[19]
`United States Patent
`5,841,201
`[11] Patent Number:
`[45] Date of Patent: Nov. 24, 1998
`Tabata et al.
`
`
`
`U8005841201A
`
`[54] HYBRID VEHICLE DRIVE SYSTEM HAVING
`A DRIVE MODE USING BOTH ENGINE AND
`ELECTRIC MOTOR
`
`[75]
`
`Inventors: Atsushi Tabata, Okazaki; Yutaka
`Taga, Aichi-ken; Ryuji Ibaraki,
`Toyota; Tsuyoshi Mikami, Toyota;
`Hiroshi Hata, Toyota, all of Japan
`
`[73] Assignee: Toyota Jidosha Kabushiki Kaisha,
`Toyota, Japan
`
`[21] Appl. No.: 805,164
`
`[22]
`
`Filed:
`
`Feb. 24, 1997
`
`[30]
`
`Foreign Application Priority Data
`
`Feb. 29, 1996
`May 27, 1996
`
`[JP]
`[JP]
`
`Japan .................................... 8—042943
`Japan .................................... 8—132105
`
`Int. Cl.6 ........................................................ H02P 9/04
`[51]
`[52] US. Cl.
`......................... 290/40 C; 180/654; 290/16;
`290/27; 318/143; 322/16
`[58] Field of Search .................................. 290/11, 16, 27,
`290/40 C; 180/651, 65.4; 318/139, 143,
`322/14, 15, 16
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`1/1993 Kawai et al.
`........................... 180/243
`5,176,213
`
`9/1994 Severinsky
`180/65.2
`5,343,970
`8/1996 Kotani ................................... 290/40 C
`5,545,928
`8/1996 Nii
`.......................................... 318/153
`5,550,445
`5,588,498 12/1996 Kitada .................................... 180/654
`
`5,621,304
`5,650,931
`5,656,921
`5,698,955
`5,722,911
`5,751,137
`
`4/1997 Kiuchietal.
`............................. 322/18
`7/1997 Nii
`..............
`.. 364/424.026
`
`........... 322/40
`8/1997 Farrall
`.
`
`
`12/1997 N11 ..............
`.. 318/139
`.............................. 477/3
`3/1998 Ibaraki et al.
`5/1998 Kiuchi et al.
`............................. 322/14
`
`FOREIGN PATENT DOCUMENTS
`
`A—3 — 12 1 928
`A—6—80048
`
`5/1991
`3/1994
`
`Japan.
`Japan.
`
`Primary Examiner—Steven L. Stephan
`Assistant Examiner—Nicholas Ponomarenko
`
`Attorney, Agent, or Firm—Cliff & Berridge, PLC
`
`[57]
`
`ABSTRACT
`
`A hybrid drive system for a motor vehicle, having a power
`drive state in which there is available a power drive mode in
`which an engine and an electric motor are both operated as
`a drive power source for driving the vehicle, and wherein a
`manually operated power drive selector is provided for
`selecting the power drive mode, and a power drive restrict-
`ing device is provided to inhibit the vehicle from being
`driven in the power drive state and therefore in the power
`drive mode if the power drive selector is not manually
`operated. The hybrid drive system may have an engine assist
`drive mode in which the electric motor is operated as an
`auxiliary drive power source,
`together with the engine
`operated as a primary drive power source, according to a
`selected one of different drivability modes of the vehicle
`selected by a manually operated drivability performance
`selector.
`
`12 Claims, 21 Drawing Sheets
`
`22
`
`
`
`
`ELECTRIC
`ENERGY
`STORAGE
`DEVICE
`
`
`
`
`MOTOR/
`
`ENGINE
`
`GENERATOR
`
`CONTROLLER
`CONTROLLER
`
`
`
` INTERNAL
`ELECTRIC
`
`MOTOR
`
`COMBUSTION
`
`ENGINE
`
`
`
`
`CONTROL
`DEVICE
`
`
`
`TRANSMISSION
`
`OUTPUT DEVICE
`
`SOC
`
`
`
`TE, TM, 6A
`NE, NM, No
`
`
`
`Page 1 of 43
`
`FORD 1105
`
`Page 1 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 1 0f 21
`
`5,841,201
`
`
`
`22
`
`
`
`1o
`
`
`ELECTRIC
`ENERGY
`STORAGE
`
`DEVICE
`
`24
`20
`
`
`
`MOTOR/
`
`
`GENERATOR
`CONTROLLER
`
`
`ENGINE
`CONTROLLER
`
`
`
`
`
`
`
`
`
`
`
`ELECTRIC
`MOTOR
`
`INTERNAL
`COMBUSTION
`ENGINE
`
`
`
`TRANSMISSION
`
`OUTPUT DEVICE
`
`CONTROL
`DEVICE
`
`TE, TM, 6A
`NE,NM,NO
`
`FIG 1
`
`Page 2 of 43
`
`FORD 1105
`
`Page 2 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 2 0f 21
`
`5,841,201
`
`12
`
`_I
`
`<2)
`<;L1J
`§¥DE§3
`EggLL!
