Abstract:
A fluid injection valve has: a valve body that is provided with an opening portion at one axial end thereof and is for starting and stopping a supply of a fluid out of the opening portion; and an injection port plate having a plurality of injection ports that penetrate therethrough, the injection port plate being fixed on the one axial end of the valve body to form a fluid chamber between itself and the valve body to accumulate the fluid therein and to which at least a part of the injection ports opens. A circumferential surface of the fluid chamber recedes toward the injection ports so as to decrease a cross-sectional area of the fluid chamber that is taken along a radial direction of the injection port plate and to reserve a predetermined length of distance between itself and the injection ports.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2004-310931 filed on Oct. 26, 2004 and No. 2005-275268 filed on Sep. 22, 2005, the contents of which are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a fluid injection valve suitable for injecting fuel into cylinders of an internal combustion engine (hereinafter referred to just as “engine”). 
   BACKGROUND OF THE INVENTION 
   In fuel injection valves for engines, it is important to atomize the fuel injection spray sufficiently from viewpoints of toxic substance reduction in emission gas, fuel consumption performance improvement and so on. U.S. Pat. Nos. 6,405,946-B1, 6,616,072-B2, US-2004-0124279-A1 and their counterpart JP-2001-46919-A disclose fluid injection nozzles for promoting an atomization of the fuel injection spray. 
   In the fluid injection nozzles disclosed in the above publications, a flat disc-shaped fuel chamber is formed between a valve seat and injection ports. By the fuel chamber provided between the valve seat and the injection ports, fuel, which has flown on an inner circumferential surface of the valve body, passes through an opening portion of the valve body, then forms a spread flow in the fuel chamber. Thus, at the outflow side of the injection ports, it is possible to decrease collisions among fuel spray columns that are injected out of the injection ports. 
   However, by forming the fuel chamber between the valve seat and the injection ports, a dead volume in the fluid injection nozzle increases. When the dead volume is large, a relatively large amount of fuel is left in the fuel chamber without being injected out of the injection ports. For example, in a case that a fuel injection valve is installed in an intake pipe of an engine, the fuel left in the fuel chamber is sucked by intake air that flows through the intake pipe at a large speed. Thus, a fuel ratio in the intake air increases, and it becomes difficult to control the fuel injection amount with high accuracy. 
   SUMMARY OF THE INVENTION 
   The present invention, in view of the above-described issue, has an object to provide a fluid injection valve that can promote an atomization of fluid injection spray and decrease a volume of its fluid chamber. 
   The fluid injection valve has: a valve body that is provided with an opening portion at one axial end thereof and is for starting and stopping a supply of a fluid out of the opening portion; and an injection port plate having a plurality of injection ports that penetrate therethrough, the injection port plate being fixed on the one axial end of the valve body to form a fluid chamber between itself and the valve body to accumulate the fluid therein and to which at least a part of the injection ports opens. A circumferential surface of the fluid chamber recedes toward the injection ports so as to decrease a cross-sectional area of the fluid chamber that is taken along a radial direction of the injection port plate and to reserve a predetermined length of distance between itself and the injection ports. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings: 
       FIG. 1  is a cross-sectional view showing an injection port plate of a fluid injection valve according to a first embodiment of the present invention, which is taken along a line I-I in  FIG. 3 ; 
       FIG. 2  is a cross-sectional view showing the fluid injection valve according to the first embodiment; 
       FIG. 3  is an enlarged cross-sectional view showing the fluid injection nozzle in the proximity of the injection port plate according to the first embodiment; 
       FIG. 4  is a further enlarged cross-sectional view showing a range IV in  FIG. 4 ; 
       FIG. 5  is a graph schematically showing a SMD (Sauter mean diameter) variation against an arrangement of a fuel injection port; 
       FIG. 6A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a second embodiment; 
       FIG. 6B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the second embodiment, which is taken along a line VIB-VIB in  FIG. 6A ; 
       FIG. 7A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a third embodiment; 
       FIG. 7B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the third embodiment, which is taken along a line VIIB-VIIB in  FIG. 7A ; 
       FIG. 8A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a first modified example of the third embodiment; 
       FIG. 8B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the first modified example of the third embodiment, which is taken along a line VIIIB-VIIIB in  FIG. 8A ; 
       FIG. 9A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a second modified example of the third embodiment; 
       FIG. 9B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the second modified example of the third embodiment, which is taken along a line IXB-IXB in  FIG. 9A ; 
       FIG. 10A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a third modified example of the third embodiment; 
       FIG. 10B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the third modified example of the third embodiment, which is taken along a line XB-XB in  FIG. 10A ; 
       FIG. 11A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a fourth modified example of the third embodiment; 
       FIG. 11B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the fourth modified example of the third embodiment, which is taken along a line XIB-XIB in  FIG. 11A ; 
