`TOR-O059(~769-01)-2. VOL. I
`
`Final Report
`Hybrid Heat Engine / Electric Systems
`Volume l: Sections l through 13
`
`Study
`
`71 JUN ~t
`
`Prepared for DIVISION OF ADVANCED AUTOMOTIVE
`POWER SYSTEMS DEVELOPMENT
`U. S. ENVIRONMENTAL PROTECTION AGENCY
`Ann Arbor, Michigan
`
`Contract No. F04701-70-C-0059
`
`Office of Corporate Planning
`THE AEROSPACE CORPORATION
`El .Segundo, California
`
`BMW1035
`Page 1 of 52
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`
`
`Report No.
`TOR-0059(6769-01)-2,
`Vol. I
`
`FINAL REPORT
`HYBRID HEAT ENGINE/ELECTRIC SYSTEMS STUDY
`
`Volume h Sections 1 through 13
`
`71 JUN ~1
`
`Office of Corporate Planning
`THE AEROSPACE CORPORATION
`El Segundo, California
`
`Prepared for
`
`Division of Advanced Automotive Power Systems Development
`U.S. ENVIRONMENTAL PROTECTION AGENCY
`Ann Arbor, Michigan
`
`Contract No. F04701-70-C-0059
`
`BMW1035
`Page 2 of 52
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`
`
`FOREWORD
`
`Basic to analyzing the performance of the hybrid vehicle was the inlportancc
`of understanding the characteristics of each major component since each
`would be operating in a nonstandard mode required by the hybr id arrange-
`ment. In addition, the potential for improvement had to be understood to
`predict the performance of advanced designs. This report, therefore, con-
`tains two types of information: (a) hybrid system analysis and results; and
`’(b) major component state-of-the-art discussions, characteristics used in
`this study, and advanced technology assessments. Heat engine operating
`characteristics, mechanical parameters, and exhaust emissions are covered
`extensively because of both their primary importance and the difficulty
`involved in collecting a reliable comprehensive set of data; this should relieve
`future investigators making studies of nonconventional propulsion systems of
`the necessity of repeating the burdensome task of assembling a data bank.
`
`It should be recognized that calculated results are based on data compilc.d in
`this study. The magnitude and trends were established on the basis ~,l ~’,
`comprehensive survey and evaluation of the best data fronn both the open
`literature and cm’rent available unpublished data sources. 3’hese data are
`considered suitable for use in the feasibility study conducted under this c<,n-
`tract. However, for further detailed design a substantial refinement o1 the
`data base would be necessary.
`
`l&
`
`he report is organized to give a logical build-up of information starting with
`study specification, analytical techniques, and component characteristics and
`concluding with system performance results and recommendations for develop-
`ment. However, seIective reading of major systems performance results is
`possible and to assist those so interested, the following brief guide is pre-
`sented:
`
`Section i
`
`Sections 2, 3, I0, and II
`
`Sections 3 and 4
`
`Sections 6 through 9
`
`Section IZ
`
`Section 13
`
`Summary of study results and recom-
`mentations
`
`Presentation of study objectives,
`design specifications, and results
`
`Description of computational techniques
`and performance requirements
`
`Review of contemporary and projected
`technology of major components
`
`Cost estimates for high-volume pro-
`duction of hybrid cars
`
`Presentation of a technological plan for
`component and system development
`
`-iii-
`
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`This report is published in two volumes for convenience; however, separation
`of the material is made with due regard to organization. Volume 1 consists of
`Sections 1 through 13 and presents the essential study information, while
`Volume II consists of Appendices A through F and presents supplementary
`data.
`
`The period of performance for this study was June 1970 through June 1971.
`
`-iv-
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`
`
`AC KNOW LE DG MEN TS
`
`The extensive diversity in technological capabilities necessary for a thorough
`
`evaluation of the hybrid electric vehicle has required the reliance for support
`
`and expertise on select members of The Aerospace Corporation technical
`
`staff as well as members of the national technical comn~unity. Recognition
`
`of this effort is expressed herewith:
`
`The Aerospace Corporation
`
`Mr,
`Mr.
`Mr.
`
`Dan Bernstein
`Lester Forrest
`Gerald Harju
`
`Mr.
