| 摘要 |
PROBLEM TO BE SOLVED: To improve assembling performance and productivity, and to provide sufficient rigidity by integrally and continuously casting/molding a head pipe and a seat pipe having the mutually parallel axes in a down frame. SOLUTION: A car body frame 10 has a head pipe 11 on the front end, a down frame 12 extending backward and downward from the head pipe 11 and a seat post 13 extending upward from a rear end upper part of the down frame 12 in parallel to the head pipe 11. The head pipe 11, the down frame 12 and the seat post 13 are integrally cast and molded by an aluminum alloy. The down frame 12 is formed in a lower part opening almost U shape. This constitution can enhance rigidity of the car body frame 10, can obviate fastening work, and can improve assembling performance and productivity of a bicycle with an auxiliary engine.
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