DIY_EFI Digest Monday, December 13 1999 Volume 04 : Number 692 In this issue: Re: maximum ON before damage Re: ECU pulse width calculations...? Pulse width, too See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Sun, 12 Dec 1999 12:45:04 -0800 From: "John Dammeyer" Subject: Re: maximum ON before damage >Date: Fri, 10 Dec 1999 02:48:38 +1100 >From: Phil Lamovie >Subject: maximum ON before damage > >Hi John et al, > [snip] > >The limiting factor with any injector is the max. time in ms available >at max. rpm. If that rpm is say 6,000 rpm we have 10 ms total. > It's at this point, Phil, that I must still disagree with you. I suspect again that it's somehow a philosophical point. Can an engine function efficiently if the injector is fired at an 80% maximum duty cycle over a 720 degree cycle? I believe it can so in fact at 6000RPM 720 degrees takes 20ms of which 80% is 16ms. >If it takes 1.2 ms to open (saturated type) and 1.1 ms to close you >only have 7.7 ms left. Just to make things difficult the first period >of 1.2 ms has NO flow. So really that 2.5 ms lower limit (for >stability's sake) >means you have 2.5 -8.9 ms to play with. Now, given that I have engine logs of the behaviour with stock Honda Injectors operating at 2.0ms at idle and the O2 sensor dancing around 0.5V (Stoich?), and the engine idles smoothly I'd say that for the first 1.2ms there is some flow. In fact, according to one of the papers I have, the amount of flow is, (at an average), 66% of the injector flow rate. This means during injector open time, of 2.0ms for example, the injector behaves as a 16 lb/hr injector. Now using our injector cleaner, with 40psi on the injector pump, I've watch a consistant and repeatable amount of fuel be dispensed from an injector running at 2ms. I've yet to do an experiment to determine the minimum pulse width before fuel is dispensed but you are probably right; 1ms is probably pretty close. This minimum pulse width is not only due to the mechanical aspects of the injector but also due to the injector inductance. It takes a certain amount of time for the current to build up and if this is longer than the pulse width, you'll never see the injector coil build up enough power to lift the pintle off the seat. BTW, there is no reason that with the same sort of circuit used for saturated injectors that someone couldn't use a 24 to 48 volt power supply and treat the saturated type of injectors as PeakHold. It's the inductance of the injector coil that prevents the rapid rise of current and increasing the voltage increases the rate of current rise in the injector. Once the maximum current is reach the electronics can reduce the voltage to 12V. This would have an impact on the minimum pulse width as now the maximum current may be reached before it's time to turn off the injector. If you've got the electronic 'smarts' a switching power supply that can take 12V and step it up to 48V would do the job. >Once again I must ask are you pulsing once per revolution or every >second / If once your figures don't add up. If every second your >choice is incorrect. The sequence is not an issue. How often do you >fire No. 1 injector ? As I stated earlier, I inject each cylinder once per engine cycle with a pulse rate from approximately 2.0ms up to 12.8ms using the stock Honda 24lb/hr injectors; we get about 126HP and peak torque is as per the engine curve as stipulated by Honda. With 28lb/hr Lucas Injectors my minimum injection time is reduced a bit, the engine still idles smoothly and my torque is also still where it's supposed to be. My top end RPM goes up from 6600RPM to 6800RPM and my HP is now at 135HP. Above 6800RPM my ignition REV Limitor cuts in and prevents further excursions. > >If you apply a table with load vs rpm values instead of you falutin' >volumetric eff. table you would find that the map sensor response of >1-3 ms is sufficiently fast to react within 1/4 of a revolution even >at moderately high rpm. If your code does a run through in under 10 ms > >you will never miss more than 1 p/w correction. > >You might be in the middle of an output event as the vacuum drops but >most throttle movements take 200 - 300 ms from start to finish and >thus many injection cycles b/w start and finish. That's a good point. I'm into a Heisenberg type situation here where if I log from the engine controller any faster to get better resolution I will be impacting the injection cycles or the higher speed output from the engine