PRESSURE COMPENSATING RALVE SPOOL POSITIONED BY DIFFERENCE IN RESSURE RECEIVING AREAS FOR LOAD AND INLET PRESSURES

摘要

This invention provides a hydraulic driving apparatus of civil engineering/construction equipment including a hydraulic pump (1), an actuator (2) driven by the pressure oil discharged from this hydraulic pump, a flow rate regulation valve (5) disposed between the hydraulic pump and the actuator, pressure compensation valves (8; 8A; 8B) equipped with a valve spool (23; 23A; 23B) for controlling the pressure difference (PZ - PLS) across this flow rate regulation valve and pump flow rate control means (9) for controlling the discharge flow rate of the hydraulic pump in accordance with the pressure difference (Pd - PLS)) between the pump pressure and the load pressure of the actuator, wherein the pressure compensation valves each include a first control chamber (30; 30A) into which the load pressure (PLS) of the actuator is introduced and which biases the valve spool in the valve opening direction by causing this load pressure to act on the first pressure receiving portion (28; 28A) of the valve spool, a second control chamber (29; 29A) into which the inlet pressure (PZ) of the flow rate regulation valve is introduced and which biases the valve spool in the valve closing direction by causing this inlet pressure to act on the second pressure receiving portion (27; 27A) of the valve spool and target pressure difference setting means (31; 50, 51; 31B, 51) for biasing the valve spool in the valve opening direction and setting the target value of the pressure difference across the flow rate regulation valve. In order to provide the actuator (2) with damping performance, the pressure receiving area (AZ) of the second pressure receiving portion (27; 27A) is made greater than the pressure receiving area (ALS) of the first pressure receiving portion (28; 28A).