Abstract:
A centrifugal fan includes: a motor; an impeller having an inlet port, the impeller being configured to be rotated by the motor and to discharge air suctioned from the inlet port outward from an outer circumferential portion of the impeller; a lower casing that is located below the impeller; a circuit board disposed between the lower casing and the impeller, the circuit board being, mounted with an electrical component including a drive circuit that drives the motor, wherein the impeller has a recessed portion formed in an annular shape around a rotational axis and on a lower face that faces the lower casing and the circuit hoard, and wherein at least a part of the electrical component is located inside the recessed portion of the impeller.

Description:
BACKGROUND 
       [0001]    1. Field of the Present Invention 
         [0002]    The present invention relates to a centrifugal fan and, more particularly, to a centrifugal fan that discharges air outward from an outer circumferential portion of an impeller with rotation of the impeller. 
         [0003]    2. Description of the Related Art (Background of the Invention) 
         [0004]    A centrifugal fan is widely used for cooling, ventilafion, air conditioning, and the like in a variety of equipment such as household electrical appliances, OA equipment, and industrial equipment or for a fan in vehicles. 
         [0005]    An example of a structure of a centrifugal fan is disclosed in JP-A-2012-189047, in which an impeller is accommodated between an upper casing and a lower casing. Such a centrifugal fan is configured to discharge air suctioned from an inlet port outward with rotation of the impeller from an outlet port formed on a side face between the upper casing and the lower casing. 
         [0006]    Recently, a decrease in size of equipment on which the above-mentioned centrifugal fan is mounted has progressed and demands for a centrifugal fan with a smaller thickness have increased. 
         [0007]    In the centrifugal fan described in JP-A-2012-189047, the lower casing also serves as a main plate of the impeller, and a motor and a circuit board are accommodated in a recessed portion formed in the lower casing. As a result, the thickness of a part above the lower casing is reduced and the overall thickness of the centrifugal fan is reduced. 
         [0008]    However, in the centrifugal fan described in JP-A-2012-189047, a manufacturing cost becomes relatively high. That is, since a gap between a partition wall of the lower casing and the blades has a great influence on air volume characteristics of the centrifugal fan, the gap should be precisely set to an appropriate value. Accordingly, dimensional accuracy of components of the centrifugal fan should be managed with high accuracy, and component costs may increase. 
       SUMMARY  
       [0009]    One of objects of the present invention is to provide a centrifugal fan with a small thickness and a low manufacturing cost. 
         [0010]    According to an illustrative embodiment of the present invention, there is provided a centrifugal fan including: a motor; an impeller having an inlet port, the impeller being configured to be rotated by the motor and to discharge air suctioned from the inlet port outward from an outer circumferential portion of the impeller; a lower casing that is located below the impeller; a circuit board disposed between the lower casing and the impeller, the circuit board being mounted with an electrical component including a drive circuit that drives the motor, wherein the impeller has a recessed portion formed in an annular shape around a rotational axis and on a lower face that faces the lower casing and the circuit board, and wherein at least a part of the electrical component is located inside the recessed portion of the impeller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    In the accompanying drawings: 
           [0012]      FIG. 1  is a plan view illustrating a centrifugal fan according to an embodiment of the present invention; 
           [0013]      FIG. 2  is a cross-sectional view taken along line A-A shown in  FIG. 1 ; 
           [0014]      FIG. 3  is a plan view illustrating an impeller; 
           [0015]      FIG. 4  is a perspective view illustrating a bottom surface of the impeller; 
           [0016]      FIG. 5  is a partial end-elevational view of an impeller according to a modified example of the embodiment; and 
           [0017]      FIG. 6  is a partial end-elevational view of an impeller according to another modified example of the embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Hereinafter, a centrifugal fan according to an embodiment of the present invention will be described. 
         [0019]      FIG. 1  is a plan view illustrating a centrifugal fan according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view taken along line A-A shown in  FIG. 1 . 
