Tutorials on 4th gen Prius fuel economy displays?

Discussion in 'Gen 4 Prius Fuel Economy' started by Awap, Apr 5, 2019.

  1. Awap

    Awap Junior Member

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    Been driving my new LE AWD-e for a few days, and I'm a bit lost trying to understand what is going on. I'm wondering if there are any tutorials to explain the various displays, like the shifting bar graph where you have green and yellow bars, broken up into little segments. And also why is it that usually it refuses to stay in EV mode if I go above ~20 mph, whereas once I'm going 40-50 mph sometimes it pops back into EV mode.

    Googling this, I see a lot of old pages on early Prius generations, and scattered comments in priuschat threads, but wondering if there is a nice "guide" somewhere online to understanding how the energy-related displays fit together.
     
  2. FuelMiser

    FuelMiser Senior Member

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    The first thing to realize is the Prius Hatchback is NOT an EV. In other words, don't stress about keeping the EV light lit. It's designed as a hybrid--both ICE and EV in play most of the time. I think you'll be very happy with your MPG if you simply drive the car as normally as possible. Accelerate moderately and anticipate slowing/stopping so you can coast as much as possible with light brake application.
     
  3. alanclarkeau

    alanclarkeau Senior Member

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    It's clearly outlined in the Owner's Manuals.

    Don't worry about whether it's going into or out of EV Mode - EV Mode doesn't mean you're necessarily going to improve economy. It does a fairly good job of that, as long as you don't drive it like a race-car.

    You can "force" it into EV Mode by the way you drive, but sometimes you find that you end up having used the Hybrid Battery charge in a circumstance where, just driving normally, would have been better, leaving ti to its own devices.

    Once you're used to the car, you might try some hypermiling. Tony Schaefer did some articles on it. Bear in mind that they're based on earlier PRIUS, but the philosophy is the same. It's more to do with how you drive than what the instruments are telling you.

    Hypermiling » What Drives Us

    Also, I found it best to ignore this display:
    upload_2019-4-6_10-7-17.png

    The EV light which I circled, is only approximate - it will sometimes be WRONG - so ignore it.

    Instead, I have this display showing where the power is going:
    upload_2019-4-6_10-5-22.png

    used in conjunction with the HUD display.

    This chap did some videos - including this one:
     
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  4. Awap

    Awap Junior Member

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    Thanks...Currently averaging about 46 mpg, mostly city driving (the AWD supposed to do about 50 mpg combined). I think I am getting the hang of gradual stops, but it's often tough to do slow acceleration with somebody behind me.

    I think I am understanding now, there are basically two modes. When energy flow display shows battery providing all the power, the solid green EV icon comes on, and simultaneously the MPG shows as "150". Other times, gas engine is used and MPG drops to maybe 40ish, EV icon goes off.

    It's pretty obvious that gas is used during strong acceleration, but I am not sure about the rest of the time - it seems a bit mysterious sometimes how it decides between gas vs. battery power.
     
  5. Awap

    Awap Junior Member

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    @alanclarkeau, thanks for that info... the hypermiling page is really interesting indeed.

    Surprised to hear the EV light can be "wrong"... I will watch for situations where it doesn't correlate with other displays in the usual way I described just above.

    It's mostly that bar graph that intrigues/puzzles me. For example, at one point I had a bar which contained a black gap in it. Was that a bug or was it telling me something?

    You're right, p. 167 of the manual (digital version at least - easier to scroll through at the moment) covers the bar graph ("Trip information" display). Most of it is clear, but I have no idea what this is saying: "Average fuel consumption for the past 15 minutes is divided by color into past averages and averages attained since the power switch was last turned to ON mode. Use the displayed average fuel consumption as a reference."

    Okay, so I see on that page, the little "E" symbol in the bars is just to indicate 30 Wh. So the E doesn't really tell you anything, it's just to emphasize that one can think of mpg in terms of Wh? Presumably there is a constant ratio between the units "Wh" and "mpg"? Curious how the math would work.
     
