Patent Publication Number: US-2013243618-A1

Title: Locking Shaft Seal Support and Methods

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Benefit is claimed of U.S. Patent Application Ser. No. 61/503,186, filed Jun. 30, 2011, and entitled “Locking Shaft Seal Support and Methods”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. 
    
    
     BACKGROUND 
     The disclosure relates to shaft seals. More particularly, the disclosure relates to compressor shaft seals. 
     Sealing a rotating shaft to a stationary housing is a common situation. In one exemplary baseline group of sealing systems, a primary seal (seal rotor) is carried by the shaft to rotate therewith. The primary seal engages a mating face (seal stator) of the housing. The primary seal may be carried by a support/carrier which resiliently biases the primary seal into engagement with the mateface so as to maintain engagement despite vibrations, excursions, and the like. In the exemplary such systems, the seal carrier itself includes an additional static seal sealing the seal carrier to the shaft. 
     In some implementations, the seal carrier may be axially held in compression against a shoulder or other structure of the shaft. One example of such a system is seen in US Pregrant Publication 2004/0113369A1 of Wright et al. However, in other situations, it is desired to clamp the carrier to the shaft. Several manufacturers produce seal supports/carriers with radial set screws in a fixed portion of the carrier to engage the shaft and secure the carrier to the shaft. Installing such a seal carrier requires radial access to the set screws. 
     SUMMARY 
     One aspect of the disclosure involves a shaft seal assembly having a support body and a seal. The support body extends from a first end to a second end and has a central passageway for accommodating the shaft. The support body has a compliant axially intermediate portion, an axially outboard portion outboard of the compliant intermediate portion, and an axially inboard portion inboard of the intermediate portion. The inboard portion has an externally threaded portion and a plurality of slots through the externally threaded portion. The seal is carried by the axially outboard portion. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an axial sectional/cutaway view of a compressor. 
         FIG. 2  is an enlarged view of a stuffing box region of the compressor of  FIG. 1 . 
         FIG. 3  is a view of a seal support. 
         FIG. 4  is a second view of the seal support. 
         FIG. 5  is a central longitudinal sectional view of the seal support of  FIG. 3 . 
         FIG. 6  is a view of external threads of a proximal member of the seal support of  FIG. 3 . 
         FIG. 7  is an axial sectional view of threads of a locking ring of the seal support. 
         FIG. 8  is a first view of a seal installation/removal process. 
         FIG. 9  is a second view of a seal installation/removal process. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  show an exemplary compressor  20 . The compressor  20  has a housing (case) assembly  22 . The exemplary compressor is driven by an engine  24  (schematically shown). The exemplary case  22  has a suction port (inlet)  26  and a discharge port (outlet)  28 . The housing defines a plurality of cylinders  30  and  32 . Each cylinder accommodates an associated piston  34  mounted for reciprocal movement at least partially within the cylinder. Exemplary multi-cylinder configurations include: in-line; V (vee); and horizontally opposed. The exemplary compressor is based upon the well known Model 05G compressor manufactured by Carrier Corporation, Syracuse, N.Y. 
     Each of the cylinders includes a suction location and a discharge location. For example, the cylinders may be coupled in parallel so that the suction location is shared/common suction plenum fed by the suction port  26  and the discharge location is a shared/common discharge plenum feeding the discharge port  28 . In other configurations, the cylinders may share suction locations/conditions but have different discharge locations/conditions. In other configurations, the cylinders may be in series. Exemplary refrigerant is R-404A. 
