Geometric design of a planetary gear train with non-circular gears

The paper presents a concept of epicyclical gear train able to generate a variable gear ratio law. The basic mechanical configuration consists of three non-circular gears in a typical planetary arrangement. Such a mechanism couples the advantages of non-circular gears with the typical performances of epicyclical gear trains. Therefore this kind of planetary gear train is useful when the synthesis of a specific torque curve or the design of a function generator involve a highly variable input/output relationship, especially if small weights and sizes are required. An application is presented, where a planetary gear train with non-circular gears is proposed in order to design a power drive mechanism for high performance bicycles. Such a device maximizes the human output during a typical low-speed way of pedalling.