EPA-460/3-74-013-d
July 1974
CURRENT STATUS
OF
ALTERNATIVE AUTOMOTIVE
POWER SYSTEMS
AND FUELS
VOLUME IV - ELECTRIC
AND HYBRID POWER SYSTEMS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Wante Management
Offire of Mobile Source Air Pollution Control
Alternative Automotive Power Systems Division
Ann Arbor, Michigan 48105
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EPA-460/3-74-013-d
CURRENT STATUS
OF
ALTERNATIVE AUTOMOTIVE
POWER SYSTEMS
AND FUELS
VOLUME IV - ELECTRIC
AND HYBRID POWER SYSTEMS
Prepared by
The Environmental Programs Group
The Aerospace Corporation
El Segundo, California 90245
Contract No. 68-01-0417
EPA Project Officer: Graham Hagey
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Alternative Automotive Power Systems Division
Ann Arbor, Michigan 48105
July 1974
-------
This report is issued by the Environmental Protection Agency, to report
technical data of interest to a limited number of readers. Copies of this
report are available free of charge to Federal employees, current contractors
and grantees, and non-profit organizations - as supplies permit - from the
Air Pollution Technical Information Center, Environmental Protection Agency,
Research Triangle Park, North Carolina 27711, or may be obtained, for a
nominal cost, from the National Technical Information Service, 5285 Port
Royal Road, Springfield, Virginia 22151.
This report was furnished to the U.S. Environmental Protection Agency
by the Aerospace Corporation, El Segundo, California, in fulfillment of
Contract No. 68-01-0417 and has been reviewed and approved for publication
by the Environmental Protection Agency. Approval does not signify that
the contents necessarily reflect the views and policies of the agency.
The material presented in this report may be based on an extrapolation of
the "State-of-the-art" . Each assumption must be carefully analyzed by
the reader to assure that it is acceptable for his purpose. Results and
conclusions should be viewed correspondingly. Mention of trade names
or commercial products does not constitute endorsement or recommendation
for use.
Publication No. EPA-460/3-74-013-d
11
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FOREWORD
This report, prepared by The Aerospace Corporation for the
Environmental Protection Agency (EPA), Alternative Automotive Power
Systems Division, summarizes available nonproprietary information on the
technological status of automotive power systems which are alternatives to
the conventional internal combustion engine, and the technological status of
nonpetroleum-based fuels derived from domestic sources which may have
application to future automotive vehicles.
The status of the technology reported herein is that existing at
the end of 1973 with more recent data in selected areas. The material pre-
sented is based principally upon the results of research and technology
activities sponsored under the Alternative Automotive Power Systems (AAPS)
Program which was originated in 1970 and which is administered by the Alter-
native Automotive Power Systems Division of EPA. Supplementary data are
included from programs sponsored by other government agencies and by pri-
vate industry. Additional information on technology and development programs
is known to the government but cannot be documented herein because the data
are proprietary.
One purpose that the AAPS Program serves is to provide a basis
of knowledge and perspective on what can and cannot be accomplished with
the use of alternative propulsion and fuels technology and to disseminate this
information to Congress, Federal policy makers, industry, and the public.
Thus, the publication of information such as that contained herein is in keeping
with this element of the mission of the AAPS Program. This is the first of a
series of reports on alternatives that are intended to be published annually.
The results of this study are presented in four volumes and
three main topical areas:
Volume I. Executive Summary
Volume II. Alternative Automotive Engines
111
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Volume III. Alternative Nonpetroleum-Based Fuels
Volume IV. Electric and Hybrid Power Systems
Volume I, the Executive Summary,- presents a concise review of important
findings and conclusions for all three topical areas. Thus, an overview of
the study results may be obtained by reading Volume I only. Volumes II, III,
and IV contain detailed, comprehensive discussions of each topical area and
are therefore of interest primarily to the technical specialist. Each of these
three volumes also contains Highlights and Summary sections pertaining to
the topical area covered in the volume.
This volume, Volume IV, presents available information per-
taining to the current technological status of electric and hybrid power
systems that may have application to future automotive vehicles.
A brief review of important findings and conclusions is presented
in the Highlights and Summary sections. The report body is divided into
two parts: Part I -- Electric Vehicles and Part II -- Hybrid Heat Engine/
Battery and Hybrid Heat Engine/Flywheel Vehicles. Section 1 of Part I
reviews the electric vehicle history, Section 2 defines the power plant
configurations, and Section 3 reviews vehicle performance characteristics.
Sections 4 and 5 discuss current and projected status of electric vehicles,
respectively. Section 1 of Part II defines a hybrid vehicle and lists various
EPA-sponsored studies, Section 2 discusses the basic hybrid concept and
vehicle powertrain operating modes, and Section 3 shows how vehicle speci-
fications influence design approaches. Section 4 describes system and
component design requirements and the analytical and test results achieved
for hybrid heat engine/battery vehicles. Section 5 provides a similar dis-
cussion for hybrid heat engine/flywheel vehicles. Section 6 briefly describes
other energy storage concepts, and Section 7 summarizes the development
status of hybrid vehicles. Appendix A presents the Air Pollution Control
Office vehicle design goals for a six passenger automobile.
IV
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ACKNOWLEDGMENTS
Appreciation is acknowledged for the guidance and assistance provided
by Mr. Graham Hagey of the Environmental Protection Agency (EPA), Alter-
native Automotive Power Systems (AAPS) Division, who served as EPA
Project Officer for this study. Appreciation is also extended to staff mem-
bers in the AAPS Division, to other EPA divisions, to various government
agencies, and to those in industry and the academic community who supplied
reference material and reviewed the contents of this report. In particular,
the efforts of Mr. Charles Pax, AAPS Division Technical Staff and Mr. H. J.
Schwartz of the NASA Lewis Research Center are gratefully acknowledged.
The following technical personnel of The Aerospace Corporation made
valuable contributions to the effort performed under this contract.
O. W. Dyke ma
L. Forrest
K. E. Hagen
J. R. Kettler
R. C. LaFrance
W. M. Smalley
Merrill G. Hinton, Director
Office of Mobile Source Pollution
D. E. Lapedes,/Study Manager
f^ ^^^ i \S f v—-"^ V^T*^ .*~*__ ^^----
Toru lura, Associate Group Director
Environmental Programs Group
Directorate
Jasrejah Meltzer, Group DTrtector
vnvironmental Prograrar^xGroup
^Directorate
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CONTENTS
Part I. Electric Vehicles
FOREWORD iii
ACKNOWLEDGMENTS v
HIGHLIGHTS H-l
SUMMARY S-l
1. INTRODUCTION 1-1
2. POWER PLANT DESCRIPTION 2-1
2. 1 Power Plant Configurations 2-1
2. 2 Design Features 2-3
2. 2. 1 Batteries 2-3
2. 2. 2 Motors and Controls 2-l£
3. VEHICLE PERFORMANCE CHARACTERISTICS 3-1
3. 1 Power, Speed, and Torque 3-1
3. 1. 1 Power and Energy Storage 3-3
3. 1. 2 Speed and Torque 3-4
3. 2 Emissions 3-4
3.3 Fuel (Energy) Economy 3-5
3.4 Noise Levels 3-7
3.5 Odor 3-7
3. 6 Maintainability 3-8
3. 7 Safety 3-8
3. 8 Drivability 3-9
4. CURRENT STATUS OF TECHNOLOGY 4-1
4. 1 Current Use 4-1
4. 2 Current Research and Development 4-1
vn
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CONTENTS (Continued)
5. PROJECTED STATUS OF ELECTRIC VEHICLES 5-1
5. 1 Required Development 5-1
5. 2 Projection for Electric Cars 5-1
REFERENCES R_ 1
VI11
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CONTENTS
Part II. Hybrid Heat Engine/Battery and Heat Engine/Flywheel Vehicles
1. INTRODUCTION
2. GENERAL CONCEPT DESIGNS AND SYSTEM
OPERATION
2. 1 Basic Concept
2. 2 Power-train Concepts
2. 3 Regenerative Braking
2.4 Vehicle Powertrain Operating Modes
2. 5 Engine Operating Modes
2. 5. 1 Series Configuration
2. 5. 2 Parallel Configuration
3. DESIGN IMPACT OF VEHICLE SPECIFICATIONS
3. 1 General Requirements and Considerations
3. 2 Road Performance Requirements
3. 3 Weight and Volume Limitations
3.4 Fuel Economy and Exhaust Emissions
3. 5 Implications of Revised Vehicle Specifications
4 HYBRID HEAT ENGINE/BATTERY VEHICLE
4 1 System Designs and Operation
4. 1. 1 TRW Systems, Inc
4. 1. 2 Minicar, Inc
4. 1.3 The Aerospace Corporation
4. 1.4 Petro-Electric Motors
4. 1. 5 General Motors Corporation
4. 1.5 Other Electric Hybirds
4.2 System Design Requirements and Achievements . . . .
4.2. 1 TRW Systems, Inc
4. 2. 2 Minicar, Inc
1 - 1
2-1
2-1
2-2
2-4
2-4
2-5
2-5
2-9
3-1
3-1
3-3
3-5
3-8
3-10
4-1
4-1
4-1
4-3
4-4
4-6
4-7
4-9
4-15
4-15
. . 4-21
IX
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CONTENTS (Continued)
4.2.3 The Aeospace Corporation 4-22
4.2.4 General Motors Corporation - Stir-Lee I 4-30
4.3 Component Design Requirements and Achievements 4-32
4.3.1 Motors and Generators 4-32
4.3.2 Control System 4-35
4.3.3 Batteries for Hybrid Vehicles 4-37
4.3.4 Heat Engines 4-45
5. HYBRID HEAT ENGINE/FLYWHEEL VEHICLE 5-1
5. 1 System Designs and Operation 5-1
5.1.1 Lockheed Missiles and Space Co., Inc 5-1
5. 1.2 Johns Hopkins University, Applied
Physics Laboratory 5-7
5.2 System Design Requirements and Achievements 5-9
5. 2. 1 Lockheed Missiles and Space Co., Inc. 5-9
5.2.2 Johns Hopkins Unitversity, Applied
Physics Laboratory 5-16
5.3 Component Design Requirements and Achievements 5-22
5.3.1 Flywheel 5-22
5.3.2 Transmission 5-35
5.3.3 Heat Engines 5-48
6. OTHER ENERGY STORAGE CONCEPTS 6-1
6. 1 Hydraulic Accumulator System 6-1
6.2 Electric Capacitor Storage Systems 6-2
6.3 Pneumatic Energy Storage Systems 6-2
6.4 Thermal Energy Storage Systems 6-2
6.5 Fuel Cell/Battery Systems 6-2
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CONTENTS (Continued)
7. ASSESSMENT OF HYBRID POWERTRAIN APPLICATION
TO AUTOMOBILES 7-1
7. 1 Technology and Economic Status 7-1
7.1.1 Major Technical Accomplishments 7-1
7.1.2 Technical Development Status 7-2
7.1.3 Economic Status 7-4
7.1.4 Critical Problem Areas 7-4
7.1.5 Alternative Vehicle Design Goals 7-5
7.2 Prognosis for Contributing to National Personal
Transportation Needs 7-6
REFERENCES R-1
APPENDIX A -- Air Pollution Control Office Advanced Automotive
Power Systems Program, "Vehicle Design Goals
Six Passenger Automobile" A-l
GLOSSARY G-l
XI
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FIGURES
Part I. Electric Vehicles
2-1. Electric Car Drivetrain Showing the Main
Components 2-2
2-2. Phantom View of the General Motors Electrovair II
Showing the Location of Major Experimental
Components 2-20
2-3. Typical Maximum Efficiency for Direct Current Motors
as a Function of Weight per Unit Horsepower 2-23
2-4. Typical Weight per Unit Horsepower as a Function of Rated
Power for Direct Current Motors Including Forced Air
Cooling 2-23
2-5. "Sundancer" Rear Quarter View 2-33
2-6. View of 1968 Mars II Electric Car 2-33
3-1. Electric System Energy Flow Diagram 3-6
Xlll
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FIGURES
Part II. Hybrid Heat Engine/Battery and Heat Engine/Flywheel Vehicles
2-1.
2-2.
2-3.
2-4.
3-1.
3-2.
3-3.
3-4.
4-1.
4-2.
4-3.
4-4.
4-5.
4-6.
4-7.
4-8.
4-9.
Simplified Schematics of Heat Engine Hybrid Vehicle
Powertrain Concepts
Various Heat Engine Operational Modes - -Series
Configuration
Heat Engine Variable Power Output Mode "Biased"
Throttle Setting Feature
Heat Engine Variable Power Output Mode- -Step Mode
Wheel Power Demands for a 4,000-lb Car
Effect of Powertrain Weight on Battery Requirements --
Family Car Series Configurations
Spark Ignition Engine SCF Map, Normalized
Emissions Effect of Spark Ignition Engine Load
Variation
TRW Electromechanical Transmission Mode I Operation • • •
Minicar Drivetrain
Phantom View of GM Stir -Lee I Hybrid System
Block Diagram of GM Stirling-Electric Hybrid System
General Motors No. 512 Hybrid Gasoline-Electric
Toyo Kogyo Wankel/Electric Car
Daihatsu Kogyo Fellow Max Hybrid Car
University of Toronto Car
Comparative Calculated Emission Levels of the Family
and Commuter Cars
2-3
2-5
2-8
2-8
3-4
3-7
3-9
3-11
4-2
4-4
4-8
4-8
4-9
4-11
4-13
4-14
4-28
4-10. Calculated Vehicle Emission Comparison, Conventional
Operation Versus Hybrid DHEW Driving Schedule --
Spark Ignition Engine 4-29
xiv
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FIGURES (Continued)
4-11. Stir-Lee I Engine Mass Emissions 4-31
4-12. Overload Capability Compensated Direct Current Motors . . . 4-34
4-13. Section Through the Various Components of the Quasi-
bipolar Plate Prior to Thermoforming 4-42
4-14. Battery Peak Discharge Currents and Associated
Power Density 4-45
4-15. Heat Engine SFC Comparison 4-51
4-16. Heat Engine Weight Comparison 4-51
4-17. Heat Engine Volume Comparison 4-51
4-18. Heat Engine Exhaust Emissions at Design Load 4-53
5-1. Lockheed Conceptual Drivetrain Arrangements 5-2
5-2. Lockheed Transaxle Fly wheel/Hybrid Transmission
Configuration 5-3
5-3. Preliminary Lockheed Flywheel Design--Family Car 5-4
5-4. Lockheed Baseline Flywheel 5-5
5-5. Lockheed Power-Splitting Transmission Configurations .... 5-6
5-6. Johns Hopkins Heat Engine/Flywheel Hybrid Com-
muter Car 5-8
5-7. Johns Hopkins Flywheel Hybrid Power Control
System 5-10
5-8. Lockheed Minimum Tractive Effort as a Function of
Speed Requirements for Flywheel Drive System 5-12
5-9. Johns Hopkins University Driving Cycle 5_17
5-10. Effect of Flywheel Rotor Weight for Otto Hybrid
Commuter Car, Johns Hopkins 5-20
xv
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FIGURES (Continued)
5-11. Effect of Drivetrain Efficiencies and External
Resistance for Otto Hybrid Commuter Car,
Johns Hopkins 5-21
5-12. Parallel and Series Configurations for Energy
Flow in Hybrid Vehicles 5-36
5-13. Sundstrand Alternate 8C Transmission 5-38
5-14. Schematic of the MTI Recommended Transmission
Design 5-42
5-15. MTI Powertrain Efficiency Comparison at Cruise
Power 5-44
5-16. MTI Comparison of Transmission Efficiencies at Cruise
Power 5-45
5-17. Transmission Efficiency at Cruising Conditions for
Different Drives, Single-Shaft Gas Turbine Engine 5-47
xvi
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TABLES
Part I. Electric Vehicles
2-1. Electric Vehicle Specifications 2-4
2-2. Electric Vehicle Summary Data for Operating
Passenger Models in the United States 2-8
2-3. Characteristics of Currently Available Secondary
Batteries 2-9
2-4. Batteries for Future Electric Vehicles 2-10
2-5. Lithium/Sulfur Laboratory Program Goals and Cell
Performance --Argonne National Laboratory 2-14
2-6. Foreign Battery Research and Development (R&D)
Efforts for All Types of Electrical Vehicles, by
Countries 2-18
2-7. Comparison of Motor Controllers 2-27
4-1. Performance of Japanese Prototype Electric
Vehicles in 1973 4-2
4-2. Comparison of the Permanent Magnet Field
Materials 4-4
xvii
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TABLES
Part II. Hybrid Heat Engine/Battery and Heat Engine/Flywheel Vehicles
3-1. Vehicle Specifications 3-2
4-1. Electromechanical Transmission Electrical Systems
4-15
4-2.
4-3.
4-4.
4-5.
Rating and Required Performance of Electrical Components,
LA-4 Driving Cycle, Parallel Configuration
Average Component Efficiency, LA-4 Driving Cycle
Effects on Overall System Efficiency, LA-4 Driving Cycle . .
Breadboard Hybrid System Emission Results, Federal
Test Procedure
4-17
4-18
4-19
4-20
4-6. Parallel Configuration, Subsystem Estimated
Performance -- Spark Ignition Engine 4-23
4-7. Parallel Configuration, Characteristics of Selected
Electrical Subsystems --Spark Ignition Engine 4-24
4-8. Preliminary Weight and Volume Summary of
Powertrain -- Family Car Parallel Mode 4-26
4-9. Resultant Hybrid Vehicle Battery
Requirements — Baseline Case 4-27
4-10. Summary of Engine Costs and Vehicle System Costs 4-30
4-11. Hybrid Vehicle Battery Preliminary Requirements 4-38
4-12. Performance Tests of Current Batteries 4-40
4-13. Family Car Heat Engine Characteristics 4-49
4-14. Commuter Car Heat Engine Characteristics 4-49
5-1. Lockheed Family Car Transmission Comparison 5-13
5-2. Lockheed Family Car Powertrain Comparison 5-14
5-3. Lockheed Vehicle Exhaust Emission Comparison 5-15
XVlll
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TABLES (Continued)
5-4. Johns Hopkins Results for Family Car Without Air
Conditioner Operating 5-18
5-5. Johns Hopkins Results for Commuter Car Without Air
Conditioner Operating 5-19
5-6. Flywheel Materials Studied by Lockheed 5-23
5-7. Flywheel Configurations Studied by Lockheed 5-25
5-8. Lockheed Comparison of Power Loss Calculations 5-26
5-9. Summary of Composite Materials, Rod Tests, Johns
Hopkins 5-30
5-10. Test Results for 1-lb Bar: Speed, Stress, and Specific
Energy at Failure, Johns Hopkins 5-33
5-11. Sundstrand Transmission Evaluation--Federal Emissions
Test Driving Cycle 5-40
5-12. Sundstrand Estimate of Constant Speed Fuel Consumption . . . 5-40
xix
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HIGHLIGHTS
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HIGHLIGHTS
Electric and hybrid power systems are unique alternatives to
heat engines for automotive propulsion. The extensive use of electric vehi-
cles would shift the burden of controlling exhaust emissions from motor
vehicles to stationary electric generating plants supplying energy for re-
charging batteries where the treatment of stack exhaust could be more easily
controlled. Furthermore, the current use of petroleum-based fuels for auto-
motive propulsion could be diminished, and personal transportation energy
needs could be supported to a large degree by coal or nuclear resources.
The most common form of system operation that has been
studied for hybrid heat engine/battery and hybrid heat engine/flywheel vehi-
cles relies on the heat engine to supply energy for vehicle cruise and for re-
charging the battery or flywheel. The additional power for vehicle accelera-
tion is supplied by the battery or flywheel. With this form of heat engine
operation, the hybrid concept offers the possibility of reduced mobile emis-
sions. A shift of exhaust emissions to stationary electric generating plants,
as in the case of electric vehicles, would be possible only if the energy for
recharging the battery or flywheel were available from an external stationary
power source, and the heat engine was then used just for supplying emergency
power or for extending vehicle range on an infrequent basis.
A status review has been made of automotive electric and
hybrid power systems in this country and, where information was available,
in foreign nations. A number of prototype vehicles have been built with
private capital, and, in some cases, federal funding has been used to evaluate
and test these systems. In particular, the results derived from EPA-funded
programs were reviewed in context with the design goals established by the
H-l
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Alternative Automotive Power Systems (AAPS) Program for personal passenger
cars. The following highlights present the essential elements of this review.
In addition to the technical problems noted, estimated high manufacturing costs
will likely be an inhibiting factor in widespread application of these systems.
Electric Vehicles
1. In electric car designs, lead-acid batteries have been used in most
cases, and the direct current electric brush motor with silicon-
controlled rectifier time-ratio controls is used by an overwhelming
majority of vehicle designers.
2. Currently, a major problem with electric vehicles is the limitation
on the amount of energy and power that can be delivered by a given
size battery; this limitation has a direct effect on vehicle range and
acceleration.
3. In general, the majority of electric vehicles do not perform up to
heat engine vehicle capabilities--particularly with respect to maxi-
mum acceleration, speed, range, and hill-climbing ability, as well
as to passenger space and accommodations such as air conditioning
and heating. The usual maximum speed is 30 to 50 miles per hour,
and range is usually limited to 50 miles under conditions of optimum
cruise speed.
4. An additional problem with the electric vehicle is the power and time
needed for recharge of the batteries. Vehicle usage will be limited
unless provisions are made for exchange of depleted batteries for
fresh batteries. The capability of residential electrical grids to
supply large power levels during daytime for a large number of
electric vehicles also may be a problem.
5. In selecting batteries for electric vehicles, a dominant parameter
has been purchase cost. Consideration also must be given to battery
replacement costs and operating costs. For these reasons, lead-
acid batteries are almost universally used.
6. No one battery has been developed yet to satisfy the combined design
requirements for low cost, long lifetime, high energy density (for
vehicle range), high power density (for vehicle acceleration), and
ease of maintenance.
H-2
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7- For near-term applications, nickel-zinc batteries offer higher energy
density possibilities, but cost and nickel availability are drawbacks
for supplanting lead-acid batteries (nickel-cadmium, batteries are even
more expensive). For far-term applications, the zinc-chlorine and
alkali-metal/high temperature battery systems, with significant in-
creases in energy and power density capabilities, appear promising if
development goals are achieved.
8. Work on batteries for electric vehicles is accelerating abroad. The
major activities are in the Federal Republic of Germany, Japan, the
United Kingdom, and the U.S. S. R. In each case, the government is
either formally participating in or is influencing the direction of the
work.
9. Excluding the special-purpose applications of golf carts, electric fork
lifts, and delivery vans, no major production of electric passenger
vehicles is expected for the next 10 years. This picture could change,
should there be a major gasoline shortage, a restriction on operating
conventional vehicles in some areas due to air quality constraints, or
a breakthrough in battery technology that would allow much improved
vehicle performance and range.
Hybrid Heat Engine/Battery and Hybrid Heat Engine/Flywheel Vehicles
1. The range limitations of electric vehicles are not found in the hybrid
heat engine vehicle concept. The hybrid vehicle under discussion
uses a small heat engine to provide road cruising power, with
acceleration power requirements provided by a battery in the case of
an electric energy storage hybrid, and by a flywheel in the case of an
inertial energy storage hybrid. By so restricting the operation of the
heat engine, early studies anticipated significant reductions in exhaust
emissions without the need for complex, costly exhaust treatment
devices, but results to date have not verified this expected performance.
2. The EPA contracted with several companies in the 1969 to 1972 period
to perform evaluations of hybrid battery and flywheel systems. This
effort encompassed the analysis and test of hybrid systems and
associated components.
3. Elements of the TRW electromechanical transmission (heat engine/
battery hybrid) were assembled into a breadboard prototype unit and
tested as a complete integrated system. Powertrain efficiency was
found to be below predicted values (though possibly correctable through
redesign), and exhaust emissions were reduced to or below the level
H-3
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of the original 1976 Federal exhaust emission standards only by the
application of an exhaust emission control system involving exhaust
gas recirculation, tricomponent catalysts, etc.
4. The Minicar, Inc. , hybrid heat engine/battery powered car was defi-
cient in meeting performance goals, and exhaust emissions were not
reduced to acceptable levels.
5. Petro-Electric Motors has an operable hybrid heat engine/battery
powered automobile that is undergoing test and evaluation at EPA
laboratories under the Federal Clean Car Incentive Program.
6. The Aerospace Corporation analytical study of hybrid heat engine/
battery powered vehicles showed that, with a spark ignition engine,
exhaust emissions could meet the original 1976 Federal exhaust emis-
sion standards only by the use of aftertreatment devices in the exhaust,
along with engine modifications. In comparison to the conventional
automobile, no improvements in fuel economy were found. Similar
conclusions were arrived at by Lockheed in its analysis of a hybrid
heat engine/flywheel system.
7. The General Motors Stir-Lee I automobile (hybrid heat engine/battery)
achieved very good fuel economy, but proved to be very limited in
acceleration and peak speed. Exhaust emissions (except for NO )
were reduced, but not enough to meet Federal 1976 standards.
8. Tyco concluded that a commercial state-of-the-art SLI (starting-
lighting-ignition) lead-acid battery was unsuited for hybrid vehicle
use because of life limitations, although required power levels were
achieved. Research tests with a revised design showed substantial
improvements in meeting required EPA lifetime.
9. It was also demonstrated by TRW/Gould that while a commercial state-
of-the-art SLI lead-acid battery approached required EPA design power
levels, it lacked the required lifetime. In a research battery design,
TRW/Gould achieved the required power density, but lifetime goals
were still not met.
Hydrocarbon (HC) = 0. 41 gm/mi
Carbon monoxide (CO) =3.4 gm/mi
Oxides of nitrogen (NO ) = 0. 40 gm/mi
H-4
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10. Lockheed concluded that 4340-grade steel was the most cost-effective
material for a flywheel in a disc configuration. E-glass and S-glass
materials were found to be best suited for bar-type flywheel geome-
tries. In tests to failure, the steel wheel exceeded specified peak
speeds, while the glass materials fell short of design goals.
11. The Johns Hopkins University Applied Physics Laboratory tested
advanced flywheels in filamentary and composite rod/bar configura-
tions with mixed results. Single-strand boron filaments, small
graphite/epoxy composite rods, and small R-glass/polyester composite
rods exceeded the energy storage design goal of 30W-hr/lb, but the
larger 1-pound S-glass/epoxy and graphite/epoxy composite bars failed
to achieve this design goal; this was attributed to inadequate material
processing techniques.
12. Sundstrand determined that a combination of mechanical, hydro-
mechanical, and hydrostatic transmissions is a practical means of
providing power for the flywheel, heat engine, and drive wheel links
in a hybrid heat engine/flywheel powered car. Computer simulation
of vehicles driven over the Federal Emissions Test Driving Cycle
showed no fuel economy advantage for the hybrid-powered automobile
when compared with a conventionally powered automobile. Mechanical
Technology, Inc. , in its transmission study, arrived at conclusions
similar to Sundstrand.
13. Although not all of the goals were met, the EPA-funded programs
resulted in some technology advancements, a much clearer definition
of critical problem areas, and the establishment of preferable system
operating modes. While the hybrid vehicle has proven to be techni-
cally feasible, it is a complex costly system when configured to match
the performance of conventional internal combustion engine powered
vehicles.
H-5
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SUMMARY
-------
SUMMARY
Electric and hybrid power systems are unique alternatives to
heat engines for automotive propulsion. A status review has been made of
such systems in this country and, where information was available, in
foreign nations. A number of prototype vehicles have been built with private
capital, and, in some cases, federal funding ;has been used to evaluate and
test these systems. In particular, the results derived from EPA-funded
programs were reviewed in context with the design goals established by the
Alternative Automotive Power Systems (AAPS) Program for personal passenger
cars.
S. 1 ELECTRIC VEHICLES
Because of the growing concern over air pollution, interest in
electric vehicles was renewed in the late 1960's and early 1970's, principally
for delivery vans and trucks in Great Britain and for compact and subcompact
cars in Japan. The primary consideration was that extensive use of electric
vehicles could shift the burden of controlling exhaust emissions from motor
vehicles to stationary electric generating plants supplying energy for re-
charging batteries, where the treatment of stack exhaust could be more easily
controlled. Furthermore, the current use of petroleum-based fuels for auto-
motive propulsion could be diminished, and personal transportation energy
needs could be supported to a large degree by coal or nuclear resources. This
renewed interest has not culminated in any extensive production of electric
cars for numerous reasons. One overriding reason is the continued limited
range of this vehicle--about 50 miles with lead-acid batteries (the only eco-
nomically viable electric energy storage device available today). Another is
that, even with lead-acid batteries, the projected purchase cost of electric
vehicles is still significantly higher than that of the gasoline-powered vehicle.
S-l
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S. 1 . 1 Power Plant Description
The basic power plant in electric vehicle designs consists of
one or more electric motors and controllers, perhaps a transmission or
other gears, and a battery system. Lead-acid batteries have been used in
most cases, and the direct current electric brush motor is used by an over-
whelming majority of vehicle designers and fabricators. In some systems,
regenerative braking is used which causes the motor to operate as a generator,
permitting recharging of the battery as the car decelerates. Figure S-l
illustrates the main components of an electric car drivetrain in schematic
form, and Figure S-2 depicts similar components as installed in the General
Motors Electrovair II electric car.
S. 1. 1. 1 Design Features --Batteries
Currently, a major problem is the limitation on the amount of
energy and power that can be delivered by a given-size battery; this limitation
has a direct effect on vehicle range and acceleration. Evidence of this problem
is seen in the restricted operation of contemporary electric vehicles as illus-
trated in Table S-l. This is a partial list of electric vehicles built to prototype
level of design or to commercial design specifications for small quantity pro-
duction in the United States. Analytical studies have shown that battery re-
quirements for powering a full-performance family car are a specific energy
density of about 135 watt -hours per pound to satisfy vehicle range, and a
specific power density of about 95 watts per pound to satisfy vehicle accelera-
tion. Current battery capabilities (Table S-2) approach the power density
requirement but fall far short of the energy density requirement. In a compact
electric car, travel distances comparable to a heat engine car (without re-
fueling) cannot be approached even with a battery system weighing about one-
third of the vehicle curb weight.
When promoting a new battery for development, with intended
application to electric vehicles, the technical comparison is most often based
on specific energy density. As electric vehicle programs proceed, other
factors, implicit in the design of battery systems, must be considered. One
S-2
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DRIVE EFFICIENCY
• DRIVE EFFICIENCY
Figure S-l. Electric Car Drivetrain Showing the Main Components
COOLING OIL RESERVOIR
l~ BATTERIES
-LOGIC CONTROLS
DC TO AC INVERTER
^»
GEARBOX
AC INDUCTION MOTOR
OIL RADIATOR AND FAN
OIL PUMP AND MOTOR
INVERTER TRIGGER CONTROLS
Figure S-2. Phantom View of General Motors Electrovair II Showing
the Location of Major Experimental Components
S-3
-------
Table S-l. Electric Vehicle Summary Data for Operating
Passenger Models in the United States
Car Name and
Manufacturer
COMUTA
Ford
GM 5U
General Motors
SUNDANCER Z
ESB
MARQUETTE
Westinghouse
HENNEY KILOWATT
Union Electric
YARDNEY
ALLECTRIC
West Penn
Power Co.
"MINI"
General Electric
American Motors and
Gulton Ind.
ESB
Renault
Rowan Electric
ALLECTRIC II
West Penn Power Co.
Model A
Garwood Si Stelber Ind.
CORTINA
ESTATE CAR
COMET
Ford
CITY CAR
PINTO
MARS II
Elect. Fuel
Prop. Inc.
ELECTROVAIR
General Motors
ELECTROVAN
General Motors
CARMEN GHIA
Allis Chalmers
SIMCA
Chrysler
Elect. Fuel
Prop. Inc.
FALCON
Linear- Alpha
"Test data
Basis of data not verifiable
C0esisn goals
Vehicle
Curb Weight,
pounds
1.200
1,250
1,600
1,730
2, 135
1,600
2, 160
2,300
1,100
--
1,300
2,300
3,086
3,800
3,200
3,640
3,400
7,100
3,440
--
3,400
--
Drive
Motor(s)
Two 5 hp
Series dc
8-1/2 hp
Series dc
(54 Ih)
8 hp Scries
dc (83 Ib)
Two 4-l/2hp
dc (45 lb|
7. 1 hp
Series dc
7. 1 hp
Series dc
7. 1 hp
72Vdc
dc Motor
10.9 hp
~~
--
Two dc
Compound
7. 1 hp dc
40 hp 100V
(150 Ib)
85 hp
40 hp
15 hp dc
100 hp
ac induction
125 hp
ac induction
"
"
"
25 hp
ac induction
motor
Maximum
Speed,
miles per hour
40a
40a
60+*
25b
40b
55b
50C
55b
50b
40b
40C
50°
52b
60b
70"
50b
55"
60 to 65C
80b
70C
--
--
85b
60b
Energy
Source and
Capacity
Lead-acid
48V (384 Ib)
Lead-acid
84V (329 Ib)
Lead-acid
86V (750 Ib)
Lead- acid
72V (800 Ib)
8 kW-hr
Lead-acid
(800 Ib)
8 k\V-hr
Silver-zinc
1? kW-hr
(240 Ib)
Lead-acid
72V (900 Ib)
9 kW-hr
Lead-acid and
Nickel- cadmium
Lithium-nickel
fluoride (150 Ib)
and Nickel-
cadmium (100 Ib)
Lead-acid
(72V)
Lead-acid
Lead-acid
(900 Ib)
(520 Ib)
Nickel- cadm lum
J900 Ib)
Sodium- sulfur
(1,086 Ib)
Lead- acid
(956 Ib)
Lead-acid
96 V (1,7,00 Ib)
30 kW-hr
Silver-zinc
530V (680 Ib)
19.5 kW-hr
Hydro gen -oxygen
fuel cell
180 to 270 kW-hr
Lead-acid
120V (1,534 lb|
Lead-acid
(1,400 Ib)
Lead-acid
cobalt
Lithium-nickel
fluoride
(360 Ib)
Range, miles
39@25 mphb
47 @30 mphb
70 to 75
on SAE
Residential1"
50b
40"
77b
50b
100 @
40 mphb
150 with
regeneration
25 to 35b
100b
50b
39. 9 @
25 mphb
--
39@
40 mphb
70 to 120b
40 to 80b
100 to 150b
60 @
60 mphb
40b
150 to 175b
75 @ 30 mphb
S-4
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Table S-2. Characteristics of Currently Available Secondary Batteries
Battery Type
Lead -Ac id
Nickel-Iron
Nickel -Cadmium
Specific
Energy
Density
W-hr/lb
20
13
12
Energy
Density,
W-hr/in3
2.0
1.2
1. 1
Specific
Power
Density,
W/lb
100
60
80
Approx.
Relative
Cost
1
3
20
Remarks
Standard
Excellent life;
poor mainte-
nance; nickel
supply limited
Good cycle life;
cadmium sup-
ply limited
W-hr/lb. Watt hours per pound W/lb = Watts per pound
W-hr/in^ = Watt -hours per cubic inch c r
objective of system design would be to reduce vehicle weight and to minimize
influences such as drag, frontal area, acceleration, and peak cruise speed,
which would allow a reduction in battery energy usage.
An additional problem with the electric vehicle is the power
and time needed to recharge the batteries. Ordinarily, recharge time will
exceed discharge time so that extensive vehicle usage •will be limited unless
provisions are made for exchange of depleted batteries for fresh batteries.
The capability of residential electrical grids to supply large power levels
during daytime for a large number of electric vehicles may also be a prob-
lem. Possible solutions are slow charging during evening hours and higher
efficiency for charge acceptance of batteries.
In selecting batteries for electric vehicles, a dominant param-
eter has been purchase cost. Cost is influenced by the basic raw material
cost and the demand/availability ratio assignable to the raw materials. In
addition to original purchase cost, consideration must be given to battery
replacement cost and operating cost. For this reason, lead-acid batteries
are almost universally used. For high-temperature batteries, cycle life
S-5
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and, especially, time at operating temperature are important factors for
determining frequency of battery replacement.
No one battery has been developed yet to satisfy the combined
design requirements for low cost, long lifetime, high energy density, high
power density, and ease of maintenance. Some of the batteries and battery
systems that are of interest are described briefly in the following paragraphs.
In recent years, the applicability of the lead-acid battery for
propelling electric highway vehicles has improved considerably. Most of the
progress in lead-acid systems has been made in the small and intermediate
sizes such as for automobile starting, golf cart propulsion, and fork lift
propulsion and power, where high production volume is possible. Little
further improvement in lead-acid battery performance is expected, except
in lifetime.
The nickel-iron system has been proposed as a low-cost
replacement for the lead-acid battery. Intensive work by Westinghouse has
improved battery life and introduced new maintenance concepts, but this
battery appears best suited for industrial applications because of cost, poor
low-temperature performance, poor charge retention, and the need for fre-
quent service. Except for lifetime, the nickel-iron battery is not competitive
in most respects with lead-acid batteries.
Nickel-cadmium batteries, when referenced to lead-acid bat-
teries, have about the same performance, longer cycle life, and cost con-
siderably more.
In contrast to the aforementioned current battery systems,
there are other systems under development with characteristics that theoreti
cally are more capable of meeting the cited battery requirements. As an
example, for near-term applications, nickel-zinc batteries .offer higher
energy density possibilities, but cost and nickel availability are drawbacks
for supplanting lead-acid batteries. A specific energy density of 30 watt-hours
per pound and a specific power density of 150 watts per pound seem possible.
Metal-gas batteries provide energy densities in the 30 to 60
watt-hours per pound range, depending on the reactants selected. The use
S-6
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of air in these batteries is advantageous for obvious reasons (e. g. , no on-
board storage required), but they require the addition of scrubbers for carbon
dioxide removal, an air blower, and a water makeup system, which negate
much of the gain. Also, a low-cost suitable air electrode has not been dis-
covered. Work on the nickel-hydrogen battery has increased, but work on
other metal-gas batteries (e.g., zinc-oxygen or zinc-air) has declined.
Alkali-metal/high-temperature batteries are theoretically
capable of meeting the goals that have been established for full-performance
vehicles. Demonstrations of high power density and high energy density have
been made, although not always in the same cell. For the far-term period
(1985 to ZOOO), such systems are most favored, but in most cases they are
still undergoing research for proof-of-principle.
The sodium-sulfur system, first announced by Ford, is
receiving international attention. The major United States program on the
sodium-sulfur battery is Ford's, although TRW Systems, General Electric,
and others have also worked on it. All sodium-sulfur ceramic electrolyte
projects face the same key problem today; namely, deterioration of the
beta-alumina electrolyte after 1000 to 2000 hours at working temperatures.
In addition, economic success will ultimately depend on finding inexpensive
ways to produce the desired ceramic and to fabricate large batteries.
The lithium-sulfur system has been under development for a
number of years at Argonne National Laboratory, with a smaller effort at
Atomics International. Test results show the system has the desired charge
and discharge rate characteristics for a vehicle battery, although the life is
limited and sulfur utilization has been too low to allow high energy densities
to be sustained. Obtaining low-cost materials compatible with this battery
environment continues to be a major problem.
The lithium-chlorine system was the first one investigated by
General Motors. It showed high power densities, but was hampered by dif-
ficult corrosion problems at the 700-degree-centigrade operating temperature.
Later, a modified system was investigated by Sohio.
S-7
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Organic electrolyte batteries offer the possibility of high energy
densities at ordinary temperatures and are attractive for this reason; however,
power densities are low. To date, no long-cycle-life, rechargeable organic
electrolyte cell has been built.
Zinc-halogen cells have been investigated in two laboratories.
The Zito Company reports long cycle life for an aqueous zinc-bromine cell,
but the energy density is too low to be of interest. A different concept has been
demonstrated by Occidental Petroleum that uses a zinc-chlorine battery in which
chlorine is stored as a solid hydrate at 8-degrees centigrade or below. For far
term applications, this battery appears promising if development goals are
achieved.
Work on batteries for electric vehicles is accelerating abroad.
The major activities are in the Federal Republic of Germany, Japan, the
United Kingdom, and the U.S.S.R. In each case, the government is either
formally participating or influencing the direction of work. In at least five
other countries (France, Switzerland, Sweden, Italy, and Czechoslovakia),
vehicle battery projects are known to be under way. The most dramatic
achievement of the past year was the use of a sodium-sulfur battery to power
a small van. This was accomplished by the Electricity Council Research
Centre at Capenhurst in the United Kingdom.
S. 1. 1.2 Design Features --Motors and Controls
A wide selection of motor design and controller combinations
has been used in past and present electric cars. The controllers vary in
complexity from the use of simple carbon-pile resistance stacks employed
on early streetcars to complex three-phase, silicon-controlled rectifier time-
ratio controls used in some of the advanced experimental alternating current
motor drives.
The overwhelming majority of electric vehicle builders use
the brush direct current motor. Brushes are easy to replace and are capable
of lasting 50,000 vehicle miles. For motor control, the chopper circuit
(generally using silicon-controlled rectifiers) provides an efficient means
for transforming a fixed battery voltage to a smoothly varying effective volt-
age matching the power requirement of the motor at all operating speeds.
S-8
-------
To date, there has been no mass production of motors or
motor controllers that are suitable for family-size vehicles. Because of this
status, these powertrain elements presently have a high cost, and it is this
high cost that is the greatest hurdle to their widespread use in automotive
vehicles. In addition, electric motors, particularly direct current motors,
have not been developed to provide combined optimization of efficiency, •weight,
size, and cost for vehicle propulsion. Part-load efficiency is very important
because during a typical urban driving cycle the motor is expected to operate
at part-load most of the time; this efficiency will be lower than that available
when operating at design load.
S. 1. 2 Vehicle Performance Characteristics
In general, most electric vehicles do not perform up
to heat engine vehicle capabilities, particularly with respect to maximum
acceleration, speed, range, hill-climbing ability, and passenger capacity.
The usual maximum speed varies between 30 and 50 miles per hour. When
a compact car weighing about 2, 000 pounds is converted to an electric vehicle
weighing 3, 000 pounds (including 1, 000 pounds of batteries), it cannot travel
more than 30 to 50 miles between charges in stop-and-go driving. If greater
battery weight is added to increase the range, the handling characteristics
such as steering and braking are further degraded, in addition to having poor
acceleration and an uncomfortable ride. It is therefore concluded that a
general-purpose, all-electric family car is not possible with present lead-
acid batteries.
Though some improvement can be made in aerodynamic drag
by streamlining, and in road drag by using radial ply tires, the basic power
to move and accelerate vehicles of certain weight and cross-section area
remains essentially fixed. Reducing drag to a minimum while increasing
drive system efficiency to a maximum are the only steps outside of battery
development that can be taken if the ratio of drivetrain weight to total weight
is to be maintained at feasible levels. Unfortunately, these actions can
provide only minor improvement.
S-9
-------
When energy requirements of electric vehicles are compared
to conventional cars, a careful examination must be made of the efficiencies
of the various steps of energy flow. But to avoid making assumptions re-
garding the efficiency of elements in the vehicle powertrain, road test data
for a given vehicle must be used. As one example, in a comparison of energy
expenditures between electric and gasoline engine powered vehicles used in
postal delivery service, the electric vehicle showed some advantage for this
special application. If these results were extrapolated to passenger cars,
it should be noted that for equivalent weight vehicles, the gasoline engine
powered car has superior driving range, cruise speed, acceleration, and
passenger/luggage accommodations. In favor of the electric car, however,
is the prospect that energy for propulsion can be derived directly from non-
petroleum based sources such as nuclear power or abundant supplies of coal.
Eventually, these sources can also be available indirectly through production
of synthetic fuels for heat engine powered cars.
While an electric vehicle has fewer moving parts than an
internal combustion engine powered vehicle, no definitive data are available
for passenger cars that can establish a statistical base for maintenance
requirements and cost.
In regard to safety, general requirements for an electric
vehicle will be comparable to those for a similar heat engine vehicle. Spill-
proof battery caps must be used; in the event of an accident, there must be
provision to avoid hazards from spilled electrolyte. There must be redundancy
in design to minimize shock hazard, and short-circuit protection must be
maintained.
S. 1. 3 Current and Projected Status
Electric delivery trucks or vans and electric utility vehicles
have been built in increasing numbers in Great Britain for the past decade,
and are now estimated to exceed 75,000 vehicles. Small electric cars and
electric utility vehicles are currently being produced in Japan in greater
numbers than in the United States, largely because of the ban on heat engine
S-10
-------
vehicles in Osaka during the 1970 World's Fair. Many demonstration and
prototype models have been built in the United States, but, excluding electric
golf carts and electric fork lifts, no major production of electric vehicles is
currently under way.
Excluding the special-purpose applications of golf carts,
electric fork lifts, and delivery vans, no major production of electric passen-
ger vehicles is expected for the next 10 years. Only very low production of
vehicles for use by electric utilities and an increasing number of individual
conversions to electric propulsion are expected to be the extent of passenger
cars on city streets during this time.
In addition, the electric car would have to be sold at a price
comparable to the heat engine car for general acceptance. This would require
subsidies or tax incentives, as well as mass production methods to reduce
fabrication costs. Of importance also is an acceptable cost for battery re-
placement and the assurance of low electric power rates to control vehicle
operating costs. This picture could change, should there be a major gasoline
shortage, a restriction on operating conventional vehicles in some areas due
to air quality constraints, or a breakthrough in battery technology that would
allow much improved vehicle performance and range.
S. 2 HYBRID HEAT ENGINE/BATTERY AND HEAT
ENGINE/FLYWHEEL VEHICLES
The problem of adequate operating range for electric vehicles
has been already noted. Until low-cost, high-capacity batteries become avail
able to permit operating ranges for electric cars that are nearly comparable
to those for gasoline engine-powered cars, other concepts must be examined
in the search for a low -pollution vehicle that could satisfy personal transpor-
tation needs. One such concept that has received the attention of automobile
designers in the last 5 years is the hybrid vehicle — a vehicle combining
various power delivery systems in the powertrain to use each form of power
most effectively. The most common form of system operation that has been
studied relies on a small, nearly constant power heat engine to supply energy
S-ll
-------
for vehicle cruise and for recharging a battery or flywheel. The additional
power for vehicle acceleration is supplied by the battery in the case of an
electric energy storage hybrid, and by the flywheel in the case of an inertial
energy storage hybrid. With this form of heat engine operation, the hybrid
concept offers the possibility of reduced mobile emissions. A shift of ex-
haust emissions and energy source to stationary electric generating plants,
as in the case of electric vehicles, would be possible only if the energy for
recharging the battery or flywheel was available from an external stationary
power source, and the heat engine was then used just for supplying emergency
power or for extending vehicle range on an infrequent basis.
To evaluate various hybrid concepts, the EPA under the AAPS
Program assumed the task of planning a hybrid vehicle prototype development
program. Implementation of a 3-year program began in 1970 with participa-
tion of several companies offering the required technical expertise. Em-
phasis was placed on achieving the original 1976 Federal emission standards
without the use of engine add-on control devices (e.g. , catalytic converters).
The hybrid vehicle development program was terminated because of funding
limitations imposed in Fiscal Year 1971 and because it was found that operat-
ing a spark ignition engine in a hybrid mode still required the same types of
exhaust aftertreatment needed on conventional systems. This latter fact was
of overriding importance in terminating further work on hybrids.
