Electric power steering device for a motor vehicle

Abstract

In an electric power steering device, an electric motor is drivingly connected to a steering shaft with a steering wheel for generating an assisting power to rotate the steering shaft. A memory has stored a control pattern which non-linearly varies an assisting power with variations in a steering effort. A microprocessor responsive to a vehicle speed detected by a speed sensor ascertains whether the detected vehicle speed is within a low speed range or within a high speed range. Ascertaining that the detected speed is within the low speed range, the microprocessor searches the memory for an assisting power corresponding to the steering effort detected by a torque sensor. Ascertaining that the detected vehicle speed is within the high speed range, on the other hand, the microprocessor calculates an assisting power based upon the detected steering effort and a constant. The microprocessor then outputs a control signal representing either of the searched and calculated assisting power to a signal modulator, which modulates the control signal based upon the vehicle speed from the speed sensor so that the assisting power generated by the electric motor is controlled to meet the modified signal from the signal modulator.