PROVISIONAL PATENT APPLICATION
`
`of
`
`ALEX J. SEVERINSKY
`
`and
`
`THEODORE LOUCKES
`
`for
`
`HYBRID VEHICLES INCORPORATING TURBOCHARGERS
`
`Field of the Invention
`
`This application relates to improvements in hybrid vehicles,
`
`that is, vehicles in which both an internal combustion engine and
`
`5
`
`one or more electric motors are provided to supply torque to the
`
`driving wheels of
`
`the vehicle,
`
`and wherein turbocharging is
`
`
`
`
`employed under certain circumstances.
`
`Background of the Invention
`
`This application discloses a number of improvements over and
`
`enhancements
`
`to the hybrid vehicles disclosed in U.S. patent
`
`5,343,970 (the
`
`"'970 patent")
`
`to one of the present
`
`inventors,
`
`which is incorporated herein by this reference. Where differences
`
`are not mentioned, it is to be understood that the specifics of the
`
`vehicle design shown in the '970 patent are applicable to the
`
`vehicles shown herein as well. Discussion of
`
`the '970 patent
`
`herein is not to be construed to limit the scope of its claims.
`
`Generally speaking, the '970 patent discloses hybrid vehicles
`
`wherein a controllable torque transfer unit is provided capable of
`
`20
`
`transferring torque between an internal combustion engine,
`
`an
`
`electric motor, and the drive wheels of the vehicle.
`
`The direction
`
`of torque transfer is controlled by a microprocessor responsive to
`
`the mode of operation of the vehicle,
`
`to provide highly efficient
`
`operation over a wide variety of operating conditions, and while
`
`25
`
`providing good performance.
`
`The flow of energy - either electrical energy stored in a
`
`substantial battery bank, or chemical energy stored as combustible
`
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`fuel - is similarly controlled by the microprocessor.
`
`For example,
`
`in low~speed city driving,
`
`the electric motor provides all torque
`
`needed responsive to energy flowing from the battery.
`
`In high—
`
`speed highway driving, where the internal-combustion engine can be
`
`5
`
`operated efficiently, it typically provides all torque; additional
`
`torque may be provided by the electric motor as needed for
`
`acceleration, hill-climbing, or passing.
`
`The electric motor is
`
`also used to start the internal-combustion engine,
`
`and can be
`
`operated as a generator by appropriate connection of its windings
`
`10
`
`by a solid—state, microprocessor-controlled inverter.
`
`For example,
`
`
`
`when the state of charge of
`
`the battery bank is relatively
`
`depleted, e.g., after a lengthy period of battery-only operation in
`
`city traffic,
`
`the internal combustion engine is started and drives
`
`the motor at between 50 and 100% of its maximum torque output, for
`
`efficient charging of the battery bank. Similarly, during braking
`
`or hill descent,
`
`the kinetic energy of the vehicle can be turned
`
`into stored electrical energy by regenerative braking.
`
`The hybrid drive train shown in the '970 patent has many
`
`advantages with respect to the prior art which are retained by the
`
`present
`
`invention.
`
`For example,
`
`the electric drive ‘motor
`
`is
`
`selected to be of relatively high power, specifically, equal to or
`
`greater than that of the internal combustion engine, and to have
`
`high torque output characteristics at low speeds; this allows the
`
`conventional multi-speed vehicle transmission to be eliminated. As
`
`compared to the prior art,
`
`the battery bank, motor/generator, and
`
`associated power circuitry are operated at relatively high voltage
`
`and relatively low current,
`
`reducing losses due to resistive
`
`heating and simplifying component selection and connection.
`
`The present provisional patent application also represents
`
`30
`
`further
`
`improvements
`
`over
`
`the hybrid vehicle described in
`
`Provisional Application Serial Number 60/100,095, filed September
`
`1998
`14,
`reference.
`
`(the "'095 application"), also incorporated herein by
`
`35
`
`Objects of the Invention
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`It is an object of the present invention to provide further
`
`improvements over the hybrid vehicles shown in the '970 patent and
`
`the '095 application.
