Patent Application
20240266928
The present application is related and has right of priority to German Patent Application No. 10 2023 201 006.2 filed on Feb. 8, 2023, the entirety of which is incorporated by reference for all purposes.
The invention relates generally to an arrangement for grounding a shaft, in particular a rotor shaft of an electric machine, the arrangement including a grounding hub, via which the shaft to be grounded is electrically conductively connected to a ground, preferably a housing. The invention also relates generally to a transmission, an electric drive axle unit for a motor vehicle, and to an electric machine, in each of which the aforementioned arrangement is implemented.
Electric machines are used in the automotive field in order to provide the motor vehicle as a hybrid or electric vehicle. Electric machines are also provided with some motor vehicle transmissions in order to make the motor vehicle transmission suitable for use in a hybrid or electric vehicle. Whereas the rest of the components of the transmission are enclosed and shielded by the surrounding transmission housing, the shafts guided out of the transmission housing induce electromagnetic interference, which, in the area of a motor vehicle, results in a malfunction of other electronic components. In addition, a potential difference builds up between the shaft and the transmission housing, which results in perforations on bearings of the shaft and thus, reduces the service life of these bearings. For this reason, the shaft concerned should be grounded, if possible. A shaft is also to be grounded with respect to other electric machines provided in a motor vehicle, such as, for example, electric axle drive units, in order to eliminate or reduce electromagnetic interference and to prevent the build-up of a potential difference. Grounding is usually carried out by electrically conductively connecting the shaft to be grounded to a ground, which is usually a housing.
DE 10 2019 133 677 A1 describes an arrangement for grounding a rotor shaft of an electric machine, wherein the rotor shaft in this arrangement is electrically conductively connected via a tubular grounding hub to a housing, which acts as a ground for grounding the rotor shaft. The grounding hub is supported at one axial end on the rotor shaft via a support bearing and is floatingly mounted at an opposite axial end in a housing cover of the housing. For the floating mounting, an electrically conductive, radially spring-loaded intermediate element is radially between the grounding hub and the housing cover, the intermediate element, as a conductor element, also establishing the electrically conductive connection between the grounding hub and the housing. On the rotor shaft side, an electrically conductive connection between the grounding hub and the rotor shaft is established as a sliding contact via a contact element, which is a carbon pin. The carbon pin is mounted on the rotor shaft and guided in a carbon brush holder, which is mounted on the grounding hub. Due to sliding contact between the carbon pin and the carbon brush holder, the electrically conductive connection is established between the grounding hub and the rotor shaft.
The present invention provides a reliable arrangement for grounding a shaft, characterized by the lowest possible manufacturing complexity.
According to the invention, an arrangement for grounding a shaft includes a grounding hub, via which the shaft to be grounded is electrically conductively connected to a ground, preferably a housing.
A “shaft” as set forth in the invention should be understood, in principle, as a rotatable component which transmits a rotational motion between components to be coupled. This shaft is also integral with one or both component(s) to be coupled. It is particularly preferred when the shaft to be grounded is a rotor shaft which is provided for a corotational connection with a rotor of an electric machine. The rotor and the rotor shaft are also formable as one piece or as individual components which are separate and connected to one another for conjoint rotation. The electric machine is an integral part of a motor vehicle transmission. The shaft to be grounded is also, in principle, any type of shaft, such as, for example, a transmission shaft.
In the arrangement according to the invention, the grounding hub electrically conductively connects the shaft to be grounded to the ground by the grounding hub being electrically conductively connected to the shaft to be grounded and also electrically conductively connected to the ground. The grounding hub consists of an electrically conductive material, at least in contact regions with the ground and the shaft to be grounded and in an intermediate region connecting these contact regions. The grounding hub is preferably formed completely of an electrically conductive material, however.
The grounding hub as set forth in the invention has, in particular, a rod-like shape, i.e., it is an elongate component, similarly to a shaft, in order to establish the electrically conductive connection preferably axially between the shaft to be grounded and the ground within the arrangement according to the invention. It is further preferred when the grounding hub is rotationally symmetrical.
