Patent Publication Number: US-6217290-B1

Title: Control valve for variable capacity compressors

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a control valve for a variable capacity compressor to be employed in air conditioners for vehicles, etc., and in particular to a control valve for a variable capacity compressor, which is designed to supply, upon requirements, a coolant gas from a discharge pressure region to a crankcase. 
     A variable capacity compressor provided with a cylinder, a piston, a wobble plate, etc. has been conventionally employed for compressing and discharging a coolant gas of an air conditioner for vehicles, etc. One example of this conventional variable capacity compressor is constructed such that it comprises a coolant gas passage for communicating a discharge pressure region with a crankcase, so that the quantity of coolant gas to be discharged can be changed in conformity with changes in inclination angle of the wobble plate which can be effected through an adjustment of the pressure inside the crankcase. The adjustment of pressure inside the crankcase is performed by feeding a high pressure compressed coolant gas from the discharge pressure region to the crankcase while adjusting the opening degree of a control valve disposed at an intermediate portion of the coolant gas passage. 
     FIGS. 6 and 7 show one example of such a control valve  100 ′ for a variable capacity compressor (hereinafter referred to simply as a control valve) (see Japanese Patent Unexamined Publication (Kokai) H/9-268,974). This control valve  100 ′ is disposed neighboring on the rear housing  210  of the variable capacity compressor  200  and is designed to adjust the pressure inside the crankcase  231  which is disposed in a front housing  230  and next to the a cylinder block  220  of the variable capacity compressor  200 . 
     In the interior of the crankcase  231 , there are housed a wobble plate  240  which is mounted on a driving shaft  250  in such a manner that it can slide along the axial direction of the driving shaft  250  and can incline about the driving shaft  250 , and also a guide pin  241  of the wobble plate  240 , which is made slidable along a supporting arm  252  of a rotatable supporting body  251 . The wobble plate  240  is connected via a couple of shoes  242  with a piston  260  which is slidably disposed in a cylinder bore  221 . 
     The wobble plate  240  is designed to swing in the directions indicated by the arrows so as to change its inclination angle in conformity with a difference in pressure between a suction pressure Ps inside the cylinder bore  221  and a pressure Pc inside the crankcase  231 . The stroke width of the forward and backward movement of the piston  260  in the cylinder bore  221  can be determined based on this inclination angle. Further, the inclinatory movement in the direction of arrows of the wobble plate  240  causes a cutoff body  270  contacting with a middle portion of the wobble plate  240  to move forward or backward in a housing bore  222 . 
     The rear housing  210  is provided with suction chambers  211   a  and  211   b  each constituting an inlet pressure region, and with discharging chambers  212   a  and  212   b  each constituting a discharge pressure region. When the piston  260  is moved forward and backward as a result of the inclinatory movement of the wobble plate  240 , the coolant gas in the suction chamber  211   a  is sucked into the cylinder bore  221  from a suction port  213  and then compressed to a predetermined pressure before it is discharged through a discharge port  214  into the discharging chamber  212   a.    
     An inlet passage  215  formed at the central portion of the rear housing  210  is communicated with the housing bore  222  and also with the suction chamber  211   b  through a through-hole  216 . When the wobble plate  240  is moved toward the cutoff body  270 , the cutoff body  270  is caused to move toward the inlet passage  215  thereby causing the through-hole  216  to be closed ultimately by the cutoff body  270 . 
     Between the inlet passage  215  and the upper end portion of the control valve  100 ′, there is formed a pressure-checking passage  217  for introducing the suction pressure Ps into the control valve  100 ′. The discharging chamber  212   b  is communicated with the crankcase  231  via gas inlet passages  218  and  219  of the control valve  100 ′. These gas inlet passages  218  and  219  are designed to be opened or closed by means of a valve member  106 ′ of the control valve  100 ′. In this case, it is designed such that a discharging pressure Pd inside the discharging chamber  212   b  is allowed to be introduced via the gas inlet passage  218  to a valve chamber port  113 ′, while the pressure Pc inside the crankcase  231  is allowed to be introduced via the gas inlet passage  219  to a valve chamber port  114 ′. Further, it is also designed such that the suction pressure Ps is allowed to be introduced via the pressure-checking passage  217  into a sucking pressure-introducing port  115 ′. 
     If a temperature detected by an indoor sensor  281  is higher than a set temperature of a temperature-setting device  282  at the moment when an actuating switch  280  of air conditioner is turned on, a controlling computer  283  outputs a command to magnetize the solenoid  101 ′ of the control valve  100 ′. As a result, an electric current is fed via an actuating circuit  284  to the solenoid  101 ′ thereby causing the solenoid  101 ′ to generate a suction force, due to which a movable core  102 ′ is attracted, against the urging force (biasing force) of a spring  103 ′, toward a fixed core  104 ′. 
     As the movable core  102 ′ is moved in this manner, the valve member  106 ′ attached to a solenoid rod  105 ′ is caused to move, against the urging force of a forced opening spring  107 ′, in the direction to decrease the opening degree of a valve hole  108 ′. As a result of this movement of the valve member  106 ′, a pressure-sensitive rod  109 ′ formed integral with the valve member  106 ′ is moved upward thereby pushing up bellows  111 ′ which is detachably connected with the pressure-sensitive rod  109 ′ through a pressure-sensitive rod receiver  110 ′. 
