自行車橢圓大齒盤偏心圓鏈輪系統設計及騎乘效益分析

Abstract

根據研究，自行車騎士使用橢圓大齒盤可提升騎乘效益，但僅使用單一橢圓大齒盤時，會使鏈條在運作過程中產生部分鬆弛的現象，易導致鏈條脫鏈。使用橢圓大齒盤搭配偏心圓鏈輪之設計可以改善鏈條鬆弛，當兩個鏈輪的節圓形狀同步變化，可減少橢圓大齒盤所產生之鏈條鬆弛量。本研究之目的在探討自行車使用橢圓大齒盤搭配偏心圓鏈輪之鏈條傳動系統，對於鏈條鬆弛情形的改善以及騎士騎乘效益之影響。首先，建立橢圓大齒盤偏心圓鏈輪系統幾何數學模型，發展電腦程式，進行數值分析，藉由調整偏心圓鏈輪之偏心量參數，尋求搭配不同長短軸比橢圓大齒盤的偏心圓鏈輪，以達到最小鏈條鬆弛量之設計目標。其次，建立自行車騎士腿部模擬五連桿機構運動及動力模型，配合橢圓大齒盤偏心圓鏈輪系統產生之踩踏轉速變化數據，以及不同的曲柄安裝角度，發展電腦程式模擬腿部關節驅動力矩與輸出功率的變化，進而探討橢圓大齒盤偏心圓鏈輪系統對於自效益的提升效果。最後，本研究根據關節驅動力矩和輸出功率之分析數據，提出三組可提升自行車騎乘效益之橢圓大齒盤偏心圓鏈輪系統設計參數，作為最終之設計方案。利用本研究所發展之橢圓大齒盤偏心圓鏈輪系統幾何數學模型及設計方法，可以協助分析並改善橢圓大齒盤造成之鏈條鬆弛情形，並達到降低騎士腿部關節負荷與提升踩踏效率之目的 ，此研究成果應有助於新型自行車非圓形鏈輪系統之開發設計。

The use of elliptical front sprocket can enhance the riding performance of cyclists, but would cause chain slack during operating, or lead to chain drop. The purpose of this study is to analyze the improvement of chain slack and the enhancement of riding benefits by using elliptical front sprocket combined with eccentric sprocket for bicycles. First, the geometry mathematical model of elliptical-eccentric sprockets system and the kinematic model and the dynamic model of the leg simulation planar five-bar linkage have been established. Then, with the computer program which is developed to analyze the eccentric of sprocket, the best design parameters for different major-minor axis ratio can be found, and achieve the target of minimum chain slack. And then, with the data of cadence variation and the different crank install angle, the joint moment and joint power can also be simulated by using computer programs. Finally, according to the data of joint moment and joint power, three groups of design parameters have been raised to reduce the joint loading and enhance the pedaling efficiency. The enhancement of riding benefits compared to the traditional system would be investigated. This study could be applied in practice and promote the design and research on the non-circular sprockets for bicycles.