ROAD SURFACE CONDITION ESTIMATION METHOD, AND ROAD SURFACE CONDITION ESTIMATION DEVICE

The invention provides a method and apparatus capable of accurately estimating a road surface condition under a traveling vehicle using unsprung acceleration and wheel speed data. The unsprung fore-aft acceleration (Gx) is detected by an acceleration sensor (11) attached to a knuckle (31) which is an unsprung component of a vehicle. At the same time, the wheel speed (Vw) is detected and the variation (Vw) in wheel speed is calculated. Then the fluctuation range (Ã(Vw)) of the variation in wheel speed and the fluctuation range (Ã(Gx)) of the unsprung fore-aft acceleration are calculated. And whether the road surface is a rough road surface with some bumpiness or a flat (smooth) road surface is estimated from a relationship between the fluctuation range (Ã(Vw)) of the variation in wheel speed and the fluctuation range (Ã(Gx)) of the unsprung fore-aft acceleration.