Servolenkungs-Vorrichtung für Motorfahrzeuge

A motor-driven type power steering apparatus for assisting a driver in manipulating a steering wheel of a motor vehicle includes a steering-wheel return state decision circuit for deciding whether the steering wheel is in the state to be returned to a center position, a control quantity generating and selecting circuit for generating control quantities corresponding to respective driving modes on the basis of a control quantity of the electric motor and selecting one of the control quantities in dependence on the result of the decision made as to the return state of the steering wheel, and a conversion circuit for converting the control quantities into PWM duty ratios, respectively. In the normal steering operation, switching elements for energizing the motor are driven with the PWM duty ratio corresponding to a first driving mode, while upon return of the steering wheel to the center position, the switching elements are driven with the PWM duty ratio corresponding to a second driving mode. A smooth steering torque control is realized with the steering-wheel return characteristic being improved.