Examination of the weak excavator on the right, failure phenomenon found when the Caterpillar EX90 hydraulic excavator was found to be weak on the right during the operation; when the road was walking, it obviously shifted to the right; when turning to the right, it was normal. Running, and turning is very slow.
cause of issue:
According to the walking power transmission sequence of the excavator, we do the following inspections in the order:
1. Check that the excavator hydraulic pump right travel motor is supplied by the hydraulic pump. In addition to the travel drive device, the hydraulic pump also supplies oil to the bucket cylinder. Since the bucket cylinder works normally, it can be determined that there is no problem with the pump.
2. Check the symptoms of the control valve failure of the excavator control valve: the valve stem of the walking valve is not pushed or the stroke is small; the cooperation gap between the valve stem and the valve hole is large, there is a leakage; the safety valve pressure is reduced. The above failures will cause weakness in right walking.
3. The inspection shows that the valve stem travel is the same for left and right walking, indicating that there is no problem with the operation of the valve stem, but it is difficult to determine whether there is leakage inside or whether the pressure value of the safety valve is reduced. The verification method is to exchange the left and right walking tubing, but the disassembly of some tubing is very difficult, so the failure of the control valve is temporarily a doubt, and no disassembly inspection will be done first.
4. Check the excavator walking motor. Because the excavator is noisy when walking, it is very inconvenient and unsafe to listen and touch the walking motor and the oil pipe. Therefore, use the bucket to support the right walking track, and slowly operate the right walking joystick at the engine idling speed. When the drive wheel has not yet turned, you can hear the right walking motor sizzle. The oil pipe feels that there is oil flow in the return pipe; when the joystick continues to move, the track starts to rotate but is very slow; when the engine accelerates, the sound of "hiss" also increases. There is no such abnormal phenomenon when operating the left travel in the same way. It can be explained that the internal leakage of the right travel motor connects the inlet and return paths, which reduces the pressure of the inlet of the travel motor and reduces the output torque of the motor. Therefore, the right travel motor needs to be disassembled for inspection.
5. Check that the hydraulic oil of the rotary joint of the excavator passes from the upper part of the excavator to the lower driving device. It must pass through the rotary joint. If there is leakage inside the rotary joint, a certain amount of high-pressure oil will flow to the oil return pipe, which will also cause walking weakness, but There is no leakage, it is difficult to judge without disintegration, so this part can only be used as a doubt.
6. Check the walking speed reduction device of the excavator. Because the power transmission from the walking motor to the walking driving wheel is normal and there is no abnormal noise. In addition, the oil temperature, oil quality and oil level in the speed reduction device are also normal, so the existence of the walking speed reduction device can be ruled out malfunction. Based on the above analysis and inspection results, it was decided to dismantle and repair the right travel motor first. After repairing and disassembling the right travel motor, it was found that its distribution bushing had been detached at the high and low pressure oil passages, which connected the oil inlet and return, thereby reducing the output torque of the right travel motor and weak walking, which is consistent with the results of inspection and listening . Due to the difficulty in repairing the bushing, it was decided to replace the right travel motor. After installation, the right travel returned to normal.
