For Hybrid Cars, a Hybrid Invention

From The New York Times

July 26, 2010, 7:45 am

For Hybrid Cars, a Hybrid Invention
By MATTHEW L. WALD

A company with a different approach to the electric car battery problem got a small boost recently when the Patent Office said it would issue a patent on its concept: using a storage device called a capacitor in conjunction with a traditional battery.

The company, AFS Trinity, plans an announcement on Monday.

Capacitors store only small amounts of electricity, but they can accept it or deliver it very quickly without damaging themselves. By contrast, lithium ion batteries, the kind now favored for cars, can store large amounts but have trouble delivering it fast enough to allow good acceleration. What is more, they don’t capture energy very well, a problem in electric cars. Electric cars are designed so that when a driver hits the brake pedal, the electric motors switch functions and become generators, converting momentum back into current. But the current flows very fast.

Engineers refer to these two qualities – the ability to store energy, and the ability to deliver it quickly, as energy and power. Lithium ion has good energy storage but poor power; capacitors are the opposite.

So AFS Trinity marries lithium ion and capacitors.

The result is that the demand for current from the lithium ion battery rises and falls more gently; the big jolts in or out are handled by the capacitors. As I wrote in late 2008, the company has been demonstrating the technology with a Saturn Vue Green Line, a small hybrid sport utility vehicle that it converted.

Saturn production was halted by G.M. as part of its reorganization last year, but the technology would fit well in a Ford Explorer or other midsize S.U.V., the company says.

Edward W. Furia, chief executive, said his company filed for the patent in 2006 and that it can now be licensed to automakers, just as “Dolby licensed its noise reduction technology to every company in the audio business.” But none have signed up yet.

Mr. Furia says that his technology could allow a plug-in hybrid or an electric car to get by on a smaller battery pack. Some of those vehicles are designed now with huge battery packs so that they can draw enough energy out of each battery to get sufficient acceleration; with a capacitor to help out in high-demand times, they could do with fewer batteries. Carrying a lot of batteries means greater weight and costs, plus beefier brakes and suspension.

He said the zippy performance of a car with capacitors offered “fun without guilt” because it did not burn gasoline and did not damage the batteries.

But the part of the tax code written to promote pure electric cars and plug-in hybrids favors extra batteries, the executive said, providing a $2,500 credit if the vehicle has at least five kilowatt-hours and another $417 for each additional kilowatt-hour. The maximum credit is $7,500, which works out to 16 kilowatt-hours. Perhaps not coincidentally, that is what the Chevy Volt, due out this fall, will carry.

“It was written for the Volt,” contends Mr. Furia, who would like the law amended to reflect not just energy, which the batteries provide, but power, which his capacitors provide.