Vane pump having a side member including a triangular-shaped protruding opening portion in communication with a back pressure opening portion for preventing wear of an inner circumference cam face

A vane pump having a discharge region, comprising:

• a rotor having a plurality of slits formed in a radiating pattern, the rotor being rotationally driven;
• a plurality of vanes received in the slits in a freely slidable manner;
• a cam ring having an inner circumference cam face with which tip end portions of the vanes are brought into sliding contact;
• a side member brought into contact with one-side surfaces of the rotor and the cam ring;
• pump chambers formed by the rotor, the cam ring, and adjacent vanes;
• and
• back pressure chambers formed in the slits by base-end portions of the vanes, wherein the side member is provided with:
• a back pressure opening portion opening at a sliding-contact surface in sliding contact with the rotor in the discharge region where the pump chambers are caused to contract as the rotor rotates, the back pressure opening portion being configured to communicate with the back pressure chambers and having an inner-side arc-shaped surface and an outer-side arc-shaped surface that are respectively formed along a circumferential direction of the rotor;
• and
• a protruding opening portion protruding along a rotating direction of the rotor from an end portion of the back pressure opening portion on a communication finishing side, where communication between the back pressure opening portion and the back pressure chambers finishes as the rotor is rotated, wherein
• the protruding opening portion has an inner-side inner circumferential surface that is continuous with the inner-side arc-shaped surface of the back pressure opening portion.