Abstract:
A fuel injection valve includes a valve member, a first stop member, a second stop member, a movable core, a fixed core, and a coil. The valve member opens and closes an injection nozzle. The first stop member protrudes radially outward from said valve member. The second stop member protrudes radially outward from said valve member. The movable core is sandwiched between said first and second stop members. The movable core and one of said first and second stop members defines a fuel chamber. The fixed core is axially displaced from said movable core. The coil causes reciprocal axial displacement of said valve member such that said movable core axially reciprocates toward and away from said fixed core therewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2004-164359, filed on Jun. 2, 2004 and Japanese Patent Application No. 2005-41934, filed on Feb. 18, 2005, the contents of which are incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a fuel injection valve and, more particularly, a fuel injection valve having a movable core.  
       BACKGROUND OF THE INVENTION  
       [0003]     In a conventional type of injector, a valve member formed as an integral part of a movable core is driven using magnetic attraction generated between a fixed core and the movable core in response to energization of a coil. In such an injector, the valve member moves back and forth in the axial direction according to whether or not the coil is energized. Consequently, when the movable core moves towards the fixed core, it collides with the fixed core, whereas when the movable core moves away from the fixed core, the integral valve member collides with the valve seat. As a result, the impact of the collisions causes so-called bouncing of the movable core and the valve member.  
         [0004]     In an injector, bouncing of the valve member results in variation of opening time and closing time of the injection nozzle. This results in uncontrollable and irreproducible injection of fuel from the injection nozzle. The effect of bouncing is particularly marked when the length of the energizing pulse applied to the coil is small, making it impossible to precisely control the amount of fuel injected and the shape of the fuel spray. Accordingly, an injector has been proposed in which two stoppers are provided on the valve member, with the movable core disposed between these stoppers (see Published Japanese Translation of PCT application No. 2002-528672).  
         [0005]     In the injector disclosed in the Published Japanese Translation of PCT application No. 2002-528672, the movable core is able to move in the axial direction between the two stoppers. Consequently, when the valve member collides with another member, opposing inertial forces are generated in the valve member and the movable core. This moderates the impact force at the point of collision. In addition, by providing buffer springs between the movable core and the stoppers, the impact of the collisions is moderated, and the occurrence of bouncing is reduced.  
         [0006]     However, with the technology disclosed in the Published Japanese Translation of PCT application No. 2002-528672, two stoppers must be provided in the valve member, and the movable core must be interposed between the two stoppers in such a manner as to be movable relative to the valve member. In addition, buffer springs must be provided between the movable core and the stoppers. This leads to a more complicated construction and increases the some number of components. Furthermore, long term operation of the injector can cause spring fatigue and abrasion and the like. Consequently, the characteristics of the springs vary over time, and it is difficult to ensure stable fuel injection characteristics over an extended period.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, an object of the present invention is to provide an injector which uses a simple construction to reduce bouncing of the movable core and the valve member, with increasing the minimum number of components, and which displays little variation in fuel injection characteristics over its lifetime.  
         [0008]     In one aspect of the invention, the movable core is sandwiched between stop members provided on the valve member, forming a fuel chamber between the movable core and the stop members. Consequently, the fuel that collects in the fuel chamber formed between the movable core and the stop members functions as a damper, which moderates the impact between the movable core and the stop members. Thus, it is not necessary to provide stopper or buffer springs, and bouncing of the movable core, as well as the valve member on which the stop members are provided, can be reduced using a simple construction, with increasing the minimum number of components. Furthermore, the damping effect of the fuel in the fuel chamber does not vary greatly over time. Accordingly, variation in the fuel injection characteristics can be minimized.  
         [0009]     In another aspect of the present invention, the movable core has a cylindrical portion protruding towards the injection side, and one of the stop members forms a fuel chamber in combination with this cylindrical portion. Consequently, a separate member is not required to form the fuel chamber. Accordingly, bouncing of the movable core and the valve member can be reduced using a simple construction, with increasing the minimum number of components.  
         [0010]     In another aspect of the present invention, a fuel aperture is formed between the outside edge in the radial direction of the stop member and the inner circumferential surface of the cylindrical portion. This fuel aperture restricts the flow of fuel in and out of the fuel chamber. Consequently, by adjusting the surface area of the opening of the fuel aperture formed between the stop member and the cylindrical portion, the flow rate of fuel in and out of the fuel chamber can be controlled easily. As a result, the surface area of the opening of the fuel aperture controls the damping effect of the fuel in the fuel chamber. Accordingly, it is possible to easily control and reduce bouncing in accordance with the operating characteristics of the valve member and the movable core, and the fuel injection characteristics that are required.  
         [0011]     In still another aspect of the present invention, the stop member has an aperture portion that penetrates through the stop member in the through-thickness direction. This aperture portion is either a cylindrical hole that passes through the stop member, or a notch-shaped groove formed at the radial outer edge of the stop member. This aperture portion restricts the flow of fuel in and out of the fuel chamber. Consequently, by adjusting the surface area of the opening of this aperture portion, the flow rate of fuel in and out of the fuel chamber can be controlled easily. As a result, the characteristics of the damping effect produced by the fuel in the fuel chamber are controlled by the surface area of the opening of the aperture portion. Accordingly, it is possible to easily control and reduce bouncing in accordance with the operating characteristics of the valve member and the movable core, and the fuel injection characteristics that are required.  
         [0012]     In still another aspect of the present invention, the movable core has an injection side recess, recessed away from the injection nozzle, in an end portion at an injection side of the movable core, and one of the stop members forms the fuel chamber together with this injection side recess. Thus, a separate member is not required to form the fuel chamber. Accordingly, bouncing of the movable core and the valve member can be reduced using a simple construction, with increasing the minimum number of components.  
         [0013]     In still another aspect of the present invention, a fuel aperture is formed between the outside edge in the radial direction of the stop member and the inner circumferential surface of the injection side recess. This fuel aperture restricts the flow of fuel in and out of the fuel chamber. Consequently, by adjusting the surface area of the opening of the fuel aperture formed between the stop member and the injection side recess, the flow rate of fuel in and out of the fuel chamber can be controlled easily. As a result, the surface area of the opening of the fuel aperture controls the damping effect of the fuel in the fuel chamber. Accordingly, it is possible to easily control and reduce bouncing in accordance with the operating characteristics of the valve member and the movable core, and the fuel injection characteristics that are required.  
