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`760121
`
`Hybrid Vehicle for
`Fuel Economy
`
`L. E. Unnewehr, J. E. Auiler, L. R. Foote,
`D. F. Moyer, and H. L. Stadler
`ResearchStaff, Ford Motor Co.
`
`system« principally in Increased initial
`coat as compared to conventional systems.,
`but this cost differential may be reduced
`as improved electrical components are
`developed and. as automotive production, and
`marketing techniques are applied to thé
`electrical components.» Other potential
`limitations of this hybrid system are
`reduced driving range at very low speeds
`and reduced capability tó supply vehicle
`auxiliaries at standstill¿
`Xn general:,
`the .replacement of a conventional drive
`train hy this particular hybrid train will
`not increase the vehicle curb weight.
`From almost the beginning of the
`Automotive Age, various1 combinations of
`drive systems luve 'been cried in order to
`achieve vehicle performance
`characteristics superior to those that can
`be obtained using a single type of drive.
`These efforts have been made in the name
`of many worthwhile goals * such as
`increased vehicle acceleration capability,
`audible noise reduction, operation of an
`engine or turbine at optimum efficiency,,
`reduction of noxious emissions, and
`improved fuel economy,
`these efforts have
`so far not led to any commerciai
`
`and amissions characteristics, and has
`been compared with eatieting internai
`combustion engine drive trains and other
`types of hybrid drives.
`A prototype
`system has been assembled and evaluated on
`a dynamometer test stand and has
`corroborated the computer analysis end
`predictions.,.
`-Problems and limitations of
`this system are discussed.
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`A HEAT ENGINE/ELECTRIC drive train has
`been evaluated as a means of improving the
`fuel economy of various types of
`automotive vehicles. Computer simulation
`studies and dynamometer tests on a
`prototype system indicate that
`improvements in CVS-Hot fuel economy
`(miles/gallon> of from 30% tö 100% can be
`realized with this system in a vehicle of
`identical weight and performance
`characteristics. Preliminary test data
`also indicates that these fuel economies
`may be realisable while meeting the
`1975/76 Federal Emission Standards (1.5HC,
`15CO, 3.1NOx) with the use of external
`emissions controls such as catalytic
`converters. Although similar in
`configuration to a standard parallel
`hybrid drive train, the control strategies
`and energy flow of this system are
`considerably different from any known
`hybrid drives. This system does not
`appear to be of equal merit for all
`classes of vehicles, but gives the
`greatest fuel economy improvements when
`applied to delivery vans, buses, and large
`passenger cars. There are certain
`drawbacks to this particular hybrid
`
`ABSTRACT-
`
`A heat engine/electteU hybrid drive
`train is proposed as a means for !improving
`CVS-Hot fuel economy by an estimated 3OH!
`tô 100% in various types of automotive
`vehicles,
`Sfhia dJfive train, classified as
`à parallel hybrid, has been analysed by
`means of computer simulation studies to
`evaluate its fuel economy, performance,
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`applications, although several
`experimental hybrid buses and rapid
`transit vehicles are being evaluated at
`the present time (1,2,3). For private
`vehicle applications, hybrid drive systems
`have generally been found to offer
`insufficient improvement in meeting one or
`more of the goals stated above to justify
`the added coat and complexity compared to
`a singular drive system, particularly
`compared to the conventional Otto cycle
`internal combustion engine drive system.
`Two extensive EPA-sponsored studies of
`heat engine/electrical hybrid systems have
`been published (4,5) and generally concur
`in this conclusion, as does the more
`recent JFL Report. (6)
`It is therefore with some trepidation
`that the subject of this paper, a heat
`engine/electric hybrid drive system, is
`proposed as a viable drive train for
`modern automotive vehicles of many
`varieties. However, this proposition has
`been developed - and to large extent,
`confirmed - on premises somewhat different
`from those upon which the EPA studies were
`based:
`
`1.The critical fuel situation in the
`U.S. and moat Western countries has
`placed increased emphasis on improved
`fuel economy for all types of vehicles
`since the initiation of the EPA
`studies of Reference 3 and 4. Recent
`large increases in gasoline prices
`have led to the conclusion that a
`sizable increase in initial vehicle
`cost (resulting from the use of a
`hybrid drivetrain) can be justified if
`a sufficient improvement in vehicle
`fuel economy is realized.
