Analysis and Troubleshooting of 2 Bulldozer Fault Cases

1． One of our company's TY220 bulldozers could not be started. It ran normally when it was first started in the morning. However, it only ran for about 30 seconds before it automatically shut down and then could not be started again. At that time, the temperature was about -5°C, and the No. 10 light diesel used in the machine did not freeze (other machinery could be started). It took until the afternoon for the diesel engine to start and run normally, but the same situation occurred again the next morning. Fault analysis and troubleshooting: The TY220 bulldozer is powered by a Cummins NT855-C280 diesel engine and is equipped with a PT fuel system. Based on the fault symptoms, it can basically be concluded that there is a fault in the fuel system, causing the PT pump to be unable to continuously supply fuel. The main reasons why the PT pump cannot supply fuel are: the PT pump itself or the filter is clogged, the cut-off valve cannot be opened, there is no oil in the fuel tank or the fuel is frozen, etc. After disassembly and inspection, it was found that there were no problems with the above-mentioned parts, but the viscosity of the fuel was very high and the flow rate was slow. Reminiscent of the phenomenon that the engine could start normally in the afternoon (the temperature was about 5°C), it was determined that the filter in the group pump was blocked due to the high viscosity of the diesel fuel No. 10. The quality was not up to standard. Therefore, use boiling water to preheat the filter and PT pump housing, and the diesel engine will start soon. When the construction unit used genuine No. 10 diesel, the above failures never occurred again. 2． The right steering clutch cannot be separated. When the machine is working, the left steering is normal, but the right steering is sometimes normal and sometimes abnormal; when braking (the steering lever is pulled to the position and the brake is linked), the engine emits black smoke and changes the sound; when the machine is reported for repair, the right steering clutch cannot be separated at all. Fault analysis and troubleshooting: Based on the above symptoms, following the principle of easy first and then difficult, we first checked the right brake, hydraulic transmission oil volume, joystick clearance adjustment, main safety valve and steering valve left and right axis rotation, and the results were all normal. Then the steering system was checked for air and oil leaks. The small covers on the left and right brake covers were opened respectively, and then a person squatted on the ripper frame to walk and observe; when the right steering lever was pulled, there was an obvious oiling sound inside the brake cover. Disassemble the rear cover of the central transmission, shake the left and right S-pipes (the oil inlet pipes of the steering clutch) respectively by hand, and feel that the movement gaps of the S-pipes on both sides are almost the same. Then pull the left and right steering rods respectively, and see that there is not much difference in the amount of oil returned from the left and right steering systems to the central transmission housing, so it can be ruled out that there is air leakage or oil leakage in the pipeline system. In order to further clarify the source of the oily sound and the working condition of the steering clutch, the diesel tank, right brake cover, and brake wheel cylinder were removed successively, and the right brake oil inlet pipe was placed in the box (to prevent the test engine oil from flowing out). The diesel engine was started. When the right steering lever was pulled, a large amount of oil was found outward from the joint between the bearing seat and the central transmission connection plate. At this point, we have made the following judgment on the cause of the failure: it is because the sealing ring here is damaged, causing the hydraulic oil to enter the right bearing seat through the S tube. However, when we lowered the cab, lifted out the right steering clutch, and pulled out the connecting plate, we found that the two sealing rings were not damaged, and the bearing seat and the central rotating disc bearing were not damaged either. We had to disassemble and inspect the right steering clutch assembly. We only found that two large springs had been broken, but the piston and the groove were not damaged. After replacing two large springs (used symmetrically), piston rings and sealing rings, the right steering component was reassembled and tested. As a result, when the brake was released, the right steering could barely separate. It was only slightly better than before the repair, but it still could not work normally, indicating that the main cause of the failure had not been eliminated. According to the exclusive principle, the problem can only lie inside the steering control valve. Therefore, the steering control valve was completely disassembled and inspected. When the right scroll was disassembled, it was finally discovered that the threads on the air cylinder had become loose, causing the spring pressure to decrease. After re-adjusting the spring pressure, reinstall the steering valve and test the engine again. The fault has been eliminated.