Shaft Grounding Device and Electric Drive Unit Comprising Such a Device

Abstract

A shaft grounding device (X) for the electrical grounding of a shaft (1) with respect to a housing (2) includes an electrically conductive rectangular ring (4) arranged in a rectangular groove (3) formed in the shaft (1). The rectangular ring (4) is in electrically conductive contact with the housing (2) via a metallic sleeve (5). A preloading device presses the rectangular ring (4) axially against the rectangular ring groove (3) and radially outward against the sleeve (5).

Claims

1-12: (canceled)

13. A shaft grounding device (X) for electrical grounding of a shaft (1) with respect to a housing (2), comprising: an electrically conductive rectangular ring (4) arranged in a rectangular groove (3) formed in the shaft (1), a metallic sleeve (5), the rectangular ring (4) in electrically conductive contact with the housing (2) via the metallic sleeve (5); and a preloading device pressing the rectangular ring (4) axially against the rectangular ring groove (3) and radially outward against the sleeve (5).

14. The shaft grounding device (X) of claim 13, wherein the rectangular ring (4) is silver-coated.

15. The shaft grounding device (X) of claim 13, wherein the preloading device comprises: a piston (6) that is wedge-shaped; and a radially preloaded base spring (7), wherein the piston (6) and the base spring (7) are arranged in the rectangular ring groove (3), and the base spring (7) presses the piston (6) against the rectangular ring (4) such that the rectangular ring (4) is pressed axially against the rectangular ring groove (3) and radially outward against the sleeve (5) by the wedge-shape of the piston (6).

16. The shaft grounding device (X) of claim 15, wherein the piston (6) defines an installation opening (9).

17. The shaft grounding device (X) of claim 15, wherein the piston (6) is a one-piece piston or a two-piece piston.

18. The shaft grounding device (X) of claim 13, wherein the rectangular ring (4) is additionally configured as an oil sealing ring.

19. The shaft grounding device (X) of claim 18, wherein: on a side facing away from the rectangular ring (4) in an installed state, a piston (6) defines grooves (8) distributed over a circumference of the piston (6); the grooves (8) configured for allowing oil to enter the rectangular ring groove (4) such that the rectangular ring (4) is pressed axially onto the rectangular ring groove (3) and radially outward against the sleeve (5) for a seal.

20. An electric drive unit (G1, G2) for a motor vehicle, comprising: a housing (2); a shaft (1) mounted in the housing (2); and the shaft grounding device (X) of claim 13, wherein an electrically conductive contact is established between the housing (2) and the shaft (1) by the shaft grounding device (X).

21. The electric drive unit (G2) of claim 20, wherein the shaft grounding device (X) is arranged in an oil chamber (GR) of the electric drive unit (G2).

22. The electric drive unit (G2) of claim 21, wherein the rectangular ring (4) of the shaft grounding device (X) operates as a sealing ring for sealing the oil chamber (GR).

23. The electric drive unit (G2) of claim 22, wherein: the preloading device comprises a piston (6) that is wedge-shaped and a radially preloaded base spring (7), the piston (6) and the base spring (7) are arranged in the rectangular ring groove (3), and the base spring (7) presses the piston (6) against the rectangular ring (4) such that the rectangular ring (4) is pressed axially against the rectangular ring groove (3) and radially outward against the sleeve (5) by the wedge-shape of the piston (6); and the piston (6) is configured such that a pressure prevailing in the oil chamber (GR) acts on the piston (6) to increase a sealing effect of the rectangular ring (4).

24. The electric drive unit (G1) of claim 20, wherein the shaft grounding device (X) is arranged in a dry space (GT) of the electric drive unit (G1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Example aspects of the invention are explained in greater detail in the following, by way of example, with reference to the attached figures, wherein:

[0021] FIG. 1 and FIG. 2 each show a drive train of a motor vehicle;

[0022] FIG. 3 shows a diagrammatic sectional view of a shaft grounding device in the installed state; and

[0023] FIG. 4 shows a perspective view of a piston of the shaft grounding device.

DETAILED DESCRIPTION

[0024] Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

[0025] FIG. 1 shows a drive train of a motor vehicle including an electric drive unit G1. The electric drive unit G1 includes an electric machine having a rotationally fixed stator ST and a rotary rotor RO. The stator ST is secured at a housing 2. The rotor RO is secured on a shaft 1, which is mounted in the housing 2. Via a transmission not represented in FIG. 1, the power applied at the rotor RO is transmitted onto a differential gear AG, which splits the power onto driving wheels DW of the motor vehicle.

[0026] During the operation of the electric machine, currents can be coupled into the rotor RO, which are electrically insulated with respect to the housing 2 due to the mounting of the shaft 1. In order to ensure a return conducting path of these currents, the electric drive unit G1 includes a shaft grounding device X. Due to the shaft grounding device X, an electrically conductive contact is established between the shaft 1 and the housing 2. The shaft grounding device X is arranged, by way of example, in a dry space GT of the electric drive unit G1.

