Patent Publication Number: US-10781804-B2

Title: Displacement control valve

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/JP2017/029833, filed on Aug. 22, 2017, and published in Japanese as WO 2018/043186 on Mar. 8, 2018 and claims priority to Japanese Application No. 2016-166844, filed on Aug. 29, 2016. The entire disclosures of the above applications are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a displacement control valve that variably controls the displacement or pressure of a working fluid, and in particular, relates to a displacement control valve that controls the discharge rate of a variable displacement compressor or the like used in an air-conditioning system of an automobile or the like, according to pressure load. 
     Related Art 
     A swash-plate variable displacement compressor used in an air-conditioning system of an automobile or the like includes a rotating shaft rotationally driven by the torque of an engine, a swash plate connected to the rotating shaft such that its inclination angle to the rotating shaft can be changed, compression pistons connected to the swash plate, and others. The compressor controls the discharge rate of refrigerant gas by changing the inclination angle of the swash plate and thereby changing the stroke of the pistons. 
     The inclination angle of the swash plate can be continuously changed by properly controlling the pressure in a control chamber, using a displacement control valve that is driven by an electromagnetic force to open and close, and thereby adjusting the balance of pressures acting on opposite faces of the pistons, while using the suction pressure in a suction chamber for sucking the refrigerant gas, the discharge pressure in a discharge chamber for discharging the refrigerant gas pressurized by the pistons, and the control chamber pressure in the control chamber (crank chamber) accommodating the swash plate. 
     As such a displacement control valve, there is known one that includes, as shown in  FIG. 5 , second communicating passages  73  and a valve hole  77  that communicate a discharge chamber and a control chamber, a second valve chest  82  formed at an intermediate point in a discharge-side passage, third communicating passages  71  and a circulation groove  72  that communicate a suction chamber and the control chamber, a third valve chest  83  formed at an intermediate point in a suction-side passage, a valve element  81  formed such that a second valve section  76  that is disposed in the second valve chest  82  to open and close the second communicating passages  73  and the valve hole  77  and a third valve section  75  that is disposed in the third valve chest  83  to open and close the third communicating passages  71  and the circulation groove  72  reciprocate in an integrated manner while performing opening and closing operation in opposite directions, a first valve chest (displacement chamber)  84  formed close to the control chamber, a pressure-sensitive element (bellows)  78  that is disposed in the first valve chest and exerts a biasing force in the extending (expanding) direction and contracts with an increase in ambient pressure, a valve seat element (engaging portion)  80  that is provided at a free end of the pressure-sensitive element in the extending and contracting direction and has an annular seat surface, a first valve section (opening valve connection portion)  79  that moves with the valve element  81  in an integrated manner in the first valve chest  84  and can open and close the suction-side passage by being engaged with and disengaged from the valve seat element  80 , a solenoid S that exerts an electromagnetic drive force on the valve element  81 , and others (Hereinafter, it is referred to as a “conventional art.” See JP 5167121 B1, for example). 
     A displacement control valve  70  is configured to be able to adjust the pressure in the control chamber (control chamber pressure) Pc by communicating the discharge chamber and the control chamber when there arises a need to change the control chamber pressure during displacement control, without having to provide a clutch mechanism to the variable displacement compressor. The displacement control valve  70  is also configured to open the suction-side passage by disengaging the first valve section (opening valve connection portion)  79  from the valve seat element (engaging portion)  80  and thereby communicating the suction chamber and the control chamber when the control chamber pressure Pc increases in the variable displacement compressor in a stopped state. 
     When the swash-plate variable displacement compressor is started after it has been stopped and left for a long period of time, liquid refrigerant (refrigerant gas cooled and liquefied while the compressor being left) accumulates in the control chamber (crank chamber). Thus, unless the liquid refrigerant is discharged, a discharge rate as set cannot be achieved by the compression of the refrigerant gas. 
     To perform desired displacement control immediately after startup, it is necessary to discharge liquid refrigerant in the control chamber (crank chamber) as rapidly as possible. 
