A comparison of highway driving methods for the Toyota NHW20 Prius

[JimboK]

After much procrastination, I've finally finished and posted the results of a Prius highway driving method comparison from several months ago:

http://priuschat.com/forums/showthread.php?t=40966

[xcel]

Hi Jim:

___I believe you may have put to much credence into WS? Just last weekend I was driving Larry’s Prius-II and pulled a 70.2 mpg run over 38 miles of Interstate during a blizzard, temps in the 20’s and head/side winds in the 10 mph area while running 95% Highway. RPM’s in the 1250 – 1350 RPM range while running SHM yet again although that is not 60 mph either. Speed limits in Chicago are 55 mph fortunately or not and with the snow, speeds were down in the 40 – 50 mph range so that certainly helped. I know Marc had a recent 80 + mph run somewhere and still pulled > 50 mpg’s which was truly surprising but I have no idea what he was doing other than WS on every slow down with a transition to standard glide below 41?

___The 1.5 should be inefficient as hell at those low RPM’s but I do not see it in the real world.

___Good Luck

___Wayne

[JimboK]

Hi, Wayne. Thanks for the comments.

Any credence I put in WS was before you even planted the seeds for SHM. The testing and the first draft of the writeup have been on my back burner since the first part of July.

Now I want to look more closely at SHM in a test environment. I've had respectable results with SHM at lower speeds and on flat terrain, and I know you're sold on it. Hobbit of course still advocates WS. I'd like to add to the body of knowledge with some solid data from a head-to-head comparison. But almost certainly not until spring.

[xcel]

Hi Jim:

___I completely understand. There is no way to hold 50 + mph in a climb at 1250 RPM and the only way to get back the burn is WS on the other side. Preferably pop it into N before you crest at 40 and enjoy the ride back up to 62 (max) without burning anything on the backside other than the 500 – 600W overhead. Make sure you add that to the discussion because it is indeed a fuel saver in the hills when and where it can be applied.

___Good Luck

___Wayne

[sup'd]

I'll have to re-read your write-up a couple of times, but on the back side of hills in your manual runs did you hold WS or SHM per the same way the computer passes through in CC? (edit: oops you said you did manual first)

If you drive the same route in the same way every day, SoC should be about the same at each point when you do it. The WS or SHM decision the computer makes as it glides for a split second is most likely the best decision you can make in manual mode based on speed and SoC.

Although if you WS for a while when the computer doesn't, the SoC won't be exactly the same when you're making the next decision to WS or SHM. So perhaps as you're building the best manual way on a frequently traveled route, start with manual for first hill then cc the rest, then do two manual then next time, cc the rest, to find the decision the computer would make at each point if you were in CC when going down the backside of a hill.

[mparrish]

Jim,

Great writeup. I've read it once, and probably will many times again. I've been planning on doing my own testing at some point just for my own knowledge & fun. We'll see how those results compare to yours. I may add them to this thread.

I'm a bit partial to SHM simply because of my 66.4mpg RT to Houston to visit Dan at an average 60mph. Now, maybe ECC would have matched that. I honestly don't know.

I found this part of your test interesting:

"The RGPC segments were completed first. A speed of 65 MPH was achieved before crossing the start point. Speed was then maintained between 55 MPH and 65 MPH and RPM between approximately 1400 and 2400 as displayed by CAN-View, staying as close as possible to a presumed ideal of approximately 1700 RPM when terrain allowed. On downhills where speed seemed likely to exceed the maximum despite RPM held at 1400+, “warp stealth” (WS) was applied. (The link describes WS in depth, but in brief, it is a term often used to describe a Prius driving technique where the go-pedal is completely released at speeds above 41 MPH, allowing the internal combustion engine, or ICE, to completely cut off, followed by immediate slight pedal pressure to release regenerative drag. The effect is similar to coasting with the car in neutral.) On uphills, progressively more pedal pressure was applied to keep speed at or above 55 MPH. If 2400 RPM was insufficient to maintain 55 MPH, then more accelerator pedal pressure would be applied; 55 MPH was deemed the lowest safe speed for the test."

