New technique works pretty well for me

Sounds like it's working, keep it up!

You may be able to do a bit better by accelerating at slightly higher RPMs and then slowing down sooner - but if you're really getting close to 70mpg, you are already doing better than 99% of the people here.

 

I DONT KNOW WHAT THE RED LINE IS FOR THE PRIUS ice, BUT I'D GUESS ITS SOMEWHERE AROUND 6000 (sorry didnt see caps were on), i've always taken all my ICE's to the red line for brief periods from time to time, for various good reasons..just a thought

 

Hi Lefat etal.,

The Red Line on the second generation Prius is 5500 rpm, and the first generation I think is 5000 rpm. If you do a google on the THS II and Prius you should find the Toyota paper on the THS II improvements (what is called HSD now), which has this information in it.

I have recently gotten some additional instumentation for my Prius (mycanscan - eeepc) and find its really neccassary to do a peak BSFC (specific fuel consumption) accelleration. This is in normal traffic, with cars in front of me.

There is a trade-off with RPM and BSFC. The higher the RPM, the more the pumping losses per unit time. But the engine also has an internal aerodynamic design which effects how much energy from the exhaust is used to pull in a fresh charge. This helps to offset the pumping losses. So, BSFC tends to peak about mid RPM to slightly higher in a traditionally tuned engine when one is upshifted.

The Prius engine is somewhat different than this. Somewhere on here are plots of the Prius BSFC Torque/RPM curves. I seem to remember the peak BSFC (energy out for fuel consumed) performance is around 2000 RPM, which is less than 1/2 the RPM range. And assuming the Prius computers load the torque for max fuel efficiency, that has been what my target has been.

Syyycko, my best guess as to why this is working for you is the engine-on consumption. Each time the engine starts, its been said it uses a tablespoon of fuel, which would otherwise run the engine at the low level for a minute or so. At the lower RPM, it takes longer to charge the battery, before the car will turn off the engine and run on battery. Depending on the time between stops on the road, you could have found an advantagous situation. The Prius engine design is specifically targetted at not loosing as much efficiency at lower power levels, than other engines, so running it longer at these levels, might have an advantage over running it at higher efficiency higher RPM, if the circumstance of the number of on/off cycles during the period would be more. The Prius computers will also load the engine so that the throttle valve has to run quite wide open, even though the engine RPM is low.

On reflection, this might have something to do with the battery size. The Prius battery might be too small, to run the engine at peak efficiency, long enough, to make the engine-on consumption inconsequential. I believe I read somewhere that some people have put in bigger battery packs, but not charged them externally, have also gotten much better mileage. This may be the reason.

With a 10 mph tail wind, I can cruise at 60 mph with 1350 RPM. And only on occaision need to blip the peddle to no more than 2000 rpm to crest a small hill. Unfortunately, this rarely happens this time of year, as the wind is mild in the morning, when I am north bound, and the prevailing winds out of the south-south-west would help. And the wind is quite heavy in the evening when I am southbound, into it.

 

syyykko, I think you're doing a great job.

Explore these threads for more info:

http://priuschat.com/forums/fuel-ec...ccelerate-fast-slow.html?highlight=sweet+spot

http://priuschat.com/forums/prius-main-forum/42496-gas-only-mpg.html?highlight=sweet+spot

http://priuschat.com/forums/newbie-...ve-break-procedure.html?highlight=engine+load

I assume you have a Scangauge II to be getting RPM's. When the engine is warm you might try pulsing @ 1500+ up to speed and then get it into glide for ICE completely off, and see how that works for you. Driving slow all the time tends to p.o. other drivers while not fully utilizing the abilities and aerodynamics of the car.

 

my only concern for running up to or near red lines (ocassionally) on ICE's is: 1-max hp is there and unless there is a significant difference with respect to the Prius ICE, the Prius ICE will never see its full potential 2-this being said, i have dyno'd many ICE's and found that those that have been red-lined, have consistantly run more efficientally and with higher hp throughout the power bandwidth. not sure i'd want a prius that has say 75k miles on it that only maxed at 1200rpm thru its lifetime, maybe i'm way off, but i still give mine a kick in the nice person now and again, i get 50+mpg, ICE runs and sounds great at 10k miles...now for some vance and hines long shots and a lowering kit..lol

 

This makes me wonder whether, when you were doing pulse and glide, you were gliding properly. In the context of the P&G technique, a glide is not something the battery "kicks into." In fact, a properly executed glide is designed to minimize battery draw as much as possible. It is done by completely releasing the go-pedal and then immediately applying just enough pedal pressure for all the arrows to disappear from the Energy display -- in other words, no current either to or from the battery. (In reality, you're actually pulling a few amps, but that's minimal in the big scheme of things.) This is roughly equivalent to putting a conventional car in neutral and killing the ignition, allowing it to freewheel.

What you seem to be describing is "stealth" mode. The car will do that on its own in steady-state driving with sufficient battery charge, as you obviously have found. And you can call it up on demand with a little more pressure on the pedal than what it takes for a glide. Whether spontaneous or driver-induced, the Energy display will show arrows flowing to the battery.

Stealth is not as efficient as gliding. If your first attempts at P&G were done to maximize stealth (intentionally or otherwise), that might have been part of the problem.

Regardless, congratulations of your efforts and your results. They will only get better!:cheer2:

 

Here is a BSFC graph for the Prius, don't know which gen:

http://us1.webpublications.com.au/static/images/articles/i1102/110216_5lo.jpg

The accompanying text reads: "The Toyota Prius petrol electric hybrid
uses its pseudo-CVT and strong low-rpm electric assist to keep the 4
cylinder internal combustion engine working as much as possible in the
area of low SFC (red line)."

