Research For The Steering System Of Wheel Loader Based On Electronic Proportional Directional Valve As Pilot Control

Recent years ,a rapid increase in demand for construction machinery with the expansion of the scale of construction and resource development. So there is a higher demand on its reliability, maintainability, safety and fuel economy. With microelectronic technology deep into the field of mechanical engineering, the modern engineering is marching for electrical and mechanical machinery integration. During the times with an important sign of microelectronics and Internet, we constantly developed an intelligent system which is integrated with hydraulic, integration of microelectronics and information technology. The intelligent system we developed is widely used in the product design of mechanical engineering, and also further improves the performance and high-tech.As the hinge of ensuring the safe driving and the efficient working, steering system should increase the electronic information technology, improve intelligent and its performance. Although working in poor conditions, the system is required to get higher control targets, accuracy and response speed. Because of the low prices but high antipollution ability, electro-hydraulic proportional control being paid much more attention by the industrial vehicle. Therefore, this paper designed a new steering system with the Flow Enlarge Valve controlled by Electronic Proportional Directional Valve, based on the original flow enlarge steering system of wheel loader. Traditional steering system works with much high-pressure flow controlled by little low-pressure, especially for large, medium-power models. There are two main types of steering system: independent ordinary and type-priority groups. They are the same both in principles and structure. The former is an independent, and unloading valve fitted on the latter , priority to the steering system, redundant systems to the working system. This will reduce the working pumps displacement, meanwhile meet the working require under the much low-pressure conditions.Flow enlarging steering system has its own outstanding advantages : the smooth operation, compact structure also to flexible and reliable; Supported feedback control theory, the margin pressure and the load pressure always to a certain value and efficient. Reasonable power uses; Hydraulic spacing a decrease of mechanical shock; structural layout flexibility. However, the CAT-flow valve exists certain properties of defects, for example, Signal oil streaming off valve spring cavity condition not associated with the loader, resulting in the hydraulic steering system overflows under pressure , causing power lose; depending on the pressure caused by oil flow through both ends of the spool ,to promote valve spool movement, the steering characteristics is affected by the oil temperature error and the impact etc.Reasonable flow from the original amplification, the working principle of the new steering system with the Flow Enlarge Valve controlled by Electronic Proportional Directional Valve as followed: steering wheel rotates, different electromagnet to control the corresponding ratio of Flow Enlarge Valve, the vehicle steering.Building a mathematical model of flow enlarge valve using the transfer function, analysing the static and dynamic characteristics and inducing mathematical model of flow enlarge valve controlled by Electronic Proportional Directional Valve.The conclusions as followed:1. Speed magnification factor k_v = k_q/A_c, k_v depends on k_q, when Ac fixedness. it shows the sensitivity of control speed on the cylinder, and directly affects the stability and the response speed of the closed-loop system . Magnify factor of the closed-loop system can increase the speed of response speed, but stability of the system would be worse.2. Hydraulic natural frequencyω_h has the relationship ofβe,V_t,A_c,M. In practice, magnifies factor adopting various measures to guarantee the stability, thus improving response time.3. Damping ratio is the flow-pressure coefficient of the system caused by the leakage and friction losses. More Leak, more friction, energy consumption would be huge, damping powerful would be strong.4. Dynamic stiffness, whenω< 2ω_hξ_h, it is to some tune viscous damping, with the lower frequencies, the increasing influence of significant leakage. Dynamic stiffness ratio decreased frequency until clean. When the frequency changes between 2ξ_hω_h andω_h, Due to the high frequency interference, there is not enough time to flow through leakage. Hydraulic cylinder would be deemed as a simple and closed one, hydraulic spring stiffness should be the stiffness. Whenω>ωh, HF inertia load is great, which stops the movement of the piston. Dynamic stiffness increases with the frequency of the secondary side. Whenω=0,static stiffness is clear. This is because continuous static load disturbance will cause leakage , keep the piston moving.5. Whenω<ωh, the influence of the import and export pressure significantly with the frequencies low down. Dynamic stiffness drops down by the frequency ratio. Whenω>ωh, dynamic stiffness increases with the frequency of the secondary side, but seldom work in this frequency range. In order to verify the validity of theoretical analysis. We made an experiment for testing the static characteristics of the Flow Enlarge Valve and the steering system with the Flow Enlarge Valve controlled by Electronic Proportional Directional Valve. The results supplies the objective evidence for the defects reason of the Flow Enlarge Valve , the influence of various factors on the Flow Enlarge Valve, and the rationality of the steering system with the Flow Enlarge Valve controlled by Electronic Proportional Directional Valve.Although, in nature, the Electronic Proportional Directional Valve controlling the Flow Enlarge Valve depends on the pressure caused by oil flow through both ends of the spool ,to promote valve spool movement, connecting and controlling the various components of the system with microelectronic technology replace the traditional mechanical or hydraulic link. Canceling some mechanical link between the steering wheel and steering wheel. Compared with the original flow enlarge system, the new system has certain characteristics of times and technological advantages :1. Simplify the system. Electro-hydraulic proportional control, simplifying the system architecture greatly, and good performance, speed ratio can be achieved, smooth switch avoiding a major vibration, and shock.2. Flexible design. In Engineering Machinery, the hydraulic valves are often installed together. It makes the connecting pipe extended, the system complex, pipeline lost, and do nothing with the dynamic characteristics. With the electro-hydraulic proportional valve, the valves can be installed in the most appropriate place to overcome these shortcomings.3. Rapid and stable open-loop speed control, but also precision, quasi-closed loop speed control.Although the new steering system with the Flow Enlarge Valve controlled by Electronic Proportional Directional Valve we designed is not making huge technical innovations, the control method we making up is fresh. And we are sure that it helps for improving performance of the control system, improving the intelligent, and designing advanced steering system.