FEV's xDCT family - extremely compact 7- and 10-speed DCTs

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FEV's xDCT family - extremely compact 7- and 10-speed DCTs

Ruschhaupt, Johannes / Hellenbroich, Gereon

Current production DCTs feature a maximum of seven speeds, which can easily be realized using three main shafts and four shift sleeves. To increase the number of gears with conventional means, more gears, shift sleeves and shafts have to be added thus increasing size, weight and cost. With the "xDCT" family, FEV has developed a series of DCT concepts which effectively minimize mechanical complexity for any given number of gears by combining two innovative ideas: "Gear generation" and "supported shifts". In order to "generate gears", a switchable connection between the two input shafts is installed which allows to use all gears inside the transmission with both clutches. The main challenge then is to effectively use the large number of resulting gears in a shift schedule without torque interruption. The solution is to incorporate "supported shifts" during which torque fill-in for an AMT-style gear shift is provided by the next higher gear. Only the combination of these two ideas allows to effectively use the theoretically available gears. The "10-xDCT" is a 10-speed dual clutch transmission for transverse installation with only four shift sleeves. A smaller version, the "7-xDCT", features seven speeds using only three shift sleeves and 14 gear wheels in total, setting a new benchmark for "functionality per complexity". In a detailed 3D concept study, a transmission based on the "7-xDCT" concept has been laid out and designed for an input torque of 280 Nm. It features a launch ratio of above 16, a ratio spread of around 7.5 and a compact axial length of only 361 mm including dry dual clutch system and dual mass flywheel.