Page - 35 - 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 2.4.4. Comparison of the Upper Level Controllers This chapter compares simulations carried out with the upper level controllers of chap- ters 2.4.3.1 to 2.4.3.4. The control laws are given in eqs. (2.28), (2.41), (2.42) and (2.47), and the controller parameters are listed in appendix C.1. The ego vehicle was simulated with eq. (2.26) with the initial condition x0 = [ 0 30 0 ]T . The target vehicle model reads x˙T = [ 0 1 0 0 ] xT+ [ 0 1 ] uT, (2.48) with the state vector xT = [ 0xx 0vx ]T describing the position and velocity in the global coordinate system. The initial condition of the target vehicle was set to xT,0 =[ 200 14 ]T . The acceleration of the targetuT was held constant to zero for the first 20s of thesimulation. It thenacceleratedwith1m/s2 for10s, followedbydrivingatconstant speed for another 10s. The target then decelerated with−3m/s2 for 5s, followed again by constant driving for 15s. Figure 2.21 shows the output for this manoeuvre. From fig. 2.21, it is clear that the fuzzy controller has the worst performance. It has an undershoot in the velocity vvx and is not really able to settle the distance error er. The simulation with the lowest acceleration vaxwas the MPC, which controls the vehicle very smoothly. The CTG and the SMC methods have similar results, but the low complexity of the CTG control law leads to a better evaluation of the CTG than the SMC approach. Of course, all four controllers could have better performances if more suitable parameters were identified. The performance of the MPC could be improved if constraints were included in the control law. In this way, the big negative slope at the beginning could be avoided by limiting the change of ades between two time steps. 2.5. Actuators The following two sections focus only on the functional requirements of the ACC system. The actuators have to fulfil many additional requirements regarding functional safety and fault detection. 2.5.1. Drive Actuators Asshownineq. (2.19), amongother factors, thedrive torquedependsonthegear ratio ig of the selected gear. For the drive actuators, the engine and the gear box form one unit. Theactuation isperformedwiththeacceleratorpedalpositionud. Toensuretherequired comfort of theACCvehicle, gear shiftingoperationsduringcontroller oscillations should beprevented, [WDS09]. Insomecases, itmightbepossible that the lower level controller (chapter 2.4.2) generates the sum of the drive torque at all wheels of eq. (2.19). In such 35