United States Patent [19]
`Ibaraki et al.
`
`US006098733A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,098,733
`Aug. 8,2000
`
`[54] HYBRID DRIVE SYSTEM FOR MOTOR
`VEHICLE
`
`[75] Inventors: Ryuji Ibaraki, Toyota; Yutaka Taga,
`Aichi-ken; Atsushi Tabata, Okazaki, all
`of Japan
`
`[73] Assignee: Toyota Jidosha Kabushiki Kaisha,
`Toyota, Japan
`
`[21] Appl' NO‘: 08/728’378
`[22] Filed:
`Oct. 9, 1996
`
`Foreign Application Priority Data
`[30]
`Oct. 13, 1995
`[JP]
`Japan .................................. .. 7-265412
`
`[51] Int. Cl.7 ..................................................... .. 1360K 6/04
`[52] US. Cl.
`.. ISO/65.2; 180/65.8; 318/376;
`701/55
`[58] Field of Search ................................ .. 180/652, 65.1,
`180/653, 654, 658; 318/8, 376; 701/22,
`51, 55
`
`[56]
`
`References Cited
`
`us‘ PATENT DOCUMENTS
`6/1982 Kawakatsu ....................... .. 180/652 X
`
`4,335,429
`
`. . . . .. 180/652
`9/1984 Hunt . . . . . . . . . . . . .
`4,470,476
`..... .. 180/652
`9/1994 Severinsky
`5,343,970
`180/65-2 X
`9/1994 Gardner ----- -
`5,346,031
`..... .. 180/652
`9/1996 Sherman ..
`5,558,175
`180/652 X
`8/1997 Farrall ........ ..
`5,656,921
`5,697,466 12/1997 Moroto et al. ....................... .. 180/652
`
`FOREIGN PATENT DOCUMENTS
`
`0 552 140
`5-50865
`6-38304
`
`7/1993 European Pat. Off. .
`3/1993 Japan .
`2/1994 Japan .
`OTHER PUBLICATIONS
`Patent Abstracts of Japan, vol. 95, No. 003, JP—A—07
`067208, Mar. 10, 1995.
`Primary Examiner—Michael Mar
`Attorney, Agent, or Firm—Oblon, Spivak, McClelland,
`Maier & Neustadt, RC.
`[57]
`ABSTRACT
`
`A hybrid vehicle drive system including an engine, an
`electric motor Operated by an 618mm: energy sIored in a
`storage device charged by operation of the engine, and a
`controller for selecting a loW-load drive mode for driving the
`Vehicle by the electric motor When the vehicle running
`condition is in a predetermined loW-load range, and a
`high-lead drive mode for driving the Vehiele by the engine
`When the running condition is in a predetermined high-load
`range in Which a load acting on the hybrid drive device is
`higher than that in the loW-load range, and Wherein the
`controller includes an emergency drive control device oper
`ated in the event of a failure of the ?rst and second drive
`poWer sources, for operating the other, normal drive poWer
`Seuree to drive the meter Vehiele, and a range Changing
`
`device for changing one of the low-load and high-load
`ranges Which corresponds to the normal drive poWer source
`When the normal drive poWer source is operated by the
`emergency drive Control device_
`
`6 Claims, 9 Drawing Sheets
`
`10
`
`OPTIONAL“
`OPERATED
`DEV'CE
`38)
`
`ELECTRIC
`f. MOTOR
`4O
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`ELECTRIC ENERGY
`STORAGE DEVICE.»\36
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`Page 1 of 23
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`FORD 1238
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`

`

`US. Patent
`
`Aug. 8, 2000
`
`Sheet 1 0f 9
`
`6,098,733
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`Page 2 of 23
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`FORD 1238
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`Page 2 of 23
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`FORD 1238
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`

`

`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 2 0f 9
`
`6,098,733
`
`FIG.2
`START
`I
`
`I
`
`READING 6A0,
`Ne Ni, No, soc,
`TEANDTM
`
`S1
`
`S2
`
`FAILURE
`OF ENGINE I2 ?
