[Bulk] Re: [Diy_efi] Donegan ECU

[Bernd Felsche]

On Friday 05 January 2007 12:26, Steven P. Donegan wrote:
> On Thu, 2007-01-04 at 18:37 -0700, Tom Visel wrote:

> > It's trading mechanical complication for electronic complication.
> > Mechanical fuel pressure regulators are a mature technology, and the
> > math for injectors that have manifold-referenced fuel pressure is
> > simpler than that for injectors with static pressure, or for
> > computer-controlled feedback-requiring variable pressure systems. 
> > Also, anything with the pressure control at/near the tank is going to
> > have hysteresis problems which will tend to minimize the gains that
> > might have been found by the increased complexity.

> For me doing just about anything in electronics and software is
> far easier than doing it in metal (and I am a fully qualified machinist
> as well as an electronics/software dude). Given this will require one
> more mostly passive input conditioning circuit and one PWM output
> circuit I may add it on general principles.

The control system aspects of the long delay via a fluid connection
between the pump and the injector is very complex. This is
especially so because the delay isn't a constant. The pressure
signal will pass in either direction at the speed of sound in the
medium, taking into account the present speed of flow in the pipe,
the speed of sound varying with pressure and temperature.

It takes an enormous amount of code and auxiliary hardware to
"replace" a very simple and cheap mechanical regulator in this
application.

It would be _possible_ to build and integrate the necessary sensors
as well as implement the necessary fluid-dynamic and control system
(differential) equations in a sophisticated microcontroller.  One
would also have to take into account the opening and closing
injectors, where pressure pulses are returned, requiring filtering,
again depending on the conditions of the fluid, and the time that
the injectors are open.

You are of course aware that all control algorithms have to be
inherently safe; i.e. failure of one or more components cannot cause
catastrophic events such as leaving injectors open indefinitely to
hydraulically lock an engine, etc.  Plausibility of all inputs has
not only to be determined, but also determined very quickly.

-- 
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