The present invention relates to pre-stressed 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 example, those used in a steering column for automotive vehicles, industrial electric motors or electromechanical actuators .

A steering co lumn o f an automotive vehicle generally comprises a tube or shaft having one of its end portions linked with a steering wheel actuated by the driver and the other of its end portions linked to mechanical elements, such as a toothed rack. The shaft of the steering column is mounted inside an outer tube via two rolling bearing assemblies. Each o f said ro lling bearing assemblies generally comprises a ro lling bearing, for example a ball bearing, with an outer ring and an inner ring between which the rolling elements or the balls are mounted and maintained by a cage element. The rolling bearing is mounted inside the outer tube o f the steering column.

In such applications, the bearings are loaded radially and axially with important loads. Moreover, because of the geometric characteristics o f the shaft and the tubular housing, misalignments between the two rolling bearings and between the inner ring and the outer ring may exist.

French patent application FR 2915543 (SKF) discloses a pre- stressed rolling bearing comprising an inner ring and two outer half rings surrounding a row of rolling elements. Each o f the outer half rings comprises an inner axial portion, a first oblique portion extending from the axial portion radially towards the housing, a second oblique portion extending from the first oblique portion radially towards the housing, and a radial portion extending from said second oblique portion towards the housing. The rolling bearing comprises a pre-stressing element, made of synthetic material, having a rectangular cross-section. At least one pre-stressing element allows to axially preload the rolling bearing by exerting an axial force on at least one outer half ring.

Such a rolling bearing does not allow radial and angular movements between the inner ring and the housing o f the outer ring . Such movements are necessary in view of constraints of the assembly of the rolling bearing during operation, for example, of a steering co lumn and in view o f possible manufacturing defects or large tolerances.

The present invention seeks to provide a pre-stressed rolling bearing particularly adapted for example to a steering column, adapted to support important axial and radial loads, while allowing a tilting movement between the inner and outer rings in order to support a misalignment between the non rotating part and the rotating part which are supported by the rolling bearing.

In an embodiment o f the present invention, a rolling bearing comprises an inner ring, an outer ring comprising two outer half rings mounted in an outer housing, a row of rolling elements between the inner and outer rings, and at least one pre-stressing element mounted in said housing and acting on one of said outer half rings.

The pre-stressing element comprises an inner portion and an outer portion. Said outer portion may be more flexible than said inner portion, so as to allow a radial and an angular or tilting movement between said inner ring and said housing.

The inner portion of the pre-stressing element allows to axially preload the rolling bearing by exerting an axial force on the outer half rings and the outer portion allow a radial and tilting movement between the axis o f the inner ring and the axis o f the housing. Such movements are necessary in order to accommo date high loads or compensate for possible manufacturing defects or large tolerances or assembly constraints which can lead to misalignments between the rotating part and the non-rotating part and to malfunction o f the rolling bearing. By allowing axial, radial and tilting movement between the inner ring and the housing of the outer ring, any misalignments between the rotating part and the non-rotating part are compensated for inside the rolling bearing which is able to function normally without any compromise o f its lifespan.

For example, the at least one pre-stressing element is made from synthetic material.

Advantageously, the axial dimension o f the outer portion of the pre-stressing element may be smaller than the axial dimension o f the inner portion of the pre-stressing element so as to provide good flexibility to the outer portion of the pre-stressing element.

The outer portion o f the pre-stressing element may be ring- shaped.

Advantageously, several recesses may be provided on the outer surface of the outer portion of the pre-stressing element. Recesses may increase flexible properties of the flexible portion.

For example, the recesses provided on the outer portion o f the pre-stressing element may be, in a free state, of semi-circular cross- section so as to define teeth linked together by concave surfaces. In another embodiment, recesses and teeth may be of triangular cross- section.

The pres-stressing element may be mounted between the housing and one outer half ring.

In an embodiment, the housing comprises two radial flanges, one o f which is in contact with the inner portion o f the pre-stressing element.

Advantageously, each of said outer half rings may have an inner axial portion, a first oblique portion extending from the axial portion radially towards the housing, a second oblique portion extending from the first oblique portion radially towards the housing, and a radial portion extending from said second oblique portion towards the housing. The inner portion of the pre-stressing element contacts the first oblique portion of one outer half ring.

One o f the radial flanges of the housing may contact the radial portion of one outer half ring.

