Abstract:
A blower for use with a hand dryer and the like has a motor; an impeller driven by the motor; a diffuser for directing air from the impeller; and a housing accommodating the motor, the impeller and the diffuser. The motor has a rotor and a stator. The rotor has a shaft, a rotor core fixed to the shaft, a ring magnet fixed to the rotor core, and a protective sleeve surrounding the ring magnet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201020140173.0 filed in The People&#39;s Republic of China on Mar. 22, 2010. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to an electric blower and in particular, to a blower suitable for use in a hand dryer or air cleaner. 
       BACKGROUND OF THE INVENTION 
       [0003]    A known blower includes a motor with a rotor and a stator, an impeller driven by the motor and a housing with an air inlet and an air outlet and in which the motor and the impeller are accommodated. The rotor has a ring magnet made of bonded NdFeB (neodymium iron boron) rare earth and adhered to a rotor core of the rotor. The blower has a disadvantage of low reliability and usability, because the ring magnet may breakdown when the rotor is rotating at high speed, such as over 15000 rpm (revolutions per minute). At this speed the bonded rare earth magnet tends to disintegrate due to the forces on the magnet. Even sintered rare earth magnets become physically unstable at rotational speeds above 40,000 rpm. However, modern appliances, such as hand dryers and air cleaners are requiring motors with high rotation speeds and light weight. 
       SUMMARY OF THE INVENTION 
       [0004]    Hence there is a desire for a blower having a permanent magnet rotor which can withstand high speed rotation so as to be suitable for use with a hand dryer or the like. 
         [0005]    Accordingly, in one aspect thereof, the present invention provides a blower comprising: a motor with a rotor and a stator; an impeller driven by the motor; a diffuser for directing air from the impeller; and a housing accommodating the motor, the impeller and the diffuser and having an air inlet and an air outlet, wherein the rotor comprises: a shaft, a rotor core fixed to the shaft, a ring magnet fixed to the rotor core, and a protective sleeve tightly surrounding the ring magnet. 
         [0006]    Preferably, the protective sleeve is made of metal. 
         [0007]    Preferably, the protective sleeve is made of stainless steel plate. 
         [0008]    Preferably, thickness of the protective sleeve is between 0.1 mm and 0.3 mm. 
         [0009]    Preferably, the ring magnet is a bonded NdFeB rare earth ring magnet or a sintered NdFeB rare earth ring magnet. NdFeB rare earth magnets provide a higher magnetic energy in a smaller lighter package and thus can reduce the size and thus weight of the motor. 
         [0010]    Preferably, the rotor has a pair of balance rings that press against the axial ends of the ring magnet to prevent axial movement of the ring magnet with respect to the rotor core. 
         [0011]    Preferably, the ring magnet has an axial length that is longer than the axial length of the rotor core and each of the balance rings has a boss that locates within the respective axial end of the ring magnet. 
         [0012]    Preferably, the ring magnet is keyed to the rotor core by a tongue in groove connection to prevent rotation of the ring magnet about the rotor core. 
         [0013]    Preferably, the diffuser is disposed between the impeller and the motor for directing air from the impeller to the motor via a plurality of air passages and wherein the diffuser supports a bearing for the shaft. 
         [0014]    Preferably, the rotor is configured to rotate at a speed greater than 25,000 rpm, preferably greater than 40,000 rpm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Preferred embodiments of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labelled with a same reference numeral in all the figures in which they appear. 
           [0016]    Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0017]      FIG. 1  shows a blower in accordance with the preferred embodiment of the present invention; 
           [0018]      FIG. 2  is a view of the blower of  FIG. 1 , with a housing removed; 
           [0019]      FIG. 3  is a side view of the blower in  FIG. 2 ; 
           [0020]      FIG. 4  is a view from below of the blower of  FIG. 3 , showing an impeller and a diffuser, being parts of the blower; 
           [0021]      FIG. 5  is a partially exploded view of a rotor of the blower; and 
           [0022]      FIG. 6  is an exploded view of a rotor assembly without a shaft, according to a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIGS. 1 to 4  illustrate a blower  100  in accordance with the preferred embodiment of the present invention. The blower comprises an impeller  200 , a diffuser  300 , a motor  400  and a housing  500 . 
         [0024]    The housing  500  comprises a first housing member  510  and a second housing member  520 . The first housing member  510  accommodates the impeller  200  and the diffuser  300  and forms a volute for the impeller. A second housing member  520  accommodates the motor  400 . The first housing member  510  comprises a circular side wall  512  and a bottom wall  514 . The second housing member  520  comprises a hollow cylinder  522  with an end plate  524 . A flange  526  extends outwardly and radially from the lower open end of the cylinder  522  adjacent to the first housing member  510 . The flange  526  is fixedly assembled with the side wall  512  of the first housing member  510 , preferably by crimping the side wall  512  to the flange. An air inlet  516  is formed at the center of the bottom wall  514  of the first housing member  510  and air outlets  523  are formed on the hollow cylinder  522  of the second housing member  520 , at the upper, closed end thereof. A boss  525  is formed in the end plate  524  with a hole arranged for holding a bearing  433 . Preferably, the first housing member  510  is a stamped sheet metal part while the second housing member  520  is an injection molded plastics material part. 
