[s-cars] EDL vs ELD explained....

[Keith Maddock]

Varon,

You make a very good point, unless you can get into the ABS/ELD software itself and make a change, I dont think there would be any way to disable ABS braking without also disabling the EDL functionality.

Your comment about stopping better sans ABS in the snow is spot-on.  Deformable surfaces, such as snow and gravel, get the best stopping distance with a LOT of slip so you can build up the wedge of road material in front of the tire which increases your friction quite a bit.  This much slip on any other surface would kill your stopping distance.  These surfaces continue to be on of the biggest challenges facing ABS engineers, as 100% accurate detection  of this kind of a surface is near impossible.    This is the only type of surface where I would personally de-activate a decent ABS system while driving.   If I had such a switch in a EDL car, then I guess I'd have to hit the switch to stop, then re-activate it to launch again...

Most vehicle manufacturers accept the fact that with ABS on, your stopping distance will be increased on loose snow and gravel.  Most do, however, require that the ABS equal or improve the stopping distance on all other surface conditions, given a set of stability and steerability constraints to the comparison of ABS on vs. ABS off (aka driver's best effort)

Now to translate from what they require to what they allow into production, depends on the auto manufacturer, the supplier they choose, and how much time and money they allow for the supplier to apply the ABS to the specific vehicle.   Granted, ABS systems now are in general much much better than they were even 5 years ago

Keith "I better get back to work" Maddock

Disclaimer:  The contents of the message above reflect only the opinions of the author, and are not to be construed as reflecting the opinion of TRW Automotive in any way. blah blah blah



****************************************************************
Keith Maddock, TRW Automotive,  Koblenz, Germany
Slip Control Systems, Systems Design, Traction Control
+49 (0)261/ 895 2474     -    -    keith.maddock at trw.com

>>> "Varon H. Fugman" <vfugman at globaldialog.com> 18:07:52 10.09.2002 >>>
Yes, Keith, thanks for the great write-up!

One more benefit of the mechanical diff lock over EDL is that you can use it
even with ABS disabled... and my car seems to stop a lot better in the snow
without ABS.

I had been thinking of trying to disable the automatic rear diff-lock
drop-out at 15MPH so I could have it locked longer for running ice trials
(on a frozen lake in January/February in Wisconsin), but then I realized
that even with the differential unlocking at 15MPH I was getting pretty good
straight-line acceleration on ice (Nokian Hakka Q's 215/55R16)... it's
turning and braking two tons of quattro on a slippery surface that is the
problem!

And while the Torsen center diff is absolutely fantastic in regular on-road
winter driving conditions (heck, the car is a regular snowmobile on
snowy/slushy streets), on smooth ice it makes handling in corners somewhat
tricky... sometimes more power in a turn causes the rear to come around
nicely, but other times it just understeers.  I suspect that with the
extremely low coefficient of friction all around that the Torsen may be
hunting for traction--sometimes shifting maximum torque to the front
(causing understeer) and other times to the rear (leading to oversteer.)

It has taken me two winters running the car on ice to feel like I might
finally be starting to get the hang of it.  Much harder to drive fast on ice
than my old FWD car (except for the initial launch, that is!)

Varon
'95 urS6

P.S. Here's a picture from last January... we had a lot of water on top of
the ice that day!
http://www.w-a-g.org/events/ice/2002/2002-01-20/batch1/photos/MVC-111S.JPG


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