Shaft grounding device

Abstract

A shaft grounding device (1) comprising a housing (2), the housing (2) containing a shaft (3) and a fluid, the shaft (3) being assigned a grounding ring (4) for establishing a conductive contact between the shaft (3) and the housing (2), the grounding ring (4) having a disk-shaped contact body (5) mounted in a lip-like manner on the circumferential surface of the shaft (3), a first contact surface (6) being formed from the contact body (5) and a second contact surface (7) being formed from the shaft (3), at least one of the contact surfaces (6, 7) being provided with a surface patterning portion (8).

Description

[Technical Field]

[0001] The present invention relates to a shaft grounding device comprising a housing which accommodates a shaft, the shaft being assigned a grounding ring which brings about an electrically conductive contact between the shaft and the housing. [Background technology]

[0002] Such a device is known, for example, from German Patent Application No. DE 10 2016 010 926 A1, and is used to ground a shaft mounted in a housing. To improve the electromagnetic compatibility of, for example, a vehicle's mechanisms, a grounding ring forms a conductive connection between the shaft and the housing, preventing electromagnetic waves, especially high-frequency electromagnetic signals, from propagating outward through the shaft and the housing. Such electromagnetic signals can also adversely affect the vehicle's electronic components or electronic equipment carried with the vehicle. Voltage flashovers can also cause mechanical damage, especially to bearings.

[0003] However, in this case, the previously known shaft grounding devices require that the grounding ring is not affected by fluids, such as lubricating oil or lubricating grease. In the previously known systems, there is a 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 mounted on the shaft in a sliding manner, will lose its conductive properties. This increases the electrical resistance of the device and impairs its function. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem underlying the present invention is to provide a shaft grounding arrangement that is robust and ensures reliable electrical contact between the ground ring and the shaft. [Means for solving the problem]

[0005] This problem is solved by the features of claim 1. Advantageous configurations are set out in the dependent claims.

[0006] The shaft grounding device of the present invention comprises a housing, which accommodates a shaft and a fluid, and which is assigned a grounding ring that establishes a conductive contact between the shaft and the housing, and which has a disk-shaped contact body mounted in a lip-like manner on the circumferential surface of the shaft, with a first contact surface formed from the contact body and a second contact surface formed from the shaft, and at least one of the two contact surfaces has a surface patterning portion.

[0007] In the shaft grounding device according to the present invention, a fluid is present in the housing next to the shaft. This fluid may be, for example, a lubricating oil or lubricating grease. In this case, the lubricating oil may be in contact with both the shaft and the grounding ring. A surface patterning on at least one of the contact surfaces ensures conductive contact between the shaft and the grounding ring even if fluid present in the housing reaches between the two contact surfaces. This ensures conductive contact between the shaft and the housing even when fluid acts on the grounding ring. This allows the grounding ring to be located inside the housing. Furthermore, the grounding ring can be located directly in the housing, without being shielded from the fluid by a sealing ring or the like.

[0008] This configuration also allows the shaft to be supported in the housing via ball bearings, with a grounding ring assigned to the ball bearings on the side facing the housing interior. This arrangement allows the grounding ring to guide current and electromagnetic signals supplied to the shaft into the housing before they reach the ball bearings. This protects the ball bearings from the effects of voltage flashovers and spark erosion caused by circulating currents. This improves smooth operation and service life, and also allows for longer maintenance intervals. Overall, failures of the entire device can be avoided.

[0009] The grounding ring of the shaft grounding device of the present invention is located directly within the fluid-fed housing, eliminating the additional dynamic sealing points that encapsulate the grounding ring in conventional grounding systems, thereby eliminating friction-generating sealing points and thereby increasing the efficiency of the system.

[0010] The shaft grounding device according to the invention is particularly suitable for use in vehicles, in particular electric vehicles, in which the shaft grounding device may be arranged, for example, in the electric motor housing or in the transmission housing.

