Patent Publication Number: US-11028927-B2

Title: Wide differential pressure range air riding carbon seal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation claiming priority to U.S. patent application Ser. No. 14/990,252 filed Jan. 7, 2016, which claims priority to U.S. Provisional Patent Application No. 62/102,304 filed Jan. 12, 2015, the contents of which are hereby incorporated in their entirety. 
    
    
     FIELD OF TECHNOLOGY 
     The present disclosure relates to a wide differential pressure range carbon seal, such as an air riding carbon seal, and a method thereof. 
     BACKGROUND 
     Carbon seals generally may be used to seal a fluid leakage path between a static component and a rotating component, for example in a gas turbine engine for sealing oil within a gearbox. Carbon seals may be either contacting or air riding, and generally may include a stator fixed and sealed to the static component, and a rotor fixed and sealed to the rotating component. A carbon ring may be mounted axially between the stator and the rotor with a spring to force the carbon into contact or proximity with the rotor. 
     In an air riding carbon seal, the rotor may be designed with hydropads, which cause separation of the carbon ring and the rotor with a fluid (air) film. The design of an air riding carbon seal and the hydropads may be dependent on such factors and parameters as rotational speed of the rotating component, force of the spring loading the carbon ring against the rotor, and pressure differential across the seal. If an air riding carbon seal is operated outside its design point (range), it may leak or become, effectively, a contacting face seal. Common air riding carbon seals are generally designed for a specific range of load conditions, i.e., lower pressure differential across the seal, and therefore may not be as effective with load conditions outside of that range. 
     Therefore, it would be helpful to provide a carbon seal, such as an air riding carbon seal, that may accommodate a wide range of design conditions, such as differences in pressure differential and speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the claims are not limited to a specific illustration, an appreciation of the various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, exemplary illustrations are shown in detail. Although the drawings represent the illustrations, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an example. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricted to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows: 
         FIG. 1  is a schematic cross-sectional view of an exemplary gas turbine engine employing a carbon seal assembly; 
         FIGS. 2-7  are schematic views of the carbon seal assembly of  FIG. 1  according to different exemplary approaches; and 
         FIG. 8  illustrates an exemplary method for installing the carbon seal of  FIGS. 2-7 . 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary carbon seal assembly generally may include a stator fixable to a static component, and a rotor fixable to a rotating component, where the rotating component is rotatable relative to the static component. The carbon seal assembly may also include a carbon ring and a spring attached thereto positioned between the stator and the rotor, where the spring may be configured to move the carbon ring fore and aft between the stator and the rotor. The carbon seal assembly may further include a diaphragm operatively attached to stator and to the carbon ring and spring combination. 
     An exemplary gas turbine engine generally may include a mechanical housing and a shaft rotatable relative to the housing. The gas turbine engine may also include a carbon seal assembly having a stator fixed to the housing, and a rotor fixed to the shaft. The carbon seal assembly may also include a carbon ring and a spring attached thereto positioned between the stator and the rotor, where the spring may be configured to move the carbon ring between the stator and the rotor. The carbon seal assembly may further include a diaphragm operatively attached to an unfixed end of the stator and to the carbon ring. 
     An exemplary method for installing a carbon seal assembly may include first attaching a diaphragm to the stator and to the carbon ring and spring combination to form a static assembly. The method may then include fixing the static assembly to a static component, such as the mechanical housing of the gas turbine engine or gearbox, and fixing a rotor to a rotating component, such as the shaft of the gas turbine engine or other shaft, that is rotatable relative to the static component. The carbon ring and spring combination generally may be positioned between the stator and the rotor such that the carbon ring may move toward and away from the rotor. 
     Referring now to the figures, an exemplary gas turbine engine  101  is shown in  FIG. 1 . The gas turbine engine  101  generally may include a compressor section  102 , a combustor section  103 , and a turbine section  104 . The compressor section  102  and the turbine section  104  may be mounted on a common shaft or spool. While the gas turbine engine  101  is depicted in  FIG. 1  as a multi-shaft configuration, it should be appreciated that the gas turbine engine  101  may be a single-shaft configuration as well. In addition, while the gas turbine engine  101  is depicted as a turbofan, it should further be appreciated that it may be, but is not limited to, a turbofan, a turboshaft, or a turboprop. The compressor section  102  may be configured to receive and compress an inlet air stream. The compressed air may then be mixed with a steady stream of fuel and ignited in the combustor section  103 . The resulting combustion gas may then enter the turbine section  104  in which the combustion gas causes turbine blades to rotate and generate energy. 
     The gas turbine engine  101  may also include a gearbox  105  connected to the common shaft. As seen in  FIGS. 2-4  and described in more detail hereinafter, a carbon seal assembly  110  may be implemented in the gearbox  105 . While the carbon seal assembly  110  is described hereinafter with respect to the gearbox  105 , it should be appreciated that the carbon seal assembly  110  may be applicable to other parts of the gas turbine engine  101  in which it may be desirable to prevent leakage from entering a particular compartment, for example with the mainline shaft of the gas turbine engine  101 , an internal gearbox, or a sump, and further, in other applications other than a gas turbine engine, for example reciprocating engines, or any other applicable machinery in marine, aerospace, or industrial applications. 