`
`It is a more specific object of
`
`the present
`
`invention to
`
`5
`
`provide a hybrid drive system for vehicles that does not require
`
`the controllable torque-transfer unit shown in the '970 patent,
`
`while providing the functional advantages of the hybrid vehicles
`
`shown in the '970 patent and the '095 application,
`
`together with
`
`further improvements.
`
`10
`
`other aspects of and improvements provided by the present
`invention will appear below.
`
`Summa
`
`o
`
`the
`
`vention
`
`According to the invention of
`
`the '095 application,
`
`the
`
`controllable ‘torque-transfer' unit.
`shown.
`in ‘the
`'970 patent
`is
`eliminated by replacing the single electric motor shown therein by
`two separate motors, both operable as generators when appropriate,
`
`connected by a
`
`functionally-conventional clutch or mechanical
`
`interlock operated by
`
`the microprocessor
`
`responsive
`
`to the
`
`vehicle's mode of operation and to input commands provided by the
`
`operator of the vehicle.
`
`As
`
`in the '970 patent,
`
`an internal
`
`combustion engine is provided, sized to provide sufficient torque
`for the maximum cruising speed desired, and is used for battery
`charging' as needed.
`According to the invention of
`the '095
`
`application,
`
`a
`
`relatively high-powered
`
`"traction" motor
`
`is
`
`
`
`connected directly to the output shaft of the vehicle; the traction
`
`in low-speed
`the vehicle
`to propel
`torque
`motor provides
`situations, and provides additional torque when required, e.g., for
`acceleration, passing, or hill-climbing during high-speed driving.
`A relatively low-powered starting motor is also provided, and can
`
`be used to provide torque propelling the vehicle when needed. This
`
`second motor
`
`is connected directly to the internal combustion
`
`engine for starting the engine. Unlike a conventional starter
`
`motor, which rotates an internal combustion engine at low speed (60
`-100 rpm) for starting, necessitating provision of a rich fuel/air
`
`30
`
`35
`
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`mixture for starting,
`
`the starter motor according to the invention
`
`spins the engine at relatively high speeds (300 - 1500 rpm)
`
`for
`
`starting;
`
`this
`
`allows
`
`starting the
`
`engine with
`
`a
`
`near—
`
`stoichiometric mixture,
`
`significantly
`
`reducing
`
`undesirable
`
`5
`
`emissions and improving fuel economy at start-up.
`
`As noted,
`
`the two motors are separated by a functionally—
`
`conventional clutch, that is, a clutch which either joins the two
`
`motors together for rotation at the same speed, or separates them
`
`completely.
`
`As the motor shafts can be controlled to rotate at
`
`10
`
`essentially the same speed when the clutch is engaged,
`
`the clutch
`
`
`
`need not
`
`allow for
`
`significant
`
`slipping before
`
`engagement.
`
`Accordingly,
`
`a friction clutch, as normally provided for
`
`road
`
`vehicles, may not be
`
`required,
`
`and a
`
`less-expensive simple
`
`mechanical interlock may alternatively be employed.
`
`Engagement of
`
`the clutch is controlled by the microprocessor, e.g., controlling
`
`a hydraulic actuator, responsive to the state of operation of the
`
`vehicle and the current operator input.
`
`For example, during low-speed operation,
`
`the clutch will be
`
`disengaged, so that the traction motor is disconnected from the
`
`engine;
`
`the vehicle is then operated as a simple electric car,
`
`i.e., power
`
`is drawn from the battery bank and supplied to the
`
`traction motor.
`
`If the batteries become depleted,
`
`the starter
`
`motor is used to start the internal combustion engine, which then
`
`runs at relatively high torque output (e.g.,
`
`between about 50 -
`
`100% of its maximum torque),
`
`for efficient use of fuel, and the
`
`starting motor is operated as a high-output generator to recharge
`
`the kmttery bank.
`
`If the operator calls for more power
`
`than
`
`available from the traction motor alone, e.g.,
`
`in accelerating onto
`
`a highway, the starter motor starts the internal combustion engine,
`
`30
`
`and the clutch is engaged, so that the engine and starter motor can
`
`provide additional torque. The engine is sized so that it provides
`
`sufficient power
`
`to maintain a suitable highway cruising speed
`
`while being operated in a
`
`torque range providing good fuel
`
`efficiency;
`
`if additional power is then needed, e.g.,
`
`for hill—
`
`35
`
`climbing or passing,
`
`the traction and/or starter motors can be
`
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`engaged as needed.
