Method for joining hollow conductors

Abstract

A method for joining hollow conductors is provided, comprising the steps: inserting hollow conductors into a stator of an electric machine, and joining ends of at least some of the hollow conductors by means of soldering in order to electrically connect these hollow conductors to one another, wherein before or during the joining step, the hollow conductors are acted upon in such a manner that solder is prevented from penetrating into or adhering to a hollow channel of the hollow conductor.

Description

[0001] 1 277 223 pl / mfa hyperdrives GmbH

[0002] Winterstrasse 6, 81543 Munich, Germany

[0003] METHOD FOR JOINING SHELL CONDUCTORS

[0004] TECHNICAL AREA

[0005] The invention relates to a method for joining waveguides, in particular waveguide pins, to a stator and / or an electric machine. Furthermore, the invention relates to an electric machine with such a stator. This method can be used, for example, in the fields of drive technology, the automotive and transport industries, aircraft and ships, energy technology, and various other applications.

[0006] used in various industrial sectors.

[0007] STATE OF THE ART

[0008] The use of waveguide windings and thus the integration of effective cooling directly into the winding of an electric machine enables a significant increase in current density and consequently a higher power density, as well as better efficiency.

[0009] The pin or hairpin design is a proven, industrialized, and cost-effective construction method primarily used in stators for electric vehicles. Applying hairpin manufacturing processes to waveguide windings would enable more automated and cost-effective production, even for directly cooled waveguide stators. The technical challenge of transferring the pin / hairpin design to waveguide windings lies in electrically contacting the numerous ends of the individual pins or hairpins in pairs. This must be done in a way that neither constricts nor obstructs the inner hollow channel of the windings, which is crucial for cooling.

[0010] DE 10 2020 201 748 A describes an electric machine comprising a stator having slots for receiving an electrical plug-in winding, wherein the electrical plug-in winding is a distributed multiphase winding and is formed from electrical conductor elements lying in the slots, each of which projects from the slots at the two end faces of the stator, each of which is connected at least at one of its two conductor ends 5e to one of the other conductor elements via a joining connection, in particular a welded connection, and which together with the preceding sections form two winding heads, characterized in that a plurality of the conductor elements of the plug-in winding are designed as waveguides and that a coolant distributor is provided at one of the two winding heads, which is electrically insulated from the hollow conductor elements, and an inlet for supplying an electrically non-conductive coolant, in particular oil.from a coolant supply and from which the coolant can be conducted into several of the hollow conductor elements.

[0011] The joint described here is a weld, which in practice is achieved through end-face laser welding. However, this method has the disadvantage that either the weld penetration depth is very shallow, or a more substantial weld bead or weld bead can impair the hollow channel, necessitating an additional tap from the side for coolant introduction. A soldered joint, particularly one produced by wave soldering, does not have this disadvantage of limited penetration depth. The wave soldering process allows for joints with a significantly larger contact area between the waveguide ends than would be possible with laser welding. These soldered joints are characterized by lower electrical contact resistance and higher mechanical strength and robustness.

[0012] However, inserting a pair of waveguides to be contacted into the stream of liquid solder results in solder ingress into the hollow channel. This ingress of solder may lead to the blockage of the hollow channel and thus to the loss of such a stator, and must therefore be prevented.

[0013] SUBJECT OF THE INVENTION

[0014] The aim of the invention is to develop a manufacturing process with which a reliable electrical connection can be established without impairing the functionality of the waveguide structure.

[0015] A method for joining waveguides according to claim 1 provides a solution for this. The method according to the invention comprises the steps of: inserting waveguides into a stator of an electric machine, and joining the ends of at least some of the waveguides by soldering in order to electrically connect these waveguides to one another, wherein, before or during joining, the waveguides are acted upon in such a way as to prevent the penetration or adhesion of solder into a hollow channel of the respective waveguide. The method can be applied to various topologies of electric machines (axial, radial, transverse flux machines, internal and external rotors, topologies with a plurality of stators or rotors).The same applies to various electrical machines that are not designed in pin / hairpin construction, such as machines with a large number of wound waveguide coils, both as tooth coils for a concentrated winding and as form coils for a distributed winding, which must be interconnected to form the winding.

