Patent Publication Number: US-2018038317-A1

Title: Gas fuel supply apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-154424 filed on Aug. 5, 2016, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical field 
     This disclosure relates to a gas fuel supply apparatus incorporating a linear solenoid to regulate a flow rate of gas fuel to be supplied from a fuel container to a supply destination. 
     Related Art 
     As one of gas fuel supply apparatus, conventionally, there is an apparatus that incorporates a linear solenoid to regulate a flow rate of gas fuel to be supplied from a fuel container to a supply destination. The linear solenoid used in such an apparatus is for example disclosed in Patent Document 1. This linear solenoid is provided with a coil, a fixed core, a movable core to be attracted to a fixed core by energization of the coil, a yoke surrounding an outer circumference of the movable core and the fixed core, and a bearing slidably supporting the movable core. In the fuel supply apparatus, the linear solenoid operates to change the distance of a valve element provided at an end of the movable core from a valve seat, i.e. the dimension of a gap between the valve seat and the valve element, to adjust an opening degree in order to regulate a flow rate of gas fuel. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     JP 2010-267749A 
     SUMMARY 
     Technical Problems 
     However, when a linear solenoid is incorporated in a gas fuel supply apparatus, this apparatus needs a large valve-opening force for valve opening. In other words, when a load acting in a valve closing direction is generated by the pressure of gas fuel, that is, under the influence of gas fuel pressure, a large electromagnetic attraction force is required to move the movable core in a valve opening direction. Reversely, when a load acting in the valve opening direction is generated by the pressure of gas fuel, a load of a compression spring for urging the movable core in the valve closing direction needs to be set large and thus a large electromagnetic attraction force is required to move the movable core in the valve opening direction. In particular, for high-pressure gas fuel, the valve-opening force needs to be set remarkably high. Therefore, the linear solenoid simply applied as in the conventional art could not generate sufficient magnetic attraction force, leading to deterioration in valve-opening property. It is to be noted that upsizing of a coil may increase the magnetic attraction force, but this causes a problem with an increase in size of the gas fuel supply apparatus itself. 
     This disclosure has been made to address the above problems and has a purpose to provide a gas fuel supply apparatus capable of achieving an improved valve-opening property without any increase in overall size even when a linear solenoid is incorporated therein. 
     Means of Solving the Problems 
     To achieve the above-mentioned purpose, one aspect of the present disclosure provides a gas fuel supply apparatus comprising: a linear solenoid section including: a coil; a fixed core; a movable core to be attracted to the fixed core when the coil is energized a spring urging the movable core in a direction away from the fixed core; a pair of hearings slid ably supporting the movable core at both ends in an axial direction of the movable core; and a yoke covering the coil; a valve element to be operated by the linear solenoid section to move together with the movable core; a housing; and a valve seat fixed to the housing, the fuel supply apparatus being configured to change a distance between the valve element and the valve seat to regulate a flow rate of gas fuel, wherein the movable core includes a large-diameter portion and a small-diameter portion, wherein the fixed core includes a large-diameter recessed portion in which the large-diameter portion is slidable and a small-diameter recessed portion in which the small-diameter portion is slidable, wherein when the coil is energized, a first magnetic circuit is formed allowing a magnetic flux to flow between a large-diameter-portion corner that is a corner of the large-diameter portion and a large-diameter recessed-portion corner that is a corner of the large-diameter recessed portion, and a second magnetic circuit is formed allowing a magnetic flux to flow between a small-diameter-portion corner that is a corner of the small-diameter portion and a small-diameter recessed-portion corner that is a corner of the small-diameter recessed portion. 
