Abstract
多段變速自行車的後變速系統包含四個子系統： 後飛輪組、變速機構、鏈條以及撥桿機構。 變速換鏈的動作可分為上鏈與下鏈兩種，而由於目前的撥桿市場多為定格 (Index) 撥桿所佔有，此類撥桿某一檔位的鋼索拉伸量是固定的， 到達某一檔位可能是由上鏈動作所形成，也可以是由下鏈動作所造成， 所以該檔位的撥桿行程，必須滿足上鏈與下鏈動作的完成以及平順性，穩定區的問題因而產生。本文首先定義穩定區的現象， 然後根據鏈節與導鏈導輪的卡緊模式來建立穩定區的數學模式，並以數值的方法求解現有變速系統的穩定區。在實驗方面， 本文設計一套量測穩定區的設備，以及量測穩定區的流程，以便與理論方面相比較，驗證理論的可行性。最後， 本文結合穩定區考量，對於現有變速系統作改良設計，經測試發現本文所做的下鏈基板改良設計， 確實能發揮良好的功效，所以本文所建立的穩定區數學模式， 確實能預估穩定區的座落點，也可以提供變速系統設計作為參考。The rear derailleur system of a multi-speed bicycle consistsof a freewheel, a derailleur system, chain, and shiftlevel. Because of the distinctive performance, the indexshift levels have been very popular. This thesis proposed aconcept of "stable region" that is physically existenceand can be used for determining the traveling distanceof the shift level to guarantee a smooth up- anddown-shifting characteristic. Beginning with the definitionof the stable region as a range of cable displacement, amathematical model for the stable region was createdaccording to the contact conditions among the chain, guidepulley, and freewheel. On the basis of this model, thestable region of an existing rear derailleur system wasfound numerically. For the sake of verifying the validity ofthe mathematical model, an equipment for measuring the stableregion of a certain type of derailleur was constructed for thecomparison between the theoretical and experimental results. Byanalyzing the characteristics of the stable region, amodified design was made for the existing rear derailleursystem. According to the test results, the modified designillustrated a remarkable improvement for the shiftingperformance.