Tshift comparos

[QSHIPQ <QSHIPQ@aol.com>]

Steve B writes:
>In my understanding VC stands for viscous coupled ... I do not believe that
>there is ever a direct connection between the input and output of a VC ...
>the coupling fluid tends to heat up as the differential speed increases and
>the fluid is designed such that it gets more viscous as the temperature
>increases.  It sounds like you are talking about a magnetically coupled
>locking coupling in your post though, not a VC.  If a magnetically coupled
>device were to be used, it would have to be controlled in some way based on
>input from wheel speed sensors.  I am by no means an expert on all of the
>various means that have been called to the task for creating an AWD vehicle,
>but I've never heard of it being used in anything other than automatic
>tranny torque converters.  

Specifically the v8 early automatics.  Bottom line is this in terms of
acceleration and torque:  Both use either the front or rear drive axles as the
PRIMARY drive axles.  Slip, rotation or traction transfers torque to the
secondary drive axles.  In this respect they are *free*, though all rotational
differences are interpreted as a reason to shift torque.  What differentiates
a VC, magnet, or clutch pack from the torsen is the primary drive axles are on
one or the other end of the car, not both, as in a torsen.  So, inherent
chassis dynamics can stay the same.  A simple and more successful effort than
the torsens, and can be predictable as well.  

Since we haven't really mastered torque transfer on accel, I'm hardly going to
address the differences on braking. Not relevent yet.
 
>As much as open diffs and torsens have been called a simple minded means to
>keep us going in the snow, my impression of the VC AWD systems is that it is
>the same animal if not more so. 

Not sure that statement is clear.  I read that the VC AWD system is the same
animal as a torsen, or more so.  IOW, a VC has distinct advantages over a
torsen in terms of chassis dynamics in a turn.  If that is the read, I totally
agree.  And can handle more torque than a torsen as well.  And is sealed, and
is a lifetime part.  Nothing touches.  Simple and dumb, beats dumb and dumber
(tm).

VC do require rotational differences to lock.  Some torsen proponents would
like us to believe that is a bad thing.  Retaining the inherent chassis
character in a turn, makes a VC more of a good thing than any rotational
shortcomings.  We could certainly extend the argument to say that the torsen
is quicker to react to slip and relative slip than a VC.  Good or bad?

I really believe that the argument is in terms of chassis dynamics in a turn.
There a torsen has many faults, the least of which is slip angle.  The
confusion this thread has created centers here.  This is the first time Dave
E. has admitted that a torsen can be fooled in a turn.  Given that, it's a
'when', not an 'if', in terms of chassis dynamics in a turn.  It's inherent in
the design of every audi chassis with a torsen.  If a torsen can be fooled, so
can the chassis it's attached to.  All you need are the right set of
variables.

Scott Justusson