| 摘要 |
A bicycle transmission with one or two driving sprockets on a pedal shaft, selectively connectable with any one of several driven sprockets of progressively varying diameters on a rear-wheel axle, is controlled by a gear-shifting lever rigid with one or two cam disks each coacting with a cam follower on an associated rocker arm. Each rocker arm is tied to a flexible link, such as a Bowden cable, serving for the relative axial shifting of the chains and a respective sprocket set to let the chain jump from one driven (or driving) sprocket to an adjoining one. Each cam disk has a plurality of peripheral lands whose distances from the disk axis determine the engagement of the chain with one of the sprockets of the associated group. With two driving sprockets and five driven sprockets, providing ten different speed ratios, each disk has ten lands divided into two groups; on one disk the two groups of lands lie on a low dwell and on a high dwell, respectively, whereas on the other disk the lands are identically stepped in the two groups. At least one land of each pair of lands simultaneously engaged by the two cam followers is formed as a notch yieldably retaining the shift lever in its selected position.
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