United States Patent
`
`119]
`
`[11] Patent Number:
`
`5,789,882
`
`[45] Date of Patent:
`Aug. 4, 1998
`Ibaraki et al.
`
`
`US005789882A
`
`[54] VEHICLE CONTROL APPARATUS ADAPTED
`TO SELECT ENGINE-OR MOTOR-DRIVE
`MODE BASED ON PHYSICAL QUANTITY
`REFLECTING ENERGY CONVERSION
`EFFICIENCIES 1N MOTOR-DRIVE MODE
`
`A-63-284031
`A—1-153330
`A-6-48222
`A-6-80048
`6-217413
`WO 95/13201
`
`Japan.
`11/1933
`Japan.
`6/1989
`Japan.
`2/1994
`Japan.
`3/1994
`Japan.
`8/1994
`5/1995 VVIPO.
`
`[75]
`
`Inventors: Ryuji Ibaraki. Toyota; Yutaka Taga.
`Aichi-ken; Hiroshi Hata. Toyota;
`Atsushi Tabata. Okazaki; Seitoku
`Kubo. Toyota. all of Japan
`
`[73] As signee:
`
`Toyota Jidosha Kabushiki Kaisha.
`Toyota. Japan
`
`[21] Appl. No.: 685,102
`
`[22] Filed:
`
`Jul. 22, 1996
`
`[30]
`
`Foreign Application Priority Data
`
`Jul. 24, 1995
`Dec. 18,1995
`
`[JP]
`[JP]
`
`Japan .................................... 7-186852
`Japan
`..... 7-328444
`
`
`
`............................... H02P 7/66
`Int. Cl." .
`[51]
`[52] US. Cl. ......................... 318/148; 318/146; 180/653;
`ISO/65.4; 290/40 C; 322/14
`[58] Field of Search ..................................
`ISO/65.1. 65.2.
`180/653. 65.4; 290/40 C. 40 R. 40 F. 36 R;
`318/140. 141. 143. 146. 148. 151. 802.
`799. 806; 322/14. 38. 39
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`_
`4,351,405
`9/1982 Fields et a1.
`........................... 180/652
`
`iflggzgg 132333 fiwakatsu e‘ a].
`' 1312::
`
`6/1994 32:23:: """"
`" 180/65‘3
`5,318,142
`
`5’343’970
`9/1994 Seven—Mk};
`ISO/65:2
`. 290,40 C
`5:545:92];
`8/1996 Kenn] .......
`
`5,566,774 10/1996 Yoshida .................................. ISO/65.4
`FOREIGN PATENT DOCUMENTS
`
`OTHER PUBLICATIONS
`
`I.E.E. Proceedings—D/Control Theory & Applications. vol.
`134. No. 6. Nov. 1987.
`
`“Fiat Conceptual Approach to Hybrid Cars Design”. Inter-
`national Electric Vehicle Symposium. Anaheim Dec. 5—7.
`1994. pp. 458—469.
`
`Primary Examiner—John W. Cabeca
`Attorney, Agent, or Firm—Cliff & Berridge. PLC
`
`[57]
`
`ABSTRACT
`
`A drive control apparatus for an automotive vehicle having
`an electric motor and an engine operated by combustion of
`a fuel. the drive control apparatus including a drive source
`selecting device for selecting an engine drive mode or a
`motor drive mode on the basis of a first value in the engine
`drive mode of a physical quantity relating to a condition of
`the engine and a second value of the same physical quantity
`reflecting energy conversion efliciencies of the electric
`motor. an electric generator and an electric energy storage
`device during an electricity generating mode. The physical
`quantity is preferably a fuel consumption amount by the
`engine. The drive control apparatus may also include an
`engine output determining device that optimizes the effi—
`ciency of the system by determining the output of the engine
`so as to power the vehicle and also provide surplus power to
`operate the electric generator and charge the electric energy
`storage device. An enlarging device may also be included to
`increase the output of the electriC motor to Prevent excessive
`charging of the electric energy storage device.
