CROSS-REFERENCE TO RELATED APPLICATIONS, IF ANY  
       [0001]     This application claims priority of Japanese Application No. 2004-097964 filed on Mar. 30, 2004 and entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR”.  
       BACKGROUND OF THE INVENTION  
       [0002]     (1) Field of the Invention  
         [0003]     The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor which is suitable for controlling refrigerant displacement of a variable displacement compressor for an automotive air conditioner.  
         [0004]     (2) Description of the Related Art  
         [0005]     A compressor used in a refrigeration cycle of an automotive air conditioner is driven by an engine whose rotational speed varies depending on a traveling condition of the vehicle, and hence incapable of performing rotational speed control. To eliminate the inconvenience, a variable displacement compressor capable of changing the discharge amount of refrigerant is generally employed so as to obtain an adequate refrigerating capacity without being constrained by the rotational speed of the engine.  
         [0006]     In a typical variable displacement compressor, a wobble plate is disposed within a gastightly-formed crankcase such that the inclination angle thereof can be changed, and driven by the rotational motion of a rotational shaft, for performing wobbling motion, and pistons caused to perform reciprocating motion in a direction parallel to the rotational shaft by the wobbling motion of the wobble plate draw refrigerant from a suction chamber into associated cylinders, compress the refrigerant, and then discharge the same into a discharge chamber. In doing this, the inclination angle of the wobble plate can be varied by changing the pressure in the crankcase, whereby the stroke of the pistons is changed for changing the discharge amount of the refrigerant. The control valve for a variable displacement compressor provides control to change the pressure in the crankcase.  
         [0007]     In general, the control valve for variably controlling the displacement of the compressor introduces part of refrigerant discharged at discharge pressure Pd from the discharge chamber into the gastightly-formed crankcase, and controls pressure Pc in the crankcase through control of the amount of refrigerant thus introduced. The amount of introduced refrigerant is controlled according to suction pressure Ps in the suction chamber. That is, the control valve senses the suction pressure Ps, and controls the flow rate of refrigerant introduced at the discharge pressure Pd from the discharge chamber into the crankcase, so as to maintain the suction pressure Ps at a constant level.  
         [0008]     To this end, the control valve is equipped with a pressure-sensing section for sensing the suction pressure Ps, and a valve section for causing a passage leading from the discharge chamber to the crankcase to open and close according to the suction pressure Ps sensed by the pressure-sensing section. Further, a type of control valve for a variable displacement compressor, which is capable of freely externally setting a value of suction pressure Ps to be assumed at the start of the variable displacement operation, is equipped with a solenoid that enables the set point of the pressure-sensing section to be varied by external electric current. The pressure-sensing section is generally implemented by a bellows, but there has also been proposed a control valve using a diaphragm.  
         [0009]     In the control valve having a pressure-sensing section implemented by a diaphragm, the relative pressure between the suction pressure Ps and atmospheric pressure is sensed, and hence due to a change in atmospheric pressure between when the vehicle is running on a road at a high altitude and when the vehicle is running on a road at a low altitude, there occurs a control error. To solve this problem, a control valve has been proposed in which suction pressure is sensed as an absolute pressure and the control error due to the difference in altitude is thereby eliminated (see Japanese Unexamined Patent Publication (Kokai) No. 2004-36596).  
         [0010]     This control valve is formed by arranging a vacuum chamber sealed by a diaphragm, a valve section for controlling the flow rate of refrigerant introduced from a discharge chamber into a crankcase, and a solenoid for setting a value of suction pressure Ps to be received by the diaphragm, in the mentioned order.  
         [0011]     However, the conventional control valve is configured such that refrigerant flows through the valve section and the solenoid, and hence metal dust contained in the refrigerant circulating through a refrigeration cycle tends to affect the solenoid, particularly movable parts thereof.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention has been made in view of this point, and an object thereof is to prevent the movable parts of a solenoid of a control valve for a variable displacement compressor, in which a diaphragm is used as a pressure-sensing section, from being adversely affected by metal dust contained in refrigerant.  
         [0013]     To solve the above problem, the present invention provides a control valve for a variable displacement compressor, which is mounted on the variable displacement compressor for control of pressure in a gastightly-formed crankcase by sensing suction pressure by a diaphragm, wherein a core of a solenoid and a plunger urged in a direction away from the core are accommodated in a bottomed sleeve, and an open end of the bottomed sleeve is sealed by the diaphragm such that an inside of the bottomed sleeve is kept gastight.  
         [0014]     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  
       [0015]      FIG. 1  is a central longitudinal cross-sectional view of the arrangement of a control valve for a variable displacement compressor, according to a first embodiment of the present invention.  
