[19]
`United States Patent
`6,116,363
`[11] Patent Number:
`[45] Date of Patent: *Sep. 12, 2000
`Frank
`
`
`
`US006116363A
`
`[54] FUEL CONSUMPTION CONTROL FOR
`CHARGE DEPLETION HYBRID ELECTRIC
`VEHICLES
`
`[75]
`
`Inventor: Andrew A. Frank, El Macero, Calif.
`
`[73] Assignee: Frank Transportation Technology,
`LLC, El Macero, Calif.
`
`[*] Notice:
`
`This patent is subject to a terminal dis-
`claimer.
`
`[21] Appl. No.2 09/063,995
`
`[22]
`
`Filed:
`
`Apr. 21, 1998
`
`Related US. Application Data
`
`[63]
`
`Continuation—in—part of application No. 08/963,037, NOV. 3,
`1997, Pat. No. 5,842,534, which is a continuation of appli—
`cation No. 08/455,104, May 31, 1995, abandoned.
`
`Int. Cl.7 ....................................................... B60K 6/04
`[51]
`[52] US. Cl.
`........................ 180/652; 180/654; 180/658
`[58] Field of Search .................................. 180/651, 65.2,
`180/653, 65.4, 65.8; 318/587; 701/22,
`36
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`8/1977 Horwinski.
`4,042,056
`4,180,138 12/1979 Shea.
`4,269,280
`5/1981 Rosen.
`4,335,429
`6/1982 Kawakatsu.
`
`8/1983 Fiala .
`4,400,997
`8/1985 Heidemeyer et a1.
`4,533,011
`4,697,660 10/1987 Wu et al. .
`5,115,183
`5/1992 Kyoukane et a1.
`5,117,931
`6/1992 Nishida .
`5,343,970
`9/1994 Severinsky .
`5,923,025
`7/1999 Ellers .
`
`.
`
`.
`
`FOREIGN PATENT DOCUMENTS
`
`2310238
`2494642
`4206360
`
`France .
`1/1977
`France .
`5/1982
`9/1993 Germany .
`
`OTHER PUBLICATIONS
`
`Wood’s Gas—Electric Car, Instruction No. 80, Dyke’s Ency-
`clopedia, 1935.
`Frank et al., “Computer Simulation of the University of
`Wise. Hybrid—Electric Vehicle Concept”, May 1973.
`
`Primary Examiner—Michael Mar
`Attorney, Agent, or Firm—John P. O’Banion
`
`[57]
`
`ABSTRACT
`
`A charge depletion method and apparatus for operating the
`electric motor and auxiliary power unit, such as an internal
`combustion engine,
`in a hybrid electric vehicle (HEV)
`separately or together depending upon the driving condi-
`tions. Operation of the electric motor and auxiliary power
`unit are coordinated as a function of a control policy for the
`auxiliary power unit based on desired least fuel consumption
`and/or vehicle emissions characteristics.
`
`6 Claims, 7 Drawing Sheets
`
`16
`
`18
`
`20
`
`22
`
`
`MULTI—SPEED
`TRANSMISSION
`
`
`
`OR
`
`
`DRIVE WHEELS
`
`
`
`
`28
`
`
`
`BATTERIES
`
`
`
`INTERNAL
`
`COMBUSTION
`
`ENGINE
`
`
`
`26
`
`GENERATOR -----
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`1of15
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`US. Patent
`
`Sep. 12, 2000
`
`Sheet 1 0f 7
`
`6,116,363
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`US. Patent
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`Sep. 12,2000
`
`Sheet 2 0f7
`
`6,116,363
`
`12
`CLUTCH
`
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`
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`100%
`
`FIG. — 4
`
`3of15
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`3 of 15
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`US. Patent
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`Sep. 12, 2000
`
`Sheet 3 0f 7
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`6,116,363
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`

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`US. Patent
`
`Sep. 12, 2000
`
`Sheet 4 0f 7
`
`6,116,363
`
`% of
`
`Travelers
`
`Commuters
`
`
`
`FIG. — 5
`
`0
`
`40
`Miles
`
`250
`
`Total Fuel
`Used (gal.)
`
`
`
`70 gal.