`
`44 30 670 Al
`
`3/1995 Germuy .
`
`19 Claims, 9 Drawing Sheets
`
`CLUTCH
`CONTROL
`ACTUATOR
`
`INTERNAL COMBUSTION ENGINE
`
`SPEED
`859g?“
`
`120
`
`DRIVE
`
`FUEL
`
`
`
`
`‘26
`sum
`POSITION
`“”50“
`ENGINE BRAKING
`SHIFT POSFTION
`SIGNAL
`
`CONTROLLER
`
`9A
`I
`ACCELERATOR SIGNAL
`‘28
`
`CONTROu
`CONTROL
`ACTUATOR ACTUATOR
`
`ass.
`ACTUATOR
`
`VALVE
`mag;
`
`I BRAKE PEDAL FORCE SIGNAL
`
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 1 of 9
`
`5,789,882
`
`22
`
`FIGI
`
`
`
`ELECTRIC
`SUPPLY
`
`DEVICE
`
`
`
`
`
`M/G
`ICE
`
`
`CONTROL
`CONTROL
`
`
`DEVICE
`DEVICE
`
`
`
`
`
`
`
`INTERNAL
`COMBUSTION
`ENGINE
`
`OUTPUT DEVICE
`
`
`
`MEMORY
`MEANS
`
`
`
`
`34
`
`COMPARING
`MEANS
`
`
`FIRST
`CALCULATING
`MEANS
`
`
`
`
`
`
`SECOND
`
`CALCULATING
`
`MEANS
`
`
`
`
`
`32
`
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 2 of 9
`
`5,789,882
`
`FIGS
`
`READING INPUT SIGNALS
`TE, TM, 0A, ETC.
`
`SI
`
`
`CALCULATING FUEL
`CONSUMPTION AMOUNTS
`
`Mfce AND Mfcm
`
`$2
`
`
`
`
`
`
`
`ENGINE
`DRIVE
`MODE
`SUB-ROUTINE
`
`
`
`
`MOTOR
`DRIVE
`MODE
`SUB-ROUTINE
`
`
`
`ELECTRICITY
`
`GENERATING
`
`
`DRIVE MODE
`SUB-ROUTINE S7
`
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 3 of 9
`
`5,789,882
`
`FIGA
`
`
`
`
`ELECTRICITY GENERATING DRIVE MODE SUB-ROUTINE
`
`
`
`
`PICE = PL IN IST CYCLE
`PICE = PICE + APICE
`IN 2ND AND SUBSEQUENT
`
`CYCLES
`
`
`RI
`
`
`
`CALCULATING 771CE
`
`R2
`
`
`
`CALCULATING AND
`STORING 77?
`
`
`
`R3
`
`
`
`
`
`
`
`
`R5
`
`
`FIB
`
`SELECTING PICE WHOSE
`77T IS MAXIMUM
`
`OPERATING ENGINE WITH
`PICE AND SETTING PGEN
`
`
`
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 4 of 9
`
`5,789,882
`
`FIGS
`
`filCEmax
`
`
`
`
`
`ENGINE SPEED NE
`
`
`
`ENGINETORQUETE
`
`MOTOR
`
`TORQUETM
`
`MOTOR SPEED NM
`
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 5 of 9
`
`5,789,882
`
`FIG.7
`
`
`
`ENGINETORQUETE
`
`(PICE— PL)
`
`
`
`
`PICE
`
`ENGlNE SPEED NE
`
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`

`US. Patent
`
`Aug. 4, 1998
`
`Sheet 6 of 9
`
`5,789,882
`
`o:
`
`
`
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`
`55%$555
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`memfim55288222$3.wa6528
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`
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`
`
`7of25
`
`FORD 1403
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`7 of 25
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`
`
`
`
`
`
`
`
`

`

`US. Patent
`
`Aug. 4, 1998
`
`Sheet 7 of 9
`
`5,789,882
`
`FIGS
`
`F’“ ——J"
`DRIVE SOURCE
`SELECTING MEANS
`
`
`
`164
`
`
`ENGINE
`DRIVING
`
`MEANS
`
`
`DRIVESOURCE
`
`SELECTING
`DATA MAP
`
`MEMORY MEANS
`
`.
