Abstract:
A sonic nozzle is disclosed that is positioned between an evaporator and compressor in an air conditioning system. The sonic nozzle limits refrigerant flow rate to that allowed by sonic velocity at a throat area of the sonic nozzle. The sonic nozzle may have a by-pass flow area that allows for less pressure drop at lower flow rates where the by-pass flow area is sealed off at a predetermined pressure drop to force all flow through the sonic nozzle. Another embodiment that is disclosed features a thermally actuated suction throttling valve that is attached to a sonic nozzle. A power element of the throttling valve contains thermally active fluid, such as water, when frozen activates a piston member into the throat portion of the sonic nozzle to restrict fluid flow.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application No. 60/368,059 filed Mar. 26, 2002, the contents of which is incorporated herein in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates generally to vapor compression refrigeration systems that utilize a fixed a variable restrictor for flow control. More particularly, the present invention relates to vapor compression refrigeration systems for automotive systems that use a compressor that varies capacity with engine speed. 
   BACKGROUND OF THE INVENTION 
   Automotive and light commercial air conditioning systems generally use either a piston type or a scroll compressor. In operation, the scroll compressor differs from the piston compressor in that the volumetric efficiency of the scroll compressor goes up as rotational speed is increased while the volumetric efficiency of the piston compressor goes down as rotational speed is increased. Accordingly, the scroll compressor produces very high head pressures when a vehicle is accelerated in hot ambient temperature. Thus, the high side pressure switch may trip, causing system cooling performance to suffer. 
   While the piston compressor may produce 30,000 BTU/hr at high rotational speeds, the scroll compressor may produce 50,000 BTU/hr. Air conditioning systems that incorporate a suction accumulator aggravate the challenges with the scroll compressors due to violent boiling of the accumulator refrigerant when suction pressure is suddenly dropped by the scroll pumping capacity on acceleration of the vehicle. This results a greater mass flow rate to the compressor as compared to a thermostatic expansion valve system with no accumulator. While a suction throttling valve may solve this problem, most are cost prohibited and complex to install. 
   Sonic nozzles have been used for years in fluid flow measurement. At flow rates below sonic, the nozzle can recover up to 94% of pressure loss. In comparison, a square edge orifice recovers only 12% of pressure loss. Pressure recovery is essential as each 1.0 psi drop in suction plumbing reduces capacity by approximately 1%. A ¼ inch diameter square edged orifice may produce a 7 psi drop at a given flow rate while the sonic nozzle may be 1 psi at similar flow and throat size. 
   SUMMARY OF THE INVENTION 
   A sonic nozzle for use in air conditioning and refrigeration systems is disclosed. In a first embodiment, the sonic nozzle of the present invention includes a first opening having a first predetermined diameter, a second opening having a second predetermined diameter, an aperture extending through the first and second openings. The aperture further includes a first tapered section and a second tapered section. The first tapered section is positioned adjacent to the first opening and converges inwardly to a throat portion having a third predetermined diameter. The first tapered section converges at a first predetermined diameter. The second tapered section diverges from the third predetermined diameter at a second predetermined angle. The second tapered section terminates at the second opening. 
   In one embodiment, the sonic nozzle is a fixed nozzle. That is, once installed in a fluid conduit or intake valve of a compressor in an air conditioning system, it does not move. To “fix” the nozzle in place, in one embodiment, the outer diameter of the nozzle includes a groove formed in the outer diameter of the nozzle. A seal, such as an O-ring is provided. 
   In another embodiment, the sonic nozzle is a movable nozzle. In accordance with this aspect of the invention, a sonic nozzle is provided, and a biasing spring is positioned adjacent the second opening of the sonic nozzle to limit the movement of the nozzle when in use. At least one set of spring shoulders, which also serve as guides for the nozzle, are also provided. When there is no or low flow rate of fluid in the conduit of the air conditioning system, fluid is permitted to enter a by-pass flow area around the outer periphery of the nozzle. As flow and pressure drop across the sonic nozzle increases, the biasing spring permits movement of sonic nozzle to seal off the by-pass flow area. 
   In addition to a pressure actuated sonic nozzle, in accordance with another aspect of the invention, a thermally activated throttling valve is disclosed. The throttling valve assembly is positioned adjacent and secured to the first opening of the sonic valve. The throttling valve includes a power element housing that contains thermally active fluid that acts upon a flexible member to move a throttling piston into the throat portion of the sonic nozzle to restrict fluid flow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description: 
       FIG. 1  is a schematic representation of a refrigeration system utilizing a sonic nozzle as a capacity control device in accordance with the present invention. 