[0016] For various topologies of electrical machines with waveguide windings and direct cooling, a method for joining the waveguide ends is provided. Soldering, and in particular wave soldering, represents a process-stable and cost-effective joining method that has become established in many industrial sectors, for example, the manufacturing of printed circuit board-based electronics.

[0017] Wave soldering is a soldering process in which a constant flow of molten, hot solder emerges from a nozzle and is fed to the joint between the two components. The nozzle is typically surrounded by an inert gas to prevent the excess solder flowing around or behind the nozzle from reacting with atmospheric oxygen and becoming contaminated with oxides. The outgoing solder is then reheated and pumped back through the nozzle to be recirculated to the joint. A key difference between wave soldering and, for example, laser soldering or soldering with a soldering iron, is that the nozzle not only supplies the solder but also provides a constant flow of heat, which is continuously absorbed and dissipated by the components being joined. The flow of the solder to, around, and into the gap between the components is subject to gravity, meaning that wave soldering is primarily a vertical process.with a vertically arranged nozzle, is practical.

[0018] When inserting a pair of waveguides to be joined, especially waveguide pins, into the flow of liquid solder, the problem arises that the solder is forced into the hollow channel by the flow pressure from the nozzle and may clog it. In narrow hollow channels, as is the case in the windings of electric motors, the capillary effect of the hollow channel further exacerbates the problem of solder ingress and clogging.

[0019] A method according to the invention for preventing solder from penetrating the hollow channel can consist of mechanically sealing the respective ends of the waveguides before joining. By selectively crimping the ends, the hollow channel is pre-sealed in such a way that no solder can penetrate the hollow channel during the soldering process. This method can be implemented cost-effectively, and the cycle time for crimping a pin end section is very short.

[0020] The mechanical sealing process, however, requires that the pressed area be mechanically removed after joining to expose the hollow channel again. Mechanical removal of the sealed area can be achieved by cutting, shearing, or machining, e.g., sawing, turning, milling, or grinding. To protect the contacted pins from mechanical stress during the machining process, it is advantageous to grip and support the waveguide pairs on the respective stator side with a device. Contamination of the stator with chips or other residues from this process can also be prevented by such a device. Another method to prevent solder penetration can be to apply a solder mask, particularly a solder resist, to the hollow channel or to the end face of a respective waveguide before joining.The solder mask must possess properties that prevent it from decomposing or dissolving under the abrasive conditions of the joining process. This may include flux treatment and repeated immersion in the hot solder stream.

[0021] This method also requires that the solder mask be mechanically removed after joining, e.g., by brushing or scraping. An advantage over mechanical crimping is that no part of the waveguide, especially copper with a solder layer, needs to be removed and recycled.

[0022] Another method for preventing solder from sealing the hollow channel can be to create a passivated surface in at least one section of the hollow channel. This can be achieved by selectively oxidizing the copper surface so that the solder cannot adhere in this area. The passivation of the hollow channel and the end section of the waveguide must be carried out in such a way that the outer surfaces of the conductor to be contacted are not affected. It can be advantageous to selectively mask these areas during passivation or to subsequently treat the areas to be soldered with flux to remove the passivation in a specific area and ensure the quality of the solder joint there. This method has the advantage that no further process step to remove sealing components is necessary after joining.A similar method to prevent solder from adhering to the hollow channel can consist of applying a thin, non-solderable coating, at least in sections. The thickness of this coating must be such that no significant narrowing of the hollow channel occurs, since this coating remains in the end section of the waveguide even after assembly.

[0023] Another design for preventing solder from entering the hollow channel involves mechanically sealing the conductor ends with a sealing device. This device can, for example, be attached to and seal the entrance of the hollow channel by means of a conical bolt or, alternatively, on the end face of the hollow conductor. It must be designed and shaped such that only minimal mechanical pressure is required to achieve a seal. The materials used for the sealing device can also be selected so that the abrasive current from the solder does not degrade it. Depending on the soldering process, such a sealing device is inserted into the nozzle or solder bath along with the conductor pair to be joined and can be removed once the joining process and the supply of solder are complete. The mechanical preload at the sealing point between the hollow channel and the device can be, for example,This is generated by a spring mechanism. Furthermore, the positioning of the sealing elements must be able to compensate for a certain amount of play, as the position of the waveguides themselves is subject to certain manufacturing tolerances and play.

