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EV Model for Simulation: GM Volt. Design your own EV.

9622 Views 20 Replies 9 Participants Last post by  EJ_San_Fran
The attached model is a simulation of the Dynamics and Range of the GM Volt. You can also design your own EV by using the model with different design parameters.

The model estimates that the Acceleration Performance of the Volt is 0 to 60 mph in 8.6 seconds :) and the Single Charge "Highway" Range @70 mph cruise is 26 miles. :(

See model details at http://www.leapcad.com/Transportation/GM_Volt_Simulation.pdf.

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Road Grade Drastically Reduces Single Charge Range

A road grade of 3% drastically reduces Single Charge Range @70mph from 26 to 14 miles. Range @40mph is reduced from 46 to 19 miles :( See attached range curves. Grades of 6% are not uncommon. The Tour De France has an average grade of 7%.

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The size of the motor determines acceleration, not battery range.

my guess is that they are useing a different electric motor that we don't know about. GM did not says any thing about the motor at all.
Motor size and mass primarily determine how fast you get from point A to B. It needs different amounts of energy depending on the profile of changes from one speed to another. Once you get to a given cruise velocity, the battery drain is determined by mechanical and efficiency factors: mass, drag, tires, road surface, wind, road grade, regen, efficiency of drive electronics and motor and battery resistance. Changing the motor shouldn't much effect on battery range. :)
Volt Drag Coefficient Assessment

GM has not disclosed the value of the Volt Cd. As you know, the EV-1 had a Cd of 0.19 and GM was aware of the value of the Prius Cd. I originally used a value of 0.25 for my simulation. Later I saw a number of articles about GM engineers doing fine tuning of Cd in wind tunnel testing and concluding that Cd must be minimized to get high speed performance. From this, I hypothesized that they wanted to aggressivly best the Prius Cd. I tried simulations with Cd of 0.25 and could not get the claimed Volt high speed performance. I considered the above and guessed at a Cd of 0.22. I know that there are tradeoffs between performance and body styling (mirrors, sharp corners are "in", etc.). My purpose in publishing my model and parameters was to subject it to review and correction. If you or anyone has a technical rationale for changing any of my parameters I would be more than delighted to improve the model. What are your thoughts about 0.22?

The frontal area came from the height and width "Specifications" on the GM-Volt home page. I suspect the actual number is less than this. Once again, if you have a better number give me a shout.

Tom
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Requested Modified Model Parameters - Thanks for the feedback

Guys,

I have modified the parameters per your posts. I also did a model for the Tesla (fixed first gear). The Tesla model appears to agree with performance specs. See attachments.

nieder
I have revised Cd upward. This decreased single charge range significantly. See below. Yes you can link/copy charts.

HAVACMAN
Changed Cd to 0.25. There is always an “average wind.” See discussion under Engineering, “EPA Ratings ...”
Bottom line: the data at http://www.awea.org/faq/usresource.html suggests 7 mph is reasonable. I will change it if anybody has statistical data to support rationale for a better value.

The Volt and Tesla power draw at 60 mph at 500W is ~ 14.9kW. See attachment for Tesla.

Rooster
Used 92.4% motor efficiency. The DC-DC converter is only used to supply accessory power. It’s efficiency does not affect traction power. If they use a separate 12V the DC-DC converter losses would not apply.

I don't know if the Li Fe battery 16/53 kWh energy spec includes battery losses. Battery loss, if not accounted for, could be a significant model error.

Pnieder, Koz
Used 2.16 m^2 = 23.25 ft^2 and Shape Correction Factor of 0.85. Changed tire rolling resistance to 0.011.

Tom

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