Abstract:
A mixed-flow fan features a housing ( 42 ); an impeller ( 43 ) journaled rotatably with respect to the housing, and equipped with fan blades ( 54 ); a generally cylindrical air conduit ( 50 ) defined between the fan housing and the impeller, the fan blades extending into the air conduit in order, during operation, to transport air; an external-rotor motor ( 75 ) having an internal stator ( 100 ) and an external rotor ( 74 ) which includes a tubular ferromagnetic yoke ( 63 ) partly embedded in material of the impeller. A cup-shaped yoke ( 72 ) fits into a central cavity ( 68 ) of the tubular yoke ( 63 ) and accommodates a permanent magnet arrangement ( 66 ) which interacts with the stator. The tubular yoke ( 63 ) and the cup-shaped yoke ( 72 ) together serve as a magnetic return path for the external-rotor motor. The structure minimizes damage during final assembly, and simplifies insertion of balancing weights.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from our German application DE 20 2010 015 749.8, which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a mixed flow fan which outputs air partly in an axial direction and partly in a radial direction. 
       BACKGROUND 
       [0003]    Such a mixed-flow or “diagonal” fan is known from DE 41 27 134 84 and corresponding U.S. Pat. No. 5,695,318, HARMSEN, issued 9 Dec. 1997. The fan has a housing that defines, together with the fan wheel of the mixed flow fan, an air flow conduit, within which the fan blades provided on the fan wheel rotate. The fan wheel is also often referred to as an “impeller.” 
         [0004]    The enveloping curve of the fan wheel has, for example, a frusto-conical shape, or the shape of a spherical cap. If the drive motor is an external-rotor motor, the hub of the fan wheel is nonrotatably connected to the external rotor of the motor. There remains, between the outer side of the external rotor and the outer side of the fan wheel, an annular cavity, on whose periphery are provided pockets for insertion of balancing weights. It is well known, in the rotating machine art, that rotors wobble the least, and operate most smoothly, when the rotor&#39;s center of mass coincides with the central axis of the rotor, and supplemental balancing weights are inserted, when necessary, to adjust for undesired asymmetries which may occur due to manufacturing variations and the like. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the invention to provide a novel mixed-flow fan structure. 
         [0006]    According to the invention, this structural object is achieved with an external-rotor drive motor in which the rotor includes a tubular ferromagnetic yoke, embedded at one point in material of the impeller of the fan, and defining a central cavity in the impeller, into which fits a generally cup-shaped yoke having a permanent magnet arrangement inside, with the result that the permanent magnet arrangement magnetically interacts with the internal stator of the motor, and the tubular yoke and the cup-shaped yoke together serve as a ferromagnetic return path for the external-rotor motor. 
         [0007]    The tubular ferromagnetic yoke performs, on the one hand, a magnetic function for the motor and, on the other hand, forms a kind of mechanical reinforcing backbone for the impeller; these functions do not interfere with one another. At the same time, this part also acts as a cooling element for the motor, which dissipates heat outward, and thereby tends to prevent or counteract formation of hot spots in the interior of the impeller. 
         [0008]    Another manner of achieving the stated object is to structure the fan wheel with blades projecting outward from a generally concave or hemi-spherical hub formed with a first plurality of pockets for insertion of balancing weights, in a first plane near the air inlet end, and a second plurality of pockets for insertion of balancing weights, in a second plane near the air discharge or outlet end of the fan wheel, and to connect the respective portions, formed with the balancing pockets, by a first plurality of generally curved longitudinal ribs and at least one second rib, extending circumferentially, and connecting together the longitudinal first ribs. The facts that, on the one hand, ribs are provided in the annular cavity and extend therein from inside to outside and, on the other hand, that at least one rib proceeding in a circumferential direction is provided, which rib connects at least some of the ribs proceeding from inside to outside into a kind of ribbed vault, for example such as a reticulated vault, define between the ribs many small pockets that, in contrast to large pockets as found in the prior art, do not cause strong turbulence. The reason this novel structure was chosen is that strong turbulence would decelerate the fan wheel, and thereby cause a considerable power loss, which would decrease the fan performance and cause the external-rotor motor and its electronics to reach their upper performance limit already at low rotation speeds, so that the fan performance would be low. 
