Abstract:
In the compressor of the present invention, the first discharge chamber is divided into m first discharge sections, where m is an integer satisfying m≧2, and the second discharge chamber is divided into m second discharge sections. N out of the first discharge sections, where n is an arbitrary integer satisfying 1≦n&lt;m, are defined as specified first discharge sections, and n out of the second discharge sections are defined as specified second discharge sections. When viewed from an axial direction of the drive shaft, at least one of the specified first discharge sections and at least one of the specified second discharge sections are disposed at positions shifted from each other. N first discharge passages each communicates with each of the specified first discharge sections and the merging portion, and n second discharge passages each communicates with each of the specified second discharge sections and the merging portion.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a double-headed piston type compressor. 
       BACKGROUND ART 
       [0002]    Japanese Patent Laid-Open No. 10-103228 discloses a conventional double-headed piston type compressor (hereinafter, simply referred to as a compressor). The compressor comprises a drive shaft, a housing that rotatably supports the drive shaft, and five double-headed pistons. 
         [0003]    The housing has five first cylinder bores and five second cylinder bores. The first cylinder bores are disposed at one side of the drive shaft. The second cylinder bores are disposed at the other side of the drive shaft and face the respective first cylinder bores. The double-headed pistons reciprocate in the first cylinder bores and the second cylinder bores respectively. 
         [0004]    The housing has also an annular first discharge chamber, an annular second discharge chamber, a merging portion, a first discharge passage and a second discharge passage. Refrigerant that has been compressed in the respective first cylinder bores is discharged into the first discharge chamber. Refrigerant that has been compressed in the respective second cylinder bores is discharged into the second discharge chamber. The refrigerant discharged into the first discharge chamber and the refrigerant discharged into the second discharge chamber flow into and merge together in the merging portion. The merging portion is capable of discharging the merged refrigerant to the outside. The first discharge passage provides communication between the first discharge chamber and the merging portion. The second discharge passage provides communication between the second discharge chamber and the merging portion. 
         [0005]    In this compressor, when the respective double-headed pistons reciprocate by rotation of the drive shaft, the refrigerant that has been compressed in the respective first cylinder bores is successively discharged into the first discharge chamber and reaches the merging portion through the first discharge passage, and the refrigerant that has been compressed in the respective second cylinder bores is successively discharged into the second discharge chamber and reaches the merging portion through the second discharge passage. Then, the refrigerant from the first discharge chamber merges with the refrigerant from the second discharge chamber in the merging portion, and the merged refrigerant is discharged outside. At this time, pressures in the first and second discharge chambers momentarily increase at every discharge, and this causes discharge pulsation. When the discharge pulsation is analyzed using a fast Fourier transform (FFT), it is found that the pulsation includes various frequency components from a first-order to quite a high-order of rotation components. If the refrigerant is discharged outside from the merging portion without reducing the discharge pulsation, components in a refrigeration circuit such as a condenser vibrate and noise is generated. 
         [0006]    In this regard, in this compressor, among the frequency components of the discharge pulsation, the fifth-order rotation component corresponding to the number (five) of the double-headed pistons (where, the fifth-order rotation component is a five-cycle fluctuation component during one rotation of the drive shaft) in the first discharge chamber differ in phase by 180° from the fifth-order rotation component in the second discharge chamber. Therefore, in the merging portion, the refrigerant which has passed through the first discharge passage merges with the refrigerant which has passed through the second discharge passage in a state where the phases of their fifth-order rotation components are shifted from each other, and this reduces the amplitude of fifth-order rotation component in the merging portion. 
         [0007]    Furthermore, in this compressor, countermeasures are taken against other factors that may increase the fifth-order rotation component. That is, the timing of discharging the refrigerant from any one of the first cylinder bores is made different from any of the timing of discharging the refrigerant from the respective second cylinder bores. In addition, in this compressor, a pair of pulsation reducing means are provided; one consisting of the first discharge chamber and the first discharge passage, and the other consisting of the second discharge chamber and the second discharge passage. The pulsation reducing means are configured such that the reduction rate of the discharge pulsation at one side of the drive shaft is made equal to the reduction rate of the discharge pulsation at the other side of the drive shaft in the housing. By employing such a configuration, this compressor attempts to reliably reduce the fifth-order rotation component of the discharge pulsation. 
         [0008]    The inventors of the present application intensively analyzed various frequency components of discharge pulsations and reached the findings that, in the case of employing the configuration in which refrigerant compressed in the first and second cylinder bores are respectively discharged into the annular first and second discharge chambers, not only a m th -order rotation component corresponding to the number m of double-headed pistons, but also (m±1) th -order rotation components reach a high level depending on the conditions at the time of operation and become the factor of generating vibration and noise of the refrigeration circuit unit. Furthermore, the inventors confirmed that, with the conventional compressor described above, the (m±1) th -order rotation components of the discharge pulsation are difficult to reduce. That is, in the conventional compressor, it is difficult to reliably reduce the vibration and noise at the time of operation. 
         [0009]    The present invention has been made in view of the conventional situation described above, and an object of the invention is to provide a double-headed piston type compressor capable of reliably reducing vibration and noise at the time of operation. 
       SUMMARY OF THE INVENTION 
       [0010]    A double-headed piston type compressor of the present invention comprises: a drive shaft; a housing that rotatably supports the drive shaft and has m first cylinder bores, where m is an integer satisfying m≧2, at one side of the drive shaft and m second cylinder bores facing the respective first cylinder bores at the other side of the drive shaft; m double-headed pistons that reciprocate in the respective first and second cylinder bores by rotation of the drive shaft; a first discharge chamber that is formed into an annular shape in the housing and into which refrigerant compressed in the first cylinder bores is discharged; a second discharge chamber that is formed into an annular shape in the housing and into which refrigerant compressed in the second cylinder bores is discharged; a merging portion in which the refrigerant discharged into the first discharge chamber and the refrigerant discharged into the second discharge chamber merge together, the merging portion being capable of discharging the merged refrigerant to the outside; at least one first discharge passage that provides communication between the first discharge chamber and the merging portion; and at least one second discharge passage that provides communication between the second discharge chamber and the merging portion. The first discharge chamber is divided into m first discharge sections that correspond to the respective first cylinder bores. The second discharge chamber is divided into m second discharge sections that correspond to the respective second cylinder bores. N out of the first discharge sections, where n is an arbitrary integer satisfying 1≦n&lt;m, are defined as specified first discharge sections, and n out of the second discharge sections are defined as specified second discharge sections. When viewed from an axial direction of the drive shaft, at least one of the specified first discharge sections and at least one of the specified second discharge sections are disposed at positions shifted from each other. The at least one first discharge passage is n in number and each communicates with each of the specified first discharge sections and the merging portion. The at least one second discharge passage is n in number and each communicates with each of the specified second discharge sections and the merging portion. 
