Hairpin conductor for a stator winding with improved insulation and method for manufacturing such a hairpin conductor and stator

Abstract

A hairpin conductor (12, 12a.12w) for a stator winding (6) of an electric machine (1) is disclosed. The hairpin conductor (12, 12a.12w) comprises a metal core (14) with a surrounding basic insulation (15) and an additional insulation (16) on the basic insulation (15), wherein a surface energy of the additional insulation (16) is lower than a surface energy of the basic insulation (15). Further on, a stator winding (6) with such a hairpin conductor (12, 12a.12w), an electric machine (1) with such a stator winding (6), a vehicle (20) with such an electric machine (1) and methods for manufacturing such a hairpin conductor (12, 12a.12w) and a stator with such hairpin conductor (12, 12a.12w) are disclosed.

Description

[0001] Hairpin conductor for a stator winding with improved insulation and method for manufacturing such a hairpin conductor and stator

[0002] TECHNICAL FIELD

[0003] The invention relates to a hairpin conductor for a stator winding, wherein the hairpin conductor has a metal core with a surrounding basic insulation. Moreover, the invention relates to a stator for an electric machine, comprising a stator lamination pack with notches and stator windings, which are arranged in said notches and which are made of a plurality of hairpin conductors of the above kind. In addition, the invention relates to an electric machine with such a stator and a vehicle with such an electric machine for propelling or driving the vehicle. For example, a vehicle may be a land craft, a watercraft or an aircraft. Finally, the invention relates to a method of manufacturing a hairpin conductor for a stator winding and a method of manufacturing a stator for an electric machine.

[0004] BACKGROUND ART

[0005] The aforementioned elements, devices and methods are generally known in prior art. Hairpin conductors are used for manufacturing a stator winding without a dedicated winding process. Instead, a plurality of hairpin conductors is interconnected, for example by means of welding, so as to form the stator winding. The basic insulation avoids short circuits and partial discharges between the hairpin conductors under different voltages, in particular between hairpin conductors of different electrical phases. In this context, there are regions, which are particularly prone to such partial discharges, namely the winding heads or ends. In these regions, the hairpin conductors of different electrical phases lay over one another and side by side with punctually very short distances in-between. Quite regularly, the hairpin conductors of different electrical phases even touch each other so that there is no air gap at all and where is only the basic insulation, which avoids said short circuits. The basic insulation can be made thicker to avoid the risk of partial discharges further, however, to the disadvantage of low current density in the stator notches. Further on, the risk of cracks in the basic insulation is increased if the windings in the region of the winding head stick to each other because of a thick basic insulation. Both, logically undermine the goal of avoiding partial discharges, short circuits and arc flashes. Yet another problem is the glue or resin, which is often used to fix the stator windings to the stator notches. Generally, the glue or resin can be applied by hot dipping or by means of a trickling process. It interconnects the hairpin conductors even in the region of the winding heads and hinders movement between the different hairpin conductors what can result in excessive shear forces and thermal stress between the hairpin conductors. These regions are very prone for initiation of cracks. This interconnection of the hairpin conductors even can lead to complete peel off of the basic insulation resulting in a complete break down of the insulation function and in turn to a break down of the electric machine. Quite often, repairing such a damage is not economical leading to the total loss of the electric machine as a consequence.

[0006] DISCLOSURE OF INVENTION

[0007] An object of the invention is to provide an improved hairpin conductor for a stator winding, an improved stator for an electric machine, an improved electric machine, an improved vehicle with such an electric machine, an improved method of manufacturing a hairpin conductor for a stator winding and an improved method of manufacturing a stator for an electric machine.

[0008] The object of the invention is solved by a hairpin conductor as disclosed in the opening paragraph, which comprises an additional insulation on the basic insulation, wherein a surface energy of the additional insulation is lower than a surface energy of the basic insulation. In a more mathematical language this means: Surface energy of the additional insulation < Surface energy of the basic insulation.

[0009] Moreover, the object of the invention is solved by a stator for an electric machine, which comprises a stator lamination pack with longitudinal and in particular axial notches and stator windings, which are arranged in said notches and which are made of a plurality of hairpin conductors as presented above.

