Patent Publication Number: US-11652392-B2

Title: Method for forming a crown from a plurality of U-shaped electrically conductive hairpins

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a division of U.S. Ser. No. 16/624,107 filed Dec. 18, 2019 and claims the benefit of the International Application No. PCT/DE2018/100574, filed on Jun. 20, 2018, and of the German patent application No. 10 2017 113 617.7 filed on Jun. 20, 2017, the entire disclosures of which are incorporated herein by way of reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a pre-fitting nest and a method for forming an annular crown from a plurality of U-shaped electrically conductive hairpins in order to then be able to install the crown in a machine element of an electric machine. The invention further relates to a device for manufacturing a machine element of an electric machine. 
     BACKGROUND OF THE INVENTION 
     Electric machines are understood to be, in particular, machines for converting electrical energy into kinetic energy and machines for converting kinetic energy into electrical energy. In particular, this term is to be understood to mean electric motors and generators. 
     When manufacturing machine elements of such electric machines, such as stators and rotors, for example, it is often necessary to connect ends of electrical conductors formed from wires with each other or otherwise process them together, such as cut them or shape them together, for example. 
     For instance, there are electric motors in which coil windings, particularly of the stator, are formed from a plurality of wire pieces whose ends are connected together. Such wire pieces are often referred to as pins or hairpins. The wire from which the hairpins are formed may, in particular, have a rectangular cross section, be configured as a flat, rectangular or profile wire, or be provided in the form of flat strip steel or the like. 
     For example, a stator member with a plurality of grooves serves for accommodating the hairpins. 
     An example of a known hairpin is shown in a lateral view in  FIG.  2   a   . The hairpin  1  has two legs  1   a ,  1   b  extending parallel to each other, and several angles resulting in the shape of a roof, which is also referred to as a house roof shape. In order to fit a plurality of hairpins in as densely packed a manner as possible when manufacturing stators, the hairpins are often bent, in their roof regions, in a direction extending perpendicularly to the plane of the hairpin, i.e. perpendicular to the drawing plane of  FIG.  2     a.    
       FIG.  2   b    shows the hairpin in an enlarged view from above onto its roof. In this view, the two legs  1   a ,  1   b  of the hairpin  1  extend perpendicularly to the drawing plane. The wire bent in this manner has a three-dimensional shape or 3D shape. 
     In order to manufacture, for example, a stator using hairpins as electrical conductors, the different hairpins often must be installed in the stator so as to form one or several annular crowns. At their ends, or the ends of their legs, the individual hairpins are electrically connected to one another and thus form a densely packed coil winding in the shape of one or several crowns. The ends of the hairpins are commonly connected by welding. 
     In order to connect the phases of the stator to a power electronic system, an element for a corresponding interconnection, for example, is electrically connected to the crown assembly. 
     In the methods for producing a stator with hairpin technology known thus far, the hairpins are manually fitted into the stator directly. 
       FIG.  3   a    shows, by way of example, a known stator  200  in a view from above, which has a plurality of grooves  211  for accommodating hairpins  1 . The legs  1   a ,  1   b  of the hairpins  1  are positioned by fitting them into the grooves  211 . 
       FIG.  3   b    shows an enlarged section of the known stator in a partial view from above. The two legs  1   a ,  1   b  of an individual hairpin or pin are fitted into a respectively assigned groove  211   a ,  211   b . These two grooves are spaced apart, so that the hairpin or pin extends with its roof across several grooves  211  situated between them, into which further hairpins are fitted, so as to result in a crown-shaped arrangement of superposed hairpins. In order to obtain a high packing density of the hairpins and thus of the stator windings, the hairpins have to be positioned very close to each other. 
     The known techniques for producing machine elements, such as stators, for example, using hairpins present the following drawbacks, in particular: 
     Manually fitting the hairpins into the stator is time-consuming and incurs high costs. 
     Due to the grooves  211  being arranged in a radiating shape, viewed from the center of the stator, the U-shaped pins or hairpins barely have clearance in the respective groove. For the fitting process, however, the outer leg of the hairpin has to be fitted at a radius that is farther outside than is the case later in the stator, after all hairpins have been fitted into the stator and are in their final position. With an arrangement of grooves in a radiating shape in the stator, this is not possible in a reliable manner. 
