Why does the ICE rev up for no reason?

Discussion in 'Clarity' started by dannieboiz, Apr 16, 2019.

  1. dannieboiz

    dannieboiz New Member

    A few times now in EV mode the ICE engine would kick in and rev up for no appearantly reason under normal driving condition.

    This commonly happen shortly after I'm off the freeway for a couple miles. I don't think the ICE should kick in for ANY reason unless the battery drained, each time my battery is almost full and has only been driving for less than 10 miles since fully charged.
  2. KentuckyKen

    KentuckyKen Well-Known Member

    That’s a trick question since it’s programmed to start for perfectly good reasons.
    You have to remember that you bought a PHEV not a BEV and that there is no pure EV only mode you can select. The ICE can and will start up even when you are not in HV or HV Charge for various reasons listed on page 13 of your manual that include but are not limited to a System Check that keeps the ICE healthy and ready to start on demand.
    Also it is well known (but not mentioned in the manual) that immediately after a full charge, regen is limited to protect the battery from over charging and will start the ICE after a hard braking or 4 chevron regen to in some manner keep the excess charge away from the battery.

    Additionally, whenever the ICE is started, it is programmed to stay on until it reaches operating temperature in order to prevent condensation in the oil and exhaust system. You should not try to circumvent this by trying to turn it off. It’s best to let it run and turn itself off.

    Don’t worry about the occasional ICE start up. I have found it possible to drive 9,000 miles on 15 gal of gas and almost all the gas was used on trips out of town. The occasional gas consumption while in “pseudo EV Mode” (not an actual mode as you have found out) is so low that I haven’t even lost a bar on the gas gauge between out of town trips. Just do as much of your driving on the battery as possible and don’t worry about the occasional ICE runs.
    Hope you enjoy your Clarity and the gas savings as much as I do.
    Last edited: Apr 16, 2019
  3. insightman

    insightman Well-Known Member

    You're thinking of the Chevy Volt--it uses up its battery and then starts it's "range-extender" ICE. The Clarity is designed to maximize overall efficiency--a marked difference in philosophy from the Volt. You can keep it in EV drive almost all the time (as @KentuckyKen mentioned) by simply using ECON Mode and avoid pressing the accelerator beyond the click point. Many on this forum have gone months without activating the ICE.
    ken wells, KentuckyKen and dannieboiz like this.
  4. insightman

    insightman Well-Known Member

    I agree that the Clarity's penchant for starting up the ICE when the battery is fully charged and regen braking occurs is frustrating and counter-intuitive. In my opinion, it's the most mysterious part of the Clarity's operation and I've been waiting for Honda to provide the definitive explanation about why it happens.

    My personal theory is not shared universally on this forum (to say the least). I believe that Honda's engineers wanted to provide regen braking capability even when the battery is fully charged rather than switch to mechanical braking alone. Whereas regular ICE-powered cars can use engine braking on a long, steep decline, the Clarity cannot. So when the battery is fully charged I believe the regen power from the traction motor (operating as a generator) goes to the starter motor/generator (operating as a motor) and is used to resist the rotation of the activated ICE. The lesser Honda i-MMD hybrids don't do this. Instead, they use the excess energy from the traction motor to power the starter motor/generator to turn the ICE, but the ICE is NOT activated.

    The only reason I can come up with for the Clarity PHEV to activate its ICE in this situation is that the Clarity's greater weight requires the additional resistance the activated ICE can provide. The shakiest part of my theory is that the starter motor/generator is operating to slow down the ICE. Nothing I've read has confirmed this idea. The power path for this mode appears in the bottom right diagram in the chart I put together last summer.

    vin seeram, Mowcowbell and ClarityDoc like this.
  5. melklim

    melklim New Member

    Dumb question but how do I get into Engine Drive Mode?
  6. ClarityDoc

    ClarityDoc Active Member

    It's a cruising mode that kicks in automatically at hughway speed. You'll see a "gear" icon appear in the center of the Clarity display's energy flow diagram. It just happens, not something you can select.

