Troubleshooting of faults such as overheating of the torque converter in bulldozers and lack of power in bulldozers

A TY165 bulldozer has been experiencing faults such as overheating of the torque converter and lack of power since it was put into use. After working for five months, the bearing was burned out and the torque converter was damaged due to lack of oil. After replacing the torque converter assembly and working for a period of time, it was found that the problem of the torque converter overheating still remained unsolved. Based on the principle of "starting with the easy tasks and moving on to the difficult ones", the following steps were followed for the investigation.

Due to the fact that sometimes the fault phenomena reported by users during the after-sales service process do not match the actual situation, in order to verify the accuracy of users' judgment of the problem, it is necessary to understand the earth-moving condition of the bulldozer on site. Therefore, before earth-moving, the basic index parameters of the transmission oil in the rear axle box, such as the oil level, oil quality, oil viscosity and gas, were first checked. It was found that the oil was relatively viscous, and the oil level was significantly higher than the standard line on the dipstick. There was no unpleasant smell when smelled. The driver reported that due to the overheating of the torque converter and the sluggishness of the bulldozer, a comprehensive inspection of the bulldozer was carried out not long ago, and the torque converter, transmission, etc. were disassembled, but the root cause of the problem was not found. During this inspection, no abnormalities were found in the diesel engine after starting the bulldozer. When the bulldozer is in the forward I gear for pushing soil, the resistance to pushing soil is relatively large, and the guide wheels of the bulldozer slip. When the temperature of the bulldozer rises or it starts hot, the slippage of the guide wheels is particularly severe.

After a preliminary analysis of the phenomenon of the bulldozer's guide wheels slipping, it is believed that the power transmitted through the engine can be effectively transmitted by the hydraulic torque converter. However, if the guide wheels slip under heavy load, it indicates that the engine power is insufficient. After analysis and determination, it was found that there was a problem with diesel supply when the throttle was increased. This might be related to multiple factors such as the low pressure of the PT pump and the clogging of the diesel filter. After disassembling the oil pipe of the diesel fine filter, it was found that the oil volume was relatively small. When the oil pipe before the fine filter was disassembled again, it was found that there was a large amount of oil, so it was suspected that the fine filter was clogged. After replacing the fine filter and resuming the earth-moving operation, it was found that the phenomenon of weak earth-moving had improved, but the torque converter was still overheating. To further confirm the cause of the torque converter's overheating, it was decided to use the pressure test method to determine whether it was caused by factors inherent to the torque converter itself.

The purpose of testing the inlet and outlet pressures of the torque converter is to verify whether the pressure is within the standard range. The test results prove that the pressure of the pressure regulating valve of the transmission clutch is normal. When the engine is at high speed, the pressure of the safety valve and the regulating valve of the torque converter is relatively high. Moreover, there is a pressure difference between the safety valve and the regulating valve at both low and high speeds of the engine, with no internal leakage. The springs and gaskets of the safety valve and the regulating valve are normal. Whether the test was completed in a cold state or not, the high pressure of the engine at high speed is related to the viscosity of the oil to some extent. As the temperature rises, the inlet and outlet pressures of the torque converter decrease at full speed of the engine. It is understood that there is another bulldozer of the same model at the construction site that also has a problem of excessively high oil temperature, but it can push earth normally. By checking the random data of these two bulldozers, it was found that the oil used in the chassis oil circuit system of the bulldozers is CD-grade 40 diesel engine oil, which is inconsistent with the 6 diesel engine oil required for the hydraulic transmission system and the 6 or 8 hydraulic transmission oil required for the hydraulic transmission system. In addition, after investigation, it is found that the oil used in the chassis oil circuit system of domestic TY165 =TY160 bulldozers is basically CD grade 30 or 40 diesel engine oil. Users generally report that the probability of torque converter overheating on these two models is relatively high. So, the oil used in the chassis oil circuit system was replaced with No. 6 hydraulic transmission oil, and then the machine was re-tested. It was found that the pressure before and after the torque converter had dropped. Among them, the inlet pressure of the torque converter was 0.48MPa and the outlet pressure was 0.30MPa, which met the technical conditions. The 1.5-hour operation of the bulldozer indicates that the pressure of the safety valve and the regulating valve of the torque converter remains normal and unchanged, and the temperature of the torque converter is normal (the oil temperature is approximately 90℃). The phenomenon of the bulldozer being weak and overheating has been completely eliminated.

Analysis suggests that the use of No. 40 diesel engine oil with a relatively high kinematic viscosity and a relatively low viscosity index in the chassis oil circuit system of this machine is the main reason for the high heating of the working oil, low transmission efficiency, and ultimately the inability of the bulldozer to push earth. At the same time, due to the inlet and outlet pressures of the torque converter being much higher than the opening pressure of the safety valve, the safety valve leaks a large amount of oil, resulting in a serious shortage of oil supply to the torque converter and failing to meet the normal working requirements of the torque converter. Moreover, the excessive oil leakage through the safety valve generates a considerable amount of heat, further raising the oil temperature. This is another reason for the weakness of the bulldozer.