Shaft grounding components, transmissions, and electric axle drives

Abstract

The present invention relates to a shaft grounding assembly (X) comprising a housing (GG), a shaft (W, GW2, DS1, DS2) supported in the housing (GG), a shaft grounding device (E) for establishing an electrically conductive contact between the shaft (W, GW2, DS1, DS2) and the housing (GG), and a cover element (C) fixedly connected to the shaft (W, GW2, DS1, DS2) for protecting the shaft grounding device (E) from environmental influences, wherein the cover element (C) at least partially surrounds the shaft grounding device (E), wherein the shaft grounding device (E) is fixedly connected to the housing (GG), wherein the electrically conductive contact is established by sliding contact (SK) between a contact element (EK) of the shaft grounding device (E) and a surface of the cover element (C), and a transmission (G) having such a shaft grounding assembly (X). The present invention also relates to an electric axle drive (EA) having such a transmission (G).

Description

Technical Field

[0001] The invention relates to a shaft grounding assembly, a transmission for a motor vehicle having such a shaft grounding assembly, and an electric axle drive for a motor vehicle having such a transmission. Background Art

[0002] It is known in the prior art to electrically ground a shaft relative to the housing by means of a shaft ground. This can, for example, prevent damage to the shaft bearings due to currents flowing through the shaft bearings. Furthermore, by grounding the shaft relative to the housing, electromagnetic radiation of interfering signals from the shaft can be avoided or at least reduced.

[0003] For example, patent application JP 2000-244180 A teaches a device for reducing electromagnetic interference signals in electric vehicles. Here, the rotating shaft of the electric drive is electrically coupled to the housing of the electric drive via sliding contacts. These sliding contacts are protected from contamination by a cover connected to the housing. However, this fixed cover solution is only possible in the area of ​​the shaft end.

[0004] Patent application DE 10249770 A1 describes a solution for grounding a shaft remote from the shaft end of a transmission. In this solution, a protective cap is fixedly connected to the shaft together with a lead-out ring. The lead-out ring, at its maximum diameter, presses against the housing and slides along it, thus establishing an electrically conductive contact between the shaft and the housing. However, there is a risk that liquid and dirt particles could enter the area of ​​the sliding contact, causing the electrical conductivity of the sliding contact to deteriorate over time. Furthermore, the large sliding contact diameter results in high circumferential speeds of the sliding contact, which increases wear and frictional power of the sliding contact. Summary of the Invention

[0005] The object of the present invention is therefore to provide an assembly for shaft grounding which is suitable for applications remote from the shaft end, is distinguished by a high resistance to environmental influences and ensures reliable electrical contact between the shaft and the housing.

[0006] This object is achieved by a shaft grounding assembly according to the present invention. The shaft grounding assembly comprises: a housing; a shaft supported in the housing and extending from the housing; a shaft grounding device for establishing an electrically conductive contact between the shaft and the housing; and a cover element fixedly connected to the shaft for protecting the shaft grounding device from environmental influences, wherein the cover element at least partially surrounds the shaft grounding device, the shaft grounding device being fixedly connected to the housing, wherein the electrically conductive contact is implemented by sliding contact between a contact element of the shaft grounding device and a surface of the cover element, the cover element having an axially oriented section that surrounds an axial projection of the shaft grounding device, and a radial gap between the axially oriented section and the axial projection, the shaft grounding assembly being designed such that water penetrating through the radial gap can pass into the interior of the shaft grounding assembly until it penetrates the sliding contact. An advantageous design solution is derived from a preferred embodiment.

[0007] To achieve this objective, a shaft grounding assembly is provided, comprising a housing, a shaft, a shaft grounding device, and a cover element. The shaft is supported in the housing, with an axial end of the shaft extending from the housing. The shaft grounding device is configured to establish an electrically conductive contact between the shaft and the housing. The cover element is fixedly connected to the shaft such that the cover element and the shaft rotate at the same speed. The cover element at least partially surrounds the shaft grounding device, thereby protecting the shaft grounding device from environmental influences such as dust and splashing water.

