A synchronous drive assembly with toothed belt

An assembly (20) for transmission comprising: a first pulley (22) toothed, -A second pulley (24) toothed, -A toothed belt (21) meshed around the pulleys, the first pulley (22) being connected to a drive member while the second pulley (24) is connected to a driven member, the engine and driven members being such as to cause vibration of the toothed belt (21) when in motion, - a circular eccentric pulley (30) toothed, driven by the toothed belt (21) but not connected to a device to be driven, characterized in that the diameter, the angular setting (α) and the eccentricity (e) of the eccentric circular pulley (30) are chosen such that the eccentric sheave (30) produces a fluctuation in belt length which reduces or cancels a predetermined harmonic by the selected diameter, vibration resulting from movement of organs taken as a whole.