noted,
however,  that the higher correction factors associated with the more effi-
cient catalyst would be applied to  a lower hot engine emission level. Figure
11-98 is shown to illustrate the tradeoffs that can occur between equivalent
cold start time,  catalyst efficiency, and  ratio of cold to hot engine emission
level.  It also illustrates that as catalytic converters are utilized, the  cold
start effect can become more pronounced unless considerable effort is
expended  to minimize these factors by decreasing effective cold start time.
Although  cold start data are still scarce, and the factors  affecting cold start
merit considerable investigation,  the following cold start correction factors
were chosen to  represent typical values that could be applied to the vehicle
emission levels  calculated.   The improved correction factor shown for  the
spark ignition engine  projected technology case (with catalyst)  was based on
minimization of engine cold start  emissions through a programmed engine
start as well as shortening  of the  catalyst warm-up time.  Table  11-5 presents
the values of the spark ignition engine,  the diesel engine,  and the gas turbine
engine.
                                   11-68

-------
                   COLD  START CYCLE EMISSIONS
                    HOT  START CYCLE EMISSIONS
o


-------
                               Table 11-5
               Cold Start Emission Correction Factors

HC
CO
NO 2
Spark Ignition
Current
Technology
(No Catalyst)
1.3
1. 3
0.95
Projected
Technology
(With Catalyst)
1.2
1. Z
0.95
Diesel
1.0
1.0
0.95
Gas
Turbine
1.2
W
1.2
0.90
Jtilizing the factors listed in the table, the vehicle emission levels presented
sarlier can then be corrected for the cold start effect.  As  more information
is obtained on cold start effects, these factors will undoubtedly change.
                                    11-70

-------
11.5      REFERENCES
1.    J. G. Hansel, "Lean Automotive Engine Operation -- Hydrocarbon
      Exhaust Emissions  and Combustion Characteristics, " SAE Paper
      71-164, January 1971.

2.    Matsumoto,  Toda, Nohira, "Oxides of Nitrogen from Smaller
      Gasoline Engine, " SAE Paper No. 700145, January  1Z,  1970.

3.    Tanuma, Sasaki,  Kaneko, and Kawasaki,  "Ignition,  Combustion,
      and Exhaust Emissions of Lean Mixtures  in Automotive  Spark
      Ignition Engines," SAE Paper 710159, January 1971.

4.    I. N.  Bishop and A.  Simko, "A New Concept of Stratified Charge
      Combustion  -- the Ford Combustion Process  (FCP), " SAE Paper
      680041, January 1968.

5V    H. K. Newhall and I. A. El Messiri, "A Combustion  Chamber
      Designed for Minimum Engine Exhaust Emissions, " SAE Paper
      700491, May 1970.
                                 11-71

-------
              SECTION 12
VEHICLE PRODUCTION COST COMPARISON

-------
                              CONTENTS


12    VEHICLE PRODUCTION COST COMPARISON	     12-1
      1Z. 1   Conventional Car Cost	     12-1
      12.2   Hybrid Car Cost  	     12-5
            12.2. 1    Vehicle Component Costs	     12-5
            12.2.2    Powertrain Component Costs	     12-5
                       12.2.2.1    Heat Engine Costs	     12-5
                       12.2.2.2    Exhaust Emission Control
                                  Costs	     12-15
                       12.2.2.3    Battery Cost  	     12-15
                       12.2.2.4    Electrical Component Costs.  .     12-18
                       12.2.2.5    Drive Line and Fluid
                                  System Costs	     12-19
      12. 3   Application of Results from Cost Analysis   	     12-20
      12.4   References	     12-22
                                 12-i

-------
                                TABLES



1Z-1.  Cost Comparison of Conventional and Hybrid Family Cars .  .  .     12-2

12-2.  Characteristics of the Conventional Family Car	     12-3

12-3.  Spark Ignition Engine Cost Parameters   	     12-9

12-4.  C.I. Vs S. I. Engine Component Cost Differentials	     12-12

12-5.  Heat Engine Cost Comparison	     12-21




                               FIGURES



12-1.  Automobile Population Weight Distribution	     12-4

12-2.  Spark Ignition Engine Cost Characteristics	     12-6

12-3.  Estimated OEM Prices of Regenerated Gas Turbines	     12-8

12-4.  Compression Ignition Engine  Cost Characteristics
       (Current)	     12-13

12-5.  Estimated OEM Prices of Rankine  Engines	     12-16

12-6.  Estimated OEM Prices of Stirling Engines	     12-17
                                 12-i.i

-------
                               SECTION 12
               VEHICLE PRODUCTION COST COMPARISON


Cost estimates for the major subsystems of an advanced hybrid vehicle in
volume production were prepared by judging system complexity and perfor-
mance requirements using current hardware cost data wherever available.
The powertrain and vehicle component cost estimates were then used to
construct a total-vehicle-cost comparison between conventional and hybrid
system designs for the family car.  The results are presented in Table 12-1
and an explanation of these  cost estimates is offered  in the succeeding dis-
cussion.
Because the cost estimates reflect assumptions evolved from the current
feasibility study,  a more detailed cost analysis based on one specific hybrid
vehicle design is necessary  in order to refine the figures presented herein.
A study incorporating this analysis  should also link costs with exhaust emis-
sions and fuel consumption.   In this manner, the value  of design trade-offs
can be assessed directly in terms of reduced pollutants  to the atmosphere
as well as vehicle operating economy.
12.  1        CONVENTIONAL CAR COST
The conventional family car is defined as a 3900-lb  (curb weight),  four-door
sedan, equipped with a 230-hp engine,  automatic transmission, air condi-
tioning, power steering, and radio.  These and other features are  shown in
Table 12-2.  The curb weight is  a mean quantity derived from the  U.S.
automobile population weight distribution (see Fig. 12-1),  excluding imports,
compact cars,  station wagons, and prestige automobiles.  The  Plymouth
Fury  I,  the  Ford Custom 500,  and the  Chevrolet Bel Air are prime examples
of U.S.  automobiles which fit this weight category (when equipped  with the
accessories mentioned above).  Each of these vehicles  is offered with a choice
of either a straight six (150 hp) or  a  V8 (230-265 hp) engine at a cost differen-
tial of about $90.  The V8 was  taken  as the standard in  consideration of the
additional engine power required to operate the  standard set of accessories.
                                   12-1

-------
                    Table 12-1.  Cost Comparison of Conventional and Hybrid Family Cars,  $
COMPONENT
• Vehicle
Body
Trim
Glass
Suspension
Steering
Tires
Wheels
Brakes
Miscellaneous
• Power Train
Heat Engine
Fluid Systems
Radiator
Fuel Tank
Exhaust
Electrical
Battery
Battery Charge Control
Starter
Generator
Motor(s)
Generator Control
Motor Control
Ac Rectifier
Drive Train Logic
Electrical Cooling
Gearing (HE to Gen)
Transmission
Drive Line
Different! al(s)
Rear Axle
• Hybrid Sensors & Display Instr.
Air Conditioning
Power Steering
Radio
• Emission Control Equipment
• Total Cost
• Cost Ratio
CONVEN-
TIONAL
VEHICLE

•\



1260



J

635

50
90
30

30
10
45
55
0
0
0
0
0
0
0
205

245

0
I
j 545
j
50
3250
1.0
SERIES HYBRID-
BASELINE
CONFIG.
(S. 1. ENGINE)

•\



1300



J

495

35
90
25

560
125
30
250
400
50
350
30
100
50
60
0
}
245
I
30
|

1
125
4895
1.5
SERIES HYBRID-
BASELINE
CONFIG.
(GAS TURBINE
ENGINE)

-



• 1300



J

920

0
115
35

560
125
30
250
400
50
350
30
100
50
60
0

245

30
]
545
}
50
5245
1.6
PARALL. HYBRID-
BASELINE
CONFIG.
(S.I. ENGINE)

•



1300



J

480

35
90
25

560
125
30
200
350
200
275
30
125
50
60
205
)
350
J
30
1
| 545
j
125
5190
1.6
PARALL. HYBRID -
DUAL MOTOR
CONFIG.
(S.I. ENGINE)

•v



1300



J

480

35
9O
25

560
IZ5
. 0
)
| 500
1
I 250
/
0
ISO
50
0
0
1
i 350
I
30
J
I 545
J
125
4615
1.4
I
PO

-------
       Table  12-2.  Characteristics of the Conventional
                   Family Car
Body Style
Transmis s ion
Engine
Accessor ies

