760121
`
`Hybrid Vehicle for
`
`Fuel Economy
`
`L. E. Unnewehr, J. E. Auiler, L. R. Foote.
`D. F. Moyer, and H. L. Stadler
`Research Stafl. Ford Motor Co.
`
`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% to 1002 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 realizable while meeting the
`1975/76 Federal Emission Standards (1.5HC,
`15C0, 3.lN0 ) with the use of external
`emissions cdntrols 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
`
`system, principally in increased initial
`cost 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 the
`electrical components. other potential
`limitations of this hybrid system are
`reduced driving range at very low speeds
`and reduced capability to supply vehicle
`auxiliaries at standstill.
`In general,
`the replacement of a conventional drive
`train by this particular hybrid train will
`not increase the vehicle curb weight.
`From almost the beginning of the
`Automotive Age, various combinations of
`drive systems have been tried 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 comercial
`
`ABSTRACT __.._.—__..————————_-_—....———~-——----——————————————————————
`
`A heat engine/electric hybrid drive
`train is proposed as a means for improving
`CV8-Hot fuel economy by an estimated 302
`to 1002 in various types of automotive
`vehicles. This drive train, classified as
`a parallel hybrid, has been analyzed by
`means of computer simulation studies to
`evaluate its fuel economy, performance,
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`and emissions characteristics, and has
`been compared with existing internal
`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 and
`predictions. Problems and limitations of
`this system are discussed.
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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 cost and complexity compared to
`a singular drive system, particularly
`compared to the conventional Otto cycle
`internal combustion engine drive system.
`Two extensive EPArsponsored studies of
`heat engine/electrical hybrid systems hve
`been published (4,5) and generally concur
`in this conclusion, as does the more
`recent JPL Report.(6)
`It is therefore with some trepidation
`that the subject of this paper, a eat
`engine/electric hybrid drive system,
`is
`proposed as a viable drive train for
`mdcrn automotive vehicles of many
`varieties. However,
`this proposition has
`been developed — and to large extent,
`confirmed a on premises somewhat different
`from those upon which the EPA studies were
`based:
`
`1.
`
`The critical fuel situation in the
`u.s. and most 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) Egg be justified if
`a sufficient improvement in vehicle
`fuel economy is realized.
`2. Studies performed during the
`development of this system have 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.
`The nodus operandi or control
`philosophy of a hybrid can have a
`profound influence on both fuel
`economy and emissions. Past hybrid
`developments have tended to use the
`heat engine primarily as a battery
`charger;
`the subject hybrid reverses
`this philosophy and makes minimu use
`of the electric system.
`
`3.
`
`It is hoped that the validity of
`these principles will be amplified by
`subsequent sections of this paper.
`
`SYSTEM DESCRIPTION
`
`A block diagram of the system
`illustrating functional performance and
`energy flow paths is shown in Figure 1.
`This drive system is intended to replace
`the engine-transmission system in
`conventional vehicles with the result of
`increasing the vehicle CV3-Hot fuel
`economy (miles/gallon) from 302 to 100% at
`1975/76 Federal emission levels using the
`CVS-Hot cycle while maintaining
`approximately equivalent accelerating,
`braking, and passing characteristics.
`hybrid-electric system consists of the
`following major components:
`1.
`A different internal combusion engine,
`considerably smaller in displacement,
`and, hence, horsepower capability,
`than the engine in the original drive
`train.
`
`The
`
`An electric motor/generator (oe unit)
`which may be on a common shaft with
`the engine output shaft or connected
`to the engine output shaft by means of
`a gear, belt, or chain system. The
`motor/generator may be of the DC
`commutator, DC homopolar, synchronous,
`or induction types.
`A means of controlling power flow
`between the motor/generator and
`battery. This may be an electronic
`controller using power thyristors 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 eergy efficiency.
`An energy storage device. This may be
`any device capable of handling the
`high bursts of power required by the
`drive train during acceleration and
`braking and of supplying the energy
`needs for low-speed driving and the
`operation of vehicle auxiliaries at
`low speeds and standstill. At the
`aresent tie, batteries are the most
`practical energy storage device. with
`the nickel-cadmium battery having
`alost ideal characteristics for this
`
`application but suffering a cost
`penalty. Flywheels, fuel cells in
`combination with batteries, closed
`loop cryogenic expander systems, are
`other possibilities.
