Patent Publication Number: US-2005116579-A1

Title: Motor for blowers

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a motor for blowers.  
      2. Description of the Prior Art  
      Disclosed in the prior art is a blower motor wherein the front end of the boss of the rotor is in the shape of a cone so that air can smoothly be sucked into the impeller. Thus, the blower motor improves the blast performance of blowers and lowers the blast noise levels of blowers.  
      When the blower motor with the front end of the boss of the rotor in the shape of a cone is mounted to a blower, however, its impeller has to be elongated in the axial direction to achieve an improved blast performance of the blower fitted with the blower motor. Thus, the blower becomes bulky.  
     SUMMARY OF THE INVENTION  
      The object of the present invention is to provide a blower motor capable of reducing the noise level of blower and improving the blast performance of the blower without making the blower bulky.  
      According to the present invention, there is provided a blower motor comprising a housing, a motor shaft supported in a bearing which is supported in the housing, a rotor which is fixed to the motor shaft and tapers off toward an air inlet, a stator which is fixed to the housing and tapers off toward the air inlet, and a magnet fixed to an internal circumferential surface of the rotor.  
      In the blower motor, because the rotor tapers off toward the air inlet, air flows along the side surface of the cone-shaped rotor; accordingly, the noise level of the blower is low. Besides, the blower is given high blast performance without making the blower bulky. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a blower fitted with a blower motor of the present invention;  
       FIG. 2  is a section taken along the line A-A of  FIG. 1 ;  
       FIG. 3  is an illustration of the workings of the blower of  FIGS. 1 and 2 ;  
       FIG. 4  is a sectional view of a blower fitted with another blower motor of the present invention;  
       FIG. 5  is a sectional view of a blower fitted with yet another blower motor of the present invention; and  
       FIG. 6  is a sectional view of a blower fitted with a further blower motor of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      By referring to  FIGS. 1 and 2 , a blower fitted with a blower motor of the present invention will be described below. An air inlet  4  is provided on one sidewall of a casing  2 , an outlet  6  is provided on an outer circumferential surface of the casing  2 . A cylindrical housing  8  is fixed to the casing  2 . A motor shaft  14  is supported in an oil-retaining plain bearing  16 , which is supported in the housing  8 . A boss  18  is fixed to the motor shaft  14 . A rotor  20  is secured to the boss  18 . A ring-like magnet  22  is fixed to an inner circumferential surface of the rotor  20 . The magnet  22  is multi-polarized circumferentially. An outer circumferential surface of the rotor  20  tapers off toward the air inlet  4 , or a portion of the motor shaft  14  fixing the boss  18  of the rotor  20 . The ratio of the minimum outside diameter to the maximum outside diameter of the rotor  20  is 0.7 to 0.9. An inner circumferential surface of the magnet  22  tapers off toward the air inlet  4 . A stator  10  is fixed to the housing  8 . The stator  10  is provided with motor windings  12 . Namely, the motor windings  12  are housed in the slots of the stator  10 . An outer circumferential surface of the stator  10  tapers off toward the air inlet  4 . The gap between the stator  10  and the magnet  22  is uniform in size. The stator  10 , rotor  20 , etc. constitute a brushless blower motor of an outer-rotor type. The rotor  20  and a support  24  for an impeller  28  are made as a single piece. A plurality of blades  26 , for example 80 blades, are supported on the support  24  to constitute the impeller  28 .  
      When a power supply connected to the motor windings  12  is switched on, the rotor  20  of the blower motor and the impeller  28  of the blower rotate. As shown in  FIG. 3 , the centrifugal force caused by the rotation of the impeller  28  causes an air flow from the air inlet  4  to the outer circumference of the impeller  28  and high-pressure air is discharged through the outlet  6 .  
