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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