BEARING

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a preloadable rolling bearing comprising at least two rings, each ring having a raceway, and rolling elements which are interposed between the rings and which travel along both raceways. Besides, the present invention relates to a method for preloading such a rolling bearing upon its installation within a mechanical system, like a rolling bearing assembly.

BACKGROUND ART OF THE INVENTION

It is sometimes required that a rolling bearing be in a condition such that a preloading, that is to say a negative clearance, always exists inside the bearing during its operation. Such a requirement exists for instance in a rolling bearing of the radial kind, when axial forces are applied onto the rolling bearing alternatively in one direction or in the opposite direction. Indeed, in the absence of preloading, an axial clearance exists inside the rolling bearing, so that the rolling elements can have small axial displacements back and forth between the rings, thus generating a click noise and vibrations which can alter the lifespan of the rolling bearing.

This problem is also well known for instance in a Power steering system for a motor vehicle, where this click noise can be heard by the occupants of the vehicle and the vibrations be felt by the driver through the steering wheel. A solution consists of using an already preloaded rolling bearing, that is to say a bearing which has been manufactured in such a way as to create an internal preloading during its manufacturing operation. It is however expensive and complex to manufacture such a rolling bearing.

US-B-6 682 226 describes a rolling bearing equipped with cylindrical rollers and with a preloading mechanism allowing an elastic deformation of one ring along a radial direction. The rolling bearing of US-B-6 682 226 decreases or eliminates the radial clearance between the inner ring and the outer ring.

However, such a prior art rolling bearing does not handle the axial clearance. SUMMARY OF THE INVENTION

One object of the present invention is to overcome the aforementioned drawbacks, by providing a rolling bearing which has an increased limit of tolerance to axial clearance and which particularly permits modification of the internal clearance, either positive or negative, inside the rolling bearing in its assembled state.

To achieve this object, a subject matter of the present invention is a rolling bearing comprising an inner ring, an outer ring and rolling elements arranged between the inner ring and the outer ring so as to rotate around a rotation axis, wherein at least one of the inner ring and the outer ring is engraved with at least one groove, the or each groove being of a substantially annular shape, the or each groove being empty, the or each groove being arranged to allow an elastic deformation of the or each engraved ring upon application on the or each engraved ring of a preloading force along a direction parallel to the rotation axis so as to reduce a clearance, either positive or negative, inside the rolling bearing.

In other words, such a rolling bearing has at least one ring which can be slightly bent and compressed around the or each groove, in order to modify the clearance inside the bearing..

According to advantageous but optional features, considered on their own or in any technically feasible combination:

- at least one groove is engraved on the outer ring;

- at least one groove is engraved on the inner ring;

- at least one groove is engraved on a surface oriented towards the rolling elements;

- at least one groove is engraved on a surface oriented opposite the rolling elements;

- at least one groove is engraved on a rolling surface delimiting at least one raceway for the rolling elements, the rolling surface belonging to the surface oriented towards the rolling elements;

- at least one of the inner ring and the outer ring is engraved with at least two grooves, at least one groove being located on the surface oriented towards the rolling elements and at least one groove being located on the surface oriented opposite the rolling elements;

- at least one groove extends all around the rotation axis;

- at least one groove extends symmetrically with respect to a median plane of the rolling elements;

- at least one groove has a substantially U-shaped cross section, considered in a plane comprising the rotation axis;

- at least one groove has a cross section, considered in a plane comprising the rotation axis, substantially in the shape of a trapezoid, preferably of an isosceles trapezoid, the sides of the trapezoid diverging towards the open end of the groove;

- the or each groove has a radial depth representing between 20% and 80%, and preferably between 40% and 60%, of the radial height of the corresponding engraved ring;

- the or each groove has an axial width representing between 1 % and

20%, and preferably between 5% and 10%, of the axial width of the corresponding engraved ring.

- the rolling elements are balls;

- every rolling element has two points of contact respectively with the raceway of the inner ring and with the raceway of the outer ring, when considered in a plane comprising the rotation axis; and

- the rolling bearing comprises two rows of rolling elements.

Besides, another object of the present invention is to provide a method for mounting a rolling bearing as here-above described, so as to preload the rolling bearing in order to compensate for axial clearance.

