Patent ID: 7392653
Filing Date: 2008-07-01
Classification: F15B,F16H

Abstract:
1. A hydraulic control system for a working machine, comprising: a hydraulic actuator; a hydraulic pump for supplying working oil to said hydraulic actuator through a control valve; means for supplying a pilot pressure to the control valve; a relief mechanism disposed on the discharge side of said hydraulic pump, said relief mechanism is set to an open state in such a manner that said relief mechanism allows a passage of said working oil from said hydraulic pump when a pump discharge pressure of said hydraulic pump which varies according to a pump flow rate in said hydraulic pump exceeds a predetermined pressure and is set to a closed state in such a manner that said relief mechanism does not allow the passage when said pump discharge pressure becomes the predetermined pressure or lower; an ordinary control means for controlling said pump flow rate in accordance with said pilot pressure; a pressure feedback control means for controlling said pump flow rate in accordance with a comparison of said pump discharge pressure with a preset pressure value; a PQ control means for controlling said pump flow rate inversely to said pump discharge pressure; and selecting means for selecting a pump flow rate based on a smaller one of the pump flow rates controlled by said ordinary control means, said pressure feedback control means and said PQ control means.