Abstract:
An electronically commutated electric motor has an internal stator ( 18 ) and an external rotor ( 24 ). They are separated by an air gap ( 23 ). A circuit board ( 68 ) equipped with openings ( 58′, 70′, 72′ ) is arranged on the internal stator ( 18 ). The internal stator ( 18 ) has a lamination stack ( 22 ) that is equipped with a winding arrangement ( 60; 86, 88 ) whose terminals are implemented at least in part as wire segments ( 86 E,  88 E,  90 ). The lamination stack ( 22 ) of the internal stator ( 18 ) is covered, at least locally, by an insulating layer ( 20 ) made of a thermally stable plastic. Implemented on said layer are supporting elements ( 58; 70, 72 ) that project from the internal stator ( 18 ) toward the circuit board ( 68 ) and serve to secure wire segments ( 86 E,  88 E,  90 ) of the winding arrangement ( 86, 88 ). These supporting elements ( 58, 70, 72 ), with the wire segments mounted thereon, are each arranged in an associated opening ( 58′, 70′, 72′ ) of the circuit board ( 68 ) and are there soldered thereto.

Description:
CROSS-REFERENCE 
       [0001]    This application is a sec. 371 of PCT/EP2006/002785, filed 27 MAR. 2006, claiming priority from DE 10 2005 024 770, filed 20 MAY  2005 . 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an electronically commutated electric motor, in particular to a subminiature motor, and to a method for the manufacture thereof. 
       BACKGROUND 
       [0003]    Subminiature motors serve, inter alia, to drive mini-fans. The latter serve, for example, to cool processors in computers, for equipment cooling in small equipment, etc., and they have very small dimensions. For example:
       fans of the ebm-papst 250 series have dimensions of 8×25×25 mm;   those of the ebm-papst 400F series have dimensions of 10×40×40 mm;   those of the ebm-papst 400 series have dimensions of 20×40×40 mm; and   fans of the ebm-papst 600 series have dimensions of 25×60×60 mm.       
 
         [0008]    The power consumption of such fans is 0.2-0.6 W for the 250 series, 0.6 to 0.9 W for the 400F series, and 0.4-3.0 W for the 400 and 600 series. Their weight is, for example, approximately 5 (five) g for the 250 series, between 17 g and 27 g for the 400/400F series, and approximately 85 g for the 600 series. 
         [0009]    In motors of this miniature size, which must be very inexpensive, it is important to make assembly as simple as possible, so that the highest possible degree of automation becomes possible during manufacture. Only extensive production automation makes possible the uniform quality that is a prerequisite for a long average service life. 
         [0010]    A further complicating factor with such subminiature motors is that their components, entirely analogously to those of a mechanical clock mechanism, are very delicate and therefore not very robust. The rotor shaft, for example, is often only as thick as a knitting needle and can therefore easily be bent if handled carelessly, rendering the motor unusable. This danger exists in particular during assembly. 
         [0011]    With such very small motors, automated production is difficult and often requires additional manual work. This applies especially to the connection of elements of the winding arrangement arranged on the stator lamination stack to the associated circuit board. As shown by  FIG. 10  below, metal pins that are secured in an insulator which is located on the stator lamination stack have hitherto been used for this. Such pins are pressed, in a separate working step, into holes in the plastic of the injection-embedded lamination stack. They are called “Autosplice” pins. 
         [0012]    A metal pin of this kind has one wire end of the winding arrangement of the motor wound around it, and is introduced, through an opening, into the circuit board and then soldered thereto. This method reaches its limits, however, at a maximum wire diameter of approximately 0.24 mm, since with thicker wires a pin of this kind bends, or the orifice in the insulating material of the injection-embedded lamination stack becomes enlarged and destroyed. 
         [0013]    In such cases, it is then possible, for example, to solder the enameled copper wire manually onto solder pads of the circuit board. In another method, so-called insulation displacement contacts are used, but, for this, the wire diameter must be greater than approximately 0.17 mm. 
       SUMMARY OF THE INVENTION 
       [0014]    It is therefore an object of the invention to make available a novel electric motor and a novel method for the manufacture thereof. 
