What if the bulldozer breaks down? (Part 1)

1. Unable to start

The bulldozer has been unable to start during the unsealing process of the hangar.

After ruling out no electricity, no oil, loose or blocked fuel tank joints, etc., it is finally suspected that the PT fuel pump is faulty. Check the AFC air fuel control device. After opening the intake pipeline and supplying air to the intake pipeline with an air compressor, the machine can start smoothly. If the air supply is stopped, the machine will turn off immediately. Therefore, it is concluded that the AFC air fuel control device is faulty.

Loosen the fixing nut of the AFC fuel control device, turn the AFC fuel control device clockwise with a hexagonal wrench, and then tighten the fixing nut. When starting the machine again, it can start normally and the fault disappears.

2. Fuel supply failure

During a season-changing maintenance, the bulldozer needs to be driven out of the hangar, but it cannot be driven.

Check the fuel tank, the fuel is sufficient; unscrew the switch at the lower part of the fuel tank, the car will automatically turn off after 1 minute; connect the fuel tank to the PT pump fuel pipe directly with the filter oil inlet pipe, the fuel will not pass through the filter, and the car will not start again after restarting ;Turn the manual screw of the fuel cut-off solenoid valve to the open position, but it still cannot be started.

When installing the filter, turn the fuel tank switch for 3 to 5 turns, and find that a small amount of fuel flows out of the oil inlet pipe of the filter, but the fuel will flow out after a while. After careful observation and repeated comparisons, it was finally found that the fuel tank switch was not turned on. The switch is a spherical structure, the oil circuit is connected when it is rotated 90°, and the oil circuit is cut off when it is rotated 90° again. The ball valve switch has no handle and no limit device, but the square iron head is exposed. The driver mistakenly uses the ball valve switch as a throttle switch. After turning 3 to 5 times, the ball valve returns to the closed position. During the rotation of the ball valve, although a small amount of fuel enters the oil circuit, the car can only be operated for 1 minute. When the fuel in the pipeline is burned out, the machine will turn off.

3. Winch oil leakage

During the construction of the bulldozer, oil seepage occurred at the wire rope winch. After pulling out all the wire ropes, it was found that the hydraulic oil leaked from the bolts on the winch seat, and when the accelerator was increased, the leak was faster, and there was almost no oil seepage at idle speed.

Preliminary analysis may be caused by loose bolts or damaged gaskets, but after replacing the gaskets and tightening the bolts, the fault remains the same. Further analysis of the hydraulic schematic diagram suggests that the cause may be poor oil return and high back pressure. Therefore, replace the oil return pipe from the winch to the control valve, that is, weld a short oil return pipe on the upper part of the inner side of the fuel tank, and replace it with a rubber hose that is thicker than the oil return pipe of the original machine, so that the end of the oil return pipe is not connected to the control valve. Connect directly to the new oil return short pipe to reduce oil return back pressure. Tried the machine again, the fault disappeared.

4. The hot engine cannot walk

During use, the cold machine starts and bulldozers are normal, but after working for 50 minutes, as the oil temperature gradually rises, the bulldozer becomes weaker and weaker, and it is even difficult to walk without load. If you stop and rest for 2 hours at this time, start the engine again after the oil temperature drops, and the starting and bulldozing will return to normal.

During the operation, the engine throttle did not decrease, and the speed did not decrease, indicating that the powerlessness of the bulldozer had nothing to do with the engine. Preliminary analysis believes that the reason is that the torque converter is short of oil, the oil circuit is blocked, or the transmission and steering clutch are malfunctioning.

Check that the torque converter is normal; loosen the exhaust screw on the fine filter of the variable speed, and find that there are air bubbles in the discharged oil, which cannot be exhausted for a long time. According to the analysis, if there is a place where the air enters, both the cold machine and the hot machine should take in air, so that the machine is working normally in the cold machine state, and it can be concluded that the low-pressure oil circuit is in good sealing condition. The air intake of the high-pressure oil circuit of the heat engine causes the machine to fail to walk, which should be caused by the excessive vacuum of the low-pressure oil circuit.