     Referring now to  FIGS. 2-7 , a carbon seal assembly  110  is depicted in the gearbox  105  of the gas turbine engine  101 . The gearbox  105  generally may have a mechanical housing  106 , or static component, and an accessory shaft  107 , or rotating component, rotatable relative to the mechanical housing  106 . The carbon seal assembly  110  may be positioned between the housing  106  and the accessory shaft  107 , and may be configured to seal the gearbox  105  to prevent leakage of a fluid, such as oil, out of the gearbox  105 . 
     The carbon seal assembly  110  may include a stator  112  fixed and sealed to the mechanical housing  106 , and a rotor  114  fixed and sealed to the accessory shaft  107 , such that the rotor  114  rotates with the accessory shaft  107  while the stator  112  remains static. The mechanical housing  106  may have a retaining ring  113  disposed therein to position the carbon seal assembly  110  and to retain it axially in place. The carbon seal assembly  110  may also include an O-ring  115  or other sealing mechanism between the stator  112  and the mechanical housing  106 , and between the rotor  114  and the accessory shaft  107 . 
     The carbon seal assembly  110  may also include a carbon ring  116  and a spring  118  mounted between the stator  112  and the rotor  114 . The carbon ring  116  generally may extend annularly around the accessory shaft  107 . The spring  118  may be configured to move the carbon ring  116  fore and aft, i.e., toward and away from the rotor  114 . With a contacting carbon seal, the spring  118  may press the carbon ring  116  against the rotor  114  to provide the seal. With an air riding carbon seal, the spring  118  will press the carbon against the rotor and during operation the hydropads (shaped depressions in the rotor) pump air sufficient to create and maintain a small gap between the carbon ring  116  and the rotor  114 , while maintaining the seal. The carbon ring  116  and the spring  118  may be at least partially disposed within a casing  120 , as seen in  FIGS. 2, 3, and 5-7 . Alternatively, the spring  118  may be attached to the exterior of the casing  120  and only the carbon ring  116  partially disposed within the casing  120 , as seen in  FIG. 4 . In either approach, there may be at least one O-ring  115  providing a seal between the casing  120  and the carbon ring  116 , either at an inner diameter of the carbon ring  116  or an outer diameter of the carbon ring  116 . 
     The carbon seal assembly  110  may further include a diaphragm  124  attached to the stator  112  and to the casing  120 . The stator  112  may have a ledge  126  extending axially from an end of the stator  112 , and to which the diaphragm  124  may be attached. The diaphragm  124  generally may be made of any flexible material, including but not limited to, elastomers, metals, and the like, that have sufficient strength to withstand the pressures associated with the gearbox  105 , while allowing the diaphragm  124  to stretch or extend in order to accommodate varying pressure differentials. Alternatively or in addition, the diaphragm  124  may be configured to allow further expansion, such as with the bellows configuration shown in the figures. 
     Generally, there is a pressure differential across the carbon seal assembly  110 . This pressure differential may have a wide range depending upon different operating conditions of the gas turbine engine  101 , for example increases in engine speed and resultant gas turbine engine bleed air into the gearbox system. However, carbon seals that only incorporate the spring and carbon ring without a diaphragm may only be able to accommodate a relatively narrow pressure/speed range condition. As the pressure differential decreases below the design point (range) of the carbon seal, it may leak and/or as the differential pressure increases beyond the design range in the case of an air riding carbon seal, may force the carbon spring against the rotor, thereby turning it into a contacting carbon seal increasing temperature and wear and defeating the purpose of an air riding carbon seal. The diaphragm  124  may act as a variable rate spring to accommodate increasing pressure differentials that fall outside of the design point of the primary spring  118  thus also providing the system with a dual rate spring. As the pressure differential increases, the diaphragm  124  may expand, thereby applying load with increasing pressure as opposed to a simple carbon ring  116  and the spring  118  assembly without a diaphragm. As such, the diaphragm  124  may allow the carbon ring  116  to set itself to seal the rotor  114  at a low pressure design point, requiring a lower rate spring  118 , and then mechanically and automatically self-adjust the carbon ring load with increasing pressures inside the gearbox  105 . 
