US Patent 7322654 Bracket angle adjustment mechanism

Disclosed is a bracket angle adjustment mechanism which includes external-tooth and internal-tooth gears having improved tooth shapes allowing an operating force for rotating a control shaft to be reduced. In the bracket angle adjustment mechanism, each of external teeth (14b) of the external-tooth gear 14 has a half-round shape having a center defined by a single point “a” on a reference circle PC (14), in a region of an addendum T1 between the reference circle PC (14) and a tip circle AC (14), and an undercut shape in a region of a dedendum T2 between the reference circle PC (14) and a root circle DC. Further, each of internal teeth (15b) of the internal-tooth gear (15) has an arc shape free of interference with the half-round-shaped addendum region.