Abstract:
A motor structure resistant to liquid intrusion features two modules, the first having an electronically commutated external-rotor motor ( 20 ), which motor comprises an internal stator ( 22 ) that is arranged on a bearing tube ( 30 ) and is separated by a first air gap ( 24 ) from an external rotor ( 26; 92 ), which latter comprises a rotor cup ( 40 ) that is open at one end and is joined at its other end to a shaft ( 46 ) that is journalled in the bearing tube ( 30 ), further having a permanent-magnet arrangement ( 76 ), arranged at the open end of the rotor cup ( 40 ), for magnetic interaction with a second permanent-magnet rotor ( 92 ), forming part of the second module. The first module is separated from that second rotor ( 92 ) by a second air gap and forms therewith a magnetic coupling ( 94 ), so that a rotation of the permanent-magnet arrangement ( 76 ) brings about a rotation of that second rotor ( 92 ). A hermetic separation of the two modules is accomplished using a non-ferromagnetic separating element ( 82 ) arranged in the second air gap. The second module can safely be used to handle liquid, e.g. as a pump.

Description:
FIELD OF THE INVENTION 
   The invention relates to an arrangement having an electronically commutated external-rotor motor. 
   BACKGROUND 
   Thanks to their simple design, great reliability, and long service life, motors of this kind are used nowadays for a wide variety of drive functions. 
   Typical applications are as drives for so-called equipment fans that are used to remove heat from computer housings, also as drives for small fans for direct cooling of microprocessors, drives for vacuum cleaners, etc. 
   When an external-rotor motor of this kind is used for combined drive functions, the problem exists that although a compact design is desirable, on the other hand the motor must not be negatively affected by a part that is to be driven. For example, if this motor is driving a liquid pump or a compressor, no medium from the pump or compressor can be permitted into the motor, since that medium might otherwise damage the electronic systems of the motor or cause corrosion or the like in it. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide a motor structure with first and second rotor modules hermetically separated from each other, but magnetically coupled together. 
   According to the invention, this object is achieved by providing a first external rotor separated by a first air gap from an internal stator, on one side of a liquid-tight non-ferromagnetic separating element, coupled magnetically to a second external rotor on the other side of a second air gap, in which the separating element is located. A compact design is thereby obtained: the non-ferromagnetic separating element, in addition to its magnetic and mechanical separating function in the second air gap, can additionally act as a carrier of the shaft for journalling the second rotor, and as a carrier for the bearing tube of the external-rotor motor. This allows a design having few parts, as well as simple and economical installation. It also allows tight production tolerances and, as a result, quiet running and a long service life. 
   An essential aspect of the invention is enhancement of the integrity of the unit made up of the external-rotor motor, magnetic coupling, and driven element (e.g. pump or compressor). This is attained by the consistent application of modern technological capabilities in order to achieve minimized manufacturing costs, excellent process reliability during manufacture, minimized imbalance in particular of the external rotor but also of the second rotor, and a minimization of parts count and production costs. 

   
     BRIEF FIGURE DESCRIPTION 
     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. 
       FIG. 1  is a longitudinal section, enlarged approximately twice, through an arrangement according to a preferred implementation of the invention, looking in the direction of line I-I of  FIG. 2 ; 
       FIG. 2  is a plan view looking in the direction of arrow II of  FIG. 1 ; 
       FIG. 3  is a variant of  FIG. 2  in which a compressor  99 , e.g. a piston pump, is used instead of a centrifugal pump; 
       FIG. 4  is a first depiction to explain how the rolling bearings of the external rotor are assembled in the case of the arrangement according to  FIGS. 1 and 2 ; 
       FIG. 5  is a second depiction showing the bearings in a state shortly before assembly is completed; 
       FIG. 6  is a depiction showing how a plain bearing can be installed from one end of motor  20 ; and 
       FIG. 7  shows a detail of  FIG. 6  that is labeled VII therein. 
