Self-correcting hydrodynamic seal

Abstract

To provide a segment of a seal assembly for improving a life of a seal and preventing deterioration of integrity of an engine.SOLUTION: A segment 100 of a seal assembly 10 for forming a hydrodynamic seal against a rotating member can include a main body extending between first and second sides and defining a radial internal surface for forming a hydrodynamic seal with the rotating member. The main body can include a main surface extending between the main body first and second sides, a fluid inlet portion recessed from the main surface, and a hydrodynamic pad region located adjacent the fluid inlet portion and extending in a circumferential direction. The hydrodynamic pad region can include a first section and a second section separated by a land portion, and the first and second sections are recessed from the main surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Patent Application No. 62 / 950,647, filed on Dec. 19, 2019, the disclosure of which is hereby incorporated by reference in its entirety.

Background Art

[0002] Radially segmented seals have been successfully used for many years in aerospace and industrial applications in aircraft engines, gearboxes, and compressors. Current segmented seals, hydrodynamic, and contacts are designed to prevent significant leakage and decompression of process fluids within aircraft engines, compressors, and gearboxes. When properly designed, the seals function properly. Part of this design cycle is to calculate, measure, or estimate the taper of the engine shaft, match this taper angle to the inner diameter of the segmented seal, and thus minimize leakage. This prediction of the tapering is a complex and laborious task as it requires an accurate combination of finite elements of structure and heat, as well as viscous and frictional heating predictions at the interface between the seal inner diameter and the shaft outer diameter. In the case of hydrodynamic radial seals, the accuracy of this calculation takes precedence over good seal performance. If the taper opens towards the system pressure side, sufficient lift - off may not occur, and the hydrodynamic pad may become at or very near system pressure, which causes it to operate as a conventional contact radial seal. This raises the system temperature and limits the seal's life. Conversely, if the taper opens towards the atmosphere side, system fluid from the system side is vented to the atmosphere, and no pressure build - up occurs in the hydrodynamic seal pad area. In this situation, the seal's life and the engine's integrity are significantly impaired. Improvements are desired.

Summary of the Invention

[0003] A segment of a seal assembly for forming a hydrodynamic seal for a rotating member can include a body that extends between first and second sides and defines a radially inner surface for forming a hydrodynamic seal with the rotating member. The body can include a main surface that extends between the first and second sides of the body, a fluid inlet portion recessed from the main surface, and a hydrodynamic pad region positioned adjacent to the fluid inlet portion and extending circumferentially, the hydrodynamic pad region including a first section and a second section separated by a land portion, the first and second sections being recessed from the main surface, the hydrodynamic pad region.

[0004] The hydrodynamic seal assembly can include a flange and a plurality of segments as described above supported by the flange to form a ring.

[0005] The machine can include a rotatable shaft and a hydrodynamic seal assembly including a flange and a plurality of segments as described above supported by the flange to form a ring through which the rotatable shaft extends.

[0006] In some embodiments, one or both of the first and second sections have a constant width.

[0007] In some embodiments, the first and second sections have a depth that decreases in a direction away from the fluid inlet portion.

[0008] In some embodiments, the segment is formed from a carbon material.

[0009] In some embodiments, the first and second sections have equal lengths with respect to each other.

[0010] In some embodiments, the segment further includes a circumferential groove adjacent to the main surface.

[0011] In some embodiments, the combined width of the first and second sections is at least half of that of the main surface.

Brief Description of the Drawings

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[0027] The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate some aspects of the present disclosure. A brief description of the drawings is as follows.

Mode for Carrying Out the Invention

[0028] Various embodiments will be described in detail with reference to the drawings, and like reference numerals in the drawings represent like parts and assemblies throughout several views. References to various embodiments are not intended to limit the scope of the claims appended hereto. Further, none of the embodiments described herein are intended to be limiting, but rather are merely illustrative of some of the many possible embodiments of the appended claims. Referring to the drawings, like reference numerals correspond to like or similar components throughout several views.

[0029] Referring to FIGS. 1-14, a segment 100 of a seal assembly 10 for sealing against a rotating member is disclosed. Segment 100 can be used in a seal assembly of the type shown and described in U.S. Pat. No. 7,770,895, which is hereby incorporated by reference in its entirety. As shown in FIGS. 1 and 2, segment 100 can be used in a circumferentially segmented seal assembly 10. In one aspect, the circumferential seal assembly 10 is shown as including a plurality of adjacent segments 100 supported by a flange assembly 12. As can be seen by continued reference to FIGS. 1 and 2, the seal assembly 10 defines an annulus 10a through which a shaft 14 (see FIG. 3) can extend such that the segments 100 are oriented about the shaft 14 to provide a seal.

