One 52T port specific large hydraulic excavator found that after the engine automatic idle function was turned on during use, the rotating speed would suddenly increase when the working device did not act. After running for a period of time, it returned to the automatic idle state. When the excavator working device does not act, this phenomenon occurs repeatedly, and the failure time interval is uncertain.
1. Working principle of automatic idle
The purpose of setting the automatic idle function of the excavator is to reduce the engine speed when the working device of the excavator does not act, so as to reduce the engine power loss and achieve energy saving and consumption reduction. The working principle of the automatic idle function is that the controller detects the pilot pressure of the excavator and judges whether the pilot handle acts according to the state of the pilot pressure switch. If the pilot handle does not act, reduce the engine speed to the set idle state. When the controller detects that the state of the pilot pressure switch changes and judges that the pilot handle acts, it immediately increases the engine speed to the working speed. In order to adapt to the port environment and reduce the manufacturing cost, the excavator is not equipped with a lower traveling device, so one of the two oil ports of the pilot pressure switch is idle.
2. Failure cause analysis
According to the working principle of the engine automatic idle function of the excavator, we believe that the main reasons for the failure of the engine automatic idle function are as follows: first, there is a problem in the controller control program, resulting in abnormal engine speed signal; Second, the pilot pressure switch is faulty, resulting in the pressure switch can not correctly reflect the working condition of the excavator; Third, there is a virtual connection in the electrical control circuit, resulting in the signal distortion detected by the controller; Fourth, the pilot hydraulic control circuit is blocked, resulting in the pilot pressure switch can not reflect the real operation.
3. Troubleshooting
According to the above failure cause analysis, the following troubleshooting can be carried out:
Turn on the automatic locking function, observe the automatic idle state of the engine without operating the pilot handle, and confirm that the level 3 automatic idle function of the engine can be realized. However, the engine will automatically increase the speed after running at automatic idle for a period of time, and then return to automatic idle state. This phenomenon occurs repeatedly and the time of occurrence is not fixed.
Unplug the connector of the pilot oil circuit pressure switch, and the signal collected by the controller is high level. When the pilot handle does not act, the engine still enters the automatic idle state without failure. Short circuit both ends of the connector, and the signal collected by the controller is low level. When the pilot handle does not act, the engine does not enter automatic idle operation. This inspection shows that there is no problem with the controller program and electrical control circuit.
Connect the pilot pressure switch at the oil port and idle oil port interchangeably, and the fault disappears after commissioning. This indicates that the pilot pressure switch has been damaged. After replacing the new pilot pressure switch, the fault is completely solved.
Based on the analysis of the working principle, the fault location was quickly determined through measures such as short circuiting, disconnecting the line and changing the component installation method, which improved the repair speed and quality and saved the maintenance time and cost.
