| Vehicle safety is not only an impetus to promote the automobile technology but also an important field for vehicle technological innovation.In recent years,many automotive active safety technologies have been developed and applied.Both the electronic stability program(ESP)and the integrated control of vehicle dynamics system are significant active safety technologies that can improve the motion performance effectively.The sideslip angle,a crucial indicator for the stability of the automobile,is obtained by estimation technology.Although many estimation methods of vehicle sideslip angle have been studied,the applicability of complex driving conditions,high estimation accuracy and on-line calculation requirement restrict the application of the sideslip angle estimation technology.The research motivation of this dissertation is put forward based on this background.Main objectives of this dissertation include two aspects.One is establishing a vehicle dynamics model which is applicable to complex driving conditions,can effectively describe the characteristics of the dynamic system and is control-and estimation-oriented.On this basis,a sideslip angle estimation method is proposed to meet the needs of on-line calculation.The main contents of this dissertation are as follows:Considering that the tire force model is the foundation and core of vehicle dynamics modeling,the characteristics of tire force and expressions of several typical tire force models are analyzed firstly.Aiming at the problem that the existing t ire models are too complex to be used for the observer design,a noval PWA modeling method for the tire lateral force is proposed in this dissertaiton.By introducing the parametric variable depicting influence of the road adhesion coefficient on the tire lateral force and combing with the theoretical model,we establish a tire lateral force PWA model characterizing influences of the load transfer and road adhesion coefficient completely.The proposed PWA modeling method can describe characteristics of the tire lateral force under pure lateral slip condition accurately with a simple structure and is convenient for the vehicle dynamics modeling.Based on the established tire lateral force PWA model under pure lateral slip condition,influence factors and action laws of vertical dynamics and parameters on lateral dynamics are analyzed,and a lateral dynamics modeling method is proposed that can characterize the vertical / lateral coupling effect effectively.Besides,a threedegree-of-freedom(3DOF)lateral dynamics PWA model considering roll motion is established.For the residual nonlinear terms of the model,the Takagi Sugeno(T-S)fuzzification method is used,and switched T-S fuzzy model of the lateral dynamics is obtained.Then,a synchronous switched T-S observer design method for the sideslip estimation is proposed.The simulation and experimental results show that the designed switched T-S sideslip angle observer has high estimation accuracy and low computational cost.In addition,the estimation performance of observers based on3 DOF model and 2DOF(without roll motion)model respectively is compared.Results show that these two observers have a similar estimation performance owing to the used output variables that can reflect the characteristic of the roll dynamics.As a result,the dynamics modeling and observer design can be simplified.To sum up,this work provides a new idea and method for solving the sideslip angle estimation problem by means of the switched T-S observer.When the switched T-S fuzzy model is used to design the sideslip observer,there is the case that the actual vehicle state and the observer state are not in the same region,which will lead to asynchronous switching.To overcome this issue,an asynchronous switched T-S observer design method for the sideslip angle is proposed.By constructing the augmented system and using the linear matrix inequality approach,an asynchronous switched T-S observer is designed so that the sideslip estimation error system is asymptotically stable.Although asynchronous observer has a more complex design process,an increased computational burden and a greater conservatism,a wider maneuver applicability and better stability are with it.The estimation performance of asynchronous and synchronous observers are compared through experiments and simulations under different maneuvers.The results show that the asynchronous observer has better estimation performance than synchronous observer when the actual system state changes near the region boundary.Based on this work,characteristics and application scope of different observers can be clarified.In order to meet the demand of vehicle motion integrated control technology development,the sideslip angle estimation method under combined slip condition is studied.Based on the above research work,the PWA model of the tire lateral force and sideslip angle estimation method are proposed.The relationship between tire lateral force and nominal lateral force is established by introducing parametric variables representing the effects of slip ratio and adhesion coefficient.Combined with the tire force theoretical model,the PWA model of tire lateral force is proposed,and the lateral dynamic PWA model with varying longitudinal speed is established.To solve the problem of multiple time-varying parameters,the lateral dynamics PWA model is transformed into a switched T-S fuzzy model by introducing premise variables.Based on this model,the sideslip angle observer is designed.The simulation and experimental results under different maneuvers show that the designed observer has a higher estimation accuracy and a better real-time calculation performance.In this dissertation,vehicle dynamics modeling and sideslip angle estimation methods with applicability for complex driving conditions,high estimation accuracy and real-time calculation performance are developed,which provides a noval idea and method for the sideslip angle estimation technology to meet application requirements. |
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