Patent Publication Number: US-11644022-B2

Title: Variable displacement compressor

Description:
TECHNICAL FIELD 
     The present invention relates to a variable displacement compressor which varies discharge displacement by adjusting the pressure of a control pressure chamber, and particularly to a variable displacement compressor which, having a supply passage which causes a discharge chamber and a control pressure chamber to communicate with each other, adjusts the pressure of the control pressure chamber by adjusting the degree of opening of the supply passage with a control valve provided on the supply passage. 
     BACKGROUND ART 
     A variable displacement compressor adopts a mechanism whereby the inclination angle of a swash plate is changed by adjusting the pressure of a control pressure chamber, adjusting the amount of stroke of a piston, thereby varying discharge displacement. As this kind of compressor, a configuration is known such that a discharge chamber and the control pressure chamber are caused to communicate with each other via a supply passage, while the control pressure chamber and a suction chamber are caused to communicate with each other via a release passage, and a control valve which adjusts the degree of opening of the supply passage is provided on the supply passage, and that the release passage is caused to communicate continuously via an orifice passage, and the degree of opening of the supply passage is adjusted by the control valve on the supply passage, adjusting the amount of refrigerant flowing into the control pressure chamber, thereby controlling the pressure of the control pressure chamber. 
     In this kind of configuration, when the supply passage is closed by the control valve, there is no more high pressure gas to be led into the control pressure chamber from the discharge chamber, and the control pressure chamber communicates continuously with the suction chamber via the release passage, so that the pressure of the control pressure chamber decreases to a value substantially the same as that of the pressure of the suction chamber, meaning that the compressor is operated at the maximum displacement. Also, when the supply passage is opened by the control valve, the high pressure gas is led into the control pressure chamber from the discharge chamber, and refrigerant gas is caused to flow out to the suction chamber from the control pressure chamber via the release passage, but the pressure of the control pressure chamber is increased, so that the discharge displacement of the compressor is controlled by the control valve adjusting the degree of opening of the supply passage. 
     At this time, when the passage cross-sectional area of the orifice passage is large, the amount of refrigerant gas caused to flow out to the suction chamber from the control pressure chamber via the release passage also increases, so that it is necessary to increase the amount of refrigerant gas to be led into the control pressure chamber from the discharge chamber, and when the passage cross-sectional area of the orifice passage is small, blow-by gas (gas wherein the refrigerant gas compressed in a compression chamber flows into the control pressure chamber via the clearance between the piston and a cylinder bore) stays in the control pressure chamber, and there is a disadvantage in that the piston cannot be fully stroked even when the supply passage is closed by the control valve. 
     In the meantime, when the compressor is at a stop for a long time without being put into operation, it happens that the pressure in a refrigeration cycle becomes balanced and the refrigerant in the refrigeration cycle is liquefied in a lowest temperature portion in the refrigeration cycle. The compressor is highest in heat capacity among the components configuring the refrigeration cycle and is hard to warm as following a change in outside temperature, so that the event of liquefaction of the refrigerant in the refrigeration cycle occurs in the compressor. Then, when the refrigerant is liquefied in the compressor, it happens that the liquid refrigerant also accumulates in the control pressure chamber. 
     When the compressor is started with the pressure balanced, the pressure of the suction chamber decreases by putting the compressor into operation, along with which the refrigerant in the control pressure chamber becomes exhausted into the suction chamber via the release passage. When the liquid refrigerant accumulates in the control pressure chamber, however, the inside of the control pressure chamber reaches equilibrium in which gas phase refrigerant and liquid phase refrigerant exist together, so that even though the refrigerant in the control pressure chamber is exhausted into the suction chamber via the release passage, it happens that the pressure of the control pressure chamber is maintained remaining as saturation pressure. Therefore, a disadvantage is known in that the pressure of the control pressure chamber does not decrease until all the liquid refrigerant is liquefied and exhausted from the release passage, hindering discharge displacement control from being carried out (impeding an increase in discharge displacement). 
     That is, when adopting a structure in which the control pressure chamber and the suction chamber are caused to communicate with each other by the release passage via the orifice passage, there is a disadvantage in that when the passage cross-sectional area of the orifice passage is large, it is necessary to lead a large amount of refrigerant gas into the control pressure chamber from the discharge chamber, resulting in a deterioration in the performance when at mid-stroke, while there is a problem in that when the passage cross-sectional area of the orifice passage is small, the refrigerant in the control pressure chamber cannot be swiftly exhausted into the suction chamber, leading to a deterioration in startability. 
     Therefore, a configuration such as shown in  FIG.  13    has heretofore been proposed in order to solve the above described problems (refer to PTL 1). 
     A first heretofore known technology shown in  FIG.  13    is such that a first control valve  104  which adjusts the degree of opening of a supply passage  103  is provided on the supply passage  103  which connects a discharge chamber  101  and a control pressure chamber  102 , and that a second control valve  107  is provided on a release passage  106  which connects the control pressure chamber  102  and a suction chamber  105 . The second control valve  107  is configured having a spool holding hollow portion  108  formed in a housing, a spool  109  movably housed in the spool housing hollow portion  108 , a rear pressure chamber  110  defined and formed in a portion of the spool holding hollow portion  108  in the rear of the spool  109 , and a biasing spring  112  which biases the spool  109  in a direction away from a valve plate  111 . The spool hosing hollow portion  108  and the suction chamber  105  are adjacent to each other, and a leakage into the suction chamber  105  from the rear pressure chamber  110  of the spool holding hollow portion  108  is kept small by the clearance between the inner wall of the spool holding hollow portion  108  and the spool  109 . Also, a constant aperture  113  is provided in a portion of the supply passage  103  on the downstream side of the first control valve  104 , and a configuration is such that an intermediate region K between the first control valve  104  and the constant aperture  113  is connected to the rear pressure chamber  110  via a branch passage  114 . 
     According to this kind of configuration, at the time of start-up when the difference between a pressure Pd of the discharge chamber  101  and a pressure Ps of the suction chamber  105  is small, the first control valve  104  puts the supply passage  103  into a fully closed state, closing off the communication between the discharge chamber  101  and the control pressure chamber  102 . Then, a pressure Pd′ of the intermediate region K of the supply passage  103  on the downstream side of the first control valve  104 , that is, the pressure of the rear pressure chamber  110  is maintained substantially equal to the pressure Pc of the control pressure chamber  102 , and the spool  109  puts the release passage  106  into a fully open state with the spring force of the biasing spring  112 . 
     As a result, even though liquid refrigerant accumulates in the control pressure chamber  102 , the pressure of the control pressure chamber  102  is caused to escape to the suction chamber  105  via the release passage with a high degree of opening, thereby enabling an early decrease in the pressure of the control pressure chamber  102  (shortening the time needed until the liquid refrigerant accumulating in the control pressure chamber  102  is all evaporated and exhausted into the suction chamber  105 ), and it is possible to avoid a disadvantage in that the time needed until discharge displacement control can be carried out is elongated. Consequently, the pressure Pc of the control pressure chamber  102  decreases swiftly by the first control valve  104  being fully closed, and the inclination angle of a swash plate increases swiftly, enabling an increase in discharge displacement. 
