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I debated about putting these questions in two different threads but I didn't want to lose track of one because of having a separate post for it. I thought maybe a comparison of these two techniques on the two vehicles would be interesting?

It is no secret that my high numbers have all resulted from heavy use of P&G techniques on the roads I travel. There is a limit to what I can achieve with my (relatively) inefficient engine when compared to say a Civic, Corolla, or Yaris, and certainly in comparison to a hybrid. Naturally I'm curious about the P&G characteristics of the HCHII and the Prius.

So my two questions are this:


Can P&G be used effectively in an HCHII? I know that it is rather quick to add assist, so does this make P&G pretty much impossible to use to any large extent?
How practical is WS in a Prius at highway speeds? Can it be used for P&G or is it too hard to hit for this? Does this relegate P&G to nothing more than the speeds under 41mph for this vehicle?

I would absolutely love to own either one of these cars and I'm pretty sure I'd do significantly (10-15mpg) better than I do currently in my Elantra. I can't afford either at the moment but it is fun to weigh pros and cons. :) To be absolutely clear I've no interest in a bashing thread... I just want to explore the limits of these vehicles when faced with the road conditions I deal with every day.

Essentially, my current commute is pretty evenly balanced between hwy and surface roads. It was more heavily leaning toward hwy travel until last week when I started my new job. The new commute has quite a few stops on the surface roads and stretches of hwy with varying levels of congestion but mostly free flowing. Which vehicle might have the advantage?

My IMPRESSION is that the HCHII is more efficient at hwy speeds but gets killed in the stop and crawl by the Prius. So what about not bad slow and go traffic? It is also my impression that the Prius is a P&G monster at speeds under 41mph but not at higher speeds. Can WS help overcome this? Is the HCHII really unable to utilize P&G because it is so ready to bring on the assist when accelerating?

This may be kind of on the fringe of usable techniques on these vehicles but I'm interested ... so bring on the numbers! I'd love to hear any and all experiences with any of the above questions!!

(Apologies for the long post :o)

Sean--

I can only speak of my experience in my HCH-II, so Prius owners follow up...

My commute is 7.5 miles and all mid-speed surface roads (35-45 mph) with a few steep hills but mostly rolling. There are 11 traffic lights, though only about a half of them are really in play as the others are on sensors or really long timers. This summer, a bad day for me has been 55mpg round-trip and most days I hit 65 depending on the lights. 2007 EPA is 49/51, less for 2008+. Tank averages have been in the high 50s. I do a modified P&G -- mostly my strategy is to get the car in EV-Glide whenever and as much as I can. Oh, and lots of DWB and DWL.

On a long highway drive to SE Minnesota this summer I got 61mpg on a tank by drafting and coasting.

What's it all mean? It sounds like your commute isn't that different from mine with the addition of some highway traffic. Not having driven a Prius that much I don't know how it would compare, but by simply driving moderately and using the HCH's tools, I think you could easily continue your 115% of EPA (especially if you get an 08 with the lower EPA estimate!).

Be mindful that the HCH-II has a tough payback if you dip into the pack much. The reason I don't P&G much is that I haven't mastered how to do it without burning through the pack and getting a dreaded forced charge. --RN

For WS in the Prius, it seems to be dependent on terrain. On the flat at highway speeds, it seems to hang around mostly in efficient RPM ranges with cruise control. Gentle hills don't seem to change that much. I recently did a test comparing CC to manual pedal control, including WS where possible, on a 50 mile stretch of highway with gently rolling hills (results soon to be posted somewhere when I find time for some final editing of the writeup). At 60 MPH the results were nearly identical at ~ 60 MPG. On the other hand, I've gotten better than 60 MPG on other highways with more hills and mostly faster speeds (though not in a test setting), making liberal use of WS on downhills.

Hi Sean,

WS in the P-II will improve your results for the "middle speed" range, 42-55 or so, and as JimboK mentioned, if used according to terrain (use on the backside of a hill, for example). Hobbit has a write-up with some technical info here:

http://techno-fandom.org/~hobbit/cars/warpstealth.html

As you increase speed beyond 55 on flat terrain though, you're probably better off going for a DWL/steady-state than trying to actually P&G.

