Abstract:
Disclosed are a stator ( 10 ) for an electric machine ( 12 ) and a method for manufacturing a stator of said type which comprises a stator body ( 34 ) that has radial stator teeth ( 14 ); each stator tooth ( 14 ) accommodates exactly one coil section ( 18 ) of an electric winding ( 16 ); the winding ( 16 ) consists of exactly two separate winding strands ( 24, 25 ) which are wound from exactly two separate winding wires ( 22 ) and each of which has three phases ( 26 ) comprising at least two coil sections ( 18, 17 ) each.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a stator for an electric machine, and to an electric machine, and to a method for producing a stator. 
         [0002]    DE 10 2012 224 153 A1 has disclosed a stator of an electric machine, in the case of which an insulating lamination and an interconnect disk are arranged axially on a lamination stack. The stator is for example enwound with needle windings, wherein the individual sub-coils are connected to one another by means of connecting wires at the outer circumference of the interconnect disk. Here, the entire winding is wound continuously in unipartite fashion by means of a single winding wire. 
         [0003]    For safety-critical electric motor applications, for example in power steering systems, the intrinsic safety of such electrical windings is a recurrent point of discussion. Here, there is the risk that, in the event of damage to the insulating lacquer of the winding wire, for example, a short circuit of the winding can arise, which leads to blockage of the electric motor. It is sought to eliminate such a risk by means of the solution according to the invention. 
       SUMMARY OF THE INVENTION 
       [0004]    The apparatus according to the invention and the method according to the invention have the advantage in relation to this that, by means of the embodiment of the electrical stator winding as two electrically entirely mutually separate winding strands, it is ensured that, even in the event of a short circuit of one winding strand, the motor can continue to be operated by means of the other winding strand. Here, the power of the electric motor may duly be reduced, but it remains possible to continue reliably implementing safety-relevant applications, such as for example the steering of a vehicle, possibly by imparting an increased manual force. If the winding is formed with two sets of three phases, the motor can, in the event of a short circuit, continue to be operated with the remaining three phases, wherein each phase is made up of at least two sub-coils which are wound onto different stator teeth. 
         [0005]    Accordingly, the stator body is preferably formed as a continuous ring in a circumferential direction, wherein the individual stator teeth are integrally formed radially inwardly on said stator body. The stator preferably has twelve stator teeth, though embodiments with 18 or 24 stator teeth are also possible. 
         [0006]    The stator body is advantageously constructed in layered fashion from individual sheet-metal laminations which together form a lamination stack. To reduce the detent torque of the electric machine, the individual stator laminations are particularly expediently rotationally offset with respect to one another in the circumferential direction, such that the longitudinal direction of the stator teeth deviates from the axial direction by a certain skew angle. Here, in each case all of the stator teeth form, with the outer yoke ring of the stator, in each case one unipartite stator lamination which is closed in the circumferential direction. 
         [0007]    To achieve intrinsic safety of the electric motor, the first winding strand is arranged geometrically entirely on a first stator half, and the second winding strand is arranged entirely on the opposite stator half. In this way, the motor is divided into two motor halves, wherein, in the event of a short circuit, it is always the case that one motor half (angular region of 180° of the stator body) remains functional. In this embodiment, it is particularly advantageous that, in the case of the interconnect plate, there are no crossing points of the connecting wires between the individual sub-coils, whereby the likelihood of a short circuit is further reduced. On both axial face sides of the stator body, there is arranged in each case one insulating lamination for the purposes of insulating the electrical winding with respect to the sheet-metal laminations. Here, at least one of the two insulating laminations has guide elements which are formed in unipartite fashion on the insulating lamination and into which the connecting wires can be laid between the sub-coils during the winding process. In order that the individual connecting wires do not make contact, they are arranged on the insulating lamination in axially different planes. To minimize the interconnection complexity of the individual sub-coils, it is always the case that in each case two sub-coils situated geometrically directly adjacent to one another in the circumferential direction are connected to form a so-called sub-coil pair, which, for example in the case of a 12-toothed stator, forms one complete phase in each case. It is particularly advantageously the case here that two immediately adjacent sub-coils are wound directly in succession in terms of time without interruption, whereby a very short connecting wire between said two sub-coils of the sub-coil pair is formed. 
