Patent ID: 7015803

Claim:
A tire air pressure detecting device for monitoring a tire air pressure by transmitting a signal representing the tire air pressure detected at a wheel to a vehicle body and receiving the signal representing the tire air pressure at the vehicle body comprising: tire air pressure detecting means on the wheel for detecting the tire air pressures main transmitting means on the wheel for transmitting an air pressure signal representing the tire air pressure detected by said tire air pressure detecting means to the vehicle body; main receiving means on the vehicle body for receiving the air pressure signal transmitted from said main transmitting means; main switch turn-on detecting means on the vehicle body for generating a main switch ON signal when the turn-on of a main switch is detected; vehicle body side control means on the vehicle body for receiving the air pressure signal received by said main receiving means and the main switch ON signal generated by said main switch turn-on detecting means; auxiliary transmitting means on the vehicle body for transmitting a transmission instruction signal to the wheel to transmit a new air pressure signal from said main transmitting means to said main receiving means based on a vehicle body side control signal from said vehicle body side control means when said vehicle body side control means receives the main switch ON signal; auxiliary receiving means on the wheel for receiving the transmission instruction signal transmitted from said auxiliary transmitting means; wheel side control means on the wheel for generating a wheel side control signal to read a new air pressure signal from said tire air pressure detecting means and transmit the air pressure signal to said main transmitting means based on the transmission instruction signal received by said auxiliary receiving means, and in addition to transmitting the transmission instruction signal received by said auxiliary receiving means, the main transmitting means also transmitting the air pressure signal repetitively at a predetermined constant frequency, the predetermined constant frequency of transmitting the air pressure signal varying depending on a vehicle speed.