Transmission for a motor vehicle and electric axle drive device

Abstract

The invention relates to a transmission (G) for a motor vehicle, having: a housing (GG); shafts (W, GW2, DS1, DS2) supported in the housing (GG) and protruding from the housing (GG); a radial shaft seal ring (DR) having a sealing lip for sealing an oil chamber (NR) within the housing (GG) relative to the environment; a shaft grounding device (E) arranged on the ambient side of the radial shaft seal ring (DR), the shaft grounding device for forming an electrically conductive sliding contact (SK) between the shafts (W, GW2, DS1, DS2) and the housing (GG); and a sleeve-shaped covering element (C) fixedly connected to the shafts (W, GW2, DS1, DS2), the covering element for protecting the sliding contact (SK) from the environment, wherein the shaft grounding device (E) is fixedly connected to the housing (GG), and wherein the covering element (C) together with the grounding device (E) forms a labyrinth seal. The invention also relates to an electric axle drive device (EA) having such a transmission (G).

Description

Technical Field

[0001] The present invention relates to a transmission for a motor vehicle and an electric axle drive device for a motor vehicle having such a transmission. Background Art

[0002] In the prior art, it is known that a transmission shaft is electrically grounded relative to a housing through a shaft ground connection. Thereby, for example, damage to the shaft bearing caused by current flowing through the shaft bearing can be avoided. In addition, by grounding the shaft relative to the housing, electromagnetic radiation of interference 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 of an electric vehicle. Here, the rotating shaft of the electric drive device is electrically coupled to the housing of the electric drive device through a sliding contact. The sliding contact is protected from contamination by a cover connected to the housing. However, such a fixed covering solution is only possible in the region of the shaft end.

[0004] In patent application DE 10249770 A1, a solution for shaft grounding away from the shaft end of a transmission is described. In this solution, a protective cap is fixedly connected to the shaft together with a lead-out ring. The lead-out ring presses against the housing at its maximum diameter and slides therealong, thereby forming an electrically conductive sliding contact between the shaft and the housing. However, there is a risk that liquid and dirt particles reach the region of the sliding contact, such that the conductivity of the sliding contact deteriorates with increasing operating time. In addition, due to the large sliding contact diameter, there is a high circumferential speed of the sliding contact, whereby the wear and frictional power of the sliding contact increase. Summary of the Invention

[0005] Therefore, an object of the present invention is to provide a transmission whose shaft grounding is suitable for applications away from the shaft end and which is characterized by high resistance to environmental influences.

[0006] This object is achieved by the features of the present invention. Advantageous design solutions are derived from the preferred embodiments.

[0007] To achieve this object, a transmission for a motor vehicle is proposed. The transmission includes a housing and a shaft supported in the housing. At least one axial end of the shaft projects from the housing. The transmission has a radial shaft seal ring having a sealing lip for sealing an oil chamber arranged in the housing relative to the surrounding environment. In addition, the transmission has a shaft grounding device and a covering element fixedly connected to the shaft, the shaft grounding device being configured to form an electrically conductive sliding contact between the shaft and the housing, and the covering element being used to protect the sliding contact from environmental influences.

[0008] According to the present invention, it is now proposed that the grounding device is fixedly connected to the housing, wherein the covering element fixedly connected to the shaft and the grounding device together form a labyrinth seal. The labyrinth seal thus formed is used to protect the sliding contact from the environment and does not form a seal for the oil chamber. To seal the oil chamber, a sealing lip of a radial shaft seal ring is provided. Thus, a clear functional separation is achieved between the radial shaft seal ring and the labyrinth seal, enabling these two components to be designed only for their respective purposes.

[0009] Preferably, the covering element has an axially oriented section that surrounds the axial protrusion of the shaft grounding device. In this way, a "simple" labyrinth can be formed, which already protects the sliding contact from the environment.

