Abstract:
A shaft sealing assembly for a compressor includes first and second lip rings, each of which is disposed around a shaft of a compressor to provide sealing. A retainer ring is disposed between the two lip rings to retain the shape of the first lip ring, which serves to allow leakage of fluid when the shaft rotates and prevent the leakage when the shaft is stopped. The three rings are held together at the radial portions of the rings. Each of the radial portions of the two lip rings extends outwardly beyond the radial portion of the retainer ring, providing an annular contact area. The two lip rings resiliently contact one another in the contact area. An annular projection is provided on at least one of the lip rings in the contact area to ensure the sealing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a shaft sealing assembly. More specifically, the present invention pertains to a shaft sealing assembly that prevents fluid such as refrigerant and lubricant from leaking from a compressor. 
     A typical shaft sealing assembly  50  is structured as follows. As shown in FIGS. 4 and 4A, the sealing assembly  50  is located between a drive shaft  61  and a compressor housing to prevent leakage of fluid from the inside to the outside of the compressor. A first lip ring  51 , which is made of synthetic rubber, includes a lip  51   a . The lip  51   a  is formed at the radially inner area of the first lip ring  51 . A retainer ring  52 , which is made of metal, retains the position of the lip  51   a  to contact a drive shaft  61 . A second lip ring  53 , which is made of fluororesin, includes a lip  53   a . The lip  53   a  is formed at the radially inner area of the second lip ring  53  and is curved toward the inside of the compressor (right side in FIG.  4 ). A spiral pump slit  53   b  is formed in the lip  53   a  about the axis of the second lip ring  53 . A third lip ring  54 , which is made of synthetic rubber, includes a lip  54   a . The first lip ring  51 , the retainer ring  52 , the second lip ring  53 , and the third lip ring  54  are arranged in this order from the inside to the outside of the compressor as shown in FIG.  4 . 
     The rings  51 - 54  are tightly held together in a cylindrical case  55 . Accordingly, the first and the second lip rings  52 ,  53  contact the retainer ring  52  and the case  55 . 
     When the drive shaft  61  is rotating, or when the compressor is operating, high pressure gas in the compressor is applied to the lip  53   a  of the second lip ring  53 . Accordingly, the lip  53   a  is pressed against the drive shaft  61  by a predetermined force, which prevents leakage of fluid from the compressor. In this state, the pump slit  53   b  of the lip  53   a  has a spiral pumping effect and positively sends fluid back between the lip  53   a  and the drive shaft  16 . This also improves the fluid-sealing performance of the second lip ring  53 . 
     When the drive shaft  61  is not rotating, or when the compressor is not operating, the lip  51   a  of the first lip ring  51  resiliently contacts the drive shaft  61 . This prevents leakage of fluid from the compressor. When the drive shaft  61  is not rotating, the pressure in the compressor is relatively low and the lip  53   a  of the second lip ring  53  is pressed against the rotational shaft  61  by a relatively small force. Accordingly, the shaft sealing assembly includes the first lip ring  51  to compensate for the weak sealing ability of the second lip ring  51 . 
     When the drive shaft  61  is rotating, the lip  51   a  of the first lip ring  51  allows fluid in the compressor to flow toward the second lip ring  53 . The position of the lip  51   a  with respect to the drive shaft  61  is retained by the retainer ring  52  when high pressure is applied to the inside of the first lip ring  51 . 
     The fluid (mainly lubricant) that leaks by the lip  51   a  of the first lip ring  51  lubricates and cools the lips  51   a ,  53   a  of the first and second lip rings  51 ,  53 . Accordingly, the lips  51   a ,  53   a  are not worn by friction. This extends the life of the first and second lip rings  51 ,  53 . 
     The lip  54   a  of the third lip ring  54  resiliently contacts the drive shaft  61  and prevents foreign particles from entering. Accordingly, foreign particles do not enter between the lip  53   a  and the drive shaft  61 , which prevents the performance of the second lip ring  53  from deteriorating. When the rotation of the drive shaft  61  is stopped, the third lip ring  54  prevents leakage of fluid that remains between the first lip ring  51  and the second lip ring  53 . 
