Discharge device for discharging electric current, and machine comprising such discharge device

Abstract

The invention relates to a discharge device (1) for discharging an electric current from a rotor part of a machine (100) having a shaft (2), comprising an axially displaceable contact element (3) which is at least partially received in a guide unit (6) and 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, the contact element (3) is connected in an electrically conductive manner to the guide unit (6) and / or to a holding element of the machine and is preloaded by a spring element to the shaft contact surface, the contact element (3) being wetted at least partially, in particular at least in the region of the sliding contact surface (4) thereof, by an oily fluid, in at least part of the guide unit (6) and / or in at least part of the contact element (3) there is at least one duct (19) for the oily fluid, which duct (19) is formed by the guide unit (6) and the contact element (3).

Description

[0001] The invention relates to a discharge device for discharging electric current from a rotor part of a machine having a shaft, the discharge device comprising a contact element which is in particular axially displaceable, is at least partially received in a guide unit and is used for establishing an electrically conductive sliding contact between a sliding contact surface of the contact element for establishing a sliding contact and a shaft contact surface of the shaft, the contact element being connected in an electrically conductive manner to the guide unit and / or a retaining element of the machine, the contact element being preloaded toward the shaft contact surface by a spring element.

[0002] Such discharge devices are known in various embodiments. In particular, it is known to discharge low-frequency currents using carbon brushes, which are distributed axially or radially around the shaft and are connected to the stator via connecting wires. Due to the low resistance of the carbon brushes, which are mounted in a holding unit and / or a brush holder, the current can be discharged directly, thus avoiding undesired conduction of currents via the bearing points of the shaft, which could cause surface damage to the bearing body or the bearing rings due to spot welding.

[0003] The term "shaft" as used herein is a synonym for the term "rotor part" or "axis line". Thus, the term "shaft" refers to all rotating machine parts that can discharge electric current to stationary stator parts and / or machine parts.

[0004] Discharge devices are also often used in railway technology, where alternating current or even operating current can flow via the wheel axle. Discharge devices of this type are described in DE 10 2010 039 847 A1, for example.

[0005] Discharge measures are also required for general electric machines, such as motor vehicles. Continuously fluctuating AC voltages and / or currents and high-frequency current pulses may occur on the engine drive shaft or the connected transmission shaft and / or other functional components, which may also damage the bearing points of the rotor shaft or transmission shaft, so discharge equipment is often required here.

[0006] One problem with the above-described discharge devices and machines having such discharge devices is that the electrical and mechanical losses generate a large amount of heat, which results in a high thermal load on the discharge device and the machine (e.g. engine, transmission). In order to solve this problem to a certain extent, ventilation systems have been used so far to dissipate the generated heat. However, such ventilation systems can only partially reduce the thermal load on the components. Another disadvantage of such ventilation systems is that the installation space required for integrating such ventilation systems into the machine increases dramatically.

[0007] The object of the present invention is to overcome the above-mentioned disadvantages of the prior art. In particular, the object of the present invention is to minimize the thermal load on the components when dissipating parasitic currents while keeping the required installation space to a minimum.

[0008] According to the invention, this object is achieved by a discharge device as described above, which is characterized in that the contact element is wetted at least partially, in particular at least in the region of the sliding contact surface of the contact element, with an oily fluid, and that at least one duct for the oily fluid is provided in at least part of the guide unit and / or at least part of the contact element, the duct being formed by the guide unit and the contact element.

[0009] With the discharge device according to the invention, it is ideally possible to discharge capacitively coupled high-frequency voltages (so-called parasitic AC voltages) which are formed by the electric drive using power electronics (pulse width modulation), while the heat generated can be controlled and / or discharged with the aid of an oily fluid. In particular, the invention does not require special cooling equipment, such as ventilation equipment, and the heat load can be minimized. As a result, the design of machines such as electric motors can be simpler and therefore cheaper than in currently known systems, and the cooling of the engine can also be more effective. For example, friction losses caused by radial shaft seals and others can also be eliminated. In addition, as mentioned above, the overall machine size can be smaller (the moment of inertia of the rotating parts is reduced).

