Rotor for an electric machine, electric machine and motor vehicle

Abstract

Rotor (14) for an electric machine (10) comprising: - a rotor shaft (16); - a laminated core arranged on the rotor shaft (16), wherein the laminated core is non-rotatably connected to the rotor shaft (16); and - a heat pipe (20) in which a cooling medium is contained, wherein - the heat pipe (20) is at least partially arranged in the rotor (14), wherein - the heat pipe (20) is designed to absorb heat and dissipate it to an environment; wherein the heat pipe (20) has at least two end segments (24; 26) at one end which is arranged outside the laminated core, wherein a first end segment (24) of the at least two end segments (24; 26) at least partially surrounds a second end segment (26) of the at least two end segments (24; 26), wherein the first end segment (24) and the second end segment (26) are arranged coaxially, characterized in that the second end segment (26) is tubular in shape, wherein the first end segment (24) and the second end segment (26) are fluidically connected to each other, wherein the remainder or other part of the heat pipe (20) is fluidically coupled or connected to the first and the second end segment (24, 26), such that the cooling medium condenses within the two end segments (24, 26) and subsequently flows back into the area of ​​the heat pipe (20) within the laminated core.

Description

[0001] The invention relates to a rotor for an electric machine, in particular for a motor vehicle. The rotor comprises a rotor shaft, a laminated core arranged on the rotor shaft, the laminated core being connected to the rotor shaft in a rotationally fixed manner, and a heat pipe in which a cooling medium is accommodated. The heat pipe is designed to absorb heat and dissipate it to the environment. For this purpose, the heat pipe is arranged at least partially within the rotor.

[0002] Electrical machines, such as electric drives, with a certain power density require cooled rotors, which usually function with cooling media introduced into the rotor.

[0003] In order to reduce or dissipate heat generated during operation of an electric machine, it is generally known from the state of the art to equip the electric machine with an integrated cooling circuit. The disadvantage of an integrated cooling circuit is that pressure losses occur in the cooling media used, which reduces the efficiency of the electric machine. Furthermore, an integrated cooling circuit increases the complexity, assembly effort, and cost of the electric machine. For example, additional components are required to implement the integrated cooling circuit, such as coolant-conveying components and seals.

[0004] Instead of integrating a cooling circuit into the electrical machine, a heat pipe can also be used to cool the electrical machine.

[0005] For example, US 2014 / 0306450 A1 describes an electric machine. The electric machine comprises a stator with a stator winding, a rotor arranged on one side of an inner diameter of the stator with a clearance between the rotor and the stator, and a shaft attached to and coupled to the rotor. Furthermore, the electric machine has a heat pipe arranged from an inner part to an outer part of the shaft.

[0006] US 2014 / 0368064 A1 further describes an electric motor cooling system for this purpose. The electric motor cooling system includes a heat pipe housed in a hollow area within a rotor shaft of the motor. One end of the heat pipe, extending from the end of the rotor shaft, is coupled to a heat exchanger. During motor operation, the heating of the rotor causes heat energy to be absorbed by the heat pipe within the rotor shaft and transferred to the heat exchanger for efficient dissipation.

[0007] US 2014 / 0292121 A1 discloses an electric motor for an electric vehicle drive unit. The electric motor consists of a rotor and a magnetic assembly. The rotor is rotatably mounted in a stator. The magnetic assembly is designed to drive the rotor. The rotor is provided with a heat pipe with at least one condensation zone for condensing a heat transfer fluid and at least one evaporation zone for evaporating the heat transfer fluid.

[0008] The disadvantage of such heat pipes used in electrical machines is that, on the one hand, the structure of the electrical machine is particularly complex and elaborate and, on the other hand, sufficient heat dissipation during operation of the electrical machine is not guaranteed.

[0009] US Pat. No. 3,842,596 A describes an electric motor rotor in which a shaftless heat pipe is installed, which cools the rotor. A working fluid circulates within the heat pipe. The working fluid is conveyed from a condenser section to an evaporator section adjacent to the rotor by accelerated centrifugal forces. The evaporator section arranged next to the rotor has a substantially conical shape. This document was used to formulate the preamble of patent claim 1.

