STATOR COOLING

Description

[0001] The invention relates to the cooling of a stator for an electric machine and a corresponding method for operating an electric machine.

[0002] When an electric machine is operated, heat is generated in the electric machine, firstly due to the ohmic losses in the electrical conductors that form the windings of the machine, and secondly also due to eddy currents and hysteresis in the laminated cores of the electric machine.

[0003] In this context, it is known, for example, to cool the stator of such an electric machine using a water jacket that surrounds a stator support and is sealed against a housing. In this design, the heat conduction path from the electrical conductors of the windings, through the stator's laminated core, to the water jacket is relatively long. A further disadvantage is that the windings, arranged in slots of the stator, are surrounded by an electrical insulating material, such as insulating paper, which has a significantly lower thermal conductivity than the metals in the stator. This results in a considerable temperature gradient across the cross-section of the insulating material. Despite cooling by the water jacket, the temperature of the electrical conductors in the slots is therefore relatively high during continuous operation, leaving little room for additional heating during short-term peak load operation.It should also be taken into account that the specific electrical resistance of copper and aluminium, the materials commonly used for electrical conductors, increases with increasing temperature; thus, the efficiency of the electrical machine decreases with increasing temperature of the electrical conductors.

[0004] Another approach in this context is waveguide cooling, which is also known, for example, from German patent application DE 10 2017 119 033 A1. With pure waveguide cooling, the heat from the laminated core is also dissipated via the waveguides, which means that the corresponding amounts of heat must first pass through the insulating paper around the conductors and the conductor itself before reaching a coolant inside the waveguide.

[0005] Electrical machines with cooled electrical conductors arranged in slots are known from DE1017265B and EP3223394A1.

[0006] Due to assembly tolerances, clearance adjustments are required in the stator's laminated core and other components, which leads to corresponding air gaps, including in the stator slots. Since air acts as a thermal insulator, this exacerbates the problem described above.

[0007] The aforementioned thermal stresses, which can occur during the operation of an electric machine, must be taken into account in the machine's design and therefore necessitate appropriate redesign. For example, reducing temperature fluctuations could significantly increase the service life of materials, and it might also be possible to use more cost-effective materials.

[0008] The object of the invention is therefore to improve the cooling of a stator of an electric machine.

[0009] This problem is solved by a stator according to claim 1, a corresponding electrical machine according to claim 4, and an associated method for operating an electrical machine according to claim 7.

[0010] The subclaims each contain advantageous further developments.

[0011] The stator according to the invention for an electric machine comprises a laminated core and windings of an electrical conductor guided at least partially in slots of the stator. According to the invention, a spacer is provided which ensures a defined distance between the electrical conductor and the laminated core in a slot. Preferably, a corresponding spacer is provided for each slot.

[0012] Due to the defined distance, a gap is created in the slot between the electrical conductor and the stator's laminated core. This gap provides a path for coolant, which can flow through it during operation of the electric machine. In this way, heat from the electrical conductor can transfer across the entire conductor area in the slot into the coolant. Conversely, heat from the laminated core can also transfer across the entire slot area into the coolant. This enables efficient cooling of the stator, i.e., of both the electrical conductor and the laminated core, even with low heat transfer coefficients between the coolant and the conductor or laminated core, and at low flow rates. The spacer ensures the conductor's positioning in the slot and thus keeps the coolant flow path open.

[0013] Since the spacer ensures the defined distance between the electrical conductor and the laminated core, it transmits forces between the conductor and the core. Consequently, the spacer also serves to hold and transmit the drive torque of the electric motor.

[0014] According to the invention, the spacer is provided by two fixing disks, preferably made of electrically insulating material, located at axially opposite ends of the stator; "axial" here refers to an axis of rotation around which a rotor of the electric machine rotates during operation. The fixing disks have locking lugs for the electrical conductor, which secure the conductor and thus achieve a defined position of the conductor in a respective groove. The fixing disks can also serve as stator supports.

[0015] In one embodiment of the stator, at least one cap sealed against the stator's laminated core is provided, defining a coolant receiving area in the vicinity of the stator's winding heads. In this configuration, the winding heads are completely surrounded by coolant, and coolant can flow from the defined area into the stator's slots. In particular, a coolant receiving area can be defined at each end of the stator, each by a corresponding cap sealed against the laminated core.

[0016] If fixing discs are used as spacers, each fixing disc preferably has a closed contour on the inner circumference of the stator, resulting in improved sealing with the caps.

[0017] In a stator that is ready for operation, a coolant is located in a slot, preferably in all slots, between the electrical conductor and the laminated core. This coolant is preferably a non-conductive fluid, for example, transformer oil.

[0018] The electric machine according to the invention has a stator as described above. In one embodiment, a coolant separator is provided, which is designed to return coolant that has escaped from the stator to a cooling circuit of the stator.

