PRE-COMPRESSION DUAL SPRING PUMP CONTROL

摘要

A variable capacity vane pump (20) is provided having a pump control ring (44) that is moveable to alter the capacity of the pump (20). A control chamber (60) is formed between the pump casing (22) and the control ring (44). The control chamber (60) is operable to receive pressurized fluid to create a force to move the control ring (44) to reduce the volumetric capacity of the pump (20). A primary return spring (56) acts between the control ring (44) and the casing (22) to bias the control ring (44) towards a position of maximum volumetric capacity. A shaft is coupled at one end to the control ring and a second end of the shaft is positioned a predetermined distance from the casing (22). A secondary return spring (62) is mounted about the shaft and is configured to engage the control ring (44) after the control ring (44) has moved a predetermined amount. The secondary return spring (62) biases the control ring (44) towards a position of maximum volumetric capacity. The secondary return spring (62) acts against the force of the control chamber (60) to establish a second equilibrium pressure.