Weight-optimised star disc for a rotor of an externally excited electric machine

Abstract

The invention relates to a star disc (1) for a rotor of an externally excited electric machine for arranging on an end face of a rotor core of the rotor and for supporting winding heads of the rotor, having a main body (3) with a star disc yoke (5) for arranging on a rotor yoke of the rotor core, star disc arms (7) protruding radially from the star disc yoke (5) for arranging on rotor teeth of the rotor core and star disc roofs (8) protruding tangentially and axially on the star disc arms (7) for arranging on pole shoes of the rotor core, wherein an underside (2) of the main body (3), which underside can be placed against the end face of the rotor core, has weight-reducing depressions (10a, 10b, 10c) for forming air-filled cavities in the arranged state of the star disc (1) on the rotor core.

Description

[0001] Weight-optimized star disk for a rotor of a separately excited electrical machine

[0002] The invention relates to a star disk for a rotor of a separately excited electrical machine for arrangement on an end face of a rotor core of the rotor and for supporting winding heads of the rotor, comprising a base body with a star disk yoke for arrangement on a rotor yoke of the rotor core, star disk arms projecting radially from the star disk yoke for arrangement on rotor teeth of the rotor core, and star disk roofs projecting tangentially and axially from the star disk arms for arrangement on pole pieces of the rotor core. The invention also relates to a rotor and a separately excited electrical machine.

[0003] In this case, the focus is on separately excited or current-excited electrical machines for electrified motor vehicles, such as electric or hybrid vehicles. Such separately excited machines have a stationary stator with energizable stator windings and a rotor mounted rotatably relative to the stator with energizable rotor windings. The rotor has a rotor core, for example, a laminated core, which supports the rotor windings. Winding conductors of the rotor windings can, for example, be designed as wires wound around salient poles of the rotor core, which is manufactured in a salient-pole design. The rotor windings form winding heads on opposite end faces of the rotor core.

[0004] In order to mechanically support the winding heads of the rotor 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 are arranged on the axially opposite end faces of the laminated core so that the star disks are also wound with the wires and, after winding, are arranged between the end faces and the winding heads. The star disks are each surrounded by a support ring so that the star disks and the support rings together absorb the mechanical load caused by the centrifugal force. The star disks can, for example, have a base body made of steel, which is partially over-molded with a plastic. While such a base body has high mechanical strength, it also has an undesirably high weight.

[0005] It is an object of the present invention to provide a mechanically stable, weight-reduced rotor for a separately excited electrical machine of a motor vehicle.

[0006] This object is achieved according to the invention by a star disk, a rotor, and a separately excited electric machine having the features according to the respective independent patent claims. Advantageous embodiments of the invention are the subject of the dependent patent claims, the description, and the figures.

[0007] A star disk according to the invention for a rotor of a separately excited electrical machine is designed to be arranged on an end face of a rotor core of the rotor and to support winding heads of the rotor. The star disk comprises a base body with a star disk yoke for arrangement on a rotor yoke of the rotor core, star disk arms projecting radially from the star disk yoke for arrangement on rotor teeth of the rotor core, and star disk roofs projecting tangentially and axially from the star disk arms for arrangement on pole pieces of the rotor core. An underside of the base body, which can be placed against the end face of the rotor core, has weight-reducing recesses for forming air-filled cavities when the star disk is arranged on the rotor core.