The inner portion of the pre-stressing element may contact the radial portion of one outer half ring.

In another embodiment, a pre-stressed rolling bearing may comprise two pre-stressing elements, each mounted on one side of the row of rolling elements.

Advantageously, each radial flange of the housing may be in contact with one pre-stressing element.

In another aspect of the invention, a steering column for an automotive vehicle comprises an outer tube, an inner tube or shaft and at least one rolling bearing according to one aspect of the invention.

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

Figure 1 is an axial half-section, along line I-I of Figure 2, of a rolling bearing according to the invention ;

- Figure 2 represents a perspective view of the pre-stressing element used in the ro lling bearing o f Figure 1 ;

Figures 3 a, 3b and 3 c represent three preferred embodiments o f a pre-stressing element used in a ro lling bearing according to the invention ;

- Figures 4a, 4b and 4c illustrate the axial cross-section o f three preferred embodiments o f a pre-stressing element used in a rolling bearing according to the invention ;

Figure 5 is an axial half-section o f the rolling bearing o f Figure 1 mounted in a steering column showing a radial displacement of the inner ring with respect to the outer ring ;

Figure 6 is an axial half-section o f a rolling bearing o f Figure 1 mounted in a steering column showing an angular displacement in the longitudinal plane of the outer ring with respect to the inner ring;

Figure 7 is an axial half-section of another embodiment of rolling bearing according to the invention.

Referring first to Figure 1 , which illustrates an embodiment o f a pre-stressed rolling bearing 1 according to the invention, the bearing 1 has an inner ring 2 and an outer ring 3 with a row of rolling elements in the example balls 4, held by a cage 5 between the inner ring 2 and the outer ring 3.

In this examp le, the inner ring 2 is designed to be mounted on a rotary member not illustrated in this figure. It thus constitutes the rotating ring of the bearing while the outer ring 3 constitutes the non- rotating ring. The inner ring 2 is so lid and has a toroidal groove 6, the radius o f curvature of which is slightly greater than the radius of the balls 4 and forms a bearing race for the balls 4. The inner ring 2 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 2 its geometric characteristics and its final surface finish.

The outer ring 3 comprises two separate half rings 3 a, 3 b mounted on each side of the row of rolling elements 4 and are surrounded by an outer housing 7. The two half rings 3 a and 3b o f the outer ring 3 are preferably identical and symmetrical with respect to the axial plane of symmetry o f the bearing, in order to reduce the manufacturing costs . Since the two half rings 3 a, 3b, formed by the two separate parts, are identical in this example, only one half ring 3 a will be described here.

The half ring 3 a comprises an inner axial portion 8 connected to a first oblique portion 9. The first oblique portion 9 extends radially towards the housing 7 and axially towards the balls 4, and is connected to a second oblique portion 10. The second oblique portion 10 extends radially towards the housing 7 and axially away from the balls 4. In the illustrated embodiment, the second oblique portion 10 is connected to a radial portion 1 1 . The first oblique portion 9 comprises a toroidal inner bearing race 12. The radius of curvature of the bearing race 12 is slightly greater than the radius o f the balls 4.

The housing 7 has a generally U-shaped section and comprises a cylindrical portion 13 , two radial lateral flanges 14 and 15 , so as to surround the two half rings 3 a, 3b. The cylindrical portion 13 remains at a significant radial distance from the radial portion 1 1 . Furthermore , the lateral flange 15 has a radial dimension smaller than the dimension of the lateral flange 14 and can be slightly curved towards the row of rolling elements 4 so as to contact the radial portion 1 1 of the half ring 3b and to axially prelo ad the bearing 1 .

A pre-stressing element 16 is mounted on the outer half ring 3 a in the housing 7. The pre-stressing element 16 has an L-shaped section comprising an inner portion 17 and an outer portion 1 8. The inner portion 17 extends axially towards the radial flange 14 of the housing 7 and the outer portion 1 8 extends radially towards the cylindrical portion 1 3 of the housing 7. The inner portion 17, having a shape o f an annular rib, is in contact axially with the radial flange 14 of the housing 7 and the first oblique portion 9 of the outer half ring 3 a and radially with the axial portion 8 of the outer half ring 3 a. The outer portion 1 8 the pre-stressing element 1 6 is in contact with the radial portion 1 1 of the outer half ring 3 a.

