Collecting device for collecting electric current and an apparatus equipped with such a collecting device

Abstract

The invention relates to a discharge device (1,1',1'') for discharging electric current from a rotor part having a shaft (2) of an equipment, the discharge device (1,1',1'') comprising an axially movable contact element (3) at least partially accommodated in a guide device (6), the contact element (3) forming an electrically conductive sliding contact between a 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) being electrically conductively connected to the guide device (6) and / or the holding element (7) of the equipment (100), the contact element (3) being biased towards the shaft contact surface (5) by a spring element (9), the contact element (3) being at least partially, in particular at least in the region of the sliding contact surface (4) by an oil-based fluid (20).

Description

[Technical field]

[0001] A discharge device according to the invention for discharging current from a rotor part having a shaft of an equipment, the discharge device comprising a contact element at least partially accommodated in a guide device and movable in particular in the axial direction, the movable contact element 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, the contact element being electrically conductively connected to the guide device and / or to a holding element of the equipment, the contact element being biased towards the shaft contact surface by a spring element. [Background technology]

[0002] Such discharge devices are known as different embodiments from the prior art. In particular, it is known to use carbon brushes for the discharge of low-frequency currents, which are distributed in the axial or radial direction of the shaft and connected to the stator via a twisted wire connection. Due to their low electrical resistance, the carbon brushes housed in a holding device or brush holder allow a direct discharge of the current, thus avoiding an undesirable current conduction through the bearing points of the shaft, which can lead to damage of the bearing body or the surface of the bearing rings due to spot welding.

[0003] The term "shaft" is used herein as a synonym for the terms "rotor part" or "axis." Thus, the term "shaft" refers to any rotating machine part through which current can be discharged to a fixed stator or machine part of the machine.

[0004] Discharge devices are also commonly used in railway technology, where alternating currents or operating currents can flow through the axles. A discharge device of this kind is described, for example, in DE 10 2010 039 847 A1.

[0005] Methods for discharging electric currents are also required in electrical equipment in general, for example in motor vehicles, where discharge devices are usually required, since constantly fluctuating AC voltages or currents and high-frequency current pulses can occur in drive shafts or gear shafts and other functional elements connected to said drive shafts, which can also damage the bearing points of the rotor shaft or gear shaft. Summary of the Invention [Problem to be solved by the invention]

[0006] One problem with the described discharge device and with the equipment comprising such a discharge device is the high heat generated by electrical and mechanical losses, which leads to a high thermal load on both the discharge device and the equipment (e.g. motor, gearbox). To control this problem to some extent, the generated heat has been removed up to now, in particular through ventilation devices. However, such ventilation devices can only partially minimize the thermal load of the elements. Another disadvantage of such ventilation devices is the considerable increase in the installation space required to incorporate such a ventilation device in the machine considered.

[0007] The object of the present invention is therefore to overcome the drawbacks known from the prior art mentioned above, in particular to minimize the required installation space while minimizing the thermal load of the elements when discharging parasitic currents. [Means for solving the problem]

[0008] According to the invention, this problem is solved by the above-mentioned discharge device, which is characterized in that the contact elements are at least partially wetted by an oily fluid, in particular at least in the region of the sliding contact surfaces.

[0009] The discharge device according to the invention allows an ideal discharge of the capacitively coupled high frequency voltage (so-called parasitic AC voltage), which is generated by the electric drive for the power electronics used (pulse width modulation), while containing or dissipating the heat generated in the process by using an oil-based fluid. In particular, the invention does not require special cooling devices, such as ventilation devices, to minimize the thermal load. Thus, the construction of the equipment, such as an electric motor, can be simpler and thus more cost-effective, and the cooling of the electric motor can be more effective compared to known systems. For example, friction losses due to radial shaft seals are also avoided. In addition, as already mentioned above, the overall dimensions of the machine can be reduced (lower moment of inertia of the rotating parts).

[0010] Typically the oil-based fluid is motor oil and / or gear oil, which is usually already present in the motor or gear in which the discharge device according to the invention is provided.