`
`Both motors can be operated as generators,
`
`e.g.,
`
`to transform the vehicle's kinetic energy ito electrical
`
`power during descent or deceleration.
`
`In each of these aspects of the operation of the vehicle, and
`
`5
`
`as
`
`in ‘the
`
`'970 patent,
`
`the. operator of
`
`'the ‘vehicle need. not
`
`consider the hybrid nature of the vehicle during its operation, but
`
`simply provides control inputs by operation of the accelerator and
`
`brake pedals.
`
`The microprocessor determines the proper state of
`
`operation of
`
`the vehicle based on these and other
`
`inputs and
`
`10
`
`controls
`
`the various
`
`components of
`
`the hybrid drive train
`
`accordingly.
`
`According to the present
`
`invention,
`
`the engine is further
`
`provided with
`
`a
`
`turbocharger,
`
`also
`
`controlled
`
`by
`
`the
`
`microprocessor,
`
`and operated only
`
`under
`
`extended high-load
`
`conditions.
`
`In low-speed driving,
`
`the turbocharger is bypassed and
`
`is inactive, so that the vehicle is operated as in the prior '095
`
`application; similarly, when the torque provided by the engine is
`
`inadequate for short-term high loads, such as during overtaking on
`
`the highway, the traction motor is employed to propel the vehicle.
`
`The second starting motor may also be employed to provide torque as
`
`needed. However,
`
`according to the present
`
`invention, when
`
`conditions demand production of high torque for extended periods,
`
`for example, when towing a trailer, climbing a long hill, or
`
`driving at sustained high speed,
`
`the microprocessor activates the
`
`turbocharger, so that additional torque is produced by the internal
`
`
`
`combustion engine when needed.
`
`More
`
`specifically,
`
`in
`
`the
`
`'095
`
`application,
`
`during
`
`substantially steady-state
`
`operation,
`
`e.g.,
`
`during
`
`highway
`
`cruising, the control system operates the engine at varying torque
`
`30
`
`output levels, responsive to the operator's commands.
`
`The range of
`
`permissible engine torque output levels is constrained to the range
`
`in which the engine provides good fuel efficiency. Where the
`
`vehicle's torque requirements exceed the engine’s maximum efficient
`
`torque output, e.g., during passing or hill-climbing, one or both
`
`35
`
`of the electric motors are energized to provide additional torque;
`
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`where the vehicle's torque requirements are less than the minimum
`
`torque efficiently provided by the engine, e.g., during coasting,
`
`on downhills or during braking,
`
`the excess engine torque is used to
`
`charge the batteries.
`
`Regenerative charging may be performed
`
`5
`
`simultaneously, as torque from the engine and the vehicle's kinetic
`
`energy both drive either or both motors in generator mode.
`
`The
`
`rate of change of torque output by the engine may be controlled in
`
`accordance with the batteries' state of charge.
`
`According to the present
`
`invention,
`
`the above control
`
`10
`
`strategy is retained and employed under substantially all "normal"
`
`
`
`driving conditions; addition of a turbocharger controlled by the
`
`microprocessor according to the invention allows additional control
`
`flexibility. More specifically, when conditions demand
`
`power in
`
`excess of the engine's normally-aspirated maximum output for a
`
`relatively long period of time, e.g., for climbing long hills, for
`
`towing, or when driving at high speed,
`
`the turbocharger, which is
`
`normally bypassed and thus inactive,
`
`is energized by supply of the
`
`engine's exhaust gas stream.
`
`The engine then produces additional
`
`torque as required.
`
`If power
`
`in excess of the engine's normal
`
`capacity is required for a shorter period of
`
`time, e.g., when
`
`passing, at
`
`least
`
`the traction motor, or both of
`
`the electric
`
`motors, are energized by power from the battery.