         [0008]    Furthermore, a sub-coil pair may also be produced by virtue of a first sub-coil with a wire start firstly being wound and then an adjacent stator tooth being wound in the circumferential direction at the end of a winding strand, wherein then, the wire end is connected to the wire start, such that said connection likewise forms a short connecting wire of a sub-coil pair. Here, the wire start and the wire end are clamped into corresponding receptacles of the insulating lamination in order to reliably fix these. For this purpose, the receptacles may be of labyrinthine form. 
         [0009]    After the winding process, the short connecting wires of the respective sub-coil pairs all lie in the same axial plane. For the interconnection of the individual sub-coils, a so-called interconnect plate is mounted axially onto the insulating lamination, wherein different interconnection concepts can be realized by means of different interconnect plates. Here, the connecting wires laid in the guide elements form a defined interface, which connecting wires are connectable to corresponding fastening sections of the conductor elements. Here, it is for example possible for an interconnect plate to electrically connect two sub-coil pairs to form a common phase with a total of four sub-coils, or else to actuate all sub-coil pairs in each case as separate phases with only two sub-coils. For this purpose, the interconnect plate has different conductor elements, which altogether have only three or else for example six terminal plugs for the motor control unit. 
         [0010]    The interconnect plate is in the form of a plastics ring which is arranged axially on the sub-coils. The internal opening of said plastics ring corresponds in this case approximately to the internal stator opening into which the rotor can then be inserted. The outer diameter of the plastics ring is smaller than the outer circumference of the insulating lamination, such that the plastics ring can be inserted radially within the outer circumference of the insulating lamination. By means of this embodiment, the interconnect plate does not take up any additional radial structural space. 
         [0011]    For the reliable positioning of the terminal plugs, axial projections are formed in unipartite fashion on the plastics ring, which projections serve as plug bases for the terminal plugs. The terminal plugs are angled approximately at right angles on the conductor elements, the other ends of which are electrically contacted, via the fastening sections, with the connecting wires of the winding. Here, the fastening sections form a defined connecting interface with the connecting wires, wherein the central part of the conductor elements and the terminal plugs may be designed in accordance with customer demands. If two sub-coil pairs are interconnected to form a common phase, the interconnect plate has a total of only three conductor elements in each case of unipartite form. By contrast, if it is sought for all sub-coil pairs in each case to be actuated as six separate phases, six separate conductor elements with a total of six terminal plugs are arranged on the plastics ring. The conductor elements may advantageously be formed as bent and punched parts or else as bent wires. 
         [0012]    It is particularly expedient if always two terminal plugs are guided in a common holding element such that, both in the case of six terminal plugs and in the case of three terminal plugs, in each case only three axial projections are formed as holding elements. Here, the two adjacently arranged terminal plugs are electrically insulated with respect to one another by the plastics guides of the holding elements. Furthermore, the central parts of the conductor elements run in radially offset fashion in axially different planes, such that, in this case, too, contact between the conductor elements is prevented. In this way, it is for example the case that the first terminal plug of a holding element is electrically contacted with a sub-coil pair which is situated radially exactly opposite a further sub-coil pair (180° in the stator) which is connected to the terminal plug of the other conductor element in the same holding element. 
         [0013]    The conductor elements can be fastened on the plastics ring in a very simple and reliable manner by means of hot stamping. For this purpose, axial rivet pins are formed on the plastics ring, which rivet pins engage through corresponding holes in the conductor elements, wherein the ends of the rivet pins are subsequently plastically deformed to form rivet heads. Alternatively, the conductor elements may be fixed by means of detent elements integrally formed on the plastics ring. If the conductor elements are formed as bent and punched parts from sheet metal, the terminal plugs can be formed very inexpensively as an installation-displacement connection, into the end-side notches of which a corresponding clamping part of the connecting plug to the control unit can be inserted. 