[0010] The object of the present invention is therefore to provide improved heat dissipation for a rotor.

[0011] This object is achieved by a rotor, an electric machine with a rotor, and a motor vehicle having the features of the independent patent claims. Advantageous embodiments with expedient and non-trivial refinements of the invention are specified in the dependent patent claims.

[0012] Accordingly, the invention proposes a rotor for an electrical machine, in particular for a motor vehicle. The rotor has a rotor shaft and a laminated core arranged on the rotor shaft, wherein the laminated core is connected to the rotor shaft in a rotationally fixed manner. In other words, the laminated core can be connected or coupled to the rotor shaft in such a way that, during operation of the electrical machine, the rotor shaft rotates with the laminated core. In particular, the laminated core can at least partially surround the rotor shaft. In other words, the rotor shaft can be accommodated or arranged in the laminated core.

[0013] Furthermore, the rotor has a heat pipe in which a cooling medium is accommodated and which is designed to absorb heat and dissipate it to an environment. The heat pipe is preferably designed to dissipate the heat generated during operation of the electrical machine, in particular the heat in the rotor and / or in the laminated core, to an environment of the electrical machine or the rotor. For this purpose, the heat pipe is at least partially arranged or accommodated in the rotor. The heat pipe can, for example, be arranged or accommodated within the rotor shaft and / or the laminated core. For example, the rotor shaft can have a cavity in which the heat pipe is at least partially accommodated, or the rotor shaft can be at least partially designed as a hollow shaft. The heat pipe preferably extends in the direction of a rotational axis of the rotor shaft.Preferably, the heat pipe is formed from a thermally conductive material, in particular from aluminum and / or copper.

[0014] A "heat pipe" specifically refers to a heat exchanger. The heat pipe has an evaporation region or evaporation zone and a condensation region or condensation zone. In relation to the rotor, the evaporation region is located in the area or within the rotor's laminated core, and the condensation region is located outside the rotor or the rotor's laminated core. When heat is introduced, the cooling medium begins to evaporate. This locally increases the pressure in the vapor space above the liquid level, leading to a slight pressure gradient within the heat pipe. The resulting vapor therefore flows to a lower-temperature location—the condensation zone—where the vapor or evaporated cooling medium condenses. At this location, the temperature rises due to the released condensation heat. The previously absorbed heat is released into the environment.The now liquid cooling medium then returns to the point where the heat is introduced or transferred, the evaporation area.

[0015] The invention is characterized in that the heat pipe has at least two end segments at one end, which is arranged outside the laminated core or rotor. In other words, the heat pipe divides into at least two end segments at the end or end region or end section of the heat pipe, which is arranged outside the laminated core. A first end segment of the at least two end segments at least partially surrounds a second end segment of the at least two end segments of the heat pipe. The term "end segment" refers in particular to a section or part of the heat pipe. The outer section - the first end segment - can surround, enclose, or enclose the inner section - the second end segment. The end of the heat pipe, which is arranged outside the laminated core, has the condensation region or condensation zone of the heat pipe.Preferably, the first end segment and the second end segment of the heat pipe, as well as the remaining part or section of the heat pipe, enclose a closed volume within which the cooling medium is accommodated. Additionally or alternatively, the heat pipe may also have further end segments that are at least partially, i.e., completely or partially, enclosed by the first end segment.

[0016] In the region or section of the heat pipe located within the laminated core, the heat generated during operation of the electrical machine is absorbed, causing the cooling medium in the heat pipe to evaporate. The evaporated cooling medium is then conducted to the end of the heat pipe located outside the laminated core. The evaporated cooling medium enters the at least two end segments—the first end segment and the second end segment—of the heat pipe. The at least two end segments are fluidically connected to one another. The remainder or the remaining or other part of the heat pipe is fluidically coupled or connected to the first end segment and the second end segment. The interior of the heat pipe preferably forms a closed volume. The cooling medium condenses within the at least two end segments and then flows back into the region of the heat pipe within the laminated core.

