Rotor comprising a cooling device with tolerance and heat transfer regions

Abstract

The invention relates to a rotor (1) for a separately excited electric machine of a motor vehicle, comprising: - a rotor body (2) comprising axial grooves (4) that extend between two end faces (6) of the rotor body (2); - rotor windings (5) for exciting a rotor magnetic field, wherein first winding portions are arranged within the grooves (4) and second winding portions project axially on the end faces (6) of the rotor body (2) and form end windings (7); - a cooling device for cooling the rotor windings (5), which comprises heat-conducting rods (16) arranged in the grooves (4) for axially dissipating waste heat from the first winding portions and two cover elements (10) designed as heat sinks (22) for absorbing the waste heat carried off by the heat-conducting rods (16), wherein rod ends (20) of the heat-conducting rods (16) protrude axially on the end faces (6) and wherein the cover elements (10) for axially covering the end windings (7) are arranged to overlap with the end faces (6) and comprise pot-shaped receiving regions (24) on an underside (23) facing the relevant end face (6), wherein, in each case, one rod end (20) is inserted into a pot-shaped receiving region (24), forming a tolerance and heat transfer region (33), and the tolerance and heat transfer regions (33) are formed by an axial gap (34) and an annular gap (35) between the relevant rod end (20) and an inner face (32) of the relevant pot-shaped receiving region (24).

Description

[0001] Rotor with a cooling device with tolerance and heat transfer ranges

[0002] The invention relates to a rotor for a separately excited electric machine of a motor vehicle, comprising a rotor body with axial slots extending between two end faces of the rotor body. The rotor also includes rotor windings for exciting a rotor magnetic field, wherein first winding sections are arranged within the slots and second winding sections project axially from the end faces of the rotor body and form winding heads. Furthermore, the rotor includes a cooling device for cooling the rotor windings. The invention also relates to a separately excited electric machine.

[0003] The present case concerns separately excited electric machines, which can be used, for example, as drive motors for electrified motor vehicles. Such separately excited electric machines typically have a stator with a stator body and current-carrying stator windings, and a rotor rotatably mounted relative to the stator, with a rotor body and current-carrying rotor windings. Both the stator and the rotor can heat up during operation of the electric machine due to power losses, so it is common practice to equip the rotor and the stator with cooling devices. For example, as shown in DE 102017213 960 A1, the rotor can have tubular cooling channels running along rotor grooves of the rotor body, containing a heat-conducting medium, such as a coolant, to dissipate heat from the rotor body via at least one end face of the rotor body.However, connecting the rotor-integrated cooling channels to a cooling circuit of the vehicle that supplies the coolant is complex due to the rotation of the rotor.

[0004] The object of the present invention is to provide an alternative, simple, rotor-integrated cooling system for an electric motor vehicle.

[0005] This problem is solved according to the invention by a rotor and a separately excited electrical 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.

[0006] A rotor according to the invention for a separately excited electric machine of a motor vehicle comprises a rotor body with axial slots extending between two end faces of the rotor body, as well as rotor windings for exciting a rotor magnetic field. First winding sections are arranged within the slots, and second winding sections project axially from the end faces of the rotor body, forming winding heads. The rotor also includes a cooling device for cooling the rotor windings. This device has heat-conducting bars arranged in the slots for axially dissipating waste heat from the first winding sections and two cover elements designed as heat sinks for absorbing the waste heat transported by the heat-conducting bars. The ends of the heat-conducting bars project axially from the end faces of the rotor body.The cover elements are arranged overlapping the end faces for axial covering of the winding heads and have cup-shaped receiving areas on one underside facing the respective end face, with one rod end being immersed in a cup-shaped receiving area, forming a tolerance and heat transfer zone. The tolerance and heat transfer zones are each formed by an axial gap and an annular gap between the respective rod end and an inner surface of the respective cup-shaped receiving area.

[0007] An externally excited electric machine according to the invention is in particular a current-excited synchronous machine (SSM) and comprises a stator and a rotor according to the invention rotatably mounted with respect to the stator. The electric machine is in particular designed as a drive machine for an electrified motor vehicle. The electric machine is preferably designed as an internal rotor machine in which the rotor is rotatably mounted within the stator.