     Subsequently, when the difference between the pressure Pd of the discharge chamber  101  and the pressure Ps of the suction chamber  105  gradually comes to increase after the liquid refrigerant accumulating in the control pressure chamber  102  is all evaporated and exhausted into the suction chamber  105 , the fully closed state of the first control valve  104  is released, opening the supply passage  103 , and the pressure Pd′ of the intermediate region K (the pressure of the rear pressure chamber  110 ) becomes higher than the pressure Pc of the control pressure chamber  102 . Then, the spool  109  moves against the biasing spring  112  and comes closest to the valve plate  111 , and the release passage  106  comes into the state of being severely narrowed by a communication groove  109   a  formed in the leading end portion of the spool  109 . Consequently, the amount of refrigerant led out into the suction chamber  105  from the control pressure chamber  102  via the release passage  106  is greatly decreased, and the pressure Pc of the control pressure chamber  102  increases, leading to a decrease in the inclination angle of the swash plate, resulting in a decrease in the discharge displacement. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-2002-021721 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the heretofore known configuration described above, however, it is necessary, between the control valve and the control pressure chamber, to form two passages, which open into the control pressure chamber, in a cylinder block or a rear head, and to form the passage which, being the intermediate region K, is branched from the downstream side of the first control valve, and in order to thus form the passages, it is required to secure a sufficient region in the housing. Also, in order to reduce as much as possible the leakage of refrigerant into the suction chamber  105  from the intermediate region K, it is required to reduce the clearance between the spool holding hollow portion  108  and the spool  109 , and a disadvantage occurs in that when a foreign substance in the refrigerant intrudes into the clearance, the spool is prevented from sliding smoothly, the spool is immobilized and goes out of control, and so on. 
     When the clearance between the spool holding hollow portion  108  and the spool  109  is set large in order to avoid this kind of disadvantage, the amount of refrigerant leaking into the suction chamber  105  from the intermediate region K increases, resulting in a deterioration in the performance when at mid-stroke. 
     Therefore, the present invention has as its main object to provide a variable displacement compressor which includes a mechanism which, while preventing the movement of a valve element from being inhibited by a foreign substance in refrigerant, can suppress a leakage of the refrigerant into a suction chamber when supplying the refrigerant to a control pressure chamber from a discharge chamber via a supply passage and thus enhance the control performance when at mid-stroke. 
     Solution to Problem 
     In order to achieve the above-mentioned object, a variable displacement compressor according to the present invention comprises a compression chamber which compresses working fluid; a suction chamber which houses the working fluid to be compressed in the compression chamber; a discharge chamber which houses the working fluid compressed in and discharged from the compression chamber; a control pressure chamber which, having passed therethrough a drive shaft, houses a swash plate which rotates along with the rotation of the drive shaft; a supply passage which causes the discharge chamber and the control pressure chamber to communicate with each other; and a supply control valve which adjusts the degree of opening of the supply passage, wherein the pressure of the control pressure chamber is adjusted, thereby changing the swing angle of the swash plate, varying discharge displacement, and the variable displacement compressor is characterized in that 
     a branch passage which branches off from a portion of the supply passage on the downstream side of the supply control valve and communicates with the suction chamber is provided, that a release control valve which allows the working fluid to flow from the downstream side of the supply control valve to the control pressure chamber and which moves in response to a difference between the pressure of the downstream side of the supply control valve and the pressure of the control pressure chamber is provided on the supply passage, that the control pressure chamber and the branch passage can be caused to communicate with each other by way of a portion of the supply passage on the downstream side of the release control valve, and the degree of opening of the communication can be adjusted depending on the position of the release control valve, and that the release control valve, being provided on the supply passage and housed in a valve housing space to which the branch passage is connected, has a valve element including a valve body which, being disposed in the valve housing space so as to be movable in an axial direction thereof, varies the degree of opening of the communication between the control pressure chamber and the branch passage and a flange which seals between the valve body and the inner peripheral wall of the valve housing space by being abutted, in the axial direction of the valve housing space, against a shoulder formed on the inner peripheral wall of the valve housing space, wherein a configuration is such that the branch passage is covered by the valve body in a state in which the flange is abutted against the shoulder. 
     Consequently, the release control valve which moves in response to the differential pressure between the pressure of the downstream side of the supply control valve and the pressure of the control pressure chamber is provided on the supply passage, and the degree of opening which causes the control pressure chamber and the branch passage to communicate with each other by way of the portion of the supply passage on the downstream side of the release control valve can be adjusted depending on the position of the release control valve, so that when the pressure of the downstream side of the supply control valve is lower than the pressure of the control pressure chamber, the release control valve is moved by the differential pressure so as to increase the degree of opening of the portion which causes the control pressure chamber and the branch passage to communicate with each other, thereby enabling the pressure of the control pressure chamber to be swiftly exhausted into the suction chamber. 
     Also, when the pressure of the downstream side of the supply control valve is higher than the pressure of the control pressure chamber, the release control valve is moved by the differential pressure therebetween so as to decrease the degree of opening of the portion which causes the control pressure chamber and the branch passage to communicate with each other, and thereby it is possible to obtain the original function of the supply passage whereby the working fluid is caused to flow from the upstream side to the downstream side via the release control valve and led into the control pressure chamber. 
     At this time, the release control valve has the valve element, the flange of which is abutted, in the axial direction of the valve housing space, against the shoulder formed on the inner peripheral wall of the valve housing space, so that it is possible, even when the clearance around the valve element is set large, to reliably carry out a seal between the circumference of the valve element and the inner wall of the valve housing space by axial abutment between the shoulder and the flange, so that the valve element can be housed in the valve housing space with a sufficient clearance such as not to be clogged with a foreign substance. 
     Also, the valve element is such that the branch passage is covered with the valve body with the flange abutted against the shoulder, so that it is possible to eliminate or reduce the state of communication between the control pressure chamber and the branch passage, and possible to swiftly increase the pressure of the control pressure chamber. 
     In this way, according to the above described configuration, in order to secure the start-up performance of the compressor, there is no more need to form two passages, which communicate with the control pressure chamber, on the downstream side of the supply control valve, and the passages opening into the control pressure chamber can be integrated into one. 
     “The release control valve which moves in response to the differential pressure between the pressure of the downstream side of the supply control valve and the pressure of the control pressure chamber” means that the release control valve can move by changing of the pressure of the downstream side of the supply control valve and the pressure of the control pressure chamber which act on the release control valve, and this does not preclude pressure other than these from acting on the release control valve. 
     Here, a configuration may be such that a valve element fitting portion in which the downstream side end portion of the valve element can be fitted is formed in the end portion of the valve housing space to which is connected a portion of the supply passage on the downstream side of the valve housing space, and the flange is abutted against the shoulder, the downstream side end portion of the valve element is fitted in the valve element fitting portion. 
     In this kind of configuration, when the flange abuts the shoulder and the branch passage is covered by the valve body, the downstream side end portion of the valve element is fitted in the valve element fitting portion, so that it is possible to seal between the valve element and the valve element fitting portion with the downstream side portion of the valve element, and it is possible to further suppress the leakage of refrigerant into the suction chamber, and possible to effectively carry out the supply of the working fluid to the control pressure chamber from the downstream side of the supply control valve. 
     Also, a configuration may be such that the valve element includes inside an internal passage which allows the working fluid to flow from the downstream side of the supply control valve to the control pressure chamber, and that a sub-valve element which is biased in the direction of closing the internal passage from the downstream side is housed in the internal passage. 
     In this kind of configuration, the sub-valve element is housed in the internal passage of the valve element, and the sub-valve element is biased so as to close the internal passage from the downstream side, so that when the downstream side pressure of the supply control valve changes from low to high, it does not happen, before the valve element moves, that the sub-valve element moves in the direction of opening the internal passage against the biasing force, and it is possible to reliably abut the flange of the valve element against the shoulder of the valve housing space. 
