Patent ID: 8257057

Claim:
A variable displacement vane pump comprising: a rotor formed with a plurality of slots each having a backpressure chamber, and provided with a plurality of vanes each slidably received in one of the slots and arranged to be urged radially outwards by a pressure in the backpressure chamber; an annular cam ring receiving therein the rotor rotatably, the cam ring being arranged to swing, and to define a plurality of pumping chambers with the vanes between the rotor and the cam ring; a pump body encasing the cam ring and the rotor and including an end wall; a pressure plate disposed between the end wall of the pump body and the rotor, the pressure plate including: a sliding surface facing toward the rotor and the cam ring, a backup surface opposite to the sliding surface, an inlet port formed in the sliding surface, to supply an operating fluid into the pumping chambers, an outlet port formed in the sliding surface, to discharge the operating fluid from the pumping chambers, and a backpressure groove formed in the sliding surface to communicate with the backpressure chambers; and a first seal member which is provided between the backup surface and the end wall, the first seal member including: an inlet-side segment extending on a radial inner side of the inlet port and a radial outer side of the backpressure groove, and an outlet-side segment extending on the radial outer side of the outlet port; wherein the outlet-side segment of the first seal member includes an outer circumference including first and second convex portions, and a concave portion which is located circumferentially between the first and second convex portions, and which is recessed so that a radial distance from a center axis of the pressure plate is smaller at the concave portion than at the first and second convex portions.