Patent Publication Number: US-2011057529-A1

Title: Mounting method for fitting a permanent magnet in a retaining element

Description:
FIELD OF THE INVENTION 
     The present invention relates to a mounting method for fitting a permanent magnet in a retaining element. 
     BACKGROUND INFORMATION 
     The use of so-called “buried magnets” in rotors in synchronous machines having permanent magnet excitation is generally discussed in German patent document DE 101 31 474 A1, for example. In this type of affixation, magnets are axially inserted into a lamellar pack assembled from individually stamped lamellae and fixed in place in the correct position using various fixation arrangements. The advantage of this technique is that it allows the use of cost-effective block-shaped magnets. Disadvantageous is the complex assembly and fixation technology due to unfavorable manufacturing tolerances of the magnets. 
     SUMMARY OF THE INVENTION 
     The provided solution endeavors to simplify and shorten the mounting processes and to increase the process stability of the fixation technology. If prior to the fitting in a retaining element (e.g., the rotor of an electric machine), the at least one permanent magnet is first at least partially coated by an elastic coating material and only then installed in the retaining element in a subsequent step, it is possible to achieve preliminary fixation of the permanent magnet in the retaining element via the elastic coating material. This prevents the permanent magnets from sliding in the retaining element and not achieving their setpoint positions prior to the introduction of an impregnation arrangement. Elastomers, copolymers made of duroplast and thermoplast, for example, as well as polymer mixtures have shown to be suitable coating materials. For example, it is provided that the coating material covers the permanent magnet on one side or multiple sides, which also may amount only to partial coating, for instance. Then, the coated permanent magnet is placed in the seat of the electromagnetically excitable component of an electric machine. Sliding of the permanent magnets in the seat is avoided solely by the increased friction between seat and coating material. Changes in the position of the permanent magnets in the electromagnetically excitable component are then prevented even better if the dimensions of the coating material are adapted in such a way that a press-fit exists between the permanent magnets provided with the coating material, and the seat. In this case, the coating material gives a little during the insertion into the seat, and shavings are produced at the same time as a result of pressing the permanent magnet and its coating into the seat. A press-fit, for example, is easily verifiable in this way. 
     An additional, improved fixation of the permanent magnet in the seat of the electromagnetically excitable component of the electric machine is achieved by applying an additional adhesive layer on the permanent magnet and its coating material. This adhesive layer improves the adhesion between the permanent magnet or its coating material and the seat of the electromagnetically excitable component. On the one hand, this is able to improve the adhesion; on the other hand, a type of form-fit between the adhesive layer, and thus the permanent magnet, and the seat may be achieved by an expansion of the adhesive layer and/or the coating material, for example. The expandable material may expand under the action of an internal or external reaction-triggering arrangement, for instance. Such an internal reaction-triggering arrangement may, for example, be a crosslinking structure or arrangement contained in the coating material. An external reaction-triggering arrangement may be the action of radiation or heat, for instance. 
     Finally, an electric machine having a permanent magnet is provided, which is mounted according to a mounting method outlined above. 
     The exemplary embodiments and/or exemplary methods of the present invention will be elucidated in greater detail in the following text based on the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an electric machine having a rotor and a rotor reciprocator element. 
         FIG. 2  shows a mounting method in schematic form. 
         FIG. 3   a  shows an example of a coated permanent magnet. 
         FIG. 3   b  shows another example of a coated permanent magnet. 
         FIG. 3   c  shows another example of a coated permanent magnet. 
         FIG. 3   d  shows another example of a coated permanent magnet. 
         FIG. 4  shows a side view of a retaining element having a recess and a permanent magnet disposed therein, the permanent magnet being provided with a reactive coating material. 
         FIG. 5  shows a side view of a retaining element having a permanent magnet in a recess, the permanent magnet being coated both by a coating material and an adhesive layer. 
     
    
    
