The present invention relates to the field of ro lling bearings, in particular rolling bearings having an inner ring and an outer ring with one or more rows of contact rollers therebetween.

The invention relates more particularly to a large-diameter rolling bearing adapted to be used in a wind turbine.

In such application, rolling bearings are used to angularly orient the rotor of the turbine according to the direction o f the wind, and to orient the blades of the turbine around their longitudinal axes . Such rolling bearings are loaded both axially and radially, often with a relatively strong load.

US patent 3 , 948 , 578 discloses a rolling bearing for a wind turbine comprising two concentric inner and outer rings, two rows of oblique contact rollers and two cages for maintaining the circumferential spacing of the rollers. Each row of rollers is located in an annular space defined between the rings, said space being delimited by two opposite raceways for the rollers and two non-loaded surfaces.

Under the action o f the lo ads to which such a rolling bearing is subj ected during operation of the wind turbine, the ro llers o f a row may slightly skew or tilt with respect to the raceways of the inner and outer rings . Accordingly, the service life o f the ro lling bearing reduces .

One aim o f the present invention is to overcome this drawback.

It is a particular object of the present invention to provide a rolling bearing, notably adapted for a wind turbine, which is simp le to manufacture, economic and having a good reliability.

A further object of the present invention is to provide a ro lling bearing having good static and dynamic carrying capacities.

In one embodiment, the rolling bearing comprising an inner ring, an outer ring and at least one row of rollers disposed between raceways provided on the rings, each roller comprising a rolling surface in contact with said raceways and two opposite end faces . Guiding faces coming into contact with the end faces of the rollers are provided on the inner ring and the outer ring. The guiding faces may be disposed opposite with one another.

In one preferred embodiment, the ratio o f the clearance between the guiding faces and the end faces of the rollers with respect to the length of said rollers is from 0. 1 % to 5 %, and preferably from 0.5 % to 0.9% .

Preferably, the guiding faces are formed directly on the inner ring and the outer ring.

In one embodiment, the guiding faces and the raceways of the rings are disposed perpendicular with respect to one another.

Preferably, the rotation axes of the rollers of the same row converge in one single point located on the longitudinal axis of the bearing.

The guiding faces are advantageously disposed parallel with one another. The guiding faces may extend radially relative to the rotation axes o f the ro llers.

Advantageously, the length of the guiding faces is smaller than the one of the raceways . Preferably, the guiding faces are straight. The entire length o f the ro lling surface o f each roller may be in contact with the raceways o f the rings.

In one embodiment, the rolling bearing further comprises spacers disposed circumferentially between the rollers . Each spacer may comprise two parallel cavities having the shape of the ro llers and at least one hole inside which a lubricant is lo cated and putting the two cavities into communication.

In one embodiment, the rolling surfaces of the rollers have a cylindrical profile . Alternatively, the rolling surfaces may have a spherical profile or a logarithmic pro file.

Preferably, the ro lling bearing comprises at least two rows of rollers, the rotation axes o f the ro llers o f one row crossing the rotation axes o f the ro llers o f the other row.

The ro lling bearing may further comprises seals provided between the inner and outer rings and having in cross section the overall shape of a H, each of the seals comprising internal lips and external lips forming the two substantially parallel branches of said H. The inner and outer rings may comprise opposite radial ribs located axially between the internal and external lips of each seal.

In one embodiment, each of the inner and outer rings comprises one guiding face.

The ro llers may have a ro lling surface for ro lling on the raceways with a cylindrical, or a spherical or a logarithmic pro file.

In one embodiment, the rolling bearing further comprises plugs provided on the outer ring for closing filling orifices through which the rollers have been introduced during the assembly of the bearing.

The ro lling bearing as previously defined may be particularly useful as a bearing for a wind turbine comprising a mast ho lding a nacelle where blades are installed, in particular for rotating the nacelle with respect to the mast and/or for rotating/pitching each blade around its longitudinal axis .

The present invention and its advantages will be better understood by studying the detailed description o f specific embodiments given by way o f non-limiting examp les and illustrated by the appended drawings on which:

- Figure 1 is a half section o f a ro lling bearing according to a first example o f the invention,

- Figure 2 is a section o f the ro lling bearing of Figure 1 according to another section plan,

- Figure 3 is a perspective view of a spacer of the rolling bearing of Figures 1 and 2, and

- Figure 4 is a half section o f a rolling bearing according to a second examp le o f the invention.