Shipping Weight,  Ib
Accessory Weight, Ib
Fluid Weight, Ib
Curb Weight,  Ib
Dealer Cost, $
List Price,  $
Customer Price,  $
Federal  Tax,  $
Freight (average), $
Total Customer Price,  $
Four-door Sedan
Automatic
230 hp, V8
Air Conditioning,  Power
Steering,  Radio
3600
130
170
3900
2850
3650
3250
158
130
3538
                           12-3

-------
M
I
         o
         t/J
2000

1800


1600


1400
         en* I20°
         LU
         y 1000
         LU
         r  800
         S   600
         CD
             400


             200


               0
                             U.S., EXCL. COMPACTS
                             AND STATION WAGONS
                             U.S. COMPACTS
I/// U.S. STATION WAGONS
                           y*x
                   1500   2000   2500    3000   3500    4000   4500   5000    5500
                                          CURB WEIGHT, Ib

                  Figure 12-1.  Automobile Population Weight Distribution  (based on 1969
                                        new car registrations)

-------
The vehicle cost to the customer  was set midway between the dealer cost
and the retail price,  thus allowing 12 to 15 percent for dealer profit.  By
this method, the cost of the conventional vehicle was found to be $3250
(exclusive  of federal tax and freight charges).   The cost of the components
comprising the powertrain,  accessory set,  and emission control equipment
for the conventional vehicle was set midway between dealer cost and the
retail  price.  The resulting figure of $1990 when subtracted from $3250
yields  $1260 for the cost of the remaining elements designated as vehicle
components (body, suspension, wheels,  etc.).
12. 2        HYBRID CAR COST
12. 2. 1     Vehicle Component Costs
The costs of the vehicle components in  the hybrid system (not including the
powertrain) cannot be estimated accurately at this time, but it seems  likely
that these costs will not differ significantly from those of the  conventional
vehicle. Hence, a value of $1300, which provides a  small allowance for
hybrid-peculiar structural  details,  has been assigned to the vehicle-associated
component set for each of the hybrid cost tabulations.  Additional explanatory
notes concerning the cost breakdown of the powertrain components follow.
12.2.2     Powertrain Component  Costs
12.2.2.1    Heat Engine Costs
The series configuration engine is rated' at 92  hp while  the parallel configu-
ration  engine  is rated at  84 hp.  The costs for the spark ignition engines
were evaluated from the data given in Table 12-3 and plotted in Fig.  12-2
where  specific cost data for automotive  spark ignition engines  are  correlated
with engine rated horsepower.  The  data fit is given  by  the line with the OEM
(Original Equipment Manufacturer) designation,  representing the cost of the
engine as  purchased by a dealer or  distributor from  the  factory.  As a rule of
thumb, the list price can be taken as twice the OEM  cost and this charac-
teristic is  shown in the figure  for information purposes.  The vehicle - installed
purchase price is difficult to estimate.   It is neither  the OEM cost nor the list
 bare engine peak power  output at the engine flywheel

                                    12-5

-------
ro
i
     O.
     .C


     -CO-
     CO
     O
     CJ>

     O
o
UJ
Q_
CO
         10
           1C
                                                                               I     I
                                      ENGINE LIST PRICE
                                            ENGINE INSTALLED PRICE
                                        v  r ENGINE ORIGINAL EQUIPMENT
                                               MANUFACTURE COST
                                                                               I	L
                                           10 2
                                   RATED HORSEPOWER, hp
10
                       Figure 12-2.  Spark Ignition Engine Cost Characteristics

-------
price of the engine purchased as a component, but may lie between these
two quantities.  The  installed-price characteristic shown in  the figure is i\
crude estimate based on  the OEM cost, to which has been added a 25 percent
allowance for assembly-line  installation expense and manufacturer /dealer
profit.
For  the gas turbine there is no production base from which high production
engine prices inay be estimated.  Various estimates have been made which
give relative costs between engine types, but these are of limited usefulness
unless all of the hardware details are clearly established.  In this report,
costs for the gas turbine engine are based on a dual  shaft,  free turbine,
recuperative engine design that does not require a transmission for delivering
torque to the rear wheels.  It has a  bsfc under 0. 6 Ib/hp-hr  at design rating.
In the absence  of any definitive study on the  subject,  the following technique
was  used in estimating costs.  Costs were predicated on a dollars per pound
basis with  consideration  of the type  of materials being used.   A factor was
employed to account  for the  fixed per unit costs for such items as controls,
ignition system,  lubricant pumps, and other accessories.  These costs do
not include the amortization of the fixed cost of development  and  initial tooling,
but are  based on  strictly the recurring costs of production.
The  gas turbine costs are shown as  a function of engine brake horsepower
for three different production levels in Fig.  12-3.  For purposes of estimating
costs in Table  12-1,  it was assumed that engine production rates exceeded
100,000 units per  year,  and  a 25 percent  allowance for assembly-line instal-
lation expense  and manufacturer/dealer  profit has been added on to the costs
given in Fig. 12-3.
Although not pertinent to the  cost breakdown given in Table 12-1,  data for
compression ignition engines were acquired in the course of  this study and
are included in the current discussion since future studies may benefit from
this  information.  These costs were used to estimate rough comparative
values shown in Table 12-4.  The OEM cost and list  price characteristics
for compression  ignition engines are shown  in Fig.  12-4.  As seen by  com-
paring these  data with those in Fig.  12-2, current cost/price levels for
                                   12-7

-------
   200
    00
e-  50
CO
o
0  20
     10
              PRODUCTION  RATE
                     1-100
                                        lOK/yr
                                        lOOK/yr
             20                100         300
                   BRAKE  HORSEPOWER OUTPUT
       Figure 12-3.
Estimated OEM Prices of Regenerated
Gas Turbines
                            12-8

-------
                             Table 12-3.  Spark Ignition Engine Cost Parameters
Make
Alfa Romeo
American Motors
American Motors
American Motors
American Motors
American Motors
American Motors
American Motors
American Motors
American Motors
American Motors
Br iggs-Stratton
Br iggs-Stratton
Br iggs-Stratton
Br iggs-Stratton
Br iggs-Stratton
Model
Giula 1300
Jeep 4L
Jeep 4F
Hornet
Jeep 155
V6-225
Hornet SST
Ambassador
Ambassador SST
AMX
Rebel SST
200-400
233-400
243-430
300-420
370-420
Application
A
A
A
A
I
A
A
A
A
A
A
I
I
I
I
I
Rated'11
HP
89
60
70
128
136
142
145
150
210
245
330
8
9
10
12
14
Cost
($ List)
1100


800
750

850




244
247
258
320
334
Cost
($ OEM)

403
407
350
412
412
336
348
461
489
625





$ OEM



0.44
0.55

0.40









$ OEM**
HP
6. 19*
6. 72*
5.82*
2.74*
3.02
2.90*
2.32*
2.32*
2.20*
1.99*
1.90*
15. 10
13. 70
12.90
13.30
11. 92
i
sO

-------
                       Table 12-3.  Spark Ignition Engine Cost Parameters (Continued)
Make
Ford
Ford
Ford
Ford
Ford
Ford
Ford
Ford
Ford
Ford
Ford
General Motors
General Motors
General Motors
Model
V4-91
4-172
V4-104
Mustang
Galaxie
6-300
330HD
361EHD
391EHD
V8-477
V8-534
Chev. 250L6
Chev. 292L6
Chev. 366V8
Application
I
I
I
A
A
I
I
I
I
I
I
T, B
T, B
T, B
Rated11 >
HP
58
68
70
120
150
165
190
200
235
253
266
155
170
235
Cost
($ List)
818
918
858
936
1110
1144
1122
1462
1620
2644
Z704
729
753
1196
Cost
($ OEM)
409
459
429
468
555
572
561
731
810
1322
1352


$ OEM
$ List
0. 50
0. 50
0. 50
0. 50
0.50
0. 50
0.50
0. 50
0. 50
0.50
0.50


**
$ OEM
HP
7.05
6.75
6. 12
3.90*
3.68*
3.47
3.06
3.65
3.45
5.06
4.86
2.35*
2.21*
„<.
2.54"
tSJ
I

-------
                          Table 12-3.   Spark  Ignition Engine Cost Parameters  (Concluded)
Make
International
Tecumseh
Toyota
Toyota
Toyota
Volkswagen
Volkswagen
Volkswagen
Model
BO-308
H4-120
Corolla
Corona
Corona Mkll
1200
1600
1500
Application
T
I
A
A
A
A
A
A
Rated'1'
HP
154
12
60
90
108
36
53
65
Cost
($ List)
1278
252
819
858
957
500
600
575
Cost
{$ OEM)








