An autonomous safety system for road departure prevention based on combined path and sideslip control

Practical limits on vehicle speed in curves depends on many factors: road friction, lateral maneuvering room, driving skill and the willingness of a driver to brakewhile cornering. This is in addition to multiple vehicle design and performance characteristics, including the classical understeer behaviour. The current paper considers an active safety control system to protect against the major effects of over-speed in curves, especially lateral drift leading to lane or road departure. The concept is to use available information about various vehicle and environmental factors-e.g. surface friction, lane and shoulder widths-and compute control interventions which will protect against lane and road departure. The proposed system is based on the optimal control of particle motions, as described previously for a Parabolic Path Reference (PPR) which provides a control reference for combined cornering and braking under computer control. The earlier work assumed very simple road geometry which is generalized in the present analysis. Further, we make use of a novel control algorithm based on nonlinear optimal control theory, capable of delivering the required integrated control of speed, path curvature and yaw stability. This paper describes the key concepts for designing and implementing such a system