       FIG. 12A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a fifth modified example of the third embodiment; 
       FIG. 12B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the fifth modified example of the third embodiment, which is taken along a line XIIB-XIIB in  FIG. 12A ; 
       FIG. 13A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a fourth embodiment; 
       FIG. 13B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the fourth embodiment, which is taken along a line XIIIB-XIIIB in  FIG. 13A ; 
       FIG. 14A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a first modified example of the fourth embodiment; 
       FIG. 14B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the first modified example of the fourth embodiment, which is taken along a line XIVB-XIVB in  FIG. 14A ; 
       FIG. 15A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a first modified example of the fourth embodiment; 
       FIG. 15B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the first modified example of the fourth embodiment, which is taken along a line XVB-XVB in  FIG. 15A ; 
       FIG. 16A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a first modified example of the fourth embodiment; 
       FIG. 16B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the first modified example of the fourth embodiment, which is taken along a line XVIB-XVIB in  FIG. 16A ; 
       FIG. 17A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a fifth embodiment; 
       FIG. 17B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the fifth embodiment, which is taken along a line XVII-XVII in  FIG. 17A ; 
       FIG. 18A  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to a sixth embodiment; 
       FIG. 18B  is a cross-sectional view showing an injection port plate of the fluid injection valve according to the sixth embodiment, which is taken along a line XVIII-XVIII in  FIG. 18A ; and 
       FIG. 19  is an enlarged cross-sectional view showing a fluid injection nozzle in the proximity of the injection port plate according to another embodiment. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   First Embodiment 
     FIG. 2  depicts a fluid injection valve (hereinafter referred to as injector)  10  according to a first embodiment of the present invention. The injector  10  is for injecting fuel at an intake port of a gasoline engine, that is, for a port fuel injection engine. The injector  10  shown in  FIG. 2  is merely an example, and may be modified to have other driving mechanism therein, to be applied to other types of engine, and so on. 
   The injector  10  has a casing  11 , a magnetic pipe  12 , a fixed core  13  and a driving portion  30 . The casing  11  is a resinous mold that covers the magnetic pipe  12 , the fixed core  13 , the driving portion  30  and so on. At one end portion of the magnetic pipe  12  is installed a nozzle  20 . Between the magnetic pipe  12  and the fixed core  13  is installed a nonmagnetic pipe  14  against a magnetic short circuit. The fixed core  13  and the nonmagnetic pipe  14 , and the nonmagnetic pipe  14  and the magnetic pipe  12  are respectively connected with each other by laser welding and the like. One axial end portion of the fixed core  13  is formed a fuel inflow port  15 . Fuel is supplied from a fuel pump (not shown) to the fuel inflow port  15  of the injector  10 . The fuel supplied to the fuel inflow port  15  flows via a fuel filter  16  into an inner space of the fixed core  13 . The fuel filter  16  is for removing foreign matters contained in the fuel. 
   The valve body  21  is installed on one end of the magnetic pipe  12  opposite from the fixed core  13 . The valve body  21  is connected with the magnetic pipe  12  by laser welding and the like. As shown in  FIG. 3 , the valve body  21  is cylinder-shaped and has an opening portion  22  at its axial end opposite from the fuel inflow port  15 . The valve body  21  has a cone-shaped inner circumferential surface  23 , which is tapered so that its inner diameter gradually decreases as coming closer to the opening portion  22  at its leading end. The valve body  21  further has a valve seat  24  on the cone-shaped inner circumferential surface  23 . On the leading end of the valve body  21 , which is at the side of the opening portion  22 , is installed an injection port plate  40  to cover the leading end portion of the valve body  21 . The Injection port plate  40  has injection ports  41  that penetrate the injection port plate  40  in its thickness direction to communicate its one surface at the side of the valve body  21  with its another surface. 
   The needle (valve member)  25  is installed on the inner circumferential side of the magnetic pipe  12  and the valve body  21  to be slidable in its axial direction. The needle  25  is aligned approximately coaxial to the valve body  21 . One axial end of the needle  25 , which is opposite from the fuel inflow port  15 , is provided with a seal portion  26 . The seal portion  26  is for coming in contact with a valve seat  24  formed in the valve body  21 . The needle  25  and the valve body  21  form a fuel passage  27  therebetween. 
   As shown in  FIG. 2 , the injector  10  is provided with a driving portion  30  for driving the needle  25 . The driving portion  30  includes a spool  31 , a coil  32 , a fixed core  13 , a magnetic pipe  12 , a plate housing  33  and a movable core  34 . The spool  31  is installed on an outer circumferential side of the magnetic pipe  12 , the fixed core  13  and the nonmagnetic pipe  14 . The spool  31  is cylinder-shaped and made of resin. On outer circumference of the spool  31  is wound the coil  32 . The coil  32  is connected to a terminal portion  36  of a connector  35 . The fixed core  35  is installed on the inner circumferential side of the coil  32 . The fixed core  13  is cylinder-shaped and made of magnetic material such as steel. The plate housing  33  is made of magnetic material and covers an outer circumference of the coil  32 . The plate housing  33  is magnetically connected with the fixed core  13  and the magnetic pipe  12 . The outer circumference of the spool  31  and the coil  32  is covered by the casing  11 , which is integrally formed with the connector  35 . 
