Tire inflation pressure monitoring apparatus

Abstract

A tire inflation pressure monitoring apparatus comprises a reference magnet fixed to a wheel, a movable magnet whose position shifts depending on the inflation pressure of a tire, and a magnetic sensor for detecting the magnetism of the magnets. The reference magnet can be moved in the axial direction of the wheel by means of a position adjusting mechanism. Thus, a relative distance from the reference magnet to the movable magnet can be adjusted to a fixed value (e.g., zero) at the time of calibration. An electric circuit section is stored with a computation formula or a map indicative of the relationships between outputs of the magnetic sensor and minimum distances from the magnets to the magnetic sensor. In detecting the inflation pressure of the tire, data associated with the minimum distances from the magnetic sensor to the magnets are obtained according to the computation formula or map on the basis of the outputs obtained by means of the magnetic sensor. Based on these data, the inflation pressure of the tire is obtained according to a pressure computation formula or a map indicative of the relationship between the tire inflation pressure and the distance between the magnets.