Abstract:
A balancing system for different compressors utilizes a counterweight having a common exterior configuration. The mass of the counterweight is optimized for each compressor by changing the size of a recess located in the counterweight. In one embodiment, the recess is an arcuately shaped recess; and in another embodiment, the recess is a plurality of holes.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the balancing of rotary machines. More particularly, the present invention relates to counterweights which are used to balance rotary machines where the counterweight includes a variable sized cavity which is used to optimize the mass of the counterweight. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     A class of machines exists in the art generally known as “scroll” apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc., and many features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a hermetic refrigerant compressor. 
     Generally speaking, a scroll apparatus comprises two spiral scroll wraps of similar configuration, each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced  180  from the other. The apparatus operates by orbiting one scroll member (the “orbiting scroll”) with respect to the other scroll member (the “fixed scroll” or “non-orbiting scroll”) to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation; i.e., the motion is purely curvilinear translation (i.e., no rotation of any line in the body). The fluid pockets carry the fluid to be handled from a first zone in the scroll apparatus where a fluid inlet is provided, to a second zone in the apparatus where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time, there will be at least one pair of sealed pockets; and when there are several pairs of sealed pockets at one, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally in the apparatus, the first zone being located at the outer periphery of the apparatus. 
     Two types of contacts define the fluid pockets formed between the scroll members: axially extending tangential line contacts between the spiral faces or flanks of the wraps caused by radial forces (“flank sealing”), and area contacts caused by axial forces between the plane edge surfaces (the “tips”) of each wrap and the opposite end plate (“tip sealing”). For high efficiency, good sealing must be achieved for both types of contacts. 
     The concept of a scroll-type apparatus has, thus, been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and, hence, are relatively small and lightweight for a given capacity. They are quieter and more vibration-free than many compressors because they do not use large reciprocating parts (e.g., pistons, connecting rods, etc.), and because all fluid flow is in one direction with simultaneous compression in plural opposed pockets, there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relatively low velocity of movement between the scrolls, and an inherent forgiveness to fluid contamination. 
     The orbiting of the one scroll member with respect to the other scroll member creates an imbalance which is typically counteracted using one or more counterweights. When designing new compressors and/or redesigning and modifying existing compressors, it is sometimes necessary to design a new counterweight. The need for a new counterweight is typically required when the mass of the counterweight needs to be optimized for a specific application. Each time a new counterweight of a new mass is required, new molds for the counterweight of the specific mass must be developed. The development of the new molds incurs development time and capital costs associated with the new mold. 
     The present invention provides the art with a counterweight which includes a recess. The size and/or depth of the recess can be varied to vary the mass of the counterweight. Thus, a counterweight having common outer dimensions can be manufactured in various masses by changing the size and/or depth of the recess in the counterweight to meet the required mass for the counterweight. The fact that counterweights having different masses can still maintain common outer dimensions eliminates the need for the tooling on the assembly line which assemble the counterweights to the compressor assembly to be modified and/or changed when different masses of counterweights are used. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a vertical cross-sectional view through the center of a scroll-type refrigeration compressor incorporating the variable mass counterweights in accordance with the present invention; 
         FIG. 2  is a perspective view looking down on the counterweight illustrated in  FIG. 1  and the mold or die used to manufacture the counterweight; 
         FIG. 3  is a perspective view looking up on the counterweight and mold or die illustrated in  FIG. 2 ; 
         FIG. 4  is a view similar to  FIG. 3 , but showing the counterweight having a different mass; 
         FIG. 5  is a perspective view looking up on a counterweight and forming mold or die in accordance with another embodiment of the present invention; 
         FIG. 6  is a perspective view of a mold assembly which produces the counterweight illustrated in  FIGS. 2 and 3 ; and 
         FIG. 7  is a perspective view of a mold assembly which produces the counterweight illustrated in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     The balancing system of the present invention is applicable to any type of rotary apparatus. For exemplary purposes only, the present invention is described in conjunction with a rotary compressor and, in particular, with a scroll-type refrigerant compressor. 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in  FIG. 1  a scroll compressor which incorporates the balancing system in accordance with the present invention which is designated generally by reference numeral  10 . Compressor  10  comprises a generally cylindrical hermetic shell  12  having welded at the upper end thereof a cap  14  and at the lower end thereof a base  16  having a plurality of mounting feet (not shown) integrally formed therewith. Cap  14  is provided with a refrigerant discharge fitting  18  which may have the usual discharge valve therein (not shown). Other major elements affixed to the shell include a transversely extending partition  22 , which is welded about its periphery at the same point that cap  14  is welded to shell  12  a main bearing housing  24  which is suitably secured to shell  12  and a lower bearing housing  26  also having a plurality of radially outwardly extending legs, each of which is also suitably secured to shell  12 . A motor stator  28 , which is generally square in cross-section but with the corners rounded off, is press fitted into shell  12 . The flats between the rounded corners on the stator provide passageways between the stator and shell, which facilitate the return flow of lubricant from the top of the shell to the bottom. 
     A drive shaft or crankshaft  30  having an eccentric crank pin  32  at the upper end thereof is rotatably journaled in a bearing  34  in main bearing housing  24 , and a second bearing  36  in lower bearing housing  26 . Crankshaft  30  has at the lower end a relatively large diameter concentric bore  38  which communicates with a radially outwardly included smaller diameter bore  40  extending upwardly therefrom to the top crankshaft  30 . Disposed within bore  38  is a stirrer  42 . The lower portion of the interior shell  12  defines an oil sump  44  which is filled with lubricating oil to a level slightly above the lower end of a rotor  46 ; and bore  38  acts as a pump to pump lubricating fluid up the crankshaft  30  and into bore  40 , and ultimately to all of the various portions of the compressor which require lubrication. 