`
`Mer r ill Hinton
`
`Dr. Toru lura
`
`Mr. Dennis Kelly
`
`Mr. Jack Kettler
`
`Mr. Harry Killian
`
`Mr. Robert La France
`
`Electrical System- Control System
`Heat Engines (Internal Combustion)
`Programming for Computations
`
`Vehicle Specifications/Conceptual Des ign
`and Sizing Studies
`
`Heat Engines (Internal Combustion’)
`Heat Engine Exhaust Emissions
`Vehicle Exhaust Emissions Test Progranl
`Electrical Systenn - Motor and (]enerator
`
`Electrical Systenl - Batteries
`Heat Engines (External Combustion)
`
`Computational Techniques
`Electrical System - Batteries
`Electrical System - Motor, Generator,
`Control Systems
`
`Mrs. Roberta Nichols
`
`Vehicle Exhaust Emission Test Program
`
`Mr. Wolfgang Roessler
`
`Dr. Henry Sampson
`
`Mr. Raymond Schult
`
`Heat Engine Exhaust Emissions
`Vehicle Exhaust Emission Test Program
`
`Vehicle Specifications
`Computational Techniques
`Vehicle Power Requirements
`Electrical System - Motor, Generator,
`Control Systems
`
`University of California, Berkeley
`
`Dr. Rober t Sawyer
`
`Heat Engine Exhaust Emissions
`
`University of California, Irvine
`
`Dr. Robert M. Saunders
`
`Electrical System -
`Control Systems
`
`Motor Generator,
`
`-V-
`
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`
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`It is to be noted that considerable data of great value to this study were
`
`kindly provided by individuals in industry, universities, and government
`
`agencies. Acknowledgment of these data sources is given in Appendix F
`
`to this report.
`
`Donald E.
`Manager, Hybrid Veh
`
`.~ Progr am
`
`~rograms
`Office of Corporate Planning
`
`-vi-
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`
`
`SECTION I0
`
`CONCEPTUAL DESIGN AND SIZING STUDIES
`
`10.1
`
`CONCEPTUAL DESIGNS
`
`1 0. I. 1
`
`Introduction
`
`Heat engine/electric hybrid powerplant concepts can be grouped into two
`
`broad classes: series and parallel configurations, as previously defined in
`
`Section 3 and further discussed in Section 6.
`
`In all cases, the difference between power required for vehicle propulsion
`
`and power supplied by the heat engine must be supplied by the batteries.
`
`Hence, at the outset, it should be recognized that once the vehicle maximum
`
`power requirements have been established, the battery design goals can be
`
`markedly influenced by the heat engine power output profile. This effect is
`
`shown in Fig. 10-1 where vehicle maximum power (for maximum acceleration)
`
`and cruise power requirements are illustrated, along with three different
`
`vehicle-velocity varying power profiles delivered by the heat engine. Pro-
`
`file #Z is defined as that power output profile which will result in the batteries
`
`being fully recharged at the end of the driving cycle.
`
`It is clear that profile #1 imposes far less severe requirements on the battery
`
`(in terms of power demand) than profiles #2 and #3, but it also requires a
`
`higher level of sustained heat engine power output at lower vehicle speeds, and
`
`is in excess of that heat engine power level required to maintain the battery
`
`state-of-charge, thus resulting in higher heat engine exhaust emissions and
`
`increased fuel consumption.
`
`An alternative type of power profile to those shown in Fig. 10=l can be en-
`
`visioned wherein the heat engine is required to accelerate (change power output)
`
`rapidly, as in conventional SI engine-powered vehicles. The heat engine could
`
`have a power output profile similar to profile #3 for constant velocity operation,
`
`and accelerate to a maximum power level (similar to the level of profile #l)
`
`10-1
`
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`
`
`during periods of vehicle acceleration, thus reducing battery peak demand
`requirements. However, for purposes of this study, it was assumed that
`this form of engine performance might not be attainable with low-pollution
`engines with possible "driveability" (i. e., smooth power-output profiles
`under instantaneous load changes) constraints.
`
`Therefore, all subsequent discussion is directed toward conceptual approaches
`
`in which heat engines are not subjected to large instantaneous changes in power
`
`output. In the following illustrative cases which depict power output varying
`
`with time, vehicle velocity, or step changes, it is assumed that these power
`
`changes take place over finite time intervals commensurate with the acceler-
`
`ation capability of the engine under load.
`
`MAXIMUM POWER REQUIRED
`(MAXIMUM VEHICLE ACCELERATION)
`
`MAXIMUM
`POWER SUPPLIED
`BY BATTERIES
`
`0
`(zu
`
`HEAT ENGINE POWER PROFILE
`No. I
`
`¯ ,
`
`REQUIRED
`CRUISE SPEED
`
`No. 2
`
`SPEED
`
`CRUISE POWER REQUIRED
`
`Figure 10-1.
