自行車變速齒盤設計之研究

Abstract

傳統的自行車變速齒盤未經適當排列，變速時容易發生鏈條在齒尖跨騎現象，產生的振動、噪音將影響騎乘的舒適性。本論文提出二個設計方法來改善變速之換鏈效率及平順性。第一種方法係將電腦輔助設計軟體與設計最佳化程式整合成一系統，再利用此系統完成換鏈路徑模擬之最佳化，產生減少上鏈(down-shifting)干涉的輔助換鏈切削面。此方法已獲得中、美二國專利，並有產品量產；但此法須要大量的電腦運算，所產生的複雜斜面，增加製造的困難度及模具成本。第二種方法運用較簡易的上鏈模擬及最佳化運算，求得多上鏈模式時之最佳相位角及一般化的輔助上鏈切削面，以有效縮短設計流程。另外本文並針對齒盤的齒尖導角模式及輔助下鏈切削面作一深入研究。 本文並根據上述方法加工出二型八速飛輪及一型九速飛輪之原型品，藉由自行車測試系統，與目前市面上三型八速飛輪及一型九速飛輪之產品作比較。所得結果有助於產業界產品功能的提升及學術界後續之研究。

The overwhelming majority of bicycles are equipped with sophisticatedderailleur systems that serve the same purpose as transmissions in motor vehicles: enabling more efficient use of input power through selection of suitable gear reduction ratios. This thesis presents two design methods for improving the performance of bicycle derailleur systems by modifying sprocket shape to eliminate jerkiness, slippage and rattling noise, and guide chain movement from one gear to another more quickly and directly. In the first method, a systematic design procedure is proposed to generate the chain-guided portion on the side of larger sprocket to improve the down-shifting performance. However, the method needs large quantities of computer time in three-dimensional simulation and optimization process. Moreover, the chain-guided portions increase manufacturing difficulty because of their complex pressing surface. The second method, a modified method of the first one, generates chain-guided portions more efficiency. In the new model a modified shape is selected to replace the original chain-guided portion, i.e., a unique shape of chain-guided portion is generated by geometric topology with concept of design for manufacture (DFM). It decreases the design time and manufacture difficulty of bicycle sprockets. Benefits of shifting with the optimized sprocket shapes include improved efficiency and smoother, more accurate shifting. Moreover, chamfers of sprocket-tooth tips and auxiliary disengagement design are discussed too. According to this study, two prototypes of eight-speed and one prototype of nine-speed freewheels are manufactured and tested to compare with three types of eight-speed and one type of nine-speed freewheels products.