   The movable core  34  is installed inside the fixed core  13  to be slidable in its axial direction. The movable core  34  is cylinder-shaped and made of magnetic material such as steel. One end of the movable core  34  opposite from the fixed core  13  is integrally connected to the needle  25 . Another end of the movable core  34  at the side of the fixed core  13  is in contact with a spring (elastic member)  17 . The spring  17  is in contact with the movable core  34  at one end and with an adjusting pipe  18  at another end. The adjusting pipe  18  is press-fitted in the fixed core  13 . 
   The spring  17  has a restitutive force to extend in the axial direction. Thus, the spring  17  pushes the movable core  34  and the needle  25  toward the valve body  21 . The load that the spring  17  applies to the movable core  34  and the needle  25  can be modified by adjusting a press-fitting amount of the adjusting pipe  18  press-fitted into the fixed core  17 . When the coil  32  is not energized, the spring  17  pushes the movable core  34  and the needle  25  toward the valve seat  24 , and the seal portion  26  is seated on the valve seat  24 . In the present embodiment, a coil spring is shown as an example of the spring  17 . Alternatively, the spring  17  may be realized by other elastic members such as a leaf spring, an air damper, a fluid damper and so on. 
   The injector  10  in the proximity to the injection port plate  40  is described in detail in the following. 
   The injection port plate  40  is disposed on the leading end of the valve body  21 . As shown in  FIG. 3 , a spacer  50  is disposed between the valve body  21  and the spacer  50 . The spacer  50  is disc-shaped and interposed between the valve body  21  and the injection port plate  40 . As shown in  FIGS. 1 and 3 , the spacer  50  has a fuel chamber opening  51  that open to the combustion chamber of the engine. An inner circumferential surface  50   a  of the spacer  50  surrounds the fuel chamber opening  51 . Thus, an end surface  21   a  of the valve body  21  at the side of the injection plate  40 , an end surface  40   a  of the injection port plate  40  at the side of the valve body  21  and the inner circumferential surface  50   a  of the spacer  50  define a space for a fuel chamber  52 . The fuel chamber  52  is provided between the opening portion  22  of the valve body  21  and the injection ports  41  of the injection port plate  40 . At least a part of the fuel chamber  52  overlaps with the opening portion  22  of the valve body  21 . Thus, the fuel that has passed through the opening portion  22  of the valve body  21  flows via the fuel chamber  52  into the injection ports  41 . 
   As described above, the inner circumferential surface  50   a  of the spacer  50  forms a perimeter of the fuel chamber  52 . Thus, a shape of the fuel chamber opening  51  and the inner circumferential face  50   a  of the spacer  50  determine a cross-sectional shape of the fuel chamber  51 . In the first embodiment, the injection ports  41  formed on the injection port plate  40  are aligned on two coaxially disposed fictive circle lines as shown in  FIG. 1 . The injection ports  41  include four inner injection ports  411   a - 411   d , which are aligned on the inner fictive circle line, and eight outer injection ports  412   a - 412   h , which are aligned on the outer fictive circle line. The four inner injection ports  411   a - 411   d  and the eight outer injection ports  412   a - 412   h  are respectively disposed at a regular intervals on the fictive circle lines. One ends of the injection ports  41  open to the fuel chamber  52 . Alternatively, the injection ports  41  may be aligned at irregular intervals in a circumferential direction of the injection port plate  40 . 
   The inner circumferential surface  50   a  of the spacer  50 , which forms the fuel chamber  52 , is at a specific distance from fuel inflow side openings of the outer injection ports  412   a - 412   h . Here, the fuel inflow side openings of the outer injection ports  412   a - 412   h  are ends of them at the side of the fuel chamber  52 . As shown in  FIG. 4 , distances from the fuel inflow side openings of the outer injection ports  412   a - 412   h  and the inner circumferential surface  50   a  of the spacer  50  are set to satisfy a relation of d 2 /d 1 ≧1, in which d 1  denotes inner diameters of the fuel inflow side openings of the outer injection ports  412   a - 42   h , and d 2  denotes distances from the outer injection ports  412   a - 412   h  to the inner circumferential surface  50   a  of the spacer  50 . As shown in  FIG. 5 , as d 2 /d 1  decreases, distances from the fuel inflow side openings of the outer injection ports  412   a - 412   h  to the inner circumferential surface  50   a  of the spacer  50  become smaller. Then, the fuel that is not so highly turbulent in the fuel chamber  52  flows into the outer injection ports  412   a - 412   h . Accordingly, the atomization performance of the fuel is spoiled, and a Sauter outer diameter (SMD) variation ratio increases. The relation of d 2 /d 1 ≧1 is a measure against this issue. 
