PROVISIONAL PATENT APPLICATION
`
`of
`
`ALEX J. SEVERINSKY
`
`for
`
`IMPROVEMENTS IN HYBRID VEHICLES
`
`Field of the Invention
`
`This application relates to improvements in hybrid vehicles,
`
`that is, vehicles in which both an internal combustion engine and
`one or more electric motors are provided to supply torque to the
`driving wheels of the vehicle.
`
`Background of the Invention
`
`This application discloses a number of improvements over and
`
`enhancements to the hybrid vehicles disclosed in the inventor's
`
`U.S. patent 5,343,970 (the
`
`"'970 patent"), 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.
`
`5:
`'
`
`
`
`Generally speaking,
`
`the '970 patent discloses hybrid vehicles
`
`wherein a controllable torque transfer unit is provided capable of
`
`transferring torque between an internal combustion. engine,
`
`an
`
`20
`
`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
`
`providing good performance.
`
`25
`
`The flow of energy - either electrical energy stored in a
`
`substantial battery bank, or chemical energy stored as combustible
`
`fuel - is similarly controlled by the microprocessor.
`
`For example,
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`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
`
`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
`
`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
`
`aspects and 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.
`
`Objects of the Invention
`
`It is an object of the present
`invention to provide further
`improvements over the hybrid vehicle shown in the '970 patent.
`It is a more specific object of
`the present
`invention to
`provide a hybrid drive system for vehicles that does not require
`the controllable torque-transfer unit shown in the '970 patent,
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`while providing the functional advantages of the hybrid vehicle
`
`shown in the '970 patent.
`
`Other aspects of and improvements provided by the present
`
`invention will appear below.
`
`Summary of the Invention
`
`According to the present invention,
`
`the controllable torque-
`
`transfer unit shown in the '970 patent is eliminated by replacing
`
`the single electric motor shown therein by two separate motors,
`
`10
`
`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,
`
` vehicle when needed. This second motor is connected directly to
`
`sized to provide sufficient torque for the maximum cruising speed
`
`desired, and is used for battery charging as needed.
`
`A relatively
`
`high-powered "traction" motor is connected directly to the output
`
`shaft of the vehicle; the traction motor provides torque to propel
`
`the vehicle in low—speed 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
`
`the internal combustion engine for starting the engine. Unlike a
`
`25
`
`conventional starter motor, which rotates an internal combustion
`
`engine at low speed for starting, necessitating provision of a rich
`
`the starter motor according to the
`fuel/air mixture for starting,
`invention spins the engine at relatively high speeds for starting;
`this allows starting the engine with a near-stoichiometric mixture,
`significantly reducing undesirable emissions and improving fuel
`
`30
`
`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
`
`35
`
`completely.
`
`As the motor shafts can be controlled to rotate at
`
`3
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`essentially the same speed when the clutch is engaged,
`
`the clutch
`
`need not allow for slip therebetween. Accordingly,
`a friction
`clutch, as normally provided for road vehicles,
`is not required,
`and a less-expensive simple mechanical interlock can alternatively
`be employed.
`Engagement of
`the clutch is controlled by the
`microprocessor, e.g., by 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 is
`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 battery 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,
`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-
`climbing or passing,
`the traction and/or starter motors can be
`
`Both motors can be operated as generators,
`engaged as needed.
`e.g.,
`to transform the vehicle's kinetic energy ito electrical
`power during descent or deceleration.
`
`5
`
`10
`
`
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`25
`
`In each of these aspects of the operation of the vehicle, and
`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
`controls
`the various
`components
`of
`the hybrid drive train
`
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`accordingly.
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`In the preferred embodiment,
`
`the engine and the two motors all
`
`the same speed when the clutch is engaged, avoiding
`rotate at
`intermediate gear trains or
`like mechanical components and the
`
`5
`
`attendant cost, complexity, weight, audible noise, and frictional
`
`It is nonetheless within the scope
`losses occasioned by their use.
`of the invention to operate one or more of these components at
`differing rotational speeds; for example,
`the starter motor might
`drive the engine through a small pinion geared to a relatively
`large toothed flywheel, as conventional. Similarly, it might be
`desirable to provide the traction motor as a relatively high-speed
`unit, driving the road wheels through a belt or gear reduction
`unit. However,
`in all cases,
`the rotational speeds of
`the two
`
`motors and the engine, and of
`
`the road wheels, are fixed with
`
`respect to one another;
`
`no multi-speed transmissions between the
`
`motors and engine and the road wheels are required by the hybrid
`power train of the invention.
`
`other improvements provided according to the invention include
`
`providing the batteries in two series-connected battery banks, with
`the vehicle chassis connected to the batteries at a central point,
`between the banks. This "center—point-chassis" connection reduces
`
`the voltage between various circuit components and the vehicle
`
`chassis by half, significantly reducing the electrical insulation
`
`issues as Iheat-sinking' of power
`required, and simplifying such.
