Electric machine with sliding contact

Abstract

In an electric machine (1), in particular in the form of a separately excited synchronous motor, a sliding contact (3) is formed by the interaction of a brush (2) with a slip ring (7), which comprises tungsten, the tungsten being the main component of at least one region of each slip ring (7) forming the sliding contact (3).

Description

Technical Field

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

[0002] Such an electric motor is known, for example, from DE 101 13 673 A1, which discloses a claw-pole generator, which is used in motor vehicles. The electric motor described in DE 101 13 673 A1 includes an internal cooling device, in which a liquid-gas mixture flows as a cooling medium around the components to be cooled, including the sliding system. The sliding system includes brushes and slip rings, which are covered with a cooling medium. As described in DE 101 13 673 A1, oxygen is thereby prevented from entering the sliding contact, which usually results in the required oxidation protection layer being eroded more quickly and reduces the service life of the sliding system. In order to reduce this adverse effect, DE 101 13 673 A1 proposes to manufacture the slip ring from an alloy, which contains copper as the main component and also includes an oxygen-philic alloy component. According to the teaching of DE 101 13 673 A1, the oxygen-philic alloy component is a metal and / or semi-metal that is less noble than copper. In particular, the metals are magnesium, zirconium, titanium, hafnium, tungsten, molybdenum, vanadium and iron and the semimetals tellurium, silicon and boron. The oxygen-philic alloying components should preferably be added in a weight ratio of about 0.05% to 3%, in particular 0.3% to 0.9%. In addition, the alloy may contain accompanying elements in the parts per thousand or ppm range, such as oxygen and / or phosphorus.

[0003] CN 106654782 A discloses the production of brushes for electric motors. In addition to graphite, it is proposed to use metal powders, in particular, to produce the brushes, which according to the embodiment contain copper and a small amount of tungsten, wherein a possible mixing ratio is 3:1. Another embodiment provides a mixture of tin and tungsten in a ratio of 2:2. In both embodiments, epoxy resin is to be used as a molding agent.

[0004] For possible embodiments of brush modules in electric machines of motor vehicles, reference is made, for example, to DE 10 2020121 291 A1. The known brush module comprises a plurality of brush holders which are arranged on an intermediate element made of plastic.

[0005] DE 10 2015 214 204 A1 discloses a brush assembly for an electric motor, which comprises brushes made of a graphite metal composite. In this case, there are a plurality of brush pairs for different directions of rotation of the electric motor. Summary of the invention

[0006] The object of the present invention is to improve an electric machine having sliding contacts suitable for motor vehicles compared to the prior art, wherein a particularly favorable relationship between equipment outlay, installation space requirement and long service life is sought.

[0007] According to the invention, this object is achieved by an electric machine having the features of claim 1. The electric machine operates according to the known basic principle by means of sliding contacts, which are formed in particular by slip rings, which contain tungsten. According to claim 1, tungsten is the main component of at least one region of each slip ring that forms the sliding contact. In this context, the term "main component" means that the tungsten content (in weight percent) in the relevant region of the slip ring is at least 50%. As a result, the slip ring according to this document is significantly better than the known slip rings, which contain a much smaller amount of tungsten.

[0008] The invention is based on the consideration that tungsten is particularly suitable for electrical components where arcs may occur due to its high temperature resistance. It has been found to be particularly advantageous if a component forming the slidable contact, in this case a slip ring cooperating with the brush, consists predominantly of tungsten.

[0009] In this case, the tungsten can be present in metallic form, in particular as a component of an alloy. Likewise, the tungsten can be present in the form of tungsten carbide in the slip ring. Tungsten carbide is not only characterized by its hardness, but also by good electrical and thermal conductivity. Slip rings containing tungsten in metallic form and in the form of tungsten carbide can also be used. In these cases, the majority of the tungsten can be present as tungsten carbide and only a smaller portion of the tungsten can be present as metallic tungsten.

[0010] The slide ring containing tungsten can be constructed with a uniform material or with a non-uniform material. In the latter case, multi-part designs, platings or coatings are particularly conceivable, wherein the coated base body can be free of tungsten compared to the coating.

[0011] Independent of the specific design of the slip ring, the slip ring together with the brush forms a sliding contact. The brush is, for example, a carbon-based mechanical element or a metal element, in particular a metal element made of steel or a non-ferrous metal alloy. In particular in the case of metal brushes, i.e. brushes, the sliding contact can be operated in an oil-lubricated manner. The radial force of the brush against the slip ring can be applied in a known manner by means of a spring. In principle, other methods of generating force, such as pneumatics, are also suitable for pressing the brush against the tungsten-containing slip ring with a defined force.

