Electric machine with detachable brush module, brush module and motor vehicle

Abstract

Electric machine (1) comprising a rotor (2) with a rotor shaft (3) and a brush module (10) with a brush carrier (6) with at least one brush (5) for supplying current to the rotor (2), characterized in that the brush module (10) comprises a shaft journal (4) which can be mechanically coupled reversibly to the rotor shaft (3) and on which the brush (5) rests.

Description

The invention relates to an electric machine comprising a rotor with a rotor shaft and a brush module with a brush carrier with at least one brush for energizing the rotor.Such an electric machine is used in various fields, for example in electrically operated motor vehicles. A common design is that of the externally excited synchronous machine, in which the rotor is electrically energized via slip rings on the rotor shaft and brushes. The brushes are pressed by springs against the sliding contacts of the rotor in order to make electrical contact possible and to supply the rotor with current for field generation.A specific field of application for such electric machines is battery-electric all-wheel vehicles. Boost axles are installed here, which are not continuously involved in the driving task. The rotor of the electric machine of this boost axle therefore only needs to be energized temporarily during the boost process and the remaining time is dragged along.Since the brushes are pressed continuously by springs onto the slip rings of the rotor shaft and the latter also rotates permanently outside the boost process, friction losses and wear of the brushes occur continuously at the contact points with the slip rings. In order to enable good electrical contacting of the slip rings by the brushes, the brushes usually contain a material with high electrical conductivity (e.g. copper, silver or gold). These materials are particularly expensive.By temporarily separating the brushes spatially from the slip rings, it is possible to reduce wear and thus the operating costs. The brushes can thus only wear during the boost process when they are in electrical contact with the slip rings.In order to enable such a temporary and spatial separation of a brush from a slip ring of a rotor, it is known from EP 3 159 980 A1 to use, in addition to a spring, also a fillable balloon element which is fixed via a bracket to a frame fixed in position in the radial direction of the rotor shaft. By filling or emptying the balloon element with a compressor, a brush can be pressed against its slip ring or lifted off it in the radial direction of the rotor shaft. It is thus possible to establish or separate an electrical contact between the brush and a slip ring of the rotor shaft by lifting or pressing a brush in the radial direction of a rotor shaft.Furthermore, it is known from CN 111987868 A that a brush can be lifted from its slip ring or pressed against it approximately radially to the axis of rotation of a rotor by using a rotary disk and a rotatable brush carrier on which the brush is mounted. In this case, the brush carrier is rotatable about an axis which is parallel to the axis of rotation of the rotor and offset therefrom. By means of a rotating disk which is likewise rotatable, the brush with the brush carrier is rotated away from the slip rings or pressed against the latter. In this case, the rotation of a plurality of brushes with rotary disks can be effected by a cable which is moved by a motor and a spring. The electrical brush contact can thus be disconnected and one or more brushes can be moved in this way approximately radially with respect to the axis of rotation of the rotor, wherein the direction of movement is arcuate.The invention is therefore based on the problem of specifying decoupling brushes from a rotor of an electric machine, which decoupling is improved in comparison therewith.To solve this problem, it is provided according to the invention in an electric machine of the type mentioned at the beginning that the brush module comprises a shaft journal which can be reversibly mechanically coupled to the rotor shaft and on which the brush bears.The invention proposes, in a brush module in which one, preferably two, or more brushes are held by a brush carrier, also providing a shaft journal which can be mechanically coupled to the rotor shaft of the electric machine or can be mechanically separated therefrom. In the coupled state, the shaft journal represents an axial extension of the rotor shaft. The one or more brushes can thus bear permanently against slip rings of the shaft journal without generating unnecessary wear or friction, since the shaft journal rotates only when it is mechanically coupled to the rotor shaft of the electric machine. A brush holder serves to hold all brushes in position and, for example by springs, to press on one or more slip rings on the shaft journal. To generate a directed current flow, at least two brushes and two separate slip rings are required. The spatial separation of the brushes from a continuously rotating rotor shaft is no longer effected radially but axially by mechanical decoupling of the shaft journal. Preferably, the shaft journal and the rotor shaft are arranged coaxially with respect to one another in order to enable simple mechanical coupling.In addition to the reversible mechanical coupling ability of the shaft journal to the rotor shaft, the electrical machine according to the invention is also distinguished in that a contact structure is provided on the shaft journal, which contact structure, when the shaft journal and the rotor shaft are mechanically coupled or decoupled, can be electrically contacted simultaneously with a contact structure provided on the rotor shaft side or can be separated