| 摘要 |
PURPOSE:To keep a required discharge quantity of a variable displacement pump, by providing a by-pass valve controlled by the pressure in a closed circuit in a circuit for controlling a servo valve connected directly to a control pump. CONSTITUTION:When a load higher than a prescribed value is applied to a variable displacement pump 1 and pressure in a closed circuit 3 becomes almost equal to the set pressure of a relief valve 6, a by-pass valve 18 is switched to a communicating position (b) by the above pressure functioning as a pilot pressure, and circuits 16, 17 connected respectively to pilot operated portions 9d, 9e of a servo valve 9 are communicated with each other via a restriction. Resultantly, a servo cylinder 8 returns near to a neutral position by the force of a spring and the discharg quantity of the variable displacement pump 1 is reduced, so that power loss due to relief of fluid is reduced. Here, since the differential pressure between the two circuits 16, 17 is compensated by the restriction of the by-pass valve 18 and the servo valve 9 and hence the servo cylinder 8 does not return completely to the neutral position, the pump 1 is enabled to supply a required quantity of fluid in the direction of normal rotation (circuit 3). |
