SOLVED- Unexpected ICE Turns On

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

  1. insightman

    insightman Well-Known Member

    Do you mean with brake-pedal only? I can't tell when the exclusively regen braking stops and the calipers kick in. I've not experienced the "notch" that some people report when they suspect regen braking cuts out, leaving only the mechanical brakes to slow the car below about 15 mph.

    It would not be good for the car to rely solely on the brakes when coming down a long grade because the brakes might overheat, not to mention the excess wear. I believe the Clarity uses the traction motor to generate electricity to provide supplemental regen braking whenever it's time to slow the car down.

    When the battery is fully charged the system needs to dispose of any regen electricity coming from the traction motor, no matter whether the regen is activated by the minus paddle or the brake pedal. I wish we could find a patent that describes the Clarity's behavior when the battery is fully charged vs the Accord Hybrid/Insight when their batteries are fully charged.
  2. mhillier

    mhillier New Member

    I live at the top of a hill, fairly steep road for three-quarters of a mile to the bottom of the hill. The only time I've had the ICE turn on after a full charge is when using the regen paddles going down (happened right away). When I use the brakes, at least so far in five months of ownership, no unexpected ICE.
  3. AnthonyW

    AnthonyW Well-Known Member

    Found it! The attached patent application is directly related to the original patent at the beginning of this post but has been updated to describe operations in a series/parallel HEV. It was just published on the 09/20/2018. What is really funny is that Honda seems to know that customers would freak out when the ICE comes on and specifically talks about how all the steps they take to prevent the use of engine braking until it is the last resort. (Bold emphasis is mine)

    Section [0049]
    In the second braking control illustrated in FIG. 4B, the second motor generator MG2 operates as a generator by the braking force of the vehicle, and the first motor generator MG1 is subjected to power-running by the regenerative power generated by the second motor generator MG2 to reverse the engine ENG. At this time, the engine ENG functions as the load of the first motor generator MG1, and the regenerative power is consumed for the power traveling operation of the first motor generator MG1.

    Section [0003]
    In a hybrid vehicle described in Japanese Patent No. 5965459, when engine braking is started after charging a traveling battery, after a braking situation immediately continued thereto, for example, after a braking situation when a hybrid vehicle goes down a slope or sloping land immediately after the start, there is a case where a driver misunderstands that no pure electric operation mode occurs.

    Section [0005]
    The hybrid vehicle disclosed in Japanese Patent No. 5965459 does not inhibit the engine brake when charging of the traveling battery is not permitted, that is, it is considered that the engine braking is performed. Therefore, when going down a slope or a sloping land after charged until the charging level of the traveling battery becomes a value greater than the charging threshold value, noise due to engine braking is generated. This noise causes a sense of incompatibility to the driver who tends to think that the quietness of the hybrid car is high due to the electric driving. In particular, since the driver is apt to feel a sense of incompatibility with the engine sound generated immediately after the charging of the traveling battery has been completed, the traveling comfort for the driver is deteriorated.

    Section [0006]
    An object of the present invention is to provide a control device for a hybrid vehicle which can improve driving comfort for a driver even when charging of a battery cannot be permitted

    Section [0012]
    the engine is utilized as a load of the first motor generator, is executed when a variable representing a charging state of the battery by a level of a value is equal to or greater than a predetermined value and use of a mechanical brake of the hybrid vehicle is restricted.

    Section [0018]
    ...Therefore, even in a state in which charging of the battery cannot be permitted, if the use of the mechanical brake is not restricted, it is possible to improve the traveling comfort for the driver, without causing the driver of the vehicle to feel uncomfortable.

    Section [0058]
    Further, it is to be noted that the present invention is not limited to the above-described embodiment, but may be appropriately modified, improved, and the like. For example, the vehicle is not limited to the HEV capable of switching between the series type and the parallel type, but may be a series type HEV or a parallel type HEV.

