On a recent 3k plus trip where I pulsed and glided a ton, when the PIP was in HV mode but gliding in the sweet spot where I had thought the engine would stop turning, no matter how I tweaked the glide, the ICE always turned at a minimum of 998 RPM per my torque app. The display was always showing 999 mpg in that situation so I assume it wasn't using fuel but just rotating freely. Is that the default behavior for HV mode? I,e, always rotating at 998 minimum rpm perhaps so it can kick in quickly if need be without vibration?? If so, the 10k oil change interval seems dicey as the engine is technically turning all the time when in HV mode. I was planning to change at 5k anyway.
There could many reasons for the engine to be running. heat cycle (unlikely), more but I'm not an expert, engine braking (depends if you were in "B" range), certain speeds. I come across about a mile down hill every day and I can feel my engine turn off usually, and then feel the vibration when it turns back on. I'm also very interested about this because my lexus seems to do it more often than my prius.
I'm not sure about the plug-in, but with our regular Prius the rpms always kick back in, when speed is climbing, somewhere just under 80 kmh (50 mph). For us there's a long downhill run where you can see it happen on the ScanGuage. The SG continues to indicate zero fuel being consumed (until we hit the bottom of the hill and start applying the gas). Not sure how that works.
When coasting above about 45-50mph, the engine will continue to rotate, but it will not be using any gasoline. This is to protect the various MG devices from over rotation.
In this situation, the ICE is free-wheeling, isn't it? That is, no compression, no fuel. And using very little power.
I wouldn't mind to understand that better. No compression would necessitate holding the valves open somehow, wouldn't it??
I thought the Plug In had a threshold of 62 MPH before the engine had to run even if there was no load. But I may have misunderstood that, on the normal Prius it is about 42 MPH depending on model. (v,c liftback, gen 2, etc)
That is correct. The valves are kept open and the engine just freewheels at around 1000rpm. I am not able to talk knowledgeably about the plug-in.
The gasoline engine in the Prius (Plug-in and standard) was designed specifically for the Prius. The control system plays all sorts of games with the valve timing; thus the designation of "Atkinson-like". This is one reason that the Prius can run on regular-octane gasoline.
When the "B" setting is selected with the shift-lever, does it alter the engine valve operation to work like an engine-brake?
It advances the valve timing, yes. It has no valves always open or always closed setting, but it can adust the timing by about 25 degrees.
This must be the answer then because come to think of it when I was using the torque app I was gliding a lot at these speeds. I would imagine the 1k rpm rotation also must make it safer to reengage at those speeds. Either way, the MPG is showing 999 in those glides so I assume you're right that it's using no gas.
If the ICE is rotating, the car is NOT gliding. Old timers called your situation 'warp-stealth.' This may sound like nitpicking but it is the heart of truly impressive fuel economy.
The Atkinson Cycle engine is great for saving fuel, but not so great for idling, therefore the speeds are kept higher, off-set by the motor-generator running in reverse.
