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So I did a roughly 160 mile drive that was primarily highway again but stuck to 75 MPH. The last 20 miles I put it in EV mode and ended at my house with about a mile to spare. Overall MPG was 42 going off of how much it took to fill the tank.
 

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So I did a roughly 160 mile drive that was primarily highway again but stuck to 75 MPH. The last 20 miles I put it in EV mode and ended at my house with about a mile to spare. Overall MPG was 42 going off of how much it took to fill the tank.
You'd be amazed at the mi/gal difference between 75 and 65 mi/hr. The physics of air resistance shows that drag is a function of the square of speed. Twice the speed yields four times the drag. That seemingly minor difference of 10 mi/hr can yield significant savings. I usually sit in the number two or three lane, and tuck in behind a truck, if there's one going 60-65 mi/hr with any consistency. I've found that Swift-branded trucks seem to go about 60 mi/hr pretty consistently. (I suspect that they have tattle-tale devices built into the tractor.)
 

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You'd be amazed at the mi/gal difference between 75 and 65 mi/hr. The physics of air resistance shows that drag is a function of the square of speed. Twice the speed yields four times the drag. That seemingly minor difference of 10 mi/hr can yield significant savings. I usually sit in the number two or three lane, and tuck in behind a truck, if there's one going 60-65 mi/hr with any consistency. I've found that Swift-branded trucks seem to go about 60 mi/hr pretty consistently. (I suspect that they have tattle-tale devices built into the tractor.)
The power requirements go up as the cube of the speed.
 
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So when the traction battery is depleted, the HV is the most efficient mode because EV is not available.
my bad, I didn't read that before posting, it should have said:

"I don't agree, the HV mode is designed to operate the way it does (as a generator) automatically at low speeds not because it is the most efficient. The lower speed use of the ICE to generate electricity and drive the car is required by the lack of a transmission."
 

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However one thing you will notice when watching the energy screen is that it constantly pops in and out of direct drive mode, basically any time there is any change in power needed, as direct drive only works when the power demand is steady. So that means that even at highway speeds the engine will still be acting like a generator part of the time, and directly driving the wheels at other times. And sometimes even shutting off completely and switching to EV mode for a brief period, even a highway speeds it will do that. But I'm sure it's more efficient to be in direct drive as much as possible otherwise they would not have included that functionality. The Chevy Volt did something similar (obermd correct me if I am wrong about that).
perhaps my driving conditions are significantly different here on the Oregon coast (max. highway speed limit is 55mph, almost never need AC, very few other cars/trucks on the road) but when my Clarity is in HV mode it stays in direct drive mode almost all the time over about 46mph and especially over 55mph. I can hear the engine sound change and see the 'gear' on the energy screen vanish if it drops out direct drive and it almost never happens, even when going up uphill on Hwy101.

because I select EV at below 46mph, our Clarity basically operates in either EV or HV direct drive all the time. ¯\(ツ)
 

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perhaps my driving conditions are significantly different here on the Oregon coast (max. highway speed limit is 55mph, almost never need AC, very few other cars/trucks on the road) but when my Clarity is in HV mode it stays in direct drive mode almost all the time over about 46mph and especially over 55mph. I can hear the engine sound change and see the 'gear' on the energy screen vanish if it drops out direct drive and it almost never happens, even when going up uphill on Hwy101.

because I select EV at below 46mph, our Clarity basically operates in either EV or HV direct drive all the time. ¯\(ツ)
I’m sorry. I’m having a hard time understanding your logic and maybe it’s because the printed word doesn’t correctly convey it. I’m truly not trying to be confrontational but why do you need to “select EV at below 46mph”? Are you saying that you always manually select HV charge maintaining mode whenever your speed is over 46 mph? And then do you manually switch this mode off when you fall below 46 mph? And are you basically saying it is more efficient to run in HV charge maintaining mode when driven above 46 mph?
 

