Fault Analysis and Elimination of TY220 Bulldozer Not Turning

During the operation of a TY220 bulldozer, it was found that when either side of the steering tie rod was pulled, the bulldozer did not turn. However, if both the left and right steering tie rods were pulled simultaneously, the bulldozer could still move forward in a straight line. It is initially determined that the steering system has malfunctioned.

First, check whether the steering control mechanism is in good condition. This machine adopts a fully mechanical control mechanism in the steering system. Check that all the pull rods and springs are well connected and the clearances between the rods are also appropriate. It is thus determined that the fault lies in the steering hydraulic circuit.

The steering pump 10 is connected to the transfer case, converting mechanical energy into hydraulic energy. Even if the oil is sucked out from the rear axle box 8 and filtered through the coarse filter 9 and fine filter 11 before entering the distribution valve 12, the distribution valve will distribute the liquid flow rate to the steering valve and the braking circuit in a ratio of 3:1. The working pressure of the steering valve is 1.25MPa, which is guaranteed by the sequence valve 3. The oil overflowing from the sequence valve enters the speed change circuit and then converges with the oil in the speed change circuit, and then enters the torque converter.

Under normal circumstances, when the steering handle is not operated, the pressure oil flowing from the diverter valve to the left or right steering valve is sealed in the steering valve and does not supply oil to the steering clutch. At this time, the steering clutch is in the engaged state. There is a small hole on both the left and right steering valves. Through this small hole, a small amount of oil is continuously replenished to the left and right steering clutches to keep the clutch working chamber always filled with oil. Once the steering valve is operated, the clutch disengages immediately, enhancing the sensitivity. By operating valve 4 or 5 respectively, the left or right clutch can be disengaged to achieve left or right steering. If valves 4 and 5 are operated simultaneously to disengage the left and right clutches at the same time, the bulldozer will stop.

When troubleshooting, the oil pressure measured at the fine filter was 2.3MPa, indicating that the steering pump 10 was fine and capable of providing 1.25MPa of pressure oil to the steering hydraulic oil circuit. In addition, since the braking and steering hydraulic circuits of this machine are both provided with hydraulic pressure by the steering pump, the braking effect is very good, which also indicates that the steering pump is in good condition.

Then, inspect the combination of the diverter valve, sequence valve and steering valve, that is, remove the upper cover of the rear axle box, disassemble each valve and check the valve core of each valve. At this point, it was found that the valve core of the sequence valve was jammed by debris. When removing this valve core, it was also discovered that the piston inside the valve core was jammed by debris. It can be seen from this that the sequence valve is always in an overflow state at this time.

At this point, the oil pressure in the steering circuit is too low. When operating the steering valve, the oil pressure in the steering circuit is far from being able to overcome the elastic force of the steering clutch spring, thus preventing the steering clutch from disengaging. As a result, the bulldozer cannot steer.

After cleaning the sequence valve and valve core, the machine was reinstalled and tested. The bulldozer turned smoothly and the fault was eliminated.