F1technical.net

Hey folks!

Sorry, that's not Formula 1 (but F1 area is more visited than "other racing series", so I hope for a helpfull answer). As maybe a few of you are knowing, I'm working on an Audi R18TDI currently. Now I've found something strange.
At the gearbox calculations, I recognised something, what I cant really believe. Is it possible, that (the R18s) drive shafts are tilted forwards? (differential behind rear wheel centre line) That sounds to me not really logical - especially at racing cars.
The R18 ones are defenitively tilted about 10 degrees upwards. But that's nothing strange - the RB7 ones are also tilted upwards.

Thank's for helping.

Cheers, Paul

The half shafts do indeed tilt upward and forward on both cars..

...I fail to see how X degrees upwards is normal but X degrees forward is strange. What difference does it make as far as the diff is concerned? Both seem perfectly normal to me.

Jersey Tom wrote:...I fail to see how X degrees upwards is normal but X degrees forward is strange. [...]

That's the reason why I asked.
I thought you also try to keep the half shafts as straight as possible (horizontal and vertical). For a lower COG it's usefull to keep the diff as low as possible and put up with the upward tilted shafts. But I still see no logical reason, to tilt the shafts forward... (appart from a (very) little more weight on the rear, but that can hardly be the reason) Maybe to build the car a little shorter.

Thanks to both of you.

Cheers,
Paul

PaulB wrote:But I still see no logical reason, to tilt the shafts forward

When you design a car (or anything) you can't get everything 100% the way you want it. There are compromises to be made for packing, component layout, whatever.

Whatever they came up with is what they felt was the best total package - even if it means some individual components aren't "ideal."

I agree with most said here, but I pulled out my trusty pen and paper and attempted to see where torque would be applied relative to the center-line of where the drive-shaft exits the transmission. Correct me if I'm wrong, but if the wheels are ahead of the transmission, torque is vectored downwards, giving an anti-squat under acceleration. As far as the wheels being below the transmission, I believe it's all because of the need to get all that heavy mass of the transmission as low as possible.

DaveKillens wrote:Correct me if I'm wrong, but if the wheels are ahead of the transmission, torque is vectored downwards, giving an anti-squat under acceleration.

Hmm. Not sure if that is the case. For a typical open wheel car with the gearbox / differential rigidly fixed to the body I think those forces are all resolved internally to the structure. The anti's would come into play through control arm geometry, or in the case of a stock car where the axle housing is separate from the body.

Torque knows only direction, not point of application.

Jersey Tom wrote:

DaveKillens wrote:Correct me if I'm wrong, but if the wheels are ahead of the transmission, torque is vectored downwards, giving an anti-squat under acceleration.

Hmm. Not sure if that is the case.
...

I agree, believe it or not, the conveyed torque itself is never attached to neither suspension nor structure outside of the diff, why the chassis will never see any of it?

However, does anyone know something about powerloss from out-of-angle drive-joints?

I've heard one manufacturer quote 4% at 12 degrees, the maximum they specify for that particular type of CV joint.

Lycoming wrote:[...] 4% at 12 degrees, the maximum they specify for that particular type of CV joint.

Yep, that's a usefull information. Thanks!

rjsa wrote:Torque knows only direction, not point of application.

True but kind of deceiving. There are suspension topologies where the torque from the engine is resolved internally and/or there are no anti's and it's all nice and easy.

There are others where you can have significant longitudinal anti's, body roll with drive torque, etc... all which has to be accounted for. The torque ultimately has to become a force at the ground after all.

do you also get slightly sinusoidal rotation speed from the geometry of CV joints?

...In answer to my own question, no, CV joint == constant velocity

tommylommykins wrote:do you also get slightly sinusoidal rotation speed from the geometry of CV joints?

You do indeed with a conventional joint, but that is directly neutralized with two joints on the same shaft interacting.

this for Saab fans:

http://www.google.de/url?sa=t&rct=j&q=t ... JPksxq_qbQ

as I understand at low angularities up to 5° the losses for tripod joints are below 1%