Abstract:
A solenoid valve comprises a diaphragm type valve member installed in a casing. The valve member is movable between an open position wherein the valve member is separated from a valve seat thereby to open the same and a close position wherein the valve member is seated on the valve seat thereby to close the same. The valve member has thereon a magnetic material. A biasing member is provided for biasing the valve member in a direction to cause the valve member to assume the close position. An electromagnetic actuator is installed in the casing. The actuator has a work part that faces the valve member. The work part produces a magnetic force to attract the valve member causing the same to assume the open position against a biasing force of the biasing member when the actuator is energized and producing no magnetic force to leave the valve member causing the same to assume the close position due to the biasing force of the biasing member when the actuator is deenergized.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The present invention relates in general to solenoid valves, and more particularly to the solenoid valves of a type that is suitable for use as a purge control valve of an evaporation purge system for automotive internal combustion engines.  
           [0003]    2. Description of Related Art  
           [0004]    One of automotive emission control systems is an evaporation purge system that captures any fuel vapors coming from the fuel tank. It prevents the vapors from escaping into the atmosphere. That is, when the engine is shut off, the fuel vapors feed from the fuel tank into a charcoal canister. The activated charcoal in the canister traps or adsorbs the fuel vapors. Later, when the engine starts and becomes to take a certain operation condition, a purge control valve is opened permitting fresh air to flow through the canister and pick up the fuel vapor. The air then flows into the intake manifold and becomes part of the air/fuel mixture entering the engine cylinders.  
           [0005]    In the system, there is arranged an evaporation purge line that extends between the intake manifold and the canister. The purge control valve is installed in the evaporation purge line and when the purge control valve takes its open position, the fuel vapor, that has been trapped by the canister, is drawn into the intake manifold for burning in the engine cylinders together with the air/fuel mixture. Usually, a solenoid valve is used as the purge control valve, which is equipped with an electromagnetic actuator for electromagnetically controlling open/close action of a valve proper.  
           [0006]    However, due to its inherent construction, it is difficult to provide the solenoid valve with a responsive open/close operation especially when the valve proper thereof is of a slider type that frictionally slides in a bore. Furthermore, it is often seen that the power produced by the electromagnetic actuator is not effectively used for moving the valve proper.  
         SUMMARY OF THE INVENTION  
         [0007]    It is therefore an object of the present invention to provide a solenoid valve or purge control valve that ensures a responsive open/close operation of a valve proper and ensures effective usage of a power produced by an electromagnetic actuator.  
           [0008]    According to a first aspect of the present invention, there is provided a solenoid valve which comprises a casing defining therein inlet and outlet passages and a valve seat, the valve seat establishing a fluid communication between the inlet and outlet passages when opened and blocking the fluid communication when closed; a diaphragm type valve member installed in the casing, the valve member being movable between an open position wherein the valve member is separated from the valve seat thereby to open the same and a close position wherein the valve member is seated on the valve seat thereby to close the same, the valve member having thereon a magnetic material; a biasing member that biases the valve member in a direction to cause the valve member to assume the close position; and an electromagnetic actuator installed in the casing, the actuator having a work part that faces the valve member, the work part producing a magnetic force to attract the valve member causing the same to assume the open position against a biasing force of the biasing member when the actuator is energized and producing no magnetic force to leave the valve member causing the same to assume the close position due to the biasing force of the biasing member when the actuator is deenergized.  
           [0009]    According to a second aspect of the present invention, there is provided a solenoid valve which comprises a casing defining therein inlet and outlet passages and a valve seat, the valve seat establishing a fluid communication between the inlet and outlet passages when opened and blocking the fluid communication when closed; a diaphragm type valve member installed in the case, the valve member being movable between an open position wherein the valve member is separated from the valve seat thereby to open the same and a close position wherein the valve member is seated on the valve seat thereby to close same, the valve member having hereon a magnetic material; a biasing coil that biases the valve member in a direction to cause the valve member to assume the close position; and an electromagnetic actuator installed in the casing, the actuator comprising a core rod, an electromagnetic coil coaxially mounted on the core rod through a coil bobbin and a yoke member including two arm members by which the core rod is held, wherein the arm members have inwardly extending lower portions whose leading ends face each other with a given clearance left therebetween, and wherein the lower portions face an upper surface of the valve member thereby to serve as a work part of the electromagnetic actuator, the work part producing a magnetic force applied to the magnetic material of the valve member when the actuator is energized.  