         [0014]     In still another aspect of the present invention, the stop member has an aperture portion that penetrates through the stop member in the through-thickness direction. This aperture portion is either a cylindrical hole that passes through the stop member, or a notch-shaped groove formed at the radial outer edge of the stop member. This aperture portion restricts the flow of fuel in and out of the fuel chamber. Consequently, by adjusting the surface area of the opening of this aperture portion, the flow rate of fuel in and out of the fuel chamber can be controlled easily. As a result, the characteristics of the damping effect produced by the fuel in the fuel chamber are controlled by the surface area of the opening of the aperture portion. Accordingly, it is possible to easily control and reduce bouncing in accordance with the operating characteristics of the valve member and the movable core, and the fuel injection characteristics that are required.  
         [0015]     In still another aspect of the present invention, the movable core has a non-injection side recess, recessed towards the injection side, in the end portion of the movable core on the opposite side from the injection side. The non-injection side recess forms the fuel chamber with an end stop member. The end stop member is the one provided at the opposite end of the valve member from the injection nozzle. Thus, a separate member is not required to form the fuel chamber. Accordingly, bouncing of the movable core and the valve member can be reduced using a simple construction, with increasing the minimum number of components.  
         [0016]     In still another aspect of the present invention, the base of the movable core and the opposing face of the end stop member, which oppose each other, are both flat surfaces. Consequently, a so-called squeezing force occurs between the opposing face and the base. Accordingly, bouncing of the movable core and the valve member can be reduced using a simple construction, with increasing the minimum number of components.  
         [0017]     In still another aspect of the present invention, the end face of the movable core and the end face of the stop member, which face each other, form the fuel chamber. Consequently, there is no need to form a recess or the like in the movable core, for example. This further simplifies the shape and manufacture of the movable core. Furthermore, when the movable core and the stop member move apart, the fuel in the fuel chamber formed between the movable core and the stop member generates a squeezing force that acts to prevent them from moving apart. In addition, when the movable core and the stop member collide, the fuel in the fuel chamber generates a damping force that moderates the impact of the collision. Accordingly, bouncing of the movable core and the valve member can be reduced using a simple construction.  
         [0018]     In still another aspect of the present invention, fuel flows in and out of the fuel chamber past the radial outer edge of an end face of the movable core and an end face of the stop member. Consequently, by adjusting the distance between the end face of the movable core and the end face of the stop member at the radial outside edge of the movable core, the flow rate of fuel in and out of the fuel chamber can be controlled easily. Accordingly, it is possible to easily control and reduce bouncing in accordance with the operating characteristics of the valve member and the movable core, and the fuel injection characteristics that are required.  
         [0019]     In still another aspect of the present invention, fuel passages are formed on the inner circumferential side of the valve member. Thus, fuel from the fixed core side passes through the inside of the valve member. Furthermore, by forming these fuel passages, the valve member takes the form of a cylinder. Consequently, the weight of the valve member is reduced, which improves the responsiveness of the valve member to coil energization.  
         [0020]     In still another aspect of the present invention, the valve member and the movable core are capable of relative movement in the axial direction. Consequently, when the movable core and the fixed core collide, the valve member has an inertial force which acts to keep the valve member moving in the direction of the fixed core. In contrast, the impact of the collision gives the movable core an inertial force in the opposite direction to the fixed core. In this case, because the movable core and the valve member form the fuel chamber, the opposing inertial forces of the movable core and the valve member are absorbed by the damping effect of the fuel in the fuel chamber. Thus, when the movable core and the fixed core collide, the impact force at the point of collision is moderated. Furthermore, in a similar manner, when the movable core and the valve member move away from the fixed core, and the valve member collides with the valve seat, the impact force at the point of collision is moderated. Accordingly, bouncing of the movable core and the valve member can be reduced using a simple construction, with increasing the minimum number of components.  
         [0021]     Other features and advantages of the present invention will be appreciated, as well as methods of operation and the function of the related parts from a study of the following detailed description, appended claims, and drawings, all of which form a part of this application. In the drawings: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a cross-sectional view showing the vicinity around a movable core of an injector according to the first embodiment of the present invention;  
         [0023]      FIG. 2  is a cross-sectional view of an injector according to the first embodiment of the present invention;  
         [0024]      FIG. 3  is a cross-sectional view showing the vicinity around the movable core of the injector according to the first embodiment of the present invention, wherein a second stop member and the movable core are separated;  
         [0025]      FIG. 4  is a cross-sectional view showing a first modification of the injector according to the first embodiment of the present invention;  
         [0026]      FIG. 5  is a cross-sectional view showing a second modification of the injector according to the first embodiment of the present invention;  
         [0027]      FIG. 6  is a cross-sectional view showing the vicinity around a movable core of an injector according to a second embodiment of the present invention;  
         [0028]      FIG. 7  is a cross-sectional view showing the vicinity around a movable core of an injector according to a third embodiment of the present invention;  
         [0029]      FIG. 8  is a cross-sectional view showing the vicinity around a movable core of an injector according to a fourth embodiment of the present invention;  
         [0030]      FIG. 9  is a cross-sectional view showing the vicinity around a movable core of an injector according to a fifth embodiment of the present invention;  
         [0031]      FIG. 10  is a cross-sectional view showing the vicinity around a movable core of an injector according to a sixth embodiment of the present invention;  
         [0032]      FIG. 11  is a cross-sectional view showing the vicinity around a movable core of an injector according to a seventh embodiment of the present invention;  
         [0033]      FIG. 12  is a cross-sectional view showing the vicinity around a movable core of an injector according to an eighth embodiment of the present invention; and  
         [0034]      FIG. 13  is a cross-sectional view showing the vicinity around a movable core of an injector according to a ninth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     A plurality of embodiments of the present invention are described below with reference to the drawings.  
