Abstract:
An apparatus for manipulating the air temperature within an interior compartment of a vehicle includes a compressor, a condenser, and an evaporator interconnected in a manner to remove heat from air in the interior compartment. A thermostatic expansion valve is connected between the condenser and evaporator, and includes an inlet and an outlet. A silencer screen is positioned at the outlet of the thermostatic expansion valve to reduce turbulence in refrigerant flow exiting the thermostatic expansion valve.

Description:
TECHNICAL FIELD 
     The present invention relates to an exit flow silencer device for reducing turbulence in refrigerant flowing through a thermostatic expansion valve in an air conditioning system, such as in a vehicle. 
     BACKGROUND OF THE INVENTION 
     Vehicle air conditioning systems typically include a compressor, condenser, and evaporator interconnected in a manner to remove heat from air in the interior compartment of the vehicle. Some vehicle air conditioning systems include a thermostatic expansion valve connected between the evaporator and condenser to reduce pressure and control flow of refrigerant flowing to the evaporator. By dropping pressure of refrigerant entering the evaporator, this enables the refrigerant to start boiling off or evaporate so that heat absorption can begin. 
     The thermostatic expansion valve has a capillary sensor that monitors refrigerant temperature flowing out of the evaporator. Expansion valves are described and calibrated to specific super heating settings. The purpose of the sensor and super heating setting is to allow the evaporator to get as cold as possible without freezing up and to assure that all liquid refrigerant entering the evaporator is a vapor when it exits. 
     Most automotive air conditioning compressors cannot accept liquid refrigerant because liquids cannot be compressed. Most systems with expansion valves will also have a thermostat control that assists in keeping the evaporator from icing up. The thermostat cycles the compressor when the evaporator approaches freezing, which is about the same time an expansion valve would start reducing flow of refrigerant. In combination, the expansion valve and the thermostat keep the evaporator as close to freezing as possible for maximum heat absorption. The expansion valve is designed to only regulate a solid liquid flow. Hissing sounds coming from the expansion valve indicate vapor bubbles passing through, which is normally the result of poor sub-cooling, a low charge or restriction in the high side. This also means the evaporator will not reach its optimum low temperature. 
     Most noise associated with the expansion valve occurs when sub-cooling is lost in the condenser. This may occur at vehicle idle or at low front end air flow and low compressor speed, which is run by the engine. In a vehicle having a rear air conditioning system, the thermostatic expansion valve in the rear part of the system experiences lower sub-cooling than the front because it is further from the condenser, and there are restrictions in the line. 
     It is desirable to provide an improved air conditioning system wherein noise from the thermostatic expansion valve is abated. 
     SUMMARY OF THE INVENTION 
     The invention provides a silencer screen positioned at the outlet of the thermostatic expansion valve to reduce turbulence in refrigerant flow exiting the thermostatic expansion valve. 
     More specifically, the invention provides an apparatus for manipulating the air temperature within an interior compartment of a vehicle. The apparatus includes a compressor, a condenser, and an evaporator interconnected in a manner to remove heat from air in the interior compartment. A thermostatic expansion valve is connected between the condenser and evaporator. The thermostatic expansion valve has an inlet and an outlet. A silencer screen is positioned at the outlet of the thermostatic expansion valve to reduce turbulence in refrigerant flow exiting the thermostatic expansion valve. 
     Preferably, the silencer screen is cylindrical in shape and supported by a cylindrical cage structure. Other shapes are contemplated within the scope of the present invention. The silencer screen is positioned within an end of an evaporator inlet tube which is connected to the thermostatic expansion valve. 
     The cylindrical cage structure preferably has a closed end and includes a flange which is connected to the outlet of the thermostatic expansion valve. The silencer screen is a mesh configuration having an opening size range between approximately 10 and 500 microns with 25% to 90% open flow area within the mesh configuration. 
     The silencer screen may be metal or plastic. The silencer screen may be connected to the cage structure, for example, by a plastic injection over-mold process. 
     The silencer screen is most preferably attached to an outlet of the thermostatic expansion valve adjacent a rear evaporator in a vehicle air conditioning system which includes front and rear evaporators. 
     The above objects, features, advantages, and other object, features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic flow diagram illustrating an air conditioning system for a vehicle in accordance with the invention; 
     FIG. 2 shows a partially exploded side view of a thermostatic expansion valve, silencer screen, and evaporator inlet tube for use with the embodiment of FIG. 1; 
     FIG. 3 shows a vertical cross-sectional view of an assembly of the components shown in FIG. 2; 
     FIG. 4 shows a side-view of a silencer screen and cage assembly in accordance with the invention; 
     FIG. 5 shows a top view of the silencer screen and cage assembly of FIG. 4; and 
     FIG. 6 shows a longitudinal cross-sectional view taken at line  6 - 6  of FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a schematic illustration of an air conditioning system  10  for use in a vehicle. As shown, the air conditioning system  10  includes a compressor  12  which pumps refrigerant through the system. Super heated vapor refrigerant exits the compressor  12  at high pressure and enters the condenser  14 , which exchanges heat to the ambient and condenses the vapor to a sub-cooled liquid at high pressure. 
