| 摘要 |
<p>A hydraulic drive system for a civil-engineering and construction machine, comprising an unloading valve (17) connected to a discharge line (15) of a hydraulic pump for relieving a hydraulic fluid from the hydraulic pump (9) to a tank (16) when a differential pressure between a delivery pressure of the hydraulic pump and a load pressure of an actuator (2) exceeds a first predetermined value, for controlling the differential pressure. The unloading valve has a spool (18), a first receiving chamber (19) at the one end of the spool receiving the delivery pressure of the hydraulic pump, and a second pressure receiving chamber (19) arranged at the other end of the spool receiving the load pressure of the hydraulic actuator. Restrictive communication means (30, 31, 32) selectively communicate the first and the second pressure receiving chamber with each other, whereby when a phase deviation exists between the delivery pressure and the maximum load pressure, oscillation of the unloading valve is prevented. <IMAGE></p> |
