Patent Publication Number: US-2006006598-A1

Title: Seal mechanism in compressor

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a seal mechanism for sealing a gap between a rotary shaft and a housing in a compressor, for example, of a scroll type, a piston type and a vane type.  
      A scroll compressor used as a refrigerant compressor includes a housing, a fixed scroll member and a movable scroll member. A back pressure chamber is defined behind the fixed scroll member for enhancing the sealing between the fixed and movable scroll members. The back pressure chamber is the space which is formed between a fixed wall provided in the housing and the movable scroll member The pressure in the back pressure chamber (or back pressure) is increased and applied to the movable scroll member. A gas compressed to a high pressure by a compression unit is introduced into the back pressure chamber. In the back pressure chamber is disposed an orbital mechanism that converts the rotation of a rotary shaft into the orbital movement of the movable scroll member. A known lip seal or tip seal is provided between the fixed wall and the rotary shaft to seal the back pressure chamber for preventing the introduced high-pressure gas in the back pressure chamber from leaking to a low-pressure region behind the fixed wall.  
      Meanwhile, besides the lip seal and the tip seal, there have been known other seal mechanisms such as a labyrinth seal and a seal mechanism for a rotary valve as disclosed in Unexamined Japanese Patent Publication No. 11-63244.  
      Recently, chlorofluorocarbon-based refrigerant used as refrigerant for the refrigerant compressor has been replaced by carbon dioxide. When carbon dioxide is used as the refrigerant, the pressure of the refrigerant becomes extremely high in operation of the compressor in comparison with the case of using chlorofluorocarbon-based refrigerant. The same is true of the scroll compressor. Therefore, in the scroll compressor, the pressure in the back pressure chamber is also much higher when using carbon dioxide in place of chlorofluorocarbon-based refrigerant.  
      When a conventional contact type seal member such as the lip seal and the tip seal is provided between the fixed wall and the rotary shaft, the seal member is pressed strongly against the rotary shaft because of the extremely large pressure difference between the back pressure chamber and the low-pressure region behind the fixed wall. Thus, the sealing may be enhanced, but sliding resistance between the seal member and the rotary shaft is extremely large when the seal member slides relative to the rotary shaft. Accordingly, the torque of the rotary shaft is increased, thereby inviting a wear of the seal member. Meanwhile, when another seal mechanism such as the non-contact type labyrinth seal is used as an alternative of the lip seal and the tip seal, the sliding resistance between the seal member and the rotary shaft is small. However, such seal mechanism does not function properly when the above pressure difference is large. Thus, the high-pressure gas in the back pressure chamber easily leaks into the low-pressure region. Though the leaking itself is not a serious problem, if the high-pressure gas leaks too much, the back pressure chamber does not perform its intended function, so that satisfactory sealing between the fixed and movable scroll members is not ensured.  
      A seal mechanism for a rotary valve is disclosed in Unexamined Japanese Patent Publication No. 11-63244. However, it is designed primarily for sealing and its sliding resistance is large as the aforementioned lip seal and tip seal. In addition, the seal mechanism formed with a protrusion and having a coil spring is complicated in structure. Therefore, such seal mechanism is not suitable for use in the compressor.  
      The present invention is directed to a compressor having a seal mechanism that ensures the sealing and is simple in structure, as well as reduces the sliding resistance between a seal member and a sliding surface.  
     SUMMARY OF THE INVENTION  
      According to the present invention, a compressor for compressing gas includes a housing, a rotary shaft, a compression unit, and a seal member. The housing has a high-pressure region and a low-pressure region. The rotary shaft is rotatably supported by the housing. The compression unit is provided in the housing and is actuated by the rotation of the rotary shaft to perform the gas compression. The seal member has an annular and plate-like shape and is provided in the housing for preventing the gas from leaking from the high-pressure region to the low-pressure region via a gap between the rotary shaft and the housing. Pressure of the gas in the high-pressure region is applied to the seal member thereby generating a seal function. The seal member is fixed to one of the housing and the rotary shaft and in contact with an edge that is formed in the other of the housing and the rotary shaft and connects a first surface facing the high-pressure region and a circumferential surface coaxial with the rotary shaft in the other of the housing and the rotary shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
       FIG. 1  is a longitudinal cross-sectional view of a motor-driven scroll compressor of a first preferred embodiment according to the present invention;  
       FIG. 2  is an enlarged partial cross-sectional view showing part of the compressor which is enclosed by the dotted oval line A in  FIG. 1 ;  
       FIG. 3  is a partially enlarged cross-sectional view of a compressor showing a seal mechanism of an alternative embodiment;  
       FIG. 4  is a partially enlarged cross-sectional view of a compressor showing a seal mechanism of an alternative embodiment; and  
       FIG. 5  is a partially enlarged cross-sectional view of a compressor showing a seal mechanism of an alternative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The following will describe a first preferred embodiment, in which the present invention is applied to a motor-driven scroll compressor for use in the refrigerant circuit of a vehicle air-conditioner and using carbon dioxide as the refrigerant of the refrigerating circuit.  
