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

[QSHIPQ at aol.com]

Well Keith, I'm all for calling a v8 EDL, cuz it's more so than the now atypical ascription of EDL.  In a v8, it's an open diff until slip occurs, then it activates the "electronic differential lock".  An open diff becoming a locked diff via  electronic activation.  Certainly purists would agree that's exactly the definition of EDL.  

As audi has it's own nomenclature for it's quattro systems, it's no surprise that EDL has taken on a new meaning.  In fact, abs based traction control isn't a electronic locking differential in any manner whatsoever, it's just using heat (braking) to absorb torque on the slipping side of an open differential, so that the other drive axle (T1 + T2 - on audis either front or rear, but not over center axle) can support more torque.  That's not locking anything, since the differential is still open by definition.  I'm sure even Keith M would agree with torsen boy on this point.

WRT your techie questions:  1) it's binary, albiet very smooth in doing so.  This was the first attempt by audi to eliminate the interactive switch approach to center differential locking on the flagship quattro.  2)  In normal mode center diff is open, without any bias F/R, in lockup mode, it's "locked" again without bias.  My only sense of it's dynamic interaction is going from a locked to an abs type stop, where the delay of the unlock is tad a bit behind the 8-ball.

IMO the audi v8 auto uses the best of the awd differentials available, electronically locked center with torsen rear.  This gives all the advantages of a locker center, with all the abs advantages of a torsen center.  Having driven just about all the combinations in the Audi lineup, there is no question in my mind that the v8 has the best quattro advantage:  portly weight, seemless electronic center locker, torsen rear, abs defeat, a svelty 32v v8 w/ flat TQ/HP curve, and all the correct external bells and whistles (front washer wipe, F/R fogs, great suspension).  The level of competency this machine exuded, I have not seen matched in my 24 years of quattro exposure (including 13 years of direct ownership)in clicking off winter mired miles.  It may be an expensive driveline audi ditched in favor of simpler and cheaper, but it has few equals in real world driving.

I understand too that scoobie and Mitsu want to lock up that front diff.  With a low lock front VC, you might gain a slight advantage in absolute tractive terms, but there are also chassis dynamic issues and driving style that would dictate this to be more toy than 'advantage'.  Certainly we can look at Audisports own use of the 20%VC in the 80's WRC efforts and see that many a driver either wanted it open or locked (usually open tho).  Finding documentation of the 20% VC in WRC is just about as common as finding a WRC torsen.  What audis don't need is any more understeer.  Also, locking up front diffs in awd cars tend to eat clutches at a much higher rate.

Scott J, aka Torsen Boy


In a message dated 12/27/2004 12:56:40 PM Eastern Standard Time, Keith Maddock <keith.maddock at gmail.com> writes:

>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
>