Abstract: In hinge structures for seats having adjustable backrests, a hinge piece attached to the fixed seat (12) and a hinge piece (6) attached to the adjustable backrest (13) are connected on a pivot axle (7) with an eccentric portion (7a). One hinge piece has inwardly projecting teeth (6a) defining a toothed zone into which extend the outwardly projecting teeth (8a) of a spur gear zone of the second hinge piece, thus forming a wobble-plate gear unit. In addition to both of these toothed zones, there is provided on the first hinge piece a second inwardly projecting toothed zone (6b) concentric with an axially displaced from the first inwardly projecting toothed zones and meshed with a second spur gear zone (8b) concentric with and axially displaced from the first spur gear zone.

Abstract: Hinge structures are disclosed which are useful in seats with adjustable krests, the structures including a gear unit (6, 8) in which indented and protruding tooth systems (6a, 8a) are punched into the hinge pieces using the precision blanking process, the diameter as well as the tooth contour of the protruding tooth system (8a) being at least partially smaller than the diameter and the tooth contour of the associated indented tooth system (6a) so that material can then flow from the unused tooth system produced during precision blanking and into the effective tooth system, thus enlarging the tooth width (b) of the effective tooth system to be greater than the thickness (d) of the initial material. See FIGS. 4a and 5a.