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Title:
ROLLING BEARING AND METHOD FOR MANUFACTURING THE SAME
Document Type and Number:
WIPO Patent Application WO/2011/091853
Kind Code:
A1
Abstract:
Method of manufacturing a rolling bearing having an inner ring (1), an outer ring (2), at least one row of rolling elements (3) between the inner and outer rings, and an annular housing (5) surrounding at least one of said rings (1, 2), said at least one ring (2) defining with the housing (5) at least one space (18a, 18b), said method comprising the steps of: inserting the inner and outer ring (1, 2) with said rolling elements (3) in an L-shaped structure (28) having an outer cylindrical part (29); spinning said cylindrical part (29) over said one space (18a) and said one ring (2) until it encloses said one ring (2) and said rolling elements (3).

Inventors:
CORDIER, Stéphane (36 rue de la Fuye, Tours, Tours, F-37000, FR)
LAPINTE, Julien (74 rue Ronsard - Apt 14, Tours, Tours, F-37100, FR)
LIVERATO, Yves-André (Les Petites Gaudières, Saint Paterne Racan, F-37370, FR)
MANCEAU, Alexandre (51 rue fleurie, Saint Cyr Sur Loire, Saint Cyr Sur Loire, F-37540, FR)
MASSOTEAU, Charles (La Garenne, Louans, F-37320, FR)
Application Number:
EP2010/051070
Publication Date:
August 04, 2011
Filing Date:
January 29, 2010
Export Citation:
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Assignee:
AKTIEBOLAGET SKF (Hornsgatan 1, Göteborg, S-415 50, SE)
CORDIER, Stéphane (36 rue de la Fuye, Tours, Tours, F-37000, FR)
LAPINTE, Julien (74 rue Ronsard - Apt 14, Tours, Tours, F-37100, FR)
LIVERATO, Yves-André (Les Petites Gaudières, Saint Paterne Racan, F-37370, FR)
MANCEAU, Alexandre (51 rue fleurie, Saint Cyr Sur Loire, Saint Cyr Sur Loire, F-37540, FR)
MASSOTEAU, Charles (La Garenne, Louans, F-37320, FR)
International Classes:
F16C19/06; B21D22/16; F16C33/60; F16C35/067; F16C43/04
Domestic Patent References:
WO2003056197A12003-07-10
WO2009059979A12009-05-14
WO2006041040A12006-04-20
WO2009059979A12009-05-14
Foreign References:
US3758930A1973-09-18
EP1935528A12008-06-25
GB1245451A1971-09-08
DE867777C1953-02-19
FR2897126A12007-08-10
US20010052184A12001-12-20
DE376136C1923-05-24
US4016642A1977-04-12
FR1111621A1956-03-02
DE102005033566A12007-01-25
DE102005016404A12005-10-27
DE102005033566A12007-01-25
GB1245451A1971-09-08
EP0769631A11997-04-23
Attorney, Agent or Firm:
CASALONGA, Axel (Bureau D.a. Casalonga-Josse, 8 avenue Percier, Paris, F-75008, FR)
Download PDF:
Claims:
CLAIMS

1 . Method of manufacturing a rolling bearing having an inner ring ( 1 ), an outer ring (2), at least one row of rolling elements (3) between the inner and outer rings, and an annular housing (5) surrounding at least one o f said rings ( 1 , 2), said at least one ring (2) defining with the housing (5) at least one space ( 1 8a, 1 8b), said method comprising the step of :

- inserting the inner and outer ring ( 1 , 2) with said rolling elements (3) in an L-shaped structure (28) having an outer cylindrical part (29), characterized in that said method comprising the step of :

- spinning said cylindrical part (29) over said one space ( 1 8a) and said one ring (2) until it enclo ses said one ring (2) and said rolling elements (3) .

2. Method according to claim 1 , characterized in that said spinning step is performed by deforming plastically said cylindrical part (29) in order to define at least one curved portion ( 19) by deforming said cylindrical part (29) within said space ( 1 8a) .

3. Method according to claims 1 or 2, in which said ro lling bearing comprises at least one axial internal portion (20a, 20b) defining with the housing (5) at least one space ( 1 8a, 1 8b), two curved portions ( 19a, 19b) being formed during said spinning step, by deforming said cylindrical part (29) .

