Patent Application
20060193545
The present invention relates generally to bearing assemblies and more specifically to bearing assemblies with rolling element bearing cages having axial grooves in the bore web surfaces and a centrifugal lubricant catcher.
High speed rolling element bearings require high strength separators (cages) to maintain relative position of the rolling elements during the bearing's high speed operation. These separators generally rotate at speeds that are roughly half of the average rotational speeds of the inner and outer rings. Thus, the separator rotational speeds are also high, and a separator piloting surface is required for smooth operation. The separator piloting surfaces can be either on the outer ring or the inner ring of the bearing, and are typically on either side of the rolling elements. In turbine engine rolling element bearings, there is a certain advantage to piloting the separator on the inner ring.
High speed rolling element bearings of the type utilized in gas turbine engines often exhibit wear between the rolling element separator pilot surfaces and the bearing inner ring lands. This wear is due to the difficulty in maintaining and replenishing the hydrodynamic lubrication film between these surfaces. The wear problem becomes more pronounced with increasing bearing speed, cage mass and pilot clearance. This wear can be severe enough to result in bearing failure in a matter of minutes. One way to resolve this wear problem is to introduce the lubricant between the shaft and the inner ring of the bearing, and use feed holes to centrifugally distribute the lubricant to the piloting surfaces. Such lubrication is called ‘under-race’ lubrication. However, in many designs ‘under-race’ lubrication cannot be incorporated. In such cases, an alternative solution is needed to improve the lubrication and eliminate wear of inner land piloted separators.
U.S. Pat. No. 3,597,031 discloses a ball bearing having a lubricant transfer recess or reservoir between the journal portions (or piloting surfaces) of the bearing cage. During operation of the ball bearing, a lubricant centrifugally collects in the reservoir and then passes to a bearing ball pocket through radial passages. The lubricant may also pass to the journal portions due to centrifugally developed pressure in the lubricating film. However, the transfer recesses are not designed to uniformly provide lubrication to the journal potions of the cage. Their primary purpose is to supply sufficient lubrication to the ball bearings during operation.
U.S. Pat. No. 5,106,209 discloses a bearing assembly including a split inner race having a plurality of center feed passages at the split line of the inner race along with at least one radial pilot passage in one of the inner race halves. The bearing assembly of the '209 patent lubricates bearing balls, raceways and bearing cage pilot surfaces with lubricant supplied at the inner diameter surface of the inner ring. There are no features, however, to bring lubricant in from an external jet and subsequently to enhance lubrication of the bearing cage pilot surfaces.
As can be seen, there is a need for a bearing assembly having enhanced lubrication of bearing cage pilot surfaces by bringing in lubricant from an external jet. It would also be desirable to have a bearing assembly that uniformly provides lubrication to bearing cage pilot surfaces.
In one aspect of the invention there is provided a bearing cage for a rolling element bearing, the bearing cage comprising an inner surface; a plurality of cage pockets at predetermined intervals along the circumference of the bearing cage; a plurality of web bore surfaces on the inner surface, the plurality of web bore surfaces separating the plurality of cage pockets; a first centrifugal lubricant catcher running circumferentially around an edge of the inner surface of the bearing cage; and a plurality of axial grooves, the plurality of axial grooves extending axially along the plurality of web bore surfaces.
In another aspect of the invention there is provided a bearing cage for a rolling element bearing, the bearing cage comprising an inner surface; a plurality of cage pockets at predetermined intervals along the circumference of the bearing cage; a plurality of web bore surfaces on the inner surface, the plurality of web bore surfaces separating the plurality of cage pockets; a first centrifugal lubricant catcher running circumferentially around an edge of the inner surface of the bearing cage; a circumferential groove, the circumferential groove running circumferentially around the inner surface of the inner ring and adjacent to the centrifugal lubricant catcher; and a plurality of axial grooves, the plurality of axial grooves extending from the circumferential groove along the plurality of web bore surfaces.
In a further aspect of the present invention there is provided a bearing cage for a rolling element bearing, the bearing cage comprising an inner surface; a plurality of cage pockets at predetermined intervals along a circumference of the bearing cage; a plurality of web bore surfaces, the plurality of web bore surfaces separating the plurality of cage pockets; a first piloting surface and a second piloting surface, the first and second piloting surfaces being on the inner surface of the bearing cage and connected by the plurality of web bore surfaces; a centrifugal lubricant catcher, wherein the centrifugal lubricant catcher comprises a lip running circumferentially around an edge of the inner surface of the bearing cage adjacent to the first piloting surface; and a plurality of axial grooves extending axially from adjacent the centrifugal lubricant catcher along the first piloting surface and the plurality of web bore surfaces to the second piloting surface, wherein the axial grooves extend over from about 50% to about 75% of the second piloting surface.
In yet another aspect of the present invention there is provided a rolling element bearing assembly comprising an inner ring; an outer ring; a bearing cage concentrically disposed between the inner ring and the outer ring, the bearing cage comprising an inner surface, a plurality of cage pockets at predetermined intervals along a circumference of the bearing cage, a plurality of web bore surfaces, the web bore surfaces separating the plurality of cage pockets, a centrifugal lubricant catcher, wherein the centrifugal lubricant catcher comprises a lip running circumferentially around an edge of the inner surface of the bearing cage, and a plurality of axial grooves extending from adjacent the lip of the centrifugal lubricant catcher along the plurality of web bore surfaces; and a plurality of rolling elements, the rolling elements being disposed within the plurality of cage pockets.
