Active rotational systems
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.