What are adjustable magnetorheological dampers

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The new coupling principle "MRF ball coupling" is a combination of a ball safety coupling and an axial MRF actuator. With mechanical ball safety couplings, the torque is transmitted via balls that are held in recesses by cup springs. The stronger the spring force, the higher the clutch release torque. With the MRF ball coupling, the holding force applied by the spring is supplied by an axial MRF actuator. This is constructed similarly to a single-tube shock absorber. A coil creates a magnetic field in the gap between the tension and compression side and prevents the MRF from flowing through the gap. As a result, the piston of the actuator is blocked and thus provides the required holding force. As a functional demonstrator, a torque wrench was set up at Fraunhofer LBF, which confirms the potential of the coupling concept.

The advantages over conventional safety clutches are the adjustable release torque of the clutch during operation and the EMERGENCY STOP function. Compared to MRF disc or MRF bell-shaped couplings, the MRF ball coupling impresses with its lower energy requirement, better temperature behavior and a significantly lower drag torque. One disadvantage is that targeted slip operation is not possible (e.g. 50% slip). Furthermore, coupling is only possible at a standstill without additional technical measures. As part of the Fraunhofer System Research Electromobility (FSEM), a safety coupling based on this coupling principle is currently being developed for the motor-generator unit of the AutoTram test vehicle (see Fig. 2). It sits between a 180kW V8 diesel engine and a generator. The motor delivers a maximum torque of 560Nm, the maximum speed is 4000rpm. The power requirement of the coupling is only 6W.

Potential areas of application for the MRF ball coupling are fast-switching safety clutches, for example in machine tools, conveyor systems or for automotive applications.