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

[insightman]

I enjoy this discussion, but it does seem that we're all staring at the elevator floor indicator wondering why it didn't stop for us

All we can do is press our ears against the elevator door, hoping to catch some of the conversation on the elevator as it passes us by.

 

[ab13]

Honda wrote in a recent Insight press release, "the Insight is capable of all-electric driving for short distances of roughly a mile." So the traction motor in that car will do more than just get the car off the line.

In the Engine Drive mode segment in Figure 11 from the referenced paper (see the figure in my original post in this thread), the starter motor/generator is in "Zero torque" mode and the traction motor is in generator mode. We know the starter motor/generator is turning whenever the engine is turning because the two are always connected, so I assume that "Zero torque" really means that the starter motor/generator is electrically disconnected to prevent it from robbing the engine of any of the torque it is trying to send to the wheels. It is simply spinning and doing essentially nothing. Meanwhile in this segment of the figure, the traction motor is working as a more powerful generator to recharge the battery (and yes, robbing the engine of some of the torque it is trying to send to the wheels).

If the starter motor/generator can do the "Zero torque" thing, abandoning the electricity it could be generating in Engine Drive mode, then why couldn't the traction motor do the same thing when decelerating to prevent overcharging the battery?

You can do that, you just have to go to friction brakes, which I think is what the Leaf does when fully charged. The system doesn't have a B button mode like the Accord, so it may be automatically engaging a similar mode.

 

[KentuckyKen]

Well, I have to add that on two occasions when ICE came in immediately after a full charge and I pulled over and poped the hood, the engine was definitely running at idle with the car stopped. And my inductive pick up hour meter continued to register time so the spark plugs are being energized.

 

[insightman]

We need Honda to explain how running the engine protects the battery from overcharging and how starting the engine with a full battery serves their dedication to overall efficiency.

Does the engine remain running on all the way down a mountain to accomplish this mysterious form of engine braking?

 

[KentuckyKen]

We need Honda to explain how running the engine protects the battery from overcharging and how starting the engine with a full battery serves their dedication to overall efficiency.

Does the engine remain running on all the way down a mountain to accomplish this mysterious form of engine braking?

I would drive to Honda HQ and pay for the engineer’s lunch if he or she would explain such things!

 

[KentuckyKen]

There is, isn't there? -- the engine icon at the top of the display?

Yes, but I find it all to easy to miss since when lit it’s harldy brighter than when not. I would greatly prefer a separate light on the DII directly in front of me.

 

[KentuckyKen]

It’s safe to say that nobody has an ironclad explanation yet on exactly how the ICE coming on in the fully charged scenario is protecting the battery/aiding braking. So I’m not even going to try.

But allow me to spit ball here and throw this out to the Clarity Brain Trust assembled on this forum as to perhaps why it only happens sometimes.
What if the battery is fully charged at one temp and then the battery temp decreases later before driving away. Then at the lower temp it hold less charge so the BMS set point considers it a little overcharged. Then it more readily triggers the ICE/full charge/no regen thing. Could it be that it’s more likely to happen when the battery for whatever reason is slightly more charged that at other times.
Just guessing here after noticing that it’s not happening to me any more after garage charging and leaving w a/c on.
What do you guys think?

 

[insightman]

I'm hoping someone can answer this question: If the battery is fully charged at the top of a mountain, does the engine start and remain running all the way down to prevent overcharging the battery? This extreme situation could provide reproducible evidence of the engine burning gas to prevent overcharging the battery.

Or does the Clarity instead perform the Accord Hybrid's engine-braking trick of using the starter motor/generator as a motor to turn the unfueled engine to use up all the unwanted electricity coming from the traction motor working as a generator to slow the car? And does the engine icon light up if the engine is turning, but unfueled?

 

[ab13]

We need Honda to explain how running the engine protects the battery from overcharging and how starting the engine with a full battery serves their dedication to overall efficiency.

Does the engine remain running on all the way down a mountain to accomplish this mysterious form of engine braking?

My theoretical guess at one option is that the generator motor can burn electrical power while also using the ICE to create pumping resistance. However, I guess it needs to warm the oil.

 

[insightman]

My theoretical guess at one option is that the generator motor can burn electrical power while also using the ICE to create pumping resistance. However, I guess it needs to warm the oil.

