Patent Publication Number: US-2015086391-A1

Title: Swash plate type variable displacement compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a swash plate type variable displacement compressor. 
     Japanese Unexamined Patent Application Publication No. 5-172052 discloses a swash plate type variable displacement compressor (hereinafter, referred to as the compressor). The compressor has a housing which includes a front housing, a cylinder block and a rear housing. Each of the front housing and the rear housing has therein a suction chamber and a discharge chamber. The rear housing has therein a pressure regulation chamber which is formed in the center of the rear housing. The suction chamber is formed radially outward of the pressure regulation chamber and the discharge chamber is formed radially outward of the suction chamber. 
     The cylinder block has therein a swash plate chamber, a plurality of cylinder bores and a main shaft insertion hole. Each cylinder bore has a first cylinder bore which is formed in the rear of the cylinder block and a second cylinder bore which is formed in the front of the cylinder block. The main shaft insertion hole is formed in the rear of the cylinder block and communicates with the swash plate chamber and the pressure regulation chamber. 
     A drive shaft is disposed extending in the housing and rotatably supported in the cylinder block. A swash plate is mounted on the drive shaft for rotation therewith in the swash plate chamber. A link mechanism is provided between the drive shaft and the swash plate which permits the inclination of the swash plate. The angle of inclination refers to an angle of the swash plate with respect to a plane extending perpendicular to the axis of rotation of the drive shaft. 
     A plurality of pistons is received in the respective cylinder bores so that the pistons are movable in the reciprocating manner. Specifically, each piston has a first piston head which reciprocates in the first cylinder bore and a second piston head which reciprocates in the second cylinder bore. Therefore, the compressor has a first compression chamber formed by the first cylinder bore and the first piston head and a second compression chamber formed by the second cylinder bore and the second piston head. The compressor further includes a conversion mechanism that converts the rotation of the swash plate into reciprocal movement of the pistons in the respective cylinder bores with a stroke length that is determined by the inclination angle of the swash plate. The inclination angle of the swash plate can be controllably changed by an actuator, which is controlled by a control mechanism of the compressor. 
     The actuator is disposed on the first cylinder bore side of the swash plate chamber. The actuator includes a non-rotating movable body, a movable body and a thrust bearing. The actuator has therein a pressure control chamber. The non-rotating movable body is disposed in the main shaft insertion hole so that the non-rotating movable body is not rotatable with the drive shaft and covers the rear end of the drive shaft. This non-rotating movable body rotatably supports on the inner peripheral surface thereof the rear end of the drive shaft. The non-rotating movable body is movable back and forth in the main shaft insertion hole in the axial direction of the rotating shaft in sliding contact with the inner peripheral surface of the main drive shaft hole. The non-rotating movable body is configured so as not to slide about the axial center of rotation. The movable body is connected to the swash plate and is movable therewith in the axial direction of the drive shaft. The thrust bearing is disposed between the non-rotating movable body and the movable body. 
     The main shaft insertion hole in the cylinder block is partitioned by the non-rotating movable body, thereby forming the pressure control chamber on the rear end side of the main shaft insertion hole. The rear end of the drive shaft is rotatably supported on the inner peripheral surface of the non-rotating movable body at a position frontward of the pressure control chamber. The pressure control chamber communicates with the pressure regulation chamber in the rear housing. A pressure spring is provided in the pressure control chamber so as to urge the non-rotating movable body in the frontward direction. 
     The control mechanism includes a control passage and a control valve provided in the control passage. The control passage provides communication between the discharge chamber and the pressure regulation chamber. By regulating the opening of the control passage, the control valve varies the pressure in the pressure control chamber thereby to move the non-rotating movable body and the movable body move together in the axial direction of the drive shaft. 
     The link mechanism has the movable body and a lug arm fixed on the drive shaft. The lug arm has at the rear end thereof an elongated hole that extends in the direction perpendicular to the axis of the drive shaft and also radially inwardly from the outer periphery thereof to the axial center. The swash plate is supported at the front thereof such that the swash plate is allowed to pivot about a first pivot pin inserted through the elongated hole. The movable body also has at the front end thereof an elongated hole which extends in the direction perpendicular to the axis of the drive shaft and also in the direction approaching the axis of the drive shaft from the outer periphery thereof. The swash plate is also supported at the rear end thereof such that the swash plate is allowed to pivot about a second pivot pin which is parallel to the center of the first pivot pin and inserted through the elongated hole. 
     In the compressor, by adjusting the opening of the control passage with the control valve, the pressure in the pressure regulation chamber and hence the pressure in the pressure control chamber can be controlled by the pressure of the refrigerant gas in the discharge chamber. 
     Specifically, increasing the pressure in the pressure regulation chamber by the control valve increases the pressure in the pressure control chamber higher than the pressure in the swash plate chamber. As a result, the non-rotating movable body and the movable body in the main shaft insertion hole advance in the axial direction of the rotating shaft. Then, the inclination angle of the swash plate is increased and the stroke of the pistons is increased. Accordingly, the displacement of the compressor per one rotation of the drive shaft is increased. 
     By reducing the pressure in the pressure regulation chamber by the control valve, the pressure in the pressure control chamber becomes almost the same as the pressure in the swash plate chamber. Accordingly, the non-rotating movable body and the movable body in the main shaft insertion hole retreat in the axial direction of the rotating shaft. Therefore, the inclination angle of the swash plate is reduced and hence the stroke of the pistons is reduced, with the result that the displacement of the compressor per one rotation of the drive shaft is decreased. 