         [0015]    According to the invention, this object is achieved by a method comprising forming an insulating layer of thermally stable plastic on the lamination stack, forming plastic projections integrally with the plastic layer, wrapping a segment of the winding around the plastic projections, introducing the wire-wrapped projection through a hole in a circuit board and soldering the wire segment to the circuit board. There is no need here for metal pins that must first be pushed into the insulating layer; instead, a securing part manufactured from plastic during the injection-molding operation is used, on which part a wire segment of the winding is secured in suitable fashion, and the combination of plastic securing part and wire segment is then inserted through an associated opening of the circuit board and then soldered to it. 
         [0016]    Another manner of achieving the stated object is to arrange a circuit board, formed with openings, on the internal stator, to form plastic projections on an insulating layer covering the lamination stack, to wrap segments of the winding on the plastic projections, to arrange the wrapped projections in the holes in the circuit board and to there solder the wire segments to the circuit board. The fact that the Autosplice pins are omitted from a motor of this kind results in substantially simplified and thus less expensive manufacturing, together with less waste. 
         [0000]    A wire segment can be connected to the associated plastic securing part, for example, by being wound onto it. Alternatively, particularly with thicker wires, the wire segment can be at least temporarily mechanically secured in the associated plastic securing part, for example by being pressed into a groove that is provided in said plastic securing part, by adhesive bonding, or in another manner. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0017]    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. 
           [0018]      FIG. 1  is a partial sectioned depiction of an internal stator for a motor and a method according to the present invention, before the internal stator is wrapped; 
           [0019]      FIG. 2  is a depiction analogous to  FIG. 1 , after wrapping; 
           [0020]      FIG. 3  shows the stator arrangement according to  FIG. 1  or  2 , in which a plastic securing part is introduced, together with a wire segment wound onto it, into a opening of a circuit board; a portion of an external rotor is indicated with dot-dash lines in  FIG. 3 ; 
           [0021]      FIG. 4  is a section viewed along line IV-IV of  FIG. 5A ; in this depiction, a total of three plastic securing parts are visible, which project into associated openings of a circuit board and are soldered there; 
           [0022]      FIG. 5A  is a plan view of the stator lamination stack of  FIGS. 1 to 4  that is injection-embedded into a plastic layer on which is wound a so-called bifilar winding whose terminals are connected to associated plastic securing parts; 
           [0023]      FIG. 5B  shows the associated circuit board in the state prior to assembly thereof; 
           [0024]      FIG. 6  shows a stator lamination stack analogous to  FIG. 5A  in its state prior to wrapping; 
           [0025]      FIG. 7  is a section viewed along line VII-VII of  FIG. 6 ; 
           [0026]      FIG. 8  is a greatly enlarged depiction of a plastic securing part that is equipped with a longitudinal groove, and of a wire segment of the winding arrangement secured on said longitudinal groove by being clamped in; 
           [0027]      FIG. 9  is a section viewed along line IX-IX of  FIG. 8 ; and 
           [0028]      FIG. 10  is a section, analogous to  FIG. 4 , through the internal stator of a motor according to the prior art. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  shows, at greatly enlarged scale, stator lamination stack  22 , injection-embedded into a plastic layer  20 , of an internal stator  18  for an external-rotor subminiature motor whose rotor ring magnet  24  is indicated with dot-dash lines in  FIG. 3 . Said ring magnet is separated from lamination stack  22  by an air gap  23 . 
         [0030]    To illustrate approximate size, a length of 1 cm is indicated in the usual fashion in  FIG. 1 , i.e. the stator lamination stack  22  that is depicted can be, for example, approximately one centimeter high. Considerable enlargement is necessary in order to show any details to be depicted. 
         [0031]    The shape of lamination stack  22  depicted by way of example is evident from  FIG. 5A . This shape has four salient poles  26 ,  28 ,  30 ,  32 , between which are slots  34 ,  36 ,  38 , and  40 . The poles are implemented on their periphery in such a way that they generate a so-called reluctance torque during operation. In  FIG. 5A , rotor  24  (not depicted therein) rotates in a clockwise direction  41 . 
