Patent Publication Number: US-6663355-B2

Title: Variable displacement compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a variable displacement compressor having single-headed pistons, which is used, for example, in a vehicular air conditioning system. 
     A variable displacement swash plate clutch compressor shown in FIG. 8 has a solenoid clutch  101 , which can interrupt power transmission from a vehicular engine Eg. The compressor also has a displacement control mechanism, which can reduce the displacement so that the solenoid clutch is not be turned on and off frequently when the cooling load is low. 
     The displacement control mechanism has a swash plate  103  connected to pistons  102  through shoes  102   a . A rotary support  105  is fixed to a drive shaft  104 . The swash plate  103  is connected to the rotary support  105  through a hinge mechanism  106 . The swash plate  103  is housed in the crank chamber  107 . The differential pressure between the crank chamber  107  and the cylinder bores  18  varies to change the inclination angle of the swash plate  103 . As the inclination angle of the swash plate  103  is changed, the stroke of each piston  102  is changed to change the displacement. 
     For example, when the pressure of the crank chamber  107  is increased to increase the difference between the pressure of the pressures of the cylinder bore  108 , the inclination angle of the swash plate  103  is reduced, which reduces the compressor displacement. In FIG. 8, the swash plate  103  indicated by the broken double-dashed line is at the minimum inclination position, where it abuts against a regulating ring  109  attached to the drive shaft  104 . When the internal pressure of the crank chamber  107  is reduced to reduce the differential pressure the cylinder bores  108 , the inclination angle of the swash plate  103  is increased to increase the compressor displacement. 
     Generally, in the step of compressing a refrigerant gas, the piston  102 , the swash plate  103 , the hinge mechanism  106 , the rotary support  105  and the drive shaft  104  transmit force to the internal wall surface of a housing  110  (leftward in FIG. 8) through a thrust bearing  111  due to the compression load on the piston  102 . 
     The internal pressure of the crank chamber  107  remains high so that the compressor can be started from the minimum displacement state, at which the load torque is minimized, even if the solenoid clutch is turned on soon after it is turned off. Further, control of the compressor displacement is performed to minimize the displacement, regardless of the cooling load, to reduce load of the engine Eg during rapid acceleration of the vehicle. 
     When the internal pressure of the crank chamber  107  is increased rapidly to minimize the displacement, the swash plate  103  may be pressed against the regulating ring  109  with excessive force, or the rotary support  105  may be pulled strongly to the rear side of the compressor through the hinge mechanism  106 . Thus, the drive shaft  104  is caused to slide or shift backward (rightward in FIG. 8) along the axis L. 
     Upon such movement of the drive shaft  104 , the top dead center position of the piston  102  shifts toward the valve plate  112 . Therefore, the piston  102  may impinge upon the valve plate  112  when reaching the top dead center position. This impingement causes vibrations and noise and may damage the pistons  102  or the valve plate  112 . 
     Also, when such backward movement of the drive shaft  104  takes place when the solenoid clutch  101  is turned off, an armature  101   a  of the solenoid clutch  101  moves toward a rotor  101   b  to eliminate a clearance between the armature  101   a  and the rotor  101   b  or to bring the armature  101   a  into contact with the rotor  101   b , which causes rattling or vibration and unnecessary power transmission. 
     To solve the above problems, a spring  113  is located between the housing  110  and the drive shaft  104 . The spring  113  urges the drive shaft  104  axially forward. 
     Japanese Unexamined Patent Publication No. Hei 11-62824 discloses a compressor having a restricting member for restricting axial shifting of the drive shaft. The restricting member is located in a hole in which the rear end of the drive shaft is fitted. The hole communicates with a suction chamber through a space. A sealing member, which prevents communication between a crank chamber and the space through the hole is applied around the rear end of the drive shaft. 
     To securely prevent backward axial shifting of the drive shaft  104  shown in FIG. 8, it is essential to use a very stiff spring  113 . As a result, the thrust bearing  111  receives a great load from the spring  113 , which reduces the life of the thrust bearing  111  and increases the power loss of the compressor at the thrust bearing  111 . The increased power loss adversely affects the fuel consumption rate of the engine Eg that drives the compressor. 
