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Field-Controllable Fluids - Magneto- and Electrorheological Fluids

Brief Description

Field-Controllable Fluids consist of particles suspended in a carrier fluid. The particles are either magnetizable in case of magnetorheological (MR) fluids or polarizable in case of electrorheological (ER) fluids.

Fig. 1: Material behaviour with and without external field

Interestingly, these fluids change their fluidic characteristics depending on the influence of an external field, specifically an electric field in case of ER fluids or a magnetic field in case of MR fluids, see Fig. 1. The particles form chains that line up along the field lines. Those particle chains have the ability to withstand external load forces, see Fig. 2. As a consequence the fluids become solids. This effect is reversible and highly dynamic, which means that changing the behaviour only takes a few microseconds.

Fig. 2: Forming chains due to external field

Field-controllable fluids can be used for adjustable dampers which are already used in automotive applications, or clutches that have the ability of an adjustable slipping torque.

Research objective

For applications like vibration isolation it would be highly beneficial if the controllable dissipative properties could be combined with controllable compliant properties resulting in a compact device having variable damping and stiffness.
One concept for such a system is shown in Fig. 3. The system contains three fluid chambers filled with magnetorheological fluid. One of the chambers is connected to a piston that transforms an input force to fluidic pressure. The other chambers are connected to springs with different stiffness values. The connection between the chambers is designed in such a way that an external field can be generated in this area. Changing the field strength changes the amount of fluid passing through the canal. If field strength is high enough to fully inhibit fluid flow then the input force has only one spring to act at. For zero field strength the apparent stiffness is less then each of the stiffness values. Damping variation can be done by small field strengths that don’t suppress flow but slows it down. As Fig. 3 shows there is already a laboratory test setup. First experiments indicate that this concept is valid.
The challenge now is to improve the activation in order to get continuous stiffness variation as well as actual viscous damping rather than friction effects which are inherent to the MR and ER fluids.

Fig. 3: Structure of the system having variable stiffness and damping

Publication list

  • Greiner-Petter, C.; Sattel, T.; Mock, R.
    A Novel Control Approach for Semi-Active Vibration Isolation of Multi-Degree-of-Freedom Rotor Systems Utilizing Magneto- or Electrorheological Dampers. Actuator 2012
  • Greiner-Petter, C.; Tan, A. S.; Sattel, T.
    A semi-active magnetorheological fluid mechanism with variable stiffness and damping. Smart Materials and Structures 23 (2014).
    http://dx.doi.org/10.1088/0964-1726/23/11/115008
  • Silge, M.; Sattel, T.; Greiner-Petter, C.
    A Concept for Vehicle Suspension Systems with Variable Mechanical Impedance Based on Magneto- and Electrorheological Fluid Actuators. Actuator 2014

Patent list

  • Greiner-Petter, C.; Mock, R.; Sattel, T.
    Verfahren zur Minderung der Resonanzschwingungen eines Rotoraggregats, 2012, WO/2013/113688 A1
  • Greiner-Petter, C.; Mock, R.; Sattel, T.
    Steuereinrichtung, Maschine mit Rotoraggregat und Verfahren zur Steuervorschriftsermittlung, 2012, DE 102012210039 A1