The recovery of wheel loader stick is slow and all other parts are normal. Generally speaking, if it should be accompanied by boom, bucket, walking or boom, reverse, full walking phenomenon. By comparing the hydraulic system diagram, it is found that the Komatsu loader is different from other companies. There is a solenoid valve in the circuit called the stick half-flow valve, which is specifically used to switch the single main pump or double main pump oil supply when the stick is recovered.
Check the solenoid valve, the electrical signal operation is normal when doing the arm recovery action, but there is no oil at the outlet of the solenoid valve. Differentiating the valve, it was found that the P, T, and A ports of the valve were reversed, and the double pump confluence during normal operation became the flow rate of the single pump. Therefore, the action is full. After the correct installation of the P, T and A ports, test the machine and the arm recovery action is normal. When the display on the dashboard is sometimes absent, it should be judged that the circuit is unhealthy. Check according to the circuit schematic: the circuit to the instrument panel is normal, and the circuit to the computer board is properly investigated. Investigate the two plugs on the computer board. After loosening and tightening, the problem did not appear again. Afterwards analysis should be that the plug is loose and the contact is bad, and sometimes there is no phenomenon when the loader makes a sensation.
After the repair, investigate the machine. It may be used for crane work in Japanese companies, and the stick recovery action is intentionally modified to make it full, so as to adapt to the fine-tuning action when lifting.
The hydraulic system oil temperature is very high when the loader is in operation. After the detection system found that the main pump no-load pressure was 10Mpa, when the engine reached the rated transfer, the no-load pressure exceeded 20Mpa, and the speed of the actuator on the pump side was full during operation. Analytical studies suggest that this phenomenon is opposed to each other. First look at the no-load high-pressure problem; the multi-way valve on the rear pump side is not stuck in the neutral position. It simply shows that the standby valve with the valve stem not in the neutral position is on the front pump side, which has nothing to do with it. It is understood that the hydraulic main pump has been overhauled not long ago, so after doubt, the variable fork of the main pump may trip and shift, forming a swash plate at a small displacement position. This can explain the problem of full speed. Why is the pressure higher at lower displacements?
Differentiated the main pump and found that the open variable shift fork tripped and shifted, forming a swash plate at a smaller displacement position. It is caused by insufficient tightening force and failure to add thread locking glue. After repairing and testing the machine, there is still no-load high-pressure phenomenon. Analyze the hydraulic system diagram and find that the biggest reason for the high pressure of the back pump is the b port logic valve. If there is an additional signal pressure at the b port during no load, the main circuit can be cut off to form high pressure. Unscrew and disconnect the b-port signal hose, start the engine and check that there is still high pressure. Studying the structure of the logic valve, it was found that there was a filter screen at the rear of the throttle valve. After disassembly, it was found that the filter screen had been blocked by foreign objects.
