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RE: Controlling torque v Marketing


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
>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
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
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
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