     Each of the pistons  34  is coupled via an associated connecting rod  36  to a crankshaft  38 . The exemplary crankshaft  38  is held within the case by bearings for rotation about an axis  500 . Each piston  30 ,  32  is coupled to its associated connecting rod  36  via an associated wrist pin  44 . The exemplary case includes a main member  50  (e.g., casting of a housing) which forms a cylinder block. A lower end of the main member is closed by a sump plate/cover  52 . One or more heads  54  may cover the cylinders. At a front end (e.g., a “distal” end meaning away from the engine), a bearing body  56  (optimally integrated with an oil pump or other system) closes the case and bears a bearing  58  which engages a forward end portion  60  (schematically shown) of the crankshaft near a forward end  61  of the crankshaft. A rear end of the case is closed by a flange  62  and gland plate  64  mounted to the main member  50 . The flange  62  and gland plate  64  are mounted along a rear wall  66  of the main member which bears/carries a bearing  68  in a bore/compartment  70 . The bearing  68  engages a first intermediate portion  72  of the crankshaft. A rear/second end portion  80  of the crankshaft (near the second end  81  of the crankshaft) is external to the case. The second end portion  80  may bear features (e.g., splines or a keyway  82 ) for coupling to the engine (including any intervening structure).  FIG. 2  shows a second intermediate portion  86  of the crankshaft between the end portion  80  and the first intermediate portion  72 . 
     Where the crankshaft penetrates the case, the crankshaft must be sealed relative to the case. An exemplary sealing system is shown as a modification of the compressor of US2004/0113369 of Wright et al. The Wright et al. primary seal (primary seal system) involves a first ring (seal rotor) which rotates with the shaft and a mating ring (seal stator) which is fixed to the housing (i.e., mounted in the gland plate  64 ). In Wright et al., the rear/proximal end wall of the case is formed by the rear wall  66  of the main member, and the flange/gland plate combination. An inboard portion  88  of the rear wall  66  defines the bearing compartment  70 . Extending outboard (axially) of the bearing compartment  70 , the rear wall  66  surrounds most of a seal compartment or “stuffing box”  90  in which the primary seal rotor  200  ( FIG. 2 ) and support  202  are mounted. The gland plate  64  (or stuffing box cover) covers the end of the seal compartment  90  and has an aperture  92  through which the crankshaft extends. Inboard (axially) of the aperture  92 , the gland plate has an annular compartment  94  into which a secondary seal  95  is mounted. The exemplary secondary seal  95  may be a lip seal as in Wright et al. The exemplary gland plate has a mating ring (seal stator) compartment  96  inboard of the secondary seal compartment  94  and containing a mating ring (seal stator)  97  which engages the seal rotor  200 . The primary seal is “primary” in that it is exposed to the internal compressor pressure at the outboard end of the bearing. The pressure difference (delta P) across the primary seal would be a majority of the pressure difference between sump and atmosphere (e.g., 50-100% of such difference or, more narrowly, 90-100%). If the secondary seal compartment is exposed to the ambient environment-as for example if the leaked oil is allowed to be collected into oil retention container, then the pressure in the secondary seal compartment would essentially be equal to the atmospheric pressure and the primary seal would see essentially 100% of the difference in pressure. The secondary seal is “secondary” in that it intervenes between the primary seal and the external environment. The designation of a seal as “primary” does not require that there be a secondary seal. The exemplary mating ring (seal stator) compartment  96  and secondary seal compartment  94  form a larger stepped compartment with a step or shoulder  98  separating the two. The mating ring (seal stator)  97  may be press fit its compartment  96 . 
     The exemplary mating ring  97  comprises a generally annular rectangular-sectioned member  100  having an inner diameter (ID) surface  101 , an outer diameter (OD) surface  102 , an (axially) inboard face  103 , and an (axially) outboard face  104 . A channel  105  in the OD surface carries a resilient seal  106  (e.g., an O-ring) for sealing the mating ring  97  to the gland plate. 
     The exemplary secondary seal may have a resilient (e.g., elastomeric or PTFE) member  110  (e.g., having a pair of lips  111 ,  112 ) and a radial spring  114 . The exemplary secondary seal will not be expected to experience the pressure differences of the primary seal. The main purpose of the secondary seal is to prevent the contamination of the primary seal by foreign objects from the outside environment (e.g., dust particles). A space  120  between the primary and secondary seals can trap small amounts of oil that leak through the primary seal. An optional collection passageway  122  (schematically shown in  FIG. 1 ) may communicate with the space  120  to pass such oil to an optional oil collection bottle  124 . The passageway  122  and collection bottle  124  prevent oil migration over the secondary lip seal to the outside environment. 
