Patent Publication Number: US-9903354-B2

Title: Variable displacement swash plate compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable displacement swash plate compressor. 
     Japanese Laid-Out Patent Publication Nos. 2-19665 and 5-172052 describe conventional variable displacement swash plate compressors (hereafter simply referred to as the compressors). The compressors each have a housing including a suction chamber, a discharge chamber, a swash plate chamber, and pairs of cylinder bores. A rotatable drive shaft is supported in the housing. A swash plate that is rotatable together with the drive shaft is arranged in the swash plate chamber. A link mechanism is located between the drive shaft and the swash plate to allow the inclination angle of the swash plate to change. The inclination angle refers to an angle relative to a direction orthogonal to the rotation axis of the drive shaft. 
     Each cylinder bore pair accommodates a piston. The piston is reciprocated in the cylinder bore pair and defines compression chambers in the cylinder bore pair. Each cylinder bore pair includes a first cylinder bore, which is located at a first side, or front side, of the swash plate, and a second cylinder bore, which is located at a second side, or rear side, of the swash plate. Each piston includes a first head, which reciprocates in the first cylinder bore, and a second head, which is formed integrally with the first head and which reciprocates in the second cylinder bore. 
     A conversion mechanism coverts rotation of the swash plate to reciprocation of the piston in each cylinder bore pair. The stroke when the piston reciprocates is in accordance with the inclination angle of the swash plate. The inclination angle of the swash plate is changed by an actuator, which is controlled by a control mechanism. 
     The compressors described in Japanese Laid-Out Patent Publication Nos. 2-19665 and 5-172052 each include a pressure regulation chamber in a rear housing member, which is an element of the housing. A cylinder block, which is also an element of the housing, includes a control pressure chamber, which is in communication with the pressure regulation chamber. The actuator is located in the control pressure chamber. The actuator is not rotated integrally with the drive shaft. 
     In the same manner as each second cylinder bore and each second head, the actuator is located at the second side, or rear of the housing. The actuator includes a non-rotation movable body that covers the rear end of the drive shaft. The non-rotation movable body includes an inner wall surface that supports the rear end of the drive shaft so that the rear end is rotatable. The non-rotation movable body is movable along the rotation axis of the drive shaft. Although the non-rotation movable body moves in the control pressure chamber along the rotation axis of the drive shaft, the non-rotation movable body is not allowed to rotate about the rotation axis of the drive shaft. A spring that urges the non-rotation movable body toward the front is arranged in the control pressure chamber or the pressure regulation chamber. The actuator includes a movable body, which is coupled to the swash plate and movable along the rotation axis of the drive shaft. A thrust bearing is arranged between the non-rotation movable body and the movable body. A pressure control valve, which changes the pressure of the control chamber, is arranged between the pressure regulation chamber and the discharge chamber. A change in the pressure of the control pressure chamber moves the non-rotation movable body and the movable body in the axial direction of the drive shaft. 
     A link mechanism, which is located in the swash plate chamber, includes a movable body and a lug arm, which is fixed to the drive shaft. The rear end of the lug arm includes an elongated hole, which extends in a direction orthogonal to the rotation axis of the drive shaft and in a direction intersecting the rotation axis of the drive shaft. The front of the swash plate is supported by a pin inserted through the elongated hole so that the swash plate is pivotal about a first pivot axis. 
     In the compressor of Japanese Laid-Open Patent Publication No. 5-172052, the front end of the movable body also includes an elongated hole that extends in a direction orthogonal to the rotation axis and in a direction intersecting the rotation axis. The rear end of the swash plate is supported by a pin inserted through the elongated hole so that the swash plate is pivotal about a second pivot axis, which is parallel to the first pivot axis. 
     In each of these compressors, the pressure control valve opens to connect the discharge chamber and the pressure regulation chamber so that the pressure of the control pressure chamber becomes higher than that of the swash plate chamber. This moves the non-rotation movable body and the movable body toward the front. Thus, the inclination angle of the swash plate increases, the piston stroke is lengthened, and the compression displacement is increased for each rotation of the drive shaft. When the pressure control valve closes to disconnect the discharge chamber and the pressure regulation chamber, the pressure of the control pressure chamber becomes low and about the same as that of the swash plate chamber. This moves the non-rotation movable body and the movable body toward the rear. Thus, the inclination angle of the swash plate decreases, the piston stroke is shortened, and the compressor displacement is decreased for each rotation of the drive shaft. 
