Abstract:
Scroll compressors include a tap for communicating a compressed refrigerant to a back pressure chamber to resist a separating force. A restriction is placed within this tap to slow build-up of the back pressure chamber at start-up. Further, the restriction smoothes out any fluctuations in the back pressure force as the pressure in the compression chamber from which the refrigerant is tapped may fluctuate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a scroll compressor having a restriction in the back pressure chamber tap to provide more control over the operation of the back pressure chamber.  
           [0002]    Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, opposed non-orbiting and orbiting scroll members face each other. Each of the scroll members have a base and a generally spiral wrap extending from the base. The wraps interfit to define compression chambers. The orbiting scroll is caused to orbit relative to the non-orbiting scroll, and compression chambers defined between the wraps are reduced in size to compress an entrapped refrigerant.  
           [0003]    The scroll compressor combination generally includes one of the two members being able to move for a limited axial distance relative to the other. The compression of the refrigerant between the wraps presents a separating force tending to force the two scroll members away from each other. Historically, this separating force has been resisted by tapping a compressed refrigerant to a “back pressure chamber” defined behind the base of one of the two scroll members. The back pressure chamber creates a force forcing the base of the axially movable scroll member toward the other scroll member, thus resisting the separating force.  
           [0004]    While the use of the back pressure chamber does address the separating force issue, there are certain challenges that remain. As one challenge, it may sometimes be desirable to not have the back pressure chamber operable for a period of time at start-up of the compressor. As an example, under certain conditions, it may be difficult to begin movement of the compressor members. In such a situation, it would be desirable to not have the back pressure chamber operable for a short period of time after start-up. In this way, the scroll members are not in contact with each other, and there will be leakage reducing the load on a motor for driving the orbiting scroll for a period of time.  
           [0005]    Another challenge with back pressure chambers is that during operation, there is some fluctuation in the pressure at the point in the compression chambers from which the back pressure chamber refrigerant is tapped. These fluctuations cause fluctuations in the back pressure force, which may result in somewhat non-smooth operation. Furthermore, the fluctuations in pressure also result in high pressure refrigerant flowing from the compression chambers to the back pressure chamber. Since the back pressure chamber is at a lower pressure, this gas gets expanded, then later recompressed when the pressure tap moves to a lower pressure chamber. This recompression results in a power loss. Because the restrictor minimizes the flow of gas, it also minimizes the power loss due to recompression.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention presents a tap for back pressure refrigerant which has a restriction. The restriction provides a dual benefit. First, the restriction resists flow of refrigerant at start-up such that there will be a period of time after start-up before the back pressure chamber is fully operational. This provides a reduction of load at start-up. Further, when fluctuations in pressure occur during operation of the compressor, the restrictions limit the back and forth movement of the refrigerant, thus tending to level out any such fluctuations.  
           [0007]    In one embodiment, a simple slip fit pin is inserted into the passage to provide a restriction. In another embodiment, a pin is provided with a groove. Other embodiments include a dowel with a small orifice, a hollow tube having a ball, a porous member, a screw with a slot in its threads, etc.  
           [0008]    In general, the various restrictions provide the benefit such as mentioned above.  
           [0009]    These and other features of the present invention may be best understood from the following specification and drawings, the following of which is a brief description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a cross-sectional view of a prior art scroll compressor incorporating the present invention.  
         [0011]    [0011]FIG. 2 is a cross-sectional view showing the FIG. 1 embodiment on an enlarged portion.  
         [0012]    [0012]FIG. 2 shows a second embodiment restriction.  
         [0013]    [0013]FIG. 3 shows another restriction embodiment.  
         [0014]    [0014]FIG. 4 shows yet another restriction embodiment.  
         [0015]    [0015]FIG. 5 shows another embodiment.  
         [0016]    [0016]FIG. 6 shows another embodiment.  
         [0017]    [0017]FIG. 7 shows various locations for the restriction.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    A scroll compressor  20  is illustrated in FIG. 1 having an orbiting scroll  22  with wraps  23 . A non-orbiting scroll  24  includes its wraps  25 . As known, the wraps  23  and  25  interfit to define compression chambers. The crankcase  26  supports the orbiting scroll  22 . Seals  28  and  30  define a back pressure chamber  32  rearward of the base of the orbiting scroll  22 . A tap  34  taps refrigerant from an intermediate pressure chamber  36  to the back pressure chamber  32 . This structure is generally as known. In the prior art, these structures had problems such as mentioned above.  
         [0019]    As shown in FIG. 2, a tap  38  communicates the pressure from the chamber  36  to a crossing tap  40  which in turn communicates with the tap  42  extending through the back pressure chamber  32 . A plug  44  is typically positioned to plug the end of the passage  34 . To form the complex passage, holes are generally drilled at  38 ,  42  and  34 . The hole  34  is then plugged by the plug  44 . As shown in this embodiment, a slip fit pin  46  is positioned within the passage  34  to restrict the flow of refrigerant from the tap portion  38  to the tap portion  42 . There is clearance between passage  34  and the outer diameter of pin  46 . During operation, this will cause a slow build-up of the pressure in the back pressure chamber  32  reducing the load on the compressor at start- up. Moreover, fluctuations in the back pressure chamber pressure  32 , as the pressure in the chamber  36  varies, will also be reduced.  
         [0020]    [0020]FIG. 3 shows another embodiment  48  wherein the slip fit pin has a groove  50  to provide a flow passage. By sizing the passage  50 , the present invention allows a designer to achieve an optimum flow restriction.  
         [0021]    [0021]FIG. 4 shows another embodiment  52  wherein a ball  54  is generally movable within the hollow tube. End stops  56  are formed at each end of the tube. Refrigerant can flow through the tube  52 , but is restricted by the ball  54 .  
         [0022]    [0022]FIG. 5 shows another embodiment  58  which is generally a dowel plug having a small restriction orifice  60  at its inner periphery.  
         [0023]    [0023]FIG. 6 shows another embodiment  70  wherein the restriction is formed of a porous material having openings such as schematically shown at  72 . Examples of ways to form the porous materials would be utilizing sintered metal, or other porous “filter” materials.  
         [0024]    [0024]FIG. 7 shows an embodiment  74  formed of a screw, having a thread  76  with a cut passage  78  along the length of the thread. This member could thus be threaded into the opening, ensuring desired positioning. Other types of labyrinth seals may also be utilized for this purpose.  
         [0025]    [0025]FIG. 8 shows embodiments  80  and  82  the restriction is placed in other locations in the passages. Alternatively, several restrictions such as are illustrated in FIG. 8 could be utilized.  
         [0026]    In general, the restriction thus provides a restriction on a portion of the passage  34 , but not the entirety of the passage  34 . This allows the designer to achieve the desired amount of restriction. Moreover, it would be difficult in many applications to form the passage  34  of a very limited size, due to machining challenges. Further, it would be difficult to form various diameters within the passage  34  due to machining challenges. Thus, the provision of a separate plug element or restriction into the passage  34  provides valuable benefits.  
         [0027]    While the proposed invention is shown in the tap for a scroll compressor having its back pressure chamber behind the orbiting scroll, it is also well known in the scroll art to have back pressure chambers behind the non-orbiting scroll. This invention provides benefits as fully apparent to compressors with a back pressure chamber behind the non-orbiting scroll. Thus, the scope of this invention is not limited to scroll compressors wherein the back pressure chamber is defined behind the non-orbiting scroll, but rather extends to scroll compressors wherein the back pressure chamber is also defined behind the non-orbiting scroll.  
         [0028]    Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications 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.