‘ sAE TECHNICAL
`PAPER SERIES
`
`950231
`
`Development of a New Hybrid
`System - Dual System
`
`Kozo Yamagtlchi, Shuzo Moroto, Koji Kobayashi,
`' Mutsumi Kawamoto, and Yoshinori Miyaishi
`-
`Equos Research 00., Ltd.
`
`'
`
`Reprinted from: Strategies in Electric and Hybrid Vehicle Design
`*
`(SP-1156)
`
`
`International Congress 8; Exposition
`' Q. ngfgggfiggfilgfiifg
`'
`Detroit, Michigan
`Land Sn Air and Space”
`Februaryaeozsdsss
`INTERNATIONAL ,
`.m
`‘ meommonwaflh Drive, Warrendala, PA 15096-0001 USA. Tel:(412)776-4841 Fax:(412)776~5760
`
`.
`
`Page 1 of 11
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`TheoppeamceoimelSSNcodemmebouomotmismoktdmsm'emem
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`960231
`
`Development of a New Hybrid
`System - Dual System
`
`Kozo Yamaguchi, Shuzo Moreto, Kali Kobayashi,
`Muteumi Kawamoto, and Yoshinori Miyaishl
`Equos Research 00.. Ltd.
`
`Copyright 1996 Society of Automotive Engineers. Inc.
`
`ABSTRACT
`
`A new hybrid vehicle system has been developed. the Dual
`System. which combines the series and parallel hybrid
`systems.
`-
`'
`'
`Combination with a motor has reduced the engine size.
`only using the most efficient range of the engine. A transaxle
`employing a generator motor and a traction motor in one
`compact package is applicable to currently produced vehicles
`with little modification. Use of the generator as a motor
`realizes multiple control functions.
`A prototype vehicle'with this new Dual System was built
`and tested.
`lts driving performance and the fuel economy
`were measured. and the fuel economy results were analyzed.
`
`INTRODUCTION
`
`Toward the let century. energy conservation has keen
`global interest due to an expected sharp increase in energy
`demands according to ever increasing population and global
`warming caused by an increasing volume of generated C02.
`To decrease the energy used for vehicles, there are activities
`in various countries to find ways to greatly reduce the fuel
`consumption of vehicles. such as the "80 mpg Super Car
`Concept" in the US. It is required to adapt a completely new
`system, not just make a simple modification to the current
`system, to realize a dramatic improvement in fuel economy.
`It is recognized that one' promising field is hybrid systems.
`. Both series and parallel hybrid systems are well known.
`This paper discusses a new hybrid system based on the "split"
`system which splits energy from the engine using a planetary
`gear [1] [2] [3]. the new system being called the Dual System.
`
`COMPARISON OF VARIOUS HYBRID SYSTEMS
`
`Not only used as a range extender of electric vehicles. the
`hybrid system. employing both an engine and an electric
`motor. can improve fuel economy using the engine through
`
`its combination with the motor [4]. The hybrid system can
`improve fuel economy in light of the following:
`1. Operation of the engine in optimum efficiency range
`2. Transmission efficiency between the engine and the
`driving wh‘eels is improved
`.
`.
`3. Regeneration of deceleration energy
`Figure l shows the four different hybrid systems.
`
`(A) SERIES SYSTEM - This system supplements
`electricity generated by the engine. It is most commonly used
`as a range extender for electric vehicles. Since the engine is
`not mechanically connected to the drive wheels. this system
`has an advantage of controlling the engine independently of
`the driving conditions. Accordingly. the engine is used in its
`optimum efficiency and low emission range. This system is
`particularly suited to engines which are hard to mechanically
`connect to the drive wheels such as gas turbine engines.
`Disadvantages, however, include large energy conversion.
`losses because of the necessity of full electricity conversion
`of the engine output. Further. a generator large enough to
`convert the maximum engine output islrequired.
`‘
`
`(B) PARALLEL SYSTEM - With the parallel system. an
`elecuic motor which supplements the engine torque. is added
`tothe conventional driveline system of the engine and
`u'ansmission. Accordingly. operations of the engine are quite
`similar to those ofan engine in a normal vehicle. This system
`requires no generator. and there is a ‘direct mechanical
`connection between the engine and the drive wheels. providing
`an advantage of less energy being lost through conversion to
`electricity.
