Patent Publication Number: US-2019195078-A1

Title: Contacting face seal

Description:
TECHNICAL FIELD 
     The application relates generally to face seals and, more particularly, to contacting face seals for a gas turbine engine. 
     BACKGROUND OF THE ART 
     In a contacting face seal, the resultant axial force acting on the face seal is generally a combination of a pressure gradient across a sealing contact surface of the face seal and an axial force from a spring or magnet acting on the face seal. Therefore, the resultant axial force can vary significantly with the pressure gradient acting on the face seal across the contact surface. Consequently, the pressure gradient across the contact surface may affect the durability of the face seal and may deteriorate the tightness of the seal. 
     SUMMARY 
     In one aspect, there is provided a contacting face seal component comprising a circumferential body defined as an annulus extending between an outer periphery and an inner periphery around a center axis, the circumferential body including a contact surface configured for face-sealing engagement with a relatively rotating member, an annular groove defined in the contact surface about the center axis, the annular groove defining in the contact face a sealing lip and at least one load distribution pad radially spaced from one another by the annular groove; and at least one passage extending between the annular groove and the outer periphery to fluidly connect with an outside of the circumferential body. 
     In another aspect, there is provided a sealing assembly for a gas turbine engine, the sealing assembly comprising a first fluidic environment adapted to have a first pressure; a second fluidic environment adapted to have a second pressure lower than the first pressure; a relatively rotating member disposed between the first and second fluidic environments; and a circumferential sealing element disposed between the first and second fluidic environments opposite of the relatively rotating member, the sealing element comprising a circumferential body defined as an annulus extending between an outer periphery and an inner periphery around a center axis, the circumferential body including a contact surface configured for face-sealing engagement with the relatively rotating member, an annular groove defined in the contact surface about the center axis, the annular groove defining in the contact face a sealing lip and at least one load distribution pad radially spaced from one another by the annular groove, at least one passage extending between the annular groove and the first fluidic environment to fluidly connect the annular groove with the first fluidic environment; and a bias member biasing the contact surface and the relatively rotating member toward each other. 
     In a further aspect, there is provided a method for sealing a space between a first fluidic environment and a second fluidic environment of a gas turbine engine, the first fluidic environment having a first pressure and the second fluidic environment having a second pressure, the first pressure being higher than the second pressure, the method comprising sealingly engaging a contact surface of a circumferential body of a contacting face seal with a relatively rotating member in the space between the first fluidic environment and the second fluidic environment; directing a flow of the first fluidic environment into an annular groove defined in the contact surface between a radially inner annular sealing lip of the circumferential body and at least one radially outer load distribution pad of the circumferential body such that the at least one load distribution pad is entirely surrounded by the first fluidic environment; balancing a closing hydraulic pressure with an opening hydraulic pressure across the at least one load distribution pad resulting from surrounding the at least one load distribution pad with the first fluidic environment; and biasing the contacting face seal and the relatively rotating member toward each other. 
     In a further aspect, there is provided a contacting face seal component comprising a circumferential body of contact material defined as an annulus extending between an outer periphery and an inner periphery around a center axis, the circumferential body of contact material, the contact material defining a contact surface configured for face-sealing engagement with a relatively rotating member, an annular groove defined directly in the contact material and in the contact surface about the center axis, the annular groove defining in the contact face a sealing lip and at least one load distribution pad radially spaced from one another by the annular groove; and at least one passage defined in the circumferential body and extending between the outer periphery and the groove such that the groove is fluidly connected with an outside of the circumferential body. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
         FIG. 2  is a schematic cross-sectional view of a sealing assembly in accordance to a particular embodiment; 
         FIG. 3  is a cross-sectional view of a contacting face seal in accordance to another particular embodiment; 
         FIG. 4  is a transverse cross-sectional view of a sealing assembly including the contacting face seal taken along line  4 - 4  of  FIG. 3 ; 
         FIG. 5A  is a schematic view illustrating axial pressures acting on the face seal of  FIG. 4 ; 
         FIG. 5B  is a schematic view illustrating non-balanced axial pressures acting on the face seal of  FIG. 5 ; and 
         FIG. 6  is a cross-sectional view of the sealing assembly of  FIG. 4  in accordance to another particular embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. 