`A differential and a drive shaft.
`general, it is desired to use the
`original drive shaft and differential
`of the vehicle.
`The system can be classified as a
`
`In
`
`3.
`
`4.
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`SI
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`parallel hybrid with engine on—o£f
`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
`mwrmmmuugmflflwenmemmuh
`and carburetor; sensors for converting
`vehicle speed, battery voltage and charge
`level, component temperatures, 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 performace but usually add some
`cost penalties:
`1.
`The use of an automatically-controlled
`decouple: 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).
`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.
`
`2.
`
` \~\'.\\\\\\\\~
`///llllf-‘II’
`
`BATTERY
`
`Fig.1 -Ford parallel hybrid
`
`SYSTEM OPERATION
`
`The system has six modes o£
`operation.
`The first five modes are shown
`in Figure 2. Mode 1 is all electric at
`speeds below 10 to 15 Min.
`In Mode 11 the
`engine is the primary source of propulsion
`and there is no energy in or out of the
`
`ELECTRICAI
`SYSTEN
`
`
`
`Fig.2 —Five hybrid modes of operation
`
`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 demands 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 752 of full charge. This strategy
`prevents deep discharge cycles on the
`battery. Te 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
`have 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 and 4 show that the fuel
`economy for both a conventional and hybrid
`system can be expressed as follows:
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`where n3 is the average engine brake
`termal efficiency, HPT is the average
`transmission efficiency,
`(Q/Gal) is the
`energy content per gallon gasoline
`consumed and (
`lMi1e) is the total energy
`requirement at
`c 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 is 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 he clearly seen.
`In order to provide
`an :Lncrease in fuel economy over a
`conventional system the quantity nE n
`/(
`/Mile) must be increased. The present
`hyb id system will be described in terms
`of hw 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 202
`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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`Enema srncuzucv
`
`rolnmma emcnsucv
`
`7;:--5-'-9-
`
`IN
`
`w;”--—%-
`
`5w
`svstsu Erncusncv
`gm-—-5-i;
`
`mu
`nuts I canon
`nu>c-
`MPG= (Ew/MILE)
`
`
`
`mm
`
`II
`
`VI
`
`77: 775-1'(QIu/GAL)
`
`Fig.3 -Average fuel economy for a conven-
`tional vehicle in terms of system efficien-
`cies
`
`
`
`mm: emcnsuev
`
`7; - -5-‘?-
`
`IN
`
`E
`
`ELEGIIIIGAL svsreu emcuzacv
`
`'17: -59--
`
`L Ecu
`
`menmm smczsncv
`
`7;"--E-E-IC
`
`svsm smcnsm
`
`IPG (MILES /GALLON)
`
`106-
`
`IN
`
`7;573
`'q§¢7,,.,(0mIGI4L)
`u:',,/me)
`
`Fig.4 -Average fuel economy for a hybrid
`vehicle in terms of system efficiencies
`and energies
`
`_ "3 "PT ( Gal
`we ' (Ew7Mi1e)
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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 node
`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,
`this
`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
`low-speed efficiencies.
`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.
`
`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
`
`4.
`
`5.
`
`B.
`
`C.
`
`torque level at which the
`electrical system is called upon
`corresponds to a high-engine
`efficiency point.
`The effect on
`transmission efficiency must also
`be considered since a lower engine
`torque requires more electrical
`energy.
`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 — when the electrical
`system is not in use,
`the nergy
`from the engine is transmitted
`directly to the rear wheels
`through the differential. This is
`Mode II in Figure 2.
`The
`instantaneous transmission
`
`The
`
`efficiency during this node is
`essentially equal to the
`differential efficiency.
`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 a minimum,
`the motor is used only when
`needed.
`The two modes requiring
`the motor are the all electric
`
`mode at low speed 0Mode I) and
`during heavy accelerations Glode
`IV).
