Prius Prime EV Indicator vs Charging Screen

• On page 212 of the Owner's Manual, Item 5 describes the EV indicator: "The EV indicator comes on when the vehicle is driven using only the electric motor (traction motor) or the gasoline engine is stopped."
• You can also watch the energy flowing on the Energy Monitor (which shows arrows to indicate where energy is flowing).

I have noticed that, at times, the EV indicator is off even though the arrows showing flow from the engine to the wheels or battery are gone (no energy flowing from engine). I had thought that no arrows from the engine would mean the engine is off, but I think it is still on in these cases because the engine is still illuminated on the Energy Monitor and I don't think I've felt it turn off (hard to feel). This tends to happen if I'm going above 75 mph and downhill. If I slow below 72 mph (fairly accurate value) down the hill with adequate HV battery, EV will illuminate and the engine on the Energy Monitor will no longer be illuminated (no arrows from it in either circumstance). I also believe I feel the engine turn off.

What does it mean for the engine to be illuminated on the Energy Monitor but no arrows flowing from it? Is it on and somehow in a "standby" mode? Is the engine on and the drivetrain in neutral while coasting? I understand that at these speeds it doesn't make sense in general to allow the engine to cut off because it will be needed very soon (unlike lower speeds), but shouldn't it at least always be charging if not propelling?

 

It seems to me that if fuel was being injected, some power is being produced and must either be generating electrical energy or powering the wheels. If it is potentially "freewheeling" as you suggest, wouldn't that steal energy to overcome the compression in the cylinders? I wonder if the VVT-i is adjustable enough to allow intake/exhaust valves to be open during the combustion/compression strokes such that there is not as much parasitic loss in turning the engine without fuel being injected. It'd be nice to know exactly what is going on.