METHOD AND APPARATUS FOR ESTIMATING ROAD SURFACE STATE AND TIRE RUNNING STATE

The frequency of an information signal indicative of the vibration of a wheel detected by an acceleration sensor 11 mounted to a wheel 1 or the frequency of an information signal indicative of a change in the pressure of a gas in a tire detected by a pressure sensor 31 installed in the tire is analyzed by frequency analyzing means 14 (34), the band value of the obtained vibration spectrum or pressure change spectrum is detected, and a vibration level or pressure change level at the detected frequency band is compared with a vibration level table 15T showing the relationship between road friction coefficient µ and vibration level stored in vibration level storage means 15, or a pressure change level table 35T showing the relationship between road friction coefficient µ and pressure change level stored in pressure change level storage means 35 to estimate a road friction coefficient µ. Therefore, it is possible to estimate the value of road friction coefficient µ accurately and improve the safety of a car.