how to drive the car

Discussion in 'Clarity' started by victor_2019, Jul 29, 2019.

  1. neal adkins

    neal adkins Active Member

    There's climbing a hill and then there's climbing a mountain. In many driving situations i agree that it is fine to go down to zero ev range. I sometimes climb a mountain thats a 6% grade for more than 14 miles. And you can definitely tell the difference when i have no ev range left. Not always angry bees but ice revving high by design.
    Also reguarding hv charge mode: maby some of the techies can wiegh in. If my mpg drops 40ish to 28ish in hv mode, for say 26 miles on the freeway (60 mph for 26 min), but i gain about 25 miles hv range, my gross mpge would now be 28(hv charge mode) + the 25ev range i gained = 53. Not bad for a 4k pound car. In situations where i cant stop and charge that actually makes sense to use hv charge. Also since my charging at home is not free, usually about .10cents per kwh. Theres not much lost in terms of cost. Great dialogue. I appreciate everyone's perspective.
     
  2. 2002

    2002 Well-Known Member

    Those almost seem like magical numbers, assuming you have seen this I assume the mpg values are what is displayed by the system, as is the 25 estimated EV range that is gained. Now if all of those numbers can be confirmed as being even close to accurate then we should all be driving in charge mode all the time.

    28 mpg (charge mode) for 26 miles = 0.93 gallons used, then you drive another 25 earned EV miles (new acronym EEVM) for a total of 53 miles on that 0.93 gallons of gas. Whereas regular HV mode at say 42 mpg would use 1.26 gallons to go the same 53 miles. If that's true then that means we are much, much smarter than the computer. But I suspect that the displayed values just aren't accurate enough to help us figure it out.

    Measuring true mpg requires measuring actual gasoline used during a specific distance where SOC is the same beginning and end. Nearly impossible to start and end with exact SOC so that's one problem. Also accurately measuring gas used for practical purposes means filling up at the beginning of the test, running the test, then filling up again. So the test run has to begin and end at a gas station. And you are never sure how exactly the fuel cutoff is topping off your tank. And then for the EV range the actual end of the test is driving out the EV miles to see exactly how many miles you really earned.

    With some effort and multiple tests in as close to identical driving conditions, then the real values would be known. I would expect charge mode to be less efficient than just running straight HV the whole way but I can't prove that other than running those tests.

    Circling back to one of your points though, if charge mode turns out to be only slightly less efficient, then the extra cost is minor and may very well be worth it just for the peace of mind and better enjoyment of the car by spreading out the revs more, i.e. some of the high revs in hill climb would instead be experienced during charge mode, but charge mode is only slightly noisier than regular HV and hill climb would still be noisy but less agitating. So spreading out the noise over more miles with a slight but acceptable loss in efficiency.
     
    Last edited: Aug 6, 2019
  3. neal adkins

    neal adkins Active Member

    Great analysis. I have a long stretch of freeway i drive and i didnt write down actual hv range gained. I do now recall i turned hv charge on about 29 miles from my exit. So my numbers were a little off. But i do remember that i was close to 50 percent soc when i got home. I hope to do another test soon.
     
  4. MrFixit

    MrFixit Active Member

    Let's say you guys are right about no difference in performance (either audible or drivability) with a commanded HV (higher SOC) vs a defaulted HV (2 bars)...
    Isn't there still a reason to 'preserve' some battery in the sense that a typical drive will entail some stop-and-go driving until you reach the freeway, then some freeway, then some more stop-and-go from the freeway exit until your destination? For best efficiency, you wouldn't want to run the battery down to 2 bars while on the freeway because then your post-freeway stop-and-go cannot be done in EV mode. The presumption is that EV is best for 'local' driving, and not so good on the freeway (particularly at high speeds).
     
    David Towle likes this.
  5. 2002

    2002 Well-Known Member

    Yes and that's the reason I usually switch to HV on the freeway, because I hardly notice it, and then the post-freeway driving is more pleasant. AFAIK in the situation that I am talking about the overall efficiency is the same, it's just a decision when you want to use your EV miles. So for me it's just about aesthetics, nothing to do with efficiency which I don't think it affects. Some have in the past said it's also more effient to do it that way but I'm not sure what they are basing that on. Yes going 70 mph on the freeway burns EV range, but it burns more gas also. Surface streets in HV mode the car is pretty efficient also.
     
