When the oil from the travel control valve flows into the oil port BV, the oil flows around the spool 2, opens the one-way valve 3, and flows into the motor oil 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 of the oil port BV increases, the hydraulic oil flows into the oil chamber G through the small oil hole F of the spool 2, and pushes the spool 2 to the left over 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, causing the motor to rotate. When the walking joystick returns to the neutral position, the hydraulic oil at ports AV and BV flows back to the hydraulic tank through the control valve. Therefore, the oil pressure in the oil chamber G drops. Under the action of the spring force, the spool 2 will Return to the original position, so the oil circulation circuit is blocked, and the walking motor stops rotating.
1. Hitachi excavator downhill walking operation
When the excavator is walking downhill, the weight of the excavator forces the walking motor, so the motor sucks oil like an oil pump. When the motor sucks in oil, the oil pressure of the oil port BV and the oil cavity G drops, so that the spool 2 moves to the right. Then, the return oil from the motor is throttled by the spool, and the oil pressure at the oil port AM increases. The increase in oil pressure at port AM also brakes the motor. Therefore, the throttled return oil again increases the oil pressure at port BV and pushes the valve again.
Post 2 back to the left. This repetitive movement of the spool (hydraulic braking action) can prevent the excavator from overspeeding.
2. Circuit protection device
When the circuit oil pressure increases above the set pressure of the overload safety valve 1, the valve opens to release 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 stops.
When the motor has the function of a pump and sucks oil, the one-way valve 3 opens to compensate for the vacuum generated by the sucking oil, so that the circuit does not produce cavitation and cavitation.
