Patent ID: 8330594

Claim:
A tire pressure measuring system in which a control unit mounted on a vehicle body is connected by radio to a sensor unit mounted on a tire of the vehicle body, for transmitting data regarding at least air pressure and temperature of the tire, measured by the sensor unit, to the control unit, wherein the control unit comprises an electromagnetic field generation circuit for generating a transmission electromagnetic field varying at a predetermined transmission frequency, and a data receiving circuit for detecting transmission data from the sensor unit, based on variation of the transmission electromagnetic field, the variation caused due to the sensor unit, the sensor unit comprises a plurality of kinds of sensors including at least a pressure sensor for measuring the air pressure and a temperature sensor for measuring temperature, an antenna for receiving the transmission electromagnetic field, and through interaction with the transmission electromagnetic field, affecting the transmission electromagnetic field such that the transmission electromagnetic field varies, to thereby communicate with the control unit, and a data transmission circuit for changing an antenna current flowing in the antenna to thereby cause the transmission electromagnetic field to vary, and alternately transmitting a plurality of kinds of transmission data corresponding to output of the plurality of kinds of sensors, the kinds of transmission data including at least pressure data and temperature data, and the data transmission circuit detects a rotation cycle of the tire, based on change of strength with which the transmission electromagnetic field is received, and carries out a transmission operation while switching among the kinds of transmission data in synchronism with the rotation cycle.