The Efficiency Standard - The Audi A8 Hybrid
MILTON KEYNES, UNITED KINGDOM – April 7, 2010:
Summary
Audi presents the A8 hybrid as a technology concept at
the Geneva Motor Show. Its two engines – a 2.0 TFSI and an electric
power unit – develop a combined total of 245PS and deliver 480 Nm
(354.03 lb-ft) of torque, enabling them to provide the confident driving
performance of a large six-cylinder engine. And combined with the
advantages of electric power, the consistent downsizing also pays
substantial benefits in fuel economy – up to 45.6mpg is possible,
corresponding to a CO2 value of 144 grams per km.
The Audi A8 hybrid utilizes a parallel hybrid system – a highly efficient principle that avoids any unnecessary friction and power losses. Interposed between the four-cylinder petrol engine, which delivers 211PS, and the eight-speed tiptronic is a powerful electric motor. It develops 45PS of power and a very ample 211 Nm (155.63 lb-ft) of torque. The two power units together develop a system power of 180 kW and 480 Nm (354.03 lb-ft). This enables the Audi A8 hybrid to accelerate in 7.6 seconds from zero to 62mph and to achieve a top speed of 146mph.
The A8 concept car is a full hybrid. This means that it can be propelled by either the gasoline engine or the electric motor alone – or by the combined power of both. During coasting or braking, the electric motor acts as a generator that converts kinetic into electric energy and recharges the battery. The hybrid drive can propel the car on electric power alone at up to 40mph with a range of over two kilometers – enough for urban stop-and-go traffic.
The efficiency standard – the Audi A8 hybrid
Full
version
Power like a big V6, fuel economy like a modest
four-cylinder unit – Audi presents the A8 hybrid as a technology
concept at the Geneva Motor Show. Its two propulsion units – a 2.0
TFSI and an electric motor – develop a total output of 245PS of
system power and 480 Nm (354.03 lb-ft) of torque. This enables the Audi A8
hybrid to accelerate in 7.6 seconds from zero to 62mph and to achieve a top
speed of 146mph. Yet average economy amounts to up to 45.6mpg – the
CO2 equivalent is 144 grams per km.
The technology of the Audi A8 hybrid
The combustion engine of
the Audi A8 hybrid is the 2.0 TFSI – a high-tech powerplant. This
four-cylinder unit, which has been named “Engine of the Year”
five times in a row since 2005, is an example of Audi’s downsizing
philosophy. It combines direct fuel injection with turbocharging and the
AVS Audi valvelift system, which regulates the valve lift in two stages. In
combination with the adjustable intake camshaft, the Audi valvelift system
improves cylinder charging and ensures spontaneous and powerful torque
build-up. The 2.0 TFSI delivers 211PS and 350 Nm (258.15 lb-ft); the torque
value remains constant from 1,500 to 4,200 rpm.
In the crankcase of the four-cylinder unit, which has a displacement of 1,984 cc, two balancer shafts offset second-order inertial forces to ensure virtually vibration-free and pleasantly quiet operation that goes well with the luxurious character of the A8. All components are optimized to minimize friction. The flow-rate-regulated, pressure-controlled oil pump further reduces fuel consumption.
Electric motor with ample propulsive power
A hydraulically
operated wet clutch links the 2.0 TFSI with the electric motor. Its control
requires the utmost precision, and a great deal of know-how has been
expended to achieve its smooth, precise and swift operation. The
synchronous motor, which is continually excited, also serves as a generator
that develops 45PS of power and 211 Nm (155.63 lb-ft) of torque. Its full
power is available practically right from standstill and contributes to a
sportily powerful start-up. Since an electric motor also develops heat, its
housing is furnished with cooling ducts. Interposed between the electric
motor and the wheelset of the eight-speed tiptronic, which is controlled
entirely by electronics, is an additional cut-out clutch. In conjunction
with the electric unit, this functions as a torque converter. The
propulsive power of both drive systems is applied to the road through the
front wheels.
Lithium-ion technology – the battery
The energy storage
system of the Audi A8 hybrid is mounted in the rear section. This
state-of-the-art lithium-ion battery is more compact and weighs less than
other types but is substantially more powerful. It is protected by a
high-strength housing, and a ventilation module ensures that it always
operated within the ideal temperature range. Yet the A8 hybrid also
provides ample luggage space of 400 litres (14.13 cubic feet)
Several subsystems that operate on engine power in a conventional car have been modified right from the start for use in the Audi A8 hybrid. The compressor in the climate control system runs entirely on electric power. The steering system is electromechanical as well. The brake booster too is supplied by a demand-controlled electric vacuum pump. During electrical – i.e. recuperative – braking actions, a sophisticated control system ensures that the ABS and ESP functions operate properly.
The power electronics unit manages the interaction of the systems. Its pulse control inverter regulates the interplay of the battery and the electric motor. The DC-DC converter supplies power to users on the onboard network. The power electronics unit, which is connected to the battery and the electric motor by high-voltage cables, is located in the engine compartment.
The smooth interaction of these components and their high level of integration attest to the specialized know-how Audi has accumulated. The technology architecture already provides a glimpse of a future production model – the Audi Q5 hybrid, which will be introduced later this year.
Driving experience
The Audi A8 hybrid, which weighs 1,885
kilograms (4,155.71 lb), drives as if it had a big six-cylinder gasoline
engine or a TDI under its bonnet. From zero to 62mph the vehicle
accelerates in 7.6 seconds, and it can continue to accelerate up to 146mph.
Yet fuel economy of up to 45.6mpg is possible, corresponding to 144 grams
CO2/km (231.75 g/mile). In city traffic, the hybrid drive uses about 20
percent less fuel than a conventional drive. Both the car’s
performance and its fuel economy benefit substantially from a major
advantage of the A8 model series – its lightweight aluminum body
based on the Audi Space Frame principle (ASF).
The hybrid drive is designed for fully electric-powered driving up to 40mph and for a distance exceeding two kilometers – especially well-suited for driving in the city or residential suburbs. When conditions permit, the driver can also select the electric mode by actuating a separate e-key in the cockpit. Both the display screen of the instrument cluster and the large monitor of the MMI operating system on the dashboard present all momentary power flows in brilliant graphics.
When the Audi A8 hybrid starts moving, both of its engines interoperate closely to suit varying power demands. Above 40mph the combustion engine alone does all the propulsive work, while the electric motor supplies onboard users and recharges the battery.
When the driver lets up on the gas, the combustion engine is disconnected from the drivetrain, so the Audi A8 hybrid ”coasts”. In braking and slow-down phases, the e-motor functions as a generator – recuperating energy efficiently and feeding it into the battery.
When the driver floors the pedal, the engine management temporarily controls the entire system power, and now the electric motor is boosting power. 245PS and 480 Nm (354.03 lb-ft) endow the big saloon with enormous thrust. The intermediate sprint between 37mph and 75mph in fifth gear for instance is accomplished in 7.5 seconds. The Audi A8 hybrid is an extremely dynamic car – with a fuel efficiency that is setting new standards. This is especially true in everyday user activities. Even its looks betray the power of this near-production concept car with its big 21-inch wheels and their 265/35 tyres.
The design of the Audi A8 hybrid
This near-production concept
car has 21-inch, two-colour wheel rims styled with highly three-dimensional
surface areas. The exterior paint job of the A8 hybrid is in “Prism
Silver” with “Spectra Flair” as an accent colour –
a rainbow effect that’s accentuated in reflected light along creases
and seams on the body. The prominently located “hybrid”
lettering on both front wings leaves no doubt about what kind of car this
is. The accentuation of its width by a prominent low horizontal spoiler
edge and a chrome strip conveys the vehicle’s solid stance on the
road.
The engine compartment cover with its high-gloss finish and the glass cover of the battery in the boot also provide visual links to hybrid technology. And the illuminated doorsteps bear the “hybrid” insignia as an elegant touch to underscore the electric aspect whenever the doors are opened – using LED technology to minimize energy consumption.
The passengers also see the prominent hybrid logo displayed on the dashboard. The "Powermeter" in addition shows the energy flow in the instrument cluster.