Abstract:
An operating rod is subjected to a surface hardening heat treatment without a post finishing process which enhances a responsiveness of the operating rod by preventing powders from being attracted to a sliding surface of the operating rod. The capacitive control valve includes a solenoid rod portion communicating with a moveable core of the solenoid portion, an operating rod connected with the solenoid rod portion, the operating rod including a valve body used for opening or closing a control fluid passage hole, and a fixed core arranged opposite relative to the moveable core. The fixed core includes a guide hole defined therein which guides the operating rod through the guide hole in a freely moveable manner, the operating rod extending longitudinally through an internal bore. The operating rod being subjected to surface hardening treatment at a relatively low temperature that does not exceed 500° C.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a capacity control valve for variably modulating a capacity or a pressure of a process fluid in a control chamber through a valve body which is connected with an operating rod. More particularly, the invention relates to a capacity control valve in which anti-abrasion capability of the operating rod in an opening or closing action of the valve body is improved and its slide resistance is decreased where the valve body is integrally attached to the operating rod. 
   2. Description of the Related Art 
   There have been known as a relative art  1  of the present invention capacity control valves for a variable displacement type swash plate compressor. In a capacity control valve of this kind, an operating rod mounting a valve body thereon is connected with a solenoid portion or a pressure sensitive device, thus the rod results in a long structure. The operating rod is also connected with a solenoid rod which is guided in a freely slidable manner through a bore inside a fixed iron core of a solenoid portion. Further, the capacity control valve accommodates the operating rod which is integrally connected with the solenoid rod of a large longitudinal length and a small radius. 
   A capacity control valve  100  shown in  FIG. 5  is similar to the capacity control valve of the related art  1 . Therefore the related art  1  is described through  FIG. 5 . A valve housing  105  in  FIG. 5  has a through hole which axially extends therethrough. The through hole disposes a discharge valve hole  110 C, suction valve hole  110 D, a first guide hole  110 E, and a second guide hole  110 F therein. Also a valve chamber  111  is disposed between the discharge valve hole  110 C and the suction valve hole  110 D. Further, a first suction pressure passage  110 B 1  is arranged to communicate with the suction valve hole  110 D. Also a discharge pressure passage  110 A is arranged to communicate with the discharge valve hole  110 C. Described at the bottom of the figure is a second suction pressure passage  110 B 2  which is arranged to communicate with the through bore. 
   In the valve housing  105 , a first valve housing  105 A and a second valve housing  105 B are integrally connected with each other at their respective end portions by means of screw thread. A spring container  120  is formed within an end portion of the first valve housing  105 A. An opening end of the spring container  120  is screw-engaged with a spring seat  122 . A spring means  121  is disposed between the spring seat  122  and the operating rod  101 , and a spring force of the spring means  121  is adjusted by rotating the screw thread of the spring seat  122 . This spring means  121  provides the operating rod  101  with a resilient, urging force which is pointing upward, as indicated in the figure. 
   The through hole of the valve housing  105  contains the operating rod  101  therewithin. The operating rod  101  forms an integral construction which includes a first stopper  110 E which slides relative to the first guide hole  110 E, a valve body  101 A which is disposed within a valve chamber  111 , a second stopper  101 F which slides relative to the second guide hole  110 F, and a solenoid rod  101 C which is fitted to a rod hole  132 A of the fixed iron core  132  in a freely slidable manner. The valve body  101 A has valve faces thereon and the respective valve faces disposed at both end faces of the valve body  101  are brought into contact with or lifted from the opposing valve seats of the valve housing  105  to adjust the opening degree of the discharge valve hole  110 C and the suction valve hole  110 D, respectively. 
   Displacement of the valve body  101 A in opening direction of the discharge valve hole  110 C allows the fluid of discharge pressure in the discharge pressure passage  110 A to rigorously flow into a crank case pressure passage  110 G. This, at the same time, creates a movement of the valve body  101 A in closing direction of the suction valve hole  110 D, which throttles the fluid of suction pressure of the first suction pressure passage  110 B 1  flowing into the crank case pressure passage  110 G. The operating rod  101  integrally built with the valve body  101 A makes a movement with the first stopper  101 E sliding relative to the first guide hole  110 E and with the second stopper  101 F sliding relative to the second guide hole  110 F. Further, the valve body  101 A is brought into contact with or is lifted from the valve seat. For this reason, the valve body  101 A as well as the first stopper  110 E and the second stopper  101 F must be hardened through heat treatment to prevent wear. Also the heat treated surfaces need to be finished by a grinding process. 
