Sliding contact arrangement and brush module for an electric machine

Abstract

A sliding contact arrangement of an electric machine is composed of a plurality of sliding contacts which are each formed by a slip ring (14, 19, 21) and a brush (2, 18, 10, 22), wherein the different sliding contacts are designed differently depending on the polarity.

Description

[0001] P240584 DE

[0002] - 1 -

[0003] Sliding contact arrangement and brush module for an electric machine

[0004] The invention relates to a sliding contact arrangement configured according to the preamble of claim 1, which comprises several sliding contacts. The invention further relates to a brush module of an electric machine operating with sliding contacts.

[0005] A generic sliding contact arrangement is known, for example, from US 2007 / 0080603 A1. The known sliding contact arrangement comprises sliding brushes of different polarities, which are designed differently to selectively influence their wear behavior. For this purpose, for example, the contact surfaces with which the sliding brushes bear against a slip ring can be of different sizes. According to the teaching of US 2007 / 0080603 A1, it is also possible to apply different forces to different sliding brushes.

[0006] Another slip ring and brush arrangement, exhibiting the features of the preamble of claim 1, is disclosed in DE 1 184 412 A. DE 1 184 412 A assumes that it is generally known to reverse the polarity of slip rings after certain operating periods in order to even out wear. However, this measure is not practical in some applications, for example in aircraft construction. Instead, DE 1 184 412 A proposes a different design for various sliding contacts. A conventional copper ring is used as the positive slip ring, which contacts an impregnated carbon brush. The negative slip ring is comparatively complex, consisting of an inner copper ring and an outer carbon ring, and contacts a sliding brush whose copper content is specified in DE 1 184 412 A as being between 80 and 90%.The entire sliding contact assembly is intended for use in a generator installed in an aircraft. P240584 DE.

[0007] - 2 -

[0008] CN 207853143 U also deals with sliding contacts in a generator.

[0009] The potential for spark formation is a particular focus here. To minimize spark formation, the use of grinding brushes with a grooved surface is suggested.

[0010] DE 10 2022 133 605 A1 discloses a grinding brush for an electric machine and a method for manufacturing a grinding brush. The grinding brush comprises a stack of layers which has a curved dynamic contact surface intended for contacting a shaft of the electric machine and is formed from alternating layers of different types, wherein a first subset of the layers describes a first cylindrical surface tangent to the surface of the shaft, whereas a second subset of the layers is raised from the cylindrical surface, forming lubricant grooves.

[0011] DE 10 2021 122 065 B3 discloses a brush holder for mounting at least two brushes for a sliding contact arrangement of an electric machine. The brush holder according to DE 10 2021 122 065 B3 comprises a substantially ring-shaped intermediate element and two contact elements for electrically contacting at least one of the brushes, i.e., sliding brushes. The contact elements are arranged on opposite sides of the intermediate element. The intermediate element is electrically insulating, and a cooling channel is formed inside the intermediate element. The device according to DE 10 2021 122 065 B3 is intended for use in a motor vehicle.

[0012] A commutator device for an electric machine, disclosed in AT 514830 A1, comprises several brushes installed in holders. At least one brush is made of a material containing a filling of Teflon and / or carbon fibers and is provided with an indicator of its degree of wear. P240584 DE

[0013] - 3 -

[0014] A holding device for a slip ring assembly, described in EP 3 788 683 B1, is intended for use in an electric machine used in a wind turbine. The holding device can accommodate two or more slip ring brushes, which are referred to as slip ring brushes in EP 3 788 683 B1. Suitable materials for manufacturing the holding device include plastic, a ceramic material, and metals such as brass or copper.

[0015] German patent DE 23 41 477 A1 concerns a sliding contact in a servo motor. Tungsten or a gold-containing alloy, for example an alloy with copper, is proposed as a material for manufacturing the brushes.

[0016] The invention is based on the objective of further developing means for current transmission between rotating and non-rotating parts of an electrical machine, i.e. an electric motor or a generator, compared to the prior art, particularly with regard to wear.

[0017] This problem is solved according to the invention by a sliding contact arrangement with the features of claim 1. According to claim 6, the sliding contact arrangement can in particular be realized by a brush module of a separately excited electric machine.

[0018] The sliding contact arrangement intended for use in an electric machine comprises several sliding contacts, each consisting of a slip ring and a sliding brush, with the different sliding contacts being designed differently depending on the polarity.

[0019] The invention is based on the understanding that wear patterns on sliding contacts can be pole-dependent. This applies in particular to oil-lubricated P240584 DE

[0020] - 4 -

[0021] Sliding contacts, even when using metal brushes. It has been observed that increased wear is found on the slip ring at the negative terminal, while the corresponding brush shows hardly any wear. Conversely, the positive terminal shows hardly any wear on the slip ring, whereas the corresponding brush exhibits comparatively heavy wear.

