Abstract:
A refrigeration suction mechanism used in a piston type compressor. The compressor comprises a rotary shaft, a plurality of pistons, a compression chamber and a rotary valve. The pistons are arranged in a circumference of the rotary shaft to reciprocate in conjunction with a rotating motion of the rotary shaft through a cam member. An end surface of one of said pistons reciprocates in the compression chamber. The rotary valve includes an introducing passage which allows refrigerant to flow into the compression mechanism through an end opened on an outer surface of the rotary valve. The refrigeration suction mechanism comprises a suction passage and a reactive force transmitting mechanism. The suction passage communicates with the cylinder bore and intermittently communicates with the end of the introducing passage in conjunction with a rotating motion of the rotary valve. The reactive force transmitting mechanism transmits a reactive force applied on one of the pistons that is in a discharging stroke so as to press the rotary valve against a mouth of the suction passage which communicates with a cylinder bore that contains the piston in the discharging stroke.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a refrigeration suction mechanism for a piston type compressor. The refrigeration suction mechanism according to the present invention comprises a rotary valve which has a refrigerant introducing passage communicating with a passage extending through a rotary shaft to introduce refrigerant into a compression chamber within a cylinder bore.  
           [0002]    A piston type compressor has a plurality of pistons each disposed in a cylinder bore in the circumference of a rotary shaft, so as to convert a rotation of the rotary shaft into reciprocating linear motion of the pistons through a cam.  
           [0003]    Piston type compressors disclosed in Japanese Laid-Open Patent Publication 5-113174 and Japanese Laid-Open Patent Publication 7-63165 comprise a rotary valve for introducing refrigerant into the cylinder bores. A variable discharge swash plate type compressor disclosed in Japanese Laid-Open Patent Publication 5-113174 comprises a rotary valve which is separately formed from and connected to a rotary shaft. The rotary valve is rotatably contained in a valve chamber so as to allow rotational motion of the rotary shaft.  
           [0004]    Japanese Laid-Open Patent Publication 7-63165 discloses a swash plate type compressor using double-headed pistons. The compressor has a suction passage radially extending in a journal portion of a rotary shaft and communicating with a refrigerant passage extending through the rotary shaft. The suction passage communicates with a suction port of one of cylinders that is in suction stroke as the suction passage rotates. In other words, the rotary shaft acts as a rotary valve. The suction port disclosed in the above publications is selectively opened by the rotary valve to introduce refrigerant into the cylinder bore. This improves volume efficiency compared to the compressor with a suction port selectively opened by a suction valve that can be distorted.  
           [0005]    However in any of the compressors disclosed in the above publications, refrigerant contained in a cylinder bore which is in suction stroke is inclined to leak from the suction passage along the outer surface of the rotary valve. More specifically, while the compressor disclosed in Japanese Laid-Open Patent Publication 5-113174 preferred to have a least possible gap between the inner surface of the valve chamber and the outer surface of the rotary valve in order to minimize refrigerant leakage, manufacture of such is very difficult. The compressor disclosed in Japanese Laid-Open Patent Publication 7-63165 has a similar problem with respect to a gap between the through hole provided in a cylinder block and the outer surface of the rotary valve. Such leakage of the refrigerant lowered the volume efficiency of the compressor.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to improve volume efficiency in a piston type compressor using a rotary valve.  
           [0007]    In order to achieve the above objectives, the present invention provides a refrigeration suction mechanism used in a piston type compressor, wherein a cam member mounted on a rotary shaft for the integral rotation with the rotary shaft converts a rotation of the rotary shaft to a linear reciprocating movement of pistons in cylinder bores arranged around the rotary shaft, wherein a compression chamber is defined in each of the cylinder bores by the associated piston, and wherein refrigerant is introduced to, compressed in and discharged from the compression chamber when the piston is in a suction stroke, a compressing stroke and a discharge stroke respectively, said compressor having a refrigerant passage for allowing the refrigerant to flow toward the compression chamber, said mechanism comprising:  
           [0008]    a rotary valve integrally formed with the rotary shaft, said rotary valve including an introducing passage that is in communication with the refrigerant passage;  
           [0009]    a suction passage having a first end and a second end , said first end being connected to each cylinder bore, and said second end being selectively connected to and disconnected from the introducing passage in accordance with the rotation of the rotary valve;  
           [0010]    a means for transmitting a reaction force acting on the piston to the rotary valve, wherein said reaction force is generated in the compression chamber when the piston is in the discharge stroke, whereby the rotary valve is urged against the second end of the suction passage connected to the cylinder bore.  
           [0011]    Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    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:  
         [0013]    [0013]FIG. 1 is a cross sectional side view showing a compressor according to the first embodiment of the present invention.  
         [0014]    [0014]FIG. 2A is a cross sectional view taken along a line  2 A- 2 A in FIG. 1.  
         [0015]    [0015]FIG. 2B is an enlarged cross sectional side view of a part of a refrigerant passage shown in FIG. 2A.  
