Page - 37 - in Integration of Advanced Driver Assistance Systems on Full-Vehicle Level - Parametrization of an Adaptive Cruise Control System Based on Test Drives

2.5. Actuators cases, theud is calculated in the engine and gear controller and is not part of the ACC, [WDS09]. 2.5.2. Brake Actuators In most of the vehicles, the brake actuation is done via the ESC. Although it is possible to do this with the brake booster, this is not common due to higher costs and much higher delay for building up brake pressure, [Fei13]. For the following considerations, which actuation is used is not relevant. Ineq. (2.21), it is evidentthatthebraketorqueTbandthereforethe longitudinalaccelera- tion vax of the vehicle are proportional to thebrakepressurep. Winner et al. mentioned in [WDS09] that a change in the brake pressure of 1bar will lead to a change in the longitudinal acceleration of 0.07 to 0.14m/s2 for a standard vehicle. Regarding comfort, the brake actuation should be able to control the pressure in steps smaller than 0.5bar, andapressureovershoothas tobeavoided. ForFSRA, the taskofpreventingmovement when the vehicle has stopped is very important. To meet this requirement, Laiou et al. showed in [LP08] that this is possible by increasing the brake pressure at a vehicle speed near 0m/s. If the brakes are applied too early, there will be high accelerations, which will not satisfy the driver. On the other hand, if the brakes are applied too late, the vehicle might move backwards, which must be prevented under all circumstances. When the FSRA starts to move from zero speed, the wheel torque has to be increased before the brake is released, [LP08]. The coordination of these operations places high demands on both the brakes and the drive controllers. 37