[pasei]

Hey guys,

Gasoline engine tend to be the most efficient at around their peak torque, which is for the 3rd Gen Insight 99 lb-ft @ 5000 rpm. It's true for both Otto and Atkinson cycles. In conventional cars, it's impractical to be in these high RPMs, but in the Insight it's not really an issue because the ICE is not directly connected to the gears (unless at constant speed on the highway).So you would think you would generate electricity the most efficiently by revving the engine at high RPMs while somehow maintaining a constant speed.

Now we can't really control the RPMs vs. actual acceleration other that playing with the ECON/ Sport buttons et the battery charge. I've read that some people use Sports mode when going flat to charge the battery in anticipation of an upcoming hill. I suppose that makes the ICE work less harder when going up the hill. But what if going uphill was a perfect case of high RPM and constant speed? Which would mean best efficiency?

Basically what I'm wondering is if there are cases when high RPMs (loud engine) would be beneficial in terms of mpgs. And using uphill with the cruise control seems like a good example to me, where it would actually be more beneficial to have a low battery at the start of the hill.

This is just a theory that went through my mind (as you guys know by now I love weird theories haha). What do you guys think?

 

[insightfully]

Basically what I'm wondering is if there are cases when high RPMs (loud engine) would be beneficial in terms of mpgs. And using uphill with the cruise control seems like a good example to me, where it would actually be more beneficial to have a low battery at the start of the hill.

I wish this were the case. I have a 500 ft hill in my daily drive, which is great on the descent (full battery on arrival) but hard on the return trip.

Climbing back up the hill is laborious, and reduces the 'instant fuel economy' for every combination tried (hi/lo speed, hi/lo battery, mode). The "least MPG hurt" I've seen on the climb is with ample HV battery, to minimize use of the gas engine. The "most MPG hurt" (and noisiest ride) has been from low HV battery level on the climb.

However there's note in the Owners Manual that one of the "severe" operating conditions is low speeds (electric motor running?) on hills/mountains, since the transmission operating temperature increases and degrades the transmission fluid faster than normal conditions. - https://www.gen3insight.com/forum/25982-post26.html

 

[maynyrd150]

So what do you mean by efficient? it could be that the least amount of fuel for any given rpm is reached at peak torque rpm but if that is a significantly higher rpm, you are belching more air and fuel out the engine than you would at a lower speed and stabbing economy in the face like Booth on Seward.

great if the goal is maximum torque all the time but i dont think that's that we're all after

 

[insightfully]

Good point. If max torque is the objective, that happens at lower (3000) RPM and with the electric motor, rather than the gas engine.

GAS ENGINE ONLY = In-Line 4-Cylinder
107 HP @6000 RPM -- 99 lb-ft torque @5000 RPM

ELECTRIC MOTOR ONLY = AC Synch Magnet
129 HP @4000-8000 RPM -- 197 lb-ft torque @0-3000 RPM

 

[maynyrd150]

Good point. If max torque is the objective, that happens at lower (3000) RPM and with the electric motor, rather than the gas engine.

elec motor can make all the torque at zero rpm but doesn't matter here. i think what the OP is after is economy instead of efficiency, but they could mean the same thing under the right circumstances.

maximum economy for an individual should be achieved when the driver is conveyed from A to B with conditions that are just above intolerable (speed and acceleration) so that the car uses the least amount of energy (horsepower or kilowatts, whatever unit you want to use, not distinguishing between gas or electric).

if you always drive a 100hp car like it only has 40hp (constrained to that limit) it will have economy closer to a 40hp car, minus losses due to larger rotating and reciprocating components (friction and larger air/fuel ratio). not a rule, but how i like to visualize it.

 

[pasei]

I wish this were the case. I have a 500 ft hill in my daily drive, which is great on the descent (full battery on arrival) but hard on the return trip.

Climbing back up the hill is laborious, and reduces the 'instant fuel economy' for every combination tried (hi/lo speed, hi/lo battery, mode). The "least MPG hurt" I've seen on the climb is with ample HV battery, to minimize use of the gas engine. The "most MPG hurt" (and noisiest ride) has been from low HV battery level on the climb.

However there's note in the Owners Manual that one of the "severe" operating conditions is low speeds (electric motor running?) on hills/mountains, since the transmission operating temperature increases and degrades the transmission fluid faster than normal conditions. - https://www.gen3insight.com/forum/25982-post26.html

Thank you! I guess I missed the notification for your reply.

By efficient I mean at which rpm of the ICE, you get the most kWh produced by gallon of fuel. But then there is the generator efficiency also. I supposed Honda reasonably optimized all of this already so probably not much we can do, except as you said, bank battery before climbing hills.

 

[pasei]

I wish this were the case. I have a 500 ft hill in my daily drive, which is great on the descent (full battery on arrival) but hard on the return trip.

Climbing back up the hill is laborious, and reduces the 'instant fuel economy' for every combination tried (hi/lo speed, hi/lo battery, mode). The "least MPG hurt" I've seen on the climb is with ample HV battery, to minimize use of the gas engine. The "most MPG hurt" (and noisiest ride) has been from low HV battery level on the climb.

However there's note in the Owners Manual that one of the "severe" operating conditions is low speeds (electric motor running?) on hills/mountains, since the transmission operating temperature increases and degrades the transmission fluid faster than normal conditions. - https://www.gen3insight.com/forum/25982-post26.html

So for your big hill, speed has no huge impact? There is no optimum speed?

 

[insightfully]

So for your big hill, speed has no huge impact? There is no optimum speed?

Temperature has more of an effect than speed on HV battery charge for me. I get to full battery faster/easier in warm weather; in cool weather, the battery is slower to charge and/or doesn't end up as 'full' while driving the same driven speed.

 

[pasei]

Temperature has more of an effect than speed on HV battery charge for me. I get to full battery faster/easier in warm weather; in cool weather, the battery is slower to charge and/or doesn't end up as 'full' while driving the same driven speed.

Oh yes, but I meant in terms of mpgs, what speed gives you the best results uphill?

 

[insightfully]

Oh yes, but I meant in terms of mpgs, what speed gives you the best results uphill?

I have yet to find a 'good' combination of speed and again, it also depends on starting battery level and ambient temperature conditions. Anything uphill results in fuel economy loss. I've just accepted it and try to get the best mpg I can on the downhill drive in to offset.

 

[andrew28]

https://youtu.be/y4Z1CihGNR4?t=143
Toyota recommends letting the incline decrease your speed instead of trying to maintain a set speed.

 

[pasei]

https://youtu.be/y4Z1CihGNR4?t=143
Toyota recommends letting the incline decrease your speed instead of trying to maintain a set speed.

I'll try that tomorrow on the left lane of I-93 :grin::grin::grin:

Joke apart, yes, I did that with my Mazda too. But for long hills it'd be good to know what's the impact of speed.