The axial thickness of the inner portion 1 8 is smaller than the axial thickness o f the outer portion 1 7 in order to increase the flexibility o f the outer portion 1 8. The pre-stressing element 16 is made from synthetic material and is obtained for example by moulding.

The curved portion o f the lateral flange 15 presses the radial portion 1 1 of the outer half ring 3b, so as to exert an axial compression force on the inner portion 17 of the pre-stressing element 15 and to preload the rolling bearing 1 both axially and radially. Referring now to Figure 2, the pre-stressing element 16 is annular and comprises an extruded portion referred to as the inner portion 17 and the outer portion 1 8. Upon misalignment between the inner ring 2 and the outer ring 3 , for instance in the longitudinal plane, the outer portion 1 8 can come into contact with the housing 7. In the event of contact thereof, the outer portion 1 8 is deformed easily thanks to several recesses 19 provided on the outer surface of the outer portion 1 8. In the embodiment of Figure 3 a, the recesses 19 may be, in a free state, of substantially identical semi-circular cross-section so as to define protrusions or teeth 20 linked together by concave surfaces 21 of the outer portion 1 8.

As illustrated on Figure 3b, the recesses 19 may be, in another example, of a triangular cross-section so as to define bosses 20 linked together by flat surfaces 21 . Such recesses increase the flexible properties of the inner portion 1 8.

As illustrated on Figure 3 c, the recesses 19 may be, in another example, of a triangular cross-section so as to define triangular protrusions or teeth 20 linked together by flat surfaces 21 .

The recesses 19 may be o f any shape allowing good flexible properties of the pre-stressing element 16.

Figures 4a, 4b and 4c illustrate the axial cross-section o f three preferred embodiments of the pre-stressing element 16.

As illustrated on Figure 4a, the pre-stressing element 16 comprises an inner portion 17 having a shape o f an annular rib extending axially, and an outer portion 1 8 extending radially from the outer portion 17. The axial thickness o f the inner portion 17 is, in this example, larger than the axial thickness of the outer portion 1 8. Thanks to its thickness and to the recesses 19 made at one end portion of the outer portion 1 8 , the outer portion 1 8 is more flexible than the inner portion 17.

Depending on the material used, the inner portion 17 and the outer portion 1 8 may have the same axial thickness, as shown in Figure 3b. The pre-stressing element 16 thus comprises an inner portion 17 having a rectangular cross-section extending radially, and an outer portion 18. The outer portion 18 comprises recesses 19 and teeth or bosses 20 as shown on Figures 3a, 3b or 3c. The flexibility of the pre-stressing element 16 is ensured by the recesses 19 of the outer portion 18.

As illustrated on Figure 4c, the pre-stressing element 16 comprises an inner portion 17 having a shape of an annular rib extending axially, and an outer portion 18 extending radially from the outer portion 17. The axial thickness of the inner portion 17 is, in this example, larger than the axial thickness of the outer portion 18. Further, the radial thickness of the outer portion 18 is larger than the radial thickness of the inner portion 17. Therefore, the outer portion 18 is more flexible than the inner portion 17, in the sense that the outer portion 18 can easily bend around the inner portion 17, for instance in the longitudinal plane.

As illustrated on Figure 5, a steering column 22 for an automotive vehicle comprises an inner tube 23 to which a non- illustrated steering wheel can be attached on an end of smaller diameter. The steering column 22 also has an outer tube 24, which is arranged around the inner tube 23. The outer tube 24 is supported on the inner tube 23 by two rolling bearings 1, at least one of which has the structure already disclosed in the embodiment of Figure. 1, references to the same elements being reproduced on Figure 5.

In the mounted position illustrated on Figure 5, a high load is exerted radially on the rolling bearing. The inner ring 2 is moved radially in a Y direction with respect to the outer ring 3. The axial section of the rolling bearing 1 is made in the plane of the radial movement of the inner ring 2. The axis A ₂ of the inner ring 2 is parallel to the axis Ai of the housing 7 of the outer ring 3. The rolling elements 4 held by the cage 5 on the inner ring 2 are moved in the Y direction which moves the outer half ring 3a in the same direction. The outer portion 18 of the pre-stressing element 16 located in the direction of the radial movement is pressed against the cylindrical portion 13 of the housing 7 so as to be deformed at least radially. The curved portion of the lateral flange 15 of the housing 7 presses the radial portion 11 of the outer half ring 3b. The inner portion 17 of the pre-stressing element 16 being in contact with the lateral flange 14 of the housing 7 and the first oblique portion 9 of the outer half ring 3a, an axial force is exerted to the inner portion 17 so as to preload the rolling bearing 1.

