Abstract:
A fan having an electronically commutated drive motor ( 27 ) has a bearing tube ( 62 ) having an inner side and an outer side. The internal stator of the drive motor ( 27 ) is arranged in the region of the outer side. An external rotor ( 28 ) of said motor interacts during operation with the internal stator ( 72 ). Fan blades ( 26 ) of the fan ( 22 ) are arranged on the outer periphery of the external rotor ( 28 ). Bearing elements ( 52, 54 ), by means of which a shaft ( 46 ) connected to the external rotor ( 28 ) is journaled, are arranged on the inner side of the bearing tube ( 62 ). Conduits ( 90 ), which enable coolant to flow through the bearing tube ( 62 ) during operation of the fan ( 22 ), are provided in the bearing tube ( 62 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a fan having an electronically commutated drive motor. 
       BACKGROUND 
       [0002]    Such fans are used principally as so-called “equipment fans” for cooling electronic devices, for example for cooling computers, servers, circuit boards, etc. Such fans must be extremely inexpensive, but, on the other hand, are expected to be highly reliable and to have a service life at least as long as the service life of the device cooled by the fan. 
         [0003]    Such fans contain a variety of elements, for example Hall sensors, ICs, transistors, capacitors, etc., as well as bearings, for example plain bearings, rolling bearings, etc. 
         [0004]    That element which is most greatly jeopardized by high operating temperatures is referred to as the “performance-determining element.” Depending on the construction of the fan, this can therefore be an electronic or a mechanical element. 
         [0005]    Higher temperatures occur in particular in fans having a plastic housing, since the heat created during operation can be dissipated only very poorly by the plastic, so that hot regions, which can also be referred to as “hot spots,” can be produced in the interior of such a fan. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the invention to make a novel heat-dissipating fan structure available. 
         [0007]    This object is achieved, according to the invention, by a fan having an internal stator, an external rotor coupled to a central shaft, rotatably journaled inside a bearing tube containing a plurality of bearings, wherein, to facilitate cooling and avoid “hot spots,” the cylindrical wall of bearing tube is formed with a plurality of conduits through which a coolant, for example air, can pass, thereby dissipating heat. Preferably, the conduits are longitudinal and mutually parallel. 
         [0008]    Coolant (i.e. generally air) can flow through the conduits, provided in the wall of the bearing tube between the internal stator and the bearing elements, so that the waste heat created in the lamination stack cannot be transferred directly to the bearing elements in the bearing tube. This is the case, in particular, for the bearing element adjacent the rotor shaft base, the temperature of which bearing element is lowered by the coolant, so that the temperature at this sensitive location can be reduced, thereby correspondingly extending the service life of the bearing element there, and thus the service life of the fan as a whole. 
         [0009]    With an appropriate design, a bearing tube of this kind can be implemented to be very light and very economical of material, but still sufficiently rigid and functionally suitable, for example in terms of cooling at critical locations. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0010]    Further details and advantageous refinements of the invention are evident from the exemplifying embodiment, in no way to be understood as a limitation of the invention, that is described below and depicted in the drawings. 
