Earthing device for an electric machine and method of electrically contacting a rotating shaft

Abstract

The invention relates to an earthing device (1) for an electric machine (10), in particular an electric motor, comprising an annular carrier element (2) which is constructed from two mutually rotatable ring elements (8, 9) concentrically nested one inside the other and is designed to surround a shaft (6) of the electric machine (10), and a flexible, electrically conductive discharge section (7), one end of which is connected to the first ring element (8, 9) and the other end of which is connected to the second ring element (9, 8).

Description

[0001] Earthing device for an electric machine and method for electrically contacting a rotating shaft

[0002] The invention relates to a grounding device for an electrical machine, i.e., an electric motor or a generator. Furthermore, the invention relates to a method for electrically contacting a rotating shaft, in particular a shaft of an electric machine.

[0003] DE 10 2022 202 004 A1 discloses a grounding brush arrangement for grounding the shaft of an electric motor. The grounding brush arrangement comprises a grounding brush and a brush mounting plate which holds the brush. The brush includes a carrier and several electrically conductive individual fibers which are fixed in the carrier.

[0004] Further earthing brush arrangements for electrical machines can be found, for example, in documents DE 102023 200 385 A1 and DE 10 2023 200 386 A1.

[0005] The invention is based on the objective of providing grounding devices and methods for electrical machines that are further developed compared to the aforementioned prior art, robust and simply constructed, and offer an adjustment option.

[0006] This problem is solved according to the invention by an earthing device for use in an electric machine, comprising the features of claim 1. Likewise, the problem is solved by a method for electrically contacting a rotating shaft, as designed according to claim 10. The embodiments and advantages of the invention explained below in connection with the contacting method also apply mutatis mutandis to the devices, i.e., the earthing device and the electric machine equipped therewith, and vice versa. The earthing device according to the application comprises a multi-part, overall ring-shaped support element, which is constructed from two concentrically nested, rotatable ring elements.The support element is designed to surround a shaft of the electric machine. Furthermore, the support element comprises a flexible, electrically conductive discharge cable, one end of which is connected to the first ring element and the other end of which is connected to the second ring element. Electrical charges can be dissipated from the shaft via the discharge cable and at least one of the ring elements. It is also possible to extend the discharge cable beyond the ring elements and use it as a conductor for grounding the shaft.

[0007] In any case, a preload between the drain string and the shaft can be adjusted by displacing one end of the drain string by rotating one of the two ring elements on the circumference of the support element and then fixing it in place. The rotatable ring element can be either the outer or the inner ring element. In both cases, the outer ring element can form at least one axial stop relative to the inner ring element.

[0008] Screw connections, which can also serve as electrically conductive connections, are suitable for attaching the non-rotating ring element to the housing of the electric machine. The ring element can be connected to the grounded housing either directly or via intermediate elements, such as metal clamps, sleeves, or other adapters. A friction-fit, detachable connection between the ring element of the grounding device and the housing is also conceivable. If a press fit is formed between the ring element and the housing, this fit can include a stop geometry that determines the axial position of the ring element within the housing. In cases where a metallurgical connection, particularly in the form of a weld, solder, or adhesive bond, is provided between the ring element and the housing, this connection can also be used for dissipating electrical charges.In the latter case, an electrically conductive adhesive must be used. Optionally, an additional electrically conductive connection can be made via a separate element, in particular a cable.

[0009] According to one possible embodiment of the grounding device, the ring elements interact with each other in the manner of a bayonet fitting, wherein at least one radially outwardly projecting extension of the inner ring element, in particular two opposing extensions in the manner of wings, is guided in at least one slot-shaped recess extending tangentially in the outer ring element. By guiding the inner ring element in slots of the outer ring element, any axial displacement of the inner ring element is prevented, apart from any possible play.

[0010] Axial stops in both directions, which at least largely prevent any axial displacement of the inner ring element, can also be provided in embodiments in which the outer ring element or each ring element is designed as a sheet metal part. In this case, for example, a ring-shaped circumferential or only partially formed edge region of the outer ring element is crimped inwards, so that the inner ring element is irrevocably positioned between the crimped region of the outer ring element and a base of the same ring element opposite this region.

