Abstract:
An easy-to-assemble electric motor ( 21 ) features an internal stator ( 50 ), an external rotor ( 22 ) having a shaft ( 34 ), which external rotor is configured as a rotor cup or bell ( 24 ) having an outer side and an inner side ( 25 ), a bearing tube ( 70 ) for receiving a bearing arrangement ( 60 ) journaling the shaft ( 34 ), which bearing tube ( 70 ) has a first end portion ( 71 ) facing toward the inner side ( 25 ) of the external rotor ( 22 ) and being formed with an inwardly protruding stop ( 73 ), the bearing tube having a second end portion ( 75 ) facing away from the first end portion ( 71 ) and being joined to a plastic part ( 80 ) that likewise forms an inwardly protruding stop ( 77 ) adjacent a second end portion ( 75 ), the bearing arrangement ( 60 ) being located in the bearing tube ( 70 ) in a chamber defined between said two inwardly protruding stops ( 73, 77 ).

Description:
FIELD OF THE INVENTION 
   The invention relates to an electronically commutated motor, in particular to a miniature and subminiature motor. Such motors are preferably used in miniature or subminiature fans. 
   BACKGROUND 
   Miniature and subminiature fans of this kind have very small dimensions and correspondingly weigh very little. Fans of the ebm-papst 250 series, for example, have dimensions of 8×25×25 mm and weigh approx. 5 g. For fans of the ebm-papst 400 series, the dimensions are 20×40×40 mm and the weight is &lt;30 g. The fan motors are accordingly even smaller and weigh even less than the fan as a whole. 
   With such motors, assembly must be simple and uncomplicated, in order to allow cost-effective manufacture and a high level of automation. Uniform quality, which is a prerequisite for a long average service life, can be achieved by extensive automation. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to make available an improved miniature or subminiature motor whose assembly steps can readily be automated. 
   According to the invention, this object is achieved by a motor having an external rotor whose central shaft is journaled in a bearing tube containing first and second ball bearings in a chamber defined between a first inwardly protruding shoulder or stop at the top of the chamber and a second inwardly protruding shoulder or stop at the bottom of the chamber, the second stop being preferably formed by an injection-molding step during assembly. 
   A motor according to the present invention can, in particular, be built in a very compact manner. Nevertheless, automated manufacture of small fans of uniformly high quality can be achieved. 

   
     BRIEF FIGURE DESCRIPTION 
     Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as a limitation of the invention, that are described below and shown in the drawings. 
       FIG. 1  is a longitudinal section through a fan that is driven by a subminiature motor; 
       FIG. 2  is an exploded depiction of the fan of  FIG. 1 ; 
       FIG. 3  is a sectioned view of the bearing tube of  FIGS. 1 and 2 ; 
       FIG. 4  is a sectioned view of the bearing tube of  FIG. 3 , having a bearing arrangement according to  FIG. 5  arranged therein; 
       FIG. 5  is an exploded depiction of the bearing tube of  FIG. 3 , including the bearings; 
       FIG. 6  is a sectioned view of the arrangement according to  FIG. 5 , having a plastic part in the form of a flange injection-molded onto it; and 
       FIG. 7  is a top view of an arrangement analogous to  FIG. 6 . 
   

   DETAILED DESCRIPTION 
   In the description that follows, the terms “left,” “right,” “top,” and “bottom” refer to the respective figure of the drawings and can vary from one figure to the next, depending on the orientation (portrait or landscape) selected in each case. Identical or identically functioning parts are labeled with the same reference characters in the various figures, and are usually described only once. 
     FIG. 1  is a longitudinal section, at greatly enlarged scale, through a radial fan  20  having a motor  21  according to a preferred embodiment of the invention. In a practical embodiment of the fan such as the one shown in  FIG. 1 , height H was 15 mm and dimension D was 51 mm, i.e.  FIG. 1  shows this fan enlarged approximately 4.5 times. 