[0010] Preferably, there is a radial gap between the axially oriented section of the covering element and the axial protrusion of the shaft grounding device. Due to the relative speed between the covering element rotating with the shaft and the non-rotating shaft grounding device, a flow is generated in the radial gap, which improves the sealing effect of the labyrinth seal.

[0011] Preferably, the covering element has a radially oriented protrusion. Through this radial protrusion, the flow path of the labyrinth seal can be extended, thereby improving the sealing effect of the labyrinth seal.

[0012] Preferably, there is a radial gap between the radially oriented protrusion of the covering element and the housing. The liquid invading the labyrinth can escape in a simple manner through this radial gap, in such a way that the relative movement between the covering element and the housing causes the liquid to be thrown out through the gap. Since the gap is designed radially rather than axially, dripping into the gap is avoided in a simple manner.

[0013] The radially oriented protrusion is preferably connected to the axially oriented section. Thus, a simple and compact structure of the covering element can be achieved.

[0014] Preferably, the diameter of the shaft on which the covering element is fixed is larger than the diameter of the sliding contact. The particularly reliable torque transmission between the shaft and the covering element is ensured by the large fixing diameter, so that a simple press fit between the covering element and the shaft is sufficient.

[0015] According to a preferred design, the surface of the covering element forms the working surface on the shaft side of the sliding contact. For this purpose, the covering element has a radial section on its inner diameter, and the inner diameter of this radial section abuts against the shaft. On the axially opposite side, the radial section forms the working surface of the sliding contact. Advantageously, in this design, the covering element is made of stainless steel.

[0016] The shaft earthing device can for example be designed as a brush. The brush end forms a conductive sliding contact with the shaft here. The brush is fixed to a conductive holder, wherein the holder is conductively connected to the housing. Instead of the embodiment as a brush, the sliding contact can be formed by a conductive PTFE element. The conductivity of the PTFE can be achieved by a correspondingly conductive filler.

[0017] Preferably, the shaft of the transmission is formed by its output shaft. Usually, a further shaft outside the transmission is coupled to the output shaft of the transmission in order to transmit the torque converted by the transmission to other components, for example to the drive wheels of a motor vehicle. Therefore, the shaft end of the output shaft cannot simply be covered, and thus the solution with the labyrinth seal proposed here is particularly advantageous.

[0018] Preferably, the transmission has an electric motor and an inverter assigned to the electric motor. Since the inverter supplies the electric motor in pulses, electromagnetic interference signals can be generated, and these electromagnetic interference signals are coupled into the shaft. Through the shaft earthing device, these interference signals can be coupled in a simple path to the housing of the transmission, which is usually connected to the electrical ground of the motor vehicle. Thereby, a simple return path for the interference signals can be achieved, thus improving the electromagnetic compatibility of the transmission.

[0019] The transmission can for example be an automatic transmission based on a planetary gear set, a dual clutch transmission, an automated transmission, or a CVT transmission. All these transmissions can be exposed to environmental influences (such as splash water, salt, and dust) in a motor vehicle, and thus the solution with the labyrinth seal proposed here is particularly advantageous.

[0020] Alternatively, the transmission proposed here can be part of an axle drive for an electric vehicle. Such an axle drive is also exposed to splash water, salt, and dust, such that the solution with the labyrinth seal proposed here is particularly advantageous for such an application. Description of the Drawings

[0021] Embodiments of the invention are described in detail based on the subsequent drawings. In the drawings:

[0022] Figure 1 and Figure 2 show the powertrain of a motor vehicle with a transmission respectively;

[0023] Figures 3 to 6 show detail cross-sectional views of the transmission according to the first embodiment to the fourth embodiment respectively; and

[0024] Figure 7 shows a view of the output side of the transmission according to the fourth embodiment.