     In the compressor disclosed in Japanese Unexamined Patent Publication No. Hei 11-62824, a sealing member is located in the hole in which the rear end of a drive shaft is supported. The sealing member prevents entry of refrigerant into the hole. Therefore, lubricant cannot be supplied fully to the radial bearing, which shortens the life of the bearing. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a variable displacement compressor having a simple constitution and being capable of maintaining sufficient lubrication of the radial bearing. 
     To achieve the above objective, the present invention provides a variable displacement compressor. The compressor comprises a housing having a suction chamber and a discharge chamber. A crank chamber is defined in the housing. A drive shaft has a front end and a rear end. The shaft is supported in the housing so that the front end protrudes from the housing. A cylinder block forms part of the housing. Cylinder bores are defined in the cylinder block. A valve plate assembly includes a suction port, a suction valve, a discharge port and a discharge valve for each cylinder bore. Single-headed pistons are housed in the cylinder bores, respectively. A drive plate is housed in the crank chamber and is connected to the pistons to convert rotation of the drive shaft into reciprocating motion of the pistons. The drive plate rotates integrally with the drive shaft. A control mechanism controls inclination of the drive plate by controlling the pressure of the crank chamber to change the volume of a refrigerant discharged from each cylinder bore into the discharge chamber. A radial bearing supports the rear end of the drive shaft. The refrigerant flows through the radial bearing. A holding bore houses the rear end of the drive shaft and the radial bearing. The holding bore is connected to a holding space. The holding space is defined by the valve plate assembly. A passage connects the holding space and the suction chamber. A restricting member is located in the holding space. The restricting member restricts axial movement of the drive shaft and divides the holding space into a first region and a second region. The first region and the second region communicate with each other. A clearance is formed between the drive shaft and the restricting member or between the restricting member and the valve plate assembly in a normal compressing operation. The clearance disappears when the pressure of the crank chamber is increased rapidly by the control mechanism. 
     The present invention also provides a variable displacement compressor. The compressor comprises a housing having a suction chamber and a discharge chamber. A crank chamber is defined in the housing. A drive shaft has a front end and a rear end. The shaft is supported in the housing so that the front end protrudes from the housing. A cylinder block forms part of the housing. Cylinder bores are defined in the cylinder block. A valve plate assembly includes a suction port, a suction valve, a discharge port and a discharge valve for each cylinder bore. Single-headed pistons are housed in the cylinder bores, respectively. A drive plate is housed in the crank chamber and is connected to the pistons to convert rotation of the drive shaft into reciprocating motion of the pistons. The drive plate rotates integrally with the drive shaft. A control mechanism controls inclination of the drive plate by controlling the pressure of the crank chamber to change the volume of a refrigerant discharged from each cylinder bore into the discharge chamber. A radial bearing supports the rear end of the drive shaft. The refrigerant flows through the radial bearing. A holding bore houses the rear end of the drive shaft and the radial bearing. The holding bore is connected to a holding space. The holding space is defined by the valve plate assembly. The holding space is connected to the suction chamber. Means for restricting restricts axial movement of the drive shaft. The restricting means are located in the holding space and divides the holding space into a first region and a second region. A clearance is formed between the drive shaft and the restricting means or between the restricting means and the valve plate assembly in a normal compressing operation. The clearance disappears when the pressure of the crank chamber is increased rapidly by the control mechanism. A passage connects the first region to the second region. 