           [0010]    According to a third aspect of the present invention, there is provided a solenoid valve which comprises a casing defining therein inlet and outlet passages and a valve seat, the valve seat establishing a fluid communication between the inlet and outlet passages when opened and blocking the fluid communication when closed; a diaphragm type valve member installed in the case, the valve member being movable between an open position wherein the valve member is separated from the valve seat thereby to open the same and a close position wherein the valve member is seated on the valve seat thereby to close same, the valve member having hereon a magnetic material; a biasing coil that biases the valve member in a direction to cause the valve member to assume the close position; and an electromagnetic actuator installed in the casing, the actuator comprising a core rod, an electromagnetic coil coaxially mounted on the core rod through a coil bobbin and a yoke member including two arm members by which the core rod is held, wherein the arm members have upper portions connected through a bridge member and inwardly extending lower portions whose leading ends face each other with a given clearance left therebetween, wherein the core rod has an upper end secured to the bridge member and a lower end positioned between the leading ends of the inwardly extending lower portions of the arm members with a given clearance left therebetween, and wherein the inwardly extending lower portions of the arm members and the lower end of the core rod face the upper surface of the valve member thereby to serve as a work part of the electromagnetic actuator, the work part producing a magnetic force applied to the magnetic material of the valve member when the actuator is energized.  
           [0011]    Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a vertically sectioned view of a solenoid valve which is a first embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a sectional view taken along the line “II-II” of FIG. 1;  
         [0014]    [0014]FIG. 3 is an external view of the solenoid valve of the first embodiment, which is taken from the same direction as in FIG. 1;  
         [0015]    [0015]FIG. 4 is an external view of the solenoid valve of the first embodiment, which is taken from the direction of the arrow “IV” of FIG. 3;  
         [0016]    [0016]FIG. 5 is an exploded view of essential parts of an electromagnetic actuator employed in the solenoid valve of the first embodiment;  
         [0017]    [0017]FIG. 6 is a schematic view showing a closed magnetic circuit provided by the electromagnetic actuator of the solenoid valve of the first embodiment;  
         [0018]    [0018]FIG. 7 is a graph showing a relation between a strength of electric current fed to the electromagnetic actuator of the solenoid valve of the first embodiment and an attractive force produced by the electromagnetic actuator;  
         [0019]    [0019]FIG. 8 is an external view similar to FIG. 3, but showing a solenoid valve of a second embodiment of the present invention;  
         [0020]    [0020]FIG. 9 is an external view of the solenoid valve of the second embodiment, which is taken from the direction of the arrow “IX” of FIG. 8;  
         [0021]    [0021]FIG. 10 is a vertically sectioned view of a solenoid valve which is a third embodiment of the present invention;  
         [0022]    [0022]FIG. 11 is a sectional view taken along the line “XI-XI” of FIG. 10;  
         [0023]    [0023]FIG. 12 is an external view of the solenoid valve of the first embodiment, which is taken from the same direction as in FIG. 10;  
         [0024]    [0024]FIG. 13 is an external view of the solenoid valve of the third embodiment, which is taken from the direction of the arrow “XIII” of FIG. 12;  
         [0025]    [0025]FIG. 14 is an exploded view of essential parts of the electromagnetic actuator employed in the solenoid valve of the third embodiment; and  
         [0026]    [0026]FIG. 15 is a schematic view showing a magnetic circuit provided by the electromagnetic actuator of the solenoid valve of the third embodiment. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0027]    In the following, three embodiments  100 ,  200  and  300  of the present invention will be described in detail with reference to the accompanying drawings.  
         [0028]    For ease of understanding, various directional terms, such as right, left, upper, lower, rightward and the like are used in the description. However, such terms are to be understood with respect to only a drawing or drawings on which the corresponding part or portion is shown. Throughout the drawings, substantially same parts or portions are denoted by the same numerals.  
         [0029]    Referring to FIGS.  1  to  7 , particularly FIGS. 1 and 2, there is shown a solenoid valve  100  of a first embodiment of the present invention, which is used as a purge control valve.  
         [0030]    In FIGS. 1 and 2, denoted by numeral  11  is a split-type casing made of a molded plastic. As is understood from these drawings, casing  11  generally comprises two parts, which are a lower part  14  that has inlet and outlet pipes  12  and  13  which are aligned, and an upper part  15  that is detachably mounted on lower part  14  in an after-mentioned manner.  
         [0031]    It is now to be noted that when the solenoid valve  100  is used as a purge control valve, inlet pipe  12  is connected to a carbon canister (not shown) and outlet pipe  13  is connected to an intake manifold (not shown) of an associated internal combustion engine. That is, inlet and outlet pipes  12  and  13  constitute part of the evaporation purge line.  
         [0032]    As is seen from FIG. 1, lower part  14  is integrally formed with a cylindrical valve seat portion  14 A that projects upward. Denoted by “O1-O1” is a center axis of which part constitutes an axis of the cylindrical valve seat portion  14 A.  
         [0033]    As is seen from FIGS. 1 and 2, lower part  14  is integrally formed at its upper portion with an annular supporting portion  14 B that surrounds cylindrical valve seat portion  14 A. As is seen from FIG. 2, a top surface of annular supporting portion  14 B is slightly higher than that of cylindrical valve seat portion  14 A.  
