Ulllted States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,842,534
`
`Frank
`
`[45] Date of Patent:
`
`Dec. 1, 1998
`
`US005842534A
`
`[54] CHARGE DEPLETION CONTROL METHOD
`AND APPARATUS FOR HYBRID POWERED
`VEHICLES
`
`76
`
`]
`
`[
`
`I
`
`: A d
`A. F
`k P.O. B
`nvemor Mgcgfy Califrggéis
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`i
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`2103 El
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`
`OX
`
`[21] Appl. No‘, 963,037
`
`[221
`
`Ffled:
`
`NOV‘ 3’ 1997
`Related U.S. Application Data
`
`[63] Continuation of Ser. No. 455,104, May 31, 1995, aban—
`doned.
`
`2494642
`4206360
`
`France .
`5/1982
`9/1993 Germany ~
`
`OTHER PUBLICATIONS
`
`“Renault launches NEXT, an interesting hybrid car”, Road
`& Track, pp. 47, 49, Aug. 1996.
`
`Woods.Gas—Electric Car, Instruction No. 80, Dyke’s Ency-
`clopedia, 1935.
`Frank et al., “Computer Simulation of the University of
`W’
`.Hb'd—El
`' Vh'l C
`” M 1973.
`ISC
`y H
`ecmc
`6 ,1C 6 ,0nCept ’
`, ay
`,
`,
`Volkswagen AG, “Golf with Diesel/Electric Hybriddrive”,
`undated
`
`Int. Cl.5 ....................................................... B60K 6/04
`......
`............................. 180/16856fi6;5180/6655.24
`ie
`0
`earc
`................................ ..
`.
`,
`.
`,
`180/65.3, 65.4, 65.8; 318/587
`
`Ji'd:V:‘i“;\‘/‘lat
`Attorney) Agent) or Fl.rm_J0hn P. O,Bani0n
`[57]
`ABSTRACT
`
`Alcharge dCplCI10(I1l rnetllilod and apparatus foroperailing the
`e ectric motor an
`sma
`auxi iary power unit, suc
`as an
`internal combustion engine,
`in a hybrid electric vehicle
`separately or together depending upon the driving
`conditions. Operation of the electric motor and auxiliary
`power 111111. are coordinated so that the vehicle operates as
`zero emissions Vehicle (ZEV) or electric car at all speeds
`below a highway cruising threshold, unless the depth of
`discharge of the batteries exceeds a charge threshold in
`which case the vehicle operates in an HEV rnode. Further,
`the vehicle operates in an HEV mode at speeds above the
`-
`-
`-
`-
`cruising threshold. The batteries are depleted during opera-
`t.
`d
`t h
`d b th
`.1.
`.t
`t
`1°“. a“ are “O 9 “g?
`Y.
`C “X1 1aryP°W‘°'r.““1>‘°'X°‘°*P
`durmg emergencles 1“ Whlch C356 the bafierles are Only
`charged enough to provide a performance enhancement to
`the small auxiliary power unit.
`
`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 ....................... .. 180/65.2 X
`4,400,997
`8/1983 Fiala.
`4,533,011
`8/1985 Heidemeyef 6131- -
`4>697>660 10/1987 Wu 61 a1~ ~
`4921025
`5/1990 Elle“ ‘
`5,115,183
`5/1992 Kyoukane et al.
`.
`.
`6/1992 Nishida . . . . . . . . . .
`5,117,931
`6/1992 Scott
`. . . . . . . . . .
`5,125,469
`12/1992 Suzuki et al.
`5,172,006
`9/1994 severinsky .
`5,343,970
`FOREIGN PATENT DOCUMENTS
`
`
`
`. . . .. 180/65.2
`. . . .. 180/65.2
`...................... 180/65.2 X
`
`.............. .. 180/65.2 X
`
`2310238
`
`1/1977
`
`France .
`
`31 Claims, 5 Drawing Sheets
`
`[51]
`
`[56]
`
`
`
`1 4
`
`22
`
`
`
`
`
`
`
`
`MULTI—SPEED
`TRANSMISSION
`
` ENGINE
`:I
`
`
`
`DRIVE WHEELS
`
`III II
`
`26
`
`GENERATOR - - - - -
`
`28
`
`BATTERIES
`
`
`
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`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 2 0f5
`
`5,842,534
`
`12
`
`BRUSHES
`
`24
`
`
`
`
`TRANS—.