`
`As compared to the turbochargers in normal use, which are
`
`constantly active,
`
`the turbocharger according to the present
`
`invention is used only when needed, that
`
`is, as noted, only when
`
`torque in excess of
`
`that available from the engine when
`
`in
`
`"normally—aspirated" mode is required for a relatively long period
`
`of
`
`time.
`
`This allows both the engine and turbocharger to be
`
`designed 113 meet relatively well-defined objectives, providing
`further efficiency in use of fuel. Furthermore, because according
`
`30
`
`to the invention the turbocharger is employed in a hybrid vehicle
`
`having one or more electric motors available to provide additional
`
`torque substantially immediately upon demand,
`
`the vehicle overall
`
`does
`
`not
`
`exhibit
`
`the
`
`slow response
`
`time
`
`of
`
`conventional
`
`35
`
`turbocharged vehicles.
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`In a further refinement,
`
`the amount of time during which the
`
`motors will be used to supply torque in excess of that availble
`
`from the engine in normally-aspirated mode before the turbocharger
`is activated is controlled responsive to the state of charge of the
`vehicle battery bank.
`
`Brief Description of the Drawings
`
`The invention will be better understood if reference is made
`
`to the accompanying drawings,
`
`in which:
`
`Fig. 1 shows a schematic diagram of the principal components
`of the hybrid vehicle drive system according to the invention;
`Fig. 2 is a diagram in which engine torque is plotted against
`engine speed for
`a
`typical engine in normally—aspirated and
`turbocharged modes of operation, and also shows typical road loads
`
`encountered;
`
`Fig.
`3 is a diagram illustrating differing modes of vehicle
`powertrain operation, plotted on
`a
`three dimensional chart,
`illustrating that the mode of vehicle operation is a function of
`
`the state of charge of the battery bank,
`
`the instantaneous road
`
`load, and time; and
`
`Fig. 4 is a timing diagram showing road load, engine torque
`output,
`the state of charge of
`the battery bank,
`and engine
`operation in normally-aspirated and turbocharged modes of operation
`as functions of time,
`thus illustrating a typical control strategy
`employed during
`low-speed city driving, highway cruising,
`and
`extended high-load driving.
`
`5
`
`10
`
`
`
`Description of the Preferred Embodiments
`
`As
`indicated above,
`this application discloses certain
`modifications,
`improvements,
`and
`enhancements of
`the hybrid
`vehicles shown in U.s. patent 5,343,970 (the
`"'970 patent") to one
`of
`the present
`inventors, which is incorporated herein by this
`reference; where not otherwise stated,
`the design of the vehicle of
`the present invention is similar to that shown in the '970 patent.
`Components
`commonly numbered in this application and the '970
`
`30
`
`35
`
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`patent are functionally similar in the corresponding systems, with
`
`detail differences as noted.
`
`The
`
`advantages of the system shown
`
`in the ‘970 patent with respect to the prior art are provided by
`
`that of the present invention, with further improvements provided
`
`5
`
`by the latter, as detailed herein.
`
`The present provisional patent
`
`application also represents further improvements over the hybrid
`
`vehicle described in
`
`Provisional Application
`
`Serial Number
`
`60/100,095, filed September 14, 1998 (the "'095 application"), also
`
`incorporated herein by reference.
`
`10
`
`As shown in the '970 patent with reference to Figs.
`
`1 and 2
`
`thereof, typical modern automobiles operate at very low efficiency,
`
`due principally to the fact that internal combustion engines are
`
`very inefficient except when operating at near peak torque output;
`
`this condition is only rarely met.
`
`(The same is true,
`
`to greater
`
`or
`
`lesser degree, of other
`
`road. vehicles powered. by internal
`
`combustion engines.)
`
`According to an important aspect of
`
`the
`
`invention of the '970 patent, substantially improved efficiency is
`
`afforded by operating the internal combustion engine only at
`
`relatively high torque output levels,
`
`typically at least 35% and
`
`preferably at least 50% of peak torque. When the vehicle operating
`
`conditions require torque of this appoximate magnitude,
`
`the engine
`
`is used to propel the vehicle; when less torque is required,
`
`an
`
`electric motor powered by electrical energy stored in a substantial
`
`battery bank drives the vehicle; when more power is required than
`
`provided by either the engine or the motor, both are operated
`
`simultaneously.
