Measurements of the torque in a rotating shaft are often required for automotive power-train and engine control systems. Conventional shaft torque measurement techniques involve strainn gages and slip rings. While this approach is often used for prototypes and vehicles under development, it is too expensive and not rugged enough for production vehicles. A rugged noncontact shaft torque sensor was produced at a cost which will allow its use for automotive applications. The system uses a novel capacitive torque sensor, which is attached to the rotating shaft. The capacitive sensor forms part of a rotating resonant circuit which is excited across an airgap by means of inductive coupling. Variations in torque cause changes in the resonance frequency of the tuned circuit. The resonance frequency is detected as a change in referred impedance at the exciting coil.
