A High-Expansion=Ratio Gasoline
`Engine for the TOYOTA Hybrid System
`
`Toshifumi Takaoka**
`Katsuhiko Hirose*
`Tatehito Ueda*
`
`Yasushi Nouno**
`Hiroshi Tada**
`Hiroshi Kanai*
`
`BEST AVAILABLE COPY
`
`Abstract
`A 50% reduction in CO2 and fuel consumption in comparison with a vehicle with the same engine displace-.
`ment has been achieved by the newly developed gasoline engine for the Toyota Hybrid System. This is
`achieved by a combination of an electric motor and an internal-combustion engine that is optimized in
`terms of its displacement and heat cycle. Delaying the closing of the intake valve effectively separates the
`compression ratio and expansion ratio, so that the expansion ratio, which is normally set to 9:1 to 10:1 to
`suppress knocking, can be set to 13.5:1. Motor-assisted quick start, improved catalyst warm-up, and the
`elimination of light-load firing allow the system to achieve emissions levels that are only one-tenth of the
`current Japanese standard values.
`
`Keywords: hybrid, low fuel consumption, low emissions, low friction, variable valve timing
`
`engine output and the motor output by means of a planetary gear sys-
`tem to control the power split. One notable feature is that because the
`drive power is the combined power of the engine and the motor, the
`engine output can be set to a relatively low value without reducing ve-
`hicle performance..
`
`1. Introduction
`
`The earth’s remaining reserves of fossil fuels are said to total approx-
`
`imately two-trillion barrels, or about a 50-year supply, The electric ve-
`
`hicle, because of its zero emissions level and the diversity of sources to
`
`supply electrical energy, is regarded as a promising automobile for the
`
`future. On the other hand, the energy limitations of on-board batteries,
`
`which is to say, their inferior energy density in comparison with fossil
`
`fuels, has meant that the electric vehicle has remained no more than just
`
`one future technology. The internal-combustion!electric hybrid system
`
`Gaso’ine engine~ 1~=i=~
`
`is promoted as a technology that compensates for this shortcoming of
`
`the electric vehicle, but it is also the object of attention as a system that
`
`eliminates the problems of the internal-combustion engine.
`
`Because the drive energy of the hybrid system comes either from
`
`electrical generation by the internal-combustion engine or from the en-
`gine’s direct drive of the axle, the efficiency of the engine, the primary
`
`power source, strongly influences the efficiencY’ of the entire system.
`
`In the development of the Toyota Hybrid System, a newgasoline en-
`
`gine was developed with more emphasis on thermal efficiency than on
`specific output. Because priority was given to the total efficiency of
`
`the entire system, it was decided that a high-expansion-ratio cycle
`
`would be used, and the engine displacement and maximum output
`
`were chosen to reduce friction loss. This paper describes the inves-
`
`tigative .process and the results that were obtained.
`
`!g
`
`I
`
`"
`
`power path
`
`Hybrid transmission
`
`Fig. 1 Toyota Hybrid System Configuration
`
`Fig. 2 shows the relationship between output and efficiency. One
`
`issue for the engine was how to raise the net thermal efficiency from
`point A topoint B.
`
`2.2 Engine Specifications ’ ’~
`
`2. Hybrid System and Engine Specifications
`
`In order to achieve the thermal efficiency objective, the engine for
`
`the hybrid vehicle was planned with the following three points in
`
`2.1 Hybrid System
`
`/
`
`mind: ."
`
`The configuration of THS is shown in Fig. 1. The system links the
`
`* Engine Engineering Oiv. II
`** Power Train Engineering Div. II
`
`(I) The only restriction to be placed on the choice of engine displace-
`ment would 6e that it be within a range that satisfies the engine
`
`output and installability requirements. This makes it possible to
`
`use a high-expansion-ratio cycle with delayed intake valve clos-
`
`TOYOTA TechnicalReview Vol. 47 No, 2 Apr. 1998
`
`53
`
`_=_._,__ I..
`Power split device G~
`
`G
`
`, L
`
`, L,~ ......... ,Battery,
`
`Page 1 of 8
`
`FORD 1206
`
`

`
`l
`
`THS vehicle
`
`g
`
`80%
`improvement
`Average efficiency
`
`Conventional
`vehicle
`
`z
`
`o
`
`A: Optimized engine operating range
`
`B: Improved engine efficiency
`
`es, it is possible to reduce friction loss by reducing both the load on
`
`the valve system springs and the tensile strength of the piston rings
`
`while maintaining the same output.
