[torsen] Re: Haldex differential

[QSHIPQ at aol.com]

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In a message dated 11/19/02 7:27:14 AM Central Standard Time, Kei
th.Maddock at trw.com writes:


Scott,

>I see where you are going with "torque shift" in terms of moving torque, as >
opposed to "torque capacity".  Though by your own rules, since the rear axle
has >0% torque in the no-slip, and is then capable of receiving 100% torque
at full lock >(assuming strong enough clutch), wouldn't you call that a
"shift" of 100% torque?

Keith, you have to envision that in terms of what's happening.  In the case
of 100/0, that's a capacity argument that lasts exactly the length of the
wheelbase.  In the case of a torsen, it would be 0/0 for the length of the
wheelbase. Is either relevent or reflected in "torque shift"?  If so, we need
to be consistent with all limited slip devices in addressing shift AND
capacity, currently it's not common practice.  I'll leave that up to the SAE
boys to figure out whilst defining awd.

>I understand if this was a locking or torsen diff, that since the no-slip
torque >transfer characteristic is 50/50, you're only "shifting" up to 50%
more to either >end, but the LSC isn't a differential based system like the
torsen.

Exactly, it is a 95f/5r or a 50f/50r diff.  The real gray area comes into
play here because with any ls/locked diff/coupling, capacity is hugely
different than torque shift.

>To-mayto, To-mahto? :)
Maybe,  I think the vision is that you can shift torque from one axle to the
other and anywhere in between.  The coupling can only "slip" in one direction
as you said with 1 input and 1 output.  A LSD can slip in either direction 1
input/2ouputs.  A nice marketing arena that audi uses fully to their
advantage.

>I'll see what I can find out from the Haldex boys this winter :)   We'll be
working >with a Golf R32 and a few Saabs with Haldex Gen I's, and a S3 with a
Haldex Gen >II transplant, so I'm sure we'll have more than a few
conversations with them!

Looking forward to it.  Keith, right now, the system is deactivated and
reactivated on the fly based on a variety of control inputs from the ecu.  I
really don't see any difference between that intervention and the ability for
the throttle valve to regulate the system more "aggressively".  Remember, as
with ANY center coupling device, a turn is a traction argument.  With <15% of
rotational differences, I would argue that the  haldex system is active (but
throttled open) as soon as you move the car from straight ahead.  This would
support a more complete electronic control of the device.

The hackers will figure this out if the engineers don't.  No question in my
mind that the TT can be run in "locked" mode with the simple override of the
throttle valve (the "switch" they describe in the application section).  We
know that the throttle valve can completely unlock the coupling, which the
device can't do by definition, unless it is the locking device as well.  One
could argue we need some sort of slip to activate the lock, but once locked,
it certainly could stay that way, pick and choose your other included ECU
standard interventions.  At steamboat for example, you default the diff to be
locked all the time, except under braking (or including braking), add in EDL,
ESC, or ABS algorithums based on track times.

Get those boys talking man.  Right now the TT is one of the worst performers
at steamboat, btinstructed that.  I'm thinking it can be better than the
lockers (or be one)  with a simple understanding of the pinouts to the
Tvalve.

SJ