`2.Studies performed during the
`development of this system heve shown
`that the relative size and power
`rating of the hybrid drive train
`components with respect to the vehicle
`weight and performance rating have an
`important influence on vehicle fuel
`economy, Hybrid drive trains may not
`improve fuel economy for vehicles of
`every size, weight, and application
`category. Stated in another way,
`hybrid drive trains are not "scalable"
`as a function of vehicle size or
`weight as are singular drive trains.
`3.The modus operandi or control
`philosophy of a hybrid can have a
`profound influence on. both fuel
`economy and emissions.. Fast hybrid
`developments have, tended to use the
`heat engine primarily as a battery
`charger; the subject hybrid reverses
`this philosophy and makes minimum use
`of the electric system.
`
`It is hoped that the validity of
`these principies will be amplified hy
`subsequent sections of this paper.
`SYSTM DESCRIFTIOH
`
`The
`
`A block diagram of the system
`illustrating functional performance and
`energy flow paths is shown in Figure U
`This drive system is intended to replace
`the engine-transmission system in
`conventional vehicles with the result of
`increasing the vehicle CVS-Hot fuel
`economy .(miles/gallon) from .3OjE to 100% at
`1?75/76 Federal emission levels using the
`CVSHttot cycle while maintaining
`approximately equivalent accelerating,
`braking, and passing characteristics.
`hybrid-electric system consists of the
`following major componente;
`1.A different internal combusion engine,
`considerably smaller in displacementf
`and, hence, horsepower capability,
`than the engine in the originel drive
`train.
`2.An electric motor/generator (one unit.)
`Which may he on a common shaft with
`the engine output sheft or connected
`to the engine output shaft hy means of
`a gear, belt, or chain system. The
`motor/generator may he of the BG
`commutator, DC homopolar, synchronous,
`or induction types..
`3.A means of controlling power flow
`between the motor/generator and
`battery. This may be an electronic
`controller using power thyriators or
`transistors, contactor controller
`using battery switching techniques, or
`similar devices. The controller must
`be. capable of two-way power flow and
`Should have high energy efficiency.
`4.An energy storage device. This may he
`any device capable of handling the
`high bursts of power required by the
`drive train during accélération sad
`braking and of supplying the energy
`needs for low-speed driving end the
`operation of vehicle auxiliaries at
`low speed's and standstill, At the
`¿resent time» batteries are the most
`practical energy storage device, with
`the nickel*cadmium battery having
`almost ideal characteristics for this
`application hut suffering a cost
`penalty.. Flywheels, fuel celie, in
`combination With batteries., closed
`loop cryogenic expander systems/ are
`other possibilities..
`5.A differential and a drive shaft,
`In
`general, it is desired to use the
`original drive shaft and differential
`of the vehicle.
`The system can be classified as a
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`parallel hybrid with engine on-off
`control, and bears some similarity in
`configuration with two other recent hybrid
`developments.
`(9),(10)
`In addition to these major power
`components, other components required by
`the hybrid drive train include:
`control
`circuitry for the proper operation of the
`power controller; modified engine throttle
`and carburetor; sensors for converting
`vehicle speed, battery voltage and charge
`level, component temperaturas, etc., to
`electrical signals suitable for use in
`control and protection systems; protection
`systems for both engine and electrical
`system emission controls; and an overall
`vehicle control system.
`Two modifications of the above system
`(Figure 1) have capabilities for improved
`system performance but usually add some
`cost penalties:
`1.
`The use of an automatically-controlled
`decoupler to permit
`the engine to be
`detached from the electrical motor
`drive shaft when the vehicle is
`operating in an all-electric drive
`mode or in a braking mode.
`It has
`been shown that the use of such a
`clutch will result in a further
`improvement in fuel economy (see
`Figure 5).
`2. The use of an electrically-controlled
`gear changing system. This will often
`result in a reduce electrical system
`weight and an improved electrical
`system efficiency.
`
`SYSTEM OPERATION
`
`The system has six modes of
`operation.
`The first five modes are shown
`in Figure 2. Mode I is all electric at
`speeds below 10 to 15 MPH.
`In Mode II the
`engine is the primary source of propulsion
`and there is no energy in or out of the
`
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`electrical system. Mode III is the
`battery charging mode. The engine still
`drives the rear wheels; however, excess
`energy is used to charge the battery.