     Then, after the flange of the valve element abuts the shoulder of the valve housing space, the sub-valve element which closes the internal passage is displaced against the biasing force, so that it is possible to further narrow the communication between the control pressure chamber and the branch passage, and possible to more effectively lead the working fluid on the downstream side of the supply control valve into the control pressure chamber. 
     Here, a configuration may be such that a sub-valve element fitting portion in which the downstream side end portion of the sub-valve element can be fitted is formed in the end portion of the valve housing space to which is connected a portion of the supply passage on the downstream side of the valve housing space, and that the downstream side end portion of the sub-valve element is fitted in the sub-valve element fitting portion with the sub-valve element positioned on the most downstream side of the valve element housing space. 
     In this kind of configuration, the branch passage is covered with the valve element, and the downstream side end portion of the sub-valve element is fitted in the sub-valve element fitting portion, enabling a seal between the sub-valve element and the sub-valve element fitting portion to be formed by the side surface of the downstream side end portion of the sub-valve element, so that it is possible to further reduce the leakage of refrigerant into the suction chamber. 
     Also, a configuration may be such that the sub-valve element, by axially abutting the perimeter of an end face opening into which the portion of the supply passage on the downstream side of the valve housing space opens, can seal the perimeter of the opening. In this kind of configuration, the perimeter of the end face opening into which the portion of the supply passage on the downstream side of the valve housing space opens is axially sealed by the downstream side end face of the sub-valve element, so that it is possible to effectively suppress the leakage of refrigerant into the suction chamber. 
     A configuration may be such that a communication passage which causes the internal passage to communicate continuously with the upstream side of the valve element is provided in the release control valve, and a configuration may also be such that a communication passage which causes the internal passage to communicate with the upstream side of the valve element is formed when the internal passage is closed. In these kinds of configurations, the upstream side of the valve element and the internal passage communicate continuously with each other, so that even when the internal passage is closed by the sub-valve element, it does not happen that the movement of the release control valve is inhibited. 
     Also, in order to adjust the movement of the valve element, a configuration may be such that a stopper which regulates the movement of the valve element is provided on the upstream side of the valve housing space. 
     Advantageous Effects of Invention 
     As described above, according to the present invention, the release control valve which is housed in the valve housing space provided on the supply passage has the valve element including the valve body which, being disposed in the valve housing space so as to be movable in the axial direction of the valve housing space, varies the degree of opening of the communication between the control pressure chamber and the branch passage; and the flange which is abutted, in the axial direction of the valve housing space, against the shoulder formed on the inner peripheral wall of the valve housing space, sealing between the valve body and the inner peripheral wall of the valve housing space, wherein a configuration is such that the branch passage is covered by the valve body in a state in which the flange of the valve element is abutted against the shoulder, so that even when the clearance between the valve element and the inner peripheral wall of the valve housing space is set large, it is possible, by abutting the shoulder against the flange, to secure the seal between the release control valve and the inner wall of the valve housing space, so that it is possible to, while preventing the movement of the valve element from being inhibited by a foreign substance in refrigerant, suppress the leakage of the refrigerant into the suction chamber when supplying the refrigerant to the control pressure chamber from the discharge chamber via the supply passage, and possible to enhance the control performance when at mid-stroke. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a sectional view showing a variable displacement compressor according to the present invention, and is a view showing the state of the compressor when at a stop and at the initial stage of start-up. 
         FIG.  2    is a sectional view showing the variable displacement compressor according to the present invention, and is a view showing the state when at full stroke. 
         FIG.  3    is a sectional view showing the variable displacement compressor according to the present invention, and is a view showing the state when under discharge displacement control at mid-stroke. 
         FIG.  4    is a sectional view showing the variable displacement compressor according to the present invention, and is a view showing the state when in OFF operation. 
         FIG.  5 ( a )  is a view showing an end face of a cylinder block facing a valve plate, and  FIG.  5 ( b )  is a sectional view seen from the line K-K of  FIG.  5 ( a ) . 
         FIGS.  6 ( a ) and  6 ( b )  are views showing a release control valve, wherein  FIG.  6 ( a )  is a sectional view showing the state of the release control valve provided on a supply passage, and  FIG.  6 ( b )  is an exploded perspective view showing component parts. 
         FIGS.  7 ( a ) to  7 ( d )  are views showing operating conditions of the release control valve, wherein  FIG.  7 ( a )  is a view showing the state of the compressor when at a stop, at the initial stage of start-up, and when in maximum discharge displacement operation,  FIG.  7 ( b )  is a view showing the state in which when the compressor is in displacement control operation, a flange of a valve element is in abutment with a shoulder, closing an internal passage of the valve element with a sub-valve element,  FIG.  7 ( c )  is a view showing the state in which when the compressor is in displacement control operation, the flange of the valve element is in abutment with the shoulder, and the downstream side end portion of the sub-valve element starts to fit in a sub-valve element fitting portion, and  FIG.  7 ( d )  is a view showing the state in which when the compressor is in displacement control operation, the flange of the valve element is in abutment with the shoulder, and the downstream side end portion of the sub-valve element is in abutment with the bottom surface of the sub-valve element fitting portion. 
         FIG.  8    is a comparison table into which supply control valve state, piston stroke, valve element position, and sub-valve element position are compiled for each operation mode of the compressor. 
         FIG.  9    is a sectional view showing a modification example of the release control valve. 
         FIGS.  10 ( a ) to  10 ( c )  are views showing another example of the release control valve, wherein  FIG.  10 ( a )  is a sectional view showing the state in which the release control valve is provided on the supply passage,  FIG.  10 ( b )  is an enlarged sectional view showing the state in which the top wall of the valve element and the tope wall of the sub-valve element are in abutment with each other, and  FIG.  10 ( c )  is a perspective view showing a valve element used in the release control valve of  FIG.  10 ( a ) . 
         FIGS.  11 ( a ) and  11 ( b )  are views showing still another example of the release control valve, wherein  FIG.  11 ( a )  is a sectional view showing the state in which the release control valve is provided on the supply passage, and  FIG.  11 ( b )  is an enlarged sectional view showing the state in which the top wall of the valve element and the top wall of the sub-valve element are in abutment with each other. 
         FIGS.  12 ( a ) and  12 ( b )  are views showing still another example of the release control valve, wherein  FIG.  12 ( a )  is a sectional view showing the state in which the release control valve is provided on the supply passage, and  FIG.  12 ( b )  is an enlarged sectional view showing the state in which the top wall of the valve element and the top wall of the sub-valve element are in abutment with each other. 
         FIG.  13    is a view showing a heretofore proposed configuration of the variable displacement compressor. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a description will be given, while referring to the accompanying drawings, of an embodiment of the present invention. 
       FIGS.  1  to  4    show a clutchless type variable displacement compressor which is belt driven by a power source such as an engine. The variable displacement compressor is configured having a cylinder block  1 , a rear head  3  assembled on the rear side (the right side in the drawings) of the cylinder block  1  via a valve plate  2 , and a front housing  5  which, being assembled so as to close the front side (the left side in the drawings) of the cylinder block  1 , defines a control pressure chamber  4 , wherein the front housing  5 , cylinder block  1 , valve plate  2 , and rear head  3  are axially fastened by a fastening bolt  6 , configuring the housing of the compressor. 
