This invention relates to bearings and in particular to bearings which can carry both radial and axial loads.

The terms 'thrust bearing' or 'axial thrust bearing' generally relate to bearings which are capable of supporting axial loads (that is, loads along the axis of rotation of the bearing). The term 'radial load bearings' generally relate to bearings which are capable of supporting radial loads (that is, loads perpendicular to the axis of rotation of the bearing).

This invention relates to bearings which can support both axial and radial loads. Thus both of the terms 'thrust bearing ¹ and 'radial load bearing' could be used to refer to the bearings of the present invention.

Journal bearings come in many forms ranging from plain bearings to those that comprise an inner race, an outer race, and a plurality of balls or rollers equispaced around a common pitch circle. The balls or rollers are often mounted in a metal cage that retains the balls or rollers at the correct positions around the common pitch circle, and the balls or rollers are dimensioned and positioned to run on the confronting bearing surfaces of the inner and outer races.

Roller bearings running on cylindrical bearing surfaces can carry larger radial loads than ball bearings running in fixed concave bearing tracks because the radial loads are distributed along the length of the rollers, whereas radial loads on ball bearings are transmitted through point contact with the bearing surfaces. Hence, roller bearings can be manufactured with a smaller overall radial section thickness than ball bearings of a similar radial load capacity.

In some designs of bearings, such as "tapered roller" bearings, the races have complementary shaped part-conical bearing surfaces on which inclined cylindrical (i.e. tapered) rollers run.

In the case of cylindrical roller bearings which support a greater radial load than an axial load (and wherein generally the axis of rotation of each of the regular cylindrical rollers of the bearings run parallel to the axis of rotation of the bearing itself), there is a need to combine the advantages of the high radial load carrying capacity of the cylindrical roller bearing with an axial load carrying capability. Prior known solutions include: a. Providing a separate thrust plate alongside the cylindrical roller bearing. A thrust plate comprises a second set of rollers disposed parallel to the first so that the first set of rollers support a primarily radial load and the second set of rollers support a primarily axial load. Not only is this heavy, and costly, but the overall size of the combined bearings may be too large for some applications (for example in high performance gearboxes and transmission systems where weight and size are an important issue). b. Use of a tapered roller bearing. This type of bearing generally requires a continuous axial force to maintain the bearing assembly, and features inherent internal friction as a product of radial load thereby reducing the efficiency of this type of bearing. c. Use of a ball bearing. The ball elements will need a radial section large enough to support the required load. As mentioned above, roller bearings can be manufactured with a smaller overall radial section

thickness than ball bearings of a similar radial load capacity. When the size, dimensioning and weight of a bearing are considerations, ball bearing can be unsuitable choices. d. Use of a cylindrical roller bearing with thrust flanges (sometimes called ribs or collars) on both inner and outer races.

Prior known solution (d.) is illustrated in Figure 1. Figure 1 shows a cross section of part of a prior known cylindrical roller bearing 10 wherein the axis of rotation of each of the cylindrical rollers 14 of the bearing 10 run parallel to the axis of rotation of the roller bearing itself 10. The bearing 10 comprises rollers 14, an inner race 12, an inner race flange 112, an outer race 11, two outer race flanges 116, 116b and cage 13 for spacing the rollers 14. In the design of cylindrical roller bearings of the type shown in Figure 1, the rollers 14 are set in a bearing track in the outer race 11 that has a side wall or flange 116, 116b at both sides of the track. The inner race 12 has one side face 112 that confronts one of the side flanges 116b on the outer race as shown in Figure 1. In this way, axial loads are transmitted from the side flange on one race axially through the rollers to the flanges on the other race. As will be clear, however this bearing is able to support higher radial than axial loads. The radial height of a bearing is the difference between the outer radius and the inner radius of the bearing. The overall radial height RH ₁ of the roller bearing shown in Figure 1 is defined by the sum of; the thickness of the inner race 12, the thickness of the flange 112 protruding from the inner race 12, the spacing between that inner race flange 112 and the cage flange 15, the thickness of the cage flange

15, the spacing between the cage flange 15 and the confronting flange 116 protruding from the outer race 11, the thickness of the flange 116 protruding from the outer race 11 and the thickness of the outer race 11. The roller 14 thickness of the roller bearing 10 of Figure 1 is therefore dependant on the space between the inner and outer races 12, 11, which in turn is dependant on the aforementioned cage flange 15 thickness and flange 112, 116 thicknesses.

There are situations that call for bearings with a smaller radial height than have been possible with prior known bearings to meet a predefined design specification (for example, load capacity) without jeopardising or compromising performance. An example is that of high performance transmission systems such as used in gearboxes of racing cars without prejudicing performance. An important consideration in this sort of application is that of reducing weight and space without jeopardising performance. Therefore there is a need for smaller, lighter bearings. An object of the present invention is to provide a bearing that is compact and capable of supporting axial and radial loads.