   The SMD is a value to indicate an average diameter of a fuel injection spray, and the SMD variation ratio, which is shown in  FIG. 5 , is a value to indicate a variation ratio of the average diameter of the fuel injection spray. An increase of the SMD variation ratio means an increase of the average diameter of the fuel injection spray. In the present embodiment, the SMD variation ratio of 1% or smaller is accepted to secure an atomization performance of the fuel. Accordingly, a minimum threshold of d 2 /d 1  is set to 1, which corresponds to the SMD variation ratio of 1%. When d 2 /d 1  is 3 or larger, the SMD variation ratio is 0.5% or smaller. Accordingly, it is further desirable that d 2 /d 1  is 3 or larger to secure the atomization performance of the fuel further. 
   The distances between the outer injection ports  412   a - 412   h  and the inner circumferential surface  50   a  of the spacer  50  are set as described above. Thus, as shown in  FIG. 1 , the inner circumferential surface  50   a  of the spacer  50  may be disposed between the outer injection ports  412   a - 412   h  in the circumferential direction as long as the relation of d 2 /d 1 ≧1 is satisfied. In the alignment of the injection ports  41  on the injection port plate  40  as shown in  FIG. 1 , a part of the inner circumferential surface  40   a  of the spacer  40 , which forms the fuel chamber  52 , juts radially inward at the intervals between the outer injection ports  412   a - 412   h . In this case, the fuel inflow side openings of the outer injection ports  412   a - 412   h  and the inner circumferential surface  50   a  of the spacer  50  satisfy the relation of d 2 /d 1 ≧1. The inner circumferential surface  50   a  of the spacer  50  juts from the intervals between the outer injection ports  412   a - 412   h  toward the inner injection ports  411   a - 411   d.    
   By the inner circumferential surface  50   a  of the spacer  50  that juts radially inward, an entire volume of the fuel chamber  52  decreases, and a dead volume in the fuel chamber  52  decreases. If the inner circumferential surface  50   a  of the spacer  50  does not juts radially inward, d 2 /d 1  is excessively large at the intervals between the outer injection ports  412   a - 412   h . As shown in  FIG. 5 , even when d 2 /d 1  is excessively large, a turbulence degree of the fuel flowing into the outer injection ports  412   a - 412   h , and the atomization performance of the fuel injected out of the outer injection ports  412   a - 412   h  are not improved so much. Thus, if the inner circumferential surface  50   a  of the spacer  50  does not juts radially inward, the fuel chamber  52  is regarded as including a dead volume at the intervals between the outer injection ports  412   a - 412   h  that does not serve the atomization performance. Correspondingly, in the first embodiment, the inner circumferential surface  50   a  of the spacer  50  that juts radially inward decreases the dead volume not serving the atomization performance. Accordingly, a fuel amount left in the fuel chamber  52  decreases. The fuel chamber  72  is formed only at the periphery of the outer injection ports  732   a - 732   h , so that a dead volume in the injector  10  decreases, and the fuel sucked into the intake air decreases, so that it is possible to limit an air-fuel ratio variation of the intake air. 
   An operation of the injector  10  having the above-described construction is described in the following. 
   When the coil  32  is not energized, the fixed core  13  and movable core  34  generate no electromagnetic attraction force therebetween. Thus, the restitutive force of the spring  17  pushes the movable core  34  and the needle  25  away from the fixed core  13 . Accordingly, when the coil  32  is not energized, the seal portion  26  of the needle  25  is seated on the valve seat  24  and no fuel is injected out of the injection ports  41 . 
   When the coil  32  is energized, a magnetic field generated by the coil  32  forms a magnetic circuit in the plate housing  33 , the magnetic pipe  12 , the movable core  34  and the fixed core  13 . Thus, the fixed core  13  and the movable core  34  generate electromagnetic attraction force therebetween. When the electromagnetic attraction force generated between the fixed core  13  and the movable core  34  exceeds the restitutive force of the spring  17 , an integrated body of the movable core  34  and the needle  25  moves toward the fixed core  13 . Accordingly, the seal portion  26  of the needle  25  lifts off the valve seat  24 . 
   As shown in  FIG. 2 , the fuel that has entered the injector  10  through the fuel inflow port  15  flows via the fuel filter  16 , an inside of the fixed core  13 , an inside of the movable core  34 , a clearance formed between the movable core  34  and the needle  25 , an inside of the magnetic pipe  12  and the fuel port  191  of the stopper  19  into a fuel passage  27 . The fuel in the fuel passage  27  further flow via a gap between the valve seat  24  and the seal portion  26 , and the fuel chamber  52  into the injection ports  41 . Thus, the fuel is injected out of the injection port  52 . 
   When the power supply to the coil  32  is interrupted again, the electromagnetic attraction force between the fixed core  13  and movable core  34  vanishes. Thus, the restitutive force of the spring  17  pushes the integrated body of the movable core  34  and the needle  25  away from the fixed core  13 . Accordingly, the seal portion  26  of the needle  25  is seated on the valve seat  24  again to interrupt the fuel flow between the fuel passage  27  and the fuel chamber  52 , and the fuel injection stops. 