`semiconductors used in the inverter circuitry.
`Providing dual
`battery banks and dual electric motors, as above, also provides a
`degree of redundancy, permitting certain component failures without
`loss of vehicle function.
`
`In the preferred embodiment, both the traction and starting
`motors are AC induction motors of
`four or more poles and the
`accompanying power circuitry provides current of three or more,
`preferably five, phases, allowing the vehicle to function even
`
`after failure of one or more components.
`
`During substantially steady-state operation, e.g., during
`highway cruising,
`the control system operates the engine at varying
`
`5
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`torque 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
`
`5
`
`efficient torque output, e.g., during passing or hill-climbing, one
`
`or both of the electric motors are energized to provide additional
`
`torque; 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
`
`10
`
`is used to charge the batteries. Regenerative charging may be
`
`performed 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
`
`vdth the batteries' state of
`
`charge.
`
`Brief Description of the Drawings
`
`The invention will be better understood if reference is made
`
` to the accompanying drawings,
` the drive system of the invention,
`
`in which:
`
`Fig.
`
`1 shows a schematic diagram of the principal components
`
`of the hybrid vehicle drive system according to the invention;
`
`Fig.
`
`2 shows a block diagram of the principal components of
`
`illustrating various control
`
`signals provided;
`
`25
`
`Fig.
`
`3 shows a partial schematic diagram of the battery bank,
`
`inverter, and motor circuitry;
`
`Fig.
`
`4 is a diagram illustrating a typical control strategy
`
`employed during highway driving; and
`
`Fig.
`
`5 is a generally similar diagram illustrating a typical
`
`30
`
`control strategy employed during low-speed city driving.
`
`Description of the Preferred Embodiments
`
`As
`
`indicated above,
`
`this application discloses certain
`
`modifications,
`
`improvements,
`
`and
`
`enhancements
`
`of
`
`the hybrid
`
`35
`
`vehicles shown in the inventor's U.S. patent 5,343,970; where not
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`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 patent are
`
`functionally similar in the corresponding systems, with detail
`
`5
`
`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 by the
`
`latter, as detailed herein.
`
`As shown in the '970 patent with reference to Figs.
`
`1 and 2
`
`10
`
`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
`
`
`
`25
`
`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
`
`the engine and motor is transferred to the drive wheels of the
`
`30
`
`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.
`
`This unit, while entirely practical, comprises gears for power
`
`35
`
`transfer, which, are inevitably' a source of audible noise and
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`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
`
`microprocessor controller responsive to operator
`
`commands
`
`and
`
`5
`
`sensed operating conditions.
`
`As
`
`shown in Fig.
`
`1 of the present application, a traction
`
`motor 25 is connected directly to the vehicle differential 32, and
`
`thence to the road wheels 34.
`
`A starting motor 21 is connected
`
`directly to the internal combustion engine 40.
`
`The motors 21 and
`
`10
`
`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
` the system,
`
`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
`
`in accordance with the operational state of the vehicle
`
`and the operator's input commands.
`
`25
`
`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
`
`state of charge of
`
`the batteries,
`
`and other variables.
`
`For
`
`example, during low—speed operation, such as in city traffic, the
`
`30
`
`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.
`
`Under
`
`these
`
`circumstances,
`
`the charging current is provided by starting motor
`
`21,
`
`operated
`
`as
`
`a generator
`
`by
`
`appropriate operation of
`
`35
`
`inverter/charger 23. Accordingly, clutch 51 is disengaged, so that
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`the road speed of the vehicle is independent of the speed of engine
`
`40; engine 40 can thus be operated at high torque,
`
`for
`
`fuel
`
`efficiency.
`
`As shown in Fig. 2, shaft encoders 18 and 19 may be mounted on
`
`5
`
`the shafts 15 and 16 of starting motor 21 and traction motor 25,
`
`respectively,
`
`to provide signals to microprocessor controller 48
`
`indicative of the relative rotational speeds of the shafts, and
`
`their respective rotational positions.
`
`Such shaft encoders are
`
`well—known and commercially available. Alternatively,
`
`signals
`
`10
`
`indicative of the rotational speeds of the shafts may be derived
`
`from the inverter control signals,
`
`in accordance with well-known
`
`principles of control of "sensorless" motor drives
`
`(see,
`
`for
`
`example, Bose, "Power Electronics and Variable Frequency Drives",
`
`IEEE, 1996). However, provision of encoders 18 and 19 will allow
`
`better low—speed torque characteristics of motor 21 and 25, and
`
`thus reduction in cost.
