Importance

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Abstract

A bicycle transmission system includes an input (2) constituted by a bicycle crankshaft, which is connected, in use, to the pedals (4) of a bicycle, and an output (32), which is connected, in use, to a bicycle sprocket wheel (34). The input (2) and output (32) are connected to respective shafts of a three branch epicyclic gearset including a sun gear (18), which is in mesh with a plurality of planet gears (16), which are rotatably carried by a common planet carrier (12) and are in mesh with an annulus gear (20). The rotors of first and second electric motor/generators (22, 24) are connected to respective shafts of the gearset via respective step-up gearing (26, 18; 28, 20) with step-up ratios of at least 5 and at least 8, respectively. The electrical connections of the stators of the motor/generators are connected together via a controller (30) arranged to selectively control the electrical power transmitted to or from an electrical energy store (31) to the motor/generators or between them. The R.sub.o ratio of the gearset, that is to say the ratio of the speed of the annulus gear (20) to the speed of the sun gear (18) when the planet carrier (12) is held stationary, is between -2 and -4.

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First Claim