[0008] The rotor comprises the rotor body or rotor core, which is preferably designed as a laminated core of axially stacked electrical steel laminations. A rotor shaft can pass axially through the rotor body and be rotationally fixed to the rotor body. Preferably, the rotor body is designed as a salient-pole structure and has a rotor yoke and radially extending salient poles with pole teeth and pole shoes, spaced apart from each other in the circumferential direction. The pole teeth are wound with winding conductors, for example, wires, to form the rotor windings. A slot is formed between each pair of adjacent pole teeth, in which the first, slot-internal winding sections of two adjacent rotor windings are arranged. A pole gap is formed between two adjacent pole shoes, the diameter of which is smaller than the diameter of the slot and which forms an access opening to the respective slot.

[0009] The grooves extend axially between the two axially opposite end faces of the rotor body. The rotor preferably has groove closure elements for closing the grooves. A groove closure element, which can also be called a cover slide, can be arranged in each groove and mechanically connected to the rotor body. The groove closure elements can, for example, be injection-molded parts made of a plastic. For instance, the groove closure elements can be designed as groove closure wedges, which have a wedge-shaped radial section arranged in the groove and a tangential section for bearing against the rotor body. The tangential section can, for example, bear against the pole shoes of two adjacent salient poles and close the pole gap.For example, the tangential area and the pole shoes can have corresponding connecting elements, which form a connection, at least in the radial direction, between the slot closure elements and the rotor body. The slot closure elements can be inserted axially or radially into the slots. In particular, axially opposite end regions of the slot closure elements project out of the slots on both sides, so that the end faces of the slot closure elements are axially raised relative to the end faces of the rotor body. These end regions of the slot closure elements are arranged circumferentially between the winding heads, thus projecting axially into a space between two adjacent winding heads.

[0010] The heat-conducting bars are arranged in the slots of the rotor body. These heat-conducting bars, or heat-conducting pins, are preferably made of solid metal. The heat-conducting bars extend axially through the slots and project beyond the end faces of the rotor body. The axial length of the heat-conducting bars is therefore greater than the axial length of the rotor body. In particular, the axial length of the bar ends is greater than the axial height of the winding heads, so that the bar ends also project beyond the winding heads. Preferably, the heat-conducting bars are designed as round bars and thus have a circular, and in particular axially constant, cross-section. In the case of a salient-pole rotor, the heat-conducting bars are arranged in the slots between the internal winding sections of the two adjacent rotor windings.Each slot can contain a heat-conducting rod, which is axially segmented to prevent an electrically conductive path leading axially through the slots. In other words, each heat-conducting rod can be multi-part and consist of at least two rod segments arranged axially spaced apart from each other in the respective slot.

[0011] Preferably, the heat-conducting bars are held in the grooves by the groove closure elements, with each closure element being mechanically connected to a heat-conducting bar, either axially continuous or axially segmented, for example, by a material bond. In the case of groove closure elements in the form of groove closure wedges, the heat-conducting bars can be integrated into the radial areas. For example, the heat-conducting bars can be material-bonded to the groove closure elements by being partially overmolded with the plastic of the groove closure elements. The mechanical connection between the groove closure elements and the heat-conducting bars thus occurs during the injection molding of the groove closure elements. A groove closure element and a heat-conducting bar therefore form an assembly. By arranging the assembly in a groove, both the groove closure element and the heat-conducting bar are thus positioned within the groove.The axial length of the heat-conducting rods is greater than the axial length of the slot closure elements, so that the axially opposite rod ends of the heat-conducting rods protrude axially at the end faces of the slot closure elements.

[0012] The heat conduction bars are designed to cool the rotor windings by absorbing the operational waste heat from the rotor windings within the slot and dissipating it axially towards the bar ends and thus towards the end faces of the rotor body. For this purpose, it is advantageous if the slot closure elements only partially encase the respective heat conduction bar for retention, so that the heat conduction bars have encased sections and exposed sections along the axial direction that absorb waste heat.