     At this moment, the displacement of bellows  111 ′ is caused in conformity with changes of the suction pressure Ps to be introduced via the pressure-sensitive passage  217  into the interior of the pressure-sensitive chamber  112 ′, thereby giving a load to the pressure-sensitive rod  109 ′. Thus, the control valve  100 ′ is designed such that the opening degree of the valve hole  108 ′ by means of the valve member  106 ′ is determined by a balance among the suction force of the solenoid  101 ′, the urging force by the bellows  111 ′ and the urging force by the forced opening spring  107 ′. 
     If the cooling load is large in this case for instance, i.e. if a difference between the temperature detected by the indoor sensor  281  and the set temperature of the room temperature-setting device  282  is large, the suction force between the movable core  102 ′ and the fixed core  104 ′ is increased whereby increasing the force of the valve member  106 ′ to bias the valve hole  108 ′ in the direction to decrease the opening degree thereof, thus making it possible to perform the opening and closing of the valve member  106 ′ with the lower suction pressure Ps. 
     When the opening degree of valve by means of the valve member  106 ′ is decreased, the quantity of coolant gas to be fed to the crankcase  231  from the discharging chamber  212   b  via the gas inlet passages  218  and  219  is decreased, thus lowering the crankcase pressure Pc in the interior of the crankcase  231 . 
     Further, if the cooling load is large, the suction pressure Ps inside the cylinder bore  221  is increased whereby generating a difference in pressure between the suction pressure Ps inside the cylinder bore  221  and the crankcase pressure Pc inside the crankcase  231 , thus enlarging the inclination angle of the wobble plate  240 , whereby causing the cutoff body  270  to keep away from the inlet passage  215  to open the passage  216 . 
     In the aforementioned conventional control valve  100 ′, it is designed such that the discharge pressure Pd is introduced via the gas inlet passage  218  into the valve chamber port  113 ′ of the control valve  100 ′ as shown in FIG.  7 . Since the discharge pressure Pd is high and the coolant gas generating such the high discharge pressure Pd releases an intense heat as it is compressed up to a predetermined pressure by the forward and backward movement of the piston  260 , the control valve  100 ′ itself is heated to high temperatures by the intense heat released from the coolant gas. 
     When the control valve  100 ′ itself is heated to high temperatures in this manner, the temperature of the solenoid  101 ′ is also risen so that the suction force of the movable core  102 ′ which is originating from the solenoid  101 ′ is weakened, thereby raising a problem that the opening or closing accuracy of the valve hole  108 ′ by means of the valve member  106 ′ is deteriorated. Furthermore, in the case of the conventional control valve  100 ′, the bellows  111 ′ is required to be incorporated into the pressure sensitive chamber  112 ′ with the interior of the pressure sensitive chamber  112 ′ being maintained in a closed state. Therefore, there is no space for introducing an adjusting jig into the pressure sensitive chamber  112 ′ from outside, thereby making it impossible to perform the adjustment of loading force of the bellows  111 ′. 
     Additionally, since the application point of suction from the solenoid  101 ′ to the solenoid rod  105 ′ is kept away from the application point of the urging force by the bellows  111 ′, not only there is a possibility that the solenoid rod  105 ′ may be rattled as it is moved at the occasion of closing the valve, but also the valve member  106 ′ may possibly be non-uniformly contacted with the valve hole  108 ′ due to the aforementioned rattling of the solenoid rod  105 ′ because the distal end portion of the valve member  106 ′ for closing the valve hole  108 ′ is simply made flat, and hence the opening or closing accuracy of the valve is hindered from being improved. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been made under the circumstances mentioned above, and therefore an object of the present invention is to provide a control valve for a variable capacity compressor, which is capable of improving the opening or closing accuracy of valve and also capable of easily performing the adjustment of the loading force of bellows. 
     The aforementioned object can be achieved by this invention by providing a control valve for a variable capacity compressor; wherein the opening degree of a valve member disposed in a coolant gas passage for communicating a discharge pressure region of the variable capacity compressor with a crankcase thereof is made adjustable by the magnetization action of a solenoid disposed in the solenoid housing which is mounted on a main valve body, thereby causing the inclination angle of the wobble plate disposed inside the crankcase to be changed and at the same time, causing the discharging capacity of the compressor to be changed; and which is characterized in that said main valve body is integrally incorporated in a rear housing of the variable capacity compressor, and that a low temperature coolant gas-introducing space communicating with a suction pressure region of the variable capacity compressor is formed between the solenoid housing and the rear housing. 
     In the control valve for a variable capacity compressor of this invention which is constructed as mentioned above, a low temperature coolant gas is introduced not only into a pressure sensitive chamber of the main valve body from the suction pressure region, but also into a low temperature coolant gas-introducing space formed between the solenoid housing and the rear housing, so that the entire side walls of the solenoid housing can be cooled by this low temperature coolant gas, thus making it possible to inhibit the solenoid disposed inside the housing from being deteriorated in magnetization force thereof due to heat, etc. 
     Further, since the main valve body is provided with a pressure sensitive chamber communicating with the suction pressure region of the variable capacity compressor, with bellows housed in the pressure sensitive chamber and functioning to move the valve member in the direction to reduce the opening degree thereof as the pressure of the suction pressure region is increased, and with an adjusting screw holder hermetically attached to the pressure sensitive chamber and provided with an adjusting screw for adjusting the strength of the bellows, it is now possible to easily perform the adjustment of strength of the bellows in the pressure sensitive chamber while maintaining the closed state of the interior of the pressure sensitive chamber. 
