Shaft grounding device and electric drive unit having the same

Abstract

The present invention relates to a shaft grounding device (X) for electrically grounding a shaft (1) relative to a housing (2), wherein a conductive rectangular ring (4) is provided for establishing electrical contact with the shaft (1), the rectangular ring being arranged in a rectangular groove (3) constructed in the shaft (1), wherein the rectangular ring (4) is in conductive contact with the housing (2) through a metal sleeve (5), wherein the shaft grounding device (X) has a pre-tightening device that axially presses the rectangular ring (4) against the rectangular ring groove (3) and radially outwards against the sleeve (5), and the present invention relates to an electric drive unit (G1, G2) for a motor vehicle having such a shaft grounding device (X).

Description

Technical Field

[0001] This invention relates to a shaft grounding device for electrically grounding a shaft relative to a housing. The invention also relates to a transmission for a motor vehicle having such a shaft grounding device. Background Technology

[0002] Axle grounding devices are commonly used in the electrified powertrains of motor vehicles, such as hybrid drives or electric axles, to conduct alternating current from conductive components (such as the drive or driven shaft and rotor of a gearbox) in order to avoid damage due to current flow in components, such as bearings, and / or reduce the formation of electromagnetic radiation from the shaft. It is necessary to keep the resistance (also known as impedance) between the rotating component (shaft) and the stationary housing in which the shaft is housed as low as possible.

[0003] As is known from the prior art, to achieve the required contact between a stationary shaft grounding device and a rotating shaft, a slider in the form of a carbon brush, coated conductive plastic, or non-woven fabric is used. To keep the contact resistance as low as possible, a larger contact bearing is required on the shaft.

[0004] As is known from US6608410B2, when the rotor shaft is arranged in a housing, grounding is achieved by venting current through a sealing element implemented in a conductive manner between the shaft and the housing. Summary of the Invention

[0005] Based on the following objective, this invention provides an alternative shaft grounding device.

[0006] To address this issue, a shaft grounding device is proposed for electrically grounding a shaft relative to a housing. This device includes a conductive rectangular ring arranged in a rectangular groove constructed within the shaft to establish electrical contact with the shaft. The rectangular ring makes conductive contact with the housing via a metal sleeve.

[0007] This invention is based on the concept of applying the known principle of rectangular ring for shaft sealing to shaft grounding. Electrical contact between the shaft and the rectangular ring is ensured by an additional pre-tightening device.

[0008] According to one embodiment of the invention, the preload device has a wedge-shaped piston and spring element, particularly a radially preloaded tension circular spring, the piston and the tension circular spring being arranged in a rectangular annular groove, wherein the tension circular spring presses the piston against the rectangular annular groove, which in turn presses the rectangular annular groove axially against the rectangular annular groove in a stationary state and radially outward against the sealing sleeve or support due to the wedge shape.

[0009] In order to integrate the required components, namely the piston and the tension spring, the existing rectangular annular groove needs to be enlarged.

[0010] The following advantages are achieved by the scheme according to the invention: the rectangular ring always has a preload relative to the shaft, especially relative to the shaft shoulder and relative to the sleeve, which, combined with the conductive design of the rectangular ring, is a prerequisite for current conduction between the shaft (via the rectangular ring, via the sleeve) and the housing.

[0011] Because the bushing is typically pressed into the housing, current can flow well to the housing for grounding. Another advantage of this invention is that it requires only two additional components compared to existing technologies: a tension spring and a piston, resulting in lower manufacturing and assembly costs. Furthermore, the mounting space required for installing the tension spring and piston is very small.

[0012] According to an extended embodiment of the invention, the rectangular ring may be configured to have a silver coating in order to keep the contact resistance as small as possible, wherein the cost for this purpose is advantageously low because the silver coating is limited to a relatively small component.

[0013] Preferably, the rectangular ring functions as an oil sealing ring in addition to its role in the shaft grounding device. This structure eliminates the need for additional seals that would otherwise be required.

[0014] Furthermore, an electric drive unit for a motor vehicle is proposed, wherein the electric drive unit has a housing and a shaft supported within the housing. The electric drive unit may have a shaft grounding device according to one of the foregoing designs to provide conductive contact between the housing and the shaft.

[0015] An electric drive unit can be, for example, an electric axle drive for a motor vehicle. Alternatively, the electric drive unit can be formed from a transmission having an electric motor for driving the vehicle, such as an automatic transmission or a dual-clutch transmission.

