RE: Haldex and Viscous Couplings

["Dave Eaton" <Dave.Eaton@clear.net.nz>]

perhaps you could explain how a physically locked differential (to all
intents and purposes a solid shaft at this point) can do anything else but
allow 100% torque transfer to either end?

you should understand also that audi's edl works *across* the open front and
open rear differentials.  it does not work across the centre differential.
for example, it will not allow *both* wheels on an axle to be braked, but
will brake one wheel when the other is spinning up.  hence 100% torque to
the rear with the haldex.

or, perhaps this press release from vw will help?
(http://www.vwvortex.com/news/4motion/page3.html)

"With a multi-plate clutch running in the oil bath, it sets up a direct
drive between the front and rear wheels as soon as the input and output
shafts of the multi-plate clutch do not rotate at the same speed and a slip
occurs between the front driving wheels and the rear wheels. In this way,
the power of the V6 engine is always transferred to the wheels with the
maximum possible traction reserve. The Haldex coupling, depending on the
difference in rotational speed, infinitely regulates the distribution of the
drive between the front and rear wheels; under extreme conditions, the
**entire drive** is transferred to the rear wheels."

anyway, now that we have established that, i'd be very intersted in your
driving experiences of the haldex.

fwiw, (and i certainly have no interest in getting back into the wrc cars
debate), the toyota wrc car had no centre differential, but a hang-on clutch
(a la haldex), mounted (surprise) at the rear.  not a centre vc.  in fact no
centre differential at all.  check out the "racecar engineering" article on
the "class of 98" wrc cars.  it's all in there. yes, the hang on clutch was
replaced, but only with a fully active setup.

hence also my advice to take it easy on stating that the haldex is not a
hi-tech quattro system...

hth,
dave
'95 rs2
'90 ur-q
'88 mb 2.3-16

-----Original Message-----
From: owner-audi-s-cars@lists.boldfish.com
[mailto:owner-audi-s-cars@lists.boldfish.com]On Behalf Of QSHIPQ@aol.com
Sent: Sunday, 12 September 1999 01:14
To: AUDI S Cars Discussion List
Subject: Re: Haldex and Viscous Couplings


In a message dated 9/10/99 3:23:10 PM Central Daylight Time,
Dave.Eaton@clear.net.nz writes:

> you're misunderstood the effect of a locked clutch between the axles.
once
>  that sucker is locked, the effect is exactly like a generation 1 locker.
>  solid link, and torque can flow front to rear 100%:0 and visa-versa.
>  depending upon grip of course.  examination of the haldex documentation
also
>  makes this clear.

Any differential that is physically joined to another is "capable" of
supporting 100% of engine torque under the right conditions.  This isn't the
accepted practice of defining a "locking" differential.  You can't have the
syncro/audi differential actively or  mechanically control locking beyond
50%
to the rear.

>  certainly edl operating across either axle could limit the torque
transfer
>  but for example, picture the front 2 wheels on ice and the rear on
tarmac.
>  pretty much 100% torque to the rear regardless of edl operating across
the
>  front axle.  only when edl operates across the axles with the torque
>  transfer be limited all the time.

If both front wheels are going for traction on ice, Trg reduces via EDL.  To
rephrase your argument, 100% of available torque goes to the rear.  The
difference is, in a locked center  100% of Trg goes to the rear axle, in the
EDL car (regardless of center diff), it is less, a lot less that 100% of
Trg.

>  > Again, looking at the comparo, I'm convinced that Haldex should take on
>  the
>  > gen I locker locked in position 2.  I'm not enamored with the Haldex,
>  sorry.
>  > It's a step from the torsen, but 180 degrees from the norm.  One major
>  flaw
>  > in the logistics, IMO.  Audi hasn't had big gains in proving btdt wrong
in
>  > the torsen arena.  Better luck here?  I'm not as optimistic as you.
>  Another
>  > 6 years of "proving" everyone wrong, that makes a total of 16.  Even if
>  they
>  > prove to be batting 1000 with the Haldex, that's still less than a .500
>  > batting average.  Quattro advantage indeed.
>
> >> mmm... toyota's performance with a hang-on-clutch in the wrc machine
would
> >> differ about state-of-the-art.  with their haldex copy they were within
a
> >> whisker (500metres) of the world championship last year.