Patent ID: 6540043
Filing Date: 2003-04-01
Classification: B62D

Abstract:
A steering system for an automotive vehicle having two front wheels and two rear wheels, said steering system comprising:a speed sensor for sensing the speed of said vehicle; means for steering said two front wheels at a desired steering angle; at least one steering angle sensor for sensing the steering angle of said two front wheels; an axially displaceable rear rack, linked between said two rear wheels, for steering said two rear wheels at a determined steering angle; a centering resilient member, extending along the length of said rear rack, having a resiliency enabling said rear rack to return said two rear wheels to a neutral steering angle position; a rear transmission mechanism connected to said rear rack; an actuator connected to said rear transmission mechanism for axially displacing said rear rack via said rear transmission mechanism against said resiliency of said centering resilient member; at least one steering angle sensor for sensing the steering angle of said two rear wheels; an electronic control unit capable of determining a steering angle for said two rear wheels from electric signals received from said vehicle speed sensor, each said font wheels steering angle sensor, and each said rear wheels steering angle sensor and capable of supplying a level of electric current to said actuator to thereby electrically empower said actuator to steer said two rear wheels at said determined steering angle; and an electronic power regulation unit capable of selectively and electrically disabling said actuator according to electric signals received from said vehicle speed sensor, said level of said electric current supplied by said electronic control unit to said actuator, and a predetermined electric current limiting function; wherein said actuator comprises a brushless, direct-current electric motor for actuating said rear transmission mechanism to axially displace said rear rack and thereby steer said two rear wheels; an electronic power stage, electrically connected between said electronic power regulation unit and said motor, for providing electric power to operate said motor as electrically enabled by said electronic power regulation unit; and an electronic controller, electrically connected between said electronic control unit and said electronic power stage, capable of generating pulse-width modulated electric control signals based on said level of said electric current supplied by said electronic control unit to said actuator and capable of transmitting said generated electric control signals to said electronic power stage to ultimately control said motor and the actuating torque produced thereby; and wherein said electronic power stage comprises six field-effect transistors connected in three half H-bridge configuration stages.