         [0014]    After the installation and contacting of the interconnect plate with the connecting wires, the stator body can be installed axially into a motor housing, for example by being pressed in, shrink-fitted in or adhesively bonded in. Thereafter, a bearing bracket can be joined axially onto the interconnect plate, wherein the bearing bracket has, at the locations of the holding elements, corresponding cutouts for receiving the plug bases with the terminal plugs. Said cutouts in the bearing cover then form the electrical leadthroughs from the motor control unit to the electrical winding of the stator. 
         [0015]    The electrical winding of the stator is preferably formed by means of a needle winding machine, in which a winding head lays the winding wire in along the oblique stator grooves and leads the connecting wires between the sub-coils into the corresponding guide elements of the insulating lamination. Here, for example in the case of a twelve-toothed stator, six stator teeth on the radially first stator half are wound with a first winding wire and, subsequently, the remaining six stator teeth are wound with a second, separate winding wire. Here, the wire start and the wire end of a single winding strand are preferably arranged adjacent to one another in parallel in the insulating lamination, such that said two adjacent wires can be electrically contacted jointly through the fastening sections of the conductor elements, in the same way as the individual short connecting wires of the continuously wound sub-coil pairs. In this way, two electrically insulated motor halves are realized which, depending on requirements, can also again be electrically interconnected with one another in a simple manner via a corresponding interconnect plate by means of the defined interfaces of the connecting wires. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Exemplary embodiments of the invention are illustrated in the drawings and discussed in more detail in the following description. In the drawings: 
           [0017]      FIG. 1  schematically shows a winding diagram according to the invention, 
           [0018]      FIG. 2  shows an interconnection according to the invention of the individual phases, 
           [0019]      FIG. 3  shows a first exemplary embodiment of a wound stator with insulating lamination, 
           [0020]      FIG. 4  shows a corresponding plan view as per  FIG. 3 , 
           [0021]      FIGS. 5 and 6  show an exemplary embodiment as per  FIG. 3  with a mounted interconnect plate, and 
           [0022]      FIG. 7  schematically shows the conductor elements of the interconnect plate without a plastics body. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  schematically illustrates a cut-open stator  10 , on the stator teeth  14  of which the winding diagram of the electrical winding  16  according to the invention is illustrated. The stator  10  has for example twelve stator teeth  14 , wherein in each case always exactly one sub-coil  18  is wound onto each stator tooth  14 . Here, in each case two sub-coils  18  situated immediately adjacent to one another are connected by means of a short connecting wire  31  to form an adjacent sub-coil pair  20 , which in this embodiment forms in each case one distinct phase  26  V 1 , U 1 , W 1 , V 2 , U 2 , W 2 . Here, the three phases  26  V 1 , U 1 , W 1  form a distinct winding strand  24  which is wound from a separate winding wire  22 . The three phases  26  V 2 , U 2  and W 2  form a second winding strand  25  which is wound from a second, separate winding wire  22  and which is electrically insulated with respect to the first winding strand  24 , as illustrated by the dash-dotted line between the sixth and seventh stator teeth  14  in  FIG. 4 . The electrical winding  16  begins for example with a first wire start  28  on the second stator tooth  14 , and a connecting wire  30  is led to the fifth stator tooth  14 . Immediately after the fifth stator tooth  14 , the sixth stator tooth  14  is wound, such that said sub-coil pair  17  is connected by means of the short connecting wire  31  for the sub-coil pair  17 . After the sixth stator tooth  14 , the winding wire  22  is led by means of the connecting wire  30  to the third stator tooth  14 , in order there to form a sub-coil pair  17 , which is connected by means of the connecting wire  31 , together with the fourth stator tooth  14 . From the fourth stator tooth  14 , the winding wire  22  is led via the connecting wire  30  to the first stator tooth  14 , where the wire end  29  of the first winding strand  24  is arranged immediately adjacent to the wire start  28 . The second winding strand  25  is wound, with a separate winding wire  22 , correspondingly to the winding of the first winding strand  24 , such that a further three sub-coil pairs  17  of immediately adjacently arranged sub-coils  18  are formed, which are connected by means of a short connecting wire  31 . The wire start  28  and the wire end  29  of the two winding strands  24 ,  25  are in each case electrically connected to one another. It is thus possible for six phases to be actuated separately from one another. 
