Discharge device for conducting electrical currents

Description

[0001] The invention relates to a discharge device for discharging electrical currents from a rotor part of a machine, in particular one formed with a shaft, into a stator part of the machine, and to a machine with a discharge device comprising a contact element, a holding device and a spring device, wherein the holding device can be electrically connected to a stator part, wherein the contact element is predominantly made of carbon, wherein the contact element is axially displaceable on the holding device and electrically connected to it, wherein the contact element can be subjected to a contact force by means of the spring device to form an electrically conductive sliding contact between a sliding contact surface of the contact element provided for forming the sliding contact and an axial shaft contact surface of the shaft.

[0002] Discharge devices of the type mentioned above are known in various embodiments from the prior art. In particular, it is known to use carbon brushes for discharging low-frequency direct currents. These brushes are arranged radially around a shaft on a slip ring and are contacted with a stator via connecting leads. Due to their low electrical resistance, the carbon brushes, which are held in a retaining device or brush holder, allow for the direct dissipation of electrical currents and can thus prevent unwanted current flow through the shaft's bearing points, which could lead to surface damage of the bearing bodies or bearing rings due to spot welding.

[0003] The term "shaft" is used here as a synonym for "rotor part" or "shaft". Therefore, the term "shaft" encompasses all rotating machine parts through which current can be transferred to a stationary stator part or machine part of a machine.

[0004] Current-discharge devices are also regularly used in railway technology, where alternating currents or operating currents can flow away via wheel axles. For example, DE 10 2010 039 847 A1 discloses a current-discharge device in which an electrically conductive end cap is mounted at the axial end of a shaft or wheel axle of a wheelset. This end cap can be contacted by a plurality of carbon brushes arranged axially relative to the shaft and held by brush holders. Each carbon brush is connected directly to a grounding cable via a wire, and a spring exerts a contact force on the sliding contact surfaces of the carbon brushes.

[0005] Similar measures for current dissipation are also necessary for electrical machines in general, such as those used in motor vehicles. Continuously fluctuating alternating voltages or currents and high-frequency current pulses can occur in motor drive shafts or connected transmission shafts, as well as in other functional components. These can damage the bearings of a rotor shaft or transmission shaft, which is why discharge devices are regularly required. A disadvantage of known discharge devices, however, is that their design requires a comparatively large amount of installation space. While solutions are known that use fiber or wire braids instead of carbon brushes, these braids exhibit high contact resistance due to the very small contact surface of a sliding contact, and only low currents can be dissipated.To create a large contact surface with the shaft, however, a plurality of carbon brushes are required, which, due to their arrangement, each require brush holders with a comparatively large installation space and a corresponding assembly effort.

[0006] DE 10 2015 110428 A1 discloses a discharge device with several spring elements. DE 199 20 384 C1, JP S51 133913 U, and EP 1 136 340 A2 each disclose a discharge device with the features of the preamble of claim 1.

[0007] The present invention therefore aims to propose a discharge device that has a low contact resistance and is easy to mount in a small installation space. This objective is achieved by a discharge device with the features of claim 1 and a machine with the features of claim 22.

[0008] The inventive conduction device for conducting electrical currents from a rotor part of a machine, in particular one formed with a shaft, into a stator part of the machine comprises a contact element, a holding device, and a spring device, wherein the holding device is electrically connectable to a stator part, wherein the contact element is predominantly made of carbon, wherein the contact element is axially displaceable and electrically connected to the holding device, wherein the contact element can be subjected to a contact force by means of the spring device to form an electrically conductive sliding contact between a sliding contact surface of the contact element provided for forming the sliding contact and an axial shaft contact surface of the shaft, wherein the contact element is disk-shaped, wherein the sliding contact surface is at least annular, preferably circular,is designed and can be arranged coaxially relative to the shaft contact surface, wherein the holding device has a base plate, wherein the spring element is arranged between the base plate and a contact surface side with the pressure side of the contact element facing away from the sliding contact surface.

