Shaft grounding arrangement structure

Abstract

The invention relates to a shaft grounding arrangement (1) having a housing (2) which receives a shaft (3) and a fluid, a grounding ring (4) is associated with the shaft (3), which grounding ring establishes an electrically conductive contact between the shaft (3) and the housing (2), the grounding ring (4) having a disc-shaped contact body (5) which lies on a circumferential surface of the shaft (3) in a lip-shaped manner, a first contact surface (6) is formed by the contact body (5) and a second contact surface (7) is formed by the shaft (3), at least one of the two contact surfaces (6, 7) being provided with a surface structure (8).

Description

Technical Field

[0001] The invention relates to a shaft grounding arrangement having a housing which receives a shaft, wherein a grounding ring is assigned to the shaft and which produces an electrically conductive contact between the shaft and the housing. Background Art

[0002] Such an arrangement is known, for example, from DE 10 2016 010926 A1 and is used for grounding a shaft supported in a housing. In order to improve the electromagnetic compatibility of an apparatus, such as a vehicle, a grounding ring establishes an electrically conductive connection between the shaft and the housing so that electromagnetic waves, in particular high-frequency electromagnetic signals, cannot propagate through the shaft beyond the housing to the outside. Such electromagnetic signals can adversely affect electronic components of the vehicle or electronic devices carried along with the vehicle. Mechanical damage can also occur, in particular at the bearings, due to voltage breakdown.

[0003] However, in previously known shaft grounding arrangements, it is necessary that the grounding ring is not affected by fluids, such as lubricating oil or grease. In previously known systems, there is the risk that the conductive contact between the grounding ring and the shaft will be interrupted by the influence of the fluid, or that the conductive ring, which is slidingly resting on the shaft, will lose its conductive properties. This would increase the electrical resistance of the arrangement and impair its function. Summary of the invention

[0004] The object of the present invention is to provide a shaft grounding arrangement which is robust and ensures reliable electrical contact between the grounding ring and the shaft.

[0005] This object is achieved with the features of claim 1. The dependent claims relate to advantageous embodiments.

[0006] According to the present invention, the shaft grounding arrangement has a housing, which accommodates a shaft and a fluid, wherein a grounding ring is provided for the shaft, which establishes an electrically conductive contact between the shaft and the housing, wherein the grounding ring has a disk-shaped contact body, which rests in a lip-shaped manner on the circumference of the shaft, wherein a first contact surface is formed by the contact body and a second contact surface is formed by the shaft, wherein at least one of the two contact surfaces is provided with a surface structuring portion.

[0007] In the shaft grounding arrangement according to the invention, a fluid is located next to the shaft in the housing, which fluid can be, for example, a lubricating oil or a lubricating grease. Here, the lubricating oil can contact the shaft and also come into contact with the grounding ring. By means of the surface structuring introduced into at least one contact surface, an electrically conductive contact between the shaft and the grounding ring is also ensured in the following case, i.e., the fluid in the housing reaches between the two contact surfaces. An electrically conductive contact between the shaft and the housing is thus also ensured in the following case, i.e., the grounding ring is loaded with fluid. It is thus possible to arrange the grounding ring inside the housing. It is also conceivable that the grounding ring is arranged directly in the housing and is not shielded from the fluid by a sealing ring or the like.

[0008] This design also allows the shaft to be supported in the housing via a ball bearing, wherein a grounding ring is provided for the ball bearing on the side facing the interior of the housing. With this arrangement, the grounding ring conducts the current and electromagnetic signals introduced into the shaft into the housing before they reach the ball bearing. This protects the ball bearing from the effects of voltage breakdown and spark erosion due to circulating currents. This improves running stability and service life and also allows for extended maintenance intervals. Overall, failures of the overall arrangement can be avoided.

[0009] By arranging the grounding ring of the shaft grounding arrangement according to the invention directly in the housing subjected to the fluid, additional dynamic sealing points which encapsulate the grounding ring in conventional grounding systems can be eliminated. This eliminates friction-generating sealing points, which is accompanied by an increase in the efficiency of the system.

[0010] The shaft grounding arrangement according to the invention is particularly suitable for use in vehicles, in particular electric vehicles, where the shaft grounding arrangement can be arranged, for example, in an electric motor or a transmission housing.