         [0024]    This is shown for example for a delta connection in  FIG. 2 , in the case of which the first winding strand  24  with the three phases  26  V 1 , U 1 , W 1  is electrically entirely separate from the second winding strand  25  with the three phases  26  V 2 , U 2 , W 2  (whereby two separate delta connections are formed). Here, the six phases  26  are fed with current in each case via the short connecting wires  31 , which are arranged in each case between two adjacently arranged sub-coils  18  on immediately adjacently arranged stator teeth  14 . In the exemplary embodiment, the stator  10  has a total of  12  stator teeth  14 , though embodiments are also conceivable in which each of the six phases  26  has for example a total of three or four sub-coils  18 , which are correspondingly wound onto 18 or 24 stator teeth  14 . 
         [0025]      FIG. 3  now shows a three-dimensional view of a stator  14  which has been wound correspondingly to the winding diagram from  FIG. 1 . The stator  14  has a stator body  34  which is for example assembled from individual sheet-metal laminations  36 . Here, the stator body  34  comprises a ring-shaped closed return yoke  38  on which the stator teeth  14  are radially inwardly integrally formed. In the interior, the stator  14  has a circular cutout into which a rotor (not illustrated) can be inserted, as can be seen more clearly in  FIG. 4 . The stator teeth  14  extend inward in a radial direction  4  and along the rotor axis in an axial direction  3 . In the exemplary embodiment, the stator teeth  14  are formed so as to be skewed in the circumferential direction  2  in order to reduce the detent torque of the motor. For this purpose, it is for example the case that the sheet-metal laminations  36  are correspondingly rotationally offset with respect to one another in the circumferential direction  2 . Before the stator body  34  is enwound, insulating laminations  40  are mounted onto the two axial face sides  39  in order to electrically insulate the winding wire  22  with respect to the stator body  34 . At least one of the two insulating laminations  40  has a ring-shaped closed circumference  41 , from which insulating teeth  42  extend in the radial direction  4 , which insulating teeth cover the face sides  39  of the stator teeth  14 . On the ring-shaped circumference  41  of the insulating lamination  40 , there are formed guide elements  44  in which the connecting wires  30 ,  31  are led between the sub-coils  18 . For this purpose, it is for example the case that grooves  45  in the circumferential direction  2  are formed on the outer circumference  41 , such that the connecting wires  30 ,  31  are arranged in axially offset planes in order to prevent the connecting wires  30 ,  31  from crossing over. The short connecting wires  31  between the sub-coil pairs  17  are arranged in the uppermost axial plane, wherein in particular all six short connecting wires  31  for the contacting of the phase terminals all run in the same axial plane. For this purpose, two axial projections  46  are always formed between two sub-coils  18  of a sub-coil pair  17 , which projections are separated from one another by an interposed radial aperture  47 . Thus, the short connecting wires  31  of the sub-coil pairs  17  are freely accessible from all sides and, in particular in the region of the radial aperture  47 , do not bear against the insulating lamination  40 . The two wire starts  28  and wire ends  29  are, in this exemplary embodiment, fixed in a labyrinth arrangement  50 , which labyrinth arrangements are each arranged immediately adjacent, in the circumferential direction  2 , to the two axial projections  46  which are spaced apart by a radial aperture  47 . It can thus be seen in  FIG. 3  that the wire start  28  of the first winding strand  24  runs, over the circumferential region of the radial aperture  47 , parallel and immediately adjacent to the wire end  29  of the first winding strand  24 . Here, the wire start  28  is arranged in a first labyrinth arrangement  50  on one side of the radial aperture  47 , and the wire end  29  of the first winding strand  24  is arranged in a second labyrinth arrangement  50  opposite the radial aperture  47  in the circumferential direction  2 . By means of this parallel arrangement of the short connecting wires  31 , these can be electrically contacted in the same way as the individual connecting wires  31  of the continuously wound sub-coil pairs  17  for the purposes of the phase actuation. 
