Flywheel/Encoder patterns

kleenair at ix.netcom.com kleenair at ix.netcom.com
Fri Dec 6 18:07:28 GMT 1996


Walters Chris wrote:
> 
> >This is exactly what I was thinking about when I decided to use 180
> >teeth.  I figured if I use a lower resolution, I would have to calculate
> >RPM (which I have to do anyway), then calculate time elapsed per degree
> >of rotation (which is estimated), and load my counter.  By going to 180
> >teeth, I've eliminated the last two steps, and all events happen once
> >per degree based on an actual signal, not an estimated value.  I realize
> >that this approach also generates more interrupts per revolution, but it
> >seems easier to work with.
> 
> I thought 60 was the practical limit on number of teeth on a timing gear -
> above that and you'd start to lose resolution.
> 
> Rather than counting pulses, has anybody thought about encoding the timing
> gear such that you can read crank position directly off the gear? Sortof
> like a shaft encoder.
> 
> Snake
> no cool Fords yet, one cool Dodge



The tooth wheel operates by generating an interrupt which in effect tells 
the processor the engine has advanced an X amount of degrees.
Using the interrupt method is preferred because regardless of what is 
going on, the processor will stop what it's doing and attend to engine 
needs (i.e. load a counter, advance degree count, etc...).  If we do away 
with the interrupt, depending on what kind of calculations are being 
performed, system performance will suffer.  If we keep the interrupt 
(i.e. generate an interrupt based on encoder state change) what have we 
gained?  We still need the cam sensor to tell us if we are in power or 
intake strokes.



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