Housing for accommodating a stator of an electrical machine

Abstract

Housing (2) for accommodating a stator (3) of an electrical machine (1), wherein at least one structure-borne sound (8) absorbing element (10) made of a cellular metallic material is arranged within the housing (2), and the housing (2) forms a cooling channel (7) of the electrical machine (1), within the cooling channel (7) the structure-borne sound (8) absorbing element (10) made of a cellular metallic material is arranged, and the housing (2) forms the cooling channel (7) together with a cooling channel insert (11).

Description

[0001] The invention relates to a housing for accommodating a stator of an electrical machine. Furthermore, the invention relates to an electrical machine comprising the housing and a stator accommodated within the housing.

[0002] The noise from electrical machines is playing an increasingly significant role. This noise must be limited for various reasons. For example, standards must be adhered to that stipulate that the noise level must not exceed certain limits. Furthermore, customer benefits suffer from unwanted noise, particularly in comfort applications.

[0003] The causes of noise in electrical machines are diverse. Very often, problems arise from structure-borne noise, which is also transmitted through the machine structures and ultimately becomes audible through sound radiation. Structure-borne noise is primarily caused by electromagnetic and mechanical effects, but also by the supply of harmonic-rich currents.

[0004] The fundamental, active process involved in sound generation in a magnetic circuit is the conversion of electrical energy into mechanical energy. The resulting forces excite the mechanical structure and cause vibrations, which ultimately lead to sound radiation.

[0005] The housing which houses the stator can also be excited to generate structure-borne noise by the circulating force waves, whereby the structure-borne noise is emitted through the housing and appears as airborne noise.

[0006] The most efficient way to reduce noise is to prevent it from occurring in the first place, or at least to reduce its generation. There are various ways to identify a noise source. One approach is theoretical. The machine is mentally broken down into its individual components and then classified according to their machine acoustic properties. The result of this analysis is evaluation tables for the sound sources, sound transmitters, and sound emitters. These culminate in a sound flow plan that graphically illustrates which components of the machine need to be the starting point for noise reduction. The greater the influence of a source, or the more strongly a body transmits or radiates noise, the sooner intervention is necessary. For this purpose, the components are marked with lines of varying thickness depending on the extent of their influence.The thicker such a line is, the more critical the impact on noise and the more urgent the need for noise reduction. This type of analysis is suitable for both designs and existing machines. It shows where intervention by an acoustic engineer is necessary and appropriate.

[0007] The closest DE 10 2010 039 463 A1 describes a housing for an electrical machine, wherein the housing comprises a sound-damping material made of a foam.

[0008] CN 2 03 301 294 U describes the noise reduction of large turbo generators for power generation companies.

[0009] DE 10 2005 044 575 A1 refers to the noise reduction of steering systems in motor vehicles.

[0010] WO 2012 / 103 882 A2 relates to a rotor for an electric motor.

[0011] It is an object of the invention to reduce structure-borne sound emitted by the housing, which appears as airborne sound, and thus to reduce the noise in an electrical machine.

[0012] The object is achieved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0013] According to the present invention, vibration damping (energy absorption) of a stator housing can be achieved through design, joining, or material-related measures. Energy absorption in the form of vibration damping contributes to improving the utility value of the electrical machine.

[0014] Structure-borne sound damping specifically refers to the absorption of vibration energy through thermal, magnetic, or atomic rearrangements of the molecules of the applied damping material. A parameter for the absorption of structure-borne sound is the so-called "loss factor," which is a measure of the material's ability to absorb energy under dynamic loading (especially during bending vibrations). Cellular metallic materials are particularly suitable for structure-borne sound damping in electrical machines, as they enable high levels of airborne and structure-borne sound damping and are therefore suitable as passive damping elements in the design of the electrical machine.

[0015] When it comes to components in a functional chain of a structure, a distinction can be made between force excitation and velocity excitation. Force-excited components are typically located in a closed force flow and are excited to structure-borne sound vibrations by elastic deformations (in particular, the stator of an electrical machine). Velocity-excited components, on the other hand, are located outside of a force flow. They are not load-bearing parts. However, they are coupled to components in the force flow and are set into structure-borne sound vibrations via a coupling point (for example, the housing of an electrical machine).

