Abstract:
A compressor including a compressing mechanism accommodated in a housing. The mechanism draws refrigerant from an intake chamber into a compression chamber and discharges the refrigerant from the compression chamber to the discharge chamber. A seal device prevents leakage of refrigerant from the internal space to the atmosphere between the drive shaft and the housing. An isolation chamber, which is separately formed in the housing, accommodates the seal device. A pressure reducing passage reduces the pressure of the isolation chamber to reduce the pressure difference applied to the seal device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to compressors. More particularly, the present invention relates to compressors that have shaft seals for preventing leakage of refrigerant from the internal space,of the compressor about the drive shaft. 
     In compressors that perform compression and intake by rotation of a drive shaft, a seal is typically provided for preventing leakage of refrigerant from the inner space about the drive shaft. Generally, this kind of seal is positioned to seal between the intake pressure area, which has a lower pressure than the discharge pressure area, and the atmosphere. Or, in a variable displacement compressor having an inclining swash plate, the seal device is positioned to seal between the operating chamber, which accommodates the swash plate, and the atmosphere. 
     However, as described in Japanese Unexamined Patent Publication No. 8-110104, the seal must withstand a great burden when carbon dioxide (CO 2 ), the refrigerant pressure of which is ten times greater than that of fluorocarbon-based refrigerant, is used as refrigerant. The great burden shortens the life of the seal. In a variable displacement compressor that controls the inclination of the swash plate by varying the pressure of the operating chamber, the pressure of the operating chamber is higher than the intake pressure of a fixed displacement compressor, thus increasing the burden on the seal. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to improve the reliability of the seal device of a compressor that uses a high-pressure refrigerant like CO 2  by decreasing the burden on the seal device. 
     To achieve the above objective, the present invention provides a compressor having a shaft seal. The compressor includes a housing, an intake chamber located within the housing, a discharge chamber located within the housing, an operating chamber located within the housing, and a gas compressing mechanism located within the housing. At least a portion of the compressing mechanism is located within the operating chamber. The compressing mechanism draws refrigerant gas from the intake chamber and discharges the refrigerant gas to the discharge chamber. The compressor further includes a drive shaft extending between the interior of the housing and the exterior of the housing. The drive shaft drives the compressing mechanism. The compressor further includes a seal for preventing leakage of refrigerant gas from the interior of the housing to the atmosphere. The seal seals a gap between the drive shaft and the housing. One side of the seal is exposed to the atmosphere. The compressor further includes an isolation chamber formed in the housing to surround a portion of the drive shaft. One side of the seal is exposed to the interior of the isolation chamber. A pressure difference is applied to the seal by the difference between the pressures of the isolation chamber and the atmosphere. The compressor further includes a pressure reducing device for reducing the pressure in the isolation chamber when the compressor is operating. The pressure reducing device reduces the pressure difference applied to the seal and lowers the pressure in the isolating chamber with respect to that of the operating chamber. 
     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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 cross-sectional view of a compressor according to a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view taken on line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view taken on line  3 — 3  of FIG. 
     FIG. 4 is a partial cross-sectional view showing a second embodiment; 
     FIG. 5 is a partial cross-sectional view showing a third embodiment; 
     FIG. 6 is a partial cross-sectional view showing a fourth embodiment; 
     FIG. 7 is a cross-sectional view of a compressor according to a fifth embodiment; 
     FIG. 8 is a cross-sectional view of a compressor according to a sixth embodiment; 
     FIG.  9 ( a ) is a partial cross-sectional view of the compressor of FIG. 8 when the intake stroke starts and the pressure of the isolation chamber  123  is being reduced; 
     FIG.  9 ( b ) is a partial cross-sectional view of the compressor of FIG. 8 when the pressure of the isolation chamber  123  is not being reduced; and 
     FIG. 10 is a cross-sectional view of a compressor according to a seventh embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will now be described with reference to FIGS. 1-3. 