[0008] The invention further relates to a rotor for a separately excited electric machine of a motor vehicle. The rotor has a rotor core with a rotor yoke and salient poles projecting radially from the rotor yoke, each having a rotor tooth and a pole shoe. Furthermore, the rotor comprises two star disks according to the invention, which are arranged on axially opposite sides of the rotor core, with the cavities formed between the end faces and the recesses. Furthermore, the rotor comprises rotor windings, the winding conductors of which are wound around the salient poles and the star disks and form winding overhangs on an upper side of the star disks. A separately excited electric machine according to the invention has a stationary stator with energizable 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 designed in particular as an internal rotor. The rotor core is designed, for example, as a laminated core made of axially stacked electrical steel laminations and manufactured in a salient pole design. For this purpose, the rotor core has the ring-shaped rotor yoke, which has an axial through-opening for receiving a rotor shaft of the rotor. The rotor shaft, which passes through the through-opening, is connected in a rotationally fixed manner to the rotor core. Several salient poles are arranged on the rotor yoke in a distributed manner in the circumferential direction. Rotor teeth or rotor shafts of the salient poles protrude radially from the rotor yoke. The rotor teeth can, for example, be designed with parallel flanks. Pole shoes are arranged radially on the outside of the rotor teeth.Between two circumferentially adjacent rotor teeth, grooves are formed for receiving axial winding sections of the winding conductors of the rotor windings. The pole pieces of two adjacent salient poles close the grooves except for a pole gap formed between the pole pieces, which forms an access opening to the corresponding groove for inserting the winding conductors.

[0009] A star disk or star-shaped end disk is arranged on each end face of the rotor core. Each star disk has a base body with a top side and a bottom side. The bottom side is placed against the respective end face of the rotor core. The base body is preferably made of steel. The base body can be manufactured, for example, using a forging process. The metallic base body is covered with an electrically insulating layer, at least in those areas that come into contact with the winding conductors, i.e., at least on a top side and on axially extending side areas. For example, the steel base body can be partially overmolded with a plastic.

[0010] The shape of the star disk corresponds to the shape of the rotor core determined by the salient pole design. The frontal, annular surface of the rotor yoke is covered by the annular star disk yoke. The star disk yoke also has an axial feedthrough for the rotor shaft. The star disk arms protrude radially from the star disk yoke, with each star disk arm covering a frontal surface of a rotor tooth. The star disk arms can also be designed with parallel flanks. The star disk roofs are arranged radially on the outside of the star disk arms and protrude axially from an upper side of the base body and tangentially from the side areas or flanks of the star disk arms. Each star disk roof covers a frontal surface of a pole shoe. In the area of ​​the star disk arms, the base body has an axial extension orThickness which is less than the axial extension of the base body in the area of ​​the star disk yoke and the star disk roofs. The star disk yoke and the star disk roofs therefore protrude radially inward and outward from an upper side of the star disk arms and, together with the star disk arms, form winding chambers for accommodating the winding overhangs. 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 slots on the flanks of the rotor teeth and the end-face winding conductor sections, which form the winding overhangs, are arranged on the upper sides of the star disk arms and are held between the star disk yoke and the star disk roofs. In particular, the axially projecting star disk roofs prevent the winding bodies from slipping due to centrifugal force.The electrically insulating layer, which partially covers the base body, insulates the winding conductors from the steel base body. The electrically insulating layer can, for example, have corrugations for wire guidance in the area of ​​a transition between the side sections and the top of the star disk arms.

[0011] To reduce the weight of the star disk, the underside of the base body, with which the base body is attached to the front side of the rotor core, has weight-reducing depressions or indentations. The surface of the underside of the base body is therefore not flat or planar, but has a height profile. Due to the depressions, the underside of the base body does not lie fully against the respective front side, but only in the area of ​​a contact surface on the underside away from the depressions. When the star disk is attached to the rotor core, the front side of the rotor core covers the depressions in the underside of the base body and thus forms the air-filled cavities or hollow spaces. For example, the depressions can be introduced during the forging process of the steel base body.Alternatively, the recesses can be created after forging the base body by machining the underside. The recesses are arranged rotationally symmetrically, so they do not introduce any imbalance.

[0012] The recesses not only advantageously reduce the weight of the star disks themselves, but also prevent the potting compound used to support the rotor windings from running into the air pockets created by the recesses between the respective base body and the end face of the rotor core, thus increasing the rotor's weight. The loads on the star disk with the recesses are not significantly higher at the critical points than on star disks without recesses. Furthermore, the deformation of the windings, especially of the connecting wire, is not significantly increased. Furthermore, no permanent deformation occurs on the outer surface of the rotor.

