Re: Torsen defined

[Orin Eman <orin@wolfenet.com>]

> >3) neither the locker or the torsen have any knwoledge of slip angles.  they
> >proportion torque based solely on tractive differences between the front and
> >rear axles (front/rear slip).  both allocate torque to the axle with the
> >most traction.
> NO.  A torsen is fooled into allocating torque based on a turning radius.  
> The conclusion is *not* that the torsen is allocating torque to the axle with 
> the most traction.  It's only allocating torque to the axle with the highest 
> resistance to torque.  That *can be* based on either a traction or a slip 
> angle variable.

...agreeing with Scott here, but adding some more.

Firstly, the claim that torque is proportioned solely on tractive
differences is false.  What the torsen sees at the output shafts is:

traction at wheel + I * dw/dt

where I is the moment of inertia of that shaft and everything it's
connected to and dw/dt is the angular acceleration of that shaft.
That I BTW, isn't insignificant.  It's what you are reducing by
putting lighter wheels/tires on a car.

Secondly, another input to the torsen is the relative movement
of the output shafts.  Frictional forces inside the torsen are
always such as to oppose such relative motion, meaning torque
is always transferred to the slower turning output shaft,
_regardless_ of traction available at that shaft.

This means that if a slower moving shaft loses traction,
then the I * dw/dt term becomes significant.  Ie, that shaft
spins up - until the shaft speeds are matched, at which point,
torque is transferred to the shaft with traction..

What Scott presents as slip angle differences translates directly
to shaft speed differences.   The torsen doesn't know why
the shafts are turning at different speeds, it just tries to
make them turn at the same speed.

Orin.