Road Friction Coefficient Estimation For Vehicle Path Prediction

This paper is part of an on-going research toward the development of a lane-departure warning system [1], one of the most technology-demanding active safety systems. The basic concept of the lane-departure warning system is to project vehicle trajectory, and compare with the perceived road geometry (obtained from vision systems) to calculate a performance metric termed "time to lane crossing" (TLC). When the calculated TLC is less than a threshold value, the control system will either issue warning signals or take intervention actions. To project the vehicle future trajectory accurately, we need to update vehicle parameters (speed, cornering stiffness, etc.) and estimate external disturbances (road super-elevation, wind gust, etc.). The estimation of external disturbances further depends on the vehicle parameters. Therefore, on-line estimation of road/tire characteristics is crucial for the TLC calculation and the overall lane-departure warning system. It is important to note that accurate road/tire friction estimation can also improve the performance of many other vehicle control/safety systems such as ABS, traction control, and 4WS systems. Recently, various methods to identify the road friction coefficients have been developed. Dieckmann [2] developed a method which allows the exact measurement of wheel-slip in the order of 10 -4 . From the information of measured wheel slip the road surface variation is detected. Eichhorn and Roth [3] used optical and noise sensors at the front-end of the tire and stress and strain sensors inside the tires tread and studied both "parameter-based" and "effect-based" road friction estimation methods. Ito et al. [4] uses the applied traction force and the resulting wheel speed difference between driven and non-driven wheels to estima...