SOLVED- Unexpected ICE Turns On

Discussion in 'Clarity' started by AnthonyW, Sep 25, 2018.

  1. PHEV Newbie

    PHEV Newbie Well-Known Member

    They just have zero regen so braking is 100% friction braking. Honda wanted to give us consistent brake feel under all conditions (like with a full battery) for safety sake so they designed this rather complex system. All other EVs, hybrids, and PHEVs simply give you friction braking when the battery is full. Hence the many chorus of complaints on how bad the brakes feel when reviewed by car magazines. The Hondas have gotten rave reviews for how natural and consistent the brakes feel.
    insightman likes this.
  2. bobcubsfan

    bobcubsfan Active Member

    Not true. The Nissan Leaf we had certainly did have regen. On many trips, the car visibly went into regen and going downhill really added on the miles. Reg worked immediately even with a full charge.
    Last edited: Feb 14, 2019
  3. Ray B

    Ray B Active Member

    I thought the OP kind of captured the essence of the situation with ICE coming on during braking in some situations. Not sure if this paper ( was referenced in the discussions yet, but I thought that it also explained the concept and the rationale behind it well enough.

    "The SPORT HYBRID i-MMD system consists of various components, and each component is subject to constraints in order to secure reliability. For example, these constraints include a motor torque limit, generator torque limit, and battery power limit. In particular regarding the battery power limit, accurate control is demanded from the viewpoint of securing Li-ion battery durability, and this limit is known to greatly influence the driving performance of a system using a series hybrid. Therefore cooperative control between each component to support various environmental and operating conditions is described below using the battery power limit as an example.
    The power management control obtains the acceleration and deceleration intent of the driver (accelerator and brake pedal operations) and the power and torque limit information from each component, and performs the appropriate cooperative power control within the limit range. Under conditions where battery power is limited, such as in low temperature environments, and the acceleration and deceleration intent cannot be satisfied by battery power alone, power management control selects Hybrid drive mode and accurately balances the motor, generator and engine outputs to both satisfy the battery power limit and achieve sufficient driving performance.
    Power management control first calculates the target vehicle driving force from the acceleration and deceleration intent of the driver and the motor torque limit requirement. Next, it calculates the target engine power that matches the sum target of the motor power calculated from the target vehicle driving force and the target battery power calculated from the energy management control. The target engine power is corrected as necessary by the battery power regulator. After that the target engine speed and the target engine torque are calculated from the corrected target engine power. Hence the target engine speed and torque values select the point at which the engine efficiency is maximized. Finally, the engine power, generator power, and motor power are corrected in consideration of various constraints including the battery power limit. This control system configuration balances the acceleration and deceleration intent of the driver, the battery SOC convergence properties, the battery power limit performance, and the constraints of other components."

    Sorry for the text wall, but I thought it was all relevant. YMMV
  4. bobcubsfan

    bobcubsfan Active Member

    Still, the Clarity mucks up having the ICE come on when not necessary. The full battery issue is bunk. If that were true, it would happen all the time, but it doesn't. And the post above stating that EV cars don't have regen is definitely not true. The purpose of regen in EV cars is to help with braking and to charge the battery. This happens even if the battery is fully charged.
  5. Robert_Alabama

    Robert_Alabama Well-Known Member

    I somewhat concur with @bobcubsfan's sentiment. I find myself thinking Honda could have added another kWh or two to the battery (surely they could have crammed some in somewhere) that you couldn't charge with EVSE to be better able to withstand more regen when fully charged without starting the ICE. This running of the ICE because the fully charged battery can't stand the regen is a little hard for me to accept as a logical design. I know they were struggling with weight of the car, but hey, probably less than 50 lbs of additional lithium battery would fix this problem.
  6. KentuckyKen

    KentuckyKen Well-Known Member

    I don’t agree that the “full battery issue” is bunk since that’s the only time my ICE comes on (coupled with hard braking or calling for 4 chevron regen). And I’ve gone over 6 months and 5,000 miles without losing a bar on the gas gauge. And I don’t begrudge the Clarity for the very occasional short ICE run because it is keeping the ICE healthy and ready to run when needed.
    I’m sorry yours misbehaves so much.
    Cash Traylor and insightman like this.
  7. MNSteve

    MNSteve Well-Known Member

    There exists this amazing electronic component named The Resistor that, seems to me, could solve this problem. If the battery is charged, the energy from regen cannot be captured, and must go somewhere. Starting the engine seems like an amazingly complex solution to that problem when you could just dump the power into this component whose entire mission in life is to convert electrical power to heat. Yes, it would be necessary to dissipate the heat but that doesn't seem a huge challenge.
  8. Ok, hang on - those that read my other posts know I can get lonnggg wind---edd.

