GB2489456A

GB2489456A - A device for axially loading a rotating shaft with respect to a first component

Info

Publication number: GB2489456A
Application number: GB201105238A
Authority: GB
Inventors: David Anthony Edwards; Richard Nicholson; David Peter Scothern
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2011-03-29
Filing date: 2011-03-29
Publication date: 2012-10-03
Also published as: GB201105238D0

Abstract

A device 10 is provided for axially loading a rotating shaft 12 with respect to a first component 24. The device 10 comprises an annular channel 40 surrounding the rotating shaft 12 which comprises a first portion 16 axially fixed with respect to the shaft 12 and having a first annular wall 16 extending in the radial direction of the shaft 12; and a second portion 28 axially fixed with respect to the first component 24 and having a second annular wall 30 axially spaced from the first wall 16 and extending in the radial direction of the shaft 12. The device further comprises a fluid supply means 14 for supplying fluid 44 to the annular fluid channel 40 and a rotator 16 rotationally fixed with respect to the shaft 12. In use the fluid 44 is supplied to the annular fluid channel 40 when the shaft 12 is rotated, the rotator applying an angular momentum to the fluid 44 thereby generating a radial force on the fluid 44 which generates an axial force between the first annular wall 16 and the second annular wall 30, thereby axially loading the shaft 12 with respect to the first component 24.

Description

I

DEVICE FOR AXIALLY LOADING A ROTATING SHAFT

The present invention relates to a device for axially loading a rotating shaft, in particular, a device for axially loading a rotating shaft by applying angular momentum to a fluid.

Rotating shafts are often supported by rolling element bearings such as ball or roller bearings. If the axial load on the shaft is insufficient the bearing is prone to skidding, that is, relative sliding movement between the balls or rollers of the bearing and the surfaces which they engage. Such skidding is highly undesirable in view of the bearing damage which it causes and it can, in certain circumstances, lead to bearing failure. Skidding is known to increase with the magnitude of the radial clearances between the various components of a bearing and consequently previous attempts to reduce skidding have centered around the reduction of these radial clearances by appropriate dimensioning of the component parts of the bearing. However this is expensive to achieve and has limited applications.

In a further attempt to overcome skidding, it is known to axially load the inner race of the bearing using a spring. However, a slave bearing is required in order to transmit the load of the spring to the inner race of the primary bearing.

Whilst this ensures reliable contact between the bearing races and the rolling elements, the cost and weight is increased due to the use of a slave bearing.

It is therefore desirable to prevent the skidding of bearings whilst minimising both weight and cost.

According to one aspect of the present invention there is provided a device for axially loading a rotating shaft with respect to a first component, comprising: a generally annular fluid channel surrounding and concentric with the rotating shaft, the annular fluid channel comprising: a first portion axially fixed with respect to the shaft and comprising a first annular wall extending at least partially in the radial direction of the shaft; and a second portion axially fixed with respect to the first component and comprising a second annular wall axially spaced from the first wall and extending at least partially in the radial direction of the shaft; and a fluid supply means for supplying fluid to the annular fluid channel; wherein when in use and fluid is supplied to the annular fluid channel and the shaft is rotated, rotator means, constrained to rotate with the shaft, applies angular momentum to the fluid, thereby generating a radial force on the fluid which generates an axial force between the first annular wall and the second annular wall to axially load the shaft with respect to the first component.

Preferably the first portion is rotationally fixed with respect to the shaft and comprises the rotator means.

The annular fluid channel may comprise an cylindrical portion generally extending in the axial direction of the shaft and positioned between the first and second annular walls. In a preferred arrangement the annular fluid channel is generally in the form of an annular trough defined by the first and second annular walls and the cylindrical portion. The first or second portion may comprise the base portion.

In a preferred embodiment the device further comprises a seal that restricts the flow of fluid out of the annular fluid channel between the first and second portions.

Fluid may be supplied to the annular fluid channel from the inside of the shaft through apertures in a wall of the shaft.

In use the second portion and the first component may be stationary.

In a particularly preferred embodiment the first component is an outer race of a rolling element bearing and the inner race of the rolling element bearing is rotationally and axially fixed with respect to the shaft.

The present invention also relates to a gas-turbine engine comprising a

device according to any statement herein.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 schematically shows a device for axially loading a shaft according to an embodiment of the invention; and Figure 2 schematically shows the device of Figure 1 in use.

Figure 1 shows generally at 10 in cross-section a rotatable shaft 12 of a gas-turbine engine supported by a ball bearing 20. The ball bearing 20 is of a conventional type and comprises an inner race 22, an outer race 24 and a ring of balls 26 disposed between the inner and outer races 22, 24. In other embodiments the bearing may be a different type of rolling element bearing such as a roller bearing. The inner race 22 is axially and rotationally fixed to the shaft 12 in a conventional manner such as by the use of a shoulder (not shown) and a locking ring (not shown).

An annular (otherwise known as a circumferential) fluid trough (or channel) 40 is provided that surrounds and is concentric with the shaft 12. The fluid trough 40 is defined by a first annular side-wall 16, a second annular side-wall 30 axially spaced from the first side-wall 16, and a cylindrical base portion 32. The first and second annular side-walls 16, 30 extend generally in the radial direction of the shaft 12 and the base portion 32 extends generally in the axial direction of the shaft 12. The opening of the fluid trough 40 faces the shaft 12.

In other embodiments the side-walls 16, 30 may extend obliquely, for example 45°, to the radial direction of the shaft 12.