  6. MrFixit

    MrFixit Active Member

    Thus my simple modus operandi :
    • If you can make it back home (or to the next charging station) on your EV miles, then just stay in EV the whole time (even if there is some freeway).
    • If your trip is longer than the EV range, use up 1/2 of the battery, then switch to HV. Remain in HV until you reach a point where your remaining ~1/2 battery can get you home (or to the next charging station), then switch back to EV for the balance of the trip.
    The 1/2 battery is just an easily recognized condition to serve as a reminder to switch modes.
    The goal is to always empty the battery as you roll into the next charging station, giving you maximum use of electricity (assuming your electric is cheaper per mile than gas). It also tends to leave you with some EV when you are driving "locally".
     
    2002 likes this.
  7. craze1cars

    craze1cars Well-Known Member

    Yup. That's another theory that has been mentioned here many times. That the car is most efficient in EV around town, and HV on freeway. So everyone does it that way. I admit I do the same frequently.

    But who has actually tested it? Who (as a random hypothetical example) has measured actual gallons used per repeatable/systematic 80 mile commute that is 59 miles freeway and 21 miles in town? And who has done it first while doing what most people think is most efficient, and again by just leaving the car do all the decision making and run the battery to the ground and letting the engine do the work after the battery is depleted?

    I have no recollection of anyone actually testing it and reporting "this is how many gallons and/or KWH per month I save by driving this way, vs that way". Maybe I missed it.

    There is NOTHING repeatable about how I drive, so I have no opportunity to test such a thing with any true consistency, or I might. I suspect people are saving much less $$ to propel themselves than they realize by making this very common driving decision. And just MAYBE it is not saving a single penny and maybe it is even wasting some energy. Only a true test can prove or disprove.

    Who will do it?
     
  8. Ray B

    Ray B Active Member Subscriber

    Hopefully this image gets attached. It is from the previous iMMD Accord PHEV which shows the effect of more battery charge on fuel efficiency as a function of speed. Obviously, it has no impact at high speed, but under 40 mph or so it becomes helpful, so city driving is best to use EV if available.

    20190806_172630.jpg
     
  9. craze1cars

    craze1cars Well-Known Member

    Cool chart. Thanks. No numbers on either axis, so it offers no specifics of amount of savings. But regardless I’m still not sure it provides any answer for the net result of my hypothetical 80 mile mixed commute. Certainly saving some charge for around town makes engine run less, or not at all, and therefore saves fuel. That’s what I see in the chart and this is obvious. Shutting engine off more frequently and for longer times saves fuel. Battery reserve allows this.

    But does the amount of fuel saved doing it that way fully offset the amount of fuel that otherwise would have been saved had the engine had some extended “off time” while the car was previously driven on the interstate instead? Then allowed to run on/off in hybrid mode around town on a dead battery?

    That’s the question I’m not convinced has been proven answered, while most of us have made our assumptions on the answer for no other reason than the battery depletes faster on the interstate.

    Maybe it is true and it seems to make sense. But I still don’t see where anyone has tested and proven it. Results sometimes surprise.
     
    2002 likes this.
  10. ClarityBill

    ClarityBill Active Member

    It looks like that drive system uses up to 7 KW of battery for hybrid mode. My data indicates the Clarity only uses 8% of the battery, or less than 1.5 KW.

    This chart shows our system would be more efficient if the algorithm allowed it to use more of the battery.

    I do not think the Clarity uses more battery, even if there is more charge available. (EV range would vary by over 10 miles if it used 7 KW in HV mode.)
     
    Last edited: Aug 7, 2019
  11. MrFixit

    MrFixit Active Member

    @Ray B
    I don't understand this chart...
    • First of all, it expresses 'battery charge' as kW. Is that really supposed to be kWh (let's assume it is)?
    • Second, I think it may suffer from the deceptive definition of fuel economy where MPG gets falsely inflated by electric use. Is this saying that at low speeds, and with a large battery 'charge', the system uses the battery a lot and therefore uses the ICE much less? To me, that is not a greater MPG, but rather, a different use case where you are essentially operating in EV mode. This does use less gas, but I don't consider it to be more MPG... The fuel is electricity.
    • What is "Intermittent Hybrid Mode"? Hybrid mode, by definition, alternates between EV and running the ICE. It is intermittent by it's very nature. What else is happening that comprises "Intermittent Hybrid" operation vs. "Hybrid Mode"?
    • The graph has some quantitative elements (the Battery 'charge' with the wrong units), but nothing else shows any quantitative values. It is too cartoonish to explain much.
    What was the source of this graph? Perhaps some additional context from the article would help explain this a little better?
     
