Bosch/automotive brakequattro (To: Robert Deis et. al.)

[Louis A. Mulieri]

On Fri, 8 Feb 2002 quattro-request at audifans.com wrote:

> Message: 2
> On Fri, 8 Feb 2002, Dave Glubrecht wrote:
> >
> > Not my understanding,
> >  ABS provides better braking under almost all conditions AND allows for the
> > driver to steer while panic braking.  ABS pumps the brakes faster than
> > humanly possible which keeps the tires at the max possible braking ability.
>
> True, except for highly skilled drivers.
>
> Maximum brake performance actually comes when "threshold braking," which
> is a point where the tire is actually rotating slower than the vehicle is
> travelling, but traction has not yet been broken.  Trained drivers know
> how to feel this point and can use it to get maximum brake force.
>
> As a bonus, since the wheel is never locked, we get improved steering
> under braking.  But don't get cocky- I nearly slid into a mailbox at 5mph
> in my 5kTQw last week. The ABS was buzzing just like it should, but the
> steering just didn't work- too slick.

Hi Rob,
	Your explanations comply with my recent, harrowing experience. I
live at the bottom of a 1/4 mile dirt road with 15 degree slope and a lake
at the bottom. Last week it was iced as well as a Zamboni could have done
it. This is the first winter driving my 88 5kCSTQ that is a hand-me down
from my wife (now sorrowly driving a new Subaru Legacy 4WD). I have four
hakkepelita, studded snows on mine. As I started down the hill this night
the ABS started popcorning. I thought...just like I've heard about. I
followed my brainwashing that one must just keep steady pressure on the
pedal if you have ABS (before this I drove an 81 Rabbit deisel for 9 years
on this same road with never a mishap). To my horror I found that I was
popping along maintaining perfectly straight steering BUT going faster and
faster. The lake at the bottom, the lake at the bottom! I pressed harder
and harder to the point of almost dislocating my him. The intellect had me
locked away from seat-of the pants driving. Fortunately, the engine
finally stalled and I turned off the key to re-start. The bomb pressure
probably fell considerably and the ABS also stopped it's overriding
control. Without ABS I found I had exquisite control with my practiced,
"Saint Vitis Dance" foot action on the heavy brake pedal. I could bring
the car to a complete stop if I wanted to. And I continued on down to the
bottom in complete control. I now turn off the ABS before starting down
my road and it's a "piece of cake" even in worse, snow on top of ice
conditions.
	This is an extreme case of needing stopping power more than
needing steering power. Since the ABS had no input about speed of car with
respect to ground it could not do what my eye/seat of pants/brain/footwork
could do. That is, to simultaneously maximize BOTH braking and steering
control. For a computer to do as well, it would need to somehow have info
on chassis velocity independent of wheel rpms. Perhaps this could be
achieved by: a. Onboard accelerometers whose output signals could be
periodically integrated to obtain instantaneous velocity in forward and
sideward directions, or b. A GPS link when GPS achieves inch-scale
resolution and precision, or perhaps c. A hybrid ABS/Human system that
includes driver input by sensing pressure applied to brake pedal (human
instinct causes greater pressure the greater the need to reduce forward
body velocity.
	Comments???

Lou Mulieri
'88 5000CS Turbo Quattro...a beauty!!!
Hinesburg, VT