[0009] The discharge device is designed for mounting on a rotating shaft or axle of a machine. It is intended that the discharge device be positioned at an axial end of the shaft and that the electrically conductive sliding contact be formed by contacting the axial shaft contact surface at the axial end of the shaft or at an end face of the shaft with the contact element. The spring mechanism then applies a contact force to the contact element, acting axially in the direction of the shaft's axis of rotation, so that the contact element's sliding contact surface is pressed against the shaft contact surface. Since the contact element is disc-shaped, or in the form of a disk or plate, space can be saved compared to a conventional grinding wheel, as the contact element is then comparatively short and thin with respect to its axial extent.The disc or plate shape of the contact element makes it possible to design the contact element with at least an annular sliding contact surface, which can then be arranged coaxially relative to the shaft contact surface. The circular shape of the sliding contact surface results from a rotational movement of the shaft or shaft contact surface. This allows for a comparatively large sliding contact surface, enabling the formation of a sliding contact with low contact resistance. However, the disc or plate shape of the contact element can also be chosen such that a contour of the contact element extends beyond the sliding contact surface. The contact element can therefore also be polygonal and still have a circular sliding contact surface.Since abrasive wear of the sliding contact is reduced relative to the large sliding contact area, the contact element can also be designed in a disc-shaped or thin form without wearing out significantly sooner than a contact element with a small sliding contact area and a large length, as known from the prior art. Furthermore, it is no longer necessary to mount multiple contact elements on the shaft to achieve low contact resistance, since a single disc-shaped contact element can already form a sufficiently large sliding contact. The discharge device thus requires little installation space and can also be easily mounted.

[0010] The holding device according to the invention has a base plate, wherein the spring element is arranged between the base plate and a contact surface side of the contact element, the contact surface being the side with the pressure side facing away from the sliding contact surface. The spring element is thus simply arranged between the base plate and the contact element. In a particularly simple embodiment of the discharge device, it can then consist of only three components that can be plugged into one another. This makes assembly of the discharge device particularly easy. If the spring device or spring element is a particularly flat spring, such as a disc spring, the installation space required for the discharge device can be reduced even further. The base plate can be easily attached to a stator part of a machine by means of a screw, plug, or adhesive connection.An electrically conductive connection of the base plate can be formed via this connection with the stator part or via a direct connection of a grounding cable to the base plate.

[0011] The outer diameter, or maximum outer dimension, of the disc-shaped contact element can be a multiple of its thickness. The contact element can have an outer dimension-to-thickness ratio of 2:1, 3:1, 4:1, 5:1, or 10:1.

[0012] For example, the sliding contact surface, or an end face of the contact element, can be dimensioned so large relative to the axial end of the shaft that its radial dimensions exceed the diameter of the shaft at the axial end. Furthermore, the sliding contact surface can also be shaped like a full circle. The contact element can also be designed so that its radial extent approximates or corresponds to the diameter of the axial end of the shaft, as this allows for a particularly large sliding contact area.

[0013] The contact element can be formed in one piece and consist predominantly of carbon. For example, the contact element can be a carbon component formed by pressing and firing or sintering. The contact element can consist of graphite, carbon black, carbon fibers, or a mixture of these materials, and may also contain particles of the metals iron, nickel, manganese, copper, zinc, silver, aluminum, and / or chromium, and a binder or binder phase.

[0014] The holding device can be made of metal, preferably steel, aluminum, copper, or an alloy of these materials. The holding device can then be easily and cost-effectively manufactured in large quantities, for example, by injection molding or simple machining of semi-finished products made from these materials. The holding device can be directly and securely connected to a stator component or a housing component of a machine, for example, by bolting it together. A grounding cable can also be easily attached or mounted to the holding device. For example, the holding device can be manufactured as a single piece or in multiple parts.

[0015] The holding device and the contact element together can form an anti-rotation device for the contact element. This allows the holding device to be firmly attached to the stator part, and the contact element can then also be firmly positioned relative to a rotating shaft on the holding device and made contact with the shaft. In particular, due to the annular shape and coaxial arrangement of the sliding contact surface, the contact element could otherwise follow the rotation of the shaft, resulting in no sliding contact with the shaft. The anti-rotation device can be easily achieved by a positive-locking connection of the contact element to the holding device, which allows axial movement of the contact element on the holding device but prevents radial movement of the contact element relative to the holding device.

