RE: torsens & 'torque split'

["Lawson, Dave" <dlawson@ball.com>]

>Orin writes:
>>
>In summary, open diff means 50/50 torque split at the output,
>locked diff means the split varies between 100/0 and 0/100
>at the output.
>>

>I believe this statement is backwards, an open diff means 100/0
>and 0/100. And a locked diff is set at 50/50, because both outputs 
>are now connected as a unit and they both rotate at the same speed.

 glen writes:
>
>  Torque and 'torque split' are not related to the speed or relative
> speeds of the two shafts with an open or a locked diff. The 'torque
> split' is purely a function
> of the relative counterforce applied to each axle and this is a
> function of the relative
> traction or lack of traction available at the two road/tire interfaces
> on the axle
> in question. Equal traction = equal torque split. Zero traction at one
> wheel = zero
> total torque and zero forward vehicle acceleration/motion with an open
> diff. 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.
>
>  
I thought about this last night and pretty much came to the same
conclusion, Orins example
of 50/50 with an open diff was based on equal 'good' traction condition
for the wheels in question 
and my 100/0 or 0/100 was based on a 1 wheel slip condition. And it
stays that way, that is, 
once that 1 wheel starts to spin it will continue to spin using 100% of
the applied torque. 

Now for the locked diff, both output shafts are 'locked  together' and
will rotate at the same speed.
I think we agree here. So in the equal 'good' traction condition, it
produces the same 50/50 torque split
as the open diff. In our Gen I quattro system, this means that each tire
is applying 25% of 
the engine outptut torque by turning that tire on the ground, with the
center diff being either 
an open or locked. And I think we agree that in a very low 'poor'
traction condition, the engine can produce
enough torque to overcome the available friction between the tire and
the ground, causing wheel spin, 
and with the center diff locked, 1 front wheel and 1 rear wheel will
each be spinning and our quattro
will stand still. I say that in this case with the 2 spinning wheels,
the torque split is 50/50. Even though
they are spinning, each wheel is still getting torque applied to it to
keep it spinning and exceeding the
available traction the ground is providing.

Now for the period in between having equal 'good' traction conditions to
the time we very low 'poor' traction 
conditions. Orin, Steve, glen and others believe with a locked center
diff the torque split varies between 
100/0 and 0/100 with 100% of the torque being applied to the wheel with
the 'better' traction. I disagree with 
this (look ma no buzzers). With the locked center diff there is no
differential, that is, both output shafts rotate
at the same speed, thereby making the wheels on the two axles rotate at
the same speed. Now one of the 
wheels starts to spin because the torque applied to that wheel exceeds
its traction condition. The remaining 
wheel which still has traction is still receiving the same amount torque
that it was previously when both wheels
had the same equal 'good' traction. The wheel with 'poor' traction is
using it's torque to keep it spinning and the 
wheel 'good' traction is using it's torque to propel the vehicle forward
and maintain its velocity. And both wheels 
are rotating at the same speed. Now with the same net torque being
applied, if the wheel with 'good' traction 
were to suddenly have 'poor' traction, the torque applied exceeds the
traction condition for both wheels and
they both spin at the same speed. In fact they will accelerate together.

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.

>
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.

>
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