HYBRID VEHICLE DRIVE SYSTEM

Abstract: In order to better control a four wheel vehicle which is normally driven only by the front wheels (10), there is provided an electric motor (16) associated with each of the rear wheels (15). The operative state of the vehicle is sensed and signals are passed to a control arrangement by which the electric motors independently driveable to bring about improved driving characteristics of the vehicle.

Description: HYBRID VEHICLE DRIVE SYSTEM This invention relates to vehicle drive systems and in particular drive systems for use with vehicles having front wheels and rear wheels, the front wheels being driven to provide a front wheel drive vehicle. Front wheel drive vehicles offer some advantages over rear wheel drive vehicles and rear wheel drive vehicles also offer some advantages over front wheel drive vehicles. In order to combine the benefits of front and rear wheel drive vehicles it has been proposed to provide vehicles in which all wheels are driven. However there is a significant cost penalty with all wheel drive vehicles and some all wheel drive vehicles are arranged so that drive is usually through one set of wheels, usually the front wheels, and only when required are the rear wheels driven. It has further been proposed to provide differentials between the front driven wheels and the rear driven wheels of vehicles in order to be able to improve driving stability but again the provision of such differentials has cost penalties. An object of the invention is to provide a front wheel drive vehicle which is normally driven from the front wheels but which has the facility to improve the driving characteristics of such vehicles. According to the invention, in one aspect there is provided a vehicle drive system for vehicles having front wheels and rear wheels which comprises a prime mover for driving the front wheels, an electric motor for driving each of the rear wheels, sensing means for sensing the operative state of the vehicle, and control means for controlling the operation of the electric motors so that the motors are each operable independently of one another according to the operative state of the vehicle. It is intended that the electric motors remain inoperative during normal driving conditions of the vehicle, so that the vehicle is driven solely by the prime mover, for example an internal combustion engine, driving the front wheels only. When the vehicle is under extreme driving conditions, for example when cornering fast, taking evasive action round obstacles, skidding, or the like, one of the electric motors or both motors are operated. Operation may be to drive only one of the rear wheels, one of the wheels may be driven at a higher drive torque than the other, both wheels may be driven at the same drive torque, or one wheel may be driven in a different direction to the other. The sensing means may sense several parameters which can indicate a requirement for the rear wheels to be driven, and the control means relates the sensed parameters together to establish a need to activate the motors in a particular manner, according to the sensed parameters. Such parameters may include yaw rate, lateral acceleration of the vehicle, the steering angle of the steerable wheels or the steering wheel position, the speed of the wheels and/or the speed of the vehicle over the ground, and the longitudinal acceleration of the vehicle. By suitable programming of the control means a combination of these parameters, or some of them, will define the operational state of the vehicle and will generate signals to provide the required action of the electric motors to bring about improved driving characteristics of the vehicle, for example to control a skid, to improve negotiation of a corner, or to negotiate an obstacle. The control means may be arranged to selectively adjust the driving torque to each of the electric motors, each of the drive motors being driveably engageable with the associated wheel. When the motors are not operated they may be drivingly disconnected from the associated wheel. The vehicle will usually be provided with electrical storage means for supplying electrical power to each of the electric motors independently of the usual vehicle battery, and the electrical storage means may be charged from the vehicle alternator or by regeneration during progress of the vehicle. According to a further aspect there is provided a method of operating a vehicle drive system for vehicles having front wheels and rear wheels wherein each of the rear wheels is driveable by an electric motor, the operative state of the vehicle is sensed and signals are passed to control means and the control means control the operation of the electric motors so that the motors are each operable independently of one another and are operated in accordance with the operative state of the vehicle, the front wheels being driven by a prime mover. Further features of the invention will appear from the following description of an embodiment of the invention given by way of example only and with reference to the drawing which is a schematic plan view of a vehicle. Referring to the drawing a vehicle is shown which is in several respects a conventional front wheel drive vehicle having a pair of front wheels 10 driven by a prime mover 11 in the form of a transversely mounted internal combustion engine driving the front wheels 10 through the usual clutch and gear box arrangement. The front wheels 10 are, in usual manner, the steerable wheels of the vehicle and are moved by a steering wheel 12 through a steering rack 13. The vehicle has a pair of rear wheels 15 located towards the rear of the vehicle which are not driven by the prime mover 11. Each of the wheels 15 driveably engageable by an electric motor 16, driving engagement between the motor 16 and the associated wheel 15 is usually being effected when the associated motor 16 is operated. The motors 16 are supplied with power for their operation by a battery 17 or other energy storage system, usually separate from the usual vehicle battery. The vehicle carries means for sensing various parameters indicating the driving characteristics of the vehicle. Thus there is a steering sensor 18 which detects the position of the steering wheel 12 in relation to a predetermined datum. In addition there is an accelerometer 19 which is able to detect the lateral acceleration and the longitudinal acceleration of the vehicle during driving. Other sensors may be provided for determining the speed of the vehicle and/or the speed of the wheels 10 and/or 15, and a yaw rate sensor may be provided. The various sensors 18, 19 etc. feed signals according to the parameters sensed to an electric controller 20 which is pre-programmed to collect the signals sensed and to calculate from these signals the operational state of the vehicle. The controller 20 also provides output signals to each of the electric motors 16 to operate the motors at the desired torque, speed and direction. In practice the controller 20 will operate the motors 16 only when the driving characteristics of the vehicle require which is when the parameters sensed indicate that the driving characteristics of the vehicle may be improved by operation of the motors 16. Under normal driving conditions the motor 16 would not be operated and would not be drivingly connected to the associated wheels 15. Under certain driving conditions the driving conditions of a vehicle would be improved by driving the rear wheels 15, for example imparting the same drive torque to the wheels 15, imparting a drive torque to one of the wheels which is greater than the other, or imparting a drive torque to only one of the wheels and not the other. There may even be circumstances in which one of the rear wheels 15 is driven in the opposite direction to the other. It will be appreciated that the controller 20 is able to initiate drive of the wheels 15 without intervention of the driver and, in effect, the vehicle is arranged to behave in such a way that it aids and enhances the driver's ability to remain in control of the vehicle during certain vehicle manoeuvres. These are usually extreme driving manoeuvres for emergencies or for improved driver control during cornering. Due to each rear wheel being independently driven the torque transmitted through one rear wheel will not be affected by that to the other even if the other wheel cannot transmit power for example, due to loss of grip on the road surface. The invention may also find application in rear wheel drive vehicles, drive from the prime mover being to the rear wheels in this case and the front wheels each being driveable by an electric motor.