   A solenoid portion  130  is disposed at the other end of the valve housing  105 . The solenoid portion  130  consists of a fixed iron core  131 , a moveable iron core  132  and an electromagnetic coil  135 . The moveable iron core  132  operates through an energization of the solenoid portion  130 , which forces the solenoid rod  101 C to move. Movement of the solenoid rod  101 C is guided by the rod hole  132 A of the fixed iron core  132 . A portion of the fluid of suction pressure from the first suction pressure passage  110 B 1  is allowed to flow into a moveable iron core chamber  136  after passing through a clearance gap on the outer perimeter surface of the solenoid rod  101 C. This equalizes the suction pressure Ps inside the moveable iron core chamber  136  and the suction pressure Ps of the suction pressure fluid flowing into the spring chamber  120  through the second suction pressure passage  110 B 2 , both of which equally act on the operating rod from its both sides. 
   In a capacity control valve  100  of this kind, the valve body  101 A opens and closes the discharge valve hole  110 C and the suction valve hole  110 D in mutually exclusive a manner as the result of an upward motion of the operating rod  101  which is created by an action force being proportional to the electric current given to the solenoid portion  130  and a reaction force of the spring means  121 . The mutually exclusive control of the opening and closing of the discharge valve hole  110 C and the suction valve hole  110 D causes the fluid of discharge pressure Pd and the fluid of suction pressure Ps to flow into a crank case of a compressor for controlling a swash plate thereof wherein the compressor is not included in the figure. 
   The operating rod  101  of the capacity control valve  100  needs to be arranged to have a hard surface because the operating rod  101  is subject to sliding movement relative to the first guide hole  110 E and the second guide hole  110 F. A valve face of the valve body  101 A also requires a hard surface because the valve face is brought into contact with a valve seat. Further, the first stopper  101 E and the second stopper  101 F are aligned with each other in a coaxial manner in order to reduce a slide friction. Also the valve face needs to be fabricated perpendicular to the axis of the operating rod  101 . In order to do so, the operating rod  101  is machined by grinding after a heat treatment process. The operating rod  101 , however, has a body of large longitudinal length and the heat treatment often causes an axial bending of the rod. In addition, a small diameter of the operating rod  101  imposes difficulty on the use of grinding process. In particular, a great difficulty resides in the grinding process of the valve face to arrange the valve face perpendicular to the rod axis. This may cause a deficiency of the operating rod  101  in that the operating rod  101  is no longer able to keep up with the spring force of the spring portion  121  or the electric current of the solenoid portion  130  when the spring portion  121  acts on the operating rod  101  or the solenoid portion  130  is energized through the modulation of the current. Therefore the control of the capacity control valve  100  affects operation of the compressor. 
   Problems remaining in the relative art  1  and relative art  2  are clarified in the following description. In the relative art  1  (for the relative art  2 , corresponding members should be referred to in  FIG. 5 ), the fixed iron core  132  is magnetic and iron powder contained in a fluid under suction pressure Ps is attracted to an inner surface of the magnetized bore before reaching the moveable iron core chamber  136  by passing through the clearance gaps in the second guide hole  110 F and in the rod hole  132 A of the fixed iron core  132 . The attracted iron powder remains on the slide surface and causes abrasion of the inner surface of the bore as well as of the operating rod  101  during relative sliding movement. In particular, the iron powder deposited on the second guide hole  110 F of the valve housing  105  causes a trouble on the operation of the operating rod  101  (connecting rod retainer in case of the relative art  2 ). Also iron powder and the like tend to be accumulated in a region close to the second stopper  101 F of the rod hole  132 A in the fixed iron core  132 . The accumulated iron powder hampers the operation of the operating rod  101 . If the solenoid rod  101 C and the operating rod  101  are defined as separate members and their respective contact surfaces are brought into contact with each other, the iron powder accumulated in the region close to the second stopper  101 F of the rod hole  132 A in the fixed iron core  132  is introduced into an interface between the two contact surfaces of the solenoid rod  101 C and the operating rod  101  as the operating rod  101  operates, which deteriorates the opening/closing performance of the valve body  101 A. This causes the capacity control valve  100  to lose control over the fluid under the crank chamber pressure Pc. 