[0016] The spring assembly comprises a spring element, the spring element being arranged coaxially relative to the sliding contact surface or a rotational axis of the shaft. According to the invention, the spring element is designed as a disc spring or a diaphragm spring. In unclaimed embodiments, it is designed as a coil spring, compression spring, leaf spring, conical spring, or ring spring.

[0017] This makes it possible to exert a pressure or spring force on the contact element in the direction of the axis of rotation of the shaft by means of the spring device, thus forming the contact force.

[0018] The contact element can be formed from at least two layers with different material mixtures. The contact element can therefore have at least two layers that exhibit different physical properties and thus different functionalities.

[0019] The layers can be arranged successively in the axial direction, with the sliding contact surface consisting of a sliding layer with a copper content of < 60% by mass and the contact surface consisting of a bonding layer with a copper content of > 80% by mass, preferably with an expansion layer formed between the sliding layer and the bonding layer. For example, the bonding layer can be solderable and weldable with a copper content of 90 to 99% by mass, with additions of tin or zinc up to 9% by mass, and a graphite content of a maximum of 3% by mass. This makes the bonding layer particularly wettable with lead-free solders and also weldable. In addition, the bonding layer exhibits a high flexural strength of over 100 MPa, thus giving it high resistance to tensile, shear, and compressive stresses.The sliding layer can also contain ≤ 50% copper by mass or even be completely copper-free. This results in good sliding properties with low wear, and thus a long service life and chemical stability. Structurally, the different layers can also differ in their isotropy / anisotropy. The bonding layer can be isotropic, while the sliding layer can be either isotropic or anisotropic. The lubricating effect of the graphite used in the sliding layer can then be optimally utilized, particularly by orienting the graphite preferentially parallel to the sliding plane. The thermal expansion behavior of the sliding layer can be controlled by the isotropy / anisotropy. The optional expansion layer can serve to equalize the different coefficients of thermal expansion between the sliding layer and the bonding layer.

[0020] The contact element can be formed with a contoured transition zone between the layers by sintering. When the contact element is formed by sintering, the individual layers can be easily formed using appropriately selected powder mixtures. Furthermore, a contour can be formed in the transition zone between the respective layers so that the layers interlock in the axial direction. This contour can be formed by first compacting a layer in a mold using a suitably contoured die, and then filling and compacting the second layer as a powder mixture.

[0021] The holding device can have at least one guide element arrangement extending axially, along which the contact element is axially displaceable. The guide element arrangement can have a profile that is continuous in the axial direction or along a rotational axis of the shaft, thus ensuring the axial displaceability of the contact element. The length of the guide element arrangement in the axial direction can always be dimensioned such that the contact element can be partially or completely worn away by abrasive wear without the contact element being able to detach from the guide element arrangement during axial displacement by means of the spring mechanism.

[0022] The contact element can have a guide contour on its circumference, which is inserted into the guide element assembly. The guide element assembly can therefore partially or completely encompass the contact element around its circumference. The circumference or guide contour of the contact element can be polygonal or partially or completely circular. Notches or grooves can also be formed on the circumference in the axial direction, into which the guide element assembly engages. In principle, it is possible to design the contact element so that it is held on the base plate solely by the guide element assembly around its circumference.

[0023] The contact element can also have a guide recess into which the guide element assembly or a guide pin of the shaft can engage. The guide recess can be designed along a longitudinal axis of the contact element in the form of a bore, so that the contact element then forms the annular sliding contact surface. The guide recess can be a through-hole in the contact element or a blind hole. Optionally or alternatively, the guide recess can be designed as a central bore in the contact element, so that the contact element can be mounted onto a guide pin or a stepped diameter of the shaft. The shaft can thus serve to radially fix the contact element.

[0024] The guide recess and the guide element assembly can have matching cross-sections. This makes it possible to guide the contact element and thus allow axial movement. Depending on the selected cross-sectional shape, the matching cross-sections can also provide anti-rotation protection. For example, the cross-section can be circular, square, rectangular, or polygonal. Instead of a round bore, a polygonal guide recess with a matching guide pin can be provided, together forming an anti-rotation device. A clearance fit can also be formed between the guide recess and the guide element assembly.

