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'[EE]: Ignition design question'
2001\03\21@104329 by John Pearson

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As the first step toward my traction control device, I want to build a
circuit that will cut out cylinders with the push of a button.

I want to use a pic that will count and pass along the pulses from the
distributor points - to the ignition box, and determine which pulses to
intercept and not pass along to cut cylinders.

My distributor uses an armature and reluctor for triggering the ignition
box. The wave form goes positive, then cuts  straight down negative. I
assume the ignition box looks for the negative edge.

I need a circuit so that the pic can see the signal from the reluctor. What
would be a good place to start with that.

Then I need a circuit so the pic can trigger the ignition box. I can use
the points input on the box for that, so all I need there is a good 12v
square wave. What would be a good starting point for that type of circuit.

Or perhaps, could the pic 'shunt' the signal from the reluctor? Would that
be easier?

Thanks

John

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2001\03\21@105826 by David VanHorn

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>
>I need a circuit so that the pic can see the signal from the reluctor.
>What would be a good place to start with that.

Op-amp to amplify and square up the signal.


>Then I need a circuit so the pic can trigger the ignition box. I can use
>the points input on the box for that, so all I need there is a good 12v
>square wave. What would be a good starting point for that type of circuit.

Skipping ignition pulses isn't very fuel efficient.
If it's injection, you could turn off the injectors on a
cylinder-by-cylinder basis, and then save that fuel.

There are also some interesting things that can happen with a slug of
fuel-air mix in the exhaust system when the next cylinder fires.. :)

>Or perhaps, could the pic 'shunt' the signal from the reluctor? Would that
>be easier?

You could probably take the signal away from the ignition, but don't take
it away from yourself too!
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2001\03\21@112717 by Steven J. Devine

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> Skipping ignition pulses isn't very fuel efficient.
> If it's injection, you could turn off the injectors on a
> cylinder-by-cylinder basis, and then save that fuel.

Also, overheats the catalytic converter (if so equipped).  Possibly detonates it :)  
Even if not equipped with one, raw fuel air mixture hitting hot exhaust often detonates in the manifold blowing out the muffler (don't ask me hoe I know THAT one... ).

Steve

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2001\03\21@185225 by Neil Bradley

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> As the first step toward my traction control device, I want to build a
> circuit that will cut out cylinders with the push of a button.
> I want to use a pic that will count and pass along the pulses from the
> distributor points - to the ignition box, and determine which pulses to
> intercept and not pass along to cut cylinders.

YEOUCH! DON'T CUT IGNITION!

This is a sure fire way to erode your exhaust manifolds, piston heads, and
valves (or apex seals if you're in a rotary engine'd vehicle). It'll also
cause quicker failure of the catalytic converter, possible backfires, and
premature wearing of the O2 sensor.

It is FAR better to cut specific fuel injectors. Also make sure that the
cut injectors are on opposite sides of the stroke at even/opposite
distances on the crank to minimize crank flexing (and wear on the crank
bearings).

FWIW, My background was designing a computer for drag racing that had to
run to 15KRPMs and account for engine knock, timing, and fuel injection
control. It used an AVR micro and a Philips XA micro.

-->Neil

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Synthcom Systems, Inc.
ICQ #29402898

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2001\03\22@041934 by Martin Hill

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It's all true.  If your engine is not fully upto temperature you will get  a
lean mixture when you turn the injectors on again due to the lack of
fuel puddling which was there before.  Obviously you have to re-
enable the injector when it is turned off.

Have you looked at retarding the spark to reduce power output?

Martin

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2001\03\22@044518 by Roman Black

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Steven J. Devine wrote:
>
> > Skipping ignition pulses isn't very fuel efficient.
> > If it's injection, you could turn off the injectors on a
> > cylinder-by-cylinder basis, and then save that fuel.
>
> Also, overheats the catalytic converter (if so equipped).  Possibly detonates it :)
>
> Even if not equipped with one, raw fuel air mixture hitting hot exhaust often detonates in the manifold blowing out the muffler (don't ask me hoe I know THAT one... ).


Absolutely. Guys on motorcycles often hit the
"kill button" on the handlebar, this cuts ignition
for a fraction of a second, then when you put it
back on that fuel detonates with a loud explosion
through the exhaust system. I don't do it as it can
bend exhaust valves on the cylinder head, but some
young hoons do it to get attention from their buddies.

If you want to control traction for anti-wheelspin
might I suggest retarding the timing, you can still
burn the fuel safely, but with the spark occuring
when the piston is further down the bore there will
be a big decrease in power. :o)

More info needed??
-Roman

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2001\03\22@094616 by John Pearson

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Yes, retarding the spark is my preffered method of power reduction. Many
Street Class drag racers, who must use street rires, use computers to
tailor a 'soft' power curve. But too expensive and too difficult to make.

Thanks

----------
{Quote hidden}

detonates it :)
> >
> > Even if not equipped with one, raw fuel air mixture hitting hot exhaust
often detonates in the manifold blowing out the muffler (don't ask me hoe I
know THAT one... ).
{Quote hidden}

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2001\03\22@103755 by Roman Black

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John Pearson wrote:
>
> Yes, retarding the spark is my preffered method of power reduction. Many
> Street Class drag racers, who must use street rires, use computers to
> tailor a 'soft' power curve. But too expensive and too difficult to make.


John, is this really that hard? Surely the traction
control will only be needed in a narrow rev-band
near the motor's peak power. Say 6000-9000rpm for
a 9000rpm redline motor?

So what's hard about spark retard as your rev limiter,
why not just add a preset delay to the signal, taking
it from a few degrees BTDC to well after TDC. If you
want to get fussy you can use the PIC to measure revs
and adjust the spark delay accordingly, this is not
that hard either as there are finite rates that an
engine can accelerate and decelerate, and mechanical
averaging.

It would be pretty scary to selectively cut spark
to some cylinders of a carburetted engine, you really
risk flash and backfire and other scary problems.
My racing motorcycle has inbuilt revlimiting, where
the fuel injection AND spark are cut. Cutting spark
and leaving fuel scares me... BOOOMMM!! :o)
-Roman

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