WO2016066224A1

WO2016066224A1 - Thrust bearing

Info

Publication number: WO2016066224A1
Application number: PCT/EP2014/073483
Authority: WO
Inventors: Jerome Dubus; Christian Boch
Original assignee: Aktiebolaget Skf
Priority date: 2014-10-31
Filing date: 2014-10-31
Publication date: 2016-05-06

Abstract

This thrust bearing (1) comprises two rings (2, 4), rotating relatively one to the other in two parallel planes that are perpendicular to a rotation axis (X1) and including each a rolling track (20, 40) for a series of rollers (6). Each rolling track (20, 40) has grooves for receiving complementary ribs of the rollers (6).

Description

THRUST BEARING

The invention concerns a thrust bearing.

A thrust bearing includes two rings that are configured to rotate relatively one to the other in two parallel planes, which are both perpendicular to a rotation axis of the bearing. A series of rolling elements, such as balls or rollers, is interposed axially between the two rings and allow one ring to rotate independently from the other. To that end, the two bearing rings include each a rolling track for the rolling elements.

Standard thrust bearings cannot be used in applications wherein a high load capacity is required. For example, it is actually impossible to use a thrust bearing in a roller screw mechanism. A roller screw mechanism includes an outer threaded screw and an inner threaded nut between which a plurality of outer threaded rollers is arranged. The nut is then coaxially disposed around the screw. An outer cap covers the screw head and a slight bearing is interposed between the screw head and the cap so as to support the axial load transmitted by the screw. For robustness purpose, it might be interesting to replace the slide bearing by a thrust bearing. However, standard thrust bearings do not have a sufficient load capacity to support the screw axial load. Indeed, a larger thrust bearing would be needed to fulfil the requirements regarding axial load capacity.

The invention intends to solve this drawback by proposing a thrust bearing having a greater axial load capacity, while remaining compact.

To this end, the invention concerns a thrust bearing comprising two rings, rotating relatively one to the other in two parallel planes that are perpendicular to a rotation axis and including each a rolling track for a series of rollers. According to the invention, each rolling track has grooves for receiving complementary ribs of the rollers.

Thanks to the invention, the grip of the rollers on the rolling tracks is improved as the contact points are more numerous than in standard thrust bearings. Each roller groove is delimited between two adjacent ribs. The load capacity of each roller is equivalent to that of a series of balls of same dimension. In practice, the load capacity of the roller is equivalent to as many balls as ribs are provided on the roller. This allows increasing the global load capacity of the thrust bearing. Moreover, in comparison to standard rollers having a contact surface with the rings, grooved rollers only have contact points with the rings, thereby reducing the friction between the rollers and the rings.

Further aspects of the invention which are advantageous but not compulsory are specified below:

- The grooves are delimited between the rollers ribs and these grooves extend each circumferentially around a rolling axis of the roller. - The roller grooves are V-shaped.

- The bottom of the roller grooves is curved.

- The side walls of the roller grooves are curved.

- The side walls of the roller grooves are concave.

- The rolling tracks grooves are V-shaped.

- The bottom of the rolling tracks grooves is curved.

- The side walls of the rolling tracks grooves are frustoconical.

- The side walls of the rolling tracks grooves form a right angle.

- The side walls of the rolling tracks grooves are each inclined of 45° relative to an axis parallel to the rotation axis.

- The rollers have a cylindrical jacket surface.

- The rollers have a frustoconical jacket surface.

- The rollers are arranged within the bearing so that the jacket surface of the rollers converges in a centripetal direction with respect to the bearing rotation axis.

- A convergence angle of the roller jacket surface is the same as the angle of the rolling tracks with respect to an axis that is radial to the rotation axis.

The invention will now be explained in correspondence with the figures, and as an illustrative example, without restricting the object of the invention. In the figures:

- figure 1 is an axial section of a thrust bearing, according to a first embodiment of the invention,

- figure 2 is a side view of a roller belonging to the thrust bearing of figure 1 ,

- figure 3 is an enlarged view of detail III of figure 2,

- figure 4 is a section of a ring belonging to the thrust bearing of figure 1 ,

- figure 5 is an enlarged view of detail V of figure 4,

- figure 6 is a section similar to figure 1 , for a second embodiment of a thrust bearing according to the invention, and

- figure 7 is a view similar to figure 2, of a roller belonging to the thrust bearing of figure 6.

Figure 1 represents a spherical roller thrust bearing 1 having a rotation axis X1 . The thrust bearing 1 includes two parallel rings 2 and 4 rotating relatively one to the other in two parallel planes P2 and P4 that are perpendicular to rotation axis X1 . These two parallel planes are axially offset, along rotation axis X1 . The rings 2 and 4 face each other symmetrically with respect to a medium plane P1 of the bearing 1 . Rings 2 and 4 include each a rolling track, respectively 20 and 40, for receiving a series of rollers 6. Rollers 6 are axially interposed between the rings 2 and 4. Bearing 1 further includes a cage 8 for holding the rollers 6 on the rolling tracks 20 and 40.