         [0016]    [0016]FIG. 3A is a cross sectional view taken along a line  3 A- 3 Ain FIG. 1.  
         [0017]    [0017]FIG. 3B is an enlarged cross sectional view of a part of a refrigerant passage shown in FIG. 3A.  
         [0018]    [0018]FIG. 4 is an enlarged cross sectional view showing a front end portion of the rotary shaft.  
         [0019]    [0019]FIG. 5 is an enlarged cross sectional view showing a rear end portion of the rotary shaft.  
         [0020]    [0020]FIG. 6A is a cross sectional side view showing a compressor according to a second embodiment of the present invention.  
         [0021]    [0021]FIG. 6B is an enlarged cross sectional side view showing a rotary valve partially taken from FIG. 6B.  
         [0022]    [0022]FIG. 7 is a cross sectional view taken along a line  7 - 7  in FIG. 6A.  
         [0023]    [0023]FIG. 8 shows a cross sectional view taken along a line  8 - 8 in FIG. 6A.  
         [0024]    [0024]FIG. 9 is a cross sectional side view showing a compressor according to the third embodiment of the present invention.  
         [0025]    [0025]FIG. 10 is a cross sectional view taken along a line  10 - 10  in FIG. 9.  
         [0026]    [0026]FIG. 11 is a cross sectional view taken along a line  11 - 11  in FIG. 9.  
         [0027]    [0027]FIG. 12A is a cross sectional view showing a double-headed piston according to another embodiment.  
         [0028]    [0028]FIG. 12B is a cross sectional view showing a single-headed piston according to another embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    A first embodiment of the invention is described by referring to FIGS. 1 through 5. The first embodiment relates to a fixed-discharge compressor comprising a double headed piston.  
         [0030]    As shown in FIG. 1, a front housing  13  and a rear housing  14  are respectively connected to cylinder blocks  11  and  12 , which are connected to each other. A discharge chamber  131  is defined within a front housing  13 . A discharge chamber  141  and a suction chamber  142  are defined in a rear housing  14 .  
         [0031]    In the front portion of the compressor, a valve plate  15 , a valve forming plate  16  and a retainer forming plate  17  are interposed between the cylinder block  11  and the front housing  13 . A valve plate  18 , a valve forming plate  19  and a retainer forming plate  20  are interposed between the cylinder block  12  and the rear housing  14 . Discharge ports  151  and  181  are respectively formed in the valve plates  15  and  18 . Discharge valves  161  and  191  are respectively formed in the valve forming plates  16  and  19 . The discharge valve  161  selectively opens the discharge port  151 . A retainer  171  regulates an opening size of the discharge valve  161 . Likewise, in the rear portion of the compressor, a valve plate assembly having a discharge port  181  and a discharge valve  191  is disposed between the cylinder block  12  and a rear housing  14 . The discharge valve  191  selectively opens the discharge port  181 . A retainer  201  regulates an opening size of the discharge valve  191 .  
         [0032]    A rotary shaft  21  is rotatably supported in cylinder blocks  11  and  12 . The rotary shaft  21  is passed through holes  112  and  122  that are formed through cylinder blocks  11  and  12 . The rotary shaft  21  is directly supported by the cylinder blocks  11  and  12  at the positions of the through holes  112  and  122 .  
         [0033]    A shaft seal  22  is interposed between front housing  13  and rotary shaft  21 . A swash plate  23 , which acts as a cam member comprising aluminum (including aluminum alloy), is mounted on the rotary shaft  21  in a swash plate chamber  24  that is defined between the cylinder blocks  11  and  12 . The swash plate  23  has a plate-shaped portion  235  for slidably contacting shoes  301  and  302 . An angle (swash plate tilt angle) between the plate-shaped portion  235  and a plane orthogonal to an axle  211  of the rotary shaft is fixed. A pair of thrust bearings  25 ,  26  are respectively interposed between edges of the cylinder blocks  11 ,  12  and both sides of a circular base portion  231  of the swash plate  23 . The swash plate  23  is interposed between a pair of the thrust bearings  25  and  26  so that the swash plate  23  and the rotary shaft  21  which is fixed to the swash plate  23  are adjusted with respect to a relative movement in the direction of the axis  211  of the rotary shaft  21 .  
         [0034]    As shown in FIG. 4, the thrust bearing  25  includes a pair of races  251  and  252  and a plurality of rollers  253  disposed therebetween. A projection  111  is formed in an edge surface of the cylinder block  11 . The race  251  abuts the projection  111 . The race  252  of the thrust bearing  25  contacts an end surface  232  of a base portion  231  of the swash plate  23 . When a thrust bearing  25  is observed from one end to the other end with respect to the rotary shaft  21 , an area in which the projection  111  and the race  251  contact and an area in which the end surface  232  and the race  252  contact substantially overlap. Accordingly, the races  251  and  252  are not distorted by a thrust loading. Therefore, the thrust bearing  25  is not provided with a function to absorb the thrust loading.  
