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

[M.M.]

No, I meant exactly what I typed.

Re-reading what you said, I think I follow now. And I suspect you're correct, that it's technically possible, with the mechanical transmission engaged, at some particular speed under some particular set of circumstances, the ICE puts out X horsepower (with X < maximum theoretical) through the clutch and the electric motor puts out Y horsepower (with Y < maximum because of the relatively high speed), and X + Y = 212hp.

The slight difference between theoretical maximums is probably as simple as that the horsepower curve for the ICE with mechanical transmission (which goes up with speed for the most part) plus the horsepower curve for the electric motor (which drops at higher speeds) peaks at a point where neither is quite at its maximum.

Certainly not meaningful in any real world sense, regardless. It is, as noted, suspect that it's the same number as a car with significantly different ICE and battery output capability.

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.

I had missed that, so yeah, I take back anything I said about that graph, it's garbage and completely meaningless.

This is not really contributing to the discussion here (I'm out of my depth past the theoretical physics of it), but this dyno graph of a Tesla and a Dodge Charger between 0 and 155mph is a much better illustration of why torque and particularly horsepower measurements between an ICE and an EV are a poor comparison at best when talking about how a car drives in the real world.


It doesn't say what year Challenger SRT that is, or if the P85D was in its drag-race mode or not, but in any case on this dyno the ICE is peaking at around 640hp and the Tesla at 550hp, but the way the cars will perform is wildly different. From a standing stop through 40mph the Tesla is producing drastically more torque and power so is going to accelerate faster, while at faster-than-highway speeds the transmission in the ICE is keeping it at near-maximum torque and power while the EV falls way off. And of course the ICE bounces around as it shifts (though the torque is quite smooth because this is an extremely high-performance ICE with a very flat torque curve). Basically why Teslas boast preposterous 0-60 times but aren't going to perform at the same level as an ICE with a similar horsepower rating at speeds over 90mph.

The Clarity PHEV (and presumably Accord PHEV) will probably look different from this with some sort of discontinuity around 50mph because the mechanical transmission may come into play at higher speeds if you're using the ICE.

 

[JeffJo]

Here is my problem with the modes in the diagram provided by LegoZ. I took the following diagram from a paper titled "Development of SPPORT HYBRID i-MMD Control System for 2014 Model Year Accord." I realize that it is a cartoon, and there are more details that go into it. It is a newer version of the one I posted yesterday. Some values probably have changed a little, but that doesn't really matter since the values were not provided.

The green region is where EV mode can be selected. The top value should be 232.2 ft-lb, the maximum torque the drive motor is rated for. The boundary with the blue region approximates a constant HP curve; supposedly 121 HP.

• But as drawn, it has to be much, much less than 121 HP.

The blue and red regions are where the ICE is running, but the clutch is not engaged. Along the boundary between them, the ICE is providing exactly enough power for propulsion; any surplus (blue) or deficit (red) is matched by the battery. That boundary also looks like a constant HP curve, but nobody has claimed to know what that HP is. In fact, it should depend on how much power the ICE is producing, which is completely independent of car speed. But what is drawn is a constant HP curve.

• The difference between your 103 HP Clarity, and my 143 HP Accord, is that my boundary will be placed higher than yours. So there is no problem with the HP values as labeled.

The red curve represents the limit of the drive motor. Since both the Clarity and Accord claim 181 HP, it is in the same place for both.

• This would mean that both ICEs, when supplemented by the battery, are capable of exceeding that 181 HP limit. But the combined power is limited by what the drive motor can handle.

The brown rectangle is where the clutch is engaged. It does not represent a constant HP. I suspect mph is shown with 10 mph intervals, so this plot goes up to only 90 mph.

• If 212 HP represents a point in the brown region, then it has to extend out to 167 mph for my Accord, and probably a little less for your Clarity. I've added those numbers, and they combine to 202 HP for my Accord, and something much less for your Clarity.
• If 212 HP represents extending the brown region up - that is, if the clutch would stay engaged under higher power requirements - then it should be extended to a different point for my Accord than for your Clarity. So we can't both have 212 total HP.

I think the green line is much less than 121 HP; in fact, to accelerate to 25 mph without crossing the green line requires much less than the 121 HP claimed.