     Further, since the main valve body is integrally incorporated in the rear housing of the variable capacity compressor with the adjusting screw holder being kept directed toward outside, even if the main valve body is mounted in the rear housing, the adjustment of strength of the bellows in the pressure sensitive chamber can be easily performed from outside. 
     Since the main valve body is constructed such that a solenoid is disposed at the center thereof, that a pressure sensitive chamber provided with bellows is disposed at one end thereof, that a valve chamber provided with the valve member is disposed at the other end thereof, that one end of a stem is fixed at one end of the plunger of the solenoid, that a stopper of the bellows placed in the pressure sensitive chamber is detachably disposed at the other end of the stem, that a rod to be contacted with the valve member is fixed at the other end of the plunger, and that a spring for urging the plunger of the solenoid toward the valve member is disposed at one end of the plunger, the valve member can be normally kept in a state of maximum opening degree, without being influenced by the action of the bellows inside the pressure sensitive chamber, during the period when the plunger is not magnetized by the solenoid. 
     Additionally, since the pressure sensitive chamber is disposed close to the solenoid, the distance between the application point by the suction of the solenoid and the application point by the bellows can be shortened, whereby the rattling of an operating bar constituted by the aforementioned rod and stem can be minimized as these rod and stem are moved in the direction of closing the valve. 
     Further, since the valve member is spherical in shape, the valve member can be uniformly contacted with the valve hole even if the operating bar is inclined at the occasion of closing the valve. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a longitudinal sectional view illustrating a variable capacity compressor provided with a control valve according to one embodiment of the present invention, wherein the discharge passage thereof is being opened; 
     FIG. 2 is a longitudinal sectional view illustrating the variable capacity compressor of FIG. 1, wherein the discharge passage thereof is being closed; 
     FIG. 3 is an enlarged longitudinal sectional view of the control valve of the variable capacity compressor shown in FIG. 1; 
     FIG. 4 is an enlarged longitudinal sectional view illustrating the details of the control valve of the variable capacity compressor shown in FIG. 3; 
     FIG. 5 is a longitudinal sectional view illustrating a main portion of a control valve of variable capacity compressor according to another embodiment of the present invention; 
     FIG. 6 is a longitudinal sectional view illustrating a variable capacity compressor provided with a conventional control valve; and 
     FIG. 7 is a longitudinal sectional view illustrating in detail the control valve for the variable capacity compressor which is shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be further explained with reference to the drawings depicting one embodiment of a control valve for a variable capacity compressor according to one embodiment of the present invention. 
     FIGS. 1 and 2 show longitudinal sectional views of a variable capacity compressor  1  provided with a control valve  100  according to this embodiment, wherein FIG. 1 shows a state where the discharge passage of the variable capacity compressor  1  is opened, while FIG. 2 shows a state where the discharge passage is closed. 
     To one end face of the cylinder block  2  of the variable capacity compressor  1  is attached, via a valve plate  2   a,  a rear housing  3 , while to the other end face of the cylinder block  2  is attached a front housing  4 . The cylinder block  2  is provided with a plurality of cylinder bores  6  which are arranged about a shaft (rotational axis)  5  at predetermined intervals along the circumferential direction. In each of these cylinder bores  6 , a piston  7  is slidably housed. 
     The front housing  4  is provided therein with a crankcase  8  in which a wobble plate  10  is housed. The wobble plate  10  is provided with a sliding surface  10   a  to which a shoe  50  for rotatably supporting a spherical end portion  11   a  of a connecting rod  11  is sustained by means of a retainer  53 . This retainer  53  is mounted via a radial bearing  55  on the boss  10   b  of the wobble plate  10 , and is made rotatable in relative to the wobble plate  10 . The radial bearing  55  is prevented from being come off by means of a stopper  54  which is fixed with a screw  45  to the boss  10   b.    
     The shoe  50  is constituted by a main shoe body  51  rotatably supporting a fore-end face of the spherical end portion  11   a  of the connecting rod  11 , and by a washer  52  rotatably supporting a rear-end face of the spherical end portion  11   a  of the connecting rod  11 . 
     The rear housing  3  is provided with a discharge chamber  12  and with a suction chamber  13 . The suction chamber  13  is disposed to surround the discharge chamber  12 . The rear housing  3  is also provided with an inlet port (not shown) which is communicated with an outlet port of an evaporator (not shown). FIG. 1 illustrates a state where the discharge passage  39  is being opened, while FIG. 2 illustrates a state where the discharge passage  39  is being closed. This discharge passage  39  which is disposed for communicating the discharge chamber  12  with a discharge port  1   a  is provided at an intermediate portion thereof with a spool valve (discharge controlling valve)  31 . This discharge passage  39  is constituted by a passage  39   a  formed in the rear housing  3  and by a passage  39   b  formed in the valve plate  2   a.  The passage  39   b  is communicated with the discharge port  1   a  formed in the cylinder block  2 . 