         [0011]    Other aspects and advantages of the present invention will be apparent from the embodiments disclosed in the following description and the attached drawings, the illustrations exemplified in the drawings, and the concept of the invention disclosed in the entire description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a sectional view of a compressor according to Embodiment 1. 
           [0013]      FIG. 2  relates to the compressor according to Embodiment 1, showing a sectional view taken along line A-A of  FIG. 1 . 
           [0014]      FIG. 3  relates to the compressor according to Embodiment 1, showing a sectional view taken along line B-B of  FIG. 1 . 
           [0015]      FIG. 4  relates to the compressor according to Embodiment 1, showing a schematic perspective view of a first discharge chamber, a second discharge chamber, a merging portion, a first discharge passage, and a second discharge passage. 
           [0016]      FIG. 5  relates to the compressor according to Embodiment 1 and is a series of graphs showing fifth-order rotation components of discharge pulsations in the first and second discharge chamber. 
           [0017]      FIG. 6  relates to the compressor according to Embodiment 1 and is a series of graphs showing fourth-order rotation components of the discharge pulsations in the first and second discharge chambers. 
           [0018]      FIG. 7  relates to the compressor according to Embodiment 1 and is a series of graphs showing sixth-order rotation components of the discharge pulsations in the first and second discharge chambers. 
           [0019]      FIG. 8  relates to the compressor according to Embodiment 1; (A) is a graph showing a fourth-order rotation component of a discharge pulsation in the merging portion; (B) is a graph showing a fifth-order rotation component of the discharge pulsation in the merging portion; and (C) is a graph showing a sixth-order rotation component of the discharge pulsation in the merging portion. 
           [0020]      FIG. 9  relates to a compressor of a comparative example; (A) is a graph showing a fourth-order rotation component of a discharge pulsation in a merging portion; (B) is a graph showing a fifth-order rotation component of the discharge pulsation in the merging portion; and (C) is a graph showing a sixth-order rotation component of the discharge pulsation in the merging portion. 
           [0021]      FIG. 10  relates to a compressor according to Embodiment 2, showing a schematic view of a first discharge chamber, a second discharge chamber, a merging portion, a first discharge passage, and a second discharge passage. 
           [0022]      FIG. 11  relates to the compressor according to Embodiment 2; (A) is a graph showing a fourth-order rotation component of a discharge pulsation in the merging portion; (B) is a graph showing a fifth-order rotation component of the discharge pulsation in the merging portion; and (C) is a graph showing a sixth-order rotation component of the discharge pulsation in the merging portion. 
           [0023]      FIG. 12  relates to a compressor according to Embodiment 3, showing a schematic view of a first discharge chamber, a second discharge chamber, a merging portion, a first discharge passage, and a second discharge passage. 
           [0024]      FIG. 13  is shows a sectional view of a compressor according to Embodiment 4. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0025]    Hereinafter, Embodiments 1 to 4 of the present invention will be described with reference to the drawings. The compressors of Embodiments 1 to 4 are all mounted on vehicles and constitute refrigeration circuits of air-conditioning apparatus for the vehicles. 
       Embodiment 1 
       [0026]    As shown in  FIG. 1 , the compressor in Embodiment 1 comprises a housing  1 , a drive shaft  3 , a swash plate  5 , and five double-headed pistons  7 . 
         [0027]    The housing  1  has a first housing  11 , a second housing  13 , a first cylinder block  15 , a second cylinder block  17 , a first valve formation plate  19 , and a second valve formation plate  21 . In the present embodiment, the front-rear direction of the compressor is defined on the assumption that the side on which the first housing  11  is disposed is the front side of the compressor, and the side on which the second housing  13  is disposed is the rear side of the compressor. The front side of the compressor corresponds to “one side of the drive shaft” in the present invention, and the rear side of the compressor corresponds to “the other side of the drive shaft” in the present invention. 
         [0028]    The housing  1  is formed by aligning the first housing  11 , the first valve formation plate  19 , the first cylinder block  15 , the second cylinder block  17 , the second valve formation plate  21 , and the second housing  13  in this order from the front side to the rear side of the compressor and joining them all together using five through-bolts  14  shown in  FIGS. 1 to 3 . 
         [0029]    As shown in  FIG. 1 , the first housing  11  has a boss  11   a  that protrudes frontward. A shaft seal device  23  is provided in the boss  11   a . As shown in  FIGS. 1 and 2 , a first suction chamber  25  and a first discharge chamber  27  are formed in the first housing  11 . The first suction chamber  25  is disposed in a center portion of the first housing  11 . The first discharge chamber  27  is disposed at an outer circumferential side of the first suction chamber  25 , and is formed into a substantially annular shape to surround the first suction chamber  25 . Furthermore, as shown in  FIG. 1 , the first housing  11  has recesses  11   b , in which front end portions of the respective through-bolts  14  can be accommodated, and bolt holes  11   c  that communicate with the recesses  11   b.    
         [0030]    As shown in  FIGS. 1 and 3 , a second suction chamber  26  and a second discharge chamber  28  are formed in the second housing  13 . The second suction chamber  26  is disposed in a center portion of the second housing  13 . The second discharge chamber  28  is disposed at an outer circumferential side of the second suction chamber  26 , and is formed into a substantially annular shape to surround the second suction chamber  26 . Furthermore, as shown in  FIG. 1 , the second housing  13  has bolt holes  13   a . The bolt holes  13   a  are formed with threads (not illustrated) to be screwed with the through-bolts  14 . 
