Honda Hybrid - the best explanation I've seen!

At the risk of disrupting the revelation on the 212hp mystery, do we really believe it takes 200-212hp to propel a relatively aerodynamic, 4000lb sedan along a freeway at 80-85mph?

As a point of reference, a document from Caterpillar demonstrates that a 34,000lb motorhome equipped with a C7 diesel engine rated at 350hp and 860tq would require 200hp to propel the coach along a smooth, flat surface with no wind at 72mph. This is a vehicle that has 90 sq/ft of frontal area and a Cd of .60.

I’ve hit ~80mph in EV mode, which is 121hp at most, and the car is reportedly capable of going 100mph in EV mode (121 hp).

I’ve also driven hundreds of miles at a time at ~80mph while achieving 36-40mpg. What would the fuel consumption rate be if the car was continuously producing 200hp for 3-4 hours?

I’ll take a stab and suggest that less than 50hp is required to keep a Clarity moving along at ~80mph.

 

Your estimate of less than 50hp to drive ~80mph (assumed steady state, flat highway, dry road surface, no headwind, etc) seems reasonable, although I have not done the math to confirm. Higher power levels are only needed to accelerate, or maintain highway speeds up a hill or mountain, or against a headwind, etc.

I've driven 85mph and accelerated up to about 90+mph (shhh, don't tell) while remaining in EV mode; which means this was done on battery power and therefore within the ~121hp battery power limit.

Alex on Autos excellent video was using the Accord Hybrid primarily in his discussion examples, which has a much smaller battery, but larger 2.0 liter engine compared to our Clarity. The Accord Hybrid small battery means its contribution to high power can only be sustained for a short burst after which max power drops to the 143hp engine limit. A Clarity PHEV with a full charge could sustain peak power for a longer burst (within heat dissipation/cooling limits) after which max power drops to the 103hp engine limit. The balance of at what speed and for how long high power levels can be maintained for these two cars varies, but neither can sustain 200+hp for 3 to 4 hours (I estimate a few minutes for the Clarity, less than a minute for the Accord). I believe Alex's point is that in real world driving, most of us will never use the ~212hp peak and will only experience the 181hp electric motor max power, but because of the overall powertrain efficiency and high torque available nearly instantly, the car still feels like a car with good power.

I enjoy zipping around, especially in town where its fast and quiet, but also on the freeway for high speed cruising or passing. The car feels like it has more than "~212hp" for a 4,000+lb sedan.

 

I was tempted add the phrase 'maximum horsepower' in my discussion... and it is clear that I should have added it.

At 85 mph, the drive system can develop 212 HP at the synchronous speeds. It can also produce 50 HP, depending on the amount of gas/electric supplied to the engines. It is the difference between flooring a manual transmission to go up a hill, and feathering the throttle on an open road: The engine RPM and road speed are the same, but the HP generated are very different.

 

I looked at the Caterpillar document again and it had data for an “automobile” as well as various diesel powered motorhomes.

At 80mph the car would require 43 hp to overcome aerodynamic and rolling resistance. The 34,000lb motorhome would require 184hp at 70mph.

 

How is it that Honda rates the Clarity PHEV, the Accord Hybrid and the CR-V Hybrid all at 212 hp when they all have 181-hp motors, but the Clarity has a smaller engine? That 212-hp rating drives me crazy, just like having the Clarity start up its engine and burn fuel to expend excess electricity from regen braking when the battery is fully charged (when the Accord Hybrid simply uses the starter motor/generator to spin a deadened engine).

 

Good point. I think Honda engineers will have to answer why the three have the exact same rating. I think part of the answer is the much larger stored energy and power rating of the Clarity battery (17kWh and 121hp or 90kW) compared to the Accord Hybrid's much smaller battery (1.3kWh and assumed 69hp or 51kW, though only for a very short burst). I assume 69hp or 51kW because that is minimum needed to add up to the claimed 212hp with the 143hp 2.0 liter engine.

