Variable displacement vane pump having connection groove communicating with suction-side back pressure port thereof

1. A variable displacement vane pump used as a fluid pressure source comprising:

a rotor that is linked to a shaft rotationally driven by motive force from a motive-power source;

a plurality of slits formed in a radiating pattern so as to open at an outer circumference of the rotor;

vanes respectively received in the slits in a freely slidable manner;

a cam ring that has an inner circumferential cam face with which tip end portions of the vanes are brought into sliding contact, the cam ring is made eccentric to a center of the rotor and the tip end portions being end portions of the vanes in direction projecting from the slits;

pump chambers defined by the rotor, the cam ring, and the adjacent vanes;

a suction port configured to guide working fluid that is to be sucked into the pump chambers;

a discharge port configured to guide the working fluid that is discharged from the pump chambers;

back pressure chambers formed in the slits and partitioned by base-end portions of the vanes, the base-end portions being end portions at the opposite side from the tip end portions;

a plate that has a sliding contact surface and a penetrating hole, the sliding contact surface being in sliding contact with a side surface of the rotor and the penetrating hole being configured such that the shaft is inserted thereinto;

a suction-side back pressure port formed on an outer circumferential side of the penetrating hole on the sliding contact surface, the suction-side back pressure port being configured to guide the working fluid in the suction port to the back pressure chambers in a suction section in which the pump chambers are in communication with the suction port;

a discharge-side back pressure port formed on an outer circumferential side of the penetrating hole on the sliding contact surface, the discharge-side back pressure port being configured to guide the working fluid that is discharged from the discharge port to the back pressure chambers in a discharge section in which the pump chambers are in communication with the discharge port;

both ends of the suction-side back pressure port and the discharge-side back pressure port are separated from each other, without being communicated;

an additional groove provided on the sliding contact surface so as to extend from between the discharge-side back pressure port and the penetrating hole to between the suction-side back pressure port and the penetrating hole; and

a connection groove that communicates the additional groove with the suction-side back pressure port.

2. The variable displacement vane pump according to claim 1 , wherein a cross-sectional area of the connection groove is smaller than a cross-sectional area of the additional groove.

3. The variable displacement vane pump according to claim 1 , wherein the additional groove is formed so as to have a ring shape over the entire outer circumferential side of the penetrating hole on the sliding contact surface.

4. The variable displacement vane pump according to claim 1 , wherein the plate is provided on at least one of side surfaces of the rotor.