| 摘要 |
PURPOSE:To transmit a stable detection signal to a car body side in a non- contact state regardless of the rotation or the non-rotation of a wheel, by respectively providing induction coils to a tire rotation side and a car body stationary side and detecting the air pressure state of a tire by one induction coil to transmit the same to the other induction coil. CONSTITUTION:A first induction coil 11 has a primary coil 12 and a secondary coil 13 and fixed to a car body stationary side while a secondary induction coil 21 has coils 22, 23 and fixed to a tire rotation side. When an alternating signal 30 is supplied to the primary coil 12, said signal traverses the magnetic field coil 22 formed to the primary coil 12. At this time, if the air pressure of a tire is sufficient, because a switch 10 is opened, no induced magnetic field is formed in the coil 21. When the air pressure of the tire is lowered, the switch 10 is closed and the coil 21 forms a closed circuit. By this method, the magnetic field of the primary coil 12 generates induced voltage in the coil 22 and, therefore, the coil 23 also forms an induced magnetic field. The coil 13 outputs a signal to a terminal 31 by a change in said induced magnetic field.
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