     The spool valve  31  which is constituted by a bottomed cylindrical body is provided therein with a spring (an urging member)  32 . One end of the spring  32  is contacted with a stopper  56  which is secured to the rear housing  3  by means of a cap  59 , while the other end of the spring  32  is contacted with the bottom surface of the spool valve  31 . The inner space  33  of the spool valve  31  is communicated via a passage  34  with a crankcase  8 . 
     It is designed that one side (upper side) of the spool valve  31  is subjected to an urging force from the spring  32  and to a pressure from the crankcase  8  both of which are directed to close the valve  31  (a direction to reduce the opening degree of valve). At the moment when the spool valve  31  is being opened, the discharge port  1   a  is allowed to communicate with the discharge chamber  12  through the discharge passage  39  (see FIG.  1 ). Therefore, the other side of the spool valve  31  is subjected to a pressure from the discharge port  1   a  and to a pressure from the discharge chamber  12  both of which are directed to open the valve  31  (a direction to enlarge the opening degree of valve). However, when a difference in pressure between the crankcase  8  and the discharge port  1   a  is decreased to less than a predetermined value, the spool valve  31  is moved in the valve-closing direction thereby to shut off the discharge passage  39 , thus allowing only the pressure from the discharge chamber  12 , which is directed in the valve-opening direction, to act on the lower side of the spool valve  31 . Namely, the pressure from the discharge port  1   a  is no more acted on the lower side of the spool valve  31 . 
     The discharge chamber  12  is communicated via a second passage  57  with the crankcase  8 . This second passage  57  is provided at an intermediate portion thereof with a control valve (for a variable capacity compressor)  100  of this embodiment as will be explained in detail hereinafter. When a heat load is large, an electric current is transmitted to the solenoid  131 A of the control valve  100  thereby to actuate the valve member  126  to shut off the second passage  57 . On the other hand, when a heat load is small, the transmission of electric current to the solenoid  131 A is stopped thereby to cause the valve member  126  to keep away from the valve seat, thus opening the second passage  57 . The operation of the control valve  100  is controlled by means of a computer (not shown). 
     The suction chamber  13  is communicated via a first passage  58  with the crankcase  8 . This first passage  58  is constituted by a combination of an orifice (a second orifice)  58   a  formed in the valve plate  2   a,  a passage  58   b  formed in the cylinder block  2 , and a through-hole  58   c  formed in a ring (an annular body)  9  which is fixed to the shaft  5 . The suction chamber  13  is communicated with the crankcase  8  also through a third passage  60 . This third passage  60  is constituted by a combination of a passage  60   a  formed in the front housing  4 , a front side bearing-receiving space  60   b,  a passage  60   c  formed in the shaft  5 , a rear side bearing-receiving space  60   d,  the passage  58   b  formed in the cylinder block  2 , and the orifice  58   a  formed in the valve plate  2   a.  Namely, the passage  58   b  in the cylinder block  2  and the orifice  58   a  in the valve plate  2   a  constitute not only part of the first passage  58  but also part of the third passage  60 . 
     The passage  60   c  is provided at the rear side end portion thereof with an internal thread  61  into which a screw  62  is fitted. This screw  62  is provided with an orifice (a first orifice)  62   a  having a cross-sectional area which is smaller than that of the second orifice  58   a  formed in the valve plate  2   a  and constituting part of the first passage  58 . Therefore, only when the through-hole  58   c  of the ring  9  is nearly closed by the boss  10   b  of the wobble plate  10  and hence the cross-sectional area of the first passage  58  is extremely reduced, a coolant in the crankcase  8  is permitted to enter the suction chamber  13  through this third passage  60 . 
     The valve plate  2   a  is provided with discharge ports  16  for communicating a compression chamber  82  with the discharge chamber  12 , and with inlet ports  15  for communicating a compression chamber  82  with the suction chamber  13 , these inlet ports  15  and discharge ports  16  being provided at predetermined intervals along the circumferential direction. The discharge ports  16  are adapted to be closed or opened by means of the discharge valve  17  which is secured together with a valve-holding member  18  to a rear housing side end face of the valve plate  2   a  by making use of a bolt  19  and a nut  20 . The suction ports  15  are adapted to be closed or opened by means of the suction valve  21  which is interposed between the valve plate  2   a  and the cylinder block  2 . 
     The rear side end portion of the shaft  5  is rotatably supported by a radial bearing (a rear side bearing)  24  and a thrust bearing (a rear side bearing)  25 , both bearings being housed in the rear side bearing-receiving space  60   d  formed in the cylinder block  2 . The front side end portion of the shaft  5  is rotatably supported by a radial bearing (a front side bearing)  26  which is housed in the front side bearing-receiving space  60   b  formed in the front housing  4 . In addition to the radial bearing  26 , a shaft seal  46  is also housed in the front side bearing-receiving space  60   b.    
     The cylinder block  2  is provided at the central portion thereof with an internal thread  1   b  into which an adjust nut  83  is fitted. When this adjust nut  83  is tightened, a preload can be given to the shaft  5  through the thrust bearing  25 . A pulley (not shown) is fixed to the front side end portion of the shaft  5 . 
     A thrust flange  40  for transmitting the rotational movement of the shaft  5  to the wobble plate  10  is also fixed to the shaft  5 . This thrust flange  40  is sustained on the inner wall of the front housing  4  by means of a thrust bearing  33 . The thrust flange  40  is connected with the wobble plate  10  by means of a hinge structure  41 , so that the wobble plate  10  can be inclined relative to an imaginary surface perpendicular to the shaft  5 . Namely, the wobble plate  10  is slidably and inclinably mounted on the shaft  5 . 