`
`Based on these considerations, the relationship between displace-
`
`ment and fuel consumption was calculated. The results are shown in
`
`Fig. 5 and Fig. 6. From Fig. 5 it can be seen that in the high-output
`
`range, thermal efficiency rises as the displacement becomes larger, but
`
`in the low-output range, thermal efficiency is higher with a small-dis-
`
`placement engine. Both the indicated thermal efficiency and the me-
`
`chanical efficiency (friction loss) improve as displacement becomes
`
`larger, but in the low-output range, because of the effect of the pump-
`
`ing loss that results from the shift to a partial load, thermal efficiency
`
`Engine output
`
`is better with a small-displacement engine.
`
`Fig. 2 Relationship of Engine Output and Efficiency
`
`sumption. For the reasons cited above, 1500 cc was deemed the opti-
`
`Fig. 6 shows the relationship between displacement and fuel con-
`
`mum engine displacement, given the curb weight of the THS vehicle.
`
`Z
`
`o
`
`g
`
`5
`
`4
`
`3
`
`2
`
`1
`
`0
`
`0
`
`5 10
`
`20
`
`40
`
`Output (kW)
`
`Fig. 4 Relationship of Displacement and Friction
`
`ing, as well as to reduce friction loss by lowering the engine
`
`speed.
`
`(2) In order to achieve a major reduction in emissions, the engine
`
`would operate with 2, = I over its entire range, and the exhaust
`
`system would use a 3-way catalyst.
`
`(3) Active measures would be taken to reduce weight and in~rease ef-
`
`ficiency,
`
`Fig. 3 shows the relationship between the SlY" ratio (the ratio of
`
`combustion chamber surface area to combustion chamber volume) and
`
`the indicated mean effective pressure. The smaller the S/V ratio, the
`
`less heat is dissipated into the coolant, raising the indicated mean ef-
`
`fective pressure. Since the S/V ratio tends to decrease as the displace-
`
`ment per cylinder increases, this also raises the indicated mean effec-
`
`tive pressure.
`
`Fig. 4 shows the relationship between displacement and friction
`
`loss in two engines designed to have identical output. Because the
`
`maximum engine speed can be set lower as the displacement increas-
`
`Pc: Brake mean effective pressure
`Pi*=Pe+Pfm+Pfp Pfm: Friction mean effective pressure
`Pfp: Pumping mean effective pressure
`
`1.40
`
`1.35
`
`1,30
`
`40
`
`’D
`
`-~ 30
`
`20
`
`.,~/,/
`
`t
`
`JV /
`
`Suburban mode
`
`t//
`
`100
`
`1000cc /
`
`Brake efficiency ~L.J~_~
`I/ i
` 8ooc
`I
` ,baomode I
`, ooocr,//
`i/
`
`2
`
`’="
`
`-A I IH - omo,at,ve ..
`( I t11 !|!11 ,eque.cv
`",LIIIIllllll. I1. tts0occ)
`
`1,25 ~ i
`0,22
`0,2
`
`~
`
`0.24
`
`,,
`
`0.26
`
`0.28
`
`S/V ratio (llmm)
`
`10
`
`20
`
`30
`
`Engine output (kW)
`
`0
`40
`
`Fig. 3 Relationship of S/V Ratio and Indicated Mean
`Effective Pressure
`
`Fig. 5 Displacement and Engine Efficiency
`
`54
`
`Page 2 of 8
`
`FORD 1206
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`

`
`10
`
`~=E
`
`0
`
`1
`Vehicie fuel economy
`I
`
`.....or--- ---o~
`
`J
`
`i 1000 1200
`
`Engine maximum efficiency
`
`I !
`
`1400 1600 , 1800
`
`40
`
`"G
`
`35
`
`¢0
`
`A H~gh-Expansion-Ilatio GasolLne Engine for tha TOYOTA " "
`!lyo~ :d SVsttm’~
`
`3.2 Relationship of Mechanical Compression Ratio,
`Valve Timing, and Brake Thermal Efficiency
`
`Before a prototype of the high-expansion-ratio engine was built, the ef-
`fects of the mechanical compression ratio and valve, timing on brake thor.
`real efficiency were studied. An in-line four-cylinder, 2164-cc Toyota 5S-
`FE engine was used in the experiments.
