Significant Drag Torque Reduction and Improved Clutch Dynamics by Innovative, Very Compact Separating Springs for Wet Clutches

Due to the CO₂ limits, which are becoming even harsher, losses in automatic transmissions must be drastically reduced. Furthermore, electrification of the drivetrain requires better controllability in order to improve interaction between combustion engine and electric motor. Mubea separating springs offer a good solution to achieve these goals. In order to minimize clutch losses, separating springs are accepted as an innovative component of current transmission programs in which discs in the clutch system are actively separated from each other. Extensive investigations have shown that drag torque losses can be reduced by 40% and more and that CO₂ savings of 0.5 g/km (in WLTP) can be achieved. First of all, this lecture presents the validation of earlier simulation results regarding a positive effect of separating springs on shifting comfort through measurement of real starting-up with a dual clutch transmission. Here shift comfort and NVH behaviour could be greatly improved by the use of separating springs. In addition to well-known wave-shaped separating springs, a new type of so-called “torsional separating spring” is presented for the first time, which offers the same technological advantages by improving the installation space requirement. Furthermore, excerpt from test results will be presented with the new torsional separating spring. In addition to already known advantages in reducing drag torque, it offer further important advantages with regard to clutch dynamics. Tests were carried out at the IPEK and IAE on a clutch test bench with near-series hardware. All results show a better controllability and a more stable control behaviour with separating springs, when engaging the clutch due to a better linearity of the torque/pressure curve. When clutch is disengaged, a higher dynamic is achieved by a faster separation of the discs.