Patent Abstract:
A seal assembly for separating a relatively high pressure area from a relatively low pressure area includes a first seal carrier having a circumferential body that has a land thereon and a seal. The seal has a circumferential body located within the first seal carrier, the seal having a first surface for sealing against the first land and a second surface and wherein one of the first surface or the first land has an unmachined wear coating that resists fretting and vibration.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a sealing arrangement for a bearing compartment in a turbine engine and more particularly, to a coated seal for use therewith. 
     BACKGROUND 
     A bearing compartment in a multiple spool gas turbine engine may contain oil that lubricates bearings that support an inner rotor shaft and an outer rotor shaft. The inner and the outer rotor shafts are separated by a gap filled with working medium gas. The working medium gas provides cooling for the rotor shafts, but is warmer than the temperature inside the bearing compartment. An intershaft seal prevents the working medium gas from leaking into the oil compartment and prevents the oil from leaking out of the compartment. The intershaft seal traditionally employs two face seals, to seal to the shafts, and a ring seal therebetween, to limit leakage between the face seals. 
     SUMMARY 
     According to an embodiment disclosed herein, a seal assembly for separating a relatively high pressure area from a relatively low pressure area includes a first seal carrier having a circumferential body, the first seal carrier having a first land thereon; and, a seal having a circumferential body located within the first seal carrier, the seal having a first surface for sealing against the first land and a second surface and wherein one of the first surface or the first land has an unmachined wear coating that resists fretting and vibration. 
     According to any previous claim made herein, the seal does not contact the first seal carrier but for contact of the first surface with the first land. 
     According to any previous claim made herein, the coating is electroless nickel. 
     According to any previous claim made herein, the first surface has an unmachined wear coating that resists fretting and vibration. 
     According to any previous claim made herein, the first land has an unmachined wear coating that resists fretting and vibration. 
     According to any previous claim made herein, a second seal carrier has a circumferential body that moves relative to the first seal carrier the second seal carrier having a second land upon which the second surface is disposed thereupon. 
     According to any previous claim made herein, the second seal carrier extends around the first seal carrier. 
     According to any previous claim made herein, the second surface may move across the second land when forced by a pressure differential between the high pressure area and the low pressure area. 
     According to any previous claim made herein, the second surface has an unmachined wear coating that resists fretting and vibration. 
     According to any previous claim made herein, the second land has an unmachined wear coating that resists fretting and vibration. 
     According to a further non-limiting embodiment disclosed herein, a seal for separating a relatively high pressure area from a relatively low pressure area includes a seal having a circumferential body, the seal having a first surface for sealing against a land and a second surface wherein the first surface has an unmachined wear coating that resists fretting and vibration. 
     According to any previous claim made herein, the coating is electroless nickel. 
     According to any previous claim made herein, the second surface has an unmachined wear coating that resists fretting and vibration. 
     According to any previous claim made herein, further including a seal carrier having a land thereon for cooperating with the first surface. 
     According to any previous claim made herein, the seal carrier houses the seal but does not touch it but for contact between the land and the first surface. 
     According to any previous claim made herein, the first surface is radially aligned. 
     According to any previous claim made herein, the first surface the second surface are perpendicular to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
         FIG. 1  shows a gas turbine engine in which an embodiment of an invention is shown. 
         FIG. 2  shows an embodiment of a coated seal for use in a bearing compartment shown in  FIG. 1 . 
         FIG. 3  shows an embodiment of a coated seal taken along the lines  3 - 3  of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flowpath B while the compressor section  24  drives air along a core flowpath C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three (or more) spooled architectures. 
     The engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure (or first) compressor section  44  and a low pressure (or first) turbine section  46 . The inner shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The geared architecture comprises a gear assembly  60  enclosed within a gear housing  62 . The gear assembly  60  couples the inner shaft  40  to a rotating fan structure. The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure (or second) compressor section  52  and high pressure (or second) turbine section  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  supports one or more bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
     The core airflow C is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than ten (10), the geared architecture  48  is an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about 5. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
     Referring now to  FIG. 2 , a bearing compartment  65  having a given static pressure (e.g., a low pressure) therein is adjacent the side  70  of the gas turbine engine  20  having a second static pressure (e.g., a high pressure) greater than the given pressure (e.g., the low pressure). Oil  75  is disposed within the bearing compartment  65 . 
