Patent ID: 7794217

Claim:
A variable capacity vane pump having a pump control ring which is moveable to alter the capacity of the pump, the pump being operable at least two selected equilibrium pressures, comprising: a pump casing having a pump chamber therein, said pump chamber having an inlet port and an outlet port; a pump control ring moveable within the pump chamber to alter the capacity of the pump; a vane pump rotor rotatably mounted within the pump control ring, said vane pump rotor having a plurality of slidably mounted vanes engaging an inside surface of said pump control ring, the vane pump rotor having an axis of rotation eccentric from a centre of said pump control ring, the vane pump rotor rotates to pressurize fluid as the fluid moves from the inlet port to the outlet port; a first control chamber between the pump casing and the pump control ring, the first control chamber operable to receive pressurized fluid to create a force to move the pump control ring to reduce the volumetric capacity of the pump; a second control chamber between the pump casing and the pump control ring, the second control chamber selectively operable to receive pressurized fluid to create a force to move the pump control ring to reduce the volumetric capacity of the pump; and a return spring acting between pump ring and the casing to bias the pump ring towards a position of maximum volumetric capacity, the return spring acting against the force of the first and second control chambers to establish an equilibrium pressure and wherein the supply of pressurized fluid to the second control chamber is varied to change the equilibrium pressure of the pump.