[0008] According to the present invention, the shaft grounding device is fixedly connected to the housing, thereby achieving electrically conductive contact via sliding contact on the shaft side. However, the shaft-side running surface for sliding contact is not formed by the shaft itself, but rather by a surface of the cover element. This allows the function of providing a running surface suitable for electrical sliding contact to be decoupled from the shaft design and instead transferred to the cover element. Consequently, sliding contact considerations no longer need to be factored into the shaft design. Thus, the shaft can be made of steel, for example, and the cover element can be made of another material. The cover element can be provided with a coating to improve sliding contact, although the application of this coating may impair the heat treatment of the shaft.

[0009] Preferably, the covering element is pressed against the circumference of the shaft. Here, the circumference of the shaft is preferably provided with a coating to improve the electrical conductivity between the circumference and the covering element pressed against the circumference.

[0010] Preferably, the cover element is made of stainless steel. Stainless steel offers good electrical conductivity and is particularly corrosion-resistant, making this material particularly well-suited for forming the cover element.

[0011] The cover element preferably has a C-shaped cross section. This allows the cover element to at least partially surround the shaft grounding device. The radially inner side of the C-shape can press against the circumference of the shaft, while the radially outer side of the C-shape surrounds a section of the shaft grounding device and thus protects it from environmental influences.

[0012] The contact element of the shaft grounding device can be designed, for example, as a brush. The brush end forms an electrically conductive sliding contact with the cover element. The brush is attached to a conductive holder, which is electrically conductively connected to the housing. Instead of a brush, the contact element can be formed from a conductive PTFE element. The electrical conductivity of the PTFE can be enhanced by a correspondingly conductive filler.

[0013] The shaft grounding device can be part of a transmission for a motor vehicle, such as an automatic transmission based on a planetary gear set, a dual-clutch transmission, an automated transmission, or a CVT transmission. All of these transmissions can be exposed to environmental influences (e.g., splash water, salt, and dust) in a motor vehicle, making the proposed solution for the shaft grounding device particularly advantageous.

[0014] Preferably, the transmission shaft, on which the shaft grounding assembly is provided, is formed by the transmission's driven shaft. Often, a further, transmission-external shaft is coupled to the transmission's driven shaft in order to transmit the torque converted by the transmission to other components, such as a differential of a driven axle of a motor vehicle. Therefore, the shaft ends of the driven shaft cannot be simply covered, making the proposed solution particularly advantageous.

[0015] The transmission preferably includes an electric motor and an inverter associated with the electric motor. Since the inverter supplies pulsed power to the electric motor, electromagnetic interference signals may be generated, which are coupled into one or more of the transmission shafts. The shaft grounding device allows these interference signals to be coupled over a simple path to the transmission housing, which is typically connected to the electrical ground of the motor vehicle. This allows for a simple return path for the interference signals, thereby improving the electromagnetic compatibility of the transmission.

[0016] The transmission can be a component of an electric axle drive. Such axle drives are also exposed to splash water, salt and dust, making the solution proposed here particularly advantageous for such applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The embodiments of the present invention are described in detail with reference to the accompanying drawings. In the drawings:

[0018] Figure 1 and Figure 2 A powertrain with a transmission of a motor vehicle is shown separately; and

[0019] Figure 3 A detail view of a transmission with a shaft grounding assembly is shown.

