| 摘要 |
PROBLEM TO BE SOLVED: To reduce adhesion of mud and dirt to the magnets and stators and to reduce the work for removing mud or the like from the magnets and the stators. SOLUTION: A concave portion 6 is formed at a center of a rear face of a fly wheel 3 mounted on a front portion of a crank shaft 2. On a peripheral surface 6a of the concave portion 6, a magnet 7 is provided. A stator 8 is fixed to a front face of a crank case 1, and the stator is arranged a faces opposite the magnet 7 with a prescribed space therebetween. An opposing face 7a of the magnet 7 and an opposing face 8a of the stator 8 are configured, such that they are included toward an outer peripheral side of a fly wheel 3 as the surfaces which approach the reverse face of the fly wheel 3. Furthermore, venting means 10 for venting toward the front side of the opposed faces 7a, 8a are installed, and air flows from the front side of the fly wheel 3 toward the back side between the opposed faces 7a, 8a.
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