A VARIABLE CAPACITY PUMP WITH DUAL SPRINGS

摘要

A variable capacity vane pump has a pump control ring that is moveable to alter the capacity of the pump. A control chamber is formed between the pump casing and the control ring. The control chamber is operable to receive pressurized fluid to create a force to move the control ring to reduce the volumetric capacity of the pump. A primary return spring acts between control ring and the casing to bias the control ring towards a position of maximum volumetric capacity. A secondary return spring is mounted in the casing and is configured to engage the control ring after the control ring has moved a predetermined amount. The secondary return spring biases the control ring towards a position of maximum volumetric capacity. The secondary return spring acts against the force of the control chamber to establish a second equilibrium pressure.