         [0035]    A thrust bearing  26  includes a pair of races  261  and  262  and a plurality of rollers  263  disposed therebetween as shown in FIG. 5. A projection  121  is formed on an end surface of cylinder block  12 . The race  261  abuts the projection  121 . A projection  234  is formed in an edge surface  233  of the base portion  231  of a swash plate  23 . The race  262  abuts the projection  234 . The distance between the rotary shaft  21  and a point at which the projection  234  and the race  262  abuts is longer than the distance between the rotary shaft  21  and the point at which the projection  121  and the race  261  abuts. When the thrust bearing  26  is observed from one end to the other end with respect to the rotary shaft  21 , an area in which the projection  121  and the race  261  contacts and an area at which the projection  234  and the race  262  contacts do not overlap. Accordingly, the races  261  and  262  are distorted by a thrust loading. Therefore, thrust bearing  26  is provided with a function to absorb thrust loading.  
         [0036]    A plurality of cylinder bores  27  and  27 A are formed in cylinder block  11  to be angularly spaced from one another in a circumference of the rotary shaft  21  as shown in FIG. 2A. Likewise, a plurality of cylinder bore  28 ,  28 A and  28 B are formed in cylinder block  12  to be angularly spaced from one another in a circumference of the rotary shaft  21  as shown in FIG. 3A. The cylinder bores  27  and  27 A are opposed to the cylinder bores  28 ,  28 B and  28 A respectively to accommodate double-headed pistons  29  and  29 A.  
         [0037]    The rotation of the swash plate  23 , which rotates integrally with the rotary shaft  21 , is transmitted to each of the double-headed pistons  29  and  29 A through shoes  301  and  302  so as to linearly reciprocate the double-headed piston  29  and  29 A within the associated cylinder bore  27 ,  27 A,  28 ,  28 B and  28 A. Compression chambers  271  and  281  are defined in the cylinder bores  27 ,  27 A,  28 ,  28 B and  28 A.  
         [0038]    Through holes  112  and  122  are formed respectively in the cylinder blocks  11  and  12  for allowing the rotary shaft  21  extending therethrough. Each of the through holes  112  and  122  extend with the different radii along the longitudinal direction of the rotary shaft  21 . Sealing surfaces  113  and  123  are formed in contact with the rotary shaft  21  in a portion in which the through hole has the smallest radius. The rotary shaft  21  is directly supported by cylinder blocks  11  and  12  on the sealing surfaces  113  and  123 .  
         [0039]    A passage  212  is formed through the rotary shaft  21 . An end of the passage  212  is in inside edge of the rotary shaft  21  and opens into the suction chamber  142  defined within the rear housing  14 . Introducing passages  31  and  32  are respectively formed within the rotary shaft  21  in fluid communication with the passage  212 .  
         [0040]    Suction passages  33  and  33 A are formed in the cylinder block  11  to allow cylinder bores  27  and  27 A to be in communication with the through hole  112  as shown in FIGS. 2A, 2B and  4 . A mouth  331  of suction passages  33  and  33 A opens on a sealing surface  113 . Suction passages  34  and  34 A are formed in the cylinder block  12  to communicate cylinder bores  28 ,  28 B and  28 A with hole  122  as shown in FIGS. 3A, 3B and  5 . A mouth  341  of suction passages  34  and  34 A opens in a sealing surface  123 . Ends  311  and  321  of the introducing passage  31  and  32  intermittently communicate with the mouths  331  and  231  of suction passages  33 ,  33 A,  34  and  34 A in conjunction with the rotation of the rotary shaft  21 .  
         [0041]    An end  311  of an introducing passage  31  and a mouth  331  of the suction passages  33  and  33 A communicate while refrigerant is introduced into the cylinder bores  27  and  27 A (namely the double-headed piston  29  and  29 A moves from the left hand side of FIG. 1 toward the right). The refrigerant in the passage  212  of the rotary shaft  21  is introduced into the compression chamber  271  of the cylinder bores  27  and  27 A, by way of the introducing passage  31  and the suction passages  33  and  33 A.  
         [0042]    The fluid communication between the end  311  and the mouth  331  of suction passages  33  and  33 A are prohibited while the refrigerant in the cylinder bores  27  and  27 A is compressed (namely the double-headed piston  29  and  29 A move from the right hand side of FIG. 1 toward the left). The refrigerant compressed in the compression chamber  271  is discharged into the discharge chamber  131  from the discharge port  151  by pushing the discharge valve  161 . The refrigerant discharged into the discharge chamber  131  is expelled into an external refrigerant circuit not shown in the figures.  
         [0043]    An end  321  of an introducing passage  32  and a mouth  341  of the suction passage  34  and  34 A are kept in communication with each other while refrigerant is introduced into the cylinder bores  28 ,  28 B and  28 A (namely the double-headed piston  29  and  29 A moves from the right hand side of FIG. 1 toward the left). The refrigerant in the passage  212  of the rotary shaft  21  is thus introduced into the compression chamber  281  of the cylinder bores  28 ,  28 B and  28 A by way of the introducing passage  32  and the suction passages  34  and  34 A.  
