Patent Publication Number: US-7721757-B2

Title: Discharge check valve assembly for use with hermetic scroll compressor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Provisional Patent Application Ser. No. 60/565,463 filed on Apr. 26, 2004. 

   FIELD OF THE INVENTION 
   The invention relates to a discharge check valve assembly for use with a hermetic scroll compressor. 
   BACKGROUND OF THE INVENTION 
   Scroll compressor machines, which have two intermeshed involutes or scrolls, provide an efficient way to compress fluids, including gases or mixtures thereof. In operation, one of the scrolls is fixed and the other, an orbiting scroll, is driven by a motor so that it orbits in relation to the fixed scroll. Fluid enters the compressor shell through a low-pressure fluid inlet port and exits through a high-pressure discharge port. The low pressure fluid enters the outer pockets defined by the intermeshed scrolls and is moved toward the center of the intermeshed scrolls or spirals, thereby decreasing in volume and increasing in pressure. The compressed fluid is exhausted through the high-pressure discharge port to the refrigeration or cooling system. 
   Discharge check valves may be installed in the high-pressure discharge port of the compressor shell to prevent the return of high-pressure refrigerant fluid that may cause reverse movement of the orbiting scroll upon shut down of the compressor. 
   U.S. Pat. No. 5,141,420 and U.S. Pat. No. 6,171,084 both disclose disc type check valves in the discharge port area of a scroll type hermetic compressor. These valves contain a plurality of components, such as a valve housing, a valve seat element, a valve stop, and a valve disc, each of which must be precisely machined to ensure free movement of the valve disc. Typically, these disc type check valves include an unbiased, planar valve disc. 
   Such disc type discharge valves are mounted prior to, or in connection with, the welding or permanent attachment of a discharge fitting to the compressor shell. The discharge fitting allows the attachment of suitable conduits to the compressor shell from the rest of the refrigeration system. With these known discharge check valves, once the discharge fitting is attached to the compressor shell, the discharge check valves cannot then be added. Moreover, once these known discharge check valves are assembled to the compressor shell, they cannot be removed without also detaching the discharge fitting from the compressor shell. 
   Further, these disk type valves are not completely tight, due to insufficient closure force on the unbiased valve element and manufacturing tolerances for the valve element and the valve seat. Even if reverse rotation of the compressor can be avoided when the compressor stops, a certain amount of refrigerant will leak back from the high-pressure side of the refrigeration system into the compressor shell. 
   In multi-compressor systems, this leads to preservation of high pressure in the discharge compartment inside the hermetic shell of the compressor, when the compressor stops. Due to this elevated pressure, restarting the compressor requires a higher than normal starting torque. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a leak tight discharge check valve assembly for a hermetic scroll compressor, which is easy and inexpensive to manufacture and to install. 
   It is a further object of the invention to provide a discharge check valve assembly having a discharge valve subassembly which may be introduced through the discharge fitting after attachment of the discharge fitting to the compressor. 
   It is another object of the invention to provide a discharge check valve assembly having a discharge valve subassembly which may be removed from the compressor without requiring removal of the permanently attached discharge fitting. 
   It is even another object of the invention to provide a hermetic scroll compressor with a pressure equalization element for reducing pressure in the high-pressure compartment when the compressor is not operating. 
   In a first embodiment, a discharge check valve assembly for use with a hermetic scroll compressor having a compressor shell is provided. The discharge check valve assembly includes a valve housing and a valve seat located within the valve housing. The valve housing is configured to mount the discharge check valve assembly to the compressor shell. The discharge check valve assembly also includes a discharge fitting and a valve subassembly. The discharge fitting is configured to mount to the compressor shell and configured to connect to a connecting tube in fluid communication with a high-pressure system. The valve subassembly has a valve member movable between an open position and a closed position. Additionally, the valve subassembly is configured to be inserted through the discharge fitting into the valve housing. 
   In one aspect, the valve subassembly further includes a valve body defining a bore, a valve member defining a guiding portion slidably receivable in the bore to allow guided movement of the valve member, and a biasing element positioned between the valve member and the valve body for urging the valve member towards the closed position. 
   In other aspects, the discharge fitting may be integral with the valve housing, or the discharge fitting may be configured to mount to the compressor shell via the valve housing. 
   In another aspect, the valve housing may be configured such that when the valve housing is mounted to the compressor shell, the valve housing is located substantially outside the compressor shell. Further, the valve subassembly may be configured such that when the valve housing is mounted to the compressor shell, the valve subassembly is located substantially outside the compressor shell. 
