Abstract:
A backup ring is provided adjacent a seal apparatus for delivering a controlled space between two relatively moving parts. The backup ring provides protection against seal extrusion and failure, and can provide an auxiliary seal when needed. The backup ring includes either an arcuate surface that deforms under pressure, or a cantilever portion that deforms under pressure, or both.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims the benefit under 35 U.S.C. §119 of Provisional Application Ser. No. 60/108,797 filed Nov. 14, 1998 by the same inventors. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a backup ring and more particularly to a backup ring having a convex shape and/or cantilever portion for providing a controlled space between the backup ring and a relatively moving part when in a pressurized state. 
     2. Description of the Related Art 
     Sealing devices between two relatively moving parts are well known in the art. When the two moving parts include a shaft and a concentric housing, the sealing device typically comprises a first annular seal ring, and an energizer ring working in combination with the seal. Both the seal ring and the energizer ring are typically disposed in a gland or a groove carved into the housing, and face the rotatable shaft to form a sealing relationship with the shaft. Some sealing arrangements provide for only a seal to be used as the sealing device. However, if both a seal ring and an energizer ring are used, the seal ring is generally disposed adjacent the rotatable shaft, and the energizer ring disposed along the opposing bottom of the gland or groove. 
     Often, a seal ring serves to retain lubrication fluid on one side of the seal, preventing the leakage of that fluid even in pressurized states. However, under operation, and especially when high-pressure fluids are involved, a seal ring has a potential to extrude from its position in the gland. This condition, known as a seal blow-out, can halt the operation of the shaft, damage the shaft and housing, and proximately cause significant secondary damage, depending on the application of the shaft and housing. 
     In part to alleviate the potential for seal extrusion, a backup ring is utilized in many sealing device applications in the art. The backup ring is disposed along the gland wall that carries the seal device during operation. It is common during operation, especially in high-pressure fluid applications, for a seal to shift toward one side of the gland, thereby exerting most of its lateral pressure on a wall of the gland. It is at this time that the potential for seal extrusion is highest. 
     Placing a backup ring between the sealing device and that gland wall provides a means for further securing the sealing device inside the gland. This is accomplished by providing a seal ring having a concentric annular hole that is either sized to fit around the diameter of the rotating shaft, or it is slightly larger. Physical properties such as elastomeric properties and design tolerances allow the backup ring to substantially prevent seal failure and seal extrusion. 
     However, it is a potential disadvantage of current backup rings that when a shaft-contacting backup ring is utilized, the system is subjected to additional friction due to the contact between the shaft and the backup ring. 
     Alternatively, when radially spaced backup rings are used, less protection against seal extrusion is provided, and a means must be implemented in order to engage the backup ring with the shaft thereby preventing fluid leakage. Furthermore, due to varying design tolerances and varying pressures within a pressurized system, an optimal clearance between the backup ring and the shaft is not always consistently achieved. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to a seal arrangement for sealing a gap between two relatively moving parts, such as a shaft and a housing that is concentric with the shaft. While the following descriptions pertain to a shaft relatively moving within a housing, the present invention is not limited by such an embodiment, and other configurations for two relatively moving parts are within the scope of this disclosure. 
     A seal arrangement is typically comprised of a primary seal apparatus that is disposed within a gland located between the shaft and the housing, and a backup ring that is disposed between the primary seal apparatus and a wall of the gland. It should be noted that while the following description discloses a preferred embodiment having a gland defined within the housing, it is within the scope of the present invention to have a gland defined in the shaft, wherein the primary seal apparatus and backup ring face the housing and form a sealing relationship therebetween. 
     The present invention, in one form thereof, comprises a backup ring for providing auxiliary sealing to a primary seal arrangement disposed between a first member having a first contact surface and a second member having a second contact surface, the backup ring comprises a washer shaped member having a perimeter in contact with the first contact surface, the washer having a convexly shaped portion. According to the invention, the convex shape is deflected when subjected to pressure, such that it extends the member into a more linear shape or otherwise changes its shape in a controlled manner, thereby either closing out or opening the seal clearance to a desired gap. 