4. Method according to any o f the preceding claims, in which the spinning step comprises the steps o f:

- inserting the rolling bearing in a mandrel (27) ;

ho lding axially the rolling bearing by a rotating shaft (3 1 ) ; rotating said mandrel (27) and said rotation shaft (3 1 ) in a first rotary direction ;

rotating a spinning tool (33) in a second rotary direction opposite to the first rotary direction ;

pressing the spinning tool (33) against said cylindrical part

(29) .

5. Method according to any preceding claims, in which the housing (5) is first grooved on its inner surface in order to create a weakening zone for facilitating the spinning step.

6. Method according to any preceding claim, in which said at least one ring (2) is made in two separate parts (2a, 2b) and the housing (5) is grooved on its outer surface in order to set a desired preload or clearance inside the bearing.

7. Method according to claim 4, in which the spinning tool (26) has a feed speed of 780 mm/mn, a rotational speed of 600 rev/mn and an attack angle of 30°.

8. Rolling bearing having an inner ring (1), an outer ring (2), at least one row of rolling elements (3) between the inner and outer rings, and an annular housing (5) surrounding at least one of said rings (1, 2), said at least one ring defining with the housing (5) at least one space (18a, 18b), said housing (5) comprising a cylindrical bottom part (14c) and two radial lateral flanges (14a, 14b), characterized in that one of said radial lateral flanges (14a, 14b) comprises at least one curved portion (19).

9. Rolling bearing according to claim 8, comprising at least one axial cylindrical portion (20a, 20b) defining with the housing (5) at least one closed space (18a, 18b) and in which said one radial lateral flange (14a) comprises two curved portions (19a, 19b) with a convexity in the direction of the closed space (18a), one of which (19a) is located within said closed space (18a) and the other (19b) is located between said inner cylindrical portion (20a) and the other one of said rings (1).

10. Rolling bearing according to claim 8 or 9, in which said at least one ring (2) is made in two separate parts (2a, 2b) surrounded by the housing (5), each of the two parts (2a, 2b) of said ring (2) defining a closed space (18a, 18b), and the cylindrical bottom part (14c) of the housing (5) comprising an annular ridge (25) on its surface facing said two parts, said annular ridge (25) allowing to set a preload or a clearance inside the bearing.

11. Rolling bearing according to one of claims 8 to 10, in which both spaces (18a, 18b) contain a lubricant and act as lubricant reservoirs.

12. Rolling bearing according to claim 11, in which each of said separate parts (2a, 2b) comprises passage means for the lubricant contained in the spaces (18a, 18b).

13. Rolling bearing according to one of claims 8 to 12, in which said at least ring (2) is the outer ring of the bearing.

14. Rolling bearing according to one of claims 8 to 12, in which said at least ring (2) is the inner ring of the bearing.

15. Rolling bearing according to one of claims 8 to 12, in which said inner and outer rings (1, 2) are both surrounded by an annular housing (5a, 5b).

Description:
ROLLING BEARING AND METHOD FOR MANUFACTURING THE SAME

The present invention relates to rolling bearings, in particular rolling bearings having an inner ring and an outer ring with one or more rows of rolling elements, for example, balls . The rolling bearings may be, for examp le, those used in industrial electric motors or in motor vehicle gearboxes . In such applications, the bearings are mainly lo aded radially, often with a relatively weak load compared to the capacity o f the bearings used. The rotational speeds in such applications are o f the order of 3000 rpm. In such applications, the service life of the ro lling bearing is essentially related to the lubrication and to the stiffness o f the bearing. For instance, a known Deep Groove Ball Bearing has two seals delimitating with the inner and outer rings a chamber inside which a lubricant such as grease has been introduced during the assembly of the bearing. Such a bearing is called lubricated "for life". However, in the long term, the mixing o f grease, combined with its ageing and with the heating cycles that the bearing undergoes, causes the grease to degrade . It is possible to envisage periodic regreasing operations for this type o f ro lling bearings . However, these operations are expensive.

Patent application WO 2006/04 1040 (NTN) and German patent application DE 10 2005 016 404 disclose a rolling bearing which has an independent lubricant reservoir that can be housed between the two rings o f the bearing. The lubricant can be supplied onto the balls o f the bearing by a radial duct delimited partly by a face of one of the rings o f the rolling bearing and by a wall of the lubricant reservoir. Such a construction is complicated and expensive.