[0024] For all the aforementioned embodiments of the invention, wave soldering is a preferred soldering method, whereby the conductor pairs to be joined can be soldered sequentially, i.e., individually and one after the other, as well as simultaneously as a group. The nozzle for a wave soldering system can be adapted to the configuration of the conductor pairs as a recurring group along the stator. To solder all the pins to be joined on a respective side of a stator simultaneously, soldering in a solder bath instead of wave soldering is a good alternative and is particularly suitable for smaller stators.

[0025] To improve the quality of soldered joints, it is advantageous to pre-tin the individual ends of the waveguides (pin ends) before inserting them into a stator and to apply flux before each soldering application to remove oxide residues or other impurities from the copper. Applying flux before final joining with waveguides already inserted into the stator can be achieved, in particular, by simultaneously immersing the ends of the waveguides in a flux bath.

[0026] The described methods were each described using a pair of conductors, in particular waveguide pins. The method can also be applied to a joining process of bundles of conductors together, or a hybrid form of waveguides with waveguide bundles, or when joining one of the respective waveguides to a solid pin, solid pin bundle, or other conductor element, for example, a phase terminal, a star point, a star point ring, or a delta connector, or any other type of internal interconnection within a winding. This can be the case, in particular, for an electrical machine with waveguide coils instead of pins, which must be interconnected. According to another aspect, an electrical machine is provided.The electric machine comprises a stator, the stator comprising waveguides, the ends of at least some of the waveguides being joined by soldering so that these waveguides are electrically connected to one another, with one hollow channel of the respective waveguide being solder-free. Such a stator can be manufactured by a method according to any of the aforementioned aspects.

[0027] The electric machine can be an axial, radial, or transverse flux machine, have an internal or external rotor, and / or employ topologies with a multitude of stators or rotors. This also applies to various electric machines that are not designed in a pin / hairpin configuration, such as machines with a multitude of wound waveguide coils, both as tooth coils for a concentrated winding and as form coils for a distributed winding, which must be interconnected to form the winding.

[0028] BRIEF DESCRIPTION OF THE FIGURES

[0029] The invention will now be explained in more detail with reference to several exemplary embodiments and the drawings.

[0030] They show:

[0031] Fig. 1a shows a stator of an electrical machine equipped with a plurality of waveguide pins (conductors);

[0032] Fig. 1b shows a detailed representation of a single pair of conductors to be electrically contacted;

[0033] Fig. 2 shows the joining of a conductor pair according to a further embodiment by soldering, in particular wave soldering, when the waveguide ends are immersed in the wave of liquid solder;

[0034] Fig. 3a shows the end section of a pair of conductors to be joined with mechanically crimped ends,

[0035] Fig. 3b shows the pair of conductors according to Fig. 3a in the ^-section view, where the closed hollow channel in the front end area is shown in more detail;

[0036] Fig. 4 shows the pair of conductors according to figures 3a, 3b after soldering and after mechanical separation of the sealed area;

[0037] Fig. 5 shows a pair of conductors according to a further embodiment before soldering in a further embodiment to prevent the penetration of solder into the hollow channel, wherein a solder mask, in particular of a bast-like type, is applied in front of or into the hollow channel of the respective conductor;

[0038] Fig. 6 shows a pair of conductors according to a further embodiment before soldering in a further embodiment to prevent adhesion of solder in the hollow channel, wherein at least one section of the hollow channel has a passivated surface;

[0039] Fig. 7 shows a pair of conductors before soldering in a further embodiment to prevent solder from adhering to the hollow channel, in which at least in sections a thin non-solderable coating was applied;

[0040] Fig. 8 shows a pair of conductors before soldering in a further embodiment to prevent solder from entering the hollow channel, the ends of the conductors being sealed by means of a device. DESCRIPTION OF THE EXECUTIONS

[0041] The figures below describe exemplary embodiments of the invention. Features of the respective embodiments can be combined to create further variants.