[0030] In one aspect, segment 100 includes an arcuate body 102 that extends between a first and a second side 102a, 102b and between a first and a second end 102c, 102d. In one embodiment, body 102 is formed from a material that includes carbon. The first and second ends 102c, 102d are oriented at an angle with respect to each other such that a number of segments can be combined to form a ring. Thus, the angular range defined between the first and second ends 102c, 102d is typically a divisor of 360 degrees, such as 72 degrees, 90 degrees, 120 degrees, or 180 degrees. In the embodiments shown in FIGS. 1 and 2, three segments 100 are provided, each forming a 120-degree (θ1, θ2, θ3 = 120 degrees) divided portion of the seal ring. Further, as shown in FIGS. 2-6, segment 100 may include cooperating features 112, 114 intended to overlap or interconnect with adjacent segments. Body 102 is further shown as defining a radial or circumferential outer surface 102e and a radial or circumferential inner surface 102f. The radial inner surface 102f may be characterized as having a partial main surface 102h. The radial inner surface 102f corresponds to the hole side of segment 100 and provides a sealing surface for a rotating member such as a shaft or a runner.

[0031] Referring to FIG. 3, a schematic cross-sectional view of seal assembly 10 is shown, with seal assembly 10 mounted on shaft or runner 14 and seal segment 100 disposed about shaft or runner 14. As depicted, each seal segment 100 is shown as having a body 102 provided with a circumferential pressure balance groove 102g, a seal dam 102o, and an axial pressure balance groove 102i. Seal segment 100 includes additional features that are shown and described later. Seal assembly 10 is also shown as including a flange 22 that houses seal segment 100. Coil spring 24, washer 26, and retainer 28 are provided to axially bias seal segment 100, while circumferential garter spring 30 is provided about the outer surface of seal segment 100 to hold seal segments 100 together.

[0032] In one aspect, the radially inner surface 102f of each segment 100 is defined by one or more hydrodynamic arrangements 105 for facilitating sealing by controlling hydrodynamic fluid flow. For example, as schematically shown in FIGS. 1 and 2, each of the segments 100 is provided with four hydrodynamic arrangements 105 to obtain a total of twelve hydrodynamic arrangements 105. The segment 100 can comprise a single hydrodynamic arrangement 105 or any desired number of arrangements 105. For example, the particular embodiment segment 100 shown in FIGS. 4-6 is provided with three hydrodynamic arrangements.

[0033] In one aspect, as most readily seen in FIGS. 7 and 10, the hydrodynamic arrangement 105 can include an inlet portion 102h that extends transversely across the radially inner surface 102f between the first side 102a and the pressure balance groove 102g. The inlet portion 102h enables fluid to be fed to the radially inner surface 102f of the seal segment, thereby ensuring that the hydrodynamic seal has a continuous supply of system fluid. In the embodiment shown, the inlet portion 102h is recessed lower than the main surface 102h and is tapered from the side 102a towards the pressure balance groove 102g. Other configurations are possible. For example, the inlet portion 102h can have a constant width or can be provided with a number of radially drilled holes.

[0034] In one aspect, the hydrodynamic arrangement 105 has a hydrodynamic pad region 102j adjacent to the inlet portion 102h. The hydrodynamic pad region 102j is recessed lower than the main surface 102h and is shown as including a draw-in portion 102k and first and second circumferentially extending sections 102m, 102n separated by a land portion 102p. In the illustrated embodiment, the land portion 102p is part of the main surface 102h. This configuration can be referred to as a fork-like configuration having first and second sections 102m, 102n that define the tine of the hydrodynamic pad region 102j. Generally, the draw-in portion 102k has a depth that is tapered in the direction towards the first and second sections 102m, 102n, while the first and second sections 102m, 102n also have a depth that continues to taper in the direction towards the second end 102d, with the first and second sections 102m, 102n becoming shallower in the direction towards the second end 102d. In the illustrated embodiment, the sections 102m, 102n have equal length and width. However, the land portion 102p can be configured such that the sections 102m, 102n have different lengths from each other and / or different widths from each other. The sections 102m, 102n are also shown as having a constant width. However, one or both of the sections 102m, 102n can have various widths, for example, a width that is tapered towards the second end 102d. Further, the disclosed sections 102m, 102n are shown as being symmetrically disposed on the main surface 102h such that they are equidistant from the centerline of the main surface 102h, and the main surface 102h is defined as a surface extending from the side portion 102a to the circumferential groove 102g. However, the sections 102m, 102n can be disposed asymmetrically, with one of the sections 102m, 102n being disposed closer to or farther away from the centerline of the main surface 102h compared to the other of the sections 102m, 102n. Accordingly, the land 102p can be disposed and shaped with various widths to conform to such an arrangement. Generally, the width of the sections 102m, 102n can be 0.02 inches or more.The width of the land portion 102p can be selected such that the desired widths of the sections 102m, 102n are achieved. In the illustrated embodiment, the combined width of the first and second sections 102m, 102n is at least half of the width of the main surface. In one embodiment, the combined width of the first and second sections 102m, 102n is wider than half of the width of the main surface.