     For this, the above conventional art provides an auxiliary communicating passage  85  in the valve seat element (engaging portion)  80  to enable communication from the displacement chamber  84  through the auxiliary communicating passage  85  and an intermediate communicating passage  86  to the third communicating passages  71  under a suction pressure (see an arrow). When the variable displacement compressor is started for cooling, this configuration can vaporize refrigerant liquid in the control chamber at 1/10 to 1/15 the speed of a displacement control valve without the auxiliary communicating passage  85 , to bring the compressor into cooling operation. 
       FIG. 5  is a state where a current flows through the solenoid unit S. On the other hand, when no current flows through the solenoid unit S, an opening spring means  87  brings the third valve section  75  into a closed state, which is not shown. At this time, the second valve section  76  is in an open state. The first valve section  79  opens under the suction pressure Ps and the control pressure Pc. 
     The first valve section  79  and the valve seat surface of the valve seat element  80  are configured such that they cannot open widely for functional reasons. Refrigerant liquid in the control chamber is vaporized, and fluid at the control pressure Pc flows through first communicating passages  74  into the first valve chest  84 . In this state, the control pressure Pc and the suction pressure Ps are high, and thus the pressure-sensitive element (bellows)  78  contracts, opening a space between the first valve section  79  and the valve seat surface of the valve seat element  80 . Only with this valve opening state, however, the vaporization of the refrigerant liquid in the control chamber  84  is accelerated only in small quantities. The provision of the auxiliary communicating passage  85  communicating with the intermediate communicating passage  86  allows the refrigerant liquid in the control chamber to be vaporized rapidly. 
     In the above conventional art, however, the refrigerant gas flows from the control chamber into the suction chamber even when the space between the first valve section  79  and the valve seat surface of the valve seat element  80  is closed and the flow of fluid through the auxiliary communicating passage  85  is unnecessary, for example, during the control of the variable displacement compressor thus resulting in a reduction in the operating efficiency of the variable displacement compressor. 
     This point will be described in detail with reference to  FIG. 6 . 
     In  FIG. 6 , the conventional art is designed as follows: 
     S 2 &gt;S 1   
     L&gt;LS 
     where S 1  is the (fixed) area of the auxiliary communicating passage  85 , S 2  is the maximum opening area of the third valve section  75 , L is the maximum stroke of the valve element  81  (stroke from full closing to full opening), and LS is the stroke of the valve element  81  in a control area. 
     Therefore, as shown by a solid line in  FIG. 6 , refrigerant gas defined by the area S 1  of the auxiliary communicating passage  85  flows from the control chamber into the suction chamber in the whole control area, and the flow of the refrigerant gas is restricted only after the valve element  81  exceeds the control area and approaches the maximum stroke. Thus, a reduction in operating efficiency during control of the variable displacement compressor is unavoidable. 
     The present invention has been made to solve the above-described problem of the conventional art, and its object is to provide a displacement control valve that is provided with an auxiliary communicating passage to be improved in the function of discharging liquid refrigerant in a control chamber at the time of startup of a variable displacement compressor. The displacement control valve can achieve a reduction in startup time and an improvement in operating efficiency during control of the variable displacement compressor simultaneously by setting the opening area of a third valve section for opening and closing third communicating passages and a circulation groove during the control of the variable displacement compressor smaller than or equal to the opening area of the auxiliary communicating passage. 
