Can using CHG Mode be more efficient?

Discussion in 'Prime Technical Discussion' started by Salamander_King, Oct 8, 2021.

  1. Salamander_King

    Salamander_King Senior Member

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    In different thread @KYBlue reported a case in which use of CHG mode and then EV mode from the SoC gained on his trip made the overall efficiency measured by MPG better than just driving the same route on HV mode without using CHG mode.

    See his comment in this thread:
    Question about battery charging while on the go | Page 2 | PriusChat

    I was very intrigued by his finding and wanted to confirm his observation. Unfortunately, I do not do often enough repeated longer distance drives right now, so that my chance to do the testing was very limited. Testing on a shorter trips less than 30 miles is likely to cause the comparison difficult due to more pronounced variations in numbers. I just made a 65 miles/one way drive yesterday and had a chance to make initial comparison.

    This is what I did. On my way to the destination, entire 65 miles was driven on HV mode. The EV range was already depleted at start, so that gave me a chance to test driving this distance all on HV mode. The route I took was rural highway with one lane on each side with top speed limit of 55mph. Very light traffic but had a few in town sections with slower speed limit and traffic lights. Overall, rolling hills up and down with slight elevation hike of ~400' to the destination. The entire distance was driven uninterrupted at average speed of 45mph with EV ratio of 65%. This trip resulted in average efficiency of 65.5mpg all from the dash.

    Then, on my way home, I started my trip with CHG mode until it stopped at 80% EV SoC. This took 29 miles at average speed of ~45mph and displayed efficiency was 37.5mpg. Then using the 80% SoC, I switched to EV mode and drove next 28miles all on EV until it depleted the EV range. I needed to finish the return trip on HV mode for the last 8 miles. This return trip was also uninterrupted at average speed of 45mph, but EV ratio displayed was 49% and the average efficiency shown on the dash was 72.3mpg.

    The summary of the result is shown in the table below:
    upload_2021-10-8_11-53-23.png

    Now, it is comparing the same distance, but not in the same direction, so it can not be taken as a direct comparison, especially because there is a slight decline in elevation on the return compared to the incline that had to be driven on HV mode on the way to the destination. It was very calm day so head and tail wind are not likely the contributing factors. But I think there is a situation in which the use of CHG mode and using the SoC acquired by the CHG mode to drive on EV mode later on the same trip may increase the overall efficiency.

    I would love to try the same drive again with using CHG/EV mode on the way to the destination, and use HV mode on the return for the same trip, but I don't have plan for another visit to the destination again anytime soon. I have to wait for next repeated longer trips for more controlled experiment.
     
    #1 Salamander_King, Oct 8, 2021
    Last edited: Oct 8, 2021
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  2. dig4dirt

    dig4dirt MoonGlow

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    One thing I had to check up on was CHG mode and regen.

    I have only used CHG mode while on highway, and turned it off before exiting.

    I had to check @john1701a yt channel to see the CHG mode in action and which was the case
    while letting off gas pedal and coasting. And I do see that the engine behaves like a standard Prius
    and the engine stops and regen happens like normal with and w/o brake.

    So I am assuming with more moderate driving patterns, the mpg can increase verses hwy driving etc.

    Your EV %'s can show this tune also.

    Hope this thread is healthy and I also can contribute.....hmm now where can I go for a few 50mi+ trips for fun?....:whistle:
     
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  3. Salamander_King

    Salamander_King Senior Member

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    Yeah, I have not tried using CHG mode in any of my usual ~35miles round trip commuting drives. I do think longer distance but not overly long trips are needed to distinguish the real difference from daily variation. The ideal distance seems to 60-80 miles trip. Either round trips, or do one way experiment on both legs of the trips twice. But it maybe not. I may have to try a few drives with CHG mode and without to see if it makes noticeable differences for the same ~35 miles trips I routinely make.

    My main question is to answer this:

    My initial thought was that it would be impossible to use CHG mode to make the car run more efficiently than just using the HV mode, but now I think I was wrong.
     
    #3 Salamander_King, Oct 8, 2021
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  4. sam spade 2

    sam spade 2 Senior Member

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    This mode, that mode, another mode........
    All of that not withstanding, it is NEVER more efficient to run the gas engine to charge a battery and THEN use the battery to propel the car.
    NEVER.
     
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  5. vvillovv

    vvillovv Senior Member

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    I'm not surprised that Charge Mode can be just as efficient or more so than HV mode. I've just never had that experience myself. Now that I've read about it twice here, I'll have to keep it in mind if I ever get better at switching modes during a trip.
    I think of Charge Mode as a special feature! Yes it typically costs me MPGs, about 10 or 15 of um. It also charges to 80% of full EV range twice as fast as a Level 2 plug in varying pulses instead of a steady controlled slower charge from the plug Although, Very handy for those times when you want it.
     
    #5 vvillovv, Oct 8, 2021
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  6. dig4dirt

    dig4dirt MoonGlow

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    I think we need to not get caught up in the standard hybrid Prius thought of efficiency.

    I think Toyota may have made the Prime much more efficient than we first think.

    Imagine....hmmm...well we are not there yet.

    the MPGe is on the table now.
    The CHG charge rate is on the table now.

    In that thread, I was leaning on the OP with belief. Still am.
    I cannot work out the math with this 999mpg on EV tho.
    ~40mpg on CHG mode+PLUS+999mpg or 133MPGe of EV gained at the same time.
    equals what?
    Math kinda works out to be more than 55-65mpg on straight HV mode?
     
