How can the Clarity Plug-In Hybrid produce 212 hp?

Discussion in 'Clarity' started by insightman, May 24, 2018.

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  1. M.M.

    M.M. Active Member

    Where are you getting that spec? Everything I'm finding says it has a 6.7kWh battery pack to the Clarity's 17kWh (both rated, not usable). In any case, though, it's significantly smaller.

    Actually, that torque comparison graph exactly matches what I would expect given identical drivetrains, the Accord having a smaller battery pack, and the Clarity having a ~100HP@5500RPM ICE with the Accord making up for its smaller battery with a ~150HP@6200RPM ICE.

    At the bottom, the torque curves are identical, because the battery pack and ICE combined in both cases are supplying sufficient power to max out the capability of the electric motor. Farther up the curve, the higher power output capability of the Clarity's larger battery pack makes its curve a bit flatter, since the ICE in the Accord can't output enough power until it gets up to higher RPMs to compensate for its smaller battery pack. The different-looking falloff at the very top looks to be directly proportional to the different power curve of the ICEs, though it could just be the electronic limits set differently or an artifact of the way the dyno works.

    The power curves, likewise, peak exactly where you'd expect them to--at 5500RPM for the Clarity and 6200RPM for the Accord PHEV. The actual measured peaks are at the same point because they're both limited by the electric motor--it's just a matter of at what RPM the ICE assist can supply the most power.

    Now, in practice both ICEs could be running at their max power RPM through the entire torque curve, so both torque curves should look identical if the mechanical transmission isn't coming into play and the drivetrain is otherwise identical. Since "RPM" for the torque curve is not defined on these graphs, I suspect that the difference may just be an artifact of the way the dyno is measuring it--it's entirely possible that they are in fact identical but because the dyno is factoring in ICE RPM rather than showing electric motor RPM it looks different when you graph it.
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  3. ab13

    ab13 Active Member

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  4. M.M.

    M.M. Active Member

    Ahh, sorry, I had failed reading comprehension on your post; since the recent discussion was comparing the Clarity PHEV to the Accord PHEV, I had incorrectly assumed you were comparing those two, not the Clarity EV and Clarity PHEV.
  5. JeffJo

    JeffJo Member

    Actually, I think whoever put that torque/HP curve together didn't understand how the iMMD system works. It is ambiguous which power plant the RPMs refer to.
    • In parallel mode the speeds of the engine and drive motor differ by a factor of about 3. I think. The gearing ratios are 2.545 and 0.805, respectively. That isn't made clear in the Clarity's specs, but it is in both the Accord's and Insight's. The numbers are identical for all three.
      • My Accord would have to be going about 165 mph for the engine to hit 6200 rpm in parallel mode.
      • The drive motor does operate in that range, since it spins three times as fast as the engine at the same road speed.
      • This puts the 5K-6K RPM range of the drive motor, where it is spec'ed at 181 HP, around 45 to 55 mph. Which makes the most sense. And the red-line of the motor (I have 12500 RPM in my notes, but don't know where I got it) around a max speed of about 110 mph.
    • But this is irrelevant. Even at these speeds, the car shifts into serial mode if it requires power. In serial mode, there is no relationship between the speeds of the two power plants.
    I think they combined the two power plants in parallel mode, but used the RPMs of the engine. So the drive motor should red-line at about 4000 in those plots. And the higher curves for the Clarity that you noticed are probably because the engine's max HP is at a different speed for the Clarity (0-5500 RPM instead of 0-6200 RPM). Something still doesn't quite add up, but this isn't my field. That's why I asked here.

