APPARATUS FOR ESTIMATING FRICTION COEFFICIENT μ OF ROAD- SURFACE

PROBLEM TO BE SOLVED: To estimate the friction coefficient μ or physical quantities related to the μvalue. SOLUTION: An apparatus is constituted of a wheel-speed computing part 14 which computes the wheel speed ω(n) of every tooth of a rotor on the basis of the wheel speed signal of a wheel speed sensor 11. In addition, it is constituted of a differentiator 16 which computes the wheel angular acceleration y(n) of every tooth on the basis of the wheel speed ω(n). It is constituted of a high-pass filter 18 which removes an offset component from the wheel angular acceleration y(n) and which outputs the change amplitude y(n) of a tire uniformity in the reciprocal direction. It is constituted of a low-pass filter part 21 which averages and computes the change amplitude Δy(n) of every tooth and which is prepared in every tooth. It is constituted of a squaring device 32 which squares the output of the low-pass filter part 21. It is constituted of a totalizer 34 which totalizes squared and computed results of every tooth and which computes a tire uniformity level. It is constituted of a level computing part 36 which sets a tire uniformity level in a high μ road. It is constituted of a road-surface μestimation part 42 which compares the computed tire uniformity level with the set tire uniformity level and which estimates a road-surface μvalue.