The Lateral Dynamic Optimal Control Of Four Wheel Steering Vehicle And The Research Of Inner Loop Controller And Outer Loop Controller Cooperate Simulation

The contribution of four wheel steering vehicle for handling and stability in extremecondition is obviously. However, in order to make the four wheel steering vehicle toimprove the potential performance, we have to consider the nonlinear characteristics of tirewhen designing the control strategy. With the development of computer technology and thesimulation and test method, it is necessary to establish a simulation platform to predict andanalysis the performance of four wheel steering vehicle in the earlier. It not only saves thedevelopment cost, shorten the development cycle, the most important is it can help theengineers to analysis and predict the design scheme and control strategy, which can help todesign the hardware and software system. We carried out the research work as follows inthis paper.A lateral dynamics model of eight degrees of freedom of four wheel steering vehiclewas established, which considered the movement of longitudinal, lateral, yaw, roll and therotate of four wheels. The tire of research vehicle was tested, and the tire parameters wereidentified using the magic formula for the following study. The eight degrees of freedomvehicle model was verified by the commercial software Carsim, and the accuracy of bothmodels were same.A steering resistance torque calculation model was established, and the model wasverified using the test data of the wheel force sensor. The movement of the rear wheelsteering actuator was analyzed, and using the mathematical model of brushless DC motor toestablished a rear wheel steering actuator model. Use the slide mode control theory toestablished a control algorithm which can control the rear wheel steering actuator. A rearwheel steering control system model was established to analysis the responsecharacteristics of the rear wheel steering system, through the bench test and simulationanalysis which gave a good agreement.According to the characteristics of the tire cornering stiffness, the lateral stiffness oftire was divided into three zones: the linear zone, the intermediate zone, and the flat zone.Using the weighted function to transit the three tire cornering stiffness smooth together toconsider the tire nonlinear cornering stiffness, and the curve was compared with the magicformula of tire, and give a good agreement. Based on the weighted function and the threezones of tire cornering stiffness, and using the linear quadratic optimal control theory to establish the optimal control strategy for the four wheel steering vehicle based on theweighted function. Through the comparative analysis with the linear optimal controlstrategy of four wheel steering vehicle, the optimal control strategy for the four wheelsteering vehicle based on the weighted function can give a good performance when the tireslip angle is larger or driving on low adhesion road, and when the tire cornering stiffnesswas down the control strategy can give a bigger rear wheel angle to maintain the desiredtarget.Three lateral velocity estimation models of vehicle were established using the kalmanfiltering algorithm and the extended kalman filtering algorithm, which are the lateralvelocity estimation model based on kinematics, the lateral velocity estimation model basedon the linear dynamics model of the three degrees, and the lateral velocity estimation modelbased on two degrees nonlinear dynamics model. Considering the advantages anddisadvantages of the above three kinds of lateral velocity models, a joint estimation modelwas established using lateral velocity estimation model based on kinematics and the lateralvelocity estimation model based on nonlinear dynamics model of two degrees. A switchlogic algorithm of joint estimation model was put forward and the result of estimationmodel was good on all kinds of road.The four wheel steering control system and the wheel force sensor testing system wereintroduced, and the principle of the wheel force sensor was introduced also. A simulationplatform was built which considered the joint control of four wheel steering control strategyand the rear wheel steering system. According to the field test on typical driving condition,the simulation platform was verified using the real vehicle, the both achieved betterconsistency, which indicated that the simulation platform was effective. At last a simulationstudy was performed using the optimal control strategy for the four wheel steering vehiclebased on the weighted function.