     The hinge structure  41  is constituted by a combination of a bracket  10   e  attached to the front face  10   c  of the wobble plate  10 , a linear guiding groove  10   f  formed in the bracket  10   e,  and a rod  43  engaged with the wobble plate side side-wall  40   a  of the thrust flange  40 . The longitudinal axis of the guide groove  10   f  is inclined to a predetermined angle in relative to the front face  10   c  of the wobble plate  10 . The spherical portion  43   a  of the rod  43  is slidably fitted in this guide groove  10   f.    
     Next, the control valve  100  for a variable capacity compressor (hereinafter referred to simply as a control valve) according to this embodiment will be explained in detail. FIG. 3 shows the longitudinal sectional view of a state where the control valve  100  is incorporated into a variable capacity compressor  1 , while FIG. 4 is a sectional view illustrating the details of the control valve  100  shown in FIG.  3 . 
     The control valve  100  shown in FIG. 3 is mounted on the rear housing  3  side of the variable capacity compressor  1  shown in FIGS. 1 and 2. A main valve body  120  of the control valve  100  is disposed in a space  84  communicating with the discharge chamber  12  to be kept at the discharging pressure Pd of coolant in such a manner that it is hermetically sealed therein by means of O-rings  121   a  and  121   b.  To the upper end portion of the main valve body  120  is fittingly secured a strainer  122 , through which the coolant gas for generating the high discharging pressure Pd in the interior of the valve chamber  123  formed in the main valve body  120  is designed to be introduced. 
     In the interior of the valve chamber  123 , a spherical valve member  126  for effecting the closing or opening of the stopper  124  and of the valve hole  125  is disposed, and at the same time, a valve-closing spring  127  for urging the spherical valve member  126  in the direction of closing the valve is interposed between the stopper  124  and the spherical valve member  126 . 
     The main valve body  120  is also provided with a port  114  to which the pressure Pc of the crankcase  8  is to be introduced. Accordingly, a coolant gas of high pressure which has been introduced into the interior of the valve chamber  123  through the strainer  122  can be introduced into the crankcase  8  through this port  114  and the passage  57  when the valve hole  125  is opened by the movement of the spherical valve member  126 . 
     Furthermore, the main valve body  120  is provided with a suction port  129  which is communicated via a passage  80  shown in FIG. 1 with the suction chamber  13  and to which the suction pressure Ps of the suction chamber  13  is to be introduced. This suction port  129  is also communicated not only with a pressure sensitive chamber  145  via a suction passage  130  but also with a suction pressure-introducing space  85  which is located between the rear housing  3  and the solenoid housing  131 . This suction pressure-introducing space  85  is hermetically sealed by means of an O-ring  131   b  mounted on a projected portion  131   a  formed on a side wall portion of the solenoid housing  131 . With the provision of this suction pressure-introducing space  85 , the side wall of the solenoid housing  131  can be entirely cooled by a low temperature coolant gas to be fed from the suction chamber  13  thereby inhibiting the solenoid  131 A housed in the solenoid housing  131  from becoming high in temperature. 
     In the solenoid housing  131 , there is also disposed a plunger  133  linked to the rod  132  which is disposed to contacted with and thereby to retain the spherical valve member  126 . The plunger  133  is slidably sustained by a pipe  136  which is fixed to a pipe holder  135  hermetically contacted, through an O-ring  134 , with the end portion  120   a  of the main valve body  120 . The aforementioned rod  132  functions together with a stem  138  (to be explained hereinafter) as an operation bar. 
     The plunger  133  is provided at the rear end  133   a  thereof with a receiving hole  137  into which one end portion  139  of the stem  138  is inserted and secured thereto. The other end portion  140  of the stem  138  is slidably introduced into and sustained by a suction member  141  in such a manner that it is inserted through the receiving hole  142  of the suction member  141  and projected from the receiving hole  143  of the suction member  141 . A spring  144  for urging the plunger  133  to keep away from the suction member  141  is interposed between the receiving hole  137  of the plunger  133  and the receiving hole  142  of the suction member  141 . 
     Bellows  146  disposed in the pressure sensitive chamber  145  is provided on both sides thereof with a pair of stoppers  147  and  148 , and one of the stoppers, i.e. the stopper  147  is detachably connected with the aforementioned other end portion  140  of the stem  138 . A spring  150  for urging the stopper  147  to keep away from the suction member  141  is interposed between the flange  149  of the stopper  147  and the receiving hole  143  of the suction member  141 . 
     It is designed that the maximum displacement of the bellows  146  is to be regulated by the contact between this pair of stoppers  147  and  148  as the bellows  146  is contracted due to an increase in the suction pressure Ps in the pressure sensitive chamber  145 . It is also designed that the maximum displacement of the bellows  146  is smaller than the maximum fitting distance between the aforementioned other end  140  of the stem  138  and the stopper  147  of the bellows  146 , thereby preventing the aforementioned other end  140  of the stem  138  from being disengaged out of the stopper  147  of the bellows  146 . 
