| 摘要 |
PURPOSE:To stably supply necessary flow and pressure to an actuator during its operation and hold the circuit pressure at a fixed level in a neutral condition of the actuator, by controlling a pump by means of a restrictor operated with an auxiliary pump, and a differential pressure control valve. CONSTITUTION:Pressurized oil from a variable displacement pump 1 is allowed to flow into an actuator 10 and a pilot chamber 32 of a differential pressure control valve 30 in accordance with the changeover amount of a selector valve 2. In a case such that a delivery pressure of the pump 1 is higher than the sum of a pressure in a pilot chamber 33 and tension of a spring 34, a differential pressure control valve 30 is switched to the left and the delivery amount is reduced by a tilt angle cylinder 37. While in the reverse case, the valve 30 is switched to the right and the cylinder 37 is communicated to a tank 38 causing the increase in the delivery amount of the pump 1. Even if the load on the actuator 10 is changed, the difference between pressures before and behind the selector valve 2 is held at a fixed level. If the selector valve 2 is returned to a neutral position, oil from an auxiliary pump 18 is allowed to flow into a tank 39 to generate a difference between pressures before and behind a restrictor 22, while oil of the pump 1 is communicated to a tank 21 by operating a throttle valve 20, and the pump 1 is held at a pressure in accordance with action of the differential pressure control valve 30 due to a difference between pressures generated before and behind a restrictor 26. |