         [0020]    Referring to  FIGS. 1 and 2 , a centrifugal fan  1  includes a casing  10 , an impeller  30 , and a motor  60 . The centrifugal fan  1  has a rectangular parallelepiped shape having a substantial square shape in a plan view as a whole. The centrifugal fan  1  has a small thickness in which the size in the vertical direction (height) is relatively small. 
         [0021]    The impeller  30  is attached to a rotor  61  which rotates along with a shaft  62  of the motor  60 . The centrifugal fan  1  rotates the impeller  30  using the motor  60 . The centrifugal fan  1  discharges air suctioned from an inlet port  33  to a lateral side of the impeller  30  with the rotation of the impeller  30 . That is, air suctioned from the inlet port  33  passes between blades  51  of the impeller  30  and is discharged outward from an outer circumferential portion of the impeller  30 , by a hydrodynamic force resulting from a centrifugal action accompanying with the rotation of the impeller  30 . The air is discharged outward from outlet ports  19  which are formed on four side faces of the casing  10 . 
         [0022]    As illustrated in  FIG. 2 , the casing  10  includes an upper casing  11  and a lower casing  21 . The upper casing  11  is disposed above the impeller  30  and the lower casing  21  is disposed below the impeller  30 . The upper casing  11  and the lower casing  21  are coupled to each other using fastening members  18  which are tapping screws via supports  17  disposed at four corners in a plan view. The supports  17  are formed by integral molding with the upper casing  11  and the fastening members  18  are tightly fastened to pilot holes formed in the supports  17 . A through-hole may be formed in the support  17  and the upper casing  11  and the lower casing  21  may be coupled to each other by inserting a bolt as the fastening member  18  through the through-hole and fixing the bolt with a nut on the other side. The fastening members  18  are not limited to these configurations. The supports  17  may be members which are formed independently of the upper casing  11  or the supports  17  may not be necessarily formed. 
         [0023]    The upper casing  11  is formed, for example, a resin such as engineering plastic. An opening  16  is formed at the center of the upper casing  11 . The opening  16  has a circular shape in a plan view and air is introduced into the inlet port  33  of the impeller  30  from the opening  16 . Plural small-thickness portions  13  are formed on the top surface side of the upper casing  11 . 
         [0024]    The lower casing  21  is formed of, for example, a metal sheet such as a steel sheet. An accommodating portion  22  which is concave downward from the parts of the lower casing  21  coupled to the supports  17  is formed at the center of the lower casing  21 . A part (lower part) of the motor  60  and the circuit board  76  are accommodated in the accommodating portion  22 . 
         [0025]    A side plate  23  which is bent in a rotation axis direction (hereinafter, simply referred to as an axial direction) of the impeller  30  is disposed in the outer circumferential portion of the lower casing  21 . Since the side plate  23  is formed, the rigidity of the lower casing  21  is improved. 
         [0026]    In the centrifugal fan  1 , areas between the upper casing  11  and the lower casing  21  other than the fastened portions (support portions) of the upper casing  11  and the lower casing  21  in four side portions of the casing  10  serve as the outlet ports  19  of air. 
         [0027]    The material of the lower casing  21  is not limited to a metal sheet such as a steel sheet, and may be a resin material. 
         [0028]    The motor  60  is, for example, an outer rotor type brushless motor. 
         [0029]    A rotor  61  of the motor  60  includes a cup-like rotor yoke  63  which is opened downward, an annular magnet  64  which is attached on the inner circumferential surface of the rotor yoke  63 , and a shaft  62  which is attached to the center of the rotor yoke  63 . 
         [0030]    The shaft  62  is rotatably supported by a pair of bearings  66  and  67  attached to a bearing holder  65 . A stator  70  is formed on the outer circumferential portion of the bearing holder  65 . 