[0010] In addition, the object of the invention is solved by an electric machine with such a stator and a vehicle with such an electric machine for propelling or driving the vehicle. Further on, the object of the invention is solved by a method of manufacturing a hairpin conductor for a stator winding, wherein the hairpin conductor has a metal core with a surrounding basic insulation, comprising the step of applying an additional insulation on the basic insulation, wherein a surface energy of the additional insulation is lower than a surface energy of the basic insulation. For example, the additional insulation can be applied by spray coating or immersion coating.

[0011] Finally, the object of the invention is solved by a method of manufacturing a stator for an electric machine, comprising the steps: providing a stator lamination pack with longitudinal and in particular axial notches for stator windings and a) mounting a plurality of hairpin conductors as presented hereinbefore into said notches and forming stator windings by electrically connecting the hairpin conductors or b) mounting a plurality of hairpin conductors each with a metal core with a surrounding basic insulation, forming stator windings by electrically connecting the hairpin conductors and applying an additional insulation on the basic insulation of the hairpin conductors, wherein a surface energy of the additional insulation is lower than a surface energy of the basic insulation.

[0012] By the proposed measures, the insulation of hairpin conductors can substantially be improved. On the one hand, the risk for partial discharges, short circuits and arc flashes can be reduced by thickening the insulation layer, on the other hand, the risk for cracks in the basic insulation is kept low as well. The reason is the loose connection between the additional insulation and the basic insulation. Accordingly, even if a crack occurs in the additional insulation, it does not continue through the basic insulation and uncover the metal core. In a more scientific language, the difference in surface energy means less adhesion than cohesion. A breaking point, if there is one at all, shall be arranged between the different materials of the additional insulation and the basic insulation. So, even in case of cracks in the additional insulation, there is a basic function of the insulation, which is sufficient to withstand the different voltages between the different hairpin conductors.

[0013] In particular, a surface energy of the additional insulation can below 40 mN / m or below 40 mJ / m2respectively. For example, the additional insulation can be made of thermo- plastistic elastomers (TPE), Polyamide (PA), fluoroplastics such as Polytetrafluoroethylene (PTFE) or silicone(s) (SI). Moreover, the basic insulation can be made of enamel. By use of such materials and / or material combinations the above advantages can be provided on a very high level.

[0014] It is advantageous if the additional insulation is applied only in a first hairpin region of the hairpin conductor, which (only) comprises a center bending and adjacent legs of the hairpin conductor. In this way, the thickness of the insulation is kept low in the region of the hairpin conductor, which is arranged within the stator lamination pack. The voltage drop or potential difference between different hairpin conductor is not very high there, and so a very high current density can be obtained in the stator notches.

[0015] In one embodiment, the additional insulation is arranged in the whole first hairpin region of the hairpin conductor. In this way, the additional insulation is easy to produce, for example by immersion coating.

[0016] In another embodiment, the additional insulation is arranged (only) in half the first hairpin region of the hairpin conductor or on one of the legs adjacent to the center bending of the hairpin conductor respectively. In this way, material can be saved and less additional space in winding ends is needed, nevertheless keeping the insulating function on a high level.

[0017] In yet another embodiment, the stator windings can be fixed to the notches in the stator lamination pack by means of a glue. In this way, the stator windings are kept in position during operation of the electric machine. For example, the glue can be made of or can comprise resin and may also be denoted as “varnish” or “impregnation resin”.

[0018] Advantageously, a surface energy of the additional insulation can be lower than a surface energy of the glue. In this way, the advantages claimed for the combination of the basic insulation and the additional insulation hereinbefore equally apply to the combination of the additional insulation and the glue. Again, there is just a loose connection between the additional insulation and the glue which lowers the risk for the formation of cracks and peel off.