         [0031]    The first cylinder block  15  is disposed at the front side of the second cylinder block  17  in the compressor. As shown in  FIGS. 1 and 2 , the first cylinder block  15  has five first cylinder bores  151  to  155  that extend in an axial direction, i.e., in the direction of an axis O of the drive shaft  3 . The first cylinder bores  151  to  155  are arranged at equiangular intervals around the axis O of the drive shaft  3 . 
         [0032]    As shown in  FIG. 1 , the first cylinder block  15  has a first shaft hole  15   a  through which the drive shaft  3  is inserted. A first radial bearing  29   a  is provided in the first shaft hole  15   a . Furthermore, the first cylinder block  15  has a first retainer groove  15   b  that restricts the maximum opening degree of first suction reed valves  191   a , which will be described later, and also has bolt holes  15   c  through which the through-bolts  14  are inserted. 
         [0033]    As shown in  FIGS. 1 and 2 , the first cylinder block  15  has five first communication paths  31   a . The first communication paths  31   a  are arranged at equiangular intervals around the axis O of the drive shaft  3 . Furthermore, the first cylinder block  15  has a first connecting passage  33   a . The first communication paths  31   a  and the first connecting passage  33   a  all extend in the axial direction, and front ends thereof are opened to a front end surface of the first cylinder block  15 . In  FIG. 2 , illustration of the first valve formation plate  19  is omitted for ease of explanation. 
         [0034]    As shown in  FIG. 1 , the second cylinder block  17  is disposed at the rear side of first cylinder block  15  in the compressor. As shown in  FIGS. 1 and 3 , the second cylinder block  17  has five second cylinder bores  171  to  175  that extend in the axial direction. The first cylinder bores  171  to  175  are arranged at equiangular intervals around the axis O of the drive shaft  3 , and are respectively paired with the above described first cylinder bores  151  to  155 . Thereby, the first cylinder bore  151  faces the second cylinder bore  171  in the direction of the axis O of the drive shaft  3 . Similarly, the first cylinder bores  152  to  155  face the corresponding second cylinder bores  172  to  175  in the direction of the axis O of the drive shaft  3 . 
         [0035]    As shown in  FIG. 1 , the second cylinder block  17  has a second shaft hole  17   a  through which the drive shaft  3  is inserted. A second radial bearing  29   b  is provided in the second shaft hole  17   a . Furthermore, the second cylinder block  17  has a second retainer groove  17   b  that restricts the maximum opening degree of second suction reed valves  211   a , which will be described later, and also has bolt holes  17   c  through which the through-bolts  14  are inserted. 
         [0036]    As shown in  FIGS. 1 and 3 , the second cylinder block  17  has five second communication paths  31   b . The second communication paths  31   b  are arranged at equiangular intervals around the axis O of the drive shaft  3 . Furthermore, the second cylinder block  17  has a second connecting passage  33   b . The second communication paths  31   b  and the second connecting passage  33   b  all extend in the axial direction, and rear ends thereof are opened to a rear end surface of the second cylinder block  17 . In  FIG. 3 , illustration of the second valve formation plate  21  is omitted for ease of explanation. 
         [0037]    As shown in  FIG. 1 , by joining the first cylinder block  15  and the second cylinder block  17  with each other, a swash plate chamber  35 , an inlet port  350 , a connection passage  37 , a merging portion  39  and an outlet port  390  are formed therebetween. 
         [0038]    The swash plate chamber  35  is disposed substantially at a center of the housing  1  in the front-rear direction of the compressor. Rear ends of the first communication paths  31   a  and front ends of the second communication paths  31   b  respectively communicate with the swash plate chamber  35 . The inlet port  350  also communicates with the swash plate chamber  35 . 
         [0039]    In  FIG. 1 , the first connecting passage  33   a , the second connecting passage  33   b , the connection passage  37  and the merging portion  39  are schematically illustrated, and the actual shapes thereof are as shown in  FIG. 4 . That is, the connection passage is formed into a circular arc shape and extends in a circumferential direction of the housing  1 . One end of the connection passage  37  is connected to a rear end of the first connecting passage  33   a , and the other end of the connection passage  37  is connected to a front end of the second connecting passage  33   b . Furthermore, the merging portion  39  is connected to a center of the connection passage  37  in the circumferential direction. 
         [0040]    In this configuration, the connection passage  37  is divided into the following two portions: a first portion  37   a , which is the portion extending from the position where the first connecting passage  33   a  is connected to the position where the merging portion  39  is connected; and a second portion  37   b , which is the portion extending from the position where the second connecting passage  33   b  is connected to the position where the merging portion  39  is connected. In this compressor, the first connecting passage  33   a  and the first portion  37   a  of the connection passage  37  form a first discharge passage  41 . Similarly, the second connecting passage  33   b  and the second portion  37   b  of the connection passage  37  forma second discharge passage  43 . 
         [0041]    In the present embodiment, a length L 1 , which is the length of the first connecting passage  33   a , and a length L 2 , which is the length of the second connecting passage  33   b , are made equal. Furthermore, a length L 3 , which is the length of the first portion  37   a  of the connection passage  37 , and a length L 4 , which is the length of the second portion  37   b  of the connection passage  37 , are also made equal. Accordingly, the length of the first discharge passage  41  (L 1 +L 3 ) and the length of the second discharge passage  43  (L 2 +L 4 ) are equal. 
         [0042]    As shown in  FIG. 1 , the first valve formation plate  19  is disposed between the first housing  11  and the first cylinder block  15 . The first valve formation plate  19  has a first valve plate  190 , a first suction valve plate  191 , a first discharge valve plate  192  and a first retainer plate  193 . The first valve formation plate  19  is provided with a first discharge communication hole  190   a  and five first suction communication holes  190   b . Furthermore, the first valve formation plate  19  is also provided with a communication hole  190   c  and bolt holes  190   d . Additionally, although not illustrated, the first valve formation plate  19  is also provided with five first suction ports and five first discharge ports that respectively correspond to the first cylinder bores  151  to  155 . 