The ground, with which the electrically conductive connection of the shaft to be grounded is established via the intermediate grounding hub, is, as set forth in the invention, an electrically conductive body, to which, in particular, the potential zero is assigned as reference potential. Preferably, this ground is present as a housing. The electrically conductive connection of the grounding hub is specifically established at this housing, a housing part, or a component which is permanently electrically connected thereto. It is particularly preferred when the grounding hub establishes an electrically conductive connection of the shaft to be grounded with a housing cover of a housing.
Within the scope of the invention, “axial” means an orientation towards an axis of rotation of the shaft or of a longitudinal axis of the grounding hub, whereas “radial” means an orientation in the diameter direction from the axis of rotation of the shaft to be grounded or from the longitudinal axis of the grounding hub.
As set forth in the invention, an “electrically conductive” connection should be understood as a connection in which a current flow is made possible between the connected components. With respect to the arrangement according to the invention, this electrically conductive connection is formed between the ground and the grounding hub, and between the grounding hub and the shaft to be grounded, wherein this connection is implementable directly or indirectly via further, intermediate components.
In particular, a bearing is between the grounding hub and the shaft to be grounded, via which bearing the shaft to be grounded is mounted for rotation with respect to the grounding hub. This bearing is, in particular, a radial bearing, this radial bearing preferably being a roller bearing and, particularly preferably, a grooved ball bearing. Within the scope of the invention, the intermediate bearing could be a different bearing, such as, for example, a roller bearing, or even a plain bearing.
The invention now encompasses the technical teaching that a separate guide element is mounted on the grounding hub, the guide element rotationally fixing the grounding hub in a direction of rotation and/or limiting a displacement of the grounding hub in at least one axial direction. In other words, a guide element is a separate component, via which the grounding hub is secured against rotation or via which an axial displacement of the grounding hub is limited in at least one axial direction or via which the grounding hub is secured against rotation and an axial displacement of the grounding hub is limited in at least one axial direction. This guide element is mounted on the grounding hub, i.e., the guide element and the grounding hub are fixed to one another, preferably the guide element is directly mounted on the grounding hub.
Such an embodiment of an arrangement has the advantage that the grounding hub is reliably securable against rotation and/or an axial displacement of the grounding hub is reliably limitable. Due to the fact that the guide element is present as a separate component which is mounted on the grounding hub, a complex formation of a section for preventing rotation of the grounding hub and/or axially securing the grounding hub is dispensed with on the grounding hub side. Therefore, the arrangement is achieved with low manufacturing complexity and, in addition, a reliable grounding of a shaft is provided. According to one embodiment of the invention, the guide element secures the grounding hub against rotation on the ground side by at least one rib formed on the guide element or on the ground, each of the at least one rib projects radially and extends in the circumferential direction over a subsection, and projects into a respective recess, each recess being delimited on both sides of the at least one rib in the circumferential direction and formed on the ground or on the guide element. As a result, rotation prevention is achieved easily by positive engagement. It is particularly preferred when the at least one rib projects radially with respect to the rest of the guide element, while the associated recess is defined on the ground side, in particular by a corresponding configuration of the housing which forms the ground. In particular, the guide element is equipped with multiple ribs, particularly preferably with two ribs.
According to one example aspect of the invention, the guide element is ring-shaped and mounted via an inner diameter on an outer diameter of the grounding hub. In this case, the guide element is therefore mounted on the grounding hub such that the guide element radially surrounds the grounding hub, for the purpose of which the guide element has a ring-shaped configuration. In addition to the ring-shaped configuration, the guide element additionally preferably has a disk-shaped character such that the guide element is a ring-shaped guide disk.
In one development of this example aspect, the guide element is pressed or press-fit onto the grounding hub. Advantageously, a reliable mounting of the guide element on the grounding hub is achieved as a result. If the grounding hub has been produced using an extrusion process, the guide element may have also been integrated in the shaping process of the grounding hub. In addition, mounting via welding, soldering, or via unfolding is also conceivable.
Alternatively, it is conceivable that the guide element is ring-shaped due to an alternative configuration and is mounted via an outer diameter on an inner diameter of the grounding hub.
In another embodiment of the invention, the grounding hub is electrically conductively connected to the ground via an intermediate conductor element. In this case, the grounding hub is therefore not directly electrically conductively connected to the ground. Instead, the electrically conductive connection is established via an intermediate component as a conductor element.