    Here's what I conclude, and why:
    • The Accord and Clarity both claim the drive motor has 181 HP at 5K to 6K RPM.
    • The Accord and Clarity both claim the drive motor produces 232.2 lb-ft of torque at 0 to 2K RPM.
      • The ranges should be about 4K to 6K RPM, and 0 to 4K RPM. (Since the crossover point is at 232.2*4094/5252=181)
    • I think that this means it is the same motor in each.
      • For reference, the Insight claims 129 HP and 197 lb-ft.
    • The 181 HP is not a limitation of the drive motor when isolated from the rest of the system. It can produce 212 HP, and must be in serial mode to do so.
    • I conjecture that the 181 HP number comes from a maximum power rating of 135 kW for the battery system. This isn't related to the capacity of the battery, it is the maximum that the system will try to pull from the battery.
      • The Insight would have a limit of 96 kW.
    • The gas engine can provide additional power beyond the battery system's limit. But the two can't both be at their maximum, there is still an overall limit of 212 HP (or about 158 kW) for the combined system.
      • It could be that this is the power limit of the motor, not of the system supplying the power.
    The point is that the 212 HP limit seems to be a property of the drive motor, while the 181 HP limit is a property of the electrical system when the gas engine is off. The first is not derived from the second in any way.


    Edit: I found the source of the drive motor's red-line. From an earlier paper titled "Development of Motor and PCU for a SPORT HYBRID i-MMD System", there was this spec for an earlier version of the motor:
    Last edited: Mar 6, 2019
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  6. ryd994

    ryd994 Active Member

    I believe it's because of the clutch. 181hp is achievable when both engine and battery are providing power to the motor. And then the clutch engage, providing extra 20hp over the shaft.
    Under certain circumstances...…
    I'm sure this needs some tricky condition, and shouldn't be used for general discussion.
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  8. JeffJo

    JeffJo Member


    The hybrid power train works in two ways:
    1. The clutch is not engaged.
      1. In engineering terms, this is called "serial hybrid mode."
      2. It is characterized by having only the drive motor propel the car.
      3. Honda's literature calls it "hybrid mode."
      4. If the ICE is running, it generates electricity thru the motor/generator:
        1. If the ICE generates a surplus, that surplus charges the battery.
        2. If the ICE doesn't generate enough, the battery supplies the rest.
    2. The clutch is engaged.
      1. In engineering terms, this is called "parallel hybrid mode."
      2. It is characterized by having the ICE propel the car, at least in part.
      3. Honda's literature calls it "engine drive mode."
        1. If the ICE supplies too much power, the drive motor acts as a generator to charge the battery.
        2. If the ICE can't supply enough power, the drive motor kicks in (powered from the battery).
    181 HP applies to the drive motor alone, without the ICE running. The issue I have is whether it is a limitation of the drive motor, or the battery's ability to drive it.

    The ICE can provide power thru the shaft ("parallel" mode) or thru the motor/generator ("serial" mode). Changing modes can't change the amount power it produces, although it can change how efficient it is. "Serial" mode is better, since it can optimize the RPMs. But the clutch can only change how the power is distributed, not increase it. And it is less versatile, since it fixes the RPMs.
    Last edited: Mar 6, 2019
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  9. M.M.

    M.M. Active Member

    I believe JeffJo probably typo'd there and meant to say that the 212HP number may be some theoretical maximum when the mechanical linkage is engaged and the electric motor is also producing its maximum drawing from the battery. This was discussed earlier in this thread, although I am not knowledgable enough to do more than speculate.

    It is interesting that those dyno graphs do seem to show the expected >200HP peak, regardless of how it's being generated or how the heck they got an RPM number for the torque curve (I don't know enough about dynos to speculate, but clearly the RPM number associated with the torque curve is not in any way related to actual output of the ICE, nor can the power curve be supplied exclusively by the ICE). It would be fun to see what the dyno results were if the car were running in EV mode only, with no ICE assist.

    An aside, dyno graphs like that are funny when it comes to EVs because in an ICE you're looking at thee performance of the engine separate from the transmission, while you get a wildly different graph (with a bunch of dips and peaks) if you graph the performance at the wheels factoring in the transmission. I think that's what you were getting at with your original comments about "horsepower" not being equivalent to an ICE.