      Firstly, the motor-driven scroll compressor (referred to as “compressor” hereinafter) will be described. Referring to  FIG. 1 , the compressor has a housing  11  that includes a first housing component  12  and a second housing component  13 . In  FIG. 1 , the left side of the compressor (or the side adjacent to the first housing component  12 ) and the opposite right side thereof (or the side adjacent to the second housing component  13 ) correspond to the rear side and the front side of the compressor, respectively. The housing  11  also includes a shaft support member  14  that is formed integrally with the first housing component  12  on the front side thereof. The shaft support member  14  has a cylindrical portion  15  through which a rotary shaft  17  is inserted. The rotary shaft  17  is rotatably supported by the housing  11  through a radial bearing  18  disposed in the first housing component  12  and a radial bearing  19  disposed on the inner circumferential surface  15 a of the cylindrical portion  15  of the shaft support member  14 .  
      A motor chamber  20  as a low-pressure region is defined in the housing  11  on the rear side of the shaft support member  14 . An electric motor  21  is provided in the motor chamber  20  and electric power is supplied to the electric motor  21  to drive the rotary shaft  17 .  
      A fixed scroll member  23  is accommodated in the housing  11  on the front side of the shaft support member  14 . The fixed scroll member  23  includes a disc-shaped fixed base plate  24 , a cylindrical outer peripheral wall  25  and a fixed scroll wall  26 . The outer peripheral wall  25  extends rearward from the outermost peripheral portion of the rear surface  24 a of the fixed base plate  24 . The fixed scroll wall  26  extends from the rear surface  24 a of the fixed base plate  24  and is located inside the outer peripheral wall  25 . A tip seal  27  is installed in the distal end surface of the fixed scroll wall  26 . The fixed scroll member  23  is joined at the rear surface of the outer peripheral wall  25  to the front surface  14 a of the shaft support member  14 .  
      A crankshaft  28  is provided at the front end of the rotary shaft  17  in offset relation to the axis L of the rotary shaft  17 . The compressor includes a balancer  29  having a boss  29   a  which is fixedly fitted on the crankshaft  28 . A bearing  30  is mounted on the boss  29   a  of the balancer  29  on the outer peripheral side thereof. A movable scroll member  31  is supported by the bearing  30 .  
      The movable scroll member  31  includes a disc-shaped movable base plate  32 , a movable scroll wall  34 , and a boss  33 . The movable scroll wall  34  extends from the front surface  32   a  of the movable base plate  32 , which faces the fixed base plate  24 . A tip seal  35  is installed in the distal end surface of the movable scroll wall  34 . The boss  33  extends from the center of the rear surface  32   b  or the back surface of the movable base plate  32 . The boss  33  is rotatably supported by the bearing  30 . The movable base plate  32  is in slide contact with the front surface  14   a  of the shaft support member  14  at the outer peripheral portion of the rear surface  32   b  thereof. A tip seal  36  is installed in the rear surface  32   b  in slide contact with the front surface  14   a  of the shaft support member  14 .  
      The fixed and movable scroll walls  26 ,  34  are engaged with each other, so that compression chambers  37  are defined by the fixed and movable base plates  24 ,  32  and the fixed and movable scroll walls  26 ,  34  of the fixed scroll member  23  and the movable scroll member  31 . Plural rotation preventing mechanisms  38  that are generally known are provided between the front surface  32   a  of the movable base plate  32  of the movable scroll member  31  and the rear surface  24   a  of the fixed base plate  24  of the fixed scroll member  23  (Only one shown in  FIG. 1 ).  
      A suction chamber  39  is defined between the outer peripheral wall  25  of the fixed scroll member  23  and the outermost peripheral portion of the movable scroll wall  34  of the movable scroll member  31 . The shaft support member  14  has a suction port  40  in the outer peripheral portion thereof, which connects the suction chamber  39  to the motor chamber  20 . The first housing component  12  has an inlet  50  that connects the motor chamber  20  with an external refrigerating circuit (not shown). Therefore, low-pressure refrigerant gas is introduced from the external refrigerating circuit into the suction chamber  39  through the inlet  50 , the motor chamber  20  and the suction port  40 .  
