Noncontact capacitive torque sensor for use on a rotating axle

The measurement of the torque in a mechanically loaded axle is often required for automotive power-train and engine-control systems. Torque sensing has been performed by mainly using strain gauges connected to the axle with slip rings to allow the electrical contacting. Noncontact magnetic and optical techniques have also been used. In the proposed capacitive torque sensor, two angular displacement sensors are spaced apart at a well-defined distance. The rotor of each of these capacitive displacement sensors is composed of an array of electrodes and sine-wave voltages with phase angles in the sequences 0°, 90°, 180°, 270° applied to it. These voltages are capacitively coupled from the stator to the rotor. The stator is also equipped with a readout electrode. The phase angle of the sine wave on this readout electrode is proportional to the rotor-to-stator electrode overlapping and thus proportional to the angular position. The phase difference between the output signals of the angular displacement transducers is a direct measure of the twist angle and thus of the torque in the axle. The sensor allows the noncontact torque measurement on a 10-mm-diameter steel axle in the 0-100-N-m range