     SUMMARY OF THE INVENTION 
     To attain the above object, a displacement control valve according to a first aspect of the present invention, which controls a flow rate or pressure in a working control chamber according to a degree of opening of a valve unit, includes a valve body having a first valve chest that communicates with first communicating passages for passing fluid at control pressure and has a first valve seat surface and a second valve seat surface, a second valve chest that has a valve hole communicating with the first valve chest and communicates with second communicating passages for passing fluid at discharge pressure, a third valve chest that communicates with third communicating passages for passing fluid at suction pressure and is next to a third valve seat surface, a valve element disposed in the valve body and having an intermediate communicating passage that communicates the first valve chest and the third communicating passages, a second valve section that separates from and comes into contact with the second valve seat surface to open and close the valve hole communicating with the first valve chest and the second valve chest, a third valve section that opens and closes opposite to and in conjunction with the second valve section and has a communicating hole that slides relatively to the third valve seat surface to open and close communication between the intermediate communicating passage and the third communicating passages, and a first valve section that is disposed in the first valve chest and opens and closes opposite to and in conjunction with the second valve section, a pressure-sensitive element that is disposed in the third valve chest and extends and contracts in response to suction pressure, the pressure-sensitive element having, at an extending and contracting free end thereof, a valve seat that separates from and comes into contact with the third valve section to open and close communication between the third valve chest and the intermediate communicating passage, an auxiliary communicating passage provided in the first valve section in the first valve chest for enabling communication between an interior of the first valve chest and the intermediate communicating passage, and a solenoid unit mounted to the valve body and actuating the valve element in a travel direction to open and close the valve sections of the valve element according to a current, in which an opening area S 2  between the communicating hole in the third valve section and the third valve seat surface in a control area to control the flow rate or pressure in the working control chamber is set smaller than an area S 1  of the auxiliary communicating passage. 
     According to this aspect, the displacement control valve, which is provided with the auxiliary communicating passage to be improved in the function of discharging liquid refrigerant in the control chamber at the time of startup of the variable displacement compressor, can reduce the minimum area of a Pc-Ps flow path in the control area, and can achieve a reduction in startup time and an improvement in operating efficiency during control of the variable displacement compressor simultaneously. 
     Further, the displacement control valve, in which the auxiliary communicating passage is provided in the first valve section in the first valve chest in which fluid at the control pressure acts, and the pressure-sensitive device and the third valve section for discharging liquid refrigerant are disposed in the third valve chest in which fluid at the suction pressure acts, can reduce the minimum area of the Pc-Ps flow path in the control area by the simple configuration of providing the communicating hole in the third valve section of the valve element. 
     According to a second aspect of the present invention, in the displacement control valve in the first aspect, a maximum opening area S 2 max between the communicating hole in the third valve section and the third valve seat surface when the second valve section is in a closed state is set equal to or smaller than the area S 1  of the auxiliary communicating passage. 
     According to this aspect, the minimum area of the Pc-Ps flow path at the time of liquid refrigerant discharge can be made as large as that in the above-described conventional art. 
     Effects of the Invention 
     The present invention achieves the following outstanding effects.
     (1) The opening area S 2  between the communicating hole in the third valve section and the third valve seat surface in the control area to control the flow rate or pressure in the working control chamber is set smaller than the area S 1  of the auxiliary communicating passage, so that the displacement control valve, which is provided with the auxiliary communicating passage to be improved in the function of discharging liquid refrigerant in the control chamber at the time of startup of the variable displacement compressor, can reduce the minimum area of the Pc-Ps flow path in the control area, and can achieve a reduction in startup time and an improvement in operating efficiency during control of the variable displacement compressor simultaneously.   

     Further, the displacement control valve, in which the auxiliary communicating passage is provided in the first valve section in the first valve chest in which fluid at the control pressure acts, and the pressure-sensitive device and the third valve section for discharging liquid refrigerant are disposed in the third valve chest in which fluid at the suction pressure acts, can reduce the minimum area of the Pc-Ps flow path in the control area by the simple configuration of providing the communicating hole in the third valve section of the valve element.
     (2) The maximum opening area S 2 max between the communicating hole in the third valve section and the third valve seat surface when the second valve section is in a closed state is set equal to or smaller than the area S 1  of the auxiliary communicating passage, so that the minimum area of the Pc-Ps flow path at the time of liquid refrigerant discharge can be made as large as that in the above-described conventional art.   

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front cross-sectional view showing a displacement control valve according to a first embodiment of the present invention. 