Keep in mind: kWh is an amount of energy, and power is the rate of doing work (the rate energy is used to do work).

Assuming each car's control system allows use of up to 80% of the battery kWh (and neglecting thermal management limitations):
17kwh x 80% = 13.6kWh, and 13.6kwh / 90kW = 9 minutes Note: Assumes full battery and neglects heat buildup; in reality it probably cannot do this.
1.3kWh x 80% = 1.04kWh, and 1.04kWh / 51kW = 1.2 minutes Note: It is less than this because the Accord Hybrid tries to keep its small battery somewhere in the middle of its capacity range, so a more realistic time is probably about half a minute, maybe even less.

Anyway, the Clarity's larger battery provides a greater percentage of the power, and that's how it can reach 212hp with only a 103hp 1.5 liter engine. And yes, I realize 121hp from the battery plus 103hp from the engine is more than 212hp. I assume there are system losses and/or the powertrain control system limits it to the 212hp published.

 

Not to insight further debate on the 212hp mystery.

When the 103hp ICE is in Engine Driving Mode it operates in a very narrow window of hp and torque. EDM quickly disengages when additional power is demanded. I believe we can conclude that EDM is not a factor in the peak hp calculation.

EV Driving Mode, on its own, can be ruled out as it can only provide 121hp.

This leaves us in HV Driving Mode. In this mode, the ICE drives a generator which provides 60hp to the traction motor. Combined with the Lithium batteries, which provide 121hp, we are now at 181hp. The rated output of the traction motor is 181hp.

The SAE International document, titled: Development of Electric Powertrain for Clarity PHEV, contains the following sentence:
“When the vehicle is driving at high speeds or is operating under high loads, such as when climbing a hill, the VCU boosts voltage in order to drive the motor.”

Is it possible that this boosted voltage can increase the output of the 181hp motor by 17% to 212hp for brief periods of time?

 

I disagree with the 'intention' of this statement.

"Very narrow window of hp and torque" is a subjective statement, but when my Clarity is in Engine Drive Mode (gear showing) the power meter ranges from zero to right about double the power output shown when the ICE is running alone. I would not define that as a narrow window of HP and torque.

"EDM quickly disengages" is also subjective. The EDM disengages when the battery state of charge drops about 5% from the HV set point. The battery SOC drops quickly when there is a large draw on the battery, but it will maintain double power of the ICE for several minutes.

I still believe the 212 HP is a legitimate claim for the Engine Drive Mode.

It would have been nice if the Honda engineers had allowed us to use the full 80% range for Engine Drive Mode, or even 20% of the battery. This would allow us to experience the 212 HP for longer periods.

If they did optimize the power output to 88 mph, I would forgive all of their other engineering weaknesses.

I agree that the boosted voltage could increase HP of the motor, but I would be surprised if that increased HP was not given as the rated HP of the motor.

 

Totally agree. Why would Honda undersell the power of their electric motors when they're willing to claim an unexplained total of 212 hp?

 

Figure 7 on page 4 of the aforementioned document, displays what I view as a very narrow window for EDM operation.

The complete statement was: “EDM quickly disengages when additional power is demanded.” This is based on my experience and observations. I have nursed the car to 85mph in EDM. It appears that Honda designed the car to reach ~100mph in EDM.

Other conditions may exist that cause EDM to disengage. I mentioned one that I have observed which occurs with impeccable consistency.

I have to disagree with this claim. The only way the car is going to produce 212hp is when the pedal hits the metal. EDM is out of the picture when that happens.

 

Here’s the document.

 

I know this is a three-year-old thread - I just found it. I just can't leave all of this misinformation uncorrected, even though I have explained it elsewhere (and I'm not sure I was believed). Also, I'm not trying to talk down to anyone, which I think may have been the impression there.