[0020] List of Reference Numerals

[0021] VM internal combustion engine

[0022] EA electric axle drive

[0023] G transmission

[0024] GW1 input shaft

[0025] GW2 driven shaft

[0026] RS gear set

[0027] RS2 reduction gear set

[0028] EM motor

[0029] INV Inverter

[0030] BAT battery

[0031] AG differential

[0032] DS1 output shaft

[0033] DS2 output shaft

[0034] DW drive wheels

[0035] X-axis grounding assembly

[0036] GG housing

[0037] WL ball bearings

[0038] DR radial shaft sealing ring

[0039] NR oil chamber

[0040] E Grounding device

[0041] EK contact elements

[0042] SK sliding contact

[0043] E1 Axial protrusion

[0044] C Covering element

[0045] C1 axially oriented segment

[0046] SP1 radial clearance DETAILED DESCRIPTION

[0047] Figure 1The schematic diagram shows a powertrain for a motor vehicle. The powertrain includes an internal combustion engine VM, the output of which is connected to the input shaft GW1 of a transmission G. The driven shaft GW2 of the transmission G is connected to a differential AG. The differential AG is configured to distribute the power applied to the driven shaft GW2 to the drive wheels DW of the motor vehicle. The transmission G includes a gear set RS, which is connected to the output shaft GW1 of the transmission G. Figure 1 The gear set RS, along with shifting elements (not shown), is configured to provide different transmission ratios between the input shaft GW1 and the output shaft GW2. The gear set RS is enclosed by a housing GG, which also houses the electric motor EM connected to the input shaft GW1. The electric motor EM is configured to drive the input shaft GW1. An inverter INV is attached to the housing GG. The inverter INV is connected to the electric motor EM on one hand and to the battery BAT on the other. The inverter INV is used to convert the direct current from the battery BAT into alternating current suitable for operating the electric motor EM and, for this purpose, includes multiple power semiconductors. The conversion between direct current and alternating current is achieved through controlled, pulsed operation of the power semiconductors.

[0048] Figure 2 A powertrain for a motor vehicle is schematically shown, with Figure 1 Unlike the embodiment shown in FIG, this powertrain is a purely electric powertrain. The powertrain includes an electric axle drive EA. The electric axle drive EA includes an electric motor EM, whose power is transmitted to the drive wheels DW of the motor vehicle via a transmission G. The transmission G includes a reduction gear set RS2 and a differential AG. The output shafts DS1 and DS2 of the differential AG are connected to the drive wheels DW. The transmission G of the electric axle drive EA is surrounded by a housing GG. An inverter INV is fixed to the housing GG. The inverter INV is connected to the electric motor EM on the one hand and to the battery BAT on the other hand. The inverter INV is used to convert the direct current of the battery BAT into alternating current suitable for operating the electric motor EM and has a plurality of power semiconductors for this purpose. The conversion between direct current and alternating current is achieved by controlled pulsed operation of the power semiconductors.

[0049] Figure 1 and Figure 2 The powertrain shown in FIG. 1 is to be considered as exemplary only.

[0050] Due to the pulsed operation of power semiconductors, electromagnetic interference signals may be generated. These electromagnetic interference signals are, for example, Figure 1 The power train is coupled into the driven shaft GW2 or in accordance with Figure 2 The power transmission system is coupled to the output shafts DS1 and DS2. Figure 1 and Figure 2The output shaft GW2 or output shafts DS1 and DS2, not shown, are supported electrically insulated from the housing GG because the lubricating oil inside the housing GG has electrically insulating properties. Therefore, interference signals coupled into the output shaft GW2 cannot flow through a short path into the housing GG, which is connected to the vehicle's electrical ground. Instead, the interference signals are electromagnetically radiated back to the electrical ground, potentially disrupting other electronic components of the vehicle. The output shaft GW2 or output shafts DS1 and DS2 extending from the housing GG can form an antenna that facilitates the electromagnetic radiation of interference signals.

[0051] In order to improve electromagnetic compatibility, according to Figure 1 The transmission G has a shaft grounding assembly X configured to electrically connect the driven shaft GW2 to the housing GG. Figure 2 The transmission G of the axle drive EA has two shaft grounding assemblies X, which are provided for electrically conductively connecting the output shafts DS1 , DS2 to the housing GG.

[0052] Figure 3 A detailed view of a transmission G with a shaft grounding assembly X is shown. Figure 3 The support and sealing of the shaft W extending from the housing GG are shown in detail in FIG. Figure 3 The axis W shown in FIG may be, for example, according to Figure 1 The driven shaft GW2 or according to Figure 2 The shaft W is a multi-piece structure and is supported on the housing GG via a ball bearing WL. The ball bearing WL is located in the oil chamber NR of the transmission G. In order to seal the oil chamber NR from the environment, a radial shaft sealing ring DR with a sealing lip is provided. A shaft grounding device E is provided on the circumference of the radial shaft sealing ring DR. The shaft grounding device E is mechanically and electrically connected to the housing GG. For this purpose, a Figure 1 The shaft grounding device E is mechanically and electrically connected to the housing GG via contact and fixing projections (not shown). The contact element EK of the shaft grounding device E forms an electrically conductive sliding contact SK. The contact element EK can be, for example, a brush or an electrically conductive PTFE element.