   In the first embodiment, the inner circumferential surface  50   a  of the spacer  50  juts radially inward, that is, toward the inner injection ports  411   a - 411   d , so that a dead volume of the fuel chamber  52  at the periphery of the outer injection ports  412   a - 412   h  decreases. Thus, after the injection of a regulated amount of fuel, the fuel amount left in the fuel chamber  52  is decreased. As a result, the fuel amount sucked into the intake air decreases, and an air-fuel ratio variation of the intake air is limited. Further, by keeping the relation of d 2 /d 1 ≧1, the spiral flow inertia of the fuel flowing into the outer injection ports  412   a - 412   h  is kept. Accordingly, it is possible to secure a fuel atomization performance and to decrease the dead volume in the combustion chamber  52 . 
   Further, in the first embodiment, the shape of the fuel chamber opening  51  can be changed by replacing the spacer  50  with another one. Thus, fuel atomization property of the fuel injected out of the injection ports  41  can be adjusted by replacing the spacer  50 . 
   Second Embodiment 
     FIGS. 6A and 6B  depict a nozzle  20  of the injector  10  according to a second embodiment of the present invention. In the second embodiment, components that are substantially equivalent to those in the first embodiment are assigned reference numerals in common with each other not especially described in the following. 
   In the first embodiment is disclosed an example in which the spacer  50  having the fuel chamber opening  51  is disposed between the valve body  21  and the injection port plate  40  to provide the fuel chamber  52  between the valve body  21  and the injection port plate  40 . 
   Correspondingly, as shown in  FIGS. 6A and 6B , the valve body  21  in the second embodiment is provided with a recess  28  to provide the fuel chamber  62 . The recess  28  has a shape equivalent to that of the fuel chamber opening  51  of the spacer  50  in the first embodiment. Thus, the fuel chamber  62  is formed by attaching the injection port plate  40  on the leading end of the valve body  21 . As a result, an inner circumferential surface  21   b  of the valve body  21  determines an outer perimeter of the fuel chamber  62 . Accordingly, the spacer  50  is not necessary in the second embodiment, and the number of parts of the injector  10  is decreased. 
   Third Embodiment 
     FIGS. 7A and 7B  depict a nozzle  20  of the injector  10  according to a third embodiment of the present invention. In the third embodiment, components that are substantially equivalent to those in the first embodiment are assigned reference numerals in common with each other not especially described in the following. 
   In the third embodiment, a recess  71  is formed on the injection port plate  70  in contrast to the second embodiment in which the recess  28  is formed on the valve body  21 . The recess  71  of the injection port plate  70  and the valve body  21  provides a fuel chamber  72  therebetween. As shown in  FIG. 7B , the injection port plate  70  has a plurality of injection ports  73 . Specifically, the injection ports  73  include inner injection ports  731   a - 731   d  and outer injection ports  732   a - 732   h , which are aligned on two coaxially disposed fictive circle lines. The recess  71  is defined by inner and outer circumferential wall surfaces  71   a ,  71   b , which are coaxially disposed to the fictive circle lines on which the inner injection ports  731   a - 731   d  and the outer injection ports  732   a - 732   h  are aligned. Thus, the recess  71  is ring-shaped on the injection port plate  70  at the side of the valve body  21 . 
   In the third embodiment, the outer injection ports  732   a - 732   h  are communicated with the fuel chamber  72  at their fuel inflow side openings. A distance from the outer injection ports  732   a - 732   h  to the outer and inner circumferential wall surfaces  71   a ,  71   b  of the recess  71  of the injection port plate  70  satisfies the relation of d 2 /d 1 ≧1, in which d 1  denotes inner diameters of the fuel inflow side openings of the outer injection ports  732   a - 732   h , and d 2  denotes a distance from the fuel inflow side openings of the outer injection ports  732   a - 732   h  to the outer or inner circumferential wall surfaces  71   a ,  71   b . Thus, the fuel that has passed through the opening portion  22  of the valve body  21  forms a highly turbulent flow, then flows into each of the outer injection ports  732   a - 732   h.    
   The spiral fuel flow along a cone-shaped inner circumferential surface  23  of the valve body  21 , which has the opening portion  22  at its leading end, directly flows into the inner injection ports  731   a - 731   d . A distance from the fuel inflow side openings of the inner injection ports  731   a - 731   d  to the inner circumferential wall  23  of the valve body  21 , which provides the opening portion  22  is enough to flow highly turbulent fuel into the inner injection ports  731   a - 731   d.    
   In the third embodiment, the outer injection ports  732   a - 732   h  and the outer and inner circumferential wall surfaces  71   a ,  71   b  of the recess  71  of the injection port plate  70  satisfies the relation of d 2 /d 1 ≧1 as described above. Thus, highly turbulent fuel flows into each of the outer injection ports  732   a - 732   h . Accordingly, an enough fuel atomization performance is secured. 
   Further, in the third embodiment, fuel inflow side openings of the inner injection ports  731   a - 731   d  open on the surface of the injection port plate  70  directly to the opening portion  22  of the valve body  21 . That is, the inner injection ports  731   a - 731   d  are not adjacent to the fuel chamber  72 . The fuel chamber  72  is formed only at the periphery of the outer injection ports  732   a - 732   h , so that a dead volume in the injector  10  decreases, and the fuel left in the fuel chamber  72  also decreases. 
