Hydraulic control device of construction machine

摘要

A hydraulic control device of construction machine is provided with a control valve (16) lying between a hydraulic pump (10) and a hydraulic actuator (12) for opening and closing a meter-in control flow path, and a flow rate control valve (18) lying between a pump discharge line on the upstream side of the above control valve and a tank. The above flow rate control valve receives a pump pressure and a load sensing pressure corresponding to a pressure on the downstream side of the meter-in control flow path as a pilot pressure, and is activated for opening and closing so as to maintain a constant differential pressure therebetween. The above flow rate control valve is maintained in a closed state by a pilot pressure switching valve when the load sensing pressure is low. The above control valve opens a bypass line when the meter-in control flow path is closed.