RE: torsens & 'torque split'

[glen powell <gpowell@acacianet.com>]

>Now for glens comment:
>>
>>Equal traction = equal torque split. Zero traction at one wheel = zero
>>total torque and zero forward vehicle acceleration/motion with an open
>>diff.
>>
>Well,  zero traction at one wheel != zero total torque, it equals 100%
>total torque being applied to that wheel
>which causes it to spin and accelerate. Just because a wheel has
>exceeded its current traction condition, 
>doesn't mean that the torque applied to that wheel disappears.

Actually, yes it does - in a zero traction scenario as I described above. Consider again, 
open diff, zero traction at one wheel = zero counteractive force at that wheel = zero torque
at that wheel. There can be no torque without counteractive force and no counteractive force 
exists if there is no traction. (for the sake of simplicity I have ignored the effects of friction
in the bearings, seals, brakes, etc.) This easily could slide into a discussion of terms and
semantics.....

>>Zero traction at one wheel = 0/100 'torque split' with a locked diff
>>with the 100% going to the wheel 
>>with traction - exactly what you want if you want the vehicle to
>>accelerate and move.
>>
>The car will accelerate because with a locked diff, 50% of the torque is
>going to a wheel with better traction, 
>instead of 100% of the torqe going to a wheel with the least traction.

Actually, no. Consider again, locked diff, zero traction at one wheel = zero counteractive 
force = zero torque at the wheel with zero traction. . There can be no torque without 
counteractive force and no counteractive force exists if there is no traction. The wheel
with the traction receives 100% of the torque - exactly what you want in this situation.
The car accelerates and 100% of the torque is applied to the wheel with the traction and
0% to the wheel with zero traction. The car can accelerate at the maximum rate that can
be supported by the traction of the one tire with traction. If both tires had (equally good)
traction then the car could accelerate at a maximum of 2x what could be supported by the
traction of one tire. With an open diff no torque is applied to either wheel when one wheel has
no traction, no counteractive force, no torque - hence no motion - you're stuck!

>>Torque and 'torque split' are not related to the speed or relative
>>speeds of the two shafts with an open or a locked diff. 
>>
>In our quattros, torque is needed to keep our wheels rotating at a
>constant speed. To keep our wheels 
>turning at a constant speed we need to apply enough torque to offset the
>frictional forces of our drivetrain 
>and a rolling tire. If our net torque is zero, the wheel stays at a
>constant speed. If net torque is positive, 
>the tire/wheel accelerates and if net torque is negative the tire/wheel
>slows down.

>Dave Lawson  

Agreed. I elected to ignore the effects of friction to simplify an understanding
of what is happening that actually moves the car in various scenarios. I believe
that it is more valuable to consider the real-world effects of getting the car
moving without the added complication of considering friction. Perhaps the
friction component is more important to consider in torsen scenarios Vs
open diff/locked diff scenarios?

Just to belabor a point and to make it clear to all:

POS 0 - both center and rear diffs open - one wheel with zero traction and you are stuck [1WD]
POS 1 - center diff only locked - one front wheel + one rear wheel with zero traction and you are stuck [2WD]
POS 2 - both center and rear diffs locked - one front wheel and both rear wheels with zero traction and you are stuck [3WD]

-glen

>Dave Lawson