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

1. You suggested a formula that requires input values from two devices: the traction motor, and the gas engine.
2. We know the result of this formula for both the Clarity and the Accord: 212 HP.
3. If these input values are determined by only those two devices, the gas engine's values will be higher form the Accord than the Clarity.
4. Obvious conclusion: there is a third device that limits the contribution from the gas engine, to the same value for both cars.

I didn't catch that you are suggesting that the clutch has a limitation. Again, this is not my area, but I don't see why that should be so. Besides, there is no practical way that the maximum power is achieved in Engine Drive Mode. The clutch disengages before even a quarter of that power is achieved.

If that were the cause, we should get different numbers. Not the same numbes.

Again, it seems obvious to me that (and I have argued that) the 232.2 lb-ft and 181HP limitations represent a limit placed on the throughput of either battery system, regardless of what the battery could do outside of the car. We have even graphical evidence that the motor is capable of operating above the (232.2lb-ft,181 HP) line, but the specs do not permit it.

Except maybe in Hybrid Drive mode, where there is an additional electrical push supplied by the generator. This could enable the combined system to beyond the (232.2 lb-ft,181 HP) line, but the throughput limitation is again the same in the two cars.

Here's my made-up example: The plot Ray B provided suggests the motor can go at least as high as 250 lb-ft and 250 HP. But...

Clarity:

• In EV mode, say the larger battery is capable of powering 300 lb-ft, or 250 HP.
  • The PCU limits the throughput of the single device to 232.2 lb-ft, or 181 HP
• In Hybrid mode, the ICE could potentially add 103 HP of electricity.
  
  • The PCU ups it power limit on the throughput to 212 HP.
  • The two devices could each operate at less than the known limitations; say, 80 HP from the ICE and 132 from the battery.

Accord:

• In EV mode, say the smaller battery is capable of powering 250 lb-ft, or 200 HP.
  • The same PCU again limits the throughput of the single device to 232.2 lb-ft, or 181 HP
• In Hybrid mode, the ICE could potentially add 143 HP of electricity.
  • The PCU ups it power limit on the throughput to the same 212 HP.

 

I'm not sure which plot you are referring to. If you mean the one where I overlaid the engine torque plots, then at ~6000 RPM the plot shows that the system is producing 250 N*m of torque (184.4 ft-lb). So the power would be ~210 hp. When I estimated the RPM at 225 N*m I got ~6700 RPM which is 212 hp. So it appears that this overlaid plot represents the actual performance that Honda claims.

I think your description of the attribution of the power is right, and does explain how the Accord and Clarity end up at the same power figure. The flowchart I showed in my earlier message tells a similar story about how the motor draws power from the generator (i.e. from the ICE) as well as the battery, and the PCU and DC-DC converter manages the power to deliver on the demand.

 

Hi @insightman - can you link to the Honda descriptions of the Hybrid = 181 hp and the EV = 121 hp. I believe the numbers, but I just want to read up on it a little more, and figure you have some sources I haven't read yet.

Every reference on Engine Mode makes it clear that it is strictly for efficiency while driving on the highway at relatively constant speed and flat grades (ie very modest power demands), and as you and others note, once you ask for a sudden acceleration it immediately switches to Hybrid Mode, as that provides more power.

Anyway, there is surely some confusing info coming from Honda, and we have to be like forensic investigators to piece together what they publish, and what is observable fact, and what assumptions are reasonable. Although almost none of it comes without reasonable doubt.

 

I have a different feeling. While I have no explicit reason to doubt the 121 HP number, I have no reason to believe it, either. All I have seen is people claiming that it is what "Honda says," but never with a reference to Honda actually saying that. I've even asked for a reference, but none is forthcoming.

And there are reasons that imply it can't be. For one, that should mean that the Clarity should have either a 181 HP max (the traction motor's rating), a 121+103=124 HP max (simple addition), or some linear combination such that 121*x+103*y=212. But in each case, the same logic applied to the Accord gives a number that is not 212, and not the same as the Clarity's.

 

Thanks @insightman - I have read plenty of references to the 181 hp rating of the traction motor, as you mentioned.

My thinking is, and I doubt anyone here agrees with me, the 181 hp rating is for maximum continuous hybrid mode output, and the 212 hp is surge power for no more than 5-10 seconds. It may be a moot argument since 181 hp cannot be sustained for much longer than that before the car would top out at maximum speed. The exception would be for a steep incline, but it would probably have to be pretty steep to be able to hold a power level of 181 hp for a significant period of time.

Anyway, that is my conclusion when looking at all the plots and data. I welcome other points of view, as I don't think I have definitive proof by any means.

I ran acceleration tests today in ECON and SPORT mode, and hit a maximum power of 183 hp at the wheels in SPORT mode. When Googling around I found that the difference between the "at the wheels" versus the "at the flywheel" is about 15% less due to transmission and other losses in a standard ICE car. For this car we can debate about how much loss would be reasonable between the advertised power and the power "at the wheels" - if it is ~10% loss then the 212 hp would be ~190.8 hp.