[0017] The at least two end segments increase the condensation surface of the heat pipe, allowing more of the absorbed heat to be dissipated into the environment. The improved heat dissipation from the rotor or the electric machine increases the efficiency and thus the continuous power of the electric machine. The structural design of the heat pipe with the at least two end segments means that the dimensions of the heat pipe can be retained. No closed cooling circuits for heat dissipation are required. Improved efficiency can either increase the continuous power of the electric machine with the same installation space or, with the same power, reduce or downsize the installation space of the electric machine.

[0018] According to the invention, it is provided that the first end segment and the second end segment are arranged coaxially, in particular at a predetermined distance from one another. In other words, the first end segment and the second end segment can be arranged coaxially and at a distance from one another. “Coaxial” means in particular that the first end segment and the second end segment have a common axis. The axis can in particular be an axis of rotation of the rotor shaft. Particularly preferably, the first end segment and the second end segment of the heat pipe are designed and / or arranged rotationally symmetrically to one another. By arranging the first end segment and the second end segment in this way to one another, the surface area of ​​the heat pipe is increased. Heat can be dissipated or released via the surface of the first end segment and via the surface of the second end segment.

[0019] Advantageously, the first end segment is designed as a double-walled tube. In other words, the first end segment can in particular have an annular space. The first end segment preferably has an inner wall and an outer wall, which are arranged in particular coaxially to one another. The outer wall surrounds in particular the inner wall or wall of the first end segment. The cooling medium flows or is located in particular between the inner wall and the outer wall of the first end segment. Preferably, the first end segment designed as a double-walled tube is closed on one side. By designing the first end segment as a double-walled tube, the surface area of ​​the heat pipe can be increased in a particularly simple manner, whereby heat dissipation in this area can be further improved.Furthermore, the design of the first end segment as a double-walled tube results in the advantage that the first end segment has a particularly simple shape to manufacture.

[0020] According to an advantageous development, it is provided that the second end segment is tubular. In other words, the second end segment can have the shape of a tube. Particularly preferably, the tubular second end segment is surrounded by the first end segment designed as a double-walled tube. In this case, the inner wall of the first end segment can face the second end segment. The inner wall of the first end segment can be arranged at a predetermined, in particular uniform, distance from the second end segment, in particular a wall of the second end segment. In this case, an annular gap can preferably be formed between the first end segment and the second end segment. Alternatively, it can be provided that the inner wall of the first end segment forms the wall or walls of the second end segment. Preferably, the second end segment designed as a tube is closed on one side.Particularly preferably, the closed ends of the first end segment and the second end segment form an end face or end surface of the heat pipe. The tubular design of the second end segment offers the advantage that the second end segment has a particularly simple shape to manufacture.

[0021] A further advantageous embodiment provides for the heat pipe, in particular the at least two end segments, to be formed in one piece. "Integral" specifically means that the heat pipe, in particular the heat pipe with the first end segment and the second end segment, is formed in one piece, i.e., as a single part or piece. This results in the advantage that the heat pipe is particularly stable. Furthermore, the one-piece design eliminates process steps in the manufacture of the heat pipe.

[0022] According to an alternative embodiment, it is provided that the heat pipe, in particular the at least two end segments, is formed from multiple parts, particularly preferably two parts. In other words, the heat pipe, in particular the first end segment and the second end segment of the heat pipe, can be formed from multiple parts or pieces, preferably from two parts. Particularly preferably, the first end segment can form one part of the heat pipe in one piece with the rest of the heat pipe, and the second end segment can form another part. To form the heat pipe, in particular the end of the heat pipe, the second end segment can be connected to the first end segment or the other part of the heat pipe in a form-fitting manner, for example by pressing in, or in a material-fitting manner, for example by gluing or welding.

