| 摘要 |
PURPOSE:To smooth running over an obstacle and cornering at a soft ground by varying the set pressure of a safety valve to specify the maximum pressures of first and second main circuits, decreasing the set pressure during ordinary running, and increasing the set pressure during running over of an obstacle and cornering on a soft ground. CONSTITUTION:During ordinary running, a solenoid 73b is demagnetized and a switching valve 73 is brought into a drain position (m). Since a chamber 71a of a cylinder 71 is communicated to a tank, the spring force of a spring 70 is low, and a safety valve 36 is brought into a first set pressure. During running over of an obstacle and cornering on a soft ground, a switch 74 of a lever 15 is turned ON, the solenoid 73b is magnetize, and the switching valve 73 is brought into a pressure oil feed position (n). As a result, pressure oil delivered from an auxiliary hydraulic pump 13 is fed to the chamber 71a to compress the spring 70, resulting the increase of a spring force. Therefore, the set pressure of the valve 36 is increased to a second set pressure higher than the first set pressure, and the maximum pressures of first and second main circuits 3 and 4 is increased to a value higher than that during ordinary running, and a running traction force is increased. |