`.
`'
`On the other hand. this system requires a transmission
`because no speed adjustment mechanism is installed. though
`the motor supplements the torque. When an automatic
`transmission is used. a'torque converter. oil pump. and other
`auxiliary components can reduce the transmission efficiency.
`Although the engine torque can be controlled by the motor.
`the engine speed is determined by gear ratios like a
`
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`(A) SERIES
`
`.
`
`“"0""
`.
`
`‘
`
`(8) PARALLEL
`
`(C-l) SWITCHING SYSTEM - Application and release
`of the clutch switches between the series and parallel systems.
`For driving as by the series system, the clutch is released.
`
`separating the engine and the generator from the driving
`wheels. For driving with the parallel system, the clutch is
`engaged. connecting the engine with the driving wheels.
`For example. since city driving requires low loads for
`driving and low emissions. the series system is selected with
`the clutch released. For high speed driving where the Series
`system would not work efficiently due to higher drive loads
`and consequently higher engine output is required, the parallel
`system is selected with the clutch applied.
`
`(02) SPLIT SYSTEM - This system acts as the series
`and parallel systems at all times. The engine output energy is
`split by the planetary gear into the series path (from the engine
`to the generator) and the parallel path (from the engine to the
`driving wheels). It can control the engine spud under variable
`control of the series path by the generator while maintaining
`the mechanical connection of the engine and the driving
`wheels. through the parallel path.
`Correlation between the vehicle speed V and the engine
`speed NE.is shown in Figure 2. When the engine is operating
`at a relatively constant torque in an optimum efficiency range.
`the energy from the engine is almost proportional to the engine
`speed NE. Accordingly, Figure 2 also indicates correlation
`between the vehicle speed and the engine output energy. In
`Figure 2, the engine speed NE15
`NE: NEP + NES
`
`where NEP is the engine speed by the parallel path and NBS
`the engine speed by the series path. As the parallel path engine
`speed NEP increases in proportion to the vehicle speed, the
`output energy from the engine increases as the'vehicle speed
`becomes higher. The higher the speed, the more energy is
`required for driving. it being appropriate that the parallel path
`
`energy becomes larger for higher speeds. For high speed
`
`
`
`Mechaniml Connection
`
`- - - - - - Electrical Connection
`
`G : Generator M: Motor 8: Battery
`EG :Engine
`TM :Transmission C: Clutch
`PG: Planetary Gear
`
`Figure I: Four Different Hybrid Systems
`
`conventional vehicle. Accordingly, the engine operation IS
`
`linked to the drivingconditions.
`(C) SERIES-PARALLEL COMBINED SYSTEM- This
`combined type. having a generator and a motor. features
`characteristics of both the series and parallel systems, and the
`following two systems are possible:
`
`.
`
`NE 'PARALLEL
`
`
`PATH
`
`.
`
`O
`
`.
`.
`- 20
`
`. —_J___—‘
`40
`$0
`80‘
`103nm12°
`(
`)
`
`Figure 2: Engine Speeds in Split Hybrid System
`
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`driving. most of the output from the engine is supplied by the
`parallel path: consequently the energy conversion is small and
`not such u large generator as for the series system. is required.
`Since the engine speed N58 with the sari .s path is variable
`within the generator capacity. it is‘ possible to control the
`engine conditions into ranges favorable for engine efficiency
`and lower emissions. it is also possible to control the amount
`of electricity charging the batteries.
`
`OBJECTIVES OF THE DUAL SYSTEM
`
`_
`
`The maximum efficiency of the conventional reciprocating
`engine reaches 35% [5] and this could be increased to 40%
`through combination with a hybrid system. Other engines.
`for example. a gas turbine engine. may not easily exceed
`such an efficiency. We therefore consider it more realistic to .
`take advantage of very developed reciprocating engine
`technologies so that the system can maximize the advantages
`of such engines.
`Based on the comparison of various hybrid systems.
`recognizing that the split type has the largest potential among
`the hybrid systems. we developed the Dual System which
`maximizes the advantages of the split hybrid system. Features
`- of this system are:
`
`1. Compact Transaxic package design requires minimal
`modification of vehicles currently available.
`2. Combination with a motor enables the engine to be small
`and lightweight. The engine can be operated in an
`optimum efficiency range.
`3. The motor can operate as a generator. realizing a variety
`of control functions.
