| 摘要 |
PROBLEM TO BE SOLVED: To provide a hydraulic control device of a construction machine preventing a problem caused by negative pressure of a back pressure of a hydraulic actuator, and reducing power loss as much as possible.SOLUTION: The hydraulic control device supplies and discharges a hydraulic fluid to the hydraulic actuator 7 arranged on the front end of a work attachment, and it includes a direction selector valve 23 arranged between the hydraulic actuator and a hydraulic pump 21 for returning the hydraulic fluid from the hydraulic pump to a tank 27 through a center bypass oil passage 28 at a neutral position c, and moreover, making the hydraulic actuator communicate with the center bypass oil passage, a magnetic proportional relief valve 31 arranged in the center bypass oil passage for enabling adjustment of the back pressure of the hydraulic actuator, a height position detecting means 35 for detecting the height position of the hydraulic actuator, and a control means 32 for controlling the relief valve to adjust the back pressure of the actuator in accordance with the height position of the actuator detected by the height position detecting means. |
