The development of a thick-film non-contact shaft torque sensor for automotive applications

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Abstract
The system described uses a novel thick-film capacitive torque sensor, which is applied to the rotating shaft. The capacitive sensor forms part of a rotating resonant circuit, which is excited across an air gap by means of inductive coupling. Variations in torque cause changes in the resonance frequency of the tuned circuit. The torque may be detected as a change in the resonance frequency, or as a change in referred impedance measured at the exciting coil. The prototype capacitive torque transducer was constructed from flexible printed circuit boards, which were bonded to the shaft. Subsequent sensors have been formed by printing thick-film conductor patterns. This novel approach provides a much simpler method of manufacturing the sensor. Two telemetry systems are discussed, one using a sweep frequency oscillator and one using a bridge circuit. It is shown that for most applications the bridge circuit is preferable.

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