| 摘要 |
A brake drum 15 is secured to a rotational shaft, and an annular guide frame B having an annular inner space 20 of a rectangular shape in section is secured to a vehicle body. The guide frame B projects into the brake drum 15. On a portion of the guide frame B, facing to an inner peripheral surface of the brake drum 15, disposed a cylindrical body 14 formed from a thin plate of a nonmagnetic material, and on a portion not facing to the inner peripheral surface of the brake drum 15, disposed a frame body 6 of a ferromagnetic material. A magnet support cylinder 9 is axially movable supported on the inner space 20 of the guide frame B, and a plurality of permanent magnets 8 are fastened to the peripheral surface of the magnet support cylinder 9 at a circumferentially spaced apart positions of uniform pitch, the polarities of the permanent magnets facing to the inner peripheral surface of the brake drum alternating circumferentially. <IMAGE> |
