Abstract:
It is an object of the invention to provide a method of working an injection hole of an electromagnetic type fuel injection valve so that when extrusion by using a punch is adopted, the punch does not break, even in the case where a central axis line of the injection hole of the electromagnetic type fuel injection valve is inclined to a line perpendicular to a face of a plate-like material to be punched. A front end, tapered portion of the punch is inclined in a direction opposed to a plate-like material relative to a central axis line of the punch to facilitate the punch along a sliding, inner face of a punch holder. While achieving a reduction in production cost, the divergent-shaped injection hole can accurately be formed in the plate-like material. A side force (Fs) is produced when the front end portion of the punch impinges on the plate-like material. The side force (Fs) is canceled by a reaction force (Fr) on a side opposed to the plate-like material and a bending moment potentially causing breakage of the punch is avoided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on an incorporates herein by reference Japanese Patent Application No. 2000-303137 filed on Oct. 3, 2000. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of working an injection hole of a fuel injection nozzle plate of a fuel injection valve for injecting fuel into an internal combustion engine. The injection hole having a diverging shape with an increasingly larger diameter from a fluid inlet to a fluid outlet. 
     2. Description of the Related Art 
     Generally known in the art is an electromagnetic type fuel injection valve arranged with a thin plate having a plurality of injection holes on a downstream side of a fuel valve portion. The fuel injection valve portion further possesses a nozzle needle and a valve seat of a valve body for injecting fuel from the respective injection holes. It is conventional that the injection holes formed in a plate for fuel injection are provided with a diameter which stays the same from a fuel inlet to a fuel outlet, however, according to U.S. Pat. No. 4,907,748, there is shown a plate with an injection hole formed in a diverging shape, that is, injection holes that increase in diameter from the fuel inlet to the fuel outlet. 
     In recent years, there has been expedited needs for highly small particle formation of sprayed fuel in an electromagnetic type fuel injection valve and there has been requested high precision working of an injection hole formed in a orifice plate integrated to a front end face of a valve body to close an opening formed at a front end portion of the valve body. Heretofore, small particle formation of sprayed fuel in an electromagnetic type fuel injection valve has been dealt with by miniaturization and large angle formation of an injection hole. 
     However, as a method of working an injection hole for forming an injection hole in a diverging shape in a plate-like material, removal machining such as electric discharge machining (EDM) has been used which takes a working time period of several tens of seconds. Experience with EDM proves that the dimensional accuracy is poor as is the accuracy of a flow rate of sprayed fuel. At the same time, when the number of electric discharge machines is increased for the purpose of producing a number of parts to meet market demands, large expenses are required in plant and equipment investment resulting in increased production costs. 
     Hence, there is conceivable a method of extrusion using a punch for working an injection hole which is capable of resolving the above-described problem. However, when a central axis line of an injection hole is at an angle to a line perpendicular to a face of a plate-like material before working the desired injection hole, there is a possibility of breaking the punch due to the existence of a side force exerted on the punch when the front end of the punch impinges on the plate-like material (this is a force orthogonal to the central axis line of the punch). Therefore, it has been difficult to adopt extrusion methods using a punch as the method of working the injection hole. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to realize a method of working an injection hole of a fluid injection nozzle capable of reducing production costs and capable of increasing productivity. Further, it is an object to achieve dimensional accuracy of the injection hole and accuracy of a fluid flow rate which has not been achievable by removal working methods such as electric discharge machining (EMD) or press-punching. Further, it is an object to realize an apparatus of working an injection hole of a fluid injection nozzle in which even when extrusion using a punch is adopted, the punch will not break. 
     According to a first aspect of the invention, there is adopted an apparatus of working an injection hole of a fluid injection nozzle having a die mounted with a plate-like material, a punch substantially in the shape of a truncated circular cone, a shape of a front end portion of which is provided with a first inclination angle and a second inclination angle relative to a line perpendicular to a face of the plate-like material, a punch guide having a support hole slidably supporting the punch such that a central axis line of the punch is inclined to a perpendicular line of the face of the plate-like material, and punch driving means for advancing the punch in a direction of a central axis line of the punch guide. 