In a further aspect of the present invention there is provided a bearing sump of a turbine engine comprising a shaft; a coupling shaft connected to the shaft; a bearing assembly comprising an inner ring, the inner ring connected to the coupling shaft, an outer ring, and a bearing cage concentrically disposed between the inner ring and the outer ring, the bearing cage comprising an inner surface, a plurality of cage pockets at predetermined intervals along a circumference of the bearing cage, a plurality of web bore surfaces, the plurality of web bore surfaces separating the plurality of cage pockets, a centrifugal lubricant catcher, wherein the centrifugal lubricant catcher comprises a lip running circumferentially around an edge of the inner surface of the bearing cage, and a plurality of axial grooves extending from adjacent the lip of the centrifugal lubricant catcher along the plurality of web bore surfaces; a bearing support housing, the bearing support housing connected to the outer ring of the bearing assembly; and a lubricant jet, the lubricant jet being positioned in the bearing support housing such that lubricant is delivered by the lubricant jet directly to the bearing assembly in such a way that the lubricant is captured by the centrifugal lubricant catcher.
In another aspect of the invention there is provided a method of lubricating a first piloting surface and a second piloting surface of a bearing cage of a bearing assembly comprising the steps of spraying a lubricant towards one side of the bearing cage; capturing the lubricant in a centrifugal lubricant catcher wherein the centrifugal lubricant catcher is on the side of the bearing cage sprayed with lubricant; centrifugally distributing the lubricant to a first piloting surface, wherein the first piloting surface is adjacent to the centrifugal lubricant catcher; capturing additional lubricant from the centrifugal lubricant catcher in a plurality of axial grooves, wherein the axial grooves extend axially from the centrifugal lubricant catcher across the first piloting surface and a web bore surface to a second piloting surface; and lubricating the second piloting surface from the axial grooves by centrifugal force.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Broadly, the present invention provides a bearing cage for a bearing assembly which may have improved lubrication of piloting surfaces of the bearing cage, thereby decreasing wear and increasing the lifespan of the bearing assembly. The bearing cage may comprise a centrifugal lubricant catcher on the inner surface of one end of the bearing cage and a plurality of axial grooves in a plurality of bore web surfaces of the bearing cage to distribute lubricant more uniformly to the piloting surfaces. The bearing cage of the present invention may be useful in high speed rolling element bearings utilized in high-speed turbo machinery such as, but not limited to, high-speed gas turbine engines, machine tool spindles, turbo-pumps, and gas compressors.
Conventional high speed rolling element bearings often have a short lifespan due to wear between the bearing cage piloting surfaces and the bearing inner rings lands. This wear is due to the difficulty in maintaining and replenishing the hydrodynamic lubrication film on these surfaces. The wear may be severe enough to result in bearing failure within a matter of minutes. One way to resolve this wear problem is to introduce the lubricant between the shaft and the inner ring of the bearing, and use feed holes to centrifugally distribute the lubricant to the piloting surfaces. Such lubrication is called ‘under-race’ lubrication. However, in many designs, ‘under-race’ lubrication features cannot be incorporated. The present invention addresses the problems associated with wear between the bearing cage piloting surfaces and the bearing inner ring lands found in a conventional high speed rolling element bearings by providing improved lubrication of the bearing cage piloting surfaces that does not require under-race lubrication, thereby reducing wear and bearing failure.
Illustrated in
Bearing assembly 20 is illustrated in more detail in
As illustrated in
Bearing cage 24 may further comprise a centrifugal lubricant catcher 34 and a plurality of axial grooves 36 as illustrated in
The dimensions of centrifugal lubricant catcher 34 and/or axial grooves 36 may be determined using computational fluid dynamics (CFD) to provide the amount of lubrication desired for first piloting surface 38 and/or second piloting surface 40. Non-limiting examples of commercial CFD programs that may be used are FLUENT and FEMEHL. The dimensions of centrifugal lubricant catcher 34 and/or axial grooves 36 may also be dependent on the dimensions of bearing cage 24. In one illustrative embodiment, centrifugal lubricant catcher 34 has a radial height of from about 0.003 inches to about 0.100 inches and a width of from about 0.010 inches to about 0.100 inches. In another illustrative embodiment, axial grooves 36 may have a depth of from about 0.010 inches to about 0.040 inches and a width of from about 0.005 inches to about 0.050 inches. It will be appreciated that it may be desirable to have axial grooves 36 that are fairly shallow and narrow in width so that the integrity of bearing cage 24 is not compromised. The number of axial grooves 36 necessary for the desired amount of lubrication may also be calculated using CFD. In one illustrative embodiment, there is an axial groove 36 on each web bore surface 44 of bearing cage 24. In an alternative illustrative embodiment, there is an axial groove on alternating web bore surfaces 44.
In an alternative embodiment shown in
As illustrative in
In another embodiment of the present invention, bearing cage 24 may comprise centrifugal groove 46 and both first and second centrifugal lubricant catchers 34, 45 wherein axial grooves 36 may extend axially from circumferential groove 46 across first piloting surface 38, bore web surface 44 and second piloting surface 40 to the edge of second centrifugal lubrication catcher 45. In a further embodiment, bearing catcher 24 may further comprise a second circumferential groove adjacent to the second centrifugal lubricant catcher, wherein axially grooves 36 may extend axially from circumferential groove 46 to the second circumferential groove.
The present invention also provides a method of lubricating a first piloting surface and a second piloting surface of a bearing cage of a bearing assembly. Method 100, shown in
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
