Eccentric gear and process for making such a gear

Eccentric gear comprising first and second, cooperating gear rings (7,10) of which one (7) has a certain number of internal, straight cogs and the other (10) has a smaller number of external, equally straight cogs, and of which at least one has a conical form with a large end (A--A) and a small end (B--B), the second gear ring (10) having a smaller pitch diameter than the first one (7) and being eccentrically mounted in bearings relative to the first in order to roll off upon the internal cogs of the latter, and the axes of symmetry (24,25) of each respective gear ring forming an angle (.alpha.) with each other, characterized in that the locations of engagement between the flanks of the cogs in the one gear ring and the opposed flanks of the cogs in the other gear ring are substantially located along a helical line that extends in axial direction between said large and small ends, and the angular positional values of the locations of engagement--seen in infinitesimally thick axial sections along the longitudinal extension of the cogs--increases from a first value (.gamma..sub.A) at the large end (A--A) to a second, larger value (.gamma..sub.B) at the small end (B--B).