Winding conductor for an electric machine

Abstract

The invention relates to a winding conductor (L) for an electric machine, said winding conductor having a quadrangular cross-sectional area with two parallel first sides (a) and two second sides (b), and rounded corners (e), wherein each of the first and second sides (a, b) has at least one straight portion. According to the invention, the rounded corners (e) at the surface of the winding conductor (L) have a rounding radius (R) which has been selected such that the centre of a circle contour (K), defined by the rounding radius (R), coincides with the centroid (F) of the cross-sectional area of the winding conductor (L).

Description

[0001] Winding conductor for an electrical machine

[0002] The invention relates to a winding conductor for electrical machines according to the preamble of claim 1.

[0003] Electric machines are used to convert electrical energy into mechanical energy or vice versa. An electric machine designed as a prime mover for a motor vehicle is particularly suitable for use within the drivetrain of a hybrid or fully electric motor vehicle.

[0004] Winding conductors for electrical machines, which are inserted into corresponding slots, are well known in a wide variety of designs. For example, there are windings with conductors made of solid individual wires with a round or any rectangular cross-section. A winding conductor can be designed as a long conductor strand that is bent several times according to the specified winding pattern, thus forming, for example, a winding in the electrical machine. However, the winding conductor can also consist of a plurality of different bent conductor pieces (shaped conductors), the conductor legs of which are inserted into the slots and then form the conductor strand via welded ends.

[0005] Winding conductors designed as square wires are used when a better slot coverage is to be achieved compared to round wires with the same cross-sectional area. However, a slight tilt of the square wire during the radial insertion of the winding into the slots can result in compression of the insulating paper previously inserted into the slots. To reduce this tendency to build up, you can either increase the edge radius of each edge or increase the thickness of the insulating paper. This first measure rounds off the edges, which means that less frictional forces act on the insulating paper when the winding is inserted into the slots, thus significantly reducing entrainment and therefore compression of the insulating paper. The second measure increases the kink resistance of the insulating paper, which also reduces the tendency for the paper to be entrained. However, when using thicker insulating paper, the slot width must also be increased or reduced.The conductor width must be reduced. However, a resulting change in the slot geometry would impair the electrical machine's power balance. Rounding and thus flattening the edge radii, on the other hand, results in a reduction in the conductor cross-section, and thus in particular in the copper cross-section of the electrically conductive base body of the winding conductor. If a certain maximum current density in the copper conductor is required for an electrical machine to avoid thermal overload, a reduced conductor cross-section would also require the current through the winding conductor to be reduced, which in turn would impair the electrical machine's power balance.

[0006] Various conductor cross-sections are known from DE 11 2008 000 175 T5. DE 11 2008 000 175 T5 discloses a conductor wire with a square cross-section comprising corners or edges at right angles, a conductor wire with an elongated cross-section comprising corners at right angles, a conductor wire with a substantially square cross-section comprising rounded corners, a conductor wire with a substantially elongated cross-section comprising rounded corners, and a conductor wire with a "racetrack-like" cross-section, which has one pair of opposite sides parallel to each other and the other pair of opposite curved sides. Depending on their design, the conductor cross-sections shown have one or more of the disadvantages described above.For example, especially with winding conductors with an elongated cross-section without rounded edges, as well as with the rounded edges shown with a small rounding radius, the difficulties mentioned above can be expected when inserting the winding conductors into the slots. In contrast, with the winding conductor shown with a "racetrack-like" cross-section, the conductor cross-section is significantly reduced, which excessively increases the current density in the conductor for the same required power of the electrical machine.

[0007] The object of the invention is to provide a winding conductor that has a cross-sectional shape that is both optimized for production technology and optimized for the electrical machine's performance. According to the invention, this object is achieved by the winding conductor according to claim 1.

[0008] Advantageous developments of the invention are defined in the respective dependent claims.

[0009] Because in a winding conductor for an electrical machine, which has a quadrangular cross-sectional area with two parallel first sides and two second sides as well as rounded edges, each of the four sides has at least one straight section and the rounded edges - i.e. corners between two sides - on the surface of the winding conductor have a rounding radius which is selected such that the center point of an outer circle spanned by the rounding radius coincides with the center point of the cross-sectional area of ​​the winding conductor, an optimized winding conductor can be provided for windings of electrical machines which provides a maximized conductor cross-sectional area both from the point of view of the power balance of the electrical machine and a more optimal conductor surface without angular edges from the point of view of assembly and production of the electrical machine.

[0010] The invention thus relates, as in DE 11 2008 000 175 T5, to winding conductors with various rounded edges. However, in the elongated cross-sections disclosed in DE 11 2008 000 175 T5, the rounded edges have rounding radii that do not share a common reference point, and furthermore, this reference point does not coincide with the center of the cross-sectional area of ​​such an elongated winding conductor. Furthermore, in the disclosed conductor wire with a "racetrack-like" cross-section, the cross-sectional area of ​​the conductor is significantly reduced compared to the elongated conductor wire with the same wire width.

[0011] The invention, on the other hand, provides a solution in which, with the same or almost the same conductor width and conductor height (determined by the first and second sides of the cross-sectional area), the cross-sectional area is optimized due to the rounding radius provided according to the invention and thus represents a compromise with regard to assembly as well as current density.