[0013] The end faces of the rotor body are fitted with cover elements that form the cooling elements. These cover elements can be actively cooled, for example, by means of oil cooling of the electric motor. The cover elements cover one end face of the rotor body as well as the winding heads of the rotor windings. Each cover element may have an axial through-opening for the rotor shaft and screw holes for mechanically connecting the cover elements to the rotor body. Additionally, the rotor may have two support bands that radially surround the winding heads and extend axially between the respective end face and the respective cover element. These support bands, which are, for example, made of steel, together with the cover elements form hood-like covers that are located on the end faces of the rotor body and cover the winding heads radially and axially.For example, the support bands can be mechanically connected to the end sections of the slot closure elements and to the rotor's star-shaped discs, which are located on the end faces of the rotor body and are designed to hold the winding heads. The support bands and the star-shaped discs form support structures for the rotor, which brace the winding heads against centrifugal forces during rotor rotation.

[0014] The undersides of the cover elements feature cup-shaped receiving areas for the ends of the heat-conducting rods. These cup-shaped receiving areas may have blind-hole-like openings, each surrounded by a side wall. The cover elements may also have shell-like receiving areas on their underside for partially receiving the winding heads. The cup-shaped receiving areas for the rod ends and the shell-like receiving areas for the winding heads can be arranged alternately around the circumference. The surface profile of the undersides of the cover elements is thus adapted to the end-face shape of the rotor body, which is fitted with the rotor windings and the assemblies. The cover elements can, for example, be cast parts, with the respective surface profile incorporated into their undersides, particularly during the casting process.The top surfaces of the cover elements can, for example, be flat.

[0015] The cup-shaped receiving areas are, for example, cylindrically designed for the round heat-conducting bars. These receiving areas have a base and a side wall. The side walls of the receiving areas, which are formed as axial protrusions on the underside of the cover elements, can, when the cover elements are in place, project axially into the spaces between two adjacent winding heads and are thus arranged circumferentially between the winding heads. The bar ends are inserted into these cup-shaped receiving areas without touching either the base or the side wall of the respective receiving area. This creates axial gaps as spaces between the tip of the inserted bar end and the base of the cup-shaped receiving area, and annular gaps as spaces between the outer surface of the inserted bar end and the side wall of the cup-shaped receiving area.To form the axial gaps, the axial immersion depth of the heat-conducting rods or the length of the rod ends is less than the depth of the receiving areas, and to form the annular gaps, the outer diameter of the rod ends is less than the inner diameter of the receiving areas. The axial and annular gaps can be filled with a potting compound when the rotor is encased.

[0016] The axial gaps and the annular gaps form tolerance and heat transfer zones. In other words, these spaces serve both to provide tolerances during the assembly of the cover elements and during the operation of the electric machine, and to improve heat transfer between the heat-conducting bars and the cover elements. Without the cup-shaped receiving areas, only tolerance-related axial gaps would form between the bar ends and the cover elements. Due to the rotor's high axial positional tolerance, these gaps could exhibit a high thermal resistance between the bar ends and the cover elements, thus impairing heat transfer and cooling efficiency. To improve cooling efficiency, the blind-hole-like receiving openings also provide annular gaps, which can likewise be used for heat transfer.These annular gaps can have a smaller dimension than the axial gaps due to the higher radial positional accuracy when mounting the cover elements, thus significantly reducing the heat transfer resistance between the heat conducting rods and the cover elements acting as heat sinks.

[0017] It is advantageous if the tolerance and heat transfer zones are only partially filled with a thermally conductive, electrically insulating material, particularly silicone, to improve heat transfer between the heat-conducting bars and the respective cover element and to provide positional tolerance between the heat-conducting bars and the respective cover element. Thus, the tolerance and heat transfer zones are not completely filled with the thermally conductive, electrically insulating material. Preferably, the thermally conductive material is arranged only in a portion of the annular gap between the shell of the bar end and the side wall of the receiving area and is arranged concentrically to the bar end, so that at least in the region of the axial gap an air cavity is formed to enable axial positional tolerance between the heat-conducting bars and the cover element.For example, the thermally conductive, electrically insulating material can be positioned at the rod ends before the cover elements are mounted, thus concentrically surrounding the rod ends. During the mounting of the cover elements, the material is positioned in the receiving area between the rod end and the side wall of the receiving area, forming a thermal bridge between the heat-conducting rods and the heat sinks, which promotes heat transfer and also electrically decouples the heat-conducting rods and the cover elements. Furthermore, the material forms a sealing ring that seals the heat-conducting rods and the heat sinks against each other, ensuring that the axial gaps remain free of potting compound, for example, when the rotor is potted. These unfilled axial gaps allow for tolerances of operational axial changes in spacing and advantageously prevent the cover elements from being axially displaced under thermal stress.

