Friday, July 15, 2011

Electric cars - Karma chameleon

Jul 13th 2011

THE first Fisker Karma, a luxury four-seater high-performance electric car, will be delivered to its first customer, one Leonardo di Caprio, on July 21st. The Hollywood film star will find that unlike other electric cars, the Karma has been designed to be driven like a conventional combustion-engined vehicle, but also with the ability to change its character and use electricity for a different driving style.
The Karma is being built by Fisker Automotive, a Californian company led by Henrik Fisker, who has designed cars for BMW, Ford and Aston Martin. Fully charged and with the car switched to what Fisker calls “stealth” mode, a 20kWh lithium-ion battery, hidden beneath the floor, gives it a range of about 80km (50 miles) and a top speed of 153kph. Like many hybrids, a petrol engine is installed to extend its range. Yet unlike those that use a range extender when the battery runs down, such as the Chevrolet Volt (Opel/Vauxhall Ampera in Europe), the Karma's two-litre turbocharged petrol engine, which sits under the bonnet in the front, never drives the wheels directly. Instead, it is perpetually connected to a generator which powers the car's two electric motors in the rear wheels.
As a result, besides its range-extending function, the petrol engine can improve the car's performance by delivering extra electricity whenever the driver flips on the vehicle's sport mode. This boosts acceleration and takes the top speed to 200kph. Switching between the different modes is done by one of a pair of paddles on the steering wheel. In a conventional modern sports car these are used to change gear. (As is often the case with such novelties, the paddles came from Formula 1.) But the Karma has no need of a gearbox, required by cars (hybrid or otherwise) whose petrol engines turn the wheels. That is because unlike petrol engines, which need to rev up before producing the torque necessary to budge a vehicle from a standstill or accelerate it quickly from a cruising speed, as in overtaking, electric motors provide full torque at the first touch of the accelerator pedal.

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