`
`Effect of Heat Engine Power Profile on
`Required Maximum Battery Power
`
`IO-Z
`
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`
`
`10.1.2
`
`Series Configuration
`
`IO. 1. Z. 1
`
`Basic Subsystems/Components
`
`A heat engine/electric hybrid powerplant configured for the series mode,
`
`as
`
`defined above, requires certain basic subsystems/components which can
`
`vary as to type and/or number according to designer’s choice.
`
`For example, a single electric drive motor can be utilized with a central
`
`differential drive to the driving wheels, or multiple drive motors could be
`
`used with a drive motor at each wheel, negating the need for the differential
`
`drive. However, aside from this configurational design option, the remaining
`
`options in the series configuration primarily center around selection of the
`
`specific type of subsystem/component to be used, and the control system to
`
`be used for the preferred mode of operation.
`
`The selected series configuration used as a baseline in the present study for
`
`all vehicles is as shown in Fig. 10-2. A single electric drive motor is used
`
`to supply power to the rear wheels through a central differential drive unit.
`
`Where appropriate, the differential drive unit is envisioned to contain an
`
`overdrive unit to provide a step change in electric drive motor rpm to allow
`
`high-speed cruising at near-maximum drive motor efficiency levels.
`
`The generator is mechanically-driven by the heat engine through a gearbox
`
`(speeder/reducer) which allows the generator (or alternator as the case may
`
`be) and the heat engine to operate at different rpm levels. The other two
`
`major subsystems (i.e., battery, control system) are then electrically-
`
`connected to the generator and drive motor as schematically represented in
`
`Fig. 6-1.
`
`10. 1.2.2
`
`Operational Modes
`
`With the foregoing series configuration arrangement, a number of modes of
`
`operation are conceivable. Several of the more significant modes are shown
`
`in Fig. 10-3 and discussed in the following paragraphs in terms of the mode
`
`of operation of the heat engine. The heat engine mode of operation was
`
`10-3
`
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`
`(, WHEEL )
`
`~6EN ESPEEDER I REDUCER
`
`o
`I
`
`HEAT
`ENGINE
`
`---P-OWER
`A.C CONDITIONING
`RAzoR*-* ~ CONTROL *--*
`SYSTEM
`
`D.C. ELECTRIC ]
`
`I
`
`I
`
`BATTERY
`
`DIFFERENTIAL
`DRIVE UNIT
`
`I /
`
`L~
`
`Figure lO-Z. Selected Baseline Series Configuration
`
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`CONSTANT POWER OUTPUT
`
`-CONTINUOUS OPERATION
`OF HEAT ENGINE
`
`TIME--,-.-
`
`ON-OFF OPERATION
`OF HEAT ENGINE
`
`{3C
`i,i
`
`0
`{3_
`
`CL
`
`0
`
`rF
`ill
`
`0
`(cid:128)3_
`
`CI_
`I--
`
`0
`
`o
`!
`ljrl
`
`VARIABLE POWER OUTPUT
`
`OUTPUT POWER:
`f (VELOCITY)
`
`/
`/
`/
`/
`/
`/
`/
`J
`
`I:E
`111
`
`0
`I:L
`
`I---
`
`t--
`
`0
`
`VEHICLE VELOCITY
`
`TIME
`
`Figure 10-3. Various Heat Engine Operational Modes
`Series Configuration
`
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`selected as the descriptor in that heat engine exhaust emission determination,
`
`a principal objective of this study, is more directly-relatable to this descrip-
`
`tor.
`
`Constant Speed (rpm) and Power Output
`
`Heat Engine Operated Continuously
`
`In this mode of operation, a severe problem arises in relation to sizing the
`
`heat engine. If the heat engine is sized only to produce a total energy required
`
`in the time duration of the emission driving cycle (including inefficiencies of
`
`the powerplant system), then the heat engine may not provide the proper
`
`continuous high-speed power demand for highway operation. This results in
`
`discharge of the batteries at high speeds (if the heat engine size is too
`
`small). Conversely, if the heat engine is sized for the maximum continuous
`
`power demand for highway operation, excessive energy loss to a heat-dump
`
`can occur (if heat engine size is too large).
`
`This mode of heat engine operation is of course attractive from the stand-
`
`point of heat engine exhaust emissions per se, in that it should be possible
`
`to select an operating point (i.e., rpm, air/fuel ratio, etc. ) most amenable
`
`to reduced emissions. However, its apparent inflexibility with regard to
`
`heat engine sizing and meeting both design driving cycle as well as emission
`
`driving cycle vehicle performance led to its discard as a viable series mode
`
`of operation for the particular classes of vehicles under consideration.
`
`However, this mode may still be suitable for vehicles with reduced top
`
`speeds and/or revised specification requirements.
