Injector Control Options

[jharvey]

Awesome and thanks for the reply(s). There's certainly allot I don't know about this. One of the better ways I've learned about it has been from talking to people. So here I am chatting it up.

tpsretard had the link I was looking for. I was looking for the typical / ball park uH of an injector, also I was looking for the curve that shows the bumps when the injector hits bottom.



This curve shows this isn't quite the same as a solenoid, but is quite close. The pin absorbs some of the energy, changing the curves some. I see the bounce on the back of the pin as it opens. When it comes to closing the injector, it's possible we could give it a soft landing if we give it some extra energy just before it bottoms out, but I suspect the spring and other such mechanical aspects typically take care of that mostly. However, letting the field collapse uncontrolled, with the fuel pressure behind it, I suspect EssEss is right. I would guess that, it shortens the injectors life. I would also guess that if we have a pressure meter on our fuel, we would see some large pressure spikes from "water hammer". I wonder what the resonant frequency of this pin would be. Hopefully not near 5khz or 6khz. Those frequencies or near those frequencies could trigger the knock sensor when we eventually have it.

On the opening side of the cycle, I can't help but feel that the change in mH could correlate to the inertia of the pin. This fellow shows it as 32.8 mH off, 23.5 mH when on. So the pins energy was equivalent to about 9.3mH. If we knew the inertia of the injector, we could soften the open, and soften the close of the injector, as well as predicted dead bands, and other parameters.

While we can approximate the dead band, and mostly remove it with software delays and preemptive turn on times, other features are much harder to do in basic software, or hardware. Like softening the on and off times, or preventing noise by decreasing water hammer effects. That's part of the reason why I'm a bit more of a fan of piping current sense data back to the brain, and letting the brain control these things in software.

I suspect hardware P&H circuits have some problems in the 1 to 2 mS range. The drive hard, then decrease your drive approach at these times would likely cause the injector to vary it's fuel squirt. Even if it doesn't completely close, I would bet as the pin bounces back, it limits the flow. I see software config of these parameters as very handy.

Any one interested in attempting to make an equation for the injector? I can't help but want to see an equation, that when plugged into a spread sheet program will produce the same curve shown in the above picture.

I think it's kind of interesting to see the low impedance injectors don't appear to bounce.

[EssEss]

everything bounces .. low or high .. so my knock sensor zip-tie method tells me. I don't think it's important to worry about softening needle landings - OEMs have different reasons for doing what they do. I don't think diy'ers have to worry about getting a million more cycles out of an injector. I'd just rather buy a new injector for pennies on the dollar at the junkyard.

once you figure out all these neat tricks, will an end user is actually tweak the current profiles ? I won't be interested - let alone do a custom bench setup to figure out what those values are. will the results be worth the effort ? for academic reasons, yes! for real world application, I'd say no.

you should work on your f/w skills - I think you'd appreciate the challenges involved with what you're proposing and understand why the f/w guys have to make some tradeoffs which may not make immediate sense. It's really a lifelong skill that would let you experiment to your hearts desire. I'm going to get off my soapbox and bow out for now Do what you feel - you're the only one doing h/w right now, I vote for throwing some simple drivers on there and be done with it. Let me know if I can help with any f/w questions you might have.

Once again, in addition to your efforts, I appreciate what everyone has contributed - after fred checks in I hope to do my fair share. my t/a board is sitting right here beside me

[tpsretard]

+1 vote for the simple drivers

[WTDeuce]

Water hammer in the fuel rail would be hard to detect if there is a fuel pressure dampener on there. Also depends on the injection setup ie sequential vs batch.

[Fred]

Water hammer in the fuel rail would be hard to detect if there is a fuel pressure dampener on there. Also depends on the injection setup ie sequential vs batch.

Yep, and they all have them! Even my modified setup retained that ;-) I sought advice from an expert and kept it, that simple.

+1 on Jared learning firmware skills.
+1 on high impedance simple drivers for the short term at the very least.