`1000 Vehicles
`
`FIG. — 6
`
`0
`
`40
`Miles
`
`250
`
`129
`
`
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`
`ICETURN—ONSPEED(KPH)
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`BATTERY DEPTH OF DISCHARGE (%DOD)
`
`FIG. — 7
`
`5of15
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`US. Patent
`
`Sep. 12,2000
`
`Sheet 5 017
`
`6,116,363
`
`129
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`US. Patent
`
`Sep. 12, 2000
`
`Sheet 6 0f 7
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`6,116,363
`
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`US. Patent
`
`Sep. 12, 2000
`
`Sheet 7 0f 7
`
`6,116,363
`
`FIG. — 11
`
`I’
`
` I
`I EMII
`II
`,’ TORQU+E
`CONTROL
`
`330
`
`
`ACCELERATOR PEDAL
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`6,116,363
`
`1
`FUEL CONSUMPTION CONTROL FOR
`CHARGE DEPLETION HYBRID ELECTRIC
`VEHICLES
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of application
`Ser. No. 08/963,037 filed on Nov. 3, 1997, now Pat. No.
`5,842,534 which is a continuation of Ser. No. 08/455,104
`filed on May 31, 1995, now abandoned.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This invention pertains generally to hybrid powered
`vehicles employing both electric motors and auxiliary power
`units, and more particularly to controlling fuel consumption
`in a charge depletion hybrid electric vehicle.
`2. Description of the Background Art
`As discussed in my copending US. application Ser. No.
`08/963,067, a hybrid electric vehicle (HEV) is a vehicle with
`electricity as the primary energy source and an auxiliary
`power unit (APU) as the secondary source. The APU is
`typically an internal combustion engine (ICE) utilizing
`reformulated gasoline, methanol, ethanol, diesel, com-
`pressed natural gas or other hydrocarbon as a fuel source.
`The electrical energy is stored in chemical storage batteries
`or capacitors. A series hybrid electric vehicle uses the ICE
`to drive a generator which supplies power to the electric
`motor (EM) or charges the batteries, whereas a parallel
`hybrid uses the ICE and EM together to directly drive the
`wheels. In both configurations, the ICE is used to supple-
`ment the energy capacity and power capability of the battery
`pack.
`Most parallel hybrid vehicles are configured with a large
`ICE. The EM is selected for urban driving and acceleration,
`since the ICE may not be used provide the power required
`for this driving demand. In emergency situations, the ICE
`can provide “limp-home” capability when the batteries reach
`a depth of discharge (DOD) where the EM can no longer
`accelerate the vehicle.
`
`Various control strategies have been previously developed
`for operating the EM and ICE in hybrid vehicles. None of
`the existing control schemes, however, integrate the opera-
`tion of the EM and ICE in a hybrid vehicle in a way which
`maximizes both efficiency and range on the batteries while
`maintaining performance of the vehicle;
`that is, using a
`“charge depletion” control method in accordance with the
`present invention. Conventional control schemes operate on
`the principle of sustaining the charge on the batteries, rather
`than depleting the batteries as in the present invention. The
`present invention satisfies the need for a control method and
`apparatus that will provide for integration of the EM and
`ICE in an efficient manner without sacrificing vehicle per-
`formance.
`
`Furthermore, government regulating agencies such as the
`Environmental Protection Agency (EPA) and the California
`Air Resources Board (CARB), as well as users of a “charge
`depletion hybrid electric vehicle” (CDHEV) in accordance
`with the present invention, may want to change the relative
`amounts of liquid or hydrocarbon fuel and electric energy
`used by a fleet of CDHEVs, since the cost and technology
`of each commodity may change over time. For example,
`electric energy is currently less expensive for powering a
`vehicle per mile than gasoline. On the other hand, emissions
`from electrical powerplants may be less clean and less
`
`10
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`15
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`20
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`25
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`35
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`2
`environmentally friendly than from gasoline engines. The
`present invention further satisfies the need to provide for
`changing the manner in which operation of the EM and ICE
`are controlled so as to allow for adjustment of the relative
`amounts of combustible fuels and electric energy consumed
`during operation of the vehicle fleet.
`The EPA currently specifies to vehicle manufacturers
`what is referred to as a “corporate average fuel economy”
`(CAFE) as well as individual vehicle emissions. A CDHEV
`in accordance with the present invention permits the EPA to
`also specify and regulate both emissions and fuel consump-
`tion for a fleet of hybrid electric vehicles. On the other hand,
`local regulations may be different since air quality and
`performance requirements change depending upon traffic
`and road infrastructure.
