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High-voltage on the asphalt

The Audi e-tron concept car gives you a foretaste of the sports-oriented future of electromobility. A test drive with watts, volts and emotions.

COPY/MICHAEL KIRCHBERGER

A Delicate hum fills the air. The selector lever clicks into the “Forward” position and a gentle jolt causes the body to tremble. And then the pressure on the accelerator in the footwell dials up the thrust that quickly brings the car up to speed from a standing start. The high-tech drive system accelerates the car, which weighs around 1,600 kilograms, from 0 to 100 kilometers per hour in 4.8 seconds. The pressure pushing your upper body back into the contoured seat must be similar to that in a supersonic jet. Yet all you can hear is the mumbling of the passenger. Isolated words like “unbelievable” or “amazing” can be plainly heard because the drive keeps the noise down to a subdued whistle hardly louder than when a computer fan is switched on. At higher speeds the only sounds are the rolling noise of the tires or the tempestuous rush of the slipstream. There’s no multi-cylinder V engine screaming under the sloping rear hatch of the vehicle – the heart of this car is a battery. The drivetrain puts out 230 kW (313 hp) and 4,500 newton meters of torque. For comparison: Among the ranks of the supercars and muscle engines, torque values greater than 1,000 newton meters are considered to be physically difficult to contain. Audi therefore drew upon long-standing virtues. The wheels are powered directly by electric motors. The short distances that the torque has to travel between its generation and meeting the asphalt reduce friction losses. Hardly a newton meter is left behind. As much as the acceleration promotes the rush of adrenaline, the innovative drive system does just as much to bring the pulse back down. Depending on the driving situation, the assembly supports, brakes or corrects. The intelligent electronics direct power to the wheels to always ensure the best possible dynamics and safety. This also provides maximum enjoyment for the driver when they discover how delivering more torque to the outside wheels while accelerating out of a corner pulls the car around the corners as if it were on rails. The e-tron is glued to the road and pulls through corners as if the gods of driving physics had braced their hands against the flanks of the tires in support. The electronics already begin monitoring traction while accelerating from rest because “there isn’t a mass-produced tire available today that could withstand it if the motors delivered their maximum torque unfettered,” explains an Audi engineer. The controller therefore monitors the steering angle of the wheels – to prevent damage to the suspension mountings, for example – and measures wheel slip, from which it derives the grip on the road surface.

The suspension plays along charmingly. Taut, but not uncomfortable. Very few prototypes exhibit such balance – and even more can be expected of the production vehicle. The brakes bite hard and powerfully, yet their calipers are applied with great precision to the four lightweight composite disks. The disks shimmer with a delicate gray through the spokes of the high-performance wheels developed specifically for the e-tron. They are however only used for severe braking. As soon as the driver backs off the thrust, the polarity of the electric motors is reversed and they act as generators. The recuperated energy is fed back into the batteries as electric current. This is good for a few more kilometers of range. The Audi e-tron electric supercar is based on the lightweight aluminum body of the R8, which is ideally suited as the platform for the innovative electric technology. Lightweight construction and sophisticated aerodynamics are important properties that reduce energy consumption and thus increase range. The e-tron has to lug around a heavy load, which is located directly behind the tailored seats covered in soft, exquisite leather. The lithium ion battery weighs in at 470 kilograms (a powerful V8 engine weighs barely half that), has an electrical capacity of 42.2 kilowatt hours at a voltage of 400 volts and is good for a range of 248 kilometers. The placement of the battery is excellent in terms of driving dynamics and is also safe in the event of a crash, as already computed by the developers in countless computer simulations.

But the charged battery has another entirely different set of requirements and exhibits almost human traits. Its capacity decreases if it gets too hot or too cold. 25 degrees Celsius is optimal. The battery therefore has its own water-filled cooling loop. Three additional loops provide thermal management for the motors and the power electronics. A series of flaps in the single-frame grille and in the flanks, as well as extensible cooling ribs above the rear of the 4.26-meter-long and only 1.23-meter-tall electromobile direct cooling air from the slipstream to the motors. Side mirrors are death to aerodynamics, which is why the designers have done away with them on the e-tron. Instead, tiny cameras snuggle tightly against the outside of the A-pillars and project their images into the cabin. The small four-inch displays sit at the exact point to which the driver’s eyes move while changing lanes: to the front window frame of the driver’s and the passenger’s door. The break with our viewing habits shouldn’t be too sharp. A heat pump system regulates the cabin temperature to relieve some of the burden on the energy system. Lightweight, quiet and very responsive, the heat pump helps e-tron drivers to keep a cool head, while an LED charge status indicator mounted on the center console (which no longer houses a cardan shaft but gives the body greater torsional rigidity) keeps them informed at all times. The charge status of the battery is represented by either a flashing red light or a steady green light. Although the e-tron units in existence already have a decidedly sporty character, the developers still have a long way to go. The car is scheduled to go into series production in 2012.

Automotive journalist Michael Kirchberger enjoyed the test drive in the Audi e-tron along the Pacific coast of California.