Patent ID: 7993116

Claim:
A variable displacement vane pump comprising: a drive shaft; a rotor which is adapted to be driven by the drive shaft, which is formed with a plurality of slots and which is provided with a plurality of vanes each of which is slidably received in one of the slots; an annular cam ring receiving therein the rotor rotatably, the cam ring being arranged to swing about a swing axis, and to define a plurality of pumping chambers with the vanes between the rotor and the cam ring; a pressure control device; and a pump casing encasing the cam ring and the rotor, the pump casing including, first and second side walls disposed on both sides of the cam ring so that the cam ring is located axially between the first and second side walls, an inlet port formed in at least one of the first and second side walls, an outlet port formed in at least one of the first and second side walls, a circumferential wall surrounding the cam ring and defining first and second pressure chambers formed between the circumferential wall and the cam ring, one of the first and second pressure chambers being connected with the pressure control device so that a fluid pressure is controlled by the pressure control device, and a pressure introduction groove formed in a sliding contact surface between the cam ring and one of the first and second side walls, and arranged so that an intermediate pressure lower than an outlet pressure and higher than an inlet pressure is introduced into the pressure introduction groove.