Abstract:
A method of rapidly assembling the rotor ( 22 ) of an external-rotor motor ( 20 ) onto a bearing support tube ( 70 ) and in a predetermined axial position relative to the latter, includes the steps of: beginning at a rotor cup portion ( 24 ) of the rotor ( 22 ), mounting on a rotor shaft ( 28 ): a compression spring ( 48 ), a retaining washer ( 50 ), and a plurality of rolling bearings ( 52, 60 ); then pressing into the bearing support tube ( 70 ), by means of a pressing-in force (K), the rotor ( 24 ), with the elements mounted thereon, the compression spring ( 48 ) being compressed so that the rotor cup presses the washer ( 50 ) into the tube ( 70 ); subsequently removing the pressing-in force (K), and displacing the rotor shaft ( 28 ) by means of the compression spring ( 48 ) within the bearings ( 52, 60 ) so that the rotor ( 24 ) assumes the desired predetermined axial position, relative to the tube ( 70 ).

Description:
CROSS-REFERENCE 
   This application is a § 371 of PCT/EP03/010139, filed 12 Sep. 2003 and published 10 Jun. 2004 as WO 2004/048791-A1. The application claims priority from DE 102 54 949.4, filed 26 Nov. 2002, the entire disclosure of which is incorporated by reference. 
   FIELD OF THE INVENTION 
   The invention concerns an external-rotor motor, and it concerns a method for assembling an external-rotor motor. 
   BACKGROUND 
   In many external-rotor motors, the shaft of the external rotor is supported in a so-called bearing support tube on whose outer side a stator lamination stack is mounted. The shaft is usually mounted on the hub of a so-called rotor cup, and is supported within the bearing support tube by means of bearings, e.g. sintered bearings or rolling bearings. The type of bearing system depends principally on the desired service life of the motor and the desired smoothness. 
   For installation of the shaft, the bearing support tube usually has, on its side facing away from the rotor cup, an opening where components are located that serve to retain or support the shaft, e.g. a thrust bearing, spring member, retaining washer, bearing cover, or the like. Dirt can penetrate through this opening and shorten the service life of such a motor. Time is also needed for assembly, making such motors more expensive. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to make available a novel external-rotor motor, and a new method for assembling such a motor. 
   According to a first aspect of the invention, this object is achieved by means of an external-rotor motor in which a compression spring, a retaining washer, and a pair of rolling bearings are pre-mounted on the shaft of the rotor, and assembly can be completed by simply sliding the rotor assembly into a bearing support tube in the stator assembly, the lip of the retaining washer serving as a pawl to latch the structure together. In such a motor, the bearing support tube can be largely closed, so that dirt cannot penetrate there. It is also inexpensive to install. 
   According to another aspect of the invention, this object is achieved by applying compression force to the rotor assembly to compress the spring and to drive the bearings and retaining washer into the bearing support tube, then removing the pressure, thereby allowing the spring to clamp the rolling bearings in place, relative to the rotor shaft. Assembly in this fashion requires only a small number of working steps and can be largely or even completely automated. An advantageous refinement of this method is to provide an annular axial projection on the rotor cup, surrounding the spring, to transfer the pressing force to an outer ring of the nearest rolling bearing. The risk of damage to the rolling bearings upon installation is thus reduced. 

   
     BRIEF FIGURE DESCRIPTION 
     Further details and advantageous refinements of the invention are evident from the exemplary embodiment, in no way to be understood as a limitation of the invention, that is described below and depicted in the drawings. 
       FIG. 1  depicts, in longitudinal section, the essential parts of the external rotor of an external-rotor motor; 
       FIG. 2  is a depiction analogous to  FIG. 1  in which, however, various elements for a subsequent installation operation are pre-installed on the shaft of the external rotor; 
       FIG. 3  is a longitudinal section through a bearing support tube provided on the stator of the motor, viewed along line III—III of  FIG. 4 ; 
       FIG. 4  is a plan view of the open, proximal end of the bearing support tube, viewed in the direction of arrow IV of  FIG. 3 ; 
       FIG. 5  is a depiction analogous to  FIG. 4  in which, however, a circuit board and a stator lamination stack provided with a stator winding are pre-installed on the bearing support tube; 
       FIG. 6  is a schematic depiction showing a snapshot during the “marriage” of stator and rotor; 
       FIG. 7  is a longitudinal section through an assembled motor that can be used, for example, to drive an equipment fan; 
       FIG. 8  is a section through a so-called retaining washer, viewed along line VIII—VIII of  FIG. 9 ; and 
       FIG. 9  is a plan view of the retaining washer, viewed in the direction of arrow IX of  FIG. 8 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows an external rotor  22  for an external-rotor motor  20  as depicted in  FIG. 7 . External rotor  22  has a rotor cup  24  that is usually manufactured from plastic or a lightweight metal. 