       FIG. 2   a  is an end view of a sonic nozzle in accordance with the present invention. 
       FIG. 2   b  is an elevational view of the sonic nozzle of  FIG. 2   a  in accordance with the present invention. 
       FIG. 3   a  is end view of an alternative embodiment of the sonic nozzle in accordance with the present invention. 
       FIG. 3   b  is an elevational view of the sonic nozzle of  FIG. 3   a  in accordance with the present invention. 
       FIG. 4   a  is an end view of a thermally actuated suction throttling valve attached to the sonic nozzle of the present invention. 
       FIG. 4   b  is an elevational view of the thermally actuated suction throttle valve in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   Turning now to  FIGS. 1–3 , the details of the present invention will be described.  FIG. 1  depicts an automotive air conditioning system  10 . System  10  includes a compressor  12 , condenser  14 , and an evaporator  16 . A liquid line conduit  18  connects the compressor  12 , condenser  14  and evaporator  16 , in series. An expansion tube or orifice  20  may also be included in system  10 . Orifice  20  is positioned between condenser  14  and evaporator  16 . System  10  may further include an accumulator  22 . 
   In accordance with one aspect of the invention, system  10  includes a sonic nozzle  24 . Sonic nozzle  24  is positioned between evaporator  16  or accumulator  22  and compressor  12 . Sonic nozzle  24  may be formed in conduit  18 , formed as part of a fitting to be added to conduit  18 , or as a separate part. Further, sonic nozzle  24  may also be formed in the intake port  26  of compressor  12 . 
   Turning now to  FIGS. 2   a – 2   b , the details of sonic nozzle  24  will be discussed. Sonic nozzle  24  is designed as a separate part that is inserted into conduit  18 . In accordance with the invention, conduit  18  includes first and second diameter sections,  28   a ,  28   b . Second diameter section  28   b  is slightly larger than first diameter section  28   a , such that a step  29  is formed. Step  29  serves as a stop for securing sonic nozzle  24  within conduit  18 . 
   As seen best in  FIG. 2   a , in one embodiment where sonic nozzle is formed as a separate part, sonic nozzle  24  has an outside diameter  30  that is slightly smaller than an inside diameter  32  of conduit  18 . Outside diameter  30  includes a groove or notch  33  formed on the outside surface. Notch  33  has a predetermined depth. A sealing O-ring  34  having a predetermined diameter that is larger than the depth of notch  32  is also provided. When O-ring  34  is positioned in notch  32  and sonic nozzle  24  is secured in conduit  18  against step  29 , O-ring  34  serves to secure sonic nozzle  24  in conduit  18 . 
   Sonic nozzle  24  includes a first opening  36  that opens into an inlet portion  38 , a throat portion  40 , and an outlet portion  42  that diverges into a second opening  44 . Second opening  44  may further include a flange portion or lip (not shown) that contacts step  29 . 
   In accordance with the present invention, sonic nozzle  24  has a venturi contour such that first opening  36  opens into inlet portion  38  that converges into throat portion  40 . Outlet portion  42  diverges to second opening  44 . As can be seen, inlet portion  38  generally has a circular arc that passes through throat portion  40  to a tangent point A. At this point, outlet portion  42  becomes conical. It is preferred that the surface finish of inlet portion  38 , throat portion  40  and outlet portion  42  is generally smooth with no irregular defects such as waviness and steps. 
   Sonic nozzle  24  may be sized to limit the cooling capacity of compressor  12  and thus solve the high head pressure problem of the scroll compressor. With the scroll compressor and other types of compressors  12 , sonic nozzle  24  could be used to limit system  10  cooling capacity thus reducing compressor  12  horsepower at certain high load, high speed conditions resulting in improved fuel economy. 
   In accordance with the invention, under sonic velocity in throat portion  40 , sonic nozzle  24  recovers up to 94% of the static pressure drop between inlet portion  38  and throat portion  40 . At sonic velocity, fluid flow is limited to sonic of the gas (R-134A refrigerant is 40 ft/sec), regardless of how low downstream pressure drops. Accordingly, a low pressure drop flow control with a defined flow limit that depends on throat flow area, is achieved. 
