Differential torque measuring device

Device for measuring the torsional moment being exerted on a shaft, the device including two magnetic circuits, essentially cylindrical and arranged around the shaft, each of said circuits being equipped with at least one permanent magnet generating a magnetic flux and each of said circuits including, on a rotor, a variable air gap having two facing relative parts each fastened to the shaft at respective points offset with respect to each other in the longitudinal direction of the shaft in such a manner that torsion of the shaft leads to modification of the air gap which differs depending on the direction of the torque exerted, the two magnetic circuits including a common central yoke part in which magnetic fluxes of each of the circuits pass in opposite directions, the device including at least one measurement means sensitive to the algebraic sum of the magnetic fluxes.