       FIG. 2  illustrates a sealing assembly  20  in accordance to a particular embodiment. The sealing assembly  20  can be used in the gas turbine engine  10  to seal a space between a high pressure environment  22  and a low pressure environment  24 . The high pressure environment  22  can be a first fluidic environment of the gas turbine engine that contains pressurized air and the low pressure environment  24  can be a second fluidic environment of the gas turbine engine  10  that contains air at a lower pressure than a pressure of the pressurized air of the first fluidic environment. The air in the second fluidic environment can also be pressurized, however, at a lower pressure than the “pressurized” air of the first fluidic environment. The pressure difference between the high and low pressure environments  22 ,  24  is referred to herein as a pressure differential. 
     The sealing assembly  20  includes a contacting face seal  26 , a relatively rotating member  28  and a bias member  30  to bias the face seal  26  and the relatively rotating member  28  toward each other. The relatively rotating member  28  is a member that rotates relative to the face seal  26 . By “relatively rotating”, it is understood that in operation at least one of the face seal  26  and the member  28  rotates. The relatively rotating member  28  can be known as a seal runner when it rotates. 
     The face seal  26  is disposed within the space between the high and low pressure environments  22 ,  24  opposite the relatively rotating member  28 . The bias member  30  of the sealing assembly  20  is shown as a spring. The spring applies a force to bias the face seal  26  toward the seal runner  30  to sealingly engage a contact surface  32  of the face seal  26  with the relatively rotating member  28 . In the embodiment shown in  FIG. 2 , a housing  34  of the sealing assembly  20  receives the spring and a portion of the face seal  26 . An O-ring  36 , or any appropriate type of seal or seals, is received in a slot  38  of the face seal  26  between the face seal  26  and the housing  34 , to prevent or to reduce air leakage therebetween. The contact between the face seal  26  and the housing  34  may be generally airtight, whereby no additional seal may be required. 
     The spring applies a mechanical axial force Fm on the face seal  26  in a direction X 1 . Moreover, the face seal  26  can be affected by hydraulic forces due to the pressure differential. The hydraulic forces include an axial closing force as a resultant of closing pressure Pc and an opposite axial opening force as a resultant of opening pressure Po. The total net forces acting axially on the face seal  26  can be expressed as the sum of the mechanical force Fm and the hydraulic opening and closing forces. The pressure differential causes a pressure gradient of the opening pressure Po. The term “pressure gradient” is intended to indicate that an opening pressure (i.e. force per unit area) acting axially on the contact surface  32  toward the high pressure environment  22  is larger than a pressure acting axially on the contact surface  32  toward the low pressure environment  24 . Thus, the net axial hydraulic force acting on the face seal  26  can vary radially along the contact surface  32  and consequently the net force (mechanical force Fm and hydraulic forces) acting on the face seal  26  varies radially along the contact surface  32 . Hence, frictional forces resulting from the pressure gradient on the face seal  26  during relative rotation between the face seal  26  and the relatively rotating member  28  may be proportional to the net forces. In operation, as the pressure differential increases between the high and low pressure environments  22 ,  24 , the hydraulic opening force applied across the contact surface  32  can develop the pressure gradient. In a particular embodiment, as the pressure differential increases, the pressure gradient consequently increases. 
     Referring to  FIG. 3 , a face seal  40  is shown in accordance to another particular embodiment. The face seal  40  includes a body  42  defined as an annulus between an outer periphery  44  and an inner periphery  46  around a center axis  48  of the face seal  40 . The body  42  may be referred to as a surrounding body as it surrounds a shaft, an annular body as it may have an annular shape as in  FIG. 3 , or a circumferential body as it circumscribes around a shaft. The outer periphery  44  is radially outward from the inner periphery  46  relative to the center axis  48 . The body  42  has two or more spaced-apart opposite surfaces extending between the outer and inner peripheries  44 ,  46 . One of the two opposite surfaces is a contact surface  50  that extends in a single plane  52  and configured for sealing engagement with the relatively rotating member  28 . The contact surface  50  can be made from the same material and/or be coated with any suitable material. According to an embodiment, the contact surface  50  is formed by contact material of the body  42 . The contact material may be any appropriate material configured to seal while rotating relative to another component, such as the relatively rotating member  28 . In an embodiment, the contact material is a monolithic or monoblock component, with subcomponents defined by grooves therein, as described below. Stated differently, the contact material may be an annular plate or disc of a single make, with static subcomponents therein resulting from grooves, such as a sealing lip, load distribution pad(s), etc. Such subcomponents of the contact material are static relative to one another, as they are integral to the body  42 . In an embodiment, the contact surface  50  is flat, and is part of a single plane. In another embodiment, the contact surface  50  is frustoconical. 