     The carbon seal assembly  110  may further include a limit stop  128  to ensure that the minimum spring load on the carbon ring  116  may be maintained while still allowing air through to act on the diaphragm  124  for the higher pressure operating points. The limit stop  128  generally may extend axially from the stator  112  to the rotor  114 . The positioning of the limit stop  128  may depend upon which of the internal pressure and the external pressure of the gearbox  105  is greater. As seen in  FIGS. 2, 4, and 5 , where the internal pressure may be greater, the limit stop  128  may be positioned axially above (i.e., further away from the shaft  106 ) the casing  120 . In such an approach, the limit stop  128  may have a lip  130  extending radially inwardly from an inner surface of the limit stop  128 , and the casing  120  may have a fore stop  132  and an aft stop  134  extending radially outwardly from an outer surface of the casing  120 , as seen in  FIGS. 2 and 4 . The lip  130  may be positioned between the fore and aft stops  132  and  134  such that the lip  130  may engage with the stops  132  and  134  to control the limits of the carbon ring  116  movement. Alternatively, as seen in  FIG. 5 , the lip  130  may extend radially outwardly from the outer surface of the casing  120 , and the fore and aft stops  132  and  134  may extend radially inwardly from the inner surface of the limit stop  130 . In either approach, there may be a gap between the lip  130 , the stops  132  and  134 , and the contacting surfaces to enable the high pressure air to flow to the diaphragm  124 . In addition or alternatively, the limit stop  128  may be porous, for example, may have at least one vent hole  136 , to allow the high pressure air to flow through it to the diaphragm  124 . 
     On the other hand, as seen in  FIG. 3 , where the external pressure of the gearbox  105  may be greater, the limit stop  128  may be positioned radially below (i.e., closer to the shaft  107 ) than the casing  120 . In such a scenario, the lip  130  may extend radially outwardly from an outer surface of the limit stop  128 , and the fore and aft stops  132  and  134  may extend radially inwardly from an outer surface of the casing  120 . The lip  130  and the fore and aft stops  132  and  134  may engage with each other in the same manner described above to limit the movement of the carbon ring  116 . In addition, the stator  116  and/or the limit stop  130  may include vent holes  136 . While only this exemplary approach is shown for the scenario in which the external pressure of the gearbox  105  is greater than the internal pressure, it should be appreciated that any of the variations depicted in  FIGS. 4 and 5  may be incorporated. For example, the lip  130  may extend radially inwardly from an outer surface of the casing  120  while the fore and aft stops  132  and  134  may extend radially outwardly from the limit stop  128 . As another example, the spring  118  may be located outside of the casing  120 , and there may be an O-ring between the casing  120  and the carbon ring  116 . 
     Referring now to  FIGS. 6 and 7 , the limit stop  128  may be unidirectional, positioned between the stator  112  and the casing  120 . As with the limit stop  128  in  FIGS. 2 and 3 , the limit stop  128  may similarly have at least one vent hole  136  to allow the high pressure air to flow through it to the diaphragm  124 . Where the internal pressure of the gearbox  105  is higher than the external pressure, the limit stop  128  may be positioned radially above the ledge  126 , as seen in  FIG. 6 , such that there may be an air flow path for the high pressure air to flow to the diaphragm  124 . Where the external pressure of the gearbox  105  is higher than the internal pressure, the limit stop  128  may be positioned at an unfixed end of the stator  112 , as seen in  FIG. 7 , to similarly allow the high pressure air to flow to the diaphragm  124 . As with the example depicted in  FIG. 3 , the stator  112  may also have vent holes  136  or other ventilation methods to further allow the high pressure air to flow to the diaphragm  124  to equalize the air pressure. 
     Referring now to  FIG. 8 , an exemplary method  200  for installing the carbon seal assembly  110 , for example, in the gas turbine engine  101 , is shown. Method  200  may begin at block  202  in which the diaphragm  124  may be attached to the stator  112  and to the carbon ring  116 /spring  118  combination, for example by attaching the diaphragm  124  to the casing  120 , to form a static assembly. The diaphragm  124  may be attached via gluing, welding, crimping, or any other process known to a person of ordinary skill in the art. At block  204 , the rotor  114  may be fixed to a rotating component, such as the shaft  107 , after which the rotor and rotating component (e.g., shaft  107 ) assembly may be installed, for example, in the gas turbine engine  101 . At block  206 , the stator assembly may be fixed to a static component, for example by fixing the stator  112  to a mechanical housing  106 . The stator assembly and the rotor  114  may be fixed to the static component and the rotating component, respectively, via any processes known to a person of ordinary skill in the art, including, but not limited to, gluing, welding, crimping, spanner nuts, interference fits, friction fits including secondary seals, and the like. 
     The carbon ring  116 /spring  118  combination generally may be positioned between the stator  112  and the rotor  114  such that the spring  118  may move the carbon ring  116  toward and away from the rotor  114 , as described above. The carbon ring  116  and the rotor  114  may already be machined such that they are ready to mate at assembly, for example, flat and square to the axis of rotation. The static assembly may be installed or fixed before or after the rotor  114  and static component are installed, depending on whether the installation is a new build or is for service purposes, for example for a seal replacement without opening the mechanical housing to access the seal from inside. 
     Method  200  may further include providing a limit stop  128  attached to or extending from the stator  112  to ensure that the minimum spring load on the carbon ring  116  may be maintained. As described above, the positioning of the limit stop  128  may depend upon which of the external pressure of the gearbox  105  and the internal pressure is higher. 
     With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claims. 
     All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.