When I came back from HF '07, I would go to 55 mph and would let the speed slowly bleed off down to 45-50. I would accelerate to 55 at a TPS of ~25 and bleed off speed at TPS of 18. I ended up with a trip of 72.5 mpg.

Hey, great info from all!! That link from Hobbit was especially helpful.

And Larry... for Pete's sake, man, is there some kind of law that keeps you from getting anything less than 75mpg in your Prius??? :eek:

So, it sounds as though WS in a Prius is quite accessible as long as the SOC is high enough -- that would seem to make it a very useful tool at high speeds as long as the terrain is well known.

RN, the numbers you are quoting from your HCHII are very encouraging! I actually had one heck of a commute for the first part of my drive home today (high of 59.7mpg!!) but the traffic the rest of the way just crushed me down to 46.6mpg :( -- wish I could borrow an HCHII to see how it would do in that situation!

Is anyone else using P&G in an HCHII?

Hey, great info from all!! That link from Hobbit was especially helpful.

And Larry... for Pete's sake, man, is there some kind of law that keeps you from getting anything less than 75mpg in your Prius??? :eek:
So, it sounds as though WS in a Prius is quite accessible as long as the SOC is high enough -- that would seem to make it a very useful tool at high speeds as long as the terrain is well known.

RN, the numbers you are quoting from your HCHII are very encouraging! I actually had one heck of a commute for the first part of my drive home today (high of 59.7mpg!!) but the traffic the rest of the way just crushed me down to 46.6mpg :( -- wish I could borrow an HCHII to see how it would do in that situation!

Is anyone else using P&G in an HCHII?

Well, there was some paperwork I signed at the dealer that I didn't read over real well...:D
But seriosly, I have a pesonal goal to get no less than 70 mpg for any segment. The really short segments usually make that impossible but anything over a mile or two I usually make the goal.

I must say that my HCHII does fine in highway driving. But I find that when I hit some decent slow-n-go traffic, or as I have started calling it pulse-n-glide traffic, I don't see my FE drop at all. It's actually a blessing - traffic may make me get home 20 min late, but my FE won't hurt for it. Just gotta be careful to leave good buffers and avoid the brakes. It's almost been a forced training in p&g, which I didn't really have much faith in before.

I don't get the chance to do much highway/interstate driving in the HCH II, but I do have a few observations from the chances I do get. In nice weather, I am able to get in the low 70s on mild hills by DWL with a lower speed limit of 50 mph. Kenny over at GH had a full tank at 71.65 mpg where most of his driving was interstate with CC at 48 mph.

http://www.greenhybrid.com/discuss/showthread.php?t=14301

His results illustrate well how the HCH II can do in these steady state conditions at moderate speeds.

As for P&G in the HCH II, I know xcel broke 100 mpg in the HCH II, but I am not sure of his conditions. The assist can be an issue. It will diminish as you get to 4 bars and pretty much go away at 3 bars SOC. However, this will be an issue if you go from a road where you can freely P&G to one where you need to maintain a steady state speed. This is when you will really get the forced charging hit.

Thanks for the reply, John! That pretty much confirms what I thought I remembered. Is assist more a problem at low as opposed to high speed P&G? I was wondering if it might be possible to use P&G for the in-town traffic where the speeds are really low anyway but there is more traffic. My guess was that maneuvers at that speed would be darn near impossible because that is when the engine has the least torque and the car would be most ready to throw assist into the equation to help out.

Good or bad guess?

It wouldn't be too hard for me to drop the P&G routine for a car that was able to pull the high stuff without it, but I'm kinda thinking for fairly frequent slowdowns at city speeds there isn't anything to beat it...

Hi Sean,

On my daily commute,
- I tend not to use P&G on purpose in the city portion of the commute - rather just DWB and maintaining steady posted speed limits while trying to keep assist/regen at zero balance. This typically nets me 50-60.