         [0031]    The stator  70  includes a stator core  71 , an insulator  72 , and a coil  75 . The stator core  71  is formed by stacking plural cores each including plural salient poles extending in the outward radial direction from an annular yoke. The insulator  72  has a configuration in which an upper insulator  73  and a lower insulator  74  are attached from both sides in the axial direction of the stator core  71 . The coil  75  is wound on the salient portion of the stator core  71  with the insulator  72  interposed therebetween. The bearing holder  65  is inserted into an opening formed at the center of the annular yoke of the stator core  71  and thus the stator  70  is disposed outside the bearing holder  65 . The outer circumferential surface of the stator core  71  faces the inner circumferential surface of the magnet  64  with a predetermined air gap in the radial direction (the left-right direction in  FIG. 2 ) therebetween. 
         [0032]    The motor  60  is attached to a bottom surface  22   a  of the accommodating portion  22  using a fastening member  68  such as a screw or a bolt. The motor  60  is attached to the lower casing  21  by inserting one end of the bearing holder  65  into an opening formed in the bottom surface  22   a  of the accommodating portion  22  and tightly fastening the fastening member  68  such as a bolt to the bearing holder  65 . A flange  65   a  is formed in the lower end portion of the bearing holder  65  and the fastening member  68  is fastened to the flange  65   a . The number of fastening positions of the fastening member  68  is, for example, three, but is not limited to this value. The motor  60  may be attached to the lower casing  21  by fixing the lower portion of the bearing holder  65  to the bottom surface  22   a  of the accommodating portion  22  by caulking instead of using the fastening member  68 . 
         [0033]    The circuit board  76  provided with a drive circuit for driving the motor  60  is attached to the lower insulator  74 . A part of the circuit board  76  along with a part of the motor  60  is accommodated in the accommodating portion  22 . An electronic component  77 , such as an electrical device and a control IC for controlling driving of the motor  60 , is mounted on the circuit board  76 . Winding ends of the coil  75  are electrically connected to a wiring pattern of the circuit board  76 . 
         [0034]    The impeller  30  is disposed within the casing  10 . The impeller  30  has a disk shape as a whole. The impeller  30  includes an annular shroud  31 , a hub  41 , a main plate  42 , and plural blades  51  disposed between the annular shroud  31  and the main plate  42 . The inlet port  33  is formed at the center of the annular shroud  31 . The hub  41  attached to the rotor  61  is disposed at the center of the impeller  30 . The main plate  42  is connected to the hub  41  and has a disk shape extending in the radial direction from the outer circumferential surface of the hub  41  and being centered on the hub  41 . 
         [0035]    The rotor yoke  63  of the motor  60  is inserted into the hub  41 . The rotor yoke  63  is attached to the impeller  30  by inserting plural bosses  41   a  formed in the hub  41  into plural through-holes formed on the top surface of the rotor yoke  63  and heating the tips of the bosses  41   a  to caulk the through-holes. 
         [0036]      FIG. 3  is a plan view illustrating the impeller  30 . 
         [0037]    In  FIG. 3 , the rotation direction of the impeller  30  is indicated by arrow RD. 
         [0038]    As illustrated in  FIG. 3 , the plural blades  51  are arranged regularly at predetermined intervals on a circumference in a plan view. The blades  51  have the same curved shape and are backward-curved blades (so-called turbo blades) which are obliquely curved and inclined backward with respect to the rotation direction. Each blade  51  extends downward in the axial direction from the annular shroud  31  and is coupled to the main plate  42 . The shape and the number of blades  51  are not limited to this example. 
         [0039]    In this embodiment, the annular shroud  31  and the blades  51  are formed, for example, by integral molding using a resin. The hub  41  and the main plate  42  are formed, for example, by integral molding using a resin. The impeller  30  is formed by joining two members formed by integral molding in this way. The joining is performed as follows. That is, two members are joined by inserting the lower ends of the blades  51  into the recessed portion formed in the main plate  42 , inserting pins formed at the lower ends of the blades  51  by integral molding into holes formed in the recessed portion, and heating the tips of the pins to caulking the recessed portion. 
         [0040]      FIG. 4  is a perspective view illustrating a bottom surface side of the impeller  30 . 
         [0041]    As illustrated in  FIG. 4 , in this embodiment, a recessed portion  45  is formed on the bottom surface (surface facing the lower casing  21 ) of the main plate  42 . The recessed portion  45  is formed in an annular shape around the rotation shaft of the impeller  30 . The recessed portion  45  is a groove having a substantially U-shaped cross-section. 