[0016] According to one possible embodiment, the shaft grounding device is arranged in the oil space of the electric drive unit. The oil space is the space in the electric drive unit where oil is located, for example, for lubricating and / or cooling the components of the electric drive unit. In such a design, the rectangular ring of the shaft grounding device can function as a sealing ring for sealing the oil space.

[0017] If the shaft grounding device of the electric drive unit has the aforementioned wedge-shaped piston, the piston is preferably oriented such that the pressure acting in the oil space acts on the piston to increase the sealing effect of the rectangular ring.

[0018] Alternatively, the shaft grounding device can be placed in the dry space of the electric drive unit. Attached Figure Description

[0019] The invention will now be explained in more detail by way of example with reference to the accompanying drawings. In the drawings:

[0020] Figure 1 and Figure 2 The power transmission systems of motor vehicles are shown separately;

[0021] Figure 3 A schematic cross-sectional view of the shaft grounding device in its assembled state is shown; and

[0022] Figure 4 A perspective view of the piston of the shaft grounding device is shown. Detailed Implementation

[0023] Figure 1 The diagram illustrates the powertrain of a motor vehicle equipped with an electric drive unit G1. The electric drive unit G1 comprises a motor with a non-rotatable stator ST and a rotatable rotor RO. The stator ST is fixed to a housing 2. The rotor RO is fixed to a shaft 1 supported within the housing 2. Power applied to the rotor RO is transmitted through… Figure 1 The transmission (not shown) transmits power to the differential transmission mechanism AG, which distributes power to the drive wheels DW of the vehicle.

[0024] During motor operation, current can be coupled into the rotor RO, and this current is electrically isolated from the housing 2 via a support member of shaft 1. To ensure a return path for these currents, the electric drive unit G1 has a shaft grounding device X. Conductive contact is established between shaft 1 and housing 2 via the shaft grounding device X. The shaft grounding device X is, for example, located in the dry space GT of the electric drive unit G1.

[0025] Figure 2 The diagram illustrates the powertrain of a motor vehicle with an electric drive unit G2. This powertrain is now configured as a hybrid powertrain. The electric drive unit G2 is formed by a transmission that is connected to the internal combustion engine VM on the input side. This transmission has… Figure 2 A gear set (not shown) is provided to offer different transmission ratios between input shaft GW2 and shaft 2. The transmission has a motor with a rotor RO and a stator ST, the stator ST being connected to the housing 2 of the electric drive unit G2, and the rotor RO being connected to the input shaft GW1. On the driven side, the transmission is connected to a differential transmission mechanism AG via shaft 1. The differential transmission mechanism AG is configured to distribute the power applied to shaft 1 to the individual drive wheels DW of the vehicle.

[0026] During motor operation, current can be coupled into the rotor RO, and this current is electrically isolated from the housing 1 through the supports of shafts GW1 and GW2. To ensure the return path of these currents, the electric drive unit G2 has a shaft grounding device X. Conductive contact is established between shaft 1 and housing 2 through the shaft grounding device X. The shaft grounding device X is arranged, for example, in the oil space GR of the electric drive unit G2.

[0027] Figure 1and Figure 2 The powertrain and electric drive units G1 and G2 shown are only examples.

[0028] Figure 3 A schematic cross-sectional view of the shaft grounding device X for the electric drive unit G2 is shown. The oil space GR is sealed relative to the housing 2 and the shaft 1 by a conductive rectangular ring 4 arranged in a rectangular annular groove 3 constructed in the shaft 1, wherein the rectangular ring 4 can be axially pressed into the rectangular annular groove 3, especially onto the shaft shoulder, by oil pressure and can be radially outwardly pressed against a sleeve 5 made of metal to achieve a sealing effect.

[0029] According to the present invention, the shaft grounding device X has a pre-tightening device that, even when the shaft 1 is stationary, presses the rectangular ring 4 axially against the rectangular ring groove 3 and radially outward against the sleeve 5, wherein, in Figure 3 In the example shown, the shaft grounding device has a wedge-shaped piston 6 and a radially preloaded tension circular spring 7, the piston and the tension circular spring being arranged in a rectangular annular groove 3. The rectangular ring 4 may be implemented with a silver coating to keep the contact resistance as low as possible.

[0030] The piston 6 is pressed against the rectangular ring 4 by the force of the stretching circular spring 7, wherein, when the shaft 1 is stationary, the rectangular ring 4 is thus pressed axially against the rectangular ring groove 3 and radially outward against the sleeve 5 due to the wedge shape of the piston 6, thereby ensuring the preload of the rectangular ring 4 on the shaft 1 and the sleeve 5 required for current discharge.

