ABS brakes
in [Drive]
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From: Ashton Crusher on 25 Apr 2010 16:47 On Sun, 25 Apr 2010 14:41:23 -0500, russotto(a)grace.speakeasy.net (Matthew Russotto) wrote: >In article <0rr8t5935sf8ejbiduealdjju2ksp44joi(a)4ax.com>, >Scott in SoCal <scottenaztlan(a)yahoo.com> wrote: >> >>In reality, it's a quantized approximation of threshold braking. That >>pulsation you feel in the pedal is the brakes being applied and >>released several times per second as the wheels go into and out of >>lockup and the system modulating the braking pressure to compensate. >>TRUE threshold braking would not involve the wheels locking up, even >>for a few milliseconds. > >Remember also that "locking up" is not as binary as we normally make it out to >be. The slip ratio actually varies continuously (but nonlinearly) >between near-1 (not braking) and near 0 (locked up). There's an ideal >slip ratio for maximum braking, and good ABS will keep the tires near >(but oscillating around) that ratio; if you have stability control as >well, it will also try to keep the car straight (which may result in a >longer stopping distance... would you rather stop short sideways or >stop a little longer straight? The answer unfortunately is dependent >on the situation). I don't think the design goal is to be "oscillating around" peak friction, that would be highly unstable. I believe it is to be very close to it on the "approach" side since that is normally the flatter side of the curve and also would never lead to lock up, which is something you really want to avoid.. I could be wrong but my intuition says oscillating around the peak would be a disaster.
From: Alan Baker on 25 Apr 2010 17:32 In article <dp67t55v3elj8vebi9ti24rlrqtr2hhl8b(a)4ax.com>, Ashton Crusher <demi(a)moore.net> wrote: > On Thu, 22 Apr 2010 21:48:20 -0700, Scott in SoCal > <scottenaztlan(a)yahoo.com> wrote: > > >Last time on rec.autos.driving, Ashton Crusher <demi(a)moore.net> said: > > > >>On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge > >><a_rogge(a)yahoo.com> wrote: > >> > >>>Nick Naim wrote: > >>>> I pegged her at 70 years old plus minus. > >>>> She pulled out of a fast food on my left in a heart beat > >>>> I,m in the left lane of thru traffic. > >>>> I,m on the binders on ABS and they are working on overtime. > >>> > >>>The ABS should not be activating on a dry surface, as this increases > >>>your stopping distance. > >>> > >> > >>ABS will activate on a dry surface the same as on a wet surface > >>whenever the tire is about to lock. And in the process it shortens > >>your stopping distance, not increases it. > > > >It shortens your stopping distance vs. screeching to a stop with > >locked brakes, sure. > > > >But true threshold braking is the shortest stopping distance of all. > > ABS is threshold braking. And any decent ABS is able to do it far > better then a human can, particularly on wet pavement. No. ABS is very close to threshold braking, but it is not. It is a very rapid sequence of going slightly beyond the threshold and then back to less than the threshold. -- Alan Baker Vancouver, British Columbia <http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>
From: Ashton Crusher on 25 Apr 2010 21:18 On Sun, 25 Apr 2010 14:32:51 -0700, Alan Baker <alangbaker(a)telus.net> wrote: >In article <dp67t55v3elj8vebi9ti24rlrqtr2hhl8b(a)4ax.com>, > Ashton Crusher <demi(a)moore.net> wrote: > >> On Thu, 22 Apr 2010 21:48:20 -0700, Scott in SoCal >> <scottenaztlan(a)yahoo.com> wrote: >> >> >Last time on rec.autos.driving, Ashton Crusher <demi(a)moore.net> said: >> > >> >>On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge >> >><a_rogge(a)yahoo.com> wrote: >> >> >> >>>Nick Naim wrote: >> >>>> I pegged her at 70 years old plus minus. >> >>>> She pulled out of a fast food on my left in a heart beat >> >>>> I,m in the left lane of thru traffic. >> >>>> I,m on the binders on ABS and they are working on overtime. >> >>> >> >>>The ABS should not be activating on a dry surface, as this increases >> >>>your stopping distance. >> >>> >> >> >> >>ABS will activate on a dry surface the same as on a wet surface >> >>whenever the tire is about to lock. And in the process it shortens >> >>your stopping distance, not increases it. >> > >> >It shortens your stopping distance vs. screeching to a stop with >> >locked brakes, sure. >> > >> >But true threshold braking is the shortest stopping distance of all. >> >> ABS is threshold braking. And any decent ABS is able to do it far >> better then a human can, particularly on wet pavement. > >No. ABS is very close to threshold braking, but it is not. It is a very >rapid sequence of going slightly beyond the threshold and then back to >less than the threshold. Where you are getting that definition from? It makes no sense to me and is contrary to what people have claimed in the past. What's your definition of the "threshold" point?
