| 摘要 |
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 ( 14 b) 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 T 1 between the reference circle PC ( 14 ) and a tip circle AC ( 14 ), and an undercut shape in a region of a dedendum T 2 between the reference circle PC ( 14 ) and a root circle DC. Further, each of internal teeth ( 15 b) of the internal-tooth gear ( 15 ) has an arc shape free of interference with the half-round-shaped addendum region.
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