HYDRAULIC DRIVE FOR HYDRAULIC WORK MACHINE

摘要

PURPOSE:To provide a hydraulic drive for hydraulic work machine which can secure superior metering characteristics even in the case of heavy loading as well as light loading. CONSTITUTION:A hydraulic pump 2 and an actuator 3 are connected to each other via metering passes 30b1 and 30b2 provided on a direction switch valve 30. A throttle valve 4 is provided at the lower reaches of a center bypass 30a provided on the direction switch valve 30. Bypass piping 32 is provided parallel to a set piping of the throttle valve and a variable throttle valve 31 is provided in the piping. Loading pressure from a loading pressure signal line 33 is introduced to the variable throttle valve. In the case of light loading, spring force of a spring 31a becomes predominant over the loading pressure so as to close the bypass piping and a control pressure signal 5 for lowering pumping force and pump flow rate is transmitted to a regulator 6. In the case of heavy loading, the loading pressure is predominant over the spring force so as to open the bypass piping and a control pressure signal for raising pumping pressure and pump flow rate is transmitted to the regulator 6.