1. Failure phenomenon
When working on a Hitachi excavator, the right side is weak to walk; when walking on a flat road, it obviously shifts to the right: when turning to the right, the engine must run at a higher speed than when turning to the left, and the turn is very slow.
2. Check the cause of the failure
According to the power transmission sequence of excavator walking, check as follows:
(1) Check the hydraulic pump
The right travel motor is supplied by a 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 control valve
Symptoms of control valve failure are generally: the valve stem of the walking valve cannot be pushed or the stroke is small; the gap between the valve stem and the valve hole is large, there is a leakage; the pressure of the safety valve is reduced. The above failures will cause weakness in walking on the right.
After inspection, it shows that the stem travel of the left and right operation valves is the same, indicating that there is no problem with the operation of the stem, but it is difficult to determine whether there is any leakage inside and whether the pressure value of the safety valve is reduced. The verification method is to interchange the left and right walking tubing, but the disassembly of some tubing is very difficult, so whether the control valve is faulty is temporarily a doubt, and no disassembly check will be done first.
(3) Check the rotary joint
The hydraulic oil passes from the upper part of the excavator to the lower driving device, and must pass through the rotary joint. If there is leakage inside the rotary joint, a certain amount of high-pressure oil flows to the oil return pipe, which will also lead to weak walking, but there is no leakage inside, and it will not disintegrate. It is difficult to judge in the case of, so this part can only be used as a doubt.
(4) Check the walking motor
Because the excavator is noisy when walking, it is very inconvenient and unsafe for listening and touching the walking motor and the oil pipe.
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 rotated, you can hear the right walking motor sizzle. Touch the oil return pipe with your hand. There is oil flow in the oil return pipe (from the working principle of the motor, when the motor is not working, that is, when there is no walking, the oil return pipe should be free of oil flow); when the joystick continues to move, the track starts to rotate but is very slow: when the engine accelerates, " The "hissing" voice is also enhanced. When the same method is used to operate the left travel, there is no such abnormal phenomenon. It can be explained that the internal leakage of the right travel motor communicates the inlet and return paths, resulting in a reduction in the inlet pressure of the travel motor, which reduces the motor output torque. Therefore, the right travel motor needs to be disassembled for inspection.
(5) Check the walking deceleration device
Because the power transmission from the travel motor to the travel drive wheels is normal and there is no abnormal noise, and the oil temperature, oil quality and oil level in the reduction gear are also normal, it can be ruled out that the travel reduction gear has a fault.
Based on the above analysis and inspection results, it was decided to dismantle and repair the right travel motor first.
3. Troubleshooting
After disassembling the right travel motor, it was found that its valve sleeve had fallen off at the interval between the high and low pressure oil passages, making it communicate with the oil return, thereby reducing the output torque of the right travel motor and walking weak, 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.
