Antiskid apparatus

An antiskid apparatus comprising:

• a wheel speed detecting means for detecting a wheel speed of at least one wheel,
• a first filter circuit having a predetermined cut-off frequency with respect to said wheel speed for filtering said wheel speed and producing a first filtered wheel speed,
• a first wheel deceleration detecting means for detecting an acceleration and deceleration of said at least one wheel based on said first filtered wheel speed,
• a vehicle body speed estimating means for estimating a vehicle body speed on the basis of said first filtered wheel speed,
• a slip quantity calculating means for calculating a slip quantity on the basis of said vehicle body speed and said first filtered wheel speed,
• a second filter circuit having a cut-off frequency which is variable with respect to said wheel speed for filtering said wheel speed and producing a second filtered wheel speed,
• a second wheel deceleration detecting means for detecting an acceleration and deceleration of said at least one wheel based on said second filtered wheel speed,
• a cut-off frequency changing means for changing said cut-off frequency of said second filter circuit in accordance with a state of road surface .mu., said state of road surface .mu. being estimated on the basis of an output of said first wheel deceleration and an output of said slip quantity calculating means,
• a control quantity calculating means for calculating and outputting a pressure reduction quantity signal at the time of detecting the wheel locking on the basis of the logical product of said output of said first wheel deceleration detecting means and an output of said second wheel deceleration detecting means or an output of said slip quantity calculating means, and
• a braking force adjusting means for adjusting the braking force of said at least one wheel in accordance with said pressure reduction quantity signal such that said braking force is decreased to avoid wheel locking and is increased when said wheel speed is restored.