| Summary: | 碩士 === 國立清華大學 === 動力機械學系 === 84 === The rear derailleur system of a multi-speed bicycle consists
of a freewheel, a derailleur system, chain, and shift
level. Because of the distinctive performance, the index
shift levels have been very popular. This thesis proposed a
concept of "stable region" that is physically existence
and can be used for determining the traveling distance
of the shift level to guarantee a smooth up- and
down-shifting characteristic. Beginning with the definition
of the stable region as a range of cable displacement, a
mathematical model for the stable region was created
according to the contact conditions among the chain, guide
pulley, and freewheel. On the basis of this model, the
stable region of an existing rear derailleur system was
found numerically. For the sake of verifying the validity of
the mathematical model, an equipment for measuring the stable
region of a certain type of derailleur was constructed for the
comparison between the theoretical and experimental results. By
analyzing the characteristics of the stable region, a
modified design was made for the existing rear derailleur
system. According to the test results, the modified design
illustrated a remarkable improvement for the shifting
performance.
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