Patent ID: 7318705

Claim:
A variable displacement pump, comprising: a rotor rotated by a driving shaft, the rotor comprising a plurality of vanes mounted to be retractable radially; a cam ring arranged on a periphery of the rotor to be swingable with respect to the rotor; a pair of closing members arranged on both sides of the cam ring, the closing members making slide contact with the cam ring, at least one closing member having an end face on a side of the cam ring, the end face being formed with a suction port; a seal member arranged in a chamber formed between a pump housing and the cam ring, the seal member dividing the chamber into two portions that define first and second working chambers; a spring arranged in the second working chamber, the spring biasing the cam ring to the first working chamber in the direction that increases volumes of pump chambers defined between the cam ring, the rotor, and the vanes; a suction passage which introduces a working fluid into a suction area within the cam ring, the suction area serving to suck the working fluid through the suction port, the suction passage and the second working chamber being always in fluid communication during pump operation; a discharge passage which supplies the working fluid from a discharge area within the cam ring to the outside; a communication passage formed in the at least one closing member substantially along the end face thereof, the communication passage providing fluid communication between the suction port and the second working chamber; an orifice provided to the discharge passage; and a control valve operated by a pressure difference between upstream and downstream sides of the orifice, the control valve controlling a pressure of the working fluid to be introduced into the first working chamber and being isolated from the second working chamber.