Abstract:
A compressor may include non-orbiting scroll, an orbiting scroll, and a bearing housing. The non-orbiting scroll may include a recess. The orbiting scroll may be intermeshed with the non-orbiting scroll to from a plurality of compression pockets therebetween. The orbiting scroll may include first and second apertures. The first aperture may communicate with one of the compression pockets. The second aperture may communicate with the recess. The bearing housing may support the orbiting scroll and cooperate with the orbiting scroll to define a chamber therebetween. The chamber may communicate with the first and second apertures.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/528,285 filed on Jun. 20, 2012, which is a continuation of U.S. patent application Ser. No. 12/938,848 filed on Nov. 3, 2010, now U.S. Pat. No. 8,226,387, which is a continuation of U.S. patent application Ser. No. 12/420,519 filed on Apr. 8, 2009, now U.S. Pat. No. 7,837,452, which is a continuation of U.S. patent application Ser. No. 11/259,237 filed on Oct. 26, 2005, now abandoned. The disclosure of each of the above applications is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure is directed toward a scroll compressor. 
     BACKGROUND AND SUMMARY 
     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. 
     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 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. 
     A compressor may include a shell assembly, a first scroll member located within the shell assembly and including a first end plate and a first spiral wrap extending from the first end plate, and a second scroll member located within the shell assembly, supported for orbital movement relative to the first scroll member and including a second end plate and a second spiral wrap extending from the second end plate and meshingly engaged with the first spiral wrap to form compression pockets. The first scroll member may define a fluid injection port and the second scroll member may define a passage in communication with the fluid injection port and at least one of the compression pockets to provide pressurized vapor from the fluid injection port to the at least one of the compression pockets. 
     The compressor may additionally include a drive shaft engaged with the second scroll member and the fluid injection port may extend through the first end plate and the passage may extend through the second end plate and may be intermittently in communication with the fluid injection port. Initial communication between the fluid injection port and the passage may occur just after an outermost one of the compression pockets is formed by being sealed off from a suction pressure region of the shell assembly. Communication between the fluid injection port and the passage may be terminated after ninety degrees of rotation of the drive shaft after the initial communication between the fluid injection port and the passage occurs. Communication between the fluid injection port and the passage may be terminated after ninety degrees of rotation of the drive shaft after an outermost one of the compression pockets is formed by being sealed off from a suction pressure region of the shell assembly. The first scroll member may be axially fixed relative to the shell assembly and the second scroll member may be axially displaceable relative to the shell assembly and the first scroll member. 
     The passage may include a first axial passage extending partially through the second end plate and in communication with the fluid injection port, a radial passage extending from the first axial passage through the second end plate and a second axial passage extending from the radial passage and in communication with the at least one of the compression pockets. The compressor may include a third axial passage extending from the radial passage and in communication with another one of the compression pockets. 
     The compressor may additionally include a vapor injection system having a pressurized vapor source in communication with the fluid injection port. The shell assembly may include an end cap and the vapor injection system may include a fluid line extending through the end cap and providing the pressurized vapor source to the fluid injection port. The compressor may include a drive shaft engaged with the second scroll member and the fluid injection port may extend through the first end plate and the passage may extend through the second end plate and may be intermittently in communication with the fluid injection port. Initial communication between the fluid injection port and the passage may occur just after an outermost one of the compression pockets is formed by being sealed off from a suction pressure region of the shell assembly. Communication between the fluid injection port and the passage may be terminated after ninety degrees of rotation of the drive shaft after the initial communication between the fluid injection port and the passage occurs. Communication between the fluid injection port and the passage may be terminated after ninety degrees of rotation of the drive shaft after an outermost one of the compression pockets is formed by being sealed off from a suction pressure region of the shell assembly. The first scroll member may be axially fixed relative to the shell assembly and the second scroll member may be axially displaceable relative to the shell assembly and the first scroll member. 
     In another form, the present disclosure provides a compressor that includes a non-orbiting scroll, an orbiting scroll, and a bearing housing. The non-orbiting scroll may include a recess. The orbiting scroll may be intermeshed with the non-orbiting scroll to from a plurality of compression pockets therebetween. The orbiting scroll may include first and second apertures. The first aperture may communicate with one of the compression pockets. The second aperture may communicate with the recess. The bearing housing may support the orbiting scroll and cooperate with the orbiting scroll to define a chamber therebetween. The chamber may communicate with the first and second apertures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a vertical cross section of a scroll compressor in accordance with the present teachings; 
         FIG. 2  is an enlarged view of the scroll members of the scroll compressor illustrated in  FIG. 1  showing the biasing system; 
         FIG. 3 a    is an enlarged view of the biasing system illustrated in  FIG. 1 ; 
         FIG. 3 b    is an enlarged view of a biasing system in accordance with another embodiment of the present invention; 
         FIGS. 4 a -4 c    are plan views of the scroll members and the biasing system illustrated in  FIG. 3   a;    
         FIG. 5  is an enlarged view of the scroll members of the scroll compressor illustrated in  FIG. 1  showing the pressurization port; 
         FIG. 6  is an enlarged view of the scroll members of the scroll compressor illustrated in  FIG. 1  showing an optional vapor injection system; 
         FIGS. 7 a -7 c    are plan views of the scroll members and the vapor injection system illustrated in  FIG. 6 ; 
         FIG. 8  is an enlarged view of the scroll members of the scroll compressor illustrated in  FIG. 1  showing an optional high pressure oil biasing system; 
         FIG. 9  is a side cross-sectional view of an oil pressure regulator used for the optional oil pressure biasing system for the compressor illustrated in  FIG. 8 ; 
