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Got a few Q's on a gearbox

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sweeneyp View Drop Down
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    Posted: Sep/26/2014 at 1:47am
So better lead off with that I'm an EE designing the gearbox (single speed, 2 stage gear reduction) for this years car at Lipscomb University. So chances are I'm going to say or have done something stupid in terms of mechanical stuff lol. We're trying to get away from the heavy/high inertia dana gearbox to drop overall vehicle weight this year. So the single speed gearbox with brake mount will be on this years car and a more complex gearbox will be used next year which is a senior design project this year.

Anyway, Q's involve gear oil and spacing around gears in the enclosure.

-I've hidden the front cover (which is simply a plate to hold bearings/seals, no cutouts like the side with the gears) and the large gear of the 1st stage to show the internals better. I left 1/8" of space between the gears and the case (on all sides, except for input gear). Is that clearance too tight? Questions have come up about that possibly building up pressure inside the gearbox while in operation from oil. It has an area to pool on the main output gear as there is a 5/8" space between it and the other side of the case. I can do all the calculations for strength of gears/shafts/whatever but some things like this, I'm simply not sure on as its a bit out of my league lol
uploads/2619/gear_internals.jpg
http://i802.photobucket.com/albums/yy306/sweeneyp/Misc%20for%20use%20in%20forums/gearboxinternals_zps2925418c.jpg

-As for gear oil, I'm worried about foaming with those cutout in the gears. So I was thinking of either using ATF fluid or 0W-20 engine oil. Anybody have experience with those? I know ATF is heavy on detergents will that possibly eat into normal shaft seals or RTV? I have a fill hole to fill it where the fluid level sits right at the bottom of the teeth on the small gear of the 2nd stage.

Thanks!

EDIT: hmm, I can't seem to get the picture to embed...or at least its simply showing up as text on my end...




Edited by sweeneyp - Sep/26/2014 at 2:06am
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Richie_Dagger View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richie_Dagger Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2014 at 2:12am
1/8" is plenty of clearance. I think I've ran 0.020-0.060" clearance without issues. This assumes there is no play in the mounting of the gears on the shafts. 

I suggest you fill the gear box with oil only up until it touches the teeth of the final drive gear. This way the gearbox is not churning through oil, causing excess heat and oil foaming. I can assure the oil will make its way from the very bottom of the case all the way to the input pinion and keep the whole thing very well lubed, in fact it will piss oil out the input shaft seal if you give it a chance to. We've always used 0W Royal Purple in the trannies to reduce frictional losses.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rasmuet Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2014 at 12:19pm
We have used ATF and it does not eat into the RTV or case/bearing seals.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Rivera Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2014 at 11:01pm
Keep in mind that it is usually a good idea to have a vent. I usually like to run my vent hose as high as possible to keep it out of water, and put a loop in it in case of roll over
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sweeneyp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sweeneyp Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2014 at 11:44pm
Originally posted by Richie_Dagger Richie_Dagger wrote:

1/8" is plenty of clearance. I think I've ran 0.020-0.060" clearance without issues. This assumes there is no play in the mounting of the gears on the shafts. 

Wow...your braver than I am lol. Well I think I'll play it safe on our first gearbox and give it a little more room than .02" lol. But thanks for putting that 1/8" into perspective.
 

Originally posted by Richie_Dagger Richie_Dagger wrote:

We've always used 0W Royal Purple in the trannies to reduce frictional losses.

Originally posted by rasmuet rasmuet wrote:

We have used ATF and it does not eat into the RTV or case/bearing seals.

So either works, that's good.We have some old ATF laying around, probably end up using that over buying new oil.

Originally posted by Tony Rivera Tony Rivera wrote:

Keep in mind that it is usually a good idea to have a vent. I usually like to run my vent hose as high as possible to keep it out of water, and put a loop in it in case of roll over

Awesome, that was the next question I had. From most teams I had talked too its been 50/50 whether they run simply sealed or with a vent of some kind. We were already leaning toward some-kind of vent. The dana H12 has a small pressure relief valve that I was looking into, but a long bit of hose will work too...not to mention cheaper.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zglazer Quote  Post ReplyReply Direct Link To This Post Posted: Sep/27/2014 at 1:50am
1/8" is a good amount of clearance. Keep in mind that less clearance (around the perimeter and the sides as well) also means you don't need to put as much oil into the gearbox to fill it up to the level of the gear teeth. It's an easy way to eliminate a bit of dead weight.

As for venting, we used to use pressure relief valves, but switched to vent bellows like this one a few years ago to avoid having oil get spat out through the valve: http://www.pscmotorsports.com/vent-bellow.html
Zack Glazer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brad SXT Quote  Post ReplyReply Direct Link To This Post Posted: Sep/27/2014 at 6:30pm
I think 1/8 inch of clearance is a safe-ish plan. What if you have wibbly wobbly gears and shafts and case?
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zglazer View Drop Down
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Post Options Post Options   Thanks (2) Thanks(2)   Quote zglazer Quote  Post ReplyReply Direct Link To This Post Posted: Sep/27/2014 at 6:34pm
Then you should find yourself a better machinist. Tongue
Zack Glazer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote paasch Quote  Post ReplyReply Direct Link To This Post Posted: Sep/28/2014 at 12:13pm
Originally posted by zglazer zglazer wrote:

Then you should find yourself a better machinist. Tongue

Or better design. The gearbox case halves need to have features that accurately locate the two halves relative to each other when you assemble them. Don't depend on the bolts to locate, bolts are for clamping. Machine the locating features and the bearing bores in the same set up.

Bob Paasch
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