Torque generation apparatus

A torque generation apparatus comprising:

• a magnetic disc configured to rotate about a rotation axis;
• a first yoke and a second yoke disposed opposite sides of the magnetic disc in a first direction parallel to the rotation axis;
• an annular member fixed to a periphery of the first yoke;
• a magnetic viscous fluid placed between the magnetic disc and the first yoke and between the magnetic disc and the second yoke;
• a coil disposed so as to overlap with the magnetic disc when viewed along the first direction;
• and
• a third yoke having a side wall, the side wall having an area adjacent to the magnetic disc at least outside the magnetic disc and the coil, the third yoke constituting a magnetic path of a magnetic field generated by the coil together with the first yoke and the second yoke,
• wherein the magnetic disc includes a torque increasing portion at at least one of a surface facing the first yoke and a surface facing the second yoke,
• the torque increasing portion is disposed in an outer circumferential area of the magnetic disc in a second direction that is a radial direction perpendicular to the first direction, the torque increasing portion is configured to increase a shearing force for a cluster of the magnetic viscous fluid as compared with an inner circumferential area of the magnetic disc inside the outer circumferential area,
• the third yoke has a magnetic gap between the third yoke and the first yoke,
• the magnetic gap is disposed outside an outer circumferential edge of the magnetic disc or at a position overlapping with the outer circumferential edge of the magnetic disc as viewed along the first direction,
• a periphery of the second yoke is in contact with the side wall of the third yoke, and the second yoke is magnetically connected to the third yoke, and
• the first yoke is fixed to an upper wall of the third yoke in the first direction, and a periphery of the annular member is in contact with an inner surface of the side wall of the third yoke,
• wherein the magnetic a extends from a bottom surface of the coil to an upper surface of the second yoke along the first direction,
• the annular member is made of a non-magnetic material, and the annular member is circular-shaped and has a first outside diameter,
• the coil is disposed on a step in the first yoke, and the coil has a second outside diameter that is substantially the same as the first outside diameter of the annular member, and
• a lower surface of the annular member is substantially flush with a bottom surface of the first yoke.