   Modified Examples of Third Embodiment 
   Modified examples of the third embodiment are described in the following. In these modified examples, components that are substantially equivalent to those in the third embodiment are assigned reference numerals in common with each other not especially described. 
   In a first modified example of the third embodiment shown in  FIGS. 8A and 8B , the injection port plate  70  may have no injection port at a projection  700  radially inside of the fuel chamber  72 . In this case, the fuel that has passed through the opening portion  22  flows into the fuel chamber  72  formed by the recess  71  radially outside of the projection  700 . 
   In a second modified example of the third embodiment shown in  FIGS. 9A and 9B , the injection port plate  70  is composed of a first injection port plate  710  and a second injection port plate  720 . The first injection port plate  710  has a flat ring shape. The first injection port plate  710  is integrally formed with the projection  700 , which is disposed at the center of the first injection port plate  710 . Specifically, two beams  713  connect the projection  700  at both sides thereof with the injection port plate  710 . The second injection port plate  720  also has a flat ring shape, and is fixed on the first injection port plate  720  at a side opposite from the valve body  21 . By fixing the second injection port plate  720  on the first injection port plate  710 , the projection  700  protrudes from the second injection port plate  720  to face the opening portion  22  of the valve body  21 , and the fuel chamber  72  is formed around the projection  700 . The outer injection ports  732   a - 732   h  open to the fuel chamber  72 . The inner circumferential side surface of the first injection port plate  710  forms an outer circumferential wall surface  711 , that is, an outer perimeter of the fuel chamber  72 . The outer circumferential side surface of the projection  700  forms an inner circumferential wall surface  712 , or an inner perimeter of the fuel chamber  72 . On the projection  700  are formed the inner injection ports  731   a - 731   d.    
   In a third modified example of the third embodiment shown in  FIGS. 10A and 10B , the second injection port plate  720  of the injection port plate  70  has a flat disc shape. The first injection port plate  710  has a construction approximately as that in the second modified example except for being provided with no inner injection port on the projection  700 . 
   In a fourth modified example of the third embodiment shown in  FIGS. 11A and 11B , the first injection port plate  710  is not provided with the beams  713  in the second modified example. Similarly, in a fifth modified example of the third embodiment shown in  FIGS. 12A and 12B , the first injection port plate  710  is not provided with the beams  713  in the third modified example. In the second and third modified examples shown in  FIGS. 9A ,  9 B,  10 A and  10 B, the projection  700  is integrally formed with the first injection port plate  710 , so that it is possible to handle with the first and second injection port plates  710 ,  720  separately until they are fixed on the valve body  21 . Correspondingly, in the fourth and fifth embodiments shown in  FIGS. 11A ,  11 B,  12 A and  12 B, the projection  700  is separated from the first injection port plate  710 , so that the first injection port plate  710  and the projection  700  are fixed on the second injection port plate  720 , then they are fixed on the valve body  21 . 
   Fourth Embodiment 
     FIGS. 13A and 13B  depict a nozzle  20  of the injector  10  according to a third embodiment of the present invention. In the fourth embodiment, components that are substantially equivalent to those in the third embodiment are assigned reference numerals in common with each other not especially described in the following. 
   In the fourth embodiment, recesses  71  ( 71   a - 71   d ) are formed on the injection port plate  70  to provide fuel chambers  72  ( 72   a - 72   d ) in an analogous way to the third embodiment. As shown in  FIG. 13B , the injection port plate  70  has inner injection ports  731   a - 731   d  and outer injection ports  732   a - 732   h , which are aligned on two coaxially disposed fictive circle lines. The fuel inflow side openings of the inner injection ports  731   a - 731   d  open on the surface of the injection port plate  70  directly to the opening portion  22  of the valve body  21  as in the third embodiment. 
   In the fourth embodiment, the injection port plate  70  has four recesses  71  ( 71   a - 71   d ). The fuel inflow side openings of the outer injection ports  732   a - 732   h  open to the recesses  71  of the injection port plate  70  to be communicated with the fuel chambers  72 . Every two of the eight outer injection ports  732   a - 732   h  constitute one injection port group. Specifically, the outer injection ports  732   a ,  732   h  constitute an injection port group  74 A, the outer injection ports  732   b ,  732   c  constitute an injection port group  74 B, the outer injection ports  732   d ,  732   e  constitute an injection port group  74 C, and the outer injection ports  732   f ,  732   g  constitutes an injection port group  74 D. Thus, the eight outer injection ports  732   a - 732   h  constitute four injection port groups  74 A- 74 D. 
   The injection port plate  70  has four recesses  71   a - 71   d  that respectively correspond to the four injection port groups  74 A- 74 D. That is, the outer injection ports  732   a ,  732   h  open to the recess  71   a , the outer injection ports  732   b ,  732   c  open to the recess  71   b , the outer injection ports  732   d ,  732   e  open to the recess  71   c , and the outer injection ports  732   f ,  732   g  open to the recess  71   d . Accordingly, four fuel chambers  72   a - 72   d  are formed between the injection port plate  70  and the valve body  21 . As a result, the fuel chambers  72   a - 72   d  are provided respectively to the injection port groups  74 A- 74 D that are composed of a plurality of the outer injection ports ( 732   a ,  732   h ), ( 732   b ,  732   c ), ( 732   d ,  732   e ), ( 732   f ,  732   g ). 
