Vehicle Stability Control Strategy Based On Optimal Sliding Mode Control Theory

In recent years, the development of automotive electronic technology promoted the rapid development of modern automotive technology. Vehicle Stability Control (VSC) system is a new active safety control system, which can not only prevent the wheels spin during baking or driving, but also maintain the vehicle stability during steering. It has an important role in improving the active safety of vehicles. As an advanced mechanical-electrical integration product, VSC control algorithm is becoming a research focus at home and abroad.Basis on the summary of the domestic and foreign research achievements, this paper focuses on improving the accuracy and robustness of VSC system. And a domestic passenger car in Class B is chose as benchmark. The modeling of stability control system, estimation of vehicle sideslip angle, researching of control algorithm, off-line simulation and hardware in the loop test are carried out in detail. The test results show that the VSC algorithm can effectively improve the vehicle's lateral stability, and guarantee a high adaptability with respect to the change of road surface condition and various severe driving conditions. The main contents are as follows:1) Vehicle Dynamics Model8-DOF vehicle model has been established by the application of modular design, which is chose as a simulation model of VSC. Based on the requirements of VSC, 2-DOF dynamic model and the wheel rotational model are established, which provide a good model basis for the research of VSC strategy.2) Analysis of Vehicle Stability Control Theory and Estimation of Sideslip AngleThe basic principles of VSC are analyzed form the theoretical, including the selection of control variables and the relationships between stability and control variables. And the control criteria of yaw rate and sideslip angle is established. For that the sideslip angle is difficult to measure directly in practical application, a state observer of the sideslip angle is designed based on Recursive Least Squares (RLS). The simulation results show that this method can effectively improve the estimation accuracy of sideslip angle in nonlinear region.3) The research of VSC AlgorithmBased on optimal control theory, the optimal decision of vehicle yaw moment is achieved by building a linear quadratic regulator. The allocation method of wheel slip ratio is proposed for achieving a reasonable distribution of yaw moment. A wheel slip controller is built based on sliding mode control theory, which makes VSC system realizes the control of the wheel slip ratio. Meanwhile, an original VSC algorithm is formed.4) The research of Off-line SimulationFor verifying the effectiveness of the developed control algorithms, VSC off-line simulation platform is built in MATLAB/SIMULINK environment, and on which the off-line simulation is carried out. The simulation results show that the algorithm can effectively improve the vehicle's lateral stability and its control effect is better than PID control.5) The research of the hardware in the loop testTo further verify the effectiveness and robustness of VSC algorithm, the hardware in the loop test is carried out using the VSC test bed in discussion group. The test results show that the algorithm can effectively improve vehicle handling and stability, and guarantee a high adaptability with respect to the change of road surface condition and various severe driving conditions.Through the above research, we can achieve the following conclusion:(1) Based on the Recursive Least Squares (RLS), this paper has presented a body slip angle state observer estimation method. This method can achieve the on-line identification between the tire cornering stiffness and body slip stiffness mutually, and significantly increase the estimation accuracy of sideslip angle. The results have has high reference value for VSC strategy.(2) This paper plans out the optimal wheel slip ratio based on optimal control theory and liner 2-DOF dual model, and establishes the wheel slip controller by application of sliding mode control theory. The proposed controller is used to improve handling and stability of the vehicle by controlling the wheel slip ratio effectively. The results show that the algorithm can effectively improve the vehicle's lateral stability and has strong adaptability and robustness.