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perhaps my driving conditions are significantly different here on the Oregon coast (max. highway speed limit is 55mph, almost never need AC, very few other cars/trucks on the road) but when my Clarity is in HV mode it stays in direct drive mode almost all the time over about 46mph and especially over 55mph. I can hear the engine sound change and see the 'gear' on the energy screen vanish if it drops out direct drive and it almost never happens, even when going up uphill on Hwy101.

because I select EV at below 46mph, our Clarity basically operates in either EV or HV direct drive all the time. ¯\(ツ)
Could very well be the driving conditions. In my case there are always other cars around, I use radar cruise and most of the time it's following a car in front of me. On the highway that's not so bad because most people use cruise control on the highway or at least a lot of them do. But on urban freeways most people don't so my speed varies at least a couple of mph, sometimes more. I don't notice it from a driving standpoint but if I look at the power needle it is almost always moving. Also where I'm at is not level, not a lot of hills but there is constant slight changes in elevation.
 

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I’m sorry. I’m having a hard time understanding your logic and maybe it’s because the printed word doesn’t correctly convey it. I’m truly not trying to be confrontational but why do you need to “select EV at below 46mph”? Are you saying that you always manually select HV charge maintaining mode whenever your speed is over 46 mph? And then do you manually switch this mode off when you fall below 46 mph? And are you basically saying it is more efficient to run in HV charge maintaining mode when driven above 46 mph?
At the risk of jumping in the middle, I think I get what he is referring to. He is pointing out that if you know that you will have to use HV during part of your trip, it's more efficient to do the HV portion of the trip above 46 mph and the EV portion below 46 mph whenever possible, as a way to maximize the amount of direct drive HV as opposed to electricity generating HV. In other words if it's a 125 mile trip and you have 50 miles EV range, then you expect that about 75 miles of the trip will be in HV. Following what he is saying your goal is to have as many of those 75 HV miles to be in direct drive mode as possible, which can be accomplished by doing as much of the HV driving as possible above 46 mph, and using EV for speeds below that. Of course how much you can use EV below 46 mph will depend on how many EV miles you have available. If you are getting low on EV miles (or reach 0) then of course you will need to use HV even below 46 mph. Also you want to eventually use up all of your EV miles by the end of the trip, so in some cases you may need to use EV above 46 mph in order to use it up.

By the way I think I have heard of the 46 mph direct drive minimum before, but I don't think I have paid enough attention to notice if that's the exact cut-off when I am driving in HV.

The idea behind all of this is that the engine in direct drive is more efficient than when it's generating electricity which has to be transferred to the electric motor, leading to some inevitable losses. Although I have heard opinions that the losses aren't all that much. But without any actual data we can only guess how much efficiency difference there might be.

I do the same thing in principle, just not to that level of detail. When I know I will be doing some HV on a trip I try to do the HV portion on the freeway, and EV on surface streets. For me freeway driving is almost always well over 46 mph (unless heavy traffic) and surface street speed limits in my area are usually 45 mph, although on those I usually go about 50.

In theory if I am on a trip where I know I need to use some HV, and if during the freeway portion of the trip traffic slows below 46 for some reason, I could switch to EV, then when traffic speeds back up again switch back to HV. And if during the surface street portion of the trip if I am driving at 50 I could switch to HV, then when I slow back down below 46 switch back to EV. Adding that extra bit of finesse would probably eke out some additional efficiency gain, but for me that's too much micromanaging. Now there's nothing wrong with micromanaging, it only becomes a problem when someone micromanages other people. But if someone wants to micromanage their car I say go for it if that's what they like doing and if it leads to some efficiency gains. It's all relative really, there are people who think that we are micromanaging our cars by using the HV button at all, their philosophy is just drive the car it will figure it out. Can't argue with that either, if they prefer driving that way and don't mind the engine noise when they run out of EV miles halfway through the trip, good for them, even though I suspect they might give up a little bit of efficiency, but if they prefer driving that way that's okay.

As for me I don't mind pushing a few buttons every once in a while but I have my limits. The great thing about the Clarity is that you can drive it however you want, either as a hypermiler, or as a carefree ne'er-do-well, or somewhere in the middle, either way it will be still be efficient, even if to somewhat varying degrees.
 

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I’m sorry. I’m having a hard time understanding your logic and maybe it’s because the printed word doesn’t correctly convey it. I’m truly not trying to be confrontational but why do you need to “select EV at below 46mph”? Are you saying that you always manually select HV charge maintaining mode whenever your speed is over 46 mph? And then do you manually switch this mode off when you fall below 46 mph? And are you basically saying it is more efficient to run in HV charge maintaining mode when driven above 46 mph?
Negative. I have never needed to use "HV Charge" mode. I have tested it and observed how it works but no need to use it.