     In the above-described swash plate type variable displacement compressor, the suction chamber is disposed radially outward of the pressure regulation chamber. Since the temperature of the refrigerant gas in the suction chamber is lower, the pressure regulation chamber is cooled and, therefore, the temperature of the refrigerant gas in the pressure regulation chamber drops, thus liquefying part of the refrigerant gas in the pressure regulation chamber. Thus, refrigerant of two phases, namely gaseous refrigerant and liquefied refrigerant is present in the pressure regulation chamber. If the proportion of the liquefied refrigerant increases, the pressure in the pressure regulation chamber increases less quickly by the refrigerant flowing from the discharge chamber into the pressure regulation chamber. Due to an increase of the proportion of the liquefied refrigerant, the pressure in the pressure regulation chamber decreases less quickly by the refrigerant flowing from the pressure regulation chamber into the suction chamber. In the compressor of the above-cited publication, therefore, it is difficult to move the non-rotating movable body and the movable body in a desirable manner. Specifically, in the compressor, it is difficult to vary the inclination angle of the swash plate quickly according to a change of the operating conditions of the vehicle on which the compressor is mounted and also the discharge displacement of the compressor is less controllable. 
     The present invention, which has been made in view of the above-identified circumstances, is directed to providing a swash plate type variable displacement compressor that offers improved controllability. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, the swash plate type variable displacement compressor includes a housing having therein a suction chamber, a discharge chamber, a swash plate chamber, and a plurality of cylinder bores; a drive shaft rotatably supported in the housing; a swash plate which is rotatable in the swash plate chamber with the rotation of the drive shaft; a link mechanism which is disposed between the drive shaft and the swash plate and allows a change in an inclination angle of the swash plate with respect to the direction perpendicular to the axis of the drive shaft; a plurality of pistons which is reciprocally received in the respective cylinder bores; a conversion mechanism which converts the rotation of the drive shaft into reciprocal movement of the pistons in the respective cylinder bores in conjunction with the swash plate with a stroke length according to the inclination angle of the swash plate; an actuator for changing the inclination angle of the swash plate; and a control mechanism which controls the actuator. The housing has therein a pressure regulation chamber. The pressure regulation chamber is disposed radially inward of the discharge chamber, which is disposed radially inward of the suction chamber. The actuator includes a fixed body, a movable body, and a pressure control chamber. The fixed body is fixed on the drive shaft in the swash plate chamber. The movable body is connected to the swash plate and movable relative to the fixed body in the direction of the axis of rotation. The pressure control chamber is defined by the fixed body and the movable body and the pressure in the pressure control chamber is changed by introducing the pressure in the discharge chamber into the pressure control chamber such that the movable body is moved. The control mechanism has a control passage and a control valve. The control passage provides communication between the discharge chamber and the pressure control chamber via the pressure regulation chamber. The control valve adjusts an opening of the control passage to vary pressure in the pressure regulation chamber such that the movable body is moved. At least a part of the control passage is formed in the drive shaft, and the drive shaft projects into the pressure regulation chamber such that the control passage connects the pressure regulation chamber and the pressure control 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 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 embodiments together with the accompanying drawings in which: 
         FIG. 1  is a longitudinal sectional view of a compressor according to an embodiment of the present invention, showing the maximum displacement of the compressor; 
         FIG. 2  is a schematic diagram of a control mechanism of the compressor of  FIG. 1 ; 
         FIG. 3  is a transverse sectional view of the compressor as viewed in arrow direction III-III in  FIG. 1 ; and 
         FIG. 4  is a longitudinal sectional view of the compressor of  FIG. 1  in the minimum displacement. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following will describe a compressor embodying the present invention with reference to the drawings. The compressor of the embodiment is a swash plate type variable displacement compressor which is mounted on a vehicle and forms a part of a refrigeration circuit for an air conditioning system of the vehicle. 
     Referring to  FIG. 1 , the compressor according to the present embodiment includes a housing  1 , a drive shaft  3 , a swash plate  5 , a link mechanism  7 , a plurality of double-headed pistons  9 , pairs of shoes  11 A,  11 B, an actuator  13  and a control mechanism  15  which is shown in  FIG. 2 . 
     The housing  1  includes a front housing  17  disposed on the front side of the compressor, a rear housing  19  disposed on the rear side of the compressor, first and second cylinder blocks  21 ,  23  disposed between the front housing  17  and the rear housing  19 , and first and second valve forming plates  39 ,  41 . 
     The front housing  17  has a boss  17 A projecting frontward. The boss  17 A has a shaft sealing device  25 . The front housing  17  has therein a first suction chamber  27 A and a first discharge chamber  29 A. The first suction chamber  27 A is formed in a radially inner region inward of the front housing  17 . The first discharge chamber  29 A is formed in an annular shape and disposed outward of the first suction chamber  27 A in the front housing  17 . 
     The front housing  17  has therein a first front communication passage  18 A which communicates at the front end thereof with the first discharge chamber  29 A and opens at the rear end thereof at the rear end of the front housing  17 . 
     The control mechanism  15  is disposed in the rear housing  19 . As shown in  FIG. 3 , the rear housing  19  has therein a second suction chamber  27 B, a second discharge chamber  29 B, and a pressure regulation chamber  31 . Specifically, the pressure regulation chamber  31  is disposed in the center of the rear housing  19 . The second discharge chamber  29 B is formed in an annular shape and formed radially outward of the pressure regulation chamber  31  in the rear housing  19  so as to surround the pressure regulation chamber  31 . The second suction chamber  27 B is formed into a substantially C shape and disposed radially outward of the second discharge chamber  29 B in the rear housing  19 . 
     Furthermore, the rear housing  19  has therein a first rear communication passage  20 A which communicates at the rear end thereof with the second discharge chamber  29 B. As shown in  FIG. 1 , the front end of the first rear communication passage  20 A is open at the front end of the rear housing  19 . 
