Most efficient speed for best MPG?

[ken1784]

Hi Bob,

Thank you for the data.
It looks the majority(for 25 minutes vs 40 minutes total) period is about 75 mpg which meets Wayne's chart.

However, your total average shows 99.9 mpg.
My math tells me you have to record more than 200 mpg on the rest of 15 minutes to achieve the 99.9 mpg average.
What happened on another 15 minutes?

Ken@Japan

[bwilson4web]

Hi Ken,
<div class='quotetop'>QUOTE(ken1784 @ Mar 11 2007, 11:06 AM) [snapback]403791[/snapback]</div>

Thank you for the data.
It looks the majority(for 25 minutes vs 40 minutes total) period is about 75 mpg which meets Wayne's chart.

However, your total average shows 99.9 mpg.
My math tells me you have to record more than 200 mpg on the rest of 15 minutes to achieve the 99.9 mpg average.
What happened on another 15 minutes?
[/b]

During this test, I didn't have the Graham scanner recording the data. But during the whole of the test, the MPG numbers were never less than 95 MPG at the end of the engine runs. I suspect but do not have the supporting data, yet, that the graphical display follows a different summary approach from the numerical value. At the end of this note, I'll describe some of my limited testing.

I am sorry for not posting both the spreadsheet, calculated_MPG_Rev_A.xls, as well as the graph:



In this revision, I added a second MPG graph based upon my measured 511 W. of fixed overhead power. Regardless, folks can pickup my spreadsheet and easily do 'what if' analysis by changing engine efficiency, fixed power overhead and easily make fully metric graphs. Certainly, analysis of my formulas is fair-game to see if I may have made a mistake. But what is most important, critical to any model, is getting benchmarks since it is testing and testing alone that lets us validate a model.

I have a couple of suggestions for folks who plan to add benchmark data. The NHW20 and NHW11 models have different rolling and coefficients of drag. Also, vehicle maintenance, tires and lubricants, have significant impacts. Finally, the North American NHW11 has an ICE coolant, lower limit of 60C and without a thermistor hack, should be used only for higher speed benchmarks where, sad to say, the differences between the two curves is moot. However, all other NHW11s and all NHW20s should provide valuable, low-speed data. In particular, one hour tests at a constant speed of 15-20 mph on a flat, empty parking lot would be very helpful.

As I mentioned earlier, I'm suspicious of the MFD display 'graphical' bars. I found that if I keep the speed below 6 mph, the graphical display, 5 minute interval appears to use some combination of the instant graphical display bar on the right for each 5 minute summary. This means you can use the battery to reach 6 mph to trigger a 100 MPG bar and back off. This fools the graphical display into displaying a solid, set of 100 MPG bars:

DISTANCE: 0.3 miles
MODIFICATION: thermistor hack (critical in cool weather!)
METHODOLOGY:
(1) fully warm up car and charge battery (~20 minutes above 42 mph)
(2) regen slow down to enter a flat, empty parking lot
(3) put car in "N" and coast to a stop with minimum electrical load and reset MFD
(4) after 'mileage bar' updates, put car in "D" and gently accelerate to 6 mph to get 99.9 'current' bar and then put in "N" and coast to a stop
(6) repeat step #4 until all bars show 99.9 MPG
(7) take photos and have a happy

My plan is to refine the Graham scanner analysis and see if that data can be used to cross-check the graphical and numerical values from the MFD. Then perform as series of tests to see if we can reverse-engineer the algorithms.

Bob Wilson

[mwbueno]

Hi all,

Find below a graph depicting what the latest Prius Energy Use Simulator outputs. Over the last 3 years I have gone out and performed several low speed tests to get better low speed data which was quite lacking before. A surprising things to note is that 20 MPH is the absolute best speed for high mileage in a Prius. This actually surprised me so, I tested for it several times. All tests were done without implementing pulse & glide techniques. I simply kept the speed on a level test track on non-windy days & let the HSD cycle through several full SOC patterns before taking the average. The graph below is based upon the following input variables:

Temp: 88 F -- About as hot as one can do without A/C & windows up for several hours.
Elevation: 400 feet above sea level
Humidity: 59%
Barometer: 30.03 in/hg
Wind: NONE
Auto A/C: OFF
Fuel: Summer Blend 114,500 BTU per Gallon US
Road Rolling Resistance: Smooth Dry Asphalt
Tire Rolling Resistance: 0.0077 -- OEM Integrity @ OEM pressures






Best Regards,
Wayne -- http://privatenrg.com

[usbseawolf2000]

Thanks for your hard work Wayne with all these testing. Oh wow! 110 MPG at 20 MPH.