`When acceleration demande exceed the power
`input of the engine,
`the motor provides
`the needed additional power. This is
`shown as Mode IV. Mode V is regenerative
`breaking. The deceleration energy of the
`vehicle is used to charge the battery.
`Fuel is shut off to the engine during the
`all electrical mode and during braking.
`The battery state of charge is maintained
`between fairly narrow limits by the
`control system around a state of charge of
`about 75% of full charge. This strategy
`prevents deep discharge cycles on the
`battery. The sixth mode is at vehicle
`standstill, during which condition both,
`the engine and electrical motor are
`inoperative or "dead". Required vehicle
`auxiliaries are supplied electrically at
`standstill.
`The objective of this system is to
`provide an increase in fuel economy over a
`conventional automotive drive system while
`maintaining equivalent acceleration
`performance. Comparisons between the
`hybrid system and conventional systems
`heve been stressed in all studies. The
`manner in which this comparison is viewed
`from an overall systems standpoint is
`important in understanding the
`significance of this particular hybrid
`configuration and its operation.
`Figures 3 end 4 show that the fuel
`economy for both a conventional and hybrid
`system can be expressed as follows:
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`where ?E is the average engine brake
`termal efficiency, ?PT is the average
`transmission efficiency,
`(Q/Gal) is the
`energy content per gallon gasoline
`consumed and (EW/Mile) is the total energy
`requirement at the drive wheels per mile
`necessary to accelerate the vehicle and to
`overcome vehicle friction and aerodynamic
`drag. The quantities in this expression
`represent average values over a prescribed
`driving cycle.
`It should be noted that
`the average powertrain efficiency is
`defined as the ratio of total positive
`engine shaft work to total positive energy
`requirement at the drive wheels. Stated
`in another way, this represents the
`fraction of total engine work used to
`propel the vehicle. For the hybrid drive
`train state of charge ie assumed to be the
`same at the beginning and end of the drive
`cycle,
`thus the net energy input to the
`transmission from the battery is zero.
`The task facing the hybrid system can
`now be clearly seen.
`In order to provide
`an increase in fuel economy over a
`conventional system the quantity?E ?PT
`/(EW/Mile) must be increased, The present
`hybrid system will be described in terms
`of how it strives to maintain high average
`engine efficiency, high average
`transmission efficiency and low work
`requirements at the drive wheels while
`maintaining the equivalent acceleration
`performance of the conventional system it
`replaces.
`A. High Average Engine Efficiency
`1.Small engine - The engine used in
`the conventional system is
`replaced by a much smaller engine
`in the hybrid system. The smaller
`engine operates at higher load
`factors, resulting in increased
`efficiencies. The hybrid engine
`is sized to meet vehicle cruise
`requirements up to a specified
`road speed. This enables the
`vehicle to be propelled by the
`engine alone for extended cruise
`periods. This corresponds to Mode
`II in Figure 2.
`2.Fuel off during idle and
`deceleration - Approximately 20%
`of the CVS-H fuel consumption is
`used during idle and braked
`deceleration for the conventional
`vehicles with automatic
`transmission considered in this
`study. Elimination of idle and
`braked deceleration fuel flow in
`the hybrid configuration results
`in significant improvements in
`average engine efficiency.
`3.Fuel off during low speed
`operation - Since the engine is
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`geared directly to the drive
`Wheels the fuel is shut off at low
`vehicle speeds and the vehicle is
`propelled by the electrical
`system. This corresponds to Mode
`I in Figure 2.
`The fuel savings
`must be weighed against, the
`electrical energy dissipated that
`must be replaced by charging the
`battery later in the driving
`cycle. Since this charging is
`done at a higher engine
`efficiency, this mode has a
`positive effect on the average
`engine efficiency. However, thie
`charging has an adverse effect on
`the average transmission
`efficiency since a lower fraction
`of the engine work shows up as
`useful work at the drive wheels.
`The total gasoline used to replace,
`the battery energy expended during
`this mode can actually exceed the
`amount of gasoline used In a
`conventional vehicle in
`accelerating up to the
`corresponding vehicle speed. The
`energy requirements of this mode
`can be substantially improved by
`lowering the work required to
`motor the engine by opening the
`throttle, collapsing the valves or
`by de-clutching the engine. Other
`approaches include gear changes or
`USe of motors with better
`lew-speed efficiencies.
