Re: real quattro...more debate!

["Robert P. Wunderlich, D.P.M." <robert@Wunderlich.com>]

Here is a nice torsen vs. haldex piece (from another list, courtesy of Doug
Carter at VWVortex):
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Interesting ideas concerning the Quattro vs. Haldex systems, but there
are some other things to consider. Yes, the sizes of the systems
dictates how and where they are used, but that, through different
engineering can be easily adjusted.

The Haldex/4-motion system is an electronically controlled system, which
means that you can control it with an ECU (similar to the Tiptronic). VW
engineers have informed us that you can program this diff to completely
control the application of power to the wheels. This does mean that you
can make a Haldex system completely rear-wheel drive. The 18-year old
Quattro system has been updated and greatly improved over the years, but
it is still mechanically controlled for power application. Only the
newest of Quattro systems contain the Electronic Differential Locking
system, and even that is just a fancy term for ABS. The Quattro can
still mechanically only apply up to 66% of the power to an individual wheel.

The European press is in love with the Haldex system. An A3 with Haldex
and an A4 with Quattro were lined up in sand, and under power
application, the A3 left the A4 mired in the sand. The Quattro system
responds slower to power transition than does Quattro.


Consider the weight savings in Haldex over Quattro, plus these other
benefits:

* It guarantees directionally stable acceleration and neutral to
slightly understeering behavior in normal driving, but still permits a
degree of oversteer if excessive power is applied.

* It guarantees directionally stable acceleration and neutral to
slightly understeering behavior in normal driving, but still permits a
degree of oversteer if excessive power is applied.

* Its behavior when coasting is consistent, it does not tend to lock up
when maneuvering, it copes with different wheel and tire circumferences
(for instance the temporary spare wheel) and it enables the car to be
towed away with the front axle raised.
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Let the debate continue...

Bob W.


-----Original Message-----
From: Levis-Fithian, Jeff E <LevisJE@LOUISVILLE.STORTEK.COM>
To: 'Dave.Eaton@clear.net.nz' <Dave.Eaton@clear.net.nz>; 'Quattro-List'
<quattro@audifans.com>
Date: Thursday, September 09, 1999 11:39 AM
Subject: RE: real quattro


>So if the Haldex system is computer controlled, does that mean with the
>right computer that you could control the front/rear torque split?  It sure
>would be fun to have a 225hp TT that is primarily rear wheel drive, and
then
>send some torque to the front wheels when necessary, a la Porsche, Lambo,
>etc...  In effect, the opposite of what it is now.
>-Jeff
>95 A6Q
>
>------------------------------
>
>Date: Thu, 9 Sep 1999 11:13:40 +1200
>From: "Dave Eaton" <Dave.Eaton@clear.net.nz>
>Subject: RE: real quattro
>
>yes this is correct - the haldex is basically a "hang-on clutch".
>
>but in defence of the unit, there are a number of very ruputable
>manufacturers who use very similar technology.  the big advantage of the
>haldex is that it is computer controlled which means that the circumstances
>governing activation, duration of engagement etc are decided by computer,
>rather than my simple mechanics as in a torsen or a vc.
>
>hth,
>dave
>'95 rs2
>'90 ur-q
>'88 mb 2.3-16
>