The CAT-D8R bulldozer adopts hydraulic transmission. The hydraulic torque converter, transmission speed and brake are controlled by the hydraulic system. If the hydraulic system fails, the bulldozer will not be able to perform the bulldozing operation or reach the normal driving speed. The following mainly introduces 3 A troubleshooting method for failure of a hydraulic system leading to inability to work.

1: Distinguish engine or transmission system failure

For bulldozers with weak walking failure, we should first distinguish whether it is engine weakness or transmission weakness. The bulldozer test machine can be carried out when the bulldozer blade is at its maximum load. When the bulldozer cannot push the soil, observe whether the engine speed drops. If the engine speed drops and the two tracks of the bulldozer are still rotating slowly, it means that the engine is weak and the transmission system is not malfunctioning. If the engine speed does not change, the two tracks of the bulldozer do not rotate, indicating that the engine is not malfunctioning, but the transmission system is weak.

There may be four reasons for the power failure of the bulldozer transmission system: one is the internal leakage of the variable-speed brake pump in the triple pump due to wear and tear, and the pressure cannot be built; the other is the brake valve core is worn out or adjusted incorrectly, causing the brake to be released Insufficient pressure; thirdly, the transmission valve is worn, stuck, or the oil passage in the valve is blocked, resulting in insufficient pressure in the transmission control oil circuit, and the clutches of each gear of the transmission are in a semi-connected state. Fourth, the torque converter is faulty, resulting in insufficient torque converter transmission torque.

2: Test the pressure of the variable speed brake pump

Measure the pressure from the variable speed brake pump to the filter. The normal pressure is about 3200kPa. If the pressure is 1000kPa lower than the normal pressure, the bulldozer may be weak. In the process of pressure measurement, it is also necessary to observe the speed of the offset movement of the pressure gauge pointer during the pressure increase process to determine the working condition of the variable speed brake pump. If the pressure gauge rises slowly, it means that the pump's internal wear, internal leakage or blockage of the pump inlet, resulting in a decrease in pump displacement, and insufficient system pressure. The problem can be solved by removing foreign matter at the pump inlet or repairing the variable speed brake pump.

3: Measure the brake system pressure

The bulldozer transmission control system realizes the brake priority through the priority valve. The priority valve test point is shown as 5 in Figure 1b. The normal pressure should be 2900kPa. If the pressure is too low, the brake valve is discharged.

The bulldozer realizes the brake of the bulldozer through the brake valve. The test points for measuring the pressure of the brake valve are shown as point 3 in Figure 1b. When measuring the pressure at this point, pay attention: there is no pressure at the pressure measurement point after the engine is started, and the pressure at this point is about 3200kPa when the hand brake (locking handle of the gear shift mechanism) is released. If the pressure is lower than 2200kPa, it will cause the bulldozer to be weak and the transmission oil temperature will increase. When the pressure is lower than 1000 kPa, the bulldozer cannot walk. During the test, the bulldozer can feel forward impulsive but cannot walk.

If the cause of the bulldozer’s failure to travel is the leakage of the priority valve to the brake cylinder, the solution is as follows: first check whether the adjustment of the lever of the lock handle and the foot brake lever is in place. If the adjustment lock cap on the lever is loose and out of the adjustment position, It will change the spool stroke so that the spool cannot be opened and the brake cannot be released. Secondly, clean and check the brake valve assembly. If the valve core and valve seat are not severely worn, as long as the stuck or blocked valve core is cleaned, the fault can be eliminated.