[0019] Generally, glue or resin can be applied by hot dipping or by means of a trickling process. In one embodiment, the winding head shall be kept free of the glue or the resin. However, it is nearly impossible that glue or resin unintentionally is also applied to parts of the winding head. In a second embodiment, the winding head is intentionally coated with the glue or resin. In both cases, the material choice for the additional insulation allows for micro movements between the hairpin conductors. That is why excessive shear forces and thermal stress between the hairpin conductor can be avoided or at least can be reduced. In turn, the risk for the formation of cracks and the risk for peeling of the whole insulation is substantially be reduced. In a more mathematical language the above means: Surface energy of the additional insulation < Surface energy of the glue or resin.

[0020] BRIEF DESCRIPTION OF DRAWINGS

[0021] The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

[0022] Fig. 1 shows a sectional view of an exemplary electric machine;

[0023] Fig. 2 a schematic view on a stator winding made of a plurality of hairpin conductors;

[0024] Fig. 3 a plurality of hairpin conductors laying over one another in the region on the winding heads and forming critical zones there;

[0025] Fig. 4 a first example of a hairpin conductor, where the whole first hairpin region, which forms the winding head, is coated with an additional insulation;

[0026] Fig. 5 a second example of a hairpin conductor, where only a half of the first hairpin region is coated with an additional insulation;

[0027] Fig. 6 an example how the hairpin conductor of Fig. 4 can be built into a stator lamination pack;

[0028] Fig. 7 an example how the hairpin conductor of Fig. 5 can be built into a stator lamination pack;

[0029] Fig. 8 like Fig. 6 but with the winding heads being coated with glue or resin;

[0030] Fig. 9 like Fig. 7 but with the winding heads being coated with glue or resin; Fig. 10 illustrates how cracks can be stopped at the basic insulation and

[0031] Fig. 11 shows a schematic view of an electric vehicle.

[0032] DETAILED DESCRIPTION

[0033] Generally, same parts or similar parts are denoted with the same / similar names and reference signs. The features disclosed in the description apply to parts with the same / similar names respectively reference signs. Indicating the orientation and relative position is related to the associated figure.

[0034] Fig. 1 shows a half section through a schematically drawn electric machine 1 . The electric machine 1 comprises a rotor shaft 2 with a rotor 3 mounted thereon. The rotor 3 comprises a rotor lamination stack, in which rotor windings or rotor magnets are arranged. The rotor lamination stack is not shown in detail in Fig. 1 , but instead the rotor lamination stack schematically is shown as simple solid block.

[0035] Further on, the electric machine 1 comprises a stator 4 with a stator lamination pack 5, which comprises a plurality of stator laminations stacked over another in an axial direction parallel to a stator axis or rotor axis A. The stator laminations are not shown in detail in Fig. 1 , but instead the stator lamination pack 5 schematically is shown as simple solid block, too. In addition to the stator lamination pack 5, the stator 4 comprises stator windings 6, which are arranged in notches in the stator lamination pack 5 (notches are not shown in Fig. 1 but see Figs. 6 to 9). The stator windings 6 comprise two winding heads B1 , B2 protruding out of the stator lamination pack 5 on its front faces.

[0036] The rotor shaft 2 is rotatably supported around the stator axis or rotor axis A relative to the stator 4 by means of a first and a second (rolling) bearing 7a, 7b. The first bearing 7a is mounted to a first bearing shield 8 and the second bearing 7b is mounted to a second bearing shield 9. The electric machine 1 also comprises a middle housing part 10, which surrounds the stator 4 and connects the first bearing shield 8 and the second bearing shield 9. The first bearing shield 8, the second bearing shield 9 and the middle housing part 10 together form the housing 1 1 of the electric machine 1 . It should be noted that the housing 1 1 may be shaped differently and may have a different number of parts. Fig. 2 now shows a schematic view on a couple of hairpin conductors 12a..12c, which are interconnected by means of welding joints 13 and together form a part of the stator windings 6. In this example, each hairpin conductor 12a..12c comprises a center bending C and adjacent legs D1 , D2. For example, the legs D1 , D2 may be straight or at least approximate a straight shape.

[0037] Fig. 3 shows couple of hairpin conductors 12u..12w in the region of the first winding head B1. The characters “u”, “v” and “w” denote the different electrical phases, which are later under different voltages in the operation of the electric machine 1 . Fig 3 furthermore shows that the hairpin conductors 12u..12w lay over one another and form critical zones E, which are prone to short circuits, partial discharges and arc flashes if an insulation of the hairpin conductors 12u..12w is defective.