`MISSION "
`
`
`HI
`
`INTERNAL
`COMBUSTION
`ENGINE
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`14
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`FIG. — 4
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`

`
`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 4 0f5
`
`5,842,534
`
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`U.S. Patent
`
`Dec. 1,1998
`
`Sheet 5 0f5
`
`5,842,534
`
`FIG. - 6
`
`I
`
`,
`
`330 I
`,: CONTROL
`
`TORQUE
`
`ACCELERATOR PEDAL
`
`I
`
`TORQUE
`
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`
`5,842,534
`
`1
`CHARGE DEPLETION CONTROL METHOD
`AND APPARATUS FOR HYBRID POWERED
`VEHICLES
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of application 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 the relative opera-
`tion of the electric motor and an auxiliary power unit such
`as an internal combustion engine, fuel cell, or external
`combustion engine in a parallel or series hybrid powered
`vehicle for maximizing range and efficiency while minimiz-
`ing pollutants.
`2. Description of the Background Art
`A hybrid electric vehicle (HEV) is a vehicle with elec-
`tricity 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, or compressed natural gas 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 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.
`A series hybrid is the most common powertrain configu-
`ration choice among HEV designers due to its low emissions
`capability, fuel economy, and simple EM/ICE integration. A
`series hybrid has the capability to use the ICE to charge the
`batteries while driving. Ideally, the ICE is point-tuned to
`operate under constant load and speed at the point of lowest
`specific fuel consumption, which could produce low tailpipe
`emissions. The EM and ICE are only electrically connected,
`allowing each power source to be independently placed in
`the vehicle, further adding to the simplicity of a series
`hybrid. Series hybrids, however, suffer from inherent energy
`losses due to the many energy conversions required to
`convert chemical fuel energy to motive energy at the wheels.
`Thus, what
`is gained from engine efficiency is lost
`to
`electrical and/or electrochemical inefficiency.
`Aparallel hybrid on the other hand, using a properly-sized
`ICE to directly transmit torque to the drive wheels, can
`provide better overall efficiency than a series hybrid. The
`engine can be sized so that, at wide-open throttle, the ICE
`maintains steady-state highway speeds and operates at its
`peak efficiency.
`In addition,
`the ICE can be tuned for
`excellent fuel economy and low tailpipe emissions. Most
`parallel hybrid vehicles are configured with a large ICE,
`however, leading to poor fuel economy and high cost. The
`EM is selected for urban driving and acceleration, since the
`ICE may not 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. For
`
`10
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`2
`example, U.S. Pat. No. 5,343,970 discloses a hybrid vehicle
`where, at low speeds or in traffic, the EM alone is used to
`drive the vehicle. Under acceleration and during hill
`climbing, both the EM and ICE are used. At steady state
`highway cruising, only the ICE is used. The control system
`also senses battery charge and uses the ICE to charge the
`battery when necessary. U.S. Pat. No. 4,923,025 discloses a
`hybrid vehicle which operates on an EM until a predeter-
`mined cruising speed is reached. The ICE is then brought on
`line and the EM is turned off. U.S. Pat. No. 4,042,056
`discloses a hybrid vehicle which is powered by an EM
`except
`in circumstances where the battery charge is
`depleted, in which case an ICE is brought on line.
`None of the existing control schemes, however, integrate
`the operation of the EM and ICE in a hybrid vehicle in a way
`which maximizes efficiency and range while maintaining
`performance of the vehicle; that is, using a “charge deple-
`tion” control method in accordance with the present inven-
`tion. Conventional control schemes operate on the principle
`of sustaining the charge on the batteries, rather than deplet-
`ing the batteries.
`The foregoing patents refiect the state of the art of which
`the applicant is aware and are tendered with the view toward
`discharging applicant’s acknowledged duty of candor in
`disclosing information which may be pertinent in the exami-
`nation of this application.
`It
`is respectfully stipulated,
`however, that none of these patents teach or render obvious,
`singly or when considered in combination, applicant’s
`claimed invention.
`
`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. 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 efficiency. Typically, the vehicle can
`be driven in all driving conditions until the batteries reach a
`state of approximately 85% depth of discharge or more. 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 entire
`vehicle will satisfy the needs of over 99% of the drivers.
`The ICE in accordance with the present
`invention is
`typically very small (e.g., 0.016 kW/vehicle kg and is
`typically sized to power the vehicle for freeway cruise at
`speeds above approximately 113 kph for a range of 690 km
`or more. However, in typical city driving conditions, driving
`with the ICE alone produces less-than-desirable perfor-
`mance because of its small size. This is an important aspect
`of the invention since it encourages the driver to periodically
`charge the vehicle batteries at home. Additionally, the vary-
`ing driving conditions inherent in city driving will cycle the
`engine and reduce efficiency. Emissions would increase and
`fuel efficiency would decrease.
`In accordance with the present invention, as long as the
`battery depth of discharge is less than approximately 50%
`and the vehicle speed is less than approximately 113 kph,
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`3
`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
`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 approximately 50%, 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. 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.
`
`Control of vehicle speed is accomplished using a two-
`stage accelerator pedal. Approximately the first ‘/3 of pedal
`travel controls the throttle position of the ICE and the last 2/3
`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.