         [0034]    As will be described in detail hereinafter, a diaphragm type valve member  18  is operatively put on the top surface of cylindrical valve seat portion  14 A.  
         [0035]    Between cylindrical valve seat portion  14 A and annular supporting portion  14 B, there is thus defined an annular passage  14 C. As is seen from FIG. 1, annular passage  14 C is exposed to an interior of the above-mentioned inlet pipe  12 . An interior of cylindrical valve seat portion  14 A constitutes an inner passage  14 D that is exposed to an interior of the above-mentioned outlet pipe  13 .  
         [0036]    As is described hereinabove, on lower part  14 , there is mounted upper part  15 . This upper part  15  of plastic has an electromagnetic actuator  21  integrally installed therein. For this installation, a so-called insert molding technique is used.  
         [0037]    As is seen from FIG. 2, upper part  15  has a rounded lower part that comprises an annular ring portion  15 A that is mated with the above-mentioned annular supporting portion  14 B, an annular stepped portion  15 B that extends radially inward from an upper part of the annular ring portion  15 A and presses an after-mentioned resilient plate  19  against the top surface of annular supporting portion  14 B, a cylindrical stopper portion  15 C that is coaxial with the center axis “O1-O1” and projects downward and an annular recess  15 D that is defined about stopper portion  15 C. As shown, annular recess  15 D has an upper wall to which an upper end of a coil spring  27  abuts.  
         [0038]    As will become apparent hereinafter, when, due to energization of electromagnetic actuator  21 , valve member  18  is lifted to assume its open position, cylindrical stopper portion  15 C functions to stop an excessive upper movement of valve member  18 . Thus, a lift or open degree of valve member  18  is restricted by stopper portion  15 C. As shown, spring  27  is compressed between the upper wall of annular recess  15 D and an upper surface of valve member  18 . That is, due to function of coil spring  27 , valve member  18  is biased toward its close position. As is seen from FIG. 2, annular recess  15 D has an outer diameter “S” which will be described in detail hereinafter.  
         [0039]    As is seen from FIG. 3, upper part  15  of casing  11  is integrally formed with a connector portion  15 E which has two terminal pins  16  and  16  installed therein. These two terminal pins  16  and  16  are used for feeding an electric power to an after-mentioned electromagnetic coil  24  that is also installed in upper part  15  of casing  11 .  
         [0040]    Referring back to FIG. 1, denoted by numerals  17  and  17  are two brackets that are integrally provided by upper part  15 . As is seen from FIG. 3, these brackets  17  and  17  are positioned at a back side of upper part  15  and extend in parallel with inlet and outlet pipes  12  and  13 . By means of these brackets  17  and  17 , the casing  11 , that is, a unit including the lower part  14  and upper part  15  is connected to a desired position of an associated internal combustion engine (not shown).  
         [0041]    As is best understood from FIG. 2, valve member  18  located on the top surface of cylindrical valve seat portion  14 A comprises a circular plate  18 A that is made of a magnetically attractive metal and a circular elastic cover member  18 B that covers a lower surface of metal plate  18 A. The above-mentioned annular resilient metal plate  19  resiliently holds the metal plate  18 A to the top surface of annular supporting portion  14 B. A slit O-ring  20  is pressed between the top surface of annular supporting portion  14 B and the lower surface of the annular stepped portion  15 B, holding a peripheral edge of annular resilient metal plate  19  at its slit part. The metal plate  18 A is made of a magnetic steel, magnetic stainless steel or the like. The elastic cover member  18 B is made of a soft plastic, natural rubber, synthetic rubber or the like. As shown, elastic cover member  18 B is formed at its center portion with a boss that is plugged in a center opening of metal plate  18 A to be exposed to the upper surface of metal plate  18 A. The boss has a flat upper end that faces a lower end of the above-mentioned cylindrical stopper portion  15 C.  
         [0042]    As will be described in detail hereinafter, the magnetic metal plate  18 A constitutes part of a closed magnetic circuit. If desired, the annular resilient metal plate  19  may be replaced with a resiliently deformable plastic plate.  
         [0043]    In response to ON/OFF operation of the electromagnetic actuator  21  which will be described in the following, valve member  18  is moved up and down from and to the top surface of cylindrical valve seat portion  14 A thereby to open and close the fluid communication between annular passage  14 C connected to inlet pipe  12  and inner passage  14 D connected to outlet pipe  13 . It is to be noted that the upward and downward movement of valve member  18  is carried out along the center axis “O1-O1”.  
