Patent Publication Number: US-2013230421-A1

Title: Centrifugal fan

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a centrifugal fan having high static pressure. 
     2. Description of the Related Art 
     Centrifugal fans designed to achieve increased static pressure are known. 
     US 2009/0301485, for example, describes a blower in which a shroud is arranged at a top portion of an impeller. 
     JP 2005-510663 describes a turbine including an annular compression chamber which is in communication with a compression chamber. 
     In the blower described in US 2009/0301485, the shroud arranged at the top portion of the impeller serves to prevent a gas, which has flowed once into a space below the impeller through an air inlet, from flowing backward toward the air inlet. This leads to an increase in ventilation resistance inside an air channel portion, resulting in an increase in static pressure. 
     However, when there is a demand for an additional increase in the static pressure, it is necessary to further increase the ventilation resistance inside the air channel portion by increasing the diameter of the impeller or by increasing the area of the shroud, which is arranged at an upper end of the impeller. In this case, an increased size of the blower, which is a centrifugal fan, cannot be avoided, and it is difficult to achieve a decrease in the size of the blower. In particular, a decrease in the size of centrifugal fans is demanded in the field of medical appliances, such as respirators and sputum aspirators, since greater portability or the like is demanded in the field. 
     In the turbine described in JP 2005-510663, air flows into the annular compression chamber (i.e., a space below a plurality of blades), and this causes an increase in ventilation resistance inside the space below the blades. This contributes to preventing the air, which has flowed once into the space below the blades, from flowing backward toward an air inlet, leading to an increase in static pressure of the turbine. 
     However, the air that has flowed once into the space below the impeller stays in the space temporarily. The air staying in the space is caused to circulate primarily by continuous suction of air through the air inlet. Accordingly, a large circumferential whirl velocity component does not act on the air which has flowed into the space below the impeller. Therefore, circumferential circulation of air (i.e., a flow of air toward an air outlet) is not easily promoted. It is therefore difficult to achieve an improved air volume characteristic. Incidentally, in the field of the medical appliances, such as the respirators and the sputum aspirators, centrifugal fans having high static pressure are desired because of a demand concerning a starting characteristic. 
     SUMMARY OF THE INVENTION 
     A centrifugal fan according to a preferred embodiment of the present invention includes an impeller arranged to rotate about a rotation axis; a motor arranged to rotate the impeller; and a case arranged to accommodate the impeller and the motor. The case includes an upper case; a lower case including a motor accommodating portion arranged to cover an outer circumference of the motor; and a joint portion at which the upper and lower cases are fixed to each other. An interior of the case includes a first annular space positioned radially outward of the motor. The first annular space includes a second annular space defined by a portion of a space defined by an annularly continuous collection of imaginary circles each of which including a diameter which is a shortest distance between an inner circumferential edge of the joint portion and a radially outermost circumferential portion of the motor accommodating portion and each of which touches the inner circumferential edge of the joint portion, the portion of the space being defined by a portion of an inner wall of the upper case and a portion of an inner wall of the lower case. A portion of the impeller is arranged in the second annular space. 
     In the centrifugal fan according to the above preferred embodiment of the present invention, a portion of the impeller is arranged in the second annular space, so that ventilation resistance in the second annular space is increased. This contributes to preventing a gas which has been drawn in through an air inlet from flowing backward toward the air inlet. Moreover, when the gas which has been drawn in through the air inlet circulates in the second annular space, the portion of the impeller which is arranged in the second annular space serves to add a circumferential whirl velocity component to the gas in the second annular space. This leads to efficient circumferential circulation of the gas (i.e., an efficient flow of the gas toward an air outlet). The centrifugal fan is thus able to achieve both an increased static pressure and an improved air volume characteristic while also maintaining a small size. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating the structure of a centrifugal fan according to a preferred embodiment of the present invention. 
         FIG. 2  is a partial cross-sectional view illustrating a first annular space and its vicinity of the centrifugal fan illustrated in  FIG. 1  in an enlarged form. 