It should be noted that many of the study guidelines that resulted
in specific powertrain design constraints for these programs have since been
under revision. Revised guidelines for vehicle range, acceleration perfor-
mance, cruise speed, exhaust emissions, and fuel economy could result in
modifications to system designs as well as to study conclusions.
S. 2. 1 General Concept Designs and System Operation
Hybrid vehicle powertrain concepts can be grouped into two
broad classes (Figure S-3). The first class, series configuration, is charac-
terized by the principle that all energy flowing from the heat engine to the
S-12
-------
In contrast to the electric system, the hybrid heat engine/
flywheel design provides higher energy densities resulting in system weights
and volumes that are a smaller fraction of the allowable value for the total
propulsion system.
S. 2. 3 Hybrid Heat Engine/Battery Vehicle
S.2.3.1 System Designs
Two major hybrid heat engine/battery system concepts funded
under the AAPS Program were the TRW Systems, Inc., electromechanical
transmission system (Figure S-4) and the Minicar, Inc. , heat engine/battery
vehicle (Figure S-5). This included the building of a breadboard prototype
system by TRW and a vehicle-mounted prototype system by Minicar. Under
the EPA Federal Clean Car Incentive Program, Petro-Electric Motors
installed a heat engine/battery powertrain in a 1972 Buick Skylark. Another
AAPS-funded study was performed by The Aerospace Corporation to provide
an analytical evaluation of hybrid heat engine/battery vehicles. This effort
did not include building a breadboard or prototype device. In addition,
General Motors built its own prototype system called Stir-Lee (modified
Opel-Kadett). Figure S-6 shows the major components as located in the
vehicle, and Figure S-7 is a schematic diagram of the hybrid power system.
S.2.3.2 System Design Requirements and Achievements
TRW performed computer simulation studies to evaluate the
automotive propulsion systems on the basis of total weight, volume, and
efficiency over the Federal Emissions Test Driving Cycle. The system
modeling used manufacturer's data for major components and included
analysis of generators, traction motors, power conditioning unit, gearing,
and batteries. A dynamometer demonstration breadboard was also built as
proof-of-principle hardware. Poor correlation was found between computer-
predicted results and breadboard testing results. A reduction in overall
powertrain efficiency (road demand/engine output) from the predicted 76.7
percent to a nominal test value of 50 percent is the most encompassing
S-15
-------
INTERNAL
COMBUSTION
ENGINE
SPEED
ENGINE
ERROR
I I
SPEEDER POWER
CONDITIONING
UNIT
W0 T0
TRACTION OR
REGENERATION
POWER
TORQUER POWER
CONDITIONING
UNIT
DRIVING
WHEELS
OPERATOR
"COMMAND
Figure S-4. Schematic, TRW Electromechanical Transmission
Mode I Operation
TORQUE: CONVERTER
2/1 STALL RATIO
AXLE
3.57/1 RATIO
TRANSMISSION
I.8I/ I LOW
I / I HIGH
6.90 X 13
TIRES
BATTERY PACK
LEAR SIEGLER G-22-C
DC MOTOR/GENERATOR
INTERNAL COMBUSTION
ENGINE 6 CYL.
OPPOSED 164 CU.IN.
AIR COOLED
Figure S-5. Minicar Drivetrain
S-16
-------
HEAT ENGINE/BATTERY HYBRID
HEAT ENGINE/FLYWHEEL HYBRID
HEAT
ENGINE
GENERATOR
So
«;:
8
MOTOR
BATTERIES
TRANS-
MISSION
FLYWHEEL
TRANS-
MISSION
WHEELS
HEAT ENGINE/BATTERY HYBRID
HEAT
ENGINE
o
-------
rear wheels first passes through an intermediate energy conversion device or
devices. The second class, parallel configuration, is characterized by the
principle that some of the energy flowing from the heat engine passes directly
to the rear wheels, with the balance of the energy directed in a parallel path
through an energy conversion device or devices.
Different operating modes have been considered for the hybrid
vehicle powertrain. The majority of designs are based on the unimodal con-
cept, whereby a portion of the heat engine energy is used continually to replace
energy drained from the on-board energy storage device (battery or flywheel).
Another design is the bimodal operating scheme, whereby the vehicle is driven
in an all-battery (or all-flywheel) mode or all-engine mode. The bimodal
vehicle •would normally be driven in the battery/flywheel mode with recharging
provided by a source external to the vehicle; the engine in this case is used
merely to extend vehicle operating range whenever required.
S. 2. 2 Design Impact of Vehicle Specifications
Early in the AAPS program, vehicle specifications for each of
a number of urban automotive applications were developed jointly by EPA and
the several contractors involved in the hybrid system study effort. In general,
the propulsion system weight limitations impose upper bounds on the ability of
the system to furnish power and energy required to operate the vehicle for
extended durations at the specified road performance levels.
Certain power plants are not applicable to the hybrid electric
family car under the propulsion system weight allocation defined by the EPA
specification, and only the spark ignition engine (reciprocating or rotary) and
gas turbine engine result in realistically achievable values for battery power
and energy densities. It should be noted, however, that more recent develop-
ment work could result in some modifications to these conclusions; e. g. ,
Stirling engine weight and size have been reduced markedly from former
levels.
Generator, motor, and battery in electric system, or flywheel and trans-
mission in inertial system.
S-14
-------
DC TO AC MODULATING INVERTER
BATTERY CHARGING CONTROL
HYDROGEN RESERVOIR
STIRLING ENGINE
RADIATOR
AND FAN
COMMUTATING
CAPACITORS:
LOGIC 4 INVERTER CONTROLS
INDUCTION MOTOR (3-PHASE)
STARTER MOTOR
ALTERNATOR
w
•COMBUSTION AIR BLOWER
Figure S-6. Phantom View of General Motors Stir-Lee I
OPERATOR
CONTROL
3 PH
ALTERf
i
FIE
CON
ASE
-IATOR
ID
TROL
RECTIFIER
—
BATTERY
LOGIC
CONTROLS
1
MODULATING
INVERTER
3 PHASE
AC MOTOR
G
DIFFERENTIAL
Figure S-7. Schematic, General Motors Stirling-Electric Hybrid System
S-17
-------
departure. The test program allowed the major contributors to system losses
to be identified. TRW stated, "In most cases, the losses can be reduced
significantly by design refinement."
A Chevrolet Vega engine modified for intake manifold fuel
injection was used for the heat engine element in the TRW powertrain system.
The emission control system proved very effective in terms of hydrocarbon
and oxides of nitrogen control. The combined use of the hydrocarbon accumu-
lator and three-component catalyst resulted in HC emissions ranging from
34 to 73 percent of the original 1975 Federal emission standards. The NO
X
results ranged from 15 to 80 percent of the original 1976 standards. The CO
standard -was met with a seven percent margin on one occasion, but was ex-
ceeded during all other tests.
The first configuration tested by Minicar did not provide
sufficient electric power to reduce emissions significantly. After many
improvements, a final prototype configuration, the Hybrid C-l, was built.
Its electric system provided up to 27 horsepower at the drive wheels, which
was short of the 40-horsepower goal. Operating performance did not match
that of many equivalent-size standard vehicles, and emissions were not
reduced to acceptable levels. The results of measured emissions over the
Federal Emissions Test Driving Cycle were HC = 3.15 grams per mile,
CO = 29. 6 grams per mile, and NO =1.0 grams per mile.
.X
The Petfo-Electric hybrid automobile was delivered to EPA
in February 1974 and is currently undergoing test and evaluation.
The Aerospace Corporation study was aimed at determining
the feasibility of using a hybrid heat engine/electric propulsion system as
a means of reducing exhaust emissions from street-operated vehicles.
Analytical results from computer calculations are as follows:
a. The study indicated that only the spark ignition engine and the
gas turbine engine offer reasonable weight margins for the
battery system. After all component weights were subtracted
from the 1500 pounds allocated powertrain weight, the weight
available for batteries requires that they deliver a power
S-18
-------
density of just over 200 watts per pound and an energy density
of just over 20 watt-hours per pound for the spark ignition
engine powered parallel hybrid.
b. Fuel economy estimated for the family car series configura-
tion was 11 miles per gallon and for the parallel configuration
was 12. 5 miles per gallon. These estimates are based on a
fully warmed-up vehicle driven over the Federal Emissions
Test Driving Cycle. The results are equivalent to the mileage
expected for a conventional, similar-size 1970 car.
c. For a parallel configuration with spark ignition or gas turbine
engines, most emissions were predicted to be reduced to
levels below the original 1975-1976 Federal emissions
standards. The one exception was oxides of nitrogen from
the spark ignition hybrid. The spark ignition engine utilized
lean operation, an oxidation catalyst, and exhaust gas
recirculation.
d. An estimate of vehicle system costs for the family car, as
ratioed to a conventional car, ranged from about 1. 15 for a
hybrid spark ignition engine system to 2. 25 for a hybrid
Stirling engine system. The conclusion drawn was that the
hybrid vehicle would require a significant increase in expendi-
tures by the consumer for first costs.
For General Motors' Stir-Lee I car, a readily available 8
horsepower Stirling engine was used to drive a three-phase alternator
delivering rectified power for recharging batteries. Battery power was
delivered to a three-phase alternating current motor through a modulating
inverter. The total weight of the Stir-Lee I powertrain was 1, 189 pounds,
which compared with 498 pounds for the standard Opel Kadett powertrain;
a total vehicle weight was 3, 200 pounds compared with the standard weight
of 1,990 pounds for the Opel Kadett.
At about 30 miles per hour on a level road, the General Motors
Stir-Lee I vehicle achieved a fuel economy of 30 to 40 miles per gallon. Bat-
tery capabilities limited the range to about 30 to 40 miles at 55 miles per hour.
Acceleration from 0 to 30 miles per hour took about 10 seconds. It achieved
a top speed of 30 miles per hour with engine power only and a top speed of
55 miles per hour if battery power was added. General Motors noted that
HC and CO emissions (in grams per horsepower-hour) were low, but NO
3C
emissions were much higher than expected for this engine; 1976 Federal
S-19
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standards were exceeded for all three species. The expectations were that
engine modifications could provide major reductions in NC>x levels.
S.Z.3.3 Component Design Requirements and Achievements
S. 2. 3. 3.1 Motors, Generators, and Control System
There were no EPA contracts awarded for development of
rotating electrical equipment and associated controls. Therefore, the dis-
cussion is limited to general design considerations and the state of the art of
these components as related to hybrid vehicles.
The motor overload capability is very important in the parallel
hybrid configuration. At cruise velocity, all the power is mechanically trans-
ferred from the heat engine to the wheels. Since the motor is not supplying
continuous power for cruise, it can be sized for supplying transient power
only, resulting in a small, lightweight unit. On the other hand, the series
hybrid configuration requires that the motor be sized for the more rigorous
requirement of continuous cruise power and is much heavier than the parallel
system motor. Allowable temperature rise is the long-term constraint which
must be met by sufficient sizing or adequate cooling system.
The motor control system for the series configuration hybrid
electric vehicle is identical to that for the all-electric vehicle. However, a
simple separate control of the generator field is required in the series
configuration hybrid to modulate the power output from the heat engine for a
fixed engine speed and convert it to electrical energy to be delivered to the
motor. The motor controller for the parallel configuration hybrid system,
by contrast, is more complex than the series hybrid because it requires
special logic to control the electric motor which is augmenting power from
the heat engine.
S.2.3.3.2 Batteries for Hybrid Vehicles
As part of the hybrid heat engine/electric vehicle program,
two investigations were initiated to study the application of lead-acid batteries
to hybrid vehicles. Contracts were awarded to Tyco Laboratories, Inc. , and
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to TRW Systems (with Gould as subcontractor ) to fill a need for data on such
batteries when operated under the unique conditions imposed by the hybrid
vehicle. Preliminary results of investigations by The Aerospace Corporation
and TRW Systems were used to establish battery operating requirements as
documented in the EPA Statement of Work.
In the initial effort, each contractor studied the applicability
of commercial lead-acid batteries to the hybrid vehicle under simulated
operating conditions. It was concluded that commercial SLI (starting-lighting-
ignition) batteries of conventional design were unsuitable because of their short
life. However, the results did indicate that, with certain design modifications,
lifetimes might be satisfactory.
Based upon these test findings, along with measured and
calculated power losses in the battery, TRW/Gould concluded that, with
limited optimization, an advanced design SLI battery could be developed to
deliver 150 watts per pound for 75 seconds. Additionally, TRW/Gould pro-
jected that with more extensive optimization, which would include the use of
lower resistivity materials and a new grid design, the battery could be re-
designed to produce 200 watts per pound for 75 seconds, and this could be
achieved without any major changes in existing manufacturing methods or cost.
In its lead-acid research battery design for the hybrid vehicle,
Tyco Laboratories used a quasi-bipolar arrangement. Under the same test
conditions as the commercial SLI battery, the research battery lasted for
1,000 high-rate hybrid test cycles, compared with 350 of the same test cycles
achieved by the commercial battery. Since the hybrid operation is expected
to involve 500 such high-rate cycles, this achievement of triple the life is
significant; however, the contract duration did not permit verification of over-
all cycle life and calendar life.
Based on tests of the SLI battery, TRW/Gould made selective
changes to the SLI cell design and, for a research battery design, was able
to increase specific power density to 150 watts per pound for 75 seconds and
'Gould supplied the batteries tested by TRW.
S-21
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204 watts per pound for 20 seconds. The higher power density was obtained
by using a greater number of thinner plates per unit volume and by using higher
conductivity lead alloy grids and conductors. Tests of the new design indicated
cell lifetimes of 8, 000 to 12, 000 charge and discharge pulses consisting of
30 low rate shallow pulses for each high rate pulse. The conventional SLI
battery laeted for 6, 859 pulses under the same test conditions.
TRW/Gould also designed and built several bipolar cells for
the hybrid vehicle. Cycle life of the best bipolar positive plate was 6,000
pulses, with 600 deep discharge cycles to 1.0 volt. This was judged by TRW/
Gould to be as good as could be expected from a high-quality conventional bat-
tery. Based upon the bipolar single-cell test results, TRW/Gould conserva-
tively estimated that a prototype battery could be built which would have a
specific power density of 164 watts per pound and a power density of 21 kilo-
watts per cubic foot for a 7 5-second discharge. Such a battery could be
available in 2 years and in production in 4 years. Projections by TRW/Gould
indicate a specific power density of 300 watts per pound could be achieved in
about 5 years.
In a study supported by EPA under an interagency agreement,
the U.S. Army Electronics Command tested nickel-zinc battery cells for the
hybrid vehicle. Power densities up to 300 watts per pound for 5 seconds were
achieved. These tests demonstrated that this battery could be designed to
provide adequate specific energy density (watt-hours per pound) and specific
power density (watts per pound) for the hybrid vehicle application, but that
considerably more development would be needed to obtain satisfactory life.
S.2.3.3.3 Heat Engines
Systems studies by TRW have shown that even conventional
engines operating in the hybrid mode can have lower emissions and improved
fuel economy in comparison with these same types of engines in con-
ventional automobiles. Since the engine in a hybrid vehicle need provide
Lockheed Missiles and Space Company in its hybrid heat engine/fly wheel
vehicle study arrived at similar results.
S-22
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only the maximum power required for cruising (and not acceleration), it can
be smaller than the engine for the conventional automobile. Engine power is
expected to be 90 to 110 horsepower for a full-size passenger car.
Based on engine weight and volume and allowable propulsion
system weight and volume, The Aerospace Corporation determined that only
the gas turbine and the spark ignition reciprocating and spark ignition rotary
engines were feasible for installation in a hybrid heat engine/battery auto-
mobile. Recent reductions in Stirling engine weight and volume might revise
the conclusions related to this engine.
In engine testing supported by EPA under an interagency agree-
ment, the Bureau of Mines Fuel Combustion Research Group measured emis-
sions of two conventional 350-CID engines under simulated hybrid operating
conditions. The results indicated that the emission levels of the original 1976
Federal emission standards would not be achieved by these engines operating
in the hybrid mode without exhaust after treatment.
S.2.4 Hybrid Heat Engine/Flywheel Vehicle
S. 2. 4. 1 System Designs
Work was performed by Lockheed Missiles and Space Company
in the investigation of inertial energy storage under two separate contracts.
The first, Flywheel Feasibility Study and Demonstration, had as its objectives
the analytical determination of the feasibility of the flywheel hybrid as a low-
emission propulsion system for urban vehicles and the demonstration and
performance evaluation of full-scale flywheels for hybrid applications. The
second, Flywheel Drive Systems Study, as applied to the family car, was
directed toward advancing the development of flywheel systems technology.
In the Lockheed concept, the drivetrain consists of a heat
engine coupled to the flywheel and the vehicle wheels through a planetary/
hydrostatic power-splitting transmission. The heat engine provides cruise
power, drivetrain losses, accessory power, and flywheel recharging power;
the flywheel provides the power required for vehicle acceleration.
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The configuration selected by Lockheed for the family car
flywheel was an 18. 6-mch-diameter conical section with a constant radius
Hare at the periphery. This disc-shaped flywheel configuration was fabri-
cated of 4340 steel and tested during the feasibility study. Flywheel selection
was predicated on the use of available materials, and it was designed to operate
in a partial vacuum within a burst containment structure. The energy storage
capacity of the flywheel is 0. 5 kilowatt-hours at a design speed of 24, 000
revolutions per minute. The weight of the flywheel alone is 86 pounds, which
constitutes approximately 46 percent of the weight of the complete flywheel
assembly.
Concurrent with the work done by Lockheed, an experimental
and analytical study of high specific energy density flywheel systems for use
in automotive propulsion systems was conducted by Johns Hopkins University
(Applied Physics Laboratory). This study had two objectives: (a) the proof-
of-principle demonstration of the use of filamentary or composite materials
of high uniaxial tensile strength in rotor configurations that would have very
high specific energy densities (i.e., 30 watt-hours/pound), and (b) the theo-
retical evaluation of the performance of such flywheels alone and in combina-
tion with heat engines. Figure S-8 illustrates the general arrangement of
components in the Johns Hopkins heat engine/flywheel hybrid concept.
HATCH BACK DOOR
CURB VKIIGHT
LOADED wtiGHT
HCAT ENGINE
FLYWHEEL SYSTEM
1400 POUNDS
I TOO POUNDS
32BHP
70 POUND ROTOR
2 kV» h
Figure S-8. Johns Hopkins Heat Engine/Flywheel Hybrid Commuter Car
CONTINUOUSLY
VARIABLE
TRANSMISSION
AND DIFFERENTIAL
S-24
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S. 2. 4. 2 System Design Requirements and Achievements
The main conclusions reached by Lockheed with regard to the
flywheel/hybrid vehicle were as follows:
a. A comparative analysis of heat engine emissions for a
hybrid flywheel drive contrasted with a conventional
three-speed automatic transmission shows that without
a catalyst, the flywheel drive offers HC, CO, and NOX
emission reductions. With a catalyst, HC and CO
emissions -were generally equivalent between hybrid
and conventional drives; the flywheel drive offered a
significant reduction for only NO emissions.
b. Fuel economy over the Federal Emissions Test Driving
Cycle for the flywheel transmission is predicted to be
roughly equivalent to that of a conventional transmission.
c. The estimated cost of ownership, size, and weight of a
family car flywheel drive falls within established EPA goals.
The primary conclusions reached by Johns Hopkins with regard
to the flywheel/hybrid vehicle were as follows:
a. The heat engine/flywheel hybrid propulsion systems satisfy
the vehicle performance requirements.
b. The spark ignition engine is the near-term choice for the
heat engine.
c. The gas turbine engine seems to offer the greatest promise
for the future because of its low specific weight, its potential
for minimizing emissions, and its operating speed, which is
close to that of the flywheel.
S. 2. 4. 3 Component Design Requirements and Achievements
S.2.4.3.1 Flywheel
Concurrent with the overall vehicle applicability and configura-
tion tradeoff studies, preliminary flywheel design studies were conducted by
Lockheed prior to fabricating and testing candidate flywheels. Six basic fly-
wheel geometries were investigated in the studies. These included the pierced
uniform disc, an unpierced uniform disc, a constant-stress disc, a truncated
conical disc, a rim-type flywheel, and the bar-type configuration. Only those
materials that could be obtained in mill-run quantities were considered. The
S-25
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most cost-effective were found to be E-glass, S-glass, and 4340-grade steel.
The filamentary composites, however, seemed readily applicable only to the
bar-type flywheel geometry. The 4340-grade steel was felt to be an excellent
candidate for low-cost flywheels in a disc configuration.
In tests to failure, the steel disc-shaped flywheel was accel-
erated until disintegration occurred at 35, 590 revolutions per minute. This
represented a peripheral velocity of 3, 170 feet per second, a specific energy
density of 26. 1 watt-hours per pound, and a total stored energy of 1. 1 kilowatt-
hours, which exceeded the design specification by a factor of about two, and
accordingly provided a margin of safety.
Disintegration of the glass composite bar-shaped flywheel of
unidirectional construction occurred prior to reaching a design speed of
ZO, 000 revolutions per minute. The maximum energy storage capacity at
failure (15,070 revolutions per minute) was 0. 568 kilowatt-hours, as com-
pared with the design point of 1.0 kilowatt-hours.
Lockheed conclusions regarding the steel flywheel were as
follows:
a. The production cost of complete family car flywheel assemblies
was projected to range from $85 to $115, depending on flywheel
configuration.
b. All the elements of a practical family car flywheel assembly
are available without further technology development.
c. Early estimates of flywheel system losses as provided to the
transmission contractors were proved by hardware testing to
be highly conservative. Flywheel windage, bearing, seal, and
vacuum pump losses were substantially lower than earlier
predictions.
d. Prevention of flywheel burst due to overspeed can be obtained
by allowing the flywheel to grow plastically into the contain-
ment ring. Total containment of a flywheel burst at energy
levels representative of what might be the case for a full-size
vehicle was not successfully demonstrated with lightweight,
low-cost materials.
Experimental work conducted by Johns Hopkins University was
directed toward a demonstration of the "superflywheel" concept in which
energy densities of 30 watt-hours per pound could be achieved. Spin tests of
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small-diameter composite rods (up to 0. 25 inches) and filamentary single
strands were conducted in which the several candidate materials exceeded
the specific energy density goal of 30 watt-hours per pound. Follow-on tests
of 30-inch-long, 1-pound rods or bars achieved 82 to 94 percent of the desired
goal.
Johns Hopkins reached the following conclusions regarding the
testing of filamentary and composite rods and bars.
a. Spin tests demonstrated the ability to achieve 48 watt-hours
per pound (without failure) with boron single strand filaments;
at burst, 36 watt-hours per pound was achieved with small
graphite/epoxy composite rods, and 31 watt-hours per pound
was achieved with small R-glass/polyester composite rods.
b. The larger 1-pound composite bars did not meet the desired
30 watt -hours per pound. The best sample S-glass/epoxy
achieved 28 watt-hours per pound, while the graphite/epoxy
achieved 26 watt -hours per pound.
c. Tensile tests indicated that the graphite/epoxy material was
substandard. While the S-glass/epoxy bars achieved satis-
factory stress levels in tensile tests, numerous surface
defects may have contributed to the inability of this material
to meet 30 watt-hours per pound requirements. With im-
proved processing techniques, Johns Hopkins felt confident
that energy densities in excess of 30 watt-hours per pound
could be achieved.
S.2.4.3.2 Transmis sions
Under AAPS Program sponsorship, two studies were conducted
on transmission designs for a parallel configuration flywheel hybrid system by
Sundstrand Aviation and Mechanical Technology, Inc. Both studies examined
the development of total energy transfer systems from the hybrid engine to
the drive wheels, and the management of the energy storage system.
Sundstrand selected a combination mechanical, hydromechanical,
and hydrostatic transmission system for linking the engine-flywheel-drive
wheels together. This transmission is made up of a five-element differential,
several hydraulic units (variable and fixed displacement), clutches, controls,
and associated gearing.
S-27
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At the conclusion of its study, Sundstrand stated that:
a. A combination of mechanical, hydromechanical, and
hydrostatic transmissions is a practical means of
providing power for the flywheel, heat engine, and
drive wheel links.
b. The selected transmission provides an infinitely variable
ratio between the flywheel and the vehicle wheels, and a
nonlinear ratio (fixed by vehicle speed) between the heat
engine and flywheel. Although the engine speed is not
independent of the flywheel speed, it does operate near
its minimum specific fuel consumption (pound fuel/horsepower -
hour) line.
c. The specified spark ignition heat engine with the selected
transmission has a greater computed fuel consumption over
the Federal Emissions Test Driving Cycle than that of a
typical three-speed automatic transmission. Cruise fuel
consumption is greater than for the three-speed automatic
below 50 miles per hour and less above this speed.
d. The theoretical fuel economy benefits that can be gained from
the flywheel energy storage concept over a "light-duty" cycle,
such as the Federal Emissions Test Driving Cycle, are
minimal because of the small amount of energy available for
storage and reuse. In fact, when the "cost" of storage in
terms of power loss is included, there is no benefit. The
more "severe" the acceleration/braking duty cycle relative
to maximum vehicle capability, and the heavier the vehicle,
the greater are the benefits derived from the flywheel energy
storage concept.
The study performed by Mechanical Technology arrived
basically at the same conclusions as Sundstrand. Mechanical Technology
proposed a power-splitting transmission. This transmission is an infinitely
variable, stepless unit that obtains torque multiplication and control by
hydraulic principles.
In a calculated comparison between the efficiencies of power-
trains for flywheel hybrid and the standard automobile for cruise operation,
the flywheel/hybrid powertrain was found to be substantially lower; even
though the transmission efficiency for the hybrid transmission was estimated
to be higher. The fuel economy of the hybrid automobile, compared with the
standard automobile, is poor up to a cruise speed of 50 miles per hour, but at
higher speeds it has superior fuel economy.
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S. 2. 5 Assessment of Hybrid Powertrain Application
to Automobiles
At the time of program suspension, EPA funds expended on
the hybrid vehicle development program had resulted in some major technology
advancements, a much clearer definition of critical problem areas, and the
establishment of preferable system operating modes. These results are
indicative of information acquired in the very early phases of development,
namely, proof -of -principle. Some forms of hybrid systems could represent
an intermediate step between current automobile powerplants and a future
system that relies totally on an energy storage device for delivering power
to the drive wheels.
The powertrain has been tested as an integrated system for
only the heat engine/battery hybrid, not for the heat engine/flywheel hybrid.
Test results showed that the concepts were technically feasible and could
operate over the desired power and speed range. System efficiencies were
lower than desired and exhaust emissions from the spark ignition engines
could only approach the original 1976 Federal emission standards by means
of the application of a catalytic converter, exhaust gas recirculation, and
lean operation. This additional complexity compromises one of the original
hopes for the hybrid vehicle; i.e. , that these engine changes would not be
required. The EPA contractors claimed that with further development some
system deficiencies could be corrected.
In regard to heat engine/battery hybrids, tests of commercial
lead-acid batteries showed relatively poor life at the performance required
for this application. Battery redesigns and advanced concepts for lead-acid
cells resulted in the achievement of power and energy levels that represent
a major increase over standard batteries for this application, leading to
optimism regarding the ability of these designs to meet most of the established
performance specifications. However, cycle life, while greatly improved,
is still short of specified goals.
For heat engine/flywheel hybrids, both conventional steel disc-
shaped flywheels and advanced material concept bar-shaped flywheels were
S-29
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tested to destruction. The conventional design met the specified goals for
energy storage level before failing. Results with the advanced filamentary
and composite rod/bar configurations were mixed, with a number of test
samples failing at rotational speeds short of planned levels. Fabrication
problems with the advanced concepts and difficulties in avoiding undesirable
stress concentrations led to early failure.
Only a limited investigation was made of the estimated
consumer purchase cost for a hybrid vehicle. Based on preliminary coarse
estimates, the purchase cost of hybrid vehicles is expected to be significantly
higher than that of current automobiles, particularly for hybrid vehicles with
advanced concept engines (e.g. , gas turbines). However, an analysis of
lifetime costs for the hybrid vehicle has not been performed wherein vehicle
4
first cost, maintenance cost, engine fuel cost, and battery replacement or
flywheel replacement cost could be assessed.
Some additional system design considerations are worth
mentioning at this point. First, some of the vehicle performance specifica-
tions adhered to during the EPA contractor studies could be relaxed for evalua-
tion of a special-purpose rather than a general-purpose car. Allowing a
reduction in acceleration levels and peak cruising speeds is expected to yield
marked reductions in the required level of battery or flywheel power density.
This result stems from two sources: (a) reduced power required and (b)
additional weight and volume available because of reductions in the size of
the heat engine and transmission and, for the hybrid battery vehicle, reduc-
tions in the size of the generator and electric drive motor. Thus, rather
than considering a hybrid vehicle designed to replace general-purpose
personal passenger cars in use in the United States, the objective rather would
be to determine just what percentage of all the various transportation needs
could be fulfilled by this special-purpose, limited-use type of vehicle.
Depending on cycle life.
Depending on fatigue life.
Particularly for the series configuration.
S-30
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Second, consideration could be given to the multimode form
of hybrid vehicle operation. As an example, recharging of the energy storage
device (battery or flywheel) could be accomplished wholly or in part by an
external stationary power source rather than solely by the on-board heat
engine. This bimodal design would permit independent operation whereby the
vehicle is powered either by the battery (or flywheel) alone or by the heat
engine alone. The most important impact could be the transfer of the energy
resource base from petroleum-based fuels to coal or nuclear power, because
electric generating plants would now supply all or part of the recharge energy.
Conservation benefits that would accrue to the limited supply of petroleum-
based fuels are obvious.
The hybrid vehicle has been proven to be a valid functioning
system, both by analysis and limited experimental tests, although not all of
the original program goals were met. At the inception of the EPA hybrid
vehicle program, emphasis was placed mainly on reduction of exhaust emis-
sions to the then promulgated 1976 Federal standards. If the program were
to be reactivated, the vehicle designs would have to strike a balance between
fuel economy and exhaust emissions, and system performance would have to
be re-evaluated in light of the revised standards.
S-31
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PART I
ELECTRIC VEHICLES
-------
1. INTRODUCTION
-------
1. INTRODUCTION
The electric car came into prominence in the early decades
of the 20th century. Initially, it seemed to offer many advantages over the
gasoline -powered car: it was quieter, issued no detectable fumes, acceler-
ated more smoothly and, even at 15 mi/hr, exceeded the speed of gasoline -
powered cars. However, in time, the gasoline engine underwent successive
design changes that increased power output and resulted in smoother vehicle
acceleration. Larger fuel tanks extended the driving range well beyond that
achievable with the battery-powered electric car. The electric car's share
of the market diminished, and it eventually became a novelty when the
gasoline -powered automobile claimed the major share of the consumer mar-
ket. This change was brought on largely by the economic advantages occa-
sioned by Henry Ford's mass production techniques, the reliability of the
spark ignition engine, and the use of muffled engine exhausts.
Because of concern with air pollution, interest in electric
vehicles was renewed in the late 1960's and early 1970's, principally for
delivery vans and trucks in Great Britain and for compact and subcompact
cars in Japan. More recently, the diminishing domestic petroleum-based
energy resources have placed further emphasis on reconsideration of the elec-
tric car. The primary arguments for renewed interest in these cars are
(a) that air pollutants can be removed from the exhaust of millions of indi-
vidual automobiles and transferred to stationary power plants where treat-
ment of the exhaust from stacks could be more easily controlled, and (b) that
more abundant nonpetroleum-based energy resources can be used for
transportation (i. e. , shifting the energy base from oil to coal or nuclear
power).
This viewpoint has not culminated in any extensive production
of electric cars for numerous reasons. One reason is the continued limited
range of this vehicle -- about 50 miles with lead-acid batteries (the only
economically viable electric energy storage device available today for this
1-1
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application). Another reason is that, even with lead-acid batteries, the
projected purchase cost of electric vehicles is still significantly higher
than the gasoline-powered vehicle.
Nonetheless, with projected improvements, the electric vehicle
can be viewed as a potential contributor to the national inventory of transport
vehicles. As such, this report reviews electric vehicle development world-
wide, but with emphasis on domestic requirements. Following a description
of the design features, and performance characteristics of the primary elements
in the electric vehicle powertrain, the status of technology is reviewed,and the
potential for national transportation needs is assessed. In this context, the
succeeding discussion is addressed to electric powered personal passenger
cars and not to special performance vehicles such as milk trucks, postal
vans, buses, etc.
1-2
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2. POWER PLANT DESCRIPTION
-------
2. POWER PLANT DESCRIPTION
The basic power plant consists of one or more electric motors
and controllers, perhaps a transmission or other gears, and a battery system.
In electric car designs, lead-acid batteries have been used in most cases and
the direct current electric brush motor is used by an overwhelming majority
of vehicle designers and fabricators. It is self-commutating and requires only
variable voltage to obtain a wide speed and torque range. Several types of
direct current motors employed include (a) series wound, (b) separately excited
(c) compound wound, and (d) the permanent magnet motor. The alternating cur-
rent induction motor has also been tried, but the requirement for multiphase con-
version of power from the battery to produce variable voltage and frequency for
the motor introduces excessive complexity and weight and, therefore, is cur-
rently lagging as a potential design approach.
In some systems regenerative braking is used; this causes the
motor to operate as a generator and recharges the battery as the car deceler-
ates. It provides equivalent and sometimes greater braking than that provided
by compression braking from conventional heat engines, and is especially use-
ful to control vehicle velocity while descending mountain roads. One study
(Ref. 2-1) estimated the average energy recovery at 7 percent.
2. 1 POWER PLANT CONFIGURATIONS
Electric vehicles built and proposed to date have used a variety
of power plant configurations. Electric cars that were built on the chassis of
production models of heat engine cars were generally forced to place the bat-
teries where room was already available and to use one large electric motor
coupled to the transmission and mounted where the heat engine is normally
located. On the other extreme is a specially designed electric car using
unsprung, gear motors mounted to each wheel and having a specially designed
cavity for battery containment, which provides for quick change of the batteries.
Between these two limits are many configurations which have
been use or proposed. The following list gives some typical examples,
2-1
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beginning with minimum modification of a present heat engine car and
progressing to specially designed cars.
a. Motor front mounted in heat engine position and using remainder of
existing drivetrain. Batteries mounted in trunk and around motor.
b. Motor front mounted in heat engine position, but coupled to
synchromesh transmission without clutch.
c. Motor front mounted in heat engine position, but coupled to
drive shaft without a transmission.
d. Single rear motor either coupled to transmission or directly
to the differential of a transaxle rear mounted heat engine car.
e. Two motors driving individual wheels with no differential gear.
The motors are frame mounted and drive the wheels through non-
slip belts that allow for vertical wheel motion. Batteries are
mounted principally in front trunk area.
f. Two frame-mounted, high-speed motors driving belts that drive
individual wheel-mounted planetary reduction gears. Batteries
are in a longitudinal well that is loaded from the rear of the car.
g. Two wheel-mounted, unsprung gear motors driving rear wheels.
Flexible power cables permit vertical wheel motion with respect
to the frame. Batteries under seat and in trunk.
h. Four unsprung, wheel-mounted minimum-size gear motors.
Batteries under passenger floorboard.
A typical electric car drivetrain that replaces the drivetrain
of a heat engine is shown in Figure 2-1.
ACCESSORIES
ELECTRICAL
POWER
SOURCE
DRIVE EFFICIENCY
• DRIVE EFFICIENCY .
Figure 2-1. Electric Car Drivetrain Showing the Main Component!
2-2
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2.2 DESIGN FEATURES
2. 2. 1 Batteries
Various studies such as.the one by A. D. Little (Ref. 2-2) have
indicated that a high performance electric vehicle will need 200 to 300 W-hr
of installed battery capacity per ton-mile. A chart showing design require-
ments for electric vehicles as established in the A. D. Little study is given
in Table 2-1. Comparisons between these derived values and specified values
for existing electric vehicles give reasonable correlation. One objective of
system design would be to reduce vehicle weight and to minimize influences
such as drag, frontal area, acceleration, and peak cruise speed, which would
allow a reduction of battery energy usage in the form of Watt-hours/vehicle
ton-mile.
2.2.1.1 Battery Design Factors
When promoting a new battery for development, with intended
application to electric vehicles, the parameter most often compared is spe-
cific energy density (W-hr/lb). As electric vehicle programs proceed, other
factors, implicit in battery system design, must be considered. These are
discussed below.
2.2. 1. 1. 1 Cost
In selecting batteries for electric vehicles, the dominant
parameter has been cost, and for this reason, lead-acid batteries are
almost universally used. Cost is influenced by the basic raw material cost
and demand/availability ratio assignable to the raw materials. In addition to
the cost and availability of primary electrode materials, consideration must
be given to the cost of electrode preparation, the container and seal costs if
the electrolyte is corrosive, the cost of the electrolyte, and battery replace-
ment and operating costs. Cycle life, and especially time at operating tem-
perature for high-temperature batteries, is an important factor for determin-
ing battery replacement frequency. A potential problem with some batteries,
especially those that use gas electrodes (e.g., zinc-oxygen/air or the nickel-
hydrogen) is the need for noble metal catalysts. Another cost-related
2-3
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Table 2-1. Electric Vehicle Specifications (Ref. 2-2)
Parameters
Assumptions
I. Acceleration to
2. Acceleration in
1. Range
4. Seats or payload
5. Loaded weight2
6. Curb weight
7. Weight assignable to pro-
pulsion, energy storage.
controls
«. conventional construction
b. lightweight construction
8. Frontal area
9. Drag coefficient
10. Elec. transmission efficiency
Derived Parameters
11. Maximum power delivered
by motors
12. Maximum output of power
source
13. Maximum velocity
14. Delivered energy
15. Stored energy
16. Weight of motors, trans-
mission, and controls
17. Weight assignable to
power source
a. conventional construction
b. lightweight construction
Power Source Requirements
IB. With conventional construction
energy density
power density
1 ^*. With lightweight construction
energy density
power density
20. M'ati-hr/ion mile
Units
mi/hr
seconds
mi
Ib
Ib
Ib
Ib
ft2
%
kW
hp
kW
mi/hr
kWh
kWh
Ib
Ib
W-hr/lb
W/lb
W-hr/lb
W/lb
--
Family
Car
60
15
200
6
4,000
3, 500
1, 250
1,750
25
0. 35
82
70
94
85
100
100
122
348
902
1,402
135
94
87
60
305
Commuter
Car
60
30
100
4
2,500
2, 100
750
1,050
18
0.25
77
22
30
29
80
20
26
118
632
932
41
46
28
31
208
Utility
Car
30
10
50
2
1,700
1,400
500
700
18
0.25
72
12
16
17
65
8
11
82
418
618
26
40
18
28
259
Delivery
Van
40
20
60
2, 500
7,000
4,500
1,400
2,000
42
0.85
79
49
66
62
56
45
57
259
1, 141
1,741
50
55
33
36
271
City
Taxi
40
15
150
6
4,000
3, 500
1,250
1,750
25
0.35
76
36
48
47
77
75
99
210
1,040
1,540
96
45
64
30
330
City
Bus
30
15
120
10,000
30,000
20,000
5,000
7,000
80
0.85
85
135
180
159
55
300
353
615
4,385
6,385
81
36
55
25
196
The loaded weights ^iven for the cars and taxi are not the maximum that they are capable of carrying but
r»!her reflect tvpical ^sage.
Derived f.-,.n. Ref. 2-2 data above by calculation oj
1000 x Stored energy (kWb.)
(Vehicle loaded weight (lb)/2000) x Range (mi)
2-4
-------
selection criterion is the ability to reclaim and reprocess the basic battery
materials.
2. 2. 1. 1. 2 Energy and Power Density
In the electric vehicle, the energy storage and drive system is
usually allocated a portion of the total volume and curb weight. These values,
along with battery energy and power capabilities, result in important param-
eters that are used in estimating a vehicle's range and drivability. These
•}
are: specific energy density (W-hr/lb), energy density (W-hr/in. ), and
specific power density (W/lb).
In consideration of energy density, a distinction must be made
between that now achieved with commercially available batteries and that
which is projected on the basis of either theoretical reactions or small-scale,
single-cell tests.
While some batteries might have excellent specific energy
densities, their energy density might be low if (a) considerable thermal
insulation is needed, (b) low molecular weight electrodes are used, or
(c) gaseous reactants are used, as in the fuel cell or the metal-gas battery.
2. 2. 1. 1. 3 Operating Temperature
Battery systems which have high-temperature electrode
couples or undergo a phase change (melt) when heated from room temperature
to operating temperature, can have significant parasitic losses and can con-
sume considerable energy and time for start-up.
2.2.1.1.4 Voltage Characteristics
Since the vehicle drive motor will be more efficient if operated
over a narrow voltage range, those battery systems that achieve their high
energy densities with a high voltage variation must be penalized by the cost
of additional power conditioning components or by a lower drive system
efficiency. Increased power conditioning will impact cost, also. Of further
concern is the degradation of cell voltage with time which will affect battery
performance and system design.
2-5
-------
2.2.1.1.5 Charge /Discharge Rate
An inherent problem with the electric vehicle is the energy
and time needed to recharge the batteries. Ordinarily, recharge time will
exceed discharge time so that extensive vehicle usage will be limited unless
provisions are made to exchange depleted batteries for fresh batteries.
This simply involves a trade-off between cost and convenience. The capa-
bility of residential electrical grids to supply large power levels during day-
time for a large number of electric vehicles may also be a problem. Possible
solutions are slow charging during evening hours and higher-efficiency for
charge acceptance of batteries.
High-rate batteries are probably not needed, since the large
installed capacity of an electric vehicle will usually have the capability to
supply high currents for moderately short periods.
2.2.1.1.6 Corrosion
Most high-energy batteries, and especially those containing
Group I metals (lithium, sodium, potassium) and sulfur, have formidable
corrosion problems. Molten sulfur attacks every metal, although some
alloys and refractory metals are corroded at low enough rates to allow
their consideration as container materials. Some electrode and electrolyte
materials attack the separators, react with impurities (including those in
the grain boundaries), and react violently with water.
It is likely that corrosion and the resultant materials problems
will be the limiting factor in the development of high-energy batteries.
2.2. 1. 1.7 Material Conservation
Battery materials which can easily be reclaimed and reused
at the end of battery life are desirable; they should be plentiful and, if
possible, not a secondary extraction material such as cadmium, which is a
biproduct of zinc smelting. Increased demand of such a material would
severely disrupt present markets-.
2-6
-------
2.2.1.1.8
Because electrode materials that are most reactive provide
the highest specific energy densities, safety can be a problem during mainte-
nance or in the event of an accident. The effect of internal cell failures on
battery operation (such as a separator rupture) should be minimized during
design studies to avoid an unstable condition.
2.2.1.2 Battery State of the Art
Currently, a major problem is the limitation on the amount of
energy and power that can be delivered by a given size battery. Evidence of
this problem is seen in the restricted operation of contemporary electric
vehicles as illustrated in Table 2-2 (Ref. 2-3). This is a partial list of
electric vehicles built to prototype level of design or to commercial design
specifications for small quantity production in the United States. Analytical
studies (Ref. 2-2) have shown that battery requirements for powering a full
performance family passenger car are: a specific energy density of about
135 W-hr/lb and a specific power density of about 95 W/lb. Table 2-3 shows
that current battery capabilities fall far short of the energy goals. A summary
of characteristics for battery systems that have been suggested for future
electric vehicles is given in Table 2-4.
2.2.1.2.1 Improved Conventional Batteries
In recent years, the lead-acid battery has improved consider-
ably (Ref. 2-2) in directions relevant to electric vehicle highway applications.
Most of the progress in lead-acid systems has been made in the small- and
intermediate-size area, where high-production volume applications exist such
as for automobiles, golf carts, and forklifts. But of note is that the hybrid
vehicle in an automotive oriented study for EPA, where high power density
for acceleration was specified, TRW Systems, Inc., and Gould showed that a
modern SLI (starting, lighting, ignition) battery capable of 18.7 W-hr/lb
under a slow rate could deliver 94 W/lb for 25 seconds (Ref. 2-4). (By
contrast, a decade ago battery power densities of 40 to 50 W/lb were
considered to be the best available). TRW Systems/Gould and another EPA
2-7
-------
Table 2-2. Electric Vehicle Summary Data for Operating
Passenger Models in the United States (based
on Ref. 2-3)
r»r Name and
V.anuJicturcr
COMUTA
Ford
CM 512
Gcri* r*I Motor*
SUNDANCER 2
ESB
MARQUETTE
Westinghousc
HKK\'KY KILOWATT
Union MI-M rlr
YARDNEY
ALLECTRIC
Wc.1 Pcnn
Power Co.
"MINI"
General Electric
Aiiirruan Motor* and
Gulion Ind.
ESB
Renault
Rowan Electric
ALLECTRIC II
West Penn Power Co.
Super-electric
Model A
Garwood fc. Stelber Ind.
CORTINA
ESTATE CAR
COMET
Ford
CITY CAR
PINTO
MARS II
Elect. Fuel
Prop. Inc.
ELECTROVA1R
General Motor*
ELECTROVAN
General Motor*
CARMEN GHLA
Allis Chalmers
SIMCA
Chrysler
Elect. Fuel
Prop. Inc.
FALCON
Linear- Alpha
Tr»t data
IV»ipr, goat*
Vehicle
Curb Weight,
pound*
1.200
1.2SO
1,600
1,730
2, 135
1.600
I. 160
2,300
1, 100
..
1,300
2.300
__
3, 086
3,800
3.200
3.640
3,400
7,100
3.440
—
5,400
--
Drive
Motor(s)
Two 5 hp
Series dc
8-1/2 hp
Series dc
{54 Ib)
8 hp Series
dc (83 Ib)
Two 4-1/2 hp
dc (45 Ib)
7. 1 hp
Serle* dc
7.1 hp
Serie* dc
7. 1 hp
72Vdc
dc Motor
10.9 hp
_.
Two dc
Compound
7.1 hp dc
Two 2 hp
40 hp 100V
{150 Ib)
85 hp
40 hp
15 hpdc
100 hp
ac induction
125 hp
ac induction
-
--
__
25 hp
ac induction
motor
Maximum
Speed,
mile* per hour
40l
40*
60+*
25»
40b
55b
50C
55b
50b
40°
40C
50C
52b
60°
70b
50b
551
60 to 65C
80b
TO*
-
-
85°
60b
Energy
Source and
Capacity
Lead-acid
48V (384 Ib)
Lead-acid
84V (329 Ib)
Lead-acid
86V (750 Ibl
Lead-acid
72V (800 Ib)
8 kW-hr
Lead- acid
(800 Ib)
8 kW-hr
Silver- line
12 kW-hr
(240 Ib)
Lead-acid
72V (900 Ib)
9 kW-hr
Lead-acid and
Nickel- cadmium
Lithium-nickel
fluoride (150 Ib)
and Nickel-
cadmium (100 Ib)
Lead-acid
(72V)
Lead- acid
Lead-acid
(900 Ib)
Lead-add
(520 Ib)
Nickel- cadmium
(900 Ib)
Sodium- sulfur
(1,086 Ib)
Lead-acid
(956 Ib)
Lead-acid
96 V (1,7.00 Ib)
30 kW-hr
Silver-zinc
530V (680 Ib)
19.5 kW-hr
Hydrogen-oxygen
fuel cell
180 to 270 kW-hr
Lead-acid
120V (1,534 Ib)
Lead-add
(1,400 Ib)
Lead-acid
cobalt
Lithium- nickel
Quo ride
(360 Ibl
Range, miles
39@25 mphb
47 @30 mphb
70 to 75
on SAE
Residential0
50b
40b
77°
50b
100 @
40 mph"
150 with
regeneratlonb
25 to 35b
100b
50°
39. 9 @
25 mphb
39@ ,
40 mph°
70 to I20b
40 to B0b
100 to I50b
60 @
60 mph°
40b
ISO to 175°
75 % 30 mph°
2-8
-------
Table 2-3. Characteristics of Currently Available
Secondary Batteries
Battery Type
Lead-Acid
Nickel- Cadmium
Nickel-Iron
Characteristics
Specific
Energy
Density,
W-hr/lb
20
12
13
Energy
Density,
W-hr/lb
2.0
1. 1
1.2
Specific
Power
Density,
W/lb
100
80
60
Approximate
Relative
Cost
1
20
3
Remarks
Standard
Good cycle
life; cadmium
supply limited
Excellent life;
poor mainte-
nance; nickel
supply limited
contractor; Tyco Laboratories, Inc. (Ref. 2-5), indicated that lead-acid
batteries could be developed to deliver power densities as high as 300 W/lb.
