40 or 28 miles? Which AER driving profile did GM choose?

18071 Views 35 Replies 12 Participants Last post by Tom, Mar 4, 2009

Tom

Discussion Starter · Jun 3, 2008 (Edited)

4

What is your normal driving profile? It will have a huge effect on the Volt’s Average Electric Range, AER. Compare three common driving profiles the EPA75, HWY, and US06. We note that these profiles are dynamometer profiles. They are not done in the wind, rough roads, or on road grades, all of which lower AER. Nor are they done with max power (209 motor hp) to simulate passing. The goal of these profiles was to check and compare emissions, not evaluate EV performance, such as AER.

The EPA Federal Test Procedure, EPA75, is called the City Cycle. It consists of the Urban Driving Cycle, UDDS, followed by the first 505 seconds of the UDDS. It has a top speed of 56.7 mph. It uses a maximum of 37 hp road power. See attachment.

The EPA Federal Test Highway Procedure, HWY, has a top speed of 59.9 mph. It uses a maximum of 30 hp road power. See attachment.

The US06 Supplemental Federal Test Procedure (SFTP) was developed to address the shortcomings with the FTP-75 test cycle in the representation of aggressive, high speed and/or high acceleration driving behavior, rapid speed fluctuations, and driving behavior following startup. It represents an 8.01 mile (12.8 km) route with an average speed of 48.4 mph, maximum speed 80.3 mph, and a duration of 596 seconds. It uses a maximum of 89 hp road power. See attachment.

I did a detailed second by second Volt simulation with these three profiles. The results were an AER of 40.2, 39.6, and 28 miles for the EPA75/UDDS, HWY, and US06 profiles, respectively.

Does anybody have a recommendation for a representative EV driving profile? Google did some work for improved EV fuel economy profiles. I'll check into that.

The simulation is attached below.

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21 - 36 of 36 Posts

cie_lab

· #21 · Nov 18, 2008

I think this is one of the better threads I've read so far (still have a long way to go).

As mentioned, this is just the start. We will see such a tremendous increase in capacity from batteries that we will be laughing at 40 mile range and telling our kids "I remember when..."

Still, it's important to keep it real. One thing this could mean short term is that folks will become much more aware of their driving habits.

Rooster, I particularly appreciate your numbers regarding oil consumption. The irony here could be oil prices so low the it could fool people into believing the oil crisis is over. However, once volt hits the road, I don't think it will matter how low the price of gas gets.

Rooster

· #22 · Dec 6, 2008

Favor to ask

Tom:

Would you mind halving the weight of the Volt in your simulation, to see what it does to EV range, against the 3 EPA test profiles?

The question I'm trying to answer is what percent improvement in EV performance would a light weight composite vehicle allow for in the Volt, all else being equal. If it's not too much trouble, maybe 3 runs using different % weights for the vehicle (50%, 60% and 70% of the 3140 lbs vehicle in your model), plus the weigh of the driver (170 lbs).

You're model, by far, has the most fidelity of any I've seen. I attempted to make one in Excel, but it is no where near as comprehensive as yours. So I trust your numbers more than mine.

BTW, what program are you using? I'm guessing it's not Excel.

Thanks

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pdt

· #23 · Dec 6, 2008

Prius

Tom,

It would also be interesting to see if your model can reproduce the 37% tank-to-wheels efficiency for the Prius published by Toyota.

jrigg

· #24 · Dec 7, 2008

gripperdon said:
Can't people get the message GAS is TOO High, Longer range is the key to selling more, Volume is what GM needs DESPERATELY. Volume will cure most ills. Quit fighting it and making excuses get more range.

Range? I think the Volt is set up to go 40 miles on all electric... and with an 8 gallon tank, it will most likely go another 300-400 miles. That's pretty good range.

Tom

Discussion Starter · #25 · Dec 8, 2008 (Edited)

AER vs Curb Weight

Rooster,

Results are in attachment.

I used Mathcad. Any programming language with numerical integration will work.

pdt,

Compared to an electric motor, an ICE has many functional factors (e.g. air intake/exhaust, octane rating) that need to be modeled to get a reasonable MPG estimate. Additionally, control parameters for parallel operation would also have to be known.

Regards,
Tom

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Rooster

· #26 · Dec 9, 2008 (Edited)

Tom said:
Rooster,

Results are in attachment.

I used Mathcad. Any programming language with numerical integration will work.