`
`The same advantages are provided by the system of
`
`the present invention, with further improvements and enhancements
`
`described in detail below.
`
`
`
`In the system of the '970 patent,
`
`torque from either or both
`
`30
`
`the engine and motor is transferred to the drive wheels of the
`
`vehicle by a controllable torque-transfer unit.
`
`This unit also
`
`allows torque to be transferred between the motor and engine, for
`
`starting the engine,
`
`and between the wheels
`
`and motor,
`
`for
`
`regenerative battery charging during deceleration of the vehicle.
`
`35
`
`This unit, while entirely practical, comprises gears for power
`
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`transfer, which are inevitably a source of audible noise and
`
`frictional
`
`losses.
`
`According to the present
`
`invention,
`
`the
`
`controllable torque-transfer unit
`
`is eliminated.
`
`Instead,
`
`two
`
`electric motors are provided,
`
`each separately controlled by a
`
`5
`
`microprocessor controller
`
`responsive to operator
`
`commands
`
`and
`
`sensed operating conditions.
`
`As shown in Fig.
`
`1 of the present application, and as also
`
`shown in the '095 application, a traction motor 25 is connected
`
`directly to the vehicle differential 32, and thence to the road
`
`10
`
`wheels 34.
`
`A starting motor 21 is connected directly to the
`
`internal combustion engine 40. The motors 21 and 25 are functional
`
`as motors or generators by appropriate operation of corresponding
`
`inverter/charger units 23 and 27, respectively. The two motors are
`
`
`
`controllably connected for
`
`torque transfer
`
`by
`
`a clutch 51,
`
`conventional
`
`in the sense that it is either engaged, wherein the
`
`shafts of motors 21 and 25 are connected and rotate together, or
`
`disengaged, wherein the
`
`shafts may
`
`rotate separately.
`
`(The
`
`respective positions of motor 21 and engine 40 with respect
`
`to
`
`clutch 51 could be reversed as compared to their positions in Figs.
`
`1 and 2 without affecting the function of the system, although as
`
`engine 40 would then require torque transmitting connection at both
`
`ends of its crankshaft,
`
`some additional complexity would result.)
`
`The clutch 51 is operated by microprocessor 48, e.g.,
`
`through a
`
`known hydraulic actuator 53,
`
`together with the other components of
`
`the system,
`
`in accordance with the operational state of the vehicle
`
`and the operator's input commands.
`
`As in the case of the hybrid vehicle system shown in the '970
`
`patent, and as indicated above,
`
`the vehicle of the invention is
`
`operated in different modes depending on the torque required,
`
`the
`
`30
`
`state of charge of
`
`the batteries,
`
`and other variables.
`
`For
`
`example, during low-speed operation, such as in city traffic, the
`
`vehicle is operated as a simple electric car, where all power is
`
`provided to road wheels 34 by traction motor 25; engine 40 is run
`
`only as needed to charge battery bank 22.
`
`(In this connection,
`
`35
`
`essentially conventional
`
`lead-acid batteries
`
`are
`
`currently
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`preferred for battery bank 22, since the infrastructure to provide
`
`and dispose of these batteries is already in place; that is,
`
`lead—
`
`acid batteries are widely available, readily recycled, and so on.
`
`More advanced batteries may be used if and when they become widely
`
`5
`
`available and economically competitive.) Under these circumstances,
`
`the charging current is provided by starting motor 21, operated as
`
`a generator by appropriate operation of
`
`inverter/charger 23.
`
`Accordingly, clutch 51 is disengaged, so that
`
`the road speed of
`
`the vehicle is independent of the speed of engine 40; engine 40 can
`
`10
`
`thus be operated at high torque,
`
`for
`
`fuel efficiency.
`
`The
`
`operating modes of
`
`the vehicle of
`
`the invention are further
`
`discussed below.
