| 摘要 |
PCT No. PCT/JP92/00589 Sec. 371 Date Jan. 5, 1993 Sec. 102(e) Date Jan. 5, 1993 PCT Filed May 8, 1992 PCT Pub. No. WO92/19821 PCT Pub. Date Nov. 12, 1992.A hydraulic drive system for a construction machine comprising a plurality of distribution compensating valves (7a, 7b) for controlling the respective differential pressures across the plurality of flow control valves (6a, 6b), the distribution compensating valves respectively having first pressure bearing chambers (52a, 52b) acting in a valve-closing direction, second pressure bearing chambers (53a, 53b) acting in a valve-opening direction, and third pressure bearing chambers (54a, 54b) acting in the valve-closing direction to reduce target values of differential pressures across a plurality of associated flow control valves (6a, 6b). The system further comprises a fourth pressure bearing chamber (55a, 55b) provided in at least one of the plurality of distribution compensating valves (7a, 7b) and subjected to a second control pressure (PCT) for acting in the valve-opening direction to set a target value ((Delta)PT) of the differential pressure across the associated flow control valve (6a, 6b). This enables the target value of the differential pressure across the flow control valve to be freely changed whereby an allowable maximum flow rate passing through the flow control valve can be freely changed so that a maximum driving speed may be freely set dependent upon the capacity of a hydraulic actuator used and/or the forms of work to be carried out.
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