Second, the earth gear bearings need to play an active function in torque transfer. Planetary systems split the torque insight from sunlight gear amongst the earth gears, which transfer torque to a world carrier linked to the gearbox result. 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 of which are made to withstand axial loads.
In planetary gearboxes, however, it’s a lot more difficult to design around these axial forces 
for just two related reasons. 1st, there is typically very little area in a planetary gearbox to include the type of bulky bearings that may tolerate high axial forces.
The presence of axial forces makes things very different for the bearings that support helical gears. But it’s important to make a distinction Helical Gearbox between fixed-axis and planetary gearboxes. In fixed-axis gearboxes, the additional axial forces amount to little more than an inconvenience. Gearbox designers will most likely upsize the bearings to accommodate the additional forces.
Since they don’t need to withstand any axial forces, spur gear bearings play just a supporting function in the functioning of the gearbox. The bearings simply need to support the rotating gear shafts, but they do not really play an active part in torque transfer.
Helical Gears Place Greater Demand on Bearings