Steering device for steering electric current, and machine comprising steering device of this type

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 (5), having a displaceable contact element which is at least partially accommodated in a guide unit (2) and for forming an electrically conductive sliding contact between a sliding contact surface (4) of the contact element provided for forming a sliding contact and a shaft contact surface (6) of the shaft, the contact element (3) is connected in an electrically conductive manner to the guide unit and / or a holding element of the machine and is preloaded by means of a spring element (7) towards 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 means of a lubricating and cooling fluid, the guide unit (2) comprising a guide (8, 8 ', 8' ', 8' ') and a holding part (9), the guide (8, 8', 8 '', 8 '') being in contact with the contact element (3). 8 '' ') for receiving the contact element (3) and a holder (9) for receiving the guide, the holder and the guide forming a conduit (15) for a lubricating and cooling fluid.

Description

[0001] The invention relates to a discharge device for discharging a current having the features of the preamble of claim 1 .

[0002] Such discharge devices are known from the prior art in various embodiments. In particular, it is known to discharge low-frequency currents using carbon brushes, which are arranged in an axial or radial distribution around the shaft and are connected to the stator via connecting wires. Due to their low electrical resistance, the carbon brushes accommodated in a holding unit and / or a brush holder allow direct discharge of the current and thus avoid undesired current conduction via the bearing points of the shaft and / or transmission connections (such as gears or the like), which could lead to surface damage to the bearing body or bearing rings due to spot welding.

[0003] The term "shaft" is used herein as a synonym for the term "rotor part" or "shaft". The term "shaft" therefore refers to all rotating machine parts, whose current can be discharged to the stationary stator part and / or machine parts of the machine.

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

[0005] Generally speaking, discharge measures are also required for electric machines, such as in motor vehicles. Continuously fluctuating AC voltages and / or currents and high-frequency current pulses can occur in the motor drive shaft or in the connected transmission shaft and / or other functional components and can also damage the bearing points of the rotor shaft or the transmission shaft, so that discharge devices are often required here.

[0006] One problem with the described discharge devices and machines having such discharge devices is the high heat development caused by electrical and mechanical losses, which leads to a high thermal load on the discharge device and the machine (e.g. motor, transmission). In order to partially solve this problem, 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 mentioned machines increases dramatically.

[0007] In order to minimize the above-mentioned disadvantages, WO2022 / 135715A1 proposes wetting the contact element with a lubricating and cooling fluid in the area of ​​the sliding contact surface of the contact element. In this way, the high-frequency voltage (so-called parasitic AC voltage) formed by the capacitive coupling of the power electronics (pulse width modulation) used by the electric drive is discharged, and at the same time, with the help of the lubricating and cooling fluid, the heat generated in the process is suppressed or released. No special cooling equipment, such as a ventilation system, is required to reduce the thermal load. As a result, the design of machines, such as motors, can be simpler and therefore cheaper, and the cooling of the motor is more effective than previously known systems. For example, friction losses caused by radial shaft seals, as well as others, are also eliminated. In addition, as mentioned above, the overall machine size can be smaller (the moment of inertia of the rotating part is reduced).

[0008] This known discharge device has an axial fluid guide in the form of an axial channel which opens into the space between the shaft and the guide unit.

[0009] A disadvantage of such discharge devices with axial fluid flow is that, for a given volume flow, the output depends on the cross-sectional area and the flow velocity of the fluid. At very large volume flows, the cross-sectional area may be too small and / or the flow velocity too high. As a result, there is a disadvantage that generally not enough fluid reaches the area between the shaft and the guide unit for cooling. Furthermore, the known guide units are somewhat complex and cost-intensive to manufacture.

[0010] It is therefore an object of the present invention to overcome the disadvantages of the prior art.

[0011] According to the invention, this object is achieved by the above-mentioned discharge device, which is characterized in that the guide unit comprises a guide part for accommodating the contact element and a holding part for accommodating the guide part, the holding part and the guide part forming a duct for a lubricating and cooling fluid.

[0012] Using 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 due to the power electronics used (pulse width modulation) and at the same time suppress and / or discharge the generated heat with the help of lubricating and cooling fluids. In particular, the invention does not require special cooling equipment, such as ventilation equipment, which allows the heat load to be reduced. As a result, the design of machines such as electric motors can be simpler and therefore cheaper, and the cooling of the electric motors can also be more effective than in currently known systems. For example, friction losses caused by radial shaft seals, among others, are also eliminated. In addition, as mentioned above, the overall machine size can be smaller (the moment of inertia of the rotating parts is reduced).