`4.Charging the battery at
`high-engine efficiency - When the
`battery requires charging from the
`engine as represented by Mode III
`in Figure 2, the basic strategy is
`to provide the charging energy at
`the most efficient engine
`operating point. This contributes
`to a high overall engine energy
`efficiency; however, this effect
`must be weighed against the effect
`on transmission efficiency since
`the optimum engine efficiency will
`not in general correspond to the
`most efficient charging torque
`level for the electrical system.
`Additional trade-offs appear when
`the effect of engine torque on
`emissions is discussed in a later
`section.
`5.Accelerate at high-engine
`efficiency ¦- When the vehicle
`acceleration demands exceed the
`power capacity of the engine,
`the
`electrical system is used to
`provide the extra needed power.
`This is described as Mode IV in
`Figure 2.
`In general the engine
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`torque level at which the
`electrical system is called upon
`corresponds to a high-engine
`efficiency point. The effect Ort
`transmission efficiency must also
`be considered since a lower engine
`torque requires more electrical
`energy..
`B.Transmission Efficiency - the
`transmission in a hybrid drive train
`is the portion of the system that
`transmits useful work from the engine
`to the drive wheels. Since all the
`energy needed to propel the vehicle
`ultimately comes from the engine
`(assuming the battery ends the drive
`cycle at the same state of charge) the
`basic objective of the transmission is
`to minimize the amount of engine
`.energy used for other purposes. This
`is achieved as follows:
`1.Engine geared directly to rear
`wheels for primary source of
`propulsion r· When the electrical
`system is not in use,
`the energy
`from the engine is transmitted
`directly to the rear wheels
`through the differential. This is
`Mode II in Figure 2. The
`instantaneous transmission
`efficiency during this mode is
`essentially equal to the
`differential efficiency.
`The
`engine is sized to provide
`sufficient torque in this mode for
`extended high-speed cruise.
`2.Use of electrical system only when
`needed - To keep the use of the
`electrical system to 4 minimum,
`the motor is used only when
`needed..
`The two modes requiring
`the motor are the. all electric
`mode at low speed (Mode I) and
`during heavy accelerations Kode
`m*
`3· Ose of regenerative braking During
`braking the kinetic energy of
`the vehicle is used tó charge the
`battery. This is described as Hode
`V in Figure 2. This has a substantial
`effect on transmission efficiency
`by reducing the charge energy
`required from the engine. C.
`DriveWheel Energy - In converting a conventional
`vehicle to a hybrid configuration
`the total energy requirements
`at the drive wheel must also
`be considered in assessing thepotential
`fuel economy gains. The primary
`factors that could reduce fuel economy
`are an increase in the vehicle weight
`and an increase in the rotational
`inertia due to higher
`rotational
`speeds of the engine and
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`motor. System weights will vary
`considerably with the vehicle
`acceleration requirements. For the
`hybrid configurations considered in
`this study small weight savings were
`realised. These differences were
`generally not enough to change the
`inertial weight class of the vehicle
`and were not considered in the fuel
`economy projections. The effects of
`increased rotational inertias were
`also seen to be minimal for the
`configurations investigated.
`METHOD OF ANALYSIS
`A computer program was developed to
`simulate all elements of the drive train
`for the six basic modes of operation over
`an arbitrary drive cycle. The required
`power at the drive wheel is computed from
`the drive cycle data,
`the vehicle
`friction, aerodynamic drag, inertial
`The
`acceleration and rotational inertias.
`corresponding power levels are computed
`throughout the drivetrain based on
`rotational speeds and torques and
`component performance characteristics.
`Motor/generator and controller
`efficiencies are computed from efficiency
`tables in terms of torque and RPM. The
`efficiency tables used for the D.C. system
`are based on experimental data from
`reference (7). Similar tables for a
`brushless synchronous motor system are
`based on experimental data from reference
`(8). Battery efficiency is computer from
`equivalent circuit models for specific
`battery types as described in Reference
`16).
`The engine is sized to provide
`sufficient power for extended cruise
`without the electrical system. Fuel flows
`axe computed in terms of engine speed and
`torque.