    In actual performance the engine in an ICE will jump all over the place on that curve as it accelerates during each shift action, and actual performance (particularly during hard acceleration) will have a lot to do with transmission gearing and how much of the time the car is spending near the peak of the torque curve and how well that matches up with the peak of the power curve--even for ICEs horsepower is just one metric and the actual real-world performance of the car is based on many factors.

    Most EVs of course have only a single gear and a torque curve that is virtually flat over a good chunk of its range, while their horsepower curve instead of peaking at one very high point (that in performance driving you only hit briefly in each gear) is flat through a broad chunk of the range, so perform much differently than an ICE.

    Horsepower, while it technically means the same thing in both cases, is not a directly equivalent metric for a variety of factors, just as you can't really compare a diesel ICE to a gas ICE based only on horsepower, or even two identical ICEs with significantly different transmissions attached.
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  10. JeffJo

    JeffJo Member

    No, I meant exactly what I typed.

    The 181 HP rating for the drive motor applies when the clutch is not engaged, and is drawing electric power from the electrical system that is built into the car. This information alone does not indicate whether or not some of that power is drawn from the ICE+generator, but later inferences seem to answer that question.

    They are simulated graphs. Read the header above the figure: "The Horspower / Torque Curve below was generated by the ProfessCars™ software, based on the factory data". No dynamometer data was used. The low end is obviously based on the 232.2 lb-ft rating of the same drive motor, sans ICE. What I'm trying to decipher is how the high-end was determined, and if it should be determined some other way.

    The following is for the Accord, but the fact that the same things happen for the Clarity, based on its numbers, supports my inferences. My educated guess is that they took the statements in the spec, "232 lb.-ft @ 0-2000 rpm" and "181 @ 5000-6000 rpm" to literally mean the drive motor's torque drops off from 232.2 lb-ft at 2000 rpm to 190 lb-ft (and so 181 HP) at 5000 rpm. And that if they could work together at the same speed, which they don't, the drive motor and ICE achieve a combined 212 HP at 6200 rpm. All that simulated dyno curve does, is connect these three pieces of information.

    But from Figure 18 of the paper referenced in the first post of this thread, and the more detailed version of the same figure that I posted, we know that data was incomplete. Those figures were for an earlier version of the drive motor, but it is clear that the same plot for the current version (and I have seen it in later papers) would show that the drive motor has 232.2 lb-ft from 0 to 4094 rpm, and T=(181*5252/RPM) lb-ft from 4094 rpm to some maximum speed around 12500 rpm. This plot is obviously generated from specified limits, and not a dynamometer. But still unclear, again based on the information so far in this post, how the ICE combines with that curve to make 212 HP, and what the car's speed is when it applies.

    I described what actually happens with, and without, the clutch engaged earlier. For reference, the speed of the car in mph is (drive motor rpm)/113 and, when the clutch is engaged, (ICE rpm)/37. But since we know that the clutch is never engaged at low speeds, or when power is required at high speeds, it is not possible for the 212 HP @ 6200 rpm figure to apply to when the clutch is engaged. This proves that the drive motor is capable of producing more that 181 HP, and that it is not hard-wired to a specific drive motor speed.

    The 181 HP must be derived from a power limit of the battery system alone. The 212 HP is the maximum the ICE+generator can add to that 181 HP. Since they can produce 143 HP in the Accord, and 103 HP in the Clarity, yet still add up to the same 212 HP, it seems clear that not all of the theoretical electrical power can be used to propel the car.

    So my conclusions are:
    1. Either the battery system alone can't produce more current than what is required to make 232.2 lb-ft of torque, or the drive motor can't accept more than that current.
    2. The battery system alone can't produce more power than 181 HP = 135 kW.
      1. This has nothing to do with capacity; but my 1.3 kWh battery can't do it for more than 6 minutes
    3. The drive motor can't accept more than 212 HP from the combined battery+ICE+generator.
    4. As a mostly irrelevant point, the torque/HP curve of these cars should be plotted based on the drive motor's rpms, not the ICE's. It's 3.05 times faster.
      1. It looks much like that figure 18. Exactly what it looks like depends on the answer to the question suggested in conclusion #1.
    Clearly the curve itself is, since its maximum is at the max-rpms of the ICE. Just as clearly, it shouldn't be. That curve is pretty meaningless.

