WO2025237450A1

WO2025237450A1 - Slip ring device for an inside of a shaft, shaft comprising the device, and traction motor comprising the shaft

Info

Publication number: WO2025237450A1
Application number: PCT/CZ2024/050034
Authority: WO
Inventors: Frantisek MERICKA; Roman SVACH; Ivana FOJTIKOVA; Yann Tremaudant; Alexander Maier; Philip Moerth; Jerome Ragot; Christoph Seidenberger
Original assignee: Cebes AS; Bayerische Motoren Werke AG
Current assignee: Cebes AS; Bayerische Motoren Werke AG
Priority date: 2024-05-13
Filing date: 2024-05-13
Publication date: 2025-11-20
Anticipated expiration: 2026-11-13

Abstract

Slip ring device (100) for an inside of a traction motor (200) shaft (221), shaft (221) with the device (100) and traction motor (200) with the shaft (221). The device (100) comprises a rotor part (110) and a stator part (130). The rotor part (110) comprises a hollow body (111) with a chamber (112) divided by a flange (114) into an inner section (115) and an outer section (116). The stator part (130) comprises a rod (131) fixable to a stator (229) of the traction motor (200) and extending through the outer section (116) of the chamber (112) into the inner section (115). The rotor part (110) further comprises two contact rings (117) attached to opposite sides of the flange (114). The stator part (130) comprises brushes which are in a sliding contact with the contact rings (117).

Description

Slip ring device for an inside of a shaft, shaft comprising the device, and traction motor comprising the shaft

Technical field

The present invention relates to traction motors, more specifically to motors where a slip ring for providing electrical current to the rotor is placed inside of the rotor’s shaft.

Background of the Invention

Traction motors generally require a DC current to be supplied to the rotor in order to create a magnetic field with its windings, and thus a rotary electrical connection is needed. Permanent magnets can be used to avoid the need for the rotary electrical connection, but they are not as strong as electromagnets and require rare elements, such as neodymium, so they are not practical for some applications. Rotary electrical connection can operate with a contactless energy transfer, but this approach is not suitable for motors with higher power, e.g., above 150 kW. Sliding contact energy transfer, i.e., slip ring contact, is thus used in most applications.

Examples of slip rings suitable for traction motors can be found in documents CN21267658111 or WO2023208259A1 . It is common to place slip rings on the outer surface of a rotor shaft, as is the case in the aforementioned documents. This approach is much simpler to design and manufacture than placing the slip ring on the inside. A drawback of this approach is that the slip ring then takes up space in the motor which cannot be occupied by rotor windings, and it therefore limits the power of the magnetic field which can be created and therefore limits the power of the motor. A slip ring located inside of a shaft is disclosed in document W02021/003360. However, in this document, a liquid contact is used, which can make the device more expensive and more prone to malfunctions and can limit a maximum current that can be transferred. It would therefore be desirable to provide a slip ring construction which would enable the slip ring to be mounted inside of the shaft, such that it does not limit space on the outside, while being relatively easy to design and manufacture and while being practical for use in electric vehicles.

Summary of the Invention

The shortcomings of the solutions known in the prior art are to some extent eliminated by a slip ring device mountable to the inside of a traction motor shaft. The device comprises a rotor part intended for rotating together with rotor of the motor and a stator part intended to be fixedly connected to a stator of the motor. The rotor part and the stator part thus can rotate with respect to each other during operation of a traction motor comprising the device. Rotatable connection between the parts can be defined by a part of the device but is preferably provided by the traction motor, i.e., by fixing the rotor part to the rotor and the stator part to the stator, where the rotor is rotatably connected to the stator.

The rotor part comprises a hollow body for mounting into a cavity in the shaft. The body comprises a chamber which has an open end and is divided by a flange into an inner section and an outer section. The body thus has a wall delimiting the chamber, wherein the outer surface of the wall is then in contact with the walls of the shaft cavity. The wall can be metallic and is then preferably provided with an insulation on the inside to keep any electrical components of the device insulated from each other. The flange is a protruding portion on the inside of the body, preferably made from one piece with the wall of the body. Preferably, the flange has a rectangular cross-section when viewed from the side and an annular cross-section when viewed along the device’s longitudinal axis (which coincides with the rotor’s axis of rotation when the device is mounted to the traction motor). The outer section is delimited at one end by the flange and at an opposite end by the open end of the chamber. The inner section is thus between the flange and the bottom end of the chamber, which is preferably closed. The sections can have similar lengths, i.e. , the flange can be close to the middle of the chamber’s depth. The inner section can be slightly longer to accommodate a fan which will be described further below.

