Variable displacement pump with communication passage

1. 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.

2. The variable displacement pump as claimed in claim 1 , wherein the communication passage comprises a groove formed in the end face of the at least one closing member.

3. The variable displacement pump as claimed in claim 2 , wherein the groove comprises a terminal-groove portion which opens to the second working chamber in the vicinity of a swinging end of the cam ring in the direction that the cam ring is reduced in an amount of eccentricity with respect to the rotor, and a connection-groove portion which provides fluid communication between the suction port and the terminal-groove portion substantially along the direction of oscillation of the cam ring.

4. The variable displacement pump as claimed in claim 2 , wherein the communication passage is configured to open to the second working chamber when the cam ring swings maximally within an operation range in the direction that the cam ring is reduced in an amount of eccentricity with respect to the rotor.

5. The variable displacement pump as claimed in claim 4 , wherein the communication passage is isolated from the second working chamber when the cam ring swings over the operation range.

6. A variable displacement pump with a rotor rotated by a driving shaft and 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 seal member arranged in a chamber formed between a pump housing and the cam ring and for dividing the chamber into two portions that define first and second working chambers, a spring arranged in the second working chamber and for 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, a discharge passage which supplies the working fluid from a discharge area within the cam ring to the outside, 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, wherein the suction passage and the second working chamber are always in fluid communication during pump operation, the variable displacement pump comprising:

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 through which the suction area sucks the working fluid; and

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.