`3. Use of regenerative braking -
`During braking the kinetic energy
`of the vehicle is used to charge
`the battery. This is described as
`Mode V in Figure 2. This has a
`substantial effect on transmission
`efficiency by reducing the charge
`energy required from the engine.
`Drive wheel Energy - In converting a
`conventional vehicle to a hybrid
`configuration the total energy
`requirements at the drive wheel must
`also be considered in assessing the
`potential fuel economy gains.
`The
`primary factors that could reduce fuel
`economy are a 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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`System weights will vary
`motor.
`considerably with the vehicle
`acceleration requirements. For the
`hybrid configurations considered in
`this study sell weight savings were
`realized. 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
`
`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.
`
`DYNAMOEDZTER TESTS
`
`The
`
`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
`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 torqe 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
`are 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 and 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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`
`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 recognized. Also,
`emission measurements and engine strategy
`for emission control were 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 ust 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.
`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.
`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.
`To determine that the selected battery
`was adequate.
`To determine that the engine is
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`basically suited to the unique or
`uusual operations in this concept,
`such as:
`
`a. Motoring the engine between 0 and
`800 RPM as required by the direct
`coupling to the wheels. Normally
`an engine is cranked and
`immediately accelerated to a idle
`speed of 700 RPM or more.
`b. Operation at high torque most of
`the times
`
`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 mtor was on a common shaft with
`the engine, and the driveahaft was
`directly coupled to a dynamometer and
`inertia wheel
`to simlate the vehicle
`road, aerodynamic, and inertial loads.
`The principal components used were:
`'74
`1. Engine: Ford 2.3L, 4—cy1inder,
`production engine, modified for fuel
`off operation.
`2. Motor: Westinghouse, AOHP, 240 V.,
`1750 RPM industrial shunt motor;
`blower cooled.
`
`SCR chopper for motor
`3. Controller:
`armature control during motoring and
`regenerative braking (designed and
`assembled at Ford); separate power
`supply for field control.
`6. Battery:
`150 cells connected in
`series of Marathon,
`type 209120, Nicd;
`auxiliary forcedwair cooling to
`maintain cells at approximately 20 C;
`plus required monitoring equipment.
`5. Loading Device: Absorptfion
`dynamometer of 150 1b—£
`inertia ad
`a flywheel of 360 1b~ft
`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 MWH (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 C0, C0 , HC, 0
`and NOX and intake 002 were ma e.
`Foe
`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 was
`accomplished by means of a smell
`solenoid valve to block fuel flow in
`
`2.
`
`the idle jet, removal of the throttle
`stop to permit full closure of the
`throttle plate, 5 means of admitting
`air below the throttle, and PCV
`modification.
`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.
`
`5.
`6.
`
`In a
`4. Low~speed engine friction:
`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
`1ow—speed friction torques of the 2.3L
`engine were measured.
`Low—speed lubrication was evaluated.
`The EGR valve and plumbing were
`enlarged to permit large EGR flow at
`wide-open thrott1e operation.
`Another interesting problem for which
`there was almost no precedent was the
`measurement of HG emissions during the
`frequent engine off/on transitions that
`the engine passes through during a typical
`driving cycle.
`Since CV5 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 “driveab1e" 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 n the
`experimental hybrid system mounted on e
`dynamometer test stand.
`The SAE driving
`cycle is a simplified version of the CV8-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 some 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 much
`simpler than over the CV5-H cycle, and
`since the control of the system was not
`fully autoated 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 tries, 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 ecoomy.
`The engine
`throttle positions were likewise made to
`correspond between the measure and
`calculated test runs.
`The results are
`summarized below:
`
`TABLE I
`COMWARISON OF MEASURED AND CALCULATED
`DYNAMIC FUEL ECONOMY OF HYBRID
`
`Simulated vehicle
`
`inertia weight
`Length of test run
`
`Calculated fuel economy
`Measured fuel economy
`
`7500 lbs
`3 SAE cycles
`(3 miles)
`15.2 mpg
`15.8 mpg
`
`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 same
`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 summarized in Figure 5.
