Electric machine with sliding contacts

Abstract

In an electric machine (1), in particular in the form of a separately excited synchronous motor, sliding contacts (3) are formed by sliding brushes (2) in conjunction with slip rings (7) which comprise tungsten, wherein tungsten constitutes the main component of at least one area of ​​each slip ring (7) forming the sliding contact (3).

Description

[0001] The invention relates to an electrical machine having a plurality of sliding contacts according to the preamble of claim 1.

[0002] Such an electrical machine is known, for example, from DE 101 13 673 A1, which discloses a claw-pole generator intended for use in a motor vehicle. The electrical machine according to DE 101 13 673 A1 comprises internal cooling, in which a liquid-gas mixture flows around the components to be cooled, including a grinding system, as the cooling medium. The grinding system comprises brushes and slip rings covered by the cooling medium. As explained in DE 101 13 673 A1, this hinders oxygen access to the sliding contacts, which can generally lead to a desired oxide protective layer being worn away more quickly and the service life of the grinding system being reduced. To mitigate this adverse effect, DE 101 13 673 A1 proposes manufacturing slip rings from an alloy containing copper as the main component and an additional oxygen-affinity alloy component.According to the teaching of DE 101 13 673 A1, the oxygen-affine alloy component can be a less noble metal than copper and / or a semi-metal. Specifically, the metals magnesium, zirconium, titanium, hafnium, tungsten, molybdenum, vanadium, and iron, as well as the semi-metals tellurium, silicon, and boron, are mentioned. The oxygen-affine alloy components should preferably be added in a weight fraction of approximately 0.05 to 3%, in particular 0.3 to 0.9%. Furthermore, the alloy can contain accompanying elements such as oxygen and / or phosphorus in the per mille or ppm range.

[0003] AT 303 880 B specifies the use of tungsten as a contact material for commutators and slip rings. Tungsten is to be a component of a two-component composite material.

[0004] CN 1 06 654 782 A deals with the production of a grinding brush for an electric motor. It is proposed to use, in addition to graphite, a metal powder for the production of grinding brushes, which, according to one described embodiment, contains copper and—to a lesser extent—tungsten, with a possible mixing ratio of 3:1 being specified. Another embodiment provides for the mixture of tin and tungsten in a ratio of 2:2. In both of these embodiments, epoxy resin is to be used as the imprint.

[0005] Regarding a possible design of a brush module in an electric motor of a motor vehicle, reference is made to DE 10 2020 121 291 A1 as an example. The known brush module comprises several brush holders arranged on an intermediate element made of plastic.

[0006] A brush arrangement for an electric motor comprising brushes made of a graphite-metal combination is known from DE 10 2015 214 204 A1. In this case, several pairs of brushes are provided for different directions of rotation of the electric motor.

[0007] The invention is based on the object of further developing an electrical machine having sliding contacts, suitable for use in a motor vehicle, for example, compared to the cited prior art, whereby a particularly favorable ratio between equipment expenditure, installation space requirement and longevity is sought.

[0008] This object is achieved according to the invention by an electrical machine having the features of claim 1. The electrical machine operates in a known basic concept with sliding contacts, which are formed, among other things, by slip rings containing tungsten. According to claim 1, tungsten is the main component of at least one region of each slip ring forming the sliding contact. The term "main component" in this context means that the tungsten content (in percent by weight) in the relevant region of the slip ring is at least 50%. This significantly distinguishes the slip ring according to the application from known slip rings, which contain a much smaller proportion of tungsten.

[0009] The invention is based on the idea that tungsten, due to its high temperature resistance, is particularly suitable for electrical components where arcing can occur. It has been found that this advantage is particularly evident when a component forming a sliding contact—in this case, a slip ring in conjunction with a brush—is predominantly made of tungsten.

[0010] Tungsten can be present in metallic form, particularly as a component of an alloy. Tungsten can also be present in the slip ring in the form of tungsten carbide. Tungsten carbide is characterized not only by its hardness but also by its good electrical and thermal conductivity. Slip rings containing tungsten in both metallic and tungsten carbide forms are also possible. In these cases, the majority of the tungsten can be present as tungsten carbide, with only a comparatively small proportion as metallic tungsten.

[0011] The tungsten-containing slip ring can be constructed of a single or mixed material. In the latter case, a multi-part design, plating, or coating are possible options. Unlike the coating, a coated base body can be tungsten-free.

[0012] Regardless of its precise design, the slip ring, together with a brush, forms the sliding contact. The brush can be, for example, a carbon-based machine element or a metallic element, particularly made of steel or a non-ferrous metal alloy. Particularly in the case of metallic brushes, i.e., grinding brushes, the sliding contacts can be operated with oil. A radial force that presses the brushes against the slip rings can be applied in a conventional manner using springs. In principle, other methods of force generation, such as pneumatics, are also suitable for pressing the grinding brushes against the tungsten-containing slip rings with a defined force.