[0035] During operation, fluid (e.g., air) enters laterally from the inlet 102h and then is directed circumferentially and compressed in the draw-in portion 102k. From the draw-in portion, the fluid is divided by the land portion 102p and enters the first and second sections 102m, 102n where the fluid travels along the lengths of the sections 102m, 102n and is further compressed. As can be seen schematically from FIG. 4, in a situation where the shaft 14 and the main surface 102h are completely parallel, the upward pressure P1 resulting incrementally from the fluid traversing the length of the section 102m is approximately equal to the pressure P2 generated by the fluid traversing the length of the section 102n. Thus, the pressures generated by the compressed fluid in the sections 102m, 102n are in a substantially balanced state and do not create a moment force that would cause the seal segment 100 to vibrate towards either the first or second side portions 102a, 102b about the longitudinal axis X of the seal segment 100.

[0036] Referring to FIG. 13, when there is a slight shaft taper or wobble in shaft 14, surface 102h will necessarily not be parallel to the outer surface of shaft 14. The slight tapering is on the order of ±0.001 inches or less. Such a condition, as can be seen from FIG. 13 and in contrast to FIG. 12 where no taper has yet occurred, results in a non-uniform pressure between P1 and P2 in each of sections 102m, 102n. Thus, the pressure associated with sections 102m, 102n closest to the side having a shorter separation distance between shaft 14 and surface 102 becomes greater than the pressure on the other sections 102m, 102n, and thus creates a corrective or restoring force to rotate seal segment 100 about either the longitudinal axis X or another axis such as an axis parallel to axis X to the other side. Generally, the side having a shorter separation distance between shaft 14 and surface 102 can be referred to as the closed side, and the other side as the open side. Regardless of the taper direction, the segments 102m, 102n on the open side of the taper produce less film stiffness and thus less hydrodynamic force than the segments 102m, 102n on the closed side. The closed side produces a stiffer hydrodynamic film and thus a higher lift-off force. This situation results in a corrective moment, i.e., the seal attempts to reach equilibrium. Thus, regardless of which side the taper is on, if fluid is being fed to the seal, a hydrodynamic corrective force is produced. As illustrated in FIG. 12, when the inner diameter surface 102h of seal segment 100 is parallel to the shaft surface, it provides a more stable hydrodynamic film as opposed to a tapered shaft that can destabilize the hydrodynamic film.

[0037] Compared to a seal segment provided by a conventional hydrodynamic pad region having only a single large segment without intervening land portions, the disclosed closed-side segments 102m, 102n are more protected from fluid exiting the open sides of segments 102m, 102n. In a conventional single pad shape, the separation distance between the shaft and the edge of the pad on the open side defines a range where undesired wear occurs. With the disclosed design, the open-side segments 102m, 102n have substantially the same separation distance at this location, and thus, the open-side segments 102m, 102n experience the same wear dynamics. However, the closed-side segments 102m, 102n are protected by the land portions 102p, which have a separation distance to the shaft that is significantly shorter than the above-described separation distance and, in the illustrated embodiment, less than half of this separation distance. Thus, the closed-side segment (segment 102m in FIG. 13) is able to compress the fluid and keep the seal operational. Thus, not only does it generate a desirable corrective force, but the disclosed design also maintains a higher level of functionality compared to conventional designs where the shaft is tapered or under oscillation.

[0038] Referring to FIG. 14, the corrective force is further illustrated, and from the pressure profile generated by a computational fluid dynamics model, the generation of the high-pressure region P1 at segment 102m can be easily visualized. In contrast to the disclosed design, as can be seen with reference to FIG. 15, a seal segment P100 provided with a conventional hydrodynamic pad region having only a single large segment without the intervention of land portions cannot generate the same corrective force as the disclosed design that can discharge the compressed fluid from the open side.

[0039] From the foregoing detailed description, it will be apparent that modifications and variations can be made in the aspects of the present disclosure without departing from the spirit or scope of the aspects. While the best modes for carrying out many aspects of the present teachings have been described in detail, those skilled in the relevant art will recognize various alternative modes for practicing the present teachings within the scope of the appended claims.

Claims

1. A segment of a seal assembly for forming a hydrodynamic seal for a rotating member, a) a body extending between a first and a second side and defining a radially inner surface for forming a hydrodynamic seal with the rotating member, wherein (i) the body has a main surface extending between the first and second sides of the body, (ii) a fluid inlet portion recessed from the main surface, (iii) a hydrodynamic pad region positioned adjacent to the fluid inlet portion and extending circumferentially, the hydrodynamic pad region including a first section and a second section separated by a land portion, the first and second sections being recessed from the main surface, the first and second sections having a depth that gradually decreases as the first and second sections extend circumferentially away from the fluid inlet portion and terminating at the main surface, defining a hydrodynamic pad region; a segment of a seal assembly comprising a body.

2. The segment according to claim 1, wherein one or both of the first and second sections have a constant width.

3. The segment according to claim 1, wherein the segment is formed from a carbon material.

4. The segment according to claim 1, wherein the first and second sections have equal lengths with respect to each other.

5. The segment according to claim 1, further comprising a circumferential groove adjacent to the main surface.

6. The segment according to claim 1, wherein the combined width of the first and second sections is at least half of that of the main surface.

7. The segment according to claim 1, wherein the segment is one of a plurality of segments constituting a hydrodynamic seal assembly.

8. The segment according to claim 7, wherein the hydrodynamic seal assembly includes a flange that supports the plurality of segments such that the plurality of segments form a ring.

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