The New 7-Speed S-Tronic from Audi
THE NEW 7-SPEED S-TRONIC FROM AUDI
Dipl.-Ing. Mario Schenker
Head of dual clutch transmission design
Audi AG, Germany
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ABSTRACT
Following the considerable success of the 6-speed S tronic in the A3 and TT models, Audi
is launching the new 7-speed S tronic in midsize and luxury models in 2008. This will be
the first time that a dual-clutch transmission has been combined with the company’s
superior quattro_ drive. The 7-speed S tronic will thus be continuing the range of
completely newly developed, innovative transmissions from Audi. This innovative
transmission concept’s extremely short shift times, high-rev stability, individually adaptable
wide gear ratios and high performance combine efficiency and sportiness in an
outstanding manner, thus making a considerable contribution to the brand essence of
“Vorsprung durch Technik”.
The paper describes the design of the transmission and deals specifically with the
components dual clutch, gearset, mechatronics and oil supply. The advantages of the
solutions realised in the transmission are illustrated. In addition, the hydraulics concept –
a completely new development – and other innovative detail solutions specially designed
for the demands of the luxury car class are presented. The paper concludes with a list of
the transmission’s performance data and a feedback from the first introduction during the
2008 International Geneva Motor Show…
INTRODUCTION
Audi has been offering models with a dual-clutch transmission since 2003, having already
made it available for both the Audi TT and the Audi A3. This transmission variant stands
out for the way it expertly combines the high efficiency of a manual transmission with the
smoothness of an automatic, whilst placing the emphasis on sportiness at the same time.
The success of this transmission technology is evident from the significant increase in the
market share of automatic vehicles in this class since its introduction. The share of Audi
A3 models with an automatic transmission, for instance, has more than doubled since the
launch of the dual-clutch transmission.
Audi intends to extend this success to further model series with the new 7-speed S tronic.
This technology will now be offered in midsize and luxury models in conjunction with the
superlative quattro_ drive system for the first time…
DEVELOPMENT GOALS
The new 7-speed S tronic has been developed in-house by AUDI AG. Series production is
taking place at Volkswagen's Kassel plant. This new transmission generation is the latest
in a line of innovative transmission concepts which have been completely newly
developed for the Modular Longitudinal Platform at Audi…
… The necessary control pressure is produced by an efficiently designed oil pump positioned
directly next to the dual clutch unit, from which it is driven via a set of gears. In order to
attain the stability at high rev speeds as stipulated in the specifications manual, the pump
was designed as an external-gear pump.
Figure 1: cut-away diagram of the 7-speed S tronic
The demands placed by this transmission's individual components on the lubricant usedvary tremendously. The dual clutch, for instance, requires a lubricant that maintains
constantly good friction coefficient ratios at the contact surfaces of the plates throughout
the transmission's service life. The mechatronics and oil pump need a fluid with a viscosity
that is as low as possible, even at low temperatures, while the gearwheels,
synchromeshes and bearings call for a lubricant that guarantees good lubrication even at
high temperatures and when subject to high compression forces. Other aspects such as
tendency to foam, compatibility with the materials used, thermal stability, etc., are only
mentioned here as examples. In order to satisfy all of these criteria without incurring any
major disadvantages for the layout of the individual components, the seven-speed S tronic
features two separate oil circuits.
Whereas the dual clutch, the mechatronic module and the oil pump are supplied with
approx. 7.5 litres of full-synthetic ATF (Automatic Transmission Fluid) by a dedicated oil
circuit, the gearsets as well as the centre and front-axle differentials are kept lubricated
with around 4.3 litres of hypoid transmission oil (see Figure 2 and 3).
Figure 2: oil chamber division (hypoid transmission oil chamber)
Figure 3: oil chamber division (automatic transmission oil chamber)
..... away under high loads, very high quantities of oil are required which cannot be supplied
by the oil pump alone. When starting off, therefore, an ejector pump cuts in which
provides extra cooling oil at low pressure. This enables the quantity of oil for cooling the
clutches to be approximately doubled if required, without the need for additional pump
capacity. This concept has already proven itself at Audi in the multitronic_ transmission.
(Figure 5)
Figure 4: dual clutch
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