     In the description that follows, the terms “left,” “right,” “top,” and “bottom” refer to the respective Figure. Identical or identically functioning parts are labeled in the various Figures. with the same reference characters, if applicable with an appended apostrophe, e.g.  26 ′ rather than  26 , and are usually described only once. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows, at approximately twice actual size, an arrangement having an electronically commutated external-rotor motor  20 . The latter has an internal stator  22  of conventional design, e.g. a stator having salient poles or a claw pole stator, and the latter is separated from an external rotor  26  by a substantially cylindrical air gap  24 . During operation, external rotor  26  rotates about internal stator  22 , this being the reason that such motors  20  are referred to as external-rotor motors. 
   Internal stator  22  is mounted on a bearing tube  30 , usually by being pressed on. A circuit board  32  is located to the right of internal stator  22 . Located on this board are the electronic components (not shown here) that are needed for electronic commutation of motor  20 , as well as a rotor position sensor  34  that is controlled by a permanent ring magnet  36  of external rotor  26 . Ring magnet  36  is radially magnetized, and preferably has four rotor poles. Sensor  34  is controlled by a leakage field of this ring magnet  36 , enabling non-contact sensing of the position of rotor  34 . 
   External rotor  26  has a design using a so-called rotor cup  40 , which is implemented here as a deep drawn cup-shaped sheet-metal part made of soft ferromagnetic material. Ring magnet  36  is mounted in this sheet-metal part  40  so that the latter constitutes a magnetic yoke for rotor magnet  36 . 
   Sheet-metal part  40  has a hub  44  in which a shaft  46  is mounted in the manner depicted. It is journalled in two ball bearings  48 ,  50  whose outer rings are held at a distance from one another by a spacer  52  (cf. also the schematic depictions in  FIGS. 4 and 5 ). These ball bearings  48 ,  50 , together with shaft  46 , are pressed from the left into bearing tube  30  upon assembly, and retained there by a latching member  54 . An axial projection  56  of flange part  44  is used to press in latching member  54 . Located between said part and the inner ring of rolling bearing  48  is a compression spring  58  that, after assembly, pushes rotor  26  sufficiently far to the left that a snap ring  59  mounted at the right end of shaft  46  makes contact against the inner ring of rolling bearing  50 . Shaft  46  is therefore displaceable in the inner rings of the two rolling bearings  48 ,  50 . 
   This mounting method makes it possible to install rotor  26 , together with its completely preassembled bearings  48 ,  50 , from the left into bearing tube  30 , so that right end  60  of the inner opening of bearing tube  30  can be closed off, as shown, in liquid-tight fashion. This mounting method will be explained in further detail with reference to the Figures. that follow. 
   Fan blades  64  are secured by plastic injection molding, in the manner depicted, on the exterior of sheet-metal part  40 . During operation, they rotate in an opening  66  of a fan housing  68  (cf.  FIG. 2 ). Fan housing  68  has, for example, the usual square shape of an equipment fan, and has a mounting hole  70  in each of its corners. 
   Also mounted on the exterior of sheet-metal part  40  by plastic injection molding is an annular extension  76  made of a plastic material having embedded particles of hard ferrite. This is referred to as a plastic-matrix ferrite magnet, from which rotor magnet  36  can also be manufactured. 
   This ferrite magnet  76  is manufactured in a corresponding injection-molding tool, and in a second process step, if applicable in the same injection-molding tool, the actual fan wheel with its blades  64  can be injection-molded around component  40 . A procedure of this kind is referred to as a “2K” (=two plastics) method. With this procedure, in particularly advantageous fashion, it is possible to minimize manufacturing costs, the “original imbalance” that can be achieved, the number of process steps, and the logistical outlay for manufacture. Alternatively, a hard ferrite ring magnet could also be mounted separately on sheet-metal part  40 , e.g. by being adhesively bonded or pressed on. 
   Bearing tube  30  transitions to the right into a flange-like portion  80  that proceeds perpendicular to the rotation axis of rotor  26  and transitions at its periphery into a cylindrical portion  82 , which here has the function of a so-called gap tube and is therefore referred to hereinafter as gap tube  82 . The right end of ferrite magnet  76  extends around the exterior of gap tube  82  and parallel to it. 
