Method of fabricating a rim gear, such as a starter rim gear made of

Abstract

The method of fabricating a rim gear, such as a starter rim gear made of sheet metal, such as sheet steel, comprises cold forming an outer surface of a substantially cylindrical rim portion of a dished blank according to the well known Grob method to effect an external or exterior gear tooth system with proper gear or gear wheel characteristics thereon, thereby also effecting an internal or inner tooth system on the inner surface of the substantially cylindrical rim portion. This method is performed such that at the fabricated rim gear the quotient of the different between an addendum circle diameter or outer diameter of the external gear tooth system and a crown circle diameter or inner diameter of the internal tooth system divided by the wall thickness of the substantially cylindrical rim portion before the start of cold forming is at least 1.6 and that the quotient of the thinnest portion of the tooth flank wall of the fabricated rim gear divided by that wall thickness is at most 0.4. By appropriately reducing the thickness of the material blank at the region of the free edge of its substantially cylindrical rim portion it is possible to at least partially precompensate the formation of undesired beading or axial beads laterally of the formed rim gear teeth. This member of fabrication also ensures that sheet metal can be used which is susceptible to surface hardening, for example, induction hardening. High quality fabrication is now possible in an economical, advantageous and reproducible manner with only a minimum of empirical work involved, thereby avoiding the innumerable trials heretofore required.