         [0044]    Due to provision of elastic cover member  18 B, valve member  18  establishes a hermetic sealing against the top surface of valve seat portion  14 A when it is seated on the top surface. Due to provision of stopper portion  15 C to which the boss of valve member  18  can abut, lift degree or open degree of valve member  18  is restricted. For obtaining a sufficient upward and downward movement of valve member  18 , a stepped circular recess “G” is defined in the rounded lower portion of upper part  15 , as is best shown in FIG. 2.  
         [0045]    As will be understood from the foregoing description, the valve member  18  is of a so-called diaphragm that is operatively placed between lower part  14  and upper part  15  to selectively open and close the fluid communication between inlet and outlet pipes  12  and  13 .  
         [0046]    For actuating valve member  18 , the electromagnetic actuator  21  is employed, which, as is seen from FIGS. 1 and 2, comprises generally a core rod  23 , the above-mentioned electromagnetic coil  24  and a yoke member  25 . The coil  24  is concentrically held by a plastic coil bobbin  22  that is concentrically disposed about core rod  23 . The coil bobbin  22  is formed with a center bore  22 A that tightly receives therein core rod  23 .  
         [0047]    As is seen from FIG. 1, upon assembly, an axis “O2-O2” of core rod  23  extends perpendicular to the center axis “O1-O1” of cylindrical valve seat portion  14 A. In other words, the center bore  22 A of coil bobbin  22  extends in parallel with a common axis of the two brackets  17  and  17 .  
         [0048]    As shown, coil bobbin  22  is positioned above valve member  18 , and center bore  22 A of coil bobbin  22  extends along the axis “O2-O2” that is perpendicular to the center axis “O1-O1”.  
         [0049]    As is best seen from FIG. 5, core rod  23  is cylindrical in shape and made of an iron, magnetic stainless steel or the like. The core rod  23  has both ends tightly held by two L-shaped arm members  26  and  26  of yoke member  25 . Caulking, press fitting, welding or the like may be used for securing core rod  23  to arm members  26  and  26 . As shown, these two arm members  26  and  26  extend in parallel with core rod  23 .  
         [0050]    Referring back to FIG. 1, electromagnetic coil  24  held by coil bobbin  22  is arranged to concentrically surround core rod  23 . Terminal ends of coil  24  are connected to the above-mentioned terminal pins  16  and  16  (see FIG. 3). Thus, when an electric connector plug (not shown) is connected to the connector portion  15 E, electric power can be fed to coil  24  for energizing the same.  
         [0051]    As is seen from FIG. 5, the two arm members  26  and  26  of yoke member  25  have inwardly extending lower portions  26 A and  26 A whose leading ends face each other with a certain clearance left therebetween. The length of the clearance is “S”. These two arm members  26  and  26  are made of an iron, magnetic stainless steel or the like. As will become apparent as the description proceeds, the lower portions  26 A and  26 A serve as a work part of the electromagnetic actuator  21 .  
         [0052]    As is seen from FIGS. 5 and 6, the length “S” of the clearance is smaller than an outer diameter “D” of the circular magnetic plate  18 A of valve member  18 , but larger than an after-mentioned gap “G”. That is, G&lt;S&lt;D is established. As will be understood from FIG. 2, the diameter “S” of annular recess  15 D of upper part  15  is equal to the length “S” of the clearance defined between the lower portions  26 A and  26 A of yoke member  25 .  
         [0053]    As is seen from FIGS. 2 and 6, the gap “G” is a clearance defined between an upper surface of the circular magnetic plate  18 A and a lower surface of each lower portion  26 A of yoke member  25  when the valve member  18  assumes its close position.  
         [0054]    It is now to be noted that due to provision of the clearance “S”, the two lower portions  26 A and  26 A are magnetically insulated from each other and function to attract circular magnetic plate  18 A of valve member  18  when electromagnetic coil  24  is energized.  
         [0055]    Referring to FIG. 6, there is schematically shown the solenoid valve  100  of the first embodiment that has the above-mentioned construction.  
         [0056]    When now electromagnetic actuator  21  is energized, there is produced a closed magnetic circuit that is depicted by the arrows “H 1 ”. It is to be noted that circular magnetic plate  18 A of valve member  18  constitutes part of the closed magnetic circuit.  
         [0057]    Upon energization of actuator  21 , valve member  18  is lifted up toward lower portions  26 A and  26 A of yoke member  25  inducing an open condition of solenoid valve  100 . While, upon deenergization of actuator  21 , the closed magnetic circuit disappears thereby inducing a close condition of solenoid valve  100  with the aid of coil spring  27 .  
         [0058]    In the following, operation of solenoid valve  100  of the first embodiment will be described with reference to the drawings, particularly, FIGS. 1, 2 and  6 , in a case wherein the valve  100  is used as a purge control valve of an evaporation purge system of an internal combustion engine.  
         [0059]    For ease of understanding, description will be commenced with respect to a close condition of solenoid valve  100 .  