[0019] In one embodiment, the stator is mechanically connected to the housing of the electric machine via an electrically insulating torque support. This achieves basic insulation of the stator without requiring any insulating material in the slots, thereby significantly improving heat dissipation by the coolant. This method of achieving basic insulation is described in more detail in German patent application DE 10 2019 118 122. In this case, it is sufficient to limit the insulation in the slots to functional insulation of the electrical conductor.

[0020] The inventive method for operating an electric machine described above is characterized in that a coolant flows through a space between the electrical conductor and the laminated core in a slot of the stator of the electric machine. This space is defined by the distance between the electrical conductor and the laminated core, which is ensured by the spacer.

[0021] The invention and its advantages are described in more detail below with reference to the accompanying drawings. Figure 1 shows a cross-section through a groove of a stator according to the invention. Figure 2 shows an embodiment of a groove insert not according to the invention. Figure 3 shows a perspective view of a groove insert not according to the invention inserted into a groove. Figure 4 shows a top view of a groove insert not according to the invention inserted into a groove. Figure 5 shows a perspective view of a stator according to the invention. Figure 6 shows a section through a part of a stator according to the invention. Figure 7 shows an embodiment of a stator according to the invention. Figure 8 shows a section of a fixing disk. Figure 9 shows a top view of a groove. Figure 10 shows an embodiment of an electric machine according to the invention. Figure 11 shows a further embodiment of an electric machine according to the invention.

[0022] The schematic figures are merely examples of how the invention can be implemented, without limiting the invention to the specific examples shown. Reference numerals used in the description of the figures refer generally to all the figures. Fig. 1Figure 1 shows a cross-section through a groove 12 in a partially shown laminated core 11 of a stator according to the invention. Electrical conductors 2 are located in the groove 12 and are surrounded by an insulating coating 21 for functional insulation. A defined distance 22 is maintained between the conductors 2 and between the conductors 2 and the laminated core 11, i.e., the wall of the groove 12. This distance is achieved by a spacer (not shown). The defined distance 22 ensures that the coolant 100 can distribute itself around all electrical conductors 2 and also make contact with the boundaries, i.e., the wall, of the groove 12 as completely as possible, in order to achieve optimal heat exchange between the conductors 2 and the coolant 100, as well as between the laminated core 11 and the coolant 100. Fig. 2Figure 1 shows an embodiment of a slot insert 3 made of an electrically insulating material, not according to the invention, which can be used as a spacer in the stator. The slot insert 3 is cage-like and comprises a plurality of webs 31. The webs 31 ensure the defined distance 22 between electrical conductors 2 and between electrical conductors 2 and the boundaries of the slot 12 within a slot 12. The spaces between the webs 31 provide room for the flow of a coolant 100. On one side of the slot insert 3, it has a closed surface 32. In an electric machine, this side is oriented towards an air gap to the rotor and thus seals the slot 12 against the air gap to prevent leakage of coolant 100. Fig. 3Figure 1 shows a perspective view of part of a laminated core 11 with a groove 12 into which a non-inventive groove insert 3 is inserted. Electrical conductors 2 are also visible in the groove 12. In this example, the groove insert 3 is fastened to the laminated core 11 by a locking lug 33. Fig. 4 Figure 1 shows a top view of a portion of a sheet metal stack 11 with a groove 12. A non-inventive groove insert 3, as described above, is inserted into the groove 12. The closed surface 32 formed on the groove insert 3 is also shown in particular. Fig. 5Figure 1 shows a perspective view of a stator 1 according to the invention with a laminated core 11. The winding heads 23 of the electrical conductors are shown. In the illustrated embodiment, caps 5 are provided which, in the assembled state of the arrangement shown, define a coolant 100 area around the winding heads 23. Sealing rings 51 are provided to seal between the coolant 100 area and the laminated core 11 of the stator 1. The caps 5 have an inlet and outlet 52 for coolant 100. Fig. 6 Figure 1 shows a section through part of a stator 1. The figures show winding heads 23, caps 5 and areas 53 defined by the caps 5 for coolant 100 around the winding heads 23. Fig. 7Figure 1 shows an embodiment of a stator 1 according to the invention with a laminated core 11. Here, the spacer is provided by two fixing discs 4 at the axial ends of the stator 1. For perspective reasons, only one fixing disc 4 is visible. The fixing disc 4 has locking lugs 41 for fixing the electrical conductor 2 in order to ensure the defined distances 22 in the grooves 12. In the embodiment shown, the fixing disc 4 also has a closed contour 42 on the radial inner circumference of the stator 1, which promotes the sealing of the laminated core 11 and the tight connection with the caps 5. Fig. 8 shows an excerpt from one of the in the Fig. 7 The embodiment shown uses fixing discs 4. The locking lugs 41 and the closed contour 42 can be seen. Fig. 9Figure 1 shows a top view of a groove 12 with a fixing disc 4 above it, of which only a portion is shown. Also shown are the electrical conductors 2 of the stator 1 windings, which are placed in the groove 12 and secured by locking lugs 41. A portion of the closed contour 42 is also visible. Fig. 10Figure 1 shows an embodiment of an electric machine 200 according to the invention. The electric machine 200 comprises a stator 1, a rotor 300, a housing 400, and a shaft 301 of the rotor 300 according to the invention. A torque support 13 made of electrically insulating material is provided, which mechanically connects the stator 1 to the housing 400, in the embodiment shown, without limiting the invention thereto, by means of a screw connection 14. This achieves a mechanical fixation of the stator 1 to the housing 400 without creating an electrically conductive connection between the stator 1 and the housing 400. Therefore, the necessary basic insulation is achieved without having to insert insulating material in the slots 12 of the stator 1. By omitting the insulating material in the slots 12, the heat transfer from the electrical conductor 2 to the coolant 100 is improved.