     Further, in each of these compressors, when the inclination angle of the swash plate changes, the link mechanism is configured so that the top dead center of the first head of each piston is shifted by a greater distance than the top dead center of the second head. More specifically, when the inclination angle of the swash plate is changed, the top dead center of the second head of each piston remains at substantially the same position but the top dead center of the first head is shifted over a relatively long distance to another position. Thus, as the inclination angle of the swash plate approaches zero degrees, each piston slightly performs compression with the second head and does not perform compression with the first head. 
     In each of these conventional compressors, the actuator is located at the second side of the swash plate, that is, the same side as the second cylinder bores as viewed from the swash plate. Thus, in these compressors, it is difficult to provide open space in the housing at the second side of the swash plate to allow for forward and rearward movement of the non-rotation movable body and the movable body. Further, since the size of the actuator is limited in the radial direction, displacement control is difficult. Moreover, when enlarging the housing in the radial direction so that the inclination angle of the swash plate is easily changed, it may become difficult to install the compressor in a vehicle or the like. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a compact compressor capable of performing superior displacement control. 
     One aspect of the present invention is a variable displacement swash plate compressor including a housing, a drive shaft, a swash plate, a link mechanism, a piston, a conversion mechanism, and actuator, and a control mechanism. The housing includes a suction chamber, a discharge chamber, a swash plate chamber, and a cylinder bore pair. The drive shaft is rotationally supported by the housing in a rotatable manner. The swash plate is rotatable together with the drive shaft in the swash plate chamber. The link mechanism is arranged between the drive shaft and the swash plate. The link mechanism allows for changes in an inclination angle of the swash plate relative to a direction orthogonal to a rotation axis of the drive shaft. The piston is reciprocally accommodated in the cylinder bore pair. The conversion mechanism is configured to reciprocate the piston in the cylinder bore pair with a stroke that is in accordance with the inclination angle of the swash plate when the swash plate rotates. The actuator is capable of changing the inclination angle of the swash plate. The control mechanism is configured to control the actuator. The cylinder bore pair includes a first cylinder bore, which is located at a first side of the swash plate, and a second cylinder bore, which is located at a second side of the swash plate. The piston includes a first head, which reciprocates in the first cylinder bore, and a second head, which is formed integrally with the first head and reciprocates in the second cylinder bore. The link mechanism is configured to shift a top dead center of the first head over a longer distance than a top dead center of the second head when the inclination angle of the swash plate changes. The actuator is located at the same side as the first cylinder bore as viewed from the swash plate, and the actuator is rotatable integrally with the drive shaft. The actuator includes a partitioning body, which is loosely fitted to the drive shaft in the swash plate chamber, a movable body, which is coupled to the swash plate and movable relative to the partitioning body along the rotation axis, and a control pressure chamber, which is defined by the partitioning body and the movable body. The pressure of the control pressure chamber moves the movable body. The control mechanism is configured to change the pressure of the control pressure chamber to move the movable body. 
     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 cross-sectional view showing a compressor of a first embodiment when the displacement is maximal; 
         FIG. 2  is a schematic diagram showing a control mechanism in the compressor of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view showing the compressor of  FIG. 1  when the displacement is minimal; and 
         FIG. 4  is a schematic diagram showing a control mechanism in a compressor of a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First and second embodiments will now be described with reference to the drawings. Compressors of the first and second embodiments are each installed in a vehicle to form a refrigeration circuit of a vehicle air conditioner. 
     First Embodiment 
     Referring to  FIGS. 1 and 3 , a compressor of the first embodiment includes a housing  1 , a drive shaft  3 , a swash plate  5 , a link mechanism  7 , pistons  9 , front and rear shoes  11   a  and  11   b , an actuator  13 , and a control mechanism  15 , which is shown in  FIG. 2 . Each piston  9  is provided with a pair of the shoes  11   a  and  11   b.    
     As shown in  FIG. 1 , the housing  1  includes a front housing member  17 , which is located at the front of the compressor, a rear housing member  19 , which is located at the rear of the compressor, and first and second cylinder blocks  21  and  23 , which are located between the front housing member  17  and the rear housing member  19 . 
     The front housing member  17  includes a boss  17   a , which projects toward the front. A sealing device  25  is arranged in the boss  17   a  around the drive shaft  3 . Further, the front housing member  17  includes a first suction chamber  27   a  and a first discharge chamber  29   a . The first suction chamber  27   a  is located in a radially inner portion of the front housing member  17 , and the first discharge chamber  29   a  is located in a radially outer portion of the front housing member  17 . 
     The rear housing member  19  includes the control mechanism  15 . The rear housing member  19  includes a second suction chamber  27   b , a second discharge chamber  29   b , and a pressure regulation chamber  31 . The second suction chamber  27   b  is located in a radially inner portion of the rear housing member  19 , and the second discharge chamber  29   b  is located in a radially outer portion of the rear housing member  19 . The pressure regulation chamber  31  is located in a radially central portion of the rear housing member  19 . A discharge passage (not shown) connects the first discharge chamber  29   a  and the second discharge chamber  29   b . The discharge passage includes a discharge port, which is in communication with the outer side of the compressor. 