`
`I0. I. 2.2. I. 2 On-Off Operation of Heat Engine
`
`As an alternative to continuous operation, it is possible to operate a constant
`
`power output heat engine in an "on-off" mode. Here, the heat engine would
`
`be sized to meet the continuous high-speed power demand for highway opera-
`
`tion, and would operate intermittently during urban driving conditions. The
`
`heat engine could be turned on or off in response to (a) a battery voltage and/
`
`or state-of-charge signal, (b) a power demand from the electric drive motor,
`
`or (c) a combination of both.
`
`10-6
`
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`In this manner, various total energy requirements can be matched by the
`
`"pulse" mode operation of the heat engine, which would allow the engine to
`
`be off more in low-energy portions of urban driving cycles.
`
`Preliminary calculations, however, indicated that this mode of operation
`
`resulted in very high energy losses during those time periods when drive
`
`motor demand is low due to battery charge rate limitations, i.e., a good
`
`portion of heat engine power output must be dumped because the battery
`
`simply cannot accept the power at the rate being supplied. This same
`
`limitation applies to the continuous heat engine operation mode previously
`
`discussed.
`
`There is one further disadvantage of intermittent or on-off operation. When
`
`operating continuously, power from the heat engine/generator can go directly
`
`to the drive motor during periods of power demand and bypass the battery
`
`loop entirely. When operating in the on-off mode, it would only be fortuitous
`
`if drive motor power demand occurred at the same time the engine was on.
`
`Therefore, more of the heat engine power output flows through the battery
`
`circuit in the "on-off" mode than in the continuous operation mode. Even if
`
`battery recharge efficiency is high, the on-off mode of operation would be
`
`less efficient than the continuous mode of operation. It was concluded that
`
`while on-off operation of the heat engine at constant power output was more
`
`flexible than continuous operation at constant power output, it was not
`
`adequate for the wide range of vehicle driving requirements under considera-
`
`tion.
`
`10. 1. 2.2. Z
`
`Variable Power Output
`
`10. 1. 7.2.7. 1 Heat Engine Operated Continuously
`
`Many of the deficiencies of the constant-power output mode of operation can
`
`be avoided by allowing the power output of the heat engine to vary. In this
`
`case, the heat engine can be sized for the maximum continuous power
`
`requirement and allowed to operate at lower power levels for those periods of
`
`10-7
`
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`vehicle driving cycles which require less power. If heat engine rpm is also
`
`allowed to vary to produce this variation in power output (as in conventional
`
`internal combustion engines), it is envisioned that the control system can
`
`effectively vary throttle setting response time constants so that engine rpm
`
`and power changes take place at a controlled rate in such a manner that no
`
`true vehicle acceleration demands are imposed on the heat engine in the
`
`conventional sense.
`
`Such a mode of operation would allow the energy requirements of a variety
`
`of urban driving cycles to be more closely matched (than with constant power
`
`output mode), although the matching of all duty cycle energy requirements
`
`may not be possible. To overcome this difficulty, it has been suggested
`
`that the heat engine power output be scheduled as a function of vehicle
`
`velocity (heat engine produces more power as road load increases} with a
`
`throttle "bias" feature in the heat engine fuel control system to increase or
`
`lower the baseline heat engine power output schedule in accordance with an
`
`input signal related to battery voltage and/or state-of-charge as illustrated
`
`in Fig. i0-4.
`
`With these features, the continuous operation of the heat engine on a variable
`
`power output basis appears to be a highly versatile and accommodating mode
`
`of operation for the series configuration of a heat engine/electric hybrid
`
`powerplant.
`
`10. 1. Z. Z. g. 2
`
`"Step-Mode" Operation
`
`Another technique for varying heat engine power output is to schedule power
`
`output in discrete steps. Figure 10-5 illustrates one such approach, wherein
`
`three levels of power output are used. A "low" level would be scheduled
`
`for a low-velocity range (e.g., 0-30 mph), an "intermediate" level for
`
`velocities between the low-velocity range and vehicle top speed, and a "peak"
`
`level for cruising at maximum continuous power conditions.
`
`Again, battery voltage and/or state-of-charge signals could be used to over-
`
`ride the nominal schedule of power output versus velocity.