To achieve this object, a subject matter of the present invention is a method for mounting a rolling bearing as here-above described in a rolling bearing assembly, wherein the method comprises the steps of:

a) installing the rolling bearing in the rolling bearing assembly;

b) applying an axial force on the or each engraved ring along a direction parallel to the rotation axis, so as to reduce a clearance, either positive or negative, inside the rolling bearing.

According to advantageous but optional features: - the axial force is appl ied until a predetermined axial preloading of the rolling bearing is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be well understood on the basis of the following description, which is given an illustrative example, without restricting the scope of the invention, and in relation with the annexed drawings among which:

- Figure 1 is a cross section of a rolling bearing according to a first embodiment of the present invention, considered in a plane comprising the rotation axis;

- Figure 2 is a view, at a larger scale, of detail II on figure 1 ;

- Figure 3 is a view similar to figure 2 of a rolling bearing assembly according to the present invention and comprising the rolling bearing of figure 2;

- Figure 4 is a view similar to figure 2 of the rolling bearing according to a second embodiment of the present invention;

- Figure 5 is a view similar to figure 2 of the rolling bearing according to a third embodiment of the present invention; and

- Figure 6 is a view similar to figure 2 of the rolling bearing according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Figure 1 and figure 2 depict a ball bearing 100 which forms a rolling bearing and which comprises an inner ring 1 10, an outer ring 130 and balls 150 as rolling elements.

Balls 150 are arranged between inner ring 1 10 and outer ring 130 so as to rotate around a rotation axis X-X'. Balls 150 are held apart from one another by a cage 151 . Every ball 150 forms a rolling element which comprises only one spherical surface. Indeed, every ball 150 is in the shape of a sphere.

Inner ring 1 10 has an internal surface 121 , an external surface 122 and two lateral surfaces 123 and 124. Internal surface 121 is oriented towards balls 150. Internal surface 121 comprises a rolling surface 125 which delimits at least one raceway for the balls 150. External surface 122 is oriented opposite balls 150. Both internal surface 121 and external surface 122 extend between the two lateral surfaces 123 and 124, along an axial direction.

Likewise, outer ring 130 has an internal surface 141 , an external surface 142 and two lateral surfaces 143 and 144. Internal surface 141 is oriented towards balls 150. Internal surface 141 comprises a rolling surface 145 which delimits at least one raceway for the balls 150. External surface 142 is oriented opposite balls 150. Both internal surface 141 and external surface 142 extend between the two lateral surfaces 143 and 144, along an axial direction.

Inner ring 1 10 is engraved with a groove 1 1 1 . Groove 1 1 1 is arranged to allow an elastic deformation of the inner ring 1 10 along an axial direction upon application on the inner ring 1 10 of a preloading force along axis X-X' so as to reduce a clearance, either positive or negative, inside rolling bearing 100. Groove 1 1 1 has an annular shape. Groove 1 1 1 extends all around the rotation axis X-X'. Groove 1 1 1 is engraved on the internal surface 121 . Such a position of groove 1 1 1 allows an axial elastic deformation of the region of inner ring 1 10 which is located farthest from the rotation axis X-X'.

The word "engraved" means that the groove forms a recess or a cavity into a surface of the inner ring or of the outer ring and that the groove emerges at this surface, i.e. opens to the outside. The world "engraved" shall not be construed as directed to a particular manufacturing process, because the groove can be made by any suitable manufacturing process, for instance by turning, by milling, by electro-erosion or even by molding. The word "engraved" solely refers to the recess form of the groove.

Groove 1 1 1 is empty, which means that it is not filled with any stiff, solid material which could hinder the axial elastic deformation of the engraved ring. In the example of figures 1 and 2, groove 1 1 1 does not contain any material. Yet, the word "empty" also means that the groove can be filled with a resilient material, such that the groove can be compressed to allow an axial elastic deformation of the engraved ring.

In the present application, the adjective "axial" refers to a direction which is parallel to the rotation axis X-X'. In the present application, the adjective "radial" refers to a direction which is second and perpendicular to the rotation axis Χ-Χ', like axis Y-Y' on figure 2. Likewise, a surface is said to be "axial" or "radial" by reference to the direction which is locally or globally perpendicular to that surface.

Precisely, groove 1 1 1 is engraved on a rolling surface 125 which delimits at least one raceway for balls 150. Rolling surface 1 25 belongs to the internal surface 121 .