`
`YES
`
`N 0 83
`
`I
`FAILURE
`OF ELECTRIC MOTOR 14 ?
`
`MOTOR
`FAILURE
`SPECIAL
`CONTROL
`ROUTINE
`
`S4
`
`NO
`
`NORMAL
`CONTROL
`ROUTINE
`
`S5
`
`END
`
`ENGINE
`FAILURE
`SPECIAL
`CONTROL
`ROUTINE
`
`Page 3 of 23
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`FORD 1238
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`

`

`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 3 0f 9
`
`6,098,733
`
`( NORMAL CONTROL ROUTINE )
`
`F|G.3
`
`CALCULATiNG
`REQUIRED
`POWER PL
`
`55-7
`
`MOTOR
`SUBMRCEPE
`
`'
`
`UT'NE
`
`ss-a
`ELECTRICITY
`GENERATING
`MODE
`
`SUB-ROUTINE
`
`MODE
`
`SUB-ROUTINE
`
`SUBMFQDUTINE
`
`‘
`
`NORMALSHIFT
`CONTROLOF
`TRANSMISSION16 85-9
`
`(
`
`RETURN
`
`)
`
`Page 4 of 23
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`FORD 1238
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`

`

`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 4 of9
`
`6,098,733
`
`FIGA
`( ENGINE-FAILURE SPECIAL CONTROL ROUTINE )
`
`CALCULATING
`REQUIRED
`POWER PL
`
`86-1
`
`S6-4
`INDICATION OF DRIVE
`SYSTEM FAILURE
`
`66-5
`OPERATING ELECTRIC
`MOTOR TO PRODUCE
`POWER CORRESPONDING
`TO THRESHOLD D
`
`OPERATING ELECTRIC
`MOTOR TO PRODUCE
`THE CALCULATED
`REQUIRED POWER PL
`
`ENGINE-FAILURE
`SPECIAL SHIFT
`CONTROL OF
`TRANSMISSION S6-6
`
`I
`
`RETURN
`
`I
`
`Page 5 of 23
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`FORD 1238
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`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 5 of9
`
`6,098,733
`
`FIGS
`( MOTOFI—FAILUFIE SPECIAL CONTROL ROUTINE )
`
`CALCULATING
`REQUIRED
`POWER PL
`
`S4-I
`
`S4-4
`INDICATION OF DRIVE
`SYSTEM FAILURE
`
`S4-5
`OPERATING ENGINE
`TO PRODUCE
`POWER CORRESPONDING
`TO THRESHOLD E
`
`OPERATING ENGINE
`TO PRODUCE
`THE CALCULATED
`REQUIRED POWER PL
`
`MOTOR-FAILURE
`SPECIAL SHIFT
`CONTROL OF
`TRANSMISSION S4-6
`
`I
`
`RETURN
`
`I
`
`Page 6 of 23
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`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 6 of9
`
`6,098,733
`
`A
`
`FIG.6
`
`
`
`DRIVE TORQUE
`
`
`
`ACCELERATOR ()PERATION AMOUNT 6A0
`
`I
`
`VEHICLE SPEED V
`
`_ I I\ ,9 I Q
`K “n
`| I | (DU 0
`\ _ I
`
`I
`
`I . \I\ l I
`
`VEHICLE SPEED V
`
`Page 7 of 23
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`

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`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 7 of9
`
`6,098,733
`
`SON
`
`FIG. 8
`
`2, /
`
`CONTROLLER
`
`/12
`I
`INTERNAL
`COMBUSTION
`ENGINE
`
`K52
`ELECTRIC
`Ne GENERATOR
`
`[/36
`ELECTRIC
`ENERGY
`STORAGE
`DEVICE
`
`14
`
`" /
`ELECTRIC
`MOTOR
`
`Ni
`
`DRIVE WHEELS
`\2o
`
`SPCEEEERREEHEIEIG NO TRANSMISSION 1
`L18
`\16
`
`I
`
`START
`
`I
`
`FIGO
`
`READING (9A0,
`Ne Ni, N0, SOC,
`TEANDTM
`
`RI
`
`R2
`
`FAILURE
`OF ENGINE 12 OR ELECTRIC
`GENERATOR 52?
