Torsen LSD

[C M Smith <cmsmith@domain.elided>]

I downloaded a tech paper on the Torsen LSD and from my inexpert reading I 
conclude that the Torsen does indeed permit differential slippage under 
drive force, and that the rate of slippage is predetermined by the cut of 
the helical gears that replace the normal bevel spider gears. In other 
words the Torsen can be "preloaded" to deliver  different amounts of slip 
under load. In theory the Torsen permits unlimited slip in overrun. An open 
differential can transmit one half of the torque available at the wheel 
with lower traction, unfortunately often close to half of zero. The Torsen 
transfers the torque available to the wheel with the higher traction, but I 
do not think it ever actually locks up. The transition of torque applied 
across the differential gears is supposed to be smooth and imperceptible to 
the driver. The Torsen is correctly described as an Automatic Torque 
Biasing differential. Torque is applied to the wheel with more grip until 
that wheel slips and the torque is then seamlessly transferred across to 
the other wheel and so forth, feeling as if no slippage at all is occurring.

Anybody out there with the necessary engineering and literary skills to 
correct my understanding (or confirm it as the case may be)? Torsen LSD are 
of particular interest to owners of fwd vehicles because it is the only LSD 
that promises minimal steering effects. I have considered putting one in my 
SAAB Aero. The 164 doesn't really have the torque to justify one, except 
for the top line 24 valve engine. Audi uses a Torsen center differential in 
their excellent Quattro drive package, and it works great.
Michael Smith
Calgary, Alberta,Canada
91 Alfa 164L
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