EV vs HV mode

Discussion in 'Clarity' started by peterkronenberg, May 16, 2018.

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  1. peterkronenberg

    peterkronenberg New Member

    I know there has been much discussion on this, but I still have lots of questions. What exactly does HV mode do? What is the difference between
    1) Driving in EV mode until the battery runs out and it automatically switches to the ICE
    2) Driving in HV mode

    Other than the regenerative breaking and paddles, does HV mode charge the battery?

    And what is the point to HV Charge mode? Why use gasoline to charge the Electric motor instead of just using gasoline to power the car? If my battery runs out, why does it makes sense to charge it with HV charge mode (assume this is a long trip and I won't have the opportunity to charge up). Why not keep driving with the gas-powered engine?

    P.S. I usually leave it in Econ mode, so just to keep things simple, let's leave that as constant for now. Similarly, I have no use for Sport mode
    AndyBA likes this.
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  3. ab13

    ab13 Active Member

    HV mode will use the ICE to charge the battery and/or drive the wheels. The vehicle doesn't have "full" power if the battery ev range is empty so HV charge mode can quickly add charge faster than HV mode. Basically if you are going to drive uphill you'd want the battery somewhat charged.
    Steve H Truong likes this.
  4. jdonalds

    jdonalds Well-Known Member

    Driving in EV mode is 100% electric. Best for around town, not highway speeds where the electric mode is less efficient.
    Most on this forum recommend using EV until you get on the freeway, then switching to HV.

    HV is Hybrid Vehicle mode where the car alternates between pure EV and running the gas engine as needed. It will not drain the battery, rather it maintains the current level of the battery when you switch to HV mode. One exception is a fully charged battery will slowly drop to 58% as that is the maximum the car is designed to charge the battery.

    So if HV mode sometimes puts the car in EV mode then isn't EV mode efficient at high speeds? Well yes if there is little load on the car. For example if you're going down a hill, even a very slight drop in elevation, then it doesn't take much energy to keep the car going so it will switch to EV mode. Then if the battery level drops slightly the engine will start back up and charge that little bit to bring the battery back to the original level. This is exactly how a Prius Hybrid operates below a certain speed.

    HV mode has two states. First it is running to drive a generator to make power so the electric motor can drive the wheels, and so the battery can be recharged to keep it steady. Second at certain higher speeds, and not under a heavy load like going up a hill, the gas engine will connect directly to the wheels and provide power to propel the car.

    Last but not least is the HV Charge mode which you can manually activate by pushing the HV mode button a second time. That will charge the battery until it reaches 58% full. You are right that it isn't likely efficient to charge the battery using the gas engine. I do it sometimes on a trip because I do like to maintain at least 5 bars of charge on the battery so I have a little reserve.

    Unfortunately HV mode doesn't stick if you turn the car off like EV mode does so you have to put it back in HV mode after you restart the car. Unfortunate because if you're not in EV mode and also not in HV mode you're in "normal" mode which will drain the battery. I really wish HV mode would persist.

    All of this sounds like a lot to be concerned about but it really is simple. EV around town. HV on the highway.

    Also if you simply drive the car it will take care of itself. Yes it will run until the battery is depleted, then start the engine in HV mode. However there seems to be building evidence that when that happens the battery will show two bars only and it won't have sufficient power to play the EV <--> HV game well. So the car may run the gas engine a bit faster so it can do it's best to supply power to the electric motor, and to add some charge to the battery. When it is running extra fast it makes a sound we have come to call "angry bees". So if you want to avoid that sound you'll want to keep an extra bit of charge on the battery.

    Our son's school is 12 miles from home. The drive to school involves some city and some highway driving. It's about 50-50. But the 24 mile round trip, plus a few stops at the gym and some stores, falls well within the electric range of the Clarity. So we stay in EV mode 100% of the time around town even though we drive some highway miles. Only when we take trips out of town do we play with the HV button.
    markc, Steve H Truong and atr like this.
  5. M.M.

    M.M. Active Member

    I would say more accurately if you're going to be driving more than 45 miles then EV around town and HV on the highway. Save battery for when you get to another patch of lower speed or stop-and-go driving.