[0011] In particular, in a preferred embodiment of the discharge device according to the invention, the guide device can be electrically connected to a stator part of the machine, which can be used, for example, as a holding element of the discharge device. When the current is discharged, it is discharged from the corresponding shaft to the contact element of the discharge device and to the guide device. Then, in the described embodiment, the discharge current flows to the aforementioned stator of the machine.

[0012] Advantageously, the contact element is conductively connected to the guide device by means of a stranded wire, preferably of low resistance, which is preferably pressed or pressed onto the contact element at one end and is preferably welded, soldered or crimped onto the guide device at the other end. The guide device is preferably made at least partially using a low resistance material, in particular a metal, preferably aluminium, an aluminium alloy, copper and / or brass.

[0013] In a particularly preferred embodiment of the discharge device according to the invention, the contact element is substantially formed using a carbon-metal mixture, in particular a mixture of graphite and a metal with high electrical conductivity, at least in the region of the sliding contact surface of the contact element, preferably silver is provided as the metal, and in the rear region of the contact element, preferably copper is provided as the metal, the contact element being preferably copper-free in the region of the sliding contact surface. The proportion of metal contained in the contact element is preferably at least 30% by volume. The contact element is preferably copper-free in the region of its surface, since this metal can cause catalytic changes in the oil-based fluid when an electric current flows through it, with the result that the physical properties of this fluid can be adversely affected. For this reason, the shaft of the device according to the invention, which will be described in detail below, is also copper-free, at least in the region where the shaft contacts the contact element.

[0014] In order to keep the system resistance as low as possible under all operating conditions, it is desirable to select the resistance of the discharge device according to the invention to be low as well. The above-described embodiment using a low-resistance material and contact elements made of a metal-carbon mixture allows the resistance of the entire device to be kept low. On the other hand, the resistance of the system is mainly influenced by the voltage drop between the shaft surface and the sliding contact surface of the contact element. This accounts for the largest proportion of the total system. It is therefore desirable to keep this low as well. To ensure that continuous lubrication is performed, it is advantageous for the specific contact pressure of the contact element on the shaft to be high. This value should be at least 10 N / cm 2 On the other hand, it is desirable that no electrochemical reactions occur in the area of ​​the sliding contact surface due to contact with the oily fluid on the contact elements, which is ensured by the use of silver-graphite materials in the areas of the contact elements that are subject to wear over their entire service life.

[0015] Advantageously, the contact element has recesses, in particular openings or slits, in the region of the sliding contact surface, so that the contact can be prevented from floating above the oil film. Advantageously, the contact element is perforated in the region of the sliding contact surface, which contributes to the prevention of poor electrical contact between the shaft and the contact element and to the minimization of the floating of the contact element on the oil film.

[0016] Typically the contact elements are pin- or bolt-shaped brushes, which are usually formed by compression molding followed by heat treatment.

[0017] Advantageously, the spring element is a compression coil spring, one end of which rests against an end face of the contact element, preferably located opposite the sliding contact face, such that a compression coil spring makes it easy to always press the contact element against the shaft with a specific desired contact pressure.

[0018] The invention also relates to an appliance, in particular an electric drive motor or transmission, having a rotor part with a shaft and a discharge device according to any one of claims 1 to 9, wherein a contact element of the discharge device contacts the shaft with a sliding contact surface to form a sliding contact. This appliance according to the invention has the above-mentioned advantages of significantly reducing thermal stresses while keeping the installation space small and being of simple design.

[0019] In the device according to the invention, the discharge device can be completely placed in an oily fluid, in particular in motor oil or gear oil. Preferably, this oily fluid is provided in the space bridged by the contact elements, in particular between the shaft and the guide device. In this embodiment, in particular the place where the highest heat is generated, i.e. the area between the shaft and the contact elements, is cooled by the oily fluid.

[0020] This discharge device can be arranged at least partially in a fluid guide, in particular an oil guide, so that the oily fluid preferably first flows into the space between the shaft and the guide device and is then discharged through the shaft. In this embodiment, heat generated in the contact area between the shaft and the contact element can be instantly removed by the flow of the oily fluid in the fluid guide.

[0021] It is further conceivable that the oil-based fluid is sprayed, dripped or applied in a mist onto the discharge device, in particular onto the contact elements of the discharge device.

