Shaft grounding device, transmission, electric axle drive unit and motor

Abstract

The utility model relates to a shaft grounding device used for establishing conductive connection between a rotatable shaft and a shell, the shaft grounding device is configured to be annular and is provided with a plurality of bending elastic and conductive contact elements so as to form conductive sliding contact with the circumferential surface of the shaft or a sleeve applied to the shaft. Each of the contact elements has a hinge section and a sliding contact section with a wear region, and at least one flexurally elastic contact element only serving as a cleaning element is provided in addition to the flexurally elastic and electrically conductive contact element, the contact element comprises a hinge section and a sliding contact section with a wear region, the length of the contact element corresponds to the length of the electrically conductive contact element and the contact element has a smaller width with the same pressing force as the bending-elastic and electrically conductive contact element and thus has a smaller contact surface with the shaft or with the sleeve in order to achieve an increased surface pressure.

Description

Technical Field

[0001] The utility model relates to a shaft grounding device for establishing an electrically conductive connection between a rotatable shaft and a housing, a transmission for a motor vehicle having the shaft grounding device, an electric axle drive unit for a motor vehicle having the shaft grounding device, and a motor having the shaft grounding device. Background Art

[0002] DE 10 2016 010 926 A1 describes a shaft grounding ring for conducting an induced voltage from a shaft into a machine element. The known shaft grounding ring has a housing and a plurality of conduction elements arranged on the housing, wherein an elastically bent edge region of each of the conduction elements rests on the shaft, thereby forming an electrically conductive sliding contact with the shaft, wherein the conduction element is a disk-shaped conduction body extending over at least part of its circumference.

[0003] Furthermore, a shaft grounding device is known which is mechanically and electrically connected to the housing and which has a flexurally elastic and electrically conductive contact element which forms an electrically conductive sliding contact with the circumference of the shaft or with a sleeve applied to the shaft, wherein the contact element is arranged and constructed such that it causes a preload of the sliding contact due to its own flexural elasticity and each of the contact elements has an articulated section and a sliding contact section with a wear region. The radial force of the contact element for generating the preload is adjusted by the articulated thickness at the turning point between the articulated section and the sliding contact section.

[0004] According to the prior art, shaft grounding requires a small but constant pressing of a material having good electrical conductivity onto the clean and ground shaft surface during its service life.

[0005] In order to improve the electrical conductivity, contact elements consisting of a combination of a plastic carrier material with conductive particles (such as graphite) and an additional conductive layer of a silver surface are proposed according to the prior art. In this case, the plastic carrier material should be worn to a defined extent in order to be able to renew the silver contact surface, which is particularly conductive.

[0006] During operation of the shaft grounding device, the contact elements wear out, so that the contact elements become shorter with increasing operating time. This reduces the preload of the sliding contact. In order to ensure reliable electrical contact during the service life, the initial preload of the contact elements must be selected to be correspondingly high.

[0007] As described in the prior art, a small compression may lead to the disadvantage that undesirable operating materials, such as transmission oil, corrosion inhibitors and grease, may lead to the floating of the contact elements. It has been observed within the scope of tests that operating materials with low viscosity, such as transmission oil, lead to the floating of shaft sealing rings for a longer time. Such shaft sealing rings are used to seal bearings. The rotatable shaft to be grounded is usually supported on the housing by means of a ball bearing, wherein the ball bearing is located in an oil chamber, and in order to seal the oil chamber from the surroundings, a radial shaft sealing ring with a sealing lip is provided, which is in sliding contact with the shaft, wherein the shaft grounding device is arranged on the surroundings side of the radial shaft sealing ring.

[0008] The effect of this floating is a short-term (approximately 15 hours of operating time) significant increase in the electrical resistance, wherein the floating effect becomes greater the lower the viscosity of the interfering working material.

