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The Natural: smart fortwo electric drive

#Bosch #HP #smart


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If there was ever a car that appeared as though it would be a natural for an electric powertrain, it is the smart fortwo. After all, it is certainly a diminutive car—measuring 106.1 in. long, 61.4 in. wide, 60.7 in. high, and with a 73.5 in. wheelbase—and when you think of electric vehicles (EVs) prior to things like the Tesla Model S and the Nissan LEAF, chances are something that is small and cute—and quite possibly a toy—comes to mind.

The smart fortwo certainly isn’t a toy, though it is small and cute.

An interesting aspect of the design of the vehicle is that alternative powertrains had been considered from its very conception. The engineers protected for more than just gasoline and diesel variants. Consequently, to transform a smart fortwo with a gasoline-powered, 999-cc, 70 hp engine to a smart fortwo electric drive with a 55-kW electric motor (that’s the top end, which it can generate for about two minutes; it provides a continuous 35-kW) and energy stored in a lithium-ion battery pack, it is essentially a swap-out: engine for motor back between the rear wheels; gas tank for battery pack, underfloor, between the front and rear wheels. Otherwise, the vehicles are essentially the same visually and structurally.

Daimler has been working on the development of what is now the second-generation smart EV for a number of years. In 2007, it had a fleet of 100 electric fortwos rolling around in London. Those cars were fitted with high-temperature sodium-nickel-chloride batteries. One not exactly user-friendly characteristic of that battery chemistry is that the batteries needed to be preheated prior to use, and because they operate at a high temperature—around 600°F—they are packaged in a Thermos-like container.

Two years later, a fleet of 2,000 smarts with lithium-ion batteries made their way into 18 markets around the world, including the U.S. And it is worth noting that in this second tranche of test vehicles, some were seeded to the car2go (car2go.com) carsharing service that is a Daimler company. These cars, like their predecessors, had a range of approximately 63 miles.

All of the learnings from these exercises led to today’s car, which feature an electric motor produced by EM-motive (em-motive.com), a joint venture between Daimler and Bosch, and batteries provided by Deutsche ACCUmotive (accumotive.de), a Daimler subsidiary. The batteries provide 17.6-kW/h of electrical power.

The smart electric drive provides 122 MPGe. The EPA-tested range is 76 miles in city driving, although smart personnel note that in European testing, the car has an approximately 90-mile range and said that this is more reflective of what one might get in real-world driving. City performance is improved through regenerative braking, which can put up to 30 kW back into the battery. 

The car can be recharged from a 110-V wall socket, or, more likely (and more efficiently) with a 240-V system. In that case, the battery can be charged from 20% to 80% in 3.5 hours; a full charge from a depleted battery can be achieved in six hours.—GSV

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