     A seal assembly  80  separates the high pressure side  70  from the low pressure bearing compartment  65 . The seal assembly  80  comprises a forward seal carrier  85  which may be circumferential, an aft circumferential seal carrier  90 , a forward land  95  cooperating with the forward seal carrier  85  and an aft land  100  cooperating with the aft seal carrier  90 . The forward seal carrier  85  has circumferential body  105 , an L-shaped radially outwardly extending seal holder  110  extending from a forward end  115  of the forward seal carrier  85 . A forward seal  120  is disposed within the L-shaped radially inwardly extending seal holder  110 . A U-shaped seal holder  125  extends from an aft end  130  of the circumferential body  105 . A piston ring  135  is disposed within the U-shaped seal holder  125  as will be discussed infra. 
     The aft seal carrier  90  includes a circumferential body  140 , an L-shaped radially outwardly extending seal holder  145  extending from an aft end  147  thereof. A seal  149  fits within the L-shaped radially inwardly extending seal holder  145  to engage the land  100 . The seal also has a sealing land (or surface)  150  which engages the land  100 . The seals  149  and  120  are typically carbon made of carbon but other materials may be used. The aft seal carrier  90  may act as a piston and move axially relative to the forward seal carrier  85   
     Referring now to  FIG. 3 , the seal holder  125 , which may be U-shaped, holds a radial inner area of body  155  of the piston ring  135 . The body  155  has a radial inner profile  160  that does not touch the seal holder  125 . The piston ring  135  has an axially forward face  170  for cooperating with the radially outer wall  175  of the seal holder  125  that is parallel to, but not in plane with a radially inner wall  180  of the seal holder  125 . The body  155  has a radially outward surface  185  engaging land  150  on the aft carbon carrier. 
     The body of the piston ring  135  has an axially aft extending portion  189  that prevents the piston ring from being inserted in the seal holder  125  in a backwards position. Such installation is not possible because if there is contact between the aft extending portion  189  and the radially outer wall  175 , the body  155  will not fit in seal holder  125 . 
     During operation, as the pressure of flow C increases on the high pressure side  70 , and the pressure urges the piston ring  135  axially forward across the land  150  so the axially forward face  170  engages the radially outer wall  175  of the seal holder  125  to effectuate a seal therebetween. The relative pressure also tends to force the piston ring  135  radially outer face  185  against the land  150 . 
     This piston ring  135  is usually made of carbon. However, the Inventors have discovered that the piston ring  135  is subject to fret wear and vibratory wear as the upstream and downstream carbon carriers  80  and  90  move relative to each other. Where the piston ring  135  is subject to rubbing and chafing caused by “fretting” along with regular vibratory modes caused by vibratory modes that are normally experienced in rotating machinery premature failure of a sealing function may occur. 
     As a result, the applicants have coated the radially outer wall  175  and the radially outer face  185  of the piston ring with electroless nickel  190  that can withstand the fret and vibratory wear experienced by the piston ring. A electroless plating process is followed by using a reducing agent such as sodium hypophosphite to produce a negative charge on the piston ring  135  that draws nickel ions in solution thereto to coat the part. The piston ring  135  may be masked to coat only the desired portions thereof like the axial forward face  170 . 
     One of the advantages of electroless nickel is that it does not require machining and other coatings that are known to resist fretting and vibratory modes that do not require machining (e.g., “unmachined”) may be used herein. Furthermore, instead of coating the axial forward face  170  and radially outer face  185  of the piston ring  135 , one may choose to coat the radially outer wall  175  or the land of the forward seal carrier  85  or the land  150  of the axially aft seal carrier  90 . The surfaces subject to the fretting and vibratory forces (e.g., axial forward face  170 , radially outer face  185 , or the radially outer wall  175  or the land  150 ) may be the only ones coated. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.

Technology Classification (CPC): 5