Using EV Charge Mode

Discussion in 'Clarity' started by WindsorBoy, Jun 16, 2018.

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  1. WindsorBoy

    WindsorBoy New Member

    This time of year I do two trips a month between my home in Markham, Ontario to my cottage up near North Bay. The trip is about 290 km (180 miles) one way. I typically leave with a full charge, let the battery range drop down to zero at which point the ICE kicks in. Pretty much immediately I select HV Charge mode. Over the next 40-60 minutes of highway driving I end up back to about 60% charge at which point I switch back to EV mode and drive on battery until its back to zero km, then back to EV Charge mode again, repeating this until I arrive at my destination. I do a full change at 120v when I arrive so that I can do trips into town on battery and so that I have a full charge on the battery when I leave to go home. Returning home I pretty much repeat the process on my return trip. On these trips I've been averaging between 2 and 3 liters per 100 km (80 to 120 mpg).

    I am curious if others have tried this technique on long trips and what your experiences have been like.

    FYI, I typically drive these long trips using the ACC (cruise control) set for maybe 5 to 10 km/h above the speed limit.
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  3. jdonalds

    jdonalds Well-Known Member

    I tried it on a long trip and found it was not worth the effort. However it depends on the miles traveled and if you can end on electricity. On some distances that method can be beneficial.

    We are in the car now on vacation. I just ran charge mode only because I like to have battery power available when we exit the freeway. I don't really care if it's efficient or not.

    We just passed 1,000 miles traveled on this trip, getting about 46 mpg while driving 70-75 mph 95% of the time.
    dstrauss and WindsorBoy like this.
  4. jorgie393

    jorgie393 Well-Known Member

    Hm. I think in your effort to be helpful you are depriving the Clarity of some of its efficiency tricks. I also think your brain can be better put to use doing something the Clarity can't do: seeing the future. I'll explain. There are those who understand the drive train better than I do, but here is my understanding. You may already know all this, so my apologies, but perhaps it will help someone.

    1) First of all--forget what I say, why not try different things and find out which works best? As long as you compare trips without big differences in traffic, climate control use, and final battery status, you can try different strategies and see which leaves you with the most gas!

    2) Until then, here is why I think you are potentially either breaking even or even hurting efficiency with your approach: (see also

    All internal combustion engines have a most efficient RPM. On a long trip, where you are going to have to use the ICE, you want to run that ICE at its most efficient RPM....or have it off. The way the Clarity makes this happen while cruising is (and this requires being in regular HV mode, so it's allowed to run the ICE or the battery, or both): It runs the ICE at maximally efficient RPM....which usually generates more electricity* than is needed to drive the wheels directly. The remainder goes into the battery. Then, once battery charges up a bit, the ICE turns off, the car draws from the battery. In a bit, when the battery is drained some, the ICE turns back on in maximally efficient RPM. This cycle repeats, with the ICE always running at high efficiency The exact ratio of engine on to engine off (duty factor) depends on your speed, and there are other tweaks....but this is the idea. This is trick 1. How about your approach? When you turn of HV mode, and force the car into EV mode, you aren't letting it choose when to turn the engine on and off. Then when you put it into HV charge mode, engine has to run double, or at least continuously, in order to both drive the car and recharge the battery. This *might* be OK. At best, you might just be forcing a very long engine on/engine off cycle (vs. the short engine on/off cycles that the car does on its own in regular HV mode). But if all you are doing is what the car would do in HV mode, except longer cycles, then why not let the car do it (by leaving it in HV mode)? No advantage to doing it manually.

    The other trick you MIGHT be losing out on: at the proper vehicle speed, the engine (still at or near its most efficient RPM) can grab mechanically onto the drive shaft, and drive the wheels directly through the mechanical clutch. This is particularly desirable, since it cuts out the generator "middleman". (The generator, since it's not 100% efficient itself, is a step with energy loss between the engine and the wheels). (The clutch is engaged when there is a little circle icon in the power flow diagram). Figuring out how to engage the clutch or not to maximize this sweet spot is beyond the driver's control, or ability; good to let the car decide how to do this, which it can do in HV mode. Again, it might be able to do it during your long HV Charge cycle, but why not let the car decide? At best you will do as well as the car would, at worst you will lose some efficiency.

    What about HV Charge mode then? I think it is designed to be used *in anticipation* of very heavy engine loads, such as crossing mountains. In those cases you'll need more power, very often, then the engine can provide, and for a long time. You build up the battery in anticipation of this (hence why it is called "mountain mode" for other cars, though I think it should be called "a steep uphills coming up" mode, where if you don't sock away some battery energy during the brief flat stretches you are going to be running a battery deficit).

    So what is the role of the driver? As I said the one thing the car can't do is see the future...but you can. *Only you* know if this current trip is going to exceed the range of the battery; or when you are getting close to your destination.

    My belief re. where your brain is most useful, and the best overall strategy:

    1) Run car in EV mode in the city at start of your trip, and during stop-and-go traffic. If the trip is going to be short (within battery range) jsut keep it that way.
    2) When you are on a trip that you know will exceed battery range, put it in HV mode *once you are cruising on the highway*.
    [2a: If mountains are coming up, and battery is low or you are going to be drawing on it for a while, put it in HV Charge mode to get the battery charged up and ready, including during any breaks in the uphills].
    3) When you are getting close to your destination, turn HV mode off and drive on battery mode, such that you arrive with a near-empty battery.

    Again, this is what I've gathered from the forum and from theory. This approach should require the least intellectual effort from you, but give the most gasoline efficiency. I'm sure others will correct my errors here.

    *Simplifying the generator steps here.
    ClarityDoc, insightman and lordsutch like this.
  5. WindsorBoy

    WindsorBoy New Member

    Perhaps. In April I did a trip between my home and Windsor, ON which is about 390 km each way. On that drive I used HV mode for most of the trip. If memory serves I believe I averaged about 5.2 liters/100 km, or 45 mpg, which similar to what my 2010 Prius would do on a similar trip around that time of year.
  6. insightman

    insightman Well-Known Member Subscriber

    Are you a Honda engineer? I believe your strategy makes perfect sense. If you are a Honda engineer, you're in for a lot of questions!

    The best part about using HV mode and (hopefully) having the clutch engaged is that you achieve the normalcy of the engine speed being tied to the road speed, which makes for a much more pleasant sound than that of the engine in HV Charge mode. The second-best part is that you don't have to think about a driving strategy--just drive the car. (Well, you have to remember to re-select HV mode after you take a break.)
    Johnhaydev likes this.
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  8. jdonalds

    jdonalds Well-Known Member

    Yea that part about remembering to re-select HV after shutting the car off is irritating. I wish Honda would simply retain the mode used when the car was shut down and reapply it the next time it is started. On our trip this week we forgot once to set HV and the "normal" mode drained the battery. Darn.

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