         FIG. 3  is a partial cross-sectional view illustrating an example spatial shape of a second annular space according to a preferred embodiment of the present invention. 
         FIG. 4  is a partial cross-sectional view illustrating the structure of an impeller according to a preferred embodiment of the present invention. 
         FIG. 5  is a partial cross-sectional view illustrating the structure of an impeller according to a preferred embodiment of the present invention. 
         FIG. 6  is a partial cross-sectional view illustrating the structure of an impeller according to a preferred embodiment of the present invention. 
         FIG. 7  is a plan view illustrating the structure of the impeller according to a preferred embodiment of the present invention. 
         FIG. 8  is a cross-sectional view illustrating the structure of a centrifugal fan according to another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the preferred embodiments, it is assumed that a direction parallel or substantially parallel to a rotation axis is referred to by the term “axial direction”, “axial”, or “axially”, that directions perpendicular or substantially perpendicular to the rotation axis are referred to by the term “radial direction”, “radial”, or “radially”, and that a circumferential direction about the rotation axis is referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”. It is also assumed that an axial direction is a vertical direction, and that a side on which an impeller is arranged with respect to a motor is defined as an upper side. The shape of each member or portion and relative positions of different members or portions will be described based on the above assumptions. Also note that the present invention is not limited to the preferred embodiments described below. It is to be understood by those skilled in the art that variations and modifications can be made appropriately as long as desired effects of the present invention are not, or are substantially not, impaired. Also note that the preferred embodiments described below may be combined with other preferred embodiments of the present invention if so desired. 
     First Preferred Embodiment 
       FIG. 1  is a schematic cross-sectional view illustrating the structure of a centrifugal fan  100  according to a preferred embodiment of the present invention. 
     Referring to  FIG. 1 , the centrifugal fan  100  according to the present preferred embodiment preferably includes an impeller  10  arranged to rotate about a rotation axis J, a motor  30  arranged to drive and rotate the impeller  10 , and a case  19  arranged to accommodate the impeller  10  and the motor  30 . An air inlet  40  through which an outside gas is drawn into the centrifugal fan  100  is preferably defined axially above the impeller  10 . 
     The impeller  10  preferably includes a hub  11 , a plurality of first blades  12 , and a plurality of second blades  13 . The hub  11  is substantially in the shape of a circular plate, and is joined to a shaft  31  arranged to rotate about the rotation axis J. The first blades  12  are preferably arranged axially above the hub  11 . The second blades  13  are preferably arranged axially below the hub  11 . 
     A peripheral portion of the hub  11  is preferably arranged to project radially outward relative to a peripheral portion of each first blade  12 . This arrangement contributes to preventing a gas which has been drawn in through the air inlet  40  due to rotation of the first blades  12  from flowing backward toward the air inlet  40 . 
     Each first blade  12  is arranged to extend axially downward and radially outward away from the rotation axis J. A portion of an inner wall of the case  19  which covers each first blade  12  includes an inner wall surface arranged to extend along an axially upper end portion of each first blade  12 . The gas drawn in through the air inlet  40  is caused to flow axially downward and radially outward by the rotation of the first blades  12 . That is, a main function of each first blade  12  is to cause the gas drawn in through the air inlet  40  to efficiently flow into the case  19 . Moreover, the first blades  12  are arranged to extend radially with the rotation axis J as a center, with each first blade  12  having such an angle that the first blade  12  bends in the same direction as a rotation direction of the impeller  10  as it extends away from the rotation axis J in a plan view. The angle of each first blade  12  at which the first blade  12  bends in the same direction as the rotation direction of the impeller  10  is preferably not constant throughout the radial extent of the first blade  12 . Specifically, each first blade  12  is arranged to bend at an increasing angle in the same direction as the rotation direction of the impeller  10  as it extends radially outward away from the rotation axis J. This arrangement enables the rotation of each first blade  12  to easily add a circumferential whirl velocity component to the gas, which primarily includes axially downward and radially outward velocity components. As a result, the gas is more efficiently sent toward an air outlet (not shown, but which is preferably arranged, for example, in a circumferential surface of the case  19 ). 