[0023] Furthermore, the shaft 301, which carries the rotor 300, has a flange 70 made of electrically insulating material at each end. Each flange 70 is mechanically connected to a flange 81, for example, and without limiting the invention thereto, via a screw connection 71. Each flange 81, in turn, is connected to a bearing shaft 82. Each bearing shaft 82 is received in a bearing 80, which is provided in the housing 400. Thus, the shaft 301, and therefore the rotor 300, is ultimately mechanically supported in the housing 400 without an electrically conductive connection between the rotor 300 and the housing 400 along the shaft 301.

[0024] Also shown is a rotary axis 500 for the electric machine 200, around which the shaft 301 and the rotor 300 rotate when the electric machine 200 is in operation. For the sake of completeness, it is mentioned that the Figure 10Figure 1 shows a sectional view through the electric machine 200, in which only a part of the electric machine 200 is shown on one side of the axis of rotation 500. The axis of rotation 500 also defines the axial direction for the stator 1 within the meaning of this application.

[0025] Fig. 11 Figure 1 shows a further embodiment of an electric machine 200 according to the invention. The elements shown have largely already been described in the context of the Figure 10 explained. The difference between the embodiment shown here and the one in Figure 10In the illustrated embodiment, the torque support 13 is made of electrically insulating material. Here, the torque support 13 is attached to the end face of a projection 410 of the housing 400. In this embodiment, mechanical fixation of the stator 1 relative to the housing 400 is achieved without an electrically conductive connection between the stator 1 and the housing 400. The torque support 13 is connected to the stator 1 and the projection 410 by screw connections 14, although the invention is not limited to this. Reference symbol list

[0026] 1 Stator 2 Electrical conductor 3 Slot insert 4 Locking washer 5 Cap 11 Sheet metal bundle 12 Groove 13 Torque support 14 Screw connection 21 Paint finish 22 Spacing 23 Winding head 31 Web 32 Closed surface 33 Locking lug 41 Locking stud 42 Closed contour 51 Sealing rings 52 Inlet / outlet 70 Flange 71 Screw connection 80 Bearing 81 Flange 82 Bearing shaft 100 Coolant 200 Electric machine 300 Rotor 301 Shaft 400 Housing 410 Projection 500 Shaft of rotation

Claims

1. A stator (1) for an electric machine (200), the stator (1) comprising a laminated core (11) and windings of electrical conductors (2) guided at least partially in slots (12) of the stator (1), a spacer (4) which ensures a defined distance (22) between electrical conductors (2) and between the electrical conductors (2) and the laminated core (11) in a slot (12), characterised in that the spacer is provided by two fixing discs (4) which are provided at axially opposite ends of the stator (1) and in which locking projections (41) are provided for the electrical conductor (2) in order to ensure the defined distances (22) in the slots (12).

2. The stator (1) according to any one of the preceding claims, wherein at least one cap (5) is provided which is sealed with respect to the laminated core (11) and defines, in a surrounding space of end windings (23) of the stator (1), a region (53) for receiving a coolant (100).

3. The stator (1) according to any one of the preceding claims, wherein a coolant (100) is located in a slot (12) between an electrical conductor (2) and the laminated core (11).

4. An electric machine (200) having a stator (1) according to any one of claims 1 to 3.

5. The electric machine (200) according to claim 4, wherein a separator for coolant (100) is provided which is designed to return coolant (100) that has escaped from the stator (1) into a cooling circuit of the stator (1).

6. The electric machine (200) according to claim 4 or 5, wherein the stator (1) is mechanically connected to a housing (400) of the electric machine (200) via an electrically insulating torque support (13).

7. A method for operating an electric machine (200) according to any one of claims 4 to 6, wherein a coolant (100) flows through an intermediate space between an electrical conductor (2) and the laminated core (11) in a slot (12) of the stator (1) of the electric machine (200).