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Audi presents the highlight of the IAA 2009: 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.
Audi has taken a new and in some cases revolutionary approach to many of the technical modules. A heat pump is used to efficiently warm up and heat the interior. The drive system, the power electronics and the battery are controlled by an innovative thermal management system that is a crucial component for achieving the car's range without compromising its high level of interior comfort. Networking the vehicle electronics with the surroundings, which is referred to as car-to-x communication, opens new dimensions for the optimization of efficiency, safety and convenience.
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.
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.
The Audi e-tron, which is slowed by four lightweight ceramic brake discs, takes the next large step into the future. An electronic brake system makes it possible to tap into the recuperation potential of the electric motors. A hydraulic fixed-caliper brake is mounted on the front axle, with two novel electrically-actuated floating-caliper brakes mounted on the rear axle. These floating calipers are actuated not by any mechanical or hydraulic transfer elements, but rather by wire ("brake by wire"). In addition, this eliminates frictional losses due to residual slip when the brakes are not being applied.
This decoupling of the brake pedal enables the e-tron's electric motors to convert all of the braking energy into electricity and recover it. The electromechanical brake system is only activated if greater deceleration is required. These control actions are unnoticeable to the driver, who feels only a predictable and constant pedal feel as with a hydraulic brake system.
The heat pump - used here for the first time ever in an automobile - also serves to increase efficiency and range. Unlike a combustion engine, the electric drive system may not produce enough waste heat under all operating conditions to effectively heat the interior. Other electric vehicles are equipped with electric supplemental heaters, which consume a relatively large amount of energy. The heat pump used by Audi - and commonly used in buildings - is a highly efficient machine that uses mechanical work to provide heat with a minimum input of energy.
The electronics development engineers at Audi not only aimed to make the e-tron as efficient and fun to drive as possible, they were also very concerned with safety and traffic management. The technical concept car includes a prototype of an information processing system. Future generations of these systems will usher in a new era in the networking of road traffic, particularly in regions and countries with a high volume of traffic. This progress is made possible by the rapid advancements in computing power, software and communication technology.
The buzzword "car-to-x communication" refers to the direct exchange of information in flowing traffic and to the traffic environment. The letter "x" is a free variable that can refer just as easily to other vehicles as to fixed infrastructure such as traffic lights. In contrast to today's telematic systems, car-to-x communication no longer requires a central service provider to quickly and effectively pool and process information. The participants themselves perform these tasks by spontaneously networking with one another.
The future car-to-x network still needs some time before it becomes reality on the roads. This obstacle is one that can be overcome, however, as nearly every carmaker in Europe, the U.S.A. and Japan has decided to develop a common standard for hardware and software. Once all new cars are equipped with this technology, a functional network of automotive transmitters will soon be available, at least in large population centers.
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