RE: Controlling torque v Marketing

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

dave, we're in agreement i think.

however, you must accept that your "centre locked" scanario never happens in
reality.  why?  because of the weight distribution of the quattro.  with a
locked centre, torque distribution will effectively mirror weight
distribution in the *static* case (ie. straight line, no acceleration).
with acceleration, you get weight and torque shift rearwards.

there is a godd discussion of this in the audi torsen sae paper.  it
includes graphs of actual torque distributions in locked centre and torsen
audi 80's.  very interesting reading.

with regards to the haldex, effectively without slip you have no torque
shift.  as you agree, 100% torque to the rear is possible, depending upon
conditions (as scott doesn't understand).  what you seem to ave difficulty
with is that the haldex is not "active" i.e. until slip happens torque is
not shifted.  an active differential will use external means to operate the
clutch reagrdless of slip.  this is not the haldex, but closer to the system
used by nissan (attesa).

thus it is also what i would describe as an automatic "part time" system.

as is any other awd system using a vc behind a centre differential.  aka
subaru, mitsibushi "full time awd" systems.  fwd until slip occurs.  and no
computer to control things after slip occurs.

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

-----Original Message-----
From: Lawson, Dave [mailto:dlawson@ball.com]
Sent: Thursday, 23 September 1999 04:45
To: Dave Eaton
Cc: quattro list
Subject: RE: Controlling torque v Marketing


Dave,

Reread what I wrote.

>sorry dave,  when the diff is locked, you do *not* have 50:50% torque
>front/rear.  by definition.  ditto with the generation 1 system.  with a
>locked diff (haldex, or manual quattro locker whatever), you have 0:100:0%
>torque front/rear depending upon traction.  you are misunderstanding
torque.
>if it helps, with an open differential, you have 50:50% f:r torque
>distribution by definition.  all the time.

My first example said all 4 wheels on the same surface. In reference to
your quantifying statement above, "depending upon traction", is what my
example was trying to describe. I contend that when all 4 wheels have
the same tractive force, i.e. are on the same surface, weight distributed
equally over all 4 wheels, and other criteria, that there is a 50:50% f:r
torque distribution with an open differential AND with a locked
differential.
So under this scenario you CAN have 50:50% torque front/rear with a locked
differential. I never said it couldn't change under some other set of
conditions,
but that under these conditions the torque distribution is 50:50. Because
I mentioned open differential above, lets say that this paragraph applies
to the gen I quattro system.

Now lets apply the exact same conditions to a Haldex "quattro" or "4motion"
system as used on the TT or A3/S3 cars. With the haldex LSC operating
in an open/uncoupled/unlocked mode, no torque is transfered to the rear
wheels. So "very close" to 100% of the torque is distributed to the front
wheels. I say "very close" because some torque is used to keep the center
driveshaft rotating. Now we program the Haldex ECU computer to lock the
haldex LSC so the rear axle is coupled to the center driveshaft. Here the
rear wheels are now being driven and the torque distribution is 50:50 f:r.
So under these EXACT same conditions we have changed the torque
distribution from 100:0 f/r to 50:50 f/r with a few keystrokes. And I
contend
that you can't get more than 50% torque to the rear axle under the
conditions I have described. I do believe that if you change the "external"
conditions, the haldex can transfer more than 50% torque to the rear axle,
but the computer controlling the haldex operation is not responsible for
transfering this additional torque.

>this was discussed in detail on the list a few months ago.

I know I have it all archived.

>with regards the haldex and it's torque distribution potential, check out
>the graph on page 6 of the white paper i sent you.

I assume you are talking about the graph with the following text. This graph
can also been seen at http://www.haldextraction.com.

"The coloured area indicates the area within which the characteristics
of the coupling can be controlled."

I don't believe this graph is correct for haldex operation as a hang
on coupling mounted on the rear axle. You can't control the coupling
characteristics to behave like that under EVERY condition. The torque
transfer characteristics shown CAN happen if certain external conditions
exist and you can program the coupling to work within the region shown,
but I argue that you can't program the haldex to have the complete range
of those torque transfer characteristics when all 4 wheels are being
driven under the EXACT same conditions.

> -
> Dave Lawson
>
>
>