`NO
`
`NORMAL
`CONTROL
`ROUTINE
`
`END
`
`YES
`
`SPECIAL
`CONTROL
`ROUTINE
`
`Page 8 of 23
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`FORD 1238
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`

`

`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 8 of9
`
`6,098,733
`
`( NORMALCONTROL ROUTINE )
`
`CALCULATING
`REQUIRED
`POWER PL
`
`R3-1
`
`ENGINE-ON
`MOTOR
`DRIVE
`MODE
`SUB-ROUTINE
`
`R3-5
`ENGINE-OFF
`MOTOR
`DRIVE
`MODE
`SUB-ROUTINE
`
`R3-6
`ELECTRICITY
`GENERATING
`DRIVE
`MODE
`SUB-ROUTINE
`
`V
`
`NORMAL SHIFT
`CONTROL OF
`TRANSMISSION 16 83-7
`
`I
`
`RETURN
`
`I
`
`Page 9 of 23
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`FORD 1238
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`

`U.S. Patent
`
`Aug. 8,2000
`
`Sheet 9 of9
`
`6,098,733
`
`( SPECIAL CONTROL ROUTINE ) F | G 1 ‘|
`l
`CALCULATING
`REQUIRED
`POWER PL
`
`R4-1
`
`.
`
`R4-4
`INDICATION OF DRIVE
`SYSTEM FAILURE
`
`R4-5
`OPERATING ELECTRIC
`MOTOR TO PRODUCE
`POWER CORRESPONDING
`TO THRESHOLD G
`I
`
`R4‘3
`OPERATING ELECTRIC
`MOTOR TO PRODUCE
`THE CALCULATED
`REQUIRED POWER PL
`
`SPECIAL SHIFT
`CONTROL OF
`TRANSMISSION R4-6
`
`
`
`DRIVE TORQUE
`
`VEHICLE SPEED V
`
`Page 10 of 23
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`

`1
`HYBRID DRIVE SYSTEM FOR MOTOR
`VEHICLE
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates in general to a so-called
`hybrid drive system for driving a motor vehicle, Which drive
`system includes an engine and an electric motor. More
`particularly, the invention is concerned With a technique for
`permitting the motor vehicle to run to a desired destination
`even in the event of a failure of one of the engine and the
`electric motor Where the engine and the electric motor are
`disposed in parallel connection With vehicle drive Wheels, or
`a failure of one of the engine and an electric generator Where
`the engine and the electric motor are disposed in series
`connection With the drive Wheels.
`2. Discussion of the Related Art
`JP-A-5-50865 discloses an example of a hybrid drive
`system of so-called “parallel type”, Which includes (a) an
`engine operated by combustion of a fuel, (b) an electric
`energy storage device Which is charged With an electric
`energy by rotation of the engine, and (c) an electric motor
`operated by the electric energy stored in the electric energy
`storage device, and Wherein the engine and the electric
`motor are selectively used to drive the vehicle, depending
`upon the running condition of the vehicle. This type of
`hybrid drive system has a loW-load drive mode in Which
`only the electric motor is used to drive the vehicle, and a
`high-load drive mode in Which the engine is used to drive the
`vehicle. The loW-load and high-load drive modes are selec
`tively established depending upon the running condition of
`the vehicle. The loW-load drive mode is selected When the
`load acting on the hybrid drive system is relatively loW
`(namely, When the currently required poWer or output for
`driving the vehicle is relatively small), and the high-load
`drive mode is selected When the load acting on the drive
`system is relatively high (namely, When the currently
`required poWer or output is relatively large). Also knoWn is
`a hybrid drive system of so-called “series type”, Which
`includes (a) an engine operated by combustion of a fuel, (b)
`an electric generator driven by the engine for generating an
`electric energy energy, (c) an electric energy storage device
`for storing the electric energy generated by the electric
`generator, and (d) an electric motor operated by the electric
`energy generated by the electric generator or stored in the
`storage device, and Wherein the electric motor is used as a
`drive poWer source for driving the vehicle. There is also
`knoWn a hybrid drive system of so-called “parallel series
`type” Which is a combination of the parallel type hybrid
`drive system and the series type hybrid drive system,
`Wherein the engine of the series type hybrid drive system is
`used as another drive poWer source in addition to the electric
`motor.
