Abstract:
A method for mounting permanent magnets that form magnetic poles on a permanent magnet support surface of the rotor of an electric machine includes the steps of forming a mold by the placement of a mold part against the support surface in such a way that the mold cavity of the mold is bounded on one side by the support surface inserting a permanent magnet into the mold so that the inserted permanent magnet is held in the mold in a desired position with respect to the support surface, and filling the mold with a thermosetting adhesive in such that the adhesive bonds the permanent magnet with the support surface and completely fills any spaces formed between the permanent magnet and the wall of the mold cavity.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for mounting permanent magnets that form magnetic poles on a permanent magnet support surface of the rotor of an electric machine. 
     2. Description of the Related Art 
     The positionally precise and secure mounting of permanent magnets on the rotor of permanently energized electric machines, especially their mounting by adhesive bonding, leads to difficulties. Due to the high forces of attraction between the permanent magnets and the rotor, the permanent magnets cannot be easily handled. 
     Methods for mounting permanent magnets on the rotor of electric machines are described, e.g., in DE 39 13 618 A1, EP 0 410 048 B1, and EP 1 473 816 A1. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to create a method that allows a positionally precise and secure joining of permanent magnets with the rotors of electric machines. 
     The invention achieves this object by forming a mold by placing a mold part against the support surface in such a way that the mold cavity of the mold is bounded on one side by the support surface; the insertion of a permanent magnet into the mold in such a way that the inserted permanent magnet is held in the mold in a desired position with respect to the support surface; and the filling of the mold with a thermosetting adhesive in such a way that the adhesive bonds the permanent magnet with the support surface and completely fills the spaces formed between the permanent magnet and the wall of the mold cavity. 
     The mold makes it possible to mount the permanent magnet precisely in the initial position necessary for carrying out the adhesive bonding process and to produce an extremely stable adhesive bond. 
     The permanent magnet can be mounted in the mold some distance from the wall of the mold cavity in such a way that almost the entire surface of the permanent magnet is covered with cured adhesive material, so that the permanent magnet is protected from corrosion. Accordingly, it is possible to use extremely strong high-energy magnets that are susceptible to corrosion. 
     It is advantageous for a mold that is open at the top to be filled from the bottom with adhesive under light pressure. The adhesive can then rise slowly with avoidance of the inclusion of air bubbles in the mold, and air can escape at the top. 
     The permanent magnet is preferably inserted from above into a mold that is open at the top. In a preferred embodiment of the invention, the permanent magnet consists of segments, which are put together to form the permanent magnet by inserting them into the mold. This has the advantage that the smaller segments can be produced and handled more easily than a complete one-piece magnet. 
     In an especially preferred embodiment of the invention, the mold part is produced from a soft magnetic material; and in this way the force of attraction that acts on the permanent magnet or the segments of the permanent magnet and is directed towards the support surface is reduced by magnetic back-circuit with the mold part. During the insertion of the permanent magnet or segments into the mold, only relatively small frictional forces arise from attraction of the permanent magnet or permanent magnet segments towards the support surface. 
     In a further refinement of the invention, several segments to be inserted into the mold can be positioned in an initial position for the insertion operation by arranging them on a guideway of an insertion device in such a way that they are offset from one another in the direction of insertion. This offset makes it possible to avoid the repulsive forces between the segments of the permanent magnet, which hinder their arrangement on the guideway. 
     Reference magnets can be arranged in the initial positions. They provide repulsion and thus prevent the arrangement of segments in incorrect polarity in the initial positions. 
     The mold part is preferably mounted on the rotor in such a way that it can swivel about a joint axis, so that it can be lifted from the support surface by swiveling to allow the cast magnetic pole to be removed from the mold. 
     In a further refinement of the invention, the permanent magnets or segments are inserted with a small, adjustable distance of the mold part from the support surface, the mold part is then placed against the support surface, and the mold cavity is sealed by a strand seal. The small distance from the support surface facilitates the insertion of the permanent magnet or segments into the mold cavity, which is still slightly opened, thereby offering more clearance. 
     Grooves can be placed in the permanent magnet and the support surface, in which adhesive and/or escaping air can flow. This facilitates the filling of the aforementioned gaps and spaces and shortens the filling process. 
     To accelerate the curing of the adhesive in the mold, the mold can be heated. 
     The thermosetting adhesive preferably forms a permanently elastic material. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is explained in greater detail below with reference to the specific embodiment illustrated in the accompanying drawings: 
         FIG. 1  is a perspective view of a section of a rotor ring of a synchronous machine, on which a device for mounting permanent magnets on the rotor ring is mounted. 
         FIG. 2  shows a mold part used in the mounting device of  FIG. 1  in a direction of view towards the axis of rotation of the rotor ring. 
         FIG. 3  is a cross-sectional view of the mold part. 
         FIG. 4  is a perspective view of the device of  FIG. 1  with an insertion device mounted on it. 
         FIG. 5  shows the insertion device of  FIG. 4  in an isolated view that is rotated 90° from the view of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Permanent magnets  25  in the form of rectangular solids, which alternately form a magnetic north pole and a magnetic south pole, are to be mounted on a support surface  1  of a rotor ring  2  of a synchronous machine.  FIG. 1  shows a section of the rotor ring. Mounting is accomplished with a device  3  by which altogether four such magnets can be simultaneously mounted on the support surface  1  at a predetermined tangential distance from each other. 
     The mounting device  3  comprises a mold part  4 , which can be placed against the support surface  1 . The side of the mold part that faces away from the support surface  1  is reinforced by ribs  5 ,  6 . As will be explained later, the mold part  4  and the support surface  1  together form molds. The mold part is mounted on a mounting device  8 , which is connected with the rotor ring  2 , in such a way that it can be swiveled about an axis of rotation  7 . The distance between the mold part  4  and the support surface  1  can be varied by setscrews  9 ,  10 . 
