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Author Topic: ECU boost control on compound turbos - thoughts?  (Read 28787 times)
Leonhard
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« Reply #45 on: February 06, 2017, 10:17:21 AM »

no, please have a closer look,
this is your setup,
just the compressor bypass and a bigger turbinebypass at the K03 is missing
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elRey
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« Reply #46 on: February 06, 2017, 10:36:59 AM »

When one turbo is used for low-end only and big turbo is used for top-end only = sequential

Small compressor bypass = sequential. It may compound for a very short rpm range durning transition (switch-over), but it is a sequential (two-stage) system.

A full compound systen has both turbos contributing thru whole range.
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elRey
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« Reply #47 on: February 06, 2017, 10:51:59 AM »

This whole thread is off-topic.

You know what? It doesn't even matter if the system in question is sequential, compound, good design, or bad design. They all have 2 WGs that both require some 0%> duty <100% at some RPM range.

I have the opportunity and ability to control two wastegates across the full RPM range. I want to discuss strategies for a 2 N75 PID control using new code, but no one can get past the hardware. Isn't this a software forum?

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« Last Edit: February 06, 2017, 10:58:34 AM by elRey » Logged
TijnCU
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« Reply #48 on: February 06, 2017, 11:08:51 AM »

What ideas do you have for control, maybe we can think along your plans or contribute our vision on the code? What you are doing is beyond most readers capability so the group of capable readers that are willing to think with you wont be that big. It is easier to comment with offtopic replies (whether they are helpfull or not).
I am just a beginner with custom code and have no experience with compound or sequential setups at all, so my advice may not be usefull at all. But the topic interests me and my first thoughts are that you can take a shortcut by having a conditional replacement value for the original n75, that value does not need to be static.
So, can you give me a description of control that you are looking for? Which wastegate needs to do what and when?
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elRey
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« Reply #49 on: February 06, 2017, 11:09:43 AM »

@ruan - I gather from your post that you agree with me generally that compound systems shift the small turbo's compressor map x-axis to the left. However, you doubt the T3/T4 - K03 combo still fall on the adjusted K03 map. Is that correct?

I haven't (I don't think) provided what PRs I plan to operate at nor have actual K03 - T3/T4 maps been referenced in your calculations. Unless you are suggesting the gt2052 is comparable to the K03

I cannot provide opposing calculations at this time, just stating the incomplete picture on which both our assumptions are based.
« Last Edit: February 06, 2017, 11:14:20 AM by elRey » Logged
elRey
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« Reply #50 on: February 06, 2017, 11:32:08 AM »

@TijnCU -

I was breaking the discussion up into two separate parts:
1) setting target boost (one target for each turbo, or more accurately, one target for big turbo and then total manifold target) A small turbo target could be considered by subtracting big turbo boost from manifold boost.
2) PID control

First thing I would like to mention is to not get stuck on only thinking about one long WOT run. Because you'll only consider 95-100% small turbo duty and xx% big turbo duty. As I mentioned before, small turbo may have to maintain 20psi at 5500 RPM for a short period after a shift or off then back on throttle up there. And that might not mean 95-100% duty on small turbo, but full PID control.

So, I can see a full range of duty % needed at anytime for both turbos.

I think the tricky part is each turbo's response to a duty% might change based on the other turbo current pressure, and it might not change linearly.

IF it did change linearly, I could see just 4 kfdmix maps, two for each turbo. One map for when other turbo is operating at wastegate only, and 2nd  map when other turbo is operating at peak boost. Then just interpolate between the two maps based on other turbos current boost/its peak boost.

Just like KFZW1/2 and fnwue.
« Last Edit: February 06, 2017, 11:40:23 AM by elRey » Logged
ruan
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« Reply #51 on: February 06, 2017, 12:00:03 PM »

@ruan - I gather from your post that you agree with me generally that compound systems shift the small turbo's compressor map x-axis to the left. However, you doubt the T3/T4 - K03 combo still fall on the adjusted K03 map. Is that correct?

I haven't (I don't think) provided what PRs I plan to operate at nor have actual K03 - T3/T4 maps been referenced in your calculations. Unless you are suggesting the gt2052 is comparable to the K03

I cannot provide opposing calculations at this time, just stating the incomplete picture on which both our assumptions are based.

Correct on the first count certainly. That was this morning and the coffee hadn't quite got my brain working in a sensible explaining fashion. The GT2052 example was merely an example to show on a turbo that's in the same ballpark area that is being discussed which conveniently has it's axis as corrected mass flow rather than volumetric - nothing else inferred from that.

Without going into specific values for what you're wanting to do... Compounding is great if you want extreme pressures, however from my experience there is quite a trade off in terms of where that pressure can be generated - the airflow you'll likely want to support at high engine speed will (even taking into account the above) be too great for the HP unit compressor.

This is why the OEMs use systems like R2S - because you can utilise that HP unit at low RPMs and provide great transient response, generate high pressures at mid RPM whilst utilising compounding, but bypass the HP unit so that you don't overspeed it... That's why compound setups are more popular on diesel motors IME.

Point of my post being:

- Mass flow vs corrected mass flow (or simply - volumetric flow) means given a higher inlet pressure you can move a greater mass of air through the compressor.

- Doesn't mean you'll always be able to move enough even with the above.

In terms of what the original thread is here for, fraid I'm about as much use as tits on a fish - many people with vastly more experience than myself on that subject. I've a bit of experience with how I might apply this in terms of a CR diesel, however there's so much knowledge here, I don't think my input would be hugely helpful! I just find reading stuff on the subject of ME7 fascinating coming at it from a completely different angle Smiley
« Last Edit: February 06, 2017, 12:18:43 PM by ruan » Logged
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