Hi Paul




I am breadboarding up a version of your 555 circuit, and was wondering
if you could provide any ball park figures for the unvalued components
(capacitors, Leaning pot, R1 and damping resistor), or ball park pulse
width range.
I know the damping resistor was mentioned in an earlier post, but
I'm currently working from web-mail, and cannot access my archives.
I'm substituting a TLO31 for the op-amp, and a 2N6660 for the FET,
just because that's what I have laying around.
Do the injectors require fluid flows for self cooling?
Sorry to be a burden.
C. Smith

On the damping resistor ask JCP. I have no idea what
he has in mind.

Here are the remaining values.

-----------------------------------
ops forgot the drawing.
Here it is.

------------------------------

I don't think that op amp circuit is going to work.
I am going to get a Ti INA 122 instrument amp
and fool around with it. Minimum gain is 5
so I will probably try the leaning pot on the
input side of the inst. amp.

If you have a variable voltage supply I would feed that
into the TLC 555 for now. Just for demo purposes.


Paul Lamar


For a starting value, the damping resistor across the injector
should be several times the dc resistance of the injector.
The lower the value of damping resistor, the lower the kick
back voltage across Switch FET. The higher the value, the quicker
injector will close. Hence, some experimentation will be required
to optimize resistor value.

Any rail to rail capable Op-Amp should work, no need for anything fancy.

Unfortunately, this simplistic analog approach is a step backwards
to the days (late 60's early 70's) of Bosch electronic fuel injection.

(Being an "old analog engineer", I understand this circuitry very
well.  But have to admit newer digital designs (i.e. RWS) are
far more adaptable, precise and reproducable !)

Be advised, the 555 will not survive very long operating
directly off of a 12 volt aircraft bus.
Sketch is Breadboard Only, NOT FLIGHT WORTHY !

JCP

We will put in a $1 three pin low power voltage regulator
rated to 35 volts input. They come in 5, 6.2, 8.2 and 9 volts.
See the attached pdf. National semi. LM78LXX

I did not do that yet as I wanted to experiment with the power
supply voltage.

EFI computers are fine in theory but the history has shown that EFI systems
are time consuming to tune and trouble some. Some people have given
up. The car manufactures spend millions getting them working and
then all cars built have the same wiring harness and mechanical layout.

An analog circuit either works or it don't. Much easier to fix and
trouble shoot with simple tools like a VOM and a scope.

I have done both but I am better at designing and programing real
time computers in assembler. Been there done that :)

http://www.rotaryeng.net/RT1.pdf

-------------------------------------------

I added the voltage regulator to keep John happy :)
Can be anything from 5 to 9 volts.

Paul Lamar


Paul:
 A 3 terminal regulator is a good start, but still not bullet proof !
What I'm
trying to pass on to others is that every "mission critical" circuit has to
be
100 % protected.

Spikes from such sources as the starter motor turn off or an intermittent
connection induced load dump from the alternator can easily exceed the 35
volt
input rating of a 3 terminal regulator.  Once overstressed, a part can fail
instantly, or worse yet at some unknown time in the future.

Hence cascaded protection has to be built in.  The 3 term reg protects the
analog circuitry (555 and op-amp), and some combination of R/C network, low
voltage MOV and/or TransZorb (big zener) is then needed to protect the 3
term.

Agreed, the 'ole analog approach is easier to play with, and probibly more
than
adequate for this application that only has to start, idle and work under
load
from 50 to 100% throttle. No emissions, no driveability, etc, to worry
about.

Wonder if schematics exist for the old Bosch designs ?  They may yield some
good ideas.  Something to hunt for on the InterNet.

BTW, the GPH integrator needs a high impedance load, not the pot shown going
off to a DVM.

JCP


I think a 3 terminal is all Tracy uses. Upper right corner
and lower right corner in this pic. A big Zener or MOV one the
mother board would not hurt.

I had one of those old Bosch units in my VW square back and it was trouble
free for years.

Paul Lamar


Hi Paul

Here's a link to the WIPO site it's titled-
1987 (WO/1987/000581) FUEL INJECTION SOLENOID DRIVER CIRCUIT
http://www.wipo.int/pctdb/en/wo.jsp?wo=1987000581&IA=US1985001929&DISPLAY=DO
CS

I hope this is helpful?

Clive C

I was not  able to get on to that site but it sounds like the old
pulse and hold type fuel injector. Now obsolete.

Paul Lamar