Patent 7419454 was granted and assigned to Toyota on September, 2008 by the United States Patent and Trademark Office.
A ring gear is an annular gear having an annular base portion with a predetermined constant width, and the annular base portion is provided with a gear on an entire periphery thereof. The base portion includes a first wall thickness portion having a first wall thickness, and a second wall thickness portion having a second wall thickness thicker than the first wall thickness.