     A swash plate chamber  33  is defined in the first cylinder block  21  and the second cylinder block  23 . The swash plate chamber  33  is located in a central portion of the housing  1 . 
     The first cylinder block  21  includes first cylinder bores  21   a , which are arranged at equal angular intervals in the circumferential direction and which extend parallel to one another. Each first cylinder bore  21   a  corresponds to a first cylinder bore of the present invention. 
     Further, the first cylinder block  21  includes a first shaft bore  21   b . The drive shaft  3  extends through the first shaft bore  21   b . The first cylinder block  21  also includes a first recess  21   c , which is located at the rear side of the first shaft bore  21   b . The first recess  21   c  is in communication with the first shaft bore  21   b  and coaxial with the first shaft bore  21   b . Further, the first recess  21   c  is in communication with the swash plate chamber  33  and includes a stepped wall surface. A first thrust bearing  35   a  is arranged in a front portion of the first recess  21   c . The first cylinder block  21  includes a first suction passage  37   a  that communicates the swash plate chamber  33  with the first suction chamber  27   a.    
     In the same manner as the first cylinder block  21 , the second cylinder block  23  includes second cylinder bores  23   a . Each second cylinder bore  23   a  corresponds to a second cylinder bore of the present invention. Corresponding ones of the first cylinder bores  21   a  and the second cylinder bores  23   a  are coaxially aligned to form cylinder bore pairs. 
     Further, the second cylinder block  23  includes a second shaft bore  23   b . The drive shaft  3  extends through the second shaft bore  23   b . The second shaft bore  23   b  is in communication with the pressure regulation chamber  31 . The second cylinder block  23  also includes a second recess  23   c , which is located at the front side of the second shaft bore  23   b . The second recess  23   c  is in communication with the second shaft bore  23   b  and coaxial with the second shaft bore  23   b . Further, the second recess  23   c  is in communication with the swash plate chamber  33  and includes a stepped wall surface. A second thrust bearing  35   b  is arranged in a rear portion of the second recess  23   c . The second cylinder block  23  includes a second suction passage  37   b  that communicates the swash plate chamber  33  with the second suction chamber  27   b.    
     The swash plate chamber  33  is connected to an evaporator (not shown) via a suction port  330  formed in the second cylinder block  23 . 
     A first valve plate  39  is arranged between the front housing member  17  and the first cylinder block  21 . The first valve plate  39  includes a suction port  39   b  and a discharge port  39   a  for each first cylinder bore  21   a . A suction valve mechanism (not shown) is provided for each suction port  39   b . Each suction port  39   b  communicates the corresponding first cylinder bore  21   a  with the first suction chamber  27   a . A discharge valve mechanism (not shown) is provided for each discharge port  39   a . Each discharge port  39   a  communicates the corresponding first cylinder bore  21   a  with the first discharge chamber  29   a . The first valve plate  39  also includes a communication hole  39   c . The communication hole  39   c  communicates the first suction chamber  27   a  with the swash plate chamber  33  through the first suction passage  37   a.    
     A second valve plate  41  is arranged between the rear housing member  19  and the second cylinder block  23 . In the same manner as the first valve plate  39 , the second valve plate  41  includes a suction port  41   b  and a discharge port  41   a  for each second cylinder bore  23   a . A suction valve mechanism (not shown) is provided for each suction port  41   b . Each suction port  41   b  communicates the corresponding second cylinder bore  23   a  with the second suction chamber  27   b . A discharge valve mechanism (not shown) is provided for each discharge port  41   a . Each discharge port  41   a  communicates the corresponding second cylinder bore  23   a  with the second discharge chamber  29   b . The second valve plate  41  also includes a communication hole  41   c . The communication hole  41   c  communicates the second suction chamber  27   b  with the swash plate chamber  33  through the second suction passage  37   b.    
     The first and second suction chambers  27   a  and  27   b  and the swash plate chamber  33  are in communication with one another through the first and second suction passages  37   a  and  37   b . Thus, the first and second suction chambers  27   a  and  27   b  and the swash plate chamber  33  have substantially the same pressure. More accurately, the pressure of the swash plate chamber  33  is slightly higher than the pressure of the first and second suction chambers  27   a  and  27   b  due to the effect of blow-by gas. Refrigerant gas from the evaporator flows into the swash plate chamber  33  through the suction port  330 . Thus, the pressure of each of the swash plate chamber  33  and the first and second suction chambers  27   a  and  27   b  is lower than the pressure of each of the first and second discharge chambers  29   a  and  29   b . In this manner, the swash plate chamber  33  and the first and second suction chambers  27   a  and  27   b  define a low pressure chamber. 