$ OEM
$ List








$ OEM"""
HP
4. 15V
10. 50
6.80*
4.77*
4.43"
6.95*
5.67*
4.40*
ro
i
           Key:

           A     Automobile
           B     Bus
           I      Industrial
           T     Truck
           OEM  Original Equipment Manufacturer
           *     Indicates data plotted
           **     Based on $ OEM = 0. 50 $ List
            (1)
Bare engine peak power output at the engine flywheel

-------
              Table 12-4.   C.-I.  Vs S.I.  Engine Component Cost Differentials
+ C. I. Components
Component
Injection System
Turbocharger
Glo Plugs
Speed Governor
TOTAL
$ List
440
300
12
	

$ OEM
220
100
6
	

$ OEM, H. P/::
110
50
3
	

+ 25%
138
62
4
	
+204
Notes - $ List
Roosa- Master
Garrett Corporation
Four Cylinder Engine
Included in Injection Pump

- C. I. Components
Carburetor
Fuel Pump
Distributor
Coil/Spark Plugs
TOTAL
50
8
25
8

25
4
12
4






31
5
15
5
-56





Net C. I. Differential Cost = 204 - 56 = 150
'H. P. = High Production Rate  =  0. 50 ($ OEM)

-------
   100
-CO-
CA)
8
UJ
Q_
CO
10
      10
                      •   AUTOMOTIVE

                      O   INDUSTRIAL
                                                    ENGINE LIST PRICE
                                                 ENGINE OEM  COST
                                          100

                              RATED HORSEPOWER ,  hp
1000
               Figure 12-4.  Compression Ignition Engine Cost Characteristics

                            (Current)

-------
diesel engines run 2. 5 to  3. 5 times higher  than those for spark ignition
engines (ZO to 100 hp).  This is largely due, it is felt, to the influence of
production quantity on manufacturing cost.   In this  connection,  it may be
noted that the yearly production of diesel engines in the U.S. barely totals
360,000 units compared with 9  million units for spark ignition engines rated
20 hp and above  (Refs. 12-1 and 12-2).
It is postulated that if the diesel industry were appropriately geared for
high volume  production,  the cost of the basic engine (i.e., block, heads,
pistons,  crankshaft, camshafts, valves) might be reduced to a value that
would be nearly  (though perhaps not exactly) comparable to the  cost of the
basic S. I.  engine.  If this premise is accepted, then it  is possible to  define
the  differential cost of the engines (C. I. versus S. I. ) in terms of the  cost of
system-peculiar auxiliary equipment required for  engine operation.   Table
12-4 attempts to develop a reasonable estimate of this differential cost for
the  hybrid family car  application by comparing the  auxiliary equipment
requirements and costs for  small (70-100 hp)  diesel and spark ignition
engine systems.   It will be noted that a generous  (50 percent) allowance has
been made for diesel  component cost improvements which might conceivably
be brought about by the economics of high production automation techniques.
Nevertheless, the diesel engine still  shows  a cost increment of $150 relative
to the S. 1. engine (this estimate may be low).  Assuming a nominal horse-
power  requirement for the family car of, say, 80 hp, and,  using  Fig.  12-2
for  S. I. engine installed price  characteristics as a base, the C. I. engine
would cost $625  installed, compared  to $475 for  the S. I. engine (30 percent
higher ).
Since there is very limited data available for assessing costs of a Rankine
engine, the estimate must be considered very tentative.  Compared to the
gas turbine,  the  principal cost increase in  the Rankine  system will be found
with the heat exchangers; e.g.,  the boiler will probably be constructed of
stainless  steel or material of similar cost.  The cost will also  be very much
dependent upon the design bsfc specified since heat exchanger size will be a
                                   12-14

-------
function of the desired bsfc.  Rankine  cycle estimated costs based on an
engine bsfc of 0. 85 are presented in Fig. 12-5 for three levels of produc-
tion rate.  These estimates are based on data presented in Refs. 12-3,
12-4,  12-6,  12-7, and 12-8.
Figure 12-6 shows estimated cost of a Stirling engine based on data in
Refs.  12-4 through 12-8.   Here, cost  is figured at the same  dollars per
pound  as the Rankine engine.  However, there is an even higher degree
of uncertainty in this case because of the less developed state of the engine.
It is entirely  possible that the engine can be reduced in weight below that of
the Rankine engines and, since the ratio between heat exchanger and power
generator weights is  lower for  the Stirling engine, the cost would be lower.
Development  costs might be higher because of the less advanced state of
present development,  but tooling costs might  be slightly lower  than  for the
Rankine engine.
12.2.2.2   Exhaust Emission Control Costs
To the heat engine costs must be added the additional costs associated with
advanced emission control  equipment.   The emission control features of Lhc
spark  ignition engine would include lean operation, exhaust gas  rec ir culation,
and catalytic  conversion; the emission control features of the compression
ignition engine would include exhaust gas recirculation and, possibly,  cata-
lytic conversion; and the gas turbine engine assumes the utilization  of a
thermal reactor  for control of hydrocarbon emissions  for costing purposes.
At the  present time,  it is necessary to speculate that the.se costs will not
differ  significantly between  the spark ignition and compression ignition
engines.  A value.of $125 is assigned to the costs for the internal combustion
engines and a value of  $50 is assigned  to the cost for the gas  turbine engine.
12.2.2.3   Battery Cost
The battery cost for the hybrid vehicles is for a nickel-zinc system required
to meet the baseline propulsion  system weight allocation.  The cost estimate
was arrived at through consideration of  contemporary  lead-acid batteries and
                                   12- 15

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   200
   100
en
8  50
    20
     0
PRODUCTION RATE
       -100
                                        lOK/yr
                               100         300
                   BRAKE  HORSEPOWER  OUTPUT
             Figure 12-5. Estimated OEM Prices of
                         Rankine Engines
                            12-16

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   200
-co-
 o
    100
    50
    20
     10
PRODUCTION RATE
       -100
                                          lOK/yr
       lOOK/yr
              20               100         300
                  ,  BRAKE  HORSEPOWER OUTPUT
              Figure 12-6.  Estimated OEM Prices of
                          Stirling Engines
                             12-17

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the relative costs between different classes of batteries given in Section 7.
At the present time, cost of a Sears Diehard lead-acid battery to the customer
is about 2-1/2 cents per W-hr at the nameplate rating.  Golf cart batteries
will cost about twice as much.   Because of refined manufacturing techniques
and additional plate area, the battery for hybrid vehicle application will cost
more than the present day SLI battery so a figure of 3. 0 cents per W-hr was
estimated  on  an OEM basis.  Through ratio of the relative active material
costs between battery systems,  the cost of a nickel-zinc battery would then
be 7. 5 cents per W-hr and for 7470 W-hr installed battery capacity the cost
is $560.
12.2.2.4   Electrical Component Costs
The costs  of the  DC electric  drive  motor ranges from $350 to $400.   This
cost quotation is based on an estimate obtained from the General Electric
Company,  D.  C.  Motor and Generator  Department,  for quantities of 100,000
or more.  In  contrast, present low production costs of a 60 hp,  2500 rpm
base-speed motor of the type that would be used on  a hybrid vehicle  would
cost approximately  $3500 to $5000  in quantities of six or less  on the present
market, according  to General Electric.
The AC  generator costs are somewhat  less than the  DC motor costs of the
same rating due  to  the fact that  they are simpler in construction and contain
less material because they are smaller.  Also,  no overload requirement
exists for  the generator.  Based on these considerations,  the  cost range  for
generators is estimated to be from $200 to $250.
The electrical controls and logic are estimated to cost from $500 to $800 at
present  day prices  in quantity production of 100,000  or more.    These figures
are probably  the least reliable of all the cost estimates contained in the
report.  The  reasons for  this are the following:
      1.    A production cost estimate  is not available at  this  time from
            industry for even small quantities  of equivalent power  handling
            devices.  The closest device that was quoted for small quantities
            (six or  less) was from  General Electric, Automation Produc.tH,
            Salen,  Virginia.  They estimated a cost  of $7SO to $800 fur a
                                   12-18

