ahickman

OK, I was reading about the injection scheme (autoshop101.com) used by the various engines and can't quite wrap my head around how the 22re even runs. According to the diagram, cylinder 1 for example receives its dosage of fuel in two squirts. Both of which are delivered to the intake valve stem on the compression cycle. Assuming that the fuel is instantly vaporized when hitting the hot metal, how in the heck is the fuel passed to the combustion chamber? Can anyone explain in detail how and when the fuel makes it to the piston head?

Thanks,

Aaron

abecedarian

all 4 injectors on a 22re fire simultaneously.
why it works, is due to PFM (pure friggin magic)

abecedarian

seriously though, the injectors fire once each engine revolution, delivering 50% of the fuel charge each crankshaft revolution.

ahickman

Good to know that I am not off my rocker in thinking that the injection schedule for a 22re is a bit odd. Would you agree that only half of the fuel is passed to the combustion chamber? The other half gets wasted during the empty 360 degree cycle.

abecedarian

gives the ecu a small window of opportunity to correct the air/fuel mix between the next ignition cycle.

abecedarian

in general, 1/2 the fuel is injected against a closed valve, and the other 1/2 fuel is injected before the valve opens again.

abecedarian

injection timing is not strictly based on spark / ignition timing.

ahickman

Referring to how the ECM modifies/shifts the injector duration?

abecedarian

technically, yes about how the ECM modifies injector duration.
injector events happen once every crank revolution, and coolant temp, throttle position, air-flow meter, intake air temp, O2 sensor (if in closed loop), egr temp (when in closed loop) all affect injector pulse-width.
the ecu can almost 'accurately' modify injector events, but only with regard to the 'average' of the previous event. it cannot modify or enhance the injector event for any particular cylinder without adversely affecting the other cylinders.
think of it as a 'modified' throttle body injector configuration, where any modification affects all of the cylinders.

ahickman

Understand! Just don't get why one would design a simultaneous injection scheme when you have the raw power of the ECM. Splitting out the four injectors and firing each during the respective intake would be so much more efficient. Can't imagine why they got so lazy given that they have the ECM doing so much more in the way of injector duration (pulse width). Injection during intake would seem to be a much more efficient means of ensuring complete combustion. Maybe this is why the EGR came about....to clean up a sloppy fuel delivery system?

abecedarian

granted, would be more efficient, but they also had investments in sensors that were not up to responding fast enough... and given that, back in 95 even, O2 sensors were barely up to the task of responding fast enough for a bank of 4 cylinders in a v8, much less to each cylinder in an I4. Arguably, O2 sensors are still not fast enough since we are now entering the direct injection phase of 4 cycle engine design.
arguably, diagnostics are progressing much faster than fuel and spark delivery, otherwise how could an OBDII system know that #2 cylinder misfired, but the system can't fix the problem on its own.

you're also talking about a system designed in the mid 80's and with cost in mind used the most simple method available- dedicated 8 bit processor running at maybe 1 MHz, with limited non-volitile memory to account for 'corrections'. Hopefully, it would be a Z8000 with eeprom for storage, but likely it's not, and even if it were, there weren't many options for an RTOS back then. You're looking at a glorified calculator (yeah, I know you've heard it before) with simple compare and compensate routines programmed in, and menial memory to help it remember certain things it did.

ahickman

Well, I wish I had the time and energy to consider how the injector bank could be split out and fired individually. Seems a simple task with considerable rewards in terms of fuel economy, engine performance and even burn efficiency. Good night!

abecedarian

at best, I would think that firing the banks the way they are wired- (firing order is 1-3-4-2... found 1/4 and 3/2 wired as pairs).
1/4 and 2/3 would be most efficient (short of true sequential injection).
In my 88, and 91, cylinders 1 & 4 share common 'hot' and 2 & 3 share a common hot as well. And both of those commons are likewise siamesed in the harness elsewhere. So maybe someone was thinking about it, but the design was simplified by someone else.