Because the 212 HP limit does not change with the ICE, I think it is the red line.

The exact location of the blue line, which will vary, depends on the 181 HP limit and the ICE.

The brown region is determined by efficiency, not HP.

 

[David Towle]

It seems to me the ENGINE DRIVE MODE pic above is incorrect. I don't see how the traction motor could simultaneously be driving and generating, so the generator/starter motor would have to be sending power straight to the traction motor/generator (like in the HV CHARGE MODE pic) to get to a total near 212 hp.

 

[JeffJo]

It seems to me the ENGINE DRIVE MODE pic above is incorrect. I don't see how the traction motor could simultaneously be driving and generating, ...

You are misinterpreting what it is saying. In ENGINE DRIVE MODE, the double-sided arrow means that electricity can flow in either direction between the traction motor and the battery, depending on whether the ICE produces a surplus or a deficit. Not that it flows in both directions at the same time.

... so the generator/starter motor would have to be sending power straight to the traction motor/generator.

It can't. Here's a picture that provides different details. The PCU is the Power Control Unit, which is a computer that decides how to route electricity. Unlike an ICE, where there is resistance to any externally-created rotation, the generator spins freely if the PCU doesn't draw current from it.

 

[M.M.]

The green region is where EV mode can be selected. The top value should be 232.2 ft-lb, the maximum torque the drive motor is rated for. The boundary with the blue region approximates a constant HP curve; supposedly 121 HP.

• But as drawn, it has to be much, much less than 121 HP.

I'm not sure about the Accord, since it has a larger ICE, but that graph is not accurate for the Clarity, and it's sort of conceptually confusing because of its structure--you have the lines labeled correctly (the blue line will be around 100hp for the Clarity PHEV and 150hp for the Accord PHEV, minus generator efficiencies in both cases) but it implies that the EV slice at the bottom is a separate range in which the car operates, which might be true for a mild hybrid like an older Accord but does not apply to full PHEVs like the Clarity (and, I assume, the newer PHEV Accord).

Fundamentally, for a full PHEV the graph isn't showing ranges, which the under-curve-area labeling you have seems to imply, it's just multiple overlapping graphs:

• An EV Mode graph (the green line)
• A Hybrid Mode graph (the blue line, red line, and the region above and below the blue line)
• An Engine Drive Mode graph (the yellow line)
• Plus a fourth that is not shown there: Engine Drive + EV assist

Also keep in mind that while the middle of the curve will be matched to horsepower output, it's going to fall off at the right side.

In the Clarity, EV curve will be much farther to the right than the Hybrid Drive curve, because the battery can put out more power than the ICE. The Accord PHEV it will presumably be farther to the left because of the smaller battery pack and larger ICE.

The entirely separate Hybrid Drive mode will have a roughly 100hp (minus generator efficiency) line that is farther to the left than the EV curve. In the Accord PHEV it's presumably a little farther to the right than the EV curve because of the larger ICE. This is the dark blue line on your graph.

Everything underneath that "maximum ICE-only output" line (not just the region between EV and the line) would be a "capable of charging" region, in which if the electric motor is not being asked to put out maximum torque for that speed, the ICE can direct excess power to the battery (in reality it may or may not depending on state of charge and mode). Then there will be a region above/to the right of that "maximum ICE-only output" line, which is pink on your graph, that shows the region in which the battery is assisting the ICE->Gen->Motor combination.

The Engine Drive mode at the bottom there is, as drawn, a third independent graph, although I would think in reality it wouldn't be that flat because of the torque curve of the ICE.

And then there's a fourth, not-shown, graph, which is Engine Drive plus electric motor assist, which is going to start at about 45mph, be closer in shape to the other curves, but will have a different shape because of the speed-dependent torque curves of the ICE+transmission and the electric motor.

If Honda's specs are honest, that final, fourth engine drive + hybrid drive curve has one individual point on it that is 212hp.

 

[JeffJo]

I'm not sure about the Accord, since it has a larger ICE, but that graph is not accurate for the Clarity...

