Manufacturing a stator using hard soldering techniques

Abstract

The present invention relates to a method for manufacturing a hairpin winding of a stator of an electric motor for powering a motor vehicle. First, a stator body with a plurality of stator slots is provided. Then, hairpins (1) are arranged in the stator slots such that free hairpin ends (2) of the hairpins (1) protrude axially from the stator body. One of the free hairpin ends (2) is connected to a conductor (3). Finally, the free hairpin end (2) is connected to the conductor (3) by brazing. According to the invention, a brazing alloy (4) is applied to the free hairpin end (2) before connecting the free hairpin end (2) to the conductor (3).

Description

[0001] The present invention relates to a method for manufacturing a hairpin winding of a stator of an electric motor for driving a motor vehicle.

[0002] Methods for manufacturing hairpin windings for stators of electric motors for powering motor vehicles are known, in which brazing plates are arranged on a busbar and the hairpins to be connected to the busbar are bent towards the brazing plates. The brazing alloy must be positioned and fixed with exceptional precision on the busbar, for example, by spot welding or similar methods. Subsequently, the busbar must be aligned precisely with the hairpins in order to fix the hairpins to the busbar by brazing. A particular challenge here is that the hairpins must be aligned exactly with the busbar to ensure sufficient brazing alloy is available. If there is too large an offset between the hairpin and the brazing alloy, the connection between the hairpin and the busbar may have insufficient strength, thus increasing the reject rate.

[0003] Document DE 10 2012 215 309 B4 discloses a manufacturing process for a hairpin winding in which two conductor ends to be joined are arranged parallel to each other and side by side. A welding plate is placed between the conductor ends. The conductor ends are then pressed together and welded by a welding process. The welding plates can be supplied via a spool or as strips. Document CN 102 362 416 B discloses another method for soldering the conductor ends of a hairpin winding. The solder plates are arranged in recesses of a carrier strip and are positioned between the hairpin ends to be soldered using the carrier strip. After the soldering process, the carrier strip is removed. Both methods have the disadvantage that very precise alignment between the hairpin ends to be joined and the solder plates is required.

[0004] It is therefore an object of the present invention to eliminate, or at least partially eliminate, the disadvantages described above in a method for manufacturing a hairpin winding of a stator of an electric motor for powering a motor vehicle. In particular, it is an object of the present invention to provide a method for manufacturing a hairpin winding of a stator of an electric motor for powering a motor vehicle which, in a simple and cost-effective manner, has a lower reject rate and / or places fewer demands on the alignment of the hairpins when connecting them to a conductor.

[0005] The aforementioned problem is solved by the patent claims. Accordingly, the problem is solved by a method for manufacturing a hairpin winding of a stator of an electric motor for driving a motor vehicle, comprising the features of independent claim 1. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings.

[0006] According to the invention, the problem is solved by a method for manufacturing a hairpin winding of a stator of an electric motor for driving a motor vehicle. The method comprises: - Providing a stator body with a plurality of stator slots, - Arranging hairpins in the stator slots such that free hairpin ends protrude from the stator body in an axial direction, - Arrange one of the free hairpin ends on a conductor, and - Connecting the free hairpin end to the conductor by hard soldering,

[0007] According to the invention, a hard solder is arranged at the free hairpin end before connecting the free hairpin end to the conductor.

[0008] First, the stator core is provided. The stator core extends along a longitudinal axis and is preferably designed as a laminated core consisting of several coaxially arranged laminations, for example, made of electrical steel. The laminations preferably have electrical insulation, for example, a coating of enamel or the like, so that an electric current through the laminated core is prevented. The stator core preferably has several stator teeth, with a stator groove formed between each pair of stator teeth. The stator grooves are preferably uniform around the circumference of the stator and have a groove length along the longitudinal axis, a groove depth in the radial direction, and a groove width in the circumferential or tangential direction. The stator grooves are open at the two axial ends of the stator core, which are also referred to as the "stator end faces."Preferably, the stator slots are open towards the longitudinal axis of the stator.

[0009] The hairpins are then arranged in the stator slots, for example by inserting them axially from a first stator end face towards the second stator end face. According to the invention, the hairpins can be designed, for example, as I-shaped or U-shaped hairpins. The hairpins are arranged in the stator slots such that the free ends of the hairpins protrude axially from the stator body at the stator end faces. The hairpins are preferably arranged radially in several layers within the stator slots.

[0010] The free end of one or more hairpins is attached to a conductor. This conductor can be, for example, a busbar, particularly a copper busbar, for electrically connecting the stator to power electronics or a control device for operating the electric motor. The free end of the hairpin can be attached to the conductor, for example, by plastically deforming the hairpin, such as by crimping or similar methods. More preferably, the free end of the hairpin is held in a soldering position, in which the brazing process is to take place, by means of a holding device.

