Abstract:
The invention relates to an electric motor comprising a permanent magnet rotor, which is supported rotationally about a central axis, a wound stator having a cylinder ring-shaped stator winding, claw poles, which are disposed perpendicularly to ring disc-shaped stator plates and around the central axis, and a cylinder jacket-shaped yoke ring, the length of the claw poles in the axially parallel direction being clearly greater than half the inner diameter of the stator. It is the object of the invention to provide an electric motor, in which the stator is composed of the least number of components, requires simple assembly and has a robust structure and optimum efficiency, thereby enabling greater design flexibility, usability of installation space and thus an economic construction. This objective is solved according to the invention in that the magnetically conductive part of the stator comprises a cylinder jacket-shaped yoke ring and two ring disc-shaped stator plates, the stator plates are each designed as a single piece with a plurality of claw poles and the ring disc-shaped stator plates comprise ends, which are connected to one another.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to an electric motor comprising a permanent magnet rotor, which is supported rotationally about a central axis, a wound stator having a cylinder ring-shaped stator winding, claw poles, which are disposed perpendicularly to ring disc-shaped stator plates and around the central axis, and a cylinder jacket-shaped yoke ring, the length of the claw poles in the axially parallel direction being clearly greater than half the inner diameter of the stator. 
     (2) Description of the Related Art 
     The most common manner of producing claw pole stators consists in bending off the pre-punched claws from the center of a disc perpendicularly thereto. In this manner the maximum length of the claws in the axial direction is limited to approx. half the inner diameter of the stator. The achievable power of such motors is therefore limited and it is sometimes necessary to arrange a plurality of stators in succession. 
     An electric motor of the generic kind is disclosed in US 2002/0180302 A1. In the electric motor disclosed, the stator is composed of four components. The claw poles are punched out from lamellar sheet metals, and then bent to form a ring, the ends of which are connected to one another. Two of these bent claw pole sheet metals are then mounted together with two other stator sheet parts. This method is relatively cumbersome and unreliable. The large number of joints further increases the magnetic resistance and thereby reduces the efficiency of the motor. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore, the object of the invention to provide an electric motor, in which the stator is composed of the least number of components, requires simple assembly and has a robust structure and optimum efficiency, thereby enabling greater design flexibility, usability of installation space and thus an economic construction. 
     This objective is solved according to the invention in that the magnetically conductive part of the stator comprises a cylinder jacket-shaped yoke ring and two ring disc-shaped stator plates, the stator plates are each designed as a single piece with a plurality of claw poles and the ring disc-shaped stator plates comprise ends, which are connected to one another. This helps achieve a small number of parts and accordingly simpler assembly and a robust construction. Furthermore, it also enables design freedom, usability of installation space and thus an economic construction. 
     The claw poles designed as a single piece with the ring disc-shaped stator plates are connected to one another mechanically preferably by means of thin webs in a pre-assembly state. This increases the mechanical stability during the handling in the further production process or also in the assembled state. 
     In order to prevent a loss of the magnetic flux by way of the thin webs, it is greatly advantageous to the efficiency of the electric motor if the webs are cut off or removed in the assembled state. The ends of the ring disc-shaped stator plates are designed in an overlapping manner. An electric resistance welding is thus easily possible. This can be accomplished cost-effectively and is sufficiently permanent. 
     In a further improvement of this embodiment, the webs are sheet-metal webs by means of which the claw poles are connected to one another forming a single piece. This is a requirement in order to punch out both the north poles and the south poles from a single sheet-metal strip and to provide them with the cylindrical shape by rolling them together. This embodiment can be preferred for economic reasons. From the physical aspect, the sheet-metal webs can lead to magnetic short circuits, if their cross-sectional area is not dimensioned to be sufficiently small. In the case of thin sheet-metal webs, these go into magnetic saturation and thus limit the magnitude of the magnetic flux in the webs. The number of the sheet-metal webs also should be kept as low as possible. It would be possible to achieve optimum efficiency if these connecting webs are removed in the final state. 
     The yoke ring should be connected to the stator plates as far as possible without play in order to achieve low magnetic resistance and thus high efficiency. Preferably the yoke ring is caulked with the stator plates. This connection can be produced easily in that the yoke ring is slotted at several locations in its axial boundary area and that sheet-metal bridges adjoining the slots are deformed inwardly in the radial direction. Due to the deformation of the sheet-metal bridges, the yoke ring is pulled inwardly towards the ring disc-shaped stator plates, thereby reducing the magnetic resistance in this area. Furthermore, the sheet-metal bridges also form a form-fit joint between the yoke ring and the ring disc-shaped stator plates—thus also the claw poles in the axial direction. 
