Patent Publication Number: US-2004057840-A1

Title: Capacity control valve for variable displacement compressor

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY:  
       [0001] This application claims priority of Japanese Application No. 2002-278764 filed on Sep. 25, 2002 and entitled “Capacity Control Valve for Variable Displacement Compressor”.  
       BACKGROUND OF THE INVENTION  
       [0002] (1) Field of the Invention  
       [0003] The present invention relates to a capacity control valve for a variable displacement compressor, and more particularly to a capacity control valve that regulates a flow of refrigerant discharged by a variable displacement compressor.  
       [0004] (2) Description of the Related Art  
       [0005] Automotive air conditioning systems employ a compressor to compress refrigerant gases in their refrigeration cycle. Since the compressor is driven by the automobile engine, the air conditioning system is unable to vary compressor rotation speed to control its output. To obtain a required cooling capacity without being restricted by the engine speed, the system uses a variable displacement compressor designed to be able to change the capacity (i.e., the amount of refrigerant that it can discharge) on its own.  
       [0006] In a variable displacement compressor, a wobble plate (swash plate) is fitted obliquely on the compressor&#39;s drive shaft, which is rotated by the engine. Rotation of this inclined wobble plate produces displacement of pistons that are linked to that plate, where the resulting piston strokes depends on the inclination angle of the wobble plate. This means that the compressor capacity (i.e., the amount of refrigerant being discharged from the compressor) can be varied by changing the wobble plate angle.  
       [0007] To control the wobble plate angle; part of the pressurized refrigerant is introduced into the gastight crank chamber of the compressor. Changing the crank chamber pressure creates a new state of balance between opposing pressures exerted on the both ends of each piston linked to the wobble plate, making it possible to vary the wobble plate angle steplessly.  
       [0008] To change the crank chamber pressure, a capacity control valve is installed either between the refrigerant outlet and the crank chamber or between the refrigerant inlet and the crank chamber. Capacity control valves are designed to open or close themselves in such a way that a certain level of differential pressure between their inlet and outlet will be maintained. More specifically, one can set a desired differential pressure by supplying a capacity control valve with an appropriate control current from an external power source. When the engine speed rises, the capacity control valve raises the pressure of refrigerant supplied to the crank chamber so as to reduce the compressor capacity. When in turn the engine slows down, the capacity control valve decreases the crank chamber pressure so as to increase the compressor capacity. In this way, the amount of refrigerant discharged from the variable displacement compressor is regulated.  
       [0009] One method to control capacity of the above variable displacement compressors is disclosed in Unexamined Japanese Patent Application Publication No. 2001-107854 (Paragraphs (0035) to (0036), FIG. 3) This literature describes a capacity control valve that regulates the flow of refrigerant being discharged from a variable displacement compressor.  
       [0010] According to Unexamined Japanese Patent Application Publication No. 2001-107854, the flow of refrigerant that is taken into the suction chamber is determined indirectly by detecting differential pressure between two pressure monitoring points with sensors. The capacity control valve controls the flow of refrigerant supplied from the discharge chamber to the crank chamber such that the intake flow rate will be maintained at a constant level, thereby regulating the flow of refrigerant discharged from the compressor.  
       [0011] The capacity control valve that controls a flow in the way described in Unexamined Japanese Patent Application Publication No. 2001-107854 needs sensors to detect differential pressure, as well as a controller to control the capacity control valve accordingly. Those extra components push up the cost of variable displacement compressor.  
       [0012] Another noteworthy aspect of automobile air conditioning systems is what kind of refrigerant to choose for their refrigeration cycles. While HFC-134a, a chlorofluorocarbon alternative, is widely used for that purpose as of this point in time, the recent development of supercritical refrigeration cycles using, for example, carbon dioxide poses another challenge to the compressor design. The new refrigeration cycle requires refrigerant to function in a region that exceeds its critical temperature, hence the supercritical refrigeration. Let us think of a refrigeration cycle using carbon dioxide as refrigerant in which a capacity control valve is employed to control crank chamber pressure according to the compressor&#39;s discharge pressure. In this case, the differential pressure between the refrigerant outlet and crank chamber could become extremely high because the refrigerant has to be pressurized up to its supercritical region. This means that a high-power solenoid actuator will be needed to produce a sufficiently large force to deal with the high differential pressure, which leads to increased size and cost of the capacity control valve.  
       SUMMARY OF THE INVENTION  
       [0013] In view of the foregoing, it is an object of the present invention to provide a compact capacity control valve for use with a flow-controlled variable displacement compressor, which can be applied not only to ordinary refrigeration cycles using HFC-134a, but also to those using supercritical high-pressure refrigerant, without the needs for high-power solenoids or extra pressure sensors.  
       [0014] To solve the above-described problems, the present invention provides a capacity control valve that regulates a flow of refrigerant discharged from a variable displacement compressor. This capacity control valve comprises the following components formed in an integrated way: a first control valve that sets a specific cross-sectional area of a refrigerant passageway that leads to a suction chamber or a discharge chamber of the variable displacement compressor; a second control valve that senses differential pressure developed across the first control valve and controls a flow of refrigerant supplied to or coming out of the crank chamber of the variable displacement compressor in such a way that the differential pressure will be maintained at a specified level; and a solenoid unit that actuates the first control valve to set the cross-sectional area of the refrigerant passageway according to variations in a given external condition.  
       [0015] The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016]FIG. 1 is a sectional view of a variable displacement compressor.  
     [0017]FIG. 2 is a detailed sectional view of a capacity control valve for a variable displacement compressor according to the first embodiment  
     [0018]FIG. 3 is a sectional view of a capacity control valve for a variable displacement compressor according to the second embodiment.  
     [0019]FIG. 4 is a sectional view of a capacity control valve for a variable displacement compressor according to the third embodiment.  
     [0020]FIG. 5 is a sectional view of a capacity control valve for a variable displacement compressor according to the fourth embodiment.  
     [0021]FIG. 6 is a sectional view of a capacity control valve for a variable displacement compressor according to the fifth embodiment.  
     [0022]FIG. 7 is a sectional view of a capacity control valve for a variable displacement compressor according to the sixth embodiment.  
     [0023]FIG. 8 is a sectional view of a capacity control valve for a variable displacement compressor according to the seventh embodiment.  
     [0024]FIG. 9 is a sectional view of a capacity control valve for a variable displacement compressor according to the eighth embodiment.  
     [0025]FIG. 10 is a sectional view of a capacity control valve for a variable displacement compressor according to the ninth embodiment.  
     [0026]FIG. 11 is a sectional view of a capacity control valve for a variable displacement compressor according to the tenth embodiment.  
     [0027]FIG. 12 is a sectional view of a capacity control valve for a variable displacement compressor according to the eleventh embodiment.  
     [0028]FIG. 13 is a sectional view of a capacity control valve for a variable displacement compressor according to the twelfth embodiment.  
     [0029]FIG. 14 is a sectional view of a capacity control valve for a variable displacement compressor according to the thirteenth embodiment.  
     [0030]FIG. 15 is a sectional view of a capacity control valve for a variable displacement compressor according to the fourteenth embodiment.  
     [0031]FIG. 16 is a sectional view of a capacity control valve for a variable displacement compressor according to the fifteenth embodiment.  
     [0032]FIG. 17 is a sectional view of a capacity control valve for a variable displacement compressor according to the sixteenth embodiment.  
     [0033]FIG. 18 is a sectional view of a capacity control valve for a variable displacement compressor according to the seventeenth embodiment.  
     [0034]FIG. 19 is a sectional view of a capacity control valve for a variable displacement compressor according to the eighteenth embodiment.  
     [0035]FIG. 20 is a sectional view of a capacity control valve for a variable displacement compressor according to the nineteenth embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0036] Embodiments of the present invention will now be described below with reference to the accompanying drawings. The description will illustrate capacity control valves for use with a flow-controlled variable displacement compressor that is supposed to discharge refrigerant at a regulated flow rate.  
     [0037]FIG. 1 is a sectional view of a variable displacement compressor.  
     [0038] The explanation will begin with the overall structure of the variable displacement compressor  1  of FIG. 1.  
     [0039] The illustrated variable displacement compressor  1  is composed of the following three sections: a driving section  100  that receives drive power from a vehicle engine (not shown); a refrigerant compressing section  200  including a gastight crank chamber; and a capacity controlling section  300  that controls discharge capacity. The variable displacement compressor  1  has an outlet port  1   a , which is connected to a condenser (or gas cooler)  3  through a high-pressure refrigerant line  2 . The refrigerant is then routed from the condenser  3  to an expansion valve  4 , an evaporator  5 , and a low-pressure refrigerant line  6  in that order, and finally returns to the inlet port  1   b  of the variable displacement compressor  1 , thus forming a closed circuit for refrigeration cycle.  
     [0040] The driving section  100  is constructed such that the rotational power of the engine can be transmitted from a drive pulley  13  to a bracket  14 , and then to a rotating shaft  12  that protrudes out of a front housing  11 . In the refrigerant compressing section  200 , the crank chamber  15  is formed as a closed space surrounded by a front housing  11  and a cylinder block  16 . The rotating shaft  12  is rotatably installed in the crank chamber  15 , across the length of the front housing  11  and cylinder block  16 .  
     [0041] The drive pulley  13  is rotatably supported by an angular bearing  17  at the front housing  11 . A drive belt (not shown) is installed around the circumference of the drive pulley  13 . The bracket  14 , which rotates together with the drive pulley  13 , is coupled to one end of the rotating shaft  12  that protrudes from the front housing  11 . As can be seen, the rotation of the vehicle engine is directly transmitted to the variable displacement compressor  1 , with no intervening clutch mechanisms (e.g., electromagnetic clutch) between them.  
     [0042] To seal off the crank chamber  15  from the exterior space of the refrigerant compressing section  200 , a lip seal  18  is placed between the front housing  11  and the front portion of the rotating shaft  12 . The rotational support member  19  is fixed to the rotating shaft  12  in the crank chamber  15 . A swash plate  20  is supported in such a way that it can be inclined at an oblique angle to the axis of the rotating shaft  12 . The swash plate  20  has a guide pin  22 , whose spherical top portion is engaged with a support arm  21  that is mounted on the rotational support member  19  in a protruding manner. This linkage between the support arm  21  and guide pin  22  enables the swash plate  20  to rotate together with the rotating shaft  12 .  