Perhaps it's easier if I reverse it to this: I never use "HV" mode at below 46mph because it will not be in direct connect mode (ICE driving the wheels). Any trip we take that cannot be made entirely on EV, I always use EV at lower speeds because I have more than enough battery to do that. I also use EV at higher speeds all the time and always end my trips with less than 5 miles of EV left.

cheers, roger
 

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At the risk of jumping in the middle, I think I get what he is referring to. He is pointing out that if you know that you will have to use HV during part of your trip, it's more efficient to do the HV portion of the trip above 46 mph and the EV portion below 46 mph whenever possible, as a way to maximize the amount of direct drive HV as opposed to electricity generating HV. In other words if it's a 125 mile trip and you have 50 miles EV range, then you expect that about 75 miles of the trip will be in HV. Following what he is saying your goal is to have as many of those 75 HV miles to be in direct drive mode as possible, which can be accomplished by doing as much of the HV driving as possible above 46 mph, and using EV for speeds below that. Of course how much you can use EV below 46 mph will depend on how many EV miles you have available. If you are getting low on EV miles (or reach 0) then of course you will need to use HV even below 46 mph. Also you want to eventually use up all of your EV miles by the end of the trip, so in some cases you may need to use EV above 46 mph in order to use it up.

By the way I think I have heard of the 46 mph direct drive minimum before, but I don't think I have paid enough attention to notice if that's the exact cut-off when I am driving in HV.

The idea behind all of this is that the engine in direct drive is more efficient than when it's generating electricity which has to be transferred to the electric motor, leading to some inevitable losses. Although I have heard opinions that the losses aren't all that much. But without any actual data we can only guess how much efficiency difference there might be.

I do the same thing in principle, just not to that level of detail. When I know I will be doing some HV on a trip I try to do the HV portion on the freeway, and EV on surface streets. For me freeway driving is almost always well over 46 mph (unless heavy traffic) and surface street speed limits in my area are usually 45 mph, although on those I usually go about 50.

In theory if I am on a trip where I know I need to use some HV, and if during the freeway portion of the trip traffic slows below 46 for some reason, I could switch to EV, then when traffic speeds back up again switch back to HV. And if during the surface street portion of the trip if I am driving at 50 I could switch to HV, then when I slow back down below 46 switch back to EV. Adding that extra bit of finesse would probably eke out some additional efficiency gain, but for me that's too much micromanaging. Now there's nothing wrong with micromanaging, it only becomes a problem when someone micromanages other people. But if someone wants to micromanage their car I say go for it if that's what they like doing and if it leads to some efficiency gains. It's all relative really, there are people who think that we are micromanaging our cars by using the HV button at all, their philosophy is just drive the car it will figure it out. Can't argue with that either, if they prefer driving that way and don't mind the engine noise when they run out of EV miles halfway through the trip, good for them, even though I suspect they might give up a little bit of efficiency, but if they prefer driving that way that's okay.

As for me I don't mind pushing a few buttons every once in a while but I have my limits. The great thing about the Clarity is that you can drive it however you want, either as a hypermiler, or as a carefree ne'er-do-well, or somewhere in the middle, either way it will be still be efficient, even if to somewhat varying degrees.
Ok, I think the way you are explaining it I’m starting to get a better understanding. It kind of boils down to whether you want to use energy from the engine to directly drive the wheels or whether you want to use energy more indirectly by allowing the engine to charge the battery which drives the motor which drives the wheels. The idea is that it’s not as efficient to do the latter. My only question would be, how do you know that the engine in direct-drive mode is running more efficiently? You don’t have as much control over the engine anymore as it must run at a specific RPM which matches the speed of the car.

For example, if the engine runs at its most efficient around 2500-3000 RPM but the speed you’re driving in direct-drive mode has the engine running at only 2000 RPM then perhaps you are running outside of its most efficient range. Whereas if you’re simply driving in HV mode when direct-drive is not engaged, perhaps the computer can direct the engine to run at a higher RPM level that is within its more efficient range in order to charge the battery.