     Further, a pipe  151  defining the pressure sensitive chamber  145  is hermetically sustained, through an O-ring  156 , by a plate  157 , and an adjusting screw holder  152  is fitted in and secured to one end of the pipe  151 . This adjusting screw holder  152  is provided therein an adjusting screw  153  for adjusting the intensity of the bellows  146 , the adjusting screw  153  being hermetically pierced through the adjusting screw holder  152  by means of an O-ring  154 . This adjusting screw  153  is disposed such that the tip end portion  155  thereof is contacted with the stopper  148  of the bellows  146 . 
     Furthermore, a cord  158  for supplying a predetermined magnetizing current under the controlling by the controlling computer (not shown) is connected with the solenoid  131 A. 
     Next, the operation of the variable capacity compressor  1  and control valve  100  according to this embodiment will be explained. First of all, the operation entirely of the variable capacity compressor  1  will be explained before explaining the operation of the control valve  100 . 
     The rotational power of an automobile engine is transmitted from a pulley (not shown) to the shaft  5  via a belt (not shown), and the resultant rotational power of the shaft  5  is transmitted to the wobble plate  10  via the hinge structure  41  thereby causing the wobble plate  10  to rotate. 
     Due to the rotation of the wobble plate  10 , the shoe  50  is also caused to rotate along the sliding surface  10   a  of the wobble plate  10 , so that the rotational power of the wobble plate  10  is converted to a linear reciprocating motion of the piston  7 . As a result, the reciprocating motion of the piston  7  in the cylinder bore  6  is taken place, thus resulting in a change in volume of the compression chamber  82  disposed inside the cylinder bore  6 . As a result of this change in volume, the suction, compression and discharging of the coolant gas is sequentially taken place, whereby allowing the coolant gas to be discharged at a rate corresponding to the angle of inclination of the wobble plate  10 . At the process of sucking, the suction valve  21  is opened, thereby allowing a low pressure coolant gas to be discharged from the suction chamber  13  to the compression chamber  82  disposed inside the cylinder bore  6 . 
     When the heat load is decreased (which corresponds to the moment of clutch-off of a clutch compressor), the transmission of electric current to the solenoid of the control valve  100  is stopped, thus actuating the control valve  100  (the plunger  133 ) to move in the direction of opening the valve, i.e. the spherical valve member  126  of the control valve  100  is caused to move, against the urging force of the valve-closing spring  127 , in the direction of opening the valve, thus opening the second passage  57 . As a result, a high pressure coolant gas is allowed to flow from the discharge chamber  12  to the crankcase  8  via the second passage  57 , thus increasing the pressure inside the crankcase  8 . 
     The force acting on the rear surface of the piston  7  becomes larger during the compression stroke, resulting in that the total of the force imposed on the rear surface of the piston  7  exceeds over the total of the force imposed on the front surface of the piston  7 , thus decreasing the inclination angle of the wobble plate  10 . When the inclination angle of the wobble plate  10  becomes minimum, the hole  58   c  of the ring  9  is substantially closed by the boss  10   b  of the wobble plate  10 , thereby extremely reducing the cross-sectional area of the first passage  58 , thus inhibiting the crankcase  8  from being lowered in pressure. 
     When a difference in pressure between the discharge chamber  12  and the crankcase  8  is decreased to a predetermined value Po or less, or to such an extent that the power acting on the upper side of the spool valve  31 , i.e. the total power of the pressure of crankcase  8  and the urging force of the spring  32 , becomes higher than the pressure of the coolant gas of the discharge chamber  12  that is acting on the lower side of the spool valve  31 , the spool valve  31  is caused to move in the direction to close the valve thereof, thus shutting down the discharge passage  39  (FIG.  2 ). As a result, the flow of the coolant gas from the discharge port  1   a  to the condenser  88  is stopped. At this moment, although the hole  58   c  of the ring  9  is substantially closed by the boss  10   b  of the wobble plate  10 , and hence the cross-sectional area of the first passage  58  is extremely reduced, the coolant gas in the crankcase  8  is allowed to flow into the suction chamber  13  through the third passage  60 . As a result, the crankcase  8  is prevented from being excessively increased in pressure, and at the same time, the coolant gas is allowed to circulate throughout the compressor  1 . 
     At the moment of minimum piston stroke (a state shown in FIG.  2 ), the coolant gas is allowed to circulate passing successively through the suction chamber  13 , the compression chamber  82 , the discharge chamber  12 , the second passage  57 , the crankcase  8  and the third passage  60  in the mentioned order, thus returning again to the suction chamber  13 . 
     On the other hand, the coolant gas in the crankcase  8  is allowed to flow, through the passage  60   a  of the front housing  4 , the front side bearing-receiving space  60   b,  the passage  60   c  formed in the shaft  5 , the rear side bearing-receiving space  60   d,  the passage  58   b  formed in the cylinder block  2  and the orifice  58   a  formed in the valve plate  2   a,  to the suction chamber  13 . At this occasion, the coolant gas flow is restricted by the orifice  62   a  of the screw  62  which is located at an intermediate portion of the passage  60   c  of the shaft  5  at first, and subsequently restricted again by the orifice  58   a  of the valve plate  2   a,  and hence the pressure of the coolant gas is caused to reduce. 