`
`
`
`As
`
`shown in further detail
`
`in the '095 application,
`
`the
`
`microprocessor
`
`48
`
`is provided. with signals indicative of
`
`the
`
`rotational speeds of shafts 15 and 16, and controls operation of
`
`engine 40, motor 21, and motor 25 as necessary to ensure that the
`
`shafts are rotating at substantially the same speed before engaging
`
`clutch 51; therefore, clutch 51 need not be an ordinary automotive
`
`friction clutch (as illustrated schematically in Fig. 1), provided
`
`to allow extensive relative slipping before the shafts are fully
`
`engaged. More particularly, as slipping of
`
`the clutch is not
`
`required to propel the vehicle initially from rest, as is the case
`
`in conventional vehicles, clutch 51 need not allow for extensive
`
`slipping when being engaged;
`
`in some cases it may be satisfactory
`
`to provide
`
`clutch 51
`
`as
`
`a
`
`simple
`
`self-aligning mechanical
`
`interlock, wherein positive mechanical connection is made between
`
`the shafts 15 and 16 upon engagement.
`
`Such a mechanical interlock
`
`is much simpler and less expensive than a friction clutch.
`
`Additional signals input to microprocessor 48 include signals
`
`30
`
`indicative of the state of charge of the battery bank 22, and
`
`operator input commands,
`
`typically acceleration, direction, and
`
`deceleration commands.
`
`The operator input commands may be provided
`
`to microprocessor
`
`48
`
`by position-sensing encoders
`
`71
`
`and 72
`
`providing signals to microprocessor 48 over lines 67 and 68 upon
`
`35
`
`motion of accelerator
`
`and brake pedals
`
`69
`
`and 70
`
`(Fig.
`
`1)
`
`10
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`respectively. The microprocessor monitors the rate at which the
`
`operator depresses pedals 69 and 70 as well as the degree to which
`
`pedals 69 and 70 are depressed. The microprocessor uses this
`
`information,
`
`and
`
`additional
`
`information
`
`to make
`
`decisions
`
`5
`
`concerning the proper operation of the vehicle according to the
`invention.
`
`suppose the vehicle has been operated in city
`For example,
`time,
`traffic for
`some
`that
`is,
`under battery power only.
`Typically the operator will only depress the accelerator slightly
`to drive in traffic.
`If the operator then depresses accelerator
`
`10
`
`
`
`pedal 69 significantly farther than he or she had, for example,
`
`the
`
`prior few times acceleration was required, this may be taken as an
`
`indication that more torque will be required, and so starting motor
`
`21 will be used to start engine 40.
`
`If the operator does not
`
`depress pedal 69 rapidly, a heater 63 will be used to preheat a
`
`catalytic converter 64 provided in the engine exhaust system 62, so
`
`that any fuel that is not combusted during starting of the engine
`
`40 will be catalytically combusted; however,
`
`if the operator
`
`depresses the pedal 69 rapidly,
`
`indicating an immediate need for
`
`full acceleration,
`
`the traction and starting motors may be driven
`
`beyond their normal rated power briefly, so that adequate power is
`
`provided (as may be necessary for safe operation) while the
`
`catalytic converter is heated.
`
`Copending
`
`application Ser. No.
`
`incorporated
`(Attorney's Docket No. PAICE993),
`filed
`herein by reference,
`provides full details of the preheating of
`the catalytic converter.
`
`Similarly,
`
`if the operator depresses the brake pedal 70
`
`relatively gently, all braking may be provided by regenerative
`
`30
`
`charging of the batteries; if the operator instead presses rapidly
`on brake pedal 70, both mechanical and regenerative braking will be
`provided. Mechanical braking is also provided on long downhills
`
`when the batteries are fully charged.
`
`In addition to engine and starting motor speed and traction
`
`motor speed, battery voltage, battery charge level, and ambient
`
`35
`
`temperature are also either monitored directly or derived from
`
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`monitored variables.
`
`In response to these inputs, and the operator
`
`inputs, microprocessor controller 48 operates a control program and
`
`provides output control signals to engine 40, by commands provided
`
`to its electronic fuel
`
`injection unit
`
`(EFI)
`
`56 and electronic
`
`5
`
`engine management system (EEM) 55, and to starting motor 21, clutch
`
`51, traction motor 25,
`
`inverter/charger units 23 and 27, and other
`
`components.