[0010] Typically, the oily fluid is engine oil and / or transmission oil, which are usually present in an engine or transmission in which the discharge device of the present invention is installed.

[0011] The conduit can extend at least along the contact element. This allows the contact element to be cooled indirectly by the oily fluid flowing through the conduit. Furthermore, the conduit can also be formed in a small installation space. Preferably, the conduit can extend along the entire length of the contact element.

[0012] The conduit can be formed by a longitudinal recess in the guide wall of the guide unit and / or a longitudinal recess in the outer wall of the contact element. The longitudinal recess in the contact element and the longitudinal recess in the guide wall are easy to make. The longitudinal recesses can form a conduit for the oily fluid alone or together. In particular, a plurality of longitudinal recesses can be formed in the guide wall and / or a plurality of longitudinal recesses can also be formed in the outer wall, which means that a corresponding number of conduits are available for the oily fluid.

[0013] The outer wall of the contact element may abut against the guide wall of the guide unit. A tolerance is formed between the outer wall of the contact element and the guide wall of the guide unit, making it easy for the contact element to move. Likewise, the tolerance may be so sized that the contact element does not get stuck or wedged in the guide unit. Thus, at least part of the outer wall of the contact element abuts against the guide wall of the guide unit.

[0014] At least part of the longitudinal recess may have a semicircular cross section, preferably in the form of a groove. The cross section of the longitudinal recess may generally have any suitable shape. A semicircular cross section is particularly easy to produce. A groove is understood to be an indentation that is long compared to its width.

[0015] A channel can be formed in the guide unit, through which the volume flow of the oily fluid through the pipeline is limited. The channel can be a simple channel opening, for example a channel drilling on the side of the guide unit facing away from the axis. The cross section of the channel can be smaller than the cross section of the pipeline and / or the sum of the cross sections of the pipeline. Such a channel can be made particularly easily and with high precision relative to the pipeline, which means that a precise volume flow of the oily fluid through the pipeline can be set through the channel.

[0016] The groove is preferably continuous. In the pipeline, a pressure loss occurs relative to the pipeline length, so that additional contact pressure can be applied to the contact element on the contact surface of the shaft, thereby further reducing the contact resistance.

[0017] The conduit for the oily fluid may lead to the space between the shaft and the guide unit.In this embodiment, the heat generated in the contact area between the shaft and the contact element may be immediately dissipated by the flow of the oily fluid.

[0018] In a particularly preferred embodiment of the discharge device according to the invention, the guide unit is connected to the stator part of the machine in an electrically conductive manner. For example, the stator part of the machine can serve as a holding device for the discharge device. When the current is discharged, the current is discharged from the relevant shaft to the contact element and the guide unit of the discharge device. The discharged current then flows into the stator part of the machine in the described embodiment.

[0019] Advantageously, the contact element is connected to the guide unit in an electrically conductive manner via a preferably low-impedance stranded wire, one end of which is preferably pressed or punched into the contact element and the other end is preferably welded or soldered or crimped to the guide unit. The guide unit is preferably at least partially made of a low-impedance material, in particular metal, preferably aluminum, an aluminum alloy, copper and / or brass.

[0020] In a particularly preferred embodiment of the discharge device according to the invention, the contact element is essentially made of a carbon-metal mixture, in particular a mixture of graphite and a highly conductive metal, preferably silver metal is provided at least in the region of the sliding contact surface of the contact element, copper metal is provided in the rear region of the contact element, and the contact element is preferably free of copper in the region of the sliding contact surface. The metal portion in the contact element preferably accounts for at least 30% of the volume. Therefore, in the region of the sliding contact surface, the contact element is preferably free of copper, because such metal can cause catalytic changes in the oily fluid when an electric current passes through it, thereby negatively affecting the physical properties of the fluid. For this reason, the shaft of the machine according to the invention described in more detail below is also free of copper, at least in the region 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 low. By means of the above-described embodiment of the contact element made of a low-impedance material and a metal-carbon mixture, the resistance of the entire device can be kept at a low level. On the other hand, the voltage drop between the shaft surface and the sliding contact surface of the contact element has a significant influence on the system resistance. This accounts for the largest part of the entire system. Therefore, it should also be kept at a low level. In order to ensure that this is done with continuous lubrication, a high contact pressure of the contact element on the shaft is advantageous. This value should be at least 10 N / cm2. On the other hand, the contact element in the area of ​​the sliding contact surface should not react electrochemically with the oily fluid in contact. This is ensured in particular by the silver-graphite material in the wear area of ​​the contact element over the entire service life.

