Abstract:
For many applications, it is desirable to use fans which weigh less than 30 grams and are driven by electric motors not more than a few centimeters in size. Mass-producing products this small, which nevertheless must be extremely reliable, poses unique manufacturing challenges, which are best overcome by an improved structure which is susceptible to automation. Preferably, the fan motor is electronically commutated and has an internal stator ( 50 ) and an external rotor ( 22 ) supported on a central rotor shaft ( 34 ). The shaft is journaled within a bearing tube ( 70 ) supporting first and second rotor bearings ( 72, 76 ). By injection-molding the bearing tube ( 70 ) with first and second axial extensions ( 90′, 90″ ), the extensions can hold the bearings in place and insure uniform manufacturing quality and a desirably long service life. One of the extensions can also be shaped to abut against a circuit board ( 46 ) which supports components which control commutation.

Description:
CROSS-REFERENCE 
       [0001]    This application claims priority of German application DE 20 2006 002 068.3, filed 3 Feb. 2006, the entire content of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to an electronically commutated motor, in particular to a miniature or subminiature motor. Such motors are preferably used in miniature or subminiature fans. 
       BACKGROUND 
       [0003]    Miniature and subminiature fans usually 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 less than 30 grams. The motors are correspondingly even smaller and weigh even less than the fans of which they are a part. 
         [0004]    With such motors, assembly must be simple and uncomplicated, in order to allow cost-effective manufacture by means of a high level of automation. Uniform quality, which is a prerequisite for a long average service life, can moreover be achieved by extensive automation. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the invention to make available a novel miniature or subminiature motor. 
         [0006]    According to the invention, this object is achieved by an electronically commutated motor having an external rotor supported on a rotor shaft, an internal stator including a stator lamination stack defining a plurality of axial slots, and a plastic layer which extends through the slots and also forms a bearing tube for receiving the rotor shaft, the bearing tube being formed with at least one recess which holds in place a respective rolling bearing for journaling the rotor shaft. According to a method aspect of the invention, this plastic element can be injection-molded. A motor of this kind can, in particular, be made very compact, and enables operation at high rotation speeds, i.e. high output. The manufacturing steps can be automated, thereby assuring consistent results and a desirably long service life. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0007]    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 depicted in the drawings. In the drawings: 
           [0008]      FIG. 1  is a longitudinal section through a fan that is driven by a miniature or subminiature motor according to an embodiment of the invention; 
           [0009]      FIG. 2  is a greatly enlarged top view of the hub of the fan of  FIG. 1 ; 
           [0010]      FIG. 3  is a longitudinal section, shown in perspective, through the air-directing tube of the fan of  FIG. 1 , with a depiction (likewise in perspective) of the internal stator; 
           [0011]      FIG. 4  is a perspective depiction of the internal stator of  FIG. 1 , with a circuit board and MOSFET (MOS Field Effect Transistor)  48  arranged thereon; 
           [0012]      FIG. 5  is a side view of the internal stator of  FIG. 4 ; 
           [0013]      FIG. 6  is a sectioned view of the internal stator of  FIG. 4  with one of the two roller bearings, and with a stator winding; 
           [0014]      FIG. 7  is a sectioned view of the internal stator of  FIG. 6  with both rolling bearings; 
           [0015]      FIG. 8  is a side view of the internal stator of  FIG. 1  with injection-embedded connector elements  96 ; 
           [0016]      FIG. 9  is a top view of the internal stator of  FIG. 8 , looking in the direction of arrow IX of  FIG. 8 ; 
           [0017]      FIG. 10  is a section looking along line X-X of  FIG. 9 ; 
           [0018]      FIG. 11  is a section looking along line XI-XI of  FIG. 9 ; 
           [0019]      FIG. 12  is a perspective depiction of the internal stator of  FIG. 4  at approximately actual size; and 
           [0020]      FIG. 13  is a longitudinal section through the fan of  FIG. 1 , at approximately actual size. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    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. 
         [0022]      FIG. 1  is a longitudinal section through an axial fan  20  having a motor  21  according to a preferred embodiment of the invention, at greatly enlarged scale (enlarged approximately five times). To illustrate the small dimensions necessary for miniature and subminiature fans, fan  20  is shown in  FIG. 13 , by way of example, at a scale of approximately 1:1. 
         [0023]    Motor  21  is arranged in an air-directing tube  80  and has an external rotor  22  and an internal stator  50 . External rotor  22  has a rotor cup  24  on whose outer periphery is provided a fan wheel  23  having fan blades  26 . Mounted on the inner periphery of rotor cup  24 , on a soft-ferromagnetic yoke element  27 , is a rotor magnet  28  that can be magnetized, for example, with four poles. Rotor cup  24  has a base  30  in which an upper shaft end  32  of a rotor shaft  34  is mounted, which shaft has a lower, free shaft end  35 . Shaft  34  is preferably made of steel, and rotor cup  24  of plastic. Rotor cup  34  is mounted on upper shaft end  32  by plastic injection molding. 