   Motor  21  has an external rotor  22 , an internal stator  50  having a stator lamination stack  50 ′, and a bearing tube  70  mounted on a plastic part  80 . External rotor  22  has a rotor cup  24  made of deep-drawn soft iron, on whose outer periphery is provided a fan wheel  23  having fan blades  26 . A rotor magnet  28  that can be magnetized, for example with four poles, is mounted on the inner periphery of rotor cup  24 . Rotor cup  24  has a base  24   a  having a central opening  24   b  that is joined via a hub  30  (made of a die-cast alloy, e.g. ZAMAK 1  or the like) to upper end  32  of a rotor shaft  34  that has a lower free end  35 .  1 Reg. Trademark of Horsehead Industries Inc. for Zinc-base alloys. 
   Internal stator  50  of motor  21  is mounted on the outer side of bearing tube  70 . Also arranged there is a circuit board  46  having a Hall sensor integrated circuit (IC)  48 , on which board are located components for electronic commutation of motor  21 , for example an IC  46 ′. As is apparent from  FIG. 1 , circuit board  46  is arranged between rotor magnet  28  and stator lamination stack  50 ′ on the one hand and IC  46 ′ on the other hand. 
   A bearing arrangement  60  is arranged in a chamber defined by bearing tube  70 , for purposes of journaling shaft  34 . Said arrangement has, at its top, a first rolling bearing  72  and, at its bottom, a second rolling bearing  76 , which are arranged at a predetermined distance from one another. This distance is defined by an annular spacing member  74 , for example an annular disk as shown. Bearing arrangement  60  is, however, not limited to a specific bearing type; instead, a variety of bearing types can be used, for example plain bearings. 
   Upper (in  FIG. 1 ) end portion  71  of bearing tube  70  faces toward inner side  25  of rotor cup  24 , and is equipped on its inner side with a stop  73 , against which outer ring  72 ″ of rolling bearing  72  abuts. Lower (in  FIG. 1 ) end portion  75  of bearing tube  70  is equipped on its inner side with an enlargement  78 , in order to facilitate the introduction of rolling bearings  72 ,  76  into bearing tube  70 . 
   Lower end portion  75  of bearing tube  70  is mounted on plastic part  80  by plastic injection molding, in such a way that the plastic which is injection-molded onto bearing tube  70  forms a stop  77  against which outer ring  76 ″ of lower rolling bearing  76  abuts. Lower end portion  75 , injection-embedded into plastic part  80 , is covered by an adhered plate  98  made of metal, or another suitable cover. Adhered plate  98  can serve as an identification plate. 
   Bearing tube  70  and bearing arrangement  60  are described in detail with reference to  FIGS. 3 to 5 . 
   As  FIG. 1  shows, shaft  34  is held by a snap ring  92 , serving as a support member or retaining element, and by a schematically depicted compression spring  94 . Snap ring  92  is snapped into an annular groove at free end  35  of shaft  34 . Compression spring  94  is arranged between inner ring  72 ′ of rolling bearing  72  and hub  30 . Compression spring  94  presses second rolling bearing  76  against snap ring  92 , so that ball bearings  72 ,  76  are tensioned with respect to each one another. 
     FIG. 2  is an exploded three-dimensional depiction of fan  20  of  FIG. 1 , illustrating the assembly process. Components of fan  20  are depicted as preassembled components, which are assembled in accordance with steps schematically shown in  FIG. 2 . 
   In a first working step, internal stator  50  is arranged, together with circuit board  46 , on the outer surface of bearing tube  70 , as indicated by an arrow  1 . As  FIG. 2  shows, plastic part  80  has an upwardly-directed wall  49  on which outwardly-directed latching hooks  47 ′,  47 ″ are arranged. 
   In a second working step, compression spring  94  is arranged on bearing arrangement  60  arranged in bearing tube  70  (cf.  FIG. 1 ), as indicated by an arrow  2 . Alternatively, compression spring  94  can be mounted on shaft  34  on external rotor  22 . 
   In a third working step, shaft  34  of rotor  22 , whose fan wheel  23 , having blades  26 , is shown by way of example in  FIG. 2 , is introduced through compression spring  94  into bearing tube  70 , as indicated by an arrow  3 , so that rotor cup  24  surrounds internal stator  50  like a bell. Shaft  34  is then secured within bearing arrangement  60  by snap ring  92 , so the shaft cannot be pulled out. 