     Thus, tensions in the hairpins may arise after they have been fitted into the stator, which may have disadvantageous effects. 
     In addition, the known arrangement generates a force pulling the fitted pins or hairpins towards the center of the accommodating means. This is disadvantageous in subsequent working processes. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to enable, in the production of a machine element, such as a stator, for example, an automated fitting of the hairpins and ensure a reliable fitting process with a high packing density. 
     In order to achieve this object, the invention provides a pre-fitting nest for forming an annular crown from a plurality of U-shaped electrically conductive hairpins in order to then be able to install the crown in a machine element of an electric machine, comprising an accommodating member with a plurality of grooves for accommodating the legs of the U-shaped hairpins, wherein the grooves are annularly disposed about a center Z and extend perpendicularly to the plane of the accommodating member, and the grooves are configured in such a way, with respect to their size and geometry, that in each case a first leg of a hairpin can be rotated within the groove in order thus to enable an unconstrained positioning of the second leg of the hairpin in another groove. 
     By forming one or several crowns of U-shaped hairpins in advance by means of a pre-fitting nest, i.e., before the hairpins are installed in a stator, for example, an automated and reliable fitting with a high packing density can take place, e.g., by means of a robot. The invention further makes it possible to collect or fit the pins in an accommodating means to form a crown. For example, the different crowns may be collected in an accommodating means in order to then be able to insert them into a machine element, particularly into a stator. 
     Advantageously, the grooves of the accommodating member are considerably larger than the cavities of the machine element or stator for accommodating the hairpins. This enables the automatic fitting of the U-shaped pins or hairpins in an even better manner. 
     The grooves of the accommodating member are configured in such a way that the hairpins are moved into their intended position in the accommodating member by the influence of gravity. Thus, the hairpins fall into their intended positions even better, resulting in an even easier positioning process. 
     Preferably, the grooves of the accommodating member are disposed in a radiating shape about the center Z. In particular, they may have side walls that extend in the radial direction in relation to the center Z. For example, the grooves may have a width B that increases outwards in the radial direction. 
     Advantageously, the grooves of the accommodating member are disposed offset or slightly offset with respect to one another, e.g., in the shape of a turbine. Thus, the one leg of a hairpin is more easily able to rotate about the center of the other leg in the accommodating member. Thus, the hairpins are protected even better from damage when they are fitted. They have more space in the accommodating member and are not subjected to any force. 
     The grooves of the accommodating member may, in each case, have side walls that extend in the direction of a point P outside the center Z. In particular, the points P of the individual grooves may, for example, be disposed on a circle around the center Z. 
     These actions improve the non-constrained positioning of the hairpins even more, and reduce the risk of possible damage even further. 
     Preferably, the accommodating member has an inner ring on whose outer face the side walls of the grooves are formed in order to retain the hairpins in their respective positions. 
     Advantageously, the accommodating member has an outer ring on whose inner face the side walls of the grooves are formed in order to retain the hairpins in their respective positions. 
     In particular, the accommodating member may be configured in such a way that there is no inner ring or no outer ring. In this case, the hairpins are retained in their position by the geometry of the accommodating member. 
     In particular, the accommodating member may have an inner ring and an outer ring between which the grooves are formed as cavities. 
     For example, the accommodating member has holding members disposed on the inner ring and/or the outer ring in order to form the grooves. In particular, it may have holding members configured as bolts, studs or metal sheets or the like in order to accommodate the hairpins or to form the grooves for accommodating the hairpins. 
     Advantageously, the grooves are configured in such a way that several annular crowns of individual hairpins are formed by accommodating the legs of the hairpins. For example, after a crown has been completed, the individual crowns may be joined, e.g., in an accommodating member configured as a collection receptacle. 
     For example, the grooves may have an inclined portion and/or one or more offsets in order to position one or several hairpins or hairpin crowns in the radial direction. The radial positioning of the individual crowns ensures the joining of several crowns in the accommodating member. Moreover, a crown to be joined is prevented from colliding with a crown that was already joined. 