   In a capacity control valve of this kind, the following drawbacks remain due to the arrangement constructed as above. First, an operating rod of the capacity control valve requires a quenching process as heat treatment in order to increase hardness of the slide surface for preventing wear thereof. Such a heat treatment process, however, raises problems such as axial bending or strains. Therefore, this necessitates not only a polishing process of the heat treated surface after the original heat treatment process but also a re-grinding process in order to correct the axial bending. In addition, a small radius of the operating rod makes it difficult to apply a grinding process thereto. Further, the valve face also requires to be processed by grinding after heat treatment to ensure perpendicularity of the valve face with respect to the longitudinal axis. This grinding process is also demanding due to its necessity of machining in a perpendicular direction relative to the longitudinal axis, which increase a production cost. 
   Further, iron powders magnetized between the solenoid rod and the rod hole of the fixed iron core are attracted to the fixed iron core and makes the solenoid rod difficult to operate normally. Such contaminants like the iron powders or the like are hard to be gotten rid of because they are introduced in a source fluid to begin with. Also wear of the fixed iron core is tough to be avoided because of the limited availability of its material. As a result, the abrasion powders attracted to the rod hole make the solenoid rod difficult to operate under a normal condition. 
   The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to prevent wear in sliding motion by hardening an operating rod and to achieve dimensional accuracy for the normal operation of the operating rod. Another goal is to decrease the production cost of the operating rod. Yet another goal is to ensure the normal operation of the operating rod by preventing impurities from being attracted to between the sliding surfaces of the rod hole of the fixed core and the solenoid rod. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is made to alleviate the above technical problems and a solution to such problems is embodied as follows. A capacity control valve retains a solenoid portion, and the capacity control valve comprises a solenoid rod portion communicating with a moveable core of the solenoid portion, an operating rod retaining the solenoid rod portion, a valve body defined in the operating rod and opening or closing a control fluid passage hole and a fixed core oppositely arranged relative to the moveable core, the fixed core retaining a guide hole, the guide hole guiding the operating rod in freely moveable a manner which longitudinally extends through an internal bore wherein the operating rod is processed at no more than 500° C. by a surface hardening treatment. 
   According to a capacity control valve of the present invention, the operating rod is processed at no more than 500° C. by a low temperature surface hardening treatment. The low temperature surface hardening treatment applied to the surface of the operating rod in which a surface thickness of less than 10×10 −6  m is processed at no more than 500° C. can provide an improved anti-abrasion, anti-sticking and a low surface roughness of the operating rod. More particularly, a sliding friction of the operating rod improves since the operating rod is free from strains caused by the heat treatment. Roundness of the operating rod after the surface hardening treatment is approximately less than 0.5×10 −6  m, thus a leakage of control fluid in the closing action of the valve body from a gap between the fit surfaces of the operating rod is effectively prevented. Further, anti-abrasion ability of the operating rod will improve. Machining cost of the operating rod is also decreased. Overall shape of the operating rod after the heat treatment exhibits little deformation caused by the heat treatment, and field experiments of the operating rod do not reveal any potential problem. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of a capacity control valve as a preferred embodiment relative to the present invention. 
       FIG. 2  is an enlarged front view of an operating rod shown in  FIG. 1 . 
       FIG. 3  is an enlarged front view of a solenoid rod portion shown in  FIG. 1 . 
       FIG. 4  is a cross sectional view of a capacity control valve relative to the present invention attached to a variable displacement compressor. 
       FIG. 5  is a cross sectional view of a control valve for a variable displacement compressor as a relative art similar to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Described below is details of the figures of preferred embodiments of a capacity control valve constructed in accordance with the principles of the present invention. All the figures explained below are constructed according to actual design drawings with accurate dimensional relations. 
     FIG. 1  is a cross sectional view of a capacity control valve as a preferred embodiment relative to the present invention. In  FIG. 1 , a reference numeral  1  signifies a capacity control valve. The capacity control valve  1  disposes a valve housing  2  which forms an outer perimeter shape of the valve  1 . The valve housing  10  disposes a through hole which defines respective portions of different diameters therein. The valve housing  10  is made of metal such as brass, aluminum or stainless, synthetic resin or the like. 
   The valve housing  10  retains an widely open end at one end of the through hole thereof. The open end is fitted with an end adjusting portion  24  which forms a pressure sensing chamber  17  therewithin. Outer circumference of the other end of the valve housing  10  forms a connecting portion with which the solenoid portion  30  is connected. The end adjusting portion  24  is fitted with the valve housing  10  at a certain relative location. However, arranging screw thread on the end adjusting portion  24  enables a desired spring force of the pressure sensing device  20  to be modulated. 