     The face seal  40  includes a groove  54  defined in the contact surface  50  such that the groove  54  separates and defines “protruding portions” of the contact surface  50 . The term “protruding portion” refers to the portion of the contact surface  50  that appears to extend from the face seal  40  because of the groove  54  or concave depression formed in the contact surface  50 . The term “protruding portion” is not intended to indicate a portion that extends beyond the plane  52  of the contact surface  50 . The groove  54  can be machined, molded or cast in the contact surface  50  (or provided by any suitable method) to define the portions. These portions are referred to as a sealing lip  56  “portion” and a load distribution pad or pads  58  “portion”. 
     In the particular embodiment shown in  FIG. 3 , the sealing lip  56  may be a continuous annular sealing lip  56  disposed radially inward from the load distribution pads  58  relative to the center axis  48 . The groove  54  circumferentially surrounds the entire sealing lip  56 . In an alternate embodiment, the sealing lip  56  can have a different shape or form, such as square, non-circular, etc. The sealing lip  56  may extend radially between the inner periphery  46  and the groove  54 . The sealing lip  56  may have several functions. One of these functions is to provide air tightness of the contact surface  50  with the relatively rotating member  28 . 
     The face seal  40  may also include one or more access grooves  60  defined in the body  42  and extending between the outer periphery  44  and the groove  54 . The access groove(s)  60  acts as a channel to fluidly connects the groove  54  with high pressure environment  22 , for a pressure of the groove  54  to be at or close to the pressure of the high pressure environment  22 . In the embodiment shown in  FIG. 3 , the access grooves  60  are defined in the contact surface  50  across the load distribution pad  58 . The access groove  60  separates the load distribution pad  58  into pad segments, pads, or “protruding portions” at the contact surface  50 . The access groove  60  can be formed in the contact surface  50  by any suitable method (e.g., machined, molded, cast). In the embodiment shown in  FIG. 3 , the access groove  60  extends radially in a straight line relative to the center axis  48  between the outer periphery  44  and the groove  54 . In an alternate embodiment, the access groove  60  can be curved and/or extend at angle relative to a radial straight line. However, a radially straight line of the access groove  60  can maximize a surface contact area of the load distribution pad  58 . In an alternate embodiment, the access groove  60  can be a passage formed by a drilling process, or the like, through the load distribution pad  58 . As a result, the passage is circumscribed by the pad  58 . The passage can be circular or any other suitable shape. 
     Referring to  FIG. 3 , the face seal  40  includes four access grooves  60  that are equally spaced circumferentially and define four uniformly shaped load distribution pads  58 . Equally spacing the access grooves  60  can evenly distribute pressure loads on the load distribution pads  58 . In an alternate embodiment, the face seal  40  includes any suitable number of access grooves  60  or passages. The contact surface  50  is thus formed from the sealing lip  56  in conjunction with the one or more load distribution pads  58  in the single plane  52 . That is, no other parts of the face seal  40  form part of the contact surface  50  or engage the relatively rotating member  28  for sealing purposes. In a particular embodiment, the sealing lip  56  and the load distribution pads  58  do not move or rotate relative to the plane  52 . They are integrally formed together to form the face seal  40  as described above. 
     In another particular embodiment, the load distribution pad or pads  58  extend along, or cover, at least 50% of an entire span  62  of the plane  52  at a radial position  64 . The span  62  in this example represents an imaginary diameter that passes through the radial position  64 . The radial position  64  can be chosen along a radii between the center axis  48  and the outer periphery  44 , radially outwardly from the groove  54 . Stated differently, the span  62  in the plane  52  is at least 50% covered by the load distribution pads  58 . In another embodiment, the load distribution pads  58  make up at least 50% of the footprint of the face seal  40  from the axial point of view of  FIG. 3 . The area or areas not covered by the load distribution pads  58  may be covered by the access grooves  60 . In another embodiment, the load distribution pad or pads  58  extend along at least 75% of the entire span  62  at the radial position  64 . Although in the embodiments shown the sealing lip  56  is described and shown to be inwardly from the load distribution pads  58 , in other embodiments, the sealing lip  56  can be disposed radially outwardly from the load distribution pads  58  and the first fluidic environment can be the low pressure environment  24  and the second fluidic environment can be the high pressure environment  22 . 