[bwilson4web]

Hi Wayne,
<div class='quotetop'>QUOTE(mwbueno @ Mar 21 2007, 05:52 PM) [snapback]409821[/snapback]</div>

. . . Over the last 3 years I have gone out and performed several low speed tests to get better low speed data which was quite lacking before. A surprising things to note is that 20 MPH is the absolute best speed for high mileage in a Prius. This actually surprised me so, I tested for it several times. . . .
[/b]

I've done one benchmark at 15 mph in my NHW11 that pegged the MFD mileage number at 99.9. I was wondering at what speeds under 30 mph you've run benchmarks?

The reason I ask is I was planning to run benchmarks at:
<blockquote>10 mph
15 mph
20 mph</blockquote>

Thanks,
Bob Wilson

[Mister Swigart]

I would like to raise a question along the same lines as was proposed here:

If you put a Prius up on rollers and made a chart of the performance for this car and perhaps using the cruise control to maintain each given speed above 25 mph, at what point would it peak? I am talking about the ICE and not trying to run off the battery or using pulse and glide. I think there must be charts or graphs of such things. It would be interesting to make such a chart at 1 mph increments from 25 to say 70mph. Anyone got the rollers you put one on? The instantaneous mpg will still change somewhat from moment to moment, I predict, but the changes could be recorded to find the mean for equal intervals of time, say 10 minutes. Keeping the engine at a constant temperature might be tricky, but a well-warmed up car could be tested by the lay-person, I would think.
Anyone?

The Lone Ranger

[ken1784]

<div class='quotetop'>QUOTE(mwbueno @ Mar 22 2007, 07:52 AM) [snapback]409821[/snapback]</div>

Find below a graph depicting what the latest Prius Energy Use Simulator outputs.[/b]

Hi Wayne,

Nice to see the updated graph.

Thank you,
Ken@Japan

[mwbueno]

[quote=bwilson4web @ Mar 21 2007, 10:30 PM) [snapback]409972[/snapback]</div>

Hi Wayne,
I've done one benchmark at 15 mph in my NHW11 that pegged the MFD mileage number at 99.9. I was wondering at what speeds under 30 mph you've run benchmarks?

The reason I ask is I was planning to run benchmarks at:
<blockquote>10 mph
15 mph
20 mph</blockquote>

Thanks,
Bob Wilson
[/b]

Hi Bob & All,

I have done 5, 10, 15, 20 & 25 benchmarks under 30 MPH... I will add 30, 35 & 40 MPH since I have them also. I will be glad to share the results but, because they were done over a period of several months (I had to wait for windless days; each test takes over 4 hours) so, one will need to note the temperature differences. I will post the actual data along with the Temperature for that day & then another column with the temperature corrected to a 77 °F baseline which the initial 5 MPH test was done at.

I also corrected for humidity & barometric pressures on each test to match test one] 5 MPH. One other thing that I did for the raw test data is ran my tire pressure @ 50 psi all the way around. I have driven over 230,000 miles in Prius vehicles fitted with 44 psi sidewall posted maximum tires always @ 50 psi so; I will show another column with Integrity tires running at OEM pressures.

All data below was gathered based upon the following variables -- These variables are important to note as some of them can make quite a large difference in mileage outcome:

Temp: 77 °F -- Unless otherwise noted
Wind: NONE
Barometer: 30.03 -- Raw data adjusted in simulator to match baseline when necessary
Humidity: 59% -- Raw data adjusted in simulator to match baseline when necessary
Elevation: 400' above sea level
Air Cond: OFF
Load: 450 lbs. above OEM vehicle weight
Fuel: Gasoline Summer Blend -- 144,500 BTU or 120.804 MJ per Gallon-US
Tire Rolling Resistance: .006 -- Goodyear Integrity tires, 80% worn @ 50 psi unless otherwise noted
Road Rolling Resistance: .001144 -- Dry Smooth Asphalt


......................ACTUAL.................MPG @.....................MPG @...........................MPG @
SPEED.........TEST TEMP...........TEST TEMP..........Adjusted to 77 °F..........OEM TIRE PSI
..5 MPH............77 °F...................51.11........................ 51.11............................48.32
10 MPH............80 °F...................90.01........................ 88.81............................82.57
15 MPH............71 °F...................99.23......................10 2.15............................94.37
20 MPH............88 °F.................116.90......................110 .36..........................101.78
25 MPH............92 °F.................111.70......................103 .11............................95.18
30 MPH............86 °F.................100.05.......................95 .49.............................88.38
35 MPH............79 °F...................89.91.......................8 9.02.............................82.69
40 MPH............89 °F...................88.93.......................8 3.79.............................78.16

Best Regards,
Wayne -- http://privatenrg.com

[bwilson4web]

[quote=mwbueno @ Mar 22 2007, 02:35 PM) [snapback]410344[/snapback]</div>

. . .