`30(J
`
`i T I.
`
`ELECTRICMOTOR 104/
`
`FIG.2
`
`112\106120
`
`118a
`
`Page 3 of 43
`
`FORD 1105
`
`Page 3 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 3 of 21
`
`5,841,201
`
`SOC
`
`
` POWER DRIVE
`
`
`POWER DRIVE
`RESTRICTING
`MODE INHIBITIN
`G
`
`
`MEANS
`MEANS
`
`
`
`
`
`
`
`
`POWER-
`NORMAL
`SWITCHING
`MEANS
`
`
`
`
`
`
`
`
`ENGINE
`DRIVE
` POWER
`
`
`
`NORMAL
`& CHARGING
`
`DRIVE
`DRIVE
`CONTROL
`08A[\%%%L
`
`
`CONTROL
`
`
`
`
`MEANS
`
`MEANS MEANS
`
`
`
`38
`
`FIG. 3
`
`Page 4 of 43
`
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`
`Page 4 of 43
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`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 4 0f 21
`
`5,841,201
`
`
`
`MEMORY
`MEANS
`
`
`
` FIRST
`
`CALCULATING
`
`MEANS
`
`COMPARING
`
`
`MEANS
`
`SECOND
`
`CALCULATING
`
`MEANS
`
`5O
`
`
`
`48
`
`FIG. 4
`
`Page 5 of 43
`
`FORD 1105
`
`Page 5 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 5 0f 21
`
`5,841,201
`
`81
`
`
`
`
`READING INPUT SIGNALS
`
`
`SP, TE, TM, 6A, NE, NM, NO, soc, ETC.
`
`FIG. 5
`
`
`
`82
`
` POWER DRIVE
`SELE%E%IGNAL
`
`
`TURNED ON
`
` POWER DRIVE
`
`MODE OFF
`INDICATOR 30
`
` ENGINE DRIVE
`& CHARGING
`
`MODE
`
`SUB-ROUTINE
`MOTOR DRIVE
`MODE
`
`SUB-ROUTINE
`
` ENGINE DRIVE |
`
`
`RETURN
`
`
` ENGINE°MOTOR
`
`DRIVE MODE
`
`SUB-ROUTINE
`
`
`
`
`MODE
`SUB-ROUTINE
`
`
`
`
`Page 6 of 43
`
`FORD 1105
`
`Page 6 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 6 0f 21
`
`5,841,201
`
`FIG. 6
`
`ENGINE DRIVE & CHARGING MODE SUB-ROUTINE
`
`
`
`
`
`PICE = PL IN IST CYCLE
`PICE = PICE + APICE
`IN 2ND AND SUBSEQUENT
`CYCLES
`
`R1
`
`CALCULATING meg
`
`R2
`
`CALCULATING AND
`STORING m
`
`R3
`
`
`
`
`R4
`
`YES
`
`SELECTING PICE WHOSE
`77T IS MAXIMUM
`
`
`
`
`
`
`
`
`OPERATING ENGINE WITH
`PICE AND SETTING PGEN
`
`
`R5
`
`R5
`
`
`
`END
`
`Page 7 of 43
`
`FORD 1105
`
`Page 7 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 7 0f 21
`
`5,841,201
`
`
`
`
`MICEmaX
`
`ENGINE SPEED NE
`
`
`
`MOTOR SPEED NM
`
`.2
`LLJ
`
`D 0 g
`
`|._.