         [0036]      FIG. 2  shows a fuel injection valve (hereafter, referred to as an “injector”) according to a first embodiment of the present invention. An injector  10  of the first embodiment can be applied to direct-injection gasoline engines, for example. However, the injector  10  is not limited to applications within direct-injection gasoline engines, and may also be applied to premixing type gasoline engines or diesel engines. When applied to a direct-injection gasoline engine, the injector  10  is fitted to a cylinder head, not shown in the diagrams.  
         [0037]     A housing  11  of the injector  10  is formed as a cylinder. The housing  11  comprises a first magnetic portion  12 , a non-magnetic portion  13 , and a second magnetic portion  14 . The non-magnetic portion  13  prevents magnetic shorting of the first magnetic portion  12  and the second magnetic portion  14 . The first magnetic portion  12 , the non-magnetic portion  13 , and the second magnetic portion  14  are connected together by laser welding or the like to form a single integrated body. It is also possible to mold the housing  11  from a magnetic material as an integrated cylindrical product, and then demagnetize the portion corresponding to the non-magnetic portion  13  using a heat treatment.  
         [0038]     An inlet member  15  is provided at one end in the axial direction of the housing  11 . The inlet member  15  is press-fit inside the inner circumference of the housing  11 . The inlet member  15  has a fuel inlet  16 . Fuel is supplied to the fuel inlet  16  from a fuel pump, not shown in the figure. The fuel supplied to the fuel inlet  16  flows into the inside of the housing  11  through a fuel filter  17 . The fuel filter  17  removes foreign matters from the fuel.  
         [0039]     A nozzle holder  20  is provided at the other end of the housing  11 . The nozzle holder  20  is formed in the shape of a cylinder, on the inside of which is provided a nozzle body  21 . The nozzle body  21  is also in the form of a cylinder, and is fixed to the nozzle holder  20  by a method such as press-fitting or welding, for example. The nozzle body  21  has a valve seat  22 , which is formed on a conically shaped internal surface, the inside diameter of which narrows towards the tip. The nozzle body  21  has an injection nozzle  23  positioned at the tip on the opposite side from the housing  11 , and this nozzle passes through the nozzle body  21  and connects the inside wall of the nozzle body with the outside wall.  
         [0040]     A needle  30 , which functions as the valve member, is housed inside the housing  11 , the nozzle holder  20  and the nozzle body  21 , and is able to move back and forth in the axial direction. The needle  30  is positioned substantially coaxially with the nozzle body  21 . The needle  30  has a shaft portion  31  and a seal portion  32 . The seal portion  32  is provided at the opposite end of the shaft portion  31  from the fuel inlet  16 . The seal portion  32  is capable of contacting the valve seat  22  provided in the nozzle body  21 . The needle  30  forms a fuel passage  33  through to the nozzle body  21 , through which fuel flows.  
         [0041]     The injector  10  has an actuator  40  that drives the needle  30 . The actuator  40  comprises a spool  41 , a coil  42 , a fixed core  43 , a plate housing  44 , and a movable core  50 . The spool  41  is positioned outside the housing  11 . The spool  41  is formed from resin in a cylindrical shape, and the coil  42  is then wound around the outside of the spool  41 . The coil  42  is connected to a terminal  46  of a connector  45 . The fixed core  43  is disposed inside the coil  42 , with the housing  11  sandwiched therebetween. The fixed core  43  is formed in a cylindrical shape from a magnetic material such as iron, and is fixed to the inside of the housing  11  by press-fitting, for example. The plate housing  44  is also made of a magnetic material, and covers the outside circumference of the coil  42 .  
         [0042]     The movable core  50  is provided inside the housing  11 , in a manner that enables movement back and forth in the axial direction. The movable core  50  is formed in a cylindrical shape from a magnetic material such as iron. At the end of the movable core  50  on the side of the fixed core  43 , the movable core  50  contacts a spring  18 , which acts as energizing means. One end of this spring  18  contacts the movable core  50 , and the other end contacts an adjusting pipe  19  which is press-fit into the fixed core  43 . The spring  18  applies a force that extends along the axial direction. Consequently, the movable core  50  and the needle  30  are pushed by the spring  18  towards the seating position on the valve seat  22 . The load of the spring  18  can be controlled by adjusting the degree to which the adjusting pipe  19  is press-fit into the fixed core  43 . When the coil  42  is not energized, the movable core  50  and the needle  30  are pushed against the valve seat  22 , and the seal portion  32  is seated against the valve seat  22 .  
         [0043]     Next, the movable core  50  of the actuator  40 , and the needle  30  are described in further detail.  
         [0044]     The needle  30  is inserted into the movable core  50  in a manner that enables movement back and forth in the axial direction. As shown in  FIG. 1 , the movable core  50  has a hole  51  which passes through the radial center of the movable core  50  in the axial direction. The fixed core  43  side of the hole  51  connects to a recess  52 . The recess  52  is recessed from the fixed core  43  side of the movable core  50 , that is, from the end of the movable core  50  on the opposite side from the injection nozzle  23 , towards the injection nozzle  23 . The inside diameter of the recess  52  is larger than that of the hole  51 . Consequently, a ring-shaped stepped portion  53  is formed between the hole  51  and the recess  52 . Here, the recess  52  corresponds to the non-injection side recess in the claims, and the stepped portion  53  corresponds to the base described in the claims. Furthermore, at the end of the movable core  50  on the opposite side from the fixed core  43 , that is, the injection nozzle  23  end of the movable core  50 , a cylindrical portion  54  is provided that protrudes towards the injection nozzle  23 . Both the inside and outside diameter of this cylindrical portion  54  are larger than the hole  51 . Consequently, a ring-shaped stepped portion  55  is formed between the hole  51  and the cylindrical portion  54 . Furthermore, the outside diameter of the cylindrical portion  54  is typically smaller than that of the movable core  50 , although may also be substantially the same as that of the movable core  50 . Fuel passages  501  which link the inner circumferential surface of the movable core  50  that forms the recess  52  to the outer circumferential surface are formed in the cylindrical movable core  50 . A plurality of these fuel passages  501  are formed around the circumferential direction of the movable core  50 .  
         [0045]     A first stop member  61  and a second stop member  62  are provided on the shaft portion  31  of the needle  30 . The first and second stop members  61  and  62  are positioned apart from each other along the axial direction of the needle  30 . The movable core  50  is sandwiched between the first and second stop members  61  and  62 . The inside diameter of the hole  51  of the movable core  50  is slightly larger than the outside diameter of the shaft portion  31  of the needle  30 . Thus, the needle  30  and the movable core  50  are capable of relative movement in the axial direction.  
