Patent ID: 7391307

Claim:
A tire alarm device that gives a warning against a runflat operation limit of a pneumatic tire during runflat operation having a reinforcement layer disposed in each sidewall thereof for enabling the run flat operation, comprising: a tire temperature sensor disposed on an inner surface of one of the sidewalls facing the reinforcement layer therein, the tire temperature sensor being used to warn of the runtlat operation limit, a processing means that determines whether or not the tire has reached a zone of the runflat operation limit based on a signal detected by the temperature sensor; a warning means that gives a warning if the processing means determines that the tire has reached the runflat operation limit zone; a tire side unit having the tire temperature sensor; and a transmitting means that transmits the signal detected by the tire temperature sensor, and a vehicle side unit having a receiving means that receives the signal from the transmitting means, the processing means and the warning means, wherein the vehicle side unit has a memory that stores a preset limit temperature data according to the runflat operation limit zone, and wherein the processing means compares a temperature data value of the signal detected by the tire temperature sensor with a value of the limit temperature data, and determines that the tire has reached the runflat operation limit zone if the temperature data value of the detected signal exceeds the limit temperature data value, wherein the tire side unit has a tire inner pressure sensor for detecting pressure in a cavity of the pneumatic tire, and wherein the processing means determines whether or not a value of the pressure detected by the tire inner pressure sensor is below a prescribed threshold value, and determines that the tire is operated in a runflat condition if the detected pressure value is less than the prescribed threshold value, and determines whether or not the tire has reached the runflat operation limit zone if the processing means determines that the tire is operated in the runflat condition, and wherein the memory stores time history data of the temperature detected, and wherein the processing means calculates a sectional approximate function of the temperature time history data by using at least four consecutive temperature data including a latest temperature data in the temperature time history data stored in the memory if the processing means determines that the tire has not reached the runflat operation limit zone, and estimates values of the temperature after the latest temperature data in time series by an extrapolation method using the sectional approximate function, and calculates a time interval reaching the limit temperature data value on the basis of the estimated temperature values.