     A drive shaft  7 , one end of which protrudes from the front housing  5 , passes through the control pressure chamber (also referred to as a crankcase)  4  which is demarcated by the front housing  5  and the cylinder block  1 . A drive pulley which is rotatably fitted onto a boss portion  5   a  of the front housing  5  via a not-shown relay member is connected to a portion of the drive shaft  7  which protrudes from the front housing  5 , and a configuration is such that rotary power is transmitted from the engine of a vehicle via a drive belt. Also, the one end side of the drive shaft  7 , a portion of which between the drive shaft  7  and the front housing  5  is hermetically sealed via a seal member  8  provided between the drive shaft  7  and the front housing  5 , is rotatably supported by a radial bearing  9 , and the other end of the drive shaft  7  is rotatably supported by a radial bearing  11  housed in a housing bore  10  formed substantially in the center of the cylinder block  1 . 
     As also shown in  FIGS.  5 ( a ) and  5 ( b ) , the housing bore  10 , in which the radial bearing  11  is housed, and a plurality of cylinder bores  15 , which are disposed at even intervals on a circumference centered on the housing bore  10 , are formed in the cylinder block  1 , and a single head piston  16  is reciprocally slidably inserted in each of the cylinder bores  15 . 
     A thrust flange  17  which rotates integral with the drive shaft  7  in the control pressure chamber  4  is securely provided on the drive shaft  7 . The thrust flange  17  is rotatably supported on the inner surface of the front housing  5  via a thrust bearing  18 , and a swash plate  20  is connected to the thrust flange  17  via a link member  19 . 
     The swash plate  20 , being provided so as to be tiltable about a hinge ball  21  slidably provided on the drive shaft  7 , is configured to rotate integral in synchronism with the rotation of the thrust flange  17  via the link member  19 . Then, an engaging portion  16   a  of the single head piston  16  is anchored to a peripheral edge portion of the swash plate  20  via a pair of shoes  22 . 
     Consequently, a configuration is such that when the drive shaft  7  rotates, the swash plate  20  rotates along therewith, and that the rotary motion of the swash plate  20  is converted to reciprocal linear motion of the single head piston  16  via the shoes  22 , changing the volume of a compression chamber  23  formed between the single head piston  16  and the valve plate  2  in the cylinder bore  15 . 
     A suction port  31  and a discharge port  32  are formed in the valve plate  2  so as to correspond to each of the cylinder bores  15 , and a suction chamber  33 , in which is housed working fluid to be compressed in the compression chamber  23 , and a discharge chamber  34 , in which is housed the working fluid compressed in and discharged from the compression chamber  23 , are demarcated in the rear head  3 . The suction chamber  33 , being formed in the central portion of the rear head  3 , can communicate with a not-shown inlet communicating with the outlet side of an evaporator and can communicate with the compression chamber  23  via the suction port  31  which is opened/closed by a not-shown suction valve. Also, the discharge chamber  34 , being formed around the suction chamber  33 , can communicate with the compression chamber  23  via the discharge port  32  which is opened/closed by a not-shown discharge valve. The discharge chamber  34  communicates with a discharge space  35  formed in the circumference of the cylinder block  1  via passages  2   a  and  1   a  which are formed respectively in the valve plate  2  and the cylinder block  1 . The discharge space  35  is defined by the cylinder block  1  and a cover  36  attached thereto, and an outlet  37  communicating with the inlet side of a condenser is formed in the cover  36 , while a discharge check valve  38  which prevents refrigerant flowing rearward from the condenser to the discharge space  35  is provided in the cover  36 . 
     The discharge displacement of the compressor is determined by the stroke of the piston  16 , and the stroke is determined by an inclination angle of the swash plate  20  to a plane perpendicular to the drive shaft  7 . The inclination angle of the swash plate  20  balances itself at an angle at which zero is the sum of the moment derived from the differential pressure between the pressure of the compression chamber  23  (the pressure in the cylinder bore) acting on each of the pistons  16  and the pressure of the control pressure chamber  4 , the moment derived from the inertial forces of the swash plate  20  and the piston  16 , and the moment derived from the biasing forces of a destroking spring  24  and a stroking spring  25  which bias the hinge ball  21 . A configuration is such that the piston stroke is thereby determined, thus determining the discharge displacement. 
     That is, when a pressure Pc of the control pressure chamber  4  increases and the differential pressure between the compression chamber  23  and the control pressure chamber  4  decreases, the moment acts in the direction of reducing the inclination angle of the swash plate  20 . Consequently, as shown in  FIG.  1   , when the inclination angle of the swash plate  20  decreases, the hinge ball  21  moves in the direction away from the thrust flange  17 , and the amount of stroke of the piston  16  decreases, reducing the discharge displacement. 
     On the contrary, when the pressure Pc of the control pressure chamber  4  decreases, the differential pressure between the compression chamber  23  and the control pressure chamber  4  increases, so that the moment acts in the direction of increasing the inclination angle of the swash plate  20 . Consequently, as shown in  FIG.  2  or  3   , when the inclination angle of the swash plate  20  increases, the hinge ball  21  moves to the thrust flange side against the biasing force from the destroking spring  24 , and the amount of stroke of the piston  16  increases, increasing the discharge displacement. 
     Then, in the present configuration example, a supply passage  40  which causes the discharge chamber  34  and the control pressure chamber  4  to communicate with each other is formed by passages  1   b ,  2   b , and  3   a  formed respectively in the cylinder block  1 , the valve plate  2 , and the rear head  3 . Also, an release passage  41  is formed which causes the control pressure chamber  4  and the suction chamber  33  to communicate with each other via the housing bore  10  formed in the cylinder block  1 , an orifice  2   c  which, being formed in the valve plate  2 , communicates with the housing bore  10 , a passage  7   a  formed in the drive shaft  7 , and the like. 
     A supply control valve  42  is provided on the supply passage  40 , adopting a configuration such that the flow rate of refrigerant flowing into the control pressure chamber  4  from the discharge chamber  34  via the supply passage  40  is adjusted by the supply control valve  42 , controlling the pressure of the control pressure chamber  4 . In this example, the supply control valve  42 , having a solenoid coil (not shown), is configured so as to be able to adjust the degree of opening of the supply passage  40  based on the amount of energization of the solenoid coil. 
     Here, the supply control valve  42 , being fitted in the rear head  3 , adjusts the degree of opening of the supply passage  40  so that a suction pressure Ps reaches a target value, controlling the pressure Pc of the control pressure chamber  4 , and the supply control valve  42 , by stopping the energization, puts the supply passage  40  into a fully open state, increasing the pressure of the control pressure chamber  4  and minimizing the discharge displacement. Also, at the initial stage of start-up, the supply control valve  42 , by maximizing the amount of energization (raising a duty ratio to 100%), carries out the operation of, for example, putting the supply control valve  42  into a closed state and stopping the supply of pressure to the control pressure chamber  4 . 
     Consequently, when the energization of the supply control valve  42  is at a stop with the compressor being rotary driven, an internal circulation pathway is formed in which the refrigerant discharged from the compression chamber  23  into the discharge chamber  34  circulates in the compressor by flowing through the supply passage  40  (the supply control valve  42  exists on the way), the control pressure chamber  4 , the release passage  41 , the suction chamber  33 , the suction port  31 , the compression chamber  23 , and the discharge port  32  in this order, and returns again to the discharge chamber  34 . A configuration is such that refrigerant gas which circulates through the internal circulation pathway lubricates and cools slide portions inside the compressor. 
     In this kind of compressor, a valve housing space  50  is formed in a portion of the supply passage  40  on the downstream side of the supply control valve  42 , and a release control valve  51  is slidably housed in the valve housing space  50 . 
