HV vs. HV Charge
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There aint no such thing as a free lunch. The ICE is burning gasoline to propel the car. If you want to charge the battery as well as propel the car the ICE has to do extra work, in order to do the extra work the ICE has to consume extra gas. When you think about it burning extra gas is just common sense. If you were driving at a steady 55 MpH on a flat road and you had to climb up a hill you are going to press down on the accelerator further going up the hill in order to maintain your speed of 55 MPH. More work requires more energy usage in the form of gas, The extra work it takes to charge the battery works on the same principle of requiring extra gas to do the extra work to charge the battery. I hope I was able to explain things in away that made sense and was understandable.
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Out of the curiosity, a few weeks ago I did try the "HV charge" on a trip with about 180 miles. It did have less mileage than the automatic "HV" mode. As a result, I would not run "HV charge" again.
Yes my gas millage on a long trip(Ontario to FL) was around 42MPG but when we tried the charge mode it went down to the low 30,s so it is not practical to ever use!
What we did do was find a old motel on way down that had doors to our room,on main floor, ran plug cord inside and charge battery over night.
What we did do was find a old motel on way down that had doors to our room,on main floor, ran plug cord inside and charge battery over night.
It is expected that while in HV Charge mode that mpg will drop way down, but at the same time you are building EV range for later use, so it generally should work out to similar overall mpg, just slightly lower.
As an example, lets says you get 42 mpg and drive 42 miles in HV mode. You would use one gallon of gas to drive those 42 miles. Now lets say you do the same drive but this time in HV charge mode, and let's say you get 30 mpg while in in HV Charge mode. In that case you will use up one gallon of gas in only 30 miles. However during that time you will have been building EV range, let's say during those 30 miles running in HV Charge mode you build up 11 additional EV miles on top of whatever you had before. So at the 30 mile mark you shut off HV Charge and switch to EV and drive the next 11 miles in EV. So you have now gone 41 miles on one gallon of gas, or 41 mpg. Just slightly less efficient. This example is based on tests people have done on a repeated route like a daily commute, where they find that running in HV Charge is only slightly less efficient than running regular HV.
Okay so if it is slightly less efficient then why would you ever use it? You use it any time you want to have additional EV miles for whatever reason, generally related to improving the driving experience. It is most often used on trips, like when climbing grades when the gas engine can be pretty noisy in HV mode, especially with 0 EV range. So what some people do is if they know they don't have enough EV miles to make it up an upcoming hill climb in EV mode, then prior to getting to the hill they run in HV Charge to build up additional miles, so that when they climb the hill they can switch to EV and climb the hill quieter. Even if overall it is slightly less efficient it is worth it to them to reduce the noise and make the drive more enjoyable.
Another example would be if you were on a trip and stopped at a rest stop or for lunch or whatever, and when you left the rest stop you forgot to switch to HV mode, and by the time you realized this you used up all of your EV miles, which you had planned to use when you arrive at your destination city as you prefer to drive in EV mode around town. In this case you can use HV Charge to build up some EV miles to be used later. Again this is slightly less efficient, but then again so is driving at 70 mph vs driving at 65 mph, but at some point we make decisions that are based on comfort and convenience not solely on squeaking out maximum efficiency.
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HV charge will consume more energy - the laws of thermodynamics require this because you're adding an (gas to electric) energy conversion into the mix. However, if you're expecting to do some serious hill climbing you need both battery and gas power in the Clarity PHEV, as neither engine is big enough by itself. HV Charge gives you a way to restore the needed battery power for this purpose.
Are you converting from MPL to MPG?
I recently drove from New Orleans to NYC (1300 miles) - with no opportunity to charge - in HV mode. Going up I used 1/3 of the battery's charge and averaged 48.5 mpg. On the way back I used 1/3 of the charge and averaged 48.3 mpg. ACC was set for the posted speed limit +4.
