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GM Continues Series vs. Parallel Hybrid Debate
Feb 15, 2008 (From the CalCars-News archive)
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GM in promoting the Volt, which it calls an "Extended Range Electric Vehicle" (E-REV), and most observers describe as a series PHEV, is continuing to make the strong case that this architecture is superior to parallel hybrids. In a presentation at the Society of Automotive Engineers Hybrid Conference in San Diego, GM's Peter Savagian, Hybrid Powertrain Engineering Director, compares the benefits of the different alternatives, especially in fuel used and cold starts to parallel hybrids and to today's aftermarket conversions of Priuses. (GM is also working on the Saturn Vue, a "blended" parallel PHEV.)

The quick explanation: series PHEVs are easier to design and build; advocates of full parallel systems say they can be better optimized. Our Technology Lead, Ron Gremban, may have comments in a few days, on returning from the conference; meanwhile, here's Savagian's posting to GM's Fastlane blog and a link to a PDF of his 35-slide presentation. You can also read a report and comments at GreenCar Congress http://www.greencarcongress.com/­2008/­02/­gm-study-shows.html . If you pick and choose among the many comments and look for the serious ones that are on-topic and not sarcastic, you'll note that what jumps out for several posters is that the comparisons seem to be between a Volt with more than twice as much energy storage as the other two vehicles.


Driving the Volt By Pete Savagian, Engineering Director, GM Hybrid Powertrain Engineering http://fastlane.gmblogs.com/­archives/­2008/­02/­driving_the_vol.html

The public's appetite for information on the Volt never ceases to amaze me. The concept obviously struck a chord, although I probably shouldn't be surprised; I was one of the chief engineers for our last battery electric vehicle -- the EV1. The public's reaction to the Volt is somewhat similar, although on an even larger scale, to the reaction we received when we built the EV1 -- the first modern electric vehicle.

The EV1 was one of the most technologically advanced vehicles for its time with a passionate, loyal group of customers. We learned an awful lot from the EV1 program, knowledge that's being put to use right now on the development of the Chevy Volt. The fact is, reducing our dependence on petroleum requires vehicles that provide the petroleum-free benefits we know electric vehicle drivers are passionate about, but we also need to offer the flexibility to be able to drive hundreds of miles at a time between fill-ups. People expect that type of freedom every time they take the wheel.

We believe an Extended-Range Electric Vehicle (E-REV) like the Volt is that kind of vehicle. E-REVs are electric vehicles that provide full performance on electric power alone and only engage energy from the gas in the tank after the battery is discharged. Based on our studies, a vehicle like this offers tremendous potential to reduce petroleum use and emissions.

Earlier today at the Hybrid Vehicle Technologies 2008 Symposium in San Diego, Calif., I shared some results from our analysis of what an E-REV could do in the hands of regular drivers. We used real world data from the Regional Travel Survey conducted by the Southern California Association of Governments over the past few years. The survey measured the daily driving habits of over 600 commuters in the Los Angeles area, one of the world's busiest, most congested driving regions.

What we learned was pretty telling. If everyone in this study drove a vehicle like the Volt:

  • Sixty-four percent of the drivers in this study would never use a single drop of gas during their daily travels.
  • On average, Volt drivers commuting less than 75 miles a day would use 1/5th the fuel compared to drivers using a conventionally-powered vehicle.
  • Drivers of the Volt would have 70 percent fewer initial engine starts than conventionally-powered vehicles. Initial engine starts are a large factor in the total emissions produced.

Please take a look at the presentation, "Driving the Volt." http://fastlane.gmblogs.com/­PDF/­presentation-sm.pdf I think you'll agree, the potential of the E-Flex technology to improve every day driving is real and something we can all get excited about. I'm excited about this and it is this potential that "drives the Volt" team each and every day.

Thanks, Pete

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