       FIG. 2 , which shows the side of the mold part  4  that faces the support surface  1 , reveals four compartments  11  for the insertion of one permanent magnet  25  each. The permanent magnets  25  consist of magnet segments  12  arranged in thirteen rows and four columns, so that in the present embodiment, each permanent magnet  25  consists of fifty-two segments  12 . 
     The compartments  11 , which are open towards the support surface  1 , are closed only at their undersides by a boundary wall  14 . They are open at the top. The base  22  of each compartment  11  is furnished with a Teflon coating. 
     In the arrangement of the mold part  4  shown in  FIG. 4 , segments  12  can be inserted by a motor-driven insertion device  15  into four chambers formed by the compartments  11  and the support surface  1 . The insertion device  15  has a guideway  16  for eight segments. The segments can be arranged on the guideway  16  in an initial position for the insertion process through windows  17  in a cover  20 , such that the initial positions are offset from one another in the direction of insertion, so that that arrangement of the segments in the initial position is not hindered by mutual repulsion. 
     A lower section  18  of the insertion device  15  serves to join the insertion device  3  with the mounting device. A motor-driven slide  19  moves the four segments  12  arranged in the initial position in the direction towards the mold part  4  by means of drivers  21 . During this operation, the segments are held on the guideway  16  by the cover  20 . 
     In the specific illustrated example here, all together 4992 segments are to be mounted on the circumference of the rotor ring  2 , which form permanent magnets or poles composed of fifty-two segments each. For the simultaneous mounting of four permanent magnets, the mounting device  3  is mounted in the necessary position on the rotor ring  2  and brought into the swivel position shown in  FIGS. 1 and 4 . The setscrews  9 ,  10  are used to produce the desired distance between the mold part  4  and the support surface  1 . In the desired spaced position produced in this way, the segments  12  are pushed into the compartments  11 , whose open sides face the support surface  1 . Eight segments at a time can be simultaneously inserted by the insertion device  15  into the chambers  11  formed by the compartments and the support wall  1 . Reference magnets (not shown) on the rear side of the guideway  16  opposite the windows  17  ensure that the segments  12  can be arranged only in correct polarity in the initial position on the guideway  16 . 
     The guideway  16 , which comprises several individual tracks, consists of material that is not soft magnetic. Therefore, during the advancing of the segments  12  on the guideway; there are no frictional forces to be overcome due to attraction of the segments to the guideway. Stops  26  are formed at the transition to the compartments  11  or chambers and serve to align the segments  12  in a straight row to allow them to enter the chambers simultaneously. Alternatively or additionally, the alignment of the segments could be carried out by producing an end section of the guideway from soft magnetic material. 
     During the entrance of the segments into the compartments  11  or chambers intrinsically strong forces of attraction act in the direction towards the support surface  1 . However, these forces of attraction are largely compensated by virtue of the fact that the mold part consists of a soft magnetic material, so that there is a magnetic back-circuit to the mold part  4 . With suitable magnetizability of the material of the mold part, the force of attraction in the direction of the support surface could be completely overcome, and it would even be possible to produce a force of attraction in the direction of the mold part. The reduction of the force of attraction means that even when the segments are being inserted into the chambers, no large frictional forces arising from forces of attraction need to be overcome. 
     During the advancing of the first row of segments, the segments are stopped against the boundary wall  14 . The following rows of four segments each are stopped against the segments that have previously been inserted. 
     After four permanent magnets have been assembled from segments by inserting segments into the chambers, the mold part  4  is lowered farther towards the support surface  1  by means of setscrews  9 ,  10 , and elastomer seals seal the molds formed by the mold part  4  and the support wall. Two lateral edges of the rectangular solid segments  12  lie against the slightly rounded support surface  1 , with a gap being formed between each segment and the support surface. In addition, gaps with a slightly conical shape are present between the lateral surfaces of the outer segments and the webs  13 . The Teflon-coated base surfaces  22  of the compartments  11  are also separated by a small distance from the sides of the segments  12  that face away from the support surface  1 . 
     A liquid adhesive is introduced under slight pressure through connectors  24  on the underside of the mold part  4 . The adhesive slowly rises to the top in the aforementioned gaps and spaces. The ascent of the adhesive is assisted by longitudinal grooves in the segments  12 , as indicated in  FIG. 2 . Air can also escape through the longitudinal grooves and exit at the top. Grooves  23  running transversely to the longitudinal grooves can be formed in the support surface  1 . The filling with adhesive is ended when the adhesive level rises above the upper ends of the uppermost segments. 
     It is now necessary to wait for the adhesive to cure. The curing can be accelerated by heating the mold, especially the mold part  4 . 
     After the curing is complete, the mold part  4  is swiveled about the axis of rotation  7  to release the four permanent magnets  25  from the mold. The permanent magnets are not merely adhesively bonded with the support surface  1  but rather are also almost completely embedded in the cured adhesive and protected from corrosion. 
     The release of the permanent magnets from the mold is made possible by the Teflon coating on the base  22  of the compartments  11  and by the application of parting agent to the sides of the webs  13  and the boundary wall  14 . The Teflon coating ensures that the segments  12  can slide smoothly without any jerking motion into the mold during the insertion process. 
     To arrange the segments  12  in the initial position on the guideway  16 , a hammer-like tool can be used, whose head consists of a soft magnetic material with a nonmagnetizable coating. The thickness of the coating can be selected in such a way that a desired force of attraction develops between the segment and the head of the hammer. 
     The magnetic poles adhesively bonded with the support surface  1  can be additionally secured against detachment by a band or other suitable cover. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.