  6. alanclarkeau

    alanclarkeau Senior Member

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    "covers the bar graph ("Trip information" display)" yes, I don't really use that, it's not a lot of use that I could ascertain in stop-start traffic. Once on a long trip with a couple of hilly then downhill and easy cruising sections - I could work out what it was doing. But in reality, I rarely look at it. Maybe next long trip?

    As far as acceleration is concerned, yes, it's important not to annoy the cars behind. That said, if it's a PORSCHE behind, I tend to find that they're not impatient - it's the guys in big, barely roadworthy trucks which are aggressive.

    If I'm at the lights, and only one car behind, I take off moderately, to ensure that they guy behind gets through. If there are a dozen cars behind, I'll floor it across the intersection then ease up, to let as many behind the opportunity to get through (only to discover that the car behind doesn't take off because she's looking at her phone!!). Hypermiling is best done when there is little or no traffic around.
     
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  7. The Professor

    The Professor Senior Member

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    After a year of ownership, and keeping quite a close geek-eye on that EV light, I've never once personally found that light to ever be wrong. It's always been on when the ICE is off, and vice versa.

    I've seen a number of references to it being wrong, but only seen one person ever stating they've actually seen it wrong in person, and even then it turned out later on in the thread they were actually referring to the acceleration guage been in the lower half of the display, rather than the green light being on.

    I'm really not convinced this light of wrong. It's consistent with data from the OBDII (e.g. rpm greater than 0, etc).

    I do, however, think it's been misunderstood sometimes (e.g. one person thought it meant EV Mode is on so was puzzled why the EV light came on when not in EV Mode), and/or confused with other guages, and since then everyone has been taking their word for it being "wrong". :D
     
    #7 The Professor, Apr 6, 2019
    Last edited: Apr 6, 2019
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  8. Harters

    Harters Active Member

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    After 2 years of ownership I have come to the exact same conclusion. Quite often I know the engine is running and the EV light is off (correct), but if I switch to the energy flow it will show the engine as being off (incorrect), so in my experience as well I find the energy flow is often incorrect.

    I much prefer the HSI as I think it gives lots of useful information.

    Having come from an Electric car to the Prius, I much prefer the Prius, all the benefits of electric power in low speed and crawling traffic, then all the advantages of an ICE at all other times (y)
     
  9. The Professor

    The Professor Senior Member

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    Ah, but there are some things to take into consideration here. The energy flow diagram can show the engine off, even when it's moving. When the battery gets towards being full, the ICE will be used for engine braking (via adiabatic heating / compression) as the charging system limits or prevents energy being sent to the batteries. So you hear the engine, because it's moving, but it's not producing any energy. In this scenario, the EV light is off, and no arrows are shown next to the ICE on the diagram, and you can hear the ICE. You can force this mode by switching to B mode.

    You can also have the ICE on but all the energy it's producing is used for engine heating. You can simulate this mode by having the car in P (parked), while in Ready mode, and holding the accelerator down. The energy flow will show no energy going anywhere, because the diagram can't show energy being lost as heat. Again, ICE is running, EV is off, but the diagram doesn't show any energy coming out of the ICE, even though it is clearly running. The Prius will go into this mode, running the ICE to maintain its temperature, and the cabin temperature, and doesn't always charge the battery. So the diagram just can't represent this.
     
    #9 The Professor, Apr 6, 2019
    Last edited: Apr 6, 2019
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  10. alanclarkeau

    alanclarkeau Senior Member

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    Another screen you can check is this one. No point having it up all the time, but I sometimes flick across to it at the end of a longer trip:
    upload_2019-4-6_22-31-53.png

    It will usually show a figure between about 20% and 40%, though for short trips it won't be particularly useful.
     
  11. Tideland Prius

    Tideland Prius Moderator of the North
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    Basically the car keeps a record of previous trips in addition to the current trip (previous Prius versions would reset every time the car is turned off).

    There’s a yellow section and a green section. IIRC, green is your previous consumption bar graphs and yellow is current.

    The E tells you how much you’ve regenerated via regenerative braking. Go down a steep hill and you’ll see a lot of Es (until your battery is full).
     
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