     The present invention also provides a variable displacement compressor. The compressor comprises a housing having a suction chamber and a discharge chamber. A crank chamber is defined in the housing. A drive shaft has a front end and a rear end. The shaft is supported in the housing so that the front end protrudes from the housing. A cylinder block forms part of the housing. Cylinder bores are defined in the cylinder block. A valve plate assembly includes a suction port, a suction valve, a discharge port and a discharge valve for each cylinder bore. Single-headed pistons are housed in the cylinder bores, respectively. A drive plate is housed in the crank chamber and is connected to the pistons to convert rotation of the drive shaft into reciprocating motion of the pistons. The drive plate rotates integrally with the drive shaft. A control mechanism controls inclination of the drive plate by controlling the pressure of the crank chamber to change the volume of a refrigerant discharged from each cylinder bore into the discharge chamber. A radial bearing supports the rear end of the drive shaft. The refrigerant flows through the radial bearing. A holding bore houses the rear end of the drive shaft and the radial bearing. The holding bore is connected to a holding space. The holding space is defined by the valve plate assembly. A passage connects the holding space and the suction chamber. A cylindrical body is located in the holding space. One end of the cylindrical body is fixed to the drive shaft, and the other end of the cylindrical body abuts against the valve plate assembly. The cylindrical body restricts axial movement of the drive shaft and divides the holding space into a first region and a second region. The cylindrical body has a hole to connect the first region to the second region. A clearance is formed between the drive shaft and the cylindrical body or between the cylindrical body and the valve plate assembly in a normal compressing operation. The clearance disappears when the internal pressure of the crank chamber is increased rapidly by the control mechanism. 
     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 examples the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view of the variable displacement compressor according to a first embodiment of the present invention; 
     FIG.  2 ( a ) is an enlarged partial cross-sectional view of the compressor shown in FIG. 1; 
     FIG.  2 ( b ) is an enlarged cross-sectional view showing actions of the passage at the portion shown in FIG.  2 ( a ); 
     FIG.  3 ( a ) is an enlarged partial cross-sectional view of the compressor according to a second embodiment of the present invention, showing a portion corresponding to that in FIG.  2 ( a ); 
     FIG.  3 ( b ) is a cross-sectional view taken along the line  3   b — 3   b  in FIG.  3 ( a ); 
     FIG. 4 is an enlarged cross-sectional view showing actions of the passage at the portion shown in FIG.  3 ( a ); 
     FIG.  5 ( a ) is an enlarged cross-sectional view of the compressor according to a third embodiment of the present invention, showing a portion corresponding to that in FIG.  2 ( a ); 
     FIG.  5 ( b ) is a cross-sectional view taken along the line  5   b — 5   b  in FIG.  5 ( a ); 
     FIG. 6 is an enlarged cross-sectional view showing actions of the passage at the portion shown in FIG.  5 ( a ); 
     FIG.  7 ( a ) is an enlarged cross-sectional view of the compressor according to a fourth embodiment of the present invention, showing a portion corresponding to that in FIG.  2 ( a ); 
     FIG.  7 ( b ) is an enlarged cross-sectional view of the compressor according to a fifth embodiment of the present invention, showing a portion corresponding to that in FIG.  2 ( a ); and 
     FIG. 8 is a cross-sectional view of a variable displacement compressor of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The variable displacement compressor according to the first embodiment of the present invention is part of a vehicular air conditioning system and is described below referring to FIGS.  1  and  2 ( b ). 
     As shown in FIG. 1, a front housing member  11  is connected to the front end of a cylinder block  12 . A rear housing member  13  is connected to the rear end of the cylinder block  12  through a valve plate assembly  14 . The front housing member  11 , the cylinder block  12  and the rear housing member  13  are fastened together with through-bolts (not shown). The front housing member  11 , the cylinder block  12  and the rear housing member  13  form a housing of the compressor. The left side and the right side in FIG. 1 correspond to the front end and the rear end, respectively. 
     The valve plate assembly  14  includes a main plate  14   a , a first sub plate  14   b , a second sub plate  14   c  and a retainer plate  14   d . The first sub plate  14   b  and the second sub plate  14   c  are superposed on the front side and on the rear side of the main plate  14   a , respectively. The retainer plate  14   d  is superposed on the rear side of the second sub plate  14   c . The first sub plate  14   b  of the valve plate assembly  14  is connected to the cylinder block  12 . 
