Control device for variable displacement pump

摘要

A control device for a variable displacement pump in which a discharge flow rate of a hydraulic operating fluid is varied by changing a variable element comprises a first negative feedback circuit 24 for controlling a pressure of the hydraulic operating fluid fed from the variable displacement pump, a second negative feedback circuit 24a, and change-over control means 88. The first negative feedback circuit 24 has first pressure detecting means 13 for detecting the pressure of the hydraulic operating fluid, second pressure detecting means 114 for detecting a vent pressure of an electromagnetic relief valve, and a differential pressure calculation circuit 122 for calculating a difference between the pressures detected by the first and second pressure detecting means 13 and 114. The change-over control means 88 performs change-over control by utilizing a differential pressure signal sent from the differential pressure calculation circuit 122 in such a manner that a relief flow rate of the hydraulic operating fluid is reduced when the pressure detected by the first pressure detecting means 13 is higher than a target pressure.