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.

(4) Wear of the rotary motor

After the operation of the pilot valve is stopped, the oil pressure inside the rotary motor at this time plays the role of hydraulic braking and works simultaneously with the brake pad 11 to brake, causing the movement of the turntable to stop. When the sliding shoes, distribution plates and other components of the rotary motor wear out, the oil film that should form hydrostatic support at these parts is damaged. Due to the decline in sealing performance, the pressure oil in the plunger leaks through the worn parts and cannot play the role of hydraulic braking, resulting in slow braking of the turntable.

From the above analysis and monitoring, it is known that the focus of fault detection should be placed on the rotary motor.

2. Troubleshooting

Through the pressure detection at points A (BH) and B (LH) of the rotary motor, it is known that the rotary table can only start to rotate when the initial pressure of the rotary motor's rotation reaches 16MPa, indicating that the rotary resistance is too large. When the bucket was placed on the ground and the pilot valve was operated, the maximum measured pressure value was only 20MPa, which was significantly different from the standard value of 26MPa.

When the exhaust filter element 7 was removed, a lot of metal shavings were found on the filter element, and it was determined that it was caused by the wear of the rotary motor. So, when the rotary motor was disassembled, it was found that there were a large amount of metal shavings inside. There were scratch marks on the surface of the distribution plate, the sealing ring behind the distribution plate had been squeezed out, and there were obvious scratch marks on the surface of the plunger slipper, the swash plate and the nine-hole plate. The metal on the surface of the lower bearing had also fallen off in large quantities.

After measurement, it was found that the height of the worn bearing was still 29.7mm, while the standard height value of similar bearings was only 29.0mm. Therefore, it was determined that an unqualified bearing was used during installation. Due to overly tight axial installation, the radial force on the bearing was too large, causing abnormal wear of the motor. The metal shafilings worn off entered the mating surfaces and scratched them.

So, the standard bearings were replaced, and the sliding boots, distribution plates, swash plates and nine-hole plates, etc. were ground by hand. In addition, the pipelines and the hydraulic oil tank were cleaned, and the hydraulic oil filter element and hydraulic oil were replaced. During the test run after reassembly, the fault had disappeared. There are a large amount of metal shavings. There are scratch marks on the surface of the distribution plate. The sealing ring behind the distribution plate has been squeezed out. There are obvious scratch marks on the surface of the plunger slipper, the swash plate and the nine-hole plate. A large amount of metal on the surface of the lower bearing has also fallen off.

After measurement, it was found that the height of the worn bearing was still 29.7mm, while the standard height value of similar bearings was only 29.0mm. Therefore, it was determined that an unqualified bearing was used during installation. Due to overly tight axial installation, the radial force on the bearing was too large, causing abnormal wear of the motor. The metal shafilings worn off entered the mating surfaces and scratched them.

So, the standard bearings were replaced, and the sliding boots, distribution plates, swash plates and nine-hole plates, etc. were ground by hand. In addition, the pipelines and the hydraulic oil tank were cleaned, and the hydraulic oil filter element and hydraulic oil were replaced. During the test run after reassembly, the fault had disappeared.