   An alternative embodiment of the present invention is shown in  FIGS. 3   a – 3   b . More specifically,  FIGS. 3   a  and  3   b  illustrate a movable sonic nozzle assembly  100  that includes a sonic nozzle  102 , a biasing spring  104 , a by-pass flow area  106  and a plurality of guides  108 . In accordance with one aspect of the invention, sonic nozzle  100  is shown as a separate unit that is placed in conduit  18  in system  10 . Again, conduit  18  has a first diameter section  28   a  and a second diameter section  28   b  such that a step  29  is formed. Step  29  serves as a stop to secure sonic nozzle assembly  100  within conduit  18 . Step  29  further serves to limit movement of sonic nozzle  102  and seal by-pass flow area  106 , as will be explained in further detail below. 
   Sonic nozzle  102  includes a first opening  110  that opens into an inlet portion  112 , a throat portion  114  connected to inlet portion  112 , and an outlet portion  116  that diverges into a second opening  118 . In accordance with the present invention, sonic nozzle  102  has a venturi contour such that first opening  110  opens into inlet portion  112  that converges into throat portion  114 . Outlet portion  116  diverges to second opening  118 . As can be seen, inlet portion  112  generally has a circular arc that passes through throat portion  114  to a tangent point A. At this point, outlet portion  116  becomes conical. It is preferred that the surface finish of inlet portion  112 , throat portion  114  and outlet portion  116  is generally smooth with no irregular defects such as waviness and steps. 
   Sonic nozzle assembly  100  further includes a plurality of spring shoulders  120  that are positioned a predetermined distance upstream of step  29  in second diameter section  28   b  of conduit  18 . Biasing spring  104  is positioned between spring shoulders  110  and step  29 , and around second opening  118  of sonic nozzle  102 . Guides  108  are provided within second section  28   b  of conduit  18 , adjacent first opening  110  of sonic nozzle. Guides  108  and spring shoulders  120  cooperate to maintain the proper orientation of sonic nozzle  102  during operation. 
   During operation, at no or low flow of fluid in conduit  18 , fluid is able to enter by-pass flow are  106 , as is shown in  FIG. 3   b . As flow and pressure drop across sonic nozzle  102  is increased, biasing spring  104  permits movement of sonic nozzle  102 . Due to the movability of sonic nozzle  102 , a lower pressure drop at low flow conditions, such as at idle conditions, may be achieved. Moreover, at higher flow rates, the flow capacity may be limited to a lower value by engagement of an outer periphery  122  of second opening  118  to step  29 , thereby sealing off by-pass flow area  106  and limiting flow area to the venturi shaped passage of sonic nozzle  102 . 
     FIGS. 4   a  and  4   b  illustrate an alternative embodiment of a thermally actuated suction throttling valve  200  that is attached to sonic nozzle  24 . In accordance with one aspect of the invention, throttling valve  200  includes a throttling piston  202 , a flexible membrane  204 , and a power element housing  206 . Throttling piston  202  includes an actuation end  208 , a flange member  210 , a sealing end  212 , and a spring  213 . Flexible membrane  204  is positioned around actuation end  208  of throttling piston  202 . Power element housing  206  is secured to a distal end  214  of a housing  216  for sonic nozzle  24 . In one embodiment, power element housing  206  is attached to distal end  214  via attachment pins  218 , although it is understood that any suitable means for attaching power element housing  206  may be employed. 
   In accordance with one aspect of the invention, deposited within power element housing  206  and outside of flexible membrane  204  is a fluid such as water (possibly with additives therein) which, when frozen, expands and deforms flexible membrane  204  around actuation end  208 . Flexible membrane  204  thereby acts upon actuation end  208  of throttling piston  202 , thereby forcing piston  202  to act against spring  213  and forcing sealing end  212  of throttling piston  202  through first opening  36  and inlet portion  38 , into throat portion  40 , thereby restricting flow through sonic nozzle  24  when the temperature of the fluid in conduit  18  upstream of sonic nozzle  24  falls to a predetermined level. 
   The advantages associated with employing a suction throttling device include a reduction in compressor clutch cycle frequency resulting in colder, more stable, evaporator discharge air temperatures. Sonic nozzles that are temperature actuated have advantages over pressure actuated valves due to a time delay that is beneficial in certain driving conditions with an automotive orifice type air conditioning system. 
   Preferred embodiments of the present invention have been disclosed. A person of ordinary skill in the art would realize, however, that certain modifications would come within the teachings of this invention. Therefore, the following claims should be studied to determine the true scope and content of the invention.