[0042] Fig. 1a shows an example of a stator 10 of an electric machine with a waveguide winding according to the invention, here implemented as a radial flux machine in an internal rotor design with I-pin waveguides 20 (hereinafter also referred to as "waveguides"). The stator core 15 can comprise a soft magnetic material, for example, stacked electrical steel sheets. The individual waveguides 20, here I-pins, can be inserted into the slots of the stator core 15 and twisted at the ends so that the waveguide elements of the conductors 20 can be electrically connected in the slots to form a meandering winding. Slot insulation is provided, for example, between the winding and the slots, and the individual conductors 20, made of copper (alternatively aluminum), are themselves surrounded by an electrically insulating coating.

[0043] Fig. 1b shows in detail a single pair of waveguides 20 from the winding head of one side of the I-pin winding. The waveguides 20 shown are already joined. In the front straight section 21 of each waveguide 20, where the waveguides 20 lie on top of each other, the insulation layer of the waveguides 20 has been removed. This process takes place before or after pin bending, even before the waveguides 20 are sealed, pre-tinned, and inserted into the stator 10. The largest part, ideally the entire exposed portion, is coated with solder after the joining process. The end face 22 of the pair of waveguides 20 shows the two hollow channels 23, which, according to the invention, are designed such that the penetration or adhesion of solder into a hollow channel 23 of the respective waveguide 20 is prevented.

[0044] Fig. 2 illustrates the joining of a pair of waveguides 20a by wave soldering. By immersing the conductor ends in the wave of liquid solder L, optimal conditions are created for a high-quality soldering of the two waveguides 20 together: a constant flow of fresh solder L and constant process heat. The immersion of the pair of waveguides 20 is achieved by positioning and moving the entire stator 10 over the solder wave or by moving the wave into the stator 10. An example of sequential soldering of the waveguides 20, in particular the ends 21a of the waveguides 20, is shown. To reduce the process time during joining, a nozzle 100 adapted to a group of waveguides 20 can be used. As an alternative to wave soldering, a solder bath can be used to solder the entire winding head on one side of the stator 10 simultaneously.

[0045] Fig. 3a shows the end section of a pair of waveguides 20b to be joined, with mechanically crimped ends 21b, before joining by soldering. Fig. 3b shows the same pair of waveguides 20b in a cross-sectional view, where it is more clearly visible that the hollow channel 23b of the waveguides 20 is tapered and sealed in the front end region such that no solder can penetrate the respective inner hollow channel 23b during soldering. Fig. 4 shows the same pair of waveguides 20b with mechanically sealed waveguides 20b before soldering and after the sealed area has been mechanically separated following soldering. The respective hollow channel 23b is exposed by separating the sealed waveguide areas, so that the cooling fluid can flow into or out of the winding through the hollow channels 23b during operation of the electric machine without interference.

[0046] Fig. 5 shows a pair of waveguides 20c before soldering in another embodiment. To prevent solder from penetrating the hollow channel, a solder mask, particularly a paste-like one, is applied in front of or into the hollow channel of the respective waveguide 20c, for example by coating, dipping, or spraying. After soldering, this material must be removed mechanically, e.g., by brushing or scraping. In contrast to mechanical crimping, no copper waveguide needs to be held in place and removed, which may reduce the manufacturing costs of such a stator.

[0047] Fig. 6 shows another embodiment of a pair of waveguides 20d before soldering, and describes a further advantageous method. This method, in contrast to the methods described above, has the advantage that no sealing step is required after soldering. Adhesion of solder to the hollow channel 23d is prevented by the fact that at least a section of the hollow channel 23d has a passivated surface. Fig. 6 optionally illustrates that the end face 22d of each waveguide 20d also has a passivated surface. The precise surface properties can be determined by the interplay of masking and flux application.

