Subject: Re: Quattro Differentials?

[C1J1Miller@aol.com]

Luis Marques wrote:
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T*rsens simply don't lock.  They actively distribute torque up to a

~20/80% limit.  This means that the wheel with more traction gets up to

fourt times the power as the wheel with less traction, but if that wheel

has no traction, zero times four is still zero ;)  Under normal driving

conditions, ALL quattros send 1/4 of the power to each wheel.
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Lets be a little more accurate:  pre-electronic differential lock (EDL) cars,
which were phased in circa '95?, back to '88, t*rsen's were used in center
differential applications, except for all V8s, which have rear T*rsen diffs,
or the '91 V8 manual, which used a T*rsen center _and_ rear differential.
Front differentials are open in all of the cars.  (EDL uses the anti-lock
brake function to slow a spinning wheel until it regains traction.)

A center T*rsen shifts torque between the front and rear axle, only.  The rear
differential is normally open, but can be locked with an electric switch,
which which is designed to unlock at speeds over 15 mph.

If one front wheel loses traction, the open front diff shifts power to that
wheel, causing it to spin.  If both front lose traction, one side will spin.
The t*rsen center will shift torque towards the rear diff/axle until either
traction up front is restored (less torque should help stop wheel spin/slip),
or the maximum shift of 78% rear is reached.  The car will still put 78% of
the engine torque to the rear axle; the other 22% goes to keep the front
spinning faster and faster...

Same for the opposite scenario; if a rear wheel slips, it will do the same,
transfering power to the front.  This is not what pre-t*rsen cars did; they
would shift the power to the one wheel that slips; technically, you'd stay
still if one wheel was on wet ice.  Even open diffs transfer a little power to
the other wheels, however.

Now, if you drove a T*rsen center car where both driver's side or both
passenger's side wheels had no traction, you'd get the same results as a pre-
T*rsen car.  In both cases, locking the rear diff will get you moving again.
Now, if both rears and one front lose traction, you're in trouble.  Usually
you slow down, or get onto ground with better traction, or both.

Under normal driving conditions, the T*rsen will split torque 50-50 between
front and rear axles; however, I've been told that open diffs typically send
more torque to one side than the other, so you're mostly 2 wheel drive, which
is double what most front or rear wheel drive cars give you...  Isn't that
what torque steer is, when the open diff sends power to mostly one wheel
(especially with unequal length front driveshafts...)

Before the debate about locking versus T*rsen diffs (and others) starts, there
was a fairly heated debate on the list for about the last year, involving
t*rsen operation, whether they were used in racing or not, and whether they
cause rapid understeer/oversteer/understeer changes during extreme cornering
(or cornering in low traction conditions).  That debate has been sent off list
and is extensive in the archives; start there first.  That's why T*rsen is
spelled with a * versus an o; I believe Dan's put up a filter to limit WOB.
Hopefully this wasn't such in your eyes...

Clear as a night lit by audi's DOT headlights?
Chris Miller,Windham NH, c1j1miller@aol.com
http://members.aol.com/c1j1miller/index.html