- The longer part of my commute is hiway at 60 or 55mph using mostly steady CC. Some trucks get in the way of the wind for me and tend to get 65-75mpg at these speeds.

- Running naked into the wind and no AC, I usually get about 66 at 55mph, 62 at 60 and 53 at 65. I suppose 50mph would net about 70 or so. Kennys tank at 48mph/71mpg seems to be in line with this.

Those are some pretty solid numbers there, SpartyBrutus!

It is sounding more and more like P&G is pretty much out for the HCHII. That's too bad... I did see the post from Wayne with the 103mpg trip in and HCHII but if you can't avoid the forced regen afterwards, what's the point?

Sounds like what is really needed is the Assist Inhibit that MSantos is working on. Hitting that when you are in good P&G situations would make acceleration sluggish but keep you from depleting the pack.

Tara, if you are reading this thread what results have you had from P&G?

I’ve been following this thread and certainly haven't ignored it, just no time to sit and write a deserving reply. Thanks for your patience, Sean.

First off, for the HCH-II I put down a lot of thoughts about P&G, and also got some excellent feedback here:
http://www.cleanmpg.com/forums/honda/t-pg-techniques-for-the-hch-ii-4521.html

Like SB, I also don’t use P&G much in the city – I rely more on DWB, and simply maintaining the iFCD high as possible. I might P&G from stoplight to stoplight, but it’s very difficult to build mileage that way. This is where the Prius shines. In the HCH, each acceleration will steal from 1-3mpg, and each coast will give back maybe 1-4mpg so it takes a string of really perfect cycles to get much over 50 in the city.

However there is this “golden stretch” of a couple miles on my way home where I can hold a glide forever, the lights are timed, the traffic is light, and there is just enough downward slope to keep the car going at a constant 30-35mph. This is the only city driving my HCH likes and I can count on this street to always raise my FE by 1 or 2 mpg on top of whatever I had a few minutes ago on the freeway. However obviously the pulses are few and short, it’s mostly all “glide”. :)

The major part of my commute is freeway driving at 50-55mph (without CC). On the way to work my route is slightly net downhill and this is where I get the best numbers. It is the sheer continuity of speed that seems to makes the difference. When I find a truck, bus or other large, slowmoving object to drive behind, that combination of ‘pace car’ and ‘windbreaker’ is unbeatable. Traffic or an accident simply tends to slows cars to a constant speed, and for some reason there are few contractions, so "traffic" means I’m able to cruise over 10 miles at a steady 43mpg, and again the car is in its element. Of course I realize this is also the beginning of the segment, where numbers can build quickly.

On the way home it’s slightly more uphill, and there are more traffic contractions here than on the way to work so here I use P&G the most to naturally flow with the traffic. If the glides are long and timed right I can do pretty well here also. But often I’m just barely able to maintain the same FE I got going to work. I’ve lost count many times I’ve cracked 70mpg going to work, but ended up at 68-69mpg for the RT getting home :(. So bottom line is, I think the car (and I) are happier maintaining even speed than with P&G. P&G done with any sloppiness seems more damaging than no P&G.

Msantos seems to have figured out how to use P&G to best advantage in his HCH-II however, so you may want to review his methods in the link I cited above.

Excellent information, Tara! That was an outstanding thread you linked to as well. Thank you!

It sounds as though P&G in the HCHII is quite doable but extremely finicky. The pack depletion is what really worries me, and it would seem that the driver would have to be extremely deft with foot control to avoid it.

Very interesting! Now I just need some time in each car to try it out for myself. ;)

Excellent information, Tara! That was an outstanding thread you linked to as well. Thank you!

It sounds as though P&G in the HCHII is quite doable but extremely finicky. The pack depletion is what really worries me, and it would seem that the driver would have to be extremely deft with foot control to avoid it.

Very interesting! Now I just need some time in each car to try it out for myself. ;)

I can help you out with one of them.;)

I can help you out with one of them.;)

Sweet!!! :D I'm really looking forward to the 25th. :woot: