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

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

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  1. insightman

    insightman Well-Known Member Subscriber

    I guess if the traction motor that actually drives the wheels does not contribute to the 212 HP rating, Honda could have thrown out any number they wanted for the maximum HP. I've always been suspicious that every one of Honda's most powerful IMMA hybrids (Clarity, Accord, CR-V) produces the same 212 HP, despite differences in their hybrid components.
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  3. JeffJo

    JeffJo Member

    Since some seem to actively refuse to understand it, "produce" means to convert energy that is stored somehow (and here that means a chemical potential energy in gasoline or a lithium-ion battery) into power (which is energy that is flowing, hence the time dimension).

    The traction motor does not do this in hybrid drive. It converts electrical power into mechanical power (yes, that can be called kinetic power, and yes, I do mean power). The ICE turns the chemical potential energy stored in gasoline into mechanical power, and the generator turns that mechanical power into electrical power. The battery turns chemical potential energy into electrical power. The two power flows are combined into one power flow by in the PCU. Wherever you think this power should be measured (before or after the PCU), this is the power flow that has a maximum of 212 HP.

    It may well be true that their individual maximums sum to more than 212 HP. It may be true that the PCU in the Accord or Clarity - if they are different - could produce more. That is irrelevant; it won't. The specifications for the combination, wherever it is measured, say 212 HP.

    He explicitly said it was based on the outputs of the (engine driven) generator and the battery. No mention of the motor. The only ambiguity here is whether that is before or after the PCU; but it is when the PCU is drawing from both, so its specs do apply.

    With no disrespect intended, do you really misunderstand what I am trying to say that badly? The traction motor can only turn electrical power, that is already "produced," into mechanical horsepower. IT CANNOT ADD ANY POWER TO THE FLOW.

    Right. Sorry I didn't acknowledge that before.
    Close. 181 HP, or about 85% of that 212, is allocated for use by the traction motor. The loss budget accounts for part of the remaining 15%. There are many peripherals that also need power, and that still has to come through the PCU.

    Whether the loss in the motor in included, I don't really care. The point is that there is a point in the electrical power flow where specs say 212 HP. They say that because there is a point in the flow through the motor where specs say 181 HP, and the electrical power flow is spec'ed so that this181 HP is 85% of its spec.

    With still no disrespect intended, do you really misunderstand it that badly? PRODUCEABLE_POWER is the maximum power available to the car. For the use of every part of the car (except what produces power - see definition above) that takes power, including losses. Convention says that the wheels get 85% of PRODUCEABLE_POWER. If you design an EV with a 181 HP motor, you want PRODUCEABLE POWER to be 181/0.85=212. It is a specific property of these cars, and has meaning that do not seem to want to see.

    This is exactly analogous to the SAE Net power rating of a conventional car. It is not wheel power, it is the power available to every part of the car that takes power. This isn't like trying to use the same units for MPG and MPGe. Ignoring how propulsion works differently in gas and electric drives, it is the precisely correct number for comparison to conventional cars when they publish the HP of their ICE.
    David Towle and lessismore like this.
  4. insightman

    insightman Well-Known Member Subscriber

    Yes, no disrespect perceived. I DID have a difficult time understanding. Now I've finally abandoned the idea that the motor driving the wheels represents the horsepower of the system. It's easier now to accept horses running around in the PCU. Thank you for your persistence (and your restraint).
    David Towle likes this.
  5. Random.Clarity

    Random.Clarity New Member

    Jeffjo, you really are just arguing semantics here. Yes, the terminology of "...despite the fact that that power is being used to generate the 60 extra horsepower produced by the traction motor?" is incorrect. But all of us understand what the intended meaning of that statement is.

    Now, I will admit I'm terrible at multi quotes on this forum so I'll just quote you below:

    All I am saying it that the designer of a conventional car will budget 15% of the engine's maximum power to peripherals and losses in transmission, and 85% of it to propulsion. So if he thinks the car needs 181 HP, he will try to build a 181 SAE net HP engine.