German patent application DE 10 2005 033 566 (Schaeffler), moreover, disclo ses a rolling bearing without clearance, in which the outer ring is in two parts . One of the parts of this ring is obtained by stamping sheet metal and delimits, together with a housing ho lding the two parts of the ring, a space, inside which an axially preloaded resilient element is housed. However, this document provides no particular means o f lubricating the ro lling bearing.

British patent application GB 1 245 45 1 (SKF) also disclo ses a rolling bearing with two rings and an annular housing surrounding one of the rings, and also a clo sed space filled with lubricant. European patent application EP 0 769 63 1 (Snecma), for its part, shows a ball bearing having lubricant passages made in one of the rings. None o f these known constructions allows satisfactory lubrication o f the rolling elements in a genuinely effective, long lasting and economic manner.

International patent application WO 2009/059979 (SKF), which aims at so lving these problems, disclo ses a rolling bearing having an inner ring and an outer ring with at least one row of rolling elements, an annular housing surrounding at least one of said rings . Said ring forms with the housing at least one closed space, inside which a lubricant is located. The clo sed space functions as a lubricant reservoir. Passage means for the lubricant, comprising axial holes at least partly facing one another, are made in the thickness of a radial portion of each of the two parts of said ring in order to put the two closed spaces into communication. This thus provides a rolling bearing which is able to operate for a long time by virtue of effective internal lubrication. This document also disclo ses a method of manufacturing such a ro lling bearing comprising the steps of inserting the inner and outer ring with the rolling elements in an L shaped envelope having an outer cylindrical part and folding said cylindrical part over one closed space and one ring until it encloses said one ring and said rolling elements.

The stiffness of such a rolling bearing may however be insufficient in some cases and lead to the dislocation of the outer ring, which could cause the malfunction o f the rolling bearing itself.

An obj ect of the present invention is to provide an improved method of manufacturing a rolling bearing. The method is more particularly useful for rolling bearings having a lubricant reservoir such as the one disclosed in the patent application WO 2009/059979. The present invention aims at so lving, in a simple way, the stiffness problems in this type o f rolling bearing by increasing the rolling bearing stiffness with no additional difficulty in comparison to the manufacturing method described hereinabove.

In one embodiment, the invention provides a method of manufacturing a rolling bearing having an inner ring, an outer ring, at least one row of rolling elements therebetween, and an annular housing surrounding at least one of said rings, said at least one ring defining with the housing at least one space, said method comprising the steps of:

inserting the inner and outer rings with said ro lling elements in an L-shaped structure having an outer cylindrical part ;

spinning said cylindrical part over said one space and said one ring until it enclo ses said one ring and said ro lling elements.

Said spinning step is performed by deforming p lastically said cylindrical part in order to define at least one curved portion by deforming said cylindrical part within said space.

Preferably, the rolling bearing comprises at least one axial cylindrical portion defining with the housing at least one space, two curved portions being formed during said spinning step, by deforming plastically said cylindrical part.

The stiffness o f the bearing is therefore increased in a simp le way by forming said curved portion.

During the spinning step, the rolling bearing is preferably inserted in an open cavity located on a mandrel and held axially by a rotating shaft. Said mandrel and said rotating shaft are rotated in a first rotary direction and a spinning tool is rotated in a second rotary direction opposite to the first rotary direction. The spinning tool is pressed against said cylindrical part so as to deform it plastically.

The housing may be grooved or recessed on its inner surface in order to create a weakening zone for facilitating the spinning step .

In a preferred embodiment, said at least one ring is made o f two separate parts or half rings. Advantageously, once the spinning step has been completed, the housing is grooved on its outer surface in order to reduce the preload or even create a clearance inside the rolling bearing. For example, the clearance can be increased between said two parts.

The spinning tool may have a feed speed between 700 mm/mn and 800 mm/mn, preferably between 750 mm/mn and 790 mm/mn, for example o f 780 mm/mn, a rotational speed between 550 rev/mn and 650 rev/mn, for example of 600 rev/mn and an attack angle between 25 ° and 35 ° , for example o f 30° .