     The swash plate  5 , the actuator  13 , and a flange  3   a  are arranged on the drive shaft  3 . The drive shaft  3  is inserted through the boss  17   a  toward the rear and inserted through the first and second shaft bores  21   b  and  23   b  in the first and second cylinder blocks  21  and  23 . The front end of the drive shaft  3  is located in the boss  17   a , and the rear end is located in the pressure regulation chamber  31 . The first and second shaft bores  21   b  and  23   b  support the drive shaft  3  in the housing  1  so that the drive shaft  3  is rotatable the rotation axis O. The swash plate  5 , the actuator  13 , and the flange  3   a  are each located in the swash plate chamber  33 . The flange  3   a  is located between the first thrust bearing  35   a  and the actuator  13 , more specifically, between the first thrust bearing  35   a  and a movable body  13   b . The flange  3   a  restricts contact of the first thrust bearing  35   a  and the movable body  13   b . Radial bearings may be arranged between the drive shaft  3  and the walls of the first and second shaft bores  21   b  and  23   b.    
     A support member  43  is fitted to the rear portion of the drive shaft  3 . The support member  43  includes a flange  43   a , which is in contact with the second thrust bearing  35   b , and a coupling portion  43   b , which receives a second pin  47   b . The drive shaft  3  includes an axial passage  3   b  and a radial passage  3   c . The axial passage  3   b  extends through the drive shaft along the rotation axis O toward the front from the rear end of the drive shaft  3 . The radial passage  3   c  extends from the front end of the axial passage  3   b  in the radial direction and opens in the outer surface of the drive shaft  3 . The axial passage  3   b  and the radial passage  3   c  define a communication passage. The rear end of the axial passage  3   b  is connected to the pressure regulation chamber  31 , or the low pressure chamber. The radial passage  3   c  is connected to a control pressure chamber  13   c . Further, the drive shaft  3  includes a step  3   e.    
     The swash plate  5  is an annular plate and includes a front surface  5   a  and a rear surface  5   b . The front surface  5   a  of the swash plate  5  faces the front side of the compressor in the swash plate chamber  33 . The rear surface  5   b  of the swash plate  5  faces the rear side of the compressor in the swash plate chamber  33 . The front surface  5   a  and the rear surface  5   b  of the swash plate  5  respectively correspond to a first surface and a second surface of the present invention. In the compressor, the first cylinder bores  21   a  are each located at the same side as the front surface  5   a  of the swash plate  5 , that is, the front side (first side). The second cylinder bores  23   a  are each located at the same side as the rear surface  5   b  of the swash plate  5 , that is, the rear side (second side). 
     The swash plate  5  is fixed to a ring plate  45 . The ring plate  45  is an annular plate. An insertion hole  45   a  extends through the center of the ring plate  45 . The drive shaft  3  is inserted through the insertion hole  45   a  to couple the swash plate  5  to the drive shaft  3 . This arranges the swash plate  5  in the swash plate chamber  33  at the same side as the second cylinder bores  23   a , that is, at a position located toward the rear in the swash plate chamber  33 . 
     The link mechanism  7  includes a lug arm  49 . The lug arm  49  is arranged at the rear side of the swash plate  5  in the swash plate chamber  33  and located between the swash plate  5  and the support member  43 . The lug arm  49  is generally L-shaped. The lug arm  49  contacts the flange  43   a  of the support member  43  when the swash plate  5  is inclined relative to a direction orthogonal to the rotation shaft O at the minimum angle. In the compressor, the lug arm  49  allows the swash plate  5  to be maintained at the minimum inclination angle. The distal end of the lug arm  49  includes a weight  49   a . The weight  49   a  extends over one half of the circumference of the actuator  13 . The weight  49   a  may be designed to have a suitable shape. 
     A first pin  47   a  couples the distal end of the lug arm  49  to a top region of the ring plate  45 . Thus, the distal end of the lug arm  49  is supported by the ring plate  45 , or the swash plate  5 , so that the lug arm  49  is pivotal about the axis of the first pin  47   a , namely, a first pivot axis M 1 . The first pivot axis M 1  extends in a direction perpendicular to the rotation axis O of the drive shaft  3 . 
