Abstract:
A compressor apparatus has a housing ( 22 ) having first ( 53 ) and second ( 58 ) ports along a flowpath. One or more working elements ( 26, 28 ) cooperate with the housing to define a compression path between suction and discharge locations along the flowpath. A check valve ( 70 ) has a valve element having a first condition permitting downstream flow along the flowpath and a second condition blocking a reverse flow. Sound suppressing means ( 120, 220, 320 ) at least partially surround the flowpath upstream of the valve element ( 70 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to compressors. More particularly, the invention relates to compressors having check valves. 
   Screw-type compressors are commonly used in air conditioning and refrigeration applications. In such a compressor, intermeshed male and female lobed rotors or screws are rotated about their axes to pump the working fluid (refrigerant) from a low pressure inlet end to a high pressure outlet end. During rotation, sequential lobes of the male rotor serve as pistons driving refrigerant downstream and compressing it within the space between an adjacent pair of female rotor lobes and the housing. Likewise sequential lobes of the female rotor produce compression of refrigerant within a space between an adjacent pair of male rotor lobes and the housing. The interlobe spaces of the male and female rotors in which compression occurs form compression pockets (alternatively described as male and female portions of a common compression pocket joined at a mesh zone). In one implementation, the male rotor is coaxial with an electric driving motor and is supported by bearings on inlet and outlet sides of its lobed working portion. There may be multiple female rotors engaged to a given male rotor. 
   When one of the interlobe spaces is exposed to an inlet port, the refrigerant enters the space essentially at suction pressure. As the rotors continue to rotate, at some point during the rotation the space is no longer in communication with the inlet port and the flow of refrigerant to the space is cut off. After the inlet port is closed, the refrigerant is compressed as the rotors continue to rotate. At some point during the rotation, each space intersects the associated outlet port and the closed compression process terminates. The inlet port and the outlet port may each be radial, axial, or a hybrid combination of an axial port and a radial port. The compression pocket opening and closing (particularly discharge port opening) are associated with pressure pulsations and resulting sound. Sound suppression has thus been an important consideration in compressor design. Many forms of compressor mufflers have been proposed. 
   Additionally, various transient conditions may tend to cause reverse flow through the compressor. For example, upon a power failure or other uncontrolled shutdown high pressure refrigerant will be left in the discharge plenum and downstream thereof in the refrigerant flowpath (e.g., in the muffler, oil separator, condenser, and the like). Such high pressure refrigerant will tend to flow backward through the rotors, reversing their direction of rotation. If rotation speed in the reverse direction is substantial, undesirable sound is generated. For some screw compressors, damage to mechanical components or internal housing surfaces can also occur. Accordingly, a one-way valve (a check valve) may be positioned along the flowpath to prevent the reverse flow. Other forms of compressor (e.g., scroll and reciprocating compressors) may include similar check valves. 
   SUMMARY OF THE INVENTION 
   A compressor apparatus has a housing having first and second ports along a flowpath. One or more working elements cooperate with the housing to define a compression path between suction and discharge locations along the flowpath. A check valve has a valve element having a first condition permitting downstream flow along the flowpath and a second condition blocking a reverse flow. Sound suppressing means at least partially surround the flowpath upstream of the valve element. 
   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 
       FIG. 1  is a longitudinal sectional view of a compressor. 
       FIG. 2  is a partial sectional view of a discharge housing of the compressor of  FIG. 1  including a first sound suppressing means. 
       FIG. 3  is a partial sectional view of a discharge housing of the compressor of  FIG. 1  including a second sound suppressing means. 
       FIG. 4  is a partial sectional view of a discharge housing of the compressor of  FIG. 1  including a third sound suppressing means. 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a compressor  20  having a housing assembly  22  containing a motor  24  driving rotors  26  and  28  having respective central longitudinal axes  500  and  502 . In the exemplary embodiment, the rotor  26  has a male lobed body or working portion  30  extending between a first end  31  and a second end  32 . The working portion  30  is enmeshed with a female lobed body or working portion  34  of the female rotor  28 . The working portion  34  has a first end  35  and a second end  36 . Each rotor includes shaft portions (e.g., stubs  39 ,  40 ,  41 , and  42  unitarily formed with the associated working portion) extending from the first and second ends of the associated working portion. Each of these shaft stubs is mounted to the housing by one or more bearing assemblies  44  for rotation about the associated rotor axis. 