   The through hole of the valve housing  10  disposes a sliding hole  12  therein which communicates with the pressure sensing chamber  17  and is arranged smaller in diameter than the pressure sensing chamber  17 . The through hole further retains a control fluid passage hole  14  which communicates with the sliding hole  12 . Also a valve chamber  4  is disposed so as to communicate with the control fluid passage hole  14  wherein the valve chamber  4  is arranged larger in diameter than the control fluid passage hole  14 . The other end of the through hole defines a mounting bore  19  which communicates with the valve chamber  4  and can be fitted to the fixed iron core (fixed core)  31  wherein the mounting bore  19  has two step shoulders and is arranged larger in diameter than the valve chamber  4 . In addition, a planar valve seat  13  is defined at the interface between the valve chamber  4  and the control fluid passage hole  14 . The valve seat  13  can be arranged to form a tapered surface toward the control fluid passage hole  14 . By doing this, a contact width with the corner of a valve portion surface  3 A can be made small. 
   The valve housing  10  defines a first communication passage  18  which communicates with the valve chamber  4 . The first communication passage  18  communicates with a passage of a fluid under control pressure Pd, e.g., a passage of a fluid under discharge pressure (control pressure) Pd in case of a variable displacement compressor. This first communication passage  18  reaches the perimeter surface of the valve housing  10  wherein four of the first communication passages  18  are disposed in equally spaced a manner. The number of the first communication passages  18  disposed on the perimeter surface in equally spaced a manner can be three, four or such depending on necessity. 
   The control fluid passage hole  14  communicates with a second communication passage  16  which allows the inflow fluid under control pressure Pd to flow out to the control chamber (crank chamber  55  in  FIG. 4 ) which is not shown in the figure. The second communication passage  16  defines a through hole extending from the outer circumference of the valve housing  10  to the control fluid passage hole  14  at two or four locations which are equally spaced along the outer circumference. 
   The valve housing  10  also retains a third communication passage  15  which communicates with the pressure sensing chamber  17 . A fluid under suction pressure (Ps) of an external device (compressor) is introduced into the pressure sensing chamber  17  through the third communication passage  15 . The outer circumference of the valve housing  10  has protruding step shoulders thereon and these protruding step shoulders at two locations dispose mounting grooves for O-ring therein. Each mounting groove mounts an O-ring thereon to provide a seal between the valve housing  10  and an installation bore of a casing, which does not appear in the figure (see  FIG. 4 ), with which the valve housing  10  is fitted. 
   The pressure sensing chamber  17  disposes a pressure sensing device  20  therewithin. A resiliently urging bellows element  21  which is made of metal forms an outer circumference of the pressure sensing chamber  17 . One end of the bellows element  21  is attached to a bellows guide  23 . The other end of the bellows element  21  is connected with a mounting plate in an integral manner. Further, a resiliently urging first spring  22  is disposed within the bellows element  21  and the internal chamber of the bellows element  21  is sealingly kept in a vacuum state. The bellows guide  23  is sealingly fitted to a sliding surface of the end adjusting portion  24  and is resiliently urged by a second spring  25 . The bellows element  21  is made of phosphorous bronze or the like and its spring coefficient is designed to a desired value. If the spring coefficient of the bellows element  21  is not strong enough, the first spring  22  which is arranged in a coil form provides an urging force. The first spring  22  exerting an urging force in an opening direction of the valve body  3  can be disposed in some other location instead of within the pressure sensing device  20 . If the first spring  22  is disposed in some other location, then the pressure sensing device  20  can be constituted by a diaphragm. 
   The pressure sensing device  20  is so designed that its action of expansion or contraction is determined based on a relative force balance between a resilient, urging force of the pressure sensing device  20  and a contracting force due to the suction pressure Ps. The suction pressure Ps which acts on an effective pressure receiving area of the pressure sensing device  20  produces the contraction force against the pressure sensing device  20 . The valve housing  10  disposes an introduction hole  17 A (represented by a broken line) which communicates from the pressure sensing chamber  17  to a large diameter portion of the mounting bore  19 . The introduction hole  17 A is capable of introducing an external fluid under suction pressure Ps through the pressure sensing chamber  17  into an internal bore  31 B of the fixed iron core  31 . The large diameter portion of the mounting bore  19  is arranged to receive a flange portion  31 C. The respective slide surfaces located in the through bore of the valve housing  10  can dispose seat films thereon which are not shown in the figure. The seat films are made of a low friction material. As an example of such a low friction material, a fluoric-resin film can be coated over the slide surface. With this seat film introduced, an overall operational response of the operating rod  2  can be improved. 
