Patent Publication Number: US-2021190208-A1

Title: Self-Correcting Hydrodynamic Seal

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/950,647, filed on Dec. 19, 2019, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     Radial segmented seals have been used successfully in aerospace and industrial applications for many years in aircraft engines, gearboxes and compressors. Current segmented seals, hydrodynamic and contacting, are designed to prevent significant leakage and de-pressurization of process fluids in aircraft engines, compressors and gearboxes. When designed properly the seals function adequately. Part of this design cycle is to calculate, measure, or estimate the taper in the engine shaft and match this taper angle with the segmented seal inside diameter thus minimizing leakage. Prediction of this tapering is a complicated effort as it in requires an accurate combined structural and thermal finite element and viscous and friction heating prediction at the interface between the seal inside diameter and the shaft outside diameter. For hydrodynamic radial seals, the accuracy of this calculation is paramount to successful seal performance. If the taper is open to the system pressure side the adequate liftoff may not occur and the hydrodynamic pad would be at or very close to the system pressure and this would operate as a conventional contacting radial seal. This would increase system temperature and limit seal life. Conversely, if the taper were to open to the atmosphere side then system fluid from the system side would be vented to atmosphere and no pressure build up would occur in the hydrodynamic seal pad area. Seal life and engine integrity would be significantly compromised in this situation. Improvements are desired. 
     SUMMARY 
     A segment of a seal assembly 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, a hydrodynamic pad region located adjacent the fluid inlet portion and extending in a circumferential direction, 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. 
     A hydrodynamic seal assembly can include a flange and a plurality of segments in accordance with the above supported by the flange to form a ring. 
     A machine can include a rotatable shaft and a hydrodynamic seal assembly including a flange and a plurality of segments in accordance with above supported by the flange to form a ring through which the rotating rotatable shaft extends. 
     In some examples, one or both of the first and second sections have a constant width. 
     In some examples, the first and second sections have a decreasing depth in a direction away from the fluid inlet portion. 
     In some examples, the segment is formed from a carbon material. 
     In some examples, the first and second sections have an equal length to each other. 
     In some examples, the segment further includes a circumferential groove adjacent the main surface. 
     In some examples, a combined width of the first and second sections is at least half that of a width of the main surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a circumferential segmented seal assembly within which multiples hydrodynamic seal segments are secured. 
         FIG. 2  is a schematic representation of a plurality of seal segments of the assembly shown in  FIG. 10 . 
         FIG. 3  is a schematic cross sectional view of the seal assembly shown in  FIG. 1  in an installed application with a rotating shaft. 
         FIG. 4  is a perspective view of a hydrodynamic seal segment of the seal assembly shown in  FIG. 1 . 
         FIG. 5  is a first side view of the hydrodynamic seal segment shown in  FIG. 4 . 
         FIG. 6  is a face side view of the hydrodynamic seal segment shown in  FIG. 4 , in which the segment is provided with three hydrodynamic seal arrangements. 
         FIG. 7  is a face side view of a portion of the hydrodynamic seal segment shown in  FIG. 4 , as indicated at reference  7  on  FIG. 6 , showing features of one of the hydrodynamic seal arrangements. 
         FIG. 8  is a first side view of the hydrodynamic seal segment portion shown at  FIG. 4 . 
         FIG. 9  is a second side view of the hydrodynamic seal segment portion shown at  FIG. 4 . 
         FIG. 10  is a face-side perspective view of the hydrodynamic seal segment portion shown at  FIG. 6 . 
         FIG. 11  is a cross-sectional view of the hydrodynamic seal segment portion shown at  FIG. 4 , taken along the line  11 - 11  at  FIG. 5 . 
         FIG. 12  is a schematic cross-sectional view of the hydrodynamic seal segment shown at  FIG. 4  illustrating a face-side perspective view of the hydrodynamic seal segment portion shown at  FIG. 6 , wherein the hydrodynamic seal arrangements maintain the seal segment in a balanced state. 
         FIG. 13  is a schematic cross-sectional view of the hydrodynamic seal segment shown at  FIG. 4  illustrating a face-side perspective view of the hydrodynamic seal segment portion shown at  FIG. 6 , wherein self-correcting forces of the hydrodynamic seal arrangements act to return the seal segment to a balanced state. 
         FIG. 14  is a computational fluid dynamic analysis of the radial segmented seal with a hydrodynamic seal arrangement of the type disclosed herein, illustrating the localized self-correcting forces generated by the disclosed design. 
         FIG. 15  is a computational fluid dynamic analysis of a prior art radial segmented seal without localized self-correcting forces. 
     
    
    
     The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the present disclosure. A brief description of the drawings is as follows: 
     DETAILED DESCRIPTION 
     Various examples will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various examples does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible examples for the appended claims. Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures. 
