Patent Grant
7770895
The present invention relates to segmented radial seal assemblies.
Segmented carbon radial or circumferential seals have been employed in a number of environments associated with compressible fluids, such as gases. They have been used, for example, in connection with gas turbine engines. Such radial seals typically act to, among other things, seal high pressure areas from low pressure areas. For some applications, Rayleigh steps or pads have been included to generate hydrodynamic opening force that enables a segmented seal to operate in a “non-contact” condition. The hydrodynamic opening force generated by a plurality of pads can distribute the associated force more evenly along a circumferential direction providing, among other things, a better balancing of forces. However, it has been found that an abrupt flow transition can occur with respect to the entrance of Rayleigh steps or pads and the transverse groove that helps to provide appropriate pressure balance. An abrupt transition between the transverse groove and the steps or pads can, among other things, cause associated flow losses and reduced efficiency.
A segment of a seal assembly for sealing a higher pressure area from a lower pressure area is disclosed. The segment comprises a radial external surface, a radial internal surface for sealing against a rotating member, a transverse groove for maintaining a pressure around portions of the segment, and one or more pads including a scooping groove. The scooping groove is positioned at or in proximity to an edge of the transverse groove and provides for a transition flow between the one or more pads and the transverse groove.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:
Reference will now be made in detail to embodiments of the present invention, examples of which are described herein and illustrated in the accompanying drawings. While the invention will be described in conjunction with embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.
A partial cut plane view of a seal ring segment 10 according to an embodiment of the invention is generally shown in
As generally illustrated in connection with
For example, without limitation, ramp 18 can be configured to transition into a plateau 17 (e.g., at 26) at a distance that is more than one-half the length of the pad 15 (viewed along its associated inner circumference). In an embodiment, ramp 18 may be configured to transition into a plateau 17 (e.g., at 26) at a distance that is more than about 2/3RDS of the distance along the pad 15 from the associated groove 16.
The pads 15, which are configured on the inner diameter, i.e., on the radial internal surface 14, permit high pressure air to migrate down channels as a shaft rotates, the air or fluid may then be channeled into grooves by the pads. The associated pressure may be used to offset assembly or system closing forces. Essentially, air under the seal can be used to generate a pressure that may be used to at least partially offset contact pressure.
In some conventional assemblies, air that moves axially down a shaft is forced to make an abrupt 90° turn as it is forced under the segment. Such an abrupt turn can cause a loss of momentum in flow and, potentially, a drop-off in feed (i.e., a situation in which there is no air working). The inclusion of a scooping groove 19 (or “undercut” in the ramp 18), of the type generally illustrated, can serve as a reservoir to provide the airflow with more room to make the necessary turn, thereby improving the efficiency of the air that is pumped into ramp 18 from the transverse groove 16. Typically, one enlarged volume portion, or scooping groove 19, is provided per pad.
It is noted that many of the dimensions are dictated by the application and various manufacturers. Nevertheless, by way of further example, in an embodiment of the invention, such as that shown in
Among other things, an appropriately configured scooping groove 19 can help improve the ability of a pad 15 to generate and hold hydrodynamic pressure near the end of the member. The scooping groove at the entrance of the pad 15 can smooth the transition from a groove that, in conventional ring segments may have previously been very shallow near the leading edge of the member. For example, such a groove depth previously may have been around 0.001 inches, while the scooping groove 19 may have a depth that is about 0.030 inches. The present invention, among other things, serves to reduce the effects of abrupt transition from the transverse groove 16 to the sloped portion or ramp 18.
Moreover, since the associated rotating shaft is not perfectly round, and the seal tracks the shaft, the configuration of the scooping groove (acting in part as a reservoir) can help prevent momentary starvation of fluid supply, which can lead to contact and wear. Consequently, the scooping groove 19—having an increased depth (or scoop) proximate the transverse groove 16—can serve to not only reduce entrance losses, but can provide a more continuous and smooth supply of fluid for the pad 15.
Turning again to
In an embodiment of the invention, the ramp 18 and scooping groove 19 do not flow all the way through in an axial direction. Rather, the ramp 18 and scooping groove 19 may be bounded or guarded by sidewalls 30 on both the high-pressure and low-pressure sides, with the scooping groove introduced to serve as a reservoir to feed ramp 18. Heat generation and removal can be effectively addressed and improved by the present invention. That is, the segments and assembly can be configured to create sufficient opening force to lift the segment off the shaft and significantly reduce heat generation so that the useful life of the seal is extended.
In an embodiment of the invention, each segment 10 may be one of a plurality of segments that together comprise a segmented seal ring or assembly. A general representation of an assembly 40 of seal ring segments 10 is shown in
As generally illustrated in
In an embodiment, the radial external surface of each segment, i.e., the surface opposing the bore-side surface shown in
Additionally, for some embodiments, an element, such as a carbon pin, may be used to connect the assembly to a housing so that the assembly does not rotate relative to the housing.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and various modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and its practical application, to thereby enable others skilled in the art to utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
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| Number | Date | Country |
|---|---|---|
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| Number | Date | Country | |
|---|---|---|---|
| 20080272552 A1 | Nov 2008 | US |