         [0032]    Because lamination stack  22  has four salient poles, rotor ring magnet  24  is also magnetized in four-pole fashion in the variant depicted. Different numbers of poles can, of course, also be used for stator  22  and rotor  24 , for example a version having two stator poles and two rotor poles. Similarly, a winding having only one strand, or a three-strand winding, would also be possible instead of the two-strand winding depicted in  FIG. 5A . 
         [0033]    Lamination stack  22  has on its inner side an opening  42  that serves for securing on, for example, a bearing tube (not depicted). Lamination stack  22  is constructed in the usual way from individual laminations  44 , and it is injection-embedded in plastic layer  20  on its upper side  46 , on its outer periphery  48 , and on its lower side  50 . 
         [0034]    Plastic layer  20  transitions on its upper side into a collar  52 , on its lower side into a collar  54 , and is equipped on its lower side with plastic securing parts  56  that project downward in  FIGS. 1 and 3 . These have approximately the shape of a pin or post, and in the example depicted have a square cross section with an edge length d of approximately 1.5 mm. Alternatively, other elongated shapes are also possible, for example that of a cylinder having a diameter of approximately 1 mm, which can also be slightly conical. 
         [0035]    The plastic used for layer  20 , for the two collars  52 ,  54 , and for plastic securing parts  56  is preferably a high-strength and high-temperature-resistant plastic, for example a liquid crystal polymer into which glass fibers are mixed in order to increase strength and reduce anisotropy. One such polymer is offered under the TICONA brand, e.g. VECTRA T 135 grade. A plastic of this kind has a bending moment of approx. 16,000 MPa and a heat deflection temperature under load (HDT (A) per ISO 75-1,2 at 1.8 MPa) of approx. 300° C. This temperature can be briefly exceeded, e.g. up to 370°, without causing this plastic to melt. 
         [0036]    This type of plastic is also referred to as LCP. These are thermotropic (i.e. melt-processable) liquid crystal polymers (LCP) with very high temperature resistance. Their molecular structure is characteristic. These polymers are made up of rigid, rod-shaped macromolecules that, in the melt, become parallel and form liquid crystal structures. When this polymer melt is subjected to a shear flow or elongation flow, for example in the context of injection molding, the rigid molecules then arrange themselves into fibers and fibrils, which are “frozen in” upon cooling. This produces the specific morphology of the liquid crystal polymers in their solid state, which is not dissimilar to the morphology of wood. The LCP matrix has fibers of the same polymer embedded in it. 
         [0037]    Such polymers are therefore also referred to as “self-reinforcing polymers.” In contrast to the known amorphous structure of conventional thermoplastic polymers, the rigid, rod-shaped polymer structure leads to a considerable improvement in mechanical properties and results in some other unusual properties, namely a continuous service temperature of up to 300° C., a melting temperature of up to 370° C., very high tensile strength and a high modulus of elasticity in the flow direction, and high impact toughness. 
         [0038]    The more greatly the melt is oriented in one direction, the higher the values obtained for tensile strength, rigidity, and toughness in the flow direction. Thin parts therefore have a particularly pronounced anisotropy. This can be reduced to a certain extent, for example by 50%, by mixing glass fibers into the polymer. The positive material properties are nevertheless largely retained in this context, for example low viscosity in the molten state that enables particularly easy processing. 
         [0039]    It is very advantageous that very thin plastic layers (e.g. 0.2 mm) can be generated with such a plastic, since it flows very readily in the molten state and has a low viscosity similar to that of water. This makes possible a very thin slot insulation  20 N (see  FIGS. 6 and 7 ), so that once lamination stack  22  has been injection-embedded, more winding room is available in slots  34 ,  36 ,  38 ,  40  than when plastics having a higher melt viscosity are used, so that a larger number of windings can be accommodated therein (greater copper fill factor), thus enabling higher motor performance. A continuous plastic layer with a thickness of, for example, 0.2 mm can likewise be provided on periphery  48  of lamination stack  22 , without requiring any increase in the size of air gap  23 . This proves to be highly advantageous especially in IP 54-rated motors and for motors that must be protected from salt mist (e.g. for shipboard use). 