just won't show up. My alternative is to put a data acquisition system on the engine and log on a 100uSec interval all my sensors including my Hall Effect CAM sensors. I use two sensors under the CAM shaft timing pulley with magnets on the pulley to give me a Grey Code 2 bit output to identify which cylinder is on what part of the cycle. However, I don't think my client wants to pay for that, they just want an acceleration that works. Catch-22. >As to the 40 ms pulse... I don't think so. The maximum fuel required >is more a function of poor combustion at low rpm than anything else >but given a max. p/w of 8.5 at 6000 rpm then the pulse width at full >load 1000 rpm would be 8.5 plus the excess fuel required due to poor >tumble, swirl, vaporization etc. etc. Probably no worse than 4 -5 ms >extra will be required. Don't forget to decay this in proportion to >the rate of change of rpm (derivative of PID ) I still disagree with your maximum pulse rate but in either case, the point is well taken. How much extra fuel is required when the throttle is suddenly opened and the MAP goes from 9" to 29". My sensor acquisition loop is more than fast enough to calculate new values at an idle speed so it's more a matter of figuring out how much extra fuel to pour in. And yes, I do decay the enrichment. > >This still points to a short coming that you have imposed with your >12.7 ms upper limit. Full load plus cold air plus cold water plus >acc enrichment will put you badly in debt even at low rpm. I suspect you are correct. My next experiment will set in max PW as a dependant parameter of RPM so that at low RPM I will be able to increase dramatically the amount of fuel and at high RPM not have my software blow up if the requested pulse rate is too long. > Cheers, John ------------------------------ Date: Sun, 12 Dec 1999 12:07:47 -0800 From: "John Dammeyer" Subject: Re: ECU pulse width calculations...? > >Date: Sat, 11 Dec 1999 13:38:23 -0800 >From: "Andrew Brownsword" >Subject: ECU pulse width calculations...? [snip] >scaling back the injector values by the ratio of the flow rates of the old >and new injectors. > >Doing this, as I understand it, should have reduced the pulse widths >controlling the injectors and therefore decreased the amount of fuel being >injected. We cut the numbers by fully half and measured the effect using a >(high end) A/F meter. We expected to see the engine lean out significantly >at idle... instead it leaned out slightly. From 11.5 up to 13.2 or so. It >would momentarily jump up to around 14.5 and then slowly drop back down to >13.1 or so. > >Does anyone have theories, advice, hints, etc? You haven't mentioned what the actual pulse widths were with the old injectors and then after you scaled them. The Open/close time of injectors remains somewhat fixed and if the pulsewidth is made too short the injectors operate erratically. So if the pulse width with the old injectors was, say, 2.5ms and you change it to 1.7ms by your scaling algo. then you just barely get the pintle off the seat before it starts to close again. This causes erratic mixture as sometimes it opens more than other times. Been there done that. It's for this very reason that picking an injector for an engine is so touchy. Big enough for gobs of power at high end and you dispense, with those injectors, too much fuel at idle. It's for this reason that the concept of staged injection is used by some performance enthusiests. Small injectors for idle and midrange and large injectors for high end. This is much like a two barrel carburetor. One alternative, is to use a throttle body injector for idle and cold start enhancement and use the multiple injectors for high end. The throttle body injector has to supply all cylinders and so has a much better chance of never being asked to be open less than a minimum time. The new problem introduced with that is then you need carb heat and an ability to make a smooth transition between the two injector set. Cheers, John ------------------------------ Date: Sun, 12 Dec 1999 17:41:10 -0600 (CST) From: digi Subject: Pulse width, too I'm wondering how you can calculate the amount of fuel that is injected from fuel pressure/duration. I'm assuming it is not a static flow, as the injector opens and closes the flow decreases for the same time unit versus fully open. Any help is appreicated. ------------------------------ End of DIY_EFI Digest V4 #692 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".