    If you compare two ICE's with similar architecture, the max-HP point should give you a good approximation to how the two compare in any one set of circumstances. Comparing different ICEs makes a poor approximation, but still has some applicability. Comparing them to an EV is mext to meaningless.

    BTW, here is an approximation of my ICE's curve; I eyeballed it from a low-resolution plot, but it did have the axes labeled. It only went up to 4000 rpm, so I interpolated out to the maximum 142 HP @ 6200 rpm. I also included the points that the computer will aim for based on the power it wants from the generator.

    Attached Files:

  11. LegoZ

    LegoZ Active Member

    Does that work for you mine kept power cycling when running in ev.
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  13. LegoZ

    LegoZ Active Member

    This part is simple and supported by the EV. The PHEV can produce 121hp when in EV as this is what the battery can handle on the discharge curve. The Clarity EV has a 33% larger capacity pack and can output approximately 33% more hp (161). This supports the notion of power without ICE running being limited to 121hp.

    The generator outputs electricity to supply extra power (181) leaving 43 hp available assuming no losses. Most likely the ice only can run at peak maximum power when the clutch is disconnected due to the gearing. I assume at 99mph the combined output is 212hp.

    This also begs the question of how much power can the generator produce. This could limit power output even lower than 103hp if the pack is fully unavailable for some reason. This could be the why some are seeing the angry bees AND loss of speed. Output without the battery would be limited to what the generator could produce.

    I think mentioned in here was also engine start for decel. I know the electric heater takes a ton of power. If they activated the heater and looped it to the engine and radiator they could dissipate a significant amount of power that way without starting the gas motor.
  14. JeffJo

    JeffJo Member

    According to this site and this site, the Clarity PHEV spec's are:
    1. The 1.5L Atkinson cycle ICE produces 99 lb-ft of torque @5000 rpm, and 103 HP@ 5500 rpm.
    2. The drive motor by itself produces 232 lb-ft @ 0-2000 rpm, and 181 HP @ 5000-6000 rpm
    3. The total system horsepower is 212, at an unspecified speed or definition of "total system." Hence the title of this thread.
    All of the reviews I have seen repeat this information. So I don't know where your "121 hp" number comes from, unless somebody mistook the Prius Prime's total horsepower for the Clarity motor's. I could be wrong, but I just haven't seen it.

    My Accord, which is what I am trying to figure out, differs from that list only in the ICE: the 2.0L Atkinson cycle ICE produces 129 lb-ft of torque @3500 rpm, and 143 HP@ 6200 rpm. And it says the total horsepower max is reached at the same 6200 rpm, which makes no sense since the clutch is disengaged. But if your logic were correct, it seems my Accord should have a much higher total power than the Clarity, not the exact same number.

    That is an good suggestion. But it is consistent with what I've been trying to suggest; that it is a system limitation. While the two ICEs can produce more than 31 HP, they can only much that much through the generator. But another data point I have suggests the ICE+Generator produce about 70 HP in "hybrid mode."
  15. LegoZ

    LegoZ Active Member

    The electric side can only pull so much power from the battery pack. The gas engine start to spin the generator to feed additional power to the motor to achieve 232 lb-ft and 181 hp. Otherwise why would the gas engine need to start when you press the accelerator hard and how would power ever exceed that of the motors rating if you are under 45 mph?

