BMW is about to introduce an all-new transmission in the 3-series. The 7-speed Sports Automatic Transmission with double clutch will debut in the 335i Coupé and 335i Convertible in December this year.
Similar in concept to German rival Volkswagen’s DSG , the new 7-speeds, offers seamless gear changes which allows for faster acceleration and improved fuel economy and better emissions.
The 7-speed double-clutch will sit as an option ($3,500) above the standard six-speed manual and replace the previous optional 6-speed Steptronic gearbox.
Gears are selected automatically, via the gear selector or steering wheel-mounted shift paddles.
Although double-clutch gearboxes are now offered by most manufacturers, the idea and concept of a double clutch transmission has its roots in motor racing.
With our men in blue hanging about every corner with, what we like to call ‘revenue-raising-guns’, the point of gaining a tenth of a second in gear-changes may be seem irrelevant to most, but really, we care, and we know you care too.
The problem with double-clutch transmissions has been that they can’t handle enormous amounts of power without sacrificing reliability. Of course the Bugatti Veyron is an exception (after all, it does cost $2.7 million!) but they are getting strong enough to handle the might of BMW’s twin-turbo inline six.
BMW says its new sports automatic transmission with double clutch is designed for engine speeds of up to 9,000 rpm and torque levels of up to 520 Nm. Making it an ideal choice for the high-revving in-line 6-cylinder BMW engines (225 kW and 400 Nm of torque).
BMW says in the time it will take the best of us to disengage the clutch in a manual gearbox, the new 7-speed double-clutch gearbox has already changed gears and you’re on your way.
As a result of the new gearbox, acceleration in the automatic 335i Coupé has improved from 5.7 to 5.4 seconds for the zero to 100 km/h run. If you think the six-speed manual is still faster, you’d be wrong, the new gearbox will shame manual drivers by 0.1 second over the same 0-100km/h spring.
All the power and acceleration aside, the most amazing figure here is the fuel economy, as if the original 9.5-litre per 100km in the 335i Coupé wasn’t impressive enough, the new model, fitted with the double clutch gearbox bring that down to just 9.1 litres per 100 km! The convertible offers the same figure, down from 9.9-litres with the previous 6-speed auto.
If you’re unsure how double-clutch transmissions work, we’ll let BMW explain:
The technical core of the system is provided by two oil-cooled wet clutches. One of the two clutches is dedicated to serving the even transmission ratios (2, 4, 6), the other is for the odd numbered ratios (1, 3, 5, 7) and reverse gear.
On the move, one of the two clutches is closed and the other open. When shifting, as the first clutch disengages, the second engages simultaneously.
The transmission control system identifies the next gear that matches perfectly the relevant engine speed and road speed, selecting it in advance, poised to be engaged.
If the vehicle is accelerating in third gear the power transmission is effected through the relevant clutch and partial gearbox with the odd numbered ratios. In the part of the gearbox responsible for the even numbered ratios, fourth gear is already engaged.
It is then sufficient for the clutch responsible for the fourth gear to engage while the clutch for the third gear simultaneously disengages: within milliseconds, engine power is conveyed to the rear wheels via fourth gear. This enables a seamless, comfortable gearshift which is also incomparably fast and drive torque is completely uninterrupted.
When selecting the next gear in advance, the electronic control system always takes account of the current road conditions. Based on the accelerator pedal position, the engine speed, road speed and shift program selected, the system identifies the level of intensity of acceleration desired by the driver, or any intended reduction of speed, for example.
The transmission control always provides for as harmonious a continuation of the driving initiated by the driver as possible. Even in the event of an extremely abrupt
change of driving style, any required change of gear is effected with high speed and precision.
If, for example, acceleration has to be interrupted unexpectedly, the sports automatic transmission with double clutch instantly provides a transmission ratio which is
appropriate to the new situation.