Electronic spark timing ! PLEASE HELP !
Jose Carlos Rublescki
rublesck at ez-poa.com.br
Thu Jul 30 05:18:02 GMT 1998
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It has recently been discussed in this list something about angular =
velocity variations in the engine that would occur because of bumby =
roads. I have a problem that is very related to this and I need help.
I have sucessfully designed an injection/igniton system based on 68HC11. =
The injection part is working great. It is a sequential multipoint =
system and it even has two injector for each of the (four) cylinders to =
handle turbo boost situations. I use ethanol alcohol as fuel so I can =
use LOTS of boost and need LOTS of fuel.
The problem comes with the ignition part. In my first system, the MCU =
received from the engine one pulse each 90-degrees of engine rotation =
(on TDC's). For each 90 degree period the MCU counted the number of =
clock pulses (2 Mhz clock), let's say n, and then it did simple =
aritmethics as follows:
90 DEGREES =3D n clock pulses
x DEGREES =3D y pulses.
So if I wanted a spark to appear x DEGREES after the 90-degree mark, I =
should just have to program the MCU to generate the spark after y clock =
pulses.
(which means that I measured a 90-degree period, do math and applied the =
result to the next period, assuming both periods would both be very =
similar to each other).
I should work fine in theory, but the problem I found is that there was =
sometimes too much variation from one 90-degree period to the next. I =
thought I could devise the pattern of the variations. I tried to =
calculate angular acelerations so that my system would predict what =
would be the length of the next 90-degree period (and many other =
aproaches). All of this failed. I came to the conclusion that the =
variations were random and that I could not improve my system further. =
The amounts of variation I got on the spark generation due to the =
variation of the measurements were big enough to blow head gaskets of my =
turbo engine. (I didn't however, melted pistons as I did when I was =
working on the injection and the mixture got inadvertedly lean WITH lots =
of boost)
My BIG question is that there are here lots of cars made by Volkswagen =
where the ECU only reads one pulse each 90-degree of engine rotation. Do =
they just live with the fact that they will have spark timing variations =
or do they have some misterious way (at least to me) make this =
calculation?
After I gave up using the system above cited, I decided to use a =
40-teeth wheel attached to the engine like FIAT and GM do here (only =
they have different teeth count). I now get much better results, but =
they're still not as great as I would expect. I now get pulses every =
9-degree of engine rotation. The process remains the same.
9 DEGREES =3D n clock pulses.
x DEGREES =3D y clock pulses. (figure out what y is and delay that =
value).
Thanks in advance,
Jose Rublescki
Dim-efi (Dio-efi) -- Do it myself efi (Do it ourselves efi)
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<BODY bgColor=3D#fffff0>
<DIV><FONT size=3D2>It has recently been discussed in this list =
something about=20
angular velocity variations in the engine that would occur because of =
bumby=20
roads. I have a problem that is very related to this and I need=20
help.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I have sucessfully designed an injection/igniton =
system based=20
on 68HC11. The injection part is working great. It is a sequential =
multipoint=20
system and it even has two injector for each of the (four) cylinders to =
handle=20
turbo boost situations. I use ethanol alcohol as fuel so I can use LOTS =
of boost=20
and need LOTS of fuel.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>The problem comes with the ignition part. In my =
first system,=20
the MCU received from the engine one pulse each 90-degrees of =
engine=20
rotation (on TDC's). For each 90 degree period the MCU counted the =
number of=20
clock pulses (2 Mhz clock), let's say n, and then it did simple =
aritmethics as=20
follows:</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>90 DEGREES =3D n clock =
pulses</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>x DEGREES =3D y =
pulses.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>So if I wanted a spark to appear x =
DEGREES after=20
the 90-degree mark, I should just have to program the MCU to generate =
the spark=20
after y clock pulses.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>(which means that I measured a =
90-degree period,=20
do math and applied the result to the next period, assuming both periods =
would=20
both be very similar to each other).</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>I should work fine in theory, but the problem I =
found is that=20
there was sometimes too much variation from one 90-degree period to the =
next. I=20
thought I could devise the pattern of the variations. I tried to =
calculate=20
angular acelerations so that my system would predict what would be the =
length of=20
the next 90-degree period (and many other aproaches). All of this =
failed. I came=20
to the conclusion that the variations were random and that I could not =
improve=20
my system further. The amounts of variation I got on the spark =
generation due to=20
the variation of the measurements were big enough to blow head gaskets =
of my=20
turbo engine. (I didn't however, melted pistons as I did when I was =
working on=20
the injection and the mixture got inadvertedly lean WITH lots of=20
boost)</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>My BIG question is that there are here lots of cars =
made by=20
Volkswagen where the ECU only reads one pulse each 90-degree of engine =
rotation.=20
Do they just live with the fact that they will have spark timing =
variations or=20
do they have some misterious way (at least to me) make this=20
calculation?</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>After I gave up using the system above cited, I =
decided to use=20
a 40-teeth wheel attached to the engine like FIAT and GM do here (only =
they have=20
different teeth count). I now get much better results, but they're still =
not as=20
great as I would expect. I now get pulses every 9-degree of engine =
rotation. The=20
process remains the same.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>9 DEGREES =3D n clock =
pulses.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>x DEGREES =3D y clock pulses. =
(figure out what y=20
is and delay that value).</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Thanks in advance,</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT><FONT size=3D2>Jose =
Rublescki</FONT></DIV>
<DIV><FONT size=3D2>Dim-efi (Dio-efi) -- Do it myself efi (Do it =
ourselves=20
efi)</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV></BODY></HTML>
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