      In the housing  11 , a discharge chamber  41  is defined by the second housing component  13  and the fixed scroll member  23 . The fixed scroll member  23  has a discharge port  23   a  at the center of the fixed base plate  24  thereof. The innermost compression chamber  37  is in communication with the discharge chamber  41  through the discharge port  23   a  and a discharge valve  23   b.  The second housing component  13  has an outlet  42  in communication with the discharge chamber  41 .  
      As the rotary shaft  17  is driven to rotate, the movable scroll member  31  orbits around the axis of the fixed scroll member  23  (which axis exists on the axis L of the rotary shaft  17 ) through the crankshaft  28 . At the same time, the rotation preventing mechanisms  38  prevent the movable scroll member  31  from rotating on its axis, while allowing the orbiting movement of the movable scroll member  31 . As the compression chambers  37  are moved radially inwardly from the outer peripheral side of the fixed and movable scroll walls  26 ,  34  of the fixed and movable scroll members  23 ,  31  toward their center by the orbital movement of the movable scroll member  31 , the compression chambers  37  progressively reduce in volume. Thereby, the low-pressure refrigerant gas introduced into the compression chambers  37  from the suction chamber  39  is compressed. The compressed high-pressure refrigerant gas is discharged from the innermost compression chamber  37  into the discharge chamber  41  through the discharge port  23   a  and the discharge valve  23   b  due to the communication of the innermost compression chamber  37  with the discharge port  23   a.    
      The following will describe a mechanism for pressing the movable scroll member  31  against the fixed scroll member  23 . The movable scroll member  31  and the shaft support member  14  in the back of the movable base plate  32  of the movable scroll member  31  cooperate to define therebetween a back pressure chamber  49 . The pressure in the back pressure chamber  49  is adjusted by a back pressure regulating mechanism  43 .  
      The back pressure regulating mechanism  43  includes a fixed passage  44  formed in the outer peripheral portion of the fixed scroll member  23 , a communication groove  45  formed around the rear opening  44   a  of the fixed passage  44  in the fixed scroll member  23 , and a movable passage  46  formed in the outer peripheral portion of the movable scroll member  31 . The fixed passage  44  is in communication with the discharge chamber  41  through the front opening  44 b thereof and a filter  48 . The movable passage  46  is in communication with the back pressure chamber  49  through the rear opening  46   a.  The fixed passage  44  is brought into or out of communication with the communication groove  45  by a slight frontward or rearward movement of the movable scroll member  31 .  
      The movable scroll member  31  is movable frontward or rearward depending on the pressure difference between the pressure in the compression chambers  37  (thrust force) and the pressure in the back pressure chamber  49  (back pressure force). When the thrust force exceeds the back pressure force in operation of the compressor, the movable scroll member  31  is pressed and moved rearward by the thrust force. A clearance is then formed between the movable scroll member  31  and the fixed scroll member  23 , and the fixed passage  44  communicates with the communication groove  45  through the clearance, accordingly Therefore, high-pressure refrigerant gas is introduced from the discharge chamber  41  into the back pressure chamber  49  through the fixed passage  44 , the clearance, the communication groove  45 , and the movable passage  46 .  
      On the other hand, when the back pressure force is increased by the introduction of the high-pressure refrigerant gas into the back pressure chamber  49  and exceeds the thrust force, the movable scroll member  31  is moved frontward by the back pressure force and comes into contact with the fixed scroll member  23 . Then the clearance between the movable scroll member  31  and the fixed scroll member  23  disappears, and the communication between the fixed passage  44  and the communication groove  45  is blocked As a result of the above frontward movement of the movable scroll member  31 , a clearance is formed between the movable scroll member  31  and the shaft support member  14 . High-pressure refrigerant gas flows from the back pressure chamber  49  into the suction chamber  39  through the clearance between the movable scroll member  31  and the shaft support member  14 .  
      As described above, the back pressure regulating mechanism  43  is operable to vary the clearance between the movable scroll member  31  and the fixed scroll member  23  and also the clearance between the movable scroll member  31  and the shaft support member  14  so that the back pressure force becomes an appropriate value in response to the thrust force, thus autonomously regulating the back pressure force. By regulating the back pressure force appropriately, sealing of the compression chambers  37  is enhanced, with the result that the compression efficiency of the compressor is improved.  