[0022] Advantageously, the contact element has a recess in the region of the sliding contact surface, in particular a bore or a slit. This prevents the contact element from floating on the oil film. Advantageously, the contact element is perforated in the region of the sliding contact surface. This helps to suppress electrical contact losses between the shaft and the contact element and minimizes floating of the contact element on the oil film.

[0023] The contact element is usually a pin-shaped brush or a bolt-shaped brush. The sliding contact surface can be rectangular, polygonal or circular. The brush is usually manufactured by compression molding and subsequent heat treatment.

[0024] Advantageously, the spring element can be a helical spring, one end of which preferably abuts against the front surface of the contact element opposite the sliding contact surface. Using a helical compression spring of this type, it is easy to press the contact element against the shaft at any time with a required specific contact pressure.

[0025] The invention also relates to a machine, in particular an electric drive engine or a transmission, having a rotor part with a shaft and a discharge device according to claims 1 to 12 of the invention. The contact element of the discharge device contacts the shaft via a sliding contact surface to form a sliding contact. The machine according to the invention achieves the aforementioned advantages, namely small installation dimensions and a simple design, with a greatly reduced thermal load.

[0026] In the machine according to the invention, the discharge device can be completely installed in an oily fluid, in particular in an engine oil or a transmission oil. Preferably, the oily fluid is provided at least in the space between the shaft and the guide unit, which space is bridged by the contact element. In this embodiment, the area where the most heat is generated, i.e. the area between the shaft and the contact element, is cooled by the oily fluid.

[0027] Advantageously, the spring element always presses the contact element against the shaft with a force of at least 10 N / cm 2 . This minimizes the voltage drop between the shaft surface and the sliding contact surface of the contact element.

[0028] As mentioned above, the shaft is preferably substantially free of copper, at least in the region in contact with the contact element.

[0029] In a preferred embodiment of the machine according to the invention, the contact element contacts the front surface of the shaft, the contact element preferably being arranged substantially coaxially with the shaft. Since the axial runout of the rotating shaft is usually small, such a shaft grounding is preferred to avoid contact losses. By arranging the contact element close to the rotation point of the shaft, the peripheral speed is minimized and the actual travel distance of the contact element during its service life is also greatly reduced. This has a direct effect on the wear of the contact element, which is usually proportional to the travel distance. By minimizing the travel distance, the wear of the contact element remains low and, therefore, the force loss of the spring element over the total wear length of the contact element is also minimized. This makes it possible to use the above-mentioned low-cost helical compression springs. In addition, the low peripheral speed of the rotating shaft close to the shaft reduces the risk of forming a continuous electrically insulating lubricating film, which means that the contact pressure can be kept below the level required for high peripheral speeds. Another advantage of the front contact of the shaft close to the rotating shaft is that the friction torque generated is minimized due to the small radial distance from the rotation point. Even in the case of large friction forces, the friction torque as the product of friction force x travel radius is still small. Therefore, the friction power together with the angular speed (equivalent to the rotation speed) remains low and the system losses remain small.

[0030] In a further embodiment of the machine according to the invention, the contact element contacts the surface of the sleeve. In this embodiment, the cross section of the contact element preferably tapers geometrically towards the preferred rotation direction of the contacted shaft to suppress electrical contact losses due to float between the shaft and the contact element.

[0031] In principle, the discharge equipment is located in the part of the machine where the main operating temperature is above 50°C.

