Compact Seven- and Ten-Speed Dual-Clutch Transmissions

The need for a large number of well-stepped gear ratios without increasing the mechanical complexity of current transmissions requires new ways of gear set synthesis and optimisation. Therefore new gear sets at FEV are developed using a systematic, computer aided synthesis process. During this process, all theoretically possible solutions are analysed until the optimum solution considering all boundary conditions has been found, ❶. Open image in new window ❶ Five steps (red) of systematic gear set synthesis (upper part) but also gear set structures a, b and c of conventional DCT, FEV 10-xDCT and FEV 7-xDCT (lower part) The visualisation of gear set structures shown in the lower part of ➀ allows a very simple and fast analysis of the functionality possible with a certain transmission layout. It illustrates the degrees of freedom and the number of switchable connections between them for a given gear set [5]. The total number of theoretical possible gears is the sum of “direct gears” (direct connection between input and output) and “generated gear” (gears in which the switchable connection between the inputs is active). All possible arrangements of switchable connections can be evaluated for example with respect to the theoretical number of gears and the number of efficiency-optimum direct gears. The lower part of ➀ shows the gear set structures of 10-xDCT (b) with ten usable forward gears using a total of eight switchable connections (four synchroniser units/four shift sleeves) and the gear set structure of a smaller version, the 7-xDCT (c), which features seven forward gears using only six switchable connections (three synchroniser units/three shift sleeves).