Multi-part rail wheel and wheel set for a rail vehicle, in particular a low-floor rail vehicle

Description

[0001] The invention relates to a multi-part rail wheel with a wheel rim, with a wheel body made of a light metal material, which has a hub opening in which a contact surface is provided on which, in use, an outer ring of a rolling bearing is supported or which, in use, is connected to the outer surface of a shaft or a shaft stub, and with at least one elastic body arranged between the wheel rim and the wheel body, by means of which the wheel rim is elastically supported on the wheel body.

[0002] Such multi-component rail wheels are also known in technical language as "hybrid rail wheels" and are used particularly on so-called "inverted portal axles" for low-floor vehicles such as trams or light rail vehicles. Examples of such rail wheels are shown on the applicant's website at the URLs https: / / www.bochumer-verein.de / das-superleichte-bvv-hybridrad-mit-aluminiumfelge-zweilteilig / and https: / / www.bochumer-verein.de / dassuperleichte-bvv-hybridrad-mit-aluminium-felge-dreiteilig / , both accessed on November 17, 2021, and are described in detail, for example, in WO 2018 / 046745 A1.

[0003] The invention also relates to a wheelset equipped with such rail wheels for a rail vehicle, for example for a low-floor rail vehicle.

[0004] Examples of wheelsets for low-floor vehicles equipped with rail wheels of the type presented here in loose bearing are shown at the URL https: / / www.bochumer-verein.de / die-bvv-niederflur-radsaetze-mitlosradlagerung / , accessed on November 9, 2021.

[0005] The loose wheels of low-floor wheelsets impose specific requirements on the design of the hub opening that accommodates the wheel bearing due to the floating bearing arrangement. A brake disc, actuated by a braking device mounted on the vehicle, may be attached to the respective rail wheel, or the wheel may be coupled to a drive system to directly transfer drive energy to the wheel during operation. This attachment of a brake disc or components required for coupling to the drive system presents a significant practical challenge for hybrid rail wheels, where the wheel body is made of a lightweight metal, particularly aluminum, due to the considerably lower fatigue strength properties of these materials.

[0006] However, rail wheels of the type described here can be used not only with low-floor wheelsets, but also with conventional wheelsets or with special designs such as independent wheel suspensions.

[0007] Unless otherwise stated, all of the mechanical properties of the materials used to manufacture rail wheels according to the invention, as specified in the present text, have been determined in accordance with DIN EN 13262 and the FKM guideline "Calculation of strength of machine components".

[0008] As a rule, the wheel bodies of rubber-sprung rail wheels are manufactured from high-strength steel alloys such as 42CrMo4, 34CrNiMo6 or 30CrNiMo8 according to DIN EN ISO 683, which, with the usual surface roughness of the components, have a permissible fatigue strength of 206 MPa, 225 MPa or even 244 MPa below the safety requirements applicable to railway vehicles.

[0009] However, if the wheel bodies are manufactured from high-strength wrought aluminum alloys with sufficient corrosion resistance, such as the aluminum alloys known under EN material number EN-AW 6082 or EN-AW 6110A according to DIN EN 13981-4, only fatigue strengths of typically 35 to 55 MPa are available. To nevertheless enable permanently secure clamping of the elastic elements between the steel wheel rim and the wheel body formed from a light alloy, a hybrid wheel has been proposed in the aforementioned WO 2018 / 046745 A1. This hybrid wheel incorporates a counter bearing made of a higher-strength material, particularly steel, which is shrunk, pressed, or adhesive-shrink-fitted to the inside of the wheel body and against which the clamping action is applied.Such a counter bearing can also be used for fastening the brake disc or drive clutch by means of a suitable screw fastening and allows, for example, a wheel body made of one of the aforementioned wrought aluminum alloys to be given the required larger stress cross-sections, so that the cyclic stresses occurring in the wheel body during use are within the permissible range of the material used.

[0010] Practical testing has shown that, despite the measures explained above, hybrid rail wheels are subject to unacceptable wear, particularly in the area of ​​the hub opening of their wheel body, which (in the case of a loose wheel bearing) accommodates the rolling bearings required for the rotatable bearing of the wheel on the respective associated axle journal.

[0011] Against this background, the task arose to create a rail wheel that reliably meets the requirements placed on its wear resistance.

[0012] Furthermore, a wheelset for a rail vehicle, especially for a low-floor vehicle, should be specified that has an optimized service life.