     In order to set the distance between the two ring disc-shaped stator plates having the claw poles, the stator plates should be connected to one another by means of an electrically insulating plastic material. This is designed preferably such that the claw poles are encapsulated by injection-molding with malleably plastic material that can be processed, in the form of an insulating body for the stator winding. 
     In a further improvement of this embodiment of the invention, it is suggested to form the insulating body with insulation displacement contacts, a projection being provided on the insulating body in the axial direction for each winding wire to be connected, which projection comprises a receiving slot for a lead and a mounting opening for a contact pin. 
     The insulating body is expediently designed as a single piece with fixing means for a printed circuit board. The fixing means are composed of a stop and a snap-on means. The stop determines the axial position of the printed circuit board in relation to the insulating body and the snap-on means ensure that the printed circuit board is securely held in this position, wherein said snap-on means represents a form-fit connection in the radial direction and can be overcome only axially under a force effect. The printed circuit board comprises openings the diameters of which are adapted to the snap-on means. It is thus possible to rapidly and easily fix the printed circuit board on the insulating body, provision being further made for the contact pin to firstly comprise an insulation displacement geometry and secondly to be designed as a solder-less press-fit pin, which is electrically connected to the printed circuit board. Due to this design of the contact pin, it is possible to simultaneously produce an electrical connection between the stator winding and the printed circuit board when the printed circuit board is mounted. The contact pins are preferably press-fitted into the printed circuit board before mounting the latter. 
     The invention also comprises a centrifugal pump driven by an electric motor of the type described above. When using the electric motor in a centrifugal pump, it is suggested that the insulating body be designed as a single piece with a containment shell, which delimits a wet chamber from a dry chamber of the centrifugal pump. This helps cut down on the insulating body as an additional component. 
     In a particularly preferred further improvement of the invention, the containment shell is made of a plastic material that is transparent to laser light of a wavelength or a wavelength range, the containment shell is heat-sealed as a component of a second housing part to the first housing part and the containment shell is heat-sealed as a component of a second housing part to a motor housing part. The first housing part or the motor housing part is made of a material that absorbs the same laser light. This arrangement makes it possible to join the first housing part to the second housing part and the second housing part to the motor housing part permanently and tightly by using the laser transmission welding process. 
     The preferred method for producing claw pole stators comprises the following steps: punching out air gaps from a magnetically conductive sheet-metal strip so that webs are retained, connecting the north poles and the south poles to one another mechanically,—rolling the sheet-metal strip to form a tubular stator part,—connecting the ends of the sheet metal strip to one another,—encapsulating the tubular stator part by injection-molding with insulating plastic material and punching out the webs. 
     Additional process steps are: winding the stator and inserting the winding ends in receiving slots of an insulating body,—joining a yoke ring and mechanically fixing the yoke ring on the wound stator part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment is explained in detail below with reference to the drawings in which: 
         FIG. 1  shows a ring disc-shaped stator plate with claw poles, 
         FIG. 2  shows two stator plates that are separated from one another, 
         FIG. 3  shows two stator plate areas, which are connected to one another by means of sheet-metal bridges, 
         FIG. 4  shows a flat stator plate strip, 
         FIG. 5  shows a right side view of a tubular yoke ring, 
         FIG. 6  shows a front view of the yoke ring, 
         FIG. 7  shows a spatial representation of the yoke ring, 
         FIG. 8  shows a left side view of the yoke ring, and 
         FIG. 9  shows a side view of a centrifugal pump of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
       FIG. 1  shows a ring disc-shaped stator plate  420  having four claw poles  42 , which are bent off from the stator plate  420  perpendicularly thereto, the stator plates  420  comprising ends  421  which are welded to one another in an overlapping manner. The circumference of the ring disc  420  comprises V-shaped recesses  422 , which are distributed uniformly over the circumference. The claw poles are provided with a trapezoidal shape for the purpose of reducing a detent torque, the claw poles being tapered towards their free ends. 
