VIBRATION DAMPING ROTARY DRIVE ELEMENT

A rotary drive element for damping torsional vibration comprises an outer part (1) and an inner part (2) defining an annular space therebetween, containing a plurality of interleaved plates and a viscous fluid. The plates comprise a set of first plates (3) having internal teeth (6') which engage teeth (8) on the inner part (2) of the element substantially without circumferential clearance, and outer teeth (5) which engage teeth (7) in the outer part (1) with a circumferential clearance. The second set of plates has inner teeth which engage the teeth of the inner part with a circumferential clearance, and outer teeth which engage the teeth in the outer part (1) without a circumferential clearance. Thus the inner and outer parts are able to move angularly relative to one another according to the circumferential teeth clearances, which movement is damped by the viscous fluid between the plates. The drive element may be incorporated in a gear wheel for a vehicle transmission, or a clutch driven plate.