Shaft arrangement of axially acting shaft earthing electrode and method for earthing a shaft

Abstract

Shaft arrangement (1) with a shaft (2) supported at least on one side by bearings in a housing (9) or a bearing shield with a shaft earthing device (12), wherein an oil supply is provided, characterized in that the shaft earthing device (12) is mounted coaxially to the shaft (2) at the end face.

Description

[0001] The invention relates to a shaft arrangement comprising a shaft and bearings as well as a shaft grounding electrode.

[0002] The invention also relates to a method for grounding a shaft. State of the art

[0003] It is common practice to use a grounding device for rotating shafts in inverter-fed electric motors and other rotating electrical machines. Grounding rings or other grounding devices are used to prevent damaging current flow through the rolling bearings. If the current is not grounded, it can flow through the rolling bearings and cause electrical corrosion, reducing the bearing life. In a typical strategy, grounding devices such as grounding rings are used in a fixed housing that prevents the grounding device from rotating. Bristles or other contact elements of the fixed grounding device can then run on a rotating rotor shaft to create an electrical grounding path for excess current. The electrical current can preferably flow through the grounding device and not through the bearings, thus preventing or reducing bearing corrosion.

[0004] An electrical grounding mechanism is known from US 4,515,417 B1. This prior art provides a grounding device that prevents electrolytic corrosion in the bearings of an electric rotary machine. The grounding device has a centrifugal contact point between an electrically conductive end cover and an inner surface of a rotor shaft. The contact point includes a spring-loaded contact element that extends inward into the rotor shaft and contacts a portion of the end cover that extends into it. When the rotor is stationary or rotating at low speeds, the contact element maintains electrical contact between the rotor shaft and the end cover. However, as the rotor speed increases, inertia tends to move the contact element radially outward against the spring bias, so that it ceases to establish electrical contact between the rotating rotor shaft and the end cover.

[0005] US 2010 / 0127585A1 comprises a grounding mechanism for an electric motor rotor with a shaft stub defining a longitudinal axis and having a first axial end, a second axial end, and a plurality of axial shaft stub segments, including a mounting segment adjacent to the first axial end and adapted for press-fitting into an electric motor housing, an electrical grounding segment adjacent to the second axial end, and a sealing segment extending between the mounting segment and the grounding segment. The mounting segment has a first diameter, the grounding segment has a second diameter larger than the first diameter, and the sealing segment has a third diameter larger than both the first and second diameters.The grounding mechanism further comprises an electrical grounding ring that can be positioned around the shaft stub and is adapted to be pressed into an axially extending bore defined by the rotor shaft of an electric motor. The electrical grounding ring comprises an outer circumference with a cylindrical outer surface adapted to contact the rotor shaft within the axially extending bore, and an inner circumference with an electrical contact interface configured to electrically connect the electrical grounding ring to the shaft stub by contacting the shaft stub circumferentially around the grounding segment. The grounding mechanism further comprises a sealing element that can be positioned around the shaft stub and is also adapted to be pressed into an axially extending bore defined by the rotor shaft of an electric motor.The sealing element comprises a cylindrical outer surface and a sealing lip that extends radially inwards and is configured to form a fluid seal with the shaft stub by contacting the shaft stub circumferentially around the sealing segment.

[0006] Attempts to mount the shaft grounding electrode axially fail because the contact surface between the shaft and the electrode is located in a wet, oily environment, and sealing it is complex. Oil on the contact surface reduces conductivity and should be avoided. Reduced conductivity results in poor bearing stress suppression and increased emission of electromagnetic waves from the drive system's output shafts into the environment.

[0007] The object of the invention is to provide an improved solution for the axial mounting of a wave earth electrode. Description of the invention

[0008] The problem is solved with a shaft arrangement with a shaft supported at least on one side by bearings in a housing or a bearing shield with a shaft earthing electrode, wherein an oil supply is provided to at least one bearing, and the shaft earthing electrode is brought into contact coaxially with the shaft at its end face.

[0009] The wave end face of the shaft is axially recessed against a wave edge, and the wave ground lies axially against the wave end face.

