Patent ID: 7832997

Claim:
A variable capacity gerotor pump, comprising: a pump housing defining a pump chamber, a pump inlet and a pump outlet; an inner rotor; an outer rotor rotatably located within the pump body, the inner rotor located within the outer rotor and the lobes of the inner rotor and outer rotor engaging, the outer rotor rotates about an axis which is eccentric from an axis of rotation of said inner rotor; a drive shaft engaging the inner rotor to rotate the inner rotor and the outer rotor when the drive shaft is rotated, the inner rotor being axially displaceable along the drive shaft to alter the volumetric capacity of the pump; an active piston including non-rotating sealing surfaces acting between the inner rotor and the outer rotor and the pump housing to create a high pressure region at the pump outlet and a low pressure region at the pump inlet when the drive shaft is rotated, the active piston abutting a surface of the inner rotor and including a substantially cylindrical surface having a radial center offset from the axis of rotation of the outer rotor to provide a seal between the surface of the inner rotor and the outer rotor, when the inner rotor is axially displaced, the cylindrical surface being in contact with two lobes of the outer rotor, and the active piston including a sealing land engaging another lobe of the outer rotor at a position substantially diametrically opposed to the two lobes; and a return spring biasing the inner rotor to a position of axial alignment with the outer rotor.