A Study On Electro-hydraulic Steering-by-wire System Of HT25J Wheel Loader

Steering system is one of the critical subsystems in wheel loader, which performance directly determines the working efficiency, driving security and driver’s labor intensity.This dissertation is funded by the project named "Multi-fields Unified Modeling Simulation and Optimization Methods for Total Lifecycle of Sophisticated Products" from National Natural Foundation of China and the momentous special project named "Research on Multi-fields Optimization Design Technology and Platform Development for Multifunctional Logistic Equipment" from Bureau of Science and Technology of Zhejiang province. The traditional all-hydraulic steering system has the deficiencies of inflexible steering, unadjustable steering sensitivity and low working efficiency. On the basis of referring to relevant researches at home and abroad, a kind of electro-hydraulic control steering system which applies a proportional pressure reducing valve to control flow amplifying valve is developed. The steering system’s mathematical models are built by transfer functions, the model of control system is established and emulated in Matlab/Simulink, its physical model is built and emulated base on AMESim, the optimum design for pivot point of steering mechanism is carried out, and the graphical user interface for steering system is developed based on MATLAB GUI.The main contents of this dissertation are included as following:1. In this paper electro-hydraulic proportional control technology is applied to steering system of HT25J wheel loader, a steer-by-wire system with proportional valve to control flow amplifying valve is designed to achieve this project. The steady and dynamic characteristics of amplifying valve are analyzed, and the steering system’s mathematical models are built by transfer functions.2. The controller is built by adopting fuzzy self-tuning PID control technique, and the model of control system is established and emulated in Matlab/Simulink environment. After simulation, the responses of the system with no controller, conventional PID controller and fuzzy self-tuning PID controller under step input signal are obtained and compared. As the result shows, fuzzy self-tuning PID controller can achieve higher control precision, smaller overshoot, quicker response. Mean while it has better steady-state behavior and robust performance.3. Appropriate submodels are adopted and each component’s physical model of the electro-hydraulic steering system is established in AMESim environment after analyzing the system’s construction and working principle. The overall physical simulation model of the steering system is established by connecting components’models. After parameters setting, simulation and research on the performance of the main valve and flow dividing valve are done. The overall model is also emulated and the output of the steering jack is obtained to verify the availability of the model.4. The mathematical model of optimum design for pivot point is built in view of the working characteristic of articulated steering mechanism. The optimum design for hinge point is carried out by applying ant colony algorithm, the curves of the relationship between stroke/arm difference and steering angle are obtained and in contrast before and after the optimization. The results are also compared before and after considering the cylinder’s generality. By contrast, we can draw a conclusion that the optimization has achieved significant improvement.5. The parameter calculating interface, simulation interface and control system simulation interface are designed by using MATLAB GUIDE function, then the callback program of each GUI widget should be complied so as to achieve GUI functions.