[0022] In another embodiment of the device according to the invention or the discharge device according to the invention, a conduit for the oily fluid is provided in the guide device of the discharge device, the conduit preferably opening into the space between the shaft and the guide device.

[0023] Advantageously, the contact element is provided with a spring element having a force of at least 10 N / cm 2 This ensures that the voltage drop between the shaft surface and the sliding contact surface of the contact element is minimized.

[0024] As mentioned above, the shaft is preferably substantially free of copper, at least in the areas where the contact elements contact.

[0025] In a preferred embodiment of the device according to the invention, the contact element is in contact with the end face of the shaft, and the contact element is preferably arranged substantially coaxially with the shaft. Grounding of the shaft of this kind is preferred to avoid poor contact, since the axial runout of a rotating shaft is usually small. By arranging the contact element near the rotation point of the shaft, the circumferential speed is minimized, and thus the actual distance traveled over the service life of the contact element is also significantly reduced. This has a direct effect on the wear of the contact element, which is generally proportional to the distance traveled. By minimizing the distance traveled, the wear of the contact element is kept low, and as a result the loss of force of the spring element over the entire wear length of the contact element is also minimized. This allows, for example, the use of more cost-effective compression coil springs, as described above. In addition, due to the low circumferential speed near the axis of rotation of the shaft, the risk of continuously forming an insulating lubricant film is reduced, whereby the contact pressure can be kept lower than that required for high circumferential speeds. Another advantage of contact at the end face close to the axis of rotation of the shaft is that the friction moment is minimized due to the small radial distance from the point of rotation. Even with very large friction forces, the friction moment, which is the product of friction force and running radius, is small. Therefore, even with respect to angular velocity (corresponding to speed), the friction force is small and the system has small losses.

[0026] In a further embodiment of the device according to the invention, the contact element contacts the circumferential surface of the shaft, in which embodiment the cross-sectional shape of the contact element is preferably geometrically tapered with respect to the preferred direction of rotation of the contacting shaft in order to achieve suppression of poor electrical contact caused by lift between the shaft and the contact element.

[0027] Typically, the discharge device is located in the compartment of the equipment primarily where the operating temperature is above 50°C.

[0028] Further features of the invention will become apparent from the following description of the drawings with reference to the drawings and the dependent claims. The individual features can be implemented alone or in combination with each other. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 shows a cross section in a plane containing the axis of rotation of a device according to the invention in the contact area between a longitudinal contact element and a shaft, the contact element being arranged coaxially with the shaft. [Diagram 2] FIG. 2 shows a cross section along the axis of rotation of another embodiment of a device according to the invention in the area of ​​contact between a contact element and a shaft, the contact element being arranged radially relative to the shaft. [Diagram 3] FIG. 3 shows an embodiment of a discharge device according to the present invention. [Figure 4] FIG. 4 shows a cross-sectional view of the discharge device of FIG. 3 taken along a plane including the rotation axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In the following, the same elements or elements having the same functions are given the same reference numbers.

[0031] FIG. 1 shows a cross-section through a plane including the axis of rotation of a device 100 according to the invention. In this case, the device 100 is an electric motor with a rotor part having a shaft 2. A discharge device 1 for discharging electric current is arranged on an end face 10 of the shaft 2. This discharge device 1 comprises a contact element in the form of a carbon brush 3 for forming an electrically conductive sliding contact between a sliding contact surface 4 of the carbon brush 3 provided for forming a sliding contact and a shaft contact surface 5 of the shaft 2. The carbon brush 3 is accommodated in a guide device 6 so as to be axially movable. The guide device 6 is a cylindrical housing and is arranged in a holding element 7 of the device 100 in a likewise cylindrical recess. The carbon brush 3 is electrically conductively connected to the holding element 7 by a wire strand 8.

[0032] The carbon brush 3 is biased towards the shaft contact surface 5 by a compression coil spring 9. The carbon brush 3 is thus subjected to a contact force by the spring 9 in order to form an electrical sliding contact between the sliding contact surface 4 of the carbon brush 3 provided for forming a 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 projects slightly from the guide device 6 and contacts the shaft 2 at an end surface 10. In this case, the carbon brush 3 is arranged so that it is substantially centrally located with respect to the end surface 10 of the shaft 2 and is thus arranged coaxially with the shaft. As already mentioned above, this arrangement is particularly advantageous since it allows the wear of the carbon brush 3 to be as small as possible.