Regards,
Tom

Tom,

Mucho Gracias!

I'm going to have to bite the bullet and purchase Mathcad. When I need to integrate, I still use my trusty HP-48SX that I purchased in 1989! It still works great, but it can be a tad slow at times. ;-)

Anyway, your numbers are more in line with what I was expecting. I used a spreadsheet to try and measure the work performed in KWh (ignoring the EV component efficiencies). The bottom-line, my "model" underestimated the efficiency gains, which was my hunch.

The more I read, the more I believe GM is basing their estimates on the FTP and HWY tests alone -- so I think your model is about as accurate as it can be without having the actual performance data. In fact, the more I think about it, I'm not so sure the 2008 MPG regression corrections are going to be applicable to an EV anyway. Once you have the trons in the battery, an EV power-train should be more efficient that an ICE power-train. Consequently, the regression analysis, which is based on ICE power-trains, is likely overestimating the loss of efficiency.

Your model shows a 37% improvement in the CITY profile, and a 29% improvement in the HWY profile by halving the weight. Nothing to sneeze at. I do hope at some point in the future, GM attempts an all composite E-REV based on technology like Fibreforge -- maybe in a Cadillac? Assuming of course, they manage to stay in business.

Thanks again for running the numbers!

Cheers

Any,

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pdt

· #27 · Dec 9, 2008

Tom said:
Rooster,

Results are in attachment.

I used Mathcad. Any programming language with numerical integration will work.

pdt,

Compared to an electric motor, an ICE has many functional factors (e.g. air intake/exhaust, octane rating) that need to be modeled to get a reasonable MPG estimate. Additionally, control parameters for parallel operation would also have to be known.

Regards,
Tom

It seems like you only need to know a few parameters for what I'd like to see as validation. You need to know the drag/friction/mass numbers to determine the energy needed for the drive cycle and a regenerative braking efficiency number (probably an average would be enough, even though it's obviously going to depend on speed/decel rate). Once you have those you'd only need to compare to the published MPG to get an efficiency number, knowing the energy content of the fuel. Compare that to Toyota's published efficiency numbers and you're there. Seems like it should be relatively straightforward, but maybe I'm missing something important.

pdt

· #28 · Dec 17, 2008

Fuel economy vs weight

Interesting numbers regarding the impact of weight on fuel economy.

http://autos.yahoo.com/green_center-article_207/

Rooster

· #29 · Dec 17, 2008

Excellent Article, thanks for posting it. It follows very closely to the calculations in Tom's model of the Volt (see data below):

Volt Curb Wt (100%) = 3140 lb
Driver = 170 lb

EV Range in miles using 3 EPA Test Driving Profiles:
Curb Wt (%) / FTP / HWY / US06
50% / 63.8 / 56.3 / 32.3
60% / 56.5 / 52.1 / 35.8
70% / 51.7 / 48.5 / 32.97
80% / 46.5 / 45.3 / 31.3
90% / 42.9 / 42.7 / 28.9
100%/ 40.1 / 40.1 / 27.5

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pdt

· #30 · Dec 17, 2008

Rooster said:
Excellent Article, thanks for posting it. It follows very closely to the calculations in Tom's model of the Volt (see data below):

Volt Curb Wt (100%) = 3140 lb
Driver = 170 lb

EV Range in miles using 3 EPA Test Driving Profiles:
Curb Wt (%) / FTP / HWY / US06
50% / 63.8 / 56.3 / 32.3
60% / 56.5 / 52.1 / 35.8
70% / 51.7 / 48.5 / 32.97
80% / 46.5 / 45.3 / 31.3
90% / 42.9 / 42.7 / 28.9
100%/ 40.1 / 40.1 / 27.5

I'm still trying to understand the curvature of that data. It seems that as the vehicle mass approaches 0 that the decrease in mass should have a smaller and smaller impact on range due to the increased importance of drag and payload. I guess I'm still looking for validation of the model against some published numbers.

Tom

Discussion Starter · #31 · Dec 17, 2008 (Edited)

Alternative Viewpoint

pdt,

I guess I'm still looking for validation of the model against some published numbers.

GM’s PUBLISHED data gives no information on the US06 or other, e.g. constant velocity, driving conditions, or effects of wind conditions, accessory power loading, climbing grades, increased AER with decreased mass, estimated top speed, or effects of regen for different driving profiles. If you want answers to any of those questions, you have to do an (accurate physics based) model.