     However, the first lip ring  51  permits leakage of fluid (refrigerant gas) during the rotation of the drive shaft  61 . The seal formed between the second lip ring  53  and the retainer ring  52  and between the second lip ring  53  and the case  55  has a lower sealing performance compared to the contact area seal formed between the first lip ring  51  and the retainer ring  52  and between the first lip ring  51  and the case  55 . Accordingly, as shown by FIG. 4A, the refrigerant gas that leaks past the first lip ring  51  is likely to enter between the second lip ring  53  and the retainer ring and between the second lip ring  53  and the case  55 . 
     When the rotation of the drive shaft  61  is stopped, the third lip ring  54  prevents leakage of the fluid remaining between the first lip ring  51  and the second lip ring  53 . In other words, the fluid (especially refrigerant gas) between the second lip ring  53  and the retainer ring  52  and between the second lip ring  53  and the case  55  does not flow out of the compressor after the drive shaft  61  is stopped. When the drive shaft  61  is stopped for a relatively long period, the refrigerant gas between the second lip ring  53  and the retainer ring  52  and between the second lip ring  53  and the case  55  can be liquefied by cooler temperatures. 
     If the drive shaft  61  rotates in this state, the temperature around the shaft sealing assembly  50  increases. Then, the liquidized refrigerant between the second lip ring  53  and the case  55  vaporizes, which moves the second lip ring  53  radially inward. This may release the second lip ring  53  from the case  55 . Since the second lip ring  53  and the retainer ring  52  are held together in the case  55  by friction and compression, the release of the second lip ring  53  also releases the retainer ring  52  from the case  55 . Accordingly, the retainer ring  52  cannot retain the initial position of the lip  51   a  of the first lip ring  51  with respect to the drive shaft  61 . As a result, the first lip ring  51  may not leak fluid, which causes the first and the second lip rings  51 ,  53  to wear prematurely. 
     On the other hand, the released second lip ring  53  may lift the first lip ring  51 , through the retainer ring  52 , from the drive shaft  61 . Thus, when the drive shaft  61  rotates, the first lip ring  51  may leak too much fluid that for the second lip ring  53  and the third lip ring  54  to stop. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a shaft sealing assembly for compressors that prevents fluid from entering between the periphery of the second lip ring and the case. 
     To achieve the above objective, the present invention provides a shaft sealing assembly for a rotary shaft extending through and supported by a housing. The shaft sealing assembly includes a first lip ring placed around the shaft. The first ring has a first peripheral portion, which extends in a substantially radial direction with respect to the shaft. The first lip ring also has a first lip portion that contacts the surface of the shaft. The first lip portion resiliently contacts the surface of the shaft. The first lip ring has a predetermined shape that prevents leakage of fluids from the inside of the housing when the shaft is stopped and allows leakage of fluids from the inside of the housing when the shaft rotates. A retainer ring is placed adjacent to the first lip ring around the shaft. The retainer ring has a second peripheral portion that extends in a substantially radial direction with respect to the shaft. The retainer ring supports the first lip ring so that the first ring substantially retains its shape. A second lip ring is also placed around the shaft and adjacent to the retainer ring on the opposite side of the retainer ring from the first lip ring. The second lip ring has a third peripheral portion that extends in a substantially radial direction with respect to the shaft and a second lip portion that extends substantially along the surface of the shaft. The second lip portion resiliently contacts the surface of the shaft to substantially prevent leakage of fluids from the inside of the housing. Further, a case is included for holding the rings together by gripping the first, the second, and the third peripheral portions. The first and the third flange portions extend outwardly beyond the second flange portion to provide an annular contact area, and the first and the second lip rings resiliently contact one another in the contact area. 
     Other aspects and advantages of the present 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 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 cross sectional view of a variable displacement compressor according to one embodiment of the present invention; 
     FIG. 2 is an enlarged cross sectional view showing the shaft sealing assembly of FIG. 1; 
     FIG. 2A is an enlargement of an encircled portion of FIG. 2; 
     FIG.  3 ( a ) is a partial enlarged view of FIG. 2; 
     FIG.  3 ( b ) is a view showing a projection when no force is applied; 
     FIG.  3 ( c ) is a view showing the projection when a force is applied. 