In one development of the aforementioned embodiment, the conductor element is a spring element, via which the grounding hub is axially preloaded towards the shaft to be grounded, the spring element axially electrically contacting the grounding hub to the ground. In one development of the invention, the conductor element is placed axially between the ground and an end face of the grounding hub facing away from the shaft to be grounded. The conductor element is situated, in particular, axially between the end face of the grounding hub and an abutment shoulder formed by the ground. Advantageously, as a result, a radially compact configuration is achieved by placing the radially compact conductor element on an axial end of the grounding hub and thus on an end face of the grounding hub. Particularly preferably, an abutment surface is defined on the end face of the grounding hub, at which abutment surface an axial contact of the grounding hub with the conductor element is established. If the conductor element is a spring element, force is introduced axially at the abutment surface for preloading the grounding hub.
Alternatively, the conductor element is axially between the ground and the guide element, which is mounted on the outer diameter of the grounding hub. Therefore, the conductor element radially surrounds the grounding hub, wherein the conductor element, as a spring element, then uses the guide element to axially preload the grounding hub. This has the advantage that the diameter of the grounding hub is therefore kept small and, as a result, its production is simplified. In addition, if the grounding hub is tubular and provided for supplying lubricant, the conductor element is no longer subjected to the lubricant pressure due to the placement on the outer diameter of the grounding hub. Improved electrical contacting is to be expected as a result.
Particularly preferably, the spring element is a wave spring, as a result of which the axial electrical contact is established with a low contact length and thus also with low contact resistance. Alternatively, the spring element could also be, in principle, a helical spring, a disk spring or the like.
In another example aspect of the invention, the grounding hub is floatingly mounted on the ground side. The grounding hub is therefore axially movable with play with respect to the ground, as a result of which the axial preload of the grounding hub is easily implemented, in particular, via the spring element. This is the case because, as a result, the grounding hub is axially displaceable relative to the ground and thus also preloaded relative to the ground. In combination with the conductor element, which is a spring element, the axial electric contact between the grounding hub and the ground is then achievable via the spring element.
In one development of the aforementioned embodiment, the grounding hub forms a guide section on a subsection thereof, on which guide section the grounding hub is axially displaceably guided in a guide bore on the ground side. As a result, the floating mounting of the grounding hub on the ground is easily achieved. It is particularly preferred when the guide section is formed as an axially extending section.
It is further preferred when the guide bore is defined by a contour and lengthened axially into the region in which the conductor element is between an abutment shoulder of the ground and the guide element. The conductor element and the abutment shoulder of the ground radially surround the guide bore. This has the advantage that a sealing length in the guide area of the grounding hub on the ground is therefore lengthened. In addition, sizing the conductor element is therefore no longer dependent on an outer diameter of the grounding hub, in that the conductor element is radially further outward with respect to the grounding hub.
According to another embodiment of the invention, the guide element limits an axial displacement of the grounding hub with respect to the ground in at least one axial direction via interaction with one axial stop in each case. Advantageously, as a result, an axial movement of the grounding hub with respect to the ground in the corresponding direction is limited, wherein, when a spring element is used as the conductor element to limit the axial movement towards the spring element, excessive compression of the spring element is prevented. A limitation of the axial movement of the grounding hub in the opposite direction, specifically towards the shaft to be grounded, is advantageous for an installation of the arrangement according to the invention, however, in that the grounding hub is axially fixed within the scope of the installation prior to the establishment of axial contact with the shaft to be grounded.
In one development of the aforementioned embodiment, the one stop in each case is an abutment shoulder of the ground and/or by a snap ring. The snap ring is placed in a corresponding groove particularly preferably on the ground side and is therefore axially fixed on the ground. In both cases, a stop is realized in a simple way.
Alternatively, or in addition to the aforementioned development, an axial displacement of the grounding hub with respect to the ground towards the shaft to be grounded is limited due to the interaction of the guide element with the snap ring, whereas a limitation in an opposite axial displacement direction of the grounding hub is formed by interaction of the guide element with an abutment shoulder. In this case, therefore, axial displacements of the grounding hub are limited in both directions, wherein this is achieved in one axial direction due to the interaction of the guide element with a snap ring and in the other axial direction due to the interaction of the guide element with an abutment shoulder.