According to one aspect of the present invention there is provided an axial thrust roller bearing comprising coaxial radial-spaced inner and outer races that define confronting cylindrical bearing surfaces, and a cage of circumferentially spaced rollers that are positioned and dimensioned to engage the bearing surfaces of the inner and outer races, said inner race being provided, at a first side of the inner race, with a first radial side flange that has a side face that faces towards, and engages, a first end of the rollers, and said outer race being provided at the

opposite side of the outer race to that of the flange on the inner race, with a second radial side flange, the second radial flange having a side face that faces towards, and engages, a second end of the rollers so that axial loads from one radial flange are transmitted to the other radial flange axially through the rollers.

According to another aspect of the present invention there is provided a roller bearing comprising coaxial radially-spaced inner and outer races that define confronting cylindrical bearing surfaces, and a cage of circumferentially spaced rollers that are positioned and dimensioned to engage the bearing surfaces of the inner and outer races, said inner race being provided, at a first side of the inner race, with a first radial side flange that has a side face that faces towards, and engages, a first end of the rollers, and said outer race being provided at the opposite side of the outer race to that of the flange on the inner race, with a second radial side flange, the second radial flange having a side face that faces towards, and engages, a second end of the rollers so that axial loads from one radial flange are transmitted to the other radial flange axially through the rollers.

Preferably the cage has a first coaxial cylindrical flange located between an extremity of the first radial flange on the inner race and the bearing surface of the outer race, and a second coaxial cylindrical flange located between an extremity of the radial flange on the outer race and the bearing surface of the inner race.

Preferably, the diameter of one of the first and second cylindrical flanges of the cage is smaller than that of the other cylindrical flange of the cage.

The axial width of the cage may be substantially the same as the axial width of at least one of the races. Preferably the axial widths of each race and the cage are substantially the same. Preferably, the axial width of the bearing is substantially equal to the sum of the axial widths of the first radial side flange, the second radial side flange and the roller. This can help to minimise the overall axial width of the bearing.

The radial spacing between the confronting bearing surfaces is preferably equal to or less than the sum of the radial heights of the first and second radial side flanges and the radial height of one of the coaxial cylindrical flanges. Most preferably the radial spacing between the confronting bearing surfaces is less than the sum of the radial heights of the first and second radial side flanges and the radial height of one of the coaxial cylindrical flanges.

Preferably the cage has a first coaxial cylindrical flange located between an extremity of the radial flange on the inner race and the bearing surface of the outer race, and a second coaxial cylindrical flange located between an extremity of the radial flange on the outer race and the bearing surface of the inner race, and the diameter of one of the first and second cylindrical flanges is smaller than that of the other cylindrical flanges.

Preferably a side of the inner race which is opposite to said first side has no radial side flange adjacent to the second end of the rollers, or at least has a flange

having a lower radial height than that of the flange provided on the first side of the inner race. Preferably a side of the outer race which is opposite to the side having said second radial flange has no radial side flange adjacent to the first end of the rollers, or at least has a flange having a lower radial height than that of the second radial flange.

Preferably a side of the inner race which is opposite to said first side has a chamfer. Preferably a side of the outer race which is opposite to the side having said second radial flange has a chamfer.

Preferably the side faces of the radial flanges are substantially flat so as to engage with respective substantially flat ends of the rollers. Preferably the side faces of the radial flanges each extend in a respective plane which is generally perpendicular to the main axis of rotation of the bearing.

It will be understood that reference to the side faces engaging the ends of the rollers implies that there is direct contact between the ends of the rollers and the side faces of the radial flanges.

The bearing may be arranged so that its axial load bearing capacity is much greater in one direction than the other. The bearing may be arranged so that when axial load is applied to the inner race in one direction relative to the outer race there is greater load bearing capacity than if axial load is applied to the inner race in the opposite direction. Axial load in one direction may tend to drive the races

axially towards one another and axial load in the opposite direction may tend to drive the races axially away from one another. The bearing may have a higher resistance to compressive axial loads than tensile axial loads.

The rollers are typically regular cylinder shaped rollers as opposed to tapered rollers. Similarly the races typically have confronting bearing surfaces shaped as the surfaces of coaxial regular cylinders rather than being frusto-conical or some other shape.

The rollers are typically disposed such that their axes of rotation are each substantially parallel to the axis of rotation of the roller bearing. The rollers may be confined in the races such as to allow rotation about only a single axis.