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            72 volt maximum, 250 ampere rated chopper with pulse frequency
            control.  This would be just for the motor  control and would not
            include the generator control,  battery charge controls,  rectifiers,
            and drive train logic.
      2.    Cost estimates  of future  production are  very difficult because
            costs  of some parts have been coming down (such as SCR's)
            while  others have been increasing  and also the cost of labor
            is at best difficult to predict and is the greater part of the cost.
            The only alternative is to base a rough estimate on costs of
            labor, materials, overhead and profit, assuming present day
            prices.  Materials costs were estimated on the basis of costs
            for  similar circuits developed under U.S.  Government military
            programs.   Labor costs were estimated to be three times the
            material costs  and a 25 percent factor was added to the  combined
            labor and material costs to account for overhead and profit.
Motor/generator costs for  the series configuration  vehicles tend to  be some-
what higher than those  using the parallel configuration.  This  is because  the
drive motor and generator  for series operation must be sized to provide  or
accommodate all the power required at the wheels,  whereas,  in the parallel
case, the drive motor and generator need only be sized to supplement the
mechanical power supplied by the heat engine.   The  separate-field-
excitation feature of the dual motor configuration provides  sufficient torque to
start the heat engine,  obviating the  need for a  separate starter.  This feature
also permits a simpler motor control  circuit design and accounts for the
lower motor control cost estimates relative to the baseline (single motor concept)
parallel system which employs SCR's  for this  purpose.  In the  separately-
excited field case, only the field current passes through the control circuit,
reducing the power handling requirement.  The transmission is eliminated
in the dual motor  design since the torque characteristic of an all-electric
drive is provided  by the second motor/generator operating through the
planetary differential.
12.2.2.5   Drive Line and Fluid System Costs
The cost assigned to the drive line/differential for the  parallel system
vehicles is higher than that of the conventional vehicle  design.   In the base-
line case, this is because additional gearing linking the motor/generator  to
                                   12-19

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the output shaft is required; in the dual motor  case,  the higher cost reflects
the additional economic burden imposed by the requirement for two differ-
ential mechanisms.
Slight differences in the fluid system costs among the different vehicles
primarily reflect the influence of such factors as heat engine.size and
specific fuel consumption (SFC) characteristics.
12. 3        APPLICATION OF RESULTS FROM COST ANALYSIS
The tabulation results  (Table 12-1) given by the  Total Cost and Cost Ratio
entries should be approached with caution,  giving due regard to the precise -
ness  of the assumptions made in the cost analysis.   The numbers indicate
that the series/gas  turbine and baseline-parallel/spark ignition engine con-
figurations are most expensive at a cost ratio  of 1, 6, while the series/
spark ignition  engine and dual motor/spark ignition engine configurations
have  cost ratios  of  1. 5 arid 1.4, respectively.   The hazard of assigning
significance to the relative magnitudes  of the cost ratio is apparent when it
is recognized that to arrive at production costs it has been necessary to
estimate figures for a number of critical components which at present may
be barely classified as being in a conceptual design phase.  Therefore,  it is
recommended  that the  indicated range of the cost ratio be regarded as the
tolerance on a general estimate of 1. 5 for the  cost ratio of the  several
hybrid vehicles investigated.
The study indicates that only the spark ignition engine and the gas turbine
engine offer reasonable weight margins for the battery system  and, for  this
reason, only detail  costing of these could be justified. The theoretical
family car constructed using Diesel,  Rankine, or Stirling engines would have
higher weights and probably reduced  performance.   These car  costs could
not be realistically  compared to those in Table 12-1. However,  a  relative
vehicle cost estimate (Table  12-5) can be generated  if an oversimplifying
assumption were made that the cost differentials of these  hybrids varied by
virtue: of relative heat engine costs (remembering  that the specification*)
differ).  Relative costs for the  engines  are compared with the spark ignition
                                   12-20

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engine installed in the hybrid in the table below.   In addition,  relative vehicle
coats are compared with those of a conventional  spark ignition car.

               Table  12-5.  Heat Engine Cost Comparison

                                                     Approximate
                                 Approximate       Relative Hybrid
          Heat Engine       Relative Engine Cost    Vehicle Cost

     Conventional Car                 	               1
     Hybrid Spark Ignition            1                  1.4-1.6
     Hybrid Diesel                    1.5                1.5-1.7
     Hybrid Gas Turbine              2                  1.6
     Hybrid Rankine                  3. 75               2
     Hybrid Stirling                   5                  2. 25
                                   12-21

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12.4       REFERENCES
12-1.    "Internal Combustion Engines, 1968, "U.S. Department of Com-
         merce,  Bureau of the Census  Publication, 16 April 1970.

12-2.    Automotive Industries,  15 March 1970.

12-3.    J. W. Bjerklie and B. Sternlight, "Critical Comparison of Low
         Emission Otto and Rankine Engine for  Automotive Use, " SAE
         Paper,  13-17 January 1969.

12-4.    D.  Friedman,  "A Feasibility Study of Emission Limited Vehicles
         for Philadelphia's Central Business  District," General Motors
         Research Laboratories, 24 June 1968.

12-5.    L. R. Hafstad, "Testimony Before Subcommittee on Air and Water
         Pollution," U.S. Senate, 27 May 1968.

12-6.    Morse,  et al,  "The Automobile and Air Pollution: A Program for
         Progress. Part I&II.  Report of the Panel on Electrically Powered
         Vehicles,"  U.S. Department of Commerce.

12-7.    S. W. Gouse,  "Automotive Vehicle Propulsion," Advances in Energy
         Conversion Engineering, Transaction's 1967 ICCEC Conference,
         13-17 August 1967.

12-8.    J. A.  Hoess, et al,  "Study of Unconventional Thermal,  Mechanical,
         and Nuclear Low-Pollution Potential Power Sources for Urban
         Vehicles,"  Battelle Memorial Institute Report,  15  March  1968.
                                  12-22

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               SECTION 13






TECHNOLOGY DEVELOPMENT PROGRAM PLAN

-------
                              CONTENTS
13
TECHNOLOGY DEVELOPMENT PROGRAM PLAN 	
13. 1 Introduction 	
13.2 Recommended Hybrid Vehicle System Design
for the Family Car 	
13.3 Recommended Development Program 	
13. 3. 1 Phase I - Detailed Hybrid System Analysis
and Expanded Data Base 	
13.3. 1. 1 Vehicle Configuration 	
13.3.1.2 Powertrain Elements 	
13.3. 1.3 Expanded Data Base 	
13. 3. 1.4 Comparative Evaluation of
Hybrid Automobile 	
13.3.1.5 Hybrid System Performance
and Cost Analysis 	
13.3.1.6 Program Schedule 	
13. 3.2 Phase II - Component Advanced
Technology 	
13.3.2. 1 Advanced Internal Combustion
Engines 	
13.3.2.2 Advanced Gas Turbine 	
13.3.2.3 Batteries 	
13.3.2.4 Component Design Evaluation . .
13.3.3 Phase III - Test Bed and Prototype
Vehicle Development 	
13.3.3.1 Analyses 	
13.3.3.2 System Design Detail 	
13. 3. 3. 3 Specification Release and
Contract Definition 	
13-1
13-1

13-2
13-5

13-6
13-6
13-8
13-10

13-12

13-13
13-15

13-15

13-15
13-17
13-18
13-18

13-18
13-20
13-20

13-21
                      13.3.3.4   Hardware Design,  Development,
                                 and Fabrication	    13-21
                                 13-i

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  CONTENTS (Continued)
13. 3. 3. 5   Component Test and
           Evaluation	    13-22
13.3.3.6   Static Interfacing Tests	    13-22
13. 3. 3. 7   Vehicle Assembly and Final
           Component Integration	    13-22
13. 3. 3. 8   Vehicle System Tests and
           Evaluation	    13-23
13.3.3.9   Prototype Vehicle Program .  .  .    13-23
13.3.3.10  Test Bed Vehicle Program
           Schedule	    13-24
            13-ii

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                               FIGURES









13-1.   Hybrid Electric Recommended Development Schedule  .... 13-7




13-2.   Schedule of Work Effort -  12-Month Program  .  .	13-16




13-3.   Test Bed Vehicle Development Program Schedule	13-25
                                 13-iii

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                              SECTION 13
            TECHNOLOGY DEVELOPMENT PROGRAM PLAN
13. 1        INTRODUCTION
The intent of presenting a development program in this report is to provide
APCO with a planning document for ensuring the early availability of a low
emission, viable alternative to the conventional automobile.  This document
defines  the specific  tasks to be accomplished and the corresponding schedule
of activities.  The entire three-phase program is  directed toward the
passenger car since this vehicle is by far the major contributor of air
pollutants from  mobile sources and is expected to receive the greatest
emphasis from government and industry.   The  first phase covers a detailed
performance analysis for providing a finer definition of vehicle operating
and production costs; an expanded data base on heat engine  emissions and
battery  characteristics forms  a basic part of the effort which includes cost
and performance comparisons with advanced heat  engine-driven automobiles.
The second  phase entails the development of advanced versions of heat
engines and batteries designed to operate in the hybrid mode.  The third
phase encompasses  the hardware definition and development necessary for
an early test bed vehicle as well as  for a later prototype vehicle.
The development program recommended would result in a prototype
vehicle  that would meet performance  goals and the 1975/1976 emission
standards in approximately four  years.   An important step  in this develop-
ment is  the  construction of a test bed vehicle; it would be available for field
testing  in about  two years.  The  reasons that a test bed-type vehicle,  rather
than a sophisticated prototype, is selected are twofold:
      1.   An instrumented vehicle with tailored components for early
            field testing is essential for resolving interfacing problems
            and  for determining the  response of all components and
                                  13-1

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            subsystems to the automotive environment presented by
            actual urban driving situations.
      2.     Selection of a test bed concept allows for more flexibility
            of design goals and for gathering of more data on component
            and vehicle performance than a polished hybrid.