`.
`
`CONSTRUCTION '
`
`The complete schematic of the Dual System is shown in
`Figure 3. Figure 4 depicts the positions of major components
`within the vehicle. The vehicle is a modified “Corolla"
`
`production model. the vehicle weight being increased by 305
`kg from the production weight of 1.040 kg. to 1.345 kg.
`
`ENGINE - Since a small engine can meet requirements
`as the drive motor adds the torque. a 660cc engine for a
`commuter vehicle was used. Although a normal vehicle can
`rarely operate in the optimum efficiency range of the engine.
`engine downsizing should make it possible at all times. The
`engine throttle was disconnected from the accelerator pedal
`and computer-controlled by a throttle actuator motor.
`An average maximum cruising speedwhich does not drain
`' electricity from the batteries is determined according to the
`
`
`
`SIGNAL
`
`""""""""" 12v
`
`_
`J 288V
`
`PEDALS. LEVER
`
`3. SWITCHES
`
`
`
`DISPLAY
`
`
`COMPUTER
`
`
`
`
`CABIN
`
`TRUNK
`
`
`0/0 0/0
`.
`s.“- "nu-u... Into-linoeue-Qmooooooo
`'
`.
`
`
`- CONVERTER
`n..-
`.
`u
`a
`a
`a
`I e-I—I_o-O‘
`
`
`
`2v
`
`ue
`BATTER
`uuuuuuuuuuuuuuuuuuuuuuuuuI
`menu-uneven..." nun-uuuunusoi-e nun-en... eons-noun
`
`
`
`THROTTLE
`
`ACTUATOR
`
`ENGINE
`COMPABTMENT
`
`I1
`
`
`
`Figure 3: Complete Dual System Schematic
`
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`\ Traction Motor
`\lnverter & MCU
`
`\. Generator Motor
`\lnverter & GCU
`
`Figure 4: Major Components Positions in Vehicle
`
`engine size. This discussed system provides an average
`cruising speed in the range of 90 to 100 km/h.
`
`TRANSAXLE - A sectional view of the transaxle is shown
`in Figure 5 and its picture in Figure 6.
`The transaxle is for a.FWD. transversely mounted engine
`and is a package of a traction motor and generator motor. Its
`total length is 359 mm. shorter than the replaced production
`4-speed automatic transaxle.
`The weight of the transaxle. including the flywheel and
`damper assembly and transmission fluid, is 90 kg. 8 kg more
`than the production 4-speed transaxle. The small engine used
`eliminates both the starter and the alternator in addition to the
`oil cooler of the transaxle. The total weight of the engine and
`the transaxle is 30 kg less than those used in current production
`model.‘
`
`Lang; - The layout of the transaxlc is of a 4-axle
`construction. On the firsuaxle'. which is on the same axis as
`the engine axle. is mounted the flywheel and damper. planetary
`gear set. generator motor and generator brake. while on the ~
`second axle. the traction motor. The counter gear is mounted
`on the third axle and the differential gear on the fourth.
`Installation of the traction motor on an axle different from
`the engine axle results in a reduced total length. This also
`enables independent design of gear ratios of the engine and
`those of the tractibn motor, which permits optimum gear ratio
`designs for both. The designed engine gear ratio (including
`the planetary gear ratio) is 4. l9 and the traction motor gear
`ratio. 7.99.
`e
`
`Planetary Gear
`/
`
`Generator Motor (6kW)
`
`
`
`Flywheel & Damper
`
`
`
`Traction Motor (40kW)
`
`Differential Gear
`
`Figure '5: Sectional View ofTransaxle‘
`
`28
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`Figure 6: Picture of Transaxle
`
`The counter gear of the third axle transmits the torque of
`the first and second axles to the fourth axle.
`
`W - The planetary gear splits the engine output
`to the generator motor and output shaft. The planetary carrier
`is connected to the engine and the ring gear to the output shaft.
`The sun gear is connected to the generator motor.
`The planetary gear also works as a speedrncreasing and
`torque reducing device for the generator motor. enabling the
`latter to be small. The speed increasing gear ratio is 3.21.
