Diagnosis and detection of the fault that the bucket of the ED600T Ding underground excavator cannot be leveled

In April 1999, one of our company's ED600T underground excavators was operating during the muck removal work at the Changliangshan Tunnel. Due to a tunnel collapse, the machine was hit, causing the bucket to be unable to maintain a horizontal position when loading and lifting materials. The movement of the bucket was out of control, resulting in severe scattering of stones and inability to load muck normally.

1. Diagnosis and analysis process

To identify the cause of the malfunction, we first inspected the damaged parts on the machine's exterior and promptly repaired them. Then, through the automatic monitoring display screen and microcontroller in the cab, the pressure variation values of the main control valves in the hydraulic system with the load and the pressure values of the entire system were observed, inspected and adjusted, but no abnormal phenomena were found. Finally, the operation of the unique device in the hydraulic system of this machine - the cartridge valve - was analyzed. One of the functions of the cartridge valve is to control the automatic leveling action of the bucket. During the lifting process of the bucket, the Angle of the bucket is constantly corrected through the automatic leveling control of the hydraulic cartridge valve group, keeping it always in a horizontal state to prevent the stones from falling. The automatic leveling function is achieved by converting the displacement signal into an electrical signal through the sensor installed in the hydraulic cylinder and transmitting it to the automatic leveling control module for control.

The working principle of the automatic leveling module is as follows: There are two automatic leveling modules on the underground excavator. One module is installed on the lifting cylinder, and the other is installed on the bucket cylinder. These two modules alternately function when the bucket is lifted or lowered to keep the bucket level. When the bucket filled with stone materials is lifted to a certain height, the automatic leveling module switch on the lifting cylinder releases the electromagnet and sends a signal to the solenoid valve of the rapid unloading system, and the bucket automatically discharges the stone materials. When the bucket drops to a certain height, the switch of the automatic leveling module on the bucket cylinder releases the electromagnet, cutting off the electrical signal, and the bucket level device does not function.

Based on the function of the hydraulic cartridge valve and the working principle of the automatic leveling control module, it is initially determined that the inability of the underground excavator bucket to be level is caused by a malfunction of the automatic leveling device, that is, the control module.

2 Detection process

(1) Let the engine run at a low speed, lower the control lever of the main control device to connect the pilot pressure in the hydraulic system control circuit, fully retract the bucket cylinder and place the bucket on the ground. At this point, when using a multimeter to test the measurement points of the inner and outer arm junction box (Part 103 in the figure) with wire numbers 48 and 6, the voltage was 0. At this point, the bucket leveling module is functioning normally.

(2) Lift the large arm and use a multimeter to test the automatic leveling device module on the lifting cylinder. Under normal circumstances, during the lifting process of the bucket by the lifting cylinder, the voltage at the test points of the sensor of the leveling mechanism (part 164 in the figure) with line numbers 48 and 6 should be 24V. When the bucket is stationary at the highest position, the voltage at the measurement point with line number 48 should be 24V, while the voltage at the measurement point with line number 6 should gradually decrease. When the bucket is lower than the minimum height of the bucket set by the sensor in the lifting cylinder (generally at the upper end of the cab door), the voltage at the measurement point with line number 3 of the rapid unloading relay (Part 117 in the figure) should still be 24V, while in other cases, the output voltage at the measurement point with line number 3 of the rapid unloading relay (Part 117 in the figure) should be 0. During the actual inspection, it was found that during the bucket lifting process, the voltage at the measurement points of the leveling mechanism sensor (part 164 in the figure) with line numbers 48 and 48 was both 19V, which could not reach the normal 24V. When the bucket is stopped at the highest position, the voltage at the measurement point with line number 6 does not drop either.

After repeated testing and verification, it was determined that the automatic leveling module of the boom lifting cylinder of the underground excavator was damaged. After replacing this module, the fault of the underground excavator was eliminated and the machine worked normally.