Variable capacity vane pump

1. A variable capacity vane pump comprising:

a pump body;

a driving shaft rotatably supported by the pump body;

a rotor provided in the pump body and rotatably driven by the driving shaft;

a plurality of vanes radially extendably installed in their respective slots that are arranged in a circumferential direction in the rotor;

a cam ring rockably provided on a supporting surface in the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes, an eccentricity amount of the cam ring with respect to the rotor being changed by rotating of the cam ring on the supporting surface;

first and second members provided at both sides in an axial direction of the cam ring;

an inlet port provided at least at one of the first and second members and opening to a suction section of the pump chamber where a volume of the pump chamber increases;

an outlet port provided at least at one of the first and second members and opening to a discharge section of the pump chamber where the volume of the pump chamber decreases; and

a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring,

wherein a center of the cam ring is provided (i) so as to be positioned at an inlet port side with respect to a center of the driving shaft in a no-load state in which a pressure difference between the suction section and the discharge section does not act on the driving shaft and the rotor, and (ii) so as to be positioned at an outlet port side with respect to the center of the driving shaft in a state in which the driving shaft is elastically deformed to the inlet port side by the action of the pressure difference on the driving shaft.

2. The variable capacity vane pump as claimed in claim 1 , wherein the second hydraulic pressure chamber is supplied with at least an inlet pressure.

3. The variable capacity vane pump as claimed in claim 1 , wherein a line on which suction/discharge of the pump chamber are switched is defined as a port reference line, and the supporting surface is provided so that the supporting surface gradually separates from the port reference line in a direction from the second hydraulic pressure chamber to the first hydraulic pressure chamber.

4. The variable capacity vane pump as claimed in claim 1 , wherein a range of an angle between the supporting surface and the port reference line is 2°˜8°.