There has been no comparable effort to develop lead-acid batteries for an
all-electric vehicle which would require greater emphasis on energy delivery
capability (Watt-hours/pound).
The nickel-iron system has been proposed as a low-cost
replacement for the lead-acid battery. Intensive work by Westinghouse has
improved battery life and introduced new maintenance concepts, but this
battery appears best suited for industrial applications. The batteries have
excellent lifetimes, with many batteries having exceeded 20 years in normal
service. It is not affected by overcharge or complete discharge, but does
generate hydrogen on charge and has poor charge retention. It offers little,
if any, performance advantage over lead-acid.
A good candidate battery for the electric vehicle in the near-
term period (1975 to 1985) is the nickel-zinc system. A specific energy
2-9
-------
Table 2-4. Batteries for Future Electric Vehicles (Refs. 2-6 through 2-
System
Improved Conventional Batteries
Lead -Acid
Nickel-Iron
Nickel -Zinc
Metal -Gas
Iron - Ai r
Zinc -Air
Nickel -Hydrogen
Zinc -Oxygen
Alkali Metal-High Temperature
Sodium-Sulfur
Lithium -Sulfur
Lithium Chlorine
Metal-Halide
Zinc -Bromine
Zinc -Chlorine
Projected Maximum Performance
Specific
Energy
Density,
W.-hr/lb
20(76)a
25(121)
30(146)
50
60(614)
40(177)
60
100
100(700)
50(1,050)
30(196)
50(209)
Energy
Density,
W-hr/,n3
2.0
1. 5
2.0
2. 5
2. 5
N.A.
2. 5
8. 1
6.7
5.0
N.A.
N.A.
Specific
Power
Density.
W/lb
150
60
150
20
35
100
30
100
400
150
N.A.
60
Opt'g
Temp. ,
"C
20
20
20
20
20
20
20
300
400
650
N.A.
N.A.
Open
Cell
Voltage
2.05
1. 37
1.71
N.A.
1.65
1. 36
N.A.
1.8 to 2. 1
N.A.
3.46
1.8
2. 12
Problem Areas
Low energy density
I *ow charge efficiency, hydrogen
evolution, maintenance
Cost, life
Cathode corrosion, life recharge.
mechanical replacement, noble
metal catalyst needed
Zinc deterioration, life cost, com-
plexity, recharge, mechanical re-
placement, noble metal catalyst
needed
Volume, life, hydrogen, noble
metal catalyst needed, cost
Life (zinc and air electrode), cost,
noble metal catalyst needed
Corrosion, life (sodium and sulfur
highly reactive), startup
Corrosion, cost, materials (lith-
ium and sulfur highly reactive),
startup
Corrosion, cost, materials (lith-
ium and chlorine highly reactive),
startup
Low energy density
Early state of development, prob-
lem areas not yet fully defined
*( ) designates theoretical value
-------
density of 30 W-hr/lb and a specific power density of 150 W/lb seems
possible. Battery life, presently 100 to 200 cycles, has been a drawback,
but work is under way on new separator systems to correct the problems of
degradation of the zinc electrode and penetration of the plate separator sys-
tem by zinc dendrites. The other major question is whether costs can be
eventually competitive with the lead-acid battery.
The energy density of the nickel-cadmium battery is about
the same as the lead-acid battery and it has superior life, but its cost is
much greater -
2.2.1.2.2 Metal-Gas Batteries
These batteries provide energy densities in the 30 to 60 W-hr/lb
range, depending on the reactants selected. The use of air in these batteries
is advantageous for obvious reasons (e.g., no onboard storage required), but
they require the addition of scrubbers for CO2 removal, an air blower, and
a water makeup system, which negate much of the gain. With either air or
oxygen, an oxygen electrode catalyst is required. No catalysts exist that
are inexpensive enough for car batteries. Reduced noble metal loadings or
nonnoble catalysts might be usable if hydrogen gas is used. However, the
volume required for hydrogen gas storage presents a problem, and hydride
storage systems are heavy and either complex or expensive, depending on
the hydride selected for use. In addition, the usual problems associated with
zinc, cadmium, and iron electrodes in conventional batteries appear in these
cells. Prototype batteries have been built and tested by Gulf-General Atomics
(circulating electrolyte), Sony (pulverized zinc fuel), and General Motors
(mechanically rechargeable). The pumped circulating systems are complex.
Gulf-General Atomics concluded that their system was unattractive economi-
cally, and General Motors has declared the mechanical recharging approach
to be impractical.
The nickel-hydrogen system is receiving considerable develop-
ment emphasis for aerospace industry applications. It is believed that long
2-11
-------
lifetimes, adequate for the electric vehicle, can be achieved with this
system, but problems remain with regard to cost, safety, and energy
density.
2.2.1.2.3 Alkali Metal - High-Temperature Batteries
These systems are theoretically capable of meeting the goals
that have been established as necessary for full-performance vehicles. High
temperatures (300 to 700 °C) allow the use of relatively resistive solid ionic
conductors and molten salts as electrolytes, and permit rapid charging and
discharging. Demonstrations of high power and energy densities have been
made, although not always in the same cell. Life is 500 to 1,000 complete
discharge cycles in 1, 000 to 2, 000 hours of operation for almost all systems.
Life time limitations are generally associated with materials problems.
The sodium-sulfur system, first announced by Ford Motor
Company (Ref. 2-10) is receiving international attention. The concept uses
a beta-alumina solid electrolyte that conducts sodium ions at reasonable
rates at the operating temperature of 350°C or slightly above. The major
United States program on the sodium-sulfur battery is Ford's, although
TRW Systems, General Electric, and others have also worked on this cell.
Ford has tested single cells and a small, 200-W, 24-cell battery. The
latter reportedly ran for 2,000 cycles and 7 months total hot life--the longest
life reported to date. The battery delivered 43 W-hr/lb and 93 W/lb, exclu-
sive of insulation. A little recognized fact is that in the Ford battery design,
power and energy density must be optimized separately. Thus, a 500-W
battery optimized to delivery 135 W-hr/lb would produce 46 W/lb, while one
designed for high power would put out 40 W-hr/lb but 150 to 250 W/lb
(Ref. 2-10), again exclusive of insulation. The largest foreign programs
are in the United Kingdom (British Railways Board, The Electricity Council),
Japan (jointly between Yuasa and Toshiba), France (CGE), and Switzerland
(Battclle-Geneva). British Railways has tested both tubular and flat-plate
cells and has a 1 kW battery operational. The Electricity Council has built
2-12
-------
a 960-cell, 50 kW-hr battery and began road tests in a Bedford van in
November 1972. The battery is rated at 15.5 kW average output, has a
peak power capability of 29 kW, and weighs 1,760 Ib. The energy density
is, therefore, 28 W-hr/lb and the power density at peak output is 16.5 W/lb.
The energy density is expected to ultimately reach 91 W-hr/lb with life in
excess of 1,000 cycles. The Japanese work on this system is part of their
government-sponsored electric vehicle program. The objective is to have
a battery-powered vehicle in operation by 1975. Yuasa is testing single cells
and seven-cell units. Lifetimes in the order of 1,000 hours (166 cycles) are
common. The energy density delivered is about 50 W-hr/lb. The French
and Swiss are concentrating their efforts on operation of single cells. All
sodium-sulfur projects face the same key problem today; namely deterioration
of the beta-alumina electrolyte after 1, 000 to 2, 000 hours at working tempera-
tures. This deterioration is ascribed to a variety of causes and has led to a
number of proprietary "fixes", but no substantial increases in life have been
reported. This is the major technical hurdle to be overcome before a suc-
cessful battery can be demonstrated. Economic success will ultimately
depend on finding inexpensive ways to produce the desired ceramic and to
fabricate large batteries.
A different approach to the sodium-sulfur system is being
pursued by Dow Chemical Company. Sodium ion-conducting glass is used
as the electrolyte in the form of hollow fibers with very thin walls (typically
85-micron O. D. x 35"-micron I.D.). Thousands of these tubes are collected
in bundles to form a cell, using a glass header and aluminum for the con-
tainer and current collector. Dow has a proprietary method of treating the
current collector to prevent formation of a passivating film. Energy densi-
ties ranging from 80 W-hr/lb for small cells to 135 W-hr/lb for large cells
are predicted. Dow has attempted to develop a 40 Ah cell under a contract
cosponsored by the Navy, Army, EPA, and DOT. This development effort
may have been premature in view of the limited amount of life data and glass
compatibility experience Dow has in hand. It did prove valuable, however,
2-13
-------
in that it focused attention on problem areas that will require work. This
approach appears to have the best low-cost potential among the various
high-temperature batteries under development.
The lithium-sulfur system has been under development for
a number of years at Argonne National Laboratory, with a smaller effort
at Atomics International. Test results show the system has the desired
charge and discharge rate characteristics (Table 2-5) for a vehicle battery,
Table 2-5. Lithium/Sulfur Laboratory Program Goals and Cell
Performance--Argonne National Laboratory
Performance
Designation
Goals
Status
Single Cell Performance
Area
crr.2
350
2
13
30
Ah/
cm2
0.4
0. 70
0.74
0. 40
A/cm2
0.4
2. 0
0.2
0. 3
Volts
1. 6
1. 7
1. 5
1. 5
Cycles
1,000
>1,250
130
250
Life.
hr
26,000
>6, 500
500
800
Comments
0. 3-cm-thick cathode
1.9-cm-thick cathode
1. 3-cm-thick cathode,
sealed cell
0. 3-cm-thick cathode
although the life is limited and sulfur utilization has been too low to allow
high energy densities to be sustained. Unsealed cells have been cycled for
1, 500 cycles during 7, 000 to 8, 000 hours of operation, but these were essen-
tially tests of the positive electrode, as the lithium electrode had to be
replaced several times to correct internal shorting problems. Shorting arises
due to a "dewetting" of the anode and subsequent formation of lithium globules
between the electrodes. In sealed cells, this results in failure in 500 to 800
hours and 130 to 250 cycles. High sulfur electrode capacity losses (as much
as 75 percent in the first 60 cycles) may be correctable using a new "mixed
cathode" construction, but the required capacity densities (1 Ah/cm2) have
not been sustained. The system has some severe materials problems. In
2-14
-------
laboratory cells, niobium housings fail due to corrosion, and molybdenum
is now being used. Static diffusion block tests show chromium is virtually
the only low-cost material that might be corrosion-resistant, assuming it
can be plated and maintained void-free on a lower cost base metal. Electrical
insulators are also a problem. Current emphasis is one use of these bat-
teries for central station service to accommodate power peaks.
Currently, Argonne National Laboratory is placing emphasis
on the lithium-aluminum alloy/ferric-sulfide battery. Although this battery
does not have the energy density potential of the lithium-sulfur or sodium-
sulfur batteries, it has a less severe materials degradation problem and
should cost less.
The lithium-chlorine system was investigated by General
Motors and later, in a modified form, by Sohio. The former investigation
showed high power densities, but was hampered by difficult corrosion prob-
lems at the 700 °C operating temperature. The latter investigation progressed
to a 264 W-hr, 12-cell battery that was tested for 100 cycles. This battery
delivered 24 W-hr/lb without insulation. Due to the particular method of
storing lithium and chlorine, the outlook for high energy densities is not
promising.
2.2.1.2.4 Other Approaches
Organic electrolyte batteries offer the possibility for high
energy densities at ordinary temperatures and are attractive for this reason.
Literature research shows that primary cells can deliver 100 to 200 W-hr/lb
at low discharge rates (over a period of 100 hours or more). High rate cells
have been built but have limited wet-stand capability due to solubility of the
cathode materials used. To date, no long cycle life, rechargeable organic
electrolyte cell has been built. Much basic research is necessary on elec-
trode reactions in nonaqueous media and on electrolyte properties. Since the
most promising approaches involve soluble cathodes, work on an ion-selective
separator would improve the chances for success.
2-15
-------
Zinc-halogen cells have been investigated in two laboratories.
The Zito Company reports long cycle life for an aqueous zinc-bromine cell,
but the energy density is too low (20 W-hr/lb) to be of interest. A different
concept has been demonstrated by Occidental Petroleum which uses a zinc-
chlorine battery in which chlorine is stored as a solid hydrate at 8 "C or
below. The system developed has progressed to where a mechanically
rechargeable 1,800-lb battery has been installed in a Vega for testing. The
energy density is 30 W-hr/lb, but Occidental claims to be working on improve-
ments that will increase this value to 75 W-hr/lb, giving the car a range of
200 miles. A joint venture between Occidental and Gulf and Western Indus-
tries was recently announced to develop this battery for both vehicle and
utility industry use.
Fuel cells, which enjoyed a resurgence in development effort
in the 1960's, are usually mentioned whenever electric cars are discussed.
Their obvious advantages of high efficiency, silent operation, and harmless
exhaust products, especially where hydrogen and oxygen are the reactants,
have been well discussed by Escher (Ref. 2-11) and others. The major
problem that has prevented commercial exploitation of the fuel cell has been
cost, which can be directly related to the use of noble metal electrode cata-
lysts, particularly for the oxygen or air electrodes. Since these electrodes
are common to metal-air and metal-oxygen cells as well, a breakthrough in
low-cost electrode catalysts could make either fuel cells or metal-gas bat-
teries more attractive for electric vehicles.
2.2.1.3 Development Activities
Battery technology for electric vehicles has not advanced
rapidly in the United States for a number of reasons. Private investment
is almost nonexistent because of the lack of any market potential, while
government research and development funds are limited and the electric
vehicle has not had a high priority. The inability to find a battery that could
compete with the lead-acid except at a prohibitive cost has also slowed
progress.
2-16
-------
Work on the nickel-hydrogen battery has increased, but work
has declined on other metal-gas batteries (e.g., zinc-oxygen or zinc-air) and
on the nickel-zinc battery.
Only long-range, high-energy battery research is receiving
any significant federal support. The Ford Motor Company in collaboration
with the University of Utah and Rensselaer Polytechnic Institute has been
working on a sodium-sulfur battery under a $700,000 contract for FY 1973
from the National Science Foundation (NSF). This proof-of-concept effort is
directed toward electric utility needs and would find application to automotive
needs if a lightweight, low-volume concept evolves successfully. Stanford
Research Institute received $100, 000 from NSF in FY 1973 to work on lead-
lead oxide cells for primary application to the electrochemical industry.
Following a $300, 000 contract from NSF in FY 1973, work continues at
Argonne National Laboratory on the lithium-sulfur battery at a contract value
of about $1 million for FY 1974, with the objectives being redirected to utility
load leveling and peaking applications. This program, which had been jointly
funded by NSF and Atomic Energy Commission (AEC) in FY 1974, is now
funded solely by AEC as of February 1974. Overall, NSF expects to have
about $900, 000 available in FY.1974 for advanced battery research.
The Electric Power Research Institute, Palo Alto, California,
is also funding work at a $1 million level for FY 1974, on sodium-sulfur bat-
teries at TRW Systems and General Electric, lithium-sulfur batteries at
Atomics International, and zinc-chlorine batteries at Energy Devleopment
Associates. Although some of this effort might apply to electric vehicles,
the primary goal is for energy storage satisfying utility load leveling and
peaking needs.
On the other hand, work on batteries for electric vehicles is
accelerating aboard. Table 2-6 summarizes these programs. The major
activities are in the Federal Republic of Germany, Japan, the United Kingdom,
and the U. S. S.R. In each case, the government is either formally partici-
pating or influencing the direction of work. In at least five other countries
2-17
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Table 2-6. Foreign Battery Research and Development (R&D)
Efforts for All Types of Electric Vehicles, by
Countries (Ref. 2-6)
Country
Federal Republic
of Germany
Japan
United Kingdom
U.S.S. R.
Others
France
Sweden
Italy
Czechoslovakia
Switzerland
Formal
National
Program
No
Yes
Noa
Yes
_ _
—
--
Estimated
Budget
$650, 000
per year
$14 million
(1971-75)
$950,000
(1973)
Unknown
_ _
_ _
--
Comments
Direction influenced by
government
Includes vehicle
development
1/2 million electrics in
use - 30 companies
making electric vehicles
Experimental and proto-
type vehicles tested
_ _
_ _
--
Strong government support of R&D
(France, Switzerland, Sweden, Italy, and Czechoslovakia) vehicle battery
projects are known to be under way. The most dramatic achievement of the
past year was the use of sodium-sulfur battery to power a small van. This
was accomplished by the Electricity Council Research Center at Capenhurst
in the United Kingdom.
1. 2. 2
Motors and Controls
A wide selection of motor design and controller combinations
have been used in past and present electric cars. The controllers vary in
complexity from the use of carbon-pile resistance stacks employed on early
2-li
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streetcars to three-phase, silicon-controlled rectifier (SCR) time-ratio
controls used in some of the advanced experimental alternating current motor
drives. No specific approach has yet been universally adopted, but the brush
direct current motor controlled with a pulse-width modulation (PWM) SCR
system was overwhelmingly used for electric vehicles during 1973, followed
by the step voltage, parallel-series switching system.
Of the many motor types available, only a small number can
be considered for vehicle drive applications. Many, such as the stepper
motor and hysteresis motor, are designed for special-purpose application
much different than an electric car. Others, such as the alternating current
induction motor and the alternating current reluctance motor, require very
complex controllers that must handle large currents for the amount of torque
generated. These two types of motors must be supplied with both variable
voltage and frequency. Because of the controller complexity and the poor
motor efficiency, these motors are not considered optimum for electric
vehicles.
Despite the high power density of the alternating current
induction motor, its requirement for advanced controller technology is a
severe limitation. This was demonstrated by General Motors when they
used this motor for a converted Corvair, the "Electrovair". Its require-
ment for three separate circuits providing both variable voltage and frequency
caused the controller weight to be greater than the motor weight. Two ver-
sions of the Electrovair were built. The first required a total controller
weight of about 480 Ib, compared to 160 Ib for the motor. The Electrovair II
controller combined some functions by building voltage and frequency controls
in the same component. This unit weighed about 240 Ib, including the cooling
system. Subsequent electric cars built by General Motors used a brush
direct current motor.
The Electrovair cars (Figure 2-2) were designed and tested
by General Motors to evaluate performance and design features. The Corvair
engine was removed and replaced by an electric drive consisting of a silver-
zinc battery weighing about 600 Ib, an alternating current induction motor, and
2-19
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COOLING OIL RESERVOIR
r-BATTERIES
— LOGIC CONTROLS
AC INDUCTION MOTOR
OIL RADIATOR AND FAN
OIL PUMP AND MOTOR
INVERTER TRIGGER CONTROLS
Figure 2-2. Phantom View of the General Motors Electrovair II
Showing the Location of Major Experimental
Components (Ref. 2-12).
associated controls. The Electrovair I weighed about 3,600 Ib and demon-
strated an acceleration capability of 0 to 60 mi/hr in about 15 seconds, which
is comparable to the wide-open throttle acceleration of a production Corvair
with automatic transmission. The motor was coupled to the rear differential
through a fixed-speed reducer, and the full torque was provided by the motor
without a gear shifting transmission. The driving range at 60 mi/hr cruising
speed was 70 miles before recharging was required.
The electric power delivery system to the drive wheels con-
sists of a chopper (or modulator) to convert the fixed battery voltage to a
smoothly variable direct current voltage, an inverter to convert this variable
direct current to three-phase alternating current voltage with rectangular
waveform, and an induction motor. Thus, by controlling the chopper and
inverter simultaneously, the voltage and frequency of the motor can be varied
smoothly (Ref. 2- 12).
2-20
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2. 2. 2. 1 Design Factors
2.2. 2. 1. 1 Cost
Neither motors that are suitable for family size vehicles nor
controllers to regulate them have been mass-produced to date. Because of
this, these powertrain elements presently have a high cost, and it is this
high cost that is the greatest single hurdle to widespread use in automotive
vehicles. The mass-produced costs must not exceed 20 percent of today's
costs for the same devices presently used in aircraft or other special appli-
cations requiring high quality control in manufacture. A single compound
wound, compensated motor of the type that could drive a family car is listed
in the General Electric catalog as costing $2,300 to $3,200, depending on the
features. The controller is an additional cost. It will thus require a large
production base to make an electric family car economically viable.
2.2.2.1.2 Drive Motors
Electric motors, particularly direct current motors, have not
been developed to provide combined optimization of efficiency, weight, size,
and cost for vehicle propulsion. It is possible that they might be designed
with lighter weights than those in the market today with equal reliability and
lifetimes because weight has not been a prime consideration. Some gains
maybe effected by installing improved (low hysteresis loss) core materials,
replacing all the frame with the lightest weight materials at minimum struc-
tural rigidities that will maintain gaps and bearing integrity, and using high
energy density fields (new rare earth cobalt permanent magnet materials).
The usual motor frame structure is very thick, heavy, and strong. The
weight saved could be used to increase the motor core cross-sections, reduc-
ing core hysteresis losses and magnetizing currents. Also, increasing the
copper cross-sections will decrease the resistance I R copper losses. Motor
efficiency at design load could thus possibly be increased from 75 to 90 per-
cent at the same weight per unit horsepower. With proper design, the working
2-21
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portion of the motor can be larger for a given size and weight, as compared
to floor-mounted models where weight is unimportant.
Currently, efficiency can be traded off against motor weight.
For a given design power level, the weight per unit horsepower can be
decreased if the efficiency is allowed to decrease (Figure 2-3, Ref. 2-7).
Extrapolation from present technology indicates that power densities of 5.5
to 8 Ib/hp should be achieved at a reasonable efficiency and cost by merely
optimizing the design for the particular application and using lightweight
materials whenever possible (Figure 2-4). Based on these figures, a 4, 000 Ib
electric car capable of cruising at 80 mi/hr would require a motor weighing
almost 400 Ib (rated at 60 hp).
The following list describes motors that are candidates for
electric vehicle propulsion and their characteristics.
a. The series wound motor has its field winding connected in
series with the motor armature so the field strength is a
function of load current. This provides a very steep speed-
torque characteristic at light loads, which becomes fairly
flat at overloads. The series motor has high starting torque
capability because the field is strengthened as the load increases,
thereby compensating for the demagnetizing effect of armature
reaction. The series motor speed can be controlled by varying
the applied voltage, but since changes in load can cause
relatively large changes in speed, precise control is difficult.
For example, if the maximum speed on level terrain is reached
through application of full battery voltage to the series motor,
as soon as the vehicle reaches an incline or a headwind, it will
always slow down (series field strength increases) rather than
draw additional power from the batteries to maintain speed.
This motor is also difficult to control for power transfer during
regenerative braking.
b. The shunt wound motor has its field connected in parallel across
the motor armature. This provides a field strength independent
of load current and directly proportional to applied voltage.
This results in a fairly flat speed-torque characteristic. It is
important that this type of motor have compensating windings
to nullify the degradation that would result from armature reaction.
Without compensation, the demagnetization effect on the field
poles of armature reaction will cause field weakening. Then,
the motor draws more current, producing an avalanche effect,
which further weakens the field.
2-22
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95
c 90
0)
o
s.
UJ
o
u.
u.
ui
80
75
BASED ON CONTINUOUS
RATED POWER
SPEED RANGE
4,000 TO 8,000 rpm
I
45678
WEIGHT PER UNIT HORSEPOWER, Ib/hp
Figure 2-3.
Typical Maximum Efficiency for Direct
Current Motors as a Function of Weight
per Unit Horsepower (Ref. 2-7)
Q.
QL
O
a.
ui
a:
O
i
UJ
a.
O
4
*
SPEED RANGE
4,000 TO 8,000 rpm
I
I
I
I
I
20 40 60 80 100 120
CONTINUOUS RATED POWER, hp
140
Figure 2-4.
Typical Weight per Unit Horsepower as a Function
of Rated Power for Direct Current Motors Including
Forced Air Cooling (Ref. 2-7)
2-23
-------
To obtain good speed control with this type of motor, it is
necessary to provide an independent power control for the
separately excited field to obtain controlled field strength.
Then, voltage to the armature can be varied in order to vary
motor speed.
With constant field strength despite armature reaction, this
motor will draw additional current at a given voltage on occa-
sions of increased load (with the vehicle on an incline or
encountering a headwind) to help maintain the same velocity.
In addition, field weakening is sometimes used to increase
speed up to three times base speed. During field weakening,
the motor can operate at constant power, providing higher
speeds. The power to operate the separately excited field is
from 1 to 1 0 percent of the rated motor power. Accurately
controlled regenerative braking is available when this motor
is equipped with a separately excited field.
c. The compound wound motor provides both a shunt field and a
series field so that performance will fall somewhere between
a shunt and a series speed-torque characteristic, depending
on the ratio of field strengths selected. If additional speed
and regenerative braking control are desired, the parallel
winding can be separately controlled as in a separately excited
motor, rather than the usual shunt connection across the single-
line input.
d. The permanent magnet motor has permanent magnet pole pieces
in place of field windings. Field strength is constant and is not
affected by armature reaction as in a wound field motor. This
is due to the low permeance coefficient of the permanent magnet
material. This provides a straight line speed-torque character-
istic with relatively low no-load speed and high starting torque.
By varying the applied armature voltage, precise speed control
is obtained. Since this motor does not have a wound field,
there are no field losses. This means that for an equivalent
rating, it is more efficient at all equivalent power levels and
speeds. This motor has strong potential for electric vehicles,
but is not yet fully developed, because the permanent magnet
material has not been available in sizes and field strengths
needed for electric cars.
e. The brushless direct current motor has often been used in
fractional horsepower space applications, but has not yet been
fully developed for electric vehicle use. The integral horse-
power brushless direct current motor will use rare earth cobalt
permanent magnets and Hall effect detectors to trigger the SCRs
for commutation. The brushless motor is self commutating.
Load demand is met by variation of average current, and
velocity demand is met by a change of effective voltage through
the PWM system.
2-24
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f. The synchronous alternating current motor energized from a
battery requires a controller incorporating both voltage control
and frequency conversion. The voltage and frequency control
can be achieved either in a separate chopper followed by an
inverter or combined in a modulating inverter. The alternating
current synchronous motor will come to a stop if its maximum
torque is exceeded. A rotor position sensor can be incorpo-
rated into the motor which will force the motor to operate like
the brushless direct current motor.
g. The alternating current 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 direct
current motors can be obtained. The induction motor has the
advantage in specific power when compared to direct current
motors at the required electric vehicle horsepower levels.
The requirement for a complex device to control frequency and
voltage has restricted its use in electric vehicles.
The overwhelming majority of electric vehicle builders use the
the brush direct current motor. Brushes are easy to replace and are capable
of lasting 50,000 vehicle miles. Power input to the motor is usually through
a single circuit requiring only variable voltage; this greatly simplifies con-
troller complexity and weight. Some builders found it worthwhile to use a
two-circuit direct current motor providing control of both armature and field
circuits. This provides an increase in load, velocity, and regeneration con-
trol available from the low-power second circuit of a separately-excited
field.
2.2.2.1.3 Control Systems
In a comparison tradeoff of drivetrain designs, it is very
important to include control system cost and weight. In terms of performance
and versatility, the selection of an adequate low-cost control system is as
significant as motor selection. Because all of the contending electric motors
need variable voltage applied for varying speed, control and regulation must
include the modification of a fixed-voltage source (the batteries). This can
be achieved by means of a chopper circuit, a variable resistance in the arma-
ture circuit, or a step-voltage change combined with field control.
2-25
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The chopper circuit (generally using SCRs) provides an efficient
means for transforming a fixed battery voltage to a smoothly varying effective
voltage matching the requirement of the motor at all speeds of operation and
providing a smoothly varying speed. The chopper system provides pulse fre-
quency variation, PWM, or a combination of the two. While the chopper sees
a varying impedance for the motor (depending on motor speed), it presents a
relatively constant high impedance to the battery when used with proper filter-
ing elements. This allows the reduction of high current pulses in the battery.
Also, compared to pure direct current control, the chopper introduces losses
due to high-frequency operation. These losses can be partially reduced by
special motor design and adequate filtering. Since the forward voltage drop
of the high-current SCR is about IV, 0.5 kW would be lost in the SCR at 500A.
This power loss presents a heat dissipation problem. The higher the maxi-
mum system voltage,the lower the proportionate loss of the SCR controller
system at a given motor power.
The main disadvantage of the chopper is the high cost of the
power switching components and the associated control circuitry. 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. Recent price
reductions have already made them practical for experimental vehicles.
However, the SCR protection circuit and the current-smoothing filters will
still remain significant cost factors.
A variable resistance in the armature circuit is a simple
type of controller that was used on streetcars and some early electric cars.
Though simple, this type of control introduces high losses because of the
voltage drop across the resistance, and is an inefficient method of voltage
control for a vehicle required to operate over a wide speed range.
Step voltage systems have been used in which multiple-pole
relays switch batteries from parallel to series in steps as vehicle speed
increases. This may be undesirable, because the discrete velocity incre-
ments may prevent one vehicle from following another vehicle at the same
2-26
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velocity, and the relays are constantly working under load, thereby shortening
the operating life. 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 (i.e., by using armature current sensing to provide feedback
information for controlling the field). This would control current surges
and corresponding jerks.
A comparison of operational characteristics using the three
types of controllers is given in Table 2-7.
Table 2-7. Comparison of Motor Controllers
(Ref. 2-7)
Item
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
Power Conditioning
Characteristics
dc Chopper
All dc motors
Zero to maximum
speed
Very smooth
Solid state only-
circuit breakers and
fuses too slow
High
Medium
Complex
Heavy filter req'd
High but inefficient
Stable with shunt
motor, decreasing
with load on series
motor
High
Modulation of full
power used by motor
Variable Resistance
All dc 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
High switching currents
with much dissipation
Step Voltage
with Field Control
Only separately excited, stabi-
lized 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
With small signal field control,
high contactor currents at switch
closing but zero contactor cur-
rents on switch opening.3
aBefore 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 direct current is thus avoided.
2-27
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Of greater complexity are the controllers for the brushless
direct current and the alternating current induction motors. Controllers for
alternating current motors must provide not only variable voltage, but also
variable frequency to the motor. At present, three-phase, variable-frequency
and variable-voltage inverters at power levels associated with electric vehi-
cles are very expensive and heavy, because they are complex (twelve SCRs 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.
2. 2. 2. 1.4 Power
In the interest of saving weight, the power levels of electric
vehicles are limited. A review of prototype electric cars shows that the usual
motor used in vehicle application is driven at or above its rating to save weight.
This results in increased heating requiring a forced air cooling system (or
even oil cooling) due to the lower efficiency of the smaller motor. A forced
cooling system can almost convert the peak power rating into continuous
power rating. Hence, the rated continuous power of the motor does not
seriously constrain the short-term power capability during acceleration.
However, due to commutation limits, the overload capability decreases with
velocity.
With this approach, the efficiency is usually 65 to 75 percent
for the motor alone, as opposed to efficiencies of 90 percent with heavier
motors having a higher weight per unit horsepower. The principal power
dissipation is in core and copper losses, which is an unfortunate conversion
of electrical energy into waste heat. The heat serves no useful purpose,
except in some designs it can be vented into the vehicle interior in winter.
The batteries also constrain the power levels realized by an
electric power plant. This arises from the limitation of the power per unit
weight available in batteries. Similarly, the limitation on energy storage
also constrains power levels. This results because battery discharge
efficiencies are a function of the power level. Thus, at high discharge
2-28
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rates, the efficiency is low (just as it is at high charge rates), and the
available energy for the motor is reduced for a given battery.
2.2.2.1.5 Weight
A literature survey on electric vehicles shows that many
electric car designers build smaller and lighter weight specialty vehicles to
keep power requirements low. It becomes necessary to design the vehicle
with the objective of minimum weight of all structural and panel parts to per-
mit sufficient allocation of weight to the batteries. The "Sundancer" was
totally designed as a minimum weight, very low aerodynamic drag electric
car with a major allocation of weight to batteries. It was built for ESB, Inc.,
by McKee Co. to offer maximum range with today's batteries (Ref. 2-13).
A study by Minicars, Inc., for EPA (Ref. 2-3) projects all
designs for electric cars as being in a low performance class (similar to a
VW 1200) because of low battery power levels available in the allocated weight.
This study also points out that these limited performance vehicles can met
the real requirements of average urban driving, but are range limited for
suburban driving.
Electric drive systems have also been used on slow; heavy
vehicles that make many short duration stops. The town delivery truck or
van and the local bus are good examples. There is usually no attempt to
reduce frame weight to compensate for heavy battery weight with these vehicles.
Indeed, the overall loaded weight is so large that even the heavy batteries do
not represent over 30 percent of the overall weight.
The family car lies midway between these trends. To date
no prototype has been designed or built that would accommodate six to eight
people. Compact vehicles have been designed for two to four passengers,
and buses have been designed for 20 people and more. A family car such as
the eight to nine passenger heat engine powered station wagon weighing 4,000
to 5, 000 Ib with about 25 ft of frontal area has much larger power require-
ments than those that have been practically achieved in the lighter electric
cars. To reach this power level would require power plant weight and
volumes required for electric buses.
2-29
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2. 2. 2. 1.6 Materials
The major material in an electric motor is reasonably high
permeance core material, such as 4 percent Silicon Steel or Armco 24.
Other materials, such as Permendur, are capable of higher magnetic flux
density before saturation, but the cost generally precludes their use for large
motors. Although large direct current motors normally have steel or iron
frames around the field yoke material, these frames could be built from
aluminum or other lightweight material, since only rigidity, not magnetic
permeability is required for the frame structure as long as the yoke is present.
The raw materials used in a system to be mass produced must
be readily available in large quantities as a primary mining or refinement
process. Excluding batteries, all the metals to be used in the electric vehicle
are available in quantity, with the possible exception of copper. Aluminum is a
possible substitute for copper; it has a better conductance per unit weight than
copper, but also a lower density. Thus, when a motor is designed for the
same electrical (I R) losses using aluminum conductors, the unit will be lighter
but larger, than when using copper.
The least available material in a permanent magnet motor using
rare earth cobalt is the cobalt. Rare earth metals, samarium and praseodymium,
are plentiful in the earth's crust. Silicon for the SCRs is plentiful.
2.2.2.1.7 Pressure and Temperature Effects
Electric vehicles are expected to be relatively insensitive to
pressure changes. Brushes cannot commutate as well under reduced pressure
due to a reduction in the potential insulation gradient of rarified air. Arcing
can thus occur at lower voltages. In addition, brush wear increases with less
air molecules to act as a surface contact lubricant. Neither of these effects is
of disturbing magnitude up to 10, 000 ft altitude, which is the usual maximum
height of mountainous roads. Even the highest peaks which contain roads (such
as Pikes Peak) would not justify special design of a brush-commutation system.
2-30
-------
Air density and the motor cooling system temperature impacts
design, particularly under load. The temperature rise of the motor that would
result from climbing a mountain could be a serious constraint on all electric
vehicles. A motor would have to be sized for mountain climbing application
commensurate with its cooling system. Cold temperatures can be a severe
problem for the battery system, which has a very serious degradation in
available energy at below-freezing temperatures.
2. 2. 2. 1.8 Cooling Requirements
In the initial running period, the power output capability is
restricted by the degree of thermal lag that determines transient tempera-
tures in the motor. After continuous operation, the power is limited by
heat emission rates of the motor and its cooling system. Cooling must be
provided to ensure that the temperature rise does not exceed the temperature
rating which is dependent on the type of material used for insulation. Running
the motor above this rating will shorten its operating life due to insulation
deterioration and subsequent shorts. Motor burnout due to operation at exces-
sive temperature is a common failure with motors used in electric cars.
2.2.2.1.9 Transmissions
A method to change the gear ratio between the motor and the
drive wheel is advisable for hill climbing and start-and-stop driving. Though
direct current motors can provide their highest torque at zero velocity, the
disadvantage of high current required to accelerate one with a fixed high gear
ratio must be considered against the losses and added weight of a transmission.
2.2.2.2 Operating Characteristics
2.2.2.2.1 Power Control
Most electric vehicles built to date have used either step volt-
age series-parallel switching or a PWM system. The step voltage approach
is becoming less popular as SCRs for a PWM system become less expensive.
In step voltage control, there are a small number of discrete voltage settings.
2-31
-------
This results in power surges when changing control levels. A major shift
from step voltage to the PWM has occurred in the past year because PWM
systems provide a smoothly varying, controlled velocity and torque. Until
last year, voltage switching schemes had been used in a large variety of
electric cars such as the Sundancer (Ref. 2-13). This car, shown in Fig-
ure 2-5, weighs about 2,000 Ib (test weight including 750 Ib of lead-acid
battery). It has a constant speed driving range of 50 mi at 50 mi/hr, and
140 mi at 30 mi/hr. (The urban driving range was between 50 and 80 mi.)
The electric drive control uses both voltage switching and series resistance
control. Figure 2-6 shows another electric car, the Mars II, which used a
similar drive scheme (Ref. 2-14). However, R. R. Aronson, President of
Electric Fuel Propulsion, Corp. , which manufactured the Mars II, indicated
in 1971 that his future electric cars would be controlled by the SCR direct
current PWM system.
2. 2. 2. 2. 2 Vehicle Range Limitations
Currently, a major problem with electric vehicles is the limi-
tation on the amount of energy and power that can be stored in a given size
battery. Evidence of this problem is seen in contemporary electric vehicle
operating characteristics. In a compact electric car, travel distances com-
parable to a heat engine car (without refueling), can only be approached with
a battery system weighing about one-third of the vehicle curb weight. The
magnitude of this problem becomes evident when the energy storage capacity
of gasoline is compared with batteries. For example, at 14 mi/gal, a heat
engine requires about 145 Ib of fuel and tank to store the energy for a 280 mi
trip. At a typical 0.5 kW-hr/mi for battery energy usage of an electric car,
about 140 kW-hr is required to be stored in the battery for the same trip.
Thus, for the same travel per unit weight, the battery must store about
970 W-hr/lb. Present lead-acid batteries achieve only about 15 to 20 W-hr/lb.
So, while it is not necessary to match the storage efficiency of gasoline in all
vehicle applications, it is quite evident why electric cars are overweight with
batteries to achieve any reasonable range.
2-32
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Figure 2-5. "Sundancer" Rear Quarter View (Ref. 2-15)
Figure 2-6. View of 1968 Mars II Electric Car (Ref. 2-17)
2-33
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2.2.2.2.3 Special Requirements and Procedure^
The all-electric vehicle must have a battery state-of-charge
indicator to advise the driver of the remaining vehicle usable range. It must
also include an on-board battery charger with a standard plug for llSVac
outlet limited to a 2 kW charge rate. This could be used in emergency for a
boost charge.
Residential recharging requires about 8 hours, since home
electrical outlets will limit charging to about 2. 2 kW into the charger on a
20-A circuit. Special wiring such as used for electric stoves could cut this
time, but charging efficiency is lower at higher rates.
An alternative to recharging is a battery replacement system
that could be used for a portion of the electric automobile population that
required very rapid restoration of energy. The exhausted battery pack is
rolled out from a storage well under the vehicle and a freshly charged battery
pack is inserted. The time required is about the same as the usual gasoline
refueling period. The exhausted battery pack is recharged while the vehicle
continues on its trip (Ref. 2-15).
The standard driving foot pedals, steering wheel, and ignition
key that closes a line relay are used. When the foot throttle is raised, regen-
erative braking can be used to decelerate the vehicle at a rate similar to that
available from a heat engine. Hydraulic brakes and an effective emergency
parking brake are also required.
Current limiting provisions independent of throttle position
are of prime importance for safety. The inexperienced driver may push the
throttle to the floor with the wheel against the curb. The armature resistance
of vehicle-size motors is too low to prevent a destructive surge of current with
application of full voltage while the motor is not turning. The PWM system
must incorporate a current sensor and control logic which prevents buildup
of currents above four to five times rated current. In the step voltage con-
trol system, a current limiting line relay may be inserted with a latching
2-34
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circuit to its closing coil. This relay is opened at a predetermined maxi-
mum current, and can be reset by a turn of the ignition key to the momentary
start position. In case the throttle is fully depressed at the same time the
latching relay is being reset, the relay will chatter but no destructive cur-
rents can flow.
Each system must have circuit breakers and/or fuses mounted
as close to battery terminals as practical. By having a switch at the driver's
position which can remotely reset or trip the circuit breakers in case of
inadvertent over-loads, the vehicle need not significantly decrease velocity
before the breakers are reset and power is reapplied.
2-35
-------
3. VEHICLE PERFORMANCE CHARACTERISTICS
-------
3. VEHICLE PERFORMANCE CHARACTERISTICS
A typical approach to building electric cars has been to use
the frame and entire structure of the conventional heat engine powered car
and merely replace the heat engine with an electric motor mounted in the
same location. A manual shift transmission is often retained, and the usual
drive shaft and differential remains. In this case, batteries are often packed
in all available space. Trunk space is often sacrificed, and heavy duty
brakes, shock absorbers, and springs are installed to compensate for the
additional weight. In many cases, such as the Mars II, the resulting weight
distributions caused adverse handling characteristics (Ref. 3-1).
Currently, if high acceleration performance is designed into
the all-electric vehicle to attempt to approach that of the baseline heat engine
vehicle, then the range becomes very limited (about 30 to 40 mi between
charges for 1, 000 Ib of battery load). However, if both high performance
and long range are desired, the battery weight will result in the vehicle
weight being much larger than a heat engine powered car of similar perfor-
mance, and indeed electric cars may never fully match the heat engine
powered car performance until advanced battery systems are available.
3. 1 POWER, SPEED, AND TORQUE
Analytical studies have been conducted on the expected per-
formance of electric vehicles, but those who subsequently built prototypes
discovered that actual performance (including range) did not measure up
to the predictions based on analysis of total drivetrain efficiency, battery
performance, aerodynamic drag, and friction drag of tires. Tire drag was
often higher than anticipated since the resulting vehicles are extremely
overweight with batteries compared to the base heat engine vehicle. To
alleviate the problem, tires are over-inflated to reduce friction. Radial ply
tires have also been used to reduce friction somewhat (Ref. 3-1).
3-1
-------
In general, the majority of the electric vehicles do not
perform up to heat engine capabilities, particularly with respect to maximum
acceleration, speed, range, and hill climbing ability. The usual maximum
speed lies in the range from 30 to 50 mi/hr. Hill climbing results in a
dramatic reduction in maximum speed. For example, a 5 percent grade
would usually cause a 50 percent drop in velocity, and a 15 percent grade
can generally be ascended only if a variable gear ratio transmission system
has been included.
The range is always constrained by the total energy carried
in the vehicle, and also varies in each vehicle with the cruise velocity,
number of stops required, and the total weight. Aerodynamic drag is not a
significant factor at the lower speeds. Differences in the vehicle frontal
area become a factor above 30 mi/hr and important above 50 mi/hr. The
range variation due to velocity is very large. The range at maximum speed
can be one-half the range at the optimum speed (Ref. 3-2). In addition, the
range is approximately inversely proportional to the number of stops. Com-
parison of vehicles from a curb weight of approximately 1,200 to 4,800 Ib
shows that range is strongly affected by the weight with the ratio of the vehicle
weight to the battery weight being the controlling factor.
A typical vehicle is the converted American Motors Hornet,
"The Electro-Sport. " This vehicle had a curb weight of 5, 180 Ib including
about 2,200 Ib of batteries. It reached a speed of 69 mi/hr, accelerated from
0 to 30 mi/hr in 9- 8 seconds and from 0 to 50 mi/hr in 26. 4 seconds. Its
range at different continuous speeds was:
Speed, mi/hr Range, mi
50 56.7
40 73.4
30 87.3
20 101.6
It was able to climb an 8.4 percent grade at 21 mi/hr. At a constant cruise
speed, the energy taken out of the battery varied from 0. 277 to 0. 458 kW-hr/mi.
3-2
-------
With a severe urban driving cycle involving four start-stops per mile, it
traveled 31.2 mi (125 stop-start cycles) at an average speed of 20 mi/hr
with an energy requirement of 0.7 kW-hr/mi (Ref. 3-2). Note that, with
four stops per mile, the energy usage increased by about a factor of 2. 5
compared to continuous driving at the same average speed.
In another evaluation, over 50 Mars II vehicles were built by
converting Renault-10 sedans. Actual performance of these cars did not
match earlier predictions. Reference 2-17 predicted acceleration of 0 to
40 mi/hr in 10 seconds, a top speed of over 70 mi/hr, and ranges of 70 mi
at 70 mi/hr and 150 mi at 40 mi/hr. The curb weight of the heat engine
powered baseline design for the Renault-10 is 1, 800 Ib, while the electric
version weighed 4, 100 Ib. The test results (Ref. 3-1) state: "Most of the
shortcomings ascribed to the Mars II stem directly from its excessive
weight and adverse weight distribution due to the batteries. " It also lists the
actual test top speed at 55 mi/hr and ranges of 84 mi at 45 mi/hr, 91 mi at
37 mi/hr, and 125 mi at 31 mi/hr. The minimum acceleration time for
0 to 40 mi/hr was actually 21 to 22 seconds, neglecting time for shifting.
The large weight was a result of 1, 800 Ib of batteries employed in an effort
to achieve high performance and long range.
3.1.1 Power and Energy Storage
When a compact car weighing about 2, 000 Ib is converted to
an electric vehicle weighing 3,000 Ib (including 1,000 Ib of batteries), it
cannot travel more than 30 to 50 mi between charges in stop-and-go driving.
If greater battery weight is added to increase the range, the handling char-
acteristics such as steering and braking are degraded, in addition to having
poor acceleration and an uncomfortable ride. It is thus concluded that a
general-purpose, all-electric family car is not possible with present lead-
acid batteries.
If the battery weight is limited to 500 Ib and the range between
battery charges is 200 mi, then a compact car must carry about 100 kW-hr
for stop-and-go driving (estimated to require energy expenditures of about
3-3
-------
0.5 kW-hr/mi). This would require a battery energy density of 200 W-hr/lb.
Only further research can develop this capability, which is a very great
increase over the present level of 15 W-hr/lb of lead-acid batteries.
Though some improvement can be made in aerodynamic drag
by streamlining and in road drag by using radial ply tires, the basic power
to move and accelerate vehicles of certain weights and cross-section area
remains essentially fixed. Reducing drag to a minimum, while increasing
drive system efficiency to a maximum are the only steps outside of battery
development that can be taken if the ratio of drivetrain weight to total
weight is to be maintained at feasible levels. Unfortunately, these actions
can only provide minor improvement.
3.1.2 Speed and Torque
As discussed previously, it is not practical to achieve the
same torque and speed characteristics in an electric vehicle as in a heat
engine vehicle. However, it is possible to make improvements in the use
of electric motor capabilities.
The present peak operating speeds of electric motors sized
to drive road vehicles are approximately the same as their heat engine
counterparts. Although this feature is convenient for those firms converting
cars by simple replacement of the heat engine with an electric motor, these
speeds are not optimum for packaging of the powertrain in electric vehicles.
For example, if a 3,000 rpm motor is replaced by a motor rated for
12, 000 rpm at 20 hp, its power density would improve from about 7-1/2 to
4-1/2 Ib per continuous horsepower- Reference 2-2 indicates that 12,000
and 24,000 rpm direct current motors could achieve 1.54 Ib per peak
horsepower and 1 Ib per peak horsepower- respectively.
3.2 EMISSIONS
Gases can evolve from the battery system depending on the
type of battery and the packaging design. Lead-acid batteries containing
antimonial lead grids give off gases on charge, discharge, and on
3-4
-------
standing idle. These gases are largely hydrogen and oxygen, but small
amounts of antimony hydride, arsenic hydride, carbon monoxide, and
chlorine may also be present. Sulfuric acid can also be lost through vents
and enter the atmosphere in the form of sulphates.
Outside of the battery, the direct emissions from an electric
vehicle are primarily heat and a possible trace of ozone from the opening of
current-carrying relays. The operation of SCRs in PWM does not generate
ozone, however.
Overall emissions must also include those produced by the
electric plant that generates the energy to charge the battery. Both the type
of emissions and the total emissions must be evaluated to determine the
benefits that accrue to the pollutant levels in the atmosphere when energy is
expended at a large, fixed single source as opposed to many small, mobile
sources.
3.3 FUEL (ENERGY) ECONOMY
When energy requirements of electric vehicles are compared
to conventional cars, a careful examination must be made of the efficiencies
of the various steps of energy flow. Thus, as pictured in Figure 3-1, start-
ing with the required power or energy delivered to the wheels, we have to
consider the efficiency of each stage in the system. But to avoid making
assumptions regarding efficiency of elements in the vehicle powertrain, road
test data for a given vehicle must be used. Some of the available test reports
quote only total range at a given speed, some measure Watt-hours to the
motor, and some base range on total energy storage. Efficiencies, such as
battery discharge efficiency and motor efficiency, are a function of the
operating cycle, the temperature, etc. For example, Reference 3-1 found
a 4 to 1 variation in range between 0 and 80 F operating temperatures. For
this reason, it is very difficult to obtain a consistent set of performance
characteristics from different tests.
3-5
-------
FUEL '
__ ENERGY
TO V
ELECTRIC
fri GENERATING _
PLANT
EFFICIENCY
DELIVERY
EHICLE
TRANSMISSION
*• DISTRIBUTION
EFFICIENCY
•••
ENERGY USAGE
"" BY VEHICLE
BATTERY BATTERY
*• CHARGING —*• DISCHARGE ~
EFFICIENCY EFFICIENCY
MOTOR AND
* POWFR —
REGULATION
EFFICIENCY
(_ DRIVE WHEEL}
1
_^_ DRIVE
EFFICIENCY
1
£ DRIVE WHEEL^
Figure 3-1. Electric System Energy Flow Diagram
Some basis for comparison between electric and spark igni-
tion internal combustion engine powered vehicles is offered by test data
acquired by the United States Postal Service during evaluation trials of
intracity mail delivery service trucks in Cupertino, California (Ref. 3-3).
The Harbilt electric vans designed for this type of service are powered by
two 36-V, lead-acid batteries and can reach a peak speed of 40 mi/hr while
ascending a 2 percent grade. The conventional postal vehicle is a Jeep
powered by a four cylinder, internal combustion gasoline engine. The postal
routes ranged from 8 to 15 mi with 100 to 300 stops.
Calculations of energy expenditure (Ref. 3-3) showed the
electric vehicle using an average of 1. 3 kW-hr/mi and the Jeep using the
equivalent of an average 5. 1 kW-hr/mi (after converting from gasoline con-
sumption figures in miles per gallon). To truly offer a compatible com-
parison, the electric power plant generating efficiency and the transmission
efficiency between the power plant and the battery charging station for the
electric vehicle must be taken into account. Based on an average nationwide
3-6
-------
efficiency of 35 percent for the electric generating plant and 91 percent for
transmission and distribution (Refs. 3-4 and 3-5), the electric vehicle is
then actually using energy at the rate of about 4. 1 kW-hr/mi.
The electric vehicle indeed shows some advantage in energy
consumption for this special application; a gasoline engine powered vehicle
is at a disadvantage under conditions of low-speed stop and start driving
coupled with significant periods of engine idle. However, the advantage
shown might be reduced (or eliminated) if the Jeep engine was derated so
that vehicle performance was lowered to that of the electric vehicle; i.e.,
fuel economy of the Jeep could possibly be improved if the engine were
redesigned for this particular application.
If this comparison were extrapolated to passenger cars, it
should be noted that for equivalent weight vehicles, the gasoline engine
powered car has superior driving range, cruise speed, acceleration, and
passenger/luggage accommodations. In favor of the electric car, however,
is the prospect that propulsion energy can be derived directly from non-
petroleum based sources (e.g., nuclear power or abundant supplies of coal).
(Eventually, these sources can also be available indirectly through produc-
tion of synthetic fuels for heat engine powered cars.)
3.4 NOISE LEVELS
Aside from brush whine, the only noise sources expected
from an all-electric are gears, wind noise, and tires. In some designs
noise has also come from power transformers, but, in general, the electric
drive is the quietest mode of transportation available.
3.5 ODOR
Relay switching in the step voltage system will cause a slight
odor of ozone. Even this odor is avoided in the PWM system. Odors from
electric generating stations will occur separately from the vehicle.
3-7
-------
3.6 MAINTAINABILITY
While an electric vehicle has fewer moving parts than an
internal combustion engine powered vehicle, no definitive data are available
for passenger cars that can establish a statistical base for maintenance
requirements and costs. Some indications of relative differences may be
available from the large fleet of electric trucks and vans operating in Great
Britain. However, extrapolation of those data to passenger cars could prove
erroneous if the duty cycle and powertrain design requirements for those
trucks are markedly different than for cars.
3.7 SAFETY
General safety requirements for an electric vehicle will be
comparable to those for a similar heat engine vehicle. There will be
additional requirements for circuit breakers with provision to reset the
breakers in the event of an inadvertent overload at high speed. Spillproof
battery caps must be used; in the event of an accident, there must be pro-
vision to avoid hazards from spilled electrolyte. Provision must also be
made for opening the battery circuit for maintenance. There must be
redundancy in design to minimize shock hazard, and short-circuit protection
must be maintained.
In early work at General Motors on all-electric vehicles
(Electrovair I), they elected to ground mid-battery voltage to minimize the
shock hazard. It was subsequently determined that by not grounding the
battery to the vehicle, the risk of shock and the risk of cable shorting upon
impact are reduced. Though the drive batteries were not grounded to the
chassis, in a later vehicle the accessory battery used the frame for the
negative terminal. To achieve isolation between the drive batteries and the
accessory battery; a high impedance charging unidirectional circuit was
used.
3-8
-------
3.8 DRIVABILITY
The Cornell Aeronautical Laboratory evaluation of an electric
vehicle (Ref. 3-1) reports poor drivability due to the distribution of battery
and motor weight in the front hood and rear trunk regions. The yaw moment
of inertia is thus considerably greater than its heat engine counterparts. To
alleviate this problem, the design of an original electric (as opposed to the
conversion of a heat engine car) must include mounting most of the batteries
in the mid-car region under the floor or seats of the car. The increased
weight causes greater steering and braking effort, but usually not so great
as to require power steering or power braking.
As noted in previous sections, the electric vehicle also has
a low acceleration capability (except perhaps at very low speeds) and a
limited top speed.
3-9
-------
4. CURRENT STATUS OF TECHNOLOGY
-------
4. CURRENT STATUS OF TECHNOLOGY
4. 1 CURRENT USE
Electric delivery trucks or vans and electric utility vehicles
have been built in increasing numbers in Great Britain for the past decade
and are now estimated to exceed 75,000 vehicles. Small electric cars and
electric utility vehicles are currently being produced in Japan in greater
numbers than in the United States, largely because of the ban on heat engine
vehicles in Osaka during the 1970 World's Fair. In the United States, an
initial production of fewer than 300 vehicles has been accomplished by both
Vanguard and Electric Fuel Propulsion Corp. Battronic is producing 100 cars
for the Electric Vehicle Council and is building over 300 truck vehicles.
Many demonstration and prototype models have been built, but, excluding
electric golf carts and electric fork lifts, no major production of electric
vehicles is under way in the United States.
Under a $14 million, 5-year program initiated in FY 1971,
Japan is developing an electric car for use in city-bound transportation
(Ref. 4-1). Aside from this program, they have produced about 1200 road
qualified electric cars from 1966 to 1972 of which about 280 were used in
EXPO-70, about 520 used for golf courses, and the majority of the remainder
used in commercial and industrial applications. Table 4-1 lists the per-
formance characteristics of electric vehicles built to prototype level of
design in Japan, including trucks, vans, passenger cars, and buses.
4.2 CURRENT RESEARCH AND DEVELOPMENT
Motors holding great promise, but not yet developed to the
point of qualification for electric vehicles, are the disc-armature motor that
is being developed at the University of Warwick and the samarium cobalt
permanent magnet brushless motor designed by General Electric under a
contract through Wright-Patter son Air Force Base. These 1972 to 1973
4-1
-------
Table 4-1. Performance of Japanese Prototype Electric Vehicles
in 1973 (Ref. 4-2)
i
ro
Parameters
Passenger +
Loading Capacity, kg
Approximate Gross
Vehicular Weight,3
kg
Maximum Speed,
km/hr
Mileage per One
Recharge, km
Acceleration (0 to
30 km/hr) in seconds
Climbing Ability
(speed of climbing
an inclination of
6 deg), km/hr
Company Responsi-
ble for Development
Cargo
Lightweight
two persons
+ 200
1, 100
more than 70
130 to 150
less than 5
more than 40
Toyo Kogyo
Compact
two persons
+ 1,000
3, 500
more than 70
180 to 200
less than 5
more than 40
Nissan
Passenger Cars (and Vans)
Lightweight
four persons
(or two per-
sons + 100)
1, 000
more than 80
130 to 150
less than 4
more than 40
Daihatsu
Compact
five persons
(or three per-
sons + 300)
2,000
more than 80
180 to 200
less than 3
more than 40
Toyota
Buses
Large -Size
60 to 80 persons
15,000
more than 60
230 to 250
less than 8
more than 25
Mitsubishi
3The weight of a battery shall be less than 30 percent of the gross vehicular weight. The energy
density of a lead storage battery shall be 60 W-hr/kg. However, this is based on constant
output for 5 hours.
The mileage per one recharge is based on a value in continuous running at a constant speed
of 40 km/hr.
-------
developments are demonstrating that high-speed motors mounted in the
drive wheel with epicyclic or planetary gears are possible. Samarium
and/or praseodymium cobalt magnets represent a breakthrough in large
motor field sources, since they are high in both field intensity and field
density. That is, they provide high torque per ampere and the high coercive
strength to resist change of the high torque per ampere. They cannot be
demagnetized at any motor currents at temperatures below approximately
700 C. Hitachi Magnetics Corporation, in joint venture with General
Electric, announced an even better rare earth cobalt magnet that could
supply almost twice the torque per ampere as present motors with wire-
wound fields.
A comparison for various materials of permanent magnet
characteristics along with approximate dates of introduction are shown in
Table 4-2.
Today's heat engine car requires a mechanical linkage
between the engine (which is frame mounted) and the wheel axle (which moves
up and down relative to the frame). Unsprung motors can be directly (or
spur gear) coupled to a wheel. That is, in an advanced concept, a torque
motor armature becomes the wheel center or a high-speed motor armature
directly drives a reduction gear within the wheel hub. The electric vehicle
can use multiple electric motors without overall efficiency penalty. How-
ever, a modest increase in weight will occur per unit torque and power
when distributed among four motors. But, this may be offset by the weight
saving due to elimination of drive shaft, differential, and transmission.
There may also be an increase in vehicle cost and repair expense with this
design.
Individual drive wheel motors can be sufficiently lightweight
to avoid undue tire wear despite their unsprung vertical inertia. Therefore,
the following wheel-mounted motor configurations may prove to be feasible:
a. Four annular torque motors mounted in the wheels,
eliminating all reduction gears. The loss in power
per unit weight of this type of motor is partially
compensated by weight saving of all gears and couplers.
4-3
-------
Table 4-2. Comparison of the Permanent Magnet Field Materials
Parameter
Manufacturer
B-H Maximum
Product in
Millions
Gauss-Oersteds
Year Introduced
Characteristic*
Comment
Projected
Approximate
Large Quantity
Coat*
Material
Alnico V
General Electric
Company
5.25
Late 1940s
Coercive strength
only 600 Oersteds
Subject to
demagnetization
in large motors
i6/lb
Ferrite V
Indiana General
Corporation
3
1954
High coercive
strength about
3, 000 Oersteds
low flux
density
Low torque per
ampere
Sl/lb
Samarium
Cobalt
Hitachi Magnetics
Corporation
18
Late 1960s
An isotropic--
difficult to
radially
magnetize
High torque per
ampere; will not
demagnetize
512/lb
Rare Earth
Cobalt
Hitachi Magnetics
Corporation
50
1973
I
Isotropic also for
radial magnetization
Highest torque per
ampere; lowest
weight
f
$25/lb
Based on 100,000 magnets per year, current technology, from manufacturer's catalog and personal
communication.
4-4
-------
b. Four disc-type torque motors using rare earth cobalt
permanent magnet fields with almost linear torque-
speed curves. These motors are mounted in the wheels.
c. Four printed circuit disc motors of bipolar or homo-
polar configuration with a permanent magnet field
mounted in the wheels.
Although battery capability is recognized as the greatest
single block to a practical family electric car, improvements can and must
be made to the motor and controller systems to better utilize the power
that next generation batteries will make available. Motor performance can
be improved by designs using lightweight materials. Very few technology
improvements have been accomplished in the controllers since the late 1960's,
which marked the advent of the SCR chopper in pulsewidth modulation mode
driving a direct current series field wound motor. During the past four
years, the power handling capability of SCR systems has improved several
fold, while costs have been reduced to about one-fourth of initial costs.
In addition to the new rare earth cobalt permanent magnet
motors now being produced in developmental quantities, an advanced motor
concept that may supply the highest power density is the cryogenic motor,
which uses super-conductors for high-strength magnetic fields without
iron core materials. Its extensive development is at least a decade away.
Besides the need for long-term insulated containment of the cryogenic fluid
(such as liquid helium), development is required for a safe method of
dissipating the large amount of energy stored in the conductors if super-
conductivity is lost.
4-5
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5. PROJECTED STATUS OF ELECTRIC VEHICLES
-------
5. PROJECTED STATUS OF ELECTRIC VEHICLES
5. 1 REQUIRED DEVELOPMENT
In addition to the essential development of batteries with
higher energy and power density, other technology development is required
for mass-produced, all-electric family cars. This includes:
a. The development of low-cost manufacturing techniques
for motors and controls is necessary.
b. Development of lightweight components is required.
Motors have small bearing tolerances for maintenance
of magnetic air gaps that require rigid end bearing
mounts. The weight saving from less material and
lighter weight but more compliant material can possibly
be made by using the rigidity of the mount structure to
maintain bearing alignment.
c. The development of a standardized structure for the
battery pack mount, despite differences in manufacturer
and external appearance, would enhance usability of
electric cars.
Recent evaluations of domestic transportation needs (Ref. 5-1) call for
battery development with an energy density goal of 100 W-hr/lb, a power
density goal of 100 W/lb, a life of 1, 000 cycles, and a cost goal of $l/lb.
Also called for are motor/control packages of less than 5 Ib/kW and costing
about $l/lb. From an initial expenditure of $10 million over a 3 to 5 year
period, an overall program for electric vehicle development is estimated
to cost $250 million, resulting in a preproduction prototype vehicle at the
end of 15 to 20 years.
5.2 PROJECTIONS FOR ELECTRIC CARS
Excluding the special-purpose applications of golf carts,
electric fork lifts, and delivery vans, no major production of electric
passenger vehicles for a first-use car is expected for the next 10 years.
Small production for use by electric utilities and an increasing number of
5-1
-------
individual conversions to electric propulsion will be the extent of passenger
cars on city streets for this period.
Often, families will retain a larger car or station wagon for
trips and entire family use, and use a second compact car for work or
shopping use. The all-electric vehicle as a second commuter car is cur-
rently marginally acceptable at best. Even for this type vehicle, mass
production is not expected within the next 5 years.
In addition, the electric car would have to be sold at a price
comparable to the heat engine car for general acceptance. This would
require subsidies or tax incentives, and mass production methods to reduce
fabrication costs. Of importance also is an acceptable cost for battery
replacement and the assurance of low electric power rates to control vehicle
operating costs. A major gasoline shortage, a restriction on driving heat
engine vehicles in some areas due to emissions, or a breakthrough in
battery technology allowing much improved performance and range could
cause increased acceptance of the electric car.
5-2
-------
REFERENCES
-------
REFERENCES
PART I
2-1. Analysis and Advanced Design Study of an Electromechanical
Transmission. Report 17220.000, TRW Systems Group, Inc.,
Redondo Beach, Calif. (April 1971) (Contract EHSH 71-002 for
Office of Air Programs, EPA).
2-2. J. H. B. George, L. J. Stratton, and R. G. Acton, Prospects for
Electric Vehicles, a Study of Low Pollution Vehicles-Electric,
Report C-69260, Arthur D. Little, Inc., Cambridge, Mass.,
Prepared for National Air Pollution Control Administration,
Washington, B.C. (15 May 1968) (Contract PH86-67-108).
2-3. Donald Friedman and Jerar Andon, The Characterization of Battery-
Electric Vehicles for 1980-1990, Minicars, Incorporated, Submitted
to General Research Corporation, Prime Contract No.
EPA-68-01-2103, January 1974.
2-4. Develop High Charge and Discharge Rate Lead/Acid Battery
Technology, Report 18353-6006-RO-OO, TRW Systems Group,
Redondo Beach, Calif. (April 1972).
2-5. J. Giner, A. H. Taylor, and F. Goebel, Lead/Acid Battery Devel-
opment for Heat Engine/Electric Hybrid Vehicles, Tyco Laboratories,
Inc., Waltham, Mass. (November 1971).
2-6. H. J. Schwartz, Electric Vehicle Battery Research and Development,
Paper presented Fall Meeting Electrochemical Society, Boston
(7-11 October 1973).
2-7. Final Report-Hybrid Heat Engine/Electric Systems Study,
TOR-0059(6769-01)-2, The Aerospace Corp., El Segundo, Calif.
(1 June 1971).
2-8. Sidney Gross and Sidney Silverman, Study of Batteries for Electric
Vehicles, Boeing Co., Seattle, Wash. (13 March 1973).
2-9. E. J. Cairns, Lithium-Sulfur Batteries, Argonne National Labora-
tories, Argonne, 111., Presentation to Department of Transportation,
Electrochemical Working Group, Washington, D. C. (16-17 May 1972).
R-l
-------
2-10 S Grach. The Ford Sodium-Sulfur Battery, Ford Motor Co. ,
Dearborn, Mich. , Presentation to Advisory Committee on Advanced
Automotive Power Systems Development, Environmental Protection
Agency, Washington, D.C. (26 January 1972).
2-11. W. J. D. Escher, No Intake-No Exhaust - A Dialogue on Technology.
Escher Technology Associates, St. Johns, Mich. (1971).
2-12. R. W. Johnston, "Modulating Inverter System for Variable Speed
Induction Motor Drive-G. M. Electrovair II, " IEEE Transactions
No. 68-Tp-108 Power, New York (January-February 1968).
2-13. R. S. McKee et al, "Sundancer: a Test Bed Electric Vehicle,"
SAE Paper No. 720188, Automotive Engineering Congress, Detroit
(January 1972).
2-14. R. R. Aronson, "The Mars II Electric Car," SAE Paper No.
680429, Detroit (May 1968).
2-15. G. A. Hoffman, "Future Electric Cars," SAE Paper No. 690073,
Los Angeles (13-17 January 1969).
3-1. J. E. Greene, An Experimental Evaluation of the Mars II Electric
Automobile, CAL No. VJ-2623-K-1, Cornell Aeronautical Laboratory.
Buffalo, N. Y. , Prepared for General Motors Corp. (February 1969).
3-2. Electrosport, a Test Data report, J. R. Miller Test Center, Dana
Corp. (30 March 1972).
3-3. "4 for 1 EV Comparison Data-a Report from Cupertino, " Electric
Vehicle News, The Porter Corporation, Westport, Connecticut
(November 1973).
3-4. Statistical Yearbook of the Electric Utility Industry for 1969, No.
70-33, Edison Electric Institute, New York (September 1970).
3-5. The Comparative Environmental Impact in 1980 of Gasoline-Powered
Motor Vehicles Versus Electric-Powered Motor Vehicles, Gordian
Associates, Report prepared for Electric Vehicle Council, New York
(October 1971).
4-1. Development Program of Electric Car in Japan - National Research
and Development Program, Agency of Industrial Science &c Technology,
Ministry of International Trade & Industry, Japan, April 1971
(Revised November 1972).
R-2
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4-2. G. E. Smith, Status of Electrical Vehicles in Japan, Report
published by University of Michigan, Ann Arbor, Michigan
(October 1973).
5-1. "Research and Development Opportunities for Improved Transpor-
tation Energy Usage," U.S. Department of Transportation,
DOT-TSC-OST-73-14, September 1972.
R-3
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PART II
HYBRID HEAT ENGINE/BATTERY AND
HEAT ENGINE/FLYWHEEL VEHICLES
-------
1. INTRODUCTION
-------
1. INTRODUCTION
The problem of adequate operating range for electric vehicles
has been discussed in Part I of this volume.
Lacking the availability of low-cost, high-capacity batteries
to permit operating ranges for electric cars that are comparable to gasoline
engine powered cars, other concepts have been examined in the search for a
low-pollution vehicle that could satisfy personal transportation needs. One
concept that has received the attention of automobile designers in the last
5 years is the hybrid vehicle - a vehicle combining various power delivery
systems in the powertrain to use each form of power more effectively.
The hybrid powertrain concept for automobiles originated in
1917 when the Woods Dual Power automobile was manufactured in limited
quantities. This spark ignition heat engine/battery hybrid vehicle had a peak
speed of 20 mi/hr and was capable of operating in three distinct modes: all
electric, engine only, or hybrid with both engine and batteries supplying
power. Regenerative braking was also available.
A modern version of the hybrid vehicle was considered to offer
potential improvements in air quality and also serve as an intermediate step
between the gasoline engine powered car and the all-electric powered car.
First, the hybrid vehicle range was considered to be no more limited than
the gasoline engine powered car because the heat engine on board this vehicle,
in conjunction with a full-size fuel tank, provided a reservoir of energy
equivalent to that of the gasoline engine powered car. Second, only a small
nearly constant power engine would be required to provide road cruising
power, with acceleration power requirements provided by a battery in the
case of an electric energy storage hybrid and by a flywheel in the case of an
inertial energy storage hybrid. (Other forms of energy storage have also
1
been considered. ) It was expected that a fixed power engine could be optimized
for reductions in both exhaust pollutants and fuel consumption.
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To evaluate various hybrid concepts, the EPA under the AAPS
Program assumed the task of planning a hybrid vehicle prototype development
program. Implementation of a 3-year program began in 1970 with the partici-
pation of several companies offering the required technical expertise.
Emphasis was placed on achieving original 1976 Federal emission standards
without the use of engine add-on control devices (namely, catalytic converters).
The programs were formulated with three basic types of efforts
for both electric and inertial hybrid systems: systems analysis, systems
development, and component development. Over a 3-year period from 1970
to 1973, approximately $2 million was expended in contracts for analysis and
test of hybrid systems and components. The work was administered by two
government agencies, Department of Health, Education and Welfare (DHEW)
and Environmental Protection Agency (EPA), each chartered at the time to
perform investigations of this nature. The program was terminated because
of funding limitations imposed in FY 1971, and because it was found that oper-
ating a spark ignition engine in a hybrid mode still required the same type of
exhaust aftertreatment needed on conventional systems. At the same time,
the EPA was also forced to curtail and/or suspend active programs designed
to evaluate some other alternative systems for powering automobiles. Since
then, EPA has concentrated on the prototype development of systems offering
a greater near-term (1975 to 1985) potential, namely gas turbine and Rankine
cycle engines.
This report summarizes results from the contractor develop-
ment programs, reviews the technical achievements in context with prior
goals, and offers a prognosis for the future potential of hybrid powertrains
for automobiles. In this regard, many of the study guidelines that resulted
in specific powertrain design constraints have been under revision since the
The EPA was created by an act of Congress in April 1970. Responsibility
for the DHEW program was assumed by EPA at the time of its inception.
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period when the EPA studies were being conducted. Revised guidelines for
vehicle range, acceleration performance, cruise speed, exhaust emissions,
and fuel economy could result in modifications to system designs and to study
conclusions.
The report is based largely on documentation that had been
prepared by DHEW and EPA contractors and published at the conclusion of
each separate study effort. Other hybrid vehicle studies not federally funded
are also briefly reviewed.
A brief listing of the EPA contractors and their assigned work
effort is given below.
a. Hybrid Heat Engine/Battery System Development
1. TRW Systems, Inc. System analysis, system construe -
tion, and integrated system breadboard tests
2. Minicar, Inc. - Powertrain fabrication, installation in
automobile, and dynomometer tested
3. The Aerospace Corporation - Systems analysis including
component sizing, performance, and costs
4. Petro-Electric Motors - Leasing of a prototype vehicle
to the government for test and evaluation
b. Hybrid Heat Engine/Flywheel System Development
1. Lockheed Missiles and Space Co. Systems analysis
including component sizing and performance estimates
2. Johns Hopkins University, Applied Physics Laboratory
(APL) Systems analysis and performance estimates
c. Component Development
1. Lockheed Missiles and Space Co. Flywheel analysis,
design, construction, and test
2. Johns Hopkins University (APL) Advanced concept
flywheel analysis, design, construction, and test
3. TRW Systems, Inc. and Gould Battery Company - Lead-
acid battery redesign and test
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4. Tyco, Inc. - Lead-acid battery advanced concept design
and test
5. Bureau of Mines, U.S. Dept. of Interior - Laboratory
tests for establishing performance map for V-8 spark
ignition engine
6. Sundstrand Aviation - Transmission design evaluation
and performance analysis
7. Mechanical Technology, Inc. - Transmission design
evaluation and performance analysis.
1-4
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2. GENERAL, CONCEPT DESIGNS AND SYSTEM OPERATION
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2. GENERAL CONCEPT DESIGNS AND SYSTEM OPERATION
2. 1 BASIC CONCEPT
The basic integrated heat engine hybrid vehicle concept is
designed to permit near steady-state engine operation while it is supplying
vehicle cruise power; vehicle acceleration power is supplied from an energy
storage device that is recharged by the engine. The term near steady-state
refers to slowly varying engine power demands. In addition, the engine opera-
ting speed and/or power levels could be restricted to a narrow range or set at a
fixed point, depending on vehicle performance requirements. By virtue of this
scheme, hybrid vehicle proponents envisioned that the engine designer could be
aided in conceiving a design optimized for minimum exhaust emissions (and
possibly minimum fuel consumption as well) that would not require the use of
add-on devices such as catalysts or thermal reactors. Furthermore, under
acceleration power demands, engine hesitation, "stumble," or power lag is
quite often associated with present day techniques for control of exhaust
emissions, particularly during cold start. With acceleration power demand
removed from the engine and transferred to an energy storage device, smooth
engine operation (and thereby smooth vehicle operation) is expected. It is also
conceivable that the heat engine size can be reduced with engine auxiliaries
(pumps, fans, etc.,) need only be sized for steady .-state operation; further
size reduction could be possible if the required range in values for engine
operating speed and/or power were to be limited.
Other heat engine hybrid concepts involve independent operation
of the heat engine and the energy storage device whereby recharge of the energy
storage device is performed by energy sources external to the vehicle; i. e. ,
a recharging station or electrical outlet in the garage at each residence. This
nonintegrated version of the hybrid vehicle has not been assessed, as has the
integrated version, for application to personal passenger car needs of the nation.
Hence, only the integrated version will be discussed in this report.
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2. 2 POWERTRAIN CONCEPTS
Hybrid vehicle powertrain concepts can be grouped into two
broad classes as shown in simplified form in Figure 2-1. The first class,
series configuration, is characterized by the principle that energy flowing
from the heat engine to the rear wheels first passes through an intermediate
energy conversion device or devices. This means of decoupling the engine
from the rear wheels provides a large degree of flexibility in engine operating
modes. Although there are several energy storage concepts for a hybrid
vehicle, EPA contracted to evaluate just two--battery and flywheel. It is
these two concepts that are included in the succeeding discussion. (As
differentiated from the static battery, the flywheel stores energy and also
transfers it kinetically. Hence, the system configurations will differ some-
what. )
In the case of a series configured heat engine/battery hybrid,
the heat engine drives an electrical generator that transmits energy to the
electric drive motor and thence to the wheels. A portion of the generator
energy is directed to recharging the batteries as needed. For a series con-
figured heat engine/fly-wheel hybrid, the heat engine drives the flywheel
through a transmission and the flywheel drives the rear wheels through another
transmission.
The second class, parallel configuration, is characterized by
the principle that some of the energy flowing from the heat engine passes
directly to the rear wheels with the balance of the energy directed in a
parallel path through an energy conversion device or devices. This engine
coupling to the rear wheels is far more limited in terms of engine flexibility
than for the series configuration, but the transmission losses are less and
the overall system efficiency is higher. Furthermore, the nonenergy storing
components that are driven by the engine in the parallel configuration are
required to supply acceleration power only whereas in the series configuration
they are required to supply cruise plus acceleration power. Hence, the size
and weight of components in the parallel configuration are reduced from that
for the series configuration. This is particularly true for the electric drive
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HEAT ENGINE'BATTERY HYBRID
HEAT ENGINE/FLYWHEEL HYBRID
CONFIGURATION
HEAT
ENGINE
— *>
GENERATOR
•i
•*•
MOTOR -+ WHEELS ^^ -* JRAN^ ^FLYWHEEL-* ^^ -^ WHEELS
i
BATTERIES
N)
HEAT ENGINE/BATTERY HYBRID
,i
PARALLE
CONFIGURAT
HEAT
ENGINE
1
r
GENERATOR
-^
BATTERIES
— *•
GEARING
i
k
MOTOR
— ^- WHEELS
HEAT ENGINE/FLYWHEEL HYBRID
Figure 2-1. Simplified Schematics of Heat Engine Hybrid
Vehicle Powertrain Concepts
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motor which can operate at three to four times rated power for brief periods
(acceleration periods).
In the case of a parallel configured heat engine/battery hybrid,
the heat engine power in the parallel energy flow path drives a generator to
recharge the batteries that are used to provide acceleration power to the
electric motor that is differentially geared to the heat engine drive shaft.
For a parallel configured heat engine/flywheel hybrid, the heat engine power
in the parallel energy flow path drives the flywheel through a transmission;
the flywheel then delivers power to the vehicle drive shaft through a trans-
mission and differential gear system.
2. 3 REGENERATIVE BRAKING
The regenerative braking mode of operation for hybrid vehicles
(as well as for all-electric or all-flywheel vehicles) has the potential to be a
significant contributor to powertrain efficiency. The advantage expected from
this mode of operation is a reduction in fuel consumption compared to con-
ventionally powered cars. Because of the energy storage device inherent in
the hybrid powertrain concept, kinetic energy can be recovered and stored
during vehicle deceleration and used for supplementing power needs during
the next period of vehicle acceleration. Analytical studies have predicted
that up to 30 to 40 percent of vehicle kinetic energy could be recovered by
various regenerative braking schemes, but adequate experimental evidence
is lacking. One study (Ref. 2-1) showed an average energy recovery of only
7 percent.
2. 4 VEHICLE POWERTRAIN OPERATING MODES
Different operating modes have been considered for the hybrid
vehicle powertrain. The majority of designs discussed in this part of the
report are based on the single ("hybrid") mode concept, whereby a portion of
the heat engine energy is used continually to replace energy drained from the
on-board energy storage device (battery or flywheel). Other designs have
resulted in a form of trimodal operating scheme whereby the vehicle can be
driven alu-rnatively in the (a) "hybrid" (engine on-board recharging) mode,
(b) all-battery (or all-flywheel) mode, or (3) all-engine mode. A somewhat
2-4
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simpler version of this design is the bimodal operating scheme whereby the
vehicle is driven only in an all-battery (or all-flywheel) mode or all-engine
mode. The vehicle would normally be driven in the battery (or flywheel) mode
with recharging provided by a source external to the vehicle; the engine in
this case is used merely to extend vehicle operating range whenever required.
2.5
ENGINE OPERATING MODES
Several forms of heat engine operating modes can be conceived
for the single "hybrid" mode of vehicle operation. These modes are discussed
first for the series configuration and then for the parallel configuration. In
either case, a design can be evolved to ensure either partial or full recharging
of the on-board energy storage device.
2.5. 1
Series Configuration
With the series configuration arrangement, a number of modes
of operation are conceivable. Several of the more significant modes are
shown in Figure 2-2 and discussed in the following paragraphs in terms of
the mode of heat engine operation.
CONSTANT POWER OUTPUT
VARIABLE POWER OUTPUT
Q_
I—
:=>
o
7
CONTINUOUS OPERATION
OF HEAT ENGINE
TIME-—
o
Q_
Q_
t—
£
0
0
1-C
rH
/
)FF
EA1
•f
OPER
r ENG
\
ATI
NE
ON
OUTPUT POWER =
f (VELOCITY)
VEHICLE VELOCITY
TIME-—
Figure 2-2. Various Heat Engine Operational
Modes - Series Configuration
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2.5.1.1 Constant Speed (rpm) and Power Output
2. 5. 1. 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 the total
energy required in the time duration of a given driving cycle (including in-
efficiencies of the power plant system), then the heat engine may not provide
the proper continuous high-speed power demand for highway operation. This
results in discharge of the energy storage device 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 dissipation heat-sink occurs at lower power demands.
This mode of heat engine operation is of course attractive
from the standpoint of heat engine exhaust emissions and/or fuel economy
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 and/or improved
fuel economy. However, its apparent inflexibility with regard to heat engine
sizing removes it from consideration as a viable series mode of operation
for matching the performance of current automobiles. However, this mode
may still be suitable for vehicles with reduced top speeds and/or revised
specification requirements.
2. 5. 1. 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 operation, and would operate intermittently during urban driving
conditions. The heat engine could be turned on or off in response to vehicle
power demands or state of charge of the energy storage device.
However, this mode of operation can result in very high energy
losses during those periods when the drive motor power demand is low and a
good portion of heat engine power output must be dissipated because the energy
storage device simply cannot accept power at the rate being supplied.
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2.5.1.2 Variable Power Output
2. 5. 1. 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 be allowed to operate at lower power levels for those
periods of vehicle driving cycles that require less power. If heat engine speed
is also allowed to vary to produce this variation in power output (as in con-
ventional internal combustion engines), it is envisioned that the control system
can effectively vary throttle setting response times so that engine speed 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.
The matching of all possible vehicle duty cycle energy require-
ments may not be possible. To overcome this difficulty, the heat engine power
output might 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 decrease the baseline heat engine
power output schedule (Figure 2-3) in accordance with an input signal related
to the state-of-charge of the energy storage device.
2.5.1.2.2 "Step-Mode" Operation
Another technique for varying heat engine power output is to
schedule power output in discrete steps. Figure 2-4 illustrates one such
approach, wherein three power output levels are used. A low level could
be scheduled for a low-velocity range (e.g. , 0 to 30 mi/hr), 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.
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o
Q_
Q.
I—
ZD
O
BATTERY VOLTAGE AND/OR
STATE-OF-CHARGE SIGNAL
CAN BE USED TO DEPART
FROM NOMINAL SCHEDULE —
(WITHIN UPPER & LOWER LIMITS) /
/UPPER LIMIT
NOMINAL SCHEDULE
LOWER LIMIT
X
VEHICLE VELOCITY
Figure 2-3. Heat Engine Variable Power Output Mode
"Biased" Throttle Setting Feature
"PEAK" LEVEL
or
LU
I
INTERMEDIATE LEVEL
LOW LEVEL
I
I
I—TOP VEHICLE
, SPEED
VEHICLE VELOCITY —
Figure 2-4. Heat Engine Variable Power Output Mode
Step Mode
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2. 5. 2 Parallel Configuration
The possible heat engine operating modes are much more
limited for the parallel configuration than for the series configuration. This
restriction is imposed by the direct mechanical link between the heat engine
and the rear wheels. Therefore, the continuous, variable power output mode
is the only simple form of engine operation that is considered to be feasible.
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3. DESIGN IMPACT OF VEHICLE SPECIFICATIONS
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3. DESIGN IMPACT OF VEHICLE SPECIFICATIONS
3. 1 GENERAL REQUIREMENTS AND CONSIDERATIONS
Early in the Alternative Automotive Power Systems (AAPS)
Program, vehicle specifications for each of a number of urban automotive
applications were developed jointly by EPA and the several contractors
involved in the hybrid system study effort. Lockheed Missiles and Space Co.
(LMSC), for example, in their flywheel hybrid feasibility study report (Ref. 3-1),
published a specification summary for the vehicles being considered, as shown
in abbreviated form in Table 3-1. A similar set of specifications, based
partly on an early study by Battelle Memorial Institute (Ref. 3-2), was pub-
lished by The Aerospace Corporation in Reference 3-3. These early specifica-
tions were modified as new requirements were identified during the study efforts.
The final form of the EPA specifications for the family car (six-passenger
automobile) appeared as shown in Appendix A. It may be observed that the
grade velocity requirement changed from 65 mi/hr, as shown in Table 3-1, to
70 mi/hr, as indicated in Appendix A. The impact of these and other specifi-
cations is discussed in subsections that follow.
Most of these modifications were minor. The basic vehicle
performance requirements did not change significantly from the initial values,
which were based on matching hybrid system performance to the acceleration,
speed, and grade ability of conventional, contemporary vehicles. Likewise,
the propulsion system sizing and operational requirements for the hybrid
vehicle were designed to match similar features in conventional vehicles.
The rationale for this approach was to enhance public acceptance of hybrid
systems by providing operational, safety, and convenience features com-
parable to those of existing systems.
In addition to the above constraints, certain criteria pertaining
to the state, level, and method of energy storage and transfer were adopted.
In the battery hybrid system studied by The Aerospace Corporation (Ref. 3-3)
for example, the batteries were required to be returned to the initial
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Table 3-1. Vehicle Specifications
Item
Stop* /Mile
V operation, mi/hr
V , mi/hr
max
v grade @ grade, mi/hr ® %
Grade length, mi
7 max. mi /hr/second
At stop* seconds
range* m
wp. ib
Number of Seats
Wc. Ib
W|. Ib
W,. Ib
Vol , ft3
8
A, ft2 \
cd )
Jerk, mi /hr/second
Family Car
a
a
a
65 <9 5
Continuous
4.44 to 60
mph
a
200
6
4, 300 max
5, 300 max
1 , 600 max
35
45
A X C , 13
d
a
Commuter Car
0. 02 to 5b
4 to 62b
70
33 @ 12
4
5
60 to 300b
1 to 50b
2
1,400
1,700
600
16
60
18
0.35
5 max
Remarks
Number of stops that vehicle makes per
mile necessitated by traffic or commercial
constraints
Length of trip/route divided by time vehicle
is on trip/route B 'range/Atrange
Maximum sustained cruise velocity
Maximum sustained velocity on the specified
grade
--
Maximum acceleration achievable [propor-
tional to V (0 to cruise)/At (to reach
cruise) ]
Length of time vehicle is stopped (V - 0)
necessitated by traffic or commercial con-
siderations (such as loading /unloading
passenger from bus) only.
Length of a trip or duty cycle. Maximum
value of one trip if It is given as n variable
is the maximum length of a trip/duty cycle
possible without supplementing vehicle
energy system. Note: For the flywheel -
only city bus, 'range maV be achieved by
one duty cycle with '"recharge" between
duty cycles. The ratio of recharge time to
Payload weight for commercial vehicles
Occupant capacity (passengers and driver)
Curb weight
Fully loaded total vehicle weight
Weight assignable to all propulsion system
components including energy storage,
controls, etc.
Maximum volume assignable to propulsion
system components including energy ator-
Xime from start-up to usable power output
Frontal cross-sectional area suitable for
the calculation of aerodynamic drag
Drag coefficient
--
*Not specified.
The range (a to b) means a continuous variable bounded by a and b. Any calculations made should
be dense enough over the range {a to b) to show the effect of the variable.
NOTEfe
I. Any calculations of rolling resistance due to
tire* should be made on the basis of currently
available tire* and include the effect of tire width.
Decreasing rolling resistance due to tires by as-
suming a type of fire that has unsafe traction
characteristics by vtrftie of low rolling resistance
is not *llowed.
2. With respect to the city bus, the average ac-
celeration (T max) must not be achieved by any
mptanlaneou* ac<. derations or rate of acceler-
ation that would cause passenger discomfort.
V Any resulting weight distribution that results
in oosft.t > handling characteris tics significantly
different from the normal expected by drivers of the
vehicles should be noted specifically.
4. Any decrease in gross vehicle weight achieved.
for example in the lighter family car and the com-
muter car. must not compromise safety
considerations,
5. Operation of the vehicle should not be compro-
mised by ambient weather considerations. Ambient
weather is defined as -25* to UO'F.
6. Noise aspect* of the various components should
be considered.
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state-of-charge by the end of the vehicle driving cycle.2 In the hybrid heat
engine/flywheel studied by LMSC (Ref. 3-4), the flywheel energy level had to
be controlled to maintain a constant total kinetic energy in the vehicle/flywheel
system. Other constraints were adopted or imposed to reduce the variety of
possible design options or applications to a manageable number. These and
other constraints adopted during the hybrid vehicle program are discussed
in further detail in Sections 4 and 5 which treat system and component require-
ments applicable to each of the design configurations investigated by the
individual contractors.
In this section the specifications on vehicle emissions, vehicle
performance, and power plant sizing exemplified by the EPA requirements in
Appendix A are discussed with respect to their influence on the overall design
of the hybrid vehicle powertrain.
3.2 ROAD PERFORMANCE REQUIREMENTS
The road performance specifications (start up, acceleration,
and grade velocity performance) for the family car are given in Paragraph 8
of Appendix A. Although these specifications are in general agreement with
the performance capabilities of conventional full-size passenger cars, an
exception is the 85 mi/hr maximum cruise velocity specification—a lower
speed than the maximum velocity achievable in most conventional family cars.
However, this higher velocity may be regarded as being less of a cruise
performance specification than the consequence of sizing the engine to meet
high performance acceleration objectives. In the hybrid system, the accelera-
tion requirements are met through power supplied by the electrical or inertial
components of the drive system.
The determination of performance goals in terms of power
required at the vehicle wheels is based on the velocity-time schedules for the
maneuvers specified in Paragraph 8 of Appendix A. In general, these charac-
teristics determine the vehicle propulsion system peak power requirements,
fix the size of the heat-engine power plant, and influence the selection of
appropriate power profiles the heat engine must deliver. Figure 3-1 (from
The Federal Emissions Test Driving Cycle.
3-3
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ROAD
HORSEPOWER
10
20
30
to sn
VEHICLE SPEED (MPh)
60
70
80
90
Figure 3-1. Wheel Power Demands for a 4, 000-Ib Car (Ref. 3-5)
3-4
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Ref. 3-5) shows the typical road load power requirements for a 4, 000-Ib
vehicle. The maximum power output demand results from the acceleration
maneuver requirement; the gradability requirement is not a determining
factor. To cruise at 85 mi/hr, approximately 65 road horsepower are needed
and the powertrain must be capable of providing short-duration power
bursts at the wheels in excess of 100 hp. When powertrain losses and the
additional power required for passenger comfort and convenience features are
considered, the heat engine must be capable of providing a maximum continuous
power output of from 85 to 100 hp.
Increased vehicle weight increases the road power requirements
over the values shown in Figure 3-1. A 5,500-lb vehicle, for example,
increases the cruise power requirement at 85 mi/hr by 10 percent and in-
creases the total system peak power requirement by about 35 percent.
In the hybrid concepts examined, the difference between the
power required for vehicle propulsion and the power supplied by the heat
engine must be furnished by the flywheel or the electric-motor components
of the hybrid powertrains. Hence, with the selection of an appropriate heat
engine power profile and with overall drivetrain gear ratios established, the
characteristics shown in Figure 3-1 yield the requirements for the flywheel
or electric motor peak torque and power outputs. Additionally, the selection
of a representative vehicle-use duty cycle establishes the requirements for
installed energy storage capacity, considering the need to operate the heat
engine at low power output levels to minimize emissions.
3. 3 WEIGHT AND VOLUME LIMITATIONS
Weight and volume specifications for the family car are
covered in Paragraphs 1 through 6 of Appendix A. The weight specifications
encompass requirements for the vehicle chassis, the propulsion system, and
the vehicle gross weight. The volume requirement calls for standard engine
packageability features and limits the allowable propulsion system volume
to 35 ft3. This specification impacts the design or selection of drivetrain
3-5
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components and immediately eliminates some heat engines as viable candidates
for certain hybrid vehicle applications. Many engines require a significant
portion of the allotted 3 5 ft , thereby imposing severe volume requirements
on other components. Weight and volume trends for the various heat engine
candidates as a function of horsepower may be seen in Section 4. 3. 4.
In general, the propulsion system weight limitations impose
upper bounds on the ability of the system to furnish power and energy required
to operate the vehicle for extended durations at the specified road performance
levels (Figure 3-1). The criticality of these specifications depends in part
upon the state of the component technology for the particular hybrid system
being considered.
For the hybrid battery system, the propulsion system weight
specification is critical in that it severely impacts the battery design require-
ments and limits the selection of available heat engine alternatives. The
situation may arise as described in Ref. 3-3 as follows: once battery
power and energy requirements are defined, the power density and energy
density requirements can be established by the specified powertrain weight
less the weight of all other powertrain components and subsystems. Com-
ponent and subsystem weights will increase with increasing severity in
specified requirements for acceleration and peak cruise speed. Hence, for
a fixed powertrain weight allocation, a high-performance car will result in
a reduction of weight available for batteries and, correspondingly, this will
increase the severity of battery design requirements.
The design implications for the series hybrid battery family
car are illustrated in Figure 3-2, showing the relationship between the power-
train weight allocation and the required battery power density and energy
density for different heat engines. Certain power plants are not applicable
to the family car under the propulsion system weight allocation defined by
the specification, and only the spark ignition engine (reciprocating or rotary)
and gas turbine engine result in realistically achievable values for battery
3-6
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1000
92.5 kW PEAK
POWER DEMAND
1000 1200 1400 1600 1800 2000 2200
AVAILABLE POWERTRAIN WEIGHT, Ib
2400
2600
1000 1200 1400 1600 1800 2000 2200 2400
AVAILABLE POWERTRAIN WEIGHT, Ib
Figure 3-2. Effect of Powertrain Weight on Battery
Requirements - Family Car Series
Configurations (Ref. 3-3)
2600
3-7
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power and energy densities. It should be noted, however, that more recent
development work could result in some modifications to these conclusions;
e. g. , Stirling engine weight and size has been reduced markedly from
former levels. (See expanded discussion in Volume II, Alternative Automotive
Engines. )
In contrast to the battery system, the hybrid heat engine/
flywheel design provides higher energy densities resulting in system weights
and volumes that are a smaller fraction of the allowable value for the total
propulsion system. Thus, a broader range of heat engines may be considered
feasible for use with this design.
3.4 FUEL ECONOMY AND EXHAUST EMISSIONS
Paragraph 10, Appendix A discusses fuel economy. Although
no specific goals are identified, the best possible performance consistent with
the objectives for exhaust emissions as delineated in Paragraph 7 is obviously
desired. The fuel economy objective may impact the design of the hybrid
system in a number of ways: the choice of series versus parallel drivetrain
configurations; the selection of heat engine type, mode of operation, and
power output profile; and the type of transmission. These and other alterna-
tives also become design considerations in connection with the specifications
covering vehicle exhaust emissions.
A number of different engine operating modes may be considered
for the hybrid vehicle. For the series configuration, the choices are relatively
broad as compared with the parallel configuration. The engine may be operated
at fixed rpm and fixed power output, at fixed rpm and variable power output,
and at variable rpm and variable power output, or at mixed conditions over the
vehicle speed range. Engine operating mode selection will be influenced by
considerations of fuel economy, emissions, and transmission and control
system design complexity.
Fuel consumption characteristics differ among the various
heat engine candidates, and part load performance in some systems such as
3-8
-------
the gas turbine is relatively poor. Fuel consumption in the spark ignition
engine is highly variable and depends on the specific operating condition of
the engine. This is shown by the performance map of Figure 3-3. Normal
road load operating conditions for a conventional automobile and for the
parallel hybrid vehicle with conventional transmission are represented by
the cruise profile curve superimposed on the illustration. The fuel economy
implications of the choice of engine operating mode may be recognized by
noting that the specific fuel consumption (SFC) parameter will be minimized
by operating at or near the lower envelope of the rpm curves. Therefore,
efficient engine operation in the series hybrid vehicle may be achieved by
removing the carburetor power enrichment device and setting the engine
throttle wide open. In the parallel hybrid configuration, operation along the
minimum SFC envelope would involve the use of a multiple step, wide gear-
ratio or continuously variable transmission.
200
s 180
1 160
u_
O
55 140
co
120
00
oo o
oo^d- CD _
-o OO O OO
L2 roio r- ooo-)
- u\\\ \ \ \ \
\\\\\\ \ \ \
-CRUISE PROFILE
— \
\A
V
/\ \
; \ \ \
Xx\\ /-^
- \ x ^/
^
0 10 20 30 40 50 60 70 80
GROSS HORSEPOWER OUTPUT, % OF RATED
90 100
Figure 3-3. Spark Ignition Engine SFC Map, Normalized (Ref. 3-3)
3-9
-------
As previously noted, many of the fuel economy design con-
side rations--primarily engine selection and operating mode--apply also to
exhaust emissions. Fixed, near-constant, or slowly variable quasi-steady-
state engine operation offer the best potential for meeting the specified
exhaust emission goals by eliminating design constraints associated with
transient or widely varying engine operating conditions. Trends in the steady-
state emissions at various loads for conventionally designed spark ignition
engines are presented in Figure 3-4.
Many approaches to optimizing engine emissions are possible.
For the spark ignition engine, these include variation of spark timing, com-
bustion chamber design, air-fuel mixture preparation, water injection, and
the use of external control devices. Air-fuel ratio is a significant emissions
parameter in all of the heat engine candidates being considered. Ultralean
conditions indicate the potential of achieving low NO levels while also con-
X
trolling HC and CO to acceptable levels. Operational problems at lean
conditions tend to be minimized in the hybrid operating mode. Nevertheless,
ultralean design for the spark ignition engine may involve carburetor and
intake manifold design modifications, the use of precombustion chambers or
stratified charge devices, changes in transmission gear ratio range and step
size to minimize drivability problems, and the use of mixed fuels to improve
fuel flammability properties and to ensure proper air-fuel distribution from
cylinder to cylinder.
3. 5 IMPLICATIONS OF REVISED VEHICLE SPECIFICATIONS
Reduced levels of vehicle acceleration and highway cruise speeds
can be expected to lead to reduced consumption of automotive fuel. Hence,
with the current emphasis on conservation of domestic energy resources along
with improvements in air quality, revisions to the original hybrid vehicle
specifications could be expected to have some value in easing the rigorous
design requirements imposed on elements of the vehicle powertrain. For
example, a reduction in peak cruise speed from 80 to 55 mi/hr would
require less than half the power formerly needed at the rear wheels. The
3-10
-------
CO
O
CO
CO
UJ
Q
O
I—
o:
-------
4. HYBRID HEAT ENGINE/BATTERY VEHICLE
-------
4. HYBRID HEAT ENGINE/BATTERY VEHICLE
4. 1 SYSTEM DESIGNS AND OPERATION
Two major hybrid heat engine/battery system concepts funded
by the EPA were: the TRW Systems, Inc. electromechanical transmission
system and the Minicar, Inc. heat engine/battery vehicle. This included the
building of a breadboard prototype system by TRW and a vehicle-mounted
prototype system by Minicar. Under the EPA Federal Clean Car Incentive
Program, Petro-Electric Motors has built a hybrid heat engine/battery system
and installed the powertrain in a 1972 Buick Skylark. In addition, General
Motors built their own prototype system called Stir-Lee. Other heat engine/
battery system prototypes have also been built; these are not discussed in
detail, but are listed for general information only.
An additional EPA-funded study was performed by The Aero-
space Corporation to provide an analytical evaluation of hybrid heat engine/
battery vehicles. This effort did not include building a breadboard or pro-
totype device; however; brief tests were conducted on a separately excited
direct current motor to ascertain the magnitude of speed and load variation
that is possible with field control as a function of applied voltage.
Each of the EPA contractors studied the trade-off of system
and component designs and costs and have presented somewhat different
solutions. Since performance requirements and driving cycles were identi-
cal, the difference among various designs can be found in efficiency and cost
factors that are influenced by varying design complexities.
4.1.1 TRW Systems, Inc.
TRW considered four system designs (Ref. Z-l) and elected
to develop one of these: a parallel configuration, electromechanical transmis-
sion (EMT) system. The prototype EMT system (Figure 4-1) operates as
follows:
a. The spark ignition, reciprocating heat engine (modified
Volkswagen engine) drives the sun gear of a planetary gear
train. The carrier gear transmits power to the speeder (gen-
erator) while the ring gear transmits power to the drive shaft.
4-1
-------
INTERNAL
COMBUSTION
ENGINE
1
PLANETARY
GEAR TRAIN
ENGINE
SPEED ERROR
T0
C_3W
SPEEDER
(GENERATOR)
»
TORQUER
(MOTOR OR
GENERATOR)
SPEEDER POWER
CONDITIONING
UNIT
TRACTION OR
REGENERATION
POWER
DRIVING
WHEELS
TORQUER POWER
CONDITIONING
UNIT
OPERATOR
COMMAND
Figure 4-1. TRW Electromechanical Transmission Mode I
Operation (Ref. 2-1)
b. Power is divided as a function of demand and speed required
at the wheel. When the vehicle is at rest all the power goes
to the speeder. As the vehicle gains velocity, the speeder
decreases in speed at an inverse ratio to the wheel shaft
speed.
c. During the increase in speed to 40 mi/hr, the generator con-
tinues to turn, but does not necessarily generate power.
Since under some circumstances the demand at the wheel
shaft exceeds the constant heat engine power rating, the torquer
(a series wound direct current motor) is used to augment the
power to the wheel shaft through direct gearing to this shaft.
d. When the demand at the wheel shaft is less than the power
rating of the heat engine, the speeder provides wheel velocity
adjustment and absorbs the excess power and converts it to
electrical energy sending it through the power conditioning
unit to the battery.
4-2
-------
e. The power conditioning unit has two major functions:
controlling the speeder velocity and power conversion
rate and controlling the torquer to provide traction or
regenerative power.
f. The torquer can either augment the power at the wheels by
adding torque in the forward direction or it can reverse the
torque direction and act as a generator converting the regen-
erative braking energy into electrical energy and charging
the batteries.
g. A Mode II operation is used for velocities above 40 mi/hr
whereby the speeder is locked out by a brake at its input
shaft and the heat engine is coupled directly to the wheel
shaft. The heat engine is therefore required to change its
speed directly with the increase of vehicle velocity above
40 mi/hr. The direct current torquer may still augment
or regenerate energies in Mode II.
4.1.2 Minicar, Inc.
The principal technique used by Minicar for reducing emissions
was to prevent rapid changes in power output from a modified Chevrolet Corvair
engine. This was accomplished by augmenting engine power with power from a
separately excited motor during vehicle acceleration. The engine is run at a
lean air-fuel ratio and a throttle spring and dashpot mechanism prevent rapid
changes in power. .Exhaust gas is used to heat the intake manifold to enhance
air-fuel mixing. With a heated manifold the engine could operate at an air-
fuel ratio of 18:1, but 16.5:1 was used in vehicle performance tests (Ref. 4-2).
A parallel configuration was selected. In this configuration
the electric motor/generator was mounted about a common drive shaft from
the engine. Total power was delivered to an automatic transmission and
thence to the drive wheels. Intake manifold pressure was used to regulate the
field current in a three-step control system. In addition, a relay was used
for permitting combinations of parallel-series connection of the batteries to
provide step voltage changes to the armature. A sketch of the drivetrain is
given in Figure 4-2.
4-3
-------
. TGBOUt CCK
BATTERY PACK
INTERNAL COMBUSTION
ENGINE 6 CYL.
OPPOSED 164 CU.IN.
AIR COOLED
3.57/1 HATiO
TRANSMISSION
I.8I/ I LOW
I / I HIGH
Figure 4-2. Minicar Drivetrain
(Ref. 4-2)
4.1.3 The Aerospace Corporation
The Aerospace Corporation study (Ref. 3-3) was aimed at
determining the feasibility of using a hybrid heat engine/battery propulsion
system as a means of reducing exhaust emissions from street operated
vehicles. Several classes of vehicles and several design configurations
were considered in the study, however, only automobile designs are dis-
cussed in this report. Following a review of associated technologies, require-
ments for electrical and mechanical components were determined. In sum-
mary, the design and system operation portion of the study included the
following:
a. Energy Flow Paths--Both series and parallel configurations
were analyzed for a lightweight commuter car and a full-size,
six-passenger automobile. Operation of these vehicles was
simulated over the Federal Emissions Test Driving Cycle.
Engine/generator charging of the batteries was regulated to en-
sure a full battery charge at the end of the driving cycle. Heat
engine power levels were adjusted to meet vehicle cruising
requirements in addition to battery charging requirements.
b. Types of Components--The components investigated for use
in the heat engine/battery hybrid were:
Motors:
alternating current induction
direct current externally excited
4-4
-------
direct current series wound
direct current compound wound
torque motors
direct current brushless
Generators:
direct current
alternating current (alternators)
Power Conditioning and Control:
pulse-width modulation
frequency modulation
variable-frequency inverters
cycloconverters
integrated circuits
relays/switches
current limiters
circuit breakers and fuses
filters (inductor-capacitor)
storage battery system
Heat Engines:
spark ignition
diesel
gas turbine
Rankine
Stirling
Batteries :
lead-acid
nickel - cadmium
nickel-zinc
Design Rationale--Significant vehicle design point conditions
that affected power plant sizing and operational capability
included vehicle top speed, gradability (in terms of percent
grade, velocity on the grade, and grade length), vehicle
weight, and aerodynamic drag area and drag coefficient.
3Other batteries were considered, but were eliminated in a screening process
based primarily on near-term development status and future performance
potential.
4-5
-------
The only limitations imposed upon the powertrain were the
assigned powertrain weights and volumes. A final require-
ment was that the acceleration, grade, and speed capabilities
of each vehicle with a hybrid power plant installed were to be
equal to that of a contemporary automotive vehicle. The
rationale for this requirement was that such performance
would enhance public acceptance of the hybrid vehicle and
would also avoid the prospect of poor traffic safety.
Designs for electric motor drive systems had 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, and (e) simple, inexpensive, and
efficient regenerative braking. Designs for the battery
system included considerations of power density (W/lb),
energy density (W-hr/lb), and cost.
d. Performance Estimates--Vehicle performance estimates
were summarized in the form of figures for battery power
and energy density, vehicle exhaust emissions, vehicle fuel
economy, and a listing of component weights for each system
design. Computer calculations included analytical models of
performance for each major component.
4.1.4 Petro-Electric Motors
Early in 1971, Petro-Electric Motors, New York City,
entered into a contract agreement with EPA for development of a hybrid heat
engine/battery vehicle under the Federal Clean Car Incentive Program. Under
this program, the contractor initially assumes development cost and risk, and
is permitted to maintain car ownership and design patent rights. Following
delivery of a prototype vehicle for test and evaluation, EPA can contract for
vehicle lease and eventually purchase a limited number of vehicles. A
prototype Petro-Electric hybrid automobile was delivered to EPA in February
1974 and is currently undergoing test and evaluation.
The Petro-Electric hybrid powertrain has been installed in a
1972 Buick Skylark, 4-door sedan with a curb weight of approximately 4,150 lb.
This parallel configuration consists of the following major components:
a. An RX-2, 70 in. , 130-hp Wankel rotary engine, Model 12A
combined with a thermal reactor and exhaust gas recirculation
for exhaust emissions control (273 lb)
4-6
-------
b. Eight 12-V lead-acid batteries rated at 90 Ah (10 hr rate)
with a maximum 600 A draw (300 Ib)
c. A 20 hp (60 hp maximum) separately excited, shunt field,
direct current motor/generator rated for 115 A, 120 V (240 Ib)
d. A 1973 Chevrolet Vega manual transmission
The engine is mechanically coupled to the transmission and
the motor/generator (same shaft). Electrical power flows back and forth
between the motor/generator and the batteries, in one direction for battery
recharge and in the other direction for augmenting engine power to the trans-
mission. (Regenerative braking is also used for recharging the batteries.)
The vehicle operator pedal position controls motor/generator field current
for the battery recharging mode or power augmentation to the transmission.
Engine power range is restricted to levels designed to result in low levels of
fuel consumption and exhaust emissions. During periods of high power demand,
further depression of the accelerator pedal frees the engine from its normal
constant manifold vacuum operating mode and allows increased engine power
output.
4.1.5 General Motors Corporation
In 1969, a Stirling-Electric Hybrid car (Stir-Lee I) was devel-
oped by General Motors without government funding. A phantom view and
block diagram of the system are shown in Figures 4-3 and 4-4, respectively
(Ref. 4-3). As Figure 4-4 shows, this is a series powertrain. The Stirling
engine (see Section 4.3.4) drives a three-phase alternator, the output of which
is rectified to charge the batteries. The controller includes a modulated in-
verter to provide variable frequency and voltage to the three-phase induction
motor. The drive system is similar to the all-electric Electrovair II that
was demonstrated in 1966. The induction motor is coupled to the differential
pinion shaft through a planetary gear set with a speed reduction of 3.45 to 1
for an overall ratio of 13.4 to 1 . Cooling water at 8 psig is used to limit the
stator winding maximum temperature to 275 F; the rotor is air cooled.
The battery pack consisted of 14 automotive-grade lead-acid
batteries connected in series. The cells carry a 44 Ah rating at the 20-hr
discharge rate for a total energy capacity of 6.6 kW-hr. To increase battery
life, the depth of discharge, however, is limited to about 75 percent of this capacity.
4-7
-------
BATTERY CHARGING CONTROL
HYDROGEN RESERVOIR
STIRLING ENGINE
RADIATOR
AND FAN
STARTER MOTOR
DC TO AC MODULATING INVERTER'
LEAD ACID BATTERIES-
rcOMMUTATING
CAPACITORS:
LOGIC & INVERTER CONTROLS
INDUCTION MOTOR (3-PHASE)
ALTERNATOR
COMBUSTION AIR BLOWER
Figure 4-3. Phantom View of GM Stir-Lee I
(Ref. 4-3)
DIFFERENTIAL
Figure 4-4. Block Diagram of GM Stir-Lee I Hybrid System
(Ref. 4-3)
4-8
-------
The modulating inverter provides variable voltage and
frequency to the induction motor for smooth torque control at all speeds. It
converts the nearly constant direct current battery voltage into three-phase
alternating current power. It contains 18 SCRs and six power diodes; ram
air is used for cooling.
4.1.6 Other Electric Hybrids
Following are brief descriptions of the salient features and
characteristics of several other electric hybrid vehicles which have been
examined by a number of organizations.
4.1.6.1 General Motors No. 512 Hybrid Gasoline-Electric (Figure 4-5)
(C.1969)
Dimensions:
Curb weight:
Gasoline engine;
Electric:
66 in. length, 56 in. height, 52 in. width
1,250 Ib
12 in displacement, engaged at 10 mph,
drives through electromagnetic clutch at
steady speeds, drives 90V alternator.
Series motor delivers power to drive wheels
up to vehicle speed of ICTmiVhr. Also used for
acceleration power.
ELECTRONIC
CONTROLLER
GASOLINE
ENGINE
BATTERIES-
ELECTRIC MOTOR-
Figure 4-5. General Motors No. 512 Hybrid Gasoline-Electric
GEAR REDUCTION
& DIFFERENTIAL
4-9
-------
4. 1.6.2
Toyo Kogyo Company, Limited, EX005
(Hybrid Car)--Prototype (Figure 4-6) (C. 1970)
Characteristics:
Total length:
Total width;
Total height:
Curb weight:
Load capacity;
Maximum speed:
Generator:
Battery:
Motor:
Engine type:
This hybrid car is propelled by an electric
motor that is powered by lead-acid batteries,
In addition, it has a small rotary engine to
generate electricity for battery recharging.
93 in.
58 in.
63.5 in.
1, 000 Ib
Four persons
25 mi/hr
3 kW
Lead-acid battery (96V) 12V in eight sets
1 kW in two sets
Rotary engine, one rotor, air-cooled engine
of 200 cm3
4-10
-------
Figure 4-6. Toyo Kogyo Wankel/Electric Car
4-11
-------
4. 1. 6. 3
Daihatsu Kogyo Company, Limited Fellow Max Hybrid
Commercial Car (Figure 4-7) (C. 1970)
Body type:
Curb weight:
Load capacity:
Total length:
Total width:
Total height:
Tread of the front:
Tread of the rear:
Wheelbase:
Minimum turning radius:
Motor:
Battery:
Control:
Gasoline engine:
Generator for charge:
Maximum speed:
Modified L38V
1,874 Ib
Two persons
117. 7 in.
51. 0 in.
52. 4 in.
44. 1 in.
43.3 in.
82. 3 in.
165. 4 in
Direct current series, 5.3 kW, 55V dc,
drives rear wheels during vehicle
acceleration
Lead-acid battery, 100 Ah/5-hr in
six sets, 72V
SCR chopper
ZM type, 356 cm of piston displace-
ment, regular gasoline, drives front
wheels
Direct current series, controlled at
constant current by SCR chopper
Gasoline engine: more than 62 mi/hr
(on highway) 37 to 50 mi/hr (in the
suburbs); charge at will battery
motor: 40 mi/hr
During vehicle cruise or deceleration, rear wheels drive motor as a generator
4-12
-------
Figure 4- (. Daihatsu Kogyo Fellow Max Hybrid Car
4.1.6.4 The University of Toronto, Canada, Faculty of
Applied Science and Engineering (Figure 4-8)
The University of Toronto built this trimodal vehicle "Miss
Purity" for entry into the 1971 Clean Air Car Race.
Body:
Chassis:
Generator:
Battery:
Motor:
Engine:
Transmission:
Polyester/fiberglass, flooring and
firewall are aluminum.
Front end - 1970 Chevelle; remainder
specially built, aluminum wheels.
16 hp, 140V, 90 A alternating current with
solid-state cyclic interrupt switch.
Lead-acid 96 Ah, 12V in ten sets; one
additional for lights and field current.
16 hp, direct current shunt motor 100V,
120 A, base speed 3,700 rpm, external
fan cooled, PWM controller, speed con-
trol and pedal switching are in the field
circuit.
Chevrolet 302 -CID V-8, 11:1
compression ratio, uses platinum
catalytic muffler, propane fueled
(has a liquid/gas expansion valve).
Two-speed gearbox and clutch with
transaxle provides ten ratios to engine
and five to the electric motor.
4-13
-------
1. FIBRECLASS BODY
2. SAFETY ROLL BAR
3. CULL-VINO DOOR
4. SAFETY STEERING WHEEL
5. ELECTRIC LOGIC CIRCUITS
6. EXPANSION VALVE
'. CARBURETOR
8. SECONDARY PLENUM
9. RADIATOR HEADER TANK
10. D.C. GENERATOR AND DRIVE
11. FOREBODY (RAISED)
12. ELECTRIC FANS
13. RADIATOR
14. AIR SCOOP
15. OIL COOLER
16, ALUMINUM WHEELS
17. V-8 ENGINE
18. CATALYTIC MUFFLER
19. MAIN MUFFLER
20. BATTERIES
21. STICK SHIFTS
22. ENGINE DRIVESIIAFT
23. D.C. MOTOR AND DRIVE
24. CORVAIR TRANSAXLE
25. EQUIPMENT FANS
26. AMP-HOUR METER
27. CHOPPER CONTROL
28. PROPANE FILLF.R
29. PROPANE TANK
30. RADIAL ELY TIRES.
Figure 4-8. University of Toronto Car
4-14
-------
4.2
4.2. 1
4.2. 1. 1
SYSTEM DESIGN REQUIREMENTS AND ACHIEVEMENTS
TRW Systems. Inc.
Design Requirements
TRW performed computer simulation studies to evaluate the
automotive propulsion systems described in Section 4. 1. 1 on the basis of
total weight, volume, and efficiency over a driving cycle based upon urban
traffic flow conditions.^
The system modeling used manufacturer's data for major com-
ponents and included analysis of: generators, traction motors, power condi-
tioning unit (PCU), gearing, and batteries. Power, current, voltage, speed,
torque, and efficiency were computed over the driving cycle for a constant
battery charge and without accessories. The results are given in Table 4-1.
Table 4-1. Electromechanical Transmission Electrical
Systems Characteristics on the LA-4
Driving Cycle (Ref. 2-1)
Parameters
Predicted Values
Overall Efficiency, percent
Total Weight, W, Ib
Control Complexity
Components
Speeder (forced cooled)
Torquer
PCU
Rectifier
76.7
386.0
Dual Loop
Rated kW Weight, Ib
40
160
95
Not
Reported
10.0
22.4
22.4
10.0
'Designated as the LA-4 driving cycle; the basis for the current Federal
Emissions Test Driving Cycle.
4-15
-------
The EMT motor, unloaded during cruise, was rated on the
basis of power augmentation required for vehicle acceleration over the LA-4
driving cycle. The EMT system performance capabilities were determined
initially by analysis and then confirmed by dynamometer tests. Table 4-2
lists the ratings of the components established for a parallel configuration.
Note that without a multiple gear ratio between the motor and wheels, some
of the component ratings were exceeded. Use of a variable gear ratio lowers
the peak motor torque required, improves efficiency, and relaxes the battery
power density requirements.
The generator power rating is established by its cooling system.
Three cooling systems were considered: internal fan self cooled, external
forced air cooled, and oil spray with heat exchanger. The external forced
air system was selected for variable speed operation in the parallel configura-
tion. The rating of the EMT generator (based on the absorption of full engine
power at rest) was conservative, although its speed varied over a 10 to 1
range as the vehicle speed varied from 0 to 42. 5 mi/hr.
4. 2. 1. 2 Performance Results
A dynamometer demonstration breadboard was built as "proof-
of-principle" hardware. Poor correlation was found between computer pre-
dicted results and breadboard testing results. A reduction in overall power-
train efficiency (road demand/engine output) from the predicted 76.7 percent
to a nominal test value of 50 percent is the most encompassing departure.
The test program allowed the major contributors to system losses to be
identified. Gelb, et al stated (Ref. 4-1) that: "In most cases the losses can
be reduced significantly by design refinement."
The EPA Specifications for velocity, acceleration, and length
of run before refueling were met in driving cycle simulation calculations.
Equivalent level road speed to 85 mi/hr could be achieved, but an actual
velocity time trace taken from the LA-4 driving cycle was used in the analysis.
The cycle has a peak velocity of 47 mi/hr.
4-16
-------
Table 4-2. Rating and Required Performance of Electrical
Components, LA-4 Driving Cycle, Parallel
Configuration (Ref. 2-1)
Component
Traction Motor
RMS Power, hp
RMS Current, A
Current Maximum,
percent rated
RMS Torque, ft Ib
Motor Power Control Unit
Power, kW
Average Current, A
Peak Current, A
Generator
Average Power, kW
RMS Power, kW
Average Current, A
Peak Current, A
Rating
30
145
300
22.5
22.5
145
600
N/R
10
50
100
Requirements
Gear
Ratio
Fixed
17.2
235
N/R
55.3
8.9
182
800
N/R
4.6
34.7
100
Gear
Ratio
Variable
17.2
144
300
27
8.9
119
450
N/R
4. 1
31
98
N/R - Not Reported
4-17
-------
Table 4-3 lists the measured efficiency of components for
simulated operation during breadboard tests of a 3, 000-lb vehicle on the
LA-4 driving cycle. These results are compared with TRW claims for
efficiences obtainable with redesigned elements in the system.
Table 4-3. Average Component Efficiency, LA-4
Driving Cycle (Ref. 2-1)
Component
Gearbox
Speeder
Speeder PCU
Torquer (drive)
Torquer PCU (drive)
Torquer (regeneration)
Torquer PCU (regeneration)
Battery (at utilization)
Measured
Efficiency,
Percent
75
70
95
67
88
52
90
64
Estimated
Redesign Efficiency,
Percent
>85
90
N/R
>80
N/R
N/R
N/R
N/R
N/R - Not Reported
Other improvements in system efficiency seemed possible.
Accordingly, TRW conducted a parametric analysis to determine the effect of
gear ratio, battery impedance, regeneration, and gear efficiency on overall
system efficiency. The results are given in Table 4-4.
4-18
-------
Table 4-4. Effects on Overall System Efficiency, LA-4
Driving Cycle (Ref. 3-5)
Configuration
Series
Parallel
Percent Increase or Decrease
Use of
Variable
Gear Ratio
+ 15
+ 13
Battery Imped-
ance Changed
from 86 to
172 ohms
-7
-1.5
Absence
of Regen-
eration
-10
-13
Gear Efficiency
Changed from
98 to 87%
-7
-9
As can be seen from Table 4-4, the use of a variable gear ratio would increase
the overall efficiency due to a better match between road demand and available
power at various vehicle speeds.
An increase in internal impedance of the battery decreased the
system efficiency for both configurations, but the parallel configuration was
affected far less than the series configuration.
If regenerative braking is omitted, the vehicle kinetic energy
is lost during vehicle deceleration; this results in a decrease in overall
efficiency.
The planetary differential gear coupled with other gears may
achieve net gear efficiency values from 94 to 98 percent. With use of the
present 75 percent efficiency planetary differential, the net gear efficiency
falls from the 94 to 98 percent range down to the 87 to 90 percent range with
the resultant overall efficiency penalty shown.
The results of exhaust emission measurements for several of
the cold start tests are shown in Table 4-5. The data show the actual grams
of HC CO and NO for the three-bag results and are summarized in the
' x
next-to-the-last column in the form of gm/mi. The final column presents
some pertinent remarks about each test.
4-19
-------
Table 4-5. Breadboard Hybrid System Emission Test Results, Federal Test Procedure
(Ref. 3-5)
Test
Date
12/22/71
12/27/71
12/28/71
12/30/71
1/3/72
1/4/72
1/6/72
Cold Start Bag,
gm
HC
1.63
1.25
1.72
1.68
2. 56
17.5
2.84
CO
55.3
55.3
59.5
41.9
49.6
45.2
46.8
NO a
X
0.52
0.87
0.28
3.22
3.88
0.66
3.48
Hot Start Bag,
gm
HC
0.24
0.25
1.27
0.40
0.40
0.21
0.84
CO
1.08
2.20
22. 1
6.60
2.66
2.43
1.63
NO a
X
0. 16
0. 54
0.54
0.21
0.44
2.66
0.56
Stabilized Bag,
gm
HC
0.77
0.38
0.41
0.38
0.90
0.95
0.50
CO
14.7
4.3
4.41
4.3
9.54
6.95
2.64
NO a
X
0. 12
0.21
0.33
0.32
0.43
0.50
0.58
Emissions ,
gm/mi"
HC
0.21
0. 14
0.25
0. 18
0.30
1. 15
0.29
0.41
0.41
CO
5.22
3.92
5.65
3.47
4.33
3.69
3.20
3.4
3.4
NO a
X
0.06
0. 12
0. 10
0.24
0.31
0.31
0.32
3. 1
0.40
Remarks3
poor hot
start
excessive
enrichment
--
too slow
choke relief
--
very poor
hot start
no hydro-
carbon
accumulator
no detect-
able NH3
1975 Fed.
Standards
1976 Fed.
Standards
a
NOX as NO2
b
No fuel economy data available
ht-
I
o
-------
The emission control system consisted of a hydrocarbon
accumulator and a three-component catalyst. The accumulator was designed
to store hydrocarbon emissions during cold-start and feed these pollutants
to the catalyst after a predetermined level of engine and catalyst warm-up.
The catalyst was designed to simultaneously control hydrocarbon, carbon
monoxide, and nitric oxide emissions with precision settings for engine
air-fuel ratio. A Chevrolet Vega engine modified for intake manifold fuel
injection was used for the heat engine element in the powertrain system.
The emission control system proved very effective in terms of hydrocarbon
and oxides of nitrogen control. The combined use of the hydrocarbon accumu-
lator and three-component catalyst resulted in hydrocarbon emissions ranging
from 34 to 73 percent of the original 1975 Federal emission standards. When
the hydrocarbon accumulator was bypassed, the total HC emissions were 2.8
times greater than the standards. The NO results ranged from 15 to 80 per-
5C
cent of the 1976 standards. The lower values were associated with earlier
tests where the choke control during the cold start was more erratic and the
engine exhaust NO did not come up as rapidly as it did in later tests. The
X,
most troublesome pollutant was CO. The CO standard was met with a 7 percent
margin on one occasion; the standard was exceeded during all other tests.
Examination of the bag data shows the cold start CO to be the major factor in
the total CO emissions.
4. 2-. 2 Minicar, Inc.
4. 2. 2. 1 Design Requirements and Performance Results
The first configuration tested by Minicar did not provide suf-
ficient electric power to significantly reduce emissions. The electric system
was to have supplied 40 percent of the required power, but actually supplied
no more than 10 percent. One reason for this was that at idle the generator
voltage was less than battery voltage; therefore, the batteries were charged
during this period.
4-21
-------
A special motor/generator was ordered that could generate
48V during high idle speed (about 1000 rpm) provided the generator field was
overexcited. With an automatic transmission, excessive creeping occurred
when the engine idled at speeds above 600 rpm so a two-step voltage system
was used. At low speeds, 24V was available by use of a parallel connection.
At higher speeds, a step change to series-connected 48V was made with con-
current field control.
After many improvements, a final prototype configuration, the
Hybrid C-l. was built. Its electric system provided up to 27 hp at the drive
wheels which was short of the 40-hp goal (Ref. 4-4). The operating per-
formance did not match that of many equivalent size standard vehicles.
The adjustable orifice dashpot for heat engine power lag func-
tioned properly as a throttle delay, but optimum delay for both acceleration
and deceleration engine transients was not found.
The field control as a function of manifold vacuum was not a
closed feedback system; indeed, three steps were used. The torque and com-
manded speed of the shunt motor was, therefore, only grossly controlled and
did not accurately augment power to keep heat engine power at a constant
level.
The C-l system was tested with the electric system providing
up to 27 hp. Emissions were not reduced to acceptable levels (Ref. 4-4);
the results of measured emissions over the Federal Emission Test Driving
Cycle were HC-3. 15 gm/mi, CO-29. 6 gm/mi, and NOx- 1 . 0 gm/mi.
4. 2. 3 The Aerospace Corporation
4. 2. 3. 1 Design Requirements
Selected examples of performance requirements for hybrid
vehicles with a spark ignition heat engine are illustrated in Table 4-6 for a
family car and a commuter car for the parallel system. The values shown
are for both full-load and part-load operations. Physical and performance
characteristics for the spark ignition powered parallel configuration electrical
subsystems are shown in Table 4-7.
4-22
-------
Table 4-6. Parallel Configuration, Subsystem Estimated
Performance--Spark Ignition Engine (Ref. 3-3)
^""""~*1---^^^ Vehicle
Sizing Criteria ~>-^^_^^
Vehicle Specification
Requirements
Maximum Cruise Speed
Velocity on Grade, mph @ %
Road Horsepower @ V , hp
* max ^
Road Horsepower @ V , , hp
Selected Baseline Subsystem
Efficiencies for Design-Point
Sizing
Final-Drive (Differential), %
Automatic Transmission, %
Ele-ctric Drive Motor
-------
Table 4-7. Parallel Configuration, Characteristics of Selected Electrical
Subsystems --Spark Ignition Engine (Ref. 3-3)
~~---^^^ Vehicle
Subsystem '
Electric Drive Motor
Type
Rated Voltage, V
Rated Horsepower, hp
Volume, ft3
Weight, lb*
Efficiency ^ Rated Load, %
Motor Controller
Volume, ft
Weight, lb
Efficiency ® Rated Load, ^
Generator
Type
Maximum Speed, rpm
Rated Output, kW
3
Volume, ft
Weight, lb
Efficiency @ Rated Load, %
Alternating Current Rectifier
Volume, ft
Weight, lb
Efficiency @ Rated Load, %
Generator Controller
Volume, ft3
Weight, lb
Cables, Low Level Electronics,
Accessories. Cooling System, and
Miscellaneous
Weight, lb
Family Car
Direct Current
Chopper
Direct Current
Series
220
38
3.0
232
90
1. 5
100
95
Alternating
Current
12, 000
8. 1
0.08
19
90
0. 1
9
99 +
0. 009
2
55
Step Voltage &
Field Control
Direct Current
Shunt -Wound
220
38
3.4
250
92
0.023
12.5
99 +
Alternating
Current
12,000
7. 5
0.07
18
90
0. 1
9
99 +
0.009
2
50
c\S'.thout forced air cooling system.
Gommu tc r
Car
Direct Current
Shunt -Wound
220
12
1.2
83
92
0.023
9.5
99 +
Alternating
Current
12,000
4. 5
0.06
12
90
0.05
5
99 +
0.009
2
38
4-24
-------
A summary of subsystem weight and volume requirements for
all heat engines considered is given in Table 4-8 for the family car parallel
mode. This table also shows the value assigned as available for vehicle
propulsion system weight and volume. After all powertrain weights and
volumes were subtracted from the propulsion system weight and volume
allowances, the balance was allocated to the battery subsystem. The par-
allel configuration provides a greater weight allocation for batteries.
4. 2. 3. 2 Performance Results
Analytical results from computer calculations are as follows:
a. Battery power and energy density required for the commuter
and family cars are given in Table 4-9. (The battery depth of
discharge for each of the heat engines investigated in the study
was 5 percent or less for the vehicle operating over the DREW
Driving Schedule" and batteries recharged by the end of the
cycle.) The total powertrain weight was set at 1,500 Ib by
EPA. The peak power demand was determined to be 92. 5 kW.
Then after all other component weights were subtracted from
the 1, 500 Ib, the weight allocation to the batteries requires
that they deliver a power density of just over 200 W/lb for the
spark ignition engine powered parallel hybrid. Based on the
current draw limitations defined by conventional lead-acid
battery polarization curves, to meet the required power drain
during maximum vehicle acceleration, installed battery capacity
was established at 8.36 kW-hr. The weight allocation requires
an energy density of just over 20 W-hr/lb for the same case.
A small, but significant, reduction in power density and energy
density is possible for a gas turbine powered hybrid. The study
indicated that only the spark ignition engine and the gas turbine
engine offer reasonable weight margins for the battery system.
b. Fuel economy determined for the family car series configura-
tion was 11 mpg and for the parallel configuration was 12.5 mpg.
These estimates are based on a fully warmed-up vehicle driven
over the DHEW Driving Schedule. The results are equivalent
to the mileage expected for a conventional similar size 1970 car.
c. Figure 4-9 shows the successful reduction of emissions over the
DHEW Driving Schedule with a parallel configuration hot start to
levels below the original 1975/1976 Federal emission standards.
The one exception is NC>2 from the spark ignition hybrid. The
spark ignition engine used lean operation, an oxidation catalyst, and
exhaust gas recirculation. A cold start correction factor of 1. 2
DHEW Driving Schedule (now Federal Emissions Test Driving Cycle)
4-25
-------
Table 4-8. Preliminary Weight and Volume Summary of Powertrain--
Family Car Parallel Mode (Ref. 3-3)
o--
~~~ --^^^ Hrat-Engine
-—^^^ Class
Pnwrrlrain ~"~ __^__^
Subsystems ~"~ — -^^^^
Klectrn al Drive Motor
C oni roller (Motor)
C, e n <• r a t o r
Alternating Current Rectifier
Generator Controller
Fuel Tank (Full)
Rear Axle Drive
Heat Engine
(ip.iririR (Heat Engine to Generator)
Radiator (Full)
Exh au s t
Starter
Transmission
Drive Line
Subtotal
Assigned Value
Available for Batteries
Spark Ignition
wt.a
Z50.0
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.b
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
R a n k i n e
Wt.
755. 0
2. 0
0
27. 1
0
59. 0
70.0
1439. I
1500.0
60.9
Vol.
12.20
0. 02
0
0.44
0
0. 42
0. 15
20. 39
28.0
7.61
St i rl i nfl
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
0
aWeight in Ib
Volume in ft
-------
Table 4-9. Resultant Hybrid Vehicle Battery
Requirements--Baseline Case (Ref. 3-3)
— ^__^Vehicle Class/Mode
Area • ___^^
Peak Power Demand, kW
(From Design Driving Cycle)
Installed Energy
Capacity, kW/hr
(From Design and/or Federal
Emissions Test Driving Cycle)
Weight Available for
Batteries, Ib
- Spark Ignition
- Diesel
- Gas Turbine
- Rankine
- Stirling
Power Density
Required, W /Ib
- Spark Ignition
- Diesel
- Gas Turbine
- Rankine
- Stirling
Energy Density
Required, W-hr/lb
- Spark Ignition
- Diesel
- Gas Turbine
- Rankine
- Stirling
Family Car
Series
92.5
8.36
398
240
453
0
0
232
385
204
--
--
20
35
18.4
--
Parallel
92.5
8.36
460
334
526
61
0
201
277
176
1520
18. 1
25
15.9
137
Commuter Car
Series
28
4.40
101
53
170
0
0
279
527
165
--
—
43.8
83
25.9
--
Parallel
28
4.40
145
99
211
32
0
193
284
133
875
— —
30.3
44.5
20.9
137
4-27
-------
120 —
< 100
o
z
£ 80 —
Z
UJ
U
a:
UJ
a
1975/1976 STANDARDS0
HC
CO
0.46 gm/mi
4.7 gm/mi
N09 0.4 gm/mi
CVJ
••
— § a Values
,^« in the
"*
-
— o
I
—
—
1
?-x''
O
O
'//
//
I
Yf
/ /
//
//
//
//.
Y/,
shown were used
study; they have been
subsequently revised.
o" \
z \- 1975/1976 STANDARDS
F77I
SPARK
O
I
::x:
O
•••H
^
^
'//
//
//.
//
k
ADVANCED TECHNOLOGY
PARALLEL CONFIGURATION
HOT START
ON DHEW
DRIVING SCHEDULE
CM
GAS
O
I
•:•:•:•
0
o
M«H
{
SPARK
€
Wr
0
1
%
GAS
IGNITION TURBINE IGNITION TURBINE^
60 —
40 —
FAMILY CAR
COMMUTER CAR
Figure 4-9.
Comparative Calculated Emission Levels
of the Family and Commuter Cars
(Ref. 3-3)
for HC and CO should be applied to the hot start values. The
NC"2 correction factor is 0.95, however.
Figure 4-10 compares the emission levels over the DHEW
Driving Schedule (now Federal Emissions Test Driving Cycle)
of the conventional vehicle (cold start) with hybrids (hot start)
for different engine and exhaust control schemes: variable
air-fuel ratio from rich to lean, air-fuel ratio maintained at
15 to 16 with exhaust gas recirculation, and air-fuel ratio
maintainted at 22 with catalyst and exhaust gas recirculation.
4-28
-------
I50
O
O
UJ
ui
O
2
UJ
UJ
O
I
UJ
40
30
10
CONVENTIONAL
SPARK IGNITION
ENGINE
(variable A/F)
O
O
CONVENTIONAL
SPARK IGNITION
ENGINE
(A/F = 15 - 16)
+ RECIRC.
ADVANCED
TECHNOLOGY
PLUS
A/F = 22 + CAT.
+ RECIRC.
1970 MODEL YEAR
CONVENTIONAL
VEHICLE
(cold start)
HYBRID VEHICLE
(4,000-lb family car)
(hot start)
Figure 4-10.
Calculated Vehicle Emission Comparison,
Conventional Operation Versus Hybrid
DHEW Driving Schedule (now Federal
Emissions Test Driving Cycle)--Spark
Ignition Engine (Ref. 3-3)
d.
The first case, with simply varying engine air-fuel ratio,
did not show reductions in NOX; about a 50 percent reduction
in HC and CO occurred. Similar results were found in
Reference 4-5.
The last case, advanced technology (with lean operation, oxi-
dizing catalyst, and exhaust gas recirculation), is required to
meet the original 1976 Federal emission standards.
A summary of engine costs and vehicle system costs is given
for the family car in Table 4-10. The conclusion drawn was
that the hybrid vehicle would require a significant increase
in expenditures by the consumer for first costs. Design
requirements and unique mass production techniques might
reduce these figures somewhat.
4-29
-------
Table 4-10. Summary of Engine Costs and
Vehicle System Costs (Ref. 3-3)
Heat Engine
Conventional Car
Hybrid Spark Ignition
Hybrid Diesel
Hybrid Gas Turbine
Hybrid Rankine
Hybrid Stirling
Approximate
Relative
Engine Cost
Not
Applicable
1
1.5
2
3.75
5
Approximate
Relative
Vehicle Cost
1
1.4 to 1.6
1.5 to 1.7
1.6
2
2.25
4.2.4
4.2.4. 1
General Motors Corporation - Stir-Lee I
Design Requirements
A readily available 8-hp Stirling engine was used. It was
originally designed for the Army as a portable power unit. The 450-lb Stirling
engine uses a small amount of hydrogen as the working fluid at pressures up to
1,000 psi (full rated power). The engine idles at a working fluid pressure of
about 260 psi. The drive system includes a motor of about 20 hp over a 3 to
1 speed ratio range. Motor speed at 55 mph is 12, 500 rpm. The motor and
gear box weighed only 85 Ib. Though the three-phase alternator had a 25 hp
nominal rating at a designed speed range of 5,000-500 rpm, in this application
it produced a maximum power output of 6.75 hp. The battery pack and racks
weigh 490 Ib, the inverter weighs 82 Ib, and the control electronics weighs
24 Ib. The weight of the Stir-Lee I powertrain is 1, 189 Ib, which compares
with 498 Ib for the standard Opel Kadett powertrain. A total vehicle weight
is, therefore, 3,200 Ib compared to the standard weight of 1,990 Ib for the
Opel Kadett.
4-30
-------
4.2.4.2
Performance Results
At about 30 mi/hr on a level road the vehicle achieves a fuel
economy of 30 to 40 mi/gal. Battery capabilities limit the range to about 30
to 40 mi at 55 mi/hr. In the all-electric mode, the range varied from 1 5 to
30 mi depending upon the type of driving cycle. Acceleration from 0 to 30
mi/hr takes about 10 seconds. It achieves a top speed of 30 mi/hr with engine
power only and a top speed of 55 mi/hr if battery power is added. In Fig-
ure 4-11 the vehicle emissions data are shown both with and without preheating
of burner inlet air to 1,200 F. The HC and CO emissions are low, but the NO
ji
emissions are much higher than expected for this engine. General Motors
stated that engine modifications could be expected to provide major reductions
in the NO levels .
x
o
o
(B
o
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
NO
A—O—O Before Preheater
A- • After Preheater
Hydrocarbons
_ CO o
20
Air-Fuel Ratio
25
0.05
0.04 _
x
0.03 5
«
o
0.02 g
E
0.01 °
0
Figure 4-11. Stir-Lee I Engine
Mass Emissions
4-31
-------
4.3 COMPONENT DESIGN REQUIREMENTS AND ACHIEVEMENTS
4.3.1 Motors and Generators
There were no EPA contracts awarded for development of
rotating electrical equipment. Therefore, this section discusses general
design considerations and the state of the art of these components as related
to hybrid vehicles. A more extensive discussion for the electric vehicle was
given in Section 2 of Part I.
4.3.1.1 Design Considerations
The motor/generator performance requirements are consider-
ably greater for the series configuration than for the parallel configuration.
All the heat engine mechanical energy must be converted to electrical energy
and then back to mechanical torque at the drive wheels in the series config-
uration. In various parallel arrangements mechanical energy is transferred
directly to the drive wheels with the differences between the mechanical
level transmitted and the demand level being absorbed or supplied through
the moto r/generator. This allows a lower continuous duty rating for the
parallel system motor/generator with corresponding lower weight and lower
electrical losses than for the series system.
It can be seen, therefore, that the series hybrid configuration
design can be quite similar to the all-electric vehicle design for battery,
controller, and motor systems. The overall difference lies in the method of
charging the batteries: the all-electric vehicle must use a charger that
accepts electrical energy from a power transmission line and delivers the
energy, at the proper voltage and current, to a battery system before energy
is removed from the batteries. By contrast, the series hybrid converts
mechanical energy from a heat engine to electrical energy with a generator
that provides the proper voltage and current to both the battery system
and the drive motors . The fact that all the energy is stored before use in
the former case but during use in the latter case allows the series hybrid to
function with less energy storage capacity.
4-32
-------
4.3.1.2 Motor Rating and Overloads
Figure 4-12 shows the overload capability of compensated
brush direct current motors suitable in size for hybrid or electric vehicle
use. These overload limits are established both by commutation constraints
(which become more severe at higher speeds) and by thermal conditions.
Notice that the "Frequently Repeated" curve in Figure 4-12 allows one
minute overload of 2-1/2 to 3-1/2 times design rated continuous duty load.