     In the aforementioned gas fuel supply apparatus, when the coil is energized, the two magnetic circuits are formed in the linear solenoid section. Specifically, there are formed the first magnetic circuit in which a magnetic flux flows between the large-diameter-portion corner which is the corner of the large-diameter portion in the movable core and the large-diameter recessed-portion corner which is the corner of the large-diameter recessed portion in the fixed core and the second magnetic circuit in which a magnetic flux flows between the small-diameter-portion corner which is the corner of the small-diameter portion in the movable core and the small-diameter recessed portion corner which is the corner of the small-diameter recessed portion in the fixed core. In each of the first magnetic circuit and the second magnetic circuit; a magnetic attraction force is generated to attract the movable core toward the fixed core. Therefore, the linear solenoid section can be designed with enhanced magnetic attraction force to attract the movable core without increasing the size of a coil. This can achieve an improved valve opening property without any increase in size of the gas fuel supply apparatus even provided with a linear solenoid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a fuel injection apparatus in a first embodiment; 
         FIG. 2  is a cross sectional view to explain a first magnetic circuit and a second magnetic circuit; 
         FIG. 3  is a cross sectional view of a fuel injection apparatus in a second embodiment; 
         FIG. 4  is a cross sectional view of a fuel injection apparatus in a third embodiment; 
         FIG. 5  is a cross sectional view of a fuel injection apparatus in a fourth embodiment; and 
         FIG. 6  is a cross sectional view of a modified example of the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     First Embodiment 
     The following embodiments show a gas fuel supply apparatus of the present disclosure, applied to a fuel injection apparatus (an injector) as one of typical examples of this disclosure. This fuel injection apparatus is for example an apparatus mounted in a fuel-cell (hybrid) vehicle and operated to supply gas fuel (e.g., hydrogen gas) to a fuel cell(s) (not shown). Thus, a first embodiment of the fuel injection apparatus will be firstly described below. 
     A fuel injection apparatus  1  in the first embodiment includes, as shown in  FIG. 1 , a linear solenoid section  10 , a valve element  12 , a valve seat  14 , a housing  16 , and others. 
     The linear solenoid section  10  is provided with a coil  50 , a fixed core  52 , a movable core  54 , a compression spring  56 , a pair of bearings  58  and  59 , a yoke  60 , and others. The coil  50  is formed of a wire wound on the outer circumference of a hollow cylindrical coil bobbin  51 . In a hollow part of the coil bobbin  51 , the fixed core  52  and the movable core  54  are placed. 
     Specifically, the fixed core  52  is positioned in one end of the coil bobbin  51  in its axial direction. The fixed core  52  has a nearly cylindrical shape (including a perfect circular cylindrical shape, an elliptic cylindrical shape, etc.) and includes a large-diameter recessed portion  70 , a small-diameter recessed portion  72 , and a bearing-holding recessed portion  74 . In other words, the fixed core  52  is formed with three recessed portions arranged stepwise. The large-diameter recessed portion  70  and the small-diameter recessed portion  72  allow the movable core  54  to slide therein. The bearing-holding recessed portion  74  has a smaller diameter than the small-diameter recessed portion  72  and holds therein the bearing  58 . The fixed core  52  is made of soft magnetic material (e.g., electromagnetic stainless steel). 
     The movable core  54  has a nearly cylindrical shape (including a perfect circular cylindrical shape, an elliptic cylindrical shape, etc.) and includes a large-diameter portion  80 , a small-diameter portion  82 , a shaft portion  84 , and a valve element portion  86 . The movable core  54  is made of soft magnetic material (e.g., electromagnetic stainless steel). The movable core  54  is positioned so that a part of the large-diameter portion  80  and the valve element portion  86  are placed in the housing  16  and the shaft portion  84  is inserted in the bearing  58 . Further, the large-diameter portion  80 , the small-diameter portion  82 , and the shaft portion  84  are located in the hollow part of the coil bobbin  51 . 
     The movable core  54  is configured such that, when the valve element  12  is brought into contact with, or seated on, the valve seat  14  (in a position shown in  FIG. 1 ), a large-diameter-portion corner  81  which is a corner of the large-diameter portion  80  (i.e. a first corner of the movable core  54 ) is positioned closest to a large-diameter recessed-portion corner  71  which is a corner of the large-diameter recessed portion  70  (i.e. a first corner of the fixed core  52 ). In this state, furthermore, a small-diameter-portion corner  83  which is a corner of the small-diameter portion  82  (i.e. a second corner of the movable core  54 ) is positioned closest to a small-diameter recessed-portion corner  73  which is a corner of the small-diameter recessed portion  72  i.e. a second corner of the fixed core  52 ). 