It is another obj ect of the invention to provide a ro lling bearing comprising an inner ring, an outer ring, at least one row of rolling elements therebetween, and an annular housing surrounding at least one of said rings. Said at least one ring defining with the housing at least one space, said housing comprising a cylindrical bottom part and two radial lateral flanges . One of said radial lateral flanges comprises at least one curved portion. The curved portion thus increases the stiffness o f the corresponding lateral flange and therefore the stiffness of the rolling bearing.

Preferably, the ro lling bearing comprises at least one axial cylindrical portion defining with the housing at least one clo sed space and in which said one radial lateral flange comprises two curved portions with a convexity in the direction of the clo sed space . One o f the curved portions is lo cated within said clo sed space and the other curved portion is lo cated between said inner cylindrical portion and the other one of said rings. In such an embodiment, the stiffness obtained for the lateral flange is particularly high due to the presence of two curved portions and to the fact that the lateral flange is pressed against the axial cylindrical portion.

In a preferred embodiment, said at least one ring is made in two separate parts surrounded by the housing, each of the two parts of said ring defining a clo sed space, and the cylindrical bottom part of the housing comprising an annular ridge on its surface facing said two parts, said annular ridge allowing to set a determined prelo ad or clearance within the bearing by moving apart at least axially said two parts .

Both said spaces may, for examp le, contain a lubricant and act as lubricant reservoirs. The two separate parts comprise passage means for the lubricant contained in the spaces, so that the balls and the correspondent races can be best lubricated.

In a preferred embodiment, said one ring is the outer ring.

In another embodiment, said one ring is the inner ring.

In another embodiment, said inner and outer rings are both surrounded by an annular housing.

The present invention will be better understood with the aid o f the detailed description o f a number of embo diments given by way o f non-limiting examp le and illustrated by the attached drawings, in which:

- Figure 1 is an axial half-section o f a rolling bearing according to the invention ;

Figure 2 is an axial half-section o f a rolling bearing according to another embodiment of the invention ;

Figure 3 is an axial half-section o f another embodiment of a rolling bearing manufactured according to the invention ;

Figure 4 is an axial half-section o f another embodiment of a rolling bearing manufactured according to the invention ;

Figures 5 , 6, 7 are steps of a manufacturing method according to the invention.

Referring first to Figure 1 , which illustrates an embodiment o f a rolling bearing according to the invention; said bearing has an inner ring 1 and an outer ring 2 with a row of rolling elements that consist in the example illustrated of balls 3 , held by a cage 4 between the inner ring 1 and the outer ring 2. An annular housing 5 surrounds the outer ring 2.

In this examp le, the inner ring 1 is designed to be mounted on a rotary member not illustrated in the figure. It thus constitutes the rotating ring of the bearing while the outer ring 2 constitutes the non- rotating ring. The inner ring 1 is solid and has a toroidal groove 6, the radius o f curvature of which is slightly greater than the radius of the balls 3 and forms a bearing race for the balls 3. The inner ring 1 may be manufactured by machining or by pressing a steel blank which is then ground and optionally lapped at the bearing race 6 in order to give the ring 1 its geometric characteristics and its final surface finish.

The cage 4 has a plurality o f open cavities 7 bounded by external retaining claws 8. The cavities 7 are advantageously spherical with a diameter slightly greater than that of the balls 3 so as to receive and ho ld the latter. The cavities 7 are made around the periphery of an annular body of the cage 4, leaving a heel 9 opposite to the openings of the various cavities 7. These openings bounded in each case by two opposing claws 8 have a width slightly smaller than the diameter of the balls 3. The balls 3 are snap-fitted inside the cage 4 by moving the claws 8 apart elastically. The cage 4 can be made of moulded synthetic resin or of metal, depending on the application. The cage 4 may have other means than cavities 7 and claws 8 for retaining the balls 3.

The outer ring 2 comprises an outer cylindrical portion 10 and a radial flange portion 1 1 located in the same radial symmetry plane than the centers of the balls 3. The radial flange portion 1 1 is internally connected to an annular portion 12 having a toroidal inner bearing race 13. The radius o f curvature of the bearing race 13 is slightly greater than the radius of the balls 3. The housing 5 , which is advantageously made of a stamped metal sheet, has two radial lateral flanges 14a and 14b and a cylindrical bottom part 14c connected to the two radial lateral flanges 14a and 14b, so as to surround the outer ring 2. The radial edges 15 a and 15b forming an annular rim o f the outer cylindrical portion 10 are in contact with the two radial lateral flanges 14a and 14b o f the housing 5. The two radial lateral flanges 14a and 14b extend towards the cylindrical periphery 16 o f the inner ring 1 , so as to leave a clearance between the edges 17a and 17b o f the radial lateral flanges 14a and 14b and the cylindrical surface 16.