     [0043] Interposed between the rotational support member  19  and swash plate  20  is an inclination-reducing spring  23 , which urges the swash plate  20  in the direction that its inclination angle is reduced. The maximum swash plate angle is restricted by an inclination-limiting protrusion  20   a  of the swash plate  20  itself, which juts out toward the rotational support member  19 .  
     [0044] The rotating shaft  12  is rotatably supported at its rear end by a radial bearing  24  that is mounted at a central axis position of the cylinder block  16 .  
     [0045] The cylinder block  16  has a plurality of cylinder bores  16   a  formed in a manner that they pass through the cylinder block  16 . Those cylinder bores  16   a  house a plurality of single-headed pistons  25  (hereafter, “pistons”), one for each. The swash plate  20  engages with the head of each piston  25  via shoes  26 , which permits rotational motion of the swash plate  20  to be converted into reciprocating motion of the pistons  25 . Placed between the rotational support member  19  and front housing  11  is a thrust bearing  28 , which receives reaction forces that are caused by the compression of refrigerant and act on the rotational support member  19  via the pistons  25  and swash plate  20 .  
     [0046] The capacity controlling section  300  is attached to the refrigerant compressing section  200 , with a valve plate  27  separating them. The capacity controlling section  300  is made up of a rear housing  31  located next the valve plate  27  and a capacity control valve  30  (described later) installed and secured in a predetermined position in the rear housing  31 . The rear housing  31  provides the following separate cavities formed immediately beside the valve plate  27 : suction chambers  32 , discharge chambers  33 , and a communication passage  34 . The suction chambers  32  are cavities at suction pressure Ps. The discharge chambers  33  at discharge pressure PdH receive the refrigerant compressed by the refrigerant compressing section  200 . The communication passage  34  communicates with the crank chamber, and hence is at crank chamber pressure Pc. In addition, the rear housing  31  provides an outlet port  1   a  and an inlet port  1   b  of the variable displacement compressor  1 , as well as a housing cavity  35  for accommodating the capacity control valve  30 . Further, the rear housing  31  has several communication holes  36  to  39  formed in its body. The first communication hole  36  connects the inlet port  1   b  with the suction chambers  32 . The second communication hole  37  connects the housing cavity  35  with the communication passage  34 , which further leads to the crank chamber  15 . The housing cavity  35  can also communicate with the discharge chamber  33  through the third communication hole  38 . The fourth communication hole  39  permits the housing cavity  35  to communicate with the outlet port  1   a  of the variable displacement compressor  1 .  
     [0047] A suction relief valve  32   v  is placed at each cylinder port connecting to the suction chamber  32 , on the side of the valve plate  27  adjacent to the cylinder bores  16   a . A discharge relief valve  33   v  is placed similarly at each cylinder port connecting to its corresponding discharge chambers  33 , but on the opposite side of the valve plate  27 , remote from the cylinder bores  16   a . The suction chambers  32 , one for each cylinder bore  16   a , communicate with each other in the rear housing  31 , as well as with the first communication hole  36 . Likewise, the discharge chambers  33  communicate with each other in the rear housing  31 , as well as with the third communication hole  38 . As the pistons  25  reciprocate, the refrigerant gas in the suction chamber  32  is sucked into each cylinder bore  16   a  through its corresponding suction relief valve  32   v  and then discharged from those cylinder bores  16   a  to their corresponding discharge chambers  33  through respective discharge relief valves  33   v.    
     [0048] While not shown in FIG. 1, there is a fixed orifice between the crank chamber  15  and suction chambers  32  to release the refrigerant from the crank chamber  15  to the suction chambers  32 .  
     [0049] The following will now describe several specific examples of the proposed capacity control valve for a variable displacement compressor.  
     [0050] First Embodiment  
     [0051]FIG. 2 is a detailed sectional view of a capacity control valve for a variable displacement compressor according to the first embodiment.  
     [0052] This capacity control valve  30  is made up of a first control valve  30 A, a second control valve  30 B, and a solenoid unit  30 C.  
     [0053] The first control valve  30 A has two ports  41  and  42  formed on its body  40 . One port  41  receives a discharge pressure PdH from the discharge chambers  33  through the third communication hole  38  of the rear housing  31  shown in FIG. 1. The other port  42  outputs refrigerant at discharge pressure PdL that has been reduced at the first control valve  30 A, for delivery through the fourth communication hole  39  and then the high-pressure refrigerant line  2 . Bored between those two ports  41  and  42  is a valve hole  45  for communication of refrigerant, the upstream edge of which is intended to function as a first valve seat  45   a . In an upstream space adjacent to the first valve seat  45   a , a ball-shaped valve element (ball valve element)  46  is placed opposite to the first valve seat  45   a . This ball valve element  46  is referred to herein as the first valve element. The valve hole space communicating with the port  41  accommodates a coil spring  48  that urges the ball valve element  46  in the direction that it closes the passage, and the amount of that spring load can be adjusted by turning an adjustment screw  47 , which is screwed into the body  40 .  
     [0054] The downstream side of the ball valve element  46  is in contact with one end of a shaft  49  that extends in the axial direction of the solenoid unit  30 C through the valve hole of the first valve seat  45   a . This shaft  49  is supported by a bearing  50   a  formed in the body  40 , and the bearing  50   a  has a communication hole  50   b  to equalize the inside pressure of the solenoid unit  30 C with the discharge pressure PdL.  
     [0055] The solenoid unit  30 C contains a solenoid coil  51  that has a cylindrical cavity, in which a sleeve  52  is fitted. As the fixed core of the solenoid actuator, a core  53  is pressed into the sleeve  52  through its opening end adjacent to the first control valve  30 A. The sleeve  52  also contains a plunger  54  that can slide in its axial direction while being urged by a coil spring  55  in the downward direction as viewed in FIG. 2. The plunger  54  is fixed to the lower end (as viewed in FIG. 2) of the shaft  49  running coaxially through the core  53 . This arrangement permits the capacity control valve  30  to operate as follows. When the solenoid coil  51  is in de-energized state, the plunger  54  is set away from the core  53  due to the force of the coil spring  55 , causing the shaft  49  extending from the plunger  54  to lose contact with the ball valve element  46 . As a result, the first control valve  30 A becomes fully closed because the freed ball valve element  46  is seated on the first valve seat  45   a , being urged by another coil spring  48 . When, on the other hand, the solenoid coil  51  is energized, the plunger  54  attracted by the magnetized core  53  will pushes the ball valve element  46  via the shaft  49  in the valve-opening direction (i.e., in the direction that the valve element will leave its corresponding valve seat). The ball valve element  46  thus moves, and the amount of this movement, or the valve lift (or openness), is proportional to the electrical current being supplied to the solenoid coil  51 . This means that the control current given to the solenoid coil  51  determines the cross-sectional area of the refrigerant passageway that the first control valve  30 A provides. In other words, the first control valve  30 A functions as a variable orifice, which changes its cross-sectional size as specified by the control current to allow the discharged refrigerant to pass through it.  
     [0056] The solenoid unit  30 C described above is intended, not for directly controlling high-pressure refrigerant flow, but for controlling the first control valve  30 A so that a small differential pressure will be produced depending on the discharge flow rate Qd of the refrigerant passing therethrough. Since only a small power is needed to achieve the purpose, it is possible to reduce the size of the solenoid unit  30 C.  
     [0057] The second control valve  30 B has a body  40   a , which is screwed to the body  40  of the first control valve  30 A so that the two valves  30 A and  30 B are stacked in series. The body  40   a  has two ports  43  and  44 . One port  43  is used to apply controlled pressure Pc to the crank chamber, and the other port  44  is used to introduce discharge pressure PdL that has been reduced at the first control valve  30 A. The body  40   a  also has an opening at its bottom end, which communicates with the port  41  to receive discharge pressure PdH of the discharge chambers  33  through a communication hole  47   a  formed on an adjustment screw  47 . Between this opening and the port  43 , a second valve seat  56  is formed as an integral part of the body  40   a . Placed opposite to this second valve seat  56  in the port  43  is a second valve element  57 . The second valve element  57  is a taper-shaped member that is integrally formed with a cylindrical piston  58 , where the piston  58  can move in its axial direction within a cylinder that is bored on the axis of the body  40   a . A coil spring  60  is installed at the upper end portion of the piston  58  as viewed in FIG. 2, which urges the second valve element  57  in the valve-closing direction. This spring load depends on how much an adjustment screw  59  is screwed into the body  40   a . The adjustment screw  59  has a through hole  59   a  at its central position, and this through hole  59   a  serves as a passage for introducing the reduced discharge pressure PdL from the port  44  to the space above the piston  58 . The second valve element  57  and piston  58  thus receive different pressures at their both endfaces apart in the direction of their axis. That is, the second valve element  57  receives discharge pressure PdH from its nearest port  41 , while the piston  58  receives discharge pressure PdL from its nearest port  44 . Their differential pressure ΔP determines the lift of the second valve element  57 . More specifically, differential pressure ΔP is produced when refrigerant flows through a passage with a certain cross-sectional area that is determined by the first control valve  30 A. Then the second control valve  30 B functions as a constant differential pressure valve that controls the amount of refrigerant flowing into the crank chamber  15  in such a way that the above differential pressure ΔP will be maintained at a constant level.  
     [0058] Several O-rings are provided around the periphery of the capacity control valve  30 . They include: an O-ring  29   a  to seal up the gap between the ports  44  and  43 , another O-ring  29   b  between the ports  43  and  41 , yet another O-ring  29   c  between the ports  41  and  42 , still another O-ring  29   d  between the port  42  and solenoid unit  30 C, and yet another O-ring  29   e  to seal the solenoid unit  30 C off from the surrounding atmosphere.  
     [0059] The variable displacement compressor  1  described above operates as follows. When the rotating shaft  12  is driven by the engine power, the swash plate  20  begins to wobble while turning around that rotating shaft  12 . This wobbling produces reciprocating motion of the pistons  25  that are linked to the outer regions of the swash plate  20 , which causes refrigerant to be sucked from the suction chambers  32  into the cylinder block  16 . The refrigerant is thus compressed and discharged toward the discharge chambers  33 .  
     [0060] Suppose here that the solenoid unit  30 C is in de-energized state. Since the first control valve  30 A is fully closed in this state, the refrigerant discharged to the discharge chambers  33  is entered to the crank chamber  15  in its entirety via the second control valve  30 B. This causes the variable displacement compressor  1  to run in the minimum capacity mode.  