`¯ Fig. 9 shows the changes in thermal efficiency with different combina-
`tions of expansion ratio and valve timing. If the expansion ratio is in-
`creased and intake valve closing is delayed, brake thermal efficiency rises,
`but it reaches a lirnit at an expansion ratio of 14¯7:1. Also, the maximum
`value of the brake mean effective pressure drops as the delay in intake
`valve closing increases.
`
`2400rpm
`
`36
`
`32
`
`=o 2B
`
`E
`
`~ z4
`
`° J!/~ ..... "
`.--"
`
`’
`
`[ !""o 1
`" = 9.5
`
`U
`
`~"
`
`0 14,7
`
`Effective compression ratio 9,0
`
`20
`0,2
`
`’ ,
`0.4
`
`i
`
`0.6
`
`I ,, ,
`
`0.8
`
`,,
`
`i
`
`I
`
`Brake mean effective pressure Pine (MPa)
`
`Fig. 9 Expansion Ratio and Thermal Efficiency
`
`Fig. 10 shows the retationship between brake thermal efficiency
`and brake mean effective pressure under full load. As the expansion
`ratio increases, the timing advance becomes slower due to knocking,
`and the brake thermal efficiency drops, but if the intake valve closing
`
`35
`
`34
`
`33
`
`.o
`
`E
`~, 32
`
`m 31
`
`Intake valve
`
`1 6%
`
`Exponston
`ratio
`9.5
`12.1
`13.7
`14.7
`16.8
`
`I
`D
`
`O
`A
`
`,,,
`
`0.8
`0.9
`0.7
`1
`Brake mean effective pressure under ful! load
`
`1,1
`
`(MPa)
`
`Fig. 10 Relationship of Brake Mean Effective Pressure
`and Thermal Efficiency as Expansion Ratio and
`Compression Ratio Change
`
`Displacement {cc)
`
`Fig. 6 Displacement and Fuel Economy
`
`3. Improving Efficiency by Means of High Expansion Ratio
`
`3.1 Principle
`
`The theoretical therma! efficiency of an equivalent charge.cycle is
`
`improved by raising the compression ratio. But if the compression
`
`ratio is raised in a gasoline engine, the compression end temperature
`
`rises, and knocking occurs. To prevent knocking in the high-expan-
`
`sion-ratio engine, the timing of intake valve closing was .delayed con-
`
`siderably, thus lowering the effective compression ratio and raising the
`
`expansion ratio, which essentially controls the thermal efficiency.
`
`Fig. 7 is a pressure-volume (p-V) diagram comparing the high-expan-
`
`sion-ratio cycle with the conventional cycle when the charging effi-
`
`ciencies of the two are equal. Fig. 8 shows the same sort of compari-
`
`son when the compression end pressures are equal¯ When the
`
`charging efficiency is identical, delaying the closing of the intake
`
`valve raises the maximum pressure and increases the positive work,
`
`and also reduces pumping loss. With identical compression end pres-
`
`sure, increasing the expansion ratio raises the theoretical efficien-
`
`High-ex!~ansion-
`I ~’~ ratio cycle
`I ~K- Conventional
`
`10000
`
`1000
`
`100
`
`o
`
`o~
`
`o.
`
`10 --
`10
`
`100 1000
`
`Cylinder volume (col
`
`,
`
`i
`100 1000
`
`10
`
`Cylinder volume (ec)
`
`Fig. 7 p-V Diagrams with
`
`Equivalent
`
`Charging Efficiency
`
`Fig. 8 p-V Diagrams with
`Equivalent
`Compression End
`Pressure
`
`TOYOTA Technical Review Vol. 47 No. 2 Apr. 1998
`
`55
`
`Page 3 of 8
`
`FORD 1206
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`

`
`is delayed at the same time, knocking gradually diminishes and effi-
`
`4.2 Engine Structure
`
`ciency improves. Therefore, if the brake mean effective pressure is al-
`
`lowed to fall, the combination of high expansion ratio and delayed in-
`
`Fig. 12 is a transverse sectional view of the high-expansion-r~
`
`take valve closing achieves high efficiency. Fig. 11 is an indicator
`
`engine. An aluminum-alloy cylinder block, offset crankshaft,’" ;
`
`diagram of actual measured results showing that the heat cycle illus-
`
`trated in Fig. 7 and Fig, 8 was achieved.
`
`10000
`
`High-expansion-
`
`1000
`
`cycle .