     A second pin  47   b  couples a basal end of the lug arm  49  to the support member  43 . Thus, the basal end of the lug arm  49  is supported by the support member  43 , or the drive shaft  3 , so that the lug arm  49  is pivotal about the axis of the second pin  47   b , namely, a second pivot axis M 2 . The second pivot axis M 2  extends parallel to the first pivot axis M 1 . The lug arm  49  and the first and second pins  47   a  and  47   b  correspond to the link mechanism  7  of the present invention. 
     In the compressor, the link mechanism  7  couples the swash plate  5  and the drive shaft  3  so that the swash plate  5  rotates together with the drive shaft  3 . As described above, the lug arm  49  is located between the swash plate  5  and the support member  43 . Thus, the link mechanism  7  is located in the swash plate chamber  33  at the rear side of the swash plate  5 , that is, the same side as the second cylinder bores  23   a  as viewed from the swash plate  5 . The two ends of the lug arm  49  are respectively pivotal about the first pivot axis M 1  and the second pivot axis M 2  so that inclination angle of the swash plate  5  is changed, as shown in  FIGS. 1 and 3 . 
     The weight  49   a  extends along the distal end of the lug arm  49 , that is, the side opposite to the second pivot axis M 2  as viewed from the first pivot axis M 1 . The lug arm  49  is supported by the first pin  47   a  on the ring plate  45  so that the weight  49   a  is inserted through a groove  45   b  in the ring plate  45  and is located at the front side of the ring plate  45 , that is, the front side of the swash plate  5 . Rotation of the swash plate  5  around the rotation axis O generates centrifugal force that acts on the weight  49   a  at the front side of the swash plate  5 . 
     Each piston  9  includes a front end that defines a first piston head  9   a  and a rear end that defines a second piston head  9   b . The first piston head  9   a  corresponds to a first head of the present invention, and the second piston head  9   b  corresponds to a second head of the present invention. 
     The first piston head  9   a  is reciprocally accommodated in the corresponding first cylinder bore  21   a  defining a first compression chamber  21   d . The second piston head  9   b  is reciprocally accommodated in the corresponding second cylinder bore  23   a  defining a second compression chamber  23   d . Each piston  9  includes a recess  9   c , which accommodates the semispherical shoes  11   a  and  11   b . The shoes  11   a  and  11   b  convert the rotation of the swash plate  5  to the reciprocation of the piston  9 . The shoes  11   a  and  11   b  correspond to a conversion mechanism of the present invention. In this manner, the first and second piston heads  9   a  and  9   b  are reciprocal in the first and second cylinder bores  21   a  and  23   a  with a stroke that is in accordance with the inclination angle of the swash plate  5 . 
     The actuator  13  is located in front of the swash plate  5  in the swash plate chamber  33  and is movable into the first recess  21   c . The actuator  13  includes a partitioning body  13   a  and a movable body  13   b.    
     The partitioning body  13   a  is disk-shaped and loosely fitted to the drive shaft  3  in the swash plate chamber  33 . An O-ring  51   a  is arranged on the outer circumferential surface of the partitioning body  13   a , and an O-ring  51   b  is arranged on the inner circumferential surface of the partitioning body  13   a.    
     The movable body  13   b  is tubular and has a closed end. Further, the movable body  13   b  includes an insertion hole  130   a , through which the drive shaft  3  is inserted, a main body portion  130   b , which extends from the front of the movable body  13   b  toward the rear, and a coupling portion  130   c , which is formed on the rear end of the main body portion  130   b . An O-ring  51   c  is arranged in the insertion hole  130   a . The movable body  13   b  is located between the first thrust bearing  35   a  and the swash plate  5 . 
     The drive shaft  3  is inserted into the main body portion  130   b  of the movable body  13   b  and through the insertion hole  130   a . The partitioning body  13   a  is arranged in a movable manner in the main body portion  130   b . The movable body  13   b  is rotatable together with the drive shaft  3  and movable along the rotation axis O of the drive shaft  3  at the front side of the swash plate  5  in the swash plate chamber  33 . In this manner, the drive shaft  3  is inserted through the actuator  13 , and the actuator  13  is rotatable integrally with the drive shaft  3  about the rotation axis O. 
     The movable body  13   b  and the link mechanism  7  are located at opposite sides of the swash plate  5  in the swash plate chamber  33 . More specifically, the actuator  13 , which includes the movable body  13   b , is located in the swash plate chamber  33  at the front side of the swash plate  5 , that is, the same side as the first cylinder bores  21   a  as viewed from the swash plate  5 . 
