RE: Fire went out!

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> > > (BTW, what *does* the Hall effect sensor actually measure, and how?)
> > 
> > It doesn't actually measure anything.  It tells the ECU (which already
> > knows the angular position of the crank with great accuracy) whether
> > the TDC #1 it's just found is the firing stroke or not.
> 
> Again, how does it know? Extra acceleration upon firing?
> (in other words, what is the Hall effect?)
> (and again, wouldn't the angular position of the camshaft give
> *all* desired info at once?)
> 
... as someone (Orin ?) quite rightly pointed out there is a rubber belt
that connects the cam to the crank.  This can lead to measurement errors.
It is also a matter of convenience ... the flywheel already has those teeth
on it ... you'd need to add something to the cam to measure the angle.
Finally ... if you were measuring at the cam, then you couldn't use one of
those RPM dependent, variable cam timing pulleys ... :-)

Devices that measure angular displacement accurately are actually a bit
expensive.  It turns out that all the Hall sender does is send a signal that
provides a Yes/No like response to the question "Is the distributor pointing
to cylinder #1 right now?" which the computer software may want to know.  

The Hall Effect is something that has been discussed on the list before ...
I know I posted something about it myself ... but in any case, here's a
snippet from an old message posted by Robert Houk ...

	Umm...not really, it's more of a second-order effect, typically
using
	solid-state sensors (not "coils" -- that's just straight "EMI"), and
	it gets really hairy from there!). Check out:
	 http://arapaho.nsuok.edu/~bradfiel/advlab/Hall/HallEffect.html
	for a reasonably straight-forward explanation...

I checked and the URL still works ... HTH!

Steve Buchholz
San Jose, CA (USA)