    If you're driving less than 45 miles, I don't get why you'd use HV mode--just leave it in EV. What's the point, after all, of having a plug-in hybrid with a nearly 50 mile range if you're just going to run it on gas every time you're on the highway and get home with battery to spare?

    Also, it's not a disaster if you just let the car run down the battery and automatically switch to HV when it's empty. You'll just make more efficient use of your gasoline fuel if you know you're going to be on a longer trip and save the battery for when you're driving around town. Personally I just leave it in EV mode and don't think about it unless I'm felling like micro-managing a road trip for efficiency.

    I'm pretty sure you turn on HV Charge mode by holding down the HV button for a second or two, not pressing twice.

    HV Charge mode is basically useful if you know you're going to be driving over a mountain range (the equivalent mode on the Chevy Volt is actually called "Mountain Mode"). Because it tries to keep a bit more than 50% charge in the battery, you'll have a hefty reserve of battery to make sure the car can climb long steep hills that the gas engine alone can't handle well, and it will use flat patches or downhills to charge back up for the next climb.

    My short version:

    Driving less than 45 miles before you're going to charge? Leave it in EV.
    Driving more than 45 miles and want to be most efficient? Use EV in town, HV on the highway, but try to switch to EV so that you run out of battery right around when you'll be getting to a charger.
    Climbing a mountain? Switch to HV Charge a few minutes before the climb starts, turn it off when you get near the top.
    Feeling lazy? Just leave it in EV and let the car take care of it.
    Steve H Truong and atr like this.
  6. jdonalds

    jdonalds Well-Known Member

    I checked the manual and you are correct. Hold the HV button down to enter Charge mode.
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  8. peterkronenberg

    peterkronenberg New Member

    Thanks for the responses. So it sounds like in HV mode, it is mostly using the gas-powered engine and just saves electric for certain situations. Is that correct? And then it just charge the battery. So is the gas-engine more efficient on long trips? Also, the Honda tech told me that the gas-engine is not directly attached to the wheels. It only acts as a generator for the electric battery. So not sure I understand jdonald's response that the gas engine connects directly the wheels to provide more power.

    Also, I notice that when I run out of electric charge, it doesn't automatically indicate that it's in HV mode. In fact, I can still put it in and take it out of HV mode by pressing the button, even though there is no electric charge at all. Is this really making a difference in this case?
  9. M.M.

    M.M. Active Member


    Not exactly, depending on what you mean by efficient. The battery-electric drivetrain is always more efficient, in the technical sense, than the gasoline one. So on a relatively short (<45 mile) trip, it really doesn't matter how fast you're going, the electric drivetrain is always going to be more efficient than gas.

    What the recommendations here are getting at is that the electric drivetrain is more efficient at slower speeds than it is at faster speeds and in stop-and-go traffic. The gas engine (ICE--Internal Combustion Engine) is more efficient at constant highway speeds than it is at slower speeds, thanks to the mechanical transmission linkage. So if you don't have enough battery energy to get you from point A to point B, and some of that time is going to be spent at highway speeds, you might as well use the ICE then when you get more miles from it than at slower speeds, and save the battery energy for the times when you're driving slower when you will get more miles out of it than you will on the highway.

    This information was wrong. At speeds above about 50mph, if you are in HV mode, there is a mechanical CVT transmission that can link the ICE directly to the wheels to increase efficiency. This is explained in the manual, and is indicated on the instrument cluster power-flow display by a little circle appearing at the point the energy line coming out of the ICE connects with the line going to the wheels and the battery.

    This is basically what makes the ICE do better at highway speeds--because it is connected directly to the wheels at that point, and is geared to run most efficiently at those speeds, you get more miles per gallon than you do when it is using its generator to generate electricity, which either goes to the motor connected to the wheels or the battery for later use.

    No, it's basically not doing anything.