`
`BRIEF SUMMARY OF THE INVENTION
`
`invention generally comprises a “charge
`The present
`depletion” method and apparatus for operating the electric
`motor (EM) and internal combustion engine (ICE) in a
`hybrid electric vehicle (HEV) separately or together depend-
`ing upon the driving conditions. The invention further
`comprises a charge depletion control policy (CDCP) that can
`be modified to adjust the relative amounts of combustible
`and electric fuels used for operation of the vehicle.
`By way of example, and not of limitation, the invention
`provides for operating the hybrid powertrain in a zero
`emissions vehicle (ZEV) mode and in an HEV mode. In the
`ZEV mode, the EM provides all driving power while the ICE
`is uncoupled and turned off. In the HEV mode, operation of
`the EM and ICE is coordinated for maximum range and fuel
`efficiency.
`The ICE used in a vehicle employing the present inven-
`tion can be typically very small (e.g., approximately 0.016
`kW/vehicle kg) and typically would be sized to power the
`vehicle at its best efficiency for legal freeway cruise speeds.
`The engine can be used to cruise the vehicle at a level above
`the maximum speed limit for a range of approximately 690
`km or more. However, in typical city driving conditions,
`driving with the ICE alone produces less-than-desirable
`performance because of its small size. This is an important
`aspect of the invention since it encourages the driver to
`remember to periodically charge the vehicle batteries at
`home. Additionally, the varying driving conditions inherent
`in city driving will cycle the engine and reduce efficiency.
`Emissions would increase and fuel efficiency would
`decrease.
`
`In accordance with one CDCP of the present invention, as
`long as the battery depth of discharge (DOD) is less than a
`hybrid integration cross-over point of approximately 50%
`(i.e., the DOD is between 0% and approximately 50%), and
`the vehicle speed is less than approximately 113 kph, then
`the EM is operated alone; that is, the ICE is uncoupled and
`turned off. Here, the vehicle operates in a ZEV mode. At
`speeds greater than approximately 113 kph,
`the vehicle
`operates in an HEV mode where the ICE is used as the
`primary source of power and the EM is automatically
`activated to (i) assist the ICE during acceleration (e.g., for
`passing or climbing hills) or (ii) regenerate energy back into
`the battery during braking. Once the depth of discharge
`exceeds the hybrid integration cross-over point, the ICE is
`brought on line and turned on at varying vehicle speeds
`below approximately 113 kph. As the depth of discharge
`increases, the vehicle speed at which the ICE is brought on
`line decreases in order to increase overall range.
`In other words, as long as the battery depth of discharge
`is less than approximately 50% and the vehicle speed is less
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`6,116,363
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`3
`than approximately 113 kph, then the EM is operated alone;
`that is, the ICE is uncoupled and turned off. Therefore, the
`vehicle operates in a ZEV mode. At speeds greater than
`approximately 113 kph,
`the vehicle operates in an HEV
`mode where the ICE is used as the primary source of power
`and the EM is automatically activated to (i) assist the ICE
`during acceleration (e. g., for passing or climbing hills) or (ii)
`regenerate energy back into the battery during braking. Once
`the depth of discharge exceeds the cross-over point, the ICE
`is brought on line and turned on at varying vehicle speeds
`below approximately 113 kph.
`As a result, the invention combines the advantages of a
`ZEV vehicle in most city driving conditions as well as
`extended city range and high freeway efficiencies from the
`ICE. Typically,
`the vehicle can be driven in all driving
`conditions with full performance until the batteries reach a
`state of approximately 85% depth of discharge or more. The
`vehicle then degrades in acceleration performance can con-
`tinue to operate. The usable battery charge corresponds to a
`city driving range of approximately 160 km. Based on recent
`studies of vehicle usage, a range of approximately 115 km
`will satisfy over 80% of the typical road vehicle miles
`traveled by the public daily. Therefore, the vehicle power
`train will function as a ZEV for a majority of drivers in the
`city. Further, the vehicle will satisfy the needs of over 99%
`of the drivers when employing this CDCP. The vehicle will
`satisfy 100% of the drivers in reaching their destination;
`only 1% or less may reach their destination with degraded
`performance because they drove too far and the batteries are
`spent.
