GB2276213A

GB2276213A - Roller bearings

Info

Publication number: GB2276213A
Application number: GB9305622A
Authority: GB
Inventors: Brian Edward Earthrowl
Original assignee: Cooper Roller Bearings Co Ltd
Current assignee: Cooper Roller Bearings Co Ltd
Priority date: 1993-03-18
Filing date: 1993-03-18
Publication date: 1994-09-21
Anticipated expiration: 2013-03-18
Also published as: GB2276213B; GB9305622D0

Abstract

A roller bearing, particularly a split roller bearing, has rings (11, 12) with raceways (20, 21) with frusto-conical axial end surfaces (24). The rollers (13) have end faces composed of plane inner portions (22) and curved outer portions (23). The curved portions (23) of the rollers (13) and the frusto-conical surfaces (24) provide contact zones (P) with wedge shaped clearance spaces which, inter alia, help maintain a film of lubricant. <IMAGE>

Description

IMPROVEMENTS IN ROLLER BEARINGS The present invention relates in general to roller bearings.

Roller bearings are composed of inner and outer rings with a number of rollers therebetween. The rollers may be cylindrical, tapered or spherical and are usually held in a spaced apart relationship by a cage.

The rollers are guided by raceways which may be defined in a variety of ways, such as by grooves in or ribs or flanges on both or one of the rings.

Certain problems arise when roller bearings are subjected to thrust load and particularly in the event of tilting and skewing of the rollers with respect to the raceways and/or the cage. The axis of a roller, when rotating and progressing along the bearing raceways in an ideal path parallel to the bearing axis describes a cylindrical locus. Skewing is when the roller axis is displaced relative to this locus but maintains parallelism with the bearing axis while tilting is when this parallelism is not maintained Skewing and tilting can result in the rollers contacting and rubbing against the raceway defining means or flanges, especially when the bearing is acting under thrust load.

Such sliding and scraping metal-to-metal contact between the rollers limits the life of the bearing. Further problems then arise from the presence of metal swarf and the lack of retention of the rollers within the cage.

The dynamic performance of bearings is also reduced by this contact since when the edge zones of the end faces of the rollers rub against the raceway defining means or flange surfaces this results in reaction forces acting in a direction non-coaxial with the rollers.

Modifications of the shape or profile of the rollers and/or raceways can improve the performance of roller bearings under thrust load.

According to the invention, and as is known, there is provided a roller bearing comprising inner and outer rings with a plurality of rollers therebetween; the inner ring having a radially outwardly directed raceway and the outer ring having a radially inwardly directed raceway and the inner and outer rings having at least one circumferential flange or equivalent defining one side of one of the raceways. In accordance with the invention, the flange or equivalent has a frusto-conical surface, which may act as a thrust contact surface, lying at a predetermined angle with respect to a radial plane of the bearing and the end faces of the rollers each have a planar inner portion and a radially curvilinear outer portion relative to the rotary axis with the curvilinear portion at one end confronting the frusto-conical surface.

One or both radially curvilinear portions of each roller is thus engageable with the associated frustoconical surface in such a fashion that deleterious affects of skewing and tilting are mitigated. Preferably flanges or the equivalent are provided on both the inner and outer rings and are arranged at mutually opposite sides such that a thrust load acting through the flange of one ring is transmitted through the rollers and through the flange of the other ring. It has been found particularly advantageous for the angle of the or each frusto-conical thrust face to be in the range of 0.10 to 1.00 and more preferably to be in the range of 0.50 to 1.00 and for the radius of curvature of the curvilinear portions of the rollers to be in the range of 200mm to 1000 mm with the centre of curvature on the axis of the roller.

The frusto-conical surface(s) can be formed by machining.

A bearing constructed in accordance with the invention can be a split roller bearing with all the major components split in half radially. Clamping rings can then hold the two halves of the inner ring to a rotating component and it is possible for at least one of the clamping rings to have a frusto-conical surface acting as aforesaid.

With a bearing in accordance with the invention, wedge shape spaces exist at or about the contact areas between the rollers and the associated frusto-conical surface(s). The presence of these wedge shaped spaces aids the maintenance of a lubricant film between the frusto-conical surface(s) and the rollers.

In order that the invention may be understood more readily and various other aspects and features of the invention may become apparent, the accompanying drawings will be referred to in the following description, wherein: Figure 1 is a schematic representation of part of a roller bearing constructed in accordance with the invention; Figure 2 is an enlarged view detailing the circled portion Z of Figure 1 and Figure 3 is a schematic representation of part of a further roller bearing constructed in accordance with the invention.