[0009] Due to the wear of the carrier material of the contact element, an axial displacement of the contact path may occur, which is disadvantageous in particular when it comes to shaft materials that may cause corrosion due to external influences, wherein this disadvantage occurs when corrosion starts in the vicinity of the current running path of the contact element and the contact element encounters corroded locations due to the wear-induced axial displacement of the contact path. Corrosive surfaces lead to increased wear of the carrier material of the contact element, which can disadvantageously lead to a short service life. Utility Model Content

[0010] The object of the invention is to provide a shaft grounding device for producing an electrically conductive connection between a rotatable shaft and a housing.

[0011] To this end, the utility model proposes a shaft grounding device for establishing an electrically conductive connection between a rotatable shaft and a housing, the shaft grounding device being constructed in an annular shape and having a plurality of flexurally elastic and electrically conductive first contact elements so as to form an electrically conductive sliding contact with the circumferential surface of the shaft or a sleeve applied to the shaft, each of the first contact elements having an articulated section and a sliding contact section with a wear area, wherein the shaft grounding device has, in addition to the flexurally elastic and electrically conductive first contact elements, at least one flexurally elastic second contact element which serves only as a cleaning element, the second contact element including an articulated section and a sliding contact section with a wear area, the length of the second contact element corresponding to the length of the electrically conductive first contact element and the second contact element having a smaller width under the same pressing force as the flexurally elastic and electrically conductive first contact element and therefore having a smaller contact surface with the shaft or with the sleeve so as to achieve an increased surface pressure.

[0012] The utility model further relates to a transmission for a motor vehicle, wherein a shaft grounding device according to the utility model is provided for establishing an electrically conductive connection between a shaft of the transmission and a housing of the transmission, and the shaft grounding device is mechanically and electrically conductively connected to the housing of the transmission.

[0013] The utility model also relates to an electric axle drive unit for a motor vehicle, wherein a shaft grounding device according to the utility model is provided for establishing an electrically conductive connection between a shaft of the electric axle drive unit and a housing of the electric axle drive unit, and the shaft grounding device is mechanically and electrically conductively connected to the housing of the electric axle drive unit.

[0014] The utility model also relates to an electric motor, wherein a shaft grounding device according to the utility model is provided for establishing an electrically conductive connection between a rotor shaft of the electric motor and a housing of the electric motor, and the shaft grounding device is mechanically and electrically conductively connected to the housing of the electric motor.

[0015] Therefore, a shaft grounding device for establishing an electrically conductive connection between a rotatable shaft and a housing is proposed, wherein the shaft grounding device is constructed in an annular shape and has a plurality of flexurally elastic and electrically conductive contact elements so as to form an electrically conductive sliding contact with the circumferential surface of the shaft or a sleeve applied to the shaft, wherein each of the contact elements has an articulated section and a sliding contact section with a wear area.

[0016] According to the present invention, the shaft grounding device has at least one flexurally elastic contact element in addition to the flexurally elastic and electrically conductive contact element, which includes an articulated section and a sliding contact section with a wear area, the length of which corresponds to the length of the electrically conductive contact element and which serves only as a cleaning element for the shaft or sleeve and has a smaller width and therefore a smaller contact surface with the shaft or with the sleeve under the same pressing force as the flexurally elastic and electrically conductive contact element, which achieves an increased surface pressure, wherein the contact surface covers the current operating trajectory of the electrically conductive contact element during operation of the shaft grounding device according to the present invention.

[0017] The smaller width of the at least one cleaning element advantageously ensures that residual oil and undesired working material on the running path of the conductive contact element are removed quickly on the shaft or sleeve by increased surface pressure, so that the conductive contact element can come into contact with the shaft or sleeve more quickly.

[0018] According to an advantageous extension of the present invention, the at least one cleaning element is implemented in a manner where the contact surface with the shaft or with the sleeve is generally smaller than the conductive contact element, so that the contact surface with the shaft or with the sleeve extends over a larger axial area when viewed axially in the direction of the articulated section and thus also covers the future operating path of the conductive contact element caused by wear during operation.

[0019] According to an extension of the present invention, the at least one cleaning element is also used to specifically converge (Raffung) the wear compared to the conductive contact element, so as to serve as maintenance on the current operating trajectory and in the case where the contact surface with the shaft or sleeve extends over a larger axial area axially toward the articulated section and also covers the future operating trajectory of the conductive contact element caused by wear during operation, the conductive particles (such as graphite) and / or additives with anti-corrosion properties contained in the wear area of ​​the at least one cleaning element are also released due to wear on the future operating trajectory of the conductive contact element.

