Created on:2022-08-13 10:34

Working principle and troubleshooting of reversing valve of electric scraper

Working principle and troubleshooting of reversing valve of electric scraper

Tor0-400e electric LHD produced in Finland has high requirements for the working reliability of the reversing valve of the variable speed system during the operation of shoveling and loading ore underground. When the shovel loading is completed and retreats, if the response of the speed change system is slow, the scraper retreats and starts slowly, which is very easy to make the ore slide from the pile and cause the machine burying accident. To deal with such faults as speed change system, we must first understand the working principle and structure of directional valve.

1. Working principle and structure of reversing valve

The working principle of the scraper reversing valve is shown in Figure 1.

The electric LHD is powered by a 1000V three-phase AC asynchronous motor and adopts a hydraulic transmission system. In order to ensure smooth operation without impact, the scraper adopts Clark 5.5hr34425 gearbox, and the reversing valve adopts the design of energy storage and delayed reversing. It can be seen from Figure 1 that in order to close the transmission directional clutch 2, the oil on the main shaft must first charge the accumulator through the orifice (a). Only when the accumulator pressure reaches the set value can the overflow valve 5 be cut off, and the clutch is quickly closed under the action of pressure oil. The charging time of the accumulator is 2S, and the delayed closing of the clutch eliminates the impact caused by the direct action of the pressure oil on the disengaging device after the gear is engaged, so that the shift operation of the scraper is stable. The pressure time relationship curve of the clutch is shown in Figure 2.



As shown in Figure 4, when the reverse gear is selected, the pressure oil enters the chamber a of the regulating valve, causing the plunger 2 to move to the left, exposing the orifice. At this time, the oil drain port is also opened. With the increase of the throttle orifice, the pressure in chamber a decreases until the pressure generated by the pressure oil in chamber a is equal to the force generated by the return spring 1 in chamber B, the pressure regulating valve plunger 2 no longer moves left, and chamber a remains at a low pressure. This process corresponds to the T1 segment in the P-T curve, and the time is 0.14s.

The pressure oil continuously enters chamber a, raising the pressure in chamber a, and the rising value is determined by the return spring 1. Under the action of this pressure difference, the pressure oil enters cavity B through orifice 5, and enters the accumulator cavity from oil discharge port 6. This process corresponds to T2 segment of P-T curve, and the time is 0.30s. When the accumulator cavity is filled with pressure oil, the accumulator plunger 3 compresses the spring 4 to increase the elastic force, which increases the pressure in chamber B that fills the accumulator cavity and the pressure regulating valve plunger 2. The plunger 2 moves to the right, the orifice area decreases, and the pressure in chamber a increases, which moves the pressure regulating valve plunger 2 to the left. This dynamic process corresponds to the T1 segment of the P-T curve, with a time of 1.58s. At this time, the pressure rise is controlled by spring 4.


2. 故障诊断与排除



2. Troubleshooting

According to the analysis of the working principle of the system, there are two reasons for the failure:

(1) The transmission direction gear is leaked from the bench, and the establishment time of gear pressure is extended.

(2) The orifice of the pressure regulating valve of the reversing valve is blocked, and the hydraulic oil flow is reduced, resulting in the extension of the charging time of the accumulator.

When determining whether the directional clutch has internal leakage, a pressure test must be carried out.

In order to determine whether the clutch leaks, make a 9.525mm according to the size of the plunger space of the pressure regulating valve × The 28.565mm round plunger hits the plunger space B, so that the pressure oil in chamber a directly enters the clutch without passing through the accumulator, starts the motor, and finds that the scraper starts immediately, which proves that the clutch is well sealed, and the fault is caused by the pressure regulating valve.

Remove the forward and backward pressure regulating valves. It is found that the throttle hole on the plunger is partially blocked. Soak and clean it with cleaning fluid. After the dirt in the throttle hole is removed, the test run is normal and the repair is completed.

The treatment of this kind of fault proves that to ensure the sensitivity of electric shovel commutation, the filter element of the transmission system must be replaced regularly, the system oil pressure must be tested frequently, and the system hydraulic oil must be replaced in time according to the requirements.

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