When is switching to HV most efficient?

Discussion in 'Prime Main Forum (2017-Current)' started by lochnersm, Oct 28, 2020.

  1. lochnersm

    lochnersm Junior Member

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    My daily commute is just outside the the EV range. Would it be more efficient for me to switch to HV on a stretch I'm doing 50 rather than just run out EV and let it switch when I'm doing more start and stops?

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  2. Bob Comer

    Bob Comer Active Member

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    My commute is a lot farther than my range, so I run in HV when it's the coldest part of the day, which is also at the fastest speed. (67MPH) That seems to get the highest mileage overall.
     
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  3. jerrymildred

    jerrymildred Senior Member

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    Probably. But just make sure you use up the EV range before you get home to charge (or to work to charge if you can charge there). Otherwise, you'd be burning gas you wouldn't need to burn. Then again, with gas prices being so crazy low in much of the country, there might not be a very large difference in cost per mile between HV and EV.
     
  4. Salamander_King

    Salamander_King Senior Member

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    Which efficiency are you trying to improve? Are you looking for more EV range or better mpg under the HV mode? If you just want overall efficiency improved, you can just drive and let the car take care of the switch. I have driven my 2017 PP for my commuting of ~40 miles. It was just a few miles longer than my EV range in summer, but almost 20 miles short in winter. I have driven my car with EV until it automatically switches to HV when the EV range runs out. This gave me better HV mode mpg, but the EV range is always limited and EV efficiency could not be increased much above 5-6miles/kWh. I changed my driving style and switched to HV mode in the middle of the commute to increase EV range and efficiency. Specifically, use HV mode on uphills and quick acceleration, but trying to keep the engine warm-up cycle to minimum. With this method, I improved EV efficiency well above 8miles/kWh, but the mpg is down. For me, electricity is more expensive than gas, so better EV efficiency with less mpg gives me better overall cost/mile.
     
    #4 Salamander_King, Oct 28, 2020
    Last edited: Oct 28, 2020
  5. lochnersm

    lochnersm Junior Member

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    @Bob Comer - I hadn't thought about temp, so it may make more sense to do it on my ride in, except I won't know how close I can make it until after work.

    @jerrymildred - yeah, I'm trying to limit the gas as much as possible.

    That is a good point. I wasn't clear. I am going for overall efficiency. Electric and gas are pretty darn close to equal using the stated EV range as my comparison. I assume when the ICE is the primary driver (no EV light) that it would be most efficient at about the 50 mph mark. So I guess I'm trying to maximize efficiency of ICE while I'm using it and assuming I'm going to use up my whole charge. But I guess turning off EV at 50 could also reduce my avg mi/kWh also. So it may be 6 of one, half dozen the other example.

    Starting to think I'm thinking too hard about this and should just drive and let the car do its thing..

    Posted via the PriusChat mobile app.
     
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  6. Bob Comer

    Bob Comer Active Member

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    Temp can make a HUGE difference, though I really wouldn't try to micromanage it. I may have been able to get higher overall mpg by micromnagement, but it really is more pain than it's worth when you figure out how much gas difference there is between 100MPG and 120MPG -- it's not very much!
     
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  7. Tideland Prius

    Tideland Prius Moderator of the North
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    Are you able to charge at work?

    If not, then I'd use HV for the highway portion and use EV for the rest so that you can maximise EV use at lower speeds in both directions.

    While using up the EV range in one direction seems reasonable, warming up the engine at the end of your commute seems a bit wasteful (Even if you do end up getting a bit of charge into the battery while its doing so) because you'd have to warm up the engine again on the way home.
     
  8. Raytheeagle

    Raytheeagle Senior Member

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    I use HV for the hills I encounter and EV for the remaining sections, regardless of speed;).

    I have a 38 mile one way commute and I average 34 miles of EV each way utilizing the HV for hills approach:).

    Free charging at work helps with economics as well(y).
     
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  9. lochnersm

    lochnersm Junior Member

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    Unfortunately, no, can't charge at work right now. Hmm... that is another thing to consider. Is it better to warm the engine up just once a day? It will probably change once we get into winter, but right now, one cycle on one stretch of road, both ways, would be enough to allow me to use ev the rest of my entire commute. Am I correct that the EV would be less efficient, everything else being equal, cruising at 50 than a slower speed? And the ICE would be more efficient cruising at 50 rather than going from a stop or cruising at a slower speed?

