torsen tech 201

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

dave/orin,

ok, now we're getting some misunderstandings occurring, so we should go into
this a little deeper...

dave, you are right when you say that the torsen before the bias ratio
doesn't behave exactly like the locker.  the *effect* is exactly the same,
as i have pointed out but, if you have the graph i described in torsen tech
103, you will understand that the torsen lets the output shafts turn a
little relatively before full biasing occurs.  unlike the locker of course,
where the output shafts are joined together.  from this point on i will use
"locked" to indicate that the effect is the same, but the mechanism is
completely different.

however (and orin makes the same mistake), when the torsen is at the bias
ratio, *no* further torque biasing occurs. the diff locks at the bias ratio,
and *holds* the bias ratio, operating as an open diff.  it can't shift
torque anywhere other than where ever dictated by tractive force.  as long
as the output shafts are spinning enough relatively, *all* torque is
distributed according to the bias ratio.

when the torsen *proportions* torque, is in the period when the gradient of
the curve i described is positive and *before* the bias ratio is reached.
in other words, the torsen moves torque to the slower axle but it *only*
does this before the bias ratio is reached.  once the torsen "unlocks" (i.e.
it is at the bias ratio), the torsen becomes an axle speed differentiating
device *not* a torque differentiating one.  what differentiates it from the
locker before the bias rati is reached is that it uses it's friction gear
design to "lock", where the locker of course just joins the output shafts
together.

as should be obvious, it is only when the relative output shaft speeds of
the unit fall back into the "low speed" range, that the torsen "locks"
again.

as i said it's a very nifty little device.

btw, if you consider the above, you will see why the "torque shift" of the
torsen at the bias ratio which is fundamental to the "bite" theorists, and
which most people assumes happens, *cannot* physically occur with the diff
if it is at the bias ratio. it is simply not in the physics of the device.

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

-----Original Message-----
From: Quattromon@cs.com [mailto:Quattromon@cs.com]
Sent: Sunday, 24 October 1999 08:01
To: Dave.Eaton@clear.net.nz; quattro@audifans.com
Subject: RE: torsen tech 102

Dave,

>however, the fact is that at the point where the torsen hits the bias
ratio,
>the locker will continue to bias torque, where the torsen will *hold* the
>torque bias ratio (i didn't make this clear enough in "torsen tech 102")
for
>increasing amounts of torque coming in, while allowing output shaft speed
>differences.  the only situation where the torsen will go from (say) 75%
>rear torque to 75% front torque distribution is when traction at the rear
is
>lost.  the locker in the same situation will put 100% torque to the front.
>so the torsen exhibits much better behaviour than the locker.

And traction at the rear can fall off as the car would continue on an
oversteer slide with the rear coming around, so as the rears slow down,
torque can be biased to the front, so an oversteer, then understeer
situation could arise.

To get into the oversteer slide, some would say the driver *overcooked*
the corner, which is probably true as the driver was driving passed
the limits of the differential, and not modulating the throttle to maintain
the 4 wheel drift that you previously described. What could catch a
driver by surprise is that the torsen diff has this changing behavior
when the bias ratio is reached. One major difference I see between
the torsen and the locked diff is that from the graph you have given,
the torsen allows wheel speed difference throughout its operating
range, and the locker always maintains 0 wheel speed difference.
-

-----Original Message-----
Date: Fri, 22 Oct 1999 18:20:57 -0700 (PDT)
From: Orin Eman <orin@wolfenet.com>
Subject: Re: torsen tech 102

> What you have just described here is a behavior of the torsen to send
> the bias ratio of torque to the rear of the car which sets up an oversteer
> condition and then once the bias ratio is reached to divert torque to the
> front which sets up an understeer condition.

...only if the rear can't handle 75% and starts slipping will torque
go back up front, more specifically, if the inside rear can't handle
37.5%.  Now the condition being discussed (bite) is where the
torque got thrown back due to the rear wheels turning slower.

Consider this... if the rears do start to slip, we get major oversteer,
but it will take a little time before they catch up to the fronts
at which time torque will start moving forwards and we go back to
understeer.

So, rears break loose - major oversteer - car pointing at apex.
Rears catch up to fronts - torque goes forwards - understeer.

It was the timing that was confusing to me.  The torsen essentially
acts instantaneously... _unless_ the wheel that was turning
more slowly has broken loose and is spinning up in which case
it continues to receive the 75% until it catches up with the other
axle.

Orin.