FR2925631A1 - Conical roller bearing assembly for gear box, has rollers with small and large end faces that are in contact with contact face of ring's collar, where contact face extends until being intersected with geometry cone defined by cone distance - Google Patents

Abstract

The assembly (10) has an inner ring (12) defining a revolution geometric axis (A1), and on which a convex tronconical inner rolling path (18) defined by a cone distance (G1) is formed. The ring has a collar (14) on which a concave tronconical contact face (15) defined by another cone distance (G2) is formed. Conical rollers (20) have a conical surface (26) that is in contact with the rolling path. The rollers have small and large end faces (22, 24) that are in contact with the face (15). The face (15) radially extends until being intersected with a geometry cone defined by the distance (G1). An independent claim is also included for a method for realizing a rolling assembly.

Description

ASSEMBLY FOR TAPERED ROLLER BEARING AND METHOD FOR ITS PRODUCTION

TECHNICAL FIELD OF THE INVENTION [001] The invention relates to an assembly for a tapered roller bearing, as well as to its production method. The present invention applies to the field of bearings, and more particularly to the field of tapered roller bearings.

STATE OF THE ART [002] A tapered roller bearing inner race generally comprises a raceway and at least one support collar for radial guidance of the tapered rollers. Due to their contact with the moving rollers, the collar and the raceway must be ground. To facilitate this grinding operation, it is known in the state of the art to make a clearance groove between the raceway and the collar, so as to allow a grinding tool to reach the areas close to the intersection between the collar and the raceway. As illustrated in Figure 1, a tapered roller bearing 1 of this type comprises a clearance groove 2 which connects the collar 3 to the inner raceway 4. This groove 2 is the clearance required for the grinding tool. However, the groove 2 thus defined opens partially outside the cone defined by the generating line 5 of the raceway 4, so that the contact between the collar 3 and the rollers 6 is necessarily remote from this cone. As a result, the height of the point of contact C between the rollers 6 and the large collar 3 is high, which generates a high torque between the rollers 6 and the collar 3 and thus significantly penalizes the performance of the bearing in terms of torque and power dissipated.

OBJECT OF THE INVENTION

The present invention therefore aims to overcome the disadvantages of the state of the art by proposing a tapered roller bearing whose collar is sized to reduce the power dissipated and the resistive torque. [4] To do this, it is proposed, according to a first aspect of the invention, an assembly for a tapered roller bearing comprising an inner ring defining a geometric axis of revolution and on which is formed a convex frustoconical inner raceway defined by a first generatrix, the ring further comprising a collar on which is formed a concave frustoconical contact surface defined by a second generator. The assembly also comprises tapered rollers each having a truncated conical surface in contact with the raceway, a small end face and a large end face in contact with the concave frustoconical contact face. This frustoconical contact face extends radially to the intersection with the geometric cone defined by the first generator. The contact face is thus extended radially inwards, which makes it possible to bring the point of contact between the rollers and the collar closer to the axis of revolution, and consequently to limit the power dissipated and the resistive torque.

[5] In the context of the present application, the term "frustoconical surface" means on the one hand the truncated cone in the strict sense, that is to say the surfaces of revolution constituting a trunk of a cone whose generator is a straight line and the center of revolution, a point on this line, and on the other hand, by approximation, surfaces of which no point is more than 1 mm distant from a frustoconical surface in the strict sense given, and that one assimilate to this truncated cone. Because of this definition, include in the frustoconical surface definition surfaces of revolution generated by a line of very small curvature, the radius of curvature is in all points greater than 500 mm, and preferably greater than 1000 mm.

[6] In the context of the present application, a frustoconical surface will be called concave if the part of the part having the face in question is entirely located radially outside the frustoconical surface in question. It will be called convex if the part of the part having the face in question is located entirely radially inside the frustoconical surface.

