| 摘要 |
PROBLEM TO BE SOLVED: To provide an engine unit wherein the rotation of a crank shaft is balanced without increasing the weight and the number of components. SOLUTION: The crank shaft 11 has a crank pin 7 eccentric from a center of rotation. A connecting rod 20 is connected to the crank pin 7, and a piston 19 is connected to the end of the connecting rod 20 on the opposite side to the crank pin 7. In the axial view of the crank shaft 11, a line drawn from the center of rotation C1 of the crank shaft 11 toward a center C2 of the crank pin 7 is a reference line A. Besides, an angle from the reference line A to the side in a rotating direction B of the crank shaft 11 around the center of rotation C1 of the crank shaft 11 is a positive angle, and an angle from the reference line A to the opposite side to the side in the rotating direction B of the crank shaft 11 is a negative angle. A key groove 40 is arranged where there is an angle of X°to the reference line A (0°) around the center of rotation C1 of the crank shaft 11. X is greater than -90°and smaller than +90°. COPYRIGHT: (C)2008,JPO&INPIT
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