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Thread: VE Table Filter Factors

  1. #1
    Senior Tuner
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    VE Table Filter Factors

    As I peel away idle "actors" I still have this fuel-loop surging.
    That is, I see MAP, O2 and injector pulse width swing wide
    while RPM sort of follows along; spark, commanded AFR and
    IAC counts are steady. I look at injector PW vs MAP*RPM
    and it's a "cloud" where you'd think it should be a straight
    line fit, given that RPM isn't moving much. IPW / MAP is not
    real tight either.

    So this says to me, another actor and possibly just the
    instability (loop lag) in the airflow measurement itself.

    I see there is a time-filter for VE. But I also see this VE
    Correction Factor, Initial vs ECT Zone which appears to be
    putting huge (30%) "correction" onto the VE at lower MAP
    and lower ECT. Since this "corner" is where I have the worst
    problem I'm wondering if anyone can 'splain me some things:

    - This correction vs ECT / MAP - is it straight multiplying
    the current indexed table value? Why do I want so big and
    so variable a correction?

    - VE Corr Factor Filt - is this change-per-tick? What have
    you seen for "sensible maximum"? Does this only "smooth"
    the applied "correction factor" or does it also "smooth" the
    table-traversal?

    - Other smoothing filters - what else might "lag out" the VE
    value as the motor slides across the VE table surface? Dynamic
    Air Filt? I'd like to know how these all interact and which might
    be the most effective in tightening up open loop fueled, open
    loop IAC idle airflow/fueling.

  2. #2
    Senior Tuner
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    Dec 2004
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    what about MAF filtering?
    I've been playing with logging MAF raw vs MAF (SAE) and calculating cylinder airmass out of it. the resulting cylairmass charts are way more jumpy than the ones we get by logging the PID. the smoothness doesn't show up from nowhere, there's gotta be some filters for it, but i went thorough tunes for 99 and 01 fbody, 04 z06, 05 gto and i dont see anything about MAF smoothing functions. Is it not available to us, or is it not there at all?

  3. #3
    if you are talking about normal MAF operation there is a complex predictive filter algorithm you are missing that goes about the job of combining the MAF, VE, MAP and TPS transient information. Contains about 10 coeff's and uses the engine operating zone concept. I have discussed this eslewhere but it's something we have never added for fear of trying to explain it in detail.

    If you are talking about SD then there is no filtering, the value that gets looked up in the VE table is pumped right into the final answer of the dynamic airflow calculation. The only real lag is the MAP sensor respsonse time and processing delay.
    I count sheep in hex...

  4. #4
    Senior Tuner
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    thanks for clarification Chris,
    can we see the predictive algorithm? i wanna see what kinds of nuttyness we're up against.

  5. #5
    It goes something like:

    Cylair(t) = K1* Cylair(t-1) + K2.MAF(t) + K3.MAF(t-1) + K4.MAP(t) + K5.MAP(t-1) + K6.MAP(t-2) + K7.TPS(t) + K8.TPS(t-1) + K9.TPS(t-2) + K10.TransientCorr(t)

    There is a set of K1, K2... for each operating zone 18 total.

    TransientCorr is either MAF (for steady state), or VE*MAFVECorrFact and MAFVECorrFact is the ratio of the MAF cylair to VE cylair.

    Judging from most cals, the transient effect is lightly weighted compared to the MAF and other terms.

    while looking for the info i found this blast from the past, which i guess is common knowledge thesedays

    http://www.hptuners.com/forum/showthread.php?t=2359
    I count sheep in hex...

  6. #6
    Advanced Tuner
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    Is it something that is worth making adjustable, I.E somein has moved the Maf much farther away from the engine as in a Draw thru turbo/blower app?