`
`8
`
`lOO
`
`ladder-frame structure are used. The crankshaf~ has been made tF
`ner and lighter, and the load on the valve system springs has been
`duced, as has the tensile strength of the piston rings. The connect
`
`rod/stroke ratio has been increased, and the intake inertia effect
`
`been reduced by using a small intake manifold, The engine also u
`
`a slant squish combustion chamber. All of these features combim
`
`achieve lighter weight, lower friction, and improved combustion,
`
`1,5-1iter engine
`
`10 ’
`10
`
`’ ’ ~ "’
`t000
`!00
`
`Cylinder volume (cc)
`
`THS engine
`
`Fig, 11 Indicator Diagram of Actual Measurements
`
`4. High-expansion-ratio THS Engine
`
`Fig. 12 Transverse Section of High.expansion-ratio Eng
`
`4.1 Basic Specifications
`
`5. Experimental Results and Considerations
`
`Table 1 shows the main specifications for the high-expansion-ratio
`
`This section summarizes the ?esults of experiments cpnducte.
`
`engine, The haechanical compression ratio is set to 13,5:1. but the ef-
`
`the 1.5-1iter high-expansion-ratio engine and some considerations
`
`fective compression ratio is suppressed to the range of 4,8:1 to 9.3:1
`
`ceming them.
`
`by using intelligent variable valve timing (VVT.i) to time the intake
`
`valve closing between 80° and 120° after bottom dead center (ABDC),
`
`The ratio of 4.8:1 is obtained by the maximum delay of VVT-i and is
`
`used to counter vibration during engine restart, as explained below,
`
`Table 1
`
`Design Specifications
`
`Engine model
`
`Displacement (cc)
`
`Bore X stroke
`
`Maximum output
`
`Combustion chamber volume
`
`Mechanical compression ratio
`
`Effective compression ratio
`
`Intake valve closln’g timing
`
`Exhaust valve opening timing
`
`1NZ-FXE
`
`1497
`
`~75X84.7
`
`43kW/4,000rpm
`
`30cc
`
`13.5
`
`4.849.3
`
`80~ 120* ABDC
`
`32° BBDC
`
`"B
`
`’1
`
`! v
`
`56
`
`5.1 Relationship Of Expan.sion Ratio and Brake Ther
`Efficiency
`
`Fig.’ 13 shows the relationship of ignition tiffing to torque ar
`brake specific fuel consumption (BSFC). Expansion ratios of
`
`14:1, and 15:1 were compared,~nd it can be seen that as the ex
`
`sion ratio increases,/.he trace krroek ignition timing is delayed. V~
`
`15:1 expansion ratio, the efficiency improves at the point of mini
`
`spark advance for best torque (MBT), but the expansion ratio i
`
`stricted by the knocking that occurs due to the high effective corn
`
`sion ratio. The best results in terms of torque and BSFC wet,
`rained with an expansion ratio of 14:1.
`
`Fig. 14 shows the results of a study of thermal efficiency v
`
`engine output. A 14:1 expansion ratio showed the best results
`
`the entire output range. Ultimately, an expansion ratio of 13,5:
`
`chosen, taking into account such factors as the allowable variati
`
`Page 4 of 8
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`FORD 1206
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`

`
`combustion chamber volume and the adhesion of deposits in the com-
`
`ventional engines and thai the objective of reducing friction loss was
`
`bustion chamber, in order to leave a margin for pre-ignition.
`
`achieved.
`
`i4ioh-E×nansiun-Ratio Gasoti~le E,r~t]ine for !he (¢tw)’~’i~ H’~,nr:r~ ~ystam
`
`120
`
`IO0
`
`80
`
`E
`Z
`
`CT o
`
`E
`z
`
`#.
`
`u-
`U’)
`O3
`
`80
`
`7O
`
`60
`280
`
`26O
`
`240
`
`220
`
`1000 rpm
`
`Black points are trace knock
`
`_ I
`
`ExpansionA~)I7
`141315 rati°t
`
`I
`5
`
`!
`lO
`
`15
`
`Ignition advance (degrees BTDC)
`
`;
`
`;,
`
`;
`
`i
`
`;
`
`; ,
`
`260
`
`240
`
`1/3
`
`220
`
`I
`
`I ..... !
`
`t
`
`I
`
`I ....
