h a l f b a k e r y"This may be bollocks, but it's lovely bollocks."
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The only difference between a dry, cold road and a cold road with a microthin coating of ice is the coefficient of friction.
Reflectivity should be mostly indistinguishable from a wet road. Temperature is useless for telling dry from icy, and severely hampered in judging wet from icy by the presence
of salt on the roads.
The only possible advance warning comes from directly measuring the coefficient of friction ahead of time.
Since photons and sound waves are not up to the task, a larger particle is called for.
Specifically, a tube continually launching superballs 50 yards ahead, with a carefully calibrated backspin.
Radar measures their change in speed on bouncing. If they jump closer to the car, great, traction ahead. If they bounce on unaffected, bells and warnings and alarms.
Black Ice (under snow)
http://video.google...23&q=cars+ice&hl=en
video! [nuclear hobo, Feb 28 2007]
BMW ASC+T
http://www.318ti.or...book/asc/index.html
Info on BMWs Automatic Stabilty Control and Traction System [jhomrighaus, Feb 28 2007]
BMW DSC Info
http://www.bmwworld.../technology/dsc.htm
Info on BMWs Dynamic Stability Control [jhomrighaus, Feb 28 2007]
BMW ATC info
http://www.unoffici...adaptive_trans.html
Info on BMW ATC system [jhomrighaus, Feb 28 2007]
The Short Short Version!
http://www.bmwworld...technology/asct.htm
For Maxwell [jhomrighaus, Feb 28 2007]
[link]
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"Temperature is useless for telling dry from icy" that is wrong. |
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Why? A -5 C road can be either icy or dry, cannit? |
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Yes, but a 120 F road would be dry. |
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ABOVE freezing? Outdoors? Where do you live, Tahiti? That certainly is not an issue here. |
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But seriously. I have a theory. The ABS
sensors presumably measure wheel
rotation in some way. Could that
information not be collected by an
onboard computer and monitored to
detect the first hints of wheel slippage?
I bet you could detect black ice (or any
loss of traction) long before you actually
entered a perceptible skid, just by
noting a small amount of wheel-slip
during normal driving. Coupled with
the information from a simple
temperature sensor, this would perhaps
give a fairly reliable detection of ice. |
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I like the idea of superball's backspin. [Maxwell] has a point though. Instead of me checking with every wheel and seeing if my wheels will easily lock up I could ask the all wheel drive to check with one tire at points I specify as relativly safe. Many roads are traveled and you might as well let the cars communicate. If my car could have warned the other three I saw in the ditch that night or the other way around even after the fact, that might have been useful. |
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//I could ask the all wheel drive to
check with one tire at points I specify as
relativly safe. // You mean try braking
or driving one wheel slightly to test for
slip? |
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I was thinking more of just looking for
very small amounts of slip during
normal driving. I'm assuming that, even
on a good road and without any sudden
braking or acceration, each wheel is
likely to slip a couple of degrees now
and again due to dirt and debris,
relative to the other three wheels. |
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On black ice, this must get significantly
worse, so the wheels would show a
greater tendency to shift "phase"
relative to one another. Only when the
driver then tries to brake or turn
sharply does this slippage actually
become a real problem. |
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So, detect incipient slippage and warn
the driver. |
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I live in the The Meadow. |
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"Unless it was wet." true, but the water would evaporate within a few minutes. |
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Unless it was 99% humidity. |
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My dad taught me to just jam on the brakes to see if it's icy. This is a much better idea. |
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Regarding the whole "temperature is useless" thing, the temperature may be completely arbitrary. A road with a microthin coating of road oil and rain water is just as dangerous and slippery as an icy one, and as difficult to detect. Using the superballs may be useful for either condition. |
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I would never consider abusing this precision instrument in traffic. |
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//So, detect incipient slippage and warn the driver.// |
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By then it's too late. I'm less worried about black ice while driving than I am while walking. At least in a car there is a thousand kilos or so of metal to protect you. |
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//By then it's too late.// Betcha it isn't.
Re-read my last annotation. It is only
too
late if you try to brake, accelerate or
steer
sharply on black ice. My point is that,
while
you are pootling along in a straight line,
black ice will be causing a small and
insignificant but detectable amount of
wheel slip. Monitoring this would
provide
a warning, giving the driver time to slow
down gently. Black ice is only a
problem if
you don't know it's there. |
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Surely the best way to discover if the road ahead is slippery is to just follow another car? - preferably one without ABS or traction control. When that spins off the road, rolls down the embankment and explodes in a dramatic fireball, you'll know there's probably black ice ahead. Proceed carefully past the black ice, pull over, and wait for another car to come along which you can follow. |
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//It is only too late if you try to brake, accelerate or steer sharply on black ice.// |
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Sharp manuevers are irrelevent.
You *may* be fine as long as you don't brake, accelerate or steer. But it's not always (or ever) possible to do that. The tinest change in weight balance, road camber, grade, etc. can send you into oblivion (see link). |
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Slippage detection is part of ABS, so in essence your anno is baked. |
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//Sharp manuevers are irrelevent.// Only
on the HB would Newton get such a hard
time. I would have expected you to be
more likely to skid when you were trying
to change velocity, but there you go. |
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//Slippage detection is part of ABS, so in
essence your anno is baked.// Not, as far
as I know, in this way. But anyway, just a
thought. |
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my BMW has a traction control system that monitors the ABS sensors to determine if the wheels are behaving in a way that indicates you are driving on a slippery surface. It then will adjust the shifting behavior of the transmission as well as the power output of the engine. I believe it does this by looking for differences in the rotational speed of the wheels in relation to one another. |
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In that case, I cede utterly and thank you
for teaching me something. |
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Check the link for a more detailed discussion of the ASC+T system. |
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Is there a concise version for the
disorganised topologist? |
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I posted a Short short version for you. if you look near the end of the first one you will find the info on the ASC+T. Those systems also link to the transmission as well in the ATC system. |
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//Only on the HB would Newton get such a hard time.// |
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I assume you are talking about the famous scientist 'Fig' Newton? |
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I don't buy the idea that you slip all the time a little. There are two types of friction Static friction and the other kind. static friction is not something you commonly overcome to make any tests. |
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To test you must apply a much more significant force to overcome static friction than the non static friction that you want to ensure you have enough of in emergency situations. I doubt I slipped at all the night I slid off the road until that point. I imagine I could have detected it before that point. |
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I however have no way of testing that, but those are my working assumptions. |
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//There are two types of friction Static friction and the other kind// |
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I believe dynamic friction is the term you are looking for. Unless of course you mean the _other_ other kind. |
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Kinetic friction is between two objects moving in regard to each other. The two types of kinetic friction are sliding friction (rubbing your hands together) and fluid friction (like the space shuttle on reentry). |
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Rolling friction is static because the contact patch does not move relative to the road surface (unless of course it is sliding on black ice, in which case it becomes kinetic friction). |
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The friction behavior of the contact patch of a tire is an incredibly complex system. I believe that there are both Kinetic and dynamic friction elements depending on the location within the patch. |
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What about pulp friction? |
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<sings> There's a fraction too little friction |
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Aye, thats the rub then isnt it? |
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//I posted a Short short version for you.//
Thanks, [johmrighous]. |
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