In acceleration tests I measured 177 - 183 hp at the wheels. So if that is accurate (no guarantees of that), then for a max motor output of 181 hp, then the gearing and bearings, etc. would have ~0% loss to get that result. It seems to be more reasonable that hammering the throttle opens up the potential to go past the 181 hp maximum (continuous) power for a brief period of 212 maximum peak horsepower before it scales it back to avoid overheating. If true, and I was touching that peak hp, then I was getting about 13.7% loss to achieve the observed 183 hp at the wheels. I think 13.7% loss is more realistic than close to 0%, but again, my OBD is a crude device, so I don't think the data would stand up to intense scrutiny.

I welcome others with OBD units to try some acceleration tests, to see if my results are repeatable.

By the way, the maximum RPMs I was observing were in the 5500-5600 range (probably at the max power of the engine ... 103 hp).

Another observation is that in ECON acceleration, the power meter dial on the dashboard was always hesitating at the spot where the white section at the far right doubles in width (about 90% of the travel). In SPORT mode I noticed on the highest power run that it went immediately to the full power position (the dial went all the way over to the maximum). Perhaps the ECON mode would have eventually got there if I had continued to higher speed, but the SPORT mode allowed it to go maximum power without hesitating. Perhaps that widened section of the power meter is where it can temporarily allow to go beyond 181 hp. Again, just guessing.

Someone needs to email Shimizu-san.

 

As far as I can tell, no claim from Honda of 121 HP under EV alone power exists. I'm not doubting it, I just haven't seen it.

It is good to finally see a source, but Car and Driver could have misinterpreted something. But if it is true, either the 181 HP number or the 212 HP number is meaningless. Neither can apply when the car is in Engine Drive Mode (although 212 could apply when the clutch is forced to stay engaged despite efficiency motivations), and at least one should be different than the Accord's number.

This would be consistent with the PCU having both a current limit (torque is proportional to current until physical limitations are reached) and a power limit. I also don't believe the Accord will stay in EV mode as long as the Clarity, supporting the idea that its battery is less powerful. But barring a huge coincidence, with a more powerful ICE and a less powerful battery, then the total system powers should be different.

 

If you refer to the overlaid plot I posted the green EV area tops out at 121 hp, so this result checks out.

Calculation:

@ 150 N*m, the green EV line is at ~5700 RPM. (150 N*m = 110.6 ft-lb)

Power [hp] = Torque [ft-lb] * RPM / 5252 = 110.6 * 5700 / 5252 = 120 hp​

For the current Honda Accord Hybrid, the battery is only 1.3 kWh (1/13th of the Clarity PHEV), and there is no way it could hit the same power level, as the traction battery (even at a full charge) would be depleted extremely fast. My guess would be that the maximum power from the hybrid battery would be tens of horsepower.

Can it not be true that 181 hp represents maximum continuous power and the 212 hp represents peak horsepower (for a brief surge)? This paper (https://www.researchgate.net/publication/322454931_Electrical_Vehicles_-_Practical_Solutions_for_Power_Traction_Motor_Systems) has plots of motor power capability of a PHEV and they clearly show separate plots for peak power and continuous power for the same motor. In that case the max continuous power rating was 102 kW and the peak was 120 kW. I'm no expert on the topic, but it seems reasonable to me.

I don't see it as a coincidence. They have the same traction motor, so I assume the peak and maximum power ratings are the same. The fraction of those power levels that come from ICE/generator and EV battery are obviously going to be different. As I said, the tiny Accord hybrid battery (in comparison) will necessarily have a lower power capability, and the difference will be made up with the more powerful ICE.

 

I am lost... lol

 

I agree with you, that's what I posted 2 days ago on this thread.

 

Coming back to this after 2 1/2 years, there's a perfectly sound explanation.

The first detail that is important, is what "212 HP" would mean in a conventional gas car. It will be identified as "SAE Net," which is a standard established by the Society of Automotive Engineers. It is a rating for the engine, not the car. They put the engine on a test bench, along with whatever peripherals it needs to operate (like oil and water pumps). But no peripherals that ony the car needs, like power steering and brake compressors. SAE Net is the total power that the engine can provide to all of the things the car needs power for. There is no easy formula for how much of this power can be applied to the wheels, but a typical estimate is 85%. I won't claim that is a universal constant, but it will come up again.

Next, the 181 HP rating for the traction motor is its maximum input power. In drive mode, the traction motor doesn't produce power. It converts electrical power produced by the generator and/or the battery into kinetic power. Just like SAE Net is the power produced by a gas engine. This number does not contribute to the 212 combined HP for the Clarity/Accord, but it does establish design parameters.

The "combined HP" of any of the Honda iMMD hybrids is the total electrical power that can be produced by the combined efforts of the ICE-driven generator and the battery. It may be that the battery can produce more, but the Power Control Unit of the Accord or Clarity can't pass more than 212 HP to all of the devices that require power from the system.