    In summation, the system is working as designed - and Honda knew it would cause discomfort. Instead of explaining clearly (in the owners manual perhaps) to the customer that engine braking has to happen from time to time, they take steps to reduce the number of occurrences. What they did not understand is that this tends to create more confusion and anxiety in the customer because it causes the ICE behavior to be sporadic and not wholly predictable. So the customer is confused because logically they think if I do this (full charge) then I do that (go down a slope) then it should always do this (ICE turn on). Since that is not always the case, the customer thinks something is wrong with the car.


    Attached Files:

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  4. KentuckyKen

    KentuckyKen Well-Known Member

    @AnthonyW, the Valkyries are now carving out a niche for your statue in Valhalla. Your legend will live on forever. I’m running out of awards for you, so I’ll just say thank you, thank you, thank you!
    This will be a big help to the software guys on the forum who have been driven slightly bonkers by the ICE operation seemingly not being consistent. It also vindicates @insightman who first postulated that this was probably what’s going on.

    Now we just have to come up with a snappy name for this event of electro-mechanical engine braking when battery full.
    Texas22Step, Kestrel and AnthonyW like this.
  5. dnb

    dnb Active Member

    Great find! Now I have to find out how to drive down my hill without breaking at all so ICE doesn't turn on the whole time for my 10 mile commute ;D
    AnthonyW likes this.
  6. jorgie393

    jorgie393 Active Member

    This is great info. Thanks so much for digging it up.

    I am still disappointed with the following design choices (the second of which I think could be, though probably is not, a mistake):

    1) that the engine actually runs to consume fuel when braking, vs. passive run. (I note that this feature--that the engine is using fuel-- is not mentioned in the patent). Though it's been proposed that this is to "warm up the engine" and make it better lubricated, I am not sure, since the friction (and associated wear) IS the braking. The more lubricated it becomes, the less it brakes. Maybe the fuel consumption is to provide extra "push" back against the electric motor so it can waste more energy?

    2) And that if it runs to consume fuel, it continues to run after the braking need is over. This is really the sore point for everyone. It's been speculated that this is to satisfy emissions requirements; but if so, it is dumb even if required, since there is no way that continuing to run the engine after it is no longer needed reduces emissions. It can only generate more. This might reduce average emissions per minute, but not total emissions. I personally still wonder if this is an unintended crossover between the "run the engine for braking" and "if the engine starts to run, keep it running until it warms up" control circuits. We will never know.

    Couldn't they just burn up the extra electricity by turning on the seat warmers, or heating the engine coolant with a big resistor, or some other waste of electricity? Ah well.
    Texas22Step, JJim, Bas and 2 others like this.
  7. bfd

    bfd Active Member

    This is exactly the way the Prius PHEV works. Likely that other PHEVs behave the same way, too. What would also be interesting to find out is what happens when a BEV starts out with a full battery and immediately starts regeneration. Where does that excess go? Or is a "full" battery actually less than full to deal with that eventuality.
  8. ab13

    ab13 Active Member

    For a BEV, you shut off regeneration and use friction brakes. Not good if decending a mountain.
  9. AnthonyW

    AnthonyW Well-Known Member

    So what follows is how I believe the meeting of Honda engineers went when they met to figure out how to deal with engine braking in regards to the customers expectations:

    Fred, the visionary Honda engineer goes first:

    “Let’s educate the customer that under these conditions engine braking will and must happen. It is normal and by design. Maybe emphasize it in the owners manual and educate our sales and service people perhaps. Maybe even kick it over to Marketing and have them put a positive spin on it by saying something about it’s a good thing because it preserves the life of your engine and your battery blah blah blah...”

    Room falls silent.

    Everything looks at everyone else.