[0011] In the embodiment with an outer ring element made of sheet metal, in the embodiment of the grounding device with bayonet fitting, and in numerous other embodiments, the two ring elements can have different axial extensions. In particular, the axial thickness of the outer ring element is greater than the thickness of the inner ring element. The outer ring element can have a recess on its circumference, through which a mounting point on the inner ring element, to which one of the two ends of the grounding cable can be fixed, is exposed. The recess is realized, for example, by the outer ring element having a pot-like base shape, whereby the cylindrical rim of the ring element is only formed in segments, so that a recess is formed between each individual segment.The second end of the grounding cable can be fixed to a mounting point on the outer ring element, which is offset from the inner ring element in the axial direction of both ring elements and thus of the entire grounding device. This means that the grounding cable is wrapped around the shaft to be grounded in a manner similar to a screw thread. The grounding cable thus contacts a section of the shaft whose axial dimension is at least slightly greater than the thickness of the grounding cable.

[0012] A possible further development of the grounding device involves the ring elements being spring-loaded and rotatable relative to each other. For example, a spring-loaded tongue can be attached to or molded onto one of the ring elements, engaging with a detent contour of the other ring element. Similarly, variants are possible in which a spring-loaded pin or ball engages with a wave-shaped detent contour.

[0013] The patented method for electrically contacting a rotating shaft provides that a flexible, electrically conductive conductor, connected to the first ring element on one side and the second ring element on the other, is pre-tensioned by a relative rotation between two ring elements, which together form a support element surrounding a shaft to be contacted, in particular to be grounded, while the shaft is in contact with the conductor. The conductor is preferably made of a metallic material. It is also possible to manufacture the conductor as a composite component from different materials that differ in their mechanical and electrical properties.

[0014] In various configurations, the grounding device can be integrated into the electric machine independently of the bearing of the shaft to be grounded. This spatial separation of the bearing and grounding functions allows conventional machine designs to be easily supplemented with the device for grounding the shaft, in particular the motor shaft of an electric motor.

[0015] Several embodiments of the invention are explained in more detail below with reference to a drawing. These drawings show, in some cases simplified form:

[0016] Fig. 1 shows a first embodiment of an earthing device for an electric machine,

[0017] Fig. 2 Details of the fastening of an annular component of a support element of the grounding device according to Fig. 1 to a housing of the electric machine,

[0018] Fig. 3 shows an earthing device with modified fastening means compared to the embodiment according to Figures 1 and 2, in a view analogous to Fig. 1.

[0019] Figs. 4 and 5 show further variants of the fastening of a ring-shaped component of a support element of an earthing device to a housing of an electrical machine.

[0020] Fig. 6 shows a sectional view of two concentric, rotatable, and relative-to-each-other-fixable ring-shaped components of a support element of an earthing device.

[0021] Fig. 7 shows a further sectional view of a detail of the grounding device according to Fig. 6, Figs. 8 and 9 show an arrangement of two nested ring elements of a grounding device that are rotatable at least to a limited extent relative to each other, wherein the outer of the two ring elements has a segmented edge.

[0022] Fig. 10, 11 shows an earthing device comprising two ring elements of a support element which can be rotated relative to each other within a defined angular range.

[0023] Fig. 12 shows an earthing device with two ring elements which interact with each other in the manner of a bayonet fitting,

[0024] Fig. 13 shows the locking interaction of two ring elements of an earthing device for an electric machine.

[0025] Fig. 14 shows two ring elements of an earthing device, which are secured against each other in both axial directions.

