RPM independence

[Howard Wilkinson]

Todd:
    I would be very interested in reading the article you mentioned.
Please let me know if you find it.
    My basic thought here is to emulate the working of the Bosch
mechanical CIS fuel injection system electronically which would allow
it to be modulated by feedback, but still yield a system simple enough
to be operated by a very low cost controller.  Injector timing is
irrelevant, therefore injector firing rate is also irrelevant within
the range above engine RPM.
    Perhaps mathematical formulae are not adequate to control fuel
delivery.... maybe lookup tables are necessary.  The Bosch mechanical
system used a shaped MAF to keep fuel flow which was mechanically
controlled in line with the motion of the MAF actuator arm.  This put
the mathematical calculation into the profile of the MAF throat which
was in effect a computer (a mechanical computer).  It took far more
intelligence in my opinion to design this one part than to program
look up tables which can be done by trial and error, or by a simple
feedback system.  I believe I could sit here and flow chart out and
write a program to generate the lookup tables based on feedback, and
minimal programmer input.  I'm just looking at different possible
approaches to the problem of managing fuel delivery via computer.
                                        H.W.

-----Original Message-----
From: Todd....!! <atc347 at c-com.net>
To: diy_efi at efi332.eng.ohio-state.edu
<diy_efi at efi332.eng.ohio-state.edu>
Date: Tuesday, May 11, 1999 1:15 PM
Subject: Re: RPM independence


>Hello Howard,
>
>your theory is TOTALLY GREAT and acceptable, and a system has alread
>ybeen created, produced, and marketed, and it's gone over wiht a
pretty
>good fine tooth comb within on eof the laterChecvy Hi po mags dealing
>with all of the diff types, makes, and brands of FI for just about
any
>type engine!
>
>Will get the name of the mag, I know you already know about the mag,
>just maybe not about the article(s) within this specific issue?
>
>But the basic function of the type system I believe you are referring
to
>is based upon the use of formulas instead of tables... I think you
are
>right in line witht the way this REALLY advanced system is designed
to
>function!
>
>Will post details later, (mag's at home)!
>
>LATER!
>
>Todd....!!
>
>Howard Wilkinson wrote:
>>
>> 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.
>
>
>