| Summary: | 博士 === 國立交通大學 === 機械工程系 === 91 === The manufacturers of bicycle transmissions in Taiwan need a design procedure of the freewheel-type bicycle transmission to develop new transmissions with plenty of gear ratios to promote their competition ability. However, these manufacturers did not make a study of the design procedure of gear ratios of a freewheel-type bicycle transmission in the past. On account of this reason, this study focuses on the ergonomic and mechanical analysis on the gear ratios and then proposes a systematic design procedure of a freewheel-type bicycle transmission.
The number of gear ratios and the complexity of gear shifting increases with the number of sprockets provided by a freewheel-type bicycle transmission. The complexity may make a cyclist feel confused by when to shift gear and which gear to be shifted to. This study proposes the calculation of the shifting point and the development of the optimum shifting strategy to solve these problems. The shifting point represents the time at gear shifting. The difference between cadences before and after shifting is a cadence spread. To decrease the complexity of shifting, a cyclist may choose several gear ratios from all gear ratios provided by a freewheel-type bicycle transmission. These chosen gear ratios compose a shifting strategy. The shifting strategy whose weight sum of mean and standard deviation of cadence spreads is minimum is the optimum shifting strategy. Therefore, the ergonomic quality of a freewheel-type bicycle transmission can be defined as the weight sum of its optimum shifting strategy. On the other hand, the mechanical quality can be defined as the number of shifting path between two sprockets. The shifting time decreases while the number of shifting path increases. In this study, the weight sum of mean and standard deviation of cadence spreads in the optimum shifting strategy is defined as a cost function in the systematic design procedure. Besides, the number of shifting path between two sprockets is treated as a constraint. Meantime, the number of gears on each sprocket is regarded as a design variable. Since the design variables are integers, this procedure finds an optimum solution by genetic algorithm. Consequently, this procedure generates the freewheel-type bicycle transmission with the optimally ergonomic and mechanical qualities.
|
|---|