The outer half ring 3b remains in the same position as in the non-mounted embodiment shown in Figure 1. The rolling elements 4 are thus in contact only in a portion of the circumference of the inner bearing race 12 of the outer half ring 3b.

Such a rolling bearing is axially and radially preloaded and at the same time allows a radial displacement between the inner ring 2 and the housing 7 of the outer ring 3. The radial displacement ΔΥ may be of 0.5 mm. The radial displacement ΔΥ between the axis A ₂ of inner ring and the axis Ai of the housing may be comprised between 0mm and 1mm, more often between 0.25mm and 0.75mm, for example of 0.5 mm.

As illustrated on Figure 6, a misalignment occurs in the longitudinal plane between the housing 7 of the outer ring 3 and the inner ring 2. An angle a exists between the axis Ai of the housing 7 and the axis A ₂ of the inner ring 2.

The rolling elements 4 held by the cage 5 on the inner ring 2 are moved angularly in the a direction which moves the outer half ring 3a in the same direction. The outer portion 18 of the pre-stressing element 16 located in the direction of the radial movement is thus pressed against the cylindrical portion 13 of the housing 7 so as to deform radially its teeth or bosses 20.

The curved portion of the lateral flange 15 of the housing 7 presses the radial portion 11 of the outer half ring 3b. The inner portion 1 7 of the pre-stressing element 16 being in contact with the lateral flange 14 of the housing 7 and the first oblique portion 9 o f the outer half ring 3 a, an axial force is exerted to the inner portion 1 7 so as to preload the rolling bearing 1 . Because o f the tilting or angular movement of the inner ring 2 with respect to the outer ring 3 , the annular rib o f the inner portion 17 is pressed against the lateral flange 14 of the housing 7. The inner portion 17 being made o f synthetic material is deformed axially. In this case, the pre-stressing element is deformed axially and radially.

The outer half ring 3b remains in the same position as in the non-mounted embodiment shown in Figure 1 . The rolling elements 4 remain in contact with the inner bearing race 12 of the outer half ring 3b and the toroidal groove 6 of the inner ring 2.

Such a rolling bearing is therefore axially and radially preloaded and, at the same time, still allows an angular displacement between the axis A ₂ o f inner ring 2 and the axis Ai o f the housing 7. The angular displacement Δα may be o f 1 ° . The angle a between the axis A ₂ o f inner ring 2 and the axis Ai o f the housing 7 may be comprised between 0° and 2° , more often between 0.5 ° and 1 .5 ° , for example o f 1 ° .

Figure 7 disclo ses another embodiment of the pre-stressed rolling bearing 1 according to the invention. The main difference from the embodiment of Figure 1 in the embo diment of Figure 7, in which identical elements bear the same references, is the presence of a second pre-stressing element 16. The ro lling bearing illustrated in this figure is in a non-mounted condition. A pre-stressing element 16 is mounted on each side of the row of elements 4 between each outer ring 3 and the housing 7. Each of the two pre-stressing elements 1 6 comprises an inner portion 17 having a rectangular cross-section and an outer portion 1 8 comprising recesses 19 and teeth or bosses 20 as illustrated in Figures 2, 3 a, 3b or 3 c. Each pre-stressing element 16 is in contact axially with one o f the lateral flanges 14 or 15 of the housing 7 and the first oblique portion 9 of each outer half ring 3 a, 3b and radially with the cylindrical portion 13 o f the housing 7. The curved portion o f the lateral flange 15 of the housing 7 is pressed directly against one of the pre-stressing elements 16 so as to exert an axial force to the other pre-stressing element 16 and to axially and radially prelo ad the bearing 1 .

Such an embodiment increases the angular displacement Δα but may decrease the axial stiffness o f the rolling bearing 1 . A metallic rim (not illustrated) can be inserted between the pre-stressing element 16 and the curved portion 15 o f the housing 7 in order to increase the angular or axial stiffness o f the ro lling bearing 1 .

The specific structure of the pre-stressing element used in the rolling bearing assembly of the present invention, with its substantially ring-shaped structure comprising two portions, one of them being more flexible than the other, permits to obtain a pre- stressed or preloaded rolling bearing adapted to function with radial and angular misalignments.