[0018] The embodiments and advantages presented with reference to the rotor according to the invention apply accordingly to the externally excited electrical machine according to the invention.

[0019] 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 not only usable in the combinations specified, but also in other combinations or on their own.

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

[0021] Fig. 1 a schematic perspective view of a rotor for a separately excited electric machine;

[0022] Fig. 2. a perspective view of part of the rotor;

[0023] Fig. 3 shows a perspective view of a groove closure element with a

[0024] thermal conductivity rod;

[0025] Fig. 4 is a perspective view of a cover element of the rotor; Fig. 5 is a perspective sectional view through a first embodiment of a cooling device of the rotor;

[0026] Fig. 6 shows a perspective sectional view through a second embodiment of a rotor cooling device; and

[0027] Fig. 7 shows a perspective view of part of the cover element according to the second embodiment of the cooling device.

[0028] In the figures, identical and functionally equivalent elements are provided with the same reference symbols.

[0029] Fig. 1 shows a rotor 1 for a separately excited electric motor vehicle. The rotor 1 has a rotor body 2 with a salient pole design, through which a rotor shaft 3 passes. The rotor body 2 has axial slots 4 in which axial winding sections of rotor windings 5 ​​(see Fig. 2) of the rotor 1 are arranged. Here, axial winding sections of two circumferentially adjacent rotor windings 5 ​​are arranged in each slot 4. End-face winding sections of the rotor windings 5 ​​project from axially opposite end faces 6 of the rotor body 2 and form winding heads 7. A star disk 8 is arranged between each winding head 7 and the end faces 6, which is designed to hold the winding heads 7 and to support them against centrifugal loads. The slots 4 of the rotor body 2 are closed with slot closure elements 9.The slot closure elements 9 project axially from the slots 4 and thus protrude from the end faces 6 of the rotor body 2. Two cover elements 10 are arranged axially overlapping the end faces 6 of the rotor body 2, covering the winding heads 7. Fig. 2 shows the rotor 1 on one side without a cover element 10. Here, the cover elements 10 are fixed to the star disks 8 and thus to the rotor body 2 by means of screws 11. The cover elements 10 each have an axial through-opening 12 for the rotor shaft 3 of the rotor 1. The rotor 1 also has two ring-shaped support bands 13 that radially surround the winding heads 7. For example, the support bands 13 can be attached to axially projecting star disk roofs 14 of the star disks 8 and to axially projecting end regions 15 of the slot closure elements 9 on the end faces 6.

[0030] To cool the rotor windings 5, which heat up, for example, when energized to excite the rotor magnetic field, the rotor 1 has a cooling device. The cooling device comprises heat-conducting bars 16, which are arranged in the slots 4 and are designed to absorb the waste heat from the winding sections within the slots and dissipate it towards the end faces 6 of the rotor body 2. The heat-conducting bars 16, which are designed here as round bars, are held by the slot closure elements 9. Figure 3 shows a perspective view of a slot closure element 9 to which a heat-conducting bar 16 is attached. The slot closure element 9 has a tangential section 17, which is supported against the rotor body 2, and a radial section 18, which extends radially from the tangential section 17 into the slot 4.The heat-conducting rod 16 is mechanically connected to the slot closure element 9 by the slot closure element 9 partially encasing the heat-conducting rod 16. Here, the heat-conducting rod 16 is integrated into the radial section 18, which has tunnel-like passages 19 for the heat-conducting rod 16. Exposed, unclad sections 16a of the heat-conducting rod 16 can absorb the waste heat from the rotor windings 4 and conduct it towards the rod ends 20 of the heat-conducting rods 16. The rod ends 20 project axially beyond the end faces 21 of the slot closure elements 9. When the slot closure elements 9 are installed in the slots 4, the rod ends 20 also project beyond the end faces 6 of the rotor body 2 and extend beyond the winding heads 7 of the rotor windings 5.

