The Anti-lock Braking System (ABS) fitted to modern passenger vehicles is intended to provide reliable and efficient braking under critical road conditions or in an emergency. However, the braking dynamics of a vehicle vary greatly depending on the road surface. On an unsealed road surface an ABS equipped vehicle will behave quite differently from vehicles without ABS. The braking distance on gravel or snow covered roads is less for systems without ABS. In this situation a snow or gravel wedge is responsible for an additional braking effect with locked wheels. In an ABS system, the formation of the wedge results in the unlocking of the brakes and the vehicle rolls over the wedge. Using a laser slit line projected longitudinally on the wheel and observing deformation of this line caused by a change in the road-wheel contact wedge, the build-up of material in front of a locked wheel can be identified. An image of the laser line is acquired by a CCD camera and is then digitally analyzed to detect changes caused by a direct build-up of soil/snow in the form of a wedge. The specifically developed algorithm is used to analyse laser digital data that identifies the build-up of snow/gravel in front of the wheel in the form of a triangular wedge. This paper investigates a method of discriminating between sealed and unsealed surfaces where a switch can be developed which may be applied to the ABS so that an alternative algorithm can be applied specifically for gravel or snow covered surfaces.
Proceedings of the 7th International Conference on Urban Transport and the Environment for the 21st Century (Urban Transport VII), Lemnos Island, Greece, 14-16 May 2001 / L. J. Sucharov and C. A. Brebbia (eds.),