EP2417371A1

EP2417371A1 - Roller for a rolling bearing

Info

Publication number: EP2417371A1
Application number: EP10717184A
Authority: EP
Inventors: Olivier Blanchin; Stéphane Paillet; Christian Ronzani
Original assignee: NTN SNR Roulements SA
Current assignee: NTN SNR Roulements SA
Priority date: 2009-04-10
Filing date: 2010-04-06
Publication date: 2012-02-15
Also published as: WO2010116058A1; FR2944330A1; FR2944330B1

Abstract

The invention relates to a roller (4) for a rolling bearing, said roller having an outer surface (5) of revolution about an axis of symmetry (A) and a lateral face (6) arranged on each side of said outer surface, said roller being intended to turn in said bearing about its axis of symmetry (A) while bearing on its outer surface (5), said roller having two recesses (8) which are each produced in one lateral face (6) and extend along the axis of symmetry (A), said recesses having an opening diameter (di) measured on the lateral face (6) and being separated axially by a bridge of material (9) of length (e), said opening diameter and said length of the bridge of material (9) fulfilling the following geometric condition: 0.1 = e/d1 = 1.

Description

Roller for rolling bearing

The invention relates to a roller for a rolling bearing and a rolling bearing in which such rollers are mounted.

The invention applies in particular to rollers for an epicyclic gear bearing, in particular a planet bearing of an epicyclic reduction gearbox for a helicopter gearbox.

In this application, it is known to use solid rollers, in particular of spherical barrel geometry. Each roll has an outer surface of revolution about an axis of symmetry and a side face disposed on each side of said outer surface. These rollers are intended to be mounted in the bearing by being arranged in a retention cage so as to be able to rotate in said bearing around their axis of symmetry while bearing on their outer surface.

To do this, the lateral faces of the rollers may have a recess in which an axial projection of the cage is engaged so as to keep each of said rollers rotating about their axis of symmetry.

However, the satellite bearings according to the prior art have a significant weight, which is even more critical for an aeronautical application in which five to ten bearings are conventionally embedded in a planetary reducer equipping a gearbox.

The object of the invention is to improve the prior art by notably proposing rollers for rolling bearings which have a reduced mass while satisfying the functional requirements of the bearing, in particular with respect to the structural fatigue of said rollers under the effect of the cycles of loads that they undergo in time. For this purpose, and according to a first aspect, the invention proposes a roller for rolling bearing, said roller having an outer surface of revolution about an axis of symmetry and a lateral face disposed on each side of said outer surface, said roller being adapted to rotate in said bearing about its axis of symmetry while resting on its outer surface, said roller having two recesses which are respectively formed on a lateral face extending along the axis of symmetry, said recesses having an opening diameter di measured on the side face and being axially separated by a material bridge of length e, said opening diameter and said length of the material bridge fulfilling the following geometrical condition: 0.1 <- <1. d \

According to a second aspect, the invention proposes a rolling bearing comprising an inner member and an outer member between which are mounted such rollers, said rollers being arranged in a retention cage so as to be rotatable about their axis of symmetry. being supported on said members via their outer surface.

Other objects and advantages of the invention will appear in the description which follows, made with reference to the appended figures in which:

- Figure 1 shows in perspective cutaway a rolling bearing according to one embodiment of the invention;

- Figures 2 show a roller according to one embodiment of the invention, respectively in longitudinal section (Figures 2a and 2c) and a top view showing the contact ellipse (Figure 2b).

In relation to FIG. 1, an embodiment of a rolling bearing in the form of an epicyclic reduction gearbox bearing for a helicopter gearbox is described below. The epicyclic gear is an effective mechanical principle for transmitting power and reducing speed in a small footprint. However, the mass of the bearings This mechanical assembly is important (bearings in large numbers: generally between five and ten).

The bearing comprises an inner ring 1 and an outer ring 2. For this application, the outer surface of the outer ring 2 is provided with a gear means formed of axial teeth 3. In a variant that is not shown, a rolling bearing according to the invention may find application in another field in which in particular a weight gain of said bearing is desirable.