`
`As
`
`indicated,
`
`the control
`
`signals provided to
`
`inverter/chargers 23 and 27 allow control of the current to be
`
`provided, of direction of rotation of
`
`the motor 25, allowing
`
`10
`
`reversing of the vehicle, as well as control of operation of the
`
`
`
`motors 21 and 25 in motor or generator mode.
`
`Inverter/chargers 23
`
`and 27 are separately controlled to allow independent operation of
`
`motors 21 and 25.
`
`See the '095 application for further details.
`
`other elements of the system as illustrated in Fig.
`
`l are
`
`generally as discussed in the '970 patent and '095 application,
`
`including supply of fuel 36 from tank 38, air filter 60,
`throttle 61.
`
`and
`
`As
`
`in the '970 patent, engine 40 is sized so that its full
`
`torque output is adequate to drive the vehicle in a desired range
`
`of cruising speeds,
`
`so that
`
`the engine is operated at high
`
`efficiency during highway cruising.
`
`During’ highway cruising,
`
`therefore, clutch 51 is engaged; engine 40 then drives road wheels
`
`34 through the shafts of motors 21 and 25.
`
`If extra power
`
`is
`
`needed, e.g., for acceleration or hill—climbing, either or both of
`
`motors 21 and 25 can be powered. Similarly, under deceleration,
`
`either or both of motors 21 and 25 are operated as generators,
`
`proving regenerative recharging of battery bank 22.
`
`According to the '095 application, when the microprocessor
`
`controller 48 detects an operator requirement for additional power,
`
`30
`
`such as during transition from slow-speed to highway operation, or
`
`by measuring the rate at which the operator depresses accelerator
`
`pedal 70, engine 40 is started using starter motor 21 and brought
`
`up to speed before, clutch 51 is engaged,
`
`to ensure a
`
`smooth
`
`transition. As cruising speed is reached, power to traction motor
`
`35
`
`25
`
`(and to starter motor 21,
`
`if also used to accelerate the
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`vehicle)
`
`is gradually reduced.
`
`Provision of
`
`the clutch 51 and
`
`separate starter motor 21, as compared to using the single traction
`
`motor
`
`to start engine 40 while simultaneously accelerating the
`
`vehicle as in the '970 patent, provides much simpler operation.
`
`5
`
`Provision of the clutch 51 and separate starter motor 21 also
`
`allows another important
`
`improvement to be provided according to
`
`the '095 application, namely starting engine 40 at high speed,
`
`e.g., between about 300 and 2000 rpm,
`
`as compared to the 60 - 100
`
`rpm starts conventionally' provided.
`
`High-rpm starting allows
`
`10
`
`significant reduction of the usual necessity of providing a fuel-
`
`rich fuel:air mixture to start engine 40,
`
`reducing emission of
`
`unburned fuel and improving fuel
`
`economy at
`
`start—up.
`
`More
`
`specifically,
`
`in conventional
`
`low-rpm starts, an extremely rich
`
`mixture must be provided to ensure that some fraction of the fuel
`
`
`
`
`
`is in the vapor phase;
`
`only fuel in the vapor phase can be ignited
`
`by a spark. At high starting speeds,
`
`turbulence in the combustion
`
`chamber is sufficient to ensure the presence of vapor, particularly
`
`if the fuel
`
`is atomized by high-pressure fuel
`
`injection, as is
`
`preferred, so that a near—stoichiometric mixture can be provided to
`
`engine 40 during the starting phase. As noted,
`
`the avoidance of
`
`rich mixtures at starting significantly reduces
`
`emission of
`
`unburned fuel - since most of the fuel provided to a conventional
`
`engine at starting is immediately exhausted unburnt - and provides
`
`some
`
`improvement
`
`in fuel efficiency.
`
`Further
`
`reduction in
`
`emissions are discussed in the '095 application,
`
`and copending
`
`application Ser. No.
`
`filed
`
`(Attorney's Docket No.
`
`PAICE993).