     DETAILED DESCRIPTION 
     An electric machine  20  shown in  FIG. 1  is provided with a rotatably supported rotor  23  as electrically acting component on the one hand, and a rotor reciprocator element  26  disposed across from it, on the other, the latter normally being implemented as stator  29 . Rotor reciprocator element  26  is permanently mounted in a housing  32  of electric machine  20 . Depending on the use of electric machine  20 , be it as motor or as generator, electrical or electromagnetic forces are acting between rotor  23  and rotor reciprocator element  26 , which either have a driving effect (motor) or an inhibiting effect (generator). 
     Rotor  23  is rotatably supported in the geometrical center of rotor reciprocator element  26 , in the generally known manner. Rotor  23  is made up of a rotor core  35 , which is able to be excited with the aid of two permanent magnets  38  in the exemplary embodiment shown. 
       FIG. 2  shows the mounting method in heavily schematized form. According to first step S 1 , a permanent magnet  38  is first at least partially coated by an elastic coating material. According to step S 2 , coated permanent magnet  38  is to be inserted in a seat  41  of an electromagnetically excitable component (rotor  23 ) of electric machine  20 . According to step S 3 , fixation of permanent magnet  38  is provided. 
       FIG. 3   a  shows a prismatic permanent magnet  38 , which has a trapezoidal cross-section. This trapezoidal permanent magnet  38  has two ends, which have an oblique orientation relative to each other, i.e., at an angle not equal to 180°. In this exemplary embodiment, permanent magnet  38  is coated by coating material  47  both on these two surfaces  44  having an oblique orientation to each other, and on the surfaces adjoining surfaces  44 . The adjoining areas are designated by reference numerals  50  and  53 . Furthermore, the two other surfaces  50 ′ and  53 , which are not visible in this exemplary embodiment, are coated as well. Surface  50 ′ and surface  53 ′ are diametrically opposed to surfaces  50  and  53 . 
     The exemplary embodiment according to  FIG. 3   b  shows a cuboid permanent magnet  38 , where only four of six sides are coated. These are surfaces  53  and  53 ′ as well as  44  and  44 ′. 
     As will still be explained in the following text, these four mentioned surfaces are the surfaces that adjoin the surface of the seat. 
       FIG. 3   c  shows a permanent magnet  38 , which has a rhombic base surface  50  and likewise is prismatic. In this case the two surfaces  44  and  44 ′ are coated. These two surfaces  44  and  44 ′ are two end faces, which are coated by coating material  47 . 
     The cuboid shown in  FIG. 3   d  is coated overall and on all sides by coating material  47 . 
       FIG. 4  shows rotor  23  of electric machine  20  in a partial view. A lamella  60  of this rotor  23  is shown in a side or sectional view, which via rectangular seat  63  extending across a specific width, i.e., across a specific number of lamellae  60 , constitutes. This lamella  60  thus represents with this seat  63  retaining element  66 . In this example, a permanent magnet  38 , shown in a sectional view, is inserted according to the exemplary embodiment from  FIG. 3   d . Permanent magnet  38  is therefore surrounded by coating material  47 . This permanent magnet was inserted with the aid of the mounting method according to the present invention for fitting a permanent magnet  38  in a retaining element  66 ; permanent magnet  38  is held by a coating material  47 , the at least one permanent magnet  38  first being at least partially coated by an elastic coating material  47  prior to being fitted in retaining element  66  or seat  63 , and is mounted in the retaining element (rotor  23 ) in a subsequent step. 
     Within the scope of this mounting method, it is provided that coating material  47  is an elastomer, a copolymerized plastic of duroplast and thermoplast, or a polymer mixture, for example. 
     It is provided that coating material  47  covers permanent magnet  38  on one side or a plurality of sides  44 ,  44 ′,  50 ,  50 ′,  53 ,  53 ′. After permanent magnet  38  ( FIG. 3   d ) has been coated by coating material  47 , it has been inserted in seat  63  of the electromagnetically excitable component (rotor  23 ) of electric machine  20 , which may be the rotor. Taking coating material  47  and its dimensions into account, permanent magnet  38  is dimensionally adapted in such a way that a press-fit exists between permanent magnets  38  provided with coating material  47 , and seat  63 . 
       FIG. 5  shows permanent magnet  38  in seat  61  of rotor  23  or its packeted lamellae  60 . In this case, permanent magnet  38  has an additional adhesive layer  70  for fixing it in place in seat  63  of electromagnetically excitable component  23  of electric machine  20 , the adhesive layer having been applied on this permanent magnet  38  or its coating material  47 . This adhesive layer provides adhesion between permanent magnet  38  or its coating material  47  and seat  61  of electromagnetically excitable component  23 . 
     Starting from the exemplary embodiment according to  FIG. 4 , in order to fix permanent magnet  38  in place in seat  61  of electromagnetically excitable component  23  of electric machine  20 , it is also provided that coating material  47  is an expandable material, which expands under the action of an internal or external reaction-triggering arrangement. This means that, for example, coating material  47  is expandable and, for example, expands under the action of radiation or heat as an external reaction-triggering arrangement, and thereby expands. This would cause permanent magnet  38 , for example, to be retained in seat  61  in a more robust and particularly excellent manner due to the expansion of coating  47 . 
     According to another exemplary embodiment, which is not shown further here, and proceeding from  FIG. 4 , coating material  47  could also have an internal reaction-triggering arrangement, which is a crosslinking arrangement, for instance. Such a crosslinking arrangement, which usually crosslinks plastics, generates heat during the reaction, which thereby affects, for example, an expansive component of coating  47  such that it expands. 
     Starting from the exemplary embodiment according to  FIG. 5 , adhesive layer  70  could also include the internal reaction-triggering arrangement or react to an external reaction-triggering arrangement, as already mentioned, and expand as a result. 
     Finally, an electric machine is provided, which has a permanent magnet  38  which is mounted according to one of the above exemplary embodiments.