`
`the
`In accordance with the method of the invention,
`batteries are not charged by the ICE during operation 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 and the ICE was running, the batteries could be
`slightly charged by the ICE (e.g., 5%) 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 event, the ICE and EM would both
`be on line, and the ICE would drive the EM in a regenerative
`mode so as to charge 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 sustaining”
`hybrids which charge the batteries from the ICE. In this
`context, note that long range batteries (e.g., 130 to 160 km)
`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 efficiency.
`Another object of the invention is to provide a control
`system for a hybrid electric vehicle powertrain which can
`provide for ultra low emissions.
`
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`4
`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.
`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 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 the operation of a hybrid
`vehicle electric motor and internal combustion engine as
`function of vehicle speed and battery depth of discharge in
`accordance with the present invention.
`FIG. 5 is a block diagram of a charge depletion control
`system in accordance with the present invention.
`FIG. 6 is a diagram showing operation of a dual-mode
`accelerator pedal in accordance with the present invention.
`FIG. 7 is a diagram showing operation of a dual-mode
`brake pedal in accordance with the present invention.
`
`DESCRIPTION OF TIE PREFERRED
`EMBODIMENTS
`
`Referring more specifically to the drawings, for illustra-
`tive purposes 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-
`ventional gasoline vehicles (long range, widely available
`fuel). Referring first to FIG. 1, a hybrid powertrain configu-
`ration 10 in accordance with the present invention 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 approxi-
`mately four times that of ICE 14, may be any high power
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`5,842,534
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`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 transmis-
`sion 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
`convertor. Continuously variable transmissions may be
`employed as well. A conventional cable actuated shifting
`system (not shown) retrofitted to the transmission 18 pro-
`duces a standard shift pattern.
`Powertrain 10 shown in FIG. 1 is depicted in a generic
`form, 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. In either configuration, a controller 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
`
`10
`
`15
`
`20
`
`25
`
`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
`
`30
`
`a configuration as shown in FIG. 2. By using a reduction
`ratio of 1.5621 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 which pro-
`duces 32 kW continuous and 60 kW peak power. With that
`motor a Unique Mobility CR20-300 solid-state controller is
`preferably used to control speed and torque. The 200-volt
`controller has a current limit of 300 amperes providing up to
`60 kW intermittent power for the electric motor/controller
`pair. Note that a permanent-magnet brushless DC electric
`motor was chosen over an AC induction motor because of its
`
`superior power-to-weight and low speed characteristics. The
`CR20-300 controller also has a speed-sensitive regenerative
`braking function which can extend ZEV range by approxi-
`mately 10% during city driving.
`The charge-depletion parallel hybrid design requires that
`the ICE 14 be sized to maintain the vehicle load require-
`ments at highway cruising speeds (95—105 km/hr) as well as
`to provide the best
`fuel economy at cruising speeds.
`Additionally, the ICE 14 must have low specific fuel con-
`sumption and emissions. These requirements mandate care-
`ful 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. After comparing various engine
`characteristics,
`it was found that
`the 15 kW, 570 cc
`overhead-valve, two cylinder Briggs & Stratton Vanguard
`4-cycle engine was preferable for a prototype vehicle. To
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`further improve the performance of the stock internal com-
`bustion engine, several modifications were made. First, the
`fixed ignition timing and the carburetor of the stock engine
`were replaced by an electronic control unit (ECU) which
`governs ignition timing and fuel injection. The program-
`mable electronic control unit allowed for customizing the
`engine management scheme for the driving requirements of
`the HEV, and allowed the air-fuel ratio and spark timing to
`be custom-tailored to achieve low fuel consumption and low
`emissions in all ranges of engine operation.
`The ECU provides engine management by monitoring
`sensors attached to the ICE 14. An engine crankshaft posi-
`tion sensor enables the ECU to adjust spark timing dynami-
`cally. By varying the spark timing, an increase in both power
`and fuel economy were achieved. The ECU also monitors
`the engine for “knock and ping” or pre-detonation. Pre-
`detonation occurs when the fuel mixture does not burn
`
`resulting in lower
`smoothly but explodes prematurely,
`power output and possible engine failure. Aknock sensor is
`incorporated into the engine management system and the
`ECU retards the ignition timing to prevent knocking and
`pinging.
`A closed loop feedback electronic fuel injection system
`was the key to obtaining high fuel economy and low
`emissions. Using an oxygen sensor in the exhaust, the ECU
`monitors combustion and regulates the duration of the fuel
`injector pulses to maintain a stoichiometric air fuel
`ratio of 14.721. A stoichiometric AF ratio is important in
`reducing emissions and fuel consumption. The electronic
`controls for the engine were necessary to obtain the desired
`performance for the HEV.