Bigblock

OBDII can individually contour a specific A/F charge for a specific cyl.Can also alter spark angle for a single cylinder or all.I know your talking 22RE ,it does not.
Bigblock

ahickman

BigBlock, looking at the following diagram for injector sequence the 22re does anything but operate with efficiency.




Wondering what it would take to split the injection pulses out into pairs or even individually. Electrical separation would be relatively easy enough as Abe identified below. The trick in either case would then be to learn the crankshaft angle as well as the current stroke cycle for each of the cylinders.

Correct me if I am wrong in thinking, but if I knew the total number of Ne pulses in a 360 degree cycle of the shaft I could divide by 2 to define 180 degree and 0 degree (TDC) points. (I would also have to know exactly which Ne pulse corresponded to TDC if I needed absolute position of the shaft. Otherwise the pulse train would just be relative.)

I really would not care about TDC, but only when the injector is first opened for No. 3 or 2 cylinder and when it is closed. The difference in time would be the pulse width being instantaneoulsly applied by the ECM. If I then waited exactly 180 degrees and opened/closed the injector for the next cylinder in the firing sequence repeating this process for the remaining three cylinders I would have a much more effiicent delivery system. One that still uses the dynamically calculated pulse width by the ECM.

Sound accurate?

ahickman

Abe, forgot to ask what you do for a living? Seem to know way more about the Toyota and electronics than the average bear.

abecedarian

Currently, I work in the cellular and microwave industry.

abecedarian

being that there is no #1 trigger... even the distributor pickup mechanisim is a simple 4 lobe rotor / hall effect detector, the easiest way (least intrusive to the harness or engine) would probably be to detect #1 (or maybe all 4) cylinder ignition event(s) inductively from the spark plug wire.
what to do next though, is an intersting proposition....
perhaps detect the pulse width from the ecu, determine which cylinder is next to start the intake stroke, then fire the appropriate injector with double the pulse width from the ecu.
determining which injector to fire though... if #1 has just hit the power stroke, that means that #3 is starting compression, #4 has just finished exhaust and is starting intake, and #2 is starting the exhaust stroke. #4 would seem to be the logical choice.
hmmm

is this going to be your next project?

ahickman

Ah, ha! Are you climbing towers or engineering RF solutions? I just spent the better part of two years designing and building out a county wide RF solution for first responders. RF is definitely one of those love/hate relationships. Propagation studies indicate one thing, but actual footprints can be very different.

Well, I am wrapping up my OBD diagnostic tool and just hate to waste the remaining memory and clock time on microcontroller. Added a few extra goodies like MIL decode but am looking for more useful things to add. I learned a lot about the 22re when making this tool and hate to stop learning if you know what I mean. Sure that most readers will wonder why I want to fix something that already works. The answer is fuel economy. If I could squeze a few MPG's out with little overhead in terms of parts, why not?

The more I think about how the fuel is delivered over two different bursts and then sits in a volume (for up to two cycles) that is heated and may have valves that are not seated completely......the more I think the fuel vapor may be prematurely leaking off before the intake stoke sucks it through to the piston cavity. Way wasteful despite being recirculated by EGR. Seems this would also have adverse effects on the O2 sensor reading?

abecedarian

Mostly, I work on the towers and facilities. Sometimes I climb, but usually on the ground telling others what to do and testing / troubleshooting the path.
But I know what you mean about what the studies and software says versus what happens when you try to put it together and make it work- footprints, hand-offs, channel conflicts, etc.

batch firing the injectors keeps the driver circuit simple- only one driver is needed on the board. it also eliminates the need for synchronizing with camshaft events. firing in two short bursts as opposed to one long burst minimizes the amount of fuel that falls out of suspension and puddles in the head or on the back of the valve, making it more difficult to burn when it gets sucked into the engine.

you think your microcontroller is up to doing the job?
I wonder if your microcontroller is up to handling the task?