Magnetorheological clutch with reversed torque transmission behavior

A new magnetorheological (MR) clutch whose transmitted torque is controlled by the strength of a magnetic field is introduced. The magnetic field applied in the clutch determines the grade of stiffening of a self-made rnagnetorheological fluid. In contrast to other MR clutches which are disengaged without magnetic field and change to the engaged state by activating the magnetic field, the new MR clutch shows a reversed torque transmission behaviour, i. e. it transmits a considerable torque without magnetic field, which can be drastically reduced when the field is switched off. This advantageous behaviour is achieved by a magnetic circuit system with two circuits one of which contains a permanent magnet and the other circuit contains an electromagnet. The new MR clutch is designed with a drum-shaped rotor which shears the MR fluid. Experimental investigations of the performance of the clutch yielded a transmittable torque of 17 Nm, caused only by the permanent magnet without any energy consumption. An appropriate counter-field of the electromagnet reduced the torque to about 1 Nm. With a current of reversed polarity in the coil of the electromagnet the transmittable torque could be increased to 33 Nm.