     FIG. 4 is a cross sectional view showing a prior art shaft sealing assembly; and 
     FIG. 4A is an enlargement of an encircled portion of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A variable displacement compressor for a vehicle air-conditioning system according to one embodiment of the present invention will now be described. 
     As shown in FIG. 1, a front housing member  11  is coupled to the front end of the cylinder block  12 . A rear housing member  13  is coupled to the rear end of the cylinder block  12  through a valve plate  14 . A crank chamber  15  is defined between the front housing member  11  and the cylinder block  12 . 
     A drive shaft  16  passes through the crank chamber  15  and is rotatably supported by the front housing member  11  and the cylinder block  12 . The front end of the drive shaft  16  extends through the front wall of the front housing member  11 . The drive shaft  16  is connected to a vehicle engine (not shown) through a clutch mechanism such as an electromagnetic clutch. Accordingly, when the engine is operating and the clutch mechanism is engaged, the drive shaft  16  rotates. 
     A boss  17  extends from the front wall of the front housing  11  and surrounds the front end of the drive shaft  16 . A shaft sealing assembly  18  is accommodated in the boss  17  and seals the drive shaft  16 . The details of the shaft sealing assembly  18  will be described later. 
     A rotor  19  is secured to the drive shaft  16  in the crank chamber  15 . A swash plate  20  is supported by the drive shaft  16  to slide on the surface of the drive shaft  16  and to incline with respect to the drive shaft  16 . A hinge mechanism  21  is located between the rotor  19  and the swash plate  20 . The hinge mechanism  21  enables the swash plate  20  to rotate integrally with the drive shaft  16  and to slide axially on the surface of the drive shaft  16 . When the center of the swash plate  20  moves toward the cylinder block  12 , the inclination of the swash plate  20  decreases. When the center of the swash plate  20  moves toward the rotor  19 , the inclination of the swash plate  20  increases. 
     Cylinder bores  12   a  are formed in the cylinder block  12  around the axis of the drive shaft  16 . Each cylinder bore accommodates a single head piston  22 . Each piston  22  is coupled to the periphery of the swash plate  21  through shoes  23 . The rotation of the swash plate  20  is converted to reciprocation of each piston  22  in the corresponding cylinder bore  12   a.    
     A suction chamber  24  and a discharge chamber  25  are respectively defined in the rear housing member  13 . The valve plate  14  includes suction ports  26 , suction valves  27 , discharge ports  28 , and discharge valves  29 . When each piston  22  moves from the top dead center to the bottom dead center position, refrigerant gas in the suction chamber  24  is drawn into the corresponding cylinder bore  12   a  through the corresponding suction port  26  and the corresponding suction valve  27 . When each piston  22  moves from the bottom dead center to the top dead center, the refrigerant gas in the corresponding cylinder bore  12   a  is compressed to a predetermined pressure and is discharged to the discharge chamber  25  through the corresponding discharge port  28  and the corresponding discharge valve  29 . 
     A bleed passage  30  connects the crank chamber  15  to the suction chamber  24 . A pressurizing passage  31  connects the discharge chamber  25  to the crank chamber  15 . An electromagnetic displacement control valve  32  is located in the pressurizing passage  31 . The control valve  32  includes a solenoid  32   a  and a valve body  32   b . The excitation and de-excitation of the solenoid  32   a  caused the valve body  32   b  to open and close the pressurizing passage  31 . The excitation and de-excitation of the solenoid  32   a  is controlled by a computer (not shown) in accordance with the cooling load. Accordingly, the opening size of the pressurizing passage  31  is adjusted by the valve body  32   b , which varies the pressure in the crank chamber  15 . This adjusts the difference between the pressure in the crank chamber  15  and the pressure in the cylinder bores  12   a . As a result, the inclination of the swash plate  20  is varied, thus varying the stroke of each piston  22  and the displacement. 