     In this example, the valve housing space  50 , as also shown in  FIGS.  5 ( a ) and  5 ( b ) , is extended substantially parallel to the drive shaft  7  from an end face of the cylinder block  1  which faces the valve plate  2 , and the upstream end (the open end facing the valve plate) of the valve housing space  50  communicates with the through hole  2   b  which, being formed in the valve plate  2 , configures one portion of the supply passage  40 , while the downstream end portion of the valve housing space  50  is connected to the passage  1   b  communicating with the control pressure chamber  4 . Also, a relay passage  1   d  connected to a recess  1   c  which, being formed in the cylinder block  1 , communicates with the suction chamber  33  in the rear head  3  is connected to the vicinity of the downstream end of the valve housing space  50 . The relay passage  1   d  is drilled obliquely to the valve housing space  50  by a drill inserted in via the recess  1   c , and a branch passage  43  which branches off from the portion of the supply passage  40  on the downstream side of the supply control valve  42  and communicates with the suction chamber  33  is formed by the relay passage  1   d , the recess  1   c  in the cylinder block  1 , and a through hole  2   d  formed in the valve plate  2 . 
     The release control valve  51 , as also shown in  FIGS.  6 ( a ) and  6 ( b ) , being slidably disposed in the valve housing space  50 , is configured having a valve element  60  which moves axially along the inner wall of the valve housing space and a sub-valve element  70  which is axially movable inside the valve element  60 . 
     The upstream side (the valve plate side) of the valve housing space  50  is formed to be larger in inner diameter than the downstream side thereof, wherein the upstream side of the valve housing space  50  is formed as an enlarged-in-diameter portion  50   a , and the downstream side as a reduced-in-diameter portion  50   b . Then, a shoulder  52  formed on a plane substantially perpendicular to the axial direction of the valve housing space  50  is formed in the transition between the enlarged-in-diameter portion  50   a  and the reduced-in-diameter portion  50   b.    
     A cylindrical stopper  53  which is press-fit inserted from the upstream side open end is fixed in the enlarged-in-diameter portion  50   a . The stopper  53 , not being provided in the whole region of the enlarged-in-diameter portion  50   a , is fixed spaced a predetermined dimension from the shoulder  52 . Also, the branch passage  43  is connected so as to open into a portion of the inner peripheral surface in the vicinity of the downstream end of the reduced-in-diameter  50   b , and the release passage  40  (the passage  1   b ) on the downstream side of the valve housing space  50  is connected so as to open into the axial end face of the reduced-in-diameter portion  50   b.    
     The valve element  60  is formed of a cylindrical (for example, circular cylindrical) valve body  62 , which has inside an axially extended internal passage  61 , and a flange  63  which protrudes radially outward from all around the circumferential edge of the upstream side (the valve plate side) end portion of the valve body  62 . The valve body  62  is formed to have an outer diameter which can obtain a sufficient clearance with the reduced-in-diameter portion  50   b , that is, an outer diameter such as not to affect the movement of the valve element  60  even when an contaminant intrudes between the valve body  62  and the reduced-in-diameter portion  50   b . Also, the flange  63 , being disposed between the stopper  53  and the shoulder  52 , has a sufficient clearance with the enlarged-in-diameter portion  50   a , but comes into an axial surface-to-surface contact with the shoulder  52 , adopting a configuration such as to form a flat seal between the flange  63  and the shoulder  52 . 
     Also, the valve body  62  is set to a length such as to cover the whole of an opening portion, to which the branch passage  43  is connected, in a state in which the flange  63  is abutted against the shoulder  52 . Furthermore, a valve element fitting portion  54  in which the downstream side end portion of the valve element  60  can fit is formed in an end portion of the valve housing space  50  to which is connected a portion (the passage  1   b ) of the supply passage  40  on the downstream side of the valve housing space  50 , and the valve element  60  is configured so that the downstream side end portion thereof is fitted in the valve element fitting portion  54  in a state in which the flange  63  is abutted against the shoulder  52 . 
     Consequently, the valve element  60  is configured such that the valve element  60  can move from the state in which the flange  63  abuts the stopper  53 , restricting the movement of the valve element  60  to the upstream side, and the degree of opening of the branch passage  43  is maximized (the state in which the degree of opening which causes the control pressure chamber  4  and the branch passage  43  to communicate with each other by way of a portion of the supply passage  40  on the downstream side of the release control valve  51 ) to the state in which the flange  63  abuts the shoulder  52 , covering the branch passage  43  with the valve body  62  and fitting the downstream side end portion of the valve element  60  in the valve element fitting portion  54 . 
     Also, a top wall  64  is provided in an end portion of the valve body  62  on which the flange  63  is formed. A plurality of through holes  65  (in this example, three through holes) which are provided at circumferentially spaced intervals in portions facing the internal passage  61  are formed in the top wall  64 . Also, an orifice  66  which connects the internal passage  61  and the upstream side (that is, the intermediate region on the downstream side of the supply control valve  42 ) of the valve element  60  is formed in the center of the top wall  64 . 
     The sub-valve element  70  provided inside the valve element  60 , being provided so as to be axially movable in the internal passage  61  of the valve element  60 , includes a valve body  72  which is formed in a cylinder having inside an internal passage  71 . The downstream end of the sub-valve element is widely opened in the same way as in the valve element  60 , and a top wall  74 , in the center of which a through hole  73  is formed, is formed in an end portion of the sub-valve element facing the top wall  64  of the valve element  60 . Thereby, with the outer surface of the top wall  74  of the sub-valve element  70  in abutment with the inner surface of the top wall  64  of the valve element  60 , the through holes  65  formed in the top wall  64  of the valve element  60  are closed by the top wall  74  of the sub-valve element  70 . Also, the inner side of the sub-valve element  70  is in continuous communication with the upstream side of the valve element  60  via the through hole  73  formed in the center of the top wall  74  of the sub-valve element  70  and via the orifice  66  provided in the top wall  64  of the valve element  60 . The orifice  66  configures a communication passage which causes the internal passage  61  of the valve element  60  to communicate continuously with the upstream side of the valve element  60 . 
     Also, a sub-valve element fitting portion  55  in which the downstream side end portion of the sub-valve element  70  can fit is formed in an end portion of the valve housing space  50  to which is connected the portion (the passage  1   b ) of the supply passage  40  on the downstream side of the valve housing space  50 . The sub-valve element fitting portion  55  is formed to have an inner diameter substantially equal to the outer diameter of the valve body  72  of the sub-valve element  70 , and a configuration is such that the downstream side end portion of the sub-valve element  70  is fitted in the sub-valve element fitting portion  55  with the sub-valve element  70  positioned on the most downstream side of the valve housing space  50 . 
     Then, in this example, a compression spring  56  is elastically installed inside the sub-valve element  70 . The compression spring  56  is configured so that one end thereof is received by the perimeter of the opening portion in which the supply passage  40  (the passage  1   b ) on the downstream side of the valve housing space  50  is connected to the valve housing space  50 , and that the other end, being disposed inside the sub-valve element  70 , is received by the perimeter of the through hole  73  in the top wall  74  of the sub-valve element  70 . 
