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Blank in the 1 Min Consumption Display

Discussion in 'Gen 3 Prius Main Forum' started by jsfabb, Apr 6, 2012.

  1. RaZa

    RaZa Member

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    I've observed that the bar tends to represent what the mpg was at the moment the minute ticks by, not the average mpg for that full minute (which really makes the graph not nearly as useful or accurate as I had thought it was). I know this because I've seen the graph dip down below 20 when I know for fact I was probably in the 50's for that minute, I just happened to be accelerating at the time the graph updated... I've seen plenty of blanks on my graph, usually when I'm at a long light. In your most recent case the blank may have appeared at just that second you had stopped.

    I am just speculating though. It really has me wondering now. I'll experiment and see if I can tell what values it shows
     
  2. Sergio-PL

    Sergio-PL Member

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    It depends on how MPG is calculated (which is a bit of unknown - we don't now the source code of ECU). I'm using mpg shown in l/100km so the lower, the better. I often have empty 1-min bars (0.0 l/100km = ifninite mpg) while gliding. From time to time I get it also on 5-min bar when stuck in crawling traffic jam with full battery.
    Today I also observed on 1-min graph that "cars" from regen braking (which occured 10-15 seconds before next bar was displayed, from 80 to 0 kmh, all with 2/3 of CHG bar) was displayed 1 minute later, on next bar. So regen cars are shifted at least 30 seconds from realtime. Maybe 1-min graph of consumption is also shifted - that could explain why you get empty bars from time to time...

    Another (much simplier) explanation would be division by 0. If mpg is calculated as Distance / Consumption and consumption = 0 (due to all EV span) calculation error occurs and bar is left at 0.

    S.
     
  3. jsfabb

    jsfabb Active Member

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    I also get blanks when I'm in a traffic jam or stop for a red light.

    The bars are delayed by 1 minute. It shows how you drove, not how you are driving at that moment. That's why I call it my 1 Minute Report Card. That's what the iMPG gauge is for. Like this morning, I never stopped except maybe for 1 second at a stop sign. Other than that I was moving all of the time and at a fairly good pace.

    As far as the Div by 0. I would think that there would be an IF statement in their logic. IF miles = 0 AND CONS = 0 THEN 0 (no bar). IF Miles > 0 AND CONS = 0 THEN 100 MPG (highest bar will go). I'm not a programmer, but it's pretty simple. Besides, you stated that when you glide you get Infinity since there is no gas used over X distance.
     
  4. Big Steve

    Big Steve ramblin wreck

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    Have you moved away from this display and returned?
     
  5. Sergio-PL

    Sergio-PL Member

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    I agree about the program logic. I would do it this way. But we can't confirm that :)

    As for the graph. I know that it is a graph of past minute and is delayed by that. I've just observed that if for example in certain minute I brake regen 60 Wh (and stop), after 10-15 seconds minute graph for this minute is shown the regen cars will not appear on the graph. They will be on the next bar, one minute after the bar that covered this braking was displayed.
     
  6. jsfabb

    jsfabb Active Member

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    I don't think I did on this one, because it was near the end of my trip. Next time it happens I will try and do that!
     
  7. commuter

    commuter Untitled

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    I've observed this a few times in my travels, but have chalked it up to being in EV mode at speeds of 0-5 MPH while easing through packed traffic. Let me watch for it over the next few days.
     
  8. TwoGeeks

    TwoGeeks Junior Member

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    This seems right to me -- although not what I expected. I THOUGHT the display would be the average mpg for the past minute, but that's not consistent with how it's working.

    I also have noticed blank bars -- most often while I was stopped at a traffic light, but also for times when I was driving solidly for the past minute or so (down a long road where the speed was 45 mph). And also occasionally (but not always) when backing out of my long driveway.

    What also perplexes me is that the rough average of the bars on the consumption display doesn't square with Annette's estimate of mpg for the whole trip. I've seen the mismatch both ways: either the Consumption display suggests I'd have gotten well over 55 mpg on the trip, but at the end of the trip Annette says I got 48 mpg ... or the minute-by-minute display suggests I'd get only 45 or so mpg, but Annette says I got 55 mpg.

    I'm starting to think the Consumption display isn't very useful.
     
  9. macman408

    macman408 Electron Guidance Counselor

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    Depending on what you're observing, this is to be expected; you can't average mpg over time and get your total mpg. Here's an example to illustrate it:
    You drive for 10 minutes at 50 mpg at a constant speed of 30 mph. This means you've traveled 5 miles, and used 0.1 gallons of gas. 5 miles/0.1 gallons = 50 mpg. So what's the problem?
    OK, now you drive uphill for 10 minutes at 25 mpg, still keeping your speed constant at 30 mph. Again, you travel 5 miles, and use 0.2 gallons of gas. If you average your mpg, you'd expect to see (25+50)/2 = 37.5 mpg. However, you've traveled 10 miles total, using 0.3 gallons of gas; 10/0.3 = 33.3 mpg.

    As an even more extreme example, consider spending another 10 minutes at 100 mpg; once at 6 mph in a (very large) parking lot, and once at 90 mph coasting down a long straight mountainside while drafting a semi on the autobahn ;) . The first went 1 mile on 0.01 gallons, the second went 15 miles on 0.15 gallons. If you average 100 mpg for 10 minutes with the first 10 minutes of 50 mpg at 30 mph, you might think you'd get 75 mpg with either of these. However, the first case is 6 mi/0.11 gal = 54.5 mpg, while the second case is 20 mi/0.25 gal = 80 mpg.

    (On the other hand, if you're observing that the minute-by-minute display never shows a bar over 50 mpg, and then your trip average shows 55 mpg, then the computer's just not telling you the truth.)