         [0016]      FIG. 2  is an enlarged fragmentary cross-sectional view showing a welded portion of a diaphragm.  
         [0017]      FIG. 3  is an enlarged fragmentary cross-sectional view showing a press-fitting portion of a bottomed sleeve.  
         [0018]      FIG. 4  is a central longitudinal cross-sectional view of the arrangement of a control valve for a variable displacement compressor, according to a second embodiment of the present invention.  
         [0019]      FIG. 5  is an enlarged exploded cross-sectional view showing a diaphragm and a bottomed sleeve. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]      FIG. 1  is a central longitudinal cross-sectional view of the arrangement of a control valve for a variable displacement compressor, according to a first embodiment of the present invention.  FIG. 2  is an enlarged fragmentary cross-sectional view showing a welded portion of a diaphragm.  FIG. 3  is an enlarged fragmentary cross-sectional view showing a press-fitting portion of a bottomed sleeve.  
         [0021]     This control valve for a variable displacement compressor has a valve section provided at an upper location, as viewed in  FIG. 1 . The valve section has a body  11 , and the body  11  has a side portion thereof formed with a port  12  for communicating with a discharge chamber of the variable displacement compressor when the control valve is mounted in the compressor, to receive discharge pressure Pd from the discharge chamber. The port  12  has a strainer  13  fixed to the periphery thereof. The port  12  for receiving the discharge pressure Pd communicates with a port  14  opening in the center of the top of the body  11 , via a refrigerant passage through the inside of the body  11 . The port  14  communicates with a crankcase of the variable displacement compressor to introduce controlled pressure Pc into the crankcase.  
         [0022]     In the refrigerant passage via which the port  12  and the port  14  are communicated through the body  11 , a valve seat  15  is formed integrally with the body  11 . In opposed relation to a side of the valve seat  15 , from which the pressure Pc is introduced, a valve element  16  is axially disposed in a manner movable to and away from the valve seat  15 . The valve element  16  is integrally formed with a shaft  17  which extends downward as viewed in the figure, through a valve hole such that it is axially movably held by the body  11 . The discharge pressure Pd from the discharge chamber is introduced into a small-diameter portion which connects between the valve element  16  and the shaft  17 . The outer diameter of the shaft  17  is set to be equal to the inner diameter of the valve hole forming the valve seat  15  such that the pressure-receiving area of the valve element  16  is equal to that of the shaft  17 . This causes a force of the discharge pressure Pd which acts on the valve element  16  in the upward direction as viewed in the figure to be cancelled out by a force acting on the shaft  17  in the downward direction as viewed in the figure, so as to prevent the control of the valve section from being adversely affected by the discharge pressure Pd which is high in pressure level.  
         [0023]     The valve element  16  is urged by a spring  18  in the valve-closing direction, and load of the spring  18  is adjusted by an adjustment screw  19  screwed into the port  14 .  
         [0024]     Further, a port  20  communicating with a suction chamber of the variable displacement compressor to receive suction pressure Ps is formed in a lower portion of the body  11  as viewed in the figure.  
         [0025]     A pressure-sensing section and a solenoid are arranged below the body  11 , as viewed in the figure. More specifically, on the lower end of the body  11 , there is disposed an assembly that is formed by accommodating a plunger  22 , a core  23 , and a spring  24 , as component elements of the solenoid, in a bottomed sleeve  21  which forms a vacuum container, and sealing the opening of the bottomed sleeve  21  with a metal diaphragm  25 , and outside the bottomed sleeve  21 , there are arranged a coil  26 , a ring  27 , a case  28 , and a handle  29 , which are made of magnetic substances and constitute a yoke for establishing a magnetic circuit.  
         [0026]     In the bottomed sleeve  21 , the core  23  is rigidly press-fitted and the plunger  22  is axially movably disposed on a side of the core  23  toward the valve section. The plunger  22  is rigidly press-fitted on one end of a shaft  30  axially extending in the center of the core  23 , and the other end of the shaft  30  is supported by a bearing  31  slidably disposed in the core  23 . A stop ring  32  is fitted on an intermediate portion of the shaft  30 , and a spring-receiving member  33  is formed such that the upward movement thereof as viewed in the figure is restricted by the stop ring  32 . The spring  24  is interposed between the spring-receiving member  33  and the bearing  31 . The plunger  22  is urged by the spring  24  via the shaft  30  in a direction away from the core  23 . It should be noted that load of the spring  24  can be changed by externally adjusting the axial position of the bearing  31 . More specifically, in final adjustment after assembly of the control valve for a variable displacement compressor, the bottom of the bottomed sleeve  21  is pushed to be deformed inward, whereby the axial position of the bearing  31  in abutment with the bottom is changed to adjust the load of the spring  24 . Thus, the set point of the control valve is adjusted.  