     The movable core  54  is supported so that the shaft part  84  at one end is slidable in the hearing  58  and the valve element portion  86  at the other end is slidable in the bearing  59 . Thus, the movable core  54  is allowed to move so that the. outer peripheral surface of the large-diameter portion  80  slides along the inner peripheral surface of the large-diameter recessed portion  70 , while the outer peripheral surface of the small-diameter portion  82  slides along the inner peripheral surface of the small-diameter recessed portion  72 . Further, the valve element  12  is integrally formed at one end of the valve element portion  86 . This valve element  12  is thus moved in association with movement of the movable core  54 . 
     The compression spring  56  is placed inside the bearing  58  and between the fixed core  52  and the movable core  54 . This compression spring  56  is normally compressed, urging the valve element  12  (the movable core  54  toward the valve seat  14 , i.e., in a direction away from the fixed core  52  corresponding to a valve closing direction. 
     The yoke  60  is placed surrounding the coil  50 . An open end of this yoke  60  is closed by a lid member  62 . Those yoke  60  and lid member  62  are made of soft magnetic material (e.g., electromagnetic stainless steel) and constitute a casing of the linear solenoid section  10 . 
     The valve element  12  is integrally provided at the end of the valve element portion  86  of the movable core  54 . This valve element  12  is placed upstream of the valve seat  14  in a flowing direction of gas fuel. The valve element  12  is provided, at its end face, with a seal member  13  having a nearly circular disc-like shape. This sea member  13  is to be brought into contact with or away from the valve seat  14  (a seat portion  15 ). The seal member  13  is formed of an elastic body made of rubber, resin, or other materials. 
     The valve seat  14  is fixed to the housing  16  and provided with the seat portion  15  having a tapered outer shape. The seal member  13  of the valve element  12  is elastically deformed into contact with this seat portion  15 , thereby enhancing sealing property during stop of gas fuel supply, i.e. during valve closing. Further, the valve seat  14  is located downstream of the valve element  12  in the gas fuel flowing direction. This valve seat  14  is formed, in its central area, with an outflow port  22 . This outflow port  22  is a through hole formed through the valve seat  14  in its axial direction to form a flow passage of gas fuel. The outflow port  22  is connected to a supply destination (e.g. a fuel cell) through a fuel pipe. 
     The housing  16  has a nearly cylindrical shape and accommodates the valve element  12  (a part of the movable core  54 ), the valve seat  14 , the bearing  59 , and others. This housing  16  is made of soft magnetic material (e.g., electromagnetic stainless steel). The housing  16  is formed internally with a fuel passage  18  extending in an axial direction of the housing  16  to allow gas fuel to flow therethrough. The housing  16  is further provided with inflow ports  20  communicating sideways with the fuel passage  18 . Specifically, these inflow ports  20  are through holes radially extending through the housing  16  (in the present embodiment, two through holes in diametrically opposite positions) and serve as flow passages for gas fuel. The inflow ports  20  are connected with a fuel container (e.g., a hydrogen cylinder) through a fuel pipe. 
     A part of the housing  16  (an area in which the large-diameter portion  80  of the movable core  54  is accommodated) is positioned in the other end (an opposite side to the fixed core  52 ) of the hollow part of the coil bobbin  51 . Further, a non-magnetic annular member  64  is placed between an end (an upper end in  FIG. 1 ) of the housing  16  and an end (a lower end in  FIG. 1 ) of the fixed core  52 . 
     Operations (behavior) of the fuel injection apparatus  1  will be described below. While the coil  50  is not energized, that is, during valve closing, the seal member  13  of the valve element  12  is forced into contact with the seat portion  15  of the valve seat  14  by the urging force of the compression spring  56  as shown in  FIG. 1 . Therefore, the outflow port  22  of the valve seat  14  is disconnected from the fuel passage  18 . Thus, gas fuel is not discharged through the outflow port  22  to the outside of the fuel injection apparatus  1 . 