The stator part comprises a rod which has a fixation end for fixing to a stator of the traction motor, e.g., by a threaded connection, welding, pressing etc., and a free end which is inserted to the inner section. The rod thus extends through the outer section of the chamber into the inner section of the chamber. The inner diameter of the flange thus needs to be at least slightly larger than the outer diameter of the rod. The rod is preferably circular in cross-section. It can have substantially constant diameter along most of its length or can change its diameter. If the diameter is non-constant, it is preferably decreasing towards the free end to provide stability close to the fixing end and to provide more space for other components close to the free end. The fixing end can have a broader portion for easier/more stable fixing to the stator. The rod is preferably hollow so that it can serve for guiding other components or air, as will be described further below.

The rotor part comprises two contact rings, one attached to the flange in the inner section, and one attached to an opposite side of the flange in the outer section. I.e., the flange is placed between the contact rings. The contact rings thus serve as a + pole and - pole for powering the rotor and are separated from each other by the flange. The rod thus extends through the rings.

The stator part comprises two brush holders which are carried by the rod, wherein one brush holder is in the inner section and one brush holder is in the outer section. Each brush holder contains at least one brush, preferably multiple brushes, which is/are in a sliding contact with one of contact rings. The brushes thus slide along the contact rings, or more precisely the contact rings rotate and slide along the brushes, and transfer current between the rotor part and stator part. The brush holder can be insulated from the rod and can conductively contact the brushes, e.g., a brush connector can be connected to the brush holder which transfers current to the brushes.

The present invention thus provides a compact device which can be inserted into a hollowed shaft and can transfer electrical power to the shaft from a stator. The outer surface of the shaft can then carry more rotor windings which makes it possible to create a more powerful motor without increasing its size. A part of the windings can even be located around a part of the slip ring device, e.g., around the inner section or a part thereof. The flange makes it possible to arrange the rings next to the brushes in the axial direction which helps with keeping the device’s diameter small enough to fit into a shaft of a standard traction motor. The sliding contact via brushes and rings is relatively simple and cheap to make so the device is reliable and can transfer substantial currents needed for powering vehicles.

Each contact ring preferably has a contact surface for contact with a brush, wherein contact surfaces of both contact rings are perpendicular to a longitudinal axis of the device. The flange is thus surrounded by the contact rings from both sides in axial direction and the two rings in turn are surrounded by the brushes in axial direction. The brushes on different brush holders can thus be pushed against each other (by a spring member as described below) in axial direction. In state of the art, brushes are pushed in radial direction which increases radial dimensions of the slip rings.

Slip rings know from the state-of-the-art use radial contact between brushes and contact rings, i.e., the sliding contact surfaces have normal vectors perpendicular to axis of rotation of the slip ring and the motor. Since each brush usually has a spring pushing it towards the contact ring to maintain contact despite wear of the brush (usually a block of carbon), a substantial amount of space in the radial direction is required. Using axial contact, where the contact surfaces have normal vectors parallel to the rotor axis, means that the rings and brushes are next to each other in axial direction. This makes the slip ring device significantly smaller in the radial direction and it is thus possible to place the device inside of the shaft while using brushes and contact rings for transferring current.

Each brush holder can further contain at least one spring member for biasing the at least one brush against a respective contact ring. A helical spring or a leaf spring can for example be used as a spring member. The springs in the present invention can be placed axially next to the brushes and thus don’t increase the radial dimension of the device. Brushes are thus held slidingly by the brush holders. The slip ring device can further comprise a cooling air passage extending through the rod, around the free end of the rod, around the brush holders, between the rod and the flange, and through the open end of the chamber. The passage can be delimited by an opening in the rod and then by a space between the rod and the body.

During use, the slip ring device produces heat, e.g., roughly 20-60 W of heat for a standard traction motor. It is advantageous to transfer this heat away by convection to keep temperatures of the device, especially of the brushes, at suitable temperatures. Providing the air passage is therefore advantageous because it allows an air circulation where the air can carry away a part of the produced heat.

The slip ring can then comprise at least one fan for increasing air flow through the passage. The at least one fan can be attached to the rotor part, especially adjacent to the free end of the rod and/or adjacent to the open end of the chamber. The fan is thus rotated by movement of the rotor. The fan is preferably fixedly attached to the rotor part.