     A swash plate chamber  33  is formed between a first cylinder block  21  and the second cylinder block  23 . The swash plate chamber  33  is disposed substantially in the center of the housing  1  as seen in the longitudinal direction of the compressor. 
     A plurality of first cylinder bores  21 A is formed substantially at an equal angular distance in the circumferential direction of the first cylinder block  21 . The first cylinder block  21  has therethrough a first shaft hole  21 B through which the drive shaft  3  is inserted. The first shaft hole  21 B has a first sliding bearing  22 A, although a rolling bearing may alternatively be used. 
     The first cylinder block  21  further has therein a first recessed portion  21 C which is annular and coaxial with the first shaft hole  21 B. The first recessed portion  21 C communicates with the swash plate chamber  33 . The inner diameter of the annular first recessed portion  21 C is reduced in the form of a step toward the front end thereof. A first thrust bearing  35 A is provided in the first recessed portion  21 C at the front end thereof. The first cylinder block  21  further has therein a first connecting passage  37 A which provides communication between the swash plate chamber  33  and the first suction chamber  27 A. The first cylinder block  21  has therein a first retaining groove  21 E for regulating the maximum opening of first suction reed valves  391 A, which will be described later. 
     The first cylinder block  21  further has therein a second front communication passage  18 B which is open at the opposite front and rear ends thereof. 
     The second cylinder block  23  has therein a plurality of second cylinder bores  23 A as in the case of the first cylinder block  21 . Each second cylinder bore  23 A on the rear side is paired with its associated first cylinder bore  21 A on the front side. The first cylinder bores  21 A and the second cylinder bores  23 A are of the same diameter. It is to be noted that the second cylinder block  23  corresponds to the cylinder block of the present invention. 
     Furthermore, the second cylinder block  23  has a projection  23 F extending rearward. With the second cylinder block  23 , the second valve forming plate  41  and the rear housing  19  joined together, the projection  23 F projects into the pressure regulation chamber  31  projecting beyond the second valve forming plate  41 . The distance for which the projection  23 F projects into the pressure regulation chamber  31  may appropriately be changed according to the design. 
     Furthermore, the second cylinder block  23  has therein a second shaft hole  23 B through which the drive shaft  3  is inserted. The second shaft hole  23 B extends also in the projection  23 F and is opened to the pressure regulation chamber  31 . The second shaft hole  23 B has therein a second sliding bearing  22 B the rear end of which projects to the pressure regulation chamber  31 . The second sliding bearing  22 B corresponds to the radial bearing of the present invention. It is to be noted that the second sliding bearing  22 B may be replaced with a roller bearing. 
     The second cylinder block  23  has therein a second recessed portion  23 C which is annular and coaxial with the second shaft hole  23 B. The second recessed portion  23 C also communicates with the swash plate chamber  33 . The inner diameter of the second annular recessed portion  23 C is reduced in the form of a step toward the rear end thereof. A second thrust bearing  35 B is provided in the second recessed portion  23 C at the rear end thereof. The second thrust bearing  35 B corresponds to the thrust bearing of the present invention. The second cylinder block  23  further has therein a second connecting passage  37 B which provides communication between the swash plate chamber  33  and the second suction chamber  27 B. The second cylinder block  23  has therein a second retaining groove  23 E for regulating the maximum opening of second suction reed valves  411 A, which will be described later. 
     The second cylinder block  23  has therein an outlet port  230 , a combined discharge chamber  231 , a third front communication passage  18 C, a second rear communication passage  20 B and an inlet port  330 . The outlet port  230  and the combined discharge chamber  231  are in direct communication with each other. The outlet port  230  and the combined discharge chamber  231  are formed in the second cylinder block  23  at positions adjacent to the front end of the second cylinder block  23  so that they are disposed substantially in the longitudinal center of the housing  1 . The combined discharge chamber  231  is connected through the discharge port  230  to a condenser (not shown). 
     The third front communication passage  18 C is open at the front end thereof in the front end of the second cylinder block  23  and communicates directly at the rear end thereof with the combined discharge chamber  231 . With the first cylinder block  21  and the second cylinder block  23  joined together, the third front communication passage  18 C communicates with the second front communication passage  18 B at the rear end thereof. 
     The second rear communication passage  20 B communicates directly at the front end thereof with the combined discharge chamber  231  and open at the rear end thereof in the rear end of the second cylinder block  23 . 
     The inlet port  330  is formed at a position adjacent to the front end of the second cylinder block  23  so that the inlet port  330  is disposed substantially in the longitudinal center of the housing  1 . The swash plate chamber  33  is connected through the suction port  330  to an evaporator (not shown) connected in the external refrigeration circuit. 
     The first valve forming plate  39  is interposed between the front housing  17  and the first cylinder block  21 . The second valve forming plate  41  is provided between the rear housing  19  and the second cylinder block  23 . The second valve forming plate  41  corresponds to the valve unit of the present invention. 
     The first and second valve forming plates  39 ,  41  are formed in an annular shape. The first valve forming plate  39  is mounted on a projection at the front end of the first cylinder block  21  and the second valve forming plate  41  is mounted on the projection  23 F of the second cylinder block  23 . 
     The first valve forming plate  39  includes a first valve plate  390 , a first suction valve plate  391 , a first discharge valve plate  392 , and a first retainer plate  393 . At least one first suction hole  390 A is formed through the first valve plate  390 , the first discharge valve plate  392 , and the first retainer plate  393 . The first suction hole  390 A corresponds to each first cylinder bore  21 A. At least one first discharge hole  390 B is formed through the first valve plate  390  and the first suction valve plate  391 . The first discharge hole  390 B corresponds to each first cylinder bore  21 A. Furthermore, at least one first suction communication hole  390 C is formed through the first valve plate  390 , the first suction valve plate  391 , the first discharge valve plate  392 , and the first retainer plate  393 . At least one first discharge communication hole  390 D is formed through the first valve plate  390  and the first suction valve plate  391 . 
