Abstract
自行車後變速系統的換鏈動作可區分為上鏈及下鏈兩種：上鏈意指鏈條由小鏈輪換掛至大鏈輪；下鏈意指鏈條由大鏈輪換掛至小鏈輪。若比較此兩種變速換鏈動作的齒形設計，其設計考量在諸多方面是彼此矛盾衝突的，故設計上、下鏈合成齒形極具困難度 。由於鏈條換掛至不同鏈輪受導鏈導輪牽引，本文從後變速系統的變速機構著手分析，建立變速換鏈的數學模型，並以此為據，嘗試以非直線路徑對齒形合成作彈性配置，規範合理之上、下鏈動作，建立完整的後飛輪組齒形設計方法。本文將設計方法程式化，以數值方法求得設計參數值，導入CAD/ CAM軟體中，以CNC嘗試銑削出上鏈、下鏈及上下鏈合成齒形之雛型，分別進行換鏈的穩定性能測試。最後，本文藉由性能測試結果，探討設計理論的正確性，並評估雛型品之上、下鏈性能優劣，以提供後續研究者作為參考。The shifting motions of rear derailleur system of a bicycle areclassified as downshift and upshift. Downshift means that thechain of a bicycle is shifted from a smaller sprocket to alarger one, on the other hand, upshift motion is on thecontrary to downshift. To design a multi-speed freewheelintegrating these two motions is difficult because of theconflicts as both shifting motions are considered. This thesisbegins with the analysis of the rear derailleur system of abicycle. By applying the concept of the nonlinear shiftingpath, a reasonable shifting motion was obtained. In addition, acomprehensive shifting model and the methodology for designingthe rear derailleur system was thus established. A computer-aided design and manufacturing software was also developedbased on the proposed design methodology. Three sets ofprototypes of the freewheels were manufactured and tested. Theaccuracy of the proposed model was evaluated from theexperimental results. It clearly illustrates that the developedmodel and CAD/CAM software are very useful for designing a newrear derailleur system of a bicycle.