         [0044]    The fluid communication between an end  321  and a mouth  341  of suction passage  34  and  34 A is prohibited while the refrigerant in the cylinder bores  28 ,  28 B and  28 A is compressed (namely the double-headed piston  29  and  29 A moves from the left hand side of FIG. 1 toward the right). The refrigerant compressed in the compression chamber  281  is discharged into the discharge chamber  141  from the discharge port  181  by pushing the discharge valve  191  while the cylinder bores  28 ,  28 A and  28 B are in discharging stroke. The refrigerant discharged into the discharge chamber  141  is expelled into an external refrigerant circuit. The refrigerant that is expelled to the external refrigerant circuit is circulated into the suction chamber  142 .  
         [0045]    Portions of the rotary shaft  21  which contact the sealing surfaces  113  and  123  act as the rotary valves  35  and  36  that are integrally formed with the rotary shaft  21  as shown in FIGS. 4 and 5. Instead of contacting the rotary shaft  21  with the sealing surfaces, these can be positioned to minimize the gap between them in order to prevent leakage of the refrigerant. The rotary valves  35  and  36  contact the sealing surfaces  113  and  123  in their outer surfaces  351  and  361 . The sealing surface  113  is in an inner surface of valve accommodating portion  37  (shown in FIG. 4) which covers the rotary valve  35 . The sealing surface  123  is in an inner surface of valve accommodating portion  38  (shown in FIG. 5) which covers rotary valve  36 .  
         [0046]    When the cylinder bore  27 A shown in FIG. 1 is in discharging stroke, the lower cylinder bore  28 B shown in FIG. 3 is also in discharging stroke. A double-headed piston  29 A within the cylinder bore  27 A that is in discharging stroke receives reactive force while compressing the refrigerant in the cylinder bore  27 A and discharging the refrigerant to the discharge chamber  131 . This reactive force is transmitted to the rotary shaft  21  by way of the double-headed piston  29 A, the shoe  301  and the swash plate  23 . The reactive force transmitted to the swash plate  23  through the double-headed piston  29 A is applied to the swash plate  23  as a force shown by an arrow F1 in FIG. 1. The reactive force transmitted to the swash plate  23  through the double-headed piston  29  in the cylinder bore  28 B also is applied to the swash plate  23  as a similar force F2 shown by an arrow F2 in FIG. 1. These forces F1 and F2 force the rotary shaft  21 , which integrally supports the swash plate  23 , to tilt centered at the center of the swash plate of  23 . The rotary shaft  21  is supported by a bearing so as to be releasable from the inner surface of through holes  112  and  122 . A displacement relative to the inner surface of the through holes  112  and  122  of the rotary shaft  21  is transmitted to the rotary valves  35  and  36 . In other words, the reactive force against compression is transmitted to the rotary shaft  21  through the double-headed pistons  29 A and  29  in the cylinder bores  27 A and  28 B in discharging stroke biases the rotary valve  35  in the direction of the cylinder bore  27 A that is in discharging stroke. Similarly, the rotary valve  36  is also biased by the reactive force in the direction of cylinder bore  28 B.  
         [0047]    The shoes  301  and  302 , the swash plate  23  and the rotary shaft  21  bias the rotary valves  35  and  36  by the reactive force toward the mouths  331  and  341  of the suction passage that communicate with the cylinder bores that are in discharging stroke.  
         [0048]    An outer surface  351  of the rotary valve  35  is biased toward the cylinder bore  27 A that is in discharging stroke. The outer surface  351  is urged toward the sealing surface  113  in proximity of the mouth  331  of the suction passage  33 A. The suction passage  33 A is in communication with the cylinder bore  27 A which is in discharging stroke. An outer surface  361  of the rotary valve  36  that is biased toward the cylinder bore  28 B of discharging stroke is pushed toward the sealing surface  123  in the proximity of the mouth  341  of the suction passage  34 . The suction passage  34  is in communication with the cylinder bore  28 B in discharging stroke. As a result, the refrigerant within compression chamber  271  and  281  of the cylinder bores  27 A and  28 B in discharging stroke is prevented from leaking from the suction passages  33 A and  34 . Accordingly, the volume efficiency in the compressor is improved.  
         [0049]    While the thrust bearing  25  is not provided with a function to absorb a thrust loading, the bearing  26  is provided with a function to absorb a thrust loading. The function of the bearing  26  to absorb the thrust loading modifies election tolerance due to dimensional error of the parts. Accordingly, the bearing  26  permits the swash plate  23  to rotate in the direction of F1 and F2 shown in FIG. 1 centered at the center of the swash plate  23 . In other words, the bearing  26  permits biasing the rotary valves  35  and  36  by reactive force in the direction of the mouth of the suction passage which communicates with the cylinder bore in discharging stroke. The configuration with the thrust bearing  26  acting to transmit the reactive force is a simple so that the refrigerant in the compression chambers  271  and  281  does not leak through the suction passage.  