[0038] Generally, the hairpin conductors 12a..12c, 12u..12w have a metal core 14 with a surrounding basic insulation 15. To improve insulation of a hairpin conductor 12a..12c, 12u..12w, an additional insulation 16 on the basic insulation 15 is proposed like it is shown for the hairpin conductor 12i in the example of Fig. 4, wherein a surface energy of the additional insulation 16 is lower than a surface energy of the basic insulation 15. Such a material for the additional insulation 16 provides very low adhesion and hence just a loose connection between the additional insulation 16 and the basic insulation 15. On the one hand, this allows for micro movements between the hairpin conductors 12u..12w, and on the other hand, this reduces the risk for the formation of critical cracks in the insulation and initiation of peeling off the insulation what is explained in more detail later in combination with Fig. 10.

[0039] In particular, the surface energy of the additional insulation 16 can be below 40 mN / m or 40 mJ / m2respectively, and for example, the additional insulation 16 can made of ther- moplastistic elastomers (TPE), Polyamide (PA), fluoroplastics such as Polytetrafluoroethylene (PTFE) or silicone(s). Further on, the basic insulation 15 can made of enamel. It has turned out, that these materials and the proposed material combinations are particularly useful for the given application.

[0040] Generally, the hairpin conductor 12i of Fig. 4 comprises three hairpin regions F1..F3. The first hairpin region F1 is part of the first winding head B1 , the second hairpin section F2 runs within the stator lamination stack 5, and the third hairpin region F3 is part of the second winding head B2, where a plurality of hairpin conductors 12i are interconnected by means of the welding joints 13.

[0041] In the example of Fig. 4, the additional insulation 16 is arranged in the whole first hairpin region F1 of the hairpin conductor 12i. However, this is not the only possibility, and the additional insulation 16 can also be arranged only in half the first hairpin region F1 of the hairpin conductor 12ii or only on one of the legs D1 , D2 adjacent to the center bending C of the hairpin conductor 12ii respectively like this is shown in Fig. 5. Such an additional insulation 16 with reduced material use provides the advantages disclosed in the context of Fig. 4 as well.

[0042] In both examples of Figs. 4 and 5 the additional insulation 16 is applied only in the first hairpin region F1 of the hairpin conductor 12i, 12ii, which (only) comprises a center bending C and adjacent legs D1 , D2.

[0043] Fig. 6 shows a further embodiment by use of the hairpin conductor 12i. Concretely, Fig. 6 depicts a part of the stator lamination pack 5 and in particular shows a longitudinal notch 17, which the hairpin conductor 12i is arranged in.

[0044] The hairpin conductor 12i or the stator windings 6 made of the hairpin conductors 12i respectively are fixed to the notches 17 in the stator lamination pack 5 by means of a glue 18. The glue 18 can be made of or comprise resin. Advantageously, the surface energy of the additional insulation 16 is lower than a surface energy of the glue 18.

[0045] Fig. 7 shows an example, which is very similar to that of Fig. 6, however by use of the hairpin conductor 12ii depicted in Fig. 5.

[0046] In the examples of Figs. 5 and 6, the glue or resin 18 is only applied in the second hairpin region F2 or in the notches 17 respectively. However, this is not the only solution. In this context, Fig. 8 shows an example, which is similar to that of Fig. 6, but with the glue or resin 18 being also arranged in the first and third hairpin region F1 , F3 or in the region of the first and second winding head B1 , B2 respectively.

[0047] Fig. 9 shows an example, which is very similar to that of Fig. 8, however by use of the hairpin conductor 12ii depicted in Fig. 5. Fig. 10 now shows a detailed view on a hairpin conductor 12. Generally, it should be noted that the risk for the initiation of cracks 19 in the additional insulation 16 and for peeling of the additional insulation 16 is substantially improved by the proposed measures, in particular by allowing micro movements between the hairpin conductors 12i, 12ii. However, despite the proposed measures, a crack 19 has been formed in the additional insulation 16 in Fig. 10, for example caused by mechanical overload or thermal stress. But using a material for the additional insulation 16, whose surface energy is lower than a surface energy of the basic insulation 15, not only reduces the risk for the initiation of cracks 19 and for peeling off the additional insulation 16 but also avoids that the crack 19 continues and reaches through the basic insulation 15 or at least reduces the risk therefor. Again, the reason is that because of the material choice, there is just a loose connection between the additional insulation 16 and the basic insulation 15.

