Research On Steer-by-wire System Of Wheel Loader By Hardware-in-the-loop Simulation

The by-wire technique was primely developed in aviation&aerospace field.Generally speaking,the by-wire technique is a new technique.By-wire technique means that person can control the movement of the action-object in the form of electric signal by electric wire(cable).Obviously,the concept of by-wire technique was put forward relative to traditional mechanic operating system.At present,the in deed concept of by-wire that is accepted in the engineering field should be:the electrical control system that apply the feedback control theory to make the movement of action-object to be the parameter which is controlled. Introduce the by-wire technique into the vehicle engineering field is the necessity result of adapting the controlling request of high efficiency,high precision and high security.Main application of by-wire technique in vehicle engineering field include steer-by-wire,brake-by-wire,throttle-by-wire and active suspension. The application of steer-by-wire on articulated wheel loader will reduce the flow loss of the steering system greatly,improve the transmission efficiency of the steering system,and achieve the aim of energy conservation.Moreover,the transmission ratio of the steering system can be adjusted according to working request,and ease the working intensity of the operating crew.In addition,the application of the steer-by-wire system is important to improve the intact stability of the wheel loader especially the high-speed wheel loader.At present,the research in this field is few.Relying on the college-enterprise co-operation project named Research on Steer-by-wire Technique and The Application on Wheel Loader of it, this thesis has done the preliminary research on steer-by-wire system of wheel loader by hardware-in-the-loop simulation. The steering kinematics of articulated wheel loader is analyzed and the concept of equivalent steering arm of force is presented in this thesis.The relationship of the displacement of steering pistons and steering angle and the relationship of arm of force(and equivalent steering arm of force) and the steering angle are derived.The insitu steering process of articulated wheel loader is analyzed.And the regulations of the moment of insitu steering resistance of both the single-bridge driving and the double-bridge driving condition are studied.The simulation based on theoretic analysis has been done on Matlab.The experimental result on double-bridge driving wheel loader has indicated that the analysis of kinematics can anastomose with experimental result.Between theoretic analysis and experimental result there is little deviation of steering resistance and pressure of steering cylinders in changing event.The main reason of it is that the analysis method is static method and the dynamic factor is ignored.And the result of simulation and the result of experiment are coherent on entirety trend and data scope.The discuss of this part is the foundation of the research on steer-by-wire system of wheel loader,and the analysis of this part will provide the theoretic and data reference. The composition of the hardware-in-the-loop simulator of wheel loader's steer-by-wire system is described,and the working principles of all parts of the simulator are analyzed.The mathematical model of the hardware-in-the-loop simulator is based on transfer function,and some of the model parameters including the damping ratio of second order factor and the coefficients of the proportional valve are corrected according to relational literatures.The entire control system is fifth order system,and which can be reduced to third order system according to practical situation.The load is realized by the different pressure of the fluid to tank which is controlled by the proportional overflow valve.And in the mathematical model,the load is included in the flow-rate gain.The calculation result indicate that the system response before adjustment is much slower than the request to the steering system. The PID control algorithm is introduced to the hardware-in-the-loop simulator,and the digital simulation model is founded in MATLAB/Simulink based on the mathematical model.The parameters K P, K iand K dof the PID contrllor are adjusted by NCD(Nonlinear Control Design) module.The results of time domain analysis and frequency domain analysis indicate that system stability is fine and the...