HYDRAULIC CONTROL DEVICE FOR WORKING MACHINE

Abstract

A hydraulic control device for a working machine includes control valves; hydraulic actuators controlled by corresponding control valves and divided into groups; unified bleed-off valves disposed on discharge lines of first and second hydraulic pumps; central bypass paths provided in the control valves, the central bypass paths of each group being connected in tandem so as to form a central bypass line; and bypass-cutting valves disposed on the central bypass lines, the bypass-cutting valves being automatically switched so as to open the central bypass lines when the unified bleed-off valves are not operated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the circuit structure according to a first embodiment of the present invention;

FIG. 2 illustrates opening characteristics of a unified bleed-off valve and a bypass-cutting valve according to the first embodiment;

FIG. 3 illustrates the circuit structure according to a second embodiment of the present invention;

FIG. 4 illustrates the circuit structure according to a third embodiment of the present invention; and

FIG. 5 illustrates the circuit structure according to a fourth embodiment of the present invention.

Claims

1. A hydraulic control device for a working machine comprising: control valves switched by operating means;hydraulic actuators separately controlled by corresponding control valves, the hydraulic actuators being divided into groups, oil discharged from common hydraulic pumps being supplied to the groups;unified bleed-off valves separately performing unified bleed-off operation on the groups on the basis of signals output from controlling means according to inputs from the operating means;central bypass paths provided in the control valves, the central bypass paths of each group being connected in tandem so as to form a central bypass line for unloading operation; andbypass-cutting valves disposed adjacent to the most downstream part of the central bypass lines for opening or closing the central bypass lines, whereinthe bypass-cutting valves are automatically switched on the basis of the signals output from the controlling means, and are adapted to open the central bypass lines when the unified bleed-off valves are not operated.

2. The hydraulic control device according to claim 1, further comprising: a switching valve for switching flow channels, the switching valve controlling the oil supply to the groups, whereinthe hydraulic actuators for motors that drive left and right crawlers belong to separate groups; andthe switching valve is switched to a simultaneous-operation position where oil discharged from the common hydraulic pumps is supplied to the groups when the control valve for one of the driving motors and the control valve for one of the other hydraulic actuators included in the same group are operated at the same time.

3. The hydraulic control device according to claim 1, wherein the bypass-cutting valves are integrated into a common valve that opens or closes the central bypass lines of corresponding groups at the same time.

4. The hydraulic control device according to claim 3, wherein the bypass-cutting valves are switched on the basis of signals common with those input to the unified bleed-off valves, and are opened when the unified bleed-off valves are not operated.

5. The hydraulic control device according to claim 1, wherein the bypass-cutting valves are integrated into the control valves disposed at the most downstream parts of the corresponding groups as sub-spools.