[0033] At the other end of the guide device 6, the guide device 6 has a lid 11 having a central recess 12 through which the stranded wire 8 passes. A spring 9 is disposed between the lid 11 and the carbon brush 3 and biases the carbon brush 3 along the shaft 2.

[0034] The holding element 7 of the device 100 is provided with two oil channels 13. These oil channels 13 are arranged above and below the shaft 2 and initially run obliquely towards the shaft 2. The motor oil flows along the direction of the shaft 2, as indicated by the arrows in FIG. 1, and enters via the oil channels 13 into a space 14 between the shaft 2 and the guide device 6, which is bridged by the front end 16 of the carbon brush 3. The carbon brush 3 is thus wetted with oil in this area. In the process, oil also deposits on the sliding contact surface 4 and on the shaft contact surface 5. This "lubrication" of the carbon brush 3 and the shaft 2 allows an ideal cooling of this area. The heated oil flows further from the space 14 into two channels 15 arranged in the shaft 2, which are arranged parallel to the longitudinal axis of the shaft. This heat is thus substantially removed from the carbon brush 3 via the channels 15.

[0035] It is clear that wetting the carbon brushes 3 can also be achieved in different ways. For example, the carbon brushes, in particular the area in contact with the shaft, can be sprayed with oil or exposed to oil vapours. It is conceivable that the whole device, in particular the contact area between the shaft 2 and the carbon brushes 3, is completely immersed in oil.

[0036] The guide device 6 and the holding element 7 are made of an electrically conductive material such that there is an electrically conductive connection between the guide device 6 and the holding element 7. In this exemplary embodiment, the guide device 6 is made of aluminium.

[0037] The strands 8 are also made of a low resistance material. At one end the strands 8 are pressed into the carbon brush 3 and at the other end they are connected to the retaining element 7 by means of a crimping means.

[0038] The carbon brush 3 has a two-layer structure. In the region of the sliding contact surface 4, the carbon brush 3 is formed by a mixture of graphite and silver. This particularly affects the section 16 of the carbon brush 3 which bridges the space 14. The silver content in this part is about 3% by volume. The remaining part of the carbon brush 3 is formed by a mixture of graphite and copper. However, the section 16 of the carbon brush 3 and the shaft 2 are substantially free of copper in order to avoid undesirable reactions with the oil.

[0039] The carbon brush 3 is a cylindrical pin. In this exemplary embodiment, the carbon brush 3 has a torque of about 10 N / cm 2 is pressed against shaft 2 by a force of

[0040] FIG. 2 shows a cross-section along the direction of the rotation axis of another embodiment of the device 100' according to the invention. The main difference in this case with respect to the device 100 of FIG. 1 is that the discharge device 1' is arranged radially of the shaft 2, such that the carbon brushes 3 are in contact with the circumferential surface 17 of the shaft 2. In addition, the strands 8 are connected to the guide device 6, such that in this case the strands 8 act as an electric wire between the carbon brushes 3 and the guide device 6. In this embodiment, the discharge device 1' is also arranged in the holding element 7 of the device 100'. Here, the discharge device 1' is arranged in a partial space 18 of the oil guide. Thus, the discharge device 1' is always in contact with the oil. Thus, also in this embodiment, the thermal stresses on the individual elements, such as the shaft 2 and the carbon brushes 3, can be kept low. Here too, the resulting heat is transferred to the oil during the process of discharge.

[0041] FIG. 3 shows another embodiment of the discharge device 1″ according to the invention, and FIG. 4 shows said discharge device 1″ in another embodiment of the device 100″ according to the invention. The device 100″ and the discharge device 1″ differ from the embodiment shown in FIGS. 1 and 2 in particular in that the oil conduit 19 is arranged in the guide device 6, which runs axially from the lid 11 to the space 14 between the guide device 6 and the shaft 2 and is openly connected to said space 14. As shown in FIG. 4, the oil 20 flows from the area of ​​the lid 11 towards the space 14 and is poured out into the space 14. The bridge section 16 of the carbon brush 3 is thereby immersed in the oil. In FIG. 4, the two-layer structure of the carbon brush 3 can be clearly seen. In the front area 21, the carbon brush 3 is formed using a mixture of graphite and silver. In the rear area 22, the carbon brush 3 is formed using a mixture of graphite and copper. In this case, the strands 8 are connected to the rear area 22 of the carbon brush 3 and to the guide device 6, electrically connecting these elements.