     A crank chamber  15  is defined between the front housing member  11  and the cylinder block  12 . A drive shaft  16  passes through the crank chamber  15 . The drive shaft  16  is supported between the front housing member  11  and the cylinder block  12 , and the front end of the drive shaft  16  extends from the housing. The front end of the drive shaft  16  is supported in the front housing member  11  by a first radial bearing  17 . A holding bore  18  is defined substantially at the center of the cylinder block  12 . The rear end of the drive shaft  16  is supported by a second radial bearing  19  located in the holding bore  18 . A shaft sealing device  20  is applied around the front end of the drive shaft  16 . The device  20  prevents leakage of refrigerant. 
     A plurality of cylinder bores  12   a  (only one cylinder bore is shown in FIG. 1) are defined in the cylinder block  12 . The cylinder bores  12   a  are defined at equiangular intervals around the axis L of the drive shaft  16 . Single-headed pistons  21  are housed in the cylinder bores  12   a . Openings of each cylinder bore  12   a  are closed by the valve plate assembly  14  and the corresponding piston  21 . A compression chamber  22  is defined in each cylinder bore  12   a . The volume of each compression chamber  22  varies as the corresponding piston  21  reciprocates. 
     In the crank chamber  15 , a lug plate  23  is fixed to and rotates integrally with the drive shaft  16 . A thrust bearing  24  is located between the lug plate  23  and the internal wall surface  11   a  of the front housing member  11 . The internal wall surface  11   a  bears the load of the compressive reaction force of the pistons  21  and functions as a regulating surface that regulates axial movement of the drive shaft  16 . 
     A swash plate  25 , or drive plate, is housed in the crank chamber  15 . The swash plate  25  is supported such that it slides and on and inclines with respect to the drive shaft  16 . A hinge mechanism  26  is located between the lug plate  23  and the swash plate  25 . The swash plate  25  is connected to the lug plate  23  through the hinge mechanism  26  and to the drive shaft  16 . The swash plate  25  rotates synchronously with the lug plate  23  and the drive shaft  16 . 
     The pistons  21  are connected to the periphery of the swash plate  25  through shoes  27 , respectively. Thus, the swash plate  25  is rotated by the drive shaft  16 , and the rotational motion of the swash plate  25  is converted to reciprocating motions of the pistons  21  through the shoes  27 . 
     A regulating ring  28  is fitted to the drive shaft  16  between the swash plate  25  and the cylinder block  12 . The minimum inclination angle of the swash plate  25 , as indicated by the broken double-dashed line in FIG. 1, is determined by abutment of the swash plate  25  against the regulating ring  28 . The maximum inclination angle of the swash plate  25 , as indicated by the solid line in FIG. 1, is determined by abutment against the lug plate  23 . 
     The drive shaft  16  is connected to an engine  30  through a power transmission mechanism  29 . The power transmission mechanism  29  may be a clutch mechanism (e.g., a solenoid clutch), which transmits or interrupts of power according to an external electrical controller, or a normally transmitting type clutchless mechanism (e.g., a belt/pulley combination). Here, in this embodiment, a clutchless power transmission mechanism  29  is employed. 
     A suction chamber  31  is defined in the rear housing member  13 . A discharge chamber  32  is defined in the rear housing member  13  at a position radially outward from the suction chamber  31 . The valve plate assembly  14  has, for each cylinder bore  12   a , a suction port  33 , a suction valve  34  for opening and closing the suction port  33 , a discharge port  35  and a discharge valve  36  for opening and closing the discharge port  35 . The suction chamber  31  communicates with the cylinder bores  12   a  through the suction ports  33 . The discharge chamber  32  communicates with the cylinder bores  12   a  through the discharge ports  35 . The suction chamber  31  and the discharge chamber  32  are connected to each other through an external refrigerant circuit (not shown). 