     In other words, the de-excitation of the solenoid  32   a  causes the valve body  32   b  to open the pressurizing passage  31 , which connects the discharge chamber  25  to the crank chamber  15 . Accordingly, high pressure refrigerant gas in the discharge chamber  25  is supplied to the crank chamber  15  through the pressurizing passage  31 , which increases the pressure in the crank chamber  15 . The increase of pressure in the crank chamber  15  minimizes the inclination of the swash plate  20  and the stroke and displacement of each piston  22 . When the solenoid  32   a  is excited, the valve body  32   b  closes the pressurizing passage  31 , which lowers the pressure in the crank chamber as the bleed passage  30  releases the pressure. The decrease of the pressure in the crank chamber  15  maximizes the inclination of the swash plate  20  and the stroke and displacement of each piston  22 . 
     The shaft sealing mechanism  18  will now be described. 
     As shown in FIG. 2, a first lip ring  35 , a metal retainer ring  36 , a second lip ring  37 , a metal shape-retaining ring  38 , a third lip ring  39 , and a metal end ring  40  are arranged in this order. The first lip ring  35  and the third lip ring  39  are made of synthetic rubber such as an acrylonitrilebutadiene rubber. The second lip ring  37  is made of fluororesin such as PTFE (polytetrafluoroethylene). 
     A cylindrical metal case  41  includes a front rim  41   a  and a rear rim  41   b . The peripheries of the rings  35 - 40  are tightly held together by friction and compression between the front rim  41   a  and the rear rim  41   b  of the case  41  as shown in FIG.  2 . The case  41  and the rings  35 - 40  are accommodated in the boss  17 . Axial movement of the case  41  is limited by a step  17   a  and a snap ring  42 . 
     The first lip ring  35  is formed by a molding that covers the inner and outer surfaces of the case  41  in the vicinity of the rear rim  41   b . A peripheral part of the first lip ring  35  that covers the circumferential surface of the case  41  forms an outer seal  35   a , which contacts the inner surface  17   b  of the boss  17 . The outer seal  35   a  includes projections to improve its sealing function. An inner part of the first lip ring  35  that contacts the inner surface of the case  41  forms an inner seal  35   b , or a first peripheral portion, which is tightly held between the retainer ring  36  and the rear rim  41   b  of the case  41 . 
     A lip  35   c  is formed at the radially inner part of the first lip ring  35 . The lip  35   c  extends rearward and radially inward. A distal corner of the lip  35   c  contacts the surface  16   a  of the drive shaft  16 . As shown by FIG. 2A, a conical end surface S 1  forms a predetermined angle θ 1  with respect to the surface  16   a  of the drive shaft  16  (or the axis of the drive shaft  16 ). A side surface S 2  of the lip  35   c  forms a predetermined angle θ 2  with respect to the surface  16   a  of the drive shaft  16 . The position of the lip  35   c  of the first lip ring  35  is determined to fulfill the condition of θ 1 &lt;θ 2 . According to experiments by the present inventors, the first lip ring  35  effectively sealed the drive shaft  16  when positioned under the condition of θ 1 &lt;θ 2  while the drive shaft  16  was not rotating. However, it was also determined that, under these conditions, fluid leakage was permitted while the drive shaft  16  was rotating. 
     The second lip ring  37  is shaped like a disc with a hole in its center before installation. The second lip ring  37  is made of a sheet of fluororesin. The inner area of the second lip ring  37  is deformed to curve rearward when installed on the drive shaft  16 . The central deformed area of the second lip ring  37  forms a lip  37   a . A seal surface  37   b  of the lip  37   a , which has a predetermined axial dimension, contacts the surface  16   a  of the drive shaft  16 . A spiral pump slit  37   c  is formed on the seal surface  37   b  of the lip  37   a  about the axis L. When the drive shaft  16  is rotating, the pump slit  37   c  serves as a pump. 
     The retainer ring  36  is formed by deforming the inner area of an annular disc  36   a , or a second peripheral portion. The deformed portion forms a retaining part  36   b . The retaining part  36   b  extends rearward and is located between the lip  35   c  of the first lip ring  35  and the lip  37   a  of the second lip ring  37 . The distal end of the retaining part  36   b  contacts an inner surface of the lip  35   c  of the first lip ring  35  and supports the lip  35   c  with respect to the surface  16   a  of the drive shaft  16  (to maintain the relationship θ 1 &lt;θ 2 ). 
