| 摘要 |
<p>The following technical means are provided in order that change of chains can be performed with a minimum moving distance of a guide pulley, a change gear efficiency and a change gear controllability are improved and the change gear mechanism is prevented from projecting. In front of a multi-stage sprocket (2), a link base (8) of a pantagraph link mechanism (12) is supported by a chain stay (7), an internal link (9) and an external link (10) are extended rearwardly from the link base, a chain guide (15) is rotatably supported on a movable member (11) connected to the rear end portions of these links in a manner to be resiliently biasing, and a guide pulley movement control means (18) is provided, so that when the pantagraph link mechanism (12) is deformed, a guide pulley (13) of the chain guide (15) moves inwardly in a direction of a hub axis, and simultaneously, moves obliquely and downwardly in the forward direction, substantially along one of the radii of the aforesaid multi-stage sprocket (2).</p> |
