Patent Publication Number: US-2016237968-A1

Title: Attachment structure of fuel injection device nozzle plate

Description:
TECHNICAL FIELD 
     The present invention relates to an attachment structure of a fuel injection device nozzle plate (abbreviated below as a nozzle plate) used to atomize and inject fuel flowing from the fuel injection port of a fuel injection device. 
     BACKGROUND ART 
     An internal combustion (abbreviated below as an engine) of an automobile or the like mixes fuel injected from a fuel injection device and air introduced via an intake air pipe to generate a combustible gas mixture and burns the combustible gas mixture in the cylinder. It is known that the mixture state of fuel injected from the fuel injection device and air significantly affects the performance of this type of engine and, in particular, the atomization of fuel injected from the fuel injection device is an important factor governing the performance of the engine. 
     Accordingly, as illustrated in  FIG. 29 , a conventional fuel injection device  1000  promotes the atomization of fuel by welding a nozzle plate  1003  of metal to a valve body  1002  of metal having a fuel injection port  1001  and injecting the fuel injected from the fuel injection port  1001  into an intake air pipe via nozzle holes  1004  formed in the nozzle plate  1003  (see PTL 1 and PTL 2). 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP-A-11-270438 
     PTL 2: JP-A-2011-144731 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the conventional fuel injection device  1000  needs to use a masking jig for welding to prevent welding spatter from entering the nozzle holes  1004  of the nozzle plate  1003  and blocking the nozzle holes  1004 , so efficient welding is difficult. As a result, the manufacturing man-hours of the conventional fuel injection device  1000  increases, making it difficult to reduce the manufacturing cost. 
     An object of the invention is to provide the attachment structure of a fuel injection device nozzle plate for enabling reduction in the manufacturing man-hours and manufacturing cost of a fuel injection device. 
     Solution to Problem 
     The invention relates to the attachment structure of fuel injection device nozzle plates  3 ,  103 , and  203  having nozzle holes  7 ,  107 , and  207  for atomizing and injecting fuel flowing from fuel injection ports  4 ,  104 , and  204  of fuel injection devices  1 ,  101 , and  201 . In the invention, the fuel injection device nozzle plates  3 ,  103 , and  203  include cylindrical fitting parts  12 ,  112 , and  212  to be fitted onto front end sides of valve bodies  5 ,  105 , and  205  of metal having the fuel injection ports  4 ,  104 ,  204  and bottom wall parts  14 ,  114 , and  214  formed so as to block one end sides of the cylindrical fitting parts  12 ,  112 , and  212 , the bottom wall parts abutting against front end surfaces  13 ,  113 , and  213  of the valve bodies  5 ,  105 , and  205  and having the nozzle holes  7 ,  107 , and  207 . In addition, the cylindrical fitting parts  12 ,  112 , and  212  and the bottom wall parts  14 ,  114 , and  214  of the fuel injection device nozzle plates  3 ,  103 , and  203  are made of synthetic resin and formed integrally. In addition, the valve bodies  5 ,  105 ,  205  are provided with outer periphery around which annular interlocking grooves  108  and  208  or interlocking projections  8  and  240  are formed. In addition, arm parts  10 ,  110 ,  210 , and  241  of synthetic resin to be fitted into the interlocking grooves  108  and  208  or the interlocking projections  8  and  240  are formed integrally with the cylindrical fitting parts  12 ,  112 , and  212  and the cylindrical fitting parts  12 ,  112 , and  212  are fixed to the valve bodies  5 ,  105 , and  205  when the arm parts  10 ,  110 ,  210 , and  241  engage with the interlocking grooves  108  and  208  or the interlocking projections  8  and  240  in a state in which the bottom wall parts  14 ,  114 , and  214  abut against the front end surfaces  13 ,  113 , and  213  of the valve bodies  5 ,  105 , and  205 . 
     Advantageous Effects of Invention 
     In the attachment structure of a fuel injection device nozzle plate according to the invention, since the nozzle plate is fixed to the front end side of a valve body only by fitting the cylindrical fitting part of the nozzle plate onto the front end side of the valve body and engaging the arm part of the nozzle plate with the interlocking groove or the interlocking projection of the valve body, the manufacturing man-hours and manufacturing cost of the fuel injection device can be reduced as compared with a conventional example in which a nozzle plate of metal is fixed to the front end of a valve body of metal by welding. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates the use state of a fuel injection device  1 . 
         FIG. 2  illustrates an attachment structure of a nozzle plate according to a first embodiment of the invention.  FIG. 2A  is a front view illustrating the front end side of a fuel injection device,  FIG. 2B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 1  in  FIG. 2A ,  FIG. 2C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 1 -A 1  in the nozzle plate in  FIG. 2A , and  FIG. 2D  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 1 -A 1  in the entire fuel injection device in  FIG. 2A . 
         FIG. 3A  is a front view illustrating the nozzle plate,  FIG. 3B  is a side view illustrating the nozzle plate seen from the direction of arrow C 2  in  FIG. 3A , and  FIG. 3C  is a cross sectional view illustrating the nozzle plate taken along line A 2 -A 2  in  FIG. 3A . 
         FIG. 4A  is a front view illustrating a valve body,  FIG. 4B  is a side view illustrating the front end side of the valve body, and  FIG. 4C  is a vertical cross sectional view illustrating the front end side of the valve body taken along line A 3 -A 3  in  FIG. 4A . 
         FIG. 5  illustrates the attachment structure of the nozzle plate.  FIG. 5A  is an enlarged view illustrating a part of  FIG. 2C ,  FIG. 5B  illustrates a first state in which the difference in thermal expansion between the nozzle plate and the valve body and the manufacturing error of the nozzle plate and the valve body have been absorbed, and  FIG. 5C  illustrates a second state in which the difference in thermal expansion between the nozzle plate and the valve body and the manufacturing error of the nozzle plate and the valve body have been absorbed. 
         FIG. 6  illustrates an attachment structure of a nozzle plate according to a second embodiment of the invention.  FIG. 6A  is a front view illustrating the front end side of the fuel injection device,  FIG. 6B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 3  in  FIG. 6A , and  FIG. 6C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 4 -A 4  in the nozzle plate in  FIG. 6A . 
         FIG. 7A  is a front view illustrating the nozzle plate,  FIG. 7B  is a side view illustrating the nozzle plate seen from the direction of arrow C 4  in  FIG. 7A , and  FIG. 7C  is a cross sectional view illustrating the nozzle plate taken along line A 5 -A 5  in  FIG. 7A . 
         FIG. 8A  is a front view illustrating the valve body and  FIG. 8B  a side view illustrating the front end side of the valve body. 
         FIG. 9  illustrates the attachment structure of the nozzle plate.  FIG. 9A  is an enlarged view illustrating a part of  FIG. 6C ,  FIG. 9B  illustrates the first state in which the difference in thermal expansion between the nozzle plate and the valve body and the manufacturing error of the nozzle plate and the valve body have been absorbed, and  FIG. 9C  illustrates the second state in which the difference in thermal expansion between the nozzle plate and the valve body and the manufacturing error of the nozzle plate and the valve body have been absorbed. 
         FIG. 10  schematically illustrates the use state of a fuel injection device  101 . 
         FIG. 11  illustrates an attachment structure of a nozzle plate according to a third embodiment of the invention.  FIG. 11A  is a front view illustrating the front end side of the fuel injection device,  FIG. 11B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 101  in  FIG. 11A ,  FIG. 11C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 101 -A 101  in the nozzle plate in  FIG. 11A , and  FIG. 11D  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 101 -A 101  in the entire fuel injection device in  FIG. 11A . 
         FIG. 12A  is a cross sectional view taken along line A 102 -A 102  in  FIG. 11C  and  FIG. 12B  is a cross sectional view taken along line A 103 -A 103  in  FIG. 11C . 
         FIG. 13A  is a front view illustrating a nozzle plate according to the third embodiment of the invention,  FIG. 13B  is a side view illustrating the nozzle plate seen from the direction of arrow C 102  in  FIG. 13A , and  FIG. 13C  is a cross sectional view illustrating the nozzle plate taken along line A 104 -A 104  in  FIG. 13A . 
         FIG. 14A  is a front view illustrating a valve body according to the third embodiment of the invention and  FIG. 14B  is a side view illustrating the front end side of the valve body. 
         FIG. 15  illustrates an attachment structure of a nozzle plate according to a fourth embodiment of the invention.  FIG. 15A  is a front view of the front end side of the fuel injection device,  FIG. 15B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 103  in  FIG. 15A , and  FIG. 15C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 105 -A 105  in the nozzle plate in  FIG. 15A . 
         FIG. 16A  is a cross sectional view taken along line A 106 -A 106  in  FIG. 15C  and  FIG. 16B  is a cross sectional view taken along line A 107 -A 107  in  FIG. 15C . 
         FIG. 17A  is a front view illustrating a valve body according to the fourth embodiment of the invention and  FIG. 17B  a side view illustrating the front end side of the valve body. 
         FIG. 18  schematically illustrates the use state of a fuel injection device  201 . 
         FIG. 19  illustrates an attachment structure of a nozzle plate according to a fifth embodiment of the invention.  FIG. 19A  is a front view of the front end side of the fuel injection device,  FIG. 19B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 201  in  FIG. 19A ,  FIG. 19C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 201 -A 201  in the nozzle plate in  FIG. 19A , and  FIG. 19D  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 201 -A 201  in the entire fuel injection device in  FIG. 19A . 
         FIG. 20A  is a cross sectional view illustrating the fuel injection device  1  taken along line A 202 -A 202  in  FIG. 19C  and  FIG. 20B  is a cross sectional view illustrating the fuel injection device taken along line A 203 -A 203  in  FIG. 19C . 
         FIG. 21  illustrates the nozzle plate according to the fifth embodiment of the invention.  FIG. 21A  is a front view illustrating the nozzle plate,  FIG. 21B  is a side view illustrating the nozzle plate seen from the direction of arrow C 202  in  FIG. 21A , and  FIG. 21C  is a cross sectional view illustrating the nozzle plate taken along line A 204 -A 204  in  FIG. 21A . 
         FIG. 22A  illustrates a first engagement state of the nozzle plate and the valve body,  FIG. 22B  illustrates a second engagement state of the nozzle plate and the valve body, and  FIG. 22C  illustrates a third engagement state of the nozzle plate and the valve body. 
         FIG. 23A  is a front view illustrating the valve body according to the fifth embodiment of the invention and  FIG. 23B  is a side view illustrating the front end side of the valve body illustrated in  FIG. 23A . 
         FIG. 24  illustrates an attachment structure of a nozzle plate according to a sixth embodiment of the invention.  FIG. 24A  is a front view illustrating the front end side of the fuel injection device,  FIG. 24B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 203  in  FIG. 24A , and  FIG. 24C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 205 -A 205  in the nozzle plate in  FIG. 24A , and  FIG. 24D  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 205 -A 205  in the entire fuel injection device in  FIG. 24A . 
         FIG. 25  illustrates the nozzle plate according to the sixth embodiment of the invention.  FIG. 25A  is a front view illustrating the nozzle plate,  FIG. 25B  is a side view illustrating the nozzle plate seen from the direction of arrow C 204  in  FIG. 25A , and  FIG. 25C  is a cross sectional view illustrating the nozzle plate taken along line A 206 -A 206  in  FIG. 25A . 
         FIG. 26  illustrates an attachment structure of a nozzle plate according to a seventh embodiment of the invention.  FIG. 26A  is a front view illustrating the front end side of the fuel injection device,  FIG. 26B  is a side view illustrating the front end side of the fuel injection device seen from the direction of arrow C 205  in  FIG. 26A ,  FIG. 26C  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 207 -A 207  in the nozzle plate in  FIG. 26A , and  FIG. 26D  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 207 -A 207  in the entire fuel injection device in  FIG. 26A . 