         FIGS. 2A to 2C  are enlarged views of a Pc-Ps flow path in  FIG. 1 , and are explanatory diagrams for explaining an opening area S 2  between a third valve section and a third valve seat surface in different states. 
         FIG. 3  is an explanatory diagram for explaining the relationship between the opening area S 2  between the third valve section and the third valve seat surface and an area S 1  of auxiliary communicating passages of the displacement control valve according to the first embodiment. 
         FIGS. 4A to 4C  are enlarged views of a Pc-Ps flow path in a second embodiment, and are explanatory diagrams for explaining an opening area S 2  between a third valve section and a third valve seat surface in different states. 
         FIG. 5  is a front cross-sectional view showing the displacement control valve in the conventional art. 
         FIG. 6  is an explanatory diagram for explaining the relationship between the opening area S 2  between the third valve section and a third valve seat surface and the area S 1  of the auxiliary communicating passage of the displacement control valve according to the conventional art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter with reference to the drawings, a mode for carrying out the present invention will be described illustratively based on embodiments. However, the dimensions, materials, shapes, relative positions, and others of components described in the embodiments are not intended to limit the present invention only to them unless otherwise explicitly described. 
     First Embodiment 
     With reference to  FIGS. 1 to 3 , a displacement control valve according to a first embodiment of the present invention will be described. 
     In  FIG. 1 , reference numeral  1  denotes a displacement control valve. The displacement control valve  1  is provided with a valve body  2  forming an outside shape. The valve body  2  includes a first valve body  2 A forming a through hole provided with functions inside, and a second valve body  2 B integrally fitted to one end of the first valve body  2 A. The first valve body  2 A is made of a metal such as brass, iron, aluminum, or stainless, or a synthetic resin material, or the like. The second valve body  2 B is formed of a magnetic substance such as iron. 
     The second valve body  2 B is provided separately to be different in function from the material of the first valve body  2 A because a solenoid unit  30  is connected to the second valve body  2 B, and the second valve body  2 B must be of a magnetic substance. If this point is considered, the shape shown in  FIG. 1  may be changed appropriately. A partition adjuster  3  is connected to the first valve body  2 A at the other end of the through hole. The partition adjuster  3  is fitted to close a third valve chest (hereinafter, sometimes referred to as a displacement chamber)  4  of the first valve body  2 A. If screwed in and fixed with a setscrew not shown, the partition adjuster  3  can move and adjust the spring force of a compression spring disposed in parallel in a bellows  22 A or the bellows  22 A in the axial direction. 
     In a compartment of the through hole axially extending through the first valve body  2 A, the third valve chest (displacement chamber)  4  is formed on the one-end side. Third communicating passages  9  are connected to the third valve chest (displacement chamber)  4 . The third communicating passages  9  are configured to communicate with a suction chamber of a variable displacement compressor so that the displacement control valve  1  allows fluid at a suction pressure Ps to flow into the suction chamber and to flow out. 
     A pressure-sensitive element (hereinafter, referred to as a pressure-sensitive device)  22  is provided in the displacement chamber  4 . The pressure-sensitive device  22  has the metal bellows  22 A connected at one end to the partition adjuster  3  in a sealed state and connected at the other end to a valve seat  22 B. The bellows  22 A is made of phosphor bronze or the like, and its spring constant is designed to a predetermined value. The interior space of the pressure-sensitive device  22  is a vacuum, or contains air. The pressure-sensitive device  22  is configured such that the pressure in the displacement chamber  4  (e.g. pressure Pc) and the suction pressure Ps act on an effective pressure-receiving area Ab of the bellows  22 A to contract the pressure-sensitive device  22 . The dish-shaped valve seat  22 B provided with a first valve seat surface  22 C at an edge peripheral surface is provided at a free end of the pressure-sensitive device  22 . 
     In the compartment of the through hole, a third valve seat surface  12  with a diameter smaller than the diameter of the third valve chest (displacement chamber)  4  is provided consecutively next to the third valve chest (displacement chamber)  4  on the upper side thereof (the side of the solenoid unit  30 ) in  FIG. 1 . 
