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Frankfurt 2009: Audi E-Tron Electric Concept
Audi presents the highlight of the 2009 Frankfurt Motor Show: the e-tron, a high-performance sports car with a purely electric drive system.Four motors – two each at the front and rear axles – drive the wheels, making the concept car a true quattro. Producing 230 kW (313 hp) and 4,500 Nm (3,319.03 lb-ft) of torque, the two-seater accelerates from 0 to 100 km/h (0 – 62.14 mph) in 4.8 seconds, and from 60 to 120 km/h (37.28 – 74.56 mph) in 4.1 seconds. The lithium-ion battery provides a truly useable energy content of 42.4 kilowatt hours to enable a range of approximately 248 kilometers.
The performance figures are by no means the only evidence of the consistent and holistic strategy. The design makes it clear that the e-tron belongs in the major leagues of sports cars, and the package takes into account the specific realities of an electric vehicle. The battery is directly behind the passenger cabin for an optimal center of gravity and axle load distribution.
The e-tron is able to freely distribute the powerful torque of its four electric motors to the wheels as required. This so-called torque vectoring allows for dazzling dynamics and an undreamed-of level of agility and precision when cornering.
Drive System and Energy Supply
Four asynchronous motors with a total output of 230 kilowatts (313 hp) give the Audi e-tron the performance of a high-output sports car. The concept car can accelerate from 0 to 100 km/h (0 – 62.14 mph) in 4.8 seconds if necessary, and goes from 60 to 120 km/h (37.28 – 74.56 mph) in 4.1 seconds. The torque flows selectively to the wheels based on the driving situation and the condition of the road surface, resulting in outstanding traction and handling.
The top speed is limited to 200 km/h (124.27 mph), as the amount of energy required by the electric motors increases disproportionately to speed. The range in the NECD combined cycle is approximately 248 kilometers (154 miles). This good value is made possible by the integrated concept: technology specially configured for the electric drive system combined with state-of-the-art battery technology. The battery block has a total energy content of roughly 53 kilowatt hours, with the usable portion thereof restricted to 42.4 kWh in the interest of service life. Audi uses liquid cooling for the batteries.
The energy storage unit is charged with household current (230 volts, 16 amperes) via a cable and a plug. The socket is behind a cover at the back of the car. With the battery fully discharged, the charging time is between 6 and 8 hours. A high voltage (400 volts, 63 amperes) reduces this to just around 2.5 hours. The Audi engineers are working on a wireless solution to make charging more convenient. The inductive charging station, which can be placed in the garage at home or also in special parking garages, is activated automatically when the vehicle is docked. Such technology is already used today in a similar form to charge electric toothbrushes.
The battery is charged not only when the car is stationary, but also when it is in motion. The keyword here is recuperation. This form of energy recovery and return to the battery is already available today in a number of Audi production models. During braking, the alternator converts the kinetic energy into electrical energy, which it then feeds into the onboard electrical system.
Electric drive systems are still very much outsiders. The first vehicles of this type took to the roads around 1900, yet in 2009 no volume car manufacturer has a car powered exclusively by batteries in its lineup. Fewer than 1,500 electric vehicles are currently registered in Germany, corresponding to only 0.035 percent of all registered vehicles.
Yet electric driving potentially offers numerous advantages. Electric cars reduce the dependence of transportation and the economy on the raw material petroleum. They produce no direct exhaust emissions and thus ease the local burden on the environment. Electric drive systems are also significantly more efficient than combustion engines, consequently making them easier on the customers’ wallets. Other strengths include sportiness and the fun they bring to driving. All of the torque is essentially available the moment the driver steps on the accelerator, allowing for breathtaking acceleration.
There is still a lot of work to do before electric cars are ready for volume production, however. The greatest challenge is the integration of the energy storage system. Acceptable range and performance requires a traction battery that is heavy and takes up a lot of space. Audi is taking a new approach to offset these disadvantages – a holistic approach with a specific vehicle package, a systematic lightweight construction concept and an optimal configuration of all components for the electric drive.
The most important development related to batteries for electric drives are lithium-ion cells. Numerous experts throughout the world are working on their further development for use in cars, with the primary objectives being to reduce weight and increase capacity and performance. Audi has also opted for this technology, both for use in a hybrid production vehicle, such as the upcoming Q5 hybrid, and in the e-tron test platform.
The requirement specification for the concept vehicle goes far beyond battery technology and the replacement of the combustion engine with an electric drive system, however. The Audi development engineers decided back in the concept phase to design practically every component and technology based on the new requirements of electric mobility. The interaction of all elements has a decisive influence on the factors efficiency, range and practicality.
The vehicle body is compact. The sweeping line of the front end and the flat curved roof immediately identify the two-seater as an Audi. The contours of the flanks are familiar. The tapering of the dynamic line above the sill and the shoulder line tie together the front end, the side and the rear, lend a plastic quality to the doors and the transition to the side air intake and sharply emphasize the Audi-typical round wheel wells with the large, 19-inch tires.
1.90 meters (74.80 in) wide, just 4.26 meters (167.72 in) long and 1.23 meters (48.43 in) tall – those are the proportions of a supercar. The wheelbase of 2.60 meters (102.36 in) leaves plenty of room between the axles for people and technology. Like with a mid-engined sports car, the cabin of the e-tron is shifted far forward toward the front axle, leaving room in front of the rear axle for the roughly 470 kilogram (1036.17 lb) battery unit, the inverter and the power electronics.
The two electric motors, which have their own cooling system, are mounted behind the rear axle. The front electric motors are mounted on the front axle, with their cooling system arranged in front of them. This special package, which features a 42:58 weight distribution, ensures perfect balance, which contributes to the driving dynamics of the e-tron.
The combination of aluminum and carbon fiber-reinforced composite material guarantees supreme rigidity coupled with low weight. Audi will soon use this technology in a similar form for production vehicles. Despite the complex drive system layout with four electric motors and a high-capacity battery system, the total weight of the Audi e-tron is only around 1,600 kilograms (3527.40 lb).
Check out the rest of our Frankfurt Motor Show coverage.
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