therefrom. The rotor and the rotor shaft can thereby be electrically energized via the shaft journal. In this case, an electrical current flow is produced in the contact structure of the shaft journal by a contact between current-carrying brushes and slip rings of the shaft journal. By the mechanical coupling of the rotor shaft and the shaft journal, this current flow is continued into the contact structure of the rotor shaft and the rotor is energized. If the rotor shaft and the shaft journal are again mechanically separated from one another, the contact structures on the shaft journal and the rotor shaft are no longer in electrical contact, as a result of which the rotor is no longer energized by the shaft journal. The electrical coupling or decoupling takes place synchronously or simultaneously with the mechanical coupling or decoupling, so that both connections are produced within the scope of a common process.In a preferred embodiment variant, the shaft journal and / or the brush module are displaceable along the longitudinal axis of the rotor shaft for mechanical coupling and decoupling. Because the mechanical coupling is effected by an axial displacement of the shaft journal and / or of the brush module, an embodiment can be provided which is space-saving particularly in the radial direction of the rotor shaft and shaft journal. It is recommended that the rotor shaft and the shaft journal be arranged coaxially with respect to one another. Depending on the embodiment and module size and available installation space, either only the shaft journal or the entire brush module, comprising the shaft journal, the brush carrier and the brushes, can be displaced along the longitudinal axis of the rotor shaft for reversible mechanical coupling. In this case, it is advantageous if this displacement can be effected by an actuator, in order to be controllable, for example, with a spatially remote control unit. Coupling and decoupling can thus be controlled externally. A suitable actuator can be, for example, a linear actuator, an electric motor or a hydraulically or pneumatically controlled bolt. The actuator can act either on both sides or only in one direction, wherein in the latter case a restoring device, for example a spring, is required.One possibility for the mechanical coupling of the shaft journal to the rotor shaft without the use of additional coupling components is represented by the spur toothing. Thus, an embodiment variant of the electric machine is characterized in that the shaft journal and the rotor shaft can be reversibly mechanically coupled to a spur toothing. By axially displacing the shaft journal and / or the brush module, the teeth of the spur tooth arrangements of both shaft ends can engage in one another, whereby a reversible mechanical coupling can be produced. This coupling variant is space-saving in the radial direction of the coupling axis, since no add-on parts are required and only the surfaces of the shaft ends are required for the coupling.In a variant for spur toothing coupling, it can be provided that the shaft journal and the rotor shaft can be reversibly mechanically coupled to a switchable coupling device. The shaft journal and the rotor shaft can be coupled or disconnected by axial displacement of the shaft journal and / or the brush module with the aid of an additional coupling device. By using such a coupling device, a complicated and usually expensive post-processing of the shaft ends, as would be required, for example, for producing a spur toothing, can be avoided. The attachment of a coupling device may be less complicated than the production of couplable structures at both shaft ends. Even when a coupling device is used, a controllable actuator can advantageously be used for the axial displacement. In a further development, it is also recommended that the coupling device be switchable and be controllable from a spatial distance, for example by a control unit.In the coupled state, the rotor shaft and the shaft journal are connected to one another in a form-fitting manner by the coupling device or the spur toothing and rotate in the same direction at an identical rotational speed. By using a coupling device in combination with an axial displacement of the shaft journal and / or of the brush module, the rotor shaft and / or the shaft journal can also be provided with a particularly small diameter. The use of a coupling device requires additional installation space in the radial direction of the rotor shaft, but for this purpose allows any desired configuration of the end faces of the rotor shaft and of the journal and also the use of a rotor shaft and of a journal with small diameters.With regard to the type of coupling device for reversibly mechanically coupling the shaft journal to the rotor shaft, it can be provided in an advantageous embodiment that the coupling device is a clutch, preferably a claw clutch or a friction clutch. Couplings are usually standardized and therefore inexpensive components which can be used for the mechanical coupling of two shafts, wherein one or both shafts can rotate during the mechanical coupling. Here, a large number of generally known and tested axial couplings can be used, wherein the embodiment of the claw coupling appears particularly suitable for this purpose, since this allows a good positive fit and consequently a good mechanical connection of both shaft ends with little rotational play. In addition, there are variants of claw clutches which have a small installation space requirement in the radial direction of the coupling axis. In addition, the use of a friction clutch for mechanically coupling both shaft ends by means of frictional engagement offers the advantage that they do not synchronize, i.e. their angle of