         [0060]    In this close condition, electromagnetic coil  24  of electric actuator  21  is deenergized, and thus, there is produced no magnetic force that attracts or pulls valve member  18  toward the lower portions  26 A and  26 A of yoke member  25 . Thus, under this condition, valve member  18  is enforcedly seated on the top surface of cylindrical valve seat portion  14 A due to the biasing force of coil spring  27 , and thus the fluid connection between inlet and outlet pipes  12  and  13  is not established. Accordingly, under this close condition, the fuel vapor that has been trapped by the canister is not led into the intake manifold of the engine.  
         [0061]    When now electromagnetic coil  24  is energized, there is produced the above-mentioned closed magnetic circuit on the unit including core rod  23  and yoke member  25 . Upon this, due to the attracting force produced by lower portions  26 A and  26 A of yoke member  25 , valve member  18  is moved upward against the biasing force of coil spring  27  thereby to open the fluid connection between inlet and outlet pipes  12  and  13 . Accordingly, under this open condition, the fuel vapor that has been trapped by the canister is led into the intake manifold and burnt in combustion chambers of the engine together with the air/fuel mixture.  
         [0062]    In the following, advantages possessed by solenoid valve  100  of the first embodiment will be described.  
         [0063]    As is understood from the above and FIG. 2, in solenoid valve  100 , a diaphragm type valve member is used as valve member  18 . In response to ON/OFF operation of electromagnetic actuator  21 , the diaphragm type valve member  18  carries out the open/close operation very smoothly and responsively. That is, upward and downward movement of valve member  18  can be freely made without being interrupted by friction resistance. This induces an assured, reliable and responsive operation of the evaporation purge system of the internal combustion engine. As has been mentioned hereinbefore, if the valve proper is of a slider type that has to bear a frictional force when moved, responsive open/close operation of the valve is not expected.  
         [0064]    Due to the unique arrangement of the parts  23 ,  24 ,  25 ,  27  and  18 A of electromagnetic actuator  21  (see FIG. 6), the open/close movement of valve member  18 A is smoothly carried out without being interrupted by an undesirable magnetic resistance produced by electromagnetic actuator  21 . That is, because of production of the closed magnetic circuit as indicated by the arrows “H 1 ” in FIG. 6, energy loss at the time when the actuator  21  is energized can be minimized.  
         [0065]    [0065]FIG. 7 is a graph that shows, by a solid curve, a relation between the strength of electric current applied to the actuator  21  and the attractive force produced by the same. For comparison, the relation in case of a known solenoid valve is also shown by a broken curve. As is seen from this graph, in the present invention, due to the closed magnetic circuit, sufficiently large attractive force is obtained as compared with the known solenoid valve. Thus, if desired, the capacity and the number of turns of electromagnetic coil  24  may be reduced, which brings about a compact and inexpensive construction of solenoid valve  100 .  
         [0066]    As is seen from FIG. 1, core rod  23  and electromagnetic coil  24  are so arranged that their common axis “O2-O2” extends perpendicular to the center axis “O1-O1” in which valve member  18  is moved for its open/close operation. Accordingly, core rod  23  and yoke member  25  can have each a simple construction. Furthermore, due to usage of annular resilient metal plate  19 , valve member  18  can be resiliently held by casing  11 .  
         [0067]    Because valve member  18  includes only circular metal plate  18 A, circular elastic cover member  18 B and annular resilient metal plate  19 , entire construction of valve member  18  can be made light in weight. Thus, a responsive action of valve member  18  is achieved in response to the ON/OFF operation of electromagnetic actuator  21 .  
         [0068]    Almost all parts of electromagnetic actuator  21  are installed in plastic upper part  15  of casing  11  by means of insert-molding technique. This brings about an easiness with which solenoid valve  100  can be assembled.  
         [0069]    Referring to FIGS. 8 and 9, there is shown a solenoid valve  200  which is a second embodiment of the present invention.  
         [0070]    As is seen from the drawings, similar to the above-mentioned embodiment  100 , the solenoid valve  200  comprises a plastic casing  31  that corresponds to casing  11  of the first embodiment  100  and comprises a lower part  34  and an upper part  35 . Inlet and outlet pipes  32  and  33  of lower part  34  are arranged to extend perpendicular to each other. The upper part  35  has a connector portion  35 E which has two terminal pins  16  and  16  installed therein. Although not shown in the drawings, these terminal pins  16  and  16  are connected to an electromagnetic coil  24  installed in upper part  35  of casing  31 . As is seen from FIG. 8, the connector portion  35 E has at its left end a plug insert opening into which an electric connector plug (not shown) is inserted for feeding the electromagnetic coil with an electric power.  