The outer ring 2 defines, with the housing 5 , two annular spaces 1 8a and 1 8b, and both o f the two spaces 1 8a and 1 8b may act as lubricant reservoirs. The lubricant contained in these spaces 1 8a and 1 8b has not been shown in the figure. The lubricant contained in these spaces 1 8a and 1 8b may flow through the clearance between the annular portion 12 and the radial lateral flanges 14a and 14b towards the balls 3.

The radial lateral flange 14a comprises a curved portion 1 9 with a convexity directed axially toward the space 1 8a i.e . towards the balls 3. The curved portion 19, not being in contact with the annular portion 12, leaves a passage for the lubricant contained in the space 1 8a in the direction o f the balls 3. The curved portion 1 9 o f the radial flange 14a increases the overall stiffness of the housing 5 by at least three to five percent compared to a flat portion o f the same thickness.

In the embodiment illustrated in Figure 2, on which similar parts bear the same references, the bearing has an inner ring 1 and an outer ring 2 consisting of two separate parts 2a, 2b. The two parts or half rings 2a and 2b of the outer ring 2 are identical and symmetrical with respect to the axial plane of symmetry o f the bearing, in order to reduce the manufacturing costs. These two separate parts 2a, 2b may advantageously be manufactured by cutting and stamping a metal sheet, the pieces obtained being then hardened by heat treatment. The bearing races may be ground and/or lapped in order to give them their geometric characteristics and their definitive surface finish. Since the two half rings 2a, 2b, formed by the two separate parts, are identical in this examp le, only one o f them, having the reference "a", will be described here, it being understood that the identical elements o f the other part 2b have the reference "b" in the figures .

The half ring 2a comprises an outer cylindrical portion 10 a connected to a radial flange portion 1 1 a. The radial flange portion 1 1 a is internally connected to an annular portion 12a having a toroidal inner bearing race 13 a. The annular portion 12a extends axially towards the outside of the rolling bearing with an inner cylindrical portion 20a. The outer edge 21 a of the inner cylindrical portion 20a is in contact with the radial lateral flange 14a. Whereas the outer edge 21b o f the inner cylindrical portion 20b is in contact with the radial lateral flange 14b. The two outer half rings 2a, 2b are positioned with the axially internal radial faces 22a and 22b o f the radial flange portions 1 1 a and l i b in contact with one another, approximately in the same radial symmetry plane as the plane containing the centers o f the balls 3.

The housing 5 comprises two radial lateral flanges 14a and 14b and a cylindrical bottom part 14c, so as to surround the two half rings 2a, 2b and to hold them firmly against one another. The half rings 2a, 2b are centered in the cylindrical bottom part 14c of the housing 5 by contact between the two outer cylindrical portions 10a, 10b.

Each of the outer half rings 2a, 2b defines, with the housing 5 , an annular clo sed space 1 8a, 1 8b. More specifically, the clo sed space 1 8a is delimited by the outer cylindrical portion 10a, the radial flange portion 1 1 a, the annular portion 12a and the inner cylindrical portion 20a, as well as, adj acent to these portions, the radial lateral flange 14a of the housing 5. In the same way, the clo sed space 1 8b is delimited by the outer cylindrical portion 1 0b, the radial flange portion l i b, the annular portion 12b and the inner cylindrical portion 20b, as well as, adj acent to these portions, the radial lateral flange 14b o f the housing 5. One of the two or both spaces 1 8a and 1 8b may act as lubricant reservoirs. Both inner cylindrical portions 20a and 20b are provided with passages 23 a and 23b through which the lubricant contained in the clo sed spaces 1 8a and 1 8b can flow by gravity towards the balls 3. Further passages or holes, not illustrated in the figure, can be provided on the two half rings 2a and 2b in order to let the lubricant flow towards the balls 3. Reference is hereby made to WO 2009/059979 which description is incorporated in the present description.

