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RE: Haldex Research results
A couple of points that Doug seemed to have missed Bob:
>>Here is a nice torsen vs. haldex piece (from another list, courtesy of Doug
>Carter at VWVortex):
>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.
Not my understanding of Haldex's own literature on the synchro application.
Haldex Sweden speaks of the Haldex system as a better VC, meaning, you have a
primary set of drive wheels (the quattro/synchro systems are fwd>haldex>awd,
most past applications are rwd>haldex>awd). The only way I see making the
Haldex completely rwd is to eliminate the front axles from the driveline
(like disconnecting the rear driveshaft on a locked gen I diff to do a dyno
test, making the car "completely fwd." This statement seems to be a figure
of speech only, sorry). It "controls" torque to the front axles by enabling
EDL there, which isn't controlling torque per say, it's decreasing Total
engine Trg with abs traction control.
>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.
Not totally a truism here either. The Haldex uses the same EDL on the FRONT
axles, and has NO EDL on the rear axles in the current trim. EDL is not
"just a fancy term for ABS", it could be said that it's a fancy term for
Traction Control on an open diff. Given the Haldex system uses it (albeit on
the front drive wheels instead of the torsen EDL rear), not sure Doug should
be making this statement at all.
>The Quattro can
>still mechanically only apply up to 66% of the power to an individual wheel.
That would be 75% or 78% (depending on which audi torsen material you read).
>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.
Interesting test. Given the operating perameters of the Haldex (EDL front
open diff, open rear, haldex center vs EDL rear open diff, open front, torsen
center), I might have bet on the locked Gen I quattro for this test
>Consider the weight savings in Haldex over Quattro, plus these otherbenefits:
>* 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.
If, per Haldex, we are speaking of an electronic variable torque clutch VC
4wd (note Haldex itself calls Haldex 4wd NOT awd or quattro), based on a fwd
primary drive wheels, the most power that can go to the rear is up to 50% of
total engine torque (100% locked), then if the fronts still slip, EDL engages
and Trg is reduced. Oversteering a 50/50 diff seems rather an interesting
statement on a understeering fwd>awd car.
>* 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.-------------------------------------
A couple thoughts come to mind. First off, the coupling doesn't immediately
disable on throttle lift or coast (to avoid LTO). It does disable during ABS
activation (sounds like an interesting turn in the snow or on the track for
those who are left foot brakers). Since the computer is dead on shut off,
the front axles are the drive axles, the rear is open (uncoupled) at rest.
Since it's electronically locked, not slip locked (ala VC), tow away boys.
My own thinking is this, given the primary drive axles as fwd might limit
this applications' advantages. I think all enthusiasts here might be more
optimistic, if the Haldex was primary rwd>haldex>awd. Even better, how 'bout
rwd>haldex>awd with true 4 wheel EDL crossing the center diff? Right now, I
see some problems for those looking to do performance driving, exulting the
"quattro advantage". It's been redefined boys, in a big way.
Please do correct any of my misunderstandings folks. After hours of
researching this, my optimism wanes on the direction "quattro" is taking.
Haldex per Haldex is 4wd... An "active and variable" VC would be a better
My .02 arbitraged thru the peso