BMW double-clutches 335i

BMW is by no means a stranger to automated manual transmissions. The Bavarian elves have been tinkering with the concept since the 1990s, when the M3 Coupe offered a six-speed SMG gearbox as an alternative to the regular six-speed manual transmission.

SMG has evolved since then, to the seven-speed SMG II when it appeared in the V10-engined M5 in 2006 -- and now, to the tongue-twisting "seven-speed sports automatic transmission with double clutch" that will be introduced to Australia in the 335i Coupe and convertibles models from December this year.

The new gearbox is a more refined, smoother-shifting development of the SMG II that applies the double-clutch principle -- first seen in VWs and Audis -- to soften the transition from ratio to ratio to the extent that it matches a regular planetary auto transmission.

The double-clutch arrangement works by always having two sets of gears in mesh -- one active and the other ready to go via an electronically activated clutch. The gearbox itself is otherwise a regular manual transmission.

Because there's no torque converter involved, the direct-drive transmission is more efficient than a conventional auto. And, because the shifts are electronically controlled and involve no more than the activation of one of the double clutches, faster than any manual shift could ever dream to be. BMW claims gearshifts take place "in the time a conventional manual transmission would take merely to disengage the clutch."

The outcome is that BMW is able to claim the seven-speed sports automatic transmission with double clutch drops the 225kW 335i Coupe's zero to 100km/h acceleration times by .1 of second compared to the manual transmission, and by 0.3 of a second compared to the now-outmoded (in 335i) Steptronic six-speed auto. The 335i Coupe with seven-speed sports automatic transmission with double clutch now reaches 100km/h in 5.4 seconds.

The benefits continue: providing BMW with clear vindication of its EfficientDynamics regime, EU testing shows the Coupe's fuel consumption is also reduced, from 9.5L/100km -- for both manual and the previous auto -- to 9.1lL/100km. The convertible is even better, claiming the same 9.1lL/100km, which represents a 0.8L/100km improvement over the figures quoted for the manual and the previous auto.

The new transmission offers driver choices of selection via the regular console shifter, or by steering wheel paddles.

The seven-speed sports automatic transmission will add $3500 to the price of a manual transmission 335i Coupe or convertible.

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