[0016] In practice, force-excited and velocity-excited components can influence each other with regard to their structure-borne sound vibrations, which is why structure-borne sound should be prevented from propagating within the structure as much as possible. This can be achieved through structure-borne sound insulation and damping.

[0017] In many cases, the means of structure-borne sound insulation cannot achieve the desired prevention of structure-borne sound propagation in order to reduce noise, because without damping the energy is not dissipated.

[0018] Reducing structure-borne sound transmission through damping requires significant internal losses in the materials used. Structure-borne sound energy is converted into heat through friction at contact surfaces or through internal friction of the materials. Here, too, the closer the damping is to the source of the sound (for example, near the stator of an electric motor), the more effective it is.

[0019] In this sense, according to a first aspect of the invention, a housing for accommodating a stator of an electrical machine is provided, wherein at least one structure-borne sound-absorbing element made of a cellular metallic material is arranged within the housing. Using the structurally specific properties of the cellular metallic material in the housing for the electrical machine, a structure is created that has significantly improved damping capacity and offers the possibility of controlled energy absorption.

[0020] According to the invention, the housing forms a cooling channel for the electric machine, with a structure-borne sound-absorbing element made of a cellular metallic material arranged within the cooling channel. The structure-borne sound-absorbing element integrated into the cooling channel can, in particular, consist of an open-pore metal foam. Especially when aluminum is used as the base material for the open-pore metal foam, this enables high thermal conductivity for the housing as a heat sink. The medium flowing through the foam absorbs the heat from the metal matrix.

[0021] The efficiency of heat exchangers can be increased through active measures, e.g., by influencing the boundary layer that hinders heat transfer. The type of flow of the cooling medium, especially the cooling liquid, has a significant influence on the effectiveness of heat transfer. The turbulence of the flow determines the level of heat transfer. It is therefore desirable that the cooling channel be designed in such a way that turbulent flow (swirling) can be achieved.

[0022] Heat transfer by convection occurs when cold molecules of a cooling fluid are brought closer to a surface. In this process, new molecules must be constantly added for heat exchange to occur. The more vigorous the movement of the cooling fluid, the greater the heat transfer by convection. In turbulent flow, heat transfer is significantly better than in laminar flow.

[0023] Against this background, according to a further embodiment, flow-guiding elements made of a cellular metallic material are arranged within the cooling channel. The flow-guiding elements can be configured to guide, swirl, deflect, and channel the flow of a cooling medium (in particular the flow of a cooling liquid) conveyed through the cooling channel.

[0024] In particular, the flow guide elements can be shaped and arranged such that a cooling medium is guided in a meandering pattern through the cooling channel. This improves heat transfer by, on the one hand, repeatedly disrupting the boundary layer and, on the other hand, increasing the degree of turbulence of the flow to improve heat transfer through increased momentum and energy exchange.

[0025] Furthermore, the flow guide elements can provide barriers or rib-shaped constrictions for a cooling medium that is guided through the cooling channel. These barriers or rib-shaped constrictions can also improve heat transfer.

[0026] According to the invention, the housing forms the cooling channel together with a cooling channel insert. This creates a modular system, whereby different cooling channels can be formed with particular flexibility, particularly by exchanging the cooling channel insert. In this context, it can also be provided, in particular, that the cooling channel insert forms the flow guide elements.

[0027] In a further embodiment, the cellular metallic material is an open-pored metal foam, in particular based on an aluminum material.

[0028] Open-pore metal foam, particularly aluminum foam, exhibits structurally specific properties that enable the production of composite structures with improved rigidity, significantly improved damping capacity, and the ability to absorb energy in a controlled manner. Structures with integrated aluminum foam are also particularly lightweight, absorb high levels of energy, and dampen vibrations and noise particularly effectively. The incorporation or placement of metal foam, particularly aluminum foam, into machine parts that transmit or emit structure-borne sound enables both lightweight construction and sound damping or vibration damping. The structure-borne sound emission of the housing can thus be reduced and shifted to other frequency ranges. Cooling elements made of metal foam thus offer maximum effectiveness with minimal dimensions and weight.Due to their delicate structure, the open-pore metal foams offer an enormously large surface area for heat dissipation. In addition, the metal foam acts as a turbulator on the surface of the cooling channel, disrupting the boundary layer that impedes heat transfer.