[0013] The electrical machine according to the application can be designed as a generator or an electric motor. In the case of a motor, it can, in particular, be a separately excited synchronous motor.

[0014] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings: Fig. 1 Components of an electrical machine, namely an electric motor, in a partial perspective view, Fig. 2 shows a schematic sectional view of the structure of a slip ring of the electrical machine according to claim 1.

[0015] A generally designated with the reference number 1, in Fig. The electric motor 1, only partially shown, is designed for use as a traction motor in a motor vehicle. Alternatively, the electric motor 1 can be operated for another purpose within a vehicle or as a stationary motor. The electric motor 1 is a separately excited synchronous motor. Regarding the basic function of the electric motor 1, reference is made to the prior art cited at the beginning.

[0016] A slip ring 7 is connected to the energizable rotor of the electric motor 1. Together with the sliding brushes 2, this forms sliding contacts 3. The sliding brushes 2 are arranged in a star-shaped configuration around the central axis of the shaft of the electric motor 1 within a brush module (not shown).

[0017] Each grinding brush 2 has a cuboid-like basic shape and is displaceably mounted in a linear guide device held on a carrier (not shown) of the brush module in the radial direction of the slip ring 7 and thus also of the shaft of the electric motor 1.

[0018] For contacting the slip ring 7, each brush 2 has a concavely curved dynamic contact side. The radius of curvature is slightly larger than the radius of the slip ring 7 in the area of ​​the sliding contacts 3. The sides of the brushes 2 opposite the sliding contacts 3, which are flat in the exemplary embodiment, are referred to as their rear sides 4. Reference numerals 5, 6 denote side surfaces of the brushes 2. The side surfaces 5, 6 are, as can be seen from Fig. 1, in the exemplary embodiment, it is significantly more extensive than side 4, so that the grinding brush 2, in plan view, approximately describes an elongated rectangle oriented in the radial direction of the electrical machine 1. Electrical cables not shown can be connected to the grinding brush 2 on one of the sides 4, 5, 6, for example, soldered or welded.

[0019] In the exemplary embodiment, the grinding brushes 2 are designed as solid metal brushes. In particular, the grinding brushes 2 can be made of steel or a wrought brass alloy. The slip ring 7 contacting the metal grinding brushes 2 can be profiled in a manner not shown, just like the grinding brushes 2 on their respective contact sides.

[0020] A particularly low wear of the sliding contacts 3 is achieved not only by the choice of material for the grinding brushes 2, but also by the design of the slip ring 7. In the exemplary embodiment, the slip ring 7 is formed by a base body 8, which is provided with a coating 9, as shown in Fig. 2. The grinding brushes 2 contact the coating 9.

[0021] The base body 8 is a metallic material, in particular steel, which contains no tungsten or at most only as a melting-related impurity. In contrast, the coating 9 has tungsten as its main component. In this case, tungsten is predominantly present as tungsten carbide. In addition, a smaller amount of tungsten may be present in metallic form.

[0022] In principle, known coating methods, such as electroplating, can be used to apply the coating 9. Alternatively, plating the base body 8 with a tungsten-containing material or a multi-part design of the slip ring 7 is possible.

[0023] The bearings of the electric motor 1 are lubricated with oil, which is also present in the area of ​​the sliding contacts 3 during normal operation of the electric motor 1. The oil contributes significantly to the low-friction and low-wear function of the sliding contacts 3 without significantly impairing their current-carrying capacity. List of reference symbols 1 electric motor, electric machine 2 sanding brushes 3 sliding contact 4 Back 5 Side surface 6 side surface 7 Slip ring 8 basic bodies 9 Coating

Claims

[1] Electrical machine (1) with sliding contacts (3) which are formed, inter alia, by slip rings (7) comprising tungsten, characterized by that tungsten is the main component of at least one area of ​​each slip ring (7) forming the sliding contact (3). [2] Electrical machine (1) according to claim 1, characterized by that tungsten is present in metallic form in the slip ring (7). [3] Electrical machine (1) according to claim 1 or 2, characterized by that tungsten is present in the slip ring (7) in the form of tungsten carbide. [4] Electrical machine (1) according to one of claims 1 to 3, characterized by that the slip ring (7) is constructed from the same material. [5] Electrical machine (1) according to one of claims 1 to 3, characterized by that tungsten is contained in a coating (9) of the slip ring (7). [6] Electrical machine (1) according to one of claims 1 to 5, characterized bythat the sliding contacts (3) are formed by the tungsten-containing slip rings (7) and carbon-based grinding brushes (2). [7] Electrical machine (1) according to one of claims 1 to 5, characterized by that the sliding contacts (3) are formed by the tungsten-containing slip rings (7) and metallic grinding brushes (2). [8] Electrical machine (1) according to claim 7, characterized by that the sliding contacts (3) are wetted with oil. [9] Electrical machine (1) according to one of claims 1 to 8, characterized by that it is designed as a separately excited synchronous motor.

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