The test bed vehicle is expected to demonstrate marked improvement in
exhaust emissions over current conventional cars, but will likely not meet
all the 1975/1976 performance goals or emission standards;  the HC and CO
values are likely to be met, but NO2 values  may be exceeded by a factor
of 2 to 3.   Component advanced technology programs will be  conducted
concurrently with the  test bed phase of the program for introduction into
the later second generation vehicle.  This vehicle, a prototype design,
will have received sufficient design review to ensure that high production
rates are both feasible and cost effective.  It will  also have received the
benefits gained from  experience with the environmental test bed vehicle.

The study indicates that the bus might make an attractive hybrid heat
engine/electric vehicle (mainly because of the ease of attaining  proper
batteries).  But for this case, only more  study or analysis is warranted
at this time.  The major factors which prevented performing this analysis
during the  study were: (1) insufficient realistic driving cycle data, (2)
lack of bus  emission  standards, and (3) inadequate emission data from
current buses to be used for comparative evaluation. A bus  study  program
is recommended which would collect or generate these three factors and
use them in the computed analysis of performance and emissions.
13. 2         RECOMMENDED HYBRID VEHICLE SYSTEM
             DESIGN  FOR  THE FAMILY  CAR
Two system designs are recommended to provide  greater assurance of
early development of the hybrid prototype.  Versions using the internal
combustion spark ignition engine and the gas turbine  are the  only two
heat engines that offer the combination of near term availability with low
                                    13-2

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emissions and also provide acceptable vehicle performance without
requiring unreasonable battery power/energy density goals.  The spark
ignition engine version will make the 1975/1976 goals, but with little
margin for the family  car as specified in this study.  The turbine has the
potential of exceeding  the goals and might lead to more acceptable post-1975/
1976 vehicles.  However, the gas turbine  engine for use  in automobiles is
not as  advanced in technology as  the spark ignition engine and thereby
results in a higher  risk program.

The recommended hybrid electric vehicle configurations are as follows:
      1.    A parallel mode configuration, powered by a spark ignition
           heat engine with lead-acid batteries for energy storage, dc
           traction motor(s) for acceleration power, an SCR-augmented
           control system  designed for varying motor voltage and
           separately excited field power, and an engine-driven
           generator  (or alternator) for recharging the batteries.
      2.    A series mode configuration,  powered by a gas turbine heat
           engine with lead-acid batteries for energy storage, a dc
           traction motor for acceleration power,  an SCR-augmented
           control system  designed for varying motor voltage and
           separately excited field power, and an engine-driven
           alternator for recharging the batteries.

The rationale used  in selecting the aforementioned configurations is as
follows:
      L    The  rpm range  for a  spark ignition engine is compatible with
           transmission/wheel rpm and is merely another application of
           current design experience;  no gear  reduction system is
           required between the heat engine and the remainder of the
           powertrain.
      2.    Because the spark ignition engine operates at less than
           5000 rpm, a dc generator may prove to be as light and
                                    1 3-3

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      efficient as an alternator in recharging the batteries,
      particularly since, as vehicle speed increases,  the generator
      output will be  controlled down to lower output (almost zero);
      for the dual motor design, power generation is inherent in
      the motor/generator system and a separate generator no
      longer forms part of the design.   A dc generator can also
      use battery power directly for  starting the heat engine.
3.    The higher rpm associated with a gas turbine should prove
      to  be  compatible with the rpm range for alternators and, with
      no mechanical link to the wheels in the series mode, gear
      reduction systems are not necessary.
4.    Direct current motors appear to offer adequate performance
      for passenger car service'although they are not the lightest
      motor available (considering motor control systems as  part
      of  the weight definition).  However, the weight (and size)
      differential is not  great enough to offset the gains from  control
      system  simplicity, past experience in vehicular applications,
      and torque characteristics that are well matched to vehicle
      needs over a wide speed range.
5.    The control system  specified offers considerable flexibility
      in  application  which is essential  to solution of design problems
      that may arise once all powertrain elements are integrated  on
      the test bed vehicle.
6.    Lead-acid batteries are selected since they have the greatest
      experience factor,  are not prohibitively costly,  and appear
      to  have  the best near term potential for marked increases in
      performance.   Nickel-zinc batteries,  because of their current
      underdevelopment but future potential for  even greater
      increases in performance, might eventually replace lead-acid
      batteries.
                              13-4

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      7.     With respect to modes of operation, the parallel configuration
            appears to offer more promising performance (e. g. ,  battery
            requirements, fuel consumption).  However, it may present
            more problems in design and fabrication than the series
            configuration because of its greater complexity in some
            design areas (due, for example,  to the direct mechanical
            link between the heat engine/generator and the rear wheels).
13. 3         RECOMMENDED DEVELOPMENT PROGRAM
A  development effort contingent  on results from early analyses of the
hybrid automobile has been formulated in three phases. In brief,  the
first phase  should be aimed at a finer definition of important hybrid
parameters both via expanded analysis and data collection.   A study should
be performed to  define in greater detail  the hybrid vehicle production and
operating costs since  costs are an important parameter in determining if
the hybrid is a viable  competitor to the conventionally powered automobile.
Particular emphasis should be placed on defining in greater detail the
operating requirements  and costs for the vehicle control system.  In
addition to the cost analysis,  a performance analysis should be conducted
to a level of depth greater than was performed in this feasibility study.
Acquisition  of component test  data is needed to support this analysis.  A
very important area for expanded data collection is in the engine  emission
area.  Here,  information on engines operating in the hybrid mode are
needed to strengthen the data base used for analysis.  A comparative
analysis  between cars using hybrid heat  engine-electric powertrains and
those using  advanced internal  combustion or gas turbine engines should also
be made  to  determine the relative advantages or disadvantages of the
hybrid concept as a means of reducing auto pollution.   Recommendations
for additional work effort in Phases  II and III are  of course highly
dependent on the results of studies conducted in Phase  I.

The second  phase should consist of an intensive effort to develop  critical
powertrain  components destined for  a prototype vehicle.  This would
                                    13-5

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include advanced technology work on engines and batteries designed to
operate in the hybrid mode.