I think it's a little more complicated than that. Current battery technology is pretty impressive with respect to efficiency (something like 99%). Generators and alternators are pretty efficient - they need to be since the vast majority of electricity is produced by converting some form of rotational kenetic energy into electricity (maybe in the 85-90% range?). Internal combustion engines have notoriously poor efficiency (so there's significant room for improvement) and their efficiency is a function of RPM. Although the continuously variable transmission can adjust drive ratio to get the RPM for the best efficiency of the ICE at the current HP requirement, the RPM may still be at a point where higher HP (and corresponding RPM) would be more efficient.
I haven't been able to find actual efficiency numbers on any of the components in question. Even if we had them, HP requirements are going to be a function of speed, road, and even rolling resistance of the car. I wish the data was published, but apparently it's a secret.
With those unknowns, the car might be cruising along at a HP requirement where the resulting RPM corresponds to a point on the efficiency curve where higher RPM would result in lower efficiency or higher efficiency. Suppose it's a case where the efficiency of the ICE when operating in normal HV mode works out to 20% but with the higher load from HV charge mode the CVT can push the RPM up to a point where the ICE efficiency was 22%. If the batteries are 99% efficient and the generator/alternator is 80% efficient, you're ahead.
The problem can get even more messy if you expand the system. Suppose a tuck-under garage and an air conditioned house. Traveling the last 5 or 10 miles on electric would allow the ICE to cool before parking it in the garage, which reduces the heat dissipated into the garage and then into the house - which is then pumped out of the house via the AC.
Basically, without real numbers for efficiency of the interesting components, all someone can do is gather some empirical data and see how it looks.
I haven't been able to find actual efficiency numbers on any of the components in question. Even if we had them, HP requirements are going to be a function of speed, road, and even rolling resistance of the car. I wish the data was published, but apparently it's a secret.
With those unknowns, the car might be cruising along at a HP requirement where the resulting RPM corresponds to a point on the efficiency curve where higher RPM would result in lower efficiency or higher efficiency. Suppose it's a case where the efficiency of the ICE when operating in normal HV mode works out to 20% but with the higher load from HV charge mode the CVT can push the RPM up to a point where the ICE efficiency was 22%. If the batteries are 99% efficient and the generator/alternator is 80% efficient, you're ahead.
The problem can get even more messy if you expand the system. Suppose a tuck-under garage and an air conditioned house. Traveling the last 5 or 10 miles on electric would allow the ICE to cool before parking it in the garage, which reduces the heat dissipated into the garage and then into the house - which is then pumped out of the house via the AC.
Basically, without real numbers for efficiency of the interesting components, all someone can do is gather some empirical data and see how it looks.
I agree that in situations where running HV Charge puts the engine higher on the power curve than it would be otherwise, that this could more than offset the inherent losses that occur when storing and retrieving electricity in the battery. There are also mechanical losses from using ICE to turn the starter/generator motor to create electricity, as well as losses when the electricity is used to turn the traction motor, however that does not really factor into this equation because HV mode does exactly the same thing.
Except when running in "gear mode". That's where ICE is connected directly to the traction motor via a clutch, and since the traction motor is essentially directly connected to the wheels, then in effect ICE is directly powering the wheels. It uses a fixed overdrive gear in this situation, Clarity does not have a CVT. When not in gear mode then ICE only turns the starter/generator motor to create electricity to be used by the traction motor. Even as efficient as those two electric motors may be, it cannot be as efficient as when ICE is directly connected to the wheels with an overdrive gear. I bring this up because I am not sure if HV Charge ever uses gear mode, in which case regular HV mode would have a slight advantage over HV Charge, at least in this one aspect. Then again maybe HV Charge does use gear mode at times, I will have to pay attention next time I use HV Charge as I don't remember. By the way for anyone who doesn't know, you can tell when ICE is running in gear mode by the tiny gear icon that sometimes appears on the energy distribution display. Gear mode is used only when driving at steady speeds above 45 MPH or so.
