Patent ID: 7248958

Claim:
A road surface state estimating apparatus comprising a tire-generated sound detector configured to detect a tire-generated sound that is generated from a tire while a vehicle is running; a calculator configured to calculate at least one feature quantity corresponding to a road surface state and tire-generated sound sources from the tire-generated sound detected by the tire-generated sound detector; a storage device configured to store feature quantities, each quantity corresponding to a road surface state and tire-generated sound source, in such a manner that the feature quantities are correlated with a plurality of road surface states, respectively; and an estimating device configured to estimate a state of a road surface on which the vehicle is running on the basis of the feature quantity calculated by the calculator and the feature quantities stored in the storage device, wherein the calculator calculates at least one feature quantity corresponding to a road surface state and tire-generated sound source by calculating correlation values of a waveform of the tire-generated sound detected by the tire-generated sound detector and at least one fundamental waveform having a predetermined length.