The third phase encompasses the hardware definition and development
necessary for an early test bed vehicle as well as for a later prototype
vehicle.   Figure 1 3-1 shows a schedule of activity for the three phases of
recommended hybrid heat engine/electric system efforts.  The details of
each phase of the recommended work effort are discussed in the subsequent
sections.
1 3. 3. 1      Phase I  -  Detailed Hybrid System Analysis
             and Expanded Data  Base
A logical  progression from the current feasibility study would be a study
directed at an in-depth analysis of the hybrid vehicle powertrain in a
passenger car application.   Thus,  in a study narrowed in scope,  the more
intricate details of component operation and installation in the vehicle can
be examined.  The analysis  is fundamental to establishing a firmer basis
for objective evaluation of the hybrid electric vehicle in terms of exhaust
emissions and costs when compared to present and  projected versions of
the engine-driven passenger car.  A four-part  effort covers analysis of
vehicle/powertrain/component performance, data acquisition for an
enlarged data base, a component and system cost analysis, and a
comparison of hybrid versus engine-driven cars based on costs,  exhaust
emissions, and  fuel economy.
13.3.1.1     Vehicle Configuration
Since APCO has consistently emphasized the importance of reduced
exhaust emissions  for a general purpose passenger automobile,  the
study should be  limited to examining a. hybrid heat engine/electric version
of  this type of vehicle.  The following components should be examined in
depth in parallel and/or series powertrain configurations:
      1)    heat engine
      2)    batteries
                                    13-6

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OJ
i
                                                          YEARS
                                                      2       3
PHASE I - ANALYSIS  8 DATA
         ACQUISITION
   PERFORMANCE ANALYSIS
   DATA ACQUISITION
   COST ANALYSIS
   POWERTRAIN COMPARISONS
   DECISION WHETHER TO
   PROCEED WITH TEST BED
PHASE n-ADVANCED TECHNOLOGY
   RESEARCH
   DEVELOPMENT
PHASE m-SYSTEM HARDWARE
   TEST BED
   PROTOTYPE
                                           	L
                           Figure. 13-1.  Hybrid Electric Recommended
                                       Development Schedule

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      3)    generator
      4)    motor
      5)    transmission/gearing
      6)    control system

The  complete powertrain and the vehicle system should also be analyzed.
The  parallel configuration should be examined for both the single motor
and dual motor concepts because the dual motor concept offers superior
operating flexibility but the efficiency remains to be defined.
13.3. 1.2    Powertrain  Elements
      ( 1)    Heat Engines
             The following heat engines were selected for further
             examination in the study because of their near term
             potential for marked reduction in emissions as well
             as noted qualities.
             (a)     Internal combustion spark ignition
                         reciprocating conventional - best known and
                        most research accomplished
                         reciprocating stratified charge - good potential
                        for lean operation without weight growth
                         reciprocating dual chamber concept - good
                        potential for lean operation
                        rotary Wankel - light weight and low  cost
                        potential
             (b)     Gas turbine
                        single vs dual shaft designs -  cost vs operating
                        flexibility
                         recuperating vs non-recuperating designs  -
                        cost and weight vs fuel economy
             (c)     Internal combustion compression ignition - cursory
                    review  of dual  chamber  concept to update cost,
                                    13-8

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              weight and emissions and re-establish ranking with
              regard to other engine classes.
(2)     Batteries
       Only the lead-acid battery should be considered with the
       charge and discharge  characteristics varied in order to
       observe  the effect on exhaust emissions and energy density.
       Thus,  required operating characteristics can be specified
       in more  detail.
(3)     Generator
       Only alternators should be considered,  and their superior
       weight and efficiency to be re-examined in light of
       component cost.
(4)     Motor
       The following motors  should be considered with one to  be
       selected on the  basis of a balance between cost, weight, and
       efficiency:
             AC induction
             DC shunt  wound - externally excited field
             DC compound wound
             DC series wound
(5)     Transmission/Gearing
       A  simple fluid coupling transmission should be utilized from
       a weight and cost standpoint for  the single motor parallel
       configuration.   Both differential and planetary gears should
       be considered for motor  power transmission in the other
       configurations.
(6)     Control System
       The following elements should be considered in terms of
       effect on electric circuit cost, reliability, operating
       flexibility and efficiency:
                              13-9

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                   silicon controlled rectifiers
                   re sis tors/inductors/capacitors
                   relays/switches
             Wherever possible, manual control should be evaluated
             for cost savings potential.
1 3. 3. 1.3    Expanded Data Base
A major effort in the study program should be the establishment of an
expanded data base for the powertrain components.  This could be
accomplished in two ways:  (1) through planning and conducting of tests
on specific component hardware to define performance maps over the
entire operating range,  and (2) through consultation with component
manufacturers and reliance  on  their existing and projected data.  These
discussions with manufacturers should also provide a means of assessing
the cost factors associated with variations in component operation.

Three major subsystems appear to need markedly increased scrutiny
before a major  funding effort for hybrid vehicle hardware  can  be  initiated.
These are:  (1) heat engines (advanced internal combustion engines and
gas turbines); (2) motor/generator control systems; and (3) batteries.

Assessing and developing the full potential of the hybrid vehicle with
respect to meeting and surpassing future vehicle exhaust emission  standards
will require the acquisition of more  engine exhaust emission data.  The
variation of emissions at part-load conditions can be very critical in
determining exhaust emission characteristics of the hybrid vehicle. While
a comprehensive evaluation of all available data was made in the  present
study, it was also discovered that a  shortage o.f steady-state mass  emission
data,  particularly at part-load  conditions, existed in the open  literature.

Due to driveability constraints  in the case of the spark ignition engine-
driven automobile, the requirement  for transient acceleration power limits
the extent to which some advantage can be gained from lean operation.
But, since the  engine runs at essentially steady-state  for the hybrid vehicle,
                                    13-10

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the limit of lean air/fuel ratios can be extended to take advantage of the
reduction in CO and particularly the NOX emissions.  However,  such data
for the extreme air/fuel ratios are  limited at present,  and a more
vigorous effort should be made to examine and evaluate the options
available  to the engine designer for meeting air/fuel ratio goals  of about
1 9 and greater.

Furthermore, for all candidate heat engines,  the techniques to minimize
both exhaust emissions and fuel consumption at the desired part-load
conditions should be examined. An emission data acquisition program
should be instituted which would include the running of  selected engines
at the desired engine operating points.  Acquisition of these data would
provide a firmer base from which to determine the most  suitable heat
engine for the hybrid vehicle from the standpoint of potential for reducing
atmospheric pollution.

Data are needed for the following  engines  operating in the hybrid mode.
      (1)     Advanced internal combustion engines operating in  the lean
             regime
             (a)     Spark ignition engines
                        modified conventional engine
                        stratified charge engine
                        pre-chamber engine
                        modified rotary (Wankel) engine
             (b)     Compression ignition engine (cursory examination)
                        modified diesel engine (low NOX, lightweight)
      (2)     Gas turbine
                    single and dual  shaft
                    recuperated and non-recuperated
                                    13-11

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The complete operating maps for these engines should be compared with
the operating maps of the electrical components in order to define the
interface relationships of power and rpm that are crucial for maintaining
low emissions and high overall efficiency resulting in low fuel consumption.

Through discussions with hardware manufacturers and the further
clarification of electrical component operation in the hybrid car that will
be accomplished in the Phcise I effort, the electrical and electronic
elements of the subsystems in the overall vehicle control system can be
defined.   This step is necessary in order to confidently predict the
production costs associated with the entire  electrical system.  The
control system circuit design should also be examined from the viewpoint
of reliability and maintainability as well as first costs,  and the complexity
should be evaluated in  terms of heat engine operating modes and the degree
of manual control that  could be realizeable.

As part of the  Phase I  effort to improve  the data base, performance of the
latest lead-acid batteries should be documented.  Test data should include
charge/discharge characteristics,  temperature effects, and in particular
cycle lifetime  at shallow discharge.  These data should be supplemented
with test  results for  high power density  cells that are under laboratory
development.   If control system operation induces transient currents at
the battery terminals,  the  resultant effects on battery lifetime should be
ascertained.
1 3. 3. 1.4    Comparative  Evaluation of Hybrid Automobile
To provide an  expanded critique of the hybrid electric system one further
evaluation merits inclusion in Phase I studies.  This relates to comparing
the advanced version of the hybrid electric  passenger car with advanced
versions  of engine-driven passenger cars.  Because of near-term
potential  for use in cars, only the spark ignition and gas turbine engines
are recommended for powerplants to be  included in  each vehicle's
powertrain.  For equivalent performance in terms of acceleration,  cruise
                                    13-12

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speed, and gradeability, the respective systems  should be compared on
the basis of production cost, exhaust emissions,  and fuel consumption.
1 3. 3. 1.5    Hybrid System Performance and Cost Analysis
Finally,  in addition to establishing a solid basis for estimating comparative
hybrid passenger vehicle emission levels and production and operating
costs, the proposed work effort should also provide a definitive package
of information that is required prior to implementation of hardware
assembly for a test bed vehicle and prior to implementation of fully funded
development programs for a prototype vehicle.  This information package
should consider such items as:
      (1)     recommended powertrain design and vehicle weight and
             powertrain weight allocations,
      (2)     performance specifications for  each major component in the
             powertrain for the test bed and prototype vehicles based on
             vehicle  specifications  to be defined  for acceleration,  cruise
             speed, and gradeability,
      (3)     rationale for powertrain design and component selection
             including trade-offs between cost, exhaust emissions, fuel
             consumption,  and reliability,
      (4)     vehicle  performance capabilities including the  effect of
             various driving cycles and cold-start  on exhaust  emissions.