[0025] The guide element arrangement can be positioned coaxially with the sliding contact surface. This ensures that the contact element is always centered relative to the shaft's axis of rotation at the axial end of the shaft. Consequently, the centroid of the sliding contact surface can always coincide with the centroid of the shaft contact surface, with both centroids potentially lying on the shaft's axis of rotation. The contact element can also be rotationally symmetrical.

[0026] The guide element arrangement can comprise at least one guide element, preferably a plurality of guide elements. A guide element can, for example, be a simple pin-shaped extension of the holding device. Alternatively, the guide element can be a screw of the holding device. The guide element can also be a polygonal extension in cross-section and, in principle, have any desired cross-sectional shape. Furthermore, it is possible to use a plurality of guide elements with the cross-sectional shapes described above, if this appears appropriate.

[0027] The guide element can be integrally formed on or inserted into the base plate of the holding device. In a simple embodiment, the guide element can be a pin that is simply inserted into a bore in the base plate. Similarly, a pin-shaped guide element can be integrally formed on the base plate in the form of a projection. The base plate can also have a central bore into which a screw is inserted or screwed.

[0028] If the holding device has an integrated guide element, it can also be manufactured as a single piece. The holding device can be easily produced using an injection molding process or by machining a semi-finished product. An inner surface of the guide recess can be electrically conductively contacted with an outer surface of the guide element. This allows an electric current to be transferred from the contact element to the holding device with low contact resistance. If the guide recess is, for example, a bore, the inner surface of the bore can be contacted with an outer surface of a pin or stud as the guide element. The inner and outer surfaces, or their respective diameters, can form a clearance fit that always ensures low contact resistance.An axial displacement can be ensured simply by the carbon of the contact element and an advantageously designed friction pairing of the inner and outer surfaces.

[0029] The guide element can be arranged concentrically relative to the shaft contact surface on the holding device. Consequently, the guide element can always also be arranged centrically to the shaft contact surface.

[0030] Additionally or alternatively, the guide element can be arranged eccentrically relative to the shaft contact surface on the holding device. In this case, however, a plurality of guide elements should be present, arranged eccentrically to the shaft contact surface on the holding device, such that the guide elements are always evenly distributed relative to an axis of rotation of the shaft, for example, equidistantly spaced from one another.

[0031] The sliding contact surface can have at least one groove extending axially. Furthermore, multiple grooves can be formed in the sliding contact surface, extending radially outwards from a central point, for example. The groove can have a depth corresponding to the maximum wear depth of the contact element. Oil on the sliding contact or particles of abrasion can be collected by means of the groove and carried away radially within it. The groove can also be spirally shaped or arranged like a passer relative to a center point of the sliding contact surface.

[0032] Particularly efficient electrical current dissipation is achieved when the contact element is connected to the holding device via at least one electrically conductive wire or a flexible metal strip. The wire can be arranged within the contact element during its manufacture or attached to it, for example, by soldering or gluing. Preferably, the contact element also comprises a plurality of wires attached to its circumference and equidistant from one another. The wire can also be easily attached to the holding device by means of clamps, screws, or soldering. Using a wire can further reduce contact resistance. It is also possible to connect the wire directly to a stator part of the machine. The machine according to the invention includes a current-dissipation device according to the invention.Advantageous embodiments of a machine result from the features of the dependent claims relating back to device claim 1.

[0033] Advantageous embodiments of the invention are explained in more detail below with reference to the accompanying drawings.

