[A4] Re: Quattro, Torsen, Haldex and others...

[Brian J White]

"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 
EDL.  It
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 least.

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 
>available
>power to either the front or rear axle.  I've read many  different torque 
>split
>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 
>available, for
>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 
>diffs
>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 
>km/h.  I
>have this in my '90  CoupeQ, it works very well, never needed to lock the 
>rear
>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
>HUMVEE's  system!
>
>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 
>EDL.  It
>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 
>mainly due
>to the completely reactive  nature of the haldex system, ie, it sends 
>power to
>the rear until it detect  slips.  However I hear that Volvo has since 
>modified
>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 
>better than
>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 
>reactive, much
>worse than the  haldex system, and it places too much demand on the 
>brakes.  If
>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 
>this issue?
>  Although I must say this probably won't be a problem for daily driving, 
> it's
>  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 
>believe
>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 
>wierd stuff
>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 
>during a
>turn.
>
>Anyhow, hope this clears  things up a bit, or not... ;-)
>
>Quincy
>'01.5 S4 - quattro IV
>'90  CoupeQ - quattro II
>
>
>
>
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