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  7. bisco

    bisco cookie crumbler

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    can't a reasonable control test be done?
     
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  8. vvillovv

    vvillovv Senior Member

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    depends on your definition of "reasonable" :)
     
  9. bisco

    bisco cookie crumbler

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    i would be comfortable with driving the same 100 mile route using charge mode and not
     
  10. Rmay635703

    Rmay635703 Senior Member

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    You would need to have a depleted battery at the end regardless of mode selected to get a reasonable comparison, temp and wind variables might skew one way or another
     
  11. bisco

    bisco cookie crumbler

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    agreed, but if you look at the weather, you can probably find a couple hours with similar forecasts.

    if the difference is so small that slight variations effect the outcome, i think the point is proven
     
  12. Salamander_King

    Salamander_King Senior Member

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    From my initial observation, CHG mode on a steady 45mph drive took 29miles of driving to gain 0-80% SoC for 28miles of EV drive. If you want to test the full EV range gained by CHG mode, then you need at least 60 miles trip.

    But I am thinking that I don't have to gain 80% SoC to test the efficiency comparison. If the SoC gain is completely linear, then 40% SoC gain would need ~15miles of steady 45mph drive to gain ~14 miles of EV drive. That's only a 29miles trip. So, in theory, I can test and compare my routine ~35 miles commute (round trips) with and without using CHG mode. I may try that. But on my routine commute, I will not get an average of 45mph speed. It is more like 30mph since I don't drive a long stretch of non-stop rural highway. It is, after all, only 18 miles one way.
     
    #12 Salamander_King, Oct 8, 2021
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  13. dig4dirt

    dig4dirt MoonGlow

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    The thing I can say for that test, is that different speeds should create different results.
    Im sure there would be a cutoff for too fast or too slow or both when no longer more efficient.

    The shorter trip can still produce results, probably sufficient enough...but longer would be better.

    Being that my round trip to work is 6 miles, I dont think that is enough. lol
    Have to think of a route or same place I can go twice or more times.
     
  14. Salamander_King

    Salamander_King Senior Member

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    I agree 100%. For reference, @KYBlue stated that he was gaining 1mile EV for every 2miles he drove on CHG mode at 74mph on CC. This is vastly different from what I observed on my trip. I was gaining roughly 1mile of EV for every 1 mile of CHG mode drive at steady but not CC controlled average 45mph highway driving. I am sure this number will change if I use the CHG mode in 30mph commuting with some stop and go.

    That is exactly my problem. I am not doing much driving now except routine commuting 1-2 times a week and occasional longer out-of-town trips and my wife using PP for around-town errands. It is hard to make more than two longer trips under very similar conditions. Now going into the colder season, the weather factor can be drastically different from one day to the next.
     
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  15. vvillovv

    vvillovv Senior Member

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    I believe History data also plays a part in results from different Primes, and not a small one either.

    There are a lot of 75 to 85 mph daily drivers that report extremely high efficiency at those speeds. Much higher than I see when occasionally driving long distances at those speeds. Except maybe the first long trip I took Down south at 72 mpg in HV mode for 800 miles with 4500 miles showing on the OD.
     
    #15 vvillovv, Oct 9, 2021
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  16. sam spade 2

    sam spade 2 Senior Member

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    999 is "code" for "can't compute".
    It is not a real number.
     
  17. vvillovv

    vvillovv Senior Member

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    Should probably ignore the optimistic. as there are quite a few.
    It's way easier to visualize 199.9 than it is 999.9 and 99.9 miles per kWh while switching modes.
    Easier to crunch numbers in the boonies at night too.
    Floating Point
    The visual display shows numbers that can be used effectively to estimate how the car is performing form trip to trip, etc.
    Not sure why so many want to trick or / and treat them as written in stone per calculated algebraic equatuibs that cover all the variables of a Ready mode / Off driving session.
     
    #17 vvillovv, Oct 9, 2021
    Last edited: Oct 9, 2021
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  18. Gokhan

    Gokhan Senior Member

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    This is not a controlled experiment. What you need to do is:
    1. It needs to be round-trip.
    2. The SOC levels should be the same before and after the trip. If not, you must subtract SOC drop x 33/100 miles from the driven miles. If the SOC drop is more than about 5%, no meaningful comparison can be made even with the subtraction.
    3. You must turn on the charging mode again to bring the SOC to where it was when experimenting with it. You must do it both in the to and from legs.
    4. You must drive with the same speed in all trials.
    5. Other things I am forgetting.
    That said, I doubt it can be more efficient.
     
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  19. Salamander_King

    Salamander_King Senior Member

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    As I commented, one trial I did was not in the same direction so it can not be directly compared. But other than #1 on your list # 2-4 were all satisfied. If I make frequent enough trips of the same route of ~65miles, I can easily satisfy #1, but unfortunately, I don't make trips of that distance often enough. Also as I commented, the initial observation made by @KYBlue in another thread was on the round trips.

    I plan to do the shorter trips (~35miles) with or without CHG mode to see if that is sufficiently long enough to show a significant difference. I will post the results when I do.
     
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  20. Gokhan

    Gokhan Senior Member

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    6. You and @KYBlue should never let the SOC fall below 10% when experimenting with this because than the Prius Prime becomes a vanilla Prius, which is less efficient in optimizing the HV driving due to the smaller battery size. If you let the SOC level drop below 10%, you are losing efficiency, and by turning on the charge mode, you are cheating by increasing the SOC/effective battery size and efficiency again in that trial.​
     
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