[0034] They show: Fig. 1: a sectional view of a first embodiment of a discharge device on a shaft; Fig. 2 :a top view of a contact element according to the first embodiment of the discharge device; Fig. 3: a side view of the contact element from Fig. 2 ; Fig. 4: a top view of a base plate according to the first embodiment of the discharge device; Fig. 5: a side view of the base plate Fig. 4 ; Fig. 6: a top view of a second embodiment of a contact element; Fig. 7: a side view of the contact element from Fig. 6 ; Fig. 8: a top view of a second embodiment of a base plate; Fig. 9: a side view of the base plate Fig. 8 ; Fig. 10: a top view of a third embodiment of a contact element; Fig. 11: a side view of the contact element from Fig. 10 ; Fig. 12: a top view of a fourth embodiment of a contact element; Fig. 13: a side view of the contact element from Fig. 12 ; Fig. 14: a top view of a fifth embodiment of a contact element; Fig. 15: a side view of the contact element from Fig. 14 ; Fig. 16: a top view of a sixth embodiment of a contact element; Fig. 17: a side view of the contact element from Fig. 16 ; Fig. 18: a top view of a seventh embodiment of a contact element; Fig. 19: a side view of the contact element from Fig. 18 ; Fig. 20: a top view of an eighth embodiment of a contact element; Fig. 21: a side view of the contact element from Fig. 20 ; Fig. 22: a top view of a ninth embodiment of a contact element; Fig. 23: a side view of the contact element from Fig. 22 ; Fig. 24: a top view of a tenth embodiment of a contact element; Fig. 25: a side view of the contact element from Fig. 24 ; Fig. 26: a second embodiment of a discharge device in a sectional view on a shaft; Fig. 27: a third embodiment of a discharge device in a sectional view on a shaft; Fig. 28: a fourth embodiment of a discharge device in a sectional view on a shaft; Fig. 29 a fifth embodiment of a discharge device in a sectional view on a shaft; Fig. 30 A sixth embodiment of a discharge device in a sectional view on a shaft.

[0035] The Fig. 1 Figure 1 shows a discharge device 10 on a shaft 11 in a sectional view. The discharge device 10 is formed from a contact element 12, a holding device 13, and a spring device 14. The contact element 12 consists predominantly of carbon, is annular in shape, and has a sliding contact surface 15 that bears against an end-face or axial shaft contact surface 16 of the shaft 11, thereby forming an electrically conductive sliding contact 17. The spring device 14 is formed by a disc spring 18, which bears against a pressure side 19 of the contact element 12 and exerts a contact force on the contact element 12 in the axial direction relative to a rotational axis 20 of the shaft 11. The holding device 13 is formed from a base plate 21 with an integrally formed guide element 22, which is circular in shape.Due to its annular shape, the contact element 12 has a guide recess 23 with which the guide element 22 is designed to align such that the contact element 12 is axially displaceable relative to the axis of rotation 20 on the holding device 13. The disc spring 18 is mounted on the guide element 22 and bears against the base plate 21. The base plate 21 and the guide element 22 are formed in one piece from a single metal component and are attached to a stationary component of an electric machine, which is not shown in detail here. Overall, this allows for a good electrically conductive connection with low contact resistance from the shaft 11 to the holding device 13 via the contact element 12. The discharge device 10 can also be mounted on an electric machine particularly quickly and easily.

[0036] The Fig. 2 und 3 Figure 24 shows a contact element which is annular and rotationally symmetrical. The contact element 24 forms a sliding contact surface on one end face 25.

[0037] The Fig. 4 und 5 The figures show a holding device 27, which is formed in one piece and has a rectangular base plate 28 with a guide element 29 molded into it, which is pin- or bolt-shaped. The contact element is formed on an outer surface 30 of the guide element 29. Fig. 2 attachable.

[0038] A summary of Fig. 6 bis 9 Figure 1 shows a contact element 31, which is disc-shaped and has a central bore 32 forming a guide recess 33. A holding device 34 has a guide pin 37 on a base plate 35, which is aligned with the bore 32. Furthermore, square guide pins 38 are formed on the base plate 35, which together with the guide pin 37 form a guide element arrangement 39. The guide pins 38 can engage in grooves 40 around a circumference 41 of the contact element 31, thus forming an anti-rotation device 42 for the contact element 32 on the holding device 34.

[0039] The Fig. 10 und 11 show a contact element 43, which, unlike the contact element made of Fig. 6 The recess 44 is formed in a sliding contact surface 45 and serves to receive the screw head of a screw (not shown in detail here) which can be used to fasten and guide the contact element 43 to a holding device or base plate.

[0040] The Fig. 12 und 13 Figure 46 shows a contact element 46 with three guide recesses 47, which are formed eccentrically and equidistantly from each other in the contact element 46 relative to a rotation axis 48 of a shaft not shown here.

[0041] The Fig. 14 bis 15 show a contact element 49 with a slot-shaped guide recess 50.

[0042] The Fig. 16 und 17 show a contact element 51 with a polygonal guide recess.

