Patent Publication Number: US-7210309-B2

Title: Variable displacement compressor

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a variable displacement compressor. 
   A vehicle air conditioner includes a compressor for compressing refrigerant. One type of compressor is driven by an engine and an electric motor. Japanese Laid-Open Patent Publication No. 2002-81375 describes such a compressor. 
   The compressor includes a housing that accommodates a compression mechanism. The housing supports the end portions of a rotary shaft in a rotatable manner. The end portions of the rotary shaft project from the compressor. The rotary shaft is used to drive the compression mechanism. A pulley connects one of the end portions projecting from the compressor to the engine. The other one of the end portions projecting from the compressor is connected to the electric motor, which is arranged outside the compressor. 
   Such a compressor that is connected to an electric motor arranged outside the compressor may be made more compact than a compressor that houses the electric motor therein. Further, the housing, which accommodates the compression mechanism, and the electric motor may be assembled separately and then connected to each other. This facilitates maintenance and replacement of the electric motor. 
   To hermetically seal the housing, seals must be arranged between the housing and the two end portions of the rotary shaft. It is preferable that the seals be lubricated and cooled to reduce friction between the seals and the rotary shaft and to improve the durability of the seals. 
   As known in the prior art, a seal may be arranged along a circulation path of the refrigerant in the housing to improve lubrication and cooling. However, the known compressors with seals arranged along the circulation path do not employ rotary shafts having both of their end portions projecting from the compressor. That is, in the prior art, in a compressor having a rotary shaft with only one end portion projecting from the compressor, only the projecting end portion is sealed. However, for a compressor having a rotary shaft with both of its end portions projecting from the compressor, there are no known structures that seal both end portions. Accordingly, there is a demand for a compressor that efficiently lubricates and cools the seals arranged on both projecting end portions of the rotary shaft. 
   SUMMARY OF THE INVENTION 
   One aspect of the present invention is a compressor, connected to an external refrigerant circuit, for compressing refrigerant gas. The compressor includes a first housing, a second housing, and a cylinder block having a bore. The cylinder block is arranged between the first and second housings. A piston accommodated in the bore. The piston defines a compression chamber in the bore. A rotatable rotary shaft extends through the first housing, the cylinder block, and the second housing. The rotary shaft has a first end portion and a second end portion. A crank chamber is defined in the first housing. A crank mechanism, accommodated in the crank chamber, converts rotation of the rotary shaft to reciprocation of the piston. A suction chamber, defined in the second housing, draws in refrigerant gas from the external refrigerant circuit. A first seal seals the first housing at the first end portion of the rotary shaft. A second seal seals the second housing at the second end portion of the rotary shaft. A first lubrication chamber is defined by the first seal around the first end portion of the rotary shaft in the first housing. A second lubrication chamber is defined by the second seal around the second end portion of the rotary shaft in the second housing. A shaft passage extends axially through the rotary shaft. The shaft passage is connected to the crank chamber via the first lubrication chamber and is connected to the suction chamber via the second lubricating chamber. 
   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 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 schematic cross-sectional view of a compressor according to a preferred embodiment of the present invention; and 
       FIG. 2  is a schematic, partial cross-sectional view of a compressor according to a further embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A variable displacement compressor (hereinafter referred to as the compressor) CP according to a first embodiment of the present invention will now be described with reference to  FIG. 1 . The compressor CP is used for an air conditioner of a vehicle and connected to an external refrigerant circuit  38 , which forms part of a refrigerant cycle. The left side of the compressor CP as viewed in  FIG. 1  is defined as the front of the compressor CP, and the right side as viewed in  FIG. 1  is defined as the rear side of the compressor CP. 
   As shown in  FIG. 1 , the compressor CP includes a cylinder block  11 , a front housing  12  fixed to the front end of the cylinder block  11 , and a rear housing  14  fixed to the rear end of the cylinder block  11  via a valve plate assembly  13 . 
   A crank chamber  15  is defined in the front housing  12  in front of the cylinder block  11 . A rotary shaft  16  extends through the crank chamber  15  and is rotatably supported by the cylinder block  11  and the front housing  12 . The rotary shaft  16  is supported by slide bearing portions  11   a,    12   a  in the cylinder block  11  and the front housing  12 . A lug plate  17  is secured to the rotary shaft  16  in the crank chamber  15  and rotates integrally with the rotary shaft  16 . 
