彈簧彈性係數可變機構之設計在自行車後變速器之應用

Abstract

後變速器是一變速自行車變速系統中重要的零組件之一。由過去相關研究中，已知平面後變速器中B、P彈簧之彈性係數值大小對導輪定位及對鍊條張力大小有直接的影響。 在本論文中，根據所模擬出平面後變速器之B、P彈簧之彈性係數變化對導輪定位的影響，在給定平面後變速器P彈簧不同彈性係數值的情況下，作一實驗與理論的比較。以及利用一設計裝置，在變速系統定轉速下，測得緊邊鏈條的張力變化情形。證實當P彈簧彈性係數較小時，能使導鏈導輪與較大齒盤的間距與在較大P彈簧彈性係數時的導鏈導輪與較小齒盤的間距相等。緊邊鏈條張力的變化則與模擬結果有些許不同，而這些不同可經由不同的環境設定加以解釋。 在此我們提出三種彈性係數可變機構，其特點是在扭轉角度增大時，其彈性係數可調小。並從製造及分析上比較其優劣點，以決定其中一個較佳的設計，並針對此機構，製作一原型件進行測試，與分析結果比較及討論。此彈簧可變機構除了可應用於變速器上外，亦可應用於需要彈簧彈性係數隨作動行程增加而變小之機構中。

The rear derailleur is one of the key components in the derailed system of the multi-speed bicycle. In the past researches, it was found that the values of the B-spring stiffness and P-spring stiffness affect the tension of the chain and the positions of the guide pulley directly. According to the influence of the B-spring and P-spring stiffness, different P-springs are set to experiment and compare with the simulated results. The smaller P-spring stiffness can keep the distance between the guide pulley and the bigger freewheel with the distance between the guide pulley and the smaller freewheel in the bigger P-spring stiffness equally. The tight-side tension forces of the chain in each speed-rate are also measured in the constant rotation velocity by the designed equipment. The experimental results of the tight-side tension are different from the simulated results. However, these differences can be explained by different environment setting. Three variable stiffness mechanisms are proposed. The characters of them make the mechanism stiffness with lowering variable when the torsion angle is larger. The advantage and the disadvantage are compared from manufacture and analysis to decide a better design. And then aim to such mechanism, the prototype of this spring mechanism will be manufactured to test, analyze, and discuss. The spring mechanisms are not only applied in the planar rear derailleur, but also applied in any mechanical engineering design that want to make the spring stiffness with lowering variable.