Safe, dynamic and comfortable longitudinal control for an autonomous vehicle

Driver assistance systems are commonly available in many vehicles. There are systems for safety functions like the Electronic Stability Control, Automatic Traction Control, Anti-lock Brake System and automatic emergency braking. There are also systems for comfort functions like adaptive cruise control with stop and go functionality and combined safety and comfort functions like lane keeping and side-wind assistance. A control system consisting of all of these systems would allow comfortable automatic vehicle guidance on highways. In an urban environment, like in the Stadtpilot project, requirements on driver assistance systems are higher, especially in the case of full autonomous driving. An essential part of an autonomous vehicle control system is a longitudinal controller for acceleration and deceleration of the vehicle. This longitudinal control system has to take care of many more conditions than an assistance system. E.g. it needs to perceive and calculate road and weather conditions with its sensors, which usually is a task a human driver does instinctively. The present paper describes how the autonomous vehicle Leonie is able to adapt its longitudinal control to changing road and weather conditions by calculating a so called Grip Value and gives an outlook how this parameter affects whole vehicle guidance.