         [0050]    A portion of the rotary shaft  21  that extends away from the swash plate  23  toward the rotary valve  35  is supported only by the radial bearing including the sealing surface  113  (that is an inner surface of the valve accommodating portion  37 ) and an outer surface  351  of the rotary valve  35 . The sealing surface  113  of the valve accommodating portion  37  acts as a radial bearing to support the rotary shaft  21  through the rotary valve  35 . The sealing surface  113  biases the rotary valve  35  by transmitting a reactive force toward the mouth  331  of the suction passage  33 A that communicate with the cylinder bore  27 A in discharging stroke.  
         [0051]    A portion of the rotary shaft  21  which extends away from the swash plate  23  toward the rotary valve  36  is supported only by the radial bearing including the sealing surface  123  (that is an inner surface of the valve accommodating portion  38 ) and an outer surface  351  of the rotary valve  35 . The sealing surface  123  of the valve accommodating portion  38  acts as a radial bearing to support the rotary shaft  21  through the rotary valve  36 . The sealing surface  123  biases the rotary valve  36  by transmitting the reactive force toward the mouth  341  of the suction passage  34  that communicate with the cylinder bore  28 B in discharging stroke.  
         [0052]    The configuration with the rotary shaft  21  supported by a radial bearing disposed in a portion of the outer surface of the rotary shaft  21  which extend away from the swash plate  23  toward the rotary valve improves an effect to block the mouth  331  and  341  of the suction passage  33 A and  34 A by a rotary valve  35  and  36 .  
         [0053]    The mouths  331  and  341  of the suction passages  33 A and  34  respectively communicating with the cylinder bores  27 A and  28 B in discharging stroke are closed by the urging force applied to the rotary valves  35  and  36  and reactive force. This closed state is not effected by a size of the gap between the outer surface  351  and  361  of the rotary valve  35  and  36  and the sealing surface  113  and  123 . Accordingly, because the strict control with respect to the tolerance of the gap is not required, the leakage of the refrigerant from the compression chamber  271  and  281  through the suction passages  33 A and  34  is prevented even in the cases where the precision of the gap is low. Namely, the volume efficiency of the compressor is improved even when the gap is not precisely in tolerance.  
         [0054]    The rotary shaft  21  is pressed against the sealing surface  113  of the cylinder block  11  in a position of rotary valve  35 . The shaft  21  is pressed against sealing surface  123  of cylinder block  12  in the position of rotary valve  36 . More concretely, the shaft  21  are pressed in an opposite directions. Therefore, it is necessary that the rotary shaft  21  be inclined to tilt with its center in the cross section, i.e. the center of the swash plate  23 . The surface of the rotary shaft  21  and the inner surface of the holes  112  and  122  contact in a small area in the longitudinal direction. This makes the rotary shaft  21  easy to tilt. The configuration with the sealing surfaces  113  and  123  having a radius smaller than that of the holes.  112  and  122  makes the rotary shaft  21  easy to tilt.  
         [0055]    The configuration with the rotary valve  35  and  36  fixingly supported on the rotary shaft  21  reduces the number of parts, resulting in the simple assembly process of the compressor.  
         [0056]    A second embodiment will described hereinafter by referring to FIGS. 6A through 8.  
         [0057]    A front housing  40  and a rear housing  41  are connected to a cylinder block  39  as shown in FIG. 6A. A valve plate assembly is disposed between the cylinder block  39  and the rear housing  41 . A rotary shaft  46  is rotatably supported in the cylinder block  39  and the front housing  40  which defines a chamber  401  for which the pressure is controlled. The front housing  40  supports the rotary shaft  46  through a radial bearing  47 . The rotary shaft  46  extends through a through hole  391  formed within the cylinder block  39 , and the cylinder block  39  directly supports the rotary shaft  46 .  
         [0058]    A lag plate  48  is fixed to the rotary shaft  46 . A pair of guide holes  481  and  482  (shown in FIG. 7) are formed in the lag plate  48 . A swash plate  49 , which acts as a cam member, is supported on the rotary shaft  46  to be slidable and tiltable in the longitudinal direction. A hole  493  is formed in the swash plate  49  to pass through the rotary shaft  46 . A pair of guide pins  491  and  492  (shown in FIG. 7) are fixed to the swash plate  49 . The swash plate  49  is tiltable in the axial direction ( with respect to an axis  461 ) and is integrally rotatable with the rotary shaft  46  by the association of the guide holes  481  and  482  and the guide pins  491  and  492 . While the swash plate  49  is illustrated by a solid line and a dotted line in FIG. 6A, the solid line shows the swash plate at its maximum tilt angle and the dotted line shows the swash plate at its minimum tilt angle.  