`
`I
`
`1000
`
`2000
`
`3000
`
`4000
`
`Engine speed (rpm)
`
`Fig. 13 Relationship of Ignition Timing and BSFC
`
`Fig. 15 Torque Improvement Effect of VVT-i
`
`=o
`
`40
`
`35
`
`30
`
`io
`I°
`I~
`
`/
`/
`;s /
`l
`I
`l
`l
`10 20 30 40 50
`
`Engine output (kW)
`
`o
`
`t,k
`
`0.1
`
`0,2
`
`Conventional engin
`
`~< .~ -
`
`~ ~llr~"
`
`T~HS engine’
`
`I ,
`1600
`
`l ~. I I
`3200 .4800
`
`6400
`
`Engine speed (rpm)
`
`!
`
`Fig. 16 Comparison of,..Friction Loss’
`
`; f
`5.4 Reduction of Exhaust Emissions
`
`The advantages and disadvantages of the hybrid vehicle with re-
`
`spect to cleaner exhaust emissions are summarized below.
`
`Advantages
`l) By using the supplementary drive power of the electric motor, the
`
`il
`
`system eliminates the light-load range, where concentrations of
`
`hydrocarbons in the emissions are high and the exhaust tempera-
`
`ture is low.
`
`Fig. 14 Expansion Ratio and Brake Thermal Efficiency
`
`5,2 Torque Improvement by VVT-i
`
`Full-load torque was adjusted using VVT-i. The results are shown
`in Fig. 15. An improvement in torque of 10% or more was made pos-
`
`sible by advancing the intake valve closing by 10°. In THS, the en-
`
`gine is controlled so that intake valve closing is advanced when the
`
`load requirements are high.
`
`5.3 Friction Loss
`
`As stated previously, the engine speed was lowered in an attempt to
`reduce friction loss. The measured results are shown in Fig. 16. h
`
`can be seen that the friction loss for the high:expansion-ratio engine is
`
`at a consistently lower level than the cluster of" points plotted for con-
`
`~OYOrA Technical Review Vol. 47 No. 2 Ap’r. 1998
`
`57
`
`Page 5 of 8
`
`FORD 1206
`
`

`
`(2) By allocating a portion of the load to the electric motor, the system
`
`is able to reduce engine load fluctuation under conditions such as
`
`rapid acceleration. This makes it possible to reduce quick transients
`
`in engine toad so that the air-fuel ratio can be stabilized easily.
`
`Disadvantages
`
`(I) Because the engine is used in the high-efficiency range, the ex-
`
`haust temperatures are lower than for a conventional vehicle.
`
`(2) There is concern that the more the engine is stopped and restarted,
`
`the more unburned fuel will enter the exhaust system and the more
`
`the catalyst bed temperature will drop.
`
`Fig, 17 shows the exhaust temperature distribution for the high-ex-
`
`pansion-ratio engine. Although the exhaust temperatures are lower
`
`than for a conventional engine, a minimum temperature of 400°C is
`
`ensured for the engine operating range shown in the diagram. This is
`
`a temperature that can maintain the catalyst in an activated state,
`
`Fig, 18 shows the change in the catalyst bed temperature after the
`
`vehicle stops. In a conventional vehicle, where the engine continues
`
`to idle, the catalyst bed temperature slowly drops. But in the THS ve-
`
`hicle, the influx of low-temperature exhaust gases can be avoided by
`
`stopping the engine, making it possible to sustain a comparatively
`
`gradualdecline in temperature.
`
`Fig. 19 shows the levels of exhaust gases at the cataIyst inlet.
`
`Hydrocarbons are at the same level as a conventional vehicle, which is
`
`thought to be due to the smaller volume and higher S/V ratio of the
`
`600
`
`U
`*_,..,
`
`F_
`
`,O
`
`ro
`
`d
`
`40O
`
`200
`
`0
`
`0
`
`%
`
`I_, Engine stopped
`
`Idling at 100O rpm
`
`- -
`
`! ........
`5
`
`|
`10
`
`Time (rain,)
`
`Fig. 18 Change in Catalyst Bed Temperature with
`Engine Stopped
`
`"r
`
`1.2
`
`x 0.8
`O
`Z
`o
`
`combustion chamber. However, as explained previously, the catalyst
`
`I
`
`is maintained in an activated state that is sufficient to ensure a high
`
`rate of catalylic conversion,
`
`Exploiting the a~dvantages cited above based on these results,
`
`Toyota optimized the system to achieve the voluntary emissions target
`
`HC
`
`o o
`CO
`
`NOx
`
`of one-tenth of the current standard values.
