Fraunhofer Adaptronics Alliance

Active rotational systems

Image 1: MRF-ball clutch
Image 2: Rotational vibration actuator

The Fraunhofer LBF works on different ad­aptive and active concepts for rotational systems. The works include novel actuators deployed for conventional duties as well as innovative functions provided by conventio­nal actuators.

Ball-safety-clutches are common systems to protect drivetrains against overload. The re­lease torque is adjusted offline with a pre­loaded spring. There are many cases in which an online adjustable release torque and an emergency release of the clutch are very useful. To realize these functions the preloaded spring is substituted by an actua­tor based on a magnetorheological fluid. This new clutch design is called mrf-ball-clutch. The first application of this new clutch design is a 700 Nm safety-clutch for the powertrain of the Fraunhofer AutoTram. Further applications are for example machi­ne tools and hoisting machines. While defined rotational vibrations are desi­red in powertrain test stands, they are usu­ally not wanted in powertrains themselves. Therefore the Fraunhofer LBF develops ad­aptive as well as active systems for vibration excitation and vibration reduction.

An acti­ve example is an electromagnetic rotational vibration actuator that can excite vibrations and reduce vibrations in closed loop control. The actuator unit is arranged parallel to a passive coupling element and is not load-bearing. The electrical power supply into the rotating system is done via slip-rings. Another example is an adaptive rotational absorber for torsional vibration reduction in powertrains. The absorber is implemented as a centrifugal pendulum and can be tu­ned to different orders. Thus it is possible to change the absorber effect to the domi­nant order in the actual rotational speed range. The adaptive rotational absorber is especially designed for powertrains with combustion engines.