As shown in Figure 5-36, when the oil from the travel control valve flows into the port BV, the oil flows around the spool 2, opens the check valve 3, and flows into the motor port BM. The return oil from the motor oil port AM is blocked by the check valve 4 and the spool 2.
When the oil pressure at port BV increases, hydraulic oil flows into the oil chamber G through the small oil hole F of the spool 2, and the spool 2 is pushed to the left against the spring force. Therefore, the return oil from the motor oil port AM flows into the oil port AV through the oil discharge port H of the spool 2 to rotate the motor. When the walking joystick returns to the neutral position, the hydraulic oil at the ports AV and BV will flow back to the hydraulic oil tank through the control valve. Therefore, the oil pressure in the oil chamber G drops, and under the action of the spring force, the spool 2 will Returning to the original position, the oil circulation circuit is blocked and the travel motor stops rotating.
1. excavator downhill walking operation
When the excavator walks downhill, the excavator's own weight forcibly drives the walking motor, so the motor is like an oil pump-like oil absorption. When the motor sucks oil, the oil pressure in port BV and oil chamber G drops, causing the spool 2 to move to the right. As a result, the return oil from the motor is throttled by the spool, increasing the oil pressure at port AM. The increase in the AM oil pressure in the port causes the motor to brake. Therefore, the throttled return oil again increases the oil pressure in the port BV and pushes the valve.
Column 2 returns to the left. This repetitive movement of the spool (hydraulic braking action) can prevent the excavator from speeding.
2. Circuit protection device
When the circuit oil pressure increases above the set pressure of the overload safety valve 1, the valve opens, releasing the peak pressure to the low pressure side, thereby avoiding motor overload. The valve can also reduce the impact pressure generated by the inertial force when the motor is stopped.
When the motor has the function of a pump to suck oil, the check valve 3 opens to compensate for the vacuum generated by the oil suction, so that the circuit does not produce cavitation and cavitation.
