[V8] front diff( EDL or just plain open?0

[Keith Maddock]

Allan wrote:
> So the real
> question was suppossed to be why have a torsen rear and an open center. you
> have also answerd this. It is a type of EDL in that it Electronicly Locks
> the Diff. via the abs sensors . . Now  That I know that, I now know why mine
> is malfunctioning. My abs light is on and i have codes for all 4 abs sensors
> as well as the 12v supply. Thanks guys Allan

Thanks to Torsen-boy for pointing my eyes at this thread.

Don't shortchange the V8 Auto center LSD by calling it a type of EDL. 
There is a big difference between Audi's EDL (which is not unique to
Audi, there application was probably developed by Bosch) which uses
the ABS sensors to determine when to apply brakes (using the ABS unit
(modified for this extra task)  to the spinning side..  As Steve
noted, this can never transfer torque - just allow up to 50% of the
engine's torque to go the non-spinning side.   Using EDL across a
center diff is actually used by some of Audi's competitors, including
Mercedes (most current 4motion setups), BMW (most current AWD setups
except newer X-Drive), & Cadillac (current STS, SRV, some Escalades)

The V8 Auto center LSD would best be called an eLSD - which uses ABS
sensors to just provide information to another computer which
determines when to lockup the clutch(es?) on the planetary open diff. 
This setup does have the capability to transfer torque.  Depending on
the strength of the clutch, it could transfer 100% of the engine's
torque to the front or rear - where the torque actually goes is
dependent on the relative surface friction front vs. rear.    (you
would have to actually have zero front/rear traction for the
rear/front to get 100% torque)

This is still one of the better center diff technologies available -
this concept (planetary center with electronically controlled lockup
clutch)  is used on a lot of modern cars/trucks/SUV's - Cayenne,
Toureg, STi, & Evo8-MR included.  I have read that the Audi versions
of  the Cayenne/Toureg SUV's will use a different center diff, I'm not
sure if that means the same thing minus low-range, or if they will
actually put a Torsen in there...

Curiousity questions for the Techies out there:

1) Has it ever been established if the V8 Auto center LSD will add
proportional amounts of lock ot the clutches (ie 25%, 50%, 75%, 100%),
or if it just operates binarily only in fully locked or fully unlocked
?

2) Since the V8 Auto center diff is a planetary type unit, do we know
if they put a static rear or front torque bias on it ?

Cheers,
Keith
95.5 S6 Avant mit EDL and soon mit V8RearTorsen