Re: A grand opening in the Diffy-q's

[John Cunningham <johnc@together.net>]

There is a basic misunderstanding going on here - a confusion between spinning
axles and torque.  The explanation that finally made this clear to me was the
following -  hopefully this will help to clarify what Dave has been trying to
say...

Torque is a turning or twisting force.

An open diff equalizes torque.  In the case when one wheel is spinning (one
wheel off the ground, or on ice or whatever), IT EQUALIZES IT TO (sortof) ZERO
AT ALL WHEELS.    0 torque to the wheel off the ground that is spinning, 0
torque to the not spinning wheel with traction.  Equal torque (well, for
practical purposes, none) in both places.  There is very little twisting force
going to either wheel, DESPITE the fact that one wheel is spinning like a
b@stard.

When you realize this, the rest follows...

With a locked diff, and those same wheels, suddenly all the torque (Twisting
Force) is sent through the wheel with traction.  No (again, for practical
purposes) twisting force goes through the free wheel.  That torque then performs
work in the form of launching the car off the jackstand - doh!

Better...?   worse... ?

Dave Eaton wrote:

> i appreciate your civility (lets keep it that way), but really (once again)
> you don't understand the simple mechanics of a diff.  until you do, the fog
> will remain.  perhaps you are misunderstanding what torque is????  you need
> to think through your scenario once again.  what is "torque" without
> tractive force?
>
> once again, an open diff transmits equal torque.  by definition.  a locked
> diff (no speed difference) does not.
>
> to your example, with centre locked and wheel lifted, all torque will move
> to where the tractive force is, in this case to the rear.  100% of it.
> every time.  with the centre unlocked and wheel lift, the torque in the
> system *must* be equalised (because open diffs do that), and the torque will
> go to the spinning wheel (same torque across all open diffs, different shaft
> velocities).
>
> i'm happy to refer you to some reading if you'd like to understand this
> fundamental.  up to you.
>
> dave
> '95 rs2
> '90 ur-q
> '61 mb fintail
>
> -----Original Message-----
>
> Date: Sun, 23 May 1999 10:32:12 EDT
> From: QSHIPQ@aol.com
> Subject: RE:  An grand opening in the Diffy-q's
>
> >bzzzttt.
> >before we go on yaw'ning perhaps we should get the fundamentals all
> sortedout...
> >the generation 1 locker *must* and does shift torque when it is *locked*.
> >(0%-100%-0% torque shift front to rear is certainly possible).
> >however, when all diffs are *open* *no* torque can be shifted.  all torque
> >outputs are equal, and 25% by definition (for awd).
> >you need to think about it some more.  once you understand this fundamental
> >principle, this will help your understanding of this whole issue....
>
> I'll try my darndest to keep this one civil, but really appreciate the
> opening Dave.
>
> Ok, let's take your "understanding" to the next step.  Let's take a hot
> corner on the track, *diffs locked* in my Gen 1 urq.  Lifting the left front
> inside wheel.  How much of the torque is shifted to that wheel dave?  Let's
> *diff unlock*, run open center differential in the same turn, lifting the
> left front inside wheel, how much torque is shifted to that wheel?  Given
> your "understanding" above, why would the gen 1 rally cars run center diffs
> locked?  More understeer:)?  Maybe it would be simpler if you compared a rwd
> open diff to a detroit locker, then work the front to rear on a quattro.
>
> Geez Dave, I think I understand, but that buzzing sound....  Yikes!   In
> deference to "opposite day", I'll just give you the opportunity to correct
> yourself, then we can move on.

--

__________________________________________________________________

John J Cunningham III           Project Leader / Technical Analyst
                                             Country Home Products
johnc@together.net                            (802) 877-1201 X1242
__________________________________________________________________