Description The invention relates to an assembly with movable parts comprising a conductive fluid for earth return and avoiding the current passage in bearings.

Earth return is a major issue for electric powered machines equipped with bearings. In particular most of railway trains are powered by electricity. Electric current flows from the upper electrified contact line to the electric traction vehicle and then to the railway tracks. Electric current flows also from a carriage wagon to another one. In both cases, the current flows from the wagon body to the railway bogie, and then crosses the wheelset to the railway tracks to close the circuit.

A standard railway bogie comprises:

- a wheelset comprising an axle wherein wheels are mounted on the axle and an axlebox wherein rolling bearings are mounted for supporting the rotating axle;

- a railway bogie frame which can support the wagon body;

- suspensions mounted on an axlebox link arm and connected to the frame railway bogie via an adapter assembly; and

- an electric wire with one end attached to the frame railway bogie and the other end to the axlebox.

Inside the axlebox bearings the electrical current in combination with the rotation of the rolling elements creates some electrical arcs which can severely damage the bearing. Moreover, the structure of the lubricant inside the bearings might change under the influence of the current flow. The lifetime of the axlebox rolling bearings is then dramatically reduced.

Therefore the current must be deviated in the axlebox to avoid the bearings. The main issue is that the current has to pass from the fixed cover to the rotating axle: a specific assembly has to be provided between these two elements for the current passage. For this purpose, EP0579123 A1 discloses a contact disc rotating with the wheelset axle on which it is attached and a contact element arranged inside the axlebox cover. Then the current can flow from the axlebox cover to the contact element, and then to the contact disc attached to the wheelset axle.

However, such an earth return device presents two major drawbacks. First, the contact disk in rotation against the contact element may deteriorate. Then the contact between the two parts is not perfectly done and the current can pass whether as electric arcs from the one to the other or whether the current can go via another non- controlled path.

Second, even if the contact between the two elements is perfectly done some electric arcs can occur due to the combination of the current flow and the rotation of a conductive element.

The patent application EP0168676 A2 and the patent EP1136340 B1 disclose carbon brushes mounted outside the bearings and permitting the current passage from the axlebox cover to the wheelset axle. The major drawback of such an assembly is that the carbon brushes wear and generate carbon particles. The carbon brush size decreases with use due to the friction with rotating parts. Then additional elements such as springs have to be integrated in the axlebox in order to maintain contact between the carbon brushes and the cover. Moreover, a complex sealing assembly has to be provided in order to avoid wear carbon particles entering the rolling bearings and affecting the lubrication and the contacting surfaces between the rolling elements and the rings.

One object of the present invention is to overcome these drawbacks by providing an improved assembly with movable parts comprising an earth return assembly, so that the electrical current flow is achieved without risk of electric arcing and with a bearing optimal protection against wear particles.

According to the invention, such an assembly with movable parts is characterized in that it comprises a sealed chamber containing a conductive fluid and being located between a non-rotating element through which electric current goes and a rotatable element solidar in rotation with a rotatable axle. At least one rolling bearing supports the axle rotation. The at least one rolling bearing comprises a rotatable ring fast with the rotatable axle, a non-rotating ring fast with a housing of the assembly and a raceway sealed chamber located between the two rings wherein rolling elements are located.

The non-rotating element is not in contact with the at least one bearing, for avoiding any direct current passage between them. Moreover, the non-rotating element is electrically insulated from elements with lower electric potential, in particular any rotatable parts in the assembly. The non-rotating element is the last passage point for the electric current on non-rotatable parts of the assembly before flowing to the rotatable parts of the assembly.

In normal operation, the electric current is supplied to the non-rotating element from outside devices (i.e. railway coach, wires, axlebox cover, etc.). The electric current flows from the non-rotating element to the rotatable element via the fluid contained in the sealed chamber defined between them. Then the current flows from the rotatable element to the rotatable axle. Finally the current flows from the axle to ground, via eventual in-between devices.

According to further aspects of the invention, which are advantageous but not compulsory, such an assembly may incorporate one or several of the following features as long as there is no contradiction: - The non-rotating ring of the at least one bearing is directly maintained in position in the assembly housing by a cover. The cover and this bearing ring are non-rotatable parts.

- The non-rotating ring of the at least one bearing is maintained in position in the assembly housing by an annular spacer ring. The said annular spacer ring is fast with a cover. The cover, the annular spacer ring and this bearing ring are non-rotatable parts.