     [0061] When a predetermined amount of control current is supplied to the solenoid unit  30 C, the first control valve  30 A gives a predetermined openness (valve lift) associated with that control current. The first control valve  30 A now acts as an orifice with a certain cross-sectional size, allowing a flow of refrigerant through the high-pressure refrigerant line  2  leading to the condenser  3 . This develops a certain amount of differential pressure ΔP (=PdH−PdL) across the orifice, depending on the actual discharge flow rate Qd of the refrigerant passing through it.  
     [0062] In the second control valve  30 B, its second valve element  57  and piston  58  are responsive to the differential pressure ΔP across the first control valve  30 A, which is functioning here as an orifice. The second control valve  30 B controls the flow of refrigerant from the discharge chambers  33  to the crank chamber  15  in such a way that the differential pressure ΔP will be maintained at a constant level. This control action may vary the capacity of the variable displacement compressor  1  as needed, so as to regulate the flow of refrigerant being discharged therefrom.  
     [0063] The flow rate of refrigerant discharged from the variable displacement compressor  1  is determined depending on how much refrigeration capacity is required in the present refrigeration cycle. Actually, the refrigeration capacity is calculated from various parameters, which include: engine rotation speed, vehicle speed, accelerator pedal position, indoor and outdoor temperatures, set temperatures, and monitoring signals supplied from various temperature and pressure sensors. The amount of the electrical current that energizes the solenoid coil  51  is determined on the basis of this calculation result.  
     [0064] Suppose here that the engine rotation rises and the discharge flow rate of refrigerant is increased accordingly. This develops an increased differential pressure ΔP across the first control valve  30 A. In response to ΔP, the second control valve  30 B lifts its valve element, so that more refrigerant will be supplied from the discharge chambers  33  to the crank chamber  15 . As a result, pressure Pc in the crank chamber  15  rises, and the variable displacement compressor  1  is thus controlled in an output-reducing condition. The variable displacement compressor  1  now operates with a smaller discharge capacity, suppressing the discharge flow rate of refrigerant, and thus reducing the differential pressure ΔP. In this way, the discharge flow rate Qd of refrigerant is regulated by controlling the second control valve  30 B so that the differential pressure across the orifice (i.e., the first control valve  30 A being configured as a proportional solenoid valve) will be maintained at a constant level.  
     [0065] The engine rotation may in turn drops. This decreases the flow rate of discharged refrigerant and reduces the differential pressure across the first control valve  30 A accordingly. The refrigerant discharge pressure PdH falls, and thus the second control valve  30 B operates in such a way as to reduce the refrigerant flow from the discharge chambers  33  to the crank chamber  15 . Pressure Pc in the crank chamber  15  falls accordingly, which causes the variable displacement compressor  1  to operate in a capacity-increasing condition, thus recovering the discharge. In this way, the discharge flow rate Qd of refrigerant is maintained at the constant level.  
     [0066] As can be seen from the above description, the present invention provides a capacity control valve  30  for use with a variable displacement compressor. This capacity control valve  30  is composed of a first control valve  30 A that functions as a variable orifice controlled by a solenoid unit  30 C and a second control valve  30 B that controls the pressure in the crank chamber  15  so as to maintain a constant differential pressure across the variable orifice. The present invention combines those components in an integrated way, thus providing a compact, space-saving design for the capacity control functions (i.e., regulating the flow rate Qd of refrigerant discharged from the variable displacement compressor  1 ).  
     [0067] Second Embodiment  
     [0068]FIG. 3 is a sectional view of a capacity control valve for a variable displacement compressor according to the second embodiment of the invention. Since many of the valve components shown in FIG. 3 are identical or similar to those discussed in FIG. 2, the same reference numerals are used in FIG. 3 to designate such components, and the following section will not provide details about them.  
     [0069] The illustrated capacity control valve  30  of the second embodiment resembles that of the first embodiment (FIG. 2) in that they share the same basic structure of their first control valve  30 A and second control valve  30 B, as well as in that the two valves  30 A and  30 B are stacked in series. The second embodiment is, however, different from the first embodiment in that the ball valve element  46  of its first control valve  30 A is arranged in such a way that it will allow more refrigerant to pass through when it is displaced following the stream of refrigerant. In other words, the ball valve element  46 , or the first valve element, is placed on the downstream side with respect to the first valve seat  45   a . To make this arrangement possible, the plunger  54  and core  53  have to swap their positions in the solenoid unit  30 C.  
     [0070] The first control valve  30 A stays in a fully closed position when the solenoid unit  30 C is not energized, because the ball valve element  46  is seated on the first valve seat  45   a  due to the force of a coil spring  55  installed between the plunger  54  and core  53 . Accordingly, the refrigerant coming into the port  41  at discharge pressure PdH is led to the crank chamber  15  in its entirety through the second control valve  30 B, meaning that the variable displacement compressor  1  now operates in the minimum capacity condition.  
     [0071] When a predetermined amount of control current is supplied to a solenoid coil  51  of the solenoid unit  30 C, the plunger  54  is attracted by the core  53  and stops at the point where the attraction force associated with that control current comes into balance with the urging force of the coil spring  55 . In this state, the ball valve element  46  is lifted, keeping in contact with the shaft  49  due to the force of the coil spring  48 , and the consequent gap serves as an orifice with a designated size.  
     [0072] Variations in the engine speed affect the discharge flow from the variable displacement compressor. In this situation, the capacity control valve  30  of the second embodiment operates in the same way as in the first embodiment described earlier in FIG. 2.  
     [0073] Third Embodiment  
     [0074]FIG. 4 is a sectional view of a capacity control valve for a variable displacement compressor according to a third embodiment of the invention. Since many of the valve components shown in FIG. 4 are identical or similar to those discussed in FIGS. 2 and 3, the same reference numerals are used in FIG. 4 to designate such components, and the following section will not provide details about them.  
     [0075] Recall that a ball valve element  46  is used as the first valve element in the first and second embodiments (FIGS. 2 and 3). However, the illustrated capacity control valve  30  of the third embodiment is different in that a taper-shaped valve element  61  is placed on the upstream side with respect to the first valve seat  45   a  while receiving a force in the valve-opening direction. Another difference is that it eliminates the port  44 , which is employed in the first and second embodiments to introduce discharge pressure PdL into the second control valve  30 B. Instead, the illustrated capacity control valve  30  has a communication hole  62  formed in the body  40  to serve the purpose. To make this arrangement possible, the port  41  for discharge pressure PdH and port  42  for discharge pressure PdL have swapped their positions in the third embodiment. Yet another difference is that the crank chamber  15  receives discharge pressure PdL after orifice.  
     [0076] More specifically, the first control valve  30 A has a port  41  formed in its body  40  to receive discharge pressure PdH from the discharge chambers  33 . It has another port  42  formed in the same body  40  to supply the high-pressure refrigerant line  2  with discharge pressure PdL that is reduced by the first control valve  30 A. A valve hole  45  is bored for communication between those two ports  41  and  42 , and its upstream-side edge is intended to function as a first valve seat  45   a . A taper-shaped valve element  61  is placed in an upstream-side space, opposite to the first valve seat  45   a . This valve element  61  is referred to herein as a first valve element. A flange  61   a  is formed as an integral part of the first valve element  61 , on its circumference remote from the first valve seat  45   a.    
     [0077] The flange  61   a  retains one end of a coil spring  48  that is placed around the first valve element  61  against the first valve seat  45   a . This coil spring  48  urges the first valve element  61  in the direction that the valve will open. The valve element  61  is also coupled to an end of a shaft  49  that extends from the solenoid unit  30 C in its axial direction. When the solenoid unit  30 C is in de-energized state, the coil spring  55  makes the first valve element  61  sit on the first valve seat  45   a . The shaft  49  is supported by a bearing  50   a  at its middle portion adjacent to the first control valve  30 A, as well as by another bearing  50   c  at its bottom end. The bottom-end bearing  50   c  has been pressed into the central bore of the core  53 .  
     [0078] The second control valve  30 B is coupled in series with the first control valve  30 A, the space above the piston  58  being closed by a lid  59   b . Its body  40  has a communication hole  62  to communicate that space with the port  41 , through which discharge pressure PdH acts on the back face of the piston  58 . This arrangement of the third embodiment reduces the number of ports that should be created on the body  40 , thus making it easier to manufacture the capacity controlling section  300  of a variable displacement compressor  1 . It also eliminates some O-rings that are required when fitting the capacity control valve  30  into the housing cavity  35  of the variable displacement compressor  1 .  
     [0079] As can be seen from the above description, the illustrated capacity control valve  30  contains a first control valve  30 A composed of a first valve element  61  and first valve seat  45   a , the first valve element  61  being a taper-shaped valve element located in an upstream-side space adjacent to the first valve seat  45   a . Here, the first control valve  30 A sets a certain cross-section area for the refrigerant passageway in accordance with how much the solenoid unit  30 C is energized. The second control valve  30 B is responsive to differential pressure developed across the first control valve  30 A to control the flow rate of refrigerant supplied from the discharge chambers  33  to the crank chamber  15 . In the way described above, the capacity control valve  30  regulates the flow rate Qd of refrigerant that the variable displacement compressor  1  discharges.  
     [0080] Fourth Embodiment  
     [0081]FIG. 5 is a sectional view of a capacity control valve for a variable displacement compressor according to a fourth embodiment of the invention. Since many of the valve components shown in FIG. 5 are identical or similar to those discussed in FIG. 2, the same reference numerals are used in FIG. 5 to designate such components, and the following section will not provide details about them.  
     [0082] Compared with the first embodiment discussed earlier in FIG. 2, the capacity control valve  30  of the fourth embodiment is distinct in the following points. First, its first control valve  30 A employs a spool-shaped valve element  63  as a first valve element. Second, its second control valve  30 B uses a taper-shaped valve element  64  as a second valve element. Third, as the counterpart of the spool-shaped valve element  63  (or first valve element), a first valve seat  63   a  is provided as an integral part of the second valve element in the second control valve  30 B. This first valve seat  63   a  is designed to set a required cross-section area for refrigerant passage while moving together with the second valve element.  
     [0083] More specifically, the second control valve  30 B has a second valve seat  56  and its corresponding second valve element  64  with a tapered shape. The second valve seat  56  is formed as an integral part of the body  40 , in the middle of a refrigerant passageway between two ports  41  and  43 , the former receiving refrigerant from the discharge chambers  33  and the latter delivering refrigerant to the crank chamber  15 . Opposite the second valve seat  56 , the second valve element  64  is located in an upstream-side space, where discharge pressure PdH is available. The second valve element  64  is urged by a coil spring  66  in the valve-opening direction. Integrally formed with this second valve element  64  is a pressure responsive member  64   a , whose base portion detects differential pressure between two different discharge pressures PdH and PdL. The pressure responsive member  64   a  is installed inside the body  40  in a manner that it can come in contact with or move away from the second valve seat  56  according to the differential pressure acting thereon. The pressure responsive member  64   a  has a central cavity around its axis, the bottom end of which is open. The pressure responsive member  64   a  has also a hole  64   b  in its upper portion, which allows the discharge pressure PdH in the port  41  to reach the central cavity.  
