Mountain driving

Discussion in 'Clarity' started by clarityplugin, Mar 12, 2018.

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  1. clarityplugin

    clarityplugin New Member


    I just got a new Clarity plugin and have a long road trip coming up. First time with a non-gas car so I'm trying to figure out the best way to drive this in the mountains:

    • When I start from home, should I push HV and save the battery until I get to the mountains? It seems the battery power would be more useful going uphill.
    • When going down, the regen paddle is like engine braking. But what happens if the battery is full, does the regen just not do anything?
    • Since regen paddle setting doesn't revert in only Sport mode, it seems Sport is the best one to use for mountain driving. Maybe even for hilly cities like San Francisco.

    And a more general question about the battery/engine, when the battery goes to zero during a long drive, what is the behavior in normal mode? Does it run gas engine, charge to some minimum battery % (such as 10%), switch to battery, and keep repeating that cycle? Or does it just not charge the battery unless I push HV charging?
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  3. jdonalds

    jdonalds Well-Known Member

    We have two modes of operation.
    1) Around town. where there are hills, we stay in EV mode all the time. The engine never comes (or very rarely) on.

    2) Trips out of town. In this case we follow the general rule that electric is better at low speeds and HV is more efficient at high speeds. So if we go into a town, and care enough to try to control the car (which has a mind of it's own) we will switch to EV mode. But for highway speeds we are in HV mode when the car will try to keep the battery at a fixed level (but will drain down to about 58% first), and will alternate between the battery power or ICE power as needed. It will also switch into ICE direct drive if needed.

    Also rather than using the paddles to slow the car on down hill runs we just set the cruise control which will maintain the set speed and will apply regen as needed. I do believe if the battery is topped out going downhill (long hill) the power from regen will be dumped somehow.
  4. loomis2

    loomis2 Well-Known Member

    Have you ever driven a Prius? It basically runs like that when you run out of battery. It will run the engine and keep the battery at a small percentage of full and switch to battery when the situation calls for it, then back to engine, rinse, repeat. That is a very generic description of what happens, but bottom line is it keeps a small reserve of battery to use when it can in hv mode.
  5. bfd

    bfd Active Member

    At its core, this Clarity variant is a hybrid vehicle. So it'll always go into that mode when the battery depletes far enough. If you are thinking you want to save EV range for around town driving, then you can use the HV mode specifically and early in your trip. It'll hold 30 or so miles of EV range in the battery.

    The system as I understand it is not an either/or, it's both. As operator, you really don't have to do anything to make the system work except get in and drive it. All of the modes and the paddles are patently unnecessary - I think - and can just make driving seem more confusing for a new PHEV owner. It's supposed to work just like any other vehicle, except that it gets its power from the blending of an electric motor and a gasoline engine. I am not sure how the modes and the paddles have really enhanced the experience, but for the most part, I get in, fire it up, and drive off. I don't really think about whether it's in EV or HV - though I do like it when I can stay in EV. I use the sport mode for times I want to get off the line quickly or get into traffic on the freeway from a light. The rest of the time, I think it's just in Eco mode or whatever it is when you first start it up. I've put it into HV mode the mode that will generate more EV miles, but only once or twice in the three months I've had the car.

    If you try to use regen braking or paddles with a 'full' battery, you will likely kick the car into using ICE to bleed off some of the electricity. I've had that happen exactly once so far, but it happened quite regularly on the PHEV I had before.

    Sometimes you will be on the electric motor only, and you can drive so as to keep it in that mode until you run out of battery power. Then the car will revert to its roots as a hybrid, using both gasoline and electricity to power the wheels.
  6. MarkClarity