[0013] Particularly preferably, the contact area of ​​the base body surrounds the depressions and runs at least along one contour of the base body. The contour of the base body is formed in particular by an edge of the base body on the outer circumference and on the inner circumference. The edge on the outer circumference is formed by outer edges of the star disk yoke, the star disk arms and the star disk roofs. The edge on the inner circumference is formed by a circular inner edge of the star disk yoke, which surrounds the axial through-opening for the rotor shaft and is pressed against the rotor shaft. In the contact area of ​​the base body, the surface of the underside is raised compared to the surface in the area of ​​the depressions. The depressions are enclosed by the contact area so that this forms a barrier for the potting compound when the star disks are in contact with the rotor core.

[0014] It can be provided that first depressions are formed in the star disk yoke in alignment with the star disk arms and / or second depressions are formed in the star disk arms and / or third depressions are formed in the star disk roofs, wherein stabilizing first webs are formed between the first depressions and the second depressions and / or stabilizing second webs are formed between the second depressions and the third depressions. With the help of the webs formed in the star disk for mechanical stabilization, a comparable strength of the star disk and a comparable deformation of the winding heads, in particular of the connecting wires under centrifugal force, is achieved compared to star disks made of solid material, despite the reduced mass caused by the depression.

[0015] The first recesses formed in the star disk yoke are delimited in the radial direction by the inner circumference of the star disk yoke and the first webs at the transition between the star disk yoke and the star disk arms. In the circumferential direction, sections of the contact area can be arranged between the first recesses and extend radially from an outer edge toward an inner edge of the star disk yoke. The sections of the contact area can extend over the entire radial diameter of the star disk yoke and separate the first recesses from each other in the circumferential direction, or they can extend only over a portion of the radial diameter of the star disk yoke, so that the first recesses are connected in the circumferential direction.In the sections of the contact area between the first recesses, a screw hole can be formed for receiving a screw for securing a cap-like support ring of the rotor to the star disk. Such a support ring has a hollow cylindrical collar area, which rests against the outer sides of the star disk roofs and thus radially surrounds the star disk, and an annular disk-shaped cover area, which is arranged so as to overlap the top side of the star disk. Holes can also be formed in the cover area, which are aligned with the screw holes and via which the support ring can be screwed tightly to the star disk.

[0016] The second recesses can be formed in the star disk arms and can be circumferentially delimited by the contact area on the lateral outer edges of the star disk arms and radially delimited by the first and second webs or by the star disk yoke and the star disk roof. The third recesses can be formed in the star disk roofs and can be radially delimited by the second web and an edge of the star disk roof.

[0017] In a further development of the invention, one surface of the webs is recessed relative to a surface of the contact area. In other words, the surfaces of the webs are not at the same axial height as the surface of the support area, so that when the star disk is in its installed state, the webs do not rest against the rotor core's face. Thus, the webs increase the stability of the star disk while minimizing weight.

[0018] In a further embodiment of the invention, the base body has a positioning pin in the region of two radially opposite second webs or in two radially opposite star disk roofs for arrangement in a positioning opening in the end face of the rotor core. The positioning pins are formed integrally with the respective web or with the underside of the base body in the region of the star disk roofs. To correctly position the star disks on the end faces, the positioning pins are inserted into the corresponding positioning openings. The rotor core, equipped with the correctly positioned star disks, can then be wound with the winding conductors. The embodiments presented with reference to the star disk according to the invention and their advantages apply accordingly to the rotor according to the invention and to the electrical machine according to the invention.

[0019] Further features of the invention emerge 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 alone in the figures, can be used not only in the respective specified combination, but also in other combinations or on their own.

[0020] The invention will now be explained in more detail using a preferred embodiment and with reference to the drawings. They show:

[0021] Fig. 1 is a perspective view of a first embodiment of a star disk for a rotor of a separately excited electrical machine; and

[0022] Fig. 2 is a perspective view of a second embodiment of a star disk.

[0023] In the figures, identical and functionally identical elements are provided with the same reference numerals.