As shown on figure 2, each roller 6 is centered on a rolling axis Y6. Each roller 6 has a jacket surface S6 that is cylindrical with a circular base. The rollers 6 are grooved. More precisely, each roller 6 includes a series of peripheral ribs 60 that delimit between them some grooves 62. The grooves 62 extend each circumferentially around rolling axis Y6. In assembled state of the thrust bearing 1 , the rolling axis Y6 of each roller 6 is radial to rotation axis X1 .

As shown on figure 3, the roller grooves 62 are V-shaped. Each groove 62 includes a curved bottom 64 and two curved side walls 66. More precisely, the side walls 66 of each groove 62 are domed, that is concave, while the bottom 64 of each groove 62 is sunken, that is convex.

As shown on figures 4 and 5, the rolling track 20 includes a series of grooves 24 that are complementary to roller ribs 60. In other words, the roller ribs 60 are received in rolling tracks grooves 24. Grooves 24 are separated from each other by ribs 22. Accordingly, rolling tracks ribs 22 are received in roller grooves 62. Grooves 24 are V-shaped and include a convex bottom 26 and two frustoconical side walls 28. The frustoconical side walls 28 define together a right angle A24. In other words, angle A24 is equal to 90° . Ring 4 is identical to ring 2. As a result, the rolling track 40 of ring 4 is also provided with ribs 42 that delimit between them grooves 44 for receiving the roller ribs 60. The grooves 44 are V-shaped and include each two frustoconical side walls 48.

In the example, each roller 6 includes five ribs 60. As a result, the axial load capacity of each roller 6 is comparable to that of a series of five balls of same dimensions, in particular the same diameter. As a general rule, the axial load capacity of each roller 6 is comparable to that of a number of balls equal to the number of ribs 60 provided on the external surface of the roller. Consequently, the load capacity of the thrust bearing 1 is greater to that of a standard thrust bearing. As a result, the thrust bearing 12 may be used in applications wherein a high axial load support is required, such as a roller screw mechanism, while it remains compact as compared to a five balls bearing.

Moreover, in assembled state of the thrust bearing 1 , the side walls 28 of the rolling tracks grooves 24 form contact surfaces between the rollers 6 and rings 2. Similarly, the side walls 48 of the rolling track grooves 44 form contact surfaces between rollers 6 and ring 4. These contact surfaces are inclined of 45° relative to an axis parallel to the rotation axis X1 . The axial load is then not integrally transmitted in the axial direction between the two rings 2 and 4, which improves the stability of the thrust bearing 1 . Furthermore, positioning of the rollers 6 on the rolling tracks 20, 40 is easy, in comparison to standard thrust bearing. Thus, grip of the rollers 6 on the rolling tracks 20, 40 is improved.

Grooved rollers 6 and complementary webbed rolling tracks 20 and 40 allow increasing the axial load capacity of the bearing, without decreasing the bearing compactness. As a result, the power density, which is the ratio between thrust bearing congestion and thrust bearing load capacity, is reduced.

On figures 6 and 7, a second embodiment of a thrust bearing 1 ' is represented. Here-below, only the differences with the first embodiment represented on figures 1 to 5 are mentioned. Moreover, the components of the thrust bearing 1 ' according to the second embodiment that are identical to that of the first embodiment have the same reference, while the components that are different with respect to the first embodiment have a reference that is followed by a single quotation mark (').

Thrust bearing 1 ' is a tapered roller bearing 1 ', comprising two parallel rings 2' and 4' rotating in two parallel planes P2 and P4 and symmetrically arranged with respect to a medium plane P1 . Bearing 1 ' also includes frustoconical rollers 6' interposed axially between the rings 2' and 4'. More precisely, the rollers 6' each have a jacket surface, or enveloppe surface, S6' that is frustoconical, with a circular base, and that is centered on a rolling axis Y6. A6 denotes a convergence angle of the jacket surface S6' towards the rolling axis Y6.

Accordingly, the rings 2' and 4' each have a rolling track, respectively 20' and 40', that is inclined in a complementary manner with the jacket surface S6'. More precisely, the rolling tracks 20' and 40' are inclined, relative to an axis radial to the rotation axis X1 , with the same angle as the convergence angle A6. The rollers 6' have each an extremity E1 of small diameter and an extremity E2 of larger diameter. Extremities E1 and E2 are opposite along the rolling axis Y6. In assembled state of the bearing 1 ', extremity E1 is closer to axis X1 than extremity E2. In other words, in assembled state of the thrust bearing 1 ', the jacket surface S6' converges in a centripetal direction with respect to rotation axis X1 .