The radial lateral flange 14a comprises two curved portions 1 9a and 19b both having a convexity directed axially towards the balls 3. A first curved portion 19a with a convexity directed axially towards the space 1 8a is located between the outer cylindrical portion 10a and the inner cylindrical portion 20a along the lubricant reservoir 1 8 a formed by the outer half ring 2a. The second curved portion 1 9b, with a convexity directed axially towards the balls 3 , is located between the inner cylindrical portion 20a and the inner ring 1 . The part of the lateral flange 14a remaining between the two curved portions 19a and 19b is pressed in contact with the cylindrical portion 20a.

Thanks to two curved portions 19a and 19b, the overall stiffness o f the housing 5 is increased by five to ten percent compared to an housing with a flat portion of the same thickness . The consequence of a stiffer housing 5 is that the rolling bearing itself is stiffer, and therefore able to withstand higher lo ads. Alternatively, thanks to the two curved portions 19a and 1 9b, it is possible to use a housing 5 with a radial lateral flange l 4a thinner than a flat one but o f the same stiffness, which advantageously further reduces the weight of the bearing.

Figure 3 disclo ses another embodiment according to the invention.

The main difference from the embodiment of Figure 2 in the embodiment of Figure 3 , in which identical elements bear the same references, is that the two rings 1 and 2 of the bearing have the same structure. In other words, the ring 1 which is the inner ring of the bearing is surrounded by a first housing 5 a. The second ring 2 of the bearing is identical to that illustrated in Figure 2. It is surrounded by a second housing 5b. The housing 5 a comprises two radial lateral flanges 14d and 14e and a cylindrical bottom part 14f, so as to surround the two half rings l a, l b and to ho ld them firmly against one another. The housing 5b comprises two radial lateral flanges 14a and 14b and a cylindrical bottom part 14c, so as to surround the two half rings 2a, 2b and to hold them firmly against one another.

Both inner cylindrical portions 20a, 20b and 20c, 20d are provided with passages 23 a, 23b and 23 c, 23 d through which the lubricant contained in the closed spaces 1 8a, 1 8b, 1 8c and 1 8d can flow by gravity towards the balls 3.

The radial lateral flange 14a comprises two curved portions 19a and 19b both having a convexity directed axially towards the balls 3. A first curved portion 19a with a convexity directed axially towards the space 1 8a is located between the outer cylindrical portion 10a and the inner cylindrical portion 20a along the lubricant reservoir 1 8 a formed by the outer half ring 2a. The second curved portion 19b, with a convexity directed axially towards the balls 3 , is located between the inner cylindrical portion 20a and the inner cylindrical portion 20c o f the inner ring 1 . The outer edge 2 1 a of the inner cylindrical portion 20a is in contact with the radial lateral flange 14a. Whereas the outer edge 21 c o f the inner cylindrical portion 20c is in contact with the radial lateral flange 14d.

The radial lateral flange 14d comprises two curved portions 19c and 19d both having a convexity directed axially towards the balls 3. A first curved portion 19c with a convexity directed axially towards the space 1 8c is located between the outer cylindrical portion 10c and the inner cylindrical portion 20c along the lubricant reservoir 1 8 c formed by the inner half ring l a. The second curved portion 19d, with a convexity directed axially towards the balls 3 , is located between the inner cylindrical portion 20c and the inner cylindrical portion 20a o f the outer ring 2. The outer edge 21 c of the lateral flange 14d remaining between the two curved portions 19c and 1 9d is pressed in contact with the inner cylindrical portion 20c.

The two radial lateral flanges 14a and 14b extend towards the inner ring 1 and the two radial lateral flanges 14c and 14d extend towards the outer ring 2, so as to leave a clearance between the edges 17a and 17b o f the radial lateral flanges 14a and 14b and the edges 17c and 17d of the radial lateral flanges 14d and 14e .

Figure 4 disclo ses another embodiment according to the invention.

The main difference from the embodiment of Figure 2 in the embodiment of Figure 4, in which identical elements bear the same references, is the presence of a groove 24 made on the outer surface of the housing 5 in the same radial symmetry plane than the centers o f the balls 3. The machining of the groove 24 generates by plastic deformation a ridge 25 protruding between the two half rings 2a and 2b, so that an axial clearance is created or increased between the two half rings 2a and 2b. The effect of this is a modification of the bearing internal preload. Indeed, once the housing 5 has been spinned, it is mo st likely that the bearing races 13 a, 13b and 6 are preloaded on the balls 3.

