12.25 Number of contacts per revolution
For a single pinion in mesh with a single gear, each member has one
contact per revolution. Some gears have more than one cycle of load contact
per revolution. An epicyclic gearset (planetary or star gear) is shown
- The gear has Q contacts/rev, where Q = number of planets. For the
example shown, the sun gear has 3 contacts/rev.
- The planet gear has 1 contact/rev because the loads from the sun gear
and ring gear occur on opposite sides of the planet gear teeth. The
reverse bending that occurs on the planet gear teeth is accounted for
with the ”Loading-type Code” (See chapter 12.24).
- (planetary gear train) The internal gear has Q contacts per revolution,
where Q = number of planets. Although the internal gear in a planetary
gearset is fixed, it is analyzed as if it were rotating at the planet carrier
- (star gear train) – the internal gear has Q contacts per revolution
of the internal gear where Q = number of planets. An example of a
split-power-train (branched) gearset is shown below:
In this example, if the pinion is the driver or is driven, it has 2 contacts/rev. If the
pinion is an idler, it has 1 contact per revolution and reversed bending. The
mating gears each have 1 contact/rev.