ABS

[John Hess]

And it is this slow speed turnoff that allows so many people to skid 
(literally) hundreds of yards on ice.  How far do you think you can 
skid with the wheels locked versus reasonable application of the 
brakes on ice.  For myself (perhaps not everyone), I find it easier to 
try to keep from skidding in the first place on ice and to maintain 
some control over which end of the car hits (or, perhaps misses) the 
tree.  One has no chance of doing  this even at VERY slow speeds 
unless the wheels are turning!


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From:  Darrell Norquay[SMTP:dnorquay at iul-ccs.com]
Sent:  Wednesday, January 29, 1997 11:07 PM
To:  diy_efi at coulomb.eng.ohio-state.edu
Subject:  RE: ABS

At 10:34 AM 1/29/97 -0600, John Hess wrote:

> This is why ABS is generally found to be ineffective on ice.

Tell you what, non-ABS brakes are sure as hell ineffective on ice as 
well!
Any amount of divine intervention is usually welcome under these 
circumstances.

There must be something other than the differential speed algorithm 
involved
in the ABS control.  If a 4 wheel lockup occurred, and the VSS reading 
went
from 20MPH to 0 in, say, half a second, the ABS controller should 
know
something is fishy.  As soon as the ABS cuts in, the wheels will 
start
turning, and the differential speed thingie starts working again. 
 However,
the ABS system has to cut out below some minimum wheel speed, 
otherwise the
brakes wouldn't work at all when the vehicle is not moving.  Not a 
safe
situation, to say the least.

Also, I would think that ABS systems work in pairs, ie front wheels on 
one
modulator, and rear on another modulator.  It would be prohibitively
expensive to have a separate master cylinder connection and modulator 
valve
for each wheel.  They may still have sensors on each wheel, but 
controlling
them in pairs is (IMHO) much safer (and cheaper) than modulating each 
wheel
individually.

regards
dn
dnorquay at iul-ccs.com