Thank you for your interest in the cross-country driving scenario.

Since writing that, I have seen more data, and I agree with your assessment that the engine will probably operate at different speeds. One reason that leads me to this conclusion is that the regen braking will provide AC power back to the system at variable frequency, so the power electronics should accept a variable frequency from the generator.

I do believe that the ICE will still recharge the batteries while in operation, and may shutdown at other times. See the attached link for GM curves on planned operation.

http://www.motortrend.com/features/auto_news/2008/112_0804_chevrolet_volt_update/photo_03.html

It will be interesting to see final performance numbers for the Volt under ICE operation.

Actually, you’re right. In fluid dynamics (fluid = gas or liquid, you can use the same analysis for either), there are two type of drag:
1. surface drag (”pulls” along the surface of the vehicle, e.g. water trickling down an angled plate “tops out” at a certain speed speed, it doesn’t keep accelerating)
2. a front/rear pressure difference (”pushes” on the front of the vehicle [but not as much on the back], surface drag over the vehicle slows the air down and creates a lower pressure at the back of the car)

A spoiler will create a non-laminar/turbulent region at the back of the vehicle, which will mostly lead to less of #2, but a little less of #1 (source: my Fluid Mechanics class, and T. Gillespie’s book “Fundamentals of Vehicle Dynamics” http://www.sae.org/technical/books/R-114 )

A spoiler also creates rear downforce. Although significantly increased downforce leads to less efficiency, it may be necessary to keep the car stable at high speeds.

Thanks for linking to the piece with your 1% grade calculations, your Kansas-to-San Francisco example should be required reading for anyone talking about power requirements, etc.

I don’t believe the Volt ICE will run at 30 kW on level ground and recharge the battery to 40%, however. IMHO control logic will match ICE output to steady-state freeway road load. It’s easy to maintain near-peak efficiency over a fairly wide power band. You can do 12 kW at full-throttle low RPM and 40 kW at full-throttle medium RPM. You might give up a couple percent efficiency over this range vs. fixed RPM operation, but you get this back (and then some) by avoiding a round-trip through the battery.

The battery will always help with transient loads, of course, and the ICE will probably cycle on and off as you describe when road load is too low for efficient operation (e.g. 30 mph). Just my opinion.

My Full sized truck has a 30 gallon tank, but when I can drive over 500 miles it feels efficient, even though it costs $90 to fill it back up. A larger tank would make the Volt seem as if it hardly uses any gas, (which is nearly true).

I think a marketing advantage is being lost and GM is thinking too technical.

If we’re trying to save fuel and volume, I’d still like to see a Stirling engine.

I hope that solar cells will become even more powerful and provide another means of extending range, especially since my car would be sitting outside in the sun all day while I’m at work. That would be a great opportunity for me to get a few extra miles range.