A commutation device for commuting current and a machine equipped with this type of commutation device

Abstract

The present invention relates to a discharge device (1) for discharging an electric current from a rotor part of a machine (100) having a shaft (5), the device (1) having a displaceable contact element at least partially received within a guide unit (2), the contact element serving to form an electrically conductive sliding contact, the contact being a contact between a sliding contact surface (4) of the contact element provided to form the contact and a shaft contact surface (6) of the shaft, the contact element being conductively connected to the guide unit and / or a holding element of the machine, the contact element being preloaded towards the shaft contact surface by a spring element (7), the contact element (3) being wetted by a lubricating and cooling fluid in the region of the sliding contact surface (4) of the contact element (3), the guide unit (2) comprising guide parts (8, 8', 8'', 8''') for receiving the contact element (3) and a holding part (9) for receiving the guide parts, the holding part and the guide parts forming a duct (15) for the lubricating and cooling fluid.

Description

Technical Field

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

Background Art

[0002] Such discharge devices are known in various embodiments from the prior art. Specifically, it is known to use carbon brushes for discharging a low-frequency electric current, and these carbon brushes are arranged in an axially or radially distributed manner around a shaft and are connected to a stator via connecting wires. The carbon brushes received in a holding unit and / or a brush holder can directly discharge an electric current due to their low electrical resistance, thus avoiding undesirable current conduction through the bearing point of the shaft and / or a transmission connection such as a gear wheel, which may lead to surface damage of the bearing body or the bearing ring caused by spot welding.

[0003] In this specification, the term "shaft" is used as a synonym for the terms "rotor part" or "axle". Thus, the term "shaft" refers to a fixed stator part of a machine and / or any rotating machine part that can discharge an electric current.

[0004] Also, discharge devices are commonly used in railway technology where an alternating current or even an operating current may flow through a wheel axle. This type of discharge device is described, for example, in DE 10 2010 039 847 A1.

[0005] Means for discharging current are necessary for all electrical machines such as, for example, automobiles. There is a risk that continuously fluctuating alternating voltages and / or currents as well as high-frequency current pulses will occur at the motor drive shaft or at the connected transmission shaft and / or at other functional components, and furthermore there is a risk of damage to the bearing points of the rotor shaft or transmission shaft, so that a discharge device is usually required here.

[0006] One problem of the aforementioned discharge devices and of machines having such discharge devices is the generation of high heat caused by electrical and mechanical losses, which results in a high heat load on both the discharge device and the machine (for example, motor, transmission). To address this problem to some extent, ventilation systems have hitherto been used to dissipate the generated heat. However, such ventilation systems can only partially minimize the heat load on the components. A further disadvantage of such ventilation systems is that the installation space required to integrate the ventilation system into the machine increases dramatically.

[0007] In order to minimize the above-mentioned drawbacks, WO 2022 / 135715 A1 proposes to wet the contact elements in the area of the sliding contact surfaces of the contact elements with a lubricating cooling fluid. By doing so, the capacitive coupled high-frequency voltage (so-called parasitic alternating voltage) formed by the electrical drive using the power electronics (pulse width modulation) used is discharged, and at the same time the heat generated in this process is confined and / or dissipated with the aid of the lubricating cooling fluid. In order to minimize the heat load, no special cooling device such as a ventilation system is required. As a result, the design of a machine such as an electric motor is simplified compared to previously known systems, and thus the price can be kept lower and the cooling of the motor can be made more efficient. For example, the frictional losses caused especially by the radial shaft seal are also eliminated. Furthermore, as already mentioned above, it becomes possible to make the overall dimensions of the machine smaller (the moment of inertia of the rotating parts is reduced).

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

[0009] This discharge device with an axial fluid flow has the disadvantage that for a given volume flow rate, the output depends on the cross-sectional area and the flow velocity of the fluid. If the volume flow rate is very high, the cross-sectional area may be too small and / or the flow velocity may be too high. Therefore, there is a disadvantage that sufficient fluid for cooling often does not reach the area between the shaft and the guide unit. Furthermore, the known guide units are somewhat complex to manufacture and costly.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] Therefore, an object of the present invention is to overcome the drawbacks of the prior art.