     As shown in FIG. 1, a front housing  12  and a rear housing  13  are respectively secured to the front part and the rear part of a cylinder block  11  by bolts  30 . An operating chamber  121  as an internal space is defined between the cylinder block  11  and the front housing  12 . A drive shaft  14  is rotatably supported by the cylinder block  11  and the front housing  12  through radial bearings  15 ,  16 . The radial bearing  15  supports the drive shaft  14  in a bore  122  of the front housing  12 . The radial bearing  16  supports the drive shaft  14  in a through hole  116  of the cylinder  11 . A disk-shaped rotor  17  is fixed to the drive shaft  14  in the operating chamber  121 . A support arm  171 , which is formed on the periphery of the rotor  17 , includes a guide hole  172 . A thrust bearing  34  is located between the rotor  17  and the front housing  12 . 
     In the operating chamber  121 , a swash plate  18  is supported by the drive shaft  14  so that the swash plate slides axially and inclines with respect to the drive shaft  14 . A connecting piece  181  is fixed to the swash plate  18 . Guide pins  19  are attached to the distal end of the connecting piece  181 . The guide pins  19  engage with guide holes  172 . Each guide hole  172  guides the inclination of the swash plate  18  through engagement with the associated guide pin  19 . The guide pins and the drive shaft  14  enable the swash plate  18  to move axially along the drive shaft  14  and to integrally rotate with the drive shaft  14 . 
     As shown in FIGS. 1 and 3, cylinder bores  111  of the cylinder block  11  accommodate pistons  20 . Each piston defines a compression chamber  112 . A pair of shoes  21  is located between a neck  201  of each piston and the swash plate  18 . The rotation of the swash plate  18  is converted to reciprocal movement of each piston  20  through the shoes  21  and each piston moves back and forth in the corresponding cylinder bore  111 . 
     In the rear housing  13 , an intake chamber  131  and a discharge chamber  132  are defined. A partition plate  22  and valve plates  23 ,  24  are, located between the cylinder block  11  and the rear housing  13 . Intake ports  221  and discharge ports  222  are provided on the partition plate  22 . Each intake port  221  is opened and closed by a flexible intake valve  231  of the valve plate  23 . Each discharge port  222  is opened and closed by a flexible discharge valve  241  of the valve plate  24 . A retainer  31  limits the opening degree of each discharge valve  241 . When each piston moves to its top dead center position, refrigerant in the compression chamber  112  presses open the discharge valve  241  and is discharged through the discharge port  22  into the discharge chamber  132 . When each piston moves to the bottom dead center position, refrigerant in the intake chamber  131  presses open the intake valve  231  and is drawn into the compression chamber  112  through the intake port  221 . 
     The stroke of each piston  20  and the inclination of the swash plate  18  vary in accordance with the difference between the pressure in the operating chamber  121  and that of the compression chamber  112  (intake pressure). Thus, the inclination of the swash plate  18  varies the displacement. When the pressure of the operating chamber  121  increases, the inclination angle of the swash plate decreases. This decreases the displacement. When the pressure of the operating chamber  121  decreases, the inclination angle of the swash plate  18  increases. This increases the displacement. 
     An electromagnetic displacement control valve  25  in the rear housing  13  controls the refrigerant supply from the discharge chamber  132  to the operating chamber  121 . The refrigerant in the operating chamber  121  flows to the intake chamber  131  through a pressure release passage  113 , which is restricted. The pressure of the operating chamber  121  is controlled by the refrigerant flow from the operating chamber  121  to the intake chamber  131  through the pressure release passage  113  and by the refrigerant supply through the displacement control valve  25 . 