       FIG. 2  shows a first embodiment with two ring disc-shaped stator plates  420  with their claw poles  42  facing one another, wherein each claw pole  42  of the first stator plate  420  follows a claw pole of the second stator plate  420 . Both the stator plates  420  are shown in their correct positions; however they are not in contact with one another. In the installation state, the stator plates are held by means of an insulating body. The insulating body is made of injection-molded plastic material and is molded around the stator plates for this purpose, wherein connecting means and fixing means are also formed additionally. 
       FIG. 3  shows a second embodiment of the invention, in which the stator plates  420  with the claw poles  42  are punched out of a single sheet-metal strip, the claw poles  42  being connected to one another by means of sheet-metal bridges  423 . The sheet-metal bridges can remain in the stator in the final assembly state if they are designed to be sufficiently thin. However, they reduce the efficiency of the motor. It would be more advantageous here to remove the bridges. This is associated with higher production expenditure. The geometry of the stator with the exception of the sheet-metal bridges  423  corresponds to the arrangement shown in  FIG. 2 . Two claw poles  42  are not connected to one another by means of sheet-metal bridges; instead they form the ends of said sheet-metal strip. The ends  421  of the ring disc-shaped stator plates  420  are welded to one another similarly to  FIGS. 1 and 2 . The welding can be carried out in a welding unit in which the inner diameter of the claw pole ring is calibrated. 
       FIG. 4  shows a sheet-metal strip from which air gap areas  424  are punched out so that webs  423  and V-shaped recesses are retained. This sheet-metal strip is rolled to form a tube in the further production process and the ends are connected to one another. Then the tube is encapsulated by injection-molding with plastic material in one or more work steps in order to connect the claw poles  42  mechanically to a magnetically non-conducting material. The webs  424  are then superfluous and can be removed. This takes place preferably by means of radial punching. For this purpose, the plastic material can be recessed in the area of the webs  423  during the encapsulation by injection-molding. Alternatively, the plastic material is removed together with the webs  423  during the punching process. Since the area of this punch-out is small, there is no necessity of any additional insulating measures. 
       FIG. 5  shows a right side view of a tubular yoke ring  43 , which is punched out from a sheet-metal strip and rolled. Both the ends of the sheet-metal strip are connected to one another at a joint  437 . The joint is created here in the form of form-fitting and button-like connecting means  438  corresponding to one another. The yoke ring comprises slots  431  (seen on its back side here), which are disposed on the periphery of the yoke and in the boundary area of the yoke ring and which are tapered towards their center and the ends of which have radii. 
     As is clearly evident from  FIGS. 7 and 8 , two slots  431  are present, which are disposed in the same peripheral area but on opposing boundaries  435 ,  436 . Both the slots  431  are connected to one another by means of a connection slot  432 , which emanates from the center of each slot  431 . The slots  431  and  432  together form an H-shape. The slots  431  each delimit a web  430  from the body of the yoke.  FIGS. 5 and 7  further show open slots  433 , which are open towards an opening  434 . By means of the slots  433 , sheet-metal tongues  439  are formed, which by bending over in the radial direction (inwardly) serve for securing the stator plates  420  in the axial direction. The sheet-metal bridges  430  serve both for securing the stator plates  420  in the axial direction and for reducing the diameter of the yoke. The radial deformation of the sheet-metal bridges  430  constricts the connection slot  432 , if necessary till both the boundary areas of the connection slot  432  contact one another. 
       FIG. 6  shows a front view of the yoke ring  43  with the opening  434 .  FIG. 7  shows a spatial representation of the yoke ring  43  and  FIG. 8  shows a side view thereof (from the left). 
       FIG. 9  shows a side view of an inventive centrifugal pump  100 , with a pump housing  102  comprising a first housing part  103  and a second housing part  104  connected thereto. A motor housing part  44  delimits a dry chamber, which is filled out by a stator of an electronically commutated direct current motor and its control electronic system. The motor housing part  44  is attached to the second housing part  102  [sic;  104 ]. The first and the second housing parts  103 ,  104  delimit a wet chamber  101  of the centrifugal pump. The second housing part  104  is formed as a single piece with a containment shell  116 , which separates the wet chamber  101  from a dry chamber  99 . 
