Patent Publication Number: US-2021184530-A1

Title: Stator for an Electric Machine

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a stator for an electric machine, an enveloping element for a stator and a method for producing a coil. 
     The electrical conductors for producing the windings of, for example, stators of electric motors are usually produced by enameled wire. The enamel is in this case used for electrical insulation. For connecting the individual conductors, this insulation is stripped off at the corresponding contact points. Once the connection has been produced (for example by welding, soldering or (hot-)crimping etc.), the joint needs to be provided with insulation again. This can take place, for example, by powder coating or encapsulation with a casting resin. In the case of encapsulation with the resin, the stator is positioned, for example, in an apparatus. Then, the casting resin is introduced into the apparatus. Once the resin has cured, the apparatus is removed again. One disadvantage with this is that such casting molds wear, contaminate and need to be cleaned or even replaced from time to time. 
     One object of the present invention therefore is specifying a stator, an enveloping element and a method for producing a coil which enable effective, quick and inexpensive insulation of stators or coils. 
     This object is achieved by a stator, an enveloping element and a method according to the independent claims. Further advantages and features can be gleaned from the dependent claims and the description and the attached figures. 
     In accordance with the invention, a stator for an electric machine comprises a shaped bar winding, wherein the shaped bar winding is formed by a multiplicity of shaped bars which have connection or contact points in the region of an end winding, wherein at least the connection or contact points are enveloped by a casting layer, and wherein a thickness of the casting layer is predetermined by an enveloping element, which is arranged on or fastened to the end winding close to the contour. In this case, the expression “close to the contour” should in particular be understood to mean that a shape of the enveloping element follows a shape of the corresponding end winding as far as possible, as a result of which, in particular, a casting layer with a thickness which is as uniform as possible or a casting layer with a substantially constant thickness or wall thickness is produced. The enveloping element is in this case arranged directly, in other words immediately, on the end winding or else indirectly, in particular via the casting layer, on the end winding. In the case of the shaped bar or else hairpin technology, a corresponding shaped wire is bent in two or three dimensions to form a hairpin and introduced into a stator laminate stack of the stator. The actual end winding is then shaped by transposing of the hairpins. For this purpose, the ends of the hairpins are oppositely transposed, for example, in accordance with the desired wiring diagram, cut to the correct length and then welded, wherein the abovementioned connection points are produced, with the result that a coil running through the stator is produced. 
     Expediently, the enveloping element comprises an end section, which is oriented substantially transversely with respect to a longitudinal axis of the stator or a stator core, cf. the abovementioned laminate stack, as well as an inner and an outer enveloping section, which extend along the longitudinal axis. The inner enveloping section and the outer enveloping section are arranged radially with respect to one another in relation to the longitudinal axis and, together with the end section, form an arrangement space or an “envelope” for the end winding. Preferably, the end section and the two enveloping sections are closed, i.e. do not have any openings or the like, which is associated with some advantages, inter alia in respect of the production costs. 
     Preferably, the enveloping element is connected, at least in regions, to the at least one end winding via the casting layer. Expediently, the enveloping element is fastened, at least in regions, to the end winding via the casting layer. In this case, it is particularly advantageous that, owing to the close-to-the-contour shape of the enveloping element, a thin, but also uniform, casting layer is made possible, which primarily is also light. Preferably, the casting layer is formed over the entire area between the enveloping element and the end winding. 
     In accordance with one embodiment, the enveloping element has pockets and/or undercuts or forms pockets and/or undercuts. This makes it possible for the enveloping element to be able to follow a geometry or an outer contour of the end winding, i.e., advantageously close to the contour. In other words, the enveloping element, as already mentioned, is matched to the shape of the end winding or follows the shape of the end winding. As a result, it is also achieved in particular that a casting material or in particular a casting resin is used in a sparing manner with respect to resources. For this purpose, the enveloping element can also have, in addition to the pockets or outward bulges, inward bulges or generally projections and/or recesses. Typical casting layer thicknesses are in this case, for example, in a range of from approximately 1 to 5 mm. In this case, however, it is also unproblematic if a thickness of the casting layer is “zero”, so to speak, i.e., if the conductor elements, in particular the shaped bars, rest directly against the enveloping element. In this case, the insulation is provided directly by the enveloping element. As a result of the fact that the enveloping element remains on the end winding, this is unproblematic, however. 
     In accordance with one embodiment, the enveloping element is designed to be flexible, at least in regions. In this case, the enveloping element develops its final rigidity only once the casting layer has cured. This may be advantageous in respect of the production of the enveloping element since shape and position tolerances may possibly be larger. Alternatively, the enveloping element is a solid shape, however, which can be pushed onto the end winding. Preferably, the enveloping element is formed from a plastic, in particular a plastic which itself has good electrical insulation properties. 
     In accordance with one embodiment, the enveloping element is designed in such a way that it is also fastened in a force-fitting manner to the end winding. In this case, the enveloping element is fastened to the end winding not exclusively via the casting compound. This may be advantageous in respect of installation since the enveloping element so to speak also “holds” on the corresponding end winding although no casting compound or no casting resin has yet been arranged, for example injected. 
     The invention is also directed at an enveloping element for a stator according to the invention. 
     Furthermore, the invention is directed at a method for producing a coil, in particular for producing or insulating a stator of an electric machine, including the following steps:
         providing a coil, which has at least one end winding;   using an enveloping element for shaping a casting layer on the at least one end winding.       