The body can have a cylindrical outer shape, wherein the cylindrical shape has a first base which is open and forms the open end of the chamber and a second base which is closed. Cylindrical shape is preferred since it can be installed into a shaft symmetrically and can delimit more space than other shapes.

The rod can comprise a power supply passage containing a brush connector, wherein each brush in the inner section is connected to this electrical connector. The outer brushes can be connected via a connector guided on the outside of the rod. The power supply passage can be the same passage as the air passage described above, i.e., air can be guided around the connector. It is also possible to provide a separate passage for the connector or to have a rod with only one of the passages.

The shortcomings of the solutions known in the prior art are to some extent also eliminated by a shaft for a traction motor, the shaft comprising a cavity which is open at one end of the shaft. The shaft further comprises the slip ring device according to the present invention, wherein the body of the device is mounted in the cavity of the shaft. The shaft is thus non-movably connected to the rotor part of the device. The shaft thus provides the same advantages as described above for the device and can be used for assembling a traction motor.

The shaft can further comprise a coolant passage for circulating a coolant through the shaft. A part of the coolant passage can be delimited by the body of the device to transfer heat away from the body and thus cooling the inside of the device. It is known to cool traction motor shafts by a coolant, usually oil, circulating through the shaft. This known cooling circuit can thus be expanded with the present invention to help cooling the slip ring device as well. The passage can for example only contact a bottom of the body, or it can be also partially delimited by the curved wall of the body along the length of the device. The passage can then e.g., comprise grooves on the cavity walls and/or on the outer surface of the body.

The cooling by oil can be used together with the cooling by air. It is also possible to use one of the types of cooling in some variants of the invention.

The body of the rotor part can protrude out of the cavity of the shaft. The protruding part of the body can then comprise a cylindrical outer surface for contact with a seal. The open end of the chamber can thus be located outside of the shaft. This protrusion can be achieved by making the body longer and/or by making the shaft shorter. A seal can thus be placed onto the protruding part. The seal can especially then be fixed to a stator when the shaft is installed as a part of a motor. The seal can be any type of seal suitable for holding oil inside of a motor. The outer surface is thus preferably smooth and is preferably from a material which will not be unacceptably worn down by a sliding contact with the seal. Steel can be a suitable material for this surface. The whole body can be made from the same material. Steel is also suitable for pressing of the body into the cavity without deforming the body.

This arrangement where the oil seal is in contact with the body of the device, not with the shaft itself, is advantageous because it allows for a larger diameter of the body. For shaft seals in traction motors, a circumferential velocity of the seal-contacting surface is often a limiting factor determining a maximum diameter of the seal for given motor speed. Standard seal materials might deteriorate if higher circumferential velocities occur. Since the circumferential velocity is given by speed of the motor (i.e., revolutions per minute) and by diameter of the seal, and since decreasing the speed of the motor is often undesirable, using larger diameter of seal is often not appropriate or possible. By forming the seal-contacting surface on the body, instead of on the shaft, the outer diameter of the body, not the outer diameter of the shaft, is limited by the seal diameter. As a result, the body can have larger diameter then if it is fully surrounded by the shaft which is then surrounded by the seal. The perimeter wall of the cavity can then be made thinner. Larger diameter of the body allows for larger coolant passage, larger brushes or contact rings, easier manufacture, more insulation etc. It is also possible to use this protrusion to decrease the size of the seal, and thus also its wear, while keeping the size of the device the same.

The shortcomings of the solutions known in the prior art are to some extent also eliminated by a traction motor comprising a rotor, a stator, and the shaft according to the present invention. The rotor is attached to the shaft, the shaft is rotatably connected to the stator and the fixing end of the rod is attached to the stator, wherein a longitudinal axis of the rod (i.e., of the device) coincides with a rotational axis of the rotor. This motor thus has its slip ring located inside of the shaft. Its windings can thus be expanded over the outer surface of the shaft even above the slip ring device.

The rotor can comprise rotor winding(s) wherein at least two ring connectors are provided, where each ring connector passes through the shaft and connects one of the contact rings to the rotor winding(s).

