| Wheel loader is a kind of construction machine which is widely used in construction due to its high efficiency. It must be steered frequently in work, and the performance of steering system influence the vehicle's operation safety and work efficiency directly. Applying advanced technology of electronics, automatic control and computer, the steering by wire system is used in wheel loader. Removing the mechanism conjunction between steering wheel and steering actuator, structure of the steering system is simplified greatly.Steering sensitively, simple to operate and work stably and reliably is the basic requirement of steering system for wheel loader. Therefore, researching on the control method of steer by wire for wheel loader, and developing the intelligent control system is very important with great theoretical significance and practical values. The research work in this Ph.D. dissertation is funded by the project"Application of Steer-By-Wire technology in wheel loader"(the foundation project of Science and Technology Bureau of JILIN province, No.20040336), and the research and development project of"Application and research of Steer-By-Wire technology in wheel loader"funded by Shandong Lingong Construction Machinery Co.,Ltd.With the purpose of enhancing security and stability of the steer-by-wire sytem in wheel loader, the advanced technology of electronics, automatic control, computer, communication and network has been applied in this reseach work. Based on analysis of the work process and configure of wheel loader, study on control method of steer-by-wire for wheel loader has been made, and the intelligent control system has been developed in this Ph.D. dissertation. To meet demands and perspectiveness of technology development, the control system is designed adopted the advanced embedded system technology. The interface for vehicle-mounted network is also developed especially for meeting the requirements of intergrated control and remote management in future. These research works will provide powerful supports for applications of steer-by-wire in wheel loader.1. Due to nonlinearity of hydraulic system in the steer-by-wire system in wheel loader, its mathematical model, which is established by the conventional method based on transfer function, might not be accurate enough because of ignoring some unimportant factors to the system, such as died zone and hysteresis of flow amplifier valve and proportion directional valve. The process of model esbablishment is complicately and difficultly. Some parameters of compenents are difficult to be defined, and this might influence the simulation accuracy. The simulation model of flow amplifier valve is established in AMESim environment in this papar, and research and simulation was done based on it. Simulation and experiment results test and verified the availability of this model.2. Time domain analysis and frequency domain analysis are the basic approaches in designing control system. A thorough study and analysis on stability of the mechanic and hydraulic system in steer-by-wire system was made using the two analysis method. Based on the transfer function, the performace of the system, including stability, stability margin and steady-state error, was discussed paticularly. The analyse results indicate that the steering system is of good stability and stability margin. Theoretically, step response of the mechanic and hydraulic system is zero steady-state error, and steady-state error with the ramp signal input is constant. The results provide the theoretical basis for research and design on control method andsystem.3. The phase plane division control is a kind of intelligent control method based on error between input and output. the of adopted in this paper can solve these problems and achieved better control effect. According to trend of the phase path on phase plan, different control actions was given to the system according to values of e and÷in different area in order to get optimum control effect. The control strategy was designed according to accuracy requirement of control and work process of loader. Analysis of the steering system and its work process, the nine states controller and five states controller based on phase plane division method is designed in this paper. Applied fuzzy control method, the fuzzy five states controller based on phase plane division is introduced followed.Compared with PID and fuzzy PID controller, the control method based on phase plane division introduced in this paper has many advantages, such as simple control rules, quick response speed, strong anti-interference capability and strong robustness.4. In MATLAB/SIMULINK environment, the simulation model of nine states controller, five states controller and fuzzy five states controller is established, and the performance of the system with no calibration, conventional PID controller, fuzzy self-tuning PID controller and the controller designed in this dissertation are compared. The simulation results show that the three controller designed in this dissertation is more effective with good performance of rapid response, short transition time, less steady state error, good tracking performances and satisfied anti-interference abilities, especially to the wheel loader steer by wire system.5. Embedded system is a kind of advanced hardware platform which is widely used in control system recent years.Adopting the embedded microprocessor, the embedded control system designed especially for steer-by-wire in wheel loader is developed. The hardware of the control system is structured on the advanced ARM9 embedded chip Samsung S3C2410. To implement the control functions, the typical peripheral circuits such as digital signal conditioning circuit, analog signal conditioning circuit, output drive circuit, power supply and reset circuit and so on is designed and introduced in addition in this dissertation.6. Take into account function expansion, system upgrade and prospective research, in-vehicle network-oriented interface and node for GPRS, CAN and FlexRay is also designed in the steer-by-wire embedded control system for loader. This provides a hardware platform for the control system to connect with vehicular network and realize remote management for wheel loader in future.7. Based on the embedded hardware system, adopt the modular design method, the embedded control software is developed for steer-by-wire control system in wheel loader. The program of main program, the steering wheel location correction, steering control mode selection, realization of intelligent control method, CAN and FlexRay communication control is introduced and analyzed.8. To test the performance of the embedded control system designed for steer-by-wire system in loader and verified the validity of the control method studied in this dissertation, bench experiment was done in laboratory. The result of experiment showed that the embedded control system is more effective with good performance of rapid response, short transition time, less steady state error, good tracking performances and satisfied anti-interference abilities, especially to the wheel loader steer by wire system.The main innovations of this dissertation are as followed:1. The phase plane division control method is applied in steer-by-wire control in wheel loader for the first time domestically. Based on the control method, the nine states controller, five states controller and the fuzzy five states controller was developed in particular to wheel loader steer-by-wire system. It provides a new control method for steer-by-wire in wheel loader and opens a new field of application of phase plane division control method.2. The embedded system technology is applied in steer-by-wire control system in wheel loader for the first time domestically. Developping the embedded control system for steer-by-wire in wheel loader based on the advanced ARM9 embedded chip, embedding diffirent control method together in the embedded control system the intelligent controller is designed for steer-by-loader for wheel loader. It is more effective with good performance of rapid response, short transition time, less steady state error, good tracking performances and satisfied anti-interference abilities, especially to the wheel loader steer by wire system.3. The embedded control system apply CANBus and FlexRay in steer-by-wire control system in wheel loader for the first time domestically. It provides the hardware platform for future research works on the steering system of wheel loader, such as, connecting to vehicular network, realizing autocontrol, intelligent control, remote integrated management and unmanned vehicle in future.4. The simulation model of flow amplifier valve is established in AMESim environment in this dissertation. Based on it, research and simulation on the performance of flow amplifier valve was done. Simulation and experiment results test and verified the availability of this model.Applying the advanced technology of electronics, automatic control, computer, communication and network in the steer-by-wire control in wheel loader, the embedded control system was developedin this dissertation. The embedded control system was structured based on advanced ARM9 embedded chip, adoped the phase plane division control method and designed with interface of GPRS, CANBus and FlexRay. It provides the hardware platform for future research works on the steering system of wheel loader, such as, connecting to vehicular network, realizing autocontrol, intelligent control, remote integrated management and unmanned vehicle in future.
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