`
`DAFETVINFG
`
`MEANS
`
`166
`
`168
`
`l
`
`
`
`
`
`REGENERATIVE
`DRIVING
`
`REGENERATIVE
`CHARGING
`AMOUNT
`
`
`DETECTING
`REGENERATIVE
`
`CHARGING
`
`AMOUNT
`
`DETERMINING
`
`
`
`
`
`REGENERATIVE
`CHARGING
`AMOUNT
`MEMORY
`
`
`
`MOTOR DRIVING RANGE ENLARGING MEANS
`
`'
`
`8 of 25
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 8 of 9
`
`5,789,882
`
`
`
`READING INPUT SIGNALS
`
`01
`
`013
`
`ACCELERATOR PEDAL 02
`QNON-OPERAM
`POSITION :2
`YES
`NO
`NO
`SHIFT LEVER
`AT ”“,D "2" 0R "L" '2
`
`
`REGENERATIVE DRIVING
`MODE SUB-ROUTINE
`
`
`STORING REGENERATIVE
`CHARGING AMOUNT SOCH
`
`
`CALCULATING REQUIRED
`POWER PL
`
`03
`
`Q4
`
`@ “0
`
`YES
`SOCRT < D OR
`SOCFIT/SOC < E?
`
`05
`
`NO
`
`
`ELECTRICITY
`
`
`GENERATING
`DRIVE MODE
`
`SUB-ROUTINE 016
`
`
`
`ENGINE ' MOTOR
`ENGINE
`MOTOR
`
`DRIVE MODE
`DRIVE MODE
`DRIVE MODE
`
`
`SUB-ROUTINE
`UB-ROUTINE OII
`SUB-ROUTINE 012
`
`
`
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`US. Patent
`
`Aug. 4, 1998
`
`Sheet 9 of 9
`
`5,789,882
`
`FIG. H
`
`TORQUE
`
`VEHICLEDRIVE
`
`VEHICLE SPEED
`
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`

`5.789.882
`
`1
`VEHICLE CONTROL APPARATUS ADAPTED
`TO SELECT ENGINE-OR MOTOR-DRIVE
`MODE BASED ON PHYSICAL QUANTITY
`REFLECTING ENERGY CONVERSION
`EFFICIENCIES IN MOTOR-DRIVE MODE
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates in general to a drive control
`apparatus for an automotive vehicle. and more particularly
`to a drive control apparatus for a so—called “hybrid vehicle"
`equipped with two drive power sources consisting of an
`electric motor and an engine such as an internal combustion
`engine.
`2. Discussion of the Related Art
`
`For the purpose of reducing exhaust gas emissions. for
`example.
`there has been proposed a so-called “hybrid
`vehicle” equipped with two drive power sources. which
`consist of an electric motor operated by an electric energy
`stored in an electric energy storage device (electric power
`supply device). and an engine such as an internal combus—
`tion engine operated by combustion of a fuel. One type of
`such hybrid vehicle is adapted to run in an engine drive
`mode by operation of the engine. or in a motor drive mode
`by operation of the electric motor. depending upon the
`running condition of the vehicle. The hybrid vehicle is
`further adapted to run in an electricity generating drive mode
`in which the electric motor is operated as an electric gen—
`erator or dynamo by a surplus torque of the engine during
`running of the vehicle with the engine selected as the drive
`power source. so that an electric energy produced by the
`electric generator (i.e.. electric motor)
`is stored in the
`electric energy storage device. An example of a drive control
`apparatus for controlling such a hybrid vehicle is disclosed
`in JP—A—6—48222 (published in 1994). wherein the engine is
`controlled so as to have an ideal torque value which is
`calculated to minimize the amount of consumption of the
`fuel by the engine or the amount of exhaust gases produced
`by the engine. During running of the vehicle with the engine.
