RE: Torsen 201

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

well scott, as i understand it, you're saying that:-

1) no locked-diff quattro can oversteer.  this is certainly not my
experience.  very interested that it is your claim.  i agree that understeer
is more likely.  just as it is with the torsen.  by design with both
technologies.  as i've explained.

2) that torque doesn't follow weight shift.

really, we are still at the basics here scott.  you are failing to
understand/comprehend the following points:

1) the torsen operates as a locked diff does only *until* the bias ratio of
torque difference between the output shafts.  there is no magic here scott.
until the torque bias ratio is reached, the output shafts of the torsen are
effectively locked together.  just like the locked diff.  the effect in
torque distribution dynamics is the same as is directly proportional to
weight distribution and wheelbase and roll characteristics.

2) the only mechanism which the torsen has to proportion torque is the
*same* as the mechanism the locker uses.  it's called front/rear slip. based
only on this factor both the locked cantre diff and the torsen proportion
torque to the rear in a turn.  the only difference is that the torsen starts
the turn with a 50:50 torque ratio while the locker has a ratio which
mirrors the weight distribution of the vehicle at that point.

fwiw, the issue of torque shift in a locked centre quattro is well covered
in jeff daniels book "car suspension at work" in the chapter on 4wd.  also
j.s. freeman has written a paper "awd powertrain models for real-time
simulation" which empirically models just this behaviour on a humvee with an
open and a locked centre differential.  i quote:

"as expected the open differential case model exhibits equal torque
proportioning between the front and rear axles.  while the locked
differential model displays a greater proportion of torque being transmitted
to the front axle at low to moderate tractive loads, while at a higher
tractive loading the torque proportioning becomes greater at the rear axle.
these results are similar to those of koga ("types of 4wd vehicles and their
basic characteristics", 1988), however that study showed much more dramatic
changes in torque proportioning of the locked centre differential case.  the
change in front/rear torque proportioning is due to changes in wheel loading
... without the effects of weight transfer, the tractive torque
proportioning follows the static wheel load proportions.  in koga's study,
the static front wheel loading was proportionally much higher on the front
wheels, than it is for the humvee model in this study."

until you understand these fundamentals scott, further discussion is simply
a waste of time.

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

-----Original Message-----

Date: Thu, 28 Oct 1999 10:02:00 EDT
From: QSHIPQ@aol.com
Subject: RE:  Torsen 201

Dave writes:
>ummmmm, then if you're not talking about the torsen operating at the bias
>ratio, but before then, when the diff is locked, i'm very keen to
understand
>how it differs at this point from the fixed centre diff?
>enquiring minds want to know.....

A couple of chassis dynamic items to ponder dave:  All center diff locked
quattros understeer.  So we reasonably conclude that regardless of chassis,
wheelbase, spring rates, radius, and cf, all  lockers still understeer?  If
indeed torque follows weight shift how could that be?  If a torsen *can*
oversteer, how can *that* be if the devices operate the same?

I think you are missing something.

Scott Justusson