Brief description of drawings

A summary of the invention is further described by means of exemplary embodiments thereof, which are described with reference to the accompanying drawings, in which:

Fig 1 . Shows a sectional view of a first exemplary embodiment of a slip ring device for an inside of a shaft of a traction motor, wherein longitudinal axis of the device lies in the section plane, wherein the device comprises a rotor part mountable inside the shaft and a stator part located in the rotor part and intended for being fixed to a stator of the traction motor.

Fig 2. Shows a detailed sectional view of the stator part of the device from fig. 1 , wherein the main part of the stator part is a rod carrying brushes and an insulation and defining an air passage indicated by arrows in the figure.

Fig 3. Shows a detailed sectional view of the rotor part of the device from fig. 1 , wherein the rotor part has a body, which can be inserted into the shaft, and which delimits a chamber divided by a flange, where the flange carries contact rings and is squeezed between the brushes from fig. 2 during operation.

Fig 4. Shows the rotor part from fig. 3 inserted into a cavity inside of the shaft, wherein a coolant passage (dashed-line arrows) is formed in the shaft and between the shaft and the body of the rotor part.

Fig 5. Shows another sectional view of the device from figs. 1 to 4 mounted into a rotor shaft, wherein the shaft carries rotor windings, an oil seal and a bearing.

Fig 6. Schematically shows a sectional view of a traction motor comprising the slip ring device, wherein the rod is fixed to the stator and longitudinal axis of the rod coincides with a longitudinal axis of the whole device and with rotation axis of the rotor.

Fig 7. Shows a sectional view with a differently inclined sectional plane of a detail of brush and contact ring arrangement in the device.

Fig 8. Shows another sectional view with sectional plane perpendicular to the rotor axis and passing through coolant passage outlets, wherein one of the brush holders with three brushes arranged therein is visible in the figure.

Fig 9. Shows another sectional view with sectional plane perpendicular to the rotor axis and passing through the fan. Fig 10. Shows a fourth exemplary embodiment of the slip ring device mounted in a traction motor, wherein this embodiment differs from the first embodiment in protrusion of the body of the slip ring device out of the cavity of the shaft.

Fig 1 1 . Shows a simplified view of arrangement of an oil seal according to the first embodiment where the seal contacts the shaft.

Fig 12. Shows a simplified view of arrangement of an oil seal according to the fourth embodiment where the seal contacts the protruding body.

Description of the Preferred Embodiments

The invention will be further described by means of exemplary embodiments with reference to the respective drawings.

A first example of the invention is shown in figs. 1 to 9. The slip ring device 100 according to this example comprises a rotor part 110 and a stator part 130. During operation, the rotor part 1 10 is fixed to a rotor 228 of a traction motor 200, specifically it is mounted into a cavity formed at one end of a rotor shaft 221 (see fig. 4), while the stator part 130 is fixed to a stator 229 of the traction motor 200. The sections thus rotate with respect to each other during operation of the motor 200 and a current for creating a magnetic field by rotor windings 223 is transferred between the sections via a sliding contact of brushes 135 on contact rings 1 17.

The rotor part 1 10 is shown in fig. 3. It comprises a cylindrical hollow body 11 1 which can be pressed into the shaft 221 cavity (see fig. 4). The body 1 1 1 is made of steel and is provided with an insulation 303 on its inner surface which is made from BMC (Bulk Moulding Compound - a composite of a resin with glass fibres). The hollow inside of the rotor part 1 10 forms a chamber 1 12 for receiving the stator part 130. The body 1 1 1 comprises a flange 1 14 on its inner surface which divides the chamber 1 12 into two sections which have approximately the same depth. An inner section 1 15 is closer to the chamber’s 1 12 bottom, an outer section 116 is closer to the chamber’s 1 12 open end 1 13. This open end 1 13 allows the stator part 130 to extend into the chamber 1 12 while being fixed to the stator 229. The chamber 1 12 is thus dumbbell-shaped, with a cylindrical central portion narrower that cylindrical side portions.

On the outer surface of the body 1 1 1 , adjacent to the open end 1 13, there is a groove for a seal between the body 1 11 and the shaft 221 . The body 1 11 further comprises several passages for electrical ring connectors 224 made through the flange 1 14 (see bottom of fig. 3 where one such opening is shown and is filled by insulation 303 separating the connector from the steel material of the flange 1 14). Correspondingly, there are several shaft openings 227 made in the shaft 221 for guiding the ring connectors 224 to the outer side of the shaft 221 to the windings 223. The ring connectors 224 serve for connecting contact rings 1 17 (which will be described below) with rotor windings 223. In the first embodiment, the ring connectors 224 are from copper. The contact rings 1 17, the ring connectors 224 and the windings 223 thus form a rotor part 110 of an electrical circuit which ensures the rotation of the rotor 228.