[0012] The design of a winding conductor according to the invention in which the first sides have a length which is greater than the length of the second sides is particularly preferred. The length of a first or second side designates the maximum distance spanned by the respective second or first sides and thus represents the dimensions for the external dimensions of the winding conductor with conductor width and conductor height. Particularly in the case of flat wire conductors with elongated cross-sections in which the first sides, and thus the conductor width, are significantly greater than the second sides, and thus the conductor height, this results in curves on the edges which are significantly flatter than known conductor cross-sections with small curve radii, but which also have more conductor material in the cross-section than known winding conductors with a "racetrack-like" cross-section.Such winding conductors designed according to the invention are achieved in particular when the rounding radius is greater than half the conductor width. This means that more conductor material is retained, particularly in the transition areas between the straight, long sides, which help determine the conductor width, and the adjacent curves, than with cross-sections with rounded corners, which do not have the features according to the invention. Flat wires are used in electrical machines particularly when it is a question of achieving a good and thus optimized slot fill level with as few conductors as possible. Especially with winding conductors designed as flat wires, which lie stacked on top of one another in the slots across their conductor height, there is a risk of tilting orThe insulation paper is removed when the winding conductors are inserted into the slots during production, so that a compromise must always be found between the maximum permissible power and the production reliability of the electrical machine.

[0013] If, in the case of a winding conductor, a further surface smoothing with a radius smaller than the radius of curvature of the rounded edges is provided in the transition areas between the respective straight sections of the sides and the rounded edges, it is possible to avoid sharp edges that may arise on the surface at these transitions, which could damage the insulation paper when the winding conductors are inserted into the slots or even just take it with them and thus compress it.

[0014] If the winding conductor's conductor cross-section consists of an electrically conductive base body and an electrically insulating material that surrounds the base body, and if the surface of the winding conductor is determined by the external dimensions of the insulating material, additional insulating paper can be omitted in the slots, or at least a thinner insulating paper can be used. In both cases, the design of the winding conductor, namely that on the conductor surface - i.e. on the external surface of the insulating material - each of the four sides has at least one straight area or straight section, and the rounded orrounded edges on the surface of the winding conductor have a rounding radius that is selected so that the center of an outer circle defined by the rounding radius coincides with the center of the cross-sectional area of ​​the winding conductor, also has the advantage that such an insulated conductor is optimized both in terms of its cross-section for maximum current and for safe insertion during assembly. An electrically insulating sheath formed by insulating material around the electrically conductive base body can be provided, for example, an insulation made of PEEK varnish or a varnish made of polyamideimide (PAI), polyimide (PI), polyetherimide (PEI), or even a suitable multi-layer varnish. The base body can be, for example, a copper core made of Cu ETP, Cu ETP1, Cu OF, Cu OF1, Cu OFEs or even an aluminum core.However, any other type of material and sheath is also conceivable, as long as the previously described inventive criteria are met.

[0015] The cross-sectional areas can have any shape, with second sides having side lengths that differ from the first sides and / or the first sides having side lengths that differ from the second sides. What is essential in all these embodiments is that at least the more prominent edges are rounded according to the invention, thus facilitating the insertion of the winding conductors into the slots and thus assembly, while also maintaining the largest possible conductor cross-sectional area.

[0016] The invention is explained in more detail using a figure, which is schematic and not to scale:

[0017] Fig. a cross section through a rectangular and coated winding conductor according to an embodiment of the invention.

[0018] The cross section of a winding conductor L designed according to the invention, sketched in Fig., has an electrically conductive base body G and a layer of an electrically insulating material M that surrounds the base body G. The rectangular winding conductor L, which is designed rectangularly here, has two parallel first sides a and two parallel second sides b, wherein the sides a determine the conductor width and the sides b determine the conductor height of the winding conductor L. Such a winding conductor L with a substantially elongated cross section is often also referred to as a ribbon conductor and can be introduced in one or more pieces into slots of the stator and / or rotor of an electrical machine.According to the invention, it is provided here that the four rounded edges e on the surface have a rounding radius R which is selected such that the center of a circular outer line K spanned by the rounding radius R coincides with the center point F of the cross-sectional area of ​​the winding conductor L. In order to avoid sharp edges on the surface, in the cross-section sketched in the figure, a further surface smoothing with radii smaller than the rounding radius R is provided in the transition areas between the respective straight sections of the sides a and b and the corners e rounded according to the invention.

Claims

Patent claims 1 . Winding conductor (L) for an electrical machine, which has a quadrangular cross-sectional area with two parallel first sides (a) and two second sides (b) and rounded edges (e), wherein each of the first and second sides (a, b) has at least one straight section, characterized in that the rounded edges (e) on the surface of the winding conductor (L) have a rounding radius (R) which is selected such that the center point of an outer circle line (K) spanned by the rounding radius (R) coincides with the center point (F) of the cross-sectional area of ​​the winding conductor (L).

2. Winding conductor (L) according to claim 1, characterized in that in transition areas between the respective straight sections of the sides (a, b) and the rounded edges (e) a further surface smoothing with radii smaller than the rounding radius (R) is provided.

3. Winding conductor (L) according to claim 1 or 2, characterized in that the winding conductor (L) consists in cross section of an electrically conductive base body (G) and an electrically insulating material (M) surrounding the base body (G) in a planar manner, the surface of the winding conductor (L) being determined by the external dimensions of the insulating material (M).

4. Winding conductor (L) according to one of the preceding claims 1 to 3, characterized in that the second sides (b) have side lengths that differ from the first sides (a) and / or the first sides (a) have side lengths that differ from the second sides (b).

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