rotation does not have to be matched to one another. Stress peaks and forces which could arise during the mechanical coupling are also significantly lower in the case of a friction clutch.Depending on the design of an electric machine according to the invention and the available installation space, an axial displacement of the shaft journal and / or of the brush module may or may not be possible. In a development of an electric machine according to the invention described at the beginning, it can therefore be provided that the shaft journal and the brush module are fixed in position along the longitudinal axis of the rotor shaft, wherein the shaft journal and the rotor shaft can be reversibly mechanically coupled to a switchable coupling device. In contrast to the coupling variants explained above, the mechanical coupling of the shaft journal and the rotor shaft must be effected by an axial displacement of a coupling device, since in this embodiment both shaft ends are positionally fixed along the coupling axis. As a result, installation space can be saved in the axial direction of the rotor shaft and the shaft journal, since neither the shaft journal nor the brush module are axially displaced, wherein the shaft ends to be connected are as close as possible to one another. A suitable coupling device is preferably designed here as switchable too. The actuation of the coupling device can be effected, for example, via an actuator which can be controlled by an external control unit. For this purpose, a linear actuator, an electric motor or a hydraulically or pneumatically controlled bolt can be provided, for example. The actuator can thereby effect the back and forth movement or only one of the movements, wherein a restoring device, for example a spring, moves the coupling device back into the starting position.In a particularly advantageous embodiment variant, the coupling device is a sliding sleeve. With conventional sliding sleeves, which have a suitable internal geometry, it is possible to bring about a positive, reversible mechanical coupling of the rotor shaft and the shaft journal. Typically, the shaft ends each have external longitudinal tooth arrangements, while the sliding sleeve has an internal longitudinal tooth arrangement which engages in the shaft-side longitudinal tooth arrangements.In addition to the variants of the mechanical coupling, a preferred embodiment of an electric machine according to the invention with regard to the electrical contacting of the rotor shaft is distinguished in that the contact structures on the shaft journal and the rotor shaft have at least two, preferably annular, contact elements for the electrical contacting or separation, which contact elements are provided on the end face on the shaft journal and the rotor shaft or a contact structure is provided on the coupling device, which contact structure simultaneously electrically contacts or separates the contact structures on the shaft journal and the rotor shaft during mechanical coupling or decoupling. In order to ensure a desired direction of rotation of the rotor shaft and rotor, correct polarity must be ensured during the electrical contacting. It is therefore recommended to use contact elements or contact structures which make possible a definable electrical contact-connection independently of the angle of rotation. Particularly suitable for this purpose are annular contact elements which are provided on the end sides of the rotor shaft and of the shaft journal. Preferably, two ring-shaped contact elements are provided per end face in order to allow a directed current flow. These end-face contact elements can also protrude away from the end faces, so that reliable electrical contacting is possible even if the end faces of the rotor shaft and of the shaft journal do not bear exactly flush against one another. This can already be achieved by projecting the contact elements by a few tenths of a millimeter. For example, by means of end-face contact elements in the form of an inner ring with a small radius and an outer ring with a large radius, it can always be ensured with purely axial displacement of one shaft end and by means of the radial offset that the inner ring of one shaft end can electrically contact only the inner ring of the other shaft end. The same applies to the two outer rings. Thus, at no time can contact be made between an inner ring and an outer ring, thereby preventing incorrect electrical polarity.In a further development, end-face contact elements can also be realized by an outer and an inner annular groove, wherein the annular grooves of the rotor shaft and of the shaft journal engage in one another when mechanically coupled, whereby an electrical contact is produced. The type of contacting is similar to the already described electrical contacting by end-face annular contact elements. When using annular grooves, annular folds are provided on one of the two shaft ends, which protrude from the end face and slide into annular grooves of the second shaft end when the shaft ends are mechanically coupled. The cross section of the annular grooves, or folds, is preferably trapezoidal in this case in order to enable easy mechanical coupling. The electrical contact elements can be provided either on the groove bottoms and the end faces of the folds or on the groove side faces and the side faces of the folds. Due to the spatial offset of the contact elements in the radial direction and the separation by grooves and folds, incorrect electrical polarity is also avoided with this type of electrical contacting, wherein at the same time, due to a positive connection between grooves and folds, additional fixing of the mechanical coupling in the radial direction takes place. In addition to the use of