[A4] Re: Quattro, Torsen, Haldex and others...
Brizax at aol.com
Brizax at aol.com
Tue Dec 28 11:07:51 EST 2004
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
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
Anyhow, hope this clears things up a bit, or not... ;-)
'01.5 S4 - quattro IV
'90 CoupeQ - quattro II
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