         FIG. 27  is a cross sectional view illustrating the fuel injection device taken along line A 208 -A 208  in  FIG. 26B . 
         FIG. 28  illustrates an attachment structure of a nozzle plate according to an eight embodiment of the invention.  FIG. 28A  is a front view illustrating the front end side of the fuel injection device,  FIG. 28B  is a cross sectional view illustrating the front end side of the fuel injection device taken along line A 209 -A 209  in  FIG. 28A , and  FIG. 28C  is an enlarged view illustrating a part of the fuel injection device illustrated in  FIG. 28B . 
         FIG. 29  is a cross sectional view of the front end side of a fuel injection device illustrating a conventional attachment structure of a nozzle plate. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the invention will be described below in detail with reference to the drawings. 
     First Embodiment 
     Fuel Injection Device 
       FIG. 1  schematically illustrates the use state of a fuel injection device  1  (see  FIG. 2 ). As illustrated in  FIG. 1 , the fuel injection device  1  of port injection type is installed at an intermediate point on an intake air pipe  2  of an engine, injects fuel into the intake air pipe  2 , mixes air introduced to the intake air pipe  2  and the fuel, and generates a combustible gas mixture. 
       FIG. 2  illustrates the front end side of the fuel injection device  1  to which a fuel injection device nozzle plate  3  (abbreviated below as the nozzle plate) has been attached.  FIG. 2A  is a front view illustrating the front end side of the fuel injection device  1  and  FIG. 2B  is a side view illustrating the front end side of the fuel injection device  1  seen from the direction of arrow C 1  in  FIG. 2A . In addition,  FIG. 2C  is a cross sectional view illustrating the front end side of the fuel injection device  1  in a plane of the nozzle plate  3  including line A 1 -A 1  in  FIG. 2A . In addition,  FIG. 2D  is a cross sectional view illustrating the front end side of the fuel injection device  1  in a plane of the entire fuel injection device  1  including line A 1 -A 1  in  FIG. 2A . 
     As illustrated in  FIG. 2 , in the fuel injection device  1 , the nozzle plate  3  of synthetic resin is attached to the front end side of a valve body  5  of metal in which a fuel injection port  4  is formed. The fuel injection device  1  has a needle valve  6  opened or closed by a solenoid (not illustrated) and, when the needle valve  6  is opened, fuel in the valve body  5  is injected from the fuel injection port  4 , and the fuel injected from the fuel injection port  4  is injected externally via nozzle holes  7  of the nozzle plate  3 . The valve body  5  is circular in front view (see  FIG. 4A ) and an annular interlocking projection  8  is formed in the circumferential direction on the outer peripheral surface on the front end side (see  FIGS. 4A and 4B ). The interlocking projection  8  has a rectangular cross section (cross section along the bus line of the valve body  5 ) and an arm part  10  of the nozzle plate  3  snaps onto the interlocking projection  8  (see  FIGS. 2C and 2D  and  FIG. 4C ). The nozzle plate is injection-molded using synthetic resin such as PPS, PEEK, POM, PA, PES, PEI, or LCP. 
     (Attachment Structure of Nozzle Plate) 
     The attachment structure of the nozzle plate  3  according to the embodiment will be described with reference to  FIGS. 2 to 5 .  FIG. 3A  is a front view illustrating the nozzle plate  3 ,  FIG. 3B  is a side view illustrating the nozzle plate  3  seen from the direction of C 2  in  FIG. 3A , and  FIG. 3C  is a cross sectional view illustrating the nozzle plate  3  in a plane including line A 2 -A 2  in  FIG. 3A .  FIG. 4A  is a front view illustrating the front end side of the valve body  5 ,  FIG. 4B  is a side view illustrating the front end side of the valve body  5 , and  FIG. 4C  is a vertical cross sectional view illustrating the valve body in a plane including line A 3 -A 3  in  FIG. 4A . In addition,  FIG. 5A  is an enlarged view illustrating a part of  FIG. 2C ,  FIG. 5B  illustrates a first state in which the difference in thermal expansion between the nozzle plate  3  and the valve body  5  and the manufacturing error of the nozzle plate  3  and the valve body  5  have been absorbed, and  FIG. 5C  illustrates a second state in which the difference in thermal expansion between the nozzle plate  3  and the valve body  5  and the manufacturing error of the nozzle plate  3  and the valve body  5  have been absorbed. 
     As illustrated in  FIGS. 2 and 3 , the nozzle plate  3  is a bottomed cylindrical body integrally having a cylindrical fitting part  12  to be pressure-fitted onto a front end side outer peripheral surface  11  of the valve body  5 , a bottom wall part  14  formed so as to block one end side of the cylindrical fitting part  12 , the bottom wall part  14  abutting against a front end surface  13  of the valve body  5 , and a pair of arm parts  10  formed on the other end side of the cylindrical fitting part  12 , the pair of arm parts  10  snapping onto the interlocking projection  8  of the valve body  5 . 
     The cylindrical fitting part  12  is cylindrical and has an inner diameter slightly smaller than the outer diameter of the valve body  5  so as to be interference-fitted onto the front end side of the valve body  5 . The cylindrical fitting part  12  has one end side blocked by the bottom wall part  14  and the other end side opened so as to receive the front end side of the valve body  5 . 
     The bottom wall part  14  has a plurality of nozzle holes  7  (six nozzle holes at regular intervals in circumferential direction) for injecting fuel injected from the fuel injection port  4  of the fuel injection device  1  externally (into the intake air pipe  2 ). An inner surface  17  (surface in close contact with the front end surface  13  of the valve body  5 ) of the bottom wall part  14  is flat and an outer surface  18  is recessed in a central part  20 . That is, in the bottom wall part  14 , the central part  20  in which the nozzle holes  7  are formed is a discoid thin-walled part and an outer edge part  21 , surrounding the thin-walled part, that connects to one end side of the cylindrical fitting part  12  is a thick-walled part, which is thicker than the central part  20 . Although the number of the nozzle holes  7  formed in the bottom wall part  14  is six in the embodiment, the invention is not limited to the embodiment and the number of holes and the diameter of holes may be determined as appropriate according to requested fuel injection characteristics. 
     The pair of arm parts  10  is formed so as to project from the opening end of the other end side of the cylindrical fitting part  12  along the bus line of the cylindrical fitting part  12  and the pair of arm parts  10  is formed at intervals of 180 degrees in the circumferential direction of the other end side of the cylindrical fitting part  12 . The arm part  10  is rectangular seen from the side of the nozzle plate  3  (seen in the direction of arrow C 1  in  FIG. 2A  and the direction of arrow C 2  in  FIG. 3A ) and entirely shaped like substantially a tongue piece. In the state in which the nozzle plate  3  is not yet attached to the valve body  5 , an outer surface  22  of the arm part  10  is flush with an outer peripheral surface  23  of the cylindrical fitting part  12  (see  FIG. 3C ). The arm part  10  includes a spring action portion  24  used while being bent (elastically deformed) radially outward of the cylindrical fitting part  12  and a hook  25  formed integrally with the front end side of the spring action portion  24 . 
     An inner surface  26  (surface facing the valve body  5 ) of the spring action portion  24  of the arm part  10  is placed radially outward of an inner peripheral surface  15  of the cylindrical fitting part  12  so as not to make contact with the interlocking projection  8  of the valve body  5  in the state (particularly, the state illustrated in  FIGS. 2C and 2D ) in which the nozzle plate  3  is attached to the valve body  5 . As described above, the spring action portion  24  of the arm part  10  is thinner than the cylindrical fitting part  12  so as to be relatively elastically deformable as compared with other components. 
     The hook  25  of the arm part  10  is provided with an inclined plane  27  pushed against the interlocking projection  8  of the valve body  5  by the elastic force of the spring action portion  24 . The inclined plane  27  is tilted radially inward from the inner surface  26  of the spring action portion  24  so as to make contact with an edge  30  of both edges  28  and  30  of the interlocking projection  8 , the edge  30  being away from the front end surface  13  of the valve body  5  (see  FIG. 5A ). When a difference in thermal expansion is generated between the valve body  5  of metal and the nozzle plate  3  of synthetic resin or manufacturing error appears in the valve body  5  and the nozzle plate  3 , mainly the spring action portion  24  of the inclined plane  27  of this shape is elastically deformed like a cantilever to absorb the difference in thermal expansion between the valve body  5  and the nozzle plate  3  or the manufacturing error generated in the valve body  5  and the nozzle plate  3 , the inclined plane  27  constantly makes contact with the edge  30  of the interlocking projection  8 , and an inclined plane component force generated in the contact portion between the interlocking projection  8  and the edge  30  constantly pushes the inner surface  17  of the bottom wall part  14  against the front end surface  13  of the valve body  5  (see  FIGS. 5B and 5C ). As a result, even when a difference in thermal expansion is generated between the valve body  5  of metal and the nozzle plate  3  of synthetic resin or manufacturing error appears in the valve body  5  and the nozzle plate  3  after the nozzle plate  3  is attached to the front end side of the valve body  5 , no space is generated between the bottom wall part  14  of the nozzle plate  3  and the front end surface  13  of the valve body  5  and, even if the injection pressure of fuel acts on the nozzle plate  3 , the nozzle plate  3  is not removed from the valve body  5  (see  FIGS. 5B and 5C ). 
     On the front end side of the hook  25  on the front end side of the arm part  10 , an engaging guide surface  31  is formed to cause the hook  25  to easily engage with the front end side of the valve body  5  and the hook  25  to easily climb over the interlocking projection  8  of the valve body  5 . The engaging guide surface  31  has one end connected to an end part of the inclined plane  27  and the other end connected to a front end surface  32  of the arm part  10 . The engaging guide surface  31  is tilted toward the outer surface  22  of the arm part  10  as moving away from the inclined plane  27 . When the nozzle plate  3  is fitted onto the front end side of the valve body  5 , the engaging guide surface  31  of this shape makes contact with an edge  33  of the front end of the valve body  5  and slowly bends the spring action portion  24  and, when the hook  25  climbs over the interlocking projection  8 , the engaging guide surface  31  makes contact with the edge  28  of the interlocking projection  8  and slowly bends the spring action portion  24 . As a result, the assembling of the nozzle plate  3  and the valve body  5  can be performed smoothly and easily. 
     Effect of First Embodiment 
     In the attachment structure of the nozzle plate  3  according to the embodiment, since the nozzle plate  3  is fixed to the front end side of the valve body  5  only by press-fitting the cylindrical fitting part  12  of the nozzle plate  3  onto the front end side of the valve body  5  and causing the hook  25  of the arm part  10  of the nozzle plate  3  to snap onto the interlocking projection  8  of the valve body  5 , it is possible to reduce the manufacturing man-hours and manufacturing cost of the fuel injection device  1  as compared with the conventional example (see  FIG. 10 ) in which a nozzle plate  103  of metal is fixed to the front end of a valve body  102  of metal by welding. 
     In addition, in the attachment structure of the nozzle plate  3  according to the embodiment, when a difference in thermal expansion is generated between the nozzle plate  3  and the valve body  5  or manufacturing error appears in the nozzle plate  3  and the valve body  5 , mainly the spring action portion  24  of the arm part  10  of the nozzle plate  3  is elastically deformed to absorb the difference in thermal expansion between the nozzle plate  3  and the valve body  5  and manufacturing error of the nozzle plate  3  and the valve body  5 , the inclined plane  27  of the hook  25  of the arm part  10  is constantly pushed against the interlocking projection  8  of the valve body  5  by the elastic force of the spring action portion  24 , the bottom wall part  14  of the nozzle plate  3  is pushed against the front end surface  13  of the valve body  5  by the inclined plane component force acting on the inclined plane  27 , so the nozzle plate  3  is not removed from the valve body  5  even when the injection pressure of fuel acts on the nozzle plate  3 . 
