Re: Center Differentials

[Eliot Lim <eliot@u.washington.edu>]

On Fri, 7 Oct 1994, Barton P. Chambers wrote:

> FWIW, the new Porsche 993
> Carrera 4 (AWD) now uses a similar system to the (Fluid-based) torque splitter
> of the Vanagon Syncor rather than the entirely mechanical system used in the
> Quantum Syncro.  

this is pretty interesting.  the latest carrera 4 now has AWD that is
barely more sophisticated than those found on the vanagon syncro,
various ford and chevy minivans, the lamborghini diablo VT..

in short, it is a part time, automatically engaging 4wd system.  the press
has almost been silent in pointing this out.  porsche, during the days of
the 959 and original carrera 4 have been strongly opposed to using any
form of viscous coupling (as is audi till this day) because "they cannot
be controlled" and they hamper ABS operation. 

i have always considered the use of a viscous coupling to be a less
elegant implementation and it seems to me that the use of a VC in the 993
is due largely to its uneven weight distribution.  even when porsche used
a 33/67 split on the original C4 there were complaints about too much fwd
effects, so the latest C4 is rwd only until they slip.

there are also a few understeer inducing doo-dads thrown in when the
accelerometers detect a situation where the tail is about to swing..
this is the only thing it has over the generic VC auto engaging 4wd
implementation.


eliot