Patent ID: 7806774

Claim:
A transmission system for rotorcraft, said rotorcraft having a structure, said transmission system comprising: a shaft; and at least an active magnetic damper extending around the shaft, wherein the magnetic damper is secured to the structure of the rotorcraft via at least a non-magnetic damper that is arranged to limit radial oscillations of the shaft and of the magnetic damper, the shaft having a ferromagnetic ring secured to the shaft, the active magnetic damper comprising a mechanical damper holding four contact connections, each connection enabling pivoting about an axis orthogonal to the axis of the shaft, and also sliding in a plane perpendicular to the axis, with dry friction, said each connection also enabling pivoting about two mutually-perpendicular transverse axes that intersect on the longitudinal axis of the shaft, the active magnetic damper including four identical electromagnets having cores with respective inside faces, said four identical electromagnets being rigidly connected to one another by a structure secured to the structure of the rotorcraft via the mechanical damper, the axes of the connections coinciding substantially with the longitudinal axes of the electromagnets, and the respective inside faces of said electromagnet cores having a concave cylindrical shape of a radius equal to the outside radius of the ferromagnetic ring secured to the shaft, plus the value of an airgap, and of axis parallel to a theoretical axis of the shaft.