         FIG. 10  is an enlarged view of the scroll member of a scroll compressor in accordance with another embodiment of the present invention; 
         FIG. 11 a    is a plan view of a force diagram for the orbiting scroll member of the present invention; 
         FIG. 11 b    is a side view force diagram for the orbiting scroll member taken along the radial axis; 
         FIG. 11 c    is a side view force diagram for the orbiting scroll member taken along the tangential axis; 
         FIG. 12  is a plan view illustrating the trajectory of the forces on the orbiting scroll member illustrated in  FIG. 10 ; 
         FIG. 13  is a side cross-sectional view of the orbiting scroll member illustrated in  FIG. 10 ; 
         FIG. 14  is a plan view of the orbiting scroll member illustrated in  FIG. 10 ; 
         FIG. 15  is a side cross-sectional view of the non-orbiting scroll member illustrated in  FIG. 10 ; 
         FIG. 16  is a plan view of the non-orbiting scroll member illustrated in  FIG. 10 ; 
         FIG. 17  is a side cross-sectional view of the main bearing housing illustrated in  FIG. 10 ; 
         FIG. 18  is a plan view of the main bearing housing illustrated in  FIG. 10 ; 
         FIGS. 19 a -19 d    illustrate the relationship between the passages, the recesses and the sealing lip for the scroll compressor illustrated in  FIG. 10 ; 
         FIG. 20  illustrates the relationship between the pressure within the recesses during orbiting of the orbiting scroll member; 
         FIG. 21  illustrates a side cross-sectional view of an orbiting scroll member in accordance with another embodiment of the present invention; 
         FIG. 22  illustrates a plan view showing an orientation of the recesses of the non-orbiting scroll member in accordance with another embodiment of the present disclosure; 
         FIG. 23  illustrates a side view cross-section of a scroll compressor in accordance with another embodiment of the present disclosure; and 
         FIG. 24  is a plan view, partially in cross-section showing the oil pressure ports illustrated in  FIG. 23 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     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 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 plurality of mounting feet  16 . Cap  14  is provided with a refrigerant discharge fitting  18 . Other major elements affixed to shell  12  include a lower bearing housing  24  that is suitably secured to shell  12  and a two piece upper bearing housing  26  suitably secured to lower bearing housing  24 . 
     A drive shaft or crankshaft  28  having an eccentric crank pin  30  at the upper end thereof is rotatably journaled in a bearing  32  in lower bearing housing  24  and a second bearing  34  in upper bearing housing  26 . Crankshaft  28  has at the lower end a relatively large diameter concentric bore  36  that communicates with a radially outwardly inclined smaller diameter bore  38  extending upwardly therefrom to the top of crankshaft  28 . The lower portion of the interior shell  12  defines an oil sump  40  that is filled with lubricating oil to a level slightly above the lower end of a rotor  42 , and bore  36  acts as a pump to pump lubricating fluid up crankshaft  28  and into bore  38  and ultimately to all of the various portions of the compressor that require lubrication. 
     Crankshaft  28  is rotatively driven by an electric motor including a stator  46 , windings  48  passing therethrough and rotor  42  press fitted on crankshaft  28  and having upper and lower counterweights  50  and  52 , respectively. 
     The upper surface of upper bearing housing  26  is provided with an annular recess  54  above 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 journaled bearing  62  therein and in which is rotatively disposed a drive bushing  64  having an inner bore in which crank pin  30  is drivingly disposed. Crank pin  30  has a flat on one surface that drivingly engages a flat surface (not shown) formed in a portion of the bore 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 upper bearing housing  26  and keyed to orbiting scroll member  56  and upper bearing housing  26  to prevent rotational movement of orbiting scroll member  56 . 
     A non-orbiting scroll member  70  is also provided having a scroll wrap  72  extending downwardly from an end plate  74  that 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  that communicates with discharge fitting  18  which extends through end cap  14 . 
     Referring now to  FIGS. 1-3   a , orbiting scroll member  56  and non-orbiting scroll member  70  are illustrated in greater detail. Non-orbiting scroll member  70  is fixedly secured to two-piece upper bearing housing  26  by a plurality of bolts  80  which prohibit all movement of non-orbiting scroll member  70  with respect to upper bearing housing  26 . Orbiting scroll member  56  is disposed between non-orbiting scroll member  70  and upper bearing housing  26 . Orbiting scroll member  56  can move radially as described above in relation to the radially compliant drive for compressor  10 . Orbiting scroll member  56  can also move axially by means of a floating thrust seal  82  disposed within annular recess  54 . 
     Floating thrust seal  82  comprises an annular valve body  84 , an inner lip seal  86  and an outer lip seal  88 . Annular valve body  84  defines an inner face seal  90  and an outer face seal  92  which are urged against end plate  60  of orbiting scroll member  56  by fluid pressure supplied to recess  54  through a plurality of passages  94  extending through annular valve body  84 . Inner lip seal  86  seals against an inner wall of recess  54 , outer lip seal  88  seals against an outer wall of recess  54  and face seals  90  and  92  seal against end plate  60  of orbiting scroll member  56  to isolate recess  54  from suction pressure refrigerant within shell  12 . The design parameters for floating thrust seal  82  are selected in such a way that, under internal pressurization, annular valve body  84  stays in constant contact with end plate  60  or orbiting scroll member  56  by means of face seals  90  and  92 . The majority of the axial biasing load applied to orbiting scroll member  56  is supplied by the refrigerant gas pressure within recess  54  rather than by mechanical contact between face seals  90  and  92  and end plate  60  of orbiting scroll member  56 . This reduces mechanical friction and wear of face seals  90  and  92  and the corresponding surface of end plate  60  of orbiting scroll member  56 . Pressurization of recess  54  is achieved using one or more passages  96  which extend from an area of end plate  60  open to recess  54  through end plate  60  and through scroll wrap  58  of orbiting scroll member  56 . 
     Referring now to  FIG. 3 b   , a biasing system in accordance with another embodiment of the present invention is disclosed.  FIG. 3 b    illustrates floating thrust seal  82 ′ which is the same as floating thrust seal  82  except that annular valve body  84  is replaced by a three piece annular body  84   a ,  84   b  and  84   c.    