`
`10-8
`
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`
`
`
`o
`I
`,4)
`
`n~
`Ill
`
`0
`CL
`h--
`in_
`F-
`D
`0
`
`BATTERY VOLTAGE AND/OR
`STATE- OF- CHARGE ISIGNAL
`CAN BE USED TO DEPART
`FROM NOMINAL SCHEDULE
`(WITHIN UPPER & LOWER LIMITS),
`/
`
`/UPPER
`LIMIT
`/
`/
`/
`
`NOMINAL SCHEDULE
`
`~ t_OWER LIMIT
`
`/
`/
`/
`
`/
`/
`/
`/
`/
`/
`
`VEHICLE VELOCITY ----
`
`Figure 10-4. Heat Engine Variable Power Output Mode
`"Biased" Throttle Setting Feature
`
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`
`
`1--
`
`13_
`
`0
`
`LI_J
`
`0
`
`"LOW" LEVEL
`
`0
`I
`i--,
`0
`
`"INTERMEDIATE" IFVEL
`
`"PEAK" IFVEL
`
`¯ ",-- TOP VEHICLE
`SPEED
`
`VEHICLE VELOCITY
`
`Figure 10-5. Heat Engine Variable Power Output Mode
`Step-Mode
`
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`
`
`10. 1.2.2. 3
`
`Selected Baseline Operational Mode
`
`On the basis of the discussion of characteristics, advantages, and disad-
`
`vantages, the variable power output mode with the heat engine operating
`
`continuously throughout the driving cycle was selected for the series con-
`
`figuration. More specifically, the heat engine power output was tailored in
`
`accordance with vehicle velocity as shown in Fig. 10-6. The specific heat
`
`engine power output profile for each vehicle is a function of the power
`
`required for steady road load above a certain vehicle velocity. Below this
`
`velocity, the power output is at a constant value. This value is determined
`
`uniquely for each vehicle as the value required to result in the battery being
`
`returned to its initial state-of-charge at the end of the vehicle driving cycle.
`
`The more sophisticated approach of having battery voltage and/or state-of-
`
`charge override this value as depicted in Fig. 10-4, while offering greater
`
`system flexibility, falls outside the scope of the current study.
`
`I0. I. 3
`
`Parallel Configuration
`
`10. I. 3. I
`
`Basic Subsystems/Components
`
`A heat engine/electric hybrid powerplant configured for the parallel mode
`
`requires the same basic subsystems/components as the series mode plus
`
`the additional need for a transmission or gearbox for the mechanical drive
`
`from the heat engine to the differential drive and/or wheels. However, the
`
`sizing criteria for some subsystems are very different from those in the
`
`series mode. For example, the drive motor in the series case must be
`
`sized to provide all power required at the wheels. In the parallel case, the
`
`drive motor is supplementary to the mechanical power supplied by the heat
`
`engine, and is sized to provide acceleration torques on an intermittent basis,
`
`not continuous duty. The generator in the series case is sized to accommo-
`
`date full power output of the heat engine, while in the parallel case the
`
`generator is sized on the basis of heat engine minimum operating power level.
`
`The size of the heat engine required can differ between the two concepts,
`
`depending upon the particular subsystem efficiencies assumed. The particular
`
`choice of mechanical arrangement of the heat engine, generator, transmission/
`
`gearbox, and drive motor can also result in the requirement for more than one
`
`drive motor, or for the drive motor to have the dual function of motor and
`
`generator (motor/generator).
`
`I0-ii
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`
`VEHICLE UNDER
`ACCELERATION:
`EXCESS TO MOTOR
`VEHICLE AT CRUISE:
`EXCESS TO BATTERY
`AND/OR ENERGY
`DUMP CIRCUIT-
`
`MINIMUM
`ALLOWABLE
`
`POW R-
`
`0
`!
`
`N
`
`C=.
`~,=
`
`0
`(3-
`
`LEVEL ROAD
`
`POWER
`DELIV
`
`///~-POWER REQUIRED FOR
`STEADY ROAD LOAD
`
`J
`
`VEHICLE SPEED, mph
`
`Figure 10-6. Series Configuration- Variation of Heat Engine
`Power with Vehicle Speed
`
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`
`
`Because of the wide variation in mechanical approaches possible for the
`parallel configuration, a simple concept was selected for the baseline parallel
`configuration in the present study which more readily allowed for a direct
`comparison of the inherent features of the parallel versus series approach in
`terms of heat engine power/energy requirements and resultant exhaust
`emissions over the emission driving cycles. A discussion of various parallel
`configurations can be found in Section 6.
`
`As shown in Fig. 10-7, the baseline parallel concept utilizes an automatic
`transmission to provide the mechanical drive connection from the heat engine
`to a differential drive unit powering the drive wheels. The electric drive
`motor, used for vehicle acceleration torque demands, is geared to the output
`shaft of the transmission. The generator is similarly geared to the output
`shaft of the heat engine. The control system is postulated to have the capa-
`bility to synchronize the input and output rpm’s of the automatic transmission
`(by controlling heat engine rpm, generator load, and drive motor rpm) to the
`extent they are essentially equal and that fluid coupling losses are minimal
`(i. e. , no torque amplification used).