   Gap tube  82  transitions via a shoulder  84  into a cylindrical portion  86  that, as depicted, serves for mounting of a cover  88 , for example by means of a threaded mount (not depicted) or a sealing ring (not depicted), or by laser welding. Cover  88  can also be referred to as spiral housing  88 , since in its interior there is a spiral-shaped housing contour in which a conveying wheel  90  is arranged. 
   The latter is preferably implemented integrally with a permanent-magnet rotor  92  that is separated by gap tube  82  from ferrite magnet  76  and forms with the latter a magnetic coupling  94 ; in other words, when ferrite magnet  76  rotates, rotor  92  also rotates and thereby drives conveying wheel  90 , with the result that the latter draws in liquid via an inlet  96  and pumps it out via an outlet  98  ( FIG. 2 ). It is self-evident that instead of a spiral pump, any other unit to be driven can also be provided, for example a compressor  99  for a refrigerating agent, as shown in  FIG. 3 . Compressor  99  is also driven via a magnetic coupling  94  that can be constructed identically to the one in  FIG. 1 . 
   Permanent-magnet rotor  92  is rotatably journalled, by means of two rolling bearings  100 ,  102  between whose outer rings a spacing member  104  is located, on a stationary shaft  106  that is mounted in liquid-tight fashion, in the manner depicted, in a projection  107 , protruding to the right, of portion  80 . Mounted on the right end of shaft  106  is a snap ring  108 , and located between the latter and the inner ring of rolling bearing  102  is a compression spring  110  that imparts an axial preload to the two rolling bearings  100 ,  102 . The inner ring of left rolling bearing  100  is braced against an axial projection  112  of projection  107 . Projection  107  is hollow on its left side, and forms there the right end  60  of the internal opening of bearing tube  30 . The method depicted here for mounting bearings  48 ,  50  requires an open space  109  between the right end of shaft  46  and the bottom of opening  60 , and the configuration having projection  107  makes possible, despite this open space  109 , an axially compact design in which the space in the unit is effectively utilized. 
   Cylindrical portion  86  is joined via struts  114 ,  116 ,  118  to fan housing  68 , so that the latter constitutes an integral part with gap tube  82 , portion  80 , and bearing tube  30 ; this greatly simplifies installation of the arrangement, keeps the parts count low, and reliably separates from one another the units that are used, so that liquid cannot travel from spiral wheel  90  to motor  20  and damage it. Stationary shaft  106  likewise constitutes a component of this injection-molded part because it becomes anchored in it during manufacture, and thus likewise contributes to the compact design. 
   MODE OF OPERATION 
   During operation, external-rotor motor  20  drives external rotor  26  so that fan blades  64  rotate in housing  68  and thereby, in known fashion, generate an axial air flow therein. Alternatively, the fan can also, for example, be implemented as a diagonal fan or radial fan. An axial fan is shown. The fan design that is used depends on the requirements. 
   At the same time, ferrite ring magnet  76 , which can be magnetized e.g. with six or eight poles, drives rotor magnet  92  (which in this case will likewise be magnetized with six or eight poles) through gap tube  82 , and thus rotates conveying wheel  90  so that the latter draws in liquid through inlet  96  and pumps it out through outlet  98  ( FIG. 2 ). Such an arrangement can be used, for example, in order to draw in water in a well and pump it out; or to pump blood in a heart-lung machine; or to transport cooling fluid in a closed cooling circuit, in which case conveying wheel  90  then has the function of a circulating pump. 
   Because cover  88  is joined in liquid-tight fashion to gap tube  82 , for example by laser welding, no liquid can escape outward from housing  88 ; a principal contributing factor here is that flange-like portion  80  and its projection  107  have no openings of any kind. This is possible because external rotor  26  can be securely installed from the left, for example in the manner described below with reference to  FIGS. 4 and 5 , since it is not necessary to have access to the right end of shaft  46  during installation. Conveying wheel  90  of the centrifugal pump, with its bearings  100 ,  102 , can similarly be installed on stationary shaft  106  from the right, and secured with snap ring  108 , before cover  88  is mounted. 
