Causes and Countermeasures of Steering Faults in Construction Machinery

1 Steering mechanism

The steering mechanisms of modern construction machinery are basically realized by adopting the structure of hydraulic pump - steering distributor - steering hydraulic cylinder. The adoption of hydraulic steering makes the structure of the steering system of construction machinery simple, easy to operate and maintain, and improves the maneuverability and driving comfort of construction machinery. However, any problem in the process of hydraulic oil moving from the oil tank to the working components will cause inflexible steering or failure. Therefore, understanding the composition, structure and principle of the steering mechanism is of great significance for analyzing and eliminating steering faults and formulating countermeasures.

First, taking the three-wheel roller as an example, the structure and principle of the hydraulic steering mechanism are explained (see Figure 1).

The hydraulic oil is pressurized by the hydraulic pump from the high-position hydraulic oil tank and then enters the steering distributor. The distributor presses the hydraulic oil into the A end (or B end) of the steering hydraulic cylinder, pushing the piston in the cylinder to move to the right (left). At the same time, the hydraulic oil in the hydraulic cylinder is returned to the hydraulic oil tank through the B end (A end) of the steering hydraulic cylinder, the distributor and the return oil pipe, thus achieving the left (right) steering of the roller.

2. Causes of steering mechanism failure

2.1 Hydraulic Oil Tank

The hydraulic oil tank removes impurities and debris from the hydraulic oil through the filter screen inside it to prevent solid particles from accelerating the wear of components and causing the performance of pumps and valves to decline. If the quality of the hydraulic oil is poor, such as deterioration or water ingress and impurities, it will affect the use of the hydraulic pump and other hydraulic components.

2.2 Hydraulic pump

Only when the hydraulic pump outputs sufficient pressure and oil volume can it ensure the smooth completion of the rotation. Most steering pumps use gear pumps. When the steering is not smooth, the first step is to check the size of the pump's output pressure. The rated pressure of a general gear pump is 2.5Mpa. Either too high or too low pressure is not suitable.

2.3 Steering distributor

The steering distributor is a precision hydraulic component. Oil leakage from the distributor can cause the response speed of the steering wheel to slow down when it is turned. In severe cases, it can directly lead to steering failure.

2.4

If the oil seal on the piston of the steering hydraulic cylinder (see Figure 2) ages and is damaged, the hydraulic oil will directly enter chamber b from chamber a, and the piston cannot be pushed to the right, resulting in steering failure.

3. Countermeasures for Troubleshooting Steering faults

3.1 Hydraulic Oil Tank

The hydraulic oil in the hydraulic oil tank should be filled to the specified height, and at the same time, the opening of the oil tank valve should be large enough to avoid insufficient oil supply. The grade of hydraulic oil should be filled in accordance with the regulations. Hydraulic oil of the same type must not be mixed to avoid deterioration of the oil quality, which may lead to a decline in anti-foaming property, viscosity and fluidity. The hydraulic oil tank should be kept highly clean and the filter screen should be cleaned regularly to prevent excessive suction resistance and accelerate the wear of the pump and hydraulic cylinder.

3.2 Hydraulic pump

First of all, it is necessary to ensure that the oil pump has sufficient input power. Regularly check whether the oil pump is firmly and reliably fixed, whether the belt tension is appropriate, and observe the output pressure of the hydraulic pump in a timely manner. If the output pressure of the hydraulic pump suddenly drops, the machine should be stopped for inspection to avoid greater losses caused by pump jamming or wear and erosion. The fit clearance between the tooth top of the pump and the inner hole of the casing is 0.05 to 0.1mm, and the axial clearance is 0.03 to 0.05mm. Generally speaking, gear pumps are not highly sensitive to hydraulic oil. As long as they are used properly, they are less likely to malfunction.

3.3 Steering distributor

When the pump oil pressure is sufficient but the steering feels particularly heavy, it may be due to the wear of the distributor shaft sleeve or the misalignment of the valve body and the valve core, resulting in a jamming phenomenon. When you feel that the steering wheel turns very lightly but never reaches the end, it might be that the distributor is leaking oil due to excessive wear inside. Oil leakage from a distributor is generally difficult to repair. Usually, the solution to the problem is to replace it.

3.4 Steering hydraulic cylinder

The phenomenon of problems with the hydraulic cylinder can be seen with the naked eye as oil leakage, or when the roller travels on an uneven road, the front wheels will automatically "run around". The main reason is that the oil seal on the piston inside the hydraulic cylinder is leaking oil. At this time, a qualified oil seal should be replaced according to the product model, and it is necessary to ensure that it is highly clean during assembly. At the same time, make sure that the lips of the two oil seals on the piston are both facing outward. The problem can then be solved.

When the steering mechanism malfunctions, first, based on the symptoms, check whether it is a problem with the hydraulic pump, the steering distributor or the hydraulic cylinder. Then, carry out careful and meticulous repairs according to the maintenance standards of each component. Generally, the problem can be solved.

References

Zhang Hongjia, Huang Yi, Hydraulic Transmission, Machinery Industry Press

Engineering Construction Machinery 2005.NO.2