US Patent 7811193 Speed reduction device

A low-noise speed reduction device that is simple in structure, small-sized, and little in energy loss is provided. Two-stage gears, i.e., a large-diameter gear 65 and a small-diameter gear 66 of a third external gear 63 are supported by a supporting shaft 59, and one-stage second external gear 58 that meshes with the small-diameter gear 66 is only attached to an axial one end of a crankshaft 40. Therefore, the axial length of the whole speed reduction device becomes short, and consequently, miniaturization becomes possible. Further, since gears mesh with each other only in two places until a driving force is transmitted to the crankshaft 40 from the first external gear 54, noises can be reduced, and energy loss can also be lowered.