         [0027]     The bottomed sleeve  21  accommodating the plunger  22  and the core  23  as described above is sealed by welding the diaphragm  25  to a flange portion formed on the open end of the bottomed sleeve  21 . For example, as shown in detail in  FIG. 2 , the diaphragm  25  is placed on the flange portion of the bottomed sleeve  21  and circumferentially welded to the flange portion along the entire perimeter thereof via an annular patch  34  by laser welding, resistance welding, or the like, under vacuum atmosphere, whereby the gastight assembly is formed such that the inside thereof maintained under vacuum.  
         [0028]     This assembly is fixed to the body  11  via a reinforcing ring  35  by positioning the flange portion of the bottomed sleeve  21  in a recess formed in the lower end of the body  11  and caulking the peripheral wall of the recess. Then, the case  28  accommodating the coil  26  is fixed to the body  11  by caulking an upper end  36  of the case  28 .  
         [0029]     Further, in mounting the assembly to the body  11 , an O ring  37  is interposed between the patch  34  and the body  11  so as to seal between a chamber receiving the suction pressure Ps and the atmosphere, such that the center of the solid part of the O ring  37  is positioned at a location radially inward of a weld line  38 . Thus, stress generated by the displacement of the diaphragm is prevented from reaching the weld line  38  which has become fragile due to a change in material caused by the welding.  
         [0030]     The bottomed sleeve  21  is formed by deep-drawing of a stainless steel material, such as SUS304. The bottomed sleeve  21  is required to be formed of a non-magnetic material so as to prevent the bottomed sleeve  21  from attracting the plunger  22  during energization of the solenoid and thereby increasing sliding resistance. However, SUS304 is known to have a property that when subjected to strong cold working, it acquires magnetism due to a partial change in its metallic crystal structure. In such a case, the bottomed sleeve  21  is made non-magnetic again by subjecting the same to annealing.  
         [0031]     On the other hand, the bottomed sleeve  21  also includes a portion which is desirably magnetic in view of the magnetic circuit. The portion is in an area in which is located the handle  29  magnetically connecting between the core  23  and the case  28 . For this reason, a part of the bottom-side portion of the bottomed sleeve  21  which is formed by deep drawing to extend straight, is further drawn as shown in detail in  FIG. 3 . More specifically, the part of the bottom-side portion of the bottomed sleeve  21  is subjected to strong cold working such that its diameter is reduced, whereby the part of the bottom-side portion can be made magnetic to increase magnetic permeability. The drawn part of the bottom-side portion of the bottomed sleeve  21  has its diameter reduced to form a press-fitting portion  39  used for rigidly press-fitting the core  23  in the bottomed sleeve  21 . In this press-fitting portion  39 , the amount of press-fitting of the core  23  is adjusted to adjust the magnitude of the magnetic gap between the core  23  and the plunger  22 .  
         [0032]     It should be noted that when the bottomed sleeve  21  is made of a stainless steel, the diaphragm  25  is also made of a stainless steel material for springs, called SUS304CSP, in view of welding. Of course, the materials of the bottomed sleeve  21  and the diaphragm  25  are not limited to the stainless steel materials, but it is also possible to use copper for the bottomed sleeve  21 , and beryllium copper for the diaphragm  25 .  
         [0033]     In the arrangement described above, the ring  27 , the case  28 , and the handle  29  are formed of magnetic materials to serve as the yoke of the magnetic circuit of the solenoid. Magnetic lines of force generated by the coil  26  pass through the magnetic circuit formed by the case  28 , the ring  27 , the plunger  22 , the core  23 , and the handle  29 .  
         [0034]      FIG. 1  shows a state of the control valve for a variable displacement compressor, in which the solenoid is not energized and the suction pressure Ps is high, i.e. a state in which an air conditioner is not operating. Since the suction pressure Ps is high, the diaphragm  25  is displaced downward, as viewed in the figure, against the load of the spring  24  to bring the plunger  22  into contact with the core  23 . As a result, the valve element  16  held in contact with the diaphragm  25  via the shaft  17  is seated on the valve seat  15  by being urged in the valve-closing direction by the spring  18 , and hence the valve section is in its fully-closed state.  
         [0035]     Now, assuming that the automotive air conditioner is started and the variable displacement compressor is driven for rotation by an engine, the variable displacement compressor whose control valve is in its fully-closed state is operated with the maximum displacement.  
