Abstract: A device for estimating a road friction state in which a friction state of a wheel with respect to a road surface can be estimated accurately. A bandpass filter extracts, from a wheel speed signal detected by a wheel speed detecting unit, a portion of the wheel speed signal in a predetermined range which includes a torsion resonance point at which a frequency is greater than a low frequency regions. A vibration level computing unit computes a vibration level of the wheel speed signal. A road friction state estimating unit estimates the friction state of the wheel with respect to the road surface on the basis of a vibration level computed by the vibration level computing unit and an estimated value of a road &mgr; slope computed by a &mgr; slope computing unit, and on the basis of a relationship between the two determined for each road surface state.

Abstract: In a speed detecting apparatus for a rotating body, a correction coefficient is used to correct a detecting error in each of pulse signal periods representing speed data of the rotating body. The correction coefficient is updated so as to cancel an aberration of the corresponding pulse signal period caused by a nonstandard factor of the rotating body. Specifically, an average value of the pulse signal periods corresponding to one rotation of the rotating body is first derived, then a value indicative of a deviation between corresponding one of the pulse signal periods and the average value is derived, and further, an updating value is derived by adjusting a degree of influence of the deviation indicative value to the correction coefficient using a correction sensitivity coefficient. The correction coefficient is updated by adding the updating value to a last value of the correction coefficient.

Abstract: It is an object of the present invention to detect a tire air pressure indirectly with high detection precision.A tire air pressure detecting device includes a speed sensor for outputting a signal corresponding to a rotational speed of a tire, and an electronic control unit which inputs the signal from the speed sensor and performs predetermined arithmetic operations on that signal. The electronic control unit calculates a wheel speed based on the output signal of the speed sensor, performs a frequency analysis for the calculated vehicle speed, and derives a resonance frequency corresponding to the unsprung mass in the vertical and longitudinal directions. The tire air pressure is then detected based on this resonance frequency.

Abstract: An apparatus for controlling running of a motor vehicle by measuring respective values of acceleration of the vehicle wheels, includes a digital low-pass filter for obtaining acceleration values by excluding high-frequency noise components of successive values of instantaneous acceleration which are obtained for each wheel at successive sampling intervals. Filter parameters such as the cut-off frequency can be controlled in accordance with the current operating conditions of the respective wheels, such as wheel velocity, to thereby provide optimum filter operation and hence substantially improved accuracy for the derived values of acceleration.

Abstract: An anti-skid control system for use in a motor vehicle which includes a braking pressure adjusting device associated in common with at least first and second wheels of the motor vehicle to control braking pressures applied thereto. The anti-skid control system includes first and second wheel speed sensors for sensing rotational speeds of the first and second wheels, respectively, and a vehicle state detector for detecting a state of the motor vehicle such as a speed of the motor vehicle. Also included in the anti-skid control system is a control unit for controlling the braking pressure adjusting device on the basis of the sensed rotational speeds of the first and second wheels and the detected state of the motor vehicle. The control unit determines a weighting coefficient on the basis of the detected vehicle state and calculates a weighted average wheel speed on the basis of the determined weighting coefficient and the sensed rotational speeds.