Patent Publication Number: US-6709249-B1

Title: Recess on tip of hybrid scroll compressor wrap to compensate for uneven thermal expansion

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the provision of a shallow recess communicating discharge pressure and temperatures back across the width of a thicker portion of a hybrid wrap in a scroll compressor to compensate for the uneven thermal expansion that can occur in hybrid scroll wraps. 
     Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member has a base with a generally spiral wrap extending from the base. A second scroll member has its own base and spiral wrap. The two wraps interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and as the relative orbital movement occurs, the wraps move reducing the size of the compression chambers, thus compressing an entrapped refrigerant. 
     Scroll compressors are becoming widely utilized due to their efficiency, and other beneficial characteristics. Also, a good deal of engineering development is occurring with scroll compressors. As one major advancement, the shape of the wraps has deviated from a spiral. Originally, the scroll wraps were formed generally along an involute of a circle. However, more recently, more complex shapes to the wraps have been developed. While the wraps are still “generally spiral,” they do deviate from an involute of a circle. Various combinations of curves, involutes, etc. are utilized to form a so-called “hybrid” wrap. In a hybrid wrap, the width of the wrap varies along its circumferential dimension. Generally, in a non-hybrid wrap, the width of the wrap is uniform. 
     While hybrid wraps provide a number of benefits, they also raise a few challenges. One challenge is shown in prior art FIGS. 1 and 2. As shown in FIG. 1, a scroll compressor  20  has an orbiting scroll member  22  with a base  24  and a hybrid wrap  26 . The non-orbiting scroll  28  has its own base  32  and wrap  33 . As shown, the wrap  33  has thinner portions  30  and thicker portions  34 . The reasons for, and configuration of, the hybrid wrap are known in the art. However, a problem associated with the wraps having thicker and thinner portions is illustrated in FIGS. 1 and 2. As shown, there is a relatively low pressure and low temperature suction chamber  38  on one side of the thicker wrap portion  34 , and a higher pressure and temperature chamber  40  on the other. The chambers on each side of the thinner portion  30  would also be at distinct pressures and distinct temperatures, however, as explained below, the problem that is to be solved by this invention would not be as pronounced at the thinner portion  30 , simply because it is thinner. 
     As shown in FIG. 1 schematically, there may be thermal expansion such as shown in outline at  36  at the thicker portion  34  due to the temperature imbalance between chambers  38  and  40 . 
     As can be seen in FIG. 2, the higher pressure and higher temperature on the inner side of the thicker portion  34  causes a heat gradient across the width of the thicker portion  34 . The same would be generally true at the thinner portions, however, since the thinner portions are in fact thinner, it is more likely that the temperature gradient will be not as pronounced, and heat would transfer freely across the width of the wrap. At the thicker portion, there is greater heat resistance, and thus a greater likelihood that the heat would not transfer across the entirety of the width  34 , but would instead result in localized thermal expansion. This is the thermal expansion shown schematically and in dotted line at  36  in FIG.  1 . When this type of expansion occurs, undesirable effects such as surface wear or galling between the end of the thicker portion  34  and the opposed base  24  of the orbiting scroll  22  can occur. This is, of course, undesirable. 
     SUMMARY OF THE INVENTION 
     In the disclosed embodiment of this invention, a recess is formed into the face of the thicker portion of the wrap such that localized thermal expansion is partially compensated, but not to the extreme edge such that this refrigerant in the recess is still separated from the suction chamber. In addition, discharge temperature and pressure refrigerant is communicated along the width of the thicker portion. Thus, the recess communicates the higher pressure and temperature refrigerant along the width of the thicker portion such that the heat gradient is only over a thin portion of the wrap, thus reducing the thermal expansion imbalance. 
     In a preferred embodiment, this recess is very shallow, and on the order of 0.0005 inch. Moreover, the recess extends between two circumferential edges, and to an inner edge. The recess preferably communicates with the discharge pressure chamber along the entirety of its circumferential width, to maximize the resistance to a heat transfer gradient. 
     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 
     FIG. 1 is a cross-section through a prior art scroll compressor. 
     FIG. 2 is an end view of one portion of a prior art scroll compressor. 
     FIG. 3 is an end view of an inventive scroll compressor component. 
     FIG. 4 is a cross-sectional view to the inventive scroll compressor component shown in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 3 shows a non-orbiting scroll member  50  incorporating the present invention. As shown, a thicker portion  52  of the wrap is provided with a recess  56 . The thinner portion  54 , and other thinner portions do not receive such a recess. While a single recess is shown, a worker in this art would recognize that more than one recess could be utilized spaced throughout the thicker portions. 
     An inner circumferential extent  58  defines the recess  56  along with an outer circumferential extent  62 . A back wall  64  seals the recess  56  from the suction chamber  38 . The front end  60  of the recess  56  allows flow of refrigerant from chamber  40  throughout the recess  56 . This higher temperature refrigerant will thus serve to reduce any thermal gradient along the thicker width of the thicker portion  52 . The recess itself will partially compensate the thermal expansion at  36  in FIG.  1 . 
     As can be appreciated from FIGS. 3 and 4, the recess is formed in a portion of the wrap  52  which is spaced from a radially inner wrap portion along a line X extending from a discharge port  100 , and through the recess. That is, the recess does not communicate with the discharge port, but instead is spaced radially outwardly of the discharge port when the wraps are engaged. Also as can be seen, line X passes through a thinner wrap portion  102  before reaching recess  56 . 
     While a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in the 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.