[0043] The Fig. 18 und 19 Figure 53 shows a contact element 53 with strands 55 protruding from a circumference 54 of the contact element 53, shown here only in sections, which can be connected to a holding device (not shown here). A central guide recess 56 and an equidistant arrangement of the strands 55 ensure that the contact element 53 is centered on the holding device.

[0044] The Fig. 20 und 21 show a contact element 57, which in contrast to the contact element made of Fig. 2 The contact element 57 has grooves 60 extending radially in a sliding contact surface 58, relative to a rotational axis 59 of a shaft (not shown). A radial depth T of the grooves corresponds to a wear length of the contact element 57.

[0045] The Fig. 22 bis 23 show a contact element 61, which, unlike the contact element made of Fig. 20 a comparatively small guide recess 62.

[0046] The Fig. 24 und 25 show a contact element 63, which, unlike the contact element made of Fig. 22 has grooves 64 which run relative to a rotation axis 65 of a shaft not shown here in the manner of a passant and thus do not intersect the rotation axis 65, but are nevertheless arranged in a radial direction.

[0047] The Fig. 26 Figure 1 shows a discharge device 66 on a shaft 67, which has a central recess 69 in an end face 68. The discharge device 66 is formed from a holding device 70 with a base plate 71 and a screw 72 attached thereto as a guide element 73. A contact element 74 of the discharge device 66 has a recess 75 that serves to receive a screw head 76 of the screw 72. The recess 69 is also dimensioned such that the screw head 76 cannot come into contact with the end face 68 if the contact element 74 wears down. A disc spring 77 is arranged between the contact element 74 and the base plate 71 to generate a contact force.

[0048] The Fig. 27 Figure 1 shows a discharge device 78 with a contact element 79, which forms a conical sliding contact surface 80. A shaft 81 also forms a conical shaft contact surface 82, which is adapted to the sliding contact surface 80. This allows for simple centering of the contact element 79 on the shaft 81.

[0049] The Fig. 28 Figure 83 shows a discharge device 83 on a shaft 84, which has a pin 85 on an end face 86. The discharge device 83 comprises an annular contact element 87, which is mounted on the pin 85, a holding device 88 with a base plate 89, a disc spring 90, and wires 91 that protrude from the contact element 87 at a circumference 92 and are attached to the base plate 89. This allows for a particularly good electrically conductive connection between the contact element 87 and the base plate 89.

[0050] The Fig. 29 shows a drainage device 93, which, unlike the drainage device from the Fig. 1 The contact element 94 comprises a sliding layer 95 and a bonding layer 96. The sliding layer 95 has a copper content of < 60% by mass, and the bonding layer 96 has a copper content of > 80% by mass. A contoured transition zone 97 between the sliding layer 95 and the bonding layer 96 is formed. The contact element 94 is manufactured by sintering various powder mixtures.

[0051] The Fig. 30 shows a discharge device 98, which, unlike the discharge device from the Fig. 29 A contact element 99 comprises a sliding layer 100 and a bonding layer 101, with an expansion layer 102 formed between them. The expansion layer 102 compensates for the different coefficients of thermal expansion of the sliding layer 100 and the bonding layer 101.

Claims

1. A discharge device (10, 66, 78, 83, 93, 98) for discharging electric currents from a rotor part of a machine, in particular a rotor part realized with a shaft (11, 67, 81, 84), into a stator part of the machine, the discharge device comprising a contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99), a support (13, 27, 34, 70, 88), and a spring mechanism (14), the support being connectable to a stator part in an electrically conductive manner, the contact element being predominantly made of carbon, the contact element being accommodated on the support in an axially movable manner and being connected to it in an electrically conductive manner, a contact force being applicable to the contact element by means of the spring mechanism so as to establish an electrically conductive sliding contact (17) between a sliding contact surface (15, 26, 45, 58, 80) of the contact element, said sliding contact surface serving to establish the sliding contact, and an axial shaft contact surface (16, 82) of the shaft, the contact element being disk-shaped, the sliding contact surface being at least annular and disposable coaxially relative to the shaft contact surface, the support having a base plate (21, 28, 35, 71, 89), the spring element being disposed between the base plate and a contact pressure side (19) of the contact element, said contact pressure side facing away from a contact surface side, which has the sliding contact surface, and the spring mechanism (14) having a spring element, the spring element being disposed coaxially relative to the sliding contact surface (15, 26, 45, 58, 80), characterized in that the spring element is a a disk spring (18, 77, 90) or a diaphragm spring.