     In contrast, when the coil  50  is energized, that is, during valve opening, two magnetic circuits M 1  and M 2  are formed around the coil  50  to allow magnetic flux to circulate from the yoke  60  through the housing  16 , movable core  54 , fixed core  52 , and lid member  62  and back through the yoke  60 . In these two magnetic circuits M 1  and M 2 , the magnetic fluxes flowing between the movable core  54  and the fixed core  52  trace different paths. Specifically, as shown in  FIG. 2 , the first magnetic circuit M 1  is formed allowing a magnetic flux to flow between the large-diameter-portion corner  81  and the large-diameter recessed-portion corner  71  and the second magnetic circuit M 2  is formed allowing a magnetic flux to flow between the small-diameter-portion corner  83  and the small-diameter recessed-portion corner  73 . 
     Accordingly, in both the first magnetic circuit M 1  and the second magnetic circuit M 2 , a magnetic attraction force is generated in the fixed core  52  to attract the movable core  54 . In the linear solenoid section  10 , therefore, a magnetic attraction force to attract the movable core  54  can be increased in strength without any increase in size of the coil  50 . This can enhance the valve opening property of the fuel injection apparatus  1  without any increase in size. 
     At the start of energization, i.e. at the start of valve opening, the large-diameter-portion corner  81  and the large-diameter recessed portion corner  71  are positioned closest to each other and also the small-diameter-portion corner  83  and the small-diameter recessed-portion corner  73  are positioned closest to each other. Accordingly, the magnetic attraction force generated by each of the first magnetic circuit M 1  and the second magnetic circuit M 2 , corresponding to an axial attraction force to attract the movable core  54  in an axial direction, can be maximized. In the linear solenoid section  10 , since the axial attraction force to attract the movable core  54  in the axial direction toward the fixed core  52  (i.e. in a valve opening direction) can be increased, the valve opening property of the fuel injection apparatus  1  at the start of valve opening can be improved. 
     The movable core  54  can thus be reliably moved toward the fixed core  52 , which in turn moves the valve element  12  toward the fixed core  52 . Accordingly, the seal member  13  of the valve element  12  is separated from the seat portion  15  of the valve seat  14 . The outflow port  22  of the valve seat  14  is thus allowed to communicate with the fuel passage  18 . 
     To be concrete, the outflow port  22  is communicated with the fuel passage  18  through a gap between the seal member  13  of the valve element  12  and the seat portion  15  of the valve seat  14 . This allows gas fuel flowing in the fuel passage  18  to flow into the outflow port  22  through the gap between the seal member  13  and the seat portion  15 . Accordingly, the gas fuel is discharged from the outflow port  22  to the outside of the fuel injection apparatus  1 . At that time, a travel distance of the movable core  54  (the valve element  12 ) is changed according to (proportional to) an amount of current applied to the coil  50 . Therefore, the amount of current to be applied to the coil  50  is controlled to adjust an opening degree of the fuel injection apparatus  1  (i.e. a distance, or a gap, between the valve element  12  and the valve seat  14 ) to thereby regulate an amount of gas fuel to be supplied. 
     According to the fuel injection apparatus  1  in the present embodiment described in detail above, when the coil  50  is applied with current, two magnetic circuits M 1  and M 2  are formed in the linear solenoid section  10 . That is, the first magnetic circuit M 1  is formed allowing a magnetic flux to flow between the is diameter-portion corner  81  of the movable core  54  and the large-diameter recessed-portion corner  71  of the fixed core  52  and the second magnetic circuit M 2  is formed allowing a magnetic flux to flow between the small-diameter-portion corner  83  of the movable core  54  and the small-diameter recessed-portion corner  73  of the fixed core  52 . In each of the first magnetic circuit M 1  and the second magnetic circuit M 2 , the magnetic attraction force is generated in the fixed core  52  to attract the movable core  54 . In the linear solenoid section  10 , therefore, a magnetic attraction force to attract the movable core  54  can be increased in strength without any increase in size. This can enhance the valve opening property of the fuel injection apparatus  1 . 
