[Diy_efi] Peak cylinder pressure timing

[Bernd Felsche]

On Wed, Mar 05, 2003 at 01:17:54PM -0600, steve ravet wrote:
> Phil Lamovie wrote:
> > Lets say we log lots of incremental values into a table;
> > say pressure vs degrees crank.
> > 
> > The issue then becomes one of how to use the data acquired.

> There's a thesis that's been posted before from a graduate student
> using ion sensing to determine the peak pressure point, one of his
> applications was to use that as feedback for ignition timing so
> that the peak pressure was always at the "best" crank angle.  That
> wouldn't require any fancy math, and would eliminate the "spark
> tables" current used.

> > If you can do fast samples with an FFT function the area under
> > the curve (torque) becomes apparent.

> Instant torque is cylinder pressure times piston area times the
> "horizontal" component of the crank arm, right?  Average torque is
> the integral of that, also no fancy math required.  I'm not sure
> what use average torque would be other than display it for the
> user -- maybe traction control?

Average torque maximisation to optimise output under WOT?
i.e. by manipulating valve, injection and ignition timing, the
engine could "optimise" itself over a few driving cycles.

For cruising, i,e, driving in a high gear with relatively low revs,
the torque peaks should be minimised, reducing rotational vibration
and speed fluctuation of the crank, with resulting improvements in
"smoothness" without relying on a heavy flywheel.

If you wanted to do FFT (maybe to aid in filtering out the system's
characteristic frequencies), then there are any number of solutions
available; plenty of software libraries that were designed to run on
CPUs running at hundreds of kilohertz. A band-pass filter on the
input can go a long way to reducing the FFT required.

-- 
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