Abstract:
A discharge valve retainer is manufactured from powder metal using FLC4608, FL4405, FC0205 or FC0208 material. The finisher retainer has a density of approximately 6.8 to 7.6 gm/cc. The retainer is carbonitrided, quenched and tempered to achieve a surface hardness of Rockwell 15N 89-93. The exterior of the retainer is contoured to provide for the non-turbulent flow of pressurized gas around the discharge valve.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to refrigeration compressors. More particularly, the present invention relates to a reciprocating piston type refrigeration compressor which incorporates a unique design for the discharge valve retainers which improve the reliability and the performance of the refrigeration compressor.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Reciprocating piston type compressors typically employ suction and discharge pressure actuated valve assemblies mounted onto a valve plate assembly which is located at end of a cylinder defined by a compressor body. The valve plate assembly is typically sandwiched between a compressor head and the body of the compressor. A valve plate gasket is located between the valve plate assembly and the compressor body to seal this interface and a head gasket is located between the valve plate assembly and the compressor head to seal this interface.  
           [0003]    The discharge valve assembly typically includes a discharge valve member which engages a valve seat defined by the valve plate assembly, a discharge valve retainer to attach the discharge valve member to the valve plate assembly and a discharge spring which is disposed between the discharge valve member and the discharge valve retainer to bias the discharge valve member into engagement with the valve seat defined by the valve plate assembly.  
           [0004]    An important design objective for the reciprocating compressor is to minimize the re-expansion or clearance volume in the cylinder when the piston reaches top dead center. The minimizing of this re-expansion or clearance volume helps to maximize the capacity and efficiency of the reciprocating compressor. In order to minimize this re-expansion or clearance volume, the valving system and the cylinder top end wall should have a shape which is complimentary with the shape of the piston to enable the piston to reduce the volume of the compression chamber to a minimum when the piston is at top dead center of its stroke without restricting gas flow. While it may be possible to accomplish this objective by designing a complex piston head shape, manufacturing of this complex shape becomes excessively expensive, the assembly becomes more difficult and throttling losses generally occur as the piston approaches top dead center.  
           [0005]    Prior art suction valve assemblies and discharge valve assemblies have been developed to meet the above defined design criteria relating to re-expansion or clearance volume and these valve assemblies have performed satisfactory in the prior art compressors.  
           [0006]    One area that can provide additional benefits to the reciprocating piston type compressors is in the area of compressed gas flow. As the piston begins its compression stroke, the gas within the compression chamber is compressed and eventually the discharge valve assembly opens to allow the compressed gas to flow into the discharge chamber. The compressed gas must flow past all of the components of the discharge valve assembly and thus the design of these components are critical to ensure that the flow of compressed gas is not restricted and therefore any throttling losses are reduced or eliminated.  
           [0007]    The present invention provides the art with a unique design for the discharge valve retainer which improves gas flow to minimize and/or eliminate throttling losses associated with the compressed gas flow. The discharge valve retainer of the present invention is manufactured using a powder metal process utilizing a retainer material and density that define and optimize the retainer&#39;s structural, reliability and performance. In addition, the geometry of the discharge valve retainer has been optimized to deliver the best performance.  
           [0008]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a side view of a compressor assembly incorporating the unique discharge valve retainer in accordance with the present invention;  
         [0011]    [0011]FIG. 2 is a top view of the compressor assembly illustrated in FIG. 1;  
         [0012]    [0012]FIG. 3 is a partial cross-sectional view through the compressor assembly illustrated in FIG. 1 and  2  where each cylinder is shown rotated  90 ° about a central axis;  
         [0013]    [0013]FIG. 4 is a side cross-sectional view of the discharge valve retainer illustrated in FIG. 3 taken through the central body and the flanges of the retainer;  
         [0014]    [0014]FIG. 5 is a top view of the discharge valve retainer illustrated in FIG. 4;  
         [0015]    [0015]FIG. 6 is a bottom view of the discharge valve retainer illustrated in FIG. 4;  
         [0016]    [0016]FIG. 7 is a side cross-sectional view of the discharge valve retainer illustrated in FIG. 3 taken through the central body of the retainer;  
         [0017]    [0017]FIG. 8 is a top perspective view of the discharge valve retainer illustrated in FIG. 4; and  
         [0018]    [0018]FIG. 9 is a bottom perspective view of the discharge valve retainer illustrated in FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. There is shown in FIGS.  1 - 8  and compressor assembly  10  which incorporates the unique discharge valve retainer in accordance with the present invention. Compressor assembly  10  comprises a compressor body  12 , a compressor head  14  a head gasket  16 , a valve plate assembly  18  and a valve plate gasket  20 .  
