雅思阅读材料：Difference Engine

　　Difference Engine: Volt farce

　　FOR General Motors, a good deal of the company’s recovery from its brush with bankruptcy is riding on the Chevrolet Volt (Opel or Vauxhall Ampera in Europe), its plug-in hybrid electric vehicle launched a year ago. Not that GM expects the sleek four-seater to be a cash cow. Indeed, the car company loses money on every one it makes. But the $41,000 (before tax breaks) Chevy Volt is a "halo" car designed to show the world what GM is capable of, and to lure customers into dealers’ showrooms—to marvel at the vehicle’s ingenious technology and its fuel economy of 60 miles per gallon (3.9litres/100km)—and then to drive off in one or other of GM’s bread-and-butter models.

　　So, it is no surprise that GM should bend over backwards to mollify customers concerned by recent news of the Volt’s lithium-ion battery catching fire following crash tests. GM is offering to loan cars to Volt owners worried about their vehicle’s safety while an official investigation is underway and modifications made if deemed necessary. The company has

　　Even offered to buy vehicles back from owners who have lost confidence in the technology. There have not been many takers. As of December 5th, fewer than three dozen owners—out of 6,400 Volts sold to date in North America—had requested loan cars. And only a couple of dozen had asked for their Volts to be bought back. At a suitable price, your correspondent would have welcomed the chance to buy one of those secondhand buy-backs for himself, had they not already been snapped up by employees. Dan Akerson, GM’s chief executive, is believed to have bought one for his wife.

　　The trouble all started in May, when the National Highway Traffic Safety Administration (NHTSA) carried out a routine 20 mph (32km/h) crash test on a Volt—to simulate a sideways impact with a tree or telegraph pole followed by a rollover. Three weeks after the test, the car’s 16 kilowatt-hour battery pack caught fire in NHTSA’s car park, destroying the vehicle and several others nearby.

　　Shortly thereafter, both NHTSA and the carmaker repeated the side-impact and rollover test on at least two other cars, all to no effect. However, in subsequent tests—carried out in November by experts from the energy and defence departments as well as GM—the investigators deliberately damaged the battery packs and ruptured their coolant lines. One battery pack behaved normally. Another emitted smoke and sparks hours after it was flipped on its back. And a third exhibited a temporary increase in temperature, but then burst into flames a week later.