Abstract:
A poppet valve has a valve pin movable relative to a bore, and with a curved outside shape. A flow cross-sectional area across the poppet valve is defined between an outer diameter of the curved outside shape, and an inner diameter of the bore. Further, a vapor cycle incorporating such a poppet valve is disclosed and claimed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a poppet valve wherein a flow cross-sectional area varies linearly with movement of the valve. 
         [0002]    Valves are utilized in any number of applications. In one particular application, valves are utilized as an expansion device in a refrigerant cycle, such as a vapor cycle. Essentially, a fluid is compressed, then passed through a first heat exchanger. Fluid downstream of this heat exchanger passes through an expansion device at which the fluid flow is restricted such that the fluid expands across the restriction. This expanded fluid then passes through another heat exchanger before returning to the compressor. 
         [0003]    Some expansion device valves have used poppet valves having a conical valve pin movable relative to a valve seat. As the conical valve pin moves, a flow cross-sectional area changes. The flow cross-sectional area is defined by the valve pin outer diameter, and a valve seat orifice inner diameter. As a conical valve pin strokes, the inner radius varies linearly. However, because the area of a circle is a function of the radius squared, the area does not vary linearly with linear valve poppet movement. 
         [0004]    Controls for the position of a conical pin must be programmed to achieve a desired flow cross-sectional area with the ability to calculate the constantly varying movement. This requires precise, complex positioning of the valve pin. 
       SUMMARY OF THE INVENTION 
       [0005]    A poppet valve has a valve pin movable relative to a bore, and with a curved outside shape. A flow cross-sectional area across the poppet valve is defined between an outer diameter of the curved outside shape, and an inner diameter of the bore. 
         [0006]    Further, a vapor cycle incorporating such a poppet valve is disclosed and claimed. 
         [0007]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  schematically shows a vapor cycle incorporating an inventive valve. 
           [0009]      FIG. 2  shows the valve in a closed position. 
           [0010]      FIG. 3  shows the valve in a mid-stroke position. 
           [0011]      FIG. 4  shows the valve in an open position. 
           [0012]      FIG. 5  shows the linear changing of an effective valve flow area with valve positioning. 
           [0013]      FIG. 6  shows how the shape of the valve pin may be calculated to achieve desired flow characteristics. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    A vapor cycle  20  is illustrated in  FIG. 1 . An expansion device is provided by a poppet valve  22  having a rotary step motor  24 . The rotary step motor  24  drives a shaft  26 . Shaft  26  is received within a valve pin  28 . Valve pin  28  is constrained from rotation by a finger  32 , and is thus caused to move linearly upon rotation of the shaft  26 . The detail for achieving this rotary to linear transmission may be as known in the art. Essentially, the shaft  26  may be received within a bore  30  in the valve pin  28 . The valve pin  28  includes a head  34  which has an outer parabolic shape. The head area  34  moves within a bore  52  in a valve seat  35 . Fluid may enter the expansion device  22  from an inlet  38 , pass across a restriction defined between the head  34  and the bore  52  of the valve seat  35 , and then pass to an outlet  36 . The fluid is expanded while crossing this restricted area. 
         [0015]    As shown, the vapor cycle  20  may include a compressor  44  delivering a compressed refrigerant to a first heat exchanger  42 . Downstream of the heat exchanger  42 , the refrigerant passes through the poppet valve  22 , the inlet  38 , to the outlet  36 , and to a second heat exchanger  40 . Downstream of the second heat exchanger  40 , the refrigerant returns to the compressor  44 . While a simple vapor cycle having two heat exchangers is shown, in practice, many more heat exchangers and other refrigerant system components could be included into the system. 
         [0016]      FIG. 2  shows the poppet valve  22  in a closed position at which there is no flow cross-sectional area. In the  FIG. 2  position, the head  34  of the valve pin  28  sits fully in the valve seat  35 , blocking flow through the bore  52 . 
         [0017]      FIG. 3  shows the poppet valve  22  in a mid-stroke position at which there is a limited flow cross-sectional area, and thus restriction as the fluid crosses between the outer diameter of the head  34 , and the inner diameter of bore  52 . As shown, the parabolic shape  50  of the valve pin  28  defines a changing cross-sectional area. The cross-sectional area is defined at the smallest area, and thus typically at the upper surface of the valve seat  35  as shown in this position. 
         [0018]      FIG. 4  shows the poppet valve  22  generally open, and not restricting fluid flow. In the  FIG. 4  position, the valve pin  28  is retracted from the valve seat  35 , and generally has little or no restriction on the flow of fluid through the bore  52 . 
         [0019]      FIG. 5  is a graph showing the change in the effective flow area with changing valve position. As shown, this change is generally linear due to the parabolic outer shape of the valve pin  28 . 
         [0020]      FIG. 6  shows the outer periphery of the head  34 , and the inner bore  52  in the valve seat  35 . As shown, an orifice diameter D of the orifice  52  can be defined, and a valve stroke S is also defined. 
         [0021]    The desired shape for the parabolic curve  50  is defined by the standard parabolic equation form: 
         [0000]        y=ax   2   ⇄bx+c   Equation 1
       c=valve stroke   b=shifts along x axis   b=0   a affects the “width” of parabola       
 
         [0026]    To determine “a”: 
         [0000]      bx=0 as b=0 
         [0000]    
       
      
       y=ax 
       2 
       +bx+c  
      
     
         [0000]      0= ax   2 +(−valve stroke)
 
         [0000]      0= a (½ orifice Dia) 2 +(−valve stroke)
 
         [0000]        a (½ orifice Dia) 2 =(valve stroke)  Equation 2
 
         [0000]    
       
         
           
             a 
             = 
             
               
                 ( 
                 
                   valve 
                    
                   
                       
                   
                    
                   stroke 
                 
                 ) 
               
               
                 
                   ( 
                   
                     
                       1 
                       / 
                       2 
                     
                      
                     
                         
                     
                      
                     orifice 
                      
                     
                         
                     
                      
                     Dia 
                   
                   ) 
                 
                 2 
               
             
           
         
       
       
         
           
             y 
             = 
             
               
                 
                   
                     ( 
                     
                       valve 
                        
                       
                           
                       
                        
                       stroke 
                     
                     ) 
                   
                   
                     
                       ( 
                       
                         
                           1 
                           / 
                           2 
                         
                          
                         
                             
                         
                          
                         orifice 
                          
                         
                             
                         
                          
                         Dia 
                       
                       ) 
                     
                     2 
                   
                 
                  
                 
                   x 
                   2 
                 
               
               + 
               
                 ( 
                 
                   
                     - 
                     valve 
                   
                    
                   
                       
                   
                    
                   stroke 
                 
                 ) 
               
             
           
         
       
     
         [0027]    With the above calculations, one can define a desired parabolic shape for a valve pin that is particularly useful in a poppet valve such that a linear change in cross-sectional area can be achieved. In this manner, very simple drive transmissions can be utilized to achieve a desired flow cross-sectional area as necessary for a refrigerant circuit, or for some other application. In the prior art, since the flow cross-sectional area did not change linearly, one needed a more complex drive arrangement, as a simple step motor would not necessarily be able to easily provide a desired location. 
         [0028]    While a parabolic shape is described in the preferred embodiments, the invention would extend to a valve pin having a head with a curved outer surface such that the flow cross-sectional area changed would be approximately linear, or closer to linear than the conical prior art valve pin heads. 
         [0029]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.