     Consequently, when an upstream side pressure Pce of the valve element  60  is substantially equal to the downstream side pressure Pc, the top wall  74  of the sub-valve element  70  abuts the top wall  64  of the valve element  60  with the biasing force of the compression spring  56 , closing the through holes  65  in the valve element  60  with the top wall  74  of the sub-valve element  70 , and the valve element  60  and the sub-valve element  70  are displaced in an integrated manner. On the contrary, when the upstream side pressure Pce of the valve element  60  is higher than the downstream side pressure Pc, and the difference in pressure between the front and the rear of the valve element is larger than the biasing force of the compression spring  56 , the valve element  60  and the sub-valve element  70  are displaced integrally until the flange  63  of the valve element  60  abuts the shoulder  52 . After that, when the flange  63  of the valve element  60  abuts the shoulder  52 , regulating the movement of the valve element  60 , the upstream side pressure Pce of the valve element  60  acts on the sub-valve element  70  via the through holes  65 , so that the sub-valve element  70  is further depressed against the spring force of the compression spring  56 . When the depression pressure is high, the downstream side end portion of the sub-valve element  70  fits in the sub-valve element fitting portion  55 , forming a seal between the outer peripheral surface of the downstream side end portion of the sub-valve element  70  and the inner peripheral surface of the sub-valve element fitting portion  55 . Also, a configuration is such that when the sub-valve element  70  abuts the bottom surface of the sub-valve element fitting portion  55 , a flat seal is formed between the downstream side end surface of the sub-valve element  70  and the bottom surface of the sub-valve element fitting portion  55 . 
     In the above configuration, with the compressor at a stop for a long time (when the engine stops), a pressure Pd of the discharge chamber  34 , the pressure Pc of the control pressure chamber  4 , and a pressure Ps of the suction chamber  33  are substantially equal to each other, and liquefied refrigerant stays retained in the control pressure chamber  4 . Also, the supply control valve  42  is in a fully open state as the energization stops, so that the pressure (the supply control valve downstream pressure Pce) of the intermediate region of the supply passage  40  on the downstream side of the supply control valve  42  (the region of the supply passage  40  between the supply control valve  42  and the release control valve  51 ) is also substantially equal to the pressure Pc of the control pressure chamber  4 . In this state, as shown in  FIG.  1   , the swash plate  20  is biased by the biasing forces of the destroking spring  24  and the stroking spring  25  so that the inclination angle to a plane perpendicular to the drive shaft  7  decreases, and as shown in  FIG.  7 ( a ) , the sub-valve element  70  abuts the top wall  64  of the valve element  60  with the spring force of the compression spring  56 , closing the through holes  65  in the valve element  60  with the top wall  74  of the sub-valve element  70 , putting the internal passage  61  into the state of being closed from the downstream side. Also, the valve element  60  is also biased by the compression spring  56  via the sub-valve element  70 , so that the flange  63  comes into abutment with the stopper  53 . Consequently, as also shown in  FIG.  8    “Engine stop”, the downstream side leading end portion of the valve element and the downstream side valve element portion of the sub-valve element  70  come into an open state in which neither of them is sealed, and the degree of opening of the communication between the control pressure chamber  4  and the branch passage  43  is highest. 
     When the engine of the vehicle is started in this state, even with the energization of the supply control valve  42  stopped, the rotary power of the engine is transmitted to the drive pulley of the compressor via the drive belt, rotating the drive shaft  7  of the compressor, and the piston  16  reciprocates in the cylinder bore  15  with a short stroke. Thereby, a small amount of refrigerant is discharged into the discharge chamber  34 , but the supply control valve  42  keeps the supply passage  40  in an open state, so that the pressure Pce of the intermediate region of the supply passage  40  on the downstream side of the supply control valve  42  increases, displacing the valve element  60 , together with the sub-valve element  70 , against the spring force of the compression spring  56 , and bringing the flange  63  of the valve element  60  into abutment with the shoulder  52 , and at the same time, the downstream side end portion of the valve element  60  fits in the valve element fitting portion  54 . Subsequently, after the flange  63  of the valve element  60  abuts the shoulder  52 , the pressure Pce of the intermediate region acts on the top wall of the sub-valve element  70  via the through holes  65  in the valve element  60 , so that the sub-valve element  70  is further displaced against the spring force of the compression spring  56 , and the top wall  74  of the sub-valve element  70  comes out of contact with the top wall  64  of the valve element  60 , releasing the pressure Pce of the intermediate region to the downstream side of the release control valve  51  via the respective internal passages  61  and  71  of the valve and sub-valve elements  60  and  70 . Therefore, the refrigerant discharged into the discharge chamber  34  is all led to the control pressure chamber  4  via the supply passage  40  and circulates in the compressor via the previously described internal circulation pathway, and no refrigerant is supplied to an external refrigeration cycle. 
     After that, when an air conditioning unit of the vehicle is switched on, the energization of the supply control valve  42  is started, and the supply passage  40  comes into a closed state (the supply control valve  42  comes into a closed state), there is no more flow of refrigerant into the suction chamber  33  via the internal circulation cycle, so that the pressure Ps of the suction chamber  33  decreases slightly. At this time, the control pressure chamber  4  is supplied with no more refrigerant from the discharge chamber  34  via the supply passage  40 , but the liquid refrigerant accumulating in the control pressure chamber  4  continues to be evaporated, so that the pressure Pc of the control pressure chamber  4  comes into the state of being maintained instead of being decreased. 
     On the other hand, the intermediate region between the supply control valve  42  and the release control valve  51  is such that the supply of refrigerant from the discharge chamber  34  into the region is suspended by the supply control valve  42 , and that the pressure in the region is released to the control pressure chamber  4  via the orifice  66  formed in the valve element  60  and via the portion (the passage  1   b ) of the supply passage  40  on the downstream side of the release control valve  51 . That is, the pressure of the intermediate region (the supply control valve downstream pressure Pce) is substantially equal to the pressure Pc of the control pressure chamber  4 . As a result, as shown in  FIGS.  1 ,  7   ( a ), and  8  “Initial stage of start-up (when liquid refrigerant stagnates)”, the sub-valve element  70  in the release control valve  51  is maintained in the position in which the through holes  65  in the valve element  60  are put into a closed state by the biasing force of the compression spring  56 , and the valve element  60  comes into abutment with the stopper  53 . That is, when the downstream side pressure of the supply control valve (the supply control valve downstream pressure Pce) is substantially equal to the pressure Pc of the control pressure chamber  4 , the valve element  60  and the sub-valve element  70  are maintained in the position in which the degree of opening of the branch passage  43  is maximized. Thereby, the vaporized refrigerant in the control pressure chamber  4  is caused to flow out to the suction chamber  33  through the portion (the passage  1   b ) of the supply passage  40  on the downstream side of the release control valve  51  and through the branch passage  43 . 
     In this way, while the liquid refrigerant accumulating in the control pressure chamber  4  is evaporating, the vaporized refrigerant continues to be caused to flow out to the suction chamber  33  via the branch passage  43  in addition to via the heretofore known release passage  41  through which the vaporized refrigerant flows via the orifice  2   c , so that the refrigerant in the control pressure chamber  4  can be caused to escape swiftly to the suction chamber  33  via two lines: the release passage  41  and the branch passage  43 , enabling an early decrease in the pressure Pc of the control pressure chamber  4  (a disadvantage of taking a long time until discharge displacement control can be carried out can be avoided by shortening the time needed until the liquid refrigerant accumulating in the control pressure chamber  4  all evaporates and is discharged into the suction chamber  33 ), a swift increase in the inclination angle of the swash plate  20 , and an increase in the discharge displacement. 