`W - The generator motor is a DC brushless
`motor with a maximum output of 6 kW. Using a motor with
`8 poles. which'rs more than usual. the generator brake and the
`planetary gear are arranged inside the coil ends, causing the
`total length to be shortened
`The generator motor is used as a motor. leading to it being
`the center of multiple control functions of the Dual System:
`when functioning as a generator. it eliminates the necessity
`of an alternator. and a starter as well since it also functions as
`
`an engine starter. it functions as a starting device, clutch and
`a kind of CVT together with the traction motor. resulting in
`not requiring a transmission.
`mm- The traction motor. outputting a
`maximum 40 kW. is a 4-pole DC brushless motor. it iunctions
`as the engine torque leveling device of the parallel hybrid
`system.
`W - Under lowload conditions such as
`constant speed cruising. the system used is the parallel hybrid
`one with the brake engaged, preventing the generator motor
`from causing energy conversion losses: The cooling oil of
`the brake plate is also used for cooling the generator motor.
`The generator motor uses "soft-landing” control for which a
`cushion plate is simply applied instead of an accumulator to
`
`prevent hard brake engagement.
`W--ATF (Automatic Tmnmira'icn Fluid}
`iii used. affecting cooling. lubrication and engaging pressures
`of the generator brake. The valve body is small. having only
`one solenoid for the brake. Cooling ofthe numeric is realized
`by radiating heat using transartle case tins along with the
`internal circulation of the ATP which cqualizcs thermal
`distribution within the rransaxlc. No oil cooler is installed
`such as a radiator. outside the transaxlc. Cooling of the motors
`is done with the ATP being showered on the stator coil ends.
`
`BATTERIES — in the hybrid vehicle using a small engine.
`acceleration and deceleration are done by discharging and
`charging of the batteries. As a result. the batteries require
`power density more than energy density. The prototype
`vehicle involved is mounted with lead-acid batteries which
`are low in cost and relatively high in power density. Those
`used are Cyclon-ZSC VRLA batteries. their capacity being
`25Ah each. The number of batteries used is 24 with a total
`voltage of 288V and a total weight of 240 kg.
`
`DlSPLAY - The display connected to the vehicle
`controller enables monitoring vehicle conditions including the
`energy flows of each component and engine conditions. on a
`real-time basis.
`
`SYSTEM CONTROL
`
`ROLE OF EACH CONTROL UNIT - The Dual System
`has four control units. including one for the engine. VCU
`(vehicle control unit) gives instructions. depending on drivi..g
`conditions. to ECU (engine control unit). GCU (generator
`motor control unit), and MCU (traction motor control unit).
`The engine is so controlled as to follow the Optimum efficiency
`curve. The generator motor controls the engine speed. and
`the output torque is controlled by the traction motor.
`W - VCU controls the throttle actuator by
`determining throttle openings from the engine speed so that
`the optimum efficiency curve be followed.
`it also turns the
`ECU on and off. taming the engine on and off.
`W - VCU gives instructions as to
`the desired generator motor speed. NG". to GCU on the basis
`of accelerator pedal movement. vehicle speed and banety SOC
`(state-of-charge)
`GCU uses feedback control for the generator torque in
`order to make the actual generator motor speed NG NG‘ Pl
`(Proportional-integral) feedback control is applied for high
`responsiveness and compensation of steady-state error
`W VCU determines the output
`torque of the traction motor from accelerator pedal movement
`and vehicle speed. Further. it computes the generator motor
`torque to determine influence of the engine torque on the
`output torque (because the torque of the engine. generator
`motor and output reaction are proportional to each other). and
`then compensates the output torque of the traction motor so
`that the output torque remains constant whatever the engine
`
`29
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`conditions are. When the brake pedal is applied. the engine
`is released. with regeneration torque of the traction motor is
`determined according to the amount of brake pedal application
`and the vehicle speed.
`MCU controls the traction motor to make the traction
`motor torque. TM. equal to the desired torque. TM“. from
`VCU.
`
`ENGINE CONTROL STRATEGIES - For high efficiency
`and low emissions of the engine. the throttle openings are so
`designed to be a constant 35% for NE for values of 2.000 rpm
`and greater. The fixed point control of the engine can be
`applied for an optimum efficiency point. while it increases
`losses due to energy conversion of motors and batteries. As
`the production engine efficiency is not so sensitive with respect
`to the engine speed. the engine speed of the Dual System is
`controlled depending on the driving load.