         [0043]    The first suction valve plate  191  is provided on the rear surface of the first valve plate  190 . The five first suction reed valves  191   a , which can open and close the respective first suction ports by elastic deformation, are formed on the first suction valve plate  191 . The first discharge valve plate  192  is provided on the front surface of the first valve plate  190 . Five first discharge reed valves  192   a , which can open and close the respective first discharge ports by elastic deformation, are formed on the first discharge valve plate  192 . The first retainer plate  193  is provided on the front surface of the first discharge valve plate  192 . The first retainer plate  193  restricts the maximum opening degree of the first discharge reed valves  192   a.    
         [0044]    The first cylinder bores  151  to  155  shown in  FIG. 2  communicate with the first suction chamber  25  through the respective first suction ports (not illustrated) and communicate also with the first discharge chamber  27  through the respective first discharge ports (not illustrated). As shown in  FIG. 2 , the first discharge chamber  27  of the present embodiment is divided into first to fifth front side discharge sections  271  to  275  equiangularly around the axis O of the drive shaft  3  so as to correspond to the respective first cylinder bores  151  to  155 . The first to fifth front side discharge sections  271  to  275  correspond to first discharge sections in the present invention. 
         [0045]    Specifically, the first front side discharge section  271  corresponds to the first cylinder bore  151 ; the second front side discharge section  272  corresponds to the first cylinder bore  152 ; the third front side discharge section  273  corresponds to the first cylinder bore  153 ; the fourth front side discharge section  274  corresponds to the first cylinder bore  154 ; and the fifth front side discharge section  275  corresponds to the first cylinder bore  155 . 
         [0046]    As shown in  FIG. 2 , when viewed from the direction of the axis O of the drive shaft  3 , the first connecting passage  33   a  is provided at a position overlapping with the first front side discharge section  271  of the first discharge chamber  27 . The first connecting passage  33   a  communicates with the first front side discharge section  271  through the first discharge communication hole  190   a  shown in  FIG. 1 . Thereby, as shown in  FIG. 4 , the first discharge chamber  27  communicates with the first discharge passage  41  at the first front side discharge section  271 . Among the first to fifth front side discharge sections  271  to  275 , the first front side discharge section  271  corresponds to a specified first discharge section in the present invention. 
         [0047]    As shown in  FIG. 1 , the first suction chamber  25  communicates with the respective first communication paths  31   a  through the first suction communication holes  190   b  and thus communicates with the swash plate chamber  35 . Therefore, the pressure in the swash plate chamber  35  is substantially equal to the pressure in the first suction chamber  25 . The drive shaft  3  is inserted through the insertion hole  190   c , and the bolts  14  are inserted through the bolt holes  190   d.    
         [0048]    The second valve formation plate  21  is disposed between the second housing  13  and the second cylinder block  17 . The second valve formation plate  21  has a second valve plate  210 , a second suction valve plate  211 , a second discharge valve plate  212  and a second retainer plate  213 . The second valve formation plate  21  is provided with a second discharge communication hole  210   a  and five second suction communication holes  210   b . Furthermore, the second valve formation plate  21  is also provided with bolt holes  210   c . Additionally, although not illustrated, the second valve formation plate  21  is also provided with five second suction ports and five second discharge ports that respectively correspond to the second cylinder bores  171  to  175 . 
         [0049]    The second suction valve plate  211  is provided on the front surface of the second valve plate  210 . The five second suction reed valves  211   a , which can open and close the respective second suction ports by elastic deformation, are formed on the second suction valve plate  211 . The second discharge valve plate  212  is provided on the rear surface of the second valve plate  210 . Five second discharge reed valves  212   a , which can open and close the respective second discharge ports by elastic deformation, are formed on the second discharge valve plate  212 . The second retainer plate  213  is provided on the rear surface of the second discharge valve plate  212 . The second retainer plate  213  restricts the maximum opening degree of the second discharge reed valves  212   a.    
         [0050]    The respective second cylinder bores  171  to  175  shown in  FIG. 3  communicate with the second suction chamber  26  through the respective second suction ports (not illustrated) and communicate with the second discharge chamber  28  through the respective second discharge ports (not illustrated). As shown in  FIG. 3 , the second discharge chamber  28  of the present embodiment is divided into a first to fifth rear side discharge sections  281  to  185  equiangularly around the axis O of the drive shaft  3  so as to correspond to the respective second cylinder bores  171  to  175 . The first to fifth rear side discharge sections  281  to  285  correspond to second discharge sections in the present invention. 
         [0051]    Specifically, the second rear side discharge section  281  corresponds to the second cylinder bore  171 ; the second rear side discharge section  282  corresponds to the second cylinder bore  172 ; the third rear side discharge section  283  corresponds to the second cylinder bore  173 ; the fourth rear side discharge section  284  corresponds to the second cylinder bore  174 ; and the fifth rear side discharge section  285  corresponds to the second cylinder bore  175 . 
         [0052]    As shown in  FIG. 3 , when viewed from the direction of the axis O of the drive shaft  3 , the second connecting passage  33   b  is provided at a position overlapping with the third rear side discharge section  283  of the second discharge chamber  28 . The second connecting passage  33   b  communicates with the third rear side discharge section  283  through the second discharge communication hole  210   a  shown in  FIG. 1 . Thereby, as shown in  FIG. 4 , the second discharge chamber  28  communicates with the second discharge passage  43  at the third rear side discharge section  283 . Among the first to fifth rear side discharge sections  281  to  285 , the third rear side discharge section  283  corresponds to a specified second discharge section in the present invention. 
         [0053]    As shown in  FIG. 4 , when the first discharge chamber  27  and the second discharge chamber  28  are viewed from the direction of the axis O of the drive shaft  3 , the first front side discharge section  271  is located at a position facing the first rear side discharge section  281 . Similarly, the second front side discharge section  272 , the third front side discharge section  273 , the fourth front side discharge section  274 , and the fifth front side discharge section  275  are located at positions facing the second rear side discharge section  282 , the third rear side discharge section  283 , the fourth rear side discharge section  284 , and the fifth rear side discharge section  285 , respectively. 
