MAF based understanding

[Hentai]

MAF Mass Air Flow

Air goes in you get a voltage or frequency output, ecu translate this from a transfer function into a known number of air mass in grams a second or pounds a minute. Personally I would stick with grams a second.
With said number the ECU can add the right amount of fuel at the various rpms and load sights, you just need to tell it what Lambda to target.

Why I prefer it is because it is a lot easier to tune and get going with a wideband then compared to trying to tune all the spots of the speed density VE table. Also the load repsents engine efficiency and corsponds with tq output while MAF follows horse power output so you have a good idea of where your tq and hp are being produced at. Plus with a little math you can figure a range that your car can be in. Also throw a map sensor in and you can tell better where you are at on turbo compressor maps. Another reason is a MAF sensor handles varying exhaust and intake setups with better ease then a speed density setup, esp if you have variable geotermy turbos or exhaust flaps or etc devices to increase engine breathing efficency. You basically tune the transfer function based on lambda output on a working car if you have no curve for it presently. car to reading to lean on the wideband, take the lambda value and multiple it with the grams a second value to get the new updated grams a second for that voltage or adc point, This method works just fine when you run at lambda 1 in your commanded fuel table.

In another post I will post up how I suggest it be implemented


Despite what people may think I don't agree on it being that much of a restriction for a normal daily driven car. The biggest objection aganist it that I can see valid is how much space a maf sensor takes to plumb in for a correct setup. the looks of one in a setup.

[Hentai]

The maf transfer function has to be proper for maf fueling and spark to be correct.
There is good and bad with maf tuning.

Disadvantages

-If you have any issues with a certain area of your map despite having a proper tuned in maf, trying to tune the maf transfer function for that area can and probably will throw the calucations off for any other area.
-Spacial issues take place when trying to position in a maf.
-People suggest that maf sensors become dirty easily though I've seen not that issue if proper maintence is done, changed air filters over time. I've yet to seen one of mine and my families car's maf sensor fail or be out of spec.
-Possible intake resistriction
-changing sensor area can effect the maf transfer function and effect fueling\spark
-cost
-laminar flow needed

Advantages

-A more accurate view of engine efficecny and output
-Proper tuned in maf curve\implementation can adapt better to changing engine conditions
-knowledge of air consumption over time
-ease of tuning
-engine load ( VE ) can be instantly shown as
VE = MAF
-------------
(displacement * Pstp * Speed)
-Knowing exact air mass flow makes fuel demand calculations simple as well
fuel flow rate =
MAF * (desired A/F ratio)

[Hentai]

Inputs
MAF
TPS
CHT
IAT - while the way most maf's work you they could be used without IAT, still need IAT for things such as timing retard incase of high IAT's which I've seen.
Crank signal

outputs
spark
fuel

For Calculated Load I would say ( maf grams a second * 15 ) / RPM = Grams a Cylinder


So for a N\A vehicle you would have 0 to 1 in your load section and a forced induction would be 0 to 2 or 3 or 4 depending on the ammount of power output.


tables
lets see
for fueling I would say we might not even need a table or if we do it will be a flat 2d table

Main Commanded Lamba table

RPM 500 - 1000 - 1500 - 2000 - 2500 - 3000 - 3500 - 4000 - 4500 -5000 - 5500 - 6000 - 6500 - 7000 - 7500
Lambada 1 1 1 1 1 1 1 1 1 .96 .96 .96 .96 .96 .96

Power Enrichment commanded lambda table
Basically same thing and better look can be seen in the picture.



PE mode throttle area %
This map is rpm vs throttle area %, this map with hysteris dictates when to enable PE mode and when to disable PE mode

I think that there should only be a MAF transfer function only, no other correction table for it, if possible this should be a live editable table on the fly. 1024 points would be good indeed, but I think you should have starting areas and let the software interoplate the rest points for starting out.
Maybe 32 points and the software fills in the other 32 points between each of those and you have the option to go in and change those points if needed.


I will introduce the spark tuning in my next post

[Fred]

Hentai, focus on that one box. Forget IAT. Forget PE. Focus, my son, and good thing will come to you from above :-)



The one box, I tell you! Focus your energy there!

Re PE, see this: viewtopic.php?f=8&t=1768

You have:

• MAF 0-5V input
• RPM value
• Lambda 3d table
• MAF 1024 point lookup

You feed 0-5V into 1024 pt lookup and get a single value back. This is the total airflow in mass / time.

What is second axis of lambda table? It's (total airflow in mass / time ) / (individual inductions / time). Inductions per time = (RPT / 2) / cyl count. RPT = Revs Per Time. Insert time units of choice and scalers to match.

What else do you need and/or want? Nothing?

Fred.

[Fred]

Updated slightly:

[Fred]

Anyone: what's a sensible variable max range for MAF in g/s? is 2000 enough? 1g/s ~= 1hp?

[Hentai]

yeah 2000g's is plenty.

The math so far is fine unless I come across something different.

at this point nothing else needed.

around 7.5~g\s = 1 hp

[Fred]

"around 7.5~g\s = 1 hp" - from the fairly brief research that I did this seems way wrong. Got references?

[Hentai]

My bad around 10hp I meant
usually I use 1lb/min to 10hp~
1lb/min = 7.5~g/s

[Fred]

Thanks :-)