   In the exemplary embodiment, the motor is an electric motor having a rotor and a stator. One of the shaft stubs of one of the rotors  26  and  28  may be coupled to the motor&#39;s rotor so as to permit the motor to drive that rotor about its axis. When so driven in an operative first direction about the axis, the rotor drives the other rotor in an opposite second direction. The exemplary housing assembly  22  includes a rotor housing  48  having an upstream/inlet end face  49  approximately midway along the motor length and a downstream/discharge end face  50  essentially coplanar with the rotor body ends  32  and  36 . 
   The exemplary housing assembly  22  further comprises a motor/inlet housing  52  having a compressor inlet/suction port  53  at an upstream end and having a downstream face  54  mounted to the rotor housing downstream face (e.g., by bolts through both housing pieces). The assembly  22  further includes an outlet housing  56  (specifically the discharge case) (shown as an assembly) having an upstream face  57  mounted to the rotor housing downstream face and having an outlet/discharge port  58 . The exemplary rotor housing, motor/inlet housing, and outlet housing  56  may each be formed as castings subject to further finish machining. 
   Surfaces of the housing assembly  22  combine with the enmeshed rotor bodies  30  and  34  to define inlet and outlet ports to compression pockets compressing and driving a refrigerant flow  504  from a suction (inlet) plenum  60  to a discharge (outlet) plenum  62 . A pair of male and female compression pockets is formed by the housing assembly  22 , male rotor body  30 , and female rotor body  34 . In the pair, one such pocket is located between a pair of adjacent lobes of each associated rotor. 
     FIG. 2  shows further details of the exemplary flowpath at the outlet/discharge port  58 . A check valve  70  is provided having a valve element  72  mounted within a boss portion  74  of the outlet housing  56 . The exemplary valve element  72  is a front sealing poppet having a stem/shaft  76  unitarily formed with and extending downstream from a head  78  along a valve axis  520 . The head has a back/underside surface  80  engaging an upstream end of a compression bias spring  82  (e.g., a metallic coil). The downstream end of the spring engages an upstream-facing shoulder  84  of a bushing/guide  86 . The bushing/guide  86  may be unitarily formed with or mounted relative to the housing and has a central bore  88  slidingly accommodating the stem for reciprocal movement between an open condition (not shown) and a closed condition of  FIG. 3 . The spring  82  biases the element  72  upstream toward the closed condition. In the closed condition, an annular peripheral seating portion  90  of the head upstream surface seats against an annular seat  92  at a downstream end of a port  94  from the discharge plenum. 
   For capacity control/unloading, the compressor has a slide valve  100  having a valve element  102 . The valve element  102  has a portion  104  along the mesh zone between rotors. The exemplary valve element has a first portion at the discharge plenum and a second portion at the suction plenum. The valve element is shiftable to control compressor capacity to provide unloading. The exemplary valve is shifted via linear translation parallel to the rotor axes. 
   The opening and closing of the compression pockets at suction and discharge ports produce pressure pulsations. As the pulsations propagate into the gas in the discharge plenum and downstream thereof, they cause vibration and associated radiated sound which are undesirable. This pulsation may be at least partially addressed by modifications involving the discharge plenum upstream of the check valve. Exemplary modifications involve modifications to the discharge plenum at the port  94  to incorporate one or more resonators tuned to suppress/attenuate one or more sound/vibration frequencies at one or more conditions. An exemplary frequency is that of the compression pockets opening/closing at the designed compressor operating speed and at the designed refrigeration system operating condition. Thus examples of otherwise identical compressors may feature differently-tuned resonators for use in different systems or conditions thereof. Exemplary modifications make use of existing manufacturing techniques and their artifacts. Exemplary modifications may be made in a remanufacturing of an existing compressor or a reengineering of an existing compressor configuration. An iterative optimization process may be used to tune the resonator(s). 
