Patent ID: 7168246
Filing Date: 2007-01-30
Classification: E02F,F15B

Abstract:
1. A hydraulic control device for a working machine, comprising: a plurality of hydraulic actuators; a hydraulic pump which functions as a hydraulic power source of the hydraulic actuators; a plurality of operating means which may be manipulated by a control amount; a plurality of control valves which control the actuators on the basis of operations by the operating means, wherein the control valves have center bypass passages which function as individual bleed-off passages which open when the control valves are in neutral states; a common bleed-off valve which returns excess oil discharged from the hydraulic pump to a tank via an unload passage on the basis of the operations by the operating means, wherein the common bleed-off valve has a position for closing the unload passage when the common bleed-off valve is in a non-operating state; and control means for controlling the common bleed-off valve and the control valves based on an operating signal of the operating means, such that the center bypass passages are closed in initial stroke periods in which the control valves move toward operating positions and the unload passage of the common bleed-off valve is opened immediately before the center bypass passages of the control valves close.