Oyvind:

Modern ABS systems use hydraulic pressure, temperature, and each wheel's
rotational velocity to compute a skid condition before it happens. The
brake hydraulic pressure is modulated and or reduced to equalize the
rotation of all wheels. Below a certain speed the ABS affect is near
zero (as when stopped or slowing to a stop from a low speed).
Many systems (like the Boeing 747 I worked on in the early 70's) use
cross or diagonal wheel (or wheel carriage or bogie) systems such that
even with a system error the braking fails to a balanced set of normally
braked wheels.

- Wayne Foletta
BMI - Saratoga, CA

> ----------
> From:         Oyvind Kaurstad[SMTP:oyvind.kaurstad@NOFAC.ABB.NO]
> Reply To:     pic microcontroller discussion list
> Sent:         Friday, January 23, 1998 4:11 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [Way OT] ABS brakes.
>
> This is way off topic, but it is related to electronics, and
> could theoretically be related to PIC's... :-)
>
> Modern cars have ABS brakes, which is a system made to
> prevent the wheels from locking up.
>
> This system have sensors on the wheels that senses whether
> it is rotating or not. Usually it is sensing on a toothed disk of
> some kind. (Probably some kind of hall-effect gadget)
>
> This is perfectly suited to sense if there is rotation or not.
>
> But here comes the interesting part:
>
> How can a car with ABS brakes come to a stop in a hill?
>
> Why don't the ABS-system release the brakes when the car stops?
>
> And now you might say that the ABS-system is deactivated below
> a certain speed, which is absolutely correct.
>
> But what if a car standing still starts to slide? Will the ABS-system
> be able to release the brakes?
>
> Just wondering....
>
>
> -Oyvind
>