Conical hub bearing for scroll machine

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.

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.

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'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'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.