RE: Torsen tech

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

mmmm.... curiouser and curiouser....

at low speeds (low torque inputs), the vehicle is highly unlikely to reach
the bias ratio (by design).  at higher torque inputs and tighter turns it
will.

to illustrate, take your favourite torsen quattro and proceed at moderate
pace (say 50km/hr) on a wide and deserted road, and proceed to pull a
full-lock "u" turn.  what happens?

on corner entry torque goes to the rear but as the car continues to tighten
the turn the bias ratio is reached.  this causes the front to spin up and
front tyres to squeal.  why?  the torsen refuses to pass more than 75% of
the torque to the back, despite the tractive conditions *requiring it*.
this means that traction is much more likely to be lost at the front than at
the rear, because the fronts are already receiving more torque than their
traction can sustain (i.e. they are already at very high slip due to the
steering and lateral forces).

do the same manoeuvre at low speeds and the bias ratio is not reached, so no
front tyre squeal...

another way of looking at this is that the torsen is conserving rear slip
angles, despite sending torque to the rear.

btw, i pull this manoeuvre every time i come home due to the road my house
is on.

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

-----Original Message-----
From: Orin Eman [mailto:orin@WOLFENET.com]
Sent: Wednesday, 3 November 1999 23:46
To: Dave.Eaton@clear.net.nz
Cc: orin@WOLFENET.com; quattro@audifans.com
Subject: Re: Torsen tech



> sorry orin, but the confusion here is that scott is explicitly discussing
> the audi sae 885140 "case" where the car is *not* at the bias ratio (it is
> proportioning torque 38/62%).  scott has said that the bite can occur this
> point, hence my post on thursday for clarification (see below)...

Actually, I thought it was the "...small cornering radii and at low
speeds the extent of torque redistribution can increase to the
torque split limit of 25/75%" case that he was considering.

Also "On a high-grip surface the torque split limit is reached
at a radius of about 15 meters".

Answering my own question on the speed of the car for the 38/62% case:

Radius = 40m
lateral acceleration = 4 m/s^2
v^2/40 = 4 (lateral acceleration is v^2/R)
v = 12.6 m/s or about 45 km/h or just over 28 mph.

This unfortunately represents just one moment in time
since the paper claims the car is accelerating at 4 m/s^2.
If they maintain constant radius, then lateral acceleration
must be increasing.  If they maintain constant lateral acceleration,
then their radius must be increasing.

Orin.