[0029] Furthermore, the metal foam can comprise hollow sphere structures. The hollow sphere structures can, in particular, be metallic. The metal foam can be characterized by a combination of open and closed porosity, and the hollow sphere structures can be formed by spherical cells with precisely adjustable cell diameters and cell wall thicknesses.

[0030] The hollow sphere structures offer the possibility of dissipating vibration energy. As soon as a wave front reaches the hollow sphere shells, the sphere shells begin to vibrate against each other. Vibration energy is converted into heat through friction and partially elastic collisions. Since vibration energy is converted into heat through internal friction during structure-borne sound damping, it can also be referred to as "internal damping." The hollow sphere structures enable high levels of structure-borne sound and vibration damping for fast-moving machine parts and under extreme conditions. The metallic hollow sphere structures can be manufactured using special technologies and flexibly processed. For example, they can be cast in place, but also joined by bonding, soldering, or sintering.

[0031] In a further development, freely movable ceramic particles can be present in the interior of the hollow sphere structures described above. In this sense, in a further embodiment, the metal foam can comprise hollow sphere structures which are filled with particles, in particular with ceramic particles. The particles, in particular the ceramic particles, act as vibration dampers. Sintered individual spheres can be filled into the structure-borne sound absorbing element (e.g. in the form of a molded body) and fixed there by gluing or soldering. The further processing of the molded bodies or also of individual hollow sphere structures into sandwich structures or casting in polymers or metals is also possible. When a component with particle-filled hollow sphere structures is set into vibration, the movement of the base material transfers the energy into the particle bed.The particles are ejected from the cavity wall, absorbing the vibration energy. Through collisions and friction between the particles, the kinetic energy is converted into heat. The damping values ​​achieved in this way can be approximately ten times higher than those of aluminum foam, which can be used as a vibration-damping lightweight material (see above).

[0032] According to a second aspect of the invention, an electric machine is provided. The electric machine comprises a housing according to the first aspect of the invention and a stator accommodated within the housing.

[0033] In the following, embodiments of the invention are explained in more detail with reference to the partially schematic drawing. Fig. 1 a longitudinal section of a known electrical machine, Fig. 2 a longitudinal sectional view of an embodiment of an electrical machine according to the invention with a structure-borne sound absorbing element in a cooling channel, Fig. 3 a longitudinal sectional view of an embodiment of an electrical machine according to the invention with coolant guide elements made of structure-borne sound-absorbing, open-pore metal foam integrated into a cooling channel, Fig. 4 a perspective exploded view of an embodiment of a housing according to the invention with a cooling channel insert made of a structure-borne sound-absorbing, open-pore metal foam, Fig. 5 an enlarged perspective view of the cooling channel insert according to Fig. 4 and Fig. 6 a longitudinal sectional view of an upper part of a further embodiment of an electrical machine according to the invention with structure-borne sound-absorbing, open-pore metal foam in a cooling channel.

[0034] Fig. 1 shows an electric machine 1 which can be used, for example, to drive a motor vehicle (not shown). The electric machine 1 comprises a housing 2 which accommodates a stator 3. The stator 3 radially surrounds a rotor core 4 which is mounted in a rotationally fixed manner on a rotor shaft 5. The rotor shaft 5 is rotatably mounted within two bearings 6, which in turn are mounted in a rotationally fixed manner by the housing 2. The housing 2 further forms a cooling channel 7, within which a medium can circulate in order to cool the electric machine 1. The housing 2 can be excited by circulating force waves to produce structure-borne sound 8. This structure-borne sound 8 can in turn be emitted through the housing 2 and appear as (unwanted) airborne sound 9.

[0035] Fig. 2 and Fig. 6 show an electrical machine 1 which has the same basic structure as the electrical machine according to Fig. 1. The electrical machine 1 according to the invention according to Fig. 2 or 6, however, additionally has a structure-borne sound absorbing element 10, which consists of a cellular metallic material, in particular of an open-pore metal foam ( Fig. 6), and which is arranged within the cooling channel 7 of the housing 2. The cellular metallic material dampens structure-borne noise 8 of the housing 2 and thereby reduces airborne noise 9, which results from the structure-borne noise 8 and leaves the electrical machine 1.

