| 摘要 |
A plastic gear having a gear peripheral portion including a tooth portion is constituted by a plastic material, and a gear inner circumferential member with an annular shape or a disk shape is provided at the inner circumferential side of the gear peripheral portion. The gear peripheral portion includes an inner core and a surface layer member, the inner core being covered with the surface layer member and made of plastic with high elastic modulus and high strength, and the surface layer member being made of plastic with relatively low elastic modulus. The inner core is revolvably fitted around the gear inner circumferential member so as to revolve around the gear revolving axis, and an engaging portion is provided at an interface of the surface layer member and the gear inner circumferential member for preventing relative revolution around the gear revolving axis.
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