   Alternatively, the valve housing may be configured such that when the valve housing is mounted to the compressor shell, the valve housing is located at least partially inside the compressor shell, and further, the valve subassembly may be configured such that when the valve housing is mounted to the compressor shell, the valve subassembly is located at least partially inside the compressor shell. 
   The valve body may be attached to the valve housing by one of a brazing method, a welding method, a press-fit method, an adhesive method, or other suitable connecting methods, including the use of mechanical fasteners. 
   In another aspect, the valve subassembly can be removably inserted through said discharge fitting into the valve housing. 
   In a further aspect, the valve subassembly also includes a sealing member coupled to the valve member and interposed between the valve member and the valve seat so that, when the valve member is in the closed position, the sealing member is compressed between the valve member and the valve seat. 
   In an even further aspect, the guiding portion of the valve member extends through the bore of the valve body and a retaining element is coupled to the guiding portion of the valve member to prevent the guiding portion from sliding out of the bore. 
   In another embodiment, a hermetic scroll compressor may include the inventive discharge valve assembly. 
   In even another embodiment, a hermetic scroll compressor includes a compressor shell, a compression stage, a delivery valve arrangement, an orifice, a discharge fitting, and pressure equalization means, e.g. at least one pressure equalizing passage. The compressor shell defines an interior volume divided into a low-pressure fluid compartment and a high-pressure fluid compartment. The compression stage has a fixed spiral element and a movable spiral element, the fixed spiral element having an outlet. The delivery valve arrangement is in fluid communication with the outlet of the fixed spiral element. The orifice is formed in the compressor shell to exhaust high-pressure fluid from the compressor. The discharge fitting is affixed over the orifice and configured to provide fluid communication between the high-pressure fluid compartment and a connecting tube in fluid communication with a high-pressure system. The pressure-equalization passage is configured to provide fluid communication between the high-pressure fluid compartment and the low-pressure fluid compartment, wherein the pressure equalization passage is configured to equalize pressures in the high-pressure and low-pressure fluid compartments when the compressor stops. 
   The hermetic scroll compressor further includes a discharge check valve assembly and a valve subassembly. The discharge valve assembly has a valve housing and a valve seat located within the valve housing, with the valve housing being mounted within the orifice formed in the compressor shell. The valve subassembly includes a valve member movable between an open position and a closed position. Moreover, the valve subassembly is configured to be inserted through the discharge fitting into the valve housing. 
   The pressure equalization passage may include a lateral passage arranged on the circumferential surface of the fixed spiral element. 
   In another aspect, the fixed spiral element may include an end plate and an outlet opening extending therethrough, and the pressure equalization passage may be in fluid communication with the outlet opening. 
   Further, the delivery valve arrangement may include a valve plate coupled to the fixed spiral element, and the pressure equalization passage may extend through the valve plate. 
   In one aspect, the pressure equalization passage includes a throughbore extending through the end plate of the fixed spiral element. A capillary sleeve may extend at least part-way through the throughbore. Furthermore, the capillary sleeve may project above an upper surface of the end plate. 
   In another aspect, the end plate of the fixed spiral element may include a protrusion on an upper surface and the pressure equalization passage may extend therethrough. 
   These and other objects, features and advantages of the present invention will become apparent in light of the drawings and detailed description of various embodiments provided below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a longitudinal cross sectional view of a hermetic scroll compressor with an inventive discharge check valve assembly; 
       FIG. 2  shows a cross sectional view of a first embodiment of the discharge check valve assembly according to the invention; 
       FIG. 3  shows a second embodiment of a discharge check valve assembly according to the invention; 
       FIG. 4  shows a third embodiment of a discharge check valve assembly according to the invention; 
       FIG. 5  shows a fourth embodiment of a discharge check valve assembly according to the invention; 
       FIG. 6  shows a longitudinal cross sectional view of a hermetic scroll compressor equipped with a delivery valve arrangement and a pressure equalizing passage; and 
       FIGS. 7-11  show other embodiments of pressure equalizing passages. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a hermetic scroll compressor  1  including an enclosure or shell  2 , an upper part of which is formed by a cap  3 . The volume inside the enclosure  2  is separated into two compartments, a low-pressure fluid-inlet compartment  4 , and a high-pressure compartment  5  for outlet of compressed fluid. These two compartments,  4  and  5 , are separated by a fluid compression stage  6 . Fluid is admitted into the low-pressure compartment via an inlet orifice  7  and compressed fluid is discharged from the high-pressure compartment  5  via an orifice  8  in cap  3 . A discharge check valve assembly  20  is arranged in orifice  8 . 
