US Patent 8702558 Planetary gear transmission unit

A planetary gear transmission unit (10) includes a ring gear (17), a sun gear (18) and a planet carrier (19) driving a plurality of planet shafts (12) onto which planet gears (11) are rotatably mounted by way of planet bearings (13). The planet shafts are flexpin shafts (12) and each flexpin shaft (12) includes a pair of planet gears (11), each planet gear (11) of the pair being of the single helical type having a helix angle opposite to that of the other planet gear (11) of the pair. A gearbox (20) including a planetary gear transmission unit (10) according to embodiments of the invention and a wind turbine including such a gearbox (20) are also described.