     Further, in the compartment of the through hole, a second valve chest  6  is provided next to the third valve seat surface  12  on the upper side (the side of the solenoid unit  30 ) in  FIG. 1 . Furthermore, in the compartment of the through hole, a first valve chest  7  communicating with the second valve chest  6  is provided consecutively next to the second valve chest  6  on the upper side (the side of the solenoid unit  30 ) in  FIG. 1 . Between the second valve chest  6  and the first valve chest  7 , a valve hole  5  with a diameter smaller than the diameters of these chests is provided consecutively. A second valve seat surface  6 A is formed around the valve hole  5  on the side of the first valve chest  7 . 
     A space between the third valve seat surface  12  and the second valve chest  6  is sealed by a sealing means. 
     Second communicating passages  8  are provided consecutively to the second valve chest  6  in the valve body  2 . The second communicating passages  8  are configured to communicate with the interior of a discharge chamber of the variable displacement compressor (not shown) so that the displacement control valve  1  allows fluid at a discharge pressure Pd to flow into a control chamber. 
     Further, first communicating passages  10  are formed at the first valve chest  7  in the valve body  2 . The first communicating passages  10  communicate with the control chamber (crank chamber) of the variable displacement compressor to allow fluid at the discharge pressure Pd flowing in from the second valve chest  6  to flow out to the control chamber (crank chamber) of the variable displacement compressor, which will be described later. 
     The first communicating passages  10 , the second communicating passages  8 , and the third communicating passages  9  are two to six in number, for example, and are spaced evenly around a peripheral surface of the valve body  2 , extending therethrough. Further, an outer peripheral surface of the valve body  2  is formed into four-stage surfaces. The outer peripheral surface is provided with O-ring fitting grooves at three locations in the axial direction. In each fitting groove, an O-ring  46  is fitted to seal a space between the valve body  2  and a fitting hole of a casing (not shown) into which the valve body  2  is fitted. 
     A valve element  21  is disposed axially movably in the through hole axially extending through the first valve body  2 A. 
     A third valve section  21 A that opens and closes with the first valve seat surface  22 C of the valve seat  22 B is provided at one end of the valve element  21 . The third valve section  21 A is provided with a third valve section surface  21 A 1  that opens and closes with the first valve seat surface  22 C. 
     The outside diameter of the third valve section  21 A is set slightly smaller than the inside diameter of the third valve seat surface  12 . 
     Further, at least one communicating hole  23  is provided in the third valve section  21 A in such a position to slide on the third valve seat surface  12 , and is opposite the third valve section surface  21 A 1 . The at least one communicating hole  23  is communicated with an intermediate communicating passage  26  to be described below that axially extends through the valve element  21 , and is provided circumferentially of the third valve section  21 A to face the third valve seat surface  12 . 
     Further, a second valve section  21 B is provided as a connecting portion, opposite the third valve section surface  21 A 1  of the third valve section  21 A of the valve element  21 . The outside diameter of the second valve section  21 B is made smaller than the diameter of the valve hole  5  so that fluid at the discharge pressure Pd can pass through the second valve chest  6  and the first valve chest  7  when the second valve section  21 B is open. 
     The second valve section  21 B at an intermediate portion of the valve element  21  is disposed in the second valve chest  6 . The second valve section  21 B is provided with a second valve section surface  21 B 1  to be joined to the second valve seat surface  6 A. 
     A first valve section  21 C above the second valve section  21 B of the valve element  21  is disposed in the first valve chest  7 . The first valve section  21 C opens and closes with a first valve seat surface  31 A formed at a lower end face of a fixed iron core  31 . 
     The intermediate communicating passage  26  is provided in the interior of the valve element  21 , extending from the first valve chest  7  to the third valve chest  4 . When the first valve section  21 C opens from the first valve seat surface  31 A, control fluid Pc can flow out from the first valve chest  7  into the third communicating passages  9 . 
