CONSTRUCTION-MACHINERY HYDRAULIC CIRCUIT, AND CONTROL DEVICE THEREFOR

摘要

A hydraulic circuit for a construction machine including a direction control valve group having multiple direction control valves that are provided in tandem to a center bypass passage of the construction machine, a bleed-off valve provided to the center bypass passage downstream of the direction control valve group, and a control valve that controls an amount of pressure oil to be supplied to the direction control valve. The direction control valve includes a first internal passage that flows out the pressure oil supplied to the direction control valve to the center bypass passage, and a second internal passage that supplies the pressure oil to a hydraulic actuator of the construction machine. The first internal passage causes pressure oil discharged from the hydraulic pump to flow out to the center bypass passage downstream of the direction control valve, so that the center bypass passage and the first internal passage form a parallel passage. The bleed-off valve performs bleed-off control on pressure oil supplied by way of the parallel passage by changing an opening area of the bleed-off valve. The control valve controls the amount of the pressure oil to be supplied to the second internal passage by changing an opening degree of the control valve.