     [0084] The first control valve  30 A, on the other hand, has a first valve seat  63   a  formed around the rim of the bottom opening of the pressure responsive member  64   a , which operates together with a spool-shaped valve element (or a first valve element)  63  located below the bottom opening. The first valve seat  63   a  and first valve element  63  set an appropriate cross-sectional area for a passageway that delivers refrigerant from one port  41  to another port  42  via the hole  64   b  of the pressure responsive member  64   a.    
     [0085] The spool-shaped valve element  63 , or the first valve element, is integrally formed with a pressure responsive piston  63   p  having the same cross-sectional area as the valve hole of the first valve seat  63   a . A flange  63   b  is formed around this valve element  63 , on a downstream-side portion remote from the first valve seat  63   a . This flange  63   b  is used to receive a force of a coil spring  48 , which urges the valve element  63  in the value-opening direction. Another coil spring  60  is disposed between the pressure responsive piston  63   p  and the pressure responsive member  64   a  of the second valve element  64 . The pressure responsive piston  63   p  is slidably supported by a plug  40   b , which seals the bottom of the body  40 . The pressure responsive piston  63   p  may also be pressed upward by a shaft  49 . This shaft  49  extends from the solenoid unit  30 C in its axial direction and reaches the bottom endface of the pressure responsive piston  63   p . A pressure balancing hole  65  is bored through the pressure responsive piston  63   p  to introduce a back pressure from the upstream-side cavity adjacent to the first valve seat  63   a . This structure permits the discharge pressure PdH from the port  41  to act equally on both the bottom end of the pressure responsive piston  63   p  and the top end of the spool-shaped valve element  63 . Since those two opposing forces cancel each other out, the discharge pressure PdH never disturbs the solenoid unit  30 C when it controls the position of the valve element  63 .  
     [0086] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and shaft  49  upward as viewed in FIG. 5, making the spool-shaped valve element  63  fit into the central opening of the pressure responsive member  64   a . The first control valve  30 A is fully closed in this state, while the second control valve  30 B fully opens itself in attempt to obtain a predetermined differential pressure between discharge pressures PdH and PdL acting on the pressure responsive member  64   a.    
     [0087] When the solenoid unit  30 C is energized, the shaft  49  moves downward as viewed in FIG. 5. This movement of the shaft  49  allows the spool-shaped valve element  63  to come out of the first valve seat  63   a  and maintain a certain amount of gap between itself and the first valve seat  63   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the pressure responsive member  64   a  of the second valve element  64  receives differential pressure between discharge pressures PdH and PdL, which moves the second valve element  64  so that the differential pressure will become a predetermined level. With this movement of the second valve element  64 , the second control valve  30 B controls the refrigerant being delivered from its port  43  to the crank chamber  15 .  
     [0088] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. The increased differential pressure causes the second valve element  64  to move in the valve-opening direction, so that the second control valve  30 B supplies more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in a valve-closing direction, thus reducing the refrigerant flowing into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges.  
     [0089] Fifth Embodiment  
     [0090]FIG. 6 is a sectional view of a capacity control valve for a variable displacement compressor according to a fifth embodiment of the invention. Since many of the valve components shown in FIG. 6 are identical or similar to those discussed in FIG. 5, the same reference numerals are used in FIG. 6 to designate such components, and the following section will not provide details about them.  
     [0091] The capacity control valve  30  of the fifth embodiment is similar to that of the fourth embodiment (FIG. 5) in that their first control valve  30 A employs a spool-shaped valve element  63  as a first valve element. The fifth embodiment, however, is different from the fourth embodiment in that the port  41  for discharge pressure PdH and port  42  for discharge pressure PdL have swapped their positions. While the second control valve  30 B of the fourth embodiment has a taper-shaped valve element  64  as a second valve element, the fifth embodiment employs a ball valve element  67  for that purpose. This ball valve element (or the second valve element)  67  is located downstream with respect to the second valve seat  56 , while being urged in the valve-opening direction by a stem that extends through the valve hole and the first control valve  30 A.  
     [0092] More specifically, the second control valve  30 B has a second valve seat  56  formed as an integral part of its body  40 , and a ball valve element  67  is located in a downstream-side space adjacent to the second valve seat  56 . The ball valve element  67  is urged by a coil spring  60  in the valve-closing direction, the spring load of which can be adjusted by turning an adjustment screw  59 . The adjustment screw  59  has a through hole  59   a  in its central portion, and this through hole  59   a  serves as a port  43  for delivery of refrigerant to the crank chamber  15 .  
     [0093] The first control valve  30 A has a first valve seat  63   a  at the bottom end of a pressure responsive member  64   a . The pressure responsive member  64   a  is integrally formed with a shaft  68  that extends in the axial direction of the second control valve  30 B, passing through the valve hole of same. The upper end of this shaft  68  is in contact with the ball valve element  67  of the second control valve  30 B.  
     [0094] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and shaft  49  in the upward direction as viewed in FIG. 6, making the spool-shaped valve element  63  fit into the central opening of the pressure responsive member  64   a . The first control valve  30 A is fully closed in this state, while the second control valve  30 B is fully opened because of the differential pressure that acts on the pressure responsive member  64   a.    
     [0095] When the solenoid unit  30 C is energized, the shaft  49  moves downward as viewed in FIG. 6. This movement of the shaft  49  allows the spool-shaped valve element  63  to come out of the first valve seat  63   a  and maintain a certain amount of gap between itself and the first valve seat  63   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the pressure responsive member  64   a  receives differential pressure between discharge pressures PdH and PdL, which moves the ball valve element  67  so that the differential pressure will become a predetermined level. With this movement of the ball valve element  67 , the second control valve  30 B controls the flow rate of the refrigerant being delivered from its port  43  to the crank chamber  15 .  
     [0096] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure, the ball valve element  67  gives a greater openness, so that the second control valve  30 B supplies more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in a valve-closing direction, thus reducing the refrigerant flowing into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges.  
     [0097] Sixth Embodiment  
     [0098]FIG. 7 is a sectional view of a capacity control valve for a variable displacement compressor according to a sixth embodiment of the invention. Since many of the valve components shown in FIG. 7 are identical or similar to those discussed in FIG. 2, 4, or  6 , the same reference numerals are used in FIG. 7 to designate such components, and the following section will not provide details about them.  
     [0099] As in the third embodiment (FIG. 4), the capacity control valve  30  of the sixth embodiment is different from that of the fifth embodiment (FIG. 6) in that its first control valve  30 A employs a taper-shaped valve element  61  as a first valve element, and in that the valve element  61  is located in an upstream-side space adjacent to the first valve seat  63   a , being urged in the valve-opening direction.  
     [0100] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and shaft  49  upward as viewed in FIG. 7, making the taper-shaped valve element  61  sit on the first valve seat  63   a . The first control valve  30 A is fully closed in this state, while the second control valve  30 B is fully opened because of the differential pressure that acts on the pressure responsive member  64   a.    
     [0101] When the solenoid unit  30 C is energized, the shaft  49  moves downward as viewed in FIG. 7. This movement of the shaft  49  allows the taper-shaped valve element  61  to leave the first valve seat  63   a  and maintain a certain amount of gap between itself and the first valve seat  63   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the pressure responsive member  64   a  receives differential pressure between discharge pressures PdH and PdL, which moves the ball valve element  67  so that the differential pressure will become a predetermined level. With this movement of the ball valve element  67 , the second control valve  30 B controls the flow rate of the refrigerant being delivered from its port  43  to the crank chamber  15 .  
     [0102] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure, the ball valve element  67  gives a greater openness, allowing the second control valve  30 B to supply more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in a valve-closing direction, thus reducing the refrigerant flowing into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges.  
     [0103] Seventh Embodiment  
     [0104]FIG. 8 is a sectional view of a capacity control valve for a variable displacement compressor according to a seventh embodiment of the invention. Since many of the valve components shown in FIG. 8 are identical or similar to those discussed in FIG. 6 or  7 , the same reference numerals are used in FIG. 8 to designate such components, and the following section will not provide details about them.  
     [0105] The illustrated capacity control valve  30  of the seventh embodiment is different from that of the sixth embodiment (FIG. 7) only in that its first valve element  61  is designed to cancel the back pressure in order to prevent the discharge pressure PdH from affecting operation of the first control valve  30 A. This concept is what has been described in the fifth embodiment (FIG. 6). The capacity control valve  30  of the seventh embodiment operates basically in the same as that of the sixth embodiment.  
     [0106] More specifically, when the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and shaft  49  in the upward direction as viewed in FIG. 8. This makes the taper-shaped valve element  61  sit on the first valve seat  63   a . Accordingly, the first control valve  30 A is fully closed, while the second control valve  30 B is fully opened.  
     [0107] When the solenoid unit  30 C is energized, the shaft  49  moves downward as viewed in FIG. 8. This movement of the shaft  49  allows the taper-shaped valve element  61  to leave the first valve seat  63   a  and maintain a certain amount of gap between itself and the first valve seat  63   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the pressure responsive member  64   a  receives differential pressure between discharge pressures PdH and PdL, which moves the ball valve element  67  so that the differential pressure will become a predetermined level. With this movement of the ball valve element  67 , the second control valve  30 B controls the flow rate of the refrigerant being delivered from its port  43  to the crank chamber  15 .  
     [0108] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure, the ball valve element  67  gives a greater openness, allowing the second control valve  30 B to supply more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in a valve-closing direction, thus reducing the refrigerant flowing into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges.  
     [0109] Eighth Embodiment  
     [0110]FIG. 9 is a sectional view of a capacity control valve for a variable displacement compressor according to an eighth embodiment of the invention. Since many of the valve components shown in FIG. 9 are identical or similar to those discussed in FIG. 2 or  5 , the same reference numerals are used in FIG. 9 to designate such components, and the following section will not provide details about them.  