In one embodiment of the invention, the grounding hub is tubular at least in sections and, via an internal volume, connects a supply connection for lubricant and/or coolant on the ground side to the shaft to be grounded. As a result, in addition to establishing the electrically conductive connection between the shaft to be grounded and the ground, the grounding hub also performs the function of supplying lubricant and/or coolant to the shaft to be grounded, for the purpose of which the grounding hub is tubular at least in sections.
The lubricant and/or coolant is guided via an internal volume of the grounding hub, which is tubular at least in sections, and a resultant defined supply line to the shaft to be grounded. The medium is preferably oil, the medium is provided for cooling the shaft, which is, in particular, a rotor shaft. The grounding hub is tubular at least over a portion of its axial extension, an internal volume being delimited by the surrounding material of the grounding hub at least in the tubular portion and thus the supply line being defined in this region. Particularly preferably, however, the grounding hub is entirely a tube, in order to therefore enable the lubricant and/or coolant to be supplied via the entire axial extension of the grounding hub and thus also to achieve guidance of the medium from the one axial end of the grounding hub to the other axial end. This embodiment is combined, in particular, with the development of the invention, in which the grounding hub is permanently secured against rotation, since, as a result, a flow of the lubricant and/or coolant via the grounding hub is simplified because the grounding hub does not rotate.
In one development of the aforementioned embodiment, the internal volume of the grounding hub is connected to a radial outer region of the grounding hub via at least one bore. As a result, a portion of the lubricant and/or coolant conducted via the internal volume is also directable into the radial outer region of the grounding hub, in order to also supply other components in addition to the shaft to be grounded, such as, for example, bearings and/or gears, etc. It is particularly preferred when the at least one bore is axially adjacent to an inner ring of a bearing, which connects the grounding hub to the shaft to be grounded. Furthermore, the at least one bore lies vertically below, in particular in the installed position of the grounding hub, in order to allow a portion of the lubricant and/or coolant to easily flow out via the at least one bore.
In one development of the invention, the grounding hub has a diameter reduction, on which a bearing having an inner ring is placed, the bearing connecting the grounding hub to the shaft to be grounded. As a result, a projection and thus also an abutment shoulder are defined on the grounding hub side, via which abutment shoulder an axial force introduced into the grounding hub is transmittable onto the inner ring of the bearing. This diameter reduction, in combination with the aforementioned embodiment, in which the grounding hub supplies lubricant and/or coolant to the shaft to be grounded, is also usable to change the flow cross-section and thus to adjust the amount of lubricant and/or coolant conducted to the shaft. Alternatively, or additionally, a sleeve is provided in the grounding hub on the side of the shaft to be grounded in the region of a mouth of the interior space of the grounding hub, via which sleeve the flow cross-section is also changeable and thus the amount of lubricant and/or coolant is also adjustable.
According to one advantageous embodiment of the invention, a bearing electrically conductively connects the grounding hub to the shaft to be grounded. In this case, the electrically conductive connection is therefore established between the grounding hub and the shaft to be grounded via an intermediate bearing, as a result of which a separate connecting element is eliminated and thus the manufacturing complexity is reduced. This is the case because the bearing is placed on a small diameter between the grounding hub and the shaft to be grounded, as a result of which low peripheral speeds arise at the bearing. Due to these low peripheral speeds, an insulating effect of lubricant of the bearing, which otherwise increases as the speed increases, is avoided, which could otherwise make the electrically conductive connection via the bearing more difficult. Within the scope of the invention, the electrically conductive connection is established between the grounding hub and the shaft to be grounded equally well via a separate contact element, such as, for example, a carbon brush.
According to one example aspect of the invention, the grounding hub is made of aluminum. This has the advantage that, due to the grounding hub being made of aluminum, a high conductivity of the grounding hub for alternating current is achieved. In addition, the grounding hub therefore has a low weight, such that weight is reduced overall in the arrangement. Preferably, the grounding hub has been manufactured in an extrusion process. Alternatively, the grounding hub could also consist of copper or be a plastic body with an electrically conductive coating. It is particularly preferred when the guide element, which is separate and mounted on the grounding hub, also consists of aluminum.