     The cylinder block  12  and the rear housing member  13  contain an gas supply passage  37  that connects the crank chamber  15  and the discharge chamber  32 . A control valve  38 , which is a solenoid valve, is located in the gas supply passage  37 . The control valve  38  has a valve chamber forming part of the gas supply passage  37 . Energization of a solenoid  38   a  opens the gas supply passage  37 , and deenergization of the solenoid  38   a  closes the gas supply passage  37 . Further, the opening degree of the gas supply passage  37  is adjusted depending on the level of the current energizing the solenoid  38   a.    
     A holding space  40  is defined behind the holding bore  18 . A restricting member  39  is housed in the holding space  40 . The restricting member  39  restricts backward movement of the drive shaft  16 . The holding space  40  is connected at one end the holding bore  18  and is closed at the other end by the valve plate assembly  14 . The holding space  40  and the suction chamber  31  communicate with each other through a passage  41  defined in the valve plate assembly  14 . The passage  41  is aligned with the axis L of the drive shaft  16 . 
     The drive shaft  16  has an axial passage  42  that connects the holding space  40  and the crank chamber  15 . An inlet  42   a  and an outlet  42   b  of the axial passage  42  open at the rear of the first radial bearing  17  and to the rear end face of the drive shaft  16 , respectively. The axial passage  42 , the holding bore  18 , the holding space  40  and the passage  41  form a bleed passage for connecting the crank chamber  15  and the suction chamber  31 . The passage  41  functions as a restrictor. 
     The restricting member  39 , which is a cylindrical, is fixed to the rear end of the drive shaft  16 . The restricting member  39  is designed to have an outside diameter that is smaller than the inside diameter of the second radial bearing  19 , and the restriction member  39  is fixed to a small-diameter portion  16   a  formed at the rear end of the drive shaft  16 . 
     As shown in FIG.  2 ( b ), in a normal compressing operation, a small clearance Δ is defined between the restricting member  39  and the valve plate assembly  14 . When the internal pressure of the crank chamber  15  is increased suddenly, the clearance Δ disappears, and backward movement of the drive shaft  16  is restricted. The clearance Δ is, for example, about 0.1 mm. This clearance Δ is smaller than the clearance between the piston  21  at the top dead center position and the valve plate assembly  14 . 
     As shown in FIGS.  2 ( a ) and  2 ( b ), the restricting member  39  divides the holding space  40  into a first region A and a second region B. The resistance of the refrigerant gas passing from the second region B to the first region A through the clearance Δ is greater than the resistance of the refrigerant gas flowing from the crank chamber  15  through the second radial bearing  19  into the holding space  40 . 
     A plurality of holes  43  are defined in the restricting member  39  to form passages connecting the first region A and the second region B. The holes  43  are defined such that the resistance of the refrigerant gas passing through is smaller than that passing through the second radial bearing  19 . 
     The operation of the compressor described above will be described below. 
     When the drive shaft  16  is rotated, the swash plate  25  is rotated integrally through the lug plate  23  and the hinge mechanism  26 , and the rotation of the swash plate  25  is converted into reciprocating motion of the pistons  21  through the shoes  27 . Consequently, suction, compression and discharge of the refrigerant are repeated sequentially in each compression chamber  22 . Refrigerant supplied from an external refrigerant circuit into the suction chamber  31  is drawn through the suction port  33  into the compression chamber  22 . Travel of the piston  21  to the top dead center compresses the refrigerant in the compression chamber  22  to a predetermined pressure and discharges the compressed refrigerant through the discharge port  35  into the discharge chamber  32 . The refrigerant discharged into the discharge chamber  32  is fed through a discharge passage to the external refrigerant circuit. 
     A controller (not shown) adjusts the valve position of the control valve  38 , i.e., the opening degree of the gas supply passage  37 , depending on the cooling load. As a result, the flow rate of gas between the discharge chamber  32  and the crank chamber  15  is changed. 