two or more contact elements per shaft end, only one contact element per shaft end can also be provided for the electrical energization of the rotor, wherein the current flow is then possible only by providing an additional contact on the rotor or the rotor shaft.If the rotor shaft and the shaft journal are fixed in position with respect to one another along the longitudinal axis of the rotor shaft, as described above, so that their end faces do not touch one another in the coupled state, the electrical contacting via the mechanical coupling device is possible. Accordingly, the contact structure on the rotor shaft is brought into electrical contact with the contact structure on the shaft journal simultaneously with the mechanical coupling by a suitable contact structure of the coupling device. In this case, correct electrical polarity must also be ensured. For this purpose, contact elements with a face surface, preferably annular, can furthermore be provided on the shaft ends, or the contact elements are designed in the form of encircling rings on the outer cylindrical lateral surfaces of the shaft ends.From the viewpoint of the economical operation of an electric machine, the saving of weight and the reduction of rotating masses are preferred. In an advantageous embodiment of an electric machine according to the invention, it can therefore be provided that the shaft journal and / or the rotor shaft are a hollow shaft. With this construction, both the performance and the efficiency of the electric machine can be improved.In addition to the electric machine described at the beginning, the invention also relates to a brush module for an electric machine according to the invention, comprising a brush carrier having at least one brush. The brush module is characterized in that it has a shaft journal which can be reversibly mechanically coupled to a rotor shaft and on which the brush bears. All embodiments of the electric machine according to the invention can be transferred analogously to the brush module according to the invention, so that the corresponding advantages also result for the brush module.As described at the beginning for an electric machine according to the invention, it is advantageous if the shaft journal of the brush module is displaceable along its longitudinal axis for mechanical coupling and decoupling. The axial coupling, which can also be controllable, for example, via an actuator and a remote control device, enables the brush module according to the invention to be used in construction spaces which are constricted in the radial direction of the shaft journal. Here too, the mechanical coupling and the installation space requirement of the brush module are facilitated by a coaxial arrangement of rotor shaft and shaft journal.A brush module according to the invention can advantageously be characterized in that the shaft journal has a spur toothing, via which it can be reversibly mechanically coupled to the rotor shaft. As a result, coupling of the rotor shaft and the shaft journal is possible with the smallest possible installation space requirement radially with respect to the coupling axis.Analogously to the electric machine according to the invention, it is also advantageous for the brush module according to the invention if a switchable coupling device is provided on the shaft journal, via which the shaft journal can be reversibly mechanically coupled to the rotor shaft. As a result, a post-processing of the rotor shaft and the shaft journal, as would be required, for example, in the case of spur gearing, is avoided.Advantageously, the coupling device can be a clutch, preferably a claw clutch or a friction clutch. As explained for the electric machine according to the invention, the use of proven clutches is recommended for realizing a reversible mechanical coupling of rotor shaft and shaft journal. This allows a positive coupling of the shaft journal to the rotor shaft, wherein mechanical connections with little rotational play are possible. Alternatively, a friction clutch can also be provided in order to mechanically couple the shaft ends by means of frictional engagement. Thus, synchronization of the shaft ends is no longer required for the coupling. Undesired coupling forces arising during the coupling can be reduced. In the radial direction of the rotor shaft and the shaft journal, installation space can be saved depending on the type of coupling.Likewise, an alternative embodiment of a brush module according to the invention consists in the fact that the shaft journal is fixed in position along its longitudinal axis, wherein a switchable coupling device is provided on the shaft journal, via which the shaft journal can be reversibly mechanically coupled to the rotor shaft. This embodiment variant allows the use of a brush module according to the invention even if sufficient installation space is not available along the longitudinal axis of the shaft journal in order to enable its displacement.Against this background, a further advantageous embodiment of a brush module according to the invention is characterized in that the coupling device is a sliding sleeve. The coupling device, or the sliding sleeve, is preferably switchable and can be switched via an actuator, for example with an external switching unit.As described at the beginning for an electric machine according to the invention, a brush module according to the invention is also advantageously distinguished in that a contact structure is provided on the shaft journal, which contact structure, when the shaft journal and the rotor shaft are mechanically coupled or decoupled, can be electrically contacted simultaneously with a contact structure provided on the rotor shaft side or can be separated from the latter. In