         [0059]    A plurality of single-headed pistons  51  and  51 A respectively are accommodated in a plurality of cylinder bores  50  and  50 A formed in the cylinder block  39  as shown in FIGS. 6A and 8. A compression chamber  501  is defined within each of the cylinder bores  50  and  50 A. Rotational motion of the swash plate  49  is transmitted to the single-headed pistons  51  and  51 A through shoes  521  and  522  and converted into linear reciprocating motion of the single-headed pistons  51  and  51 A within the cylinder bores  50  and  50 A.  
         [0060]    A discharge chamber  411  and a suction chamber  412  are formed within the rear housing  41  as shown in FIG. 6A. A discharge port  421  and a discharge valve  431  are included in the valve plate assembly. The discharge valve  431  selectively opens the discharge port  421 . A retainer  441  is formed to regulate the opening size of the discharge valve  431 .  
         [0061]    A thrust bearing  53  is disposed in between the lag plate  48  and the front housing  40 . A shaft seal  45  is interposed between the front housing  40  and the rotary shaft  46 . A passage  462  is formed through the rotary shaft  46 . An end of the passage  462  is in the inside edge of the rotary shaft  46  to open into the suction chamber  412  within the rear housing  41 .  
         [0062]    A discharge chamber  411  and a chamber  401  are in communication through a refrigerant passage  54 . A displacement control valve  55  is disposed on the refrigerant passage  54 . The displacement control valve  55  controls the amount of the refrigerant which flows out from the discharge chamber  411  into the chamber  401 , pressure of which is controlled. The chamber  401  and the suction chamber  412  are in communication through the passage  462  and the refrigerant passage  56 . The refrigerant in the chamber  401  flows out to the suction chamber  412  through the refrigerant passage  56 . The tilt angle of the swash plate  49  is decreased as the pressure in the chamber  401  increase, and the tilt angle increases as the pressure in the chamber  401  is reduced. The displacement control valve  55  controls the tilt angle of the swash plate by adjusting the pressure within the chamber  401 .  
         [0063]    The radius of the through hole  391  allowing the rotary shaft  46  to extend therethrough varies in the longitudinal direction and a portion of the inner surface of the hole acts as a sealing surface  392 . The radius at the sealing surface  392  is smaller than that at other portions of the inner surface of the through hole  391 . The rotary shaft  46  is directly supported by the cylinder block  39  through the sealing surface  392 .  
         [0064]    A plurality of suction passages  58  and  58 A are formed in the cylinder block  39  to allow the cylinder bores  50  and  50 A to communicate with the through hole  391  as shown in FIG. 8. Mouths  581  of the suction passages  58  and  58 A open in the sealing surface  392 . An introducing passage  57  is formed in the rotary shaft  46  to be in communication with the passage  462 . An end  571  of the introducing passage  57  intermittently communicate with the mouths  581  of the suction passages  58 , and  58 A in accordance with the rotation of the rotary shaft  46 .  
         [0065]    An end  571  and the mouths  581  of the suction passages  58  and  58 A communicate while the refrigerant is introduced into the cylinder bores  50  and  50 A (namely the single-headed pistons  51  and  51 A move from the right hand side of FIG. 6A toward the left). The refrigerant in the passage  462  of the rotary shaft  46  is introduced into the compression chamber  501  of the cylinder bores  50  and  50 A through the introducing passage  57  and the suction passages  58  and  58 A while the cylinder bores  50  and  50 A are in suction stroke.  
         [0066]    The fluid communication of the end  571  and the mouths  581  of the suction passages  58  and  58 A are prohibited while the refrigerant in the cylinder bores  50  and  50 A is compressed (namely the single-headed pistons  51  and  51 A move from the left hand side of FIG. 6A toward the right). The refrigerant is compressed in the compression chamber  501  in a compression stroke, and is discharged into a discharge chamber  411  from a discharge port  421  by pushing the discharge valve  431 . The refrigerant discharged into the discharge chamber  411  is expelled out into an external refrigerant circuit not shown in the figures. The refrigerant expelled into the external refrigerant circuit is circulated into the suction chamber  412 .  
         [0067]    A portion of the rotary shaft  46  which contacts the sealing surface  392  acts as a rotary valve  59  integrally formed with the rotary shaft  46  as shown in FIG. 6B. Instead of contacting the rotary shaft with the sealing surfaces, these can be positioned to minimize the gap between them in order to prevent leakage. A sealing surface  392 , to which the outer surface  591  of the rotary valve  59  contacts, is an inner surface of the valve accommodating portion  60  in which the rotary valve  59  is contained.  