In compiling this information package, it is estimated that the following
work effort will have to be accomplished: First, establish minimally
acceptable vehicle  operating specifications for cruise speed, acceleration
and gradeability so that effect on  reduced requirements for component
performance can be assessed.   Then, allow vehicle and powertrain weight
to vary for establishment of an optimum  configuration using complete
component operating  maps and link hybrid vehicle powertrain elements
through combined factors of power, efficiency, and rpm.
                                    13-13

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Next, define the effect of variations in component weight and performance
on system cost and review preliminary operational requirements in detail
with component manufacturers  to assess cost trade-offs and to acquire
latest data on component operating maps; viz. emissions and fuel consumption
versus power output and rpm for heat engines.

Next, vary part-load characteristics of each component in order to
optimize overall  powertrain efficiency and establish vehicle  optimum
weight for a  general purpose passenger automobile.  Also,  evaluate the
effect of different driving  cycles on powertrain operation, fuel consumption,
and exhaust emissions  and determine if the control system demonstrates
suitable flexibility.

Finally,  calculate system performance in terms  of exhaust  emissions
and fuel consumption for advanced heat engine-driven automobiles (spark
ignition and gas turbine) and compare to results for the hybrid electric
powertrain.  Use the same heat engines and driving cycles as those used
in analysis of the hybrid powertrain in providing this comparison between
hybrid powertrain cars and advanced heat engine-driven cars with
evaluation factors of cost,  exhaust emission levels, and fuel consumption.
This effort is necessary to establish whether the hybrid electric powertrain
cost margin  over the heat engine-driven car is adequacy balanced by the
performance delivered in  terms of exhaust emissions and fuel  economy.

Furthermore,  establish prototype conceptual designs for two alternative
hybrid heat engine/electric automobiles specifying the required operating
map characteristics of each component in the  powertrain, the exhaust
emissions, and the fuel consumption.   One vehicle shall use a  selected
"best" spark ignition engine while the other vehicle shall use a selected
"best" gas turbine.  Provide a  detailed cost breakdown for each
recommended hybrid vehicle design using improved component hardware
;xnd with an optimized powertrain and vehicle weight.  Provide  trade-off
factors  between costs,  exhaust emission levels,  and fuel consumption
involved with the selected hybrid vehicle.
                                    13-14

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1 3. 3. 1.6    Program Schedule
The  schedule of work effort for all activities associated with Phase I
is  given in Figure 13-2.   Component specifications and production cost
estimates are shown as being available within 9 months following program
inception in addition to a  comparative evaluation with advanced heat engine
driven automobiles.
13. 3. 2       Phase II -  Component Advanced Technology
A  research and development program is recommended to provide power-
train components with performance markedly improved over contemporary
hardware.   Because of the influence on vehicle performance,  all  com-
ponents and subsystems are  to be designed for low weight and volume with
due regard for effect on part-load to full-load efficiency.  In order to
ensure that the 1975/76 emission goals are met or exceeded,  effective
research is needed in several areas,  but the effort should lie predominantly
in  the areas of heat engine emissions  and battery lifetimes.

Initially, the program emphasis should be on research with limited funding
until the Phase I study results  in the form of comparative vehicle
performance and cost as  well as component specifications are available
for review.  Should these Phase I results still favor the development of
a hybrid electric automobile, then the Phase II effort  should be expanded
rapidly with increased funding  and eventual initiation of the  hardware
development portion of the program.  The required work effort is presented
in  the following discussion.  Component development goals are discussed
more extensively at the end of Sections 6 through 9 of  the report.
13. 3. 2. 1     Advanced Internal Combustion Engines
To select the optimum engine to be  used in the advanced prototype vehicle,
a state-of-the-art evaluation should be conducted of lean (high air/fuel
ratio) engine technology.  The  current hybrid studies have indicated that
this  type of spark ignition engine shows promise; however,  more data and
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OJ
I
TASK
SELECTION OF CONFIGURATIONS TO BE DESIGNED
SPECIFICATION GENERATION SYSTEMS LEVEL
COMPONENT DATA ACQUISITION 8 REVIEW
ENGINES
BATTERIES
MOTOR /GENERATOR 8 CONTROLS
COMPONENT TESTS
COMPONENT PARAMETRIC COST/ PERFORMANCE
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COMPARATIVE ANALYSIS WITH ADVANCED HEAT
ENGINE DRIVEN AUTOMOBILE
DECISION TO COMMIT TO HARDWARE
FINAL REPORT PREPARATION
MONTHS
1

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                         Figure  13-2.  Schedule of Work Effort - 12-Month Program
                                      (Phase I)

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evaluation of current developments must be accomplished to determine
the best approach.  In this regard, efforts should be made to design for
low specific mass emissions at part-load engine  operation.  Lean air/fuel
ratio engines should be evaluated to select the best approach towards
achieving low emission goals consistent with fuel economy.  Approaches
to be evaluated should include  the stratified charge engine, pre-chamber
engine, and engines with  optimized induction system design.  The rotary
combustion (Wankel)  engine, because of its low weight and volume and its
potential for  operating in the lean air/fuel ratio regime,  should also be
investigated.  Diesel engine technology should be investigated to assess
its potential for reducing NO   emissions and engine weight.  A  2-year
engine R&D program should be conducted with efforts also directed towards
incorporating efficient catalytic converters,  thermal reactors,  and
exhaust gas recirculation.

The lean engine evaluation program should delineate engine developments
to be conducted as well as identify technology and data gaps.  Following
this development period,  an engine should be selected for the hybrid
system based not only on the results of this program,  but on results from
other, concurrent spark ignition engine programs that have been  conducted
for non-hybrid applications.  Efforts  should be also directed to developing
efficient catalytic  converters and techniques to reduce cold start  emission
effects.
1 3. 3. 2. 2     Advanced Gas Turbine
A  burner  development program should be instituted to minimize the NC>2
emissions of the gas  turbine by means of  optimizing primary and secondary
zone air/fuel ratios and the residence time  of the gases  in the primary
zone.  Studies  should be conducted to select the optimum gas turbine
design for the hybrid vehicle and to further  the development necessary to
meet the requirements of the prototype vehicle.  The gas turbine developed
with the hybrid vehicle in mind should have  good  part-load emission
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characteristics, and provide optimum matching of the heat engine with
the electrical drive system.
1 3. 3. 2. 3    Batteries
The battery research and development program should consist of parallel
laboratory studies of a lead-acid battery and a nickel-zinc battery optimized
to the hybrid vehicle requirements in terms of power density,  energy density,
lifetime,  and charge acceptance.  It is anticipated that nickel-zinc batteries
will demonstrate  superior performance  characteristics than lead-acid but
will be more expensive.   It is also anticipated that selection of an optimum
battery for the prototype vehicle will be  made at the end of 2 years.
Reduction in packaging volume is also necessary for realistic installation
with other components in  a restricted powertrain-allocated volume within
the vehicle chassis/body combination.

Early implementation of this program is needed to determine whether
such factors as increased plate area, thinner plates,  stirred electrolyte,
reduced internal resistance,  and minimum (or zero) maintenance  can be
combined in a long life, low cost design  that will be compatible with the
automotive environment.
1 3. 3. 2. 4    Component Design Evaluation
Design concepts generated in this  Phase II program should eventually be
introduced into  the hybrid vehicle  test bed program for evaluation, and
field test results  should be used to tailor the later development work
effort.  The test bed program is discussed next in Phase III of the
overall development effort.
1 3. 3. 3       Phase III  - Test Bed and Prototype Vehicle
             Development
The discussion  that follows is highly dependent on the results of studies
conducted in Phase I and the success of  component research and development
efforts in Phase II.  If the cost and performance analyses indicate that
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the hybrid heat engine/electric automobile should remain as a strong
contender in the APCO advanced powerplant program,  then the philosophy
guiding the formulation of the  subsequent development program is to
confidently provide as soon as possible a mobile test bed for the hybrid
electric vehicle.   This instrumented test vehicle will permit evaluation of
the adequacy of the integrated system under combined environmental
conditions that cannot be simulated either in the laboratory or by "breadboard"
simulation systems.   The resulting data will be reflected in realistic
specifications being imposed upon components and subsystems  that are in
evolutionary stages and destined for the second generation vehicle (a
prototype of the production passenger car).   An approach of this nature
will ensure that development funds are  efficiently expended throughout the
program and permit expenditures to be curtailed or expanded at critical
evaluation points.