`an instantaneous torque value of the engine which is
`required for running the vehicle under the current running
`condition of the vehicle is calculated. If the ideal torque
`value is larger than the required torque value. that is. if the
`engine has a surplus torque. the vehicle is driven in the
`electricity generating drive mode. that is. the electric motor
`is driven by the surplus torque of the engine to charge the
`electric energy storage device. It will be understood that the
`electric motor also functions as the electric generator or
`dynamo.
`The vehicle drive control apparatus as described above is
`further adapted to be placed in a regenerative drive mode
`wherein the electric generator is driven by a kinetic energy
`of the running vehicle to generate an electric energy for
`charging the electric energy storage device as well as to
`apply a brake to the vehicle. This regenerative drive mode is
`established when a predetermined regenerative driving con-
`dition is satisfied. for example. when the operating amount
`of the accelerator pedal is zero.
`In the known vehicle drive control apparatus described
`above. the operating condition of the engine is controlled on
`the basis of only the fuel consumption rate (fuel consump-
`tion amount g/kWh per unit power) or the exhaust gas rate
`(exhaust gas amount per unit power) of the engine. This
`arrangement does not necessarily assure minimization of the
`fuel consumption amount or exhaust gas amount for a
`certain amount of electric energy to be stored in the electric
`
`2
`
`the
`energy storage device. Described more particularly.
`efliciency of conversion of the kinetic energy into the
`electric energy by the electric generator varies with the
`operating speed and torque of the engine. and the conversion
`efliciency upon storing the electric energy in the electric
`energy storage device varies with the electric power (electric
`energy per unit time). Accordingly. the efficiency in charging
`the electric energy storage device is not sufficiently high
`under some operating condition (speed. torque. power. etc.)
`of the engine. A similar problem is encountered in deter—
`mining whether the vehicle should be run by the engine in
`the engine drive motor or by the electric motor in the motor
`drive mode. To efiect this determination in order to minimize
`the fuel consumption amount or the exhaust gas amount. for
`example. the fuel consumption amount or the exhaust gas
`amount when the engine is operated in the electricity gen-
`erating drive mode while driving the electric motor so as to
`charge the electric energy storage device is compared with
`that when the engine is operated in the engine drive motor
`for the sole purpose of driving the vehicle. The vehicle is run
`in the motor drive mode if the fuel consumption amount or
`exhaust gas amount in the electricity generating drive mode
`is smaller than that in the engine drive mode. The vehicle is
`run in the engine drive mode if the fuel consumption amount
`or exhaust gas amount in the engine drive motor is smaller.
`However.
`the fuel consumption amount or exhaust gas
`amount could not be sufliciently reduced if the energy
`conversion etficiencies of the electric generator and the
`electric energy storage device would not be taken into
`account in selecting the engine drive mode or the motor
`drive mode.
`
`The rule for selecting the engine drive mode or the motor
`drive mode remains unchanged even where the vehicle runs
`on a mountain path. During running of the vehicle on a
`mountain path. the vehicle load is generally high. and the
`vehicle is more frequently operated in the engine drive
`mode. whereby the electric energy storage device tends to be
`excessively charged by the engine through the electric
`generator while the vehicle is less frequently operated in the
`motor drive mode. Excessive charging of the electric energy
`storage device may lead to reduction of the energy conver-
`sion efliciency (charging and discharging efficiencies). and
`may even cause a failure to charge the electric energy
`storage device. Thus. the known arrangement for selecting
`the engine or the electric motor as the drive powm‘ source
`does not permit effective utilization of the electric energy.
`resulting in an increase in the fuel consumption amount or
`the exhaust gas amount during running of the vehicle on a
`mountain path.