The graphed red line seems to be sitting right on the 1184 RPMs noted by
OP.

How are the BSFC graph and OP's experience related?. Help anyone?

Graph and text extracted from:

AutoSpeed Apr2008

NB: I see potential for confusion here as "red line" has been used for two
different things: red line = max RPM, and the red line on the graph. I've
edited the above to say "Graphed red line" to set it apart.
Recommend others do the same.

 

Hi syyykko!
Good job finding a technique that works well for your driving conditions!
After all, what counts is the results. I'll let the others argue the theory.

I have a tip for possibly further enhancing your technique.
Instead of letting it "kick into glide when ever it wants to", try coaxing it into glide whenever you are going downhill and whenever you have to slow down.

 

Hi Rokeby,

I think that redline graph is for the first generation Prius, as its max RPM is 4500 RPM.

Also, note that the contour lines are the BSFC curves in grams of fuel per KWH mechanical shaft energy generated. The minimum (best economy) grams/KWH is at about 2600 RPM.

The Red Line on the graph is the line that computer tries to run the engine at to get best economy . At the 1100 RPM, the curve starts at 500 grams/KWH, or more than twice the fuel used per KWH than at 2600 RPM. This is the socalled granny syndrome - super slow accelleration delivers very poor fuel economy. By the time the red line is at 1250 RPM, its up to 240 grams/KWH, and the improvement to 2600 RPM is only up to maybe 227 grams/KWH. So, engine-start consumption probably has a great impact there. Its a harry edge (1100 rpm to probably 1184 rpm) between the granny syndrome, and best mileage in the stop-and-go enviorment.

Also, the curve shows its probably OK to breifly accellerate up to 3500 RPM (if you can do so without using up battery), as long as your not going to have to stop the engine for a long time. Since this has the same engine efficiency as at 2200 RPM. Like getting onto the highway at an on-ramp. But, the rest of the system might not have the best effiiciency at these power levels, due to heating of the conductors, and battery size.

Another possible explanation is the pedal control programing. When first accellerating, the Prius brings on the battery and the engine power. Hold the pedal stationary, and in about a second the battery drops out, and the engine maintains. Best mileage will have the least amount of electric energy swaps. So, holding the pedal steady will minimize the electric energy swaps, as the car will drop out of electric assist faster that way. Resulting in less electric energy o be replaced later.

 

I think you are definitely on the right track. I drive in a similar manner and had 76.8 mpg on my last tank of 530.8 miles. I will begin keeping a closer eye on my rpm's to see if I'm staying in the same range as you. Keep up the good work as you are obviously on the road to pulling the full potential out of these great cars.:clap2:

 

Judging from your numbers and RPM, I assume your cruising at about 45 mph correct? 45 mph at < 1200 RPM will likely put you "Super Highway Mode" even though your in the city. Thread on the subject is here: New Prius - "Super Highway Mode" Technique (SH). - CleanMPG Forums .

Your right to look at IGN. I'd keep that up, and be willing to guess your at 13 of 14. This should yield between 70-75 mpg over extended periods. The trick is not to fall off of that IGN number. It's sometimes like chasing a magnet and you'll see IGN stick at 17 down at that level. If it does your MPG will rot. Once you get the IGN at 13 or 14, so long as you hold TPS and RPM it should stay right there.

As a side note, I definitely agree with Jimbo. P&G should yield some big numbers so long as your maximum speed is below 40 mph. You also have to keep an eye out for the false glides. No lines on the MFD but the engine is running at 1000 rpm. Only the SG will tell you if your in a real glide or a false glide.

11011011

 

It's fascinating that Julian Edgar used a shrunken and colorized
rehash of a graphic *I* hung out there quite a while ago, as opposed
to digging a fresh copy out of the SAE paper it originally came
from. It's on page 7 of SAE paper 2004-01-0064, a copy of which
is in the "files" section of the toyota-prius-sat1 yahoogroup
[which you have to log into yahoo to access, unfortunately].
When I snarfed it I added the SAE number to indicate credit.
.
I wouldn't put 100% credence in that chart's numbers. There's
the theoretical curve of the engine alone, but from a SYSTEMS
perspective I think a lot of us have found that the optimal RPM
range is shifted significantly downward in real life due to
fewer losses elsewhere. Exactly where that range peaks has been
the subject of years of debate, but it's fairly broad and flat
so people who get anywhere into it generally do pretty well.
.
Over 2400 RPM frequently yields way more acceleration than you
might want under many circumstances, too. Personally, I don't
like launching myself across intersections because of the, uh,
wireless communications enthusiast barreling toward me from some
other direction. In fact I try to use 2400 as my *upper* limit
unless I need to go up a big hill.
.
_H*

 

I'm doing P&G pretty much exclusively. I pulse at ~1100-1700 rpm's or so up to a high of 40 mph then glide down to ~30 mph or lower when I'm coming to a stop sign. Your technique seems similar to the steady state cruise testing that is being discussed in another thread.

 

Hey syyykko and others,
Just wondering, about how many MPH are you guys going when you're at ~1184 RPM? Is this on the freeway?

And what might you recommend for freeway driving for those that don't have the Scangauge? (I don't have scan gauge, but I can get 50+ MPH if I stick to around 55 miles an hour.)

I do pulse and glide on city streets when possible.

Thanks so much!