This could provide adequate acceleration of an all-electric or hybrid electric
car to highway speeds. Bursts of power for up to 5 seconds allow 3-1/3 to
5-1/2 times overload which is "Occasionally Repeated".
The overload capability is very important in the parallel
hybrid configuration. At cruise velocity, all the power is mechanically
transferred from the heat engine to the wheels. Since the motor is not
supplying continuous power for cruise, it can be sized for supplying tran-
sient power, resulting in a small, lightweight unit. It was thus determined
in Reference 3-3 for a 4, 000-lb passenger car, that a 38-hp motor, rated for
continuous duty would, at a factor of three overload, provide 114 hp for
acceleration to maximum vehicle speed. It can also provide a starting
torque for one minute of 3-1/2 times the rated current torque. Since the
curves in Figure 4-12 assume continuous duty at 100 percent of rated load
before the overloads occur, the temperature rise of the motor in the parallel
hybrid configuration would be lower since the motor is not continuously
loaded.
On the other hand, the series hybrid configuration requires
that all continuous and overload power be provided by the electric motor.
This motor must be sized for the more rigorous requirement of continuous
cruise power and is much heavier than the parallel system motor. Refer-
ence 3-3 thus calls for the use of a continuous duty rating of 61 hp in a 4, 000-lb
passenger car for this configuration. This is the minimum input power
required to provide vehicle cruise at 80 mi/hr.
4-33
-------
c
900 r-
800
700
600
50°
ct
O 400
< 300
200
100
, INSTANTANEOUS LOADS
1,4
.^OCCASIONALLY REPEATED LOADS 2'4
FREQUENTLY REPEATED LOADS3'4
I
50 100 150
BASE SPEED, percent
200
1. Instantaneous loads are defined as 0.5 seconds duration or less,
repeated not oftener than once every minute.
2. Occasionally repeated loads are defined as 5 seconds duration
or less, repeated not oftener than once every 5 minutes.
3. Frequently repeated loads are defined as 1 minute duration or
less, repeated not oftener than once in a period of 20 times
the duration.
4. Curves are for assumed continuous duty at 100 percent of
rated load prior to onset of overload. They apply regardless
of whether speed is obtained by armature voltage or shut field
control, and they also apply for regenerating operations.
Figure 4-12. Overload Capability Compensated Direct Current
Motors (Ref. 4-6)
4-34
-------
The size and rating of both hybrid motors were imposed by the
specifications under the EPA design guidelines of 80 mi/hr cruise and equiva-
lent acceleration and gradability of 1970 type family-size heat engine
passenger cars. Relaxation of the specifications could have a marked effect
on major components. If the cruise speed specification were reduced from
80 to 55 mi/hr for the family car, the series hybrid configuration motor
continuous input rating could be reduced from 61 to 22 hp. This would
result in a much smaller motor and more space for batteries. Note, how%-
ever; that the gradability requirement would have to be reduced to correspond
to the lower power rating. Since peak acceleration (requiring 114 hp) could
only be obtained for five seconds in a five minute interval with the smaller
motor, the acceleration specification would also have to be relaxed.
To summarize, the most rigorous duty demanded of a motor
or generator establishes its size and in turn its weight, peak power, and
maximum torque capabilities. Allowable temperature rise is the long-term
constraint that must be met by sufficient sizing or adequate cooling system.
4.3.2 Control System
4.3.2.1 Comparison of Motor Controller
The motor control system for the series configuration hybrid
electric vehicle is identical to that for the all-electric vehicle. However, a
simple separate control of the generator field is required in the series
configuration hybrid to modulate the power output from the heat engine for a
fixed engine speed and convert it to electrical energy to be delivered to the
motor. A more complex control logic will have to be inserted for a heat
engine-generator system with variable engine speed that is designed for
transmitting higher levels of power to the motor to enable the vehicle to
operate at high speed on level roads or at sustained speeds on grades.
4-35
-------
The motor controller for the parallel configuration hybrid
system, by contrast, is more complex than the series hybrid because it
requires special logic to control the electric motor that is augmenting
power from the heat engine. That is, the road power demand less the
mechanical power provided by the heat engine must be supplied by the
electric motor. A sensor and logic system must, therefore, be capable
of accepting foot throttle position information and heat engine power output
information to provide the difference. Therefore, it is a heavier, costlier
system by virtue of the increased logic, but it is lighter and cheaper on the
basis of reduced power handling requirements.
4.3.2.2 Generator Control
A battery charge rate sensor and generator control is needed
for both the series and parallel hybrid systems. (The all-electric vehicle
has no generator and, hence, no generator controller.) In the series hybrid,
power is being continuously converted from mechanical torque from the
heat engine to electrical energy at the generator output. The logic for the
series hybrid is simpler because it need only sense the battery back voltage
and regulate generator field strength accordingly (as is done with current
conventional 12-V alternator, regulator systems).
The parallel hybrid, however, must contain logic to control
the field strength in the generator so that batteries are charged only when
surplus power is available from the heat engine. That is, in the parallel
system, batteries will never be charged at the same time that electrical
energy is being delivered by the generator to the motor and this occurs only
when heat engine power is less than road demand (typically in a vehicle
acceleration mode).
4.3.2.3 Regeneration Mode
In the all-electric vehicle, braking force is supplied when
kinetic energy is converted back to electrical energy through the motor/
generator and directed to recharging the battery system. The braking drag
4-36
-------
is limited, therefore, by both the short-term over-current rating of the motor
and the charge acceptance rate capability of the batteries. In both hybrid
configurations, the heat engine-generator system may be charging the
batteries at the same time braking drag is required. The simultaneous
supply of electric energy from both the heat engine-generator and motor-
generator during regenerative braking can exceed the charge acceptance
rate of the battery system. In addition, the battery is kept near a full
charge in the hybrid mode. Therefore, both the state of charge of the
battery and its charge acceptance rate are two severe constraints to utili-
zation of regenerative braking energy in the hybrid vehicle.
4.3.3 Batteries for Hybrid Vehicles
4.3.3.1 Battery Requirements
As part of the hybrid heat engine/electric vehicle program,
two investigations were initiated to study the application of lead-acid batteries
to hybrid vehicles. Contracts were awarded to Tyco Laboratories, Inc.
(Ref. 4-7) and to TRW Systems, Inc. with Gould as subcontractor (Ref. 4-8).
These contracts were awarded to fill a need for data on lead-acid batteries
when operated under the unique conditions imposed by the hybrid vehicle
(i.e. , the battery is charged by an engine-driven generator and is used only
to supply pulse power needs during acceleration) as contrasted with the all-
electric vehicle battery that supplies all vehicle power demands.
Before the start of the battery investigations, independent
contracts had been awarded by EPA to The Aerospace Corporation and TRW
Systems for studies of hybrid heat engine/battery system vehicles. The pre-
liminary results of these investigations (Refs. 3-3 and 2-1) were used to
establish battery operating requirements shown in Table 4-11 (Ref. 4-9).
7TRW Systems, Inc. tested batteries supplied by Gould.
4-37
-------
Table 4-11. Hybrid Vehicle Battery Preliminary
Requirements (Ref. 4-9)
Parameters
Specification
Power
Voltage, V
55 kW discharge for
25 seconds, twice
within 60 seconds
30 kW recharge for
90 seconds after
above two discharges
200 to 220 open circuit
150 minimum
Life
5-years; 200,000 cycles
Number
of
Cycles
Rate, kW
Discharge
Charge
Discharge
Energy
Per Cycle
W/hr
500
3000
3000
Balance of
200, 000
55
55
55
10
30
30
30
380
130
80
30
Weight, Ib
Maximum
Goal
Cost
Operation
550
450
$550
Safe
No undue care or
maintenance
4-38
-------
4.3.3.2 Commercial Lead-Acid Batteries
Prior to the Tyco and TRW/Gould programs, there was a
considerable amount of published information on the discharge and charge
current rates and cycle life characteristics for starting-lighting-ignition
(SLI) and golf cart type battery applications to electric vehicles. However,
there was little information that could be used to predict performance of
these batteries during hybrid vehicle operation.
In the initial effort, each contractor tested commercial SLI
batteries to establish a reference performance case. Test battery character-
istics, test conditions, and test results are presented in Table 4-12.
In the Tyco reference tests, the battery cells were to have been
cycled at conditions representative of those in the preliminary hybrid specifi-
cation--55 kW discharge and 30 kW charge; however, test equipment limita-
tions reduced the rates slightly to 48 kW discharge and 26 kW charge.
A maximum of 350 of these high-rate cycles were sustained by
the positive plates prior to failure. Positive plates averaged 72 percent
capacity loss after 300 cycles. The capacity loss and positive plate failures
were caused by plate expansion and consequent poor paste adhesion, particularly
in the positive battery terminal region. An individual cell plate was used in
tests against oversized counterelectrodes . The SLI test battery results showed
that negative plates lost only 30 percent of their capacity after 500 cycles and
also confirmed the positive plate problems that were revealed in the cell tests.
In the TRW Systems/Gould tests of conventional SLI batteries,
a life of 221 high-rate cycles (55 kW, 25 seconds) plus 6638 low-rate cycles
(10 kW, 10.8 seconds) was obtained.
It was demonstrated by these tests that a commercial SLI
battery of conventional design was unsuited for hybrid vehicle use due to life
limitations although it did have required power and rate performance when new.
4-39
-------
Table 4-12. Performance Tests of Current Batteries
Parameters
Battery
Size, in.
Length
Width
Height
Volume, in.
Weight, Ib
Specific Energy
Density,
W-hr/lb
Energy Density,
W-hr/in.3
Cell
No. of positive
plates
(plate thickness,
in.)
No. of negative
plates
(plate thickness,
in.)
Plate Size, in.
lest Conditions
(Scaled to full-size
hybrid battery)
Discharge Rates
Charge Rates
Test Results
Maximum Cycle
Life
Contractor
Tyco Laboratories,
Incorporated
96 Ah
Not specified
Not specified
Not specified
Not specified
55
20.9
Not available
7 (0.060)
8 (0.050)
5. 2 by 6. 1
47.4 kW rate,
25 seconds
25. 9 kW rate,
61 to 67 seconds
Complete discharge
at C/5 rate every
100 cycles for capac
ity determination
350 cycles
72 percent capacity
loss after 300 cycles
TRW Systems/Could
61 Ah,
22 F
Gould 22F-CP-G1
9-7/16
6-7/8
7-5/8
480
35.9
18.7
1.52
5 (0.
6 (0.
073)
053)
Not specified
Cycle Type 1
10 kW rate,
10.8 seconds
5 kW rate,
22 seconds
6638 Type 1 +
Cycle Type 2
55 kW rate,
25 seconds
30 kW rate,
50 seconds
221 Type 2
6859 cycles total (30 cycles of
Type 1, one cycle of Type 2,
and repeat)
No capacity retention
measurements
4-40
-------
4.3.3.3 Research Battery Designs for Hybrid Vehicles
4.3.3.3.1 Lead-Acid Batteries
4.3.3.3.1.1 Tyco Laboratories, Incorporated
Tyco Laboratories (Ref. 4-7) used a quasi-bipolar arrangement
(Figure 4-13) in its lead-acid battery design for the hybrid vehicle. Vertical
lead strips are placed on both sides of an insulating substrate, and these strips
are then connected at the top, above the electrolyte level. The positive (lead
oxide) paste is applied on one side, and the negative (lead) mass is applied on
the other side. A number of these plate assemblies when stacked together
(each separated by a thin polyethylene sheet) form a battery. Because the
plate assemblies are relatively thin, a high voltage can be obtained in a short
length. Capacity is obtained by adding parallel battery modules. Plastics are
used extensively in the battery to reduce weight and prevent loss of strength
due to corrosion during life.
Under the same test conditions as the commercial SLI battery,
a quasi-bipolar battery lasted for 1, 000 cycles, compared with the 350 cycles
achieved by the commerical battery. Capacity loss after 300 and 1,000 cycles
averaged 8 and 48 percent, respectively, compared to a 72 percent capacity
I
loss for the SLI battery after 300 cycles. In contrast to the plate failure of the
commerical battery, after 1,000 cycles the positive plate was in good condi-
tion, while the nagative plate did have some blistering and shedding.
4.3.3.3.1.2 TRW Systems, Inc./Gould
Based on the tests of the modern SLI battery, TRW Systems,
Inc./Gould (Ref. 4-8) made selective changes to the SLI cell design and was
able to increase power density to 150 W/lb for 75 seconds and 204 W/lb for
20 seconds. The higher power density was obtained by using a greater number
of thinner plates per unit volume and by using higher conductivity lead alloy
grids and conductors. Tests of the new design indicated cell lifetimes of 260
to 390 high-rate cycles plus 7,740 to 11,610 low-rate cycles. Under the same
test conditions, the commercial SLI battery lasted 221 high-rate cycles plus
6,638 low-rate cycles.
4-41
-------
LEXAN
GRIDS
LEXAN BORDER
LEXAN BORDER
\
\ /
M i
3
/I
3
', \
\
'•
\
^*>
^^ f-\*—** 1 »^ ^ * 1 «V MM • •
| ANTI-SPLASH RIM
PASTING
AREA
"^LEAD CONDUCTOR EXTENDING
THROUGH THE BASE PLATE
LEXAN
BASE PLATE
Figure 4-13. Section Through the Various Components of the
Quasi-bipolar Plate Prior to Thermoforming
(Ref. 4-7)
4-42
-------
TRW/Gould also designed and built several bipolar cells for
the hybrid vehicle. Cycle life of the best bipolar positive plate was 6,000
cycles that included 60 deep discharge cycles to 1.0 V. This was judged
by TRW/Gould to be equivalent to what could be expected from a good
conventional positive plate.
4.3.3.3.2 Other Batteries
4.3.3.3.2.1 Nickel-Zinc
In a study supported by EPA under an interagency agreement,
the U.S. Army Electronics Command (Ref. 4-10) tested nickel-zinc battery
cells for the hybrid vehicle. Cells for testing were received from Eagle-
Picher, General Electric, Energy Research Corporation, and NASA Lewis
Research Center. An individual cell rated at 24 Ah yielded up to 26, 000
Ah total output, which is calculated in Ref. 4-10 as being equivalent to
3/8 of the cycle life called for in Ref. 3-3.
The principal failure mode observed with the nickel-zinc cells
was degradation of the cellulose cell plate separator material. Inorganic
separators (designed for another application) were supplied by NASA Lewis
Research Center, but in the thicknesses available proved to be unsatisfactory
for this application. The nickel electrodes were unaffected by the testing,
while the zinc electrodes showed a low (10 to 20 percent) shape change.
Power densities up to 300 W/lb for five seconds were achieved.
The nickel-zinc battery tests demonstrated that the nickel-zinc battery could
be designed to provide adequate specific energy density (W-hr/lb) and power
density (W/lb) for the hybrid vehicle application, but that considerably more
development would be needed to obtain satisfactory life.
4.3.3.3.2.2 Nickel-Hydrogen
Metal-gas batteries, particularly nickel-hydrogen, could find
application in the hybrid vehicle. Prototype nickel-hydrogen cells have been
built with specific energy densities above 30 W-hr/lb and specific power
densities of more than 200 W/lb, and are considered feasible (Ref. 4-11).
4-43
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The nickel electrode in the nickel-cadmium battery has proven to be
relatively trouble-free; the hydrogen electrode of the hydrogen-oxygen fuel
cell has also proven to be reliable (Ref. 4-12). The combination of the two
could be expected to have good life and performance if the experience with
fuel cells can be reliably extrapolated to batteries. Over 2,000 complete
discharges have been made with nickel-hydrogen cells without any significant
degradation. It has been also shown that the cells can accept charge and
can discharge over a wide range of current levels.
The main concerns in the development of the cell would be
large volume, safety, and cost. Safety problems may arise from the poten-
tial leakage of hydrogen through seals and cases, although such leakage is
generally associated with high-pressure and high-temperature systems that
are not required in the hybrid application.
4.3.3.4 Impact of Vehicle Requirements on Battery Design
Figure 4-14 (Ref. 3-3) shows the characteristics of the most
severe operating cycle in the DHEW Driving Schedule (now Federal Emissions
Test Driving Cycle) based upon a 4,000-lb family automobile. In this case,
severity is defined by the duration of discharge, ampere hours delivered, and
peak battery current. The battery power density needed to meet this demand
is about 100 W/lb and the ampere hours delivered are 0.62 Ah.
Based upon these findings, it appears that the lead-acid battery
will be adequate for the hybrid to negotiate the DHEW Driving Schedule on a
repetitive basis provided its cycle life can be improved. A reduction in the
requirements specified for vehicle peak acceleration (0 to 60 mi/hr in
13 . 5 seconds) and top speed (80 mi/hr) will also make the lead-acid battery
more suitable for the hybrid vehicle. Further battery weight reductions
might be achieved by use of advanced battery systems.
4-44
-------
1 I I I I
4,000 Ib FAMILY CAR
OHEW EMISSION DRIVING SCHEDULE
GENERATOR OUTPUT = 38 amp
38 Ah LEAD-ACID BATTERY
190-206 seconds
7448-465 seconds
120
80
8
CM
a
z
o
o
in
£
\
40
to
Z
Ul
a
ui
10 15
ELAPSED TIME, seconds
4.3.4
4.3.4. 1
Figure 4-14.
Heat Engines
Introduction
Battery Peak Discharge Currents
and Associated Power Density
(Ref. 3-3)
System studies by TRW Systems (Ref. 2-1) have shown that
even conventional engines operating in the hybrid mode can have lower emis-
sions and improved fuel economy in comparison with these same types of
Q
engines in conventional automobiles. Since the engine in a hybrid vehicle
need only provide the maximum power required for cruising (and not accel-
eration), it can be smaller than the engine for the conventional automobile.
8
Lockheed Missiles and Space Company (LMSC) in its hybrid heat engine/
flywheel study arrived at similar results (Ref. 3-1).
4-45,
-------
Engine power is expected to be 90 to 110 hp for a full-size passenger car
(Refs. 3-1 and 3-3). Because rapid transient power requirements for ac-
celeration are met by an energy storage device, such as a flywheel or
battery, the engine operates at or near steady-state conditions. Under these
conditions, the engine may be designed with unique features and operating
characteristics in an attempt to achieve significant reductions in exhaust
emissions and fuel consumption.
4.3.4.2 Candidate Heat Engines
A number of heat engine types have been considered by EPA
contractors for use in hybrid vehicles: the Otto cycle (spark ignition
engine), the Diesel cycle (compression ignition engine), the Brayton cycle
(gas turbine engine), the Rankine cycle ("steam" engine), and the Stirling
cycle. These engines are discussed in the following paragraphs.
4.3.4.2.1 Otto Cycle
The sequence of operations in the reciprocating spark ignition
engine involves four piston strokes: intake, compression (during which
ignition and combustion of the charge occur), power or expansion, and
exhaust. A rotating lobe in the Wankel engine undergoes a similar operating
sequence. Typically, a carburetor supplies an air-fuel mixture to the engine
intake at a near-constant, near-stoichiometric ratio over a broad range of
engine operating conditions. Engine output to meet load requirements is con-
trolled by throttling the air flow, which in turn controls the fuel flow to the
engine. At a fixed throttle setting, the engine delivers a relatively constant
torque, and its output power is roughly proportional to engine speed (rpm).
4.3.4.2.2 Diesel Cycle
The diesel cycle employs a four-stroke sequence of engine
operations made up of an air-only intake stroke, a compression stroke that
raises the air temperature above the autoignition point of the fuel, followed
by combustion of an injected fuel charge, a power or expansion stroke, and
an exhaust stroke. Fuel under high pressure is delivered to the cylinder
4-46
-------
through individual cylinder nozzle injection valves by an injection pump
driven by the camshaft. Unlike the spark ignition engine, the charge mixture
is not regulated and overall air-fuel ratios ranging from 20 to 75 or higher
may be encountered over the normal engine operating range. Load and speed
control are achieved by adjusting the amount of fuel injected.
4.3.4.2.3 Bray ton Cycle
In the basic Brayton cycle, inlet air is compressed and heated
at constant pressure in a combustion process; combustion products are
expanded through a power turbine and discharged to the atmosphere, eventu-
ally reaching equilibrium with the environment. The engine design
arrangement can be either single-shaft or dual-shaft (free turbine). In the
single-shaft arrangement, a turbine supplies power to both the compressor
and the load. In the dual-shaft arrangement, separate turbines supply
power for the load and for the compressor.
Cycle efficiency and engine fuel economy can be improved by:
(a) increasing the maximum cycle temperature, (b) improving component
efficiencies, and (c) using a regenerator to recover some of the rejected
heat. Optimum cycle efficiencies are obtained at high compressor pressure
ratios (8 to 12) without regenerators, and at low compressor pressure
ratios (4 to 6) with regenerators (Ref. 4-13).
The most advanced operational gas turbine is Chrysler's
sixth generation gas turbine engine for automobiles that is being developed
further under an EPA-sponsored contract. The Chrysler design is a low
pressure ratio, free turbine, regenerative engine with a compressor
pressure ratio of 4:1, maximum turbine speed of 45,700 rpm, and first
stage turbine inlet temperature of 1,850 F.
4.3.4.2.4 Rankine Cycle
The Rankine cycle engine is an external combustion power
plant using water or other working fluids. In this cycle, the working fluid
is vaporized and superheated at high pressure in a boiler. The fluid is
then expanded in a power absorbing reciprocating piston or rotating turbine;
the exhaust is condensed and the liquid is pumped back to the boiler.
4-47
-------
In the water-base vehicular engine, steam design pressures
and temperatures of about 1,000 psia and i,000°F are planned. Organic
working fluid systems under development range in pressure from 700 to
1,000 psi with temperatures of about 600 F.
The EPA has sponsored four Rankine cycle development pro-
grams. These programs are:
a. Water-base Rankine--reciprocating expander and turbine
expander.
b. Organic Rankine--reciprocating expander and turbine
expander.
Components for these engines have been under test since January 1973
(Ref. 4-14).
4.3.4.2.5 Stirling Cycle
The Stirling cycle engine is a closed-cycle external combustion
engine with a reciprocating expander. The working fluid can be any gas.
Ideally, the Stirling cycle consists of two constant volume processes joined
by an isothermal expansion and an isothermal compression process.
The Stirling cycle has a very high efficiency approaching the
Carnot cycle efficiency; the basic problem has been excessive weight and
volume. Improvements have been made in recent years in reducing both
weight and volume. Several European companies (N.V. Philips of Holland,
and United Stirling of Sweden) have worked on Stirling engines for automo-
biles. Currently, N.V. Philips and Ford Motor Company are in the process
of designing a 170-hp Stirling engine for a Torino automobile. Changes that
have lead to the compactness and reduced weight of the engine include the use
of a swash-plate (for converting reciprocating motion of the piston to rotary
drive shaft motion) and the use of high pressure (200 atm) gaseous hydrogen
as the working medium (Ref. 4-15).
4.3.4.3 Fuel Consumption, Weight, and Volume Characteristics
Specific fuel consumption (SFC), weight, and volume charac-
teristics for each of the candidate heat engine types are shown in Table 4-13
for the hybrid family car and in Table 4-14 for the hybrid commuter car.
4-48
-------
Table 4-13. Family Car Heat Engine Characteristics
(Ref. 3-3)
Heat Engine
Spark Ignition Engine -
Reciprocating Piston
Spark Ignition Engine -
Rotary Piston
Compression Ignition Engine
Brayton Cycle Engine
Rankine Cycle Engine
(Positive Displacement)
Stirling Cycle Engine
(Rhombic Drive)
SFC, Ib/hp-hr
0.50
0.50
0.43
0.57
0.87
0.42
Weight, Ib
335
216
493
310
846
1,153
Volume, ft
11.8
5.8
15. 1
10.4
13.5
22.8
Table 4-14. Commuter Car Heat Engine Characteristics
(Ref. 3-3)
Heat Engine
Spark Ignition Engine -
Reciprocating Piston
Spark Ignition Engine -
Rotary Piston
Compression Ignition Engine
Brayton Cycle Engine
Rankine Cycle Engine
(Positive Displacement)
Stirling Cycle Engine
(Rhombic Drive)
SFC, Ib/hp-hr
0.56
0.56
0.45
0.65
0.93
0.43
Weight, Ib
180
116
228
125
322
432
Volume, ft
6.1
4.0
8.9
3.9
5.5
8.6
4-49'
-------
These characteristics are representative of information available at the
time the study reported in Ref. 3-3 (C. 1970). The SFCs for the spark
ignition 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 entire oper-
ating map. It is noted that these data may be compared on an equal basis
without great error since the SFC characteristic for design-optimized
systems used in the hybrid application would tend to be relatively flat over
a •wide load range.
The weights and volumes for each engine type represent
technology current at the time of the hybrid study. Values shown for the
rotary piston spark ignition engine were estimated from Curtiss-Wright data,
appropriately adjusted to reflect a consistent set of automotive accessories
for all engines. Weights and SFCs for the compression ignition engine are
based on turbocharged, divided-chamber designs. Weight and volume values
for the Rankine cycle reflect positive displacement expander systems. The
Stirling cycle characteristics are representative of engines using Rhombic
drive devices. As noted earlier, more recent designs using swash-plate
mechanisms and double-acting pistons are lighter and more compact.
A broader view of the tabulated results may be obtained by
referring to the plots of Figures 4-15, 4-16, and 4-17, where the data are
grouped by heat engine characteristic and are plotted over a range of engine
horsepower. The SFC plot, Figure 4-15, shows that the Stirling and com-
pression ignition engines provide the lowest fuel consumption over the
horsepower range. 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, Figure 4-16, 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. The reciprocating piston spark ignition engine is
4-50
-------
Figure 4-15.
Heat Engine SFC
Comparison
(Ref. 3-3)
04
RANKINE
BRAYTON
SPARK IGNITION
COMPRESSION IGNITION
STIRLING
50 100 150 200
ENGINE RATED HORSEPOWER
250
3000
2500
2000
O
1500
UJ
z
z 1000
UJ
500
STIRLING
(rhombic!
RANKINE
(positive
displacememi
Figure 4-16.
COMPRESSION
IGNITION
BRAYTON
SPARK IGNITION
reciprocating)
SPARK IGNITION
(rotary)
J
50 100 150 200 250
ENGINE RATED HORSEPOWER
300
Figure 4-17.
Heat Engine Volume
Comparison
(Ref. 3-3)
50
- 40
uT
i30
Ul
5 20
UJ
10
Heat Engine Weight
Comparison
(Ref. 3-3)
STIRLING
(rhombic)
RANKINE
(positive
displacementl
COMPRESSION
IGNITION
SPARK IGNITION
(reciprocating)
BRAYTON
SPARK IGNITION
rotary)
50 100 150 200 250
ENGINE RATED HORSEPOWER
300
4-51
-------
competitive with the Brayton cycle for the family car and is superior to the
Brayton cycle for higher horsepower applications. The Stirling (rhombic
drive technology) and Rankine (positive displacement) engines run signifi-
cantly heavier than other heat engine types and, in view of the criticality
of weight in relation to battery power density requirements, these systems
would appear to be unsuitable for hybrid use without further development.
4.3.4.4 Emissions
Hydrocarbon (HC), carbon monoxide (CO), and oxides of
nitrogen (NOX) emission are given as design-load specific mass emissions
for each of the five engine types in Figure 4-18 (Ref. 3-3). These charts
allow a comparison of specific mass emissions for each engine category
for both 1970 state of the art and projected technologies. The values indi-
cated do not provide a direct correlation to vehicle emission, since the
latter depend on the part-load operating cycle and its attendant emission
characteristics.
The spark ignition engine values may be compared with
results obtained by the Bureau of Mines using standard 350-CID engines
in a test program conducted for EPA with the goal of supplying information
for a hybrid vehicle engine design (Ref. 4-16). At steady-state conditions
with exhaust control equipment consisting of a catalytic converter and
exhaust gas recirculation (EGR), minimum HC and CO emissions were
obtained at air-fuel ratios between 16 and 17. At these conditions, the
emissions in gr/bhp-hr were:
HC 0.2 to 0.4
CO 1.5 to 2.5
NO 1.0 to 1.5
X.
The HC compares quite well with the engine design load values
in Figure 4-17 for projected technology. Both CO and NOX exceed the pro-
jected technology levels by a factor of two or more. Nonetheless, at the
4-52
-------
0.8
0.6
| 0.4
0.2
f 10
Q.
0-5
(a)
-i iiMit-OF-THE
J ART TECHNOLOGY
PROJECTED
TECHNOLOGY
I fa i I fa
: (bi
^ <->
2
- 1 —
CVJ CO
CSI =3
»
-------
measured levels, it would appear that, if this engine were operated in a
hybrid vehicle, the 1976 interim Federal emission standards could be met.
But the referenced work estimates that EGR alone would not be sufficient to
reduce NO enough to meet the original 1976 Federal emission standards.
Diesel engine emissions compare favorably with spark ignition
engine emissions for the 1970 technology case. High-pressure, high-temper-
ature combustion in the diesel may, for the projected technology, limit the
reduction in NO to a level somewhat higher than that achievable with the
spark ignition engine operating at ultralean conditions.
Satisfactorily low levels of both HC and CO are achievable
in current Brayton cycle systems. The major problem in gas turbine
design for low emissions relates to NO . The EPA AAPS Brayton program
is currently supporting the development of new lean-combustion burner
designs that show promise of meeting 1976 emission objectives.
The emission levels shown for the Rankine cycle engine were
based largely on General Motors research engines, Doble automobile tests,
Williams system steam data, and burner data from various sources. The
most critical emission specie of the Rankine engine is NO . Possible
X.
techniques for reducing NO are being examined in the EPA AAPS Rankine
cycle program that is supporting the investigation and development of new
burner types and control techniques such as EGR.
The Stirling engine provides very low emission levels. The
CO and HC levels are presently below the 1976 standards and various
methods, such as exhaust gas recirculation, are being tested to reduce NO
X
emissions.
4.3.4.5 Hybrid Operation
A number of possible engine operating modes for the hybrid
vehicle were discussed in Section 2.4. As a rule, the selection of mode
will depend on a number of considerations, among which are the requirements
4-54
-------
for vehicle performance under urban and highway operating conditions,
vehicle exhaust emissions and fuel economy. These conditions, in turn,
will interact with the choice of drivetrain arrangement, series or parallel.
In general, the fixed speed, fixed power output mode does
not provide the necessary flexibility required to meet vehicle energy require-
ments. Two other modes of hybrid operation for the engines under con-
sideration are feasible. One is the constant rpm and variable power output
mode. This mode is frequently used in engine/generator power units and
may be applied to the series configuration of the hybrid vehicle for all of
the heat engines under consideration. It may be particularly suitable for the
gas turbine (single-shaft design), with variable turbine nozzle or compressor
inlet guide vanes to maintain control over turbine inlet temperature and
air-fuel ratio. Generally, the parallel hybrid configuration will require
variable rpm and variable power operation.
The variable rpm and variable power output mode at optimum
throttle setting suggests an interesting possibility: attainment of an optimum
SFC level over the complete engine load range. The low SFC may favorably
influence vehicle exhaust emissions provided that the air-fuel ratio require-
ments for low SFC can be maintained compatible with the requirements for
low emissions.
4.3.4.6 Engine Feasibility for Hybrid Vehicles
Based on engine weight and volume and allowable propulsion
system weight and volume, only the gas turbine, spark ignition reciprocating
and spark ignition rotary engines are considered feasible for installation
into a hybrid heat engine/battery automobile (Ref. 3-3). The other engines
would impose excessive performance requirements on other components
because of reduced weight and volume available on board the vehicle. This
is particularly true for battery systems, where performance requirements,
in the form of power and energy density, are much higher than any future
expectations for advanced battery designs. Recent reductions in Stirling
engine weight and volume might permit use of this engine in a hybrid, but the
4-55
-------
desirability of such use has not been examined in sufficient depth to revise
the conclusions cited.
It is of interest to note that all performance and physical
characteristics for these engines are based upon designs that meet the rapid
response and wide range in engine speed and power required for current
conventional automobiles. Engines designed specifically for a hybrid
automobile may possibly be reduced in size and weight. Improvements in
exhaust emissions and fuel economy might also result from a new design.
Verification of these projections is not currently available.
4-56
-------
5. HYBRID HEAT ENGINE/FLY WHEEL VEHICLE
-------
5. HYBRID HEAT ENGINE/FLYWHEEL VEHICLE
5. 1 SYSTEM DESIGNS AND OPERATION
5.1.1 Lockheed Missiles and Space Co. , Inc.
Work was performed by Lockheed Missiles and Space Co. (LMSC)
in the investigation of inertial energy storage under two separate contracts. The
first, Flywheel Feasibility Study and Demonstration (Ref. 3-1), had as its
objectives the analytical determination of the feasibility of the flywheel hybrid
as a low-emission propulsion system for urban vehicles (family car, commuter
car, delivery van, and intracity bus) and the demonstration and performance
evaluation of full-scale flywheels for hybrid applications. The second, Fly-
wheel Drive Systems Study (Ref. 3-4), as applied to the family car, was
directed toward advancing the development of flywheel systems technology
including: (a) the experimental development of final designs of flywheel auxil-
iary equipment (housings, bearings, seals, etc.), (b) the experimental
demonstration of positive energy containment in burst tests of flywheels,
(c) safety"analyses, (d) use of engine emission data supplied by the U.S. Bu-
reau of Mines (Ref. 4-16) in analyses of hybrid vehicle emissions, and (e)
systems coordination for the transmission studies (see Section 5. 3.2) con-
ducted by Mechanical Technology, Inc. (MTI) and Sundstrand (Refs. 5-1 and
5-2, respectively).
Two conceptual drivetrain arrangements (Figure 5-1) were
examined by Lockheed for the heat engine/flywheel family car. The first
replaces the conventional hydrokinetic transmission with the flywheel drive
transmission in an engine-mounted configuration. In the second arrange-
ment, the conventional transmission was replaced by a torque damper and
the flywheel drive transmission was incorporated into an independent rear
suspension transaxle package. Since it resulted in packaging advantages,
Lockheed favored the latter configuration.
5-1
-------
Drivetrain Arrangement for Engine-Mounted
Flywheel /Transmission
FUEL
FLYWHEEL
TRANSAXLE
Drivetrain Arrangement for Transaxle
Flywheel/Transmission
Figure 5- 1.
Lockheed Conceptual Drivetrain Arrangements
(Ref. 3-1)
5-2
-------
The drivetrain (Figure 5-2) consists of a heat engine coupled
to the flywheel and the vehicle wheels through a planetary/hydrostatic power
splitting transmission.
0.5 KW-HR
16,000 TO 24,OOORPM
CRUISE POWER
3:1 RATIO RANGE
PEAK ROAD POWER
15:1 RATIO RANGE
• ROAD
•40% NORMAL
HP RANGE
2:1 RPM RANGE
FLYWHEEL TRANSAXLE PACKAGE
•PLANETARY/HYDROSTATIC POWER
SPLITTING TRANSMISSION
Figure 5-2. Lockheed Transaxle Fly wheel/Hybrid
Transmission Configuration (Ref. 3-1)
The heat engine provides cruise power, drivetrain losses,
accessory power, and flywheel recharging power. An internal combustion,
spark ignition, reciprocating engine was selected by LMSC for use in the
flywheel/hybrid passenger car for operation under variable speed (2:1) and
load conditions.
The flywheel provides the power required for vehicle
acceleration. Flywheel charging is accomplished by the heat engine and
by regenerative braking of the rear wheels during deceleration. The flywheel
was fabricated of 4340 steel and was sized on the basis of the vehicle kinetic
energy at maximum speed. The preliminary configuration selected by
Lockheed for the family car flywheel (Figure 5-3) was a 20.4-in. -dia con-
ical section with a constant radius flare at the periphery. This flywheel
configuration was fabricated and tested during the feasibility study (see
Section 5. 3. 1). However, the incorporation of the burst containment struc-
ture dictated a reduction in flywheel diameter to comply with automotive
5-3
-------
BEARING A
BEARING B
SEAL
Figure 5-3. Preliminary Lockheed Flywheel Design --
Family Car (Ref. 3-4)
space requirements. Accordingly, the baseline flywheel configuration
(Figure 5-4) was selected and mounted in the transaxle configuration (Fig-
ure 5-1). The energy storage capacity of the flywheel is 0. 5 kW-hr at a
design speed of 24, 000 rpm. The weight of the flywheel alone is 86 Ib,
which constitutes approximately 46 percent of the weight of the complete
flywheel assembly.
Flywheel selection was predicated on the use of available
materials and near-term (5 to 10 years) technology. This precluded the
use of the more advanced materials investigated by Johns Hopkins Univer-
sity (Ref. 5-3) for flywheel application. In addition, Lockheed imposed cer-
tain design constraints as screening criteria within the general volume and
weight limitations imposed by the EPA Vehicle Design Goals, Appendix A.
These constraints included the following: (a) the flywheel assembly maximum
weight should not exceed 50 percent of the 1,600 Ib specified for the entire
propulsion system, (b) the flywheel assembly volume should not exceed
50 percent of the total 35 ft volume specified for the propulsion system,
(c) the flywheel assembly radius should not exceed 2 ft and the assembly
height should not exceed 1 ft, (d) a speed constraint of 24,000 rpm based
5-4
-------
CONTAINMENT RING
8.4 in.
FLYWHEEL
Figure 5-4. Lockheed Baseline Flywheel (Ref. 3-4)
on the availability of relatively inexpensive seals and bearings, and (e) the
flywheel assembly cost should not exceed $0. 50/W-hr of energy storage
capacity. The flywheel assembly was assumed to incorporate a housing
suitable for maintaining the required vacuum, bearings, and seals. Fly-
wheel assembly cost was estimated at three times flywheel material cost
plus $3. 00/lb for the housing.
The flywheel was designed to operate in a partial vacuum
of 0.01 atm (7.6 mm Hg) to reduce windage losses since rim speeds would
be supersonic. Lockheed determined that the flywheel gyrodynamic
forces in the family car were only a minor consideration. It was further
concluded that the choice of flywheel spin axis orientation (i.e. , vertical,
longitudinal, transverse) can be based primarily on vehicle packaging
considerations. The effect of these forces on a vehicle operating on
icy roads was not investigated and would require further study.
5-5
-------
Two flywheel drive transmission configurations (Figure 5-5)
were considered by Lockheed. The double transmission (series configura-
tion) was preferred to the single transmission (parallel configuration)
because it offered greater control flexibility by allowing the heat engine
speed to be controlled independently of either flywheel speed or vehicle
speed. The power-splitting transmission favored by Lockheed is a
combination of a mechanical-differential and hydrostatic transmission.
DOUBLE TRANSMISSION
ENGINE
TRANS MISSION
C3-.\ RANGE)
FLYWHEEL
»OWER SPLITTING
IRAN? MISSION
GEARBOX AND
DIFFERENTIAL
VEHICLE
SINGLE TRANSMISSION
ENGINE
FLYWHEEL
POWER SPLITTING
TRANSMISSION
VEHICLE
Figure 5-5. Lockheed Power-Splitting Transmission
Configurations (Ref. 3-1)
The basic control concept proposed by Lockheed (total kinetic
energy) is intended to control the heat-engine output so as to hold the sum of
the kinetic energies of the flywheel and the vehicle at a constant value. This
value is essentially equal to the kinetic energy of the fully loaded vehicle at
maximum cruise velocity (where flywheel kinetic energy can be zero). The
actual levels of vehicle and flywheel kinetic energies are monitored and
summed. The difference between this sum and the constant reference value
constitutes an error signal to the engine to recharge the flywheel. Recharging
5-6
-------
continues until the actual summed kinetic energies match the predetermined
value. According to Lockheed, this system will account for energy reclaimed
by regenerative braking and minimize the size of the flywheel.
5.1.2 Johns Hopkins University, Applied Physics
Laboratory
Concurrent with the work done by Lockheed, an experimental
and analytical study of high specific energy flywheel systems for use in
automotive propulsion systems was conducted by Johns Hopkins University,
Applied Physics Laboratory. This study had two objectives: (a) proof-of -
principle demonstration of the use of filamentary or composite materials
of high uniaxial tensile strength in rotor configurations that would have
significantly higher specific energies (i.e., 30 W-hr/lb) and (b) theoretical
evaluation of the performance of such flywheels alone and in combination
with heat engines, in four classes of vehicles: family car; commuter car,
delivery van, and intracity bus.
Vehicle evaluation studies by Johns Hopkins indicated that the
city bus was the only one of the four classes that could meet performance
specifications using a flywheel-only propulsion system. Heat-engine/flywheel
hybrid propulsion systems would satisfy the performance requirements for all
four classes.
The near-term heat engine choice was the spark ignition
engine, but the gas turbine engine was considered to offer the greatest
promise for the future because of its low specific weight, its potential
for minimizing emissions, and its higher operating speed, which is close
to that of the flywheel.
The general details of a hybrid propulsion system selected
by Johns Hopkins for a commuter car is shown in Figure 5-6. This car has
a curb weight of 1,400 Ib and a loaded weight of 1,700 Ib. A series config-
uration powertrain is envisaged by Johns Hopkins with the heat engine
mounted in the front of the car and the flywheel-transmission system mounted
5-7
-------
HATCH BACK DOOR
CURB WEIGHT 14OOPOUNDS
LOADED WEIGHT 1700 POUNDS
HEAT ENGINE 32 BHP
FLYWHEEL SYSTEM 70 POUND ROTOR
2kW-h
CONTINUOUSLY
VARIABLE
TRANSMISSION
AND DIFFERENTIAL
Figure 5-6. Johns Hopkins Heat Engine/Flywheel Hybrid Commuter Car
(Ref. 5-3)
in the rear, essentially equalizing the weight distribution. The continuously
variable transmission is integrated with the differential. All of the power-
train components in the rear of the car are rigidly connected to one another
and are shock mounted on the spring mass. The rear wheels are indepen-
dently suspended. This arrangement provides space for a disc flywheel of
2 kW-hr or a bar of approximately 1. 5 kW-hr, although the use of a system
with this amount of energy will depend on the ability to contain the rotor,
acceptable vehicle handling characteristics, and the development of low-
friction bearings and seals.
In evaluating each of the four types of vehicles, Johns Hop-
kins made the following assumptions:
a.
Composite discs would be superior to bars with respect to
packaging volume and would have approximately the same
specific energy (these were assumed for the applications
studies).
5-8
-------
b. The heat engine would be operated in an on-off mode
in supplying energy to the flywheel; all drive wheel
power is supplied by the flywheel in the proposed series
configuration.
c. A 72 percent overall transmission efficiency (engine-
to-flywheel-to-drive wheels) for all driving modes.
A continuously variable transmission of the power-splitting
type was felt by Johns Hopkins to best satisfy the requirements for a hybrid
vehicle. (Lockheed recommended the same type transmission.)
The drivetrain schematic is shown in Figure 5-7. The power
required for accessories (power steering, power brakes, air conditioning,
fans, pumps, and lights) is taken from the central gearbox, and an input
shaft is provided for externally supplying power to charge the flywheel
in the event of a rundown or while the vehicle is parked. To conserve the
stored energy, the clutch of the flywheel is disengaged whenever the vehicle
is parked. When the flywheel and drive clutches are engaged, power can be
transmitted from the gearbox to the drive wheels, or vice versa (for
regeneration).
The operator controls are analogous to those on present vehicles.
An "ignition" switch engages the flywheel clutch, a selector lever positions the
transmission for drive, neutral, or reverse, and accelerator and brake
pedals command vehicle accelerations and decelerations. (A conventional
parking brake, not shown, would be provided. ) A central control box called
the power programmer, translates operator commands into the desired
mechanical responses.
5.2 SYSTEM DESIGN REQUIREMENTS AND ACHIEVEMENTS
5.2. 1 Lockheed Missiles and Space Company, Inc.
5. 2. 1. 1 Design Requirements
Propulsion system performance requirements, based on
Revision C to the EPA Vehicle Design Goals (see Appendix A), were calculated
in terms of tractive effort to provide a common basis to the contractors for
5-9
-------
ELECTRICAL
FLYWHEEL
CHARGE UNIT
HEAT ENGINE
2 1
SPEED RANGE
ON
OFF
MECHANICAL BRAKES
DIFFERENTIAL
ENGINE
CLUTCH
(ONE-WAY)
(1500-3000)
I
h-^
o
CONTINUOUSLY
VARIABLE
TRANSMISSION
(DRIVE. NEUTRAL.
REVERSE)
FLYWHEEL
CLUTCH
WHEEL SPEED
10:1 SPEED
REDUCER
VEHICLE
START-UP
AND SHUT DOWN
POWER
SETTING
FLYWHEEL
(15 000-300001
FLYWHEEL
SPEED
POWER
PROGRAMMER
FLYWHEEL RE-CHARGE COMMAND
LEGEND
POWER LINKS
PRIMARY CONTROL LINKS
(REDUNDANT LINKS AND
INTERLOCKS NOT SHOWN)
SHAFT RPM TYPICAL VALUES
FOR FAMILY CAR
OPERATOR COMMANDS
VEHICLE ON-OFF
DRIVE. NEUTRAL. REVERSE
ACCELERATE
BRAKE
EMERGENCY BRAKING
Figure 5-7. Johns Hopkins Flywheel Hybrid Power Control System (Ref. 5-3)
-------
transmission design. Average values of vehicle weight were assumed
(i. e. , test weight of 4, 300 Ib and gross weight of 5, 000 Ib); both are 300 Ib
below the maximum allowable. The tractive effort profile for vehicle accel-
eration and cruise requirements is shown in Figure 5-8.
The heat engine was sized on the basis of a sustained 70 mi/hr
on a 5 percent grade. This requires 93 road hp, which, when combined with
drivetrain losses (10 percent) of 10. 3 hp and accessory power requirements
of 5 hp brings the total required to 108 hp. The vehicle performance require-
ments of Appendix A could, therefore, be met as follows: from a standing
start, the heat engine power rises to a constant value of 108 hp at 26 mi/hr,
remains at this value to 70 mi/hr, and then declines from 70 to 85 mi/hr.
To match current automotive capabilities, however, Lockheed increased the
low-speed tractive effort requirement from 1,523 Ib to one-half the test
weight, or 2, 150 Ib. This level of tractive effort provides a capability for
acceleration from 0 to 15 mi/hr in 6 seconds on a 30-percent grade.
5.2.1.2 Performance Results
A comparison of several types of family car transmissions
studied by Lockheed in both the single and double configuration (See Figure 5-5)
is presented in Table 5-1. The efficiency is calculated for operation of the
Q
family car over a DHEW Urban Dynamometer Driving Schedule with the
assumption that all braking is regenerative. The best transmission on the
basis of highest efficiency (which minimizes emissions) and the lowest cosf:-
was the power-splitting transmission. The weight and volume of the power-
splitting transmission, although greater than for the hydrostatic trans-
mission, were not considered excessive by Lockheed.
As part of the Flywheel Feasibility Study (Ref. 3-1), a con-
ventional spark ignition heat engine was selected by Lockheed on the
combined basis of comparative costs, brake specific fuel consumption (BSFC),
Department of Health, Education, and Welfare (predecessor to EPA),.