         [0020]    Compressor body  12  defines a pair of compression cylinders  22  within which a piston  24  is slidably disposed. Each compression cylinder  22  is in communication with both a discharge chamber and a suction chamber through valve plate assembly  18 .  
         [0021]    Valve plate assembly  18  comprises an upper valve plate  26 , a lower valve plate  28 , and an annular spacer  30 . Valve plate assembly  18  defines a pair of suction passages  32  which is in communication with the suction chamber of compression assembly  10  and a pair of discharge passages  34  which are in communication with the discharge chamber of compressor assembly  10 . Each discharge passage  34  is defined by a radially inclined or beveled sidewall  36  extending between an upper surface  38  and a lower surface  40  of valve plate assembly  18 . Beveled sidewall  36  is formed from upper valve plate  26 . A surface  42  of side wall  36  provides a valve seat for a discharge valve member  44  which is urged into sealing engagement therewith by discharge gas pressure and a spring  46  extending between discharge valve member  44  and a bridge-like retainer  48 .  
         [0022]    As shown, discharge valve member  44  is of a size and a shape relative to discharge passage  34  so as to place a lower surface  50  thereof in substantially coplanar relationship to lower surface  40  of valve plate assembly  18 . Spring  46  is located in a recess  52  provided in retainer  48 . Discharge valve member  44  is essentially pressure actuated and spring  46  is chosen primarily to provide stability and also to provide an initial closing bias or preload to establish an initial seal. Other types of springs, other than that illustrated may of course be used for this purpose. Retainer  48 , which also serves as a stop to limit the opening movement of valve member  44  is secured to valve plate assembly  18  by a pair of suitable fasteners  54 .  
         [0023]    Annular spacer  308  is disposed between upper valve plate  26  and lower valve plate  28  and annular spacer  30  forms suction passage  32  with upper valve plate  26  and lower valve plate  28 . Valve plate assembly  18  is secured to compressor body  12  when compressor head  14  is secured to compressor body  12 . Valve plate assembly  18  is sandwiched between compressor head  14  and compressor body  12  with valve plate gasket  20  being sandwiched between valve plate assembly  18  and compressor body  12  and head gasket  16  being sandwiched between valve plate assembly  18  and compressor head  14 .  
         [0024]    A plurality of bolts  60  extend through compressor head  14 , head gasket  16 , upper valve plate  26  of valve plate assembly  18 , annular spacer  308  of valve plate assembly  18 , lower valve plate  28  of valve plate assembly  18 , valve plate gasket  20  and are threadingly received by compressor body  12 . The tightening of bolts  60  compresses valve plate gasket  20  to provide a sealing relationship between valve plate assembly  18  and compressor body  12  and comprises head gasket  16  to provide a sealing relationship between valve plate assembly  18  and compressor head  14 .  
         [0025]    Valve plate assembly  18  defines an annular valve seat  70  and sidewall  36  defines an annular valve seat  72  located at its terminal end. Disposed between valve seat  70  and valve seat  72  is suction passage  32 .  
         [0026]    Valve seat  72  of sidewall  36  is positioned in coplanar relationship with valve seat  70  of valve plate assembly  18 . A suction reed valve member  76  in the form of an annular ring sealingly engages, in its closed position, valve seat  72  of sidewall  36  and valve seat  70  of valve plate assembly  18  to prevent passage of fluid from compression cylinder  22  into suction passage  32 . A central opening  78  is provided in suction reed valve member  76  and is arranged coaxially with discharge passage  34  so as to allow direct gas flow communication between compression cylinder  22  and lower surface  50  of discharge valve member  44 . Suction reed valve member  76  also includes a pair of diametrically opposed radially outwardly extending tabs  80 . One tab  80  is used to secure reed valve member  76  to valve plate assembly  18  using a pair of drive studs  82 .  
