simple analog fuel injection

[Chris Morriss]

In message <01bd9e4a$a47d8560$53198fd1 at nacelp>, Bruce Plecan
<nacelp at bright.net> writes
>
>
>
>%TPS change per amount of time.  Or change of voltage per amount of time.
>Remember you have 70% throttle opening at 20% throttle
>travel.  Then cold coolant correction.  Air temp correction.  RPM
>Correction, gee gettin complex quick.  I'm not at all trying to rain
>on your parade.  Within the last 6-7 months I think this very issue
>accleration pump has been talked about.  Think the final thoughts were 5
>tables, corrections for it.
>  You can minimize these corrections IMHO by using a fuel pressure
>regulator referenced to engine vac.  But, still complex, to do right.
>Also, intake tract ducting can help (ie real long in lenght).
>  If I had to do something along these lines I rack a bunch of 555's
>together.  Base Pulse width, then temp correction, then air correction
>accleration/TPS, accleration temp, accleration MAP etc etc.  add'em
>up and then fire the injector(s).
>Just some thoughts
>Bruce     One similiar project here at CSH, HQ was a traction
>               control device worked really nice then one night temp
>               dropped on test drive a couple degrees, and the car
>               could not be made to move, disable TCD and drove
>               home.  Put device in freezer wouldn't work.  Thaw to
>               34+ and it was fine.  Could not be made not temp
>               sensitive.  Months of work down the drain...  Tandy
>               Corp stock rose $2/share over what I spent at radio
>               shack
>
Air temperature correction?  Come on, I was using this to replace two
old 1.25 inch SU carbs.  They didn't have any water or air correction
methods.  Like I said, I wouldn't use the system on a car that needed
stringent emissions checks.

Regarding rpm correction; take a look at most published 3d graphs of
injection pulse width, versus MAP, versus rpm.  Apart from a slight
increase in PW around the best torque rpm (best VE), then the curves
show almost straight lines with very little variation with rpm.  MAP is
the dominant variable.  I agree that water temp needs a large
correction, but that can be done with the equivalent of a manual 'choke'
control.  (We kept manual chokes in the UK for many years).  My
prototype was a bugger to keep running after starting when cold, but
that was because I didn't have a fast idle arrangement.  I've got a
heated bypass valve now to try off a Volvo 760 K-jet system. (and a
separate cold start injector,  This could use the thermo-time switch
from a K-jet system to provide enrichment on cold starts with a cold
engine.)

If instead you want to use MAF for a simple system, with an injector
pulse every rev, then you have to perform a correction for rpm.  (PW
proportional to 1/rpm)  The original L-jetronic did this by a very crude
mechanism.)

I am not suggesting that an analogue system is ideal.  It's a lot of fun
to play with though.  BTW, the old Microdynamics analogue system used
virtually the same technique, with gain, offset, and transient
enrichment pots.

I didn't use 555 chips.  I had a voltage controlled pulse-width
generator triggered at TDC.  All of the processing was done on the
voltage signal prior to it going to the pulse generator section. I did
use temperature corrected MAP sensors though from Farnell components
(UK)

-- 
Chris Morriss