     A third pin  47   c  couples a bottom region of the ring plate  45  to the coupling portion  130   c  of the movable body  13   b . Thus, the ring plate  45 , or the swash plate  5 , is supported by the movable body  13   b  so as to be pivotal about the axis of the third pin  47   c , namely, an action axis M 3 . The action axis M 3  extends parallel to the first and second pivot axes M 1  and M 2 . In this manner, the movable body  13   b  is coupled to the swash plate  5 . The movable body  13   b  contacts the flange  3   a  when the swash plate  5  is inclined at the maximum angle. In the compressor, the movable body  13   b  allows the swash plate  5  to be maintained at the maximum inclination angle. 
     The control pressure chamber  13   c  is defined between the partitioning body  13   a  and the movable body  13   b . The radial passage  3   c  extends into the control pressure chamber  13   c . The control pressure chamber  13   c  is in communication with the pressure regulation chamber  31  through the radial passage  3   c  and the axial passage  3   b.    
     As shown in  FIG. 2 , the control mechanism  15  includes a bleed passage  15   a , a gas supplying passage  15   b , a control valve  15   c , and an orifice  15   d . The bleed passage  15   a  and the gas supplying passage  15   b  form a control passage. 
     The bleed passage  15   a  is connected to the pressure regulation chamber  31  and the second suction chamber  27   b . The pressure regulation chamber  31  is in communication with the control pressure chamber  13   c  through the axial passage  3   b  and the radial passage  3   c . Thus, the control pressure chamber  13   c  and the second suction chamber  27   b  are in communication with each other through the bleed passage  15   a . The bleed passage  15   a  includes the orifice  15   d.    
     The gas supplying passage  15   b  is connected to the pressure regulation chamber  31  and the second discharge chamber  29   b . Thus, in the same manner as the bleed passage  15   a , the control pressure chamber  13   c  and the second discharge chamber  29   b  are in communication with each other through the axial passage  3   b  and the radial passage  3   c . In this manner, the axial passage  3   b  and the radial passage  3   c  form portions of the bleed passage  15   a  and the gas supplying passage  15   b , which serve as the control passage. 
     The control valve  15   c  is arranged in the gas supplying passage  15   b . The control valve  15   c  adjusts the open degree of the gas supplying passage  15   b  based on the pressure of the second suction chamber  27   b . A known valve may be used as the control valve  15   c.    
     The distal end of the drive shaft  3  includes a threaded portion  3   d . The threaded portion  3   d  couples the drive shaft  3  to a pulley or an electromagnetic clutch (neither shown). A belt (not shown), which is driven by a vehicle engine, runs along the pulley or a pulley of the electromagnetic clutch. 
     A pipe leading to the evaporator is connected to the suction port  330 . A pipe leading to a condenser is connected to a discharge port (none shown). The compressor, the evaporator, an expansion valve, the condenser, and the like form the refrigeration circuit of the vehicle air conditioner. 
     In the compressor, the rotation of the drive shaft  3  rotates the swash plate  5  and reciprocates each piston  9  in the corresponding first and second cylinder bores  21   a  and  23   a . Thus, the volumes of the first and second compression chambers  21   d  and  23   d  change in accordance with the piston stroke. This draws refrigerant gas into the swash plate chamber  33  through the suction port  330  from the evaporator. The refrigerant gas flows through the first and second suction chambers  27   a  and  27   b  and is compressed in the first and second compression chambers  21   d  and  23   d , which then discharge the refrigerant gas into the first and second discharge chambers  29   a  and  29   b . The refrigerant gas in the first and second discharge chambers  29   a  and  29   b  is discharged out of the discharge port and sent to the condenser. 
     During operation of the compressor, centrifugal force, which acts to decrease the inclination angle of the swash plate, and compression reaction, which acts to decrease the inclination angle of the swash plate  5  through the pistons  9 , are applied to the rotation members, which include the swash plate  5 , the ring plate  45 , the lug arm  49 , and the first pin  47   a . The compressor displacement may be controlled by changing the inclination angle of the swash plate  5  thereby lengthening or shortening the stroke of the pistons  9 . 
     More specifically, in the control mechanism  15 , when the control valve  15   c  shown in  FIG. 2  decreases the open degree of the gas supplying passage  15   b , the pressure of the control pressure chamber  13   c  becomes substantially equal to the pressure of the second suction chamber  27   b . Thus, the centrifugal force and the compression reaction acting on the rotation members move the movable body  13   b  toward the rear. This contracts the control pressure chamber  13   c  and decreases the inclination angle of the swash plate  5 . 
     As a result, referring to  FIG. 3 , the swash plate  5  pivots about the action axis M 3  of the swash plate  5  and the two ends of the lug arm  49  respectively pivot about the first and second pivot axes M 1  and M 2  so that the lug arm  49  moves toward the flange  43   a  of the support member  43 . This shortens the stroke of the pistons  9  and decreases the compressor displacement for each rotation of the drive shaft  3 . The inclination angle of the swash plate  5  in  FIG. 3  is the minimum inclination angle of the compressor. 