    MarkClarity Active Member

    As I understand it (I may be wrong a there is a lot of conflicting info out there), there is no transmission, only a single gear links the engine to the drivetrain, so the engine can only directly drive the wheels at highway speeds +/- some amount. At slow speeds I don't believe the engine can directly drive the wheels as the rpm would be too slow. At slow speeds, the engine will likely rev at a reasonably efficient RPM and only generate electricity to drive the wheels. This is likely why there are comments about high revs and unexpectedly loud engine noise at low speed.
    jdonalds likes this.
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  8. aapitten

    aapitten Active Member

    Not to hijack the thread, but @MarkClarity I have literally been trying to find a definite answer to this 'conflicting info' since before I bought my Clarity in mid-December and can't find a concrete answer. Some people say CVT, I've heard planetary gear-set, I think everyone is confused. You would think Honda might make this better known at least at a high-level.
  9. bpratt

    bpratt Active Member

    I don't remember where I found this information, but the explanation said there is a clutch between the engine and the electric motor that will only engage at highway speeds. The other end of the electric motor drives the wheels through a set of gears and is always connected. There is no transmission, CVT or otherwise.
  10. Fidzio

    Fidzio Member

    This video gives a good explanation of the Honda Accord PHEV from which the Honda Clarity PHEV was derived. My understanding is that the mechanical arrangement is the same, although the gear ratios etc may be different.

    Aaron_Menchions likes this.
  11. MarkClarity

    MarkClarity Active Member

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  13. KentuckyKen

    KentuckyKen Well-Known Member

    FWIW, I found it states on Honda’s EV Owners web site that the Clarity has an “electronic continuously variable transmission E-CVT...”
    Here is the link

    And then I found this at

    TRANSMISSION Plug-In Hybrid Plug-In Hybrid Touring
    Fixed, single speed • •
    Ratio 2.454 ~ 0.805 2.454 ~ 0.805
    Final Drive 3.42 3.42

    Here is that link

    So if both these sites are official Honda sites, then even Honda is putting out conflicting info on our Claritys.
    No wonder we’re all left wondering!
  14. Viking79

    Viking79 Well-Known Member

    As Ken and others point out, the clarity has a CVT (referred to as e-CVT). It is nothing like a belt driven CVT, but it is a CVT in that it can continuously vary the gear ratio (the definition of CVT). It uses 2 electric motors (main traction motor and generator motor), a planetary gear set, and a couple clutches. Planetary gears are great as you can have multiple inputs or outputs and they are meant for blending or splitting power.

    For technical details of how the transmission operates see the technical paper in post #7 from ab13:
    KentuckyKen likes this.
  15. KentuckyKen

    KentuckyKen Well-Known Member

    Viking79, I think you hit the nail on the head and the ball out of the park!!

    We have what Honda calls an E-CVT or CVTe (I’ve seen it both ways) that is physically a planetary gear set and I believe is unique to the Clarity model among Hondas (some other mfgs also use this).
    In fact, I’ll send $10 to the first person to prove us wrong.
  16. Fidzio

    Fidzio Member

    So I wish to (politely as I'm in Canada) disagree with your statement about the planetary gear set (and Kentucky Ken, I'll settle for a 10 smileys instead of $10). The Chevy Volt has two planetary gear sets, but the Honda Clarity has none - it only has a single gear train to the wheels, with a clutch which is engaged when the car has reached the speed at which the engine can directly drive the wheels.

    See the "This Honda has No Transmission" video a few posts above this one, which I posted earlier today, and which does a good job explaining how the car works.

    The use of the E-CVT term is misleading - at speeds below the clutch engagement speed, the car is driven by the electric traction motor which is supplied with current from the engine driven generator which is continuously driven by the engine when it is running.
    KentuckyKen likes this.
  17. KentuckyKen

    KentuckyKen Well-Known Member

    Thanks for the Canadian kindness, Fidzio. But I will have to stand with Viking79 on this and politely agree to disagree.
    I have viewed the video you reference but I have to point out that it is not from corporate Honda and is just this person’s opinion (although a very informed opinion), while the references I cited are actually from Honda and specific to the Clarity. So I guess I’m going to claim that my source can beat up your source (in a gentle Canadian kind of way, eh).
    And if you can find an official Honda document to prove me wrong I will insist on sending you 10 Canadian dollars. And if you disassemble your transmission and post pix to remove all doubt, I’ll triple that offer. Haha.
  18. Fidzio

    Fidzio Member

    Dear Kentucky Ken, thanks for your polite rebuttal.

