ON A STUDY OF BICYCLE SPROCKETS DESIGN
|關鍵字:||自行車;飛輪;電腦輔助設計;最佳化設計;導鏈槽;Bicycle;Freewheel;CAD;Optimization Design;Chain-guided portion|
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.
|Appears in Collections:||Thesis|