How do I know this? Well, it is consistent with everything Honda has published. Then, I had a private correspondence with Alex Dykes (from Youtube's "Alex on Autos"). He passed on part of a conversation he had with Takeshi Wakamatsu, a senior engineer at Honda. I had dropped that name to demonstrate that I had read a certain research paper. By coincidence, he had talked with TW that week about this very issue. TW's response was "it [212 hp] can be achieved at any speed by the generator at max output and the battery at max output."

But to validate what I have said, let's look at all of the iMMD hybrids that Honda has produced in the States:

• 2014-15 Accord PHEV.
  • Combined 196 HP
  • 166 HP traction motor
  • 85% of 196 HP is 166.6 HP
• 2017+ Accord Hybrid, CR-V Hybrid, Clarity
  • Combined 212 HP
  • 181 HP traction motor
  • 85% of 212 HP is 180.2 HP
• 2019+ Insight
  • Combined 151 HP
  • 129 HP traction motor
  • 85% of 151HP is 128.4 HP

 

You’ve validated what you’ve said by using your own, contrived estimate.

Hell, a gas engine doesn’t make power either. It just converts the energy that’s stored in gasoline.

And, it’s kinetic energy, not kinetic power.

 

There are two devices here that extract stored, chemical energy and turn it into electrical power ("power" because it is a rate of energy transfer). Both feed a device called the Power Control Unit, or PCU. Which sends electrical power to the traction motor. And maybe I should have said the motor adds to the kinetic energy of the vehicle by sending mechanical power, but that can be called kinetic power.

I'm saying that the power budget PCU allocates about 15% of its maximum possible output to peripherals, and 85% to electric propulsion. And I didn't make these numbers up, it is a common convention. And one that Honda is clearly using here.

I'm saying that this is a design consideration for the PCU and Traction Motor. I don't know which device determines their sizes (it probably is the motor), but they have a fixed relationship: The Traction Motor's power rating (which is the maximum input power) is 85% of the maximum output power of the PCU.

I'm saying that it may not (despite Takeshi Wakamatsu's exact words) have anything to do with the specific power capabilities of the two sources of electrical power to the PCU (ICE-driven generator and battery); except that their sum should be capable of meeting or exceeding it.

181 HP (or if you prefer, 135 kW) is the maximum power that the PCU will pass to the traction motor.

 

It seems like a lot of folks here are making the same argument, just from different perspectives.

Lets word it differently: The battery + engine can produce 212hp. 181 of that is output by the motor due to losses in the power electronics and electric motor efficiency.

212hp total power -> power electronics -> electric motor -> 181hp output.

Assume the power electronics are 95% efficient and the motor 90%:

212*0.95 = 201.4
201.4*0.90 = 181.26

I'll also note that electric motor input is typically measured in kW, not horsepower. So when Honda says hybrid mode boosts the electric motor to 181hp, they're talking about the output of the motor. Consider that we don't list gas engine power as the energy the gasoline it burned contained and these numbers make more sense.

 

Also noting the use of kW vs horsepower, you'd also typically measure battery output in kW, but I assume Honda did not here to avoid a split rating (103hp+81kw total power) that most consumers wouldn't understand.

Also noteworthy is that the accord hybrid and clarity each have a unique PCU. So why they both are rated the same power is either a limit on the electric motor or simply marketing. Why have the weird phev (that you don't really want to sell many of because you lose money on each) outshine the mass market, more profitable model?

And since I can't edit my previous post, I'll add here that the Honda press kit states:

Propulsion motor peak output: 181 horsepower and 232 lb.-ft. of torque

Therefore the motor input must exceed 181hp, further supporting the claim that total power is 212hp, prior to entering the power electronics.

 

I'll try one last time, but it seems to me that many don't want to accept anything that contradicts their initial impressions.

First, I'll admit that I may have confused motor input and output power ratings. I did read that somewhere, but there is little significance to the distinction- the motor is at least 95% efficient over most useful ranges. But I also wouldn't put faith in the exact words of a document that says 212 is the "Total system horsepower as measured by the peak, concurrent output of the two electric motors and gasoline engine," when an accurate combination can't use all three at once.

What I'm saying is that a conventional car's power flow looks like this:


I didn't include losses that can occur in each gray box. The blue circles indicate where a power that is important to propulsion can me measured. And I did not make up that 85% number, You can find it in many places. Like here:


The maximum horsepower of a Honda iMMD hybrid can only be obtained in Hybrid Drive It clearly it can't be in EV Drive, and Engine Drive is only for low power situations. So here is a similar diagram for Hybrid Drive:



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.

But SAE Net HP is not the equivalent design goal for a serial hybrid car. What can come out of the PCU is. If the same 85%. Since it was determined that our cars need a HP motor (whether that is input or output of the motor is irrelevant), the same rule of thumb says the components that convert stored energy (gasoline and lithium) to flowing energy (power, electrical in this case) should be capable of 181 HP. Yes, electrical power is conventionally expressed in kilowatts, but a car's power production is conventionally expressed in horsepower.

Note that the traction motor does not contribute to this 212 HP rating.