`In the event of a failure of the engine or electric motor in
`the parallel type hybrid drive system, the motor vehicle
`cannot be driven at all or cannot be driven a distance
`sufficient to reach the desired destination. If the engine
`becomes defective, the vehicle should be driven by the
`electric motor. Since the torque produced by the electric
`motor is relatively small, the vehicle cannot be driven by the
`electric motor With a sufficient torque Where the required
`poWer is relatively large, for instance, Where the vehicle is
`required to climb an uphill. It is also noted that the electric
`energy is stored in the storage device by the engine as Well
`as by utiliZing regenerative braking of the electric motor, the
`failure of the engine results in an insufficient amount of the
`
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`electric energy stored in the storage device, making it
`impossible to operate the electric motor for driving the
`vehicle over a distance sufficient to reach the desired des
`tination. If the electric motor becomes defective, the vehicle
`should be driven by the engine. Since the drive system is
`designed to select the engine drive mode only When the
`vehicle is in a high-load condition, the vehicle cannot be
`driven by the engine in the engine drive mode When the
`vehicle is in a loW-load condition, for example, immediately
`after the vehicle has been started or immediately before the
`vehicle is stopped. Where the hybrid drive system of the
`parallel type is equipped With a transmission Which is shifted
`to change its speed ratio depending upon the running con
`dition of the vehicle, a failure of one of the engine and the
`electric motor causes deteriorated running performance of
`the vehicle. That is, the poWer transmitted from the normal
`drive source (normally functioning engine or electric motor)
`to the transmission does not match the selected speed ratio
`if the transmission is shifted to change its speed ratio
`depending upon the amount of operation of the accelerator
`pedal or other running condition of the vehicle in the same
`manner as in the normal state of the drive system. In this
`case, the vehicle may not be driven at all, or the running
`distance is considerably limited.
`In the event of a failure of the electric motor as the drive
`poWer source in the series type hybrid drive system, it is
`certainly impossible to drive the vehicle. HoWever, a failure
`of the engine or electric generator also causes a problem.
`Namely, the failure of the engine makes it impossible to
`operate the electric generator to generate the electric energy,
`and the electric energy that can be used by the electric motor
`to drive the vehicle is limited to that stored in the electric
`energy storage device. If the vehicle is run under a relatively
`high load, the running distance is limited particularly since
`the energy efficiency is relatively loW in the high-load
`running condition. If the ratio of the electric energy neces
`sary to operate the electric motor to the electric energy
`stored in the storage device is controlled, the failure of the
`electric generator to generate the electric energy results in
`shortage of the electric energy to be used by the electric
`motor, leading to a possibility of running failure of the
`vehicle due to an insufficient output of the electric motor.
`
`SUMMARY OF THE INVENTION
`It is therefore an object of the present invention to provide
`a hybrid drive system for a motor vehicle, Which permits the
`vehicle to run to a desired destination even in the event of
`a failure of the engine or the electric motor of the parallel
`type drive system or a failure of the engine or the electric
`generator of the series type drive system.
