Abstract
Keywords - dual-clutch, double-clutch, transmission, gearbox, Efficient Dynamics
With its new dual-clutch-transmission BMW succeeds once again in combining efficiency and dynamics in one package. The gearbox first shown in the new BMW M3 and later also used in highly-powered BMW AG models shines in both disciplines - joy of driving and fuel economy.
The high-revving engine concept used in the M3 necessitated the use of automated manual transmissions until now. These have the disadvantage of noticeable torque breaks during the shifts. The achievable shift-speeds are very high, though, which leads to drastic losses in comfort. The torque-break-free dual-clutch transmission dissolves this compromise completely.
For this gearbox a sport-oriented design with 7 gears and a low ratio-spread of 4.8 was chosen to underline the sporty character of the target-vehicles. At the same time a fuel consumption advantage of 5% is realized through the transmission in the NEFZ-cycle.
Through the use of wet clutches with a high torque capacity of up to 600 Nm and their use as strategy-enabling launch-devices, the gearbox is extremely flexible in its character. Depending on the type of vehicle it can be adapted to be supremely comfortable or extremely sporty, all with the same hardware variant. It can also be adapted by the driver via ample personalization possibilities to suit his/her personal and momentary driving style.
Due to package restrictions the gear-set was realized with an output-gear constant. This means higher rotational speeds in the gear-set but at the same time less torque, which enables a very compact design. The gears are divided into the groups of 1, 3, 5, 7, R and 2, 4, 6 respectively. The hydraulic unit is vertically mounted on the side of the gearbox to achieve a valuable gain in ground clearance. Lubrication is accomplished via a dry-sump system with a combination of a gear- and a jet-pump in order to cope with cooling demands in sustained high-load manoeuvres. A dual-clutch unit with minimized drag completes a highly compact and efficient gearbox design.