The present invention will now be described by way of example, with reference to the accompanying drawings, in which: -

Figures 1 shows a cross sectional view of a prior known bearing and Figure 2 shows a cross sectional view of a bearing embodying the present invention.

The bearings of Figures 1 and 2 are drawn to approximately the same scale.

The bearings shown in Figures 1 and 2 each have the same inner race bore diameter. Figure 1 is separated from Figure 2 by the dotted line A extending between the two Figures. The dotted line A represents the axis of rotation of each of the bearings 10, 20.

Figures 1 and 2 show bearings 10 ,20 that are designed to the same specification so that certain bearing parameters are kept exactly the same for the

purposes of meaningful comparison between them. These certain parameters include rotation speed, bearing materials used, lubricants, radial loads and axial loads.

Referring to Figure 1 a prior known cylindrical roller bearing 10 comprises an outer race 11, two outer race flanges 116, 116b, an inner race 12, an inner race flange 112 and a roller cage 13 that accommodates a set of rollers 14 that run on cylindrical bearing surfaces of both races. The roller cage 13 is of symmetric shape and has flanges 15 and 16 that extend around a common pitch circle diameter (PCD). The flanges 15 and 16 both have the same radial height, the same inner cylindrical diameter and the same outer cylindrical diameter. The axis of rotation of each of the cylindrical rollers 14 of the bearing 10 run parallel to the axis of rotation A of the roller bearing 10.

As mentioned above the roller 14 thickness of the roller bearing 10 is dependant on the space between the inner and outer races 12, 11, which in turn is dependant on the cage flange 15 thickness and flange 112, 116 thicknesses at what is the left hand side of the bearing in the orientation shown in Figure 1.

Referring to Figure 2 there is shown a bearing embodying the present invention. It will be seen that although both bearings are designed to the same internal bore diameter, the bearing of Figure 2 is of a much smaller outer radius (R) than the bearing of Figure 1 which has an outer radius of (R + r). The difference in the outer radius of the bearing of Figures 1 and 2 is the distance 'r\ The distance Y is shown in Figure 1 as being equivalent to the radial height of the radial side flange 112 on the inner race 12.

Radial height is generally measured perpendicular to the axis of rotation of a bearing. For example, the radial height of the aforementioned flanges 15, 16 of the cage 13 of the bearing 10 can be seen in Figure 1 to be equal. Another example is the radial height of the radial side flange 26 of Figure 2 (as will be described in more detail below). This radial height of this flange 26 is the difference between; a) the distance from the outer race inner cylindrical confronting bearing surface 124 to the axis of rotation A; and b) the distance from the extremity 226 of the flange 26 to the axis of rotation A.

The bearing 20 of Figure 2 comprises an inner race 21 of the same inside and outside diameters as the inner race 12 of the bearing 10 of Figure 1. The inner race 21 has a flange 22 at only one side end of the race that engages one end of each roller. The flange 22 is located on the first side of inner race 21. The other side end of the inner race 21 opposite to the first side has a chamfer 23 that eases assembly of the bearing.

The outer race 24 which is coaxial to the inner race 21 has a smaller diameter inner cylindrical bearing surface 124 than that of the outer race 11 of Figure 1.

The inner cylindrical bearing surface 124 of the outer race 24 confronts with the inner cylindrical bearing surface 121 of the inner race 21 with rollers 25 in between. The rollers 25 are positioned and dimensioned to engage these surfaces 121, 124. The outer race 24 has a flange 26 on the opposite end of the race 24 to

that of first side of the inner race 21. This second radial side flange 26 can be seen on the right of Figure 2. The first radial side flange 22 can be seen on the left of Figure 2. A chamfer 23a on same end of the race 24 as that of the first side of the inner race 21 eases assembly of the bearing. The rollers 25 of the bearing 20 of Figure 2 are of a much smaller diameter than the rollers 14 of the bearing 10 of Figure 1. The difference in the size of the diameter of the rollers 25 and the rollers 14 is approximately equal to V.

The rollers 25 are mounted in a roller cage 27 that has a cylindrical flange 28, 29 on each side of the cage 27. The first cylindrical flange 28 is coaxial with the second cylindrical flange 29. The first flange 28 is of a larger diameter than that of the second flange 29 so that the flanges 28, 29 are positioned between the flanges 22, 26 of the inner and outer races. Thus the first cylindrical flange 28 of the cage 27 is located between the extremity 222 of the radial flange 22 on the inner race 21 and the bearing surface 124 of the outer race 24. The bearing surface 124 may comprise the chamfer 23 a. Furthermore, the second cylindrical flange 29 of the cage 27 is located between the extremity 226 of the radial flange 26 on the outer race 24 and the bearing surface 121 of the inner race 21. The bearing surface 121 may comprise the chamfer 23.

