I have to try testing this a bit more, but I haven't read definitive results here. I have about a 4 mile incline on the way to work in an 80 mile commute. On the way back I regen. I can get anywhere from 55mpg (displayed) or 61 mpg depending on the season. I try to disengage EV at high speeds to pulse and glide. I try to use EV up the hill because I know I average 15-20mpg uphill otherwise. What's the consensus though? Is it more efficient to use EV on flats or it really doesn't matter as long as I use it?
I'm of the belief that EV uphill is counterproductive. You want the gasoline engine to do the climbing and accelerating with its "direct drive" through the power split, although instantaneous MPG is quite low while doing so. I believe using EV for times of high energy demand is counter-productive, since the system must then recoup all that energy loss. My strategy would be to use EV for short durations of low energy demand (or not at all). It's easy to get carried away thinking that more EV=better. In reality, the car manages the systems pretty optimally without any mode-button input. Too much EV causes the car to run the gasoline engine more than usual to regenerate the consumed charge.
EV up hill is very inefficient uphill. On my hill it costs me 3 EV miles to go 1 mile. If the engine is hot I always use HV going up the hill to home. If not (that is for short trips) I do use EV up the hill rather than run the ICE such a short time that it doesn't get up to operating temperature. On long trips I switch to HV uphill and save the EV miles for slow speed level parts of the trip. And of course for downhill to get regeneration charging. I generally get about 62 mpg on a long trip that has a significant amount of slower back roads.
Gas engine for when more throttle is needed, EV for when less throttle is needed. Gasoline engines are much more efficient towards full throttle operation, and much less efficient at partial throttle operation. The Atkinson-like design of the Prius engine plus variable gearing mitigates some of the inefficiencies of partial throttle operation, but cannot fully overcome them.
Going uphill always requires more energy than the same distance on flat road, regardless of immediate energy source. On top of that, your car does not have 4 miles of EV range, so it cannot make it up that hill in just EV, it must turn on the gas engine regardless. Because your 2010 isn't a plugin, all EV energy ultimately comes from the gas engine anyway, and the extra energy conversions to and from the battery come at a cost. Therefore, it should be marginally more efficient to get that climbing energy directly from the gas engine, rather than being laundered through the battery system. The Gen3 Prius' gas engine runs quite close to its peak efficiency over a very wide load and RPM range, much wider than traditional non-hybrids, so don't fear letting the car decide when to run it. The computers are very good at making the trade-off decisions without the human operator overriding them. Your tank MPG depends on your overall trips, uphill and downhill combined, not on the separate segments. My experience is that there is little one can do to improve the uphill portion, as the engine is pretty much already at its peak efficiency. Downhill is more important, where it is easier for common driving habits to sabotage things by not making use of the most efficient glide opportunities. Thus, focus most of your attention on the downhill side. Don't settle for just 100 MPG when the car could do 250 to Infinite MPG, as revealed by aftermarket engine monitors.
Add multiple vehicles to your signature like I have (see below). So assuming your this is your PIP on the commute, daily mpg readings should answer your question. I've done similar with routes to see which delivers the best mpg vs time.
I think EV efficiency difference may be negligible. The better question is the wear on the battery vs. the ICE. I'd rather climb with ICE to give the battery easy life.
In Ma, Iv'e found a route to work consisting of backroads that wind and go up and down small hills. In my 33 mile trip, I can get 62 mpg in the winter and 68 in the summer, and rarely 75. I'm going to work so I try and keep my overall average speed at 45 mph, to keep the trip quick. During the winter I turn the heater to max temperature, but turn the fan off to keep it from turning on the ICE. When approaching an up hill, I throttle up for the pulse portion of my "modified pulse and glide". When the ICE is engaged, I turn the heater fan on max (this is a form of heating pulse and glide). I accelerate to about 15 mph over the speed limit until, I get to the crest. Then the heater fan goes off, I feather the accelerator to get into Ev and glide into the next hill. The route is not far from the minimum distance route found by my gps. Some roads I don't go on because of potholes, some roads are not plowed very well, and some T intersections are difficult to turn on, so I avoid those.
As long as you can stay in "eco" up the hill, efficiency will be more or less the same. The more you have to rev the engine, the more power goes through the two MGs and the more efficiency drops, although it's not a huge difference in that case.