[0011] The contact piece may have a nonwoven substrate. In this case, the contact piece with the nonwoven substrate may be impregnated with PTFE and provided with conductive particles. The conductive material may be, for example, silver and / or graphite, and may be applied in the form of threads, particles, or powder. In principle, highly conductive materials, such as copper, nickel, gold, or the like, are also possible. Depending on the configuration, the nonwoven fabric may already be conductive, and in this case, the conductivity can be improved by adding the aforementioned additives. In this configuration, the contact piece can be produced simply and inexpensively, and has good electrical conductivity in addition to low-friction, low-wear sliding properties.

[0012] The contact body may be formed as a disk, the outer periphery of which is provided with radially inwardly extending notches, which may be oriented in the main direction of rotation. The notches may be in the form of slots.

[0013] According to a first embodiment, a surface pattern is machined on the second contact surface, and correspondingly, on the circumferential surface of the shaft, whereby the surface pattern is advantageously particularly durable and only suffers from minimal wear.

[0014] The surface patterning may be directly machined onto the shaft. Alternatively, the shaft may be fitted with a sleeve, in which case the sleeve is conductive and preferably press-fitted onto the shaft. In this configuration, the surface patterning may be applied to the outer surface of the sleeve, and the ground ring is in contact with the sleeve.

[0015] In this case, the surface patterning may comprise a circumferentially extending groove, which may extend circularly or spirally around the axis.

[0016] It has been found that the surface patterning ensures that the grounding ring is always in contact with the shaft, thereby establishing electrical contact between the shaft and the housing. When a fluid, such as a lubricant, reaches the area of the contact surfaces, the surface patterning causes the fluid to be transported so that the fluid does not remain between the contact surfaces and thus does not move the grounding ring away from the shaft. Accordingly, the surface patterning can achieve a pumping effect. This constant transport ensures that the grounding ring is always in contact with the shaft. It is also advantageous if the surface patterning is non-directional and has any pattern, such as that produced by roughening or grinding.

[0017] According to a second embodiment, a surface pattern is machined onto the first contact surface. In this embodiment, the surface pattern is machined onto the contact body accordingly. In this embodiment, the surface pattern can also have a groove extending concentrically on the contact surface that is assigned to the axis. The groove can be machined onto the first contact surface in the form of concentric rings, sine waves, or spirals. This embodiment has the advantage that the surface pattern can be machined onto the contact body particularly easily and inexpensively. This can be done, for example, during the shaping process of the contact body, which is particularly easy if the contact body is made of a polymer material.

[0018] However, it is also possible, in particular, for the surface patterning to be indented into the first contact surface, so that the surface patterning can be applied to the contact surface even after it has been shaped into the contact body.

[0019] According to a third aspect, the first and second contact surfaces are provided with a surface patterning, which ensures a conductive contact between the shaft and the housing even under unfavorable conditions, such as during particularly vigorous contact with fluids.

[0020] The contact body may be assigned a spring means that presses the contact body against the shaft with an elastic preload. This spring means ensures continuous contact of the grounding ring with the shaft. In this case, the spring means may be formed by an annular elastomer lip that surrounds the contact body on its outer periphery. This elastomer lip may have a fluid-conveying pattern. In particular, the elastomer lip may have a thickened portion that extends into the intermediate chamber of the contact body formed by the notch. If the elastomer lip has a convection pattern in the region of the thickened portion, a particularly good convection effect is achieved.

[0021] The surface patterning on the first contact surface and / or the second contact surface may form a wave-shaped transition when viewed in cross section, for example in the form of a sine wave, a square wave or a trapezoidal wave.

[0022] The contact body may have a recess into which the spring means protrudes. In this configuration, it is possible, in particular, for the surface pattern to be processed into the spring means. In this case, it is particularly advantageous that the surface pattern can be particularly easily produced.

[0023] A long lifespan as well as reliable electrical contact between the contact body and the shaft can be achieved particularly when the height of the surface patterning portion, i.e., the distance between the peak and the valley, is 1 μm to 20 μm. The depth is particularly preferably 5 μm to 15 μm. The width of the groove-like pattern of the surface patterning portion, for example, the distance between one peak and the adjacent peak, is preferably 50 μm to 200 μm. The width is particularly preferably 75 μm to 150 μm.