`When the load increases, the generator motor speed is
`raised to supplement the energy from the engine. This control
`reduces the electricity passing through the batteries.
`consequently reducing the energy conversion losses of the
`. batteries and also protecting the batteries from exceSsive
`discharge. As the accelerator pedal is depressed. the engine
`speed increases. and the driving feeling is natural to the driver.
`Battery current accumulation is used as SOC. maintaining
`the initial value by generator motor control. if the SOC lowers
`
`from the initial value. the generator motor speed increases.
`making the engine speed increase for higher engine output
`energy. if SOC becomes higher. the generator motor speed is
`decreased.
`During transient conditions for turning the engine and
`brake on and off. the generator motorcontrols the engine speed
`so that changes are gradual in order to prevent any excessive
`change in engine operation.
`
`VEHICLE CONTROL OF EACH STATE . As shown in
`Figure 7. each control mode is specifically applied depending
`on driving conditions:
`a)WM: - When the vehicle is stopped at a
`standstill. the engine stops.
`b) MQmLMnde - Until the vehicle reaches a speed of 8
`ltm/h after starting or it decelerates to 5 ltm/h or lower when
`driving. the engine stops and the motor alone works.
`c) 29W - The generator brake is engaged and the
`system drives using the parallel hybrid system. The generator
`motor does not operate during this time.
`d)W - Accelerator pedal movement
`and the SOC determine the generator motor speed NO. The
`engine speed NE is obtained from the formula:
`. NE = N5? + 3.212 f NG
`where NEP is the engine speed of parallel path which is
`proportional to the vehicle speed. NE should be increased by
`
`MOTOR DRIVE
`(CREEPING SPEED)
`
`b) MOTOR MODE
`
`DRIVE
`
`9) ENGINE START
`CONTR01.
`
`VEHICLE
`CONTROL
`
`”WE
`
`
`
`
`
`hl ENGINE STOP
`CONTROL
`
`9) ENGINE START
`\LUNTROL
`
`
`
`
` ENGINE DRIVE
`
`It) ENGINE STOP
`CONTROL
`
`(&?'"‘%h I
`
`
`
`ORDINARY
`
`OPERATION
`
`e} PARALLEL
`MODE
`
`i) 8 OFFCONTROL
`
`‘) 8 ON CONTRO.
`
`
`
`HIGH LOAD or
`tow soc
`
`
`
`d) SPLIT MODE
`(PosmVEi
`
`
`
`
`
`
`OECELEMTE
`
`”REGENERATION
`MODE
`
`Figure 7: Vehicle Control
`
`30
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`increasing N6 according to the degree of low SOC. This
`leads to an increase of energy supply from the engine. As the
`accelerator is depressed. NE is increased. raising the energy
`supply from the engine.
`..
`As the efficiency of the generator motor reduces in a low
`speed range. the generator brake is engaged to change to
`parallel mode when calculated NG” reaches 1.500 rpm or less.
`The parallel mode is not applied when the vehicle speed is
`lower than 25 lam/h because the engine speed becomes too
`low. To avoid any possible worsening of emissions due to a
`sharp change in the engine speed. the maximum rate of the
`generator motor speed change is limited to 300 rpm/second
`while in the split mode.
`e)W - When the SOC becomes too
`high. the generator motor functions as a motor and not a
`generator. with the generator motor rotating in the negative '
`direction. controlling the engine speed to be lower than the
`parallel speed NE?
`f) EsmemmMQdeWhen the brake pedalts applied.
`the regeneration mode comes on. The regenerated electricity
`depends on the degree of pedal application. The upper limit
`of the regeneration is 20 kW for battery protection. almost
`taking care of LA#4 (Los Angeles No.4: Federal Urban
`
`7000 _~————~————.———-———E'
`4
`
`5000'.
`
`_ if,”
`
`3
`
`En ine-t-Motor
`
`5000: /
`
`0)1%.! l
`
`(N)
`
`
`
`TractionForce
`
`i
`
`
`
`
`o
`20
`4o
`60
`so 100120 .140.
`
`Vehicle speed
`
`(km/h)
`
`Figure 8: .Vehicle Traction Performance
`
`
`
`Driving Cycle) mode deceleration. The engine stops to
`eliminate its resistance and consequently the regeneration
`energy is maximized.