Most of what non-automotive engineers think they know about an ICEV's drivetrain is pretty superficial. And that's not a bad thing, because they don't need to know more. The problems come up when they try to translate that superficial knowledge to Hybrid Electric Vehicles and Battery Electric Vehicles. Those drivetrains simply do not work the same way, and the knowledge does not apply, even superficially.

POINT #1: Electric Motor Generators (MGs) do not perform the same task as Internal Combustion Engines (ICEs). Or more accurately, an ICE performs two tasks, and an MG performs only one of them - arguably the less significant one. The ICE (1) converts stored energy into usable power and (2) converts that usable power into mechanical power in the form POWER=TORQUE*RPM. An MG needs some other device to turn stored energy into usable power in the form POWER=VOLTAGE*CURRENT, and the MG changes that into POWER=TORQUE*RPM.

POINT #2: The power rating of an ICEV is the maximum power that the ICE can put out. It applies at only one rpm, so it is almost never possible to achieve. I suppose a perfect CVT could do it, but I'm not sure that any will choose that rpm. And it is measured at the crankshaft, with the ICE taken out of the car and put on a test bed. The point here is that this power rating is meant for comparison only, not to suggest it can be applied to propulsion.

POINT #3: Other devices in the car need power, and in an ICEV they take it from the crankshaft. Then there are losses in transmission. So even if the ICE runs full throttle at the right rpm, not all of that power can reach the wheels. An estimate that I have heard in several places (one is here) is that at most 85% of the ICE's maximum power can reach the wheels. I don't know how good that is, or how commonly it is used, but I do know Honda uses it.

POINT #4: The power rating of an MG in an HEV or BEV is completely different. It is the power that the MG can convert to mechanical power, and it is applied after all other power draws and most other losses. Essentially, it can be considered to be propulsion power. While I'm not suggesting that the power curves work the same way in ICEVs and EVs, the simplest comparison is that an ICEV "has the same power" as an EV whose MG is rated at 85% of the ICE rating.

POINT #5: These Honda iMMD hybrids achieve maximum power in Hybrid Drive, not Engine Drive. That is, clutch open, not closed. That is the 181 HP MG in the Clarity, Accord, and CR-V. In order to fully power this MG, using the same 85% rule, the electrical system would need to provide 181/0.85=212 HP of electrical power. This is where the 212 HP rating comes from. It is a value for comparison, not a rating of any part of the system. It can probably make more, but (according to the estimation rule) never needs to. Before 2023, every Honda iMMD hybrid used this same method - the HP rating of the HEV was the HP rating of the drive motor, divided by 0.85.

POINT #6. Only a serial hybrid can use this simple method; other types mix ICE power and MG power. I don't know when it happened, or how it works, but there now is an ISO standard for the HP rating of an HEV. It makes some measurement of performance, and gives the HEV the rating of an ICEV with the same measure. Like I said earlier, since the power curves are very different, this really isn't meaningful. But the pre-2023 Accords and CR-Vs were "downgraded" to 202 HP. I don't know about the Clarity.

 

Thanks for resurrecting this thread to provide more information. I probably questioned the 212 HP rating more often than anyone else on this forum--especially questioning why the 212 HP rating applied to all Honda hybrids (gen 3 Insight excepted), regardless of engine size and HP. Where did the 85% rule come from?

 

That was probably the strongest clue that the 212 HP rating is based entirely on the 181 HP motor, since the power production (ICE-->Generator plus battery) is so different in the two cars. Then the fact that the 2014 Accord (196 and 166 HP) and Insight (151 and 129 HP) had the same ratio cemented it.

I don't know. It seems to be entirely empirical. Based on the discussion in that link, I'd say it was an estimate made by "tuners" of the best observed wheel HP, compared to the ICE's rating. But I have seen it in multiple places, and that link called it "universal." So whatever estimation accuracy applies seems to apply across platforms.