     The present invention, in another embodiment thereof, further comprises a generally arcuate cantilever portion extending from the perimeter of the washer. As disclosed in the invention, the cantilever portion extends at an angle from the plane defined by the washer during an unpressurized state, and when pressurized, deforms into a position disposed between a surface of the gland and the primary seal arrangement such that the cantilever portion extends substantially perpendicularly from the plane defined by the washer. 
     The present invention, in another form thereof, comprises a seal arrangement for sealing a gap between a shaft and a housing, the seal arrangement having a pressurized state and a non-pressurized state, the seal arrangement comprising a primary seal apparatus disposed within a gland between the shaft and the housing, and a backup ring disposed between the primary seal apparatus and a wall of the gland, the backup ring extending substantially radially between the shaft and a gland bottom, and having a convex portion in the non-pressurized state. 
     The present invention, in yet another form thereof, comprises a method of sealing and gap between a first member and a second member comprising the steps of: providing a primary seal arrangement disposed between the first member and the second member, and providing a backup ring disposed between the first member and the second member adjacent to the primary seal arrangement, the backup ring having a convexly shaped portion that deflects when subject to compressive forces. 
     The present invention, in a further embodiment thereof, comprises a backup ring disposed between a first member having a first contact surface and a second member having a second contact surface, the backup ring comprising a washer having a cantilever portion extending from the washer at an angle from a plane substantially defined by the washer. According to this embodiment of the invention, the cantilever portion extends at an angle from the plane substantially defined by the washer when the system is in an non-pressurized state, and is deformed into a configuration wherein the cantilever portion extends substantially perpendicularly from the plane defined by the washer in a pressurized state. 
     During an unpressurized state of the present invention, a primary seal apparatus contacts the shaft on an inner surface of the seal apparatus, and contacts the gland bottom on an outer surface of the said apparatus. The primary seal apparatus may only include a seal ring, or it may include a seal ring and an energizer, the energizer circumscribing the seal ring. In either case, the backup ring is placed adjacent the seal arrangement, such that it is disposed between the primary seal apparatus and a gland wall, on a non-pressurized side of the primary seal apparatus. 
     In one embodiment of the present invention, the backup ring maintains a convex shape during a non-pressurized state, while being radially spaced from the outer surface of the shaft. However, during a pressurized state, the primary seal apparatus exerts pressure on the backup ring in an axial direction, thereby deforming and radially elongating the backup ring, and consequently encouraging the inner surface of the backup ring to move closer to the shaft. Depending on the application, the backup ring can be designed to engage and seal the shaft during a pressurized state, or provide an optimal clearance between the shaft and the backup ring during the pressurized state. 
     It is an advantage of the present invention that the backup ring, in one form thereof, provides a substantially frictionless convex shaped design during periods of low pressure operation and provides a selectable positioning with relation to the shaft during a high-pressure state, when the likelihood of seal failure or extrusion is greatest. 
     It is a further advantage of the present invention, in one form thereof, that the wear on the backup ring during normal operation is greatly reduced because of the clearance provided between the shaft and the backup ring when it is in its convex shape. 
     It is a further advantage of one embodiment of the present invention that extrusion of the primary seal apparatus and the backup ring is further minimized by the providing a consistently achievable clearance between the backup ring and the shaft. 
     Yet another advantage of this embodiment is that the axially protruding lip portion provides for a lifting of the backup ring from the shaft, thereby reducing friction and wear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a sectional view on an axial plane illustrating one form of the invention; 
     FIG. 2 is a sectional view of the invention of FIG. 1 in a pressurized state; 
     FIG. 3 is a sectional view of another embodiment of the present invention wherein a cantilever portion is provided in addition to a concave surface. 
     FIG. 4 is a sectional view of another embodiment of the present invention wherein the backup ring forms a concave surface facing toward the seal element; 
     FIG. 5 is a sectional view of an embodiment of the invention wherein two backup rings are provided; 
     FIG. 6 is a sectional view of an embodiment of the invention wherein a cantilever portion is provided; 
     FIG. 7 is a sectional view of the embodiment of FIG. 6 during a pressurized state; and 
     FIG. 8 shows the results of a finite element analysis comparing the prior art seal arrangement to the present invention. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and particularly to FIG. 1, there is shown a typical seal arrangement  10  which includes a primary seal apparatus  12  disposed within a gland  14  for creating a sealing relationship between a first member  16  and a second member  18  having motion relative to each other. 