[0011] Finally, the free hairpin end(s) attached to the conductor are brazed to the conductor. This creates both a mechanical and an electrical connection between the hairpin(s) and the conductor. The retaining device is then removed from the hairpin.

[0012] According to the invention, a hard solder is arranged at the free hairpin end beforehand, so that even with larger deviations of a predefined relative position of the free hairpin end to the conductor during arrangement, it is always ensured that the hard solder is arranged as intended between the free hairpin end and the conductor.

[0013] An inventive method for manufacturing a hairpin winding of an electric motor stator for powering a motor vehicle has the advantage over conventional methods that a soldered connection between the hairpin and the conductor can be produced using simple means and in a cost-effective manner. By positioning the brazing alloy at the free end of the hairpin, it is ensured that the brazing alloy is favorably positioned for the brazing process after the hairpin end is attached to the conductor. This allows for greater tolerance when attaching the free end of the hairpin to the conductor, thus eliminating the need for complex, precise alignment operations. Consequently, high product quality is guaranteed with reduced manufacturing effort.

[0014] According to a preferred embodiment of the invention, a method for manufacturing a hairpin winding of a stator may include fixing the brazing alloy as a brazing alloy plate at the free end of the hairpin. The brazing alloy plate may, for example, have a rectangular, and preferably square, base. Preferably, the brazing alloy plate has a constant thickness. The length and / or width of the brazing alloy plate is preferably at least five, and preferably at least ten times, its thickness. The length and / or width of the brazing alloy plate is preferably a maximum of forty, and preferably a maximum of twenty, times its thickness. The brazing alloy plate may, for example, be fixed to the hairpin end by means of an adhesive bond. This is done in such a way that the electrical coupling between the hairpin and the conductor is still ensured after brazing.Accordingly, for example, an adhesive can be used that only wets a relatively small area of ​​the brazing alloy, thus maintaining direct contact between the brazing alloy and the hairpin. Alternatively or additionally, an adhesive can be used that evaporates during brazing, so that no electrical insulation is formed between the hairpin and the conductor. This has the advantage of ensuring reliable positioning and a secure hold of the brazing alloy at the hairpin end in a simple and cost-effective manner.

[0015] According to the invention, it is preferred that the brazing alloy is fitted over the free hairpin end as a brazing alloy cap. Within the scope of the invention, a cap is understood to be a brazing alloy in which the free hairpin end can be surrounded on at least three sides. Preferably, the cap is designed to surround the free hairpin end on four or five sides. The cap can, for example, have an approximately ring-shaped form with two free openings. According to the invention, the cap can also have a plate-shaped main surface and several wire-shaped secondary surfaces, the main surface being provided for placement between the free hairpin end and the conductor. The secondary surfaces thus serve only to fasten the main surface to the free hairpin end.The cap preferably has an inner cross-section that corresponds in shape and size to, or at least substantially corresponds to, the outer cross-section of the free hairpin end, so that the cap can be easily slipped onto the free hairpin end. Preferably, the cap has a widening at a free opening to facilitate its placement on the free hairpin end. Preferably, an inner cavity of the cap tapers away from the free opening in such a way that the cap can be clamped onto the free hairpin end when slipped over it. This has the advantage of ensuring reliable placement and secure retention of the brazing alloy on the hairpin end in a simple and cost-effective manner.

[0016] Preferably, the brazing alloy is fixed to the free end of the hairpin by spot welding or brazing. It is particularly advantageous for the brazing alloy to be in the form of a brazing plate. Spot welding is preferably performed via a central point on the brazing alloy. Spot welding securely holds the brazing alloy to the free end of the hairpin. This has the advantage of ensuring reliable positioning and secure retention of the brazing alloy at the hairpin end using simple and cost-effective methods.

[0017] In a particularly preferred embodiment of the invention, a method for manufacturing a hairpin winding of an electric motor stator may include fixing the brazing alloy to the free end of the hairpin by plastic deformation. This plastic deformation can be achieved, for example, by crimping, staking, or the like. It may be provided, for instance, that the brazing alloy has a projection on both sides of the free end of the hairpin in the width direction, which is bent around the free end of the hairpin by plastic deformation, forming a clamp. Alternatively, a point-like or line-like compressive force may be applied to the brazing alloy, displacing a portion of the brazing alloy into the hairpin end, thus creating a mechanical staking connection between the brazing alloy and the hairpin end.To reduce the process forces required, a surface treatment such as roughening, knurling, or similar processes may be performed on the free hairpin end beforehand. This has the advantage of ensuring reliable positioning and secure retention of the brazing alloy at the hairpin end in a simple and cost-effective manner.