      The following will describe a seal mechanism  51  of the preferred embodiment of the present invention with reference to  FIG. 2 .  FIG. 2  shows an enlarged cross-sectional view showing part of the compressor which is enclosed by the dotted oval A in  FIG. 1 . The seal mechanism  51  is adapted to seal a gap  67  that is formed between the shaft support member  14  and the rotary shaft  17  in the front of the radial bearing  19  provided in the shaft support member  14 . As shown in  FIG. 2 , the seal mechanism  51  is positioned to separate the back pressure chamber  49  as a high-pressure region and the motor chamber  20  as a low-pressure region. The rotary shaft  17  is formed adjacently to the shaft support member  14  with a large-diameter portion  60  having a diameter greater than that of the rear part of the rotary shaft  17  and serving to restrict the frontward movement of the radial bearing  19 , a medium-diameter portion  62  extending frontward from the large-diameter portion  60  by way of a first stepped portion  61 , and a small-diameter portion  64  extending further frontward from the medium-diameter portion  62  by way of a second stepped portion  63 . The aforementioned crankshaft  28  is formed on the front end of the small-diameter portion  64 .  
      The large-diameter portion  60  has a circumferential surface  60   b  facing the inner circumferential surface  15   a  of the cylindrical portion  15  of the shaft support member  14 , and a front surface  60   c  facing the rear surface  52   a  of a fixed wall  52  which will be described later. The medium-diameter portion  62  has a circumferential surface  62   b  that faces the inner circumferential surface  52   b  of the fixed wall  52  and is coaxial with the rotary shaft  17 . The medium-diameter portion  62  also has a front surface  62   c  as a first surface that faces back pressure chamber  49 . The second stepped portion  63  has a chamfered edge  66  connecting the front surface  62   c  and the circumferential surface  62   b.  The small-diameter portion  64  has a circumferential surface  64   b  that is exposed to the back pressure chamber  49 .  
      The fixed wall  52  is formed integrally with the shaft support member  14  that forms a part of the housing  11 . The fixed wall  52  is formed protruding inwardly or toward the rotary shaft  17  in the space between the radial bearing  19  and the balancer  29 . The fixed wall  52  has the rear surface  52   a  facing the motor chamber  20 , the inner circumferential surface  52   b  facing the circumferential surface  62   b  of the medium-diameter portion  62 , and a front surface  52   c  as a second surface facing the back pressure chamber  49 . The fixed wall  52  has a stepped portion  59  in the front of the front surface  52   c.  The fixed wall  52  has at the stepped portion  59  an accommodation surface  56  whose inner diameter is larger than that of the inner circumferential surface  52   b.  An annular groove  56   a  is formed in the accommodation surface  56  of the fixed wall  52  for receiving therein a seal member  53 .  
      The seal member  53  has an annular and plate-like shape and made of a flexible material such as resin. The seal member  53  has an inner peripheral portion  53   a  whose inner diameter is smaller than the outer diameter of the  2 o medium-diameter portion  62  and larger than the outer diameter of the small-diameter portion  64 , and an outer peripheral portion  53   b  whose outer diameter that is larger than the inner diameter of the accommodation surface  56 . The seal member  53  is installed with the outer peripheral portion  53   b  thereof set in the annular groove  56   a  and held in place by a circlip  55  that is fitted in the annular groove  56   a  in the front of the outer peripheral portion  53   b,  as shown in  FIG. 2 . Thus, the seal member  53  is fixed to the shaft support member  14  in contact with the front surface  52   c.    
      The front, surface  52   c  of the fixed wall  52  is located rearward of the front surface  62   c  of the medium-diameter portion  62 , so that, when the seal member  53  is installed in place, its inner peripheral portion  53   a  is bent forward to be in contact with the edge  66  connecting the circumferential surface  62   b  and the front surface  62   c,  as shown in  FIG. 2 .  
      The gap  67  between the inner circumferential surface  52   b  of the fixed wall  52  and the circumferential surface  62   b  of the medium-diameter portion  62  corresponds to a gap between the housing  11  (the fixed wall  52 ) and the rotary shaft  17  in the present invention, and the seal member  53  blocks the fluid communication between the back pressure chamber  49  and the motor chamber  20  via the gap  67 .  
      As described above, high-pressure refrigerant gas is introduced from the discharge chamber  41  into the back pressure chamber  49  in operation of the compressor, and the pressure in the back pressure chamber  49  becomes higher than that in the motor chamber  20 , thus a pressure difference being created therebetween. Due to this pressure difference, the back pressure in the back pressure chamber  49  is applied to the seal member  53 . In operation of the compressor, the seal member  53  slides relative to and in pressing contact with the edge  66 , thereby to seal the gap  67 .  
      According to the above-described first preferred embodiment, the following advantageous effects are obtained.  