[0012] The electrical machine according to the present invention can be designed as a generator or as an electric motor. In the case of an electric motor, it is in particular a separately excited synchronous motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be described in detail below with reference to the accompanying drawings. It is shown in the drawings:

[0014] Figure 1A partial perspective view of a component of an electric machine, i.e. an electric motor, is shown,

[0015] Figure 2 A schematic cross-sectional view shows the structure of a slip ring of an electric machine according to claim 1 . DETAILED DESCRIPTION

[0016] exist Figure 1 1, only part of the electric motor, which is designated as a whole by the reference numeral 1, is shown, which is designed to be used as a traction motor of a motor vehicle. Alternatively, the electric motor 1 can be used for other purposes in the vehicle or can be operated as a stationary electric motor. The electric motor 1 is a separately excited synchronous motor. For the basic function of the electric motor 1, reference is made to the prior art cited at the beginning.

[0017] The slip ring 7 is connected to the energizable rotor of the electric motor 1. Together with the brushes 2, a sliding contact 3 is thus formed. In a brush module (not shown in detail), the brushes 2 are arranged overall in a star shape around the center axis of the shaft of the electric motor 1.

[0018] Each brush 2 has a square basic shape and is mounted so as to be displaceable in a linear guide in the radial direction of the slip ring 7 and thus of the shaft of the electric motor 1 , which is held on a support (not shown) of the brush module.

[0019] In order to contact the slip ring 7, each brush 2 has a concavely curved dynamic contact side. The bending radius is slightly larger than the radius of the slip ring 7 in the region of the sliding contact 3. The side of the brush 2 opposite the sliding contact 3, which is flat in this embodiment, is called its rear side 4. The side faces of the brush 2 are denoted by the reference numerals 5 and 6. Figure 1 It can be seen that the side surfaces 5, 6 in this embodiment are significantly more extensive than the side 4, so that the brush 2 appears approximately as an elongated rectangle oriented in the radial direction of the electric machine 1 in a top view. Electrical lines (not shown) can be connected to the brush 2 on one side of the side 4, 5, 7, for example, by soldering or welding.

[0020] In this exemplary embodiment, the brush 2 is designed as a full metal brush. In particular, the brush 2 can be made of steel or of a forged brass alloy. The slip ring 7 contacting the metal brush 2 can be designed in a manner not shown, just like the brush 2 on its respective contact side.

[0021] The particularly low wear of the sliding contact 3 is achieved not only by the material selection of the brush 2, but also by the structural design of the slip ring 7. In this embodiment, the slip ring 7 is formed by a base body 8, which is provided with a coating 9, such as Figure 2 As shown, the brush 2 contacts the coating 9.

[0022] The substrate 8 is a metallic substance, in particular steel, which contains no tungsten or at most tungsten as an impurity caused by melting. In contrast, the coating 9 has tungsten as the main component. In this case, tungsten is mainly present as carbide. In addition, tungsten can be present in a smaller proportion in metallic form.

[0023] In principle, the coating 9 can be applied using known coating methods, for example galvanic methods. Alternatively, it is conceivable to coat the base body 8 with a tungsten-containing material or to design the slide ring 7 in multiple parts.

[0024] The bearings of the electric motor 1 are lubricated with oil, and when the electric motor 1 is operating as intended, the oil is also present in the region of the sliding contact 3. The oil contributes significantly to the low friction and low wear effect of the sliding contact 3 without significantly impairing the conductive properties of the sliding contact.

[0025] Reference numerals list

[0026] 1 Electric motors

[0027] 2 Brushes

[0028] 3 Sliding contacts

[0029] 4 Rear

[0030] 5 Side

[0031] 6 Side

[0032] 7 Slip Rings

[0033] 8 Matrix

[0034] 9 Coating

Claims

1. An electric machine (1) having a sliding contact (3), the sliding contact being in particular formed by a slip ring (7) comprising tungsten, characterized in that: Tungsten is the main component of at least one region of each slip ring (7) which forms the sliding contact (3).

2. The electric machine (1) according to claim 1, characterized in that Tungsten is present in the slip ring (7) in the form of metal.

3. The electric machine (1) according to claim 1 or 2, characterized in that The tungsten is present in the slip ring (7) in the form of tungsten carbide.

4. The electric machine (1) according to any one of claims 1 to 3, characterized in that The slide ring (7) is constructed of a uniform material.

5. The electric machine (1) according to any one of claims 1 to 3, characterized in that The coating (9) of the slip ring (7) contains tungsten.

6. The electric machine (1) according to any one of claims 1 to 5, characterized in that The sliding contact (3) is composed of a slip ring (7) containing tungsten and a carbon-based brush (2).

7. The electric machine (1) according to any one of claims 1 to 5, characterized in that The sliding contact (3) is composed of a slip ring (7) containing tungsten and a metal brush (2).

8. The electric machine (1) according to claim 7, characterized in that The sliding contact (3) is wetted with oil.

9. The electric machine (1) according to any one of claims 1 to 8, characterized in that The motor is configured as a separately excited synchronous motor.

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