Discharge device for discharging electric currents, and machine comprising a discharge device of this kind

Abstract

The invention relates to a discharge device (1) for discharging electric currents from a rotor part of a machine (100), the rotor part being formed with a shaft (2), comprising an axially displaceable contact element (3), which is at least partially accommodated in a guide device (6), for forming an electrically conductive sliding contact between a sliding contact surface (4) of the contact element (3) and a shaft contact surface of the shaft, wherein the contact element (3) is electrically conductively connected to the guide device (6) and / or a holding element of the machine and is preloaded in the direction of the shaft contact surface by means of a spring element, wherein the contact element (3) is at least partially wetted, in particular at least in the region of its sliding contact surface (4), with an oil-like fluid, wherein at least one line (19) for the oil-like fluid is provided at least in sections in the guide device (6) and / or in the contact element (3), wherein the line (19) is formed by the guide device (6) and the contact element (3).

Description

[0001] Discharge device for discharging electrical currents and machine with such a discharge device

[0002] The present invention relates to a diverting device for diverting electrical currents from a rotor part of a machine formed with a shaft, comprising a contact element which is at least partially received in a guide device and is in particular axially displaceable for forming an electrically conductive sliding contact between a sliding contact surface of the contact element provided for forming the sliding contact and a shaft contact surface of the shaft, wherein the contact element is electrically conductively connected to the guide device and / or a holding element of the machine and wherein the contact element is prestressed in the direction of the shaft contact surface by means of a spring element.

[0003] Such diverting devices are known in various designs from the prior art. In particular, it is known to use carbon brushes to divert low-frequency currents. These brushes are arranged axially or radially around a shaft and connected to a stator via connecting strands. Due to their low electrical resistance, the carbon brushes, housed in a holding device or brush holder, enable direct diversion of electrical currents and can thus prevent unwanted current flow through the shaft's bearings, which could lead to surface damage to the bearing bodies or bearing rings due to spot welding.

[0004] The term "shaft" is used here as a synonym for the term "rotor part" or "axle." Therefore, the term "shaft" refers to all rotating machine parts for which currents can be diverted to a stationary stator or machine part of a machine.

[0005] Diversion devices are also regularly used in railway technology, where alternating currents or a working current can flow through wheel axles. Such diversion devices are described, for example, in DE 10 2010 039 847 A1.

[0006] Measures for current dissipation are also required for electrical machines in general, such as those used in motor vehicles. Motor drive shafts or connected transmission shafts or other functional components can be subject to continuously fluctuating alternating voltages or currents and high-frequency current pulses, which can also damage bearings on a rotor shaft or transmission shaft, which is why discharge devices are regularly required.

[0007] A problem with the described discharge devices and the machines incorporating such devices is the high heat generation caused by electrical and mechanical losses, which leads to high thermal loads on both the discharge device and the machine (e.g., motor, gearbox). In order to somewhat control this problem, the resulting heat has so far been dissipated, particularly via ventilation systems. However, such ventilation systems can only partially minimize the thermal load on components. A further disadvantage of such ventilation systems is the drastic increase in the installation space required to integrate such ventilation systems into the machines in question.

[0008] The present invention is based on the object of overcoming the above-described disadvantages of the prior art. In particular, the invention is based on the object of minimizing thermal component stress when dissipating parasitic currents while simultaneously keeping the required installation space as small as possible.

[0009] This object is achieved according to the invention by a discharge device of the type mentioned at the outset, which is characterized in that the contact element is at least partially wetted with an oily fluid, in particular at least in the region of its sliding contact surface, wherein at least one line for the oily fluid is provided at least in sections in the guide device and / or in the contact element, wherein the line is formed by the guide device and the contact element.

[0010] The discharge device according to the invention ideally enables the dissipation of capacitively coupled high-frequency voltages (so-called parasitic alternating voltages) generated by electric drives due to the power electronics used (pulse width modulation). At the same time, the resulting heat can be contained or dissipated using the oily fluid. In particular, the present invention eliminates the need for a special cooling device, such as a ventilation system to minimize thermal stress. This allows the design of a machine, such as an electric motor, to be simpler and thus more cost-effective, and the cooling of the motor to be more efficient than with previously known systems. For example, friction losses caused by radial shaft seals, among other things, are also eliminated.In addition, as already mentioned above, the overall machine dimensions can be smaller (the moment of inertia of the rotating parts is reduced).

