Research For Kinetic Characteristics Of Steering System Of Articulated Wheel Loader

As the only nation brand ruling the inland market of engineering, wheel loader is the most powerful brand to export. However, with the foreign companies pulling in, the nation companies realize the serious situation. Paying more attention to the technique, taking different tech-route and doing more tech-innovation in order to improve the technological content of products, build its own brand, and enhance products'competitiveness in the international and domestic.To solve the existing problems is the first task for increasing the technological content, and then to propose the better solution. So experts from domestic and foreign have been always concerned on the wheel loader with the focus on the important part of it—the steering system.The performance of the steering system is directly related to the safety of the loader and operational efficiency. Generally, it contains of main regulating valve and control valve constitute which is very complicated. It is typical inertia load hydraulic servo control loop.According to the reference of the past research results, a large number of test curve will appear such a recurring phenomenon: At the beginning of steering for wheel loader, the pressure of steering hydraulic system changes fierce. The long-term impact not only affects the performance stability and reliability of hydraulic steering hydraulic system, but also leads to vibration, noise and connector loose, and so even the pipeline rupture, There would be much more dangerous results in the high pressure and large flow system. If we could find the reason and the impact factors with dynamic analysis methods, we can improve the design of steering system, avoid duplication of tests and the high processing costs, and determine the dynamic characteristics of the weak links in time.Based on the basic principle of wheel loader and taking into account the inertia load, Bridge Dutch distribution, and tire stiffness, we convert the original system into the equivalent model with quality and flexibility components. With the equivalent model, we deduce the transfer function of the Steering angle input with the location of cylinder output, the Steering angle input with cylinder power output and the only inertial load. And then make a dynamic performance analysis. To get more data certification, some test is on demand such as dynamic performance testing of hydraulic steering under simulated load when different steering turn input, the dynamic performance testing of steering system on the sandy road, Asphalt Pavement with empty or fully loaded; the dynamic performance testing of steering system with hanging up the front or back drive bridge etc. Finally, the conclusion of the main reasons of pressure fluctuations as followed:1. The elastic deformation effect of tire and the effect of inertial load during the steering process cause a resonant system between the structural stiffness and the load quality. The resonator between the resonant system and hydraulic system causes a new system called hydraulic -- mechanical resonator system. Compared with the hydraulic frequency and the structure frequency, the new frequency is much lower. If the structure frequency too low, it would limit system bandwidth. That is the important reason of pressure fluctuations. To improve the structure frequency, it is necessary to reduce the load equivalent quality, or the equivalent increased stiffness.2. The damping ratio is the leak damping caused by flow pressure coefficient. Increasing the overall damping ratio will enhance the relative stability of system.It is impossible to improve the damping ratio by magnifying k ce directly for the steering system of wheel loader in practice. Therefore, we could improve the natural hydraulic frequencies and integrated damping ratio by using the dynamic pressure feedback device. With the dynamic pressure feedback device, the transfer function keeps the same except adding thedamping ratio . Under a stable situation, it is near zero which is to do nothing for the steady-state performance. During the dynamic process, the additional damping caused by the change of load pressures would changes along with the significant change of load pressure. At this time, the system will keep the k Ge = C sl + kce as small as possible, in order to improve the static stiffness. The system stability may be protected by the pressure feedback device. This could satisfy the static and dynamic characteristics of both requirements.3. Magnify Speed magnification factor of the closed-loop system can increase the speed of response speed, but stability of the system would be worse. It could get the appropriate Speed magnification factor, if the appropriate selection of the steering is being choosen.4. Step input, the steady-state error of system is zero; Isokinetic speed input, Steady-state error rate is proportional to input speed, and is inversely proportional to enlarge coefficient of the open-loop system. Meanwhile, the input signal and the external load force work in the system, the total system error is equal to the sum of follow error and the loaded error. It is beneficial for reducing the speed error and load error to improve open-loop magnification factor. However, the improvement of speed magnification factor is limited by the system stability. To cater for the accuracy requirements, it has to compensate the system. To reduce the load error, it should reduce flow pressure coefficient by doing which will cause the decrease of damping ratio. In all, there is a contradiction between reducing load error and increasing damping ratio.