    This is nonsense. For the most part, in modern manufacturing you don't have the luxury to build a spec engine for every model you make. You pick what engine is available closest to your desired power characteristics, then try to engineer (within your budget) as much of that power as you can to the wheels. Keep in mind you won't know the actual % loss until you have designed the entire driveline and run the simulations. Maybe your driveline team had an unlimited budget and you get 90% of it down on pavement, maybe you build an AWD and only get 75%. See point 3 in the below bullets for more on why this number varies.

    I've also attached a revised ICE power flow.

    Please note:
    • SAE net HP is measured at the crank and includes all installed engine components, belts, and accessories, hence the X for that in the image. On an ICE the only other substantial power draw reducing the published SAE net hp would be the A/C compressor, and that would max out a a few hp when the compressor clutch is engaged. But, when you floor it in an ICE the A/C compressor clutch is disengaged so that it doesn't reduce power.
    • The 85% figure post transmission is crossed out as that number varies widely. Really, no one measures hp at the transmission output shaft either. But if they did the number would still vary based on transmission type. A torque converter automatic not in lockup would have much higher loss number (with additional variance depending on the transmission) compared to a wet clutch DCT. However, I believe you intended the 85% number to be power at the wheels, in which case:
    • Post transmission you have additional losses from driveshafts, differentials, axles, etc. A 15% loss from crank hp to wheel hp is certainly accurate for some vehicles, yes. You can look up drivetrain losses for RWD, FWD, and 4WD -- they are all different. Go look up a dyno for a Subaru and see how much higher the losses are there. As I said, it is pretty dang close in some cases, but that number is not some standard to use as in your examples.

    As this relates to the clarity, there is zero need to 'hold back' 15%, nor use this as any sort of metric (though I will admit it lines up nicely with my previous calculations). As in the ICE design, the goal is to get as much of the total system power to the wheels. In this case Honda is able to get 181hp output from the electric motor from a total system power of 212hp. I'm not qualified to argue exactly what gets lost where (none of us are) so lets consider it like this:

    212 total system hp -> [black box of mystery losses] -> 181hp electric motor output

    If you look up the Clarity and Accord hybrid transmissions, you'll find the design is strikingly similar. I don't know for sure but would speculate that they probably do share the same electric motor and a number of electric components, and this is why we see the 212hp/181hp numbers for both.

    Also noteworthy is how much harder Honda runs the Accord hybrid HV battery. Had they used the same power cells in the Clarity and pulled the same current you'd have Tesla like power in the Clarity (they'd have to make a whole new driveline, but one can dream).

    Attached Files:

    Last edited: Sep 17, 2021
  6. insightman

    insightman Well-Known Member Subscriber

    The Clarity's motor (unless Honda upgraded it) is an earlier design than the Accord Hybrid's motor. Honda says the i-MMD Accord Hybrid's motor uses no rare-earth elements. @JeffJo says the motor doesn't matter in the total horsepower calculation so it's strange that Honda specifies 212 total hp for both the Clarity PHEV the Accord Hybrid despite the Accord Hybrid's more powerful (143 hp vs 103 hp) engine. The Clarity's larger battery must perfectly balance out its smaller engine to generate exactly the same total horsepower?
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  8. Guess this wasn’t your last try after all.
  9. Random.Clarity

    Random.Clarity New Member

    Your guess on the motor is as good as mine.
    The Clarity is on the 2nd gen system, yes. The motor could be the older or the newer design. We can also debate everything covered in this thread indefinitely. The difference between the 2nd and 3rd gen systems could be as simple as Honda just liking the 212/181 numbers.

    As we'll likely never know which explanation of the 212/181 numbers is right, and can keep beating this horse indefinitely, I'm calling it quits here.
  10. insightman

    insightman Well-Known Member Subscriber

    I thank you and everyone who participated in this thread. Honda could have made this thread unnecessary had they simply explained how they arrived at their magical 212-hp number. To those I frustrated, I am sorry that my years of reading horsepower ratings for ICE vehicles left me unprepared to comprehend Honda's logic.

    One last question: The purpose of numerical ratings is to enable customers to compare one vehicle with another. Do other hybrid vehicle manufacturers use the same method to rate their vehicles' horsepower?
  11. Random.Clarity

    Random.Clarity New Member

    In general, hybrids and plug ins give the equivalent of total system power and electrics give the motor output. Honda is the exception here by providing both.
    insightman likes this.
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