[0036] Fig. 3 shows an electrical machine 1, which has the same basic structure as the electrical machine according to Fig. 1. The electrical machine 1 according to the invention according to Fig. 3, however, additionally has a cooling channel insert 11, which represents a separate component and together with the housing 2 forms the cooling channel 7 (cf. Fig. 4). The cooling channel insert 11 consists of a cellular metallic material and forms a structure-borne sound-absorbing element. The cellular metallic material dampens structure-borne sound 8 from the housing 2 and thereby reduces airborne sound 9, which results from the structure-borne sound 8 and leaves the electric machine 1.

[0037] Fig. 4 and Fig. 5 show a cooling channel insert 11, which, for example, together with the housing 2 of the embodiment according to Fig. 3 can be used. The cooling channel insert 11 comprises a cellular metallic material which dampens structure-borne noise 8 of the housing 2 and thereby reduces airborne noise 9 resulting from the structure-borne noise 8 and leaving the electrical machine 1.

[0038] The housing 2 comprises according to Fig. 4 a first housing part 12 with a cooling channel groove, a second housing part 13 with a flow connection 14 and a return connection 15 as well as a bearing plate 16. The cooling channel insert 11 also comprises a flow connection 17 and a return connection 18, several flow guiding elements in the form of transverse ribs 19 arranged at a distance from one another in the circumferential direction as well as a molded part partition wall 20. The first housing part 12 and the cooling channel insert 11 form the cooling channel 7 in the assembled state of the housing 2 in the assembly direction M (cf. Fig. 3).

[0039] The molded part partition wall 20 connects two adjacent transverse ribs 19 in the region of the connections 17 and 18 in the circumferential direction. In this way, coolant entering the cooling channel 7 via the supply connection 17 cannot immediately leave the cooling channel 7 again via the return connection 18. Instead, the coolant entering via the supply connection 17 is guided in a meandering manner around the transverse ribs 19 through the circumferentially running cooling channel 7 and is discharged from the cooling channel 7 again via the return connection 18. The transverse ribs, on the one hand, repeatedly tear open the boundary layer of the coolant flow and, on the other hand, increase the degree of turbulence of the flow, resulting in an increased momentum and energy exchange, which improves heat transfer.

[0040] The metal foam shown in the figures described above may comprise hollow sphere structures, in particular hollow sphere structures filled with particles, e.g. with ceramic particles.

Claims

[1] Housing (2) for accommodating a stator (3) of an electrical machine (1), wherein at least one structure-borne sound (8) absorbing element (10) made of a cellular metallic material is arranged within the housing (2), and the housing (2) forms a cooling channel (7) of the electrical machine (1), within the cooling channel (7) the structure-borne sound (8) absorbing element (10) made of a cellular metallic material is arranged, and the housing (2) forms the cooling channel (7) together with a cooling channel insert (11). [2] Housing (2) according to claim 1, wherein flow guiding elements (19, 20) made of a cellular metallic material are arranged within the cooling channel (7). [3] Housing (2) according to claim 2, wherein the flow guiding elements (19, 20) are shaped and arranged such that a cooling medium is guided in a meandering manner through the cooling channel (7). [4] Housing (2) according to claim 2 or 3, wherein the flow guiding elements (19, 20) provide barriers (20) or rib-shaped constrictions (19) for a cooling medium which is guided through the cooling channel (7). [5] Housing (2) according to one of claims 2 to 4, wherein the cooling channel insert (11) forms the flow guiding elements (19, 20). [6] Housing (2) according to one of the preceding claims, wherein the cellular metallic material is an open-pore metal foam (10). [7] Housing (2) according to one of the preceding claims, wherein the metal foam (10) comprises hollow sphere structures. [8] Housing (2) according to one of the preceding claims, wherein the metal foam (10) comprises hollow sphere structures filled with particles. [9] Electrical machine (21) comprising a housing (2) according to one of the preceding claims and a stator which is accommodated within the housing (2).

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