[0013] Typically, the lubricating and cooling fluid is an oily fluid, in particular an engine and / or transmission oil, which is normally present in any way in an engine or a transmission provided with the discharge device according to the invention.

[0014] The fact that the guide unit comprises a guide part for accommodating the contact element and a holding part for accommodating the guide part, and the holding part and the guide part form a duct for the lubricating and cooling fluid, makes it possible to create fluid ducts of various shapes and sizes in a simple manner. For example, by integrating a guide part with an outer circumference deviating from the cylindrical shape into a holding part with a cylindrical recess, a fluid duct can be produced extremely simply. This inevitably leads to a cavity, the shape and size of which can be determined by correspondingly adjusting the outer circumference of the guide part.

[0015] Typically, the fluid conduit extends at least along the guide portion, preferably along the entire length of the guide portion. This achieves excellent cooling of the rotor in a particularly advantageous manner. In this embodiment, the lubricating and cooling fluid can flow over the entire length of the guide portion into the space between the shaft and the contact element.

[0016] Advantageously, the duct for the lubricating and cooling fluid is formed by a longitudinal groove in the outer wall of the guide part and / or in the inner wall of the retaining part in contact with the outer wall of the guide part. Such a longitudinal groove makes it extremely easy to manufacture the fluid duct.

[0017] In a particularly preferred embodiment of the discharge device according to the invention, the inner wall of the holding part is cylindrical, and the outer wall of the guide part has a shape deviating from the cylindrical shape, preferably has a cross section deviating from the circular shape, and at least one, preferably three or four grooves extend in the longitudinal direction of the guide part and have in particular a semicircular cross section provided in the outer circumference of the guide part. This embodiment is particularly easy to manufacture and is characterized by a simple flexibility in creating fluid conduits of different shapes and sizes. In this way, fluid conduits can be manufactured by means of which large amounts of oil can be conveyed to the location where cooling is required.

[0018] In a further embodiment of the discharge device according to the invention, the outer wall of the guide part has a substantially circular cross section and is preferably cylindrical, and the inner wall of the retaining part has a shape deviating from a cylindrical shape, preferably a cross section deviating from a circular shape. Thus, the described embodiment features substantially cubic or triangular prism guide parts, whose sides are curved inwards, i.e. concave. These guide parts can be manufactured particularly advantageously by extrusion or continuous casting and form an optimal fluid conduit with the retaining part.

[0019] In a further embodiment of the discharge device according to the invention, the outer wall of the guide portion has a substantially circular cross section and is preferably cylindrical, and the inner wall of the retaining portion has a shape deviating from a cylindrical shape, preferably a cross section deviating from a circular shape. This embodiment can also be used to create fluid conduits of different shapes and sizes in a simple manner.

[0020] Advantageously, the guide is an extruded profile, preferably an aluminum extruded profile or a continuous casting profile. Such a guide is particularly easy to manufacture and has low cost.

[0021] At least one channel-shaped fluid conduit is provided in the guide part, which channel preferably opens in the front face of the guide part, which front face defines the space between the shaft and the discharge device. By this embodiment, even more lubricating and cooling fluid can be directed to the location to be cooled. For example, such a fluid conduit can be a conduit extending parallel to the longitudinal axis of the discharge device, such as a fluid guide channel.

[0022] Advantageously, the guide is substantially completely contained in the retaining portion. This makes it possible to create a conduit channel for a lubricating and cooling fluid extending along the entire length of the guide. This fluid can then flow into the space between the shaft and the discharge device.

[0023] 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, this stator part of the machine can be used as a holding device for the discharge device. When the current is discharged, it is discharged from the relevant shaft to the contact element and the guide unit of the discharge device. Then, in said embodiment, the discharged current flows into said stator part of the machine.

[0024] Advantageously, the contact element is connected to the guide unit in an electrically conductive manner by means of a preferably low-impedance stranded conductor which is preferably pressed or stamped into the contact element at one end and preferably welded or soldered or crimped to the guide unit at the other end. The guide unit is preferably at least partially made of a low-impedance material, in particular plastic or metal, preferably aluminum, an aluminum alloy, copper and / or brass.