`the
`It will be appreciated that, by altering the CDCP,
`overall amount of combustible fuel burned by the vehicle in
`comparison to the amount of electric energy used can be
`increased or reduced to meet governmental or user mandated
`standards. If the DOD parameter in the CDCP is decreased,
`the amount of combustible fuel burned will
`increase,
`whereas increasing the DOD parameter in the CDCP will
`decrease the amount of combustible fuel burned and the
`
`vehicle will be powered by the EM more often thereby
`decreasing the high performance range.
`For example, assume that
`typical commuters travel
`approximately 40 miles and that a fleet of conventional
`vehicles driven by such computers uses approximately 2500
`gallons of gasoline per 1000 vehicles. The CDCP described
`above with a crossover point of approximately 50% DOD
`would reduce fleet consumption of gasoline to approxi-
`mately 70 gallons per 1000 vehicles for an approximate
`gasoline savings of 97%. By lowering the hybrid integration
`crossover point from 50% to 20%, only a 95% gasoline
`savings would be realized. If the hybrid integration cross-
`over point is further reduced, and the speed cross-over point
`is lowered from 113 km/hr to approximately 65 km/hr, the
`gasoline savings would be reduced to 85, and by further
`lowering the speed cross-over point to approximately 20
`km/br, only a 60% gasoline savings would be realized.
`Therefore,
`the threshold speeds and adjustment of the
`threshold speeds, as well as the charge depletion of the
`batteries (DOD characteristics), are a function of a control
`policy for the auxiliary power unit based on desired fleet fuel
`consumption and/or fleet vehicle emissions characteristics.
`In accordance with another aspect of the invention, con-
`trol of vehicle acceleration and speed is preferably accom-
`plished using a two-stage accelerator pedal when in hybrid
`mode where both the engine and the electric motor are
`powering the vehicle. Approximately the first 1/3 of pedal
`travel controls the throttle position of the ICE and the last 2/3
`
`5
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`60
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`65
`
`4
`controls the torque of the EM. When operating in the HEV
`mode the ICE operates at high throttle settings and, when the
`ICE is operating at wide open throttle (WOT) but additional
`power is still required, the driver depresses the pedal further
`and the EM torque is automatically added. Therefore,
`vehicle acceleration is proportional to the accelerator pedal
`position as in a conventional car. Transmission shifting is
`accomplished similar to conventional cars.
`Since vehicle “launch” is performed by the EM, an
`automatic transmission would not need a torque converter.
`Further, a computer is not needed to coordinate the ICE
`throttle and EM torque control. Operation of the brake pedal
`is similar to the accelerator pedal, where the first part of the
`pedal depression provides regenerative braking by the EM,
`and the continued deflection eventually activates mechanical
`brakes which simply adds to the braking effort already
`available from regeneration.
`In accordance with another aspect of the invention, the
`batteries are not charged directly by the ICE during opera-
`tion of the vehicle, except during emergency conditions, in
`which case charging would only be partial and solely to
`maintain performance. For example, if the batteries were
`completely depleted (e.g., 100% DOD or 0% state of charge)
`and the ICE was running, the batteries could be slightly
`charged by the ICE (e.g., 5% state of charge) only to provide
`additional performance to get home or to a charging station.
`The manner of doing so would be for the driver to pull off
`to the side of the road, place the transmission in neutral, and
`depress both the accelerator pedal and the brake pedal at the
`same time so as to allow the ICE to operate at high rpm for
`several minutes. In such an event, the ICE and EM would
`both be on line, and the ICE would drive the EM in a
`regenerative mode so as to recharge the batteries. In normal
`operation, however, the batteries are charged only from an
`external power source. Thus, the hybrid control method of
`the present invention will be referred to herein as a “charge
`depletion” hybrid, in contrast to conventional “charge sus-
`taining” hybrids which charge the batteries directly from the
`ICE.
`In this context, note that
`long range batteries are
`required to make the vehicle practical. No controls are
`available to the driver of the vehicle other than an accelera-
`
`tor pedal, brake pedal and, if desired, a transmission clutch
`pedal. Operation in the ZEV and HEV modes are automatic,
`and the driver does not have control over those modes of
`
`operation.
`An object of the invention is to provide a control system
`for a hybrid electric vehicle powertrain which can provide
`super fuel and energy efficiency.
`Another object of the invention is to provide a control
`system for a hybrid electric vehicle powertrain which can
`provide for ultra low tailpipe emissions in a fleet.
