RPM independence

[Howard Wilkinson]

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.