[0032] Further features of the present invention will be described below in conjunction with the accompanying drawings and the dependent claims. The various features can be implemented individually or in combination with each other.

[0033] Figure 1 : A first embodiment of the discharge device is shown.

[0034] Figure 2 : Shows Figure 1 A longitudinal section of the discharge device on a section of the machine in the contact region between the contact element and the shaft, the contact element being arranged coaxially with the shaft.

[0035] Figure 3 : Shows Figure 1 Cross-sectional view of a discharge device.

[0036] Figure 4: A front view of a second embodiment of the discharge device is shown.

[0037] Figure 5 : A front view of a third embodiment of the discharge device is shown.

[0038] Figure 6 : A front view of a fourth embodiment of the discharge device is shown.

[0039] Figure 7 : A front view of a fifth embodiment of the discharge device is shown.

[0040] Figure 8 : A front view of a sixth embodiment of the discharge device is shown.

[0041] Fig. 9 : A front view of a seventh embodiment of the discharge device is shown.

[0042] Fig.10 : A front view of an eighth embodiment of the discharge device is shown.

[0043] Fig.11 : A front view of a ninth embodiment of the discharge device is shown.

[0044] Fig.12 : A front view of a tenth embodiment of a discharge device is shown.

[0045] Fig.13 : A front view of an eleventh embodiment of the discharge device is shown.

[0046] Fig.14 : A front view of a twelfth embodiment of a discharge device is shown.

[0047] Figures 1 to 3 The schematic diagram shows a cross section of a machine 100 according to the invention, which has a discharge device 1. In the present case, the machine 100 is an electric motor, the rotor part of which has a shaft 2. The discharge device 1 for discharging electric current is arranged on the front surface 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 a sliding contact surface 4 of the contact element 3 for forming a sliding contact and a shaft contact surface 5 of the shaft 2. The contact element 3 is received in a guide unit 6 in an axially displaceable manner. The guide unit 6 is designed as a cylindrical housing and is located in a likewise cylindrical recess of the machine 100 (not shown). The contact element 3 is electrically conductively connected to the guide unit 6 via a litz wire 8.

[0048] The contact element 3 is preloaded toward the shaft contact surface 5 by means of a helical compression spring 9. The contact element 3 is therefore subjected to the contact force of the spring 9 so as to form an electrically conductive sliding contact between the sliding contact surface 4 of the contact element 3 for forming a sliding contact and the axial shaft contact surface 5 of the shaft 2. On the side of the guide unit 6 facing the shaft 2, the carbon brush 3 slightly protrudes from the guide unit 6 and contacts the shaft 2 at the front surface 10 of the shaft. In this case, the contact element 3 is arranged substantially in the center of the front face 10 of the shaft 2 and is therefore coaxial with the shaft. As mentioned above, this position is particularly advantageous because it minimizes the wear of the contact element 3.

[0049] At the other end of the guide unit 6 there is a cover 11 to which the strands 8 are connected. A spring 9 is provided between the cover 11 and the contact element 3 for preloading the contact element 3 toward the shaft 2.

[0050] The guide unit 6 is made of an electrically conductive metal, so that an electrically conductive connection is established between the guide unit 6 and a component group (not shown) of the machine 100, which holds the guide unit 6. In the present exemplary embodiment, the guide unit 6 is made of aluminum.

[0051] The stranded wire 8 is also made of a low impedance material. One end of the stranded wire 8 is pressed into the contact element 3, and the other end is connected to the cover 11 by crimping, resistance welding or soldering. The stranded wire 8 can also pass through the cover 11 and be fed in another way.

[0052] The contact element 3 has a two-layer structure. In the region of the sliding contact surface 4, the contact element 3 consists of a graphite-silver mixture. This particularly affects the portion 21 of the contact element 3. The silver content in this region is about 3% by volume. The remaining region of the contact element 3 consists of a graphite-copper mixture. However, the portion 21 of the contact element 3 and the shaft 2 are substantially free of copper to avoid adverse reactions with oil. The contact element 3 is designed as a cylindrical pin. In the present exemplary embodiment, a force of about 10 N / cm2 is used to press the contact element 3 against the shaft 2.

