[s-cars] EDL fails (but my new 22's worked great!)

[Keith Maddock]

Torsen on a 92-95 (non-EDL) car really doesn't buy you much when
you're stuck in deep snow.  Generally here (at least part of ) your
problem is that you have one wheel with nearly zero traction.

For simplicity's sake just consider the rear axle (which is quite
dominant on an 18% grade anyway...)

With an open diff (IE broken locker on 92-95's), the most torque you
can transmit (for any appreciable amount off time) to the wheel with
traction is the same as the wheel without traction.
Zero Traction on one wheel, zero traction on the other wheel: STUCK.

With a torsen (retrofitted 92-95), the most torque you can transmit
(for any appreciable amount off time) to the wheel with traction is 4
times the amount as the wheel without traction.
Zero Traction on one wheel, zero traction on the other wheel: STUCK.

With EDL and an open diff (95.5) , the most torque you can transmit
(for any appreciable amount off time) to the wheel with traction is
the same as the wheel without traction.  However EDL tricks the diff
into seeing a brake application as traction.  So you can get torque on
the "good wheel" up to the lowest value of:
A) max brake torque EDL will apply (or can apply if your brake pad is
on fire from doing this...)
B) 1/2 the engine torque.
C) surface traction available (Mu * Normal Force!)
Zero Traction on one wheel, up to 1/2 engine power on the other wheel:
SOMETIMES STUCK.

With EDL and a torsen, you are nearly golden!  It's the same as above
but the limiatations of torque to the "good wheel" are now the lesser
of :
A) 4x Max brake EDL will (or can) apply
B) 4/5 the engine torque
C) surface traction available (Mu * Normal Force!)
Zero Traction on wheel, up to 4/5 engine power to the other wheel:
RARELY STUCK

With a locker, you are completely golden.  100% of the torque can go
to the good wheel.
Zero Traction on one wheel, up to full engine power on the other wheel:
NEARLY NEVER STUCK

Of course of both rear wheels don't have much traction, you'll be
fairly stuck anyway on a 18 percent grade with 9.5" of snow,
regardless of what rear axle bits you've got...

In this case consider that with the center torsen, your front axle
torque is limited to 4x rear axle total traction.  If rear axle
traction is zero, front axle traction is zero.
STUCK :-) 

Cheers,
Keith





On Tue, 1 Mar 2005 18:27:53 -0500, Taka Mizutani <t44tqtro at gmail.com> wrote:
> I don't agree with that statement at all- Torsens do not work as well
> as lockers in low traction situations, just a lot more friendly
> driving on the street and turning.
> 
> Too bad there is no Audi application for the new Eaton diff-
> electronic locker that is a Torsen LSD when not locked.
> 
> Taka
> 
> On Tue, 01 Mar 2005 13:54:21 -0500, Serge Filanovsky
> <s6serge at verizon.net> wrote:
> > on 3/1/05 10:04 AM, LL - NY at larrycleung at gmail.com wrote:
> >
> > > IMHO, wouldn't have needed the shovel if I had diff lock.
> >
> > Or a torsen rear diff.
> >
> > Serge Filanovsky
> >
> > 95.5 S6 Avant
> >
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