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Future bodies

BMW dotting its i's with carbon fibre, a material with many automotive pluses

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BMW's i brand will lead the company toward its goal of producing sustainable urban transportation.

There are two very different cars under this umbrella, at this point -- the i3 and i8. The former is an all-electric four-seater that can be equipped with a range-extending three-cylinder gasoline engine, if so desired. The latter is a swoopy plug-in series/parallel hybrid that represents a greener take on a flat-out sports car.

Both vehicles feature BMW's LifeDrive chassis. The Drive module is an aluminum frame that houses the drivetrain components and serves to protect the main lithium-ion battery.

Sitting atop that is the Life portion -- the carbon-fibre passenger cell. It's this aspect that will become the subject of the longest production line in the world since the ill-fated Cadillac Allante, which was built in Italy by Pininfarina and shipped 5,300 kilometres in specially modified Jumbos to Cadillac's Hamtramck, Mich., assembly line.

With the BMW i-cars, it all starts in Japan, hits North America and ends up in Germany.

The starting point is the delicate fibre, produced in Japan. These fibres are shipped to SLG Automotive Carbon Fibers, a joint venture between BMW and SGL Group, located in Moses Lake, Wash. It's here that the transformation begins.

Unlike other facilities that produce carbon fibre, this plant uses electricity, a sustainable energy resource, to heat the various ovens that change the base fibre into one of the lightest and strongest materials currently used in the automotive industry.

After being stretched, washed, carbonized, impregnated and heat-treated, the freshly minted carbon-fibre strands are finally wound onto spools that are shipped to a facility in Germany, where they're woven into the mat material that will be used to manufacture the Life cell in yet another plant.

It's a long process, but one that has a very good reason for being so -- the availability and cost of electricity. You see, SLG Carbon Fibers' new facility sits beside hydroelectric plants that harvest their energy from the Columbia River. This cuts the cost of electricity appreciably.

In Germany, the ovens would consume power costing 19 cents a kilowatt-hour. In Washington, the company is paying just three cents per kilowatt-hour.

That's an important consideration, because BMW's goal is to produce a carbon-fibre body for the same price as an aluminum body. It's a tall order, but something BMW insists will happen in the nearer term -- likely before the end of the decade. This will represent an enormous step forward, as cost is one of the bigger issues that plagues the electric automobile.

The other major hurdle facing the electrification of the car is driving range. Not surprisingly, one of the biggest factors affecting range is vehicle mass. The heavier the vehicle, the higher the draw on the battery's finite supply of electrons.

The use of carbon fibre drops the mass of the i3's Life cell to the point where it is 50-per-cent lighter than a comparable steel body and 30-per-cent lighter than one built of aluminum.

Carbon fibre is not only incredibly strong, it is very good at absorbing the impact energy generated in a crash. Steel and aluminum bend and deform to absorb the enormous loads involved in a crunch. Carbon fibre breaks, but in the process it absorbs the impact energy just as effectively.

One need only look at a Formula One car. Here, weight is paramount, but it would be pointless using a material because of its lightweight appeal if the driver was rolled into a horrible little ball after an impact. In fact, it's the strength of the carbon-fibre monocoque that protects the driver, despite the extreme speed typical of a Formula One crash.

Yet another carbon-fibre advantage is the simplicity of the assembly process. The BMW X5 has between 350 and 400 different parts that must be welded together to form the body. In contrast, the i3 has but 35 components that need to be glued together to produce the Life cell.

There are other significant cost savings in the use of carbon fibre. Obviously, the reduction in manufacturing complexity helps, but so do reductions in the electricity consumed and the amount of water used in the production process. BMW's current 1 Series consumes 60-per -ent more water during production than the i3.

Another key influence on price is market size. At this point, carbon fibre is a niche commodity that's more or less limited to the aerospace industry, a few exotic cars, select automotive parts such as the M3's optional carbon-fibre roof panel and a few kitschy items such as Lance Armstrong's Tour de France bike.

But the i3, which will hit the road this year, will increase the world's production capacity by 10 per cent, a big step toward bringing it closer to the mainstream.

So what is beyond the use of carbon fibre in the body?

It will soon be possible to build a 40-horsepower electric motor that weighs just three kilograms. The use of carbon fibre and the shift toward compact in-wheel electric motors look very promising. Four of these lightweight motivators would give the next-generation electric vehicle a combined output of 160 hp from a 12-kg power source. That, by today's standards, is an enormous step forward -- a typical four-cylinder gas engine weighs somewhere around 150 kg.

BMW's carbon-fibre initiative is a bold move, and it's one that has to be applauded.

-- Postmedia News

Republished from the Winnipeg Free Press print edition February 22, 2013 F8

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