[0020] In this way, the future running path of the electrically conductive contact element can be pre-maintained during operation of the shaft grounding device, so that reduced corrosion formation can be achieved in the contact area on the shaft or sleeve. Corrosion on the future running path of the electrically conductive contact element is thus prevented without using rust-proof materials; the electrical conductivity of stainless steel is, for example, up to 20 times worse than that of ordinary alloy steels, wherein stainless steel is also expensive and requires cost-intensive production.

[0021] In the case where the shaft grounding device has a plurality of cleaning elements, the cleaning elements are preferably arranged equidistantly in the circumferential direction of the shaft grounding device.

[0022] The proposed shaft grounding device can be, for example, a component of a transmission for a motor vehicle, such as an automatic transmission or an automated transmission, in order to ground a shaft of the transmission, for example a transmission output shaft, relative to a housing of the transmission.

[0023] Furthermore, the arrangement according to the invention can be used for grounding a shaft of an electric axle drive unit for a motor vehicle or for grounding a rotor of an electric machine, for example an electric machine of a drive train of a motor vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is explained in more detail below by way of example with the aid of the accompanying drawings, wherein only the features that are important to the present invention are described in detail and the same reference numerals are used for the same components. In the accompanying drawings:

[0025] Figure 1 and Figure 2The powertrain of the motor vehicle is shown respectively;

[0026] Figure 3 The motor is shown;

[0027] Figure 4 A perspective detailed view showing a design of a shaft grounding device according to the present invention;

[0028] Figure 5 Show according to Figure 4 a perspective detail view of the shaft grounding device in the assembled state; and

[0029] Figure 6 Show according to Figure 4 Detailed cross-section of a shaft grounding device. DETAILED DESCRIPTION

[0030] Figure 1 The schematic diagram shows a powertrain for a motor vehicle. The powertrain has an internal combustion engine VM, the output of which is connected to the input shaft GW1 of a transmission G. The output shaft GW2 of the transmission G is connected to a differential AG. The differential AG is designed to distribute the power present on the output shaft GW2 to the drive wheels DW of the motor vehicle. The transmission G has a gear set RS, which together with the gear set in Figure 1 The switching element not shown in the figure is designed 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, which also accommodates the motor EM connected to the input shaft GW1. The motor EM is designed to drive the input shaft GW1. An inverter INV is fixed to the housing GG. The inverter INV is connected to the 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 motor EM, and has a plurality of power semiconductors for this purpose. The conversion between direct current and alternating current is carried out by controlled pulsed operation of the power semiconductors.

[0031] Figure 2 A powertrain for a motor vehicle is schematically shown, which is connected to the Figure 1Compared with the embodiment shown in , it is a purely electric powertrain. The powertrain has an electric axle drive unit EX. The electric axle drive unit EX includes an electric motor EM, the power of which is transmitted to the drive wheel DW of the motor vehicle through a reduction gear set RS2 and a differential AG. The output shafts DS1 and DS2 of the differential AG are connected to the drive wheel DW. The electric motor EM, the reduction gear set RS2 and the differential AG are surrounded by a housing GA. An inverter INV is fixed to the housing GA. 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 carried out by controlled pulsed operation of the power semiconductor.

[0032] exist Figure 1 and Figure 2 The powertrain shown in FIG. 1 is to be considered as exemplary only.

[0033] Due to the pulsed operation of the power semiconductors, electromagnetic interference signals may be generated, which may be generated, for example, according to Figure 1 The power train is coupled to the output shaft GW2 or according to Figure 2 The power transmission system is coupled to the output shafts DS1 and DS2. Figure 1 and Figure 2 The supporting structure of the driven shaft GW2 or the output shaft DS1, DS2, which is not shown, is electrically insulated relative to the housing GG or the housing GA, because the lubricating oil inside the housing GG, GA has electrically insulating properties. Therefore, the interference signal coupled into the driven shaft GW2 or coupled into the output shaft DS1, DS2 cannot flow into the housing GG or the housing GA connected to the electrical ground of the motor vehicle over a short path. Instead, the interference signal returns to the electrical ground through electromagnetic radiation, which may interfere with other electronic components of the motor vehicle. The driven shaft GW2 or the output shaft DS1, DS2 extending from the housing GG or the housing GA can form an antenna, which is conducive to the electromagnetic radiation of the interference signal.

