| 摘要 |
PROBLEM TO BE SOLVED: To provide a power assisted bicycle with a mounted hub driving device for contribution to reducing the size in the direction of an axle without applying overload on a planetary gear device. SOLUTION: The planetary gear device as a reducer is formed in a two-stage structure with a large external gear 31 and three small planetary gears 30 in a hub casing 21. One of the planetary gears 30 is overhung by a motor cover 28 serving as a planetary gear carrier 36 and the shaft of the other planetary gear 30 is held in linkage with a planetary gear plate 32. The planetary gear plate 32 has a central portion to be thrust and supported by a fixed side casing 22. A pinion gear 33 is formed at one end of a rotatable motor shaft to which a rotor 27 is fixed, and it is put in engagement with the planetary gear 30. The planetary gear 30 is put in engagement with the external gear 31 to reduce the rotating force of the rotor 27 and transmit it to the hub casing 21 via a free clutch 34 on the outer periphery of the external gear 31.
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