The Steering Stability Control Of Four-wheel-drive Electric Vehicle

Nowadays,four-wheel-drive electric cars have been generally regarded as one of the most important means of transport for the future social development among the public,because they own the advantages of zero emission,less noise and lower energy consumption compared with traditional cars.Moreover they have equipped with more efficient power output and improved their performance of the structure,transmission and control.Therefore,this kind of flexible drive format opens up more space for the management and makes the vehicle easier to handle.In the future,four-wheel-drive electric vehicles will be considered as one of the indispensable tools to build a smart city.The main content of this article is to study the steering stability strategy of four-wheel-drive electric vehicle.It mainly solves the problems of distributed drive electric vehicles regarding steering and operating stability so that it can realize the safe drive.This paper aims for the safety issue of the car when the driver is steering at a medium or high speed and provides a method of torque coordination control based on distributed electric drive system in order to improve the stability of the vehicle.To enhance the stability of electric vehicles under steering conditions,this paper firstly establishes a nonlinear seven-degree-of-freedom dynamic model and uses the three degrees of freedom of transverse and longitudinal direction and vehicle yaw to design a sliding mode controller.The tire lateral force MAP table obtained from the tire magic formula has been improved,and the force table is used to replace the complex tire formula model,which can reduce the difficulty of calculation and increase the speed of solving nonlinear optimization problems.Aiming at solving the problem that the vehicle body sideslip angle cannot be measured in real-time,a vehicle state estimation method based on Kalman filtering theory is proposed when considering the nonlinear characteristics of tire forces.In the article,the application steps of this estimation method are introduced in detail,and the effectiveness of the estimator is verified by simulation experiments.When the car is practically driving,the problem of the tire slip seriously affects the stability of the vehicle due to excessive driving.So this paper designs a lower-level torque distribution controller based on model predictive control,which state is the longitudinal slip rate of the four tires and constrained within the stable range.This solution can accurately track the additional yaw moment required for the upper yaw stability while considering the tire slip.And the sum of the input torque of the four tires is taken as the objective function of optimization,which guarantees the optimal energy and maintains the safe steering of the vehicle.The validity of the controller is proved by simulation.