MPG in Hybrid Mode

Discussion in 'Prime Technical Discussion' started by CEJ, May 13, 2019.

  1. CEJ

    CEJ Member

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    Good job scoping this out, SK! Find it interesting that the EV icon on HSI and Engine icon on EM can both be unlit. This would be confusing without your explanation. Actually, today as I was driving in HV with engine icon unlit, I am pretty sure I could hear the engine running, which would have to be the case if it's still supplying energy to the motor and the wheels.

    I assume this same type of light show will also occur with zero SOC.

    I am now driving short-trips around town in HV and SOC has dropped to less the 50% as I discussed happening to me before. I assume that the mpg reading on the Main Display in this case is pretty meaningless. However, in the trips you take keeping SOC near 100% (where it started), wouldn't one expect the mpg reading to be more reliable since essentially no net charge is depleted? I realize the best results would be found, as you have said, by doing a calculation starting with a full tank and then refilling it. But even this probably doesn't mean much in the case you have depleted the charge substantially.
     
  2. utsug

    utsug Member

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    few days ago temperature here was 107 degrees F and within a minute of switching from EV to HV, the warm-up cycle was done.
     
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  3. CEJ

    CEJ Member

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    Does anyone know any way to get around the start-up video (prius driving on snow-covered terrain) on the big screen, so you can get to the control screen faster?
     
  4. jerrymildred

    jerrymildred Senior Member

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    That would be nice. That thing is slower than Windows 3.1!
     
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  5. Raytheeagle

    Raytheeagle Senior Member

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    What’s Windows 3.1:p.
     
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  6. jerrymildred

    jerrymildred Senior Member

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    A bad memory that I can't seem to completely forget. :oops:
     
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  7. CEJ

    CEJ Member

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    Just finished an in-town (shorter trips) run of 182.9 mi in "pure" HV (0%SOC) starting with full tank. AC on most of the time. Mpg on main display showed 64.9 after the run. Refill of 2.745 gallons gave a calculated result of 182.9/2.745=66.63 mpg, about a 2.5% difference. I think SK found 5% or so difference earlier in the thread (but less, rather than more). The difference here can be explained if the refill amount was just .073 gallons less than the original full level. I think such a refill discrepancy should be less important if the experiment is conducted over a greater distance. Be interesting to see if the calculated and displayed mpg become closer in that case or whether there is some other factor causing a difference between these two numbers.
     
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  8. jerrymildred

    jerrymildred Senior Member

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    Quite true about the small refill being prone to larger error. Also, having several fill ups and averaging them will get you an even better picture.

    Mine is much closer to being right than previous Prii I've had. Here's what we got on our vacation. As you can see, the error varied quite a bit. (Blanks are when I forgot to get a picture of that number when I filled up.)
    Screen Shot 2019-06-23 at 6.59.17 AM.png
     
  9. Prius from Dad

    Prius from Dad Senior Member

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    I agree that you need a big sample to get a good average. These are the results for the 2012 v that I traded in on my Prime:

    Miles 123,670
    Fill ups 246
    Displayed 51.60 mpg
    Calculated 48.86 mpg
    Difference -2.74 mpg
    % difference -5.31%

    This agrees with the general consensus of 5%-6% optimistic, that I've read in these forums.
     
  10. Salamander_King

    Salamander_King Senior Member

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    The hand calculated mpg being better than the displayed mpg is rare, but it can happen. As pointed out, a small amount of refill makes more error-prone, especially if two fillings before and after are done at different gas stations. I try to use the same gas station, same pump repeatedly, but that is not always possible. What I read is that while most of the pumps are accurate for the amount of gas delivered, the auto shut off sensitivity may differ causing a difference in the "full" point if you use two different pumps. It is also conceivable that even using the same pump, filling technique can vary the shut-off point to cause some discrepancy.

    Edit: Here is my data from my Gen3 Prius.

    Miles 35,061
    Fill ups 77
    Displayed 52.4 mpg
    Calculated 49.2 mpg
    Difference -3.2 mpg
    % difference -6.1%

    As for the PRIME, my data points are too small to be meaningful for pure HV drives for I usually don't drive a full tank of gas without charging. However, I suppose for the comparison of the displayed mpg vs. calculated mpg purpose, one can include all of the fill-ups regardless of charging status. So, here is my current data.

    Miles 29,513
    Fill ups 39
    Displayed 84.7 mpg
    Calculated 80.7 mpg
    Difference -4.0 mpg
    % difference -4.7%
     
    #230 Salamander_King, Jun 23, 2019
    Last edited: Jun 23, 2019
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  11. Salamander_King

    Salamander_King Senior Member

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    For PRIME, the lifetime mpg for the HV drive portion only can be calculated if you have the data for the lifetime miles/kWh for EV drive portion from "Drive Monitor 2" and the total amount of wall charge you have used plus, of course, the total amount of gas used.

