GB2111608A - Lubrication of a bearing assembly - Google Patents

Abstract

A bearing assembly 34 separates two co-rotating shafts (8, 16). Both races (34, 36) rotate, as does the surrounding structure (shaft 16). An annular oil catcher (70) is fixed to the outer race (36) to catch oil which has traversed the rolling elements (40). Oil catcher 70 is an integral member which has no joints which are exposed to oil which is being acted upon by centrifugal force. Oil is piped from the oil catcher to a space (52) bounded by a non rotary casing (54) which absorbs the kinetic energy in the oil. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a bearing assembly This invention relates to a bearing assembly in which both races rotate.

';This engine has particular efficacy in a gas turbine engine.

It is the accepted practice, to pass lubricating oil to bearings which support a shaft for rotation, by injecting the oil into the shaft interior and using the centrifugal force developed on rotation of the shaft, to drive the oil against and along the shaft wall. The oil then passes radially outwards through orifices formed in the shaft wall at strategic points, or over annular lips at the shaft end, onto the bearing assembly.

In those arrangements where only the inner race of a bearing rotates, oil which has passed therethrough, is flung off into a catching space, bounded by fixed structure from which it returns along the wall of the structure, to drains, by virtue of the pressure still behind it. Where however, both races of a bearing rotate, e.g. in a situation where the bearing supports adjacent ends of two co-rotating shafts on the oil being flung into the scavanging space, it is still acted upon by centrifugal forces, by virtue of the rotation of the structure bounding the scavanging space.

In multi shaft gas turbine engines, the rotational speed of such shafts, is commonly many thousands of revolutions per minute. It follows that the centrifugal forces generated therein, are of considerable magnitude. If the structure bounding the catching space includes radial joints, e.g. flange inter faces, oil leakage may occur, via those interfaces.

The present invention seeks to provide a bearing assembly including improved scavenging means.

According to the present invention, a bearing assembly comprises inner and outer races spaced by rolling elements and including on a side face of the outer race for co-rotation therewith, an annular feature which has an annular groove formed in its bone for the receipt of lubricating oil which in operation has traversed the rolling elements and centrifuged therefrom, and passage means for connecting the groove bottom to an oil scavage area.

The invention will now be described, by way of example and with reference to the accompanying drawings.

In the drawing, a first shaft 8 comprises a first portion 10 and a second portion 12, splined together at 14, for the transmission of rotary drive from one to the other.

Shaft 8 provides the drive connection between a low pressure turbine and a fan, neither of which is shown.

Shaft 8 rets in coaxial manner, within a further shaft 1 6 which comprises a portion 1 8 and a portion 20 joined by bolted flanges 22, 24.

Shaft 1 6 provides the driving connection between a high pressure turbine and compressor, neither of which is shown.

Shaft 16 is supported by a bearing assembly 26 the rotor race 28 of which is boited to fixed, non rotary structure 30. Shaft 1 6 is thus positively located for rotation about axis 32.

Shaft 8 is supported for rotation about axis 32, by a bearing assembly 34.

Bearing assembly 34 has an outer race 36 bolted to flange 24 of shaft i 6 and thus in operation rotates therewith.

Bearing assembly 34 has an inner vane 38 which is bolted to portion 10 of shaft 8 and thus in operation, rotates therewith.

Although shafts 8 and 1 6 both rotate in the same direction, there is also relative rotation between races 36 and 38, by virtue of shaft 8 being driven by the low pressure turbine (not shown) which rotates more slowly than the high pressure turbine (not shown), which drives shaft 16.

Lubrication of the rolling elements 40, 42, is achieved by injecting oil under pressure onto the inner surface of shaft portion 20, where it stays under the action of centrifugal force derived from rotation of the shaft portion. The oil moves along the shaft inner surface as depicted by arrows 44 and, on reaching radial holes 46 in the shaft wall, some of the oil passes therethrough to radial passages 48 in inner race 50 of bearing assembly 26 via which the oil reaches rolling elements 42.

The oil is then centrifuged from the rolling elements 42, into a scavange chamber 52, which is bounded by a casing 54.