When I am SHM'ing it, I target lower RPMS than that. If I'm keeping her between 55mph & 65mph, I will try to "pulse" @ ~2000 RPMs to keep iMPG as high as possible, and then "glide" @ ~1200 RPMs to maximize the iMPG above 100mpg (99.9mpg on the FCD and ~120-140mpg on SGII).

Obviously, on sufficiently hilly terrain it may not be possible to pulse @ 2000 RPMs without falling below 55mph, which traffic may or may not allow. But I do wonder how this lower demand SHM would compare to your higher demand test. Sounds like a good test for me to experiment. More testing, less yakking.

FYI.............since Wayne mentioned it, I should probably offer more details on my high speed / adequate mpg trip:

Austin to Houston:
150 total miles
75 miles of US highway at 75mph
75 miles of US interstate at 80mph
SHM (on the flats) & WS (on the hills) within mph bands of 72-78mph & 77-83mph
A few small towns / lights on the US highway with lower speed SHM & P&G
A small amount of city driving in Austin & Houston
ScangaugeII read 50.3mpg upon arrival in downtown Houston.
AND IMPORTANTLY! Temps were around 60-65F. It is Texas after all.
ALSO! Net downhill of 600 feet over 150 miles. Maybe 50.3 wasn't so good after all.

[locutus]

Hi Jim,

Great writeup! It reads like a [good] science paper. I'll have more empirical SHM-in-cold-weather-possibly-with-snow this weekend, but I really need to get some SHM vs CC vs some-sort-of-HS-P&G data myself in more controlled conditions.

The hills on my route back to see family (particularly right around the MN-WI border) make for interesting adjustments - 2400 RPM and a truck lane, still just trying to keep it above 40.

[JimboK]

Hi, all. Thanks for all the comments!

As I told Wayne, I really want to do what some of you suggest -- a controlled test comparing SHM to WS and CC. Ideally I'd like to make multiple comparisons using a variety of average speeds and terrains.

I also want to repeat this test on a road with steeper hills. My hunch is that WS is still the way to go there. But I prefer hard data to hunches and anecdotes.

Not sure when I'll have time to do all this though. I do have a life.

A key to an apples-to-apples test, but somewhat problematic in comparing SHM to WS, is maintaining the same average speeds (or at least keeping them very close) with each comparison. With CC it's easy: figure the average speed for the manual run and then set CC at that speed. Any ideas?

[hobbit]

I think I espouse WS simply because it's easier for me to find
and hold it with the battery current meter. And it seems to do
pretty well for me. I've made a few honest attempts to do SHM and
it just doesn't seem to keep me going along any better than
judiciously applied WS, although I will try to do more tests
as time permits.
.
I love warp neutral [i.e. start < 42 mph downill in neutral and
keep the engine off]. I was doing a lot of that on the summer
road trips and kicking relative butt. It doesn't last long in
the bigger hills, though, since that would be tantamount to
freefall and we do have to maintain a modicum of control. That's
when the "just how much elevation can this battery suck up"
studies started.
.
_H*

[JimboK]

Originally Posted by hobbit

I think I espouse WS simply because it's easier for me to find
and hold it with the battery current meter.

Even after having CAN-View for several months, it's been only recently (and after this study) that I've discovered an extremely narrow range of pedal pressure where current flow out of the battery during WS can be maintained at 5A or less. It's such a fine pedal adjustment that it often takes several seconds to get it and it's tough to hold it; even a little bump in the road can throw it off. (For the benefit of those without a current meter, 10A or more is the more typical WS scenario.)

I assume you know this. If so, is this your typical WS? And if it is, how much do you suppose that contributes to your favorable WS results? That additional 5A wouldn't seem to make much difference, but through dozens of WS segments over hundreds of miles, maybe it does. Has it ever been -- or can it even be -- quantified?