         [0054]    The first front side discharge section  271  is located apart from the third rear side discharge section  283  by 144°, which is twice as large as 360°/5, in the direction of the dashed arrow R 1  in  FIG. 4  around the axis O of the drive shaft  3 . That is, the first front side discharge section  271  is most apart from the third rear side discharge section  283  across the axis O of the drive shaft  3  in the direction of the dashed arrow R 1 . In other words, when the first discharge chamber  27  and the second discharge chamber  28  are viewed from the direction of the axis O of the drive shaft  3 , the first front side discharge section  271  and the third rear side discharge section  283  are disposed at positions shifted from each other. Consequently, in this compressor, when viewed from the direction of the axis O, the position where the first connecting passage  33   a  of the first discharge passage  41  communicates with the first front side discharge section  271  of the first discharge chamber  27  is shifted from the position where the second connecting passage  33   b  of the second discharge passage  43  communicates with the third rear side discharge section  283  of the second discharge chamber  28 . 
         [0055]    As shown in  FIG. 1 , the second suction chamber  26  communicates with the respective second communication paths  31   b  through the second suction communication holes  210   b  and thus communicates with the swash plate chamber  35 . Therefore, the pressure in the swash plate chamber  35  is also substantially equal to the pressure in the second suction chamber  26 . The bolts  14  are inserted through the bolt holes  210   c.    
         [0056]    The drive shaft  3  is inserted into the housing  1  so as to extend in the direction of the axis O. A front side of the drive shaft  3  is inserted through the shaft seal device  23  in the boss  11   a  and supported by the first radial bearing  29   a  in the first shaft hole  15   a  of the first cylinder block  15 . A rear side of the drive shaft  3  is supported by the second radial bearing  29   b  in the second shaft hole  17   a  of the second cylinder block  17 . The housing  1  supports the drive shaft  3  so as to be rotatable around the axis O of the drive shaft  3 . 
         [0057]    A threaded portion  3   a  is formed at a front end of the drive shaft  3 . The drive shaft  3  is connected to a pulley or an electromagnetic clutch (not illustrated) via the threaded portion  3   a.    
         [0058]    The swash plate  5  includes a cylindrical portion  5   a  and a swash plate main body  5   b . An insertion hole  5   c  is formed through the cylindrical portion  5   a . The swash plate main body  5   b  is formed into a plate shape and has a front surface  501  and a rear surface  502 . The swash plate main body  5   b  is inclined at a predetermined angle with respect to the axis O of the drive shaft  3  and formed integrally with the cylindrical portion  5   a . By press-fitting the drive shaft  3  to the insertion hole  5   c , the swash plate  5  is integrated with the drive shaft  3  and rotatable in the swash plate chamber  35  along with the rotation of the drive shaft  3 . 
         [0059]    In the swash plate chamber  35 , a first thrust bearing  45   a  is provided between the swash plate  5  and the first cylinder block  15 . Furthermore, in the swash plate chamber  35 , a second thrust bearing  45   b  is provided between the swash plate  5  and the second cylinder block  17 . The first thrust bearing  45   a  receives a frontward thrust force acting on the drive shaft  3  at the time of operation of the compressor, and the second thrust bearing  45   b  receives a rearward thrust force acting on the drive shaft  3  at the time of operation of the compressor. 
         [0060]    The double-headed pistons  7  each has a first head portion  7   a  at a front end thereof a second head portion  7   b  at a rear end thereof. The first head portions  7   a  are reciprocally accommodated in the respective first cylinder bores  151  to  155 . First compression chambers  47   a  are defined by the respective first head portions  7   a  and the first valve formation plate  19  within the first cylinder bores  151  to  155 . The second head portions  7   b  are reciprocally accommodated in the respective second cylinder bores  171  to  175 . Second compression chambers  47   b  are defined by the respective second head portions  7   b  and the second valve formation plate  21  within the second cylinder bores  171  to  175 . 
         [0061]    The double-headed pistons  7  each has an engaging portion  7   c  at a center thereof. Semispherical shoes  49   a  and  49   b  are provided in the respective engaging portions  7   c . The shoes  49   a  slide on the front surface  501  of the swash plate main body  5   b . The shoes  49   b  slide on the rear surface  502  of the swash plate main body  5   b . In this way, the shoes  49   a  and  49   b  convert rotation of the swash plate  5  into reciprocation of the double-headed pistons  7 . Therefore, when the drive shaft  3  rotates, the first head portions  7   a  of the respective double-headed pistons  7  reciprocate in the respective first cylinder bores  151  to  155 , and the second head portions  7   b  reciprocate in the respective second cylinder bores  171  to  175 . 
         [0062]    In this compressor, a pipe  201 , which is connected to a condenser  101 , is connected to the outlet port  390 . The condenser  101  is connected to an evaporator  102  via a pipe  202 . Furthermore, an expansion valve  103  is provided on the pipe  202 . The evaporator  102  and the inlet port  350  are connected via a pipe  203 . In this manner, the refrigeration circuit of vehicle air-conditioning apparatus is configured. Detailed explanation on configurations of the condenser  101 , the evaporator  102 , the expansion valve  103 , and the pipes  201  to  203  are omitted. 
         [0063]    In the compressor configured as above, by rotation of the drive shaft  3 , the swash plate  5  rotates and the double-headed pistons  7  reciprocate in the first cylinder bores  151  to  155  and the second cylinder bores  171  to  175 . At this time, a suction phase for sucking refrigerant gas that has passed through the evaporator  102  into the compression chambers  47   a  and  47   b  of the first cylinder bores  151  to  155  and the second cylinder bores  171  to  175  respectively, a compression phase for compressing the refrigerant gas in the first and second compression chambers  47   a  and  47   b , and a discharge phase for discharging the compressed high-pressure refrigerant gas into the first and second discharge chambers  27  and  28  take place repeatedly. The high-pressure refrigerant gas discharged into the first and second discharge chambers  27  and  28  reaches the merging portion  39  through the first and second discharge passages  41  and  43  and is then discharged to the condenser  101  through the outlet port  390 . 