         [0024]    Internal stator  50 , which is described in detail in  FIGS. 2 to 11 , has a stator lamination stack  52  having a plastic coating  77 , which together form a bearing tube  70  for journaling of rotor shaft  34 . Arranged for this purpose at one end  71 ′ of stator lamination stack  52  is a plastic part  90 ′ therein, in the form of a first axial extension of plastic coating  77 , having a bearing  72 . Arranged at the other end  71 ″ of stator lamination stack  52  is a plastic part  90 ″ in the form of a second axial extension in which a bearing  76  is present. 
         [0025]    According to a preferred embodiment of the invention, plastic coating  77  and extensions  90 ′ and  90 ″ are formed integrally, bearing  72  being held in extension  90 ′ by plastic injection molding, the shape of the molded element form-lockingly defining the alignment of the bearing with respect to the rotor shaft which it journals. As an alternative thereto, extension  90 ′ can be formed as a separate component, in such a way that bearing  72  can be anchored in it by being pressed in. Extension  90 ′ can, in this case, be manufactured independently of plastic coating  77  and, in a simple working step, e.g. press-fitted thereon. Extension  90 ′ can comprise, for this purpose, one or more guidance elements that facilitate such a press-fitting operation. Bearing  76  can likewise optionally be injection-embedded into extension  90 ″ or pressed into it. 
         [0026]    Bearings  72  and  76  are preferably implemented as rolling bearings, but are not limited to a specific bearing type. A variety of bearing types can instead be used, for example, plain bearings. Rolling bearing  72  has an inner ring  72 ′ and an outer ring  72 ″, and rolling bearing  76  has an inner ring  76 ′ and an outer ring  76 ″. Rotor shaft  34 , rotatably journaled in rolling bearings  72  and  76 , is held therein by means of an abutment or retaining element  92  and a compression spring  94 . Abutment  92 , for example a snap washer or other latching member, is snapped into an annular slot at lower end  35  of shaft  34 . Tensioned spring  94  is held between inner ring  72 ′ of rolling bearing  72  and latching member  92 . A conical extension of base  30  of rotor cup  24  is pressed by said spring against inner ring  76 ′ of rolling bearing  76 , so that shaft  34  is held with dynamic tension in rolling bearings  72  and  76  of internal stator  50 . This action of spring  94  is assisted by the fact that rotor magnet  28  is offset downward, with respect to stator lamination stack  52 , thereby creating a magnetic pull on external rotor  22  which pulls the latter upward with reference to  FIG. 1 . 
         [0027]    Arranged on outer periphery  74  of extension  90 ′ is a circuit board  46  having a relatively large electronic component  48 , e.g. a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), that is provided to control the current in a stator winding  97  of motor  21 . Further electronic components, e.g. a Hall IC (Integrated Circuit), can likewise be arranged on circuit board  46 , onto which connector elements  96  for stator winding  97  are soldered. These connector elements  96  are supported in a shoulder  95  of extension  90 ′ by plastic injection molding. 
         [0028]    The lower end of extension  90 ′ is secured to a hub  85  by being pressed in, and can additionally be adhesively bonded and/or welding thereonto. Struts  86 ′ and  86 ″, which support air-directing tube  80 , extend from this hub  85 . 
         [0029]      FIG. 2  is a top view of hub  85  of fan  20  of  FIG. 1 .  FIG. 2  illustrates struts  86 ′,  86 ″, and  86 ″′ arranged between hub  85  and air-directing tube  80 , as well as extension  90 ′ whose exposed end is connected to hub  85 . 
         [0030]      FIG. 3  is a perspective longitudinal section through air-directing tube  80  of fan  20 , with a perspective depiction of internal stator  50 .  FIG. 3  illustrates the assembly of fan  20  according to a preferred embodiment, in which, in a first step, circuit board  46  having component  48  thereon is arranged on internal stator  50 , and the latter is then mounted on hub  85  in a further step. As is apparent from  FIG. 3 , internal stator  50  comprises, for example, four spacers  59 ′,  59 ″,  59 ″′,  59 ″″. These serve to prevent damage to stator winding  97  when internal stator  50  is pressed into hub  85 . 
         [0031]      FIG. 4  is a three-dimensional view of internal stator  50  ( FIG. 3 ) enlarged approximately ten times. Internal stator  50  is shown for illustrative purposes in  FIG. 12 , by way of example, at a scale of approximately 1:1. 
         [0032]      FIG. 4  shows circuit board  46 , abutting against shoulder  95  of extension  90 ′, onto which board connector element  96 ′ is soldered, and also shows rolling bearing  76  mounted in extension  90 ″. To facilitate the pressing of rolling bearing  76  into extension  90 ″, the latter has two recesses  75 ′ and  75 ″ at its upper end. 
         [0033]    Stator lamination stack  52  contains laminations, three of which are labeled  55 ′,  55 ″, and  55 ″′. Stator lamination stack  52  is “packeted,” i.e. its plates or laminations have small holes that are stamped with mating bosses, so that they form an aligned, unitary block. The plastic of plastic coating  77 , which plastic is injected into stator lamination stack  52  and, together therewith, forms bearing tube  70 , can also stabilize and contribute to the strength of this block. As shown in  FIG. 4 , this plastic constitutes strip-shaped plastic facings  79  (two plastic facings being labeled  79 ′ and  79 ″ by way of example) at locations on the outer side of lamination stack  52 , which facings further enhance strength. 
