BEARING RACEWAY AND A METHOD OF MANUFACTURING A BEARING

Abstract

A component 2 for a bearing, the component 2 comprising a bearing surface 4, wherein the bearing surface 4 is formed so as to be tapered at rest, thereby offsetting deformation of the bearing during an operational condition which generates an induced angle in the bearing surface 4 or an opposing surface of the bearing. A method of manufacturing a bearing is also provided. The method comprises: determining an induced angle of a component 2 of the bearing caused by deformation of the bearing during an operational condition: and providing a surface 4 of the component 2 or an opposing component with a taper at rest so as to offset the induced angle generated during the operational condition.

Claims

1. A cylindrical bearing for a shaft, comprising: a rolling element, an inner or outer race having a bearing surface against which the rolling element rolls in use. wherein the bearing surface includes a taper angle so as to be angled relative to the rotational axis of the shaft at rest, the taper angle being equal to the deformation of the bearing during an operational condition which generates an opposing induced angle in the bearing surface such that the bearing surface is at an angle with respect to the rolling element at rest, and parallel to the bearing surface during the operational condition.

2. A cylindrical bearing as claimed in claim 1, wherein the bearing surface has a taper angle of approximately 0.5 to 5.0 mrads.

3. A cylindrical bearing as claimed in claim 1, wherein the inner or outer race is installed with an interference fit between two mating surfaces and wherein at least one of the mating surfaces of the interference fit has a profile which causes the component to deform during installation, thereby creating the taper angle in the bearing surface.

4. A cylindrical bearing as claimed in claim 1, wherein the rolling element is a roller or ball bearing.

5. A cylindrical bearing as claimed in claim 1, wherein the tapered bearing surface is angled with respect to an opposing surface of the rolling element at rest and is brought closer toward being parallel with the opposing surface during the operational condition.

6. A cylindrical bearing as claimed in claim 5, wherein the bearing surface is parallel to the opposing surface of the rolling element during the operational condition.

7. A cylindrical bearing as claimed in claim 1, wherein the bearing surface is angled toward the opposing surface at rest and is parallel with or angled away from the opposing surface during the operational condition.

8. A gas turbine engine comprising the bearing as claimed in claim 1 wherein the operational condition is a cruise condition for the engine.

9. A method of manufacturing a bearing, the method comprising: determining an induced angle of an inner or outer race of the bearing caused by deformation of the bearing during an operational condition; and providing a bearing surface of the inner or outer race with a taper at rest so as to offset the induced angle generated during the operational condition.

10. A method of manufacturing a bearing as claimed in claim 9, wherein a taper angle of the bearing surface is selected so as to provide the bearing surface with an operating angle during the operational condition which is within a predetermined misalignment range.

11. A method of manufacturing a bearing as claimed in claim 10, wherein the bearing surface is provided with a taper by installing the component so that a mating surface of the component abuts against a mating surface of another structure to form an interference fit and wherein at least one of the mating surfaces of the interference fit has a profile which causes the component to deform during installation, thereby creating the tapered bearing surface.

12. A method of manufacturing a bearing as claimed in claim 11, wherein a taper angle of the bearing surface is selected based on relative times in the operational condition and in a rest condition.

Description

DESCRIPTION OF DRAWINGS

[0037] For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0038] FIG. 1 is a cross-sectional view of a bearing race according to an embodiment of the invention at rest;

[0039] FIG. 2 shows the bearing race of FIG. 1 during an operational condition;

[0040] FIG. 3 is a cross-section view of a prior art bearing race at rest; and

[0041] FIG. 4 shows the bearing race of FIG. 3 during an operational condition.

[0042] FIG. 5 shows a bearing arrangement having the bearing race of FIGS. 1 and 2.

[0043] FIG. 6 shows a bearing race which is tapered on installation.

[0044] FIG. 7 shows an alternative arrangement to that shown in FIG. 6.

[0045] FIG. 8 shows a conventional gas turbine engine.

DETAILED DESCRIPTION

[0046] FIGS. 1 and 5 show a bearing race 2 (component) of a roller bearing. The bearing race 2 is annular and is arranged concentrically with a further bearing race 5 having a different diameter to that of the bearing race 2 to form inner and outer races. Rollers 6, which may be cylindrical, are disposed between the inner and outer races of the bearing to permit relative rotation between the inner and outer races. The inner and outer races are mounted on to or within a supporting structure such as a housing 7, or a shaft 8. It will be appreciated that the bearing arrangement may also include other parts such as a bearing cage or the like,

[0047] The bearing race 2 comprises a raceway 4 (bearing surface) which contacts the rollers. The raceway 4 is therefore either an inner surface of the outer race or an outer surface of the inner race.

