why did the engine continue to rev high, even after we started going downhill...and when we were driving on flat road?
I would think it was trying to do maximum battery charging, in addition to what you were getting from regen. Now why it thought it needed maximum battery charging at that moment is hard to say. I always try and remind myself that the car is essentially driving blind, it goes only by "feel". Yes there are cameras for LKAS and such, and yes maybe NAV is running, but those are separate systems, the power system only lives for the moment, based somewhat on past experience with this particular "rider" and it is trying to predict, completely blindly, what is coming next. And of course when I say "it" I am really referring to software designers who have to sit in a room and imagine a nearly infinite number of scenarios, including someone driving up Divisadero street after driving in from Tahoe, on a battery that is not quite empty yet but getting there. As far as the computer knows you were starting up Pikes Peak. Probably at times the computer is overcautious, but again that is easier said from our viewpoint with our eyes and ears and knowledge of San Francisco streets and also knowing what our next turn will be and where we will be driving next.
I sometimes think that in the future there will be smarter PHEV's that integrate the drive system with the cameras and NAV so that it can make better decisions about battery and power management. Until then.....
It's just really unpleasant to drive when the engine is revving that high when it shouldn't be. There's a reason why we all maximize charge on this car!!
Some people say, not always politely in these type of discussions, well then you should be driving an EV. I think saying it that bluntly isn't always helpful, but I think there is a point that a PHEV is a hybrid, and that the system has to make constant decisions between efficiency and giving us the EV only driving that we expect when we have what we think is enough battery charge.
I have no doubt that the high engine revs are the most efficient at that moment. We tend to equate high revs with something being wrong, or even harmful to the engine, which is understandable because it is loud, and not what we are used to hearing in a normal car except maybe a Mustang showing off. I don't drive a stick shift very often anymore, when I do I worry more about under-revving which harms an engine, and knowing that I am somewhat out of practice I lean a little more toward over-revving, which might use a little more fuel but doesn't harm the engine (I'm not talking about redlining it). But when someone is riding with me, I notice that they could care less when I accidentally lug the engine, but if I over-rev even for a few seconds they think I have just killed the car.
Dedicated hybrids are certainly different cars, for one thing the ICE engine is not-typical, it's an Atkinson cycle engine, a type of engine that is extremely efficient due to its unusual power-stroke, but if you put one in a regular non-hybrid car people would go crazy because it is not the smooth quite engine we have grown accustomed to.
I'm sure the engineers could have put an RPM limit on the car to keep us from becoming anxious, just as they could have used normal rear fender skirts. But they seem to have been given a mandate to lean towards efficiency, not normalcy, yet meanwhile without skimping on weight that affects passenger comfort and quietness. Ironically it's the quietness that makes us even more aware that we have a lawnmower under the hood.
That being said, a few rare people have had problems with ICE running way too often, but with just one incident, or even an occasional few, your car is likely operating as designed.
