Abstract:
A miniature fan, particularly an axial fan, has a space-conserving structure which permits sophisticated electronic control circuits within a limited amount of space. It features an electronically commutated motor (ECM) including an internal stator  68 , an external rotor  27  on a shaft  62 , and a fan wheel  28  mounted on the rotor and bearing fan blades  26 . The motor flange  40 ′ supports a bearing tube  60  which rotatably journals the rotor shaft  62  and is formed with a cavity  84  which receives a first circuit board  86  devoted to control of motor speed and/or voltage, and a second circuit board  96  which supports a galvanometric sensor  100  which senses the rotational position of the rotor, for purposes of triggering commutation of the motor stator windings  68  at appropriate times.

Description:
CROSS-REFERENCE 
     This application claims priority from German Utility Model application DE 20 2007 018 178.7, filed 17 Dec. 2007, the disclosure of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a miniature fan, and in particular to a miniature fan having improved electronic capabilities, e.g. rotation speed regulation or rotation direction reversal. 
     BACKGROUND 
     Miniature fans of this kind usually have a square fan housing as depicted in partial section in  FIG. 1 , and the dimension L ( FIG. 1 ) can be, for example, 20, 25, 30, 40, 50, or 60 mm, so that a fan housing of this kind has sizes from approximately 20×20 mm to approximately 60×60 mm; for known miniature fans, the housing depth T is usually between 8 mm and 25 mm. The 20×20 mm and 25×25 mm sizes are ordinarily referred to as micro-fans or subminiature fans, and the 30×30 to 60×60 mm sizes as miniature fans, the terminology differing by company and by country. 
     Miniature fans of this kind have become very popular in numerous application sectors, for example in the fields of cooling of circuit boards or the cooling of components in which a high level of power dissipation occurs. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to make available a new miniature fan which has sufficient internal space for its control circuits. 
     According to the invention, this object is achieved by providing an internal stator with a stator winding arrangement, an external permanent-magnet rotor, and a fan wheel mounted on the rotor. In order to utilize space optimally, a mounting flange of the motor supports a bearing tube in which the central shaft of the external rotor is journaled, and the flange is formed with a cavity which receives a first circuit board with components which control motor voltage and/or direction and a second circuit board with a galvanometric sensor which detects the rotational position of the rotor for purposes of triggering commutation. A miniature fan having an enlarged component space is thus obtained, and, in this enlarged component space, it is possible to accommodate complex electronics, since it is possible in this fashion to accommodate two or more circuit boards, even in a miniature fan. The interface of the circuit boards to the motor can be limited to the galvanomagnetic sensor that senses the instantaneous position of the permanent-magnet arrangement, and to the electrical connections from at least one circuit board to the stator winding; this substantially simplifies assembly since, in a motor having, for example, only one winding strand, only two electrical connecting leads from that winding strand to a circuit board are required. 
     On the same principle, it is also possible to accommodate more than two circuit boards in (or in the region of) the fan flange(s). The depth T ( FIG. 1 ) of the relevant fan is thereby increased, and that enables a larger axial extension of the fan blades—also referred to as “blade depth”—and thus a greater volumetric air flow rate (V/t) and a greater differential air pressure or “head” (Δp), with the overall result that a miniature fan having improved properties is obtained. 
    
    
     