this way, the rotor shaft can be energized by a mechanical contact to the shaft journal of the brush module via an electrical contact connection of the contact structures of shaft journal and rotor shaft, which contact connection is formed or separated simultaneously with the mechanical coupling. The electrical contacting is enabled at all by the mechanical coupling or separation.With regard to the electrical contacting of the rotor shaft by the shaft journal, it is advantageous if the contact structure on the shaft journal has at least two, preferably annular, contact elements for electrical contacting or isolation, which contact elements are provided on the end face of the shaft journal or a contact structure is provided on the coupling device, which contact structure simultaneously electrically contacts or separates during mechanical coupling or decoupling. The contact structure of the shaft journal of a brush module according to the invention can thus be brought into electrical contact with the contact structure of the rotor shaft via contact elements on its end face and the end face of the rotor shaft. For this purpose, it is recommended to provide ring-shaped contact elements, for example an inner ring and an outer ring, which allow contact with always correct electrical polarity independent of the angle of rotation. The contact structures of the rotor shaft and of the shaft journal can also be electrically conductively connected to one another via a coupling device having a contact structure and contact elements, for example having a sliding sleeve. In conjunction with a coupling device, it is also possible to provide the contact elements on the lateral surfaces of the shaft journal and / or rotor shaft. By axial displacement of the coupling structure, such contact elements can be electrically contacted with contact elements of the coupling structure or separated from one another.An advantageous embodiment variant is also characterized for a brush module according to the invention in that the shaft journal is a hollow shaft. This allows material and weight to be saved.In particular, an electric machine according to the invention and / or a brush module according to the invention can be used in an electric drive train of a motor vehicle.Finally, the invention also relates to a motor vehicle which comprises at least one electric machine according to the invention.Further advantages and details of the present invention are evident from the exemplary embodiments described below and on the basis of the drawings. The following are shown:FIG. 1 shows an electric machine according to the invention with an axially displaceable shaft journal, an axially positionally fixed rotor shaft and a coupling device in the uncoupled state, FIG. 2 shows an electric machine according to the invention with an axially displaceable shaft journal, an axially positionally fixed rotor shaft and a coupling device in the coupled state, FIG. 3 shows an electric machine according to the invention with an axially positionally fixed rotor shaft and an axially positionally fixed shaft journal and an axially displaceable coupling device in the uncoupled state, FIG. 4 shows an electric machine according to the invention with an axially positionally fixed rotor shaft and an axially positionally fixed shaft journal and an axially displaceable coupling device in the coupled state, FIG. 5 shows an electric machine according to the invention with an axially positionally fixed rotor shaft and an axially displaceable shaft journal with spur gearing, in the decoupled state, FIG. 6 shows an electric machine according to the invention with an axially positionally fixed rotor shaft and an axially displaceable shaft journal with spur gearing, in the coupled state, FIG. 7 shows an electric machine according to the invention with an axially positionally fixed rotor shaft and an axially positionally fixed shaft journal and a sliding sleeve in the decoupled state, FIG. 8 shows an electric machine according to the invention with an axially positionally fixed rotor shaft and an axially positionally fixed shaft journal and a sliding sleeve in the coupled state, FIG. 9 shows shaft ends with contact elements projecting from the end face, and FIG. 10 shows contact elements on the end faces of two shaft ends with annular grooves and folds.FIG. 1 shows an exemplary embodiment of an electric machine 1 according to the invention having a rotor 2 with a rotor shaft 3 and a brush module 10 which is not coupled to the rotor shaft 3. The brush module 10 shown comprises a shaft journal 4 and two brushes 5 and a brush carrier 6, which holds the brushes 5 and presses them against the circumferential surface 24 of the shaft journal 4. The rotor shaft 3 fixed in position in the axial direction and the shaft journal 4 are positioned coaxially with respect to one another along the coupling axis 40 and can be mechanically coupled to one another reversibly by the coupling device 9 by displacing the shaft journal 4 to the left along the coupling axis 40. An axial displacement of the shaft journal 4 can be effected with the aid of an actuator 8, wherein the displacement is possible in both directions and can be effected by an actuator acting on both sides or an actuator acting on one side with a restoring device.For the electrical energization of the rotor 2, an electrically conductive contact structure 12 is provided on the rotor shaft side, which contact structure can be energized via contact elements 13 on the end face 11. Similarly, the shaft journal 4 also has an electrically conductive contact structure 22, which in turn can be supplied with current by the brushes 5 via the two slip rings 7, when these are in electrical contact with the brushes 5.Due to