Electronic (uC ccontrolled) ignition

[Johnny]

Shane Eric Taylour wrote:
> 
> Hi,
> 
> Does anyone know how the ignition timing is done on distributorless
> ignition systems when cranking the engine? How is the ignition timed when
> the crank is not turning over at constant revs?
> 
> It may take several attempts at cranking the engine before the ignition
> fires. How then, do any reference marks on the crankshaft/flywheel apply
> when starting?
> 
> Any thoughts on the subject appreciated.
> 
> Best Regards,
> 
> Shane,
> (taylour at minyos.its.rmit.edu.au)

It usually takes one full revolution to sync on whatever the sync device
might be (like a couple of missing teeth on the crank wheel). After that
each tooth is counted and it doesn't really matter if it occurs at
cranking speed or not. Cranking speed is fast enough for accurate tooth
count. It doesn't matter that it's not occuring at a constant speed. In
the most technical terms, piston engines are never turning at a constant
speed. The crankshaft is always either increasing or decreasing in
speed. The CPU counts each tooth regardless. Measuring the time since
the last tooth went by is how it knows if the engine is speeding up or
slowing down, even after just a few degrees of rotation. Especially if
there are 60 teeth on the crank wheel. This gives a fairly fine
resolution to base engine speed and crank position on.

-j-