[0018] Preferably, the brazing alloy is applied to the free end of the hairpins before they are placed in the stator slots. The hairpins are thus treated before being placed in the stator slots, during which the brazing alloy is applied to their free ends. The brazing alloy is preferably applied in such a way that it does not impede the placement of the hairpins in the stator slots and remains in place during this process. For example, a brazing alloy with a chamfer can be provided, which facilitates smoother sliding of the hairpin in the stator slot. This has the advantage that the hairpins can be pre-finished using simple and cost-effective methods, eliminating the need to apply the brazing alloy during the final stator assembly.This can further improve production efficiency.

[0019] According to a preferred embodiment of the invention, the hairpins are separated and / or twisted before or during the application of the brazing alloy to the free hairpin ends. In this context, it is preferred that the brazing alloy is applied after the hairpins have been positioned in the stator slots. The process sequence can, for example, be as follows: first, the hairpins are positioned in the stator slots; then, the brazing alloy is applied to the free hairpin end and preferably fixed; and finally, the free hairpin ends are separated and / or twisted. Alternatively, the separation and / or twisting of the free hairpin ends can be carried out after the hairpins have been positioned in the stator slots, whereby the brazing alloy can only be applied to the free hairpin ends in the separated or twisted state.According to another alternative, the brazing alloy can be positioned at the free hairpin end using the separating or set tool, so that the positioning of the brazing alloy at the free hairpin end occurs simultaneously with the separation or settling. This has the advantage that reliable positioning and a secure hold of the brazing alloy at the hairpin end are ensured with simple means and in a cost-effective manner.

[0020] It is particularly advantageous to apply a hard solder to each of the free hairpin ends. For example, it may be necessary to connect other free hairpin ends to the conductor in pairs, in addition to fixing them to the conductor, such as to form a winding head of the stator. This can also be done by hard soldering. Applying the hard solder to all free hairpin ends reduces the number of hairpin variations, making them easier to manufacture in a pre-production stage where the hard solder is applied to the free hairpin end. The hairpin ends to be joined already have the hard solder applied, so the hard soldering process can be carried out directly after separation and forming. This has the advantage of further improving the efficiency of stator manufacturing using simple and cost-effective methods.

[0021] According to the invention, it is preferred that the brazing alloy be provided with a width that is less than or equal to the width of the free hairpin end. It is further preferred that the brazing alloy be provided at the free hairpin end in such a way that it is flush with the free hairpin end laterally or at least has no lateral projection beyond the free hairpin end. This has the advantage that reliable positioning and secure retention of the brazing alloy at the hairpin end are ensured simply and cost-effectively. Furthermore, this avoids wasting brazing alloy.

[0022] Preferably, a recess is formed at the free end of the hairpin before the brazing alloy is applied, with the brazing alloy being at least partially placed in the recess. The recess can, for example, be designed as a flattened area, with the free hairpin having a thinner section in the area of ​​the flattened section than adjacent to it. Alternatively, the recess can be designed as a contour in which the thickness of the free hairpin remains constant, resulting in a corresponding elevation on one side of the free hairpin opposite the recess. The recess preferably extends over the entire width of the free hairpin. More preferably, the recess extends longitudinally along the hairpin to the edge of the free hairpin. Alternatively, the recess can be spaced apart from one or more edges of the free hairpin.The hard solder is preferably positioned by pressing it into the recess, so that the hard solder is held at the free end of the hairpin. This has the advantage that reliable positioning and a secure hold of the hard solder at the hairpin end are ensured using simple and cost-effective means.

[0023] A method according to the invention for manufacturing a hairpin winding of a stator of an electric motor for driving a motor vehicle is explained in more detail below with reference to the drawings. The drawings schematically show: Fig. 1. A conductor designed as a busbar in a top view during the execution of a process in accordance with the state of the art, Fig. 2 in a top view a free hairpin end during the execution of a preferred first embodiment of a method according to the invention, Fig. 3 in a top view a free hairpin end during the execution of a preferred second embodiment of a method according to the invention, Fig. 4 in a top view a conductor designed as a busbar during the execution of a preferred embodiment of a method according to the invention, and Fig. 5 in a flowchart a preferred embodiment of a method according to the invention.

[0024] Elements with the same function and mode of operation are in the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5 each with the same reference numerals.

[0025] In Fig. Figure 1 is a schematic top view of a conductor 3 designed as a busbar during the execution of a prior art process. The conductor 3 has three brazing plates 4 designed as brazing discs, which are arranged at defined positions on the conductor 3 at intervals from one another. Furthermore, three free hairpin ends 2 of three hairpins 1 are indicated, which are aligned with the conductor 3 during the stator manufacturing process. A hairpin 1 on the left in this view has the correct alignment with the associated brazing plate 4. A hairpin 1 in the middle in this view has an alignment with the associated brazing plate 4 with a small offset to the left. A hairpin 1 on the right in this view has an alignment with the associated brazing plate 4 with a larger offset to the left.These offsets can easily occur when aligning the hairpins 1 to the conductor 3 and can lead to faulty brazed connections between the hairpin 1 and the conductor 3.

