1.  Field of the Invention
The present invention relates to the tire trouble detection technology of detecting the occurrence of troubles in the tires of an automotive vehicle. 
2.  Description of the Related Art
In order to make the automotive vehicle run safely, it is indispensable to keep the states of the tires normal.  If a trouble occurs in any of the tires, it is necessary to detect it exactly and take the suitable measures to eliminate it.  Conventionally, the technology of detecting the occurrence of troubles in the tires is known. 
For example, Japanese Laid-Open Patent Application No.  7-081337 discloses a tire trouble detection device in which the electrodes are arranged in the tread portion and the rim portion in the air cell of the tire, respectively, and the distortion of the tire is detected based on the static capacitance that varies according to the distance between the electrodes. 
Moreover, Japanese Laid-Open Patent Application No.  7-081341 and Japanese Laid-Open Patent Application No.  9-193627 disclose the technology similar to the above-mentioned device. 
According to the conventional technology disclosed in Japanese Laid-Open Patent Application No.  7-081337, it is possible to detect the occurrence of troubles, such as the drop of the air pressure of the tire or the rapid unusual deformation of the tire.  However, it is difficult to detect the partial plastic deformation in the carcass, the inner liner, etc.  of the tire inside. 
When the tire steps on the curbstone on the road or the safety rivet (called the cat's eye) embedded in the road surface or the road center line, the layered composition portion in the tire inside, such as the carcass, may be damaged and the swelling (or bulging) of the sidewall portion of the tire may occur, although it does not result in the rapid unusual deformation. 
If it results in the rapid unusual deformation, the possibility that the driver notices the trouble in the tires is high.  In such a case, the conventional technology can detect the occurrence of the trouble.  However, if it does not result in the rapid unusual deformation and the trouble occurs in the tire inside only, the possibility that the driver does not notice the trouble even by visual inspection remains.  In such a case, the conventional technology cannot detect the occurrence of the trouble.