the axial offset of the shaft journal 4 along the coupling axis 40, its slip rings 7 are not in electrical contact with the brushes 5, as a result of which the contact structure 22 and the contact elements 23 arranged on the end face 21 of the shaft journal 4 are not energized.If not only the shaft journal 4 but the entire brush module 10 and thus also brush carrier 6 and brushes 5 were displaced by the actuator 8, these would be in continuous electrical contact with the slip rings 7 and the contact structure 22 with the contact elements 23 would be energized. Even if the contact structure 22 were to conduct electric current, the contact structure 12 of the rotor shaft 3 would remain uncurrentd in the illustration, since the contact elements 13 on the rotor shaft side are not in electrical contact with the contact elements 23 of the shaft journal 4 as a result of the axial distance. The current flow from the brushes 5 into the rotor 2 and vice versa is interrupted.FIG. 2 shows the machine 1 from FIG. 1, wherein the shaft journal 4 is now mechanically coupled to the rotor shaft 3 by displacement along the coupling axis 40. The mechanical coupling is effected with the aid of the coupling device 9. In the coupled state, the end faces 11 and 21 abut each other, whereby the contact elements 13 of the rotor shaft 3 form an electrically conductive connection with the contact elements 23 of the shaft journal 4. As a result, simultaneously with the mechanical coupling of both shaft ends, an energization of the rotor 2 is possible, wherein the electric current from the brushes 5 is conducted through the frictional contact provided in this position into the slip rings 7 and the contact structure 22 connected thereto with the contact elements 23 is energized. As a result of the electrical connection to the contact elements 13 of the rotor shaft 3, the current is passed on via the contact structure 12 into the rotor 2. The electric current can also flow back from the rotor 2 into the brushes 5 in the opposite direction.An axial displacement of the shaft journal 4 or of the entire brush module 10 to the right would mechanically decouple the shaft journal 4 from the rotor shaft 3 again and consequently also interrupt the electrical current flow via the end-face contact elements 13 and 23.The exemplary embodiment of the electric machine 1 according to the invention in FIG. 3 differs from the preceding examples in that the entire brush module 10, comprising the shaft journal 4 and the brush carrier 6 with brushes 5, is fixed in position along the coupling axis 40. Since the rotor 2 is also fixed in position with the rotor shaft 3 along this axis, the mechanical coupling and the electrical contacting can only be effected by a coupling device 9. In the illustration, this is axially displaceable along the coupling axis 40, wherein the displacement is possible in both directions and can be effected by an actuator acting on both sides or an actuator acting on one side with a restoring device. The rotor shaft 3 and the shaft journal 4 are arranged coaxially. An open coupling device 9 is shown, by means of which the shaft journal 4 and the rotor shaft 3 are neither mechanically coupled nor electrically contacted. Because the shaft journal 4 is axially fixed in position, the brushes 5 are pressed permanently onto the slip rings 7 by the brush carrier 6 and the contact structure 22 with the contact elements 23 of the shaft journal 4 is continuously energized. In the opening position of the coupling device 9 shown, the contact elements 23 do not form an electrically conductive connection with the contact elements 33 of the coupling device 9. The contact structure 32, which is required for generating an electric current flow from the shaft journal 4 into the rotor 2, thus does not carry any current and the contact structure 12 on the rotor shaft side and its contact elements 13 remain uncurrentd.The electric machine 1 according to the invention of FIG. 3 is shown in a coupled state in FIG. 4. In this case, the coupling device 9 which is displaceable along the coupling axis 40 is displaced to the left and is in the closed state. The rotor shaft 3 and the shaft journal 4 are mechanically coupled to one another via the coupling device 9. Simultaneously, an electric energization of the rotor 2 is also possible. For this purpose, the current flows via the brushes 5 of the brush carrier 6 into the slip rings 7, as a result of which the contact structure 22 of the shaft journal 4 is energized. The electrical current is forwarded into its contact structure 32 by electrical contact of the contact elements 23 with the contact elements 33 of the coupling device 9 and from there is forwarded again via contact elements 33 to the contact elements 13 of the rotor shaft 3. The contact structure 12 of the rotor shaft 3 and finally also the rotor 2 is therefore energized, wherein a current flow in the reverse direction from the rotor 2 into the brushes 5 is also possible.A further embodiment variant of an electric machine according to the invention with spur gearing for the reversible mechanical coupling of the shaft journal 4 to the rotor shaft 3 is illustrated in FIGS. 5 and 6. FIG. 5 shows the decoupled state. On the rotor shaft 3 of the rotor 2 and on the shaft journal 4 the spur gear teeth 15 and 25 are provided. The shaft journal 4 is displaceable along the coupling axis 40 by an actuator 8 and positioned coaxially with respect to the rotor shaft 3. In the illustrated state, the spur tooth arrangements 15 and 25 do not engage in one another on account of the axial offset, as a result of which there is no mechanical coupling between the rotor shaft 3 and the shaft journal 4 and consequently no electrical current flow is possible between