From: gpsman on 25 Apr 2010 23:44 On Apr 25, 9:18 pm, Ashton Crusher <d...(a)moore.net> wrote: > On Sun, 25 Apr 2010 14:32:51 -0700, Alan Baker <alangba...(a)telus.net> > wrote: > > > > >In article <dp67t55v3elj8vebi9ti24rlrqtr2hh...(a)4ax.com>, > > Ashton Crusher <d...(a)moore.net> wrote: > > >> On Thu, 22 Apr 2010 21:48:20 -0700, Scott in SoCal > >> <scottenazt...(a)yahoo.com> wrote: > > >> >Last time on rec.autos.driving, Ashton Crusher <d...(a)moore.net> said: > > >> >>On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge > >> >><a_ro...(a)yahoo.com> wrote: > > >> >>>Nick Naim wrote: > >> >>>> I pegged her at 70 years old plus minus. > >> >>>> She pulled out of a fast food on my left in a heart beat > >> >>>> I,m in the left lane of thru traffic. > >> >>>> I,m on the binders on ABS and they are working on overtime. > > >> >>>The ABS should not be activating on a dry surface, as this increases > >> >>>your stopping distance. > > >> >>ABS will activate on a dry surface the same as on a wet surface > >> >>whenever the tire is about to lock. And in the process it shortens > >> >>your stopping distance, not increases it. > > >> >It shortens your stopping distance vs. screeching to a stop with > >> >locked brakes, sure. > > >> >But true threshold braking is the shortest stopping distance of all. > > >> ABS is threshold braking. And any decent ABS is able to do it far > >> better then a human can, particularly on wet pavement. > > >No. ABS is very close to threshold braking, but it is not. It is a very > >rapid sequence of going slightly beyond the threshold and then back to > >less than the threshold. > > Where you are getting that definition from? It makes no sense to me > and is contrary to what people have claimed in the past. What's your > definition of the "threshold" point? If a tire slips under braking force the braking threshold of the tire has been exceeded. ABS allows tires to slip, however briefly. ----- - gpsman
From: Ashton Crusher on 26 Apr 2010 02:18
On Sun, 25 Apr 2010 14:32:51 -0700, Alan Baker <alangbaker(a)telus.net> wrote: >In article <dp67t55v3elj8vebi9ti24rlrqtr2hhl8b(a)4ax.com>, > Ashton Crusher <demi(a)moore.net> wrote: > >> On Thu, 22 Apr 2010 21:48:20 -0700, Scott in SoCal >> <scottenaztlan(a)yahoo.com> wrote: >> >> >Last time on rec.autos.driving, Ashton Crusher <demi(a)moore.net> said: >> > >> >>On Thu, 22 Apr 2010 21:47:45 +0000, Alexander Rogge >> >><a_rogge(a)yahoo.com> wrote: >> >> >> >>>Nick Naim wrote: >> >>>> I pegged her at 70 years old plus minus. >> >>>> She pulled out of a fast food on my left in a heart beat >> >>>> I,m in the left lane of thru traffic. >> >>>> I,m on the binders on ABS and they are working on overtime. >> >>> >> >>>The ABS should not be activating on a dry surface, as this increases >> >>>your stopping distance. >> >>> >> >> >> >>ABS will activate on a dry surface the same as on a wet surface >> >>whenever the tire is about to lock. And in the process it shortens >> >>your stopping distance, not increases it. >> > >> >It shortens your stopping distance vs. screeching to a stop with >> >locked brakes, sure. >> > >> >But true threshold braking is the shortest stopping distance of all. >> >> ABS is threshold braking. And any decent ABS is able to do it far >> better then a human can, particularly on wet pavement. > >No. ABS is very close to threshold braking, but it is not. It is a very >rapid sequence of going slightly beyond the threshold and then back to >less than the threshold. Where you are getting that definition from? It makes no sense to me and is contrary to what people have claimed in the past. What's your definition of the "threshold" point? |