Most efficient speed for best MPG?

[jayman]

Last summer, there was a lot of road construction on the highway that runs north of the Trans Canada to my hobby farm. A lot of 70 km/h speed limits.

With the car at 70 km/h - about 42 MPH - the MFD claims a consistent 3.7 l/100km: 76 MPG Imperial gallon

[FreshAirGuy]

Originally posted by tomdeimos@Jan 25 2006, 12:12 PM
You're correct there are other efficiency improvements in the Prius.  But the battery is a major one at low speeds.

You can't get the super mpgs by using the engine.  I have tried at various speeds.  I always get better mpg on battery driving on flat roads at 40 mph than on engine at 43 mph.    My best mpg is always when I am on battery about 2/3 or more of the time and I can drive at a steady speed. 

Any time the engine is going  full time I generally get mpg's that are always below 70 mpg.  This includes  slow driving in winter too, when it is too cold for the engine to stop.

[snapback]197045[/snapback]

Someone else has already asked. Nonehtless are you referring the MPG shown on the display while driving or the MPG derived by dividing total miles by number of gallons used? Since the original inquiry referred to effciency which is most commonly an outcome variable rather than a process variable, the changing MPG is not a good measure of efficency. Others have already pointed out that gliding displays 99 MPG but that has little or nothing to do with actual number of gallons of fuel consumed.

[tomdeimos]

Originally posted by FreshAirGuy@Jan 26 2006, 06:09 PM
Someone else has already asked. Nonehtless are you referring the MPG shown on the display while driving or the MPG derived by dividing total miles by number of gallons used? Since the original inquiry referred to effciency which is most commonly an outcome variable rather than a process variable, the changing MPG is not a good measure of efficency. Others have already pointed out that gliding displays 99 MPG but that has little or nothing to do with actual number of gallons of fuel consumed.

[snapback]198232[/snapback]

What I refer to as my mileage is my total trip mileage. I reset the display regularly except when I am checking over many tanks to check the mpg accuracy. (I'm doing that again now, to see if the code update changed anything.)

So it includes my trip, usually to work via back routes that are quite repeatable. 15 miles or so total. I never measure going home, because traffic then is just too variable.

Instant readouts of 80 plus are easy to get and mean nothing, as does the 99 when on battery. But battery use pays well when you are on gas only 1/2 or less of the time and are still getting 50 or better. I go by the total result.

And now that I have my code upgrade I am on battery even more, and my mpg has gone up noticably as a result, except in the cold weather where the engine just has to run full time anyway to keep warm.

For mpg 30 mpg is better than 40 due to air drag alone. And under 40 you will be on battery anyway if your car is working right. Only way to avoid it is in the country with pulse and glide but not practical around where I am.

I am quite happy running on battery trying for 75 mpg or better instead of pulse and gliding and trying not to charge the battery to get 100 mpg with my speed varying all over the place.

[tochatihu]

I have a copy of the US gallons/oF page from the spreadsheet, but could not find the entire spreadsheet, to give due credit to the author. Wayne Brown's program (HSD version) was used. I will try to atatch the image here.

[windstrings]

Originally posted by efusco@Jan 24 2006, 01:25 PM
The 64mph "Sweet spot" once proposed on his site is not true.
The best MPG will be on level terrain b/w 30-40mph.  Lower forces the ICE to run too much in a low efficiency state.  Higher and drag becomes the bigger factor.  It's a linear thing and there's nothing magical about 64mph or 53mph or any other number.

[snapback]196388[/snapback]

Yea.. between those speeds you can utilize the "pulse and glide" technique that has shown to get up to 110mph?
http://hybridcars.about.com/od/owner...seandglide.htm

Of course thats not too practicle for driving on the freeway!

[hobbit]

Seconded. Read up on what the Pittsburgh Marathoners did. It is
nowhere near as simple as a sweet-spot speed -- you have to take into
account what modes the system is running in. The idea with P&G is
that you're running the engine efficiently, or not at all, and NOT
cranking a lot of energy in and out of the battery but using your
momentum to best advantage. For most people, above 41 mph and most
bets are off WRT efficient engine use, unless you know how to use
"warp stealth" that allows the engine to turn but not burn gas.
.
Wayne's site is http://privatenrg.com -- recommended reading indeed.
.
_H*

[vincent1449p]

Originally posted by tochatihu@Jan 27 2006, 09:33 AM
I have a copy of the US gallons/oF page from the spreadsheet, but could not find the entire spreadsheet, to give due credit to the author.  Wayne Brown's program (HSD version) was used. I will try to atatch the image here.

[snapback]198301[/snapback]

The author of the spreadsheet is Didier LUSUARDI and it was created using Wayne Brown's program.

[jdjeep98]

Originally posted by tomdeimos@Jan 25 2006, 08:39 AM
The best mpg is on battery only at around 30 mph.
You should easily achieve over 70 mpg.

[snapback]196983[/snapback]

Is it me, or does it seem odd to you, too, that you would get any reading below max (99.9) when you are using "battery only"...

[kDB]

Originally posted by jdjeep98@Jan 27 2006, 07:10 AM
:blink:  Is it me, or does it seem odd to you, too, that you would get any reading below max (99.9) when you are using "battery only"...  :blink:

[snapback]198541[/snapback]

this happens when the ICE is running but is not helping move the car. usually when the ICE is warming up.

[jdjeep98]

Originally posted by tomdeimos@Jan 25 2006, 09:57 AM
The battery is why the Prius works.

[snapback]196997[/snapback]

Actually, Energy Management is why the Prius works. The battery gets all its energy from the ICE, which burns gasoline. What makes the car efficient is not the conversion, which loses some of the energy in the process, but the management of the car's energy requirements.

That management includes all the little weirdnesses like stopping the ICE when it's not required, regenerating electricity from the car's kinetic energy (something a gas-only vehicle cannot do ever), and balancing the use of electricity and gasoline. ALL the energy used by the car comes from gasoline. The battery is just a big (not big enough, in my opinion) energy buffer.

Technically, you are correct, but it's like saying that the hammer is what makes a house.