   The crank chamber  15  accommodates a cam plate, or a swash plate  18 . The swash plate  18  is supported by the rotary shaft  16  to slide along and incline with respect to the rotary shaft  16 . A hinge mechanism  19  is located between the lug plate  17  and the swash plate  18  to rotate the swash plate  18  integrally with the lug plate  17  and the rotary shaft  16  while permitting the swash plate  18  to slide along the rotary shaft  16  in the direction of the rotary shaft axis L and incline with respect to the rotary shaft  16 . 
   A plurality of cylinder bores  20  (only one shown in  FIG. 1 ) extends through the cylinder block  11  around the rotary shaft  16 . A single headed piston (hereinafter referred to as the piston)  21  is accommodated in each cylinder bore  20 . Each piston  21  and the corresponding cylinder bore  20  define a compression chamber  22 . Reciprocation of the piston  21  varies the volume of the compression chamber  22 . Each piston  21  is engaged with the peripheral portion of the swash plate  18  via a pair of shoes  23 . Therefore, when the rotary shaft  16  rotates the swash plate  18 , the rotation of the swash plate  18  is converted to the reciprocation of each piston  21 . The lug plate  17 , the swash plate  18 , the hinge mechanism  19 , and the shoes  23  define a crank mechanism for converting the rotation of the rotary shaft  16  to the reciprocation of each piston  21 . 
   An annular suction chamber  40  and an annular discharge chamber  41  are defined in the rear housing  14  at the rear side of the cylinder block  11 . A through hole  14   a  extends axially through the center of the rear housing  14 . The suction chamber  40  is formed to surround the through hole  14   a , and the discharge chamber  41  is formed to surround the suction chamber  40 . 
   The suction chamber  40  is connected to the discharge chamber  41  via the external refrigerant circuit  38 , which forms part of the refrigerant cycle. When each piston  21  moves from the top dead center position to the bottom dead center position, refrigerant gas in the suction chamber  40  is drawn into the corresponding compression chamber  22  via a corresponding suction port  42  and suction valve  43 , which are formed in the valve plate assembly  13 . When each piston  21  moves from the bottom dead center position to the top dead center position, the refrigerant gas in the compression chamber  22  is compressed to a predetermined pressure and is discharged to the discharge chamber  41  via a corresponding discharge port  44  and discharge valve  45 , which are formed in the valve plate assembly  13 . 
   The inclination angle of the swash plate  18  is adjusted by changing the balance between the pressure in the compression chamber  22  and the pressure in the crank chamber  15  (crank pressure) that acts on each piston  21 . In the preferred embodiment, the inclination angle of the swash plate  18  is adjusted by positively changing the crank pressure. 
   The compressor CP includes a supply passage  60  and a control valve  61 . The supply passage  60  connects the discharge chamber  41  to the crank chamber  15 . The control valve  61  is located in the supply passage  60 . Adjustment of the opening degree of the control valve  61  controls the flow rate of highly pressurized refrigerant gas supplied from the discharge chamber  41  to the crank chamber  15  through the supply passage  60 . This determines the crank pressure. The inclination angle of the swash plate  18  changes in accordance with the change in the crank pressure. Accordingly, the stroke of each piston  21 , or the displacement of the compressor CP is adjusted. The crank mechanism of the preferred embodiment has a variable displacement structure that controls the displacement by adjusting the flow rate of the refrigerant gas delivered to the crank chamber. 
   When the opening degree of the control valve  61  is decreased to lower the crank pressure, the inclination angle of the swash plate  18  is increased. Accordingly, the displacement of the compressor CP is increased. Conversely, when the opening degree of the control valve  61  is increased to increase the crank pressure, the inclination angle of the swash plate  18  is decreased. Accordingly, the displacement of the compressor CP is decreased. 
   The rotary shaft  16  has a first end portion, or a front end portion  16   a,  projecting from the front housing  12  through a through hole  12   c  formed in a front wall  12   b  of the front housing  12 . The front end portion  16   a  of the rotary shaft  16  is connected to a pulley  25  via a first one-way clutch  24  outside the front housing  12 . The first one-way clutch  24  is rotated in one direction to permit power transmission from the pulley  25  to the rotary shaft  16  and prevent power from being transmitted from the rotary shaft  16  to the pulley  25 . 