`The above object may be achieved according to a ?rst
`aspect of the present invention, Which provides a hybrid
`drive system (10) for a motor vehicle, comprising: (a) an
`engine operated as a ?rst drive poWer source by combustion
`of a fuel; (b) an electric energy storage device Which is
`charged With an electric energy by operation of the engine;
`(c) an electric motor operated as a second drive poWer
`source by the electric energy stored in the electric energy
`storage device; and (d) a controller for selecting a loW-load
`drive mode in Which only the electric motor is operated to
`drive the vehicle is selected, When a running condition of the
`vehicle is in a predetermined loW-load range, and a high
`load drive mode in Which at least the engine is operated to
`drive the vehicle, When the running condition is in a prede
`termined high-load range in Which a load acting on the
`hybrid drive device is higher than that in the predetermined
`loW-load range, and Wherein the controller includes emer
`
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`3
`gency drive control means operated in the event of a failure
`of one of the engine and the electric motor as the ?rst and
`second drive poWer sources, for operating the other of the
`?rst and second drive poWer sources to drive the motor
`vehicle, and range changing means for changing one of the
`predetermined loW-load and high-load ranges Which corre
`sponds to the other of the ?rst and second drive poWer
`sources, When the other of the ?rst and second drive poWer
`sources is operated by the emergency drive control means.
`The hybrid drive system according to the ?rst aspect of
`the invention is of the parallel type adapted such that in the
`event of a failure of one of the engine and the electric motor,
`the emergency drive control means activates the other of the
`engine and the electric motor to drive the vehicle, and the
`range changing means changes the corresponding loW-load
`or high-load range in Which the normally functioning engine
`or electric motor is operated in the loW-load or high-load
`drive mode. Accordingly, the present hybrid drive system
`permits the vehicle to be run even in a condition in Which the
`normally functioning motor or electric motor could not be
`operated in the prior art hybrid drive system. The present
`hybrid drive system is therefore effective to increase the
`distance of running of the vehicle by the normally function
`ing drive poWer source, making it possible to run the vehicle
`to the desired destination even in the event of a failure of the
`engine or electric motor.
`According to a ?rst preferred form of the hybrid drive
`system described above, the range changing means com
`prises loWer limit changing means for enlarging the prede
`termined high-load range by reducing a loWer limit of the
`high-load range, When the engine is operated as the normal
`drive poWer source by the emergency drive control means.
`In this case, the vehicle can be driven by the engine under
`a loWer load than in the normal state of the drive system, and
`can be smoothly started and stopped. According to a second
`preferred form of the hybrid drive system, the range chang
`ing means comprises upper limit changing means for enlarg
`ing the predetermined loW-load range by increasing an upper
`limit of the loW-load range, When the electric motor is
`operated as the normal drive poWer source by the emergency
`drive control means. In this case, the vehicle can be driven
`by the electric motor under a higher load than in the normal
`state of the drive system, and can be run on an uphill road.
`According to a third preferred form of the present hybrid
`drive system, the range changing means may comprise
`upper limit changing means for narroWing the predeter
`mined loW-load range by reducing an upper limit of the
`loW-load range, When the electric motor is operated as the
`other drive poWer source by the emergency drive control
`means. In this case, the amount of the electric energy
`consumed by the electric motor is reduced, and the distance
`of running of the vehicle by the energy stored in the storage
`device can be accordingly increased.
`The running condition of the motor vehicle may be
`represented by an amount of poWer currently required by an
`operator of the vehicle to drive the vehicle. For instance, the
`amount of poWer currently required by the operator is
`represented by a currently required output of the drive
`system (Which may be represented by a currently detected
`amount of operation of an accelerator pedal by the operator)
`and a currently detected speed of the vehicle. In this
`instance, the loW-load and high-load ranges may be respec
`tive loW-load and high-load areas Which are de?ned by
`predetermined relationships betWeen the currently required
`output and the currently detected vehicle speed.
