Research On Longitudinal And Lateral Coupling Dynamic Control Of Motor-Wheel Driving Electric Vehicle Based On Coordination Of Four Wheels

Compared with the internal combustion engine vehicle and the electric vehicle driven by a single motor, the motor-wheel driving electric vehicle with hub motor has, the unique technical characteristics and the advantage on drive unit configuration, chassis structure and vehicle handling stability, and then is a unique development direction of the electric vehicle. The lightweight, integrated and high performance motor-wheel driving electric vehicle will be a kind of clean, energy saving and safe ideal electric vehicle in the future. According to the feature that the speed and torque of each motor-wheel can be controlled independently, the longitudinal and lateral dynamic coupling relation and coupling control of the motor-wheel driving electric vehicle are researched in this dissertation in order to improve its handling stability.According to the feature that the torque of each motor-wheel can be controlled independently, three degree of freedom, four degree of freedom vehicle linear dynamic model and sixteen degree of freedom vehicle nonlinear dynamic model involving the longitudinal force difference between left and right wheels are built. In terms of these models, this dissertation researches the longitudinal and lateral dynamic indirect coupling relation that the longitudinal force difference between left and right wheels forms the yaw moment to affect the vehicle yaw rate and then indirectly affects the vehicle lateral motion, and the longitudinal and lateral dynamic direct coupling relation that the longitudinal force difference between left and right front-wheels forms the steering torque to rotate the front-wheel round its king pin and to change the front-wheel steering angle and then directly affects the vehicle lateral motion. The "Magic Formula" empirical tyre model, the differential adjusting single point preview optimal curvature driver model, the electric drive system EMR (Energetic Macroscopic Representation) and MCS (Maximum Control Structure) model and the sixteen degree of freedom vehicle nonlinear dynamic model are integrated into the system model of the motor-wheel driving electric vehicle to simulate its comprehensive performance.According to the feature that the speed of each motor-wheel can be controlled independently, the motor-wheel driving electric vehicle can realize the electronic differential. The differential relationship among four wheels is analyzed according to the Ackerman steer model, and then the method for determining the differential relationship through the push and steer test is proposed. The feedforward control and the incremental PID feedback control are combined to regulate the motor speed. Each motor speed can meet the differential relationship through four parallel control of motor speed regulation. Hereby, the electronic differential control method applied to the real motor-wheel driving electric vehicle is developed. This electronic differential control based on the differential relationship determined through the push and steer test for the in-wheel motor drive electric vehicle is validated through the road tests of different conditions.The motor-wheel driving electric vehicle can realize the direct yaw-moment control by means of the longitudinal force difference between left and right wheels. Through the reasonable torque distribution among four motor-wheels, the longitudinal force difference between left and right wheels forms the additional yaw moment applied to the vehicle by the ground to improve the vehicle handling stability in the mode of the longitudinal and lateral dynamic indirect coupling. In order to determine the reasonable longitudinal force difference between left and right wheels, the direct yaw-moment control based on the feedforward of the front-wheel steering angle or the feedback of the vehicle yaw rate is researched. These two methods can improve the vehicle handling stability, but the latter is better than the former on the adaptability and the anti interference performance. The yaw-moment control test of the real motor-wheel driving electric vehicle validates that the longitudinal force difference between left and right wheels can form the additional yaw moment to affect the vehicle yaw rate and the vehicle steering performance.The motor-wheel driving electric vehicle can realize the differential drive active steering by means of the longitudinal force difference between left and right front-wheels. This dissertation puts forward the concept of the differential drive active steering that the longitudinal force difference between left and right front-wheels forms the steering torque to rotate the front-wheel round its king pin and to make the front-wheel steer actively. The mechanism of the differential drive active steering is researched through the kinematic and dynamic analysis of the steering motor-wheel and the steering mechanism. Through the reasonable torque distribution between left and right front-wheels, the longitudinal force difference between left and right front-wheels forms the steering torque to rotate the front-wheel round its king pin and to change the front-wheel steering angle in order to improve the vehicle handling stability in the mode of the longitudinal and lateral dynamic direct coupling. In order to determine the reasonable longitudinal force difference between left and right wheels, the combined control of the differential drive active steering and the direct yaw-moment control based on the linear quadratic output tracking control is researched. This combined control can fully exert each advantage to improve the vehicle handling stability. The differential drive active steering test of the real motor-wheel driving electric vehicle validates that the longitudinal force difference between left and right front-wheels can form the steering torque to make the front-wheel steer actively and then affect the vehicle steering performance. The combined control test of the differential drive active steering and the direct yaw-moment control of the real motor-wheel driving electric vehicle validates that when the longitudinal force difference between left and right front-wheels makes the front-wheel steer actively, the reverse yaw-moment can weaken the vehicle yaw rate caused by the differential drive active steering so that the trend of oversteering during the differential drive active steering is reduced.In short, according to the feature that each motor-wheel can be controlled independently, the longitudinal and lateral coupling dynamic and its control of the motor-wheel driving electric vehicle based on the coordination of four wheels are researched and analyzed, and the proposed electronic differential control, direct yaw-moment control and differential drive active steering control are validated through the test of the real motor-wheel driving electric vehicle. These research results can be used as reference for the research and development of the motor-wheel driving electric vehicle.