         [0042]    As illustrated in  FIG. 2 , an upper portion of the electronic component  77  mounted on the circuit boar  76  is accommodated in a part of the recessed portion  45 . Accordingly, even when the electronic component  77  having a relatively large height is mounted on the circuit board  76 , it is possible to dispose the impeller  30  and the circuit board  76  so as to be close to each other while preventing interference (contact) between the impeller  30  and the electronic component  77 . 
         [0043]    As illustrated in  FIG. 3 , the diameter D 1  of the impeller  30  is greater than the diameter D 2  of a circle C 2  passing through the outermost circumferential edges of the blades  51 . The gap size in the axial direction between the annular shroud  31  and the main plate  42  gradually increases from the position of the outermost circumferential edge of each blade  51  to the outer circumferential edge of the impeller  30  (gradually increases toward the outer circumferential edge of the impeller  30 ). Accordingly, air guided to the outermost circumferential edges of the blades  51  is smoothly guided so as to spread outward from the impeller  30  and is discharged from the impeller  30  through the outlet ports  19 . Therefore, it is possible to suppress noise generated around the outlet ports  19 . 
         [0044]    In this embodiment, as illustrated in  FIG. 2 , a part on the outer circumference side of the lower surface of the annular shroud  31  is curved to form a wing upper surface shape. That is, the lower surface on the outer circumference side of the annular shroud  31  has a slowly-curved shape which is convex downward. In other words, the lower surface of the outer circumference side of the annular shroud  31  has a curved shape like a horn (a bell shape (a trumpet shape) of a brass instrument). Accordingly, air flowing outward from the outer circumferential edges of the blades  51  is not easily separated from the surface of the annular shroud  31  and can be more effectively guided and smoothly discharged so as not to cause disturbance of an air flow. 
         [0045]    Since the centrifugal fan  1  has the above-mentioned configuration, the following advantages are obtained. That is, a part of the electronic component  77  on the circuit board  76  is accommodated in a part of the recessed portion  45  formed on the bottom surface of the main plate  42  (a part of the annular recessed portion  45  corresponding to a part in which the electronic component  77  is formed). Accordingly, it is possible to avoid interference between the impeller  30  and the electronic component  77  and to dispose the circuit board  76  and the impeller  30  so as to be close to each other. Therefore, it is possible to decrease the thickness of the centrifugal fan  1 . 
         [0046]    The main plate  42  is disposed below the blades  51 , and the centrifugal fan  1  has a structure different from the structure in which the lower casing is also used as the main plate of the impeller in the related art. Accordingly, since the dimensional accuracy (flatness) of the lower casing  21  does not need to be managed with high accuracy and the lower casing  21  can be formed, for example, using press working, it is possible to reduce the manufacturing cost of the centrifugal fan  1 . 
         [0047]    The impeller  30  includes the main plate  42  and is formed by joining two members. Accordingly, the number of components of the centrifugal fan  1  is greater than that in the structure in which the lower casing is also used as the main plate of the impeller. However, the decrease in cost due to the manufacturing of the lower casing  21  using press working is greater than the increase in cost due to the increase in the number of components and thus it is also possible to decrease the manufacturing cost in this embodiment. 
         [0048]    The diameter D 1  of the impeller  30  is greater than the diameter D 2  of the circle C 2  passing through the outermost circumferential edges of the blades  51 . The gap size in the axial direction between the annular shroud  31  and the main plate  42  gradually increases from the position of the outermost circumferential edge of each blade  51  to the outer circumferential edge of the impeller  30 , and the bottom surface on the outer circumferential edge side of the annular shroud  31  is curved to form a wing upper surface shape. Accordingly, air output from the outer circumferential edges of the blades  51  is smoothly discharged outward along the lower surface of the annular shroud  31 , thereby suppressing generation of noise around the outlet ports  19 . 