[0053] A duct 19 is formed in the guide unit 6, extending from the cover 11 in the axial direction to the space 14 between the guide unit 6 and the shaft 2, and communicating with the space 14. Figure 2 As can be seen in FIG. 1 , the oil 20 flows from the region of the cover 11 in the direction of the space 14 and is injected into it. As a result, the portion 21 of the contact element 3 is surrounded by the oil 20. The portion 22 of the contact element 3 consists of a graphite-copper mixture. In this case, the litz wire 8 is connected to the portion 22 of the contact element 3, the guide unit 6 and / or the cover 11 and connects these elements in an electrically conductive manner.

[0054] The part of the duct 19 formed in the guide unit 6 is also formed and / or limited by the contact element 3. In particular, the duct 19 is formed by a longitudinal recess 23 in a guide wall 24 of the guide unit 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 the area between the outer wall 26 and the longitudinal recess 23 forms a cross section 27 of the duct 19 through which the oil 20 flows.

[0055] When the oil 20 flows into the space 14, the oil 20 reaches the sliding contact surface 4 and / or the shaft contact surface 5. This "oiling" of the contact element 3 and the shaft 2 achieves optimal cooling of this area. The heated oil then flows from the space 14 into the channel (not shown) of the machine 100. Therefore, the heat energy of the contact element 3 is effectively dissipated.

[0056] Figure 4 A discharge device 30 is shown, with Figures 1 to 3 Unlike the discharge device in FIG. 3 , a pipe 31 is formed in the device. The discharge device 30 is symmetrical.

[0057] Figure 5 A discharge device 32 is shown, with Figures 1 to 3 Unlike the discharge device in FIG. 1 , the contact element 33 of the device is arranged asymmetrically with respect to the longitudinal axis 34 of the guide unit 35. Therefore, the contact element 33 can be designed to have a particularly large cross section.

[0058] Figure 6 A discharge device 36 is shown, with Figures 1 to 3 Unlike the discharge device in , a duct 37 with a kidney-shaped cross section 38 is formed in the device, adapted to the outer edge 39 of the guide device 40. Therefore, the cross section 38 can be particularly large.

[0059] exist Figure 7 In the illustration of the discharge device 41 in FIG. 1 , a plurality of pipelines 37 are formed so that a particularly large amount of oil can be conveyed through the pipelines 37 .

[0060] Figure 8 The discharge device 42 in FIG. 4 has two semicircular ducts 43 which face toward a substantially flat outer wall 44 of a contact element 45 .

[0061] Fig. 9 A discharge device 46 is shown in which two ducts 47 are arranged transversely to an outer wall 48 of a contact element 49 .

[0062] Fig.10 A discharge device 50 is shown, whose contact element 51 has a polygonal cross section 52. At each edge 53 of the contact element 51, a duct 54 is formed in a guide unit 55 of the discharge device 50.

[0063] Fig.11 A discharge device 56 is shown, having a contact element 57 forming a duct 58 .

[0064] exist Fig.12 In the discharge device 59 shown in FIG. 1 , a plurality of channels 58 are formed in a contact element 60. The contact element 60 is symmetrical.

[0065] and Fig.12 The discharge equipment is different. Fig.13 The guide unit 62 in the discharge device 61 also forms a part of the duct 63. The discharge device 61 is symmetrical.

[0066] Fig.14 A discharge device 64 is shown, wherein Fig.11 Unlike the discharge device of FIG. 6A , a separate conduit 66 and / or a portion thereof is formed in the guide unit 65 .

