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

9599 Views 20 Replies 9 Participants Last post by EJ_San_Fran, May 20, 2008

Tom

Discussion Starter · May 14, 2008 (Edited)

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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pnieder

· #8 · May 17, 2008

Tom,

Thank you for this excellent document. I'm writing an article about EV range, especially as it is reduced by higher speeds and accessory loads, so this is perfect!

A couple of questions: I see you used a Cd of .22. That seems optimistic. The Prius is .26, and I understood that was the target for the Volt. And what did you use for the frontal area?

Are you an engineer; and in the EV field? Can I feel confident about using this chart in an article?

Thanks for any further answers.

Paul

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pnieder

· #10 · May 17, 2008

Tom,

the height and width may not be accurate for determining total frontal area, as there is substantial "tumblehome" in cars like the Volt (wider in the midsection than at the top, and perhaps bottom). Also, it appears from the model that the final Volt will be tallere than the very low-slung concept.

I distinctly remember reading that Lutz said that they had attained their goal of equaling the Prius' cd number. I can't find it now.

For modeling purposes, I would use the Prius's total CX (cd x frontal area), because I suspect it will be close to that. I think a cd of .22 is overly ambitious.

Would making those changes alter the results much?

Also, I assume I can link/insert your charts in an article about EV range I'm writing?

Paul

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pnieder

· #12 · May 17, 2008

hvcman: spoilers can be for looks, downforce (racing cars), and improved aerodynamics (look at a gen1 Prius). It all depends on how they're designed.

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pnieder

· #15 · May 18, 2008

Koz (and Tom),

The Tesla Cd may be higher, but don't forget, it's total aero drag (CD x frontal area) that counts. The Tesla is very low and small, and has a much smaller fronat area than the Volt or Prius. I would expect its Cx to be substantially lower than both. That's one of the reasons they chose the Elise to base it on, light weight and low total aero drag.

I will repeat what I said earlier; I am certain that Lutz said somewhere that they had "equaled the Prius' aero drag" with their redesign of the Volt. I think the safest number to use is the Prius' FA, which my notes show to be 2.16 square meters. Does that sound right?

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pnieder

· #17 · May 19, 2008

Tom,

Here is a calculation someone made for the Tesla. Note the higher efficiency numbers assumed for the drivetrain.

Also, I have numbers for the total aero drag for the Tesla: between 5.7 and 6.12 feet square.

Robin wrote on May 16th, 2007 at 1:45 am
CdA and range for tesla roadster:

Dimensions:

1.127 x 1.7 (-mirrors estimate) = 1.9 m²
X 85% (standard shape correction factor) = 1.63 m²
Cd = 0.3 (mentioned in online article)
CdA = 0.3 x 1.63 = 0.49

(9.81 x 1350 x 0.011 + 0.49 x 50% x 1.293 x 26.5²)

x 75% / 3.6 = 136 wh/km

Efficiency: (batteries, charger, drive train) 0.93 x 0.93 x 0.9 = 0.78. minus 3% for lights, AC, heating gives a 75% average efficiency to work with

9.81 = gravity
1350 = weight in kg of roadster including 300 lbs (total = about 3000 lbs = 1350 kg) passenger and cargo average
Rolling resistance estimate: 0.011
1.293 = air density
26.5 = average speed in m/s that compensates for regen braking. Calculated this speed by analyzing EV1 speed and range data.
Divide by 3.6 to get wh/km

Range: 50 kW (battery pack energy estimate) / 0.136 = about 370 km or 230 miles

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pnieder

· #20 · May 20, 2008

Tom, my article about the Volt's range is here:
http://www.thetruthaboutcars.com/chevrolet-volt-home-home-on-the-range/
It includes your calculations and graphs (embedded). Thanks for your efforts, and shedding light on the issue of the easily-affected Volt's AER.

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

Tom

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