Abstract:
A scroll compressor is provided with spaced grooves in a base of one of the two scroll members. A recess is formed in a wrap tip of the other scroll member. The recess in the wrap tip bridges a space between the grooves of the other scroll member. This bridging equalizes pressure between two parallel intermediate compression chambers. Pressure equalization between the chambers improves compressor efficiency.

Description:
RELATED APPLICATIONS 
   The application claims priority to U.S. Provisional Application No. 60/685,854 which was filed on May 31, 2005. 

   BACKGROUND OF THE INVENTION 
   Scroll compressors typically include two interfitting scroll members, each having a base and a generally spiral wrap extending from the base. The two wraps interfit to define a pair of compression chambers in which refrigerant is compressed in a parallel manner. 
   Refrigerant ideally enters the chambers in equal amounts, and the chambers then seal and move toward a compressor discharge. Additional refrigerant can be added to the compression chambers by various options, such as the injection of an economizer fluid or liquid injection. 
   An economizer fluid is returned to the compressor when an economizer cycle is in operation. Essentially, an economizer cycle taps a flow of refrigerant downstream of a heat exchanger which receives a compressed refrigerant from a compressor. The tapped refrigerant is expanded, and passed through an economizer heat exchanger where it cools a main refrigerant flow. This increases the cooling capacity of the main refrigerant flow. The tapped fluid, having passed through the economizer heat exchanger, is returned to the compressor. Typically, the returned fluid is injected into the compression chambers at an intermediate point in the compression cycle. 
   Efforts are made to ensure that the pressure of refrigerant to be compressed in each of the opposed compression chambers is equal. However, in practice, it has been difficult to ensure that the pressure is equal. It becomes particularly difficult to ensure equal pressure when the economizer function is in operation and vapor is being injected into the compression chambers. It is also difficult to assure that pressure remains equal within the compression chambers when liquid injection is used to reduce the compressor discharge temperature. 
   Different pressure in the two intermediate compression chambers leads to additional losses during porting, as the refrigerant streams of different pressure will merge into a common discharge chamber as the refrigerant exits form each of the intermediate compression chambers. This results in additional mixing losses as two streams of different pressure merge together during porting. Having different pressure at each compression chamber during porting also makes it impossible to achieve an optimum built-in volume ratio for a rating point, because at least one parallel compression path during compression will operate at the non-optimum built-in pressure ratio. 
   Historically, scroll compressors had wraps which were of a generally constant thickness. However, with further design development, much study went into the shape of the wraps. The wraps are now often of a varying shape for many different design reasons. These varying shapes have varying thicknesses. Such varying thickness shaped wraps are known as “hybrid” wraps. The problem mentioned above becomes especially acute for a hybrid-type scroll wrap profile, as the injection ports for the economizer fluid have different geometry and sizes for each compression chamber. Having different geometry ports makes it especially difficult to achieve equal pressure in each compression chamber, because depending on the operating condition it would be difficult to inject the same amount of refrigerant into each chamber. 
   It is known in the prior art to have a groove, which connects the two opposed compression chambers in an attempt to equalize pressure between the chambers. An example is illustrated in U.S. Pat. No. 6,171,086. However, this prior art method only communicates the two chambers for a short period of time. 
   SUMMARY OF THE INVENTION 
   A scroll compressor includes a first scroll member and a second scroll member. Each scroll member has a base and a generally spiral wrap extending from the base. One of the two scroll members is caused to orbit relative to a non-orbiting scroll member. As is known, the wraps interfit to define compression chambers. The two compression chambers are reduced in size as the orbiting scroll orbits relative to the non-orbiting scroll. A method of equalizing the pressure in these two compression chambers is disclosed, and provides pressure equalization for a greater period of an orbiting cycle than was the case in the prior art. 
   In a disclosed embodiment of this invention, spaced grooves are formed in the base of one of a first scroll member and a second scroll member. A recess is formed in the wrap tip of the other. During a portion of the orbiting cycle, the recess bridges a space between the grooves as the wrap of the orbiting scroll orbits relative to the non-orbiting scroll. Refrigerant is thus selectively communicated between the first and second compression chambers and pressure in the two can equalize. Due to the recess, this communication will occur over a greater period of time than is the case in the prior art. It should be pointed out that the geometry of the grooves and recess is selected to assure that there is a communication between the two intermediate parallel chambers via the recess. At the same time, the geometry of the grooves and the recess is selected such that there is no or just minimal unwanted communication between the intermediate chambers and discharge chamber to minimize high to low leak. 