5-11
-------
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-------
Table 5-1. Lockheed Family Car Transmission Comparison
(Ref. 3-1)
Item
DHEW Schedule
Efficiency
(Normalized)
Volume, ft3
Weight, Ib
Cost, $
Electric
Single
0. 588
3.4
488
641
Double
0.369
4.0
536
689
Hydrostatic
Single
0.745
3.3
280
403
Double
0.626
3.7
289
469
Power Splitting
Single
1.000
3.7
311
261
Double
0.835
5. 1
391
341
weight, and volume. A summary of these parameters, together with the
analytically derived emissions and BSFC are presented in Table 5-2 for
each engine type considerd by Lockheed. Vehicle emissions calculated by
Lockheed in the Feasibility Study for the family car were based on EPA-
supplied parametric curves of best and worst emissions as a function of
horsepower. From these, emissions were calculated for the best and worst
cases for each of the candidate heat engines during simulated operation over
the DHEW Urban Driving Schedule. The effect of cold starts was not included
and the results were regarded as very preliminary. Fuel consumption, desig-
nated as Cruise Specific Fuel Consumption, is based only on the trend curve
developed from single values of BSFC plotted as a function of horsepower
as obtained from a survey of engine manufacturer's data. Such horsepower
and BSFC values are frequently for wide-open throttle operation; hence,
these results were regarded as extremely preliminary because they
represent a single wide-open throttle BSFC case for the heat engine required
power level of 108 hp.
In contrast, during the Flywheel Drive Systems Study
(Ref. 3-4) Lockheed calculated BSFC on the basis of an EPA-supplied
BSFC map for a medium-sized V-8 engine and EPA-furnished accessory
5-13
-------
Table 5-2. Lockheed Family Car Power-train Comparison (Ref. 3-1)
Item
0
Volume, ftj
Weight, Ib
Cost, $
Vehicle Cruise
Specific Fuel
Consumption,
Ib/hp-hr
Calculated Hot
Start Vehicle
Emissions,
gm/mia '
HC
CO
NOX
1970
Family
Car
16
817
958
0.47
3. 25
36.9
3.22
Engine Plus Power Splitting Transmission
Spark Ignition
21.0
1, 034
1,050
0.486
Best
0.083
1.42
0. 591
Worst
0.695
2.57
1. H
Diesel
24.2
1,,390
1,771
0.424
Best
0.278
0.308
1.39
Worst
0.487
11.6
4. 52
Turbine
8.5
672
5,749
0.919
Best
0.016
0. 503
1. 94
Worst
0. 127
5. 84
3.43
Rankine
37.2
1,492
1,476
0.774
Best
0. 229
1.88
0.434
Worst
0.347
2.85
0.650
Includes air conditioning and other accessories. Does not include any
cold start allowance or catalyst exhaust treatment. Engine specific
emissions provided by EPA.
power loads. A number of computer runs were made over the DREW Urban
Driving Schedule to determine fuel economy for various drive configurations
and engine speed curves. Results of these runs showed that average fuel
economy values over the urban driving cycle ranged from 7. 3 to 13. 7 mpg
for the hybrid heat engine/flywheel vehicle, depending on assumed values
for transmission efficiency and the operating regime over the engine BSFC
map. Comparable figures for the conventional passenger car with auto-
matic transmission ranged from 11 to 12 mpg, depending on the assumed
transmission efficiency.
5-14
-------
Subsequent emission calculations made by Lockheed, as a
part of the Flywheel Drive Systems Study (Ref. 3-4), were based on
emissions data provided by the U.S. Bureau of Mines (Ref. 4-16). These
data were taken on two 350-CID engines at various engine speeds, percent
power, air-fuel ratios, spark advance, EGR rates, and with and without
an Engelhard oxidizing catalyst (type unspecified).
Results of the computer simulations over the DHEW Urban
Driving Schedule are shown in Table 5-3 for both a conventional three-speed
automatic transmission and a flywheel/hybrid vehicle. Results are predi-
cated on both vehicles being equipped with an oxidizing catalyst and with
EGR. Cold start effects are not included because of a lack of data.
Table 5-3. Lockheed Vehicle Exhaust Emission
Comparison (Ref. 3-4)
Drive Systema
Conventional Three -Speed
Automatic Transmission
Hybrid Heat Engine/
Flywheel Vehicle
Calculated Hot Start Emissions,
gm/mi
HC
0.39
0.38
CO
0. 95
1. 12
NO
X
3.98
1.21
a4, 300 Ib family car spark ignition engine with oxidation catalyst
and EGR. Engine specific emissions from U.S. Bureau of Mines
data.
5-15
-------
The main conclusions reached by Lockheed with regard to
the flywheel/hybrid vehicle were as follows:
a. A comparative analysis of heat engine emissions for a hybrid
flywheel drive contrasted with a conventional three-speed
automatic transmission shows that without a catalyst the fly-
wheel drive offers HC, CO, and NOX emission reductions.
With a catalyst, HC and CO emissions were generally equiva-
lent between hybrid and conventional drives; the flywheel
drive offered a significant reduction only for NOX emissions.
b. Fuel economy over the DHEW Urban Driving Schedule for the
flywheel transmission is predicted to be roughly equivalent to
that of a conventional transmission.
c. The estimated cost of ownership, size, and weight of a family
car flywheel drive falls within the established EPA Vehicle
Design Goals.
5. 2. 2 Johns Hopkins University, Applied Physics
Laboratory
The analytical studies made by Johns Hopkins for each of the
four types of vehicles were predicated upon the EPA-supplied vehicle per-
formance parameters. These are summarized in Appendix A. Both fly-
wheel only and hybrid configurations were considered. For each vehicle
class, an appropriate driving "cycle" is represented as the sum of a num-
ber of discrete cruise, acceleration, and deceleration phases in terms of
the percentage of time spent in each (Figure 5-9).
The operating mode of the flywheel-hybrid vehicle essentially
decouples engine operation from the time sequence of vehicle operation.
The engine is either on (at full load and nearly fixed speed) to charge the
flywheel, or off. For passenger cars, the high rotor energy density allows
energy storage for at least seven accelerations from 0 to 60 mi/hr, which, with
regeneration, allows the vehicle to negotiate with ease a trip on any of the
cycles without the possibility of the energy use rate being greater than the
charge rate. Therefore, the time sequence of the modes is immaterial, and
the resulting performance and emission estimates are based on average
horsepower and velocity for the various phases.
5-16
-------
DU
1
E
£ 25
8
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\ \ \
V = 22.1 mi/hr
r"\ /
/ \ /
!\ \ \
0 0.2 0.4 0.6
/\
\
\ _
\
, \
0.8 1.
FRACTION OF TOTAL TIME
Figure 5-9. Johns Hopkins University
Driving Cycle (Ref. 5-3)
The analytical results for the family car and commuter car
are summarized in Tables 5-4 and 5-5. The heat engine was sized to
permit cruise at the design speed with all accessories operating. Emissions,
fuel economy, and ranges are quoted without the air conditioner operating.
Fuel economy figures were calculated by Johns Hopkins from BSFC data
reported in Reference 5-4. Note that the flywheel subsystem weight (which
includes a protective housing in addition to the flywheel) is a significant per-
centage greater than the weight of the flywheel alone.
Emissions were calculated on the basis of EPA-supplied data
in the form of a band of brake specific emissions (Ib/hp-hr) applicable for
several types of engines.
The spark ignition engine hybrid commuter car was selected
by Johns Hopkins for the purpose of investigating the influence of variations
in various parameters. The base case refers to the spark ignition engine
hybrid reported in Table 5-5 without the air conditioner operating. As
examples, when the flywheel rotor weight Wr is increased, Figure 5-10
shows that fuel economy decreases and total emissions increase due to the
increased curb weight. The upswings in the hydrocarbon (HC) and carbon
monoxide (CO) emissions for the smaller rotors are due to the effects of
start-up emission penalties.
5-17
-------
Table 5-4. Johns Hopkins Results for Family Car Without Air Conditioner Operating
(Ref. 5-3)
Performance Parameters
Gross Engine Horsepower
W, /W.,
fw (fw+e)
Flywheel Rotor Weight, W lb
Wfw - WR« lb
Fuel Economy at V , mpg
' max ^&
Flywheel Only Range at 40 mi/hr, mi
Flywheel Only Range on Grade, mi
No. of Accelerations per Flywheel Charge
Flywheel Charge Time, minutes
Cycle Performance
Fuel Economy, mpg
HC Emission Ratio
NO Emission Ratio
CO Emission Ratio
Flywheel Cycles per 100 Miles
Flywheel Only Range, mi
Percentage of Time Engine On
Flywheel Only
NA
1.0
584
239
NA
42.3
5. 5
49
NA
NA
NA
NA
NA
4. 5
22.4
NA
Hybrids
Gas Turbine
91. 0(200. 0)a
0.62(0. 52)
353(389)
159(143)
9.2(11.8)
25.6(21.0)
3.3(2.7)
30(24)
7.7(2.9)
11. 3(14.4)
0.02(0.01)
1.97(1.97)
0.20(0. 15)
7.4(9.0)
13.5(11. 1)
21. 1(9.6)
Otto
94. 0
0. 31
163
92
11. 8
12. 2
1. 5
13
3. 5
14.4
0. 31
1.73
0. 58
16.0
6.2
21. 1
Steam
91.0
0.27
138
85
10. 0
10.0
1. 3
11
3.0
12. 2
0.46
0.88
0. 57
18.9
5. 3
21. 1
Numbers in parenthesis are for a gas turbine engine sized for same fuel economy as Otto engine.
Emissions ratioed to the original 1976 Federal emission standards.
NA = Not Applicable
W- = weight of flywheel subsystem, lb
W,, = weight of flywheel subsystem plus engine, lb
\ iv/ T e i
WD = weight of rotor, lb
H.
CD
-------
Table 5-5. Johns Hopkins Results for Commuter Car Without Air Conditioner
Operating (Ref. 5-3)
vO
Performance Parameters
Gross Engine Horsepower
W /W
fw' (fw+e)
Flywheel Rotor Weight, W , Ib
Wfw - WR' lb
Fuel Economy at V , mpg
' max ^6
Flywheel Only Range at 40 mi/hr, mi
Flywheel Only Range on Grade, mi
No. of Accelerations per Flywheel Charge
Flywheel Charge Time, minutes
Cycle Performance
Fuel Economy, mpg
HC Emission Ratiob
NO Emission Ratio
X
CO Emission Ratio
Flywheel Cycles per 100 Miles
Flywheel Only Range, mi
Percentage of Time Engine On
Flywheel Only
NA
1.0
217
112
NA
38.3
4.9
42
NA
NA
NA
NA
NA
4.7
21.5
NA
Hybrids
Gas Turbine
32.2(109)a
0. 53(0. 33)
103(64)
72(45)
10.9(25. 5)
18. 5(11. 5)
2.3(1.4)
20(12)
6.4(1.2)
13. 0(30.6)
0.01(0.01)
0.76(0.76)
0. 10(0.08)
9.9(15.8)
10.2(6.3)
23. 1(6.8)
Otto
33.2
0.41
74
61
25.5
13. 1
1.6
14
4.6
30.6
0. 11
0.67
0.22
13.8
7.3
23. 1
Steam
32.2
0.25
35
49
17.8
6.2
0.8
6
2.2
21.2
0.20
0.34
0.24
28.9
3. 5
23. 1
Numbers in parentheses are for a gas turbine engine sized for same fuel economy as Otto engine.
Emissions ratioed to the original 1976 Federal emission standards.
NA = Not Applicable
Wr = weight of flywheel subsystem, lb
W,, = weight of flywheel subsystem plus engine, lb
W = weight of rotor, lb
XV
-------
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<
o
(-
IU
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cc
LU
a.
20
0
-20
-100
0 100 200 300
CHANGE IN ROTOR WEIGHT (%)
400
Figure 5-10. Effect of Flywheel Rotor Weight
for Otto Hybrid Commuter Car,
Johns Hopkins (Ref. 5-3)
The effects of the drivetrain efficiencies and the external
resistance (drag and tire friction) on fuel economy are shown in Figure 5-11,
The emissions on a gm/mi basis will vary inversely with fuel economy.
Increasing the regeneration efficiency by 20 percent (from 50 to 60 percent)
is seen to result in a 12 percent increase in fuel economy. The direct linear
effects of drive and charge efficiencies are equivalent: a 10 percent increase
in either results in a corresponding 10 percent increase in fuel economy.
Because of the nature of the driving cycle assumed (small percentage of high
speed cruise time) the effects of drag variations are not pronounced. A
20 percent drag decrease results in a 6.2 percent increase in fuel economy.
Conclusions reached by Johns Hopkins regarding the flywheel
only or flywheel/hybrid vehicles were as follows:
a.
The heat engine /flywheel hybrid propulsion systems satisfy
the performance requirements for all four classes of
5-20
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20
10
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oc
-10
-20
REGENERATION
EFFICIENCY
CHARGE OR DRIVE
EFFICIENCY
-20
-10
10
20
PERCENT CHANGE
Figure 5-11.
Effect of Drivetrain Efficien-
cies and External Resistance
for Otto Hybrid Commuter
Car, Johns Hopkins (Ref. 5-3)
vehicles (i.e., family car, commuter car, delivery van,
and intracity bus).
b. The spark ignition engine is the near-term choice for the
heat engine.
c. The gas turbine engine was believed to offer the greatest
promise for the future because of its low specific weight,
its potential for minimizing emissions, and its operating
speed, which is close to that of the flywheel.
d. The Johns Hopkins University hybrid system emission anal-
yses were considered inconclusive because of the lack of
data at the time of their study on the operation of engines at
single design points or over a very limited speed range. 1"
10
Since that time, data on a spark ignition engine was acquired by the Bureau
of Mines (Ref. 4-16).
5-21
-------
5. 3 COMPONENT DESIGN REQUIREMENTS AND ACHIEVEMENTS
5. 3. 1 Flywheel
5.3.1.1 Lockheed Missiles and Space Co., Inc.
Concurrent with the overall vehicle applicability and
configuration tradeoff studies conducted by Lockheed (Ref. 3-1), flywheel
design studies were conducted prior to fabricating and testing candidate
flywheels (Ref. 3-4). Six basic flywheel geometries were considered in
the Lockheed preliminary design studies for automobiles and buses. These
included the pierced uniform disc, an unpierced uniform disc, a constant-
stress disc, a truncated conical disc, a rim-type flywheel, and the bar-type
configuration. Although this volume of the report addresses hybrid auto-
mobile technology, the work performed by Lockheed on flywheels for buses
is of significance and will be included in discussions in this section.
Only those materials that could be obtained in mill-run quanti-
ties were considered for the flywheel design studies. Eleven materials were
chosen on the basis of high strength and/or low cost, as shown in Table 5-6.
Recommended working stress was derived from studies for a hybrid fly-
wheel design life of 10 million cycles. To facilitate a quantitative comparison,
Lockheed calculated a normalized cost as follows: material cost was divided
by the working-stress-to-density ratio and then divided by the resulting value
for the least expensive material. Thus, the normalized cost represents the
cost for each material to provide an equivalent energy storage capability for
a given flywheel configuration. These normalized costs, shown in the right-
hand column of Table 5-6, indicate that the most cost-effective materials
are E-glass, S-glass, and 4340-grade steel. The filamentary composites,
however, seem to be readily applicable to only the bar-type flywheel
geometry. These filamentary composites might be used in a rim-type
flywheel, but in Lockheed's opinion the web attachment and balancing
requirements appeared to present significant problems. The 4340-grade
steel was felt to be an excellent candidate material for application to low-
cost flywheels in a disc configuration.
5-22
-------
Table 5-6. Flywheel Materials Studied by Lockheed (Ref. 3-1)
Material
18NI-400
(Maraging Steel)
18NI-300
(Maraging Steel)
4340 Steel
1040 Steel
1020 Steel
Cast Iron
2021-T81
(Aluminum)
2024-T851
(Aluminum)
6A1-4V
(Titanium)
E -Glass
S -Glass
Density
(P) ,
(Ib/in/)
0.289
0.289
0.283
0.283
0.283
0.280
0.103
0. 100
0. 160
0.075
0.072
Poisson's
Ratio
<")
0.26
0.30
0.32
0.30
0.30
0.30
0.33
0.33
0.32
0.29
0.293
Ultimate
Tensile
(Ftu) ksi
409
307
260
87
68
55
62
66
150
200
260
Yield
Tensile
(Fty) ksi
400
300
217
58
43
37
52
58
140
-
-
Working
Stress
(cr)ksi
260
200
130
36
25
20
26
35
82
67
87
(S
(x 106)
0.900
0.692
0.459
0.127
0.088
0.071
0.252
0.350
0.512
0.890
1.210
Material
Cost
($/lb)
2.25
2.25
0.60
0.30
0.30
0.30
0.53
0.50
4.00
0.42
0.75
Normalized
Cost
($/lb)
5.30
/
6.S9
2.78
5.00
7.23
8.94
4.45
3.03
16. 55
1.00
1.31
-------
The design capacity of the family car was placed at 0. 5
kW-hr based on a required 0. 395 kW-hr capacity. Similarly, the design
capacity of the bus flywheel was set at 1. 0 kW-hr capacity based on a
required capacity of 0.604 kW-hr.
A total of 24 hybrid flywheel designs were found to be
suitable based on the design constraints. These are summarized in
Table 5-7, where it will be seen that 11 were suitable for application
to the family car with an energy storage capacity of 500 W-hr. The
optimum design for the family car from the standpoint of minimum
assembly cost, size, and weight is the constant-stress disc of 4340-grade
steel. The cost shown represents the projected assembly cost in auto-
motive quantities after amortization of necessary tooling. On the basis
of this preliminary screening, the decision was made by Lockheed to
fabricate two 46-Ib, 24, 000 rpm flywheels from 4340-grade steel in the
exponential geometry.
Similarly, the acceptable hybrid flywheel configurations
for the city bus are seen in Table 5-7 to cover essentially the same
range of geometries and materials as for the family car with the exception
of the two filamentary composite flywheels. Again, the optimum flywheel
for the city bus appeared to be the 4340-grade steel flywheel in the constant-
stress disc configuration. However, it was decided by Lockheed that little
additional information would result from fabrication and test of the 1. 0 kW-hr
flywheel in essentially the same configuration and of the same material as
chosen for the 0. 5 kW-hr flywheel, Therefore, the decision was made to
fabricate a bar flywheel of S-glass filamentary composite bonded with
epoxy having a 1 kW-hr capacity.
The intial constant-stress disc configuration was an
exponential disc design. The early dropoff of both the radial and tangential
stresses in this design indicated that more mass could be added to the
periphery of the wheel, increasing the stresses throughout most of the
flywheel and thereby improving the overall efficiency. Accordingly, a
small rim was added, approximately 0. 5 in. thick and tapering back into
5-24
-------
Table 5-7. Flywheel Configurations Studied by Lockheed (Ref. 3-1)
Capacity
(kw-hr)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Material
4340
4340
1040
2021-T81
2024-T851
4340
2021-T81
2024-T851
4340
2021-T81
2024-T851
4340
4340
1040
2021-T81
2024-T851
4340
2021-T81
2024-T851
4340
2021-T81
2024-T851
E-Glass
S -Glass
Geometry
Pierced Disc
Solid Disc
Solid Disc
Solid Disc
Solid Disc
Conical
Conical
Conical
Constant -Stress
Constant -Stress
Constant -Stress
Pierced Disc
Solid Disc
Solid Disc
Solid Disc
Solid Disc
Conical
Conical
Conical
Constant -Stress
Constant -Stress
Constant -Stress
Bar
Bar
Flywheel
Speed
(rpm)
21,749
22.821
13, 453
13, 394
21,940
23,410
18, 698
22,970
24, 000
24, 000
24, 000
17, 308
21,746
10,678
13, 394
17,714
22,873
18,097
20,857
24, 000
24, 000
24, 000
15, 132
19, 199
Flywheel
Weight
-------
the flywheel. With this design, the configuration was nearly conical from
the hub out to a radius of 7. 25 in. For ease in manufacture, it was decided
to let this part of the configuration become conical, with a constant radius
flare from that point to the rim. The final diameter, as fabricated, was
20.466 in. with a maximum disc thickness of 0. 576 in. This is the same
configuration as shown in Figure 5-3 and discussed in Section 5. 1. 1 for
the family car hybrid/flywheel vehicle.
Tests on the first steel flywheel were conducted to verify
windage losses and to determine the energy density at disintegration speed.
Various levels of pressure in the test pit were used to determine the windage
losses of the flywheel. The flywheel was driven by an air turbine; driving
torque was estimated at various speeds from the power output curves of the
turbine and the turbine inlet line air pressure. (An alternate means of
determining torque was by use of a disc brake. ) A comparison of the power
losses calculated from measurements of torque and speed with the losses
calculated using an EPA-supplied empirical equation is shown in Table 5-8.
In the test-to-failure, the flywheel was accelerated until
disintegration occured at 35,590 rpm. This represented a peripheral velocity
of 3, 170 fps, an energy density for the flywheel rotor of 26. 1 W-hr/lb, and a
total stored energy of 1. 1 kW-hr •which exceeded the design specification by a
factor of about two and accordingly provides a margin of safety. Lockheed
indicated that failure may have been initiated at an occlusion on the surface
of the flywheel.
Table 5-8. Lockheed Comparison of Power Loss Calculations (Ref. 3-1)
Flywheel
Speed,
rpm
14, 110
12, 530
Test Pit
Pressure,
psia
8.35
14.7
Loss (Calculated
from Turbine Char-
acteristics), hp
14
13
Loss (Calculated
from EPA
Equation), hp
15.3
17.3
5-26
-------
Power density, spindown, and acoustic noise tests were
conducted on the second steel flywheel. Power density measurements
verified that at least 5, 000 W/lb of usable power could be extracted from
the 20.4 in. flywheel at various speeds. Spindown tests were conducted by
taking the flywheel to 24, 000 rpm and uncoupling it from the turbine. The
test pit was evacuated to 0. 2-mm Hg for this test. After 20 minutes of
spindown, flywheel speed was down to 8,700 rpm, at which time the pit
was vented to the atmosphere. At this low pressure the flywheel windage
losses are essentially nonexistent, and the bearing and the brake disc were
the major sources of drag (approximately 3 hp between 24, 000 and 20, 000
rpm). Bearing losses were high because of oil-flooding of the bearings.
Two glass flywheels were fabricated using the same bar-type
configuration, but different layup procedures. Both were constructed of Ferro
Corporation S-1014 glass fiber with 828/1031/NMA resin. Resin content was
22 percent by volume. The fabricated weight and dimensions were not reported
by Lockheed for the bar-type flywheels. However, analysis of the test results
indicates that the flywheel weight was approximately 77 Ib. Design speed for
the bar-type flywheels was 20, 000 rpm with an energy storage capacity of
1. 0 kW-hr.
The No. 1 glass flywheel of unidirectional construction was
tested to demonstrate energy density, power density, spindown, and disinte-
gration speed. Disintegration occurred prior to reaching the design speed
of 20, 000 rpm. The maximum energy storage capacity at failure (15, 070 rpm)
was 0. 568 kW-hr as compared to the design point of 1. 0 kW-hr. Lockheed
reported that the massive disintegration that occurred after failure made it
difficult to determine the failure mode. The break in the hub was stated to
have the appearance of a tensile failure, indicating that a high transverse
force was involved. This might have been attributable to transverse
delamination.
5-27
-------
During the energy density test of the No. 2 flywheel,
disintegration occurred at 14,690 rpm. Again, the flywheel and hub were
completely destroyed, although the added transverse fibers did serve to
hold most of the longitudinal fibers together. Similar to the first flywheel,
the hub had the appearance of a tensile failure. Lockheed reported that the
failure may have occurred by means of the fiberglass moving longitudinally
out of the hub.
Lockheed conclusions regarding the steel flywheel for use
in the family car were as follows:
a. The production cost of complete family car flywheel assemblies
was projected to be $100, plus or minus $15 depending on
flywheel configuration.
b. All the elements of a practical family car flywheel assembly
are available without further technology development.
c. Early estimates of flywheel system losses as provided to the
transmission contractors were proved by hardware testing to
be highly conservative. Flywheel windage, bearing, seal, and
vacuum pump losses were substantially lower than earlier
predictions.
d. Prevention of flywheel burst due to overspeed can be obtained
by allowing the flywheel to grow plastically into the contain-
ment ring. Total containment of a flywheel burst at energy
levels representative of what might be the case for a full-size
vehicle were not successfully demonstrated with lightweight,
low-cost materials. Containment of a burst at 0. 86 hp-hr
was demonstrated with a 192-lb steel ring and at 0.46 hp-hr
with a 167-lb composite ring.
5. 3. 1.2 Johns Hopkins University, Applied Physics
Laboratory
Experimental work conducted by Johns Hopkins University
was directed toward a demonstration of the "superflywheel" concept in which
energy densities of 30 W-hr/lb for flywheel rods or bars could be achieved.
Spin tests of small diameter composite rods (up to 0. 25 in.) and filamentary
single strands were conducted in which the several candidate materials ex-
ceeded the flywheel rod energy density goal of 30 W-hr/lb. Follow-on tests
of 30-in.-long, 1-lb rods or bars achieved 82 to 94 percent of the desired
goal.
5-28
-------
The results of the 30-in. -long, small diameter rod tests
conducted at Johns Hopkins are summarized in Table 5-9. The 4- and 8-mil
boron single strand filaments were tested prior to the installation of a diffu-
sion pump in the test chamber vacuum system and were tested at 8 X 10
Torr and 4. 7 X 10 Torr, respectively. All other tests were conducted at
_3
a nominal pressure of 1 X 10 Torr (1 Torr = 1 mm Hg abs).
The boron filaments were tested in a spin fixture powered by
a motor having a rated speed of 39, 000 rpm. This was insufficient to fail
the boron filament rods, all of which were intact after spindown. The
indicated energy densities for these materials are at the maximum indicated
rpm and do not represent the energy density at failure. All other materials
were tested to failure with higher speed drive systems.
Results from these tests indicated that the flywheel rod energy
density goal of 30 W-hr/lb could be achieved with composite rods; valuable
information was acquired on the selection of materials for subsequent tests
of 1-lb bars. In reviewing the failure mode of the small rods, Johns Hopkins
stated that a significant portion of their kinetic energy was dissipated by
microfracture or vaporization of the matrix material.
Based upon the test results of the small rods, a joint decision
was made by Johns Hopkins and EPA to fabricate the 1-lb bars or two mate-
rials: S-glass fiber in an epoxy matrix and a graphite/epoxy composite.
The S-glass fiber was selected because of its low cost ($1. 00/lb) and known
characteristics. The filamentary graphite was selected over the filamentary
boron because it has equivalent strength and potential for future price re-
duction (Johns Hopkins stated current prices of about $200/lb, but indicated
an order of magnitude reduction would be possible in the near future for the
graphite). The EPA/Johns Hopkins selection of the two markedly different
materials (S-galss and graphite) was made to compare the strength levels
and modes of failure.
Bars of each composite material were obtained from Hercules,
Inc. Fabrication of the bars by molding (which would obviate the need for
any surface machining) was considered, but was not used because of high
5-29
-------
Table 5-9. Summary of Composite Materials, Rod Tests, Johns
Hopkins (Ref. 5-3)
Teat
Drive
Syatem1
Mounting
Syctem?
AVCO Boron FlUmenU
4-mll
8-mll
Gene
Dlehl
Dlehl
ral Technolog;
Tube
Tube
r Corp. Boron/
Magnesium 20-Mil Preform
1
Here
Dlehl
ulea Graphite/
1 /8-lnch Square
1
2
3
Foth
S/I
G/S
G/S
crgill & Harve
1/16 Inch Square
1
2
3
4
5
6
7
PPG
S/I
S/I
S/I
S/I
S/I
S/I
G/S
/BBI Type 525
Epoxy
Epoxy
RTV
RTV
Epoxy
y Graphlte/Epo
RTV
RTV
RTV
RTV
RTV
RTV
Epoxy
E-Glaa«/Poly«
0. 098 Inch in Diameter
1
2
3
4
5
6
PPC
G/S
G/S
G/S
G/S
G/S
G/S
/BBI Type 10J
Epoxy
Epoxy
Epoxy
RTV
RTV
RTV
5 E-Glass/Pol;
0. 018 Inch in Diameter
1
2
PPC
G/S
G/S
,/BBI R-Comp.
Epoxy
RTV
osition Glaaa/P
0. OUB Inch in Diameter
1
2
3
4
Coh
G/S
G/S
G/S
G/S
jmbia Product
Epoxy
Epoxy
RTV
RTV
> (Shakeapeare)
Epoxy, 0. 250 Inch In Diameter
1
2
S/I
S/I
RTV
RTV
Max. Speed
(rpm)
W -
38 000
34 000
Wr'
31 500
Wr
24 500
19 000
31 300
51
w =
22 400
22 BOO
22 400
28 900
26 200
22 100
33 000
•ater (48% Fiber
W *
r
23 600
23 400
24 000
-19 800
24 000
23 200
pester (58% Fibe
W '
27 000
26 700
olyester (55% F
W =
28 900
30 700
< 1 8 000
26 400
E-Glass/
W -
r
14 400
14 600
Max. Stress
(kai)
D. 00035 and 0. 000
424
340
). 00075 pound
254
0. 027 pound
105
66
180
0. 0066 pound
91
94
91
151
124
88
195
Volume)
0. 015 pound
116
118
123
-84
123
115
r Volume)
0. 016 pound
165
1GO
ber Volume)
0. 015 pound
177
194
<65
149
0. 091 pound
41
42
E/W3
(W-h/lb)
1 4 pound
48
.18
31
20
12
33*
17
18
17
28
23
1C
3(i4
19
IB
19
-13
19
18
24
24
28*
31<
<11
23
7
7
Remarks
lind did not fail; spei'il
limited by motor
No failure; speed
limited
Counter slopped just
before rod failure
Failure before slroln
synchrom/alion
Some mihcntioiis mil
pulled mil uf lutlilri
5-30
-------
Table 5-9. Summary of Composite Materials, Rod Tests (Continued)
Test
Drive
System1
Mounting
System*
Max. Speed
(rpm)
Max. Stress
(ksi)
E/W'
(W-h/lb)
Remarks
Corning Glass Rods, 0. 106 Inch in Diameter.
30. 9 Inches Long
0. 026 pound
G/S
G/S
G/S
G/S
G/S
G/S
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
9 240
9 480
9 780
9 900
9 540
10 260
29
28
26
32
30
36
Failed awav from point
of max. stress
d.o.
PPG Glass Rods in
Steel Holder
G/S
Acrylic
W , =0. 0015 pound; W , = 0. 32 pound
glass K steel
25 100
165
14
E/W based on equivalent
full circular brush (see
text)
1 Drive System:
2 Mounting System:
Si I: Speed increaser
G/S: Globe motor with spindle
Diehl: Diehl motor
RTV: Dow Corning Silastic 734, room temperature vulcanizing
Epoxy: Armstrong epoxy
Acrylic: Acrylic cement
Tube: Stainless steel tube support with epoxy cement
3 Stress and specific energy calculations assume constant rod cross-section, uniform
mass distribution, and 30-inch length (spin diameter) except where noted; 1 ksi 1000 lb/in2.
4 For the graphite/epoxy and R-glass/polyester materials, the better results were obtained
with the Globe motor and epoxy mounting system.
5-31
-------
tooling costs. The bars, therefore, were fabricated by laying up the
composite tape to the required thickness and forming a plate from which the
bars of square cross section were cut. Curing problems associated with the
scotch ply tapes resulted in the S-glass/epoxy plate final form being less than
the desired thickness. As a result, the square bars cut from the plate
weighed only 3/4 Ib instead of the desired 1 Ib.
Results of the tests are shown in Table 5-10. The first test
JH-1 was, as indicated, a facility check-out run using an available E-glass
bar. Because of the leaks in the vacuum system (believed by Johns Hopkins
to be attributable to the turbine drive spindle seal), it was not possible to
achieve the desired vacuum levels. The vacuum achieved for each test is
shown in Table 5-10, where it will be noted that the highest pressure,
25 X 10" Torr, was experienced on test No. JH-4. Johns Hopkins expressed
the opinion that this was satisfactory for the short duration test, however,
since the bending stresses induced in the rod by aerodynamic drag were
less than 50 psi.
It will also be noted that all bars in spin tests failed to meet
the expected stress levels (260,000 psi for S-glass; 200,000 psi for graphite)
and the energy storage capacity of the flywheel bar of 30 W-hr/lb. Tensile
tests of the two materials indicated that although the S-glass met or exceeded
the expected stress level, the graphite/epoxy samples achieved an average
stress of only 164,000 psi (84 percent of expected). Johns Hopkins indicated
that the most probable reason for the lower tensile strength of the graphite/
epoxy was the fact that the prepregnated tape, which was not that normally
used by Hercules because of scheduling problems, resulted in only a 53 per-
cent fiber volume instead of the expected 59 percent.
In the opinion of Johns Hopkins, differences between the stress
levels achieved in the tensile tests and those achieved in the spin tests were
attributable to several factors. Among these are: maintaining fiber align-
ment and fiber content, and achieving more uniform properties.
5-32
-------
Table 5-10. Test Results for 1-lb Bar: Speed, Stress, and Specific
Energy at Failure, Johns Hopkins (Ref. 5-3)
Parameters
Material
Cross Section
Weight, Ib
Speed, rpm
Stress
ksi
percent
E/W, W-h/lb
Vacuum, Torr
Test Number
JH-la
E-Glass/
Polyester
13/16-in.-
dia
1. 10
19,900
89
--
13.2
1.8 X 10"2
JH-2
S-Glass/
Epoxy
0.57-in.-
square
0.73
29, 100
204
79
28.2
6. 3 X 10"2
—
S-Glass/
Epoxy
0. 56-in.-
square
0.72
b
b
b
b
b
JH-3
Graphite/
Epoxy
0.79-in.-
square
1.00
28,000
136
68
26.1
17 X 10~2
JH-4
Graphite/
Epoxy
0.78-in.-
square
0.99
28,200
137
69
26. 5
25 X 10"2
JH-5
S-Glass/
Epoxy
0. 57-in.-
square
0.72
27,200C
178
69
24.7
19 X 10~2
Facility and instrumentation checkout
No test- -facility failure
°Test aborted at this speed. Rod subsequently failed at 24,700 rpm
Percent of expected value quoted by Hercules
in
i
oo
-------
High-speed photographs of the failure mode for each of the
two types of rods tested revealed a significant feature of filamentary fly-
wheel failure compared to metal flywheels. The photographs showed that
both types of rods were essentially destroyed in less than 1 ms and before
motion of the containment ring was detected. Analysis of the relative rates
of rod destruction and containment ring response by Johns Hopkins revealed
that only 1 to 2 percent of the kinetic energy of the rod was transferred to
the containment ring, with the remainder of the energy being dissipated by
pulverization of the rod itself. In contrast, a steel disc rotor will generally
fracture into several large fragments with transfer of nearly all energy to
the containment ring.
The following conclusions were reached by Johns Hopkins re-
garding the testing of filamentary and composite rods and bars:
a. Spin tests demonstrated the ability to achieve 48 W-hr/lb
(without failure) with boron filaments; at burst, 36 W-hr/lb
was achieved with small graphite/epoxy composite rods, and
31 W-hr/lb was achieved with small R-glass/polyester
composite rods.
b. The larger 1-lb composite rods did not meet the desired
30 W-hr/lb. The best sample S-glass/epoxy achieved
28 W-hr/lb while the graphite/epoxy achieved 26 W-hr/lb.
c. Tensile tests indicated that the graphite/epoxy material
was substandard. While the S-glass/epoxy bars achieved
satisfactory stress levels in tensile tests, numerous sur-
face defects may have contributed to the inability of this
material to meet 30 W-hr/lb requirements. With improved
processing techniques, Johns Hopkins felt confident that
energy densities in excess of 30 W-hr/lb could be achieved.
d. Analysis of the failure modes of both the filamentary and
composite materials tested showed that only 1 to 2 percent
of the kinetic energy of the rod was transferred to the
containment ring.
5-34
-------
5.3.2 Transmission
The transmission converts energy output of the engine to
useful levels of torque at the vehicle wheels. Ideally, the transmission
should have the following characteristics:
a. High efficiency over the normal operating range
b. Control simplicity for optimum performance
c. Low volume for compactness
d. Low noise
e. Low specific weight
f. Reverse-power and braking capability
g. Capability of absorbing road shocks
h. Low power consumption during engine start and at idle
The operational and economic feasibility of a hybrid system depends in
large part on the above features and on a reasonable low cost for the
transmission.
The selection or design of a transmission for a hybrid system
will depend primarily on the type of hybrid powertrain arrangement, the energy
storage method used, and the relative speed between various powertrain elements.
In a heat engine/fly wheel hybrid, the transmission links three main components:
engine, flywheel, and drive wheels. Figure 5-12 shows the power connection
for both a parallel and series hybrid configuration. In the parallel system
shown, power can be delivered to the drive wheels directly from the engine or
through a flywheel. Because the flywheel spins at very high speeds, unique
forms of wide speed range transmissions are required.
In a heat engine/battery hybrid, the electric drive motor acts
as the transmission for the series configuration. Hence, the discussion in
this section addresses the subject of unique transmission for heat engine/
flywheel hybrid vehicles only.
5-35
-------
ENGINE
LINK 1
c
LINK 2
FLYWHEEL
LINK
DRIVE
WHEELS
PARALLEL SYSTEM
ENGINE
LINK 1 ^
pi YWMFFI
r i_ T vwntt L.
LINK 2
DRIVE
WHEELS
SERIES SYSTEM
Figure 5-12. Parallel and Series Configurations for Energy
Flow in Hybrid Vehicles (Ref. 5-2)
5. 3.2. 1
Parallel Configuration Operation
Under EPA sponsorship two studies were conducted on
transmission designs for a parallel configuration flywheel hybrid system.
These studies were conducted by Sundstrand Aviation (Ref. 5-2) and
Mechanical Technology, Inc. (MTI) (Ref. 5-1). Both studies examined
(a) the development of total energy transfer systems from the hybrid
engine to the drive wheels and (b) the management of the energy storage
system.
As shown in Figure 5-12, for parallel operation, two types
of transmissions are required. From flywheel to the load an infinitely
variable transmission is needed (Ref. 5-2). A standard three-speed
transmission is adequate between the engine and the load for all engines
5-36
-------
considered, except for a single-shaft gas turbine. It requires a continuously
variable speed transmission - a transmission that has not been fully
developed.
5.3.2.1.1 Sundstrand Aviation Study
The Sundstrand study assessed the practicality of a trans-
mission for use in a heat engine/flywheel hybrid system for a full-size
family car- In this study, a number of possible types of links between
the engine, flywheel, and drive wheels were analyzed: mechanical, hydro-
static, and hydromechanical.
An infinitely variable hydromechanical transmission was
selected between the flywheel and the drive wheels. For the engine-flywheel
transmission, the engine speed was fixed at each power level to ensure
operation near minimum SFC or minimum emission levels. A fixed speed
ratio between the engine and the flywheel was not sufficient and hence a
transmission was required. Sundstrand selected a combination mechanical,
hydromechanical, and hydrostatic transmission system for links 1, 2, and
3, respectively (Figure 5-12). This transmission, called Baseline 8A, is
made up of a five-element differential, several hydraulic units (variable
and fixed displacement), clutches, controls, and associated gearing. By
controlling the displacement of the variable hydraulic unit, it is possible
to control the reaction torques in the five-element differential. By con-
trolling these torques, it is possible to control the direction of power flow
and hence extract energy from the flywheel and supply this energy to the
"output" or take energy from the "output" and supply it to the flywheel, as
required.
In considering the Federal Emissions Test Driving Cycle
it was discovered that with the Baseline 8A transmission the engine was
not running continuously at minimum fuel consumption conditions. But
the required engine speed versus vehicle speed characteristics for minimum
SFC could be very closely approximated by putting a clutch on the input, such
that at light accelerator pedal loads below 50 mi/hr; the engine input comes
5-37
-------
into the variable hydraulic unit (V-unit), and at heavy accelerator pedal loads
below 50 mi/hr, or at any load above 50 mi/hr, the engine input comes directly
into the differential gear set. This arrangement, the alternate 8C transmission,
shown in Figure 5-13, allows the engine to run at a slower and more economi-
cal speed at the slower road speed and lighter load conditions, but allows
higher engine speed operation (when the engine would otherwise be power
limited) at the higher load and/or higher road speed conditions.
INPUT
CLUTCH
ENGINE
OVER-RUNNING
CLUTCH
MODE 2
CLUTCH
MODE 1
CLUTCH
f— OUTPUT
^-OUTPUT
CLUTCH
V
F
FW
£5
- VARIABLE DISPLACEMENT HYDRAULIC UNIT
- FIXED DISPLACEMENT HYDRAULIC UNIT
- FLYWHEEL
- FIVE ELEMENT DIFFERENTIAL
- MECHANICAL CLUTCH
Figure 5-13. Sundstrand Alternate 8C Transmission (Ref. 5-2)
5-38
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On the basis of fuel consumption calculations utilizing ideal
energy storage versus ideal non-energy storage transmission systems oper-
ated over the Federal Emissions Test Driving Cycle, Sundstrand concluded
that the amount of energy available for storage and reuse, as regenerated on
deceleration by a light vehicle operated over the Federal Emissions Test
Driving Cycle, was relatively small. This fact was reflected in Federal
Emissions Test Driving Cycle fuel consumption calculations made for the
Baseline 8A and Alternate 8C transmission and for a typical three-speed
automatic. These results, shown in Table 5-11, indicate that the Baseline
8A system has a poorer fuel economy than the Alternate 8C system, and
that both of these have poorer fuel economy than the standard transmission
when transmission losses are estimated and included in the energy compu-
tation ("real" case).
The results of constant speed fuel consumption calculations
for the two hybrid storage/transmission systems compared with results for
a typical three-speed transmission are shown in Table 5-12. As expected,
transmission 8C has fuel economy that is superior to transmission 8A up
to approximately 50 mi/hr. It can also be seen that the three-speed auto-
matic transmission has better fuel economy below 50 to 60 mi/hr. Above
this value, the two hydromechanical flywheel transmissions exhibit superior
fuel economy. These results largely reflect the fact that the flywheel trans-
missions are configured to permit the engine to operate at or near minimum
SFC at higher speeds.
In conclusion, Sundstrand stated that:
a. A combination of mechanical, hydromechanical, and hydrostatic
transmissions is a practical means of providing power for the
flywheel, heat engine, and drive wheel links.
b. The selected transmission provides an infinitely variable ratio
between the flywheel and the vehicle wheels, and a nonlinear
ratio (fixed by vehicle speed) between the heat engine and fly-
wheel. Although the engine speed is not independent of the
flywheel speed, it does operate near its minimum SFC line.
5-39
-------
Table 5-11. Sundstrand Transmission Evaluation -- Federal
Emissions Test Driving Cycle (Ref. 5-2)
Transmission
"Real" (with estimated
transmission losses)
"Ideal" (zero trans-
mission losses, fly-
wheel losses are
included)
Results, mpg
Flywheel Energy
Storing Transmission
Baseline
8A
7. 96
9.78
Alternate
8C
9.26
12.66
Nonenergy Storing
Three-Speed Automatic
Transmission
11. 14
11.99
Note: Vehicle weight 4,300 Ib
Table 5-12. Sundstrand Estimate of Constant Speed Fuel
Consumption (Ref. 5-2)
Constant
Speed,
mi/hr
20
30
40
50
60
70
80
Results, mpg
Baseline 8A
9. 82
11.41
14.42
16.04
16. 59
16. 25
13. 32
Alternate 8C
12.62
12.47
15. 59
16.80
16. 59
16.25
13. 32
Three -Speed Automatic
15. 58
17. 86
17.92
16.92
14.30
11. 91
10.34
Note: Vehicle weight 4, 300 Ib
5-40
-------
c. The specified spark ignition heat engine with the selected
transmission has a greater computed fuel consumption over
the Federal Emissions Test Driving Cycle than that of a typical
three-speed automatic transmission. Cruise fuel consumption
is greater than for the three-speed automatic below 50 mi/hr
and less above this speed.
d. The theoretical fuel economy benefits that can be gained from
the flywheel energy storage concept over a "light duty" cycle
such as the Federal Emissions Test Driving Cycle is minimal
because of the small amount of energy available for storage and
reuse. In fact, when the "cost" of storage in terms of power
loss is included, there is no benefit. The more "severe" the
acceleration/braking duty cycle relative to maximum vehicle
capability and the heavier the vehicle, the greater are the bene-
fits derived from the flywheel energy storage concept.
5.3.2.1.Z Mechanical Technology, Inc. Study
The study performed by MTI basically arrived at the same
conclusions as Sundstrand. Mechanical Technology proposed a power split-
ting transmission (Ref. 5-1). This transmission is an infinitely variable,
stepless unit that obtains torque multiplication and control by hydraulic
principles. It is intended for use in a medium-size automobile.
The unit differs from the torque converter or fluid coupling
hydrodynamic-type transmissions in that the power in the hydraulic circuit
is transferred by fluid static pressure at low flow rates, whereas the hydro-
dynamic unit uses high flow rates and the inertial motion of the fluid to
transfer power. Basically, the transmission system consists of a flywheel
planetary gear train, hydraulic variable displacement elements, connecting
drive gears, an output planetary gear train, and a control system.
As shown in schematic form, Figure 5-14, three planetary
gear trains are used in the assembly to (a) provide a power path for the
flywheel, (b) direct the output power when the vehicle is in the high-ratio
range, and (c) provide a low-ratio range power path.
5-41
-------
PUnrtiry "A"
Primary
. Swshplitf
Input
1200 UM
to
RPM
ro
\\\\\\\
1 '
\
24,000 RPM
10,000 IPX
\
I I /
////// /
Secondary TranavlsalOD
Pliaectr?
1
_
6.5 J
2.75
.1.0
=
=
/]
1.00
1.00
\
\
1.27
1.00
Variable Displacement
+ 3200 RPM
~ 3200 PSI
7.5 In3/r«v.
ELEMENT 1
l_
\
\
Variable Displacement
+ 3400 RPM
3400 PSI
6.0 In3/rev.
ELEMENT III
Variable Displacement
+ 3200 RPM
i2OO PSI
7.5 1 r>. 3 ' T *v .
ELEMENT II
)
/,,,
Variable Displacement
f 3400 RPM
" 3400 PSI
6.0 InVrev.
ELEMENT IV
1.00
1.10
/
/
1.00
1.62
1.00
1.00
l.OQ
IT"
Planetary 'V
Trlniallllon
Output
0 RFM
to
4470 RPM
f*^- Low Range Brake
High Range Clutch
Notes: 1. Rear Axle Differential Katie - j.55:l
2. Rear Wheel Diameter - 2.1 -t.
3. Vehicle Speed Equals '-it*. - ^ph
at TransalseioTi Output Spee^
f, e /./. Tn ___
Figure 5-14. Schematic of the MTI Recornmended Transmission Design (Ref. 5-1)
-------
The overall transmission consists of two separately controlled
split-path hydrostatic links: the primary path that establishes a given ratio
between the engine and vehicle for optimum torque-speed loading of the engine
in a steady-state mode, and the secondary path that controls the direction and
magnitude of power flow to and from the flywheel during vehicle velocity
transient. In each of the primary and secondary sections, the hydrostatic
transmission consists of two identical positive displacement units - Elements I
and II for the primary and Elements III and IV for the secondary circuits.