[0023] Advantageously, a first surface of the first end segment and / or a second surface of the second end segment has a predetermined gradient, in particular a gradient of 0.25° to 5°, preferably of 1° to 3°. The outer wall of the first end segment and / or the wall of the first end segment preferably has a gradient of 0.25° to 5°, preferably of 1° to 3°. Gradient means, in particular, that the wall or walls of the first end segment and / or of the second end segment have a bevel. The respective gradient of the first surface of the first end segment and / or of the second surface of the second end segment is inclined in the direction away from the rotor shaft in the direction of the laminated core. In the direction of the laminated core, the diameter of the first end segment and / or of the second end segment, in particular the inner diameter, becomes larger due to the gradient.Due to the respective slope, the first end segment and / or the second end segment can have the shape of a cone. The first surface and / or the second surface is, in particular, the surface or inner surface of the first end segment and / or second end segment that faces an interior space of the heat pipe. The slope can ensure that the condensed cooling medium within the heat pipe flows or flows back into the part of the heat pipe within the electrical machine.

[0024] An advantageous development provides that the heat pipe has cooling fins arranged at the end of the heat pipe located outside the laminated core. The cooling fins extend, in particular, perpendicular to the rotor shaft. The individual cooling fins can be arranged at a predetermined, in particular uniform, distance from one another in the direction of the rotation axis. The cooling fins can be coupled to the first end segment and / or the second end segment. The cooling fins serve, in particular, to enlarge the surface area of ​​the heat pipe, in particular in the condensation area, in order to improve heat transfer to the environment and thus cooling.

[0025] The invention also includes an electric machine with the rotor according to the invention. The electric machine can be designed, for example, as a motor, in particular as an electric motor for a motor vehicle.

[0026] Finally, the invention also includes a motor vehicle with an electric motor. The motor vehicle is preferably designed as a motor vehicle, in particular as a passenger car.

[0027] The invention also includes combinations of the features of the described embodiments.

[0028] The invention also includes further developments of the electric machine according to the invention and the motor vehicle according to the invention, which have features as already described in connection with the further developments of the rotor according to the invention. For this reason, the corresponding further developments of the electric machine according to the invention and the motor vehicle according to the invention are not described again here.

[0029] Exemplary embodiments of the invention are described below. Shown are: Fig. 1 is a schematic representation of an electrical machine comprising a stator, a rotor and a heat pipe; Fig. 2 an enlarged view of a section of the heat pipe of Fig. 1; and Fig. 3 a schematic representation of the rotor of Fig. 1 with another embodiment of the heat pipe.

[0030] The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that can be considered independently of one another, each of which also develops the invention independently of one another. Therefore, the disclosure is intended to encompass combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0031] In the figures, the same reference symbols designate elements with the same function.

[0032] Fig. 1 shows a schematic representation of an electric machine 10. The electric machine 10 can be, for example, an electric motor, in particular for a motor vehicle, particularly preferably for an electric vehicle. The electric machine 10 has a stator 12 and a rotor 14. The rotor 14 further has a rotor shaft 16. The stator 12 surrounds the rotor 14. In other words, the rotor 14 can be at least partially received in the stator 12. The rotor 14 further has a laminated core and a short-circuit ring (not shown in the figures). Accordingly, the rotor 14 can be designed as a squirrel-cage rotor or a cage rotor. Furthermore, the rotor 14 is arranged on the rotor shaft 16 such that, during operation of the electric machine 10, the rotor 14 rotates with the rotor shaft 16. In other words, the rotor 14 is located inside the stator 12 and is connected in a rotationally fixed manner to the rotor shaft 16.The rotor shaft 16 is mounted in the stator 12 so as to be rotatable about a rotation axis.

[0033] During operation of the electric machine 10, heat is generated inside the electric machine 10, which must be dissipated to an environment 18 of the electric machine 10 in order to avoid efficiency losses or even damage to the electric machine. For this purpose, the electric machine 10 or the rotor 14 has a heat pipe 20, which can also be referred to as a heat pipe. The heat pipe 10 is at least partially accommodated within the electric machine 10. The heat pipe 20 can be accommodated or arranged in the rotor, in particular the rotor shaft 16 or the laminated core. Fig. As can be seen from Figure 1, one end 22 or a section of the heat pipe 20 is arranged outside the laminated core of the rotor 14. In other words, the end 22 of the heat pipe 20 protrudes from the electrical machine 10, in particular the laminated core of the rotor 14. The heat pipe 20 is arranged in particular in or on the rotor shaft 16 of the electrical machine 10 or is held thereon. The rotor shaft 16 preferably has a cavity in which the heat pipe 20 is received.

