| 摘要 |
PURPOSE:To attain a lighter weight and effectively suppress the film vibration of a wall part enclosed by a rib by curvedly forming the wall part of a grid rib so that the peripheral part is thicker than the center part in the circumferential direction of a cylindrical case to form an outside surface axially having a curvature larger than the circumferential thickness change. CONSTITUTION:A wall part 24, 24... enclosed by a grid rib 22 is curvedly formed with the outside surface having a curvature R so that the peripheral part close to a horizontal rib 22a, 22a... is thicker than the center part of each wall part 24, 24... to the circumferential direction of a cylindrical case 10. To the axial direction of the cylindrical case 10, the wall part 24, 24... is formed with an uniformed thickness or a fixed thickness, namely, with the outside surface having an infinite curvature. According to this constitution, the outside form of the wall part 24,24... enclosed by the grid rib 22 of the cylindrical case 10 is formed with the curvatures being varied between the circumferential and axial directions of the cylindrical case 10, so that anisotropy is given to the rigidity of the wall part 24, 24... in the circumferential and axial directions.
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