   For bearings  100 ,  102 , it is preferred to use so-called hybrid bearings. These have balls made of ceramic and bearing rings made of a corrosion-resistant special-steel alloy. They are manufactured, for example, by the GRW company and are used especially for blood pumps and dental drills. With such bearings, the desired service life is obtained even in unusual media. 
   As an alternative to  FIG. 1 , it is possible to provide, for the journalling of conveying wheel  90 , a rotating shaft that, exactly like shaft  46  of motor  20 , is journalled in a bearing tube (not depicted) that then, like bearing tube  30 , is implemented integrally with portion  80  and protrudes to the right from it, i.e. in mirror-image fashion with respect to bearing tube  30 . With this variant, installation is performed in the same way as described for the installation of external rotor  26 , i.e. by pressing into that bearing tube (not depicted). Installation in this fashion proceeds more quickly than the installation of spring  110  and snap ring  108  in the version according to  FIG. 1 , since pre-assembly in this case can occur outside the pump in a special apparatus, and can be largely automated. 
   In this case as well, stator  22  of external-rotor motor  20  can be sealed in fluid-tight fashion. This can be done by insert-molding with polyurethane or with hot-melt adhesive. In this case the stator can be mounted in the cavity labeled  120  in  FIG. 1  on the bearing tube described (as a variant) in the previous paragraph, and can directly drive rotor  92  of magnetic coupling  94 . Fan wheel  64  is, in this case, driven via a magnetic coupling, i.e. in this case ring magnet  76  directly drives blades  64  of the fan. This enables an even more compact design, since in this case cavity  120  is filled up by the internal stator of the external-rotor motor. It is then also possible to journal fan wheel  64  at its outer circumference in a bearing directly in housing  68 , as is occasionally the practice with such fans. What then results from this is an extraordinarily short design, which is required in many devices. In this case blades  64  are connected at their periphery by a ring. 
   According to  FIG. 4 , which differs slightly from  FIG. 1 , various components are preinstalled on shaft  46  prior to the assembly of motor  20 . 
   Beginning with projection  56 , these are firstly compression spring  58  of preferably conical shape, whose larger-diameter end rests in a depression  39 . 
   Spring  58  is followed below by the annular securing member in the form of securing washer  54 . Spring  58  preferably does not rest against this securing member  54 . 
   Securing member  54  is followed by rolling bearing  48  with its outer ring  48   e  and its inner ring  48   i . The latter is displaceable in an axial direction on shaft  46 . The lower end of spring  58  rests against the upper end of inner ring  48   i . Rolling bearing  48  is followed by spacer  52 , which is guided displaceably on shaft  46  by means of a radially inwardly protruding projection  53 , and whose upper end, as depicted, rests against the lower end of outer ring  48   i.    
   Spacer  52  is followed by lower rolling bearing  50 , with its outer ring  50   e  that rests with its upper end against spacer  52 , and with its inner ring  50   i  that is displaceable in an axial direction on shaft  46  and rests with its lower end against snap ring  59 , as depicted, when motor  20  is completely assembled. 
   It is readily apparent that, if one pushes upwardly with a force F on lower rolling bearing  50 , spring  58  can be compressed and the two bearings  48 ,  50 , spacer  52 , and securing washer  54  can thereby be displaced upward on shaft  46 , so that inner ring  50   i  is no longer resting against snap ring  59  but ends up at a distance from it. In this case, projection  56  of rotor  22  comes to rest against securing washer  54  and makes it possible, by means thereof, to transfer an axial force in a distal direction to securing washer  54 , outer ring  48   e , spacer  52 , and outer ring  50   e  when rotor  26  is pushed downward by a force K during installation. This is depicted below in  FIG. 5 . 
     FIG. 5  shows, so to speak, a snapshot during the “mating” procedure in which shaft  46  of rotor  26 , with rolling bearings  48 ,  50  present thereon, is introduced for the first time into internal opening  77  of bearing tube  30 . 
