HYDRAULIC DRIVE DEVICE OF WORKING MACHINE

摘要

To permit forcedly stopping combining flows of pressure fluid from two hydraulic pumps when a load pressure on a combined-flow-driven actuator in which the flows of pressure fluid are combined together exceeds a predetermined pressure and hence to permit driving the combined-flow-driven actuator with the pressure fluid from only one of the hydraulic pumps, a hydraulic drive system is provided with a flow-combining valve 2 connected to a directional control valve 1 in a first group of directional control valves via a center bypass passage 3, a flow-combining circuit 5 communicating the flow-combining valve 2 and a supply port of a flow-combining directional control valve 4 with each other, and a combined-flow-driven actuator 20 controlled by the flow-combining directional control valve 4, and performs overall power control such that a total value of input torques to the two hydraulic pumps 15,18 does not exceed an output torque from an engine 30. The hydraulic drive system is provided with a canceling valve 10 to cancel the combination of flows by the flow-combining valve 2 when a load pressure on the combined-flow-driven actuator 20 becomes higher than a predetermined pressure.