[0048] The proposed measures inter alia provide the following advantages: the risk for the formation of critical cracks 19 in the basic insulation 15 and the risk for initiation of peeling off the basic insulation 15 is substantially reduced, the risk for the formation of critical cracks 19 in the glue or resin 18 and the risk for initiation of peeling off the glue or resin 18 is reduced as well, limiting the additional insulation 16 to the first hairpin region F1 allows for high current densities within the notches 17, where insulation is less critical because of only low voltage differences between the single hairpin conductors 12, 12a..12w and micro movements between the hairpin conductors 12, 12a..12w do not induce very high shear stress which reduces the formation of cracks 19 in the additional insulation 16 and initiation of peeling off the additional insulation 16.

[0049] Generally, a method of manufacturing a hairpin conductor 12, 12a..12w for a stator winding 6 having a metal core 14 with a surrounding basic insulation 15, can comprise the step of applying an additional insulation 16 on the basic insulation 15, wherein a surface energy of the additional insulation 16 is lower than a surface energy of the basic insulation 15.

[0050] Further on, a method of manufacturing a stator 4 for an electric machine 1 generally can comprise the steps: providing a stator lamination pack 5 with longitudinal notches 17 for stator windings 6 and a) mounting a plurality of hairpin conductors 12, 12a..12w as into said notches 17 and forming stator windings 16 by electrically connecting the hairpin conductors 12, 12a..12w or b) mounting a plurality of hairpin conductors 12, 12a..12w each with a metal core 14 with a surrounding basic insulation 15, forming stator windings 6 by electrically connecting the hairpin conductors 12, 12a..12w and applying an additional insulation 16 on the basic insulation 15 of the hairpin conductors 12, 12a..12w, wherein a surface energy of the additional insulation 16 is lower than a surface energy of the basic insulation 15.

[0051] The method may also comprise the additional step of fixing the stator windings 6 to the notches 17 in the stator lamination pack 4 by means of a glue 18.

[0052] Fig. 11 finally shows an electric vehicle 20 with a drivetrain comprising an electric machine 1 as defined hereinbefore, which is provided to propel the electric vehicle 20. In detail, the electric machine 1 is coupled to gearbox 21 , side shafts 22 and finally to the wheels 23. The electric machine 1 may be provided for powering the electric vehicle 20 permanently in a pure electric car or intermittently, e.g. in combination with a combustion engine in a hybrid car.

[0053] It is noted that the invention is not limited to the embodiments disclosed hereinbefore, but combinations of the different variants are possible. In reality, the electric machine 1 and the electric vehicle 20 may have more or less parts than shown in the figures. It is also noted that the electric machine 1 and the electric vehicle 20 or parts thereof are not necessarily drawn to scale in the Figs. Moreover, the description may comprise subject matter of further independent inventions.

[0054] It should also be noted that the term "comprising" does not exclude other elements and the use of articles "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims. List of References

[0055] 1 electric machine

[0056] 2 rotor shaft

[0057] 3 rotor

[0058] 4 stator

[0059] 5 stator lamination pack

[0060] 6 stator winding

[0061] 7a, 7b (roller)bearing

[0062] 8 first bearing shield

[0063] 9 second bearing shield

[0064] 10 stator housing

[0065] 11 machine housing

[0066] 12, 12a..12w hairpin conductor

[0067] 13 welding joint

[0068] 14 metal core

[0069] 15 basic insulation

[0070] 16 additional insulation

[0071] 17 (stator) notch

[0072] 18 glue / resin

[0073] 19 crack

[0074] 20 vehicle

[0075] 21 gearbox

[0076] 22 side shaft

[0077] 23 wheel

[0078] A rotor axis

[0079] B1 , B2 winding head

[0080] C center bending

[0081] D1 , D2 leg

[0082] E critical zone

[0083] F1..F3 hairpin region

Claims

Claims1. Hairpin conductor (12, 12a..12w) for a stator winding (6), wherein the hairpin conductor (12, 12a..12w) has a metal core (14) with a surrounding basic insulation (15), characterized in an additional insulation (16) on the basic insulation (15), wherein a surface energy of the additional insulation (16) is lower than a surface energy of the basic insulation (15).

