| 摘要 |
PROBLEM TO BE SOLVED: To make change of the relation between air pressure of a tire and a resonance frequency of the tire, by characteristic change of a tire material with the lapse of time, not taken into account. SOLUTION: A rotational speed of a wheel is detected, and the resonance frequency fr is extracted from a detected signal detected therein (S102-S114). The resonance frequency fr is corrected in response to lapsing days after tire fitting (S116, S118), and the air pressure of the tire is estimated based on the corrected resonance frequency fr (S120).
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