Abstract: A sealing structure has a permanent magnet and a magnetic-flux guiding member for guiding magnetic flux of the permanent magnet to a brake shaft of a brake rotating member. The magnetic-flux guiding member surrounds an outer periphery of the brake shaft so as to form a sealing gap around the brake shaft. The sealing gap is communicated to a fluid chamber, in which magnetic viscous fluid is filled. A fluid sealing member is provided at the brake shaft at a housing outer side of the magnetic-flux guiding member to form an intermediate fluid chamber, in which an intermediate fluid made of non-magnetic liquid is filled.

Abstract: A fluid brake device has a brake shaft which penetrates a case. The case provides a fluid chamber for a magneto-rheological fluid. A magnetic seal has a magnetic seal sleeve which holds a small amount of the magneto-rheological fluid by magnetic flux. In addition to the magnetic seal, an axially pumping element is provided on an axial outside of the magnetic seal. The axially pumping element is provided by a shaft helical groove formed on an opposing wall of the brake shaft and/or a case helical groove formed on a surrounding wall. As the brake shaft rotates, the helical groove pushes the magneto-rheological fluid back to the magnetic seal. A combination of the magnetic seal and the axially pumping element may reduce leakage of the magneto-rheological fluid.