Jump to content

Base/typical values for closed loop boost PID


M1tch
 Share

Recommended Posts

Hi all,

Currently road tuning my car to build up a good open loop wastegate duty cycle base table, next phase will be to then use this as the base table and drop it into closed loop boost control.

Plan will be to have boost by gear and also lower/reduce boost at lower throttle as well as when the engine is not up to full temperature.

Just looking at some of the base maps that have PID enabled as well as the help file I can see that the integral gain is usually set to 0.3 with the derivative gain set to 3.

Looking at a few of the base maps for other cars like the TT and Celica ST205 however the integral gain is set to 0.08 and the derivative gain is set to 0.5.

My question is, what should I start my closed loop PID to as a starting point? Will mainly be working on getting the open loop table sorted out first but would be great to get some basic settings sorted for closed loop.

Engine is currently fitted with the weakest wastegate spring during some shake down running (around 6-7psi) and planning to target something like 10-12psi as the 'higher' boost setting initially although the gearbox is rated to hold the torque of over 20psi so the current boost levels aren't going to really concern the engine if I 'overshoot' the boost to say 14psi although I would doubt it with such a weak spring.

Link to comment
Share on other sites

There are really no "typical settings", even basic stuff like the size of the hole through the boost source nipple or ignition timing has a big influence on the response of the turbo control system.  There are some examples in the help file which I have attached below but I even see big differences in very similar cars so I wouldnt take it as gospel.

I suggest following the guide in the help file here:  

G4+ ECU Tuning Functions > Boost Control > Closed Loop Boost Control > Closed Loop Boost Setup Guide

 

s0Q5TWL.png

Link to comment
Share on other sites

Thanks for that Adam, will look to perhaps set the initial settings within those ranges and see what the results are, ideally with a well tweaked open loop base map the closed loop part shouldn't need to do much heavy lifting to get to the boost targets etc.

Link to comment
Share on other sites

  • 1 month later...

I have now roughed out the open loop map and am sorting out the closed loop map - and it works most of the time, I have noticed that with stage 2-3 enabled that sometimes the stage 3 or indeed the 'D' part is sometimes too aggressive with the P and I values getting me there in terms of boost level requested.

I am tempted to just run stage 2 rather than stage 2-3, I am running 2 boost levels based on gear, 180kpa in 1st, 2nd, 5th and 6th with 220kpa target for 3rd and 4th (due to my gearbox setup).

I have noticed that on I might need to bump the base map by around 3% duty cycle on the solenoid to get a perfectly stable 180kpa, once I then change gear sometimes the value of D gets pulled over to the higher boost target and means it undershoots then back to the lower boost the D value adjusts the value away and it doesn't boost as high.

Example below is a lower boost pull, I can see that I need to adjust the duty cycle by around 3% on the base table but thats fine:

image.png.0fc84639451b081acea784196aa84240.png

On a slightly higher boost level I can see that it boosts ok, minor overshoot but thats fine - think I am near the limit of the wastegate spring but again needs about 3% more duty cycle on the base table.

image.png.4c0c1fd1d5be57f6d156ca8efa11cc37.png

Further on and boosting again in 3rd to 220kpa the D is pulling out 3% overall (the wrong way), I can see the D value is pulling out 3%, 6%, 9% and even 12% in later pulls even at lower boost and its not even hitting target anymore with an undershoot of 40kpa in some of the higher boost gears.

image.png.a275546127b5387c7f62371de6cda303.png

I can only partly guess that it might be fighting the wastegate spring a bit, although it seems to be ok to boost up to 220kpa and has gone higher than that before - only at around 60% duty cycle at 220kpa.

Wastegate trim increase of 35% in 2nd and 3rd to get the higher boost levels

Is it worth me doing the following:

1. Check the logs and add in 2-3% duty cycle to the base table to mean the closed loop system doesn't need to work almost at all for the target boost levels

2. Change over to stage 2 only rather than stage 2-3

Settings for the closed loop are here:

image.png.588df7787bc5dcd3c2e10ba93364a9f7.png

Link to comment
Share on other sites

I have looked back again at some of the maps vs logging for various pulls, I think the issue is that the initial cells when coming onto boost are slightly too high meaning that the derivative gain is pulling duty out of the map to avoid an overshoot but when it actually gets to the cells where the turbo is spooling up they are basically correct.

I have found a fair few pulls where the derivative gain is at 0 when the turbo is on boost but I can see it pulling duty beforehand - I have adjusted the wastegate duty basemap during the spooling area of the map to match off the actual wastegate duty cycle being commanded by the closed loop system which should hopefully mean that the closed loop system doesn't panic as it sees the turbo build boost quickly.

I am seeing stage 1 spool, stage 2 as well as stage 3 operate back and forth so I think my PID gains are ok, it doesn't overshoot and boost comes on quite strongly but smoothly - I can see that the Integral %DC is only up to around 5% at the max so well within the integral clamp - have dropped the clamp to +/- 15% although it doesn't get near it which is good.

I did originally have some of the pre spool duty cycle cells higher than they are currently which might have caused this issue over the past week or so - my thought was to get the turbo to spool up quicker but I know stage 1 goes to 90% duty cycle to get the spool up anyway.

Link to comment
Share on other sites

Stage 2 uses P & D only, this stage is to control the approach to target.  Think of "D" as kind of like putting on the brakes as you approach target to prevent it overshooting. The faster you are approaching the target the more DC D will pull out.   Stage 3 disables D and uses P & I only, this stage is to remove any remaining error off target.    

So the main problem appears to be sometimes it is not reaching the stage 3 threshold.  That could be too much D or base DC too low.