     Second Embodiment 
     A second embodiment will be described below, referring to  FIG. 3 . Like parts or components to the first embodiment are designated by same reference numerals and will not be further explained. The following description is therefore made with a focus on differences from the first embodiment. 
     A fuel injection apparatus  101  in the second embodiment differs from the first embodiment in the shapes of a fixed core  152  and a movable core  154  as shown in  FIG. 3 . To be concrete, the fixed core  152  is provided with a large-diameter recessed portion  170  and a small-diameter recessed portion  172 . In other words, the fixed core  152  is formed with only two recessed portions arranged stepwise. Correspondingly, the movable core  154  is provided with a large-diameter portion  180  a small diameter portion  182 , and a valve element  86 . 
     The small-diameter recessed portion  172  also serves as one of the bearings slidably supporting the movable core  154 . Specifically, one of the bearings is constituted of the small-diameter recessed portion  172  and provided integral with the fixed core  152 . Accordingly, the fuel injection apparatus  101  is reduced in component count by the number of bearings as compared with the fuel injection apparatus  1 . 
     In this fuel injection apparatus  101 , when the coil  50  is energized, that is, during valve opening, two magnetic circuits M 1  and M 2  are formed around the coil  50  to allow magnetic flux to circulate from the yoke  60  through the housing  16 , movable core  154 , fixed core  152 , and lid member  62  and back through the yoke  60 . In these o magnetic circuits M 1  and M 2 , the magnetic fluxes flowing between the movable core  154  and the fixed core  152  trace different paths. Specifically, the first magnetic circuit M 1  is formed allowing a magnetic flux to flow between a large-diameter-portion corner  181  and a large-diameter recessed-portion corner  171  and the second magnetic circuit M 2  is formed allowing a magnetic flux to flow between a small-diameter-portion corner  183  and a small-diameter recessed-portion corner  173 . In the linear solenoid section  110 , therefore, a magnetic attraction force to attract the movable core  154  can be increased in strength without any increase in size. 
     According to the fuel injection apparatus  101 , consequently, the linear solenoid section  110  can increase the magnetic attraction force to attract the movable core  154  and enhance the valve opening property. The component count can also be reduced. 
     Third Embodiment 
     A third embodiment will be described below, referring to  FIG. 4 . Like parts or components to the first embodiment are designated by same reference numerals and will not be further explained. The following description is therefore made with a focus on differences from the first embodiment. 
     A fuel injection apparatus  201  in the third embodiment differs from the first embodiment in the shape of a movable core  254  as shown in  FIG. 4 . To be concrete, the length L of a small-diameter portion  282  in an axial direction in the movable core  254  is shorter (smaller) than that in the first embodiment. While the valve element  12  is in contact with the valve seat  14 , accordingly, the small-diameter-portion corner  283  is away from the small-diameter recessed-portion corner  73 . Then, when the movable core  254  is moved toward the fixed core  52  by a predetermined distance, the small-diameter-portion corner  283  comes closest to the small-diameter recessed-portion corner  73 . 
     Herein, the axial length L can be set for example based on the predetermined distance determined based on a travel distance of the movable core  254  moved in the valve opening direction at which the axial attraction force generated by the first magnetic circuit M 1  to attract the movable core  254  in the axial direction starts declining or weakening. In the present embodiment, the axial length L is set so that, before the axial attraction force generated in the first magnetic circuit M 1  starts declining, the small-diameter-portion corner  283  comes closest to the small-diameter recessed-portion corner  73  so that the axial attraction force generated by the second magnetic circuit M 2  is maximum. 
