PID Explanation and Tuning

[MarkMc]

I have attached a document I have written to explain PID control and give a guide to tuning. It will help give some background on what is going on with closed loop boost control, idle, servo motor, cam control, etc. Feel free to comment.

[Wolf_Tm250]

Thanks a lot !

[figgie]

Mark

Realy appreciate this!

It is one thing to follow directions for say an LS2 DBW install by pluggin in numbers for PID. Now I UNDERSTAND what this actually means

[Pascal]

Mark teh Magnificent! Great work with very simple explanation easy to underestand!

Thanks!

[MarkMc]

Hmmmm DBW, sounds like "official MoTeC annnouncement" time.

DBW throttle bodies are characterized here by our head designer. There is actually a lot of things to take into account when doing PID, beyond what I have talked about in the document. DBW throttles need a heap of extra work to make sure they are safe. Just make sure no one gets the idea that they should be setting their own PID for DBW.....there are a few other settings for the DBW other than the actual P, I and D which are all important parts of the control. If anyone asks about them I will get suspicious.

Stick with the servo, idle, boost and cams and no one will get hurt....except for possibly Pascal...I have been driving with him, haha. Crazy.

[SPowers]

Thanks Mark, nice little quick and dirty for the 'ole back pocket!

Sean

[figgie]

Mark

lol

sorry about spooking you.

I was in no way saying to muck with the DBW PID settings that you guys charachterized That would be, literally, suicidal

I got the PID charachterization from Simon Wagner for the LS2 DBW and Electronic Throttle (off a 2006 Chevy Corvertte in the US&A).

[MarkMc]

Good boy, Figgie.

[pnanassy]

Great explanation,thanks!

I have a real life case.Boost control with PID.As you can see,it works very well in 4th gear,but in 5th it starts to "overshoot",and while it trys to "brake",it begins to hunting.
Should i lower the "P" and sacrifice the systems reaction in the lowergears?
Could you please give me your suggestions which direction to go?

Boostlog_160to250kmh

Boost_PID_160to250kmh.JPG (109.3 KiB) Viewed 136534 times

[MarkMc]

Looks like you may have a bit too much D once you get to 5th. You can see the duty cycle drop right off which gives you the drop in boost pressure. You then see the duty cycle go back up as the boost undershoots but the boost takes ages to recover, the duty looks like it has flat lined at the max allowable (about 65-ish%). You could need to have a bit more allowable duty cycle in fifth gear.

If you are using version 3 M800 software you can set everything as a table. Perhaps you need a gear position input into the ECU so you can tweak everything based on gear.