RE: torsen = torque sensing !=rotation sensing

[David Eaton <david.eaton@computerland.co.nz>]

scott,

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.

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.

i quote from the recently tabled paper  - uncut and the author is
anonymous folks ;-)...

"When the car goes around a corner and one wheel needs to go faster, the
*force* [ie. torque reaction, oops, i've just cut the quote] from the
faster outer wheel goes *into* the differential through the output gear.
 Now we have a situation where a force is being applied from a worm gear
to a ring gear.  Relative motion between these two gears is allowed when
the force is in this direction."

apply this thinking to your model scott and it changes, a lot.

btw, just in case it needs to be stated in this public forum, i welcome
this discussion as it helps us all understand our cars.  no ill-feelings
or heat from this kiwi bloke.  my (longstanding) invite to scott, jeff
and others for a drive in a station wagon shopping basket in godzone is
still on the table....

dave
'95 rs2
'90 ur-q


>-----Original Message-----
>------------------------------
>
>Date: Thu, 5 Mar 1998 09:38:32 EST
>From: QSHIPQ <QSHIPQ@aol.com>
>Subject: KISTT
>
>Dave E.:
>Excellent report on the differences between locked and torsen centers thru a
>turn with wheel lift.  Great archive material.  For ABSOLUTE traction, torsen
>is proven and continues to be better than a locked center, per your post, and
>mine.  
>
>One point in relation to that .8 statistic to consider....
>Now that you've gone through that exercise.  Let's Keep It Simpler Than That.
>You've assumed cf a constant front to rear, and WOT (Trg = max, T1 + T2 =
>Trg).  I can show that same Torsen to Tshift-max 170lb/ft with NO WHEEL LIFT
>at all, forward back, AND back forward in the same turn, and a locker to
>Tshift = 0.  Ok, let's forget traction for a minute and concentrate on
>chassis
>dynamics for just a minute.  Thinking on that wheel lift issue, what does
>that
>exactly say about who might be cornering harder, you with wheel lift, or me
>with none?  
>
>Scott Justusson
>QSHIPQ@aol.com
>
>------------------------------
>
>Date: Thu, 5 Mar 1998 10:00:16 EST
>From: QSHIPQ <QSHIPQ@aol.com>
>Subject: *T*max
>
>Torsens are great absolute traction devices.  I would put one in ANY fwd/rwd
>that has high horse power.  Where I would argue it doesn't do so well, is
>before wheel lift.  There, by physics alone, we can have Tshift=max.  When
>you
>think of that in terms of traction, you have maximum traction while that
>Tshift occurs.  OR maximum Trg with a low traction situation.  That can get
>ugly.   When a wheel lift happens, Torsen center is just like Torsen in a
>straight line, it becomes a great absolute traction device.  I would expect
>it
>to be so, because that is exactly it's design.  
>
>So, enjoy that WOT turn.  Remember, per Dave E's and my own posts, Center
>Torsens are absolute traction devices.  NOTHING more.  In a Center Torsen
>diff, WOT, constant cf, you have a lot of torque that slides fore and aft
>before you lift a wheel.  Never thought of 'advocating' wheel lift before...
>
>I also fully accept the presentation that 44 chassis cars are more
>noticeable.
>Why?  Because you have more weight, a worse f/r dist, a longer wheelbase, and
>softer effective spring rates.  This all makes for a larger COG "egg".  And
>slower reactions to any given torque shift in terms of chasis dynamics.
>Unfortunately for all of us, that doesn't change the physics, just puts one's
>bite at a lower set of variables.
>
>The variables are chassis dynamics, Slip Angle (and track), Trg, and cf.
>Since a small shift in one, creates a large effect on the other, this isn't a
>chartable or predictable event for the matrix of the four.  So, the "Don't
>get
>bitten" advice, however obsurd, right now is the only answer.  Ironic and
>somewhat uncomfortable for this driver, I must admit.
>
>