| 摘要 |
PURPOSE:To reduce audible noise by forming plural ribs which extend to both end parts while which are outwradly projected in positions which divide a circumference non-uniformly, on the side wall of the cylindrical part of an enclosed case, and moving the natural frequency of said enclosed case to a higher zone. CONSTITUTION:An enclosed case 22 is formed by joining a cylindrical part 23 and cup-shaped cover parts 24, 25 together, while plural ribs 23a which extend to both end parts and which are outwardly projected in positions which divide a circumference non-uniformly projected in positions which divide a circumference non-uniformly, are formed on the outer peripheral surface of the side wall of the cylindrical part 23. By forming these ribs 23a, rigidity of the enclosed case 22 having sectional deformation in its axial direction can be increased, and its natural frequency is moved to a higher frequency zone, thereby, enabling natural frequency is an audible frequency zone, thereby, enabling natural frequency in an audible frequency zone to be reduced, reducing the generation of noise. |
