| 摘要 |
PROBLEM TO BE SOLVED: To provide a power transmission device for an electric power assist bicycle, which causes unpleasant feeling to be hardly generated by response delay and impact when a tread force is transmitted, eliminates offensive hitting sound and simplifies structure. SOLUTION: This power transmission device includes an inner ring 12 formed integrally with a first tubular part 10 penetrated through a crank shaft 106 and having an outer peripheral surface 12a of a circular shape in cross section, an outer ring 24 having an inner peripheral surface 24a of a circular shape in cross section opposed to the inner ring 12 and formed integrally with a second tubular shape 20, and a sprag 30 disposed between the outer ring 24 and the inner ring 12. The inner peripheral surface 24a and the outer peripheral surface 12a have simple circular shapes in cross section and are formed integrally with the first tubular part 10 and the second tubular part 20, and thereby the structure can be simplified. Since play between the inner peripheral surface 24a, etc. and an engaging surface of the sprag 30 is reduced to substantially zero, the response delay and impact can be prevented when the tread force is transmitted, unpleasant feeling can be hardly generated, eliminating offensive hitting sounds. COPYRIGHT: (C)2011,JPO&INPIT
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