     In this fuel injection apparatus  201 , when the coil  50  is energized, that is, during valve opening, two magnetic circuits M 1  and M 2  are formed around the coil  50  to allow magnetic flux to circulate from the yoke  60  through the housing  16 , movable core  254 , fixed core  52 , and lid member  62 , and back through the yoke  60 . In these two magnetic circuits M 1  and M 2 , the magnetic fluxes flowing between the movable core  254  and the fixed core  52  trace different paths. Specifically, the first magnetic circuit M 1  is formed allowing a magnetic flux to flow between the large-diameter-portion corner  81  and the large-diameter recessed-portion corner  71  and the second magnetic circuit M 2  is formed allowing a magnetic flux to flow between the small-diameter-portion corner  283  and the small-diameter recessed-portion corner  73 . In a linear solenoid section  210  of the fuel injection apparatus  201 , therefore, a magnetic attraction force to attract the movable core  254  can be increased in strength without any increase in size of the linear solenoid section  210 . However, the magnetic attraction force of the second magnetic circuit M 2  at the start of valve opening is weaker than in the first embodiment. 
     According to the fuel injection apparatus  201 , consequently, the magnetic attraction force attracting the movable core  254  at the start of valve opening is lower than in the first embodiment but is larger than in the conventional art. Thus, the valve opening property can be enhanced. 
     As the current to be applied to the coil  50  is gradually increased and accordingly the movable core  254  is moved toward the fixed core  52 , in the first magnetic circuit M 1 , a radial attraction force attracting the movable core  254  in a radial direction becomes higher and then, before the axial attraction force attracting the movable core  254  in an axial direction in the first magnetic circuit M 1  starts declining, the axial attraction force attracting the movable core  254  in the second magnetic circuit M 2  can be maximized. 
     According to the fuel injection apparatus  201 , therefore, the travel distance (the movable range) of the movable core  254  in a proportional region (a control area) of the linear solenoid section  210  can be set large. This makes it possible to improve controllability at the valve opening, thus enabling controlling the amount of gas fuel to be supplied with high precision. 
     Fourth Embodiment 
     A fourth embodiment will be described below, referring to  FIGS. 5 and 6 . Like parts or components to the first embodiment are designated by same reference numerals and will not be further explained. The following description is therefore made with a focus on differences from the first embodiment. 
     A fuel injection apparatus  301  in the fourth embodiment differs from that in the first embodiment in the shapes of a fixed core  352  and a movable core  354  as shown in  FIG. 5 . To be concrete, the fixed core  352  is provided with a large-diameter recessed portion  370 , a small-diameter recessed portion  372 , a bearing recessed portion  374 , and a through hole  376  allowing the bearing recessed portion  374  to communicate with outside. Correspondingly, the movable core  354  is provided with a large-diameter portion  380 , a small-diameter portion  382 , a shaft portion  384 , and a valve element portion  386 . 
     Herein, the shaft portion  384  is provided with an annular seal member  385  (e.g., an O ring) for sealing against the fixed core  352  (the bearing recessed portion  374 ). Further, an area of the bearing recessed portion  374  in which the compression spring  356  is placed is communicated with the outside through the through hole  376 . Accordingly, the pressure of gas fuel (primary pressure) does not act on an end face  384   a  of the shaft portion  384 . 
     A sealing diameter SR 1  (corresponding to an inner diameter of the seat portion  15 ) defined by the seal member  13  of the valve element  12  brought into contact with, or seated on, the seat portion  15  of the valve seat  14 , thus sealing off the outflow port  22 , is equal to a sealing diameter SR 2  of the annular seal member  385  (corresponding to an outer diameter of the annular seal member  385 ) (SR 1 =SR 2 ). Accordingly, the pressure-receiving area of the movable core  354  to be subjected to the pressure of gas fuel (primary pressure) acting in the valve closing direction (that is, a total area of the end face  380   a  of the large-diameter portion  380  and the end face  382   a  of the small-diameter portion  382  located close to the fixed core  352 ) is equal to the pressure-receiving area of the movable core  354  to be subjected to the pressure of gas fuel (primary pressure) acting in the valve opening direction (that is, a total area of the end face  380   b  of the large-diameter portion  380  located close to the valve element portion  386  and a part of the end face  386   a  of the valve element portion  386  more outside than the seat portion  15  (the outflow port  22 )). Consequently, the force generated by the gas fuel pressure (primary pressure) urging the movable core  354  (the valve element  12 ) in the valve closing direction can disappear (be balanced out). 
