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

18072 Views 35 Replies 12 Participants Last post by Tom, Mar 4, 2009

Tom

Discussion Starter · Jun 3, 2008 (Edited)

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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Koz

· #8 · Jun 6, 2008

Tom said:
As the Section “Find the Single Charge (@SOC = 50%) Cruise Range for a given Velocity”, in my attachment states, TInvE, is defined as the Traction Inverter Efficiency and GPE is the Gear Power Efficiency. Their product is 83.2%.

Consider all the Power Train elements in this product. Let’s take the highest estimates for these Power Train components: Battery IR losses (98%), Buck Inverter Efficiency (97%), Motor Efficiency (92.5%), and Gear Power Losses (95%). This product is 83.5%. Without any evidence to the contrary, I don’t think it is reasonable to assume higher efficiencies.

I believe the 8KWh that has been bantered about is for energy out of the battery and not totak diminished. Not that 2% will make a huge difference but every little bit helps. GM has said 40 miles end of life is their goal and beginning of life will be more like 50. Hopefully that pans out and must mean more than 8KWh in the beginning. I can't wait for them to start divulging more information, but this tidbit will probably not be divulged until late in the game. I do think they could tell us the cross sectional drag (Cd*A) without giving away too much. Maybe Lyle could ask for this in his next interview with GM

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Koz

· #11 · Jun 6, 2008

Tom said:
Koz,

With the large currents (peak ~ 400A, cruise @ 50mph ~ 30A), I would think that I^2R power losses in general, (cabling, battery terminals, connections) could easily be 2%. 100milliohms and 50A average current ~ 3% power loss.

I thought you were referring to internal losses in the battery. 2% seems like a reasonable swag for line and terminal losses.

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Koz

· #16 · Jun 6, 2008

Tom said:
I ran the program with 10Hz data files and required program changes for 10 Hz sampling. I got the same numbers as the 1 Hz files within 0.05%. Apparently, with a large enough 1 Hz data sample, the 1 Hz sampling errors average out.

I increased the Regeneration Efficiency from 80% to 90% (I doubt if it's this efficient). I got a Pre2008 City and Highway AER of 44.4 and 40.3 miles, respectively, and a post 2008 City (33.5) and Hwy (28.7) AER for a combined of 31.4 miles, an 21.5% difference from 40 miles.
The results imply that when wind speed, road grade, road roughness, etc. are considered, that the Volt cannot meet the 40 mile AER per post 2008 EPA testing specs.

What is the source of the discrepancy with the specified 40 mile AER for the Volt? Koz, you opened up a can of worms. But I suspect you have a habit of doing this.

My wife calls it something else, but it wasn't me this time. Blame the Rooster crowing.

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

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