   A joint element is fixedly attached to a concave portion of the mounting plate located at the one end of the pressure receiving device  20  wherein a protruding portion of the joint element is fixedly fitted with the concave portion. The joint element also has a concave portion therein which has a shape of truncated cone. The operating rod  2  whose one end is fittingly connected with the concave portion of the joint element extends through the through bore. The operating rod  2  retains a pressure sensing rod portion  2 B which undergoes a sliding motion against the sliding hole  12 . The operating rod  2  also retains a joint rod portion  2 C which is integral with the pressure sensing rod portion  2 B. The joint rod portion  2 C is arranged smaller in diameter than the control fluid passage hole  14  such that, when the valve body  3  opens, a fluid under control pressure Pc is allowed to communicate between the control fluid passage hole  14  and the joint rod portion  2 C. The operating rod  2  further retains the valve body  3  at the end portion of the joint rod portion  2 C in an integral manner. The valve body  3  includes a valve seat  13  and a valve portion surface  3 A. A valve body rod portion  2 A extends from the valve body  3 . Diameter of the valve body rod portion  2 A is arranged slightly larger than that of the control fluid passage hole  14 . A protruding joining portion  2 E is formed at an end surface  2 A 2  (see  FIG. 2 ) of the valve body rod portion  2 A. The joining portion  2 E of the valve body rod portion  2 A is arranged to be engaged with an engagement hole disposed in a solenoid rod portion  2 D. The joining portion  2 E can be fabricated to a conical shape or a square rod shape with which the engagement hole of the solenoid rod portion  2 D is engaged. The operating rod  2  is made of stainless steel or possibly a nonmagnetic material or special steel. 
   The solenoid rod portion  2 D is formed a circular rod shape and retains the engagement hole at its one end which is engaged with the joining portion  2 E of the operating rod  2 . And the other end is fixedly connected to a fit bore of the moveable iron core (moveable core)  32 . The solenoid rod portion  2 D is made of stainless steel. The operating rod  2  is processed with a low temperature surface hardening treatment whose temperature is less than 530° C., more preferably less than 500° C. The moveable iron core  32  is arranged to form a conical surface at the fixed iron core  31  side. On the other hand, an opposite side of the moveable iron core  32  relative to the solenoid rod portion  2 D retains a concave portion and a third positive spring  36 A is disposed in the concave portion. The third positive spring  36 A always provides the moveable iron core  32  with a resiliently urging force toward the valve body  3 . The moveable iron core  32  is fitted to a bottomed cylindrical tube  33  in a freely moveable manner. 
   The fixed iron core  31  fitted to the tube  33  retains a conical-shaped concave portion at its one end which is engaged with a conical surface of the moveable iron core  32 . The flange portion  31 C is located to the valve body  3  side of the fixed iron core  31  wherein the flange portion  31 C serves a part of a main electromagnetic circuit driven by the electromagnetic coil  34  and an end portion located to the valve body  3  side relative to the flange portion  31 C defines a rod support portion  31 A. This rod support portion  31 A is not a part of the main electromagnetic circuit. And a central portion of the fixed iron core  31  is defined as the internal bore  31 B with which the solenoid rod portion  2 D is fitted in a moveable manner. The inner diameter of the internal bore  31 B is arranged to have a certain clearance gap such that the bore  31 B does not come into contact with the solenoid rod portion  2 , thus the bore  31 B loosely fits with the solenoid rod portion  2 . On the other hand, an inner diameter of a guide hole  31 A 1  extending through the center of the rod support portion  31 A is arranged to undergo a slide movement relative to the valve body rod portion  2 A. The valve body rod portion  2 A and the solenoid rod portion  2 D are joined with each other at a location where the valve body rod portion  2 A further extends out of the guide hole  31 A 1  to within the internal bore  31 B. This enables the suction pressure Ps to act on the end surface  2 A 2  of the valve body rod portion  2 A. 