By my understanding, the Clarity is a PHEV. That means it operates in two phases. The first uses only EV mode - the ICE will not turn on. The second begins when the battery is depleted to a certain level, and then it acts as a "full hybrid" just like the Accord. That means it alternates between EV, Hybrid,and Drive modes as appropriate. The graph is accurate for that period, and that period is the subject of this thread.

...you have the lines labeled correctly (the blue line will be around 100hp for the Clarity PHEV and 150hp for the Accord PHEV, ...

The Accord is not a Plug-In Hybrid Vehicle, or PHEV. It is just a Hybrid, and operates only in the second phase I described. And the blue line applies to situations requiring more HP than just EV mode, which you claimed was 121 HP for the Clarity.

...minus generator efficiencies in both cases ...

All the values I've mentioned assume efficiencies have already been applied.

... but it implies that the EV slice at the bottom is a separate range in which the car operates, which might be true for a mild hybrid like an older Accord but does not apply to full PHEVs like the Clarity

The graph was taken from a paper describing how Honda engineers implemented a full hybrid, and applies to both the Clarity PHEV (in its hybrid phase) and the newer Accord (at all times). Not to a mild hybrid, which by definition has no EV mode.

In the Clarity, EV curve will be much farther to the right than the Hybrid Drive curve.

Not in the Hybrid phase I described.

Everything underneath that "maximum ICE-only output" line

There is no such line. The brown region is where the clutch's overdrive gear - Engine Drive - is more efficient than hybrid mode. It has nothing to do with maximums.

The Engine Drive mode at the bottom there is, as drawn, a third independent graph, although I would think in reality it wouldn't be that flat because of the torque curve of the ICE.

Tell that to the engineers who wrote the paper describing i-MMD.

And then there's a fourth, not-shown, graph, which is Engine Drive plus electric motor assist, which is going to start at about 45mph,

That is the brown region.

 

[Ray B]

I don't have a good answer for the original question, but I found a few charts on the i-MMD system of the previous generation with the 124 kW motor and the current 135 kW motor, and a few other supporting graphs and details. It doesn't get to the root of the question but it may resolve a couple unanswered questions.

First, although the parallel mode of engaging the clutch and at the same time driving the wheels by pushing EV battery power to the traction motor (so called 'Engine Drive Mode') would seem to be the logical way to add up power to push beyond the motor limit of 135 kW, this does not appear to be the case as some have already stated. In one of the papers from the Honda Accord iMMD with the similar propulsion design ("Development of Motor and PCU for a SPORT Hybrid i-MMD System") you can see that the amount of electric motor torque present in Engine Drive Mode is pretty limited:

So I think we can rule out Engine drive mode as a potential to get up to 158 kW / 212 hp.

Also, I found charts of the torque vs RPM for the older 124 kW motor and the current 135 kW motor, and one that has both plotted together:


If we overlay that chart and the Torque vs speed chart for the Clarity PHEV that they have published in various papers, including the SAE paper, you get this:


Which appears to show that the total system power will exceed the published motor torque vs RPM curves (comparing the black line to the red line). When you calculate where the new black line for torque vs RPM is you can calculate ~158 kW of power (just eyeballing the line and reading numbers from the axes and then calculating power). So it does appear that they show power exceeding what the motor can do. And the result lines up very well with what they say is the maximum combined power level.

But they do call out the "max torque" in at least one translated source as "target". So perhaps the system is engineered to stay at or below that limit but can exceed it under the right conditions. One Google translated source said that "According to the test results of the Japanese energy department, the Accord has a fuel efficiency of 30 km/L petrol and a combined output of 158 kW." So perhaps this external entity ran a test or simulation based on Honda data to come up with the 158 kW number. Who knows?

In another source, they show a plot with motor efficiency figures which go beyond the "max torque" - so perhaps it can be "overclocked" (Accord iMMD motor with 124kW max power, 307 Nm max torque):


In other references they show that the torque they achieve is due to the voltage amplification of the EV voltage achieved by the VCU (again this chart like many of the others is for the Accord iMMD 128 kW motor with 307 Nm max toque):


So perhaps by juicing it up a little more with power from the generator and the battery combined it can go beyond the 700V to get to the 158 kW power level. Also, I believe there is a maximum voltage of the Clarity PHEV motor as 650V rather than this 700V for the Accord. There is about 100x as much data and charts for the previous iMMD cars compared to the current Clarity PHEV drivetrain.

