Good Points Chris. There are already many simple schemes that can perform the
required motion detection duties. Sensor technology is a highly advanced field
with a multitude of solutions offered.
Jim
Chris Kotting wrote:
> Paul -
>
> Aha! You've discovered ABS's weak point. Allow me to ask a question:
> How does ABS know that a wheel is locked? Think about this for a second
> before reading the next line.
>
> Ready for the answer?
>
> By comparing rotional speeds of the four wheels.
>
> Now for the next question: How can an ABS system tell the difference
> between these two states (a) all four wheels locked and sliding, and (b)
> stopped?
>
> Answer? It can't. And, until they come up with a sensor to pick up on
> the abruptly rising adrenaline level in the driver's bloodstream, no
> amount of software tweaking will help. (Okay, a fuzzy logic system that
> compared pre-braking wheel rotation speeds to post-braking wheel
> rotation speeds, AND from that figure out that the indicated rate of
> deceration was impossible, AND conclude correctly that you were indeed
> sliding, COULD do it, but don't count on that getting implemented for a
> while.)
>
> Herein lies the problem: ABS (current technology) helps a bunch when
> you're in a slightly tricky situation (one or more wheels sliding),
> particularly if its the front wheels sliding and you need to steer. BUT
> it can engender a false sense of confidence in the machine's ability to
> take care of you, which will fail you totally when you are in a
> situation where you really need all the help you can get (all 4 wheels
> sliding).
>
> In effect, it raises the threshold at which one is aware one is in
> trouble to the level at which uyou are in REALLY deep doo-doo. Some
> people prefer a car with high adhesion at the limit, even if it gives
> little warning of an impending slide, others will trade a little
> adhesion for a little warning.
>
> ABS is okay, so long as you are fully aware of its limits. I happen to
> think that too few people are. I'm still not convinced that it's better
> FOR ME, than a close awareness of the capability of my car's braking
> systems, unenhanced by a computer.
>
> Chris Kotting
> ckotting@iwaynet.net
>
> > Date: Thu, 20 Jan 2000 19:46:00 -0500
> > From: cgmoog@ibm.net
> > Subject: Re: ABS experience (long)
> >
> > My limited experience with ABS leads me to believe that its is good in
> > most but not all situations. About 5 years ago I was on a business trip
> > to Rochester and Buffalo. Left Rochester in a rental GM vehicle
> > (A-body) with ABS. The NYS Thruway was closed east of Rochester due to
> > heavy snow.
> >
> > The ABS allowed me to brake much more aggressively then I would have
> > thought possible (I'd apply the brakes until I felt the ABS cycle and
> > then ease up slightly).
> >
> > Once in Buffalo with snow still falling I drove around the city
> > completing my work. At one intersection (which I was approaching at ~10
> > mph) I braked normally to stop for a stationary snowplow. Applying the
> > brakes did not slow the vehicle at all. I kept pressing the brakes
> > harder and harder while rolling toward the plow. I was about to through
> > the transmission into park when the pedal suddenly sunk and inch or so
> > all four wheels locked up and I slid to a halt inches from the plow.
> >
> > Further experimenting showed that in very low friction driving (at low
> > speeds) I could get the ABS to malfunction in one of ten stops.
> >
> > So while I liked it in most situations I would rather have a switch to
> > disable it (or be convinced that the software has improved since the
> > early 90's) before I'll purchase a vehicle with it.
> >
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