Road friction information is very important for vehicle active braking control systems such as ABS, ASR, or ESP. It is not easy\nto estimate the tire/road friction forces and coefficient accurately because of the nonlinear system, parameters uncertainties, and\nsignal noises. In this paper, a robust and effective tire/road friction estimation algorithm for ABS is proposed, and its performance\nis further discussed by simulation and experiment. The tire forces were observed by the discrete Kalman filter, and the road friction\ncoefficient was estimated by the recursive least square method consequently. Then, the proposed algorithmwas analysed and verified\nby simulation and road test. A sliding mode based ABS with smooth wheel slip ratio control and a threshold based ABS by pulse\npressure control with significant fluctuations were used for the simulation. Finally, road tests were carried out in both winter and\nsummer by the car equipped with the same threshold based ABS, and the algorithm was evaluated on different road surfaces. The\nresults show that the proposed algorithm can identify the variation of road conditions with considerable accuracy and response\nspeed.
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