Abstract: An electric power steering apparatus in which the steering force of a steering wheel is assisted by an electric motor is disclosed. The number of revolution of the electric motor is detected, and the counter electromotive force of the electric motor is calculated on the basis of the detected number of revolution. A voltage which is to be applied to the electric motor and corresponds to the driving current instruction value determined in accordance with the steering torque is corrected on the basis of the calculated counter electromotive force. In the electric power steering apparatus, the period of the detection of the number of revolution of the electric motor is made longer than the period of the feedback control of the driving current of the electric motor, and the period of the feedback control of the driving current of the electric motor is synchronized with the period of the correction of the voltage to be applied.

Abstract: In an electric power steering apparatus using a direct drive electric motor for assisting steering force, the electric motor is operated with three-phase alternating current obtained from a direct-current power supply through an inverter, the three-phase alternating current being controlled by detecting the value of the direct current being supplied to the inverter. The difference between the detected direct current and a target current calculated on the basis of detected vehicle speed and steering torque is determined, based on which the three-phase alternating current is controlled.

Abstract: A power steering apparatus for eliminating the counter electromotive force generated upon stopping the motor for assisting steering force includes a circuit for opening all of the commutation-controlled switches (power transistors) each connected to an end of one of the coils of the motor and to disconnect and isolate the one ends from each other and prevent the production of a counter-electromotive force.