[0011] The contact body can have a matrix consisting of a nonwoven fabric. The contact body having a matrix consisting of a nonwoven fabric can be impregnated with PTFE and provided with conductive particles. The conductive material is, for example, silver and / or graphite and can exist in the form of a thread, particles or powder. In principle, highly conductive materials such as copper, nickel, gold or the like can also be envisioned. According to the design, the nonwoven fabric is already conductive, wherein the conductivity can be improved by adding the additive. In this design, the contact body is simple and can be manufactured at low cost and has good conductivity in addition to the sliding properties of low friction and low wear.

[0012] The contact body can be designed as a disk, wherein a recess extending radially inwards is introduced into the outer circumference. It is also conceivable that the recess is oriented in the direction of the main rotational direction. The recess can be designed in the form of a slot.

[0013] According to a first embodiment, the surface structure is introduced into the second contact surface. Correspondingly, the surface structure is introduced into the circumference of the shaft. Advantageously, the surface structure is particularly durable and is subject to only slight wear.

[0014] The surface structured portion can be introduced directly into the shaft. Alternatively, it is conceivable that a sleeve is pushed onto the shaft, wherein the sleeve is electrically conductive and is preferably fastened to the shaft in a press fit. In this design, the surface structured portion can be applied to the sleeve on the outside and the grounding ring is in contact with the sleeve.

[0015] In this case, the surface structuring can have grooves which extend in the circumferential direction. In this case, the grooves can extend in an annular or spiral manner around the shaft.

[0016] It has been shown that the surface structuring ensures that the grounding ring always lies on the shaft and thus produces an electrical contact between the shaft and the housing. If a fluid, such as lubricating oil, reaches the region of the contact surface, the surface structuring causes the fluid to be transported so that it does not remain between the two contact surfaces and thus lifts the grounding ring off the shaft. A corresponding pumping action can be achieved by the surface structuring. The durable transport ensures that the grounding ring always lies on the shaft. Advantageous effects also occur when the surface structuring is also non-directional and has an arbitrary structure, for example produced by roughening or grinding.

[0017] According to a second design, the surface structuring is introduced into the first contact surface. In this design, the surface structuring is correspondingly introduced into the contact body. In this design, the surface structuring can also include grooves, which in this design extend concentrically on the contact surface assigned to the shaft. The grooves can be introduced into the first contact surface in the form of concentric rings, sine waves or in the form of a spiral. In this design, it is advantageous that the surface structuring can be introduced into the contact body particularly simply and inexpensively. This can be done, for example, directly during the molding process of the contact body, which is particularly simple when the contact body is made of a polymer material.

[0018] In particular, however, it is also conceivable that the surface structuring is stamped into the first contact surface. Thus, the surface structuring can also be introduced into the contact surface after the contact body has been shaped.

[0019] According to a third embodiment, the first contact surface and the second contact surface are provided with a surface structuring. This embodiment ensures an electrically conductive contact between the shaft and the housing even under unfavorable conditions, for example in the case of particularly intensive contact with a fluid.

[0020] The contact body can be provided with a spring mechanism which presses the contact body onto the shaft with an elastic prestress. The spring mechanism ensures permanent contact of the grounding ring with the shaft. The spring mechanism can be formed by an annular elastomer lip which surrounds the contact body on the outer circumference. The elastomer lip can be provided with a fluid conveying structure. In particular, it is conceivable that the elastomer lip is provided with a thickening which extends into the gap formed by the recess of the contact body. A particularly good conveying effect is achieved when the elastomer lip is provided with a conveying structure in the region of the thickening.

[0021] The surface structuring introduced into the first contact surface and / or the second contact surface can have a wave-like course when viewed in cross section and be designed, for example, in the form of a sinusoidal wave, a rectangular wave or a trapezoidal wave.

[0022] The contact body can have a recess into which the spring means projects. In this design, it is particularly conceivable that the surface structuring is introduced into the spring means. It is particularly advantageous here that the surface structuring can be manufactured particularly simply.

[0023] In particular, a reliable electrical contact between the contact body and the shaft is produced with a long service life when the height of the surface structuring, i.e. the distance between high points and low points, is between 1 μm and 20 μm. The depth is particularly preferably between 5 μm and 15 μm. The width of the groove-shaped structures of the surface structuring, for example the distance between high points to adjacent high points, is preferably between 50 μm and 200 μm. The width is particularly preferably between 75 μm and 150 μm.