     When the cooling load is high, the opening degree of the gas supply passage  37  is reduced to reduce the flow rate of the refrigerant gas supplied from the discharge chamber  32  into the crank chamber  15 . When the amount of refrigerant gas supplied to the crank chamber  15  decreases, the internal pressure of the crank chamber  15  is reduced gradually due to the release of refrigerant gas through the axial passage  42  into the suction chamber  31 . Thus, the differential pressure between the pressure of the crank chamber  15  and that of the cylinder bore  12   a  decreases, which moves the swash plate  25  to the maximum inclination position. Therefore, the stroke of the piston  21  is increased, which increases the displacement. 
     When the cooling load is low, the control valve  38  is opened to increase the flow rate of refrigerant gas from the discharge chamber  32  into the crank chamber  15 . If the amount of refrigerant gas supplied to the crank chamber  15  exceeds the flow rate of refrigerant gas flowing out through the axial passage  42  into the suction chamber  31 , the internal pressure of the crank chamber  15  increases gradually. Thus, the differential pressure between the crank chamber  15  and the cylinder bore  12   a  increases, which moves the swash plate  25  to the minimum inclination angle position. This reduces the stroke of each piston  21 , and reduces the displacement. 
     The compression load of the refrigerant gas acting upon each piston  21  is applied to the internal wall surface  11   a  of the front housing member  11  through the shoes  27 , the swash plate  25 , the hinge mechanism  26 , the lug plate  23  and the thrust bearing  24 . Generally, in the compressing operation, forward movement of the drive shaft  16 , the swash plate  25 , the lug plate  23 , and the pistons  21  along the axis L is restricted by the internal wall surface  11   a  of the front housing member  11  through the thrust bearing  24 . When the wall surface  11   a  restricts the forward axial movement of the drive shaft  16 , a clearance Δ exists between the restricting member  39  and the valve plate assembly  14 . Accordingly, the restricting member  39  does not interfere with the rotation of the drive shaft  16 . 
     When the compressor is operating at the maximum displacement and is subjected to displacement restricting control, the control valve  38  causes the gas supply passage  37  to open suddenly from a closed state. Thus, the high-pressure refrigerant in the discharge chamber  32  is supplied rapidly to the crank chamber  15 . The pressure of the crank chamber  15  increases rapidly, since additional refrigerant can not be rapidly through the axial passage  42 . The sudden increase in the pressure of the crank chamber  15  rapidly reduces the inclination angle of the swash plate  25 . This causes the swash plate  25  (indicated by the broken double-dashed line in FIG. 1) to be pressed against the regulating ring  28  with an excessive force, which pulls the lug plate  23  strongly backward through the hinge mechanism  26 . Thus, the drive shaft  16  slides backward along the axis L. The restricting member  39  thus abuts against the valve plate assembly  14  to restrict backward movement of the drive shaft  16 . Therefore, the distal end of the piston  21  is prevented from connecting the valve plate assembly when the piston  21  reaches the top dead center position. 
     During rotation of the drive shaft  16 , some refrigerant flows from the passage  41  into the suction chamber  31  through the axial passage  42  and the holding space  40  due to the differential pressure between the crank chamber  15  and the suction chamber  31 . Atomized lubricant in the refrigerant lubricates the thrust bearing  24  and the first radial bearing  17 . 
     Some of the refrigerant gas in the crank chamber  15  flows through the second radial bearing  19  into the second region B of the holding space  40 . The second radial bearing  19  is lubricated by the atomized lubricant contained in the refrigerant flowing from the crank chamber  15  toward the holding space  40 . During normal operation of the compressor, there is a very small clearance Δ present between the restricting member  39  and the valve plate assembly  14 . If the second region B and the first region A could communicate with each other only through the clearance Δ, the refrigerant would not move smoothly from the second region B to the first region A. Thus, the amount of refrigerant passing through the second radial bearing  19  would decrease and the second radial bearing  19  would not be adequately lubricated. Particularly, in the case of clutchless compressors, the second radial bearing  19  is lubricated insufficiently during minimum displacement operation. 
