Control apparatus for reversible motor and motor-driven power steering

Abstract

A motor-driven power steering control system of a motor vehicle for assisting a driver in manipulating a steering wheel by making use of an assist torque generated by a reversible motor which is operatively coupled to a steering mechanism of the motor vehicle includes an electric reversible motor mechanically coupled to a steering system of the motor vehicle through an electromagnetic clutch, a motor drive circuit, an H-bridge switching driver circuit for driving the electric reversible motor in forward or reverse direction under the control of the motor drive circuit, and a clutch control circuit for controlling the electromagnetic clutch. A motor voltage detection circuit for detecting terminal voltages at both terminals of the electric reversible motor is provided for generating a voltage signal of high level and subsequently a fail-safe signal of a low level on the basis of the high-level voltage signal when both of the terminal voltages are approximately zero, while generating a voltage signal of a low level and subsequently a fail-safe signal of high level on the basis of the low-level voltage signal unless both of the terminal voltages are approximately zero. A switch is connected between an electric power source and the switching drive circuit and the clutch control circuit. A microcomputer fetches the fail-safe signal from the motor voltage detection circuit to thereby open the switch for interrupting the power supply to the reversible motor and the clutch control circuit when the fail-safe signal is at the low level.