| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a hydraulic circuit for a working machine of a hydraulic backhoe, which can be easily switched over a breaker mode. SOLUTION: The hydraulic circuit for connecting a direction switching valve (6g) to the working machine (10), is comprised of one side circuit (11) and the other side circuit (12). In the one side circuit (11), a three-way switching valve (34) for switching return oil from a breaker (10a) to a circuit for draining the same to an oil tank (4), is arranged. In the other side circuit (12), a pressure variable safety valve (30) for lowering relief pressure when the working machine (10) assumes a breaker (10a) mode, is arranged. Then, a circuit switching solenoid valve (45) for actuating the pressure variable safety valve (30) and the three-way switching valve (34) is arranged in a pilot circuit (35) for connecting a pilot initial pressure circuit (22) of a pilot pressure proportional control valve (20) to the pressure variable safety valve (30) and to the three-way switching valve (34). The pilot initial pressure circuit (22) has a proportional pressure solenoid control valve (51) arranged therein, for controlling pilot pressure applied to the direction switching valve (6g).</p> |