     Because of the inclined portion and/or the offsets, which are formed, for example, on the upper side of the accommodating member in the region of the grooves, the hairpins or hairpin crowns are brought to an outer diameter and positioned there by gravity or a force acting from outside. 
     Advantageously, the pre-fitting nest has a frustoconical shape in the region of the grooves. 
     In particular, the grooves may have side walls at whose upper ends an inclined portion and/or one or more steps are formed. 
     For example, the pre-fitting nest is configured as a multiple pre-fitting nest for forming several crown layers. 
     In particular, due to the geometry of the accommodating member, the invention makes it possible, with a robot in an automated manner, to fit the hairpins together to form crowns, and also to collect several crowns in an accommodating means. 
     According to one aspect, the invention provides a device for manufacturing a machine element of an electric machine, comprising a pre-fitting nest for forming a crown from a plurality of U-shaped electrically conductive hairpins, a machine element housing for accommodating the hairpins, and an apparatus for delivering and inserting the crown of U-shaped hairpins into the machine element housing. 
     In particular, the pre-fitting nest may, in this case, be configured in accordance with the invention. 
     According to another aspect, the invention provides a method for forming a crown from a plurality of U-shaped electrically conductive hairpins in order to then be able to install the crown in a machine element of an electric machine, comprising the steps of: 
     providing a plurality of U-shaped electrically conductive hairpins; 
     joining the hairpins by fitting the legs of the hairpins into an accommodating member, so that the hairpins together form a crown; 
     wherein, when the respective hairpin is fitted into the accommodating member, a first leg of the hairpin is rotatably held in the accommodating member in order to position the second leg of the hairpin in the accommodating member by rotation about the first leg; 
     then providing the crown of hairpins for introduction into a hairpin accommodating means of the machine element. 
     Advantageously, the accommodating member has grooves for accommodating the hairpins which are larger than the grooves of the machine element or the stator for accommodating the hairpins. 
     For example, the grooves may be disposed in a radiating shape. They may also be disposed in an offset manner relative to one another. 
     Preferably, the hairpins fall into their respectively intended position due to the influence of gravity. 
     Advantageously, several crowns are formed and joined to form a multi-layer crown member. 
     Preferably, a crown or several crowns, subsequent to their manufacture, are inserted into a machine element or stator. The insertion of several crowns into the machine element or stator may take place individually and one after the other, or also together as an assembly of several crowns. 
     In particular, the method is carried out with a pre-fitting nest according to the invention. 
     According to another aspect of the invention, a pre-fitting nest according to the invention is used for carrying out the method according to the invention. 
     According to an additional aspect, a device according to the invention is used for carrying out the method according to the invention. 
     Advantages and details of the invention mentioned in connection with the pre-fitting nest according to the invention also apply to the device according to the invention and the method according to the invention, just as advantages and details mentioned in connection with the method according to the invention or the device according to the invention also apply to the pre-fitting nest according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a schematic illustration of a pre-fitting nest of the invention according to a preferred embodiment, as a view from above; 
         FIGS.  2   a  and  2   b    show a schematic illustration of a known hairpin in a lateral view ( FIG.  2   a   ) and in a view from above onto the roof of the hairpin ( FIG.  2   b   ); 
         FIGS.  3   a  and  3   b    show a schematic illustration of a known stator as a top view in a total view ( FIG.  3   a   ) and in an enlarged partial view ( FIG.  3   b   ) with a plurality of grooves for accommodating hairpins; 
         FIGS.  4   a  and  4   b    show a schematic illustration of a pre-fitting nest of the invention with offset webs, as a view from above ( FIG.  4   a   ) and as an enlarged partial view from above ( FIG.  4   a   ); 
         FIG.  5    shows a schematic illustration of a pre-fitting nest of the invention with offset webs or grooves, as an enlarged view from above; 
         FIGS.  6   a  and  6   b    show a schematic illustration of the upper part of a pre-fitting nest with inclined portions formed, as a view from the front ( FIG.  6   a   ) and as a view from above ( FIG.  6   b   ); 
         FIGS.  7   a  and  7   b    show a schematic illustration of the upper part of a pre-fitting nest with steps formed, as a view from the front ( FIG.  7   a   ) and as a view from above ( FIG.  7   b   ); 
         FIG.  8    shows a schematic illustration of a pre-fitting nest of the invention without an outer ring, as a view from above; 
         FIG.  9    shows a schematic illustration of a pre-fitting nest of the invention without an inner ring, as a view from above. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG.  1    shows a pre-fitting nest  100  according to a preferred embodiment of the invention in a view from above. The pre-fitting nest  100  serves for forming at least one crown from a plurality of U-shaped electrically conductive hairpins, so that the crown can then be installed in a machine element of an electric machine. In this example, the crown is to be installed in a stator which is suitable particularly for an electric motor of a motor vehicle. 