     In one embodiment of the invention, as shown in FIG. 1, gland  14  is defined within first member  16 , facing second member  18 . Although the preferred embodiment describes first member  16  as a shaft housing that has a concentric relationship with a shaft, second member  18 , other configurations and placements for the gland  14  are within the scope of the invention. For example, gland  14  could be defined within second member  18 , whereby primary seal apparatus  12  is arranged to be facing first member  16 , and first member  16  and second member  18  could have planar or other geometries. 
     While primary seal apparatus  12  is shown in FIG. 1 to include a seal ring  20  and an energizer ring  22 , the present invention may alternately utilize only a seal ring as the primary seal apparatus  12 , thereby omitting energizer ring  22 . 
     The invention, in its most important portion, further comprises backup ring  24  disposed between primary seal apparatus  12  and wall surface  26  of gland  14 . Backup ring  24  can be composed of polytetrafluoroethylene, or any other elastomeric compound that provides a deformable medium, such as thermoplastics or thermosets including, but not limited to UHMWPE or thermoset, Nylon, polyetheretherketone, polyphenylsulfide, phenolic, epoxy, thermoplastic elastomer, and polyurethane. 
     According to the embodiment of the invention as disclosed in FIG. 1, backup ring  24  extends radially between second member  18  and a bottom surface  28  of gland  14 . In an unpressurized state, the backup ring  24  of FIG. 1 maintains a convexly shaped portion  30  having an inner arcuate surface  32  and outer arcuate surface  34 . In an unpressurized state, backup ring  24  contacts primary seal apparatus  12  along at least one contact surface  36  disposed on outer arcuate surface  34  of backup ring  24 , and contacts first member wall surface  26  at contacts  38 ,  40 . Importantly, backup ring  24  is disposed and constructed such that in an unpressurized state, a clearance  42  is left between inner contact surface  44  of backup ring  24  and a perimeter of second member  18 , the clearance  42  providing for frictionless relative movement between first member  16  and second member  18 , at least with respect to backup ring  24 . Additionally, during an unpressurized state, backup ring  24  is not subjected to wear as would be expected if it were in constant contact with second member  18 . 
     FIG. 2 depicts the embodiment of FIG. 1 in a pressurized state, wherein fluid pressure is being introduced into the system through passageway P. As indicated by the arrows  52  depicting pressure, a pressurized state is characterized by internal fluid pressure on seal ring  20  and energizer ring  22 , the pressure shifting seal ring  20  and energizer ring  22  toward backup ring  24 , causing convexly shaped portion  30  to deflect into a more linear and extended shape. As pressure in the system increases, inner arcuate surface  32  is forced closer to wall surface  26 , and backup ring  24  radially expands, causing inner contact surface  44  of backup ring  24  to come in close proximity with outer surface of second member  18 . If desired in the application, backup ring  24  can be designed to close the gap between inner contact surface  44  and second member  18  when pressurized. 
     Furthermore, backup ring  24  can be manufactured with different tolerances and materials, such that the pressure range at which deflection occurs is appropriate for the particular application. For instance, if it is desirable in the application to have backup ring  24  become substantially linear at a lower pressure, a more elastomeric compound can be used, and/or a backup ring  24  with a smaller thickness or different geometries can be used. 
     As pressure increases in the system and backup ring  24  becomes more linear, its relationship with second member  18  and more particularly seal ring  20  substantially prevents primary seal apparatus  12  from extruding. This is caused by the controllability or close out of the clearance space between backup ring  24  and second member  18 . Additionally, backup ring  24  can provide a secondary seal in the event that the primary seal apparatus  12  fails or leaks in some manner. 