    I'd like to present a short extract from the corporate Honda press kit for the Clarity: ( which states that the Intelligent Multi-Mode Drive (i-MMD) two-motor hybrid system is used in the Clarity.


    "The 2018 Clarity Plug-In Hybrid's utilizes the second generation of Honda's Intelligent Multi-Mode Drive (i-MMD) two-motor hybrid system. This highly efficient powertrain selects the optimal drive operation under a wide range of driving conditions to combine fun-to-drive performance with outstanding efficiency."

    This i-MMD (which I understand was first used in the 2014 Accord hybrid) is further described in the following Car & Driver document:
    which is subtitled: "Making It Simple: There's no transmission—really."

    and in the following corporate Honda video:

    These documents all point to the "no transmission" except for a single gear ratio which is connected through a clutch when the car reaches the appropriate speed.

    Do I get my 10 smileys? :)
    KentuckyKen likes this.
  19. MarkClarity

    MarkClarity Active Member

    Toyota Prius also describes their single gear ratio transaxle with a single planetary gear set as a eCVT. With only one gear ratio the only variable part is from the electronic control of the variable speed electric motor, and/or the RPM of the ICE.
    KentuckyKen likes this.
  20. ab13

    ab13 Active Member

    Here is an article that has a video interview with Honda engineering about the 2 motor hybrid. It has a pretty good cutaway motor model. Based on the view, the 2 electric motors seem as separate entities with what appear to be housings around each one. They appear to only be connected in rotation when the ICE is clutched in. The design is really a full EV attached to a ICE/generator for serial hybrid mode, but they added mechanical clutch mode since they found it provides some additional efficiency.
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  21. MarkClarity

    MarkClarity Active Member

    Good video finally have an explanation for the eCVT term.

    A normal CVT keeps a constant efficient ICE RPM and has a variable drive ratio to the wheels. A eCVT has a constant ICE RPM generating power connected via wire to a variable speed electric motor driving the wheels. So a CVT is a physical device and a eCVT is an abstract design concept.
    Last edited: Mar 14, 2018
    KentuckyKen likes this.
  22. KentuckyKen

    KentuckyKen Well-Known Member

    Dear Fizdio, I can’t think of a nicer guy (or gal?) to disagree with. I think if everyone had a Canadian mindset, we’d all get along much better.
    However, I’m not quite ready to send you your 10 dollars or 10 smileys just yet.

    I politely submit the following for your consideration:
    1. Although your first reference is from an official Honda source and is specific to the Clarity and does state we have the i-MMD, it also states “Unlike most competing hybrid and plug-in hybrid vehicles, the Clarity does not use a conventional transmission, which saves weight and minimizes complexity while improving efficiency.”. I submit that this may be a different statement from saying it doesn’t have any transmission at all. Also the i-MMD system is the motive or energy producing part of the drive train and I don’t think it includes any downstream components for directing the motive force to the wheels. So proving we have the i-MMD may or may not prove anything about presence or absence of any kind of transmission. Unless of course if the I-MMD itself includes all forms of transmission, then my arguments moot.

    2. Honda specifically states the Clarity has an eCVT in the link I provided. That seems pretty clear to me and a little hard to just completely ignore.

    3. I respect and trust Car and Driver very much, but I must point out that the article you cited is from 2013 and is about the Accord not the present day Clarity. I can find no Information from Honda that we have the same i-MMD as was being discussed in 2013 about an Accord.

    So I can’t quite yet agree with you on the no transmission concept, but I am willing to admit we don’t really know with 100% certainty. And I’ll go out on a limb here and claim I’ve got a slightly better argument and “evidence” but it is in no way iron clad and I am willing to be convinced otherwise.
    You definitely deserve much more than 10 smileys from me for attitude and effort, but I’m holding off on the smileys and dollars for winning the argument until I hear your re-re-rebuttal (or whatever we’re up to now!).
    And if I lose, it couldn’t be to a nicer guy or gal, and no matter what’s under the hood we all come out winners on this wonderful hybrid. Also, it’s kinda fun trying to unravel all the mechanical and software puzzles in our Claritys.
    Last edited: Mar 14, 2018
  23. cowgomoo

    cowgomoo New Member

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