Dwell Control

[Ward]

On Sun, 11 Apr 1999 09:47:13 -0400, Bruce Plecan wrote:
Good question, I can only guess that they also have a problem during start
up.

If you look close, you will see taht the module (early ver's) have two
functions:

1) Convert an analog disrtibuter signal to a rectangular 0/5 VDC pulse.

2) Ignition Amplifer to charge and fire the coil, from a rectangualar pulse
comminf from the PCM/ECM. The coil charges when the ECM/PCM sig is high and
fires on the falling edge. 


Anouther note is that you must allow time for the firing to ringm\ prior to
charging the coil for the next cycle, or you will shorten the firing period,
(Bad).

As to why so many is there are but two big cap types in the same form
factor, and they have different zero corssing dectector phasing, which
affect the pasing of the output DRP. The early units had a high RPM problem
and were not long in service.

The Small cap HEI's have only ont type, Mech form factor

The LT1 has a slightly different version, No provisions for processing the
DRP, thats done by the Opto Spark directly.

All of the DIS systems are functionaly the same as the HEI,s. 


> 
> ----- Original Message -----
> From: Ward <wspoonemore at excite.com>
> To: <gmecm at efi332.eng.ohio-state.edu>
> Sent: Sunday, April 11, 1999 1:20 AM
> Subject: Re: Dwell Control
> 
> Then why with the Haltech ecm ([E6GM] a direct replacement for the aussie
> 165) do they mention to use it with a ignition module that performs the
> dwell controll?.
>   Then why are there so many different ignition modules?.
> How can the ecm perform a closed loop dwell controll with no feedback
from
> the coil?.
> Bruce
> 
> > Bruce, the only time that dwell is controled by the module it when the
> > system is in by-pass, (set init timing) or durring the 1st. part of
start
> > up, (when RPM lt 400).
> >
> > If you work it out, in usec it a tough job for an analog ckt. The math
for
> a
> > V8 is sec = 15/RPM, this will be the time for a single cyl ecvent, or
90
> > degrees of crank.
> >
> > Let use 3000 RPM. 15/3000 = 0.005 seconds or 5000 usec for 90 degrees
of
> > crank, if we have 20 degrees of spark advance, that say's we will fire
the
> > coil 20 degrees before the next Dist Ref Pulse, (DRP) or in fact, (90 -
> 20)
> > or 70 degrees after the last DRP. each degree is 5000/90 or 55.5
> > usec/degree.
> >
> > The interesting thing is that the coil is an electrical circuit and
could
> > care less about degrees of crank, but it tends to retarad (as in
resist)
> the
> > flow of electrical current, and therefore requires time to charge
up,(sort
> > of like filing the bucket).
> >
> > So the dwell issue is an old hold over from point's. In fact the coild
> don't
> > care as long as you giveit enough time to charge, In the case of most
GM
> > coils the min time is about 1 500 usec.
> >
> > I am sure you will chatch on that I'm working this out as I go, I had a
> > tough time when I ws desiging a computer ignition system abiout 10
years
> > back, get the time travel issue under contol.
> >
> > As an aside thanks for the other info.
> >
> > Ward
> >
> >
> >
> >
> >
> > On Sat, 10 Apr 1999 10:01:25 -0400, Bruce Plecan wrote:
> >
> > > Well, I posted some time ago about the dwell control being in the
> module,
> > > and was corrected that it is actually in the ecm program.  Tada, well,
I
> > was
> > > correct, as well as the correction.  In the DIS Teachers manual they
> > mention
> > > that the dwell control is in the module, and that it is a closed loop
> > dwell
> > > control.  Meaning if the module doesn't sense that the coil (s) were
> > fully
> > > charged, then the dwell was adjusted.  What the ecm must do is try to
> > > account for this correction, hence it has what looks to be dwell
control
> > in
> > > it.  Again all of the above, IMHO, and from the GM DIS Teacher's
Manual.
> > >    Bruce
> > >
> >
> >
> >
> >
> >
> > _______________________________________________________
> > Get your free, private email at http://mail.excite.com/
> >
> 





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