 

Can Alex, or anyone else explain how the 103hp engine in the Clarity can produce 212hp while operating in EDM?

Isn’t the engine the sole source of power in Engine Drive Mode?

 

<Sigh.>I thought I had, numerous times. Alex does a very good job, but he still gets this detail wrong. I even wrote him an email explaining it, where I cited a Honda research paper about the ICE in the Accord. All the data I will present will be about the Accord specifically, since that is what I have. But the same concepts apply to the Clarity.

The lead author of that paper was Takeshi Wakamatsu - I dropped that name in my email just to prove that I had the actual paper. This is important because Alex wrote back (emphasis added):

Thanks for the email, I was actually at dinner with Takeshi Wakamatsu last night at the CR-V launch event. We discussed the system in great detail and he has no general issues with our video.
...
The only area that Wakamatsu-san pushed back on any front was their claim of total system HP. The claim is that it can be achieved at any speed by the generator at max output and the battery at max output, however he admitted only 181HP can come from the traction motor. It’s a game of semantics because even in this mode they like to say the system makes “212” horsepower while some would say no, it is only making 181.​

No. Wakamatsu-san confirms it, but few seem to comprehend it. Even Alex.

• No, the engine is not the sole source of power in Engine Drive. The electric motor can add to it, but seldom will. If more than, oh maybe 40 to 50 HP is needed, the car will drop out of Engine Drive and into Hybrid Drive.
• This is because Engine Drive uses a fixed gear ratio. In the Accord, that means RPM=37*MPH. At 54 mph, this puts the engine at its maximum efficiency speed, 2000 rpm and 40.6% thermal efficiency. But it gets 40.6% only at 34 HP. The maximum power it can produce at that speed is about 44 HP, and efficiency drops. At 75 MPH, this changes to 2750 rpm, maybe 40.4% best efficient at 48 HP, and a max of 66 HP.
• To get the engine's max power, it has to run at 6200 rpm. That would be 167 mph.

Maybe a graphical description would help. I drew this up maybe a year ago (and no, I don't think the transmission is driven by a belt; I think I drew it that way to compare to a BEV).


Like Wakamatsu-san, the 212 HP power produced is the electrical power than can be sent to Power Control, just like in a 212 HP conventional ICE vehicle it is the SAE Net power of the ICE. The max power on the road is estimated to be 85% if that. Honda simply uses this estimation backwards: the motor can put 181 HP on the road, but to do that it needs electrical power of 181/0.85=212 HP at the same point where SEA Net power occurs.

Alex gets the "semantics issue" he mentioned wrong. The ICE and the battery are the only devices that "produce" power. The motor acts more like the transmission in a conventional car; it transfers power from one place to another, transforming it in the process. A transmission transforms it by applying a variable gear ratio. A motor converts it from electrical to mechanical power.

 

<Sigh.> lol

 

Did you seriously attempt to explain this numerous times?

You’ve now explained the 212hp as being produced from the electrical power that can be sent to Power Control.

I’ve maintained throughout, that maximum power can only be achieved by utilizing the electricity from the battery and ICE driven generator and that EDM is a non-factor in that situation.

Perhaps we’re not understanding each other, but I’d enjoy hearing your explanation of how the car can produce 212hp or 181hp while in EDM.

 

Maybe you haven't seen the other thread, but the person I was replying to was quite active on it. But there are two here.

I didn't say it happened in Engine Drive. It happens in Hybrid Drive. ICE+generator (Accord) produces about 140 HP. Battery produces over 70 HP. JUST LIKE THE LEAD ENGINEER ON THE ENGINE DEVELOPMENT SAID. By "the generator at max output, and the battery at max output." I even drew a diagram using the exact same two sources you named for the combined power.

What's the problem?

 

Well, I asked the question above. You quoted it and provided the exasperated answer above. From that, it sounds as though you’ve explained numerous times how the Clarity can make 212hp while operating in EDM mode.

Is that clear enough?