In any event, I doubt there is a practical way for the average driver to get up to that level of torque and power unless it was under very specific conditions.

Anyway, I am not sure I got anywhere in all of this but I thought I would at least push out what I have found in Googling and Google-translating many of the Japanese and Chinese sites.

As a last chart, I will show how the iMMD system figures out how to manage the flow of energy to provide what is 'asked for':

 

[M.M.]

Ray B posted some good graphs there, particularly that layered one in which the engine drive mode looks like what I'd expect it to, and how it feels in practice.

The determination that the max HP number may indeed not be due to point with combined mechanical and electric drivetrain output is interesting. And at least in theory it is certainly possible--an electric motor can handle higher than rated maximum power for a brief period of time before overheating, so its totally possible that in Sport mode during hard acceleration it will briefly be allowed to hit a higher power output before it gets thermally limited. Sort of a very low-key version of Tesla's ludicrous mode, which pre-cools the motors and battery pack for short-term rapid acceleration.

As for what I had posted previously, caveat: I can only speak for the Clarity PHEV, and my understanding is based on a combination of driving the thing, general understanding as an electric controls engineer with a physics degree, and documentation in this thread and elsewhere about the vehicle's drivetrain.

By my understanding, the Clarity is a PHEV. That means it operates in two phases. The first uses only EV mode - the ICE will not turn on. The second begins when the battery is depleted to a certain level, and then it acts as a "full hybrid" just like the Accord. That means it alternates between EV, Hybrid,and Drive modes as appropriate. The graph is accurate for that period, and that period is the subject of this thread.

We might really be saying the same thing here and just looking at it differently, but how the Clarity PHEV behaves depends entirely on what mode it's in and the current state of the battery. If it's in EV mode and you don't push the accelerator past the detent, it operates as a full EV within the limits of the electric motor and battery output capability.

If you put it in sport or normal mode, it will behave like an EV unless you push the accelerator past a certain point, at which point it behaves as an EV with additional assist from energy generated by the ICE/generator. This is sort of the mode thatI think we're discussing, since we're looking at maximums, although because the mechanical transmission can still engage while in this mode at higher speeds it is not necessarily differentiated from the engine drive mode.

If you put it in hybrid mode OR deplete the battery to the point it automatically drops out of EV mode, it operates roughly like you described; it generally will attempt to generate as much power as is going to the wheels with the ICE, but depending on state of charge may run the ICE harder to recharge the battery or use more energy from the battery if there is excess. In the event the battery is very depleted, it will be limited to energy supplied by the ICE. But, again, it will engage the mechanical transmission if and when it thinks it's efficient, so in practice this mode gets blended with the brown region.

And when the mechanical transmission is engaged, the vehicle can and will supplement the output of it with the battery and electric motor, based on the power flow graph the car displays and perceived performance. This effectively blends into the two above modes based on speed and what torque region you're operating in. Conversely, if the torque requirements are low (such as going downhill) I believe it will disengage the mechanical linkage, so it will never run in part of the region under the brown line. I could be wrong about that last bit, though, I haven't driven the car in that mode very much.

My description of what the Clarity's graph probably looks like is based on the above, and could of course be mistaken.

Not in the Hybrid phase I described.

Again speaking only for the Clarity, that EV region in hybrid mode is not a single defined line, it moves around constantly based on the state of charge of the battery and maybe other factors. If we're talking about maximum performance acceleration (which anything toward the top of the torque curves basically is), and you're in Sport mode, I'm pretty sure it will start the ICE proactively for hard acceleration even if it can't make use of the extra power for the first 20mph or so of acceleration because of the electric motor being torque rather than power limited.

On the flip side, if the state of charge is low, the ICE could be running at 5000rpm putting nearly its full output into the battery and the remainder to the wheels even though you're driving at 20mph on a slight downhill and the torque is almost zero.

There is no such line. The brown region is where the clutch's overdrive gear - Engine Drive - is more efficient than hybrid mode. It has nothing to do with maximums.

