I knew being a grad student in michigan would come in handy someday....
A number of cars use accelerometers, but NOT for axial deceleration measurement
generally. They are for lateral acceleration - i.e. cornering. The ABS
operates slightly differently when cornering than when going straight (more
braking on the inside wheels I think, but I could be way off base on that.
Don't remember the specifics). Anyway, my guess based on my limited
measurements experience is that accelerometers (or at least reasonably priced
ones) are just too noisy to be used very well for axial deceleration.
Oh, the cars that I know of that do use lateral accelerometers, are Caddy
Sevilles, Corvettes, Jaguar S series (though that one is rolled into their
traction control stuff) and a bunch more I'm sure.
YMMV, my .02, etc.
Adam Arabian
Stuck in michigan for 4 more months, then off to Sunny Wash. DC with a
disassembled '52 TD
Max Heim wrote:
> This is all very interesting. The question is, do any current ABS systems
> use accelerometers? If so, which ones?
>
> (sorry to butt in)
>
> Matt Pringle had this to say:
>
> >Even on ice the car will be slowing (albeit extremely slowly).
> >Acceleromters can be extremely sensitive.
> >
> >Matt
> >
> >Bob Howard wrote:
> >>
> >> Matt,
> >> I can follow your logic if the skid is on pavement where at least one
> >> wheel has good grip. If all four wheels were on ice, how would it sense
> >> deceleration?
> >> Bob
> >>
> >> On Fri, 21 Jan 2000 08:43:47 -0500 Matt Pringle <pringlmm@mcmaster.ca>
> >> writes:
> >> > Actually sensing the difference between being stopped and skidding
> >> > with
> >> > all wheels locked is very simple and I'd be very surprised if they
> >> > don't
> >> > do it already. When you're skidding, you're still slowing down and
> >> > so
> >> > an accelerometer could easily sense this.
> >> >
> >> > Matt
> >> >
> >> > 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.
> >
>
> --
>
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the red one with the silver bootlid.
|