         [0009]    In a mixed flow fan of this kind, the improved fan wheel can be manufactured with little outlay, for example as a cast or an injection-molded part, and once the fan wheel has been connected to the rotor of the external-rotor motor, it needs only to be balanced, which in this case is particularly simple, because balancing pockets for two parallel, spatially-separated, balancing planes (each orthogonal to the rotor axis) are reachable from the air-discharge side of the fan wheel. Procedures for two-plane balancing are known, for example from the document published Jan. 18, 2011 at the National Instruments website, www.ni.com, entitled “ Two - Plane Balancing Using LabVIEW PDA and NI CF -6004  CompactFlash Data Acquisition Card.”   
         [0010]    A further manner of achieving the stated object is to structure the external-rotor motor with an internal stator and an external rotor, the rotor including a tubular ferromagnetic yoke formed near the air inlet end with a splayed or widened end which is accessible, during the assembly process, from the air inlet side of the fan wheel. A smaller-diameter cup-shaped ferromagnetic yoke, which accommodates, in its interior, a permanent magnet arrangement, is adapted to be press-fitted into one end of the tubular yoke. The tubular yoke and the cup-shaped yoke together serve as a magnetic return path for the permanent magnet arrangement. Assembly of the fan is made substantially easier as a result of this configuration, since introduction of the cup-like ferromagnetic yoke into the tubular ferromagnetic yoke sometimes requires considerable force, which could result in damage to the impeller; and because the tubular ferromagnetic yoke is accessible from the outer side of the impeller, it can be braced directly from the outer side of the impeller so that, with this structure, no deforming mechanical forces are exerted on the impeller during assembly, and damage to the impeller is thus reliably avoided. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0011]    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. 
           [0012]      FIG. 1  is a three-dimensional depiction of a preferred embodiment of a mixed flow fan, 
           [0013]      FIG. 2  is an exploded depiction of parts of the fan and its axis, 
           [0014]      FIG. 3  is a plan view of the upper side of the fan, and of the impeller mounted on the rotor, in the context of the mixed flow fan of  FIG. 1 , looking in the direction of arrow III of  FIG. 1 , 
           [0015]      FIG. 4  is a plan view of the lower side of the rotor and the impeller of the fan of  FIG. 3 , and of the networked or ribbed vault provided there, 
           [0016]      FIG. 5  shows a highly enlarged portion of  FIG. 4 , 
           [0017]      FIG. 6  is a three-dimensional depiction of the ribbed vault of  FIGS. 4 and 5 , 
           [0018]      FIG. 7  shows an enlarged portion of  FIG. 6 , 
           [0019]      FIG. 8  is a three-dimensional depiction analogous to  FIG. 7 , 
           [0020]      FIG. 9  is a three-dimensional depiction analogous to  FIG. 6 , 
           [0021]      FIG. 10  is a longitudinal section through the blank of an impeller in the state prior to installation thereof, according to a preferred embodiment of the invention, looking along line X-X of  FIG. 3 , 
           [0022]      FIG. 11  is a longitudinal section, analogous to  FIG. 10 , during press-fitting of the external rotor into the impeller, 
           [0023]      FIG. 12  depicts the impeller, after the external rotor has been press-fitted, but before installation of a radial fan wheel whose function is to transport cooling air through the drive motor of the mixed flow fan, 
           [0024]      FIG. 13  is a longitudinal section through a first variant of the impeller, and 
           [0025]      FIG. 14  is a longitudinal section through a second variant of the impeller. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  is a perspective depiction of a mixed flow fan  40 , and  FIG. 2  shows parts of such a fan in an exploded view, in order to facilitate comprehension. 