[0024] Fig. 1 and Fig. 2 show perspective views of different designs of a star disk 1 for a rotor of a separately excited electrical machine. The electrical machine can be used, for example, as a drive motor for an electrified motor vehicle. The star disk 1 can be placed with an underside 2 against an end face of a rotor core, for example a laminated core, of the rotor and hold winding heads of rotor windings of the rotor there. The star disk 1 has the task, in particular together with a support ring (not shown here) surrounding the star disk 1, of dissipating the high centrifugal forces that act on the winding heads at high speeds of the electrical machine. The star disk 1 has a metallic base body 3, which is made in particular of steel and is partially covered with an electrically insulating layer 4, for example a plastic.The star disk 1 has a star disk yoke 5 with a through-opening 6 for a rotor shaft of the rotor, parallel-flanked star disk arms 7 projecting radially from the star disk yoke 5, and star disk roofs 8 arranged radially on the outside of the star disk arms 7. The star disk arms 7 carry the winding heads. The star disk roofs 8 and the star disk yoke 5 protrude in the axial direction on an upper side of the star disk arms 7, so that the winding heads arranged on the star disk arms 7 are radially enclosed by the star disk yoke 5 and the star disk roofs 8. In order 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, all sides of the base body 3, except for the underside 2 and outer side regions 9 of the star disk roofs 8, are covered with the electrically insulating layer 4.The support ring, which is made of stainless steel for example and surrounds the star disc 1 like a bandage, can be pressed onto the uncovered outer side areas 9 of the star disc 1.

[0025] Because the base body 3 is made of steel, it exhibits high strength, reliably dissipating centrifugal force loads and minimizing deformation of the rotor windings, particularly of a connecting wire of the rotor windings. A further advantage of the star disk 1 with the ferrous steel base body 3 is that, unlike an aluminum base body, the thermal expansions of the ferrous laminated core, the copper wires, and the steel base body 3 are aligned. Adapted thermal expansions have the advantage of reducing relative deformations between the components inside the rotor.

[0026] A disadvantage of the steel base body 3, however, is its high weight. To reduce this high mass, weight optimizations are implemented on the star disk 1 in the form of recesses 10a, 10b, 10c or pockets in the underside 2 of the base body 3. The recesses 10a, 10b, 10c are separated from the surrounding area 11 of the star disk 1 by a contact area 12 on the underside 2 that is raised relative to the recesses 10a, 10b, 10c. The contact area 12 extends at least along a contour 13 of the base body 3, so that the contact area 12 has at least one inner edge 14 and outer edge 15 of the base body 3 that is raised relative to the recesses 10a, 10b, 10c. An inner side of the star disk yoke 5 also serves to form a press fit between the star disk 1 and the rotor shaft of the rotor passed through the passage 6, wherein the press fit between the star disk 1 and the rotor shaft ensures axial stability.The contact area 12 forms a contact surface which, when the star disk 1 is in the arranged state, rests against the rotor core's end face and is pressed against the rotor core by the windings. In this arranged and pressed-on state, the recesses 10a, 10b, 10c covered by the end face of the rotor core form air-filled cavities which remain free of potting compound even when the rotor is potted with a potting compound.

[0027] A first area that can be used for weight optimization is the star disk yoke 5. First recesses 10a can be arranged here. The first recesses 10a are distributed in the circumferential direction and arranged in alignment with the star disk arms 7 in the star disk yoke 5. In the radial direction, the first recesses 10a are delimited by the inner edge 14 and a respective first web 16 between the star disk yoke 5 and the star disk arms 7. Sections 17 of the contact area 12 are arranged between the recesses 10a along the circumferential direction. In the exemplary embodiment according to Fig. 2, the sections 17 extend between the inner edge 14 and the outer edge 15 and separate the first recesses 10a from one another. In the exemplary embodiment according to Fig. 1, the sections 17 extend from the outer edge 15, but are arranged at a distance from the inner edge 14.This connects the first recesses 10a in the circumferential direction. The sections 17 between the first recesses 10a also have screw holes 18 for receiving screws, by means of which the support ring can be attached to the respective star disk 1.