   Inner circumferential wall surfaces  75   a - 75   d  of the injection port plate  70  define the peripheries of the fuel chambers  72   a - 72   d . The correspondence between the outer injection ports  732   a - 732   h  and the inner circumferential wall surfaces  75   a - 75   d  are as described above. Distances from the outer injection ports  732   a - 732   h  to the inner circumferential wall surfaces  75   a - 75   d  of the recesses  71   a - 71   d  of the injection port plate  70  satisfies the relation of d 2 /d 1 ≧1, in which d 1  denotes inner diameters of the fuel inflow side openings of the outer injection ports  732   a - 732   h  communicated with the fuel chambers  72   a - 72   d , and d 2  denotes distances from the fuel inflow side openings of the outer injection ports  732   a - 732   h  to the inner circumferential wall surfaces  75   a - 75   d.    
   In the fourth embodiment, each of the injection port groups  74 A- 74 D is provided with the fuel chamber  72   a - 72   d , and no fuel chamber is formed at the intervals between the injection port groups  74 A- 74 D. Thus, a dead volume formed at the intervals between every adjacent two of the injection port groups  74 A- 74 D. Accordingly, it is possible to decrease a fuel amount left in the fuel chambers  72   a - 72   d.    
   Modified Examples of Fourth Embodiment 
   Modified examples of the fourth embodiment are described in the following. In these modified examples, components that are substantially equivalent to those in the fourth embodiment are assigned reference numerals in common with each other not especially described. 
   In a first modified example of the fourth embodiment shown in  FIGS. 14A and 14B , the injection port plate  70  may have no injection port at a projection  700  surrounded by the fuel chambers  72  ( 72   a - 72   d ). In this case, the fuel that has passed through the opening portion  22  flows into the fuel chambers  72  ( 72   a - 72   d ) formed by the recesses  71  ( 71 A- 71 D). 
   In a second modified example of the fourth embodiment shown in FIGS.  15 A and  15 B, the injection port plate  70  is composed of a first injection port plate  710  and a second injection port plate  720 . The first injection port plate  710  has four opening portions  710   a - 710   d  respectively in accordance with the fuel chambers  72   a - 72   d . By fixing the second injection port plate  720  on a surface of the first injection port plate  710  opposite from the valve body  21 , the recesses  71  ( 71 A- 71 D) are formed between the valve body  21 , the first injection port plate  70  and the second injection port plate  720 . In the second modified embodiment shown in FIGS, the projection  700  is provided with no injection port (the inner injection port). Correspondingly, in the third modified example of the fourth embodiment shown in  FIGS. 16A and 16B , the second injection port plate  720  has a flat ring shape, so that the projection  700  of the first injection port plate  710  are formed the injection ports, that is, the inner injection ports  731   a - 731   d.    
   Fifth Embodiment 
     FIGS. 17A and 17B  depict a nozzle  20  of the injector  10  according to a fifth embodiment of the present invention. In the fifth embodiment, components that are substantially equivalent to those in the first embodiment are assigned reference numerals in common with each other not especially described in the following. 
   In the fifth embodiment, recesses  81  ( 81   a - 81   d ) are formed on the injection port plate  80  to provide fuel chambers  82  ( 82   a - 82   d ) in an analogous way to the third embodiment. The injection port plate  70  has a plurality of injection ports  83 . Specifically, the injection ports  893  include inner injection ports  831   a - 831   d  and outer injection ports  832   a - 832   h , which are aligned on two coaxially disposed fictive circle lines as shown in  FIG. 17B . 
   In the fifth embodiment, the injection port plate  80  has four recesses  81  ( 81   a - 81   d ). Three injection ports including one of the four inner injection ports  831   a - 831   d  and two of the eight outer injection ports  832   a - 832   h  constitute one injection port group. Specifically, the inner injection port  831   a  and the outer injection ports  832   a ,  832   h  constitute an injection port group  84 A, the inner injection port  831   b  and the outer injection ports  832   b ,  832   c  constitute an injection port group  84 B, the inner injection port  831   c  and the outer injection ports  832   d ,  832   e  constitute an injection port group  84 C, and the inner injection port  831   d  and the outer injection ports  832   f ,  832   g  constitute an injection port group  84 D. Thus, the four inner injection ports  831   a - 831   d  and the eight outer injection ports  832   a - 832   h  constitute four injection port groups  84 A- 84 D. 