Means for Solving the Problems

[0012] According to the present invention, this object is achieved by a discharge device of the above-described type, characterized in that the guide unit comprises a guide part for receiving the contact element and a holding part for receiving the guide part, and these holding parts and guide parts form a duct for the lubricating and cooling fluid.

[0013] By using the discharge device according to the present invention, it is ideally possible to discharge the capacitively coupled high-frequency voltage (so-called parasitic alternating voltage) formed by the electrical drive using the power electronics (pulse width modulation) used, and at the same time to confine and / or release the heat resulting from the assistance of the lubricating and cooling fluid. In particular, the present invention does not require a special cooling device such as a ventilation device in order to minimize the heat load. As a result, the design of a machine such as an electric motor, for example, is simplified compared to previously known systems, and thus the price can be kept lower and the cooling of the motor can be made more efficient. For example, the frictional losses caused especially by the radial shaft seal are also eliminated. Furthermore, as described above, it is possible to make the overall dimensions of the machine smaller (the moment of inertia of the rotating parts is reduced).

[0014] Generally, the lubricating and cooling fluid is an oily fluid, in particular engine oil and / or transmission oil, and these are usually present in some way in the engine or transmission in which the discharge device according to the present invention is provided.

[0015] The guide unit includes a guide part for receiving a contact element and a holding part for receiving the guide part, and these holding part and guide part can easily produce a fluid duct in various shapes and sizes by forming a duct for a lubricating and cooling fluid. For example, by incorporating a guide part having an outer peripheral part deviating from a cylindrical shape into a holding part having a cylindrical recess, a fluid duct can be produced very easily. As a result, a cavity is necessarily obtained, and its shape and size can be determined by appropriately adapting the outer peripheral part of the guide part.

[0016] Generally, the fluid duct extends at least along the guide part, and preferably extends along the entire length of the guide part. Thereby, excellent cooling of the rotor is achieved in a particularly advantageous manner. In this embodiment, the lubricating and cooling fluid can flow into the space between the shaft and the contact element over the entire length of the guide part.

[0017] Advantageously, the duct for the lubricating and cooling fluid is formed by a longitudinal recess in the outer wall part of the guide part and / or a longitudinal recess in the inner wall part of the holding part in contact with the outer wall part of the guide part. Such longitudinal recesses make the manufacture of the fluid duct extremely easy.

[0018] In a particularly preferred embodiment of the discharge device according to the present invention, the inner wall part of the holding part is cylindrical, the outer wall part of the guide part has a shape deviating from a cylindrical shape, preferably has a cross-section deviating from a round shape, and at least one, preferably three or four grooves extend in the longitudinal direction of the guide part, particularly having a semi-circular cross-section and being provided in the outer peripheral part of the guide part. This embodiment is particularly easy to manufacture and is characterized by simple flexibility in producing fluid ducts of different shapes and sizes. By doing so, it becomes possible to manufacture a fluid duct capable of transporting a large amount of oil to the position to be cooled.

[0019] In a further embodiment of the discharge device according to the invention, the outer wall part of the guide part has a substantially round cross-section, preferably is cylindrical, and the inner wall part of the holding part has a shape deviating from a cylindrical shape, preferably has a cross-section deviating from a round shape. Thus, the described embodiment features a guide part that is substantially cubic or triangular prism-shaped, and the sides of this guide part are curved inwards, i.e., concave. These guide parts can be manufactured particularly advantageously by extrusion or continuous casting and form an optimal fluid duct together with the holding parts.

[0020] In a further embodiment of the discharge device according to the invention, the outer wall part of the guide part has a substantially round cross-section, preferably is cylindrical, and the inner wall part of the holding part has a shape deviating from a cylindrical shape, preferably has a cross-section deviating from a round shape. This embodiment can also be used to easily produce fluid ducts of different shapes and sizes.

[0021] Advantageously, the guide part is an extruded profile, preferably an aluminum extruded profile or a continuous casting profile. Such guide parts are particularly easy and inexpensive to manufacture.

[0022] At least one fluid duct in the shape of a channel is provided in the guide part, and the channel preferably opens on the front face of the guide part, which front face delimits the space between the shaft and the discharge device. This embodiment enables more lubricating and cooling fluid to be sent to the location to be cooled. For example, this fluid duct can be a duct extending parallel to the longitudinal axis of the discharge device, such as a fluid guide channel.