         [0046]     The first stop member  61  is positioned closer to the injection nozzle  23  than the second stop member  62 . The first stop member  61  protrudes outward in a radial direction from the shaft portion  31  of the needle  30 . The first stop member  61  is formed as part of a single integrated body with the needle  30 . The first stop member  61  protrudes from the needle  30  in a continuous ring shape in the circumferential direction.  
         [0047]     On the other hand, the second stop member  62  is positioned further away from the injection nozzle  23  than the first stop member  61 . In other words, the second stop member  62  is an end stop member provided at the opposite end of the needle  30 , in the axial direction, from the seal portion  32 . The second stop member  62  protrudes outward in a radial direction from the shaft portion  31  of the needle  30 . The second stop member  62  is formed as a separate body from the needle  30 . The second stop member  62  is press-fit onto a small-diameter portion  34  formed at the opposite end of the needle  30  from the injection nozzle  23 . The second stop member  62  comprises a press-fitting portion  621 , which is press-fit onto the small-diameter portion  34  of the needle  30 , and a protruding portion  622 , which protrudes in a radial direction from the press-fitting portion  621 , forming a continuous ring shape. The position of the second stop member  62  along the axial direction is determined by a step  35  formed between the shaft portion  31  of the needle  30  and the small-diameter portion  34 . The end of the spring  18  positioned away from the adjusting pipe  19  contacts the protruding portion  622  of the second stop member  62 , thereby pushing the movable core  50  in the direction of the injection nozzle  23 .  
         [0048]     The needle  30  is inserted into the movable core  50  from the opposite side of the movable core  50  to the fixed core  43 , and the second stop member  62  is attached to the needle  30 . As a result, the movable core  50  is sandwiched between the first stop member  61  and the second stop member  62 . When the second stop member  62  is in contact with the stepped portion  53  of the movable core  50 , a gap of a predetermined length forms between the first stop member  61  and the stepped portion  53  of the movable core  50 . Thus, the needle  30  and the movable core  50  are able to undergo relative movement in the axial direction, equivalent to the length of this gap.  
         [0049]     When the needle  30  and the movable core  50  undergo relative movement in the axial direction, the first stop member  61  moves back and forth in the axial direction inside the cylindrical portion  54  of the movable core  50 . Consequently, a fuel chamber  56  is formed between the stepped portion  55  of the movable core  50 , an inner circumferential surface  54   a  of the cylindrical portion  54 , and the surface of the first stop member  61  that faces the fixed core  43 . When axial movement of the needle  30  and the movable core  50  causes the first stop member  61  to move back and forth inside the cylindrical portion  54 , the capacity of the fuel chamber  56  changes. The outside diameter of the first stop member  61  is slightly smaller than the inside diameter of the cylindrical portion  54 . Consequently, when the capacity of the fuel chamber  56  changes, fuel enters and leaves the fuel chamber  56  through the slight gap formed between the radial outer edge of the first stop member  61  and the inner circumferential surface  54   a  of the cylindrical portion  54 . In other words, the radial outer edge of the first stop member  61  and the inner circumferential surface  54   a  of the cylindrical portion  54  form an aperture portion  57 , which functions as a fuel aperture for restricting the flow of fuel in and out of the fuel chamber  56 .  
         [0050]     The gap between the inner circumferential surface of the movable core  50 , which forms the hole  51 , and the outer wall of the needle  30 , is smaller than the aperture portion  57 . Consequently, fuel enters and leaves the fuel chamber  56  through the aperture portion  57  formed between the first stop member  61  and the cylindrical portion  54 .  
         [0051]     When the needle  30  and the movable core  50  undergo relative movement in the radial direction, the second stop member  62  moves back and forth in the axial direction inside the recess  52  of the movable core  50 . Consequently, as shown in  FIG. 3 , a fuel chamber  58  is formed between the stepped portion  53  of the movable core  50 , the inner circumferential surface of the movable core  50  that forms the recess  52 , and an opposing face  62   a , which is the surface of the second stop member  62  on the side of the stepped portion  53 . When the axial movement of the needle  30  and the movable core  50  causes the second stop member  62  to move back and forth inside the recess  52 , the capacity of the fuel chamber  58  changes. The outside diameter of the second stop member  62  is slightly smaller than the inside diameter of the recess  52 . Thus, when the capacity of the fuel chamber  58  changes, fuel enters and leaves the fuel chamber  58  through the tiny gap formed between the radial outer edge of the second stop member  62 , and the inner circumferential surface of the movable core  50  that forms the recess  52 . In other words, the radial outer edge of the second stop member  62 , and the inner circumferential surface of the movable core  50  that forms the recess  52 , form an aperture portion  59 , which functions as a fuel aperture for restricting the flow of fuel in and out of the fuel chamber  58 . The stepped portion  53  of the movable core  50  and the opposing face  62   a  of the second stop member  62  are both flat. Thus, when relative movement of the needle  30  and the movable core  50  causes the opposing face  62   a  to move away from the stepped portion  53 , a mutually attracting force, that is, a squeezing force, occurs between the opposing face  62   a  and the stepped portion  53 .  
         [0052]     Next, the impact moderating effect of the injector  10  according to the above construction is described.  
         [0053]     When the movable core  50  is drawn towards the fixed core  43 , leading to a collision between the fixed core  43  and the movable core  50 , the impact of the collision causes the movable core  50  to move away from the fixed core  43 , that is, towards the injection nozzle  23 . On the other hand, when the fixed core  43  and the movable core  50  collide, an inertial force means the needle  30  has energy moving towards the fixed core  43 . This means that while the movable core  50  has movement energy directed in the opposite direction to the fixed core  43 , the needle  30  has movement energy directed towards the fixed core  43 . In other words, the energy of the movable core  50  and the energy of the needle  30  are acting in opposite directions. As a result, by allowing relative movement of the movable core  50  and the needle  30 , the kinetic energy produced in the movable core  50  and the needle  30  when the fixed core  43  and the movable core  50  collide can be canceled out.  
