Star disc for a rotor of an externally excited electric machine, having a thermally conductive insulation layer

Abstract

The invention relates to a star disc (1) for a rotor of an externally excited electric machine for mounting on an end face of the body of the rotor and for supporting winding heads of the rotor, having - a metal main part (3) with a star disc yoke (5) for mounting on a yoke of the rotor body, star disc arms (7) protruding radially from the star disc yoke (5) for mounting on teeth of the rotor body, and star disc roofs (8) protruding tangentially and axially from the star disc arms (7) for mounting on pole shoes of the rotor body, a winding space (10) for receiving the associated winding head being formed, for each rotor pole, by outer lateral regions of the star disc yoke, the inner face of the star disc roofs (8), and the upper face of the star disc arms (7), and - an insulation layer (4) which is provided on the main part (3) at least in the region of the winding spaces (10) for electrically insulating the winding heads from the main part (3), the insulation layer (4) consisting of a thermally conductive plastic (13) with a specific thermal conductivity of at most 0.5 W / m-K and a layer thickness of at most 1 mm in order to dissipate waste heat of the winding heads to the metal main part (3).

Description

[0001] 24-1036

[0002] 1

[0003] Star disk for a rotor of a separately excited electric machine with a thermally conductive insulating layer

[0004] The invention relates to a star disk for a rotor of a separately excited electric machine, for mounting on an end face of the rotor body and for supporting the winding heads of the rotor windings. The star disk comprises a metallic base body with a star disk yoke for mounting on a rotor yoke of the rotor body, star disk arms projecting radially from the star disk yoke for mounting on rotor teeth of the rotor body, and star disk roofs projecting tangentially and axially from the star disk arms for mounting on pole shoes of the rotor body, wherein a winding space for receiving the associated winding head is formed for each rotor pole by outer regions of the star disk yoke, an inner side of the star disk roofs, and an upper side of the star disk arms.Furthermore, the star disk includes an insulating layer which, at least in the area of ​​the winding spaces, is arranged on the base body for electrical insulation of the winding heads from the base body. The invention also relates to a rotor and a separately excited electrical machine.

[0005] The focus here is on separately excited or electrically excited electric machines for electrified motor vehicles, such as electric or hybrid vehicles. Such separately excited machines have a stationary stator with current-carrying stator windings and a rotor with current-carrying rotor windings, which is rotatably mounted relative to the stator. The rotor has a rotor body, for example, a laminated core, which supports the rotor windings. The winding conductors of the rotor windings can, for example, be wires wound around the salient poles of the salient-pole rotor body. The rotor windings form winding heads on opposite end faces of the rotor body.

[0006] To mechanically support the rotor winding heads against high centrifugal forces during rotor rotation, star disks and support rings are known from the prior art, for example from DE 10 2018 128 521 A1. The star disks 24-1036

[0007] Two star disks are positioned on the axially opposite end faces of the lamination stack before the rotor body is wound, so that after winding the star disks are located between the end faces and the winding heads. Each star disk is surrounded by a support ring, so that the star disks and the support rings together absorb the centrifugal force-induced mechanical load. The star disks can, for example, have a steel base body that is partially overmolded with an insulating material, such as a plastic. Such a base body exhibits high mechanical strength.

[0008] To enable cooling of the winding heads, the star disks can be at least partially overmolded with highly thermally conductive, temperature-resistant insulating materials. To achieve high thermal conductivity in the plastic, materials with high filler content are used. These fillers generally impair the material's flowability during injection molding, necessitating high minimum thicknesses of the insulating layer to ensure flawless overmolding of the base body. This results from the rapid heat dissipation and thus rapid solidification of the plastic during overmolding. These high minimum thicknesses of the insulating layer negatively impact the dissipation of waste heat from the winding heads into the base body via the insulating layer. Furthermore, a high filler content reduces mechanical properties, particularly elongation at break. Material costs also increase.

[0009] The object of the present invention is to provide a mechanically stable, thermally conductive and electrically resistant star disk for a rotor of a separately excited electric machine of a motor vehicle.