`In general, automatic calibration
`fuel island data is used with simulated
`exhaust system, fan on, alternator
`operated at one-half charge end power
`steering pump loaded. Engine motoring
`torque is computed as a function of engine
`RPM from experimental data.
`Axle ratio between the engine and
`drive wheels and gear ratio between the
`motor and engine are varied in the
`analysis until a suitable compromise is
`reached between fuel economy,
`top speed,
`acceleration, maintaining battery charge
`and, in some cases, emissions.
`Comparisons with conventional
`drivetrains are made by applying the same
`basic technique of starting at the rear
`wheels and describing each element
`individually. Transmission efficiencies
`are computed for each gear from output
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`speed. Automatic transmission shift
`schedules are determined from driveshaft
`RPM and manifold vacuum. Manifold vacuum
`must be implied from engine torque which
`cannot be computed until the proper gear
`is determined. The engine torque and
`transmission shift schedule must,
`therefore, be matched iteratively.
`The approach is similar to techniques
`described in Reference (11) for
`conventional vehicles and in Reference
`(16) for electric vehicles.
`DYNAMOMETER TESTS
`Early in the course of the computer
`simulation and other analytical studies of
`the hybrid concept,
`the need for some
`experimental evidence to support the
`computer predictions of fuel economy and
`performance was recognised. Also,
`emission measurements and engine strategy
`for emission control ware required. The
`first step in such experimental
`evaluations has been the testing of an
`engine-electric drivetrain with a
`dynamometer and inertia wheel as loading
`devices. Ultimate evaluation of any
`alternate engine or other drivetrain
`component must of necessity by made
`through a long series of vehicular tests
`under typical or prescribed driving
`conditions. However, for systems so far
`removed from conventional automotive
`practice as a hybrid drivetrain,
`dynamometer testing appears essential
`before vehicular testing is initiated.
`The principal goals of the hybrid
`dynamometer tests were:
`1.To test the computer predictions of
`fuel economy, performance, and
`emissions using a production engine.
`2.To establish that the fuel economy
`improvement is attainable at
`acceptable emission levels. This
`required that near optimum engine
`strategy regarding spark, air-fuel
`ratio, and exhaust gas recirculation
`be developed. This was done by
`dividing the speed torque plane in a
`grid pattern, studying each area in
`the grid and summing the total for
`hybrid operation. This process is
`called engine mapping in subsequent
`discussions.
`3.To determine that the on-off fuel
`control required by the hybrid was
`practical at acceptable performance,
`emissions and cost. This was
`determined using a carburetor and
`minor modifications.
`4.To determine that the selected battery
`was adequate.
`5.To determine that the engine is
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`basically suited to the unique or
`unusual operations in this concept,
`such as:
`a.Motoring the engine between0 and
`800 RPM as required by the direct
`coupling to the wheels. Normally
`an engine is cranked and
`immediately accelerated to an idle
`speed of 700 RPM or more.
`b.Operation at high torque most of
`the time.
`C. Higher than normal total use and
`long duration of high torque at
`high speed.
`The experimental hybrid drivetrain
`was configured as in the block diagram of
`Figure 1 with two exceptions: The
`electric motor was on a common shaft with
`the engine, and the driveshaft was
`directly coupled to a dynamometer and
`inertia wheel to simulate the vehicle
`road, aerodynamic, and inertial loads.
`The principal components used were:
`1. Engine: Ford 2.3L, 4-cylinder,
`'74
`production engine, modified for fuel
`off operation.
`2. Motor: Westinghouse, 40HP, 240 V.,
`1750 RPM industrial shunt motor;
`blower cooled.
`3. Controller:
`SCR chopper for motor
`armature control during motoring and
`regenerative braking (designed and
`assembled at Ford); separate power
`supply for field control.
`4.Battery:140 cells connected in
`series of Marathon,
`type 20D120, NiCd;
`auxiliary forced-air cooling to
`maintain cells at approximately 20 C;
`plus required monitoring equipment.
`5.Loading Device: Absorption
`dynamometer of 150 lb-ft2 inertia and
`a flywheel of 360 lb-ft2 inertia.
`The combined inertias of the rotating
`members of the experimental system are
`equivalent to a vehicle of 7500 lb.
`inertia weight based upon an engine
`RPM/vehicle MPH (N/V) ratio of 53.5.