    Sent using Inside EVs mobile app
  7. fotomoto

    fotomoto Active Member

    Hybrids also can and do do this. Why can't the Clarity? Unlike previous Honda hybrid designs, the Clarity is more like others (Toyota, GM, and Ford) using the transaxle as a power split device (toyota term) between the ICE and motor/generators.

    Yes, hybrids can use the ICE as an "air pump" to provide gas-less engine braking if the battery is too full or other reasons (too hot, more regen than the batt can accept, etc). The prius has a "B" on the gear selector that stands for Braking which activates this behavior when manually selected. NOTE: in these modes, the ICE sounds normal (as if it's running and burning gas). In fact, on the first startup, there's a possibility it is burning gas to warmup; need scanguage or other OBD device to determine that.
  8. insightman

    insightman Well-Known Member

    To perform true engine braking, the ICE needs to be able to use its compression to slow the wheels through the transmission. The Clarity doesn't have a multi-speed mechanical transmission that would enable this to happen. When the Engine drive ("gear-mode") clutch connects the Clarity PHEV's ICE to the wheels, it is operating through the equivalent of 6th gear in a multi-speed transmission, and such a high gear wouldn't provide much engine-braking at all. Those other hybrids have multi-speed transmissions.
    Last edited: Apr 17, 2019
  9. fotomoto

    fotomoto Active Member

    Most use a variation of the CVT design (volt, clarity, energi, prius, etc) but some manufactures (Koreans for example) have used a conventional trans with the EV motor placed between it and the ICE.

    Honda also calls it an Electronic Continuously Variable Transmission (E-CVT) with Sport Mode and Deceleration Paddle Selectors.


    Looking at the powerflow chart above and the REGEN mode on the bottom right in particular, the energy flow can go back to the ICE via the starter motor so that the starter motor is consuming the excess electricity by spinning the (non-firing) ICE. This is how most hybrids burn off excess regen. NOTE: all of these designs use slightly different methods and terms to A) avoid patents and B) marketing. Ford and Toyota actually shared some hybrid tech in the beginning (10-15 years ago).

    Another method is to simply bypass everything and apply 100% friction braking and this is used for hard braking. The Tesla brake pedal is only connected to the hydraulic brakes while regen is controlled by the accelerator pedal. Without an ICE, Tesla can only turn off or greatly reduce regen when the pack is too full/hot, etc.
    Last edited: Apr 17, 2019
  10. insightman

    insightman Well-Known Member

    But the Clarity, unlike every other hybrid, starts its ICE (the exhaust manifold gets warm) when regen braking occurs if the battery is fully charged. There is no mechanical transmission that can effect engine-braking--Electronic Continuously Variable Transmission refers to the two electric motor/generators, not to a multi-speed mechanical transmission (I count a conventional CVT as a multi-speed mechanical transmission).
    Last edited: Apr 17, 2019
  11. petteyg359

    petteyg359 Active Member Subscriber

    The 212hp diagram seems wrong. The traction motor can't spin both ways at the same time. Clutch + engine power + battery charge would use both motors/generators, shouldn't it?
  12. insightman

    insightman Well-Known Member

    Yes, clutch + engine power + battery charge would use the starter motor/generator as a generator and the traction motor as a motor. The traction motor would not be operating as a generator--it does that only when regen braking occurs. So it would not "spin both ways."

    I started a thread long ago, How can the Clarity Plug-In Hybrid produce 212 hp? Although there were many suggestions, there were no solid answers.

    Honda says the traction motor can produce up to 181 hp when powered by the combination of the high-voltage battery and ICE-powered starter motor/generator. If the traction motor can actually achieve 212 hp for short bursts, why would Honda say it can produce only 181 hp? So in what mode can the Clarity come up with the 31 hp needed to achieve Honda's claim of 212 hp?