`
`As discussed in detail in the '095 application,
`
`the primary
`
`consideration in selecting the torque of starting motor 21 is that
`
`30
`
`it be capable of rotating the engine 40 at about 300 — 2000 rpm for
`
`starting, and that it be capable of accepting at least about 30% of
`
`the engine's maximum torque output when operated as a generator, so
`
`that the engine can be be efficiently employed when charging the
`
`battery bank during extended
`
`low-speed operation;
`
`the main
`
`35
`
`consideration in specification of the torque of engine 40 is that
`
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`5
`
`for highway cruising’ while being
`it provide sufficient. power
`operated at high efficiency, i.e., that its maximum power output be
`approximately equal to that required to maintain a range of desired
`cruising speeds; and the principal consideration defining the power
`required of
`the traction motor 25 is that it be sufficiently
`powerful to provide adequate acceleration in combination with the
`
`engine 40 and starting motor 21. Stated differently,
`the total
`power
`available provided by all
`of
`these
`torque-producing
`components should be at least equal to and preferably exceeds the
`
`10
`
`engines of
`combustion
`internal
`the
`power provided by
`peak
`conventional vehicles of similar intended use, both as measured at
`
`the wheels. Moreover, as set forth in the '970 patent,
`
`the total
`
`torque provided by motors 21 and 25 should be at least equal to
`that produced by engine 40;
`this is important
`is achieveing
`adequate low—speed performance
`in a vehicle not
`including a
`variable-ratio transmission.
`
`At
`
`the same time, motors 21 and 25 are also sized to be
`
`
`
`capable of recovering 65 - 90% of the vehicle's kinetic energy when
`operated as generators
`in the regenerative braking mode.
`A
`, particularly high fraction of the vehicle's kinetic energy can be
`recovered during low-speed operation; as compared to high—speed
`operation, where air
`resistance and road friction consume
`a
`
`in low
`relatively large fraction of the total energy required,
`speed operation much energy is lost by conventional vehicles as
`
`heat released during braking.
`
`the following are typical
`Given the above considerations,
`power specifications for the engine 40, starting motor 21 and
`traction motor 25 of a 3000 pound vehicle having performance
`approximately equivalent to that of a "mid-size" sedan of United
`
`30
`
`States manufacture;
`it
`should be understood that
`in these
`specifications,
`reference is made
`to rated peak power of
`the
`various components,
`that
`is,
`the components are rated. at
`'the
`combination of torque and rpm yielding the maximum torque produced
`per unit time.
`
`35
`
`Engine 40: 40 to 50 horsepower at 6000 rpm
`
`14
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`Starting motor 21: 10 - 15 horsepower at approximately 1500
`rpm and higher speeds
`
`5
`
`Traction motor 25: 50 - 60 horsepower from 1500 to 6000 rpm.
`The same starting motor would be satisfactory for a larger,
`4000 pound sedan, but the engine would typically provide 70 — 90
`horsepower at 6000 rpm and the traction motor 75 - 100 horsepower.
`In both cases,
`the total
`rated power available from the
`electric motors should equal, and preferably exceeds,
`the maximum
`power available from the engine.
`
`10
`
`These components would provide acceleration much superior to
`that of
`typical
`similarly—sized automobiles of United States
`
`It will be apparent that these specifications may
`manufacture.
`vary over relatively wide ranges depending on the intended use of
`
`the vehicle of the invention, and should not be construed to limit
`
`the scope of the invention.
`
`in the preferred embodiment, both the
`indicated above,
`As
`starting and traction motors are AC induction motors, although
`other
`types may also be
`employed.
`These motors,
`and the
`inverter/chargers driving them, should be chosen and operated such
`that the motors have torque output characteristics varying as a
`function of rpm as illustrated in Fig. 14 of the '970 patent; that
`is,
`the motors should produce constant torque up to a base speed,
`typically 1500 - 2000 rpm, and should produce constant power at
`higher speeds.
`The ratio of the base to maximum speed can vary
`between about 3 to 1 and about 6 to 1.
`By comparison,
`the series-
`wound DC 'motors conventionally’ used as engine starter motors
`provide very high torque, but only at very low speeds; their torque
`output drops precipitously at higher speeds.
`Such conventional
`starter motors would be unsatisfactory in the present system.
`As noted, each of the torque—producing components (that is,
`engine 40 and starting and traction motors 21 and 25) preferably
`operate at
`the same speed,
`so that no gear—reduction units or
`similar he