We need some mountaineer to tell us if the Clarity (with its battery as fully charged as the design allows) always starts its engine at the beginning of the descent while using the Clarity's pseudo engine-braking. Said mountaineer can then tell us if the engine stops burning fuel part-way down the mountain after the oil is warmed up. Finally, we need a Honda engineer to tell us how a running engine can resist the starter motor/generator to use up the excess power generated by the traction motor as the descent begins.

 

[PHEV Newbie]

For the Clarity PHEV, Honda says the 1.5-liter, 103-hp engine and 181-hp traction motor (121-hp on battery power only) combination can produce up to 212 horsepower. For the 2018 Accord Hybrid, Honda says its 2.0-liter, 143-hp engine and 181-hp traction motor (unrevealed horsepower on battery power only) also produces a maximum of 212 hp, despite the Accord Hybrid's more powerful engine. Is Honda simply picking a number for the hybrid that's unchallengingly 40-hp less than the Accord 2.0-liter Turbo's 252 hp?

Honda says the 1.5-liter engine in the 2019 Insight hybrid combines with a traction motor of unrevealed power to produce up to 151 horsepower. If that's the same 1.5-liter, 103-hp engine from the Clarity PHEV, then the Insight's traction motor must not be very powerful. Perhaps it's very lightweight compared to the Clarity's traction motor or to the Accord's even newer-design rare-earth-free traction motor. Still, Honda claims the 2019 Insight will "deliver the best power-to-weight ratio in its class."

The difference between the Accord and Insight hybrids to the Clarity is that the Clarity has a battery 10 times that of the hybrids so the combined power from the battery and ICE is equal to the Accord and greater than the Insight despite the Accord and Insight having more powerful and equivalent ICE's, respectively. The bigger the battery, the more power you have to drive the electric motor. That's why Teslas with larger optional battery packs are much faster than models with the same drive motors and base batteries. Thus, the Clarity's battery contributes much more power to the traction motor than possible in either the Accord or Insight.

 

[ab13]

Finally, we need a Honda engineer to tell us how a running engine can resist the starter motor/generator to use up the excess power generated by the traction motor as the descent begins.

Recall that the generator motor is the starter for the ice which means it can take electrical power and turn the ice. So that's why I say theoretically it can pull electricity from the battery or possibly the regen from the drive motor. So by burning electricity by running and using the ice to be a load, it could burn off excess power. The direct gear ratio between the two is for high torque, as compared to the clutched ICE gear, which is for high speed.

 

[insightman]

Recall that the generator motor is the starter for the ice which means it can take electrical power and turn the ice. So that's why I say theoretically it can pull electricity from the battery or possibly the regen from the drive motor. So by burning electricity by running and using the ice to be a load, it could burn off excess power. The direct gear ratio between the two is for high torque, as compared to the clutched ICE gear, which is for high speed.

When the i-MMD starter motor/generator is being used to burn off excess electricity produced by the traction motor slowing the car, why would the Clarity run its engine while the Accord Hybrid simply spins the unfueled engine? I'm sure the gearing is equivalent. The only rationale I can come up with is that the Accord Hybrid's engine and oil will already be warmed up while the Clarity's engine might not.

 

[Pushmi-Pullyu]

The video linked below won't tell you how much horsepower the Clarity's electric motor nor the gasoline engine put out, nor will it help any at all in calculating the combined horsepower put out by the powertrain when both are engaged.

But it will explain how the motor and the engine work both separately and together in different driving modes. The video specifically references the Honda Accord Hybrid, but my understanding is it applies equally well to the Clarity PHEV.

 

[Pushmi-Pullyu]

For those interested in the logic determining when the engine runs during cruising, this paper describes how intermittently charging and discharging the battery provides the highest efficiency (and efficiency, not extended EV driving, is the ultimate goal of the i-MMD system).

Unfortunately, this paper does not describe why the engine might be activated soon after setting out with a fully charged battery.

This ought to be #1 on an FAQ for any forum dedicated to the Clarity PHEV. We certainly have seen a lot of questions about why the Clarity PHEV often turns on the gas engine at the beginning of a drive, even when there doesn't seem to be any logical reason to do so!

​

 

[JeffJo]

I want to understand how Honda calculates the combined horsepower ratings for i-MMD two-motor hybrid systems. Specifically, how the Clarity Plug-In Hybrid can produce Honda's claim of 212 horsepower.

