At the Geneva show Audi revealed the S5 S-tronic, a seven-speed DSG matched to the S5’s longitudinal V8 and quattro transmission and which is entirely an Audi in-house design. The principle is the same as in the transverse DSG, with a hollow input shaft running concentrically around a solid one and each shaft connecting to alternate gears, but this time there’s no need to squeeze it into a short package as there’s a whole transmission tunnel to play with.
So the clutches can have their own compartment, separate from the gears, which means the clutches can bathe in ATF lubricant and the gears in normal hypoid gear oil to the benefit of both. The inner input shaft, engaged by the larger clutch, is mated to first, third, seventh and fifth gears (that’s the order, working rearwards), while the outer shaft, whose clutch sits within that of the inner shaft, carries fourth, sixth and second gears. The centre Torsen differential sits on the back of the output shaft, which runs below the input shaft. The first three gears plus reverse, that is the gears with the biggest gap to the next ratios and thus the biggest loads on their synchromesh, have triple-cone synchronisers.
Sport mode speeds the shifts (to 100 milliseconds from 200), livens up the kickdown and locks out seventh gear. Manual mode feels near-instant and of course there’s the impression of a continuous torque delivery during the shift.