It was not clear to me that the brown region was most efficient, rather than the whole region of where it runs in engine drive mode, but the little spike in the graph visible in the stacked one Ray B just posted looks a lot more like what I'd expect it to look like in practice based on limited experience driving in that mode.

At least as you have it labeled, the dark blue line--the curve over which the ICE running at peak horsepower output can exactly supply the needs of the electric motors--is the line I'm describing. That line will be a blend of the torque limitations of the electric motor at lower speeds and the horsepower-limited curve of the ICE at higher speeds. At all torque/speed combinations below that line, there is excess power available from the ICE to charge the battery if desired, and everything above it cannot be achieved without additional power from the battery. So, minus efficiencies, the middle part of that blue line would be the horsepower limit of the ICE.

 

[Ray B]

If you put it in hybrid mode OR deplete the battery to the point it automatically drops out of EV mode, it operates roughly like you described; it generally will attempt to generate as much power as is going to the wheels with the ICE, but depending on state of charge may run the ICE harder to recharge the battery or use more energy from the battery if there is excess. In the event the battery is very depleted, it will be limited to energy supplied by the ICE. But, again, it will engage the mechanical transmission if and when it thinks it's efficient, so in practice this mode gets blended with the brown region.

Yes, and I think the highest EV battery power available is at the highest state of charge, preferably for a warm battery:


If the EV battery is depleted, I think the amount of power available will drop by a considerable fraction of a fully charged battery. But then again, there is a lot of controls in between as shown in the flow chart I showed at the end of my post. So it is anyone's guess how it is managed by the PCU computer.

At least as you have it labeled, the dark blue line--the curve over which the ICE running at peak horsepower output can exactly supply the needs of the electric motors--is the line I'm describing. That line will be a blend of the torque limitations of the electric motor at lower speeds and the horsepower-limited curve of the ICE at higher speeds. At all torque/speed combinations below that line, there is excess power available from the ICE to charge the battery if desired, and everything above it cannot be achieved without additional power from the battery. So, minus efficiencies, the middle part of that blue line would be the horsepower limit of the ICE.

I think so but I am not certain. The ICE tops out the power at 103 hp at 5500 RPM. For the car's top speed of 100 mph (I think), with the clutch in (Engine Drive Mode) that would be ~3750 RPM engine speed which would be a lot less than 103 hp - probably ~75 hp. So to get higher power you can ask the battery to crank the electric motor, but that only provides a modest amount of boost. To get more power, you need to disengage the clutch and ask the ICE to spin faster to drive the generator and combine that energy with a high energy flow from the battery, preferably with a high SoC I would think.

 

[insightman]

The Accord is not a Plug-In Hybrid Vehicle, or PHEV. It is just a Hybrid

Back in 2014, Honda made a limited number of Accord Plug-In Hybrid cars. The 6.7 kWh battery was good for 13 miles of EV travel.

 

[JeffJo]

...In one of the papers from the Honda Accord iMMD with the similar propulsion design ("Development of Motor and PCU for a SPORT Hybrid i-MMD System") you can see that the amount of electric motor torque present in Engine Drive Mode is pretty limited:

All that means, is that outside of that range the clutch disengages.

My point is that, while the Clarity PHEV and the 2018+ Accord HEV have the same traction motor, the Accord's ICE is 33% larger (and 143 HP to 103 HP). Yet they have the same combined power of 212 HP. So that number can't be a result of simply adding the ICE's horsepower to the traction motor's, no matter where in that plot you do it.

Also, I found charts ....appear(s) to show that the total system power will exceed the published motor torque vs RPM curves (comparing the black line to the red line).

The black line in that plot consisyt of three portions: a constant TORQUE= 232.2 lb-ft from RPM=0 to about 4100, a functional TORQUE=181*5252/RPM curve from RPM=4100 to 12,500, and a red-line form RPM at 12,500. To me, that means it is a property of the Power Control Unit (PCU). Since TORQUE is proportional to the current I, there must be a maximum I that the PCU can draw from the battery; I don't know what limit is. But there is also a maximum power it can draw from the battery, P=I*V=135 kW=181 HP (yes, I know this ignores efficiency).

But when you add in electrical power from the ICE+generator, the power limit goes up to the same number, 212 HP, for both vehicles. The ICE+generator could make more, but the system won't accept it. There really is not other explanation that makes sense.

