Most car buyers haven't even heard the term "range extender" yet.
But over time, expect it to become more familiar, as electric cars like the 2011 Chevrolet Volt introduce the concept of a gasoline engine that turns a generator to produce electricity to power the vehicle.
Tiny, powerful, efficient
At the 2009 Frankfurt Motor Show, Lotus Engineering unveiled a tiny, 1.2-liter three-cylinder gasoline engine designed solely for use as a range extender.
Now, 18 months later, Lotus has taken the wraps off an improved version of its engine, plus a new, more powerful supercharged model. Both designs have been heavily revised in response to customer feedback.
And the company says it has "significant interest" in the new 1.3-liter engines from three separate automakers about supplying its Range Extender for use in future extended-range electric cars now on the drawing boards.
Projected volumes are in the tens of thousands, Lotus said, along with smaller numbers that might potentially go to specialty makers.
Close to Volt power
The first version of the Lotus Range Extender used an aluminum monoblock, meaning the engine block, cylinder head, and even the exhaust manifold are cast as a single element, reducing both weight (just 125 pounds) and parts count.
The version shown at the Geneva Motor Show in September 2009 produced 47 horsepower (35 kilowatts) running at a maximum of 3500 rpm. The new supercharged version raises power output to 67 hp (50 kW).
Proton Concept platform showing battery pack and Lotus range-extender engine, 2010 Geneva Motor Show
That puts it close to the 74 hp (55 kW) of the Volt's 1.4-liter four-cylinder engine, which was adapted from a high-volume General Motors engine used in many other models.
Lotus expects its engine to offer considerably higher efficiency and lower fuel consumption, though no third-party test data has been provided as yet.
The Volt itself is rated by the EPA at 37 mpg in range-extending mode.
More conventional engineering
The newly revised version now has a more conventional separate head, making it far easier to manufacture. The exhaust manifold is still an integral part of the block casting, however, and a balance shaft is now optional.
And Lotus has cut the weight even further, to 112 pounds in standard form or 128 pounds with the supercharger, as well as making the engine-generator combination more compact. It can now be fitted either vertically or horizontally.
Proton Country concept, 2010 Geneva Motor Show
The company is also working on a two-cylinder version of the engine.
Already a variety of manufacturers have fitted the Lotus Range Extender in concept vehicles.
Lotus itself showed its Evora 414E Hybrid prototype; Jaguar used it in a prototype "LimoGreen" full-size luxury sedan; and Malaysian maker Proton, which owns Lotus, showed the engine in a range of EMAS minicar concept vehicles.