     In the compressor, the centrifugal force acting on the weight  49   a  is applied to the swash plate  5 . Thus, in the compressor, the swash plate  5  easily moves in the direction that decreases the inclination angle of the swash plate  5 . Further, when the movable body  13   b  moves toward the rear along the rotation axis O of the drive shaft  3 , the rear end of the movable body  13   b  is arranged at the inner side of the weight  49   a . As a result, in the compressor, when the inclination angle of the swash plate  5  decreases, the weight  49   a  covers about one half of the rear end of the movable body  13   b.    
     When the control valve  15   c  shown in  FIG. 2  increases the open degree of the gas supplying passage  15   b , the pressure of the control pressure chamber  13   c  becomes substantially equal to the pressure of the second discharge chamber  29   b . Thus, the movable body  13   b  of the actuator  13  moves toward the front against the centrifugal force and the compression reaction acting on the rotation members. This enlarges the control pressure chamber  13   c  and increases the inclination angle of the swash plate  5 . 
     As a result, referring to  FIG. 1 , the swash plate  5  pivots in the opposite direction about the action axis M 3  of the swash plate  5  and the two ends of the lug arm  49  respectively pivot in the opposite direction about the first and second pivot axes M 1  and M 2  so that the lug arm  49  moves away from the flange  43   a  of the support member  43 . This lengthens the stroke of the pistons  9  and increases the compressor displacement for each rotation of the drive shaft  3 . The inclination angle of the swash plate  5  in  FIG. 1  is the maximum inclination angle of the compressor. 
     In the compressor, the link mechanism  7  couples the swash plate  5  and the drive shaft  3  so that the swash plate  5  is located near the second cylinder bores  23   a  in the swash plate chamber  33 . Thus, in the compressor, when the inclination angle of the swash plate  5  is maximal and the stroke of the pistons  9  is maximal, the top dead center of each first piston head  9   a  is located closest to the first valve plate  39 , and the top dead center of each second piston head  9   b  is located closest to the second valve plate  41 . As the inclination angle of the swash plate  5  decreases and shortens the stroke of the pistons  9 , the top dead center of each first piston head  9   a  is gradually separated from the first valve plate  39 . However, the top dead center of each second piston head  9   b  remains at substantially the same position as when the stroke of the pistons  9  is maximal and is kept close to the second valve plate  41 . 
     In this manner, in the compressor, when the inclination angle of the swash plate  5  is changed, the top dead center of the second piston head  9   b  of each piston  9  remains at substantially the same position but the top dead center of the first piston head  9   a  of each piston  9  is shifted over a relatively long distance to another position. In the compressor, a relatively large open space is provided in the swash plate chamber  33  near the first cylinder bores  21   a . Further, the actuator  13  is located near the first cylinder bores  21   a  in the swash plate chamber  33 . Accordingly, the compressor allows the actuator  13  to be enlarged in the radial direction without the need to enlarge the housing  1  in the radial direction. This allows the control pressure chamber  13   c  to be large. Thus, in the compressor, the movable body  13   b  is moved in a preferred manner by a change in the pressure of the control pressure chamber  13   c.    
     In the compressor, the partitioning body  13   a  is loosely fitted to the drive shaft  3 , and the movable body  13   b  easily moves relative to the partitioning body  13   a . Thus, in the compressor, the movable body  13   b  is moved in a preferred manner along the rotation axis O. 
     In the compressor, the link mechanism  7  is located at the same side as the second cylinder bores  23   a  as viewed from the swash plate  5 . In other words, the link mechanism  7  and the movable body  13   b  are located at opposite sides of the swash plate  5 . As described above, when the inclination angle of the swash plate  5  is changed, the top dead center of the second piston head  9   b  of each piston  9  remains at substantially the same position. Thus, the open space that is provided in the swash plate chamber  33  is relatively narrow near the second cylinder bores  23   a . However, the link mechanism  7  of the compressor is only used to change the inclination angle of the swash plate  5 . Further, the lug arm  49  is L-shaped so that the lug arm  49  is reduced in size while obtaining a sufficient pivoting range. Accordingly, even if the link mechanism  7  is arranged in the swash plate chamber  33  near the second cylinder bores  23   a  where open space is limited, the link mechanism  7  sufficiently functions. 
     Further, in the compressor, the link mechanism  7  is located at the same side as the second cylinder bores  23   a  as viewed from the swash plate  5 . This increases the open space near the first cylinder bores  21   a  in the swash plate chamber  33 . 
     Accordingly, the compressor of the first embodiment is compact, easy to install in a vehicle, and allows for superior displacement control. 