         [0025]    In  FIGS. 2 to 4 , the blower is shown with the housing removed to show the impeller, diffuser and motor disposed within the housing. The impeller  200  is fixed to and rotates with a shaft  442  of the motor  400 . The impeller  200  comprises a cover  220 , a base  240  and a plurality of curved blades  260 . The cover  220  has an opening  222  formed at center thereof and opposite to the air inlet  516 . The plurality of blades  260  are disposed between the cover and the base, extending in a generally radial manner from the opening and evenly distributed circumferentially to form a plurality of flow passages through which air passing through the opening  222  flows when the impeller is rotating. Each blade  260  has a plurality of tabs  262  on each of the two long edges and holes corresponding to the tabs  262  are formed in the cover  220  and the base  240 . A tab  262  and a corresponding hole constitute a clamp structure. The blades  260  are firmly fixed between the cover  220  and the base  240  by crimping or otherwise deforming the tabs after they have been inserted into the holes to prevent their removal, in a manner generally known in the art. 
         [0026]    The diffuser  300  is arranged between the impeller  200  and the motor  400  and fixedly mounted to the housing  500 . The diffuser  300  is provided with a circular body  320  which has an outer diameter larger than the impeller  200  and is fitted to an inner surface of the circular side wall  512  of the first housing member  510 . A bearing holder with a through hole is formed at center of the circular body  320  for holding a bearing  445  for the shaft  442 . A plurality of diffusing structures  340  integrally formed with the circular body  320  are evenly arranged at outer periphery of one surface of the circular body  320  facing the impeller  200 . Each diffusing structure  340  and the inner surface of the circular side wall  512  of the first housing member  510  defines a diffusing passage  342  which guide the air flow axially as well as circumferentially. A plurality of air guides  360  integrally formed with the circular body  320  are evenly arranged on one surface of the circular body  320  facing the motor  400 . Air passages  362  are formed between adjacent air guides  360  and guide the air flow from the diffusing passages into the hollow body  522  of the second housing  520 , to be exhausted from through the outlets  523 . Thus the diffuser  300  channels or guides the air flow from the impeller  200  into the hollow body  522 . Pressured air exiting from the impeller  200  flows into the air passages  362  via the diffusing passages  342  and then are guided to the motor  400  by the air passages  362  so as to be expelled from the blower  100  through the air outlets  523  of the second housing member  520 . 
         [0027]    The motor  400  is a brushless motor with a permanent magnet rotor  440  and a stator  420  surrounding the rotor  440 . The stator  420  is fixed to the second housing member  520  and comprises a stator core  422  and windings (not shown in the figures) wounded on teeth  424  of the stator core  422 . In the embodiment shown, there are six stator poles formed by six teeth  424 . The rotor  440  comprises a shaft  442 , a rotor core  444  fixed to the shaft  442 , and a ring magnet  446  fixed to the rotor core  444 . The shaft  442  is rotatably supported by two bearings  443  and  445 . The ring magnet  446  is a bonded NdFeB rare earth ring magnet to lower the cost of the blower  100 . Alternatively the ring magnet  446  may be a sintered NdFeB rare earth ring magnet. A pair of balance rings  441  are attached to the shaft at respective axial ends of the ring magnet  446  to clamp the ring magnet  446  in an axial direction. A protective sleeve  448  is applied to the ring magnet  446  and the pair of balancing rings  441 . The protective sleeve  448  is preferably made of stainless steel plate with a thickness of about 0.1 mm-0.3 mm, which will not significantly effect performance of the motor but has good mechanical strength to endure centrifugal and electromagnetic forces to prevent the ring magnet  446  from breaking up when the rotor  440  is rotating at high speed over 25,000 rpm (even over 40,000 rpm). 
         [0028]      FIG. 6  illustrates an exploded view of a rotor assembly of a second embodiment with the shaft omitted. In use, the rotor assembly shown would be fitted to a rotor shaft such as shaft  442  of  FIG. 5 . The rotor assembly comprises a rotor core  444  which has a central hole for being press fitted onto the shaft. A ring magnet  446  is fitted to the rotor core. The ring magnet is coupled to the rotor core by a tongue and groove connection comprising two grooves  451  formed in the inner surface of the ring magnet which receive or mate with two ridges or tongues  450  formed on the outer surface of the rotor core. Of course the locations of the tongues and grooves may be reversed and the number of tongues and grooves may be different. The tongue and groove connection prevents the ring magnet from rotating about the rotor core. The axial length of the rotor core may be less than the axial length of the ring magnet such that a small chamber may be formed at each the end of the magnet once fitted to the rotor core. The balance rings each have a boss  449  which locates within a respective chamber when fitted to the rotor core. The balance rings may be pressed onto the shaft to hold the ring magnet axially with respect to the shaft and the rotor core. However, preferably the balance rings  441  are fixed to the rotor core with the bosses  449  contacting the rotor core. Fixing may be by any suitable means such as by bolts passing through the rotor core from one balance ring to the other. The protective sleeve  448  which fits over the ring magnet  446  to support the ring magnet against the forces trying to destroy the ring magnet during high speed rotation. The protective sleeve, in this embodiment, has the same axial length as the ring magnet. 
         [0029]    The blower in accordance with the present invention is particularly suitable for air processing apparatus such as hand dryers and air cleaners. 
         [0030]    The advantages of embodiments of the present invention include that reliability of the blower can be improved because the added protect sleeve can prevent the ring magnet from being broken and cost of the blower is low because a ring magnet made of bonded NdFeB rare earth is adopted. 
         [0031]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
         [0032]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.