- The rotatable ring of the at least one bearing is maintained in position on the rotatable axle between two contact surfaces defined with a backing ring on the one end, and the non-rotating element on the other end. This contact with the rotatable element may allow the electric current passage. - An electrically insulator ring made from a non-electrically conductive material (polymer or synthetic) is mounted between the cover and the non-rotating ring of the at least one bearing. Then the two elements are electrically insulated from each other. The current coming from the wire connected to the cover cannot pass from the cover to the bearing non-rotating ring which is electrically insulated.

- The rotatabie element is provided with surrounding edges and the non-rotating element is located on the surrounding surface of the rotatabie element for defining a sealed chamber.

- The non-rotating element defines a sealed chamber with the outside surrounding surface of the rotatabie element edges.

- The non-rotating element defines a sealed chamber with the inside surrounding surface of the rotatabie element edges.

- The rotatabie element is provided with a base supporting the surrounding edges. Openings are done on said base for engaging fixation means made in conductive material and attaching the rotatabie element to the axle. The electric current can flow from the rotatabie element to the axle via the conductive fixation means.

- The non-rotating element is blocked in rotation by a lock pin provided on the cover. The contact surface between the cover and the non-rotating element allows the electric current passage.

- Plain bearings are mounted between the rotatabie element and the non-rotating element for allowing the rotation of the said rotatabie element.

- The seal rings and the plain bearing are made from a non-electrically conductive material, such as synthetic or polymer material (not necessary the same material). The non-rotatable and the rotatabie elements are electrically insulated from each other.

- The sealed chamber is sealed by sealing rings located between the non-rotating element and the rotatabie element.

- The conductive fluid has a low ohmic resistance.

- The conductive fluid is a liquid with low viscosity. Indeed in case of high temperature due to friction, a high-viscosity fluid such as grease can change of state

(liquefaction) and be deteriorated.

- The non-rotating element and/or the rotatabie element is provided with at least one opening and at least one plug in order to fill up with the conductive fluid the sealed chamber. - An insulator ring is mounted between the rotatable element and the rotatable ring of the at least one bearing at their contact surface for avoiding any direct current passage between them.

- The electric current is coming from an outside device and is transferred to the non- rotating element thanks to an electric wire.

- The non-rotating element is an extension of the cover and both together form one piece.

The present invention is a carbon-less assembly without carbon particles allowing a lighter bearing sealing assembly. Moreover electrical arcs cannot occur since the volume between the non-rotatable parts and the rotatable parts is full of conductive fluid.

Another advantage of the present invention is that the earth return assembly comprising the rotatable element directly maintains the bearing inner ring without additional device.

Even if the sealed chamber contains a limited volume of conductive fluid, the sealed chamber is in contact with an important annular surface between the rotatable and the fixed part. Moreover, the empty volume remaining between the surrounding sealed chamber allows the fixation means mounting without any additional device or more complex parts.

Such an assembly with movable parts can be an axlebox mounted on railway bogie with a rotatable axle or any other type of assembly with rotatable or translatable parts without being a limitation of the invention.

According to a further embodiment, the invention concerns a railway bogie comprising at least one railway axlebox according at least one of the preceding embodiments.

Further advantages, features and details of the invention will be described with reference to the appended and non-limiting drawings wherein:

- Figure 1 is a perspective view of a railway axlebox; and

- Figure 2 is a longitudinal cross section of the railway axlebox. According to the non-limiting Figures 1 and 2, the assembly 1 with movable parts is a railway axlebox comprising a housing 2. The housing 2 extends to the left and the right side by two link arms 3 on which suspensions (not shown) are mounted on each of said link arms 3.

An electric wire 4 has a first end connected to the frame railway bogie (not shown) and a second end connected to the axlebox cover 5. This second end of the wire 4 is held by a bolt 6 on the cover 5. The cover 5 closes the axlebox housing 2 wherein two rolling bearings 7 are mounted. The rolling bearings 7 are each provided with an outer ring 8 in close abutment with the inner surface of the housing 2 and an inner ring 9. A raceway sealed chamber is defined between the two rings 8 and 9 wherein rolling elements 10 are located.