`
`Fig. 19 Comparison Of Emissions at Catalyst Inlet
`
`THS engine operating range
`
`120
`
`100
`
`80
`
`60
`
`4O
`
`20
`
`z
`
`~r
`
`F.-
`
`0 -
`800
`
`Exhaust temperature (*C)
`,, l, ,,I I
`1600 2400
`3200
`
`4000
`
`Engine speed from)
`
`Fig. 17 Exhaust Temperature Map
`
`58
`
`5.5 Vibration Countermeasures When Starting an
`
`Stopping
`
`Stopping the engine when the vehicle stops contributes greatly
`fuel economy, realizing a 20% improvement in the 10-15 mode. (
`the other hand, problems have be’~m raised with vibration as the engi
`
`speed passes through the resonartce"point of the drive train, as well
`
`vibration due to the brief continuation of the compression and expa
`
`sion cycle when the engine stops. The drive train ~tesonance proble
`
`is solved by using the motor to raise the engineJspeed in a shor~
`time. It was thought that the compression and expansibn cycle cot
`
`be moderated by reducing the vohime of air when the: engine is st
`
`off. The VVT-i function is used to reduce the volume of the intake
`
`Fig. 20 shows floor vibration when the engine starts. The large a
`
`plitude of acceleration seen in area A in the diagram is due to the co
`
`pression reaction force. This amplitude can be reduced considerably.
`
`shown in area A’, by using VVT-i to set the timing of intake valve cl,
`
`ing to 120" ABDC. The vibration seen in area B arises from the rai
`
`increase in engine torque after the engine’ starts firing. This is elimir,
`
`ed by controlling the ignition timing delay, as shown in area B’.
`
`Page 6 of 8
`
`FORD 1206
`
`

`
`A High-Exgsnsicr,.R~tio GnsoHno Engine for [he TO"CT,’~ Hybrid S~’sI.em
`
`lO
`
`m
`
`~ ,lO
`o
`
`~ooo
`
`Intake valve
`closing 120°
`ABDC.
`
`lO
`
`E
`g
`o .~
`
`-lO ~,
`¢J
`<
`
`2
`
`o.
`
`T~
`L}
`
`tu -0,2
`
`o
`
`0.2
`
`0.4
`
`0.6
`
`Time (sec.)
`
`I i
`0.8
`
`Fig. 20 Vibration When Engine Starts
`
`400
`
`800
`
`1200
`
`Engine speed (rpml
`
`Fig. 21 Relationship of Engine Speed and Cylinder
`Pressure
`
`5.6 Low-temperature Starting
`
`40
`
`[n the THS system, the generator is used as a starter motor to start
`
`the engine turning. For this purpose, the generator uses the large-ca-
`
`pacity nickel-metal hydride battery as a power supply. However, as
`
`the temperature drops, the battery power also drops, reducing the
`
`20 "
`
`cranking speed. On the other hand, the significant delay in intake
`
`ca
`
`10.15 mode
`
`Li
`
`30 ~,
`
`valve closing in the high-expansion-ratio engine reduces the compres-
`
`sion end pressure (the maximum pressure within the cylinder) during
`
`cranking. The relationship between cylinder pressure and engine
`
`.speed is shown in Fig. 21, using intake valve closing timing as a para-
`meter. Given the combustion characteristics of the engine, the maxi-
`
`mum pressure at which ignition is possible is approximately 0.85
`
`MPa. In the THS system, the engine speed and intake valve closing
`
`timing are coordinated so that this pressure is maintained even under
`
`low-temperature conditions.
`
`5,7 Vehicle Fuel Economy
`
`Fig. 22 shows the efficiency distribution of the developed high-ex-
`
`pansion-ratio engine when it is combined with the THS system and
`
`stopped, so thatt it is used only in the high-efficiency range. Fig. 23
`
`iI driven in the 10. 15 mode. In the low-output range the engine is
`
`10
`20
`Engine output lk.W)
`
`3O E
`
`Fig. 22
`
`Engine Operating Range and Efficiency in
`10- 15 Mode
`
`e~
`
`’35
`
`30
`
`25
`
`r~
`
`{;~ tTt ¯
`
`shows the relationshl" ’p between fuel economy and the charge balance
`
`
`tk
`
`of the battery before and after mode driving. In the hybrid vehicle, the
`
`fuel economy chat~ges as the battery charges and discharges, so the
`
`vehicle’s fuel economy is defined as the value when the charge bal-
`
`ance is zero.