      In the blower having the blower motor shown in FIGS.  1  and  2 , because the outer circumferential surface of the rotor  20  tapers off toward the inlet  4 , an extreme outside diameter of the rotor  20  is small, the effective area of the air inlet  4  is large. Besides, air flows along the side surface of the cone-shaped rotor  20 ; accordingly, the direction of the air flow changes smoothly and air flows up to the vicinity of the support  24 . Thus, the noise level of the blower is low. Furthermore, the ratio of the effective length “A” of blades  26  to their overall length is as large as 90%; therefore, the capacity of the blower is large for the axial length of the impeller  28  and the thickness of the blower. Thus, the blower is given high blast performance without extending the axial length of the impeller of the blower or making the blower bulky. Therefore, the blast performance of the blower can be improved without making the blower bulky. In addition, because attraction is generated between the stator  10  and the magnet  22 , the axial positional slippage of the magnet  22  because of conditions on the installation of the blower, or undesirable installed position, or posture, of the blower, and axial thrust due to the rotation of the impeller  28  can be prevented if an inexpensive oil-retaining plain bearing  16  is used to support the motor shaft  14 . Accordingly, there occurs no positional slippage between the center of the stator  10  and that of the magnet  22 , reducing the axial vibration in the direction of the motor shaft  14  and the noise level of the blower and achieving a low noise level in a high static-pressure range.  
       FIG. 4  shows a blower fitted with another blower motor according to the present invention. A housing  30  is fixed to a casing  2 , and a stator  10  is fixed to the housing  30 . A motor shaft  14  is supported in an oil-retaining plain bearing  16 , which is supported in the housing  30 . An outer circumferential surface of the housing  30  tapers off toward an air inlet  4 .  
      The blower motor of  FIG. 4 , too, has a low noise level of the blower and high blast performance for its dimensions, and there occurs no positional slippage between the center of the stator  10  and that of a magnet  22 . Besides, the diameter of part of the housing  30  supported by the casing  2  is large; accordingly, a rotor  20  is supported rigidly and the vibration of an impeller  28  is light. The effect of reducing noise levels is large, particularly when a large blower is fitted with the blower motor.  
      The stator  10  shown in  FIGS. 2, 3 , and  4  has a plurality of main magnetic poles and each of the main magnetic poles has a motor winding  12 . If the stator yoke of the stator  10  is divided for each main magnetic pole, each divided stator yoke is provided with a motor winding, and the divided stator yokes with motor winding are connected, a blower motor can easily be made.  
       FIG. 5  shows a blower fitted with yet another blower motor according to the present invention. A motor shaft  14  is supported in a rolling bearing  38 , which is supported in a housing  8 . A center yoke  32  and two divided stator yokes  34  are fixed to the housing  8 . The two divided stator yokes  34  constitute a stator  40 . An outer circumferential surface of the stator  40  tapers off toward an air inlet  4 . The two divided stator yokes  34  are divided for each main magnetic pole. Each of the two divided stator yokes  34  has a main magnetic pole extending radially from the center toward outside. The main magnetic poles of the two divided stator yokes  34  are offset from each other by 180 electrical degrees. The center yoke  32  establishes a short circuit between the center portions of the two divided stator yokes  34  magnetically. A motor winding  36  is supported by each of the two divided stator yokes  34 , and the center yoke  32  is placed in the center of the motor winding  36 . The motor winding  36  is wound around a bobbin. The motor winding  36  is of ring-like shape and an outer circumferential surface of the motor winding  36  tapers off toward the air inlet  4 .  
      The blower motor of  FIG. 5 , too, has a low noise level and high blast performance for its dimensions. In addition, because axial attraction is generated between the stator  40  and a magnet  22 , there occurs no positional slippage between the center of the stator  40  and that of the magnet  22 .  
       FIG. 6  shows a blower fitted with yet another blower motor according to the present invention. A housing  42  is fixed to a casing  2 , and a stator  40  is fixed to the housing  42 . A motor shaft  14  is supported in a rolling bearing  38 , which is supported in the housing  42 . An outer circumferential surface of the housing  42  tapers off toward an air inlet  4 .  
      The blower motor of  FIG. 6 , too, has a low noise level and high blast performance for its dimensions. In addition, there occurs no positional slippage between the center of the stator  40  and that of a magnet  22 . Besides, the diameter of part of the housing  42  supported by the casing  2  is large; accordingly, a rotor  20  is supported rigidly and the vibration of an impeller  28  is light.  
      In the above embodiments, the housings  8 ,  30 , and  42  are fixed to their respective casings  2 . However, the casing and the housing may be made as a single piece.