[0025] 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, silver is preferably the metal provided at least in the region of the sliding contact surface of the contact element, copper is preferably the metal provided in the rear region of the contact element, the contact element preferably being free of copper in the region of the sliding contact surface. The metal portion in the contact element is preferably at least 30% by volume. Therefore, in the region of the sliding contact surface, the contact element is preferably free of copper, since such metal can lead to catalytic changes in the lubricating and cooling fluid, together with the passage of electric current, thereby causing negative changes in the physical properties of this 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.

[0026] 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 using the above-mentioned embodiments with low-impedance materials and contact elements made of metal-carbon mixtures, the resistance of the entire device can be kept low. 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 low. In order to ensure this continuous lubrication, a high specific contact pressure of the contact element on the shaft is advantageous. This value should be at least 10N / cm 2 On the other hand, no electrochemical reactions should occur in the contact element in the region of the sliding contact surface together with the lubricating and cooling fluid. This is ensured in particular by the silver-graphite material in the region of the contact element which is subject to wear over the entire service life.

[0027] Advantageously, the contact element has a recess, in particular a bore or a slot, in the region of the sliding contact surface. This prevents the contact 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.

[0028] The contact element is usually a pin-shaped or 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.

[0029] Advantageously, the spring element can be a helical spring, one end of which is preferably close to the front side of the contact element opposite to the sliding contact surface. Using this type of helical compression spring, it is easy to press the contact element onto the shaft at any time using a specific desired contact pressure.

[0030] The invention also relates to a machine, in particular an electric drive motor 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 bringing the shaft into contact with its sliding contact surface to form a sliding contact. The machine according to the invention achieves the advantages described previously, with a small installation size and a simple design which significantly reduces the thermal load.

[0031] In the machine according to the invention, the discharge device can be completely installed in a lubricating and cooling fluid, in particular in a motor or transmission oil. Preferably, the lubricating and cooling fluid is provided at least in the space between the shaft and the guide unit bridged by the contact element. In this embodiment, the area where the greatest heat is generated, i.e. the area between the shaft and the contact element, is cooled by the lubricating and cooling fluid.

[0032] Advantageously, the contact element is always loaded by the spring element 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.

[0033] As mentioned above, the shaft is preferably substantially free of copper at least in the region in contact with the contact element.

[0034] In a preferred embodiment of the machine according to the invention, the contact element is in contact with the front face of the shaft, the contact element being preferably arranged substantially coaxially with the shaft. This type of shaft grounding is preferred in order to avoid 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 speed is minimized and the actual travel distance during the service life of the contact element is 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 is kept low, and therefore the force loss of the spring element over the total wear length of the contact element is also minimal. This makes it possible to use the low-cost helical compression springs mentioned above. 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 lower than required at high peripheral speeds. Another advantage of the front contact of the shaft close to the rotating shaft is that the friction torque is minimal due to the small radial distance from the rotation point. Even in the case of large friction forces, the friction torque, which is the product of the friction force and the travel radius, is still small. Therefore, the friction power is kept low together with the angular velocity (equivalent to the rotation speed) and the system losses are kept small.

[0035] In a further embodiment of the machine according to the invention, the contact element is in contact with the jacket surface of the surface. In this embodiment, the cross section of the contact element is preferably geometrically inclined towards the preferred direction of rotation of the shaft to be contacted, so as to achieve suppression of electrical contact losses due to float between the shaft and the contact element.

[0036] Typically, the discharge device is located in a part of the machine where the main operating temperature is above 50°C.

[0037] Further features of the invention are shown in the following description of the drawings together with the drawings and the dependent claims. The individual features can be realized both individually and in combination with one another.

[0038] In the attached picture:

[0039] Figure 1 : A perspective view of a discharge device having a guide portion and a retaining portion according to the present invention is shown.

[0040] Figure 2-Figure 5 : shows a guide portion according to a further embodiment of the discharge device of the present invention.

[0041] Figure 6 : Shows Figure 1 A perspective view of a guide portion of a discharge device.

[0042] Figure 7 : Shows Figure 1 Front view of the discharge device.

[0043] Figure 8 : It shows that the Figure 1 A longitudinal section of a machine of a discharge device is shown.

[0044] In the following, identical or functionally identical elements are identified with the same reference numerals.