         [0036]     When the variable displacement compressor continues to operate with the maximum displacement to make the suction pressure Ps from the suction chamber sufficiently low, the diaphragm  25 , sensing the suction pressure Ps, moves upward as viewed in the figure. With this upward motion of the diaphragm  25 , the plunger  22  moves away from the core  23  in a state abutted to the diaphragm  25 . At this time, if control current supplied to the solenoid coil  26  is set to a value of cooling capacity corresponding to a temperature set for air conditioning, the plunger  22  stops in a position where the suction pressure Ps, the loads of the springs  18  and  24 , and the attractive force of the solenoid are balanced. This causes the valve element  16  held in contact with the diaphragm  25  via the shaft  17  to be pushed upward by the diaphragm  25  to move away from the valve seat  15  so as to be set to a predetermined valve lift. Therefore, refrigerant at the discharge pressure Pd is introduced into the crankcase at a flow rate controlled to a value dependent on the valve lift, whereby the variable displacement compressor is controlled to perform operation with the displacement corresponding to the control current.  
         [0037]     When the control current supplied to the coil  26  of the solenoid is constant, the diaphragm  25  senses the suction pressure Ps as an absolute pressure to thereby control the valve lift of the valve section. For example, when the refrigeration load increases to make the suction pressure Ps high, the diaphragm  25  is displaced downward as viewed in the figure, so that the valve element  16  is also moved downward to decrease the valve lift of the valve section, causing the variable displacement compressor to operate in a direction of increasing the displacement. On the other hand, when the refrigeration load decreases to make the suction pressure Ps low, the diaphragm  25  is displaced upward as viewed in the figure to increase the valve lift of the valve section, causing the variable displacement compressor to operate in a direction of decreasing the displacement. Thus, the control valve controls the displacement of the variable displacement compressor such that the suction pressure Ps becomes equal to a value set by the solenoid.  
         [0038]      FIG. 4  is a central longitudinal cross-sectional view of the arrangement of a control valve for a variable displacement compressor, according to a second embodiment of the present invention.  FIG. 5  is an enlarged exploded cross-sectional view showing a diaphragm and a bottomed sleeve. It should be noted that component elements in  FIG. 4  identical or similar in function to those in  FIG. 1  are designated by identical reference numerals, and detailed description thereof is omitted.  
         [0039]     The control valve for a variable displacement compressor of the second embodiment is distinguished from the control valve for a variable displacement compressor of the first embodiment in that the shape of the diaphragm  25  is modified. As shown in detail in  FIG. 5 , the present diaphragm  25  comprises three component parts. First, a base part  40  having a largest diameter has a central portion thereof formed with a hole, and is welded to the flange portion of the bottomed sleeve  21 . An intermediate connecting part  41  in the form of a funnel is disposed on the base part  40 , and a disk  42  is disposed on the intermediate connecting part  41  in a manner covering the upper opening of the same. The base part  40 , the intermediate connecting part  41 , and the disk  42  are formed e.g. of beryllium copper. The base part  40  and the intermediate connecting part  41  have inner peripheral portions thereof welded to each other along the entire perimeters thereof e.g. by forming a protuberance along the inner peripheral edge of the base part  40  and projection-welding the inner peripheral portions of the two, and the intermediate connecting part  41  and the disk  42  have outer peripheral portions thereof welded to each other along the entire perimeters thereof e.g. by laser-welding. The diaphragm  25  is thus formed. In this case, the bottomed sleeve  21  is formed of the same copper material as the diaphragm  25 , and the base part  40  of the diaphragm  25  is welded to the flange portion of the bottomed sleeve  21  along the entire perimeter thereof under vacuum atmosphere e.g. by laser-welding.  
         [0040]     This diaphragm  25  can have a larger stroke in the direction of displacement than that of the control valve of the first embodiment in which the pressure-sensing section is formed by a single thin metal plate, and hence the control range of the valve section can be expanded.  
         [0041]     The control valve for a variable displacement compressor, according to the present invention, is configured such that an assembly is separately formed by sealing the bottomed sleeve containing the movable parts of the solenoid with the diaphragm such that the assembly has a vacuum inside, and the assembly is fixed to the body of the valve section. Further, the assembly is fixed to the body of the valve section with the solenoid coil arranged therearound. Therefore, the control valve is advantageous in its ease of construction.  
         [0042]     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.
To prevent the movable parts of a solenoid of a control valve for a variable displacement compressor, in which a diaphragm is used as a pressure-sensing section, from being affected by metal dust contained in refrigerant. A core, a plunger, and a spring of a solenoid are accommodated in a bottomed sleeve. A diaphragm is welded to an open end of the bottomed sleeve under a vacuum ambience, whereby an assembly that makes the inside a vacuum is formed. As a result, suction pressure Ps can be sensed as an absolute pressure with reference to a vacuum. The movable parts of the solenoid are housed in the vacuum container, so that they are free from the influence of metal dust contained in refrigerant circulating through a refrigeration cycle.