Systematic design and analytical evaluation of a novel multi-speed bicycle rear transmission hub with a permanent magnet assisted gear shifting mechanism

This study presents a systematic design approach for a multi-speed bicycle rear transmission hub, which consists of a gear speed-changing mechanism and a rotary-type gear-shifting mechanism to enhance functional performance and optimize space utilization. The design process encompasses structural synthesis, gear stage arrangement, gear teeth synthesis, and clutch configuration, ensuring optimal power transmission and seamless gear shifting. A 9-speed rear transmission hub is used as an example to illustrate the design process. A compound planetary gear train with a new permanent magnet assisted gear-shifting mechanism was presented to provide nine forward gears, including four underdrive gears, a direct drive gear and four overdrive gears. The proposed design was verified through computer simulations, confirming its functional feasibility and mechanical integrity. Key performance results demonstrate that the system achieves a speed ratio ranging from 0.56 to 1.80 with a step jump no greater than 20%. Furthermore, the design maintains a compact dimension within a diameter of 200 mm and an axial length not exceeding 190 mm, while keeping the total weight under 3 kg. The results indicate that the system effectively meets performance specifications while addressing limitations associated with traditional spring-based gear shifting mechanisms. This study contributes to the advancement of multi-speed transmission hubs, providing a structured framework for next-generation bicycle transmission systems.