Centrifugal fan and noise reduction method in centrifugal fan

Abstract

A centrifugal fan having a sound reduction effect for noises in a wide frequency range is provided. The centrifugal fan comprises a motor to which an impeller is connected, a casing which surrounds the impeller and which has a bell-mouth-like suction port, and a bell-mouth-like orifice which has a suction port being concentric with the suction port of the casing and having a diameter as large as that of the suction port of the casing, in an outer shell, providing a plurality of protrusions in a resonant space surrounded by the orifice, the casing, and the outer shell, and providing depressions which are formed so as to be interposed between the protrusions.

1 . A centrifugal fan comprising:
 an outer shell having an opening portion,   an impeller that is supported rotatably in the outer shell,   a motor for driving and rotating the impeller,   a casing that has a first suction port and that is placed in the outer shell so as to surround the impeller, and   a bell-mouth-like orifice that is placed on the opening portion of the outer shell so as to have a gap between the orifice and the first suction port of the casing and that has a second suction port providing communication between the opening portion of the outer shell and the first suction port of the casing, wherein   a resonant space that communicates with the first suction port through the gap between the first suction port and the second suction port and that effects resonance silencing against noises emitted from the first suction port is defined by the orifice, the casing and the outer shell that serve as definition walls, and wherein a plurality of protruding portions are formed on the definition walls for the resonant space.   
     
     
         2 . The centrifugal fan as defined in  claim 1 , wherein
 the plurality of protruding portions comprise sloped surfaces sloping relative to a surface of the definition walls for the resonant space in positions where the protruding portions are formed, and wherein   the sloped surface of one protruding portion and the sloped surface of another protruding portion adjacent to the one protruding portion are connected to each other so that a recessed part is formed by the sloped surfaces between both the protruding portions.   
     
     
         3 . The centrifugal fan as defined in  claim 2 , wherein connected parts of the sloped surfaces in each recessed part form an acute angle. 
     
     
         4 . The centrifugal fan as defined in  claim 2 , wherein the protruding portions each have a flat surface on a top part thereof. 
     
     
         5 . The centrifugal fan as defined in  claim 2 , wherein the protruding portions each have a shape such that a depth thereof is longer than a height and a width thereof. 
     
     
         6 . The centrifugal fan as defined in  claim 5 , wherein a plurality of protruding portion groups in each of which a plurality of protruding portions are arranged with depthwise directions thereof being parallel to one another are arranged so that depthwise directions of adjacent protruding portion groups intersect with each other. 
     
     
         7 . The centrifugal fan as defined in  claim 5 , wherein a plurality of protruding portion groups in each of which a plurality of protruding portions are arranged with depthwise directions thereof being parallel to one another are arranged so as to have different depthwise directions. 
     
     
         8 . The centrifugal fan as defined in  claim 5 , wherein the plurality of recessed parts formed between the plurality of protruding portions are formed so as to extend along the surfaces of the definition walls and are arranged so that directions in which the recessed parts extend are different from at least one of radial directions, a circumferential direction and an axial direction of the impeller. 
     
     
         9 . The centrifugal fan as defined in  claim 1 , wherein the plurality of protruding portions have the same shape and wherein the plurality of recessed parts formed between the plurality of protruding portions have the same shape. 
     
     
         10 . The centrifugal fan as defined in  claim 1 , wherein the protruding portions have a plurality of different shapes and wherein the recessed parts formed between the plurality of protruding portions have a plurality of different shapes. 
     
     
         11 . The centrifugal fan as defined in  claim 1 , wherein the plurality of protruding portions are provided on the orifice in the resonant space. 
     
     
         12 . The centrifugal fan as defined in  claim 1 , wherein the plurality of protruding portions are formed integrally with the definition walls of the orifice, the casing and the outer shell. 
     
     
         13 . The centrifugal fan as defined in  claim 1 , wherein the protruding portions are detachably provided on the definition walls. 
     
     
         14 . The centrifugal fan as defined in  claim 13 , wherein the protruding portions are formed of sound absorbing material. 
     
     
         15 . The centrifugal fan as defined in  claim 1 , wherein the protruding portions are formed so as to have cavities inside and wherein holes that provide communication between the cavities and the resonant space are formed on the protruding portions. 
     
     
         16 . A noise reduction method in a centrifugal fan comprising an outer shell having an opening portion, an impeller that is supported rotatably in the outer shell, a casing that has a first suction port and that is placed in the outer shell so as to surround the impeller, and a bell-mouth-like orifice that is placed on the opening portion of the outer shell so as to have a gap between the orifice and the first suction port of the casing and that has a second suction port providing communication between the opening portion of the outer shell and the first suction port of the casing, the method comprising:
 making acoustic waves of noises occurring in the casing with rotational drive of the impeller incident, through the gap between the first suction port and the second suction port, on a resonant space that communicates with the first suction port through the gap between the first suction port and the second suction port and that is defined by the orifice, the casing and the outer shell that serve as definition walls, and   reducing acoustic wave levels of the noises incident on the resonant space by air column resonance, and reducing acoustic wave levels of the noises by diffused reflection of the acoustic waves of the noises in the resonant space.