The rotor part 1 10 further comprises two contact rings 1 17, one for a positive side of the slip ring contact and the other for a negative side. In this embodiment, the positive side is in the inner section 1 15 of the chamber 1 12 while the negative side is in the outer section 1 16. The contact rings 1 17 are made from bronze and contain contact surfaces which are oriented perpendicularly to the rotor axis 230 which is also a longitudinal axis of the device. The device is almost rotationally symmetric around the rotor axis 230, with smaller asymmetrical parts such as connectors, passages and openings, brushes 135, fan 1 18 etc.

Both contact rings 117 are fixed to the flange 1 14, the inner contact ring 1 17 on the inner side of the flange 1 14 and the outer contact ring 1 17 on the outer side of the flange 1 14. The flange 1 14 with its insulation 303 separates the contact rings 117 sufficiently to prevent any short-circuiting or arc-forming between the contact rings 117. Each contact ring 1 17 is connected to at least one ring connector 224.

The rotor part 110 further comprises a fan 1 18 fixed to the bottom of the chamber 1 12, i.e., the end opposite to the open end 113. The fan 118 serves for drawing air 301 from the outside through an air 301 passage formed by the rotor part 1 10 and stator part 130 which will be described below. The fan 1 18 comprises several blades and rotates together with the rotor 228. The fan 1 18 with its six blades is depicted in fig. 9.

The stator part 130 is shown in fig. 2. It comprises a hollow rod 131 made from aluminium which has a fixation end 132, which is to be fixed (e.g., pressed into, welded, screwed etc.) to the stator 229, and a free end 133 which is inserted into the chamber 112 adjacent to the fan 1 18 such that air 301 can be drawn through the hollowed rod 131 into the chamber 1 12. The outer surface of the rod 131 is covered by insulation 303 which is also made from BMC. The stator part 130 further comprises two brush holders 134, each with three brushes 135 made of carbon and three spring members 136 for pressing the brushes 135 towards the contact rings 117. Both brush holders 134 are attached to the rod 131 at positions corresponding to positions of the contact rings 1 17. The positive side brushes 135 are in the inner section 1 15 when the stator part 130 is placed in the rotor part 110. The negative side brushes 135 are then in the outer section 116. The spring members 136 bias the brushes 135 such that the contact rings 117 with the flange 1 14 in between are squeezed by the brushes 135. The inner brushes 135 are connected via the brush holder 134 and via conductive leads 304 to a brush connector 137 - an insulated copper wire located inside of the hollow rod 131 and extending from the fixed end to the inner brush holder 134. The inside of the rod 131 thus serves for guiding the brush connector 137 as well as for guiding cooling air 301 towards the fan 118. The outer brushes 135 have their brush connector 137 located on the outside of the rod 131 . The shape of the brush holder 134, and arrangement of brushes 135 and their leads 304 and their spring members 136 is depicted in fig. 8.

When the rotor part 1 10 and the stator part 130 are assembled (fig. 1 ), the rod 131 is centred with respect to the chamber 1 12 walls by fixing the rod 131 to the stator 229 and connecting the shaft 221 with the rotor part 1 10 to the stator 229 via bearings 226. The only contact between the stator part 130 and the rotor part 1 10 is thus between the brushes 135 and the contact rings 117. There is an air gap everywhere else around the rod 131 in the chamber 1 12. There is thus a cooling air 301 passage starting at the fixing end of the rod 131 (where the passage can be open to the inside of the stator 229 or to the outside of the stator 229 (see fig. 6)), extending through the rod 131 towards the fan 1 18. The air 301 is guided through and around the fan 1 18 to the outer surface of the rod 131 where the air 301 passage continues around the inner brush holder 134, around the flange 1 14 (where the passage is at its narrowest), around the outer brush holder 134 and then out from the device into the stator 229.

The passage and the air 301 inside of the passage are indicated by solid-line arrows in the attached drawings. The air 301 thus cools the inside of the device, especially the brushes 135 and contact rings 1 17 which are the main source of heat of slip rings due to higher electrical resistance at the sliding contact. The heated air 301 is expelled from the device at the open end 113. It can thus be guided towards a stator 229 wall which can then efficiently dissipate the heat transferred from the heated air 301 to the outside. As can be seen in fig. 1 , the fan 1 18 is partially covered by the insulation 303 which separates it from the rod 131 . Part of the fan 118 is extending into the free end 133 of the rod 131 so that air 301 can be drawn more effectively from the rod 131 .