    I thought 121 hp EV was well established at this point, but I could be wrong.
    " Honda says that EV Drive mode produces up to 121 hp" from

    It also is less clear when you compare discharge rates for the PHEV (121hp(90KW) it is 5.29C) and for EV (161hp(120KW) it is 4.7C)
  16. LegoZ

    LegoZ Active Member

    Maybe we can get someone to reach out to Honda of Japan engineers to explain these things... @Domenick you have any connections? I know that with the Urban EV stuff Fully Charged met with some of them so maybe they have contacts and can prode and obtain more information?
  17. LegoZ

    LegoZ Active Member

  18. JeffJo

    JeffJo Member

    But the exact same diagram (except maybe the 121 HP, which is based on hearsay as far as I can tell), with the exact same numbers, applies to my Accord. So why do I have a 2.0L, 143 HP gas engine to achieve the same output that a 103 HP one can? (Except possibly needing to turn it on sooner. I can only conjecture that, if 121 HP is correct in that spot, my car has the same or less).

    The source seems to be post #11 (and maybe #9) where insightman claimed it was what Honda says. But such a source is what I am trying to find, not someone claiming somebody else said it.

    Here's a slightly different version of that diagram, taken from a paper titled "Development of Motor and PCU for a SPORT HYBRID i-MMD System". I added the HP ratings where I think they apply. I' not convinced about the 121 HP number, so I can't put it anywhere. Note that engine drive mode applies only in an overdrive gear, so it can't be anywhere near the maximum rated HP. I fudged the numbers from the following plot that showed where the clutch is engaged, but didn't label the values.
    upload_2019-3-8_16-10-53.png upload_2019-3-8_16-13-6.png
  19. LegoZ

    LegoZ Active Member

    Please explain why the output is rated at 180hp, by Honda, when power is being delivered by both the gas and battery then?
    “Power comes from a 181-horsepower electric motor producing 232 lb.-ft. of torque and drawing power from both the gasoline engine and a 17-kilowatt hour (kWh) battery pack.

    There are three power outputs two known, one uncertain:
    Full EV: uncertain maybe 120hp
    Battery and Generator running:181hp see source above
    unknown combination of factors: 212hp

    I have driven the first gen two motor setup of the accord hybrid and you don't get much power without the gas engine running. A large limiting factor is draw rate on the battery, which is a function capacity and cell design. It is unlikely that you can draw the power from your battery at the same rate as the Clarity can due to the smaller capacity, thus the larger gas motor and likely higher output generator (the other wild card)
    Last edited: Mar 8, 2019
  20. LegoZ

    LegoZ Active Member

  21. LegoZ

    LegoZ Active Member

  22. LegoZ

    LegoZ Active Member

    “Engine Drive Operation
    When cruising at medium to high speeds, the high-efficiency Atkinson-cycle i-VTEC gasoline engine provides propulsion via a high capacity lock-up clutch, which connects the generator motor (always linked to the engine) and the electric drive motor, effectively sending motive power directly from the engine to the drive wheels. In this type mode, the system works as a "parallel hybrid" where both the gasoline engine and, when required – for instance upon quick acceleration – the electric propulsion motor, both provide power to the wheels.
    I think in this mode it works like the IMA system all power from the gas engine does mechanically go to the wheels through a very long gear combined with the max power from the battery being fed to the traction motor increasing the twisting force.

    The problem is I really don’t want to fire up the gas engine to test this lol. This would require going fast enough that lockup mode would work.
  23. JeffJo

    JeffJo Member

    I added the underlining to that footnote. It was a footnote to the "212 HP @ 6200 rpm" spec.

    The same spec in the 2018 model references the same "1" footnote, but so does the emissions spec. The footnote provided there is for the emissions.

    In the 2019 model, the corrected footnote says "Total system horsepower as measured by the peak, concurrent output of the two electric motors and gasoline engine." This might be getting somewhere, but still seems like "fake news." As far as I know, the motor/generator (as opposed to the drive motor) shouldn't ever contribute to this issue. And it doesn't explain how the Clarity and Accord get the total HP same values, with (I assume) the same two motors but different ICEs.
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