Analysis and Elimination of Brake Faults in Loaders

At present, the braking systems of domestic loaders generally adopt the air-to-oil and caliper disc braking form, which consists of two parts: service brake and parking brake, and also serves the function of emergency braking. Its structural principle is shown in Figure 1.

In actual working conditions, there are also the following typical phenomena in the use of loaders. When loaders are performing high-intensity operations in coal yards and mining areas, frequent braking is required. During the operation process, in order to simplify the operation and improve the operation efficiency, there is a phenomenon of braking while stepping on the accelerator. Specifically, due to the short transportation distance, in order to quickly lift the boom into position within a short distance while keeping the overall machine's traveling speed slow, this operation must be carried out. On the surface, the movements seem very coordinated. In fact, during this process, the torque converter, transmission, and brake discs are all in a "suppressed" state. The torque converter operates in the low-efficiency zone, and the brake discs are in a high-pressure sliding friction state. The temperatures of both the torque converter and the brake discs rise rapidly. The temperature of the brake disc heats the brake fluid through conduction and radiation, causing the brake fluid to vaporize. This results in the oil circuit of the brake system being blocked by gas, and the pressure cannot be transmitted in time. The caliper piston does not return to its original position due to the "back pressure" of air resistance and gets stuck. The power cylinder also experiences oil spraying due to the "back pressure" of air resistance. The hotter it is, the more severe the vaporization becomes. The greater the "back pressure", the higher the friction temperature, and the more severe the oil spraying phenomenon. The more brake fluid is wasted. When the brake system is short of oil and the oil is not replenished and vented in time, air will enter the brake fluid line, causing air lock and resulting in brake failure, which poses a safety hazard. Therefore, higher requirements have been put forward for the reliable performance of vehicle service braking, emergency braking during service, and parking braking performance.

Through investigation and analysis, it was found that in order to adapt to the high-intensity operation and frequent braking in coal mines, the adoption of the power cut-off function can reduce the heat converted during braking and is conducive to reducing the occurrence of brake failure. However, during the actual driving process of the vehicle, especially when going uphill or downhill, sometimes the cut-off valve fails to recover properly when the power is cut off during braking. After the braking is released, the machine slides down, causing danger. In view of the above situation, the original system was improved. The working principle after the improvement is shown in Figure 2.

The compressed air discharged from air compressor 1 enters the air storage tank 3 through the combination valve 2. When the foot brake is applied, the compressed air enters the booster pump 5 through the foot brake valve 4 to brake the loader. At the same time, it is controlled by the selection valve 11 to cut off the pneumatic stop valve 12, cutting off the cylinder 9 to unload the pressure oil controlled by the transmission, thereby cutting off the output power of the engine. When the selection valve 11 is at another position, the pneumatic stop valve 12 will cut off the air intake, and the cylinder 9 will not cut off the driving power. This situation is applicable when the loader is going uphill or downhill, which can prevent the loader from sliding due to the loss of power. The parking brake valve 8 is a manual control valve. It is mainly used for parking braking, but it can also be applied in emergency braking.

After the above-mentioned improved system was applied to the loader, its braking performance became more stable. It not only reduced the brake failure faults of the loader under heavy load and harsh working conditions, but also avoided the landslide phenomenon caused by the inadequate recovery of the shut-off valve when going uphill and downhill. The application effect was remarkable.