In some applications, it is preferred that the rolling bearing has an internal prelo ad, that it to say a preload both in the radial and axial directions. For instance, in an Electric Power Assisted Steering system for a vehicle, such a bearing advantageously supports in rotation the rotor of the electric motor in order to prevent any click noise.

In other applications though, it is desired to use a rolling bearing with no internal preload i. e. with an internal clearance, in order for instance to reduce friction and to compensate thermal expansion o f the rings .

The ridge 25 allows a radial clearance of about 60μιη to 70μιη can advantageously be created within the rolling bearing.

The method of manufacturing such types of bearings will now be described on the basis o f Figures 5 to 7. On the Figure 5 , the inner ring 1 o f the rolling bearing is mounted in an open cavity 26 located on a mandrel 27. The housing 5 has, at this stage of the manufacturing method, an L-shaped structure 28 , with an outer cylindrical part 29 and a first lateral radial flange 14a. The radial lateral flange 14b and the cylindrical bottom part 14c, which is part of the L-shaped structure 28 , are facing the inside o f the open cavity 26. The half ring 2b is positioned in the L-shaped structure 28 , with the edge 1 5b of the outer cylindrical portion 10b resting on the radial lateral flange 14b . The balls 3 are inserted in the cavities 7 of the cage 4 and the whole assembly is fitted on the inner ring 1 . The inner ring 1 is held axially by a shoulder 30 o f a rotating shaft 3 1 . The half ring 2a is positioned in the L-shaped structure 28 with the radial face 22a of the radial flange portion 1 1 a in contact with the radial face 22b of the radial flange portion l i b of the half ring 2b .

The outer cylindrical part 29 of the housing 5 comprises a groove 32 located on its inner surface in the same plane than the radial edge 15 a of the half ring 2a. This groove 32 allows an easy spinning o f the outer cylindrical part 29 o f the housing 5 , in order to form the radial lateral flange 14a and to ho ld the two half rings 2a, 2b firmly against one another by way o f their respective outer cylindrical portions 10a and 10b . The groove 32 can have a width o f 20mm to 30mm, preferably o f 25mm.

A spinning tool 33 has a roller 34 adapted on a rotating shaft 35. The spinning tool 33 can move in a direction X, parallel to the symmetry plane of the inner ring 1 and in a direction Y, parallel to the radial symmetry plane of the balls 3. The roller 34 may have a trapezoidal shape in cross section, with rounded edges 34a and a plane surface 34b .

As illustrated in Figure 6, the mandrel 27 and the rotating shaft

3 1 are rotated in a first rotary direction referenced by the arrow F l with a rotational speed between 550 rev/mn and 650 rev/mn, preferably of 600 rev/mn. The assembly of the inner ring 1 and the reshaped structure 29 is thus rotated together with the mandrel 27. The rotating shaft 35 o f the spinning tool 33 is rotated in a second rotary direction referenced by the arrow F2. The direction F2 is preferably opposite to the first rotary direction F l . Rotating the spinning tool 33 in an opposite direction F2 o f the rotation of the rolling bearing accelerate the manufacturing method. The roller 34 o f the spinning tool 33 has, preferably, a diameter of 175 mm. The attack angle a o f the roller 34 is between 25 ° and 35 ° , preferably o f 30° . The attack angle a is the angle between the surface 34b of the spinning tool 33 and the Y-axis . The feed speed, i. e. the speed of movement in direction Y, o f the spinning tool 33 is between 700 mm/mn and 800mm/mn, preferably of 780 mm/mn and is constant during the manufacturing method. The force P and the feed speed of the spinning tool 33 are maintained constant during the manufacturing method by regulation means not shown in the figure.

During the spinning step illustrated in Figure 7, the spinning tool 33 is moved along directions X and Y towards the housing 5 until it contacts the outer cylindrical part 29. When the rounded edge 34a contacts the outer cylindrical part 29 of the housing 5 , the outer cylindrical part 29 is pressed against the radial edge 15 a with the force P . The spinning tool 33 is moved in direction X with its force P and its feed speed maintained constant. The outer cylindrical part 29 is thus pushed towards the space 1 8a. Thanks to the groove 32 shown in Figure 5 , the spinning requires fewer efforts as compared to a non grooved surface. However, it must be understood that the cylindrical part 29 can be spinned towards the space 1 8a even if no groove 32 is made on the surface of the housing 5.

