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Computer MPG Calculation

Discussion in 'Gen 2 Prius Main Forum' started by corysold, Mar 8, 2007.

  1. corysold

    corysold New Member

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    Maybe this should be in the MPG forum and maybe it has already been discussed. However, during gliding, electric motor use, braking, etc. when the MPG readout is 99.9, what number is the computer using to calculate MPG? Is it using 99.9, infinity, something in the hundreds it doesn't show? Just thinking this might be a reason my calculations are different than the computer.
     
    #1 corysold, Mar 8, 2007
  2. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(corysold @ Mar 8 2007, 03:44 PM) [snapback]402427[/snapback]</div>
    We know it's capable of reading significantly higher than 99.9 and it's believed it uses that number....but not infinity. There was a miniscanner used for the original Prius Marathon run and I wanna say the high readout was 140mpg or so....but don't sue me if that's not correct.
     
    #2 efusco, Mar 8, 2007
  3. ken1784

    ken1784 SuperMID designer

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    <div class='quotetop'>QUOTE(corysold @ Mar 9 2007, 06:44 AM) [snapback]402427[/snapback]</div>
    some miles / zero gallon = infinity mpg
    What kind of calculations did you use?

    Ken@Japan
     
    #3 ken1784, Mar 8, 2007
  4. efusco

    efusco Moderator Emeritus
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    Ken, how high does the super mid read?

    does it use L/100km and that's why the calculations were higher.
     
    #4 efusco, Mar 8, 2007
  5. JimboK

    JimboK One owner, low mileage

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    If the ICE is not spinning the ScanGauge shows 9999.9 MPG. I figured it was using infinity. Evan, if not, how do you account for such a high number? Not challenging you, oh Great One, just trying to learn.

    I've seen the SG show up to ~200 MPG when the ICE is spinning.
     
    #5 JimboK, Mar 8, 2007
  6. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(JimboK @ Mar 8 2007, 03:58 PM) [snapback]402434[/snapback]</div>
    No offense, I'm not sure of the actual max. But, as for the 9999.9 on the scan guage it may be substituting that for infinity so as to avoid the mathematical errors of calculating mpg that infinity would introduce.
     
    #6 efusco, Mar 8, 2007
  7. qbee42

    qbee42 My other car is a boat

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    The infinity vs. 99.9 or some other large number is really only an issue for instantaneous mileage. No self respecting engineer would ever calculate average mileage by totaling up a bunch of instantaneous mileage calculations. Doing so invites all sorts of error accumulation. Average mileage is calculated by maintaining total miles and total fuel used over the average period. I can't say how Toyota does it with the Prius, but any other way is virtually unimaginable.

    Tom
     
    #7 qbee42, Mar 8, 2007
  8. Allannde

    Allannde Just a Senior

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    <div class='quotetop'>QUOTE(qbee42 @ Mar 8 2007, 02:12 PM) [snapback]402442[/snapback]</div>
    Of course.

    That tall bar on the MFD simply means that for the moment, the car is effectively not consuming fuel.
     
    #8 Allannde, Mar 8, 2007
  9. jeneric

    jeneric New Member

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    <div class='quotetop'>QUOTE(corysold @ Mar 8 2007, 01:44 PM) [snapback]402427[/snapback]</div>
    So, yeah, that shouldn't be the reason. Computer just tracks Miles and Gallons. Gallons is not 0, so there's no problem. Display of 99.9 is just that, a "display" of a number, maybe where Gallons was zero and Miles wasn't.

    How many Gallons are you off?

    How much fuel evaporates as you're filling your tank? How well are the pumps calibrated?
     
    #9 jeneric, Mar 8, 2007
  10. ken1784

    ken1784 SuperMID designer

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    <div class='quotetop'>QUOTE(efusco @ Mar 9 2007, 06:54 AM) [snapback]402431[/snapback]</div>
    My SuperMID shows max 99.99 km/L (235 mpg) when it exceeds 99.99 km/L including infinity.

    Ken@Japan


    <div class='quotetop'>QUOTE(qbee42 @ Mar 9 2007, 07:12 AM) [snapback]402442[/snapback]</div>
    It is not only for instantaneous mileage, but also average mileage as well.

    Ken@Japan

    [​IMG]
     
    #10 ken1784, Mar 8, 2007
  11. corysold

    corysold New Member

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    I am not off by a whole lot, same as most everyone else it seems, a couple miles per gallon here or there. I was more just curious as to how the system works.
     
    #11 corysold, Mar 9, 2007
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