   The injection port plate  80  has four recesses  81   a - 81   d  that respectively correspond to the four injection port groups  84 A- 84 D. That is, the inner injection port  831   a  and the outer injection ports  832   a ,  832   h  open to the recess  81   a , the inner injection port  831   b  and the outer injection ports  832   b ,  832   c  open to the recess  81   b , the inner injection port  831   c  and the outer injection ports  832   d ,  832   e  open to the recess  81   c , and the inner injection port  831   d  and the outer injection ports  832   f ,  832   g  open to the recess  81   d . Accordingly, four fuel chambers  82   a - 82   d  are formed between the injection port plate  80  and the valve body  21 . As a result, the fuel chambers  82   a - 82   d  are provided respectively to the injection port groups  84 A- 84 D that are composed of a plurality of the inner and outer injection ports ( 831   a ,  832   a ,  832   h ), ( 831   b ,  832   b ,  832   c ), ( 831   c ,  832   d ,  832   e ), ( 831   d ,  832   f ,  832   g ). 
   The correspondence between the inner and outer injection ports  831   a - 831   d ,  832   a - 832   h  and the inner circumferential wall surfaces  85   a - 85   d , which define the peripheries of the fuel chambers  82   a - 82   d , are as described above. Distances from the inner and outer injection ports  831   a - 831   d ,  832   a - 832   h  to the inner circumferential wall surfaces  85   a - 85   d  of the recesses  81   a - 81   d  of the injection port plate  80  satisfies the relation of d 2 /d 1 ≧1, in which d 1  denotes inner diameters of the fuel inflow side openings of the inner and outer injection ports  831   a - 831   d ,  832   a - 832   h  communicated with the fuel chambers  82   a - 82   d , and d 2  denotes distances from the fuel inflow side openings of the inner and outer injection ports  831   a - 831   d ,  832   a - 832   h  to the inner circumferential wall surfaces  85   a - 85   d.    
   In the fifth embodiment, each of the injection port groups  84 A- 84 D is provided with the fuel chamber  82   a - 82   d , and no fuel chamber is formed at the intervals between the injection port groups  84 A- 84 D, which include not only the outer injection ports  832   a - 832   h  but also the inner injection ports  831   a - 831   d . Thus, a dead volume formed at the intervals between every adjacent two of the injection port groups  84 A- 84 D. Accordingly, it is possible to decrease a fuel amount left in the fuel chambers  82   a - 82   d.    
   Sixth Embodiment 
     FIGS. 18A and 18B  depict a nozzle  20  of the injector  10  according to a sixth embodiment of the present invention. In the sixth embodiment, components that are substantially equivalent to those in the first embodiment are assigned reference numerals in common with each other not especially described in the following. 
   In the sixth embodiment, recesses  91  ( 91   a - 91   d ) are formed on the injection port plate  90  to provide fuel chambers  92  ( 92   a - 92   d ) in an analogous way to the third embodiment. As shown in  FIG. 18B , the injection port plate  90  has injection ports  93   a - 93   d , which are aligned on a fictive circle line. 
   In the sixth embodiment, the injection port plate  90  has four recesses  91   a - 91   d  that respectively correspond to the four injection ports  93   a - 93   d . That is, the injection port  93   a  opens to the recess  91   a , the injection port  93   b  opens to the recess  91   b , the injection port  93   c  opens to the recess  91   c , and the injection port  93   d  opens to the recess  91   d . Accordingly, four fuel chambers  92   a - 92   d  are formed between the injection port plate  90  and the valve body  21 . As a result, the fuel chambers  92   a - 92   d  are provided respectively to the injection ports  93   a - 93   d . The correspondence between the injection ports  93   a - 93   d  and the inner circumferential wall surfaces  95   a - 95   d , which define the peripheries of the fuel chambers  92   a - 92   d , are as described above. Distances from the injection ports  93   a - 93   d  to the inner circumferential wall surfaces  95   a - 95   d  of the recesses  91   a - 91   d  of the injection port plate  90  satisfies the relation of d 2 /d 1 ≧1, in which d 1  denotes inner diameters of the fuel inflow side openings of the injection ports  93   a - 93   d  communicated with the fuel chambers  92   a - 92   d , and d 2  denotes distances from the fuel inflow side openings of the injection ports  93   a - 93   d  to the inner circumferential wall surfaces  95   a - 95   d.    
   In the sixth embodiment, each of the injection ports  93   a - 93   d  is provided with the fuel chamber  92   a - 92   d , and no fuel chamber is formed at the intervals between the injection ports  93   a - 93   d . Thus, a dead volume formed at the intervals between every adjacent two injection ports  93   a - 93   d . Thus, a dead volume formed at the intervals between every adjacent two injection ports  93   a - 93   d . Accordingly, it is possible to decrease a fuel amount left in the fuel chambers  92   a - 92   d.    
   Other Embodiments 
   In the above-described embodiments are described constructions in which any one of flat plate-shaped spacer  50  and an injection port plate  40 ,  70 ,  80 ,  90  is attached on the leading end of the valve body  21 . Alternatively, as shown in  FIG. 19 , the injector may have a construction in which the leading end of the valve body  21  is capped with an approximately cup-shaped injection port plate  100  that has a cylindrical portion  101  and bottom portion  102  on which injection ports  41  are formed. 
   This description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.