| 摘要 |
PROBLEM TO BE SOLVED: To prevent the discharge side from having an abnormally high pressure when the uncontrollable period of pump discharge quantity is present in the switching of a solenoid valve by providing a structure for directly introducing the pump discharge pressure to a pressure control valve in a pump switchable to low-pressure large-flow rate pump operation and high-pressure small flow rate pump operation. SOLUTION: When a pump 10 is operated as a low-pressure large flow rate pump in the state where a solenoid valve 18 is OFF, a low-pressure pressure control valve 16 and a high-pressure pressure control valve 17 are in returned positions by spring, and a swash plate 12 is in a maximum discharge quantity position, a pump unit 11 is driven by an electric motor M as the solenoid valve 18 is still in OFF state. At this time, the discharge oil partially acts on the low-pressure pressure control valve 16 as pilot pressure to raise the load pressure, and when it reaches a set value, the valve 16 is switched to introduce the discharge pressure to the pressurization chamber of one operating piston 14a. According to this, the operating piston 14a displaces a swash plate 12 in the direction of reducing its inclination to limit the discharge quantity.
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