Without any empirical evidence I'm guessing about 1-5 mph if there is no one around you, you don't mind looking like an idiot, and you aren't having to run the HVAC at a very high level. On a more practical note: When driving through subdivisions at the standard 25 mph speed limit I have no problem doing about 10-15 mph if there is no one behind me.
If raw MPG is the goal, I'm going to guess that the peak is somewhere in the 10-20 mph area. All the electrics and electronics consume some overhead load. At really low speed, the power for this will exceed the actual propulsion power, and mpg will plummet. Somewhere in the PC archives is a graph of early Prius mpg vs speed, from a national lab. It clearly shows this low speed dropoff. Bob Wilson's GenIII mpg vs speed graph from three years ago doesn't go low enough to find that peak, but just shows mpg pegged at 100 at 25 mph.
IMHO, EV mode in the regular Prius is basically a stunt--though one I love showing to my friends. This is because all the energy in the regular Prius eventually comes from gasoline. I don't think I am smart enough to do better than the computer at deciding when to turn on the gas engine and when to keep it off to maximize economy. The only exception to this might be when going such a short distance that I don't want the gas engine coming on at all and wasting gas heating itself up--e.g., when moving it to a more convenient place in the parking lot for loading/unloading. Here I think speed is more a matter of driving conditions than economy. Operating on electric power only in Plug-In Prius is very different, because there are lots of useful places you can go at varying speeds on electric power only. Unfortunately, as to your question about speed vs. efficiency in the PiP--I just don't know. Someone may have addressed it in the Plug-In Prius forum.
Even with radio and DRL's but nothing else on (parked) I am only seeing a current pull of about .5 amps.
Following is my study. We see approx 1 amp base consumption of HV battery when parked, so it is approx 0.2 kW base consumption. I learn Prius driving force (N) at speed (m/sec) is ... N = 0.4 X (speed ^ 2) + 160 (Newton) Column 1 0 [tr][th]mph[/th][th]drive kW[/th][th]base kW[/th][th]total kW[/th][th]kWh/mile[/th][/tr] 1 [tr][td]5[/td][td]0.36[/td][td]0.2[/td][td]0.56[/td][td]0.1121[/td][/tr] 2 [tr][td]10[/td][td]0.75[/td][td]0.2[/td][td]0.95[/td][td]0.0948[/td][/tr] 3 [tr][td]15[/td][td]1.19[/td][td]0.2[/td][td]1.39[/td][td]0.0926[/td][/tr] 4 [tr][td]20[/td][td]1.71[/td][td]0.2[/td][td]1.91[/td][td]0.0955[/td][/tr] 5 [tr][td]25[/td][td]2.34[/td][td]0.2[/td][td]2.54[/td][td]0.1015[/td][/tr] 6 [tr][td]30[/td][td]3.10[/td][td]0.2[/td][td]3.30[/td][td]0.1100[/td][/tr] So, the optimum speed is approx 15 mph, and my math tells me the peak is 14.1 mph. Ken@Japan
Anyone know if this result applies to the Plug-in Prius as well? While it seems to me it should, empirical testing is always best.
I don't watch the speed as it varies with terrain. When accelerating from a stop I watch HSI and try to keep it at the trunk of the "EV" car symbol, then after just a few seconds I drop throttle to about 20% of the HSI area, and then try to go to none or even charge on coasting. Usually its around 18-24 mph for me. I have about 1.3 miles of residential commute most trips out and back.
Thanks Ken. 15 mph also feels like the right speed. Good to get data to back it up. I was curious as I was going for my best mpg on a fill-up and wanted to make sure I was doing everything I could to boost the mpg. I ended up with 72.3 mpg and 700.7 miles. But that was just an experiment and was stressful to maintain, so I'll go back to 55-60 mpg with more normal driving.
Not ALL the energy. I drive to the gym every morning. The most of the first mile is down hill so I pick up 2 to 3 bars on the HV battery. With the right gas pedal operation (as everyone knows) I can use that energy for much of the flat land distance. If I just let the computer decide, it will run the ICE at low efficiency, low rpm some of the time on the flat land.
Not picking on you or anything but that made me remember something funny. This guy at work took the elevator at work to the gym (2 floors down), to use, drum roll please, the Stair Master.
I quite agree with Ken although my earlier studies of the NHW11 suggests 18 mph is the peak speed range. I would add that this area of the performance curve is so flat that +/- 3 mph gives effectively the same result. At these speeds it takes a dead calm as even low winds can move the optimum speed point lower or higher. Bob Wilson
That is good to know. Knowledge is usually good. I also have a PiP now and it is amazing how much driving you can do with a 12 mile range. We are getting 42%. If the battery size were doubled, I think that number could go up to 75% easily. Can't wait to trade my Gen III in for the next Gen of the PiP.
