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

Tue Dec 28 13:48:58 EST 2004

	interestingly, i'm seriously considering an X3.

At 8:29 AM -0800 12/28/04, Brian J White wrote:
>"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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