Electric motor assisted power steering device

Abstract

An electric motor assisted power steering device for an automobile is disclosed which comprises a dupicate torque direction determination system. The power steering device comprises, in addition to a microcomputer for determining the amount and direction of the auxiliary torque which is to be provided by the electric motor, an analog direction determiner circuit for determining the direction of the auxiliary torque. The torque sensor outputs a voltage which is substantially in linear relationship with the steering torque applied by the operator. The direction determiner circuit includes: a first comparator which outputs a right direction signal when this output voltage of the torque sensor exceeds a first reference level; and a second comparator which outputs a left direction signal when the output voltage of the torque sensor is below a second reference level which is lower than the first level. These reference voltages, selected at upper and lower ends of the non-sensitive region, may be obtained by a voltage divider. The microcomputer determines, on the basis of the output of the torque sensor, the direction of the auxiliary torque and outputs a corresponding right or left direction signal. A first AND gate performs an AND operation on the two right direction signals outputted from the microcomputer and the analog circuit; a second AND gate performs an AND operation on the two left direction signals. The motor driver circuit controls the direction of the current supplied to the electric motor in accordance with the output of the first and the second AND gate.