         [0071]    Because of similar construction to the above-mentioned solenoid valve  100  of the first embodiment, solenoid valve  200  of the second embodiment has substantially the same advantages as those of the first embodiment.  
         [0072]    Referring to FIGS.  10  to  15 , particularly FIGS. 10 and 11, there is shown a solenoid valve  300  of a third embodiment of the present invention, which is used as a purge control valve.  
         [0073]    In FIGS. 10 and 11, denoted by numeral  11  is a split-type casing made of a molded plastic. Similar to the above-mentioned first embodiment  100 , casing  11  generally comprises two parts, which are a lower part  14  that has inlet and outlet pipes  12  and  13  which are aligned, and an upper part  15  that is detachably mounted on lower part  14 . Inlet pipe  12  is connected to a carbon canister (not shown) and outlet pipe  13  is connected to an intake manifold (not shown) of an associated internal combustion engine. That is, inlet and outlet pipes  12  and  13  constitute part of an evaporation purge line.  
         [0074]    As is seen from FIG. 10, lower part  14  is integrally formed with a cylindrical valve seat portion  14 A that projects upward. Denoted by “O1-O1” is a center axis of cylindrical valve seat portion  14 A.  
         [0075]    As is seen from FIGS. 10 and 11, lower part  14  is integrally formed at its upper portion with an annular supporting portion  14 B that surrounds cylindrical valve seat portion  14 A. As is seen from the drawings, a top surface of annular supporting portion  14 B is slightly higher than that of cylindrical valve seat portion  14 A.  
         [0076]    A diaphragm type valve member  18  is operatively put on the top surface of cylindrical valve seat portion  14 A in such a manner as will be described in detail hereinafter.  
         [0077]    Between cylindrical valve seat portion  14 A and annular supporting portion  14 B, there is thus defined an annular passage  14 C. As is seen from FIG. 10, annular passage  14 C is exposed to an interior of inlet pipe  12 . An interior of cylindrical valve seat portion  14 A constitutes an inner passage  14 D that is exposed to an interior of outlet pipe  13 .  
         [0078]    On the lower part  14 , there is mounted the upper part  15 . This upper part  15  of plastic has an electromagnetic actuator  21  integrally installed therein.  
         [0079]    As is seen from FIG. 11, upper part  15  has a rounded lower part that comprises an annular ring portion  15 A that is mated with the above-mentioned annular supporting portion  14 B, an annular stepped portion  15 B that extends radially inward from an upper part of the annular ring portion  15 A and presses an after-mentioned resilient plate  19  against the top surface of annular supporting portion  14 B, a circular recess  15 C that is coaxial with the center axis “O1-O1” and perpendicularly exposed to the top surface of cylindrical valve seat portion  14 A and an annular plastic plug member  15 D that is snugly received in circular recess  15 C. As shown, annular plastic plug member  15 D has at its lower end an annular groove (no numeral) into which an upper end of a coil spring  27  is received. As shown, coil spring  27  is compressed between annular plastic plug member  15 D and circular valve member  18 . That is, due to function of spring  27 , valve member  18  is biased toward its close position.  
         [0080]    As is seen from FIG. 12, upper part  15  of casing  11  is integrally formed with a connector portion  15 E which has two terminal pins  16  and  16  installed therein. These two terminal pins  16  and  16  are used for feeding an electric power to an after-mentioned electromagnetic coil  24  that is also installed in upper part  15  of casing  11 .  
         [0081]    Referring back to FIG. 10, denoted by numerals  17  and  17  are two brackets that are integrally provided by upper part  15 . As is seen from FIG. 12, these brackets  17  and  17  are positioned at a back side of upper part  15  and extend in parallel with inlet and outlet pipes  12  and  13 . By means of these brackets  17  and  17 , the casing  11 , that is, a unit including lower part  14  and upper part  15  can be fixed to a desired position of an associated internal combustion engine (not shown).  
         [0082]    As is best seen from FIG. 11, valve member  18  seated on the top surface of cylindrical valve seat portion  14 A comprises a circular plate  18 A that is made of a magnetically attractive metal and a circular elastic cover member  18 B that covers upper and lower surfaces of the circular plate  18 A. The above-mentioned annular resilient metal plate  19  resiliently holds metal plate  18 A to the top surface of annular supporting portion  14 B. A slit O-ring  20  is sandwiched between the top surface of annular supporting portion  14 B and the lower surface of the annular stepped portion  15 B, holding a peripheral edge of annular resilient metal plate  19  at its slit part. The metal plate  18 A is made of a magnetic steel, magnetic stainless steel or the like. The elastic cover member  18 B is made of a soft plastic, natural rubber, synthetic rubber or the like. As shown, elastic cover member  18 B is formed with a center stud portion through which lower and upper flat portions (no numerals) are connected. For receiving the center stud portion, the metal plate  18 A is formed with an opening (no numeral). The upper flat portion of elastic cover member  18 B faces the top surface of the above-mentioned circular recess  15 C.  
