Research On Drift Control Of Rear-Wheel Drive Vehicles

The drift state of a vehicle has always been a condition that conventional vehicle control aims to avoid.The Electronic Stability Control(ESC)system in vehicle control is designed to prevent the vehicle from entering an unstable state and aims to limit the vehicle’s kinematic constraints.It allows the vehicle to stay within the controllable range of an average driver.However,such control range is limited,and studying the motion mechanics under extreme vehicle conditions can expand the stability boundaries of vehicle control.In professional racing competitions,through extensive training,drivers usually have a more professional understanding of the vehicle’s state and tire adhesion conditions.Race drivers often induce the vehicle into a drift state by coordinating steering,acceleration,and braking.Typically,the rear wheels reach the tire’s adhesion limit,accompanied by countersteering,to maintain the vehicle’s state near an unstable equilibrium while enabling it to run on a predetermined trajectory.This is a common driving technique used by drivers in professional vehicle races.Due to the saturated state of the rear tires during drift,the vehicle experiences significant sideways slip,a large yaw angle,lateral acceleration,and the average driver cannot quickly take the correct actions to keep the vehicle within a safe and controllable range.In the drift state,the lateral and longitudinal tire forces are limited by the tire’s friction ellipse,and the tires experience deep saturation.The lateral and longitudinal forces become strongly coupled,and their relationship no longer follows a linear change,thus leading to the study of non-linear dynamics in control.At this point,the vehicle experiences high lateral acceleration,which,on one hand,puts the vehicle in an unstable state,and on the other hand,provides it with higher maneuverability.However,the existence of maneuverability must be based on the vehicle’s controllability.This article primarily focuses on the following research aspects:1.This article establishes an improved Fiala tire model for combined lateral and longitudinal slip conditions,simplifying the model’s complexity.The tire’s adhesion ellipse is simplified,and a simplified tire force curve model is introduced to simulate the variation of the tire’s adhesion coefficient with slip ratio within the saturation range.Based on the parameters of a D-class SUV whole vehicle model in Car Sim,a three-degree-of-freedom single-track vehicle model is established,considering the load transfer between the front and rear axles.2.The phase plane analysis of the three-degree-of-freedom single-track model is conducted to study the vehicle’s state variation with the front wheel’s steering angle under a given vehicle speed.Ultimately,the parameter information at the unstable equilibrium point of the vehicle is obtained.The analysis results verify the characteristic that the vehicle,in a drift condition,experiences deep saturation in the rear wheels,and the front wheel’s steering angle and the vehicle’s yaw angle are opposite to the actual direction of vehicle motion.3.Based on the phase plane and state transition diagram of the drift equilibrium state,the equilibrium state is determined.A drift controller is designed using a sliding mode control structure.The control tracking target,which is the desired yaw rate of the vehicle,is redefined based on the path curvature.Simulations are conducted on multiple different trajectories,and the results demonstrate that the control algorithm can track the predetermined trajectory while drifting.Additionally,the control algorithm can smoothly exit the drift and transition to classical steering control.