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Thread: Tackling Torque Correlation

  1. #1
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    Tackling Torque Correlation

    So I am trying to back into how the PCM is calculating torque and airflow, I see how HP Tuners laid it out in the formulas, but the math is simply not working.

    Here is the math...

    Airflow (g/sec) = (commanded torque (Nm) - Torque/Airflow Offset (Nm))/Torque/Airflow Factor (Nm/g/sec)

    When you divide the NM of torque by the factor, NM units cancel out and youre just left with g/sec...

    I have been logging the following channels:
    Powertrain Thottle TqReq - matches exactly to the table found in Engine>Torque Management>Auto Trans TqMgt, this is essentially your COMMANDED TORQUE for all intensive purposes
    Trans Engine Torque - appears to be your CALCULATED TORQUE

    So here is just one exact spot...

    900RPMS in gear at a stop
    Powertrain Thottle TqReq: 48Nm
    Trans Engine Torque: 101Nm
    Total Airflow: 19.2g/sec
    ECT: 181*F
    MAP: 68.4 kPa

    At 900RPMS, my tune has the following parameters:
    Torque/Airflow Offset: -14.84 Nm
    Torque/Airflow Factor: 11.75875 Nm/g/sec
    Friction Torque Loss: 39.5 Nm
    Flywheel Req. Tq - DR: 52 Nm

    So first off, a bit of a rounding issue but the Flywheel Req. Tq - DR is essentially equal to the Powertrain Throttle TqReq, which is what I expect...

    Now the Trans Engine Torque I am guessing is ACTUAL flywheel torque, either that or it is POST torque convertor torque multiplication, would would make some sense as most are around 2x multiple. But I see it move around a TON more than the torque commanded, and in fact when in park/neutral the commanded torque goes to zero but yet the trans engine torque remains populated, telling me its actual torque calculated.

    So now when I attempt to do the airflow calc using either one I don't get even close:

    Using Powertrain Throttle Torque: (52Nm - (-14.84Nm))/11.75875 Nm/g/sec = 5.68 g/sec

    Compare to my logged total airflow of 19.2 g/sec Not even close

    Ok so I thought maybe total airflow is calculated on actual torque calculated, could make more sense, here is that calc:

    Using Trans Engine Torque: (101Nm - (-14.84Nm))/11.75875 Nm/g/sec = 9.85 g/sec

    Still confused...anyone have any insight?

  2. #2
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    To me the math works if I just do:

    [commanded torque (Nm) / Torque/Airflow Factor (Nm/g/sec)] - Torque/Airflow Offset (Nm)

    (52Nm/11.75875) - (-14.84) = 19.26

    The math works, but then that means the "Offset" table is a g/sec offset not a torque offset.

  3. #3
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    Looks like my hunch is right, unless by some magic MIRACLE it works at every data point. Excel attached, if someone could populate their tunes info and check this against a log, it would be helpful, I going to try to dig up some tunes and logs from people and run it through this model.

    Based on this you have 3 ways to change your commanded airflow (commanded torque, factor, or offset). I had support map out the commanded torque in drive for my tune, not sure if others can see it.

    Commanded Airflow.xlsx

  4. #4
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    Seems to all be working out, I added modeling to the excel sheet based on the commanded airflow the expected TPS voltage, verified its working and matches my tune exactly.

    Commanded Airflow.xlsx
    Last edited by 06300CSRT8; 05-26-2016 at 04:46 PM.

  5. #5
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    Quote Originally Posted by 06300CSRT8 View Post
    Seems to all be working out, I added modeling to the excel sheet based on the commanded airflow the expected TPS voltage, verified its working and matches my tune exactly.

    Commanded Airflow.xlsx
    Pardon my ignorance but what does this allow you to do? Scale the Desired airflow and desired tq?

  6. #6
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    Thanks for sharing this.

  7. #7
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    Thumbs up Pretty Cool!

    Quote Originally Posted by 06300CSRT8 View Post
    Seems to all be working out, I added modeling to the excel sheet based on the commanded airflow the expected TPS voltage, verified its working and matches my tune exactly.

    Commanded Airflow.xlsx
    I'm looking at this for torque mutiplication for a current Dodge tune and this was exactly what I needed. thanks for posting