HV Charge Mode - observations/questionsfrom one day Road Trip!

No argument here... It's just a matter of degree.
The impact of running in HV Charge has been demonstrated to be smaller than you might expect.

 

I find alternating HV Charge with EV to be a positive for gas mileage when under 50 mph (where gear drive is mostly unavailable) and a negative at highway speeds where gear drive is available most of the time in HV.

 

Completely agree based on my multiple experiments.


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Is there really any advantage to using HV Charge mode besides avoiding a screaming engine? I did a long road trip on highways, and ran the car in default (EV) on the way out, and HV mode on the way back. The only advantage I found to using HV was that the engine revved up to noisy levels less often. Running it in EV mode w/ the battery @ 2 bars, it didn't seem to kick into EV mode much less than it did in HV mode w/ the battery at half charge. The car was able to climb steep mountains, even in HV mode w/ depleted battery.

 

I've started to use HV charge mode to avoid screaming engine on long climbs recently as suggested, and so far it seems to work. Besides being a more pleasant driving experience, I wonder if this also contributes to slightly better fuel economy (haven't verified that though) - it seems this should be the case assuming that engine is operating less efficiently in "screaming RPM" mode, compared to regular 2000-3000 rpm.

 

It is likely that the engine RPM at which you achieve maximum efficiency is surprisingly high. With a conventional vehicle it is not really possible to stay at the maximum efficiency point because of the constraints of vehicle speed and fixed gear ratios. With the Hybrid / PHEV it is possible to decouple the speed from the RPM's and better utilize the maximum efficiency of the ICE. I think this is why it seems odd to some when the ICE is revving for no apparent reason. In actuality, the RPM regime is likely designed to maximize efficiency of the generator. The Angry Bees may be beyond maximum efficiency, but what is perceived as 'high' rev's could very well be the most efficient condition possible for a given circumstance.

 

HV Charge mode is useful if you want to keep the battery charged so you can use the remote climate control. It's also useful if you are planning to stop on a road trip and want to maximize how much gas you can pump.

 

I've been so EV-focused with our Clarity PHEV that this prudent idea never occurred to me. Thanks!

 

My theory (picked up from some other posts in this forum if I remember right) for using HV charge mode during long climbs is that this is effectively changing the circumstance/constraints the car operates in: The goal of regular/non-charge HV mode is to maintain some specific state of charge (set when HV mode is first activated), and therefore it will rev harder if battery state of charge drops too far below this set point. The goal of HV charge mode (presumably) is just to achieve ~58% state of charge by running the engine slightly harder than needed, for however long it takes; therefore HV charge mode will actually allow (somewhat paradoxically) to drop state of charge further than HV mode would (if needed due to continued high-powered climbing), without triggering additional increase in engine RPM. After experimenting with this for a day, I can confirm that this appears to be the behavior, although I will need more experience with it to be sure. (Might be awhile, since this isn't easy to test - one needs climbs long & fast enough to require more battery drain than provided by the extra charge from HV charge mode.)

The effect on gas mileage would require further testing, but I still think it's plausible that it should be better with HV charge mode, because it allows the car to use the entire battery capacity as a buffer (vs the ~2 bars available in regular HV mode), so it can keep engine load constant (= more efficient) for longer independent of terrain.