[0045] Figure 1 , 7 and 8 show a discharge device 1 according to the present invention, Figure 8 The discharge device 1 is integrated in a machine 100 according to the invention. The discharge device 1 is used to discharge current from a rotor part of the machine 100 having a shaft 5. The discharge device 1 comprises a pin-shaped displaceable brush 3 accommodated in a guide unit 2 for forming an electrically conductive sliding contact between a sliding contact surface 4 of the brush 3 provided for forming a sliding contact and a shaft contact surface 6 of the shaft. The shaft 5 is as shown in FIG. Figure 8 The brush 3 is preloaded towards the shaft contact surface 6 by means of a helical compression spring 7. This can also be done in Figure 8 In the region of the sliding contact surface 4 , the brushes 3 are wetted by the lubricating and cooling fluid.

[0046] The guide unit 2 includes a guide portion 8 for accommodating the brush 3 and a holding portion 9 for accommodating the guide portion 8. In the example shown, the inner wall 10 of the holding portion 9 is cylindrical. On the other hand, the outer wall 11 of the guide portion 8 has a shape different from the cylindrical shape. For example, the guide portion 8 is designed as a triangular prism, and the cross section of the guide portion 8 is basically triangular and has a flat angle 12, and the sides of the triangle are bent inward, that is, concave. Since the side surface 13 of the guide portion 8 is also concave, the guide portion 8 has three semicircular grooves 14 extending in the longitudinal direction of the guide portion 8. These grooves 14 extend along the entire length of the guide portion 8.

[0047] from Figure 1 , 7 8, it can be clearly seen that the guide 8 is accommodated in the holder 9, and its flat corners 12 contact the inner wall 10 of the holder 9. In this case, the grooves 14 in the outer circumference of the guide 8 together with the inner wall 10 of the holder 9 form a total of three fluid ducts 15. These fluid ducts 15 serve as flow channels for lubricating and cooling fluids, which flow from the back side 16 of the discharge device 1 in the direction of the sliding contact surface 4 of the brush 3.

[0048] A continuous receiving channel 17 for the brush 3 is also provided in the guide 8. Both the brush 3 and the receiving channel 17 have a substantially square cross section with rounded corners.

[0049] like Figure 8 As shown, on the side of the guide unit 2 facing the shaft 5, the brush 3 protrudes slightly from the guide 8 and contacts the shaft 5 at its end face 18. In this case, the brush 3 is arranged substantially centrally to the end face 18 of the shaft and is therefore coaxial to the shaft 5.

[0050] At the other end of the guide 8, there is a cover 19 to which a chain 20 is attached. A spring 7, which preloads the brush 3 toward the shaft 5, is arranged between the cover 19 and the brush 3. The chain 20 is made of a low-impedance material and is pressed into the brush 3 at one end and connected to the cover 19 at its other end.

[0051] The brushes are made of a graphite-metal mixture.

[0052] Figure 2 , 3 5 and 6 show other possible shapes of the guide. Figure 2 The guide 8' is shown, which has a semicircular cross section, wherein the flat surface 22 adjoins the curved jacket surface 21. Figure 1 In the holding part 9 with a cylindrical inner wall 10, the inner wall 10 of the holding part 9 together with the plane 22 of the guide part 2' forms a fluid conduit. Figure 2The lines shown in 2 are intended to illustrate further longitudinal grooves which can be produced in the curved surface 21 and which, together with the inner wall 10 of the holder 9 , can form further fluid ducts.

[0053] Figure 3 A further embodiment of a guide 8" with a circular cross section is shown. The guide 8" is particularly suitable for holding parts with an inner wall cross section which deviates from a circular shape. For example, the guide 8" would thus form four fluid ducts in a holding part with a cubic body and inner walls with a square cross section.

[0054] Figure 5 A further embodiment of the guide portion 8"' is shown. The guide portion 8"' can be Figure 1 The guide portion 8'' has a square cross section and flat angles 12, the sides of the square being concave. The guide portion 8'' therefore has a substantially cubic shape, the sides 13 of the cube being concave. If the guide portion 8'' is integrated in the holder 9, the concave sides 13 therefore form a total of four fluid ducts together with the cylindrical inner circumference 10 of the holder 9.

[0055] Figure 4 The guide portion is shown, which is similar in shape to Figure 1 The guide portion 8 corresponds to Figure 1 The guide part 8 of FIG. 8 differs only in that it has three continuous fluid ducts 23, which are circular in cross section. These fluid ducts extend along the entire length of the guide part 8 and are used to deliver more lubricating and cooling fluid to the space between the shaft 5 and the guide part 8. Figure 5 The guide part 8"' in the embodiment also has this type of conduit. Figure 3 The guide part 8″′ in the embodiment also has two such ducts 23 ′, each of which has a longitudinal, curved cross section. Each of the ducts 23 , 23 ′ opens in the front face 24 of the corresponding guide part.