    For this calculation, I make an assumption that actual traction battery SOC used for EV portion (not the displayed SOC) is 62% (from 18%-80%) or 5.46kWh (8.8kWh x 62%) and a full charge from the wall is 6.5kWh with 84% charge efficiency thus giving 5.46kWh of charge to the traction battery each time it is charged from zero EV range to full. I have this calculation set on my spreadsheet to track the change.

    Miles 29,513
    Calculated lifetime mpg for EV/HV combined: 80.7 mpg
    Displayed lifetime miles/kWh for EV: 4.5 miles/kWh
    Calculated lifetime mpg for HV: 53.95 mpg

    Screenshot 2019-06-23 at 9.05.23 AM.png
     
    #231 Salamander_King, Jun 23, 2019
    Last edited: Jun 23, 2019
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  12. Tideland Prius

    Tideland Prius Moderator of the North
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    I know you're joking but for our younger members...

     
  13. Raytheeagle

    Raytheeagle Senior Member

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    I always like older references that some may not get;).

    I had an interviewee that we toured on Friday and we talked about one of our pieces of equipment that when you take off a screen looks like Lite Brite:whistle:.

    When I made the reference, I got the blank stare:rolleyes:.

    Made me feel a bit older :oops:.
     
  14. CEJ

    CEJ Member

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    Just finished a roughly 1000 mile round trip. Starting with full charge and driving in HV from the start, SOC hung very closely in the high 90's. This was very satisfying since the AC was on constantly due to hot weather. On the return trip (also starting with 100% SOC), I was observing the same thing until after a lunch stop when I forgot to punch the HV/EV button and drove some miles before noticing a drop in the SOC to the mid 80's. Realizing what I had done, I then quickly pressed the button. This occurred at around 150 or so miles into the 500 mile return trip. But from there on, staying religiously in HV, the SOC never got more than a percentage or two above the 80% level it had dropped to. Seems like I vaguely remember something like this being mentioned much earlier in this thread. But also that the level to which SOC charge could be replenished was not capped.
     
  15. jerrymildred

    jerrymildred Senior Member

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    Right. It'll try to maintain the SOC available at the time you went to HV mode, but will borrow and repay energy from the battery, so that level will fluctuate as you go. As for replenishing it, it will normally replenish up to a little above that baseline SOC. But, on a long enough descent, it can replenish right up to 100% and you can lock in that new SOC by quickly going to EV and back to HV. Charge mode, has an upper limit and I think it's 80%.
     
  16. CEJ

    CEJ Member

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    Thanks, Jerry, for that clear explanation. That is fascinating! Do you have any idea why it works that way? That is, why it normally won't go much above the level it dropped to when you go back to HV, and that it won't capture the gain from a downhill episode unless you lock it in by switching to EV and then back to HV?
     
  17. Tideland Prius

    Tideland Prius Moderator of the North
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    I thought it will capture the gain from a downhill section, it just won't hold it at that new, higher % SOC; that's what the HV --> EV --> HV trick is for. (Ratcheting).

    From a computer logic standpoint, it makes sense since that's how the Toyota Hybrid System has always functioned - keep the charge at around 60% of true SOC (for older Prius owners, that's 6 bars). I suspect that logic carries over to the Prime where when you exit EV mode and enter HV mode, it treats that SOC as the target SOC so it will fluctuate around it but will try to keep it at the SOC value when you entered HV mode.
     
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  18. jerrymildred

    jerrymildred Senior Member

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    What @Tideland Prius said.

    When you put the car in HV mode, it's acting like a regular Prius hybrid. A regular Prius hybrid would not push the battery from (for example) 2 kWh to 6 kWh because it could not; the battery isn't that big. The regular Prius has a much narrower range of battery power available. The Prime pretty closely emulates that in HV mode although I think it does push the edges a little more than the regular Prius, at least compared to previous generations.
     
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  19. CEJ

    CEJ Member

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    Thanks, Jerry and Tideland. It's all making much more sense to me! Can't imagine where else I could have found such good info.
     
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  20. jerrymildred

    jerrymildred Senior Member

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    One other likely rational for the system working the way it does is that you'll get terrible gas mileage while the car is filling up the battery. The car allows you to fill it with CHARGE mode if you see an upcoming need for more EV range. But it won't assume you'll need it because, for all the car knows, it might finish filling the battery just as you arrive home and you'd be parking with a full battery and an empty gas tank rather than the other way around, so to speak. It's almost always best to get home with little to no EV range left.
     
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