How do you make a carbon-fiber electric car? Ask BMW. According to Automotive News Europe, “BMW i3 pioneers use of carbon fiber in mass-produced cars.”
Why use carbon fiber? Carbon fibers are characterized by high stiffness, high tensile strength, low weight, high chemical resistance and temperature tolerance, and low thermal expansion. The low weight of carbon-fiber reinforced plastic compensates for the heavy lithium-ion battery, making all-electric cars a closer reality for everyone.
The result? BMW i3 weights only 2,755 pounds. “BMW i3 weighs 20 percent less than Nissan Motor Co.’s Leaf, the world’s best-selling electric car. That helps the vehicle accelerate to 100 kilometers per hour in 7.2 seconds, more than 4 seconds faster than the Leaf.”
How do they make it? Due to the high cost of carbon fiber, BMW has done it from scratch, with mass carbon fiber production. The production is designed to be environmentally friendly whenever possible. BMW formed a partnership with SGL Carbon SE in 2009 and opened a carbon-fiber producing plant in September, 2011, in Moses Lake, Wash., using renewable hydropower.
The industrial process of carbon fiber production starts with polyacrylonitrile, a synthetic, semicrystalline organic polymer resin. Polyacrylonitrile fibers are first thermally oxidized in air at 230 degrees Celcius, then carbonized above 1,000 degrees Celcius in an inert atmosphere. In the resulting carbon fiber (a thin tube with a diameter of 5–8 micrometers) carbon atoms are bonded together in crystals, aligned with the direction of the fiber. Next, the fibers are bundled together and woven into a fabric. Here is how SGL Automotive Carbon Fibers LLC describes the process:
The raw material, polyacrylonitrile, is produced in Japan through a joint effort between SGL and Mitsubishi Rayon. The material is then shipped to Washington, where it is converted into strands of carbon fibers in high-temperature furnaces. Then the fiber, up to 3,300 tons per year, is transferred to Germany, where it is processed into carbon fiber reinforced plastics (CFRP) parts and components to be used in BMW’s auto factories. Each vehicle utilizes about 660 pounds of carbon fiber.
The BMW i3 is produced in Leipzig, Germany, in a plant that is powered by wind turbines and uses 160 robots in the assembly process. Carbon fiber reinforced plastics (CFRP) are used to make the “passenger cell” (see the image above). The chassis, carrying the suspension, steering, and drivetrain, and the battery case are made of partially recycled aluminum; body panels are plastic; and wool and fast-growing wood are used in the interior. After touring the plant, Andrew English described the car details in an article in Popular Mechanics:
The 507-pound, 22-kilowatt-hour square battery pack sits under the floor and is cooled by both ambient air and the air conditioning. It consists of 96 Samsung-made cells, but the installation, the aluminum-alloy case, and the control electronics and software are BMW’s design. The cells have a squared-off shape to aid packaging and cooling […] During an impact, the main battery that’s carried under the floor automatically disconnects using an explosive fuse, the residual system charge is drained, and the motor regeneration electronics are isolated. Carbon fiber is also cheaper to repair […] BMW says that more than 95 percent of typical accidents will affect only the outer skin panels, which can be easily replaced, with just 2.5 percent affecting the aluminum rolling chassis and 2.5 percent the inner carbon-fiber body.
As a result, according to Green Car Reports, BMW i3 will be “Cheaper to Repair, Insure Than You’d Expect,” as the exterior plastic panels can be easily interchanged. BMW i3 is considered greener than almost any other car. With a range of 80 to 100 miles, and up to 120 miles in the most efficient driving mode, it will become a choice of many environmentally-conscious customers in the U.S.A. once it becomes available next year.
Source: BMW i3 pioneers use of carbon fiber in mass-produced cars, autonews.com, November 16, 2013
Source: SGL Automotive Carbon Fibers LLC, commerce.wa.gov
Source: Inside BMW’s Ultra-Green i3 Factory, Andrew English, PopularMechanics.com
Source: The BMWi3 is officially much greener than almost any other car, jalopnic.com, November 12, 2013
Source: 2014 BMW i3 will be Cheaper To Repair, Insure Than You’d Expect, Anthony Ingram, greencarreport.com, December 12, 2013
Image BMW i3 all-electric concept car by mariordo59
Video BMW i3 LifeDrive by BMWi