Abstract:
A scroll compressor has its back pressure chamber defined by two seals. The two seals are on different planes. Locating the seals on two distinct planes allows a more direct connection for a tap through a compression chamber and the back pressure chamber. In addition, the volume of the back pressure chamber can be made significantly larger, reducing resistance at start-up of the scroll compressor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a scroll compressor wherein a back pressure chamber is defined by inner and outer seals, with the seals on different planes. The formation of a tap for the back pressure chamber is simplified, and there is also less resistance at startup. 
         [0002]    Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member has a base and a generally spiral wrap extending from the base. A second scroll member has a base and a generally spiral wrap extending from its base. The wraps interfit to define compression chambers, and one of the two scroll members is caused to orbit relative to the other. As the scroll member orbits, the size of the compression chambers decreases and an entrapped refrigerant is compressed. 
         [0003]    Generally, at least one of the two scroll members is allowed to move axially away from the other. As compression occurs a separating force is created which tends to drive the two scroll members apart. To address the separating force, scroll compressor designers have typically provided a “back pressure chamber.” 
         [0004]    A back pressure chamber typically includes a sealed chamber into which compressed refrigerant is tapped. This compressed refrigerant works in opposition to the previously mentioned separating force, causing the two scroll members to be held in contact with each other. 
         [0005]    In the prior art, the back pressure chamber has typically been formed by two radially spaced seals which are mounted in seal recesses in a face of a crankcase. The prior art back pressure chamber has required that a tap from an intermediate compression chamber to the back pressure chamber go through a plurality of drilled holes. This has resulted in some difficulty in machining the tap. 
         [0006]    In addition, due to seal location in a crankcase seal face, and the part geometry (crankcase and orbiting scroll), the prior art back chamber pressure volume is limited to a relatively small volume. Thus, at startup of the compressor, the back pressure chamber fills quickly driving the scroll members into contact, and causing resistance to the orbiting movement from a point relatively soon after startup. This raises challenges under differential pressures for an electric motor that drives the scroll member to orbit. 
       SUMMARY OF THE INVENTION 
       [0007]    In the disclosed embodiment of this invention, one of the two seals for defining the back pressure chamber is at a surface which is spaced away from the plane which receives the other seal. In this manner, the seals may be spaced radially further from each other such that a more direct path from the compression chamber to the back pressure chamber can be utilized, and a simple drilled hole can provide the tap. 
         [0008]    Further, the radially innermost of the seals can be spaced axially from the radially outermost of the seals to define a relatively large volume back pressure chamber. Thus, it will take a relatively longer time for the back pressure chamber to fill, and for the scroll members to be brought in contact with each other at startup. In this manner, resistance to movement of the scroll member at startup is significantly reduced. This new arrangement also provides greater flexibility to tailor back chamber volume for optimized starting versus compression ramp-up. 
         [0009]    The seals may be in the crankcase or in the orbital scroll. 
         [0010]    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 
         [0011]      FIG. 1  shows a prior art scroll compressor. 
           [0012]      FIG. 1B  shows a detail of the prior art. 
           [0013]      FIG. 2  shows the inventive scroll compressor. 
           [0014]      FIG. 3  shows a second embodiment. 
           [0015]      FIG. 4  shows a third embodiment. 
           [0016]      FIG. 5  shows a fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    A prior art scroll compressor  20  is illustrated in  FIG. 1 . As known, a crankcase  22  is fixed to a non-orbiting scroll member  24 . Non-orbiting scroll member  24  has a base  26  and a generally spiral wrap  28  extending from its base. An orbiting scroll member  29  has a base  30  and a generally spiral wrap  32  extending from its base. The orbiting scroll member  29  is supported on the crankcase  22 . The wraps of the orbiting scroll and non-orbiting scroll interfit to define compression chambers such as  42 . A boss  44  extends rearwardly away from the base  30  and receives a driveshaft  46  through an intermediate slider block  48 . As known, the orbiting scroll member is caused to orbit relative to the non-orbiting scroll member. As this occurs, the size of the compression chambers  42  is decreased to compress an entrapped refrigerant. 
         [0018]    A separating force is created in the compression chambers as the refrigerant is compressed. To address this separating force, a back pressure chamber  34  is provided. A radially outer seal  36  and a radially inner seal  38  are mounted within recesses in a face of the crankcase  22 . Refrigerant is tapped through a tap  40  from an intermediate pressure compression chamber  42 . As shown in  FIG. 1B , the tap  40  typically includes three sub portions  40 A,  40 B and  40 C. This is necessary since a compression chamber of significantly high pressure tends to be more radially centered, and the crankcase face which receives the innermost seal is not sufficiently centered. Typically, the crossing path  40 B must be drilled from an outer surface of the orbiting scroll and then plugged. The creation of this three-part path is somewhat complex. 
         [0019]    In addition, as can be appreciated, the back pressure chamber  34  is very small in volume. At startup, refrigerant sufficient to fill the back pressure chamber  34  is quickly directed through the tap  40  increasing the back chamber pressure and pushing the orbiting scroll member  29  into contact with the non-orbiting scroll  24 . At this point, the motor  100  rotating the driveshaft  46  is still starting up, and it is somewhat difficult for it to overcome the compressive resistance. Therefore, a relatively high torque exists to begin compressing refrigerant. This situation is worst when discharge pressure is significantly higher than suction pressure. 
         [0020]      FIG. 2  shows a scroll compressor  50  which is modified to address the concerns mentioned above. Scroll compressor  50  modifies the boss  52  such that it has an outwardly extending flange  54 . Flange  54  defines an enlarged chamber  56  between a lower surface  60  of the crankcase  22  and an upper surface  62 . Lower surface  60  receives a seal  58 , while upper surface  62  receives a seal  64 . In this manner, the radially inner seal  58  may be positioned more radially inwardly than in the prior art. Thus, the tap  66  can extend directly through the base of the orbiting scroll member. Forming the tap  66  is much simpler than forming the tap  40 . In addition, the volume of the chamber  56  is much larger than the volume of the prior art back pressure chamber  34 . A longer period of time is required after startup for the back pressure chamber  56  to pressurize and push the orbiting scroll member  51  into contact with the non-orbiting scroll member  24 . The volume that controls this start-up torque can be adjusted by several methods, including, as an example, thickening of flange  54  or boss  52  or adding additional boss to upper surface  62 . Thus, the start-up torque resistance on the motor is reduced until the motor is rotating at a significantly higher speed. 
         [0021]    An embodiment  150  is shown in  FIG. 3 , wherein the radially inner seal  156  is in the hub  154  of the orbiting scroll  152 . The radially outer seal  64  remains in the crankcase. Of course, the two seal locations could be reversed, with the radially outer seal in the orbiting scroll and the radially inner seal in the crankcase. 
         [0022]      FIG. 4  shows another embodiment  250  wherein the orbiting scroll  252  has the hub  254  receiving the radially inner seal  258 . The base of the orbiting scroll  252  receives the radially outer seal  256 . 
         [0023]      FIG. 5  shows another embodiment  300  wherein the orbiting scroll  302  includes a hub  305  with a separate member  308  that contacts the radially inner seal  306 . The radially outer seal  304  sits in the crankcase in this embodiment. In this embodiment, the formation of the orbiting scroll is simplified in that the hub need not have the radially outwardly extending lowermost portion, but can instead receive a separate component to provide that function. 
         [0024]    Although a preferred 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.