But they do call out the "max torque" in at least one translated source as "target". So perhaps the system is engineered to stay at or below that limit but can exceed it under the right conditions. One Google translated source said that "According to the test results of the Japanese energy department, the Accord has a fuel efficiency of 30 km/L petrol and a combined output of 158 kW." So perhaps this external entity ran a test or simulation based on Honda data to come up with the 158 kW number. Who knows?

SAE J2908, which is implied to be the standard for combined power that Honda uses, seems to say a hybrid's combined power shod be measured at the axle. That is not inconsistent with my hypothesis, except including the ICE's rpm rate in the statement. Not all statements do.

In any event, I doubt there is a practical way for the average driver to get up to that level of torque and power unless it was under very specific conditions.

Rated horsepower never is. I estimated that my 2001 Accord manual transmission had to find a hill so steep that I had to downshift into second to maintain 55mph, in order to achieve its rated 150 HP. But few drives realize that they never use the rated power, it is for comparison to similarly-designed power plants only. Which is why comparing the Accord and Clarity, or other i-MMD systems, is really the only valid use of the number. Which is part of my point here.

As for what I had posted previously, caveat: I can only speak for the Clarity PHEV, and my understanding is based on a combination of driving the thing, general understanding as an electric controls engineer with a physics degree, and documentation in this thread and elsewhere about the vehicle's drivetrain.

Same for me with the Accord. But, while I conjecture that either PCU can take 135 kW (181 HP) from the battery alone, I doubt very much that my puny battery can do so for any significant amount of time. Yours might, but mine needs help from the ICE sooner. On the other hand, your squirrels probably won't like boosting it up to 212 HP for very long, while mine might. This is the takeaway I'm looking at.

We might really be saying the same thing here and just looking at it differently, but how the Clarity PHEV behaves depends entirely on what mode it's in and the current state of the battery.

I'm mostly talking about after you start using the ICE. But I think there is potential for a small misunderstanding here:

If it's in EV mode and you don't push the accelerator past the detent, it operates as a full EV within the limits of the electric motor and battery output capability.

If you put it in sport or normal mode, it will behave like an EV unless you push the accelerator past a certain point, at which point it behaves as an EV with additional assist from energy generated by the ICE/generator.

"EV with additional assist from energy generated by the ICE/generator" is Hybrid Mode.

For the Accord at least, Honda uses ambiguous terminology. I usually try to use this set:

• "Drive" defines what powers the wheels, and how. So ...
  • "EV Drive" means the car uses battery power only, to drive the traction motor and hence the wheels.
  • "Hybrid Drive" means the ICE is powering the generator, and the traction motor is powering the wheels. The battery adjusts the power flow up or down to meet the need. So it still "behaves as an EV."
    
  • "Engine Drive" means the clutch is engaged, so the ICE is powering the wheels. The traction motor+battery system adjusts the power flow up or down to meet the need.
• "Mode" defines how the car mixes the Drives.
  • "EV Mode" uses EV Drive only.
    
  • "Hybrid Mode" means the car oscillates between the three drives, as needed.

The Accord is always in Hybrid Mode unless you press the "EV" button on the console. I assume the Clarity PHEV starts in EV Mode, and drops into Hybrid Mode if the charge gets low, or you press the pedal past the detent. And yes, I've been discussing only Hybrid Mode.

Again speaking only for the Clarity, that EV region in hybrid mode is not a single defined line, it moves around constantly based on the state of charge of the battery and maybe other factors.

See where I said "other details." At least, I think that is what I called them.

It was not clear to me that the brown region was most efficient, ...

Hybrid Drive lets the ICE run within a small range of efficient rpms, even if the power there is not the same as the need. Engine Drive is for when it is the same. That's why it isn't for higher torques - switching to Hybrid Drive lets the engine run faster than the wheels to produce more power. Just like down-shifting in a manual transmission.

 

[ryd994]

?????

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.

For example, engine provides 50hp over the clutch and 50hp as electricity. Then battery provides 112hp, so that the motor can provide 162hp.
162+50=212
Actual composition vary, but this looks totally valid for me.

