Page - 30 - in Maximum Tire-Road Friction Coefficient Estimation

2 Estimation of the friction potential depends on the vehicle’s longitudinal speed vx and the measurement range dM, see Fig- ure2.9. Often, extra sensors arenecessary, whichcauseadditional cost andmaintenance efforts. Sensors that measure the vehicle reactions incorporate the current vehicle condi- tionandthusenable thecalculationof the safetymargin. Theycannotdeliverpredictive estimates, as they require a vehicle reaction, and they may or may not cause additional costs, depending on the kind of sensor and the accuracy needed. A trade-off between robustness, accuracy and time delay has to be negotiated for all vehicle-fixed methods. ! I v x v x d M Figure 2.9.: Identification of the friction potential using (top) car-to-x (C2x) commu- nication systems such as car-to-car (C2C) and car-to-infrastructure (C2I) communication, (centre)on-boardenvironmentalsensorsthatscantheroad surface ahead or (bottom) on-board sensors that estimate the friction po- tential based on the measured vehicle reaction Figure 2.10 shows a classification of vehicle-fixed methods, which will be discussed in the Sections 2.2.1 and 2.2.2. Thereafter, infrastructural systems and sensorfusion-based systems are discussed in Sections 2.2.3 and 2.2.4. 2.2.1. Cause-based approaches The friction potential µmax is determined by the influencing parameters shown in Ta- ble 2.1. For cause-based approaches, the conditions that have the highest influence on µmax (e.g. the presence and condition of intermediary layers, road roughness) are observed, see Figure 2.10. Efforts have been made to detect the following conditions: 30