[0013] With regard to the rail wheel, the invention has solved this problem by providing such a rail wheel with at least the features specified in claim 1.

[0014] With regard to the wheelset, the invention has solved the aforementioned problem by equipping such a wheelset with rail wheels designed according to the invention.

[0015] Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below, as is the general concept of the invention.

[0016] Accordingly, a multi-part rail wheel according to the invention, in accordance with the prior art described above, comprises a wheel rim (preferably made of a wear-resistant steel alloy), a wheel body made of a light metal material, which has a hub opening in which a contact surface is provided on which, in use, an outer ring of a rolling bearing is supported or which, in use, is connected to the outer surface of a shaft (e.g., of a wheelset) or a shaft stub (e.g., of an independent wheel suspension), and an elastic body arranged between the wheel rim and the wheel body, by means of which the wheel rim is elastically supported on the wheel body. Particularly in the case of a loose wheel bearing, at least two contact surfaces are preferably provided in the hub opening on which, in use, the outer rings of two rolling bearings are supported.For use with a rigid wheelset, a single contact surface in the hub opening is sufficient to create a secure connection (especially a force-fit or friction-fit connection) between the contact surface and the outer surface of a shaft or shaft stub. It may be provided that two or more elastic elements are arranged between the wheel tread and the wheel body, by means of which the wheel tread is elastically supported against the wheel body.

[0017] According to the invention, at least the contact surface in the hub opening of the wheel body is coated with an oxide layer produced by electrochemical anodizing. If two or more contact surfaces are provided in the hub opening of the wheel body, it can be provided that all contact surfaces are coated with an oxide layer produced by electrochemical anodizing.

[0018] According to the invention, a wheelset for a rail vehicle comprises two rail wheels designed according to the invention, the contact surfaces of which are connected to the outer surface of a shaft or shaft stub. The connection is preferably a force-fit or friction-fit connection, which can be produced, for example, by press-fitting and / or shrink-fitting.

[0019] The wheelset can, for example, be a wheelset for a low-floor rail vehicle. According to the invention, a wheelset for a low-floor rail vehicle comprises a portal axle, which has an axle center section extending along a longitudinal axis and two axle journals, one of which is located on a first end section of the axle center section and a second of which is located on a second end section of the axle center section opposite the first end section, wherein the axle journals are oriented outwards away from the axle center section, as well as two rail wheels designed according to the invention, which are rotatably mounted in a floating bearing on the axle journals of the portal axle via at least one rolling bearing each, the bearing having an inner ring on the respective axle journal and bearinging with a circumferential surface of an outer ring against the contact surface provided in the hub opening of the wheel body of the rail wheel.

[0020] The invention is based on the understanding that, in the case of a hybrid wheel whose wheel body is made of a light metal material and which is to be mounted loosely on an axle of a wheelset for a rail vehicle, additional measures are necessary to prevent interactions between the inner surface of the hub opening of the wheel body and the outer ring of the rolling bearings by which the rail wheels are mounted on the axle journal of the wheelset. According to the invention, these measures consist of subjecting the hub opening of the wheel body, which serves as a receptacle for the rolling bearing, in particular designed as a roller bearing, to a special surface treatment, namely electrochemical anodizing.

[0021] According to the invention, this treatment, also known in technical language as "anodizing", selectively creates an oxide layer at least on the contact surface forming a section of the inner surface of the hub opening of the wheel body, on which the outer ring of the rolling bearing rests during use or which is connected during use to the outer surface of a shaft or shaft stub, the thickness and density of which exceeds the thickness and density of the natural oxide layer that forms naturally on the surface of the wheel body as a result of contact between the light metal material of the wheel body and the ambient atmosphere.

[0022] Surprisingly, it has been shown that this artificial oxide layer, forced through targeted treatment, is sufficient to increase the wear and abrasion resistance of the contact surface to such an extent that the requirements placed on the service life of the rail wheel are reliably met.

[0023] This is also aided by the fact that the oxide layer provided according to the invention ensures high corrosion resistance in the area of ​​contact between the wheel body, which consists of light metal, and the outer ring of the rolling bearing, which is usually made of a rolling bearing steel known for this purpose, or the material of the outer surface of the shaft or shaft stub.

[0024] A further advantage of the oxide layer produced by electrochemical anodizing, which is provided according to the invention at least in the area of ​​the contact surfaces for the respective rolling bearing or for the shaft or for the shaft stub in the bearing opening of the wheel body, is that the oxide layer acts as an electrically insulating barrier layer. In this way, it prevents unintentional current flow – for example, from the wheel body via the wheel bearing to the axle journal – and thus reliably prevents bearing damage that could otherwise be caused by current flow.