    Discounting the possibility of a 212-hp traction-motor burst, I figured that the 212 hp number can only happen in Engine Drive mode, when the clutch has connected the ICE to the wheels through the single-speed gearbox. The battery must be contributing its max (which can provide 121 hp from the traction motor), the ICE must be providing its 60-hp electrical bump from the starter motor/generator to the traction motor, AND the ICE must also be delivering 31 hp directly to the wheels. That would mean the ICE is generating 60 hp worth of electricity and contributing 31 hp of mechanical drive. The ICE must therefore be effectively delivering 91 hp. The number is lower than the ICE's claimed 103 hp due to losses within the system.

    I would love it if Honda would fess up and explain that 212-hp number. Isn't it interesting that Honda says the 2019 Accord i-MMD Hybrid, with its 143-hp ICE and a 181-hp traction motor (numbers from Car & Driver) produces the same maximum of 212 hp?

    The irony is that you never see any significant performance in Engine Drive mode because the Clarity blips back to Hybrid Drive mode the instant you get aggressive with the accelerator pedal.
    Last edited: Apr 17, 2019
    KentuckyKen likes this.
  13. ken wells

    ken wells Member

    When you have your car in HV Charge mode and you are going over 45 mph, can you ever get in a situation where the engine is driving the wheels (clutch engaged) and also sending torque to the generator / stater motor to provide electricity to charge the battery? This would seem to be more efficient than any other way of charging the battery with the engine while driving.

    Also, the diagrams above are simplified and somewhat misleading because they show the battery directly connecting to the two motors. The electronic control module has been left out. the ECM connects to the battery and also has two 3-phase inverters that connect to the two motors. Thus it is possible for electricity generated by the generator / starter motor to flow to the traction motor without sending / drawing electricity to/from the battery.
  14. insightman

    insightman Well-Known Member

    I didn't know that. Is there a name for that mode?
  15. David in TN

    David in TN Active Member

    Yes, the elusive gear icon drive. May not be the best name, but that's when it is occurring.

    Sent from my SM-N960U using Inside EVs mobile app
  16. insightman

    insightman Well-Known Member

    Honda calls the gear-icon drive mode Engine Drive mode. However, it does not fit the non-battery mode definition you were describing. The battery does provide power and is recharged in Engine Drive mode.

    The three underlying drive modes Honda describes are EV Drive mode (battery-power only), Hybrid Drive mode (battery-power + ICE-generated electric power), and Engine Drive mode (battery-power + ICE-generated electric power + ICE mechanical power through the clutch). In all of those modes, the traction motor performs regen charging of the battery when the car slows. I would expect that there is an instant of no battery involvement between when the battery is providing power and when the battery is receiving power, but I don't believe that constitutes a fourth drive mode.
    Last edited: Apr 18, 2019
  17. David in TN

    David in TN Active Member

    I was under the impression that Engine Drive mode was taking ICE and sending directly to the wheels (through the various clutches, eCVT tranny, etc.,) and therefore not charging or discharging the battery as @ken_wells had asked. If this in incorrect, then I stand corrected. :)
  18. David in TN

    David in TN Active Member

    From the Honda Clarity PHEV Press Kit:

    In Engine Drive mode, which is typically engaged when cruising at medium to high speeds, the Clarity functions as a parallel hybrid. A lock-up clutch connects the engine (always linked to the generator motor) and the traction motor to send power directly from the engine to the front wheels.

    Maybe I'm reading more into this than I should, but I'm seeing that the ICE is providing the power to the front wheel under this condition?
  19. insightman

    insightman Well-Known Member

    Yes, in a parallel hybrid, the power is coming from both the electrical and mechanical sources (as opposed to the power sources combining to provide electrical power only). If only the ICE was providing power, then the Clarity PHEV would not be operating as a hybrid.
  20. KentuckyKen

    KentuckyKen Well-Known Member

    My head is swimming from taking in all this engineering, but I have seen all the power flows with the gear icon illuminated. I’ve seen power go to and from the battery with a slight pause between. And any downhill that triggers regen seems to turn off Engine Drive Mode and then it comes back on after a longer pause.
    MPower likes this.

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