Tshift

[QSHIPQ <QSHIPQ@aol.com>]

Dave E. writes:
>thanks!
>btw, it is still not accepted by me that you can get t(shist)=t(max) by
>a torsen without losing traction as you describe.  i simply cannot see
>how this can possibly occur.

Put your car on gravel road, narrow grippy M&S tires.  Get the thing sideways.
You didn't lift a wheel, and the forces of gravity in relation to slip angle
still apply.  By your own argument you have to agree that you have a Tshift
max will occur.  So, by extension, your same argument is that cf HAS to be
low.  Ok, 'cept I've btdt on a dry track 110degree right, WOT,  no wheel lift.

>central to this point is whether the torsen uses *rotational* shaft
>speed differences as the determinant of the torque bias to apply, or
>whether it uses forces *from* the driveshafts *into* the diff to do this
>(ie. effective traction, or torque reaction).  I am convinced that it is
>the later.
>it is called a "torque sensing" differential after all.
>i am sure this is the basis of your misunderstanding.

To the Center Diff, what's the difference Dave?  What "other" forces are
there?   In a Center diff that can be traction OR slip angle, by definition of
both.  They ultimately tell the center torsen the same thing.  The torsen is a
dumb device, it doesn't know the difference between the two.  What's the
difference between a Center and a fwd/rwd?  Slip Angle relative to the drive
wheels is a constant in the fwd/rwd, a variable in the Center.

Try looking at it this way.  Slip Angle in fwd/rwd relative to the torsen is a
constant.  Slip Angle relative to the opposing wheels is irrelevent to the
operation of the Torsen.  A Center Torsen, the Slip Angle of the rear tires is
critical to how f/r torque is distributed.  And the Slip Angle of the front
tires in relation to the rears is as well.  So, with all tires on the ground,
ONLY if your slip angles are the SAME in the front and the rear, will a Torsen
center behave as an absolute traction device.  OR you lift a wheel, then
torsen operates as a traction device, however, slip angle is still an issue,
just a smaller problem.  Opposing that argument, lifting a wheel on snow is
almost impossible, so slip angle and relative slip angle becomes the problem
to the definition of torque/traction to the Torsen Center.

As you well pointed out, wheel lift creates an absolute traction issue.
Torsen is a very effective absolute traction device.   No wheel lift, on the
other hand, doesn't necessarily create a traction problem.  The key to
understanding this whole issue is how Slip Angle is percieved by the torsen.  
  

HTH

Scott Justusson
QSHIPQ@aol.com