Abstract:
A floating seal has a lower plate, an upper plate and a pair of seals disposed between the two plates. The lower plate, the upper plate or both plates include a backer which projects outward from the plate to engage one or both of the seals to support the seal during operation.

Description:
FIELD 
     The present invention relates to floating seal designs for the axially movable scroll member of a scroll machine. More particularly, the present invention relates to a unique floating seal design for the axially movable non-orbiting scroll member of the scroll machine. 
     BACKGROUND AND SUMMARY 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     A class of machines exists in the art generally known as “scroll” machines for the displacement of various types of fluids. Such machines may be configured as an expander, a displacement engine, a pump, a compressor, etc., and the 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. 
     Scroll-type apparatus have been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and hence are 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.). All fluid flow is in one direction with simultaneous compression in plural opposed pockets which results in 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. 
     Generally speaking, a scroll machine 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 machine 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 relative rotation between the scroll members is typically prohibited by the use of an Oldham coupling. 
     The moving fluid pockets carry the fluid to be handled from a first zone in the scroll machine where a fluid inlet is provided, to a second zone in the machine 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 where there are several pairs of sealed pockets at one time, 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 machine, the first zone being located at the outer periphery of the machine. 
     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. 
     One of the difficult areas of design in a scroll-type machine concerns the technique used to achieve tip sealing under all operating conditions, and also at all speeds in a variable speed machine. Conventionally, this has been accomplished by (1) using extremely accurate and very expensive machining techniques, (2) providing the wrap tips with spiral tip seals, which, unfortunately, are hard to assemble and often unreliable, or (3) applying an axially restoring force by axial biasing the orbiting scroll or the non-orbiting scroll towards the opposing scroll using compressed working fluid. 
     The utilization of an axial restoring force first requires one of the two scroll members to be mounted for axial movement with respect to the other scroll member. This can be accomplished by securing the non-orbiting scroll member to a main bearing housing by means of a plurality of bolts and a plurality of sleeve guides as disclosed in Assignee&#39;s U.S. Pat. No. 5,407,335, the disclosure of which is hereby incorporated herein by reference. Second, a biasing load needs to be applied to the axially movable non-orbiting scroll to urge the non-orbiting scroll into engagement with the orbiting scroll. This can be accomplished by forming a chamber on the side of the non-orbiting scroll opposite to the orbiting scroll member, placing a floating seal in the chamber and then supplying a pressurized fluid to this chamber. The source of the pressurized fluid can be the scroll compressor itself. This type of biasing system is also disclosed in the aforementioned U.S. Pat. No. 5,407,335. 
     The prior art floating seal is an assembly of two metal plates and one or more polymer seals. The lower plate is an as-cast aluminum part with vertical posts that fit through holes in the upper cast iron plate. The upper plate has a feature incorporated into its top surface that acts as a face seal with a muffler plate whenever the two components are in contact. The polymer seals are located by and held between the two plates. The assembly process for the prior art floating seal involves stacking the pieces together and then plastically deforming the aluminum posts such that the top ends locally spread out over the iron plate to form a rigid attachment. 
     When assembled, the one or more polymer seals are retained by the two plates in a first plane and the sealing interface with the non-orbiting scroll member occurs along a surface of the non-orbiting scroll member that is generally perpendicular to the plane of retention by the two plates. Thus, the one or more polymer seals bend through an approximately ninety-degree angle to achieve their sealing. 
     The present invention provides the art with an improved seal design by providing a backer or backing plate which supports the polymer seal at the point of bending. The additional support provided by the backer significantly reduces the stresses associated with the seal during operation of the compressor and thus significantly improves the durability of the polymer. 
     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. 
    
    
     