[0056] The guides 8, 8', 8" and 8'" shown are all extruded aluminum sections.

Claims

1. A discharge device (1) for discharging an electric current from a rotor part of a machine (100) having a shaft (5), the discharge device (1) comprising a displaceable contact element at least partially accommodated in a guide unit (2) and for establishing an electrically conductive sliding contact between a sliding contact surface (4) of the contact element provided for forming a sliding contact and a shaft contact surface (6) 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 towards the shaft contact surface by a spring element (7), The contact element (3) is at least partially wetted by a lubricating and cooling fluid, in particular at least in the region of its sliding contact surface (4), Features The guide unit (2) comprises a guide portion (8, 8', 8", 8'") and a retaining portion (9), wherein the guide portion (8, 8', 8", 8'") is used to accommodate the contact element (3), and the retaining portion (9) is used to accommodate the guide portion, and the retaining portion and the guide portion form a conduit (15) for lubricating and cooling fluid.

2. The discharge device according to claim 1, Features The fluid conduit (15) extends at least along the guide portion (8, 8', 8", 8'"), and the fluid conduit (15) preferably extends along the entire length of the guide portion (8, 8', 8", 8'").

3. The discharge device according to claim 1 or 2, Features The fluid conduit (15) is formed by a longitudinal groove (14) in the outer wall (11) of the guide part (8, 8', 8", 8'") and / or a longitudinal groove (14) in the inner wall of the retaining part in contact with the outer wall of the guide part (8, 8', 8", 8'").

4. A discharge device according to any one of the preceding claims, Features The inner wall (10) of the retaining portion (9) is cylindrical, and the outer wall (11) of the guide portion (8, 8', 8", 8'") has a shape deviating from the cylindrical shape, preferably has a cross section deviating from the circular shape, at least one, preferably three or more grooves (14) extend in the longitudinal direction of the guide portion and in particular have a semicircular cross section provided in the outer circumference of the guide portion (8, 8', 8", 8'").

5. A discharge device according to any one of the preceding claims, Features The cross section of the guide portion (8, 8', 8", 8'") is substantially triangular or square and has straight or rounded corners (12), and the side faces (13) of the triangle or square are preferably substantially concave.

6. A discharge device according to any one of claims 1 to 3, Features The outer wall of the guide part (8, 8', 8", 8'") has a substantially circular cross section, and is preferably cylindrical, and the inner wall (10) of the retaining part (9) has a shape deviating from the cylindrical shape, and preferably has a cross section deviating from the circular shape.

7. A discharge device according to any one of the preceding claims, Features The guide part (8, 8', 8", 8'") is an extruded profile, preferably an aluminum extruded profile or a continuous casting profile.

8. A discharge device according to any one of the preceding claims, Features At least one channel-shaped fluid conduit (23, 23') is provided in the guide (8, 8", 8'"), the channel preferably opening in the front side (24) of the guide.

9. A discharge device according to any one of the preceding claims, Features The guide portion (8, 8', 8", 8'") is substantially completely accommodated in the retaining portion (9).

10. A discharge device according to any one of the preceding claims, Features The guide part (8, 8', 8", 8'") is connectable to the stator part of the machine (100) in an electrically conductive manner.

11. A discharge device according to any one of the preceding claims, Features The contact element is a pin-shaped or bolt-shaped brush (3), and the sliding contact surface (4) is preferably rectangular, polygonal or circular.

12. A discharge device according to any one of the preceding claims, Features The spring element is a helical spring (7), one end of which is preferably in close contact with the front side of the contact element (3) opposite to the sliding contact surface (4).

13. A machine (100), in particular an electric drive motor or a transmission having a rotor part with a shaft (5) and a discharge device (1) according to any one of the preceding claims, the contact element (3) of the discharge device (1) being in contact with the shaft (5) with its sliding contact surface (4) to form a sliding contact.

14. The machine according to claim 13, Features A lubricating and cooling fluid, in particular motor or transmission oil, or a water-based cooling medium is provided at least in the space between the shaft (5) and the guide unit (2) bridged by the contact element (3).

15. A machine according to claim 13 or 14, Features The contact element (3) is in contact with the front face of the shaft (5), the contact element being preferably arranged substantially coaxially with the shaft.

16. A machine according to any one of claims 13 to 14, Features The contact element contacts the jacket surface of the shaft.

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