     Each first cylinder bore  21 A is communicable with the first suction chamber  27 A through its associated first suction hole  390 A. Each first cylinder bore  21 A is communicable with the first discharge chamber  29 A through its associated first discharge hole  390 B. The first suction chamber  27 A and the first connecting passage  37 A are communicable with each other through the first suction communication hole  390 C. The first front communication passage  18 A and the second front communication passage  18 B are communicable with each other through the first discharge communication hole  390 D. 
     The first suction valve plate  391  is provided on a rear surface of the first valve plate  390  and has the plurality of first suction reed valves  391 A which are elastically deformable to open and close the first suction holes  390 A. The first discharge valve plate  392  is provided on a front surface of the first valve plate  390  and has a plurality of first discharge reed valves  392 A which are elastically deformable to open and close the first discharge holes  390 B. The first retainer plate  393  is provided on the front surface of the first discharge plate  392  for regulating the maximum opening of the first discharge reed valves  392 A. 
     The second valve forming plate  41  includes a second valve plate  410 , a second suction valve plate  411 , a second discharge valve plate  412  and a second retainer plate  413 . At least one second suction hole  410 A is formed through the second valve plate  410 . The second suction hole  410 A corresponds to each second cylinder bore  23 A. At least one second discharge hole  410 B is formed through the second valve plate  410  and the second suction valve plate  411 . The second discharge hole  410 B corresponds to each second cylinder bore  23 A. Furthermore, at least one second suction communication hole  410 C and at least one second discharge communication hole  410 D are formed through the second valve plate  410  and the second suction valve plate  411 . 
     Each second cylinder bore  23 A is communicable with the second suction chamber  27 B through its associated second suction hole  410 A. Each second cylinder bore  23 A is communicable with the second discharge chamber  29 B through its associated second discharge hole  410 B. The second suction chamber  27 B and the second connecting passage  37 B are communicable with each other through the second suction communication hole  410 C. The first rear communication passage  20 A and the second rear communication passage  20 B are communicable with each other through the second discharge communication hole  410 D. 
     The second suction valve plate  411  is provided on the front surface of the second valve plate  410  and has a plurality of second suction reed valves  411 A which are elastically deformable to open and close the second suction holes  410 A. The second discharge valve plate  412  is provided on the rear surface of the second valve plate  410  and has a plurality of second discharge reed valves  412 A which are elastically deformable to open and close the second discharge holes  410 B. The second retainer plate  413  is provided on the rear surface of the second discharge valve plate  412  for regulating the maximum opening of the second discharge reed valves  412 A. 
     In the compressor, a first communication passage  18  is formed by the first front communication passage  18 A, the first discharge communication hole  390 D, the second front communication passage  18 B, and the third front communication passage  18 C. A second communication passage  20  is formed by the first rear communication passage  20 A, the second discharge communication hole  410 D, and the second rear communication passage  20 B. 
     In the compressor, the swash plate chamber  33  communicates with the first and second suction chambers  27 A,  27 B via the first and second connection passage  37 A,  37 B and the first and second suction communication holes  390 C,  410 C. Therefore, the pressures are substantially the same among the first suction chamber  27 A, the second suction chamber  27 B, and the swash plate chamber  33 . Since the refrigerant gas which has passed through the evaporator is introduced into the swash plate chamber  33  through the inlet port  330 , the pressures in the first and second suction chambers  27 A,  27 B and the swash plate chamber  33  are lower than the pressures in the first and second discharge chambers  29 A,  29 B. 
     The drive shaft  3  includes a drive shaft body  30  (a drive shaft main body  30 ), a first support member  43 A and a second support member  43 B. The drive shaft body  30  extending rearward from the boss  17 A is inserted through the first and second sliding bearings  22 A,  22 B. The drive shaft  3  is supported in the first and second cylinder blocks  21 ,  23  so as to be rotatable about the axis of rotation O. The front end of the drive shaft body  30  extends into the boss  17 A, and the rear end of the drive shaft body  30  projects beyond the projection  23 F and the second sliding bearing  22 B and into the pressure regulation chamber  31 . 
     The first support member  43 A is press-fitted on the front end part of the drive shaft body  30 . With the rotation of the drive shaft  3  about the axis of rotation O, the first support member  43 A is rotated with the drive shaft  3  in sliding contact with the first sliding bearing  22 A. The first support member  43 A is formed at the rear end part thereof with a flange  430  and a mounting (not shown) into which a second pin  47 B, which will be described later, is inserted. The flange  430  serves as a retainer for the first thrust bearing  35 A. Specifically, the flange  430  and the inner wall surface of the first recessed portion  21 C cooperate to hold therebetween the first thrust bearing  35 A. The front end of a first return spring  44 A is fixed on the first support member  43 A. The first return spring  44 A extends in the direction of the axis of rotation O toward the swash plate chamber  33  from the flange  430  of the first support member  43 A. 
     The second support member  43 B is press-fitted on the rear end part of the drive shaft body  30  so that the rear end surface of the second support member  43 B is flush with the rear end surface of the drive shaft body  30 . The rear end of the second support member  43 B projects beyond the projection  23 F and the second sliding bearing  23 B and into the pressure regulation chamber  31 . 
     With the rotation of the drive shaft  3  about the axis of rotation O, the second support member  43 B is rotated in sliding contact with the second sliding bearing  22 B. A flange  431  is formed at the front end of the second support member  43 B. The flange  431  is disposed between the second thrust bearing  35 B and the actuator  13  and serves as a retainer for the second thrust bearing  35 B. Specifically, the flange  431  and the inner wall surface of the first recessed portion  21 C cooperate to hold therebetween the second thrust bearing  35 B. The second support member  43 B corresponds to the cap of the present invention. 