The Base DC mode only changes what is used from the base DC table in stage 3.  I would generally leave in in stage2-3.

Link to comment
Share on other sites

Will keep it as stage 2-3, D might be too high although it is preventing an overshoot ok, have pulled back the DC on the spool part of the map and will see if that helps - sometimes its fine though and the DC for the part of the map on boost seems to be about right.

Should I increase the stage 3 on KPa value? I can see all 3 stages being used in the logs so everything is triggering.

Link to comment
Share on other sites

1 hour ago, M1tch said:

Should I increase the stage 3 on KPa value?

You may have to, but 15-20kpa is around where I have usually ended up.  

 

1 hour ago, M1tch said:

I can see all 3 stages being used in the logs so everything is triggering.

In that last log pic above it is stuck in stage 2, so it would never try to correct that last bit of error.  Not sure why it hasnt reached the threshold though.  You have to study logs to find what causes it to not reach the threshold sometimes - it may be gear, air temp, a certain cell in the DC table, a driver related influence such as how quickly the throttle is moved etc...  

Link to comment
Share on other sites

17 minutes ago, Adamw said:

You may have to, but 15-20kpa is around where I have usually ended up.  

 

In that last log pic above it is stuck in stage 2, so it would never try to correct that last bit of error.  Not sure why it hasnt reached the threshold though.  You have to study logs to find what causes it to not reach the threshold sometimes - it may be gear, air temp, a certain cell in the DC table, a driver related influence such as how quickly the throttle is moved etc...  

In that last log where its undershot the target is at 220kpa, kpa at that point is 198 so 2kpa under where stage 3 will trigger (20kpa under the target) - will perhaps bump this to 25kpa for stage 3.

Have adjusted some of the DC during spool up to avoid the D value needing to pull DC to avoid the overshoot - some of these 3rd gear pulls are from a lower rpm rather than shifting at higher RPMs so might be another issue - unable to really rev out much more in 3rd due to road logging and speed limits.

Link to comment
Share on other sites

I have increased the stage 3 to 30kpa to see if it can 'reset' itself a bit, still seem to have the issue that the D value is pulling out too much duty making the turbo quite lazy and missing its boost target and which is cyclic as it undershoots and then never turns off as its undershot.

I have 1/4 mile drag track time booked in for this weekend so I can hopefully get to the bottom of this - car sometimes runs at the boost level I have set but not all of the time, kinda want to only have the 'D' duty cycle below a certain point for the initial spool until it hits its boost target.

Link to comment
Share on other sites

Still battling with this, might revert back to the original settings - boost controller thought it would be funny to just randomly chuck in another 7.5% duty cycle to spike it into boost cut after undershooting again at the RPM where its at maximum torque whilst pulling out duty cycle before hand to make it not actually hit target.

image.png.758a43713f59bcab788eb2fcfae12ae1.png

Link to comment
Share on other sites

Dropped the duty cycle back slightly inline with how the system was commanding the turbo, its now just completely ignoring the target - its 40kpa off and not correcting anything?

image.png.549298e80ee61b839e98f4029bde1827.png

Link to comment
Share on other sites

I have attached a log file from the drag strip this morning which will give you 2 sets of some full throttle pulls in both normal boost at 180kpa and higher boost 220kpa, I pulled out boost control in 1st near the end of the runs but the duty cycle is the same I believe.

You can see from the start of the week screenshot that at 58% duty cycle it was sitting at 180kpa with boost being controlled at 220kpa at 65% duty cycle.

 

Link to comment
Share on other sites

The wastegate is tapped out at the max 90% and the boost hasnt reached target.  You need to make some mechanical or plumbing adjustments so that your target boost is achievable with less than about 75% DC.  The Mac valves are generally fully open at about 75-80%, so giving it more DC after that makes no difference.  I would also generally have no zeros in my boost target table.  If 180Kpa is the lowest boost you are going to run then 180kpa is the smallest number I would have anywhere in the target table.  Example table from my car below.  

UcOx4pq.png

 

m6Hsn24.png

Link to comment
Share on other sites

I will check over all of the plumbing and check the preload on the wastegate as well to see whats happening - it was previously holding 220kpa at 65% duty cycle which is why I was wondering what had happened when it was maxxing out at less than that.

With regards to my boost targets, I am limiting boost levels by gear due to having slightly stronger 3rd and 4th gear, I have worked out that I think the max torque the other gears is at around 180kpa - this is why the base table is at 180kpa with a boost by gear modifier for 3rd and 4th. I also left some cells blank below say 50% throttle as I don't really need the turbo to spool up when on cruise or around town etc, have also seen that this is also the case so that it doesn't try and spool up mid corner on lighter throttle.

My plan for boost by gear is:

1st - wastegate spring pressure to allow for easier launches

2nd - 180kpa

3rd - 220kpa+

4th - 220kpa+

5th - 180kpa

6th - 180kpa

To your point though, I might look to set the whole base table to 180kpa, unsure what spring I currently have in the wastegate at the moment but might see if I can run something like a 9psi spring to then boost up to 12psi easier (but not overshoot which could damage the gearbox) but make it easier to get to higher boost levels where I can.

I think I have worked out that I can run around 220-240kpa maybe to 260kpa at higher RPMs in 3rd and 4th in terms of torque rating but currently I am just after 180kpa base bumping up to 220kpa for 3rd and 4th.

Link to comment
Share on other sites

Will check the preload once the engine cools down a bit, have changed over the BOV, checked all leaks for both exhaust and boost hoses, not allowed to attach the log file as its too large it seems but its still pulling duty even when its still far under target and not really increasing that fast.

image.png.8f09b18e8cd6980efd6c11c7c01bde75.png

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...