    I'm guessing the only difference there would be that if you went down a really long downhill and the regeneration generated a few miles worth of EV range, in EV mode the car would use that energy before starting up the ICE again. If you had it in HV mode, I'm guessing it would keep using the ICE once the road flattened out and hold onto that extra charge, at least until you went up a hill or something.
  10. THIS! Very well said. I'm copying this for future use.
  11. Viking79

    Viking79 Well-Known Member

    Great answers already covering when to use those modes and how they work. Short answers:
    HV Mode = Hold current battery charge as possible without charging
    HV Charge Mode = Charge then Hold at 58%
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  13. Timothy

    Timothy Active Member

    peterkronenberg, I am repeating this because it might be easy to assume that a Honda tech is right and a poster on a forum is wrong (and I apparently can't stop myself from beating a dead horse). M.M. (and jdonald) is correct above 45mph the ICE can directly drive the wheels. Though this is at a fixed ratio and there is no CTV.

    These videos (which have been posted often on this forum) are very useful if you want to know more details. The Clarity basically has the Accord Hybrid tech with a bigger battery.

    Last edited: May 17, 2018
    Steve H Truong likes this.
  14. JimW

    JimW Active Member

    It is somewhat amusing how we all have slightly different understanding of how our Clarities work.

    For the new poster, a few key points:

    -When driving on highway or hilly roads with zero battery (2 bars), the Clarity is not a pleasant driving experience. The small gas engine revs high and the car does not perform as you would expect from driving "normal" luxury sedans. This is why most of us recommend switching to HV mode on long trips rather than waiting for the battery to run down and have the car make that decision. In HV mode with ~50% battery, it is pleasant and quiet on the highway with good performance.

    -For in-town daily driving, even with Interstate driving, if less than 40-50 miles per day, leave in EV econ mode. No need for HV mode.

    -While on a trip, put on the energy flow display and watch it as you go up and down hills and change speeds. This is the best way to learn how the system really works. Watch for the tiny gear icon in the center of the energy flow - this shows when the ICE gets clutched to the drive train, only at highways speeds and it is constantly engaging and disengaging. Going down a long grade, the ICE will turn off. Going down a steep mountain, you will actually build charge in the battery from regen braking (using paddles to control speed). As someone else mentioned, the Clarity does not have a CVT, the ICE is clutched to a non-variable gearbox. Honda uses the marketing term "E-CVT" to explain the series hybrid concept.
    atr likes this.
  15. M.M.

    M.M. Active Member

    Well I've learned something today. Thanks!
  16. LAF

    LAF Active Member

    don't knock the sport mode - it makes the care drive much more responsively around town even when you don't need much acceleration. If you set the regen paddles to 4 they will stay there in sport mode and this combination I have found is just as efficient as eco mode. I have been getting 65 miles using sport mode now that the temp is ~70.
  17. Rajiv Vaidyanathan

    Rajiv Vaidyanathan Active Member

    You can see this in the second post of this thread where I tracked mileage using HV mode on the highway:

  18. KentuckyKen

    KentuckyKen Well-Known Member

    OK, I have the definitive, perfect, and indisputable answer of all time for peterkronenberg.
    And here it is...

    Just take jdonalds’, M.M’s, viking79’s, and JimW’s posts, stir them together and you have what should have been written in the owner’s manual!

    Well played sirs, well played!
    CyberDyneSystems likes this.
  19. peterkronenberg

    peterkronenberg New Member

    Hmm, that's interesting about the re-gen paddles. So you get the quicker response of Sport Mode, but you get more regeneration. I wonder why the paddles stay enabled in Sport mode?
  20. peterkronenberg

    peterkronenberg New Member

    Absolutely! This forum is a great (only!) source of information for the Clarity
  21. jdonalds

    jdonalds Well-Known Member

    Just a note: I use cruise/ACC around town often. It kills regen in Sport mode.
    Rajiv Vaidyanathan likes this.
  22. dstrauss

    dstrauss Well-Known Member

    Just for grins: we live in Midland, TX, 20 miles from Odessa (kind of like Minneapolis-St. Paul for you northerners). Had to make a quick run for a package pickup (about 30 miles round trip), so for the first time I left it in EV at 75 mph - that was a sweet and quiet ride - and had 17 miles to spare when I got back home! It does eat through the battery quickly (compared to my usual commute accuracy it was gobbling about 1.4 miles EV range for each mile driven), but it was a VERY INTERESTING taste of what it must be like to BEV all the time.

    Still prefer my PHEV because my long range trips are more long range, but it was a hoot.
    atr and jdonalds like this.
  23. Maggie

    Maggie New Member


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