[7] Preferably, the assembly for a roller bearing comprises a groove situated in the radial extension of the contact face, inside the geometrical cone defined by the first generating line and transversely inside the second defined geometrical cone. by the second generative right. This groove connects the truncated conical inner race to the concave frustoconical contact face and makes it possible to bring the useful bearing surface of the conical rollers on the collar closer to the axis of rotation of the bearing.

[8] According to a particularly advantageous method of assembly, the angle formed by the two generating lines is between 85 ° and 95 ° and each roll contacts the frustoconical contact face in at least one point

respecting the inequality i <0, 026, where H is the height of the point of contact considered and E the height of the point of intersection between the two generating lines, the heights being measured with respect to the geometric axis of revolution of the inner ring. The assembly mode thus offers the possibility of reducing the height H of the point of contact in question and consequently of saving material while increasing the performance of the bearing.

[9] According to a particularly advantageous embodiment, the assembly comprises a roller holding cage, and an outer ring defining a geometric axis of revolution and on which is formed a concave frustoconical outer raceway. Advantageously, the geometric axis of revolution of the outer ring coincides with the geometric axis of revolution of the inner ring, and the rollers each comprise a connection profile on the outer edge of the large end face. Such an assembly for tapered roller bearing can be installed in particular in a gearbox device, and reduce the torque and the power dissipated by the rolling friction. Of course, other applications are possible.

Finally, the invention relates to a method of making such an assembly for tapered roller bearings. The method consists of producing, by the hard turning technique, at least the generatrix of the collar, then the groove in the extension of the generatrix of the collar. During hard turning, the amount of heat transmitted to the machined part is much less than in a grinding operation, and problems of surface burn are avoided. When the cutting edge of the hard turning tool starts to wear out, a characteristic white surface layer appears when micrographically analyzing a section of the workpiece. This white layer constitutes an area composed of tempered and hardened martensite, which is explained by the elevation of the surface temperature and the difference in temperature between this surface and the underlying layers. The level of tempering and hardening depends mainly on the process parameters and the wear of the cutting tool, which results in a greater or lesser thickness of this characteristic white layer. In any case, it is preferable that the white layer has a thickness of less than 15 μm in the groove and 10 μm in the collar.

BRIEF DESCRIPTION OF THE FIGURES [0011] Other features and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, in which:

- Figure 1 (already commented) is a sectional view of a tapered roller bearing according to the state of the art; - Figure 2 shows a sectional view of a tapered roller bearing assembly according to the present invention; ,

FIG. 3 represents a conical roller of the assembly of FIG. 2, and

FIG. 4 represents a schematic section comparing the device of FIG. 2 and that of FIG. 1.

EXAMPLE OF REALIZATION

In Figure 2 is shown a sectional view of an assembly for tapered roller bearing according to the present invention.

The assembly for tapered roller bearing 10 comprises an inner ring 12 defining a geometric axis of revolution Al. On the inner ring 12 are formed a large collar 14 and a small collar 16, and a frustoconical raceway. 18. The convex frustoconical inner raceway 18 and the large collar 14 are respectively directed along a first generating line G1 and a second generating line G2. The assembly also comprises a plurality of rollers 20 each having a large end face 22, a small end face 24 and a frustoconical contact surface 26.

The contact faces 22, 26 of each conical roller 20 are able to come into contact with the inner ring 12. The large end face 22 comes into contact with the concave frustoconical face 15 of the large collar 14 , and the frustoconical contact surface 26 with the inner raceway 18.

The frustoconical face 15 is connected to the raceway 18 by a groove 28, located in the radial extension of the frustoconical face 15 along the generating line G2 of the large collar 14. It also extends inside the geometric cone of revolution defined by the generating line G1 of the inner raceway 18, so that the groove 28 connects the frustoconical surface 26 and the large collar 14 leaving a space without material. In the exemplary embodiment, the angle formed by the two generating lines G1 and G2 being between 85 and 95 °, and in this example substantially equal to 90 °, the groove 28 thus defined makes it possible to obtain a average height of the point of contact C between the large collar 16 and the large end face 22 of each tapered roller 20 lowered and of the order of 0.8 millimeters.