Groove 1 1 1 extends symmetrically with respect to a median plane P of the balls 150. Median plane P corresponds to the equatorial plane of inner ring 1 10 and outer ring 1 30. In other words, groove 1 1 1 extends about the mid-l ine between lateral surfaces 123 and 124. Such a position of groove 1 1 1 provides a symmetrical elastic deformation of the two halves of inner ring 1 10 located on both sides of groove 1 1 1 or of median plane P.

Groove 1 1 1 has a substantially U-shaped cross section when considered in a plane comprising the rotation axis, like the plane of figure 2. In other words, groove 1 1 1 is substantially in the shape of a flat annulus. Such a shape of groove 1 1 1 is relatively easy to produce by a suitable manufacturing process. .

Groove 1 1 1 has a radial depth D1 1 1 representing approximately 40% of the radial height H 1 1 0 of inner ring 1 10. The radial depth D1 1 1 and the radial height H 1 1 0 are measured along a radial direction, like axis Y-Y' . Such a percentage of radial depth D1 1 1 over radial height H1 10 allows a determined elastic deformation of inner ring 1 10 upon application of a force along axis X-X'.

This elastic deformation is also determined by the material constituting inner ring

1 10. Inner ring 1 10 can for instance be made of 100Cr6.

Groove 1 1 1 has an axial width W1 1 1 which represents 5% of the axial width W1 10 of inner ring 1 10. Axial width 1 10 and axial width 1 1 1 are measured along an axial direction, for instance along axis X-X'. Such an axial width W1 1 1 of groove 1 1 1 allows a determined elastic deformation of inner ring 1 10 along an axial direction.

Ball bearing 100 is a so called "four points of contact" ball bearing. Indeed, every ball 150 has two points of contact with the raceway 125 of inner ring 1 10 pl us two points of contact with the raceway 1 45 of outer ring 130, when considered in a plane comprising the rotation axis X-X', like the plane of figure 2. When balls 150 rotate around rotation axis X-X', the contact between balls 150 and raceways 125 and 145 take place along four circles to which belong the four points of contact.

Ball bearings having four points of contact are designed to bear loads having both an axial component and a rad ial component. To ach ieve such contact on fou r poi nts or fou r circles, rol l ing su rfaces 125 and 145 are respectively defined by the junction of two truncated tori at the middle of the inner ring 1 10 and of the outer ring 130. The not-shown centers of these tori are located on the rotation axis X-X'. The centers of these tori are offset from one another. Rolling surface 125 or 145 is a concave surface.

Figure 3 illustrates a rolling bearing assembly 1 comprising the rolling bearing 100, a shaft 160 and a nut 170. Shaft 160 defines a receiving surface 161 having a cylindrical shape in order to receive the external surface 122 of inner ring 1 10. Receiving surface 161 and external surface 122 approximately have the same diameter. Shaft 160 has a thread 162 onto which nut 170 can be screwed.

Shaft 160 also has a shoulder 162 extending radially in front of a portion of lateral surface 123. A counterbore or recess 165 extends radially on the annular internal surface of shoulder 162. Recess 165 extends from the receiving surface 161 towards outer ring 130 but only partially along shoulder 162. Thus, the radial end of shoulder 162 defines an axially protruding surface 163 which is intended to bear against lateral surface 123 of inner ring 1 10.

Likewise, nut 170 has a recess 175 similar and symmetric to recess 165. Thus, the radial end of nut 170 defines an axially protruding surface 174 which is intended to bear against lateral surface 124 of inner ring 1 10.

When nut 170 is tightly screwed on thread 162, axially protruding surfaces

163 and 174 apply pressures respectively upon lateral surfaces 123 and 124 of inner ring 1 10. These pressures induce a resultant couple of forces F160 and F170. The magnitudes of forces F160 and F170 depend on the tightening torque applied on nut 170. Forces F160 and F170 apply approximately at the same application radius.

Besides, the positions and dimensions of axially protruding surfaces 163 and 174 are selected so as to permit an elastic deformation of inner ring 1 10. In the example of figures 1 to 3, this elastic deformation is an elastic bending. To achieve such a bending, the distance DF separating the bottom of groove 1 1 1 from the application radius of forces F1 60 and F1 70 is greater than the height D1 1 1 of groove 1 1 1 . The greater the distance DF is, the larger the bending will be.