`When the vehicle running condition is in the high-load
`range, the vehicle is driven by at least the engine in the
`
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`high-load drive mode, Which may consist of an engine drive
`mode in Which only the engine is operated to drive the
`vehicle, or an engine'motor drive mode in Which both of the
`engine and the electric motor are operated to drive the
`vehicle. The electric energy storage device is charged as
`needed by an electric generator, Which may be the electric
`motor or a dynamo separate from the electric motor. The
`electric generator is driven by the engine or regenerative
`braking. When the vehicle running condition is in the
`loW-load range, the vehicle is driven by only the electric
`motor in the loW-load drive mode. In this loW-load drive
`mode, the electric motor is operated by only the electric
`energy Which has been stored in the electric energy storage
`device, or by not only the stored electric energy, but also the
`electric energy generated by the electric generator operated
`by the engine. The electric motor may be provided for each
`of tWo or more drive Wheels of the vehicle, or may be used
`commonly for the tWo or more drive Wheels. Where the
`engine and the electric motor are disposed in parallel con
`nection With a transmission Whose speed ratio is variable,
`the tWo or more drive Wheels are desirably driven by the
`single electric motor.
`As indicated above, the loW-load drive mode or the
`high-load drive mode is selected depending upon Whether
`the vehicle running condition falls in the predetermined
`loW-load range or in the high-load range in Which the load
`acting on the hybrid drive system is higher than in the
`loW-load range. The vehicle running condition may be
`represented by an amount of poWer currently required to
`drive the vehicle, Which may be represented by the drive
`torque and the running speed of the vehicle. The loW-load
`and high-load ranges of the vehicle running condition (e.g.,
`currently required poWer) are usually determined so as to
`reduce the amount of fuel consumption by the engine and the
`amount of electric energy consumption by the electric motor.
`The loW-load and high-load ranges may be de?ned by upper
`and loWer limits of the currently required output of the
`engine or electric motor. For instance, the range changing
`means may be the loWer limit changing means or the upper
`limit changing means as described above. Where the hybrid
`drive system includes a transmission Whose speed ratio is
`variable, the range changing means may be adapted to
`change the speed ratio of the transmission so that the
`loW-load or high-load range is shifted to increase the drive
`torque and reduce the vehicle running speed, or to reduce the
`drive torque and increase the vehicle running speed. The
`capacity or nominal or maXimum output of the electric
`motor is generally determined depending upon the amount
`of electric energy generated by regenerative braking by the
`electric motor, and the upper limit of the loW-load range in
`Which the electric motor is operated is considerably loWer
`than the maXimum output of the electric motor. This means
`that it is possible to operate the electric motor even When the
`upper limit of the loW-load range is increased to enlarge the
`loW-load range as described above With respect to the
`second preferred form of the invention.
`The emergency drive control means of the hybrid drive
`system according to the present ?rst aspect of this invention
`may be adapted to be operated only in the event of a failure
`of the electric motor, to drive the vehicle by the engine, or
`only in the vent of a failure of the engine, to drive the vehicle
`by the electric motor. Alternatively, the emergency drive
`control means may be adapted to operated in both of these
`cases.
`Regarding the preferred forms of the present ?rst aspect
`of the invention described above, the enlarged high-load
`range for operating the engine in the event of a failure of the
`
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`6,098,733
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`5
`electric motor, and the enlarged or narrowed loW-load range
`for operating the electric motor in the event of a failure of
`the engine may be stored in a memory as a data map.
`Alternatively, a predetermined value may be added to or
`subtracted from the upper or loWer limit of the normal
`high-load or loW-load range, to enlarge or narroW the range.