`
`In either embodiment,
`
`the microprocessor controller 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 slipping
`
`before the shafts are fully engaged. Alternatively, clutch 51 may
`
`
`
`25
`
`be a simple self-aligning nmchanical
`
`interlock (as illustrated
`
`schematically in Fig. 2), wherein positive mechanical connection is
`
`made between the shafts
`
`15
`
`and 16 upon engagement;
`
`such a
`
`interlock is much simpler and less expensive than a
`mechanical
`friction clutch.
`
`30
`
`Additional signals input to microprocessor controller 48, as
`
`shown
`
`in Fig.
`
`2,
`
`include operator
`
`input
`
`commands,
`
`typically
`
`acceleration, direction,
`
`and deceleration commands. Position-
`
`sensing encoders 71 and 72 (which could be configured as rheostats,
`
`Hall-effect
`
`sensors,
`
`or
`
`otherwise)
`
`provide
`
`signals
`
`to
`
`35
`
`microprocessor controller 48 over lines 67 and 68 upon motion of
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`accelerator and brake pedals 69 and 70 (Fig. 1) 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 to make
`
`5
`
`decisions concerning the proper operation of the vehicle according
`
`to the invention.
`
`For example,
`
`suppose the vehicle has been operated in city
`
`traffic for
`
`some
`
`time,
`
`that
`
`is,
`
`under battery power only.
`
`Typically the operator will only depress the accelerator slightly
`
`10
`
`to drive in traffic.
`
`If the operator then depresses accelerator
`
`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 preheating step may be omitted. Similarly,
`
`if the operator depresses the brake pedal 70 relatively gently, all
`
`braking may be provided by regenerative charging of the batteries;
`
`if the operator instead presses rapidly on brake pedal 70, both
`
`mechanical and regenerative braking will be provided. Mechanical
`
`
`
`25
`
`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, monitored by shaft encoders 18 and 19 as discussed
`
`above,
`
`battery voltage, battery charge
`
`level,
`
`and
`
`ambient
`
`30
`
`temperature are also either monitored directly or derived from
`
`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
`
`35
`
`engine management system (EEM) 55, and to starting motor 21, clutch
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`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
`
`5
`
`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, although the duplicate control lines required are
`
`not illustrated in Fig. 2.
`
`Inverter/charger operation is discussed
`
`10
`
`further below in connection with Fig. 3.
`
`other elements of the system as illustrated in Figs. 1 and 2
`
`are generally as discussed in the '970 patent,
`
`including supply of
`
`fuel 36 from tank 38, air filter 60, and throttle 61.
`
`As
`
`in the '970 patent, engine 40 is sized so that its full
`
`torque output is adequate to drive the vehicle at a desired top
`
`speed, so that the engine is operated at high efficiency during
`
`highway cruising. During highway cruising, therefore, clutch 51 is
`
` recharging of battery bank
`
`engaged; engine 40 then drives road wheels
`
`of motors
`
`21
`
`and 25.
`
`If extra power
`
`34 through the shafts
`
`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
`
`22.
`
`Fig.
`
`4,
`
`discussed below,
`
`illustrates operation in this mode in further detail.
`
`25
`
`When the microprocessor controller 48 detects a continued
`
`operator
`requirement
`for
`additional
`power,
`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
`
`30
`
`before clutch 51 is engaged,
`
`to ensure a smooth transition.
`
`As
`
`cruising speed is reached, power
`
`to traction motor 25
`
`(and to
`
`starter motor 21,
`
`if also used to accelerate the vehicle)
`
`is
`
`gradually reduced. Provision of the clutch 51 and separate starter
`
`motor 21, as compared to using the single traction motor to start
`
`35
`
`engine 40 while simultaneously accelerating the vehicle as in the
`
`11
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`'970 patent, provides much simpler operation.
`
`In a particularly
`
`preferred embodiment, both motors 21 and 25 and clutch 51 may be
`
`provided in a single sealed housing, possibly bathed in oil for
`
`cooling and protection from dust and the like. Connection of the
`
`5
`
`engine 40 to the drive wheels through motors 21 and 25 also serves
`
`to damp out any vibration of engine 40.
`
`Provision of the clutch 51 and separate starter motor 21 also
`
`allows another important improvement to be provided according to
`
`the present
`
`invention, namely starting engine 40 at high speed,
`
`10
`
`e.g., between about 500 and 2000 rpm,
`
`as compared to the 60 - 200
`
`rpm starts conventionally' provided.
`
`High-rpm starting allows
`
`elimination of
`
`the usual necessity of providing a
`
`fuel-rich
`
`air/fuel mixture to start engine 40, reducing emission of unburned
`
`fuel and improving fuel economy at start-up. More specifically,
`
`in
`
`conventional
`
`low-rpm starts, a rich mixture must be provided to
`
` to a conventional engine at starting is immediately exhausted
`
`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,
`
`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
`
`unburnt - and provides some improvement in fuel efficiency.
