| 摘要 |
PCT No. PCT/JP92/00463 Sec. 371 Date Sep. 29, 1992 Sec. 102(e) Date Sep. 29, 1992 PCT Filed Apr. 13, 1992 PCT Pub. No. WO92/18710 PCT Pub. Date Oct. 29, 1992.A hydraulic drive system for a construction machine comprising a hydraulic pump (1) of variable displacement type, a pump regulator (2) for controlling a delivery rate of the hydraulic pump, a plurality of hydraulic actuators (7) driven by a hydraulic fluid supplied from the hydraulic pump, a plurality of directional control valves (4A-4D) for controlling respective flows of the hydraulic fluid supplied from the hydraulic pump to the plural hydraulic actuators, a low-pressure circuit (22), a center bypass line (23) for connecting in series center bypasses of the plural directional control valves (4A-4D) to the low-pressure circuit (22), a plurality of bleeding-off restrictors (26) in the center bypass line and having their openings variable in accordance with respectively associated directional control valves, a fixed restrictor (5) disposed in the center bypass line for producing a control pressure (PZ), and a pressure sensor (8) for detecting the control pressure and outputting a corresponding electric signal (E). The hydraulic drive system further comprises a memory unit (9c) for storing a plurality of preset pump flow rate characteristics (40, 41, 42) that define relationships between a value of the electric signal (E) outputted from the pressure sensor (8) and a delivery rate (Q) of the hydraulic pump (1), a selector (12) for outputting a command signal (ES) to select one of the plural pump flow rate characteristics (40, 41, 42) preset in the memory unit, and an arithmetic unit (9b) for determining the delivery rate (Q) corresponding to the value of the electric signal (E) outputted from the pressure sensor means (8) based on the pump flow rate characteristic selected by the command signal (ES), and outputting a drive signal (ED) corresponding to the determined delivery rate. The pump regulator is driven with the drive signal.
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