    Manager at the head of the table says, “Okay Fred you’re fired. Hank, you are in charge now. Your job is to design a system that is so complicated that it requires a patent and make sure it effectively freaks the customer out by making it random and unpredictable. John, throw in an Active Noise Cancellation system so the customer can’t hear the engine in the first place. Maybe we can gaslight them into thinking that the engine isn’t even really coming on. Any questions? Good, you have a couple of years and a couple of million dollars to get this done. Okay, next order of bus-, Fred why are you still here?”

    Sent from my iPhone using Inside EVs
    eagle8 likes this.
  10. Atkinson

    Atkinson Active Member

    Our Bolt EV has a feature called location based charging for people who live or charge at the top of a hill.
    In the locations you specify, charging will end at your specified level (ex. 80%) so that you are charged, but have room for regen when you leave.
    Best case - we all move to location well below sea level so we coast in the last few miles on "fumes" and head out with a full battery.
    Then there's the flood insurance issues.....
    Otherwise, you might be able to just stop charging well before 100% and keep your house with the panoramic mountain views.
    VTSAX, jorgie393 and insightman like this.
  11. insightman

    insightman Well-Known Member

    Thank you so much for finding this recent patent, AnthonyW! I wish it explicitly indicated the ECU starts the engine to provide pseudo engine braking when the battery is fully charged. However, you identified the key paragraph that implies the engine is started.

    The key phrase in the key paragraph is "reverse the engine ENG." For the non-plug-in i-MMD hybrids, there is no need to reverse the engine because the engine provides a sufficient power-wasting load simply by shutting off its fuel injectors and closing its valves--the starter motor/generator can spin the unfueled engine just as it does when it is starting the engine. So, without explicitly saying so, reverse the engine ENG implies the engine is running and the torque from the starter motor/generator is applied in the reverse rotational direction from the torque it uses to start the engine.

    Ha, ha! Paying the price for allowing your battery to become fully charged by getting a hot-seat!
  12. bfd

    bfd Active Member

    So, this should no longer be thought of as an "unexpected" ICE turn-on, and rather a "programmed" energy dump. Now, onto figuring out why ICE engages at other random times that are yet to be as well-explained as this one was.
    EmZ and AnthonyW like this.
  13. ab13

    ab13 Active Member

    The diagram shows its based on the brake usage, the actual values of course are not given. The issue is the system didn't no how long you will be driving. If you use a lot of brake for 2 to 3 minutes it's should be okay to stay in friction mode if you are only driving 10 or 15 minutes. The car doesn't know if you are driving 10 minutes or 10 hours. The should provide an option that pops up where you can dismiss "engine braking" or let it go on if needed.
  14. Dmiko

    Dmiko New Member

    I live on a top pf a hill and descent with regen produces about 8 miles of EV range. So I just calculate charging time so that the battery is charged to an indicated 42 miles instead of 5x. I wish Honda had a "hilltop reserve" mode of the Chevy Bolt where you can specify max charge percentage...
    LegoZ, Cash Traylor and insightman like this.
  15. insightman

    insightman Well-Known Member

    In their response to the possibility of gas mixing with the Clarity's oil, I hope Honda's doesn't introduce an update that lengthens the minimum time the engine runs to warm up. It would increase "engine anxiety" to "engine paranoia."
    KentuckyKen likes this.
  16. Cash Traylor

