Abstract:
A compressor has first and second enmeshed rotors rotating about first and second axes to pump refrigerant to a discharge plenum. The compressor includes a muffler system comprising a sound absorbing first element and a sound absorbing second element. The second element at least partially surrounds the first element and defines a generally annular flow path portion between the first element and the second element At least one of the first and second elements comprises an expanded bead material.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Continuation-in-Part of PCT Application No. PCT/US04/34946, filed Oct. 20, 2004 and entitled “COMPRESSOR SOUND SUPPRESSION”. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to compressors. More particularly, the invention relates to sound and vibration suppression in screw-type compressors. 
         [0003]    In positive displacement compressors, discrete volumes of gas are: trapped at a suction pressure; compressed; and discharged at a discharge pressure. The trapping and discharge each may produce pressure pulsations and related noise generation. Accordingly, a well developed field exists in compressor sound suppression. 
         [0004]    One class of absorptive mufflers involves passing the refrigerant flow discharged from the compressor working elements through an annular space between inner and outer annular layers of sound-absorptive material (e.g., fiber batting). US Patent Application Pub. No. 2004/0065504 A1 discloses a basic such muffler and then improved versions having integral helmholtz resonators formed within the inner layer. The disclosure of this &#39;504 publication is incorporated by reference herein as if set forth at length. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, one aspect of the invention involves a compressor having first and second enmeshed rotors rotating about first and second axes to pump refrigerant to a discharge plenum. The compressor includes a muffler system comprising a sound absorbing first element and a sound absorbing second element. The second element at least partially surrounds the first element and defines a generally annular flow path portion between the first element and the second element At least one of the first and second elements comprises an expanded bead material. 
         [0006]    In various implementations, at least one of the first and second elements comprises a plurality of rings of porous expanded polypropylene. Along a majority of total longitudinal spans of the first and second elements, the first and second elements may have inboard and outboard surfaces that are essentially non-convergent and non-divergent. The muffler system may include a perforated sheet metal first sleeve between the first and second elements and a first wire reinforcement secured to the first sleeve. The first sleeve may be at an inboard boundary of the generally annular flow path portion. A perforated sheet metal second sleeve may be at an outboard boundary of the generally annular flow path portion and a second wire reinforcement is secured to the second sleeve. 
         [0007]    Another aspect of the invention involves a compressor muffler element. The element has a stack of a plurality of rings of an expanded bead material. 
         [0008]    In various implementations the expanded bead material may be porous expanded polypropylene. A foraminate metallic sleeve may be concentrically within or surrounding the rings. A spiral metallic reinforcement may be secured to a first surface of the sleeve. The reinforcement may contact an adjacent surface of the element. A first such element according may be an outer element and a second such element may be an inner element at least partially nested within the first element to define a flowpath segment between an inner surface of the first element and an outer surface of the second element. First and second such elements may be separated by a metallic divider and a third such element may be an inner element at least partially nested within the first and second elements to define a flowpath segment between an inner surface of the first element and an outer surface of the second element. 
         [0009]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a longitudinal sectional view of a compressor. 
           [0011]      FIG. 2  is a longitudinal sectional view of a muffler of the compressor of  FIG. 1 . 
           [0012]      FIG. 3  is a downstream end view of the muffler of  FIG. 2 . 
           [0013]      FIG. 4  is a longitudinal sectional view of a first metal subassembly of the muffler of  FIG. 2 . 
           [0014]      FIG. 5  is a longitudinal sectional view of a second metal subassembly of the muffler of  FIG. 2 . 