     However, in this embodiment, the restricting member  39  includes the holes  43 , and the refrigerant thus passes from the second region B to the first region A smoothly. As a result, the refrigerant flowing from the crank chamber  15  toward the holding space  40  through the second radial bearing  19  thoroughly lubricates the second radial bearing  19 . 
     This embodiment has the following effects. 
     A reduction in the amount of refrigerant passing through the second radial bearing  19  is avoided by forming holes  43  between the first region A and the second region B. Thus, impingement of the pistons  21  against the valve plate assembly  14  caused by backward movement of the drive shaft  16  is avoided, even in the absence of the spring  113  shown in FIG.  8 . Further, the second radial bearing  19  is thoroughly lubricated. In addition, the load acting upon the thrust bearing  24  is reduced compared with constitution compressors that employ the spring  113 . This reduces friction and thus reduces the power loss of the compressor, which improves the fuel consumption of the engine  30 . The present invention has a particularly significant effect in clutchless compressors. 
     Use of the restricting member  39  in which holes  43  are formed permits thorough lubrication of the second radial bearing  19  and restricts backward movement of the drive shaft  16 . The number and the diameter of the holes  43  can be changed arbitrarily. 
     The restricting member  39  is fitted on the drive shaft  16 . Therefore, the assembly is simple. 
     The outside diameter of the restricting member  39  is smaller than the inside diameter of the second radial bearing  19 . Therefore, during assembly of the compressor, the restricting member  39  can be installed in the compressor after it is fitted on the drive shaft  16 . This facilitates assembly. 
     The holding space  40  is located between the holding bore  18  and the valve plate assembly  14 . Therefore, the space used for housing the spring  113  shown in FIG. 8 is used as the holding space  40 . Thus, space for the restricting member  39  is available, and there is no need to enlarge the compressor. 
     A second embodiment will be described referring to FIGS.  3 ( a ) to  4 . This embodiment has the same construction as in the embodiment shown in FIGS. 1 to  2 ( b ), except that the passages between the second region B and the first region A are different from that in the foregoing embodiment. Therefore, the same or like parts as in the embodiment shown in FIGS. 1 to  2 ( b ) are affixed with the same reference numbers respectively, and a detailed description of them will be omitted. 
     A cross-shaped hole  44  is defined in the first sub plate  14   b  of the valve plate assembly  14 . The hole  44  is defined when forming of the suction valve  34  by using different press dies. 
     As shown in FIG. 4, the clearance between the restricting member  39  and the valve plate assembly  14  corresponds to the clearance Δ shown in FIG.  2 ( b ). The size of the clearance between opposing parts of the restricting member  39  and the hole  44  is the sum of the clearance Δ and the thickness t of the first sub plate  14   b . The refrigerant flows smoothly from the second region B into the first region A through this clearance Δ+t). 
     This embodiment has the following effects in addition to those of the embodiment shown in FIGS. 1 to  2 ( b ). 
     The hole  44  can be defined simultaneously when the first sub plate  14   b  is formed by slightly changing the dies used for forming the first sub plate  14   b . Further, the passage between the second region B and the first region A can be defined easily, which reduces costs compared with the case where the holes  43  are defined in the restricting member  39  by drilling or the like. 
     This embodiment may be modified as follows. 
     If the passage connecting the second region B and the first region A is defined in the valve plate assembly  14 , both the first sub plate  14   b  and the main plate  14   a  may be machined. For example, as in a third embodiment shown in FIGS.  5 ( a ),  5 ( b ) and  6 , a circular first hole  45  and a plurality of second holes (four holes in this embodiment)  46  are defined in the first sub plate  14   b . The first hole  45  is defined concentrically with the passage  41  and has a diameter smaller than the inside diameter of the restricting member  39 . The second hole  46  is defined radially outside of the restricting member  39 . 
