BMW electric i3: Here’s how it works

Published Jul 10, 2013

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BMW has finally released full details of what it says is the first premium car to be designed from the ground up as a battery-powered vehicle - although electric carmakers such as Tesla and Fisker might have something to say about that.

What is true, however, is that the i3 is not adapted from an existing conventional design with an engine compartment, space for a fuel tank or similar design constraints - it's essentially a carbon-fibre box with a battery-pack underneath, a wheel at each corner and an electric motor just ahead of the rear axle.

BMW calls this the LifeDrive architecture; using the light stuff for the bodyshell offsets the extra weight of the lithium-ion batteries, putting them under the middle of the floor gives the car a very low centre of gravity and perfect 50:50 weight distribution, and the whole thing weighs just 1195kg.

Having the motor directly driving the rear axle not only prevents transmission losses but also improves traction, while obviating the need for a transmission tunnel and increasing cabin space, especially for rear-seat passengers, which has long been an issue with smaller BMW models.

BMW is only showing ghost pictures for now, but its styling will not stray far from the i3 concept car - CLICK HERE for pics.

250NM AT JUST ABOUT ZERO REVS

BMW's claim that it has developed the motor, the battery and all the ancillaries in-house is backed by the numbers. The hybrid synchronous motor weighs only 50kg but spins to a dizzy 11 400rpm, while delivering a claimed 125kW and 250Nm at just about zero revs.

That will take the i3 from 0-100km/h in 7.2 seconds, it says, and on to 150km/h flat out.

The 360V lithium-ion battery pack consists of eight modules, each containing 12 individual cells (which can be replaced individually) and weighs in at a creditable 230kg - but its capacity is only 22kWh, which means that the i3 has a limited range.

BMW quotes 130-160km in normal usage, or about 190km in Eco Pro+ mode; previous experience with similar setups suggests that enthusiastic application of the right foot could see the i3 coasting to a halt at the side of the road within 80-100km.

EXTENDED RANGE

Which is why there is also a range-extended model, with a 25kW 650cc twin-cylinder motorcycle engine (also right over the rear axle), fed by a nine-litre fuel tank at the front of the car and driving the same generator that charges the battery under braking, to push the limit out to a more practical 300km.

Charging time from a flat battery to 100 percent, using a 220-volt BMW Wallbox installed in the owner's garage, is a full eight hours, but that drops to a much more practical 30 minutes using a 50kW street charging pole belonging to one of Germany's more than 70 commercial energy retailers.

The i3's running gear is actually quite conventional; its wheelbase is a longish 2570mm, front suspension is by McPherson strut, and the rear by a five-link independent set-up that uses a lot of aluminium components to save weight.

The electric power steering, however, needs no more than an Alfa Romeo-like 2.5 turns from lock to lock which, given a claimed turning circle of only 9.86 metres, will make the i3 steer like a go-kart, especially as it runs on special large-diameter but unusually narrow 155/70 R19 tyres to minimise rolling resistance.

THE FULLY NETWORKED CAR

Each i3 comes with a dedicated sim card, which not only hooks it up to BMW's ConnectedDrive internet service but also enables the factory to monitor your car in real time, so that a roadside assistance vehicle with an on-board 50kW charger can be despatched to you wherever you are, with the correct spares on board for whatever ails your i3.

In addition, smartphone apps will tell you remotely what your car's state of charge is, guide you from wherever you've parked to your final destination and even help you plan your journey before you get into the car.

The car's navigation system also ties into both car-sharing and public-transport networks (in Germany anyway!) as well as real-time traffic information services to help you plan every journey to be as energy-efficient as possible.

BMW also plans to conclude agreements with as many energy retailers across the EU countries as possible, so that you can plug your i3 into any street-charging pole in Europe and receive just one monthly invoice from BMW.

All of which makes the i3 sound more like a cellphone with wheels than a conventional car - maybe that’s the idea.

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