   The compression stage  6  includes a fixed spiral element  9  and a movable spiral element  10 , these two spiral elements having interpenetrating parts and defining compression pockets  12 . A shaft  13  drives the movable spiral element  10  in an orbital movement. Movement of shaft  13  is provided by a motor  14 . During the orbital movement of the spiral element  10 , the compression pockets  12  define a volume that gradually decreases from the outside, where the fluid is admitted into the low-pressure compartment, towards the inside, the compressed fluids exiting at the centre of the compression stage  6  to the high-pressure compartment  5  through a central outlet opening  11  in the fixed scroll element  9 . 
   The discharge check valve assembly  20  prevents return flow of fluid from the high pressure side of a refrigeration system into the high-pressure compartment  5  and into the compression pockets  12 . High pressure in compartment  5  could cause detrimental reverse rotation of the movable scroll element  10  when the compressor stops. 
   In one embodiment shown in  FIG. 2 , the discharge check valve assembly  20  includes a valve housing  21  having a through passage. Valve housing  21  is externally attached to the upper cap  3  of the compressor shell  2 . In this embodiment, the tubular end portion  41  of the substantially tubular valve housing  21  opposite the end attached to cap  3  also serves as a discharge fitting  45 , i.e. a fitting for connecting the compressor  1  to the refrigeration or cooling system. 
   The valve assembly  20  includes an annular valve seat  22 , a valve body  23  having a stop surface  24 , a valve member  25  biased towards the valve seat  22  by a biasing element or resilient valve spring  26  arranged between the valve member  25  and the valve body  23 . The valve member  25  has an elongated guiding portion  27  slidingly movable within a central bore  28  of the valve body  23 . 
   In  FIG. 2  the valve assembly  20  is shown with the valve member  25  in a closed position. The valve member  25  includes a plate shaped base part  29 . A central boss  30  projects from the base part in a direction towards the valve seat  22 . An annular sealing member  31  is arranged on the base part  29  and surrounds the central boss  30 . The sealing member is held on the base part  29  by use of a back-up ring  32 . The back-up ring presses the sealing member towards the base part and may be secured by a deformation or flanging of the boss  30 . In the closed position of the check valve the sealing member  31  abuts the valve seat  22  which projects from the valve housing  21  and surrounds a discharge opening  33 . 
   The valve housing  21  includes a first connecting portion  34 , which is inserted in the orifice  8  formed in the upper cap  3  of the compressor shell  2 . A welding portion  36  comprises a contact surface  37  abutting the outer surface of the upper cap  3 . The valve housing  21  is fixed to the cap  3  by welding seam  38 . A portion  39  of the housing  21  of increased diameter surrounds the valve member  25 , the valve body  23  and the resilient spring  26 , and delimits a valve chamber  40 . A tubular end portion  41  of valve housing  21  includes on its inner surface a stop flange  42  for the valve body  23 . The tubular end portion  41 , acting as a discharge fitting  45 , further accommodates a connecting tube  60  to provide fluid communication to the refrigeration system (not shown). 
   The valve body  23  includes a guiding portion  43  defining a central bore  28  and having a radial outer surface  44 . The surface of the bore  28  serves as a sliding bearing for the guiding portion  27  of the valve member. The radial outer surface  44  is adapted to the inner diameter of spring  26 . An axial end face  24  of the guiding portion serves as a stop surface for the base part  29  and limits the opening movement of the valve member  25 . An annular fixation portion  46  having a flange  47  projecting in a radially outward direction and abutting stop flange  42  of the valve housing  21  determines the position of the valve body within housing  21 . A plurality of leg members  48  connect the guiding portion  43  and the fixation portion  46  of the valve body, without overly disturbing the flow path of the discharge fluid. 
   The valve spring  26  is arranged between a surface  49  of the valve body  23  and the base part  29  of the valve member  25 . In one aspect of the invention, the spring constant of the valve spring  26  is relatively weak, as the spring essentially only has to compensate for friction losses in the valve body to ensure that the check valve closes when the compressor is not operating. Spring  26  need not be limited to a spiral wound compression spring, as shown in  FIG. 2 , but may be any elastically deformable element having a suitable spring constant. 