`SUMMARY OF THE INVENTION
`
`It is therefore an object of this invention to provide a drive
`control apparatus for a hybrid vehicle equipped with an
`electric motor and an engine as drive sources. which appa-
`ratus permits effective reduction in the fuel consumption
`amount or exhaust gas amount of the engine.
`According to a first aspect of the present invention. there
`is provided a drive control apparatus for an automotive
`vehicle having an electric generator for generating an elec-
`tric energy. an electric energy storage device for storing the
`electric energy generated by the electric generator. an elec-
`tric motor operated as a first drive power source by the
`electric energy. and an engine operated as a second drive
`power source by combustion of a fuel. the apparatus having
`an engine drive mode in which the vehicle is driven by the
`engine. a motor drive mode in which the vehicle is driven by
`the electric motor. and an electricity generating mode in
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
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`35
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`
`50
`
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`
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`3
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`5,789,882
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`which the electric generator is operated by the engine to
`charge the electric energy storage device.
`the apparatus
`selecting one of the engine drive mode. the motor drive
`mode and the electricity generating mode. depending upon
`a running condition of the vehicle. the apparatus being
`characterised by drive source selecting means for selecting
`one of the engine drive mode and the motor drive mode. on
`the basis of a first value in the engine drive mode of a
`physical quantity relating to a condition of the engine and a
`second value of the physical quantity reflecting energy
`conversion efliciencies of the electric generator. the electric
`motor and the electric energy storage device in the electricity
`generating mode. and according to a predetermined rule
`associated with the first and second values.
`
`In the vehicle drive control apparatus constructed accord-
`ing to the first aspect of this invention. the drive source
`selecting means selects the engine drive mode for running
`the vehicle with the engine or the motor drive mode for
`running the vehicle with the electric motor. according to the
`predetermined rule associated with the first and second
`values of a selected physical quantity relating to a condition
`of the engine. such as an amount of consumption of the fuel
`by the engine or an amount of exhaust gases produced by the
`engine. The first value is the physical quantity value in the
`engine drive mode. while the second value is the physical
`quantity value in the electricity generating mode in which
`the electric generator is operated by the engine to generate
`the electric energy which is stored in the electric energy
`storage device and which is used by the electric motor in the
`motor drive mode. The drive source selecting means obtains
`the second value while taking into account of the energy
`conversion efficiency values of the electric motor. electric
`generator and electric energy storage device in the electricity
`generating mode. The use of this second value which reflects
`the energy conversion efliciency values in the electricity
`generating mode permits adequate selection of the engine
`drive mode or the motor drive mode so as to effectively
`increase or decrease the physical quantity of the engine. for
`example. minimize the fuel consumption amount or exhaust
`gas emission amount of the engine. Where the fuel con—
`sumption amount
`is used as the physical quantity. for
`instance. the engine drive mode is selected it the first value
`of the fuel consumption amount in the engine drive mode is
`smaller than the second value in the electricity generating
`mode. while the motor drive mode is selected if the second
`value is smaller than the first value. This arrangement is
`effective to minimize the fuel consumption amount of the
`engine. Where the exhaust gas emission amount is used as
`the physical quantity. the engine drive mode and the motor
`drive modes are selected on the basis of the first and second
`values as compared with each other in the same manner as
`described above. so as to minimize the exhaust gas emission
`amount.
`
`In one preferred form of the present drive control
`apparatus. the drive source selecting means comprises: (a)
`first calculating means for obtaining the first value of the
`physical quantity in the engine drive mode; (b) second
`calculating means for obtaining the second value of the
`physical quantity which second value reflects the energy
`conversion efficiencies in the electricin generating mode in
`which the electric generator is operated by the engine to
`generate the electric energy to be stored in the electric
`energy storage device and used by the electric motor in the
`motor drive mode; and (c) comparing means for comparing
`the first and second values of the physical quantity obtained
`by the first and second calculating means. and selecting one
`of the engine drive mode and the motor drive mode depend-
`
`ing upon whether one of the first and second values is
`smaller than the other.
