| 摘要 |
PROBLEM TO BE SOLVED: To provide a crank folding-up mechanism of a bicycle compactly foldable and easy in folding-up operation. SOLUTION: A sprocket tooth part is formed so that the inner peripheral surface is mounted with a chain wheel 5 for forming a guide rail part 7 having a recessed cross section, a guide ring 8 for journalling plural guide rollers 9 rollingly inserted along the guide rail part of the inner peripheral surface of the chain wheel by an annular connecting rod 10 and a guide shaft body 10 in an opposed position of the connecting rod of the guide ring. A crankshaft holding part 1 is installed on the guide shaft body so as to be freely rotatable in a 90-degree range of an orthogonal position from a position opposed to an installing surface of the chain wheel and to become concentric with the axis of the crankshaft holding part for installing these chain wheel, guide ring and crankshaft when the crankshaft holding part rotates to the orthogonal position to the installing surface of the chain wheel.
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