     Floating thrust seal  82 ′ comprises annular valve bodies  84   a ,  84   b  and  84   c , an inner lip seal  86  and an outer lip seal  88 . Annular valve body  84   a  defines an inner face seal  90  and an outer face seal  92  which are urged against end plate  60  of orbiting scroll member  56  by fluid pressure supplied to recess  54  through a plurality of passages  94  extending through annular valve body  84   a . Inner lip seal  86  is located between annular valve body  84   a  and  84   b  and it seals against an inner wall of recess  54 , outer lip seal  88  is located between annular valve body  84   a  and  84   c  and it seals against an outer wall of recess  54  and face seals  90  and  92  seal against end plate  60  of orbiting scroll member  56  to isolate recess  54  from suction pressure refrigerant within shell  12 . The use of the three piece annular valve bodies  84   a ,  84   b  and  84   c  allows lip seals  86  and  88  to operate independently from each other. The design parameters for floating thrust seal  82  are selected in such a way that, under internal pressurization, annular valve body  84   a  stays in constant contact with end plate  60  or orbiting scroll member  56  by means of face seals  90  and  92 . The majority of the axial biasing load applied to orbiting scroll member  56  is supplied by the refrigerant gas pressure within recess  54  rather than by mechanical contact between face seals  90  and  92  and end plate  60  of orbiting scroll member  56 . This reduces mechanical friction and wear of face seals  90  and  92  and the corresponding surface of end plate  60  of orbiting scroll member  56 . Pressurization of recess  54  is achieved using one or more passages  96  which extend from an area of end plate  60  open to recess  54  through end plate  60  and through scroll wrap  58  of orbiting scroll member  56 . 
     During orbiting motion of orbiting scroll member  56  with respect to non-orbiting scroll member  70 , the end of the one or more passages  96  extending through scroll wrap  58  connects to one of the moving pockets defined by scroll wraps  58  and  72  by means of a recess  98  which is machined into end plate  74  of non-orbiting scroll member  70 . The location, size and shape of the one or more passages  96  and recess  98  will determine the opening and closing of gas communication between the compressed gas in the moving pocket and recess  54 . In addition, the transition time of the pressure equalization between the moving pocket and recess  54  is controlled by the location, size and shape of the one or more passages  96  and recess  98 . The timing of the opening and closing in conjunction with the transition time can be selected such that it will minimize excessive axial force applied to end plate  60  of orbiting scroll member  56  but at the same time the axial force will keep orbiting scroll member  56  in constant contact with non-orbiting scroll member  70 .  FIG. 4 a    illustrates the beginning of the opening of communication,  FIG. 4 b    illustrates an opened communication and  FIG. 4 c    illustrates the closing of communication between recess  98  and one passage  96 . 
     Referring now to  FIG. 5 , an axial pressure biasing system  110  is illustrated. During the operation of compressor  10 , suction gas is sucked into scroll members  56  and  70  where it is compressed and then discharged from discharge passage  76  through discharge fitting  18  that extends through cap  14 . Because the axial force from the compressed gas is located primarily in the center of orbiting scroll member  56 , and axial support for orbiting scroll member  56  from floating thrust seal  82  is located at the periphery of orbiting scroll member  56 , end plate  60  of orbiting scroll member  56  experiences bending such that the upper surface of end plate  60  becomes concave. At the same time, due to the thermal field, orbiting scroll wrap  58  as well as non-orbiting scroll wrap  72  are experiencing thermal growth, with the higher growth being in the center of scroll members  56  and  70 . The lower surface of end plate  74  of non-orbiting scroll member  70  also becomes concave due to the axial separating force from the compressed gas in the moving pockets. However, gas pressure behind end plate  74  of non-orbiting scroll member  70  can also influence the deflection of end plate  74 . 
     Non-orbiting scroll member  70  is sealingly secured to end cap  14  using a seal  112 . Non-orbiting scroll member  70  and end cap  14  define a pressure chamber  114  which is supplied intermediate pressurized gas from one or more of the moving pockets defined by wraps  58  and  72  through a passage  116  extending through end plate  74 . At a given operating condition, determined by suction and discharge pressure, it is possible to determine the value of gas pressure in pressure chamber  114 . The gas pressure in pressure chamber  114  influences the deflection of end plate  74  in such a way that the tips of orbiting scroll wrap  58  as well as the tips of non-orbiting scroll wrap  72  will be as close to a uniform contact as possible. The necessary gas pressure to achieve the uniform contact with the respective end plates  60  and  74  can be selected by properly positioning passage  116  in end plate  74 . 
     Referring now to  FIGS. 6 and 7   a - 7   c , a vapor injection system  120  in accordance with the present invention is illustrated. The source for vapor injection is located external to compressor  10  and it is supplied from a fluid line (not shown) which extends through cap  14 . Non-orbiting scroll member  70  defines a fluid injection port  122  to which the fluid line is attached to supply the pressurized vapor to scroll members  56  and  70 . Fluid injection port  122  is in communication with an axial passage  124  in orbiting scroll member  56 . Axial passage  124  is in communication with a radial passage  126  which is in turn in communication with a pair of axial passages  128  which open into the moving fluid pockets defined by scroll wraps  58  and  72 . In order to achieve the necessary amount of vapor introduced into the moving pockets, opening and closing of communication between port  122  and passage  124  must be controlled. The opening of port  122  to passage  124  should begin just after the moving pocket is formed by being sealed from the suction area of compressor  10 . The closing of port  122  to passage  124  should happen after approximately ninety degrees of rotation of orbiting scroll member  56 . Because of the relative orbiting motion of orbiting scroll member  56  with respect to non-orbiting scroll member  70 , the proper selection of relative locations of port  122 , passage  124  and passages  128  make it possible to control the opening and closing of vapor injection system  120 . Opening and closing of vapor injection system  120  to provide vapor to the moving pockets can be achieved by either lowering and uncovering passages  128  on end plate  60  of orbiting scroll member  56  by scroll wrap  72  of non-orbiting scroll member or by opening and closing communication between port  122  and passage  124  or by a combination of both. 
