Patent ID: 7614858

Claim:
A variable displacement vane pump comprising: a pump rotor having a plurality of moveable vanes; a pump housing defining a pump chamber with the rotor being located within the chamber; a displacement varying ring pivotally mounted in the pump chamber, the ring enclosing the pump rotor to define a high pressure area and a low pressure area about the rotor, the pump housing having an inlet to admit working fluid into the low pressure area and an outlet to deliver pressurized working fluid from the high pressure area; a control mechanism pivoting the ring within the pump chamber to vary the volumetric displacement of the pump in response to outlet pressure of said working fluid; and wherein the outlet also provides working fluid to a first portion within the pump chamber outside the ring, the working fluid in the first portion acting on an area substantially similar to the area inside the ring acted upon by the working fluid in the high pressure area of the pump to reduce the net force exerted on the ring by the high pressure working fluid.