         [0064]    More specifically, in this compressor, by rotation of the drive shaft  3 , the high-pressure refrigerant gas compressed in the compression chamber  47   a  of the first cylinder bore  151  is discharged into the first front side discharge section  271  of the first discharge chamber  27 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   a  of the first cylinder bore  152  is discharged into the second front side discharge section  272 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   a  of the first cylinder bore  153  is discharged into the third front side discharge section  273 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   a  of the first cylinder bore  154  is discharged into the fourth front side discharge section  274 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   a  of the first cylinder bore  155  is discharged to the fifth front side discharge section  275 . Discharging operation is repeated in this order. 
         [0065]    Similarly, by rotation of the drive shaft  3 , the high-pressure refrigerant gas compressed in the compression chamber  47   b  of the second cylinder bore  171  is discharged into the first rear side discharge section  281 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   b  of the second cylinder bore  172  is discharged into the second rear side discharge section  282 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   b  of the second cylinder bore  173  is discharged into the third rear side discharge section  283 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   b  of the second cylinder bore  174  is discharged into the fourth rear side discharge section  284 . Subsequently, the high-pressure refrigerant gas compressed in the compression chamber  47   b  of the second cylinder bore  175  is discharged to the fifth rear side discharge section  285 . Discharging operation is repeated in this sequence. 
         [0066]    During the discharging operation, the pressures in the first and second discharge chambers  27  and  28  momentarily increase every time the high-pressure refrigerant gas is discharged, and this causes discharge pulsation. In this compressor, since the number of the double-headed pistons  7  is five, a fifth-order rotation component is the main component among various frequency components of the discharge pulsation. As shown in  FIG. 5 , the fifth-order rotation component on the side of the first discharge chamber  27  differs in phase by 180° from the fifth-order rotation component on the side of the second discharge chamber  28 . Accordingly, when, for example, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point A 1  in  FIG. 5  at a certain point in time, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the third rear side discharge section  283  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point A 2  in  FIG. 5 . Therefore, in this compressor, the high-pressure refrigerant gas from the first discharge passage  41  merges with the high-pressure refrigerant gas from the second discharge passage  43  in the merging portion  39  in a state where the phases of their fifth-order rotation components differ from each other by 180°, and this reduces the amplitude of the fifth-order rotation component of the discharge pulsation in the merging portion  39  as shown in  FIG. 8(B) . As compared with the fifth-order rotation components in the first and second discharge chambers  27  and  28  shown in  FIG. 5 , the amplitude of the fifth-order rotation component in the merging portion  39  is surely reduced to almost zero. 
         [0067]    In this compressor, since the number of the double-headed pistons  7  is an odd number, the timing of discharging the high-pressure refrigerant gas from any one of the compression chambers  47   a  of the first cylinder bores  151  to  155  differs from any of the timing of discharging the high-pressure refrigerant gas from the respective discharge chambers  47   b  of the second cylinder bores  171  to  175 . Furthermore, in this compressor, as shown in  FIG. 4 , the length of the first discharge passage  41  (L 1 +L 3 ) is equal to the length of the second discharge passage  43  (L 2 +L 4 ). Accordingly, the reduction rate of the discharge pulsations of the high-pressure refrigerant gas is substantially equal between the first discharge passage  41  and the second discharge passage  43 . Therefore, even if there are other factors which may increase the fifth-order rotation component as described in Japanese Patent Laid-Open No. 10-103228, the compressor of the present embodiment is capable of reliably reduce the fifth-order rotation component of the discharge pulsation. 
         [0068]    Furthermore, in this compressor, the first and second discharge chambers  27  and  28  are formed into the substantially annular shapes. The high-pressure refrigerant gas compressed in the compression chambers  47   a  of the first cylinder bores  151  to  155  is discharged into the first discharge chamber  27 . The high-pressure refrigerant gas compressed in the compression chambers  47   b  of the second cylinder bores  171  to  175  is discharged into the second discharge chamber  28 . In such a compressor, depending on the conditions of operation, fourth-order rotation components of the discharge pulsations in the first and second discharge chambers  27  and  28  also increases to a high level as shown in  FIG. 6 . Similarly, depending on the conditions of operation, sixth-order rotation components of the discharge pulsations in the first and second discharge chambers  27  and  28  also increases to a high level as shown in  FIG. 7 . 
         [0069]    In this regard, as shown in  FIG. 4 , when the compressor is viewed from the direction of the axis O of the drive shaft  3 , the position of the first front side discharge section  271  where the first discharge passage  41  communicates with the first discharge chamber  27  is shifted from the position of the third rear side discharge section  283  where the second discharge passage  43  communicates with the second discharge chamber  28 . 
         [0070]    Accordingly, when, for example, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point B 1  in  FIG. 6  at a certain point in time, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the third rear side discharge section  283  of the second discharge chamber  28  and flowing into the merging point  39  through the second discharge passage  43  corresponds to the point B 2  in  FIG. 6 . Therefore, in the merging portion  39 , the high-pressure refrigerant gas which has flowed through the first discharge passage  41  from the first front side discharge section  271  merges with the high-pressure refrigerant gas which has flowed through the second discharge passage  43   d  from the third rear side discharge section  283  in a state where the phases of their fourth-order rotation components are shifted from each other, and this reduces the amplitude of the fourth-order rotation component of the discharge pulsation in the merging portion  39  as shown in  FIG. 8(A) . As compared with the fourth-order rotation components in the first and second discharge chambers  27  and  28  shown in  FIG. 6 , the amplitude of the fourth-order rotation component in the merging portion  39  is surely reduced. 
         [0071]    Furthermore, when, for example, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point C 1  in  FIG. 7  at a certain point in time, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the third rear side discharge section  283  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point C 2  in  FIG. 7 . Therefore, in the merging portion  39 , the high-pressure refrigerant gas which has flowed through the first discharge passage  41  from the first front side discharge section  271  merges with the high-pressure refrigerant gas which has flowed through the second discharge passage  43  from the third rear side discharge section  283  in a state where the phases of their sixth-order rotation components are shifted from each other, and this reduces the amplitude of the sixth-order rotation component of the discharge pulsation in the merging portion  39  as shown in  FIG. 8(C) . As compared with the sixth-order rotation components in the first and second discharge chambers  27  and  28  shown in  FIG. 7 , the amplitude of the sixth-order rotation component in the merging portion  39  is surely reduced. 