     In the attachment structure of the nozzle plate  3  according to the embodiment, since the nozzle plate  3  is fixed to the front end side of the valve body  5  only by press-fitting the cylindrical fitting part  12  of the nozzle plate  3  onto the front end side of the valve body  5  and causing the hook  25  of the arm part  10  of the nozzle plate  3  to snap onto the interlocking projection  8  of the valve body  5 , a failure (a nozzle hole  104  is blocked by welding spatter) does not occur unlike the conventional example in which the nozzle plate  103  of metal is fixed to the front end of the valve body  102  of metal by welding and all nozzle holes  7  surely achieve the function of atomizing fuel (see  FIG. 10 ). 
     In the attachment structure of the nozzle plate  3  according to the embodiment, the shape (the shape of the cross section along an central axis  16 ) of the cross section of the hook  25  on the inside (facing the valve body  5 ) is a triangle formed by the inclined plane  27  and the engaging guide surface  31  and the ridge formed by the inclined plane  27  and the engaging guide surface  31  is disposed radially inward (close to the central axis  16 ) of the other part (the part of the hook  25  excluding the ridge). 
     In addition, in the attachment structure of the nozzle plate  3  according to the embodiment, the inclined plane  27  of the hook  25  has an inclined angle of 45 degrees (see  FIG. 3C ). However, the invention is not limited to the embodiment and the inclined angle may be adjusted to an optimum angle according to the difference in thermal expansion between the nozzle plate  3  and the valve body  5  and the like. 
     In addition, in the attachment structure of the nozzle plate  3  according to the embodiment, the front shape of the nozzle plate  3  and the valve body  5  is not limited to a circle and may be a polygon such as a hexagon, D-shape, ellipse, or the like. 
     Second Embodiment 
       FIGS. 6 to 9  illustrate an attachment structure of the nozzle plate  3  according to a second embodiment of the invention. In the description of the attachment structure of the nozzle plate  3  according to the embodiment, the same components in  FIGS. 6 to 9  as in the attachment structure of the nozzle plate  3  according to the first embodiment are given the same reference numerals and duplicate description as in the nozzle plate  3  according to the first embodiment is omitted. 
     In the attachment structure of the nozzle plate  3  according to the embodiment, an inclined plane  34  is formed on the interlocking projection  8  of the valve body  5  and the hook  25  of the arm part  10  of the nozzle plate  3  is elastically pushed against the inclined plane  34  of the interlocking projection  8  by the spring action portion  24  of the arm part  10  (see  FIG. 9A ). 
     In the attachment structure of the nozzle plate  3  according to the embodiment, when a difference in thermal expansion is generated between the valve body  5  of metal and the nozzle plate  3  of synthetic resin or manufacturing error appears in the nozzle plate  3  and the valve body  5 , the spring action portion  24  is elastically deformed like a cantilever to absorb the difference in thermal expansion between the nozzle plate  3  and the valve body  5  and the manufacturing error of the nozzle plate  3  and the valve body  5 , the elastic force of the spring action portion  24  causes the hook  25  to constantly make contact with the inclined plane  34  of the interlocking projection  8 , and an inclined plane component force generated in the contact portion between the inclined plane  34  of the interlocking projection  8  and the hook  25  can push the inner surface  17  of the bottom wall part  14  against the front end surface  13  of the valve body  5  (see  FIG. 9B ). As a result, even when a difference in thermal expansion is generated between the valve body  5  of metal and the nozzle plate  3  of synthetic resin or manufacturing error appears in the valve body  5  and the nozzle plate  3  after the nozzle plate  3  is attached to the front end side of the valve body  5 , no space is generated between the bottom wall part  14  of the nozzle plate  3  and the front end surface  13  of the valve body  5  and, even if the injection pressure of fuel acts on the nozzle plate  3 , the nozzle plate  3  is not removed from the valve body  5  (see  FIGS. 9B and 9C ). 
     In the attachment structure of the nozzle plate according to the embodiment, it is possible to obtain effects similar to those in the attachment structure of the nozzle plate  3  according to the first embodiment. 
     In the attachment structure of the nozzle plate according to the embodiment, the shape of the cross section of the hook  25  on the inside is a triangle projecting radially inward of the nozzle plate  3  and the apex of the triangle makes contact with the inclined plane  34  of the interlocking projection  8 . 
     In addition, in the attachment structure of the nozzle plate according to the embodiment, the inclined plane  34  of the interlocking projection  8  has an inclined angle of 45 degrees (see  FIG. 8 ). However, the invention is not limited to the embodiment and the inclined angle may be adjusted to an optimum angle according to the difference in thermal expansion between the nozzle plate  3  and the valve body  5  and the manufacturing error of the nozzle plate  3  and the valve body  5  and the like. 
     Modification 1 of First and Second Embodiments 
     Although the first embodiment and the second embodiment indicate aspects in which the pair of arm parts  10  is formed at intervals of 180 degrees in the circumferential direction on the other end side of the cylindrical fitting part  12 , the invention is not limited to the aspects and the number of the arm parts  10  may be at least one (one or more). 
     Modification 2 of First and Second Embodiments 
     In the first embodiment and the second embodiment, the part corresponding to the edge  28  of the interlocking projection  8  illustrated in  FIG. 4B  and  FIG. 8B  is chamfered (C-chamfered or R-chamfered), so that the hook  25  makes contact with the chamfered portion of the interlocking projection  8  and slowly bends the spring action portion  24  when the hook  25  climbs over the interlocking projection  8 . As a result, the assembling of the nozzle plate  3  and the valve body  5  can be performed easily and smoothly. 
     Third Embodiment 
     Fuel Injection Device 
       FIG. 10  illustrates the use state of a fuel injection device  101  (see  FIG. 11 ). As illustrated in  FIG. 10 , the fuel injection device  101  of port injection type is installed at an intermediate point on an intake air pipe  102  of the engine, injects fuel into the intake air pipe  102 , mixes air introduced to the intake air pipe  102  and the fuel, and generates a combustible gas mixture. 
       FIG. 11  illustrates the front end side of the fuel injection device  101  to which the fuel injection device nozzle plate  103  (abbreviated below as the nozzle plate) has been attached.  FIG. 11A  is a side view illustrating the front end side of the fuel injection device  101 .  FIG. 11B  is a side view illustrating the front end side of the fuel injection device  101  seen from the direction of arrow C 101  in  FIG. 11A .  FIG. 11C  is a cross sectional view illustrating the front end side of the fuel injection device  101  taken along line A 101 -A 101  in the nozzle plate  103  in  FIG. 11A .  FIG. 11D  is a cross sectional view illustrating the front end side of the fuel injection device  101  taken along line A 101 -A 101  in the entire fuel injection device  101  in  FIG. 11A . 
     As illustrated in  FIG. 11 , in the fuel injection device  101 , the nozzle plate  103  of synthetic resin is attached to the front end side of a valve body  105  of metal in which a fuel injection port  104  is formed. The fuel injection device  101  has a needle valve  106  opened or closed by a solenoid (not illustrated) and, when the needle valve  106  is opened, fuel in the valve body  105  is injected from the fuel injection port  104  and the fuel injected from the fuel injection port  104  is injected externally via the nozzle holes  107  of the nozzle plate  103 . The valve body  105  is circular in front view (see  FIG. 14A ) and the annular interlocking groove  108  is formed in the circumferential direction on the outer peripheral surface on the front end side (see  FIGS. 14A and 14B ). The interlocking projection  108  has a rectangular cross section (cross section along the bus line of the valve body  105 ) and the front end of the arm part  110  of the nozzle plate  103  engages with the interlocking projection  108  (see  FIGS. 11C and 11D ). The nozzle plate  103  is injection-molded using synthetic resin such as PPS, PEEK, POM, PA, PES, PEI, or LCP. 
     (Attachment Structure of Nozzle Plate) 
     The attachment structure of the nozzle plate  103  according to the embodiment will be described below with reference to  FIGS. 11 to 14 .  FIG. 12A  is a cross sectional view taken along line A 102 -A 102  in  FIG. 11C  and  FIG. 12B  is a cross sectional view taken along line A 103 -A 103  in  FIG. 11C .  FIG. 13A  is a front view illustrating the nozzle plate  103 ,  FIG. 13B  is a side view illustrating the nozzle plate  103  seen from the direction of arrow C 102  in  FIG. 13A , and  FIG. 13C  is a cross sectional view illustrating the nozzle plate  103  taken along line A 104 -A 104  in  FIG. 13A . In addition,  FIG. 14A  is a front view illustrating the front end side of the valve body  105  and  FIG. 14B  is a side view illustrating the front end side of the valve body  105 . 
     As illustrated in  FIGS. 11 to 14 , the nozzle plate  103  is a bottomed cylindrical body integrally having a cylindrical fitting part  112  to be pressure-fitted onto front end side outer peripheral surfaces  111   a  and  111   b  of the valve body  105 , the bottom wall part  114  formed so as to block one end side of the cylindrical fitting part  112 , the bottom wall part  114  abutting against the front end surface  113  of the valve body  105 , and the pair of arm parts  110  formed on the other end side of the cylindrical fitting part  112 , the pair of arm parts  110  engaging with the interlocking groove  108  of the valve body  105 . Although the pair of arm parts  110  is formed on the other end side of the cylindrical fitting part  112  in the aspect in the embodiment, the invention is not limited to the aspect and at least one arm part  110  only needs to be formed on the other end side of the cylindrical fitting part  112 . 
     The cylindrical fitting part  112  is cylindrical and has an inner diameter slightly smaller than the outer diameter of the valve body  105  so as to be interference-fitted onto the front end side of the valve body  105 . The cylindrical fitting part  112  has one end side blocked by the bottom wall part  114  and the other end side opened so as to receive the front end side of the valve body  105 . In addition, the cylindrical fitting part  112  has a small-diameter hole part  115  on one end side to be press-fitted onto a front end side small-diameter part  116  of the valve body  105  and a large-diameter hole  117  on the other end side to be press-fitted onto a front end side large-diameter part  118 . In the valve body  105  onto which the cylindrical fitting part  112  is to be press-fitted, the interlocking groove  108  is formed between the front end side small-diameter part  116  to be connected to the front end surface  113  and the front end side large-diameter part  118  positioned away from the front end surface  113 . The cross section of the interlocking groove  108  of the valve body  105  is a rectangular recess taken along a central axis  120  of the valve body  105  (see  FIGS. 11C and 11D  and  FIG. 14 ). 
     The bottom wall part  114  has a plurality of nozzle holes  107  (six nozzle holes at regular intervals in circumferential direction) for injecting fuel injected from the fuel injection port  104  of the fuel injection device  101  externally (into the intake air pipe  102 ). An inner surface  121  (surface in close contact with the front end surface  113  of the valve body  105 ) of the bottom wall part  14  is a flat surface and an outer surface  122  is recessed in a central part  123 . That is, in the bottom wall part  114 , the central part  123  in which nozzle holes  107  are formed is a discoid thin-walled part and an outer edge part  124 , surrounding the central part  123 , that connects to one end side of the cylindrical fitting part  112  is a thick-walled part, which is thicker than the central part  123 . Although the number of the nozzle holes  107  formed in the bottom wall part  114  is six in the embodiment, the invention is not limited to the embodiment and the number of holes and the diameter of holes may be determined as appropriate according to necessary fuel injection characteristics. 
     The arm part  110  includes an arm part main body  125  having a front end  125   a  engaging with the interlocking groove  108  of the valve body  105 , a projection  126 , formed on an inner surface  125   c  of the arm part main body  125 , that makes contact with the outer peripheral surface  111   b  of the valve body  105  at a rear end  125   b  of the arm part main body  125 , and an arm part main body supporting portion  127  elastically supporting the arm part main body  125  with respect to the cylindrical fitting part  112 . 