   The parts that are facing toward rotor cup  24  will be referred to hereinafter, by analogy with medical terminology, as “proximal,” and the parts facing away from rotor cup  24  as “distal.” 
   Mounted in the center of rotor cup  24 , i.e. on its hub  36 , is proximal end  26  of a shaft  28  at the distal end of which is provided an annular groove  30  that serves, as shown in  FIG. 2 , for mounting of a snap ring  32 . The distal end of shaft  28  is labeled  34 . Shaft  28  has a cylindrical cross section, and its diameter is constant over practically the entire length. Located on hub  36  is an axial projection  38  that protrudes in the distal direction away from hub  36  and has a depressed region  39  in its center. 
   A magnetic yoke in the form of a sheet-metal ring  40  made of soft iron is mounted in rotor cup  22 , and on the ring&#39;s inner side is located a (usually flexible) ring  44  made of permanent-magnetic material, usually a so-called rubber magnet, i.e. a mixture of ferromagnetic particles and an elastomer. Ring  44  is magnetized in the radial direction with the requisite number of magnetic poles, e.g. with four poles as is common practice in the art. 
   As shown in  FIG. 2 , a variety of components are pre-installed on shaft  28  prior to the assembly of motor  20 . 
   Beginning at projection  38 , the first is a compression spring  48  of approximately conical shape whose proximal, larger-diameter end lies in depression  39 . 
   Following spring  48  in the distal direction is an annular retaining member in the form of a retaining washer  50 , as described in more detail below with reference to  FIGS. 8 and 9 . Spring  48  preferably is not in contact against this retaining member  50 . 
   Retaining member  50  is followed by a proximal rolling bearing  52  comprising an outer ring  54  and an inner ring  56 . The latter is displaceable in the axial direction on shaft  28  with a small clearance. The distal end of spring  48  is in contact against the proximal end of inner ring  56 . Rolling bearing  52  is followed in the distal direction by a spacer  58 , which is guided displaceably on shaft  28  by means of a radially inwardly protruding projection  59 , and whose proximal end is in contact, as depicted, against the distal end of outer ring  54 . 
   Spacer  58  is followed by a distal rolling bearing  60  comprising an outer ring  62  that is in contact with its proximal end against spacer  58 , and comprising an inner ring  64  that is displaceable in the axial direction on shaft  28  with a small clearance and is in contact with its distal end, as depicted, against snap ring  32  when motor  20  is completely assembled. (optionally, a spacer or the like can also be located between snap ring  32  and rolling bearing  60 , e.g. in order to compensate for tolerances.) 
   It is immediately apparent that by pressing with a force F in the proximal direction on distal rolling bearing  60 , spring  48  can be compressed and the two rolling bearings  52  and  60 , spacer  58 , and retaining washer  50  can be displaced in the proximal direction on shaft  28 , so that inner ring  64  is no longer in contact against snap ring  32  but becomes spaced away from it. In this case projection  38  of rotor cup  24  comes into contact against retaining washer  50  and allows an axial force to be transferred via the latter, in the distal direction, onto retaining washer  50 , outer ring  54 , spacer  58 , and outer ring  62  when rotor cup  24  is pressed downward, i.e. in the distal direction, by a force K upon assembly. This is depicted below in  FIG. 6 . 
     FIG. 3  shows bearing support tube  70  of external-rotor motor  20 , which tube is usually manufactured from plastic or a lightweight metal. In this embodiment it has at the bottom a flange  72  that serves to mount motor  20 , e.g. to mount it on a fan housing or some other device to be driven. 