The output torque is a function of the hydraulic pressure and
the displacement of the hydrostatic units. If the torque increases, the dis-
placement or pressure of the units must increase.
The secondary or flywheel drive section operates over a
relatively small speed ratio and only operates for short bursts of power.
The major power to and from the flywheel is transmitted by the planetary.
The hydrostatic drive functions on both sides of the mechanical drive serve
only as a positive speed control.
Figure 5-15 shows a comparison between the efficiencies of
powertrains for flywheel hybrid and the standard automobile for cruise
operation. As shown, the efficiency of the flywheel/hybrid powertrain
is substantially lower even though the transmission efficiency for the
hybrid transmission is higher (Figure 5-16). The fuel economy of the
hybrid automobile compared to the standard automobile is poor up to a
cruise speed of 50mi/hr, butat higher speeds it has superior fuel economy.
5.3.2.2 Series Configuration Operation
In the series configuration for the hybrid heat engine/flywheel
vehicle as discussed in Reference 5-3, the engine drives the flywheel and
the flywheel drives the car. In such a scheme, an infinitely variable
transmission is required between the engine and the flywheel as well as
between the flywheel and the load. Mechanical Technology, as did Sundstrand,
selected a hydromechanical infinitely variable transmission for this configu-
ration.
5-43
-------
100
•Standard Automatic Transmission
(Without Flywheel)
80
o 60 —
Flywheel/Hybrid Transmission Power Train
(With Inline Pierced Flywheel, P = 2.94 psi)
£ 40 *~4
E '
Cruise Power Train Efficiency =
40 50
Vehicle Speed, MPH
70
80
90
Figure 5-15. MTI Powertrain Efficiency Comparison at Cruise Power (Ref. 5-1)
-------
100
Flywheel/Hybrid Transmission
(With Inline Pierced Flywheel, P = 2.94 psi)
--! ~ t f
• --Standard Automatic Transmission (Without Flywheel)
J "Vehicle Weight = 4600 Ibs
1 0% Grade
H—Engine Accessories Include Air Conditioner-
(HP + HP , , ) x 100
out Fly-loss
Transmission Efficiency (Cruise)
40 50
Vehicle Speed, MPH
Figure 5-16. MTI Comparison of Transmission Efficiencies at Cruise Power (Ref. 5-1)
-------
5.3.2.3 Other Transmission Designs
There are several other types of transmissions that have
been evaluated. In an EPA-sponsored program "Automobile Gas Turbine
Optimization Study" several contractors studied transmission systems for
use with gas turbine automotive power plants. The single-shaft gas turbine
requires an infinitely variable speed transmission. Traction and belt
transmissions are two types of infinitely variable speed transmissions that
are discussed in Reference 5-5 and summarized in Reference 4-13. These
transmissions, which are candidates for use in the hybrid vehicle, are
briefly discussed below.
5.3.2.3.1 Traction Transmission
Traction transmissions are not currently commercially
available for large power output devices. A recent company development
effort in this area by Tracer, Inc. has resulted in the design of a special
metal traction device for transmitting torque at the high power levels
associated with automotive drives (Ref. 5-5).
The Tracor design uses toroidal discs and rollers, special
hydrostatic thrust bearings, and a specially prepared lubrication oil
(Monsanto's Santotrac 30). Roller position is controlled so that the trans-
mission can operate in a speed step-up, or in a speed step-down, or in a
direct-drive mode. According to Tracor, the favorable features of the
traction transmission include low noise, high-speed operation (up to
10,000 rpm input speed), compact size, a wide speed range capability,
and comparatively low cost.
The estimated efficiency of the Tracor traction transmission
serving a 250-hp engine is shown in Figure 5-17. Over a wide range of
vehicle speed, the transmission efficiency is between 85 and 90 percent,
somewhat lower than the performance of the hydromechanical system
shown in Figure 5-16.
5-46
-------
100
-------
5.3.3 Heat Engines
The discussion on this subject can be found in Section 4.3.4
for heat engine/battery hybrid vehicles. Though equally applicable to heat
engine/flywheel vehicles, it will not be repeated here.
5-48
-------
6. OTHER ENERGY STORAGE CONCEPTS
-------
6. OTHER ENERGY STORAGE CONCEPTS
6. 1 HYDRAULIC ACCUMULATOR SYSTEM
Some recent studies of hydraulic accumulators with application
to hybrid engines are reported in Refs. 6-1 and 6-2. Reference 6-1 reports
on a simple, basic accumulator system built and tested in the laboratory.
For straight hydraulic power transmission, pump-to-motor, an efficiency
of 80 to 85 percent is estimated in simulated steady, high-speed cruise.
Reference 6-2 also reports on studies involving a laboratory accumulator
hybrid engine system. References 6-3 and 6-4 report on studies of methods
of improving accumulator efficiency by reducing the thermal losses. Basically,
the approaches involve the use of metallic or fibrous materials in the high-
pressure gas to act as heat sink regenerators. Condensible gases greatly
improve the efficiency. Either method tends to maintain isothermal conditions
in the gas during compression and expansion cycles. Reference 6-3 indicates
reduction of losses to less than 2 percent using a foam fill. Reference 6-4
reports performance improvements of 15 to 40 percent using fine copper
strands. Any accumulator design that reduces the magnitude of the gas
pressure change with volume change results in improved accumulator
performance.
While some of these studies of hydraulic accumulators concern
simple laboratory hybrid engine systems, none considers the performance,
size, weight and practicality of such a system installed in a vehicle. A
preliminary analytical evaluation of a vehicular system proposed by the
U.S. Navy, Pacific Missile Range (PMR) is reported in References 6-5
and 6-6. Although several types of heat engines are applicable in the sys-
tem, the example studied involved a Rankine cycle. The system was
assumed to be installed in a 4, 000-lb automobile.
6-1
-------
6.2 ELECTRICAL CAPACITOR STORAGE SYSTEMS
These systems, at least with current state-of-the-art
capacitor technology, would have to be very large in volume to store the
necessary energy. Practical energy densities in capacitors are about one
ten thousandth that of a good battery. Because of high internal energy
leakage rates, energy storage in very high voltage capacitors could only be
for brief periods. Even if they could be built, the power transfer efficien-
cies would probably be very low.
6.3 PNEUMATIC ENERGY STORAGE SYSTEMS
These systems (not involving a liquid system, as in a
hydraulic accumulator) are inherently inefficient because of the large work
required to pump gases to high pressures.
6.4 THERMAL ENERGY STORAGE SYSTEMS
These systems are subject to the same large thermodynamic
efficiency losses suffered by the heat engine during initial energy generation.
No other temporary energy storage schemes have been proposed.
6.5 FUEL CELL/BATTERY SYSTEMS
These systems have been proposed, but these are subject to
the limitations imposed by the large volume, high cost, and limited lifetime
of current fuel cell systems.
6-2
-------
7. ASSESSMENT OF HYBRID POWERTRAIN
APPLICATION TO AUTOMOBILES
-------
7. ASSESSMENT OF HYBRID POWERTRAIN
APPLICATION TO AUTOMOBILES
7. 1 TECHNOLOGICAL AND ECONOMIC STATUS
At the time of program suspension, EPA funds expended on
the hybrid vehicle development program had resulted in some major tech-
nology advancements, a much clearer definition of critical problem areas,
and the establishment of preferable system operating modes. These re-
sults are indicative of information acquired in the very early phases of
development--namely, proof-of-principle. To date, the major portion of a
full prototype development program for Hybrid personal passenger cars has
never been performed. Some forms of hybrid systems could represent an
intermediate step between current automobile power plants and a future sys-
tem that relies totally on an energy storage device for delivering power to
the drive wheels.
7. 1. 1 Major Technical Accomplishments
Both heat engine/battery and heat engine/flywheel hybrid sys-
tems have been analyzed extensively. Operation of these systems for power-
ing an automobile on grades, at highway speeds, and in urban traffic has
been simulated on computers. This effort has resulted in the definition of
performance requirements and size and weight for components and subsys-
tems that make up the powertrain system. Exhaust emission levels and
fuel consumption levels were then determined analytically for various degrees
of design sophistication, and performance specifications were established for
critical components such as batteries, flywheels, and control systems.
Two heat engine/battery hybrid systems were built and tested.
One was a complete laboratory breadboard model and the other was installed
in a research automobile. In both cases, exhaust emissions were measured
and component, subsystem, and system efficiencies were determined on the
basis of experimental data acquired in system tests.
7-1
-------
Dual development programs were initiated for the energy
storage devices. These programs for development of batteries and flywheels
were divided into near-term and advanced concepts. The programs pro-
gressed beyond the design stage to the point where laboratory models were
tested to evaluate the concepts. Data •were acquired that showed how well
each design met the previously established specifications.
Concepts for fly-wheel transmission systems were analyzed
and designs were formulated to meet speed and power requirements. Per-
formance of these designs was simulated in analytical studies of vehicle
operation in stop-and-go driving and highway cruising.
7.1.2 Technical Development Status
7. 1. 2. 1 Systems
The powertrain has only been tested as an integrated system
for the heat engine/battery hybrid, not for the heat engine/flywheel hybrid.
Test results showed that the concepts were technically feasible and could
operate over the desired power and speed range. System efficiencies were
lower than desired and exhaust emissions from the spark ignition engines
could only approach the original 1976 Federal emission standards by means
of the application of a catalytic converter, exhaust gas recirculation, and
lean operation. This additional complexity compromises one of the original
hopes for the hybrid vehicle; i. e. , that these engine changes would not be
required. The contractors claimed that with further development some sys-
tem deficiencies could be corrected.
In assessing the results objectively it must be recognized that
the systems involved the use of contemporary hardware for components.
These powertrain elements had not been designed specifically for applica-
tion to a hybrid vehicle and, therefore, marginal performance levels might
be expected. This is particularly true for the heat engines and electric
motors. Test results might have been more encouraging had these systems
benefited from a comprehensive component development program aimed at
7-2
-------
optimization of performance levels for hybrid powertrains. An effort of
this type was initiated to develop more efficient lead-acid batteries.
Based on reasonably attainable performance for near-term
design of components and energy storage devices, only three heat engines
•were found to be feasible for installation in engine compartments of current
automobiles converted to a hybrid system. These power plants are the
spark ignition reciprocating engine, the spark ignition rotary engine, and
the gas turbine engine. Diesel, Stirling, and Rankine cycle engines proved
to be too heavy and too bulky. However, as these engines undergo succes-
sive development stages this conclusion may have to be revised, particularly
for new versions of the Stirling engine. An automobile designed specifically
for hybrid operation might also relieve the problem of differences between
required space/weight and allowable space/weight for the powertrain.
7.1.2.2 Components
Tests of commercial lead-acid batteries showed relatively
poor life at the performance required for this application. Battery rede-
signs and more advanced concepts for lead-acid cells resulted in the achieve-
ment of power and energy levels that represent a major increase over stan-
dard batteries for this application, leading to optimism regarding the ability
of these designs to meet most of the established performance specifications.
However, cycle life, while greatly improved, is still short of specified goals.
Resolution of this deficiency would require further development work for both
lead-acid and other battery types. Changes in heat engine operating modes
might result in reduced requirements in battery specifications.
Both conventional steel disc-shaped flywheels and advanced
material concept bar-shaped flywheels were tested to destruction. The
conventional design met the specified goals for energy storage level before
failing, but the advanced concepts failed at rotational speeds short of planned
levels. Fabrication problems with the advanced concepts and difficulty in
avoiding undesirable stress concentrations led to early failure. Resolution
of some of these problems by EPA contractors appeared to be possible,
7-3
-------
but suspension of the hybrid vehicle program prevented verification of the
proposed corrective action.
7-1.3 Economic Status
Only a limited investigation was made of the estimated con-
sumer purchase cost for a hybrid vehicle. The limitation to establishment
of a more precise figure was caused by the lack of a definitive system de-
signed specifically for mass production and by the paucity of data for costs
of mass produced components such as advanced concept flywheels, large
electric drive motors, and sophisticated electronic control systems. (The
greatest potential for cost reduction was found to reside with the control
system.) Based on preliminary coarse estimates, the purchase cost of
hybrid vehicles is expected to be significantly higher than that of current
automobiles, particularly for hybrid vehicles with advanced concept engines
(e.g., gas turbines). However; an analysis of lifetime costs for the hybrid
vehicle has not been performed wherein vehicle first cost, maintenance cost,
engine fuel cost, and battery replacement cost would be assessed.
7.1.4 Critical Problem Areas
Some critical problems which must be addressed before a
successful prototype hybrid vehicle is developed are:
a. Achievement of battery performance goals in terms of
power density, energy density, cycle life, and low cost.
b. Achievement of advanced concept flywheel goals in terms
of energy density and cycle life.
c. Demonstration of low-cost flywheel transmissions meeting
performance requirements in terms of efficiency, power
extraction, and durability over the entire operating range.
Assuming flywheel fatigue life exceeds vehicle life, no flywheel
replacement cost is involved.
7-4
-------
d. Development of lightweight, production type electric drive
motors and generators that have high efficiency at part-load
operation as well as at design load operation.
e. Design of an efficient, low cost, versatile, control system
and demonstration of its capabilities.
f. Development of a heat engine designed specifically for hybrid
mode operation and determination of any improvement in
exhaust emissions and fuel consumption.
g. Integration into a system of all improved components in a
gradual, step-wise fashion and verification of system per-
formance and durability.
The aforementioned goals for technical achievement would
necessarily have to be coupled with a continual reassessment of hybrid power
train production and operating costs. Failure to achieve any one of the stated
goals within a carefully planned prototype development program for a battery
or a flywheel hybrid would seriously jeopardize successful development of
this vehicle.
7.1.5 Alternative Vehicle Design Goals
Some additional system design considerations are worth men-
tioning at this point. First, some of the vehicle performance specifications
adhered to during the EPA contractor studies could be relaxed for evaluation
of a special purpose rather than a general purpose car. Allowing a reduction
in acceleration levels and peak cruising speeds is anticipated to yield marked
reductions in the required level of battery or flywheel power density. This
result stems from two sources: (a) reduced power required, and (b) additional
weight and volume available because of reductions in the size of the heat
engine and transmission and, for the hybrid battery vehicle, reductions in
12
the size of the generator and electric drive motor. Thus, rather than con-
sidering a hybrid vehicle designed to replace general-purpose personal
passenger cars in use in the U.S. , the objective rather would be to determine
Particularly for the series configuration.
7-5
-------
just what percentage of all the various transportation needs could be fulfilled
by this special-purpose, limited-use type of vehicle.
Second, consideration could be given to the multimode form
of hybrid vehicle operation. As an example, recharging of the energy stor-
age device (battery or flywheel) could be accomplished wholly or in part by
an external stationary power source rather than solely by the on-board heat
engine. The bimodal design would permit independent operation whereby
the vehicle is powered either by the battery (or flywheel) alone or by the
heat engine alone.
The multimode form of operation would of course require
relaxation of the specification for vehicle range. (However, the heat engine
would continue to be available for providing range extension whenever
required.)
The most important impact could be the transfer of the energy
resource base from petroleum-based fuels to coal, because electric gener-
ating plants would now supply all or part of the recharge energy.
7.2 PROGNOSIS FOR CONTRIBUTING TO NATIONAL
PERSONAL TRANSPORTATION NEEDS
Validity of any prognosis made for future application of an
alternative automobile power plant is highly dependent on the availability of
clarifying information on system performance and cost. In this regard, the
necessary background data on hybrid vehicles is still quite limited and,
therefore, the estimates given herein will bear further scrutiny (and possible
revision) as additional data may be acquired in the future.
The hybrid vehicle has been proven to be a valid functioning
system both by analysis and limited experimental tests, although not all of
the original program goals were met. At the inception of the EPA hybrid
vehicle program emphasis was placed mainly on reduction of exhaust emis-
sions to the then promulgated original 1976 Federal emission standards.
If the program were to be reactivated, the vehicle designs would now have
7-6
-------
to strike a balance between fuel e'conomy and exhaust emissions and system
performance would have to be re-evaluated in the light of the revised standards.
System efficiency requires further improvement to match
original goals, and such improvement appears to be quite possible. Vehicle
performance is marginal when configured with a conventional chassis and
off-the-shelf hardware modified to reflect improvements that evolved from
the EPA component development program. Although tests confirmed a major
reduction in exhaust emissions compared to 1970 model conventionally pow-
ered cars, the primary objective of providing very low exhaust emission
levels without exhaust after-treatment devices has not been met. The pros-
pects for further improvement are not good unless the heat engine is de-
signed specifically to operate in the hybrid mode. Furthermore, fuel con-
sumption levels were no better than those for conventionally powered cars
even with regenerative braking; again, some improvement might be possible
with a new type of engine.
An automobile designed specifically for hybrid operation and
for packaging of advanced design components and subsystems could fulfill all
performance specifications although durability (in particular battery and fly-
wheel cycle life) is still in doubt.
The purchase cost of a hybrid vehicle is currently estimated
to be excessive, particularly when equipped with advanced engine systems.
This is a major deterrent to further system development. However, the
economic evaluation of hybrid vehicle lifetime cost was not performed. In
addition, relaxation of vehicle specifications could result in significant re-
ductions in vehicle cost.
Hybrids of the type studied by EPA do not look promising as
yet for the general passenger vehicle. They might prove to be suitable for
limited-use, special-purpose cars. The bimodal hybrid vehicle might war-
rant further evaluation in light of its ability to derive a major portion of its
energy from nonpetroleum sources and, thereby, offer benefits to urban air
quality. This form of vehicle operation might enhance the viability of hybrid
electric and hybrid flywheel vehicles as a contender for meeting a significant
portion of public transportation needs while meeting energy conservation and
environmental goals.
7-7
-------
REFERENCES
-------
REFERENCES
PART II
2-1. Analysis and Advanced Design Study of an Electromechanical Trans-
mission, Report 17220.000, TRW Systems Group, Inc., Redondo
Beach, Calif. (April 1971) (Contract EHSH 71-002 for Office of
Air Programs, EPA).
3-1. Flywheel Feasibility Study and Demonstration, Report LMSC-
D007915, Lockheed Missiles and Space Co., Sunnyvale, Calif.
(30 April 1973).
3-2. Study of Unconventional Thermal, Mechanical, and Nuclear Low-
Pollution-Potential Power Sources for Urban Vehicles, Battelle
Memorial Institute, Columbus, Ohio (15 March 1968).
3-3. Hybrid Heat Engine/Electric Systems Study, TOR-0059(6769-01)-2,
Vol. I, The Aerospace Corp., El Segundo, Calif. (1 June 1971)
(Contract EPA F04701-70-C-0059).
3-4. R. R. Gilbert et al, Flywheel Drive Systems Study, Report
LMSC-D246393, Lockheed Missiles and Space Co., Sunnyvale,
Calif. (31 July 1972) (Contract EPA 68-04-0048).
3-5. G. H. Gelb, B. Berman, and E. Koutsoukos, Cost and Emission
Studies of a Heat Engine/Battery Hybrid Family Car, Report
21054-6001-RO-OO, TRW Systems Group, Inc., Redondo Beach,
Calif. (April 1972) (Contract EPA 68-04-0058).
4-1. G. H. Gelb et al, "An Electromechanical Transmission for Hybrid
Vehicle Power Trains - Design and Dynamometer Testing," SAE
Paper No. 710235 (11 to 15 January 1971).
4-2. J. Andon and I. R. Barpal, Emission Optimization of Heat Engine/
Electric Vehicle, Report 400, Project 1010, Minicars, Inc., Goleta,
California (27 January 1971) (Contract PA-MTD-8/H-830) (APCO
Project EHS-70-107).
4-3. P. Agarwal, R. Mooney, and R. Toepel, Stir-Lee I, A Stirling
Electric Hybrid Car, Report GMR 840, General Motors Research
Laboratories, Warren, Mich. (13 January 1969).
4_4. Monthly Progress Report No. 3, Minicars, Inc., Goleta, California
(September 1973) (Contract EPA 68-01-2103).
R-l
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4-5. Sidney G. Liddle, Emissions From Hybrid Vehicles, General Motors
Research Laboratories, Intersociety Engineering Energy Conversion
Conference, August 1973.
4-6. A. Kusko, "Solid State DC Motor Drives," MIT Press, Cambridge,
Mass. (1969).
4-7. J. Giner, A. H. Taylor, and F. Goebel, Lead-Acid Battery Develop-
ments for Heat Engine/Electric Hybrid Vehicles, Tyco Laboratories,
Inc., Waltham, Mass. (November 1971).
4_8. Develop High Charge and Discharge Rate Lead/Acid Battery Tech-
nology, Report 18353-6006-RO-OO, TRW Systems Group, Redondo
Beach, Calif (April 1972).
4-9. Request for Proposal. RFP No. EHSD 71-Neg 100, Division of
Advanced Automotive Power Systems Development, Environmental
Protection Agency (October 1970).
4-10. M. J. Sulkes, Nickel-Zinc Batteries for Hybrid Vehicle Operation,
Report for U.S. Army Electronics Command, Ft. Monmouth, N. J.
(December 1972).
4-11. L. L. Swette, "A Remarkable New Battery - Nickel/Hydrogen,"
Electrochemical Society Abstracts, Boston (7-11 October 1973).
4-12. W. E. Rice and D. Bell, III, "Status of Shuttle Fuel Cell Technology
Program, Proceedings of the 7th Intersociety Energy Conversion
Engineering Conference, San Diego, California (25-29 September
1972).
4-13. Gas Turbine Engine Production Implementation Study, ATR-73(7323)-1
(DOT Report TSC-051-73-26), The Aerospace Corp., El Segundo,
Calif., Vol I and II (July 1973).
4-14. Rankine Cycle Contractors Coordination Meeting, Presentation by
Scientific Energy Systems Corp. (October 1973).
4-15. N. D. Postina et al, The Stirling Engine for Passenger Car Appli-
cation, Paper published by Ford Motor Co., Dearborn, Mich., and
N. V. Philips of Holland.
4-16. Emission Characteristics of Spark Ignition Internal Combustion
Engine Used as the Prime Mover in a Hybrid System, Report by
Bureau of Mines, Fuels Combustion Research Group, Energy
Research Center, Bartlesville, Okla., Prepared for Environmental
Protection Agency (March 1972).
R-2
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5-1.
Feasibility Analysis of the Transmission for a Flywheel/Heat Engine
Hybrid Propulsion System, Report APTD-1181. Mechanical Tech-
nology, Inc. (November 1971).
5-2. M. A. Gordan and D. H. Grimm, Hybrid Propulsion System Trans-
mission Evaluation, Report AER-640, Sundstrand Aviation, Rockford,
111. (25 February 1972).
5-3. G. L. Dugger et al, Heat-Engine/Mechanical-Energy-Storage Hybrid
Propulsion Systems for Vehicles--Final Report, Report CP Oil, The
Johns Hopkins University, Applied Physics Laboratory, Silver Spring,
Md. (March 1972).
5-4. D. J. Patterson and J. A. Bolt, "Low Pollution Heat Engines,"
Paper No. 689107, Proceedings of the 3rd Intersociety Energy
Commission Engineering Conference (1968).
5-5. Automobile Gas Turbine Optimization Study, Final Report, Report
AT-6100-R7, AiResearch Mfg. Co. of Arizona, Phoenix, Ariz.
(July 1972).
5-6. Automobile Gas Turbine - Optimum Cycle Selection Study, Final
Report, Report GESP-725FS, General Electric Space Division
(1972).
6-1. H. S. Dunn and P. H. Wojciechowski, "High-Pressure Hydraulic
Hybrid with Regenerative Braking," Proceedings of the 7th Inter-
society Energy Conversion Engineering Conference, San Diego,
Calif. (September 1972).
6-2. P. E. Tartaglia,- "Achieving High Energy Efficiency for Urban
Transportation Through Hydrostatic Power Transmission and
Energy Storage," Proceedings of the 8th Intersociety Energy
Conversion Engineering Conference (August 1973).
6-3. D. R. Otis, "Thermal Losses in Gas-Charged Hydraulic Accumulators,"
Proceedings of the 8th Intersociety Energy Conversion Engineering
Conference (August 1973).
6-4. M. P. Sherman and B. V. Karlekar, "Improving the Energy Storage
Capacity of Hydraulic Accumulators," Proceedings of the 8th Inter-
society Energy Conversion Engineering Conference (August 1973).
6-5. O. W. Dykema, Evaluation of a Novel Prime Mover Concept Pro-
posed by the Pacific Missile Range, Report by Naval Air Systems
Command Reserve Unit U-2 (February 1973).
6-6. O. W. Dykema, Evaluation of a Novel Prime Mover Concept Proposed
by the Pacific Missile Range, Addendum to Report by Naval Air
Systems Command Reserve Unit U-2 (April 1973).
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APPENDIX A
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APPENDIX A. Air Pollution Control Office
Advanced Automotive Power Systems Program
"Vehicle Design Goals — Six Passenger Automobile"
(Revision C - May 28, 1971)
The design goals presented below are intended to provide:
A common objective for prospective contractors.
Criteria for evaluating proposals and selecting a contractor.
Criteria for evaluating competitive power systems for entering
first generation system hardware.
Advisory criteria in such areas as rolling resistance, vehicle air
drag etc. are included to assist the contractor-
The derived criteria are based on typical characteristics of the class of
passenger automobiles with the largest market volume produced in the U. S.
during the model years 1969 and 1970. It is noted that emissions, volume
and =ost weight characteristics presented are maximum values while the
performance characteristics are intended as minimum values. Contractors
and prospective contractors who take exceptions must justify these exceptions
and relate these exceptions to the technical goals presented herein.
1. Vehicle weight without propulsion system - WQ.
W0 is the weight of the vehicle without the propulsion system and
includes, but is not limited to: body, frame, glass and trim,
suspension, service brakes, seats, upholstery, sound absorbing materials,
insulation, wheels (rims and tires), accessory ducting, dashboard
instruments and accessory wiring, battery, passenger compartment
heating and cooling devices and all other components not included in
the propulsion system. It also includes accessories such as, the air
conditioner compressor, the power steering pump, and the power
brakes actuating device.
W0 is fixed at 2700 Ibs.
2. Propulsion system weight - Wp.
Wn includes the energy storage unit (including fuel and containment).
power converter (including both functional components and controls)
and power transmitting components to the driven wneols. It ^°
includes the exhaust system, pumps, motors, fans and fluids necessary
for operation of the propulsion system, and any propulsion system
heating or cooling devices.
A-l
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The naximuiu allowable propulsion system weight, W , is 1600 Ibs.
However, light weight propulsion systems are highly desired.
(Equivalent 1970 propulsion system weight with a spark ignition
engine is 1300 Ibs.)
3. Vehicle curb weight - WG
Wc = W0 + Wp
The maximum allowable vehicle curb weight, Wcm, is 4300 Ibs.
(2700 + 1600 max. - 4300)
4. Vehicle test weight - Wt.
W_ = Wc + 300 Ibs. Wfc is the vehicle weight at which all accelerative
maneuvers, fuel economy and emissions are to be calculated. (Items 8c,
8D, 8e).
The maximum allowable test weight, W^, is 4600 Ibs. (2700 + 1600
max. + 300 = 4600).
5. Gross vehicle weight - Wg
WCT = Wc + 1000 Ibs. Wg is the gross vehicle weight at which sustained
cruj.se grade velocity capability is to be calculated. (Item 8f) . The
1000 Ibs. load simulates a full load of passengers and baggage.
The maximum allowable gross vehicle weight, Wgm, is 5300 Ibs. (2700 +
1600 max. + 1000 - 5300).
6. Propulsion system volume - Vp
V0 includes all items identified under item 2. Vp shall be packngable
ih such a way that the volume encroachment on either the passenger or
..., ,._• compartment is not significantly different than today's (1970)
standard full size family car- The propulsion system shall not violate
the vehicle ground clearance lines as established by the manufacturer of
the vehicle used for propulsion system/vehicle packaging. Additionally,
the propulsion system shall not violate the space allocated for wheel
jounce motions and vehicle steering. Necessary external appearance
(styling) changes will be minor in nature. Vp shall also be packagable
ir. such a way that the handling characteristics of the vehicle do not
depart significantly from a 1970 full size family car.
The rr.aximum allowable volume assignable to the propulsion systc:
V , , is 35 ft.3.
A-2
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Emission Goals
The vehicle when tested for emissions in accordance with the procedure
outlined in the November 10, 1970 Federal Register shall have a
weight of Wt. The emission goals for the vehicle are:
Hydrocarbons* - 0.14 grams/mile maximum
Carbon monoxide - 4.7 grams/mile maximum
Oxides of nitrogen** - 0.4 grams/mile maximum
Particulates - 0.03 grams/mile maximum
*Total hydrocarbons (using 1972 measurement procedures)
plus total oxygenates. Total oxygenates including
aldehydes will not be more than 10 percent by weight
of the hydrocarbons or 0.014 grams/mile, whichever is
greater.
**measured or computed as NO-.
8. Start up, Acceleration, and Grade Velocity Performance.
a. Start up:
The vehicle must be capable of being tested in accordance with
the procedure outlined in the November 10, 1970 Federal Register
without special driver startup/warmup procedures.
The maximum time from, key on to reach 65 percent full power
is 45 sec. Ambient conditions are 14.7 psia pressure, 60°F
temperature.
Powerplant starting techniques in low ambient temperatures shall
be equivalent to or better than the typical automobile spark-
ignition engine. Conventional spark-ignition engines are deemed
satisfactory if after a 24 hour soak at -20°F the engine achieves
a self-sustaining idle condition without further driver input
within 25 seconds. No starting aids external to the normal vehicle
system shall be needed for -20°F starts or higher temperatures.
A-3
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b. Idle operation conditions:
The fuel consumption rate at idle operating condition will not
exceed 14 percent of the fuel consumption rate at the maximum design
power condition. Recharging of energy storage systems is
exempted from this requirement. Air conditioning is off,the
power steering pump and power brake actuating device, if
directly engine driven, are being driven but are unloaded.
The torque at transmission output during idle operation (idle
creep torque) shall not exceed 40 foot-pounds, assuming conventional
rear axle ratios and tire sizes. This idle creep torque should
result in level road operation in high gear which does not exceed
18 mph.
c. Acceleration from a standing start:
The minimum distance to be covered in 10.0 sec. is 440 ft.
The maximum time to reach a velocity of 60 mph is 13.5 sec.
Ambient conditions are 14.7 psia, 85° F. Vehicle weight is Wt.
Acceleration is on a level grade and initiated with the engine
at the normal idle condition.
d. Acceleration in merging traffic:
The maximum time to accelerate from a constant velocity
of 25 mph to a velocity of 70 mph is 15.0 sec. Time starts
when the throttle is depressed. Ambient conditions are 14.7
psia, 85° F. Vehicle weight is Wt, and acceleration is on
level grade.
e. Acceleration, DOT High Speed Pass Maneuver:
The maximum time and maximum distance to go from an initial
velocity of 50 mph with the front of the automobile (18 foot
length assumed) 100 feet behind the back of a 55 foot truck
traveling at a constant 50 mph to a position where the back
of the automobile is 100 feet in front of the front of the 55
foot truck is, 15 sec. and 1400 ft. The entire maneuver takes
place in a traffic lane adjacent to the lane in which tha truck
is operated. Vehicle will be accelerated until the maneuver is
completed or until a maximum speed of 80 mph is attained, which-
ever occurs first. Vehicle acceleration ceases when a speed of
80 mph is attained, the maneuver then being completed at a
constant 80 mph. (This does not imply a design requirement
limiting the maximum vehicle speed to 80 mph.) Time starts when
the throttle is depressed. Ambient conditions are 14.7 psia,
85° F. Vehicle weight is Wt, and acceleration is on level grade.
A-4
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f. Grade velocity:
The vehicle must be capable of starting from rest on a 30
percent grade and accelerating to 15 mph and sustaining it.
This is the steepest grade on which the vehicle is required
to operate in either the forward or reverse direction.
The minimum cruise velocity that can be continuously maintained
on a 5 percent grade with an accessory load of 4 hp shall be
not less than 60 mph.
The vehicle must be capable of achieving a velocity of 65 mph
up a 5 percent grade and maintaining this velocity for a
period of 180 seconds when preceded and followed by continuous
operation at 60 mph on the same grade (as above).
The vehicle must be capable of achieving a velocity of 70 mph
up a 5 percent grade and maintaining this velocity for a
period of 100 seconds when preceded and followed by continuous
operation at 60 mph on the same grade (as above).
The minimum cruise velocity that can be continuously maintained
on a level road (zero grade) with an accessory load of 4 hp
shall be not less than 85 mph with a vehicle weight of Wt.
Ambient conditions for all grade specifications are 14.7 psia
85° F. Vehicle weight is Wg for all grade specifications
except the zero grade specification.
The vehicle must be capable of providing performance (Paragraphs
8c, 8d, 8e 8f)withtn5 percent of the stated 85° F values, when
operated at. ambient temperatures from -20° F to 105° F.
A-5
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9. Minimum vehicle range:
Minimum vehicle range without supplementing the energy storage
will be 200 miles. The minimum range shall be calculated for,
and applied to each of the two following modes: 1) A city-
suburban mode, and 2) a cruise mode.
Mode 1: Is the driving cycle which appears In the
November 10, 1970 Federal Register. For
vehicles whose performance does not depend
on the state of energy storage, the range
may be calculated for one cycle and ratioed
to 200 miles. For vehicles whose performance
does depend on the state of energy storage
the Federal driving cycle must be repeated
until 200 miles have been completed.
Mode 2: Is a constant 70 mph cruise on a level road for
200 miles.
The vehicle weight for both modes shall be, initially, Wfc. The
ambient conditions shall be a pressure of 14.7 psia, and temperatures
of 60° F, 85° F and 105° F. The vehicle minimum range shall not
decrease by more than 5 percent at an ambient temperature of -20° F.
For hybrid vehicles, the energy level in the power augmenting device
at the completion of operation will be equivalent to the energy level
at the beginning of operation.
A-6
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10. System thermal efficiency:
System thermal efficiency will be calculated by two methods:
A. A "fuel economy" figure based on 1) miles per gallon
(fuel type being specified) and 2) the number of Btu
per mile required to drive the vehicle over the 1972
Federal driving cycle which appears in the November
10, 1970 Federal Register. Fuel economy is based on
the fuel or other forms of energy delivered at the
vehicle. Vehicle weight is Wfc.
B. A "fuel economy" figure based on 1) miles per gallon
(fuel type being specified) and 2) the number of Btu
per mile required to drive the vehicle at constant
speed, in still air, on level road, at speeds of 20,
30, 40, 50, 60, 70, and 80 mph. Fuel economy is based
on the fuel or other forms of energy delivered at the
vehicle. Vehicle weight is Wfc.
In both cases, the system thermal efficiency shall be calculated
with sufficient electrical, power steering and power brake loads
in service to permit safe operation of the automobile. Calculations
shall be made with and without air conditioning operating. The
ambient conditions are 14.7 psia and temperatures of 60° F, 85° F
and 105° F. Calculations shall be made with heater operating at
ambient conditions of 14.7 psia and 30° F (18,000 Btu/hr).
11. Air Drag Calculation:
The product of the drag coefficient, Cj, and the frontal area,
is to be used in air drag calculations. The product CjAf has a
value of 12 ft2. The air density used in computations shall
correspond to the applicable ambient air temperature.
12. Rolling Resistance:
Rolling resistance, R, is expressed in the equation
R = W/65 [1 + (1.4 x 10-3V) + (1.2 1Q-5V2)] Ibs. V is the vehicle
velocity in ft/sec. W is the vehicle weight in Ibs.
A-7
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13. Accessory power requirements:
The accessories are defined as subsystems for driver assistance
and passenger convenience, not essential to sustaining the
engine operation and include: the air conditioning compressor,
the power steering pump, the alternator (except where required
to sustain operation), and the power brakes actuating device.
The accessories also include a device for heating the passenger
compartment if the heating demand is not supplied by waste heat.
Auxiliaries are defined as those subsystems necessary for the
sustained operation of the engine, and include condenser fan(s),
combustor fan(s), fuel pumps, lube pumps, cooling fluid pumps,
working fluid pumps and the alternator when necessary for driving
electric motor driven fans or pumps.
The maximum intermittent accessory load, Paim» is 10 hp (plus the
heating load, if applicable). The maximum continuous accessory
load, Pacm, is 7.5 hp (plus the heating load if applicable). The
average accessory load, Paa, is 4 hp.
If accessories are driven at variable speeds, the above values
apply. If the accessories are driven at constant speed, Paim
pacm wil1 be reduced by 3 hp.
A-8
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14. Passenger comfort requirements:
Heating and air conditioning of the passenger compartment shall be
at a rate equivalent to that provided in the present (1970) standard
full size family car.
Present practice for maximum passenger compartment heating rate is
approximately 30,000 Btu/hr. For an air conditioning system at 110°
ambient, 80° F and 40% relative humidity air to the evaporator, the
rate is approximately 13,000 Btu/hr.
15. Propulsion system operating temperature range:
The propulsion system shall be operable within an expected ambient
temperature range of -40° to 125° F.
16. Operational life:
The mean operational life of the propulsion system should be
approximately equal to that of the present spark-ignition engine.
The mean operational life should be based on a mean vehicle life of
105,000 miles or ten years, whichever comes first.
The design lifetime of the propulsion system in normal operation will
be 3500 hours. Normal maintenance may include replacement of
accessable minor parts of the propulsion system via a usual maintenance
procedure, but the major parts of the system shall be designed for a
3500 hour minimum operation life.
The operational life of an engine shall be determined by structural or
functional failure causing repair and replacement costs exceeding the
cost of a new or rebuilt engine. (Functional failure is defined as
power degradation exceeding 25 percent or top vehicle speed degradation
exceeding 9 percent).
A-9
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17. Noise standards: (Air conditioner not operating)
a. Maximum noise test:
The maximum noise generated by the vehicle shall not
exceed 77 dbA when measured in accordance with SAE J986a.
Note that the boise level is 77 dbA whereas in the SAE
J986a the level is 86 dbA.
b. Low speed noise test:
The maximum noise generated by the vehicle shall not exceed
63 dbA when measured in accordance with SAE J986a except
that a constant vehicle velocity of 30 mph is used on the
pass-by, the vehicle being in high gear or the highest gear
in which it can be operated at that speed.
c. Idle noise test:
The maximum noise generated by the vehicle shall not exceed
62 dbA when measured in accordance with SAE J986a except that
the engine is idling (clutch disengaged or in neutral gear)
and the vehicle passes by at a speed of less than 10 mph.
the microphone will be placed at 10 feet from the centerllne
of the vehicle pass line.
18. Safety standards:.
The vehicle shall comply with all current Department of Transportation
Federal Motor Vehicle Safety Standards. Reference DOT/HS 820 083.
A-10
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19. Reliability and maintainability:
The reliability and maintainability of the vehicle shall equal or
exceed that of the spark-ignition automobile. The mean-time-between
failure should be maximized to reduce the number of unscheduled
service trips. All failure modes should not represent a serious
safety hazard during vehicle operation and servicing. Failure
propagation should be minimized. The power plant should be designed
for ease of maintenance and repairs to minimize costs, maintenance
personnel education, and downtime. Parts requiring frequent servicing
shall be easily accessable.
20. Cost of ownership:
The net cost of ownership of the vehicle shall be minimized for
ten years and 105,000 miles of operation. The net cost of ownership
includes initial purchase price (less scrap value), other fixed costs,
operating and maintenance costs. A target goal should be to not
exceed 110 percent of the average net cost of ownership of the present
standard size automobile with spark-ignition engine as determied by
the U.S. Department of Commerce 1969-70 statistics on such ownership.
A-11
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GLOSSARY
-------
GLOSSARY
Acronyms and Units of Measurement
ac alternating current
Ah Ampere hour
Ah/cm Ampere hour per square centimeter
BSFC brake specific fuel consumption (pounds of fuel per engine
brake horsepower-hour)
Btu British thermal unit
CI compression ignition
CID cubic inches of piston displacement (reciprocating piston engines)
CO carbon monoxide
dc direct current
DHEW Department of Health, Education, and Welfare (predecessor
to EPA in studying the control of automotive emissions)
DOT Department of Transportation
EGR exhaust gas recirculation
EMT electromechanical transmission
FETDC Federal emissions test driving cycle (used in Federal emissions
test for certification of light-duty vehicles)
HC hydrocarbon
hp horsepower
kW kilowatts
MTI Mechanical Technology, Inc.
G-l
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NO
x
PCU
PWM
rms
SCR
SFC
SI
V
w
W/lb
Wh
Wh/lb
oxides of nitrogen
power conditioning unit
pulse-width modulation
root mean square
silicon controlled rectifier
specific fuel consumption
spark ignition
Volts
Watts
Watts per pound
Watt hours
Watt hours per pound
G-2
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Technical Terms
alkali-metal battery
bipolar cell
breadboard prototype
carbon-pile resis-
tance stacks
Carnot cycle
catalytic converter
chopper circuit
(for motor control)
direct current brush
motor
fuel cell
A storage battery in which the anode consists of an
alkali-metal such as lithium or sodium.
An electrode structure in which the anode of one
cell and the cathode of the adjoining cell are com-
bined to form a single member.
An experimental arrangement of selected compo-
nents to prove the feasibility of a given design and
to facilitate changes when necessary.
A variable resistor consisting of a stack of carbon
disks mounted between fixed and movable metal
plates that serve as terminals of the resistor. The
resistance value is reduced by applying pressure
to the movable metal plate.
An ideal cycle that is used to establish the maxi-
mum thermal efficiency of a heat engine operating
between two temperature limits.
As applied to automotive heat engines, a device
relying on a catalyst process that is used to induce
or accelerate oxidizing or reducing chemical reac-
tions in the engine exhaust with the objective of
lessening pollutant emissions to the atmosphere.
An electronic solid-state circuit generally using
silicon controlled rectifiers to "chop" continuous
direct-current voltage into undulating voltage -with
an essentially square waveform for control of
power delivered to an electric motor.
Any motor that accepts power from a direct current
source and uses carbon or composition brushes both
to carry current to the armature and to mechanically
commutate current as the armature rotates.
An electrochemical energy-producing device em-
ploying inert electrodes to which are fed liquid or
gaseous reactants, and from which the reaction
products are continuously removed.
G-3
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heat engines
hydromechanical
transmission
hydrostatic
transmission
hysteresis motor
induction motor
inverter
noble metal
organic electrolyte
Otto cycle
A general term applied to a class of engines that
use heat to raise the temperature/pressure of a
working fluid to provide power (i.e. , those that
convert heat energy into mechanical energy or
motion). As opposed to those that use chemical
reactions (i. e. , batteries) to provide power.
Examples of heat engines are: reciprocating or
rotary piston, diesel, gas turbine, Rankine cycle,
and Stirling.
The hydromechanical or power-splitting transmis-
sion is a combination of mechanical differential
gearing and a hydrostatic transmission.
The hydrostatic transmission consists of a hydraulic
pump with a fluid connection to a hydraulic motor.
A small synchronous motor that starts in the hys-
teresis mode whereby a magnetic field is induced
into the rotor (secondary field) which then interacts
with the primary field to produce torque. Usually
used for light constant-speed duty.
An alternating-current motor in which the change
of current in the primary, stator winding induces
eddy currents in the passive secondary rotor which
interacts to produce torque.
A solid-state electronic or electromechanical device
that converts direct current power into alternating
current power.
A metal such as gold, silver, or platinum that has
high resistance to corrosion and oxidation.
An electrolyte embodying an organic (carbon con-
taining) solvent contrasted with normal electrolyte
that uses water as a solvent.
A four-step process for internal combustion engines
in which the first step consists of intake of an air-
fuel (explosive) charge into the cylinder, the second
step consists of compression and ignition of the
charge, the third step consists of expansion of the
gasses, and the last step is expulsion of the com-
bustion products from the cylinder.
G-4
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powertrain
pulse-width
modulation (PWM)
quasi bipolar
Rankine cycle engine
reluctance motor
series--wound motor
shunt-wound motor
silicon controlled
rectifier
stepper motor
The complete power generation and transmission
system that provides energy to the drive wheels of
an automotive vehicle.
A method for electric power control relying on the
ratio of "voltage time on" to "voltage time off."
A term devised to describe a bipolar lead-acid bat-
tery that uses the normal lead or lead alloy current
collectors in conjunction with an alternative paste
support material.
An external combustion engine in which a high-
pressure working fluid is converted to super-
heated vapor by the heat from combustion gases
and then is expanded in a piston- or turbine type
device to produce work.
A synchronous motor similar in construction to an
induction motor, in which the member carrying the
secondary circuit has salient poles, without per-
manent magnets or direct current excitation. It
starts as an induction motor, but operates nor-
mally at synchronous speed. (The rotor seeks
minimum reluctance, whence the name reluctance
motor.)
A direct-current motor in which excitation is sup-
plied by a winding or windings connected in series
with or carrying a current proportional to that in
the armature winding. Has a high starting torque,
variation in speed with load, and dangerously high
speed with no load.
A direct-current motor in which excitation of the
field circuit is supplied by a winding connected in
parallel with the armature circuit.
An electronic semiconductor device used principally
to provide control of high direct current power levels
to an electric motor.
A motor that rotates in short and essentially uniform
angular movements rather than continuously. The
angular steps, usually 30, 45, and 90 deg, are ob-
tained electromagnetically rather than by ratchet
and pawl mechanisms as in stepping relays.
G-5
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Stirling cycle An external combustion, closed cycle, piston-type
engine device that uses a gaseous internal working fluid,
usually hydrogen or helium. Cyclical heating and
cooling varies the pressure of the fluid within a
closed volume, the pressure variations being trans-
mitted to a piston, thereby developing output power.
G-6
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-460/3-74-013-d
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Current Status of Alternative Automotive Power
Systems and Fuels
Volume IV - Electric and Hybrid Power Systems
5. REPORT DATE
July 1974
6. PERFORMING ORGANIZATION CODE
7.AUTHORIS) D. E. Lapedes, M. G. Hinton, J. Meltzer,
T. lura, O. Dykema, L. Forrest, K. Hagen,
J. Kettler, R. LaFrance, W. Smalley
8. PERFORMING ORGANIZATION REPORT NO.
ATR-74(7325)-l, Vol. IV
9. PERFORMING ORGANIZATION NAME AND ADDRESS
The Environmental Programs Group
Environment and Urban Division
The Aerospace Corporation
El Segundo, Calif. 90245
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-01-0417
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Air and Waste Management
Office of Mobile Source Air Pollution Control
Alternative Automotive Power Systems Division
Ann Arbor, Michigan 48105
13. TYPE OF. REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A summarization has been made of the available nonproprietary information on
the technological status of automotive power systems which are alternatives to the
conventional internal combustion engine, and the technological status of non-
petroleum-based fuels derived from domestic sources which may have application
to future automotive vehicles. The material presented is based principally upon
the results of research and technology activities sponsored under the Alternative
Automotive Power Systems Program which was originated in 1970. Supplementary
data are included from programs sponsored by other government agencies and by
private industry. The results of the study are presented in four volumes; this
volume presents the current technological status of electric and hybrid power
systems.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Electric Cars
Hybrid Heat Engine/Battery Cars
Hybrid Heat Engine/Flywheel Cars
Batteries
Flywheels
Design Concepts
Operating Modes
Performance
Exhaust Emissions
Technology Status
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report}
Unclassified
!1. NO. OF PAGES
260
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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