   The introduction hole  17 A is allowed to communicate with the internal bore  31 B through a plurality of communication passage holes which radially extend from the outer perimeter surface of the fixed iron core  31 . Therefore, regions surrounding the fixed iron core  31 , moveable iron core  32  and the third positive spring  36 A are kept under suction pressure Ps flowing in from the pressure sensing chamber  17 . In the valve chamber  4 , a force acted on the cross section of the valve body rod portion  2 A by the discharge pressure Pd in a direction of the solenoid rod portion  2 D approximately offsets another force acted on the seal surface of the valve seat  13  of the valve body rod portion  2 A by the discharge pressure Pd in a direction of the pressure sensing rod  2 B, thus an influence of the discharge pressure Pd in the valve chamber  4  can be neglected. This implies that the operating rod  2  can be controlled by the suction pressure Ps alone without being affected by the discharge pressure Pd. 
   An electromagnetic coil  34  is located in the outer circumference of the tube  33 . The solenoid portion  30  is mainly constituted by the electromagnetic coil  34 , the moveable iron core  32  and the fixed iron core  31 . The solenoid portion  30  controls the opening degree of the valve body  3  by driving the moveable iron core  32  based on an electric current supplied to the electromagnetic coil  34 . In this case, the suction pressure Ps acted on the pressure sensing device  20  simultaneously affects the opening degree of the valve body  3  as well. In a capacity control valve  1  of this kind, the valve body  3  is opened or closed not only by the operation of the solenoid portion  30  according to the electric current supplied but also by the operation of the pressure sensing device  20  due to suction pressure Ps wherein the action of the valve body  3  modulates pressure within the control chamber by adjusting the fluid flow of the discharge pressure Pd to be introduced to the control chamber. 
     FIG. 2  shows the valve body rod portion  2 A of the operating rod  2  given in  FIG. 1 . As shown in  FIG. 1 , the operating rod  2  undergoes a sliding movement at the sliding surface  2 A 1  of the valve body rod portion  2 A against the guide hole  31 A 1 . Also the sliding surface  2 B 1  of the pressure sensing rod portion  2 B is subject to a sliding movement against the sliding hole  12 . Low temperature surface hardening treatment, however, is applied to the sliding surface  2 A 1  and the sliding surface  2 B 1 , thus bending in the longitudinal length or distortion in roundness of the operating rod  2  can be prevented. Wear on the sliding surface  2 A 1  and the sliding surface  2 B 1  also is prevented. Further, friction during the operation of the operating rod  2  is decreased as well. The operating rod  2  is made of stainless steel. A circular stainless steel rod is machined to fabricate a form shown in  FIG. 2 . The surface of the operating rod  2  is processed with a low temperature surface hardening treatment in order to increase the surface hardness. In doing so, the operating rod  2  fabricated as shown in  FIG. 2  is degreased as the first step by a degreasing process. 
   Next, the operating rod  2  is heat treated at the temperature of as low as 480° C. for approximately 120 minutes after preheating and then is oil-cooled. Heat treatment temperature is preferably no more than 500° C. and the duration is in a range of from 20 to 120 minutes. The heat treatment period varies depending on the mass and the thickness of surface treatment of the operating rod  2 . The surface may be polished after the heat treatment from necessity by means of barrel finishing or shot-peening. Finally a cleansing process concludes the entire process. In this surface hardening process, its hardening depth from the surface is less than 8×10 −6  m and a deformation of the shape of the operating rod  2  is hardly recognizable. As far as the roundness is concerned, before heat treatment and after heat treatment are, respectively, 0.28-0.46×10 −6  m and 0.37-0.47×10 −6  m. Thus the operating rod  2  hardly suffers from any distortion caused by heat treatment. And when the operating rod  2  is in operation, a leakage of the control fluid through mating sliding surfaces is negligible. Also anti-abrasion capability and anti-burning performance of the operating rod  2  under a sliding movement improves. 
   As a comparison example relative to a conventional nitriding treatment wherein an operating rod, which is made of austenite stainless steel and heat treated at 570° C. for 90 minutes, forms a nitrided layer (black layer) at the surface of the operating rod which mainly contains nitrided chrome, thus anti-corrosion performance of the stainless steel will decrease. Also the nitrided layer resulted from the nitriding treatment requires grinding finish with a grinding stone for a practical use of the operating rod  2 . Such a requirement leads to an increase in the production cost, which may in turn cause a loss of marketability. Further, stainless steel treated by a conventional quenching process must be followed by an annealing process which inevitably decreases the hardness of the sliding surface of the operating rod. An operating rod  2  of the present invention which is made of the same material and processed by a low temperature surface hardening treatment at 480° C. for 90 minutes (for example, an equivalent method to Palsonite which is a product&#39;s name of a nitriding process developed by Nihon Parkerizing Co., Ltd.), does not show an existence of black layers at its surface (the surface of the operating rod  2  in this case is called “white layer” instead). This does not require grinding finish with a grinding stone thereafter and hence its machining coat can be reduced by applying a massive, finishing method to the surfaces of the operating rods  2  such as shot-peening, honing or barrel polishing. Also a surface hardness as well as an anti-corrosion performance thereof can be improved. 