  12. 2002

    2002 Well-Known Member

    In any hybrid (setting aside EV mode for now) using electricity always means using gas. You can use gas to directly power the wheels, either via direct drive or by sending generated electricity directly to the drive motor. Or you can store gas generated electricity to be used for powering the wheels later. And lastly you can convert some of the kinetic energy that was produced by gasoline back into electricity via regenerative braking, for later use powering the wheels. Either way, the energy driving the wheels always comes from gasoline. This concept of course is very obvious in a regular hybrid, but can become a little more blurred in a PHEV.

    Looking at another example, you come across people who think regen is efficient and that is why city driving gets better mpg than highway driving. Of course we know that regen actually wastes energy, it just wastes less of it than friction brakes. Compared to a regular ICE car yes it's great and is one reason hybrids are more efficient, but it doesn't mean you can increase efficiency by purposely using regen to generate electricity.

    I think we can fall into the same trap with using gas to generate electricity and storing it, thinking that at times it can be inherently more efficient than powering the car directly . The story being that a gas engine is more efficient at a particular power band, so when you don't need that much power, run the engine at that power band anyway and store the excess to be used later, and this will be more efficient than simply driving the wheels. But that is not the case, if it was we would be using charge mode all the time.

    What makes a hybrid efficient is that for steady speed driving it can use a lightweight, relatively low power, highly efficient Atkinson cycle engine. Just using this type of engine by itself I think would make the car very efficient at steady speeds. But for accelerating it is probably not as efficient as a larger engine, not to mention it will annoy the driver. So we have a hybrid system that allows the gas engine to store electricity for use during acceleration. And that includes not only major acceleration like starting from a stop sign or signal light, but also all of the minor accelerations that occur the entire time we are driving. I think that's all it is. For most driving you don't really need to store all that much. At least that's how I understand it. Oversimplified I'm quite sure but that's how I understand the basic concept.

    There is another reason you don't want to "fill" the battery with gas generated electricity, for a regular hybrid that's to leave room for regen. No good to burn gas to fill up the battery, then miss opportunities for regen. In a similar thinking if you have a PHEV you want to leave room for grid charging since that was the point of getting a PHEV. Again you don't want to burn gas to fill up the battery, then miss an opportunity to fill up with grid power. Okay I know you probably won't actually fill up the battery, but lets say you have 55% charge when you arrive home. In that case you can put 45% SOC of grid power into the battery. But what if the system had generated a bunch of extra electricity leaving your battery at 70% charge. So now when you fill up you can only put 30% grid power into the battery. The question is, was it better for that 15% of SOC to be generated by the gas engine instead of grid power? Probably not. So the system doesn't generate more electricity than it thinks it will need. It's not an exact science since it doesn't know if you will run into hills etc. but it does the best that it can.
     
    Last edited: Aug 7, 2019
    KentuckyKen likes this.
  13. Ray B

    Ray B Active Member Subscriber

    The technical papers Honda publishes on their R&D site are somewhat technical but mostly a marketing tool. As such, the quality of some of the charts and descriptions lack a lot of detail and can be deliberately tough to interpret. My guess is that this particular chart was subcontracted to a very junior staff member (e.g. a summer intern out of high school) as the graph shows only limited sophistication. So I can see how mistakes like kW instead of kWh may have slipped in.

    Anyway, I make no strong defense of it. It seemed like a useful snippet of info in spite of the units. But if you take issue with it, so be it.

    It came from here: https://www.hondarandd.jp/point.php?pid=965&lang=en
     
  14. MNSteve

    MNSteve Well-Known Member Subscriber

    Just speaking for myself here, but at least for me you are missing the point of why I find a benefit to using HV on the highway.

    I do not do it to prevent "angry bees" or maintaining power, as I have never experienced any of those symptoms. I don't do it because it's more efficient.