[0025] Typically, rail wheels of the type according to the invention – when used in a loose wheel bearing arrangement – ​​are mounted on their respective axle journals via two rolling bearings, such as roller bearings. In this case, which is important for practical purposes, there are therefore two contact surfaces in the bearing opening, which are coated with an oxide layer produced by electrochemical anodizing in the manner according to the invention.

[0026] The resistance of a rail wheel according to the invention can be further improved when used in a loose wheel bearing by not only covering the contact surface assigned to the respective rolling bearing with an oxide layer in the manner of the invention, but also by ensuring that the contact surface forms a section of an inner surface of the hub opening of the wheel body and that the entire inner surface of the hub opening is covered with the oxide layer produced by electrochemical anodizing.

[0027] It has proven particularly advantageous if the wheel body is also coated, at least partially, on its free outer surface outside the hub opening with the oxide layer formed according to the invention by electrochemical anodizing. This has the advantage that even on the weather-exposed outer surface of the wheel body, there is high corrosion resistance and, at the same time, increased surface resistance to mechanical attacks, such as those that can occur during use, for example, from flying gravel. The resistance to corrosion and mechanical damage achieved by the oxide layer produced according to the invention is so high that additional measures, such as painting, can be dispensed with.The complex inspections for integrity required for color-coated rail wheels under current technology, and any necessary repair work, can thus be reduced to a minimum.

[0028] In order to make the most comprehensive use of the advantages of the oxide layer provided according to the invention, the entire wheel body can be covered with the electrochemically produced oxide layer.

[0029] To clamp the elastic body between the wheel tread and the wheel body, a clamping device clamped against the wheel body can be provided in a manner known per se (see WO 2018 / 046745 A1). This is typically designed as a clamping ring that sits on a suitable circumferential shoulder of the wheel body.

[0030] If the optional clamping element of a rail wheel according to the invention is also to be given optimized stability and corrosion resistance, this can likewise be achieved by coating the clamping element, at least partially, with an oxide layer produced by electrochemical anodizing. Here, it proves particularly advantageous if the clamping element is coated with an oxide layer produced by electrochemical anodizing, at least in the area of ​​its surface coming into contact with the elastic body.

[0031] If a connection zone for an electrically conductive cable connection ("current bridge") is provided on the outer surface of the wheel body and / or the optional clamping element, the outer surface of the wheel body, the wheel tread, and / or the optional clamping element, with the exception of the connection zone, may be coated with the oxide layer produced by electrochemical anodizing. The respective connection zone should be excluded from the oxide layer to ensure a minimized electrical contact resistance between the connected cable and the respective component ("wheel body" or "clamping element") to which the electrically conductive cable connection is attached.

[0032] Methods for targeted electrochemical anodizing are well known to those skilled in the art. If the wheel body, as preferred by the invention, is made of an aluminum alloy, the naturally occurring oxide layer can be thickened by a factor of 50 to 5000 using known anodizing methods. Typically, the thickness of the oxide layer thus produced, as provided for in the invention, is 10 µm to 160 µm, and in particular 30 µm to 140 µm.

[0033] For the electrochemical production of the oxide layer provided for in the invention, the wheel body to be treated is placed in a bath consisting of an electrically conductive liquid, the electrolyte, and connected to a DC voltage source, so that it serves as the anode in the electrochemical process. Sulfuric acid or oxalic acid is typically used as the electrolyte. Additionally, a cathode, for example a rod-shaped one, typically made of stainless steel, lead, or aluminum, is immersed in the electrolyte bath. In the resulting electric field, oxygen-containing anions are formed at the cathode with the release of hydrogen and migrate to the surface of the wheel body. There, they react with the aluminum material of the wheel body, forming an aluminum oxide layer that adheres firmly to the exposed surfaces of the wheel body.The oxide layer thus formed comprises a thin barrier layer, which is almost pore-free, completely dense, and electrically insulating, and a significantly thicker, slightly porous, and electrically conductive top layer, which is formed by a chemical reaction of the barrier layer with the electrolyte. Areas of the wheel body that are to remain free of the oxide layer can be masked in a known manner, for example, using a lacquer known from the prior art. Further explanations of known methods for the electrochemical anodizing of a light metal material suitable for the purposes of the invention can be found in Galvanotechnik by Nasser Kanani; Hanser-Verlag, Munich; 3rd edition 2020.