           [0011]      FIG. 1  is a perspective depiction of the housing of an axial fan prior to installation of the drive motor and the fan wheel, the bearing tube being visible at the center; 
           [0012]      FIG. 2  is a depiction analogous to  FIG. 1 , from a slightly different angle of view and at greatly enlarged scale; 
           [0013]      FIG. 3  is a depiction viewed from the underside of the depiction of  FIG. 2 , i.e. in the direction of arrow III of  FIG. 1 ; 
           [0014]      FIG. 4  depicts a rotor on which a fan wheel is arranged; 
           [0015]      FIG. 5  is a perspective depiction of housing, drive motor, and fan wheel, viewed approximately in the direction of arrow III of  FIG. 1 ; 
           [0016]      FIG. 6  is a perspective depiction of housing, drive motor, and fan wheel, viewed from a perspective similar to that of  FIG. 1 ; 
           [0017]      FIG. 7  is a longitudinal section through the assembled fan, similar to the depiction of  FIG. 5 ; 
           [0018]      FIG. 8  depicts measurement curves; this figure shows the measurements for a fan not having conduits in the bearing tube and for use of a standard rotor not having a radial fan wheel; 
           [0019]      FIG. 9  is a depiction analogous to  FIG. 8  for a fan of the same size as in  FIG. 8  but having a radial fan wheel in the rotor and having conduits in the bearing tube, although here they are closed off so that air cannot flow through them; and 
           [0020]      FIG. 10  is a depiction analogous to  FIGS. 8 and 9  for a fan of the same size as in those figures, but having a radial fan wheel in the rotor and having conduits in the wall of the bearing tube which are open, so that air can flow through them during operation, as indicated schematically in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  shows housing  20  of a typical equipment fan  22  that is depicted in the assembled state in  FIG. 6 . Fan  22  here has a fan wheel  24  having seven fan blades  26 , which are mounted on the central rotor  28  of a drive motor  27  and, in  FIG. 6 , rotate in the direction of an arrow  30 , i.e. counter-clockwise, so that in  FIG. 6  air is transported through fan  22  in the direction of an arrow  34 , i.e. from top to bottom. The result is to produce a corresponding pressure difference at fan  22 , i.e. in  FIG. 6  the pressure is greater at the bottom than at the top. Flow-through direction  34  of the transported air is also schematically depicted in  FIG. 7  for the right half of that Figure. 
         [0022]    Fan wheel  24  is depicted in  FIG. 4  from the lower (in  FIG. 6 ) side. Rotor  28  has on its outer side a pot- or bell-shaped housing  29  that is made of plastic and is integral with blades  26 , as clearly shown in  FIG. 5 . 
         [0023]    A magnetic yoke  40 , whose shape is best gathered from  FIG. 7 , is mounted in housing  29  by molding. The upper (in  FIG. 4 ) end  44  of a rotor shaft  46  is cast, by means of a suitable metal alloy  42  (e.g. ZAMAK) in a collar  41  in the center of yoke  40 . Also preferably produced in the casting operation is a small radial fan wheel  48  that keeps air moving there during operation and that improves cooling, particularly in the region of the winding ends. In some cases, such a fan wheel is not necessary, this being ascertained by experiment. Upper end  44  of shaft  46  has an annular groove  45  into which metal alloy  42  engages (see  FIG. 7 ). A multi-pole, radially magnetized ring magnet  47  is mounted in yoke  40 . 
         [0024]    Shaft  46  is journaled in two bearings  52 ,  54 , in this case in ball bearings, whose inner rings are slid onto shaft  46 . The inner ring of the lower (in  FIG. 7 ) bearing  54  is additionally retained by a snap ring  56 . 
         [0025]    The outer ring of upper bearing  52  is pressed from above into an opening  60  of a bearing tube  62  as far as a stop  64 , and the outer ring of lower bearing  54  is likewise pressed from below into an opening  66  of bearing tube  62  to the same stop  64 . The latter holds the two outer rings at a predefined spacing. 
         [0026]    Bearing tube  62  has a wall  59 , whose inner surface is designated  61  and whose outer surface is designated  63 . It is manufactured from a suitable plastic that has the requisite mechanical stability and heat resistance. It is, in this case, integral with a flange  70  whose function is to support internal stator  72  of drive motor  27  and the associated circuit board  76  for the motor electronics. This flange  70  is held by spokes  78  in outer ring  80  of housing  20 . 
         [0027]    Internal stator  72  has a lamination stack  84  equipped with a stator winding  82  (see  FIG. 7 ), which stack is pressed onto ribs  81  on the outer side  63  of bearing tube  62  as far as a stop  86  ( FIG. 2 ) so that waste heat from lamination stack  84  is transferred to wall  59  of bearing tube  62  and, via the latter, in particular to upper bearing  52  ( FIG. 7 ). 
         [0028]    Wall  59  of bearing tube  62  is equipped with, for example, ten continuous conduits  90  ( FIG. 2 ) whose angular extent alpha can be equal to, for example 25°. Extending between them are radial ribs  92  having an angular extent of, for example, 11°, i.e. the angular extent of conduits  90  is approximately 1.5 to three times the angular extent of ribs  92 . Ribs  81  are located radially outside conduits  90 . 