     The contour of the arm part main body  125  is formed substantially by a pair of first axial direction grooves  128  and  128 , a pair of second axial direction grooves  130  and  130 , and a circumferential direction groove  131  formed in the cylindrical fitting part  112 . The pair of first axial direction grooves  128  and  128  are formed along the central axis  120  (along the bus line) of the cylindrical fitting part  112  from one end  132  of the cylindrical fitting part  112  so as to be spaced apart in the circumferential direction of the cylindrical fitting part  112 . The pair of second axial direction grooves  130  are grooves like long holes disposed in the cylindrical fitting part  112  so as to be away from the first axial direction grooves  128  and  128  along extension lines of the first axial direction grooves  128  and  128  (extension grooves along the central axis  120 ) so as to face the pair of first axial direction grooves  128  and  128 . If the end parts of the second axial direction grooves  130  and  130  close to the first axial direction grooves  128  and  128  are assumed to be one end sides of the second axial direction grooves  130  and  130  and the end parts of the second axial direction grooves  130  and  130  away from the first axial direction grooves  128  and  128  are assumed to be the other end sides of the second axial direction grooves  130  and  130 , the other end sides of the pair of second axial direction grooves  130  and  130  are connected to each other by the circumferential direction groove  131  formed along the circumferential direction of the cylindrical fitting part  112 . The pair of first axial direction grooves  128  and  128 , the pair of the second axial direction grooves  130  and  130 , and the circumferential direction groove  131  penetrate the cylindrical fitting part  112  from the outer peripheral surface to the inner surface. As described above, the arm part main body  125  is separated from the cylindrical fitting part  112  except a part (the arm part main body supporting portions  127  and  127 ) by the pair of first axial direction grooves  128  and  128 , the pair of second axial direction grooves  130  and  130 , and the circumferential direction groove  131  formed in the cylindrical fitting part  112 . In addition, if the end part of the arm part main body  125  close to one end (opening end)  132  of the cylindrical fitting part  112  is assumed to be one end (rear end)  125   b  and the end part of the arm part main body  125  away from the one end (opening end)  132  of the cylindrical fitting part  112  in the direction of the central axis  120  is assumed to be the other end (front end)  125   a , the part located substantially in the middle of the part between the one end  125   b  and the other end  125   a  is elastically supported by the arm part main body supporting portions  127  and  127 . In addition, the circumferential direction groove  131  is obliquely formed so that the edge close to the outer peripheral surface is positioned closer to the bottom wall part  114  than the edge close to the inner peripheral surface of the cylindrical fitting part  112  in the embodiment. As a result, a front end surface  125   d  of the arm part main body  125  is obliquely formed so that the angle formed by the front end surface  125   d  and a virtual straight line  119  orthogonal to the central axis  120  of the cylindrical fitting part  112  is 0 (for example, 10° to 45°). The arm part main body  125  is rectangular seen from the side of the nozzle plate  103 , as illustrated in  FIG. 11B  and  FIG. 13B . 
     The arm part main body supporting portions  127  and  127  are the remaining portions formed between the pair of first axial direction grooves  128  and  128  and the pair of second axial direction grooves  130  and  130  formed in the cylindrical fitting part  112 . The arm part main body supporting portions  127  and  127  connect both sides of the arm part main body  125  (both sides in the width direction along the circumference of the cylindrical fitting part  112 ) to the cylindrical fitting part  112  and elastically supports the arm part main body  125  with respect to the cylindrical fitting part  112  so that the arm part main body  125  can swing. 
     The projection  126  is a rectangular projection disposed closer to (the one end  125   b  of the arm part main body  125 ) the one end  132  of cylindrical fitting part  112  than the arm part main body supporting portion  127  so as to make contact with a broad area in the circumferential direction of the valve body  105  when the nozzle plate  103  is press-fitted onto the valve body  105 . When one end  126   a  of the end of the projection  126  is assumed to be close to the one end  132  of the cylindrical fitting part  112  and the other end  126   b  of the projection  126  is assumed to be away from the one end  132  of the cylindrical fitting part  112  along the central axis  120 , the one end  126   a  is closer (radially inward) to the central axis  120  of the cylindrical fitting part  112  than the other end  126   b . The projection  126  of this shape lifts (moves the one end  125   b  away from the outer peripheral surface of the valve body  105  as illustrated in  FIG. 12B ) the one end  125   b  of the arm part main body  125  using the pair of arm part main body supporting portions  127  and  127  as the fulcrum when the cylindrical fitting part  112  of the nozzle plate  103  is press-fitted onto the valve body  105 , puts the other end (front end)  125   a  of the arm part main body  125  into the interlocking groove  108  (see  FIG. 12A ), elastically deforms the other end (front end)  125   a  of the arm part main body  125  so as to be crashed, and pushes the oblique front end surface  125   d  of the arm part main body  125  against an edge  135  (the edge  135  formed by a groove wall  133  of a pair of groove walls  133  and  134  of the interlocking groove  108  close to the front end surface  113  of the valve body  105  and the outer peripheral surface of the valve body  105 ) (see  FIGS. 11C and 11D ). This causes an elastic force (elastic force caused when the other end (front end)  125   a  of the arm part main body  125  is crashed) to constantly act on the nozzle plate  103  in a direction in which the bottom wall part  114  is pushed against the front end surface  113  of the valve body  105 . The inner peripheral edge close to the one end  132  of the cylindrical fitting part  112  and the one end  126   a  of the projection  126  are preferably chamfered so that the valve body  105  is easily fitted to the cylindrical fitting part  112 . In addition, as illustrated in  FIG. 14B , the end part of the front end side large-diameter part  118  close to the interlocking groove  108  may be chamfered. A chamfered surface  134   a  is formed to smoothly guide the movements of the one end  125   b  of the arm part main body  125  and the projection  126  using an inclined surface so that the valve body  105  is easily fitted into the cylindrical fitting part  112  and the chamfered surface  134   a  preferably prevents the inner surface  125   c  of the arm part main body  125  from making contact with the valve body  105 . 
     Effect of Third Embodiment 
     In the attachment structure of the nozzle plate  103  according to the embodiment, if the cylindrical fitting part  112  of the nozzle plate  103  is press-fitted onto the front end side of the valve body  105 , the projection  126  of the arm part  110  puts the front end  125   a  of the arm part main body  125  into the interlocking groove  108  of the valve body  105 , the front end  125   a  of the arm part main body  125  is pushed against the edge  135  of the interlocking groove  108  (the front end  125   a  of the arm part main body  125  engages with the interlocking groove  108  of the valve body  105 ) in the state in which the front end  125   a  of the arm part main body  125  is elastically deformed so as to be crashed, and the nozzle plate  103  is fixed to the front end side of the valve body  105  while being retained, so it is possible to reduce the manufacturing man-hours and manufacturing cost of the fuel injection device  101  as compared with the conventional example (see  FIG. 29 ) in which a nozzle plate  1103  of metal is fixed to the front end of a valve body  1102  of metal by welding. 
     In addition, in the attachment structure of the nozzle plate  103  according to the embodiment, when a difference in thermal expansion is generated between the nozzle plate  103  of synthetic resin and the valve body  105  of metal after the nozzle plate  103  is press-fitted onto the valve body  105 , the other end (front end)  125   a  of the arm part main body  125  having been elastically deformed so as to be crashed is elastically restored to absorb the difference in thermal expansion between the nozzle plate  103  and the valve body  105 , it is possible to maintain the state in which the front end surface  125   d  of the arm part main body  125  is pushed against the edge  135  of the groove wall  133  of the interlocking groove  108 , no space is generated between the bottom wall part  114  of the nozzle plate  103  and the front end surface  113  of the valve body  105 , 
     and the elastic force of the other end (front end)  125   a  of the arm part main body  125  having been elastically deformed so as to be crashed counteracts the force in a direction in which the nozzle plate  103  is removed from the valve body  105 . As a result, in the attachment structure of the nozzle plate  103  according to the embodiment, the nozzle plate  103  is not removed from the valve body  105  even when the injection pressure of fuel acts on the nozzle plate  103 , and the nozzle plate  103  achieves a desired function (function of atomizing fuel). Since the nozzle plate  103  of synthetic resin has a thermal expansion rate larger than in the valve body  105  of metal, the thermal expansion of the nozzle plate  103  is longer than in the valve body  105  of metal. 
     In addition, in the attachment structure of the nozzle plate  103  according to the embodiment, when the valve body  105  and the nozzle plate  103  have manufacturing error, the other end (front end)  125   a  of the arm part main body  125  makes contact with the edge  135  of the groove wall  133  of the interlocking groove  108  in the state in which the other end (front end)  125   a  of the arm part main body  125  is elastically deformed to absorb the manufacturing error of the valve body  105  and the nozzle plate  103 , the elastic contact between the other end (front end)  125   a  of the arm part main body  125  and the edge  135  of the groove wall  133  of the interlocking groove  108  is kept, and the elastic force of the other end (front end)  125   a  of the arm part main body  125  elastically deformed so as to be crashed counteracts on the force in a direction in which the nozzle plate  103  is removed from the valve body  105 . As a result, in the attachment structure of the nozzle plate  103  according to the embodiment, no space is generated between the bottom wall part  114  of the nozzle plate  103  and the front end surface  113  of the valve body  105  even when the valve body  105  of metal and the nozzle plate  103  of synthetic resin have manufacturing error, and the nozzle plate  103  is not removed from the valve body  105  even when the injection pressure of fuel acts on the nozzle plate  103 . 
     In the attachment structure of the nozzle plate  103  according to the embodiment, if the cylindrical fitting part  112  of the nozzle plate  103  is press-fitted onto the front end side of the valve body  105 , the projection  126  of the arm part  110  puts the other end (front end)  125   a  of the arm part main body  125  into the interlocking groove  108  of the valve body  105 , the other end (front end)  125   a  of the arm part main body  125  is pushed against the edge  135  of the interlocking groove  108  (the other end (front end)  125   a  of the arm part main body  125  engages with the interlocking groove  108  of the valve body  105 ) in the state in which the other end (front end)  125   a  of the arm part main body  125  is elastically deformed so as to be crashed, and the nozzle plate  103  is fixed to the front end side of the valve body  105  while being retained, so a failure (a nozzle hole  1104  is blocked by welding spatter) does not occur unlike the conventional example (see  FIG. 29 ) in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding and all nozzle holes  107  surely achieve the function of atomizing fuel. 
     Although  FIGS. 11A and 13A  illustrates an aspect in which the pair of arm parts  110  are formed along the circumferential direction of the cylindrical fitting part  112 , the invention is not limited to the aspect and at least one arm part  110  only needs to be formed in the cylindrical fitting part  112  or three or more arm parts  110  may be formed in the cylindrical fitting part  112 . 
     In addition, in the attachment structure of the nozzle plate  103  according to the embodiment, the front shape of the nozzle plate  103  and the valve body  105  is not limited to a circle and may be a polygon such as a hexagon, D-shape, ellipse, or the like. 
     Fourth Embodiment 
       FIGS. 15 to 17  illustrate an attachment structure of the nozzle plate  103  according to a fourth embodiment of the invention. In the description of the attachment structure of the nozzle plate  103  according to the embodiment, the same components in  FIGS. 15 to 17  as in the attachment structure of the nozzle plate  103  according to the third embodiment are given the same reference numerals and duplicate description as in the nozzle plate  103  according to the third embodiment is omitted. 
     In the attachment structure of the nozzle plate  103  according to the embodiment, of the pair of the groove walls  133  and  134  forming the interlocking groove  108  of the valve body  105 , the groove wall  133  close to the front end surface  113  is an inclined plane and, when the cylindrical fitting part  112  is press-fitted onto the front end side of the valve body  105 , the one end (rear end)  125   b  of the arm part main body  125  is pushed up by the projection  126  and the other end (front end)  125   a  of the arm part main body  125  is put in the interlocking groove  108 , the other end (front end)  125   a  (particularly, the inside in contact with the groove wall  133  as an inclined plane) of the arm part main body  125  is pushed against the groove wall  133  as the inclined plane of the interlocking groove  108  in the state in which the other end  125   a  is elastically deformed so as to be crashed, and the nozzle plate  103  is fixed to the front end side of the valve body  105  while being retained. 