         [0027]    As piston  24  within compression cylinder  22  moves away from valve plate assembly  18  during a suction stroke, the pressure differential between compression cylinder  22  and suction passage  32  will cause suction reed valve member  76  to deflect inwardly with respect to compression cylinder  22 , to its open position (shown in dashed lines in FIG. 3), thereby enabling gas flow from suction passage  32  into compression cylinder  22  between valve seats  70  and  72 . Because only tabs  80  of suction reed valve member  76  extend outwardly beyond the sidewalls of compression cylinder  22 , suction gas flow will readily flow into compression cylinder  22  around substantially the entire inner and outer peripheries of suction reed valve member  76 . As a compression stroke of piston  24  begins, suction reed valve member  76  will be forced into sealing engagement with valve seat  70  and valve seat  72 . Discharge valve member  44  will begin to open due to the pressure within compression cylinder  22  exceeding the pressure within discharge passage  34  and the force exerted by spring  46 . The compressed gas will be forced through central opening  78 , past discharge valve member  44  and into discharge passage  34 . The concentric arrangement of valve plate assembly  18  and reed valve member  76  allow substantially the entire available surface area overlying compression cylinder  22  to be utilized for suction and discharge valving and porting, thereby allowing maximum gas flow both into and out of compression cylinder  22 .  
         [0028]    The continuous stroking of piston  24  within compression cylinder  22  continuously causes suction reed valve member  76  and discharge valve member  44  to move between their open and closed positions. Compressor body  12  includes an angled or curved portion  84  at the outer edge of compression cylinder  22  adjacent the free end of suction reed valve member  16  to provide a friendly surface for suction reed valve member  76  to bend against, thereby significantly reducing the bending stresses generated within the free end tab  80 .  
         [0029]    Referring now to FIGS.  4 - 8 , the present invention is directed towards the unique design for discharge valve retainer  48 . Discharge valve retainer  48  comprises a circular central body  100  and a pair of radially outward extending flanges  102 .  
         [0030]    Each flange  102  defines a bore  104  which is utilized to secure discharge valve retainer  48  to valve plate assembly  18  using a respective fastener  54 .  
         [0031]    Circular central body  100  defines recess  52  within which spring  46  is located. A plurality of bores  106  located within recess  52  extend through circular central body  100 . Bores  106  allow for flow of compressed discharge gas to facilitate the movement of discharge valve member  44  and spring  46  as well as to direct the pressurized gas to the back side of discharge valve member  44  to bias discharge valve member  44  against the valve seat defined by surface  42  of sidewall  36 .  
         [0032]    An annular recess  110  extends into circular central body opposite to the side which defines recess  52 . Recess  110  provides for a more consistent wall thickness for discharge valve retainer which helps to achieve uniform part density, particularly in the top edge, which is a critical requirement for the functionality of the retainer.  
         [0033]    Referring now specifically to FIG. 7, the exterior configuration of circular central body  100  is illustrated. The exterior configuration of circular central body  100  is designed to provide better discharge gas flow which translates into less turbulence and thus better compressor performance. Starting at the top of recess  52 , the exterior configuration of central body  100  comprises a first contoured surface in the form of a first frusto-conical wall  112 , a blending portion  114  and a second contoured surface in the form of a second frusto-conical wall  116 . In the preferred embodiment, first frusto-conical wall  112  forms a  450  angle with the axial direction of discharge valve retainer  48  and the second frusto-conical wall  116  forms a 15° angle with the axial direction. The preferred blending portion  114  is a 0.250 inch radius. The axial direction of discharge valve retainer  48  is the axial direction of bores  106 .  
         [0034]    The preferred material for producing discharge valve member  48  from powder metal is a low alloy steel powder pre alloyed with 1.5 weight percent molybdenum and 0.2 weight percent carbon in the matrix (obtained by prealloying or admixing graphite). This material is available form Hoeganaes Corporation under the tradename Ancorsteel® 150 HP or from Hoganats AB, under tradename Astoloy Mo. which provides optimal structural properties with a preferred part density of approximately 6.8 to 7.6 gm/cc and more preferably with a part density of approximately 7.6 gm/cc. While the above described material is preferred material, alternate materials that may be used for discharge valve retainer  48  include but are not limited to FLC4608, FL4405, FC0205 and FC0208.  
         [0035]    Because surface hardness and functional strength are critical to the reliability and performance of discharge valve retainer  48 , carbonitriding, quenching and tempering of discharge valve retainer  48  is preferred to provide a surface hardness to Rockwell 15N 89-93.  
         [0036]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.