       FIG. 7 a    illustrates scroll members  56  and  70  corresponding to the point where the moving pockets defined by scroll wraps  58  and  72  are initially sealed off from the suction area of compressor  10 . Communication between port  122  and passage  124  is just starting to take place and passages  128  are just beginning to be uncovered by scroll wrap  72 .  FIG. 7 b    illustrates scroll members  56  and  70  corresponding to the position forty-five degrees of rotation after the initial sealing point illustrated in  FIG. 7 a   . Port  122  is open to passage  124  and passages  128  are not covered by scroll wrap  72  to provide for vapor injection.  FIG. 7 c    illustrates scroll members  56  and  70  corresponding to the position ninety degrees of rotation after the initial sealing paint illustrated in  FIG. 7 a   . Port  122  has just closed communication with passage  124  to stop vapor injection by vapor injection system  120 . 
     Referring now to  FIGS. 8 and 9 , a scroll compressor  210  in accordance with another embodiment of the present invention is illustrated. Scroll compressor  210  is the same as scroll compressor  10  but scroll compressor  210  includes an optional oil injection system  212 . Scroll compressor  210  includes a non-orbiting scroll member  70 ′ which replaces non-orbiting scroll member  70  and a two-piece upper bearing housing  26 ′ which replaces two-piece upper bearing housing  26 . Non-orbiting scroll member  70 ′ is the same as non-orbiting scroll member  70  except that non-orbiting scroll member  70 ′ defines an oil pressure passage  214  and an oil pressure groove  216 . Upper bearing housing  26 ′ is the same as upper bearing housing  26  except that upper bearing housing  26 ′ defines an oil supply passage  218 . 
     Oil injection system  212  injects oil into the moving chambers defined by scroll wraps  56  and  72  for cooling and lubrication through passage  94  and the one or more passages  96 . While passages  94  and  96  are illustrated as being used for oil injection, it is within the scope of the present invention to have additional or other dedicated oil injection ports if desired. Once oil is injected into the moving pockets, it is discharged together with the compressed gas and then separated from the compressed gas in an external oil separator (not shown). The separated oil is then cooled and reinjected into the moving pockets of compressor  210 . 
     A source of high pressure oil or high pressure sump  228  is connected through cap  14  to oil pressure passage  214  to provide high pressure oil to annular recess  54  and floating thrust seal  82 . In order to control the pressure of the supplied oil, an external oil pressure regulator  230  is utilized. Also, in order to provide the necessary feed back for regulator  230 , oil groove  216  and oil pressure passage  214  are connected through cap  14  to regulator  230 . When orbiting scroll member  56  is in tight contact with non-orbiting scroll member  70 ′, groove  216  is sealed from the suction area of compressor  210 . However, when scroll axial separation takes place, groove  216  opens to the suction area of compressor  210  to provide a leak path. 
     Referring now to  FIG. 9 , oil pressure regulator  230  comprises a housing  232  and a differential piston  234 . On the left side of piston  234  as shown in  FIG. 9 , there is a hydrostatic thrust bearing chamber  236  and a lubrication groove sensing chamber  238 . Lubrication groove sensing chamber  238  is connected to oil groove  216  through oil pressure passage  214 . Lubrication groove sensing chamber  238  is also connected to high pressure oil sump  228  through a metering orifice  240 . To the right of piston  234  as shown in  FIG. 9 , there is an adjustment piston  242  which is threaded into housing  232 . Adjustment piston  242  can be used to adjust the preload of springs  244  which urge piston  234  to the left as shown in  FIG. 9 . Adjustment piston  242  together with piston  234  form a chamber  246  and a chamber  248 . 
     During operation chamber  246  is connected to high pressure oil sump  228  and chamber  248  to high pressure oil sump  228  and chamber  248  is connected to the suction side of compressor  210 . There is a circular groove  250  in piston  234  which is connected by a passage  252  to hydrostatic thrust bearing chamber  236 . A radial passage  254  through housing  232  is also connected to the suction side of compressor  210 . A second radial passage  256  through housing  232  is connected to high pressure sump  228 . During operation, the position of piston  234  is determined by the balance of forces in chambers  236 ,  238 ,  246  and  248  and the forces exerted by springs  244 . The pressure in chamber  236  is controlled by oil leakage from groove  250  to/from radial passages  254  and  256 . This leakage depends on the position of groove  250  relative to the openings of passages  254  and  256 . Differential piston diameters, as well as other design parameters, are selected in such a way that the controlled pressure in chamber  236  becomes a proper combination of suction and discharge pressures and spring force resulting in the best possible pressure within annular recess  54  reacting on orbiting scroll member  56  and floating thrust seal  82  to provide the appropriate amount of biasing for orbiting scroll member  56  for the efficient operation of compressor  210 . When scroll members  56  and  70 ′ are in tight contact, the oil pressure in circular groove  216  and chamber  238  are close to the design pressure. However, in the event of scroll axial separation, oil leakage from groove  216  to the suction portion of compressor  210  will result in a drop of pressure in groove  216  and chamber  238  due to the presence of metering orifice  240 . This changes the force balance equilibrium on piston  234  resulting in groove  250  aligning with passage  256  increasing the oil pressure within chamber  236  by connecting chamber  236  to high pressure sump  228  through passage  252 , groove  250  and passage  256 . This increased oil pressure is supplied from chamber  236  to annular recess  54  resulting in an increase in the clamping force in order to bring the scrolls back together. With the scrolls back together, the pressure within groove  216  and chamber  238  will return to the pressure of high pressure sump  228  which will move piston  234  to the right as shown in  FIG. 9  until groove  250  aligns with passage  254  to bleed the increased pressure within chamber  236  to the suction area of the compressor through passage  252 , groove  250  and passage  254 . This brings the pressure within chamber  236  and thus annular recess  54  back to the design pressure. 
     Referring now to  FIG. 10 , a scroll compressor  310  in accordance with another embodiment of the present invention is illustrated. Scroll compressor  310  is the same as scroll compressor  10  but scroll compressor  310  incorporates a different biasing system for the orbiting scroll member. 
     Compressor  310  comprises generally cylindrical hermetic shell  12  having welded at the upper end thereof cap  14  and at the lower end thereof the plurality of mounting feet  16 . Cap  14  is provided with refrigerant discharge fitting  18 . Other major elements affixed to shell  12  include lower bearing housing  24  that is suitably secured to shell  12  and two piece upper bearing housing  26  suitably secured to lower bearing housing  24 . 