     By the way, since the variable capacity compressor according to this embodiment is constructed such that one end of the spool valve  31  functioning as a discharge control valve is subjected to the pressure from the crankcase  8 , while the other end of the spool valve  31  is subjected to the pressure from the discharge chamber  12 , and that a spring of relatively small resilient force is employed as the spring  32  for urging the spool valve  31  in the direction to close the valve, the spool valve  31  can be conditioned to take a minimum piston stroke (a minimum load) as the pressure of the discharge chamber  12  is gradually lowered due to a decrease in heat load, so that the spool valve  31  can be maintained in an opened state until the cross-sectional area of the first passage  58  is reduced by the wobble plate  10 . 
     On the other hand, when a heat load becomes large, an electric current is transmitted to the solenoid  131 A of the control valve  100  thereby to actuate the plunger  133  to move in the direction to close the valve and to actuate the spherical valve member  126  to move in the direction to close the valve by way of the urging force of the valve-closing spring  127 , thus stopping the passage of a coolant gas to the second passage  57 . As a result, the inflow of a high pressure coolant gas from the discharge chamber  12  into the crankcase  8  can be prevented, thus lowering the pressure in the crankcase  8 . 
     Furthermore, the force acting on the rear surface of the piston  7  during the compression stroke can be minimized, whereby the total force acting on the rear surface of the piston  7  becomes lower than the total force acting on the front surface of the piston  7 , thus increasing the inclination angle of the wobble plate  10 . When the inclination angle of the wobble plate  10  is changed from the minimum angle to the maximum angle, the boss  10   b  of the wobble plate  10  is moved away from the hole  58   c  of the ring  9 , thus allowing the first passage  58  to open fully and hence allowing the coolant gas filled in the crankcase  8  to flow into the suction chamber through the first passage  58 . As a result, the reduction in pressure of the crankcase  8  can be promoted. When the cross-sectional area of the first passage  58  is made maximum, the coolant gas is scarcely permitted to flow into the suction chamber  13  from the third passage  60 . 
     When the pressure of the discharge chamber  12  becomes higher to such an extent that a difference in pressure between the discharge chamber  12  and the crankcase  8  becomes a predetermined value Po or more, the pressure of coolant gas existing in the discharge chamber  12  and acting on the spool valve  31  becomes higher than the total power of the pressure of coolant gas in the crankcase  8  and the urging force of the spring  32 , so that the spool valve  31  is caused to move in the direction to open the valve, thus opening the discharge passage  39  (FIG.  1 ). As a result, the coolant gas in the discharge chamber  12  is permitted to flow from the discharge port  1   a  to the condenser  88 . 
     Next, the operation of the control valve  100  according to this embodiment will be explained in detail. 
     First of all, under the condition where the solenoid  131 A of the control valve  100  is magnetized, the plunger  133  is pulled, against the urging force of the spring  144 , toward the suction member  141 , so that the rod  132  linked with the plunger  133  is moved. As a result, the spherical valve member  126  attached to the rod  132  is caused to move in the direction to close the valve hole  125  of the main valve body  120 . On the other hand, a low temperature coolant gas is introduced from the suction passage  80  communicating with the suction chamber  13  to the pressure sensitive chamber  145  through the suction port  129  of the main valve body  120  and the suction passage  130 . As a result, the bellows  146  in the pressure sensitive chamber  145  is caused to displace according to the pressure of the coolant gas, i.e. the suction pressure Ps of the suction chamber  13 . This displacement is then transmitted to the spherical valve member  126  via the stem  138 , the plunger  133  and the rod  132 . In this case, the position of opening degree of the valve hole  125  of the spherical valve member  126  is determined by the displacement force of the bellows  146 , the valve-closing spring  127  and the spring  144 . 
     When the suction pressure Ps of the interior of the pressure sensitive chamber  145  becomes high, the bellows  146  is contracted according to the suction pressure Ps. Therefore, the direction of this contraction agrees with the sucking direction of the plunger  133  to be effected by the solenoid  131 A, and at the same time, the spherical valve member  126  is moved following the displacement of the bellows  146 , thus reducing the opening degree of the valve hole  125 . As a result, the quantity of a high pressure coolant gas to be introduced into the interior of the valve chamber  123  from the discharge chamber  12  via the strainer  122 , and then introduced into the crankcase  8  of FIG. 1 via the port  114  and the second passage  57  is reduced (the pressure Pc of the crankcase is lowered), thus increasing the inclination angle of the wobble plate  10  shown in FIG.  1 . 
     Further, since a low temperature coolant gas supplied from the suction passage  80  communicating with the suction chamber  13  is communicated with the suction pressure-introducing space  85  interposed between the rear housing  3  and the solenoid housing  131 , the side wall of the solenoid housing  131  can be entirely cooled by this low temperature coolant gas supplied from the suction chamber  13 , thus making it possible to inhibit the temperature rise of the solenoid  131 A disposed inside the solenoid housing  131 . On the other hand, when the suction pressure Ps in the interior of the pressure sensitive chamber  145  is lowered, the bellows  146  is expanded due to the spring  159  and to the restoring force of the bellows itself. As a result, in accordance with the displacement of the bellows  146 , the spherical valve member  126  is pushed by way of the stem  138 , the plunger  133  and the rod  132 , whereby the spherical valve member  126  is moved in the direction to increase the opening degree of the valve hole  125 . As a result, the quantity of a high pressure coolant gas to be introduced into the interior of the valve chamber  123  from the discharge chamber  12  via the strainer  122 , and then introduced into the crankcase  8  of FIG. 1 via the port  114  and the second passage  57  is increased (the pressure Pc of the crankcase is raised), thus decreasing the inclination angle of the wobble plate  10  shown in FIG.  1 . 
