Highway Driving Technique (actual)

Since you have a GenII, which adopts well to Super Highway Mode, I was going to suggest searching for details of this mode. But the old thread Scangauge: best threads for mileage improvement is rich in other high MPG details too.

 

I think your strategy is good and certainly your results are, especially this time of year. I'll add a couple of comments.

It's probably less important to keep ICE RPM constant than to keep it out of inefficiently high ranges. It seems as though you're doing that.

Do you have any added instrumentation like a ScanGauge to know your RPM? If not, here's a rule of thumb: During ICE-on conditions, keep the instantaneous MPG at least half the vehicle speed.

Instead of coasting on the downhills, which I assume you're doing with your foot completely off the go-pedal, try what has been dubbed "warp stealth." Follow Fuzzy's link and you'll find an article specific to that (among several other good links).

Super Highway Mode can get you good results on level terrain, but it's not suited for hill country. You need more climbing power from the ICE than what SHM generates. And SHM is tough to do without more gauges.

 

I think if you set the cruise control at 60 mph, you'll see 60 mpg. I'm not abdicating cruise control as an efficient means of travel, it's usually not, but I think you can do better than you currently are.
I think Jimbok is correct in telling you to keep the engine out of inefficient RPM ranges as the key. Without a tach, the best way is the instant mileage readout and of course the ECO light.

 

That can't be good for the HV battery. You are putting more miles on it, using up the cycles.

Have you tried keeping your foot stable running with gas engine? I found my Prius get better MPG (about 10%) once I settle my foot (without wild movement) for about 5 minutes.

 

I have a SG, and at least to my ears at highway speeds, 2800 rpm is obvious engine noise, less than 2200 rpm is barely audible to no engine noise, and 2200 to 2400 rpm audible but quiet noise.

I suggest you try shooting for barely audible -- audible but quiet.
This might mean you start your engine earlier than you have been, if you have to gain enough speed to get over the next hill within your stated parameter of staying above 50 mpg.

Hobbit has said that 63 mpg at 63 mph is about the best he thinks the G2 Prius can do on the highway; it is certainly better than I have ever managed, and I have the benefit of high elevation. So all in all, I think your current results are darn close to optimal, and congratulations already!

 

Try going faster.

On the downhill, at least. I find I get better mileage by not keeping the pedal pressure constant, but by letting the car slow down up the hill, and speed up down the hill.

 

Oh no... I do that too. I try not to, but more often than not, I get the yellow battery discharge arrows because its hard for me to find warp stealth at highway speeds.

 

If you have to do it, don't do it too long. Many short cycles are better than one long cycle.

Understanding NiMH hypercycles (usbseawolf2000)

 

Shouldn't the Prius be smart enough to manage the battery though? Even those that heavily pulse and glide in the Gen II aren't reporting any problems that I've seen yet.

 

Prius BMU does manage the HV battery very well. However the driver's behavior can influence and limit what it can do, especially with the EV button. Note that Gen III has more restrictions and lower speed limit for the EV mode.

The strategy of P&G is to avoid using HV battery. Use ICE to accelerate and glide without using HV battery AND ICE. If you are using HV battery during the glide, you are NOT gliding.

 

I P&G for two benefits:
- Attempt to keep ICE use in efficient range;
- Less time paying penalty of minimum ICE rpm

My HV use depends on terrain. If a trickle keeps me going without ICE use, I use it.
While it is true than HV use will incur ~10-15% penalty from conversion losses, ICE off saves about 2 kW.