     Not only when the sealing diameter SR 1  is equal to the sealing diameter SR 2 , but also even when the sealing diameter SR 1  is larger than the sealing diameter SR 2  (SRI&gt;SR 2 ) as shown in  FIG. 6 , the force generated by the gas fuel pressure (primary pressure) urging the movable core  354  (the valve element  12 ) in the valve closing direction can be reduced as compared with those in other embodiments. In this case, specifically, the pressure-receiving area of the movable core  354  to be subjected to the gas fuel pressure (primary pressure) acting in the valve closing direction (that is, a total area of the end face  380   a  of the large-diameter portion  380  and the end face  382   a  of the small-diameter portion  382  each located close to the fixed core  352 ) is larger than the pressure-receiving area of the movable core  354  to be subjected to the gas fuel pressure (primary pressure) acting in the valve opening direction (that is, a total area of the end face  380   b  of the large-diameter portion  380  and the valve element portion  386  and a part of the end face  386   a  of the valve element portion  386  more outside than the seat portion  15  (the outflow port  22 )). Consequently, the seal member  13  can be pressed against the seat portion  15  by use of the gas fuel pressure (primary pressure), so that a set load of the compression spring  356  can be reduced as compared with those in other embodiments. 
     In the fuel injection apparatus  301  configured as above, when the coil  50  is energized, that is, during valve opening, two magnetic circuits M 1  and M 2  are formed around the coil  50  to allow magnetic flux to circulate from the yoke  60 , through the housing  16 , movable core  354 , fixed core  352 , and lid member  62 , and back through the yoke  60 . In these two magnetic circuits M 1  and M 2 , the magnetic fluxes flowing between the movable core  354  and the fixed core  352  trace different paths. Specifically, the first magnetic circuit M 1  is formed allowing a magnetic flux to flow between the large-diameter-portion corner  381  and the large-diameter recessed-portion corner  371  and the second magnetic circuit M 2  is formed allowing a magnetic flux to flow between the small-diameter-portion corner  383  and the small-diameter recessed-portion corner  373 . In the linear solenoid section  310 , therefore, a magnetic attraction force to attract the movable core  354  can be increased in strength without any increase in size of the linear solenoid section  310 . 
     According to the fuel injection apparatus  301 , consequently, the force generated by the gas fuel pressure (primary pressure), urging the movable core  354  (the valve element  12 ) in the valve closing direction, is balanced out (or reduced) and thus the magnetic attraction force to attract the movable core  354  is increased. This can make it possible to reliably enhance the valve opening property. 
     The foregoing embodiments are mere examples and give no limitation to the present disclosure. The present disclosure may be embodied in other specific forms without departing from the essential characteristics thereof. For instance, the aforementioned fuel injection apparatus can also be directed to gas fuel (e.g. CNG) other than hydrogen. 
     The aforementioned embodiment describes the case where gas fuel flows from the inflow port  20  to the outflow port  22  via the fuel passage  18 . As an alternative, the present disclosure is applicable to a reverse direction of gas fuel, that is, to a case where gas fuel flows from the inflow port  20  to the outflow port  22  via the fuel passage  18 . 
     REFERENCE SIGNS LIST 
       
       1  Fuel injection apparatus 
       10  Linear solenoid section 
       12  Valve element 
       13  Seal member 
       14  Valve seat 
       15  Seat part 
       16  Housing 
       50  Coil 
       52  Fixed core 
       54  Movable core 
       56  Compression spring 
       58  Bearing 
       59  Bearing 
       60  Yoke 
       70  Large-diameter recessed portion 
       71  Large-diameter recessed-portion corner 
       72  Small-diameter recessed portion 
       73  Small-diameter recessed-portion corner 
       80  Large-diameter portion 
       81  Large-diameter portion corner 
       82  Small-diameter portion 
       83  Small-diameter portion corner 
     M 1  First magnetic circuit 
     M 2  Second magnetic circuit