[0025] List of Reference Signs

[0026] VM Internal Combustion Engine

[0027] EA Electric Axle Drive

[0028] G Transmission

[0029] GW1 Input Shaft

[0030] GW2 Driven Shaft

[0031] RS Gear Set

[0032] RS2 Reduction Gear Set

[0033] EM Electric Motor

[0034] INV Inverter

[0035] BAT Battery

[0036] AG Differential

[0037] DS1 Output Shaft

[0038] DS2 Output Shaft

[0039] DW Drive Wheel

[0040] GG Housing

[0041] WL Ball Bearing

[0042] DR Radial Shaft Seal Ring

[0043] NR Oil Chamber

[0044] E Shaft Grounding Device

[0045] EK Contact Element

[0046] EB Fixed Tab

[0047] SK Sliding Contact

[0048] E1 Axial Projection

[0049] C Covering Element

[0050] C1 Axially Oriented Section

[0051] C2 Radially Oriented Projection

[0052] SP1 Radial Clearance

[0053] SP2 Radial Clearance

[0054] O1 O-Ring

[0055] O2 O-Ring

[0056] K covering hood Detailed implementation mode

[0057] Figure 1 Schematically shows a powertrain for a motor vehicle. The powertrain has an internal combustion engine VM, and the output end of the internal combustion engine is connected to the input shaft GW1 of the transmission G. The driven shaft GW2 of the transmission G is connected to the 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 has a gear set RS, and the gear set together with the shift elements (not shown in Figure 1 is configured to provide different transmission ratios between the input shaft GW1 and the driven shaft GW2. The gear set RS is surrounded by a housing GG, and the housing also houses an 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 fixed on 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 an alternating current suitable for operating the electric motor EM, and for this purpose has a plurality of power semiconductors. The conversion between the direct current and the alternating current is achieved by the controlled pulsed operation of the power semiconductors.

[0058] Figure 2 Schematically shows a powertrain for a motor vehicle. Different from the embodiment shown in Figure 1 , this powertrain is a pure electric powertrain. The powertrain has an electric axle drive device EA. The electric axle drive device EA includes an electric motor EM, and its power is transmitted to the drive wheels DW of the motor vehicle through the transmission G. The transmission G includes a reduction gear set RS2 and a differential AG. The output shafts DS1, DS2 of the differential AG are connected to the drive wheels DW. The transmission G of the electric axle drive device EA is surrounded by a housing GG. An inverter INV is fixed on 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 an alternating current suitable for operating the electric motor EM, and for this purpose has a plurality of power semiconductors. The conversion between the direct current and the alternating current is achieved by the controlled pulsed operation of the power semiconductors.

[0059] Figure 1 and Figure 2 The powertrains shown in are only to be regarded as exemplary.

[0060] Since the pulsed operation of the power semiconductors may generate electromagnetic interference signals, these electromagnetic interference signals are, for example, coupled into the driven shaft GW2 in the powertrain according to Figure 1 or in the powertrain according toFigure 2 is coupled into the output shafts DS1, DS2 in the powertrain. However, through Figure 1 and Figure 2 the support of the driven shaft GW2 or the output shafts DS1, DS2 not shown in, the driven shaft or the output shaft is electrically insulated from the housing GG, because the lubricating oil inside the housing GG has electrical insulation properties. Therefore, the interference signals coupled into the driven shaft GW2 cannot flow into the housing GG connected to the electrical ground of the motor vehicle through a short path. Instead, the interference signals return to the electrical ground through electromagnetic radiation, thereby possibly interfering with other electronic components of the motor vehicle. The driven shaft GW2 or the output shafts DS1, DS2 extending from the housing GG can form an antenna here, which facilitates the electromagnetic radiation of the interference signals.

