Power Supply Reduction Unit (PSRU)

[thundair]

I have a project that the customer wants to use 4 gears to reduce RPM
My problem is I can't get my head around the concept of dividing load. I would think at the very lest it would pair up with two gears and cause a harmonic vibration with the other two. His idea is to replace a planetary gear.
What are the caveats so I can convince him to abandon this concept.

Thanks in advance

This is a pic of his model with the blue as the input and the green gear as the output.


I don't know anything but the people that do.

 

[MikeHalloran]

As I recall reading about it, the trick to load sharing is that the planet carrier has to be a little flexible in its least flexible direction, to allow the planet gears to advance/retard relative to each other so that they will share load despite minor tooth to tooth pitch variations.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

thundair,

Torque splitting is commonly used in aircraft gear drives to reduce weight. And as MikeHalloran noted, getting all of the gears to load share equally is the hard part.

The most reliable method is to float one of the gears. In your particular example, you would float the sun gear. This technique would give equal load sharing with 3 equally spaced planet gears, but with 4 planets as you show, perfect load sharing cannot be assured. And the more planets you have the worse the problem gets.

Load sharing can also be achieved thru precision manufacture and assembly, but this is very costly. Another technique is to use torsionally compliant elements (like quill shafts) on the planets.

If weight is not an issue, then a single gear and pinion would be a simpler, less costly, and more reliable choice.

With regards to harmonics, whether you have one gear mesh or several, the most important thing is to make sure that none of your operating gear meshing frequencies couple with a structural mode in one of your rotating components.

Hope that helps.
Terry