Abstract:
A scroll compressor has an orbiting scroll which has an end plate with a hub extending generally perpendicular from the end plate. The hub defines a bore within which a bearing is press fit. The machining of the bore in the hub is done in a conical manner to accommodate and compensate for the unequal distortion of the hub between the two ends of the hub. The conical shape and the unequal distortion provide an assembled bearing with a more cylindrically shaped inner surface.

Description:
FIELD OF THE INVENTION 
     The present invention relates to scroll machines. More particularly, the present invention relates to scroll compressors having a conical shaped bore in the hub into which the bearing is pressed. After insertion of the bearing, the conical shape of the bore in conjunction with the variation in distortion of the hub provides a straight bearing for the compressor. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Scroll type machines are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes. 
     Generally, the motor includes a stator which is secured to the shell of the compressor. The motor rotor rotates within the stator to impart rotation to a crankshaft which is normally press fit within the motor rotor. The crankshaft is rotationally supported by a pair of bearings which are supported by an upper bearing housing and a lower bearing housing. The crankshaft includes an eccentric crank pin which extends into a bore defined in a hub of the orbiting scroll. Disposed between the hub of the crank pin and the inner surface of the bore is a drive bushing which rides against a bearing that is press fit within the bore of the hub. 
     The hub of the orbiting scroll extends perpendicularly from a base plate of the orbiting scroll. The bore in the hub extends from the open end of the hub to a position generally adjacent the base plate of the orbiting scroll. Thus, the bore in the hub is a blind bore with the open end being positioned at the distal end of the hub and the closed end being positioned at the base plate of the orbiting scroll. During the manufacture of the orbiting scroll, the bore in the hub is machined and the bearing is press fit within the machined bore. Because of the press fit relationship of the bearing and the bore, both the scroll hub and the bearing will deflect during the assembly of the bearing. The total amount of deflection will be determined by the overall stiffness of the hub. The deflection of the hub at the open end of the bore will be greater than the deflection of the hub at the closed end of the bore. The main reason for this unequal deflection is because the hub at the open end of the bore is unsupported while the hub at the closed end of the bore is supported by the end plate. The unequal deflection will result in an assembled bearing having a greater diameter at the open end than at the closed end. This tapered bearing will adversely affect the long term performance of the bearing life and thus the scroll machine. 
     The present invention presents a solution to the tapered bearing problem by providing a conical bearing bore prior to the installation of the bearing. The conical shape of the bearing bore provides a smaller diameter at the open end and a larger diameter at the closed end. After assembly of the bearing the unequal deflection of the scroll hub will provide an assembled bearing that is more cylindrical than the prior art systems. Thus, the more cylindrical shape will perform longer thus increasing the long term durability of both the bearing and the compressor. The more cylindrical shape increases the durability by providing a uniform clearance between the bearing and the bushing. The uniform clearance increases the load capacity of the bearing due to more uniform pressures being exerted on the bearing. Other advantages include a more uniform press load is required to assemble the bearing and this uniform press load provides a better indication of the holding pressure of the assembly. In addition, the system of the present invention is less sensitive to the dimensional variations of the individual components and this will therefore allow some broadening of the tolerances of the individual dimensions. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 is a vertical cross-sectional view through the center of a scroll type refrigeration compressor incorporating the conical hub bearing in accordance with the present invention; 
     FIG. 2 is an enlarged cross-sectional view of the orbiting scroll hub and bearing of the compressor shown in FIG. 1; 
     FIG. 3 is an enlarged cross-sectional view of the orbiting scroll hub shown in FIGS. 1 and 2 prior to assembly of the bearing illustrating the conical hub bore according to the present invention; 
     FIG. 4 is an enlarged cross-sectional view similar to FIG. 3 but illustrating a conical hub bore in accordance with another embodiment of the present invention; and 
     FIG. 5 is an enlarged cross-sectional view similar to FIG. 3 but illustrating a conical hub bore in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 a compensation 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  by a plurality of radially outwardly extending legs 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 or hexagonal in cross-section but with the corners rounded off is press fitted into shell  12 . The flats between the rounded corners on stator  28  provide passageways between stator  28  and shell  12 , 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 inclined smaller diameter bore  40  extending upwardly therefrom to the top of 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 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  extending upward from an end plate  60 . Projecting downwardly from the lower surface of end plate  60  of orbiting scroll member  56  is a cylindrical hub having a journal bearing  62  therein and in which is rotatively disposed a drive bushing  64  having an inner bore  66  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  66  to provide a radially compliant driving arrangement, such as shown in assignee&#39;s U.S. Pat. No. 4,877,382, the disclosure of which is hereby incorporated herein by reference. An Oldham coupling  68  is also provided positioned between orbiting scroll member  56  and bearing housing  24  and keyed to orbiting scroll member  56  and a non-orbiting scroll member  70  to prevent rotational movement of orbiting scroll member  56 . Oldham coupling  68  is preferably of the type disclosed in assignee&#39;s co-pending U.S. Pat. No. 5,320,506, the disclosure of which is hereby incorporated herein by reference. 