 

[JeffJo]

For example, engine provides 50hp over the clutch and 50hp as electricity. Then battery provides 112hp, so that the motor can provide 162hp.
162+50=212
Actual composition vary, but this looks totally valid for me.

But it is obviously not how they arrived at 212 HP number.

The Accord Hybrid has the same 181 HP traction motor, and a more powerful gas engine (2.0L, 143 HP compared to 1.5L, 103 HP). So in the same situation, its engine could provide 70 HP over the clutch and 70 HP as electricity, making 232 HP. Yet it has the same 212 HP total-system power rating.

 

[LegoZ]

Max power has to be developed below 100mph as Honda cuts all electric power at the that speed. Max power above 100mph can only be 103hp. Likely the hp rating if the gas engine is at the flywheel, the electric side at the axle and combined is also at the axle.

We still need someone to rig up a go pro and do a 40-80mph full throttle run with the vehicle information screen to see if the lock up stays engaged. This, in my mind is the only way the system could work.

 

[insightman]

Max power has to be developed below 100mph as Honda cuts all electric power at the that speed. Max power above 100mph can only be 103hp. Likely the hp rating if the gas engine is at the flywheel, the electric side at the axle and combined is also at the axle.

We still need someone to rig up a go pro and do a 40-80 mph full throttle run with the vehicle information screen to see if the lock up stays engaged. This, in my mind is the only way the system could work.

When I floor the accelerator in Engine drive mode, my Clarity immediately returns to Hybrid drive mode, whereupon the 181-hp traction motor alone is turning the wheels. It appears to me that the 212-hp number is meaningless because 181-hp is the maximum available when accelerating and the car can't use the "212-hp" Engine drive mode to achieve a constant high speed that would require 212-hp because the car is electronically limited to 100 mph.

 

[JeffJo]

Max power has to be developed below 100mph as Honda cuts all electric power at the that speed. Max power above 100mph can only be 103hp. Likely the hp rating if the gas engine is at the flywheel, the electric side at the axle and combined is also at the axle.

I haven't found an actual statement from Honda declaring a top speed. Reviews at Car & Driver say my Accord's is 115 mph, which is consistent with a maximum rpm of around 12,500 for the traction motor. That's also about where the info from Honda that I have seen says it red-lines.

The Clarity supposedly has the same gear ratios and larger tires (235's to 225's), but C&D says its top speed is 101 mph, consistent with what you say. And not the 12,500 red-line. That's why I only run numbers on my Accord - I get more consistency.

FYI, in lock-up mode the Accord's engine speed is roughly RPM=37*MPH. If the only difference in the Clarity is the larger tires, it would be RPM=35.4*MPH.

When I floor the accelerator in Engine drive mode, my Clarity immediately returns to Hybrid drive mode, whereupon the 181-hp traction motor alone is turning the wheels.

Consistent with the speed/drive-force diagrams provided earlier.

It appears to me that the 212-hp number is meaningless ...

I try to distinguish between "having no meaning," "having little practical meaning," and "having comparative meaning." A conventional ICE's horsepower rating has little practical meaning, because even if you achieve the conditions where it is produced, you won't stay there for long. But it is good for comparison to similar ICEs.

So I don't expect a maximum horsepower rating to have practical meaning. But can I use this 212 HP number for comparison? My motivation, at least at first (it is mostly theoretical now) was to understand the difference between a 212 HP Accord Hybrid, and a 208 HP Camry Hybrid. The systems are quite different from each other, and the strengths of each are at different speeds, but these two numbers do seem to come close to the overall difference.

... because 181-hp is the maximum available when accelerating.

If true, it would also have to be the maximum available when maintaining a constant speed requires a lot of power (going uphill). It is drive-force, not acceleration, that determines this.

But I'm not sure that is true. As I have claimed before, I don't think the 181 HP is a physical limit of the traction motor itself. I think it is a limitation of the electrical system in between the battery and the traction motor. It just can't, or maybe just won't, let enough (battery amperes)*(battery volts) to pass through. This is consistent with the shape of the traction motor's torque curve.

But if you can add in some generator power, you might be able to push the traction motor harder. And there would be a different (total amperes)*(total volts) limit that has nothing to do with how much power the ICE can generate.

