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About the Chevrolet Volt

Tuesday, 8 September, 2009

General Motors is developing an all-new vehicle. It will be sold under almost all of their surviving brands around the world, but is typically called “Chevrolet Volt” in all press reports and releases. The car is expected to sell not before Fall, 2010. Following an unfortunate and short-lived campaign which promoted the implausible and unofficial fuel-economy rating of 230 miles per gallon, the Volt is being spoken about outside the dedicated automotive media.

These articles are universally misleading. Among the unfortunate ideas promulgated about the Chevrolet Volt:

  • It is General Motors’ interpretation of the Toyota Prius, and uses functionally similar technology.
  • It will run for 40 miles on a battery, then operates like a traditional vehicle with a gasoline engine.
  • It is an electric car with a range of 40 miles, and has a gasoline engine installed for no discernible reason.

I will attempt to clarify some of the hype and misleading impressions in terms comprehensible to folks without engineering degrees. The Toyota system combines the efforts of an electric motor and, through a particularly complicated and computer-controlled transmission, an internal combustion engine. The Toyota system is called a “parallel hybrid”, due to both engine systems working through the same transmission, and potentially at the same time. All mass-produced, modern vehicles called hybrid are parallel.

The Volt uses a different idea called “series hybrid”. In 1899 a young engineer, Ferdinand Porsche of later KdF Wagen fame, developed the Lohner-Porsche for an endurance rally. It was a fully electric car powered by a battery kept in a state of constant charge by a dynamo. That dynamo driven by a gasoline engine. This theory of automotive propulsion arose again and again over the century. The idea is that an internal combustion engine operating at peak efficiency powering a dynamo is dramatically more efficient than the same engine consistently changing its revolutions in spite of the additional weight and superficial conversion losses. Its most successful implementation is in diesel locomotives in which the arrangement is all but universal.

Battery weight and chassis strength limited practical applications for the idea, even into the 1980s by which time Volvo and GM had produced experimental vehicles which did not enter production. Over the last twenty years design, metallurgy and battery technology have advanced to the point that the idea may have become worthwhile.

The Chevrolet Volt is a fully-electric vehicle. It has an gasoline-powered engine, driving an electric generator which may power the electric motor directly, charge the batteries or both. It will not charge the battery over (roughly) 30% for reasons which are not clear. Charging the battery much more would be useful on particularly long trips and would have no effect on the vehicle’s intended operation around town. The internal-combustion engine believed to be intended for the Volt is the same 1.4 liter gasoline unit powering the upcoming garden-variety-powered Chevrolet Cruze which shall replace the poorly received Cobalt. The annoyingly named Cruze will be built on the same platform as the Volt, may be built in the same factory* (Lordstown, OH) , and comparisons between the two products are inevitable.

Importantly, the Volt has a plug-in battery system unlike the Prius and all other hybrids available in North America as I type. The charging system and it’s installation in your home is included in the sale price of the Volt. This increases the gasoline economy dramatically. The battery system, at full charge, allegedly allows the vehicle to run without consuming gasoline for 40 miles. When those 40 miles have passed, the gasoline engine starts. The vehicle is driven by the same electric system, but powered by the electric generator.

A few weeks ago, GM made more than a little noise about the number 230. This was their estimated fuel economy of the Volt in the EPA urban cycle. This number was achieved upon the assumption the Volt will use no fuel for the first 40 miles of the urban cycle, then use gas for the subsequent 11 miles. GM then divided the total number of miles traveled into the gallons of gas used. When running with the gasoline engine engaged, the Volt actually gets 51 miles per gallon which isn’t shabby for a Compact competing with Focus, Corolla, Golf, &c.

Is that fuel economy worth a $25000 premium? If you had $40000 sitting around and were intending to purchase a standard sedan, would anything called Chevrolet be on your list? I’m asking.

* Lordstown is expected to build vehicles to be sold in North America, and some vehicles sold in Europe. Plants on other continents shall build identical vehicles for sale elsewhere.

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