Motorized power steering apparatus

Abstract

A motorized power steering apparatus is equipped with a torque sensor including a primary potentiometer for detecting a steering torque applied to the steering wheel by a driver. The torque sensor further includes an auxiliary potentiometer so as to detect variations in the output voltage of a constant voltage power supply to the potentiometers. When there is a difference between the outputs of the primary and auxiliary potentiometers which is greater than a prescribed level, a fail-safe relay is turned off to nullify the power steering operation of a motor. When the output voltage of the power supply for supplying a constant voltage to the primary and auxiliary potentiometers drops below or rises above a predetermined level, the output voltage of the auxiliary potentiometer, which is not used for power steering control, is raised. This increases the difference between the output voltages of the potentiometers to a detectable level, whereby a fail-safe operation is carried out to nullify the power steering operation of the electric motor. Thus, the steering wheel is prevented, in a reliable manner, from being turned spontaneously or unintentionally against the driver's will due to variations in the neutral point of the torque sensor resulting from fluctuations in the voltage supplied thereto.