Page - 39 - in Maximum Tire-Road Friction Coefficient Estimation

3. Vehicle model This chapter derives a model for vehicle and environment that is suitable for both the sensitivity analysis (see Section 4) and the tire road friction observer (see Section 5). The focus of this work is solely limited to variables that are related to the vehicle dy- namicsandareavailable inavehicle equippedwithESC, seeSection2.3. This limitation excludes any kind of optical sensors, such as radar, laser or camera-based systems. In addition, all variables need to be measured or estimated on board a vehicle, which ex- cludes C2x applications. To ensure the transferability of the results of the sensitivity analysis in Section 4 to the observer presented in Section 5, the same model considerations apply. The sensi- tivity analysis presented in Section 4, which is used to derive the necessary parameters for the tire/road friction observer, does not need to be real-time capable, as it is only used for parameter design. Nevertheless, the model has to be suitable for the proposed procedure, and the computational effort depends on the model complexity. In compari- son, the model used for the tire/road friction observer must be designed with real-time ability and robustness, see Section 5. The two applications share the requirement that the tire/road contact has to be represented with sufficient accuracy, see Section 3.1. Section3.1 investigates thenecessarymodel complexity intermsofatrade-offbetween computational effort and accuracy, within the limitations on available variables, and Section 3.2 then presents the vehicle model derived from these outcomes. 3.1. Assessment of required model accuracy The same model considerations for both the sensitivity analysis (cf. Section 4) and the tire/road friction observer (see Section 5) are chosen in order to ensure transferability of the results of the sensitivity analysis to the observer development. This may seem lim- iting for the sensitivity analysis. However, this investigation is already limited in terms of mathematical model complexity that can be processed with the proposed method.