         [0026]    In  FIG. 4 , it can likewise be clearly seen that the two connecting wires  31  running parallel are arranged at the same radius. The free ends of the wire start  28  and of the wire end  29  end directly after the corresponding labyrinth arrangements  50 , such that they do not protrude radially beyond the connecting wires  30 ,  31 . The connecting wires  30 ,  31  all run in the circumferential direction  2  along the guide elements  44  and lie radially outside the sub-coils  18  wound onto the stator teeth  14 . In  FIG. 4 , the two motor halves  11 ,  13  are schematically separated by the dash-dotted line, wherein the left-hand motor half  11  is electrically insulated with respect to the right-hand motor half  13 . The electrical winding  16  is manufactured for example by means of needle winding, wherein the connecting wires  30 ,  31  can, by means of a winding head, be led radially outward between the sub-coils  18  and laid in the guide elements  44 . In this embodiment, all connecting wires  30 ,  31  are arranged axially on one side of the stator body  34 . In an alternative embodiment which is not illustrated, it is also possible for a part of the connecting wires  30 ,  31  to be laid onto the axially opposite side of the stator  14 . Here, it is for example possible for the short connecting wires  31  for the contacting of the phase actuation to be arranged in a first insulating lamination  40 , and for the other connecting wires  30 , which connect the different sub-coil pairs  17  to one another in each case, to be led on the axially oppositely arranged insulating lamination  40 . 
         [0027]    In  FIG. 5 , an interconnect plate  52  has been mounted onto the embodiment of the stator  10  as per  FIG. 3 , by means of which interconnect plate the electrical winding  16  is actuated. For this purpose, the interconnect plate  52  has terminal plugs  54  to which customer-specific connecting plugs  56  of a control unit can be joined. In this embodiment, exactly six terminal plugs  54  are provided, which are in each case electrically connected to one phase  26  of the electrical winding  16 . Here, each phase  26  is formed by exactly one sub-coil pair  17 , such that the six terminal plugs  54  are contacted with exactly six connecting wires  31  of adjacent sub-coil pairs  17 . For this purpose, the interconnect plate  52  has exactly six conductor elements  58  which, on an axially angled end, have the terminal plugs  54  and, on the other end, have a fastening section  60  which is electrically connected, for example welded, to the connecting wires  31 . The interconnect plate  52  has a plastics body  62  which is formed as a closed ring  61  through which the rotor can be inserted into the stator  10 . On the plastics body  62  there are integrally formed in unipartite fashion holding elements  63  which extend away from the stator body  34  in the axial direction  3 . The conductor elements  58  extend in the circumferential direction  2  along the plastics body  62 , wherein the angled terminal plugs  54  are led in the axial direction  3  within the holding elements  63 . On the other end, the conductor elements  58  have the fastening section  60 , the free end of which is formed as a loop  64  which surrounds the connecting wires  31 . Here, the loop  64  is formed from a sheet-metal material, the cross section of which is approximately rectangular. In the exemplary embodiment, the conductor elements  58  are formed as bent and punched parts  59  composed of sheet metal, such that the loop  64  can be bent out of the free end of the fastening section  60 , during the installation thereof, around the connecting wire  31 . After the arrangement of the open loop  64  around the connecting wire  31 , it is for example the case that electrodes are laid onto both radially oppositely situated surfaces of the loop  64 , which electrodes are pressed together in the radial direction while being fed with current in order to weld the loop  64  to the connecting wire  31 . Here, the insulating lacquer of the connecting wire  31  is melted, resulting in a metallic connection between the fastening section  60  and the connecting wire  31 . The loop  64  is laid around the connecting wire  31  in the region of the radial aperture  47 , because in this region, no guide element  44  is arranged between the connecting wire  31  and the loop  64 . As a result, sufficient free space is available for the electrodes to be laid on, such that a free limb end  65  of the loop  64  can be pressed against the fastening section  60 , whereby the loop  64  is closed. Here, depending on the sub-coil pair  17 , the loop  64  surrounds only a single connecting wire  31  or simultaneously surrounds 2 connecting wires  31  which run adjacent to one another in parallel and which are formed from the wire start  28  and the wire and  29  of a single winding strand  24 ,  25 . The terminal plugs  54  are for example formed as insulation-displacement connections  55  which, at their free axial end  68 , have a notch  69  into which a wire or a clamping element of the corresponding connecting plug  56  of the customer can be inserted. Furthermore, a transverse web  70  is formed in the radial direction  4  on the terminal plug  54 , which transverse web is correspondingly supported on an axial stop  72  of the holding element  63 . Furthermore, on the holding element  63 , a first guide surface  74  and a second guide surface  75  are formed which support the terminal plug  54  in the two opposite circumferential directions  2 . This prevents the terminal plugs  54  from bending over or bending out in the circumferential direction  2  during the insertion of the connecting plugs  56 , whereby the axial tolerances of the plug connection are ensured. 