`8)Wall - The generator motor starts up
`the engine. at which time the output torque is compensated
`for by the traction motor using the generator motor torque.
`h)W - The engine is stopped by caning
`the fuel.
`
`i) mm— In order to prevent harsh shock and
`emissions upon generator brake engagement, the generator
`motor gradually reducesits own speed until it is zero for "soft
`landing".
`j)W- Tire generator motor controlstts own
`speed from zero to ensure "soft taking off" to prevent harsh
`shock and emissions upon generator brake release.
`
`VEHICLE PERFORMANCE
`
`DRIVING PERFORMANCE - The traction performance
`of the Dual System vehicle is shown in Figure 8. The total
`power of the engine and the traction motor is comparable to
`approx. 50 kW. in particular. at medium and low speeds, it is
`confirmed that most of the drive torque of the vehicle is
`supplied by the traction motor, and the engine works as an
`energy supply source. The maximum speed is 125 kah.
`Table I shows the acceleration performance of the vehicle.
`
`FUEL ECONOMY - Regarding LA#4 in the us. and the
`Japanese city lO-ls mode. fuel economy tests were conducted
`on a chassis dynamometer with one vehicle having a
`production 4-speed automatic transmission and the other being
`the Dual System vehicle.
`
`(RM/l)
`
`.- LA“
`‘Cl tootsmode
`
`FUEL
`ECONOMY
`
`
`20
`
`15
`
`1°
`
`
`
`
`
`
`
`
`
`Table l: Acceleration Performance
`
`Chart 1: Fuel Economy Results
`
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`WWW
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`Vehicle Weight (kg)
`
`1000
`
`1200
`
`1400
`
`61
`
`
`
`
`
`FuelEconomy(+%)
`
`Economy
`
`
`
`Transmission Etficien
`'
`10-15
`
`
`
`(+56)
`LL Fuel
`
`A \
`
`"
`s,v
`
`> a 2
`
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`0
`LU
`753
`
`Chart 2: Relationship between Each Factor and Fuel Economy
`
`The Dual System is controlled so that the electricity
`balance of the battery is met before and after the test. Any
`difference in the electricity balance before and after the test is
`compensated for by the use of simulations.
`Euel Egooggmy Eggglt - The measured results are
`summarizedin Chart I. The Dual System vehicle testedis
`305 kg heavier than the production 4-speed automatic
`transmission vehicle. The results show that the Dual System
`vehicle provided better fuel economy than the production
`vehicle by 31% for LA#4 and 57% for 10°15 mode.
`Analysis, of tag Eesulgs -The fuel economy results are .
`analyzed using assumptions during simulations.
`influence on fuel economy of each factor)5 shown in Chart
`2. The influence of each factor in this test is summarized in
`Table 2 based on Chan 2. The lO-lS mode. compared to
`LA#4. shows the greater improvements of engine efficiency
`because of lower engine efficiency of the production vehicle
`caused by the lower vehicle speed of 10°15 mode. The
`influence of the brake regeneration represents the ratio ofthe
`regeneration energy to the total required energy. The
`improvement of fuel economy through brake regeneration will
`be reduced by energy conversion losses.
`
`LA#4 10-1 5mode
`
`
`
`
`
`
`_
`Vehicle’Weight
`Engine Efficiency
`Transmission Efficiency
`.....................................................................................................................
`Brake Regeneration
`Total
`
`
`Table 2:
`
`influence of Each Factor on Fuel Economy Results
`
`32
`
`Table 3 shows efficiency and energy distributions of each
`component. Out of the total energy output during driving.
`25% for LA#4 and 28% for IOOIS mode is input from brake
`regeneration. As well. the overall driveline efficiency.
`including electricity energy conversion. is 71% for LA#4 and
`70% for 10.15 mode.
`
`FUEL ECONOMY IMPROVEMENT - This Dual System
`is in the initial prototype stage where each component has not '
`yet been fully optimized. With respect to the fuel economy.
`all the deceleration energy is regenerated. however other
`factors also have potential for improvement. From Chart 2
`and Table 3. we will review how much fuel economy can be
`improved by upgrading each vehicle component.
`W- The Dual System
`compensates acceleration using the traction motor and
`therefore no high engine speed due to kick-down acceleration.
`is required. This helps engine design since it is focused on
`low and medium speeds. Optimization of intake and exhaust
`systems and a reduction of friction. as a result. helps improve ‘
`engine efficiency. To control the air-fuel ratio so it is .