     On the other hand, under the condition where the solenoid  131 A is demagnetized, the pulling of the plunger  133  toward the spring  144  is vanished, so that, due to the urging force of the spring  144 , the plunger  133  is caused to move in the direction opposite to the side where the suction member  141  is disposed. As a result, the spherical valve member  126  is caused to move by way of the rod  132  in the direction to open the valve hole  125  of the main valve body  120 . When the suction pressure Ps of the interior of the pressure sensitive chamber  145  is increased under this condition, the bellows  146  is caused to contract thereby decreasing the opening degree of the spherical valve member  126 . However, since the other end portion  140  of the stem  138  is detachably contacted with the stopper  147  of the bellows  146 , the displacement of the bellows  146  would not give any influence to the spherical valve member  126 . 
     As a result, the spherical valve member  126  can be kept remained in a state of maximum opening degree without being influenced by an increase in suction pressure Ps of the interior of the pressure sensitive chamber  145 . 
     Additionally, since it is designed such that the maximum displacement of the bellows  146  becomes smaller than the maximum fitting distance between the aforementioned other end  140  of the stem  138  and the stopper  147  of the bellows  146 , the aforementioned other end  140  of the stem  138  can be prevented from being disengaged out of the stopper  147  of the bellows  146 . 
     As mentioned above, according to the control valve  100  of this embodiment, at the occasion of introducing a low temperature coolant gas into the pressure sensitive chamber  145  of the main valve body  120  from the suction chamber  13 , the low temperature coolant gas is introduced at first into the suction pressure-introducing space  85  interposed between the rear housing  3  and the solenoid housing  131 , so that the side wall of the solenoid housing  131  can be entirely cooled by this low temperature coolant gas. As a result, it possible to inhibit the deterioration in magnetization of the solenoid  131 A disposed inside the solenoid housing  131 . 
     Further, since an adjusting screw holder  152  provided with an adjusting screw  153  for adjusting the strength of the bellows  146  is hermetically attached to the pressure sensitive chamber  145  so as to make it possible to perform the adjustment in strength of the bellows  146  in the pressure sensitive chamber  145  by adjusting the adjusting screw  153  from outside of the main valve body  120 , it is now possible to easily perform the adjustment in strength of the bellows  146  hermetically housed in the pressure sensitive chamber  145 . 
     Moreover, since the main valve body  120  is integrally incorporated in a rear housing  210  of the variable capacity compressor  200  with the aforementioned adjusting screw holder  152  being directed outward, it is now possible to easily perform the adjustment in strength of the bellows  146  from outside even under the condition where the main valve body  120  is kept attached to the rear housing  210 . 
     Additionally, since the stem  138  constituting part of the operating bar is located near the pressure sensitive chamber  145  and disposed in the interior of the solenoid  131 A which is designed to pull the stem  138  in the direction to reduce the opening degree of the spherical valve member  126  so as to minimize the distance between the application point to be effected on the operating bar by the suction of the solenoid  131 A and the application point to be effected on the operating bar by the urging force of the bellows  146 , the rattling of the operating bar can be minimized at the occasion of moving the operating bar in the direction of closing the valve. 
     Further, since the valve member  126  is spherical in shape, the valve member  126  can be uniformly contacted with the valve hole  125  even if the rod  132  is inclined at the occasion of closing the valve. 
     In the foregoing embodiment, the adjusting screw  153  and the adjusting screw holder  152  are respectively employed as a separate body. However, the present invention is not limited to such an embodiment. For example, these adjusting screw and adjusting screw holder can be integrated thus forming a cap structure  152   a  as shown in FIG. 5 illustrating a main portion of such an alternative embodiment. Namely, this cap structure  152   a  is provided with an external thread portion  152   b  with which the female screw portion  157   a  formed on the inner wall of a plate  157  is engaged so as to make it possible to perform an adjustment of their relative locations. The air-tightness between the external thread portion  152   b  and the female screw portion  157   a  is ensured by means of an O-ring  154 . 
     As would be clearly understood from the above explanations, according to the control valve for a variable capacity compressor of this invention, at the occasion of introducing a low temperature coolant gas into the pressure sensitive chamber of the main valve body from the suction chamber, the low temperature coolant gas is introduced at first into the suction pressure-introducing space interposed between the rear housing and the solenoid housing, so that the side wall of the solenoid housing can be entirely cooled by this low temperature coolant gas. As a result, it possible to inhibit the deterioration in magnetization of the solenoid disposed inside the solenoid housing. 
     Further, since the main valve body is constructed such that one end of a stem is fixed at one end of the plunger of the solenoid, that the stopper of the bellows placed in the pressure sensitive chamber is detachably disposed at the other end of the stem, that a rod to be contacted with the valve member is fixed at the other end of the plunger, and that a spring for urging the plunger of the solenoid toward the valve member is disposed at one end of the plunger, the valve member can be normally kept in a state of maximum opening degree, without being influenced by the action of the bellows inside the pressure sensitive chamber, during the period when the plunger is not magnetized by the solenoid.