The scenario: endurance tests in the wind tunnel
In front of the low-noise rotor measuring around five meters (16.4 ft) in diameter, the Audi e-tron prototype stares into the eye of the hurricane. On the aeroacoustics test rig in the Wind Tunnel Center in Ingolstadt, the world’s quietest vehicle wind tunnel, the Audi engineers optimize drag and noise under extreme conditions. Both are crucial for a car’s efficiency and comfort. With an output of 2.6 megawatts, the fan produces speeds of up to 300 km/h (186.4 mph). The Audi e-tron prototype was put through over 1,000 hours of testing here.
The result: When equipped with the standard exterior mirrors, the electric SUV achieves a drag coefficient of 0.28. Even with the optional virtual exterior mirrors the value is 0.27. Customers benefit directly from this low figure as drag contributes decisively to the high range of more than 400 kilometers (248.5 mi) in the WLTP cycle. A hundredth of the drag coefficient figure represents a range of around five kilometers (3.1 mi) driving under everyday conditions.
Drag: essential on long journeys
On long journeys where the Audi e-tron prototype is perfectly at home, the drag constitutes the key driving resistance – far more important than the rolling resistance and inertia. The energy is lost which the car needs to overcome this resistance. That is why good aerodynamics are so important. In urban traffic, however, other factors come into play. Here an electric car can recover a large part of the used energy when braking, thereby reducing the importance of its mass.
To achieve the low drag coefficient, the Audi engineers developed a wide range of aerodynamics measures in all body areas. Some of these technical solutions are evident at first glance, while others fulfill their purpose hidden away from sight. Thanks to these solutions, the drag coefficient for the Audi e-tron prototype is almost 0.07 less than for a comparable, conventionally powered vehicle. With a typical usage profile this set-up increases the range by around 35 kilometers (21.7 mi) per battery charge in the WLTP cycle.
Smart solutions: virtual exterior mirrors and dimples on the underbody
The optional virtual exterior mirrors will be making their world premiere in the volume-production version of the Audi e-tron prototype. They are much narrower than the standard mirrors: They reduce the vehicle width by 15 centimeters (5.9 in) and, thanks to their new shape, not only reduce drag, but also noticeably cut the nonetheless low wind noise. Each of their flat supports integrates a small camera. The captured images appear on OLED displays in the transition between the instrument panel and door. The virtual exterior mirrors can be adapted for various driving situations, thus potentially improving safety. Three views are available in the MMI system – for highway driving, turning and parking.