[0011] As a rule, the oily fluid is an engine and / or transmission oil, which is usually present anyway in the engine or transmission in which the discharge device according to the invention is provided.

[0012] The line can be configured to run at least along the contact element. This allows for direct cooling of the contact element by the oily fluid flowing through the line. Furthermore, the line can be configured even in confined spaces. The line can preferably be configured to run along the entire length of the contact element.

[0013] The line can be formed by a longitudinal recess in a guide wall of the guide device and / or a longitudinal recess in an outer wall of the contact element. The longitudinal recess in the contact element and the longitudinal recess in the guide wall can be easily manufactured. Each of these longitudinal recesses can form the line for the oily fluid on its own, or both longitudinal recesses together. In particular, it can be provided that a plurality of longitudinal recesses are formed in the guide wall or a plurality of longitudinal recesses are also formed in the outer wall, thus providing a corresponding number of lines for the oily fluid.

[0014] The outer wall of the contact element can rest against the guide wall of the guide device. A clearance can be formed between the outer wall of the contact element and the guide wall of the guide device, such that the contact element can be easily moved in the guide device in the longitudinal direction of the contact element. Likewise, the clearance can be dimensioned such that the contact element cannot jam or tilt in the guide device. The outer wall of the contact element therefore rests, at least in sections, against the guide wall of the guide device.

[0015] The longitudinal recess can be formed, at least in sections, with a semicircular cross-section, preferably in the form of a groove. The cross-section of the longitudinal recess can, in principle, have any suitable shape. A semicircular cross-section is particularly easy to produce. A groove is understood here to be a depression that is comparatively long compared to its width.

[0016] A passage can be formed in the guide device, by means of which a volume flow of oily fluid through the line can be limited. The passage can be a simple through-opening, for example a through-bore on a side of the guide device facing away from the shaft. A cross-section of the passage can be comparatively smaller than a cross-section of the line or the sum of the cross-sections of the lines. Such a passage is particularly simple and can be manufactured with a high degree of accuracy compared to the line, so that the passage can be used to precisely adjust the volume flow of the oily fluid through the line.

[0017] The groove is preferably continuous. A pressure loss can occur in the line, relative to its length, so that additional contact pressure can be exerted on the contact element against the shaft contact surface, which can further reduce contact resistance.

[0018] The line for the oily fluid can open into the space between the shaft and the guide device. In this embodiment, the heat generated in the contact area between the shaft and the contact element can be immediately dissipated by the flow of the oily fluid. In a particularly preferred embodiment of the discharge device according to the invention, the guide device can be electrically connected to a stator part of the machine. This stator part of the machine can serve, for example, as a holding device for the discharge device. When the current is discharged, it is diverted from the respective shaft into the contact element and the guide device of the discharge device. In the described embodiment, the diverted current then flows into the aforementioned stator part of the machine.

[0019] Advantageously, the contact element is electrically connected to the guide device by means of a preferably low-resistance stranded wire, wherein the stranded wire is preferably pressed or stamped into the contact element at one end and is preferably welded, soldered, or crimped to the guide device at the other end. The guide device is preferably made at least partially of a low-resistance material, in particular of metal, preferably aluminum, aluminum alloy, copper, and / or brass.

[0020] In a particularly preferred embodiment of the discharge device according to the invention, the contact element is made essentially of a carbon-metal mixture, in particular of a mixture of graphite and a metal with good electrical conductivity, wherein at least in the region of the sliding contact surface of the contact element, silver is preferably provided as the metal and wherein in a rear region of the contact element, copper is preferably provided as the metal, wherein the contact element is preferably free of copper in the region of the sliding contact surface. The proportion of metal in the contact element is preferably at least 30 vol.%. In the region of the sliding contact surface, the contact element is therefore preferably free of copper because this metal, in conjunction with the passage of current, can lead to catalytic changes in the oily fluid, which can consequently adversely change the physical properties of this fluid.For this reason, the shaft of the machine according to the invention, which is described in more detail below, is also free of copper, at least in the area where the shaft contacts the contact element.