   The white layer formed at the surface of the operating rod  2  due to the low temperature surface hardening treatment is not magnetized and does no harm to the magnetic property of austenite stainless steel, thus no iron powder is attracted to the surface of the operating rod  2 . This decreases a slide friction of the sliding surface of the operating rod  2  and improves an operational response of the operating rod  2 . The low temperature surface hardening treatment used is a nitriding method conducted under no more than 530° C., preferably no more than 500° C. A material candidate for the operating rod  2  includes a structure steel alloy, tool steel, high-speed steel and stainless steel. Use of stainless steel for the operating rod  2 , however, forms a white layer which is not magnetized and does no harm to its magnetic property. This further is capable of enhancing not only the surface hardness but also the anti-corrosion performance. Also anti-sticking as well as anti-galling (resistance against wear due to mutual galling) under sliding movement of the sliding surface is improved and an outstanding response of the operating rod  2  under operation is exhibited. 
     FIG. 3  shows an example of a joint portion  2 F of the solenoid rod portion  2 D in  FIG. 1  fitted to a mounting bore of the moveable iron core  32 . Although the solenoid rod portion  2 D is a part of the operating rod  2 , an engagement hole  2 D 1  is arranged at the end of the solenoid rod portion  2 D of this example such that the valve body rod portion  2  can be connected therewith. Surface of the solenoid rod portion  2 D does not need a low temperature surface hardening treatment unless it is brought into contact. If it is subject to a relative sliding movement, however, a low temperature surface hardening treatment stated above can be utilized as well. The white layer surface finish of the solenoid rod portion  2 D is good enough from the operational point of view with no need of extra surface finishing process. Also the white layer of the operating rod  2  is not magnetized and does no harm to the magnetic property of the solenoid portion  30 . 
     FIG. 4  shows a cross section of a compressor mounting a capacity control valve  1  of the present invention therein. The compressor  50  in  FIG. 4  retains a cylinder block  51  which disposes a plurality of cylinder bores  51 A therein, a front housing  52  being defined at one end of the cylinder block  51 , and a rear housing  53  being connected via a valve plate  54  to the cylinder block  51 . 
   The cylinder block  51  and the front housing  52  define a crank chamber  55  therein and the crank chamber  55  disposes a longitudinally extending drive shaft  56  therein. A swash plate  57  is arranged in the circumference about the driving shaft  56 . The swash plate  57  is connected via a joint portion to a rotor  58  which is securely fixed to the driving shaft  56  such that the inclined angle of the swash plate  57  relative to the driving shaft  56  can be modulated. 
   One end of the driving shaft  56  extends to an external environment through the internal of the boss portion which is protruding outward from the front housing  52 . Front end portion of the driving shaft  56  defines a screw thread to which a nut  74  is fastened in order to fixate a power transmission plate  72 . Also a belt wheel  71  is disposed through a bearing  60  in the outer circumference of the boss portion  52 A. The belt wheel  71  is joined with the power transmission plate  72  through fixing bolts  73 . This means that rotating the belt wheel  71  implies rotation of the driving shaft  56 . An oil seal  52 B is disposed between the driving shaft  56  and the boss portion  52 A in order to provide a seal between the internal and the external with respect to the front housing  52 . The other end of the driving shaft  56  is located within the cylinder block  51 , being supported by a support portion  78 . Bearings  75 ,  76 ,  77  which are arranged in parallel to the driving shaft  56  provide a support to the driving shaft  56  in a rotatable manner. 
