Study On Longitudinal And Lateral Force Coordinated Control Of Four Wheel Independent Driving / Steering Electric Vehicle

Under the dual pressure of resources and environment,the research and development of electric vehicle has become an irreversible trend.In this,the electric vehicle with four wheel independent driving,independent braking and independent steering function provides more possibilities for the energy saving control,stability control and active safety control because of it has more freedom than the general electric vehicle.Therefore it is considered to be an important direction for the development of automobile industry in the future.In order to improve the vehicle's handling stability and the active safety with the failure of the driving motor,the relevant research on the four wheel independent electric vehicle is carried out in this paper.The specific contents include:(1)A four wheel independent electric vehicle dynamics simulation model is established.The simulation model includes vehicle dynamics model with seven degrees of freedom,magic tire model,driving and braking model,steering model and so on.Finally,the correctness of the model is verified by commercial software Carsim.(2)An algorithm for estimating the adhesion coefficient of road surface is designed.The normalized Dugoff tire model is selected as the estimation model.Taking the road adhesion coefficient as the state variable,the state equation and observation equation of the system are established based on the measurement of longitudinal and lateral acceleration and yaw angle acceleration.Then use the extended Calman filter theory to linearize the system to calculate the Jacobian matrix.Finally,the validity and accuracy of the filter is simulated and verified.(3)A longitudinal and lateral force coordinated control strategy of four wheeled independent electric vehicle is designed.The upper controller is used to ensure the desired driving state of vehicle.In order to minimize the square sum of the tire load rate,the middle layer distributor is the objective function.The optimal allocation of the longitudinal and lateral forces of each wheel is realized on the premise of sufficient consideration of the related constraints.The lower executive layer transforms the longitudinal and lateral forces into electric torque and wheel corner output by means of the wheel dynamic model and the reverse model of tire cornering characteristics.Finally,the simulation verification of cooperative control is carried out.(4)A corresponding fault tolerant control strategy after driving motor failure is designed.First,the definition of failure is given,and various failure situations of the driving motor are analyzed and the failure modes are divided.Then a rule-based fault-tolerant control strategy is designed.In order to overcome its shortcomings,a fault tolerant control strategy based on control allocation is also designed.Finally,the fault tolerant control strategy is simulated and verified.