   A support cylinder  12   d  projects from the front wall  12   b  of the front housing  12  to rotatably support the pulley  25  via a radial bearing  26 . The pulley  25  is connected to and driven by the engine Eg via a belt  27 . 
   The rotary shaft  16  includes a second end, or a rear end portion  16   b , projecting from the rear housing  14  through the through hole  14   a  of the rear housing  14 . The rear end portion  16   b  of the rotary shaft  16  is connected to and driven by an electric motor  30 . 
   The electric motor  30  is a DC electric motor incorporating a brush. A rotor  33 , which forms part of the electric motor  30 , is connected to the rear end portion  16   b  of the rotary shaft  16  via a radial bearing  31  and a second one-way clutch  32 . The second one-way clutch  32  is rotated in one direction to permit power transmission from the rotor  33  to the rotary shaft  16  and prevent power from being transmitted from the rotary shaft  16  to the rotor  33 . 
   In the preferred embodiment, the second one-way clutch  32  is press-fitted to the rotor  33  and connected to the rotary shaft  16  by a key. A step  16   c  is formed on the outer surface at the rear end portion  16   b  of the rotary shaft  16  to restrict movement of the rotor  33  in the frontward direction when connecting the rotor  33  to the rotary shaft  16 . More specifically, the second one-way clutch  32  is moved frontward along the rotary shaft  16  to a position where it comes into contact with the step  16   c . This facilitates positioning of the rotor  33  with respect to the rotary shaft  16 . 
   The rotor  33  includes a coil  33   a  and a commutator  33   b . An annular stator support  35  is attached to the rear outer surface of the rear housing  14 . A stator (permanent magnet)  34 , which forms part of the electric motor  30 , is fixed to the stator support  35 . The stator  34  encompasses the rotor  33  in the stator support  35 . A brush  36 , which slides along the commutator  33   b , conducts power to the coil  33   a.  This causes the electric motor  30  to rotate the rotor  33 . The brush  36  is supplied with power from an external power source via a drive circuit (not shown), which is fixed to the rear housing  14 . 
   An electric motor case  37 , which accommodates the electric motor  30 , is fixed to the rear surface  14   b  of the rear housing  14  outside the compressor CP. The electric motor case  37  includes a plurality of ventilation holes  37   a  to release heat from the electric motor  30  out of the electric motor case  37 . 
   The compressor CP of the preferred embodiment uses the engine Eg and the electric motor  30  as a drive source. In the preferred embodiment, when the engine Eg functions as the drive source and rotates the rotary shaft  16 , the supply of power to the electric motor  30  is stopped. In this state, the second one-way clutch  32  prevents power from being transmitted from the rotary shaft  16  to the rotor of the electric motor  30 . This prevents energy loss that would result from the rotation of the rotor  33 . When the electric motor  30  rotates the rotary shaft  16  as the drive source, the first one-way clutch  24  prevents power from being transmitted from the rotary shaft  16  to the pulley  25 . Accordingly, unnecessary power is not transmitted from the electric motor  30  to the engine Eg. 
   A first seal  50  is arranged in the through hole  12   c , which extends through the front wall  12   b  of the front housing  12 , to seal the space between the front end portion  16   a  of the rotary shaft  16  and the wall defining the through hole  12   c . That is, the first seal  50  seals the inside of the compressor CP from the outside of the compressor CP at the front end portion  16   a  of the rotary shaft  16 . The first seal  50  is a lip seal. A first lubrication chamber  51  is defined in the through hole  12   c  at the inner side of the first seal  50  (toward the right as viewed in  FIG. 1 ). The first lubrication chamber  51  is located at the front side of the slide bearing portion  12   a  in the through hole  12   c . The first lubrication chamber  51  is connected to the crank chamber  15  via a communication passage  58 , which extends through the front wall  12   b  of the front housing  12 . 
   A second seal  52  is arranged in the through hole  14   a  of the rear housing  14  to seal the space between the rear end portion  16   b  of the rotary shaft  16  and the wall defining the through hole  14   a . That is, the second seal  52  seals the inside of the compressor CP from the outside of the compressor CP at the rear end portion  16   b  of the rotary shaft  16 . The second seal  52  is a lip seal. A second lubrication chamber  53  is defined in the through hole  14   a  at the inner side of the second seal  52  (toward the left as viewed in  FIG. 1 ). The second lubrication chamber  53  is located at the rear side of the valve plate assembly  13  in the through hole  14   a.    