     Non-orbiting scroll member  70  is also provided having a wrap  72  extending downwardly from an end plate  74  which is positioned in meshing engagement with wrap  58  of orbiting scroll member  56 . Non-orbiting scroll member  70  has a centrally disposed discharge passage  76  which communicates with an upwardly open recess  78  which in turn is in fluid communication with a discharge muffler chamber  80  defined by cap  14  and partition  22 . An annular recess  82  is also formed in non-orbiting scroll member  70  within which is disposed a seal assembly  84 . Recesses  78  and  82  and seal assembly  84  cooperate to define axial pressure biasing chambers which receive pressurized fluid being compressed by wraps  58  and  72  so as to exert an axial biasing force on non-orbiting scroll member  70  to thereby urge the tips of respective wraps  58 ,  72  into sealing engagement with the opposed end plate surfaces of end plates  74  and  60 , respectively. Seal assembly  84  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  70  is designed to be mounted to 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, the hub of orbiting scroll member  56  includes annular wall  90  which extends generally perpendicularly from end plate  60 . Annular wall  90  defines an internal bore  92  within which bearing  62  is located. The manufacturing process for orbiting scroll member  56  includes the machining of bore  92  and the assembly of bearing  62  within bore  92 . The dimensions for bore  92  and the dimensions for bearing  62  are chosen such that an interference fit occurs between the outside diameter of bearing  62  and the inside diameter of bore  92 . Typically, the amount of interference designed into the assembly is 0.003 inches when scroll member  56  and bearing  62  are manufactured from steel. Of course the amount of interference will change when scroll member  56  is made from a different material. These dimensions are typical for a bore diameter of approximately 30 mm for bore  92 . 
     During the assembly of bearing  62  within bore  92  both annular wall  90  and bearing  62  will deflect due to the interference fit. Typically, a steel or cast iron scroll member  56  will see annular wall  90  deflecting outward approximately 40% of the interference and bearing  62  will deflect inward approximately 60% of the interference. The relationship between the amount of deflection will change when scroll member  56  is manufactured from a different material. 
     Referring to FIG. 3, bore  92  is illustrated. Bore  92  includes a first diameter  96  at its open end and a second diameter  98  at its closed end. The shape of bore  92  between diameters  96  and  98  is a straight line relationship and diameter  96  is smaller than diameter  98 . Preferably, the difference between diameter  96  and diameter  98  is between 0.0010 inches and 0.0012 inches. 
     Referring to FIG. 4, a bore  92 ′ is illustrated. Bore  92 ′ includes a first diameter  96 ′ at its open end and a second diameter  98 ′ at its closed end. The shape of bore  92 ′ between diameters  96 ′ and  98 ′ is defined by diameter  96 ′ extending towards diameter  98 ′ for a specified distance and then a straight line relationship as shown in a solid line or a curved relationship as shown in a dashed line between diameter  96 ′ and  98 ′. Diameter  96 ′ is smaller than diameter  98 ′. Preferably the difference between diameter  96 ′ and diameter  98 ′ is between 0.0006 inches and 0.0012 inches with diameter  96 ′ extending for approximately 60% of the length between the free end and the closed end of bore  92 ′. 
     Referring now to FIG. 5, bore  92 ″ is illustrated. Bore  92 ″ includes a first diameter  96 ″ at its open end and a second diameter  98 ″ at its closed end. The shape of bore  92 ″ between diameters  96 ″ and  98 ″ is a curved line or an arcuate surface and diameter  96 ″ is smaller than diameter  98 ′. Preferably, the difference between diameter  96 ″ and  98 ″ is between 0.0006 inches and 0.0010 inches. 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.