Patent ID: 6422009
Filing Date: 2002-07-23
Classification: E02F,F04B,F15B,Y10T

Abstract:
A pump displacement control system (25) provided in a hydraulic drive apparatus comprising an engine (9) and a variable displacement hydraulic pump (1) driven by said engine for rotation and supplying a hydraulic fluid to a plurality of actuators (21, 21) through respective flow control valves (6, 6),said pump displacement control system comprising a load sensing valve (5) for controlling a displacement of said hydraulic pump so that a differential pressure between a delivery pressure of said hydraulic pump and a maximum load pressure among said plurality of actuators is maintained at a target differential pressure, a fixed displacement hydraulic pump (11) driven by said engine for rotation together with said variable displacement hydraulic pump, and a throttle (12) provided in a delivery line of said fixed displacement hydraulic pump, the displacement of said variable displacement hydraulic pump being controlled by detecting change of a revolution speed of said engine and modifying said target differential pressure in accordance with change of a differential pressure across said throttle, wherein: said pump displacement control system further comprises differential pressure detecting means (31; 50) for detecting the differential pressure across said throttle (12) and outputting, as a signal pressure, a pressure lower than the detected differential pressure by a predetermined value whereby the target differential pressure of said load sensing valve (5) is set based on the outputted signal pressure.