[A4] Re: Quattro, Torsen, Haldex and others...
Brian J White
brian at bjwhite.net
Tue Dec 28 11:29:43 EST 2004
"quattro IV - torsen center diff with open front and rear diffs, but now it
has EDL to keep side-to-side traction in check. This system combines the
proactive nature of the mechanical torsen, with reactive aspect of the
should in theory able to pass the "one wheel with traction only" test."
Key point up there. The car on which I saw the test applied was a 99 or so
A4 Quattro...obviously having Quattro IV.
Either they disabled the EDL (possible as this was a marketing exercise) or
the EDL couldn't keep up with absolutely ZERO traction on the other 4
wheels. It certainly looked like it was trying but just couldn't make it
happen. My eyes popped out of my head....I was certainly surprised to say
The BMW (the new system) AWD on the 330Xi certainly did the trick. There
are handling advantages to the 36/66 torque split as well. Biased towards
the rear for that rear wheel drive track handling feel.
At 08:07 2004-12-28, Brizax at aol.com wrote:
>GOOD INFO THERE, SOMEONE HAS BEEN PAYING ATTENTION IN CLASS THE LAST COUPLE
>YEARS HUH? :)
>NYT is wrong!!!
>On torsen based quattro system (now version 4, hence quattro IV), the
>factory torsen is a splitted 2:1, meaning it can transfer up to 2/3 of
>power to either the front or rear axle. I've read many different torque
>figures from different sources, ranging from 40:60 to 30:70, but I believe
>the 2/3 is the most correct. There're other versions of torsen
>example Stasis Engineering offers a 4:1 version, capable of splitting up to
>4/5th (or 80%) to either end.
>All torsen are normally 50:50, whereas the haldex quattro is either 100:0 pr
>95:5 normally, and it's capable of sending all power to either end. Volvo
>uses this system as well. So there, NYT got the 2 quattros confused.
>Now here's some distinction of the different versions of traditional quattro
>systems for longitudinally mounted engines (all B and C chassis cars, such
>as 4000, 80/90, 5000, 100/200, A4, A6, A8):
>quattro I - original version. All 3 diffs are open, but the center and rear
>are manually lockable. It's very simple and reliable, but it tends to eat
>tires or cause damage to the driveline when people forget to unlock the
>after they unstuck themselves.
>quattro II - introduced in '88 I believe, when torsen replaced the old open
>center diff. The rear is still manually lockable, but it's now operated
>pneumatically so that it'll unlock itself once the car reaches over 25
>have this in my '90 CoupeQ, it works very well, never needed to lock the
>diff, but this version will not pass the "one wheel with traction only" test.
>quattro III - this was only used in the V8, where both the center and rear
>diffs are torsen. Since this car wasn't sold in large quantity I don't know
>how well it actually works, but it sure sounds promising, almost like the
>quattro IV - torsen center diff with open front and rear diffs, but now it
>has EDL to keep side-to-side traction in check. This system combines the
>proactive nature of the mechanical torsen, with reactive aspect of the
>should in theory able to pass the "one wheel with traction only" test.
>On the TT, its quattro system has no version because it's not an evolution
>of the original quattro for longitudinally mounted engines. As I've said
>before, my brief drive in a TT didn't impress me much. I think it's
>to the completely reactive nature of the haldex system, ie, it sends
>the rear until it detect slips. However I hear that Volvo has since
>their haldex AWD on newer cars and they're supposed to be a cut above the
>original haldex system.
>To further continue the AWD topic, BMW's system is not as good as quattro
>due to its inability of changing torque split between front and rear, it's
>always at 38/62. However it's brand new x-drive is supposedly much
>the old AWD system, which started in '88 in the 325ix and was never
>changed/upgraded until just now.
>M-B's system is even worse. All 3 diffs are open and it relies on their
>version of EDL to control wheel spin by braking the spinning wheel(s) hence
>sending power to the ones that aren't spinning. It's completely
>worse than the haldex system, and it places too much demand on the
>Audi decided to deactivate their EDLs above 80 km/h due to potentially
>overworking the brakes, how well do you think M-B's system copes with
> Although I must say this probably won't be a problem for daily driving,
> more of a problem if you really get stuck or actually to off-roading.
>Now to chip in my $0.02 on the center versus rear applications of the torsen
>diff, they are really quite different. Hence if you've only driven quattros
>with torsen center diff, you really have no idea how it would behave when
>is't slapped onto the rear of a RWD car, of the front of a FWD car (I
>Nissan used to offer torsen on their 240SX and Maxima as part of their SE
>package). A friend of mine (240SX owner) has told me once that having a LSD
>(such as torsen) in the rear is great in the dry, but it does do some
>when it's wet and slippery, cause the diff seems to be distributing power
>from side to side as each of the rear wheels lose and regain traction
>Anyhow, hope this clears things up a bit, or not... ;-)
>'01.5 S4 - quattro IV
>'90 CoupeQ - quattro II
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>A4 at audifans.com
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