| 摘要 |
PCT No. PCT/JP93/00508 Sec. 371 Date Nov. 22, 1993 Sec. 102(e) Date Nov. 22, 1993 PCT Filed Apr. 20, 1993 PCT Pub. No. WO93/21395 PCT Pub. Date Oct. 28, 1993.The hydraulic circuit system for civil engineering and construction machines includes a first pressure adjusting device (130) arranged between first variable restrictors (107, 107a) of a left traveling directional control valve (47) and a first traveling motor (57) for controlling the pressure downstream of the first variable restrictors to a value corresponding to a first signal pressure and a second pressure adjusting device (133) arranged between second variable restrictors (108, 108a) of a right traveling directional control valve (49) and a second traveling motor (58) for controlling the pressure downstream of the second variable restrictors to a value corresponding to a second signal pressure. A shuttle valve (136) detects a higher one of load pressures of the first and second traveling motors as a maximum load pressure. When performing the combined operation in which the first and second traveling motors are driven with at least one of a plurality of working actuators (53-56) simultaneously, signal selection valves (131, 135, 170) are actuated so as to supply the maximum load pressure to the first and second pressure adjusting devices as the first and second signal pressures. Consequently, in a combined operation of traveling and performing other works, a communication circuit (110) is activated along with the operation of a working actuator whereby even if a hydraulic fluid supply circuit (104) of the second traveling directional control valve communicates with a hydraulic fluid supply circuit (103) of a first traveling directional control valve, the differential pressures across the first and second variable restrictors become almost the same, thereby achieving a stable straight traveling.
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