Abstract:
A shaft sealing mechanism is provided including a first component having a first surface and a second component having a second surface. The first component and the second component are arranged in contact such that the first surface and the second surface form a dynamic interface. The first surface includes a conformable carbon or carbon-graphite material. The second surface includes a rigid, highly polished, silicon carbide material having a plurality of graphite particles embedded therein.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Exemplary embodiments of the invention relate generally to compressor systems, and more particularly to a shaft seal for a crankshaft in a refrigerant compressor system. 
         [0002]    Refrigeration systems, such as the type used in transport refrigeration equipment, include, in the simplest form, a compressor, a condenser, an expansion device, and an evaporator serially interconnected to form a closed loop refrigeration circulation path. Various types of compressors used in a refrigeration system include a dynamic seal positioned between rotating components and adjacent stationary components to prevent refrigerant from escaping into the atmosphere. 
         [0003]    Oil is used in such compressors to lubricate various parts and interfaces there between. To retain the refrigerant within the compressor, mechanical face seals are commonly used to provide a barrier where the rotating crankshaft penetrates the housing of the compressor. The face seal is typically constructed with a flat, circular, rotating component configured to mate against a flat, circular, stationary component. Acceptably small refrigerant leak rates are generally obtained by maintaining very flat, smooth surfaces at the sealing interface and by introducing oil to the interface. An oil film that forms at the interface not only inhibits the transfer of refrigerant through the interface, but also provides lubrication and reduces potentially damaging friction and wear that may occur during operation of the compressor. 
         [0004]    Oil leakage commonly occurs at the sealing interface of the mechanical face seal as described above. If oil is allowed to leak unabated, oil transfer from the compressor can result in environmental or safety issues and/or lead to compressor failure. Typically the face seal is designed in a manner that promotes the development of a substantial oil film, however this may result in undesirable oil leakage from the contained system. Various carbon/graphite and silicon carbide formulations of the rotating component and the stationary component are available that enable seal designs with a very thin oil film thickness, and therefore low oil transfer rates. A key element of a lower leakage seal design is a hard, smooth, surface on one side of the interface, such as a highly polished silicon carbide surface for example, and a somewhat conformable carbon/graphite surface on the other side of the interface. However, if the hard surface is too smooth, the carbon/graphite surface may be damaged as a result of high shear and drag forces that occur on startup before an oil film develops. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to an aspect of the invention, shaft sealing mechanism is provided including a first component having a first surface and a second component having a second surface. The first component and the second component are arranged in contact such that the first surface and the second surface form a dynamic interface. The first surface includes a conformable carbon or carbon-graphite material. The second surface includes a rigid, highly polished, silicon carbide material having a plurality of graphite particles embedded therein. 
         [0006]    According to another aspect of the invention, a refrigerant compressor is provided including a housing. A crankshaft extends through at least a portion of the housing and is configured to rotate relative to the housing. A shaft sealing mechanism is arranged between the housing and the crankshaft to limit refrigerant from leaking from the housing. The shaft sealing mechanism includes a rotating component mounted to the crankshaft. The rotating component includes a first surface. A stationary component is mounted to the housing and is configured to receive the crankshaft. The stationary component has a second surface. The first surface and the second surface are positioned to form a dynamic interface. The first surface includes a conformable carbon or carbon-graphite material. The second surface includes a rigid, highly polished, silicon carbide material having a plurality of graphite particles embedded therein. 
         [0007]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0008]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a cross-sectional view of a compressor according to an embodiment of the invention; 
           [0010]      FIG. 2  is an cross-sectional view of a shaft seal cavity of a compressor according to an embodiment of the invention; and 
           [0011]      FIG. 3  is a detailed cross-sectional view of a portion of a sealing mechanism arranged within a shaft seal cavity of a compressor according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring now to  FIG. 1 , an example of a compressor  10  is illustrated. Though the compressor  10  described and illustrated herein is a reciprocating compressor, other types of refrigerant compressors are within the scope of the invention. The compressor includes a plurality of working pistons  14 , each of which is configured to move within a respective cylinder  16  within a housing  12 . A first end  19  of a plurality of connecting rods  20  is received about a crankshaft  18  of the compressor, and a second end  21  of each of the plurality of connecting rods  20  is coupled to a piston  14 . The first end  19  of each connecting rod  20  may be generally secured to an offset portion  22  of the crankshaft  18 . The connecting rods  20  are configured to impart the motion of the crankshaft  18  to each piston  14 , such that each of the pistons  14  translates within a respective cylinder  16  as the crankshaft  18  rotates about an axis of rotation R. A counterbalance  24  may be arranged at a first end  23  of the crankshaft  18  to balance any rotational irregularities thereof. A second end  25  of the crankshaft  18  extends through and is configured to rotate within a sleeve (not shown) and a shaft seal cavity  26  of the housing  12 . 