     Further, when a central axis line of the injection hole is inclined to a perpendicular line of the plate-like material face, by using a die structure capable of receiving a side force at a front end portion of the punch produced by working the injection hole, an inner face of the injection hole can be provided with a uniform face condition. That is, the face condition will be uniform over an entire region of the inner face of the injection hole without producing a broken face as in conventional press-punching. Therefore, a method is realized whereby working an injection hole of a fluid injection nozzle reduces production costs and improves productivity. 
     Further, by adopting extrusion using the punch, dimensional accuracy and accuracy in a flow rate is achievable. Accuracy and flow rates are not achievable by removal working methods such as electric discharge machining or press-punching. Further, the side force (force in a direction orthogonal to a central axis line of the punch) evident when the front end portion of the punch reaches the injection hole, can be opposed by a sliding face of the punch guide on a side opposed to the plate-like material. The side force is canceled by a reaction force, therefore a bending moment for breaking the punch is not created. Therefore, the punch is not broken by the side force produced when the front end portion of the punch reaches the injection hole. 
     According to a second aspect of the invention, a sliding face of the punch guide on which the front end portion of the punch slides is provided with the first inclination angle relative to the perpendicular line of the face of the plate-like material. The shape of the front end portion of the punch is constituted by a shape along the sliding face of the punch guide by inclining the front end portion of the punch guide in a direction opposed to a direction of the plate-like material relative to the central axis line of the punch. An effect (material removal effect) similar to that of the invention described in the first aspect can further be expected. 
     According to a third aspect of the invention, in working (forming) the injection hole, in a state in which the plate-like material is held between the die and the punch guide, there is carried out extrusion by pressing the front end portion of the punch into the plate-like material by advancing the punch along the central axis line of the punch guide in the direction of the plate and extruding a volumetric portion which the front end portion of the punch contacts as the punch progresses. The shape of the front end portion of the punch penetrates the plate-like material to thereby form the injection hole having the desired punch shape. An effect similar to that of the invention described in the first aspect can be expected to a further degree. 
     According to a fourth aspect of the invention, there are provided press dies setting a clearance between the front end portion of the punch and the die in a predetermined range relative to a plate thickness of the plate-like material. Further, the plate-like material is formed with the desired shape of the injection hole by executing a step of removing an extruded volumetric portion, which the front end portion of the punch presses and expels after the extrusion, by cutting, machining, or grinding the extruded portion at a level consistent with the face of the plate-like material. 
     According to a fifth aspect of the invention, there are provided press dies setting a clearance between the front end portion of the punch and the die to be equal to or smaller than a predetermined value. Further, the desired shape of the injection hole is formed in the plate-like material by pressing the punch until the extruded volumetric portion, which the front end portion of the punch presses to exclude, is separated from the plate-like material in the extrusion. The removing step is abolished and therefore, production costs are reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a schematic view showing a method of working an injection hole of an electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 1B is a schematic view showing a method of working an injection hole of an electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 2 is a cross-sectional view of the electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 3A is an enlarged cross-sectional view showing a fuel injection nozzle of the electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 3B is a plan view showing a plate with an injection hole viewed from a fuel inlet side according to an embodiment of the invention; 
     FIG. 4A is a plan view showing a shape of an injection hole of the plate according to an embodiment of the invention; 
     FIG. 4B is a cross-sectional view showing the shape of the injection hole of the plate according to an embodiment of the invention; 
     FIGS. 5A through 5C are schematic views showing a method of forming an injection hole of an electromagnetic type fuel injection valve (comparison example); 
     FIG. 6A is a schematic view showing an example of a prior art punch being forced into a plate with the resulting force being indicated (comparison example); 
     FIG. 6B is a schematic view showing an example of a prior art punch breaking as a result of the force in FIG. 6A (comparison example); 
     FIG. 7 is a schematic view showing a method of working an injection hole of the electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 8A is a schematic view showing a method of forming an injection hole of the electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 8B is a cross-sectional view taken along line VIIIB—VIIIB of FIG. 8A according to an embodiment of the invention; 
     FIG. 9A is a schematic view showing a method of forming an injection hole of the electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 9B is a schematic view showing a method of forming an injection hole of the electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 10 is a schematic view showing a method of forming an injection hole of an electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 11 is a schematic view showing a method of forming an injection hole of an electromagnetic type fuel injection valve according to an embodiment of the invention; 
     FIG. 12A is an enlarged sectional view showing a fuel injection nozzle of an electromagnetic type fuel injection valve according to an embodiment of the invention; and 
     FIG. 12B is a plane view showing a plate with an injection hole viewed from a fuel inlet side according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG.  1 A through FIG. 9B show an embodiment of the invention, FIG. 2 is a cross-sectional view showing an example of applying a fuel injection nozzle to an electromagnetic type fuel injection valve of a gasoline engine, FIG. 3A is a view showing a fuel injection nozzle of the electromagnetic type fuel injection valve and FIG. 3B is a view showing a plate with and injection hole viewed from a fuel inlet side. 