[0031] The cooling system also includes the cover elements 10, which form heat sinks 22. The cover elements 10 can, for example, be sprayed with a coolant during operation of the electric machine. The cover elements 10 are, for example, made of cast material. The cover elements 10 are designed to absorb the waste heat from the rotor windings 5 ​​transported by the heat conductors 16. For this purpose, the cover elements 10, as shown in Fig. 4, have cup-shaped receiving areas 24 on their underside 23 for the ends 20 of the heat conductors 16. The cup-shaped receiving areas 24 have blind-hole-like receiving openings 25 into which the ends 20 of the heat conductors 16 can be inserted without contact. The receiving areas 24 also have a side wall 26 that encloses the blind-hole-like receiving openings 25.

[0032] The underside 23 of the cover elements 10 also has cup-shaped receiving areas 27 for the winding heads 7 and screw holes 28 for the insertion of the screws 11. The cup-shaped receiving areas 27 have a wall 29 which surrounds a recess 30 for the partial reception of the winding heads 27. The cup-shaped receiving areas 27 for the winding heads 7 and the cup-shaped receiving areas 24 for the bar ends 20 are arranged alternately in the circumferential direction. The walls 26, 29 are raised or axially projecting relative to a contact surface 31 of the underside 23, which also has the screw holes 28 and which is placed against the star disk 8. As a result, the side walls 26 of the cup-shaped receiving areas 24 are arranged circumferentially between the winding heads 7 when the cover elements 10 are in their installed state.

[0033] Figure 5 shows a sectional view through a first embodiment of the cooling device in the area of ​​a rod end 20 protruding from a groove 4 and a receiving area 24 of the cover element 10. A tolerance and heat transfer zone 33 is formed between the rod end 20 and an inner surface 32 of the cup-shaped receiving area 24. This zone consists of an axial gap 34 and an annular gap 35 between the rod end 20 and the receiving area 24. The waste heat can thus be transferred from the rod end 20 to the cover element 10 via the respective annular gap 35 and the axial gap 34. Additionally, the tolerance and heat transfer zone 33 provides positional tolerance between the heat-conducting rods 16 and the cover elements 10 during assembly and operation of the rotor 1.

[0034] Fig. 6 shows a cross-sectional view through a second embodiment of the cooling device in the region of a rod end 20 and a receiving area 24, wherein an electrically insulating, thermally conductive material 36 is arranged in a section of the annular gap 35. The material 36 is, in particular, silicone. The material 36 forms an annular heat-conducting bridge between the rod end 20 and the cover element 10 and improves the heat transfer across the annular gap 35. In Fig. 7, the annularly arranged material 36 is shown in the blind-hole-like receiving opening 25 of the receiving area 24. Because the material 36 is not arranged within the axial gap 34, the air-filled axial gap 34 allows axial play between the heat-conducting bars 16 and the cover element 10 and ensures that the cover element 10 is not pushed away by an axially displacing heat-conducting bar 16.

Claims

Patent claims 1. Rotor (1) for a separately excited electric machine of a motor vehicle comprising: - a rotor body (2) with axial grooves (4) extending between two end faces (6) of the rotor body (2), - Rotor windings (5) for exciting a rotor magnetic field, wherein first winding sections are arranged within the slots (4) and second winding sections project axially at the end faces (6) of the rotor body (2) and form winding heads (7), - a cooling device for cooling the rotor windings (5), characterized in that the cooling device has heat conducting bars (16) arranged in the slots (4) for axially dissipating waste heat from the first winding sections and two cover elements (10) designed as heat sinks (22) for receiving the waste heat transported by the heat conducting bars (16), wherein bar ends (20) of the heat conducting bars (16) project axially onto the end faces (6) and wherein the cover elements (10) are arranged overlapping with the end faces (6) for axially covering the winding heads (7) and have cup-shaped receiving areas (24) on a lower side (23) facing the respective end face (6),wherein each rod end (20) is immersed in a cup-shaped receiving area (24) forming a tolerance and heat transfer area (33) and the tolerance and heat transfer areas (33) are formed by an axial gap (34) and an annular gap (35) between the respective rod end (20) and an inner surface (32) of the respective cup-shaped receiving area (24).