         [0049]    In this embodiment, the part on the outer circumferential edge side of the lower surface of the annular shroud  31  is formed in a wing upper surface shape, and the part on the outer circumferential edge side of the upper surface of the main plate  42  is formed in a linear shape (planar shape) in a side cross-sectional view, but the present invention is not limited to these shapes. For example, when the part on the outer circumferential edge side of at least one of the lower surface of the annular shroud  31  and the upper surface of the main plate  42  is curved to form a wing upper surface shape as will be described below, it is possible to achieve an advantage of preventing separation of air discharged from the impeller  30  as described above. 
         [0050]      FIG. 5  is a partial end-elevational view of an impeller  130  according to a modified example of this embodiment. 
         [0051]    The end elevation illustrated in  FIG. 5  shows a modified example of the impeller  30  illustrated in  FIG. 2 . As illustrated in  FIG. 5 , the impeller  130  includes an annular shroud  31 , blades  51 , a hub  41 , and a main plate  142  having a shape other than described above. The upper surface on the outer circumference side of the main plate  142  is curved to form a wing upper surface. That is, the lower surface on the outer circumference side of the main plate  142  has a slow-curved shape which is convex upward. Since the parts on the outer circumference side of the lower surface of the annular shroud  31  and the upper surface of the main plate  142  are curved to form a wing upper surface shape in this way, air of the outer circumferential edges of the blades  51  is smoothly discharged from the impeller  130 . 
         [0052]      FIG. 6  is a partial end-elevational view of an impeller  230  according to another modified example of this embodiment. 
         [0053]    The end elevation illustrated in  FIG. 6  shows another modified example of the impeller  30  illustrated in  FIG. 2 . As illustrated in  FIG. 6 , the impeller  230  includes an annular shroud  231  having a shape other than described above, blades  51 , a hub  41 , and a main plate  142 . The upper surface on the outer circumference side of the annular shroud  231  is curved in a substantially linear shape on a side cross-sectional view, which is different from the above-mentioned shape. The lower surface of the outer circumference side of the main plate  142  is curved to form a wing upper surface and a gap size in the axial direction between the annular shroud  231  and the main plate  142  gradually increases from the position of the outermost circumferential edges of the blades  51  to the outer circumferential edge of the impeller  230 . Even when the part on the outer circumferential edge side of the upper surface of the main plate  142  is curved to form a wing upper surface shape in this way, air of the outer circumferential edges of the blades  51  is smoothly discharged from the impeller  230 . 
         [0054]    The shape of the casing is not limited to the substantially square shape in a plan view. The casing may have a polygonal shape in a plan view, may have a circular shape, or may have an asymmetric shape with respect to the rotation axis. 
         [0055]    The upper casing may not be necessarily provided. For example, a motor, a circuit board, and an impeller may be attached to the lower casing to form a centrifugal fan and the lower casing is directly fixed to another apparatus to mount the centrifugal fan on the apparatus. 
         [0056]    The shape of the impeller is not limited to the above-mentioned shape. In the impeller, the parts on the outer circumference edge sides of both the lower surface of the annular shroud and the upper surface of the main plate may not be curved. The impeller is not limited to the structure in which the gap size in the axial direction between the annular shroud and the main plate gradually increases from the positions of the outer circumferential edges of the blades to the outer circumferential edge of the impeller. The diameter of the impeller may not be greater than the diameter of a circle passing through the outer circumferential edges of the blades. 
         [0057]    The shape or position of the recessed portion formed in the impeller is not limited to the above-mentioned ones. That is, the position or shape of the recessed portion may be set to correspond to the positions or shapes of members mounted on the circuit board such that the members mounted on the circuit board and the impeller do not interfere with each other when the impeller rotates. Accordingly, it is possible to dispose the circuit board and the impeller to be close to each other and thus to decrease the thickness of the centrifugal fan. 
         [0058]    It should be understood that the above-mentioned embodiment is exemplary in terms of all points of view but is not restrictive. The scope of the present invention is defined by the appended claims, not by the above description, and includes all modifications within a meaning and a scope of the claims.