Patent ID: 7798790

Claim:
A variable displacement vane pump comprising: a rotor including a plurality of vanes slidably extending radially from the rotor; a pump housing defining a pump inlet, a pump outlet and a rotor chamber receiving the rotor and including an inlet port in communication with the pump inlet and through which working fluid is introduced to the rotor and an outlet port through which working fluid exits the rotor to the pump outlet, the outlet port being connected to the pump outlet via a passage; a cam ring encircling the rotor, the ends of the vanes of the rotor engaging the inner surface of the cam ring to form variable volume pump chambers between adjacent vanes, the rotor and the cam ring, the cam ring being pivotable within the rotor chamber about a pivot point to alter the eccentricity of the cam ring with respect to the rotor to change the displacement of the pump; a regulating spring acting between the pump housing and the cam ring to bias the cam ring to a position of maximum eccentricity between the cam ring and the rotor; a first regulating chamber receiving working fluid from the pump outlet, the working fluid applying a regulating force to the cam ring to counter the bias of the regulating spring; and a second regulating chamber receiving working fluid from the first regulating chamber via an orifice, the working fluid applying a regulating force to the cam ring to counter the bias of the regulating spring and the orifice altering the pressure of the working fluid received in the second regulating chamber with respect to the pressure of the regulating fluid in the first regulating chamber, wherein the first and second regulating chambers are separated by the orifice, the orifice being formed between the cam ring and the pump housing and maintaining a substantially constant cross-sectional flow area when the cam ring moves about the pivot point.