Re: 4th gen. quattro

[Eliot Lim <eliot@u.washington.edu>]

On Thu, 14 Dec 1995, Peter Grul wrote:

> 	The A4 quattro is advertised as having the "fourth generation quattro 
> system." Here are my guesses on what the four gens. are:
> 
> 3rd:  1990 - 1991	   front:	free
>       V8		   center:	TORSEN
> 			   rear:	TORSEN

this setup is only for the 5 speed v8 (1991 model only)

slush v8's had rear torsens and computer controlled multiplate clutches
in the center.

that center diff setup in the slush v8 is also used in slush 100Qs and
presumably in slush a4q's.  the reason for doing this is because with
the slush box you have a good ready source of hydraulic pressure and
this can be controlled far more precisely and tuned.
 
> 4th:  1996 -               front:	free
>       all models	   center:	TORSEN
>                            rear:	manually lockable with
>                                         auto disengage above 15mph/25kmh
>                                         and EDL (a true autolock feature?
> 					or some kind of "brake the wheel
> 					that's spinning" thing? the owner's
> 					was confusing - possibly EDL means
> 					something different for FWD than it
> 					does for quattro?)

i believe that the a4q has what the 2wd world knows as traction
control (EDL=electronic diff lock) on both front and rear and does not
have the solid rear lock (doesn't need it anyway).  operation is
of the upmost simplicity.  inverse abs opertion.  a spinning wheel
is braked.  ta da.  

the a8 has the same setup for front and rear, and being a slush, will
have the hydraulic multiplate clutch setup for the center.

this means that the a4q/a8 will need to lose drive to ALL 4 WHEELS
before it gets stuck, and this is unprecedented in quattro history.

this appears to be the future of the quattro system.

> Anyone have any clue about why Audi didn't 
> stick with the V8's double TORSEN setup? Seems like the best to me, although 
> it takes all the fun out of manually locking the diffs.

torsen diffs are expensive.  my best guess at this point is that the v8
had the worst weight distribution and thus needed a torsen in the rear
more than any of the other models.

EDL offers the most bang for the buck.. it's nothing more than additional
electronics (and we know how cheap those are) added to the ABS control
unit.  and i'll bet that it was carried over largely unchanged from
the vr6 volkswagens.

eliot