    There is a lot already said here, first and foremost is that a Parallel PHEV is not an EV, and cannot be compared to one, completely different power trains, energy management and well, if you want the behavior of an EV, buy an EV. If you want the synergy of a Series PHEV, then buy that (BMW with Range Extender) as that is not what the Clarity is. It's a parallel electric/ICE-Generator drive train, and actually a really good one. You can even buy turbine powered hybrids (series and parallel, so the heck with an ICE) just google Capstone Microturbine cars. A full EV has no ICE to turn, so when the battery is full, no regen occurs, and the "braking" is, well - using BRAKES, it has no parallel transmission architecture to deal with, just a CVT (or none if it's a golf cart).

    Simply disabling the ICE would completely change the behavior of the car and the driver experience. I absolutely guarantee that if the regen system could have been made more fuel efficient given other design concerns, Honda would have done it as in this market - gains are small and eMPG is a big marketing concern.

    Completely disabling the ICE may be something that a few people would want to do, but auto manufacturers don't build for a few, they want to sell a lot.... so they make what ALL hardware manufacturers do (software lends itself to more customization) they make compromises based on market research. Heck, that's why I got a crappy sound system in the factory touring class Clarity (but I bet others here think the stereo is just fine, just like I am not bothered by the regen/ICE design). Hey, I'm even getting rid of those annoying low rolling friction tires for some better handling ones, don't care about the electric range penalty, have a gas engine generator if it goes dead. Honda likely believed there would be more people interested in every joule of electric motive efficiency so saved a few pounds in speaker weight and wanted the margin in COGs/BOM (I mean, that has to be it, right :confused::mad::( ?). Fortunately I could easily fix the stereo issue, and knew that when I bought the car. Changing the powertrain design and programming is likely more difficult. I think the biggest problem with the Clarity is the lack of technical information. You can youtube a full teardown to loose "bolts" of the Chevy Volt or even a Tesla (Rich Rebuilds), but digging for info on this vehicle is still difficult for a number of reasons (it's new is one).

    However, if you want to spend some money you can read all the technical info publicly available regarding the e-transmission and power train here:

    Let us know what you find out. Considering that the goal of Honda was to make a PHEV that was user indistinguishable from any other high end Honda sedan in driver experience with the exception of far less use of fuel and a reasonable choice in motive energy (for short, non highway commutes) of electricity over fuel, I think they did a good job. If you bought the Clarity PHEV wanting to never use the ICE or have it turn on, you bought the wrong car - get the Clarity Electric, a Bolt, a Tesla, etc.... However, I am not convinced that you bought the wrong car knowingly - Honda did a poor job of defining the Clarity variations from a marketing standpoint and I think they blurred the lines a bit in consumer expectations. The info is there, but as MUCH evidenced in this particular forum/thread - you really have to dig to find it.

    To put this issue to rest we need only one simple data point > drag ICE fuel burn (as that is the only concern really presented here). So, charged car, top of mountain, moderate temperatures, fuel flow meter (or electric sensor attached to all fuel injectors to read the impulse), and EGT probe (or a good ODB probe). The trick is that when the ice is triggered Honda chose to go ahead and warm up/test the motor. What you need to know is after that, does the regen energy burning and turning the ICE, actually consume gas. If not, then the ICE "warm up" fuel is inconsequential for normal drives as it happens only once and at idle for a short time. So, we warm up the engine, don't turn the car off, and then start down hill regen braking to our heart's content.... then read data. Who is up for that? I admit I am not...