[0034] The invention proves particularly advantageous when the wheel body of a rail wheel according to the invention is made of an aluminum material, in particular an aluminum wrought alloy of the type mentioned above. In this embodiment, the oxide layer produced by electrochemical anodizing consists of at least 87.1% by mass of Al₂O₃ and the remainder of other oxides formed during the electrochemical anodizing process from oxide-forming alloying elements that are present in the aluminum material of the wheel body in addition to aluminum. Maximized Al₂O₃ content proves particularly advantageous with regard to optimizing resistance. Accordingly, an advantageous embodiment of the invention provides that the oxide layer produced by electrochemical anodizing consists of at least 95.0% by mass of Al₂O₃.

[0035] A wheelset according to the invention for a rail vehicle comprises two rail wheels designed according to the invention, which are preferably connected with their contact surface to the outer surface of a shaft or of a single wheel which is connected to a shaft stub, for example by a force-fit or friction-fit connection.

[0036] A wheelset according to the invention for a low-floor rail vehicle comprises a portal axle comprising an axle center section extending along a longitudinal axis and two axle journals, one of which is located on a first end section of the axle center section and a second on a second end section of the axle center section opposite the first end section, wherein the axle journals are oriented outwards away from the axle center section, and two rail wheels designed according to the invention, which are rotatably mounted in a floating bearing on the axle journals of the portal axle via at least one rolling bearing each, which sits with an inner ring on the respective axle journal and bears with a circumferential surface of an outer ring against the contact surface provided in the hub opening of the wheel body of the rail wheel, wherein in practice typically two rolling bearings are provided for each of the rail wheels.

[0037] The invention will now be explained in more detail with reference to a drawing illustrating an exemplary embodiment. The drawing schematically shows: Fig. 1 shows a rail wheel mounted on an axle journal provided at one end section of a portal axle in a section along the Fig. 2 section line AA shown; Fig. 2 the rail wheel in a frontal view directed towards its free end face facing away from the portal axis; Fig. 3 a wheel body of the in the Figure 1 and 2 shown rail wheel in one of the Fig. 1 corresponding sectional view.

[0038] In the Figure 1 and 2A rail wheel 1 is shown, rotatably mounted on a pivot 2 of a portal axle 3. Alternatively, the rail wheel 1 can be non-rotatably connected to a shaft or a stub shaft. The pivot 2 is integrally formed with a cheek 4, which in turn is integrally formed with an axle center section 5 of the portal axle 3 such that the cheek 4 rests on an associated end section 6 of the axle center section 5, and the pivot 2 is supported laterally by the axle center section 5, pointing away from the cheek 4. To minimize the weight of the portal axle 3, a through-opening 7 is provided in the pivot 2, extending from the free end face of the pivot 2 to the side surface of the cheek 4 associated with the axle center section 5.

[0039] The portal axle 3 comprises a second arrangement of a side plate and a pivot pin, designed in the same manner, on which a rail wheel (not shown here) is mounted, designed according to the rail wheel 1. This second arrangement is mirror-symmetrical with respect to the center of the portal axle 3 compared to the arrangement formed by the side plate 4 and the pivot pin 2 with the rail wheel 1, and is provided at an end section of the axle center section 5 (also not shown here), which is formed at the end of the axle center section 5 opposite the first end section 6.

[0040] The rail wheel 1, the portal axle 3, and the second rail wheel mounted on it are part of a wheelset, which may include further components or devices in the conventional manner. These include, for example, a braking device for braking the rail wheels, a drive device for driving the rail wheels, and / or a spring-damper system by which the wheelset can be elastically coupled to the chassis of a low-floor rail vehicle, such as a tram, in a manner known per se. In this regard, Fig. 1 and Fig. 2 Only by way of example is a connecting element 26 shown, which is intended to receive a braking device (in particular a brake disc) or a drive device, and is attached to the wheel body 9 in the area of ​​a connection zone by means of clamping screws 27 which are screwed into counter bearings 27'.

[0041] The rail wheel 1 shown here as an example of the wheels of the wheelset is, in a manner known from the prior art explained at the beginning of this text, composed of several parts consisting of a wheel rim 8, a wheel body 9 and elastic bodies 10 arranged at regular intervals between the wheel rim 8 and the wheel body 9, by means of which the wheel rim 8 is elastically supported on the wheel body 9.