`Another object of the invention is to provide a control
`system for a hybrid electric vehicle powertrain which can
`provide for high performance.
`Another object of the invention is to provide a control
`system for a hybrid electric vehicle powertrain which can
`provide for low cost manufacturing due to simplicity.
`Another object of the invention is to provide a control
`system for a hybrid electric vehicle powertrain which is
`simple to operate.
`Another object of the invention is to provide a control
`system for a hybrid electric vehicle powertrain which is
`automatic.
`
`Another object of the invention is to provide for flexibility
`in the control policy of a charge depletion hybrid electric
`vehicle.
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`Another object of the invention is to provide control over
`the relative amounts of combustible fuel and electric energy
`used in a charge depletion hybrid electric vehicle.
`Further objects and advantages of the invention will be
`brought out in the following portions of the specification,
`wherein the detailed description is for the purpose of fully
`disclosing preferred embodiments of the invention without
`placing limitations thereon.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention will be more fully understood by reference
`to the following drawings which are for illustrative purposes
`only:
`FIG. 1 schematically depicts a hybrid vehicle powertrain
`in accordance with the present invention showing the pre-
`ferred embodiment with a clutch for
`a “parallel”
`configuration, and showing a generator which can replace
`the clutch and shaft for a “series” configuration.
`FIG. 2 is a schematic diagram of an embodiment of a
`parallel hybrid vehicle powertrain in accordance with the
`present invention.
`FIG. 3 is a flow chart showing an embodiment of the
`method of the present invention.
`FIG. 4 graphically depicts a control policy for the opera-
`tion of a hybrid vehicle electric motor and internal combus-
`tion engine as function of vehicle speed and battery depth of
`discharge in accordance with the present invention.
`FIG. 5 is a graph depicting the distribution density of
`travelers using vehicles in a geographical area.
`FIG. 6 is a graph depicting the total fuel used by a 1000
`vehicle fleet travelling according to the distribution density
`shown in FIG. 5.
`
`FIG. 7 is a graph depicting an alternative to the control
`policy shown in FIG. 4.
`FIG. 8 is a graph depicting a second alternative to the
`control policy shown in FIG. 4.
`FIG. 9 is a graph depicting a third alternative to the
`control policy shown in FIG. 4 showing a strategy which
`minimizes use of electric energy to extend the range of the
`vehicle in city and highway driving to a maximum.
`FIG. 10 is a block diagram of a charge depletion control
`system in accordance with the present invention for con-
`trolling the ICE, EM, clutch and transmission from an
`accelerator pedal and a brake pedal.
`FIG. 11 is a diagram showing operation of a typical
`two-stage accelerator pedal in accordance with the present
`invention.
`
`FIG. 12 is a diagram showing operation of a typical
`two-stage brake pedal in accordance with the present inven-
`tion.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Referring more specifically to the drawings, where like
`reference numerals denote like parts, for illustrative pur-
`poses the present invention is embodied in the apparatus and
`method generally depicted therein. It will be appreciated that
`the apparatus may vary as to configuration and as to details
`of the parts, and that the method of the invention may vary
`as to the steps and their sequence, without departing from
`the basic concepts as disclosed herein.
`In accordance with the present invention, a hybrid electric
`vehicle can enjoy the advantages of electric vehicles (e.g.,
`zero emissions, no idling, efficient energy usage) and con-
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`ventional gasoline vehicles (long range, widely available
`fuel). Referring first to FIG. 1 and FIG. 2, a hybrid power-
`train configuration 10 in accordance with the present inven-
`tion utilizes a large electric motor (EM) 12 and an auxiliary
`power unit (APU) 14 which is preferably a small internal
`combustion engine (ICE) integrated in a drive package.
`Alternatively, APU 14 may be an external combustion
`engine, such as a Sterling or steam engine, or a fuel cell
`which would be electrically connected to the batteries and
`throttle control. The EM 12, which typically has a power
`output of approximately four times that of ICE 14, may be
`any high power electric motor operating from batteries, such
`as a Unique Mobility SR180N brushless, permanent-magnet
`DC motor or the like with regenerative braking. The ICE 14
`may be any small gasoline engine such as a Briggs &
`Stratton Vanguard or the like. The EM 12 is typically
`coupled to a shaft 16 which transmits power to a multi-speed
`or continuously variable transmission 18 which in turn
`drives a shaft 20 which transmits power to the wheels 22.