     A first seal device  26  and a second seal device  27  are located between the front housing  12  and the drive shaft  14 . The second seal device is a lip seal. The first seal device  26  includes a seal ring  261  that contacts the wall of the bore  122 . The seal ring  261  is supported in a support ring  262 . The second seal device  27  contacts one end of the support ring  262  and the periphery of the drive shaft  14 . In the bore  122 , which accommodates the first and the second seal devices  26 ,  27 , an isolation chamber  123  is formed. The isolation chamber  123  is isolated from the operating chamber  121  by the radial bearing  15  and the first and the second seal devices  26 ,  27 . 
     As shown in FIGS. 1 and 2, a pressure reducing passage  28  is formed in the drive shaft  14 . An entrance  281  of the reducing passage  28  is open to the isolation chamber  123 , and an exit  282  of the reducing passage  28  is open to the through hole  116 . A fan  29  for moving refrigerant is secured to the end (on the side of the exit  282 ) of the drive shaft  14 . As shown in FIG. 3, the fan  29  rotates in the direction of the arrow R, thus moving refrigerant from the reducing passage  28  to the through hole  116 . Then, the refrigerant flows to the operating chamber  121  through gaps in the radial bearing  16 . 
     The isolation chamber  123  is connected to the operating chamber  121  through gaps in the radial bearing  15  and the thrust bearing  34 . The gaps in the radial bearing  15  and the thrust bearing  34  also function as oil supply passage. 
     The fan  29 , which, together with the pressure reducing passage  28 , serves as a pressure reducer driven by the rotation of the drive shaft  14  when the compressor operates. The fan  29  removes refrigerant from the isolation chamber  123  and delivers it to the through hole  116  through the reducing passage  28 . Accordingly, the pressure of the isolation chamber  123  is lower than that of the operating chamber  121 . Without such pressure reducing action, the pressure difference that applies to the first and second seal devices  26 ,  27  between the atmosphere and the isolation chamber  123  would be equal to the pressure difference between the atmosphere and the operating chamber  121 . In the present embodiment, due to the pressure reducer, the pressure in the isolation chamber  123  is lower than that of the Operating chamber  121 . Thus, the pressure difference between the isolation chamber  123  and the atmosphere is lower than that between the atmosphere and the operating chamber  121 . This reduces the burden on the first and second seal devices  26 ,  27  and improves their durability. Reducing the burden on the seals by reducing the pressure of the isolation chamber  123  is especially effective with regard to the second seal device  27 , which slidably contacts the drive shaft  14 . 
     Using the drive shaft  14  and the fan  29  as a refrigerant mover requires only a simple construction. There is no need for any special drive mechanism for driving the fan  29 . 
     The refrigerant from the operating chamber  121  flows little by little into the isolation chamber  123  through the gaps in the radial bearing  15  and the thrust bearing  34 . At the same time, lubricant mixed in the refrigerant lubricates the radial bearing  15  and the second seal device  27 . That is, the reduction of pressure in the isolation chamber  123  by the fan  29  helps lubricate the radial bearing  15 , the thrust bearing  34 , and the second seal device  27 . 
     The pressure reducing passage  28  is connected to the operating chamber  121  through the gaps in the radial bearing  16 . That is, a refrigerant circulation passage is formed through the operating chamber  121 , the isolation chamber  123 , and the pressure reducing passage  28  and the through hole  116 . The refrigerant circulation passage returns lubricant to the operating chamber  121  where it is needed. 
     The pressure of the operating chamber  121  is lower than that of the discharge chamber  132 . Though the pressure of the operating chamber  121  varies, the pressure of the operating chamber  121  is maintained higher than that of the intake chamber  131 . The pressure reduction in the isolation chamber  123  is especially suitable for reducing the burden on seal devices  26 ,  27  that seal between the operating chamber  121  and the atmosphere. 
     In a compressor using CO 2  refrigerant, the pressure of which is ten times higher than that of the fluorocarbon-based refrigerant, the pressure reduction of the isolation chamber  123  is especially suitable for reducing the burden on the seal devices  26 ,  27 . 