     A main function of each second blade  13  is to send the gas drawn into the case  19  toward the air outlet (not shown). 
     The motor  30  preferably includes a bearing  32  arranged to support a rotor magnet  33  such that the rotor magnet  33  is rotatable about the rotation axis J, a bearing support portion  35  arranged to support the bearing  32 , and a stator  34  supported by the bearing support portion  35 . The hub  11 , which is fixed to the shaft  31  arranged to rotate about the rotation axis J, includes a hub cylindrical portion  11   a  extending axially downward and being substantially cylindrical. The rotor magnet  33  is fixed to an inner circumferential surface of the hub cylindrical portion  11   a . Note that, although the motor  30  illustrated in  FIG. 1  is an outer-rotor motor, a motor according to another preferred embodiment of the present invention may be an inner-rotor motor, if so desired. 
     Regarding the centrifugal fan  100 , a torque is produced between the rotor magnet  33  and the stator  34  as a result of a drive current supplied to the stator  34 . As a result, the impeller  10  is caused to rotate about the rotation axis J. 
     The case  19  preferably includes an upper case  20 , a lower case  21  including a motor accommodating portion  22  arranged to cover an outer circumference of the motor  30 , and a joint portion  23  at which the upper and lower cases  20  and  21  are preferably fixed to each other. The upper case  20  is arranged to extend axially downward and radially outward from a peripheral portion of the air inlet  40 . The lower case  21  further includes a radially outer portion fixed to a radially outer portion of the upper case  20  at the joint portion  23 , and an intermediate portion arranged to extend axially downward and radially inward in a curve from the joint portion  23 , and joined to an upper end portion of the motor accommodating portion  22 . Note that the intermediate portion of the lower case  21  does not need to begin to curve radially inward at a junction with the joint portion  23 . That is, the intermediate portion of the lower case  21  may be arranged to begin to curve radially inward after extending axially downward by a predetermined distance from the joint portion  23 . Also note that the intermediate portion of the lower case  21  does not need to extend radially inward in a curve to be joined to the upper end portion of the motor accommodating portion  22 . That is, the intermediate portion of the lower case  21  may be arranged to first extend axially downward by a predetermined distance from the joint portion  23 , and then bend radially inward substantially at a right angle to be joined to the upper end portion of the motor accommodating portion  22 . Note that the predetermined distance is appropriately set within a range of the axial distance between the joint portion  23  and a lower end of the motor accommodating portion  22 . Also note that the intermediate portion of lower case  21  may be arranged to obliquely extend radially inward from the joint portion  23  to be joined to the upper end portion of the motor accommodating portion  22 . Also note that the intermediate portion of the lower case  21  may be arranged to obliquely extend radially inward from the joint portion  23  while changing a slant angle to be joined to the upper end portion of the motor accommodating portion  22 . At least, the intermediate portion of the lower case  21  is joined to the motor accommodating portion  22  while defining a space at an axial height lower than an axial height of the joint portion  23 . 
     An interior of the case  19  preferably includes a first annular space (an air channel portion)  50  positioned radially outward of the motor  30 . Rotation of the impeller  10  causes the gas drawn in through the air inlet  40  to whirl in a circumferential direction while passing through the first annular space  50 , which is arranged around the impeller  10 , and to be discharged through the air outlet (not shown). 
       FIG. 2  is a partial cross-sectional view illustrating the first annular space  50  and its vicinity within the centrifugal fan  100  illustrated in  FIG. 1  in an enlarged form. 
