Analysis and Elimination of Faults in Two Bulldozers

1. Cannot start

One of our TY220 bulldozers operated normally when it was first started in the early morning. However, it only ran for about 30 seconds before automatically shutting down and could no longer be started. At that time, the temperature was around -5℃, and the -10 # light diesel used on the machines had not frozen (all other machinery could be started). It was not until the afternoon that the diesel engine could start and operate normally, but the same situation occurred again the next morning.

Fault analysis and Elimination: The TY220 bulldozer is powered by a Cummins NT855-C280 diesel engine and is equipped with a PT fuel system. Based on its malfunction symptoms, it can basically be determined that the fuel system has malfunctioned, causing the PT pump to be unable to continuously supply fuel. The main reasons for the PT pump not being able to supply fuel are: blockage of the PT pump itself or the filter, the shut-off valve not being able to open, no fuel in the fuel tank or frozen fuel, etc. After disassembly and inspection, no problems were found in the above-mentioned areas, but the viscosity of the fuel was very high and the flow rate was relatively slow. Recalling the phenomenon that the engine could start normally in the afternoon (when the temperature was around 5℃), it was determined that the quality of the -10 diesel was substandard, causing the filter screen inside the group pump to be clogged due to the high viscosity of the diesel. So, the filter and the PT pump housing were preheated with boiling water, and the diesel engine could start very quickly. After the construction unit adopted genuine -10 diesel, the above-mentioned faults have never occurred again.

2 The right steering clutch cannot disengage

When the machine is working, turning left is normal, but turning right is sometimes normal and sometimes abnormal. When braking (the steering lever is pulled into place and the brake is engaged), the engine emits black smoke and makes a change in noise. When the machine was reported for repair, the right steering clutch was completely unable to disengage.

Fault analysis and Elimination: Based on the above symptoms, following the principle of starting with the easier tasks and moving on to the more difficult ones, the right brake, the oil level of the hydraulic transmission, the adjustment of the control lever clearance, and the rotation of the left and right shafts of the main safety valve and the steering valve were inspected first. All the results were normal. Then, they checked whether the steering system was leaking air or oil. They opened the small covers on the left and right brake covers respectively, and then squatted on the soil loosening frame to walk and observe. When the right steering lever was pulled, there was a distinct oiling sound inside the brake cover. Remove the rear cover of the central transmission, shake the left and right S tubes (the oil inlet pipes of the steering clutch) by hand respectively, and feel that the movable clearances of the two S tubes are almost the same. Then pull the left and right steering rods respectively, and you can see that the amount of oil returned to the central transmission housing from the left and right steering systems is not much different. Therefore, it can be ruled out that there is a situation of air or oil leakage in the pipeline system. To further clarify the source of the oil clearance sound and the working condition of the steering clutch, the diesel tank, the right brake cover and the brake caliper were successively removed. The right brake oil inlet was placed inside the box (to prevent the test engine oil from flowing out). When the diesel engine was started and the right steering lever was pulled, it was found that a large amount of oil was leaking out from the joint of the bearing housing and the central transmission connection plate. At this point, we have made the following judgment on the cause of the fault: It is due to the damage of the sealing ring here, which caused the hydraulic oil to enter the right bearing housing through the S pipe.

However, when the cab was lowered, the right steering clutch was lifted out, and the connecting plate was pulled out, it was found that the two sealing rings were not damaged, and the bearing housing and the bearing of the central rotating disc were also undamaged. We had no choice but to disassemble and inspect the right steering clutch assembly. The result was that only two large springs were broken, while 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 for a test run. The result showed that when the brake was released, the right steering could barely separate, only slightly better than before the repair, but still could not work normally, indicating that the main cause of the fault had not yet been eliminated. According to the principle of exclusivity, the problem can only lie inside the steering control valve. So, the steering control valve was comprehensively disassembled and inspected. Finally, when disassembling the right shaft, it was found that the thread on the air cylinder had loosened, causing the spring pressure to drop. After readjusting the spring pressure at this location, reinstall the directional control valve and test the machine again. The fault has been eliminated.