Research Of Steer-by-Wire Control System On Wheel Loader With Articulated-Frame

The steering system is an important subsystem in wheel loader, which determines the driving security, working efficiency, fuel consumption and the labor intensity of driver. It is an important factor for the people and the manufacturer who make an effort to improve the steer performance of the wheel loader with articulated-frame, however.The higher request is bring forward on steering system with the progress of technology, from reducing labor intensity to bring forward comfort, from locale control to remote control and information. On the other hand, to improve control precision after achieve basic steering function and the steering precision may be up to centimeter. It is that the controllability and the perfection of control on the heavy vehicle are the desire work condition of people. The steering technique of construction machinery will get more progress with the development of electro-hydraulic component.The steer-by-wire system replaces the traditional mechanical or hydraulic connect by connecting and controlling all the component of steering system through micro-electronics technology, using sensors to collect the data of steering, then transfer them to the micro computer on the vehicle. The computer processes these signals, makes decision and outputs actuating signals such as the steering degrees of vehicle. In order to avoid driver's mistake, the system will ignore the input of driver in emergency and make the vehicle in safety.This Ph.D. dissertation is funded by the project (No.20040336) named"Application of Steer-By-Wire technology in wheel loader"from Bureau of Science and Technology of JILIN province, combined project of Jilin University and Shandong Lingong Construction Machinery Co.,Ltd named"Application and research of Steer-By-Wire technology in wheel loader". In order to tackle the contradiction between higher working efficiency and the more stability at high speed, improve the labor efficiency, this paper applies the steer-by-wire technology to wheel loader. This system integrates electro-hydraulic proportion control technology, computer technology and automatic control technology etc. The steering sensitivity can be adjusted according to the different operating condition, offer appropriate"Road Feeling"and adjust the grade of"Road Feeling"according to the driver's custom. To improve the speed of construction vehicle and reduce the labor intensity of operator are the aim at progress of loader. Steer-by-wire system of wheel loader with articulated-frame can be divided into two basic sub-systems: the"Road feeling"control sub-system and the steering degree control sub-system. The"Road feeling"control sub-system explained as follow: The information such as steering resistance of loader is transfer to steering wheel, the direction of resistance torque is contrary to input, and then the driver apperceives the road state. That is the"Road Feeling". The steering angle control sub-system accepts the driver's input signal then control the output mechanism of hydraulic system (steering cylinder) to extrude corresponding displacement. The cylinder pushes the forward and backward frame to circumvolve depend on the shaft, then the steering degree of the vehicle changes. It is a typical electro-hydraulic servo position control system. This paper researches on the theory and experimentation about Steer-by-wire system of the wheel loader such as control strategy of"Road feeling"and steering cylinder position, the software and hardware of the electricity control system. The main research work and innovations in this dissertation can be summed up as following:1. The development actuality of steer-by wire is introduced. The advantages and feasibilities of steer-by-wire to be applied on the wheel loader are analyzed. According to the function of the articulated-frame wheel loader, the control project of steer-by wire is designed. The system of redirector control flow amplifier is substituted by the proportion directional valve control flow amplifier valve based the advantages and disadvantages of former steering system. The hand wheel subsystem with force feedback characteristic and adjustable steer sensitivity is developed because of there is no road feeling to the driver in the former steering system.2. The sources and the main factors influence the steering system of road feeling are analyzed. The relationship between the pressure of the working space in the steering cylinder and steering angle of the vehicle is calculated when the steering resistance torque is changeless. The dynamic compensate of the steering wheel rebound is developed when the steering direction is changed. The control scheme, the mathematic model and the strategy of road feeling sub-system. The strategy and rationality of control algorithm are validated by the simulation of Matlab software.3. The steering angle control sub-system is divided into run and work operating condition according to the obvious characteristic of the wheel loader's operating condition. The transmission ratio between the input signal of the steering wheel and output signal of the steering cylinder is different for the two operating condition. Under low work mode, the high steering sensitivity mode is adopted to increase the work efficiency and decrease operator's labor intensity because in this mode the steering wheel only rotates 180°for the full steering. While in the run mode, in order to enhance operation security and the stability, the low steering sensitivity is set. Therefore the steering wheel must rotate 900°for the full steering.The transfer function of proportion directional valve control flow amplifier valve and whole electro-hydraulic servo sub-system is educed. Then analyze the dynamic characteristics of sub-system. There is big steady state error and slow response when the digital PID controller of classical control theory is used to the non-linear and uncertain system. So the method of non-linear control is developed in the thesis and make up the deficiency of the classical PID controller, to adjust the three parameter of PID controller with the single nerve cell adaptive neural network. The switch of two controllers between Bang-Bang and single nerve cell adaptive neural network is carried out by the expert intelligence coordinator. So the control precision, the response and the stability can be improved. The work mode should not be switched when the vehicle in high speed. The expert intelligence coordinator forces the steering angel sub-system to be low sensitivity by estimating the speed of the vehicle. The system will give an alarm when the mistake is happen.4. Development of software and hardware for electronic control unit. And then, taking TMS320LF2407A DSP as control core of ECU, its main performances and interior resources are introduced. The structure of hardware, selection of electronic elements and designs of some representative function circuits is concretely explained. Finally, on the base, the structure of software adopting module design idea, the flow sheet of main controlling programs and the redundancy design for important devices are carried out with some anti-interference schemes in the process of developing electronic control system.5. Experimental study for steer-by-wire system is accomplished on test bench and road to validate the mathematical model and simulation result. The output signal response and tracking characteristic for input signal are tested separately in two sub-systems.The dissertation put forward a new control system on wheel loader with articulated-frame. The results of the thesis indicate the system can work reliably and improve the control effect clearly.This technology applied to the wheel loader can bring our construction machinery's progress a great stride. Its entire machine working performance and the mobile flexibility can be enhanced greatly, the enhancement international competitive ability will increase, and the operator's labor intensity will be decreased.