[0053] To protect the electrically conductive sliding contacts SK from environmental influences (such as liquids or dust), a cover element C is provided. The cover element C is fixedly connected to the shaft W, for example by crimping. Together, the cover element C and the shaft grounding device E form a labyrinth seal. The cover element C has an axially oriented section C1 that surrounds an axial projection E1 of the shaft grounding device E. A radial gap SP1 exists between the axially oriented section C1 and the axial projection E1. Consequently, the flow conditions in the gap SP1 between the cover element C, which rotates with the shaft, and the non-rotating shaft grounding device E create a contactless seal. If water were to infiltrate the gap SP1 and, therefore, the sliding contacts SK, it can escape again at the spatially defined lower edge of the cover element C. The design of the cover element C thus provides good protection for the sliding contacts SK against dust and corrosion.

[0054] Cover element C has a C-shaped cross-section and at least partially surrounds shaft grounding device E. The radially inner side of the C-shape forms the radially inner contact surface with shaft W, and the radially outer side forms the running surface of sliding contact SK. Cover element C is made of stainless steel and thus forms a corrosion-free running surface for sliding contact SK. To improve the electrical conductivity between cover element C and shaft W, shaft W is partially provided with a coating that improves the electrical conductivity.

Claims

1. A shaft grounding assembly (X), comprising: A housing (GG); a shaft (W, GW2, DS1, DS2) supported in the housing (GG) and extending from the housing (GG); a shaft grounding device (E) for establishing an electrically conductive contact between the shaft (W, GW2, DS1, DS2) and the housing (GG); and a cover element (C) fixedly connected to the shaft (W, GW2, DS1, DS2) for protecting the shaft grounding device (E) from environmental influences, wherein the cover element (C) at least partially surrounds the shaft grounding device (E), It is characterized in that the shaft grounding device (E) is fixedly connected to the housing (GG), wherein the conductive contact is implemented by sliding contact (SK) between the contact element (EK) of the shaft grounding device (E) and the surface of the cover element (C), the cover element (C) has an axially oriented section (C1), which surrounds the axial protrusion (E1) of the shaft grounding device (E), and a radial gap (SP1) is present between the axially oriented section (C1) and the axial protrusion (E1), and the shaft grounding component is designed so that water penetrating through the radial gap (SP1) can pass into the interior of the shaft grounding component until it penetrates the sliding contact (SK).

2. The shaft grounding assembly (X) according to claim 1, characterized in that The cover element (C) is pressed against the circumference of the shaft (W, GW2, DS1, DS2).

3. The shaft grounding assembly (X) according to claim 2, characterized in that The circumferential surface of the shaft (W, GW2, DS1, DS2) is provided at least partially with a coating in order to improve the electrical conductivity between the circumferential surface and a covering element (C) pressed against the circumferential surface.

4. The shaft grounding assembly (X) according to any one of claims 1 to 3, characterized in that: The covering element (C) is made of stainless steel.

5. The shaft grounding assembly (X) according to any one of claims 1 to 3, characterized in that: The covering element (C) has a C-shaped cross section.

6. The shaft grounding assembly (X) according to any one of claims 1 to 3, characterized in that: The contact element (EK) of the shaft grounding device (E) is realized as a brush or in the form of an electrically conductive PTFE element.

7. A transmission (G) for a motor vehicle, characterized in that: A shaft grounding assembly (X) according to any one of claims 1 to 6 is provided.

8. The transmission (G) according to claim 7, characterized in that The shaft (W) is formed by the driven shaft (GW2) of the transmission (G).

9. The transmission (G) according to claim 7 or claim 8, characterized in that The transmission (G) has an electric machine (EM) and an inverter (INV) associated with the electric machine (EM).

10. The transmission (G) according to claim 7 or claim 8, characterized in that The transmission (G) is an automatic transmission based on a planetary gear set, a dual clutch transmission or a CVT transmission.

11. The transmission (G) according to claim 7 or claim 8, characterized in that The transmission (G) is an automated transmission.

12. An electric axle drive (EA) for a motor vehicle, characterized in that: A transmission (G) according to one of claims 7 to 11 is provided.

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