[0034] Figure 3A schematic view of an electric motor EM2 is shown. The electric motor EM2 has a housing GE, which accommodates a stator S and a rotor R. The stator S is fixed in the housing GE in a rotationally fixed manner. The rotor R is coupled to a rotor shaft RW, wherein the rotor shaft RW is rotatably supported via two rolling bearings WL1, WL2 supported on the housing GE. One end of the rotor shaft RW protrudes from the housing GE. A shaft grounding device E is provided on the exposed section of the rotor shaft RW. A sealing ring DR2 is provided between the rolling bearing WL2 and the shaft grounding device. The shaft grounding device E establishes an electrically conductive contact between the housing GE and the rotor shaft RW. For this purpose, the shaft grounding device E has brushes or other electrically conductive contact elements that slide on the surface of the rotor shaft RW. The potential difference between the housing GE and the rotor shaft RW can be reduced via the shaft grounding device E. The rolling bearings WL1, WL2 are thereby protected from uncontrolled potential compensation via the rolling bodies of the rolling bearings WL1, WL2. Figure 1 and Figure 2 An exemplary arrangement of a shaft grounding device 1 is shown.

[0035] exist Figure 3 , 4 5 show a part of a shaft grounding device 1 for establishing an electrically conductive connection between a rotatable shaft 2 and a housing according to the present invention. The shaft grounding device is mechanically and electrically connected to the housing and comprises a plurality of flexurally elastic and electrically conductive contact elements 3, which form an electrically conductive sliding contact with the circumference of the shaft 2 or with a sleeve applied to the shaft 2, wherein each of the contact elements 3 has an articulated section 4 and a sliding contact section 5 with a wear region 6.

[0036] In the example shown in the figures, the contact element 3 is fixed between a holding element 7 and a clamping element 8 , wherein the holding element 8 produces a mechanical and electrically conductive contact with the housing.

[0037] According to the present invention and with reference to the accompanying drawings, the shaft grounding device 1 has at least one flexurally elastic contact element 9 in addition to the flexurally elastic and electrically conductive contact element 3, wherein the contact element includes a hinged section and a sliding contact section with a wear area, and the length of the contact element corresponds to the length of the electrically conductive contact element 3.

[0038] The contact element 9 serves only as a cleaning element for the shaft 2 or sleeve and has a smaller width and therefore a smaller contact surface relative to the shaft 2 or sleeve at the same contact force as the flexurally elastic and electrically conductive contact element 3, which achieves an increased surface pressure. In this case, the contact surface of the at least one cleaning element 9 covers the current operating path of the electrically conductive contact element 3 during operation.

[0039] According to one embodiment of the present invention, the wear region 10 of the at least one cleaning element 9 contains electrically conductive particles (such as graphite) and / or additives with anti-corrosion properties, which are released on the running path due to wear.

[0040] It is particularly advantageous if the at least one cleaning element 9 is designed so that the contact surface with the shaft 2 or with the sleeve is overall smaller than the electrically conductive contact element 3, so that the contact surface with the shaft 2 or with the sleeve extends over a larger axial area when viewed axially in the direction of the articulated section and thus also covers the future operating path of the electrically conductive contact element 3 caused by wear during operation.

[0041] This advantageously enables the future running path of the electrically conductive contact element 3 to be pre-maintained during operation of the shaft grounding device 1 in conjunction with the wear-induced release of electrically conductive particles (such as graphite) and / or additives having anti-corrosion properties.