     The swash plate  5  is a circular, flat plate having a front surface  5 A and a rear surface  5 B. In the swash plate chamber  33 , the front surface  5 A faces frontward and the rear surface  5 B faces rearward. 
     The swash plate  5  is fixed to a ring plate  45 . The ring plate  45  is a circular, flat plate having an insertion hole  45 A in the center thereof. The swash plate  5  is mounted to the drive shaft  3  with the drive shaft body  30  passed through the insertion hole  45 A of the swash plate  5 . 
     The aforementioned link mechanism  7  includes a lug arm  49 . The lug arm  49  is disposed frontward of the swash plate  5  in the swash plate chamber  33  and located between the swash plate  5  and the first support member  43 A. The lug arm  49  is formed substantially in an L shape as viewed toward the rear end thereof. When the swash plate  5  is positioned at the minimum inclination angle with respect to a plane extending perpendicular to the axis of rotation O of the drive shaft  3 , the lug arm  49  is in contact the flange  430  of the first support member  43 A, as shown in  FIG. 4 . Thus, the minimum inclination angle position of the swash plate  5  is determined by the contact of the lug arm  49  with the flange  430 . The lug arm  49  has in the rear part thereof a weight portion  49 A extending for half the circumference of the actuator  13 . It is to be noted that the weight portion  49 A may be formed in any shape appropriately through design. 
     As shown in  FIG. 1 , the lug arm  49  is connected at the rear end thereof to one end of the ring plate  45  through a first pin  47 A. With this configuration, the lug arm  49  is supported at the front end thereof so as to be swingable about a first pivot axis M1 which is the axial center of the first pin  47 A with respect to the one end of the ring plate  45 , i.e., the swash plate  5 . The first pivot axis M1 extends in the direction perpendicular to the axis of rotation O of the drive shaft  3 . 
     The lug arm  49  is connected at the front end thereof to the first support member  43 A through the second pin  47 B. With this configuration, the lug arm  49  is supported at the rear end thereof so as to be swingable about a second pivot axis M2 which is the axial center of the second pin  47 B with respect to the first support member  43 A, i.e., the drive shaft  3 . The second pivot axis M2 extends parallel to the with the first pivot axis M1. The lug arm  49 , the first pin  47 A and the second pin  47 B correspond to the link mechanism  7  of the present invention. 
     The weight portion  49 A extends rearward from the first pivot axis M1, and therefore, the weight portion  49 A of the lug arm  49  is supported on the ring plate  45  with the first pin  47 A. The weight portion  49 A is passed through a groove portion  45 B of the ring plate  45  and positioned behind the ring plate  45 , that is, on the rear surface  5 B side of the swash plate  5 . With this configuration, the centrifugal force generated by the rotation of the swash plate  5  about the axis of rotation O acts on the weight portion  49 A on the rear surface  5 B side of the swash plate  5 . 
     In the compressor, the swash plate  5  is connected to the drive shaft  3  via the link mechanism  7  for rotation with the drive shaft  3 . The inclination angle of the swash plate  5  is variable with the swinging motion of the opposite ends of the lug arm  49  about the first pivot axis M1 and the second pivot axis M2, respectively. 
     Each piston  9  has a first piston head  9 A at the front end thereof and a second piston head  9 B at the rear end thereof. Each first piston head  9 A is received in its associated first cylinder bore  21 A so as to be reciprocally movable. Each first cylinder bore  21 A has therein a first compression chamber  21 D which is formed between the first piston head  9 A and the first valve forming plate  39 . Each second piston head  9 B is received in its associated second cylinder bore  23 A so as to be reciprocally movable. Each second cylinder bore  23 A has therein a second compression chamber  23 D which is formed between the second piston head  9 B and the second valve forming plate  41 . Since the first cylinder bores  21 A and the second cylinder bores  23 A have the same diameter as mentioned above, the first piston head  9 A and the second piston head  9 B are formed to have the same diameter. 
     Each piston  9  has at the longitudinal center thereof a recessed portion  9 C and the pair of hemispherical shoes  11 A,  11 B is received in the recessed portion  9 C. The shoes  11 A,  11 B convert the rotation of the swash plate  5  into the reciprocating motion of the pistons  9  in the respective cylinder bores  21 A,  23 A. The shoes  11 A,  11 B correspond to the conversion mechanism of the present invention. The first and second piston heads  9 A,  9 B are reciprocable in the first and second cylinder bores  21 A,  23 A, respectively, for a stroke length according to the inclination angle of the swash plate  5 . 
     With the change of the stroke length of the respective pistons  9  according to the change of the inclination angle of the swash plate  5 , the top dead center of the respective first piston heads  9 A and the second piston heads  9 B is shifted. Specifically, in the state of  FIG. 1  where the inclination angle of the swash plate  5  and the stroke length of the pistons  9  are the maximum, the top dead centers of the first piston heads  9 A and the second piston head  9 B are located at positions closest to the first valve forming plate  39  and the second valve forming plate  41 , respectively. As will be appreciated from comparison of  FIGS. 1 and 4 , the top dead center of the second piston heads  9 B becomes more distant from the second valve forming plate  41  with a decrease of the inclination angle of the swash plate  5  and hence of the stroke length of the pistons  9 . Whereas, the top dead center of the first piston heads  9 A is shifted very little when the stroke of the pistons  9  is the maximum and the position which is close to the first valve forming plate  39  is maintained. In other words, in the compressor of the present embodiment, as the inclination angle of the swash plate  5  decreases, the shifting of the top dead center of the second piston head  9 B becomes greater than that of the first piston head  9 A. 