     [0111] The illustrated capacity control valve  30  of the eighth embodiment resembles that of the fourth embodiment (FIG. 5) in that both of them use a taper-shaped valve element  64  as their second valve element. The eighth embodiment is, however, different from the fourth embodiment in that its first valve seat  45   a  is not designed to move, but is constructed as an integral part of the body  40  of the first control valve  30 A. Another difference is that a plurality of ball valve elements  46  are employed to serve the function of the first valve element.  
     [0112] More specifically, the first control valve  30 A is constructed as follows. The body  40  has a plurality of valve holes  45  bored along a circle that is concentric with a cross section of the body  40  itself, the bottom-end edge of each hole serving as a first valve seat  45   a . A ball valve element  46  is placed at a downstream-side space adjacent to each first valve seat  45   a . Those ball valve elements  46  sit on the downstream-side surface of a support member  70 , which is urged by a coil spring  60  in the downward direction as viewed in FIG. 9. The support member  70  also receives a force of a coil spring  55  in the solenoid unit  30 C, via a plunger  54  and shaft  49 , which acts in the upward direction as viewed in FIG. 9.  
     [0113] The second control valve  30 B, on the other hand, has a pressure responsive member  64   a , which is urged by a coil spring  66  upward as viewed in FIG. 9. Since this pressure responsive member  64   a  is integrally formed with a second valve element  64 , the urging force of the coil spring  66  also acts on the second valve element  64  in the valve-closing direction. The pressure responsive member  64   a , in combination with the second valve element  64 , is supposed to be responsive to differential pressure ΔP between two different discharge pressures PdH and PdL, which are observed on the upstream end and downstream end of the first control valve  30 A, respectively.  
     [0114] When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and shaft  49  in the upward direction as viewed in FIG. 9. This makes the ball valve elements  46  fit with corresponding first valve seats  45   a , and thus the first control valve  30 A is fully closed. With the refrigerant at discharge pressure PdH present in the port  41 , the maximum differential pressure acts on the pressure responsive member  64   a , making the second control valve  30 B fully open. The variable displacement compressor  1  thus operates in the minimum capacity condition.  
     [0115] When the solenoid unit  30 C is energized, the shaft  49  moves downward as viewed in FIG. 9. This movement of the shaft  49 , in conjunction with the force of the coil spring  60 , allows the support member  70  to follow in the same direction while keeping in contact with the shaft  49 . Each ball valve element  46  thus leaves the corresponding first valve seat  45   a  and maintains a certain amount of gap between itself and that valve seat  45   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the pressure responsive member  64   a  adjacent to the second valve element  64  receives differential pressure between discharge pressures PdH and PdL, which moves the second valve element  64  so that the differential pressure will become a predetermined level. This movement of the second valve element  64  controls the flow rate of the refrigerant at discharge pressure PdH that flows through the second control valve  30 B, from one port  41  to another port  43 .  
     [0116] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure acting on the pressure responsive member  64   a , the second valve element  64  in the second control valve  30 B is moved in the direction that it gives a greater openness, allowing the second control valve  30 B to supply more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B reduces the refrigerant into the crank chamber  15  because the pressure responsive member  64   a  impels the second valve element  64  in the valve-closing direction. As a result of this control action, the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges.  
     [0117] Ninth Embodiment  
     [0118]FIG. 10 is a sectional view of a capacity control valve for a variable displacement compressor according to a ninth embodiment of the invention. Since many of the valve components shown in FIG. 10 are identical or similar to those discussed in FIG. 9, the same reference numerals are used in FIG. 10 to designate such components, and the following section will not provide details about them.  
     [0119] The capacity control valve  30  of this embodiment differs from that of the eighth embodiment (FIG. 9) in its first control valve  30 A, particularly in the structure of its first valve element and first valve seat.  
     [0120] More specifically, the first control valve  30 A is constructed as follows. The body  40  has a doughnut-shaped valve hole  45  hollowed along a circle that is concentric with a cross section of the body  40  itself, and the bottom-end edge of that hole is supposed to serve as a first valve seat  45   a . It should be noted that the doughnut-shaped valve hole  45  does not go through the floor of the body  40  in its entire circumference, but some middle part of the floor is left unhallowed at a few places on its circumference. This is necessary because the central portion of the floor should still be connected to  64   a  in that portion. As the counterpart of the first valve seat  45   a , a flat valve element  71  is disposed on the downstream side, together with a plug  40   b  that supports the flat valve element  71  in a way that it can slide in the axial direction.  
     [0121] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and shaft  49  in the upward direction as viewed in FIG. 10, making the flat valve element  71  abut on the first valve seat  45   a . The first control valve  30 A is fully closed in this state. With the refrigerant at discharge pressure PdH present in the port  41 , the maximum differential pressure acts on the pressure responsive member  64   a , making the second control valve  30 B fully open. The variable displacement compressor  1  thus operates in the minimum capacity condition.  
     [0122] When the solenoid unit  30 C is energized, the shaft  49  moves downward as viewed in FIG. 10. This movement of the shaft  49 , in conjunction with the force of a coil spring  60 , allows the flat valve element  71  to follow in the same direction while keeping in contact with the shaft  49 . The flat valve element  71  thus leaves the first valve seat  45   a  and maintains a certain amount of gap between itself and that valve seat  45   a . As a result, the refrigerant coming into the port  41  at discharge pressure pdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the pressure responsive member  64   a  adjacent to the second valve element  64  receives differential pressure between discharge pressures PdH and PdL, which moves the second valve element  64  so that the differential pressure will become a predetermined level. This movement of the second valve element  64  controls the flow rate of the refrigerant at discharge pressure PdH that flows through the second control valve  30 B, from one port  41  to another port  43 .  
     [0123] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure acting on the pressure responsive member  64   a , the second valve element  64  in the second control valve  30 B is moved in the direction that it gives a greater openness, allowing the second control valve  30 B to supply more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B reduces the refrigerant into the crank chamber  15  because its pressure responsive member  64   a  impels the second valve element  64  in the valve-closing direction. As a result of this control action, the variable displacement regulate the flow rate Qd of refrigerant that it discharges.  
     [0124] Tenth Embodiment  
     [0125]FIG. 11 is a sectional view of a capacity control valve for a variable displacement compressor according to a tenth embodiment of the invention. Since many of the valve components shown in FIG. 11 are identical or similar to those discussed in FIG. 2 or  4 , the same reference numerals are used in FIG. 11 to designate such components, and the following section will not provide details about them.  
     [0126] The capacity control valve  30  of this embodiment differs from that of the first embodiment (FIG. 2) in several points. The most prominent difference is that the tenth embodiment uses, in its first control valve  30 A, a diaphragm  72  to detect differential pressure between upstream and downstream.  
     [0127] More specifically, in a central region of the body  40 , a cylinder  40   c  is formed as an integral part of the body  40 , and the inner cavity of that cylinder  40   c  serves as a valve hole  45  to interconnect two ports  41  and  42 . The bottom end of the cylinder  40   c  functions as a first valve seat  45   a  for the first control valve  30 A. In the downstream-side space communicating with the port  42 , a taper-shaped valve element  61  is placed opposite the first valve seat  45   a . This taper-shaped valve element  61 , integrally formed with the plunger  54  of the solenoid unit  30 C, has a circumferential groove  61   b  around its round side surface at the boundary portion where the plunger  54  is joined. The groove  61   b  receives a piston ring  74 , which permits the plunger  54  to be slidably supported on the inner wall of the sleeve  52 , as well as centering the taper-shaped valve element  61  on the axis of the sleeve  52 .  
     [0128] In the second control valve  30 B, on the other hand, a valve hole is bored to allow a port  41  to communicate with another port  43 , the bottom end of which is supposed to function as a second valve seat  56 . In the upstream-side space adjacent to the second valve seat  56 , a taper-shaped second valve element  64  is placed. Integrally formed on top of this second valve element  64  are a shaft  64   c  and a piston  64   d . This piston  64   d  has the same outer diameter as the valve hole of the second valve seat  56 . The endface of the piston  64   d  remote from the second valve element  64  receives, through a communication hole  62 , discharge pressure PdH in the port  41 , so that the second valve element  64  can be driven with nothing but differential pressure between discharge pressures PdH and PdL, without being affected by the absolute value of discharge pressure PdH. The second valve element  64  is integrally formed also with a base member  64   e , which is larger in diameter than the second valve element  64  and has a hole  64   b  to introduce discharge pressure PdH from the port  41  to the inner cavity of the cylinder  40   c.    
     [0129] A sliding member  73  is provided around the outer surface of the cylinder  40   c  in the body  40  in a way that it can move in the vertical direction as viewed in FIG. 11. This sliding member  73  is connected with the inner surface of the bodies  40  and  40   a  via a diaphragm  72 , which is a doughnut-shaped sheet with a center hole. The outer circumference of the diaphragm  72  is clamped between two bodies  40  and  40   a , the latter  40   a  being pressed into the former  40 . The inner circumference of the diaphragm  72 , on the other hand, is clamped between the sliding member  73  and a ring  73   a  being fitted thereto. The base member  64   e  of the second valve element  64  is placed on the sliding member  73 , and two coil springs  60  and  66  urge those two members  64   e  and  73  such that they will keep in contact with each other. With the above arrangement, the diaphragm  72  receives differential pressure between discharge pressure PdH available at one port  41  and discharge pressure PdL at another port  42 . This differential pressure displaces the sliding member  73  in its axial direction, causing the second valve element  64  to move toward or away from its corresponding second valve seat  56 .  
     [0130] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54  and taper-shaped valve element  61  upward as viewed in FIG. 11, making the taper-shaped valve element  61  sit on the first valve seat  45   a . The first control valve  30 A is fully closed in this state. With the refrigerant at discharge pressure PdH present in the port  41 , the maximum differential pressure acts on the diaphragm  72 , making the second control valve  30 B fully open. The variable displacement compressor  1  thus operates in the minimum capacity condition.  
     [0131] When the solenoid unit  30 C is energized, the plunger  54  moves downward as viewed in FIG. 11. This movement of the plunger  54  allows the taper-shaped valve element  61  to leave the first valve seat  45   a  and maintain a certain amount of gap between itself and the first valve seat  45   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the hole  64   b  of the second valve element  64 , the central cavity of the cylinder  40   c , and the first control valve  30 A. Then, in the second control valve  30 B, the diaphragm  72  receives differential pressure between two different discharge pressures PdH and PdL, which moves the sliding member  73  upward as viewed in FIG. 11 so that the differential pressure will become a predetermined level. The second valve element  64  follows this movement of the sliding member  73 , thus controlling the refrigerant at discharge pressure PdH that flows through the second control valve  30 B, from one port  41  to another port  43 .  