     FIG. 2  shows one exemplary modification of a basic compressor. This modification involves providing an outlet conduit  120  having a distal/upstream protruding portion  122  extending into the discharge plenum to a rim  126 . In the exemplary implementation, the outlet conduit is separately formed from the remainder of the outlet housing (e.g., as a steel cylindrical tube having a proximal/downstream portion  127  interference fit (e.g., press-fit) into a cast iron housing member  56  within 2 cm of the head  78  in the second (closed) condition). An annular channel  128  is defined in the discharge plenum surrounding the protruding portion  122  to form an annular resonance cavity that functions as a side branch resonator. The exemplary cavity has an annular opening/port  130 . When implemented in a remanufacturing of an existing compressor or a reengineering of an existing configuration, the cavity may be associated with a change in the local discharge plenum surface  132  (e.g., from an initial/baseline surface  132 ′). In the exemplary implementation, the surface is relieved so as to deepen and broaden the cavity. The cavity is shown having a length L, an inner radius R, and a radial span ΔR. These parameters may be selected to provide desired tuning. The annular base portion of the surface  132  forms a back wall of the cavity, off which pressure waves reflect. The length L may thus be chosen to provide an out-of-phase cancellation effect relative to incident pulsations at the plane of the port  130  and rim  126 . The cancellation effect reduces pulsation magnitude at the conduit mouth and, in turn, downstream through the conduit. By changing the curved section of the baseline surface  132 ′ to the more right angle section of the surface  132 , a flat radial back wall/base is formed that provides a more coherent reflection, permitting advantageous cancellation properties. 
     FIG. 3  shows an alternative modification wherein the outlet conduit  220  has an upstream end wall  222  and a sidewall  224 . The end wall  222  includes an array of apertures  226 . The sidewall  224  includes an array of apertures  228 . The apertures  226  and  228  serve to break-up the discharge flow into many substreams passing through the aperture and recombining in the interior of the conduit  220 . This helps attenuate the downstream impact of upstream pulsations. The sizes, densities, and distributions of the apertures may be selected to provide a desired degree of attenuation. Optionally, there may be some tuning of the plenum volume surrounding the conduit  220  to also provide additional pulsation reduction within the conduit  220 . 
     FIG. 4  shows another alternative modification wherein an outlet conduit assembly  320  has a main conduit  322  extending downstream from a rim  324 . Although optionally similarly constructed to the conduit  120 , the conduit  322  has an array of apertures  326  similar to the apertures  228  of the conduit  220 . However, rather than passing a net flow, the apertures  326  serve as ports to a resonator volume  330  surrounding the conduit. The volume  330  is otherwise sealed and longitudinally and laterally bounded by an inwardly-open C-sectioned member  332  (e.g., having a pair of upstream and downstream collars  333  and  334  welded to the outboard surface of the conduit  322 ). Thus, although similarly located to the resonator volume  128 , the resonator volume  330  has a longitudinal and circumferential array of discrete radial ports provided by the apertures  326  rather than a single annular longitudinal port  130 . Optionally, the volume  330  may be filled with a sound dissipating material. The presence of that dissipative material may reduce cancellation effectiveness at a single target frequency but compensate by providing some cancellation over a wider frequency range, making tuning accuracy less critical. 
   The relative proximity of the resonator(s) to the discharge plenum is believed advantageous for several reasons. First, flow turbulence may tend to increase downstream. Turbulent conditions make tuning difficult. The relatively low turbulence of an upstream location (e.g., within the compressor housing), helps facilitate proper tuning. Second, the proximity to the pulsation source may maximize the sound/vibration cancellation effect. 
   Many known or yet-developed resonator configurations and optimization techniques may be applied. The former include, for example, Helmholtz resonators. 
   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. Implementations may involve check valves used in other locations in the fluid circuit. The principles may be applied to compressors having working elements other than screw-type rotors (e.g., reciprocating and scroll compressors). Accordingly, other embodiments are within the scope of the following claims.