         [0029]    As  FIGS. 3 and 5  show, conduits  90  extend through flange  70  so that cooling air can flow, in  FIG. 7 , from the discharge (lower) side of fan  22  upward through conduits  90 , as indicated by arrows  94  schematically and only for the right side of  FIG. 7 . This air  94  cools wall  59  of bearing tube  62  and transports, upward in  FIG. 7 , the heat that travels from lamination stack  84  into bearing tube  62 . 
         [0030]    This air flows there, along arrows  96 , over the winding ends of stator winding  82 , downward between the stator poles, and then from there along arrows  98  to a gap  100  between rotor  28  and flange  70 ; there it is entrained (Venturi effect) by the air flowing past in the direction of arrows  34 , so that a continuous and powerful air circulation takes place in internal stator  72  during operation, cooling principally the upper bearing  52  and stator winding  82  and thereby lengthening the service life of fan  22  (see  FIG. 10 ). 
         [0031]    Bearing tube  62  thus has a honeycomb structure in cross section, making it possible to lengthen the service life of the fan without additional outlay. Radial fan wheel  48  (if present) causes a distribution of the circulating air in the upper (in  FIG. 7 ) part of internal stator  72 , and thereby produces uniform cooling. 
         [0032]      FIG. 8  shows measurement curves for a standard fan in which a radial fan wheel is not provided in rotor  28 , and in which a solid bearing tube, not having a honeycomb structure, is used. 
         [0033]    The symbol P designates the electrical power level, plotted on the right-hand scale in  FIG. 8 . 
         [0034]    The measured room temperature is labeled  102 , and in this case is equal to 24° C. 
         [0035]    Curve  104  is the temperature difference of stator winding  82  ( FIG. 7 ) relative to room temperature  102 , i.e. for a volumetric flow rate of zero, this temperature difference is equal to 38° K, and at 380 m 3 /h, it decreases to 22° K. 
         [0036]    Curve  106  is the temperature difference of upper ball bearing  52 , and  108  is the temperature of lower ball bearing  54 , both relative to room temperature. It is evident that the upper (in  FIG. 7 ) ball bearing  52  is hotter than lower ball bearing  54  because the upper ball bearing is being cooled less effectively. 
         [0037]      FIG. 9  shows measurement curves for a bearing tube  62  that has a honeycomb structure, but in which conduits  90  are closed off. 
         [0038]    Once again, P designates the electrical power level, the curve for which is similar to that in  FIG. 8  and is likewise plotted on the right-hand scale in  FIG. 9 . 
         [0039]    Room temperature is labeled  112  and in this case is equal to 23° C. 
         [0040]    Curve  114  is the temperature difference of stator winding  82  with respect to room temperature. 
         [0041]    Curve  116  is the temperature difference of upper ball bearing  52  with respect to room temperature. Curve  118  shows the temperature difference of lower ball bearing  54  with respect to room temperature. It is evident that upper ball bearing  52  is approximately 5° K hotter than lower ball bearing  54 . 
         [0042]      FIG. 10  shows measurement curves for a bearing tube  62  having a honeycomb structure as depicted in  FIG. 2 , conduits  90  being open, so that air flows through conduits  90  and through motor  27  as indicated schematically in  FIG. 7  by flow arrows  94 ,  96 ,  98 . Radial fan wheel  48  ( FIG. 4 ) is also provided. Once again, P designates the electrical power level. 
         [0043]    A comparison of  FIGS. 9 and 10  shows the considerable difference. 
         [0044]    Room temperature is labeled  122  in  FIG. 10 , and is equal here to 23° C. 
         [0045]    The difference between the winding temperature and room temperature is labeled  124 , and is somewhat lower than in  FIG. 9  because winding  82  is being cooled better. 
         [0046]    The temperature difference between upper ball bearing  52  and room temperature is labeled  126 , and is 10° K lower here than in  FIG. 9 , i.e. upper ball bearing  52  is being cooled substantially better in  FIG. 10  than in  FIG. 9 . 
         [0047]    The temperature difference between lower ball bearing  54  and room temperature  122  is labeled  128 . That difference is approximately 7° K less than in  FIG. 9 , i.e. bearing  54  is also being cooled substantially better, so that what results as a whole, from the measures and features according to  FIGS. 1 to 7 , is a substantially longer service life for fan  22 , without the need for additional costs for that purpose. 
         [0048]    Numerous variants and modifications are, of course, possible within the scope of the invention.