Ecm role expanding?

[Rich Vandervoort]

Unfortunately a defeat switch would cause an instant brake lockup.  If you 
are doing threshold braking on a non ABS car you approach optimal brake 
pressure relatively slowly and modulate about that pressure.  If you defeat 
ABS during an ABS event you will usually have a large pressure head on the 
master cylinder side of the ABS unit.  This pressure will be released at ABS 
defeat and cause an instant 4 wheel lockup.  You then have to release the 
brake and recover control.  At this point you have no idea what pedal force 
is needed for threshold braking.  Also the defeat is a one shot deal you 
could not turn ABS off and then turn it back on during and ABS stop.  The 
ABS systems vehicle reference speed would loose accuracy and therefore 
couldn't control the brakes properly.  I remember once watching a car with 
four wheels locked up sliding down a hill.  I think the car got up to 15 to 
20 mph before it plowed into a snow bank and stopped.  It was common 
practise in this town to put one wheel into the snowbank to slow yourself 
while going downhill.

Rich V.


>Date: Fri, 5 Jan 2001 20:41:21 -0800
>From: "Dave Zug" <dzug at delanet.com>
>Subject: Re: Ecm role expanding?

>We have seen studies where inexperienced drivers >suddenly release the 
>brakes
>when the ABS kicks the pedal, and BAM right into the >tree. I wonder if ABS
>practice is part of driving school nowadays?

>In our minivan, there IS a defeat switch for traction >control, but not for
>ABS. I've been in a vehicle where it was ACCELLERATING >downhill with the
>brakes applied in snow. 3mph,..4,..5,...6,...  its not a >good feeling but 
>I
>dont know if defeating ABS would have helped.

>If we had a defeat switch for the seat belt buzzer >unfortunately less 
>people
>would put them on.

>in summary, I don't really know which side of the issue >I am on.

>(and yes, I am 420 email messages behind today)


>- ----- Original Message -----
>From: Walter Sherwin <wsherwin at home.com>
>To: <gmecm at diy-efi.org>
>Sent: Tuesday, November 28, 2000 6:40 PM
>Subject: Re: Ecm role expanding?


>Just my $.02 worth here............Once upon several dozen times I've been
>both spectator and participant where the main "game" was to take average
>drivers and put them into average production vehicles, and then simulate
>average typical treacherous/dangerous driving modes with either snow or
rain
>as the traction limiter.
>
>Granted, a smart/good driver will have already adequately compensated for
>such road conditions, and he/she will probably be in both good position
and
>mindset to pump/release/steer/pump/etc....  However, the rest of the
>unwashed masses are far less fortunate, and ABS really does make a
>difference for them.  For those kinds of people, I applaud the OE movement
>toward widely available ABS & Traction Control systems, and things of the
>like.
>
>Please though,  just give me (and similar like minded people) a quick
defeat
>switch for times when "I" choose to be in control.  Whether or not I can
>accomplish better than a "system" is open to debate, but, at least if I
hit
>something I'll have nobody to blame but myself during such modes.
>
>Walt.
>
>
>
> >
> > In part, they were to save lives, and that hasn't been born out in any
> > report that I've seen, ABS really allows you to steer when you would be
> > otherwise in a locked tire no steering mode.   But, folks in general
>aren't
> > maintaining an alternate path, so it's 2/3 defeated anyway
>
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