Thursday, March 18, 2010

Electric supercars

Highly charged motoring

Fast cars will go even faster with electric power

Mar 18th 2010 | From The Economist print edition
SOME people think sports cars are threatened with extinction by tightening restrictions on carbon-dioxide emissions and unacceptable fuel-guzzling. They fear the roar of the V8 will be replaced by the whirr of the electric armature—and that motoring will never be the same again. Well, it ought to be quieter, that is true. But the Jeremy Clarksons and J. Bonington Jagworths of this world need not fear that it will be slower.
The secret (whisper it, lest puritanical greens find out) is that electric motors are better than combustion engines. They have more oomph, and no need of a gearbox to deliver it. No self-respecting supercar should be without them. And, at this month’s Geneva motor show, at least three supercar-makers showed that they had got the message. Lotus, Porsche and Ferrari each unveiled vehicles driven partly by electric motors. These cars have petrol engines, too, to back the electric ones up; technically, therefore, they are hybrids. But that should change in the future as batteries’ storage capacity goes up, and charging time comes down. Most importantly they show that, sometimes, doing the right thing can be fun.
The launch of the Tesla roadster two years ago demonstrated that electric cars do not have to be slouches. The Californian company’s small plug-in sports car can accelerate from zero to 96kph in 3.7 seconds. It has a range of 393km (244 miles) once its lithium-ion battery pack is fully charged (which, admittedly, takes several hours). The Tesla’s rapid acceleration comes from the ability of an electric motor to deliver its maximum amount of torque at whatever speed the motor is turning.
Torque is the scientific term for turning force, and it is measured in newton-metres (Nm). The Tesla’s motor has a torque of 400Nm all the way to 5,100 revolutions per minute. An internal-combustion engine, by contrast, produces maximum torque only at certain speeds. The 2.0 litre engine of a Lotus Elise S2, for instance, peaks at 213Nm at 4,400rpm. And, whereas a gearbox is needed to use the torque from a combustion engine efficiently, it is unnecessary with the heft of an electric motor. Read more here....

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