         [0034]    As shown in  FIG. 9 , stator lamination stack  52  has salient stator poles  52 ′,  52 ″,  52 ″′,  52 ″″ that are separated from one another by slots  54 ′,  54 ″,  54 ″′,  54 ″″ through which plastic coating  77  extends. Stator winding  97  is arranged on stator poles  52 ′,  52 ″,  52 ″′,  52 ″″ (cf.  FIG. 4 ). 
         [0035]      FIG. 5  is a side view of internal stator  50  of  FIG. 4 , but without winding  97 , and illustrates shoulder  95  of extension  90 ′, in which shoulder connector element  96 ′ is mounted. In the region of extension  90 ′ in which component  48  is arranged on circuit board  46 , said extension has a recess  99 . 
         [0036]      FIG. 6  is a longitudinal section through internal stator  50 , and illustrates recess  99  as well as bearing tube  70  formed by plastic coating  77  and stator lamination stack  52 . 
         [0037]    Plastic coating  77  forms, at lower end  71 ′ of stator lamination stack  52 , an end layer  73 ′ on which axial extension  90 ′ is arranged. The latter has a recess or compartment  91  in which first rolling bearing  72  is arranged. Recess  91  is formed with a first shoulder  91 ′ and a second, opposing shoulder  91 ″. As mentioned with reference to  FIG. 1 , at least outer ring  72 ″ of this rolling bearing  72  is injection-embedded into the plastic of extension  90 ′. For this purpose, prior to plastic injection molding, a first tool is guided from above through stator lamination stack  52  and immobilizes the upper rim of said outer ring  72 ″. The latter&#39;s lower rim is immobilized by a second tool coming from below. The two tools seal off rolling bearing  72 , in such a way that no plastic can penetrate into bearing  72  during plastic injection. 
         [0038]    At upper end  71 ″ of stator lamination stack  52 , plastic coating  77  forms an end layer or terminal disk  73 ″ on which axial extension  90 ″ is arranged. As is apparent from  FIG. 6 , plastic coating  77  and extensions  90 ′ and  90 ″ are preferably formed integrally. Extension  90 ″ has an opening  93  for the reception of rolling bearing  76 . The latter is preferably pressed into opening  93  (cf.  FIG. 7 ). 
         [0039]      FIG. 7  is a sectioned view of internal stator  50  with both rolling bearings  72  and  76 . 
         [0040]      FIG. 8  is another side view, analogous to  FIG. 5 , of internal stator  50 . In contrast to the side view of  FIG. 5 , internal stator  50  is rotated 45° to the right in  FIG. 8 , and is depicted without circuit board  46  and component  48 . Slot  54 ″″ located between stator poles  52 ′ and  52 ″″, and connector elements  96 ″″ and  96 ″′ injection-embedded into shoulder  95 , are thus visible in  FIG. 8 . Said connector elements are preferably implemented as bronze pins. 
         [0041]      FIG. 9  is a top view of internal stator  50 .  FIG. 9  shows a preferred embodiment of stator lamination stack  52  equipped with plastic coating  77 , and illustrates slots  54 ′,  54 ″,  54 ″′, and  54 ″″ provided between poles  52 ′,  52 ″,  52 ″′, and  52 ″″. 
         [0042]    As is apparent from  FIG. 9 , end layer  73 ′ of plastic coating  77  has cutouts  56 ′,  56 ″,  56 ″′, and  56 ″″ at the axial ends of slots  54 ′,  54 ″,  54 ″′, and  54 ″″. End layer  73 ″ located opposite end layer  73 ′ analogously has cutouts  58 ′,  58 ″,  58 ″′, and  58 ″″. These cutouts at both ends allow stator winding  97  (not shown in  FIG. 9 ) to be arranged on stator lamination stack  52 . 
         [0043]    All the poles  52 ″,  52 ″,  52 ″′, and  52 ″″ have an identical configuration. To simplify matters, only the configuration of pole  52 ′ will therefore be described. The latter has a pole core  12  and a pole shoe having pole ends or pole horns  14 ,  16 . Pole horn  16 , onto which plastic facing  79 ′ is applied, has a smaller diameter than pole horn  14 . This conformation is usually referred to as a “reluctance lamination form,” and serves to generate a so-called “reluctance torque.” For interaction with this stator shape, rotor magnet  28  has a trapezoidal magnetization. 
         [0044]      FIG. 10  is a sectioned view of internal stator  50  along section line X-X of  FIG. 9 , and  FIG. 11  is a sectioned view of internal stator  50  along section line XI-XI of  FIG. 9 .  FIG. 11  illustrates cutouts  56 ′,  56 ″′ in end layer  73 ′ at end  71 ′ of lamination stack  52 , as well as cutouts  58 ′,  58 ″′ in end layer  73 ″ at its end  71 ″. 
         [0045]    It has been found that, as a result of the type of journaling described, the fan depicted in  FIG. 13  can be operated at a rotation speed of 15,000 rpm. Many variants and modifications are of course possible within the scope of the present invention.