Study On Hydraulic System Of Wheel Loader

The wheel loader is an important kind of engineering machinery. It is a kind of self-propelled machinery which is integrated with shovelling, transporting, loading and unloading. It is widely applied in many fields such as construction, road, railway, water and electricity projects, port, mining and defense, so it has played an important role in the national economic building. As a kind of self-propelled engineering machinery, it is involved in many technical fields. Among them, hydraulic system is a key transmission mode, and it takes irreplaceable place in the transmission of the wheel loader and even the whole engineering machinery. Therefore, analysis and study on hydraulic system o f the wheel loader have great significance for raising the properties and reliability of the wheel loader. This article is divided into six chapters. Chapter 1 introduces the background and the significance of the project, and the preparation and process of the experiments. Chapter 2 studies the experiment results of the working equipment system in different conditions. These experiments show that some interference phenomena exist in the working unit of this type of wheel loader. An experiment is conducted on the cantilever of the working unit during running of wheel loader, and the cantilever can cause the change of pressures in the cylinder of the working unit. The experimental results are that the change of pressures can apply on to the whole machine through the front frame and cause vibration of the whole machine. The average pressure in the lower cavity of movable arm is 2.4Mpa, and its maximum pressure can reach 3Mpa. The maximum pressure in the non-arm cavity of rotating bucket can reach 4MPa. The fluctuation of these pressures will be stronger when the shovel is filled with full load. Chapter 3 analyzes experimental results of the steering hydraulic system in different working conditions. These experiment show that the pressure loss of steering hydraulic system is higher, and its efficiency is lower. Especially when the steering pressure is not stable during steering, there is a pressure swing of 3 ~ 3.5Hz. This swing is so big that the properties and reliability of the steering system will be affect severely. Chapter 4 analyzes the characteristics of hydraulic system of working unit of wheel loader and the characteristics of the 4-way proportional valve which is used as a main directional valve to control the non-symmetric cylinder. The experimental results show that this kind of matching structure drives the loads not well, in particular, some phenomena such as cavities or backpressure will appear when it is run overloaded. At the same time, pressure leap is analyzed which is caused by the symmetric proportional valve controlling the non-symmetric cylinder during the change of directions. And when the wheel loaders are working in different loads and directions, this Chapter analyses the pressure drop of hydraulic oil which is produced when the oil passes through the multi-way directional valves owing to different types of spools. Chapter 5analyzes characteristics of steering system with the amplificatory flow unit, deduces its mathematic model, analyzes its dynamic characteristics theoretically in detail and studies the affection of properties of steering caused by the parameters of the hydraulic system. Chapter 6 summaries the research work of the project.