[0042] A clamping ring 11 is provided for clamping the elastic bodies 10 between the wheel tread 8 and the wheel body 9, which is attached to the wheel body 9 by means of clamping screws 12, which are screwed into counter bearings 12', in the manner described, for example, in WO 2018 / 046745 A1.

[0043] The wheel body 9 is electrically connected to the clamping ring 11 via the clamping screws 12 and the corresponding counter bearings 12'. The electrical connection between the wheel tread 8 and the wheel body 9 is established, for example, via a current bridge 13, as described in WO 2020 / 234286 A1. The cable lug at one end of the cable lug rests in a first connection zone 25 on the end face of the wheel tread 8 facing away from the portal axis 3, and the cable lug at the other end rests in a second connection zone 24 on the free end face of the clamping ring 11. Alternatively, the second connection zone 24 of the cable lug can rest on the free end face of the wheel body 9.

[0044] The wheel body 9 is made of an aluminum material, such as the wrought aluminum alloy standardized under the EN material number EN-AW 6082, and has a hub opening 14 through which the axle journal 2 of the portal axle 3, which is assigned to the rail wheel 1, is guided.

[0045] On the axle journal 2, two roller bearings 15, 16 are mounted in a known manner in a floating bearing arrangement. The outer rings 17, 18 of these bearings each bear against a contact surface 20, 21 provided on the inner surface 19 of the hub opening 14. The contact surfaces 20, 21 each occupy a section of the inner surface 19 of the hub opening 14. The position of the roller bearings 15, 16 on the axle journal 2 is secured by a cover 22 screwed to the end face of the axle journal 2.

[0046] The wheel body 9, made of aluminum alloy, was subjected to electrochemical anodizing before the assembly of the rail wheel 1. This anodizing was carried out in the manner already described above and is known per se. The anodizing process produced an oxide layer OX, 10 µm to 160 µm thick and consisting of at least 87.1% by mass of Al₂O₃, on the entire outer surface 23 of the wheel body 9, the inner surface 19 of its hub opening 14, and especially on the contact surfaces 20, 21.

[0047] As in Fig. 3As indicated by the outline of the wheel body 9, shown with a thicker line, the oxide layer OX completely covers the outer surfaces 23 of the wheel body 9 and the inner surface 19 of its inner opening 14 with the contact surfaces 20, 21, except for the connection surfaces for so-called grounding contacts. These contacts establish the electrical connection between the running gear of the rail vehicle and, via the current bridges 13, with the wheel tires 8 and thus with the rail. As such, the oxide layer OX not only provides optimal protection against corrosion and abrasive wear, but also, particularly in the area of ​​the contact surfaces 20, 21, electrical insulation, which prevents current flow from the axle journal 2 via the rolling bearings 16, 17 to the wheel body 8 and vice versa.To ensure an optimal electrical transition between the clamping ring 11 and the wheel body 8, the surfaces where contact occurs between the clamping screws provided for holding the clamping ring 11 on the wheel body 9 and the wheel body 9, as well as the connection points of the grounding contacts on the wheel body 9, can be covered by applying a covering agent known from the prior art, such as a suitable varnish, in order to prevent the formation of the oxide layer OX there.

[0048] Optionally, the clamping ring 11 can also be provided with an oxide layer produced by electrochemical anodizing to optimize its resistance to mechanical attacks, such as stone chips. For this purpose, the clamping ring 11 is electrochemically coated with the oxide layer in a manner known per se before the assembly of the rail wheel 1. Prior to the electrochemical treatment, the connection zones 24 on the clamping ring 11, in which the cable lugs of the current bridge 13 bear against the end faces of the clamping ring 11, are covered with a suitable covering agent, for example, a lacquer commonly used for this purpose in the prior art. In this way, the connection surfaces are kept free of the oxide layer, and an optimal electrical connection between the current bridge 13, the wheel rim 8, the clamping ring 11, and consequently the wheel body 9, is ensured.Alternatively, if the connection zone 24 is positioned not on the clamping ring 11 but directly on the wheel body 9, this zone is covered analogously to achieve an optimal electrical connection. The same procedure is followed for the connection points for the aforementioned grounding contacts on the wheel body. REFERENCE MARK LIST