[0021] In order to keep the system resistance as low as possible under all operating conditions, the resistance of the discharge device according to the invention should also be selected to be low. The above-described embodiments with low-resistance materials and a contact element made of a metal-carbon mixture allow the resistance of the entire device to be kept low. On the other hand, the system resistance is significantly influenced by the voltage drop between the shaft surface and the sliding contact surface of the contact element. This represents the largest portion of the overall system. Therefore, it should also be kept low. To ensure this under continuous lubrication, a high specific contact pressure of the contact element against the shaft is advantageous. This value should be at least 10 N / cm 2On the other hand, no electrochemical reactions should occur in the contact element in the area of ​​the sliding contact surface in conjunction with the oily fluid. This is particularly ensured by using a silver-graphite material in an area of ​​the contact element that is subject to wear over its entire service life.

[0022] The contact element advantageously has a recess, in particular a hole or slot, in the area of ​​the sliding contact surface. This prevents the contact from floating on the oil film. The contact element advantageously has an open-pore design in the area of ​​the sliding contact surface. This contributes to the suppression of electrical contact losses between the shaft and the contact element and minimizes the contact element from floating on the oil film.

[0023] Typically, the contact element is a pin- or bolt-shaped brush. The sliding contact surface can be rectangular, polygonal, or circular. This brush is typically manufactured by compression molding followed by heat treatment.

[0024] The spring element can advantageously be a helical compression spring, one end of which preferably rests against the end face of the contact element opposite the sliding contact surface. Such a helical compression spring makes it easy to always press the contact element against the shaft with a specific desired contact pressure.

[0025] The present invention further relates to a machine, in particular an electric drive motor or transmission, with a rotor part having a shaft and a deflection device according to the invention according to one of claims 1 to 12, wherein the contact element of the deflection device contacts the shaft with its sliding contact surface to form a sliding contact. The machine according to the invention achieves the advantages already described above of drastically reduced thermal stress with a small size and uncomplicated design.

[0026] In the machine according to the invention, the discharge device can be completely immersed in an oily fluid, in particular engine or transmission oil. The oily fluid is preferably provided in a space between the shaft and the guide device, which is bridged by the contact element. In this embodiment, the area of ​​greatest heat generation, namely the area between the shaft and the contact element, is cooled by the oily fluid.

[0027] Advantageously, the contact element is always actuated by the spring element with a force of at least 10 N / cm 2 pressed against the shaft. This minimizes the voltage drop between the shaft surface and the sliding contact surface of the contact element. As already stated above, the shaft is preferably essentially free of copper, at least in the area in which it is contacted by the contact element.

[0028] In a preferred embodiment of the machine according to the invention, the contact element contacts an end face of the shaft, wherein the contact element is preferably arranged substantially coaxially to the shaft. Such shaft grounding is preferably suitable for avoiding contact losses, since the axial runout of the rotating shaft is usually low. By positioning the contact element close to the rotation point of the shaft, the peripheral speeds are minimized and thus the actual running distance of the contact element over the service life is enormously reduced. This has a direct influence on the wear of the contact element, which usually correlates proportionally with the running distance. By minimizing the running distance, the wear of the contact element remains low, which consequently also means that the force loss of the spring element over the entire wear length of the contact element is also minimal.This enables, for example, the use of a cost-effective helical compression spring as mentioned above. In addition, the low peripheral speed near the shaft's axis of rotation reduces the risk of a continuous, electrically insulating lubricating film forming, meaning the contact force can be kept lower than would be necessary at high peripheral speeds. A further advantage of end-to-end contact with the shaft near the axis of rotation is the minimization of frictional torque due to the small radial distance from the point of rotation. Even with a very high frictional force, the frictional torque remains small as the product of frictional force x running radius. As a result, in conjunction with the angular velocity (equivalent to speed), the frictional power remains low and thus the system losses are small.

[0029] In a further embodiment of the machine according to the invention, the contact element contacts the lateral surface of the surface. In this embodiment, the contact element is preferably geometrically tapered in cross-section against the preferred direction of rotation of the shaft to be contacted in order to suppress electrical contact losses due to floating between the shaft and the contact element.

[0030] As a rule, the discharge device is positioned in a section of the machine where an operating temperature of over 50 °C prevails.

[0031] Further features of the invention will become apparent from the following descriptions of the figures in conjunction with the drawings and the dependent claims. The individual features can be implemented alone or in combination with one another.