     Drive shaft or crankshaft  28  having eccentric crank pin  30  at the upper end thereof is rotatably journaled in bearing  32  in lower bearing housing  24  and second bearing  34  in upper bearing housing  26 . Crankshaft  28  has at the lower end the relatively large diameter concentric bore  36  that communicates with radially outwardly inclined smaller diameter bore  38  extending upwardly therefrom to the top of crankshaft  28 . The lower portion of the interior shell  12  defines oil sump  40  that is filled with lubricating oil to a level slightly above the lower end of rotor  42 , and bore  36  acts as a pump to pump lubricating fluid up crankshaft  28  and into bore  38  and ultimately to all of the various portions of the compressor that require lubrication. 
     Crankshaft  28  is rotatively driven by the electric motor including stator  46 , winding  48  passing therethrough and rotor  42  press fitted on crankshaft  28  and having upper and lower counterweights  50  and  52 , respectively. 
     The upper surface of upper bearing housing  26  is provided with annular recess  54  above which is disposed an orbiting scroll member  356  having the usual spiral vane or wrap  358  extending upward from an end plate  360 . Projecting downwardly from the lower surface of end plate  360  of orbiting scroll member  356  is a cylindrical hub having a journaled bearing  362  therein and in which is rotatively disposed drive bushing  64  having an inner bore in which crank pin  30  is drivingly disposed. Crank pin  30  has a flat on one surface that drivingly engages a flat surface (not shown) formed in a portion of the bore 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. Oldham coupling  68  is also provided positioned between orbiting scroll member  356  and upper bearing housing  26  and keyed to orbiting scroll member  356  and upper bearing housing  26  to prevent rotational movement of orbiting scroll member  356 . 
     A non-orbiting scroll member  370  is also provided having a wrap  372  extending downwardly from an end plate  374  that is positioned in meshing engagement with wrap  358  of orbiting scroll member  356 . Non-orbiting scroll member  370  has a centrally disposed discharge passage  376  that communicates with discharge fitting  18  which extends through end cap  14 . 
     Non-orbiting scroll member  370  is fixedly secured to two-piece upper bearing housing  26  by plurality of bolts  80  which prohibit all movement of non-orbiting scroll member  370  with respect to upper bearing housing  26 . Orbiting scroll member  356  is disposed between non-orbiting scroll member  370  and upper bearing housing  26 . Orbiting scroll member  356  can move radially as described above in relation to the radially compliant drive for compressor  310 . Orbiting scroll member  356  can also move axially by means of a floating thrust seal  382  disposed within annular recess  54 . 
     Floating thrust seal  382  comprises a pair of annular valve bodies  384  with one annular body  384  sealingly engaging the interior wall of recess  54  at  386  and the other annular body  384  sealingly engaging the exterior wall of recess  54  at  388 . Annular valve bodies  384  define an inner face seal  390  and an outer face seal  392  which are urged against end plate  360  of orbiting scroll member  356  by fluid pressure supplied to recess  54 . The seal at  386  seals against the inner wall of recess  54 , the seal at  388  seals against the outer wall of recess  54  and face seals  390  and  392  seal against end plate  360  of orbiting scroll member  356  to isolate recess  54  from suction pressure refrigerant within shell  12 . The design parameters for floating thrust seal  382  are selected in such a way that, under internal pressurization, annular valve bodies  384  stay in constant contact with end plate  360  of orbiting scroll member  356  by means of face seals  390  and  392 . The majority of the axial biasing load applied to orbiting scroll member  356  is supplied by the refrigerant gas pressure within recess  54  rather than by mechanical contact between face seals  390  and  392  and end plate  360  of orbiting scroll member  356 . This reduces mechanical friction and wear of face seals  390  and  392  and the corresponding surface of end plate  360  of orbiting scroll member  356 . While not illustrated in  FIG. 10 , pressurization of recess  54  is achieved using one or more passages  96  which extend from an area of end plate  360  open to recess  54  through end plate  360  to one or more of the compression chambers formed by wraps  358  and  372  as shown in  FIGS. 1-4   c . Also, scroll compressor  10  can include the optional oil injection system  212  illustrated above for compressor  210 . 
     During orbiting motion of orbiting scroll member  356  with respect to non-orbiting scroll member  370 , a plurality of passages  396  which extend through end plate  360  control the pressure within a recess  398 . The end of each passage  396  extending through end plate  360  connects to one of a plurality of recesses  398  which are machined into end plate  374  of non-orbiting scroll member  370 . The location, size and shape of passage  396  and recess  398  will determine the opening and closing of gas communication between the compressed gas in the suction area of scroll compressor  310  and recess  398  as well as the opening and closing of gas communication between recess  54  and recess  398 . In addition, the transition time of the pressure equalization between the suction area of scroll compressor  310  and recess  398  and the transition time of the pressure equalization between recess  54  and recess  398  is controlled by the location, size and shape of passage  396  and recess  398 . The timing of the opening and closing in conjunction with the transition time can be selected such that it will minimize excessive axial force applied to end plate  360  of orbiting scroll member  356  but at the same time the axial force will keep orbiting scroll member  356  in constant contact with non-orbiting scroll member  370 . 
     Scroll compressors create a contingent axial force that tries to separate the two mating scrolls due to the compression process. This force changes in a revolution with ten to thirty percent of the fluctuation depending on the operating condition. To overcome the separating force and hold the mating scrolls together, a constant gas pressure is applied from the back side of the orbiting scroll member by using a sealing system which is typically provided on a stationary part of the scroll compressor. In order to keep the scroll members together at all times with the constant pressure acting against the fluctuating separating force, the backpressure that creates the holding force must be equal to or more than the peak value of the fluctuating force creating an excessive pressure. As a result, the excessive force will be exerted on the mating axial surfaces of the sealing system. This excessive force causes frictional losses that deteriorates the efficiency of the compressor. 
     There is another circumstance which requires an unwanted excessive force. This is due to the presence of the “scroll particular” over-turning moment which is schematically illustrated in  FIGS. 11 a -11 c   . Since the separation force F SP  and the holding force F HOLD  are separately placed by a half of the orbiting radius R OR , the centroid of the excessive force F TH  needs to occur at the opposite side of the axis (shown in X) in order to balance out the moment from the two forces F SP  and F HOLD . As seen in  FIG. 11 b   , the force balance in the axial direction can be represented by the following equation [1].
 