     A second embodiment of FIG. 4, a third embodiment of FIG. 5, and a fourth embodiment of FIG. 6 will now be described. The construction of each embodiment is similar to that of the first embodiment, and like numerals are used to refer to like members. 
     In the second embodiment, an oil supply passage  124 , which is formed in the front housing  12 , connects the operating chamber  121  to the isolation chamber  123 . When the pressure of the isolation chamber  123  is reduced, refrigerant from the operating chamber  121  flows to the isolation chamber  123 . The oil mixed in the refrigerant is effectively supplied to the isolation chamber  123  through the oil supply passage  124 . Accordingly, lubrication of the second seal device  27  is more effective. 
     In the third embodiment of FIG. 5, a bolt hole  127  for the bolt  30  in the front housing  12  and the isolation chamber  123  are connected by an oil supply passage  125 . The bolt hole  127  is located at the bottom of the operating chamber  121 . Lubricant oil that settles at the bottom of the operating chamber  121  flows to the isolation chamber  123  through the oil supply passage  125  when the pressure of the isolation chamber  123  is reduced. In this way, the second seal device  27  is more effectively lubricated. 
     In the fourth embodiment shown in FIG. 6, the bolt hole  127  and the top of the isolation chamber  123  are connected by an oil supply passage  126 . The lubricant oil accumulated at the bottom of the operating chamber  121  flows to the upper portion of the isolation chamber  123  through the oil supply passage  126  when the pressure of the isolation chamber  123  is reduced. The oil temporarily remains in the isolation chamber  123 . Accordingly, the second seal device  27  is more effectively lubricated. 
     A fifth embodiment of FIG. 7 will now be described. Like numerals are used to refer to like members of the first embodiment. 
     In the fifth embodiment, a spiral groove  283  is formed on the inner surface of the pressure reducing passage  28  in the drive shaft  14 . The spiral groove  283  moves refrigerant of the reducing passage  28  from the isolation chamber  123  to the through hole  116  when the drive shaft  14  rotates, thus reducing the pressure of the isolation chamber  123 . Employing the spiral groove  283  in the drive shaft  14  makes it unnecessary to provide a special space for a fan. 
     A sixth embodiment of FIGS. 8,  9 ( a ) and  9 ( b ) will now be described. Like numerals are used to refer to members similar to those of the first embodiment. 
     A pressure reducing auxiliary chamber  134  is formed in the rear housing  13 . The auxiliary chamber  134  is connected to the through hole  116  by a connecting port  223 , which is formed to pass through the partition plate  22 , the valve plates  22 ,  24  and the retainer  31 . Also, the auxiliary chamber  134  is connected to the compression chamber  112  by a pressure reducing port  224 , which is formed to pass through the partition plate  22 , the valve plates  23 ,  24  and the retainer  31 . The pressure reducing port  224  is opened and closed by the valve  232  of the valve plate  23 . The pressure reducing passage  28 , the through hole  116 , the connecting port  223 , the auxiliary chamber  134  and the pressure reducing port  224  form a passage for delivering refrigerant from the isolation chamber  123  to the compression chamber  112 . 
     A third seal device  32  and a lip seal type fourth seal device  33  are located between the inner surface of the through hole  116  and the drive shaft  14 . The third seal device  32  includes a seal ring  321 . The seal ring contacts the inner surface of the through hole  116  and is supported by a support ring  322 . The fourth seal device  33  contacts an end surface of the support ring  322  and the outer surface of the drive shaft  14 . The seal devices  32 ,  33  close off communication between the through hole  116  and the operating chamber  121  along the outer surface of the drive shaft  14 . That is, the seal devices  32 ,  33  form a seal between the drive shaft  14  and the cylinder block  11 . 
     An intake passage  114  is formed to connect the intake chamber  131  with the cylinder bore  111  in the cylinder block  11 . As shown in FIG. 8, the head of the piston  20 , at its top dead center position, is located closer to the partition plate  22  than the opening  115 . The intake port  221  is connected to the cylinder bore  111  by the intake passage  114 . 