         [0027]    Fan  40  has a housing  42  in which a fan rotor  43 , which is usually referred to as an “impeller,” is arranged. A plastic part  46  is installed in housing  42  on inlet side  44 . This part defines the outer edge or wall of an air conduit  50  that extends from inlet  44 , in a frusto-conical manner, to an air discharge outlet  52 . Housing  42  has an upper part  53  that is connected, via connecting elements  45 , to a base part  47  through which an electrical connector lead  49  extends outward. Base part  47  is highlighted in gray. 
         [0028]    The inner edge or wall of air conduit  50  is defined by the approximately dome-shaped or spherical-cap-shaped outer surface  56  of fan rotor  43  ( FIG. 2 ). Fan blades  58  are mounted on this outer side  56 . They rotate in the direction of an arrow  60 , i.e. clockwise with reference to  FIGS. 1 and 2 . The flow direction of the air is indicated by an arrow  61 , i.e. air is driven from top to bottom in  FIG. 1 . 
         [0029]    Fan rotor  43  has at the bottom, in  FIGS. 10 and 11 , an approximately cylindrical portion  59  on whose inner side are provided balancing pockets  62  for a first balancing plane P 1  orthogonal to the rotor axis. In a balancing operation, so-called balance weights (not shown) are inserted into these pockets, in a manner known to having ordinary skill in the art. Alternatively, other methods can also be used for balancing. 
         [0030]    Blades  58  are preferably arranged in an overlapping configuration. Together with fan rotor  43 , they form the impeller of fan  40 . The impeller is preferably manufactured by plastic casting. Mounted in it is a portion of a tubular yoke  63 , made of ferromagnetic material, that extends almost to the upper side of impeller  43 . Part  63  is part of a magnetic return path for a rotor magnet  66  that is shown in  FIG. 2 . 
         [0031]    At its outer (left) end in  FIG. 10 , tubular part  63  is deformed into an outwardly projecting flange or rim  67  that is, for example, embedded into material of impeller  43  and thereby anchored therein. For example, rim  67  can be placed in plastic which later hardens. 
         [0032]    Tubular part  63  is also referred to as a “circular blank.” It defines, within its inner surface, a cavity  68  having a wall  70 . Provided on wall  70  are flat elevations or bosses  71  that can have, for example, a height of approximately 0.1 to approximately 0.3 mm and a diameter of, for example, 5 mm. Approximately six elevations  71  are usually sufficient; in  FIG. 10  they are arranged adjacent the left end of part  63 , and are distributed evenly around the circumference of part  63 . 
         [0033]    As  FIG. 11  shows, the cup-shaped magnetic yoke  72  of an external rotor  74  is press-fitted, from the right, into cavity  68  in the interior of tubular part  63 . Serving this purpose is a press-fit force F 1  that is exerted by a suitable auxiliary tool (not shown) onto the cup-shaped yoke  72 . 
         [0034]    In order to enable press-fitting, tubular part  63  is braced by means of a counterforce F 2  that engages against the outwardly projecting rim  67  of part  63 . This rim  67  is therefore not located in the interior of impeller  43 , i.e. is not cast into it, so that a retainer (not shown) can engage against the rim  67  and can exert counterforce F 2  onto part  63 . 
         [0035]    Impeller  43  has for this reason, on its upper (in  FIG. 1 ) side  44 , an annular opening  76 ′ through which direct access to rim  67  is possible. If applicable, this annular opening  76 ′ can also be implemented in the form of a plurality of shorter openings, through which corresponding parts of a retainer can be introduced. 
         [0036]    When external rotor  74  is press-fitted, its outer side  73  is what is principally pressed into the flat elevations or bumps  71  and thereby securely connected to tubular part  63 . Rotor magnet  66  is mounted, in a suitable manner, in the interior of cup-shaped part  72 . 
