Anti-vibration suspension device having a torsion spring, for a helicopter

An anti-vibration suspension device for a main helicopter rotor comprising a rotor mast driven in rotation by a main gear box about an axis of the mast, which is the axis of rotation of the rotor, the suspension device including at least three rigid and oblique bars for supporting the gearbox on a helicopter structure, the oblique bars being distributed around the gearbox and inclined relative to the rotor axis so as to converge with one another substantially at top ends towards a point on the rotor axis, the oblique bars being articulated and joined on the one hand to the gearbox by means of said top ends and on the other hand to the helicopter structure by bottom ends and by means of rigid lever, a same number of said levers being provided as there are oblique bars, each lever supporting at least one oscillating weight at one end and being articulated and joined to the structure by an opposite end part, in the vicinity of which the bottom end of a corresponding oblique bar is articulated on the corresponding lever, the articulated joints linking each lever to the structure and to the corresponding oblique bar being articulated joints which pivot at least about axes substantially perpendicular to a corresponding radial plane containing the axis of the rotor and a longitudinal axis of the corresponding oblique bar, wherein each lever is also linked to the gearbox by at least one torsion spring, biassed about a torsion axis also substantially perpendicular to said corresponding radial plane.