     FIG. 8 shows a state when the discharge stroke of the piston  20  is completed, that is, when the piston is at the top dead center position. In this state, the piston  20  closes the opening  115  of the intake passage  114  and the valve  232  is closed. In the state of FIG.  9 ( a ), the piston  20  is about to start the intake stroke and the opening  115  is closed by the piston  20 . In this state, the refrigerant of the auxiliary chamber  134  presses open the valve  232  and flows into the compression chamber  112  by the vacuum action of the intake stroke of the piston  20 . Accordingly, the pressure of the isolation chamber  123 , which is connected to the auxiliary chamber  134  by the pressure reducing passage  28 , is reduced. In the state of FIG.  9 ( b ), the piston  20  opens the opening  115  and the refrigerant of the intake chamber  131  presses open the intake valve  231  and flows into the compression chamber  112 . The pressure of the compression chamber increases above the pressure of the auxiliary chamber  134 , therefore the valve  232  closes the pressure reducing port  224 . 
     The sixth embodiment has the following advantages. 
     At the beginning of the intake stroke, the valve  232  opens the pressure reducing port  224 , connecting the isolation chamber  123  to the compression chamber  112 . Accordingly, the pressure of the isolation chamber  123  is lowered below the intake pressure of the intake chamber  131 . The pressure of the isolation chamber  123  is reduced for a certain period, which extends into the discharge stroke. This relieves the burden on the seal devices  26 ,  27 . Further, since the valve  232  closes, the compressed refrigerant of the compression chamber  112  cannot flow into the auxiliary chamber  134 . Therefore, the output of the compressor is not reduced by leakage from the port  224 . 
     Forming part of the refrigerant delivering passage in the drive shaft  14  for connecting the compression chamber  112  to the isolation chamber  123  simplifies the structure. 
     A seventh embodiment of FIG. 10 will now be described. Like numerals are used to refer to members that are similar to those of the first embodiment. 
     In this embodiment, a passage  35  is formed in the drive shaft  14 . A restricting passage  36 , which restricts a flow rate of the refrigerant, opens at the outer surface of the drive shaft  14  in the vicinity of the radial bearing  15 . The restricting passage  36  is connected to the passage  35 . A fan  37  is attached to the drive shaft  14  in the vicinity of the restricting passage  36 . The fan  37  integrally rotates with the drive shaft  14 . The refrigerant of the isolation chamber  123  is moved by the fan  37 , and the pressure of the isolation chamber  123  is reduced accordingly. As in the first embodiment, the burden on the first and second seal devices  26 ,  27  is reduced. 
     Refrigerant from the isolation chamber  123  is sent to the operating chamber  121  through the gaps, or clearances, in the thrust bearing  34 . The lubricant oil mixed in the refrigerant lubricates the thrust bearing  34 . Refrigerant from the operating chamber  121  flows little by little to the isolation chamber  123  through the passage  35  and the restricting passage  36 . The oil mixed in the refrigerant lubricates the radial bearing  15  and the second seal device  27 . That is, the action of the fan  37  helps lubricate the radial bearing  15 , the thrust bearing  34  and the second seal device  27 . 
     In the present invention, the following embodiments are also possible. 
     The pressure reducing passage  28  of the drive shaft  14  may be connected to the intake chamber  131 . Refrigerant from the isolation chamber  123  would then be sent to the intake chamber  131 . 
     The operating chamber  121  may be completely shut off from the isolation chamber  123 . 
     The present invention may be applied to double-headed piston compressors. 
     The present invention may be applied to compressors that have seal devices in the intake chamber and in the discharge chamber in addition to the operating chamber. 
     The present invention may be applied to compressors other than piston type compressors, such as, scroll type compressors, and vane type compressors. 
     Therefore, 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 and equivalence of the appended claims.