         [0054]     A collision between the fixed core  43  and the movable core  50  causes the movable core  50  to move away from the fixed core  43 , while the needle  30  moves towards the fixed core  43 . In this case, the movement of the first stop member  61  that accompanies the movement of the needle  30  causes a reduction in the capacity of the fuel chamber  56 . Consequently, the fuel in the fuel chamber  56  is pressurized, and the pressurized fuel is discharged slowly from the fuel chamber  56 , through the aperture portion  57 . This causes the fuel in the fuel chamber  56  to generate a damping effect.  
         [0055]     In the same manner, the movement of the second stop member  62  that accompanies the movement of the needle  30  causes the capacity of the fuel chamber  58  to increase. Consequently, the pressure of the fuel in the fuel chamber  58  is reduced, and fuel is slowly drawn into the fuel chamber  58  through the aperture portion  59 . Furthermore, a squeezing force is generated between the second stop member  62  and the movable core  50 . This causes the fuel in the fuel chamber  58  to generate a damping effect. Therefore, the impact of the collision between the movable core  50  and the fixed core  43  is absorbed by relative movement of the movable core  50  and the needle  30 , as well as the damping effect provided by the fuel chamber  56  and the fuel chamber  58 . As a result, bouncing of the movable core  50 , and the needle  30  which moves in concert with the movable core  50 , is reduced.  
         [0056]     Furthermore, when the pushing force of the spring  18  causes the seal portion  32  of the needle  30  to be seated on the valve seat  22 , the impact at the time of seating causes the needle  30  to move in the direction of the fixed core  43 . On the other hand, when the seal portion  32  and the valve seat  22  collide, the inertial force produced means the movable core  50  has energy moving in the opposite direction to the fixed core  43 , that is in the direction of the injection nozzle  23 . This means that while the needle  30  has energy moving in the fixed core  43  direction, the movable core  50  has energy moving in the opposite direction. As a result, by allowing relative movement of the movable core  50  and the needle  30 , the kinetic energy produced in the movable core  50  and the needle  30  when the needle  30  and the valve seat  22  collide can be canceled out.  
         [0057]     When the needle  30  and the valve seat  22  collide, the needle  30  moves in the direction of the fixed core  43  while the movable core  50  moves in the opposite direction to the fixed core  43 . In this case, the movement of the first stop member  61  that accompanies the movement of the needle  30  reduces the capacity of the fuel chamber  56 . Consequently, the fuel in the fuel chamber  56  is pressurized, and the pressurized fuel is discharged slowly from the fuel chamber  56 , through the aperture portion  57 . This causes the fuel in the fuel chamber  56  to generate a damping effect.  
         [0058]     In the same manner, the movement of the second stop member  62  that accompanies the movement of the needle  30  causes the capacity of the fuel chamber  58  to increase. Consequently, the pressure of the fuel in the fuel chamber  58  is reduced, and fuel is slowly drawn into the fuel chamber  58  through the aperture portion  59 . Furthermore, a squeezing force is generated between the second stop member  62  and the movable core  50 . This causes the fuel in the fuel chamber  58  to generate a damping effect. Therefore, the impact of the collision between the needle  30  and the valve seat  22  is absorbed by relative movement of the movable core  50  and the needle  30 , as well as the damping effect provided by the fuel chamber  56  and the fuel chamber  58 . As a result, bouncing of the movable core  50 , and the needle  30 , which moves in concert with the movable core  50 , is reduced.  
         [0059]     Next, the operation of the injector  10  according to the above construction is described.  
         [0060]     When energization of the coil  42  is stopped, there is no magnetic attraction generated between the fixed core  43  and the movable core  50 . Consequently, the pushing force of the spring  18  causes the movable core  50  and the needle  30  to move in the opposite direction to the fixed core  43 . As a result, when energization of the coil  42  is stopped, the seal portion  32  of the needle  30  is seated on the valve seat  22 . Accordingly, no fuel is injected from the injection nozzle  23 .  
         [0061]     When the coil  42  is energized, the magnetic field produced in the coil  42  causes a magnetic flux to flow through the plate housing  44 , the first magnetic portion  12 , the movable core  50 , the fixed core  43 , and the second magnetic portion  14 , thereby forming a magnetic circuit. Accordingly, magnetic attraction is generated between the fixed core  43  and the movable core  50 . When this magnetic attraction generated between the fixed core  43  and the movable core  50  exceeds the pushing force generated by the spring  18 , the movable core  50  moves towards the fixed core  43 . At this time, the second stop member  62  provided on the needle  30  contacts the stepped portion  53  of the movable core  50 . Consequently, the needle  30  also moves in the direction of the fixed core  43 , together with the movable core  50 . As a result, the seal portion  32  of the needle  30  is unseated from the valve seat  22 .  
         [0062]     The fuel which flows into the injector  10  from the fuel inlet  16  travels via the fuel filter  17 , the inside of the inlet member  15 , the inside of the adjusting pipe  19 , the fuel passages  501  of the movable core  50 , and the inside of the nozzle holder  20 , before entering the fuel passage  33 . The fuel which flows into the fuel passage  33  flows into the injection nozzle  23  through the gap formed between the needle  30 , which has been unseated from the valve seat  22 , and the nozzle body  21 . Fuel is thus injected from the injection nozzle  23 .  
         [0063]     When energization of the coil  42  is stopped, the magnetic attraction between the fixed core  43  and the movable core  50  dissipates. Because the second stop member  62  is in contact with the stepped portion  53  of the movable core  50 , the pushing force of the spring  18  causes the movable core  50  and the needle  30  to move away from the fixed core  43  as a unit. Consequently, the seal portion  32  is once again seated on the valve seat  22 , and the flow of fuel between the fuel passage  33  and the injection nozzle  23  is cut off. Accordingly, fuel injection stops.  