`LLJ
`
`Z (
`
`‘52
`Lu
`
`5L
`
`u3 OC
`
`]:
`
`O'
`—D
`
`: O'
`
`—OE
`
`Page 8 of 43
`
`FORD 1105
`
`Page 8 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 8 0f 21
`
`5,841,201
`
`FIG. 9
`
`ENGINE
`
`TORQUETE
`
`ENGINE SPEED NE
`
`Page 9 of 43
`
`FORD 1105
`
`Page 9 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 9 0f 21
`
`5,841,201
`
`VNN
`
`LO
`(‘3
`N
`
`C0
`N F
`I
`
`_
`
`Ll.
`
`‘_
`
`Nm\N
`
`m‘—
`N
`
`(O1—
`N
`
`0
`LL
`
`(0
`
`NN
`
`Page 10 of 43
`
`FORD 1105
`
`Page 10 of 43
`
`FORD 1105
`
`

`

`taPS”U
`
`m.
`
`nMwm00mM,
`
`102,148,5
`
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`
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`
`N02:2:
`
`29229
`
`
`
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`
`HYBRID DRIVE CONTROLLER
`
`AUTOMATIC
`TRANSMISSION
`CONTROLLER
`
`.E-I
`
`
`
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`
`mom
`
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`
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`
`LEN
`
`wnm
`
`Sum
`
`Nwm
`
`mvm
`
`mum
`
`Page 11 of 43
`
`FORD 1105
`
`Page 11 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 11 0f 21
`
`5,841,201
`
`
`calm$18302022szKim
`
`NFOvmNFNo0%Illnflflafilflla;
`
`>§mzommémm$1830
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`
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`
`mm¢m>mm
`
`
`
`ml
`
`Page 12 of 43
`
`FORD 1105
`
`Page 12 of 43
`
`FORD 1105
`
`
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 12 0f 21
`
`5,841,201
`
`‘1‘“
`IVAVIAVA‘
`
`
`
`
`Page 13 of 43
`
`FORD 1105
`
`Page 13 of 43
`
`FORD 1105
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 13 0f 21
`
`5,841,201
`
`250
`
`
`
`MOTOR/
`GENERATOR
`
`258
`
`ELECTRIC
`ENERGY
`STORAGE
`DEVICE
`
`MOTOR/
`GENERATOR
`
`CONTROLLER
`
`FIRST CLUTCH
`
`CE2
`
`
`
`
`
`
`
` HYBRIDDRIVECONTROLLER ISECOND CLUTCH
`
`
`
`
`FIG. 14
`
`Page 14 of 43
`
`FORD 1105
`
`Page 14 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 14 0f 21
`
`5,841,201
`
`— FIG. 15
`REQUIRED
`S2 SELECTING
`
`ENGINE
`STARTING
`
`9
`
`YES
`
`MODE 9
`
`3
`
`BRAMNG
`REQUIRED?
`
`SS4@ NO
`
`Y 85
`SELECTING
`SELECTING S6
`
`S7 VEHICLE START YES
`MODE8
`MODE 6
`BY ENGINE
`<REQUIRED7:
`
`N0
`
`ACCELERATOR NO
`‘DEPRESSED?
`
`YES
`
`310 SELECTING
`MODE 7
`
`SH
`
`@NO
`
`515
`
`89 SELECTING
`
`MODE 5
`
`YES
`
`<P1<Pd<P2?
`
`818
`
`NO
`
`816
`
`S13
`
`SELECTING
`
`817
`
`@NO YES
`
`
`MODE 1
`
` SELECTING S19
`
`SELECTING
`MODE 2
`
`SELECTING
`MODE 3
`
`MODE4
`
`END
`
`Page 15 of 43
`
`FORD 1105
`
`Page 15 of 43
`
`FORD 1105
`
`

`

`P
`
`N
`
`10
`
`
`
`
`mm:.G_n_
`
`
`m.mmafiozmggm8:ammosmomeéoaEfim8:
`mamaEEOEQZGEEEEE.mOzam<$+m2m$zazmgaaal
`
`
`s Eésmz2E8:EEEEImozgémm>E$2m8¢gaaalmmzazimEEmdeEgaaal
`
`
`
`Page 16 of 43
`
`FORD 1105
`
`Page 16 of 43
`
`FORD 1105
`
`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 16 0f 21
`
`5,841,201
`
`VEHICLE
`REAR
`
`LEFT
`
`RIGHT
`
`VEHICLE
`FRONT
`
`FIG. 1 7
`
`246:
`
`243
`
`Page 17 of 43
`
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`
`Page 17 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 17 0f 21
`
`5,841,201
`
`P
`
`VEHICLE
`FRONT
`
`R\
`
`N
`
`3 — D —— DM
`
`258
`
`
`
`
`
`
`ELECTRIC
`ENERGY
`STORAGE
`DEVICE
`
`
`
`
`
`
`
`
`AUTOMATIC
`
`TRANSMISSION
`
`
`CONTROLLER
`
`
`
`Page 18 of 43
`
`FORD 1105
`
`Page 18 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 18 0f 21
`
`5,841,201
`
`ENGINE ASSIST CONTROL SUB-ROUTINE
`
`SAT
`
`SEPARATE?