Casing 54 is bolted to fixed structure 30 at one end and has an annular seal 56 at the other end which cooperates with an annular seal 58 on shaft portion 20. In operation, differences in air pressure across the seal, ensures that oil cannot leak from chamber 52, through the seal structure.

Oil which strikes casing 54 loses all of the energy which had been imparted to it by the centrifuging action of the rotating elements 42 and race 28. There is thus no driving force, to force the oil between the engaging faces of casing 54 and fixed structure 30.

The remaining oil centrifuges into an annular groove 60 in the inner surface of shaft portion 20, then through apertures 62, into a lip 64, from whence it further centrifuges onto the cage 66 of bearing assembly 34.

The oil traverses the rolling elements 40 and exits into an annular groove 68 which is fomed in an annular member 70 affixed to the side face of outer race 36.

It will be appreciated, that annular member 70 rotates by virtue of its rigid connection to outer race 70 and moreover, exerts a greater centrifugal force on the oil than hitherto, because of its enlarged diameter, relative to the structure diameters previously traversed by the oil. Member 70 however, has no radially aligned joint faces through which oil may leak. It does however, have an outlet passage 72 into which oil is forced to pass into a tube 74 is brazed or otherwise sealingly fixed into member 70.

Tube 74 is passed through a bore in outer race 36 and shaft portion 20 and terminates in scavange chamber 52. If desired, there may be several such tubes spaced around the race 36 and shaft portion 20.

When oil exits from tube 74, it is centrifuged into scavange chamber 52 but again, its energy is expended in striking the static wall of casing 54.

Annular member 70 includes a cap 76 which ensures than on cessation of rotation of the bearing assembly 34, oil falls under gravity only into the bottom portion of groove 68 rather than space 78. On re-start of rotation, oil is thus prevented from reaching the interface joint of flanges 22, 24 which by virtue of their co-rotating would exert a centrifugal force on any oil which did reach the interface joint. That oil would then be lost from the lubrication system.

A flanged ring 80 is located via a first flange 82 between inner race 38 and shaft portion 10. A second, outer flange 84 projects into groove 68 and is spaced therefrom. The sole purpose of flanged ring 80 is to provide a hydraulic seal, between bearing assembly 34 and air upstream of the assembly i.e. to the left of the assembly, as viewed in the drawings. It is not essential to the invention, to provide the hydraulic seal at the position shown in the drawing, for example splines 14 need to be lubricated and this would be achieved, by passing oil along the inner surface of shaft portion 12 in the manner already described.

The oil would traverse the splines 14 and pass through radial holes (not shown) in shaft portion 10, to an annular reservoir (not shown) which includes a flanged ring corresponding to flanged ring 80. The reservoir would bleed back to scavange chamber 52 via the space defined by cap 76, which would be re-shaped to embrace reservoir and would provide a hydraulic seal for both spline and bearing assembly oil path.

It should be noted, that in order to achieve assembly of annular member 70, cap 76 and flanged ring 80, it will be necessary to place flanged ring 80 inside member 70 and then weld cap 76 in position around the joint periphay 86.

Member 70, cap 76 and flanged ring 80 will thereafter remain a loose sub assembly, when the whole is dismantled for maintenance.

It shouid be appreciated, that annular member 70, could be formed integrally with outer race 36.

Claims (5)

1. A bearing assembly comprising inner and outer races spaced by rolling elements and including on a side face of the outer race for co rotation therewith, an annular feature which has an annular groove formed in its bore for the receipt of lubricating oil which in operation has traversed the rolling elements and centrifuged therefrom and passage means for connecting the groove bottom to an oii scavange area.

2. A bearing assembly as claimed in claim 1 wherein the annular feature is an integral extension on said side face.

3. A bearing assembly as claimed in claim 1 wherein said annular feature is detachably attached to said side face.

4. A bearing assembly as claimed in any previous claim including a flanged ring which is shaped and positioned so as to cooperate with said annular feature to form a hydraulic seal.

5. A bearing assembly substantially as described in this specification, with reference to the accompanying drawings.