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  10. lochnersm

    lochnersm Junior Member

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    Posted via the PriusChat mobile app.

    Mine is 18.5 each way. Right now I can get 34-35. 36 if I push the hypermiling. Hit 37 once.
     
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  11. vvillovv

    vvillovv Senior Member

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    lochnersm in response to your OP and asked again post #7, in my opinion the answer is yes, EV can be more efficient at slower mph than at faster mph. ie if you can find a flat stretch of road with few stops. no traffic. for 50 miles and drive it at creep home speed the car will deliver nearly the max EV range. The numbers look something like this 8.9 Kw traction pack takes 6.6 +/- kw to charge and delivers approximately 5.5 kw where the wheels meet the road. So take 5.5 kw * 10 M/kw = 55 miles EV
    I doubt anyone has ever achieved 55 mile true EV only range, I know I haven't, but in theory it is possible.
    So again in my mind, generally going slower in EV will get you more available EV miles and generally be more efficient than driving in EV at higher speed, for sake of argument such as EV at 84 mph which is the Primes EV only cut off mark. Run the numbers at both very low speed and very high speed and it should become more clear, minus all the other variables at play during a regular drive to work or town.
     
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  12. Bob Comer

    Bob Comer Active Member

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    There's something else to remember, the ICE is more efficient at slower speeds as well...
     
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  13. Tideland Prius

    Tideland Prius Moderator of the North
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    Possibly. I mean you'll have to test it on your route several times to see how long you need to keep the engine on to balance emissions, fuel consumption and EV range.

    Cruising? Maybe. I would imagine the acceleration up to 50mph is the bigger culprit (and why using the engine, after its warm-up cycle might be better). Once the engine has warmed up and you've accelerated to 50mph, you can just leave it in HV until you leave the highway and let the car manage power between battery and engine (it should be mostly engine since the Prime's MG2 can do highway speeds in EV).
     
  14. vvillovv

    vvillovv Senior Member

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    It might be an interesting assignment for someone interested in getting the engines real world efficiency curve
    and listing all the variables encountered while getting the results.

    I haven't looked closely, but I'm thinking the engine at - very low - speeds is not it's most efficient area.

    It's much easier to tell ( do in part to it's limited availability in Prii ) in EV how much of a difference such things as wind resistance at higher speeds, strong head winds, cold weather, rain or water on the road, etc effect range and / or efficiency.

    Just wondering, if the power split was opposite ( bigger motor and pack with a small engine that also powers the wheels ) if it would be easier to measure the engine efficiency than it would be to measure the motor efficiency as a driver in real world scenarios
     
    #14 vvillovv, Oct 30, 2020
    Last edited: Oct 30, 2020
  15. lochnersm

    lochnersm Junior Member

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    Is it better for the ICE, if I know I'm going to use it later on the drive, to let it warm up from a stop first? I've been just letting it kick on once my EV runs out regardless of where I'm at on my drive.

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  16. Bob Comer

    Bob Comer Active Member

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    It depends on what you mean by very slow speeds, but I can for sure say that I get better mileage when going 30 than when going 50, and by a decent margin. The real time MPG is just as much a hint as to efficiency as to what you're using to figure out your EV efficiency. Maybe a tad slower, but it's there. I think we're both on the same page about maximising EV to maximise total efficiency, but it's not always easy to find the best way. Trial and error is how I did it.

    My commute: Start, putting it in HV mode immeditaly, then about 15 miles at ~67MPH (at the coldest time of day too), a town, then 22 miles rural highway at 62. No charging at work. Leave work in EV mode and run it until it's out, which happens to be in the same 15 miles streatch as morning at 67 MPH. I've gotten up to 114MPG on that run, but average in the low 90s, depending on speed anywhere in my commute. The slower the better, the faster the worst unfailingly.
     
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  17. Tideland Prius

    Tideland Prius Moderator of the North
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    If you're going to use it in a "higher" stress situation like merging onto a highway or accelerate up a steep hill, I would warm it up ahead of time when you're in a lower stress situation like driving at a constant speed or over flatter terrain.
     
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