     The pre-fitting nest  100  comprises an accommodating member  10  with a plurality of grooves  11  serving for accommodating the legs  1   a ,  1   b  of U-shaped hairpins  1 . One example of such known hairpins  1  was described above with reference to the  FIGS.  2   a  and  2   b   . However, differently configured hairpins than those shown in  FIGS.  2   a  and  2   b    may also be accommodated in the device  100 . 
     In the accommodating member  10 , grooves  11  are annularly disposed about a center Z of the pre-fitting nest  100 . Here, the grooves  11  extend perpendicularly to the plane of the accommodating member  10 , i.e. perpendicularly to the drawing plane of  FIG.  1   . 
     With respect to their size and geometry, the grooves  11  are configured in such a way that in each case the first leg  1   a  of a hairpin  1  can be rotated within the groove  11 , so that an unconstrained positioning of the second leg  1   b  of the hairpin  1  in another groove  11  is thus enabled (also see  FIGS.  2   a ,  2   b   ). 
     The grooves  11  of the accommodating member  10  are disposed in a radiating shape about the center Z of the latter. They have side walls  11   a ,  11   b  that extend in the radial direction in relation to the center Z. The width B of the grooves  11  increases outwards in the radial direction. 
     The grooves  11  of the accommodating member  10  are configured to be considerably larger than the cavities or grooves of the stator in which the hairpins  1  are later to be accommodated. This facilitates fitting the U-shaped pins and can be carried out in an automated manner. 
     Due to the geometry of the arrangement of the grooves, it is possible, when inserting a respective hairpin  1  into a groove  11  of the accommodating member  10 , to rotate the hairpin  1  about the leg  1   a  thereof, which is already accommodated in the groove  11 . That means the leg  1   a  in the groove  11  forms a rotation axis. The crown of mutually superposed hairpins  1 , which will later, i.e., after the removal from the pre-fitting nest  100 , be inserted into the stator, is formed in a non-constrained manner in the pre-fitting nest  100 . 
     In contrast, in the known stator shown by way of example in  FIG.  3   , no rotation of the respective hairpin leg  1   b  about the rotation point R is possible when inserting the hairpin. That means that here, the individual hairpins  1  are unable to rotate about the leg  1   a  already fitted into the groove  211   a  of the stator  200 , so that no rotation R′ can occur. Thus, tensions arise during or after the fitting of the hairpins into the stator, which may have disadvantageous effects. 
     Due to the grooves  11  of the pre-fitting nest  100  according to the invention being enlarged as compared with the stator, and due to the geometry of the grooves  11  and their arrangement, which enables the rotation of the hairpin legs  1   a ,  1   b  in the respective groove  11  during fitting, the hairpins  1  can be positioned in the pre-fitting nest  100  in an automated manner, e.g., by means of a robot. Tensions are avoided when the hairpins  1  are fitted. 
     Then, the hairpins may be inserted in an automated manner into the future stator as a finished crown or as a crown assembly of several crowns. Thus, a reliable, automated and tension-free forming of hairpin crowns in stators is made possible by means of the pre-fitting nest according to the invention. 