`The compression ratio (CR) was increased to obtain a
`more complete combustion of the air-fuel mixture. The CR
`was increased from the stock 8.521 CR to 9.521. Compres-
`sion ratios higher than 9.521 caused knocking and pinging as
`well as excessive NOx emissions. NOx formation occurs
`
`more readily at the higher combustion temperatures caused
`by higher compression ratios. The combustion chamber
`inside the head was also reshaped to obtain optimal com-
`bustion.
`
`The complete powertrain described above, including the
`electric motor controller, weighs 133 kg and can produce
`179 N-m of torque. It has a maximum power input to the
`transaxle of 75 kW. Also, to improve the reliability of the
`drivetrain it was found desirable to redesign and remanu-
`facture some of the components for proper alignment and
`tighter tolerances. Further,
`the cooling of the drivetrain
`compartment was greatly improved, allowing for higher
`efficiencies and reliability to be realized by the electric
`motor and internal combustion engine.
`The ICE 14 was sized to power the vehicle for freeway
`cruise at 113 kph for 690 km using a 20.1 liter gasoline tank.
`In typical city driving conditions, however, driving with the
`ICE 14 alone produces less-than-desirable performance.
`Additionally, the varying driving conditions inherent in city
`driving will cycle the engine and reduce efficiency. Emis-
`sions would increase and fuel efficiency would decrease.
`In order to overcome these inefficiencies,
`the charge
`depletion control method of the present
`invention was
`developed to monitor vehicle speed and depth of discharge
`(DOD) of the battery, and to control 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
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`turned off. Typically, the vehicle can be driven in all driving
`conditions until the batteries reach a state of approximately
`100% DOD. The usable battery charge corresponds to a
`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
`
`approximately 10% charge left. If the depth of discharge is
`greater than 90%,
`then an emergency warning light
`is
`activated at step 140 so that the driver can take appropriate
`emergency measures to recharge the batteries. For example,
`the driver can stop the vehicle, put
`the transmission 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.
`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; for example,
`when the vehicle is accelerating or climbing a hill. If ICE 14
`is operating at closed throttle and the brake pedal
`is
`depressed for deceleration at step 210, then at step 220 the
`EM 12 is operated in a regeneration mode at step 230. In this
`mode, the EM 12 loads the vehicle powertrain to assist in
`slowing the vehicle, and generates electricity which will
`provide a charge to the batteries. If desired, during decel-
`eration or braking the ICE 14 could be taken off line and
`turned off by decoupling the clutch and cutting of the flow
`of fuel.
`
`Referring also to FIG. 4, the control parameters 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 is where the vehicle operates in a ZEV
`mode, with the EM 12 turned on and the ICE 14 decoupled
`and turned off. The area above the “on” threshold curve 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.
`As can be seen from FIG. 4, as long as the battery DOD
`is less than approximately 50% and the vehicle speed is less
`than approximately 113 kph, then the EM 12 is operated
`alone. This is the range of speeds typically encountered in
`city driving. Therefore, the vehicle operates as a ZEV. When
`the vehicle is operating at speeds in excess of approximately
`113 kph, which corresponds to freeway driving, the ICE 14
`is turned on and the ICE 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
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`speed/depth of discharge parameters fall below the “off”
`threshold curve, 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 and the “off” threshold curve 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.
`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 kph but stays below 120 kph (which is a speed
`where the ICE 14 alone will be insufficient to power the
`vehicle), the driver uses no battery electrical energy except
`when needed to pass someone or to climb a hill or mountain
`(a very small amount is used constantly since the EM 12 is
`always online). With the amount of energy storage in such
`a vehicle, a 3300 meter high mountain can be climbed at 115
`kph using the small gasoline engine and the large electric
`motor on highways constructed to current US standards.
`There should be energy left in the battery after such a climb
`to continue for some distance. When the vehicle is stopped
`for
`the driver or passengers to have lunch,
`it can be
`recharged, to top off the batteries if necessary or desired.
`This capability makes the configuration and control system
`of this invention generally applicable to the public and
`provides the vehicle a capability comparable to a conven-
`tional car. The difference, of course, is super fuel efficiency
`(e.g., 2.3 to 2.5 liters per 100 km) and Ultra Low Emission
`Vehicle (ULEV) capability. The fuel efficiency will be two
`to three times the economy of a conventional vehicle, while
`the performance will be equal or better.
`As indicated above, when driving in the city beyond
`approximately 50% percent DOD of the battery, the gasoline
`engine will come “on” at a lower speed depending on the
`DOD. This will extend the electric range for city driving to
`approximately 350 to 375 km. In order to drive this distance
`in the city, a driver would spend nine to ten hours behind the
`wheel. Less than 0.1 percent of the population would drive
`this far in the city. Of course, the control curve of FIG. 4 can
`be adjusted for the kind of driving done by most p