[0048] The raceway 4 is tapered at an angle α such that the raceway 4 is inclined toward an axis of rotation of the bearing race 2 when at rest, as is shown in FIG. 1.

[0049] As shown in FIG. 2, during operation of the bearing, the bearing race 2 may deform as a result of operational conditions, such as speed, load and temperature. As shown in FIG. 2, the deformation of the bearing race 2 creates an induced angle θ at the raceway 4. The taper angle α of the raceway 4 opposes and thus offsets deformation of the bearing race 2 during the operational condition. Consequently, during the operational condition, the raceway 4 has an operating angle which is equal to the induced angle θ minus the taper angle α (=θ−α).

[0050] The taper angle α of the raceway 4 thus limits the misalignment between the rollers and the raceway 4 during operation.

[0051] The taper angle α of the raceway 4 causes misalignment during start-up (before the bearing is rotating at operational speed) and so the taper angle α is selected so as to balance the level of misalignment and the relative time spent under the start-up condition and the operational condition.

[0052] The taper angle α of the raceway 4 may be formed during manufacture of the race 2 itself, such as during a machining process.

[0053] Alternatively, as shown in FIGS. 6 and 7, the taper angle α may be generated during installation of the race 2. For example, where the race 2 is a discrete component which is fitted with an interference on to a shaft or housing structure 7, the taper angle α may be generated by providing a tapered profile on either of the mating surfaces. For the inner race, the tapered profile may be provided on an inner surface of the inner race or an outer surface of the shaft. Similarly, for the outer race, the tapered profile may be provided on an inner surface of the housing 7 (FIG. 6) or an outer surface 9 of the outer race (FIG. 7). FIGS. 6 and 7 show the pre- and post-installed on left and right respectively.

[0054] The tapered profile of the mating surface causes the race 2 to deform as it is forced onto the shaft or housing, thereby generating the required taper angle α at the raceway 4. The resulting taper angle α is dependent on the relative stiffness of the mating components which therefore must be taken into account when determining the required profile of the mating surface.

[0055] By way of contrast, FIGS. 3 and 4 show a prior art bearing race 1 that has a raceway 3 which, unlike the raceway 4 of the invention, is not tapered. Accordingly, the raceway 3 is parallel to the axis of rotation when the bearing is at rest, as shown in FIG. 3. Consequently, any deformation of the bearing race 1 during the operational condition increases the operating angle of the raceway 3. The operating angle is thus equal to the induced angle θ. In extreme operating conditions, the induced angle θ may exceed the acceptable level of misalignment causing premature bearing distress.

[0056] As can be seen, the tapered raceway 4 of the invention acts to offset deformation of the race 2 during use. Therefore, at least the initial deformation of the race 2 actually acts to improve the alignment (i.e. reduce the misalignment) of the race 2 and the roller. The tapered raceway 4 is thus able to reduce misalignment during the operational condition to acceptable levels, thereby improving reliability and prolonging the life of the bearing. This is particularly beneficial where the induced angle θ exceeds a predetermined misalignment tolerance of the bearing. It will be appreciated that the operational angle of the raceway may be any desired but will preferably be parallel. This is not the case shown in FIG. 2, which has an exaggerated angle to make the effect clear.

[0057] The tapered raceway 4 does not compromise the surrounding architecture and rotor geometry which would otherwise have to be modified to reduce the bearing misalignment.

[0058] The raceway of one or both of the inner and outer races may be tapered, as described previously. Where both the inner and outer races are provided with a tapered raceway, they may taper in the same or opposing directions, depending on the nature of the deformation encountered by the respective race. A tapered raceway may also be used to offset deformation of an opposing race.

[0059] The raceway of the inner or outer race may be provided with a pair of guide ribs to maintain the axial location of the rollers as they rotate around the bearing. The guide ribs may also be angled so that they are perpendicular to the tapered surface of the raceway.

[0060] Although the operating angle of the raceway 4 has been shown as being angled away from the axis of rotation of the race 2, it will be appreciated that the taper angle α may be set such that the operating angle is in fact parallel to the axis. This may be appropriate where the race 2 reaches the operating angle very quickly and so very little time is spent in the start-up condition.

[0061] Although the invention has been described with reference to a roller bearing, it will be appreciated that the invention may be employed with other bearings, particularly ball bearings. The bearing may, for example, be a tapered roller bearing, barrel roller bearing, spherical roller bearing, spherical tapered roller bearing, needle roller bearing or spherical plain journal bearing. The invention may also be employed with other bearings which do not have rolling elements, such as plain journal bearings.

[0062] The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.