Claims: Claims 1. A vehicle drive system for vehicles having front wheels and rear wheels comprises a prime mover for driving the front wheels, an electric motor for driving each of the rear wheels, sensing means for sensing the operative state of the vehicle, and control means for controlling the operation of the electric motors so that the motors are each operable independently of one another according to the operative state of the vehicle. 2. A vehicle according to Claim 1 wherein the sensing means is arranged to sense operative parameters of the vehicle in use selected from lateral and/or longitudinal acceleration of the vehicle, steering angle of the steerable wheels of the vehicle, the steering wheel position, the speed of rotation of the wheels, and the speed of the vehicle over the ground, and the control means calculates the way in which the electric motors are to be driven having regard to the sensed parameters whereby to improve the driving characteristics of the vehicle. 3. A vehicle according to Claim 1 or 2 wherein the control means is arranged to drive the electric motors at different or the same driving torque, at the same speed, or at different speeds and/or in different directions or the same direction, according to the driving conditions of the vehicle. 4. A vehicle according to any one of the preceding claims wherein the vehicle includes electrical storage means for supplying electrical power to the electric motors which electrical storage means is independent of the vehicle battery for the prime mover. 5. A vehicle according to Claim 4 wherein the electrical storage means is recharged from the vehicle alternator and/or by energy regeneration means. 6. A vehicle according to any one of the preceding claims wherein the vehicle prime mover is arranged to drive the front wheels of the vehicle only. 7. A vehicle according to any one of the preceding claims wherein the electric motors are drivingly disengageable from their associated wheels. 8. A method of operating a vehicle drive system for vehicles having front wheels and rear wheels wherein each of the rear wheels is driveable by an electric motor, the operative state of the vehicle is sensed and signals are passed to control means and the control means control the operation of the electric motors so that the motors are each operable independently of one another and are operated in accordance with the operative state of the vehicle, the front wheels being driven by a prime mover.

Inventors: PRICE STEVEN MICHAEL, PRICE, STEVEN, MICHAEL
Applicants: PRICE STEVEN MICHAEL, PRODRIVE 2000 LTD, PRICE, STEVEN, MICHAEL, PRODRIVE 2000 LIMITED
Application year: 2001
Main classification: B60K41
IPC codes: B60K1, B60K6, B60W10, B60W20