Another interesting question then would be, if you had a continuously variable transmission where you could always get the engine to run in a most efficient mode, would it always be more efficient than a hybrid vehicle (if for the moment you leave out the benefits of regenerative braking)?
 

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Ok, I think the way you are explaining it I’m starting to get a better understanding. It kind of boils down to whether you want to use energy from the engine to directly drive the wheels or whether you want to use energy more indirectly by allowing the engine to charge the battery which drives the motor which drives the wheels. The idea is that it’s not as efficient to do the latter. My only question would be, how do you know that the engine in direct-drive mode is running more efficiently? You don’t have as much control over the engine anymore as it must run at a specific RPM which matches the speed of the car.

For example, if the engine runs at its most efficient around 2500-3000 RPM but the speed you’re driving in direct-drive mode has the engine running at only 2000 RPM then perhaps you are running outside of its most efficient range. Whereas if you’re simply driving in HV mode when direct-drive is not engaged, perhaps the computer can direct the engine to run at a higher RPM level that is within its more efficient range in order to charge the battery.

Another interesting question then would be, if you had a continuously variable transmission where you could always get the engine to run in a most efficient mode, would it always be more efficient than a hybrid vehicle (if for the moment you leave out the benefits of regenerative braking)?
good question.

first is to note that if it was more efficient to use a small ICE to generate electricity and then move the car using that electricity, there would be no need for a mechanical connection (transmission/differential). You could simply eliminate all that cost and weight and just slightly increase the size of the electric traction motors.

second, which is why the first scenario I describe isn't used, comes from thermodynamics in that when you convert energy from one type to another, there are always losses that you can't get rid of. Directly driving the wheels from the ICE, especially if you don't go through a transmission (more losses) is always more efficient than generating electricity with that same ICE and powering the wheels with that electricity.

another thing to consider with the Atkinson cycle ICE used in the Clarity, it's efficiency is very high and similar over the RPM range it operates in- there is not much change in efficiency across the usable range of RPM. What an Atkinson cycle sacrifices is low RPM torque, which makes it perfect for hybrid systems that overcome that with the electric boost.

worth noting that as speed increases above the initial Direct Connect speed, the ICE is capable of driving the wheels and generating electricity at the same time to power systems or put charge into the battery. At speeds just over 46mph, when Direct Connect starts, there isn't much excess power which is why it would go in and out of Direct Connect more until speed (and thus ICE RPM) increases. Once above about 50mph, the Clarity should be able to stay in Direct Connect most of the time.

found this great graphic of the Honda hybrid system:



from here: Explaining the Honda Accord's Shrewdly Designed New Hybrid System

thanks for attending my Sunday TED talk. lol
cheers, roger
 

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good question.

first is to note that if it was more efficient to use a small ICE to generate electricity and then move the car using that electricity, there would be no need for a mechanical connection (transmission/differential). You could simply eliminate all that cost and weight and just slightly increase the size of the electric traction motors.

second, which is why the first scenario I describe isn't used, comes from thermodynamics in that when you convert energy from one type to another, there are always losses that you can't get rid of. Directly driving the wheels from the ICE, especially if you don't go through a transmission (more losses) is always more efficient than generating electricity with that same ICE and powering the wheels with that electricity.

another thing to consider with the Atkinson cycle ICE used in the Clarity, it's efficiency is very high and similar over the RPM range it operates in- there is not much change in efficiency across the usable range of RPM. What an Atkinson cycle sacrifices is low RPM torque, which makes it perfect for hybrid systems that overcome that with the electric boost.

worth noting that as speed increases above the initial Direct Connect speed, the ICE is capable of driving the wheels and generating electricity at the same time to power systems or put charge into the battery. At speeds just over 46mph, when Direct Connect starts, there isn't much excess power which is why it would go in and out of Direct Connect more until speed (and thus ICE RPM) increases. Once above about 50mph, the Clarity should be able to stay in Direct Connect most of the time.

found this great graphic of the Honda hybrid system:



from here: Explaining the Honda Accord's Shrewdly Designed New Hybrid System

thanks for attending my Sunday TED talk. lol
cheers, roger
I get your drift now. It’s pretty much what I have done when I know I’m going to have to be in HV mode. Force it when you’re on the highway and put it back in EV mode when you’re in town.
 

