Automotive Intelligence - the web for automotive professionals and car enthusiasts
Januar 12, 2010
Its “torque vectoring” is the key to a thrilling level of active precision and excellent traction. Thanks also to its low weight, short wheelbase and perfect weight distribution for dynamic handling, the Audi e-tron has all the drivability of a go-kart – agile, good on bends and neutral right up to the very high handling limit. Lithium-ion batteries, located for an optimal center of gravity behind the passenger compartment and ahead of the rear axle, make an effective energy content of 45 kilowatt-hours available. This makes an operating range of up to 250 kilometers (155.34 miles) realistically possible.
As previously with the first e-tron concept car shown in Frankfurt, Audi again bases all components in this electric vehicle on an integral concept with many revolutionary details: a heat pump as an efficient means of heating up and maintaining the interior temperature. The drive system, power electronics and battery have innovative thermal management – crucial for maintaining a high operating range coupled with outstanding interior comfort.
Design and package Audi is presenting a further variant of an electric vehicle in the form of the Detroit showcar Audi e-tron. The vehicle body has a powerful, wide and muscular stance on the road, and looks extremely compact and puristic not least thanks to the typically short sports car wheelbase of just 2.43 meters (95.67 in) – a whole 22 centimeters (8.66 in) shorter than the R8.
1.78 meters (70.08 in) wide, just 3.93 meters (154.72 in) long and 1.22 meters (48.03 in) tall – those are the classic proportions of a sports car. That leaves space ahead of the rear wheels for the 399 kilogram (879.64 lb) battery unit, with converter and power electronics.
The two electric motors, which have their own cooling system, are mounted on the rear axle. This special package, featuring a 40:60 weight distribution, ensures perfect balance, which contributes to the driving dynamics of the Audi e-tron.
The trapeze of the single-frame grille dominates the distinctly wedge-shaped front end and is flanked by two large air intakes. The top of the grille merges into the flat strips of the adaptive matrix beam headlight modules with their clear glass covers. All light units use ultra-efficient LED technology.
One design element that is specific to electric vehicles developed by Audi – such as the Audi e-tron – are the air intakes in the single-frame grille and behind the side windows on the C-post. They are closed flush under normal circumstances and opened by retracting slats when additional cooling air is required. The slats above the drive unit then also open to provide a better through-flow of air. These measures, too, maximize efficiency – the concept car is outstanding for an already low drag coefficient that is further improved when the flaps are closed.
The ASF body Systematic lightweight construction is an even more important prerequisite for efficiency and range with electric vehicles than for conventionally powered automobiles. Lightweight construction is moreover the key to thrilling handling characteristics. Audi developers focused on a core competence of the company when creating the Detroit showcar Audi e-tron: The body structure is based on Audi Space Frame technology (ASF), with a hybrid design approach adopted. All add-on parts – doors, lids, sidewalls and roof – are made of a fiber-reinforced plastic.
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 future production vehicles. Despite the complex drive system layout with two electric motors and a high-capacity battery system, the total weight of the Audi e-tron showcar on display in Detroit is only around 1,350 kilograms (2,976.24 lb).
Characteristic for the concept of the Audi e-tron – and therefore also characteristic for a further development in an electric vehicle – is the near total elimination of switches and small components such as the ignition. The climate control unit is located to the right above the steering wheel. The display provides temperature and ventilation information. Again drawing inspiration from a smartphone, the system is controlled by means of a touch-sensitive sliding control.
The equally racing-inspired lightweight bucket seats combine excellent lateral support with comfort. Two contrasting colors delineate the various zones of the interior. The colors and the high-quality materials combine elegance and sportiness.
Drive system and energy supply Two asynchronous electric motors with a total output of 150 kilowatts (204 hp) give the Detroit showcar Audi e-tron the performance of a genuine sports car. The concept car can accelerate from 0 to 100 km/h (0 – 62.14 mph) in 5.9 seconds if necessary, and goes from 60 to 120 km/h (37.28 – 74.56 mph) in 5.1 seconds. The torque is distributed 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 250 kilometers (155.34 miles).
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. The charging time when the battery is empty is around 11 hours, but heavy current (400 volts, 32 amperes) cuts this to around just two hours.
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 recharging of the battery is already available on many Audi production models. During braking, the alternator converts the kinetic energy into electrical energy, which it then feeds into the on-board electrical system.
The Detroit showcar Audi e-tron in its further developed version goes one decisive step further into the future; an electro-mechanical brake system means the potential of electric motors for energy recovery can now be exploited. 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.
By virtue of being isolated from the brake pedal, the Audi e-tron’s electric motors can convert the entire deceleration energy into electric current 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.
Driving dynamics The drive system’s power is transferred to the road by the rear wheels, reflecting the Audi e-tron’s weight distribution of 40:60.
Both the individual motors, which are installed behind the wheels close to the vehicle’s center line as wheel drives, also enable the Detroit showcar Audi e-tron's lateral dynamics to be intelligently controlled. This also boosts traction. Similar to what the sport differential does in conventional Audi vehicles, torque vectoring – the targeted acceleration of individual wheels – makes the newly developed electric drive of the Detroit showcar Audi e-tron even more dynamic while simultaneously enhancing driving safety.