         [0064]     As described above, in the first embodiment, the movable core  50  and the needle  30  are freely movable relative to each other over a predetermined range in the axial direction. Consequently, bouncing of the movable core  50 , which occurs when the fixed core  43  and the movable core  50  collide, is absorbed by the inertial movement of the needle  30  in the direction opposite to the bouncing. Furthermore, bouncing of the needle  30 , which occurs when the needle  30  collides with the valve seat  22 , is absorbed by the inertial movement of the movable core  50  in the direction opposite to the bouncing. In addition, the relative movement between the needle  30  and the movable core  50  is moderated by the damping effect of the fuel in the fuel chambers  56  and  58  formed between the first stop member  61  or the second stop member  62  respectively, and the movable core  50 . Thus, the impact of a collision is moderated, while still ensuring that the needle  30  and the movable core  50  move as a unit. Accordingly, bouncing during operation of the needle  30  and the movable core  50  can be reduced using a simple construction, with increasing the minimum number of components.  
         [0065]     Particularly in those cases where the present invention is applied to a direct-injection gasoline engine, as with the injector  10  of the present embodiment, the pressure of the fuel injected from the injector  10  will be high, within a range from 5 to 13 MPa. Recently, higher fuel pressures have been demanded in order to better atomize the injected fuel. When the fuel pressure is increased, greater drive force is required of the actuator  40  to open the valve, that is increased magnetic attraction is required between the fixed core  43  and the movable core  50 . On the other hand, to close the valve, increased pushing force is required of the spring  18 , which functions as the energizing means. Consequently, the impact of collisions between the movable core  50  and the fixed core  43  when opening the valve of the needle  30 , and the impact of collisions between the needle  30  and the valve seat  22  when closing the valve of the needle  30 , both increase. On the other hand, with the injector  10  of the present embodiment, because the impact of the collisions is moderated, bouncing during operation is reduced. Thus, uncontrollable injection of fuel from the injector  10  is reduced. Accordingly, the amount of fuel injected from the injection nozzle  23  and the shape of the spray can be controlled with favorable precision, even if the fuel pressure is increased.  
         [0066]     Furthermore, in the injector  10  of the first embodiment, fuel enters and leaves the fuel chamber  56  through the aperture portion  57 , and the fuel chamber  58  through the aperture portion  59 . Accordingly, the characteristics of the damping effects produced by the fuel chambers  56  and  58  can be changed by adjusting either the gap between the first stop member  61  and the cylindrical portion  54 , which forms the aperture portion  57 , or the gap between the second stop member  62  and the inner circumferential surface of the movable core  50 , which forms the aperture portion  59 , respectively. Accordingly, the characteristics of the damping effects produced by the fuel within the fuel chambers  56  and  58  can be adjusted easily, and bouncing of the needle  30  can be minimized.  
         [0067]     In addition, in the injector  10  of the first embodiment, the impact of a collision during operation of the needle  30  is moderated by the relative movement of the needle  30  and the movable core  50 , and the damping effect provided by the fuel in the fuel chambers  56  and  58 . This damping effect is generated by the fuel within the fuel chambers  56  and  58 . Consequently, there is almost no variation over time in this damping effect, especially when compared with the moderating effect provided by an elastic member such as a spring. Accordingly, there is little variation in the impact moderating capabilities, meaning the injector  10  can demonstrate stable fuel injection characteristics over long periods.  
         [0068]     Modifications of the injector according to the first embodiment of the present invention are shown in  FIG. 4  and  FIG. 5 . Those structural elements that are substantially the same as in the first embodiment are given the same reference numerals, and their description is omitted.  
         [0069]     In the modification shown in  FIG. 4 , a first stop member  63  is formed as a separate body from the needle  30 . On the other hand, a second stop member  64  is formed integrally with the needle  30 .  
         [0070]     Furthermore, in the modification shown in  FIG. 5 , both a first stop member  65  and a second stop member  66  are formed as separate bodies from the needle  30 .  
         [0071]     The vicinity around the movable core of an injector according to a second embodiment of the present invention is shown in  FIG. 6 . Those structural elements that are substantially the same as in the first embodiment are given the same reference numerals, and their description is omitted.  
         [0072]     As shown in  FIG. 6 , a movable core  70  of the injector according to the second embodiment has a recess  71  at the opposite end from the fixed core  43 . The recess  71  is recessed towards the fixed core  43 . This recess  71  corresponds to the injection side recess in the claims. The inside diameter of the recess  71  is greater than that of a hole portion  72 . Consequently, a stepped portion  73  is formed between the recess  71  and the hole portion  72 . Furthermore, the movable core  70  comprises fuel passages  701  which connect the inside of the movable core  70  with the outside.  
         [0073]     During relative movement of the needle  30  and the movable core  70  in the axial direction, the first stop member  61 , which is integrated with the needle  30 , moves axially back and forth inside the recess  71 . Consequently, a fuel chamber  74  is formed between the stepped portion  73  of the movable core  70 , the inner circumferential surface of the movable core  70  that forms the recess  71 , and the surface of the first stop member  61  on the side of the fixed core  43 . When axial movement of the needle  30  and the movable core  70  causes the first stop member  61  to move back and forth inside the recess  71 , the capacity of the fuel chamber  74  changes. The inside diameter of the recess  71  is slightly larger than the outside diameter of the first stop member  61 . Thus, when the capacity of the fuel chamber  74  changes, fuel enters and leaves the fuel chamber  74  through the small gap formed between the radial outer edge of the first stop member  61 , and an inner circumferential surface  71   a  of the movable core  70  that forms the recess  71 . In other words, the radial outer edge of the first stop member  61  and the inner circumferential surface  71   a  of the movable core  70  form an aperture portion  75 , which acts as a fuel aperture for restricting the flow of fuel in and out of the fuel chamber.  
         [0074]     In the second embodiment, the fuel chamber  74  is formed in the recess  71 , which is recessed into the end portion of the movable core  70  on the opposite side from the fixed core  43 . In the construction of the second embodiment, as in the first embodiment, the fuel in the fuel chamber  74  has a damping effect. Consequently, relative movement between the needle  30  and the movable core  70  is moderated by the damping effect of the fuel in the fuel chamber  74  formed between the first stop member  61 , which is formed integrally with the needle  30 , or the second stop member  62 , and the movable core  50 . Thus, the impact of a collision is moderated, while still ensuring that the needle  30  and the movable core  70  move as a unit. Accordingly, bouncing during operation of the needle  30  and the movable core  70  can be reduced using a simple construction, with increasing the minimum number of components.  