the brushes 5 of the brush carrier 6 and the rotor 2. The electrically conductive contact structure 22 of the shaft journal 4 is not energized by the brushes 5, since they do not abut on the slip rings 7. Furthermore, the axial offset also does not allow electrical contact between the contact elements 23 and 13 of the shaft journal 4 and the rotor shaft 3. If the contact structure 22 were continuously energized, for example because the entire brush module 10 and thus also the brushes 5 were axially displaced by the actuator 8, no energization of the rotor 2 would nevertheless be possible in the illustrated state on account of the spatial separation of the contact elements 13 and 23. The contact structure 12 of the rotor shaft 3 is electroless.The coupled state of the electric machine 1 from FIG. 5 is visualized in FIG. 6. Here, the shaft journal 4 is displaced to the left by the actuator 8 along the coupling axis 40, as a result of which the spur tooth arrangements 15 and 25 of the rotor shaft 3 and shaft journal 4 engage in one another and a positive mechanical coupling exists. The shaft journal 4 is co-rotated by the continuous rotating rotor shaft 3. Simultaneously with the mechanical coupling, the rotor 2 is energized by the brushes 5 of the brush carrier 6. In this case, the contact structure 22 of the shaft journal 4 is initially energized by the brushes 5 via the slip rings 7. The mechanical contact of rotor shaft 3 and shaft journal 4 also produces an electrically conductive connection of contact structures 12 and 22 via ring-shaped contact elements 13 and 23 provided on the end face.FIGS. 7 and 8 show a further exemplary embodiment of an electric machine 1 according to the invention, in which the mechanical coupling and the electrical contacting of rotor shaft 3 and shaft journal 4 are effected by a coupling device 9 in the form of a sliding sleeve. The rotor shaft 3 and the shaft journal 4 are fixed in position along the coupling axis 40, wherein the coupling device 9 can be displaced on both sides along this axis, for example by an actuator or an actuator in combination with a restoring device. The contact structure 22 of the shaft journal 4 is continuously energized via the slip rings 7 by the brushes 5 of the brush carrier 6.In the uncoupled state, which is shown in FIG. 7, the shaft journal 4 and rotor shaft 3 are mechanically uncoupled due to the coupling device 9 being displaced to the right along the coupling axis 40 and thus opened. At the same time, the contact structures 12 and 22 of the rotor shaft 3 and of the shaft journal 4 are not in electrically conductive connection, since their contact elements 13 and 23 are not electrically bridged by the contact structure 32 and the contact elements 33 in the decoupled state by the axial offset of the coupling device 9. The rotor 2 is therefore not energized by the brushes 5.In the mechanically coupled state of the same electric machine in FIG. 8, the coupling device 9, or the sliding sleeve, is, on the other hand, displaced to the left in the direction of the coupling axis 40. Via an internal longitudinal toothing of the coupling device 9 and an external longitudinal toothing at the shaft ends of the rotor shaft 3 and of the shaft journal 4, both shaft ends are reversibly mechanically coupled to one another. Simultaneously, the contact elements 33 of the coupling device 9 also abut the contact elements 13 and 23. These are provided here as annular contact elements on the lateral surfaces 14 and 24 of the shaft ends. Depending on the shape of the coupling device 9, the contact elements 13 and 23 and the contact elements 33 of the coupling device 9 can also be provided on the end face or in the radial direction on a shaft shoulder. In the illustrated state, the contact structures 12 and 22 are electrically bridged by the contact structure 32 of the coupling device 9. As a result, a current flow from the brushes 5 into the rotor 2 and vice versa is possible.FIG. 9 shows, in the form of an exemplary embodiment, a shaft journal 4 with the end face 21, wherein two annular contact elements 23 are provided on the end face. The contact elements 23 project somewhat perpendicularly to the end face 21, the projection amounting to, for example, a few tenths of a millimeter. If such contact elements are provided on two shaft ends, a mutual electrical contacting of these shaft ends can be ensured even if their end faces are not exactly planar and / or do not bear flush against one another.As a further exemplary embodiment of an electrical contacting of two shaft ends, the contact structure 12 of a rotor shaft 3 and the contact structure 22 of a shaft journal 4 are illustrated in a decoupled state in FIG. 10. The shaft journal 4 is positioned coaxially to the rotor shaft 3 and is displaceable along the coupling axis 40, wherein the rotor shaft-side contact elements 13 and the journal-side contact elements 23 do not form an electrically conductive connection. If the shaft journal 4 is pushed to the left onto the rotor shaft 3, for example by an actuator, the contact elements 13 and 23 of the contact structures 12 and 22 contact each other. The annular shape of the contact elements 13 and 23 makes possible electrical contacting of both contact structures 12 and 22 independent of the angle of rotation, wherein the radial offset of the contact elements 13 and 23 and their attachment to annular grooves 16 and folds 26 prevents electrical faulty contacting in the case of purely axial displacement. If the rotor shaft 3 and the shaft journal 4 are brought together in end-face contact, the folds 26 on the shaft journal 4 slide into the annular grooves 16 of the rotor shaft 3, as a result of which the contact elements 13 and 23 make electrical contact.