In the first embodiment, the cooling of the device is further provided by an oil 302 coolant passage 222. This passage is formed once the slip ring device 100 is mounted into the cavity in the shaft 221 (see e.g., fig. 4). The shaft 221 is a part for a traction motor 200 with an oil 302 cooling circuit which is partially inside of the motor’s 200 rotor 228 and partially outside of the rotor 228 (see also fig. 5). It is known from the state of the art to provide a motor 200 with an oil 302 cooling circuit which extends through the shaft 221 . The present invention improves this cooling circuit by extending its oil 302 coolant passage 222 in the shaft 221 to the part of the shaft 221 carrying the device.

The coolant passage 222 starts at the outer side of the bottom of the body 1 1 1 (see fig. 4 where the oil 302 flow is marked by arrows with dashed lines) where the oil 302 contacts the whole base of the cylindrical body Hl. The passage is then divided into several branches which extend parallelly to the rotational axis towards the open end 113 of the body 1 11. The branches are distributed along the body’s 1 1 1 perimeter at equal distances. The branches are again merged into a single circular passage close to the open end 1 13 which surrounds the whole perimeter of the body 1 11. The passage then extends via several outlets (see fig. 8) in radial directions through the shaft 221 into the space between the rotor 228 and the stator 229 (see fig. 5 where there is a boundary between oil 302 and air 301 delimited by a seal 225 and depicted by a vertical dashed line). In fig. 4, one of the outlets is visible where the oil 302 coolant passage 222 leaves the shaft 221 on the upper left part of the drawing. During the motor’s 200 operation, the oil 302 is thus provided by the standard cooling circuit which is a part of the traction motor 200. The body 1 11 of the device forms a part of the coolant passage 222 and is thus cooled by contact with the oil 302. The device is thus cooled on the inside by air 301 and from the outside, it is cooled by oil 302. The oil’s 302 temperature can be for example around 70°C during the motor’s 200 prolonged operation. There is thus relatively intense cooling effect provided for the slip ring device 100. The operational temperature of the device is thus kept at low enough temperatures, preferably under 100°C, which prolongs life of the brushes 135 (which are generally fairly sensitive to high temperatures and wear out much sooner when the temperatures are high).

The slip ring device 100 mounted into the traction motor 200 is shown in figs. 5 and 6. The body 1 11 of the device is fixed into the shaft 221 which carries an oil 302 seal 225, a bearing 226 and rotor windings 223 (see fig. 5). The rotor windings 223 are connected to the contact rings 1 17 via the ring connectors 224 passing through the shaft 221 and the flange 1_1_4. In fig. 6, the stator 229 is also shown. The rotor part 1 10 of the device is shown here as a part of the shaft 221 and a seal is not shown for sake of simplicity. The rod 131 is screwed to the stator 229 and the air 301 passage extends through a stator 229 wall to the outside. Fig. 6 is only a schematical drawing but it makes it clear how the rotor 228 can carry more windings 223 thanks to space saved on the shaft 221 by placing the slip ring device 100 to the inside.

A second exemplary embodiment of the invention is the shaft 221 depicted in figs. 4 and 5 which contains the slip ring device 100 according to the first embodiment. The shaft 221 thus comprises a cylindrical cavity with dimensions complementary to the outside dimensions of the body 1 1 1. The device is pressed into the cavity and the rotor part 110 is thus fixed to the shaft 221 . Outer surface of the shaft 221 has various diameters for accommodating seals 225, bearings 226, windings 223 etc. A coolant passage 222 is made in the shaft 221 as described above. A third exemplary embodiment of the invention is the traction motor 200 from figs. 5 and 6. The motor 200 comprises standard traction motor 200 components, i.e., a rotor 228 with windings 223, shaft 221 , bearings 226, etc., and a stator 229 with a casing, power connector, air 301 intake etc. The rotor shaft 221 in this embodiment is the shaft 221 according to the second embodiment. The rod 131 of the device is fixed to a wall of the stator 229 (see fig. 6). The space inside of the stator 229 is partially filed by air 301 and partially by oil 302.