   The second lubrication chamber  53  is partitioned from the suction chamber  40 . A restriction passage  54 , which extends through a wall partitioning the second lubrication chamber  53  and the suction chamber  40 , connects the second lubrication chamber  53  to the suction chamber  40 . 
   A shaft passage  55  extends through the rotary shaft  16  along the axis L to connect the first lubrication chamber  51  and the second lubrication chamber  53 . The shaft passage  55  has an inlet  55   a  extending from the shaft passage  55  to the surface of the rotary shaft  16 . The inlet  55   a  is located in the first lubrication chamber  51  near the portion where the first seal  50  contacts the rotary shaft  16 . The shaft passage  55  further has an outlet  55   b  extending from the shaft passage  55  to the surface of the rotary shaft  16 . The outlet  55   b  is located in the second lubrication chamber  53  near the portion where the second seal  52  contacts the rotary shaft  16 . 
   In the preferred embodiment, the communication passage  58 , the first lubrication chamber  51 , the shaft passage  55 , the second lubrication chamber  53 , and the restriction passage  54  form a refrigerant passage, which is used to adjust the crank pressure for controlling the compressor displacement. The crank pressure is determined by controlling the balance between the amount of the highly pressurized refrigerant gas supplied from the discharge chamber  41  to the crank chamber  15  via the supply passage  60  and the amount of refrigerant gas sent from the crank chamber  15  to the suction chamber  40  through the refrigerant passage. The refrigerant gas and the lubricating oil included in the refrigerant gas flows through the refrigerant passage from the crank chamber  15  to the suction chamber  40 . This cools and lubricates the first and second seals  50  and  52 . 
   The shaft passage  55  of the rotary shaft  16  includes an oil separator  56 . The shaft passage  55 , which has a predetermined diameter, is partially enlarged to form the oil separator  56 . The oil separator  56  collects the lubricating oil on the wall of the shaft passage  55 . A lubricating oil drain  56   a  extends through the rotary shaft  16  from the oil separator  56  to discharge the collected lubricating oil out of the oil separator  56  and into the crank chamber  15  (outside the rotary shaft  16 ). 
   The rotary shaft  16  has a front shaft piece, which includes the front end portion  16   a , and a rear shaft piece, which includes the rear end portion  16   b . The front and rear shaft pieces are welded together to form the rotary shaft  16 . The line denoted by reference number  57  in  FIG. 1  indicates the portion where the front and rear shaft pieces are connected to each other. Before the front and rear shaft pieces are connected to each other, the shaft pieces are drilled at the end faces corresponding to line  57  to form the shaft passage  55  (excluding the inlet  55   a  and the outlet  55   b ) and the oil separator  56 . 
   The preferred embodiment has the advantages described below. 
   (1) The first lubrication chamber  51  is formed around the front end portion  16   a  of the rotary shaft  16  in the front housing  12 . The second lubrication chamber  53  is formed around the rear end portion  16   b  of the rotary shaft  16  in the rear housing  14 . Further, the crank chamber  15  is connected to the shaft passage  55  via the first lubrication chamber  51 , and the shaft passage  55  is connected to the suction chamber  40  via the second lubrication chamber  53 . 
   As a result, the refrigerant gas flows from the crank chamber  15  to the suction chamber  40  via the first lubrication chamber  51 , the shaft passage  55 , and the second lubrication chamber  53 . This cools the first and second seals  50  and  52  in a satisfactory manner. Further, the lubricating oil included in the refrigerant gas lubricates the seals  50  and  52  in a satisfactory manner. 
   If the lubrication chambers  51  and  53  were to be connected by a passage that does not extend through the rotary shaft  16  like in the preferred embodiment, a passage would have to be formed avoiding components, such as the crank mechanism, and extending across the cylinder block  11 . This would lengthen the passage and make the structure of the compressor housing complicated. However, in the preferred embodiment, the shaft passage  55  extends straight between the first and second lubrication chambers  51  and  53 . This minimizes the distance between the lubrication chambers  51  and  53  and simplifies the compressor structure. The shortened distance between the lubrication chambers  51  and  53  improves the flow efficiency of the refrigerant gas between the lubrication chambers  51  and  53 . This further increases the cooling efficiency and lubricating efficiency of the seals  50  and  52  and improves the controllability of the variable compressor displacement. 