      (1) The seal member  53  maintains its contact with the edge  66  connecting the circumferential surface  62   b  of the medium-diameter portion  62  of the rotary shaft  17  and the front surface  62   c  facing the back pressure chamber  49 . Since the seal member  53  is in contact with the rotary shaft  17  substantially in a line contact manner rather than in a surface-to-surface contact manner, the contact area and hence the sliding resistance is minimized. In operation of the compressor, the pressure in the back pressure chamber  49  is increased as described earlier, so that the seal member  53  is pressed strongly against the edge  66 . Thus, the seal member  53  which is pressed against the edge  66  by additional fluid pressure enhances its sealing capability. The seal mechanism  51  which dispenses with a coil spring is simple in structure. Accordingly, the seal mechanism  51  may be used advantageously at a position where the back pressure chamber  49  and the motor chamber  20  are separated in a scroll compressor that requires reduction of the sliding resistance and satisfactory sealing.  
      (2) The seal member  53  is fixed to the shaft support member  14  that is located round the rotary shaft  17 . Thus, the distance from the axis of the rotary shaft  17  to the sliding position of the seal member  53  is shorter in comparison with the case wherein the seal member  53  is fixed to the rotary shaft  17  and slides relative to the shaft support member  14 . As a result, the peripheral speed at the edge  66  of the rotary shaft  17  with which the seal member  53  maintains in contact is lower, with the result that the sliding resistance of the seal member  53  and the edge  66  is reduced.  
      (3) Carbon dioxide is used as the refrigerant in the compressor. Thus, the pressure in the back pressure chamber  49  becomes extremely high in operation of the compressor, and the force applied to the seal member  53  is extremely large, accordingly. However, since the seal member  53  is in contact with the edge  66 , the sliding resistance is minimized, so that the sealing of the seal member  53  is further improved. Therefore, the seal mechanism  51  of the present preferred embodiment is advantageously applicable to a compressor using carbon dioxide as the refrigerant.  
      (4) The seal mechanism  51  is also advantageously applicable to a compressor using an electric motor such as  21  wherein the sliding resistance should be as low as possible.  
      The following alternative embodiments may be practiced without departing from the scope of the present invention  
      In the first preferred embodiment, the seal member  53  is fixed to the shaft support member  14  with the outer peripheral portion  53   b  placed therein. In the alternative embodiment shown in  FIG. 3 , an annular and plate-like seal member  54  is fixed to the rotary shaft  17  with the inner peripheral portion  54   a  thereof placed in an annular groove  69  that is formed in the circumferential surface  64   b  of the small-diameter portion  64  of the rotary shaft  17 . The seal member  54  is in contact with the front surface  62   c  of the medium-diameter portion  62  as a second surface. In this case, it is so arranged that the front surface  52   c  of the fixed wall  52  is located forward of the front surface  62   c  of the medium-diameter portion  62 . The outer peripheral portion  54   b  of the seal member  54  is bent forward to be in contact with a chamfered edge  68  connecting the front surface  52   c  of the fixed wall  52  as a first surface and the inner circumferential surface  52   b  of the fixed wall  52  as the circumferential surface that is coaxial with the rotary shaft  17 . The medium-diameter and small-diameter portions  62 ,  64  correspond to a fixed portion of the rotary shaft of the present invention.  
      In the first preferred embodiment, the seal member  53  is made of a flexible material such as resin and it is made in contact with the edge  66  by bending. A seal member  70  of the alternative embodiment shown in  FIG. 4  is made of a rigid material such as rigid metal or resin which is formed in the shape similar to that of the seal member  53  when it is bent in contact with the edge  66  as in the first preferred embodiment.  
      In the first preferred embodiment, the annular and plate-like seal member  53  is used. A seal member  71  of the alternative embodiment shown in  FIG. 5  is of a funnel shape broadening rearwardly and has an annular and plate-like shape. The seal member  71  has a large-diameter portion  71   a  adjacent to the wide rear opening and a small-diameter portion  71   b  adjacent to the narrow front opening. The seal member  71  is set such that its large-diameter portion  71   a  is embedded in the fixed wall  52  and its inner circumferential surface  72  is in contact with the edge  66  at the small-diameter portion  71   b,  as shown in  FIG. 5 .  
      In the first preferred embodiment, the seal mechanism of the present invention is applied to a scroll type compressor. Alternatively, the present invention is applicable to compressors of other known types such as piston type and vane type.  
      In the first preferred embodiment, the rotary shaft  17  is driven by the electric motor  21 . Alternatively, a belt type transmission may be used, in which the rotation of a vehicle engine is transmitted to the rotary shaft through a belt to drive the rotary shaft.  
      The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.