     In the attachment structure of the nozzle plate  103  according to the embodiment, when a difference in thermal expansion is generated between the valve body  105  of metal and the nozzle plate  103  of synthetic resin, the other end (front end)  125   a  of the arm part main body  125  in contact with the groove wall  133  as an inclined plane of the interlocking groove  108  while being elastically deformed elastically restores to absorb the difference in thermal expansion between the valve body  105  and the nozzle plate  103 , the elastic contact between the other end (front end)  125   a  of the arm part main body  125  and the groove wall  133  as an inclined plane of the interlocking groove  108  is kept, and the elastic force of the other end (front end)  125   a  of the arm part main body  125  elastically deformed so as to be crashed counteracts the force in a direction in which the nozzle plate  103  is removed from the valve body  105 . As a result, even when a difference in thermal expansion is generated between the valve body  105  of metal and the nozzle plate  103  of synthetic resin after the nozzle plate  103  is attached to the front end side of the valve body  105 , no space is generated between the bottom wall part  114  of the nozzle plate  103  and the front end surface  113  of the valve body  105  and the elastic force of the other end (front end)  125   a  of the arm part main body  125  having been elastically deformed so as to be crashed counteracts the force in a direction in which the nozzle plate  103  is removed from the valve body  105 . Accordingly, even if the injection pressure of fuel acts on the nozzle plate  103 , the nozzle plate  103  is not removed from the valve body  105 . 
     In addition, in the attachment structure of the nozzle plate  103  according to the embodiment, when the valve body  105  and the nozzle plate  103  have manufacturing error, the other end (front end)  125   a  of the arm part main body  125  makes contact with the groove wall  133  as an inclined plane of the interlocking groove  108  in the state in which the other end (front end)  125   a  of the arm part main body  125  is elastically deformed to absorb the manufacturing error of the valve body  105  and the nozzle plate  103  and the elastic contact between the other end (front end)  125   a  of the arm part main body  125  and the groove wall  133  as an inclined plane of the interlocking groove  108  is kept. As a result, in the attachment structure of the nozzle plate  103  according to the embodiment, no space is generated between the bottom wall part  114  of the nozzle plate  103  and the front end surface  113  of the valve body  105  even when the valve body  105  of metal and the nozzle plate  103  of synthetic resin have manufacturing error and the elastic force of the other end (front end)  125   a  of the arm part main body  125  having been elastically deformed so as to be crashed counteracts the force in a direction in which the nozzle plate  103  is removed from the valve body  105 . Accordingly, even when the injection pressure of fuel acts on the nozzle plate  103 , the nozzle plate  103  is not removed from the valve body  105 . 
     In the attachment structure of the nozzle plate  103  according to the embodiment, it is possible to obtain effects similar to those in the attachment structure of the nozzle plate  103  according to the third embodiment. That is, in the attachment structure of the nozzle plate  103  according to the embodiment, when the cylindrical fitting part  112  of the nozzle plate  103  is press-fitted onto the front end side of the valve body  105 , the projection  126  of the arm part  110  puts the other end (front end)  125   a  of the arm part main body  125  into the interlocking groove  108  of the valve body  105 , the other end (front end)  125   a  of the arm part main body  125  is pushed against the groove wall  133  as an inclined plane of the interlocking groove  108  of the valve body  105  (the other end (front end)  125   a  of the arm part main body  125  engages with the interlocking groove  108  of the valve body  105 ) in the state in which the other end (front end)  125   a  of the arm part main body  125  is elastically deformed so as to be crashed, and the nozzle plate  103  is fixed to the front end side of the valve body  105  while being retained, so it is possible to reduce the manufacturing man-hours and manufacturing cost of the fuel injection device  101  as compared with the conventional example (see  FIG. 29 ) in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding. 
     In addition, in the attachment structure of the nozzle plate  103  according to the embodiment, if the cylindrical fitting part  112  of the nozzle plate  103  is press-fitted onto the front end side of the valve body  105 , the projection  126  of the arm part  110  puts the other end (front end)  125   a  of the arm part main body  125  into the interlocking groove  108  of the valve body  105 , the other end (front end)  125   a  of the arm part main body  125  is pushed against the groove wall  133  as an inclined plane of the interlocking groove  108  of the valve body  105  (the other end (front end)  125   a  of the arm part main body  125  engages with the interlocking groove  108  of the valve body  105 ) in the state in which the other end (front end)  125   a  of the arm part main body  125  is elastically deformed so as to be crashed, and the nozzle plate  103  is fixed to the front end side of the valve body  105  while being retained, so a failure (the nozzle hole  1104  is blocked by welding spatter) does not occur unlike the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal (see  FIG. 29 ) by welding and all nozzle holes  107  surely achieve the function of atomizing fuel. 
     In the interlocking groove  108  according to the embodiment, of the pair of groove walls  133  and  134 , the entire groove wall  133  close to the bottom wall part  114  is used as an incline surface. However, the invention is not limited to the embodiment and only a part of the groove wall  133  may be an inclined plane. In addition, although the front end surface  125   d  of the arm part main body  125  is formed so that θ in  FIG. 13C  equals 0 degrees (θ=0°) in the embodiment, θ may be larger than 0 degrees as long as the contact state between the other end (front end)  125   a  of the arm part main body  125  illustrated in  FIG. 15C  and the groove wall  133  can be kept. 
     Fifth Embodiment 
     Fuel Injection Device 
       FIG. 18  illustrates the use state of the fuel injection device  201  (see  FIG. 19 ). As illustrated in  FIG. 18 , the fuel injection device  201  of port injection type is installed at an intermediate point on an intake air pipe  202  of the engine, injects fuel into the intake air pipe  202 , mixes air introduced to the intake air pipe  202  and the fuel, and generates a combustible gas mixture. 
       FIG. 19  illustrates the front end side of the fuel injection device  201  to which the fuel injection device nozzle plate  203  (abbreviated below as the nozzle plate) has been attached.  FIG. 19A  is a front view illustrating the front end side of the fuel injection device  201 .  FIG. 19B  is a side view illustrating the front end side of the fuel injection device  201  seen from the direction of arrow C 201  in  FIG. 19A .  FIG. 19C  is a cross sectional view illustrating the front end side of the fuel injection device  201  taken along line A 201 -A 201  in the nozzle plate  203  in  FIG. 19A .  FIG. 19D  is a cross sectional view illustrating the front end side of the fuel injection device  201  taken along line A 201 -A 201  in the entire fuel injection device  201  in  FIG. 19A . 
     As illustrated in  FIG. 19 , in the fuel injection device  201 , the nozzle plate  203  of synthetic resin is attached to the front end side of the valve body  205  of metal in which a fuel injection port  204  is formed. The fuel injection device  201  has a needle valve  206  opened or closed by a solenoid (not illustrated) and, when the needle valve  206  is opened, fuel in the valve body  205  is injected from the fuel injection port  204  and the fuel injected from the fuel injection port  204  is injected externally via the nozzle holes  207  of the nozzle plate  203 . The valve body  205  is circular in front view (see  FIG. 23A ) and the annular interlocking groove  208  is formed in the circumferential direction on a front end side outer peripheral surface  211   a  (see  FIGS. 23A and 23B ). The interlocking groove  208  has a rectangular cross section (cross section along the bus line of the valve body  205 ) and the arm part  210  of the nozzle plate  203  engages with the interlocking groove  208  (see  FIGS. 19C and 19D ). The nozzle plate  203  is injection-molded using synthetic resin such as PPS, PEEK, POM, PA, PES, PEI, or LCP. 
     (Attachment Structure of Nozzle Plate) 
     The attachment structure of the nozzle plate  203  according to the embodiment will be described with reference to  FIGS. 19 to 23 .  FIG. 20A  is a cross sectional view taken along line A 202 -A 202  in  FIG. 19C  and  FIG. 20B  is a cross sectional view taken along line A 203 -A 203  in  FIG. 19C .  FIG. 21A  is a front view illustrating the nozzle plate  203 ,  FIG. 21B  is a side view illustrating the nozzle plate  203  seen from the direction of arrow C 202  in  FIG. 21A , and  FIG. 21C  is a cross sectional view illustrating the nozzle plate  203  taken along line A 204 -A 204  in  FIG. 21A .  FIG. 22A  illustrates a first engagement state of the nozzle plate  203  and the valve body  205  and  FIG. 22B  illustrates a second engagement state of the nozzle plate  203  and the valve body  205 .  FIG. 23A  is a front view illustrating the front end side of the valve body  205  and  FIG. 23B  is a side view illustrating the front end side of the valve body  205 . 
     As illustrated in  FIGS. 19 to 23 , the nozzle plate  203  is a bottomed cylindrical body integrally having the cylindrical fitting part  212  to be pressure-fitted onto the front end side outer peripheral surfaces  211   a  and  211   b  of the valve body  205 , the bottom wall part  214  formed so as to block one end side of the cylindrical fitting part  212 , the bottom wall part  214  abutting against the front end surface  213  of the valve body  205 , and the arm part  210  formed on the other end side of the cylindrical fitting part  212 , the arm part  210  engaging with the interlocking groove  208  of the valve body  205 . Although the embodiment indicates an aspect in which the pair of arm parts  210  is formed on the other end side of the cylindrical fitting part  212 , the invention is not limited to the aspect and at least one arm part  210  only needs to be formed on the other end side of the cylindrical fitting part  212 . 
     The cylindrical fitting part  212  is cylindrical and has an inner diameter slightly smaller than the outer diameter of the valve body  205  so as to be interference-fitted onto the front end side of the valve body  205 . The cylindrical fitting part  212  has one end side blocked by the bottom wall part  214  and the other end side opened so as to receive the front end side of the valve body  205 . In addition, the cylindrical fitting part  212  has a small-diameter hole part  215  on one end side to be press-fitted onto a front end side small-diameter part  216  of the valve body  205  and a large-diameter hole  217  on the other end side to be press-fitted onto a front end side large-diameter part  218  of the valve body  205 . In the valve body  205  onto which the cylindrical fitting part  212  is to be press-fitted, the interlocking groove  208  is formed between the front end side small-diameter part  216  to be connected to the front end surface  213  and the front end side large-diameter part  218  positioned away from the front end surface  213 . The interlocking groove  208  of the valve body  205  has a rectangular recessed cross section taken along a central axis  220  of the valve body  205  (see  FIGS. 19C and 19D  and  FIG. 23 ). 
     The bottom wall part  214  has the plurality of nozzle holes  207  (six nozzle holes at regular intervals in circumferential direction) for injecting fuel injected from the fuel injection port  204  of the fuel injection device  201  externally (into the intake air pipe  202 ). 
     The bottom wall part  214  is provided with a flat surface (valve body abutment part)  221  that first makes contact with the front end surface  213  of the valve body  205  when the cylindrical fitting part  212  is press-fitted onto the front end side of the valve body  205  in the central part of the inside (the side facing the front end surface  213  of the valve body  205 ). The flat surface  221  has the plurality of nozzle holes  207  and makes contact with the periphery of the fuel injection port  204  of the valve body  205 . The bottom wall part  214  has a recessed portion  222  (which is recessed from the flat surface  221 ) radially inward of the connection portion with the cylindrical fitting part  212  to the outer edge of the flat surface  221 . The recessed portion  222  is formed inside the bottom wall part  214  so that space is generated with respect to the front end surface  213  of the valve body  205  in the state in which the flat surface  221  first makes contact with the front end surface  213  of the valve body  205 . The recessed portion  222  is formed by a tapered surface  223  extending radially outward from the outer edge of the flat surface  221  and a curved surface  225  smoothly connecting the outer edge of the tapered surface  223  to an inner peripheral surface  224  of the cylindrical fitting part  212  (see  FIG. 22A ). The valve body abutment part is not limited to the flat surface  221  and may be, for example, an annular projection in contact with the periphery of the fuel injection port  204  of the front end surface  213  of the valve body  205 . 