`
`Where the physical quantity is an amount of consumption
`of the fuel by the engine or an amount of exhaust gas
`emission from the engine. the first and second calculating
`means obtain a first value and a second value of the amount
`of consumption of the fuel or the amount of exhaust gas
`emission in the engine drive mode and the electricity gen-
`erating mode. respectively.
`In this case.
`the comparing
`means may be adapted to select the engine drive mode if the
`first value obtained by the first calculating means is smaller
`than the second value obtained by the second calculating
`means. and select the motor drive mode if the first value is
`not smaller than the second value.
`In the above case. the first calculating means may be
`adapted to calculate the first value of the amount of con-
`sumption of the fuel in the engine drive mode. by using a
`speed and a torque of the engine. and the second calculating
`means may be adapted to calculate the second value of the
`amount of consumption of the fuel by the engine in the
`electricity generating mode. by using a speed and a torque
`of the electric motor.
`
`The fuel consumption amount or exhaust gas emission
`amount of the engine may be substantially represented by
`the speed and torque of the engine. Therefore.
`the fuel
`consumption amount or exhaust gas emission amount during
`running of the vehicle in the engine drive motor may be
`obtained on the basis of the engine speed and torque which
`vary with the specific running condition of the vehicle. On
`the other hand. the energy conversion efficiency during
`running of the vehicle in the motor drive mode may be
`substantially represented or determined by the speed and
`torque of the electric motor which vary with the specific
`running condition of the vehicle. The discharging efliciency
`of the electric energy storage device during use of the
`electric energy stored in this storage device in the motor
`drive mode may be substantially determined by electric
`power of the electric motor or engine. namely. an amount of
`electric energy per unit time. The charging efliciency of the
`electric energy storage device in the electricity generating
`mode in which the electric energy generated by the electric
`generator by operation of the engine is stored in the storage
`device is substantially constant where the charging is
`effected in the electricity charging mode under a predeter—
`mined constant condition. for example. when the vehicle is
`in a stop with the engine kept operating. In the light of these
`facts. the amount of fuel consumption required for charging
`the electric energy storage device in the electricity generat—
`ing mode and running the vehicle in the motor drive mode
`may be represented by the speed and torque of the electric
`motor which vary with the specific vehicle running
`condition. like the engine speed and torque. For the same
`reason. the amount of the exhaust gases emitted from the
`engine may be represented by the motor speed and torque.
`Therefore. the selection of the engine drive mode or the
`motor drive mode may be eifected on the basis of the engine
`speed and torque (motor speed and torque) and according to
`a stored data map which is formulated to select one of the
`engine drive mode and the motor drive mode which requires
`a smaller amount of consumption of the fuel by the engine
`or which results in a smaller amount of exhaust gas emission
`from the engine. This arrangement using the data map does
`not require data processing operations to calculate the first
`and second values of the fuel consumption amount or
`exhaust gas emission amount. and does not require calcu—
`lating means as described above. The drive source selecting
`means may use a parameter or parameters other than the
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`speed and torque of the engine or motor. which reflect the
`energy conversion efliciency of the electric energy storage
`device. for example. It is also noted that the rate of change
`of the energy conversion efliciency values of the electric
`system associated with the electric generator and motor and
`the electric energy storage device is generally lower than the
`rate of change of the fuel consumption rate or exhaust gas
`emission rate of the engine. In this respect. the selection of
`the engine drive mode and the motor drive mode may be
`advantageously effected according to a data map associated
`with the fuel consumption rate or exhaust gas emission rate
`of the engine.