    Cash Traylor Active Member Subscriber

    I would point out that (and this is highly speculative until I parachute into the engineering department at night with a flashlight and find the answer), the Atkinson-Generator attached to the 3 point planetary drive/clutch is not the same as a starter absorbing energy as a "mechanical-thermal" load. It is quite capable of spinning the engine up to it's red line when in motive mode versus generator mode (regardless of AC/DC Phase), and as the ICE is capable, by design, of variable compression, injection, and ignition (all computer controlled) it is possible that the ICE is not "entirely" started/running when the above events trigger it's engagement. And, more importantly would be difficult for the driver or passengers inside to tell the difference from the engine idling, or BEING idled. I would love to throw an accurate fuel transducer (bet there is one there already, just need to gain access to the data channel) pre-fuel manifold and I bet that in these events the fuel flow is very low, if at all. EGT would be another way to gauge this. It is an elegant solution to the problem of being unable to easily disengage the traction motor from the wheels when the energy flow is reversed, without the risks of the motor/gens going free wheel into the inverters. This could be solved another way, but the driver experience solution versus the industrial engineering solutions for this are not "easy." Since it is very obvious from at least my experience that Honda tried to make this Clarity PHEV drive like a "regular" car I can see why they would chose this as a solution to the energy storage problem. As others have commented about the drive battery not being "fully" charged I would only say that they are protecting the battery with a universal charge management program and using the "extra" capacity to absorb regen would violate that system, and result in reduced battery life. That and the most correct engineering answer has to do with the Li-ion chemistry and the fact that the battery's ability to absorb rapid charge rates exponentially decreases with high states of charge. It simply cannot (at 100% user, or 90% actual design) absorb regen currents easily without risk of damage. Another option for Honda would have been to put a big nichrome resister pack in the frame... but I am glad they didn't (leave that to locomotives) as a white hot kilowatt resistor in a car is a bad idea...

    Anthony, you are amazing! You win the MI6 award for this "undocumented feature" and my high praise! Congrats!

    Last edited: Nov 9, 2018
    LegoZ likes this.
  17. insightman

    insightman Well-Known Member

    How does the Clarity's engine vary its compression?

    I didn't understand that concept.

    It's been documented that the spark plugs are firing when a Clarity with a fully charged battery decelerates using the traction motor to slow the car. That qualifies as "running." Is your point that the engine does run but wastes very little fuel to provide energy-burning resistance to the regen power from the traction motor?
  18. Cash Traylor

    Cash Traylor Active Member Subscriber

    Fuel need not be injected into all, or any, cylinders. The variable "live" cylinder engine is an old concept (article below) and has been around for a long time, 8 cylinder engines running on 4, etc. Our 4 running on 2, or none, is not a stretch. An ICE that is "running" does not represent a mechanical "load" for the generator to dissipate energy into. It is also not generally a good practice to overdrive an operating engine that has combustion occurring in the cylinders (depending on design) "jake braking" the engine. So what I meant but likely did not eloquently (it's Friday, beer has occurred) state is that the engine is not fully running (on all 4) in this circumstance and "wasting" a lot of fuel. Honda seemed pretty determined in the overall design to make the vehicle efficient without sacrificing mechanical reliability.

    But again, I have not found the secret file closet yet, so this is only speculation, as I mentioned in my first line.

    As for the "programmable variability" in the Clarity's ICE, I am making a lot of assumptions based on limited actual engineering data. However, based on this:

    I think they have some undocumented features up their sleeves. But I fully admit I may be completely wrong, incorrect, full of confabulatory fiber, etc...


    Last edited: Nov 9, 2018
  19. Cash Traylor

    Cash Traylor Active Member Subscriber

    I like the point about Honda failing to provide user specified states of charge (hilltop reserve) etc. I love the Clarity, but agree the Volt is a little more technically mature, and has more geek-out features. Fortunately, in reality those are all entirely software solutions, so who knows - one can hope?!? I just hope they add it to the vehicle software and not the "app" as well...

    I did see that the range gauge application update was linked to the infotainment system as a app. This makes me wonder how much functionality is actually available in the infotainment UI (hidden/root/etc) or interface. This deserves more investigation when someone smarter than I am has the time!


  20. insightman

    insightman Well-Known Member

    I've come to believe the starter motor/generator is producing negative torque opposing the running engine's torque to use up regen energy from the traction motor when the battery is too full to accept that energy. I could be persuaded that all of the engine's cylinders are not engaged in this effort. Someone will have to attach a separate engine run-time monitor to each of the 4 spark-plug wires.

    I look forward to the results of your parachute entry to the secret vaults of Honda's secrets.

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