`The transmission 18 may be manual or automatic and, if
`automatic, would not require a torque converter. Continu-
`ously variable transmissions may be employed as well. A
`conventional cable actuated shifting system (not shown)
`retrofitted to the transmission 18 produces a standard shift
`pattern if the transmission is manually controlled.
`Note that powertrain 10 shown in FIG. 2 is depicted in a
`generic form in FIG. 1, applicable to both series and parallel
`hybrids. In a parallel hybrid configuration, ICE 14 would be
`coupled to EM 12 via an electromagnetic clutch 24 or the
`like. In a series hybrid configuration, ICE 14 would not be
`coupled to EM 12 but, instead, would drive a generator 26
`which would in turn provide electric power to drive EM 12
`but would not charge batteries 28 when using a charge
`depletion control scheme. In either configuration, a control-
`ler 30 is used to control the speed and torque of the EM 12.
`In the parallel hybrid configuration, the electromagnetic
`clutch 24 is typically a Warner SF825 or the like coupled to
`intermediate shafts 32a, 32b, and is used to engage and
`disengage the ICE 14 from the drivetrain.
`If specially
`designed, EM 12 could run at the same speed as the ICE 14
`and thus could be in line with the transmission 18 and the
`
`ICE 14 as shown in FIG. 1. Alternatively, a belt 34, such as
`a 36-mm Kevlar Gates Poly Chain GT belt or the like can be
`used to connect the EM 12 to the intermediate shaft 32b in
`
`a configuration as shown in FIG. 2. By using a reduction
`ratio of 1.56:1 or the like, the rpm range of the EM 12 is
`matched to that of the ICE 14. Either way, the EM 12 is
`always coupled to the drivetrain. This allows the regenera-
`tive braking capability of the EM 12 to be available on all
`modes, so as to load the drivetrain and produce electricity
`when desired. The regenerative braking capability of EM 12
`is activated when the brake pedal is slightly depressed.
`As indicated above, the EM 12 can be a Unique Mobility
`SR180N electric motor or the like, which is a permanent-
`magnet, brushless direct current electric motor. An AC
`induction motor or similar traction motor may also be used.
`The charge-depletion parallel hybrid design requires that
`the ICE 14 be sized to maintain the vehicle load require-
`ments at level road legal highway cruising speeds (95—120
`km/hr in the US. or other legal speeds in various countries)
`as well as to provide the best fuel economy at these cruising
`speeds. Additionally, the ICE 14 must have low specific fuel
`consumption (high efficiency) and emissions for all power
`levels. These requirements mandate careful selection of the
`ICE 14. An internal combustion engine can be made to
`operate most efficiently at wide open throttle; therefore, the
`power output of the ICE 14 must match the power required
`to maintain the vehicle at a desired highway cruising speed.
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`The ICE 14 was sized to power the vehicle for freeway
`cruise at 113 kph for in a specific example constructed. In
`typical city driving conditions, however, driving with the
`ICE 14 alone produces low performance. Additionally, the
`varying driving conditions inherent in city driving will cycle
`the engine and reduce efficiency. Emissions would increase
`and fuel efficiency would decrease.
`In order to improve performance in these conditions, the
`charge depletion control method of the present invention
`was developed by monitoring vehicle speed and depth of
`discharge (DOD) of the battery, and controlling the EM 12
`and ICE 14 as a function thereof. The invention provides for
`operating the hybrid powertrain in a zero emissions vehicle
`(ZEV) mode and in a hybrid electric vehicle (HEV) mode.
`In the ZEV mode, the electric motor provides all driving
`power while the internal combustion engine is uncoupled
`and turned off. Typically, the vehicle can be driven in all
`driving conditions until the batteries reach a state of approxi-
`mately 90% DOD. The usable battery charge corresponds to
`a ZEV range of approximately 120—160 km.