[0024] The grounding ring can be equipped with at least one fluid guiding element. The fluid guiding element is here assigned to the housing or the shaft. Preferably, the fluid guiding element is arranged on the shaft in a non-rotatable manner. In this design, the fluid guiding element acts as a centrifugal ring, and the guiding element fluiddynamically limits the amount of fluid that can enter between the two contact surfaces. According to another advantageous design, a fluid guiding element is arranged on each side of the grounding ring. It is also conceivable that the grounding ring is designed as a box ring and has fluid guiding elements on both sides, and the grounding ring is arranged between the fluid guiding elements. In this design, it is particularly conceivable that the fluid guiding element is arranged on the shaft in a non-rotatable manner, while the grounding ring is fastened to the housing in a non-rotatable manner.

[0025] Another advantageous embodiment provides that the return ring has a bearing structure which is fixedly secured to the shaft in a rotationally fixed manner and has fluid-conducting elements in the form of eccentric surfaces on both end sides. A further bearing body is arranged between the two fluid-conducting elements, which bears a spring mechanism which presses the contact body on the end side against the inner side of the fluid-conducting element. This embodiment is suitable for particularly rugged applications with a high presence of fluid agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Next, one of the above-mentioned designs of the shaft grounding arrangement according to the present invention is shown with the aid of the accompanying drawings. The drawings schematically show:

[0027] Figure 1 Cross-section of the shaft grounding arrangement;

[0028] Figure 2 Details of the grounding ring;

[0029] Figure 3 a grounding ring including a spring body in the form of an elastomeric lip;

[0030] Figure 4 a grounding ring including a fluid directing element;

[0031] Figure 5 As a grounding ring for box-type arrangements;

[0032] Figure 6 A grounding ring comprising a conveying structure introduced into a spring mechanism;

[0033] Figure 7 Details of different designs of the surface structuring. DETAILED DESCRIPTION

[0034] Figure 1 A shaft grounding arrangement 1 is shown, which has a housing 2 which accommodates a shaft 3 and a fluid 11. The shaft grounding arrangement 1 is a component of an electric motor or a transmission of an electric vehicle. The fluid 11 is a lubricating oil in this case.

[0035] A grounding ring 4 is assigned to the shaft 3, which establishes an electrically conductive contact between the shaft 3 and the housing 2. The grounding ring 4 has a disk-shaped contact body 5, which rests in a lip-shaped manner on the circumference of the shaft 3. In this case, a first contact surface 6 is formed by the contact body 5 and a second contact surface 7 is formed by the shaft 3.

[0036] The contact body 5 has a base body made of a nonwoven fabric, which is impregnated with PTFE and made of an electrically conductive material. In order to improve the electrical conductivity, an electrically conductive material is introduced into the nonwoven fabric. The electrically conductive material has silver particles according to a first design and graphite powder according to a second design. The third design has a combination of silver particles and graphite powder. The contact body 5 is fixed to a support body 12 made of an electrically conductive material, wherein the support body 12 is designed in two parts and the contact body 5 is fixed by means of a clamping connection. The support body 12 is fixed to the housing 2.

[0037] In the present design, the surface structure 8 is introduced into the second contact surface 7. The surface structure 8 has grooves, which are formed in a trapezoidal shape when viewed in section. The high points and low points (from peak to valley) of the surface structure 8 are at a distance of 10 μm from each other. The high points adjacent to each other are at a distance of 100 μm from each other.

[0038] The groove is introduced into the shaft 3 in a threaded manner. According to an alternative embodiment, the groove is introduced into the shaft 3 in an annular manner.

[0039] The contact body 5 is provided with a spring mechanism 9 which presses the contact body 5 onto the shaft 3 with elastic prestress. In the present design, the spring mechanism 9 has a plurality of metal tongues which are evenly distributed around the circumference and press the contact body 5 onto the shaft 3 in the region of the first contact surface 6.

[0040] Figure 2 Shown in Figure 1 . In this design, the surface structure 8 is introduced into the first contact surface 6 of the contact body 5. This is done by embossing in this design. The surface structure 8 has a plurality of concentrically arranged circles with protrusions and recesses. Alternatively, the surface structure 8 can also be formed in a spiral shape.