[0049] 1 Rail wheel 2 Axle journal 3 Portal axle 4 Side of portal axle 3 5 Center section of portal axle 3 6 End section of the center section of portal axle 3 7 Through opening of axle journal 2 8 Wheel tire 9 Wheel body 10 Elastic bodies 11 Tension ring 12 Tension screws 12': Counter bearing (of the tension screw 12) 13 Current bridge 14 Hub opening of wheel body 8 15, 16 Rolling bearings 17, 18 Outer rings of the rolling bearings 15, 16 19 Inner surface of hub opening 14 20, 21 Contact surfaces for the outer rings 17, 18 of the rolling bearings 15, 16 22 Cover 23 Outer surface of wheel body 9 24, 25 Connection zones for the current bridge 13 26 Connecting element 27 Tension screw 27'Counter bearing (of the clamping screw 27) OX oxide layer

Claims

1. Multi-part rail wheel having a wheel tyre (8), having a wheel body (9) which consists of a light alloy material and has a hub opening (14) in which a contact surface (20, 21) is provided, on which an outer ring (17, 18) of a roller bearing (15, 16) is supported during use or which is connected to the outer surface of a shaft or a shaft stub during use, and having at least one resilient body (10) which is arranged between the wheel tyre (8) and the wheel body (9) and via which the wheel tyre (8) is resiliently supported on the wheel body (9), characterised in that at least the contact surface (20, 21) in the hub opening (14) of the wheel body (9) is covered with an oxide layer (OX) generated by electrochemical anodizing.

2. Rail wheel according to Claim 1, characterised in that the contact surface (20, 21) forms a section of an inner surface (19) of the hub opening (14) of the wheel body (9) and in that the inner surface (19) of the hub opening (14) is covered entirely with the oxide layer (OX) generated by electrochemical anodizing.

3. Rail wheel according to one of the preceding claims, characterised in that at least a section of an outer surface of the wheel body (9) is also covered with the oxide layer (OX) generated by electrochemical anodizing.

4. Rail wheel according to one of the preceding claims, characterised in that a clamping means (11), which consists of a light alloy material and is clamped against the wheel body (9), is provided in order to clamp the resilient body (10) between the wheel tyre (8) and the wheel body (9).

5. Rail wheel according to Claim 4, characterised in that the clamping means (11) is covered with an oxide layer (OX) generated by electrochemical anodizing at least in the region of its surface that comes in contact with the resilient body.

6. Rail wheel according to one of Claims 3 to 5, characterised in that a connecting zone (24) for connecting an electrically conductive cable connection is provided on the outer surface (23) of the wheel body (9) and / or the outer surface of the clamping means (11) and in that the respective outer surface with the exception of the connecting zone (24) is fully covered with the oxide layer (OX) generated by electrochemical anodizing.

7. Rail wheel according to one of the preceding claims, characterised in that the thickness of the oxide layer (OX) respectively present is from 10 µm to 160 µm.

8. Rail wheel according to one of the preceding claims, characterised in that the wheel body (9) consists of an aluminium material and the oxide layer (OX) generated by electrochemical anodizing consists of at least 87.1% by mass Al2O3 and a remainder of other oxides, which are formed in the course of electrochemical anodizing from oxide-forming alloy constituents that are contained in addition to aluminium in the aluminium material of the wheel body (9).

9. Wheel set for a rail vehicle, having two rail wheels (1) formed according to one of the preceding claims.

10. Wheel set according to Claim 9, characterised in that the rail wheels (1) are connected with their contact surface (20, 21) to the outer surface of a shaft or a shaft stub.

11. Wheel set according to Claim 9 for a low-floor rail vehicle, having a portal axle (3), having an axle middle part (5) extending along a longitudinal axis and two axle journals (2), one of which is seated on a first end section (6) of the axle middle part (5) and a second of which is seated on a second end section of the axle middle part (5), which is formed opposite to the first end section (6), the axle journals being aligned facing outwards from the axle middle part, and having two rail wheels (1) formed according to one of the preceding claims, which are rotatably mounted in floating bearing on the axle journal (2) of the portal axle (3) in each case via at least one roller bearing (15, 16) which is seated with an inner ring on the respective axle journal (2) and bears with a circumferential surface of an outer ring (17, 18) on the contact surface (20, 21), which is provided in the hub opening (14) of the wheel body (9) of the rail wheel (1).

12. Wheel set according to Claim 11, characterised in that the rail wheels (1) are in each case rotatably mounted on their assigned axle journal (2) of the portal axle (3) by means of two roller bearings (15, 16) and in that a contact surface (20, 21) in the hub opening (14) of the wheel body (9) of the rail wheels (1) is assigned to each roller bearing (15, 16).