Patent ID: 7360619
Filing Date: 2008-04-22
Classification: B62K

Abstract:
1. A frame structure for a motorcycle, said frame structure comprising: a head pipe; a pair of right and left main pipes extending rearwardly and downwardly from an upper part of the head pipe; a down pipe extending from front parts of the main pipes and said head pipe; a head pipe gusset provided in a lower part of the head pipe and supporting a front wall side of the down pipe; a stiffener pipe gusset provided on a rear wall side of the down pipe; and a stiffener pipe extending from the stiffener pipe gusset to the main pipes; said head pipe gusset being forged integrally with said head pipe and including a tapered front fitting recess to which a front wall and front-half parts of right and left side walls of said down pipe can be fit, said front fitting recess being wider at an open outer end than at an inner end thereof; said stiffener pipe gusset being forged and including a tapered rear fitting recess in which a rear wall and rear-half parts of the right and left side walls of the down pipe can be fit, said rear fitting recess being wider at an open outer end than at an inner end thereof; wherein a cross-sectional shape of said down pipe is configured such that said right and left front-half parts of said down pipe are inclined in accordance with a non-zero acute draft angle of the front fitting recess, the draft angle being formed at the time of said forging, such that said cross-sectional shape is wider at a central portion of said down pipe than at a front wall side, and wherein said right and left rear-half parts of said down pipe are inclined in accordance with a non-zero acute draft angle of the rear fitting recess, the draft angle being formed at the time of forging; wherein the front wall and the right and left front-half parts of said down pipe are fit into the front fitting recess and a periphery of the front fitting recess is welded to the right and left front-half parts; and wherein the rear wall and right and left rear-half parts of said down pipe are fit into the rear fitting recess and a periphery of the rear fitting recess is welded to the right and left rear-half parts.