The excavator can't stop once it turns.

When the working time of a VOLVO-EC360 excavator reaches 3000h, the braking of the upper turntable fails at the beginning, which leads to the failure to stop the rotation in time. After working for 2 hours, the above failures became more and more serious. During the inspection, it was found that the turntable could not stop immediately after rapid rotation, but only after rotating in the same direction for a period of time. When the turntable rotates slowly, it must rotate slowly in the opposite direction for more than 90 degrees to stop.

1. Fault analysis

Judging from the failure phenomenon, it is mainly caused by insufficient braking force. There are several reasons for insufficient braking force, and we will investigate them item by item.

(1) The brake pads are worn and the spring force is insufficient.

Stop the machine on the slope, make the upper turntable rotate to the state perpendicular to the slope, and turn off the engine. At this time, the turntable will not rotate downward due to gravity; Cut off the oil circuit at the brake control valve PG, start the engine and operate the pilot valve. At this time, the turntable cannot rotate. The above situation shows that there is no problem with the brake pads and springs.

(2) SH(A 1

2) Pressure oil still enters the end.

Incorrect or untimely return of pilot valve; Or the reversing valve 6 is worn, so that the pressure oil of the main pump enters the pilot oil path through the shuttle valves 3 and 4 and the PAs (or PBs) and SH(A 12) pipelines; There are also leaks in other parts. Pressure oil enters SH(A 12) from AM, A 13 and Psp. , so that the brake control valve does not flow back and is always connected with the brake piston, while PG pressure oil continues to enter the brake piston cavity, resulting in the separation of the brake pad 1 1.

According to the pressure test, when the pilot valve works, the pressure at SH(A 12) is 3.6MPa, and when the pilot valve stops, the pressure drops rapidly from 3.6MPa to 0, so it is no problem to determine the above-mentioned hypothetical fault point.

(3) The throttle hole of regulating valve 2 is blocked, and the brake control valve 1 does not return.

After the pilot valve is closed, the throttle hole of the speed control valve 2 is blocked, and the brake control valve 1 is stuck in the ON position, so the pressure in the brake cylinder cannot be released, and the brake device does not work.

Through pressure detection, after the pilot valve stops, the pressure in the brake piston cavity drops from 3.6MPa to 0 (about 3 seconds), but when the pressure in the cavity is 0, the rotation of the turntable cannot be stopped. It can be confirmed that there is nothing wrong with the speed regulating valve and the brake control valve.

(4) Wear and tear of rotating electric machine

After the pilot valve stops working, the oil pressure in the swing motor plays the role of hydraulic braking, and at the same time, it plays the role of braking together with the brake pad 1 1, so that the turntable stops moving. When the sliding shoes and the port plate of the rotating motor are worn, the oil film which should form the hydrostatic support at these parts is destroyed, and the pressure oil in the plunger leaks through the worn parts due to the decrease of sealing performance, which can not play the role of hydraulic braking, resulting in slow braking of the turntable.

From the above analysis and monitoring, it can be seen that the focus of fault investigation should be on the rotating motor.

Step 2 resolve disputes

Through the pressure detection of rotating motors A(BH) and B(LH), it is known that the turntable can only start to rotate when the initial pressure of rotating motors reaches 16MPa, indicating that the rotating resistance is too large. Putting the bucket on the ground and operating the pilot valve, the maximum pressure measured is only 20MPa, which is quite different from the standard value of 26MPa.

When discharging the filter element 7, it was found that there were many metal fragments on the filter element, which was determined to be caused by the wear of the rotating motor. Results After the rotating motor was disassembled, it was found that there were a lot of metal chips in it, and there were traces of strain on the surface of the valve plate. The sealing ring behind the port plate has been squeezed out, and there are obvious strain marks on the surfaces of plunger slipper, swash plate and nine-hole plate, and the metal on the surface of the lower bearing has also fallen off a lot.

After measurement, the height of the worn bearing is still 29.7mm, while the standard height of similar bearings is only 29.0 mm. Therefore, it is concluded that the unqualified bearing was used in the installation, and the abnormal wear of the motor is due to the too tight radial force of the bearing and the too large axial force, and the ground metal chips enter the mating surface and pull.

So, the standard bearing was replaced, and the sliding shoes, port plate, swash plate and nine-hole plate were manually ground. In addition, the pipeline and hydraulic oil tank were washed, and the hydraulic oil filter and hydraulic oil were replaced. After reassembly, the fault disappeared during the trial operation. There are traces of strain on the surface of the port plate, the sealing ring behind the port plate has been squeezed out, there are obvious traces of strain on the surfaces of plunger slipper, swash plate and nine-hole plate, and the metal on the lower bearing surface has also fallen off a lot.

So, the standard bearing was replaced, and the sliding shoes, port plate, swash plate and nine-hole plate were manually ground. In addition, the pipeline and hydraulic oil tank were washed, and the hydraulic oil filter and hydraulic oil were replaced. After reassembly, the fault disappeared during the trial operation.

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