PLL on crank angle sensor input

John Hess JohnH at ixc-comm.net
Tue Mar 4 21:43:33 GMT 1997


Basically the same way GM does it on computer controlled HEI.  They 
measure the RPM and calculate the spark offset off the sensors in the 
distributor.  Note that the GM V-8s from about '82 through the LT1 
(90?) used a HEI with no vacuum or centrifugal advance;  but, had a 
separate processor for the spark system.

If you measure the time between contact closures, you have a pretty 
good idea of what the RPM is.  From this (as stated above), just 
calculate the time to fire the plugs.



----------
From:  cloud at peaches.ph.utexas.edu[SMTP:cloud at peaches.ph.utexas.edu]
Sent:  Tuesday, March 04, 1997 1:45 PM
To:  diy_efi at coulomb.eng.ohio-state.edu
Subject:  Re: PLL on crank angle sensor input

>I thought of using a PLL to phase lock a higher frequency clock to 
crank, or
>cam sensor to allow more resolution in developing ignition and fuel 
timing.
>The problem I see is the very large dynamic range required.   We 
have
>programmable on chip PLLs that would require software intervention to 
change
>the feedback as the frequency approaches range boundaries.  me

this topic surfaces every-so-often.  I've asked about it and
been told that the PLL circuit is not stable enough.  My experience
with PLL's is limited, but seems t'me that once capture is achieved,
the little guy ought track any rev changes (esp. for stock)
just fine.  Then, there's the total dynamic range, some say
it's too great.  Dunno.  I know that my Ford truck ('82) uses
a four-pointed crank pickup and manages the timing with that.
MSD offers a similar setup now as an aftermarket timing control.
How do they do that without PLL (could use some sort of time
delay from the pulse onset that's modified by rpm so degree
setting is "constant" ... but anything 'derived' is going
to experience some fluctuation).  So, how'd Ford and how
does MSD do it?

Tom Cloud <cloud at peaches.ph.utexas.edu>





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