`
`25
`
`More specifically,
`
`in normal
`
`low-rpm starting,
`
`a fuel/air
`
`mixture comprising on the order of 6 to 7 times the stoichiometric
`
`amount of fuel is provided; most of the excess fuel is immediately
`
`emitted unburned. According to the invention a mixture typically
`
`including only 1.2 times the stoichiometric amount of fuel
`
`is
`
`30
`
`provided for starting, greatly reducing these emissions. As noted
`
`above, whenever possible - that is, whenever the engine is started
`
`except when immediate full torque is required by the operator - a
`
`catalytic converter 64 is preheated before starting the engine,
`
`to
`
`prevent even this relatively small emission of unburned fuel.
`
`35
`
`Thus,
`
`the primary consideration in selecting the torque of
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`starting motor 21 is that it be capable of rotating the engine 40
`
`at about 500 - 2000 rpm for starting;
`
`the main consideration in
`
`specification of
`
`the torque of engine 40
`
`is that it provide
`
`sufficient power for highway cruising at high efficiency,
`
`i.e.,
`
`5
`
`that
`
`its maximum power output be approximately equal
`
`to that
`
`required to naintain maximum vehicle speed;
`
`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
`
`10
`
`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 peak power provided by the internal
`
`combustion engines of 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.
`
` relatively large fraction of the total energy required,
`
`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
`
`speed operation much energy is lost by conventional vehicles as
`
`25
`
`heat released during braking.
`
`Given the above considerations,
`
`the following are typical
`
`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
`
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`Starting motor 21: 10 — 15 horsepower at approximately 1500
`
`rpm and higher speeds
`
`Traction motor 25: 50 - 60 horsepower from 1500 to 6000 rpm.
`
`The same starting motor would be satisfactory for a larger,
`
`5
`
`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 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
`
`manufacture.
`
`It will be apparent that these specifications may
`
`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.
`
` typically 1500 - 2000 rpm, and should produce constant power at
`
`As
`
`indicated above,
`
`in the preferred embodiment, both the
`
`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,
`
`higher speeds.
`
`The ratio of the base to maximum speed can vary
`
`25
`
`between about 3 to 1 and about 6 to 1.
`
`By comparison,
`
`the series-
`
`wound DC nmtors conventionally used as engine starting 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.
`
`30
`
`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 heavy and power-dissipating intermediate components are
`
`needed.
`
`A maximum speed of approximately 6000 rpm is preferred, as
`
`35
`
`this represents a good compromise between cost, weight, and size of
`
`14
`
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`the key components.
`
`However, as noted above, it is within the
`
`scope of
`
`the invention to operate the starter motor,
`
`traction
`
`motor, and engine at differing rotational speeds, and connect these
`
`torque-producing components to one another and to the road wheels
`
`5
`
`by fixed-ratio gear or belt drives.
`
`In each case, no variable
`
`speed transmission between the torque-producing components and the
`
`road wheels is provided.
`
`The speed of rotation of the torque—
`
`producing components is reduced to a suitable speed for the road
`
`wheels by gear or belt drive reduction in (or incorporated with)
`
`10
`
`differential 32;
`
`the reduction ratio can be chosen to provide
`
`substantially any desired top speed.
`
`As discussed above, it is preferred that motors 21 and 25 have
`
`more than two poles, and be operated by current applied over more
`
`than three phases, so that failure of some components - such as the
`
`power
`
`semiconductors used in the inverter/charger units,
`
`as
`
`discussed below — can be tolerated without total failure of the
`
`vehicle. It is also desired that the battery bank be divided into
`
`two, with the vehicle chassis connected between them, halving the
`
`voltage between given components and the vehicle chassis, and thus
`
`simplifying their construction,
`
`insulation, and connection. Fig.
`
`3 shows a partial schematic diagram of a circuit providing these
`
`attributes.
`
`
` The functions of the inverter/chargers 23 and 27
`
`(separate
`
`inverter/chargers being required to allow independent operation of
`
`25
`
`motors 21 and 25)
`
`include control of motors 21 and 25 to operate as
`
`motors or as generators; operation of traction motor 25 in the
`
`opposite direction for reversing the vehicle; conversion of DC
`
`stored by the battery bank to AC
`
`for motor operation;
`
`and
`
`conversion of AC induced in the motors when operated as generators
`
`30
`
`to DC for battery charging. Essentially similar functions were
`
`provided by the solid-state switching AC/DC converter 44 in the
`
`'970 patent; where not specified to the contrary,
`
`the discussion
`
`there