[0010] The shaft is designed in the area of ​​the contact surface in such a way that the incoming oil for bearing lubrication is shielded due to the leading geometry.

[0011] Furthermore, any remaining oil is flung outwards by centrifugal force, and the contact area of ​​the shaft remains dry. Therefore, the function of the shaft grounding device is not impaired.

[0012] The wave edge is cylindrical or conical.

[0013] The wave grounding electrode has a spring-loaded contact cylinder that rests against the end face of the wave.

[0014] The problem is also solved by a method for grounding a shaft in a shaft arrangement, whereby supplied oil is flung away from the shaft end face over the shaft edge.

[0015] The shaft end, designed in this way, prevents the inflow of fresh oil during operation and allows existing oil to be quickly spun off. This ensures good drainage.

[0016] The discharge function is not affected. Effective bearing stress suppression is ensured, thus guaranteeing the bearings' protection against electrical erosion. Furthermore, this results in a reduction of EMC emissions via the output shafts, enabling compliance with required EMC limits. Description of the characters Fig. Figure 1 shows a wave with a wave grounding electrode.

[0017] The single figure shows a shaft arrangement 1 consisting of a shaft 2, for example a rotor shaft, and a housing 9 or a bearing arrangement.

[0018] In this embodiment, the shaft has a cavity, the shaft interior 3. The shaft 2 has a stepped diameter at the end shown in the figure. In this embodiment, two steps are visible, which terminate in a tapered shaft section 4. In this tapered shaft section 4, the shaft 2 is supported by bearings 8 in the housing 9 or in a bearing shield. The outer surface of the shaft 7 has direct contact with the bearings 8. The housing 9 contains a supply line 10 for lubricating and cooling oil, as well as a return line 11 for the lubricating and cooling oil. The lubricating oil serves at least to lubricate the bearings 8.

[0019] The end face of the shaft 2 has a shaft edge 6 that annularly surrounds a recessed shaft end face 5. A shaft grounding electrode 12 projects with its contact cylinder 15 against the recessed shaft end face 5. The contact cylinder 15 is pre-tensioned by a spring 13 in the housing of the shaft grounding electrode. The shaft grounding electrode 12 sits in a recess of the housing 9 and is pressed into the housing up to an edge 14 during assembly. Due to the pre-tension of the spring 13, the contact cylinder 15 is in contact with the shaft end face 5.

[0020] The lubricating oil flowing in via the supply line 10 flows directly into the interior space between shaft 2 and housing 9 in the area of ​​the bearings 8. The rotating shaft 2, more precisely the shaft edge 6, flings the lubricating oil outwards and away from the shaft end face 5. This keeps the shaft end face 5 largely oil-free.

[0021] The wave edge 6 in the embodiment shown is a cylindrical wall, but it is also possible to design the wave edge 6 conically to further support the ejection function. Reference sign 1 Wave arrangement 2nd wave 3 wave interior 4 tapered wave area 5 wave face 6 wavy edge 7 Outside Wave 8 bearings 9 cases 10 Oil supply line 11 Oil drainage 12 wave earth electrodes 13 spring 14 Rand 15 contact cylinders QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 4 515 417 B1

[0004] US 2010 / 0 127 585 A1

[0005]

Claims

[1] Shaft arrangement (1) with a shaft (2) supported at least on one side by bearings in a housing (9) or a bearing shield with a shaft grounding rod (12), wherein an oil supply is provided at least to the bearing, characterized by , that the wave earthing device (12) is brought into contact coaxially with the end face of the wave (2). [2] Shaft arrangement according to claim 1, characterized by , that the wave end face of the shaft (2) is axially recessed against a wave edge (6) and the wave earthing conductor (12) is axially in contact with the wave end face (5). [3] Shaft arrangement according to claim 2, characterized by , that the wave edge (6) is cylindrical or conical. [4] Shaft arrangement according to one of the preceding claims, characterized by , that the wave earthing device (12) has a spring-loaded contact cylinder (15) which rests against the wave end face (5). [5] Method for grounding a shaft (2) in a shaft arrangement (1) according to one of claims 1 to 4, wherein supplied oil is flung away from the shaft end face (5) over the shaft edge (6).

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