RE: haldex

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

no scott, you're misunderstanding the way that the haldex operates.  the
haldex can send 100% torque to the rear.  it must, as long as the clutch is
locked (i.e. solid connection).  the only way to limit this is to use edl
across the haldex to brake *both* wheels on an axle which has little or no
traction.  otherwise, you have a fixed connection (clutch fully locked) and
100-0-100 torque possibility.  just like the generation 1 quattro.

a look at the haldex literature clearly shows this to be the case ("torque
transfer characteristics" on page 6, including a graph of torque f/r
output).  it also shows the range locking/torque characteristics which are
possible.

as collaboration, all road tests i have read (including the recent one on
the new tts quattro and the s3 in "car") have commented specifically on the
advent of lift off oversteer to the performance equation.  "evo", "autocar"
ditto.

what the haldex can do of course, is to *vary* the locking rates depending
on the delta speed difference front and rear.  locking rates under straight
line acceleration (traction premium) can vary over cornering (stability
premium) can vary over braking (traction).  all by the computer controlling
the clutch.  it gives the designer a much greater repertoire to play with
than a purely mechanical device.

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

> -----Original Message-----
------------------------------
>
> Date: Thu, 9 Sep 1999 20:49:20 EDT
> From: QSHIPQ@aol.com
> Subject: What is quattro, what is "haldex"
>
> Dave E writes:
> >what interests me in the design is the ability of the processor to change
> >the handling dynamics.  i expect, at this premature time, to find the s3
and
> >ttq quite differet handling animals...
>
> not totally with you here Dave.  If Haldex can only send a maximum of
total
> Trg of 50% to the rear wheels, both should handle as the press has
reviewed.
> A slight hint of understeer all the time.  Why is that?  Because the
ability
> to induce LTO is limited by the haldex locking (specifically the delay in
> unlocking to prevent LTO), and the ability to induce on throttle oversteer
is
> limited by the interference of the EDL on the front drive axles (total Trg
is
> reduced to keep handling at slight understeer).  Without tuning (I argue
even
> with tuning of the Haldex "CAN") you can equalize one chassis dynamics to
> another (something torsen couldn't really do) with the same hardware in
the
> system.  But that only means that when you own an S3 and a TT you can
drive
> them the same.  Where too, does the Haldex leave the LFQB (left foot
quattro
> brakers)?  Quite in the "lurch" might be an understatement.  It's one
thing
> to try  controlling a variable torque torsen with LFQB, it's another to
> control a fwd>awd switch all together.