Research On The Integration And Trajectory Tracking Control Algorithm Of Full X-by-wire Chassis Vehicle Based On Distributed Drive

Traditional vehicles have become more and more perfect after more than a century of development.However,due to the increasing performance requirements of vehicles,the limitation of mechanical structure of traditional vehicles makes it difficult to improve the performance of the vehicle In recent years,with the continuous development of technologies such as drive motors,chassis-by-wire,and intelligence,the future of X-by-wire,electrification,and intelligence has become a development trend.At the same time,improving the performance of vehicles is also an effective way to reduce traffic accidents,reduce pollution,and improve driving safety and comfort.This paper takes the Full X-by-Wire chassis vehicle based on distributed drive as the research object.This type of structure combines the distributed drive-by-wire and distributed-by-wire chassis technology,cancels most of the mechanical connections,and is equipped with four wheels on the vehicle.There are hub or wheel drive motors,four-wheel independent wire-controlled steering and four-wheel independent wirecontrolled brakes,etc.,which make the vehicle with this structure have a higher degree of controllability and is suitable for the use of chassis integrated control technology.Using chassis integrated control technology,can effectively control the Steer,Drive/Brake system actuators,give full play to the performance of the vehicle At the same time,the hardware configuration of the distributed drive-by-wire chassis vehicle is also a favorable condition for realizing the unpiloted vehicle.Relying on the national key project-Multi-system efficient integration of in-wheel motor action module and vehicle torque vector distribution technology（2021YFB2500703）,this paper mainly studies the drive and chassis integrated control algorithm and trajectory tracking control algorithm with unpiloted vehicle.To sum up,the main research contents of this paper are as follows:（1）Establish a vehicle dynamics model.In order to study the dynamic characteristics of the Full X-by-Wire chassis vehicle based on distributed drive and provide the development basis for the integrated control algorithm and trajectory tracking control algorithm,a four-wheel independent steering and driving vehicle dynamics model is established.The model can reflect the coupling relationship between the longitudinal,lateral and yaw motions of the vehicle as well as the steering/drive kinematics of the four wheels.Finally,the accuracy of the vehicle model is compared and verified.A single-track dynamics model of a four-wheel-steer vehicle based on active rear wheel steering is established for the design and research of the trajectory tracking controller.（2）For the Full X-by-Wire chassis vehicle based on distributed drive,design the chassis integrated control algorithm.The designed integrated control algorithm adopts a hierarchical control architecture including centralized control layer,tire force distribution layer and actuator control layer.The integrated control layer takes the vehicles longitudinal speed,lateral speed and yaw angular velocity as the control objectives,and uses the model predictive control algorithm to find out the control variable required to respond to the drivers command,that is,the total force and total torque.The tire force distribution layer is to distribute the total force/moment calculated in the upper layer to eight independent control quantities in the lateral and longitudinal directions of the four wheels.The optimal control method is considered to transform the tire force distribution problem into a quadratic programming problem,and the tire utilization efficiency is taken as the optimization objective to solve the problem,and the longitudinal and lateral forces of each tire are obtained to improve vehicle stability.The actuator control layer is used for calculating the final actuator control commands for motor,i.e.four wheel steer angles and drive/brake moment.The longitudinal force of the tire can be directly obtained by the driving/braking force control.And the wheel steer angle needs to establish an inverse tire model,then the wheel steer angle can be obtained by calculating the tire slip angle.（3）For the Full X-by-Wire chassis vehicle based on distributed drive,design the trajectory tracking control algorithm.For the four-wheel-steering vehicle based on active rear-wheel steering,two typical four-wheel-steering vehicle trajectory tracking controllers are designed using model predictive control theory and active rear-wheel steering control strategy.Aiming at the four-wheel independent steering characteristics of the Full X-by-Wire chassis vehicle based on distributed drive,on the basis of the above chassis integrated control system,the integrated control layer in the chassis integrated control layer is switched to the trajectory tracking control layer,while the tire force distribution layers and actuator control layers keep the same.In the trajectory tracking layer,it is assumed that the vehicles driving trajectory has been given,and the vehicles longitudinal speed,lateral displacement and yaw angular velocity are used as reference targets to find out the total force and total moment of the vehicles motion,so as to follow the expected driving path.（4）In order to verify the effectiveness of the proposed algorithm,the Matlab/Simulink and Car Sim co-simulation platform is established in this paper to verify the effectiveness of the algorithm.In the experiment of the chassis integrated control algorithm,the comparison results of different working conditions and different algorithms show that the chassis integrated control algorithm can improve the driving stability of the vehicle compared with the direct yaw moment control algorithm.In the experiment of trajectory tracking control algorithm,the two typical four-wheel steering controllers designed are compared with the trajectory tracking controller proposed in this paper for the Full X-by-Wire chassis vehicle based on distributed drive.The results show that the three controllers can follow the reference trajectory basically,in which the Full X-by-Wire chassis vehicle based on distributed drive controller has better adaptability to various working conditions and higher control accuracy.