The wheeled excavator was suddenly unable to walk on the way back after working at the steel slag loading and unloading site. Check that the tires rotate well and the transmission shaft is normal. Disassemble the pilot oil pipeline that controls the high and low gears of the excavator, change the high and low gears, and observe the strong oil output from the oil pipe, which can eliminate the failure of the gear valve and hydraulic oil circuit. Turn off the engine, and the traveling device is in the stop braking state. Open the transmission case and observe the cover, check the shift fork, and you can feel that the middle of the shift fork is broken and separated from the sliding sleeve. The preliminary judgment is that the shift fork is broken.
1. Cause of failure
According to the breakage of the fork, the cause of the failure was analyzed: during the driving process, the machine switched between high and low gears before it stopped completely. The transmission box of the excavator is not equipped with a synchronizer. When the machine is running, the internal transmission gear rotates at a high speed. If the gear is shifted at this time, the sliding sleeve of the shifting fork cannot complete the meshing with the gear, and the reaction force generated by the collision directly causes the shifting. Fork damaged. It was decided to replace the fork for this reason.
2. Disassemble the gearbox
The disassembly process is carried out in several steps: first, loosen the hydraulic oil tank cover and exhaust the hydraulic system, disconnect the hydraulic line connected to the transmission case and close the oil leakage point; secondly, remove the front and rear drive shafts, and remove the handbrake The hydraulic cylinder and the front axle drive the hydraulic cylinder oil pipe; again, place the adjustable lifter at the lower part of the transmission case, adjust the lifter to support the case, remove the three fixing bolts of the transmission case, and detach the transmission case frame. Due to the large mass of the transmission box, it is necessary to confirm that the lifter is fully contained and hold the box body, and then remove the fixing bolts. Decomposition steps of the transmission case: First, disassemble the cover of the transmission case, and then remove the cylinder head lock nut, piston, O-ring, centering disc, compression spring, spring seat, pin, retaining ring, shaft, shift fork and joystick in turn . Next, replace damaged levers, forks, and aging various O-rings. Finally, check the wear of the transmission shaft and gears inside the transmission box, and confirm whether each component is in good condition.
3. Assembly test machine
Assemble the disassembled parts one by one, and assembly is the reverse process of disassembly. After assembly, install the restored transmission case to the frame and connect the corresponding hydraulic lines. Finally, tighten the hydraulic oil tank cover and start the engine, raise the bulldozer, and test the machine in high, low and reverse gears respectively, and the fault disappears.
Special attention should be paid to the test machine process: do not rush to increase the accelerator after operating the gear, first tap the accelerator pedal to feel the machine move slightly, and when the gears in the transmission box are fully meshed, then increase the accelerator to prevent the gears from meshing. Partial offset backstop.
