| 摘要 |
PURPOSE: A vehicle speed sensor is provided to precisely control an electronic device using a vehicle speed as a parameter by outputting an accurate vehicle speed during a low speed travel employing a sound wave sensor. CONSTITUTION: A vehicle speed sensor comprises a sound wave generator(10) and a sound wave sensor(20). The sound wave generator mounted in a vehicle wheel generates ultrasonic waves of a specific frequency. The sound wave sensor is fixed in a wheel housing to receive the ultrasonic waves while vehicle wheels rotate. An electronics control unit(30) outputs a signal corresponding to the frequency of the ultrasonic wave received in the sound wave sensor. While the wheels rotate, the sound wave generator also rotates. Distance between the sound wave generator and the sound wave sensor varies, and ultrasonic waves of frequency varied by the position of the wheels are received in the sound wave sensor. A wheel speed corresponding to the variation of the frequency received in the electronic control unit is outputted. Therefore, instantaneous speed of a vehicle is outputted precisely.
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