2. The discharge device according to claim 1, characterized in that the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) is realized in one piece and consists predominantly of carbon.

3. The discharge device according to claim 1 or 2, characterized in that the support (13, 27, 34, 70, 88) is made of metal, preferably of steel, aluminum, copper or an alloy of these materials.

4. The discharge device according to any one of the preceding claims, characterized in that the support (13, 27, 34, 70, 88) and the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) together form a lock against rotation (42) for the contact element.

5. The discharge device according to any one of the preceding claims, characterized in that the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) is composed of at least two layers (95, 96, 100, 101, 102) having different material mixtures.

6. The discharge device according to claim 5, characterized in that the layers (95, 96, 100, 101, 102) are formed back to back in the axial direction, the sliding contact surface (15, 26, 45, 58, 80) being formed by a sliding layer (95, 100) having a copper content of < 60 wt%, and the contact pressure side (19) being formed by a bonding layer (96, 101) having a copper content of > 80 wt%, an expansion layer (102) being preferably formed between the sliding layer and the bonding layer.

7. The discharge device according to claim 5 or 6, characterized in that the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) is realized with a contoured transition zone (97) between the layers (95, 96, 100, 101, 102) by sintering.

8. The discharge device according to any one of the preceding claims, characterized in that the support (13, 27, 34, 70, 88) has at least one guiding element assembly (39) which extends in the axial direction and on which the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) can axially slide.

9. The discharge device according to claim 8, characterized in that at its circumference (41, 54, 92), the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) has a guiding contour which is inserted into the guiding element assembly (39).

10. The discharge device according to claim 8 or 9, characterized in that the contact element (12, 24, 31, 43, 46, 49, 51, 53, 57, 61, 63, 74, 79, 87, 94, 99) has a guiding recess (23, 33, 47, 50, 52, 56, 62) into which the guiding element assembly (39) or a guiding pin (85) of the shaft (11, 67, 81, 84) engages.

11. The discharge device according to claim 10, characterized in that the guiding recess (23, 33, 47, 50, 52, 56, 62) and the guiding element assembly (39) have corresponding cross-sections.

12. The discharge device according to any one of claims 8 to 11, characterized in that the guiding element assembly (39) is disposed coaxially with the sliding contact surface (15, 26, 45, 58, 80).

13. The discharge device according to any one of claims 8 to 12, characterized in that the guiding element assembly (39) has at least one guiding element (22, 29, 36, 73), preferably a plurality of guiding elements.

14. The discharge device according to claim 13, characterized in that the guiding element (22, 29, 36, 73) is integral to a base plate (21, 28, 35, 71, 89) of the support (13, 27, 34, 70, 88) or plugged into the base plate.

15. The discharge device according to claim 13 or 14, characterized in that the support (13, 27, 34, 70, 88) is realized in one piece.

16. The discharge device according to any one of claims 13 to 15, characterized in that an inner surface of the guiding recess (23, 33, 47, 50, 52, 56, 62) is in electrically conductive contact with an outer surface (30) of the guiding element (22, 29, 36, 73).

17. The discharge device according to any one of claims 13 to 16, characterized in that the guiding element (22, 29, 36, 73) is disposed on the support (13, 27, 34, 70, 88) concentrically relative to the shaft contact surface (16, 82).

18. The discharge device according to any one of claims 13 to 17, characterized in that the guiding element is disposed on the support eccentrically relative to the shaft contact surface.

19. The discharge device according to any one of the preceding claims, characterized in that at least one groove (60, 64) running in the radial direction is formed in the sliding contact surface (58).

20. The discharge device according to any one of the preceding claims, characterized in that the contact element (53, 87) is connected to the support (88) via at least one electrically conductive stranded wire (55, 91) or a flexible flat metal tape.

21. The discharge device according to any one of the preceding claims, characterized in that the sliding contact surface (80) is conical, preferably cone-shaped, in order to come into contact with a correspondingly shaped shaft contact surface (82).

22. A machine comprising a discharge device (10, 66, 78, 83, 93, 98) according to any one of the preceding claims.