     Referring to  FIG. 2 , the first annular space  50  preferably includes a second annular space  51 , which is a portion of a space defined by an annularly continuous collection of imaginary circles each of whose diameter D is the shortest distance between an inner circumferential edge  23   a  of the joint portion  23  and a radially outermost circumferential portion  22   a  of the motor accommodating portion  22  and each of which touches the inner circumferential edge  23   a  of the joint portion  23 , the portion of the space being defined by a portion of an inner wall of the upper case  20  and a portion of an inner wall of the lower case  21 . A portion of the impeller  10  is arranged in the second annular space  51 . Each imaginary circle mentioned above refers to an imaginary circle (or shape substantially arranged in the form of a circle) positioned in a plane including the rotation axis J (i.e., a plane extending in parallel or substantially in parallel with the rotation axis J). 
     Note that, in the structure according to the present preferred embodiment, preferably no portion of the radially outermost circumferential portion  22   a  of the motor accommodating portion  22  is positioned radially inside the inner circumferential edge  23   a  of the joint portion  23  at the same axial height as the axial height of the inner circumferential edge  23   a  of the joint portion  23 . In this case, the shortest distance between the inner circumferential edge  23   a  of the joint portion  23  and the radially outermost circumferential portion  22   a  of the motor accommodating portion  22  is assumed to be the shortest distance between the inner circumferential edge  23   a  of the joint portion  23  and an axial extension  22   b  of the radially outermost circumferential portion  22   a  of the motor accommodating portion  22 . 
     Also note that, in the present preferred embodiment, the inner circumferential edge  23   a  of the joint portion  23 , at which the upper and lower cases  20  and  21  are fixed to each other, is a line determined for reasons of necessity to define the second annular space  51 . The position of the inner circumferential edge  23   a  of the joint portion  23  does not need to be determined exactly as long as the inner circumferential edge  23   a  is positioned axially below the impeller  10  and helps to define the second annular space  51 , in which a whirl occurs. 
     In the present preferred embodiment, the second annular space  51  is arranged to define an annular air channel portion which is a portion of the first annular space  50  positioned radially outward of the motor  30 , and which includes a space axially below the impeller  10 . Accordingly, a circumferential whirl velocity component caused by the rotation of the impeller  10  is added to a gas which has flowed into the second annular space  51 . Moreover, the gas drawn in through the air inlet  40  is incessantly sent into the second annular space  51  through the rotation of the impeller  10 . The density of the gas in the second annular space  51  is consequently increased. This leads to an increase in ventilation resistance in an air channel from the air inlet  40  to the air outlet (not shown), leading to an increase in static pressure of the centrifugal fan  100 . 
     Furthermore, in the present preferred embodiment, a portion of the impeller  10  is preferably arranged in the second annular space  51 . Accordingly, the circumferential whirl velocity component is added to the gas which has flowed into the second annular space  51  through the rotation of the impeller  10 . As a result, the density of the gas in the second annular space  51  is further increased. Moreover, the portion of the impeller  10  which is arranged in the second annular space  51  closes a portion of a channel arranged to contain the gas in the second annular space  51 , and this leads to an increase in the ventilation resistance. As a result, the static pressure is increased. Furthermore, arranging the portion of the impeller  10  in the second annular space  51  results in a large combined surface area of portions of the impeller  10  which are positioned in the second annular space  51 . As a result, the air volume of the centrifugal fan  100  is also increased. 
     In short, the centrifugal fan  100  according to the present preferred embodiment is able to achieve increased static pressure and an improved air volume characteristic by arranging the second annular space  51 , which is annular in shape and which includes the space axially below the impeller  10 , in the first annular space  50  positioned radially outward of the motor  30 , and arranging a portion of the impeller  10  in the second annular space  51 . 
     The gas drawn in through the air inlet  40  through the rotation of the first blades  12  flows into the case  19  and is guided to the first annular space  50  and then to the second annular space  51 . In the present preferred embodiment, the peripheral portion of the hub  11  is arranged to project radially outward relative to the peripheral portion of each first blade  12 . This makes it less likely for a gas which has been guided into the second annular space  51  to flow backward toward the first blades  12 . This leads to an increase in the density of the gas in the second annular space  51  and, because the gas is pushed in the circumferential direction, to an increase in the static pressure and the air volume. 
