Abstract:
A carbon seal assembly comprises an annular member adapted to be secured to a structure. An annular seal runner is sealingly mounted to a shaft to rotate therewith, with the seal runner being made of a material complementary to that of the annular member for magnetic attraction therebetween. An annular carbon seal element is mounted to the annular seal runner to rotate therewith and positioned in a gap between the annular member and the annular seal runner, the annular carbon seal element having an annular wear surface abutting against a face of the annular member. A cross-sectional area of the annular carbon seal element increases as the axial dimension of the annular seal runner decreases for at least a part of the seal.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to gas turbine engines, and carbon seal assemblies in gas turbine engines. 
       BACKGROUND OF THE ART 
       [0002]    Prior carbon seal technology provides sealing when a rotating seal runner is attracted to a stationary magnet and contact is made on a carbon element against the stationary magnet. When wear of the carbon element occurs, the seal runner moves closer to the magnet, increasing the force of the magnetic field on the seal runner, resulting in additional pressure on the seal runner. Moreover, the rate of wear increases as the magnetic force increases, thus reducing the service life of the seal in the seal runner. 
       SUMMARY 
       [0003]    In one aspect, there is provided a carbon seal assembly comprising: an annular member adapted to be secured to a structure; an annular seal runner adapted to be sealingly mounted to a shaft to rotate therewith, with the seal runner being made of a material complementary to that of the annular member for magnetic attraction therebetween; and an annular carbon seal element mounted to the annular seal runner to rotate therewith and positioned in a gap between the annular member and the annular seal runner, the annular carbon seal element having an annular wear surface abutting against a face of the annular member, a cross-sectional area of the annular carbon seal element increasing as the axial dimension of the annular seal runner decreases for at least a part of the seal. 
         [0004]    In a second aspect, there is provided an engine comprising: a structure; a shaft operatingly mounted to the structure to rotate relative to the structure; a carbon seal assembly comprising: an annular member secured to the structure; an annular seal runner sealingly mounted to the shaft to rotate therewith, with the seal runner being made of a material complementary to that of the annular member for magnetic attraction therebetween; and an annular carbon seal element mounted to the annular seal runner to rotate therewith and positioned in a gap between the annular member and the annular seal runner, the annular carbon seal element having an annular wear surface abutting against a face of the annular member, a cross-sectional area of the annular carbon seal element increasing as the axial dimension of the annular seal runner decreases for at least a part of the seal. 
         [0005]    In a third aspect, there is provided a carbon seal assembly comprising: an annular member adapted to be secured to a structure; an annular seal runner adapted to be sealingly mounted to a shaft to rotate therewith, with the seal runner being made of a material complementary to that of the annular member for magnetic attraction therebetween; and an annular carbon seal element mounted to the annular seal runner to rotate therewith and positioned in a gap between the annular member and the annular seal runner, the annular carbon seal element having an annular wear surface abutting against a face of the annular member, at least a part of a sectional shape of the annular carbon seal element having an increasing radial dimension along an axial direction of the annular carbon seal element from the annular wear surface toward the annular seal runner. 
         [0006]    In a fourth aspect, there is provided an engine comprising: a structure; a shaft operatingly mounted to the structure to rotate relative to the structure; a carbon seal assembly comprising: an annular member secured to the structure; an annular seal runner sealingly mounted to the shaft to rotate therewith, with the seal runner being made of a material complementary to that of the annular member for magnetic attraction therebetween; and an annular carbon seal element mounted to the annular seal runner to rotate therewith and positioned in a gap between the annular member and the annular seal runner, the annular carbon seal element having an annular wear surface abutting against a face of the annular member, at least a part of a sectional shape of the annular carbon seal element having an increasing radial dimension along an axial direction of the annular carbon seal element from the annular contact surface toward the annular seal runner. 
         [0007]    Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]    Reference is now made to the accompanying figures, in which: 
           [0009]      FIG. 1  is a cross-sectional view of a carbon seal assembly between a structure and a shaft; and 
           [0010]      FIG. 2  is a schematic view of a sectional shape of an annular carbon element of the carbon seal assembly of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0011]    Referring to  FIG. 1 , there is illustrated at  10  a carbon seal assembly. The carbon seal assembly  10  is located in a gap between a structure  12  and a rotation component, such as shaft  14 . It is pointed out that the structure  12  and the shaft  14  may be in various types of engines, such as gas turbine engines of aircraft. In the illustrated embodiment, the shaft  14  rotates about axis Y. Hence, some components of the carbon seal assembly may be annular, as described hereinafter. 
         [0012]    When used in a gas turbine engine, the carbon seal assembly  10  of the present invention may be disposed about any rotating shaft or other element thereof, such as for example about at least one of the main engine shafts. Alternately, the carbon seal assembly  10  may be employed to seal another rotating shaft in the gas turbine engine or in another turbomachine, pump, compressor, turbocharger or the like. 
         [0013]    The carbon seal assembly  10  may comprise a seal housing  20  that is secured to the structure  12 . A seal  21  may be provided between the seal housing  20  and the structure  12  to prevent fluid leaks therebetween. In the illustrated embodiment, the seal  21  is located in an annular channel  22  defined in the seal housing  20 . The seal  21  is shown as being an O-ring but any other type of seal, sealing device or gasket may be used as alternatives to the O-ring. Moreover, more than one seal could be used. The material and the shape of the seal  21  are selected as a function of the contemplated use of the structure  12  and the shaft  14  (pressures, temperatures, exposure to fluids). Also, the annular channel  22  may be defined in the structure  12  instead of in the seal housing  20 . 