   Each cylinder bore  51 A contains a piston  62  therewithin. A hollow portion  62 A located in one internal end of the piston  62  accommodates a space for the outer perimeter portion of a swash plate  57 . An outer circumferential portion of the swash plate  57  is arranged to move together with the piston  62  through a shoe  63 . Within the rear housing  53 , a discharge chamber  64  and a suction chamber  65  are separately located. Suction chamber  65  and the cylinder bore  51 A communicate with each other through a suction port  81  disposed in a valve plate  54  and a suction valve which does not appear in the figure. Discharge chamber  64  and the cylinder bore  51 A communicate with each other through a discharge valve which is not shown in the figure and a discharge port  82  disposed in the valve plate  54 . 
   A capacity control valve  1  is installed in a hollow which is formed inside the rear wall of the rear housing  53 . The capacity control valve  1  controls the fluid under discharge pressure Pd flowing to the crank chamber  55  by adjusting the opening degrees of a fluid communication passage  69  for discharge pressure Pd which communicates with the discharge chamber  64  as well as of a fluid communication passage  66  for crank pressure Pc which communicates with the crank chamber  55 . Also the fluid under crank chamber pressure Pc within the crank chamber  55  reaches the suction chamber  65  through between the other end of the driving shaft  56  and the bearing  77 , a fluid chamber  84  and a fixed orifice  83 . As a result, the capacity control valve  1  becomes capable of adjusting the opening degrees of the fluid communication passage  69  for discharge pressure Pd as well as of the fluid communication passage  66  for crank pressure Pc, which causes changes in the crank chamber pressure Pc and allows stroke of the pistons  62  to be modulated. 
   Other preferred embodiments relative to the present invention will be described below. 
   A capacity control valve as a preferred embodiment related to a second invention retains a guide hole as a part of a fixed iron core of a solenoid portion wherein the guide hole is located at such a position that a magnetic circuit of the solenoid portion does not pass through the guide hole. 
   In the capacity control valve related to the second invention, iron powders or the like are prevented from being attracted to the guide hole. This ensures a prevention of malfunctioning of the operating rod due to iron powders or the like and an exhibition of an outstanding response of the operating rod in the control of process fluid. 
   A capacity control valve as a preferred embodiment related to a third invention retains an introduction hole to make an internal bore and a pressure sensing chamber containing a pressure sensing device communicate with each other wherein a solenoid rod portion and an operating rod are defined as two separate components within the internal bore both of which are integrally joined with each other at the division end surface. 
   In the capacity control valve related to the third invention, the solenoid rod portion can be arranged nonmagnetic and the operating rod can be made of nonmagnetic material of a different kind which is suitable to the valve body because the solenoid rod portion and the operating rod are two separate components. This not only improves anti-corrosive capability of the valve body but also decreases the sliding friction during operation. Further, a suction pressure differential between the both end portions of the operating rod can be offset by making an arrangement such that the suction pressure acts on the both end faces. By doing this, the response accuracy of the operating rod due to suction pressure will improve. 
   A capacity control valve as a preferred embodiment related to a fourth invention disposes a flange portion in an outer circumferential portion of a fixed iron core and the flange portion is located closer to an electromagnetic coil than the guide hole. 
   In the capacity control valve related to the fourth invention, disposing the flange portion closer to the electromagnetic coil than the guide hole makes it possible to form a magnetic circuit passing through the fixed iron core, but away from the guide hole. This effectively prevents iron powders or the like from being attracted to the magnetized guide hole. 
   A capacity control valve as a preferred embodiment related to a fifth invention, an operating rod is made of stainless steel. 
   In the capacity control valve related to the fifth invention, use of stainless steel for the operating rod and a low temperature surface hardening treatment applied to it leads to a formation of nonmagnetic white layer on the surface, thus no harm is given to the magnetic properties of the solenoid portion. Although even a conventional nitrided layer in stainless steel suffer from a lowered anti-corrosion, the white layer formed by a low temperature surface hardening treatment does not damage anti-corrosion. Therefore, the operating rod is capable of maintaining anti-corrosive property, improving the surface hardness and anti-sticking and enhancing its bending strength. 
   Having described specific embodiments of the invention, however, the descriptions of these embodiments do not cover the whole scope of the present invention nor do they limit the invention to the aspects disclosed herein, and therefore it is apparent that various changes or modifications may be made from these embodiments. The technical scope of the invention is specified by the claims. 
   A capacity control valve  1  of the present invention, as mentioned above, is very effective for a pressure regulation of a control chamber in pneumatic machines, compressors or the like. More particularly, the capacity control valve exhibits an outstanding operational response of the operating rod, a high anti-abrasive property of relative sliding portions of the operating rod and a low production cost of the operating rod.