     In the control mechanism  15  of the compressor, the control pressure chamber  13   c  and the second suction chamber  27   b  are in communication through the bleed passage  15   a , and the control pressure chamber  13   c  and the second discharge chamber  29   b  are in communication through the gas supplying passage  15   b . Further, the control valve  15   c  allows for adjustment of the open degree of the gas supplying passage  15   b . Accordingly, in the compressor, the high pressure of the second discharge chamber  29   b  readily increases the pressure of the control pressure chamber  13   c  to a high value so that the compressor displacement is readily increased. 
     Further, in the compressor, the swash plate chamber  33  is used as a refrigerant gas passage leading to the first and second suction chambers  27   a  and  27   b . This has a muffler effect that reduces suction pulsation of the refrigerant gas and decreases noise of the compressor. 
     Second Embodiment 
     A compressor of the second embodiment includes a control mechanism  16  shown in  FIG. 4  in lieu of the control mechanism  15  used in the compressor of the first embodiment. The control mechanism  16  includes a bleed passage  16   a , a gas supplying passage  16   b , a control valve  16   c , and an orifice  16   d . The bleed passage  16   a  and the gas supplying passage  16   b  form a control passage. 
     The bleed passage  16   a  is connected to the pressure regulation chamber  31  and the second suction chamber  27   b . Thus, the control pressure chamber  13   c  and the second suction chamber  27   b  are in communication with each other through the bleed passage  16   a . The gas supplying passage  16   b  is connected to the pressure regulation chamber  31  and the second discharge chamber  29   b . Thus, the control pressure chamber  13   c  and the pressure regulation chamber  31  are in communication with the second discharge chamber  29   b  through the gas supplying passage  16   b . The gas supplying passage  16   b  includes the orifice  16   d.    
     The control valve  16   c  is arranged in the bleed passage  16   a . The control valve  16   c  adjusts the open degree of the bleed passage  16   a  based on the pressure of the second suction chamber  27   b . In the same manner as the control valve  15   c , a known valve may be used as the control valve  16   c . Further, the axial passage  3   b  and the radial passage  3   c  form portions of the bleed passage  16   a  and the gas supplying passage  16   b . Other portions of the compressor have the same structure as the compressor of the first embodiment. Same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described in detail. 
     In the control mechanism  16  of the compressor, when the control valve  16   c  decreases the open degree of the bleed passage  16   a , the pressure of the control pressure chamber  13   c  becomes substantially equal to the pressure of the second discharge chamber  29   b . Thus, the centrifugal force and the compression reaction acting on the rotation members move the movable body  13   b  of the actuator  13  toward the front. This expands the control pressure chamber  13   c  and increases the inclination angle of the swash plate  5 . 
     As a result, in the same manner as the compressor of the first embodiment, the inclination angle of the swash plate  5  increases in the compressor and lengthens the stroke of the pistons  9 . This increases the compressor displacement for each rotation of the drive shaft  3  (refer to  FIG. 1 ). 
     When the control valve  16   c  increases the open degree of the bleed passage  16   a , the pressure of the control pressure chamber  13   c  becomes substantially equal to the pressure of the second suction chamber  27   b . Thus, the centrifugal force and the compression reaction acting on the rotation members move the movable body  13   b  toward the rear. This contracts the control pressure chamber  13   c  and decreases the inclination angle of the swash plate  5 . 
     As a result, the inclination angle of the swash plate  5  decreases in the compressor and shortens the stroke of the pistons  9 . This decreases the compressor displacement for each rotation of the drive shaft  3  (refer to  FIG. 3 ). 
     In the control mechanism  16  of the compressor, the control valve  16   c  allows for adjustment of the open degree of the bleed passage  16   a . Thus, in the compressor, the low pressure of the second suction chamber  27   b  gradually decreases the pressure of the control pressure chamber  13   c  to a low value so that a suitable driving feel of the vehicle is maintained. Otherwise, the operation of the compressor is the same as the compressor of the first embodiment. 
     The present invention is not restricted to the first and second embodiments described above. 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. 
     In the compressors of the first and second embodiments, refrigerant gas is drawn into the first and second suction chambers  27   a  and  27   b  through the swash plate chamber  33 . Instead, refrigerant gas may be directly drawn into the first and second suction chambers  27   a  and  27   b  from a pipe through a suction port. In this case, the first and second suction chambers  27   a  and  27   b  may be configured to communicate with the swash plate chamber  33  in the compressor, and the swash plate chamber  33  is configured to serve as a low pressure chamber. 
     The pressure regulation chamber  31  may be omitted from the compressors of the first and second embodiments. 
     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.