Alternatively, it is also conceivable within the scope of the invention that the guide element is made of a material having higher strength in comparison to aluminum. As a result, a higher breaking elongation and thus also reliably securing the grounding hub against rotation and/or reliably delimiting an axial displacement of the grounding hub is achieved in the region of the guide element. The guide element is made of steel, although another material having a higher strength in comparison to aluminum is usable, such as, for example, a composite material, i.e., a combination of multiple materials.
The invention also relates to a transmission, which is, in particular, a motor vehicle transmission. In this transmission, at least one shaft is grounded in an arrangement according to one or more of the aforementioned variants. This arrangement is achieved, in particular, with a rotor shaft of an electric machine which is integrated into the housing. An arrangement according to the invention for grounding the shaft is also an integral part of an electric drive axle unit for a motor vehicle or of an electric machine.
Advantageous embodiments of the invention, which are explained in the following, are shown in the drawings, in which:
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.
In addition, a power inverter 12 is mounted on the housing 9. The power inverter 12 is connected to the electric machine 10 on one side and to a battery 13 on the other side. The power inverter 12 is utilized for converting the direct current of the battery 13 into an alternating current, which is suitable for operating the electric machine 10, and includes several power semiconductors for this purpose. The conversion between direct current and alternating current takes place by a pulse-like operation of the power semiconductors controlled by an open-loop system.
The shaft 11 of the electric machine 10 is grounded in order to prevent electromagnetic interference and the build-up of a potential difference during operation. This is shown in
As is apparent with reference to
On an axial end 21 (
As is also apparent from
The spring element 27 is also used, however, to establish axial contact between the grounding hub 17 and the housing cover 18 of the housing 9, in order to always maintain the electrically conductive connection between the grounding hub 17 and the housing cover 18 in this case as well. Due to the spring element 27 being a wave spring, this electrical contact is established with a short conduction path and thus, with low contact resistance.
As is apparent in
The guide element 30 is used to limit an axial relative displacement of the grounding hub 17 with respect to the housing cover 18 in both axial directions. For instance, as shown in
The guide element 30 also prevents rotation of the grounding hub 17 by the guide element 30 having a rib 40 which is apparent, in particular, in each of
Apart from establishing the electrically conductive connection between the shaft 11 to be grounded and the housing cover 18, the grounding hub 17 is also used to supply lubricant and/or coolant to the shaft 11 to be grounded in order to cool the shaft 11 and, in particular, the rotor of the electric machine. The lubricant and/or coolant is preferably oil. The lubricant and/or coolant is introduced from the axial end 21 (
Furthermore,
The abutment shoulder 45 is defined on the housing cover 18 radially inward with respect to the abutment shoulder 37, which functions as the stop 34 for the guide element 30 with respect to the variant according to
In addition,
The abutment shoulder 37 and the abutment shoulder 45 are defined by a contour 47, which is a guide bore 48 for axially guiding the grounding hub 17 on the housing cover 18. The abutment shoulder 37 projects with respect to the abutment shoulder 45 axially towards the guide element 30, as a result of which the guide bore 48 is lengthened axially into the region in which the spring element 44 extends between the abutment shoulder 45 and the end face 33 of the guide element 30. As a result, a sealing length between an outer diameter 23 of the grounding hub 17 and the guide bore 48 is correspondingly axially lengthened. In addition, the spring element 44 extends radially further outwards, as a result of which a smaller number of windings is necessary in order to provide the force necessary to preload the grounding hub 17. The contour 47 is additionally used as a spacer element during installation of the spring element 44, in order to avoid a complete compression of the spring element 44 and thus destruction of the spring element 44. The rest of the embodiment according to
Furthermore,
In the present case, a grounding of the shaft 55 is carried out within the framework of an arrangement according to the invention, the arrangement being produced similarly to one of the variants according to
Finally,
In the present case, the rotor shaft 66 is grounded within the framework of an arrangement according to the invention, the arrangement being produced similarly to one of the variants according to
Reliable grounding of a shaft is achieved by the embodiments of an arrangement according to the invention.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102023201006.2 | Feb 2023 | DE | national |
