Motor-driven power steering system for a vehicle

摘要

A motor-driven power steering system for a vehicle capable of preventing a motor-related element such as a motor itself, power elements for controlling power supply to the motor or the like from being damage due to an abnormal temperature rise or overheating thereof, thereby substantially avoiding or reducing resultant unsureness or instability in the operator's steering feeling upon change in steering mode as well as improving safety in steering operation. The motor is operatively connected with a steering rack and energizable by a power source for power assisting the steering motion caused by the operator through a steering wheel. A temperature sensor detects the temperature of the motor-related element. An electromagnetic switching clutch is interposed between the motor and the steering rack for selectively establishing and interrupting the transmission of power assisting force from the motor to the steering rack in accordance with the travelling speed of the vehicle. A control uint is provided for controlling the operation of the motor in such a manner such that when the detected temperature of the motor-related element is higher than a prescribed level, the current supplied to the motor through the motor-related element is gradually reduced to lower the temperature of the motor-related element.