The outer ring 8 is a non-rotating ring and is fast with the housing 2 between a contact surface 11 and a contact surface 13 with a annular spacer ring 12. The said annular spacer ring 12 is fast with the cover 5. One end of an axle 14 is force fitted in the inner ring 9 for coupling rotation. The inner ring 9 is a rotatable ring and is in direct contact with both a backing ring 15 and a rotatable element 17. It defines a contact surface 16 with the backing ring 15 and a contact surface 18 with the rotatable element 17. The backing ring 15 is also fast with the axle 14 by shoulders.

The rotatable element 17 has a cup shape and is provided with edges 19 and a base 20. The base 20 defined an empty volume 21 and is provided with openings 22 in which fixation means 23 are inserted for attaching the rotatable element 17 to the axle 14. An upper head of the fixation means 23 can fit in the empty volume 21 of the rotatable element 17. The fixation means 23 are made in a conductive material, such as metal

The edges 19 are provided with an outer surrounding surface wherein a groove 25 is machined between surrounding shoulders 24. A non-rotating element 26 is inserted into this groove 25 between the shoulders 24 for defining a sealed chamber 27. The sealed chamber 27 is annular and contains a conductive fluid being able to ensure the current passage.

The sealed chamber 27 is sealed by two annular sealing rings 28 located between the bottom surface of the groove 25 and the outer surrounding surface of the edges 19 of the non-rotating element 26.

A single opening with a plug 29 is provided on the non-rotating element 26 in order to fill up with the conductive fluid the sealed sealed chamber 27.

The cover 5 is provided with a lock pin 30 in order to block in rotation the non-rotating element 26.

Since the rotatable element 17 rotates with the axle 14 whereas the non-rotating element 26 is blocked in rotation, plain bearings 31 are located between the groove 25 and the non-rotating element 26. Plain bearings 31 have an L-shape for covering the lower contact surface between the bottom surface of the groove 25 and the end of the non-rotating element edge and for covering the inside contact surface between the inside surface of the shoulder 24 and the outer surface of the non-rotating element edge. The rotation of the rotatable element 17 is allowed thanks to the deformation of the conductive fluid in the sealed chamber 27.

The non-rotating element 26 and the rotatable element 17 are never in contact since seal rings 28 and plain bearings 31 are located between them. Seal rings 28 are made in a non-conductive material, such as synthetic or polymer material. Plain bearings 31 are also made in non-conductive material, such as synthetic or polymer material.

An insulator ring 32 is mounted between the cover 5 and the annular spacer ring 12. The insulator ring 32 is made in a non-conductive material, such as synthetic or polymer material.

In normal operation, the electric current is supplied to the cover 5 by the wire 4. Then the current goes to the non-rotating element 26 thanks to the lock pin 30 providing contact. The current goes from the fixed non-rotating element 26 to the rotatable element 17 via the conductive fluid contained in the sealed chamber 27. The current goes to the axle 14 whether via the fixation means 23 or whether via the bearing inner ring 9. Finally the current goes to the railway tracks from the axle 14 via the wheels. The assembly comprising the rotatable element 17 and the non-rotating element 26 wherein is located the sealed chamber 27 is entirely located inside the annular spacer ring 12 and covered from the outside by the cover 5.

An additional protection can be provided to the assembly by mounting an insulator ring between the rotatable element 17 and the inner ring 9 at the contact surface 18.

According to a further embodiment, a railway bogie may comprise at least one railway axlebox 1 according at least one of the preceding embodiments. The said railway bogie comprises:

- a wheelset having at least one rotatable axle 14, wheels being mounted on the at least one axle and the said at least one railway axlebox 1;

- at least one hydraulic suspension mounted on at least one link arm 3 on the at least one axlebox;

- a railway bogie frame; and

- an adapter assembly attached to the said railway bogie frame on one end and to the said at least one hydraulic suspension on the other end, in order to have the wheelset able to support the railway bogie frame.

Nomenclature

1. Assembly

2. Housing

3. Link arm

4. Electric wire

5. Cover

6. Bolt

7. Rolling bearing

8. Non-rotating ring

9. Rotatable ring

10. Rolling elements

11. Contact surface

12. Annular spacer ring

13. Contact surface

14. Axle

15. Backing ring

16. Contact surface

17. Rotatable element

18. Contact surface

19. Edges

20. Base

21. Empty volume

22. Opening

23. Fixation means

24. Surrounding shoulder

25. Groove

26. Non-rotating element

27. Sealed chamber

28. Sealing ring

29. Plug

30. Lock pin

31. Plain bearings

32. Insulator ring