METHOD FOR ESTIMATING ROAD SURFACE CONDITION

A method capable of estimating a snowy road surface condition during vehicular travel in finer classification. In this method, tire vibrations in the circumferential direction, road surface temperature (T), and tire-generated sound are detected by an acceleration sensor, a road surface thermometer, and a microphone, respectively. Then band values P 11 , P 12 and P 13 for a pre-leading-edge region (R1), band values P 21 , P 22 and P 23 for a leading-edge region (R2), band values P 31 , P 32 and P 33 for a pre-trailing-edge region (R3), band values P 41 and P 42 for a trailing-edge region (R4), and band values P 51 , P 52 and P 53 for a post-trailing-edge region (R5) are calculated from the tire vibration data. A sound pressure level ratio (Q) = (P A /P B ) , which is the ratio of a band power value (P A ) of a low frequency band to a band power value (P B ) of a high frequency band, is calculated from data on the tire-generated sound. And a road surface condition is estimated, using the band values (P ij ), road surface temperature data (T), sound pressure level ratio (Q), and wheel speed data.