|The Audi e-tron concept. Click to enlarge.|
At the Frankfurt Motor Show, Audi unveiled the e-tron. a high-performance electric sports car featuring four drive motors—two each at the front and rear axles—making the concept car a true quattro. Producing 230 kW (313 hp) and 4,500 Nm (3,319 lb-ft) of torque, the two-seater accelerates from 0 to 100 km/h in 4.8 seconds, and from 60 to 120 km/h (37 – 75 mph) in 4.1 seconds. The 53 kWh lithium-ion battery pack enables a range of approximately 248 kilometers (154 miles) (NECD combined cycle).
The e-tron is 1.90 meters (74.80 in) wide, 4.26 meters (167.72 in) long and 1.23 meters (48.43 in) tall. 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 kg (1,036 lb) battery unit, the inverter and the power electronics.
The two rear 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.
Battery pack and charging. The battery pack has a total energy capacity of approximately 53 kWh, 42.4 kWh (roughly 80%) of which is usable. The battery pack is directly behind the passenger cabin for an optimal center of gravity and axle load distribution. Placing the battery in front of the rear axle ensures an optimal axle load distribution without compromising the compact overall design and the generous amount of interior space.
The battery system is water-cooled. A needs-based energy management system controls all functions for the chassis, convenience equipment and other auxiliary consumers. A thermal management system with optimally matched cooling and heating components considers the cooling requirements of the battery and the drive system in addition to the interior temperature.
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 charge (400 volts, 63 amperes) reduces this to just around 2.5 hours.
Audi engineers are also working on an inductive (wireless) charging 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.
Braking. 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.
Lightweight construction. Lightweight construction was a top priority for the e-tron concept car. The Audi development engineers drew on the core competence of the company for the e-tron. The body structure is based on Audi Space Frame (ASF) technology and was realized as a hybrid construction. All add-on parts—doors, covers, sidewalls and roof—are made of a fiber-reinforced plastic.
The combination of aluminum and carbon fiber-reinforced composite material delivers 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 (3,527 lbs). An intelligent aerodynamics concept with active elements helps to reduce consumption.
Heat pump. A heat pump is used to efficiently warm up and heat the interior. The heat pump 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.
A high-efficiency climate control system is used to cool the interior. It works together with the thermal management system to also control the temperature of the high-voltage battery. The battery, the power electronics and the electric motors must be kept at their respective ideal operating temperatures to achieve optimal performance and range. As soon as the vehicle is connected to a charging station the vehicle is preconditioned as appropriate by the thermal management and other associated systems.
The drive system is heated if temperatures are cool, and cooled if hot. This preconditioning can also be extended to the interior, if necessary, so that the passengers can step into a cabin that has been heated or cooled as appropriate for their comfort.
Car-to-x.The e-tron concept car uses car-to-x communication technology developed by Audi to improve the efficiency of conventionally powered vehicles. For example, information about traffic light cycle times and the flow of traffic—provided by the infrastructure and other vehicles—is used to compute an optimal driving strategy. Audi has already modeled such a solution in Ingolstadt as part of its “travolution” project.