         [0037]      FIGS. 13 and 14  show variations of impeller  43  that are particularly suitable for experimental prototypes. In  FIG. 13 , tubular yoke part  63  is mounted in impeller  43  by means of a press-fitted or bonded in plastic ring  65 . Ring  65  is press-fitted or bonded in between part  63  and the inner wall of impeller  43 , and abuts with its left end (as shown in  FIGS. 13 and 14 ) against rim  67  from the inside. 
         [0038]    In  FIG. 14 , plastic ring  65  also has a flange extension  79  that covers the hollow inner side of impeller  43 , and thus reduces losses due to air turbulence. 
         [0039]    The bottom of yoke part  72  is labeled  77 . A shaft  90  is mounted on it, by means of a welded bushing  80  (see also  FIG. 2 ). This makes it possible for tubular part  63  and for rotor  43  to thermally expand, independently of one another. 
         [0040]    A cup-shaped yoke  72 , made of ferromagnetic material, shown in  FIG. 2 , is press-fitted into tubular part  63 . This yoke has an approximately cylindrical wall  73 , and its bottom is labeled  77  (see  FIG. 4 ). Rotor magnet  66  is arranged on the inner wall of yoke part  72  (see  FIGS. 2 ,  4 ,  10 , and  11 ). The magnet is preferably radially magnetized. Its number of poles can be, for example, 2, 4, 6, 8, 10, etc. poles, depending upon requirements. In principle, any type of electric motor can be used to drive the fan rotor, but the compact form depicted and described has proven particularly advantageous. 
         [0041]    Impeller  43  has, on the right in  FIG. 10 , an approximately cylindrical portion  59  on whose inner side are provided balancing pockets  62  for a first balancing plane P 1  orthogonal to the rotor axis. So-called balance weights (not shown) are inserted, as needed, into these pockets, in the context of a balancing operation. 
         [0042]    Blades  58  are preferably arranged in an overlapping configuration. Together with support structure  54 , they form impeller  43  of fan  40 . Impeller  43  is preferably manufactured by plastic molding and, if applicable, could also be assembled from a plurality of parts, for example by splitting in an axial direction. 
         [0043]    Impeller  43  has, on its inner side, a cylindrical extension  70 ′ (see  FIG. 5 ) that serves for mounting of the cup-shaped magnetic yoke  72  ( FIG. 2 ). This cylindrical extension  70 ′ transitions, via an annular connecting part  74 , into the support structure of impeller  43  (see  FIG. 8 ). 
         [0044]    Provided in connecting part  74  are second balancing pockets  76  ( FIGS. 4 and 5 ) in a second balancing plane P 2  orthogonal to the rotor axis, which pockets are at an axial distance and a radial distance from first balancing pockets  62 . They make possible balancing in two parallel spatially-separated planes, from the same side of impeller  43 . 
         [0045]    This kind of configuration of fan  40  thus makes it possible to balance impeller  43  from a single side, namely the air-discharge side visible in  FIGS. 5 to 9 , so that no balancing pockets need to be provided on outer side  56  ( FIG. 10 ) of impeller  43 . This enables an optimal conformation of impeller  43 , and of its fan blades  58 , the radially inner ends of which latter can be located closer to rotation axis  78  ( FIG. 2 ) of impeller  43 , thus providing noise minimization advantages; in other words, the so-called “attachment area” of fan blades  58  on impeller  43  can be particularly large in this case, which also improves aerodynamic efficiency. 
         [0046]    Fan blades  58  can also have an S-shaped profile  80  on their leading edges ( FIG. 3 ), and can have indentations  82  ( FIG. 2 ); this likewise contributes to a reduction in fan noise. 
         [0047]    As  FIGS. 4 to 9  show, ribs  83  are provided between cylindrical extension  70 ′ and cylindrical portion  60 . This enables the use of a small air gap between wall  48  of air conduit  50  and the outer ends of blades  58  (see  FIG. 1 ). 