[0028] A second area that can be used for weight optimization is the star disk arms 7. Second recesses 10b are arranged there. In the circumferential direction, the second recesses 10b are delimited by the side flank region 19 of the outer edge 15 of the star disk arms 7. As shown in the exemplary embodiment according to Fig. 2, in the radial direction, the second recesses 10b are delimited by the first webs 16 and by the outer edge 15 in the outer side region 9 of the star disk roofs 8. The second recesses 10b thus extend into the star disk roofs 8.

[0029] In the exemplary embodiment according to Fig. 1, it is shown that the second recesses 10b are delimited by the first webs 16 and by second webs 20 between the second recesses 10b and third recesses 10c in the star disk roofs 8. The webs 16, 20, which contribute to the stability of the star disk 1, also exhibit slight weight optimization in that their surface is at least partially reduced or set back from a surface of the support area 18.

[0030] Positioning pins 21 are formed radially outside of two opposing second recesses 10b in the underside 2, for example, in two radially opposing second webs 20. To position the star disk 1 on the rotor core, these positioning pins 21 are arranged in corresponding positioning openings in the end face of the rotor core.

Claims

Patent claims 1. Star disk (1) for a rotor of a separately excited electrical machine for arranging on an end face of a rotor core of the rotor and for supporting winding heads of the rotor, comprising a base body (3) with a star disk yoke (5) for arranging on a rotor yoke of the rotor core, star disk arms (7) projecting radially from the star disk yoke (5) for arranging on rotor teeth of the rotor core and star disk roofs (8) projecting tangentially and axially on the star disk arms (7) for arranging on pole shoes of the rotor core, characterized in that an underside (2) of the base body (3) which can be placed against the end face of the rotor core has weight-reducing depressions (10a, 10b, 10c) for forming air-filled cavities in the arranged state of the star disk (1) on the rotor core.

2. Star disk (1) according to claim 1, characterized in that the base body (3) consists of steel and is covered at least in regions with an electrically insulating layer (4).

3. Star disk (1) according to claim 1 or 2, characterized in that the underside (2) of the base body (3) has a contact area (12) for contact with the end face of the rotor core, which contact area surrounds the recesses (10a, 10b, 10c) and which runs at least along a contour (13) of the base body (3).

4. Star disk (1) according to one of the preceding claims, characterized in that first recesses (10a) in the star disk yoke (5) are aligned with the Star disk arms (7) are formed and / or second depressions (10b) are formed in the star disk arms (7) and / or third depressions (10c) are formed in the star disk roofs (8), wherein stabilizing first webs (16) are formed between the first depressions (10a) and the second depressions (10b) and / or stabilizing second webs (20) are formed between the second depressions (10b) and the third depressions (10c).

5. Star disk (1) according to claim 4, characterized in that a surface of the webs (16, 20) is set back from a surface of the contact area (12).

6. Star disk (1) according to claim 4 or 5, characterized in that the base body (3) in the region of two radially opposite second webs (20) or of two radially opposite star disk roofs (8) each has a positioning pin (21) for arrangement in a positioning opening in the end face of the rotor core.

7. Star disk (1) according to one of claims 4 to 6, characterized in that the contact area is arranged at least in sections between the first recesses and extends radially from an outer edge towards an inner edge of the star disk yoke, wherein in the sections of the contact area between the first recesses each has a screw hole for receiving a screw for fixing a cap-like support ring of the rotor to the star disk.

8. Rotor for a separately excited electric machine of a motor vehicle, comprising: - a rotor core with a rotor yoke and salient poles projecting radially from the rotor yoke, 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 core, wherein the air-filled cavities are formed between the end faces and the recesses (10a, 10b, 10c), - Rotor windings with winding conductors which are wound around the salient poles and form winding heads on an upper side of the star disks (1).

9. Rotor according to claim 8, characterized in that the winding conductors are cast with a casting compound, wherein no casting compound is arranged within the cavities.

10. Separately excited electrical machine for a motor vehicle comprising a stator and a rotor rotatably mounted with respect to the stator according to claim 8 or 9.

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