Diagnosis and troubleshooting methods for the fault that bulldozers cannot move

I. Fault Phenomenon:

There are two states of the bulldozer's inability to move: Cold vehicle inability to move means that when the engine is started cold and running at medium speed, and then the gear is shifted, the bulldozer cannot start immediately. The inability of the hot engine to move refers to the situation where, during the normal process of pushing earth, as the oil temperature rises (within the normal oil temperature range), the bulldozer becomes increasingly weak (at this time, the engine is working normally), and even when there is no load, it is difficult to move.

Ii. Fault Diagnosis Methods:

When a bulldozer fails to move, whether it is in a cold or hot state, first control the engine throttle at medium to high speed, then remove the left foot pedal in the cab and observe whether the output shaft of the torque converter rotates. If it rotates, then check whether the output shaft still rotates after shifting gears. At the same time, pay attention to distinguishing whether there are any changes in the sounds of the engine, torque converter and transmission before and after shifting gears. If the output shaft does not rotate after shifting gears, it indicates that the fault comes from the torque converter, such as a lack of oil in the torque converter, etc. If both the output shafts can rotate before and after shifting gears, it indicates that the torque converter is not faulty. The fault may lie in the transmission, steering clutch, brake, etc.

To distinguish whether the problem lies in the oil circuit system or the mechanical part, you can loosen the exhaust screw on the variable speed fine filter to see if there is air. If there is air and it cannot be completely discharged, it indicates that there is air intake in the low-pressure oil circuit, that is, between the oil suction port and the variable speed pump. To further accurately determine the air intake location, you should continue to loosen the exhaust screw on the steering fine filter. If there is air, This proves that the air intake position is between the oil suction day and the coarse filter, as this section of the oil circuit is shared by the gear shifting and steering. If there is no air, it indicates that the air intake should be between the coarse filter and the variable speed pump. If there is no air in the exhaust screws of the transmission fine filter and the steering fine filter, it indicates that the fault does not lie in the transmission and steering oil circuit system, but in the transmission, steering clutch or brake, etc.

Iii. Examples of Fault Diagnosis and Elimination Methods

(1) A cold vehicle cannot move:

After a bulldozer started its engine cold and shifted gears, it could not move immediately. The starting time gradually increased from the initial 5 minutes to about 30 minutes. Loosening the exhaust screw on the transmission fine filter for inspection, it was found that although there were no bubbles, oil was overflowing. The output shaft of the torque converter could be rotated. Everything was normal after the engine was warmed up. It can be known that the reason for the inability to start should be the transmission control valve. Remove the pressure plate from the transmission cover. There is a pressure gauge oil plug screw under this pressure plate. Connect it to a 0-5MPa pressure gauge. Start the engine and increase the speed to high. Then, shift the transmission control lever to the forward 1, 11, and Ill gears respectively. The measured pressures are 0.23MPa, 0.5MPa, and 0.55MPa. The pressure is clearly insufficient (the specified pressures are 1.25 MPa, 2.5 MPa, and 2.5 MPa respectively). After 10 minutes, the pressures measured again were 1.1 MPa, 2.2 MPa and 2.3 MPa respectively. Only then could the bulldozer start. From this, it can be determined that there is a leakage point in the variable speed control valve.

The assembly of the transmission control room was removed. After inspection, it was found that the O-rings on the control mechanism had been flattened and deformed, and had lost their elasticity. In particular, the two black O-rings at the five oil inlet holes on the cylinder block had aged more severely. To further identify the fault, the high-pressure air pipe of the air pump was used to supply air to the five oil inlet holes respectively. Except for the first gear (as there is no planetary carrier and it is fully enclosed, the driving and driven friction plates are not exposed), in the other forward, reverse, 11, and Ill gears, the piston could be seen pushing the driving and driven friction plates to move. When the air supply was cut off, the four-position sound of the piston under the action of the spring could be heard (the first gear's return position uses a wavy spring) It can be inferred that the sealing rings of the transmission are well sealed (with relatively low elasticity and weak noise when the piston returns to its original position). After replacing the O-rings on the control valve, the fault that the cold vehicle could not start was eliminated.

The above-mentioned malfunction has occurred on three TY220 bulldozers. Among the O-rings in the five oil inlet holes on the cylinder block, three are light red and two are black. From both disassembly and inspection, it was found that the black O-rings were of poorer quality than the red ones. The problem lies in the two black rubber O-rings. It is recommended that the manufacturer use high-quality ones during assembly to reduce unnecessary malfunctions.

(2) The vehicle cannot move when it is hot

I once encountered two bulldozers that worked for about 5,000 hours. The cold start and pushing of the bulldozer were all normal. However, after working for 45 minutes, as the oil temperature gradually rose, the bulldozer became increasingly weak. Even when there was no load, it was difficult to move (at this time, the engine throttle did not decrease and the speed did not drop, indicating that the bulldozer was weak and had nothing to do with the engine). If the machine stops at this time and rests for about 2 hours, when the oil temperature drops, start the engine again, and the starting and pushing will return to normal. When the oil temperature rises and the bulldozer shows signs of weakness, the foot pedal beside the cab is removed. It is found that the output shaft of the torque converter is still rotating at this time. Loosening the exhaust screw on the transmission fine filter, it is discovered that there are bubbles in the discharged oil, and they cannot be completely discharged for a long time. If there is a place where air enters, it can be confirmed that air should enter both cold and hot vehicles. A cold vehicle should also be unable to move. In fact, a cold vehicle works normally, so it can be confirmed that the sealing condition of the low-pressure oil circuit is good. The car cannot move due to air entering the high-pressure oil circuit when it is hot, which is caused by excessive vacuum in the low-pressure oil circuit. Upon inspection, it was found that the rubber hose between the oil suction port and the coarse filter was sucked in. The higher the engine speed, the greater the degree of suction, resulting in poor oil intake. The reason was that the inner layer of the rubber hose aged and bubbled with the increase of usage time. As the oil temperature rose, the bubbling became larger, thus blocking the oil intake channel and causing excessive vacuum. After replacing the rubber hose, the fault was eliminated.