mph (electronically limited)
(from Audi Press
Release) Frankfurt Motor Show (IAA) 2009
The Audi e-tron
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
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.
Audi e-tron – The Holistic
The most important
development related to batteries for electric drives are lithium-ion
cells. Numerous experts throughout the world are working on their
further development for use in cars, with the primary objectives
being to reduce weight and increase capacity and performance. Audi
has also opted for this technology, both for use in a hybrid
production vehicle, such as the upcoming Q5 hybrid, and in the e-tron
The requirement specification for the concept vehicle goes far
beyond battery technology and the replacement of the combustion
engine with an electric drive system, however. The Audi development
engineers decided back in the concept phase to design practically
every component and technology based on the new requirements of
electric mobility. The interaction of all elements has a decisive
influence on the factors efficiency, range and practicality.
The Audi team therefore focused its attention on the total vehicle,
which is reflected in the comprehensive requirement specification.
-- The reduction of
road resistances and the resulting increase in range plays a
major role with electric vehicles. Lightweight construction was
therefore a top priority for the e-tron concept car. The body,
in particular, combines low weight with supreme strength and
rigidity. An intelligent aerodynamics concept with active
elements helps to reduce consumption.-- The package ensures the
safe integration of the electric drive system and the battery.
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.
-- Advanced battery technology enables a practical range. The
battery system is water-cooled for optimal performance and
-- A needs-based energy management system controls all functions
for the chassis, convenience equipment and other auxiliary
-- The innovative 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.
-- Driving dynamics and road comfort are what Audi customers
have come to expect in the sports car segment.
-- Vehicle safety is on par with the best of today’s production
-- The driver is provided with clear and comprehensive
-- 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.
Design and Package
The caliber of the car
is apparent to the observer at first glance. The Audi e-tron has a
wide, powerful stance on the road. The car body seems almost
monolithic; the closed rear end appears powerful and muscular. The
trapeze of the single-frame grille dominates the 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 headlamp modules with
their clear glass covers. High-efficiency LED technology is used for
all lighting units – a matter of honor for Audi as the worldwide
pioneer in this field.
The headlamps are the core of a fully automatic light assistance
system that reacts flexibly to any situation. The new technology
recognizes weather conditions and adapts the illumination to rain or
fog. The technology at the heart of the light assistance system is a
camera that works together with a fast computer to detect oncoming
traffic, recognize lanes and measure visibilities, such as in the
event of fog.
If there is oncoming traffic, for example, the high beams are turned
off in the corresponding section of the illumination field. The
cornering light system analyzes data from the navigation system and
illuminates corners before the driver steers into them. The Audi e-tron
does not have conventional fog lamps that consume additional power.
It instead intelligently varies the low beams to widen the
illumination field, thus significantly reducing the glare from the
car’s own lights.
The variability of the headlamps is also reflected in their design.
The LED elements change appearance and thus the character of the
front end of the vehicle depending on the speed driven and the
ambient conditions. The innovative lighting technology offers the
Audi designers almost as much design freedom as the shape of the
A new design element unique to the e-tron are the air intakes in the
single-frame grille and in front of the rear wheel wells. They are
closed flush under normal circumstances and opened by means of flaps
when additional cooling air is required. Maximum efficiency is also
the reason behind this measure. The concept car has a remarkably low
drag coefficient, which gets even better when the flaps are closed.
The vehicle body is compact. The sweeping line of the front end and
the flat curved roof immediately identify the two-seater as an Audi.
The contours of the flanks are familiar. The tapering of the dynamic
line above the sill and the shoulder line tie together the front
end, the side and the rear, lend a plastic quality to the doors and
the transition to the side air intake and sharply emphasize the
Audi-typical round wheel wells with the large, 19-inch tires.
1.90 meters (74.80 in) wide, just 4.26 meters (167.72 in) long and
1.23 meters (48.43 in) tall – those are the proportions of a
supercar. 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 kilogram (1036.17 lb) battery unit, the inverter and the
The two 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.
Systematic lightweight construction is an even more important
prerequisite for efficiency and range with electric vehicles than
for conventionally powered automobiles. 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 guarantees supreme 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 (3527.40 lb).
Interior and Control Concept
Optical and functional
references to the new drive concept characterize the interior
design. They establish an advanced connection between proven Audi
genes and new formal hallmarks. Typical for the Audi design language
is the reduction of the architecture, controls and flow of
information to the essential in favor of visible lightweight
construction and a tidy overall impression.
The dash appears to float and has a curve that extends laterally
into the door panels. With no need to allow for a transmission,
shifter and cardan tunnel, the designers took advantage of the
opportunity to create a particularly slim and lightweight center
tunnel and center console. The flush gear selector, with which the
driver chooses between the modes forward, reverse and neutral,
emerges from the tunnel when the vehicle is started.
The cockpit of the e-tron is also oriented toward the driver – a
further characteristic Audi trait. Instead of the classic instrument
cluster, the concept car is the first Audi to be equipped with a
large, fold-out central display with integrated MMI functions. It is
flanked by two round dials.
The MMI is controlled via a scroll pad with a touch-sensitive
surface on the steering wheel (“MMI touch”) – an element inspired by
While an analog speedometer on the right provides speed information,
the instrument on the left tells the driver how much power is being
drawn. The central display shows the range in the status bar and
presents all key information from the infotainment and navigation
systems. It also provides the driver with relevant data from the
vehicle’s communication with its surroundings. The instruments
combine the analog and the digital worlds into a single unit.
Characteristic for the concept of the Audi e-tron 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 racing-inspired lightweight bucket seats combine excellent
lateral support with comfort. To contrasting colors – snow white and
cognac – delineate the various zones of the interior. The colors and
the high-quality materials combine elegance and sportiness.
Drive System and Energy Supply
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
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.
Making its Automotive Debut: The
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.
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.
The normal distribution
of the tractive power is clearly biased toward the rear axle in
accordance with the weight distribution of the e-tron. Similarly to
a mid-engined sports car, roughly 70 percent of the power goes the
rear and 30 percent to the front. If an axle slips, this balance can
be varied by means of the four centrally controlled electric motors.
The electric vehicle from Audi thus enjoys all of the advantages of
The four individual motors, which in the interest of greater
traction are installed behind the wheels as wheel drives, also
enable the e-tron’s lateral dynamics to be intelligently controlled.
Similar to what the sport differential does in conventional quattro
vehicles, torque vectoring – the targeted acceleration of individual
wheels – makes the e-tron even more dynamic while simultaneously
enhancing driving safety. Understeer and oversteer can be corrected
by not only targeted activation of the brakes, but also by precise
increases in power lasting just a few milliseconds. The concept car
remains extremely neutral even under great lateral acceleration and
hustles through corners as if on the proverbial rails.
The chassis has triangular double wishbones at the front axle and
trapezoidal wishbones made of forged aluminum components at the rear
axle – a geometry that has proven in motorsports to be the optimal
prerequisite for high agility, uncompromising precision and
precisely defined self-steering behavior. A taut setup was chosen
for the springs and shock absorbers, but it is still very
The direct rack-and-pinion steering gives finely differentiated
feedback. Its electromechanical steering boost varies with speed, so
that the e-tron only has to provide energy while steering, and not
while driving straight ahead.
As befitting its status, the Audi concept car rolls on 19-inch tires
with a new blade design. 235/35 tires up front and 295/30 tires in
the rear provide the necessary grip.
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
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
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.
These transmitters can be used to open up many new practical
applications. Below are just four examples showing the possibilities
offered by car-to-x communication.
Example 1 – Efficiency and range: Numerous external factors
influence energy consumption and thus the range of any vehicle. An
intelligent vehicle equipped with car-to-x technology is aware of
necessary braking or acceleration maneuvers in advance because it
combines navigational data with information about the flow of
traffic, for example. The central computer can prevent driver
actions that would use energy unnecessarily or use targeted braking
for recuperation of the battery.
Example 2 – Safety: A vehicle has spun out on a slippery road in a
blind curve and is unable to free itself under its own power. At the
same time, other vehicles are approaching quickly. The stuck vehicle
uses car-to-x to send out a warning signal reporting the precise
location of the hazardous location. A corresponding warning then
appears on the navigation system display of the approaching cars.
Example 3 – Traffic flow: Many cars are traveling between traffic
lights on an arterial road. Over and over again, they accelerate
only to have to brake again when the traffic light changes to red.
Car-to-x technology enables them to establish a network between
themselves and receive information from the traffic light
controller. The drivers can then make more judicious use of the gas
pedal because they know what to expect. The same applies for
imminent traffic jams: cars ahead provide information that results
in adjustments to the posted speed limits, noticeably spreading out
Example 4 – Convenience: The driver has entered a shopping center
with a chronic shortage of parking spaces into his navigation system
as the destination. With car-to-x, the mobile system networks with
the parking space registration system at the destination. When the
system in the parking garage reports that a convenient parking spot
is available, the navigation system can register its location and
also reserve the spot.