     The exemplary seal support  202  ( FIG. 3 ) comprises a body  222  and an internally threaded lock ring  224 . The exemplary support body  222  extends from a proximal end  210  (e.g., at a rim ( FIG. 5 )) to a distal end  212  and defines a central passageway  214  for accommodating the shaft. The exemplary support body  222  comprises an assembly of three principal pieces or members: a proximal member  226  for mounting to the shaft and whose proximal end forms the proximal end  210 ; a distal member  228  for carrying the seal rotor  200  and whose distal end forms the distal end  212 ; and a compliant axially intermediate member  230  between a distal end  232  of the member  226  and a proximal end  234  of the member  228 . The exemplary members  226  and  228  are metallic machinings (e.g., stainless steel). The exemplary intermediate member  230  comprises a welded metallic bellows (e.g., also stainless steel) assembly. The exemplary bellows is secured to the members  226  and  228  via welding. 
     The exemplary seal rotor  200  has an inboard (inner diameter or ID) surface  240 , and an outboard (outer diameter or OD) surface  242 . It has a proximal end face  244  and a distal end face  246 . As seen in the exemplary implementation, a slight annular internal rebate/shoulder  247  is formed at a junction between the surfaces  240  and  246 . In operation, the surface  246  sealingly, rotationally, and slidingly engages the adjacent surface  103  ( FIG. 2 ) of the seal stator. 
     The exemplary member  226  has an inboard (inner diameter or ID) surface  250  and an outboard (outer diameter or OD) surface  252 . Similarly, the member  228  has an ID surface  256  and an OD surface  258 . The exemplary ID surface of the member  226  has an annular channel  260  carrying a seal  262  (e.g., an elastomeric O-ring) for sealing the support to the shaft. The exemplary member  228  comprises a proximal annular flange  264  mounted to the intermediate member  230  and a sleeve  265  extending distally from the flange periphery. The exemplary member  228  is stamped or machined as a single piece of metal (e.g., stainless steel). 
     Along most of the lengths of the members  226  and  228 , the respective OD surfaces  252  and  258  have respective outer diameters shown as Ø O1  and Ø O2 . Similarly, along most of the respective lengths of the members  226  and  228  the ID faces  250  and  256  have respective inner diameters shown as Ø I1  and Ø I2 . The seal rotor has, along majorities of its length, respective outer and inner diameters shown as Ø OR  and Ø IR . The flange and sleeve respectively define an inboard axial end and an OD periphery of a compartment receiving the seal rotor (e.g., in a press fit). The sleeve has a distal end portion outwardly flared to guide seal rotor insertion, leaving the distal end face  246  of the seal rotor protruding slightly axially therebeyond with the proximal end surface/face  244  bottomed against the distal face of the flange  264 . Exemplary Ø IR  may be chosen to be equal or slightly larger than the local shaft diameter. By having Ø IR  sufficiently greater than the shaft diameter, the seal rotor may go through slight angular excursions relative to the shaft to maintain sealing engagement with the seal stator. Such clearance may be within standard engineering tolerance for seal rotors. 
     A proximal portion  270  of the proximal member  226  has an outer diameter (OD radial rebate) leaving an externally threaded portion  272  separated from a main portion by a shoulder  274 . The externally threaded portion  272  may receive the internal threads  276  of the ring  224 . The ring  224  includes a proximal face  280  and a distal face  282 . In the installed condition, the distal face  282  abuts the shoulder surface  274 . The ring  224  includes an outer diameter (OD) surface  284  bearing a circumferential array of channels  286  which may receive splines of a corresponding spline tool (described further below). The proximal portion  270  has a circumferential array of recesses or slots (through-cut slots from ID to OD)  290  extending inward from the rim  210 . Each recess  290  has a first face  292 , a second face  294 , and a base  296 . The portion  270  has a curved ID chamfer  298 . 