    I very often turn on HV mode to trigger the ICE and let it warm up while cruising the route from work on the surface roads. This lets it warm up gently (like a regular car) before I reach the toll road to head home... and well, let's just say I use all available acceleration energy available in the Clarity and prefer to not high rev a cold engine. 100mph electric limit my azz!

  9. I know this is going to sound rude, but really, you think the Honda engineers didn't know about resistors... there are probably about half a million passives in the electronics in the Clarity and resistors likely make up over a third of them.

    Well, basically due to this amazing principle of energy conversion/conservation to heat and the dissipation of that in physics... ever touched your brake rotor after just a very short deceleration from say 60 mph, once :oops::eek:?!?

    Since stopping a 4000 pound vehicle is an AMAZING amount of energy to dissipate (why regen was a good idea in the first place - lots of energy there to recover when possible), let's just make it easy in that you have a 100 hp motor accelerating you for 10 seconds, then stop at that same accel/g rate... Let's just say it's about (~750 watts/hp) 75,000 watt seconds times ten for argument sake. The best designed resistor on the planet for that would require a HUGE heatsink or it would turn into a plasma torch... Something I do not want in or around my car that also has a gas tank... Basically you need resistors with thermal masses the size of vented brake rotors and placed in the airflow... so you then cause wind resistance and add weight. Or, you could just use something already there - like the existing friction brake rotors, and the ICE-Generator, that came with the PHEV. I like reusing things that already have to be there as it is cost effective and efficient....

  10. The Gadgeteer

    The Gadgeteer Active Member

    This was surely said already... pure EVs generally use regen braking but if max battery charge is reached or braking needs exceed what regen will provide they introduce friction braking as needed.

    The exceeding the max battery charge of a pure EV which has a much larger battery than a PHEV is probably less likely but there are other reasons the battery may not take all of the regen available that I will not go into. The point is an EV and a PHEV will logically make use of regen if it can but if it cannot some of that energy needs to be dissipated somehow.

    Being a long mountain downhill and smaller PHEV battery could lead to dangerously overheated ineffective brakes, leveraging engine braking in a heavy vehicle (in trucking called a Jake Brake) is not only genius but probably required. The engine may “run” but is either not burning any fuel or not any appreciable amount of fuel. The engine is being used as a big air pump to waste the kinetic energy.
    Last edited: Feb 20, 2019
  11. The Gadgeteer

    The Gadgeteer Active Member

    To learn more on why an engine can “run” without consuming fuel when coasting or going downhill read this article...

    The key part
    “Almost all vehicles show a pulse width of zero when coasting while in gear. Zero, as in there is no fuel injected at all. Yes, the engine is turning over, the pistons are going up and down, the water pump, alternator and a/c compressor are working, so technically you can say the engine is running, sort of. But it's not consuming any fuel. And that goes for automatic or manuals”

    This is all largely because modern engines make use of a fuel cut off and electronic controls to save gas. Our PHEVs do it even better and do more of course.
    Last edited: Feb 20, 2019
    PHEV Newbie likes this.
  12. Robert_Alabama

    Robert_Alabama Well-Known Member

    After the past few posts, I feel a little like I'm being told what I don't like is no issue and all is well. I maintain that the burning of fuel to manage deceleration (maybe that is Honda making the engine burn fuel to warm up after it spins at all, but it still burns fuel, something like 0.1 gallon for my car for each occurrence) when the battery is near fully charged is not my desired design. I'd rather dissipate the energy in the rotors or have had Honda add an extra kWh or two of battery (even if I paid for it) to manage that charging energy. For my car, it is not "top of mountain" behavior, it is if I use the regen paddles more than a click or two after charging (and that is after no downgrade). I'm finding that even trying really hard to manage regen at the beginning of my commute, it is hard to keep the ICE from running. Is this incremental gas burn a big deal? No, but it's aggravating to me. I also own a Chevy Volt. I don't know how the Volt handles this, but I can go down a mountain with a full charge and no ICE, or complaints of any kind. Maybe Chevy kept more available buffer at the top of the battery so this was not an issue with charging current, or they just didn't care if it stressed the battery. If the latter, it seems the lackadaisical attitude was ok, as the batteries in the Volts have held up pretty well. Quite possibly my car is more sensitive than most for this. It does seem to have increased in frequency, or maybe I've just started to notice it more.
  13. PHEV Newbie