The rings 1, 2 each comprise a raceway between which is arranged a row of rollers 4 so as to allow the relative rotation of said rings.

In relation to FIG. 2, an embodiment of the rollers 4, which each have an outer surface 5 of revolution about an axis of symmetry A and a lateral face 6 disposed on each side of said outer surface, is described below. Given the power to be transmitted and the significant reduction ratio, the rollers 4 may be made of metal material, especially rolled steel type 100Cr6.

In the bearing, the rollers 4 are intended to rotate about their axis of symmetry A during the rotation of said bearing, said rollers bearing on the rolling tracks via their outer surface 5. Moreover, when the rotation, the side faces 6 are guided along a shoulder or the retention cage 7 so as to maintain the rollers 4 in the bearing.

In the embodiment shown, the outer surface 5 has a barrel spherical geometry of radius R (commonly called barrel roll) in which the diameter d of side faces 6 is smaller than the central diameter D of said outer surface. In addition, the lateral faces 6 extend respectively in a plane transverse to the axis of symmetry A, the diameters d being measured in the transverse planes and said planes being spaced from a length L corresponding to that of the roller 4. Alternatively not shown, the roller 4 may have a cylindrical or conical geometry.

To obtain a weight saving in the bearing, the invention proposes a relief of the rollers 4 that it incorporates. To do this, the rollers 4 have two recesses 8 which are made, in particular by drilling, turning or milling, respectively on a lateral face 6 extending along the axis of symmetry A. The recesses 8 have an opening diameter di measured on the side face 6 and are separated axially by a material bridge 9 of length e.

However, the rollers 4 are subjected to structural fatigue as a result of the load cycles they undergo over time. In order to meet the functional requirements of the bearing, particularly with respect to this fatigue, while decreasing the weight, the invention proposes to reduce the amount of material of the rollers 4 in the less mechanically stressed areas and to keep it elsewhere.

To do this, according to a first advantageous characteristic of the invention, the opening diameter di and the length e of the material bridge 9 can fulfill the following geometrical condition: 0.1 <- <1. Thus, the recesses 8 are d \ arranged to maintain a sufficient wall thickness to mechanically withstand the stresses experienced during the rotation of the bearing.

In particular, the length e of the material bridge 9 is determined according to the application to be sufficient to be certain, with the safety margins in force in said application, not to risk a fatigue failure of a roller 4 in the bearing.

In addition, to make reliable guiding on the side faces 6, the opening diameter di may be such that d -d _λ ≥ lmm, so as to maintain a sufficient guide length of the roller 4 in the bearing. According to another advantageous characteristic of the invention, each recess 8 has a convergent frustoconical geometry having a bottom diameter d ₂ on the junction zone with the diameter bridge 9, said bottom diameter being smaller than the opening diameter di . Thus, a maximum of material can be maintained in the central zone of the roll 4 which is the most stressed by the contact between the outer surface 5 and the raceways.

Indeed, the maximum diameter D of the outer surface 5 is disposed in the center of said surface, around the material bridge 9. Thus, the contact zone (called Hertz) between a roller 4 and the rolling tracks is positioned at right of the center of the roll 4, that is to say the right of the material bridge 9, the Hertz stress depth being directly related to the level of contact pressure between the roller 4 and the tracks.

In the embodiment shown, the contact zone has an elliptical shape 10 (FIG. 2b) which has a large length L _e . To optimize the mechanical strength of the rollers 4, each recess 8 may have a diameter d _e measured at a quarter of the great length L _e of the contact ellipse 10 of which is such that _e <^ ^D Â • Thus, the thickness diametral Dd _e of the material around the material bridge 9, that is to say the depth of material left in this area, is greater than W, so as to be sufficient to ensure the structural strength of the rollers 4 in fatigue.

According to another advantageous characteristic of the invention, the junction zone between the recesses 8 and the material bridge 9 has a connection radius r, said connection radius r being in particular greater than 0.1 mm. Thus, on the most stressed area of the rollers 4, there is eliminated any risk of local over-stress due to sharp angles or connections of uncontrolled surfaces. In particular, the recesses 8 extend over a depth P defined between diameters di and d ₂ , the connection radius r being formed from said bottom diameter d ₂ . To allow retention of the rollers 4 in the running space during the rotation of the bearing, said rollers are arranged in a retention cage 7 so as to be rotatable about their axis of symmetry A while bearing on the members 1 , 2 through their outer surface 5.

