RE: "Real" Quattro Operation

["Dave Eaton" <Dave.Eaton@clear.net.nz>]

ok, quick summary (you don't say what sort of audi you have)....

generation 1 system (manual locked centre diff, open front and manual locked
rear diffs)
unlocked centre: fixed torque across the diff (50% to the front, 50% to the
rear) regardless
locked centre: torque will vary depending upon traction up to 100% to either
end.

generation 2 quattro (torsen centre, open front, manual locked rear diff).
nominally 50% torque f/r, but the torsen limits the torque transfer through
the system to 28%:72% (or thereabouts) by use of internal friction gears.

generation 3 system (torsen centre, open front and rear with edl and esp)
as above but using the individual wheel brakes to limit the torque
distribution across the front and rear differentials.  no manual rear
differential lock.  esp uses engine control to limit torque to the system.

specifically not covered the v8 quattro system (torsen rear, clutch centre,
open front).

hth,
dave
'95 rs2
'90 ur-q
'88 mb 2.3-16

> -----Original Message-----

Date: Fri, 10 Sep 1999 06:34:40 -0600
From: "Clough, Samuel" <SClough@irps.atl.invesco.com>
Subject: "Real" Quattro Operation

My assumptions are:
1.  There is a Torsen differential behind the gearbox that determines that
power split front to rear.  I'm assuming it's set some where around 50/50
although I heard that the new S6 is set 45/55 so maybe it's not, I don't
know.  It would make sense to me to send more power to the rear since the
front tires are doing a lot of work, but when did Audi make sense?
2.  This center Torsen differential balances power on torque.  If more
torque is applied to one end of the car rather than the other (I assume some
variability is allowed) then the differential begins feeding power to the
other end to equalize torque (or if it's not 50/50 to bring it back into an
acceptable ratio).  An increase in torque at one end of the car is presumed
to be wheelspin, so by equalizing torque, it's actually feeding power to the
wheels that grip.
3.  Each end of the car offers a similar setup.  I don't know if Audi uses
Torsen differentials at the front and rear of the car or not, but it does
seem to offer some method of equalizing torque/wheelspin because I've
noticed in the A6 if you feed it throttle when the wheels are turned
sharply, you feel a vibration through the steering wheel until you
straighten out which I've assumed to be the front end thinking that the
outside wheel is actually slipping relative to the inside wheel and then
trying to correct the perceived problem.

Am I on target, or way off?

Samuel W. Clough
INVESCO Retirement Plan Services