[0010] This problem is solved according to the invention by a star disk, a rotor, and a separately excited electric machine with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0011] A star disk according to the invention for a rotor of a separately excited electric machine serves to be arranged on an end face of a rotor body of the rotor and to support winding heads of the rotor. The star disk comprises a metallic base body with a star disk yoke for arrangement on a rotor yoke of the rotor body, star disk arms projecting radially from the star disk yoke to 24-1036

[0012] 3

[0013] The star disk is arranged on the rotor teeth of the rotor body and has star disk roofs projecting tangentially and axially onto the star disk arms for mounting on the pole shoes of the rotor body. The outer surfaces of the star disk yoke, the inner surfaces of the star disk roofs, and the upper surfaces of the star disk arms form a winding space for each rotor pole to accommodate the associated winding head. The star disk also includes an insulating layer, which, at least in the area of ​​the winding spaces, is arranged on the base body to electrically insulate the winding heads from the base body. The insulating layer consists of a thermally conductive plastic with a specific thermal conductivity of no more than 0.5 W / m K and a layer thickness of no more than 1 mm to dissipate heat from the winding heads to the metallic base body.

[0014] The invention also relates to a rotor for a separately excited electric machine of a motor vehicle. The rotor has a rotor body with a rotor yoke and salient poles projecting radially from the rotor yoke, each of which has a rotor tooth and a pole shoe. The rotor also includes two star disks according to the invention, which are arranged on axially opposite sides of the rotor body. Furthermore, the rotor comprises rotor windings, the winding conductors of which are wound around the salient poles and the star disks and form winding heads on a top side of the star disks. The winding heads are arranged in the winding spaces of the star disks. A separately excited electric machine according to the invention has a stationary stator with current-carrying stator windings and a rotor according to the invention that is rotatably mounted relative to the stator.The electric machine is in particular a current-excited synchronous machine (SSM), wherein the rotor is in particular designed as an internal rotor which is surrounded by the stator and rotatably mounted within the stator.

[0015] The rotor body, for example, is designed as a laminated core of axially stacked electrical steel laminations and manufactured using a salient-pole design. For this purpose, the rotor body features a ring-shaped rotor yoke, which has an axial through-opening for receiving the rotor shaft. The rotor shaft, passing through the through-opening, is rotationally fixed to the rotor body. Several salient poles or rotor poles are arranged circumferentially around the rotor yoke. The rotor teeth or rotor shafts of the salient poles project radially from the rotor yoke. The rotor teeth can, for example, have parallel flanks. Pole shoes are arranged radially on the outer edges of the rotor teeth. Grooves for receiving axial [24-1036] are located between two circumferentially adjacent rotor teeth.

[0016] 4

[0017] The winding sections of the rotor windings are formed. The pole shoes of two adjacent salient poles close the slots except for a pole gap formed between the pole shoes, which provides an access opening to the corresponding slot for inserting the winding conductors.

[0018] A star disk or star-shaped end disk is arranged on each end face of the rotor body. One shape of the star disk corresponds to a shape of the rotor body determined by the salient-pole design. The annular end face surface of the rotor yoke is covered by the annular star disk yoke. The star disk yoke also has an axial passage for the rotor shaft. Radially extending from the star disk yoke are the star disk arms, with each arm covering an end face surface of a rotor tooth. The star disk arms can also have parallel flanks. Radially outward on the star disk arms are the star disk roofs, which project axially from the top surface of the base body and tangentially from the sides or flanks of the star disk arms. Each star disk roof covers an end face surface of a pole shoe.

[0019] In the area of ​​the star disk arms, the star disk has an axial extent or thickness that is less than the axial extent of the star disk in the area of ​​the star disk yoke and the star disk roofs. Thus, the star disk yoke and the star disk roofs project radially inwards and outwards from the upper surface of the star disk arms and, together with the star disk arms, form the winding spaces or winding chambers for receiving the winding heads. To form the rotor windings, the winding conductors are wound around the rotor teeth and the star disk arms, so that the axial winding conductor sections are arranged in the grooves on the flanks of the rotor teeth, and the end-face winding conductor sections, which form the winding heads, are arranged on the upper surfaces of the star disk arms and are held radially between the star disk yoke and the star disk roofs.The outer surface of the star disk yoke belonging to a winding chamber and the inner surface of the star disk roof belonging to the winding chamber form winding flanges.

