Patent ID: 7455608

Claim:
A four branch differential transmission system comprising: a first shaft and a second shaft, which constitute the input and output shafts; a third shaft connected to a first variator arranged to increase or decrease its speed and; a fourth shaft connected to a second variator arranged to increase or decrease its speed; the four shafts being connected together by a spur gear compound epicyclic gearset including a plurality of toothed gearwheels, wherein the compound epicyclic gearset comprises first and second epicyclic gearsets, the first epicyclic gearset being of positive type and comprising a first sun wheel and a second sun wheel in mesh with a respective set of first and second planet wheels, each first planet wheel being connected to rotate with a respective second planet wheel about a respective common planet shaft, the planet shafts being connected to a common planet carrier, the second epicyclic gearset being of negative type and comprising the first sun wheel and a third sun wheel, the third sun wheel being in mesh with a set of third planet wheels, each of which is connected to rotate with a respective first and second planet wheel about a respective planet shaft, the first and third planet wheels or the first and second planet wheels of each connected set of planet wheels being of different diameter and being connected together to constitute a stepped composite planet wheel.