       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 of a scroll compressor incorporating a floating seal design in accordance with the present invention; 
         FIG. 2  is an enlarged view of the floating seal illustrated in  FIG. 1 ; 
         FIG. 3  is an enlarged view of circle  3  in  FIG. 2  illustrating a seal in accordance with the present invention; 
         FIG. 4  is a plan view of the floating seal illustrated in  FIGS. 1 and 2 ; and 
         FIG. 5  is an enlarged view of circle  5  in  FIG. 2  illustrating a seal in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     There is illustrated in  FIG. 1  a scroll compressor which incorporates a floating seal arrangement in accordance with the present invention and 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 stationary main bearing housing or body  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 pressfitted into shell  12 . The flats between the rounded corners on the stator provide passageways between the stator and shell, which facilitate the 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 the crankshaft. Disposed within bore  38  is a stirrer  42 . The lower portion of the interior shell  12  is filled with lubricating oil, 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  44  passing therethrough and a rotor  46  pressfitted on the crankshaft  30  and having upper and lower counterweights  48  and  50 , respectively. A counterweight shield  52  may be provided to reduce the work loss caused by counterweight  50  spinning in the oil in the sump. Counterweight shield  52  is more fully disclosed in Assignee&#39;s U.S. Pat. No. 5,064,356 entitled “Counterweight Shield For Scroll Compressor,” the disclosure of which is hereby incorporated herein by reference. 
     The upper surface of main bearing housing  24  is provided with a flat thrust bearing surface on which is disposed an orbiting scroll member  54  having the usual spiral vane or wrap  56  on the upper surface thereof. Projecting downwardly from the lower surface of orbiting scroll member  54  is a cylindrical hub  58  having a journal bearing therein and in which is rotatively disposed a drive bushing  60  having an inner bore  62  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  62  to provide a radially compliant driving arrangement, such as shown in aforementioned Assignee&#39;s U.S. Pat. No. 4,877,382, the disclosure of which is hereby incorporated herein by reference. An Oldham coupling  64  is also provided positioned between and keyed to orbiting scroll member  54  and a non-orbiting scroll member  66  to prevent rotational movement of orbiting scroll member  54 . Oldham coupling  64  is preferably of the type disclosed in the above-referenced U.S. Pat. No. 4,877,382; however, the coupling disclosed in Assignee&#39;s U.S. Pat. No. 5,320,506 entitled “Oldham Coupling For Scroll Compressor”, the disclosure of which is hereby incorporated herein by reference, may be used in place thereof. 
     Non-orbiting scroll member  66  is also provided having a wrap  68  positioned in meshing engagement with wrap  56  of orbiting scroll member  54 . Non-orbiting scroll member  66  has a centrally disposed discharge passage  70  communicating with an upwardly open recess  72  which is in fluid communication with a discharge muffler chamber  74  defined by cap  14  and partition  22  through an opening defined by partition  22 . An annular recess  76  is also formed in non-orbiting scroll member  66  within which is disposed a floating seal assembly  78 . Recesses  72  and  76  and floating seal assembly  78  cooperate to define axial pressure biasing chambers which receive pressurized fluid being compressed by wraps  56  and  68  so as to exert an axial biasing force on non-orbiting scroll member  66  to thereby urge the tips of respective wraps  56 ,  68  into sealing engagement with the opposed end plate surfaces. 
     With reference to  FIGS. 1-3 , floating seal assembly  78  is of a coaxial sandwiched construction and comprises an annular base plate  90  formed out of aluminum or the like. Annular base plate  90  has a laterally extending upper surface  91  having a plurality of equally spaced upstanding annular projections  92  extending therefrom. Disposed on upper surface  91  of base plate  90  is an annular gasket or seal  94  having a plurality of equally spaced holes which receive projections  92 . On top of seal  94  is disposed an annular upper seal plate  96  having a plurality of equally spaced holes receiving projections  92 . Upper annular seal plate  96 , which may be formed of grey cast iron, has a laterally extending lower surface  97  and a laterally extending upper surface  99  including an upwardly projecting planar seal lip  98  disposed about the periphery thereof. The assembly is secured together by swaging the ends of each projection  92  as indicated at  100 . 
     The overall seal assembly therefore provides three distinct seals, namely, an inside diameter seal at  102 , an outside diameter seal at  104  and a top seal at  106 . Seal  102  isolates fluid under intermediate pressure in the bottom of recess  76  from the fluid under discharge pressure in recess  72 . Seal  104  isolates fluid under intermediate pressure in the bottom of recess  76  from fluid at suction pressure within shell  12 . Seal  106  isolates fluid at suction pressure within shell  12  from fluid at discharge pressure across the top of floating seal assembly  78 .  FIG. 1  illustrates a wear ring  108  attached to partition  22  which provides seal  106  between plate  96  and wear ring  108 . In lieu of wear ring  108 , the lower surface of partition  22  can be locally hardened by nitriding, carbo-nitriding or other hardening processes known in the art. 
     The diameter of seal  106  is chosen so that there is a positive upward sealing force on floating seal assembly  78  under normal operating conditions i.e. at normal pressure ratios. Therefore, when excessive pressure ratios are encountered, floating seal assembly  78  will be forced downwardly by discharge pressure, thereby permitting a leak of high side discharge pressure gas directly across the top of floating seal assembly  78  to a zone of low side suction gas. If this leakage is great enough, the resultant loss of flow of motor cooling suction gas (aggravated by the excessive temperature of the leaking discharge gas) will cause a motor protector (not shown) to trip, thereby de-energizing the motor. The width of seal  106  is chosen so that the unit pressure on the seal itself (i.e. between sealing lip  98  and wear ring  108 ) is greater than normally encountered discharge pressure, thus insuring consistent sealing. 
     The wearing of seal  94  has always been an issue which needed to be addressed. The discharge pressure of compressor  10  urges the inner lip seal portion of seal  94  into engagement with non-orbiting scroll member  66  to form the inside diameter seal at  102 . When the inner lip seal portion of seal  94  is left unsupported, the wear of seal  94  increases at the bottom due to creep. 
     Annular base plate  90  includes a first protrusion, such as an upwardly projecting backer  120  extending longitudinally outwardly away from non-orbiting scroll member  66  from upper surface  91  at a radially inner portion of annular base plate  90 . Backer  120  generally supports the side of seal  94  that is opposite to discharge pressure. As shown in  FIG. 3 , backer  120  defines a contoured surface  122  which mates with the bottom of seal  94  to support seal  94  during operation of compressor  10 . While  FIG. 3  illustrates backer  120  as being an annular triangled cross-section backer, other configurations of backer  120  can be used if needed to adequately support seal  94 . 
     The intermediate pressure within recess  76  urges the outer lip seal portion of seal  94  into engagement with non-orbiting scroll member  66  to form the outside diameter seal at  104 . When the outer lip seal portion of seal  94  is left unsupported, the wear of seal  94  may increase. 
     Upper annular seal plate  96  includes a second protrusion, such as a downward projecting backer  130  extending longitudinally inwardly toward non-orbiting scroll member  66  from lower surface  97  at a radially outer portion of upper annular seal plate  96 . Backer  130  generally supports the side of seal  94  that is opposite to intermediate pressure within recess  76 . As shown in  FIG. 5 , backer  130  defines a contoured surface  132  which mates with the top side of seal  94  to support seal  94  during operation of compressor  10 . While  FIG. 5  illustrates backer  130  as being an annular triangled cross-section backer, other configurations of backer  130  can be used to adequately support seal  94 .