In a fourth exemplary embodiment, the slip ring device 100 is as described in the first embodiment with the following differences. The body 1 1 1 is made longer that the cavity in the shaft 221 into which the body 11 1 is to be mounted, or more precisely, the cavity and the shaft 221 are shortened. The body 1 1 1 thus protrudes out of the cavity - a part of the outer section 1 16 is located on the outside. Outer wall of the body 1 11 thus has a cylindrical surface not covered by the shaft 221 . The oil 302 seal 225, which in the first embodiment was in a sliding contact with the shaft 221 , is in contact with the body 1 1 1 instead. The shaft 221 and the seal 225 have the same diameter as in the first embodiment, but the cavity and the body 11 1 have larger diameters. The body 1 1 1 is thus larger, while the seal 225 has the same size and the seal-contacting body surface 1 19 has the same velocity (for some given value of rpm) as in the first embodiment, so the increase in the size of the device has no impact on wear of the seal 225. The fourth embodiment is shown in figs. 10 and 12.

The increased size of the body 1 11 allows for using larger contact rings 1 17 and brushes 135, and also for larger coolant passage 222. The device in this embodiment thus has decreased electrical resistance of the sliding electrical contact and improved cooling. The increase in the diameter of the body 11 1 without change in size of the seal 225 or of the outer diameter of the shaft 221 can best be seen when comparing figs. 1 1 and 12. In fig. 12, which shows a schematic simplified drawing of the fourth embodiment, it can be seen that seal 225 is in contact with the seal-contacting body surface 1 19 and has the same size as in fig. 11 (depicting the first embodiment). There is however significantly more space inside of the device from fig. 12. In the fourth embodiment, there are also additional cooling ribs placed on the flange 1 14 (see fig. 10, where four ribs can be seen). The cooling air 301 passes around these ribs and thus contacts the flange 1 14 at a large surface area and thus cools it more.

Alternative embodiments:

The traction motor 200 can alternatively be made without the oil 302 circuit. The device can then be cooled by the air 301 passage only. In some embodiments, even the air 301 passage can be omitted and the heat from the slip ring device 100 can simply dissipate through the shaft 221 - these embodiments might however be limited in terms of traction power in order to not overheat the device.

Alternatively, the air 301 passage can be omitted, or at least the fan 1 18 can be omitted, and sufficient cooling can be maintained by the oil 302 coolant passage 222 only.

The oil 302 passage can in some embodiments be in contact with the body 1 1 1 only at the bottom of the chamber 112, i.e., the base of the cylindrical shape of the body 1 1 1. There are thus no passages around the body 1 1 1 in radial direction in such embodiments. Cooling through the bottom can be sufficient for keeping the device at suitable temperatures and omitting the part of the passage next to the body 1 1 1 simplifies construction of the shaft 221 and the motor 200.

In another alternative embodiment, the device can have alternative or additional fan 1 18 placed on the perimeter of the open end 1 13 of the body 1 11.

The polarity of the brushes 135 and contact rings 1 17 can be reversed in some embodiments.

The materials used in the first embodiment can be different. E.g., the bronze can be replaced by copper/aluminium or vice versa, the insulation 303 can be made from any other suitable non-conductive material, the rod 131 can be made from steel or other sufficiently strong material, the body 1 1 1 can be made from aluminium etc.

The number of brushes 135 or their shape or material, shape of the brush holder 134, number of oil 302 passage branches or outlets, outer shape of the shaft 221 , dimensions of the chamber 112 and flange 1 14, and other parameters can also be different than depicted. A skilled person can readily choose these parameters as suitable for their desired application without deviating from the scope of the invention.

Other features of each alternative embodiment can be implemented as described in another alternative embodiment and/or as described in the first embodiment or fourth embodiment.

List of reference numbers

100 Slip ring device

200 Motor

110 Rotor part 221 Shaft

111 Body 222 Coolant passage

112 Chamber 223 Winding

113 Open end 224 Ring connector

114 Flange 225 Seal

115 Inner section 226 Bearing

116 Outer section 227 Shaft opening

117 Contact ring 228 Rotor

118 Fan 229 Stator

119 Seal-contacting body surface 230 Rotor axis

130 Stator part 301 Air

131 Rod 302 Oil

132 Fixation end 303 Insulation

133 Free end 304 Lead

134 Brush holder

135 Brush

136 Spring member

137 Brush connector

Claims

1. Slip ring device (100) for an inside of a traction motor (200) shaft (221 ), wherein the slip ring device (100) comprises a rotor part (1 10) and a stator part (130) characterized in that

