Getting Started (FAQ ver. 0.1)

[thomas walter x5955]

For those looking to "Getting started on this project":


To begin with: KEEP IT SIMPLE! The first fuel injection systems
were analog designs, no microprocessors were even used! They were
not optimized for the best results, but worked well and were
pretty reliable! [411 VW with the D-jetronic was probably the
first system I came across. Even had an adjustable fuel pressure
regulator to play with!]

The later L-jetronic went with some pretty simple uC's with very
little code to them. Inputs were air flow, air temp, water temp,
two throttle position switches (idle and WOT), and battery voltage.  
Closed loop design (with a EGO sensor) came later.  

Most of the OLDER control systems are pretty straight forward MATH!

FUEL PULSE WIDTH =  injector open time + air flow + temp compensation
                    +battery_voltage
 

Each fuel width is triggered of a engine cycle (ignition), which takes
care of the rpm. The amount of fuel is determined by the amount of
time to open/close an injectors (which depends on the battery voltage),
The amount of air entering the engine, and the temperature of the engine.

[There is also the method of just DETERMINING the amount of air entering
the engine by observing the engine vacuum and not using a air vane
style measurement. Just easiest to base your STARTING system on what
hardware maybe common to your target engine]

Start with a simple BATCH fired injection system, and take it from there.

All the later & more sophisticated systems started with this simple idea
from the days of the ANALOG boxes. Obvious is a curve is not linear,
then a look up table (map) makes more sense to use rather than doing
a whole bunch of math.

Once you have the basic system RUNNING, then I would look at adding
the ignition controls to the system [ignition information is already
available to the system, just have a "loop back" on the original system
that uses the stock ignition trigger to fire the coil. Later on
use a relay (normally closed to function as a "limp home" mode)
under a uC control to fire an "optimized timing signal" with knock
sensor, and load (vacuum/boost) sensors.


A rough example of the development cycle:

SYSTEM DEVELOPMENT:

STAGE ZERO:	 System requirements! This is the MOST demanding task,
			   and should not be overlooked. Put it into writing.
			   List your goals, time line, and go from there!
 
             Purpose: determine goal and what is needed to get there!
 
			 What is YOUR goal?
			 What is the maximum amount of fuel required for WOT?
			 Determine MAXIMUM size of the injectors (+20%)
             What range of ignition advance (start & final for rpm
				and load sensor)
			 Determine what hardware will be needed for the engine
                in question. (TBI, Port, etc)
             Start getting the parts & pieces together.
             EMI, RFI, LOAD DUMPS, and other "unknowns". They exist 
               and should be planned for! (metal enclosure, filtered
               input and output signals, over voltage protection]

       
STAGE ONE:  Basic fuel control.
			Purpose: "learning to walk"
            GOAL:  Drive vehicle around the block without any 
                   engine fires or meltdowns!

            Basic control:
			Cold Start enrichment device (injects extra fuel
				timed by a "temperature sensitive relay).
			Open loop system with following inputs:
				air flow
				air temp
				water temp
                rpm signal (ignition trigger)

            Electric fuel pump relay controlled by oil pressure,
            while engine is running. (Safety first!)
				
            OBSERVE: Exhaust with a HEGO sensor & bar graph display.

STAGE TWO:	Fine Tune the fuel control
            Purpose: "learning to walk quickly"
			GOAL:  Start to tweak the system for maximum economy & power
			
            STAGE ONE, PLUS:
			idle contact switch (software for idle)
            WOT contact switch  (software to go "open loop rich" at WOT)
             
            cold start enrichment via the injectors:
					system will require a onboard timer. Hence the one
					circuit that is left running while the ignition is
					"off". 

			switched ignition
			starter engaged

STAGE THREE: Closed loop operation.
			 Purpose: increase fuel economy for cruise conditions.
             Goal: adjust fuel mixture based on the EGO signal

			 EGO added.

			 Software to DATALOG and output sensor conditions.

   3.5

			Limp home modes fully debugged! (i.e. a 555 timer fired
					off the engine rpm. Runs like trash, gets you home,
                    hint: rich mixture is less likely to warp the head!) 
            Simple diagnostics to check for open and shorted sensors. 
                   and parameters that changed TOO QUICKLY.

    3.6

			Throttle position sensor. Improved throttle response to
				changing "stomping on it" to pass.

STAGE FOUR: Development of the ignition control hardware.
			Purpose: basic ignition control.

			Observe time duration between ignition events to determine
			the engine rpm.

			Trigger the ignition (SPDT relay). Use a STOCK OEM map
			(mechanical distributor) as a starting point.
	
		    Engine vacuum sensor to adjust ignition timing (per stock
               specs).


STAGE FIVE:	Enhaunced Ignition control.

			Software changes to the system to MAP the response.

			Knock sensor added to additional control.

STAGE SIX: Full load condition.

			More software, based on IDLE AND WOT switches.
			
            Wheel sensor - speed information (if WOT == 1,
               and SPEED is decreasing... back off ignition!
               How many of you pull trailers!)

STAGE SEVEN: Getting there!

			Ignition timing now using FULL CONTROL. Software
			to optimize each cylinder with coil per cylinder:

			Ignition timing wheel (i.e. Bosch 58 tooth)
			Coil per cylinder technology, 
				[I'll use a double ended coil, to allow
				 a simpler LIMP HOME mode operation on a 4 cyl]

STAGE EIGHT: Whew!

			Adaptive technology. 
            An exercise left for the student ;-)




Your features can really
go from here, thermocouples on all the exhaust ports BEFORE you
begin may not be a bad idea at all. A simple DATALOG system to
record parameters (water temp, exhaust temps, length of time
the engine has been running, etc) maybe a good way to start this
and get your feet wet BEFORE building your own engine controller.

I realize for some on the list, this is really too basic. But with
the understanding of "How do I get started", this should help get
you one your way to THINKING about the system.

Ok, that about wraps it for the first pass of this spec. Any and
all comments welcome and appreciated: email to: 
walter at roadster.sps.mot.com

Cheers,

Tom Walter
Austin, TX.