| 摘要 |
<p>Peripheral wall ribs (34A, 34A) of a damper plate (30) rise from at least two sides out of four sides which constitute the peripheral section of the damper plate (30), said peripheral wall ribs (34A, 34A) having belt-like outer side surfaces, and said two sides being longitudinally located along the direction in which a rotation shaft (31) is disposed vertically. When the damper plate (30) is positioned in such way as to close an airway (40), the outer surface of the upper peripheral wall rib (34A) and the outer surface of the lower peripheral wall rib (34A) are positioned parallel to an upper wall surface (13A) of a retainer (13) and the lower wall surface (13B) of the retainer, respectively, with narrow gaps in between. As a result, it is possible to avoid the occurrence of abnormal sound, and the problem of a damper failing to rotate smoothly. Furthermore, the manufacture of the damper can be streamlined.</p> |
