WO2010066293A1

WO2010066293A1 - Cage for rolling bearing, in particular for rolling bearing used in a wind turbine generator.

Info

Publication number: WO2010066293A1
Application number: PCT/EP2008/067217
Authority: WO
Inventors: Thierry Adane; Stéphane CORDIER; Jean-Luc Gardelle; Jean-Marie Gerard
Original assignee: Aktiebolaget Skf
Priority date: 2008-12-10
Filing date: 2008-12-10
Publication date: 2010-06-17

Abstract

The cage 5 is adapted for a rolling bearing comprising an inner ring 2, an outer ring 3 and at least one row of balls 4 held by the cage between the rings. The cage comprises a plurality of elliptical pockets 7 for maintaining the circumferential spacing of the balls, circumferential spaces being provided between a ball and the corresponding pocket. The circumferential spaces are less than 3, 5 % of the diameter of the balls in the circumferential direction.

Description

Cage for rolling bearing, in particular for rolling bearing used in a wind turbine generator.

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 balls held by a cage between bearing races provided on the two rings.

The present invention relates more particularly to cages used in the rolling bearings and having a plurality of pockets to maintain the circumferential spacing of the balls.

The rolling bearings may be for example those used in industrial electric motors or generators such as wind turbine generators.

In such applications, with the rotational or circumferential movements of the balls relative to the cage, interferences or interactions between the balls and the edges of the spherical pockets of the retaining cage appear. In fact, the balls impact back and forth inside the pockets. Thus, some noise occurs during operation and the wear of the cage increases significantly. With the aim of avoiding these drawbacks, document US

2007/01 16395 discloses a rolling bearing having a retaining cage including elliptical pockets for the balls. The pockets define smaller and larger spaces in the axial and circumferential directions of the rolling bearing, respectively, between them and the balls so as to increase the contact area between these two elements, thereby reducing the contact pressure therebetween and the vibrations.

However, with circumferential spaces such as disclosed in this document, the cage is not stable and can move in the circumferential direction with respect to the balls. Some impacts may still occur between the balls and the cage. One aim of the present invention is to overcome the aforementioned drawback.

It is a particular object of the present invention to provide a cage for a rolling bearing which limits collisions with the balls in both an effective and economic manner.

In one embodiment, the cage is adapted for a rolling bearing comprising an inner ring, an outer ring and at least one row of balls held by the cage between the rings. The cage is provided with a plurality of elliptical pockets for maintaining the circumferential spacing of the balls, circumferential spaces being provided between a ball and the corresponding pocket. The circumferential spaces are less than 3 ,5 % of the diameter of the balls in the circumferential direction.

This thus provides a cage for a rolling bearing which is adapted to operate in a sure way with a reduction of impacts between the cage and the balls in the circumferential direction. The cage has therefore a limited risk of damage, thus increasing the reliability and service life of the rolling bearing.

Advantageously, the circumferential spaces are comprised between 1 ,5 and 2,5 % of the diameter of the balls, and preferably equal to 2 % of said diameter.

The cage may comprise a retaining portion for maintaining the balls in the axial direction. Axial spaces provided between the balls and the retaining portion may be less than 0, 1 % of the diameter of the balls, and preferably equal to 0,07 % of said diameter. The cage guides the balls in the axial direction and thus reduces the collisions in this direction even if the inner and outer rings are misaligned.

In one embodiment, the cage also comprises a guiding portion for the guiding of the cage by the balls, the retaining portion being extended by said guiding portion. In one embodiment, the cage comprises two half-cages. The cage can be formed from metal or from thermoplastic.

The invention further relates to a rolling bearing comprising an inner ring, an outer ring, at least one row of balls between said rings, and a cage comprising a plurality of elliptical pockets for maintaining the circumferential spacing of the balls, circumferential spaces being provided between a ball and the corresponding pocket. The circumferential spaces are less than 3 ,5 % of the diameter of the balls.

The present invention and its advantages will be better understood by studying the detailed description of embodiments taken as non-limiting examples and illustrated by the appended drawings wherein:

- Figure 1 is an axial half-section of a rolling bearing according to a first embodiment of the invention, - Figures 2 and 3 are views in axial section on H-II and III-III, respectively, of Figure 1 ,

- Figure 4 is a perspective view of a cage of the rolling bearing of Figure 1 , and

- Figure 5 is an axial half-section of a rolling bearing according to a second embodiment of the invention.

Figure 1 to 4 show the structure of a rolling bearing 1 comprising an inner ring 2, an outer ring 3 , between which is housed a row of rolling elements 4, which in this case are balls, and a cage 5 for retaining the circumferential space of the identical balls 4. The inner and outer rings 2, 3 are concentric and symmetric with respect to a transverse radial plane passing through the centre of the rolling bearing. The inner ring 2 is of the solid type. A "solid ring" is to be understood as a ring obtained by machining with removal o f material (by turning, grinding) from tube stock, bar stock, rough forgings and/or rolled blanks.

The inner ring 2 comprises a bore 2a of cylindrical shape delimited by opposing radial lateral surfaces 2b and 2c, and an outer cylindrical surface 2d onto which is formed a toroidal circular raceway

2e having in cross section a concave internal profile adapted to receive the balls 4, the said raceway being directed radially outwards.

The outer ring 3 , also of solid type, comprises an outer cylindrical surface 3 a delimited by opposing radial lateral surfaces 3b and 3c, and a bore 3d of cylindrical shape from which is formed a toroidal circular raceway 3e having in cross section a concave internal profile adapted to receive the balls 4, the said raceway being directed radially inwards.

