Troubleshooting methods for brake failure of Volvo EC360 excavator

(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.