[0026] Fig. Figure 2 schematically shows a free hairpin end 2 of a hairpin 1 during the execution of a preferred first embodiment of a method according to the invention in a top view. A hard solder 4, designed as a hard solder plate, is arranged at the free hairpin end 2. The hard solder 4 is fixed to the hairpin 1 by a spot weld 5.

[0027] In Fig. Figure 3 schematically depicts a free hairpin end 2 of a hairpin 1 during the execution of a preferred second embodiment of a method according to the invention in a top view. A brazing alloy 4, designed as a brazing cap, is arranged on the free hairpin end 2. The cap preferably has a slight undersize relative to the free hairpin end 2, so that the cap is clamped onto the free hairpin end 2. In addition, the brazing alloy 4 is fixed to the hairpin 1 by means of a spot weld 5, which is optional in this case.

[0028] Fig. Figure 4 schematically shows a conductor 3 designed as a busbar in a top view during the execution of a preferred embodiment of a method according to the invention. Three free hairpin ends 2 of three hairpins 1 are indicated in front of the conductor 3; these are aligned with the conductor 3 during the stator manufacturing process. Since the brazing alloy 4 is always first applied and fixed at the free hairpin end 2 during the execution of the method according to the invention, it is ensured that the brazing alloy 4 is correctly positioned between the hairpin 1 and the conductor 3, even with an offset between the hairpin 1 and the conductor 3. Thus, the requirements for aligning the hairpins 1 with the conductor 3 are significantly lower than in the prior art.

[0029] In Fig.Figure 5 shows a preferred embodiment of a method according to the invention schematically in a flowchart. In a first process step 100, a stator base body with a plurality of stator slots is provided. In a second process step 200, hairpins 1 are provided, at whose hairpin ends 2 hard solder 4, designed as a brazing plate, is arranged and fixed. In a third process step 300, the hairpins 1 are arranged in the stator slots such that the free hairpin ends 2 protrude axially from the stator base body. In a fourth process step 400, at least one of the free hairpin ends 2, at which the brazing solder 4 is arranged, is arranged on a conductor 3. In a fifth process step 500, the free hairpin end 2 is connected to the conductor 3 by brazing. Here, the brazing solder 4 arranged at the free hairpin end 2 is first melted and then solidified again. Reference symbol list 1 Hairpin 2 free hairpin ends 3 conductors 4 Hard solder 5 spot welds 100 first procedural action 200 second procedural action 300 third procedural action 400 fourth procedural action 500 fifth procedural action QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2012 215 309 B4

[0003] CN 102 362 416 B

[0003]

Claims

[1] Method for manufacturing a hairpin winding of a stator of an electric motor for driving a motor vehicle, comprising: - Providing a stator body with a plurality of stator slots, - Arranging hairpins (1) in the stator slots such that free hairpin ends (2) of the hairpins (1) protrude from the stator body in an axial direction, - Arranging one of the free hairpin ends (2) on a current conductor (3), and - Connecting the free hairpin end (2) to the conductor (3) by hard soldering, characterized by , that a hard solder (4) is placed on the free hairpin end (2) before connecting the free hairpin end (2) to the conductor (3). [2] Method according to claim 1, characterized by , that the hard solder (4) is fixed as a hard solder plate at the free hairpin end (2). [3] Method according to claim 1 or 2, characterized by, that the hard solder (4) is placed over the free hairpin end (2) as a hard solder cap. [4] Method according to any of the preceding claims, characterized by , that the hard solder (4) is fixed to the free hairpin end (2) by spot welding or soldering. [5] Method according to any of the preceding claims, characterized by , that the hard solder (4) is fixed at the free hairpin end (2) by plastic deformation. [6] Method according to any of the preceding claims, characterized by , that the brazing alloy (4) is arranged at the free hairpin end (2) before the hairpins (1) are arranged in the stator slots. [7] Method according to any one of claims 1 to 5, characterized by , that the hairpins (1) are separated and / or twisted before or during the arrangement of the hard solder (4) at the free hairpin ends (2). [8] Method according to any of the preceding claims, characterized by, that a hard solder (4) is arranged at each of the free hairpin ends (2). [9] Method according to any of the preceding claims, characterized by , that the brazing alloy (4) is provided with a width that is less than or equal to a hairpin width of the free hairpin end (2). [10] Method according to any of the preceding claims, characterized by , that before the brazing alloy (4) is arranged at the free hairpin end (2) a recess is made at the free hairpin end (2), wherein the brazing alloy (4) is at least partially arranged in the recess.

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