[0027] FIG. 2 shows a drive train of a motor vehicle including an electric drive unit G2. The drive train is now designed as a hybrid drive train. The electric drive unit G2 is formed by a transmission, which is connected on the input side to an internal combustion engine VM. The transmission includes a gear set (not represented in FIG. 2) in order to provide different transmission ratios between an input shaft GW1 and a shaft 1. The transmission includes an electric machine having a rotor RO and a stator ST, wherein the stator ST is connected to a housing 2 of the electric drive unit G2 and the rotor RO is connected to the input shaft GW1. On the output side, the transmission is connected via a shaft 1 to a differential gear AG. The differential gear AG is configured for distributing the power applied at the shaft 1 to driving wheels DW of the motor vehicle.

[0028] During the operation of the electric machine, currents can be coupled into the rotor RO, which are electrically insulated with respect to the housing 2 due to the mounting of the shafts GW1, 1. In order to ensure a return conducting path of these currents, the electric drive unit G2 includes a shaft grounding device X. Due to the shaft grounding device X, an electrically conductive contact is established between the shaft 1 and the housing 2. The shaft grounding device X is arranged, by way of example, in an oil chamber GR of the electric drive unit G2.

[0029] The drive trains and electric drive units G1, G2 shown in FIG. 1 and FIG. 2 are to be considered merely as examples.

[0030] FIG. 3 shows a diagrammatic sectional view of a shaft grounding device X for the electric drive unit G2. The oil chamber GR is sealed with respect to the housing 2 and the shaft 1 via a rectangular ring 4, which is designed to be electrically conductive and is arranged in a rectangular ring groove 3 formed in the shaft 1, wherein, in order to achieve a sealing effect, the rectangular ring 4 is pressable by the oil pressure axially onto the rectangular ring groove 3, in particular a shaft shoulder, and radially outward against a sleeve 5 made of metal.

[0031] According to example aspects of the invention, the shaft grounding device X includes a preloading device, which presses the rectangular ring 4—also when the shaft 1 is at a standstill—axially against the rectangular ring groove 3 and radially outward against the sleeve 5, wherein, in the example shown in FIG. 3, the preloading device includes a piston 6 designed to be wedge-shaped and a radially preloaded base spring 7, which are arranged in the rectangular ring groove 3. The rectangular ring 4 can be designed to be silver-coated in order to keep the contact resistance as low as possible.

[0032] The piston 6 is pressed against the rectangular ring 4 by the force of the base spring 7, wherein, as a result, when the shaft 1 is at a standstill, the rectangular ring 4 is pressed axially against the rectangular ring groove 3 and, due to the wedge shape of the piston 6, radially outward against the sleeve 5, and so the preload of the rectangular ring 4 with respect to the shaft 1 and the sleeve 5, which is necessary for dissipating current, is ensured.

[0033] The subject matter of FIG. 4 is a piston 6 of the preloading device of the shaft grounding device X. As is apparent from FIG. 4, on the side facing away from the rectangular ring 4 in the installed state, the piston 6 has grooves 8 distributed over the circumference, which, during operation, make it possible for oil to enter the rectangular ring groove 3, as the result of which the rectangular ring 4 is pressed axially onto the rectangular ring groove 3 and radially outward against the sleeve 5 in order to achieve the sealing effect.

[0034] Moreover, the piston 6 in the example shown has an opening 9 for enabling and simplifying installation; according to further example embodiments, the piston can be composed of two parts.

[0035] The shaft grounding device X according to FIG. 3 and FIG. 4 can also be utilized in the electric drive unit G1 such that the shaft grounding device X is arranged in the dry space GT of the electric drive unit G1. A hydraulic preloading of the rectangular ring 4 is therefore dispensed with.

[0036] Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. In the claims, reference characters corresponding to elements recited in the detailed description and the drawings may be recited. Such reference characters are enclosed within parentheses and are provided as an aid for reference to example embodiments described in the detailed description and the drawings. Such reference characters are provided for convenience only and have no effect on the scope of the claims. In particular, such reference characters are not intended to limit the claims to the particular example embodiments described in the detailed description and the drawings.

REFERENCE CHARACTERS

[0037] G1, G2 electric drive unit [0038] ST stator [0039] RO rotor [0040] AG differential gear [0041] DW driving wheel [0042] VM internal combustion engine [0043] GW1 input shaft [0044] GR oil chamber [0045] GT dry space [0046] X shaft grounding device [0047] 1 shaft [0048] 2 housing [0049] 3 rectangular ring groove [0050] 4 rectangular ring [0051] 5 sealing sleeve [0052] 6 piston [0053] 7 base spring [0054] 8 groove [0055] 9 opening