`
`YES
`
`8A5
`
`NO
`
`8A2
`
`Y
`
`ES
`
`FIG- 20
`
`SAG
`YES
`
`6
`
`> a
`ACT 7:
`-
`
`a
`
`
`
`8A7 NO
`ENGINE ASSIST
`CONTROL
`OF MOTOR
`
`DEFERRED
`
`-
`
`SA“
`
`.
`
`YES
`
`N0
`3A3
`POWER DRIVE
`a NORMAL DRIVE '2
`
`YES
`
`8A1 0
`
`YES
`
`NO
`
`8A4
`
`6"”
`
`._
`
`9“"
`
`NO
`
`SA15
`
`EITHER POWER DRIVE
`SHIFT PATTERN SELECTED,
`OR SHIFT LEVER PLACED
`IN MANUAL DRIVE
`POSITION "DM" ?
`
`YES
`
`0A02 Z 9a
`
`?
`
`NO
`
`T0 8A9
`
`8A9
`
`
`
`
`
`ENGINE ASSIST
`CONTROL
`OF MOTOR
`INITIATED
`
`
`
`
`
`
`TERMINATION OF
`ENGINE ASSIST
`CONTROL
`
`
`
`
`
`DEFERRED
`
`YES
`
`SA14
`
`
`ENGINE ASSIST
`CONTROL
`OF MOTOR
`TERMINATED
`
`
`
`
`
`
`
`
`Page 19 of 43
`
`FORD 1105
`
`Page 19 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 19 0f 21
`
`5,841,201
`
`FIG. 21
`
`DRIVE
`
`TORQUE
`
`ACCELERATOR PEDAL
`OPERATION AMOUNT 0A0
`
`FIG. 22
`
`AUTOMATIC
`TRANSMISSION
`
`CONTROLLER
`
`Page 20 of 43
`
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`
`Page 20 of 43
`
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`
`

`

`US. Patent
`
`Nov. 24, 1998
`
`Sheet 20 0f 21
`
`5,841,201
`
`
`
`QLU
`
`Page 21 of 43
`
`FORD 1105
`
`Page 21 of 43
`
`FORD 1105
`
`

`

`nwaPS”U
`
`S
`
`2
`
`2
`
`102,148.,5
`
`t.WNSE
`
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`
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`
`$553zo_mm_2mz<Efifiw
`Inna-IIa-IE
`
`
`
`
`:Ezomega$1830
`
`Page 22 of 43
`
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`
`Page 22 of 43
`
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`

`

`5,841,201
`
`1
`HYBRID VEHICLE DRIVE SYSTEM HAVING
`A DRIVE MODE USING BOTH ENGINE AND
`ELECTRIC MOTOR
`
`This application is based on Japanese Patent Applications
`No. 8-42943 filed Feb. 29, 1996 and No. 8-132105 filed May
`27, 1996, the contents of which are incorporated hereinto by
`reference.
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`US. patent application Ser. No. 08/685,102 filed Jul. 22,
`1996
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates in general to a hybrid drive
`system for driving a motor vehicle, and more particularly to
`such a hybrid vehicle drive system having a power drive
`state in which the vehicle is driven by both an engine and an
`electric motor, or an engine assist drive mode in which the
`electric motor cooperates with the engine to serve as a drive
`power source.