`
`Optimization of the vehicle’s integrated controls, including regener-
`mive braking, allows the THS vehicle to attain almost twice the fue!
`
`economy of a conventional vehicle of the same class.
`
`20
`-0.2
`
`-o.1
`
`0.0
`
`0.1
`
`0.2
`
`Charge balance (Ah)
`
`Fig. 23 Charge Balance and Fuel Economy
`
`TOYOTA Technical Review Vol. 47 No. 2 Apr. 1998
`
`59
`
`!
`
`Page 7 of 8
`
`FORD 1206
`
`

`
`6. Conclusion
`
`10, 9437458
`
`A lightweight, compact, high-expansion-ratio gasoline engine was
`developed for use in the internal-combustion/electric hybrid vehicle.
`
`(I) The engine output required to meet the vehicle’s weight and per-
`
`formance requirements was determined, and the engine displace-
`
`(10)Shinichi Sano, Kamiyama, Ueda: Improving Thermal Efficie~
`
`by Means of Cylinder Bore and Offset Crankshaft. JSAE Prin
`
`Materials for Presentations 966 t996-10
`
`ment was chosen to yield the optimum vehicle fuel economy from
`
`I Authors
`
`the high-expansion-ratio cycle.
`(2) A 1.5-1iter high-expansion-ratio gasoline engine was developed as
`
`the primary power source, and it attained the target fuel consump-
`
`tion rate of less than 230 gJkWh.
`(3) Emissions levels much lower than the current standard values
`
`were attained by optimum control of the motor and engine.
`
`(4) Vibration during engine starting and stopping was greatly reduced
`
`by using VVT-i.
`
`(5) The hybrid system achieved twice the fuel economy of a conven-
`
`T, TAKAOKA
`
`K. HIROSE
`
`T. UEDA
`
`tional vehicle of the same class, while cutting the volume of CO.,
`
`emissions in half.
`
`The authors wish to express their respectful appreciation to atl
`
`those who cooperated in the development of this system. We particu-
`
`larly wish to express our gratitude to the late Mr. Masahito I’,!inomiya
`
`for helping us to succeed in providing this engine to out’customers.
`
`[] References
`
`(I) YoshihiroFujiyoshi, Urata, Suzuki, Fukuo:Study of. Non-
`
`Y. NOUNO
`
`H. TADA
`
`H. KANAI
`
`Throttling Engine Using Early Intake Valve Closing Mechanism.
`
`Report No. I. Society of Automotive Engineers of Japan (JSAE).
`
`Printed Materials for Presentations 924006, 924 1992-10
`
`(2) Shinichi Nagumo, Hara: Improved Fuel Efficiency by Control of
`
`Intake Valve Closing Timing. JSAE Paper 9540921, Vol. 26 No.
`
`4, October, 1995
`
`(3) Richard Stone, Eric Kwan: Variable Valve Actuation Mechanisms
`
`and the Potential for their Application. SAE Paper 890673, 1989
`
`(4) T. Ahmad, M. A. Theobald (GMR): A Survey of Variable-Valve-
`
`Actuation Technology. SAE Paper 891674, 1989
`
`(5) T. W. Asmus: Valve Events and Engine Operation. SAE Paper
`
`820749, 1982
`
`(6) Hitomi Mitsuo, Sasaki, et al.: Mechanism of Improving Fuel
`
`Efficiency by Miller Cycle and its Future Prospects. SAE Paper
`
`950974, 1995
`
`(7) James H. Turtle: Controlling Engine Load by Means of Early
`
`Intake-Valve Closing. SAE Paper 820408, 1982
`
`(8) R. A. Stein, K. M. Galietti, T. G. Leone: Dual Equal VCT-A
`
`Variable Camshaft Timing Strategy for Improved Fuel Economy
`
`and Emissions. SAE Paper 95975, 1995
`
`(9) Naoharu Ueda, lchimaru, Sakai, Kanesaka: High Expansion Ratio
`
`Gasoline Engine Using Rotary Valve for Intake Manifold Control,
`
`Report No. 3. JSAE Printed Materials for Presentations 946 1994-
`
`f
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`60
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`Page 8 of 8
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`FORD 1206