    PHEV Newbie Well-Known Member

    Bob, sorry I wasn't clear. I was responding to the discussion of what happens to BEVs with 100% full batteries (as shown in the quote in my comment). I'm surprised to hear that the Leaf will go to regen when the battery is full. That would be pretty damaging to the battery if there's a long downhill after fully charging. I'm under the impression that BEVs (and most PHEVs) default to friction braking when the battery is 100%. I guess that's not true in all cases.
  14. PHEV Newbie

    PHEV Newbie Well-Known Member

    Thanks for the link. Now it all makes sense. The article explains that most modern ICE cars shut off fuel to the engine when coasting even though everything else is firing (electricals, etc). That would explain why folks in this forum say the engine is actually running because they can monitor the plugs firing. If it is normal behavior for regular ICE cars to shut off gasoline, it's a simple matter for the Clarity to use one of its electric motors to turn the ICE (like it would when it starts it, there is no conventional starter motor) to expend the energy from regen without using any gasoline.

    If you don't like this behavior and you live on the top of a hill, why not just charge to 90% or so? You'll recapture the energy going downhill and the ICE won't come on at all. Also, not charging to 100% will increase the life of the battery. Win-win.
  15. Robert_Alabama

    Robert_Alabama Well-Known Member

    I want to say I give up, but I'll give it one more try. The engine in the Clarity burns gas when it does this, maybe that's due to Honda's stubbornness that it is going to warm the engine whenever it starts, but it burns somewhere just shy of 0.1 gallon each occurrence from what I can tell. Second, this happens at least every other day for me even if I am trying to be careful with regen and no downhill (not living on top of hill situation). Yes you can try to watch the Hondalink app and stop charging at 80-90% to stop this, but that's a pain as well. I just want to be on the record that I think the design is dumb when Honda had other options (either a little more battery or use the friction brakes). It reminds me of the line in Jurassic Park saying the problem is that they figured out that they could run the ICE for this purpose before they thought about whether they should. Maybe every one else loves this behavior, but i kind of despise it. I do love pretty much everything else about the car, so it more than balances out...
  16. bobcubsfan

    bobcubsfan Active Member

    Hi, Robert in Alabama. I have been one of the more vocal critics on this issue. That and the insistence that oil be changed even though the ICE has only been used for about 700 miles out of the 8000 miles on the car. The ICE came on yesterday for no apparent reason, and stayed on for about 3 miles, burning gas AND depleting the battery at the same time. I said in a previous post, that I am counting the months until I can get rid of this car.
    Last edited: Feb 20, 2019
  17. Robert_Alabama

    Robert_Alabama Well-Known Member

    @bobcubsfan, it sounds like your car has a mind of it's own as to when/how it runs the engine. I do feel for you in living with that. Mine is limited to this behavior, and it really hasn't contributed that much gas burn. I've burned about 25 gallons in 4500 miles, most of it on highway trips where battery was insufficient for the trip. This designed fuel burn just seems like a bad idea to me. Again, I really love the car, but that doesn't mean I embrace this.
  18. KentuckyKen

    KentuckyKen Well-Known Member

    @Robert_Alabama, I’ve managed to stop the ICE from running after a full charge by NOT using the paddles and only using the pedal to brake. Then if I don’t have to brake hard, the ICE is not coming on for me. Don’t know if it would work on a long steep downgrade, but it works in town for me. Try it and see if it works for you.
    David Towle and Robert_Alabama like this.
  19. Robert_Alabama

    Robert_Alabama Well-Known Member

    Will try. I have gotten myself addicted to use of the paddles, so it will take conscious effort on my part. If it works for me, once I get myself retrained, that would be a great solution.
  20. MNSteve

    MNSteve Well-Known Member

    Yes, it does.

    Somehow, over the past decades, car manufacturers have figured out a way to dissipate heat from brakes. Dumping extra energy into an engine is not the only way. It is the way that the Honda engineers picked. I was suggesting, tongue in cheek, an alternative.

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