[0024] At least one fluid guide element may be assigned to the grounding ring. In this case, this fluid guide element is assigned to the housing or the shaft. Preferably, the fluid guide element is arranged non-rotatably on the shaft. In this configuration, the fluid guide element functions as a centrifugal ring that hydrodynamically limits the amount of fluid that can penetrate between the two contact surfaces. According to a further advantageous configuration, one fluid guide element is arranged on each side of the grounding ring. It is also possible for the grounding ring to be configured as a cassette ring and to have fluid guide elements on both sides, with one grounding ring arranged between the fluid guide elements. In this configuration, it is particularly possible for the fluid guide elements to be arranged non-rotatably on the shaft, while the grounding ring is attached non-rotatably to the housing.

[0025] A further advantageous configuration specifies that the grounding ring has a support structure that is fixed to the shaft and has fluid guide elements in the form of centrifugal surfaces on both end faces. Between the two fluid guide elements, a further support is arranged that supports spring means that press the contact body against the inner surface of one of the fluid guide elements on the end face. This configuration is particularly suitable for robust applications with high fluid medium consumption.

[0026] One of the configurations of the shaft grounding device according to the present invention will be shown below with reference to the drawings. [Brief explanation of the drawings]

[0027] [Figure 1]FIG. 2 is a schematic cross-sectional view of a shaft grounding device. [Figure 2] FIG. 2 is a schematic detail view of a ground ring. [Figure 3] FIG. 1 is a schematic diagram of a ground ring with a spring body in the form of an elastomeric lip. [Figure 4] 1 is a schematic diagram of a ground ring with a fluid guide element. [Figure 5] FIG. 1 is a schematic diagram of a ground ring as a cassette device. [Figure 6] 1 is a schematic diagram of a ground ring with a carrier pattern machined into the spring means. [Figure 7] 1A-1C are schematic detailed views of different configurations of surface patterning features. DETAILED DESCRIPTION OF THE INVENTION

[0028] 1 shows a shaft grounding device 1 comprising a housing 2 containing a shaft 3 and a fluid 11. In this case, the shaft grounding device 1 is a component of an electric motor or transmission of an electric vehicle. The fluid 11 is lubricating oil in the illustrated configuration.

[0029] A grounding ring 4 is assigned to the shaft 3, which provides 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 lip-like on the circumferential surface of the shaft 3. A first contact surface 6 is formed from the contact body 5, and a second contact surface 7 is formed from the shaft 3.

[0030] The contact body 5 has a base material made of a nonwoven fabric impregnated with PTFE and made of a conductive material. To improve conductivity, a conductive material is inserted into the nonwoven fabric. In a first configuration, the conductive material contains silver particles, and in a second configuration, it contains graphite powder. In a third configuration, it contains a combination of silver particles and graphite powder. The contact body 5 is fixed to a support 12 made of a conductive material, which in this case is made of two parts and fixes the contact body 5 in place by a clamping connection. The support 12 is fixed to the housing 2.

[0031] In the illustrated configuration, the second contact surface 7 is machined with a surface patterning 8. The surface patterning 8 includes grooves that are trapezoidal in cross section. The peaks and valleys of the surface patterning 8 (peak to valley) are 10 μm apart. Adjacent peaks are 100 μm apart.

[0032] The groove is machined helically on the shaft 3. According to an alternative configuration, the groove is machined annularly on the shaft 3.

[0033] The contact body 5 is assigned a spring means 9 which presses the contact body 5 against the shaft 3 with an elastic preload. In this configuration, the spring means 9 comprises a number of metal tongues which are evenly distributed over the entire circumference and press the contact body 5 against the shaft 3 in the area of the first contact surface 6.

[0034] 2 shows a second configuration of the ground ring 4 shown in FIG. 1. In this configuration, a surface pattern 8 is machined into the first contact surface 6 of the contact body 5, in this case by embossing. In this case, the surface pattern 8 includes a plurality of concentric circles with protrusions and recesses. Alternatively, the surface pattern 8 may be formed in the shape of a spiral.

