Troubleshooting methods for brake failure of Volvo EC360 excavator

A VOLVO-EC360 excavator, when the working time reached 3000 hours, initially experienced brake failure when the upper turntable rotated, preventing the rotation from stopping in time. After working for another 2 hours, the above-mentioned fault phenomenon became more and more serious. During the inspection, it was found that the turntable could not stop immediately after rapid rotation, but had to rotate in the same direction for a certain distance before it could stop rotating. When the turntable is rotating slowly, it needs to be slowly rotated in the opposite direction by more than 90 degrees before it can come to a stop.

1. Fault analysis

Judging from the fault phenomenon, it is mainly caused by insufficient braking force. There are several reasons for insufficient braking force, so they were investigated item by item.

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

Stop the machine on the slope, rotate the upper turntable to a position perpendicular to the slope, and turn off the engine. At this time, the turntable has not rotated to the lower side due to the effect of gravity. Cut off the oil circuit at PG of the brake control valve, start the engine, and operate the pilot valve. At this time, the turntable cannot rotate. The above situation indicates that there is no problem with the brake pads and springs.

(2) Due to wear and leakage in other parts, pressure oil still entered the SH(A12) end after the operation of the pilot valve was stopped

The pilot valve is not returned to the correct position or is not returned in time. Or the reversing valve 6 is worn, causing the main pump pressure oil to enter the pilot oil circuit through the wear gap via PAs(or PBs), and then enter the SH(A12) pipeline through shuttle valves 3 and 4. There is leakage in other parts. Pressure oil enters SH(A12) from AM, A1, A13, Psp, etc., causing the brake control valve not to return to its original position and remaining in a state of connection with the brake piston. However, PG pressure oil continues to continuously enter the brake piston cavity, resulting in the separation of brake pad 11 and preventing it from performing the braking function.

After pressure detection, it was found that when operating the pilot valve, the pressure at SH(A12) was 3.6MPa. When the pilot valve was stopped, the pressure rapidly dropped from 3.6MPa to 0. Therefore, it was determined that the assumed fault point above was not a problem.

(3) The throttle hole of the regulating valve 2 is blocked and the braking control valve 1 does not return to its original position

After closing the pilot valve, due to the blockage of the throttle hole of the speed control valve 2 and the brake control valve 1 being stuck in the connected position, the pressure in the brake cylinder cannot be released, and the braking device fails to function.

Through pressure detection, the pressure in the brake piston chamber dropped from 3.6MPa to 0 after the operation of the pilot valve was stopped (taking approximately 3 seconds), but when the pressure in the chamber was 0, the rotation of the turntable still could not stop. From this, it can be determined that there is no problem with the speed control valve and the braking control valve.