[0026] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0027] An earthing device, designated by reference numeral 1, is intended for use in an electric machine 10, in this case an electric motor. The earthing device 1 is installed in the electric motor 10 independently of any bearings and therefore constitutes a stand-alone shunt element. An annular support element 2 of the earthing device 1 defines an interior space 15, which is penetrated by a shaft 6 of the electric machine 10, i.e., by the motor shaft of the electric motor 10. The outer circumferential surface of the support element 2, which is at least partially cylindrical, is designated 16. In all embodiments, the support element 2 is composed of multiple parts, namely an inner ring element 8 and an outer ring element 9. Mounting clamps 3 are suitable, among other things, for attaching one of the ring elements 8, 9 to the housing of the electric motor 10, designated 5.Screws which hold the support element 2 to the housing 5 are designated 4.

[0028] A grounding conductor 7 is provided for the shaft 6, the ends of which are attached to the inner ring element 8 on one side and to the outer ring element 9 on the other. The flexible grounding conductor 7 contacts the shaft 6 with an adjustable preload, whereby the ring elements 8 and 9 are rotatable relative to each other for this purpose. The grounding conductor 7 is specifically designed as a steel cable.

[0029] In the embodiment shown in Figures 1 and 2, the outer ring element 9 is attached to the housing 5 of the electric motor 10. The inner ring element 8 can be fixed by means not shown, in particular by at least one locking screw. It is also possible to generate a torque by spring loading the inner ring element 8, which ensures automatic readjustment of the lead screw 7, so that a preload of the lead screw bearing against the shaft 6 is maintained that is largely independent of the operating conditions and any wear. This also applies to the embodiment shown in Figure 3, in which the inner ring element 8 is fixedly connected to the housing 5 instead of the outer ring element 9.

[0030] Regarding the attachment of one of the ring elements 8, 9 to the housing 5, the variant according to Figure 4 corresponds to the embodiment according to Figures 1 and 2, and the variant according to Figure 5 corresponds to the embodiment according to Figure 3. In contrast to the embodiments according to Figures 1 to 3, in the cases of Figures 4 and 5, one of the ring elements 8, 9 is directly screwed to the housing 5. In each embodiment, the inner ring element 8 is supported on the outer ring element 9 in at least one of two possible axial directions. A first axial stop surface of the outer ring element 9 is designated 11. To clamp the inner ring element 8, a fixing screw can be used, which is screwed into an opening 13 in the outer ring element 9 that has an internal thread.The opening 13 is located, for example, as shown in Figure 6, in a region of the outer ring element 9 where its outer circumferential surface 16 has its maximum diameter. In circumferential sections of the outer ring element 9 where there is no opening 13, a recess 17 on the outer circumference can be present, as shown in Figure 1. The recess 17 represents a material saving; it can also be used as a contour for aligning the ring element 9.

[0031] Such an alignment function, concerning the angular position of the non-rotatable ring element 8, 9, can also be implemented by recesses 12, which, in the embodiment shown in Figures 8 and 9, are located on the circumference of the outer ring element 9. One of the recesses 12 provides an opening 14, which is located in the inner ring element 8 and serves as a mounting point for the flexible, electrically conductive conductor 7. A second mounting point for the conductor 7 exists in the form of an opening 18, which is located in the outer ring element 9.

[0032] The embodiment shown in Figures 10 and 11 is modified compared to the embodiment shown in Figures 8 and 9 in that the inner ring element 8 has two outwardly directed wings 19, i.e., projections, which each engage in a recess 12 on the circumference of the outer ring element 9. The wings 19 are less extensive in the circumferential direction of the ring elements 8, 9 than the recesses 12, so that a limited pivoting mobility of the inner ring element 8 is maintained.

[0033] Two wings 19 of the inner ring element 8 are also present in the embodiment shown in Figure 12, whereby in this case the two ring elements 8, 9 interact in the manner of a bayonet fitting 20. Here, the wings 19 each engage in a slot 21 formed in the outer ring element 9, which represents a contour of the bayonet fitting 20.