[0020] In particular, the axially projecting star disc roofs prevent the winding bodies from slipping due to centrifugal force.

[0021] Each star disk has a metallic base body with a top and a bottom. The bottom is positioned against the respective end face of the rotor body. 24-1036

[0022] 5

[0023] The base body is preferably made of steel. It can be manufactured, for example, by forging. The metallic base body is covered with an insulating layer, at least in those areas that come into contact with the winding conductors, i.e., in the winding spaces. To attach the insulating layer to the base body, it can be overmolded, at least in certain areas, with thermally conductive plastic. This insulating layer provides electrical insulation between the winding conductors and the metallic base body.

[0024] The insulating layer material is designed to allow for thin layers or walls. The insulating layer consists of a thermally poorly conductive plastic with a specific thermal conductivity of no more than 0.5 W / m K. Specifically, the thermally conductive plastic is a thermoplastic, preferably polyphenylene sulfide (PPS), with a filler such as glass fiber. The low filler content, for example, no more than 30%, ensures the necessary flowability of the plastic to produce thin layers of no more than 1.0 mm. The thermal conductivity of the insulating layer is determined by the wall thickness and the specific thermal conductivity of the material used, resulting in comparable or even better thermal conductivity compared to the prior art.Improved properties of the insulating layer can be achieved by reducing its wall thickness and specific thermal conductivity. This allows the waste heat from the winding heads to be dissipated via the insulating layer to the metallic base body, which then transfers the heat, for example, to the rotor shaft. The rotor shaft can be designed as a hollow shaft and be permeated by a coolant flowing through it, which carries the waste heat away to a coolant-carrying cooling circuit of the vehicle. The embodiments and advantages presented with reference to the star disk according to the invention apply accordingly to the rotor and the electric machine according to the invention.

[0025] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures alone, are usable not only in the combinations specified, but also in other combinations or individually. 24-1036

[0026] 6

[0027] The invention will now be explained in more detail with reference to a preferred embodiment and the drawings. The drawings show:

[0028] Fig. 1 shows a top view of the upper surface of a star disk design for a rotor of a separately excited electric machine;

[0029] Fig. 2 shows a top view of the underside of the star disk;

[0030] Fig. 3 shows a longitudinal section through the star disk; and

[0031] Fig. 4 shows a cross-sectional view through one arm of the star disk.

[0032] In the figures, identical and functionally equivalent elements are provided with the same reference symbols.

[0033] Figures 1 and 2 show perspective views of a star disk 1 for the rotor of a separately excited electric machine. The electric machine can be used, for example, as a drive motor for an electrified motor vehicle. The star disk 1 can be placed with its underside 2 (see Figure 2) against an end face of a rotor body, for example, a laminated core, and can hold the winding heads of the rotor windings. The star disk 1, in particular together with a support ring surrounding the star disk 1 (not shown here), has the function of dissipating the high centrifugal forces that act on the winding heads at high rotational speeds of the electric machine. The star disk 1 has a metallic base body 3, which is preferably made of steel and is partially covered with an insulating layer 4.

[0034] The star disk 1 has a star disk yoke 5 with a through-opening 6 for a rotor shaft of the rotor, radially projecting, parallel-flanked star disk arms 7, and star disk roofs 8 arranged radially outside the star disk arms 7. The star disk arms 7 support the winding heads. The star disk roofs 8 and the star disk yoke 5 project axially from an upper surface of the star disk arms 7, so that the winding heads arranged on the star disk arms 7 are enclosed radially by the star disk yoke 5 and the star disk roofs 8. A star disk arm 7, the associated star disk roof 8, and an outer surface area 9 of the star disk yoke 5 form 24-1036

[0035] 7 a winding space 10 or a winding chamber for a winding head of the rotor winding wound around the associated salient pole of the rotor body.