Some people who have done tests have reported that HV Charge can at times be more efficient than HV. If so then it could be the power curve situation that you are describing. But it's so hard to measure any of this. The only way to accurately measure MPG is to calculate it based on gas purchases and miles driven. But that is only meaningful if the entire tankful is driving in HV. Even then you never know if some of the electricity used in HV mode came from a previous charging session. So you really have to start the test with a depleted battery.
Anyone using the MPG displayed on the instrument panel to figure any of this out is wasting their time as that is notoriously unreliable. Gas receipts and odometer readings are the only meaningful measurements when it comes to MPG.
Not that I plan to do any of these experiments. I just accept other people's reports that HV Charge is similar efficiency to regular HV. I mean people who have done actual testing, not people who just look at displayed MPG on the instrument panel while running in HV Charge, and don't even factor in the value of the EV miles that are generated.
If there is a situation that will make the driving experience more enjoyable by using HV Charge to build up some EV miles for later use (city driving, climbing a hill, etc.) then I have no hesitation to use HV Charge. One person reported that they use HV Charge instead of HV because it tends to result in lower overall engine noise. I realize that is counterintuitive since we automatically assume that HV Charge will add RPM on top of whatever RPM the engine is already doing, but that is not really the case. It seems more like HV Charge does "opportunity charging" during periods when ICE is not being used (slow speeds or stopped) or if ICE is being used at low power. The resulting additional battery charge is then available to help avoid the high RPM's that can occur when the battery is depleted.
Yeah, I really wish Honda made some of that data available. Does the storage system have efficiency comparable to that of home PV system storage batteries? What's the efficiency vs RPM graph look like? Sure wish that wasn't a secret.... (hint, hint)
I wonder if we're talking about different years/models. Based on the feel and what I've found on the web, my 2018 does. See the section on Acceleration and Power.
https://cars.usnews.com/cars-trucks/honda/clarity/2018/performance
Is that the display that shows an outline of a car, an engine, wheels, and a battery and shows the energy flowing into and out of the battery? I've never noticed it. Where will the gear icon be?
Honda calls their system "eCVT", but that's a serious misnomer, as there isn't an actual CVT anywhere in the system, according to Professor Kelly at Weber State. Here's an excellent breakdown of the system:
Sorry I am a couple of months late replying to this question. The gear icon is pretty tiny, but once you have seen it you can spot it again without too much trouble. You can see it in the picture on the right at the bottom of this message.
Also some more experimentation on my part seems to confirm that gear mode is not used while in HV Charge. While driving at a steady speed in HV mode I saw the gear icon, then I switched to HV Charge and the gear icon went away. Switched back to HV and the gear icon returned. I tried this several times with the same result. Note that even in HV mode the gear icon comes and goes, it seems to like steady speeds, any momentary acceleration or regen takes it out of gear mode until the speed is steady again.
Thanks - that video was helpful. From what I understood in the video, it seems the CVT in the clarity is a stretch of the definition (but maybe technically true?). So, it's (numbered by how they're presented in the video)
(#1) electric from battery -> inverter -> electric motor,
(#3) clutch-less overdrive purely mechanical connection (for speeds over 62 mph),
or (#2) eCVT with ICE driving generator -> maybe AC/DC converter -> maybe inverter from #1 -> electric motor.
Sound right?
If the power for #2 is running through the AC/DC converter and then through the inverter used it seems like the only extra loss involved in charge mode would be the charge/discharge loss of the Li Ion cells. Right?
Does it optimize the ICE speed to run as efficiently as possible and just store the excess in the batteries?
Thanks - the image helped. I see it on mine now. A couple questions this brings up... (1) the video (above) said the overdrive lock kicks in at 62, but with cruise on, I'm seeing it in the mid to upper 40's. (2) Do we assume it's charging the battery with the excess horsepower when in overdrive?
Here's a good video that shows the workings of a true CVT. There's no comparison.
From Weber Auto:
I can't say enough good things about Professor Kelly. His videos are awesome.
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He later commented that the clutch engaged around 43mph
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