     The wet chamber  101  comprises an axle  49 , which is permanently installed between a containment shell-side axle mount  48  and a suction connection-side axle mount  47 . A knurl on the end of the axle prevents a rotation of the axle  49  during the pump operation. A fixed bearing  54  is supported rotationally on the axle  49 , which fixed bearing is press-fitted into a hollow shaft  51  of the rotor  50 . The shaft  51  is designed as a single piece with a pump impeller  59 , which comprises a plurality of approximately spirally-shaped vanes  591  for conveying the liquid. The front surfaces of the fixed bearing  54  can be supported axially against the containment shell-side axle mount  48  and against the suction connection-side axle mount  47  by positioning thrust washers in between. A cylindrically hollow ferrite magnet  52  is glued on the hollow shaft  51 , an elastic adhesive being used, which is inserted in four or five axially parallel grooves  511  formed in the hollow shaft. 
     The dry chamber  99  comprises the stator  40  of the electronically commutated direct current motor  10 , which is designed in the form of a cylindrically hollow stator winding  41 , its magnetic field being guided during operation to the periphery of the containment shell  116  by means of claw poles in an alternating manner and interacting with the cylindrically hollow permanent magnet  52  in the wet chamber  101 . The magnetic circuit is closed by a yoke ring  43 , which is connected to the claw poles  42 . The claw poles  42  are provided by means of encapsulating them by injection-molding with an insulating body  46 , which connects the claw poles  42  to one another mechanically, but not magnetically. The stator  40  comprises four pairs of poles in the present example. The insulating body  46  is shaped in such a way geometrically that the winding wires of the stator winding  41  can be connected to contact pins  62  comprising insulation displacement contacts, which can be fixed mechanically in the insulating body  46 . The contact pins  62  are formed as combination contacts and their ends located opposite to the insulation displacement contact  63  are press-fitted into a printed circuit board  61 , thereby contacting the latter. For this purpose, the contact pins  62  comprise one or two deformable press-fit zones. The printed circuit board  61  comprises a Hall sensor  71 , an integrated circuit  70  (IC), a PTC for the winding shield, power components and connector pins  64  for the voltage supply. The motor housing part  44  comprises a connector housing  65  in which the connector pins  64  are disposed. Electronic components with high heat losses are cooled by means of heat conducting foils  67  in the direction of the wet chamber  101 . Conductor paths, which serve for the contacting of components to be cooled, are dimensioned so as to provide the broadest possible conductor paths  66  on the printed circuit board  61  for easier dissipation of heat. In order to achieve a particularly good utilization of the printed circuit board  61  and optimum heat dissipation, the different conductor paths  66  are designed with varying widths, depending on the amount of heat arising in the component connection to be contacted. A longitudinal groove is molded in the form of a cooling channel in the shaft  51  between a base  117  of the containment shell  116  and the pump impeller  59 . This cooling channel enforces a continuous circulation of the conveying medium even in the interior of the containment shell  116 . The printed circuit board is disposed between a front side  45  of the motor housing  44  and the base  117  of the containment shell  116  and is held in heat-conductive contact with the base  117  by means of the heat conducting foil  67 . 
     The first housing part  103  comprises a first flange  130  and a first ring  131  attached thereto. The second housing part  104  comprises a second flange  140  and a second ring  141  attached thereto. The motor housing part comprises a third ring  441 . The second flange  140  and the second ring  141  together form a T-shaped cross-section. Four sealing areas  133 ,  144 ,  145  and  444  are provided. The first sealing area is located on the radially outer side of the first ring  131  on the first housing part  103 . The second sealing area  144  is located on the opposing radially inner side of the second ring  141  and of the second housing part  104 . Likewise, the third sealing area  145  is located on the radially inner side of the second ring  141  and of the second housing part  104 . The fourth sealing area  444  is located facing the third sealing area and on the radially outer side of the third ring  441  and of the motor housing part  44 . The second housing part  104  is made of a material that is permeable to laser light of a wavelength or a wavelength range. The first housing part  103  and the motor housing part  44  are made of a material that absorbs the same laser light. A laser beam can thus be guided up to a joint without significantly heating up the transparent material. Here, the beam hits the material, which absorbs the light and converts it into heat, thereby melting the plastic and causing it to form a deep joint with the adjoining material. 
     Since both the sealing areas to be welded are located close to one another, it is easily possible to produce both the joints in one welding unit and in one work step. The welding unit can comprise two individual lasers, each laser beam being used to produce a welding seam. Alternatively, the welding unit can comprise a single laser, the output beam of which is divided by a beam splitter into two bundles of rays, each of which produces one welding seam. In the present example, the laser beams are focused radially on the pump housing. 
     Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.