Research On Predictive Stability Control Strategy For In-wheel Motor-driven Vehicles

With the advent of Industry 4.0 and Made in China 2025,the sales of new energy vehicles represented by electric vehicles in the Chinese auto market are increasing year by year.Compared with traditional centralized drive electric vehicles,in-wheel motor-driven vehicles have the characteristics of independent controllable torque and fast response speed,so they have great advantages in yaw stability control.Relying on the national key R＆D project "Key Technologies and Applications of HighPerformance In-wheel Motor and Modular Assembly Integration"（SQ2021YFB2500007）,this paper takes the in-wheel motor-driven vehicles as the object of study,and aims to improve the yaw stability of the vehicle.In-depth research has been carried out on key technologies such as scientific modeling,state estimation and prediction,steady state judgment,and the calculation and distribution of direct yaw moment.The main research work of this paper is as follows:（1）Dynamic analysis and modeling of in-wheel motor-driven vehicles.First,the sevendegree-of-freedom model,tire model,driver model,and in-wheel motor models composed of body and wheel motions are established,and the torque and power of the in-wheel motor are matched based on the dynamic index;Then the in-wheel motor is established through Car Sim to drive the car;Finally,the established vehicle dynamics model is simulated and analyzed,and the results show that the vehicle dynamics model has high accuracy in the linear region,which can provide a theoretical basis for the subsequent predictive stability control strategy.（2）Research on vehicle stability analysis and state estimation and prediction methods.Firstly,the vehicle stability principle and yaw motion control method are deeply analyzed;Then,based on the linear two-degree-of-freedom model and the road adhesion limit,the ideal state parameters are obtained,and the equivalent cornering stiffness of the front and rear axles are identified and checked;Secondly,based on the simplified nonlinear two-degree-of-freedom model and the EKF algorithm to estimate the vehicle sideslip angle;Finally,a vehicle state prediction method based on linear model and data trend is proposed,which predicts the state of the vehicle in the future cycle,and simulates it on the road surface with different adhesion coefficients.The results show that the designed prediction method has high accuracy（3）Research on vehicle hierarchical control strategy based on predictive stability judgment.First,a stability judgment method is proposed: according to the result of vehicle state prediction,the stability threshold value is used to judge the stability of the vehicle in the future cycle;Then,the upper controller is designed based on LQR,and the required yaw moment is calculated according to the vehicle state and ideal state of the current cycle,and the weight coefficient of the Q matrix is adjusted according to the vehicle sideslip angle,and the upper controller and the predictive stability judgment method are simulated and verified under the input conditions of sine and step angle.The results show that the predictive stability judgment method effectively enables the vehicle to intervene in the stability control in advance and the upper controller improves the yaw stability of the vehicle;Finally,the lower controller is designed based on the quadratic programming algorithm with the optimization objective of minimizing the sum of the squares of the tire load rate,and the driving/braking torque of the in-wheel motor is optimally distributed.The simulation results show that compared with the average torque distribution method,the optimal torque distribution method can increase the stability margin of the vehicle and improve the stability of the vehicle.（4）The driver-in-the-loop experiment verifies the predictive stability control strategy.The driver-in-the-loop real-time simulation platform was built by using d SPACE,Micro Auto Box and Logitech G27 driving simulator,and the experimental verification was carried out under step and sinusoidal angle input conditions.The results show that the predictive stability control strategy can enable the vehicle to intervene in the stability control in advance and improve the stability of the vehicle.