     At this juncture, mention will be made of the fact that the advantages mentioned in connection with the stator apply similarly and correspondingly to the method and to the enveloping element, and vice versa and between themselves. 
     In accordance with one embodiment, the method includes the following steps:
         introducing casting compound into the enveloping element prior to attaching the enveloping element to the at least one end winding;   dipping the at least one end winding into the enveloping element.       

     The enveloping element is filled with (casting) resin, for example. Then, the coil, in particular a stator of an electric machine, is dipped with the end winding to be cast into the resin. Then, the resin can cure, and the enveloping element remains on the stator. 
     In accordance with one embodiment, the method includes the following steps:
         arranging the enveloping element on the at least one end winding;   introducing casting compound between the enveloping element and the at least one end winding.       

     In this case, the enveloping element is therefore first positioned on the stator and then filled with (casting) resin. Expediently, the enveloping element does not have any fill openings or the like for the resin. Instead, in accordance with one embodiment, the resin is advantageously introduced into a gap which is provided in any case between the end winding and the enveloping element. 
     The possibility of filling the casting cap at different times or in different ways is a considerable advantage in terms of production. The enveloping element itself can in both cases have the same configuration. 
     The use of the enveloping element, which remains on the coil or on the stator even after the casting, markedly increases the stability of the stator, in particular the mechanical stability, for example in the case of oscillations, in particular also in comparison with a powder coating. Preferably, the stator is a stator of an electric machine of a motor vehicle, in particular an electric vehicle or hybrid vehicle. It is also advantageous that, in contrast to the case of a conventional injection mold, undercuts or the like can also be produced without any problems, as a result of which optimum matching of a shape of the enveloping element to a shape of the end winding is possible. In addition, cleaning of the injection-molding die, maintenance thereof etc. is no longer required, with the result that the proposed solution is also interesting in terms of costs. 
     Further advantages and features can be gleaned from the description below of embodiments of a stator and an enveloping element with reference to the attached figures. Various features can in this case be combined with one another within the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  shows a section through an embodiment of an enveloping element in a schematic illustration; 
         FIG. 2  shows a side view of a stator with an enveloping element arranged thereon in a schematic view; 
         FIG. 3  shows a further schematic view of an embodiment of an enveloping element; 
         FIG. 4  shows a plan view of a further schematic view of an embodiment of an enveloping element. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a sectional illustration of an enveloping element  20 , which has an approximately circular end section  22 , from which an inner enveloping section  24  and an outer enveloping section  26  extend along a longitudinal axis L. The longitudinal axis L runs parallel to or on a stator axis (not illustrated further here). The reference symbol  1  denotes a casting compound with which the enveloping element  20  has been filled. Thus, for example, a stator can be dipped with its end winding into an enveloping element  20  which has been prepared in this way. Once the casting compound  1 , for example the casting resin, has cured, the enveloping element  20  then remains on the stator or on the end winding. Reference symbol A also illustrates an arrangement direction. In particular, this is intended to mean a direction along which the enveloping element  20  can be pushed onto an end winding. As has already been mentioned, however, it is also possible for the end winding to be moved into the enveloping element  20  in the opposite direction to this arrangement direction A. 
       FIG. 2  shows a schematic view of a stator  10 , which has an end winding  12  at each end. The stator extends along a longitudinal axis L or along a stator axis S. The stator  10  illustrated here has, for example, a shaped bar winding, wherein the shaped bars or hairpins have been pushed into a stator core from the right-hand side. In the left-hand part, the shaped bars are then transposed or else interconnected to form the end winding  12  illustrated there. In this region, which is illustrated as a section, an enveloping element  20  is now pushed onto the end winding  12  along the arrangement direction A, with the result that, after the casting, a casting layer  2  has been formed around the end winding  12 . It can be seen at least schematically that a shape of the enveloping element  20 , in particular the arrangement space thereof, which is formed by the end section and the inner and the outer enveloping section, cf. in this regard also  FIG. 1 , follows a shape of the end winding  12 . In the region of the end winding  12 , a phase terminal  14  is furthermore also provided, which is used for making electrical contact with the stator  10 . 
       FIG. 3  shows, in a further schematic illustration, an enveloping element  20 , wherein it can be seen in the embodiment shown here that the enveloping element  20  can have pockets  28 , which extend radially or axially away from an end section  22  or from an outer enveloping section  26 . 
       FIG. 4  shows, similarly to  FIG. 3 , a multiplicity of pockets  28 , wherein it can be seen that the pockets  28  extend along a longitudinal axis L or an arrangement direction A. An enveloping element  20  is shown here in a plan view (viewed along the arrangement direction A). The pockets  28  extend radially and axially with respect to the longitudinal axis L of the enveloping element  20 . In principle, such pockets serve the purpose of making it possible for the enveloping element to follow, as precisely as possible, a shape or a geometry of the winding head therebeneath. Precisely when the end winding is connected, for example, to a phase terminal assembly, as illustrated in  FIG. 2  (reference symbol  14  in this figure), it may arise that some shaped bars practically “protrude” from the end winding. The pockets  28  or else outward bulges, undercuts or the like nevertheless enable a uniform thickness of the casting layer. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  casting compound 
           2  casting layer 
           10  coil, stator 
           12  end winding 
           14  phase terminal 
           20  enveloping element 
           22  end section 
           24  inner enveloping section 
           26  outer enveloping section 
           28  pocket 
         L longitudinal axis 
         S stator axis