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Ravigneaux Gearset Ratio Analysis

Ravigneaux Gearset Ratio Analysis

Ravigneaux Gearset Ratio Analysis

I am looking at design alternatives for a gearbox section that will need to offer one reduction ratio forward and one reverse. I know I can use a single planetary set to get the ratios (and directions) I need with a sun gear input, locking the carrier and using the ring for output (reverse) and locking the ring and outputting on the carrier (for forward), but this will require 4 clutches including 2 on the output shaft!  Not pretty from a control point of view.

Going to 2 simple planetaries is relatively easy, as I could simply shift from one sun to the other, but I would need to anchor the ring of one set and the carrier of the other to the case.  This leads me to think I could use a single ravigneaux set and just anchor the ring to the case, always outputting the carrier. One sun would drive through a second planet, giving me a reverse. Simple and maybe cheaper.

Question: When calculating ratios in a ravigneaux gearset, presuming the planets have an equal number of teeth, are ratios calculated exactly as they are with simple planetaries, that is 1 + ring/sun = ratio?   Any other references, hints and comments on the subtleties of ravigneaux geartrains would be appreciated.  

RE: Ravigneaux Gearset Ratio Analysis

I'm sorry, even after reading through the post 3 times, I see I stated my design incorrectly.

For the ravigneaux set, I plan to output from the ring and anchor the carrier!  That is the way I have it drawn.

RE: Ravigneaux Gearset Ratio Analysis

Woohoo!  My fist forum post anywhere!

Sorry, to answer your question, the ratio of the ravigneaux would be just (ring/sun) and also negative (-ring/sun).

Hope that helps

RE: Ravigneaux Gearset Ratio Analysis

ops!  I think I mispoke about the negative...  what I meant was that one ratio is negative and one is positive

I think the ratios would be

Also, the planets do not need to have the same number of teeth-- the ratios are still valid.

RE: Ravigneaux Gearset Ratio Analysis

Ops!  I assumed that one of the ratios would be (1+ring/sun) but that's only if you anchor the ring!  Sorry, it's been a while since I've thought about this stuff (that's why I have no references for you).

I guess I should be more thorough for accuracy-- that way I know I'm not making any more silly mistakes!

For a single planetary gear set:
if you hold the ring, ratio = (1+ring/sun1)
if you hold the carrier, ratio = -ring/sun1

For a planetary gear set with two sets of planets (sun meshes with one set, and ring meshes with the other).  Like a ravigneaux without one of the sun gears:
if you hold the ring, ratio = -(ring/sun2-1) = (1-ring/sun2)
if you hold the carrier, ratio = ring/sun2

So, the ratios you'd get are by anchoring the carrier and outputing the ring would be
(where sun2 is the one that is connected the ring through two sets of planets.  Usually sun2 is smaller than sun1, but I don't think it has to be)

Sorry for the silly mistakes.  This time I've been thorough, so you can see where I made the little mistakes.

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