Second, the planet gear bearings need to play an active role in torque transfer. Planetary systems split the torque insight from the sun gear amongst the planet gears, which in turn transfer torque to a world carrier connected to the gearbox output. The bearings that support the planets on the carrier have to 
bear the entire brunt of that torque transfer.
Or, in extreme cases, they may select angular get in touch with or tapered roller bearings, both which are designed to withstand axial loads.
In planetary gearboxes, however, it’s much more difficult to design around these axial forces for just two related reasons. 1st, there is typically very little space in a planetary gearbox to include the kind of bulky bearings that can tolerate high axial forces.
The Helical Gearbox existence of axial forces makes things very different for the bearings that support helical gears. But it is important to make a distinction between fixed-axis and planetary gearboxes. In fixed-axis gearboxes, the excess axial forces amount to little more than an inconvenience. Gearbox designers will most likely upsize the bearings to support the additional forces.
Since they don’t need to withstand any axial forces, spur gear bearings enjoy just a supporting function in the functioning of the gearbox. The bearings simply need to support the rotating equipment shafts, however they do not play an active function in torque transfer.
Helical Gears Place Better Demand on Bearings