         [0048]    Fan  40  is driven by an electronically commutated external-rotor motor (ECM)  75 . Magnetic yoke  72  of the rotor is, as described, connected to cylindrical extension  70 ′ of connecting part  74 . It is, in turn, drivingly connected to a shaft  90  that is journaled in a bearing tube  92 , in this case by means of two ball bearings  94 ,  96  that are tensioned against one another by means of a compression spring (not shown). Magnetic yoke  72  rotates around longitudinal axis  78  during operation. 
         [0049]    Motor  75  has an internal stator  100  that is mounted on the outer side of bearing tube  92 . Located in this instance below internal stator  100  is a circuit board  102  on which electronic components for motor  75  can be arranged. Bearing tube  92  is connected to a flange plate  106  that is in turn connected to external housing  42  in a suitable manner, usually by way of struts  103 , one of which is visible in  FIG. 1 . 
         [0050]    In practice, the bearing tube  92 , struts  103 , flange  106 , and fan housing  42  can be formed as a one-piece pressure-cast aluminum part or a one-piece plastic part. A multi-part embodiment is also possible. 
         [0051]    Because external-rotor motor  75  is arranged in the interior of impeller  43 , it is relatively poorly cooled. An additional fan arrangement  120  similar to a disk is therefore preferably provided above motor  75 , and in this case is driven directly by shaft  90 . It sits directly on external rotor  72  and draws in air through openings  122  that are provided there (see  FIG. 2 ). 
         [0052]    This air first flows through motor  75  and cools it. During operation, mixed flow fan  40  of  FIG. 1  has, at the top, a first lower pressure and, at the bottom, a higher second pressure, which pushes air upward through motor  75  and thereby cools it. 
         [0053]    From motor  75 , the cooling air flows through openings  122  of cup-shaped part  72  to air disk  120 , which is configured as a radial blower wheel. It reinforces the effect of the second pressure and draws air through openings  122 . 
         [0054]    Air disk  120  can either be manufactured directly (e.g. by injection molding) on impeller  43  upon manufacture of the latter, or can be mounted on impeller  43 . Cooling air is blown out radially from air disk  120  through exit openings  126  ( FIG. 1 ). 
         [0055]    Mixed flow fan  40  has, on its air inlet side  44 , adjacent disk  120 , a low pressure that is usually somewhat lower than the first pressure, since air is being drawn in there to inlet opening  44 . This drawn-in air flows through exit openings  126  and generates there, as a result of the Venturi effect, an additional negative pressure that intensifies the flow of cooling air through motor  75  and thereby further improves the cooling thereof. The pressure generated on exhaust side  52  by the fan itself also additionally intensifies the cooling effect. 
         [0056]    As  FIGS. 4 to 9  show, first ribs  130  extend outward from inner extension  70 ′ to part  60 . Ribs  130  each extend here from a portion between two inner balancing pockets  76 , through cavity  144 , to an approximately oppositely located portion between two outer balancing pockets  62 . In  FIG. 5 , one of the ribs  130  is highlighted in gray. 
         [0057]    Extending perpendicular to first ribs  130  (here, in a circumferential direction) are second ribs  132 ,  134  which form, with first ribs  130 , a kind of ribbed vault and are connected to the first ribs at intersection points  142 . First ribs  130  and second ribs  132 ,  134  form, with each other, small cavities,  136  that, during the operation of fan  40 , cannot cause any substantial turbulence and therefore cannot cause any large losses. 
         [0058]    First ribs  130  have angular spacings of approximately 5° to approximately 20°. As  FIGS. 6 and 7  show, the shape is adapted to the shape of cavity  144  in the interior of impeller  44 . The number of second ribs  132 ,  134  is based, among other factors, on the space situation, i.e. the size and output of mixed flow fan  40 . 
         [0059]    The configuration of ribs  130 ,  132 ,  134  thus results, without substantial additional cost, in an improvement in the performance of mixed flow fan  40 , since turbulence in the interior of impeller  66  becomes greatly reduced. 
         [0060]    Many variants and modifications are of course possible, within the scope of the present invention.