[0061] Figure 3 A detailed cross-sectional view of the transmission G according to the first embodiment of the present invention is shown. The support and sealing of the shaft W extending from the housing GG are shown in detail therein. The shaft W shown in Figure 3 may be, for example, the driven shaft GW2 according to Figure 1 or one of the output shafts DS1, DS2 according to Figure 2 . The shaft W is constructed in a multi-piece manner and is supported on the housing GG by 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 seal ring DR with a sealing lip is provided. An axial grounding device E is provided on the circumferential side of the radial shaft seal ring DR. The axial grounding device E is mechanically and conductively connected to the housing GG. For this purpose, contact and fixing protrusions not shown in Figure 1 are provided, through which the axial grounding device E is mechanically and electrically connected to the housing GG. The contact element EK of the axial grounding device E forms a conductive sliding contact SK with the circumferential surface of the shaft W. The contact element SK can be, for example, a brush or a conductive PTFE element.

[0062] As Figure 3 shown, the conductive sliding contact SK can be directly realized on the surface of the shaft W. The surface of the shaft W may be provided with a coating in the area of the sliding contact, which improves the electrical contact with the contact element SK. Instead, the working surface of the sliding contact SK can be formed by a sleeve not shown in Figure 1 , which is fixed on the shaft W, for example, a stainless steel sleeve. This applies in the same way to the embodiments according to Figure 4 and Figure 6 .

[0063] To protect the conductive sliding contact SK from environmental influences (such as liquids or dust), a covering element C is provided. The covering element C is fixedly connected to the shaft W, for example by means of crimping. The covering element C and the shaft earthing device E together form a labyrinth seal. The covering element C has an axially oriented section C1 that surrounds the axially protruding part E1 of the shaft earthing device E. A radial gap SP1 exists between the axially oriented section C1 and the axially protruding part E1. Thus, a non-contact seal is formed by the flow situation in the gap SP1 between the covering element C rotating with the shaft and the non-rotating shaft earthing device E. If water may penetrate into the gap SP1 and thus into the sliding contact SK, the water can flow out again at the spatially lower edge of the covering element C, so that a good protection of the sliding contact SK against dust and corrosion is formed by the shaping of the covering element C.

[0064] Figure 4 A detailed cross-sectional view of details of a transmission G according to a second embodiment of the invention is shown, which second embodiment corresponds essentially to the Figure 3 first embodiment shown therein. Now, the covering element C has a radially outwardly directed protrusion C2 that is coupled to the axial section C1 and thus extends the labyrinth path. A radial gap SP2 exists between the protrusion C2 and the housing GG, such that water dripping on the housing GG cannot flow into the gap SP2. If water may penetrate into the gap SP2, the water can flow out again at the spatially lower edge of the covering element C, so that a good protection of the sliding contact SK against dust and corrosion is formed by the shaping of the covering element C.

[0065] Figure 5 A detailed cross-sectional view of details of a transmission G according to a third embodiment of the invention is shown, which third embodiment corresponds essentially to the Figure 3 first embodiment shown therein. Now, the covering element C is designed in a C-shape, wherein the working surface on the shaft side of the sliding contact SK is formed by the surface of the covering element C.

[0066] Figure 6 A detailed cross-sectional view of details of a transmission G according to a fourth embodiment of the invention is shown, which fourth embodiment corresponds essentially to the Figure 3 first embodiment shown therein. To prevent moisture from penetrating into the sliding contact SK due to the interference fit between the shaft W and the covering element C, an O-ring O1 is provided. The shaping of the covering element C is correspondingly adapted so as not to damage the O-ring O1 when the covering element C is pressed onto the shaft W. Thus, now, the covering element C is first pushed onto the shaft W with a bending radius, rather than onto an independent edge.

[0067] Additionally, an O-ring O2 is provided in the transmission G according to the fourth embodiment. The O-ring O2 is arranged between a section of the housing GG and the shaft grounding device E. Thereby, moisture or dust is prevented from reaching the intermediate space between the shaft grounding device E and the radial shaft seal DR from above in a simple manner. However, if dust or the like reaches the intermediate space between the shaft grounding device E and the radial shaft seal DR from above, the dust or the like is intercepted by the dust-proof lip of the radial shaft seal DR that faces the shaft grounding device E. Dust-proof lips are arranged over the entire circumference of the radial shaft seal DR, such that dirt around the sliding contact SK can be discharged downward. The O-ring O2 can be used in any of the foregoing embodiments, regardless of the design of the covering element C.

