Boost Control - Closed Loop Setup Mode

NigeT · Post by **NigeT** » Wed Sep 14, 2016 4:45 pm

Can someone give me an overview of how this works. I have a minimum of 140kPa target and for 140kPa I have a duty bias in the twenties across the board, but much of my logs have 0 boost duty with occasional Max Duty and some periods of the expected bias duty.
Thanks in advance.

Nigel

Post by **muythaibxr** » Thu Sep 15, 2016 4:02 am

NigeT · Post by **NigeT** » Thu Sep 15, 2016 3:58 pm

Fair enough - I was just hoping for some pointers to doc.

Attached the tune file, but the logs are too big even when zipped. I've randomly cut one down - hopefully it is good enough to be some use.

NigeT · Post by **NigeT** » Wed Sep 28, 2016 3:48 pm

I think that I'm pretty much there for the boost duty bias settings for the targets that are used in my boost tables. MAP is pretty much within +-5 of target when doing full throttle sweeps through the rev range from 2000-7000+. The one thing that concerns me now is when you start at a higher rpm at low-mid throttle and then quickly open the throttle - I seem to get a boost spike that goes much further above target.

Is this normal?
Do I need to reduce my boost duty bias to cater for it?

MSQ and brief log of a sample event attached.
Thanks.

Matt Cramer · Post by **Matt Cramer** » Thu Sep 29, 2016 6:32 am

Does the boost spike happen in setup mode or only once you get out of setup mode and turn PID on?

NigeT · Post by **NigeT** » Thu Sep 29, 2016 6:42 am

I may have posted this on the wrong thread, but this was in setup mode, I was using my commute too/from work to get some more data from tinkering with my duty bias values. Thanks.

eMTea · Post by **eMTea** » Thu Sep 29, 2016 8:44 am

Not trying to hijack your thread, but is there anywhere in the manuals that describes the different use of the closed loop modes?

Post by **muythaibxr** » Sat Oct 01, 2016 4:53 am

The latest manual describes it in the boost control section.

eMTea · Post by **eMTea** » Mon Oct 03, 2016 5:07 am

muythaibxr wrote:The latest manual describes it in the boost control section.

As far as I can find (page 99-100) in the "Megasquirt 3 setting up" manual, there is no mention of the "Setup Mode" and "Bias table".

Post by **muythaibxr** » Tue Oct 04, 2016 3:47 am

Hrrm, thought it was added. Anyway, use setup mode to set up the bias table. In this mode it won't engage PID.

eMTea · Post by **eMTea** » Tue Oct 04, 2016 3:51 am

Thank you!

And sorry for hijacking the thread!

NigeT · Post by **NigeT** » Thu Oct 06, 2016 5:08 pm

Just a note to say that I'm seeing the same boost spike on sudden throttle increase when the turbo is already boosting in Basic Mode as I saw in Setup Mode. I don't have it happen on a WOT run from 2000rpm up to redline, but then boost is mechanically limited for the first 1500-2000rpm increase anyway I guess.

Do I need to change my boost target tables from essentially flat lines to curves that match what can actually be achieved from the mechanical system?

Please don't flame me - I paid for my car to be tuned and it probably worked great on the hub dyno but I'm having issues real world that I'm trying to correct.

I will try to add a cut down log and msq in the next couple of days.

As ever thanks for the patience, assistance and encouragement you all give.

Post by **muythaibxr** » Fri Oct 07, 2016 3:50 am

Yes you should tune it based on what it wants mechanically.

nathaninwa · Post by **nathaninwa** » Fri Oct 07, 2016 6:59 am

Yep, tune DC to flatline boost. I have one car that needs 5dc more from peak tq to redline and my new LS setup seems to want declining DC. It's all based on the efficiency and design of the system as a whole

NigeT · Post by **NigeT** » Fri Oct 07, 2016 5:07 pm

Thanks guys.

I think there are several different considerations here.
1) Setting boost targets to achieve the power/torque targets you want at RPMs that allow enough boost to be generated to achieve those goals.
2) Tuning boost control duty cycle to meet those upper targets.
3) Dealing with the RPM regions below the point at which sufficient boost can be generated to achieve the desired boost targets.

1 was set by the professional tuner that created my tune on the hub dyno.
I believe I have 2 covered from my weeks of trying DC % in Setup Mode. I'm pretty happy with the DCs in mid to higher RPM, there is a very slight drop off as room increases, but within about +-5kPa.
With a full 2000-7000 RPM, WOT pull I'm seeing good results in Setup Mode and in Basic Mode, maybe slightly better in Setup Mode. If I'm at medium throttle at medium RPMs and go wide open throttle I hit the overboost limiter in both Basic Mode and Setup Mode. I was wondering if that could be at least partially caused by the boost targets being unachievable at lower RPMs, simply because the turbo cannot sling fast enough to generate the boost. I.e. should the boost target ramp up from somewhere between around 30-100kPa at 1000 RPM to maybe 160 kPa at just below 3500 RPM. I don't really have any data to indicate what the ramp up might be at lower throttle openings though.

Nigel

nathaninwa · Post by **nathaninwa** » Sat Oct 08, 2016 12:44 am

Maybe now is the time to limit the valves opening. Don't go below the max duty you need to make boost, but start limiting to 90% then 80% till you see a change in spool on a 2000 to redline 3rd gear pull. Limiting the valve may help with overboost situations by not allowing 100% for ramp in

NigeT · Post by **NigeT** » Sat Oct 08, 2016 1:24 am

Good point, I've had that set at something like 85% for some time now. I'm not really finding that Basic Mode is getting to the target as well as Setup Mode could limiting max duty allow me to increase the slider for Basic Mode and is that likely to improve reaching the target?

Thank you.

NigeT · Post by **NigeT** » Sun Oct 09, 2016 1:08 pm

Latest MSQ and some log snippets (the logs are too long to upload). The morning run may have had a slightly smaller delta. This is with my lower boost targets table - maximum just 160kPa.

NigeT · Post by **NigeT** » Thu Oct 20, 2016 4:04 pm

I dropped the Max duty limit a little and got chance to run the car a little yesterday. There was little if any change to the overboost, or a wider range pull. Log snippets attached.

I had a look at the log and noticed that the overboost is occurring after the Lower Limit Delta has been exceeded and so closed loop boost control is in effect. So I wondered whether my issue was that the control algorithm had too little authority over the duty cycle - previously I was assuming it had too much. I doubled the simple mode slider to around 300 and the boost control seemed much better on the way home. I didn't provoke any overboost fuel cut. I will continue pursuing this approach for now.

I have one question though - how do I eradicate the boost duty spikes on throttle lift?

NigeT · Post by **NigeT** » Fri Oct 28, 2016 5:59 am

Quick follow up. WOT pulls from below boost (say 2000-2500rpm) up to redline have Boost Control working pretty well, but with the slider I seem to have no impact on the mid-rpm (full boost available) sudden increase to WOT form low-mid throttle. It seems like the boost delta is higher in these situations and the boost control doesn't always catch it before the overshoot exceeds the tolerance.
Should switching to Advanced Mode and just increasing the differential coefficient allow me to reign in the overshoot in this scenario?
Thanks, Nigel.

Megasquirt Support Forum (MSEXTRA)