Ign Advance on MR-2

[Diehl, Jeffrey]

I've heard a lot of talk about magnetic reluctor sensors and the associated
circuitry.  What about a Infra-Red emitter/receiver pair who's output goes
through a Schmitt trigger?  This seems easier to design around...  What am I
missing?

I could have two wheels attached to the crank pulley, one with 1 tooth, and
one with 4 teeth.  I might have to run the output through a flip-flop to
reduce the frequency 1/2...  Then use a 2-bit counter to select one of 4
transisters to turn on, which in turn charge/discharge the coil.

This seems simple, actually.  Am I missing something?

I can't use the cam gears for timing, because we intend to adjust the cam
timing on the fly; this is why we need to build a circuit which emulates the
distributer, which is run off the exhaust cam.  

As you can see, we have suffered from feature creap.  We started out simply
wanting to emulate the distributor, now we are talking about a 4-coil DIS.
<evil grin>

Any comments are more than welcome.

Thanx,
Mike Diehl.

-----Original Message-----
From: Les Newell
To: diy_efi at diy-efi.org
Sent: 8/12/2001 4:28 AM
Subject: Re: Ign Advance on MR-2


The ouput of this type of sensor is very dependent on engine speed. At
lower
revs it will be a sharp positive spike as the tooth leading edge passes
the
sensor and a sharp negative spike as the trailing edge passes the
sensor. As
the speed increases the waveform becomes more square and at very high
speed
the waveform will approximate the shape of the tooth. The wave shape is
also
dependent on the load on the sensor.
The output voltage is also highly dependent on speed. Open circuit
voltage
can be anything from a few millivolts at cranking speed to tens of volts
at
high revs. The only way to make sense of these messy signals is to
detect
the zero crossings as they will always be at the leading and trailing
edges
of the tooth.

What are you trying to do? Are you trying to replace the distributor
because
you don't have room for it or are you trying to replace the ECU?

If you are replacing the distributor it may be easier to make up toothed
wheels that can be attached to the camshaft and relocate the sensors.
The
toothed wheels could even be replaced by blobs of weld on the cam pulley
(assuming it is belt drive). Obviously you will still have to make an
electronic distributor but this should not be difficult. One way would
be to
use a set-reset latch driven by two crank position sensors, one for
piston 1
at about 10-30 deg ATDC and one for piston 2 at 10-30 deg ATDC. The
latch
would then drive substantial PNP transistors, switching the high sides
of
the coils (the ECU drives the low side). One coil would then feed pots 1
and
4 and the other pots 2 and 3, using the wasted spark system.

Les


> For all fo you who have replied and tried to help me, Thank you.  I'm
not
> trying to be difficult, but I have to really understand how this
system
> works.
>
> My dad and I are considering an engine modification which will
necessitate
> converting to a distributor-less ignition, or at least fooling the ECU
into
> thinking it has a distributor....
>
> We're thinking that as the tooth approaches the magnet, it induces a
current
> which gets larger as the tooth approaches and smaller as it passes,
forming
> (perhapse) a sin wave pattern.
>
> Now, if the ECU fires a spark plug when this current exceeds a fixed
> voltage, we could advance/retard the ignition timing by adding a bias
> voltage into this equation.  The fact that the pickup only has two
wires
> coming out of it implies that all of this math is being done inside
the
ECU
> and not by biasing the pickup itself, right?  These details are
important
to
> us when we try to build a circuit which emulates this behaviour.
>
> Any insight you may have would be most welcome.
>
> Thanx,
> Mike Diehl.
>
> -----Original Message-----
> From: Chris Conlon
> To: diy_efi at diy-efi.org
> Sent: 8/11/2001 12:46 PM
> Subject: Re: Ign Advance on MR-2
>
> At 12:42 AM 8/11/01 -0600, Diehl, Jeffrey wrote:
>
> >other with 1.  The single-toothed wheel is probably used to run the
> tach and
> >is slightly offset from the cooresponding tooth on the 4-tooth wheel.
>
> The tach should be run via a signal from the igniter. On an '87 it
> probably just takes a signal from the low voltage side of the coil.
>
> >There are no vacuum lines, so it is not doing vacuum advance.  The
only
> >moving part is the shaft on which the two wheels move.
> >
> >So, my question is: How does this mechanism manage to advance the
> spark?
>
> That ECU uses an AFM. It doesn't measure MAP directly, but can figure
> out load, based on RPM and the AFM signal. It then uses the load value
> to adjust the spark timing. The ECU controls all aspects of spark
> timing... except dwell, which is probably controlled by the igniter.
>
> Actually that ECU is old enough that the Ne signal from the dizzy
> (the one with more teeth) may go to the igniter, which then feeds a
> copy of the signal to the ECU. (Operation is pretty similar to the
> other setup, though, from the ECU's point of view.) Just a quirk to
> watch out for when you're tracing down wires.
>
>    Chris C.
>
>
------------------------------------------------------------------------
> ----
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
> quotes)
> in the body of a message (not the subject) to
> majordomo at lists.diy-efi.org
>
>
>
------------------------------------------------------------------------
--
--
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
quotes)
> in the body of a message (not the subject) to
majordomo at lists.diy-efi.org
>

------------------------------------------------------------------------
----
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
quotes)
in the body of a message (not the subject) to
majordomo at lists.diy-efi.org


----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org