Re: Marketing 101 (a vc is not a vc is not a vc)

[Dave Eaton <dave.eaton@minedu.govt.nz>]

further on scott's attempt to win hearts and minds...

a vc (aka fergusson coupling) is an all or nothing device.  it will apportion
0% or 100% when locked.  it does *not* apportion torque split as you assert.

a plain vc, (eg. as used by some synchro implementations, and some volvo
implementations) is simply as described above.  no drive to the other axle,
until slippage occurs, then the other axle is locked up.

the "vc" you blithely describe is a vc *coupled* to a split diff (usually
epicyclic) which maintains a *static* torque split.  until traction loss (or
slip) occurs.  then torque is applied to where it (thinks) it is needed.  this
rate of locking is *progressive*, although the rate is dependent upon
implementation.

you seem very pedantic wrt the operation of the torsen, and then blithely tell
everyone that the vc locks.  o-o-o or u-u-u you say.  nope.

vc's certainly are designed to *progressively* lock, but the rate of the
locking is a design peramater.  torque distribution will occur during the
locking process.  this locking time will occur *after* sufficient slip has been
detected on either axle.  the delay and the progressive locking are design
parameters.  not, as you suggest, part of a "generic" diff.

a fast locking vc will allow torque re-distribution for a shorter period of
time, and then will lock at the ratio designed into the diff.

so, in summary, a vc is quite capable of going u-o-u in a turn, or the other
other way, until the %slip is enough to heat the fluid and lock the sucker. 

you will also accept that the vc requires work-arounds to work with abs. 
right?  where the torsen doesn't.

once again, you have the audi torsen bias ratio wrong.  it's 25/75 to 75/25,
not 22/78 as you suggest.  this is the most common audi implementation, but
then you don't have any torsen cars, so you'd probably not know that.

scott, sometimes marketing to you is when the rubber meets the sky.  you're not
marketing anything are you?

dave 
'95 rs2 
'90 ur-q 
>------------------------------ > 
>Date: Mon, 4 May 1998 20:21:50 EDT 
>From: QSHIPQ <QSHIPQ@aol.com> 
> 
>AND, ABS works (this is in deference to the old lockers, which disabled the
>abs).  To jump and say that ABS works 'better' in a torsen than in a VC needs
>a lot more data than has been published.  Given Trg at a minimum, I don't
>think either claims a win, both are 'linked' to some extent (in techno terms,
>both have a decel Bias Ratio).  Racing, the Torsen was not used to any great
>extent (singular exceptions so noted) in the audis.   
> 
>What the torsen EXACTLY lacks, that a VC doesn't, is that you can get U-O-U
>(understeer = u,  oversteer = o) in the same turn with no 'traction' reasons
>for Tshift.  A torsen audi then exactly doesn't maintain chassis character
>thru a turn, since at 50/50 static distribution it understeers, at 78r/22f it 
>oversteers, and at 22r/78f it understeers.  A VC (3kgtVr4 for instance) has a
>primary set of drive wheels, and the lock is at a specific ratio, that can be 
>made to keep the inherent chassis dynamics, here O-O-O.  Even with slip angle
>variables, the chassis dynamics doesn't change, it's still oversteer.  Just as
>predictable as a locked 50/50 audi diff at U-U-U, only better (racers tend to
>use a 65r/35f split as preferred, btw)
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