     As shown in  FIG. 1 , the actuator  13  is disposed in the swash plate chamber  33 . The actuator  13  is located behind the swash plate  5  and movable into the second recessed portion  23 C. The actuator  13  includes a movable body  13 A and a fixed body  13 B and a pressure control chamber  13 C is formed between the movable body  13 A and the fixed body  13 B. 
     The movable body  13 A includes a body  130  and a peripheral wall  131 . The body  130  forms the rear part of the movable body  13 A and extends radially from the drive shaft  3 . The peripheral wall  131  is connected to the outer circumferential edge of the body  130  and extends in the axial direction of the drive shaft  3 . Furthermore, the peripheral wall  131  has at the front end thereof a connecting portion  132 . The body  130 , the peripheral wall  131  and the connecting portion  132  cooperate to form the movable body  13 A of a shape of a closed-end cylinder. 
     The fixed body  13 B is formed of a circular plate having substantially the same diameter as the inner diameter of the movable body  13 A. A second return spring  44 B is provided between the fixed body  13 B and the ring plate  45 . Specifically, the return spring  44 B is fixed at the rear end thereof to the fixed body  13 B and fixed at the front end thereof to the other end of the ring plate  45 , or the end of the ring plate  45  that is opposite from the end thereof to which the lug arm  49  is connected. 
     The drive shaft body  30  extends through the center holes of the movable body  13 A and the fixed body  13 B, so that the movable body  13 A in the second recessed portion  23 C is located opposite from the link mechanism  7  with respect to the swash plate  5 . The fixed body  13 B is disposed within the movable body  13 A at a position rearward of the swash plate  5  and the periphery of the fixed body  13 B is covered by the peripheral wall  131  of the movable body  13 A. With such configuration of the actuator  13 , the pressure control chamber  13 C is formed between the movable body  13 A and the fixed body  13 B. Specifically, the pressure control chamber  13 C is defined by the body  130  and the peripheral wall  131  of the movable body  13 A and the fixed body  13 B, thereby being separated from the swash plate chamber  33 . 
     The movable body  13 A is mounted on the drive shaft body  30  in such a way that the movable body  13 A is rotatable with the drive shaft  3  and also slidable in the swash plate chamber  33  in the axial direction O of the drive shaft  3 . Whereas, the fixed body  13 B is fixedly mounted on the drive shaft body  30  with the drive shaft body  30  inserted in the fixed body  13 B, so that the fixed body  13 B is rotatable with the drive shaft  3 , but immovable in the axial direction O. Therefore, the movable body  13 A is movable relative to the fixed body  13 B in the axial direction O of the drive shaft  3 . 
     The connecting portion  132  of the movable body  13 A is connected to the other end of the ring plate  45  through a third pin  47 C, so that the other end of the ring plate  45  is supported, that is, the swash plate  5  is supported by the movable body  13 A so as to be swingable about a pivot axis M3 of the third pin  47 C. The pivot axis M3 extends parallel to the first and second pivot axes M1, M2. The movable body  13 A is thus connected to the swash plate  5 . The movable body  13 A is in contact with the flange  431  of the second support member  43 B when the swash plate  5  is placed at the maximum inclination angle position. 
     Furthermore, the drive shaft body  30  has therein an axial passage  3 B extending in the axial direction O and opened in the rear end surface of the drive shaft body  30  and a radial passage  3 C extending from the front end of the axial passage  3 B and opened in the peripheral surface of the drive shaft body  30 . Because the rear end of the drive shaft body  30  projects into the pressure regulation chamber  31 , the rear end of the axial passage  3 B is also located and is opened to the pressure regulation chamber  31 . The radial passage  3 C is opened to the control chamber  13 C. With this configuration, the pressure control chamber  13 C communicates with the pressure regulation chamber  31  through the radial passage  3 C and the axial passage  3 B. 
     The drive shaft body  30  has at the front end thereof a threaded portion  3 D. The drive shaft  3  is connected to a pulley or an electromagnetic clutch (not shown) at the threaded portion  3 D. 
     As shown in  FIG. 2 , the control mechanism  15  includes a low-pressure passage  15 A, a high-pressure passage  15 B, a control valve  15 C, an orifice  15 D and the aforementioned axial and radial passages  3 B,  3 C. The axial passage  3 B and the radial passage  3 C correspond to the pressure-changing passages of the present invention. The low-pressure passage  15 A, the high-pressure passage  15 B, the axial passage  3 B and the radial passage  3 C correspond to the control passages of the present invention. 
     The low-pressure passage  15 A is connected to the pressure regulation chamber  31  and the second suction chamber  27 B. The pressure control chamber  13 C, the pressure regulation chamber  31  and the second suction chamber  27 B communicate with each other through the low-pressure passage  15 A, the axial passage  3 B and the radial passage  3 C. The high-pressure passage  15 B is connected to the pressure regulation chamber  31  and the second discharge chamber  29 B. The pressure control chamber  13 C, the pressure regulation chamber  31  and the second discharge chamber  29 B communicate with each other through the high-pressure passage  15 B, the axial passage  3 B and the radial passage  3 C. The orifice  15 D is formed in the high-pressure passage  15 B for restricting the flow rate of the refrigerant gas flowing in the high-pressure passage  15 B. 
     The control valve  15 C is formed in the low-pressure passage  15 A and regulates the opening of the low-pressure passage  15 A based on the pressure in the second suction chamber  27 B. 
