Principle of Operation

The M DCT consists of two sub-transmissions, each with its own clutch. Clutch 1 with sub-transmission 1 and clutch 2 with sub-transmission 2. Sub-transmission 1 consists of the gears 1, 3, 5, 7 and Reverse while sub-transmission 2 consists of gears 2, 4 and 6. This means that the your next gear is always pre-selected in the other sub-transmission, regardless of whether you are shifting up or down (with the exception of "R").

For example, while still in the acceleration phase of the currently selected gear, if on sub-transmission 1 the next logical gear on sub-transmission 2 is engaged in advance, in a process similar to the Shift Overlap function of an automatic transmission.

Precise control of the clutches when upshifting will allow the driving force to be transferred very quickly and smoothly from sub-transmission 1 to sub-transmission 2 without an interruption in driving power. This results in significant benefits not only for the available driving force but also in terms of shift comfort.

By combining the seamless driving force and comfort of the automatic with the direct connection to the engine as a manual, M DCT provides the benefits of both transmissions.

Fig 1: M DCT Functional Diagram

Courtesy of BMW OF NORTH AMERICA, INC.