     The second blades  13  are preferably arranged radially inward in the second annular space  51 . The gas drawn in through the air inlet  40  flows into a radially outer space in the second annular space  51 , and tends to easily stay in a radially inner space in the second annular space  51 . Therefore, arranging the second blades  13  radially inward in the second annular space  51  enables a gas staying in the radially inner space in the second annular space  51  to be efficiently discharged radially outward. 
     Note that the second annular space  51  according to the present preferred embodiment may have any of a variety of spatial shapes. For example, a portion of the inner wall of the case  19  which covers the second annular space  51  may be arranged to include a curved surface in a vertical section. This arrangement enables the gas drawn in through the air inlet  40  to smoothly flow into the second annular space  51 . Note that this curved surface is not necessarily required to be a spherical surface. 
       FIG. 3  is a partial cross-sectional view illustrating an example spatial shape of the second annular space  51 . The first annular space  50  further includes a space  51   a  positioned axially below the second annular space  51 , which is the portion of the space defined by the annularly continuous collection of the imaginary circles each of whose diameter D is the shortest distance between the inner circumferential edge  23   a  of the joint portion  23  and the radially outermost circumferential portion  22   a  of the motor accommodating portion  22  and each of which touches the inner circumferential edge  23   a  of the joint portion  23 , the portion of the space being defined by a portion of the inner wall of the upper case  20  and a portion of the inner wall of the lower case  21 . A gas which has been drawn in along the inner wall of the upper case  20  is guided from a radially outer portion to a radially inner portion of the space  51   a  along the inner wall of the lower case  21 , and stays therein as a whirl. A position at which the gas drawn in stays as the whirl depends on the axial dimension of the intermediate portion of the lower case  21 . Therefore, the position at which the gas drawn in stays as the whirl according to the present preferred embodiment is axially lower than in the preferred embodiment in which the first annular space  50  does not include the space  51   a . In this case, it is desirable to elongate each second blade  13  axially downward. For example, it is desirable to elongate each second blade  13  axially downward up to the same axial position as that of the joint portion  23  or that of an upper end of the radially outermost circumferential portion  22   a  of the motor accommodating portion  22  or even further downward. This causes each second blade  13  to overlap with a space in which the whirl occurs, and this enables a gas which stays as the whirl to be efficiently pushed radially outward. Note, however, that the position at which the gas drawn in stays as the whirl depends not only on the axial dimension of the intermediate portion of the lower case  21 , but also on the shape of an inner wall of the intermediate portion of the lower case  21 . Therefore, in addition to elongating each second blade  13  axially downward, the shape of the inner wall of the intermediate portion of the lower case  21  may be modified appropriately so that each second blade  13  will overlap with the space in which the whirl occurs. 
     In the present preferred embodiment, no particular limitation is imposed on the structure of the impeller  10 . For example, the impeller  10  may be modified to have a structure as illustrated in  FIG. 4 ,  5 , or  6  in place of the structure illustrated in  FIG. 1 . 
     In an impeller  10  having the structure illustrated in  FIG. 4 , the peripheral portion of the hub  11  does not project radially outward relative to the peripheral portion of each first blade  12 , but is arranged to be flush with both the peripheral portion of each first blade  12  and a peripheral portion of each second blade  13 . A reduction in the radial dimension of the impeller  10  can thus be achieved. 
     In an impeller  10  having the structure illustrated in  FIG. 5 , the peripheral portion of each first blade  12  and the peripheral portion of a corresponding one of the second blades  13  are joined to each other on a radially outer side of the peripheral portion of the hub  11 . The first and second blades  12  and  13  can thus be integrally defined with each other. 