Temp: 77 °F -- Unless otherwise noted
Wind: NONE
Barometer: 30.03 -- Raw data adjusted in simulator to match baseline when necessary
Humidity: 59% -- Raw data adjusted in simulator to match baseline when necessary
Elevation: 400' above sea level
Air Cond: OFF
Load: 450 lbs. above OEM vehicle weight
Fuel: Gasoline Summer Blend -- 144,500 BTU or 120.804 MJ per Gallon-US
Tire Rolling Resistance: .006 -- Goodyear Integrity tires, 80% worn] 50 psi unless otherwise noted
Road Rolling Resistance: .001144 -- Dry Smooth Asphalt
......................ACTUAL.................MPG @.....................MPG @...........................MPG @
SPEED.........TEST TEMP...........TEST TEMP..........Adjusted to 77 °F..........OEM TIRE PSI
..5 MPH............77 °F...................51.11........................ 51.11............................48.32
10 MPH............80 °F...................90.01........................ 88.81............................82.57
15 MPH............71 °F...................99.23......................10 2.15............................94.37
20 MPH............88 °F.................116.90......................110 .36..........................101.78
25 MPH............92 °F.................111.70......................103 .11............................95.18
30 MPH............86 °F.................100.05.......................95 .49.............................88.38
35 MPH............79 °F...................89.91.......................8 9.02.............................82.69
40 MPH............89 °F...................88.93.......................8 3.79.............................78.16

Best Regards,
Wayne -- http://privatenrg.com
[/b]

Thank you! Thank you! Thank you!

My benchmarks have not been as rigorous but your 15 mph data agrees nicely with my 10 mile test with the NHW11 thermistor hack. How do you handle warm-up?

In my case, I drive for about 20-30 minutes at speeds above 45 mph, typically 55-65 mph. Testing last summer revealed this brings the transaxle oil to thermal equilibrium at +50F of ambient. I then drive a mile or so at urban speeds, 35-38 mph, to my test area, a large, flat parking lot in a shopping mall that is undergoing renovation and do one loop, ~0.9 miles, to let the car approach steady state conditions. Although not a perfect solution, it seems enough to give reproducible results. I used the MFD display for the MPG.

When I ran my 15 mph benchmark, I was also testing a thermistor hack. The North American NHW11 has a lower coolant temperature limit of 60C that forces ICE operation even if power is not required. Ken's data from Japan indicates the NHW20 and all other NHW11s can go much lower and start ICE auto-shutdown as low as 40C. I only mention this because I don't know if there is a lower coolant temperature limit for the NHW20 that might trigger ICE operation when moving.

Great data!

Thanks,
Bob Wilson

[bwilson4web]

<div class='quotetop'>QUOTE(The Lone Ranger @ Mar 22 2007, 12:04 AM) [snapback]409990[/snapback]</div>

I would like to raise a question along the same lines as was proposed here:

If you put a Prius up on rollers and made a chart of the performance for this car and perhaps using the cruise control to maintain each given speed above 25 mph, at what point would it peak? I am talking about the ICE and not trying to run off the battery or using pulse and glide. I think there must be charts or graphs of such things. It would be interesting to make such a chart at 1 mph increments from 25 to say 70mph. Anyone got the rollers you put one on? The instantaneous mpg will still change somewhat from moment to moment, I predict, but the changes could be recorded to find the mean for equal intervals of time, say 10 minutes. Keeping the engine at a constant temperature might be tricky, but a well-warmed up car could be tested by the lay-person, I would think.
Anyone?
[/b]

Let me offer some data and an explanation:

http://hiwaay.net/~bzwilson/prius/pri_test.html

The critical data is the cycling between ICE-ON and ICE-OFF modes:


The car constantly cycles from ICE-ON to move the car and recharge the battery, and ICE-OFF when the battery alone provide motive power. During the ICE-ON time, it runs between 10-20 hp, a very efficient power range. As the speed increases, the duration of the ICE-ON times increase and the durations of the ICE-OFF times decrease. But the ICE power range remains between 10-20 hp. There is one exception, at 15 mph, it stays between 10-13 hp. But the power cycling remains the same.

One other aspect is the Power Split Device tansaxle also keeps the ICE torque gently sloping from 1,650 to 3,050 rpm and flat thereafter. This is important because it gives exceptional specific fuel consumption:




This is magical-mystery technology compared to any ordinary car:





Questions?

Bob Wilson