   In this, a force K is applied in an axial direction onto rotor  26 ; and because outer rings  48   e ,  50   e  of rolling bearings  48 ,  50  are pressed with a press fit into ribs of bearing tube  30 , spring  58  is compressed by the force K so that shaft  46  shifts in a distal direction in ball bearings  48 ,  50 , and projection  56  impinges via securing washer  54  on outer ring  48   e  of ball bearing  48 , and via spacing member  52  also on outer ring  50   e  of ball bearing  50 , thus pressing both ball bearings  48 ,  50  into bearing tube  30 . As depicted in  FIG. 5 , spring  58  is only partially compressed in this context, in order to avoid damaging it. 
   This pressing-in operation continues until outer ring  50   e  of lower ball bearing  50  is resting against the upper end of ribs  83  that are provided in bearing tube  30  at its inner end  60 . 
   In this process, as depicted, securing member  54  is displaced downward in bearing tube  30  and digs into the plastic material of bearing tube  30 , so that it latches or locks the entire bearing arrangement in bearing tube  30 . If an attempt were made to pull rotor  26  out of bearing tube  30  against force K, securing member  54  would only dig that much more deeply into the material of bearing tube  30 ; in other words, this is an extraordinarily secure attachment. There are, of course many different solutions and components for a permanent interlock of this kind, and securing element  54  depicted here therefore represents only a preferred implementation. 
   After pressing-in is complete, force K is removed and the situation according to  FIG. 1  then results, i.e. spring  58  now once again pushes shaft  46  sufficiently that snap ring  59  once again abuts against inner ring  50   i  of rolling bearing  50 . The “mating” process is then at an end. Spring  58  now clamps the two inner rings  48   i ,  50   i  of rolling bearings  48 ,  50  against one another, which is necessary for quiet running of motor  20 . 
   As already stated, the same mounting method can also be used for the installation of conveying wheel  90 , in which case a corresponding bearing tube must then also be provided for the conveying wheel; this represents an alternative (not depicted) to  FIG. 1 . 
   The great advantage of this mounting method is that, in accordance with  FIG. 4 , ball bearings  48 ,  50 , spacer  52 , and snap ring  59  can be preassembled as shown in  FIG. 4 . The preassembled parts can then be tested for reliable operation, and if that is achieved the preassembled rotor  26  (or preassembled conveying wheel  90 ) can easily be pressed into the associated bearing tube, eliminating the need for further installation work. This is therefore a very easy mounting method that contributes to a particularly compact design of the unit. 
     FIGS. 6 and 7  show an analogous rotor mounting method in the case of an external-rotor motor  20 ′ whose shaft  46 ′ is journalled in a double sintered bearing  130 . The latter is pressed into a bearing tube  132  in a predetermined axial position, and external rotor  26 ′ is preassembled in a manner such that sintered bearing  130  together with bearing tube  132  is slid onto its shaft  46 ′, and is then secured with snap ring  59 ′. 
   What is then obtained is a preassembled rotor approximately analogous to  FIG. 4  having, however, not ball bearings but instead a plain bearing  130  that is located at a predetermined axial position in bearing tube  132 . 
   A bearing tube fitting  134  is provided on portion  80 ′ (made of plastic). This fitting is preferably implemented integrally with portion  80 ′. Fitting  134  extends over only approximately half the distance between portion  80 ′ and bottom  136  of rotor cup  26 ′. 
   Pressed into this fitting  134 , as shown in  FIGS. 6 and 7 , is outer rotor  26 ′ with its bearing tube  132 , already preassembled with plain bearing  130 . Bearing tube  132  has on its exterior ribs  138  that are deformed as they are pressed in, and thereby bring about a secure fit and secure mounting. 
   As  FIG. 6  shows, coil former  140  of internal stator  22 ′ is then slid over bearing tube  132  and bearing tube fitting  134 , and brings about additional retention. 
   In this fashion, it is also possible to easily pre-assemble a rotor  26 ′ that is equipped with a plain bearing  130 , and then to mount it in the fan, in the preassembled state, by pressing it in from one side. The same mounting method is of course also possible for conveying wheel  90 , provided plain bearing  130  is compatible with the fluid being conveyed therein. 
   Many variants and modifications are of course possible within the scope of the present invention.