         [0028]    The conductor elements  58  are arranged at least partially radially adjacent to one another, whereby it is necessary for the fastening sections  60  of the inner conductor elements  58  to radially cross the outer conductor elements  58  in order to be contacted with the connecting wires  31 . Therefore, the radially inner conductor elements  58  are arranged on an axially higher path  76  of the plastics body  62 , and the radially outer conductor elements  58  are arranged on an axially lower-lying path  77 . Here, the central sections  78 , which are in the form of sheet-metal strips, of the conductor elements  58  bear areally against the plastics body  62  and are connected to the latter for example by means of rivet connections or detent elements. For this purpose, it is for example the case that axial rivet pins  79  are formed on the plastics body  62 , which rivet pins engage through corresponding axial apertures  80  of the conductor elements  58 . By means of heat, in particular ultrasound, the ends of the rivet bolts can be deformed to form a rivet head  81 , which forms a form fit with the conductor elements  58 . 
         [0029]    In the exemplary embodiment, it is always the case that two terminal plugs  54  are arranged in a common holding element  63 , wherein said terminal plugs are separated from one another in the circumferential direction  2  by a central web  82  of the holding element  63 . Here, the central web  82  forms, on both sides, in each case a first and a second guide surface  74 ,  75  for the respectively abutting terminal plugs  54 . The second and first guide surfaces  75 ,  74  situated in each case opposite the central web  82  are formed by corresponding counterpart surfaces  83  which extend in the radial direction  4  and axial direction  3 . In the region of the holding elements  63 —axially opposite these—there are integrally formed spacers  84  which support the interconnect plate  52  axially with respect to the stator body  34 . In the exemplary embodiment of  FIGS. 5 and 6 , exactly one holding element  63  has a greater width  85  in the circumferential direction  2  than the two other holding elements  63 . In this way, a rotation prevention means is realized for a bearing cover (not illustrated) which is mounted axially with correspondingly shaped axial leadthroughs onto the holding elements  63 . 
         [0030]      FIG. 6  shows how the two terminal plugs  54  bear at both sides against the central web  82 . Angled in each case in opposite circumferential directions  2 , the respective central section  78  of the conductor element  58  adjoins the terminal plug  54 . Since the conductor elements  58  situated radially adjacent to one another are arranged on axially different paths  76 ,  77 , said conductor elements do not make contact, such that they are electrically insulated with respect to one another. The inner ring of the plastics body  62  is of slightly undulating form in order that a punch tool can be engaged on the inner ends of the stator teeth  14 , directly on the side surfaces thereof. In this way, the stator  10  can be pressed into a motor housing (not illustrated). 
         [0031]      FIG. 7  shows the six conductor elements  58  once again without a plastics body  62  of the interconnect plate  52 , in order to illustrate how the six fastening sections  60 , with the respective loops  64 , feed current to the six phases  26  V 1 , U 1 , W 1 , V 2 , U 2 , W 2  in accordance with the winding diagram of  FIG. 1  via the respective terminal plugs  54 . Via the connecting plugs  56  (not illustrated), the electrical winding  16  is thus contacted with a control unit in which, for example, the interconnection configuration as per  FIG. 2  can be realized.