     In the valve element  21 , a connecting portion  25 A provided at a lower end portion of a solenoid rod  25  is fitted into a fitting hole  21 D of the valve element  21 . 
     The valve element  21  is provided with, for example, four evenly-spaced auxiliary communicating passages  21 E located below the fitting hole  21 D in the first valve chest  7 . Through the auxiliary communicating passages  21 E, the first valve chest  7  communicates with the intermediate communicating passage  26 . 
     The first valve chest  7  is formed with a surface with a diameter slightly larger than that of the outer shape of the valve element  21  to facilitate flowing of fluid at the control fluid Pc from the first communicating passages  10  into the first valve chest  7 . 
     The above-described configuration of a lower part in  FIG. 1  including the valve body  2 , the valve element  21 , and the pressure-sensitive device  22  constitutes a valve unit. 
     The area S 1  of the auxiliary communicating passages  21 E may be equal to or larger than the maximum opening area S 2 max of the at least one communicating hole  23 . 
     The diameter of the auxiliary communicating passages  21 E may vary, depending on the capacity of the air conditioner. 
     In a state where the pressure-sensitive device  22  is contracted according to the pressure of the control fluid Pc of vaporized refrigerant liquid, opening the third valve section  21 A, time to vaporize refrigerant liquid is as long as ten minutes or longer. During this, the pressure in the control chamber of the swash-plate variable displacement compressor, which is in a vaporizing state, gradually increases, thus resulting in a further delay in vaporization. However, the provision of the auxiliary communicating passages  21 E allows refrigerant liquid in the control chamber to be rapidly vaporized. When all the refrigerant liquid in the control chamber is vaporized, the displacement control valve  1  can freely control the pressure in the control chamber. 
     The at least one communicating hole  23  in the third valve section  21 A is set so as to be in an open state when the second valve section surface  21 B 1  of the second valve section  21 B is in a closed state, and to be in a closed state when the second valve section surface  21 B 1  is in an open state. 
     The other end portion opposite the connecting portion  25 A of the solenoid rod  25  is fitted into a fitting hole  32 A of a plunger  32  for connection. The fixed iron core  31  fixed to the first valve body  2 A is provided between the valve element  21  and the plunger  32 . The solenoid rod  25  is fitted movably along an inner peripheral surface  31 D of the fixed iron core  31 . 
     A spring seat chamber  31 C is formed in the fixed iron core  31  on the side of the plunger  32 . A spring means (hereinafter, also referred to as a resilient means)  28  for bringing the third valve section  21 A and the second valve section  21 B from a closed state into an open state is disposed in the spring seat chamber  31 C. That is, the spring means  28  springs to separate the plunger  32  from the fixed iron core  31 . An attraction surface  31 B of the fixed iron core  31  and a joint surface  32 B of the plunger  32  form opposing tapered surfaces, providing a gap between the opposing surfaces to enable attraction. The separation and contact between the attraction surface  31 B of the fixed iron core  31  and the joint surface  32 B of the plunger  32  depend on the strength of a current flowing through an electromagnetic coil  35 . A solenoid case  33  is fixed to a step on the one-end side of the second valve body  2 B. In the solenoid case  33 , the electromagnetic coil  35  is disposed. The solenoid unit  30  presents the above overall configuration. The electromagnetic coil  35  provided in the solenoid unit  30  is controlled by a control computer (not shown). 
     A plunger case  34  is fitted to the fixed iron core  31 . The plunger  32  is slidably fitted therein. The plunger case  34  is fitted at one end in a fitting hole in the second valve body  2 B, and is fixed at the other end in a fitting hole in an end portion of the solenoid case  33 . The above configuration constitutes the solenoid unit  30 . 
     Note that in  FIG. 1 , a thick curved line of an arrow indicates a Pc-Ps flow path from one of the first communicating passages  10  to one of the third communicating passages  9 . 
     Next, with reference to  FIG. 2 , the positional relationships between the first valve section  21 C, the second valve section  21 B, and the communicating holes  23  in the third valve section  21 A will be described in detail. 