A method accord ing to th e present invention , for mounting rolling bearing 100 according to the present invention in rolling bearing assembly 1 , comprises the steps of:

a) installing rolling bearing 100 in rolling bearing assembly 1 ,

b) applying axial forces F1 60 and F1 70 on the engraved ring, e.g. inner ring 1 10, parallel to axis X-X', so as to reduce the positive clearance inside rolling bearing 100.

Hence, rolling bearing 1 00, which initially copes with an axial positive clearance, is mounted onto shaft 160 until inner ring 1 10 abuts shoulder 162 on shaft 160. Nut 1 70 is then screwed on thread 1 62. Upon tightening of nut 170, inner ring 1 10 is under compression and axial resultant forces F160 and F170 are generated . Thus, inner ring 1 1 0 bends around groove 1 1 1 with lateral surfaces 123 and 124 moving towards outer ring 130.

Upon tightening of nut 170, the axial clearance inside rolling bearing 100 is reduced and eventually becomes null. Moreover, axial forces F160 and F170 can be applied until a predetermined axial preloading of rolling bearing 100 is obtained. Thus, upon further tightening, the axial clearance inside rolling bearing 100 becomes negative, i.e. the rolling bearing 100 is preloaded. For instance, a preload, or initial deformation, of say 5 microns to 10 microns can be reached for a rolling bearing having an internal clearance of say 20 microns before tightening of the nut.

Figure 4 depicts a ball bearing 200 according to a second embodiment of the invention. The description of the ball bearing 100 given above with reference to figures 1 and 2 can be transposed to bal l bearing 200 of figure 4. Ball bearing 200 is similar to ball bearing 100, except for the hereafter stated differences. An element of ball bearing 200 that is identical or corresponding to an element of ball bearing 100 is allocated the same reference sign plus 100.

One can thus define an inner ring 21 0, an outer ring 230, balls 250, a cage 251 , a groove 212, for inner ring 210: an internal surface 221 , an external surface 222, two lateral surfaces 223 and 224 and a rolling surface 225, and a rolling surface 245 of outer ring 230.

Ball bearing 200 differs from ball bearing 1 00 in that the groove 212 is engraved on the external surface 222 of inner ring 210, i .e. on the surface oriented opposite balls 250. Such a position of groove 212 allows an axial elastic deformation, upon application of an axial preloading force, of the region of inner ring 210 which is located closest to rotation axis X-X'. Upon tightening of not shown nut, an initial positive axial clearance inside rolling bearing 200 can be reduced and eventually made null . Besides, further tightening of this nut shall preload rolling bearing 200, because the axial clearance inside rolling bearing 200 becomes negative.

Figure 5 depicts a ball bearing 300 according to a third embodiment of the invention . The description of ball bearing 1 00 given above with reference to figure 2 can be transposed to ball bearing 300. Ball bearing 300 is similar to ball bearing 1 00, except for the hereafter stated differences. An element of ball bearing 300 that is identical or corresponding to an element of ball bearing 100 is allocated with the same reference sign plus 200.

One can thus define an inner ring 31 0, an outer ring 330, balls 350, a cage 351 , a groove 31 2, the inner ring 310 having an internal surface 321 , an external surface 322, two lateral surfaces 323 and 324, and a rolling surface 325, the outer ring 330 having a rolling surface 345.

Ball bearing 300 differs from ball bearing 1 00 in that the groove 312 is engraved on the external surface 322 of inner ring 310, like groove 212.

Besides, groove 31 2 has a cross section wh ich is substantially in the shape of a trapezoid, when considered in a plane comprising the rotation axis X- X', like the plane of figure 5. More precisely, groove 312 has a cross section in the shape of an isosceles trapezoid, the sides of which diverge towards external surface 322. Such a shape of groove 312 allows an axial elastic deformation of inner ring 310 which has greater amplitude than the elastic deformation allowed by groove 212.

Moreover, ball bearing 300 differs from ball bearing 100 in that the axial width W31 2 represents approximately 20% of the axial width W310 of inner ring 310. Such a percentage also increases the axial elastic deformation of inner ring 310 as compared to inner ring 1 10.

Upon tightening of not shown nut, an initial positive axial clearance inside rolling bearing 300 can be reduced and eventually made null. Besides, further tighten ing of th is nut shal l preload roll ing bearing 300, because the axial clearance inside rolling bearing 300 becomes negative.

