Patent ID: 8733307

Claim:
A hydraulic braking device comprising: a housing having a fluid chamber; magnetic viscous fluid filled in the fluid chamber and made of non-magnetic base fluid into which magnetic particles are dispersed, so that viscosity of the magnetic viscous fluid is changed depending on density of magnetic flux passing through the magnetic viscous fluid; a viscosity controlling unit for controlling the density of the magnetic flux passing through the magnetic viscous fluid in order to change the viscosity of the magnetic viscous fluid; a brake rotating member having a brake shaft passing through an inside of the housing in its axial direction and outwardly extending from the housing, the brake rotating member being in contact with the magnetic viscous fluid in the fluid chamber so that braking torque depending on the viscosity of the magnetic viscous fluid is applied to the brake rotating member; and a sealing structure for fluid-tightly sealing a gap between the housing and the brake rotating member, wherein the sealing structure comprises; a permanent magnet for generating magnetic flux; a magnetic-flux guiding member provided in the housing and surrounding the brake shaft, so that a sealing gap communicated to the fluid chamber is formed between the magnetic-flux guiding member and the brake shaft, the magnetic-flux guiding member guiding the magnetic flux generated at the permanent magnet to the brake shaft; a fluid sealing member provided in the housing at a housing-outer side more remote from the magnetic-flux guiding member in the axial direction and being in contact with the brake shaft so as to fluid-tightly seal a gap between the housing and the brake shaft; an intermediate fluid chamber formed in the housing between the sealing gap and the fluid sealing member; and an intermediate fluid made of non-magnetic liquid and filled in the intermediate fluid chamber.