Patent Publication Number: US-2002004008-A1

Title: Centrifugal fan

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a centrifugal fan which sucks air in the axial direction of a rotary shaft and blows it out in the radial direction. This centrifugal fan is effectively applied to an air purifier for vehicle use or an air-conditioner recessed in a ceiling.  
       [0003] 2. Description of the Related Art  
       [0004] A centrifugal fan, which will be referred to as a fan in this specification hereinafter, which is described in Japanese Unexamined Utility Model Publication No. 61-29222, is composed as follows. Outside a centrifugal multi-blade impeller, which will be referred to as an impeller in this specification hereinafter, there are provided two air passages which are formed into a spiral. Due to the above structure, air streams can be simultaneously blown out from a plurality of outlets.  
       [0005] However, in the case of the above fan having a plurality of outlets, the length of the air passage (the winding angle of the air passage) is shorter than that of a fan having one outlet. Therefore, the following problems may be encountered. The air stream in the fan is unstable, and turbulence tends to occur in the air stream. For the above reasons, noise tends to be generated, and further the total pressure of the fan can not be sufficiently increased.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention has been achieved to solve the above problems. It is an object of the present invention to decrease the occurrence of noise and increase the total pressure of a fan having a plurality of outlets.  
       [0007] In order to accomplish the above object, the present invention provides a centrifugal fan comprising: a centrifugal impeller ( 111 ) having a number of blades ( 112 ) around a rotary shaft, the centrifugal impeller ( 111 ) sucking air in the axial direction of the rotary shaft and blowing it out in the radial direction; a casing ( 113 ) for accommodating the centrifugal impeller ( 111 ), the casing ( 113 ) having a plurality of outlets ( 114 ) for blowing out air; and stator blades ( 115 ) arranged in the casing ( 113 ), extending from the outer diameter side of the centrifugal impeller ( 111 ) to the downstream side of an air current.  
       [0008] Due to the above structure, while a stream of air blown out from the centrifugal impeller ( 111 ) is being straightened by the stator blades ( 115 ), dynamic pressure of the stream of air is converted into static pressure. Accordingly, it is possible to make the stream of air flow stably onto the outlet ( 114 ) side without disturbing the stream of air. Therefore, it is possible to sufficiently increase the total pressure of the centrifugal fan and suppress the generation of noise.  
       [0009] In this connection, it is preferable that the stator blades ( 115 ) are arranged all over the circumference on the outer diameter side of the centrifugal impeller ( 111 ).  
       [0010] It is also preferable that the centrifugal impeller ( 111 ) has blades ( 112 ) arranged backward, the impeller delivery angle (β) of which is larger than 90°.  
       [0011] It is also preferable that the entrance angle (α) of the stator blade ( 115 ) is not more than 20°.  
       [0012] Further, it is preferable that the cross-section of the stator blade ( 115 ) is an airfoil shape.  
       [0013] In this connection, reference numerals in parentheses in each means described above show the correspondence to the specific means described in the embodiments which will be stated later.  
       [0014] The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] In the drawings:  
     [0016]FIG. 1 is a perspective view showing the inside of a passenger compartment of a vehicle into which an air purifier using a fan of an embodiment of the present invention is incorporated;  
     [0017]FIG. 2 is a front view showing an air purifier in which a fan of an embodiment of the present invention is used;  
     [0018]FIG. 3 is a front cross-sectional view of a fan of an embodiment of the present invention;  
     [0019]FIG. 4 is a cross-sectional view taken on line A-A in FIG. 3;  
     [0020]FIG. 5 is an enlarged view of an impeller and diffuser of a fan of an embodiment of the present invention;  
     [0021]FIG. 6 is a graph showing a relation between the total pressure ΔP and the volume of blown air and also showing a relation between the specific noise Ks and the volume of the blown air;  
     [0022]FIG. 7 is a schematic illustration showing a model of a fan of the prior art; and  
     [0023]FIG. 8 is a schematic illustration showing a model of a fan in which diffusers have been removed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0024] In this embodiment, a fan of the present invention is applied to an air purifier, for vehicle use, by which air in a passenger compartment of a vehicle is cleaned. FIG. 1 is a perspective view of the inside of a passenger compartment of a vehicle showing a state in which the air purifier  100  is incorporated onto the rear package tray  200  of the vehicle. FIG. 2 is a front view showing an air purifier  100  for vehicle use.  