       FIGS.  4   a  and  4   b    show another exemplary embodiment of the invention in a view from above or as an enlarged partial view from above.  FIG.  5    shows an enlarged view from above. In the pre-fitting nest  100  according to this example, the grooves  11  are disposed in a slightly offset manner. This arrangement may be referred to as turbine-shaped. 
     The side walls  11   a ,  11   b  of the grooves  11  each extend in the direction of a point P outside the center Z of the pre-fitting nest  100  (see  FIG.  5   ). The points P of the respective grooves  11  are disposed on a circle around the center Z. 
     The width B of the grooves  11  increases outwards in the radial direction also in this exemplary embodiment. The other details and features of this exemplary embodiment are as described above with reference to the first exemplary embodiment. 
     When a hairpin  1  is positioned, the latter is able rotate about its leg  1   a , which is located in a groove  11 . The rotation point or rotation axis is marked with an R in  FIG.  4   b   . As a result, the other end of the hairpin, i.e., its leg  1   b , is able to rotate in the accommodating member  10  or its groove  11  about the rotation point or rotation axis R. The rotary movement of the leg  1   b  about the leg  1   a  is labeled R′. 
     The geometry of the grooves  11  is configured such that this rotation is made possible. Since the pins have more space in the accommodating means and are not exposed to any force, the pins are not damaged during fitting. In addition, the pins fall into the intended positions better and more easily due to the influence of gravity. 
     The offset grooves or webs result in an even larger clearance for the hairpins. This results in an even further improved tension-free arrangement of the hairpins in the shape of one or more crowns. 
       FIGS.  6   a  and  6   b    show another possible embodiment of the invention. Here, the pre-fitting nest  100  has inclined portions  18  formed on its upper side, which extend in the radial direction. In this example, the inclined portions  18  are configured to drop off in a radially outward direction. The inclined portions  18  are each located at the upper end of the grooves  11  and have the effect that the pins or hairpins, or crowns formed from them, are brought to an outer diameter or radius of the accommodating member  10  and positioned there by the influence of gravity and/or an external force. 
       FIGS.  7   a  and  7   b    show a different possible embodiment of the invention, in which steps or offsets  19  are formed on the upper side of the pre-fitting nest  100  in the radial direction. The steps  19  are located at the upper edge of the grooves  11  and are configured to drop off in a radially outward direction in this example. Just like the inclined portions  18  described above, they have the effect that the pins or hairpins, or crowns formed from them, are brought to an outer diameter or radius of the accommodating member  10  and positioned there correspondingly by the influence of gravity and/or by an external force or force acting from outside. 
     That means that, when a single pin or a crown formed from pins is fitted into the grooves  11  from above, the pins or pin crowns are moved outwards into the intended radial position by means of the inclined portions  18  and/or the steps  19 . 
     The inclined portions  18  and steps  19  may also be combined with each other. 
     In particular, the radial positioning of the hairpins by means of the inclined portions  18  and/or the steps  19  of the grooves  11 , as described above with reference to  FIGS.  6   a  and  6   b    or  7   a  and  7   b , has the effect that, once a crown of hairpins  1  has been completed, several crowns may be joined and positioned. 
     The individual crowns formed from hairpins may be positioned in the radial direction in a defined manner in the accommodating means or the accommodating member  10  and held there, so that a crown to be joined does not collide with a crown that was already joined. 
     The reliable joining of several crowns in the accommodating means or the accommodating member  10  is thus ensured. In this case, the accommodating member  10  forms a collection receptacle for joining several crowns. 
       FIG.  8    shows yet another possible configuration of the accommodating member  10 . Here, the accommodating member  10  has an inner ring  14  but no outer ring. Instead, the pins or hairpins are retained in the required position by the geometry of the accommodating member  10 . For this purpose, the grooves  11  are formed on the outer face of the inner ring  14  of the accommodating member  10 . The side walls  11   a ,  11   b  of the grooves  11  extend radially outwards from the outer face of the inner ring  14 . 