     After that, the liquid refrigerant accumulating in the control pressure chamber  4  all evaporates and is discharged into the suction chamber  33 , whereby the refrigerant in the control pressure chamber escapes from saturation, and the pressure Pc of the control pressure chamber  4  starts to decrease. Thereby, the discharge displacement of the compressor starts to increase, and the discharge check valve  38  comes into an open state, supplying sufficient refrigerant to the external refrigeration cycle, leading to a gradual decrease in the temperature of the evaporator of the refrigeration cycle, and resulting in a decrease in the pressure Ps of the suction chamber  33 . At this time, the supply control valve  42  still keeps the supply passage  40  in a closed state (refer to  FIGS.  2 ,  7   ( a ), and  8  “when in Maximum displacement operation”), so that no refrigerant gas is supplied to the control pressure chamber  4  by way of the supply passage  40 , but one portion of the refrigerant gas compressed in the cylinder flows into the control pressure chamber  4  via the clearance between the cylinder bore  15  and the piston  16  (so-called blow-by gas), so that it is necessary to cause the blow-by gas to escape to the suction chamber  33 . Therefore, in the case of a compressor which does not include the branch passage  43 , it has been necessary to increase the area of the orifice  2   c  to a certain degree in order to enable the blow-by gas to escape fully to the suction chamber  33  through only the heretofore known release passage  41  through which the gas flows via the orifice  2   c , but in the present example, the release control valve  51  can cause the blow-by gas to escape to the suction chamber  33  via the open branch passage  43 , so that the area of the orifice  2   c  is set to be relatively small. 
     Then, when the cooling capacity in the evaporator reaches a sufficient value, the amount of energization of the supply control valve  42  is adjusted, opening the supply passage  40  (opening the supply control valve  42 ), and the refrigerant in the discharge chamber  34  is supplied to the control pressure chamber  4  via the supply passage  40 . At this time, the release control valve  51  is provided in the portion of the supply passage downstream of the supply control valve  42 , but the refrigerant led up to the release control valve  51  from the discharge chamber  34  via the supply control valve  42 , passing through the through holes  65 ,  73  and the internal passages  61 ,  71 , which are formed in the release control valve, flows into the control pressure chamber  4 . 
     Flow resistance generated when the refrigerant gas passes through the release control valve causes the difference in pressure between the upstream and downstream sides of the release control valve  51 , so that the release control valve  51  is biased to the downstream side in the figure by the difference in pressure, pressing the flange  63  of the valve element  60  against the shoulder  52 , and the branch passage  43  is closed by the valve body  62  (the degree of opening of the branch passage  43  is minimized). 
     In this state, the flange  63  of the valve element  60  is axially abutted against the shoulder  52 , so that a good sealed state of the valve element  60  is formed by the shoulder  52 , and it will not happen that the refrigerant flows around the outside of the valve element  60  and leaks into the branch passage  43  from the clearance between the valve element  60  and the inner wall of the valve housing space  50 . Therefore, it is not necessary to keep tight control over the clearance between the valve element  60  and the inner wall of the valve housing space  50 , and there is no specific disadvantage even though the clearance is set to the extent that the movement of the valve element  60  is not inhibited by contaminant intrusion. 
     Also, in this example, a check valve  75  is formed inside the valve element  60  by the sub-valve element  70  and the compression spring  56  which biases the sub-valve element  70  in the direction of closing the internal passage  61  (in the direction against the flow of refrigerant). As shown in  FIGS.  3 ,  7   ( b ) to  7 ( d ), and  8  “Displacement control operation”, the sub-valve element  70  moves in the direction of opening the through holes  65  against the spring force of the compression spring  56 , putting the check valve  75  into an open state, and at the same time, the downstream side end portion of the sub-valve element  70  moves in the direction of fitting in the sub-valve element fitting portion  55 . Therefore, with the branch passage  43  closed by the valve body  62  of the valve element  60 , when the clearance between the valve body  62  and the valve housing space  50  is set to be large, the amount of refrigerant leaking into the branch passage  43  increases, but when the downstream side end portion of the sub-valve element  70  (the valve body  72 ) reaches the sub-valve element fitting portion  55 , a seal is formed between the downstream side end portion of the sub-valve element  70  and the inner peripheral surface of the sub-valve element fitting portion  55 , and furthermore, when the downstream side end face of the sub-valve element  70  abuts the bottom surface of the sub-valve element fitting portion  55 , a flat seal is formed in this end face portion, so that as shown in  FIGS.  7 ( c ) and  7 ( d ) , it is possible to form a plurality of portions with high passage resistance in the pathway from the downstream side of the release control valve  51  to the branch passage  43 , and possible to gradually narrow the flow of refrigerant from the downstream side of the release control valve  51  to the branch passage  43 . 
     Also, the configuration wherein the check valve  75  is provided in the flow path in the release control valve  51  works so that a substantially constant difference in pressure is caused between the front and the rear of the release control valve, in response to the set load of the compression spring  56 , regardless of the amount of refrigerant passing through the supply passage  40 . That is, even when the refrigerant passing through the supply passage  40  is small in amount, the supply control valve downstream pressure Pce (the release control valve upstream pressure) can be reliably made higher than the control pressure chamber pressure Pc (the release control valve downstream side pressure), as a result of which the flange  55  of the valve element  60  can be reliably pressed against the shoulder  52 . Conversely, even when the refrigerant passing through the supply passage  40  is large in amount, the refrigerant gas can be caused to pass through the inside of the release control valve  51  only by causing a difference in pressure corresponding to the open valve pressure of the check valve  75 , as a result of which it does not happen that the supply of refrigerant gas to the control pressure chamber is impaired. 
     Consequently, the refrigerant in the control pressure chamber  4  is exhausted into the suction chamber  33  only via the release passage  41 , and high pressure gas is supplied to the control pressure chamber  4  via the supply passage  40  with the amount of refrigerant to be caused to flow out to the suction chamber  33  from the control pressure chamber  4  being considerably reduced, so that the pressure Pc of the control pressure chamber  4  increases swiftly, and the inclination angle of the swash plate  20  decreases swiftly, reducing the discharge displacement. Furthermore, as described above, the area of the orifice  2   c  in the release passage  41  is set to be relatively small compared with in the heretofore known, so that the pressure Pc of the control pressure chamber  4  can be increased by leading in a smaller amount of high pressure gas, and it is possible to reduce the internal circulation amount of refrigerant while in displacement control operation. 
     When an idle state is reached from when in maximum displacement operation or when in displacement control operation, as shown in  FIGS.  4 ,  7   ( d ), and  8  “Clutchless off operation”, in order to minimize the discharge displacement of the compressor, the supply control valve  42  is fully opened, and the high pressure refrigerant is supplied to the control pressure chamber  4  from the discharge chamber  34  via the supply passage  40 , minimizing the piston stroke. 
     In this way, it is possible to respond to individual operation modes by controlling the opening/closing of the supply passage  40  and the opening/closing of the branch passage  43  using the release control valve  51  and its inside check valve  75  which operate in response to the difference between the pressure Pce of the supply passage  40  on the downstream side of the supply control valve  42  (the supply control valve downstream pressure) and the pressure Pc of the control pressure chamber, so that it is not necessary that two passages communicating with the control pressure chamber  4  are formed on the downstream side of the supply control valve  42  in order to enhance the start-up performance of the compressor, and the passages opening into the control pressure chamber  4  can be integrated into one, enabling a reduction in the housing region required to form the passages and enabling a simplification in structure. 
     The above described configuration shows an example wherein in order to cause the difference in pressure between upstream and downstream of the release control valve  51 , the check valve  75 , being provided inside the release control valve  51 , is configured by the sub-valve element  70  which slides in the internal passage  61  of the valve element  60  and the compression spring  56  elastically installed between the sub-valve element  70  and the downstream side end face of the valve housing space  50 , but as shown in  FIG.  9   , a structure may be adopted in which the sub-valve element  70  and the compression spring  56  are housed inside the valve element  60  without being protruded outward from the valve element  60 . In this kind of configuration, means which biases the valve element  60  to the stopper  53  side does not have to be provided, but when the movement of the valve element  60  is not stable, the compression spring  59  which biases the valve element  60  to the stopper  53  side may be provided in the valve housing space  50  as needed. 
