Research On Nonlinear State Estimation Of Side-slip Angle For Vehicle Electronic Stability Program

As the development of electronic technology, electronic control device have been widely used in modern vehicle. As an active safety technology, Electronic Stability Program (ESP) can improve the vehicle handling stability completely by monitoring the vehicle's state in real time and constraining the over-steering or under-steering actively. As an important assessment indicator of vehicle handling stability, the side-slip angle of a vehicle play a great role in the research procedure of ESP. But the cost for side-slip angle measurement systems is too high compared to existing on-board sensors, it is difficult for ESP system to measure the side-slip angle. So the research on estimation of side-slip angle is important in the development procedure of ESP.This thesis is associated with the"Integrated Development of Electronic Stability Program (ESP) and Integrated Control Technology of Electronic Power Steering (EPS)"subject, supported by the project of National 863 Program"Integrated Development of Advanced Technology for X121 Passenger Car". Based on the summary of the domestic and foreign research achievements of the side-slip angle estimation method, a nonlinear state observer have been applied for the estimation of side-slip angle. Aimed on the research on side-slip angle of ESP, the modeling of vehicle body dynamic and tire dynamic, the design and modeling of nonlinear state observer, the estimation of side-slip angle, the simulation under standard testing condition are carried out in detail. The main contents are as follows:The first chapter systematically introduces the status of ESP and the role of the side-slip angle in the ESP system. This thesis also do some research and summarize the status of the estimation on side-slip angle. The widely-used estimating methods have been introduced, and their advantages and disadvantages have been compared. According to research above-mentioned, the academic background and the application background of topic selecting are elaborated. The first chapter also gives the primary coverage of this thesis.The second chapter introduces the vehicle system dynamics. In this chapter an eight degree-of-freedom vehicle dynamics model and a tire model have been systematically introduced. The model coordinate and basic concept have been described, the model have been established. According to the relationship between model properties as well as the analysis of nonlinear and non-steady-state problems, the model has been refined. The results show that the vehicle model can describe the dynamical characteristics in linear and nonlinear area correctly and accurately. The vehicle model provides a reliable foundation for researching on stability control.The third chapter introduces the basic concept and design method of nonlinear state observer. According to the particular problem that estimates the side-slip angle, an nonlinear state observer system have been designed and established to estimate the side-slip angle based on seven degree-of-freedom vehicle dynamic model. The modular method for the establishment of system model has been carried out. The vehicle body dynamic model, the Uni-Tire model and the nonlinear state observer model have been established independently, the interface is designed to implement the relationship between each model, the side-slip angle nonlinear state observer finally achieved based on the modular model.Firstly, the basic concept and the procedure of the model establishment of the seven degree-of-freedom vehicle body dynamic model have been introduced. Also the roles of the seven degree-of-freedom during the analysis of the ESP, the definition of the inner model parameters and the description of the vehicle model state function have been introduced. The theory base has been supplied for the establishment of the side-slip angle nonlinear observer with the S-function.Comprehensively considering the real-time requirement of the ESP and the accuracy requirement of tire model of the side-slip angle observer, the Uni-Tire model that describes the united condition of side-slip and longitudinal-slip has been applied as the inner tire model of the observer system. According to the analysis of the relationship between the inputs and outputs of the tire model, and considering the relationship between each modular model, this thesis establishes a tire model that is used in observer system.The design and model establishment of the side-slip angle nonlinear state observer is the key point of this thesis. Based on the seven degree-of-freedom vehicle body model, a reduced-order observer has been established. The feedback mechanism has been designed independently according to the states including longitudinal velocity, lateral velocity and yaw velocity. Generally, the side-slip angle nonlinear state observer is established.The forth chapter is the simulation of the side-slip angle nonlinear state observer system and the analysis of the consequences. The simulation condition is based on the regulation that is proposed in The Test Evaluation Methods and Goal Setting X121 Car ESP. According to the test and the analysis on the results, the side-slip angle nonlinear state observer can satisfied all the testing condition.The fifth chapter conclude the whole content of this thesis. And it put forward the direction and the keystone for the future.