     For this purpose, webs or projections  16  in the form of fins, which extend outwards or radially outwards from the outer face of the inner ring  14 , are formed on the inner ring  14 . Thus, the projections  16  form holding members for the hairpins  1 . For example, bolts, spikes, metal sheets or other holding members may also be mounted on the inner ring  14 , which accommodate the pins or form grooves for accommodating the pins. 
       FIG.  9    shows another possible configuration of the accommodating member  10 , in which only an outer ring  15  exists, but no inner ring. Webs or projections  16  in the form of fins extend inwards or radially inwards from the outer ring  15  and thus form holding members for the hairpins  1 . Also in this case, bolts, spikes, metal sheets or other holding members, for example, may be installed, which accommodate the pins or form grooves for accommodating the pins. 
     It is also possible to provide both an inner ring  14  and an outer ring  15 , between which the grooves  11  for accommodating the hairpins at their legs  1   a ,  1   b  extend. 
     A method for forming a crown from a plurality of U-shaped electrically conductive hairpins will be described below by way of example. The method serves for being able to subsequently install the crown in a machine element of an electric machine, particularly in a stator for an electric motor for motor vehicles. 
     In this method, a plurality of U-shaped electrically conductive hairpins  1  is provided first (see  FIGS.  2   a  and  2   b   ). 
     The hairpins  1  are now joined by fitting their legs  1   a ,  1   b  into the accommodating member  10  (see, for example,  FIG.  1    and  FIG.  5   ). In this way, the hairpins  1  form a crown together. 
     When the hairpins  1  are fitted into the accommodating member  10 , a first leg  1   a  of the respective hairpin  1  is rotatably held in the accommodating member  10 , so that the second leg  1   b  of the respective hairpin  1  can be positioned in the accommodating member  10  by rotation about the first leg  1   a  (see, for example,  FIG.  4   b   ). 
     For easier, non-constrained positioning, the grooves  11  in the accommodating member  10  are considerably larger than the grooves of the stator in which the hairpins are later to be accommodated. The grooves  11  may also be disposed in a radiating shape and/or in an offset manner relative to one another. 
     During the fitting process, the hairpins  1  fall into their respectively intended position due to the influence of gravity. 
     In particular, inclined portions  18  or offsets  19  are provided for improved positioning, as they are described above with reference to  FIGS.  6   a  and  6   b    or  7   a  and  7   b.    
     The crown of hairpins formed in the manner is then provided for introduction into a machine element or a hairpin accommodating means of a machine element, wherein the machine element is a stator in this example. Then, the crown may be inserted into the stator. Also, several crowns may be inserted into the stator one after the other, for instance. 
     In particular, using the pre-fitting nest  100 , several crowns may also be formed in the method by joining individual hairpins, and may be joined to form a multi-layer crown member. This assembly of several crowns may then be removed from the pre-fitting nest  100  and inserted into the stator as a complete package. 
     Moreover, several pre-fitting nests may be used for manufacturing a crown assembly consisting of several hairpin crowns. In this case, the individual crowns of hairpins are formed with different diameters in a pre-fitting nest or in several pre-fitting nests. The crowns with different diameters formed in this manner are then arranged together in a further pre-fitting nest, which in this case serves as a collection receptacle or collection pre-fitting nest and is configured for this purpose. 
     The forming of the crown or crowns from hairpins and the subsequent delivery and insertion into the housing of a machine element, which is a stator housing, for example, preferably takes place in an automated manner, e.g., by means of a robot. 
     Due to the geometry of the accommodating means or the accommodating member  10 , it is thus possible with a robot to fit the hairpins to form a crown, and to collect several hairpin crowns in an accommodating means. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Hairpin 
           1   a ,  1   b  Hairpin leg 
           10  Accommodating member 
           11  Grooves 
           11   a ,  11   b  Side walls of grooves 
           14  Inner ring 
           15  Outer ring 
           16  Projections, fins 
           18  Inclined portion 
           19  Offset 
           100  Pre-fitting nest 
           200  Stator 
           211  Grooves of stator 
           211   a ,  211   b  Grooves of stator 
         B Width of grooves 
         P Point outside the center 
         R Rotation point or axis 
         R′ Rotary movement 
         Z Center