[0023] Advantageously, the guide part is received substantially completely within the holding part. This enables the creation of a duct channel for the lubricating and cooling fluid extending along the entire length of the guide part. This fluid can then flow into the space between the shaft and the discharge device.

[0024] In a particularly preferred embodiment of the discharge device according to the invention, the guide unit can be conductively connected to a stator part of a machine. This stator part of the machine can, for example, serve as a holding device for the discharge device. When current is discharged, this current is discharged from the associated shaft into the contact element and the guide unit of the discharge device. Then, in the described embodiment, this discharged current flows into the stator part of the machine.

[0025] Advantageously, the contact element is conductively connected to the guide unit preferably by a low-impedance stranded wire, which is preferably pushed or pressed into the contact element at one end and preferably welded, 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 from plastic or metal, preferably from aluminum, aluminum alloy, copper and / or brass.

[0026] In a particularly preferred embodiment of the discharge device according to the invention, the contact element is made substantially from a carbon-metal mixture, in particular from a mixture of graphite and a highly conductive metal, preferably silver is the metal provided at least in the region of the sliding contact surface of the contact element, preferably copper is the metal provided in the rear region of the contact element, and the contact element preferably does not contain copper in the region of the sliding contact surface. The proportion of metal in the contact element is preferably at least 30% by volume. Thus, in the region of the sliding contact surface, the contact element preferably does not contain copper. This is because this metal can cause a catalytic change in the lubricating cooling fluid with the passage of current, and as a result, it may negatively change the physical properties of this fluid. For this reason, the machine shaft according to the invention, which will be described in more detail hereinafter, also does not contain copper at least in the region where this shaft contacts the contact element.

[0027] In order to keep the system resistance as low as possible under all operating conditions, the resistance of the discharge device according to the present invention should also be low. The resistance of the entire device can be kept low by using the above-described embodiment having a low-impedance material and a contact element made of a metal-carbon mixture. On the other hand, the system resistance is significantly affected by the voltage drop between the shaft surface and the sliding contact surface of the contact element. This occupies the largest part of the entire system. Therefore, the system resistance should also be kept low. In order to ensure the condition of low system resistance under continuous lubrication, a high specific contact surface pressure of the contact element against the shaft is advantageous. This value should be at least 10 N / cm 2 should be. On the other hand, in combination with the lubricating cooling fluid, an electrochemical reaction should not occur in the contact element in the area of the sliding contact surface. This is specifically ensured by the silver-graphite material in the area of the contact element that wears over the entire service life.

[0028] Advantageously, the contact element has recesses, in particular drill holes or slots, in the area of the sliding contact surface. This prevents the contact part from floating on the oil film. Advantageously, the contact element has open holes in the area of the sliding contact surface. This contributes to suppressing the electrical contact loss between the shaft and the contact element and minimizes the floating of the contact element on the oil film.

[0029] The contact element is typically a pin-shaped brush or a bolt-shaped brush. The sliding contact surface is rectangular, polygonal, or circular. The brush is usually manufactured by compression molding and subsequent heat treatment.

[0030] Advantageously, the spring element is a coil spring, and one end of the spring element preferably abuts against the front surface of the contact element located on the opposite side of the sliding contact surface. By using this type of compression coil spring, it becomes easy to press the contact element against the shaft using a specific desired contact pressure at all times.

[0031] Furthermore, the present invention 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 present invention. The contact element of this discharge device forms a sliding contact portion by contacting the shaft by means of the sliding contact surface of the contact element. The machine according to the present invention realizes the aforementioned advantage of a dramatic reduction in thermal load due to its small installation size and uncomplicated design.

[0032] In the machine according to the present invention, the discharge device can be completely installed in a lubricating and cooling fluid, specifically in motor oil or transmission oil. Preferably, the lubricating and cooling fluid is supplied at least into the space between the shaft and the guide unit, and the contact element occupies this space. In this embodiment, the region where the maximum heat is generated, that is, the region between the shaft and the contact element, is cooled by the lubricating and cooling fluid.

[0033] Advantageously, the contact element is constantly pressed against the shaft by a spring element using a force of at least 10 N / cm 2 Thereby, the voltage drop between the shaft surface and the sliding contact surface of the contact element is minimized.