The ro lling bearing as illustrated by Figure 1 is a large- diameter rolling bearing comprising an inner ring 1 and an outer ring 2 between which are housed two rows of oblique or angular contact rollers 3 and 4. The inner and outer rings 1 , 2 are concentric and extend axially along the bearing rotation axis (not shown) of the rolling bearing. The rings 1 , 2 are of the solid type. A "so lid ring" is to be understood as a ring obtained by machining with removal o f material (by machining, grinding) from metal tube stock, bar stock, rough forgings and/or rolled blanks .

The rollers 3 , 4 are identical with one another and each comprise an exterior rolling surface 3 a, 4a and opposite end transverse faces 3b and 3 c, 4b and 4c delimiting axially the rolling surface. In the illustrated embodiment, the rolling surfaces 3 a, 4a have a cylindrical profile. Alternatively, the rolling surfaces may have a spherical profile or a logarithmic profile. For each row, the rotation axes 3 d, 4d of the rollers converge in one single point located on the longitudinal axis o f the bearing, and are disposed at a determined angle with respect to the bearing axis. In the illustrated embodiment, the rotation axes 3 d, 4d of the rollers o f the two rows are arranged at an angle of 90° to each other, and of approximately o f 45 ° to the bearing axis . The angle between the rotation axis 3 d, 4d o f each ro ller and the bearing axis may be comprised for example between 20° and 70° .

The inner ring 1 has a bore l a of cylindrical shape designed to be fixed to a chassis or to a structure of a machine (not shown) and delimited by opposite radial lateral surfaces l b, l c. The inner ring 1 also includes a stepped exterior cylindrical surface I d onto which first and second annular raceways 5 , 6 are formed. The raceways 5 , 6 are mutually symmetric with respect to a transverse radial plane passing through the centre of the rolling bearing. Each raceway 5 , 6 extend obliquely inwards from the exterior cylindrical surface I d and has a frustoconical shape. Each raceway 5 , 6 has in cross section a straight internal profile in contact with the rolling surfaces 3 a, 4a of the rollers 3 , 4.

The outer ring 2 comprises an outer cylindrical surface 2a delimited by opposite radial lateral surfaces 2b, 2c. The radial lateral surface 2c is axially set back from the corresponding radial surface l c of the inner ring 1 , whereas the radial lateral surface l b of said inner ring is axially set back from the corresponding radial surface 2b of the outer ring . Alternatively, the radial lateral surfaces 2b and l b, 2c and l c of the inner and outer rings 1 , 2 could be respectively coplanar. The outer ring 2 also includes a stepped annular bore 2d of cylindrical shape into which first and second raceways 7, 8 are formed. The raceways 7, 8 are mutually symmetric with respect to the radial plane passing through the centre of the rolling bearing. The raceways 7, 8 are respectively parallel to the raceways 5 , 6. Each raceway 7, 8 extends obliquely outwards from the bore 2d and has a frustoconical shape . Each raceway 7, 8 has in cross section a straight internal profile in contact with the rolling surfaces 3 a, 4a of the rollers 3 , 4.

The dimension of the raceways 5 to 8 is adapted such that the entire length o f the rolling surfaces 3 a, 4a of each roller is in contact with said raceways. Surfaces stresses on the raceways are reduced. The raceways 5 , 6 of the inner ring and the raceways 7, 8 of the outer ring mutually face each other while at the same time being symmetric with regard to the rotation axis 3 d, 4d of the rollers 3 , 4.

The inner ring 1 also comprises annular guiding faces 9, 1 0 formed onto the exterior surface I d and coming into axial contact with the end faces 3b, 4b o f the ro llers with regard to the rotation axes 3 d, 4d. The guiding faces 9, 10 are mutually symmetric with respect to the radial plane passing through the centre of rolling bearing. Each guiding face 9, 10 is straight and disposed perpendicular to the corresponding raceway 5 , 6 and is connected to the edge of small diameter of said raceway by a concave fillet. Each guiding face 9, 10 extends obliquely outwards from said fillet and is connected to the exterior surface I d of the inner ring. The guiding faces 9, 10 extend radially relative to the rotation axis 3 d, 4d of the rollers. Each guiding faces 9, 10 and the associated raceway 5 , 6 delimit a V-shaped groove directed radially outwards .