`
`In this concept, the generator can supply power to the batteries when heat
`engine power is in excess of wheel demand, and the drive motor can also
`function as a generator during periods of deceleration, if desired (regenera-
`tive braking) Additionally, the drive motor could also function as a
`generator during vehicle cruise periods if the heat engine power output was
`prescheduled or "biased" via the throttle schedule in the control system to
`provide more power at any given speed than required by the vehicle for road
`load power. Conceptually, the baseline parallel systeln provides all of the
`operational attributes postulated for the various single motor parallel concepts.
`
`1 0. I. 3.2
`
`Operational Modes
`
`With the parallel configuration arrangement, a single mode of operation was
`selected as most compatible with the hardware arrangement and as providing
`an equitable comparison with the operational mode selected for the baseline
`series configuration. As shown in Fig. 10-8, the total power output of the
`heat engine is scheduled as a function of vehicle velocity, with that portion
`above a certain velocity equal to the steady road load power. Below this
`velocity, a minimum power level, constant with velocity, is selected. The
`
`10-13
`
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`
`
`
`HEAT
`ENGINE
`
`AUTOMAT I C
`TRANSMISSION
`
`o
`I
`
`GENERATOR
`
`MOTOR
`
`A.C. 1
`I O.C.
`Lt P°WE ;
`
`WHEEL
`
`DIFFERENTIAL --
`DRIVE UNIT
`
`CONDITIONING
`& CONTROL
`SYSTEM F
`
`BATTERY
`
`Figure 10- 7. Selected Baseline Parallel Configuration Concept
`
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`Page 20 of 52
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`
`
`LEVEL ROAD
`
`VEHICLE UNDER ACCELERATION"
`EXCESS TO WHEELS
`VEHICLE AT CRUISE :
`EXCESS TO GENERATOR
`(TO BA T TERY AND / OR
`ENERGY DUMP CIRCUIT)
`
`el::"
`t.~
`
`0
`
`o
`
`I
`
`U1
`
`MINIMUM
`ALLOWABLE
`POWER
`
`TOTAL POWER
`DELIVERED
`
`POWER TRANSMITTED
`MECHANICALLY TO REAR
`WHEELS (EQUAL TO POWER
`REQUIRED FOR STEADY
`ROAD LOAD)
`VEHICLE SPEED, mph
`
`Figure I0- 8. Parallel Configuration - Variation of Heat Engine
`Power with \;ehLcte Speed
`
`BMW1035
`Page 21 of 52
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`
`
`portion of heat engine power transmitted mechanically to the rear wheels is
`
`shown by the dashed line and is just equal to that power required for constant
`
`velocity road load demand. The difference, then, between the selected mini-
`
`mum power level and road-load demand is available to the generator, and is
`
`either used to charge the battery, go to the drive motor during acceleration,
`
`or to an energy dump circuit as appropriate to the particular driving
`
`schedule/cycle. During periods of vehicle deceleration, the mechanical
`
`power is reduced to zero and the heat engine power output is reduced to
`
`the minimum level. The motor (as a generator) and/or the generator can
`
`then utilize the heat engine power output during vehicle deceleration for
`
`battery recharging.
`
`10.2
`
`SIZING STUDIES
`
`10.2. 1
`
`Subsystem Sizing
`
`In order to conduct the desired performance and tradeoff studies, it was
`
`necessary to select subsystems, define vehicle characteristics and establish
`
`a baseline for comparing various vehicle classes. It should be stressed
`
`that, due to the complexity of factors and problems involved in analyzing
`
`various hybrid systems during the short duration of this study, it was only
`
`possible to make limited, general investigations of the wide range of sub-
`
`systems and alternative schemes possible. This report should therefore
`
`be considered in this context and as establishing the basis for more refined
`
`investigations.
`
`Component characteristics for the electrical subsystem are merely initial
`
`selections, based on the limited scope of technology review of Section 6, and
`
`do not at this time represent either optimized systems or preferred
`
`approaches. Rather they are considered to be preliminary selections serving
`
`as a baseline for comparison of various vehicles.
`
`In the case of the family car for example, to establish a baseline two types of
`
`motor voltage control were considered, namely:
`
`A solid state chopper control
`
`Voltage step switching combined with field control of the motor
`
`I0-16
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`Page 22 of 52
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`
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`Since step voltage switching combined with field control of the motor has
`
`not been extensively demonstrated for automotive application, this scheme
`
`would require thorough investigation to determine the feasibility of use in
`
`hybrid powertrains. If such a scheme is proven to be feasible, it offers the
`
`advantages of higher efficiency, lighter weight, and possibly lower cost.