Based on 181 HP, the Accord's traction motor crosses from being torque-limited (232.2 lb-ft) to power-limited at about 36 mph. At 212 HP, this goes up to 43 mph. And it produces about an extra 25 to 30 lb-ft of torque for acceleration above that 36 mph.

 

[ryd994]

But it is obviously not how they arrived at 212 HP number.

The Accord Hybrid has the same 181 HP traction motor, and a more powerful gas engine (2.0L, 143 HP compared to 1.5L, 103 HP). So in the same situation, its engine could provide 70 HP over the clutch and 70 HP as electricity, making 232 HP. Yet it has the same 212 HP total-system power rating.

Not obvious for me, please explain.

Assume Clarity and Accord Hybrid use the same electric powertrain with only ICE different.
The max power of motor is the same. The max torque through the clutch might be same as well.

Final power on wheel = power from motor + power from clutch
Since motor and clutch are the same, the max power is the same. It can be different if the clutch is different or ECU logic is different, but I won't be surprised when it's same.

On the other hand, I can also come up with another hypothesis: Accord hybrid has a much smaller battery. Although more power from ICE, there is less power from battery. At the end of the day, they add up to the same 212hp.

Maybe neither of my hypothesis is true, but all I want to say is that 212hp max combined is not impossible.

With larger engine, the advantage of Accord hybrid is where extended HV use and battery is depleted,
which is common for a hybrid, but not so common for a plug-in hybrid.

 

[Ray B]

At the risk of re-igniting the debate about power, I found this plot in the SAE paper (https://www.sae.org/publications/technical-papers/content/2018-01-0458/preview/) on the Clarity's DC-DC converter that describes three different power tests in real-world driving scenarios. The third one ("Period III") is aggressive slam the accelerator pedal to the floor type of test that one would get on a 0-60 run. In that instance, because the power demand is at its highest and the click-point in the pedal is exceeded, the engine comes on and provides the needed extra power. To be clear, there is no clutch engaged, so this is not "Engine Drive" mode, it is hybrid drive.



They do not outright say in the paper that the result is 212 hp available, but I think that it again makes it clear that the maximum power is achieved in Hybrid mode. In my limited testing I recorded almost 180 hp at the wheels in such acceleration tests (same as @Viking79 on page 1 of this thread). But those were in ECO mode - I should repeat them in SPORT mode to see if I get a different result. Stay tuned.

 

[David Towle]

My understanding is there is no difference in power with the accelerator fully floored between econ, regular, and sport. All that changes is how much power is produced per unit of accelerator travel. Is this right?

Maybe the answer is that the electric motor alone produces the 212 hp, from a combo of ICE/generator and battery, but is only able to do that for a few seconds and the 180 hp rating is continuous. If you measured 180 hp at the wheels (how?) it means the motor must be producing something more than that. That would explain why the Accord hybrid has the same exact rating.

 

[Ray B]

My understanding is there is no difference in power with the accelerator fully floored between econ, regular, and sport. All that changes is how much power is produced per unit of accelerator travel. Is this right?

That is the consensus here, but I reserve a little bit of doubt about it. I found a couple of instances in their literature which show behavior differences between SPORT and Normal (non-SPORT, non-ECO), that make me believe that yes it is mostly mapping of the pedal, but that it may also change the complex behavior of the systems which decide how much power to enable. I have no direct proof to point to, but just a couple of plots (which I will try to find) that make me suspect it may be more complex than a different pedal constant.

Maybe the answer is that the electric motor alone produces the 212 hp, from a combo of ICE/generator and battery, but is only able to do that for a few seconds and the 180 hp rating is continuous. If you measured 180 hp at the wheels (how?) it means the motor must be producing something more than that. That would explain why the Accord hybrid has the same exact rating.

I measured on flat roads in limited runs (0 to ~50 mph) using an OBD scanner. It is a crude tool, but the estimated result from Torque Pro was almost exactly the same as my calculated result. Many assumptions, so I don't say it is bullet-proof data, but it ended up looking like a realistic value. On the weekend, I'll try it on a quiet stretch of highway and bring it up to a higher speed and try to compare ECO vs normal vs SPORT. If I get anything useful I will post the result either here or in a new thread.