The outer ring 2 also comprises guiding faces 1 1 , 12 formed into the bore 2d and coming into axial contact with the end faces 3 c, 4c o f the rollers 3 , 4 with regard to the rotation axes 3 d, 4d. The guiding faces 1 1 , 12 are mutually symmetric with respect to the radial plane passing through the centre of rolling bearing. The guiding faces 1 1 , 12 and the guiding faces 9 , 1 0 mutually face each other and are respectively parallel. Each guiding face 1 1 , 12 is straight and disposed perpendicular to the corresponding raceway 7, 8 and is connected to the edge of large diameter of said raceway by a concave fillet. Each guiding face 1 1 , 12 extends obliquely inwards from said fillet and is connected to the bore 2d of the inner ring. Each guiding face 1 1 , 12 extend radially relative to the rotation axis 3 d, 4d of the ro llers. Each guiding face 1 1 , 12 and the associated raceway 7, 8 delimit a V-shaped groove directed radially inwards .

The raceway 5 and the guiding face 9 of the inner ring define together with the raceway 7 and the guiding face 1 1 of the outer ring a first annular space inside which the row of rollers 3 is disposed. Each roller 3 arranged between the raceways 5 , 7 are maintained laterally in position by the guiding faces 9, 1 1 to avoid a skewing or tilting o f said rollers with respect to the raceways. Each guiding face 9, 1 1 form a flank having a direct contact surface with the associated end face 3b, 3 c o f the rollers 3 to have a slight relative sliding between the end faces 3b, 3 c of rollers 3 and the inner and outer rings 1 , 2. According to an analysis made by the applicant, it was found that a good compromise is obtained between the lateral guiding o f the ro llers 3 and the induced friction torque when the ratio of the clearance between the guiding faces 9, 1 1 and the end faces 3b, 3 c of the ro llers 3 with respect to the length of said rollers is from 0. 1 % to 5 %, and preferably from 0.5 % to 0.9% . In order to limit the friction torque between the rollers 3 and the inner and outer rings 1 and 2, the length of the guiding faces 9, 1 1 is smaller than the one of the raceways 5 , 7.

Similarly, the raceway 6 and the guiding face 10 of the inner ring define together with the raceway 8 and the guiding face 12 o f the outer ring a second annular space inside which the row of rollers 4 is disposed. The arrangement of the rollers 4 with respect to the guiding faces 10, 12 is the same that the one previously described for the rollers 3 and the guiding faces 9, 1 1 .

The rolling bearing also comprising a plurality of spacers 1 3 (Figure 3) disposed circumferentially between the rollers 3 , 4 to maintain the circumferential spacing between them. The spacers 13 are identical with one another and each placed between two consecutive rollers 3 , 4. The spacers 13 may be made from metal or from plastic material. Each spacer 1 3 comprises two opposite cavities 14, 1 5 having the shape of cylinder segments with parallel axes . The cavities 14, 15 have a concave profile which corresponds to the profile of the rolling surface 3 a, 4a of the rollers 3 , 4. The axial length o f the cavities 14, 15 is slightly smaller than the length o f the ro llers 3 , 4. The cavities 14, 15 are delimited axially by opposite lateral surfaces 16, 17 which face the corresponding guiding faces of the rings 1 , 2. The spacer 13 also comprises two opposite planar surfaces 1 8 , 19 facing the corresponding raceways of said rings.

Each spacer 13 comprises a through-ho le 20 made inside its thickness, which opens onto the cavities 14, 15 and put said cavities into communication. A lubricant (not shown) is disposed inside the through-ho le 20, said ho le acting as lubricant reservoir for lubricating the rolling surfaces 3 a, 4a of the rollers. The lubricant used may be grease or oil. The through-ho le 20 allows the lubricant contained to emerge directly onto the rolling surface 3 a, 4a of each roller 3 , 4.

As shown on Figure 1 , the inner and outer rings 1 , 2 further respectively comprise axial ho les 21 , 22 for fixing the two rings to two parts of a machine which can rotate one with respect to the other by virtue of the rolling bearing.

