A roller bearing as well as a cage suitable for such a roller bearing FIELD OF THE INVENTION The invention relates to a roller bearing comprising at least an outer ring, an inner ring, a number of rollers and a cage, which rollers and cage are at least partially disposed between the outer ring and the inner ring, which cage comprises at least a first and a second wave shaped holding plate, which holding plates are located opposite to each other, each holding plate comprises at least two pockets and a bridge part extending between two adjacent pockets, wherein in opposite pockets of two holding plates at least one roller of the number of rollers is located, wherein the bridge parts of the holding plates comprises means to allow displacement of the holding plates with respect to each other in a circumferential direction of the outer and inner rings.

The invention also relates to a cage suitable for such a roller bearing. BACKGROUND OF THE INVENTION In such a roller bearing, known from JP2008025783A, balls are located in opposite pockets of two holding plates. Due to the bridge parts extending between two adjacent pockets, the balls located in two adjacent pockets are spaced apart in circumferential direction.

The bridge parts of the wave shaped holding plates located opposite to each other are connected to each other by means of an elastic member. The elastic member is attached to the bridge parts by means of an adhesive.

Due to the elastic member, the opposite bridge parts and thus the opposite holding plates can move with respect to each other in the circumferential direction. Such a movement will occur, when forces are applied on the balls and via the balls on the pockets surrounding the balls, whereby the forces on one pocket differ from the forces on the opposite pocket, due to which the opposite pockets are being moved with respect to each other in the circumferential direction. Such different forces on opposite pockets may occur in case the due to production tolerances the dimensions of the pockets differ.

A disadvantage of the known roller bearing is that next to the holding plates, the cage comprises a number of elastic elements, being the same number as the number of balls, whereby each elastic member must be attached with each side with an adhesive to a bridge part.

This does not only have a negative effect on the manufacturing costs, but has also the disadvantage that in use the connection between the elastic member and the bridge part may get lost whereby the elastic member will get caught between the ball and the pocket or between the ball and the inner ring or outer ring. Furthermore there is a risk that by the grease used for the lubrication in the roller bearing, the elastic capacities of the elastic member will deteriorate. SUMMARY OF THE INVENTION

One of the objects of the invention is to provide a roller bearing whereby the disadvantages of the above mentioned roller bearing have been overcome.

This object is achieved by the roller bearing according to the invention in that the bridge part of the first holding plate comprises a passage, whilst the bridge part of the second holding plate comprises a lip located at least partially inside the passage, wherein in the circumferential direction the width of the lip is smaller than the width of the passage.

Since in the circumferential direction the width of the lip is smaller than the width of the passage, the lip is movable inside the passage in the circumferential direction. The lip can be moved until the lip abuts an edge of the passage. Since the passage as well as the lip are part of the holding plates no additional elements are needed to obtain holding plates which are movable with respect to each other in circumferential direction.

If desired the holding plates of the cage are only movable with respect to each other in circumferential direction during the production of the roller bearing. After the inner ring, the outer ring, the rollers and the cage are assembled and, preferably after the inner ring and outer ring have been rotated with respect to each other, the rollers have forced the holding plates of the cage to a preferred relative position, which position can be maintained by connecting the opposite bridge parts to each other, for example by welding or clamping.

An embodiment of the roller bearing according to the invention is characterized in that the lip of the second bridge part is a bent portion of the second bridge part.

By bending a portion of the second bridge part to form the lip, a lip is obtained in a simply, cheap and reliable manner.

Another embodiment of the roller bearing according to the invention is characterized in that the bridge part of one of the two holding plates comprises at least one extension, which extension is bent over the bridge part of the other holding plate.

By means of the extension the holding plates are kept together to prevent or limit axial movement of the bridge parts with respect to each other, however thereby still allowing movement of the holding plates with respect to each other in the circumferential direction. Since the extension forms part of the bridge part, the extension does not increase the number of parts of the roller bearing.

Another embodiment of the roller bearing according to the invention is characterized in that the bridge part of the first holding plate comprises the extension, which extension is located adjacent to the passage.

When producing the first holding plate, the passage and the extension can easily be made in the holding plate, for example by punching, stamping, laser cutting etc.

Another embodiment of the roller bearing according to the invention is characterized in that the bridge part of the first holding plate comprises two of said extensions, which are located on opposite sides of the passage.