Figure 1 shows, by way of example, a bearing 10 constructed in accordance with the invention. The bearing 10 has inner and outer rings 11, 12 and a complement of rollers 13 spaced apart by cage 14 therebetween. The bearing rollers 13 have cylindrical outer surfaces 15 which are so dimensioned that the rollers 13 lie closely between the flanges 16-19 defining the sides of raceways 20, 21 of the rings 11, 12, The rollers 13 are of a general circularly cylindrical configuration. The end faces of each roller 13 comprise a planar inner portion 22 and a radially curvilinear or spherical annular outer portion 23 merging the planar portion 22 with the outer surface 15. The curvilinear portion 23 of each roller 13 comprises an annular surface of a sphere of radius 12 having a centre C on an axis A of the roller 13. The flanges 16-19 are each provided with a frusto-conical surface 24, inclined at an angle a relative to a radial plane of the bearing. There is a contact zone P between each roller 13 and the surface 24 with the centre of the contact zone P being a distance H radially from the raceway. The angle a is a design parameter set to one of a number of predetermined standard values to determine the axial and radial load capacity of the bearing 10 and is selected in conjunction with the value of the radius R of the curvilinear portion 23, and the distance H of the contact portion P radially from the raceway. Examples of these parameters a H and R are given hereinafter.

The bearing shown is of the split variety having clamping rings 30, 31.

Figure 2 details the zone 16 wherein the curvilinear surface 23 of one of the rollers 13 is in abutment with the frusto-conical surface 24 of the flange 16.

Figure 3 shows a further embodiment of the invention wherein the clamping rings 30, 31 are provided with the flanges 16, 17. As is known, such clamping rings are used when split bearings are employed and serve to clamp the two halves of the inner rings 11 together about a rotating shaft generally with a diameter in the range of 35mm to 150mm.

In operation, lubrication is provided for the rollers 13 and the contact surfaces 20, 21, 23. The rollers 13 roll within the raceways 20, 21 with the cage 14 acting to space the individual rollers about the periphery of the raceways 20, 21. Due to the configuration of the rollers 13 and the width of the raceways 20, 21 each roller 13 may assume a slightly offaxis position. The frusto-conical surfaces 24 of the end flanges 16-19 affects the skewing. As a result of the off-axis disposition of the rollers 13 with respect to the raceways 20, 21 each roller 13 will contact one of the frusto-conical surfaces 24 at a contact portion P which lies off the central axis A of the roller. The instantaneous velocity components of the roller 13 at the contact position P include a radially inward directed component. It has been found that a velocity component in such a direction tends to induce lubricant flow into a wedge shaped space surrounding the contact portion P.

This establishes and maintains a hydrodynamic lubricating film between the curvilinear surface 23 of the roller 13 and the associated frusto-conical surface 24.

It has been found advantageous to have the clearance distance between the curvilinear face 23 and the frusto-conical surface 24 to be in the range of 0.03mm to 0.06mm. Preferred values of the conical thrust face angle a are in the range of 0.5 to 1.00, whilst the preferred values of the radius R of the curvilinear portions 23 are in the range of 200mm to 1000mm.

Typically the centre of the contact zone P is a radial distance H of 2/3 the height of the associated flange 16-19 from the associated raceway 20, 21. These values have been calculated for bearings having shaft diameters between 35mm and 150mm, and will vary depending, inter alia, on the size of shaft, expected loads and the application of the bearing.

Claims

1. A roller bearing comprising inner and outer rings and a plurality of rollers disposed between the rings, the rings being relatively rotatable about a bearing axis with the rollers being guided by raceways defined at least partly by the rings; wherein the rollers have end faces each with an inner portion and a curvilinear outer portion and the raceways are delimited axially by frustoconical surfaces each of which lies at a predetermined angle relative to a radial plane extending through the adjacent inner portion of the associated end face of one of the rollers and confronts the curvilinear portions of the rollers.

2. A roller bearing according to claim I wherein the frusts-conical surfaces of the raceways are defined by flanges of the rings.

3. A roller bearing according to claim 1, wherein the frusto-conical surfaces of the raceways are defined partly by flanges of the rings.

4. A roller bearing according to claim 1, wherein the bearing is of the split type with the rollers and the rings separable about a central radial plane and the frusto-conical surfaces of the raceways are defined partly by flanges of the rings and partly by clamping rings which serve to hold the rollers and the bearing rings together.

5. A roller bearing according to any one of claims 1 to 4 wherein the inner portion of each end face of each roller is planar.

6. A roller bearing according to any one of the preceding claims wherein the pre-determined angle is in the range of 0.10 to 1.00 degrees.

7. A roller bearing according to any one of the preceding claims wherein the pre-determined angle is in the range of 0.50 to 1.00 degrees.

8. A roller bearing according to any one of the preceding claims wherein the centre of curvature of the outer portion of each end face of each roller lies on a projection of the axis of the roller and the radius of curvature of the outer portion of each end face of each roller is in the range 200mm to l000mm.

9. A roller bearing according to any one of the preceding claims wherein the curvilinear portions of the end faces of each of the rollers and the adjacent frustoconical surfaces of the raceways define contact zones each having a centre disposed at a radial distance from the adjaCi:''t cylindrical outer surface of the roller of about two thirds of the depth of the associated raceway.

10. A roller bearing substantially as described with reference to, and as illustrated in, Figures 1 and 2 or Figures 2 and 3 of the accompanying drawings.