     FIG. 3  shows another embodiment of the discharge check valve assembly  20 . In this embodiment, a valve position is illustrated, where the compressor is in operation, thus delivering compressed fluid from the discharge opening  33  towards the downstream components of the refrigeration system. The direction of fluid flow is illustrated by the arrow  50 . The valve member  25  abuts the stop surface  24  of the valve body, and the resilient spring  26  is almost completely compressed. In distinction to  FIG. 2 , the valve member  25  in this embodiment is a unitary part, preferably made of a material exhibiting sufficient sealing characteristics in connection with the metal valve seat  22 . A suitable material for the valve member may be Teflon (PTFE), which also has excellent lubrication behavior in connection with the valve body. However, the present invention is not limited in this regard and other appropriate materials known to those skilled in the pertinent art to which the present invention pertains may be substituted without departing from the broader aspect of the invention. With this design, the manufacturing costs may be further decreased. 
   To minimize pressure losses in the discharge flow, the valve member  25  has in its central portion a conically shaped boss  51 . Further, the interior shape of the valve housing  21  is adapted to the conical boss  51  to realize an undisturbed flow path for the discharge fluid within the valve chamber  40  with substantially constant flow cross section through the entire valve assembly. 
     FIG. 4  shows a third embodiment of the valve assembly  20 , where the valve member  25  includes a planar base part  29  with a boss  30 , an annular sealing member  31  and a retaining element  52 . The retaining element has a conical shape for minimization of flow resistance and covers both boss  30  and the sealing member, except for the area of the sealing member abutting the valve seat  22 . Retaining element  52  may be fixed to the base part  29  by means of a threaded bolt or a rivet (not shown) arranged in a central bore  53 . 
   Where the valve housing  21 /discharge fittings  45  in  FIGS. 2 and 3  have been represented as a unitary member, the housing  21  of  FIG. 4  is now attached to a separate tubular end portion  54  acting as discharge fitting  45 . Tubular end portion  54  may be attached to the housing in the area of stop flange  42  by any suitable fixation means, e.g. by welding or brazing. In one aspect, end portion  54  is a simple tubular part having reduced wall thickness compared to the housing. This feature simplifies the attachment of connecting tubes to the refrigeration system, which typically is done by the manufacturer of the refrigeration system. The relatively thin wall allows fast heating of the end portion  54  to the required brazing temperature. The reduced heat input leads to less heating of other components of the valve assembly and minimizes the risk of thermal damage to these parts. Preferably, the end portion  54  is made of a bi-metal-material, e.g. a stainless steel tube pre-plated on its inner surface. This further facilitates the brazing operation for the connecting tube. 
   In  FIGS. 1-4 , the discharge valve assembly  20  is configured to be mounted completely on the exterior of the compressor shell  2 , and the valve subassembly  35  is located outside the compressor. In such embodiments, no additional space inside the compressor shell is required when the discharge check valve assembly is integrated into the discharge fitting.  FIG. 5  shows another embodiment, wherein the discharge valve assembly  20  and the valve subassembly  35  are at least partially located inside cap  3  of the compressor shell  2 . Tubular end portion  41  of discharge valve assembly  20  is positioned within and extends through orifice  8 . Circumferential notch  57  is formed in the interior surface of tubular end portion  41  and incorporates stop flange  42 . Valve body  23  of valve subassembly  35  includes annular fixation portion  46  having a radial projecting flange  47 . When valve subassembly  35  is inserted within valve housing  21 , flange  47  abuts stop flange  42  of housing  20 . Retaining element  58 , e.g. a snap ring or spring clip, snaps into notch  57  and retains valve subassembly  35  with housing  20 . Other suitable retaining elements as known to person of ordinary skill in the art may be used to hold valve subassembly against stop flange  42 . Discharge fitting  45  is shown affixed to the portion of tubular end portion  41  extending from orifice  8 . Alternatively, discharge fitting could be affixed to shell  2  or to both tubular end portion  41  and shell  2 . 
   In all of the previously disclosed embodiments, the valve subassembly  35  including the valve member  25 , the valve body  23  and the spring  26  is pre-assembled prior to mounting into the valve housing  21 . For that purpose, a retaining element  55  (see  FIGS. 2 and 4 ), e.g. a spring clip, is arranged in a radial groove  56  near the axial end of the elongated guiding portion  27  of the valve member  25 .  FIG. 3  shows radial groove  56  without retaining element  55  for clarity. Element  55  prevents the valve body and the valve member from becoming separated during the mounting operation. 
   As the outer diameter of the valve member  25  and of the entire valve subassembly  35  is less than the inner diameter of the discharge fitting  45  and the inner diameter of the tubular end portion  41  of the housing, the valve subassembly  35  can be inserted into the housing from the side remote to the compressor shell  2  after the discharge fitting  45  has been affixed to the valve housing  21  or to the compressor shell  2 . Thus, the valve subassembly  35  can be inserted through the discharge fitting  45  and into the valve housing  21  after finalized, on-site mounting of the compressor. This allows greater flexibility in ordering and installing compressors, in that identical compressors may be operated with or without the discharge check valve subassembly  35  or, alternatively, a compressor originally configured for operation with a discharge check valve assembly may be simply and easily reconfigured for use without a discharge check valve assembly, or vice versa. 