[0036] To electrically insulate the electrically conductive winding conductors of the rotor windings, which are made of copper, for example, from the metallic base body 3, the base body 3 is partially covered, at least in the area of ​​the winding spaces 10, with the insulating layer 4. Here, the base body 3 is covered with the insulating layer 4 except for a bottom surface 11 and a top surface 12 of the star disk yoke 5. Because the base body 3 is made of steel, it has high strength, so that centrifugal loads are reliably absorbed and deformation of the rotor windings, especially of a connecting wire of the rotor windings, is kept to a minimum. Another advantage of the star disk 1 with the iron-containing steel base body 3 is that the thermal expansions of the iron-containing laminated core, the copper wires, and the steel base body 3 are equalized, unlike with an aluminum base body.Matched thermal expansions have the advantage that relative deformations between the components inside the rotor are reduced.

[0037] Furthermore, steel has high thermal conductivity, allowing waste heat to be efficiently dissipated, for example, to the cooled rotor shaft of the rotor. However, the waste heat from the winding heads must be conducted to the base body 3 via the insulating layer 4. This insulating layer 4 must also provide the necessary insulation between the winding heads and the base body 3. Therefore, the insulating layer 4 is made of a thermally conductive plastic 13 with a low filler content. Figures 3 and 4 show cross-sectional views through the star disk 1 along the section lines AA' (Fig. 3) and BB' (Fig. 4).If the insulating layer 4 were made of a highly thermally conductive plastic with a high filler content, the required insulation strength and minimum wall thickness from the crimping process would result in a minimum layer thickness d1 of the insulating layer 4, which would negatively affect the weight and mechanical stability of the star disk 1 and would also require a high amount of material. This minimum layer thickness d1 can be reduced to a layer thickness d2 of the insulating layer 4 if the insulating layer 4 is made of the thermally conductive plastic 13 with a low filler content, for example PPS, as provided here.

Claims

24-1036 8 Patent claims 1. Star disk (1) for a rotor of a separately excited electrical machine for arrangement on an end face of a rotor body of the rotor and for carrying winding heads of the rotor, comprising - a metallic base body (3) with a star disk yoke (5) for arrangement on a rotor yoke of the rotor body, star disk arms (7) projecting radially from the star disk yoke (5) for arrangement on rotor teeth of the rotor body, and star disk roofs (8) projecting tangentially and axially on the star disk arms (7) for arrangement on pole shoes of the rotor body, wherein a winding space (10) for receiving the associated winding head is formed for each rotor pole by outer surface areas of the star disk yoke, an inner surface of the star disk roofs (8), and an upper surface of the star disk arms (7), and - an insulating layer (4) which is arranged at least in the area of ​​the winding spaces (10) on the base body (3) for electrically insulating the winding heads from the base body (3), characterized in that the insulating layer (4) consists of a thermally conductive plastic (13) with a specific thermal conductivity of at most 0.5 W / m K and a layer thickness of at most 1 mm for dissipating waste heat from the winding heads to the metallic base body (3).

2. Star disk (1) according to claim 1, characterized in that the base body (3) is made of steel.

3. Star disc (1) according to claim 1 or 2, characterized in that the thermally conductive plastic (13) is a thermoplastic plastic. 24-1036 9 4. Star disc (1) according to claim 3, characterized in that the thermoplastic polymer is polyphenylene sulfide.

5. Rotor for a separately excited electric machine of a motor vehicle, comprising: - a rotor body with a rotor yoke and radially projecting salient poles, each having a rotor tooth and a pole shoe, - two star disks (1) according to one of the preceding claims, which are arranged on axially opposite sides of the rotor body, - Rotor windings with winding conductors which are wound around the salient poles and form winding heads on a top side of the star disks (1), wherein the winding heads are arranged in the winding spaces (10) of the star disks (1).

6. Externally excited electric machine for a motor vehicle comprising a stator and a rotor rotatably mounted with respect to the stator according to claim 5.

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