         [0068]    A single-headed piston  51 A within the cylinder bore  50 A receives a reactive force from the refrigerant while compressing and discharging the refrigerant of the cylinder bore  50 A into the discharge chamber  411 , during discharging stroke of the cylinder bore  50 A shown in FIG. 6A. A portion of the reactive force is transmitted to the front housing  40  by way of a single-headed piston  51 A, a shoe  521 , a swash plate  49 , guide pins  491  and  492 , a lag plate  48  and a thrust bearing  53 . The reactive force transmitted to the swash plate  49  through a single-headed piston  51 A is applied to the swash plate  49  as a force shown by an arrow F3 in FIG. 6A. The force F3 biases the swash plate  49  toward upper direction of FIG. 6A. The guide holes  481  and  482  are in the form of a hole directing substantially radial direction of the rotary shaft  46 . Accordingly, the engagement of the guide pins  491  and  492  to the guide holes  481  and  482  will not disturb a motion of the swash plate  49  toward upper direction shown in FIG. 6A. The motion of the swash plate  49  toward the upper direction of FIG. 6A biases the rotary shaft  46  in the upper direction of FIG. 6A through engagement of the hole  493  and the surface of rotary shaft  46 . The biasing force acts as a moment loading having a center in the position of engagement between the rotary shaft  46  and the radial bearing  47 , so that the rotary valve  59  is biased in the direction of the cylinder bore  50 A in discharging stroke. Namely, a reactive force transmitted to the rotary shaft  46  through a single-headed piston  51 A in the cylinder bore  50 A in discharging stroke biases the rotary valve  59  in the direction of the cylinder bore  50 A.  
         [0069]    A shoe  521 , a swash plate  49 , a hole  493  and a rotary shaft  46  bias the rotary valve  59  by the reactive force in the direction of the mouth  581  of the suction passage which is in communication with a cylinder bore that is in discharging stroke.  
         [0070]    An outer surface  591  of the rotary valve  59  which is biased in the direction of a cylinder bore  50 A in a discharging stroke is pushed against the sealing surface  392  so as to block the mouth  581  of the suction passage  58 A. As a result, the refrigerant within the compression chamber  501  in the cylinder bore  50 A in discharging stroke is prevented from leaking so as to improve the volume efficiency in the compressor.  
         [0071]    A portion of the rotary shaft  46  which extends from the swash plate  49  toward the rotary valve  59  is supported only by a radial bearing including a sealing surface  392  (that is inner surface of a valve accommodating portion  60 ) and the outer surface  591  of the rotary valve  59 . The sealing surface  392 , which is the inner surface of the valve accommodating portion  60 , acts as a part of radial bearing which supports the rotary shaft  46  through rotary valve  59 . Further, the sealing surface  392  transmits the reactive force from the compressed refrigerant. The structure in which the rotary shaft  46  is supported solely by a radial bearing at a portion of the rotary shaft  46  which extends away from the swash plate  49  toward the rotary valve  59  improves the effect of blocking the mouth of the suction passage by a rotary valve.  
         [0072]    A mouth  581  of the suction passage  58 A which communicates with a cylinder bore  50 A in discharging stroke is closed by pushing the rotary valve  59  by the reactive force. This closed state is not effected by the clearance size between the outer surface  591  of the rotary valve and the sealing surface  392 . Accordingly, strict control is not necessary with respect to the tolerance of this clearance and the refrigerant which pass through from a compression chamber  501  within a cylinder bore  50 A in discharging stroke to the suction passage  58 A is prevented from leaking even in the cases where the manufacturing precision of the clearance is low. Namely, the volume efficiency in a compressor is improved in the cases where the manufacturing precision of the clearance is low.  
         [0073]    In order that the rotary shaft  46  is pushed against a sealing surface  392  of the cylinder block  39  in a position of a rotary valve  59 , the rotary shaft  46  is required to be easily tilted in the direction toward the cylinder bore  50 A which is in discharging stroke. The rotary shaft  46  is more easily tilted as an area where an outer surface of the rotary shaft  46  and an inner surface of a hole  391  contact is smaller in the longitudinal direction of the rotary shaft  46 . The structure which provides a sealing surface  392  having a smaller radius compared to other portions within the through hole  391  makes the rotary shaft  46  easier to tilt.  
         [0074]    The structure in which a rotary valve  59  is integrally formed with a rotary shaft  46  reduces the number of parts and simplifies assembly process of the compressor.  
         [0075]    The third embodiment shown in FIGS. 9 through 11 are next described. Elements similar to those described in the first embodiment are numbered with like reference numerals.  
         [0076]    Rotary valves  62  and  63  are fixed to a rotary shaft  61  and are contained within valve accommodating portions  64  and  65 . Introducing passages  66  and  67  formed in rotary valves  62  and  63  are in communication with a swash plate chamber  24 . The swash plate chamber  24  is a suction chamber which communicates with an external refrigerant circuit (not shown in the figures). Ends  661  and  671  of the introducing passages  66  and  67  and mouths  331  and  341  of suction passages  33 ,  33 A,  34  and  34 A intermittently communicate along with rotation of rotary valves  62  and  63 . Refrigerant within the swash plate chamber  24  is introduced into the compression chambers  271  and  281  of the cylinder bores  27  and  28  that are in suction stroke, by way of the introducing passages  66  and  67  and suction passages  33 ,  33 A,  34  and  34 A.  