   In the disclosed embodiment, the scroll compressor may additionally include an economizer cycle and economizer injection ports extending through the wraps of the non-orbiting scroll member. While particular arrangements and shapes are disclosed, other shapes can be utilized for the grooves and recesses. 
   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 
       FIG. 1  is a cross-sectional view showing a scroll compressor. 
       FIG. 2  is a cross-sectional view showing the scroll members. 
       FIG. 3  shows an orbiting scroll member. 
       FIG. 4  shows a feature of the non-orbiting scroll. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a scroll compressor  18  having a non-orbiting scroll wrap  20  and an orbiting scroll wrap  22 . As can be appreciated, compression chambers are defined between the wraps as will be disclosed below. As shown, the compressor  18  delivers a compressed refrigerant to a condenser  15 . The refrigerant flows from the condenser  15  to an optional tap line  17  which taps the refrigerant from a main flow line. The tapped refrigerant has passed through an optional economizer expansion device  11 , and both the tapped refrigerant and a main refrigerant flow line pass through an optional economizer heat exchanger  16 . While the two flows are shown in the same direction in this figure, this is for illustration simplicity only. In practice, typically, the tapped refrigerant flows in an opposed direction through the economizer heat exchanger  16  from the main refrigerant flow. As shown, the tapped refrigerant passes back through an optional economizer injection line  101  into ports  100  (shown schematically) and back into the compression chambers defined between the orbiting and non-orbiting scroll wraps  22  and  20 . A main expansion device  19  and an evaporator  21  are downstream of the economizer heat exchanger  16 , and refrigerant from the evaporator  21  returns to a suction port in the compressor  18 . 
     FIG. 2  shows scroll compressor  18  having non-orbiting scroll wrap  20  and orbiting scroll wrap  22 . As can be appreciated, parallel compression chambers  24  and  26  are defined by the wraps  20  and  22 . Grooves  28  and  30  are formed in the base of the non-orbiting scroll. As can be appreciated in  FIG. 2 , a recess  32  formed into the wrap  22  of the orbiting scroll connects the grooves  28  and  30  during a portion of the orbiting cycle. When the grooves  28  and  30  are connected by the corresponding recess  32  on the tip of the orbiting scroll wrap, then the pressure in the chambers  24  and  26  can equalize. The use of the recess  32  ensures this equalization will occur for a greater length in the orbiting cycle than is the case in the prior art. 
   As shown in  FIG. 3 , the orbiting scroll  22  has the recess  32 . The recess  32  is shown as a simple, cylindrical recess. However, other shapes may be utilized. 
     FIG. 4  shows the grooves  28  and  30  in the non-orbiting scroll member. As can be appreciated from this figure, one of the grooves  28  is generally circular while the other groove  30  is more elongated. The shape of the grooves is selected such that there is a sufficient amount of time through which the two chambers can communicate. 
   As also shown in  FIG. 2 , optional economizer vapor injection ports  100  are formed through the non-orbiting scroll wrap  20 . As mentioned above, the present invention is particularly valuable in a scroll compressor having the vapor injection. This invention would also be important if a liquid injection is used to reduce the discharge temperature. In this case, for example, the liquid will be tapped from tap  17  and injected into line  101  and then into the intermediate compression chambers. If the liquid injection is used in conjunction with economized vapor injection then the schematic of  FIG. 1  would remain essentially the same. If the liquid injection is used as a stand alone feature then the heat exchanger  16  can be eliminated. It should be pointed out that this invention can also be applied where there is no liquid or vapor injection at all. The optional components mentioned above would then be completely eliminated from the schematic of  FIG. 1 . It also should be pointed out that the liquid injection and vapor injection schematic shown in  FIG. 1  is just an example of how vapor injection or liquid injection can be accomplished. Many other schematics are known in the prior art. Moreover, the wraps as shown in  FIGS. 1-4  are of the “hybrid” variety having a non-uniform cross-section. However this invention would also work where the wraps are generally of uniform thickness. The present invention is particularly valuable for a scroll compressor having both the economizer injection or liquid injection and hybrid wraps. It should also be pointed out that the number of grooves and/or recesses could be increased from what is shown in the Figures to further enhance the pressure balancing between the chambers. The number of injection ports can also vary from what is shown in the Figures. It is possible, for example, to have just one injection port. As known, a single injection port can communicate with one compression chamber or can be in communication with two compression chambers. It is also possible to have two or more injection ports. 
   When there is vapor injection, such as from an economizer circuit, the problem of balancing the pressure becomes particularly acute. Thus, with such a feature included in the compressor, the use of the inventive structure becomes even more valuable. 
   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.