     The aforementioned evaporator is connected to the inlet port  330  of the compressor through a tube and the condenser is connected to the outlet port  230  through a tube. The condenser is connected to the evaporator through a tube and an expansion valve. The compressor, the evaporator, the expansion valve, the condenser and the like cooperate to form the refrigeration circuit of a vehicle air conditioning system. It is to be noted that the evaporator, the expansion valve, the condenser and the tubes are omitted from illustration in the drawings. 
     During the operation of the above-described compressor, the rotation of the drive shaft  3  rotates the swash plate  5 , causing the pistons  9  to reciprocate in the first and second cylinder bores  21 A,  23 A, so that compression of refrigerant gas is performed in the first and second compression chambers  21 D,  23 D. The displacement of the compressor varies according to the stroke length of the pistons  9 . In the compressor, the suction phase in which refrigerant gas is drawn into the first and second cylinder bores  21 A,  23 A, the compression phase in which compressing the refrigerant gas is performed in the first and second cylinder bores  21 A,  23 A, and the discharge phase in which the compressed refrigerant gas is discharged from the first and second cylinder bores  21 A,  23 A are repeated. 
     In the suction phase, the refrigerant gas which is drawn from the evaporator into the swash plate chamber  33  through the inlet port  330  is flowed into the first suction chamber  27 A through the first connecting passage  37 A. The refrigerant gas in the first suction chamber  27 A is then drawn into the first cylinder bore  21 A through the first suction hole  390 A due to the pressure difference which is created between the first cylinder bore  21 A and the first suction chamber  27 A and opens the first suction reed valves  391 A. On the other hand, the refrigerant gas in the swash plate chamber  33  is also flowed into the second suction chamber  27 B through the second connecting passage  37 B and then drawn into the second cylinder bore  23 A through the second suction hole  410 A due to the pressure difference which is created between the second cylinder bore  23 A and the second suction chamber  27 B and opens the second suction reed valves  411 A. 
     In the discharge phase, the refrigerant gas compressed in the first compression chamber  21 D is discharged into the first discharge chamber  29 A and flowed toward the combined discharge chamber  231  through the first communication passage  18 . Similarly, the refrigerant gas compressed in the second compression chamber  23 D is discharged into the second discharge chamber  29 B and flowed toward the combined discharge chamber  231  through the second communication passage  20 . The refrigerant gas in the combined discharge chamber  231  is discharged out through the outlet port  230  toward the condenser. 
     During the suction phase, the compression force of the pistons  9  acts on the swash plate  5 , the ring plate  45 , the lug arm  49 , and the first pin  47 A in such a way that reduces the inclination angle of the swash plate  5 . A change in the inclination angle of the swash plate  5  increases or decreases the stroke length of the pistons  9  thereby to change the discharge displacement. 
     Specifically, when the opening of the low-pressure passage  15 A is increased by the control valve  15 C shown in  FIG. 2 , the pressures in the pressure regulation chamber  31  and hence the pressure control chamber  13 C become substantially the same as the pressure in the second suction chamber  27 B. As a result, the movable body  13 A of the actuator  13  moves frontward in the swash plate chamber  33  and, therefore, toward the lug arm  49 , as shown in  FIG. 4 , due to the compression force of the pistons  9  acting on the swash plate  5 . 
     The end of the ring plate  45  that is opposite from the end thereof to which the lug arm  49  is connected, that is, the other end of the swash plate  5  swings clockwise about the pivot axis M3 while overcoming against the urging force of the second return spring  44 B. Furthermore, the rear end of the lug arm  49  swings clockwise about the first pivot axis M1, while the front end of the lug arm  49  swings counterclockwise about the second pivot axis M2. Accordingly, the lug arm  49  moves toward the flange  430  of the first support member  43 A and the swash plate  5  swings about the first pivot axis M1 with the pivot axis M3 as the point of action and the first pivot axis M1 as the fulcrum point. The inclination angle of the swash plate  5  with respect to a plane extending perpendicular to the axis of rotation O of the drive shaft  3  decreases and the stroke length of the pistons  9  decreases. Accordingly, the displacement of the compressor per one rotation of the drive shaft  3  is decreased. It is to be noted that the inclination angle of the swash plate  5  shown in  FIG. 4  corresponds to the minimum inclination angle. 
     In this case, the centrifugal force acting on the weight portion  49 A is imparted to the swash plate  5  in such a way that the swash plate  5  tends to shift easily in the direction that reduces the inclination angle of the swash plate  5 . The movable body  13 A moves frontward in the swash plate chamber  33  to a position where the front end of the movable body  13 A is located radially inner side of the weight portion  49 A. In the compressor, when the inclination angle of the swash plate  5  is reduced to minimum, about front half of the front end of the movable body  13 A is covered with the weight portion  49 A. 
     As the inclination angle of the swash plate  5  is decreased, the ring plate  45  is brought into contact with the rear end of the first return spring  44 A. Then the first return spring  44 A is elastically deformed and the rear end of the first return spring  44 A approaches the first support member  43 A. 
     With a decrease of the inclination angle of the swash plate  5  and hence of the stroke length of the pistons  9 , the top dead center of the second piston heads  9 B is shifted away from the second valve forming plate  41 . Therefore, when the inclination angle of the swash plate  5  is approximately zero, compression for a small displacement is performed in the first compression chamber  21 D, and no compression is performed in the second compression chamber  23 D. 
     As the control valve  15 C shown in  FIG. 2  reduces the opening of the low-pressure passage  15 A, the pressure in the pressure control chamber  13 C becomes substantially the same as the pressure in the second discharge chamber  29 B. Accordingly, the movable body  13 A moves rearward in the swash plate chamber  33  against the compression force of the pistons acting on the swash plate  5 , so that the movable body  13 A is moved away from the lug arm  49 . 