[0034] The heat pipe 20 typically has a casing or wall, which is formed in particular from a heat-conducting material. For example, the wall of the heat pipe 20 can be made of copper, aluminum, stainless steel, ceramic, or glass. A cooling medium, which can also be referred to as the working medium, is accommodated within the heat pipe 20. The cooling medium is preferably water.

[0035] The function of the heat pipe 20 will be discussed in more detail below. If the heat pipe 20 assumes a higher temperature due to heat input, i.e. heat generated during operation of the electrical machine 10, the pressure increases, in particular in accordance with the vapor pressure curve of the cooling medium. If a lower temperature arises at any other point in the heat pipe 20 due to heat dissipation, this leads to a drop below the dew point at this point with immediate condensate formation. The pressure at this point drops in proportion to the temperature. The vapor in the heat pipe 20 flows, following the pressure gradient, to the colder point. The condensate flows back to the point of evaporation, driven by gravity and / or by the capillary forces of the heat pipe 20. Since the vapor phase and the liquid phase of the working medium are located in the same space or closed volume, a wet vapor region results.As a result, a specific temperature always occurs in the heat pipe 20 at a specific temperature. The location of evaporation, i.e., the evaporation region or evaporation zone, is located in particular within the electric machine 10 or the rotor 14, in particular the rotor shaft 16 and / or the laminated core. The location of condensation, i.e., the condensation region, is preferably located at the end 22 of the heat pipe 20, i.e., outside the laminated core of the rotor 14.

[0036] Heat pipes are generally tubular in shape. However, in order to increase or improve heat removal or heat dissipation at the condensation area, i.e., the end 22 of the heat pipe 20, a surface of the heat pipe 20, through which the heat is dissipated to the environment 18, can be enlarged. In connection with Fig. 1 and Fig. 2, the enlargement of the surface of the end 22 of the heat pipe 20 will be explained in more detail.

[0037] In order to enlarge the surface area of ​​the heat pipe 20, in particular the inner surface or condensation surface, at the end 22, the heat pipe 20 has at least two end segments 24, 26—first end segment 24 and second end segment 26—at the end 22. In other words, the end 22 of the heat pipe 20 is divided into at least two end segments 24, 26. In particular, the first end segment 24 and the second end segment 26 are rotationally symmetrical. The first, in particular outer, end segment 24 is designed as a double-walled tube. The first end segment 24, as a double-walled tube, has an inner wall 28 and an outer wall 30, which are arranged in particular coaxially to one another. The outer wall 30 surrounds the inner wall 28, in particular radially. The cooling medium flows or is located in particular between the inner wall 28 and the outer wall 30 of the first end segment 24.

[0038] The second end segment 26 is tubular. In other words, the second end segment 26 can have the shape of a tube. Particularly preferably, the tubular second end segment 26 is surrounded by the first end segment 24, which is designed as a double-walled tube. The inner wall 28 of the first end segment 24 can face the second end segment 26. Alternatively, the inner wall 28 of the first end segment 24 can form the wall or walling of the second end segment 26.

[0039] Furthermore, a first surface 32 of the first end segment 24 or the surface of the first end segment 24 opposite the first surface and a second surface 34 of the second end segment 26 have a predetermined gradient, in particular a gradient of 0.25° to 5°, preferably of 1° to 3°. The inner wall 28 and / or the outer wall 30 can have the gradient. By gradient, it is meant in particular that the wall or walls of the first end segment 24 and of the second end segment 26 have a bevel. The gradient extends along an extension direction of the electrical machine 10. The respective gradient of the first surface 32 of the first end segment 24 and the second surface 34 of the second end segment 26 runs away from the electrical machine 10, in particular away from the rotor 14. In other words, the respective wall runs away from the rotor shaft 16 due to the gradient in the direction of the laminated core.The gradient can ensure that the condensed cooling medium within the heat pipe 20 flows back into the part of the heat pipe 20 within the electric machine 10 or the rotor 14.