       
    
    
       [0015]    Like reference numbers and designations in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows a compressor  20  having a housing or case assembly  22 . The exemplary compressor is a three-rotor, screw-type, hermetic compressor having rotors  26 ,  28 , and  30  with respective central longitudinal axes  500 ,  502 , and  504 . In the exemplary embodiment, the first rotor  26  is a male-lobed rotor driven by a coaxial electric motor  32  and, in turn, enmeshed with and driving the female-lobed rotors  28  and  30 . In the exemplary embodiment, the male rotor axis  500  also forms a central longitudinal axis of the compressor  20  as a whole. The rotor working portions are located within a rotor case segment  34  of the case assembly  22  and may be supported by bearings  36  and sealed by seals  38  engaging rotor shafts at each end of the associated rotor working portion. When driven by the motor  32 , the rotors pump and compress a working fluid (e.g., a refrigerant) along a flowpath from a suction plenum  40  to a discharge plenum  42 . The flowpath is divided along distinct compression pockets or compression paths defined by associated pairs of the rotors between the suction and discharge plenums. Thus, the flow splits in the suction plenum and merges in the discharge plenum. 
         [0017]    In the exemplary embodiment, the suction plenum  40  is located within an upstream end of the rotor case  34  and the discharge plenum is located generally within a discharge case  46  separated from the rotor case by a bearing case  48  and having a generally downstream-convergent interior surface  49 . In the exemplary embodiment, a bearing cover/retainer plate  50  is mounted to a downstream end of the bearing case  48  to retain the bearing stacks. Downstream of the discharge case  46  is a muffler  52  in a muffler case  54 . Downstream of the muffler  52  is an oil separator unit  60  having a case  62  containing a separator mesh  64 . An oil return conduit  66  extends from the housing  62  to return oil stopped by the mesh  64  to a lubrication system (not shown). An outlet plenum  68  having an outlet port  69  is downstream of the mesh  64 . 
         [0018]    The exemplary main muffler  52  includes annular inner and outer elements  70  and  72  separated by a generally annular space  74 . These elements may be formed of sound absorption material. In the exemplary embodiment, the inner element  70  is retained and separated from the space  74  by an inner foraminate sleeve  76  (e.g., wire mesh or perforated/expanded metal sheeting) and the outer element  72  is similarly separated and retained by an outer foraminate sleeve  78 . In the exemplary embodiment, the outer element  72  is encased within an outer sleeve  80  telescopically received within the housing  54 . The sleeves  80  and  78  are joined at upstream and downstream ends by annular plates  82  and  84 . In the exemplary embodiment, the upstream end of the sleeve  76  is closed by a circular plate  86  and the downstream end closed by an annular plate  90 . In the exemplary embodiment, a non-foraminate central core  94  (e.g., steel pipe) extends through the inner element  70  and protrudes beyond a downstream end thereof. At the upstream end of the main muffler, radially-extending connectors  96  join the circular plate  86  to the annular plate  82 . At the downstream end, radially-extending connectors  98  connect the annular plates  84  and  90  to hold the inner and outer elements concentrically spaced apart to maintain the annular space  74 . 
         [0019]    In operation, compressed gas flow exits the compression pockets of the screw rotors  26 ,  28 ,  30  and flows into the discharge plenum  42 . Upon exiting the compressor discharge plenum, the gas flows down the annular space  74 . Upon exiting the muffler, the gas flow, which typically has entrained oil droplets, flows through the oil separating mesh  64 . The mesh  64  captures any oil entrained in the gas and returns it to the oil management system by means of the conduit  66 . The gas leaves the oil separating mesh and enters the plenum  68  and exits the outlet  69  toward the condenser (not shown). 
         [0020]      FIG. 2  shows further details of the main muffler  52 . The sound-absorbing material of the inner and outer elements are respectively formed by exemplary stacks of foam-like rings  110  and  112 A,  112 B. The exemplary rings  110  are formed in a single stack (e.g., of nine identical rings). The exemplary rings  112 A and  112 B are identical but positioned in distinct upstream and downstream stacks. Exemplary ring material is expanded polypropylene beads (e.g., material known as porous expanded polypropylene (PEPP)). 
