Patent ID: 7168306

Claim:
A tire air pressure detection system comprising: a transmitter provided at each of a plurality of wheels provided with tires and sending out a detection signal corresponding to air pressure of each tire attached to each corresponding wheel; and a receiver provided at a chassis side and provided with first antennas arranged near said transmitters of said plurality of wheels and a first controller receiving detection signals through the first antennas and finding the air pressures of said tires provided at said plurality of wheels based on said detection signals, wherein said receiver is designed so that said first controller measures a strength of each said detection signal, sets a power control signal in accordance with that strength, then sends the power control signal to the transmitter originating said detection signal, and each transmitter is provided with a second antenna receiving its corresponding power control signal and a second controller controlling a transmission power for sending said detection signal based on said received power control signal, wherein said first controller sets as said power control signal a signal maintaining the strength of said detection signal in state if the strength of said detection signal is within a predetermined allowable range (ΔL) with respect to a predetermined threshold value (Th), sets as said power control signal a signal for reducing the strength of said detection signal if larger than a value of said predetermined threshold value (Th) set with said predetermined allowable range (ΔL) (Th±ΔL), and sets as said power control signal a signal for increasing the strength of said detection signal if smaller than a value of said predetermined threshold value (Th) set with said predetermined allowable range (ΔL) (Th±ΔL).