[0032] The drawings show:

[0033] Fig. 1 shows a first embodiment of a discharge device;

[0034] Fig. 2: a longitudinal section through the diverter device of Fig. 1 in a section of a machine in the contact area between contact element and shaft, wherein the contact element is arranged coaxially to the shaft;

[0035] Fig. 2 : a cross-sectional view through the discharge device of Fig. 1 ;

[0036] Fig. 4 : a front view of a second embodiment of a discharge device;

[0037] Fig. 5 : a front view of a third embodiment of a discharge device;

[0038] Fig. 6: a front view of a fourth embodiment of a discharge device; Fig. 7: a front view of a fifth embodiment of a discharge device;

[0039] Fig. 8 : a front view of a sixth embodiment of a discharge device;

[0040] Fig. 9 : a front view of a seventh embodiment of a discharge device;

[0041] Fig. 10 : a front view of an eighth embodiment of a discharge device;

[0042] Fig. 11 : a front view of a ninth embodiment of a discharge device;

[0043] Fig. 12 : a front view of a tenth embodiment of a discharge device;

[0044] Fig. 13 : a front view of an eleventh embodiment of a discharge device;

[0045] Fig. 14 : a front view of a twelfth embodiment of a discharge device.

[0046] A summary of Figs. 1 to 3 shows a section of a machine 100 according to the invention with a discharge device 1. In the present case, the machine 100 is an electric motor having a rotor part with a shaft 2. The discharge device 1 for discharging electrical currents is arranged on an end face 10 of the shaft 2. The discharge device 1 comprises a contact element 3 in the form of a carbon brush for forming an electrically conductive sliding contact between the sliding contact surface 4 of the contact element 3, provided for forming the sliding contact, and a shaft contact surface 5 of the shaft 2. The contact element 3 is received in an axially displaceable manner in a guide device 6. The guide device 6 is designed as a cylindrical housing and is located in a recess (not shown here) of the machine 100 that is also cylindrical.The contact element 3 is electrically connected to the guide device 6 by means of a stranded wire 8.

[0047] The contact element 3 is preloaded in the direction of the shaft contact surface 5 by a helical compression spring 9. The contact element 3 is thus subjected to a contact force by the spring 9 to form an electrically conductive sliding contact between the sliding contact surface 4 of the contact element 3, which is provided for forming the sliding contact, and the axial shaft contact surface 5 of the shaft 2. On the side of the guide device 6 facing the shaft 2, the carbon brush 3 protrudes slightly from the latter and contacts the shaft 2 at its end face 10. The contact element 3 is arranged essentially centrally to the end face 10 of the shaft 2 and thus coaxial with the shaft. As already described above, this position is particularly advantageous because it minimizes wear on the contact element 3.

[0048] At the other end of the guide device 6, it has a cover 11 to which the stranded wire 8 is attached. Between the cover 11 and the contact element 3, the spring 9 is arranged, which preloads the contact element 3 in the direction of the shaft 2.

[0049] The guide device 6 is made of an electrically conductive metal, so that an electrically conductive connection exists between the guide device 6 and a subassembly of the machine 100 (not shown here) that supports the guide device 6. In the present embodiment, the guide device 6 is made of aluminum.

[0050] The stranded wire 8 is also made of a low-resistance material. The stranded wire 8 is pressed into the contact element 3 at one end and connected to the cover 11 at the other end by crimping, resistance welding, or soldering. The stranded wire 8 can also be passed through the cover 11 and otherwise contacted.

[0051] The contact element 3 has a two-layer structure. In the area of ​​the sliding contact surface 4, the contact element 3 consists of a graphite-silver mixture. This particularly affects a section 21 of the contact element 3. The silver content in this area is approximately 3% by volume. The remaining area of ​​the contact element 3 consists of a graphite-copper mixture. However, section 21 of the contact element 3 and the shaft 2 are essentially free of copper in order to avoid undesirable reactions with oil. The contact element 3 is designed as a cylindrical pin. In the present embodiment, the contact element 3 is pressed with a force of approximately 10 N / cm 2 pressed against shaft 2.