     Referring to  FIGS. 1 to 14 , a segment  100  of a seal assembly  10  for sealing against a rotating member is disclosed. The segment  100  may be used in a seal assembly of the type shown and described in U.S. Pat. No. 7,770,895, the entirety of which is incorporated by reference herein. The segment  100  may be used in a circumferential segmented seal assembly  10 , as shown at  FIGS. 1 and 2 . In one aspect, the circumferential seal assembly  10  is shown as including a plurality of adjacently arranged segments  100  supported by a flange assembly  12 . With continued reference to  FIGS. 1 and 2 , it can be seen that the seal assembly  10  defines an annulus  10   a  through which a shaft  14  (e.g. see  FIG. 3 ) can extend such that the segments  100  are oriented about the shaft  14  to provide a seal. 
     In one aspect, the segment  100  includes an arc-shaped main body  102  extending between first and second sides  102   a ,  102   b  and extending between a first and second ends  102   c ,  102   d . In one example, the main body  102  is formed from a material including carbon. The first and second ends  102   c ,  102   d  are oriented at an angle to each other such that multiple segments can be combined to form a ring. Accordingly, the angular range defined between the first and second ends  102   c ,  102   d  will typically be a multiple of 360°, such as 72°, 90°, 120°, or 180°. In the example shown at  FIGS. 1 and 2 , three segments  100  are provided that each form a 120° (θ 1 , θ 2 , θ 3 =120°) segment of a seal ring. Additionally, the segments  100  may include cooperating features  112 ,  114  intended to overlap or interconnect with an adjacent segment, as is depicted at  FIGS. 2 to 6 . The main body  102  is further shown as defining a radial or circumferential outer surface  102   e  and a radial or circumferential inner surface  102   f . The radial internal surface  102   f  may be characterized as having, in part, a main surface  102   h . The radial internal surface  102   f  corresponds to a bore side of the segment  100  and provides a sealing surface against a rotating member, such as a shaft or runner. 
     Referring to  FIG. 3 , a schematic cross-sectional view of the seal assembly  10  is presented, wherein the seal assembly  10  is shown as being mounted onto a shaft or runner  14  such that the seal segments  100  are arranged about the shaft or runner  14 . As depicted, each seal segment  100  is shown as having a main body  102  being provided with a circumferential pressure balance groove  102   g , a seal dam  102   o , and an axial pressure balance groove  102   i . The seal segments  100  include additional features which are shown and described later. The seal assembly  10  is also shown as including a flange  22  housing the seal segments  100 . A coil spring  24 , washer  26 , and retainer  28  are provided to urge the seal segments  100  in an axial direction while a circumferential garter spring  30  is provided about the outer surface of the seal segments  100  to hold the seal segments  100  together. 
     In one aspect, the radial inner surface  102   f  of each segment  100  is defined by one or more hydrodynamic arrangements  105  for facilitating sealing by controlling hydrodynamic fluid flow. For example, and schematically as shown at  FIGS. 1 and 2 , each of the segments  100  is provided with four such hydrodynamic arrangements  105 , for a total of twelve hydrodynamic arrangements  105 . A segment  100  can be provided with a single hydrodynamic arrangement  105  or any number of desired arrangements  105 . For example, the particular example segment  100  shown at  FIGS. 4 to 6  is provided with three hydrodynamic arrangements. 
     In one aspect, and as most easily seen at  FIGS. 7 and 10 , the hydrodynamic arrangement  105  can include an inlet portion  102   h  extending transversely across the radial internal surface  102   f  between the first side  102   a  and the pressure balance groove  102   g . The inlet portion  102   h  allows for fluid to be fed into the radial internal surface  102   f  of the seal segment, thereby ensuring that the hydrodynamic seal has a continuous supply of system fluid. In the example shown, the inlet portion  102   h  is recessed below the main surface  102   h  and tapers from the side  102   a  towards the pressure balance groove  102   g . Other configurations are possible. For example, the inlet portion  102   h  could have a constant width or could be provided by multiple radial drilled holes. 
     In one aspect, the hydrodynamic arrangement  105  has a hydrodynamic pad region  102   j  adjacent the inlet portion  102   h . The hydrodynamic pad region  102   j  is recessed below the main surface  102   h  and is shown as including a lead-in portion  102   k  and circumferentially extending first and second sections  102   m ,  102   n  separated by a land portion  102   p . In the example shown, the land portion  102   p  is the part of the main surface  102   h . This configuration may be referred to as a forked configuration with the first and second sections  102   m ,  102   n  defining tines of the hydrodynamic pad region  102   j . In general terms, the lead-in portion  102   k  has a depth that tapers in a direction towards the first and second sections  102   m ,  102   n  while the first and second sections  102   m ,  102   n  have a depth that also continues to taper in the direction towards the second end  102   d  such that the first and second sections  102   m ,  102   n  become shallower in a direction towards the second end  102   d . In the example shown, the sections  102   m ,  102   n  have an equal length and width. However, the land portion  102   p  may be configured such that the sections  102   m ,  102   n  have a different length from each other and/or have a different width from each other. The sections  102   m ,  102   n  are also shown as having a constant width. However, one or both of the sections  102   m ,  102   n  may have a varying width, for example, a width that tapers towards the second end  102   d . Furthermore, the disclosed sections  102   m ,  102   n  are shown as being symmetrically arranged on the main surface  102   h  such that they are equidistant from a centerline of the main surface  102   h , where the main surface  102   h  is defined as the surface extending from the side  102   a  to the circumferential groove  102   g . However, the sections  102   m ,  102   n  may be asymmetrically arranged such that one of the sections  102   m ,  102   n  is located either closer or farther away from the centerline of the main surface  102   h  as compared to the other section  102   m ,  102   n . The land  102   p  may be accordingly located and shaped with a varying width to accommodate such an arrangement. In general, the width of the sections  102   m ,  102   n  can be approximately 0.02 inches or wider. The width of the land portion  102   p  may be selected such that the desired width of the sections  102   m ,  102   n  is achieved. In the example shown, the combined width of the first and second sections  102   m ,  102   n  is at least half of the width of the main surface. In one example, the combined width of the first and second sections  102   m ,  102   n  is greater than half of the main surface width. 