         [0072]    A comparative example is shown in  FIG. 9 . In a compressor of the comparative example, although not illustrated, the first connecting passage  33   a  is connected to the first discharge chamber  27  at the first front side discharge section  271 , and the second connecting passage  33   b  is connected to the second discharge chamber  28  at the first rear side discharge section  281 . That is, in the compressor of the comparative example, the first front side discharge section  271  is the first specified discharge section, and the first rear side discharge section  281  is the second specified discharge section. Therefore, when the compressor of the comparative example is viewed from the direction of the axis O of the drive shaft  3 , the first front side discharge section  271  where the first discharge passage  41  communicates with the first discharge chamber  27  faces the first rear side discharge section  281  where the second discharge passage  43  communicates with the second discharge chamber  28 . The other configurations in the compressor of the comparative example are the same as those of the compressor in Embodiment 1. 
         [0073]    Also In the compressor of the comparative example, the fifth-order rotation component on the side of the first discharge chamber  27  differs in phase by 180° from the fifth-order rotation component on the side of the second discharge chamber  28 . Accordingly, when, for example, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point A 1  in  FIG. 5  at a certain point in time, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first rear side discharge section  281  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point A 3  in  FIG. 5 . Therefore, the amplitude of the fifth-order rotation component in the compressor of the comparative example is also surely reduced to almost zero as shown in  FIG. 9(B) . 
         [0074]    However, in the compressor of the comparative example, when, for example, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point B 1  in  FIG. 6  at a certain point in time, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first rear side discharge section  281  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point B 3  in  FIG. 6 . Therefore, in the merging portion  39 , the refrigerant gas which has flowed through the first discharge passage  41  from the first front side discharge section  271  merges with the high-pressure refrigerant gas which has flowed through the second discharge passage  43  from the first rear side discharge section  281  in a state where the phases of their fourth-order rotation components overlap each other, and this increases the amplitude of the fourth-order rotation component of the discharge pulsation in the merging portion  39  as shown in  FIG. 9(A) . As compared with the fourth-order rotation components in the first and second discharge chambers  27  and  28  shown in  FIG. 6 , the amplitude of the fourth-order rotation component in the merging portion  39  is significantly increased. 
         [0075]    Furthermore, when, for example, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point C 1  in  FIG. 7  at a certain point in time, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first rear side discharge section  281  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point C 3  in  FIG. 7 . Therefore, in the merging portion  39 , the high-pressure refrigerant gas which has flowed through the first discharge passage  41  from the first front side discharge section  271  merges with the high-pressure refrigerant gas which has flowed through the second discharge passage  43  from the first rear side discharge section  281  in a state where the phases of their sixth-order rotation components overlap each other, and this increases the amplitude of the sixth-order rotation component of the discharge pulsation in the merging portion  39  as shown in  FIG. 9(C) . As compared with the sixth-order rotation components in the first and second discharge chambers  27  and  28  shown in  FIG. 7 , the amplitude of the sixth-order rotation component in the merging portion  39  is significantly increased. 
         [0076]    Since the compressor of Embodiment 1 is capable of reducing the amplitudes of the fourth, fifth and sixth-order rotation components in this way, it is possible to reduce the discharge pulsation of the high-pressure refrigerant gas flowing into the pipe  201  through the merging portion  39  and the outlet port  390 . 
         [0077]    Therefore, the compressor of Embodiment 1 is capable of reliably reducing vibration and noise at the time of operation. 
         [0078]    Furthermore, in this compressor, since the first discharge passage  41 , the second discharge passage  43 , and the merging portion  39  are formed in the housing  1 , it is possible to simplify the outer shape of the compressor as well as the assembly process thereof. 
       Embodiment 2 
       [0079]    In the compressor of Embodiment 2, as shown in  FIG. 10 , the second discharge chamber  28  communicates with the second connecting passage  33   b  and thus the second discharge passage  43  at the fifth rear side discharge section  285 . That is, in this compressor, the fifth rear side discharge section  285  corresponds to the specified second discharge section of the present invention. 
         [0080]    In this compressor, the first front side discharge section  271  is located apart from the fifth rear side discharge section  285  by 72°, which is 360°/5, in the opposite direction of the dashed arrow R 1  in  FIG. 4  around the axis O of the drive shaft  3 . The other configurations in this compressor are the same as those of the compressor of Embodiment 1. Where the components are the same as Embodiment 1, same reference numerals are used and detailed explanation thereof is omitted. 
         [0081]    Also in this compressor, the fifth-order rotation component of the discharge pulsation on the side of the first discharge chamber  27  differs in phase by 180° from the fifth-order rotation component on the side of the second discharge chamber  28 . Accordingly, when, for example, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point A 1  in  FIG. 5  at a certain point in time, the phase of the fifth-order rotation component of the high-pressure refrigerant gas discharged from the fifth rear side discharge section  285  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point A 4  in  FIG. 5 . Therefore, the amplitude of the fifth-order rotation component in this compressor is surely reduced to almost zero as shown in  FIG. 11(B) . 
         [0082]    Furthermore, in this compressor, when, for example, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point B 1  in  FIG. 6  at a certain point in time, the phase of the fourth-order rotation component of the high-pressure refrigerant gas discharged from the fifth rear side discharge section  285  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point B 4  in  FIG. 6 . Therefore, in the merging portion  39 , the high-pressure refrigerant gas which has flowed through the first discharge passage  41  from the first front side discharge section  271  merges with the high-pressure refrigerant gas which has flowed through the second discharge passage  43  from the fifth rear side discharge section  285  in a state where the phases of their fourth-order rotation components are shifted from each other, and thereby, as shown in  FIG. 11(A) , the degree of increase of the amplitude of the fourth-order rotation component in the merging portion  39  can be made smaller than that of the comparative example shown in  FIG. 9(A) . 