[0022] This knowledge is used to design sliding contact arrangements pole-selectively according to various embodiments as follows:

[0023] A sliding contact at the negative terminal is formed by a grooved brush and an associated slip ring, wherein the grooved brush is made of brass. The associated slip ring is, in particular, a smooth steel ring. In these embodiments, a sliding contact at the positive terminal is formed, for example, by a porous bronze brush and a smooth slip ring.

[0024] Optionally, a sliding contact at the negative terminal is formed by a grooved brass brush and a WoCu ring, i.e., a ring made of a material containing tungsten and copper, as the corresponding slip ring. Regarding materials containing tungsten and copper intended for use in electrotechnical devices, reference is made to DD 12078 A1 as an example. In the present case, a sliding contact at the positive terminal can be formed, in particular, by a grooved WoCu brush and a smooth slip ring.

[0025] All sliding contacts can be oil-lubricated, with at least one channel for lubricant distribution being formed in a housing in which the sliding brushes are mounted. The lubricant is directed to the sliding contacts and also dissipates heat, thus also acting as a coolant. P240584 DE

[0026] - 5 -

[0027] Several embodiments of the invention (Figs. 5 to 8) and a comparative example (Figs. 1 to 4) for illustrative purposes are explained in more detail below with reference to a drawing. These figures show, in some cases schematically:

[0028] Fig. 1 shows an unclaimed example of a brush module of an electric machine in perspective view.

[0029] Fig. 2 shows a housing component of the brush module according to Fig. 1 ,

[0030] Fig. 3 shows a slip ring of the brush module according to Fig. 1 ,

[0031] Fig. 4 Components of the brush module according to Fig. 1 in a cutaway perspective view,

[0032] Fig. 5 shows a pairing of a grinding brush and a slip ring intended for the negative terminal of an electric machine as a first embodiment,

[0033] Fig. 6 shows a pairing of a grinding brush and a slip ring intended for the positive pole of the electric machine according to Fig. 5,

[0034] Fig. 7 shows a pairing of a grinding brush and a slip ring intended for the negative pole of another electrical machine as a second embodiment,

[0035] Fig. 6 shows a pairing of a brush and a slip ring intended for the positive terminal of the electric machine according to Fig. 7. P240584 DE

[0036] - 6 -

[0037] Unless otherwise stated, the following explanations refer to both exemplary embodiments as well as to the unclaimed comparative example. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0038] A brush module, designated as a whole by reference numeral 1, is intended for use in an electric machine, in this case a traction motor of an electrically powered vehicle. The electric motor, i.e., the traction motor, which comprises the brush module 1, is designed as a separately excited synchronous motor. Alternatively, the brush module 1 can be used in a stationary electric machine.

[0039] The brush module 1 comprises a total of six sliding brushes 2, which are also referred to simply as brushes, and are designed to contact a slip ring 14, which is rigidly connected to a shaft of the electric motor's rotor. The slip ring 14 comprises a current transmission section 15, which is also referred to as the slip ring in the narrower sense, and a mounting section 16 held on the electric motor shaft.

[0040] A first group of three brushes 2 is arranged on one side of a carrier plate 3 of the brush module 1. The carrier plate 3 is part of a plastic housing 7 of the brush module 1. Covers of the housing 7 are not shown in the figures. A second group of three brushes 2 is arranged on the opposite side of the carrier plate 3. The brushes 2 are each mounted in a linear guide 4 and are spring-loaded by springs 5. In these cases, the brushes 2 are metal brushes. In all cases, the sliding contacts at the negative terminal differ from those at the positive terminal to minimize wear. All sliding contacts through which the rotor of the electric motor is energized are lubricated with oil. The brush module 1 therefore represents a wet current transmission system. For the oil supply, P240584 DE

[0041] - 7 - which also serves as a coolant, oil channels 17 are provided which supply lubricants specifically to the individual sliding contacts.

[0042] Each group of three brushes 2 is located on a pole plate 6. Sandwiched between the two pole plates 6 is a plate section 8 of the carrier plate 3. The pole plates 6 and the plate section 8 lie in planes to which the central axis of the electric motor's rotor forms a surface normal. By definition, the rotor's central axis is aligned in the longitudinal or axial direction of the brush module 1. At the edge of the plate section 8, an edge section 9, also part of the housing 7, is formed, which projects beyond the plate section 8 and both pole plates 6 in the axial direction of the brush module 1.

[0043] Overall, the brush module 1, viewed in the longitudinal direction of the electric motor shaft, has a modified triangular shape, with the three sides of the approximately triangular support plate 3 being defined by concave-convex-concave curved regions of the edge section 9. A mounting contour 10 is formed between each pair of these three curved regions, in which a screw 11 is located. A central opening 12, designed to receive the slip ring 14, is located in the support plate 3. The central axis of the electric motor shaft is identical to the central axis of the opening 12. The brushes 2 are radially displaceable along the shaft and thus also along the brush module 1, and are arranged at angular intervals of 120° around the shaft. Electrical leads connected to the brushes 2 are generally designated 13.