`Further alternatively, the upper or loWer limit of the normal
`range is multiplied by a predetermined value, to obtain the
`enlarged or narroWed range. The upper limit changing
`means according to the ?rst preferred form is adapted to
`reduce the loWer limit of the high-load range to thereby
`enlarge the range When the engine is operated to drive the
`vehicle in the event of a failure of the electric motor. In this
`case, the loWer limit of the high-load range is reduced to
`permit the vehicle to run at a speed loW enough for smooth
`starting and stopping of the vehicle. HoWever, the loWer
`limit of the high-load range may be Zeroed. The upper limit
`changing means according to the second preferred form is
`adapted to increase the upper limit of the loW-load range to
`thereby enlarge the range When the electric motor is operated
`to drive the vehicle in the event of a failure of the engine. In
`this case, the upper limit of the loW-load range to meet a
`predetermined requirement or requirements, for instance, to
`permit the vehicle to run at a speed higher than a predeter
`mined loWer limit Y (km/h) under a given condition (e.g.,
`during running on a road surface Whose gradient is X°), or
`permit the vehicle to be accelerated at a rate higher than a
`loWer limit Z (G) after the starting under a given condition.
`While the loWer limit or upper limit changing means
`described above is adapted to change the upper or loWer
`limit of the output of the engine or electric motor, the
`changing means may be adapted to change the upper or
`loWer limit of the drive torque or running speed of the
`vehicle.
`The object indicated above may also be achieved accord
`ing to a second aspect of this invention, Which provides a
`hybrid drive system for a motor vehicle, comprising: (a) an
`engine operated as a ?rst drive poWer source by combustion
`of a fuel; (b) an electric energy storage device Which is
`charged With an electric energy by operation of the engine;
`(c) an electric motor operated as a second drive poWer
`source by the electric energy stored in the electric energy
`storage device; (d) a transmission for transferring an output
`of one of the ?rst and second drive poWer sources to a drive
`Wheel of the vehicle, When one of the ?rst and second drive
`poWer sources is selected depending upon a running condi
`tion of the vehicle; and (e) a controller for controlling the
`transmission to change a speed ratio thereof depending upon
`the running running condition, and Wherein the controller
`comprises emergency drive control means operated in the
`event of a failure of one of the engine and the electric motor
`as the ?rst and second drive poWer sources, for operating the
`other of the ?rst and second drive poWer sources, and
`emergency shift control means for changing a predetermined
`relationship betWeen the running condition of the vehicle
`and the speed ratio of the transmission, When the other of the
`?rst and second drive poWer sources is operated by the
`emergency drive control means.
`The hybrid drive system according to the second aspect of
`the invention may be of either the parallel type or the series
`type, Which is adapted such that in the event of a failure of
`one of the engine and the electric motor, the emergency
`drive control means activates the other of the engine and the
`electric motor to drive the vehicle, and the emergency shift
`control means changes the predetermined relationship
`betWeen the vehicle running condition and the speed ratio of
`the transmission When the normal drive poWer source is
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`6
`operated by the emergency drive control means. The emer
`gency shift control means permits the transmission to be
`suitably shifted so as to reduce the electric energy consump
`tion by the electric motor in the event of a failure of the
`engine, or improve the drivability of the vehicle. The hybrid
`drive system according to this second aspect of this inven
`tion has substantially the same advantages as the hybrid
`drive system according to the ?rst aspect of the invention.
`The controller may be adapted to shift the transmission to
`one of a plurality of operating positions thereof on the basis
`of an amount of operation of an accelerator pedal and a
`running speed of the vehicle.
`The object indicated above may also be achieved accord
`ing to a third aspect of this invention, Which provides a
`hybrid drive system for a motor vehicle, comprising: (a) an
`engine operated by combustion of a fuel; (b) an electric
`energy storage device Which is charged With an electric
`energy by operation of the engine; (c) an electric motor (14)
`operated by the electric energy stored in the electric energy
`storage device; (d) a transmission Whose speed ratio is
`variable; and (e) a controller for operating at least the
`electric motor to drive the vehicle, and Wherein the control
`ler comprises energy-saving shift control means operated in
`the event of a failure of the engine, for shifting the trans
`mission to change the speed ratio so as to reduce an amount
`of consumption of the electric energy by the electric motor,
`depending upon at least one of a poWer transfer ef?ciency of
`the transmission and an energy conversion efficiency of the
`electric motor.
