| 摘要 |
PURPOSE:To reduce noise by specifying a ratio of an inner surface radius of a spherical surface of a cap portion of a closed case to a circumferential radius of a cylindrical portion and a ratio of a distance between a bearing and a spherical end portion to an inner circumferential diameter. CONSTITUTION:The ratio of an inner spherical surface radius r of a cap portion of a closed case to an inner circumferential radius R of a cylindrical portion 19 is specified with the equation 1.13 <= r/R <= 1.39. And a ratio of a distance 1 between a spherical end portion 15a of the cap portion 15 to the inner circumferential diameter 2R of the cylindrical portion 19 is specified with the equation 1/R <= 0.33. As a result, the resonance of a 1st natural frequency deforming and vibrating in the axial direction of the cap portion is stabilized and reduced to reduce noise in a stabilized manner. |