         [0083]    As will be described in detail hereinafter, magnetic metal plate  18 A constitutes part of a closed magnetic circuit. A resiliently deformable plastic plate may be used as a substitute for the resilient metal plate  19 .  
         [0084]    In response to ON/OFF operation of the electromagnetic actuator  21 , the above-mentioned circular valve member  18  is moved up and down from and to the top surface of cylindrical valve seat portion  14 A. With this moving of the valve member  18 , the fluid communication between annular passage  14 C connected to inlet pipe  12  and inner passage  14 D connected to outlet pipe  13  is opened and closed selectively. It is to be noted that the upward and downward movement of the valve member  18  is made along the center axis “O1-O1”. For obtaining a sufficient upward and downward movement of the valve member  18 , a stepped circulate recess “G” is defined in the rounded lower portion of the upper part  15  of casing  11 , as is seen from FIG. 11.  
         [0085]    Like in the above-mentioned first and second embodiments  100  and  200 , the valve member  18  is a so-called diaphragm that is operatively placed between lower part  14  and upper part  15  to selectively open and close the fluid communication between inlet and outlet pipes  12  and  13 .  
         [0086]    For actuating valve member  18 , the electromagnetic actuator  21  is employed, which, as is seen from FIGS. 10 and 11, comprises generally a core rod  23 , the above-mentioned electromagnetic coil  24  and a yoke member  25 . The coil  24  is stably held by a plastic coil bobbin  22  that is arranged to surround core rod  23 . The coil bobbin  22  is formed with a center bore  22 A that tightly receives therein core rod  23 .  
         [0087]    As is seen from FIG. 10, upon assembly, an axis of core rod  23  coincides with the center axis “O1-O1” of cylindrical valve seat portion  14 A. In other words, the center bore  22 A of coil bobbin  22  extends perpendicular to a common axis of the two brackets  17  and  17 .  
         [0088]    As shown, coil bobbin  22  is positioned above the circular valve member  18 , and center bore  22 A of coil bobbin  22  extends along the center axis “O1-O1”.  
         [0089]    As is best seen from FIG. 14, the core rod  23  is cylindrical in shape and made of iron, magnetic stainless steel or the like.  
         [0090]    As is understood from FIGS. 11 and 14, core rod  23  stands vertically having its lower end exposed to circular recess  15 C. The lower end of core rod  23  faces the valve member  18  keeping a certain clearance “G” therebetween. The core rod  23  has a smaller upper end  23 A tightly fitted in an opening  26 Ca of an after-mentioned bridge member  26 C of yoke member  25 . Caulking, press fitting, welding or the like is used for securing the smaller upper end  23 A to the bridge member  26 C.  
         [0091]    Referring back to FIG. 10, electromagnetic coil  24  held by coil bobbin  22  is arranged to concentrically surround core rod  23 . Terminal ends of coil  24  are connected to terminal pins  16  and  16  of the above-mentioned connector portion  15 E. Thus, when an electric connector plug (not shown) is connected to connector portion  15 E, electric power can be fed to coil  24  to energize the same.  
         [0092]    As is understood from FIG. 14, yoke member  25  is shaped generally rectangular and arranged to surround electromagnetic coil  24  held on coil bobbin disposed on core rod  23 . Yoke member  25  comprises two side arm members  26  and  26  each having inwardly extending lower and upper portions  26 A and  26 B. As shown, leading ends of lower portions  26 A and  26 A of the two side arm members  26  and  26  are enlarged and semi-circularly shaped to concentrically surround the lower end of core rod  23 . For this surrounding, each leading end of the lower portions  26 A and  26 A has a semicircular recess that surrounds the cylindrical outer surface of core rod  23 . Designated by reference “S” is a given annular clearance that is defined between the leading ends and the core rod  23  when the actuator  21  is properly assembled.  
         [0093]    As shown, inwardly extending upper portions  26 B and  26 B of the two side arm members  26  and  26  are connected through the above-mentioned bridge member  26 C. The bridge member  26 C is connected to the upper portions  26 B and  26 B by means of welding or the like. The two side arm members  26  and  26  and bridge member  26 C are made of iron, magnetic stainless steel or the like.  
         [0094]    Referring back to FIG. 11, under close condition of the valve member  18 , there is defined a given clearance “G” between each lower portion  26 A of the side arm members  26  and  26  and the valve member  18 . The given clearance “G” is smaller than the above-mentioned annular clearance “S”. As shown, lower surfaces of lower portions  26 A and  26 A of arm members  26  and  26  are substantially flush with a flat surface defined on the lower end of core rod  23 .  