       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 depicted in the drawings, in which: 
         FIG. 1  is a greatly enlarged schematic depiction of a miniature axial fan  20 ;  FIG. 1  serves to explain miniature fans and their problems; 
         FIG. 2  is a greatly enlarged axial section through a miniature axial fan; and 
         FIG. 3  schematically depicts a circuit arrangement for operating the miniature fan according to  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows, schematically and greatly enlarged, a miniature fan  20 . The latter has a fan housing  22  of a design known in principle, which is depicted partially in section. It has a cylindrical inner side  24  inside which rotate fan blades  26  that are arranged on a fan wheel  28 . An air conduit  30  extends between fan wheel  28  and cylindrical inner side  24 . In this example, cylindrical inner side  24  expands outward in the form of conical segments  34  at the four corners  32  of fan housing  22 , only three of which corners are depicted. It must be noted, however, that in miniature fans, cylindrical inner side  24  generally extends over the entire axial extent T of fan housing  22 , i.e. conical segments  32  are usually absent therefrom for space reasons (cf.  FIG. 2 ). 
     Connected to outer fan housing  22  via struts or spokes  36  is a support flange  40  on which is mounted an electronically commutated motor ( FIG. 2 ) that serves to drive fan wheel  28  and is depicted in  FIG. 2 . 
     If fan wheel  28  rotates in the direction of an arrow  44 , i.e. counter-clockwise, fan  20  then delivers air in the direction of arrows  46 , i.e. from left to right in  FIG. 1 ; and if fan wheel  28  rotates clockwise, i.e. in the direction of an arrow  48 , fan  20  then delivers air in the direction of arrows  50 , i.e. from right to left in  FIG. 1 . 
     In miniature fans as well, this reversal of rotation direction requires a greater number of electronic components, which entails considerable difficulty due to the small size of such fans. 
       FIG. 2  shows an embodiment of a miniature fan  20  having two circuit boards. The same reference numbers as in  FIG. 1  are used for identical or identically functioning parts. Fan  20  according to  FIG. 2  has no corner expansions  34 , but instead its inner side  24  is substantially continuously cylindrical. The fan is driven by an electronically commutated motor  18 . 
     Mounted in this inner side via struts  36  is a support flange  40 ′ that is longer than flange  40  of  FIG. 1 . A bearing arrangement  60  is provided at the center of flange  40 ′, said arrangement serving to journal rotation shaft  62  of fan wheel  28  arranged on the outer side of rotor  27 , and being indicated only very schematically. There are numerous solutions in the existing art for bearing assembly  60  and for rotation shaft  62 , and for their manner of mounting on rotor  27 . The depiction in  FIG. 2  is therefore very schematic. 
     An approximately cup-shaped magnetic yoke plate  64  is arranged in rotor  27 , usually during the manufacture of fan wheel  28 . Fan wheel  28 , together with its fan blades  26 , is usually manufactured from plastic by injection molding. Mounted on the inner side of yoke plate  64  in rotor  27  is a permanent-magnet arrangement, here in the form of a radially magnetized permanent magnet  66 . Alternatively, for example, individual magnets could also be used here. This ring  66  can have, for example, two or four magnet poles, which are not depicted. This permanent-magnet ring  66  interacts magnetically with a claw pole internal stator  68  in whose interior a winding arrangement  70  is located. In the simplest case, this winding arrangement  70  contains an annular coil having two electrical terminals  72 ,  74 . Winding arrangement  70  is wound onto a coil former  76 . The latter is in turn retained between an upper claw pole piece  78  and a lower claw pole piece  80 . 
     As  FIG. 2  shows, the individual claw poles  78 A can have on one side an oblique edge  82  in order to generate, in interaction with the magnet poles of permanent-magnet ring  66 , a reluctance torque of suitable shape that serves, among other purposes, to rotate ring magnet  66 , in the currentless state, into a position from which starting is possible without difficulty. There are numerous and detailed examples of this in the literature. 
     Claw pole pieces  78  and  80  are mounted on flange  40 ′ in suitable form, e.g. on bearing arrangement  60  which in turn can be mounted in an axial projection  82 ′ from flange  40 ′. 
     Formed in flange  40 ′ is an annular recess or opening  84  which is made sufficiently large that at least a first, annular circuit board  86  can be accommodated in it; electronic components  88  are arranged on said board, and from it an electrical connector lead  90  of fan  20  is guided outward through an opening  92  of fan flange  40 ′ and through an opening  94  of fan housing  22 . Lead  90  serves to control fan  20  and to deliver current to it. 
     Located above circuit board  86 , between upper edge  41  of fan flange  40 ′ and the lower end of fan wheel  28 , is a second circuit board  96  that has an opening  98  in which a galvanomagnetic rotor position sensor  100  is arranged, specifically below rotor magnet arrangement  66 , so that said sensor  100  is located in the region of the leakage field of rotor magnet arrangement  66  and is controlled by said leakage field. Sensor  100  is normally a Hall Integrated Circuit (IC), but there are also other possibilities for it (e.g. a Giant Magneto Resistor or GMR). 
     Connector pins are soldered into second circuit board  96 ; these serve for electrical connection between terminals  72 ,  74  of annular coil  70  and the components on second circuit board  96 . Extending similarly between first circuit board  86  and second circuit board  96  are connecting pins  104 ,  106  for electrical connection between said circuit boards. Alternatively, an electrical plug connection (not shown) can also be provided there, or e.g. a wire, stranded-wire, or foil connection. 
     The use of two circuit boards  86 ,  96  makes it possible to provide an electronic regulation or control system directly in the fan, even if the latter is very small, since the space for electronic components is correspondingly enlarged. 
     As a result of the increased axial extent T ( FIG. 1 ) of fan  20 , fan blades  26  can be made correspondingly longer; they must maintain a small spacing  110  from fan flange  40 ′ in the latter&#39;s vicinity. As a result of this, an elevated air delivery volume and a greater air pressure buildup are obtained. 
     More than two circuit boards can of course also be used, in which case the axial length T of fan  20  is then correspondingly increased. 
       FIG. 3  shows a preferred circuit for fan  20  of  FIG. 2 . The fan has a circuit  119  for generating control signals FW, BW to specify whether the fan is to run forward or backward, which signals are applied to a directional controller  120 , and a target rotation speed signal n soll  which is applied to a directional controller  122 . The output signal of directional controller  120  is also applied to the rotation speed controller n_CTL  122 , along with the target rotation speed signal n_soll and the actual rotation speed n_ist of fan  20 . This controller  122 , which can be, for example, a P (Proportional) controller, a PI (Proportional Integral) controller, or a PID (Proportional Integral Differential) controller, generates at its output  124  a control output signal that is delivered to a power stage  126 , to whose outputs  72 ,  74  the winding arrangement  70  of internal stator  68  of motor  18  is connected. 
     Rotor magnet  66  drives fan wheel  28 , to which fan blades  26  are attached, and generates, by interaction with Hall IC  100 , the actual speed signal n_ist that is also applied to an input  127  of output stage  126 , in order to control commutation in the motor winding. 
     It is very advantageous that internal stator  68  can be combined with circuit boards  86  and  96  into one physical unit that, after electrical assembly thereof, can be integrated with fan flange  40 ′. 
     Fan wheel  28  is then journaled with its shaft  62  in bearing arrangement  60 , thereby automatically creating the operative connection between rotor magnet  66  and Hall IC  100 , so that no special assembly steps are necessary for this. 
     As  FIG. 3  shows, the components can advantageously be distributed so that those components  72 ,  74 ,  100 ,  127  associated directly with motor  18  are arranged predominantly on circuit board  96  next to the motor, and those components  88 ,  120 ,  122  that belong to a higher-order control system, e.g. to controller  120  for the rotation direction or to rotation speed controller  122 , are arranged on the lower circuit board  86 . 
     This makes possible a modular configuration, i.e. upper circuit board  96  can be adapted or matched to the power output, operating voltage, etc. of motor  18 , and lower circuit board  86  enables the implementation of a variety of functions, e.g. a rotation speed controller  122  or rotation direction controller  120 . 
     Many further variants and modifications are of course possible within the scope of the present invention.