[0048] Fig. 7 describes a similar embodiment to that shown in Fig. 6, wherein the adhesion of solder in the hollow channel 23e of a respective waveguide 20e can be prevented by applying at least a thin, non-solderable coating 24e within a respective hollow channel 23e and optionally on the end face, at least in sections. This coating 24e remains after soldering and must be of such thin-walled construction that it does not impede the flow of the coolant through the waveguides 20e.

[0049] Fig. 8 shows another embodiment in which the ingress of solder into a hollow channel 23f of a respective waveguide 20f for a pair of waveguides 20f to be joined can be prevented, wherein the respective ends of the waveguides 20f are closed with a sealing device 25f. The sealing device 25f is, in particular, a conical bolt which engages at the entrance region of the respective hollow channel 23f and which can achieve a sealing effect by mechanical pressure. Here, a sealing device 25f for a single pair of waveguides 20f with two hollow channels 23f to be closed is shown. Likewise, such a sealing device can be implemented for a complete stator, which is simultaneously immersed in a solder bath together with such a sealing device.

[0050] Once the joining process and the application of solder are complete, the sealing device 25f can be removed. The mechanical preload at the sealing point between the hollow channel 23f and the sealing device 25f can be generated, for example, by a spring mechanism 26f. Furthermore, the positioning of the sealing elements must be able to compensate for a certain amount of play, since the position of the waveguides 20f themselves is subject to certain manufacturing tolerances and clearances.

Claims

PATENT CLAIMS 1. Method for joining waveguides (20-20f ) , comprising the steps: Insertion of waveguides (20-20f) into a stator (10) of an electric machine, and Joining the ends of at least some of the waveguides (20-20f) by soldering in order to electrically connect these waveguides (20-20f) to each other, whereby before or during joining, action is taken on the waveguides (20-20f) in such a way as to prevent the penetration or adhesion of solder into a hollow channel (23-23f) of the respective waveguide (20-20f).

2. Method according to claim 1, wherein to prevent the penetration of solder, the respective ends of the waveguides (20b) and in particular the hollow channel (23b) are crimped.

3. Method according to claim 2, wherein the pressed area is mechanically removed after joining.

4. Method according to claim 1, wherein to prevent the penetration of solder prior to joining, a solder resist, in particular a solder mask-like, is introduced in front of or into the hollow channel of the respective waveguide (20c).

5. Method according to claim 4, wherein the solder mask is mechanically removed after joining.

6. Method according to one of the preceding claims, wherein a gas, in particular an inert gas, is passed through the respective waveguide during soldering to prevent the penetration of solder.

7. Method according to claim 1, wherein, to prevent wetting and adhesion of solder prior to joining, action is taken on at least one section of the hollow channel (23d) such that a passivated surface is formed in this area.

8. Method according to claim 1, wherein a thin non-solderable coating (24e) is applied at least sectionally within the hollow channel (23e) to prevent wetting and adhesion.

9. Method according to claim 1, wherein to prevent the ingress of solder, the ends of the waveguides (20f) are closed by means of a closure device (25f).

10. Method according to one of the preceding claims, wherein the joining is carried out by wave soldering.

11. Method according to one of the preceding claims, wherein the joining is carried out by simultaneously soldering the ends of the waveguides (20-20f) in a bath.

12. Method according to one of the preceding claims, wherein a flux is applied to the ends of the waveguides (20-20f) prior to soldering, in particular by jointly immersing the ends of the waveguides (20-20f) in a flux bath.

13. Method according to one of the preceding claims, wherein the ends of the waveguides (20-20f) are pre-tinned before being inserted into the stator (10).

14. Method according to one of the preceding claims, wherein a waveguide end is joined with a solid copper conductor, in particular phase connection, delta / star connector and / or internal interconnection.

15. Method according to one of the preceding claims, wherein a waveguide end is joined to a bundle of waveguides or a bundle of solid copper conductors.

16. Electrical machine comprising: a stator (10) , wherein the stator (10) comprises waveguides ( 20- 20f ), and wherein ends of at least some of the waveguides (20- 20f ) are joined by soldering, such that these waveguides (20- 20f ) are electrically connected to each other, wherein a hollow channel (23- 23f ) of the respective waveguide (20- 20f ) is solder-free.

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