         [0077]    The displacement of a rotary shaft  61  in the direction of the axis  611  is regulated by a pair of thrust bearings  68  and  69 . Both of the thrust bearings  68  and  69  are provided with a function to absorb thrust loading. The thrust bearings  68  and  69  act to transmit a reactive force against compression similarly as a thrust bearing  26  described with respect to the first embodiment. While the number of parts is increased in the third embodiment since the rotary valves  62  and  63  are provided separately from the rotary shaft  61 , other advantages as described with respect to the first embodiment can be obtained similarly.  
         [0078]    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 invention may be embodied in the following forms.  
         [0079]    The thrust bearing  25  of the first embodiment may be provided with a function to absorb thrust loading. By providing such function, the rotary valves  35  and  36  are more easily allowed to be pushed toward the mouth of the suction passage which communicate cylinder bores that are in discharging stroke, by the compression reactive force. As a result, the refrigerant in the compression chambers in the cylinder bores that are in discharging stroke are prevented from leaking, and the volume efficiency of the compressor is improved.  
         [0080]    In the case where the rotary valve is integrally formed with rotary shaft, the rotary shaft may be manufactured to have a maximum radius in the proximity at a position where the rotary valve is formed. In this way, a portion of the rotary shaft which extends from the swash plate toward the rotary valve is supported only by a radial bearing including a sealing surface (that is inner surface of valve accommodating portion) and an outer surface of the rotary valve so as to improve effect to block the mouth of the suction passage by the rotary valve.  
         [0081]    The pistons may have a hollow structure. Examples of such are shown in FIGS. 12A and 12B. Namely, a double-headed piston  29 A of FIG. 12A comprises a body portion  701  that is connected to shoes  301  and  302 , and cap portions  702  that are fixed at reciprocating ends of the body portion  701 . The double-headed piston  29 A has a hollow structure with a space  703 , which is enclosed by the body portion  701  and the cap portion  702 . Other double-headed pistons  29  have similar structures.  
         [0082]    A single-headed piston  51 A of FIG. 12B comprises a coupling portion  711  to be coupled with shoes  521  and  522 , and a head portion  712  that is fixed at a rear end of the coupling portion  711 . The single-headed piston  51 A has a hollow structure with a space  713 , which is enclosed by the coupling portion  711  and the head portion  712 . In this case, other single-head pistons  51  have similar structures.  
         [0083]    A piston receives an inertial force which is directed to a direction opposite to the compression reactive force. Accordingly, the forces F1, F2 and F3, which work on the swash plate  23  due to the compression reactive force, are smaller as the inertial force increases. The biasing force, which pushes the outer surface of the rotary valve toward the sealing surface in the neighborhood of the suction passage when the piston receives the compression reactive force from the refrigerant, is weakened.  
         [0084]    Accordingly, the inertial force is lowered in the case where the weight of the pistons is reduced by adopting a hollow structure, compared to a case where the pistons are solid. In this way, decrease in the volume efficiency due to leakage of refrigerant within the compression chambers that are in discharging stroke through the suction passages, is suppressed.  
         [0085]    The swash plate  23  can be made of a material such as iron (including iron alloy) having a larger specific gravity than aluminum, in the first and the third embodiments. In this way, the centrifugal force, which acts on the swash plate  23  during rotation of the rotary shaft  12 , can be increased without manufacturing larger swash plate, compared to the case where the swash plate  23  is made of aluminum.  
         [0086]    The rotary shaft  21  receives a force which acts to rotate the fixed rotary shaft  21  and the swash plate  23  in a direction in which an angle between the longitudinal direction of the plate-shaped portion  235  and the central axis of the housing increases toward 90 degrees. This direction is clockwise in FIGS. 1 and 9. In other words, such force acts upon the rotary valve  35  and  36  to be forced toward the mouth  331  and  341  of the suction passage in communication with the cylinder bore which is in discharging stroke.  
         [0087]    Since the swash plate  23  of the first and the third embodiments comprises aluminum, the swash plate has a relatively light weight. The above described effect of the centrifugal force to push the rotary valve  35  and  36  toward mouth  331  and  341  of suction passage is not fully exhibited in these embodiments. On the other hand, the force to push the rotary valve  35  and  36  toward mouth  331  and  341  of suction passage communicating the cylinder bore in the discharging stroke is increased when the swash plate  23  is formed from a material which has a relatively large specific gravity such as materials comprising iron. The refrigerant in the compression chambers that are in discharging stroke is prevented from leaking through suction chamber in this way, so that the volume efficiency of the compressor is increased.  
         [0088]    While the rotary valve of the first and second embodiments are described to be pushed against the inner surface of the valve accommodating portion, the rotary valves can be formed to decrease clearance in between to prevent leakage, instead of contacting the inner surface of the valve accommodating portion.  
         [0089]    It is also possible to apply present invention to a wobble type variable displacement compressor disclosed in Japanese Laid-Open Patent Publication 5-113174, constant displacement piston type compressor having a single-headed piston and a piston type compressor having a cam member having a shape other than swash plate, a wave cam for example.  
         [0090]    Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.