`stoichiometric instead of rich also improves the engine
`efficiency of high load range where the engine of the Dual
`System is essentially used.
`.
`The current Dual System. which uses a production engine
`as it is. is assumed to have 27% engine efficiency on an average
`(Table 3). Chart 2 indicates this can be increased to 35%.
`leading to another 30% improvement in fuel consumption
`In addition. increasing the engine efficiency to 40% should
`raise the'improvement of fuel consumption to 48%.
`lmnmementflmnsmissienflficiem- As Table 3
`shows. out of the 30% of transmission losses. approx. half
`are from the energy conversion losses of the two motors and
`
`Page 10 of 11
`Page 10 of 11
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`FMC 1021
`FMC 1021
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`

`

`Efficiency
`‘ (9/0)
`.
`
`'
`
`Energy
`
`'
`
`10-15 mode
`
`Efficiency
`('70)
`
`Energy
`(%)
`
`'
`
`Generator Motor
`
`Traction Motor
`
`Batt
`
`ies
`
`(%)
`
`.......12VAccesones
`Mechanical Losses
`
`(
`
`Table 3: Efficiency and Energy Distribution of Each Component
`
`REFERENCES
`
`l. Nims. P. T.. "GENERATOR-MOTOR DRIVING
`SYSTEM." United States Patent 2.506.809 . 1950
`
`Gelb. G. H.. Richardson. N. A., Wang. T. C. and Berman.
`B.. “An Electromechanical Transmission for Hybrid
`Vehicle Power Trains - Design and Dynamometer
`Testing? SAE Paper 7l0235. I971
`
`Mayrhofer. 1.. Kriegler. W.. Albrecht. K.. "A HYBRID
`DRIVE BASED ON A STRUCTURE VARIABLE
`ARRANGEMENT.“ EVS- I 2 SYMPOSIUM
`
`PROCEEDINGS Vol.2 p. [89-200. Anaheim. California.
`U.S.A.. I994
`
`Unnewehr, L. E.. Auiler. J. 8.. Foote. L. R.. Moyer. D. F. .
`and Stadler. H. L.. "Hybrid Vehicle for Fuel Economy."
`SAE Paper 76012l.l976
`
`Schwarzel. W., Willcnbockel, O. and Zickwolff. 5.. "Der
`
`neue Zweiliter-Vierventilmotor vin Opel." M'H‘Z. Vol.49,
`No.4. p.139. Germany. I988
`
`the batteries. the rest of the losses coming from 12V
`accessories and the mechanical losses within the transaxle.
`
`An improvement of 70% to 80% of the transmission efficiency
`should improve the fuel economy by 14%. which can be
`determined from Chart 2.
`
`Weight Bsd'aCiiQn of garages, - Out. of the total increase
`of weight of 305 kg. 240 kg is from the batteries. As it is not
`realistic to carry a few hundred kilograms of batteries, it is
`very necessary to find ways to reduce their weight. Measures
`for such reductions include power density improvements and
`electricity supplementing by generation using the engine
`through the series path. Chart 2 indicates that weight reduction
`of the batteries by 100 kg should help improve the fuel
`consumption by 5%.
`Mix; - in summary. for example. the improvement
`of the engine average efficiency to 35%. the weight reduction
`of the batteries by 100 kg and a 10% improvement of the
`transmission efficiency should further improve the fuel
`economy by another 55%.
`In light of a comparison with a
`production vehicle. the fuel economy could be double for the
`LA#4 and 2.4 times for the l0°l5 mode.
`
`CONCLUSIONS
`
`The Dual System features new characteristics that are not
`available for the conventional series hybrid system or the
`parallel system. Those features include:
`1. Free control of the engine while keeping a mechanical
`connection between the engine and the drive wheels.
`‘
`2. Compact design of the transaxle integrating two motors
`requires little modification for cunent production vehicles.
`3. Use of the generator as a motor and its combination with
`the traction motor permits the engine and the driveline to
`flexibly adapt to driving conditions.
`The prototype discussed in this paper used current production
`components such as the engine and the batteries. An optimized
`design for each component should further improve the fuel
`economy.
`'
`
`33
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`Page 11 of 11
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`FMC 1021
`FMC 1021
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