Thread Content
Causes and Countermeasures of Steering Failures in Construction Machinery Author: Li Lei, Highway Administration Bureau of Weicheng District, Weifang City, Shandong Province Abstract: By analyzing common faults in the hydraulic steering systems of construction machinery, this paper comprehensively discusses the structural characteristics of the steering mechanisms as well as the strategies for troubleshooting such faults. Keywords: steering mechanism, cause analysis, countermeasures. 1 Steering mechanism: The steering mechanisms of modern construction machinery generally use a structure consisting of a hydraulic pump, a steering distributor, and steering hydraulic cylinders to function. Hydraulic steering enables a simple structure for the steering system of construction machinery, making it easy to operate and maintain, and thereby improving the maneuverability and driving comfort of such machinery. However, any problem at any stage in the process of hydraulic oil flowing from the tank to the working components can cause sluggish steering or failure; therefore, understanding the composition, structure, and principles of the steering mechanism is crucial for analyzing and resolving steering faults as well as formulating appropriate solutions. First, taking a three-wheel roller as an example, the structure and principle of the hydraulic steering mechanism are explained (see Figure 1). Figure 1: In the hydraulic steering mechanism, the hydraulic oil from the high-mounted hydraulic tank is pressurized by a hydraulic pump and then enters the steering distributor. The distributor sends the hydraulic oil to end A (or end B) of the steering hydraulic cylinder, pushing the piston inside the cylinder to move to the right (or left). At the same time, the hydraulic oil in the cylinder returns to the hydraulic tank via end B (or end A) of the steering hydraulic cylinder, the distributor, and the return pipe, thereby enabling the roller to turn left (or right). 2 Causes of steering mechanism failures 2.1 Hydraulic tank The hydraulic tank uses the filter inside it to remove impurities and debris from the hydraulic oil, thereby preventing solid particles from accelerating the wear of components and causing a decline in the performance of pumps and valves. If the quality of the hydraulic oil is poor, such as being degraded or containing water and impurities, it will affect the performance of the hydraulic pump and other hydraulic components. 2.2 Hydraulic Pump: A hydraulic pump is necessary to ensure smooth steering, as it must be able to generate sufficient pressure and flow of oil. Most steering pumps are gear pumps; when the steering does not function properly, the output pressure of the pump should be checked first. The rated pressure of a standard gear pump is 2.5 Mpa; values that are too high or too low are not suitable. 2.3 Steering Distributor The steering distributor is a precision hydraulic component; leaks in this distributor can cause a reduction in the response speed of the steering wheel when it is turned, and in severe cases, it can lead to complete loss of steering control. 2.4 Steering Hydraulic Cylinder: If the oil seal on the piston of the steering hydraulic cylinder (see Figure 2) wears out or gets damaged, hydraulic fluid will flow directly from chamber a to chamber b, preventing the piston from moving to the right and resulting in steering failure. Figure 2: Schematic diagram of the steering hydraulic cylinder. Figure 3: Countermeasures for steering faults. 3.1 Hydraulic oil tank: The hydraulic oil in the tank should be filled to the specified level, and the valve of the tank should be opened wide enough to prevent insufficient oil supply. The hydraulic oil grade should be filled in accordance with the specifications; different types of hydraulic oil must not be mixed together, as this can cause the oil to deteriorate, leading to a decrease in its antifoaming properties, viscosity, and flow characteristics. The hydraulic oil tank must be kept very clean, and its filters should be cleaned regularly to avoid excessive resistance when drawing oil, which could accelerate wear on the pump and hydraulic cylinders. 3.2 Hydraulic Pump: It is necessary to ensure that the oil pump receives sufficient power input. Regularly check whether the pump is securely fixed in place, whether the belt tension is appropriate, and monitor the output pressure of the hydraulic pump on a timely basis. If the output pressure of the hydraulic pump suddenly drops, the machine should be stopped for inspection to prevent greater damage caused by the pump getting stuck or suffering from wear and abrasion. The clearance between the tooth tip of the pump and the inner hole of the casing is 0.05~0.1 mm, while the axial clearance is 0.03~0.05 mm. Generally speaking, gear pumps are not very sensitive to hydraulic oil, and as long as they are used properly, they are less likely to fail. 3.3 Steering distributor: When the pump pressure is sufficient yet steering feels particularly heavy, it may be due to worn distributor bushings or misalignment between the valve body and the valve spool, resulting in sticking; when the steering wheel turns easily but cannot be turned all the way, it may be because of oil leakage inside the distributor caused by excessive wear. Oil leakage in distributors is generally difficult to repair; the usual solution is to replace them. 3.4 Steering hydraulic cylinder: Problems with the hydraulic cylinder are visible to the naked eye as oil leakage, or the front wheels of the roller may move around randomly when it travels on uneven surfaces. The main reason is oil leakage from the oil seals on the piston inside the hydraulic cylinder. In such cases, a suitable oil seal should be installed according to the product model, and it is necessary to ensure a clean working environment during installation; moreover, both oil seal lips on the piston must face outward, and then the problem will be resolved. When a fault occurs in the steering mechanism, it is first necessary to determine, based on the symptoms, whether the problem lies with the hydraulic pump, the steering distributor, or the hydraulic cylinders. After that, careful and thorough repairs are carried out in accordance with the maintenance standards for each component, and this usually resolves the issue. References: Zhang Hongjia, Huang Yi, Hydraulic Transmission, Machinery Industry Press