A common engine problem of the PC-200 excavator is that the engine is running normally, but the working device moves slowly. The main reasons for this failure are: the pressure of the hydraulic oil circuit is too low, the engine speed sensor is damaged, and the displacement of the working pump is too small. . The solution is to check the engine speed sensor first. The signal from the engine speed sensor is input to the pump controller to control the displacement of the working pump. If the sensor is damaged or its connecting line is disconnected, the pump controller will be unable to issue a command to change the pump displacement due to no signal input. The solenoid valve will therefore be unable to adjust the pump flow in a timely manner, causing the entire machine’s working device to move slowly. It is known that the resistance of the speed sensor should be 500 to 1000 ohms. After testing, the resistance was normal and the electrical system was normal. Then check the pressure of the self-reducing valve, remove the pressure measuring screw plug of the oil line, and install the oil pressure gauge. When the engine is idling at high speed, the pressure should be around 3.4MPa, but the actual measurement is only 2MPa. When the valve was disassembled and inspected, it was found that there was dirt sandwiched between the poppet valve and the shell of the valve. Because the poppet valve was stuck, the pressure could not reach the set value. Therefore, no matter how the operating handle moved, the PPC valve (proportional pressure The oil pressure between the control valve and the main control valve does not change much, causing the main control valve spool to move very little, even if the hydraulic oil flow of the working device is small, causing the working device to move slowly. Therefore, as long as the self-pressure reducing valve is cleaned and the pressure is restored to 3.4MPa, the fault will be solved.
The main reason why the engine stalls when the excavator is performing heavy-load operations is that the engine automatically stalls due to overload due to the excessive displacement of the working pump. It can be seen from the hydraulic system diagram that the servo piston that detects the displacement of the working pump should be controlled first, and then the investigation should be carried out according to the complexity of the functions of each control valve. You can first check whether the connection of the solenoid valve is reversed. If the connection is reversed, it will cause the signal transmission error of the pump controller. When the machine is under heavy load operation, the pump displacement will be out of control, causing the engine to stall. If there are no errors, then check the working condition of the solenoid valve. The main technical indicator is that the resistance of the solenoid valve coil should be 7 to 14 ohms. If the solenoid valve is damaged, the valve will not be able to receive the signal from the pump controller when the machine is operating under heavy load. The command to reduce the pump displacement prevents the solenoid valve from adjusting the pump displacement, and the engine stalls due to overload. If there is no fault in the solenoid valve, check the pressure control valve (PC valve) again. The function of the PC valve is that when the change in external load is reflected as a change in the working pressure, the PC valve senses the change in pressure, and then according to the “changes in the pump and engine” According to the principle of “best match”, the displacement of the working pump is automatically adjusted. If the valve core is stuck, the pressure at the end of the rodless cavity of the servo piston will not change with the change of the external load pressure, causing the displacement of the working pump to be too large. This causes the engine to stall. If there is a fault, replacing the hydraulic oil and cleaning the PC valve can solve the problem.
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Post time: Feb-08-2024