`
`A comparison of component weights for electrical subsystems in series and
`
`parallel powertrain configurations is shown in Tables 10-1 and 10-Z for
`
`each vehicle class. All data shown are based on a control scheme using
`
`step voltage switching combined with field control of the motor except for
`
`the first column in each table which is based on a chopper scheme for
`
`controlling motor voltage. The two types of electrical control systems
`
`have been presented here in the case of the family car solely for relative
`
`comparison of weight, volume, and efficiency. This shows that the dif-
`
`ference in the total weight of electrical components in the two approaches
`
`is quite small compared to the overall family car weight.
`
`The step voltage/field control scheme was chosen [or the final analysis
`of component weights, power requirements, and costs, and was used as
`the basis for comparing the performance of various classes of vehicles. It
`is felt that the performance data obtained with this scheme applies approxi-
`mately to the chopper approach.
`
`I0. Z. I. 1
`
`Series Configuration
`
`Table I0-i denotes the characteristics of the electrical subsystems (drive
`motor, motor controller, generator, generator controller, AC rectifier)
`selected for the baseline series configuration for each of the six vehicle
`classes. Included in the table are such features as subsystem type, rating
`(where appropriate), volume, weight, and efficiency at rated load conditions.
`
`As mentioned previously, the final drive for the series configuration is
`defined as a conventional differential drive unit, adapted to contain an over-
`drive mechanism for a step-change in gear ratio during high-speed cruise
`operation for increased drive motor efficiency. The heat engine, of course,
`
`10-17
`
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`Page 23 of 52
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`
`
`Table I0-i. Baseline Series Configuration Characteristics of
`Selected Electrical Subsystems
`
`Vehicle
`
`Family Car
`
`Delive ry/Postal Van
`
`City Bus
`
`Subs~’stem
`
`Electmc Drive Motor
`
`t
`
`Type
`
`Rated Voltage, volts
`
`Rated HP, hp
`
`Volume, ft3
`
`Weight, Ib (5)
`
`Ef/;.ciency @ Rated Load, %
`
`,Motor Controller
`
`Volume. ft3
`
`Weight, lb
`
`Efficiency ~ Rated Load, %
`
`G,e r.e rato r (1)
`
`DC Choppe r
`
`Step Voltage b
`Field Control (3)
`
`Con~ mute r Car
`
`Low Speed
`
`High Speed
`
`Low Speed
`
`High Speed
`
`DC Series
`
`DC Shunt-Wound
`
`DC Shunt-Wound
`
`DC Series
`
`DC Series
`
`DC Series
`
`DC Compound
`
`220
`
`61
`
`4.3
`
`315
`
`9O
`
`1.8
`
`IZ0
`
`95
`
`220
`
`61
`
`4.80
`
`337
`
`92
`
`0.023
`
`12.5
`
`99
`
`220
`
`21
`
`2.24
`
`133
`
`92
`
`0.023
`
`9.5
`99+
`
`220
`
`30
`
`2.94
`
`15b
`
`92
`
`1.4
`
`64
`
`97.4
`
`220
`
`80
`
`6.75
`
`462
`
`94
`
`1.8
`
`84
`
`97,4
`
`440
`
`I00
`
`440
`
`175
`
`14.60
`
`14.53
`
`816
`
`94
`
`3.0
`
`135
`
`97.7
`
`968
`
`94
`
`2.5
`
`112
`
`97.6
`
`AC
`
`AC
`
`AC
`
`AC
`
`i..a
`
`O
`I
`
`O0
`
`Type
`
`Maximum-RPM
`
`Rated Output, kw
`
`Volume, ft3
`
`Weight, Ib (4)
`
`Efficiency@ Rated Load, %
`
`AC Rectifier
`
`Volume, ft3
`
`Weight, lb
`
`Efficiency~ Rated Load, %
`
`C~ne rator Controller
`
`Volume, ft3
`
`Weight, lb
`
`Cables, Low I_~vei Electronics,
`.-Xccessories, Cooling System &
`.V.~ scellaneous
`
`AC
`
`12,000
`
`54
`
`0.2
`
`84
`
`90
`
`0.15
`
`18
`99+
`
`0.02
`
`3
`
`AC
`
`12. 000
`
`AC
`
`12,000
`
`51
`
`0.16
`
`80
`
`9O
`
`0.15
`
`18
`
`99+
`
`0.02
`
`3
`
`18
`
`0.09
`
`37
`
`90
`
`0.05
`
`9
`
`99+
`
`0. 009
`
`I
`
`12,000
`
`28
`
`0.12
`
`52
`90
`
`0.1
`9
`99.6
`
`0.02
`
`3
`
`12,000
`
`12, ooo
`
`12,000
`
`71
`
`0.25
`
`103
`
`9O
`
`0.1
`
`9
`
`99.6
`
`0.02
`
`3
`
`88
`0.30
`126
`9O
`
`0.1
`
`9
`
`99.b
`
`0.02
`
`3
`
`154
`
`0.50
`
`195
`
`90
`
`0.2
`
`18
`
`99.6
`
`0.02
`3
`
`Weight, Ib (2)
`
`55
`
`50
`
`38
`
`45
`
`8O
`
`120
`
`150
`
`(1) Gear weight accounted for in Tables I0-7 through I0-12.
