| Summary: | This article proposes a new magnetic rear hub transmission for bicycles, which consists of a coaxial magnetic gear mechanism to serve as the speed-changing device and a speed control mechanism to govern the gear stage. A 3-speed magnetic hub transmission, including a low-speed gear, a direct-drive gear, and a high-speed gear, is designed and installed in the rear hub of a bicycle, which allows the rider to select different gears to adjust the pedaling force. For a new kind of rear hub transmission, kinematic analysis and power-flow path analysis are essential to validate the speed ratio and the power-flow path at each gear stage. They are also the fundamentals for the mechanical efficiency analysis. Here, a system’s kinematic equation, which is an analytical approach and analogous to the kinematics of a basic planetary gear train, for the presented coaxial magnetic gear mechanism is derived without considering the complex space harmonics of the magnetic flux density distribution presented in previous studies. Hence, the speed ratio at each gear stage of the magnetic hub transmission can be easily calculated.
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