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..... thermodynamics in that when you convert energy from one type to another, there are always losses that you can't get rid of. Directly driving the wheels from the ICE, especially if you don't go through a transmission (more losses) is always more efficient than generating electricity with that same ICE and powering the wheels with that electricity.
Inarguably. However the question remains, how much more efficient? Clearly it's at least enough of an increase in efficiency for Honda to justify including direct drive. But that still doesn't quantify the difference. The hybrid system itself including the Atkinson cycle engine provides the bulk of the efficiency, but similar to Toyota with Prius which was also something of an efficiency showcase, Honda also employed multiple additional methods to improve efficiency, many of which by themselves don't make a huge difference, but cumulatively gave them the EPA numbers that they needed for the Clarity. Things like fender skirts, air curtains for the wheels, LRR tires, underbody cover for better airflow under the car, aluminum suspension parts, and many others. Although direct drive was probably the most costly of these, but that still doesn't mean that it necessarily makes a ginormous difference in efficiency. Or maybe it does. But without any data from Honda we can only guess about it.

You could simply eliminate all that cost and weight and just slightly increase the size of the electric traction motors.
Not sure why it would need a larger traction motor, as this would imply that the car has a higher maximum speed in direct drive than in generating mode. Which in theory is possible I suppose, but I have read that in EV mode the speed is artificially limited to 100 mph. Maybe direct drive can go faster than that, but for most people that's a moot point.

I haven't maxed out my Clarity like I did with my two Prius (2002 and 2006). But on those I did it just because I got tired of people asking me if my Prius had enough power to keep up with traffic on the freeway. So each of the cars I got them very briefly to 100 mph. Thereafter anytime I got that question, rather than having to go through explanations I could now simply answer, "I've done 100 mph in it". That usually created a look of confusion on their face and they didn't ask any more about it. Only thing I didn't tell them is that I had to be on a slight downhill to get to 100 mph! On flat ground they maxed out at about 95 mph.
 

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Thank you! Taking another highway trip today so will set it right at 75 the whole way and see what happens.
Try driving slower.
Anything over 60 MPH causes more fuel to be used due to drag & loss of efficiency on that small 1.5L engine plus the extra weight of the batteries.
When I drove the Clarity on the freeway for hours at 60MPH or less, I got 48 MPG in HV - flat terrain - no A/C - no heat.
 

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I personally think that for best efficiency you just quit messing with the button and let the vehicle manage things. By switching it manually you are saying that you somehow can make it more efficient than the way the engineers designed it. I’m not saying that there is never a reason to switch to HV mode, just that in most cases the best solution is to let the car manage it.
Engineers know what's best for each condition but there's no way to predict and accommodate all those cases. If you are talking about just pure highway driving, then maybe it's okay to just let the car manage everything, you will deplete the HV battery, then use gas with 10% battery remaining that can be used only for bursts when needed. But if you know you will be stopping by in a town or you want to build up some reserve because you know there will be tons of hills up ahead, then it's probably better to plan ahead. Engineers would probably agree to those decisions, and I'm sure we have plenty of engineers in the forum.

By the way, AC doesn't use too much battery. The heater does. It's counter intuitive, but even in 70F weather, if you set the temperature to 68F and turn on the climate control, it'll use more power than setting at LO because to make 68F the car has to heat up the coolant to mix it with the AC cooled air. At LO, it's going to get chilly but at least you know the heater isn't on. I stopped thinking about the AC power usage, but the heater part always has me to hesitate using the climate control.
 

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Engineers know what's best for each condition but there's no way to predict and accommodate all those cases. If you are talking about just pure highway driving, then maybe it's okay to just let the car manage everything, you will deplete the HV battery, then use gas with 10% battery remaining that can be used only for bursts when needed. But if you know you will be stopping by in a town or you want to build up some reserve because you know there will be tons of hills up ahead, then it's probably better to plan ahead. Engineers would probably agree to those decisions, and I'm sure we have plenty of engineers in the forum.

By the way, AC doesn't use too much battery. The heater does. It's counter intuitive, but even in 70F weather, if you set the temperature to 68F and turn on the climate control, it'll use more power than setting at LO because to make 68F the car has to heat up the coolant to mix it with the AC cooled air. At LO, it's going to get chilly but at least you know the heater isn't on. I stopped thinking about the AC power usage, but the heater part always has me to hesitate using the climate control.
So you’re saying it’s better to set the temperature way low so the system doesn’t try to mix warm air in with the cool? If so, would it be good to set the temp at, say, 60 degrees and then just use the fan speed to control how cold it gets in the car?
 