Claims

Electric machine (1) comprising a rotor (2) with a rotor shaft (3) and a brush module (10) with a brush carrier (6) with at least one brush (5) for energizing the rotor (2), characterized in that the brush module (10) comprises a shaft journal (4) which can be reversibly mechanically coupled to the rotor shaft (3) and against which the brush (5) bears.Electric machine (1) according to Claim 1, characterized in that the shaft journal (4) and / or the brush module (10) are displaceable along the longitudinal axis of the rotor shaft (3) for mechanical coupling and decoupling.Electric machine (1) according to Claim 2, characterized in that the shaft journal (4) and the rotor shaft (3) can be coupled mechanically reversibly to a spur toothing (15, 25).Electric machine (1) according to Claim 2, characterized in that the shaft journal (4) and the rotor shaft (3) can be coupled mechanically reversibly to a switchable coupling device (9).Electric machine (1) according to Claim 4, characterized in that the coupling device (9) is a clutch, preferably a claw clutch or a friction clutch.Electric machine (1) according to Claim 1, characterized in that the shaft journal (4) and the brush module (10) are fixed in position along the longitudinal axis of the rotor shaft (3), wherein the shaft journal (4) and the rotor shaft (3) can be coupled mechanically reversibly to a switchable coupling device (9).Electric machine (1) according to Claim 6, characterized in that the coupling device (9) is a sliding sleeve.Electric machine (1) according to one of the preceding claims, characterized in that a contact structure (22) is provided on the shaft journal (4), which contact structure, when the shaft journal (4) and the rotor shaft (3) are mechanically coupled or decoupled, can be electrically contacted simultaneously with a contact structure (12) provided on the rotor shaft side or can be separated therefrom.Electric machine (1) according to Claim 8, characterized in that the contact structures (12, 22) on the shaft journal (4) and the rotor shaft (3) have at least two, preferably annular, contact elements (13, 23) for electrical contacting or disconnection, which contact elements are provided on the end face on the shaft journal (4) and the rotor shaft (3) or a contact structure (32) is provided on the coupling device (9), which contact structure electrically contacts or disconnects the contact structures (12, 22) on the shaft journal (4) and the rotor shaft (3) simultaneously during mechanical coupling or decoupling.Electric machine (1) according to one of the preceding claims, characterized in that the shaft journal (4) and / or the rotor shaft (3) are a hollow shaft.Brush module (10) for an electric machine (1) according to one of the preceding claims, comprising a brush carrier (6) with at least one brush (5), characterized in that the brush module (10) has a shaft journal (4) which can be reversibly mechanically coupled to a rotor shaft (3) and on which the brush (5) bears.Brush module (10) according to Claim 11, characterized in that the shaft journal (4) is displaceable along its longitudinal axis for mechanical coupling and decoupling.Brush module (10) according to Claim 12, characterized in that the shaft journal (4) has a spur toothing (25), via which it can be coupled mechanically reversibly to the rotor shaft (3).Brush module (10) according to Claim 12, characterized in that a switchable coupling device (9) is provided on the shaft journal (4), by means of which coupling device the shaft journal (4) can be coupled reversibly mechanically to the rotor shaft (3).Brush module (10) according to Claim 14, characterized in that the coupling device (9) is a clutch, preferably a claw clutch or a friction clutch.Brush module (10) according to Claim 11, characterized in that the shaft journal (4) is fixed in position along its longitudinal axis, wherein a switchable coupling device (9) is provided on the shaft journal (4), by means of which coupling device the shaft journal (4) can be coupled reversibly mechanically to the rotor shaft (3).Brush module (10) according to Claim 16, characterized in that the coupling device (9) is a sliding sleeve.Brush module (10) according to one of the preceding claims, characterized in that a contact structure (22) is provided on the shaft journal (4), which contact structure, when the shaft journal (4) and the rotor shaft (3) are mechanically coupled or decoupled, can be electrically contacted simultaneously with a contact structure (12) provided on the rotor shaft side or can be separated from the latter.Brush module (10) according to Claim 18, characterized in that the contact structure (22) on the shaft journal (4) has at least two, preferably annular, contact elements (23) for electrical contacting or disconnection, which contact elements are provided on the end face of the shaft journal (4) or a contact structure (32) is provided on the coupling device (9), which contact structure simultaneously electrically contacts or disconnects when mechanically coupling or decoupling.Brush module (10) according to one of the preceding claims, characterized in that the shaft journal (4) is a hollow shaft.Motor vehicle comprising at least one electric machine (1) according to one of Claims 1 to 10.

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