`2. Discussion of the Related Art
`
`For driving a motor vehicle, there is known a hybrid drive
`system which includes, as drive power sources, an engine
`operated by combustion of a fuel, and an electric motor
`operated by an electric energy stored in an electric energy
`storage device. Such a hybrid drive system has an engine
`drive mode in which the engine is operated to drive the
`vehicle, and a motor drive mode in which the electric motor
`is operated to drive the vehicle. The engine drive mode and
`the motor drive mode are selectively established depending
`upon the running condition of the vehicle, so as to reduce the
`amount of consumption of the fuel and the amount of
`exhaust gas emission from the engine. For further reducing
`the fuel consumption and the exhaust gas emission, there is
`proposed a hybrid drive system which has a so-called
`“power drive mode” in which the engine and the electric
`motor are both operated to drive the vehicle so as to restrict
`the maximum output of the engine. This power drive mode
`is established when a load acting on the vehicle is relatively
`high, for example, during running of the vehicle on an uphill
`road. An example of this type of hybrid drive system is
`disclosed in JP-A-6-80048, wherein the power drive state is
`established when the accelerator pedal is operated by a
`relatively large amount by the vehicle operator, namely,
`when the vehicle load is relatively high.
`However, the conventional hybrid drive system described
`above may suffer from an insufficient drive force in the
`power drive mode, due to a reduced amount of the electric
`energy stored in the electric energy storage device, which
`causes a reduced output of the electric motor even when the
`amount of operation of the accelerator pedal by the vehicle
`operator is relatively large. This tendency gives a discomfort
`to the vehicle operator who expects a sufficient drive force
`upon depression of the accelerator pedal by a relatively large
`amount.
`In other words,
`the conventional hybrid drive
`system tends to suffer from a variation in the drive force in
`the power drive mode, due to a varying amount of the stored
`electric energy, even when the running condition of the
`vehicle is substantially constant.
`There is also known a hybrid drive system wherein the
`electric motor is operated as needed, to assist the engine
`during running of the vehicle by the engine. An example of
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`this type of hybrid drive system is disclosed in JP-A-3-
`121928. In this system, the engine is normally operated as
`the drive power source for driving the vehicle, and the
`electric motor is also operated to assist the engine only when
`the engine load (as represented by the amount of operation
`of the accelerator pedal) exceeds a given upper limit. This
`system assures desired drivability of the vehicle while
`reducing the amount of fuel consumption and the amount of
`exhaust gas emission.
`In the above hybrid drive system having the engine assist
`function, however, the electric motor is necessarily operated
`as long as the engine load is higher than the predetermined
`upper limit. This arrangement tends to suffer from relatively
`high frequency of operation of the electric motor and
`relatively large amount of consumption of the electric
`energy, requiring the electric energy storage device to have
`a comparatively large capacity and to be charged relatively
`frequently by the engine.
`
`SUMMARY OF THE INVENTION
`
`It is therefore a first object of the present invention to
`provide a hybrid drive system for a motor vehicle, which
`does not give a discomfort to the vehicle operator even when
`the operation of the electric motor is limited due to reduced
`amount of the electric energy stored in the electric energy
`storage device.
`It is a second object of the invention to provide a hybrid
`drive system which is adapted to reduce the frequency of
`operation of the electric motor and minimize the amount of
`consumption of the electric energy by the electric motor,
`while permitting the motor vehicle to be driven with driv-
`ability performance or drive force as desired by the vehicle
`operator.
`The first object may be achieved according to the first
`aspect of the present 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 for storing an electric energy; (c) an electric
`motor operated with the electric energy stored in the electric
`energy storage device; (d) normal drive control means for
`controlling the engine and the electric motor so as to
`establish a normal drive state in which one of the engine and
`the electric motor is operated as a drive power source to
`drive the motor vehicle; (e) power drive control means for
`controlling the engine and the electric motor so as to
`establish a power drive state in which there is available a
`power drive mode in which both of the engine and the
`electric motor are operated as the drive power source to
`drive the motor vehicle; (f) power drive selecting means
`manually operated by an operator of the motor vehicle when
`the operator desires to drive the motor vehicle in the power
`drive mode; and (g) power drive restricting means for
`permitting the power drive control means to establish the
`power drive state if the power drive selecting means is
`operated, and inhibiting the power drive control means from
`establishing the power drive state,
`to thereby inhibit the
`motor vehicle from being driven in said power drive mode,
`if the power drive selecting means is not manually operated.
