Boost overshoot

[Wolf_Tm250]

Hi,
I'd like to have your opinion on this, as all the mods I tried seems not to work...

Boost aim is 280, but map arrives till 295 kPa...

Here is the setup:
P = 0.30
I = 0
D = 0.03

Aux 3 is the boost control valve ( external wg )

Too little the D, or it is a normal position issue?

Thanks in advance.

[MarkMc]

You probably need some I gain to get rid of the last bit of boost error. P gain alone can only work so far and D only works while the error is changing. I will wind in/out duty cycle over time when there is any left over error.

Also your normal position duty cycle may not be exact enough as well. You should always start with open loop boost control to find the duty cycle that gives the boost you want, this then becomes your Normal Position.

Did you read my PID tuning guide? it is stuck as the top subject in this forum.

[Wolf_Tm250]

You probably need some I gain to get rid of the last bit of boost error. P gain alone can only work so far and D only works while the error is changing. I will wind in/out duty cycle over time when there is any left over error.

Ok, I'll try

Also your normal position duty cycle may not be exact enough as well. You should always start with open loop boost control to find the duty cycle that gives the boost you want, this then becomes your Normal Position.

Ok

Did you read my PID tuning guide? it is stuck as the top subject in this forum.

Yes sure!
Very well done and useful!
Even if I didn't got it could be an I issue...

Thanks

[Wolf_Tm250]

You probably need some I gain to get rid of the last bit of boost error. P gain alone can only work so far and D only works while the error is changing. I will wind in/out duty cycle over time when there is any left over error.

Also your normal position duty cycle may not be exact enough as well. You should always start with open loop boost control to find the duty cycle that gives the boost you want, this then becomes your Normal Position.

I tried to add some I ( 0.01 & +/- 10% ), but with results only in the very long distance.
Then I started to increase I, but things got worst and with I = 0.05 I had a 300 kPa overshoot... so I returned at I = 0.01
After this, I tried to increase D from 0.03 to 0.055, but it didn't seem to me that it made any difference.



Could it be a Normal Position (AUX 3) issue, for example, if I understood correctly, it is too high in some positions?

Thanks.

EDIT: I just understood that I was thinking wrong about the polarity of the boost valve.
I thought that 100% BCV DC meant fully opened valve, that is to say external wastegate valve fully closed, so boost up.
So I lowered the Normal Position values to decrease overshoot, but I was wrong, and probably I increased the overshoot.

[Scott@FP]

Keep in mind most boost control solenoids effective control range is *not* 0% DC to 100% DC, some of them have a rather narrow range like 30% to 70% and below 30% and above 70% you get very iffy or no control.

To test your solenoids useable range use shop air thru a regulator and a gauge on the WG port outlet at your target boost pressure and actuate the solenoid under 'test outputs' and put it thru the entire range of output DC % at your frequency, watch the gauge as decreases (or increases) pressure to the WG port.

Try a different frequency and see if you gain some range.

Once you know the DC % limits of your particular solenoid, if your target boost pressure is at the edge of the control range, change the WG spring to get you back inside your control range.

If you are using MAP/EMAP for Effcy use it as the X axis for Normal Position instead of RPM, as it is not gear or load dependent, a more accurate measurement of the forces acting on the valve that effect its operation.

[Wolf_Tm250]

Keep in mind most boost control solenoids effective control range is *not* 0% DC to 100% DC, some of them have a rather narrow range like 30% to 70% and below 30% and above 70% you get very iffy or no control.

I'm currently using the Motec's suggested one, the Delco 3 way boost valve which has a range from 10% to 85%.

Once you know the DC % limits of your particular solenoid, if your target boost pressure is at the edge of the control range, change the WG spring to get you back inside your control range.

Ok, I'll try this test.

If you are using MAP/EMAP for Effcy use it as the X axis for Normal Position instead of RPM, as it is not gear or load dependent, a more accurate measurement of the forces acting on the valve that effect its operation.

Ok, thanks a lot

[Scott@FP]

This only works if you are using MAP/EMAP for Effcy!

For Normal Position table try (MAP/EMAP) 'Effcy' on X and Boost Aim on Y.

Not as big of a help on larger turbos that don't get below 100% Effcy but for the rest of us with small/medium 'street' turbos that spend a lot of time below 100% Effcy it makes for a Normal Position table that is smooth and predictable.

Suggested points on X are 60%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 125%, 150%. Unless the turbo is very small stock sized or you run a restrictor Effcy won't get much below 70% or so.

There will be very slight change in Normal Position DC % from 150% to 100%, then required DC% will ramp up from 95% to 75% as the turbine pressure gets higher and higher.

[Wolf_Tm250]

This only works if you are using MAP/EMAP for Effcy!

For Normal Position table try (MAP/EMAP) 'Effcy' on X and Boost Aim on Y.

Not as big of a help on larger turbos that don't get below 100% Effcy but for the rest of us with small/medium 'street' turbos that spend a lot of time below 100% Effcy it makes for a Normal Position table that is smooth and predictable.

Suggested points on X are 60%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 125%, 150%. Unless the turbo is very small stock sized or you run a restrictor Effcy won't get much below 70% or so.

There will be very slight change in Normal Position DC % from 150% to 100%, then required DC% will ramp up from 95% to 75% as the turbine pressure gets higher and higher.

I just discovered my Efficiency is #4 = MAP in kPa, so no percentages...

[Wolf_Tm250]

Hi,
need help to clear some things about boost controlling. Thanks.

Scenario:
Motec M400, software V.3, EXTERNAL wastegate.
Setup:
- EBC (Delco) valve Output to ground
- Polarity: Lo for 0%


The car was mapped by professional tuner, and never had boost problems in these years.
After changing ic pipes diameter, I got 20/25 kPa of overshooting in 3rd gear and up... ok, that's fine, as my mods probably modified engine VE.

So I started removing some P (small decrements), and adding some D (very small increments), but this had really NO impact on boost control.
I even tried to follow the advices about the I, but with no luck.

PS: yes, removing EBC does make my boost to return to wg spring setting.

I started then to INCREASE Valve Normal Position numbers (DC) from 45 to 50 and more%, as with external wastegate, with valve ON, the boost decrease.... but it was even worse!

So I decreased Normal Position numbers till 30/35%, and now I have no more overshoot:
1. could anyone please tell me why decreasing Normal Position numbers solved my problem?
If I understood correctly, the more the EBC valve is ON, the less the boost... right?
And with 100% DC, that is to say fully ON valve, the boost should return to wg spring setting!

2. I really thought PID has more influence than DC...

THANK YOU.

[Scott@FP]

Are you using the external WG with both top and bottom ports, with manifold pressure to the bottom port and the WG solenoid to the top port? Or is it bottom port only with EBC bleeding off pressure?

How is the solenoid connected, as a normally open or normally closed valve?

It appears from the logs your normal position vs actual position exceeds the settings in the Pos Int Clamp and Neg Int Clamp tables and it quits reacting. You don't have to be using I for the +/- Int Clamp tables to have an effect.

Try increasing your pos and neg int clamps to 30% and see if it starts reacting during overshoot. Your Normal Pos tables may need some adjustment.

Oh and try using Boost Aim on the Y axis of the Normal Position Table rather than Manifold Pressure, that way if it does over/undershoot the Normal Position DC% is where it should be instead of lower or higher than it should be.