     The bottom wall part  214  is recessed in a central part  226  on the outside and the plurality of nozzle holes  207  are opened in the recessed central part  226 . In the bottom wall part  214 , an annular recess  227  around the inner peripheral surface  224  of the cylindrical fitting part  212  is formed in the part (thicker than the central part  226 ) disposed radially inward of the connection portion with respect to the cylindrical fitting part  212  in the area surrounding the central part  226  on the outside, so that an annular thin-walled part  228  is formed around the inner peripheral surface  224  of the cylindrical fitting part  212  (see  FIG. 22A ). The annular recess  227  has an arc-shaped cross section to prevent concentration of stress. In addition, although a total of six nozzle holes  207  are formed in the bottom wall part  214  in the embodiment, the invention is not limited to the embodiment and the optimum number of nozzle holes  207  and the optimum hole diameter may be determined according to the necessary fuel injection characteristics. 
     The nozzle plate  203  configured in this way pushes the cylindrical fitting part  212  so as to narrow the space between the recessed portion  222  inside the bottom wall part  214  and the front end surface  213  of the valve body  205  from the state illustrated in  FIG. 22A  in which the flat surface  221  first makes contact with the front end surface  213  of the valve body  205  to the state illustrated in  FIG. 22B  and then the nozzle plate  203  is attached to the valve body  205  by engaging a front end  230   a  of the arm part  210  described later with the interlocking groove  208  of the valve body  205  (see  FIG. 19C ). At this time, the annular thin-walled part  228  of the bottom wall part  214  is elastically deformed easily to make it easy to further press-fit the cylindrical fitting part  212  onto the valve body  205 . In addition, in the embodiment, as illustrated in  FIG. 22C , the cylindrical fitting part  212  can be further press-fitted (moved) onto the front end side of the valve body  205  by the amount of the space between the recessed portion  222  inside the bottom wall part  214  and the front end surface  213  of the valve body  205  (see  FIG. 22B ). Accordingly, the force caused by the elastic deformation of the annular thin-walled part  228  of the bottom wall part  214  is maintained even when the engagement state changes according to the manufacturing error of the nozzle plate  203  and the valve body  205 , the assembling error of the nozzle plate  203  and the valve body  205 , and the difference in the linear expansion coefficient between the nozzle plate  203  and the valve body  205 . 
     The arm part  210  includes an arm part main body  230  having the front end  230   a  engaging with the interlocking groove  208  of the valve body  205 , a projection  231  formed on an inner surface  230   c  of the arm part main body  230  facing a front end side outer peripheral surface  211   b  of the valve body  205  at a rear end  230   b  of the arm part main body  230 , and arm part main body supporting portions  232  elastically supporting the arm part main body  230  with respect to the cylindrical fitting part  212 . 
     The contour of the arm part main body  230  is formed substantially by a pair of first axial direction grooves  233  and  233 , a pair of second axial direction grooves  234  and  234 , and a circumferential direction groove  235  formed in the cylindrical fitting part  212 . The pair of first axial direction grooves  233  and  233  are formed along the central axis  220  (along the bus line) of the cylindrical fitting part  212  from one end  237  of the cylindrical fitting part  212  so as to be spaced apart in the circumferential direction of the cylindrical fitting part  112 . The pair of second axial direction grooves  234  are grooves like long holes disposed in the cylindrical fitting part  212  so as to be away from the first axial direction grooves  233  along extension lines (extension lines along the central axis  220 ) of the first axial direction grooves  233  so as to face the pair of first axial direction grooves  233  and  233 . If the end parts of the second axial direction grooves  234  and  234  close to the first axial direction grooves  233  and  233  are assumed to be one end sides of the second axial direction grooves  234  and  234  and the end parts of the second axial direction grooves  234  and  234  away from the first axial direction grooves  233  and  233  are assumed to be the other end sides of the second axial direction grooves  234  and  234 , the other end sides of the pair of second axial direction grooves  234  and  234  are connected to each other by the circumferential direction groove  235  formed along the circumferential direction of the cylindrical fitting part  212 . The pair of first axial direction grooves  233  and  233 , the pair of the second axial direction grooves  234  and  234 , and the circumferential direction groove  235  penetrate the cylindrical fitting part  212  from an outer peripheral surface  236  to the inner peripheral surface  224 . As described above, the arm part main body  230  is separated from the cylindrical fitting part  212  except the parts (the arm part main body supporting portions  232  and  232 ) by the pair of first axial direction grooves  233  and  233 , the pair of second axial direction grooves  234  and  234 , and the circumferential direction groove  235  formed in the cylindrical fitting part  212 . In addition, if the end part of the arm part main body  230  close to one end (opening end)  237  of the cylindrical fitting part  212  is assumed to be one end (rear end)  230   b  and the end part of the arm part main body  230  away from the one end (opening end)  237  of the cylindrical fitting part  212  in the direction of the central axis  220  is assumed to be the other end (front end)  230   a , the part located substantially in the middle of the part between the one end  230   b  and the other end  230   a  is elastically supported by the arm part main body supporting portions  232  and  232 . Although the circumferential direction groove  235  is formed orthogonally to the central axis  220  of the cylindrical fitting part  212  in the embodiment, the invention is not limited to the embodiment and the circumferential direction groove  235  may be formed obliquely so that the edge of the cylindrical fitting part  212  close to the outer peripheral surface  236  is closer to the bottom wall part  214  than the edge of the cylindrical fitting part  212  close to the inner peripheral surface  224 . The arm part main body  230  is substantially rectangular seen from the side of the nozzle plate  203 , as illustrated in  FIGS. 19B and 21B . 
     The arm part main body supporting portions  232  and  232  are the remaining portions formed between the pair of first axial direction grooves  233  and  233  and the pair of second axial direction grooves  234  and  234  formed in the cylindrical fitting part  212 . The arm part main body supporting portions  232  and  232  connect both ends of the arm part main body  230  (both ends in the width direction along the circumferential direction of the cylindrical fitting part  212 ) to the cylindrical fitting part  212  and elastically supports the arm part main body  230  with respect to the cylindrical fitting part  212  so that the arm part main body  230  can swing. 
     The projection  231  is a rectangular projection disposed closer to the one end  237  of the cylindrical fitting part  212  (the one end  125   b  of the arm part main body  125 ) than the arm part main body supporting portion  232  so as to make contact with a broad area in the circumferential direction of the valve body  205  when the nozzle plate  203  is press-fitted onto the valve body  205 . When the end part of the projection  231  close to the one end  237  of the cylindrical fitting part  212  is assumed to be one end  231   a  and the end part away from the one end  237  of the cylindrical fitting part  212  in the direction of the central axis  220  is assumed to be the other end  231   b , the one end  231   a  is formed at a position closer (radially inward) to the central axis  220  of the cylindrical fitting part  212  than the other end  231   b . The projection  231  of this shape lifts the one end  230   b  of the arm part main body  230  using the pair of arm part main body supporting portions  232  and  232  as the fulcrum when the cylindrical fitting part  212  of the nozzle plate  203  is press-fitted onto the valve body  205 , and puts the other end (front end)  230   a  of the arm part main body  230  into the interlocking groove  208 . At this time, when the other end (front end)  230   a  of the arm part main body  230  does not engage with the interlocking groove  208  because the other end (front end)  230   a  snaps onto the front end side outer peripheral surface  211   a  of the valve body  205  due to manufacturing error of the nozzle plate  203  and the valve body  205  or the like, the cylindrical fitting part  212  is further press-fitted onto the valve body  205  within the space between the recessed portion  222  of the bottom wall part  214  and the front end surface  213  of the valve body  205 . As a result, the other end (front end)  230   a  of the arm part main body  230  surely engages with the interlocking groove  208  of the valve body  205  and the nozzle plate  203  is fixed to the valve body  205  while being retained. The inner peripheral edge of the cylindrical fitting part  212  close to the one end  237  and the one end  231   a  of the projection  231  are preferably chamfered so that the valve body  205  is easily fitted into the cylindrical fitting part  212 . In addition, as illustrated in  FIG. 23B , the end part of the front end side large-diameter part  218  close to the interlocking groove  208  may be a chamfered surface  238 . The chamfered surface  238  is formed to smoothly guide the movements of the one end  230   b  of the arm part main body  230  and the projection  231  using an inclined surface so that the valve body  205  is easily fitted into the cylindrical fitting part  212  and the chamfered surface  238  preferably prevents the inner surface  230   c  of the arm part main body  230  from making contact with the valve body  205 . 
     Effect of Fifth Embodiment 
     In the attachment structure of the nozzle plate  203  according to the embodiment, if the cylindrical fitting part  212  of the nozzle plate  203  is press-fitted onto the front end side of the valve body  205 , the projection  231  of the arm part  210  puts the front end  230   a  of the arm part main body  230  into the interlocking groove  208  of the valve body  205 . However, when the front end  230   a  of the arm part main body  230  snaps onto the front end side outer surface  211   a  of the valve body  205  and does not engage with the interlocking groove  208 , the cylindrical fitting part  212  is moved (the cylindrical fitting part  212  is further press-fitted onto the valve body  205 ) in a direction in which the space between the recessed portion  222  of the bottom wall part  214  of the nozzle plate  203  and the front end surface  213  of the valve body  205  is narrowed, the front end  230   a  of the arm part main body  230  surely engages with the interlocking groove  208 , the nozzle plate  203  can be surely fixed to the valve body  205  while being retained. Accordingly, in the attachment structure of the nozzle plate  203  according to the embodiment, it is possible to reduce the manufacturing man-hours and manufacturing cost of the fuel injection device  201  as compared with the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding (see  FIG. 29 ). In addition, in the attachment structure of the nozzle plate  203  according to the embodiment, a failure (the nozzle hole  1104  is blocked by welding spatter) does not occur unlike the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding (see  FIG. 29 ) and all nozzle holes  207  surely achieve the function of atomizing fuel. 
     Although  FIGS. 19A and 21A  illustrate an aspect in which the pair of arm parts  210  are formed along the circumferential direction of the cylindrical fitting part  212 , the invention is not limited to the aspect and at least one arm part  210  only needs to be formed in the cylindrical fitting part  212  or three or more arm parts  210  may be formed in the cylindrical fitting part  212 . 
     In addition, in the attachment structure of the nozzle plate  203  according to the embodiment, the front shape of the nozzle plate  203  and the valve body  205  is not limited to a circle and may be a polygon such as a hexagon, D-shape, ellipse, or the like. 
     Sixth Embodiment 
     An attachment structure of the nozzle plate  203  according to a sixth embodiment will be described below. 
     (Attachment Structure of Nozzle Plate) 
       FIGS. 24 and 25  illustrate the attachment structure of the nozzle plate  203  according to the sixth embodiment of the invention.  FIG. 24  illustrates the front end side of the fuel injection device  201  according to the sixth embodiment of the invention.  FIG. 25  illustrates the nozzle plate  203  according to the sixth embodiment of the invention. In the description of the attachment structure of the nozzle plate  203  according to the embodiment, the duplicate description as in the nozzle plate  203  according to the fifth embodiment is omitted. 
     As illustrated in  FIGS. 24 and 25 , the nozzle plate  203  is a bottomed cylindrical body integrally having the cylindrical fitting part  212  to be pressure-fitted onto the front end side outer peripheral surface  211   a  of the valve body  205 , the bottom wall part  214  formed so as to block one end side of the cylindrical fitting part  212 , the bottom wall part  214  abutting against the front end surface  213  of the valve body  205 , and a pair of arm parts  241  formed on the other end side of the cylindrical fitting part  212 , the pair of arm part  241  snapping onto the interlocking projection  240  of the valve body  205 . The nozzle plate  203  according to the embodiment is made of synthetic resin as in the nozzle plate  203  according to the fifth embodiment. 