Furthermore, the invention can also apply to a rolling bearing which already has a negative internal clearance before tightening of the nut is already negative, that is to say a bearing which is already in a preloaded condition. Upon tighten ing of the nut, the negative clearance will become even smaller, for instance, starting from minus 5 microns, it is possible to reach minus 20 microns of negative clearance of preloading.

Figure 6 depicts a ball bearing 400 according to a fourth embodiment of the invention. The description of the ball bearing 100 given above with reference to figures 1 and 2 can be transposed to ball bearing 400. Ball bearing 400 is sim ilar to ball bearing 1 00, except for the hereafter stated d ifferences. An element of ball bearing 400 that is identical or corresponding to an element of ball bearing 100 is allocated the same reference sign plus 100.

One can thus define an inner ring 41 0, an outer ring 430, balls 450, a cage 451 , the outer ring having an internal surface 441 , an external surface 442, two lateral surfaces 443 and 444 and a rolling surface 445, the inner ring 410 having a rolling surface 425.

Ball bearing 400 differs from ball bearing 100 in that the outer ring 430 is engraved with two grooves, i.e. an internal 431 and an external 432. Internal groove 431 is located on the internal surface, i.e. on the surface oriented towards balls 450. External groove 432 is located on the external surface 442, i.e. on the surface opposite balls 450. The location of grooves 431 and 432 on the outer ring 430 allows an elastic deformation of outer ring 430 along an axial direction. This location of grooves 431 and 432 provides an elastic deformation both of the region of outer ring 430 located closest to rotation axis X-X' and of the region of outer ring 430 located farthest from rotation axis X-X'.

Moreover, ball bearing 400 differs from ball bearing 100 in that the sum of radial depth D431 of internal groove 431 plus rad ial depth D432 of external groove 432 represents approximately 55% of rad ial height H430 of outer ring 430. Hence, internal groove 431 and external groove 432 allow a higher elastic deformation than the one allowed by groove 1 1 1 or 21 1 .

In the example of figure 6, the elastic deformation, e.g . the bending, is operated on the outer ring 130 by way of a tightening applied on a not shown nut, as here-above described in relation with figure 3.

According to further not shown embodiments:

- only one groove can be engraved on the outer ring, either on the internal surface or on the external surface;

- two grooves can be engraved on the inner ring;

- more than two grooves can be engraved on the outer ring or on the inner ring, e.g. three grooves;

- one groove can be engraved on the inner ring while one groove can be engraved on the outer ring.

According to another not shown embodiment, one groove extends on a part of the perimeter of the engraved ring, either the inner ring or the outer ring. Such a groove does not extend all around the rotation axis.

According to a further not shown embodiment, two semi-annular grooves can be engraved on the inner ring or the outer ring, which grooves do not extend all around the rotation axis, but rather extend approximately on two halves of the engraved ring with two bridges of matter disconnecting these two grooves..

The present invention has been described in relation with four points of contact ball bearings. The present invention can also be implemented to other kinds of rolling bearings, for instance a deep groove ball bearing (DGBB), a cylindrical ball bearing (CRB) or a tapered roller bearing (TRB),

According to another not shown embodiment, the rolling bearing can comprise two or more rows of rolling elements.

Depending upon the required elastic deformation along an axial direction of the inner ring or of the outer ring, the radial depth of a groove can represent between 20% and 80% of the radial height of the corresponding engraved ring. Preferably, the depth of the groove represents between 40% and 60% of its radial height. Depending upon the required elastic deformation of the inner ring or of the outer ring, the groove can have an axial width representing between 1 % and 20% of the axial width of the corresponding engraved ring. Preferably, the width of the groove represents between 5% and 10% of the width of the engraved ring.

A rolling bearing according to the present invention has an increased limit of tolerance to axial clearance. Furthermore, such a rolling bearing permits modification of the internal clearance, either positive or negative, inside the rolling bearing in its assembled state.

Besides, when the groove is engraved on an internal surface, it can serve as a lubricant reservoir storing and releasing lubricant close to the raceways, i.e. the areas of contact between rolling elements and inner ring or outer ring. Thanks to the groove or grooves in the engraved ring or rings, the mass of the rolling bearing is reduced.

A mounting method according to the present invention makes it possible to reduce the clearance in a rolling bearing or even to set a preload in a rolling bearing whenever required.