2. Rotor (1) according to claim 1 , characterized in that the underside (23) of the cover elements (10) has, in addition to the cup-shaped receiving areas (24), shell-like receiving areas (27) for partially receiving the winding heads (7), wherein the cup-shaped receiving areas (24) and the shell-like receiving areas (27) are arranged alternately to each other in the circumferential direction.

3. Rotor (1) according to claim 1 or 2, characterized in that the rotor (1) has two support bandages (19) which radially surround the winding heads (7) and which extend axially between the respective end face (6) of the rotor body (2) and the respective cover element (10).

4. Rotor (1) according to one of the preceding claims, characterized in that the cover elements (10) are designed as cast parts, in the undersides (23) of which the cup-shaped receiving areas (24) are incorporated.

5. Rotor (1) according to one of the preceding claims, characterized in that Side walls (26) of the pot-shaped receiving areas (24), which surround blind-hole receiving openings (25) of the pot-shaped receiving areas (24) for receiving the rod ends (20), project axially into a free space between two adjacent winding heads (7).

6. Rotor (1) according to one of the preceding claims, characterized in that the heat conducting bars (16) are designed as, in particular metallic, round bars and the pot-shaped receiving areas (24) are designed in a cylindrical pot shape.

7. Rotor (1) according to one of the preceding claims, characterized in that a heat conducting bar (16) is arranged in each groove (4), which is axially segmented to prevent an electrically conductive path leading axially through the groove (4).

8. Rotor (1) according to one of the preceding claims, characterized in that the rotor (1) has slot closure elements (9) which are arranged in the slots (4) for closing the slots (4) and which are mechanically connected to the heat conducting bars (16) for holding the heat conducting bars (16) in the slots (4).

9. Rotor (1) according to claim 8, characterized in that The slot closure elements (9) partially enclose the respective heat-conducting rod (16) for holding, so that the heat-conducting rods (16) have sections enclosed by the respective slot closure element (9) and exposed sections (16a) that absorb waste heat.

10. Rotor (1) according to claim 9, characterized in that the slot closure elements (9) are formed as injection-molded parts made of plastic, wherein the heat-conducting rods (16) are partially overmolded by the plastic.

11. Rotor (1) according to one of claims 8 to 10, characterized in that the slot closure elements (9) each have a wedge-shaped radial area (18) arranged in the slot (4), in which the respective heat conducting rod (16) is integrated, and a tangential area (17) for support on the rotor body (2).

12. Rotor (1) according to one of claims 8 to 11, characterized in that the rotor body (2) formed in salient pole construction has a rotor yoke and salient poles projecting radially from the rotor yoke with pole teeth and pole shoes, wherein the pole teeth are wound with winding conductors to form the rotor windings (5) and a slot (4) is formed between two adjacent pole teeth in which the first winding sections of two adjacent rotor windings (5) are arranged, wherein the slot closure elements (9) are supported on the pole shoes and the heat conducting bars (16) attached to the slot closure elements (9) are arranged between the first winding sections of two adjacent rotor windings (5).

13. Rotor (1) according to one of the preceding claims, characterized in that the tolerance and heat transfer areas (33) for improving the heat transfer between the heat conducting bars (16) and the respective cover element (10) and for providing a positional tolerance between the heat conducting bars (16) and the respective cover element (10) are only partially filled with a thermally conductive, electrically insulating material (36), in particular a silicone.

14. Rotor (1) according to claim 13, characterized in that the thermally conductive material (36) is arranged only in a partial section of the respective annular gap (35) between the rod end (20) and the inside (32) of the cup-shaped receiving area (24) and is arranged concentrically to the rod end (20), so that at least in the area of ​​the axial gap (34) an air cavity is formed to provide an axial position tolerance between the heat-conducting rods (16) and the cover element (10).

15. Externally excited electric machine for a motor vehicle comprising a stator and a rotor (1) rotatably mounted with respect to the stator according to one of the preceding claims.

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