`The hybrid drive system according to the third aspect of
`the invention may be of either the parallel type or the series
`type, Wherein the energy-saving shift control means is
`operated in the event of a failure of the engine, for shifting
`the transmission to change the speed ratio so as to reduce the
`amount of consumption of the electric energy by the electric
`motor, Whereby the electric energy consumption by the
`electric motor is reduced, and the distance of running of the
`vehicle by the electric energy stored in the storage device is
`accordingly increased, permitting the vehicle to be run to the
`desired destination.
`The transmission provided in the hybrid drive system
`according to the second or third aspect of the invention
`described above may be either a transmission having a
`plurality of operating positions having different speed ratios,
`or a continuously variable transmission Whose speed ratio is
`continuously variable. In the hybrid drive system according
`to the second aspect of the invention, the predetermined
`relationship betWeen the vehicle running condition and the
`speed ratio of the transmission is changed by the emergency
`shift control means. This predetermined relationship, When
`used for shifting the transmission having tWo or more
`operating positions, may consist of shift pattern maps
`de?ned by the operation amount of the accelerator pedal and
`the running speed of the vehicle, for eXample. When the
`predetermined relationship is used for the continuously
`variable transmission, the relationship may be represented
`by predetermined equations formulated to determine the
`speed ratio on the basis of the accelerator pedal operation
`amount and the vehicle running speed. In the event of a
`failure of one of the engine and the electric motor, the
`emergency shift control means changes the shift pattern
`maps or equations so that the transmission is shifted to a
`position suitable for the output range of the normal drive
`poWer source. In the parallel type hybrid drive system, the
`vehicle may be driven in the loW-load or high-load drive
`mode depending upon the running condition of the vehicle,
`for example, the operation amount of the accelerator pedal,
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`6,098,733
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`7
`as described above With respect to the ?rst aspect of the
`invention. For instance, the vehicle is driven by the electric
`motor in the loW-load drive mode When the accelerator pedal
`operation amount is smaller than a predetermined upper
`limit, and is driven by the engine in the high-load drive mode
`When the accelerator pedal operation amount is larger than
`a predetermined loWer limit. In the event of a failure of the
`engine, the vehicle is driven by the electric motor such that
`the maximum output of the electric motor corresponds to the
`predetermined upper limit of the loW-load range, Which may
`be increased to enlarge the loW-load range in the event of the
`engine failure as described above With respect to the second
`preferred form of the ?rst aspect of the invention. In other
`Words, the speed ratio of the transmission is selected Within
`the output range of the electric motor Whose upper limit may
`changed by the upper limit changing means as described
`above. In the event of a failure of the electric motor, the
`vehicle is driven by the engine With the transmission being
`suitably shifted so as to meet the output range of the engine,
`Whose loWer limit may be reduced to enlarge the high-load
`range in the event of the motor failure as described above
`With respect to the ?rst preferred form of the ?rst aspect of
`the invention. The data map or equation for obtaining the
`currently required poWer for driving the vehicle may be
`formulated such that the maximum output of the electric
`motor corresponds to the 100% operation of the accelerator
`pedal in the event of a failure of the engine, or the minimum
`output of the engine corresponds to the 0% operation of the
`accelerator pedal in the event of a failure of the electric
`motor.
`The emergency shift control means may be adapted to
`change the predetermined relationship so as to satisfy a
`predetermined requirement or requirements. For example,
`the shift patterns for shifting the transmission may be
`changed so that the transmission is placed in a relatively
`loW-gear position in the event of a failure of the engine, for
`the purpose of increasing the drivability of the vehicle by the
`electric motor during running on an uphill road. Further, the
`shif