| 摘要 |
PROBLEM TO BE SOLVED: To provide a hydraulic system of a construction machine capable of releasing a hydraulic oil discharged from a pump in operating an operation device to a tank without passing through a control valve, and smoothly operating an actuator even in fail.SOLUTION: A hydraulic driving system of a construction machine includes a control valve 3 constituted to gradually reduce an opening area of a center bypass passage 3a in accompany with increase of an operation signal, an operation device 4 outputting the operation signal, a bleed-ff line 6, and a bleed-off valve 7 having a pilot port to which a secondary pressure of an electromagnetic proportional valve 8 is guided, and constituted to open the bypass passage until the operation signal is over a first set value, to close the bypass passage when the operation signal is over the first set value, to open an unload passage when the operation signal is over a second set value, and to gradually reduce an opening area of the unload passage from a time when the operation signal is over the second set value to a time when it reaches a third set value.SELECTED DRAWING: Figure 1 |