       FIG. 4  illustrates a transvers cross-sectional view of the face seal  40  taken along line  4 - 4  of  FIG. 3 , and shown as part of a sealing assembly  66 . The sealing assembly  66  is disposed between the high and low pressure environments  22 ,  24  to seal the space therebetween. A sealing element  68  is shown in a sealing engagement with the relatively rotating member  28 . The sealing element  68  includes the housing  34 , the bias member  30  and the face seal  40 . In the embodiment shown, the center axis  48  is normal to the plane  52  of the contact surface  50 . In an alternate embodiment, the center axis  48  can be in an angled, non-normal, relation with the contact surface  50 . The bias member  30  is received in the housing  34  and the face seal  40  is mounted between the housing  34  and the relatively rotating member  28 . The bias member  30  biases the face seal  40  toward the relatively rotating member  28  such that the contact surface  50  sealingly engage the member  28 . In an alternate embodiment, the bias member  30  can be replaced with any suitable biasing device. For example, a magnetic seal arrangement can be used for magnetic forces to bring the face seal  40  into contacting engagement with the relatively rotating member  28 . 
     A depth  70  of the access grooves  60  is equal to a depth  72  of the groove  54  relative to the contact surface  50 . In an alternate embodiment, the depth  70  of the access groove(s) can be different from the depth  72  of the groove  54 . 
     In operation, pressurized air flows from the high pressure environment  22  into the groove  54  though the passage or access grooves  60 . As such, the one or more load distribution pads  58  are surrounded by pressurized air of the high pressure environment  22  and thus there is no pressure differential across the pads  58 . In other words, the pads  58  are surrounded by the same pressure. 
       FIG. 5A  illustrates the opening pressure acting on the face seal  40 . The opening pressure across the load distribution pads  58  becomes constant across the load distribution pads  58  since there is no pressure differential across the pads  58 . The pressure gradient is eliminated or reduced because there is no longer a pressure differential across the pads  58 . The sealing lip  56  experiences a pressure gradient because there is a pressure differential across the sealing lip  56 . The contacting area of the sealing lip  56  is smaller than the contacting area of the pads  58 . Accordingly, the pressure gradient impacts the frictional losses for a smaller portion of the face seal  40 , as the pressure gradient is present on a smaller surface of the face seal  40 , i.e., that defined by the sealing lip  56 . In a particular embodiment, the contacting area of the sealing lip  56  is at most 25% of the contacting area of the pads  58 . The term “contacting area” is intended to indicate an area of the contact surface  50  that sealingly engage the relatively rotating member  28 . 
       FIG. 5B  illustrates the pressure gradient across the sealing lip  56 . The hydraulic pressures across the pads  58  are not shown. The closing hydraulic pressure Pc is balanced by the opening hydraulic pressure Po over the load distribution pads  58 . That is, the net axial hydraulic pressure across the pads  58  is zero. 
     Referring to  FIG. 6 , a sealing assembly  74  is shown in accordance to another particular embodiment. In this embodiment, the same or similar structural elements as to the elements of the previous embodiments are designated by the same reference numerals. The relatively rotating member  28  includes a magnet. For example, the relatively rotating member  28  can be a static magnet and the face seal  40  rotates during the operation of the sealing assembly  74 . The term “magnet” is intended to include, in at least one embodiment, a body that produces a magnetic field externally unto itself. In an alternate embodiment, the relatively rotating member  28  includes internal magnets, surface mounted magnets and the like. A sealing element  76  is shown which includes a seat  78  receiving the face seal  40 . The seat  78  includes a ferrous material such that the magnet and the seat  78  are magnetically attracted. The term “ferrous” or “ferrous material” can indicate any material to which the magnet is attracted thus creating an adherent force or magnetic attraction. The ferrous material can include for example any metal or alloy that is primarily made up of iron or steel. In this particular embodiment, the magnet and the seat  78  form a biasing member  80 . Other biasing members can also be used, such as the spring. 
     In operation, according to a particular embodiment, sealing the space between the high and low pressure environments  22 ,  24  includes sealingly engaging the contact surface  50  of the face seal  40  with the relatively rotating member  28 , biasing the face seal  40  toward the relatively rotating member  28  and directing a flow of the high pressure environment  22  into the groove  54  through the access groove  60  or passage. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the pressurized air can be substituted for other fluids. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.