[0052] A line 19 is formed in the guide device 6, which extends from the cover 11 in the axial direction to a space 14 between the guide device 6 and the shaft 2 and is in open communication with the space 14. As can be seen from Fig. 2, oil 20 flows from the area of ​​the cover 11 towards the space 14 and pours into it. As a result, the section 21 of the contact element 3 is surrounded by oil 20. In a section 22, the contact element 3 consists of a graphite-copper mixture. The stranded wire 8 is connected here to the section 22 of the contact element 3 and the guide device 6 or the cover 11 and connects these elements in an electrically conductive manner.

[0053] The line 19 formed in the guide device 6 is also partially formed or delimited by the contact element 3. In particular, the line 19 is formed by a longitudinal recess 23 in a guide wall 24 of the guide device 6. The longitudinal recess 23 thus forms a groove 25 in the guide wall 24. The groove 25 is at least partially covered by an outer wall 26 of the contact element 13, so that in this area between the outer wall 26 and the longitudinal recess 23, a cross-section 27 of the line 19, through which the oil 20 flows, is formed.

[0054] As the oil 20 flows into the chamber 14, the oil 20 reaches the sliding contact surface 4 and the shaft contact surface 5, respectively. This "oiling" of the contact element 3 and the shaft 2 achieves optimal cooling in this area. From the chamber 14, the heated oil then flows into channels of the machine 100 (not shown here). This advantageously dissipates heat energy from the contact element 3.

[0055] Fig. 4 shows a discharge device 30 in which, in contrast to the discharge device of Figs. 1 to 3, lines 31 are formed. The discharge device 30 is designed symmetrically.

[0056] Fig. 5 shows a discharge device 32 which, in contrast to the discharge device of Figs. 1 to 3, has an asymmetrical arrangement of a contact element 33 relative to a longitudinal axis 34 of a guide device 35. The contact element 33 can thus be formed with a particularly large cross-section.

[0057] Fig. 6 shows a discharge device 36 in which, in contrast to the discharge device of Figs. 1 to 3, a line 37 is formed with a kidney-shaped cross-section 38, which is adapted to an outer edge 39 of a guide device 40. The cross-section 38 can thus be made particularly large.

[0058] In the illustration of a discharge device 41 in Fig. 7, a plurality of lines 37 are formed so that a particularly large amount of oil can be transported through the lines 37.

[0059] In the discharge device 42 of Fig. 8, two semicircular lines 43 are formed, which are opposite a substantially flat outer wall 44 of a contact element 45. Fig. 9 shows a discharge device 46 in which two lines 47 are each arranged transversely to outer walls 48 of a contact element 49.

[0060] Fig. 10 shows a discharge device 50 with a contact element 51 with a polygonal cross-section 52. At each edge 53 of the

[0061] Contact element 5 1, lines 54 are formed in a guide device 55 of the discharge device 50.

[0062] Fig. 11 shows a discharge device 56 with a contact element 57 in which a line 58 is formed. In the discharge device 59 shown in Fig. 12, a plurality of lines 58 are formed in a contact element 60. The contact element 60 is symmetrical.

[0063] In contrast to the discharge device of Fig. 12, the discharge device 61 of Fig. 13 also includes a portion of a line 63 in a guide device 62. The discharge device 61 is symmetrical.

[0064] Fig. 14 shows a discharge device 64 in which, in contrast to the discharge device of Fig. 11, a single line 66 or a section thereof is formed in a guide device 65.

