Bicycle Transmission Systems

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 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.

1 . A bicycle transmission system including an input constituted by a bicycle crankshaft, which is connected, in use, to the pedals of a bicycle, and an output, which is connected, in use, to a bicycle sprocket wheel, the input and output being connected to respective shafts of a three branch epicyclic gearset including a sun gear which is in mesh with a plurality of planet gears, which are rotatably carried by a common planet carrier and are in mesh with an annulus gear, and first and second electric motor/generators, the rotors of which are connected to respective shafts of the gearset via respective step-up gearing with step-up ratios of at least 5 and at least 8, respectively, and the electrical connections of the stators of which are connected together via a controller arranged to selectively control the electrical power transmitted to or from an electrical energy store to the motor/generators or between them, the R o  ratio of the gearset, that is to say the ratio of the speed of the annulus gear to the speed of the sun gear when the planet carrier is held stationary, being between −2 and −4, in which the input is connected to the planet carrier and the sun gear is rotatable with respect to the input and is connected to the first motor/generator via step-up gearing with a step-up ratio of at least 5 and the annulus gear is connected to the second motor/generator via step-up gearing with a step-up ratio of at least 8. 
     
     
         2 . (canceled) 
     
     
         3 . A transmission system as claimed in  claim 1  in which splines are integrally formed on the bicycle crankshaft, which splines are in mesh with splines on the planet carrier. 
     
     
         4 . A transmission system as claimed in  claim 1  in which connected to the rotor of the first and second motor/generator is a respective pinion gear in mesh with gear teeth on the sun gear and annulus gear, respectively. 
     
     
         5 . A transmission system as claimed in  claim 1  in which the controller is programmed selectively to direct electrical power from an electric battery to at least one of the motor/generators to cause it to operate as a motor. 
     
     
         6 . A transmission system as claimed in  claim 1  in which the controller is programmed selectively to direct electrical power from that motor/generator which is operating as a generator to an electric battery to recharge it. 
     
     
         7 . A transmission system as claimed in  claim 1  in situ on a bicycle, the crankshaft being connected to the pedals of the bicycle to be rotated thereby, the output being connected to a bicycle sprocket wheel and the controller being connected to an electric power storage medium.