EssEss, I have my computer out of storage and will be able to put some time into it in the coming week. I don't know how long it will take to bring it up to release standard, but hopefully a week should be enough. I see lots of diffing, git diffing and kdiff3ing in my future.

Fred.

[jharvey]

Water hammer in the fuel rail would be hard to detect if there is a fuel pressure dampener on there. Also depends on the injection setup ie sequential vs batch.

I don't think it's that hard to detect. Some time put in a temporary rubber T in your fuel line. Then put your automotive stethoscope in the T and tell me what you hear. Of course if you do it at the tank, several feet from the injectors, you won't hear it. It also goes away quickly when you go to the other side of the regulator. However, if you try it at the injector, it's quite noticeable.

I know rubber on the fuel line isn't good for the long term, but for test purposes, it blocks most of the mechanical noise you might here from rigid lines.

Just like a nail is designed for impact loading, so is an injector. So technically they will work, however, letting it impact like this isn't the best thing.

About firmware skills, I'm actually not all that bad at firmware. I'm just not familiar with the S12X intricacies like that PITA timer (I mean PIT timer) or intricate build environment.

[EssEss]

the cool thing about that is you don't have to worry about the build environment - fred has already set it up. and a datasheet/um will cure the other problem.

sorry, I assumed that you didn't know anything about f/w. all your previous comments about not seeing how the hip bone connected to the knee bone tipped me in the wrong way. If you think fred's code isn't clear, you should see some of the other stuff out there in the world (msqrt). there's some really bad stuff out there. fred at least cares about the maintainability/readability of his code which goes a far way in my book. I see someone else did some doxygen work ( ) which is a superb start.

[Fred]

the cool thing about that is you don't have to worry about the build environment - fred has already set it up.

Yep, all you have to worry about is the utterly vexing question "Do I know how to type 'make s19' and hit enter?" - if the answer is yes, then you are set! :-) Even if you can only type make you'll get a bunch of info out of it that shows you what you can do.

all your previous comments about not seeing how the hip bone connected to the knee bone tipped me in the wrong way.

I'm sure this is a function of two things. One, that it's not complete and some of the bones, eg, the ribs, are missing. Two, it's interrupt driven and much of the code works on it's own from or to some state variables. The non interrupt stuff is the ribs, these are the features, they'll come later. If separating things into functions causes you to find it disconnected then that is a basic issue with your code reading skills. Simple as that.

If you think fred's code isn't clear, you should see some of the other stuff out there in the world (msqrt). there's some really bad stuff out there. fred at least cares about the maintainability/readability of his code which goes a far way in my book. I see someone else did some doxygen work ( ;) ) which is a superb start.

I don't know whether to be complemented of offended! So I'll just stay confused. I've said it before, but please, rip it apart, I know there is a lot wrong, but telling me something that I already know is not an issue. I'm still keeping that semaphore register in the back of my mind as although I think my defense was right, it could easily become an issue later ;-) Thanks for that.

Fred.

[AbeFM]

Water hammer in the fuel rail would be hard to detect if there is a fuel pressure dampener on there. Also depends on the injection setup ie sequential vs batch.

I've certainly heard tales of injector starvation due to this - people removing the damper and losing a piston/valve. So perhaps you can remove the need for a mechanical damper?

I've certainly seen the pintle moving in the current vs time plots. Odds are pretty good it'll vary with the injector.

Injectors are a pain to swap on some motors, not always so cheap, and worth saving if it can be done reasonably. I would worry more about the error in delivered fuel with any funny gentle closing than the rest of it. Certainly for low-ohm injectors it would be nice to make this all work - as I start looking at 750 cc injectors on my 1.8.... more work making them behave seems worthwhile, cause it's either that or using secondaries.

[Fred]

Yep, I spoke to some injection specialists here before I went ahead and built up my rail and supply system and they urged me to retain the damper despite the boost. I did, and I'm glad I did. The other thing I retained was the check valve at the pump. Insta fuel pressure every time. A friend of mine with the same pump and better regulator has some issues with his priming pulse the first time round due to back flow/drain out.

Fred.