In this way, one end of each roller 25 engages a side face 122 of the first radial side flange 22 which is at the full depth of the flange 22 and the other end of each roller 25 engages a side face 126 of the second radial flange 26 which is at the full depth of the flange 26. The side faces 122, 126 of the radial flange are substantially flat so as to engage with the respective flat ends of the rollers 25. As

such, the side faces 122, 126 of the radial flanges 22, 26 each extend in a respective plane which is perpendicular to the axis of rotation A.

It can be seen in Figure 2 that the arrangement of the cage 27 and the inner and outer races 21, 24 are such that the axial width W of the cage 27 and races 21, 24 are substantially the same.

The bearing 20 is assembled by first mounting the rollers 25 in the cage 27, sliding the roller cage 27 with the rollers 21 onto the inner race 22, and then sliding the outer race 24 onto the rollers 25. As mentioned, the chamfers 23, 23a ease the assembly of the bearing. As mentioned above, the outer radius of the bearing 20 in Figure 2 is smaller than the outer radius of the bearing 10 in Figure 1. This smaller size of the outer radius of the bearing 20 results from the arrangement of certain structural features of the bearing 20 - namely the cage flanges 28, 29 and the radial side flanges 22, 26. The smaller size of the outer radius of the bearing 20 of Figure 2 does not result from reducing the dimensions of each of said cage flanges 28, 29 and radial side flanges 22, 26.

As mentioned above, the two bearings 10, 20 are designed to the same specification so that certain bearing parameters are kept exactly the same for the purposes of meaningful comparison between them. Certain bearing parameters that are kept exactly the same include the dimensioning of said cage flanges 28, 29 and radial side flanges 22, 26 in that; the radial heights of the cage flanges 28, 29 of Figure 2 and the corresponding cage flanges 15, 16 of Figure 1 are all the same. Similarly, the radial height of the flange 26 of the outer race 24 of the bearing 20 of Figure 2 is the same as the

corresponding radial height of the flange 116b of the outer race 11 of the bearing 10 of Figure 1. The radial height of the flange 22 of the inner race 21 of the bearing 20 of Figure 2 is the same radial height as the corresponding flange 112 of the bearing 10 of Figure 1. Due to the arrangement of the bearing 20 of Figure 2, the radial spacing between the confronting bearing surfaces 121, 124 of the bearing 20 of Figure 2 is less than the sum of the radial heights of; the first radial side flange 22; the second radial side flange 26; and one of the cage flanges 28 / 29; whereas the radial spacing between the confronting bearing surfaces of the inner race 12 and the outer race 11 of the bearing 10 of Figure 1 is more than the sum of the radial heights of the corresponding; first radial side flange 112; second radial side flange 116b; and one of the cage flanges 15 / 16; despite the corresponding features being dimensioned to be of the same size.

Parameters such as the materials used in a bearing and dimensioning of the structural features of the bearing can be changed to change the characteristics of the bearing. Such characteristics typically include radial or axial load capacity (e.g. before bearing seizure), mean time before failure etc.

Generally, such changes to the parameters are made to improve one characteristic of a bearing, but at the expense of another. For example, if the radial

height of any of the side flanges 112, 116, 116b, 22, 26 were to be increased, the axial load carrying capabilities of the roller bearing may be improved, but the overall size and weight of the bearing would increase which may be less favourable in certain conditions. If a material with a better strength-to-weight ratio than normal were to be used in the bearing, the cost of the production of the bearing may be increased.

The arrangement of the structural features of the bearing 20 of Figure 2 allows the bearing 20 to have a smaller overall radial height and lower weight than that of the bearing 10 of Figure 1 without having substantial characteristic differences

(e.g.. radial and axial load capacity of both bearings 10 and 20 are similar).

In use, the outer race 24 is mounted in a bearing support structure (not shown) and a component (not shown) that is to be mounted in the inner centre hole 30 of the inner race 21 is mounted into the inner race 21. The bearing must be correctly positioned so that, in use, the axial loads created by the component that is inserted into the inner race 21, urges the rollers 25 against the flange 26 of the outer race, and are reacted by the structure in which the outer race 24 is mounted.

The present bearing will support radial and axial loads. However, it can be seen from Figure 2 that present bearing will support significant axial loads acting in one direction only - the direction in which axial loads are supported is the direction in which the ends of the rollers 25 are urged against the sides of the flanges 22, 26. In use, this axial force is transmitted between each of the following in succession;

• the inner race 21

• the inner race first radial side flange 22

• the inside face of the inner race first radial side flange 22 which faces towards a first end of the roller 25

• the roller 25

• the inside face of the second radial side flange 26

• the outer race second radial side flange 26

• the outer race 24