The rolling tracks 20' and 40' converge towards rotation axis X1 on the inside of the bearing 1 ', that is respectively in direction of the ring 40' and 20'. The thrust bearing 1 ' further includes a cage 8 for retaining the rollers 6'.

As in the first embodiment, the rolling tracks 20' and 40' have grooves for receiving complementary ribs of the rollers 6'. 28' and 48' denote respectively a side wall of the external rolling tracks grooves 20 and 40. External rolling tracks grooves are the grooves which are radially furthest from rotation axis X1 . Side walls 28' and 48' are also the side walls that are the furthest from the rotation axis X1 . In operating conditions, the bearing 1 ' usually supports an axial load that is applied on the external face of one or two rings. In the example of figure 6, an axial load F1 is applied on an external face 41 ' of the ring 4'. By wedge effect, the load F1 is partially transmitted to the rollers 6' in a centrifugal direction F2 with respect to the rotation axis X1 . The rollers 6' are then pressed against external groove side walls 28' and 48' of the tracks 20' and 40'. Consequently, friction between the rollers 6' and the rings 2', 4' is reduced in this area.

In a non-represented alternative embodiment, angle A24 formed by the side walls 28 of the rolling tracks 20, 40 is different from 90° .

In a non-represented alternative embodiment, thrust bearing 1 or 1 ' does not include a cage 8.

In a non-represented alternative embodiment, rollers 6 or 6' may include a number of ribs 60 that is different from five.

In a non-represented alternative embodiment, side walls 28, 28' of the rolling tracks grooves 24 may be convex or concave.

In a non-represented alternative embodiment, rollers 6' are oriented in a reverse configuration, wherein the jacket surface S6' converges in a centrifugal direction with respect to rotation axis X1 . The rolling tracks 20' and 40' are then inclined in a complementary manner.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings. Rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Besides, the technical features of the different embodiments and alternative embodiments of the invention described here-above can be combined together to generate new embodiments of the invention.

Claims

1 . -Thrust bearing (1 ; 1 '), comprising two rings (2, 4; 2', 4'), rotating relatively one to the other in two parallel planes that are perpendicular to a rotation axis (X1 ) and including each a rolling track (20, 40; 20', 40') for a series of rollers (6; 6'), characterized in that each rolling track (20, 40; 20', 40') has grooves (24) for receiving complementary ribs (60) of the rollers (6; 6').

2. -Thrust bearing according to claim 1 , characterized in that grooves (62; 62') are delimited between the rollers ribs (60) and in that these grooves (62; 62') extend each circumferentially around a rolling axis (Y6) of the roller (6; 6').

3. -Thrust bearing according to previous claim, characterized in that the roller grooves (62; 62') are V-shaped.

4. - Thrust bearing according to previous claim, characterized in that the bottom (64) of the roller grooves (62) is curved.

5. - Thrust bearing according to claim 3 or 4, characterized in that the side walls (66) of the roller grooves (62) are curved.

6. - Thrust bearing according to claim 5, characterized in that the side walls (66) of the roller grooves (62) are concave.

7.- Thrust bearing according to any previous claim, characterized in that the rolling tracks grooves (24) are V-shaped.

8. - Thrust bearing according to claim 7, characterized in that the bottom (26) of the rolling tracks grooves (24, 44) is curved.

9. - Thrust bearing according to claim 7 or 8, characterized in that the side walls (28; 28') of the rolling tracks grooves (24) are frustoconical.

10. - Thrust bearing according to previous claim, characterized in that the side walls (28; 28') of the rolling tracks grooves form a right angle (A24).

1 1 . - Thrust bearing according to previous claim, characterized in that the side walls (28; 28') of the rolling tracks grooves are each inclined of 45° relative to an axis parallel to the rotation axis (X1 ).

12. - Thrust bearing (1 ) according to any previous claim, characterized in that the rollers (6) have a cylindrical jacket surface (S6).

13. - Thrust bearing (1 ') according to any claim 1 to 1 1 , characterized in that the rollers (6') have a frustoconical jacket surface (S6').

14. - Thrust bearing (1 ') according to previous claim, characterized in that the rollers (6') are arranged within the bearing so that the jacket surface (S6') of the rollers (6') converges in a centripetal direction with respect to the bearing rotation axis (X1 ).

15.- Thrust bearing (1 ') according to claim 13 or 14, characterized in that a convergence angle (A6) of the roller jacket surface (S6') is the same as the angle of the rolling tracks (20', 40') with respect to an axis that is radial to the rotation axis (X1 ).