Eddy current retarder

An eddy current retarder comprising:

• a braking member that has a cylindrical shape, and is attached to a rotary shaft;
• a plurality of permanent magnets that are disposed on an inner side of the braking member in a radial direction, and are lined up in a circumferential direction of the braking member;
• and
• a plurality of pole pieces that are disposed between the braking member and the permanent magnets in the radial direction, and are lined up in the circumferential direction,
• wherein each of the permanent magnets has magnetic poles that are arranged in the radial direction and are reversed with respect to magnetic poles of other permanent magnets adjacent in the circumferential direction,
• the permanent magnets are configured to rotate in the circumferential direction relative to the pole pieces to switch the eddy current retarder between a braking state and a non-braking state,
• each of the pole pieces includes an inner circumferential surface that faces, in the braking state, one of the permanent magnets with a gap in the radial direction, an outer circumferential surface located on an outer side of the inner circumferential surface in the radial direction, and two side surfaces connecting the inner circumferential surface and the outer circumferential surface,
• the inner circumferential surface includes:
• a first region located forward of a center of the inner circumferential surface in a rotation direction of rotation of the permanent magnets relative to the pole pieces when the eddy current retarder switches from the non-braking state to the braking state, the first region being separated in the radial direction from the permanent magnet that the inner circumferential surface faces at an increasing distance toward a front end side of the inner circumferential surface in the rotation direction in a manner such that the gap is larger on the front end side than at the center;
• and
• a second region located rearward of the center in the rotation direction, the second region being separated in the radial direction from the permanent magnet that the inner circumferential surface faces at an increasing distance toward a rear end side of the inner circumferential surface in the rotation direction in a manner such that the gap is larger on the rear end side than at the center.