Crank Position

[Gregory A. Parmer]

I had intended to just listen in and see what I could learn
about about EFIs, but suddenly I've got to throw in some 
suggestions/comments/questions that I had previously thought
were obvious.

A key question is "how many possible variations are you/we planning
on designing here?"  I would hope that the system will be designed
in modules of some sort so that the type of sensors used can vary.
It shouldn't really matter whether a person wants to use the toothed
wheel or the flying magnets, and it shouldn't matter whether it's attached
to the harmonic balancer or the flex plate. Opinions are sure to differ
about such specifics.  A reasonable design should take this into account,
and allow several options, IMHO.

>	| The angular precision will be greater for a given magnet diameter as the
>	| radius increases. 
>	
>	No, I don't agree. 
>	
...<stuff deleted>...
>	of the magnet makes *no* difference; however the placement does. You can also
>	buy ring magnets with multiple pole pairs. Each pole pair would produce one
>	pulse.


This is way over my head, but my thoughts are these.  

  If you use four magnets (assuming V8 here) that are all just alike it 
won't matter whether the trigger occurs at the beginning or the end of 
the pulse, just that it occurs at the same point for each of the four 
magnets.  Adjustments of the trigger mechanism *relative to crankshaft
position* (an obvious requirement) makes the point moot about the exact
relationship of the magnet and sensor at the time of the trigger.

  Where precision becomes a real issue is in the placement of the magnets.
If I understand the discussion correctly and you intend to use several magnets
to sense crankshaft position then the *distribution* of these magnets around
the harmonic balancer or flexplate is where the precision factor gets tricky.
It'll be *much* easier to accurately space four magnets at 90 degree intervels
around a flywheel or flexplate than around a harmonic balancer.  If you miss
by 1/4" on a 7" HB you'll be out ~4 degrees, but the same error on a 24" flyweel
results in only 1 degree of error.  The math is probably off, but you get the
picture.  I would think the diameter of the magnet itself is irrelevant but that
the diameter of the wheel they're attached to is *very* relevant.

Preparing a spot in the sand to bury my ignorant head,    :)
-greg

Greg Parmer				INTERNET:  gparmer at acenet.auburn.edu
Lead Specialist, Network Support	VOICE: (205) 844-9660
Alabama Cooperative Extension Service	FAX: (205) 844-3501
Auburn University, AL  36849-5646