     The third lip ring  39  is formed by molding to cover the front side and the radially outer end surface of a shape-retaining ring  38 . The outer diameter of the shape-retaining ring  38  is smaller than the inner diameter of the case  41 . The outer diameter of the second and third lip rings  37 ,  39  are substantially the same as that of the case  41 . Accordingly, though the shape-retaining ring  38  is located between the third lip ring  39  and the second lip ring  37 , the peripheral part of the third lip ring  39  contacts the second lip ring  37 . The lip  39   a  of the third lip ring  39  contacts the surface  16   a  of the drive shaft  16 . 
     As shown in FIG.  3 ( a ), the first and the second lip rings  35 ,  37  are pressed against each other about the outer rim of the retainer ring  36  in the case  41 . That is, contact between the inner seal  35   b  of the first lip ring  35  and an outer portion  37   e , or a third peripheral portion, of the second lip ring  37  occurs radially outward from the annular disc  36   a  of the retainer ring  36 . The outer diameter of the retainer ring  36  is smaller than the inner diameter of the case  41 . The outer diameter of the inner seal  35   b  and the outer diameter of the second lip ring  37  are substantially the same as the inner diameter of the case  41 . Accordingly, the inner seal  35   b  and the second lip ring  37  contact one another (at surfaces  35   d ,  37   d ) about the annular disk  36   a  of the retainer ring  36  in the case  41 . 
     A projection  43  is integrally formed on the facing surface  35   d  of the inner seal  35   b  of the first lip ring  35 . The projection  43  extends in the direction of the axis L. As shown in FIG.  3 ( b ), when not compressed, the length of the projection  43  in the axial direction from the surface  35   d  is greater than the thickness of the annular disc  36   a  of the retainer ring  36 , or the distance between the facing surfaces  35   d  and  37   d  after assembly. Accordingly, as shown in FIG.  3 ( a ), the projection  43 , which is made of synthetic rubber more resilient than fluororesin, is pressed against the facing surface  37   d  of the second lip ring  37  and is compressed to the thickness of the annular disc  36   a  of the retainer ring  36  when the rings  35 - 40  are held together in the case  41 . In other words, pressurized contact between the first lip ring  35  and the second lip ring  37  is mainly achieved by the compression of the projection  43  when the rings  35 - 40  are held in the case  41 . 
     Operation of the shaft sealing assembly will now be described. 
     When the compressor is operating, high pressure from the crank chamber  15  is applied to the lip  37   a  of the second lip ring  37 . Accordingly, the seal surface  37   b  of the lip  37   a  is pressed against the surface  16   a  of the drive shaft  16 , which prevents leakage of fluid (refrigerant gas and lubricant oil) from the crank chamber  15 . In this state, the spiral pump slit  37   c  performs pumping with the relatively rotating surface  16   a  of the drive shaft  16  and positively sends fluid back between the lip  37   a  and the drive shaft  16 . This improves the fluid-sealing performance of the second lip ring  37 . 
     When the compressor is not operating, the resilient contact of the lip  35   c  of the first lip ring  35  with the surface  16   a  of the drive shaft  16  prevents leakage of fluid from the crank chamber  15 . 
     When the compressor is operating, the lip  35   c  of the first lip ring  35  permits fluid from the crank chamber  15  to flow towards the second lip ring  37 . The lip  35   c  is supported by the retaining portion  36   b  of the retainer ring  36  and the position of the lip  35   c  with respect to the shaft  16  is maintained when high pressure from the crank chamber  15  is applied to the first lip ring  35 . 
     When the drive shaft  16  is rotating, the fluid (mainly lubricant oil) leaked by the lip  35   c  of the first lip ring  35  lubricates and cools the lips  35   c ,  37   a  of the first and second lip rings  35 ,  37 . Accordingly, wear of the lips  35   c    37   a  from friction and heat is limited, which extends the life of the first and second lip rings  35 ,  37 . 