Claims

Claims: A discharge device (1, 30, 32, 36, 41, 42, 46, 50, 56, 59, 61, 64) for discharging electrical currents from a rotor part of a machine (100) formed with a shaft (2), comprising a displaceable contact element (3, 33, 45, 49, 51, 57, 60) received at least partially in a guide device (6, 35, 40, 55, 62) for forming an electrically conductive sliding contact between a sliding contact surface (4) of the contact element provided for forming the sliding contact and a shaft contact surface (5) of the shaft, wherein the contact element is electrically conductively connected to the guide device and / or a holding element of the machine and wherein the contact element is biased in the direction of the shaft contact surface by means of a spring element (9), characterized in that the contact element is at least partially, in particular at least in the area of ​​its The grinding contact surface is wetted with an oil-like fluid (20),wherein at least one line (19, 31, 37, 43, 47, 54, 58, 63) for the oil-like fluid is provided at least in sections in the guide device and / or in the contact element, wherein the guide is formed by the guide device and the contact element. Drainage device according to claim 1, characterized in that the guide (19, 31, 37, 43, 47, 54, 58, 63) is designed to run at least along the contact element (3, 33, 45, 49, 51, 57, 60). A discharge device according to claim 1 or 2, characterized in that the conductor (19, 31, 37, 43, 47, 54, 58, 63) is formed by a longitudinal recess (23) in a guide wall (24) of the guide device (6, 35, 40, 55, 62) and / or a longitudinal recess in an outer wall (26, 44, 48) of a contact element (3, 33, 45, 49, 51, 57, 60). A discharge device according to claim 3, characterized in that the outer wall (26) of the contact element (3, 33, 45, 49, 51, 57, 60) abuts the guide wall (24) of the guide device (6, 35, 40, 55, 62).A drainage device according to claim 3 or 4, characterized in that the longitudinal recess (23) is formed at least partially with a semicircular cross-section (27, 28, 52), preferably in the form of a groove (25). A drainage device according to any one of the preceding claims, characterized in that... that the line (19, 31, 37, 43, 47, 54, 58, 63) for the oily fluid (20) opens into the space (14) between the shaft (2) and the guide device (6, 35, 40, 55, 62). Drainage device according to one of the preceding claims, characterized in that a passage is formed in the guide device (6, 35, 40, 55, 62) by means of which a volume flow of oily fluid (20) through the line (19, 31, 37, 43, 47, 54, 58, 63) can be limited. Drainage device according to one of the preceding claims, characterized in that the guide device (6, 35, 40, 55, 62) can be electrically connected to a stator part of the machine (100).A discharge device according to one of the preceding claims, characterized in that the contact element (3, 33, 45, 49, 51, 57, 60) is electrically connected to the guide device (6, 35, 40, 55, 62) or a holding element of the machine (100) by means of a preferably low-resistance stranded wire (8), wherein the stranded wire is preferably pressed or stamped into the contact element at one end and preferably welded, soldered, or crimped to the guide device at the other end. A discharge device according to one of the preceding claims, characterized in that the contact element (3, 33, 45, 49, 51, 57, 60) is made essentially of a carbon-metal mixture, in particular of a mixture of graphite and metal, wherein the total volume fraction of the metal is preferably at least 30 vol.%, wherein at least in a front, sliding contact surface (4) in the pointing area (16, 21) of the contact element, preferably silver is provided as a metal and in a rear area (22) of the contact element, preferably copper is provided as a metal, wherein the contact element in the area of ​​the sliding contact surface is preferably free of copper.

11. Drainage device according to one of the preceding claims, characterized in that the contact element (3, 33, 45, 49, 51, 57, 60) is a pin- or bolt-shaped brush, wherein the sliding contact surface (4) is preferably rectangular, polygonal or circular.

12. Discharge device according to one of the preceding claims, characterized in that the spring element (9) is a helical compression spring which, with one end, preferably abuts the end face of the contact element (3, 33, 45, 49, 51, 57, 60) opposite the sliding contact surface (4).

13. Machine (100), in particular an electric drive motor or gearbox with a rotor part having a shaft (2) and a discharge device (1, 30, 32, 36, 41, 42, 46, 50, 56, 59, 61, 64) according to one of the preceding claims, wherein the contact element (3, 33, 45, 49, 51, 57, 60) of the discharge device (1, 30, 32, 36, 41, 42, 46, 50, 56, 59, 61, 64) contacts the shaft with its sliding contact surface (4) to form a sliding contact.

14. Machine according to claim 13, characterized in that at least in a space (14) between the shaft (2) and the guide device (6, 35, 40, 55, 62), which is defined by the contact- The contact element (3, 33, 45, 49, 51, 57, 60) is bridged by an oily fluid, in particular engine or transmission oil (20). A machine according to claim 13 or 14, characterized in that the shaft (2) is substantially free of copper, at least in the area where it is contacted by the contact element (3, 33, 45, 49, 51, 57, 60). A machine according to any one of claims 13 to 15, characterized in that the contact element (3, 33, 45, 49, 51, 57, 60) contacts an end face (10) of the shaft (2), the contact element preferably being arranged substantially coaxially with the shaft. A machine according to any one of claims 13 to 15, characterized in that the contact element contacts a circumferential surface of the shaft.

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