The recommendations are based on results  of  the just completed feasibility
study on hybrid electric vehicles, and should be considered  solely as
generalized planning  information at this time.  As results from the Phase I
program become available,  (viz.  detailed design information from  the
expanded  analysis and data base) they can be used to refine the plans
formulated in the subsequent discussion.  In addition, refinement of plans
for the  prototype vehicle should be dependent on the success in improving
component performance demonstrated in  the Phase II research effort.

A 2-1/2 yr program is recommended for  development of two mobile test
beds for the hybrid electric  vehicle.  It is expected that specifications
can be released for component development bids 7-1/2 months after
Phase III initiation, and completely assembled vehicles will be available
for a road test program within 21 months after Phase III initiation.  The
test vehicle is expected  to demonstrate marked improvements in exhaust
emissions, but will likely not meet the 1975/1976 emission standards.
That goal is expected to be fulfilled by a prototype hybrid electric vehicle
planned for completion in the 1974-1975 time period -- a vehicle  which
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will largely benefit from the experience and component development
accrued within the test bed vehicle and advanced component technology
programs.
A logical division of the test bed vehicle program is  presented herewith.
First, the directed effort from analysis through design, development,
fabrication, test, and specification release is discussed; second, a program
schedule  is presented for major tasks to be accomplished between 1971
and  1975.
13.3.3.1    Analyses
13.3.3.1.1  Design Factors Definition
Perform  analyses  for each configuration to define design factors in detail
for  the  test bed vehicle including the  following:
      1.     Vehicle and power train  weight based on latest available
             component data.
      2.     Vehicle performance in terms of acceleration, maximum
             cruise speed,  and gradeability.
      3.     Component  and complete power train operating characteristics
             at all part-loads up to full load.
      4.     Structural loads and  component/subsystem environment.
13. 3. 3. 1. Z  Component Data Evaluation
Evaluate  test data  on components being developed for the hybrid electric
vehicle  and factor  into the vehicle performance analyses.
13.3.3.1.3  Test  Bed Data Analysis
Analyze data acquired from vehicle test bed and use  results to modify
design and tailor future component development to prototype system needs.
13.3.3.2    System Design  Detail
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J 3. 3. 3. 2. 1  Structural Load Design
Establish adequacy of chassis and body design for static and dynamic
structural loads.
1 3. 3. 3. 2. 2  Layout  Design
Design component/subsystem layout, gearing, routing of lines, weight
distribution, e.g. location,  ....
1 3. 3. 3. 2. 3  Establishment of System Interfaces
Establish control system mechanical/electrical  interfaces.
1 3. 3. 3. 3    Specification Release and Contract Definition
13. 3. 3. 3. 1  Specification Evolution
Evolve final specifications  for chassis, body, and powertrain components
and subsystems from results of analysis and design.
1 3. 3. 3. 3. 2  Specification Release and Contract Award
Release specifications to vendors for bid and subsequently contract for
development and fabrication.
13.3.3.4    Hardware Design, Development,  and Fabrication
All components and subsystems are to be designed for low weight and
volume with due regard for effects on part-load  to full load efficiency.
They will also be designed  to operate acceptably under the environmental
conditions expected for the test bed vehicle (e. g. , shock, vibration,
acceleration, temperature,  moisture, dust) as delineated in the specifications.
The following comments serve  to highlight those design factors peculiar
to the hybrid electric vehicle.
1 3. 3. 3. 4. 1  Motor/Generator
Design for low cooling requirements, for nonsteady operation, and for
an optimized balance between high part-load efficiency and efficiency
achievable at full load.
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1 3. 3. 3. 4. 2  Control System
Design  for simplicity,  reliability, and low audible noise.
13.3.3.4.3  Batteries
Design  for high power density, high energy density,  long life,  high charge
acceptance,  and minimum (or zero) maintenance.
1 3. 3. 3. 4. 4  Heat Engine
Design  for low emissions at part-load up to full load and for application of
catalytic converters and thermal reactors.
13.3.3.4.5  Body and Chassis
Design  for weight balance, c. g. control, cooling  provisions  for
electronics and batteries, and noise suppression.
1 3. 3. 3. 5    Component Test and Evaluation
During  component design and fabrication,  test data are to be acquired for
verification of adherence to specifications.  Evaluation of these data should
offer alternatives to design approaches if specifications are  not met  under
all operating conditions.  These results can then  be factored into the design
before hardware delivery.
1 3. 3. 3. 6    Static  Interfacing Tests
All components and subsystems will be assembled in a breadboard test
set-up to provide initial evaluation of  performance and interfacing
problems.  A dynamometer will be utilized to simulate road load, and
exhaust emissions will  be measured along with component performance.
Control system modifications will be incorporated at this time if necessary
to optimize reduction in exhaust emissions.
1 3. 3. 3. 7    Vehicle Assembly and Final Component Integration
All components and subsystems will be installed in a conventional
automobile chassis  modified for the hybrid electric vehicle design and
for use as an instrumented test bed.   Body and interior arrangements
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are to be tailored for esthetic reasons as well as for functional operation
in a test bed vehicle (i. e. ,  the body shell should be easily removable to
permit ready access to components or for structural alternations to the
chassis).
1 3. 3. 3. 8    Vehicle System Tests and Evaluation
13.3.3.8.]  Road Tests
Following initial checkout of the assembled test bed vehicle  for handling,
drivability, and response to power  demand, an extensive series of tests
arc to be conducted for evaluating component, subsystem, and total  system
operation in the urban and open highway environment.  Tests are to  be
run both at  steady speeds as well as in a dynamic traffic-following situation.
Data will be evaluated to:  (a)  determine how well the vehicle matches design
performance goals, and (b) determine required  design modifications to
improve performance.
1 3. 3. 3. 8. 2  Laboratory Emission  Tests
The vehicle is  to be tested in an exhaust emissions test laboratory over
the prescribed government  test driving  cycle, and  measurements are to
be made of  unburned hydrocarbons,  carbon monoxide, and oxides of
nitrogen from exhaust gas sampling.  Basic emissions  data  should also
be acquired for various operating conditions.
13.3.3.9    Prototype Vehicle Program
Based on the analysis of the advanced technology program engine results
and the test bed results, one of the two  types of engines will be selected
for prototype development.   Development of the second generation vehicle
will largely follow  the plan  given for the test bed in the preceding sections
with the  following exceptions:
      1.     Component  design and development should be directed toward
            long-range  ultimate  improvements in performance.
                                    13-23

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      2.     Component qualification tests should be introduced prior to
            vehicle assembly.
      3.     Component and vehicle specifications should be more
            restrictive, particularly those associated with affecting
            exhaust emissions.
1 3. 3. 3. 1 0   Test  Bed Vehicle Program Schedule
A  29-month program has been scheduled by major task elements for the
test  bed vehicle as shown in the accompanying chart (Fig. 13-3).  The
basic design and release of final specifications for use in soliciting contract
bids  for hardware  development is accomplished 7-1/2 months  after program
inception; a fully assembled test bed vehicle is ready for  road tests
22 months after program inception.  The prototype vehicle program is
initiated 1 to 1-1/2  yr after inception of the test bed vehicle program and
continues on for approximately 3 yr.  Based on analysis,  test bed data,
and detailed costing, the more promising of the two hybrids should be
selected for use in the prototype development program.

The  tasks for the prototype vehicle program, while not delineated, are
in essence the  same as  those  shown for  the test bed vehicle; the main
difference is the use of  more  developed  components and of design data
obtained from the test bed program.  Detailed definition of the prototype
vehicle program should not be attempted until specifications have been
released for the test bed vehicle and some data on component  performance
characteristics generated.
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OJ
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TASK
TEST BED VEHICLE PROGRAM
13.3.3.1 ANALYSES
13.3.3.2 DETAIL SYSTEM DESIGN
13.3.3.3 SPECIFICATION RELEASE
8 CONTRACT DEFINITION
13.3.3.4 HARDWARE DESIGN, DEVELOP-
MENT 8 FABRICATION
13.3.35 COMPONENT TEST a
EVALUATION
13.3.3.6 STATIC INTERFACING TESTS
13.3.3.7 VEHICLE ASSEMBLY 8 FINAL
COMPONENT INTEGRATION
13.3.3.8 VEHICLE SYSTEM TESTS
8 EVALUATION
MILESTONES
13.3.3.9 PROTOTYPE VEHICLE PROGRAM
( TASKS SIMILAR TO TEST BED
VEHICLE PROGRAM )

YEARS FROM PROGRAM INCEPTION
1
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                                Figure 13-3.  Test Bed Vehicle Development
                                              Program Schedule

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