Sorry to resurrect this thread, but I've been trying to figure out the same thing for my new Accord hybrid. And the only conclusion I can justify is that it is an apples-to-oranges comparison. But I wanted to get some feedback on my thoughts.

Horsepower ratings mean different things for different types of drive systems. Since an ICE's torque changes with RPMs, it applies only at one specific RPM value. And even then, only if one specific torque value is required. For example, to exert the advertised 148 HP, my old 2001 Accord manual-trans would have to be on a sufficiently steep hill to require me to downshift into second gear to maintain 55 mph. I never came close to that. I'm not suggesting you didn't know this; the point is that I never expected that car to exert 148 HP. The rating is meant for comparison only; a 200 HP engine in that car would be roughly 34% more powerful in any set of circumstances.

But it seems that isn't what an electric motor's rating is for. Until limits are reached, its torque at any RPM is proportional to the electrical current. Voltage needs to be increase with RPMs to maintain that torque (power is determined by the formula P=I*V) so, while the torque/horsepower curves of an ICE are physical limitations of the engine, for an electric motor they determined by three red-lines: the maximum allowable electric current establishes the constant maximum torque at low RPMs, the maximum allowable electric power establishes the constant power at intermediate RPMs, and the motor's RPM red-line establishes the cut-off.

The question is, are these physical requirements for the motor itself, or for the electrial system that provides power to the motor? The evidence I've seen suggests it is the electrical system. So, for my new Accord, the 181 HP rating "for the motor" is really the maximum power output of the battery; it increases to 212 HP when the ICE+generator assist the battery in hybrid mode. Yes, it theoretically could be 181+143=324 HP, but there are other limitations on the electrical system as a whole that keep it below 212. The Clarity has the same 181 HP motor, with the same limitations on the the electrical system as a whole even though it has a smaller ICE. So it "gets" the same 212 HP combined.

And just like my old 2001 Accord, I don't think anybody ever expects the car to actually achieve, let alone sustain, these HP levels. They are for comparison. But you can't really compare these hybrids to a 212 HP ICE; in fact, my new Accord's 0-60 times are much better than the same Accord with the 192 HP turbo (which beats the Camry's 203 HP engine).

 

[Pushmi-Pullyu]

The rating is meant for comparison only; a 200 HP engine in that car would be roughly 34% more powerful in any set of circumstances.

But it seems that isn't what an electric motor's rating is for.

I don't know if this is relevant to your question, but be aware that the way electric motors are rated for HP is very different than how ICEngines are rated for HP. For ICEngines, the HP rating is the maximum power possible. But for electric motors, the HP rating is the sustained output rating. Momentary output can be higher.

You may think this is a trivial difference, but it's quite significant. You'll see a lot of argument over what the actual conversion rate is, and it depends on the application (for example, lawnmowers need a different ratio than car motors). A brief Google survey suggests ratios between 3:1 (3 HP ICE = 1 HP electric) and 1.5:1. Since I'm not an engineer, I won't offer an opinion as what the exact ratio should be for car motors.

 

[M.M.]

The question is, are these physical requirements for the motor itself, or for the electrial system that provides power to the motor?

The short answer, as partly discussed earlier in this thread, is "both". In nonspecific terms, the maximum power and/or current input into an EV's electric motor can be limited by how much heat the motor can absorb in a short period before overheating, how much heat the motor can absorb over a long period based on its cooling system, how much power can be supplied by the battery pack over a short period before the pack overheats, and how much power can be supplied by the battery pack over a long period based on the cooling capability of the battery pack. With a PHEV you add to that how much additional energy can be supplied by the ICE. With a PHEV with a mechanical transmission like the Clarity you also add in how much energy can be supplied to the wheels directly by the ICE using the mechanical transmission.

For the Clarity, since the rating on the electric motor is higher than what it can put out in EV mode, it's pretty clear that the limit is the battery pack's output, not the motor. Add in the ICE and you have either additional generation capacity going to the electric motor, at low speeds, or maybe additional mechanical motive force at high enough speeds that the mechanical transmission can engage (although the dyno curve I link below implies that all the motive force during hard acceleration is coming from the electric motor).

