| 摘要 |
PROBLEM TO BE SOLVED: To provide a main frame of a motorcycle having a shape that can be manufactured through molding work and having a higher strength than a U-shaped molded product having a fixed opening direction. SOLUTION: A rail part 31 is molded by casting having a first direction D1 and a second direction D2 as removal directions. A reference axis M is set as a straight or curve line in a plane perpendicular to the removal directions. The rail part 31 includes a closed loop part having a first area A1, a second area A2, and a third area A3 so as to be located away from a head pipe frame in this order along the reference axis M. The first area A1 has a U-shaped cross-section that opens in the first direction D1 in the plane perpendicular to the reference axis M, the second area A2 has an inverted N-shaped cross-section that opens in the first direction D1 and the second direction D2 in the plane perpendicular to the reference axis M, and the third area A3 has a U-shaped cross-section that opens in the second direction D2 in the plane perpendicular to the reference axis M. COPYRIGHT: (C)2011,JPO&INPIT |