    I do it simply because I am selfish and I find driving in EV mode more pleasant when I am not on the highway. When I'm on the highway, I perceive no difference between HV and EV; I cannot hear the engine running. But when I am in town, I can. It's not objectionable; there's plenty of power; it's just that I enjoy the completely quiet operation of EV. So since it makes no difference to me when on the highway, but it does make a difference when I'm in town, I like to save the EV miles for in-town driving.

    If I mess up - like I forget to hit the HV button and use my EV miles on the highway - not a big deal. But I am driving an electric car, and when I can tell the difference, I want it to act like an electric car.
     
    Last edited: Aug 7, 2019
  15. MrFixit

    MrFixit Active Member

    Absolutely...

    My comments about meaningless MPG relate specifically to the PHEV because there are two energy inputs - gas, and grid electricity. If you just measure your gas input and divide by miles traveled, you will get an MPG number (of sorts). This number is rendered meaningless unless you also consider the amount of grid energy that was used during this interval. If you want to know your gas mileage, then you have to subtract out any miles from the calculation that the grid provided for you.

    You might say that you can calculate your MPG accurately only if the SOC is the same at the end of the interval as it was at the beginning. This is much better than ignoring the SOC, but not totally correct because the SOC does go up and down by some percentage during hybrid operation with energy produced by the generator from gas directly, or via regeneration. If the SOC is the same as you started with, then your MPG number will be pretty good since hybrid SOC only goes up and down by a small amount. The exception is the occasional owner who has a continuous loss of SOC when operating in HV.

    If you use the nominal 47 mile EV range with a full charge as an example - If someone starts out with a full charge, drives 94 miles and uses 1 gallon of gas, he did NOT get 94 MPG. He really got 47 miles from the grid, and 47 miles from his 1 gallon of gas, and hence his actual MPG is 47.
     
    MNSteve likes this.
  16. 2002

    2002 Well-Known Member

    Agree with all of that, including that to truly measure mpg the SOC must be the same beginning and end. Not easy to do since as you mention SOC is always varying a bit in normal usage.

    Although my last post was not quite on that topic but about whether Clarity would be more efficient if it took advantage of the larger battery to store up more gas generated electricity. If that was true a regular hybrid would benefit from even larger battery sizes, but they keep the batteries small because the extra cost and weight of a larger battery isn't worth it to store additional electricity. Now in the case of PHEV you already have the larger battery so in that sense the extra storage space is "free", well at least already paid for. And yet Clarity doesn't use that extra space to store additional electricity, it stays within the same charge range as basically a regular hybrid. Prius Prime is the same way. Not sure about other PHEV's. I think this is because generating extra electricity to be stored would not be any more efficient and it also would use storage space that was intended for grid power.
     
  17. MrFixit

    MrFixit Active Member

    Maybe another way to think about this is that you would just be allowing the hybrid mode to deviate by a greater amount +/- from it's nominal SOC. It seems to me that the amount of deviation allowed can only benefit you if you experience road conditions that would produce that amount of deviation (ie: you can establish a maximum deviation based on the 'longest hill' that you might encounter). Having a greater range of SOC beyond the 'longest hill' is non-productive because it would never be used. I suspect that you rapidly reach the point of diminishing returns because the average driver does not encounter tremendous hills and valleys regularly.
     
    2002 likes this.
  18. MNSteve

    MNSteve Well-Known Member Subscriber

    I expect that there was a team of engineers who were given this problem to solve. Seems that the question is whether to use a bit more gas to generate extra electricity if the engine is running slower than its most efficient speed. This decision has marketing ramifications since it affects what you can claim as miles per gallon in your sales literature. It may well be that the "right" answer in terms of overall efficiency was to run the engine at its sweet spot, but that decision was overruled due to the marketing aspects.
     
  19. MrFixit

    MrFixit Active Member

    Yes !! This may result in running the ICE in Angry Bee mode 100% of the time !! Certainly not a crowd-pleaser.
     
  20. 2002

    2002 Well-Known Member

    That's possible I suppose that they tuned the system for the EPA tests, at the sake of long term efficiency. If so then of course the EPA tests need to be modified/updated.

    However I still think/suspect that it's a myth that it's more efficient to run the engine at higher power than you need in order to run at the sweet spot, then use that extra power to generate electricity (with losses) then use that electricity to charge a battery (with losses) then later pull that power out of the battery (with losses) to drive the car. Seems like an assignment for the old Myth Busters team to determine if the myth is confirmed or busted.
     

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