`Referring to FIG. 3, a general flow diagram of the control
`method is shown. At step 100, the EM 12 is turned on to
`“launch” or start the vehicle and the vehicle operates in a
`ZEV mode. At steps 110 and 120, the vehicle speed and
`battery depth of discharged are sensed, respectively. At step
`130 a determination is made as to whether there is less than
`
`a low predetermined value, such as approximately 10%,
`charge left. If the depth of discharge is greater than the
`predetermine value, such as 90%, then an emergency warn-
`ing light is activated at step 140 so that the driver can take
`appropriate emergency measures to recharge the batteries or
`continue to operate the vehicle at degraded performance. For
`example, the driver can stop the vehicle, put the transmis-
`sion in neutral, push the accelerator and brake pedals
`simultaneously, and run the ICE 14 at high rpm for several
`minutes. This will partially charge the batteries and allow the
`vehicle to “limp” home for a complete recharging. Of
`course, the driver can simply continue home with lower
`acceleration capability if desired.
`At step 150 the vehicle speed and battery depth of
`discharge are compared with a control curve and, if those
`parameters exceed a predetermined threshold, the ICE 14 is
`brought on line by engaging the clutch at step 170 and
`turning the engine on at step. 180. Otherwise, the ICE 14
`remains off line and the vehicle continues to operate in a
`ZEV mode at step 160. Once the ICE 14 is operating, the EM
`12 is available for supplemental use. If ICE 14 is operating
`at wide open throttle and a call for acceleration or other
`additional power demand is sensed at step 190, then at step
`200 EM 12 is used to supply additional power such as for
`boost and control of the vehicle; for example, when the
`vehicle is accelerating or climbing a hill. If ICE 14 is
`operating at low power and the brake pedal is depressed for
`deceleration at step 210, then at step 220 the EM 12 is
`operated in a regeneration mode and the ICE clutch is
`opened. In this mode, the EM 12 loads the vehicle power-
`train to assist in slowing the vehicle, and generates electric-
`ity which will provide a charge to the batteries. If desired,
`during deceleration or braking the ICE 14 could be taken off
`line and turned off by decoupling the clutch and cutting of
`the flow of fuel. As can be seen,
`the process otherwise
`returns to step 110 from step 210.
`Referring also to FIG. 4, a preferred control policy used
`for coordinating the operation of the EM 12 and the ICE 14
`in step 150 of FIG. 3 are graphically shown. The area below
`the “on” threshold curve 250 is where the vehicle operates
`in a ZEV mode, with the EM 12 turned on and the ICE 14
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`decoupled and turned off. The area above the “on” threshold
`curve 250 is where the vehicle operates in a HEV mode with
`the ICE 14 coupled and turned on, and with the EM 12 being
`used only for accelerating, climbing hills and regenerative
`braking.
`In accordance with the control policy shown in FIG. 4, as
`long as the battery DOD is less than the hybrid integration
`cross-over point 260 of approximately 50% and the vehicle
`speed is less than the maximum speed threshold 270 of
`approximately 113 kph to 120 kph,
`then the EM 12 is
`operated alone. This is the range of speeds typically encoun-
`tered in city driving.
`Therefore,
`the vehicle operates as a ZEV. When the
`vehicle is operating at speeds in excess of approximately 113
`kph to 120 kph, which corresponds to freeway driving, the
`ICE 14 is turned on and the EM 12 is used only for
`accelerating, climbing hills, and regenerative braking.
`However, once the DOD exceeds approximately 50%, the
`ICE 14 is brought online at varying speeds as a function of
`DOD; that is, as the DOD increases, the speed at which the
`ICE 14 is brought online decreases in order to increase
`overall range. Therefore, the ICE 14 is not turned on unless
`the vehicle speed exceeds approximately 113 kph or unless
`the batteries are approximately 50% depleted. Then it is
`brought on according to the batteries’ DOD. After the ICE
`14 is turned on and vehicle is operating in a HEV mode, if
`the vehicle speed/depth of discharge parameters fall below
`the “off” threshold curve 280, the ICE 14 is decoupled and
`turned off. Then, since the EM 12 is still online, the vehicle
`again operates in a ZEV mode. The control band between the
`“on” threshold curve 250 and the “off” threshold curve 280
`
`prevents undesirable or excessive cycling of the ICE 14 due
`to fluctuations in sensed speed and depth of discharge. As an
`alternative to separate “on” and “off” thresholds, a single
`threshold could be used in combination with a time delay
`between the “on” and “off” modes to prevent frequent
`cycling. Both techniques may also be used.
`In a typical vehicle employing the present invention, the
`50% depletion point of the batteries should occur at approxi-
`mately 115 km of city driving. If a driver is on a freeway and
`exceeds 113 k