     As shown in FIGS.  5 ( a ) and  5 ( b ), four elliptic recesses  47  are defined in the main plate  14   a . The recesses  47  connect the first hole  45  to the second holes  46 . In this embodiment, the first hole  45 , the second holes  46  and the recesses  47  define the passage between the second region B and the first region A. The first hole  45  and the second holes  46  are formed when the suction valve  34  is formed in the first sub plate  14   b , and the recesses  47  are formed when forming the suction ports  33 , discharge ports  35 , etc. in the main plate  14   a . Therefore, this embodiment has the same effects as in the embodiment shown in FIGS.  3 ( a ) to  4 . 
     In the embodiment shown in FIGS.  3 ( a ) to  4 , in the state where the restricting member  39  is abutted against the valve plate assembly  14 , the end face of the restricting member  39  is brought into direct contact with the periphery of the hole  44 . In the embodiment shown in FIGS.  5 ( a ),  5 ( b ) and  6 , in the state where the restricting member  39  is abutted against the valve plate assembly  14 , the restricting member  39  is not engaged with the passage defined in the valve plate assembly  14 . 
     Instead of fitting the restricting member  39  to the small-diameter rear end portion of the drive shaft  16 , the diameter of the outlet  42   a  of the axial passage  42  may be increased so that the restricting member  39  can be fitted in the axial passage  42 . In this case, the effects of the embodiments shown in FIGS. 1 to  6  can be obtained. 
     The passage between the second region B and the first region A may be defined in the drive shaft  16 . 
     The restricting member  39  may be formed integrally at the rear end portion of the drive shaft  16 . That is, the rear end of the drive shaft  16  is abutted directly against the valve plate assembly  14 , and a hole  43  is defined in the rear end of the drive shaft  16 . 
     The cylindrical restricting member  39  may be press fitted in the holding space  40 . For example, as in a fourth embodiment shown in FIG.  7 ( a ), in the state where the drive shaft  16  is urged forward by the compressive reaction force, the restricting member  39  is fixed such that a clearance Δ is defined between the restricting member  39  and the rear end of the drive shaft  16 . The restricting member  39  is fixed in the holding space  40  such that a sufficient distance exists between the valve plate assembly  14  and the restricting member  39 . 
     A first hole  48  is defined at the center of the restricting member  39 . A plurality of second holes  49  are defined as passages between the second region B and the first region A. This eliminates the need for fixing the restricting member  39  to the drive shaft  16  and for machining the valve plate assembly  14 , and only the restricting member  39  is machined. 
     In a fifth embodiment shown in FIG.  7 ( b ), a groove  50  is formed as the passage in the cylinder block  12 . In this case, the degree of freedom in the size of the passage is increased compared with the embodiments where the passage is defined in the restricting member  39 , and the groove  50  can be formed when forming the cylinder block  12 , which simplifies the formation the restricting member  39 . 
     The axial passage  42  need not be defined in the drive shaft  16 , but a bleed passage (not shown) may be defined separately in the cylinder block  12 . In this case, the holding space  40  is allowed to communicate with the suction chamber  31  to permit flow of the refrigerant into it and to lubricate the second radial bearing  19 . 
     The present invention may be employed where power transmission from the drive source to the drive shaft  16  is achieved through a solenoid clutch. In this case, the clearance defined between the rotor of the solenoid clutch and the armature, when the solenoid is off, is larger than the clearance Δ between the restricting member  39  and the valve plate assembly  14  or between the restricting member  39  and the rear end face of the drive shaft  16 . Therefore, even if the value of clearance Δ is not changed, the rotor and the armature do not interfere with each other when the solenoid clutch is off. 
     The present invention may be applied to a wobble compressor in which the drive plate rotates relative to the drive shaft. 
     The control valve  38  for adjusting the opening degree of the air supply passage is not limited to the solenoid valve. The control valve  38  may be, for example, one disclosed in Japanese Unexamined Patent Publication No. Hei 6-123281, which has a diaphragm that moves according to the suction pressure and a valve mechanism for controlling the opening degree of the air supply passage according to the position of the diaphragm. However, an externally controllable solenoid valve is preferred in a clutchless compressor. 
     The drive source is not limited to the engine  30  but may be a motor. 
     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. 
     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 of the appended claims.