         [0014]    An annular magnet  30  may be fixed to the seal housing  20  and hence, immovable relative to the structure  12 . The seal housing  20  and the annular magnet  30  project radially inward of the structure  12  toward the shaft  14 , so as to partially close the gap between the structure  12  and the shaft  14 . In another embodiment, the magnets may be secured directly to the structure  12 . The annular magnet  30  is made of any appropriate material producing a suitable attracting force. 
         [0015]    An annular carbon element  40  is connected to a seal runner  50  that rotates with the shaft  14 . The annular carbon element  40  is shown as being axisymmetric and in contact against the annular magnet  30 , with the annular carbon element  40  rotating with the shaft  14  while the annular magnet  30  is fixed relative to the shaft  14 . The runner  50  is typically made of a metallic material that is attracted by the annular magnet  30 . Alternatively, the runner  50  could be made of a magnetic material while the annular magnet  30  could be a metallic ring. Hence, the carbon element  40  seals the gap between the annular magnet  30  and the runner  50 . The carbon element  40  is a “hard matter” seal, as opposed to a soft matter seal (e.g., flexible and elastic seals of polymers). The annular carbon element  40  may be carbon in any appropriate constitution in accordance with its use. For instance, graphite may be used. 
         [0016]    A seal  51  is located in a housing  52  of the runner  50 . The seal  51  and the housing  52  are of annular shape, as the runner  50  and seal  51  concurrently surround the shaft  14 . Accordingly, the seal  51  seals the gap between the shaft  14  and the runner  50 . The runner  50  and seal  51  are sized to remain on the shaft  14 , for instance by a resilient action of the seal  51  against the shaft  14 . The seal  51  is shown as being an O-ring but may be any appropriate type of seal or gasket. For instance, wiper seals, gaskets, cup seals, and the like are a few of the possible sealing devices that could be used between the runner  50  and the shaft  14 . The material and the shape of the seal  51  are selected as a function of the contemplated use of the structure  12  and the shaft  14  (pressures, temperatures, exposure to fluids). 
         [0017]    A shoulder  53  is defined in the runner  50  and provides an abutment surface for the annular carbon element  40 . Other configurations are considered, such as an annular channel, a flat surface, mating engagement, etc. The annular carbon element  40  may be secured to the runner  50  with adhesives, mating connectors, fasteners or the like, for the annular carbon element  40  to remain engaged to the runner  50  and rotate therewith. 
         [0018]    As the shaft  14  rotates, the carbon element  40  will rub against the annular magnet  30 . As a result, the carbon element  40  will wear over time. Due to the attraction forces between the annular magnet  30  and the runner  50 , the runner  50  will gradually move along the shaft  14  in direction Y, thereby keeping the carbon element  40  against the annular magnet  30 , to seal the gap between the annular magnet  30  and the runner  50 . 
         [0019]    The annular carbon element  40  is shown, in this example, having a five-sided section. It is observed that a sectional thickness of the annular carbon element  40  (the difference between the outer diameter and the inner diameter) increases in the axial direction (axis Y), away from the annular magnet  30 . In other words, the sectional thickness (i.e., circumferential cross-sectional area) of the annular carbon element  40  increases as the seal wears, and flares away from the annular magnet  30 . Therefore, as the annular carbon element  40  wears down over time from rubbing against the annular magnet  30 , and thus reduces in width (along the Y axis), the contact surface area between annular magnet  30  and annular carbon element  40  increases. This may result in lower stresses and a slower wear rate than a prior-art annular carbon element without a sectional thickness increase. On the other hand, by having a smaller initial sectional thickness, the friction between the annular magnet  30  and the annular carbon element  40  is maintained relatively low in comparison to the greater sectional thickness near the runner  50 . 
         [0020]    Referring to  FIG. 2 , a sectional shape of the annular carbon element  40  is schematically illustrated. The sectional shape is a five-sided polygon, made of a first trapezoid sectional shape portion  60 , and a second trapezoid sectional shape portion  61 . The first portion  60  may be referred to as a leading portion as it is closer to the wear interface with the annular magnet  30 , while the second portion  61  may be referred to as a trailing portion, as it is farther away from the wear interface with the annular magnet  30 . Despite the portions  60  and  61  being described separately, the annular carbon element  40  may be a monolithic piece. The trapezoid portion  60  is shown having its inner and outer edge surfaces  62  and  63  diverging away from one another away from the wear surface  64 . 
         [0021]    The trapezoid portion  61  has the outer edge surface  65  being generally parallel to axis Y, and thus square relative to the wear surface  64  and the abutment surface  66 . Accordingly, the square arrangement of the outer edge surface  65  and of the abutment surface  66  allow the annular carbon element  40  to be abuttingly received in the counterbore-like receptacle (including shoulder  53 ) of the runner  50 , with suitable contact surface between the annular carbon element  40  and the runner  50 . The sectional shape shown in  FIGS. 1 and 2  is one of numerous sectional shapes possible for the annular carbon element  40 . 
         [0022]    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 annular carbon element  40  may have a trapezoid shape, with the runner  50  having a corresponding shape. The annular magnet  30  may be integrated directly in the structure  12 , without housing  20  or seal  21 . The runner  50  may be sealingly connected to the shaft  14  by other means than the seal  51 , etc. 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.