| 摘要 |
PROBLEM TO BE SOLVED: To reduce weight, to increase a strength and to improve the degree of designing freedom by forming the longitudinal direction central part of a crank to be hollow, forming a recessed groove extended in a longitudinal direction on the back surface of the crank in the hollow structure and fixing a cap member in the opening surface of the recessed groove. SOLUTION: Both end parts 2, 4 of the longitudinal direction of a bicycle crank 1 are formed to be solid and also its longitudinal direction central part 3 is formed to be hollow. In the hollow structure, a recessed groove 31 extended in a longitudinal direction is formed on the back surface of the recessed groove 31 and a shape in the vicinity of both end parts of the recessed groove 31 is formed in such a manner that a groove depth is continuously made smaller toward both end parts and groove depths are smallest in both end parts. A step part 32 is formed in the opening surface side of the recessed groove 31, a cap member 33 is fitted ion this step part 33 and the surrounding of the cap body 33 and the crank 1 main body are fixed to each other by welding. Thus, weight is reduced, a strength is increased and the degree of designing freedom is increased. |
