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Old 07-17-2010, 10:17 AM   #1
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Default closed loop boost

If there is anyone here using closed loop boost control, what sort of PID numbers do you run to get to and maintain boost targets?

I have been playing with 21,12,0 tonight. Before this, I have been keeping close to the suggested 5,0,5 with no luck.

Boost comes on hard and fast with the big numbers but i'm curious to know whats "normal"

Would love to see a screeny of your wastegate tab!
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Old 07-17-2010, 10:55 AM   #2
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I want to play with this badly but have not yet done it. How well is it reaching and holding your target boost without overshooting? I'd like to see some logs if you have them.

Apparently there are mathematical methods for tuning a PID based on looking at plots of their behavior. This is as opposed to trial and error. I have not bothered with learning the math for PID tuning of the idle since there is little at risk. But, with boost... I suppose I should man up and try this since I have a hybrid wastegate and it is not possible for me to go above the MBC set pressure even with the EBC locked at 100% DC.

Are you using fuel/spark cut to control catastrophic overshoot?

You know, for such a potentially useful feature it is a bit surprising from what I can tell that no one seems to know much if anything about using it. The adaptronic site does not seem to have much information if any IIRC. I would like to use it to control the boost for my low level boost set point to compensate for outside temperature changes.
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Old 07-17-2010, 02:11 PM   #3
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I bet it's similar to tuning the MS PID:

1. Set Integral and Differential Gains to 0% - To make tuning the Proportional gain easier, set the Integral and Differential gains to 0%.
2. Set Proportional gain to 150% and slowly lower - While tuning Proportional gain, higher numbers mean slower boost climb and lower final boost. For safety, start with a very high gain (150% should be sufficient). Find the RPM that typically spools quickly, and fully and quickly depress the accelerator. Note how much boost is reached. If boost overshoots the target, increase the Proportional gain. Otherwise, reduce the Proportional gain and try again. Do this until boost reaches the target with little or no overshoot.
3. Tune the Integral Gain - The next step after the target is reached consistently is to tune the Integral gain. Starting from the RPM used to tune the P-gain, fully depress the accelerator and watch the boost as the engine climbs through the RPM range. As the engine accelerates through the rev range, the boost will probably creep away from the target. Keep increasing the I gain until the controller adequately maintains the target with minimal oscillation.
4. tune the Derivative Gain - If overshoot cannot be tuned out with the P gain on a quick acceleration, increase the D gain until the overshoot is minimized. Care must be taken when increasing the D gain as too much D gain can over-dampen the effects of the P and I gains.
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Old 07-17-2010, 02:58 PM   #4
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Thanks Brain. Adaptronic uses different scaling for the PID values (I think) but the methodology should be the same.

So back when I had my MS the closed loop boost control was not working, or not correctly anyway. Is it working well now? Just curious.
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Old 07-18-2010, 11:29 AM   #5
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I just saw the post showing your mbc idea. I might try that as a further safety net as i'm only using the spark cut 10kpa above my target (176kpa)
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Old 07-18-2010, 11:33 AM   #6
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btw, i'm at PID 65,26,0 after some more play today

boost comes on hard and fast - hope i dont break ****!
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Old 07-19-2010, 10:01 AM   #7
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Quote:
Originally Posted by ZX-Tex View Post
So back when I had my MS the closed loop boost control was not working, or not correctly anyway. Is it working well now? Just curious.
PID is only on MS-II and MS-III.
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Old 08-01-2010, 02:11 PM   #8
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I tried tuning the closed loop boost today, and didn't have a lot of luck. Is it possible that the EBC can't evacuate enough pressure? I was trying to tune at a conservative 8psi. The tuning only allowed me to keep steady at 12psi. Is my problem due to the wastegate spring that came with my turbo??? It says it is set to a max of 25psi in the ad. Should I be trying to tune it at something above the stock wastegate 15psi??? Do I need to adjust my wastegate rod?

I did notice that the lower my P term got, the slower the spool. I guess it tries to bleed off air sooner.

what should I do?
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Old 08-01-2010, 05:39 PM   #9
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Which EBC do you have?

Maybe you know this, but I'll state it anyway. You will not be able to tune to a boost pressure that is lower than whatever your wastegate actuator is set at. You can look for this wastegate pressure by setting all of your open-loop columns to zero and doing say a 3rd or 4th gear pull. Whatever pressure you hit is as low as it will go.

If you want to go lower, you can loosen your wastegate actuator like you stated. There is a tradeoff to this as you probably know. it is all of the usual stuff. Too loose and your spool will suffer.

Usually wastegate actuators have a narrow range of adjustment pressure, like 7-9 psi or 12-14 psi. If the turbo you are using claims to hold to 25 psi... But it is a churbo right? Specs could be loosely rated.
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Old 08-01-2010, 11:08 PM   #10
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What kind of decrease in spool are we talking about? It might be better just to buy a 12-14 psi wastegate. Dame, I expected much more adjustablility than 2 psi. That isn't going to get me where I want to be. I really don't have the stones to tune 22psi on the street. I'd rather wait for dyno time for that. Plus, I'd like to be able to detune a little at the track when I go in October.

Is it stupid to expect a 7psi WG with EBC to be able to hold up to 20-22psi. I want the largest adjustment range that is reasonable. I'd really like from 8 to 22. It will mostly be set to 20-22psi when all is said and done.
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Old 08-02-2010, 11:56 AM   #11
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Quote:
Originally Posted by djp0623 View Post
What kind of decrease in spool are we talking about?
You may get to the point where the wastegate is so loose trying to hit your target boost pressure that you will have significant exhaust gas flow going through the wastegate (instead of the turbine) well before you reach your target. That will slow down spooling.

I have a 12 psi actuator (set to about 12-13 psi) and have boosted up to 20-21 with MBC/EBC no problem. I have not tried to go that high with a 7-8 psi actuator. That does not mean it cannot be done. I have just not tried it so I cannot say.

Dig around some more or call someone like ATP Turbo and ask them what they think.
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