`In another preferred form of the vehicle drive control
`apparatus of this first aspect of the invention. the energy
`conversion efficiencies which are reflected by the second
`value of the selected physical quantity comprise at least one
`of: efliciency of conversion of a kinetic energy into the
`electric energy by the electric generator in the electricity
`generating mode; efficiency of charging of the electric
`energy storage device with the electric energy generated by
`the electric generator in the electricity generating mode;
`efliciency of discharging of the electric energy storage
`device in the motor drive mode; and efficiency of conversion
`of the electric energy stored in the electric energy storage
`device into a kinetic energy by the electric motor in the
`motor drive mode.
`
`The electric generator and the electric motor may be
`provided as separate elements. Alternatively. the electric
`motor may function as the electric generator.
`According to a second aspect of the present invention.
`there is provided a drive control apparatus for an automotive
`vehicle having an electric generator for generating an elec-
`tric energy. an electric energy storage device for storing the
`electric energy generated by the electric generator. an elec-
`tric motor operated as a first drive power source by the
`electric energy. and an engine operated as a second drive
`power source by combustion of a fuel. the apparatus having
`an engine drive mode in which the vehicle is driven by the
`engine. a motor drive mode in which the vehicle is driven by
`the electric motor. and an electricity generating mode in
`which the electric generator is operated by the engine to
`charge the electric energy storage device. the apparatus
`being characterised by engine output determining means for
`determining a desired output of the engine in the electricity
`generating mode. on the basis of an overall efiiciency of a
`system assigned to charge the electric energy storage device
`in the electricity generating mode. the overall efficiency
`being associated with a physical quantity relating to a
`condition of the engine. and said overall efliciency reflecting
`energy conversion efliciencies of the electric energy storage
`device and the electric generator in the electricity generating
`mode.
`
`In the vehicle drive control apparatus constructed accord—
`ing to the second aspect of this invention. the engine output
`determining means is adapted to determine the desired
`engine output for operating the electric generator to charge
`the electric energy storage device in the electricity generat—
`ing mode. on the basis of the overall efficiency of a selected
`physical quantity of the engine such as the fuel consumption
`amount or exhaust gas emission amount of the engine. which
`overall efficiency reflects the energy conversion efliciencies
`of the electric energy storage device and the electric gen-
`erator in the electricity generating mode. This arrangement
`is efiective to maximize or minimize the selected physical
`quantity of the engine such as the fuel consumption amount
`or exhaust gas emission amount per unit amount of electric
`energy to be stored in the electric energy storage device in
`
`the electricity generating mode. Where the fuel consumption
`amount of the engine is used as the physical quantity. the
`desired output of the engine is determined 50 as to maximize
`the overall efliciency relating to the fuel consumption of the
`engine. In this case. the ratio of the fuel consumption amount
`of the engine to the electric energy to be stored in the electric
`energy storage device is minimized. Where the exhaust gas
`emission amount of the engine is used as the physical
`quantity. the desired output of the engine is determined so as
`to maximize the overall efficiency relating to the exhaust gas
`emission of the engine. In this case. the ratio of the exhaust
`gas emission amount to the electric energy to be stored in the
`electric energy storage device is minimized.
`In one preferred form of the vehicle drive control appa—
`ratus according to the second aspect of the invention. the
`engine output determining means determines the desired
`output of the engine such that the desired output is larger
`than a value of drive power required for the engine to drive
`the vehicle in the engine drive mode. by a predetermined
`amount which provides surplus power by which the electric
`generator is operated to charge the electric energy storage
`device.
`
`In one advantageous arrangement of the above preferred
`form of the apparatus. the engine output determining means
`comprises: calculating means for calculating values of the
`overall efliciency which correspond to different candidate
`values of the desired output of the engine. respectively. the
`values of the overall efliciency reflecting the energy con-
`version efliciencies of the electric energy storage device and
`the electric generator during operation of the electric gen-
`erator by the surplus power in the electricity generating
`mode; and determining means for selecting one of the
`different candidate values of the desired output of the engine
`which corresponds to one of the values of the overall
`efliciency which satisfies a predetermined condition. and
`determining the selected candidate value as the desired
`output of the engine. The different candidate values of the
`desired output of the engine correspond to diflerent values of
`the surplus power by which the electric generator is operated
`to charge the electric energy storage device. The determining
`means indicated above may be adapted to determine. as the
`desired output of the engine. one of the candidate values
`which corresponds to a highest one of the values of the
`overall efficiency.