There is enough EV1 history, published Volt specs, current motor, converter, and battery tech info to make intelligent guesses about values of the Volt parameters. Obviously, there are many subtleties of behavior that are not known, but their quantitative effects are small compared to known major parameters like mass, motor behavior, frontal cross section/drag, and battery energy.

With regard to the stuff we design and manufacture, in today’s world of integrated circuits and nanotechnology, instruments are incapable of making accurate measurements of some critical parameters at the device’s scale because the measurement greatly perturbs what you are trying to measure. Designers can only get/infer accurate numbers for some critical design parameters with computer models. (You just have to be sure that you model all of the relevant phenomena at that scale. Parameter extraction then becomes a critical design step.) In today’s manufacturing world and beyond, you can’t design an airplane, automobile, new chemical, drug, or nuclear weapon (Lagrangians) or power plant without a computer model. The designer validates the parameter's measured/extracted/inferred behaviour against the well tested and known physics of the computer model, not the other way around. With today's enterprise scale systems, the major present worth of a company may be tied up in its parameter extraction, design, process, and production control models. Potentially, hundreds of millions of dollars of intellectual property in a flash drive.

If you had such a flash drive (or a portion of it) what would you do with it? Your country's national security or economic health might depend on the answer.

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pdt

· #32 · Dec 17, 2008

Sorry

Sorry Tom, didn't mean to be disrespectful. I'm just trying to understand the curvature of the range vs mass data you sent. It seems from your numbers that mass becomes more important at lower mass and my intuition would say the opposite. I could be wrong, I'm just trying to understand.

I also still believe that it would be relatively easy to compare a model such as yours to published MPG/tank-to-wheels efficiency numbers, such as those for the Prius.

fishmahn

· #33 · Dec 19, 2008

Rooster said:
Excellent Article, thanks for posting it. It follows very closely to the calculations in Tom's model of the Volt (see data below):

Volt Curb Wt (100%) = 3140 lb
Driver = 170 lb

EV Range in miles using 3 EPA Test Driving Profiles:
Curb Wt (%) / FTP / HWY / US06
50% / 63.8 / 56.3 / 32.3
60% / 56.5 / 52.1 / 35.8
70% / 51.7 / 48.5 / 32.97
80% / 46.5 / 45.3 / 31.3
90% / 42.9 / 42.7 / 28.9
100%/ 40.1 / 40.1 / 27.5

This looks wrong - the US06 - All the other ranges increase as mass decreases, but the US06 goes down from 60% to 50% mass. Should it be 42.3? Or maybe 37.3?
(I know, I'm not seeing the chart just what was posted in the message - the "net nazi's" at the office don't allow downloads.)

Rooster

· #34 · Dec 20, 2008

fishmahn said:
This looks wrong - the US06 - All the other ranges increase as mass decreases, but the US06 goes down from 60% to 50% mass. Should it be 42.3? Or maybe 37.3?
(I know, I'm not seeing the chart just what was posted in the message - the "net nazi's" at the office don't allow downloads.)

Good catch, that's a typo.

I believe it should be 37.3 miles. Tom couldn't post the actual results of his model -- he's using Mathcad to model the vehicle dynamics, and the file size was too large -- so he had to type the results in a MS Word document that he could zip to keep the file size small.

pdt

· #35 · Jan 31, 2009

Link regarding weight and fuel economy

Not sure if this showed up before. These results are not for hybrid vehicles, but still interesting.

http://www.autoaluminum.org/downloads/AluminumNow/Ricardo Study_with cover.pdf

Tom

Discussion Starter · #36 · Mar 4, 2009

Carnegie Mellon Study Applied to Volt

I did the Carnegie Mellon simulation for the Volt. The results of the simulation are shown at http://www.leapcad.com/Transportation/Re-Simulation%20of%20Carnegie-Mellon%20Study.pdf. The simulation is based on the work found in http://gm-volt.com/forum/showthread.php?t=581 . The CM restudy was done with $700/kWhr and an ICE cost equivalent to the Volt’s performance. The results are that for a 12 year lifetime the Volt’s NPV Average Lifetime Cost is less than that of an equivalent ICE. However, most buyers do not consider the lifetime cost. Research has shown that they base their buying decision on the perceived cost saving only over the first two or three years. Based on this criterion, the typical buyer will not purchase a Volt.

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