     [0025] In this embodiment, the air purifier  100  is set in motion or stopped by an output signal of a smoke sensor (not shown), which detects the degree of fouling of the air in the compartment, or by a manual switch operated by a driver. When this purifier  100  is operating, air is introduced into the inlet  101  arranged at a substantial center of the air purifier  100  as shown in FIG. 1, and air, which has been cleaned, is blown out from the outlet  102 .  
     [0026] Next, the fan  110  of this embodiment will be explained below.  
     [0027]FIG. 3 is a front cross-sectional view, which is taken on line B-B in FIG. 4, of the fan  110  of this embodiment. FIG. 4 is a cross-sectional view taken on line A-A in FIG. 3. Reference numeral  111  is a centrifugal impeller, which will be referred to as an impeller hereinafter, having a number of blades  112  around the rotary shaft  111   a , for blowing out air, which has been sucked in the axial direction of the rotary shaft  111   a , in the radial direction. In this embodiment, an impeller (turbo-impeller) is adopted, the blades of which are arranged backward, the delivery angle β of each blade  112  of which is larger than 90°.  
     [0028] In this connection, the delivery angle β of each blade  112  is an angle formed between the blade  112  and the outer diameter edge L 1  of the impeller  111  as shown in FIG. 5. This delivery angle β is measured from the proceeding side of the rotary direction of the impeller  111 .  
     [0029] As shown in FIG. 3, the impeller  111  is accommodated in the casing  113  made of resin (polypropylene in this embodiment). In this casing  113 , there are provided a plurality (two in this embodiment) of outlets  114  from which air is blown out.  
     [0030] In each outlet  114  formed in the casing  113 , there is provided a filter  103  for cleaning air which has been blown out from the impeller  111 .  
     [0031] In the casing  113 , on the outer diameter side of the impeller  111 , there are provided stationary blades (diffusers)  115  extending from portions close to the outer diameter of the impeller  111  toward the downstream side of the air current, wherein these diffusers  115  are arranged around the circumference on the outer diameter side of the impeller  111 . In this embodiment, the entrance angle α of the diffuser  115  is set at not more than 20°. In this figure, the entrance angle α of the diffuser  115  is set at 20°. In this connection, as shown in FIG. 5, the entrance angle α of the diffuser  115  is defined as an angle of the inner diameter edge (the circular locus connecting the side end portions of the diffusers  115  of the impeller  111 ) L 2  of the diffuser  115  with the diffusers  115 , wherein the entrance angle α of the diffuser  115  is measured from the proceeding side of the rotary direction of the impeller  111 .  
     [0032] In this connection, reference numeral  116  is a suction port for introducing air, which has been introduced from the inlet  101 , into the casing  113 . At the inner diameter edge of this suction port  116 , there is provided a bell-mouth  117  for introducing air, which has been sucked from the suction port, onto the inner diameter side of the impeller  111 . This bell-mouth  117  is molded and integrated with the casing  113 .  
     [0033] Reference numeral  118  is an electric motor (drive means) for driving the impeller  111 . When this electric motor  118  is controlled by being turned on, the air purifier  100  is operated.  
     [0034] Next, the characteristic of this embodiment will be described below.  
     [0035] Immediately after air has been blown out from the impeller  111  into the casing  113 , its flow velocity is greatly changed, and further the thus blown air collides with the side (the inner wall of the casing  113  located on the outer diameter side of the impeller  111 ) of the casing  113 . Since a current of air on the upper face side (the suction port  116  side) of the casing  113  and a current of air on the lower face side (the electric motor  118  side) are reverse to each other, noise tends to be generated, and further it is impossible to sufficiently increase the total pressure of the fan.  
