Application of a system level model to study the planetary load sharing behavior

In planetary transmissions, the input torque is split between a number of parallel sun-pinion-ring gear paths. Under ideal conditions, each parallel path carries the same amount of torque. However manufacturing errors in the pinion pin-hole location cause unequal load sharing between the parallel paths. The nature of this load sharing behavior depends upon the number of pinions in the planetary system. This load sharing behavior is studied for 4, 5, and 6-pinion variants of a planetary transmission. Critical manufacturing tolerances are identified and loss function curves are generated. The effects of sun gear support stiffness and pinion needle bearing stiffness on the load sharing results are also studied. It is shown that as the number of pinions in a planetary transmission increases, the pin-hole position error tolerance has to be tightened in order to reap the full benefits of load sharing between the pinions. Gear system analysis modules (GSAM) is an analytical tool that can model entire gear systems and will be used in this paper to quantify the load sharing between pinions. The numerical techniques implemented in GSAM will be briefly reviewed.