     Crankshaft  30  is rotatively driven by an electric motor including stator  28 , windings  48  passing therethrough and rotor  46  press fitted on the crankshaft  30  and having upper and lower counterweights  50  and  52 , respectively. 
     The upper surface of main bearing housing  24  is provided with a flat thrust bearing surface  54  on which is disposed an orbiting scroll member  56  having the usual spiral vane or wrap  58  on the upper surface thereof. Projecting downwardly from the lower surface of orbiting scroll member  56  is a cylindrical hub having a journal bearing  60  therein, and in which is rotatively disposed a drive bushing  62  having an inner bore  64  in which crank pin  32  is drivingly disposed. Crank pin  32  has a flat on one surface which drivingly engages a flat surface (not shown) formed in a portion of bore  64  to provide a radially compliant driving arrangement, such as shown in U.S. Pat. No. 4,877,382, the disclosure of which is hereby incorporated herein by reference. An Oldham coupling  66  is also provided, positioned between orbiting scroll member  56  and main bearing housing  24 , and keyed to orbiting scroll member  56  and a non-orbiting scroll member  68  to prevent rotational movement of orbiting scroll member  56 . Oldham coupling  66  is preferably of the type disclosed in U.S. Pat. No. 5,320,506, the disclosure of which is hereby incorporated herein by reference. 
     Non-orbiting scroll member  68  is also provided, having a wrap  70  positioned in meshing engagement with wrap  58  of orbiting scroll member  56 . Non-orbiting scroll member  68  has a centrally disposed discharge passage  72  which communicates with an upwardly open recess  74  which, in turn, is in fluid communication with a discharge muffler chamber  76  defined by cap  14  and partition  22 . An annular recess  78  is also formed in non-orbiting scroll member  68  within which is disposed a seal assembly  80 . Recesses  74  and  78  and seal assembly  80  cooperate to define axial pressure biasing chambers which receive pressurized fluid being compressed by wraps  58  and  70  so as to exert an axial biasing force on non-orbiting scroll member  68  to thereby urge the tips of respective wraps  58 ,  70  into sealing engagement with the opposed end plate surfaces. Seal assembly  80  is preferably of the type described in greater detail in U.S. Pat. No. 5,156,539, the disclosure of which is hereby incorporated herein by reference. Non-orbiting scroll member  68  is designed to be mounted to main bearing housing  24  in a suitable manner such as disclosed in the aforementioned U.S. Pat. No. 4,877,382 or U.S. Pat. No. 5,102,316, the disclosure of which is hereby incorporated herein by reference. 
     Referring now to  FIGS. 2 and 3 , upper counterweight  50  is illustrated in greater detail. While the present invention is being described in relation to upper counterweight  50 , it is within the scope of the present invention to incorporate the variable mass characteristics of upper counterweight  50  into lower counterweight  52 , if desired. 
     Upper counterweight  50  is stepped and it comprises a semi-circular C-shaped section or main body  90  having circumferentially opposite end faces  92  and a pair of opposite circumferentially extended flange positions  94 , each including an opening  96  which is utilized to secure counterweight  50  to rotor  46 . C-shaped section  90  has an arcuate body portion between end faces  92  which extends circumferentially through an arc of up to, but not exceeding, 180° so as to be disposed entirely on one side of a plane extending along the axis of rotation of rotor  46 . Flange portions  94  extend circumferentially from the juncture of end faces  92  to define an angular extension exceeding 180°. 
     C-shaped section  90  defines a cavity or recess  98  which is utilized to achieve a specified mass for counterweight  50 . Recess  98  extends over a specified arc and it has a specified depth. Both the length of the arc and the depth of the recess can be varied by having different interchangeable cores  100  ( FIG. 6 ), which are inserted into a mold or die  102  ( FIG. 6 ), which is utilized to manufacture counterweight  50 . In addition, one or more ribs  104  can be formed to extend into recess  98  to adjust the mass of counterweight  50  to the specified mass. Counterweight  50 ′ illustrated in  FIG. 4  has an increased mass when compared to the mass of counterweight  50  due to the shorter arc of recess  98 , the shorter depth of recess  98  and the addition of one or more ribs  104 . This is accomplished by having a different core or pin  100 . The exterior configuration of counterweights  50  and  50 ′ are identical, thus allowing both counterweights  50  and  50 ′ to be manufactured in the same mold or die  102  ( FIG. 6 ) with different cores  100  being utilized to define the different sizes of recess  98 . Counterweight  50 ′ would replace counterweight  50  when the operating characteristics of compressor  10  change, with the change in operating characteristics requiring rebalancing of compressor  10 . 
     Referring now to  FIG. 5 , a counterweight  150  is illustrated in accordance with another embodiment of the present invention. Counterweight  150  is the same as counterweight  50 , except that recess  98  has been replaced with a plurality of holes  198 . The plurality of holes  198  are circumferentially spaced along C-shaped section  90  and each of them has a specified depth. Both the number of holes  198  and the depth of each hole  198  can be independently varied by having a core  200  ( FIG. 7 ) having different numbers and lengths of pins  200 , which are inserted into the mold or die  102  ( FIG. 7 ), which is utilized to manufacture counterweights  150 . 
     Thus, counterweights having common outer dimensions can be manufactured in different masses. This feature reduces the costs associated with additional plant capital. Prior art designs of counterweights vary by height and/or diameter thus requiring the assembly tooling for the counterweight to be modified or replaced when different masses of counterweights are used. By communizing the outer dimensions for a plurality of counterweight masses, a single set of assembly equipment can be utilized for all of the plurality of counterweight masses. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.