`Conventional gas analysis equipment was
`used to measure emissions under conditions
`of steady state engine operation.
`Measurements of exhaust CO, CO2, HC. O2,
`and NOx
`and intake CO2 were made. Fuel
`flow was measured by weight.
`Since the hybrid application requires
`operating an engine under conditions
`considerably different from those
`associated with conventional vehicles,
`preliminary evaluation and modification of
`the 2.3L engine was necessary:
`1. The engine was modified to permit fuel
`to be turned off during deceleration
`and at speeds below 15 MPH. This wee
`accomplished by means of a small
`solenoid valve to block fuel flow in
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`the idle jet, removal of the throttle
`stop to permit full closure of the
`throttle plate, a means of admitting
`air below the throttle, and PCV
`modification.
`2.A sequence control was required for
`minimum emissions and quality
`performance during engine fuel turn-on
`and turn-off. For example, during
`turn-off,
`the following sequence was
`used:
`(a) close throttle, idle
`solenoid, and PCV valve,
`(b) open
`by-pass air valve around throttle to
`permit air without fuel into intake
`manifold, (c) turn-off ignition, with
`elapsed time between these events.
`3.Removal of some engine auxiliaries;
`for example, the engine alternator is
`not required in a hybrid drive; air
`conditioner was not used. The power
`steering pump was connected and
`driven.
`4.Low-speed engine friction:
`In a
`conventional vehicle,
`the engine is
`operated below the idle speed (about
`800 RPM) for only a few seconds during
`start-up.
`In the hybrid, much longer
`operation may be required. The
`low-speed friction torques of the
`2.3L
`engine were measured.
`5.Low-speed lubrication was evaluated.
`6. The EGR valve and plumbing were
`enlarged to permit large EGR flow at
`wide-open throttle operation.
`Another interesting problem for which
`there was almost no precedent was the
`measurement of HC emissions during the
`frequent engine off/on transitions that
`the engine passes through during a typical
`driving cycle. Since CVS equipment for
`this measurement was not available a
`technique using diluted samples from the
`engine-off period was developed and
`considered to give reasonable accuracy.
`This method was used to predict the
`emissions discussed in later sections of
`this paper.
`The resulting experimental system
`proved to be very "driveable" with smooth
`transitions between the various operating
`modes.
`The system was "driven" through
`several of the standard test driving
`cycles with ease and accuracy after a few
`learning cycles by the operator.
`In order to experimentally verify the
`calculated values of fuel economy that had
`been obtained from the various computer
`simulations described above, several
`dynamic runs over both CVS-H and SAE (17)
`driving cycles were performed on the
`experimental hybrid system mounted on a
`dynamometer test stand.
`The SAe driving
`cycle is a simplified version of the CVS-H
`cycle developed mainly for the electric
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`vehicle tests. Many comparisons of the
`two driving cycles have shown that both
`result in approximately the same fuel
`consumption for both ICE and electric
`vehicles. Since the "driving" of an
`experimental drivetrain on a dynamometer
`test stand over the SAE cycle is muc h
`simpler than over the CVS-H cycle, and
`since the control of the system was not
`fully automated but required considerable
`manual control, the SAE cycle was chosen
`as the means for comparing calculated with
`measured fuel economy of the hybrid
`drivetrain.
`It was found that after only
`a few tried, manual, control was able to
`follow the required speed and acceleration
`variations specified by the SAE cycle
`almost perfectly.
`The actual efficiencies
`of the components in the electric branch
`of the hybrid and the actual road load
`simulated by the dynamometer were fed into
`the computer model to obtain the
`calculated fuel economy.
`The engine
`throttle positions were likewise made to
`correspond between the measure and
`calculated test runs. The results are
`summarized below:
`
`FUEL ECONOMY STUDIES WITH AUTOMATIC ENGINE
`CALIBRATIONS
`A variety of studies was conducted by
`applying the computer program to hybrid
`and conventional versions of the name
`vehicle using fuel island data for stock
`engines with automatic calibrations. The
`hybrid electrical systems were sized to
`provide approximately equivalent
`acceleration performance. The results of
`these studies are summarised in Figure 5.
`The purpose of this section is to discuss
`the reasons for the fuel economy
`improvement resulting from a hybrid system
`and to discuss the effects of fundamental
`system changes on fuel economy.