     In an impeller  10  having the structure illustrated in  FIG. 6 , second blades  13   a  are defined in an outer circumferential edge of the hub  11 .  FIG. 7  is a plan view of the impeller  10  illustrated in  FIG. 6 . Each second blade  13   a  is preferably defined by cutting a portion of the outer circumferential edge of the hub  11  radially inward. Each second blade  13   a  is preferably defined in an outer circumferential side surface of the hub  11 . The outer circumferential edge of the hub  11  is locally cut away up to a vicinity of the peripheral portion of each first blade  12 . In other words, a portion of the outer circumferential edge of the hub  11  begins at the vicinity of the peripheral portion of each first blade  12  and extends to a position radially outward of an adjacent one of the first blades  12 . The axial extent of the hub  11  is thus able to serve as the second blades  13   a  at the outer circumferential edge of the hub  11 . 
     The structure of the hub  11  illustrated in  FIG. 7  will now be described in more detail below. Each first blade  12  is arranged to extend radially outward in a smooth curve from a radially inner end thereof. In a plan view of the hub  11 , a portion of the outer circumferential edge of the hub  11  begins at an outer circumferential end portion of each first blade  12  and extends radially outward along this curve up to a radially outermost point of the outer circumferential edge of the hub  11  (resulting in a first side surface), and then extends in a smooth curve from the radially outermost point of the outer circumferential edge of the hub  11  to a radially innermost point of the outer circumferential edge of the hub  11  at which an outer circumferential end portion of an adjacent one of the first blades  12  is positioned (resulting in a second side surface). The impeller  10  illustrated in  FIG. 7  is arranged to rotate in a counterclockwise direction. The number of cuts defined in the outer circumferential edge of the hub  11  is preferably equal to the number of first blades  12 . Note, however, that each cut may be defined for two or more of the first blades  12  (for example, for two of the first blades  12 ). It is enough that surfaces arranged radially should be defined in the outer circumferential edge of the hub  11  to define the second blades  13   a.    
     In the impeller  10  having the structure illustrated in  FIG. 6 , portions of the outer circumferential edge of the hub  11  are cut away as described above. Accordingly, a reduction in the weight of the impeller  10  can thus be achieved. The reduction in the weight of the impeller  10  leads to quicker start of the rotation of the impeller  10  when the impeller  10  is activated. 
     Each second blade  13   a  of the impeller  10  having the structure illustrated in  FIG. 6  is arranged in the second annular space  51 . This contributes to discharging a gas which stays in the annular air channel portion efficiently radially outward. 
       FIG. 8  is a schematic cross-sectional view illustrating the structure of a centrifugal fan  110  according to another preferred embodiment of the present invention. The centrifugal fan  110  according to the present preferred embodiment is preferably a so-called mixed flow fan. 
     The structure of an impeller  10  according to the present preferred embodiment is different from the structure of the impeller  10  illustrated in  FIG. 1 . The structure of a motor  30  according to the present preferred embodiment is preferably identical or substantially identical to the structure of the motor  30  illustrated in  FIG. 1 , and a description thereof is therefore omitted. 
     The impeller  10  according to the present preferred embodiment is joined to a shaft  31  arranged to rotate about a rotation axis J, and includes a hub  11  arranged to obliquely extend axially downward and radially outward from the shaft  31 , and a plurality of first blades  12  arranged axially above the hub  11 . A portion  12   a  of each first blade  12  is arranged in a second annular space  51 . Note that the definition of the second annular space  51  according to the present preferred embodiment is the same as the definition of the second annular space  51  illustrated in  FIG. 2 . 
     In the centrifugal fan  110  according to the present preferred embodiment, each first blade  12  is arranged to obliquely extend axially downward and radially outward away from the rotation axis J. A gas drawn in through an air inlet  40  is accordingly sent axially downward and radially outward through rotation of the first blades  12 . This enables the gas drawn in through the air inlet  40  to be smoothly guided into the second annular space  51 . 
     In addition, an annular shroud  14  may be arranged on an axially upper end portion of each first blade  12 . Here, the shroud  14  is positioned axially over the second annular space  51 . This makes it less likely for the gas guided into the second annular space  51  from the air inlet  40  through the rotation of the first blades  12  to flow backward toward upper portions of the first blades  12 . This leads to an increase in the density of the gas in the second annular space  51  and, because the gas is pushed in the circumferential direction, also to an increase in the static pressure. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.