lighten torsen & FEA

[Scotto]

looking to lighten up the torsen housing.. but havin troubles doing an FEA model(COSMOS). just wondering what teams have done before to deal with this. im looking to use 7000 series Al, ive also heard stories that inserts are needed and arent needed(are the inserts really needed?) to be used for the friction surfaces(how do you model these surfaces too?)-and where are the exact loading points/loads? hope that makes sense.
any help would be grand as im a rookie on the subject

thanks
Scott

ps congrats to RMIT

[Scotto]

looking to lighten up the torsen housing.. but havin troubles doing an FEA model(COSMOS). just wondering what teams have done before to deal with this. im looking to use 7000 series Al, ive also heard stories that inserts are needed and arent needed(are the inserts really needed?) to be used for the friction surfaces(how do you model these surfaces too?)-and where are the exact loading points/loads? hope that makes sense.
any help would be grand as im a rookie on the subject

thanks
Scott

ps congrats to RMIT

[Underthefloor]

Hey Scott,

There is alot of information about the torsen if you search the forums. Personally, I would just use an open diff depending on how your suspension is set up.

John

[Scotto]

i hada bit of a peak at the forums before hand with no conclusive luck, so this was really a bit of a last resort. the info i found seemed more like just a guess design and hope for the best, as opposed to an engineering reliant design(im sure im being a little naive with that statement). i guess im chasing the appropriate design protocol and execution. as for the open diff, we already have the torsen in place and it seems to be truckin very well, perhaps next year we'll look for something else.

thanks
Scott

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Underthefloor:

Personally, I would just use an open diff depending on how your suspension is set up.

John </div></BLOCKQUOTE>

Why? I'd be curious to hear what suspension geometry you'd propsose to make this the ideal setup.

Scotto..
I may be able to help you out. I have some information about the development of the forces/loading conditions inside the Torsen. We've had good luck making our own 7075-T6 carriers in the past...never any wear problems considering the average life cycle of a FSAE car. I'll have to dig it up later though...I'm at work right now.

[jdstuff]

Scotto, what is your email?

As a new memeber, it's encouraged to provide some personal information in your profile (email, affiliation, etc). That way people know who they're talking to. and are more likely to offer advice. =)

[John_Burford]

If you have force/loading condition information, by far the best approach is to setup a Topology optimization. I have done this type of work on differential carriers before with good results.

John Burford

[Chuck Maddocks]

you won't need to model the friction surfaces since you are just performing fea on the carrier. calculate your input forces from the sprocket (and inboard brake if applicable). don't forget to include the thrust forces from the gears. you can try restraining certain surfaces if calculating the thrust forces is too challenging, but i found that i had higher stresses when actual forces were applied. plus the thrust forces due to the helix angle are unequal.

another consideration is how to split the input torque between the sprocket bolt holes. originally, i split it evenly between all six of our bolt holes, but i realize now that only 2-3 bolts are really stressed during acceleration. when approaching these kinds of things it is always good to start simple and then gradually refine your assumptions to incorperate the "realilistic" complexities. good luck

chuck
maryland

[Underthefloor]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jdstuff:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Underthefloor:

Personally, I would just use an open diff depending on how your suspension is set up.

John </div></BLOCKQUOTE>

Why? I'd be curious to hear what suspension geometry you'd propsose to make this the ideal setup.

</div></BLOCKQUOTE>

Jason,

Im not a suspension expert but here is what I know. According to our suspension guy we have very little jacking of the rear inside wheel when turning. We are also running a little softer role resistance in the back of the car.

On our 05 car we ran a torsen and had alot of trouble understeering out of corners. This year we are running an open diff with the same suspension geometry and are not having wheel spin up problems so far. The understeer problem also apears to be fixed.

Sorry I don't know the specifics of the suspension and steering geometry but the open diff seems to be working on our car. I can't say the we have the optimal setup but for our current car an open diff seems to be alot better than the torsen.

Scotto,

I made a set of equations bassed on the helic and pressure angles of the torsen gears. If you want, I can send them to you for comparison purposes.

[jdstuff]

John,

Rock on. If you can get an open to work well with your package, I think that's awesome. Personally, I have never been a fan of the torsen....I think that it is over-used and under-understood in FSAE. I think the torsen can work well in our application, just not in the configuration that most tend run. Good to hear that you've done the homework, and made an ENGINEERING decision on what diff to use. I'm willing to bet you could make a seriously light weight open diff.....what did you source the gears from?

Also, were you guys running a diff mounted brake rotor with the torsen...and has your brake configuration changed with the open?

[BeaverGuy]

I can answer some of those questions Jason. I believe that the gears are custom, selected with the help of a local gear manufacturer. As far as a torsen mounted brake, no we weren't running one before so the brake configuration has stayed the same.

Now, I have a couple questions John. Did you ever get a torsen housing made for this year to do direct comparisons with? And are you guys working going to write an SAE paper about the diff now that you have done some of the testing?

[Underthefloor]

Unfortunately the diff isn't all that light because we actually made a no preload adjustable clutch plate LSD. The idea was to find the minimum TBR that would prevent wheel spin. The car was initially set up in an open configuration and we have not run into any* wheel spin problems so we haven't run any other TBRs. I'm just hoping that it doesn't rain in Southern California in middle of June. http://fsae.com/groupee_common/emoticons/icon_cool.gif

Hey Josh, congratulations on getting accepted at Kettering. We never got the torsen fully converted and now it is unlikely that we ever will. I don't know about a paper. We "dynoed" the diff two different ways to attempt to confirm our theoretical TBR calculations. Unfortunately neither setup was able to accurately test the diff and we had some issues with the clutches acting like thrust bearings at low loads. To make a long story short, we need a working chassis dyno to test the diff accurately and in the torque/speed ranges actually seen while driving. As of now, we have no proof that the diff is working as expected. We just got the chassis back from powder coat and when the car is reassembled we will put torque wrenches on the spindle nuts but that's probably going to be the most accurate testing we get done before competition.

*On a 180 turn there was some inside wheel spin but it was not believed to affect performance too much. It was a much tighter turn than expected at competition. I'm not really sure what ramifications of this are.

John

[Scotto]

updated my profile a little now... much appreciate the input guys(and girls where applicable)... all i know is that i have a lot to learn, but its all part of the fun and gameshttp://fsae.com/groupee_common/emoticons/icon_wink.gif

Underthefloor and jdstuff, id like to hear any info you may have that could help myself out..feel free to email me... thanks again ill keep my ears out!

[RickyRacer]

Hey Jason,
Are you going to be at the Portland Race? If so, I would like to swing by and meet you. I will be there with an F2000 team.
Ricky
Cal State Long Beach FSAE

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RickyRacer:
Hey Jason,
Are you going to be at the Portland Race? If so, I would like to swing by and meet you. I will be there with an F2000 team.
Ricky
Cal State Long Beach FSAE </div></BLOCKQUOTE>

Yeah, we'll be there. Our transport is grey with black & yellow graphics...drivers Alex Barron and Alan Sciuto. Bummer that it's the same weekend as FASE West...I would have really liked to have gone with my team to competition.

[RickyRacer]

Yeah, real bummer. We could not get our car done by the deadline so instead I will be at portland working. I would rather be at Cal Speedway but we are bringing our fast driver(who is leading the championship) from the Pacific F2000 series to try and beat the entire F2000 field. I remember Sciuto, he ran F2000 last year. I would like to stop by and talk to you about Atlantics and your position there. I will see you there.

Ricky
Cal State Long Beach FSAE