Patent ID: 7818968
Filing Date: 2010-10-26
Classification: F15B

Abstract:
1. A hydraulic control device of construction machine, comprising: a hydraulic pump; a hydraulic actuator to which working oil is supplied from said hydraulic pump; an operation member operated by an operator; a control valve having a meter-in control flow path lying between said hydraulic pump and said hydraulic actuator, the control valve working so as to change a flow rate of the working oil supplied from said hydraulic pump to said hydraulic actuator through said meter-in control flow path following the operation of said operation member; a flow rate control valve lying between a pump discharge line on the upstream side of said control valve and a tank, the flow rate control valve for changing a flow rate of the working oil returned from said pump discharge line to said tank; flow rate control means for activating said flow rate control valve for opening and closing in the direction of maintaining a constant differential pressure between a pressure of the working oil in said pump discharge line and a pressure on the downstream side of said meter-in control flow path; closed valve maintaining means for maintaining said flow rate control valve in a closed state irrespective of the differential pressure when the pressure on the downstream side of said meter-in control flow path is lower than a set pressure which is preliminarily set; a bypass line for communicating with said pump discharge line and said tank on a different route from said flow rate control valve; and bypass switching means for opening said bypass line when said control valve closes said meter-in control flow path, and decreasing a flow path area of said bypass line following an increase in a flow path area of said meter-in control flow path.