   Bearing support tube  70  has on its outer side a shoulder  74 , and adjacent thereto in the proximal direction a circumferential surface  76  that tapers toward the top in frustoconical fashion. 
   On its inner side  78 , bearing support tube  70  has six longitudinal ribs  80  that end at a distance d from the closed distal end  82  of bearing support tube  70 . They are followed in the distal region by a total of eight ribs  84  whose proximal ends form, during assembly, a stop for outer ring  62  of distal ball bearing  60  (see  FIG. 7 ). These ribs  84  taper in the proximal direction so that distal end  34  of shaft  28  has sufficient room during assembly (see  FIG. 6 ). The bearing support tube has projections  86  at its upper, proximal end (see  FIG. 6 ). 
     FIG. 5  shows the manner in which a stator lamination stack  90  is mounted on bearing support tube  70 . Lamination stack  90  has for this purpose a coil former  92  made of plastic into which a stator winding  94  is wound. A circuit board is indicated at  93 .  FIG. 5  shows two winding ends  95 ,  96  that are soldered respectively onto an associated metal pin  98  and  97 . Coil former  92  has, as depicted, an inwardly protruding projection  100  with which it is pressed onto outer side  76  of bearing support tube  70 . 
     FIG. 6  shows a snapshot, so to speak, during the “marrying” operation in which shaft  28  of rotor  22 , with rolling bearings  52 ,  60  located thereon, is introduced for the first time into inner recess  78  (see  FIG. 3 ) of bearing support tube  70 . 
   In this context, a force K is applied in the distal direction onto rotor  22 , and because outer rings  54 ,  62  of rolling bearings  52 ,  60  are pressed with a press fit into ribs  80  (see  FIG. 3 ) of bearing support tube  70 , spring  48  is compressed by force K so that shaft  28  is displaced in the distal direction within ball bearings  52 ,  60 , and projection  38  pushes via retaining washer  50  on outer ring  54  of ball bearing  52 , and via spacer  58  also on outer ring  62  of ball bearing  60 , and thus presses the two ball bearings  52 ,  60  into bearing support tube  70 . As depicted in  FIG. 6 , spring  48  is only partly compressed in this process in order to prevent damage to it. 
   The pressing-in operation continues until outer ring  62  of distal ball bearing  60  is in contact against the proximal ends of ribs  84 . 
   In this context, as depicted, retaining member  50  is displaced in bearing support tube  70  in the distal direction, i.e. downward, and digs into the material of bearing support tube  70  so that the entire bearing arrangement is latched or locked in bearing support tube  70 . If an attempt were made to pull rotor  22  out of bearing support tube  70  oppositely to force K, retaining member  50  would only dig that much more deeply into the material of bearing support tube  70 , so that the attachment here is therefore extraordinarily secure. There are, of course, many different solutions and components for a permanent latching system of this kind, and retention member  50  that is depicted therefore represents only a preferred embodiment. 
   After the pressing-in operation is complete, force K is removed and the result then is as shown in  FIG. 7 , i.e. spring  48  again presses shaft  28  upward in the proximal direction until snap ring  32  is again in contact against inner ring  64  of distal rolling bearing  60 . The marriage is then complete. Spring  48  now clamps the two inner rings  56 ,  64  of rolling bearings  52 ,  60  against one another, which is favorable in terms of quiet operation of motor  20 . 
     FIGS. 8 and 9  show a preferred embodiment of a retaining member  50 . This has in the middle an opening  110  for the passage of shaft  28  and of the distal end of compression spring  48 . Opening  110  is located in a flat part  112  that is adjoined toward the outside by a frustoconical portion  114  whose upper (in  FIG. 8 ) end  116  digs into the material of bearing support tube  70  upon assembly because its diameter is greater than the inside diameter of bearing support tube  70 . 
   Portion  114  could be divided, by slots that extend in the axial direction, into a plurality of individual prongs. In this case an annular retaining member of this kind can also be referred to as a prong washer or prong ring. It is usually not necessary, however, to provide such individual prongs. It can also be very advantageous to implement spring  48  and retaining member  50  together as a single component. These parts can, for example, be welded together, or spring  48  can be machined directly out of the material of retaining washer  50 . In other ways as well, many variants and modifications are possible in the context of the present invention.