Seite - 22 - in Integration of Advanced Driver Assistance Systems on Full-Vehicle Level - Parametrization of an Adaptive Cruise Control System Based on Test Drives

2. Adaptive Cruise Control 2.3. Vehicle Dynamics Sensors The Vehicle Dynamics Sensors are part of the Electronic Stability Control (ESC), which is standard equipment in every modern vehicle, [WWL+04]. For ACC systems, the yaw rate vωz, the steering wheel angle δSW, the acceleration in longitudinal vax and lateral vay directions and the wheel speeds cωi are sent to the ACC controller. According to [Rob02], the yaw rate is measured through micro-mechanical devices, which vibrate at about 2000Hz. The yaw motion introduces the Coriolis Force, which is proportional to the yaw rate. Modern vehicles use Hall sensors to detect the rotational speed of the wheels, [Rob02]. To this end, a multi-pole-ring is mounted on the wheel bearing. The Hall sensor detects thechange inthemagneticfield,whichisproportionaltothewheelspeed. Theadvantage of this sensor type is that measurements near zero speed are possible. The longitudinal and lateral accelerations are measured using the Hall Principle as well, [Rob02]. To achieve this, a permanent magnet is mounted on a spring. Due to accelerations, the spring is deflected, whereby the movement is measured with the help of a Hall sensor. The steering wheel angle δSW is measured via a potentiometer or magnetic sensors, such as Hall sensors. It is very important that the sensor can measure thesteeringwheelangle intherangeof±720°,whichrepresents fourrevolutions, [Rob02]. With the help of gearwheels, the four revolutions at the steering wheel correspond to less than one revolution at the sensor, where the actual steering wheel angle can be measured. Another possibility is to use two angular sensors, where both have different gear ratios to the steeringcolumn. Thecombinationof the twomeasuredanglesprovides clear information about the actual steering wheel angle. There are other measurement principles possible, but modern vehicles most frequently use the principles described above. 2.4. ACC Controller Usually, theACCcontrollerelectronicsareplaceddirectly inthehousingoftheenvironmental- recognition sensor, which is therefore called the ACC-Sensor and Controller Unit (ACC- SCU), [WWL+04]. The ACC controller itself consist of two levels, the ˆ upper level controller and the ˆ lower level controller. Theupper levelcontroller receivesthedistancetotheOTF srOTF anditsrelativevelocity sr˙OTF in the sensor coordinate system. The driver sets the desired speed vset and time gap τset. The lower level controller generates the drive train and brake actuation, ud and ub. Each controller receives the current state of the vehicle, the velocity vvx and the longitudinal acceleration vax. As mentioned above, the RADAR sensor requires 22