     [0036] On the other hand, in this embodiment, on the outer diameter side of the impeller  111 , there are provided diffusers  115  which extend from portions close to the outer diameter side of the impeller  111  to the downstream side of the air current. Accordingly, while a current of air, which has been blown out from the impeller  111 , is being straightened, its dynamic pressure is converted into static pressure.  
     [0037] Consequently, it is possible to make the current of air flow stably into the outlet  114  side without disturbing it. Therefore, the generation of noise can be suppressed and the total pressure of the fan  110  can be sufficiently increased.  
     [0038] After the current of air has been straightened by the diffusers  115  so that the distribution of air velocity can be made uniform, the current of air flows into the filter  103 . Therefore, it is possible to prevent the occurrence of a problem in which the clogging of the filter occurs in one portion of the filter  103  compared with the other portion. Accordingly, the life of the filter  103  can be extended.  
     [0039] In this connection, FIG. 6 is a graph showing the results of experiments on the total pressure ΔP and the specific noise Ks with respect to the conventional fan shown in FIG. 7 (having a scroll casing, the air passage length of which is small (the winding angle of the air passage of which is small)), also with respect to the fan in which the diffusers  115  are abolished from the fan of this embodiment shown in FIG. 8, and also with respect to the fan of this embodiment. As can be seen from this graph, according to the present invention, it is possible to sufficiently increase the total pressure of the fan  110  and suppress the generation of noise.  
     [0040] In this connection, the definition of terminology of total pressure ΔP and specific noise Ks is based on JIS B 0132, and the above method of the experiment is based on JIS B 8340.  
     [0041] In this connection, as shown in FIG. 6, the smaller the entrance angle α of the diffuser  115  is made, the more the level of the specific noise Ks can be decreased (by about 2 dB). However, as can be seen in this embodiment, when the entrance angle α of the diffuser  115  is set at a value not more than 20° from the viewpoint of practical use, it is possible to guide the air, which has been blown out from the impeller  111 , into the outlet  114  side while the dynamic pressure of the air is effectively converted into static pressure.  
     [0042] In this embodiment, an impeller (turbo-impeller), the blades of which are arranged backward, the delivery angle β of each blade  112  of which is larger than 90°, is adopted. Therefore, it is possible to increase the static pressure of the air itself which is blown out from the impeller  111 . Accordingly, the total pressure ΔP can be increased.  
     [0043] Another embodiment will be explained below. In the embodiment described above, the number of the outlets  114  of the fan  110  is two, however, it should be noted that the present invention is not limited to the above specific embodiment. It is possible to apply the present invention to a fan having not less than three outlets  114 .  
     [0044] In the above embodiment, the fan of the present invention is applied to an air purifier for vehicle use, however, it should be noted that the present invention is not limited to the above specific embodiment. The fan of the present invention can be applied to an air-conditioner recessed in a ceiling or to another apparatus.  
     [0045] In the above embodiment, the impeller is used, the blades of which are arranged backward and the impeller delivery angle β of which is not less than 90°. However, it possible to use an impeller, the blades of which are arranged forward and the impeller delivery angle β of which is not more than 90°.  
     [0046] In the above embodiment, the diffusers  115  are arranged around the circumference on the outer diameter side of the impeller  111 , however, the diffusers  115  may be arranged only in a portion of the circumference on the outer diameter side of the impeller  111 .  
     [0047] In the above embodiment, the each diffuser  115  is plate-shaped and the thickness is constant. However, it should be noted that the present invention is not limited to the above specific embodiment. The cross section of each diffuser  115  may be an airfoil shape, the impeller  111  side of which is a side of the chord of blade, or a streamline shape.  
     [0048] While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.