The two rings 2, 3 are separated radially from one another by an annular space 6 in which the cage 5 rotates. Radial gaps are provided between the cage 5 and the inner and outer rings 2, 3. The cage 5 is axially offset relative to the radial surface 2b, 3b and 2c, 3c of said rings towards the interior of the rolling bearing 1.

The cage 5 receives and holds the balls 4 with a uniform circumferential spacing. The cage 5 has a plurality of identical elliptical pockets 7 forming housings for the balls 4. The major axis o f each of the elliptical pockets extends in the rotational or circumferential direction of the rolling bearing 1 , and the minor axis extends in the axial direction. The cage 5 is here composed of two identical half-cages 8 , 9 having open cavities which constitute the pockets when said half-cages 8, 9 are axially fixed one relative to the other. To this end, any appropriate fixing means may be used, for example rivets 13 uniformly spaced apart in the circumferential direction as shown on Figure 4. The half-cages 8, 9 can be of the solid type and obtained by machining with removal of material (by turning, grinding) from tube stock, bar stock, rough forgings and/or rolled blanks. Alternatively, the half-cages 8, 9 may be made of another material, for example aluminium, brass or thermoplastic. In this embodiment, the cage 5 is composed of two half-cages 8, 9. It is easily understood that it could also be possible to use a cage made in one part for example by moulding.

The cage 5 comprises an upper radial portion 10 facing the outer ring 3 and radially extended by a lower conical portion 1 1 facing the inner ring 2 and extending inwards towards the balls 4. The radial portion 10 and the conical portion 1 1 define the elliptical pockets 7. The conical portion 1 1 constitutes a guiding portion for the guiding o f the cage 5 by the balls 4. The radial portion 10 is adapted to hold the balls 4 in the axial direction. To this end, the axial dimension of the elliptical pockets 7 is slightly greater than that the diameter of the balls 4. More precisely, small axial spaces provided between the balls 4 and the radial portion 10 are advantageously less than 0, 1 % of the diameter of the balls 4, for example equal to 0,07 % of said diameter.

This thus provides an axial guiding of the balls 4 which limits collisions between them and the cage 5 along the axial direction, i.e . the minor axis of the elliptical pockets 7, even if the inner and outer rings 2, 3 are misaligned. The radial portion 10 is also adapted to limits contacts between the cage 5 and the ball 4 along the circumferential direction of the rolling bearing 1 , i.e. along the major axis of the elliptical pockets 7. To this end, circumferential spaces S are defined between the balls 4 and the radial portion 10 of the cage 5. In the circumferential direction, spaces S are less than 3 ,5 % of the diameter of the balls, advantageously comprised between 1 ,5 and 2,5 % of said diameter, and preferably equal to 2 %. As shown on Figure 3 , spaces S are also provided in the circumferential direction between the balls 4 and the conical portion 1 1 of the cage 5.

The applicant has determined that with circumferential spaces less than 3 ,5 % of the diameter of the balls 4, and preferably comprised between 1 ,5 % and 2,5 %, the balls 4 does not anymore impact back and forth inside the corresponding pockets 7 but slide inside said pockets rather. Thus, their motions are smoother. The vibrations and the noise generated during operation are therefore significantly decreased. With a cage of the solid type, the resonance phenomena is also limited with such spaces. The service life of the cage 5 is increased. The embodiment illustrated in Figure 5 only differs in that the radial portion 10 of the cage 5 is extended by a toroidal portion 12 having a radius of curvature adapted to the diameter of the balls 4. The toroidal portion 12 constitutes a guiding portion for the guiding of the cage 5 by the balls 4. The disclosed rolling bearings are particularly useful as bearing for a wind turbine generator. However, the rolling bearings can be applied equally well to other generators or other applications such as electric motors.

It should be noted that the embodiments illustrated and described were given merely by way of non-limiting indicative examples and that modifications and variations are possible within the scope of the inventions. For example, 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 several rows of balls 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 bearing.

Claims

1. Cage (5) for a rolling bearing comprising an inner ring (2), an outer ring (3) and at least one row of balls (4) held by the cage between the rings, said cage comprising a plurality of elliptical pockets (7) for maintaining the circumferential spacing of the balls, circumferential spaces (S) being provided between a ball and the corresponding pocket, characterized in that the circumferential spaces are less than 3 ,5 % of the diameter of the balls in the circumferential direction.

2. Cage according to claim 1 , wherein the circumferential spaces (S) are comprised between 1 ,5 and 2,5 % of the diameter of the balls, and preferably equal to 2 % of said diameter.

3. Cage according to claim 1 or 2, comprising a retaining portion ( 10) for maintaining the balls in the axial direction.

4. Cage according to claim 3 , wherein axial spaces provided between the balls (4) and the retaining portion ( 10) are less than 0, 1 % of the diameter of the balls, and preferably equal to 0,07 % of said diameter.

5. Cage according to claim 3 or 4, comprising a guiding portion ( 1 1 ; 12) of said cage by the balls, the retaining portion ( 10) being extended by said guiding portion.

6. Cage according to any of the preceding claims, comprising two half-cages.

7. Cage according to any of the preceding claims, forming from metal.

8. Cage according to the claims 1 to 5 , forming from thermoplastic.

9. Rolling bearing comprising an inner ring (2), an outer ring (3), at least one row of rolling balls (4) between said rings, and a cage (5) according to any of the preceding claims for maintaining the circumferential spacing of the balls.

10. Electric motor or generator comprising at least one rolling bearing according to claim 9.