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

It's certainly true that more torque provides greater acceleration. I've never read anything about how much torque the engine can add to the 232 lb-ft from the Clarity PHEV's traction motor. If Honda is going to specify a combined horsepower of 212 hp, why not a combined torque rating?

More horsepower is usually associated with a higher top speed. However, as with my 2006 Insight, Honda's engineers have designed the Clarity to cut off the electric motor's contribution at 100 mph, so the ultimate benefit of more horsepower is moot. My original question was how the Clarity can produce 212 hp when it was not obvious to me that the engine and traction motor were ever propelling the car at the same time.

It appears that as much as 212 hp may be achievable between approximately 45 mph, the speed at which the Engine Drive clutch may choose to engage, and 100 mph, the speed at which Honda cuts off power contribution from the traction motor. Whether this clutch engages during an all-out, 0-60 mph acceleration run has yet to be determined.

 

The confusion that prompted me to originate this thread has been resolved. If I'd looked closer in the first place...

I kept returning to the Honda engineers' 2013 paper describing the efficiency of Honda's i-MMD two-motor hybrid system for the 2014 Accord Hybrid. I finally noticed a blue arrow I'd missed in the 3rd part of Table 2 (see below), which depicts Engine Drive mode (when the OD clutch is engaged). The diagram confirms that the engine and the traction motor can combine their outputs, even though Figure 11 in this paper implies that the traction motor always functions as a battery-charging generator during Engine Drive mode.

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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."

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.

I'm still not convinced the engine is used to somehow burn off regenerated electricity when the battery is already full--especially when the primary focus of the i-MMD system is overall efficiency. When the traction motor turns into a generator during deceleration, couldn't the i-MMD system simply electrically disconnect the generator to prevent it from sending power to a fully charged battery?

 

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?

 

The OD clutch would have to be engaged for the Clarity's engine to perform traditional engine braking, but the gearing is so high in Engine Drive mode that the clutch cannot be engaged at speeds below around 45 mph.

If, indeed, efficiency be damned and the Clarity is bound and determined to do more than use its brakes to slow down, I could imagine the electricity from the engine-powered starter motor-generator somehow being switched to drive the traction motor in reverse to slow the car.

 

Major revelations follow:

Here's what Hybrid Cars reported when they first drove the 2017 Honda Accord Hybrid (I emboldened the critical info):

The driver can freely move the shifter between the normal “D” forward drive and “B” which adds stronger regenerative braking when the accelerator pedal is released and also when the brake pedal is pressed. Cruise control can only be engaged in D. If the battery fills up due to regenerative braking in B the car will dissipate the energy by using the generator to spin the gas engine (known as “engine braking”) rather than using the friction brakes on the wheels.

So the overlooked little starter motor/generator is working in stealth-mode as a motor, turning against the resistance of the unfueled engine to burn off the excess power being generated by the traction motor, which is working as a generator to slow the car down!

It appears the Clarity PHEV provides the false impression that it is burning fossil fuel when the engine icon lights up shortly after setting out with a fully charged battery. In reality, the engine icon lights up whenever the engine is turning, even if no gas is being consumed. Premature enginulation isn't a real thing after all!

Perhaps the Clarity PHEV should not illuminate the engine icon when the engine is spinning without fuel--or use a different color for the icon in that situation. Perhaps Honda should explain this operation in the Owners Manual.

Edit: On 32nd thought, does the engine icon then go out immediately when the full-battery traction-motor regeneration ceases? I don't have enough experience with this phenomenon to answer that question.

 

There would still be air being pumped out the exhaust pipe, right? You'll have to use your nose for this test.

 

Wouldn't the engine perform all its normal lubrication activities when it is being spun by the starter motor/generator?

That evidence is, indeed, perplexing. I wonder if that means the Clarity PHEV goes further than the 2017 Accord Hybrid and actually reverses the action of the starter motor/generator after the starter motor/generator starts the engine? Otherwise, what good would a running engine be in resisting the normal spin of the starter motor/generator to burn off excess energy?

Could it be that Honda doesn't believe a cold engine can properly lubricate itself?