[0041] According to a third embodiment, both the contact surface 7 of the shaft 3 and the contact surface 6 of the grounding ring 4 are provided with a surface structuring 6. The surface structuring 6 can be introduced directly into the surface of the shaft 3. Alternatively, a sleeve can be pushed onto the shaft 3, wherein the sleeve is electrically conductive and wherein the surface structuring 6 is introduced into the sleeve on the outside.

[0042] Figure 3 Shown in Figure 1 3. A third design of the grounding ring 4 is shown in FIG. In this design, the spring means 9 is formed by an elastomer lip, which bears on the outside against the contact body 5. The radial compression of the spring means 9 is reinforced by an annular coil spring, which is arranged on the outside on the elastomer lip.

[0043] Figure 4 Shown in Figure 1A further development of the shaft grounding arrangement 1 shown in FIG. 1 is shown in FIG. 2 . In this design, the two end faces of the grounding ring are provided with disk-shaped fluid guiding elements 10 . The two fluid guiding elements 10 are fastened on the shaft 3 in a rotationally fixed manner.

[0044] Figure 5 A shaft grounding arrangement 1 in the form of a cassette seal is shown. In this design, the grounding ring 4 has a bearing structure which is fixedly secured to the shaft 3 in a rotationally fixed manner and has fluid-conducting elements 10 in the form of eccentric surfaces on both end sides. Between the two fluid-conducting elements 10, a further bearing body 14 is arranged which supports a spring mechanism 9 which presses the contact body 5 on the inner side of the fluid-conducting element 10 at the end side.

[0045] Figure 6 Shown in Figure 3 . In the present design, the surface structured portion 6 is introduced into the spring means 9. The contact body 5 has a plurality of recesses into which the spring means 9 protrude, wherein the spring means 9 has thickenings in these regions. The surface structured portion 6 of the spring means 9 is arranged in the region of the recesses.

[0046] Figure 7 Different designs of the surface structure 6 are shown.

Claims

1. A shaft grounding arrangement (1) having a housing (2) which receives a shaft (3) and a fluid, wherein: The shaft (3) is provided with a grounding ring (4), which establishes an electrically conductive contact between the shaft (3) and the housing (2), wherein the grounding ring (4) has a disk-shaped contact body (5) which rests in a lip-shaped manner on the circumference of the shaft (3), wherein a first contact surface (6) is formed by the contact body (5) and a second contact surface (7) is formed by the shaft (3), wherein at least one of the two contact surfaces (6, 7) is provided with a surface structured portion (8).

2. The shaft grounding arrangement according to claim 1, characterized in that: The contact body (5) has a base body composed of a nonwoven fabric.

3. The shaft grounding arrangement according to claim 1 or 2, characterized in that: The surface structuring (8) is introduced into the second contact surface (7).

4. The shaft grounding arrangement according to any one of claims 1 to 3, characterized in that The surface structured portion (8) has grooves which extend in the circumferential direction.

5. The shaft grounding arrangement according to claim 4, characterized in that: The groove is designed in an annular or spiral manner.

6. The shaft grounding arrangement according to any one of claims 1 to 4, characterized in that The surface structured portion (8) has no directionality.

7. The shaft grounding arrangement according to any one of claims 1 to 6, characterized in that The surface structuring (8) is introduced into the first contact surface (6).

8. The shaft grounding arrangement according to claim 7, characterized in that: The surface structure (8) is embossed into the first contact surface (6).

9. The shaft grounding arrangement according to any one of claims 1 to 8, characterized in that A spring mechanism (9) is assigned to the contact body (5), which presses the contact body (5) against the shaft (3) with elastic prestress.

10. The shaft grounding arrangement according to claim 9, characterized in that: The surface structuring (8) is introduced into the spring mechanism (9).

11. The shaft grounding arrangement according to any one of claims 1 to 10, characterized in that A fluid guiding element (10) is assigned to the grounding ring (4).

12. The shaft grounding arrangement according to claim 11, characterized in that Two fluid-conducting elements (10) are provided, wherein one fluid-conducting element (10) is respectively assigned to an end face of the contact body (5).

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