• the rotor part (1 10) comprises a hollow body (1 1 1 ) for mounting into a cavity in the shaft (221 ), the body (1 1 1 ) comprising a chamber (112) which has an open end (1 13) and which is divided by a flange (114) into an inner section (1 15) and an outer section (1 16),

• wherein the outer section (1 16) is delimited at one end by the flange (1 14) and at an opposite end by the open end (113) of the chamber (1 12),

• wherein the stator part (130) comprises a rod (131 ) which has a fixation end (132) for fixing to a stator (229) of the traction motor (200) and a free end (133), wherein the rod (131 ) extends through the outer section (1 16) of the chamber (1 12) into the inner section (115) of the chamber (112),

• wherein the rotor part (1 10) comprises two contact rings (1 17), one attached to the flange (1 14) in the inner section (1 15), and one attached to an opposite side of the flange (1 14) in the outer section (116),

• wherein the stator part (130) comprises two brush holders (134) which are carried by the rod (131 ), wherein one brush holder (134) is in the inner section (1 15) and one brush holder (134) is in the outer section (1 16) and each brush holder (134) contains at least one brush (135) which is in a sliding contact with one of contact rings (117).

2. The slip ring device (100) according to claim 1 wherein each contact ring (1 17) has a contact surface for contact with a brush (135), wherein contact surfaces of both contact rings (117) are perpendicular to a longitudinal axis of the slip ring device (100).

3. The slip ring device (100) according to any preceding claim wherein each brush holder (134) further contains at least one spring member (136) for biasing the at least one brush (135) against a respective contact ring (1 17).

4. The slip ring device (100) according to any preceding claim wherein the slip ring device (100) comprises a cooling air (301 ) passage extending through the rod (131 ), around the free end (133) of the rod (131 ), around the brush holders (134), between the rod (131 ) and the flange (1 14), and through the open end (1 13) of the chamber (1 12).

5. The slip ring device (100) according to claim 4 wherein the slip ring device (100) comprises at least one fan (1 18) for increasing air flow through the passage, wherein the at least one fan (1 18) is attached to the rotor part (1 10), wherein the fan (1 18) is adjacent to the free end (133) of the rod (131 ) and/or adjacent to the open end (1 13) of the chamber (1 12).

6. The slip ring device (100) according to any preceding claim wherein the body (1 1 1 ) has a cylindrical outer shape, wherein the cylindrical shape has a first base which is open and forms the open end (113) of the chamber (1 12) and a second base which is closed.

7. The slip ring device (100) according to any preceding claim wherein the rod (131 ) comprises a power supply passage containing a brush connector (137), wherein each brush (135) in the inner section (1 15) is connected to this brush connector (137).

8. Shaft (221 ) for a traction motor (200), the shaft (221 ) comprising a cavity which is open at one end of the shaft (221 ), characterized in that the shaft (221 ) further comprises the slip ring device (100) according to any preceding claim, wherein the body (1 1 1 ) of the slip ring device (100) is mounted in the cavity of the shaft (221 ).

9. The shaft (221 ) according to claim 8 wherein the shaft (221 ) further comprises a coolant passage (222) for circulating a coolant through the shaft (221 ), wherein a part of the coolant passage (222) is delimited by the body (1 1 1 ) of the slip ring device (100).

10. The shaft (221 ) according to any one of claims 8 or 9 wherein the body (1 1 1 ) of the rotor part (1 10) protrudes out of the cavity of the shaft (221 ), wherein a protruding part of the body (1 11 ) comprises a cylindrical outer surface for contact with a seal (225).

1 1 .Traction motor (200) comprising a rotor (228) and a stator (229) characterized in that it comprises the shaft (221 ) according to any one of claims 8 to 10, wherein the rotor (228) is attached to the shaft (221 ), the shaft (221 ) is rotatably connected to the stator (229) and the fixing end of the rod (131 ) is attached to the stator (229), wherein a longitudinal axis of the rod (131 ) coincides with a rotational axis of the rotor (228).

12. The traction motor (200) according to claim 11 wherein the rotor (228) comprises a rotor winding (223) and at least two ring connectors (224), wherein each ring connector (224) passes through the shaft (221 ) and connects one of the contact rings (1 17) to the rotor winding (223).