     As shown, the air conditioning system  10  includes a front portion  16  and a rear portion  18 . The front portion  16  includes a front thermostatic expansion valve (or orifice tube)  20  which provides a restriction that changes the pressure from high to low and changes the flow to a two-phase refrigerant at low pressure. The two-phase refrigerant enters the front evaporator  22 . The evaporator  22  draws heat from the evaporator fins into the refrigerant. As the refrigerant changes states (i.e. evaporates from two-phase to just vapor), it expands and absorbs heat. The super heated vapor exits the front evaporator  22  at low pressure and enters the accumulator  24 . 
     The rear portion  18  of the air conditioning system  10  is positioned in parallel with the front thermostatic expansion valve  20 , front evaporator  22 , and accumulator  24 . The rear portion  18  includes the rear thermostatic expansion valve  26  and the rear evaporator  28 . A refrigerant flow silencer device  30  is positioned at the outlet of the rear thermostatic expansion device  26 . Similar to the front portion  16 , in the rear portion  18 , a two-phase refrigerant at low pressure exits the silencer device  30  and enters the rear evaporator  28 . A super heated vapor at low pressure exits the rear evaporator  28  and enters the compressor  12 . 
     The rear thermostatic expansion valve  26  includes a variable restriction or orifice which is controlled based upon the characteristics of heat exchange in the rear evaporator  28 . The temperature at the evaporator outlet is measured and flow to the evaporator is optimized by the rear thermostatic expansion valve  26  to provide optimal flow through the rear evaporator  28 . The rear thermostatic expansion valve  26  is used with the rear evaporator  28  because it helps balance refrigerant flow between the front and rear portions  16 ,  18  of the air conditioning system  10 . 
     The rear thermostatic expansion valve  26  and silencer device  30  are shown in greater detail in FIGS. 2 and 3. As shown in FIGS. 2 and 3, a thermostatic expansion valve inlet tube  32  is connected to an inlet  34  of the rear thermostatic expansion valve  26 . A body  36  of the thermostatic expansion valve  26  forms a channel  38  to carry the refrigerant. The body  36  includes a threaded portion  40  which is threadedly engaged with the nut  42 . The nut  42  engages a crimped portion  44  of the inlet tube  32  to secure the inlet tube  32  to the expansion valve  26 . An O-ring seal  46  is also provided between the crimped portion  44  of the tube  32  and the body  36 . 
     The body  36  is enclosed by a housing  48 . The body  36  forms a variable orifice  50  which is adjustable via the pin  52 . The pin  52  includes a sphere  54  at its distal end which is adjustable with respect to the orifice  50  for varying flow through the orifice  50 . 
     At the outlet of the body  36 , a second nut  56  is engaged with the threads  58  of the body  36 . The nut  56  is operative to connect the evaporator inlet tube  60  by engaging the crimped portion  62  of the evaporator inlet tube  60 . O-ring seals  64 ,  66  are provided between the silencer device  30  and the body  36 . The flange  68  of the silencer device  30  is sufficiently large so that it may not enter the evaporator inlet tube  60 . Accordingly, the silencer device  30  is held in position by the nut  56 , housing  48 , and evaporator inlet tube  60  via the flange  68 . 
     The silencer device  30  is shown in greater detail in FIGS. 4-6. As shown, the silencer device  30  includes a generally cylindrical cage structure  74  which supports a cylindrical silencer screen  76 . The silencer screen is formed in a cylindrical shape (i.e. it is round in vertical cross-section to fit in the tube  60 ) and is supported by the cage structure  74 . As shown, the cage structure  74  includes an open inlet  78  through which refrigerant flow may enter, and a closed end  80  which causes the refrigerant to flow radially outward through the screen  76  in order to reduce turbulence. The cage structure  74  includes a base  82  which is connected to the flange  68 . A pair of ribs  84 ,  86  extend longitudinally from the base  82  along the length of the silencer device  30  to the closed end  80 . Screen support members  88 ,  90 ,  92  extend from the ribs  84  to support the screen  76 . 
     The screen  76  is preferably a nylon plastic material which is connected to the cage structure  74  in a plastic injection over-molding process, wherein the screen is inserted into a mold and secured in place, and molten plastic is injected into the mold and bonds with the screen as the cage structure is formed. 
     Alternatively, the screen  76  could be a metal screen. The screen may be configured in a variety of shapes, such as: a cylindrical shape with a closed exit end; a cylindrical shape with an open exit end; a cone shape; a disk shape; a flat shape; a dome shape; etc. 
     Preferably, the silencer screen is in a mesh configuration having an opening size range between approximately 10 and 500 microns with 25% to 90% open area. The screen may be held in place by a plastic injection over-molding process, a plastic holder, a metal holder, etc. The silencer device may be held in place within the evaporator inlet tube by a metal detainer, plastic detainer, adhesive, or it may be screwed or pressed in closely adjacent the thermostatic expansion valve. 
     Accordingly, the silencer device dampens the turbulent two-phase refrigerant flow impact and high-flow velocity noise characteristics as the flow exits the thermostatic expansion valve and enters the evaporator, thus attenuating refrigerant noise. The device is particularly useful when the incoming thermostatic expansion valve refrigerant quality is low (less sub-cooled) and when the exiting refrigerant flow contains more vapor and is therefore more likely to generate objectionable refrigerant noise (hissing). 
     Alternatively, the silencer screen may be positioned inside the thermostatic expansion valve, as opposed to being positioned in the evaporator inlet tube. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.