[0034] A modified version of the guide for the wing 19 in a slot 21 of the outer ring element 9 is illustrated in Figure 13. Here, a ball 23 is guided in a recess formed in the wing 19, which is designed as a blind hole and aligned axially with the ring elements 8, 9. The ball 23 projects axially beyond the contour of the wing 19. A spring 24, specifically a compression spring designed as a helical spring, is inserted into the aforementioned recess to provide spring tension to the ball 23, which contacts a wall of the slot 21 formed by the outer ring element 9. The side of the wing 19 facing away from the ball 23, which is referred to as the upper side without loss of generality, is rounded and engages in a detent contour 22, which also forms a wall of the slot 21.An additional mechanism for determining the position of the inner ring element 8 relative to the outer ring element 9 is therefore not absolutely necessary in the case of Figure 13.

[0035] The embodiment shown in Figure 14 shares similarities with the embodiment shown in Figures 12 and 13 in that the inner ring element 8 is secured against the outer ring element 9 in both axial directions. In the case of Figure 14, this securing is achieved by a crimp 26 on the outer ring element 9, which is made of sheet metal. The original, uncrimped shape of the outer ring element 9 is indicated by dashed lines in Figure 14. The crimp 26 provides a second stop surface 25, which is opposite the first axial stop surface 11. The crimp 26 can be formed around the entire circumference of the outer ring element 9 or only segmentally, i.e., in the form of individual inwardly folded tabs. (See list of reference symbols.)

[0036] grounding device

[0037] Support element

[0038] Mounting bracket

[0039] screw

[0040] Housing

[0041] Wave

[0042] Drainage strand inner ring element outer ring element

[0043] electric motor, electric machine, first axial stop surface

[0044] Recess on the circumference of the outer ring element

[0045] Opening for fixing screw

[0046] Opening in the inner ring element for the drain line, attachment point

[0047] interior

[0048] External perimeter

[0049] Recess on the outer circumference

[0050] Opening in the outer ring element for the drain line, attachment point

[0051] Wings of the inner ring element

[0052] bayonet fitting

[0053] slot

[0054] Rast contour

[0055] Bullet

[0056] spring second axial stop surface

[0057] crimping

Claims

Patent claims 1. Earthing device (1) for an electric machine (10), comprising an annular support element (2) which is constructed from two concentrically nested, rotatable ring elements (8, 9) and is designed to surround a shaft (6) of the electric machine (10), and a flexible, electrically conductive conductor (7) of which one end is connected to the first ring element (8, 9) and the other end is connected to the second ring element (9, 8).

2. Earthing device (1) according to claim 1, characterized in that the outer ring element (9) is a rotationally fixed element and the inner ring element (8) is designed as a rotatable element.

3. Earthing device (1) according to claim 1, characterized in that the inner ring element (8) is a rotationally fixed element and the outer ring element (9) is designed as a rotatable element.

4. Earthing device (1 ) according to claim 3, characterized in that at least one axial stop (11 , 25) is formed by the outer ring element (9) against the inner ring element (8).

5. Grounding device (1 ) according to claim 4, characterized in that the two ring elements (8, 9) interact with each other in the manner of a bayonet fitting (20), wherein at least one radially outwardly extending extension (19) of the inner ring element (8) is guided in a slot-shaped, tangentially extending recess (21 ) of the outer ring element (9).

6. Earthing device (1 ) according to one of claims 1 to 5, characterized in that the two ring elements (8, 9) extend to different extents in the axial direction.

7. Earthing device (1 ) according to claim 6, characterized in that the outer ring element (9) has a recess (12) on its circumference through which a fastening point (14) located on the inner ring element (8), on which an end of the discharge string (7) can be fixed, is released.

8. Earthing device (1) according to claim 6 or 7, characterized in that a fastening point (18) located on the outer ring element (9) is attached to which fixes the second end of the drain string (7), is offset in the axial direction of the ring elements (8, 9) relative to the inner ring element (8).

9. Earthing device (1 ) according to one of claims 1 to 8, characterized in that the two ring elements (8, 9) are rotatable against each other under spring preload.

10. Method for electrically contacting a rotating shaft (6), wherein a flexible electrically conductive conductor (7), which is connected on one side to the first ring element (8) and on the other side to the second ring element (9), is pre-tensioned by a relative rotation between two ring elements (8, 9) which together form a support element (2) which surrounds the shaft (6), while contacting the shaft (6).

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