By having two extensions located on opposite sides of the passage, a symmetrical construction around the passage and the lip located therein is obtained. This guarantees symmetric clockwise and counter-clockwise running of the bearing related to its clearance. The clearance is the difference between the width of the passage and the width of the lip. Another embodiment of the roller bearing according to the invention is characterized in that the at least first and second wave shaped holding plates are ring-shaped forming a ring-shaped cage.

By such a ring-shaped cage all rollers of the roller bearing can be maintained on the desired position by one single cage.

Another embodiment of the roller bearing according to the invention is characterized in that each of the at least first and second wave shaped holding plates is made as a whole.

In this manner each holding plate can easily, fast and reliable be manufactured. Furthermore, the cage is obtained by connecting the holding plates to each other without additional parts.

Another embodiment of the roller bearing according to the invention is characterized in that the rollers are balls.

Especially for balls, like in deep groove ball bearings or trust bearings, the cage as described above has proven to decrease the running noise and to increase the life of the bearing. Alignment of the two holding plates towards the balls reduces noise and friction.

The invention also relates to a cage for such a roller bearing, which cage comprises at least a first and a second wave shaped holding plate, which holding plates are located opposite to each other, each holding plate comprises at least two pockets and a bridge part extending between two adjacent pockets, wherein the bridge parts of the holding plates comprises means to allow displacement of the holding plates with respect to each other in a direction extending from one pocket to the adjacent pocket of the same holding plate, wherein the bridge part of the first holding plate comprises a passage, whilst the bridge part of the second holding plate comprises a lip located at least partially inside the passage, wherein in the circumferential direction the width of the lip is smaller than the width of the passage.

Such a cage can easily be made, for example of holding plates, each made as a whole, to allow movement of the holding plates with respect to each other, when in use different forces are applied on the opposite pockets surrounding a roller of a bearing. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective, partially cross section of a first embodiment of a roller bearing according to the invention,

figure 2 is a perspective view of a first holding plate of the roller bearing as shown in figure 1 ,

figure 3 is a perspective view of a second holding plate of the roller bearing as shown in figure 1 ,

figure 4 is a perspective view of the first and second holding plate as well as balls of the roller bearing as shown in figure 1 ,

figure 5 is an enlarged rear view of a detail of figure 4,

figure 6 is an enlarged front view of a detail of figure 4,

figure 7 is a perspective view of the first and second holding plate as well as balls of a second embodiment of a roller bearing according to the invention, during assembly of the plates,

figure 8 is a perspective view of the first and second holding plate as well as balls of the second embodiment of a roller bearing according to the invention, after assembly of the plates.

In the drawings, like reference numerals refer to like elements.

DESCRIPTION OF THE FIGURES

The figures 1 -6 show different views of an embodiment of a roller bearing 1 according to the invention. The roller bearing 1 is a deep groove ball bearing comprising an outer ring 2 with a radially inner surface providing a radially outer raceway 3, an inner ring 4 with a radially outer surface providing a radially inner raceway 5, a set of bearing balls 6 radially interposed between the outer raceway 3 and the inner raceway 5 and a cage 7 for holding the balls 6. The cage 7 comprises a first wave shaped holding plate 8 and a second wave shaped holding plate 9, which holding plates 8, 9 are located opposite to each other.

As can best be seen in the figures 2 and 4, the first wave shaped holding plate 8 is an endless ring, comprising a number of pockets 10, each with a partially hemispherical surface similar to the surface of the balls 6. Each set of two adjacent pockets 1 0 are connected to each other by means of a bridge part 1 1 .

Each bridge part 1 1 comprises at least a relatively flat base portion 12 extending in a circumferential direction indicated by double arrow P1 and in a radial direction of the rings 2, 4. The base portion 12 is provided with a passage 13 having a width WP in the circumferential direction.

On each side of the passage 13, the bridge part 1 1 is provided with an extension 14 being folded over a folding line 15 extending in the circumferential direction and located on the upper side 16 of the holding plate 8. Each extension 14 has a width WE in the circumferential direction. The width WP of the passage 14 is about the same as the width WE of the extensions.

Each passage 13 is bounded in the circumferential direction by edges

17.

As can best be seen in figures 3 and 4, the second wave shaped holding plate 9 is an endless ring, comprising a number of pockets 20, each with a partially hemispherical surface similar to the surface of the balls 6. Each set of two adjacent pockets 20 are connected to each other by means of a bridge part 21 .

