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03/11/2011
THE ELECTRIC CAR ACCORDING TO BMW

THE NEW "I" FAMILY

Soon to make its debut in the main European cities, the new i3 city car, the first totally electric vehicle from the Bavarian manufacturer, aims to be the new technical and construction benchmark for sustainable mobility: here is how it is made

Mino De Rigo

Just slightly over a year to transfer the prototype to mass production and see it driving about the centre of Munich or, rather, coping with the traffic in Milan. The BMW i3 is the first totally electric model from the German company that was unveiled at the recent motor show in Frankfurt in the form of a concept car but one that has already gone beyond the next stage in its development. It seems to have everything it takes to establish new manufacturing benchmarks in the name of sustainable mobility. Not just in terms of construction technology and methods, for which efficiency is a categorical imperative, but because of the extensive use of recycled materials and carbon fibre, both of which aim for lightness and safety. The prototype of the next city car in the premium segment, the i3 is assembled at the factory in Leipzig: Norbert Reithofer, chairman of the board of directors of the BMW Group, said - "We have combined the principles that make up our vision of tomorrow's urban mobility. Throughout its life cycle, the greenhouse gas emissions produced by i3 are potentially at least one third lower than those of a highly efficient vehicle in the same segment with an internal combustion engine, like the BMW 118d. And if the vehicle uses electricity from renewable sources, the potential for reducing CO2 emission exceeds 50%". Also envisaged at the factory in Leipzig is the installation of a wind-powered generating plant. "If the sub brand "m" indicates BMW vehicles that are the height of dynamism, then the new sub brand "i" means maximum efficiency".


Farewell conversion car
The new vehicle draws on the experience acquired by the Bavarian car manufacturer in long tests carried out in the USA and Europe on the test fleet of electric vehicles composed of the Mini E and the BMW ActivE. But there has been an obvious leap forward with respect to both of them: if the so-called conversion cars are paying the price of being developed originally to house an internal combustion engine and were then adapted to take an electric engine, then the new i3 can count on completely new architecture. There is no self-supporting body but two modules called Drive and Life, which are horizontally coupled to shape the vehicle: mostly aluminium, the chassis is designed for structural functions, anti-crash protection, and to incorporate the power accumulator and the engine. On top of it is the Carbon Fibre Reinforced Plastic (CFRP) cabin: As Klaus Draeger, a member of the BMW board, explained - "It is a genuine safety cell on the example of Formula 1 cockpits, which incorporates specific deformation elements that on minimum surfaces can absorb the energy produced by a collision or when overturning, so without the large areas required by similar constructions in metal". In the Drive module, the power accumulator cells fill the central area in order to spread the weight better between the axles and ensure a low barycentre, which has a positive effect on driving dynamics. "The weight of the batteries is amply offset by the lightness of the cabin: CFRP is almost as strong as steel, but it is half the weight, and aluminium saves another 30% in weight."


Recycled is better
"Moreover, recycled materials and natural raw materials have substituted about one quarter of the plastic in the interiors and even 25% of the thermoplastic elements in the body." Furthermore, 10% of the CFRP used in the Life module is recycled, the result of a process used to date by BMW. The use of CFRP has also made it possible to eliminate the B-pillar, so access to the interior is wider; also contributing to this are the two opposing "coach" doors. Because the transmission components are in the Drive module, there is no central tunnel in the cabin of the rear-wheel drive BMW i3, which means there is more space available for the four occupants. The vehicle is 3.84 m long, 2.01 m wide and weighs 1250 kg, the boot holds about 200 litres and there is an additional compartment in the front. Made entirely by BMW and assembled on the rear axle of the i3, the electric engine generates 125 kW (it's the same engine used in the Mini E, but in 40% less space) and torque of 250 Nm from standing. The rating plate states acceleration from 0 to 60 km/h in less than four seconds and from rest to 100 km/h in eight seconds. Efficiency is due mainly to design specifications of lightness combined with maximum use of interior space, and to safety requirements. And without doubt aerodynamics and the recovery of energy while driving also play an important role.


All-round efficiency
Narrower wheels with a wider diameter than usual and low rolling resistance tyres join the numerous other solutions: the undertray of the car is flat and coated to reduce drag that would increase consumption, rear diffusers, specially-shaped wheel arches and the characteristic aero flaps just behind the front wheels. Driving autonomy is increased not only by energy recovery when the accelerator is released, typical of electric vehicles that decelerate quickly without using the brake pedal, but also by allowing the car to freewheel by putting the accelerator pedal into neutral: the effect is the same as releasing the clutch, so the vehicle moves forward without using battery power. The lithium-ion battery packs give autonomy of about 150 km and are built to last as long as the vehicle. Constructed in a joint venture set up between Bosch and Samsung, they incorporate a specific liquid cooling system for maintaining an optimum running temperature and increasing battery output. A fast-charge will generate 80% in just one hour and a full charge takes about six hours. To increase vehicle autonomy, BMW also offers an optional range extender: a small combustion engine that powers a generator to maintain battery charge.


Smartphone controls
However, if it is difficult to adopt an appropriate style of driving that will extend range, the BMW i3 also has an Eco Pro mode for maximum efficiency. The characteristic line of the accelerator pedal is modified to use less power and the heating/air-conditioning is also optimized. Moreover, pre-setting the accumulator and heating/air-conditioning (for example, to cool the cabin in the summer before the car is unplugged) is typical of electric vehicles, as is the charge control system. The latter enables the start of recharging to be regulated, displays status, autonomy and the time required to complete the process.ECO PRO mode gears everything towards maximum efficiency: accelerator pedal and gearbox parameters as well as shift points are all optimized and the heating/air-conditioning strategy is adapted intelligently.

The Control Display indicates how the ECO PRO mode is actively reducing energy consumption, e.g. through Brake Energy Regeneration or the Auto Stop Start Function. What is more, ECO PRO tips on more efficient driving show information such as the optimum choice of gear at any point in time.

Which saving potentials are implemented is for you, the driver, to decide. Following the ECO PRO tips makes it possible to achieve a reduction in fuel consumption of up to 20%*. The bonus range in the on-board computer shows you exactly how many additional kilometres you can now drive.
The data can also be received by smartphones thanks to the remote functions included in the BMW Connected Drive package: the apps will allow owners to lock or unlock the car, sound the horn, make the indicators blink to locate the car within 1500 metres, and add an itinerary with local Google search for use with the navigation system.



• Blue as in clean efficiency, for tyres as well


The traditional BMW roundel on the bonnet is edged with a new blue ring, the distinctive symbol of the new "i" family which, together with the latest i3 electric city car, already proposes the supersporty i8, a plug-in 2+2 hybrid with overall power of 260 kW and, according to the manufacturer, capable of doing over 100 km on 3 litres of fuel; and soon new models will be included to fill the numerical gap. The same blue that is associated with efficient dynamics, cleanness, zero emissions, emphasizes certain details of the body and enhances the interior design, is also to be found in the grooves of the tread and even on the tyre beading. It is not by chance, given the contribution they make to vehicle efficiency. "Exclusive products" - said Ian Robertson, head of sales and marketing at BMW - "that are narrower than normal and not only have lower rolling resistance but also boast considerable performance in terms of lateral acceleration". The i3 tyres are 175/60 R19, the outcome of Bridgestone's Half Weight construction philosophy, and the i8 is fitted with 20" rims. "Reduced width decreases drag and their shape and tread contribute to smoothness; what's more, they take up hardly any room in the cabin, to the advantage of the passengers".

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