As a result, there is at least one point of the conical roller which

comes into contact with the large collar and respects the inequality <O, 026, H being the height of the point of contact C considered and E the height of the point of intersection between the two generating lines. These heights being measured with respect to the geometric axis of revolution of the inner ring 12, such a definition of the groove 28 reflects a lowering of the contact point C with respect to the state of the art, lowering which makes it possible to reduce the torque and power dissipated at the neck by 33%. This reduction then reduces the efficiency losses of the tapered roller bearing induced by these harmful phenomena. Furthermore, the assembly also comprises an outer ring 30 defining a geometric axis of revolution A2, advantageously confused with the axis of revolution of the inner ring 12.

On this outer ring 30 is formed a concave frustoconical outer raceway 32 in contact with the frustoconical contact face 26 of the conical roller 20.

In addition, the assembly comprises a roller retaining cage 34 ensuring the consistency and good performance of the assembly. Indeed, this cage 34, located between the inner ring 12 and the outer ring 30, 10 traps all the tapered rollers 20 without altering the contact between the frustoconical contact face 28 of each of the tapered rollers 20 and the raceways inner and outer rings 18 and 32 of the inner and outer rings 12 and 30.

[0022] Finally, on each conical roller 20 is formed a connection profile 36, consisting of a small sloping surface of small dimension connecting the small and large end faces 22 and 24 to the frustoconical contact faces 26 of the conical rollers 20 in order to eliminate the sharp edge likely to deteriorate the contact of the conical roller 20 with the raceways 18 and 32 and the collars 14 and 16.

The profile of the ring can advantageously be produced by hard turning, using a cutting tool of high tenacity, without a step of grinding the surfaces of the collar and the groove. The cutting tool is a turning plate which makes it possible to form, preferably in several passes, the collar and the groove inside the inner ring. To form the groove 28 in the extension of the second generatrix G2, the cutting edge of the wafer is directed towards the inside of the geometric cone defined by the geometric axis of the inner ring. The final surface state is distinguished by striations or helical grooves oriented in the same direction towards the axis of rotation, unlike the cross striations characteristic of the rectification. It is furthermore remarkable by the presence of a characteristic surface white layer visible on micrographic analysis of a cut of the machined part, composed of tempered and hardened martensite of a thickness of less than 15 μm in the groove and pm at the collar. In Figure 4 is shown on the one hand in solid lines the profile of the ring according to the invention and a corresponding roller, and on the other hand in fine broken lines the profile of a ring and a roll of the state of the art. The ring according to the invention is distinguished by a frustoconical contact face 15 which extends radially to the intersection with the geometric cone defined by the first generatrix G1. The useful part of the contact face 15 is therefore greater than in the state of the art, which makes it possible to modify the profile of the rollers, and significantly increase the radius of curvature of the connection profile 36 so as to bring the point of contact of the axis of rotation of the ring and the generator G1.

In principle, the connection profile 36 may be limited to what is strictly necessary to remove the sharp edge between the frustoconical surface 26 and the large end face 22. However, because of the manufacturing processes of the rollers the radius of curvature of the connection profile depends on the size of the roll. With reference to FIG. 3, it has been empirically determined that an excellent compromise between the search for a minimization of the radius of curvature and the manufacturing constraints is obtained when the radius of curvature R of the connection diameter satisfies the following inequality: R K.DW + xo

where Dw is the large diameter of the roll, and where Ro and K are constants, with Ro = 0.09mm and K = 0.03, where R and Dw are expressed in mm, this empirical relation being valid for at least Dw between 10mm and 20mm, and by extension for values between 7mm and 30mm.

