RPM independence

[Bruce Plecan]

One thing I've been musing over is something similiar.
But way over driving the injectors as a function of rpm.
That way I could use say two ecms one for timing (a v-8, as a v-8, on a v-8)
Then one for fuel at say the injector firing rate of a 6 cylinder.
Bruce



> I have given more than a little thought to the possibility of an EFI
> system that operated completely independently of engine RPM.  The idea
> being that as the injectors are batch fired anyway, the timing is
> irrelevant so long as the injectors fire at engine RPM or more.
>     Such a system could be almost entirely MAF based.  The injectors
> would begin at a very short pulse width, and simply increase pulse
> rate up to a set pulse rate where width would be increased thereafter.
> Such a system could be operated based on mathematical formulae rather
> than on look up tables.  A simple equation based on ECT could modify
> the result for cold operation, and a TPS modifier would give
> accelerator pump effect.  Map should not be necessary as air density
> should directly effect MAF output.  An O2 loop would handle minor
> dicrepancies.
>     A lot of the complexity of the common EFI systems comes from the
> desire to fire the injectors once per revolution.  Because of RPM
> dependence, the MAP, MAF, & TPS outputs are meaningful only in the
> context of RPM.  Total fuel delivery per unit time is only directly
> related to MAF.... It is not closely related to RPM, Throttle
> Position, or Vacuum individually as it is to MAF.  The MAF tells us
> how much fuel we must deliver per unit time, but the system must then
> work out the pulse rate based on RPM, and pulse width for that rate to
> achieve the desired delivery per unit time.
>     If we know that x amount of fuel is delivered at Y pulse width per
> pulse, then it becomes a simple matter to determine how many pulses
> per unit time are required to deliver that amount of fuel.  At some
> point pulse rate reaches a max practical limit, and at that point
> pulse rate can become constant, and pulse width may be modified above
> that point to control fuel delivery.  The fewer factors you are
> changing the simple the program becomes.
>     Perhaps this is a simple minded vew of the process, but then I'm a
> simple minded sort of guy.... I am of the "KISS" school of thought.
>                                 H.W.