`A. Reasons for Fuel Economy Improvement
`Resulting from a Hybrid System - The
`Econoline Van and the Mark IV
`configurations received the most
`emphasis in these studies. Figures 6
`and 7 present summaries of comparisons
`made between typical hybrid and
`conventional versions of the Econoline
`Van and Mark IV, respectively. The
`computations were done for the CVS-H
`drive cycle and both comparisons are
`based on equivalent acceleration
`performance between the respective
`hybrid and conventional
`configurations. Both hybrid systems
`represent typical configurations with
`automatic engine calibrations, DC
`motor and controller and normal idle
`throttle engine, motoring friction
`during fuel off modes.
`In Figure 6 a 4500 lb.
`conventional van with 300 CID engine
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`during braking. Gearing between the
`engine and rear "wheels gives a ratio
`of engine RPM to vehicle speed in MPH
`N/V) of 100, while the ratio of
`electric motoï SFH to engine KFM is
`1.75. The weight summary of this
`substitution is shown in Table II. The
`performance predictions (acceleration)
`for this same vehicle are given in
`Table III.
`In Figure 7 a 55O0 lb.
`conventional 1974 Mark IVwith 460 CID
`engine and automatic transmission is
`compared to a 5500 lb, hybrid Hark IV
`witha 2.3 liter engine, DC motor with
`260 ft. lb. peak torque and 80 KW of
`NiCd batteries. Accelerations are
`done at wide-open throttle, while
`battery charging is done at optimum
`fuel consumption. Fuel is shut off at
`
`and autometic transmission is compared
`to a 450D lb, hybrid van with a 1.1
`liter engine, DC motor with 130 ft.
`Ib. peak torque And 45 KW of NiCd
`batteries. Acceleration and battery
`charging axe both done at wide-open
`throttle and fuel is shut off at
`engine speeds below 1000 RPM and
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`engine speeds below 800 RPM and during
`braking. Engine RPM to vehicle MPH is
`58.66,
`and electric motor RPM to
`engine RPH is 2.27.
`The comparisons shown in
`Figures 6 and 7 illustrate the
`following important characteristics
`regarding fuel economy comparisons
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`3.
`
`system with automatic transmission
`and torque converter.
`The effect of higher rotating
`inertias on the required work at
`the drive wheels for the hybrid
`configurations is not a
`significant factor in the fuel
`
`(b)Non-emissionized.
`
`(c) Emissionized.
`(e)
`CVS-CH at 4500 lb. test weight, 25 HP
`motor, a 50 KW battery, and maximum
`speed of 81 mph.
`(g) Computer projections developed by
`Powertrain Research, PP&R, Ford Motor
`Company.
`"Time Exposed to Danger"; this is the
`time required to gain 150 ft. on a
`vehicle traveling at 55 mph.
`
`(h)
`
`between hybrid end conventional
`vehicles over the CVS-H drive cycle:
`1.For both the van and Mark IV
`configurations the improvement in
`the hybrid fuel economy is
`approximately equal to the
`improvement in overall engine
`efficiency.
`2.Average hybrid transmission
`efficiencies are comparable in
`magnitude to the transmission
`efficiencies of the conventional
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`economy, resulting in fuel economy
`penalties of less than 2%.
`Another important feature of these
`comparisons is the much greater fuel
`economy improvement shown for the
`hybrid Mark IV (66.7%) over that shown
`for the van (37.9%). Fuel economy is
`stated in miles per gallon. The
`reasons for this difference are shown
`in Figures 8 through 11 which show
`distributions of fuel utilization over
`the CVS driving cycle for the
`conventional and hybrid versions of
`the van and the Mark IV. The
`percentages of total fuel consumed at
`various engine operating points are
`indicated by the numbers enclosed by
`the dashed square regions. This
`information is superimposed on the
`engine fuel island curves which show
`contours of constant engine efficiency
`and brake specific fuel consumption in
`terms of engine RPM and brake
`horsepower for an automatic engine
`calibration. The conventional van
`does not offer as much improvement
`potential.
`In addition, it was
`necessary to charge at wide open
`throttle with the hybrid van, while in the
`case of the Mark IV charging was done at
`optimum fuel consumption resulting in a
`higher average engine efficiency. The
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`difference in engine efficiency d