`The output of the engine may be represented by the torque
`and speed of the engine. Similarly. the energy conversion
`efficiencies of the electric generator and the electric energy
`storage device may be represented by the torque and speed
`or electric power (drive power) of the engine. In view of
`these facts. the desired output of the engine in the electricity
`generating mode may be determined on the basis of the
`engine torque and speed and according to a predetermined
`relationship between the desired engine output and the
`engine torque and speed. which relationship is represented
`by a stored data map. The engine torque and speed represent
`the current running condition of the vehicle. namely. the
`drive power currently required by the engine to operate the
`elecuic motor to charge the electric energy storage device.
`The relationship is formulated to determine the desired
`output of the engine so as to maximize the overall efficiency
`of the selected physical quantity such as the fuel consump-
`tion amount of the engine. This arrangement using the data
`map does not require operations to calculate the overall
`efliciency values corresponding to different candidate values
`of the engine output. and does not require the calculating
`means as described above. The desired engine output in the
`electricity generating mode may be determined using a
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`parameter or parameters other than the engine torque and
`speed. which parameters reflect a condition of charging of
`the electric energy storage device in the electricity generat-
`ing mode. Where the electric energy storage device is
`charged under a substantially constant condition. for
`example. when the vehicle is in a stop with the engine kept
`operating.
`the engine output determining means may be
`adapted to set the desired engine output at a constant value.
`which is determined depending upon the energy conversion
`efficiencies of the electric generator and the electric energy
`storage device.
`According to a third aspect of this invention. there is
`provided a drive control device for an automotive vehicle
`having an electric generator for generating an electric
`energy. an electric energy storage device for storing the
`electric energy generated by the electric generator. an elec-
`tric motor operated as a first drive power source by the
`electric energy. and an engine operated as a second drive
`power source by combustion of a fuel. the apparatus com—
`prising: (a) engine driving means for running the vehicle by
`operation of the engine in an engine drive mode while a
`running condition of the vehicle is held within a engine
`driving range; (b) motor driving means for running the
`vehicle by operation of the electric motor in a motor drive
`mode while the running condition is held within a motor
`driving range; (c) regenerative driving means for running the
`vehicle in a regenerative drive mode in which the electric
`generator is driven by a kinetic energy of the running vehicle
`so as to store an electric energy in the electric energy storage
`device as well as to apply a brake to the vehicle.
`the
`regenerative drive mode is selected when the running con-
`dition of the vehicle satisfies a predetermined requirement;
`and (d) enlarging means for enlarging the motor driving
`range when an amount of the electric energy stored in the
`electric energy storage device by operation of the electric
`generator in the regenerative drive mode is larger than a
`predetermined threshold.
`In the vehicle drive control apparatus constructed accord-
`ing to the third aspect of the present invention. the enlarging
`means is adapted to enlarge the motor driving range when
`the amount of the electric energy stored in the electric energy
`storage device in the regenerative drive mode is larger than
`the predetermined threshold. As a result. the amount of the
`electric energy consumed by the electric motor in the motor
`drive mode tends to be increased. and the electric energy
`stored in the electric energy storage device tends to be
`accordingly reduced. Thus. this arrangement is effective to
`prevent an excessively charged state of the electric energy
`storage device which would occur during running of the
`vehicle on a mountain path and which would cause reduc—
`tion in the energy conversion efficiency or a failure to charge
`the energy storage device. Since the amount of consumption
`of the fuel by the engine is reduced by enlargement of the
`motor driving range. the amount of exhaust gas emission
`fi'om the engine is accordingly reduced.
`In one preferred form of the present apparatus. the