According to one embodiment, the cage 7 is formed in one piece, in particular by machining a metallic material, to comprise a first ring and, offset axially, a second ring, said rings having the same diameter. The cage further comprises a plurality of axial crosspieces which extend between said crowns so as to form between two adjacent crosspieces and the crowns a retention housing of a roller 4. In particular, the internal geometry of the housing is formed to fit the periphery of the roll 4 allowing its rotation about its axis of symmetry A.

In addition, each lateral face of a roll 4 is disposed facing respectively a side face of a housing, a hooking means of said roller being formed on each side face of said housing. According to one embodiment, the hooking means comprises an axial projection engaged in a recess 8 of the roll 4 so as to keep said roll in said housing in rotation.

A numerical example is given below for the characteristic geometrical dimensions of a roll 4 according to the invention: L = 30 mm

D = 20 mm

R = 50 mm d = 16 mm

Cl ₁ = 10 mm r = 3 mm e = _e = 6 mm 7 mm On this roll 4, the lightening according to the invention makes it possible to gain about 10g over 70g which is substantial and very interesting for the application in question.

Claims

Roller (4) for rolling bearing, said roller having an outer surface (5) of revolution about an axis of symmetry (A) and a side face

(6) disposed on each side of said outer surface, said roller being adapted to rotate in said bearing about its axis of symmetry (A) while resting on its outer surface (5), said roller being characterized in that it has two recesses (8) which are respectively formed on a lateral face (6) extending along the axis of symmetry (A), said recesses having an opening diameter (di) measured on the lateral face (6). ) and being axially separated by a material bridge (9) of length (e), said opening diameter and said length of the material bridge (9) fulfilling the following geometrical condition: 0.1 <- <1.

Roller for rolling bearing according to Claim 1, characterized in that the lateral faces (6) have a diameter (d) measured in a transverse plane, the opening diameter (di) being such that d -d _x ≥ \ mm.

Roller for rolling bearing according to claim 1 or 2, characterized in that each recess (8) has a convergent frustoconical geometry having a bottom diameter (d ₂ ) on the junction area with the diameter bridge (9). ), said bottom diameter being smaller than the opening diameter (di).

Roller for roller bearing according to Claim 3, characterized in that the outer surface (5) has a maximum diameter (D) and is intended to have a contact ellipse (10) in the bearing, each recess (8). having a diameter (d _e ) measured at a quarter of the great length (L _e ) of said ellipse, said diameter being such that d _e < ⁴ ^.

5. Roller for rolling bearing according to any one of claims 1 to 4, characterized in that the junction area between the recesses (8) and the material bridge (9) has a connecting radius (r).

Roller for rolling bearing according to Claim 5, characterized in that the connecting radius (r) is greater than 0.1 mm.

Roller for rolling bearing according to any one of claims 1 to 6, characterized in that the outer surface (5) has a spherical barrel geometry in which the diameter (d) of the side faces (6) is smaller than the central diameter (D) of said outer surface, said central diameter being formed around the material bridge (9).

Roller bearing comprising an inner member (1) and an outer member (2) between which are mounted rollers (4) according to any one of claims 1 to 7, said rollers being arranged in a holding cage (7). ) so as to be rotatable about their axis of symmetry (A) bearing on said members via their outer surface (5).

9. rolling bearing according to claim 8, characterized in that the retention cage (7) comprises two rings and a plurality of axial crosspieces extending between said rings so as to form between two adjacent sleepers and the crowns a housing of retaining a roller (4), each lateral face (6) of said roller being disposed opposite respectively a lateral face of the housing, a hooking means of said roller being formed on each lateral face of said housing, said hooking means comprising an axial projection engaged in a recess (8) of said roll so as to keep said roll in said housing in rotation.

10. Rolling bearing according to Claim 9, characterized in that the outer surface of the outer member (2) is provided with a gear means (3) for use in an epicyclic gear train.