ITB Alpha N Closed Loop Strategy

[Keith Tan]

HI guys,

This is with regards to tuning a ITB car with Alpha N main fuel map. Hope to learn from the more experienced tuners here.

I've previously mapped the car without any closed loop control on Alpha N and it drives well. However, Alpha N is basically using the TPS as an estimate of the load that the engine see. 

The load changes depending on road condition and which gear the car is running. There will be situations where for example 3000rpm at 15% TPS load, gear 3. The load site is tuned to stoich 14.7AFR. In another scenario when the engine is operating at the same 3000rpm, 15% TPS load but on gear 6 and there is a slight uphill slope, the actual load increases and the fueling will end up lean. 

 

So i've tuned the car for all load sites for the worse possible load. More fuel is always better than too little fuel! However, when the engine is at a light gear, that same site will end up running too rich due to the lesser load. 

I've tried using 4D fueling overlay with MAP as the load site and tried to apply corrections to this map. However, there will be overlapping situations where the same MAP cell coincides with other load demands. End up messing up the fueling and making things worse. 

Thus my decision to hook up the AEM Uego wideband sensor to make fuel trims automatically. However, i've faced a few issues while tuning today.

Tried logging a run while driving on the road. At the fuel mixture table, refreshed the logged fuel cells and applied the changes necessary. 

However, the Mixture table uses MAP as the load site. My main fuel table is TPS load site. So how does the table decide where the fuel trims are applied on my main fuel table? 

2nd issue. After applying those trims, i'll end up with a map with many spikes. I understand why such spikes appear. It is sudden lean situations due to load on that particular TPS site which the close loop strategy might not have taken into account the MAP values. I would imagine that fuel trim should be applied to the 4D overlay map instead. Would that work better?

3rd issue: Closed loop %TP Delta lockout and map Delta Lockout. These two constraints are too restrictive for Alpha N close loop control. Since my load sites are based off the TPS numbers, a delta lockout of maximum 20% means Closeloop will be disabled when there is a sudden opening of more than 20% throttle. When the main fueling map is TPS based, 20% throttle input isnt too much during acceleration. 

Map Delta Lockout: The maximum i could put in is 20kpa. With ITBs airflow is much more sudden and quicker than single throttles. A 20% throttle input would have swing the MAP way over 20kpa. I hope this can be increased so the close loop strategy isnt too limited for alpha n?

4th issue: Oscillating AFR. I've played around the Gain and AFR control for idling so the corrected AFR hovers near my target without going left and right too much. However, while driving, there are sudden lean situations and the car feels flat and the close loop strategy doesnt react quickly enough to richen the mix. Makes it very flat whenever more throttle is applied. 

5th issue: The sudden lean situation might be opposite of whats happening. IE maybe my acceleration fueling is adding more fuel which the close loop strategy is trying to lean off, since those sites my target AFR is 14.7. And acclereation fueling might end up going to 13:1 so the close loop might see this sudden rich state and trim off aggressively and overshoots into lean before it decides to richen up again. These are all happening during transcient situations. 

I was hoping that the Vipec Closed loop strategy would be able to manage all these transcient situations. Perhaps VE based tuning might do a better job at this since they can predict the fueling requirements? 

I really need a good ECU that can manage transcient throttle fueling control well for ITB cars. I hope the vipec can be tuned to reach this goal. 

 

Thanks for taking the time to read all these. Appreciate it if someone could shed some light into this?

 

Cheers!
keith

 

 

[Dave Kriedeman]

Hi Keith,

what ECU are you using, G4 or G4 + based.

Are you tuning the engine on the road or a dyno.

What do you have the fuel setting set up as, BAP MAP XOVER with TPS Y AXIS main fuel table and TARGET AFR table MAP as Y axis.

Some more info on precisely your software settings, what FW are you using etc, please.

Regards

Dave.

[Keith Tan]

Hi Dave,

Firmware is Version 4.9.9.1784

Load = MAP

I guess Load= BAP would work better?

Open Loop AFR Table Overlay = OFF

This is a Vipec V88 ecu bought 4years ago. Tried to use the iVTS software but it wouldn't work, so i went back to the standard VTS software. 

I was doing road tuning yesterday and logging the AFR and tried to get the close loop to work as efficiently as possible. 

I've done Dyno tune on ITB cars but road conditions always varies and a perfectly tuned ITB car on a dyno will always need to be touched up on the road afterwards.

Nowadays, i prefer to use the dyno to find MBT and tune the fuel map on the road instead. 

Rgds

keith

 

 

 

Dave,

Both Fuel Map and target AFR table are both on TPS Y axis. 

This is what i've set for Closed Loop Gain

Error of

0=0

0.5=8

1=10

1.5=20

2=20

2.5=20

 

Closed loop Control rate:

1000rpm = 4

2000rpm= 10

3k=10

4k=10

5k=10

8k=10

 

Thanks

Keith

 

 

 

[Dave Kriedeman]

Hi Keith,

You can actually use  BAP or MAP and span the Y axis of the FUEL MAIN TABLE with TPS.

Set the TARGET AFR table by TPS or MAP.

Normally once running above idle the MAP signal is a lot smoother unless running massive camshafts also.

So if the MAP signal is still weak or erratic then use TPS as the Y axis on the target table.

However I personally have never been able to not use MAP on the TARGET AFR TABLE.

Idle areas and light throttle cruise can be an issue but you just manually tune them to suit.

Full OPEN LOOP TUNING must be completed really before switching to full CLL control.

Also make sure you have OPEN LOOP AFR TABLE - ON.

The OPEN LOOP AFR OVERLAY TABLE CAN STAY OFF, HOWEVER you should tune with OPEN LOOP AFR TABLE -ON.

Once you have tuned the OPEN LOOP FUEL then you will find that the CLL tuning will be a lot more accurate and stable,

If using Mixture Map tuning it can be setup to use anything you like as the LOAD SOURCE.

Be careful tuning with mixture Map unless you add filters to lock out rapid throttle position changes , decal changes etc, any transient type influences to the fuel data.

I personally would have load source as MAP, FUEL MAIN Y AXIS as  TPS MAIN, TARGET AFR TABLE set as MAP.

Tune FULL OPEN LOOP and then use Quick tune or MATHS KEY TUNE from data logs.

Upgrade to firmware 4.10.2

While you are in the fuel table you can be locked on a cell press the M key and a table will open for that sight , type in the actual AFR and the ECU will change the value of the fuel cell to the correct value.

Also use less resolution, rpm every 500 and TPS every 10%, let the ECU do the work of interpolating between the cells.

When you have picky areas add more resolution to those spots by adding more refined cells.

Once you are happy with OPEN LOOP TUNING, then try your luck at CLL.

Remember CLL is really designed to keep the mixtures around stoich for economy and emissions.

By the way you can not use G4+ or iVTS on G4 or V series ECU's.

Regards

Dave.

 

Edited October 23, 2015 by Dave Kriedeman
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