         [0013]    Referring now to  FIGS. 2 and 3 , a sealing mechanism  30  arranged within the shaft seal cavity  26 , near the interface between the second end  23  of the crankshaft  18  and the housing  12 , is illustrated in more detail. The sealing mechanism  30  is a mechanical face seal and includes a generally cylindrical body  32  and an adjacent gland plate  34 , both having a central bore through which the crankshaft  18  extends. A flange  36  of the gland plate  34  is configured to mount to the housing  12 , such as with a plurality of fasteners for example, such that a first end  38  of the gland plate  34  having a diameter smaller than the diameter of the flange  36  is arranged at least partially within the shaft seal cavity  26 . In one embodiment, a gland plate gasket  37  is positioned between the outer flange  36  and the housing  12  to prevent seepage there between. Arranged at the first end  38  of the gland plate  34  is a mating ring  40  positioned between the crankshaft  18  and an inner diameter A of the gland plate  34 . The mating ring  40  is substantially cylindrical and includes seal  42 , such as an O-ring for example, configured to hold the mating ring  40  stationary within the inner diameter A of the gland plate  34  as the crankshaft  18  rotates. A lip seal  44  configured to block dirt, dust, and other debris from entering the shaft seal cavity  26  is located at a second, opposite end  39  of the gland plate  34 . The lip seal  44  is positioned generally between the crankshaft  18  and a smaller diameter B of the gland plate  34 , such that an inner disc-shaped space  46  is located between the lip seal  44  and the mating ring  34 . 
         [0014]    A primary ring  50  is arranged at an end of the cylindrical body  32 , adjacent the gland plate  34 . A biasing mechanism  52 , such as a coil spring for example, is wrapped around the exterior of the cylindrical body  32 . When installed, the biasing mechanism  52  is preloaded, or in a partially compressed state, such that the biasing mechanism  52  applies a biasing force to a crankshaft seal thrust face  54 . The biasing force causes the primary ring  50  to contact and apply an axial load to the counter face  41 , or adjacent surface of the mating ring  40 , thereby creating a refrigerant seal having a dynamic interface. Oil is generally disposed between the components of the sealing mechanism  30  and the crankshaft  18 . The engagement between the mating ring  40  and the primary ring  50  prevents the oil from entering the shaft seal cavity  26 . In one embodiment, the gland plate  34  includes a first passage (not shown) connected to a second passage formed generally through the housing  12 . If excess oil accumulates within the space  46  between the lip seal  44  and the O-ring  42  of mating ring  40 , the excess oil travels through the passages, such as to an internal cavity for example, where the oil is accumulated or absorbed. 
         [0015]    The materials selected for the primary ring  50  and the mating ring  40  are critical to the operation of the sealing mechanism  30 . The primary ring  50  is generally formed from a relatively soft material, such as carbon graphite for example. Primary rings  50  formed from other known materials are also within the scope of the invention. Exemplary materials used to form the mating ring  40  include cast iron, stainless steel, tungsten carbide, and silicon carbide for example. In one embodiment, the mating ring  40  is formed from a graphite loaded silicon carbide. The graphite within the silicon carbide effectively limits the lower bound of the surface finish attainable for the counter face  41  of the mating ring  40 . As a result, a graphite loaded silicon carbide mating ring  40  can be highly polished using conventional lapping techniques to a desired flatness without making the counter face of the mating ring  40  excessively smooth. The graphite inclusions within the silicon carbide provide dry lubricity and minor irregularities that reduce shear forces to below a level that can damage the primary ring  50  biased into contact there with. 
         [0016]    Use of a carbon/graphite primary ring  50  and a graphite loaded silicon carbide mating ring  40  results in a cost effective sealing mechanism  30  having a lower leakage rate and improved reliability compared to conventional sealing mechanisms. Because the graphite within the graphite loaded silicon carbide material limits the surface finish thereof, a mating ring  40  formed from such material will be easier to manufacture. 
         [0017]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.