RS5: crown centre diff - new quattro

[Marv]

I was intrigued by this so thought it worth stating a new thread...

Qisha mentioned it in the 'Audi RS5 Brochure' post saying its more compact and lighter (which makes a lot of sense) and has 'greater barrage values'. Qisha, can you elaborate, I've no idea what that means.

The previous torsen centre diff had a lot going for it IMO - purely mechanical, no electronics, no hydraulics, no clutches etc so very little to go wrong. It was also instant acting in transferring torque (the nature of its mechanical setup) unlike the Haldex system that requires a degree of slip to work.

Does anyone know if the new crown centre diff is a like the old mechanical torsen or does it need computers and clutches to operate. And how does it compare in the real world (apart from being lighter)?

Marv

[roadrunner]

Maybe that will help

[Qisha]

Dear Marv,

the promotional video explains the basics pretty good, thanks to roadrunner.

If you got additional questions, add them here. I will gladly respond to them.

Qisha

[Sims]

Dear Marv,

the promotional video explains the basics pretty good, thanks to roadrunner.

If you got additional questions, add them here. I will gladly respond to them.

Qisha

Excellent video. Thank you.

[Lmg]

Excellent video. Thank you.

+1! That was very informative!

[Marv]

Thanks guys - very informative. No mention of efficiency/drive train losses though. You'd hope, being newer, that there would be less power loss than the old torsen?

Do you know if this will this become the standard MLP quattro or is it for RS cars only?

[r8dream]

Awesome video and awesome new technology from Audi, very exciting.

According to the price list http://www.darkhouse.de/temp/Preisliste_Audi_RS5.pdf
Quattro Sport Differential in the rear, is an option on the RS5, so crown gear center differential is compatible with the torque vectoring rear diff.

So now, two questions please Qisha,

What is the probability of an RS5- 6 speed manual coming out in one or two years. good or not good?
and secondly please,
Can the new crown gear center differential be retrofitted to previous quattro manual gearboxes (that used the torsen 40/60 split) like the s5-0b4, rs4-0a3 or older s8-01e ? It looks physically bigger with larger splines also.

Because its 6mt or nothing, and Quattro or nothing, because it rains more than half the year here in the UK.

Thanks, John

[r8dream]

after watching the video again, i noticed that it only talks about torque vectoring through the edl system, but doesn't seem to mention what happens when the optional quattro sport diff is added,
which doesn't use the brakes to vary the torque to the individual rear wheels.

i had one of the first tv diffs on an '92 porsche 928gt, it was the psd from the 959, very similar to the qsd, and made the drive unforgettable in the rain. porsche video here, http://www.youtube.com/watch?v=_PoocIsiV2c

audi qsd video here, http://www.youtube.com/watch?v=viWJUaakMKs

porsche is using a new tv system on the new 911 turbo, called Porsche Torque Vectoring (PTV).
but this time using the brakes, not a diff like the qsd and old psd.

i would have liked to see this comparison video done with the optional qsd on the s5.
http://www.youtube.com/watch?v=EU4Mx7bT5po

[Silver Stealth]

Qisha,

Can you talk more about the brake-based torque vectoring?
Could this system lead to overheated brakes or fade in a track scenario or extended mountain pass drive by constantly using the brakes in turns?

Just curious about Audi's decision to use this rather than the sport differential concept of accelerating a wheel versus slowing it down...

[Tanner]

Just curious about Audi's decision to use this rather than the sport differential concept of accelerating a wheel versus slowing it down...

Willing to be it were the bean counters. They could have made the sport diff a standard feature with this RS.

[ChicagoAudi]

The video, while informative, does little to provide insight into why this center differential is preferable to the older Torsen-based quattro systems. The torque apportionment between front and rear axles seems to span the same range between the Torsen and crown gear center differentials..

The explanation of brake-assisted torque vectoring appears inferior to the Audi Sport Differential, and looks to significantly increase brake wear and fade. The EDL found on quattro IV does significantly increase rear brake pad wear.

Audi needs to do more to convince a fickle consumer that this version of quattro is a technical advancement and not a move to lower costs.

[Tanner]

The video, while informative, does little to provide insight into why this center differential is preferable to the older Torsen-based quattro systems. The torque apportionment between front and rear axles seems to span the same range between the Torsen and crown gear center differentials..

I think there are a couple benefits for sure - smaller package and weight. More we can save on weight the better.

As for the other reason, aren't the current torsen-based centre diffs an open-diff? While I doubt a lot of us get into the extreme case where one axle has absolutely zero grip, it's the axle with no grip that will get all the torque, assuming ESP is turned off. So this is the only other benefit I see is that it is now a self-locking differential, though correct me if I'm wrong on this.

[Jani]

Super video from Audi, excellent! Surprised about the usage of brakes in torque vectoring. Also wondering if brakes are used also if you choose the sport diff-option?

Here is the patent (in German) http://www.freepatentsonline.com/EP1906053.pdf

Im Vergleich zu bekannten Ausführungen
selbstsperrender Differenzialgetriebe ist das erfindungsgemäße
Differenzialgetriebe 1 aufgrund eines geometrisch
einfachen Aufbaus relativ kostengünstig herstellbar.
Insbesondere bei Verwendung einer Geradverzahnung
zwischen den Ausgleichsrädern 3 und den Abtriebsrädern
4, 5 ist die Sperrwirkung der Reibungsbremsen
9, 10 exakter einstellbar, und die Verzahnung weist
eine erhöhte Toleranz gegenüber einer bauartbedingt erforderlichen
Axialverschiebung der Abtriebsräder 4, 5
auf. Bei einer Verwendung des Differenzialgetriebes 1
als Mittendifferenzial ist zudem die Möglichkeit einer
asymmetrischen Verteilung des Antriebsmomehtes gegeben.

The benefits briefly compared to other previous self-locking diffs (with my non-native German translation):
-geometrically simple and cost effective to produce
-better adjustability of locking behaviour
-higher tolerances
-when acting as centre differential, the possibility of asymmetric torque distribution

So it is not only technical decision, but also simple and cost-effective.

[Marv]

I've just watched the video again with proper audio (was on a crappy notebook when I saw it first) and the background music is really cheesy .

It's interesting that both Porsche and the new Mclaren MP4-12C (maybe other manufacturers too?) are going with a brake based torque vectoring. There must be a good reason. The upside is that it's cheap and adds no weight, the downside is early brake wear, heat build up and computer control (i.e not instantaneous). Being cynical I'd immediately say it's because it's cheap but then Mclaren aren't known for penny pinching...

That said, even the Audi sport diff can suffer from overheating if it's pushed hard - if it gets too hot it goes back to being an open diff until it cools enough to work again (never overheated it in my car; suspect you need sustained track work to do that)

I've not looked through the sales spec of the RS5 yet - does anyone know if it is it actually possible to order the sport diff or is it brake based TV only?

I guess like all these things, until we get some reviews it's all speculation....

[Lmg]

I've not looked through the sales spec of the RS5 yet - does anyone know if it is it actually possible to order the sport diff or is it brake based TV only?

Yes, it is possible to order the Sport differential.

It will be very interesting to see the way that the crown diferential's torque vectoring will work together with the sport differential.