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By the way, AC doesn't use too much battery. The heater does. It's counter intuitive, but even in 70F weather, if you set the temperature to 68F and turn on the climate control, it'll use more power than setting at LO because to make 68F the car has to heat up the coolant to mix it with the AC cooled air. At LO, it's going to get chilly but at least you know the heater isn't on. I stopped thinking about the AC power usage, but the heater part always has me to hesitate using the climate control.
Just making sure that I am correctly reading your example. If you are running AC and the temperature is set to 68, and for whatever reason the AC overshoots and the cabin temperature drops to say 67, then it will shut off the AC compressor. But instead of just waiting for the cabin to naturally warm back up to 68 as heat from the 70 degree outside air slowly migrates into the cabin, instead it turns on the heater to more quickly get back to 68. And yes the only way to avoid this is to set the temperature to LO.

Although I think (but I'm not sure) that it only runs the heater in that scenario if the outside temperature is only slightly above the set temperature. If the outside air was say 80 degrees, then instead of running the heater I think it just brings in some outside air.

would it be good to set the temp at, say, 60 degrees and then just use the fan speed to control how cold it gets in the car?
Setting at LO or at 60 should do the pretty much the same thing. In either case this will keep it from using heated air to maintain exact temperature. Of course using LO or 60 you can't be in Auto mode because it will run the fan at full blast trying to reach that temperature, so as you said you have to manually control the fan.

By the way this is also good to do when using fan only. Meaning turning off the AC compressor, which you do by going into the climate screen and pressing the AC OFF button so that it is illuminated. Note that even if the AC ON button is not illuminated, the AC compressor will still run if the ACC OFF button is not illuminated. When running fan only it may still in some cases turn on the heater, setting it to LO avoids that.
 

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Engineers know what's best for each condition but there's no way to predict and accommodate all those cases. If you are talking about just pure highway driving, then maybe it's okay to just let the car manage everything, you will deplete the HV battery, then use gas with 10% battery remaining that can be used only for bursts when needed. But if you know you will be stopping by in a town or you want to build up some reserve because you know there will be tons of hills up ahead, then it's probably better to plan ahead. Engineers would probably agree to those decisions, and I'm sure we have plenty of engineers in the forum.

By the way, AC doesn't use too much battery. The heater does. It's counter intuitive, but even in 70F weather, if you set the temperature to 68F and turn on the climate control, it'll use more power than setting at LO because to make 68F the car has to heat up the coolant to mix it with the AC cooled air. At LO, it's going to get chilly but at least you know the heater isn't on. I stopped thinking about the AC power usage, but the heater part always has me to hesitate using the climate control.
Engineers work with marketing to make decisions. Sometimes, they're not "allowed" to do things the most efficient way possible.

Case in point: In my 2011 Volt, the engine runs in "Normal" mode, unless you change it to another, such as "Mountain" mode. In Mountain mode, the engine revs at a much higher rate, in order to put extra energy back into the battery, in anticipation of needing the extra battery buffer during ascent of...well...mountains. In Mountain mode, the engine noise can be quite noticeable. Some might even call it jarringly loud.

What I found was that if I played with the modes on flat ground, that the vehicle got about 10% better gas mileage if I kept it in Mountain mode while the engine was running. It required significant diligence on my part, to keep track of battery SOC, and turn on Mountain mode when the battery got down to where the GOM reported about 3 miles worth of charge. I'd then leave it in Mountain mode for about 20 minutes, while the vehicle engine (relatively loudly) added a buffer to the battery. I'd then turn it back to regular mode and run off the battery (in EV mode), until it got down to 3 mies EV range again. Repeat.

What this seems to show is that GM made a marketing decision, that drivers would prefer a quieter environment in the Volt, rather then maximizing the efficiency of the system by running the engine at a louder and higher RPM.

I suspect that the nigher RPM put the little engine more into the peak area of its power band, which can be more efficient. It's possible that the same can be said for the Clarity PHEV, but I haven't played with it to the same extent that I did the Volt.
 
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