 F   HOLD   =F   TH   +F   SP   [1]
 
The location X illustrated in  FIG. 11 b    becomes off setting from the central axis with which the holding force F HOLD  gets close to the separation force F SP  to eliminate the excessive force and its location can be represented by the following equation [2].
 
                   X   =               R   OR     2     ·     F   SP       -     C   ·     F   RAD           F   TH       +     R   OR               [   2   ]               
Substituting equation [1] into equation [2] gives us the location for X which can be represented by the following equation [3].
 
                   X   =               R   OR     2     ·     F   SP       -     C   ·     F   RAD             F   HOLD     -     F   SP         +     R   OR               [   3   ]               
The location of F TH  is also affected by the other moment balance in the tangential plane shown in the following equation [4].
 
 Y·F   TH   =C·F   TAN   [4]
 
This equation can be written as
 
                   Y   =       C   ·     F   TAN         F   TH               [   5   ]               
and substituting equation [1] in this equation gives us the position for Y.
 
     
       
         
           
             
               
                 
                   Y 
                   = 
                   
                     
                       C 
                       · 
                       
                         F 
                         TAN 
                       
                     
                     
                       
                         F 
                         HOLD 
                       
                       - 
                       
                         F 
                         SP 
                       
                     
                   
                 
               
               
                 
                   [ 
                   6 
                   ] 
                 
               
             
           
         
       
     