`121 This weight accounted for as part of vehicle body weight.
`13i This column used for final analysis results (Sections 10 and 11).
`(41 Allowing a derating factor of 15% for possible variation in heat engine speed.
`(5) W.thout forced air cooling system.
`
`BMW1035
`Page 24 of 52
`
`
`
`Table 10-2. Baseline Parallel Configuration Characteristics of
`Selected Electrical Subsystems
`
`Vehicle
`
`Family Car
`
`Delivery/Postal Van
`
`Ctty Bus
`
`Subsystem
`
`Electric Drive Motor
`
`Type
`
`Rated Voltage, volts
`
`Rated F!P. hp
`
`Volume, ft3
`
`Weight. lb (5)
`
`Efficiency~ Rated Load, %
`
`Motor Controller
`
`Volume, It3
`
`Weight, Ih
`
`Efficiency@Rated Load. %
`
`Generator (I)
`
`Type
`
`DC Chopper
`
`Step Voltage &
`Field Control (3)
`
`Commuter Car
`
`Low Speed
`
`High Speed
`
`Low Speed
`
`High Speed
`
`DC Series
`
`DC Shunt-Wound
`
`DC Shunt-Wound
`
`DC Series
`
`DC Series
`
`DC Series
`
`DC Compound
`
`Z20
`
`38
`
`3.4
`
`250
`
`92
`
`0.023
`
`IZ.5
`
`99+
`
`220
`
`38
`
`3.0
`
`232
`
`9O
`
`l.S
`
`1oo
`
`95
`
`AC
`
`2Z0
`
`12
`
`1.2
`
`83
`
`9Z
`
`0.0Z3
`
`9.5
`
`99÷
`
`AC
`
`220
`
`30
`
`2.95
`
`170
`
`92
`
`1.4
`
`64
`
`97.4
`
`AC
`
`Z20
`
`30
`
`2.95
`
`170
`
`94
`
`1.4
`
`64
`
`97.4
`
`440
`
`100
`
`14.66
`
`831
`
`94
`
`3.0
`135
`
`97.7
`
`440.
`
`30
`
`2.95
`
`170
`
`94
`
`1.4
`
`64
`
`97.4
`
`O
`!
`
`xD
`
`Maximum RPM
`
`Rated Output, kw
`
`Volume. ft3
`
`Weight. Ib (4)
`
`Efficiency @Rated Load, %
`
`AC Rectifier
`
`Volume. ft3
`
`Weight. th
`
`Efficiency@Rated Load, %
`
`Generator Controller
`
`Volume, ft3
`
`Weight, Ib
`
`Cables, Low Level Electronics.
`Accessories. Cooling System &
`Miscellaneous
`
`1Z,000
`
`8.1
`
`0.08
`
`19
`
`90
`
`0.1
`
`9
`
`99+
`
`0. 009
`
`2
`
`AC
`12,000
`7.5
`0.07
`18
`9O
`
`0.1
`
`9
`
`99+
`
`O. 009
`
`2
`
`lZ,000
`
`12.000
`
`AC
`
`12,000
`
`AC
`
`12,000
`
`4.5
`
`0.06
`
`12
`
`90
`
`O.OS
`
`S
`
`99+
`
`0.009
`
`z
`
`13
`
`0.08
`
`27
`
`90
`
`0.1
`
`9
`
`99.6
`
`13
`
`0.08
`
`27
`
`90
`
`0. I
`
`9
`
`99.6
`
`63
`
`0.19
`
`95
`
`90
`
`0.1
`
`9
`
`99.6
`
`0.009
`I
`
`0. 009
`
`1
`
`0.009
`
`1
`
`A