     In operation, as fluid (e.g. air) enters transversely at the inlet  102   h  and is then directed circumferentially and compressed at the lead-in portion  102   k . From the lead-in portion, the fluid is split by the land portion  102   p  and enters the first and second sections  102   m ,  102   n  where the fluid is further compressed travelling along the length of the sections  102   m ,  102   n . In circumstances where the shaft  14  and the main surface  102   h  are perfectly parallel, as can be seen schematically at  FIG. 4 , the resulting upward pressure P 1  increasingly generated by the fluid traversing the length of the section  102   m  will generally be equal to the pressure P 2  generated by the fluid traversing the length of the section  102   n . Accordingly, the pressure created by the compressing fluid at the sections  102   m ,  102   n  is generally balanced and does not create a moment force that would otherwise cause the seal segment  100  to rock either towards the first or second sides  102   a ,  102   b  about a longitudinal axis X of the seal segment  100 . 
     With reference to  FIG. 13 , when the shaft  14  develops a minor shaft taper or wobble, the surface  102   h  is no longer naturally parallel to the outer surface of the shaft  14 . Minor tapering would be in the order of ±0.001 inch or less. Such a condition results in an uneven pressure between P 1  and P 2  at each of the sections  102   m ,  102   n , as can be seen at  FIG. 13 , and in contrast to  FIG. 12  where a taper has not yet developed. Accordingly, the pressure associated with the section  102   m ,  102   n  that is nearest the side with the narrower clearance between the shaft  14  and the surface  102  will be greater than the pressure on the other section  102   m ,  102   n  and will thus generate a correcting or righting force to rotate the seal segment  100  to rotate towards the other side either about the longitudinal axis X or another axis, such as an axis parallel to the axis X. In general terms, the side with the narrower clearance between the shaft  14  and the surface  102  can be referred to as the closed side and the other side can be referred to as the open side. Regardless of the taper direction, the segment  102   m ,  102   n  on the open side of the taper would develop less film stiffness and thus less hydrodynamic forces than the segment  102   m ,  102   n  on the closed side. The closed side would develop a more stiff hydrodynamic film and thus a higher lift-off force. This situation would result in a correcting moment, i.e. the seal would attempt to reach equilibrium. Therefore, regardless of which side the taper exists, if the seal is being fed fluid, then a correcting hydrodynamic force would result. When the inner diameter surface  102   h  of the seal segment  100  is parallel to the shaft surface, as illustrated at  FIG. 12 , it will provide a more stable hydrodynamic film as opposed to tapered shaft which could destabilize the hydrodynamic film. 
     As compared a seal segment provided with a conventional hydrodynamic pad region with only single large segment having no intervening land portion, the disclosed closed side segment  102   m ,  102   n  is more greatly protected from fluid exhausting out the open side of the closed side segment  102   m ,  102   n . In a conventional, single pad configuration, the clearance between the shaft and the edge of the pad at the open side defines the extent to which undesirably exhaustion will occur. With the disclosed design, the open side segment  102   m ,  102   n  will generally have the same clearance at this location and thus the open side segment  102   m ,  102   n  will be subject to the same exhaustion dynamic. However, the closed side segment  102   m ,  102   n  is protected by the land portion  102   p  which has a clearance to the shaft that is significantly less than the aforementioned clearance, and in the example shown, is less than half of this clearance. Accordingly, the closed side segment (segment  102   m  in  FIG. 13 ) is able to continue to compress the fluid and keep the seal operational. Thus, not only does the disclosed design create a desirable correcting force, the disclosed design also maintains a higher level of functionality in comparison to conventional designs under shaft tapering or wobbling conditions. 
     Referring to  FIG. 14 , the correcting force is further illustrated, where the creation of a high pressure region P 1  at the segment  102   m  can be readily viewed in a pressure profile generated from computer fluid dynamics model. In contrast to the disclosed design, and referring to  FIG. 15 , it can be seen that a seal segment P 100  provided with a conventional hydrodynamic pad region with a only single large segment with no intervening land portion is unable to generate the same correcting force as the disclosed design as the compressing fluid is able to exhaust out of the open side. 
     From the forgoing detailed description, it will be evident that modifications and variations can be made in the aspects of the disclosure without departing from the spirit or scope of the aspects. While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.