Abstract:
The invention relates to a refrigeration system for an air conditioner of an automobile, the system having at least a gas cooler, an evaporator, and an expansion valve assembly. The expansion valve assembly is provided with an expansion chamber that is in fluid communication with the gas cooler and the evaporator. A valve defines an opening from the expansion chamber to the outlet conduit and a diaphragm defines another boundary of the expansion chamber. An appendage at least partially located within the expansion chamber. A variable-force mechanism is adapted to cause movement of an appendage coupled thereto, and it is at least partially controlled by an electrical signal. An appendage is moved by the variable-force mechanism, resulting in throttling of the opening.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a valve arrangement for a cooling system that uses a fluid that may be supercritical on the high-pressure side of the system. More particularly, the invention relates to a closed circuit refrigerating system including at least a compressor, a heat rejecting or gas cooling heat exchanger, an expansion valve, and an evaporating heat exchanger; where these elements are connected in series and the expansion valve is at least partially controlled by an electrical signal. 
     2. Description of Related Art 
     A conventional vapor compression cycle system for refrigeration, air conditioning, or heat pump purposes includes a compressor, a heat rejecting heat exchanger (gas cooler), an expansion valve, an evaporating heat exchanger (evaporator), and an accumulator. These elements are in fluid communication in a closed flow circuit, in which fluid, such as carbon dioxide (CO 2 ), and other known fluids, is circulated. A supercritical vapor compression cycle system generally operates as follows. The compressor increases the temperature and pressure of the fluid vapor. Vapor flows out of the compressor and into the gas cooler, which then cools the fluid with the fluid giving off heat to a secondary fluid, such as air. The fluid next flows into the expansion valve, which throttles the high-pressure fluid such that the outlet fluid has a lower pressure than the inlet fluid. The low pressure fluid flows into the evaporator, which heats the fluid such that it becomes at least partially vapor. Finally, the fluid flows into the accumulator, which is used as a vapor-liquid separator, and the fluid vapor is finally drawn into the compressor, completing the cycle. 
     The working fluid is considered to be at a high side pressure when it is located between the outlet of the compressor and the inlet of the expansion valve. Also, the working fluid is considered to be at a low side pressure when it is located between the outlet of the expansion valve and the inlet of the compressor. 
     Efficiency of a vapor compression cycle is denoted as the coefficient of performance (COP) and is defined as the ratio between the refrigerating capacity and the applied compressor drive power used. In general under typical operating conditions of a supercritical system, the refrigerating capacity obtained at the evaporator rises with increasing high side pressure, and falls with decreasing high side pressure. The COP increases with increasing high side pressure up to a certain point, but then begins to decline as the extra refrigerating effect no longer fully compensates for the extra work of compression. Thus, a maximum COP can be maintained by regulating the high side pressure with the expansion valve. 
     The prior art expansion valve assemblies control high side pressure with an expansion valve assembly that is mechanically adjusted via a rotatable handle moving a threaded body, which in turn adjusts the position of the top of a spring. Movement of the bottom of the spring controls the size of the opening within the expansion valve and thus controls the high side pressure. 
     manual valve is not suitable for control of a vapor compression system as it requires human interaction to modify the setting of the valve. Obviously this is not an option for mass-produced vapor compression systems. 
     In view of the above, it is clear that there exists a need for an expansion valve assembly with a quick and precise response mechanism and with fewer system variables. 
     It is an object of the present invention to control the valve setting with an electric signal, allowing the vapor compression system to operate without human interaction, thereby making the commercial mass production of such a system feasible. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a refrigeration system and includes a compressor, gas cooler, an evaporator, and an expansion valve assembly. The expansion valve assembly defines an expansion chamber in fluid communication with the gas cooler, by an inlet conduit, and in fluid communication with the evaporator, by an outlet conduit. The inlet conduit contains high side pressure fluid while the outlet conduit contains low side pressure fluid. Within the expansion valve assembly, the valve position defines an opening between the expansion chamber and the outlet conduit. In one preferred embodiment of the invention, the opening is tapered. The expansion valve assembly also includes a diaphragm defining a boundary of the expansion chamber, an appendage at least partially located within the expansion chamber, and a variable-force mechanism located adjacent to the diaphragm. The variable-force mechanism is capable of downward-upward movement, and the applied force is at least partially controlled by an electrical signal correlated to the desired high side pressure. 