[0042] Reference numerals

[0043] 1 Shaft grounding device

[0044] 2 Axis

[0045] 3 Conductive contact elements

[0046] 4 Articulated sections

[0047] 5 Sliding contact section

[0048] 6 Wear Areas

[0049] 7. Retaining element

[0050] 8 Clamping element

[0051] 9 Cleaning Elements

[0052] 10 Cleaning element wear areas

[0053] VM Internal Combustion Engine

[0054] EX e-axle drive unit

[0055] G Transmission

[0056] GW1 Input shaft

[0057] GW2 driven shaft

[0058] RS Gear Set

[0059] RS2 reduction gear set

[0060] EM Motor

[0061] INV Inverter

[0062] BAT Battery

[0063] AG Differential

[0064] DS1 Output shaft

[0065] DS2 Output shaft

[0066] DW drive wheel

[0067] GA Housing

[0068] EM Motor

[0069] S Stator

[0070] R Rotor

[0071] RW Rotor shaft

[0072] WL1 bearings

[0073] WL2 bearings

[0074] DR2 sealing ring

[0075] GE Housing

Claims

1. A shaft grounding device (1) for establishing an electrically conductive connection between a rotatable shaft (2) and a housing, the shaft grounding device (1) being designed in an annular shape and having a plurality of flexurally elastic and electrically conductive first contact elements (3) in order to form an electrically conductive sliding contact with the circumference of the shaft (2) or a sleeve applied to the shaft (2), each of the first contact elements (3) having an articulated section and a sliding contact section (5) with a wear zone, characterized in that The shaft grounding device (1) has, in addition to the first flexurally elastic and electrically conductive contact element (3), at least one second flexurally elastic contact element (9) which serves only as a cleaning element, the second contact element comprising an articulated section and a sliding contact section with a wear zone, the length of the second contact element corresponding to the length of the first electrically conductive contact element (3) and the second contact element having a smaller width and therefore a smaller contact surface with the shaft (2) or with the sleeve at the same pressing force as the first flexurally elastic and electrically conductive contact element (3) in order to achieve an increased surface pressure.

2. The shaft grounding device (1) according to claim 1, characterized in that: The wear region of the at least one flexurally elastic second contact element (9) which serves only as a cleaning element contains electrically conductive particles or additives with anti-corrosion properties which are released on the running path due to wear.

3. The shaft grounding device (1) according to claim 1 or 2, characterized in that: The at least one flexurally elastic second contact element (9) which serves only as a cleaning element is designed so that the contact surface with the shaft (2) or with the sleeve is smaller than the first electrically conductive contact element (3) in general, so that the contact surface with the shaft (2) or with the sleeve extends over a larger axial area when viewed axially in the direction of the articulated section and thus also covers the future running path of the first electrically conductive contact element (3) caused by wear during operation.

4. The shaft grounding device (1) according to claim 1 or 2, characterized in that: The shaft grounding device (1) has a plurality of second contact elements (9) which are arranged equidistantly in the circumferential direction of the shaft grounding device (1).

5. A transmission (G) for a motor vehicle, characterized in that A shaft grounding device (1) according to any one of claims 1 to 4 is provided for establishing an electrically conductive connection between a shaft (GW2) of a transmission (G) and a housing (GG) of the transmission (G), the shaft grounding device (1) being mechanically and electrically conductively connected to the housing (GG) of the transmission (G).

6. The transmission for a motor vehicle according to claim 5, characterized in that: The shaft (GW2) is the transmission driven shaft.

7. An electric axle drive unit (EX) for a motor vehicle, characterized in that A shaft grounding device (1) according to any one of claims 1 to 4 is provided for establishing an electrically conductive connection between a shaft (DS1, DS2) of the electric axle drive unit (EX) and a housing (GA) of the electric axle drive unit (EX), the shaft grounding device (1) being mechanically and electrically conductively connected to the housing (GE) of the electric axle drive unit (EX).

8. An electric motor (EM2), characterized in that A shaft grounding device (1) according to any one of claims 1 to 4 is provided for establishing an electrically conductive connection between a rotor shaft (RW) of the electric machine (EM2) and a housing (GE) of the electric machine (EM2), the shaft grounding device (1) being mechanically and electrically conductively connected to the housing (GE) of the electric machine (EM2).

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