         [0040]      FIG. 2  shows lamination stack  22  of  FIG. 1  onto which a winding  60  of enameled copper wire has been wound, plastic parts  20 ,  52 ,  54  forming a coil former. 
         [0041]    Winding  60  has a terminal wire  62 , and the latter is wound around plastic securing part  56  in the form of a small winding  64 . This small winding  64  can in many cases be tinned by immersion into a tin bath, which simultaneously burns off the enameling of wire  62 . 
         [0042]    According to  FIG. 3 , plastic securing part  56  having winding  64  is then introduced into an opening  66  of a circuit board  68 , and circuit board  68  is then soldered in the usual fashion, winding  64  being electrically connected by the solder to one of the conductive tracks (not shown) on circuit board  68 . 
         [0043]      FIG. 4  is a section through the completely wrapped stator lamination stack  22  and through circuit board  68 , into which latter a total of three plastic securing parts  56 ,  70 , and  72  project. The solder is indicated at  74 . 
         [0044]      FIG. 5B  shows circuit board  68  prior to its installation on the wrapped stator lamination stack  22  (installation is symbolically indicated by arrows  69 ). Circuit board  68  has three openings  58 ′,  70 ′, and  72 ′ for receiving the three securing parts  58 ,  70 , and  72 . It also has, at its center, an opening  76  into which project three protrusions  78  that serve to guide circuit board  68  on corresponding openings  80  of collar  52 , and that are asymmetrically distributed in order to preclude assembly errors. Arranged on circuit board  68  is a Hall sensor  82  that is controlled by the leakage field of rotor magnet  24  and serves to control electronic commutation. 
         [0045]      FIG. 5A  shows the two winding strands  86 ,  88  of the motor type shown by way of example. These are wound in the usual way in bifilar fashion, i.e. with two parallel wires, and have a common terminal  90  that is mechanically connected to plastic securing part  70 . Strand  86  proceeds therefrom clockwise to its end  86 E, which is mechanically connected to securing part  58 . Strand  88  likewise proceeds from terminal  90 , counterclockwise, to its end  88 E that is mechanically connected to securing part  72 . Strands  86 ,  88  are then electrically connected to corresponding conductor tracks (not depicted) of circuit board  68  by being soldered to circuit board  68 . The currents through strands  86 ,  88  are controlled in known fashion by Hall sensor  82  as a function of the position of rotor  24 . Alternatively, control on the basis of the so-called sensorless principle is possible. 
         [0046]    Located in the region of each plastic securing part  58 ,  70 ,  72  is a respective protective partition  94  ( FIGS. 6 and 7 ) that proceeds in approximately a V-shape and has at its center a depression  96  out of which the relevant plastic securing part  58 ,  70 ,  72  projects. Protective partitions  94  have two functions: 
         [0047]    a) supporting and spacing members during installation onto circuit board  68 ; 
         [0048]    b) mechanical protection to prevent damage to securing parts  58 ,  70 ,  72 . 
         [0049]      FIG. 6  shows that protective partitions  94  of this kind are also provided therein at the three-o&#39;-clock position, at which (in this example) a securing part is not necessary. These partitions, like securing parts  58 ,  70 ,  72 , are implemented from the material of insulating layer  20 . 
         [0050]      FIGS. 8 and 9  show a variant, namely a plastic securing part  56 ′ in which is provided a longitudinal groove  57  in which a connector wire  62 ′ is mechanically secured by being clamped in. This allows the securing of thicker wires, e.g. having a diameter greater than 0.6 mm. These then do not need to be wound around the relevant securing part. 
         [0051]      FIG. 10  shows securing of the connector wires onto metal pins  100  according to the prior art. These pins are pressed into orifices  102  of an insulating layer  104 , but are suitable only for very thin winding wires up to approx. 0.25 mm diameter, since they can easily be damaged by excessive mechanical stress. 
         [0052]    Numerous variants and modifications are of course possible, within the scope of the present invention.