Bicycle transmission system

摘要

A method is provided for controlling operation of a pedal cycle (10) having a rear hub-mounted electro-mechanical transmission arrangement in which a chain-driven rear sprocket (80), an input electrical machine (120) and the hub (100) are each coupled to a respective branch of a three-branch epicyclic gear set (140). Allowing for natural variations in input torque by a cyclist over a cycle of the crank arms (50), a substantially constant current is caused to exist in the input electrical machine (120) such that a change in torque applied by the cyclist results in a change in transmission ratio between the rear sprocket (80) and the hub (100), thereby providing a form of automatic and continuously variable transmission for the pedal cycle (10).