         [0075]     The vicinity around the movable core of an injector according to a third embodiment of the present invention is shown in  FIG. 7 . Those structural elements that are substantially the same as in the first embodiment are given the same reference numerals, and their description is omitted.  
         [0076]     As shown in  FIG. 7 , in a movable core  80  according to the third embodiment, a groove  81  is formed in the end portion at the opposite side from the fixed core  43 . The groove  81  is recessed into the movable core  80  in the direction of the fixed core  43 . The groove  81  is formed as a continuous ring shape, around the circumferential direction of the movable core  80 . Furthermore, a first stop member  90  provided on the needle  30  comprises an inner cylinder portion  91 , which is press-fit onto the needle  30 , an expansion portion  92 , which protrudes radially outward from the inner cylinder portion  91 , and an outer cylinder portion  93 , which rises from the radial outside edge of the expansion portion  92 , towards the fixed core  43  side. The outer cylinder portion  93  is designed to enter the groove  81  of the movable core  80 , leaving a slight gap. The movable core  80  comprises fuel passages  801  which connect the inside of the movable core  80  with the outside.  
         [0077]     By employing the above construction, a first fuel chamber  82  is formed between the outer cylinder portion  93 , and an inner circumferential surface  80   a  that forms the groove  81  within the movable core  80 . Furthermore, a second fuel chamber  83  is formed in the space enclosed by the outer cylinder portion  93 , the movable core  80 , the expansion portion  92 , and the needle  30 . In other words, in the third embodiment, two fuel chambers, namely the first and second fuel chambers  82  and  83 , are formed between the movable core  80  and the first stop member  90 .  
         [0078]     In the third embodiment, a plurality of fuel chambers  82  and  83  are formed. Consequently, by changing the characteristics of the respective damping effects of the first and second fuel chambers  82  and  83 , and combining the resulting effects, the characteristics of the overall damping effect can be easily adjusted as desired.  
         [0079]     The vicinity around the movable core of injectors according to fourth and fifth embodiments of the present invention are shown in  FIG. 8  and  FIG. 9 , respectively. Those structural elements that are substantially the same as in the first embodiment are given the same reference numerals, and their description is omitted.  
         [0080]     In the description of the first embodiment, an example was presented in which a fuel aperture was formed using the gap between the first stop member and the cylindrical portion. In contrast, in the fourth embodiment, notches  67  are formed in the radial outside edge of the first stop member  61 , as shown in  FIG. 8 . Furthermore, cylindrical holes  68  are also provided, which pass through the first stop member  61  in the through-thickness direction. The notches  67  and the holes  68  constitute the aperture portion described in the claims. Thus, in the fourth embodiment, the notches  67  and the holes  68  act as the aperture portion by which fuel enters and leaves the fuel chamber  56 . In the fourth embodiment, by adjusting the shape, number, and size of the notches  67  or holes  68 , it is possible to easily adjust the damping characteristics. These notches or holes may also be formed in the second stop member  62  as well as the first stop member  61 .  
         [0081]     In the fifth embodiment, connecting holes  541  which connect the fuel chamber  56  with the outside of the movable core  50  are formed in the cylindrical portion  54  of the movable core  50 , as shown in  FIG. 9 . In this case, it is possible to easily adjust the damping characteristics by adjusting the shape, number, and size of the connecting holes  541 .  
         [0082]     The vicinity around the movable core of injectors according to sixth and seventh embodiments of the present invention are shown in  FIG. 10  and  FIG. 11 , respectively. Those structural elements that are substantially the same as in the first or second embodiment are given the same reference numerals, and their description is omitted.  
         [0083]     The movable core  70  according to the sixth embodiment is a modification of the movable core of the second embodiment. Furthermore, the needle  30  is the same as the modification shown in  FIG. 4 .  
         [0084]     In the sixth embodiment, the recess  71  of the movable core  70  is formed with a tapered shape in which the inside diameter increases with increasing distance from the fixed core  43 , as shown in  FIG. 10 . The inside diameter of the recess  71  on the fixed core  43  side is greater than the inside diameter of the hole portion  72 . Consequently, a stepped portion  73  is formed between the recess  71  and the hole portion  72 . When the recess  71  is formed with a tapered shape, the first stop member  69 , which is formed either integrally with, or separate from, the needle  30 , is unable to move inside the recess  71 . Furthermore, the outside diameter of the first stop member  69  is greater than the inside diameter of the recess  71  at the opposite end from the fixed core  43 , and is only slightly smaller than the outside diameter of the movable core  70 . Consequently, in the sixth embodiment, the first stop member  69  moves outside the movable core  70  at the opposite end from the fixed core  43 .  
         [0085]     During relative movement of the needle  30  and the movable core  70  in the axial direction, the first stop member  69 , which is not integrated with the needle  30 , moves back and forth in the axial direction outside the movable core  70 . At this time, the fuel chamber  74  is formed between the stepped portion  73  of the movable core  70 , the inner circumferential surface of the recess  71  of the movable core  70 , and an end face  69   a  on the movable core  70  side of the first stop member  69 . When axial movement of the needle  30  and the movable core  70  causes the first stop member  69  to move back and forth, the pressure of the fuel in the fuel chamber  74  changes. A gap forms between the end face  70   a  of the movable core  70  on the opposite side to the fixed core  43 , and the end face  69   a  on the movable core  70  side of the first stop member  69 . Thus, when the pressure of the fuel in the fuel chamber  74  changes, fuel enters and leaves the fuel chamber  74  through the gap formed between the end face  70   a  of the movable core  70  and the end face  69   a  of the first stop member  69 . In other words, the end face  70   a  of the movable core  70  and the end face  69   a  of the first stop member  69  form an aperture portion  76  which functions as a fuel aperture for restricting the flow of fuel in and out of the fuel chamber.  