`In the hybrid drive system for a motor vehicle, the power
`drive mode is available in the power drive state. However,
`the power drive state is not established when the power drive
`selecting means is not manually operated. Therefore, when
`the power drive selecting means is not operated, the vehicle
`is not driven in the power drive mode in which the engine
`and the electric motor are both operated as the drive power
`source for driving the vehicle. In other words, the vehicle is
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`driven by only the engine or the electric motor when the
`power drive selecting means is not manually operated. If the
`electric motor cannot be operated to provide a sufficient
`drive force due to reduction of the electric energy amount
`stored in the electric energy storage device while the power
`drive selecting means is not operated, the vehicle is driven
`by the engine used as the drive power source. In this case
`where the manually operable power drive selecting means is
`not operated, the vehicle operator recognizes that the power
`drive mode is not available, and does not feel that the vehicle
`drive force is unexpectedly small. When the power drive
`selecting means is manually operated, the vehicle is driven
`in the power drive mode with the engine and the electric
`motor if the appropriate condition is satisfied, for example,
`the stored electric energy is sufficient to operate the electric
`motor. Thus, only when excessive reduction of the stored
`electric energy occurs while the power drive selecting means
`is operated, the vehicle driver may feel that the vehicle drive
`force is smaller than expected upon depression of the
`accelerator pedal with the power drive selecting means
`being operated to select the power drive mode.
`The principle of the first aspect of the present invention is
`applicable to various types of hybrid drive system equipped
`with the engine and the electric motor as the drive power
`source for driving the motor vehicle. One or both of the
`engine and the electric motor may be used as the drive power
`source, by selective connection and disconnection of appro-
`priate power transmission paths by selective engagement
`and disengagement of clutches, or by a synthesizer and
`distributor mechanism such as a planetary gear mechanism
`for synthesizing or distributing the outputs of the engine and
`electric motor, or by suitable means for using the electric
`motor as an auxiliary drive power source to assist the engine
`as a primary power source. In any case, the hybrid drive
`system has the normal drive state in which the vehicle is
`driven by only one of the engine or the electric motor, and
`the power drive state in which the vehicle can be driven in
`the power drive mode using both of the engine and the
`electric motor. The electric motor may be provided for each
`of the drive wheels of the motor vehicle.
`
`In the normal drive state established by the normal drive
`control means, the vehicle may be driven in an engine drive
`mode using the engine as the drive power source, or in a
`motor drive mode using the electric motor as the drive power
`source. Preferably, the engine drive mode and the motor
`drive mode are selectively established depending upon the
`running condition of the vehicle, so as to reduce the amount
`of exhaust gas emission. However, the engine is always used
`as a primary power source, with the electric motor being
`used as an auxiliary power source which is operated when
`needed. In the power drive state established by the power
`drive control means when the power drive selecting means
`is operated, at least the power drive mode is available for
`driving the vehicle with both of the engine and the electric
`motor. This power drive mode may be established irrespec-
`tive of the running condition of the vehicle, as long as the
`power drive selecting means is operated. For reducing the
`amount of exhaust gas emission, however, it is desirable that
`the power drive mode be established only when the prede-
`termined condition is satisfied while the power drive select-
`ing means is operated.
`The power drive selecting means is operated by the
`vehicle operator according to the desire of the vehicle
`operator regarding the drive force produced by the hybrid
`drive system. The power drive selecting means may com-
`prise a selector switch provided on an instrument panel of
`the vehicle, or on a pushbutton provided on a grip of a shift
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`lever for shifting a transmission provided on the vehicle. The
`power drive selecting means may be provided as one of the
`operating positions of a transmission shift lever.
`According to one preferred form of this invention, the
`power drive restricting means is adapted to command the
`normal drive control means to establish the normal drive
`
`state if the power drive selecting means is not manually
`operated.
`According to another preferred form of the invention, the
`hybrid drive system further comprises:
`(h) power drive
`mode inhibiting means for inhibiting the power drive control
`means from establishing the power drive mode and for
`operating only the engine as the drive power source for
`driving the motor vehicle, if an amount of the electric energy
`stored in the electric energy storage device is smaller than a
`predetermined lower limit, even when the power drive
`selecting means is manually operated; and (i) indicating
`means for informing the operator of the motor vehicle that
`the motor vehicle is inhibited from being driven in the power
`drive mode, when the power drive control means is inhibited
`by the power drive mode inhibiting means from establishing
`the power drive mode.
`In the above preferred form of the invention, the running
`of the vehicle in the power drive mode is inhibited when the
`stored electric energy amount is smaller than the lower limit,
`even when the power drive selecting means is operated. This
`arrangement is effective to prevent damaging of the electric
`energy storage device, and excessive reduction of the charg-
`ing and discharging efficiencies of the storage device.