     The cylindrical fitting part  212  is cylindrical and has an inner diameter slightly smaller than the outer diameter of the valve body  205  so as to be interference-fitted onto the front end side of the valve body  205 . The cylindrical fitting part  212  has one end side blocked by the bottom wall part  214  and the other end side opened so as to receive the front end side of the valve body  205 . 
     The bottom wall part  214  is provided with the flat surface (valve body abutment part)  221  that first makes contact with the front end surface  213  of the valve body  205  when the cylindrical fitting part  212  is press-fitted onto the front end side of the valve body  205  in the central part of the inside (the side facing the front end surface  213  of the valve body  205 ). The flat surface  221  has the plurality of nozzle holes  207  and makes contact with the periphery of the fuel injection port  204  of the valve body  205 . The bottom wall part  214  has the recessed portion  222  (which is recessed from the flat surface  221 ) radially inward of the connection portion with the cylindrical fitting part  212  to the outer edge of the flat surface  221 . The recessed portion  222  is formed inside the bottom wall part  214  so that space is generated with respect to the front end surface  213  of the valve body  205  in the state in which the flat surface  221  first makes contact with the front end surface  213  of the valve body  205 . The recessed portion  222  is formed by the tapered surface  223  extending radially outward from the outer edge of the flat surface  221  and the curved surface  225  smoothly connecting the outer edge of the tapered surface  223  to the inner peripheral surface  224  of the cylindrical fitting part  212  (see  FIG. 22A ). The valve body abutment part is not limited to the flat surface  221  and may be, for example, an annular projection in contact with the periphery of the fuel injection port  204  of the front end surface  213  of the valve body  205 . 
     The bottom wall part  214  is recessed in a central part  226  on the outside and the plurality of nozzle holes  207  are opened in the recessed central part  226 . In the bottom wall part  214 , the annular recess  227  around the inner peripheral surface  224  of the cylindrical fitting part  212  is formed in the part (thicker than the central part  226 ) disposed radially inward of the connection portion with respect to the cylindrical fitting part  212  in the area surrounding the central part  226  on the outside, so that the annular thin-walled part  228  is formed around the inner peripheral surface  224  of the cylindrical fitting part  212  (see  FIG. 22A ). The annular recess  227  has an arc-shaped cross section to prevent concentration of stress. In addition, although a total of six nozzle holes  207  are formed in the bottom wall part  214  in the embodiment, the invention is not limited to the embodiment and the optimum number of nozzle holes  207  and the optimum hole diameter may be determined according to the necessary fuel injection characteristics. 
     The nozzle plate  203  configured in this way pushes the cylindrical fitting part  212  so as to narrow the space between the recessed portion  222  in the bottom wall part  214  and the front end surface  213  of the valve body  205  from the state illustrated in  FIG. 22A  in which the flat surface  221  first makes contact with the front end surface  213  of the valve body  205  to the state illustrated in  FIG. 22B  and then the nozzle plate  203  is attached to the valve body  205  by engaging a hook  244  of the arm part  241  with a side surface  246  of the interlocking projection  240  of the valve body  205 . At this time, the bottom wall part  214  is elastically deformed easily in the annular thin-walled part  228  to make it easy to further press-fit the cylindrical fitting part  212  onto the valve body  205 . In addition, in the embodiment, as illustrated in  FIG. 22C , the cylindrical fitting part  212  can be further press-fitted (moved) onto the front end side of the valve body  205  by the amount of the space between the recessed portion  222  inside the bottom wall part  214  and the front end surface  213  of the valve body  205  (see  FIG. 22B ). Accordingly, the force caused by the elastic deformation of the annular thin-walled part  228  of the bottom wall part  214  is maintained even when the engagement state changes according to the manufacturing error of the nozzle plate  203  and the valve body  205 , the assembling error of the nozzle plate  203  and the valve body  205 , and the difference in the linear expansion coefficient between the nozzle plate  203  and the valve body  205 . 
     The pair of arm parts  241  is formed so as to project from the opening end (one end)  237  of the cylindrical fitting part  212  along the bus line of the cylindrical fitting part  212  and the pair of arm parts  241  is formed at intervals of 180 degrees in the circumferential direction of the opening end  237  of the cylindrical fitting part  212 . The arm part  241  is rectangular seen from the side of the nozzle plate  203  (seen in the direction of arrow C 203  in  FIG. 24A  and the direction of arrow C 204  in  FIG. 25A ) and entirely shaped like substantially a tongue piece. In the state in which the nozzle plate  203  is not yet attached to the valve body  205 , the outer surface  242  of the arm part  241  is flush with the outer peripheral surface  236  of the cylindrical fitting part  212  (see  FIG. 25C ). The arm part  241  includes the spring action portion  243  bent radially outward when the front end side climbs over the interlocking projection  240  of the valve body  205  and the hook  244  formed integrally with the front end side of the spring action portion  243 . 
     An inner surface  245  (surface facing the valve body  205 ) of the spring action portion  243  of the arm part  241  is placed radially outward of the inner peripheral surface  224  of the cylindrical fitting part  212  so as not to make contact with the interlocking projection  240  of the valve body  205  in the state (particularly, the state illustrated in  FIGS. 24C and 24D ) in which the nozzle plate  203  is attached to the valve body  205 . As described above, since the spring action portion  243  of the arm part  241  is thinner than the cylindrical fitting part  212  so as to be relatively elastically deformable as compared with other components. 
     The hook  244  of the arm part  241  is provided with an abutment surface  247  that snaps onto the side surface  246  of the interlocking projection  240  of the valve body  205 . The abutment surface  247  is a flat surface extending radially inward from the inner surface  245  of the spring action portion  243  and makes contact with the side surface  246  of both side surfaces of the interlocking projection  240  away from the front end surface  213  of the valve body  205  (see  FIGS. 24C and 24D ). 
     In addition, on the front end side of the hook  244  on the front end side of the arm part  241 , an engaging guide surface  248  is formed to cause the hook  244  to easily engage with the front end side of the valve body  205  and the hook  244  to easily climb over the interlocking projection  240  of the valve body  205 . The engaging guide surface  248  has one end connected to an end part of the abutment surface  247  and the other end connected to a front end surface  250  of the arm part  241 . The engaging guide surface  248  is tilted toward the outer surface  242  of the arm part  241  as moving away from the abutment surface  247 . The engaging guide surface  248  of this shape makes contact with an edge  251  of the front end of the valve body  205  and slowly bends the spring action portion  243  when the nozzle plate  203  engages with the front end side of the valve body  205 . The engaging guide surface  248  makes contact with the edge  252  of the interlocking projection  240  and slowly bends the spring action portion  243  when the hook  244  climbs over the interlocking projection  240 . As a result, the assembling of the nozzle plate  203  and the valve body  205  can be performed smoothly and easily. 
     Effect of Sixth Embodiment 
     In the attachment structure of the nozzle plate  203  according to the embodiment, if the cylindrical fitting part  212  of the nozzle plate  203  is press-fitted onto the front end side of the valve body  205 , the hook  244  of the arm part  241  climbs over the interlocking projection  240  and then snaps onto the side surface  246  of the interlocking projection  240 . When the hook  244  of the arm part  241  cannot climb over the interlocking projection  240  because of manufacturing error or the like of the nozzle plate  203  and the valve body  205 , the cylindrical fitting part  212  is moved (the cylindrical fitting part  212  is further press-fitted onto the valve body  205 ) in a direction in which the space between the recessed portion  222  of the bottom wall part  214  of the nozzle plate  203  and the front end surface  213  of the valve body  205  is narrowed, the hook  244  of the arm part  241  surely snaps onto (engages with) the interlocking projection  240 , and the nozzle plate  203  is surely fixed to the valve body  205  while being retained. Accordingly, in the attachment structure of the nozzle plate  203  according to the embodiment, it is possible to reduce the manufacturing man-hours and manufacturing cost of the fuel injection device  201  as compared with the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding (see  FIG. 29 ). In addition, in the attachment structure of the nozzle plate  203  according to the embodiment, a failure (the nozzle hole  1104  is blocked by welding spatter) does not occur unlike the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding (see  FIG. 29 ) and all nozzle holes  207  surely achieve the function of atomizing fuel. 
     Although  FIGS. 24A and 25A  illustrate an aspect in which the pair of arm parts  241  are formed along the circumferential direction of the cylindrical fitting part  212 , the invention is not limited to the aspect and at least one arm part  241  only needs to be formed in the cylindrical fitting part  212  or three or more arm parts  241  may be formed in the cylindrical fitting part  212 . 
     By chamfering (such as C-chamfering or R-chamfering) the part corresponding to the edge  252  of the interlocking projection  240  illustrated in  FIGS. 24C  and D, when the hook  244  climbs over the interlocking projection  240 , the hook  244  makes contact with the chamfered part of the interlocking projection  240  and slowly bends the spring action portion  243 . As a result, the assembling of the nozzle plate  203  and the valve body  205  can be performed easily and smoothly. 
     Seventh Embodiment 
     An attachment structure of the nozzle plate  203  according to a seventh embodiment of the invention will be described below. 
     (Attachment Structure of Nozzle Plate) 
       FIGS. 26 and 27  illustrate the attachment structure of the nozzle plate  203  according to the seventh embodiment of the invention.  FIG. 26  illustrates the front end side of the fuel injection device  201  according to the seventh embodiment of the invention.  FIG. 27  is a cross sectional view illustrating the fuel injection device  201  taken along line A 208 -A 208  in  FIG. 26B . In the description of the attachment structure of the nozzle plate  203  according to the embodiment, the duplicate description as in the nozzle plate  203  according to the fifth embodiment is omitted. 
     As illustrated in  FIGS. 26 and 27 , the nozzle plate  203  is a bottomed cylindrical body integrally having the cylindrical fitting part  212  to be pressure-fitted onto the front end side outer peripheral surface  211  of the valve body  205 , the bottom wall part  214  formed so as to block one end side of the cylindrical fitting part  212 , the bottom wall part  214  abutting against the front end surface  213  of the valve body  205 . The nozzle plate  203  according to the embodiment is made of synthetic resin as in the nozzle plate  203  according to the fifth embodiment. 
     The bottom wall part  214  is provided with the flat surface (valve body abutment part)  221  that first makes contact with the front end surface  213  of the valve body  205  when the cylindrical fitting part  212  is press-fitted onto the front end side of the valve body  205  in the central part of the inside (the side facing the front end surface  213  of the valve body  205 ). The flat surface  221  has the plurality of nozzle holes  207  and makes contact with the periphery of the fuel injection port  204  of the valve body  205 . The bottom wall part  214  has the recessed portion  222  (which is recessed from the flat surface  221 ) radially inward of the connection portion with the cylindrical fitting part  212  to the outer edge of the flat surface  221 . The recessed portion  222  is formed inside the bottom wall part  214  so that space is generated with respect to the front end surface  213  of the valve body  205  in the state in which the flat surface  221  first makes contact with the front end surface  213  of the valve body  205 . The recessed portion  222  is formed by the tapered surface  223  extending radially outward from the outer edge of the flat surface  221  and the curved surface  225  smoothly connecting the outer edge of the tapered surface  223  to the inner peripheral surface  224  of the cylindrical fitting part  212  (see  FIG. 22A ). The valve body abutment part is not limited to the flat surface  221  and may be, for example, an annular projection in contact with the periphery of the fuel injection port  204  of the front end surface  213  of the valve body  205 . 
     The bottom wall part  214  is recessed in a central part  226  on the outside and the plurality of nozzle holes  207  are opened in the recessed central part  226 . In the bottom wall part  214 , the annular recess  227  around the inner peripheral surface  224  of the cylindrical fitting part  212  is formed in the part (thicker than the central part  226 ) disposed radially inward of the connection portion with respect to the cylindrical fitting part  212  in the area surrounding the central part  226  on the outside, so that the annular thin-walled part  228  is formed around the inner peripheral surface  224  of the cylindrical fitting part  212  (see  FIG. 22A ). The annular recess  227  has an arc-shaped cross section to prevent concentration of stress. In addition, although a total of six nozzle holes  207  are formed in the bottom wall part  214  in the embodiment, the invention is not limited to the embodiment and the optimum number of nozzle holes  207  and the optimum hole diameter may be determined according to the necessary fuel injection characteristics. 