FIG. 4 also shows, taking into account the dimensional tolerances of manufacture, the range of variation of the point of contact C between the roll and the collar 14 with the invention (CMIN, CMOV and CMAX points). and according to the state of the art (points C'MIN, C'MOV and C'MAX). Each of these points corresponds to a height H of the point of contact considered. The table below shows the comparative values of the H / E ratio (average, minimum and maximum values) obtained experimentally, according to the process used to produce the tapered roller bearing assembly (bar turning). or hard turning), where E designates the height of the point of intersection of generators G1 and G2. EHH / E machining and milling 46.59 1.44 0.0309 min 46.59 1.03 0.0221 rectification Max 46.59 1.83 0.0393 medium 46.59 0.82 0.0176 hard turning min 46 , 59 0.37 0.0079 Max 46.59 1.24 0.0266 It can be seen that the hard turning technique used for producing the groove and the position of the groove within the inner ring allows a decrease in the height of the contact point C and the ratio H / E compared to the technique usually used for this type of machining. Thus, the lowering of the contact point C has the advantage of significantly increasing the performance of the bearing in terms of friction. In practice, such an assembly makes it possible, in the tests carried out, to reduce by one third the power dissipated at the large collar level under nominal operating conditions of the bearing. In addition, the reduction in the height of the point of contact C allows a saving of material. Indeed, the new heights of the point C accessible by the assembly allow a decrease in the outer diameter of the large collar 14, the consequence is a saving of material of the order of 12%.

Claims (9)

A tapered roller bearing assembly comprising: an inner ring (12) defining a geometrical axis of revolution (A1) and on which is formed a convex frustoconical inner raceway (18) defined by a first generatrix (G1), the ring (12) further comprising a collar (14) on which is formed a concave frustoconical contact face (15) defined by a second generatrix (G2); and tapered rollers (20) each having a frustoconical surface (26) in contact with the race (18), a small end face (24) and a large end face (22) in contact with the face concave frustoconical contact member (15); the frustoconical contact face (15) extending radially to the intersection with the geometric cone defined by the first generatrix (G1). 2. Assembly for tapered roller bearing according to claim 1, characterized in that it further comprises a groove (28) located in the radial extension of the contact face (15), inside the geometric cone defined by the first generatrix (G1) and connecting the frustoconical inner race (18) to the concave frustoconical contact face (15). 3. A tapered roller bearing assembly according to claim 2, characterized in that the groove (28) is located transversely inside a second geometrical cone defined by the second generatrix (G2). 4. A tapered roller bearing assembly according to any one of the preceding claims, characterized in that the angle 30 formed between the two generators (G1, G2) is between 85 ° and 95 °. 5. Assembly for tapered roller bearing according to any one of the preceding claims, characterized in that each roller (20) contacts the frustoconical contact face (15) at at least one point 35 respecting the inequality H <0 026, where H is the height of the point of contact considered and E the height of the point of intersection between the two generators (G1, G2), the heights being measured with respect to the geometric axis of revolution of the inner ring (Al). Tapered roller bearing assembly according to one of the preceding claims, characterized in that the rollers each have a connection profile between the frusto-conical surface (26) and the large end face (22). connection having a radius of curvature R respecting the following inequality: R <K.Dw + Ro where Dw is the large diameter of the roll between 10mm and 20mm, and where Ro and K are constants, with Ro = 0.09mm and K = 0.03, where R and Dw are expressed in mm. 7. Assembly for tapered roller bearing according to any one of the preceding claims, characterized in that it comprises a holding cage (34) of the conical rollers (20) and an outer ring (30) defining a geometric axis of revolution (A2), on which is formed a concave frustoconical outer raceway (32). Tapered roller bearing assembly according to one of the preceding claims, characterized in that the rollers (20) each have a chamfer (36) on the outer edge of the large end face (22). 9. A method of producing an assembly for a tapered roller bearing according to claims 1 to 7, characterized in that it comprises a step of producing the collar (14) and the groove (28) by a hard turning technique. .