Troubleshooting of wheel wobbling faults in loaders

The steering valve of the ZL50 loader is leaking oil due to a crack in the casing. As the casing material is cast iron, neither adhesive bonding nor heating insulation electric welding to repair the crack has solved the oil leakage problem. As this machine adopts an integrated structure of the steering gear and the steering valve, that is, the steering valve is directly installed at the lower end of the steering gear, it has been decided to replace all the steering gear and steering valve assemblies with new parts.

After replacing the steering gear and steering valve assembly, during the test run, the following occurred: The front wheels kept swinging left and right. The steering wheel is shaking, the steering is extremely flexible, and there is a feeling of drifting, so it is completely unusable. Before replacing the new part, there was only leakage due to a crack in the steering valve housing, with no other faults. However, after replacing the new part, the front wheels started to swing, so it should be a problem with the new part. So I replaced it with another new part, but during the test run, the front wheel wobbling occurred again. We speculate that the possibility of both new steering gears and steering valve assemblies simultaneously malfunctioning is not very high. It might be that there is a problem with the steering system itself. It was only after the steering gear and steering valve assemblies were replaced that the fault manifested itself.

Based on the analysis of the steering system, it is believed that the fault may occur in the flow conversion valve or the relief valve.

In this system, the function of the flow conversion valve is: when turning, it can be supplied with oil by the steering pump alone (when the engine speed is higher than 1600r /min), or it can be supplied with oil by the steering pump and the auxiliary pump together (when the engine speed is lower than 600r/min). When the engine speed is 600 to 1600r/min, the auxiliary pump supplies oil to both the steering oil circuit and the hydraulic system of the working device. This can more effectively utilize the engine power, reduce the heat generation of the hydraulic system, shorten the operation time and improve the production efficiency. The function of the relief valve is: when the pressure of the steering system exceeds 12MPa, the relief valve opens, and the hydraulic oil flows directly back to the oil tank, thus avoiding faults such as oil pipe burst, excessively high oil temperature, and damage to the hydraulic pump. When disassembling and inspecting the flow conversion valve, no abnormal phenomena were found. The maximum pressure of the steering oil circuit measured by a 0-25 mpa pressure gauge was 12MPa (the standard pressure is 12MPa), which clearly indicates that the overflow pressure is too high. Adjust the overflow pressure to 12MPa. When the machine was tested again, the front wheel wobbling fault was eliminated.

Before the steering gear and steering valve assembly were replaced, although the pressure of the steering oil circuit was high (according to the driver's recollection, the pressure of the relief valve was adjusted two years ago due to heavy steering), due to the large internal leakage caused by the wear of the steering valve and the large clearance of the steering gear, it was more suitable to use the old steering gear and steering valve assembly, and the front wheels did not sway. After replacing the new parts, due to the reduced clearance of the steering gear and the decrease in internal leakage of the steering valve, the oil circuit response during steering became overly sensitive, resulting in the front wheels swaying.