   In addition, in those embodiments wherein the valve subassembly  35  is not permanently affixed to the valve housing  21 , the valve subassembly  35  may be removed from valve housing  21  through the discharge fitting  45  without requiring removal of the permanently attached discharge fitting. This is particularly useful in case of valve failure. 
   The insertion depth of the valve subassembly  35  is limited by the abutment of flange  47  of the valve body  23  on stop flange  42  of the housing. The valve body  23  may be secured to the housing by means of a press fit, adhesive, brazing or welding between valve body and housing, or other suitable connecting methods, including the use of mechanical fasteners. 
   During operation of the compressor  1 , the high pressure of the discharge fluid from the compression stage will be exerted against the valve member  25  and thereby against the force of the valve spring  26 . The high pressure causes the valve member to move towards an open position. When fully open, the valve member may abut the valve body stop surface  24 . 
   When the compressor stops, the high pressure in the discharge line of the system will force the valve member to its closed position and prevent any refrigerant fluids from leaking back into the compressor shell. The valve assembly, according to the invention, also reduces the risk of undesirable reverse rotation of the orbiting scroll set  10  by preventing back flow of refrigerant fluid at high pressure into the compression pockets  12 , when the compressor stops. 
     FIG. 6  shows a hermetic scroll compressor which is additionally equipped with a delivery valve arrangement denoted by the general reference number  15 . Such valve arrangements, as known in the art prevent return flow of fluid from the high-pressure compartment  5  to the compression pockets  12 , when the pressure in the central compression pocket is less than the pressure in the high-pressure compartment. 
   As shown in  FIG. 6 , the compressor includes pressure-equalizing means in the form of a lateral passage  17  arranged in a circumferential surface of the fixed spiral element  9 . Lateral passage  17  provides fluid communication between the high-pressure compartment  5  and the low pressure compartment  4 . If no equalizing means were present in such a compressor, the high-pressure compartment  5  would remain at a high-pressure level when the compressor stops, due to the closing action of both the delivery valve arrangement  15  and the discharge valve assembly  20 . The pressure equalizing means serves to decrease the pressure in the compartment  5  towards the pressure level in the low-pressure compartment  4 . This in turn reduces the required starting torque for the motor, when the compressor is next operated. Further, the pressure equalizing means allows return of any lubricant separated from the refrigerant fluid flow in the high-pressure compartment  5  towards the oil sump at the bottom of the shell  2 , even during operation of the compressor. 
     FIGS. 7 to 11  show other embodiments of pressure equalizing and oil return means for a compressor. In  FIG. 7  a passage  61  is arranged in the end plate of the fixed spiral member  9 . Passage  61  provides fluid communication between high-pressure compartment  5  with the outlet opening  11  of the spiral member  9 . Pressure equalization between high-pressure compartment  5  and low-pressure compartment  4  occurs in this case by leakage through compression pockets  12 . However, in this case, oil return will only occur during a stop period of the compressor. 
   In  FIG. 8  pressure equalization and oil return occurs in a similar manner as disclosed above for  FIG. 7 . As shown in  FIG. 8 , a passage  62  is arranged in the valve plate  63  of the delivery valve arrangement  15 . Passage  62  places the high-pressure compartment  5  in fluid communication with the outlet opening  11 . 
   In  FIG. 9  a capillary tube  64  is arranged in an axial bore  65  through the radial outer portion  66  of the fixed spiral element  9 , which limits the lowest level of the high-pressure compartment  5 . The upper end portion  67  of capillary tube  64  may project from the surface of the fixed spiral element  9 , as shown in  FIG. 9 . By extending the capillary tube  64  above the surface, an oil reservoir is established at the radial outer portion  66 . This oil reservoir may also catch and retain impurities, e.g. dust or dirt particles, which could block the free passage in capillary tube  64 . 
   The same effect of preventing blockage of the pressure equalizing and oil return passage is achieved by the embodiments of  FIG. 10 , where a capillary sleeve  68  is arranged in a bore  65 , and of  FIG. 11 , where a protrusion  69  is formed on the upper surface of fixed spiral element  9 , surrounding bore  65 . 
   Although the present invention has been described with respect to discharge check valve assemblies for scroll compressors, the claimed invention may be easily adapted for used with any pressurized vessel. Father, although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the invention.