Motor-driven power steering apparatus and method

Claim 1

A motor-driven power steering apparatus for a vehicle comprising: a steering system transmitting a steering force applied to a steering wheel by a driver of the vehicle to steerable road wheels of the vehicle; a vehicle speed sensor for sensing the speed of the vehicle at which the vehicle is travelling; a torque sensor for sensing a steering torque applied to said steering system; a steering speed sensor for sensing a steering speed at which said steering wheel is turned by the driver; a motor coupled via a clutch to said steering system for generating an assisting torque which assists a driver's induced steering motion of said steering system; motor current sensing means for sensing a motor current flowing through said motor; motor voltage sensing means for sensing a motor voltage across said motor; motor control means for controlling a current supplied to said motor based on the vehicle speed and the steering torque in such a manner that the current supplied to said motor is zero when the vehicle speed is equal to or greater than a predetermined vehicle speed; clutch control means for turning said clutch on and off based on the steering torque, the vehicle speed, the steering speed and the motor voltage in such a manner that said clutch is turned off to disconnect said motor from said steering system when a system failure is determined during high speed travel of the vehicle at which the vehicle is travelling at a speed equal to or higher than the predetermined vehicle speed.

Claim 4

A method of controlling a motor-driven power steering apparatus for a vehicle in which a motor is coupled via a clutch to a steering system having a steering wheel for generating an assisting torque to assist a steering motion of said steering system induced by a driver of the vehicle, said method comprising the steps of: a) determining whether a speed of the vehicle is equal to or greater than a predetermined vehicle speed; b) deenergizing said motor with said clutch held in a connected state when the vehicle speed is equal to or greater than the predetermined vehicle speed; c) measuring the current flowing through the deenergized motor; d) measuring the voltage across the deenergized motor; e) measuring the steering torque and steering speed applied to the steering wheel by the driver; f) determining whether there is a system failure on the basis of the motor current, motor voltage, steering torque and steering speed measurements of steps c), d) and e); and turning said clutch off to disconnect said motor from said steering system if there is a system failure.

Claim 5

A method of controlling a motor-driven power steering apparatus for a vehicle in which a motor is coupled via a clutch to a steering system having a steering wheel for generating an assisting torque to assist a steering motion of said steering system induced by a driver of the vehicle, said method comprising the steps of: a) determining whether a speed of the vehicle is equal to or greater than a predetermined vehicle speed; b) deenergizing said motor with said clutch held in a connected state when the vehicle speed is equal to or greater than the predetermined vehicle speed; c) measuring the current flowing through the deenergized motor; d) measuring the voltage across the deenergized motor; e) measuring the steering torque and steering speed applied to the steering wheel by the driver; f) determining whether there is a system failure on the basis of the motor current, motor voltage, steering torque and steering speed measurements of steps c), d) and e); and turning said clutch off to disconnect said motor from said steering system if there is a system failure.