   (2) The second lubrication chamber  53  and the suction chamber  40  are partitioned from each other but connected to each other by the restriction passage  54 . Thus, the second seal  52  is less affected by the pressure fluctuation that occurs in the suction chamber  40  as the pistons  21  reciprocate in comparison to when the partitioning wall between the suction chamber  40  and the second lubrication chamber  53  is eliminated to use the suction chamber  40  as the second lubrication chamber  53  (or the second lubrication chamber  53  as the suction chamber  40 ). Accordingly, the second seal  52  stably seals the space between the rotary shaft  16  and the rear housing  14 . 
   (3) The oil separator  56  is arranged in the shaft passage  55  of the rotary shaft  16  to separate lubricating oil from the refrigerant gas and provide the separated lubricating oil to the crank chamber  15 . This prevents an excessive amount of lubricating oil from being supplied from the first lubrication chamber  51  to the second lubrication chamber  53 . Accordingly, excessive amount of lubricating oil is prevented from being supplied to the suction chamber  40 . This reduces the amount of lubricating oil discharged to the external refrigerant circuit  38  via the compression chambers  22  and the discharge chamber  41  while lubricating the crank chamber  15 . The reduction in the amount of lubricating oil discharged to the external refrigerant circuit  38  improves heat exchange efficiency in the external refrigerant circuit  38 . 
   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. Particularly, it should be understood that the present invention may be embodied in the following forms. 
   The rotary shaft  16  may be formed by a front shaft piece  70  and a rear shaft piece  71 , as shown in  FIG. 2 . 
   In this structure, the front shaft piece  70  has a rear end portion arranged in the second lubrication chamber  53 . A front passage  72   a  extends through the front shaft piece  70 . In the same manner as the shaft passage  55  of the above embodiment, the front end (not shown) of the front passage  72   a  is connected to the first lubrication chamber  51 . The rear end of the front passage  72   a  opens at the rear end face  70   a  of the front shaft piece  70 . 
   The rear shaft piece  71  has a cylindrical front end portion, which is arranged in the second lubrication chamber  53  and which accommodates the rear end portion of the front shaft piece  70 . The space in the front end portion of the rear shaft piece  71  defines a rear passage  72   b . The front passage  72   a  and the rear passage  72   b  form a shaft passage  72 . 
   The front shaft piece  70  and the rear shaft piece  71  are connected to each other via a one-way clutch  73 , which is arranged between the inner surface of the rear shaft piece  71  and the outer surface of the front shaft piece  70 . The one-way clutch  73  is rotated in one direction to permit power transmission from the rear shaft piece  71  to the front shaft piece  70  and prevents power from being transmitted from the front shaft piece  70  to the rear shaft piece  71 . A rotor  33 , which forms part of an electric motor  30 , is fixed to the rear end portion of the rear shaft piece  71 . This integrally rotates the rear shaft piece  71  and the rotor  33 . 
   In this structure, the refrigerant gas in the first lubrication chamber  51  is drawn into the rear passage  72   b  of the rear shaft piece  71  via the front passage  72   a  of the front shaft piece  70  and then further drawn into the second lubrication chamber  53  through gaps formed in the one-way clutch  73 . The flow of the refrigerant gas cools and lubricates the seals  50  and  52  and the one-way clutch  73 . 
   In the preferred embodiment, the wall partitioning the suction chamber  40  and the second lubrication chamber  53  may be eliminated. In this case, the suction chamber  40  is used as the second lubrication chamber  53  (or the second lubrication chamber  53  is used as the suction chamber  40 ). 
   The oil separator  56  does not necessarily have to be employed. 
   The electric motor  30  is not restricted to a DC electric motor incorporating a brush. For example, a motor that incorporates a brush, such as a universal motor, or a rotary magnetic field type electric motor, such as an induction electric motor and a reluctance electric motor (including an SR electric motor), may be employed. 
   The electric motor  30  may be connected to the front end portion  16   a  of the rotary shaft  16 , and the engine Eg may be connected to the rear end portion  16   b  of the rotary shaft  16 . 
   Instead of the electric motor  30 , a driven device, such as a dynamo, may be connected to the rotary shaft  16 . 
   In the preferred embodiment, the compressor CP is a variable displacement compressor. However, the present invention may be applied to a compressor having a fixed displacement. 
   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.