     [0132] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure acting on the diaphragm  72 , the second valve element  64  in the second control valve  30 B is impelled in the direction that it gives a greater openness, allowing the second control valve  30 B to supply more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the diaphragm  72  of the second control valve  30 B receives a reduced differential pressure and reduces the refrigerant flowing into the crank chamber  15  because its sliding member  73  impels the second valve element  64  in the valve-closing direction. As a result of this control action, the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges. Note here that the second control valve  30 B is controlled to be responsive only to differential pressure between two different discharge pressures PdH and PdL, because since its second valve element  64  is decoupled from variations of discharge pressure PdH.  
     [0133] Eleventh Embodiment  
     [0134]FIG. 12 is a sectional view of a capacity control valve for a variable displacement compressor according to an eleventh embodiment of the invention. Since many of the valve components shown in FIG. 12 are identical or similar to those discussed in FIGS. 2, 5, or  11 , the same reference numerals are used in FIG. 12 to designate such components, and the following section will not provide details about them.  
     [0135] The illustrated capacity control valve  30  of the eleventh embodiment resembles that of the tenth embodiment (FIG. 11) in that both of them use a diaphragm  72  as their pressure sensing element. The eleventh embodiment is, however, different from the tenth embodiment in that the taper-shaped valve element (first valve element)  61  in its first control valve  30 A is disposed in an upstream-side space adjacent to a first valve seat  45   b  formed at the top end of the cylinder  40   c . For this reason, in the solenoid unit  30 C of the eleventh embodiment, the plunger  54  and core  53  have swapped their positions on the axis. Also, a shaft  49  is employed to connect the first valve element  61  with the plunger  54  in the solenoid unit  30 C. The first valve element  61  is urged by a coil spring  55  in the valve-closing direction.  
     [0136] The eleventh embodiment operates basically in the same way as the tenth embodiment because of its similarity in structure; that is, it uses a diaphragm  72  to detect differential pressure ΔP between the upstream and downstream ends of the first control valve  30 A, so as to control the refrigerant flow in the second control valve  30 B according to that differential pressure ΔP. In this structure, the widened base member  64   e  of the second valve element  64  has a round hole  64   f  in addition to the hole  64   b  in order to deliver the discharge pressure PdH from the port  41  toward the upstream side of the first valve element  61 .  
     [0137] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54 , shaft  49 , and first valve element  61  downward as viewed in FIG. 12, making the first valve element  61  sit on the first valve seat  45   b . The first control valve  30 A is fully closed in this state. With the refrigerant at discharge pressure PdH present in the port  41 , the maximum differential pressure acts on the diaphragm  72 , making the second control valve  30 B fully open. The variable displacement compressor  1  thus operates in the minimum capacity condition.  
     [0138] When the solenoid unit  30 C is energized, the plunger  54  moves upward as viewed in FIG. 12. This movement of the plunger  54  allows the taper-shaped valve element  61  to leave the first valve seat  45   b  and maintain a certain amount of gap between itself and the first valve seat  45   b . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through round hole  64   f  and the hole  64   b  of the second valve element  64 , the first control valve  30 A, and the central cavity of the cylinder  40   c . Then, in the second control valve  30 B, the diaphragm  72  receives differential pressure between two different discharge pressures PdH and PdL, which moves the sliding member  73  upward as viewed in FIG. 12 so that the differential pressure will become a predetermined level. The second valve element  64  follows this upward movement of the sliding member  73 , thus controlling the flow rate of the refrigerant at discharge pressure PdH that flows through the second control valve  30 B, from one port  41  to another port  43 .  
     [0139] If the refrigerant flowing through the first control valve  30 A increases, a larger differential pressure will be produced across that valve  30 A. With the increased differential pressure acting on the diaphragm  72 , the second valve element  64  in the second control valve  30 B is moved in the direction that it gives a greater openness, allowing the second control valve  30 B to supply more refrigerant into the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the diaphragm  72  of the second control valve  30 B detects a reduced differential pressure acting thereon, and thus the sliding member  73  impels the second valve element  64  in the valve-closing direction. As a result, the second control valve  30 B reduces the refrigerant supplied to the crank chamber  15 , and the variable displacement compressor  1  operates with a larger displacement so as to regulate the flow rate Qd of refrigerant that it discharges.  
     [0140] Twelfth Embodiment  
     [0141]FIG. 13 is a sectional view of a capacity control valve for a variable displacement compressor according to a twelfth embodiment of the invention. Since many of the valve components shown in FIG. 13 are identical or similar to those discussed in FIG. 4, the same reference numerals are used in FIG. 13 to designate such components, and the following section will not provide details about them.  
     [0142] Recall the capacity control valve  30  of the third embodiment shown in FIG. 4. In that embodiment, the first control valve  30 A is located between the discharge chambers  33  and crank chamber  15 , and the pressure in the crank chamber  15  is controlled by varying the flow rate of refrigerant at discharge pressure PdL that is supplied from the discharge chambers  33  into the crank chamber  15 . Unlike the third embodiment, the twelfth embodiment controls the flow rate of the refrigerant returning from the crank chamber  15  back into the suction chambers  32 . In this alternative arrangement, the variable displacement compressor  1  has a fixed orifice in the middle of a passageway that delivers refrigerant from the discharge chambers  33  to the crank chamber  15 .  
     [0143] The first control valve  30 A and solenoid unit  30 C of this capacity control valve  30  have almost the same structure as those in the third embodiment. The exception is that the first control valve  30 A is designed to route the discharged refrigerant in the direction that the stream pushes the taper-shaped valve element  61  away from the first valve seat  45   a , or in short, in the valve-opening direction.  
     [0144] In the second control valve  30 B, there are two pistons  58  and  58   a  integrally formed with a second valve element  57 . The pistons  58  and  58   a  have the same outer diameter as the valve hole of the second valve seat  56 . Discharge pressure PdH acts on the piston  58   a  and discharge pressure PdL propagates through a communication hole  62  and acts on one endface of the piston  58 . Pressure Pc of the crank chamber  15  is led from the port  43  to an upstream-side cavity adjacent to the second valve element  57 . The downstream-side room, on the other hand, communicates with the suction chambers  32  at suction pressure Ps via the port  75 . With such an arrangement of the second control valve  30 B, the second valve element  57  and piston  58  are responsive to the differential pressure ΔP developed across the first control valve  30 A, which is functioning here as an orifice. The second control valve  30 B thus controls the flow rate of the refrigerant flowing from the crank chamber  15  to the suction chambers  32  in such a way that the differential pressure ΔP will be maintained at a constant level. This control action varies the capacity of the variable displacement compressor  1  so as to regulate the flow rate of refrigerant being discharged therefrom.  
     [0145] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54 , shaft  49 , and first valve element  61  upward as viewed in FIG. 13, making the first valve element  61  sit on the first valve seat  45   a . The first control valve  30 A is fully closed in this state.  
     [0146] When the solenoid unit  30 C is energized, the plunger  54  moves downward as viewed in FIG. 13. This movement of the plunger  54  allows the first valve element  61  to leave the first valve seat  45   a  and maintain a certain amount of gap between itself and the first valve seat  45   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the second valve element  57  and piston  58 , as a single integrated member, receive differential pressure between two different discharge pressures PdH and PdL, in addition to the force of the coil spring  60 . The second valve element  57  thus moves to a point at which all those forces and pressures come into balance, which allows the refrigerant in the crank chamber  15  at pressure Pc to flow back to the suction chambers  32 . The second control valve  30 B can now control the discharge capacity of the variable displacement compressor  1  by varying crank chamber pressure Pc.  
     [0147] The amount of refrigerant flowing through the first control valve  30 A may rise due to, for example, sudden acceleration of the engine. If this happens, a larger differential pressure will be produced across that valve  30 A. The increased differential pressure actuates the second control valve  30 B in the direction that it gives a smaller openness, thus reducing the flow rate of refrigerant coming out of the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in the valve-opening direction, thus increasing the flow rate of refrigerant coming out of the crank chamber  15 . As a result of this control action, the variable displacement compressor  1  operates with a larger displacement, thus regulating the flow rate Qd of refrigerant that it discharges.  
     [0148] Thirteenth Embodiment  
     [0149]FIG. 14 is a sectional view of a capacity control valve for a variable displacement compressor according to a thirteenth embodiment of the invention. Since many of the valve components shown in FIG. 14 are identical or similar to those discussed in FIG. 13, the same reference numerals are used in FIG. 14 to designate such components, and the following section will not provide details about them.  
     [0150] The third embodiment (FIG. 4) has presented a capacity control valve  30  that is designed to control the flow rate of refrigerant entering the crank chamber  15 , which is referred to as the inflow control. In contrast to this, the twelfth embodiment (FIG. 13) manipulates the flow rate of refrigerant coming out of the crank chamber  15 , which is referred to as the outflow control. The thirteenth embodiment now offers a capacity control valve  30  that employs both in-flow and out-flow control mechanisms. More specifically, the capacity control valve  30  of the thirteenth embodiment has a first control valve  30 A that is placed on a passageway leading from the discharge chambers  33  and a solenoid unit  30 C that governs the cross-sectional area of that passageway. In addition to those components, the capacity control valve  30  has second and third control valves  30 B and  30 D that detect differential pressure developed across the first control valve  30 A and control the pressure in the crank chamber  15  such that the differential pressure will become a specified level.  
     [0151] The second and third control valves  30 B and  30 D accommodate the following components in their common valve hole: a piston  58 , a second valve element  57 , and a third valve element  76 . Those components are integrally formed as a single member. One edge formed in the valve hole serves as a third valve seat  77 , and the piston  58  has the same outer diameter as that valve seat  77 . The second valve element  57  receives discharge pressure PdH on its bottom endface, while the piston  58  receives discharge pressure PdL through a communication hole  62 . The upstream-side room adjacent to the second valve element  57  is at discharge pressure PdH introduced from a port  41 . The downstream side, on the other hand, communicates with the crank chamber  15  through another port  43   a , the pressure at which is Pc1. The upstream-side space adjacent to the third valve element  76  receives pressure Pc2 from the crank chamber  15  via yet another port  43   b . The downstream-side space adjacent to the third valve element  76 , on the other hand, communicates with the suction chambers  32  at suction pressure Ps via still another port  75 .  
