THE NEW 7-SPEED S-TRONIC FROM AUDIDipl.-Ing. Mario Schenker

Head of dual clutch transmission designAudi AG, Germany

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ABSTRACTFollowing the considerable success of the 6-speed S tronic in the A3 and TT models, Audiis launching the new 7-speed S tronic in midsize and luxury models in 2008. This will bethe first time that a dual-clutch transmission has been combined with the company’ssuperior quattro_ drive. The 7-speed S tronic will thus be continuing the range ofcompletely newly developed, innovative transmissions from Audi. This innovativetransmission concept’s extremely short shift times, high-rev stability, individually adaptablewide gear ratios and high performance combine efficiency and sportiness in anoutstanding 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 thecomponents dual clutch, gearset, mechatronics and oil supply. The advantages of thesolutions realised in the transmission are illustrated. In addition, the hydraulics concept –a completely new development – and other innovative detail solutions specially designedfor the demands of the luxury car class are presented. The paper concludes with a list ofthe transmission’s performance data and a feedback from the first introduction during the2008 International Geneva Motor Show…

INTRODUCTIONAudi has been offering models with a dual-clutch transmission since 2003, having alreadymade it available for both the Audi TT and the Audi A3. This transmission variant standsout for the way it expertly combines the high efficiency of a manual transmission with thesmoothness 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 themarket share of automatic vehicles in this class since its introduction. The share of AudiA3 models with an automatic transmission, for instance, has more than doubled since thelaunch 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 thesuperlative quattro_ drive system for the first time…

DEVELOPMENT GOALSThe new 7-speed S tronic has been developed in-house by AUDI AG. Series production istaking place at Volkswagen's Kassel plant. This new transmission generation is the latestin a line of innovative transmission concepts which have been completely newlydeveloped for the Modular Longitudinal Platform at Audi…… The necessary control pressure is produced by an efficiently designed oil pump positioned

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directly next to the dual clutch unit, from which it is driven via a set of gears. In order toattain the stability at high rev speeds as stipulated in the specifications manual, the pumpwas 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 used vary tremendously. The dual clutch, for instance, requires a lubricant that maintainsconstantly good friction coefficient ratios at the contact surfaces of the plates throughoutthe transmission's service life. The mechatronics and oil pump need a fluid with a viscositythat is as low as possible, even at low temperatures, while the gearwheels,synchromeshes and bearings call for a lubricant that guarantees good lubrication even athigh temperatures and when subject to high compression forces. Other aspects such astendency to foam, compatibility with the materials used, thermal stability, etc., are onlymentioned here as examples. In order to satisfy all of these criteria without incurring anymajor disadvantages for the layout of the individual components, the seven-speed S tronicfeatures two separate oil circuits.Whereas the dual clutch, the mechatronic module and the oil pump are supplied withapprox. 7.5 litres of full-synthetic ATF (Automatic Transmission Fluid) by a dedicated oilcircuit, the gearsets as well as the centre and front-axle differentials are kept lubricatedwith 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 suppliedby the oil pump alone. When starting off, therefore, an ejector pump cuts in whichprovides extra cooling oil at low pressure. This enables the quantity of oil for cooling theclutches 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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