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My guess concerning the Root Cause
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Posted by Notnoel [Email] (#23) [Profile/Gallery] (more from Notnoel) on Sun, 25 Sep 2011 09:21:56 Share Post by Email
In Reply to: Re: What Is the Root Cause?.., Roger D [Profile/Gallery] , Sun, 25 Sep 2011 08:29:16
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My feeling is that there is really nothing wrong with the design of the ABS unit, per se. I think the problem is in the placement of everything else around it. As SaabJunkie noted, the fan from the alternator blows warm area into this corner of the engine bay, and it is located behind the antifreeze reservoir (another source of heat. Lastly, the accumulator (the "bomnb") sits up high in this little warm dead air zone, which is further insulated by the soundproofing on the hood when closed.

The fault typically occurs in very warm, humid conditions on about 95-100 degrees when stuck in a traffic jam or rush hour traffic (a double whammy of lots of use, and no air flow occurring because of the slow speed). Typically, what happens is the bomb becomes over heated, which kicks on the ABS pump, and then sets uip a vicious cycle.

A couple of years ago, I figured out that placing a wetted rag over the bomb would provide enough adiobatic cooling to remedy the situation, as long as the rag remained wet. This lead to the wetted sock solution RayF describes above. I'd given thought to setting up a sprayer so that I wouldn't have to pull over, just hit a button. But, as others have noted, there are a lot of electric connections int his area, and spraying water remotely (out of sight), might not be the best idea.

This problem only arises on the worst days of the summer (for me at least), and it seems that it only takes a very little bit of cooling to bring the ABS unit back to within its proper working temperatures. The engineering challenge is to find a workable solution that can be remotely operated via a switch in the cabin, and that doesn't use water.

Last week I got the idea of using a peltier cooler, like the one I used to have on an overclocked computer a few years back. These are about 1.5 inches square, run on 12 volts DC, and are capable of cooling to 4 degrees F. I've already spoken with an engineer at the site and selected the unit. The trouble is that the bomb is a curved surface, and the pletier cooler is a flat surface. Therefore, I need to fabricate a heatsink (perhaps I should call it a coolsink) to transfer the cooling to the bomb. To have the proper thermal conductivity, the coolsink needs to be made of aluminum or copper, so it is going to require me to do a bit of manufacturing. The actual heat sink to conduct the heat away from the peltier's other side is easy - a standard computer heat sink should be fine.

Here's a link to a little film about how Peltier coolers work (for my application it does not need to have such a giant heatsink:

http://www.youtube.com/watch?v=3x-wxLEfLEQ&feature=related

I'll place a How-to in my photos section when I am done, it it works, that is.




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