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literature and current available unpublished data sources.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
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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.
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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
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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
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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
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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. )
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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.
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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
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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.
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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.
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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.
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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.
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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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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.
-------
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
-------
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
-------
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.
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
oo
i
Key (~) Generator T Turbine
C Compressor R Regenerator
CC Combustion Chamber 1C Intercooler
-------
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
-------
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
i
U1
o
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
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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
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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
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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
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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
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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
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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
-------
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
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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
-------
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
-------
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
-------
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
-------
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
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PROJECTED TECHNOLOGY
A/F = 22, CATALYST, RECIRCULATION
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PROJECTED TECHNOLOGY
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A/F = 22
PROJECTED TECHNOLOGY
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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
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2.5
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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
-------
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
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TURBOCHARGED. PRECHAMBEft
(a) PROJECTED TECHNOLOGY
\ TURBOCHARGED, PRECHAMBER
^ ^ W/CAT 8 EGR
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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
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NAT. ASP, DIRECT INJECTION
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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
-------
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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STATE OF THE ART TECHNOLOGY
PROJECTED TECHNOLOGY
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DESIGN BRAKE HORSEPOWER
Figure 9-5. Gas Turbine Emissions, Steady State Design
Load: (a) Hydrocarbon, (b) Carbon Monoxide,
(c) Nitric Oxide
9-16
I I I
I03
-------
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
-------
CO
00 r
CO 5
-------
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
-------
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
-------
CO
40 60
PERCENT OF DESIGN LOAD
Figure 9-8. Rankine Engines - HC, CO, NO, Emissions,
Steady State Part-Load
9-23
-------
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'
-------
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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STATE-OF-THE
ART TECHNOLOGY
SPARK DIESEL
IGNITION ENGINE
ENGINE
(GASOLINE)
GAS RANKINE STIRLING
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
SECTION 11
SUMMARY OF RESULTS
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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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11-10
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11-11
-------
CURRENT TECHNOLOGY
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-
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11-12
-------
g
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S I ENGINE DIESEL GAS TURBINE RANKINE STIRLING
I?
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(1C Km,..Ion.
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S. i. ENGINE DIESEL GAS TURBINE RANKINE STIRLING
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I FL n, n,'
S.I. ENGINE DIESEL GAS TURBINE RANKINE STIRLING
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11-13
-------
n 3
'i
I CURRENT TECHNOLOGY
] PROJECTED TECHNOLOGY
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20
S I ENGINE DIESEL GAS TURBINE SANKINE STIRLING
10
CURRENT TECHNOLOGY
PROJECTED TECHNOLOGY
s i ENGINE DIESEL GAS TURBINE RANKING STIRLING
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11-14
-------
„ 3
F
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SIINGIM DILStl GAS lURBlV RANKINE STIRLING
| CURRENT TECHNOLOGY
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S I ENGINE DIESEL G« TURBINE RAHKINE STIRLING
jCURRENT TECHNOLOGY
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S U'SGINE DIFSEL GAS TURBINE RANKINE STIRLING
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BO
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BO
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] PROJECTED TECHNOLOGY
H
ru
si. ENGINE DIESEL GAS TURBINE RANKINE STIRLING
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
-------
g 5
X f
11 '•">
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11-29
-------
S _r 110
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REOURU tr
-------
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
VlH'CLl *l iGlil.lD
4000 «iriO vnu
I I
s. •,,
4?00 4JOO "00 «'///
vrmai *ri(,t(t. it
« '2
Is
4000 4100 4K» 4JOQ 44QO 4MO
-------
1700 1750
1900 IS50 1900 1950 2000 2050 1000
VEHICLE *ŁiCMT. It
II
fj-
1}
a* 10
If
1—I-
I
I
I
1850 1900 1950 2000 2050
VCKICU UTtKiHI. It
militant • C«nnml«r C>r/DK[v Crll*
IBM IBM 1900 I9SO
VlMIClf. *t'GHT. Id
../Utl»» r.t.l. .
1750
1900 11V)
f *LIGHI. ib
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
\
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.
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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
gg
S > 120
§ |
el no
080
10 so eo ra eo 90
MOTOR EFFICIENCY d|,l. %
^ no
HO Ml fO 70 BO 90 100
I i L_
l i L
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090
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•>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
-------
19
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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
p= 600
o
Q.
400
CO
rj>
UJ
CK
g 200
UJ
Q:
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
Q.
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
oc.
o
Q_
a:
«=t
CO
a
UJ
CC
400
200
S.I. ENGINE
GAS TURBINE
90kW PEAK POWER DEMAND
100
JE 80
>-
I—
CO
<_D
cc
-------
Q
or
1000
800
600
o
a.
25 400
.
CO
UJ
cc
rD
o
UJ
cc
200
0
S.I. ENGINE
"~ DIESEL
GAS TURBINE
STIRLING
RANKINE
210 kW PEAK POWER DEMAND
CO
z
UJ
O
O
CC
UJ
>-
a:
m
CO
-------
1000
800
CO
8 600
cr
o
Q-
or
UJ
cc.
cc.
400
200
0
GAS TURBINE
136 kW PEAK
POWER DEMAND
S.I. ENGINE
>-
H;
CO
^
UJ
o
o:
LiJ
I—
I—
<:Ł
CD
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
Q
o
Q_
600 -
O
UJ
:
o
UJ
oc
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
cc
o
Q_
OC
O
UJ
9E
o
LU
cc
400
200
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
I
-------
1000
800
S 600
CE
O
Q_
cr
CD
O
O
UJ
CC
400
200
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
>-
h^
CO
ce
>-
cc
m
Q
60
40
20
S.I. ENGINE
GAS TURBINE
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
UJ
CC
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
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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
-------
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:
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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
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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.
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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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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
TDAnc-ncr CTiinv
InMUt. Urr OlUUT
SPECIFICATION GENERATION- COMPONENTS
(TlCT AMAl VClC mMDHMFMTQ
UJo 1 ANALTolo LUMrUNtlN lo
SYSTEM EVALUATION 8 COST INTEGRATION
COMPARATIVE ANALYSIS WITH ADVANCED HEAT
ENGINE DRIVEN AUTOMOBILE
DECISION TO COMMIT TO HARDWARE
FINAL REPORT PREPARATION
MONTHS
1
///,
2
//////
I//
' / /
U* f
r// //
3
III
4
5
///i
f / / \
// / /
/ / / /
/ / / /
/ J
(11
6
/ /
\l
7
8
f ///i
9
////// /
i
////////// A
f/
,,
I/
/ /
1
///////
/ / /
10
/ / / / / 1
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A
/ / /
II
12
/ / // >
Figure 13-2. Schedule of Work Effort - 12-Month Program
(Phase I)
-------
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
13-17
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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
13-18
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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
13-22
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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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(Jl
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
1 1 1
" •
VEHIC
FINAL
F
DESIGN COMPL.
SPEC. RELEASE
1 1 1
2
1 l 1
•
—
LE ASSY.
SYS. INTEG.I
vv v
a ist SYS.
INTEG.
1 1 1
3
1 1 1
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/COMPLETED
v vx
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REPORT
1 1 1
4
1 1 1
FINAL
PRO
AVA
1 1 1
1
_A
TOTYPE
LABLE
|
Figure 13-3. Test Bed Vehicle Development
Program Schedule
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