     As indicated, the Y location also becomes off from the central axis by minimizing the excessive force (F HOLD -F SP ). For most of scroll compressors, the F TH  positions near the tangential line, which is extended from the center of the orbiting scroll toward the rotation direction of the orbit. As the tangential and radial axes rotate, F TH  moves along the tangential axis resulting in drawing a closed loop trajectory as illustrated in  FIG. 12  by the dashed line. If no axial surface is provided between the mating scroll members at the location of F TH , the orbiting scroll member will tilt over and thus result in the scroll compressor being inoperative. Therefore, the excessive force is allowed to be reduced only within the range of which F TH  does not go across the outer edge of the axial surface between the mating scrolls. 
     A typical approach to overcome such excessive force is to widen the axial thrust area in order to extend the outer edge of the axial surface as well as to reduce the contact force per unit area. With this approach, however, it brings about the compressor shell diameter being larger which is against the market demand for miniaturization. In addition, lubrication of this increased surface area presents additional problems. 
     The present invention addresses this issue by increasing and decreasing the fluid pressure within recess  398  which creates a pressure biasing chamber during the cycle of rotation in order to counteract the circumferential movement of F TH . The increasing and decreasing of the fluid pressure within recess  398  is described above where recess  398  is cyclically placed in communicated with the suction area of compressor  310  and the fluid pressure within recess  54 . 
       FIGS. 13-18  illustrate the positional and geometrical information about the plurality of passages  396  in end plate  360 , the plurality of recesses  398  formed in end plate  374  and an axial sealing surface  400  of annular recess  54  provided at the backside of end plate  360 . 
     Preferably, four passages  396   a - d  are arranged circumferentially around end plate  360  at a ninety degree interval at a diameter of C BH  from the center of orbiting scroll member  356 . The diameter D BH  for each passage  396  is preferred, but not limited to be matched to a seal width of outer face seal  392 . Preferably four recesses  398   a - d  are arranged circumferentially around end plate  374  at a diameter C GR . The four recesses  398  are not interconnected with each other and thus they can each be treated as an independent volume. The depth of each recess t GR  is preferred, but not limited to be considerably small such as less than a millimeter. Recesses  398  are arranged at ninety degree interval on diameter C GR  from the center of non-orbiting scroll member  370 . Recesses  398  are preferred but are not limited for each to have a width L GR  which is equal to or greater than twice the orbiting radius R OR . The diameter C GR  is preferred to be the same size of diameter C BH  of passage  396 . Also, the diameter C GR  is preferred, but not limited to be the same as the diameter C SEAL  of outer face seal  392 . The matching of diameters C GR  and C SEAL  permit the fabrication of the plurality of passages  396  by a simple vertical drilling operation. 
     An angular orientation of the four recesses  398  is preferred, but not limited to be arranged so that the symmetric axis of each recess coincides with the radial direction of a respective passage  396 . 
       FIGS. 19 a -19 d    show the positional relationship between the passages  396 , the recesses  398  and the outer sealing surface of outer face seal  392  at each ninety degree rotation of orbiting scroll member  356  with respect to non-orbiting scroll member  370 . The relative position of each passage  396  and the outer sealing surface of outer face seal  392  are successively changed as the center O os  of orbiting scroll member  356  orbits on the orbiting circle C OR  around the center O FS  of non-orbiting scroll member  370 . Each passage  396  comes across the axial sealing surface of outer face seal  392  twice during one revolution of orbiting scroll member  356 . Thus, the bottoms of passages  396  are repeatedly and alternately exposed to high pressure (e.g., discharge pressure) and low pressure (e.g., suction pressure) refrigerant environments. The exposure of each passage  396  becomes phase-delayed by ninety degrees such that the exposures occur on respective passages  396  one after another during the orbital motion. 
     The upper end of each passage  396  is in communication with a respective recess  398  at all times. Therefore, the pressures of fluid within recesses  398  fluctuates during each revolution of orbiting scroll member  356  as the result of the alternate exposure of passages  396  to the high and low pressures of the refrigerant environment. A typical pattern of the pressure fluctuation in each recess  398  is shown in  FIG. 20 . The pressure increases when passage  396  is exposed to the high pressure environment and it decreases when it is exposed to the low pressure environment. Although the rate of the increase and the decrease of the pressure within each recess  398  is affected by the volume of the recess and the flow resistance of passage  396 , the peak pressure always appears at the end of the exposure of passage  396  to the high pressure and the bottom pressure occurs at the end of the exposure of passage  396  to the low pressure. This is illustrated in  FIG. 20  where the solid line indicates recess pressure for a large volume recess  398  or a high flow resistance passage  396  and the dashed line indicates recess pressure for a small volume recess  398  or a low flow resistance passage  396 . 
     In the crank position illustrated in  FIG. 19 a   , passage  396   a  is located at the ending position of the exposure to the inside of recess  54  which holds a higher pressure than the suction area of scroll compressor  310 . Thus, at this crank position, the pressure within recess  398   a  reaches its maximum, generating a peak force to counteract the excessive force F TH , which is generated by the overturning moment. Since the pressure within recess  398  is uniform, the location of the force should be represented by the centroid of the recesses axial area, which is shown in  FIG. 16  as F GRA . 
     As illustrated in  FIG. 12 , the excessive force F TH  always appears near the tangential line, which is extended from the center of orbiting scroll member  356  toward the rotational direction of orbit. As seen in  FIG. 16 , the centroid of the counteracting force F GRA  is located close to F TH . Providing the counteracting force F GRA  close the F TH  will negate most of the excessive force F TH  and prevent a residual moment due to the presence of a minimum distance between F GRA  and F TH . 
     As the orbital motion proceed from the crank position illustrated in  FIG. 19 a    to that illustrated in  19   b , passage  396   a  comes across the outer sealing surface of outer face seal  392  and will be exposed to the suction area of scroll compressor  310 . The pressure within recess  398   a  will start to decrease and thus reduce the counteracting from recess  398   a . On the next recess  398   b , however, the respective passage  396   b  is approaching the end position of the exposure to the inside of pressurized recess  54  which is increasing the pressure within recess  398   b . In the middle position between  FIGS. 19 a  and 19 b   , therefore, both recesses  398   a  and  398   b  hold an intermediate pressure which generates intermediate counteracting forces at both F GRA  and F GRB . These two forces can also be represented by the centroid of the two recesses which is located between the two centroids of the two recesses. The location of the counteracting force therefore moves circumferentially in the direction of the orbital motion and follows the movement of F TH  which is illustrated in  FIG. 12  by the dashed line.  FIGS. 19 c  and 19 d    each illustrate an additional ninety degrees of orbital motion. 
     The passages  396   a - d  are illustrated as vertical and straight on the premise of which diameter of the concentric circles of recesses C GR  matches with the diameter of the sealing face of outer face seal  392 . This premise sometimes cannot be met due to layout restrictions in relation to the other components. Passages  396  can be replaced with passage  396 ′ illustrated in  FIG. 21  so that the bottom of passages  396 ′ are still exposed to the inside and outside of recess  54  repeatedly and alternately. As illustrated in  FIG. 22 , the angular orientation of recesses  398  can be modified within forty-five degrees from the case of the preferred embodiment with the symmetric axis of each groove coinciding with the radial direction of the respective passage  396 . This will allow shifting of the centroid of the respective recesses  398  in the circumferential direction and further minimizing the distance between the excessive force F TH  and the counteracting force F GR . While  FIG. 22  illustrated modification in a clockwise direction, it is within the scope of the present invention to modify recesses  398  in a counter-clockwise direction if desired. 
     Referring now to  FIGS. 23 and 24 , a scroll compressor  410  in accordance with the present invention is illustrated. Scroll compressor  410  is the same as scroll compressor  10  but scroll compressor  410  incorporates a hydrostatic thrust bearing. Compressor  410  comprises generally cylindrical hermetic shell  12  having welded at the upper end thereof cap  14  and at the lower end thereof plurality of mounting feet  16 . Cap  14  is provided with refrigerant discharge fitting  18 . Other major elements affixed to shell  12  include lower bearing housing  24  that is suitably secured to shell  12  and two piece upper bearing housing  26  suitably secured to lower bearing housing  24 . 