     [0152] With the arrangement described above, the piston  58  and second valve element  57  move together in response to differential pressure ΔP across the first control valve  30 A, which is functioning here as an orifice. The second and third control valves  30 B and  30 D now act as a three-way valve that controls the inflow of refrigerant from the discharge chambers  33  into the crank chamber  15 , simultaneously with the outflow from the crank chamber  15  to the suction chambers  32 , so that the differential pressure ΔP will be maintained at a constant level.  
     [0153] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54 , shaft  49 , and first valve element  61  upward as viewed in FIG. 14, making the first valve element  61  sit on the first valve seat  45   a . The first control valve  30 A is fully closed in this state.  
     [0154] When the solenoid unit  30 C is energized, the plunger  54  moves downward as viewed in FIG. 14. This movement of the plunger  54  causes the first valve element  61  to leave the first valve seat  45   a  and maintain a certain amount of gap. As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then in the second control valve  30 B, the unified valve member (i.e., second valve element  57 , third valve element  76 , and piston  58 ) receives differential pressure between two different discharge pressures PdH and PdL while being pushed by the coil spring  60 , and thus moves to a point at which all those forces and pressures come into balance. The second control valve  30 B now supplies the crank chamber  15  with refrigerant at discharge pressure PdH, and the third control valve  30 D allows the refrigerant at pressure Pc to flow back into the suction chambers  32 . The capacity control valve  30  varies the crank chamber pressure Pc in this way, thus being able to control the discharge capacity of the variable displacement compressor  1 .  
     [0155] The amount of refrigerant flowing through the first control valve  30 A may rise due to, for example, sudden acceleration of the engine. If this happens, a larger differential pressure will be produced across that valve  30 A. The increased differential pressure makes the second control valve  30 B open wider, while actuating the third control valve  30 D in the valve-closing direction. This control action brings about an increased inflow of refrigerant to the crank chamber  15 , along with a decreased outflow from the crank chamber  15 . As a result, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in the valve-closing direction, thus producing a decreased inflow of refrigerant to the crank chamber  15 . At the same time, the third control valve  30 D is impelled in the valve-opening direction, resulting in an increased outflow from the crank chamber  15 . The variable displacement compressor  1  now operates with a larger displacement, resulting in a regulated flow rate Qd of refrigerant that it discharges.  
     [0156] Fourteenth Embodiment  
     [0157]FIG. 15 is a sectional view of a capacity control valve for a variable displacement compressor according to a fourteenth embodiment of the invention. Since many of the valve components shown in FIG. 15 are identical or similar to those discussed in FIG. 13, the same reference numerals are used in FIG. 15 to designate such components, and the following section will not provide details about them.  
     [0158] As opposed to the twelfth embodiment (FIG. 13), the capacity control valve  30  of the fourteenth embodiment is designed to control how much of the discharged refrigerant to supply to the crank chamber  15 . Another difference is that the second valve element  57  of the second control valve  30 B is provided as a discrete component, not integrated with a pressure sensing member that responds to differential pressure across the first control valve  30 A.  
     [0159] More specifically, the second control valve  30 B is constructed as follows. A piston  58  is located inside the body  40 , and a communication hole  62  is bored through the body  40  to apply discharge pressure PdL to the piston  58 . A refrigerant passageway branches from the communication hole  62 , leading to a port  43  for the crank chamber  15 . In the middle of this passageway, a second valve seat  56  is formed as an integral part of the body  40 . Located downstream with respect to the second valve seat  56  is a second valve element  57 . This second valve element  57 , integrally formed with the piston  58 , can move toward and away from the second valve seat  56  in the downstream-side space. The piston  58  receives discharge pressure PdL on its distal end. In addition, a piston  78 , coil spring  79 , and spring seat  80  are installed coaxially with the second valve element  57  and piston  58  in a space formed between the port  41  and communication hole  62 . Discharge pressure PdH is available in this space. A shaft is integrally formed with the second valve element  57 , extending therefrom toward the piston  78  in a space that communicates with the communication hole  62 . The piston  78  is forced against the shaft by the coil spring  79 . Discharge pressure PdL does not affect the movement of the second valve element  57  and piston  58  because their pressure-receiving areas are substantially equal. In the second control valve  30 B, its piston  78  is responsive to differential pressure ΔP developed across the first control valve  30 A, which is functioning here as an orifice. The second control valve  30 B thus controls the flow rate of refrigerant from the discharge chambers  33  to the crank chamber  15  such that the differential pressure ΔP will be maintained at a constant level. This mechanism varies the capacity of the variable displacement compressor  1  so as to regulate the flow rate of refrigerant that it discharges.  
     [0160] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54 , shaft  49 , and first valve element  61  in the upward direction as viewed in FIG. 15, making the first valve element  61  sit on the first valve seat  45   a . The first control valve  30 A is fully closed in this state.  
     [0161] When the solenoid unit  30 C is energized, the plunger  54  moves downward as viewed in FIG. 15. This movement of the plunger  54  allows the first valve element  61  to leave the first valve seat  45   a  and maintain a certain amount of gap between itself and the first valve seat  45   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then in the second control valve  30 B, the piston  78  receives differential pressure between two different discharge pressures PdH and PdL while being pushed by two coil springs  60  and  79 , and thus moves to a point at which all those forces and pressures come into balance. This allows the refrigerant at discharge pressure PdH to flow into the crank chamber  15 , and the second control valve  30 B can now control the discharge capacity of the variable displacement compressor  1  by varying crank chamber pressure Pc.  
     [0162] The amount of refrigerant flowing through the first control valve  30 A may rise due to, for example, sudden acceleration of the engine. If this happens, a larger differential pressure will be produced across that valve  30 A, which makes the second control valve  30 B open wider. This control action produces an increased inflow of refrigerant to the crank chamber  15 , and as a result, the variable displacement compressor  1  operates with a smaller displacement, thus recovering its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in the valve-closing direction, thus producing a decreased inflow of refrigerant to the crank chamber  15 . The variable displacement compressor  1  now operates with a larger displacement, resulting in a regulated flow rate Qd of refrigerant that it discharges.  
     [0163] Fifteenth Embodiment  
     [0164]FIG. 16 is a sectional view of a capacity control valve for a variable displacement compressor according to a fifteenth embodiment of the invention. Since many of the valve components shown in FIG. 16 are identical or similar to those discussed in FIG. 13, the same reference numerals are used in FIG. 16 to designate such components, and the following section will not provide details about them.  
     [0165] The capacity control valve  30  of the fifteenth embodiment is similar to that of the twelfth embodiment (FIG. 13) in that it controls the outflow of refrigerant from the crank chamber  15  to the suction chambers  32 . The fifteenth embodiment, however, differs in that the second valve element  57  in its second control valve  30 B is provided as a discrete component, not integrated with a pressure sensing member that responds to differential pressure across the first control valve  30 A.  
     [0166] More specifically, to detect differential pressure across the first control valve  30 A, the second control valve  30 B employs a piston  78 , a coil spring  79 , and a spring seat  80 . Ports  43  and  75  are disposed to communicate with the crank chamber  15  and suction chambers  32 , respectively, and between these two ports, a second valve seat  56  is formed as an integral part of the body  40 . A second valve element  57  is installed in an upstream-side space near the port  43  such that it can move toward and away from the second valve seat  56 . Integrally formed with this second valve element  57  is a piston  58  with the same diameter as the valve hole of the second valve seat  56 . Discharge pressure PdL propagates through a communication hole  62  and acts on one endface of the piston  58 . The second valve element  57  is integrally formed also with another piston  58   a  having nearly the same diameter as the valve hole of the second valve seat  56 . This piston  58   a  is held in the body  40  in an airtight manner, movably in its axial direction, receiving discharge pressure PdL. The lower end of the piston  58   a  as viewed in FIG. 16 abuts on yet another piston  78 . Discharge pressure PdL does not affect movement of the pistons  58   a  and  58  because their diameters are substantially the same. With the above arrangement of the second control valve  30 B, the piston  78  is responsive to differential pressure ΔP across the first control valve  30 A, which is functioning here as an orifice. The second control valve  30 B thus controls the outflow of refrigerant from the crank chamber  15  to the suction chambers  32  in such a way that the differential pressure ΔP will be maintained at a constant level. This control action varies the capacity of the variable displacement compressor  1  so as to regulate the flow rate of refrigerant being discharged therefrom.  
     [0167] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54 , shaft  49 , and first valve element  61  upward as viewed in FIG. 16, making the first valve element  61  sit on the first valve seat  45   a . The first control valve  30 A is fully closed in this state.  
     [0168] When the solenoid unit  30 C is energized, the plunger  54  moves downward as viewed in FIG. 16. This movement of the plunger  54  allows the first valve element  61  to leave the first valve seat  45   a  and maintain a certain amount of gap between itself and the first valve seat  45   a . As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then, in the second control valve  30 B, the piston  78  receives differential pressure between discharge pressures PdH and PdL, while being pushed by two coil springs  60  and  79 , and thus moves to a point at which all those forces and pressures come into balance. With this movement of the piston  78 , the refrigerant in the crank chamber  15  at pressure Pc is allowed to flow back into the suction chambers  32 . The second control valve  30 B can now control the discharge capacity of the variable displacement compressor  1  by varying crank chamber pressure Pc.  
     [0169] The amount of refrigerant flowing through the first control valve  30 A may rise due to, for example, sudden acceleration of the engine. If this happens, a larger differential pressure will be produced across that valve  30 A. The increased differential pressure actuates the second control valve  30 B in the direction that it gives a smaller openness, thus reducing the flow rate of refrigerant coming out of the crank chamber  15  and raising the crank chamber pressure Pc. As a result of this action, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in the valve-opening direction, thus permitting an increased outflow from the crank chamber  15 . Since the crank chamber pressure Pc goes down, the variable displacement compressor  1  now operates with a larger displacement, resulting in a regulated flow rate Qd of refrigerant that it discharges.  
     [0170] Sixteenth Embodiment  
     [0171]FIG. 17 is a sectional view of a capacity control valve for a variable displacement compressor according to a sixteenth embodiment of the invention. Since many of the valve components shown in FIG. 17 are identical or similar to those discussed in FIGS. 14 and 16, the same reference numerals are used in FIG. 17 to designate such components, and the following section will not provide details about them.  
     [0172] The capacity control valve  30  of this sixteenth embodiment is similar to that of the thirteenth embodiment (FIG. 14) in that it controls both inflow and outflow of refrigerant to/from the crank chamber  15 . The sixteenth embodiment, however, differs in that the second valve element  57  in its second control valve  30 B is provided as a discrete component, not integrated with a member that senses differential pressure across the first control valve  30 A. Regarding the pressure responsive member, the sixteenth embodiment uses a similar structure to that in the fifteenth embodiment (FIG. 16).  