     At the time of liquid refrigerant discharge (at the time of maximum displacement control) shown in  FIG. 2A , that is, when the second valve section  21 B is in a fully-closed state, the first valve section  21 C is in a fully-open state, the communicating holes  23  in the third valve section  21 A are also in an open state, and the control fluid Pc (control fluid Pc of vaporized refrigerant liquid at the time of liquid refrigerant discharge) flows through the auxiliary communicating passages  21 E, the intermediate communicating passage  26 , and the communicating holes  23  into the third valve chest  4 , and flows out from the third valve chest  4  into the third communicating passages  9 . 
     In this state, the maximum opening area S 2 max between the communicating holes  23  and the third valve seat surface  12  is produced. The position of the communicating holes  23  is set such that the maximum opening area S 2 max is equal to or smaller than the area S 1  of the auxiliary communicating passages  21 E (when there are two or more auxiliary communicating passages, the total area). In this case, the opening area S 2  is set so as to rapidly decrease in the initial stage of travel of the valve element  21 , and thereafter, to be nearly constant. 
     A thick curved line of an arrow indicates the Pc-Ps flow path. 
     In a control area shown in  FIG. 2B , the opening area S 2  between the third valve seat surface  12  and the communicating holes  23  is set to a nearly constant value smaller than that of the area S 1  of the auxiliary communicating passages  21 E, and is in a range of 10% to 30% of Sl, for example. 
     At an OFF time when the second valve section  21 B is in a fully-open state shown in  FIG. 2C , S 2  is not zero, leaving a space, whereas the Pc-Ps flow path becomes zero because the first valve section  21 C is sealed with the first valve seat surface  31 A. 
     Next, with reference to  FIG. 3 , the minimum area of the Pc-Ps flow path will be described. 
     In  FIG. 3 , the horizontal axis represents the stroke of the valve element  21 , and the vertical axis the opening area. 
     The left end in  FIG. 3  indicates the time of liquid refrigerant discharge, that is, a state where the second valve section  21 B is fully closed (the first valve section  21 C is fully open). Likewise, the right end in  FIG. 3  indicates a state where the second valve section  21 B is fully open (the first valve section  21 C is fully closed). A range from the left end to a vertical line formed by a broken line in a nearly midpoint position on the horizontal axis represents the control area. 
     A horizontal line formed by a broken line in a nearly midpoint position on the vertical axis represents the area S 1  of the auxiliary communicating passages  21 E. 
     In the present invention, since the opening area S 2  between the communicating holes  23  in the third valve section  21 A and the third valve seat surface  12  in the control area is set smaller than the (fixed) area S 1  of the auxiliary communicating passages  21 E, the minimum area of the Pc-Ps flow path is defined by the opening area S 2  between the communicating holes  23  in the third valve section  21 A and the third valve seat surface  12 . 
     Thus, the displacement control valve, in which the auxiliary communicating passages  21 E are provided in the first valve section  21 C in the first valve chest  7  in which fluid at the control pressure acts, and the pressure-sensitive device  22  and the third valve section  21 A for discharging liquid refrigerant are disposed in the third valve chest  4  in which fluid at the suction pressure acts, can reduce the minimum area of the Pc-Ps flow path in the control area by the simple configuration of providing the communicating holes  23  in the third valve section  21 A of the valve element  21 . 
     In  FIG. 3 , the opening area S 2  between the communicating holes  23  in the third valve section  21 A and the third valve seat surface  12  in the control area is shown by a solid line. At the time of liquid refrigerant discharge at the left end, that is, in a state where the second valve section  21 B is fully closed (the first valve section  21 C is fully open), the maximum opening area S 2 max is produced, and the maximum opening area S 2 max is set equal to or nearly equal to the area S 1  of the auxiliary communicating passages  21 E. As the valve element  21  starts to travel, first, the opening area S 2  is rapidly decreased from the area S 1  of the auxiliary communicating passages  21 E, and becomes a nearly constant value in a range of 10% to 30% of S 1 . 