Each bridge part 21 comprises at least a relatively flat base portion 22 extending in a circumferential direction indicated by arrow P1 and in a radial direction of the rings 2, 4. The base portion 22 is provided with a lip 23 having a width WL in the circumferential direction. De width WP of the passage 1 3 is larger than the width WL of the lip. The difference or clearance between the width WP and WL is preferably in de order of 0,5 - 1 ,5 millimeter, depending on the diameter of the bearing 1 . Preferably, a smaller bearing has a smaller clearance.

The lip 23 is obtained by providing the base portion 22 with two cuts perpendicular to the upper side 24 of the holding plate 8 and bending the lip 23 located between the two cuts over a folding line 25 located between ends of the cuts and extending parallel to the upper side 24. The lip 23 is bent in axial direction into an S-shape, whereby a lower part 26 of the lip is connected at the folding line 24 to the base portion 22 and an upper part 27 extends parallel to the base portion 12 of the bridge part 1 1 of the first holding plate 8, when the lip 23 is located in the passage 1 3.

In figure 4 the two holding plates 8, 9 are positioned opposite each other, whereby between opposite pockets 10, 20 a cavity is formed in which a ball 6 is being disposed. The opposed bridge parts 1 1 , 21 are connected to each other by means of the extensions 14 of the bridge part 1 1 , which are positioned over the upper side 24 of the base portion 22. The extensions 14 prevent the holding plates 8, 9 for moving with respect to each other in axial direction but do not prevent movement of the holding plates 8, 9 with respect to each other in the circumferential direction as indicated by double arrow P1 . By connecting the opposed bridge parts 1 1 , 21 to each other, the lip 23 of bridge part 21 is positioned inside the passage 13.

Since the width WL of the lip 23 is smaller than the width WP of the passage 13, the holding plates 8, 9 can move with respect to each other in the circumferential direction as indicated by double arrow P1 if different forces are applied by a ball 6 on the opposed pockets 10, 20 until the lip 23 is in abutment with an edge 17 of the passage 13.

Due to the clearance WP-WL in the circumferential direction indicated by arrow P1 of the holding plates 8, 9, the holding plates 8, 9 align themselves on the surfaces of the balls 6. This alignment corrects for the manufacturing errors of the tolerances of the two holding plates 8, 9, being displaceable connected to each other.

Figures 7 and 8 show perspective views of the first and second holding plate 38, 9 with balls 6 of a second embodiment of a roller bearing 31 according to the invention. The second holding plate 9 of the roller bearing 31 is identical to the second holding plate 9 of the roller bearing 1 .

The first holding plate 38 differs from the first holding plate 8 in that ends of the extensions 14 are connected to each other by a strip 39. The extensions and the strip can easily be made in the holding plate, for example by punching, stamping, laser cutting etc. In the middle the strip 39 is provided with a spring portion 40 bend towards the second holding plate 9.

In figure 7 the holding plates 9, 38 are shown during assembly, whereby the extensions 14 extend parallel to the axis of rotation of the roller bearing 31 . In figure 8 the holding plates 9, 38 are shown after assembly, whereby the extensions 14 extend parallel to the base portion 22 of the second holding plate 9. The spring portion 40 rests against the lip 23 and presses the lip 23 in a direction parallel to the axis of rotation into the passage 13 of the first holding plate 38. In this manner axial movement of the holding plates 38, 9 with respect to each other in a direction parallel to the axis of rotation is being easily prevented whilst movement of the holding plates 38, 9 with respect to each other in the circumferential direction indicated by double arrow P1 is still possible. During such a movement the spring portion 40 slides over the lip 23.

The first and second wave shaped holding plates 8, 9 are each made as whole from a metal like steel or plastic, like polyamide

It is also possible that the bridge part comprises one extension, which is bent over the bridge part of the other holding plate.

It is also possible that the extension is located adjacent to the lip.

It is also possible that instead of balls other rolling elements are being used.

Instead of a seal the sealing structure may comprise a shield.

The person skilled in the art will realize that the present invention is by no means limited to the preferred embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the scope should not be construed as limiting the scope of the claims. LIST OF REFERENCE SIGNS

1 roller bearing

2 outer ring

3 outer raceway

4 inner ring

5 inner raceway

6 ball

7 cage

8 holding plate

9 holding plate

10 pocket

1 1 bridge part

12 base portion

13 passage

14 extension

15 folding line

16 upper side

17 edges

20 pocket

21 bridge part

22 base portion

23 lip

24 upper side

25 folding line

26 lower part

27 upper part

31 roller bearing

38 first holding plate

39 strip

40 spring portion

P1 double arrow

WE width of the extension WP width of the passage WL width of the lip