Internal Gear Contact Ratio Chart?
Internal Gear Contact Ratio Chart?
(OP)
I am considering the design of a lightweight gearbox. I was hoping that by using an internal-external gear pair, I could get away with a much thinner gearset than I would with an external-external gear pair for the same torque. However I have not been able to find a good online reference for the amount of load sharing between internal and external gear teeth of a given ratio. The AGMA J factor charts give a good indication of tooth-load sharing for external gears. Does anyone know of a similar chart for internal gears?





RE: Internal Gear Contact Ratio Chart?
If you have a gear program, simply use 10000 teeth to simulate a rack.
The contact ratio will be lower than the internal external gear combo
and certainly higher than the external external como. If you need exact
numbers, someone offered excel spread sheets awhile back but I do not
know if they re still available. They were metric spread sheets, but
if you use the same combinations, the contact ratios would be the same.
If you provide, the numbers, I can send you the contact ratio of the
set. Will you be using modified addendums on the internal gear? It is
customary to truncate the internal gear addendum to avoid interference
in the root of the external gear.
RE: Internal Gear Contact Ratio Chart?
If you have a spreadsheet available, can you plug in the following ratios and let me know what you get for contact ratio? That way I can check to see if my assumption is valid:
case 1) 96 t internal, 30 tooth external
case 2) 72 t internal, 50 tooth external
compare against:
base case) 72 t external, 50 tooth external.
RE: Internal Gear Contact Ratio Chart?
case 2) 72 t internal, 50 tooth external 1.909 contact ratio internal gear must be shortened .075xModule to avoid involute interference.
compare against:
base case) 72 t external, 50 tooth external 1.783 contact ratio
Lewis Y factors at tips
30 t ext .358
50 t ext .408
72 t ext .430
72 t int .584
96 t int .441
So you are not going to get that great of an increase in bending strength.
This is a simple analysis based on tip loading. Even using a stub tooth
form, you will not gain much. You may have to look at different materials
to see the increases that you are looking for or increase the face widths.
RE: Internal Gear Contact Ratio Chart?
RE: Internal Gear Contact Ratio Chart?
Also, if efficiency or scoring/scuffing are a concern, an external gear pair would have a slight advantage over the pinion/internal ring combination. Even using lots of profile shift to produce recess action, the pinion/internal ring combination will still have greater sliding losses than the external gears will.
Lastly, in case you had not considered the issue, the relative direction of rotation from input to output is not the same with a pair of external gears and a pinion/internal ring gear pair.
Hope that helps.
Terry
RE: Internal Gear Contact Ratio Chart?
RE: Internal Gear Contact Ratio Chart?
RE: Internal Gear Contact Ratio Chart?
The root cause of the majority of the gear failures that I've seen have been associated with surface durability issues not bending strength.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181