ABS
RABBITT_Andrew at mail.orbeng.com.au
RABBITT_Andrew at mail.orbeng.com.au
Thu Jan 30 01:13:16 GMT 1997
>Unfortunately, on very slick surfaces such as ice, all four wheels
>lock up at once. Generally the ABS systems work on a speed
>differential algorithm. If a wheel is going appreciably slower than
>another (the others), then that wheel is considered locked and the
>brake system is modulated. If all four are locked at the same time
>(at least at very slow vehicle speeds), the system sees the vehicle
>as stopped and is not activated. This is why ABS is generally found
>to be ineffective on ice.
Some ABS systems have chassis mounted G-sensors which I presume are
used to compare wheel deceleration with vehicle deceleration. If all
four wheels lock instantaneously then you would be able to detect this
by such a comparison. In any case there would be a limiting value of
wheel deceleration, beyond which a lock-up condition could be
inferred.
Andrew Rabbitt
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