Aisin Aw Co., Ltd.

Kiyoshi Tajima

Atsushi Mori

Katsuhiro Maeno

Naoki Takabayashi

A ring gear that, together with a sun gear and a pinion gear that is disposed radially outward of the sun gear and meshes with the sun gear, forms a planetary gear unit, the ring gear includes: a body, internal teeth that are configured to mesh with the pinion gear and that are formed in at least a part of an inner peripheral surface of the body, and external teeth that have a lower hardness than the internal teeth and that are formed in at least a part of an outer peripheral surface of the body, wherein a surface nitrogen concentration in the internal teeth is higher than that in at least tooth surfaces of the external teeth.

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Nishio, Japan

Kiyoshi Tajima