     The nozzle plate  203  configured in this way pushes the cylindrical fitting part  212  so as to narrow the space between the recessed portion  222  in the bottom wall part  214  and the front end surface  213  of the valve body  205  from the state illustrated in  FIG. 22A  in which the flat surface  221  first makes contact with the front end surface  213  of the valve body  205  to the state illustrated in  FIG. 22B  and then the nozzle plate  203  is attached to the valve body  205  by interposing a U-ring  254  between a groove wall  268  of an arm part engaging groove portion  260  and the groove wall  270  of an interlocking groove  253 . At this time, the bottom wall part  214  is elastically deformed easily in the annular thin-walled part  228  to make it easy to further press-fit the cylindrical fitting part  212  onto the valve body  205 . In addition, in the embodiment, as illustrated in  FIG. 22C , the cylindrical fitting part  212  can be further press-fitted (moved) onto the front end side of the valve body  205  by the amount of the space between the recessed portion  222  inside the bottom wall part  214  and the front end surface  213  of the valve body  205  (see  FIG. 22B ). Accordingly, the force caused by the elastic deformation of the annular thin-walled part  228  of the bottom wall part  214  is maintained even when the engagement state changes according to the manufacturing error of the nozzle plate  203  and the valve body  205 , the assembling error of the nozzle plate  203  and the valve body  205 , and the difference in the linear expansion coefficient between the nozzle plate  203  and the valve body  205 . 
     The cylindrical fitting part  212  is cylindrical and has an inner diameter slightly smaller than the outer diameter of the valve body  205  so as to be press-fitted onto the front end side of the valve body  205 . The cylindrical fitting part  212  has one end side blocked by the bottom wall part  214  and the other end side opened so as to receive the front end side of the valve body  205 . In the valve body  205  onto which the cylindrical fitting part  212  is to be press-fitted, the interlocking groove  253  is formed in the outer peripheral surface  211  on the front end side. The interlocking groove  253  of the valve body  205  has a rectangular recessed cross section taken along the central axis  220  of the valve body  205  (see  FIGS. 26C  and D). 
     The cylindrical fitting part  212  is provided with a ring attachment groove  255  to which the U-ring (fixing ring)  254  is attached. The ring attachment groove  255  includes an arc part engaging groove portion  257  with which an arc part  256  of the U-ring  254  engages and the pair of arm part engaging groove portions  260  and  260  with which a pair of arm parts  258  and  258  extending in parallel from both ends of the arc part  256  of the U-ring  254  (see  FIG. 27 ). The depth of the arc part engaging groove portion  257  is almost the same as the wire diameter of the U-ring  254  and the arc part engaging groove portion  257  extends like an arc to the pair of arm part engaging groove portions  260  and  260  around the outer peripheral surface  236  of the cylindrical fitting part  212 . The pair of arm part engaging groove portions  260  and  260  is provided with a window  261  in the groove bottom for exposure of the valve body  205 . The window  261  formed in the bottom of the arm part engaging groove portion  260  exposes a part of the valve body  205  to the inside of the ring attachment groove  255  so that a valve body pushing portion  262  of the U-ring  254  attached to the arm part engaging groove portion  260  can make contact with a groove bottom  263  of the interlocking groove  253  of the valve body  205 . In addition, the pair of arm part engaging groove portions  260  and  260  is formed substantially in parallel with the X-axis when the virtual plane orthogonal to a central axis  264  of the cylindrical fitting part  212  (nozzle plate  203 ) is assumed to be the X-Y plane as illustrated in  FIG. 27 , and the pair of arm part engaging groove portions  260  and  260  is formed symmetrically with respect to a center line  265  orthogonal to the central axis  264  of the cylindrical fitting part  212 . A connection portion  266  between the arc part engaging groove portion  257  and the arm part engaging groove portion  260  is formed as a smoothly curved surface and functions as a guide surface for inserting the front ends of the arm parts  258  of the U-ring  254  into the arm part engaging groove portions  260  and smoothly guides the front ends of the arm parts  258  of the U-ring  254  into the arm part engaging groove portions  260 . 
     The ring attachment groove  255  of the cylindrical fitting part  212  is formed to have a groove width larger than the wire diameter of the U-ring  254 . The ring attachment groove  255  of the cylindrical fitting part  212  is positioned slightly closer to the bottom wall part  214  than the interlocking groove  253  of the valve body  205  in the state in which the nozzle plate  203  is press-fitted onto the front end side of the valve body  205  and the flat surface  221  of the bottom wall part  214  of the nozzle plate  203  makes contact with the front end surface  213  of the valve body  205 . In addition, since the cylindrical fitting part  212  is provided with the ring attachment groove  255 , a thin-walled U-ring supporting portion  267  having substantially a C-ring shape in plan view is formed in the part close to the opening end  237  of the cylindrical fitting part  212 . When the U-ring  254  is attached to the ring attachment groove  255  of the cylindrical fitting part  212  in the state in which the nozzle plate  203  is press-fitted onto the front end side of the valve body  205  and the flat surface  221  of the bottom wall part  214  of the nozzle plate  203  makes contact with the front end surface  213  of the valve body  205 , the U-ring  254  is interposed between the groove wall  268  of the arm part engaging groove portion  260  and a groove wall  270  of the interlocking groove  253  while elastically deforming the U-ring supporting portion  267  and U-ring  254  is pushed against the groove wall  270  of the interlocking groove  253  by the elastic force of the U-ring supporting portion  267 . However, when the space between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253  is too small due to manufacturing error and the like in the nozzle plate  203  and the valve body  205 , the U-ring  254  is not interposed between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253 . In such a case, when the cylindrical fitting part  212  is moved (further press-fitted onto the valve body  205 ) in a direction in which the space between the recessed portion  222  of the bottom wall part  214  of the nozzle plate  203  and the front end surface  213  of the valve body  205  is narrowed, the ring attachment groove  255  goes away from the front end surface  213  of the valve body  205 , the space between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253  can be widened, and the U-ring  254  can be easily interposed between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253 . 
     The U-ring  254  is formed by bending an elastically deformable metal wire having a circular cross section. The U-ring  254  integrally has the arc part  256  and the pair of arm parts  258  and  258  extending substantially in parallel from both ends of the arc part  256 . In addition, the arm part  258  of the U-ring  254  has the valve body pushing portion  262  formed like an arc along the groove bottom shape of the interlocking groove  253  of the valve body  205 . The U-ring  254  as described above is attached to the ring attachment groove  255  of the cylindrical fitting part  212  and the interlocking groove  253  of the valve body  205  in the state in which the U-ring  254  is elastically deformed to widen the space between the pair of arm parts  258  and  258 , elastically pinches the valve body  205  between both ends in the radial direction using the valve body pushing portions  262  and  262  of the pair of arm parts  258  and  258 , and is sandwiched between the groove wall  268  of the ring attachment groove  255  of the cylindrical fitting part  212  and the groove wall  270  of the interlocking groove  253  of the valve body  205 . This surely fixes the nozzle plate  203  to the front end side of the valve body  205  while being retained. 
     Effect of Seventh Embodiment 
     In the attachment structure of the nozzle plate  203  according to the embodiment, if the cylindrical fitting part  212  of the nozzle plate  203  is fitted onto the front end side of the valve body  205  and the U-ring  254  is attached to the ring attachment groove  255  of the nozzle plate  203 , the U-ring  254  is interposed between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253  while elastically deforming the U-ring supporting portion  267 . However, when the space between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253  is too small to interpose the U-ring  254  between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253 , only if the cylindrical fitting part  212  is moved in a direction in which the space between the recessed portion  222  of the bottom wall part  214  of the nozzle plate  203  and the front end surface  213  of the valve body  203  is narrowed, the space between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253  is widened, the U-ring  254  can be easily interposed between the groove wall  268  of the arm part engaging groove portion  260  and the groove wall  270  of the interlocking groove  253 , and the nozzle plate  203  can be surely fixed to the valve body  205  while being retained. Accordingly, in the attachment structure of the nozzle plate  203  according to the embodiment, it is possible to reduce the manufacturing man-hours and manufacturing cost of the fuel injection device  201  as compared with the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding (see  FIG. 29 ). In addition, in the attachment structure of the nozzle plate  203  according to the embodiment, a failure (the nozzle hole  1104  is blocked by welding spatter) does not occur unlike the conventional example in which the nozzle plate  1103  of metal is fixed to the front end of the valve body  1102  of metal by welding (see  FIG. 29 ) and all nozzle holes  207  surely achieve the function of atomizing fuel. 
     In an aspect of attachment structure of the nozzle plate  203  according to the embodiment, the U-ring  254  is illustrated as a fixing ring and the nozzle plate  203  is fixed to the valve body  205  while being retained by the U-ring  254 . However, the invention is not limited to the aspect, a C-ring or E-ring may be used as the fixing ring and the nozzle plate  203  is fixed to the valve body  205  while being retained using a C-ring or E-ring. 
     Modification of Fifth to Seventh Embodiments 
       FIG. 28  illustrates a modification of the attachment structure of the nozzle plate  203  according to the fifth to seventh embodiments of the invention, more specifically a modification of the bottom wall part  214  of the nozzle plate  203 . As illustrated in  FIG. 28 , in this modification, in a part radially inward of the connection portion with respect to the cylindrical fitting part  212  in the area surrounding the central part  226  on the outside, the bottom wall part  214  of the nozzle plate  203  has the plurality of annular recesses  227  formed concentrically around the inner peripheral surface  224  of the cylindrical fitting part  212  and the plurality of thin-walled parts  228  formed concentrically around the inner peripheral surface  224  of the cylindrical fitting part  212 . Accordingly, the outer peripheral part (the part close to the cylindrical fitting part  212 ) of the bottom wall part  214  is elastically deformed in multiple stages and this elastic deformation is larger than in the bottom wall part  214  of the nozzle plate  203  according to the fifth to seventh embodiments. 
     In addition, as illustrated in  FIG. 28 , when the flat surface  221  (valve body abutment part) first makes contact with the front end surface  213  of the valve body  205 , space is generated between the recessed portion  222  of the bottom wall part  214  of the nozzle plate  203  and the front end surface  213  of the valve body  205  and this space is larger than the space between the recessed portion  222  of the bottom wall part  214  of the nozzle plate  203  according to the fifth to seventh embodiments and the front end surface  213  of the valve body  205 . The recessed portion  222  includes a tapered surface  271  extending radially outward from the outer edge of the flat surface  221  and an annular groove surface  272  connecting the outer edge of the tapered surface  271  to the inner peripheral surface  224  of the cylindrical fitting part  212 . The annular groove surface  272  included in the recessed portion  222  has a depth (depth from the flat surface  221 ) large enough to prevent the annular groove surface  272  from making contact with the edge  273  on the front end side of the valve body  205  even when deformation is made until the tapered surface  271  makes contact with the front end surface  213  of the valve body  205 . 
     REFERENCE SIGNS LIST 
     
         
           1 ,  101 ,  201 : fuel injection device 
           3 ,  103 ,  203 : nozzle plate (fuel injection device nozzle plate) 
           4 ,  104 ,  204 : fuel injection port 
           5 ,  105 ,  205 : valve body 
           7 ,  107 ,  207 : nozzle hole 
           8 ,  240 : interlocking projection 
           10 ,  110 ,  210 ,  241 : arm part 
           12 ,  112 ,  212 : cylindrical fitting part 
           13 ,  113 ,  213 : front end surface 
           14 ,  114 ,  214 : bottom wall part 
           108 ,  208 : interlocking groove