[0031] Figure 4 The object is the piston 6 of the preload device of the shaft grounding device X. For example, from... Figure 4 As can be seen, when the piston 6 is in the assembled state, it has grooves 8 distributed on its periphery on the side away from the rectangular ring 4. When running, the grooves allow oil to enter the rectangular ring groove 3, so that the rectangular ring 4 is axially pressed onto the rectangular ring groove 3 and radially outward pressed against the sleeve 5 to achieve a sealing effect.

[0032] Furthermore, in the example shown, piston 6 has an opening 9 to facilitate or simplify assembly; according to other designs, the piston may consist of two parts.

[0033] according to Figure 3 and Figure 4 The shaft grounding device X can also be used in the electric drive unit G1, so that the shaft grounding device X is arranged in the dry space GT of the electric drive unit G1. Here, the hydraulic preload of the rectangular ring 4 is omitted accordingly.

[0034] List of reference numerals

[0035] G1 and G2 electric drive units

[0036] ST stator

[0037] RO rotor

[0038] AG differential transmission mechanism

[0039] DW drive wheels

[0040] VM internal combustion engine

[0041] GW1 input shaft

[0042] GR oil space

[0043] GT Dry Space

[0044] X-axis grounding device

[0045] 1 axis

[0046] 2 shells

[0047] 3 rectangular annular grooves

[0048] 4 rectangular rings

[0049] 5 sealing sleeve

[0050] 6-piston

[0051] 7. Stretch circular spring

[0052] 8 slots

[0053] 9 openings

Claims

1. A shaft grounding device (X) for electrically grounding a shaft (1) relative to a housing (2), wherein, A conductive rectangular ring (4) is provided for establishing electrical contact with the shaft (1). The rectangular ring is arranged in a rectangular ring groove (3) constructed in the shaft (1). The rectangular ring (4) is in conductive contact with the housing (2) through a metal sleeve (5). The shaft grounding device (X) has a pre-tightening device that presses the rectangular ring (4) axially against the rectangular ring groove (3) and radially outward against the sleeve (5). The pre-tightening device has a wedge-shaped piston (6) and a radially pre-tightened tension circular spring (7), the piston and the tension circular spring being arranged in a rectangular ring groove (3), such that the tension circular spring (7) presses the piston (6) against the rectangular ring (4), thereby pressing the rectangular ring (4) axially against the rectangular ring groove (3) and radially outward against the sleeve (5) due to the wedge shape of the piston (6).

2. The shaft grounding device (X) according to claim 1, characterized in that, The rectangular ring (4) is implemented with a silver coating.

3. The shaft grounding device (X) according to claim 1 or 2, characterized in that, The piston (6) has an opening (9) for facilitating or simplifying assembly.

4. The shaft grounding device (X) according to claim 1 or 2, characterized in that, The piston (6) is implemented as a single piece or consists of two parts.

5. The shaft grounding device (X) according to claim 1 or 2, characterized in that, The rectangular ring (4) additionally functions as an oil sealing ring.

6. The shaft grounding device (X) according to claim 5, characterized in that, The piston (6) has grooves (8) distributed on its periphery on the side away from the rectangular ring (4) when it is in the assembled state. These grooves allow oil to enter the rectangular ring groove (3) during operation, so that the rectangular ring (4) is axially pressed against the rectangular ring groove (3) and radially outwardly pressed against the sleeve (5) to achieve a sealing effect.

7. An electric drive unit for a motor vehicle, wherein, The electric drive unit has a housing (2) and a shaft (1) supported in the housing (2), characterized in that it is provided with a shaft grounding device (X) according to any one of claims 1 to 6, wherein a conductive contact is established between the housing (2) and the shaft (1) by means of the shaft grounding device (X).

8. The electric drive unit according to claim 7, characterized in that, The shaft grounding device (X) is arranged in the oil space (GR) of the electric drive unit.

9. The electric drive unit according to claim 8, characterized in that, The rectangular ring (4) of the shaft grounding device (X) functions as a sealing ring for sealing the oil space (GR).

10. The electric drive unit according to claim 9, characterized in that, The pressure present in the oil space (GR) acts on the piston (6), which strengthens the sealing effect of the rectangular ring (4).

11. The electric drive unit according to claim 7, characterized in that, The shaft grounding device (X) is arranged in the dry space (GT) of the electric drive unit.

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