Development of a rotating-shaft torque sensor for automotive applications

Measurements of the torque in a rotating shaft are often required for automotive powertrain and engine control systems. Conventional shaft torque measurement techniques involve strain gauges 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. The Ford Motor Company has supported work at Southampton University with the aim of producing a rugged noncontact shaft torque sensor, at a cost which will allow its use for automotive applications. The system described in the paper 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. Considerable effort has been put into the design of the capacitive torque transducer. A number of practical problems have to be overcome, such as finding a suitable method of adhesion and optimising the capacitor geometry. A satisfactory sensor has now been produced, and work is now being concentrated on improving the passive telemetry system. The torque sensor is currently the subject of a patent application by the Ford Motor Company.