Patent ID: 8226517

Claim:
A speed change mechanism, comprising: a first planetary gear set, comprising a first sun gear, a plurality of first planet pinions, a first carrier arm and a first ring gear; a second planetary gear set, comprising a second sun gear, a plurality of second planet pinions, a second carrier arm and a second ring gear; a power input connection for drivingly connecting the first and second sun gears with an output from a power source; a hub shell surrounding the first and second planetary gear sets; a first one-way clutch for transmitting drive from an output of the first planetary gear set to the hub shell in a first rotary direction only; and a second one-way clutch for transmitting drive from an output of the second planetary gear set to the hub shell in the first rotary direction only; wherein, in one of the first and secondary planetary gear sets the carrier arm is fixed and the ring gear is the output and in the other of the first and second planetary gear sets the ring gear is fixed and the carrier arm is the output.