     An electronically controlled fuel injection apparatus of an embodiment of the present invention comprises sensors for detecting a fuel supply system, an intake system, and an operating state of an internal combustion engine. Additionally, an electronic control unit (ECU) is provided for governing and controlling these components. Among them, the fuel supply system is a system capable of; 1) pressurizing fuel to a constant pressure by utilizing an electric type fuel pump (not illustrated); 2) delivering the fuel to an electromagnetic type fuel injection valve  1  (FIG. 2) via a delivery pipe (not illustrated); and 3) injecting the fuel at optimum timings. 
     The electromagnetic type fuel injection valve  1  is a fuel injector having a function of expediting a small particle formation of sprayed fuel (from a plate with an injection hole(s)) sprayed to a vicinity (intake port) of an intake valve (suction valve) in an internal combustion engine such as a gasoline engine (hereinafter, referred to as “engine”) with proper and efficient timings. Further, a number of the electromagnetic type fuel injection valves  1  in accordance with a number of cylinders of the engine, are integrated into an intake manifold (intake pipes) which supply air for internal combustion. 
     With continued reference to FIG. 2, the electromagnetic type fuel injection valve  1  is composed of a housing mold  2 , an electromagnetic coil (solenoid coil)  4  wound around an outer periphery of a coil bobbin  3  made of resin arranged in the housing mold  2 , a fixed core (stator)  5  substantially in a cylindrical shape fixed in the housing mold  2 , a movable core (armature)  6  movable in the axial direction, a valve body  7  provided at a front end side of the housing mold  2 , a nozzle needle  8  contained in the valve body  7  and a plate with injection hole (orifice plate)  10  forming a fuel path  9  between the orifice plate  10  and one end face (front end face) of the nozzle needle  8  in the axial direction. 
     The housing mold  2  is integrally molded with a resin material. At an inside of the housing mold  2 , the coil bobbin  3  and the fixed core  5  and an outside connecting terminal (terminal)  11  are integrally molded. Further, at an outer periphery of the coil bobbin  3  and the electromagnetic coil  4 , a resin mold  55  surrounding the electromagnetic coil  4  is integrally molded. Further, at an upper side of the housing mold  2 , there is provided a connector portion  12  that projects from an outer wall of the housing mold  2  at a predetermined inclination angle. Further, the outside connecting terminal (terminal)  11  electrically connected to the electromagnetic coil  4 , is embedded in the connector portion  12  and a resin mold  56 . Further, the outside connecting terminal  11  is connected to an ECU, not illustrated, via a wire harness. 
     The fixed core  5  is composed of a ferromagnetic material and is provided in the resin housing mold  2  to project upwardly from an upper end face of the housing mold  2 . Further, at an inside of the fixed core  5 , a fuel path  13  is formed in the axial direction. At an inner peripheral face of the fixed core  5 , there is provided an adjusting pipe  15  substantially in a cylindrical shape having an axial hole  14 . The adjusting pipe  15  sets a load (valve opening pressure) of a coil spring  16  by displacing the spring  16  in the axial direction at an inside portion of the fixed core  5  and is fixed to the inner peripheral face of the fixed core  5  after setting the adjusting pipe  15 . 
     Furthermore, with continued reference to FIGS. 2 and 3A, one end of the coil spring  16  is brought into contact with a front end face of the adjusting pipe  15 . The other end of the coil spring  16  is brought into contact with the movable core  6  which is fixedly welded to an upper end face of the nozzle needle  8 . The coil spring  16  seats a seat portion  22  of the nozzle needle  8  on a valve seat  21  of the valve body  7  by urging the movable core  6  and the nozzle needle  8  to a lower portion of the electromagnetic type fuel injection valve  1 . Further, when excitation current flows from the outside connecting terminal  11  to the electromagnetic coil  4  by ECU, the movable core  6  and the nozzle needle  8  are sucked in the direction of the fixed core  5 , against the spring force of the coil spring  16 . 