         [0083]    Furthermore, when, for example, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the first front side discharge section  271  of the first discharge chamber  27  and flowing into the merging portion  39  through the first discharge passage  41  corresponds to the point C 1  in  FIG. 7  at a certain point in time, the phase of the sixth-order rotation component of the high-pressure refrigerant gas discharged from the fifth rear side discharge section  285  of the second discharge chamber  28  and flowing into the merging portion  39  through the second discharge passage  43  corresponds to the point C 4  in  FIG. 7 . Therefore, in the merging portion  39 , the high-pressure refrigerant gas which has flowed through the first discharge passage  41  from the first front side discharge section  271  merges with the high-pressure refrigerant gas which has flowed through the second discharge passage  43  from the fifth rear side discharge section  285  in a state where the phases of their sixth-order rotation components are shifted from each other, and thereby, as shown in  FIG. 11(C) , the degree of increase of the amplitude of the sixth-order rotation component in the merging portion  39  can be made smaller than that of the comparative example shown in  FIG. 9(C) . 
         [0084]    Therefore, the compressor of Embodiment 2 is also capable of reliably reducing vibration and noise at the time of operation. 
       Embodiment 3 
       [0085]    Unlike the compressor of Embodiment 1, the compressor of Embodiment 3 is provided with two first discharge passages  51   a  and  51   b  and two second discharge passages  53   a  and  53   b  as shown in  FIG. 12 . 
         [0086]    The first discharge passage  51   a  communicates with the first front side discharge section  271  in the first discharge chamber  27  and the merging portion  39 . The first discharge passage  51   b  communicates with the third front side discharge section  273  in the first discharge chamber  27  and the merging portion  39 . 
         [0087]    The second discharge passage  53   a  communicates with the second rear side discharge section  282  in the second discharge chamber  28  and the merging portion  39 . The second discharge passage  53   b  communicates with the fourth rear side discharge section  284  in the second discharge chamber  28  and the merging portion  39 . 
         [0088]    The first front side discharge section  271  and the third front side discharge section  273  correspond to the first specified discharge section in the present invention. The second rear side discharge section  282  and the fourth rear side discharge section  284  correspond to the second specified discharge section in the present invention. 
         [0089]    When viewed from the direction of the axis O of the drive shaft  3 , the first front side discharge section  271  and the third front side discharge section  273 , i.e., the first specified discharge section, and the second rear side discharge section  282  and the fourth rear side discharge section  284 , i.e., the second specified discharge section, are disposed at positions shifted from each other. The other configurations of this compressor are the same as those of the compressor in Embodiment 1. 
         [0090]    With the compressor of Embodiment 3 configured as above, similarly to the compressors of Embodiments 1 and 2, it is possible to reliably reduce vibration and noise at the time of operation. 
       Embodiment 4 
       [0091]    As shown in  FIG. 13 , the compressor of Embodiment 4 employs a first discharge passage  55  and a second discharge passage  57  instead of the first discharge passage  41  and the second discharge passage  43  in the compressor of Embodiment 1. In the present embodiment, the first discharge passage  55 , the second discharge passage  57 , and the merging portion  39  are disposed outside of the housing  1 . Furthermore, the first and second valve formation plates  19  and  21  in this embodiment do not have the first and second discharge communication paths  190   a  and  210   a  provided in Embodiment 1. 
         [0092]    The first discharge passage  55  communicates with the first discharge chamber  27  at a front end  55   a  thereof and communicates with the merging portion  39  at a rear end  55   b  thereof. Furthermore, the second discharge passage  57  communicates with the merging portion  39  a front end  57   a  thereof and communicates with the second discharge chamber  28  a rear end  57   b  thereof. The front end  55   a  of the first discharge passage  55  is connected to the first discharge chamber  27  from outside of the first housing  11  at a position where the first front side discharge section  271  is located. Similarly, the rear end  57   b  of the second discharge passage  57  is connected to the second discharge chamber  28  from outside of the second housing  13  at a position where the third rear side discharge section  283  is located. The other configurations of this compressor are the same as those of the compressor in Embodiment 1. 
         [0093]    Similarly to the compressors of Embodiments 1 and 2, the compressor of Embodiment 4 is also capable of reliably reducing vibration and noise at the time of operation. Furthermore, in this compressor, since the first discharge passage  55 , the second discharge passage  57 , and the merging portion  39  do not need to be formed in the first and second cylinder blocks  15  and  17 , configurations of the first and second cylinder blocks  15  and  17  can be simplified. 
         [0094]    Although the present invention has been described in line with the embodiments above, it is needless to say that the invention is not limited to the above-described embodiments, but may be appropriately modified in application without departing from the gist of the invention. 
         [0095]    For example, selection of the specified first discharge section and the specified second discharge section is not limited to those in Embodiments 1 to 4. The compressor of Embodiment 1 may be configured such that the second discharge chamber  28  communicates with the second discharge passage  43  at the fourth rear side discharge section  284 . In this case, the first front side discharge section  271  is located apart from the fourth rear side discharge section  284  by 144° in the opposite direction of the dashed arrow R 1  in  FIG. 4  around the axis O of the drive shaft  3 . Therefore, it is possible to exhibit the same effect as the compressor of Embodiment 1. 
         [0096]    Furthermore, although m=5 and n=1 in Embodiments 1, 2 and 4 and m=5 and n=2 in Embodiment 3, the present invention is not limited to these configurations. In the present invention, the numbers m and n may be freely selected as long as the compressor is operable. For example, when m=5 and n=4, the compressor may be configured such that, when viewed from the axial direction of the drive shaft, one of the four specified first discharge sections and one of the four specified second discharge sections are disposed at positions shifted from each other, and the other three of the four specified first discharge sections and the other three of the four specified second discharge sections are disposed at positions facing each other. 
         [0097]    Furthermore, although the discharge capacity of the compressors in Embodiments 1 to 4 is fixed at a constant value by fixing the inclination angle of the swash plate main body  5   b  at a predetermined value with respect to the axis O of the drive shaft  3 , the swash plate  5  may be configured such that its inclination angle with respect to the axis O of the drive shaft  3  is changeable by pressure in the swash plate chamber  35  and an exclusive actuator.