The outer ring 2 also comprises a filling orifice 23 (Figure 2) which extends radially from the outer cylindrical surface 2a and opens into the annular space delimited by the raceways 5 , 7 and the guiding faces 9, 1 1 of the inner and outer rings. A plug 24 closes the filling orifice 23 and is held in place relative to the outer ring 2 by a pin 25 which extends axially. The plug 24 comprises two planar surfaces 24a, 24b having respectively the same shape than the raceway 7 and the guiding face 1 1 . Said raceway 7 and guiding face 1 1 are interrupted by the filling orifice and are replaced at this level by the planar surfaces 24a, 24b o f the plug without the mechanical properties thereof being impaired. The filling orifice 23 is provided in the outer ring 2 for introducing the rollers 3 and the spacers 1 3 into the first annular space defined between the inner and outer rings 1 , 2.

The outer ring 2 also comprises a second filling orifice 26 which extends radially from the outer cylindrical surface 2a and opens into the annular space delimited by the raceways 6, 8 and the guiding faces 10, 12. The outer ring 2 also comprises a plug 27 closing the filling orifice 26 and comprising two planar surfaces 27a, 27b which respectively replace locally the raceway 8 and the guiding face 12. The plug 27 is held in place by a pin 28. The filling orifice 26 enables the introduction of the rollers 4 and the spacers 13 into the second annular space defined between the inner and outer rings 1 , 2. In the illustrated embodiment, the plugs 24, 27 are provided on the outer ring 2. Alternatively, the plugs may be provided on the inner ring 1 .

The embodiment shown on Figure 4, in which identical parts are given identical references, differs from the previous embodiment in that the rolling bearing further comprising two annular seals 3 1 , 32 positioned radially between the inner and outer rings 1 , 2. The seal 3 1 is mounted axially between the rollers 3 and the radial surface 2b o f the outer ring 2. The seal 32 is positioned axially between the rollers 4 and the radial surface l c o f the inner ring 1 . The seal 32 is identical to the seal 3 1 and is positioned symmetrically with respect to the latter with regard to the radial plane passing through the centre of the ro lling bearing. A closed space is defined between the rings 1 , 2 and the seals 3 1 , 32 in which the rollers 3 , 4 are housed so as to be protected against polluting elements.

The seal 3 1 has, in cross section, the overall shape of a H. The seal 3 1 formed of an elastic material comprises an annular portion 33 , two annular internal lips 34, 35 forming one of the branches of the H, and two annular external lips 36, 37 forming the other branch of said H. The lips 34 to 37 have a certain degree of axial elasticity and join or attach directly the annular portion 33. The lips 34, 35 and 36, 37 are symmetric with respect to a radial plane passing through the centre of the seal 3 1 , the lips 34, 36 and 35 , 37 being also symmetric with respect to an axial plane passing through the portion 33. The lips 34 , 36 and 35 , 37 respectively press against annular radial protrusions or ribs 38 and 39 respectively provided on the outer cylindrical surface I d of the inner ring and on the bore 2d of the outer ring. The ribs 38 , 39 radially face each other.

The seal 3 1 is axially maintained between the inner and outer rings 1 , 2 by the opposite radial ribs 38 , 39. In order to keep in a permanent contact state the lips 34, 36 and 35 , 37 with ribs 38 and 39 , the thickness of the ribs is made larger than the axial gap between the lips in a free state . The seal 3 1 and the ribs 38 , 39 are thus resiliently coupled in the axial direction which prevents relative axial displacement between the seal 3 1 and the rings 1 , 2.

As above-mentioned, the sealing of the rolling bearing on the other side is provided by the seal 32 which is identical to the seal 3 1 and which cooperates with annular ribs 40, 41 of the inner and outer rings 1 , 2. Said ribs 40, 41 and 38 , 39 are mutually symmetric with respect to the radial plane passing through the center o f the rolling bearing.

Although the invention has been illustrated on the basis of a rolling bearing having a double row of oblique contact rollers, it should be understood that the invention can be applied to bearings having a simp le row of rollers or at least three rows of rollers. Otherwise, in the illustrated embodiments, the rolling bearings are O-type bearings . Alternatively, it may also be possible to foresee X- type rolling bearings .

Furthermore, the inner ring and/or the outer ring may comprise gearing teeth on their outer periphery, so as to be connected to driving gears for instance connected to the output shaft of a motor.

Thanks to the invention, the service life of the bearing is increased by up to 40 % and the friction o f the bearing is reduced. This is particularly advantageous in the case o f a wind turbine comprising actuation means for changing the pitch o f the blades, because it allows to downsize these actuation means since less power is required to pitch the blades, and even to reduce the response time o f this pitching action, with, as a consequence, an improved overall efficiency o f the wind turbine.