Derailleur for a bicycle

#This invention relates to a derailleur for a bicycle, and more particularly to a derailleur for a bicycle, which shifts a driving chain from one sprocket to another of a multistage sprocket assembly mounted on the bicycle frame.

#Generally, rear derailleurs use with a rear side multistage sprocket assembly are provided with a linkage mechanism comprising a fixing member fixed to a fork end of the bicycle frame, a pair of linkage members, and a movable member having a chain guide. The linkage mechanism is disposed axially outwardly of a smaller diameter sprocket at the multistage sprocket assembly, and the fixing member is fixed to the fork end. The movable member is moved in reciprocation by operating a control wire, and a driving chain engaging with pulleys at the chain guide is shifted to one sprocket at the multistage sprocket assembly, thereby changing the bicycle speed at a predetermined speed changing stage.

#Problems exist where the fixing member at the linkage member is fixed to the fork end at the bicycle frame. Since the linkage mechanism projects outwardly with respect to the bicycle frame and no guard is provided for guarding the linkage mechanism, the linkage mechanism is subject to the danger of colliding with the ground or a foreign object, for example, when the bicycle falls down, and is subjected to a force or pressure greater than a resistance against speed change. In this situation, the fixing member particularly is subject to being plastically deformed axially inwardly of the multistage sprocket assembly with respect to the frame. As a result, a problem is created in that the chain guide shifts from the proper position with respect to the multistage sprocket assembly.

#FIG. 1 is a front view of a first embodiment of a derailleur for a bicycle in accordance with the invention, which is incorporated together with a multistage sprocket assembly into the bicycle frame,

#FIG. 2 is a partial side view of the FIG. 1 embodiment,

#FIG. 3 is a bottom view of the derailleur only,

#In the drawings, a rear bicycle derailleur is shown. Referring to FIGS. 1 through 3, the rear derailleur basically comprises a linkage mechanism A comprising a fixing member 1 fixed to a fork end H at the bicycle frame F, a pair of linkage members 2 and 3 supported to the fixing member 1 such that they are swingable axially of a multistage sprocket assembly S mounted on the rear hub of the bicycle, and a movable member 5 supported to the linkage members 2 and 3 and having the chain guide 4.

#The fixing member 1 comprises a bracket member 11 fixed to the fork end H and a base 12 pivoted to the bracket member 11 through a horizontal shaft 6. A pair of mounting projections opposite to each other are provided at one side of the base 12, and the movable member 5 is pivoted to the free end of the linkage members 2 and 3 through a pair of pins 9 and 10.

#The movable member 5 is like, the base 12, provided at one side with mounting projections opposite to each other, and pivoted thereby to the linkage members 2 and 3 swingably through the pins 9 and 10. On the other side of the movable member 5, the chain guide 4, having a pulley 41, is mounted through a horizontal shaft 20 such that it is rotatable in a predetermined range only.