`The purpose of this section is to discuss
`the reasons for the fuel economy
`imrovement 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 Bcooline
`
`The
`Van and Mark IV, respectively.
`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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`
`anon
`
`(c)
`
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`van
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`Von
`
`van
`
`Van
`Va
`
`I125“ Egg: Train
`
`figs;
`1.| with closed throtle
`l.| with wide-open throttle
`Ll , valves closed
`
`1.! , clutch
`
`2.: as-an:
`
`1.} diesel, clutch
`
`1.1 . clutch
`2.) diesel. clutch
`
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`1a.:
`18,!
`19.5
`
`20.0
`
`22.0
`
`23.7
`
`13.:
`28.1:
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`14.6
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`51
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`65
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`7:
`:09
`
`(e) 6500 lb. Inertia lit.
`0:} 5500 lb. Inefua Ht.
`{c} All fuel oconeny calculations baud upon vehicle driving the Federal as-u cynic; no no: change in battery
`ltnll-of-charge.
`(01) Cllculntod Eur uoelluloatzcd, no an engine. cntculctiou holed upon the ms. enuntontud 300 cm mum: used
`on 1975 vohlcln resulted In 1 fuel econeay 0! [L6 MPG.
`(03 51141 ‘IP55? reluctance coco: developed by Ford.
`(See toinmnccn (8) and 06)).
`(:1 Calculated to: 2974 «so czo engzuc with automatic calibration.
`
`Fig.5 -Calculated fuel economy comparisons
`
`8 of 18
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`
`
`
`CV5
`HPG-I34
`
`POIERTIAII
`
`SYSTEI
`MP9
`
`
`
`0 I0 20 30 #0 50 6D'N 0
`% IIPHOVEIEIT OVER CONVENTIONAL
`
`Fig.6 —CVS-H fuel economy and efficiency
`comparison between hybrid and conventional
`econoline van
`
`5500 u
`
`Mill 1!
`‘°° °'”
`
`snot: "hf"
`mam
`um 11
`
`23 um 7)‘
`
`
`
`-.2sa
`
`mg;
`are - :o.5
`
`3:: _ "5
`
`during braking. Gearing between the
`engine and rear wheels gives a ratio
`of engine RPM to vehicle speed in NH
`(N/V) of 100, while the ratio of
`electric motor RPM to engine RPM 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 5500 lb.
`conventional 1974 Mark IV with 460 CID
`engine and automatic transmission is
`compared to a 5500 lb. hybrid Mark IV
`with a 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
`
`TABLE II
`VEHICLE WEIGHT EXCHANGE
`
`Production Systems — 1975 Nantucket Weight
`(lbs)
`
`Curb
`
`Delete:
`. 300 CID Engine
`. Cad Automatic Transmission
`. Exhaust System
`. Fuel System [22 gal. base tank)
`. Battery and Alternator
`
`993*
`. 1.1L Engine
`. Exhaust System
`. Fuel System (13.3 gal.
`base tank)
`. Motor
`(Provision
`. 2-spd. Trans.
`—— not included in fuel
`
`economy)
`. Controller
`. Battery and Cooling
`(Ni-Cad System)
`. 12V Inverter
`
`631
`155
`56
`29
`_§fl
`__9__2_§_ lbs.
`
`243
`25
`
`18
`120
`
`80
`70
`
`170
`__§
`731 lBs.
`
`mm:
`
`romnmn
`
`59 as
`
`svsm
`m
`
`sow.
`
`31 ox,
`66.7%
`
`0 10 20 50 40 50 60 70 80
`‘la IIPROVEIIHIT OVER GONVEIITIOIAI
`
`Fig.7 -cvs~H fuel economy and efficiency
`comparison between a hybrid and conventional
`Mark IV
`
`NOTE: Structural and other small
`
`component changes may alter this
`weight comparison.
`
`and automatic transmission is compared
`to a 4500 lb. hybrid van with a 1.1
`liter engine, DC motor with 130 ft.
`lb. peak torque and 45 KW of Nicd
`batteries. Acceleration and battery
`charging are both done at widewopen
`throttle and fuel is shut off at
`engine speeds below 1000 REM and
`9of18
`
`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 ec