[0034] As described above, preferably, the shaft is substantially free of copper at least in the region covered by the contact with the contact element.

[0035] In a preferred embodiment of the machine according to the invention, the contact element contacts the front face of the shaft, and the contact element is preferably arranged substantially coaxially with the shaft. This type of shaft grounding is preferred for avoiding contact losses since the axial runout of the rotating shaft is generally low. By positioning the contact element near the rotation point of the shaft, the peripheral speed is minimized and the actual running distance over the service life of the contact element is significantly reduced. This has a direct impact on the wear of the contact element and has a proportional correlation with the normal running distance. By minimizing the running distance, the wear of the contact element remains low, and as a result, the loss of force of the spring element over the total wear length of the contact element is also minimized. This enables, for example, the use of low-cost compression coil springs as described above. Furthermore, due to the low peripheral speed near the axis of rotation of the shaft, the risk of forming a continuous electrically insulating lubricating film is reduced, i.e., it is possible to maintain a lower contact pressure than the pressure required at high peripheral speeds. Another advantage of the front contact of the shaft near the axis of rotation is that the frictional torque is minimized due to the short radial distance from the rotation point. Even when the frictional force is very high, the frictional torque as the product of the frictional force and the running radius remains small. As a result, this frictional force remains low in combination with the angular velocity (equivalent to the rotational speed), and the system losses also remain low.

[0036] In a further embodiment of the machine according to the invention, the contact element contacts the jacket surface of the surface. In this embodiment, preferably, the cross-section of the contact element is geometrically tapered in the preferred direction of rotation of the shaft to be contacted in order to achieve suppression of electrical contact losses due to floating between the shaft and the contact element.

[0037] Generally, the discharge device is positioned in the section of the machine where the main operating temperature exceeds 50 °C.

[0038] Further features of the invention are shown in the following description of the figures in combination with the drawings and the dependent claims. The individual features can be realized alone or in combination with each other.

Brief Description of the Drawings

[0039]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0040] Hereinafter, elements that are the same or functionally the same are identified by the same reference numerals.

[0041] Figures 1, 7, and 8 show the discharge device 1 according to the present invention, and the discharge device 1 in FIG. 8 is incorporated into the machine 100 according to the present invention. The discharge device 1 is used to discharge current from the rotor part of the machine 100 having the shaft 5. The discharge device 1 includes a displaceable pin-shaped brush 3 received in the guide unit 2, and this brush 3 serves to form a conductive sliding contact portion, and this conductive sliding contact portion is a contact portion between the sliding contact surface 4 of the brush 3 provided to form this sliding contact portion and the shaft contact surface 6 of the shaft. This shaft 5 is shown in FIG. 8. The brush 3 is preloaded toward the shaft contact surface 6 by the compression coil spring 7. This compression coil spring 7 is also shown in FIG. 8. In the region of the sliding contact surface 4, the brush 3 is wetted by the lubricating cooling fluid.

[0042] The guide unit 2 includes a guide part 8 for receiving the brush 3 and a holding part 9 for receiving the guide part 8. In the illustrated example, the inner wall part 10 of the holding part 9 has a cylindrical shape. On the other hand, the outer wall part 11 of the guide part 8 has a shape different from the cylindrical shape. For example, the guide part 8 is designed as a certain kind of triangular prism, the cross-section of the guide part 8 is substantially triangular, has flat corners 12, and the sides of this triangle are curved inward, that is, concave. Since the side surface 13 of the guide part 8 is also concave, the guide part 8 has three semi-circular grooves 14 extending in the longitudinal direction of the guide part 8. These grooves 14 extend along the entire length of the guide part 8.

[0043] As clearly shown in FIGS. 1, 7, and 8, the guide part 8 is received in the holding part 9, and its flat corner 12 contacts the inner wall part 10 of the holding part 9. In this situation, the grooves 14 in the outer peripheral part of the guide part 8 form a total of three fluid ducts 15 in combination with the inner wall part 10 of the holding part 9. These fluid ducts 15 serve as flow paths for the lubricating cooling fluid flowing from the rear side part 16 of the discharge device 1 toward the sliding contact surface 4 of the brush 3.