         [0021]    The exemplary sleeve  80  is formed in respective upstream and downstream sections  80 A and  80 B along the ring stacks. The exemplary sleeve  78  is similarly formed in upstream and downstream sections  78 A and  78 B. Exemplary sleeve sections  78 A and  78 B are, along their outboard surfaces, circumferentially reinforced by a metallic spiral reinforcement  114 A and  114 B. Similarly, the sleeve  76  may, along its inboard surface be reinforced by a metallic spiral element  116 . 
         [0022]    In the exemplary muffler, the two stacks of outer rings  112 A and  112 B are separated by a divider  118  comprising a pair of annular plates  120  and  122 . In the exemplary muffler, each of the annular plates  82 ,  84 ,  120 , and  122  is secured to associated short inboard and outboard metal rings  126  and  128  extending partially inboard and outboard, respectively, of the adjacent ring  112 A or  112 B to form a longitudinally-open annular channel. 
         [0023]    In an exemplary sequence of muffler assembly, the annular plates  82 ,  84 ,  120 , and  122  are welded to their associated rings  126  and  128 . Respective downstream and upstream end portions of the sleeve sections  78 A and  78 B may be telescopically inserted within the central apertures of respective plates  120  and  122  and their associated inboard rings  126  and welded thereto. The reinforcements  114 A and  114 B may then be wrapped around the sleeve sections  78 A and  78 B and welded thereto. The sleeve sections  80 A and  80 B may then be installed over the plates  120  and  122  and their associated outer rings  126  and welded thereto to define annular compartments  128 A and  128 B ( FIG. 4 ). The resultant two subassemblies may then be welded end-to-end (e.g., with the downstream face of the plate  120  contacting the upstream face of the plate  122 ) to provide an outer element metallic assembly  130  ( FIG. 4 ). 
         [0024]    An inner element metallic assembly  132  ( FIG. 5 ) may also be formed. The tube  94  may be welded to the downstream face of the plate  86 . An upstream end portion of the sleeve  76  may be placed over the outer periphery of the plate  86  and welded thereto. The connectors  96  may be welded to the upstream face of the plate  82  and then to the upstream face of the plate  86  to position the plate  86  concentrically within the plate  82  and its associated rings. The reinforcement  116  may be inserted within the sleeve  76  and welded thereto. The relatively smaller diameter of the sleeve  76  compared with the sleeve  78  may provide the sleeve  76  with greater structural integrity. Thus, there may be less need for reinforcement of the sleeve  76 . Also, it is desirable that the reinforcement be opposite the space  74  so that the reinforcement does not excessively restrict the refrigerant flow. Such a location places the reinforcement  116  within the sleeve  76  and increases the difficulty of welding relative to an external placement. This difficulty, combined with a lesser need, renders the reinforcement  116  of a substantially lower cost/benefit value and makes it particularly omitable. With the two metal assemblies prepared, the muffler may be finally assembled. The stack of rings  112 A is inserted within the first annular compartment  128 A. One or more insulator rings  136  (e.g., a synthetic, non-asbestos, non-metallic, material in a resilient binder (e.g., neoprene or nitrile rubber) such as is available under the trademark BLUE-GARD 3300 of Garlock Sealing Technologies, Palmyra, New York, may be installed atop the stack or within the annular channel  134  ( FIG. 5 ) formed by the plate  82  and its associated rings. The assembly  130  may then be installed to the assembly  132  with upstream portions of the sleeves  78 A and  80 A receiving the annular plate  82  and its associated rings. The sleeves may then be welded to the annular plate. During this welding, the insulator rings  136  protect the upstreammost ring  112 A from thermal damage. The rings  112 B may then be inserted into the compartment  128 B. Also, the rings  110  may be installed over the tube  94  within the sleeve  76 . The downstream end assembly may then be put in place (insulator rings  136  being pre-installed, for example). An exemplary securing involves welding the inner aperture of the plate  90  to the tube  94  and an outer perimeter portion of the plate  84  to the downstream end portion of the sleeve  80 B. 
         [0025]    One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, in a reengineering or remanufacturing situation, details of the existing compressor may particularly influence or dictate details of the implementation. Accordingly, other embodiments are within the scope of the following claims.