[0044] In the comparative example according to Figures 1 to 4, all surfaces of the grinding brushes 2 that contact the slip ring 14 are smooth, with a curvature adapted to the dimensions of the current transmission section 15. Regarding the materials from which the grinding brushes 2 are made, there are differences in the comparative example according to Figures 1 to 4, as well as in the exemplary embodiments, between the brushes 2 arranged at the negative pole and the brushes 2 arranged at the positive pole. In all cases P240584 DE

[0045] - 8 - the grinding brushes 2 arranged at the positive pole are more wear-resistant than the grinding brushes 2 arranged at the negative pole, without considering electrical and electrochemical effects. The pole-dependent material selection results in an overall long service life of the sliding contacts formed by the brushes 2 and slip rings 14, while simultaneously ensuring reliable electrical contact.

[0046] The material pairings shown in Figures 5 and 6, as well as those shown in Figures 7 and 8, are suitable for use in the brush module 1, which has the overall shape shown in Figures 1 to 4. In particular, the grinding brushes 2 have a cuboid shape in each of these cases. Any wear on the brushes 2 is compensated for by the feed of the brushes 2 effected by the springs 5.

[0047] As shown in Figure 5, the grinding brush, designated 18 in this case, is a grooved brush, specifically a brass brush. The grinding brush 18, located at the negative terminal of the brush module 1, contacts a slip ring 14, which in this case is a smooth steel ring 19.

[0048] The brush module 1, to which the sliding contact according to Figure 5 belongs, further comprises a sliding contact formed at the positive pole, illustrated in Figure 6, which is formed on the one hand by a sliding brush 20, which is a porous bronze brush, and on the other hand by a steel ring 19. Regarding the external dimensions of the various sliding brushes 18, 20, there are not necessarily differences between the arrangement according to Figure 5 and the arrangement according to Figure 6.

[0049] In the embodiment shown in Figures 7 and 8, a grooved grinding brush 18, made of brass, is used at the negative terminal, as in the embodiment shown in Figures 5 and 6. The brass brush 18 is combined with a WoCu ring 21 as the grinding, current-transmitting component. P240584 DE

[0050] - 9 -

[0051] The sliding contact at the positive pole, belonging to the same brush module 1 as the arrangement according to Figure 7, is formed by a grooved WoCu brush 22 and a smooth steel ring 19. Thus, in this case, each of the sliding contacts has a component 21, 22 formed from a tungsten-copper alloy.

[0052] P240584 DE

[0053] - 10 -

[0054] List of reference signs

[0055] 1 brush module

[0056] 2 grinding brushes, brush

[0057] 3 Carrier plate

[0058] 4 linear guides

[0059] 5 springs

[0060] 6 pole plate

[0061] 7 cases

[0062] 8 plate section

[0063] 9. Marginal section

[0064] 10 Mounting contour

[0065] 11 screw

[0066] 12 Opening

[0067] 13 Management

[0068] 14 Slip ring

[0069] 15 Power transmission section

[0070] 16 Fastening section

[0071] 17 Oil channel

[0072] 18 Grooved grinding brushes

[0073] 19 steel rings

[0074] 20 porous grinding brushes

[0075] 21 WoCu-Ring

[0076] 22 WoCu brush

Claims

P240584 DE - 11 - Patent claims 1. Sliding contact arrangement, composed of several sliding contacts, each of which is formed from a slip ring (14, 19, 21) and a sliding brush (2, 18, 10, 22), wherein the different sliding contacts are designed differently depending on the polarity, characterized in that a sliding contact at the negative pole is formed by a grooved sliding brush (18), namely a brass brush, and an associated slip ring (19, 21).

2. Sliding contact arrangement according to claim 1, characterized in that a smooth steel ring is provided as the associated slip ring (19).

3. Sliding contact arrangement according to claim 1 or 2, characterized in that a sliding contact at the positive pole is formed by a porous bronze brush (20) and a smooth slip ring (19).

4. Sliding contact arrangement according to claim 1, characterized in that a sliding contact at the negative pole is formed by a grooved brass brush (18) and a WoCu ring (21) as the associated slip ring.

5. Sliding contact arrangement according to claim 4, characterized in that a sliding contact at the positive pole is formed by a grooved WoCu brush (22) and a smooth slip ring (19).

6. Brush module (1 ) of a separately excited electric machine, comprising a sliding contact arrangement according to claim 1.

7. Brush module (1 ) according to claim 6, characterized in that all sliding contacts are oil-lubricated, wherein at least one oil channel (17) for lubricant distribution is formed in a housing (7) in which the sliding brushes (2, 18, 10, 22) are mounted.

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