     As disclosed above, backup ring  24  can be designed with varying geometries, thicknesses, and compositions, such that a variety of applications may be served. For example, an application requiring a minimum radial clearance of 0.010 inch between backup ring  24  and second member  18  would have a certain geometry, composition, and specifications. In contrast, an application requiring the backup ring to close the radial clearance to a 0.002 inch clearance in the same gland would likely provide either more elastomeric properties, larger dimensions, or a slightly differing geometry, such as one in which inner the arcuate surfaces  32 ,  34  are altered to have a different arcuate curvature. Additionally, backup ring  24  can be provided with physical characteristics and properties that enable it to sealingly engage with second member  18  during extreme high-pressure conditions, thereby providing maximum protection against seal extrusion and failure. 
     In an alternative embodiment of the invention, a method of sealing a gap between a first member and a second member is provided, the method comprising the steps of providing a primary seal arrangement disposed between the first member and the second member, and providing a backup ring between the first member and the second member and adjacent the primary seal apparatus, wherein the backup ring has a convexly shaped portion for permitting deflection when subjected to compressive forces. 
     Another alternative embodiment of the invention is shown in FIG. 3, wherein backup ring  24  further comprises a cantilever portion  46 . According to this embodiment of the invention, cantilever portion  46 , during a non-pressurized state, extends at an angle from backup ring  24 . Under pressurization, primary seal apparatus  12  presses against backup ring  24  thereby forcing cantilever portion  46  against bottom surface  28 , and deforming it such that it extends substantially perpendicularly from backup ring  24 . By providing a cantilever portion  46 , this embodiment offers a consistent placement of backup ring  24  with relation to primary seal apparatus  12 , thereby consistently achieving the desired spaced relationship between backup ring  24  and second member  18 . 
     The present invention, in another form thereof, is shown in FIG. 4 to have a backup ring  24  with a convexly shaped portion  30  that has an inner circumference  32  that faces toward the primary seal apparatus  12 . In this embodiment, the operation of the backup ring  24  remains substantially the same as the above-discussed embodiments, wherein backup ring  24  deflects into a substantially linear or extended shape when the system is exposed to increased pressure. As pressure increases and backup ring  24  deflects, a predetermined gap is defined between backup ring  24  and second member  18 , thereby substantially preventing the extrusion of primary seal apparatus  12 . 
     Yet another embodiment of the invention is shown in FIG. 5, wherein a second backup ring  48  is disposed between primary seal apparatus  12  and a second wall surface  50 . A second backup ring  48  may be used in applications where it is desirable to have additional sealing, despite the fact that additional friction will result during a pressurized state. 
     FIG. 6 shows yet another embodiment of the present invention wherein backup ring  24  comprises a washer having a cantilever portion  46  that extends from the washer at an angle from a plane substantially defined by the washer. During a non-pressurized state, the angle at which the cantilever portion  46  extends from the washer causes cantilever tip  45  to touch bottom surface  28  of gland  14  while simultaneously leaving a gap between corner  47  of backup ring  24  and the bottom surface  28  of gland  14 . 
     When the embodiment of FIG. 6 is subjected to pressure (indicated by arrows “P”), as depicted in FIG. 7, primary seal apparatus  12  presses against backup ring  24 , thereby forcing corner  47  against bottom surface  28 , and consequently deforming cantilever portion  46  such that it extends substantially perpendicularly from the washer-shaped backup ring  24 . As corner  47  is forced against bottom surface  28 , backup ring  24  “lifts” away from second member  18 , providing a small gap  49  between backup ring  24  and second member  18 . Gap  49  provides for a frictionless relationship between backup ring  24  and second member  18 , while simultaneously preventing extrusion of primary seal apparatus  12 . Furthermore, during the pressurized state, cantilever portion  46  is fixedly disposed between primary seal apparatus  12  and first member  16  because of the pressure imparted by primary seal apparatus  12 , resulting in increased anti-extrusion properties. 
     FIG. 8 shows the advantages of the embodiment of the present invention having a backup ring with a cantilever portion, using results of finite element analysis to compare the prior art seal arrangement to the present invention. The analysis was conducted under high pressure with rotary motion. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.