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Why is my TD Integral accumulating?


iNVAR

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I had a thread over on the RR forums, not much help there. Airboy took a shot at it, but no dice. Here's the thread:

 

http://www.romraider.com/forum/viewtopic.php?f=15&t=8452&sid=4f1ac935000ac9dda7f01a251be80138

 

But I'll summarize:

 

I've been dialing in my boost and turbo dynamics for some time now and I've notice a phenomenon where the TD Proportional is obviously great enough to cover the gap between PWGDC and PWGDCMax, which I've been told should prevent TD Integral from accumulating any more. Well, I've logged it and on some occasions, that does NOT seem to be the case, which results in overboosting sometimes.

 

Here is the most recent log I took that shows the event occurring. I've logged PWGDC and PWGDC Max as well as all the TD parameters. TDI still accumulates for some reason... it's almost like it's too "stupid" to realize TDP already covered the gap.

 

Any explanations? I want to eliminate this phenomenon which would help me prevent the hard overboost that results.

 

http://www.crimetank.com/misc/what3.csv

 

If someone wants, I can post up the relevant tables for my current map, but it shouldn't be necessary. The log shows it all.

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TDi isn't accumulating, it's ramping down like it should. TDi is increasing until line 23 because there is still boost error (below target) and TDp is high enough to call for TDi to intervene.

At line 24 TD has done it's job a little too well and you tip into overboost. With negative boost error TDp immediately goes negative to catch the overboost but TDi is by nature slower to respond, but respond it does by dropping from 5.5 at line 23 to 2.3 at line 32, where boost has dropped slightly below target.

 

You could flatten the TDi response slightly to smooth this out but I'd only try lowering it a small amount. I would probably not touch it as I like to see some small amount of positive TDi pushing WGDC up to hold target boost at higher revs. Better that than have it go negative to hold it back. 2~3% TDi up there is IMO not a problem.

Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs.
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Hey! Good to hear your input but I think you're mistaken in this instance. TDI is not behaving like it's supposed to be in my logs, and I say that according to this:

http://www.romraider.com/forum/topic1814.html

 

Based on that and what I've personally observed and what others have been posting, when PWGDC is already equal to or greater than MaxWGDC, TDI should cease to accumulate. From lines 15-20, TDI should have remained 0 all the way because TDP already covered the gap to bring PWGDC up to MaxWGDC.

 

My other logs to behave appropriately that way and everything's dialed in nicely otherwise with lots of credit due to your help. (I've been meaning to send you an update.) BUT I do get an aberration like this once in a blue moon. It's very rare, but it does happen once in a while and I'm stumped.

 

It pretty much never overshoots by this much anymore in any gear. :)

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I don't know that the same logic applies in all ROMs. You can often see this phenomena in spool, where boost targets are set too high. TDi accumulates if boost error stays at the same value or gets worse, even though WGDC has reached the values set in the MWGDC table and cannot therefore increase further. I believe this is the case because your MWGDC values are not set the same through the whole rev range, and the logic is designed to allow those TDi values to remain where they are in case MWGDC suddenly rises in the next cell up on the rpm scale, without having to go through the whole process of evaluating TDp vs. boost error over time. That could make boost control very choppy indeed!

 

Also note that TDi is indeed falling while TDp is negative, and that's completely normal in my experience. The only time I see TDi values suddenly cleared to zero is as Bill mentions, when parameters pass the thresholds set for TD activity.

Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs.
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Like I said, I see the advantage in letting TDi accumulate even if the correction cannot be applied for the moment due to MWGDC being reached. Remember when Bill wrote that tutorial... understandings develop further over time and if he were free to write that again today it might be somewhat different.
Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs.
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Hmm, so you're saying there may be some other logic at work here that lets TDI accumulate for whatever reason?

 

That's... irritating I guess, because I can't consistently predict when it'll do it. If my boost behaves 95% of the time correctly, that's great, but since I'm a bit OCD, I'd like to get it behaving correctly the other 5% of the time too.

 

BUT I can't get it to behave correctly the other 5% of the time if that requires me to further reduce TDI. My TDI curve is already pretty flat. If I make it any flatter, it'll start affecting the boost the other 95% of the time.

 

I may just have to let this one go. :(

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As a fellow perfectionist wingnut, I know how hard it is to let this go, but I don't see what can be changed to fully prevent this. As I said, there is a benefit to allowing the TDi value to remain high even though max WGDC has been reached.

You can try flattening the TDi curve a bit more but expect other issues to crop up as you predicted.

Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs.
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