The first annular side-wall 16 constitutes a first portion of the fluid trough and is attached to the shaft 12 and is fixed both axially and rotationally with respect to it. The second annular side wall 30 and the base portion 32 constitute a second portion 28 of the fluid trough 40 which is attached to the outer race 24 of the ball bearing 20 and is fixed both axially and rotationally with respect to it.

The interface between the first and second fluid trough portions 16, 28, i.e. the end of the base portion 32 and the first annular side-wall 16, is provided with a seal 42.

The wall of the shaft 12 is provided with a number of circumferentially spaced apertures 14, or openings, that extend through the thickness of the wall and are aligned with the fluid trough 40. Fluid, such as oil, can be supplied to the fluid trough 40 through the inside of the shaft 12 and the apertures 14.

However, fluid may be supplied to the fluid trough 40 by other means, such as an opening in the base portion 32.

With reference to Figure 2, in use the shaft 12 is rotated and fluid 44, such as oil, is supplied to the fluid trough 40 through the apertures 14 in the wall of the shaft 12. As the shaft 12 rotates the outer race 24 and the second portion 28 of the fluid trough 40 remain stationary whilst the first annular wall 16 (otherwise known as the rotator) of the fluid trough 40 rotates with the shaft 12 and applies angular momentum to the fluid 44 located within the fluid trough 40. This generates a radial force on the fluid 44 which in turn exerts an axial force A between the first annular wall 16 and the second annular wall 30. This increases the distance between the first annular wall 16 and the base annular portion 32 and the seal 42 expands to fill the gap in order to prevent fluid from leaking out of the fluid trough 40. As the first annular wall 16 is axially fixed with respect to the shaft 12 which is axially fixed with respect to the inner race 22 of the bearing 20, and the second annular wall 30 is axially fixed with respect to the outer race 24 of the bearing 20 the arrangement axially loads the shaft 12 and inner race 22 with respect to the outer race 24.

In other embodiments the rotator applying angular momentum to the fluid may be separate from the first annular wall 16. Further, the rotator may be supplied with fins or vanes to increase the angular momentum applied to the fluid.

The loading of the bearing races 22, 24 in this way ensures reliable contact between the races 22, 24 and the rolling elements 26. This reduces the risk of the bearing skidding. The bearing 20 is axially loaded without requiring the provision of a slave bearing, thus reducing weight and cost. Further, as the rotational speed of the shaft 12 increases the axial load applied to the bearing 20 increases. This is particularly beneficial because the conditions most likely to cause bearing skidding are high speed and low axial load.

In the above described embodiment the axial load applied to the inner race 22 is in the direction indicated by the arrow marked F in Figure 2. However, as will be readily apparent to one skilled in the art, the inner race 22 could be loaded in the opposite direction using a different configuration, for example, by locating the fluid trough 40 on the opposite side of the bearing 20.

In systems with several concentric shafts, the above described arrangement could be fitted to bearings located between two shafts.

The seal 42 has not been described in detail. A number of standard types of seal would be suitable for the seal 42, including those that seal on a face or a circumference.

Further, although it has been described that the arrangement is used to apply an axial load to a race of a rolling element bearing, the arrangement may be used to apply an axial load to a rotating shaft in other applications.

A benefit of the above described arrangement is that the pressure head generated by applying angular momentum to the fluid may be used to operate an actuator elsewhere in the system.

Claims

CLAIMS: 1. A device (10) for axially loading a rotating shaft (12) with respect to a first component (24), comprising: a generally annular fluid channel (40) surrounding and concentric with the rotating shaft (12), the annular fluid channel (40) comprising: a first portion (16) axially fixed with respect to the shaft (12) and comprising a first annular wall (16) extending at least partially in the radial direction of the shaft (12); and a second portion (28) axially fixed with respect to the first component (24) and comprising a second annular wall (30) axially spaced from the first wall (16) and extending at least partially in the radial direction of the shaft (1 2); and a fluid supply means (14) for supplying fluid (44) to the annular fluid channel (40); and wherein when fluid (44) is supplied to the annular fluid channel (40) and the shaft (12) is rotated, rotator means (16) constrained to rotate with the shaft (12), applies angular momentum to the fluid (44), thereby generating a radial force on the fluid (44) which generates an axial force between the first annular wall (16) and the second annular wall (30) to axially load the shaft (12) with respect to the first component (24).
2. A device (10) according to claim 1, wherein the first portion (16) is rotationally fixed with respect to the shaft (12) and comprises the rotator.
3. A device (10) according to claim I or 2, wherein the annular fluid channel (40) comprises a cylindrical base portion (32) generally extending in the axial direction of the shaft (12) and positioned between the first and second annular walls (16, 30).
4. A device (10) according to claim 3, wherein the annular fluid channel (40) is generally in the form of an annular trough defined by the first and second annular walls (16, 30) and the base portion (32).
5. A device (10) according to claim 3 or 4, wherein the first or second portion (16, 28) comprises the base portion (32).
6. A device (10) according to any preceding claim, further comprising a seal (42) that restricts the flow of fluid out of the annular fluid channel (40) between the first and second portions (16, 28).
7. A device (10) according to any preceding claim, wherein fluid (44) is supplied to the annular fluid channel (40) from the inside of the shaft (12) through apertures (14) in a wall of the shaft (12).
8. A device (10) according to any preceding claim, wherein in use the second portion (28) and the first component (24) are stationary.
9. A device (10) according to any preceding claim, wherein the first component (24) is an outer race of a rolling element bearing (20) and the inner race (22) of the rolling element bearing (20) is rotationally and axially fixed with respect to the shaft (12).
10. A gas-turbine engine comprising a device according to any of claims 1-9.
11. A device for axially loading a rotating shaft with respect to a first component substantially as described herein with reference to the accompanying drawings.