     In one preferred embodiment, a mechanical valve interfaced with a stepper motor operates as a means to achieve the desired outcome. Changes to the valve setting are quick and precise. In another preferred embodiment, the variable-force mechanism is a solenoid. In both embodiments, the appendage is at least partially controlled by the variable-force mechanism, resulting in similar possible downward-upward movement. The applied force is at least partly proportionally related to the Sigh side pressure of the system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will be made more apparent from the following description of the preferred embodiments, with reference to the accompanying drawings wherein: 
     FIG. 1 is a diagram of a vapor compression cycle system for refrigeration, air conditioning, or heat pump purposes, embodying the principles of the present invention; 
     FIG. 2 is an enlarged schematic diagram of an electronically controlled expansion valve assembly, according to the present invention, as generally encircled within Line  2  of FIG. 1, and showing the forces acting on the expansion valve assembly during use; and 
     FIG. 3 is a schematic illustration of a mechanical setting, expansion valve assembly coupled to a stepper motor and showing the forces acting on the expansion valve assembly during use. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A vapor compression cycle system  10  is generally shown in FIG.  1 . The vapor compression cycle system  10  principally comprises a compressor  12 , a heat rejecting heat exchanger (gas cooler  14 ), an expansion valve  16 , an evaporating heat exchanger (evaporator  18 ), and an accumulator  20 . These elements are in fluid communication in a closed flow circuit, in which fluid, such as carbon dioxide (CO 2 ) is circulated. 
     Generally, the vapor compression cycle system  10  generally operates as follows. The compressor  12 , of a conventional and well known construction, increases the temperature and pressure of the fluid vapor. Vapor flows out of the compressor  12  through the compressor gas cooler conduit  22  and into the gas cooler  14  (also of a conventional construction), which then cools the fluid, causing the fluid to give off heat to a secondary fluid, such as air. The fluid next flows through an inlet conduit  24 , which has an input sensor  25  measuring the pressure of the fluid into the expansion valve  16 . Alternately, it may not be necessary to measure the high-side pressure. Knowing what electric signal corresponds to what high side pressure, and based on a corresponding control strategy, the appropriate signal is sent to the valve to achieve the desired high side pressure. A control strategy  26  is accordingly adapted to control the high side pressure into the expansion valve  16 . After the fluid exits the gas cooler, it enters the expansion valve  16 , which then throttles the high-pressure fluid such that the fluid in the outlet conduit  28  has a lower pressure than the fluid in the inlet conduit  24 . The fluid flows from the expansion valve  16  to the evaporator  18  through the outlet conduit  28 . The evaporator  18  heats the fluid such that it becomes vapor. Next, the fluid flows though the evaporator-accumulator conduit  30  into the accumulator  20 , which is used as a vapor-liquid separator. The fluid vapor is finally drawn through the accumulator-compressor pipe  32  into the compressor  12 , completing the cycle. 
     As mentioned previously, the working fluid is considered to be at a high side pressure (and therefore generally designated as high pressure fluid  36 ) when it is located between the outlet of the compressor  12  and the inlet of the expansion valve  16 . The working fluid is considered to be at a low side pressure (and therefore generally designated as low pressure fluid  38 ) when it is located between the outlet of the expansion valve  16  and the inlet of the compressor  12 . The vapor compression cycle system  10  operates such that the high side pressure becomes the supercritical pressure of the circulating refrigerant. 
     Referring now to FIG. 2, one embodiment of an electronically controlled expansion valve assembly  34  according to the present invention, generally encircled within Line  2  of FIG. 1, is seen therein. The electronically controlled expansion valve assembly  34  is coupled to the inlet conduit  24 , where the high pressure fluid  36  flows at a high side pressure, and the outlet conduit  28 , where the low pressure fluid  38  flows at a low side pressure. As described before, the maximum COP can be maintained by regulating the high side pressure of the high pressure fluid  36 . 