In all cases it's possible for throttling to occur if the battery pack (or I think motor) is hot, although the only time I've ever seen this was in the other direction when descending a very long hill and the battery pack stopped accepting regenerative charge because it was heating too much for the cooling system to offset. (Irony: Most cars overheat going up a hill; the Clarity overheats going down a hill.)

I don't know enough about the Accord to say how any of this applies to it, other than that it has a significantly larger ICE and, at least in some versions, a full CVT rather than a fixed-gear-ratio linkage like the Clarity, so the power limitations may be more closely linked to the ICE.

Of interest in general, here's a dyno curve somebody did of the 2018 Clarity: https://www.automobile-catalog.com/curve/2018/2616890/honda_clarity_plug-in_hybrid.html



It looks more or less like you'd expect--dead-flat torque from 1000-2500RPM, begins to curve downward gradually through 5500RPM, then falls off precipitously. The power curve, likewise, is a straight line up through 212HP at 5500RPM, then drops off. This aligns exactly with what you'd expect if the ICE were acting only as a generator--there's no discontinuity at all. That also explains why there would be no bump in the curve due to the lag of the ICE spooling up, since the motor is not being limited by maximum capability of the battery to until far enough up the curve for the ICE to have kicked in.

Interesting aside: Depending on design, a PHEV using the ICE has the unusual characteristic that it can essentially act as if it has a perfect CVT--the ICE can be run at its maximum power RPM and loading at any time, regardless of the speed of the wheels (and I suspect it does in the Clarity, hence the "angry bees" some people complain about with low state of charge).

 

[JeffJo]

I don't know enough about the Accord to say how any of this applies to it, other than that it has a significantly larger ICE and, at least in some versions, a full CVT rather than a fixed-gear-ratio linkage like the Clarity, so the power limitations may be more closely linked to the ICE.

The only significant differences are the battery (1.3 kWh, I think, but I've seen it quoted at both 1.1 and 1.7) and the ICE (2.0L, 143 HP to 1.5L, 103 HP). Both have the same "transmission" system. Which isn't really a conventional transmission, let alone a CVT of any kind. Honda calls both an eCVT, I guess because they need to put something that box.

Of interest in general, here's a dyno curve somebody did of the 2018 Clarity: https://www.automobile-catalog.com/curve/2018/2616890/honda_clarity_plug-in_hybrid.html

https://www.automobile-catalog.com/curve/2018/2616890/honda_clarity_plug-in_hybrid.html
Yeah, I've seen it. Here is the comparison between the Clarity and Accord (that site lists the raw data):

The Clarity is the one that is the higher of the two once it tails off, which is not consistent with the difference being the ICE. I haven't been able to interpret what it means, since as far as I can tell the two have the same gearing. But the flat portion of the torque curve - both at 232.2 lb-ft - is why I think it is a red-line for current imposed on the car.

It looks more or less like you'd expect--dead-flat torque from 1000-2500RPM, begins to curve downward gradually through 5500RPM, then falls off precipitously. The power curve, likewise, is a straight line up through 212HP at 5500RPM, then drops off. This aligns exactly with what you'd expect if the ICE were acting only as a generator.

But then the Accord's should be higher. Anyway, my conclusion was that this curve represents hybrid mode only, not direct drive.

Interesting aside: Depending on design, a PHEV using the ICE has the unusual characteristic that it can essentially act as if it has a perfect CVT--the ICE can be run at its maximum power RPM and loading at any time, regardless of the speed of the wheels (and I suspect it does in the Clarity, hence the "angry bees" some people complain about with low state of charge).

I think this is addressed in figures 15 and 16, if I recall correctly, of that research paper. There is a target "hybrid line" that goes through the most efficient parts of the range given the power requirement.

 

[ab13]

For the Clarity, since the rating on the electric motor is higher than what it can put out in EV mode, it's pretty clear that the limit is the battery pack's output, not the motor. Add in the ICE and you have either additional generation capacity going to the electric motor, at low speeds, or maybe additional mechanical motive force at high enough speeds that the mechanical transmission can engage (although the dyno curve I link below implies that all the motive force during hard acceleration is coming from the electric motor).

Clarity EV has exactly 50% more battery capacity by adding a 3rd pack module. That implies PHEV has 2/3 the pack output, the ICE fills in the top ~1/3 if need.