     [0173] More specifically, inside the second and third control valves  30 B and  30 D, a piston  58 , a second valve element  57 , and a third valve element  76  are disposed in an integrated manner. The piston  58  has the same outer diameter as the valve holes of second and third valve seats  56  and  77  so as to avoid the effect of discharge pressure PdL acting thereon. With this arrangement, the piston  58  and second valve element  57  move together in response to differential pressure ΔP across the first control valve  30 A, which is functioning here as an orifice. The second and third control valves  30 B and  30 D now serve as a three-way valve that controls the inflow of refrigerant from the discharge chambers  33  into the crank chamber  15 , simultaneously with the outflow from the crank chamber  15  to the suction chambers  32 , in such a way that the differential pressure ΔP will be maintained at a constant level.  
     [0174] The capacity control valve  30  with the above construction operates as follows. When the solenoid unit  30 C is in de-energized state, the coil spring  55  urges the plunger  54 , shaft  49 , and first valve element  61  upward as viewed in FIG. 17, making the first valve element  61  sit on the first valve seat  45   a . The first control valve  30 A is fully closed in this state.  
     [0175] When the solenoid unit  30 C is energized, the plunger  54  moves downward as viewed in FIG. 17. This movement of the plunger  54  allows the first valve element  61  to leave the first valve seat  45   a  and maintain a certain amount of gap. As a result, the refrigerant coming into the port  41  at discharge pressure PdH begins flowing out of the port  42  through the first control valve  30 A. Then in the second control valve  30 B, the unified valve member (i.e. second valve element  57 , third valve element  76 , and piston  58 ) receives differential pressure between discharge pressures PdH and PdL while being pushed by the coil springs  60  and  79 , and thus moves to a point at which all those forces and pressures come into balance. The second control valve  30 B now supplies refrigerant at pressure Pc1 to the crank chamber  15  by controlling refrigerant at discharge pressure PdL, and at the same time, the third control valve  30 D allows the refrigerant at pressure Pc2 in the crank chamber  15  to flow back into the suction chambers  32 . The capacity control valve  30  varies the crank chamber pressure Pc in this way, thus being able to control the discharge capacity of the variable displacement compressor  1 .  
     [0176] The amount of refrigerant flowing through the first control valve  30 A may rise due to, for example, sudden acceleration of the engine. If this happens, a larger differential pressure will be produced across that valve  30 A. The increased differential pressure makes the second control valve  30 B open wider, while actuating the third control valve  30 D in the valve-closing direction. This control action produces an increased inflow of refrigerant to the crank chamber  15 , together with a decreased outflow from the crank chamber  15 . As a result, the variable displacement compressor  1  operates with a smaller displacement so as to recover its original discharge flow rate. If, in turn, the refrigerant flowing through the first control valve  30 A decreases, the second control valve  30 B is actuated in the valve-closing direction, and the third control valve  30 D in the value-opening direction, thus producing a decreased inflow of refrigerant to the crank chamber  15  and an increased outflow from the crank chamber  15 . The variable displacement compressor  1  now operates with a larger displacement, resulting in a regulated flow rate Qd of refrigerant that it discharges.  
     [0177] Seventeenth Embodiment  
     [0178]FIG. 18 is a sectional view of a capacity control valve for a variable displacement compressor according to a seventeenth embodiment of the invention. Since many of the valve components shown in FIG. 18 are identical or similar to those discussed in FIG. 15, the same reference numerals are used in FIG. 18 to designate such components, and the following section will not provide details about them.  
     [0179] As in the fourteenth embodiment (FIG. 15), the capacity control valve  30  of this seventeenth embodiment is designed to control how much of the discharged refrigerant to supply to the crank chamber  15 . Another similarity is that the second valve element  57  of the second control valve  30 B is provided as a discrete component, not integrated with a member that responds to differential pressure across the first control valve  30 A. The seventeenth embodiments is, however, different in that it has no back-pressure cancellation mechanism for the second valve element  57 .  
     [0180] More specifically, the second control valve  30 B is constructed as follows. A second valve element  57  is urged by a coil spring  60  in the valve-closing direction, where discharge pressure PdL is routed through a communication hole  62  and acts only on the piston  78  and second valve element  57 . The upper end of the coil spring  60 , as viewed in FIG. 18, is supported by a lid  59   c  having a vent. An O-ring  29   b  is used for sealing of the capacity control valve  30  when it is installed in a variable displacement compressor  1 . The upper space above the level of this O-ring  29   b , as viewed in FIG. 18, will be at pressure Pc, i.e., the pressure in the port  43 , meaning that the same pressure Pc will be available in the cavity where the coil spring  60  resides.  
     [0181] The above-described capacity control valve  30  bears close resemblance to the fourteenth embodiment (FIG. 15) in terms of the structure, except for the fact that the second valve element  57  is not free from back pressures. When its solenoid unit  30 C is in de-energized state, the capacity control valve  30  operates in the same way as described in the fourteenth embodiment. This similarity in its control operations also applies when the solenoid unit  30 C is energized, as well as when the engine rotation varies.  
     [0182] Eighteenth Embodiment  
     [0183]FIG. 19 is a sectional view of a capacity control valve for a variable displacement compressor according to an eighteenth embodiment of the invention. Since many of the valve components shown in FIG. 19 are identical or similar to those discussed in FIG. 16, the same reference numerals are used in FIG. 19 to designate such components, and the following section will not provide details about them.  
     [0184] As in the fifteenth embodiment (FIG. 16), the capacity control valve  30  of this eighteenth embodiment is designed to control the outflow of refrigerant coming out of the crank chamber  15  to the suction chambers  32 . Another likeness is that the second valve element  57  of the second control valve  30 B is provided as a discrete component, not integrated with a member that senses differential pressure across the first control valve  30 A. The eighteenth embodiments is, however, different in that it has no back-pressure cancellation mechanism for the second valve element  57 .  
     [0185] More specifically, the second control valve  30 B is constructed as follows. A second valve element  57  is urged against a piston  78  by a coil spring  60  in the valve-opening direction, where discharge pressure PdL is routed through a communication hole  62  in such a way that it acts only on the piston  78  and another piston that extends from the second valve element  57 . Yet another piston  58  is integrally formed with the second valve element  57 , and the coil spring  60  is accommodated in a space between this piston  58  and a lid  59   c  having a vent. The coil spring space is pressurized at Ps through the vent in the lid  59   c.    
     [0186] The above-described capacity control valve  30  bears close resemblance to the fifteenth embodiment (FIG. 16) in terms of the structure, except for the fact that the second valve element  57  is not free from back pressures. When its solenoid unit  30 C is in de-energized state, the capacity control valve  30  operates in the same way as described in the fifteenth embodiment. This similarity in its control operations also applies when the solenoid unit  30 C is energized, as well as when the engine rotation varies.  
     [0187] Nineteenth Embodiment  
     [0188]FIG. 20 is a sectional view of a capacity control valve for a variable displacement compressor according to a nineteenth embodiment of the invention. Since many of the valve components shown in FIG. 20 are identical or similar to those discussed in FIG. 17, the same reference numerals are used in FIG. 20 to designate such components, and the following section will not provide details about them.  
     [0189] The capacity control valve  30  of this nineteenth embodiment controls both inflow and outflow of refrigerant to/from the crank chamber  15 , as in the seventeenth embodiment (FIG. 18). The nineteenth embodiment is also similar to the seventeenth embodiment in that the second valve element  57  in its second control valve  30 B is provided as a discrete component, not integrated with a member that senses differential pressure across the first control valve  30 A.  
     [0190] More specifically, the second and third control valves  30 B and  30 D are constructed as follows. A second valve element  57  and a third valve element  76 , which constitute a three-way valve, are urged by a coil spring  60  in the valve-closing direction and in the valve-opening direction, respectively, where discharge pressure PdL is routed through a communication hole  62  in such a way that it acts only on the second valve element  57  and piston  78 . A piston  58  is integrally formed with the second and third valve elements  57  and  76 , and the coil spring  60  is accommodated in a space between this piston  58  and a lid  59   c  having a vent. The coil spring space is pressurized at Ps through the vent in the lid  59   c.    
     [0191] The above-described capacity control valve  30  bears close resemblance to the sixteenth embodiment (FIG. 17) in terms of the structure, except for the fact that the second valve element  57  and third valve element  76  are not free from back pressures. When its solenoid unit  30 C is in de-energized state, the capacity control valve  30  operates in the same way as described in the sixteenth embodiment. This similarity in its control operations also applies when the solenoid unit  30 C is energized, as well as when the engine rotation varies.  
     [0192] Various types of capacity control valves  30  have been presented as preferred embodiments of the present invention. All those embodiments share a common concept that the first control valve  30 A controls the cross-section area of a passageway of discharged refrigerant, and the second control valve  30 B (and third control valve  30 D in several cases) controls pressure Pc in the crank chamber  15  in such a way that the differential pressure across the controlled passageway will be maintained at a specified level. The capacity control valves of the present invention should not be limited to the structure that uses differential pressure on the discharge side of the valves. Rather, it has to be appreciated that the invention covers the structure using differential pressure on the suction side. That is, the first control valve  30 A may control the cross-section area of a passageway of refrigerant coming into the compressor, and the second control valve  30 B (and third control valve  30 D) controls pressure Pc in the crank chamber  15  in such a way that the differential pressure across the controlled passageway will be maintained at a specified level.  
     [0193] As can be seen from the above explanation, the present invention proposes a structure that employs first and second control valves formed in an integrated way. Here, the first control valve controls the cross-section area at a midway point between low-pressure refrigerant passage and suction chamber, or between discharge chamber and high-pressure refrigerant passage, according to a given external condition. The second control valve, on the other hand, detects differential pressure between upstream end and downstream end of the first control valve and controls the crank chamber pressure in such a way that the differential pressure will be maintained at a specified level. This feature of the present invention enables us to construct a smaller variable displacement compressor at lower cost.  
     [0194] Because the first control valve has only to produce a small amount of differential pressure, the solenoid unit can drive the valve with a small power, and thus it is not necessary to increase its size to achieve the purpose. The present invention can easily be applied to refrigeration cycles using HFC-134a in a system that should operate with small differential pressure between discharge chamber and crank chamber, or crank chamber and suction chamber. In addition, the present invention can also be applied to those using high-pressure refrigerant in its supercritical region.  
     [0195] The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents.