Patent ID: 7174988

Claim:
A power steering system, comprising: a hydraulic power cylinder which assists a steering force of a steering mechanism coupled to steered wheels, the power cylinder comprising first and second pressure chambers; a reversible-type oil pump which supplies a hydraulic fluid to the first and second pressure chambers of the power cylinder through first and second passages, the oil pump comprising first and second discharge ports; an electric motor which rotates the oil pump in the normal and reverse directions; a branch passage which conveys part of the hydraulic fluid discharged from the first and second discharge ports of the oil pump to the outside of the first and second pressure chambers of the power cylinder, the branch passage having a passage sectional area greater than a total leak sectional area of the oil pump; a steering-condition sensing circuit which senses a steering condition made by a driver; and a motor control circuit which controls the electric motor, the motor control circuit outputting a drive command to the electric motor in accordance with the sensed steering condition.