Claims

1. A discharge device (1, 30, 32, 36, 41, 42, 46, 50, 56, 59, 61, 64) for discharging electric current from a rotor portion of a machine (100) having a shaft (2), the discharge device comprising a displaceable contact element (3, 33, 45, 49, 51, 57, 60) at least partially received in a guide unit (6, 35, 40, 55, 62) and for forming an electrically conductive sliding contact between a sliding contact surface (4) of the contact element for forming a sliding contact and a shaft contact surface (5) of the shaft, the contact element being connected in an electrically conductive manner to the guide unit and / or a retaining element of the machine, and the contact element being preloaded toward the shaft contact surface by a spring element (9), characterized in that The contact element is at least partially wetted with an oily fluid (20), in particular at least in the region of a sliding contact surface of the contact element, and at least one duct (19, 31, 37, 43, 47, 54, 58, 63) for the oily fluid is provided in at least part of the guide unit and / or at least part of the contact element, the duct being formed by the guide unit and the contact element.

2. The discharge device according to claim 1, characterized in that The duct (19, 31, 37, 43, 47, 54, 58, 63) extends at least along the contact element (3, 33, 45, 49, 51, 57, 60).

3. The discharge device according to claim 1 or 2, characterized in that: The duct (19, 31, 37, 43, 47, 54, 58, 63) is formed by a longitudinal recess (23) in a guide wall (24) of a guide unit (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).

4. The 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 against the guide wall (24) of the guide unit (6, 35, 40, 55, 62).

5. The discharge device according to claim 3 or 4, characterized in that: At least part of the longitudinal recess (23) has a semicircular cross section (27, 28, 52), preferably in the manner of a groove (25).

6. Discharge device according to any one of the preceding claims, characterized in that A conduit (19, 31, 37, 43, 47, 54, 58, 63) for an oily fluid (20) opens into a space (14) between the shaft (2) and the guide unit (6, 35, 40, 55, 62).

7. Discharge device according to any one of the preceding claims, characterized in that A channel is formed in the guide unit (6, 35, 40, 55, 62), through which the volume flow of the oily fluid (20) through the pipeline (19, 31, 37, 43, 47, 54, 58, 63) can be restricted.

8. Discharge device according to any one of the preceding claims, characterized in that The guide unit (6, 35, 40, 55, 62) is connected to a stator part of the machine (100) in an electrically conductive manner.

9. Discharge device according to any one of the preceding claims, characterized in that The contact element (3, 33, 45, 49, 51, 57, 60) is connected in an electrically conductive manner to a guide unit (6, 35, 40, 55, 62) or a holding element of a machine (100) via a preferably low-impedance stranded wire (8), one end of which is preferably pressed or punched into the contact element and the other end of which is preferably welded or soldered or crimped to the guide unit.

10. Discharge device according to any one of the preceding claims, characterized in that The contact element (3, 33, 45, 49, 51, 57, 60) is essentially made of a carbon-metal mixture, in particular a mixture of graphite and metal, the total volume fraction of the metal preferably being at least 30% by volume, preferably silver metal being used at least in the front region (16, 21) of the contact region with the sliding contact surface (4), and preferably copper metal being used in the rear region (22) of the contact element, the contact element preferably being free of copper in the region of the sliding contact surface.

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

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

13. A machine (100), in particular an electrically driven engine or a transmission, having a rotor part with a shaft (2) and a discharge device (1, 30, 32, 36, 41, 42, 46, 50, 56, 59, 61, 64) according to any of the preceding claims, 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) being in contact with the shaft via a sliding contact surface (4) of the contact element, thereby forming a sliding contact.

14. The machine according to claim 13, characterized in that Oily fluid, in particular engine oil or transmission oil (20), is provided at least in a space (14) between the shaft (2) and the guide unit (6, 35, 40, 55, 62), the space (14) being bridged by a contact element (3, 33, 45, 49, 51, 57, 60).

15. A machine according to claim 13 or 14, characterised in that At least in the region where the shaft (2) contacts the contact element (3, 33, 45, 49, 51, 57, 60), the shaft (2) is substantially copper-free.

16. A machine according to any one of claims 13 to 15, characterised in that The contact element (3, 33, 45, 49, 51, 57, 60) contacts the front surface (10) of the shaft (2), the contact element preferably being arranged substantially coaxially with the shaft.

17. A machine according to any one of claims 13 to 15, characterised in that The contact element contacts the sleeve surface of the shaft.

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