Claims

1. An electric device (100, 100', 100'') having a rotor portion having a shaft (2) and a discharge device (1, 1', 1''), said discharge device (1, 1', 1'') comprising a movable contact element (3) at least partially housed in a guide device (6), the movable contact element (3) forms an electrically conductive sliding contact between a 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 electrically conductively connected to the guiding device (6) and / or the holding element (7) of the electrical device (100), The contact element (3) is biased towards the shaft contact surface (5) by a spring element (9), said contact element (3) being at least partially wetted by an oily fluid (20); the contact element (3) of the discharge device (1, 1', 1'') contacts the shaft (2) with the sliding contact surface (4) to form a sliding contact, The contact element (3) contacts an end face (10) of the shaft (2); The contact element (3) is arranged coaxially with the shaft (2), At least in the space (14) between the shaft (2) and the guide device (6), said space (14) being bridged by said contact element (3); An oil-based fluid is provided in the space (14), The discharge device (1) is at least partially disposed within a fluid guide (13, 15), The oily fluid (20) first flows into the space (14) between the shaft (2) and the guide device (6); The oily fluid (20) is then discharged through the shaft (2).

2. 2. Electrical equipment according to claim 1, characterized in that the oil-based fluid is motor oil (20) and / or gear oil.

3. An electric machine according to any one of claims 1-2, characterized in that the guide device (6) can be electrically conductively connected to a stator part of the electric machine.

4. the contact element (3) is conductively connected to the guiding device (6) or the holding element (7) of the electrical device (100) by a low resistance stranded wire (8); The electrical device according to any one of claims 1 to 3, characterized in that the stranded wire (8) is pressed or pressed onto the contact element (3) at one end and welded, soldered or crimped onto the guide device (6) at the other end.

5. 5. Electrical appliance according to claim 1, characterized in that the guide device (6) is at least partially made of aluminium, an aluminium alloy, copper and / or brass.

6. said contact element (3) being made using a mixture of graphite and metal; the total volume fraction of said metal in said contact element (3) is at least 30% by volume; At least a front region (16, 21) of the contact element (3) has the sliding contact surface (4), and the front region (16, 21) is provided with silver as the metal, The rear region (22) of the contact element (3) is provided with copper as the metal, An electrical device according to any one of claims 1 to 5, characterized in that the contact elements are copper-free in the area of ​​the sliding contact surfaces.

7. the contact element (3) has openings or slits in the area of ​​the sliding contact surface (4), 7. Electrical device according to claim 1, characterized in that the contact elements are perforated in the region of the sliding contact surface.

8. The contact elements are pin-shaped or bolt-shaped brushes (3), An electrical device according to any one of claims 1 to 7, characterized in that the sliding contact surface (4) is rectangular or circular.

9. The spring element is a compression coil spring (9), The electrical device according to any one of claims 1 to 8, characterized in that one end of the compression coil spring (9) is in contact with an end face of the contact element (3) located opposite the sliding contact surface (4).

10. A conduit (19) for the oily fluid (20) is provided in the guide device (6), 2. Electrical machine according to claim 1, characterized in that the conduit (19) opens into the space (14) between the shaft (2) and the guide device (6).

11. The contact element (3) is subjected to a force of at least 10 N / cm by the spring element (9). ２ 11. The electrical device according to claim 1 or 10, characterized in that the electrical device is constantly pressed against the shaft (2) with a force of .

12. An electrical device according to any one of claims 1 or 10-11, characterized in that the shaft (2) is copper-free, at least in the area in contact with the contact element (3).

13. An electrical machine according to any one of claims 1 or 10-12, characterized in that the contact element (3) is in contact with a circumferential surface (17) of the shaft (2).

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