         [0086]     In the seventh embodiment, the first stop member  69  is molded to fit the shape of the recess  71  of the movable core  70 , as shown in  FIG. 11 . Thus, in the seventh embodiment, the first stop member  69  is capable of moving back and forth inside the recess  71 . In the seventh embodiment, the fuel chamber  74  is formed between the stepped portion  73  of the movable core  70 , the inner circumferential surface of the recess  71  in the movable core  70 , and the end face  69   a  on the movable core  70  side of the first stop member  69 . When movement of the needle  30  and the movable core  70  in the axial direction causes the first stop member  69  to move back and forth inside the recess  71 , the capacity of the fuel chamber  74  changes. A gap is formed between the inner circumferential surface of the movable core  70  and the end face  69   a  on the movable core  70  side of the first stop member  69 . Thus, when the capacity of the fuel chamber  74  changes, fuel enters and leaves the fuel chamber  74  through the gap formed between the inner circumferential surface of the movable core  70  and the end face  69   a  of the first stop member  69 . In other words, the end face  70   a  of the movable core  70  and the end face  69   a  of the first stop member  69  form an aperture portion  77  which functions as a fuel aperture for restricting the flow of fuel in and out of the fuel chamber.  
         [0087]     In the sixth and seventh embodiments, the movable core  70  and the first stop member  69  form the fuel chamber  74 , and also form the aperture portions  76  and  77 . Accordingly, the impact of collisions between the fixed core  43  and the movable core  70  is moderated, while still ensuring that the needle  30  and the movable core  70  move as a unit. Accordingly, bouncing during operation of the needle  30  and the movable core  70  can be reduced.  
         [0088]     Furthermore, in the sixth and seventh embodiments, forming the recess  71  in the movable core  70  reduces the mass of the movable core  70 . This enables a reduction in the weight of the movable core  70  and the needle  30  that needs to be attracted to the fixed core  43 . Accordingly, the responsiveness of the movable core  70  and the needle  30  to changes in the energization of the coil  42  can be improved.  
         [0089]     The vicinity around the movable core of an injector according to an eighth embodiment of the present invention is shown in  FIG. 12 . Those structural elements that are substantially the same as in the seventh embodiment are given the same reference numerals, and their description is omitted.  
         [0090]     In the eighth embodiment, as shown in  FIG. 12 , there is no recess formed in the end of the movable core  70  on the opposite side from the fixed core  43 . In other words, in the eighth embodiment, the movable core  70  has an end face  70   a  on the side of the injection nozzle  23 . This end face  70   a  is either substantially perpendicular to the axis of the movable core  70 , or may be inclined relative to the axis. The end face  70   a  may also be a stepped surface, or a curved shape. Thus, the movable core  70  forms a fuel chamber between the end face  70   a , and the end face  69   a  of the first stop member  69  that faces the movable core  70  side. When the movable core  70  and the first stop member  69  move apart, the fuel in this fuel chamber generates a force, that is, a so-called squeezing force, which acts to prevent the movable core  70  and the first stop member  69  from moving apart. Furthermore, when the first stop member  69  and the movable core  70  approach each other, the fuel in this fuel chamber generates a force, that is, a so-called damping force, which acts to hinder the approach of the first stop member  69  and the movable core  70 . Thus, when the needle  30  and the movable core  70  move back and forth relative to each other in the axial direction, the fuel in this fuel chamber between the movable core  70  and the first stop member  69  generates a force that hinders the relative movement. This fuel enters and leaves the space between the mutually opposing first stop member  69  and movable core  70  from the radial outside edge. In other words, the end face  70   a  of the movable core  70  and the end face  69   a  of the first stop member  69  form an aperture portion  78  at the radial outside edge, which acts as a fuel aperture for restricting the flow of fuel in and out of the fuel chamber.  
         [0091]     In the eighth embodiment, even if a recess is not formed in the end of the movable core  70  on the opposite side to the fixed core  43 , a squeezing force and a damping force are still generated by the fuel in the fuel chamber between the movable core  70  and the first stop member  69 . As a result, the structure and manufacture of the movable core  70  can be simplified, while still reducing bouncing of the needle  30  and the movable core  70 . Furthermore, the amount of fuel which flows into and out of the fuel chamber is controlled by the distance between the end faces  69   a  and  70   a  that form the aperture portion  78 . Accordingly, the squeezing force and the damping force that act between the movable core  70  and the first stop member  69  can be controlled easily.  
         [0092]     The vicinity around the movable core area of an injector according to a ninth embodiment of the present invention is shown in  FIG. 13 . Those structural elements that are substantially the same as in the first embodiment or the eighth embodiment are given the same reference numerals, and their description is omitted.  
         [0093]     As shown in  FIG. 13 , in the ninth embodiment, the movable core  70  is the same shape as in the eighth embodiment. However in the ninth embodiment, the shape of the needle  130  differs from the other embodiments described above. In the ninth embodiment, the needle  130  is formed with a hollow cylindrical shape. As a result, a fuel passage  131  is formed inside the needle  130 . The needle  130  has a flange  132 , which acts as an end stop member, provided at the opposite end of the needle  130  from the injection nozzle  23 . The flange  132  extends radially outward from the needle  130 , and is formed as an integral part of the needle  130 .  
         [0094]     The needle  130  has fuel holes  133 , which penetrate the side walls that form the fuel passage  131 . The fuel which flows through the fuel passage  131  flows from the inside of the needle  130 , through the fuel holes  133 , to the outside. Thus, there is no need to form a fuel passage for connecting the inside of the movable core  70  to the outside. The location of the fuel holes  133  is not limited to the movable core  70  side of the needle  130 , and they may also be located near the end of the needle  130  on the injection nozzle  23  side. Furthermore, a fuel passage may also be formed in the movable core  70  to ensure an adequate fuel flow rate.  
         [0095]     In the ninth embodiment, the needle  130  is formed as a hollow cylinder, thus forming the fuel passage  131 . Consequently, the mass of the needle  130  is reduced. This means that the weight of the movable core  70  and the needle  130  that must be attracted to the fixed core  43  can be reduced. Accordingly, the responsiveness of the movable core  70  and the needle  30  to changes in the energization of the coil  42  can be improved.  
         [0096]     In the plurality of embodiments described above, the description focused on examples in which two stop members were provided along the axial direction of the needle. However, three or more stop members could also be provided in the axial direction. If, for example, the needle has a plurality of movable cores, each movable core may be sandwiched between two stop members. Furthermore, in the plurality of embodiments above, the description focused on examples in which each embodiment was applied separately. However, a combination of a plurality of embodiments may also be used.