[0040] To further increase the surface area of ​​the heat pipe 20 in the region of the end 22, the heat pipe 22 has cooling fins 36. The cooling fins 36 can be coupled to the first end segment 24 and / or the second end segment 26.

[0041] According to the embodiment of the heat pipe 20 in Fig. 1 and Fig. 2, the heat pipe 20 is formed in one piece or in one piece. In Fig. 3, the heat pipe 20 has the same or the same structure as the heat pipe 20 in Fig. 1 and Fig.2. The heat pipe 20, particularly in the region of the end 22 of the heat pipe 20, is designed in multiple parts, in particular in two parts. The first end segment 24 is designed in one piece with the remaining heat pipe 20. The part 26' or piece of the heat pipe 20 forming the second end segment 26 is bush-shaped or has a T-shape in cross-section. The part 26' forming the second end segment 26 can be introduced onto or into the heat pipe 20 in such a way that the second end segment 26 of the heat pipe is formed. The part 26' forming the second end segment 26 can be pressed or pressed into the heat pipe 20, in particular the first end segment, or can be integrally bonded, in particular glued, welded, or soldered.

[0042] Overall, the examples show how the invention provides a heat pipe with an enlarged inner surface or condensation surface.

Claims

[1] Rotor (14) for an electrical machine (10) comprising: - a rotor shaft (16); - a laminated core arranged on the rotor shaft (16), the laminated core being connected to the rotor shaft (16) in a rotationally fixed manner; and - a heat pipe (20) in which a cooling medium is accommodated, wherein - the heat pipe (20) is arranged at least partially in the rotor (14), wherein - the heat pipe (20) is designed to absorb heat and dissipate it to an environment; wherein the heat pipe (20) has at least two end segments (24; 26) at one end which is arranged outside the laminated core, wherein a first end segment (24) of the at least two end segments (24; 26) at least partially surrounds a second end segment (26) of the at least two end segments (24; 26), wherein the first end segment (24) and the second end segment (26) are arranged coaxially, characterized byin that the second end segment (26) is tubular, wherein the first end segment (24) and the second end segment (26) are fluidically connected to one another, wherein the remainder or remaining or other part of the heat pipe (20) is fluidically coupled or connected to the first and the second end segment (24, 26) such that the cooling medium condenses within the two end segments (24, 26) and then flows back into the region of the heat pipe (20) within the laminated core. [2] Rotor (14) according to claim 1, characterized by that the first end segment (24) and the second end segment (26) are arranged coaxially at a predetermined distance from one another. [3] Rotor (14) according to claim 1 or 2, characterized by that the first end segment (24) is designed as a double-walled tube. [4] Rotor (14) according to one of the preceding claims, characterized bythat the heat pipe (20), in particular the at least two end segments (24; 26), is formed in one piece. [5] Rotor (14) according to one of claims 1 to 3, characterized by that the heat pipe (20), in particular the at least two end segments (24; 26), is formed in several parts, particularly preferably in two parts. [6] Rotor (14) according to one of the preceding claims, characterized by that a first surface (32) of the first end segment (24) and / or a second surface (34) of the second end segment (26) has a predetermined gradient, in particular a gradient of 0.25° to 5°, preferably of 1° to 3°. [7] Rotor (14) according to one of the preceding claims, characterized by in that the heat pipe (20) has cooling fins (36) which are arranged at the end (22) of the heat pipe (20) which is arranged outside the laminated core, wherein the cooling fins (36) are coupled to the first end segment (24) and / or the second end segment (26). [8] Electric machine (10) with a rotor (14) according to one of the preceding claims. [9] Motor vehicle with an electric machine (10) according to claim 8.

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