`Further, the indicating means provides an indication that the
`power drive mode is not available when the stored electric
`energy amount is smaller than the lower limit. This arrange-
`ment permits the vehicle operator to recognize that the
`vehicle is driven by only the engine even though the vehicle
`operator has manipulated the power drive selecting means to
`select the power drive mode. This arrangement does not give
`a discomfort to the vehicle operator even if the vehicle drive
`force as felt by the vehicle drive is smaller than expected.
`The lower limit of the stored electric energy amount
`below which the running of the vehicle in the power drive
`mode is inhibited by the power drive mode inhibiting means
`is determined to prevent excessive deterioration of the
`charging and discharging efficiencies of the electric energy
`storage device due to excessive reduction of the stored
`electric energy amount, which may result in damaging the
`storage device. The power drive mode inhibiting means may
`be operable only when the power drive state is established
`by the power drive control means. However, the power drive
`mode inhibiting means may be operable in both of the
`normal drive state and the power drive state. In this case, the
`electric motor is inhibited from operating or stopped, and the
`vehicle is driven by only the engine, if the stored electric
`energy amount falls below the lower limit, irrespective of
`whether the hybrid drive system is in the normal drive state
`or in the power drive state. The indicating means may be an
`indicator disposed on the vehicle instrument panel, for
`providing a visual or audible indication. The indicating
`means may be activated as long as the running of the vehicle
`in the power drive mode is inhibited. However, the indicat-
`ing means may be activated only when the power mode
`selecting means is manually operated and the running of the
`vehicle in the power drive mode is inhibited by the power
`drive mode inhibiting means.
`The second object
`indicated above may be achieved
`according to a second aspect of this invention, which pro-
`vides a hybrid drive system for a motor vehicle, comprising:
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`(a) an engine operated by combustion of a fuel; (b) an
`electric motor operated by an electric energy; (c) engine
`assist control means operable in an engine assist mode, for
`controlling the electric motor such that the electric motor is
`operated as needed, as an auxiliary drive power source,
`together with the engine, to assist the engine to drive the
`motor vehicle, during running of the motor vehicle with the
`engine operated as a primary drive power source; and (d)
`drivability performance selecting means manually operated
`by an operator of the motor vehicle, for selecting one of a
`plurality of drivability modes of the motor vehicle, and
`wherein the engine assist control means includes assist
`torque changing means for changing an amount of an assist
`torque which is produced by the electric motor and which is
`added to a torque of the engine in the engine assist mode.
`The assist torque changing means changing the amount of
`the assist torque according to the one of the drivability
`modes of the motor vehicle selected by the drivability
`performance selecting means.
`In the hybrid drive system according to the second aspect
`of this invention constructed as described above, the amount
`of the assist torque produced by the electric motor and added
`to the torque of the engine in the engine assist drive mode
`is changed by the assist torque changing means of the engine
`assist control means, according to or depending upon the
`selected one of the drivability modes of the motor vehicle
`which is selected by the vehicle operator by the drivability
`performance selecting means. Thus, the present hybrid drive
`system assures reduced frequency of operation of the elec-
`tric motor and reduced amount of consumption of the
`electric energy by the electric motor, while permitting the
`vehicle to be driven with drivability performance or drive
`force as desired by the vehicle operator.
`The principle of the above second aspect of the present
`invention is applicable to various types of hybrid drive
`system which are equipped with the engine and the electric
`motor as the drive power source for driving the motor
`vehicle and which are adapted such that one or both of the
`engine and the electric motor may be used as the drive power
`source, by selective connection and disconnection of appro-
`priate power transmission paths by selective engagement
`and disengagement of clutches, or by a synthesizer and
`distributor mechanism such as a planetary gear mechanism
`for synthesizing or distributing the outputs of the engine and
`electric motor. In any case, the hybrid drive system has the
`engine assist drive mode in which the electric motor is
`operated as an auxiliary drive power source, together with
`the engine, to assist the engine to drive the motor vehicle,
`during running of the motor vehicle with the engine operated
`as a primary drive power source. The electric motor may be
`provided for each of the drive wheels of the motor vehicle.
