torsen tech 103

["Dave Eaton" <Dave.Eaton@clear.net.nz>]

in re-reading my last post "torsen tech 102", i realise that i have not made
something as clear as i should have.

when the torsen reaches the bias ratio and then "opens" or "unlocks" to
allow axle speed differentiation, it is now operating as an open diff would,
but the torque outputs *remain* at the bias ratio.  they do not change.  so
while an open diff will allow different output shaft speeds but equal
torque, the torsen will told the bias ratio torque outputs to each shaft,
but also allow shaft speeds to change.

surplus torque gets turned into wheel spin.  as in the 4-wheel drift.

thus it is *impossible* for the torsen when at the bias ratio to "apportion
torque" front to rear as some are assuming.  at the bias ratio, it is acting
as a bevel diff with fixed torque outputs (albeit at different levels).

if it would help to illustrate, draw a graph with the y-axis the "torque
bias ratio" from 1 to 3, and the x-axis "speed difference" between the
torsen output shafts in rad/sec from 0 to 3.  draw a line from {0,1}
straight up to {0.5,3} and then straight from there to {3,3}.  the part of
the curve with the gradient is where the torsen is locked. when the speed
difference of the output shafts reaches 0.5 rad/sec, the bias ratio is
reached and thereafter stays here while the speed difference increases.
this graph is from a model of a specific torsen ("4wd powertrain models for
real-time simulation", freeman, 1991)

in torsen tech 104, i'll look at cornering with/without loss of traction
conditions...

hth,
dave
'95 rs2
'90 ur-q
'88 mb 2.3-16