Patent ID: 7155905

Claim:
A power steering apparatus comprising: a hydraulic power cylinder including first and second pressure chambers and a piston separating the first and second pressure chambers to provide a steering force to a steering mechanism connected with a steering wheel; a reversible pump including a first outlet connected with the first pressure chamber through a first fluid passage, and a second outlet connected with the second pressure chamber through a second fluid presage to supply a fluid pressure to the first pressure chamber or the second pressure chamber selectively; a motor arranged to drive the reversible pump in a forward rotational direction or a reverse rotational direction; a steering assist force sensor arranged to sense a steering assist force to be provided to the steering wheel; a pump discharge quantity measuring section configured to ascertain a pump discharge quantity of the reversible pump; a cylinder volume variation measuring section configured to ascertain a cylinder volume variation of one of the pressure chambers of the hydraulic power cylinder; a leak quantity calculating circuit configured to calculate a leak quantity of the reversible pump from a difference between the pump discharge quantity and the cylinder volume variation; and a motor control circuit configured to deliver a motor drive signal to the motor to cause the motor to produce the fluid pressure in accordance with the steering assist force and the leak quantity.