`The hybrid drive system according to the second aspect of
`the invention should have the engine assist drive mode in
`which the electric motor is used as the auxiliary drive power
`source to assist the engine which serves as the primary drive
`power source. However, the present hybrid drive system
`may have other drive modes such as an engine drive mode
`in which only the engine is operated to drive the vehicle. In
`this case, one of the drive modes is selected depending upon
`the running condition of the vehicle, such as the operation
`amount of the accelerator pedal,
`running speed of the
`vehicle, and amount of electric energy stored in an electric
`energy storage device. The engine may preferably use a
`throttle valve whose opening angle is electrically controlled
`according to the operation amount of the accelerator pedal.
`Where the engine is always used as the drive power source,
`however,
`the engine may use a throttle valve which is
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`mechanically connected to the accelerator pedal so that the
`opening angle of the throttle valve is changed as the accel-
`erator pedal is operated. In either case, the opening angle of
`the throttle valve, which represents the engine output cur-
`rently required by the vehicle operator, generally has a given
`relationship with the operation amount of the accelerator
`pedal. Therefore, the currently required output of the engine
`may be represented by the opening angle of the throttle
`valve, or an intake air quantity of the engine.
`The total vehicle drive force in the engine assist drive
`mode is a sum of the assist torque produced by the electric
`motor and the torque produced by the engine. The engine
`assist control means is adapted to control the electric motor
`in the engine assist drive mode such that the total vehicle
`drive force continuously smoothly increases with an
`increase in the currently required output of the engine as
`represented by the operation amount of the accelerator
`pedal, over substantially the entire range of the operation
`amount of the accelerator pedal, for example. The pattern of
`change of the assist torque produced by the engine with
`respect to the currently required output of the engine is
`determined with the output characteristics of the engine
`taken into account. Usually, the engine output substantially
`linearly increases with the engine load when the engine load
`is relatively low. When the engine load is relatively high, the
`rate of increase of the engine output is reduced, and the
`engine output does not substantially linearly increase with
`the engine load. In the light of this fact, the electric motor is
`not operated as the auxiliary drive power source to assist the
`engine while the engine load is relatively low, that is, while
`the currently required output of the engine is relatively
`small. When the engine load is relatively high, the engine
`assist control means operates the electric motor to assist the
`engine in the engine assist drive mode such that the total
`vehicle drive torque continuously smoothly increases with
`an increase in the engine load, namely, with an increase in
`the currently required output of the engine. In particular, the
`assist torque changing means is adapted to increase the assist
`torque so that the total vehicle drive force smoothly increase
`with the engine load.
`The drivability performance selecting means may be a
`selector switch exclusively provided for selecting a desired
`one of the two or more drivability modes of the vehicle.
`However, the drivability performance selecting means may
`be a shift pattern selector switch provided for selecting one
`of a plurality of shift patterns of an automatic transmission
`provided in the hybrid drive system. In this case, the shift
`patterns of the transmission include a power drive shift
`pattern which is selected when the vehicle driver desires to
`drive the vehicle with relatively high drivability, and a
`normal drive shift pattern which is selected when the vehicle
`operator desires to drive the vehicle with relatively high fuel
`economy, for example. Alternatively, a shift lever for shift-
`ing a transmission may serve as the drivability performance
`selecting means. That is, the shift lever has a manual-mode
`position (so-called “sporty mode”, for example) in which the
`transmission may be manually shifted to a desired position.
`In this case, the vehicle can be driven with a higher degree
`of drivability when the shift lever is placed in the manual-
`mode position, than when the shift lever is normally placed
`in the drive position in which the transmission is automati-
`cally shifted depending upon the running condition of the
`vehicle. Thus, the shift lever can serve as the drivability
`performance selecting means for selecting one of a plurality
`of drivability modes of the vehicle. In this respect, it is noted
`that the present hybrid drive system preferably includes an
`automatic transmission which has different speed ratios and
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`which is disposed between the engine and drive wheels of
`the vehicle. However,
`the automatic transmission is not
`essential.
`
`The assist torque changing means of the engine assist
`control means may be adapted to change the assist torque
`such that the amount of the assist torque is larger when the
`power drive shift pattern is selected for the automatic
`transmission or when the shift lever is placed in the manual-
`mode position is selected, than when the normal drive shift
`pattern is selected or when the shift lever is placed in the
`drive position. However,
`the engine assist control means
`may be adapted to operate the electric motor only when the
`power drive shift pattern or the manual-mode position is
`selected. In this case, the electric motor is not operated when
`the power drive shift pattern or the manual-mode position is
`not selected. That is, the assist torque may be zero in the
`engine assist drive mode.
`According to a first pre