     As is discussed further below, the recesses  290  impart additional radial compliance to the portion  270  allowing it to be compressed into clamping engagement with the shaft. The chamfer  298  guides the shaft into the passageway  214  during installation. As is discussed further below, when the ring  224  is tightened on to the member  226  and the surface  282  is bottomed against the shoulder surface  274 , further tightening produces a wedging/camming action between the threads of the ring and the threads of the portion  270 . This drives the intact segments (petals) of the portion  270  radially inward into compressive frictional engagement with the shaft so as to clamp the member  226  to the shaft. This clamping engagement secures the member  226  both axially and rotationally and allows compression of the intermediate member  230  to bias the member  228  toward the seal stator to maintain rotational sealing engagement between the seal rotor and seal stator. 
     The exemplary external thread  300  ( FIG. 6 ) has a root or base  302  at a diameter Ø R  from the centerline and an apex  304  at a diameter Ø A . The thread has a leading face  306  (axially outboard in the illustration) and a trailing face  308  (axially inboard). The leading face  306  is relatively steep/radial (e.g., within 10° of radial, more narrowly, within 5° and, most particularly, at a negative angle θ 2  of 1-5° or a nominal 3°). In contrast, the trailing face  308  is relatively shallow (e.g., relatively near axial than radial such as at an angle θ 1  off radial of 60-80°, more narrowly, 70-80° or about 75°). The internal thread  320  similarly has a root  322 , an apex  324 , a leading face  326 , and a trailing face  328 . The exemplary threads  300  and  320  are at a pitch of an exemplary eleven turns per inch (tpi), more broadly, 10-12 tpi or 8-16 tpi (4.3 turns per cm, more broadly, 4-5 or 3-6) for a nominal shift diameter of 1.5 inch (3.81 cm). 
     The exemplary internal thread is sufficiently similar in geometry to the thread  300  so as to mate therewith. In the illustrated example, ( FIG. 7 ) internal thread apex diameter is shown as Ø A ′, root diameter as Ø R ′, leading edge negative angle as θ 4 , and trailing edge negative angle as θ 3 . These dimensions and angles may be chosen so that the two threads properly mate. Exemplary θ 3  may be the same as θ 1  and exemplary θ 4  may be the same as θ 2 . 
     In a service situation ( FIGS. 8&amp;9 ), the gland plate  64  may be removed and one or both of the lip seal  95  and mating ring  97 /O-ring  106  extracted and replaced with new ones. To loosen the lock ring  224  (and subsequently re-tighten the lock ring) a tool such as a spline socket (wrench)  400  may be used. The spline socket has an annular sidewall  402  extending from a first end  404  to a second end  406  and having an inner surface  410  and an outer surface  412 . The first end bears projections  420  complementary to the recesses  286 . The spline socket has a base/web  430  with a socket  440  for receiving a socket driver/handle  450  of appropriate size. The spline socket may be installed over the support/carrier and its projections engaged to the ring recesses  286 . Thus, radial clearance may, effectively, be as small as the sidewall thickness of the spline socket. The wrench may then be turned to loosen the ring and release the clamping of the shaft by the portion  270 . The wrench may be removed and the support  202  extracted by hand and replaced with a new support  202  (or the seal rotor  200  on the support  202  may be replaced and the support reinstalled). Such replacement may involve tightening the lock ring using the spline tool/wrench. The gland plate may be reinstalled. 
     An alternative to the O-ring seal  262  involves replacing the bellows  230  with a resilient non-metallic material (e.g., an elastomer) (e.g., with a coil spring or other support) so that linear compression of the bellows causes radial sealing bias between the non-metallic material and shaft. An alternative to the slots  286  is to provide features such as through-holes or blind bores/holes in the face  182  which receive complementary features such as projections (e.g., pins) of the tool. 
     Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the reengineering of an existing compressor configuration, details of the existing configuration may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.