Re: Torsen theory for Gary

["Eric Renneisen" <renneie@hlthsrc.com>]

Orin Eman wrote:
> True.  Since this hasn't been quoted yet, here is an extract 
> from the infamous SAE 885140:
> 
> [40m radius turn, acceleration of 4 m/s^2, high-grip (uG 
> approx 0.9)]
> 
> "...the front wheels follow a wider radius than the rear 
> wheels on the circular course, so that 0.2% of forced slip 
> occurs _between_ the two axles, which reduces the wheel slip 
> under traction at the front wheels, and reduces the slip at 
> the rear wheels.  This results in the tractive forces being 
> redistributed towards the rear wheels, so that the tractive 
> force distribution is 38/62%.  The extent of this 
> redistribution decreases with increasing cornering radii and 
> road speeds. With small cornering radii and low speeds the 
> extent of torque redistribution can increase to the torque 
> split limit of 25/75%. [Orin: that shudder from the rear you 
> feel in parking lot turns.] On a high grip surface, the 
> torque limit split is reached at a radius of about 15 
> meters."

To borrow a line from Scoobie Doo, rut-roh! It seems we have a 
_major_ inconsistency here. I've suspected this ever since 
reading the hearsay about the above document, and now that 
Orin's provided the direct quote my suspicions are confirmed. 

The above makes you think that as a Torsen center car is 
turning, it gradually and progressively allocates more torque 
to the rear, until at some point (slow, tight turn) it reaches 
the max torque split.

Now take a look at section 5.2 of Stan the Man's paper at:
http://www.mindspring.com/~audidudi/Torsen.htm
"A torque division between drive axles at the bias ratio is a 
precondition for differentiation under all circumstances of 
operation."

According to Stan, if the front and rear axles are spinning 
at different rates then you are already _at_the_bias_ratio_. 
To put it another way, if a Torsen diff is differentiating, 
then the max torque will be sent to the slower driveshaft.

Either I'm missing something, or we've got a big problem with 
two of the primary sources of information on this topic. Which 
do we believe?

Eric Renneisen
'90 CQ 20V  -  my 'racing-iron'  ;^)
Chattanooga, TN