[0044] Furthermore, a continuous receiving channel 17 for the brush 3 is provided in the guide part 8. Both the brush 3 and the receiving channel 17 have a substantially square cross-section with rounded corners.

[0045] As shown in FIG. 8, on the side of the guide unit 2 facing the shaft 5, the brush 3 protrudes slightly from the guide part 8 and contacts the shaft 5 at its end face 18. In this situation, the brush 3 is arranged substantially centrally with respect to the end face 18 of the shaft, and thus is coaxial with the shaft 5.

[0046] The guide part 8 has a cover 19 to which a stranded wire 20 is attached at the other end. The spring 7 that preloads the brush 3 towards the shaft 5 is arranged between the cover 19 and the brush 3. The stranded wire 20 is made of a low-impedance material, is pushed into the brush 3 at one end, and is connected to the cover 19 at the other end.

[0047] The brush is made of a graphite-metal mixture.

[0048] FIGS. 2, 3, and 5 show other possible shapes of the guide part. FIG. 2 shows a guide part 8' having a semi-circular cross-section, where a flat surface 22 is adjacent to a curved jacket surface 21. The cylindrical inner wall portion 10 of the holding part 9 in FIG. 1 forms a fluid duct in combination with the flat surface 22 of the guide part 8' received within the holding part 9. The lines shown in FIG. 2 are intended to show that further longitudinal grooves can be made in the curved surface 21, and these longitudinal grooves can form further fluid ducts in combination with the inner wall portion 10 of the holding part 9.

[0049] FIG. 3 shows a further embodiment of a guide part 8'' having a round cross-section. The guide part 8'' is particularly suitable for a holding part having an inner wall portion cross-section deviating from a round shape. Thus, for example, the guide part 8'' forms four fluid ducts in a holding part having a cubic body and an inner wall portion having a square cross-section.

[0050] Figure 5 shows a further embodiment of the guide part 8'''. The guide part 8''' can be combined with the holding part 9 of FIG. 1. The guide part 8''' has a square cross-section and flat corners 12, and the sides of this square are concave. Accordingly, the guide part 8''' has a substantially cubic shape, and the side surfaces 13 of this cube are concave. When the guide part 8''' is incorporated into the holding part 9, the concave side surfaces 13 form a total of four fluid ducts in combination with the cylindrical inner peripheral part 10 of the holding part 9.

[0051] Figure 4 shows a guide part having the same shape as the guide part 8 of FIG. 1, but differing from the guide part 8 of FIG. 1 only in that it has three continuous fluid ducts 23 with a round cross-section. These fluid ducts extend along the entire length of the guide part 8 and serve to transport even more lubricating and cooling fluid within the space between the shaft 5 and the guide part 8. The guide part 8''' of FIG. 5 also has ducts of this type. Furthermore, the guide part 8''' of FIG. 3 also has two such ducts 23', each of which has a longitudinally curved cross-section. These ducts 23, 23' each open into the front surface 24 of each guide part.

[0052] The illustrated guide parts 8, 8', 8'', and 8''' are all aluminum extrusions.

Description of the reference numerals

[0053] 1 Discharge device 2 Guide unit 3 Brush 4 Sliding contact surface 5 Shaft 6 Shaft contact surface 7 Compression coil spring, spring, spring element 8 Guide part 8' Guide part 8'' Guide part 8''' Guide part 9 Holding part 10 Inner wall part, cylindrical inner peripheral part 11 Outer wall part 12 Flat corner, rounded corner 13 Side surface, concave side surface, side 14 Semi-circular groove, groove, longitudinal recess 15 Fluid duct, duct 16 Rear side part 17 Receiving channel 18 End face 19 Cover 20 Twisted wire 21 Curved jacket surface, curved surface 22 Flat surface 23 Fluid duct, duct 23' Fluid duct, duct 24 Front face 100 Machine

Claims

1. A discharge device (1) for discharging an electric current from a rotor part of a machine (100) having a shaft (5), wherein the discharge device (1) comprises a displaceable contact element at least partially received within a guide unit (2), the contact element serving to establish an electrically conductive sliding contact, the electrically conductive sliding contact being a contact between a sliding contact surface (4) of the contact element provided to form the sliding contact and a shaft contact surface (6) of the shaft, the contact element being electrically connected to the guide unit and / or a holding element of the machine, the contact element being preloaded towards the shaft contact surface by a spring element (7), In the discharge device (1), the contact element (3) is at least partially wetted by a lubricating and cooling fluid, particularly in the region of at least the sliding contact surface (4) of the contact element (3). The guide unit (2) comprises guide parts (8, 8', 8", 8'") for receiving the contact element (3) and a holding part (9) for receiving the guide parts, the discharge device (1) being characterized in that the holding part and the guide parts form a duct (15) for the lubricating and cooling fluid.