     Consequently, the lower end of the swash plate  5  is pulled at the pivot axis M3 by the movable body  13 A rearward in the swash plate chamber  33  through the connecting portion  132 , so that the other end of the swash plate  5  swings counterclockwise about the pivot axis M3. Furthermore, the rear end of the lug arm  49  swings counterclockwise about the first pivot axis M1, while the front end of the lug arm  49  swings clockwise about the second pivot axis M2. Accordingly, the lug arm  49  moves away from the flange  430  of the first support member  43 A and the swash plate  5  swings about the first pivot axis M1 with the pivot axis M3 as the point of action and the pivot axis M1 as the fulcrum point in the direction that is opposite to the direction that decreases the inclination angle of the swash plate  5 . Therefore, the inclination angle of the swash plate  5  increases and the stroke length of the pistons  9  is lengthened, with the result that the displacement of the compressor per one rotation of the drive shaft  3  is increased. It is to be noted that the inclination angle of the swash plate  5  shown in  FIG. 1  corresponds to the maximum inclination angle. 
     As described above, the refrigerant gas in the second discharge chamber  29 B is drawn into the pressure regulation chamber  31  through the high-pressure passage  15 B of the control mechanism  15 . The refrigerant gas in the second discharge chamber  29 B, which has been just compressed in the second compression chamber  23 D, has a high temperature and a high pressure. 
     As shown in  FIG. 3 , the pressure regulation chamber  31  is disposed in the rear housing  19  at a position radially inward of the second discharge chamber  29 B and surrounded by the second discharge chamber  29 B. In such structure of the compressor, the refrigerant in the pressure regulation chamber  31  is heated by high-temperature refrigerant gas in the second discharge chamber  29 B and part of the rear housing  19  in the vicinity of the second discharge chamber  29 B and, therefore, the refrigerant gas in the pressure regulation chamber  31  will also be heated. In the compressor wherein the second suction chamber  27 B is disposed radially outward of the second discharge chamber  29 B in the rear housing  19 , the refrigerant gas in the pressure regulation chamber  31  tends to be less cooled by the second suction chamber  27 B because the refrigerant gas in the pressure regulation chamber  31  is less susceptible to the influence of low-temperature refrigerant gas in the second suction chamber  27 B. 
     Furthermore, during the operation of the compressor when the drive shaft  3  is being rotated, the first and second cylinder blocks  21 ,  23 , the first and second sliding bearings  22 A,  22 B, and the first and second support members  43 A,  43 B are heated by friction. The drive shaft body  30  is also heated by the heat transmitted from the second support member  43 B and the like. The first and second thrust bearings  35 A,  35 B are also heated by the friction caused during the rotation of the drive shaft  3 . In the compressor wherein the second thrust bearing  35 B is provided between the second recessed portion  23 C of the second cylinder block  23  and the flange  431  of the second support member  43 B, the heat generated in the second thrust bearing  35 B is transmitted to the second cylinder block  23  and the second support member  43 B. 
     In the compressor, the refrigerant gas in the pressure regulation chamber  31  may be heated directly by the members projecting into the pressure regulation chamber  31 , such as the projection  23 F of the second cylinder block  23 , the second sliding bearing  22 B, the rear end of the second support member  43 B and the rear end of the drive shaft body  30  that project into the pressure regulation chamber  31 . 
     In the compressor according to the present embodiment, the temperature of the refrigerant gas which is drawn from the second discharge chamber  29 B into the pressure regulation chamber  31  is hard to drop. Therefore, in the compressor wherein the drive shaft body  30  is heated as described above and the rear end of the axial passage  3 B is located in the pressure regulation chamber  31 , the refrigerant gas flowed from the pressure regulation chamber  31  into the pressure control chamber  13 C is hard to be cooled in the axial passage  3 B and the radial passage  3 C. If liquefied refrigerant exists in the pressure regulation chamber  31  due to cooling, the pressure change in the pressure control chamber  13 C is inhibited. In the compressor according to the present embodiment, the refrigerant in the pressure regulation chamber  31  is hardly to be liquefied, with the result that the pressure of the refrigerant gas flowed into the pressure control chamber  13 C through the pressure regulation chamber  31  is varied quickly and the movable body  13 A is moved smoothly in response to a change of the pressure in the pressure control chamber  13 C and, therefore, the inclination angle of the swash plate is changed quickly according to a change of the operating condition of the compressor. 
     Thus, the compressor according to the embodiment exhibits good controllability. 
     Furthermore, in the compressor, the drive shaft including the drive shaft body and the cap maintains the simple form of the drive shaft main body to thereby provide a simplified manufacturing process of the compressor, while heating the refrigerant with the cap. 
     The present invention has been described according to the embodiment shown in the drawings. However, the present invention is not limited to the embodiment above, but it may appropriately be modified without departing from the gist of the invention. 
     For example, as in the case of the rear housing  19 , the first discharge chamber  29 A may be formed radially inward of the front housing  17  and the first suction chamber  27 A radially outward of the first discharge chamber  29 A. 
     The configuration of the control mechanism  15  may be such that the control valve  15 C is formed in the high-pressure passage  15 B and the orifice  15 D is formed in the low-pressure passage  15 A. In this case, the opening of the high-pressure passage  15 B is regulated by the control valve  15 C. In the compressor of such configuration, the pressure in the pressure control chamber  13 C is raised quickly by the high pressure in the second discharge chamber  29 B, so that an increase of the displacement of the compressor may be accomplished quickly. 
     The compressor may be configured such that the actuator  13  is disposed on the front surface  5 A side and the lug arm  49  on the rear surface  5 B side of the swash plate  5 . 
     The compressor may further be configured such that the compression chamber is formed in either the first cylinder block  21  or the second cylinder block  23 . 
     The present invention is applicable to an air conditioning apparatus or and the like.