Patent ID: 8142173

Claim:
A variable displacement vane pump comprising: a rotor driven by an internal combustion engine; a cam ring configured to accommodate therein the rotor and further configured to oscillate about a fulcrum of oscillating motion along two axially opposed sidewalls facing both sides of the cam ring respectively; a plurality of vanes, each of which is fitted into the rotor to slide from the rotor toward an inner peripheral surface of the cam ring and set to be kept in abutted-engagement with the inner peripheral surface of the cam ring, the vanes being configured to define a plurality of working chambers in cooperation with an outer peripheral surface of the rotor, the inner peripheral surface of the cam ring, and the two axially opposed sidewalls; a biasing member configured to force the cam ring in a direction that a geometric center of the inner peripheral surface of the cam ring and a rotation center of the rotor are spaced apart from each other; and an inlet portion and a discharge portion both formed in at least one of the two axially opposed sidewalls, the inlet portion being configured to open into a first group of working chambers of the plurality of working chambers so as to extend over the first group of working chambers within an area where volumes of the first group of working chambers increase, and the discharge portion being configured to open into a second group of working chambers of the plurality of working chambers so as to extend over the second group of working chambers within an area where volumes of the second group of working chambers decrease, wherein an only force, acting on the inner peripheral surface of the cam ring to oscillate the cam ring against the biasing member, is a pressure in the discharge portion.