[0035] According to a third configuration, both the contact surface 7 of the shaft 3 and the contact surface 6 of the ground ring 4 are provided with a surface patterning 6. This surface patterning 6 may be directly machined onto the surface of the shaft 3. Alternatively, the shaft 3 may be fitted with a sleeve, in which case the sleeve is electrically conductive and the surface patterning 6 is machined onto the outer surface of the sleeve.

[0036] Figure 3 shows a third configuration of the grounding ring 4 shown in Figure 1. In this configuration, the spring means 9 is formed by an elastomeric lip that rests against the outer surface of the contact body 5. The radial bias of the spring means 9 is reinforced by an annular helical spring that is disposed on the outer surface of the elastomeric lip.

[0037] Figure 4 shows a refinement of the shaft grounding device 1 shown in Figure 1. In this configuration, a disk-shaped fluid guide element 10 is assigned to each end face of the grounding ring. Both fluid guide elements 10 are mounted on the shaft 3 so that they cannot rotate relative to each other.

[0038] 5 shows a shaft grounding device 1 in the form of a cassette seal. In this configuration, the grounding ring 4 has a support structure which is fixed to the shaft 3 so as to be rotationally fixed relative to it and which has fluid guide elements 10 in the form of centrifugal surfaces on both end faces. Between the two fluid guide elements 10, a further support 14 is arranged which carries a spring means 9 which presses the contact body 5 against the inner surface of one of the fluid guide elements 10 on its end face.

[0039] Figure 6 shows an improved version of the ground ring 4 shown in Figure 3. In this configuration, the surface patterning 6 is machined into spring means 9. The contact body 5 has a number of notches into which the spring means 9 protrude, with the spring means 9 having thickened portions in these areas. The surface patterning 6 of the spring means 9 is arranged in the area of the notches.

[0040] In FIG. 7, different configurations of the surface patterning portion 6 are shown.

Claims

1. 1. A shaft grounding device (1) comprising a housing (2), the housing (2) containing a shaft (3) and a fluid, the shaft (3) being assigned a grounding ring (4) for establishing a conductive contact between the shaft (3) and the housing (2), the grounding ring (4) having a disk-shaped contact body (5) mounted in a lip-like manner on the circumferential surface of the shaft (3), a first contact surface (6) being formed from the contact body (5), and a second contact surface (7) being formed from the shaft (3), at least one of the contact surfaces (6, 7) being provided with a surface patterning portion (8).

2. 2. The shaft grounding device according to claim 1, wherein the contact body (5) has a base material made of nonwoven fabric.

3. 3. The shaft grounding device according to claim 1, wherein the surface patterning portion (8) is processed on the second contact surface (7).

4. 4. A shaft grounding device according to any one of claims 1 to 3, characterized in that the surface patterning (8) comprises circumferentially extending grooves.

5. 5. The shaft grounding device according to claim 4, wherein the groove is formed in a circular or spiral shape.

6. 5. A shaft grounding device according to any one of claims 1 to 4, characterized in that the surface patterning (8) is non-directional.

7. 7. The shaft grounding device according to claim 1, wherein the surface patterning (8) is machined on the first contact surface (6).

8. 8. A shaft grounding device according to claim 7, characterized in that the surface patterning (8) is pressed into the first contact surface (6).

9. 9. A shaft grounding device according to claim 1, characterized in that the contact body (5) is assigned a spring means (9) which presses the contact body (5) against the shaft (3) with an elastic preload.

10. 10. The shaft grounding device according to claim 9, wherein the surface patterning (8) is machined on the spring means (9).

11. 11. Shaft grounding device according to claim 1, characterized in that the grounding ring (4) is assigned a fluid guide element (10).

12. 12. The shaft grounding device according to claim 11, characterized in that two fluid guide elements (10) are provided, one fluid guide element (10) being assigned to each end face of the contact body (5).

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