Seite - 5 - in Maximum Tire-Road Friction Coefficient Estimation

1 Introduction driver warning. The acceptable accuracy of any estimate to be used for driver warning depends on the type and urgency of the specific warning, [HG09]. For warnings that require the driver to perfrom an action, the tolerance for a false intervention is very low. Thismeans, for example, thatwhenacollision is imminentandthedriverhas to react in order to avoid or mitigate the collision, the detection of the collision and the influencing parameters have to be highly accurate. A decrease in the friction potential requires the driver to be more attentive. In this case, false interventions are more tolerable and hence the accuracy requirement is lower. A rough but reliable resolution of three different friction potentials (high, slippery, very low) is already valuable to improve traffic safety. Further investigation on the accuracy requirements for an estimate of the friction potential that is used to adapt interventions on the vehicle level is shown in the following section. 1.3. Advanced driver assistance systems and vehicle dynamics controls The driving process consists of a complex interaction between driver, vehicle and en- vironment, see Figure 1.4. This interaction has to be considered in the intervention strategies of ADAS and VDC. However, the intervention characteristics of ADAS and VDC are very different, and hence the requirements also differ greatly. According to Donges, the tasks of the driver consist of navigation, course planning and stabilisation, [Don09]. In the navigation task, the driving route is chosen in or- der to fulfill the purpose of the planned travel. Course planning is necessary in both longitudinal and lateral direction and depend on the traffic conditions and the drivers’ preferences. Subtasks include selecting the longitudinal speed, distance to other traffic participants and the vehicle’s position in the lane. In the stabilisation task, the driver performs actions in order to adapt the actual vehicle reaction to the desired one. Sta- bilisation tasks typically lie in the time range of 0.5 to 2 seconds ahead, whereas the navigation task can begin up to several hours in advance and course planning starts when the driver is able to perceive the environment which is in the range of one minute. Typical anticipatory times for steering actions are within 1 second, whereby these times are normally higher for longitudinal manouevres, [Don09]. Drivers receive between 80 and 90 % of the driving-relevant information through visual cues, [AB09]. The lack of visual cues also explains the higher risk for accidents at night, [KH09]. 5