[0068] Additionally, a covering hood K is provided in the transmission G according to the fourth embodiment. The covering hood K is fixed to the shaft grounding device E and is made of, for example, patches (Flies). The covering hood K provides additional protection for the sliding contact SK against environmental influences. The covering hood K can be used in any of the foregoing embodiments.

[0069] Figure 7 An isometric view of the driven side of the transmission G according to the fourth embodiment is shown. It can be clearly seen therein that the shaft W projects from the housing GG. The shaft grounding device E is mechanically fixed to the housing GG by means of a plurality of fixing tabs EB, and the shaft grounding device E is also electrically connected to the housing GG by means of the fixing tabs EB. The covering element C is designed in a sleeve shape and surrounds a part of the shaft grounding device E to protect Figure 7 the invisible sliding contact SK from environmental influences.

Claims

1. A transmission (G) for a motor vehicle, wherein the transmission (G) has: a housing (GG); shafts (W, GW2, DS1, DS2) supported in the housing (GG) and protruding from the housing (GG); a radial shaft seal ring (DR) having a sealing lip for sealing an oil chamber (NR) within the housing (GG) relative to the environment; a shaft grounding device (E) arranged on the ambient side of the radial shaft seal ring (DR) for forming an electrically conductive sliding contact (SK) between the shafts (W, GW2, DS1, DS2) and the housing (GG); and a sleeve-shaped covering element (C) fixedly connected to the shafts (W, GW2, DS1, DS2) for protecting the sliding contact (SK) from the environment, It is characterized in that The shaft grounding device (E) is fixedly connected to the housing (GG), wherein the covering element (C) and the grounding device (E) together form a labyrinth seal.

2. The transmission (G) according to claim 1, characterized in that, The covering element (C) has an axially oriented section (C1) that surrounds an axial projection (E1) of the shaft grounding device (E).

3. The transmission (G) according to claim 2, characterized in that, A radial gap (SP1) exists between the axially oriented section (C1) of the covering element (C) and the axial projection (E1) of the shaft grounding device (E).

4. The transmission (G) according to any one of claims 1 to 3, characterized in that The covering element (C) has a radially oriented projection (C2).

5. The transmission (G) according to claim 4, characterized in that, A radial gap (SP2) exists between the radially oriented projection (C2) of the covering element (C) and the housing (GG).

6. The transmission (G) according to claim 2 or claim 3, characterized in that, The covering element (C) has a radially oriented projection (C2), and the radially oriented projection (C2) of the covering element (C) is connected to the axially oriented section (C1) of the covering element.

7. The transmission (G) according to one of claims 1 to 3, characterized in that, The diameter by which the covering element (C) is fixed to the shaft is greater than the diameter of the sliding contact (SK).

8. The transmission (G) according to one of claims 1 to 3, characterized in that, The face of the covering element (C) forms the working face on the shaft side of the sliding contact (SK).

9. The transmission (G) according to one of claims 1 to 3, characterized in that, The sliding contact (SK) of the shaft grounding device (E) is realized as a brush or in the form of an electrically conductive PTFE element.

10. The transmission (G) according to one of claims 1 to 3, characterized in that, The shaft is formed by a driven shaft of the transmission (G).

11. The transmission (G) according to one of claims 1 to 3, characterized in that, The transmission (G) has an electric machine (EM) and an inverter (INV) assigned to the electric machine (EM).

12. The transmission (G) according to one of claims 1 to 3, characterized in that, The transmission (G) is an automatic transmission based on a planetary gear set, a dual clutch transmission, an automated transmission, or a CVT transmission.

13. An electric axle drive device (EA) for a motor vehicle, characterized in that The transmission (G) according to one of claims 1 to 11.

Images