Patent ID: 6940399

Claim:
A tire air pressure detection device comprising: a vehicle wheel speed detecting portion ( 2 a - 2 d , 3 a ) for detecting respective vehicle wheel speeds; a rotational status value calculating portion ( 3 b ) for calculating a rotational value (D) expressing a relationship of the respective vehicle wheel speeds to cancel a wheel speed variation between left and right wheels generated due to vehicle turns; a slip status value calculating portion ( 3 c ) for calculating a slip status value (β) based on the vehicle wheel speeds detected by the vehicle wheel speed detecting portion, the slip status value depending on a slip status between driven wheels and non-driven wheels; a regression line calculating portion ( 3 d ) for calculating a regression line that is a linear function expressing a relationship between the rotational status value calculated by the rotational status value calculating portion and the slip status value calculated by the slip status value calculating portion; an ideal driving status calculating portion ( 3 e ) for calculating an ideal status value (βid) corresponding to a slip value under an ideal driving status without tire slippage; a rotational status value compensating portion ( 3 f ) for calculating an ideal rotational status value under the ideal driving status without tire slippage based on the regression line calculated by the regression line calculating portion and the ideal slip status value calculated by the ideal driving status calculating portion; and a tire air pressure decrease detecting portion ( 3 h ) for detecting a tire air pressure decrease based on the ideal rotational status value calculated by the rotational status value compensating portion.