Research On Sideslip Angle Estimation And Control Algorithm For Vehicle Electronic Stability System

As an active safety technology, Electronic Stability Control(ESC) can improve the vehicle handling stability completely by monitoring the vehicle's state in real time and constraining the oversteering or understeering actively. ESC leads the progress of the future active safety technology. So it is essential to master the advanced technology about ESC, which means taking advantages in the competition of automotive safety market in the future. Therefore, studying of the theories and key technologies in developing ESC can not only have a great realistic significance in improving the ability of developing domestic automobile industry and shortening the gap between the technological levels of our country and developed countries, but also greatly accelerate the progress of automotive industry and other related industry. And it leads to applications widely in the future prospects.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". Basis on the summary of the domestic and foreign research achievements, this thesis focuses on improving the ability of developing stability control system. And a domestic passenger car in Class A0 is chose as benchmark. The modeling of stability control system, estimation of vehicle sideslip angle, researching of control algorithm, developing of test rig, and real vehicle testing are carried out in detail. The main contents are as follows:The first chapter systematically introduces definition, principle and components of ESC. As well as the prospects and the key technologies of ESC are demonstrated. Then 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 establishes a vehicle dynamical model for simulating research of stability control. In view of characteristic features of stability control and the benchmark, a 9 degree-of-freedom nonlinear vehicle model is constructed in modularization. It is composed of engine model, powertrain model, brake system model, hydraulic regulator model, wheel dynamics model, tire model, vehicle body model and driver model. And the vehicle model is validated using the handling test data of the target vehicle. 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.Based on the vehicle lateral dynamics, the relationships between stability and yaw rate, stability and sideslip angle are studied firstly in the third chapter. And the conclusion is that: 1) Yaw rate can be used to judge vehicle state as oversteering or understeering. Sideslip angle can be used to judge vehicle state as oversteering. 2) Sideslip angle can influences the vehicle stable state greatly. Yaw rate can express the vehicle steering characteristic when sideslip angle is small. And the main point of stability control system is to constrain the sideslip angle when it grows large.For that the sideslip angle is difficult to measure directly in practical application, the estimation of sideslip angle in limited steering conditions is studied using state observer and Extended Kalman Filter(EKF). The simulating results of typical operating conditions under different road coefficients show that: 1) Due to the nonlinear characteristic of vehicle dynamics, the nonlinear state estimating methods must be adopted in sideslip angle estimation. 2) The sideslip angle estimating strategy, based on Extended Kalman Filter, can accurately estimate sideslip angle in both linear region and nonlinear region. The sideslip angle estimated is valuable for stability control system. And it provides a reliable foundation for design of stability control algorithm.The control algorithm is the key point of developing ESC system. The fourth chapter develops the framework and content of sub-modules of stability control algorithm using the hierarchic method. The control algorithm takes the nominal yaw rate and stable boundary of sideslip angle as references. The yaw moment is decided by combining threshold control method and classical PID control method. And the yaw moment is transformed into the change of longitude slip of the given wheels using the HSRI tire model. Then the yaw moment is achieved by regulating the wheel brake pressure. The control algorithm is simulated in open-loop and close-loop environments under different vehicle speed and different road coefficients. The simulation results show that the control algorithm can improve vehicle stability in various operating conditions. So the validity of the control algorithm is proved.Testing research is one of the key techniques in developing ESC system. For the purpose of developing and testing stability control system, a test rig is established in the fifth chapter. The test rig is composed of four parts: sensor, actuator, controller and monitor. The software and hardware of stability controller are designed and developed independently. The functions of sensor module of stability control system and sideslip angle estimating strategy are tested in real vehicle using the test rig. The test results show that: 1) The test rig, established in this thesis, reach the design goal and meet the requirements of developing and testing stability control system. 2) The sensor module can accurately measure vehicle state and provide an reliable information for stability control algorithm. The sensor module meets the requirements of developing stability control system. 3) The sideslip angle estimating strategy, based on Extended Kalman Filter, can accurately estimate sideslip angle in both linear region and nonlinear region. And it gets same conclusion in both simulation and vehicle test. The estimating strategy is validated preliminarily.Chapter Six conclude the whole content of this thesis. And it put forward the direction and the keystone for the future.For resolving practical issues, this thesis studies the aspects related to developing stability control system. And it has creative works following:(1) The issue of estimating sideslip angle in limited steering conditions is studied thoroughly in this thesis. Based on Extended Kalman Filter, a sideslip estimating strategy is put forward. Contrast to linear estimating method, the strategy can greatly improve the accuracy of sideslip angle estimation.(2) This thesis develops the framework and content of stability control algorithm using the hierarchic method. The control algorithm is validated by simulating under various operating conditions in open-loop and close-loop.(3) The software and hardware of stability controller are designed and developed independently using the embedded technology. Based on the controller, a test rig is established for developing and testing stability control system. And the functions of sensor module of stability control system and sideslip angle estimating strategy are tested in real vehicle using the test rig.