     The inlet conduit  24  is connected to a chamber  40  defined within the side walls  41  of the valve assembly  34  such that the condenser  14  and the chamber  40  are in fluid communication. A partition  42  valve defines the lower boundary of the chamber  40  and includes a tapered opening  44  defined therein. The opening  44  communicates the chamber  40  to the outlet conduit  28 . The opening  44  is tapered in a preferred embodiment, but it may be provided as a non-tapered or other configuration. The tapered characteristic of the opening  44  allows for a more effective control of the mass flow rate between the chamber  40  and the outlet conduit  28 . Defining the upper boundary of the chamber  40  is a diaphragm  46 . This diaphragm  46  further separates the chamber  40  from an upper chamber  48 . The diaphragm  46  preferably forms a seal between the chamber  40  and the upper chamber  48 , such that fluid cannot communicate between the two chambers. 
     Associated with and located within the upper chamber  48  is a variable-force mechanism  49 . In one preferred embodiment, a solenoid core  50 , acting as part of the variable force mechanism, is fixedly attached to the diaphragm  46 , such that the diaphragm  46  moves in a downward-upward or advanced-retracted motion as the solenoid core  50  moves. Electrical current traveling through a solenoid coil  52  creates a magnetic field that actuates the solenoid core  50 . A spring  54  may further be located between the wall  51  of the upper chamber  48  and the diaphragm  46 . The net force resulting from the spring  54  and, if present, the force from the solenoid due to the electric signal, result in the proper force balance on the diaphragm  46  to maintain the desired high-side pressure. Accordingly, the signal provided to the expansion valve assembly  34  results in the assembly  34  exhibiting a force balance situation where the desired high side pressure is maintained. The signal therefore correlated to the desired high side pressure. 
     An appendage  56  is fixedly attached to the diaphragm  46 , the solenoid core  50 , or both the diaphragm  46  and the solenoid core  50 , at an appendage base  62  such that the appendage  56  moves in a downward-upward motion as the solenoid core  50  and/or diaphragm  46  moves. The position of a distal end  60  of the appendage  56  within the opening  44  controls the mass flow rate through the tapered opening  44  by varying the cross-sectional area between the opening  44  and the end  60  of the appendage stem  56 . A protrusion may be located on the distal end  60  of the appendage  56  in order to mate with the tapered opening  44 . 
     A preferred embodiment also includes a fixed bypass orifice  58  in the partition  42  and/or a minimum closing clearance between the tapered opening  44  and the of the appendage end  60 . The bypass orifice  58  and the minimum closing clearance are designed such that if the desired high side pressure  36  cannot be achieved, the working fluid will still flow through the bypass orifice  58  allowing for continued operation of the system  10 , although perhaps at a reduced capacity or efficiency. 
     FIG. 2 also shows the forces for the illustrated construction acting on the electronically controlled expansion valve assembly  34  during use. Other force balancing construction could also be utilized. The low pressure force  70  on the appendage  56  acts upon the protrusion  60  in an upward direction (“upward” being used in reference to the orientation of the figure and not to mean a required direction referenced to horizontal) such as to create a larger opening between the protrusion  60  or appendage  56  and the tapered opening  44 . The low pressure force  70  on the appendage  56  is approximately calculated by multiplying the cross-sectional area of the protrusion  60  (A P ) or the appendage stem  56  (A S ) by the low side pressure  38  (P L ) in the outlet conduit  28 . The high pressure force  74  on the diaphragm  46  acts upon the diaphragm  46  in an upward direction. The high pressure force  74  on the diaphragm  46  is approximately calculated by multiplying the cross-sectional area of the diaphragm  46  (A D ) by the high side pressure  36  (P H ). 
     The high pressure force  72  on the appendage  56  acts upon the appendage protrusion or the appendage stem in a downward direction (such as to tend to create a smaller opening between the appendage protrusion or stem and the tapered opening  44 ). The high pressure force  72  on the appendage  56  is approximately calculated by multiplying the cross-sectional area of the appendage protrusion (A P ) minus the area of the stem (A S ) by the high side pressure  36  (P H ) in the inlet conduit  24 . A spring force  76  acts upon the diaphragm  46  in either a downward or upward direction, and the spring force  76  is approximately calculated by multiplying the spring constant (k) by the distance that the spring is compressed or extended (x). A solenoid force  78  (F S ) may act upon the diaphragm  46  in either a downward or upward direction, and the solenoid force  78  is preferably controlled by an electrical current running through the solenoid core  50 . The chamber pressure force  80  acts upon the diaphragm  46  in a downward direction, and the chamber pressure force  80  is approximately calculated by multiplying the cross-sectional area of the diaphragm  46  (A d ) by the upper chamber pressure (P C ). 
     Thus, the force balance equation for the electronically controlled expansion valve assembly  34  is approximated as follows: 
     