   In a concluding working step, a cover part  40  is mounted onto plastic part  80 , as indicated by an arrow  4 . Cover part  40  has a wall  97  directed downward (in  FIG. 2 ) on which are arranged outwardly-directed latching members  42 ′,  42 ″. The latter, upon assembly of cover part  40  with or onto part  80 , are pushed over latching hooks  47 ,  47 ″ of part  80 , form a latching connection therewith, and form a fan housing that protects the components of fan  20  from external influences. 
     FIG. 3  is a longitudinal section through bearing tube  70 . The latter has, at the top, a shoulder  73  forming a stop, and at the bottom has an enlargement  78 . Inside diameter d 1  of bearing tube  70  transitions, at enlargement  78 , to a larger inside diameter d 2  (d 1 &lt;d 2 ). Located on the external periphery of bearing tube  70 , adjacent enlargement  78 , is a shoulder  79  that, when bearing tube  70  is injection-embedded into part  80 , provides additional protection against escape of bearing tube  70  from part  80 . 
     FIG. 4  is a longitudinal section through bearing tube  70  and bearing arrangement  60  arranged therein. An upper end face  72 ″′ of outer ring  72 ″ abuts against stop  73 . Arranged between outer rings  72 ″ and  76 ″ is spacing member  74 , which abuts against a lower end face  72   IV  of outer ring  72 ″ and an upper end face  76   IV  of outer ring  76 ″. Provided at the bottom, between outer ring  76 ″ and the inner side of bearing tube  70 , is a cavity  65  that preferably is filled at least partially with plastic material upon mounting of bearing tube  70  on part  80 , forming stop  77  ( FIG. 6 ) that abuts against a lower end face  76 ″′ of outer ring  76 ″ ( FIG. 6 ). To simplify illustration, shaft  34 , and snap ring  92  thereon, have been omitted from  FIG. 4 . 
     FIG. 5  is an exploded depiction of bearing tube  70  and bearing arrangement  60 . Spacing member  74  is thicker at its outer periphery  74 ″ than at its inner periphery  74 ′. 
   For assembly, firstly rolling bearing  72  is introduced from below (in  FIG. 4 ) into bearing tube  70  in such a way that upper end face  72 ″′ of outer ring  72 ″ of said bearing  72  abuts against shoulder or stop  73  at upper end portion  71  of bearing tube  70 . Spacing member  74  is then introduced into bearing tube  70 , in such a way that its upper face  74 ″′ abuts against lower end face  72   IV  of outer ring  72 ″. Lastly, second rolling bearing  76  is introduced into bearing tube  70 , in such a way that upper end face  76   IV  of outer ring  76 ″ of said bearing  76  abuts against a lower face  74   IV  of spacing member  74 . 
   To prevent rolling bearings  72 ,  76  and spacing member  74  from sliding out of bearing tube  70 , inside diameter d 1  of bearing tube  70  can be selected in such a way that it is slightly smaller than the diameter of bearings  72 ,  76 , so that the bearings are pressed into tube  70  upon assembly. 
     FIG. 6  is a longitudinal section through bearing tube  70 , having bearing arrangement  60  arranged therein and having part  80  according to  FIG. 2 , which can be a part implemented in application-specific fashion, injection-molded onto bearing tube  70 . The plastic of part  80  that is injection-molded onto bearing tube  70  forms an outer ring  95  that rests on top of shoulder  79  of bearing tube  70 , and thus effects a solid coupling of these components. 
   As is apparent from  FIG. 6 , the plastic of part  80 , that is injection-molded in this way, also forms an inner ring  95 ′ that at least partially fills up cavity  65  with plastic  65 ′ and forms stop  77 . 
   Be it noted, however, that the injection molding of part  80  onto bearing tube  70  is described merely by way of example, as a preferred method for mounting bearing tube  70  on part  80 . Other methods are likewise possible. For example, part  80  could be manufactured independently of bearing tube  70 , which in that case would be press-fitted onto plastic part  80 . 
     FIG. 6  illustrates the implementation of stops  73 ,  77  in the end regions of bearing tube  70 , i.e. on its upper and lower end portions  71  and  75 , respectively, thereby defining the bearing chamber. 
     FIG. 7  is a three-dimensional illustration of bearing tube  70  with plastic part  80  mounted thereon, to illustrate outer ring  95 . 
   Many variants and modifications are of course possible, within the scope of the present invention.