Patent ID: 8186244

Claim:
A transmission casing for a bicycle, comprising: a left casing and a right casing, each casing comprising: a metal reinforcing member, each reinforcing member having an inner surface and an outer surface opposite the inner surface, the metal reinforcing member forming an exterior surface of the casing; a cover member which is integrally laminated to the inner surface of the reinforcing member so as to form a sidewall having an inner layer and an outer layer, the cover member forming an interior surface of the casing; and an aperture for allowing the passage of a transmission shaft, wherein a thickness of the cover member is set to a value which falls within a range of 0.7 to 1.5 mm and the reinforcing member has at least a portion thereof formed thicker than the cover member, wherein the transmission casing is divided into the left and right casings by using an approximately center portion of the transmission casing in a bicycle width direction as a boundary, the left and right divided transmission casings are integrally coupled to each other using screw members at a plurality of portions on an outer peripheral portion of the transmission casing and, at the same time, the transmission casing is coupled to a body of the bicycle at a plurality of given portions out of the plurality of portions, and wherein fiber-reinforced-plastic strip bodies are attached to the whole circumference of inner surfaces of outer peripheries of the cover members of the left and right divided transmission casings; a sealing member is fitted in a groove portion which is formed between an outer peripheral portion of the cover member in one of the left and right casings and an outer peripheral portion of the fiber-reinforced-plastic strip body; and an outer peripheral portion of the cover member in the other casing of the left and right divided transmission casings is brought into contact with the sealing member.