2. Hairpin conductor (12, 12a..12w) as claimed in claim 1 , characterized in that the additional insulation (16) is applied only in a first hairpin region (F1 ) of the hairpin conductor (12, 12a..12w), which comprises a center bending (C) and adjacent legs (D1 , D2) of the hairpin conductor (12, 12a..12w).

3. Hairpin conductor (12, 12a..12w) as claimed in claim 1 or 2, characterized in that the additional insulation (16) is arranged in the whole first hairpin region (F1 ) of the hairpin conductor (12, 12a..12w) or in half the first hairpin region (F1 ) of the hairpin conductor (12, 12a..12w) or on one of the legs (D1 , D2) adjacent to the center bending (C) of the hairpin conductor (12, 12a..12w) respectively.

4. Hairpin conductor (12, 12a..12w) as claimed in any one of claims 1 to 3, characterized in that a surface energy of the additional insulation (16) is below 40 mN / m.

5. Hairpin conductor (12, 12a..12w) as claimed in any one of claims 1 to 4, characterized in that the additional insulation (16) is made of thermoplastistic elastomer (TPE), Polyamide (PA), fluoroplastic or silicone.

6. Hairpin conductor (12, 12a..12w) as claimed in any one of claims 1 to 5, characterized in that the basic insulation (15) is made of enamel.

7. Stator (4) for an electric machine (1 ), comprising a stator lamination pack (5) with longitudinal notches (17) and stator windings (6), which are arranged in said notches (17) and which are made of a plurality of hairpin conductors (12, 12a..12w) as claimed in any one of claims 1 to 6.

8. Stator (4) as claimed in claim 7, characterized in that the stator windings (6) are fixed to the notches (17) in the stator lamination pack (5) by means of a glue (18).

9. Stator (4) as claimed in claim 8, characterized in that a surface energy of the additional insulation (16) is lower than a surface energy of the glue (18).

10. Stator (4) as claimed in claim 8 or 9, characterized in that the glue (18) is made of or comprises resin.

11. Electric machine (1 ), characterized by a stator (4) as claimed in any one of the claims 7 to 10.

12. Vehicle (20), characterized by an electric machine (1 ) as claimed in claim 11 for propelling or driving the vehicle.

13. Method of manufacturing a hairpin conductor (12, 12a..12w) for a stator winding (6), wherein the hairpin conductor (12, 12a..12w) has a metal core (14) with a surrounding basic insulation (15), comprising the step of applying an additional insulation (16) on the basic insulation (15), wherein a surface energy of the additional insulation (16) is lower than a surface energy of the basic insulation (15).

14. Method of manufacturing a stator (4) for an electric machine (1 ), comprising the steps providing a stator lamination pack (5) with longitudinal notches (17) for stator windings (6) and a) mounting a plurality of hairpin conductors (12, 12a..12w) as claimed in any one of claims 1 to 7 into said notches (17) and forming stator windings (16) by electrically connecting the hairpin conductors (12, 12a..12w) or b) mounting a plurality of hairpin conductors (12, 12a..12w) each with a metal core (14) with a surrounding basic insulation (15), forming stator windings (6) by electrically connecting the hairpin conductors (12, 12a..12w) and applying an additional insulation (16) on the basic insulation (15) of the hairpin conductors (12, 12a..12w), wherein a surface energy of the additional insulation (16) is lower than a surface energy of the basic insulation (15).

15. Method as claimed in claim 14, characterized in an additional step of fixing the stator windings (6) to the notches (17) in the stator lamination pack (4) by means of a glue (18).

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