         [0095]    Due to presence of annular clearance “S”, each lower portion  26 A and core rod  23  are magnetically insulated from each other. Upon energization of magnetic coil  24 , the lower portions  26 A and  26 A of yoke member  25  and the lower portion of core rod  23  function to attract the valve member  18  thereby opening the fluid communication between inlet and outlet pipes  12  and  13 . Because the upper end  23 A of core rod  23  are connected to bridge member  26 C, these two members  23  and  26 C and two side arm members  26  and  26  are magnetically connected.  
         [0096]    Referring to FIG. 15, there is schematically shown the solenoid valve  300  of the third embodiment that has the above-mentioned construction.  
         [0097]    When now electromagnetic actuator  21  is energized, there is produced a closed magnetic circuit that is depicted by the arrows “H 1 ”. It is to be noted that circular magnetic plate  18 A of valve member  18  constitutes part of the closed magnetic circuit.  
         [0098]    Upon energization of actuator  21 , valve member  18  is lifted up toward the lower end of core rod  23  inducing an open condition of solenoid valve  300 . While, upon deenergization of actuator  21 , the closed magnetic circuit disappears thereby inducing a close condition of solenoid valve  300  with the aid of coil spring  27 .  
         [0099]    In the following, operation of solenoid valve  300  of the third embodiment will be described with reference to the drawings, particularly FIGS. 10, 11 and  15 , in a case wherein the valve  300  is used as a purge control valve of an evaporation purge system of an internal combustion engine.  
         [0100]    For ease of understanding, description will be commenced with respect to a close condition of solenoid valve  300 , viz., the purge control valve.  
         [0101]    In the closed condition, electromagnetic coil  24  of actuator  21  is deenergized, and thus, there is produced no magnetic force that attracts or pulls valve member  18  toward the lower end of core rod  23 . Thus, under this condition, valve member  18  is enforcedly seated on the top surface of cylindrical valve seat portion  14 A due to the biasing force of coil spring  27 , and thus the fluid connection between inlet and outlet pipes  12  and  13  is not established. Accordingly, under this condition, the fuel vapor that has been trapped by the canister is not led into the intake manifold of the engine.  
         [0102]    When now electromagnetic coil  24  is energized, there is produced the above-mentioned closed magnetic circuit on a unit including core rod  23  and yoke member  25 . Upon this, due to an attracting force produced by the lower end of core rod  23  and lower portions  26 A and  26 A of the two side arm members  26  and  26 , the valve member  18  is moved upward against the biasing force of coil spring  27  thereby to pen the fluid connection between inlet and outlet pipes  12  and  13 . Thus, under this open condition, the fuel vapor that has been trapped by the canister is led into the intake manifold and burnt in combustion chambers of the engine together with the air/fuel mixture.  
         [0103]    In the following, advantages possessed by the solenoid valve  300  will be described.  
         [0104]    Also in this third embodiment, a diaphragm type valve member is used as the valve member  18 . That is, upward and downward movement of the valve member  18 , that induces open/close operation of the valve, can be freely made without being interrupted by friction resistance. Thus, assured and resonsive operation of the evaporation purge system of the internal combustion engine is established.  
         [0105]    Due to the unique arrangement of the parts  23 ,  24 ,  25 ,  27  and  18 A of electromagnetic actuator  21  (see FIG. 15), the open/close movement of valve member  18  is smoothly carried out without being interrupted by an undesirable magnetic resistance produced by actuator  21 . Because of production of the closed magnetic circuit as indicated by the arrows “H 1 ” in FIG. 15, energy loss at the time when the actuator  21  is energized can be minimized.  
         [0106]    As is seen from FIG. 10, core rod  23  and electromagnetic coil  24  are so arranged that their common axis is the same as the center axis “O1-O1” in which valve member  18  is moved for its open/close operation. Thus, core rod  23  and yoke member  25  can have each a simple construction. Due to usage of annular resilient metal plate  19 , the valve member  18  can be resiliently held by casing  11 .  
         [0107]    Because valve member  18  includes only circular metal plate  18 A, elastic cover member  18 B and annular resilient metal plate  19 , entire construction of valve member  18  can be made light in weight. Thus, a responsive action of the valve member  18  is achieved in response to the ON/OFF operation of electromagnetic actuator  21 .  
         [0108]    Almost all parts of electric actuator  21  are installed in the plastic upper part  15  of casing  11  by means of insert-molding technique. This brings about an easiness with which solenoid valve  300  can be assembled.  
         [0109]    The entire contents of Japanese Patent Applications 2002-118212 (filed Apr. 19, 2002) and 2002-118213 (filed Apr. 19, 2002) are incorporated herein by reference.  
         [0110]    Although the invention has been described above with reference to the embodiments of the invention, the invention is not limited to such embodiments as described above. Various modifications and variations of such embodiments may be carried out by those skilled in the art, in light of the above description.