       
           P   L   *A   S   +P   H   *A   D   =P   C   *A   D   +P   D *( A   P   −A   S )− kx+F   S   +C   Preset   
       
     
     If A D &gt;&gt;A P , then 
     
       
         
           P 
           H 
           *A 
           D 
           =P 
           C 
           *A 
           D 
           −kx+F 
           S 
           +C 
           Preset 
         
       
     
     Due to small changes in the movement of the diaphragm  46 , the spring force  76  remains relatively constant compared to the solenoid force  78 . Thus, A D , P C , and kx are relatively constant, and: 
     
       
         
           P 
           H 
           ∝F 
           S 
         
       
     
     Therefore, in the electronically controlled expansion valve assembly  34  embodied in the present invention, the high side pressure  36  can be substantially controlled by the solenoid force  78 . 
     FIG. 3 is a schematic sketch of another embodiment incorporating the principles of this invention. The mechanical expansion valve assembly  84  controls the high side pressure  86  by adjusting the position of the spring top  98 . The adjusting handle  90  turns the threaded cylinder  92 , which interacts with the threaded opening  94  and moves upward or downward. The spring top  98  is coupled with the threaded cylinder  92  such that the spring top  98  moves upward or downward in unison with the threaded cylinder  92 . As the spring top  98  moves upward or downward, the spring body  104  will compress and/or the spring bottom  100  will move upward or downward. The spring bottom  100  is coupled with the diaphragm  102 , and the appendage  106  is coupled with the diaphragm  102  such that the appendage  106  moves upward or downward as the spring bottom  100  moves upward or downward. The distance between the end  107  of the appendage  106  and the opening  108 , which may be tapered, controls the high side pressure  36 . 
     In order to adjust the handle  90  and accordingly the force balance setting of the assembly  84 , the handle  90  is coupled to, for example, a stepper motor  120 . The stepper motor  120  receives an electric signal s via the control strategy and, based on the signal, changes the position of the end  107  of the appendage  106  thereby creating the desired high side pressure. 
     FIG. 3 also shows the forces acting on the mechanical setting expansion valve assembly  84  during use. The low pressure force on the appendage  110  acts upon the appendage end  107  in an upward direction. The low pressure force on the appendage  110  is approximately calculated by multiplying the cross-sectional area of the appendage protrusion  107  (A P ) by the low side pressure  88  (P L ). The high pressure force on the diaphragm  114  acts upon the diaphragm  102  in an upward direction, and the high pressure force on the diaphragm  114  is approximately calculated by multiplying the cross-sectional area of the diaphragm  102  (A D ) by the high side pressure  86  (P H ). 
     The high pressure force on the appendage  112  acts upon the appendage end  107  in a downward direction. The high pressure force on the appendage  112  is approximately calculated by multiplying the cross-sectional area of the appendage end  107  (A P ) by the high side pressure  86  (P H ). The spring force  116  may act upon the diaphragm  102  in either a downward or upward direction, and the spring force  116  is approximately calculated by multiplying the spring constant (k) by the distance that the spring is compressed or extended (x−x′). The chamber pressure force on the diaphragm  118  acts upon the diaphragm  102  in a downward direction, and the chamber pressure force on the diaphragm  118  is approximately calculated by multiplying the cross-sectional area of the diaphragm  102  (A D ) by the upper chamber  99  pressure (P C ). 
     Thus, the force balance equation for the mechanical setting expansion valve assembly  84  is as follows: 
     
       
           P   L   *A   S   +P   H   *A   D   =P   C   *A   D   +P   D   *A   S   −k ( x−x′ ) +C   Preset   
       
     
     If A D &gt;&gt;A S , then 
     
       
           P   H   *A   D   =P   C   A   D     31  k ( x−x′ ) +C   Preset   
       
     
     The values for A D  and P C  are relatively constant, thus: 
     
       
           P   H ∝( x−x′ ) 
       
     
     One advantage of an electronically controlled expansion valve assembly according to this invention, is that the high-side pressure is directly proportional to or a function of the signal being sent to the valve assembly. Thus, if system parameters change (compressor speed, blower speed, etc.) the signal to the valve will not have to change, and the valve will be self-adjusting. If the system change results in higher than desired pressure, the valve will open to let more flow through until the desired pressure is achieved. If the system change results in a decrease in pressure, the valve will close, restricting flow, until the desired pressure is achieved. In either case, a new electronic signal will not have to be sent to the valve, the corrections are a result of the internal force balance. This will make the control strategy much simpler compared to a typical electronic expansion valve where the actual opening is set and controlled in order to control pressure. 
     The foregoing discussion discloses and describes two preferred embodiments of the invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the scope of the invention as defined in the following claims. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.