     The rate of change in the opening area S 2  with the travel of the valve element  21  between the communicating holes  23  in the third valve section  21 A and the third valve seat surface  12  in the control area can be changed by the shape of the communicating holes  23 . 
     In the example in  FIGS. 1 to 2C , the front shape of the communicating holes  23  is substantially circular, the cross-sectional shape thereof is a stepped shape in which the side facing the third valve seat surface  12  is a large-diameter portion and the side facing the intermediate communicating passage  26  is a small-diameter portion. In the initial stage of travel of the valve element  21 , almost all area of the large-diameter portion overlaps the third valve seat surface  12 , rapidly decreasing the gap between them, and thereafter, a radial gap between the valve element  21  and the third valve seat surface  12  is left. Thus, the opening area S 2  changes as shown by the solid line in  FIG. 3 . 
     The displacement control valve according to the first embodiment of the present invention is as described above, and achieves the following outstanding effects.
     (1) The opening area S 2  between the communicating holes  23  in the third valve section  21 A and the third valve seat surface  12  in the control area to control the flow rate or pressure in the working control chamber is set smaller than the area S 1  of the auxiliary communicating passages  21 E, so that the displacement control valve, which is provided with the auxiliary communicating passages to be improved in the function of discharging liquid refrigerant in the control chamber at the time of startup of the variable displacement compressor, can reduce the minimum area of the Pc-Ps flow path in the control area, and can achieve a reduction in startup time and an improvement in operating efficiency during control of the variable displacement compressor simultaneously.   (2) The displacement control valve, in which the auxiliary communicating passages  21 E are provided in the first valve section  21 C in the first valve chest  7  in which fluid at the control pressure acts, and the pressure-sensitive device  22  and the third valve section  21 A for discharging liquid refrigerant are disposed in the third valve chest  4  in which fluid at the suction pressure acts, can reduce the minimum area of the Pc-Ps flow path in the control area by the simple configuration of providing the communicating holes  23  in the third valve section  21 A of the valve element  21 .   (3) The maximum opening area S 2 max between the communicating holes  23  in the third valve section  21 A and the third valve seat surface  12  when the second valve section  21 B is in a closed state is set equal to or smaller than the area S 1  of the auxiliary communicating passages  21 E, so that the minimum area of the Pc-Ps flow path at the time of liquid refrigerant discharge can be made as large as that in the above-described conventional art.   

     Second Embodiment 
     With reference to  FIG. 4 , a displacement control valve according to a second embodiment of the present invention will be described. 
     The displacement control valve according to the second embodiment is different from the displacement control valve in the first embodiment in the shape of communicating holes, but is identical to that of the first embodiment in the other basic configuration. The same members are provided with the same reference numerals and letters, and will not be described redundantly. 
     In  FIG. 4 , the front shape of communicating holes  23  is a T-like shape, and the cross-sectional shape thereof is uniform. In the initial stage of travel of a valve element  21  after the time of liquid refrigerant discharge (the state in  FIG. 4A ), a large opening at a horizontal portion of the T-like shape overlaps a third valve seat surface  12 , rapidly decreasing a gap between them, and thereafter, a radial gap between the valve element  21  and the third valve seat surface  12  is left. Thus, the opening area S 2  changes as shown by the solid line in  FIG. 3 . 
     Although the above second embodiment has described a case where the front shape of the communicating holes  23  is a T-like shape, the front shape of the communicating holes  23  is not limited to this, and may be an inverted triangle, a semicircle, or an ellipse, for example. It is essential only that the front shape of the communicating holes  23  be a shape having a portion with a large area that is closed in the initial stage of travel of the valve element  21  after the time of liquid refrigerant discharge, and a portion with a small area that is closed gradually thereafter. 
     Although the mode of carrying out the present invention has been described above with the embodiments, a specific configuration is not limited to these embodiments. Any changes and additions made without departing from the scope of the present invention are included in the present invention.