During the continuation of the spinning step illustrated on Figure 6, the tool 33 is moved according to direction Y. The spinning tool 33 presses the radial lateral flange 14a towards the space 1 8a. The force P and the feed speed of the spinning tool 33 being maintained constant, the spinning tool 33 moves in a direction opposite to direction X when the radial lateral flange 14a is pressed against the outer edge 21 a o f the inner cylindrical portion 20a. The radial lateral flange 14a thus presents a curved portion 19a with a convexity in a direction towards the space 1 8a.

The second curved portion 1 9b of the radial lateral flange 14a is made in the same way as the curved portion 19a during further movement of the spinning tool 33 in direction Y. Indeed, the spinning tool 33 is moved in direction Y with its force P and its feed speed maintained constant, in order to press the radial lateral flange 14a towards the balls 3. The radial flange 14a is pressed by the rounded edge 34a of the spinning tool 33 towards the balls 3 so as to leave a clearance between the edge 17a of the radial lateral flange 14a and the cylindrical surface 16 of the inner ring 1 . The radial lateral flange 14a thus presents the curved portion 19a with a convexity in a direction towards the space 1 8a and a curved portion 19b with a convexity in a direction towards the balls 3.

Further, with the mandrel 27 still in rotation, or after the spinning step, it is possible to machine the groove 24 by pressing a rolling tool (not illustrated) against the cylindrical bottom part 14c o f the housing 5 , in the middle o f it, and in a direction perpendicular to it, so as to plastically deform radially inwards the cylindrical bottom part 14c which becomes the annular ridge 25. By virtue of the present invention it is possible to obtain a rolling bearing that is economical to manufacture, is compact, is light, has a large reserve o f lubricant enabling it to operate for a very long time without needing relubrication, has a high stiffness, and with a clearance which can be easily set according to the needs.

Although the present invention has been illustrated on the basis of ball bearings having a single row of balls, it should be understood that the invention can be applied to bearings using rolling elements that are not balls and/or to several rows of rolling elements, without major modifications. The invention can also be applied to different types of ball bearings, such as deep-groove bearings, angular contact bearings, or else to self-aligning bearings .

The invention can also be applied to rolling bearings having a housing surrounding the inner ring. In that case, it is the outer ring that is so lid while the two separate parts forming the inner ring are produced by stamping a metal sheet. The arrangement is identical to that of the embodiment of figures 1 to 2, but with the elements inverted. Of course, the manufacturing method illustrated in Figures4 5to 7 could be applied to this inverted arrangement. In this embodiment, it is advantageous for the inner ring formed by the separate parts to be the rotating element of the rolling bearing. In this case, while the rolling bearing rotates, the lubricant contained in spaces functioning as lubricant reservoirs is rej ected by centrifugal force and tends to diffuse through the passage means provided in the two separate parts forming the inner ring. In this embodiment, the outer ring is mounted in an open cavity located on a mandrel. The housing surrounding the inner ring has an L-shaped structure, with an outer cylindrical part and a first lateral radial flange. One o f the half rings o f the inner ring is positioned in the L-shaped structure with the edge o f its outer cylindrical portion resting on one of the radial flanges. The balls are inserted in the cavities o f the cage and the who le assembly is fitted on the outer ring. The inner ring is held axially by a shaft. A spinning tool moves in a direction X and in a direction opposite to the direction Y illustrated in Figures 5 to 7, towards the housing until it contacts the cylindrical part. The cylindrical part is thus spinned towards the balls. The spinning tool continues its movement according to the direction opposite to the direction Y, so as to create one or two curved portions of the radial lateral flange.

The invention can also be applied to rolling bearings in which the inner ring and the outer ring are both surrounded by an annular housing, as illustrated in Figure 3 In that case, the two rings have the same structure. In other words, the inner ring is surrounded by a first annular housing and the outer ring is surrounded by a second annular housing. In this embo diment, the rolling bearing has four closed spaces acting as lubricant reservoirs. Each housing is spinned successively by a spinning tool, so as to create two radial lateral flanges . Each radial lateral flanges can have one or two curved portions.