Motor-driven power steering system for front and rear road wheels

Claim 2

A power steering apparatus for steering rear road wheels (l5) of a vehicle in response to the steering of the front road wheels (5) of the vehicle, comprising a steering motor (24), steering condition sensing means (2l) responsive to the steering of the front road wheels (5), sensing means (23, 27) responsive to the steering condition of the rear wheels (l5), and the control means (20) arranged to control the operation on the basis of a comparison of the output signals of the sensing means (2l) for the front wheels (5) and of the sensing means (23, 27) for the rear wheels, characterised in that locking means (25) are provided for locking the rear road wheels (l5) in position, and the control means (20) control operation of the locking means to lock the steering position of the rear wheels when the said control means detects failure or abnormal operation of the power steering apparatus.

Claim 3

Power steering apparatus as claimed in claim l in which the locking means (25) is a normally-on brake arranged to brake the steering motor (24).

Claim 4

A motor-driven power steering system for front and rear road wheels of a vehicle adapted to steer the rear road wheels in response to the steering conditions of the front road wheels, said power steering system comprising: a motor electrically connected with an electric power source and mechanically connected with said rear road wheels for steering thereof; a steering condition sensor for detecting at least one of steering conditions of a steering wheel such as the direction, the steering angle, the steering torque and the steering speed of the steering wheel; a vehicle speed sensor for detecting the travelling speed of the vehicle; a motor rotation sensor for detecting the rotational direction and the rotational speed of said motor; a rear-wheel steering angle sensor for detecting the steering angle of said rear road wheels; an electromagnetic brake for braking the operation of said motor so as to lock the steering motion of said rear road wheels when the electric power supply to said electromagnetic brake is off; and a control unit adapted to receive the output signals of said respective sensors to appropriately control the electric power supply from said electric power source to said motor and said electromagnetic brake on the basis of the information obtained therefrom.

Claim 5

A motor-driven power steering system for front and rear road wheels of a vehicle adapted to steer the rear road wheels in response to the steering conditions of the front road wheels, said power steering system comprising: a motor electrically connected with an electric power source and mechanically connected with said rear road wheels for steering thereof; a steering condition sensor for detecting at least one of steering conditions of a steering wheel such as the direction, the steering angle, the steering torque and the steering speed of the steering wheel; a vehicle speed sensor for detecting the travelling speed of the vehicle; a motor rotation sensor for detecting the rotational direction and the rotational speed of said motor; a rear-wheel steering angle sensor for detecting the steering angle of said rear road wheels; an electromagnetic brake for braking the operation of said motor so as to lock the steering motion of said rear road wheels when the electric power supply to said electromagnetic brake is off; and a control unit adapted to receive the output signals of said respective sensors to appropriately control the electric power supply from said electric power source to said motor and said electromagnetic brake on the basis of the information obtained therefrom.

Claim 6

A motor-driven power steering system for front and rear road wheels of a vehicle as set forth in claim 3, wherein said control unit comprises: a fail-safe relay inserted in a power line for electrically connecting said electric power source with said motor and said electromagnetic brake and adapted to establish, when switched on, the electrical connections therebetween, and interrupt the electrical connections when switched off; a fail-safe-relay driving circuit adapted to switch said fail-safe relay on or off in a manner such that said fail-safe relay is switched on to supply electric power to said motor and said brake when there is no failure in said steering system, and switched off to interrupt the electric power supply to said motor and said brake when said steering system has failed; a power transistor unit inserted in a line electrically connecting between said fail-safe relay and said motor and adapted to selectively drive said motor in one rotational direction or in the opposite rotational direction; a first power-transistor driving circuit for driving said power transistor unit in a manner such that current is supplied from said electric power source to said motor so as to rotate it in one rotational direction; a second power-transistor driving circuit adapted to operable alternatively with said first power-transistor driving circuit for driving said power transistor unit in a manner such that current is supplied from said electric power source to said motor so as to rotate it in the opposite rotational direction; an electromagnetic-brake driving circuit for driving said electromagnetic brake for brake application when at least one of said sensors, said electric power source and the wiring electrically connecting between said sensors and said control unit or between said electric power source and said motor has failed; and a microcomputer electrically connected with said electric power source through said key switch and adapted to receive the output signals of said steering-wheel-condition sensor, said vehicle-speed sensor, said rear-wheel steering angle sensor and said motor-rotational speed sensor for determining whether or not said power steering system has failed and controlling the operations of said fail-safe driving circuit, said first and second power transistor driving circuits and said electromagnetic brake driving circuit in a manner such that said rear road wheels are appropriately steered under the action of said motor and said electromagnetic brake which are controlled by said first and second transistor circuits and said electromagnetic-brake driving circuit if it is determined that said steering system is normally operating, whereas said fail-safe relay driving circuit is operated to switch off said fail-safe relay thereby to interrupt the supply of electric power to said motor and said electromagnetic brake so that said motor is stopped and said electromagnetic brake is actuated to lock said rear road wheels against steering if it is determined that there is a failure in any of said sensors, said electric power source and the wiring connecting between said sensors and said control unit or between said electric power source and said motor.

Claim 7

A motor-driven power steering system for front and rear road wheels as set forth in claim 4, wherein said fail-safe relay comprises: a pair of normally open contacts inserted in the power line connecting said electric power source with said motor and said electromagnetic brake; and a driving coil electrically connected through said key switch with said electric power source and adapted to be energized, upon closing of said key switch, to close said pair of contacts for supplying electric power from said electric power source to said electromagnetic brake and said motor in the normal operating condition of said power steering system so that said motor is driven to rotate and said electromagnetic brake is deactuated, whereas said driving coil is deenergized by opening of said key switch or by said fail-safe relay driving circuit when said microcomputer judges that there is a failure in any of said sensors, said electric power source and the wiring electrically connecting between said sensors and said control unit or between said electric power source and said motor.

Claim 8

A motor-driven power steering system for front and rear road wheels as set forth in claim 3, 4 or 5, wherein said control unit further comprises: a steering-wheel-condition signal input circuit through which the output signal of said steering-wheel condition sensor is input to said microcomputer; a vehicle-speed signal input circuit through which the output signal of said vehicle-speed sensor is input to said microcomputer; a rear-wheel steering-angle signal input circuit through which the output signal of said rear-wheel steering angle sensor is input to said microcomputer; a motor-rotation signal input circuit through which the output signal of said motor rotation sensor is input to said microcomputer; and a power circuit through which said microcomputer is electrically connected with said electric power source.