2. The fluid duct (15) extends at least along the guide parts (8, 8', 8", 8'"), and the fluid duct (15) preferably extends along the entire length of the guide parts (8, 8', 8", 8'"). The discharge device according to claim 1, characterized in that.

3. The fluid duct (15) is formed by a longitudinal recess (14) in an outer wall part (11) of the guide parts (8, 8', 8", 8'") and / or a longitudinal recess in an inner wall part of the holding part in contact with the outer wall part of the guide parts (8, 8', 8", 8'"). The discharge device according to claim 1 or 2, characterized in that.

4. The inner wall portion (10) of the holding part (9) is cylindrical, and the outer wall portion (11) of the guide parts (8, 8', 8", 8'") has a shape deviating from a cylindrical shape, preferably has a cross-section deviating from a round shape, and at least one, preferably three or more grooves (14) extend in the longitudinal direction of the guide part, particularly having a semi-circular cross-section and being provided in the outer peripheral portion of the guide parts (8, 8', 8", 8'"). The discharge device according to any one of claims 1 to 3, characterized in that.

5. The cross-section of the guide parts (8, 8', 8", 8'") is substantially triangular or square, has flat corners or round corners (12), and the sides (13) of the triangle or the square are preferably substantially concave. The discharge device according to any one of claims 1 to 4, characterized in that.

6. The outer wall portion of the guide parts (8, 8', 8", 8'") has a substantially round cross-section, preferably is cylindrical, and the inner wall portion (10) of the holding part (9) has a shape deviating from a cylindrical shape, preferably has a cross-section deviating from a round shape. The discharge device according to any one of claims 1 to 3, characterized in that.

7. The guide parts (8, 8', 8", 8'") are extrusion profiles, preferably aluminum extrusion profiles or continuous casting profiles. The discharge device according to any one of claims 1 to 6, characterized in that.

8. At least one fluid duct (23, 23') in the shape of a channel is provided in the guide parts (8, 8", 8'"), and the channel preferably opens to the front surface (24) of the guide part. The discharge device according to any one of claims 1 to 7, characterized in that.

9. The guide parts (8, 8', 8", 8'") are substantially completely received within the holding part (9). The discharge device according to any one of claims 1 to 8, characterized in that.

10. The guide parts (8, 8', 8", 8'") are electrically conductively connectable to the stator parts of the machine (100). The discharge device according to any one of claims 1 to 9, characterized in that.

11. The contact element is a pin-shaped brush or a bolt-shaped brush (3), and the sliding contact surface (4) is preferably rectangular, polygonal, or circular. The discharge device according to any one of claims 1 to 10 is characterized in that.

12. The spring element is a coil spring (7), and one end of the spring element preferably abuts on the front surface of the contact element (3) located on the opposite side of the sliding contact surface (4). The discharge device according to any one of claims 1 to 11 is characterized in that.

13. A machine (100), particularly an electric drive motor or a transmission, having a rotor part having a shaft (5) and a discharge device (1) according to any one of claims 1 to 12, wherein the contact element (3) of the discharge device (1) forms a sliding contact portion by contacting the shaft (5) with the sliding contact surface (4) of the contact element (3). Machine (100).

14. A lubricating and cooling fluid, particularly motor oil or transmission oil, or a water-based cooling medium is supplied into at least the space between the shaft (5) and the guide unit (2), and the contact element (3) occupies the space. The machine according to claim 13 is characterized in that.

15. The contact element (3) contacts the front surface of the shaft (5), and the contact element is preferably arranged substantially coaxially with the shaft. The machine according to claim 13 or 14 is characterized in that.

16. The contact element contacts the jacket surface of the shaft. The machine according to claim 13 or 14 is characterized in that.

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