     The lip  39   a  of the third lip ring  39  resiliently contacts the surface  16   a  of the drive shaft  16  and prevents foreign particles from entering the shaft sealing assembly  18 . Accordingly, the fluid-sealing performance of the second lip ring  37  is not lowered by foreign particles entering between the surface  16   a  of the drive shaft  16  and the seal surface  37   b  of the lip  37   a . When rotation of the drive shaft  16  is stopped, the third lip ring  39  prevents leakage of fluid remaining between the first lip ring  35  and the second lip ring  37 . 
     As already mentioned, the first lip ring  35  permits leakage of fluid (refrigerant gas) while the drive shaft  16  rotates. The contact between the second lip ring  37  (made of fluororesin) and the retainer ring  36  and the contact between the second lip ring  37  and the case  41  forms a weaker seal than the contact between the first lip ring  35  (made of synthetic rubber) and the retainer ring  36  and the contact between the first lip ring  35  and the case  41 . 
     However, in the illustrated embodiment, the first lip ring  35  is pressed against the second lip ring  37  about the retainer ring  36  in the case  41 . In other words, leakage of fluid through contact between the second lip ring  37  and the retainer ring  36  and between the outer end surface of the second lip ring  37  and the case  41  is prevented. 
     Accordingly, the fluid that leaks past the first lip ring  35  during the rotation of the drive shaft  16  does not enter between the outer edge surface of the second lip ring  37  and the case  41 . As a result, the problem in the prior art is solved. That is, the second lip ring  37  is not released from the case  41  when the liquefied refrigerant leaked from the first lip ring  35  evaporates. Therefore, the rings  35 - 40  continue to be held tightly in the case  41 . The predetermined position of the first lip ring  35  with respect to the drive shaft  16  is maintained. 
     The illustrated embodiment has the following advantages. 
     The evaporation of liquefied refrigerant leaked from the first lip ring  35  does not occur at the outer edge of the second lip ring  37 , which prevents the release of the second lip ring  37  from the case  41 . Accordingly, the first lip ring  35  leaks an appropriate amount of fluid during the rotation of the drive shaft. 
     The projection  43  extends in the direction of the axis L of the drive shaft  16 . That is, the first lip ring  35  is pressed against the second lip ring  37  in the direction of the axis L. Accordingly, this achieves pressurized contact between the first lip ring  35  and the second lip ring  37  without adding a special assembly step to the prior art assembly of FIG.  4 . 
     The projection  43  is integrally formed on the first lip ring  35 , which facilitates the formation of the projection  43 . That is, if the projection  43  were formed on the second lip ring  37 , which is made of a sheet of fluororesin, the projection  43  must be formed on the sheet in advance. Also, cutting out the second lip ring  37  from the fluororesin sheet would require accuracy and would complicate the manufacturing process. However, the first lip ring  35  made of the synthetic rubber is molded around the case  41 . Accordingly, it is possible to integrally form the projection  43  with the first lip ring  35  by changing the shape of the mold. 
     The pump slit  37   c  is formed on the seal surface  37   b  to improve the sealing performance of the second lip ring  37 . The second lip ring  37  leaks very little, if any, of the fluid that leaks past the first lip ring  35  during the rotation of the drive shaft  16 . Accordingly, a relatively large amount of fluid exists between the first lip ring  35  and the second lip ring  37  during the rotation of the drive shaft  16 . In other words, in the prior art, a relatively large amount of fluid tends to enter between the outer end surface of the second lip ring  37  and the case  41 . Therefore, it is important that the first lip ring  35  leaks fluid during the rotation of the drive shaft  16 , but not too much fluid. 
     The shaft sealing assembly  18  includes the third lip ring  39 , which is located frontward of the second lip ring  37 . Accordingly, when the rotation of the drive shaft  16  is stopped, the third lip ring  39  prevents leakage of the fluid remaining between the first lip ring  35  and the second lip ring  37 . In other words, the fluid between the second lip ring  37  and the retainer ring  36  or the case  41  does not drain out of the compressor after the rotation of the drive shaft  16  is stopped. Therefore, it is important that the first lip ring  35  leaks fluid during the rotation of the drive shaft  16 , but not too much fluid. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. 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.