     Drive shaft or crankshaft  28  having eccentric crank pin  30  at the upper end thereof is rotatably journaled in bearing  32  in lower bearing housing  24  and second bearing  34  in upper bearing housing  26 . Crankshaft  28  has at the lower end the relatively large diameter concentric bore  36  that communicates with radially outwardly inclined smaller diameter bore  38  extending upwardly therefrom to the top of crankshaft  28 . The lower portion of the interior shell  12  defines oil sump  40  that is filled with lubricating oil to a level slightly above the lower end of rotor  42 , and bore  36  acts as a pump to pump lubricating fluid up crankshaft  28  and into bore  38  and ultimately to all of the various portions of the compressor that require lubrication. 
     Crankshaft  28  is rotatively driven by the electric motor including stator  46 , winding  48  passing therethrough and rotor  42  press fitted on crankshaft  28  and having upper and lower counterweights  50  and  52 , respectively. 
     The upper surface of upper bearing housing  26  is provided with annular recess  54  above which is disposed an orbiting scroll member  456  having the usual spiral vane or wrap  458  extending upward from an end plate  460 . Projecting downwardly from the lower surface of end plate  460  of orbiting scroll member  456  is a cylindrical hub having a journaled bearing  462  therein and in which is rotatively disposed drive bushing  64  having an inner bore in which crank pin  30  is drivingly disposed. Crank pin  30  has a flat on one surface that drivingly engages a flat surface (not shown) formed in a portion of the bore 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. Oldham coupling  68  is also provided positioned between orbiting scroll member  456  and upper bearing housing  26  and keyed to orbiting scroll member  456  and upper bearing housing  26  to prevent rotational movement of orbiting scroll member  456 . 
     A non-orbiting scroll member  470  is also provided having a wrap  472  extending downwardly from an end plate  474  that is positioned in meshing engagement with wrap  458  of orbiting scroll member  456 . Non-orbiting scroll member  470  has a centrally disposed discharge passage  476  that communicates with discharge fitting  18  which extends through end cap  14 . 
     Non-orbiting scroll member  470  is fixedly secured to two-piece upper bearing housing  26  by the plurality of bolts  80  which prohibit all movement of non-orbiting scroll member  470  with respect to upper bearing housing  26 . Orbiting scroll member  456  is disposed between non-orbiting scroll member  470  and upper bearing housing  26 . Orbiting scroll member  456  can move radially as described above in relation to the radially compliant drive for compressor  410 . Orbiting scroll member  456  can also move axially by means of a floating thrust seal  482  disposed within annular recess  54 . 
     Floating thrust seal  482  comprises a pair of annular bodies  484  with one annular body  484  sealingly engaging the inner wall of recess  54  at  486  and the other annular body  484  sealingly engaging the exterior wall of recess  54  at  488 . Annular valve bodies  484  define an inner face seal  490  and an outer face seal  492  which are urged against end plate  460  of orbiting scroll member  456  by fluid pressure supplied to recess  54 . The seal at  486  seals against the inner wall of recess  54 , the seal  488  seals against the outer wall of recess  54  and face seals  490  and  492  seal against end plate  460  of orbiting scroll member  456  to isolate recess  54  from suction pressure refrigerant within shell  12 . The design parameters for floating thrust seal  482  are selected in such a way that, under internal pressurization, annular valve bodies  484  stay in constant contact with end plate  460  or orbiting scroll member  456  by means of face seals  490  and  492 . The majority of the axial biasing load applied to orbiting scroll member  456  is supplied by the refrigerant gas pressure within recess  54  rather than by mechanical contact between face seals  490  and  492  and end plate  460  of orbiting scroll member  456 . This reduces mechanical friction and wear of face seals  490  and  492  and the corresponding surface of end plate  460  of orbiting scroll member  456 . Pressurization of recess  54  is achieved using the one or more passages  96  which extends from an area of end plate  460  open to recess  54  through end plate  460  and through scroll wrap  458  of orbiting scroll member  456 . 
     Scroll compressor  410  incorporates a hydrostatic thrust bearing  500  or non-orbiting scroll member  470 . Hydrostatic bearing  500  is located at a thrust surface  502  of non-orbiting scroll member  470  which mates with end plate  460  of orbiting scroll member  456 . This positions hydrostatic bearing  500  exterior to non-orbiting scroll wrap  472 . Hydrostatic bearing  500  comprises one or more recesses  504  disposed on thrust surface  502 , one or more throttling devices  506  such as orifices, tubes, valves, capillaries or other throttling devices known in the art, a high pressure oil source  508  and one or more oil passages  510  that connect high pressure oil source  508  to one or more recesses  504 . An oil-separator  512  can be used for high pressure oil source  508  and as illustrated in  FIG. 23 , oil-separator  512  is located at the discharge end of scroll compressor  410 . 
     As described above, scroll compressor can create a contingent axial force by its compression mechanism which tries to separate the two mating scrolls. This force changes during a revolution of the orbiting scroll member with ten to thirty percent of the fluctuation depending on the operating condition. To overcome the separating force and hold the mating scroll members together, a constant back pressure is generally applied from a side of the non-orbiting scroll member or from a side of the orbiting scroll member. In order to keep the scroll members together with the constant back pressure against the fluctuating separating force, the back pressure that creates a force equal to or more than the peak value of the fluctuating force is chosen. As a result, the excessive clamping force at the time of other than when the peak force occurs will be applied to the scroll members resulting in mechanical loss. This loss becomes more significant if the scroll compressor creates a large axial force relative to the useful work output (tangential force) such as a scroll compressor for CO 2  refrigerant. 
     Preferably four separate recesses  504   a - d  are provided on thrust surface  502  of non-orbiting scroll member  470 . Recesses  504   a - d  are located circumferentially to surround scroll wrap  472 . By using separate recesses  504   a - d , the capability to carry the eccentric bias-load which scroll members normally generate will be enhanced. Each recess has its own throttling device  506  to provide each recess  504  with its own independent oil carrying capacity. This feature is also necessary for the eccentric load. The land of each recess  504  is adjusted in height to be flush with the tip surface of non-orbiting scroll wrap  472 . 
     A common oil passage  514  connects to each recess  504  through a high pressure oil line  516  connected to oil separator  516 . As detailed above, a constant back pressure from recess  54  is applied to end plate  460  of orbiting scroll member  456 . 
     Hydrostatic thrust bearing  500  will provide rigidity to the load carrying capacity against the clearance between the two mating surfaces, end plate  460  and thrust surface  502 . Hydrostatic thrust bearing  500  will carry additional load as the clearance between the two surfaces decrease. When there is excessive force applied to orbiting scroll member  456  from the fluid pressure within recess  54 , orbiting scroll member  456  comes closer to non-orbiting scroll member  470 . Hydrostatic thrust bearing  500  will generate an increased reaction force as orbiting scroll member  456  comes closer to non-orbiting scroll member  470 . Both the biasing force and the reaction force will balance out at a certain clearance where orbiting scroll member  456  will stop its axial movement. As a result, orbiting scroll member  456  stays in a floating state with respect to non-orbiting scroll member  470  not transferring forces between the tips of scroll wraps  458 ,  472  and end plates  474 ,  460 , respectively. This floating state of orbiting scroll member  456  eliminates the friction loss between the scroll tips and the end plates. 
     This reduction becomes more of a significant factor when the biasing load created by the pressurized fluid in recess  54  is large. This is especially true for scroll compressors that create significant fluctuation of the separating force such as the ones for CO 2  refrigerant. Hydrostatic thrust bearing  500  accommodates this fluctuating force by allowing a change in the floating position of orbiting scroll member  456 . If this change in the floating position becomes too large, the performance of the scroll compressor may be degraded due to leakage of the compressed gas between adjacent scroll pockets. If the change in the floating position becomes too large, the prevention of gas leakage can be accomplished by designing recesses  504  and throttling devices  506  to realize the maximum rigidity which will then bring about the minimum change in the floating position in relation to the fluctuation of the load. 
     Hydrostatic thrust bearing  500  can be intentionally designed to be, more or less, too small in its load carrying capacity against the separating force. Hydrostatic thrust bearing  500  will then carry a part of the separation force at the two mating scroll members in contact. Although, in this design, hydrostatic bearing  500  does not completely eliminate the tip friction, it still reduces the friction drastically by receiving axial stress at the tip of the scroll. 
     While the present invention is illustrated with hydrostatic thrust bearing being on the non-orbiting scroll member with an axially movable orbiting scroll member, hydrostatic bearing  500  can be incorporated into an orbiting scroll member that does not move axially but which is mated with an axially movable non-orbiting scroll member. 
     The description is merely exemplary in nature and, thus, variations are intended to be within the scope of the teachings. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.