     Also, the above described example shows an example wherein the stopper  53  which regulates the movement of the valve element  60  is provided in the valve housing space  50 , but in the event that there is no specific disadvantage in processing the relay passage  1   d  which configures the branch passage  43 , the stopper  53  is omitted and may be substituted by the valve plate  2  or the like. 
     Furthermore, in the above described example, a configuration is such that the valve housing space  50  is provided in the cylinder block  1  and the release control valve  51  is housed in the valve housing space  50 , but the above described release control valve may be provided anywhere on the supply passage and may be provided in a portion of the rear head  3  in which the valve housing space  50  communicating with the suction chamber  33  can be formed. 
     Meanwhile, in the above configuration, the orifice  66  is provided in the top wall  64  of the valve element  60 , causing the internal passage  61  of the valve element  60  and the upstream side of the valve element  60  to communicate continuously with each other, thereby adopting a configuration such as not to inhibit the movement of the release control valve  51  (the valve element  60 ) even when the internal passage  61  (the through holes  65 ) is closed by the sub-valve element  70 , that is, even when the outer surface of the top wall  74  of the sub-valve element  70  is in abutment with the inner surface of the top wall  64  of the valve element  60 , but high-precision processing is required in forming an appropriate small diameter orifice in the top wall  64 , causing the disadvantage of a decrease in productivity. 
     Hence, in order to realize a similar function, as shown in  FIGS.  10 ( a ) to  10 ( c ) , a configuration may be such that arc-like through holes  65  are formed along a virtual circle centered on the center of the top wall  64  without providing an orifice in the top wall  64  of the valve element  60 , and a distance R 1  from the center of the top wall  64  to the inner circumferential edge of the through hole  65  is made slightly smaller than a radius R 2  of the through hole  73  formed in the top wall  74  of the sub-valve element  70  (R 2 −R 1 =α), and that as also shown in  FIG.  10 ( b ) , a clearance passage  80  which causes the through hole  73  of the sub-valve element  70  and the through hole  65  in the valve element  60  to communicate with each other is formed with the top wall  74  of the sub-valve element  70  in abutment with the top wall  64  of the valve element  60 . When the internal passage  61  of the valve element  60  is closed, that is, when the outer surface of the top wall  74  of the sub-valve element  70  is in abutment with the inner surface of the top wall  64  of the valve element  60 , the clearance passage  80  forms a communication passage which causes the internal passage  61  to communicate continuously with the upstream side of the valve element  60 , so that a configuration is such as not to inhibit the movement of the release control valve  51  (the valve element  60 ). 
     A configuration may be such as to regulate the movement of the valve element  60  with the stopper  53  in the same way as in the configuration shown in  FIGS.  6 ( a ) and  6 ( b ) , but in this example, the stopper  53  is omitted, and a configuration is such as to regulate the movement by press fitting a ring member  57  between the valve element  60  and the valve plate  2  or the like. The ring member  57  may be of an elastic material as long as it is a material which can regulate the movement of the valve element  60 . 
     As the other configurations are the same as in  FIGS.  6 ( a ) and  6 ( b ) , the description will be omitted by giving identical numbers to identical portions. 
     In this kind of configuration, there is no need to form the orifice  66  in the top wall  64  of the valve element  60 , so that dimensional management and manufacture are facilitated. As the orifice  66  is a minute opening, it is difficult to manage the dimensions thereof, and as the orifice  66  is difficult to form with a forming mold, boring by a drill has been required, but according to the above described configuration wherein the clearance passage  80  is formed by adjusting the shape of the through holes  65  and  73 , each of the through holes  65  and  73  can be formed with a forming mold, so that dimensional management and manufacture are facilitated. 
       FIGS.  11 ( a ),  11 ( b ),  12 ( a ), and  12 ( b )  show other configuration examples in place of the orifice  66  in  FIGS.  6 ( a ) and  6 ( b ) . The examples are such that a groove is formed in an abutment portion between the top wall  64  of the valve element  60  and the top wall  74  of the sub-valve element  70 , forming a clearance passage  80  (a communication passage) which causes the internal passage  61  of the valve element  60  to communicate with the upstream side of the valve element  60  when closing the internal passage  61  of the valve element  60 , that is, when the outer surface of the top wall  74  of the sub-valve element  70  is in abutment with the inner surface of the top wall  64  of the valve element  60 . 
     In  FIGS.  11 ( a ) and  11 ( b ) , a distance R 1  from the center of the top wall  64  to the through hole  65  formed in the top wall  64  of the valve element  60  is made larger than a radius R 2  of the through hole  73  formed in the top wall  74  of the sub-valve element  70  (R 1 −R 2 =β), based on which a groove  81  extended from the through hole  65  to the radial inner side is formed in a surface of the top wall  64  of the valve element  60  facing the top wall  74  of the sub-valve element  70 , adopting a configuration such that with the top wall  64  of the valve element  60  and the top wall  74  of the sub-valve element  70  in abutment with each other, the clearance passage  80  formed by the groove  81  causes the through hole  73  of the sub-valve element  70  and the through hole  65  in the valve element  60  to communicate with each other. 
     Here, the groove  81  may be provided all over the entire circumferential length of the through hole  65 , or one and a plurality of the grooves  81  may also be provided in one circumferential portion of the through hole  65 . 
     Also, in  FIGS.  12 ( a ) and  12 ( b ) , a distance R 1  from the center of the top wall  64  to the through hole  65  formed in the top wall  64  of the valve element  60  is made larger than a radius R 2  of the through hole  73  formed in the top wall  74  of the sub-valve element  70  (R 1 −R 2 =β), based on which a groove  82  extended from the through hole  73  to the radial outer side is formed in a surface of the top wall  74  of the sub-valve element  70  facing the top wall  64  of the valve element  60 , adopting a configuration such that with the top wall  64  of the valve element  60  and the top wall  74  of the sub-valve element  70  in abutment with each other, a clearance passage  80  formed by the groove  82  causes the through hole  73  of the sub-valve element  70  and the through hole  65  in the valve element  60  to communicate with each other. 
     Here, the groove  82  may be provided all over the entire circumferential length of the through hole  73 , and one and a plurality of the grooves  82  may also be provided in one circumferential portion of the through hole  73 . 
     In  FIGS.  11 ( a ),  11 ( b ),  12 ( a ), and  12 ( b ) , as the other configurations are the same as in  FIGS.  6 ( a ) and  6 ( b ) , the description will be omitted by giving identical numbers to identical portions. 
     In these configurations, too, it is possible to mold the groove  81 ,  82  simultaneously with when molding with a forming mold, so that dimensional management and manufacture become easier than when forming the orifice. 
     REFERENCE SIGNS LIST 
     
         
           4  control pressure chamber 
           7  drive shaft 
           20  swash plate 
           23  compression chamber 
           33  suction chamber 
           34  discharge chamber 
           40  supply passage 
           41  release passage 
           42  supply control valve 
           43  branch passage 
           50  valve housing space 
           51  release control valve 
           52  shoulder 
           53  stopper 
           56  compression spring 
           60  valve element 
           61  internal passage 
           62  valve body 
           63  flange 
           65  through hole 
           66  orifice 
           70  sub-valve element 
           71  internal passage 
           75  check valve 
           80  clearance passage 
           81  groove 
           82  groove