| 摘要 |
PURPOSE:To reduce power loss and give priority to speed control of one of the actuators that is subjected to the highest load pressure by communicating via a shuttle valve a load pressure in the rear position of each of variable orifices of a plurality of flow rate and direction control valves, with a pressure in a back pressure chamber of a pressure control valve which opens and closes the passage between two ports. CONSTITUTION:A pressure control valve 30 is operated in accordance with a difference between fluid pressure on the side of a primary port 24 and in a back pressure chamber 32, namely, a difference between pressures in front of and behind a flow rate regulating variable orifice 19 so as to open and close the passage between the secondary and primary ports 25 and 24, whereby controlling the quantity and the pressure of fluid discharged by a variable pump 1 in accordance with the opening of the flow rate regulating variable orifice 19. The pump therefore will not discharge any excess fluid and the difference between pressures in front of and behind the flow rate regulating variable orifice 19 may be controlled to exhibit a constant value which corresponds to a spring pressure of a spring 33, thereby providing small power loss. One flow rate regulating variable orifice 19a, for example, behind which the highest load pressure is exhibited is selected by shuttle valves 42a and 42b and the pressure is propagated into the back pressure chamber 32 of the pressure control valve 30 to control the difference between the front and behind pressures, so as to give priority to the speed control of an actuator 50a which is subjected to the highest load pressure. |