     Further, one side of the fixed core  6  in the axial direction is arranged with a nonmagnetic pipe  17  and a magnetic pipe  18 . The nonmagnetic pipe  17  is composed of a nonmagnetic material and is formed substantially in a cylindrical shape. The nonmagnetic pipe  17  is connected to a lower end of the fixed core  5 . Further, the magnetic pipe  18  is composed of a magnetic material and is formed using stepped portions. The magnetic pipe  18  is connected to a lower end of the nonmagnetic pipe  17 . A space inward from the nonmagnetic pipe  17  and the magnetic pipe  18  houses the movable core  6  comprising a magnetic material and formed in a cylindrical shape. 
     Further, the valve body  7  is laser welded into the magnetic pipe  18 , after facilitating the insertion of the valve body  7  with a hollow, circular disk spacer  19 , which abuts the magnetic pipe  18 . A thickness of the spacer  19  is adjusted to maintain an air gap between the fixed core  5  and the movable core  6  at a predetermined value. Here, an electromagnetic type actuator is composed of the housing mold  2 , the electromagnetic coil  4 , the fixed core  5 , the movable core  6 , the nonmagnetic pipe  17 , the magnetic pipe  18  and so forth. 
     Next, a simple explanation pertaining to the structures of the valve body  7  and the nozzle needle  8  according to the embodiment of FIGS. 2-3B will be provided. The valve body  7  and the nozzle needle  8  are formed in predetermined shapes by a metal material such as SUS. Further, inside of the valve body  7 , there is formed a fluid fuel path  20 . There is formed a clearance for passing fuel between a cylindrical face  23  of the valve body  7  and four faced portions formed at a sliding portion  24  of the nozzle needle  8 . Further, a valve portion is composed of the valve seat  21  of the valve body  7  and the seat portion  22  at a front end of the nozzle needle  8 . 
     The nozzle needle  8  is a valve member for closing the fuel path  20  by being seated on the valve seat  21  of the valve body  7  and opening the fuel path  20  by separating from the valve seat  21 . Shown in FIG. 2, a coupling portion  25  is formed at an upper portion of the nozzle needle  8 . Further, by laser welding the coupling portion  25  and the movable core  6 , the movable core  6  and the nozzle needle  8  are integrally connected. An outer periphery of the coupling portion  25  is faced to accommodate a fuel path. Further, when the movable core  6  is attracted by the fixed core  5  by generating a magnetomotive force in the electromagnetic coil  4 , the nozzle needle  8  is lifted until a flange portion  26  is brought into contact with the spacer  19 . 
     Here, a valve main body of the electromagnetic type fuel injection valve  1  is composed of the valve body  7  and the orifice plate  10  and the valve member of the electromagnetic type fuel injection valve  1  is composed of the nozzle needle  8 . Additionally, a filter  57  is mounted to an upper side of the fuel path  13  formed in the fixed core  5 . The filter  57  removes foreign matter such as dust and dirt in pressurized fuel from a fuel tank. The fuel, pressurized by a fuel pump, flows into the electromagnetic type fuel injection valve  1 . Further, a detachment preventive member  58  of an O-ring  54  is mounted to an upper end portion of the fixed core  5 . 
     Next, a simple explanation will be given pertaining to the structure of the orifice plate  10  according to the embodiment of FIG.  2  through FIG.  4 B. Here, FIGS. 4A and 4B are views showing a shape of an injection hole of the orifice plate. 
     With reference to FIG. 3A, the orifice plate  10  is fixed to a front end face of the valve body  7 , by using welding means such as laser welding, to close an opening  29  in the shape of a circular hole formed in the valve body  7 . The orifice plate  10  is composed of a metal material such as SUS. Further, FIG. 3B shows that orifice plate  10  is formed with a plurality of injection holes (orifices)  30   a  through  30   d  for controlling directions of spray fuel and expediting small particle formation of spray fuel. Four of the injection holes  30   a  through  30   d  are of a tapered shape formed by a single step of pressing according to the invention and arranged on an imaginary line of one circle centering on a central axis line of the orifice plate  10  of the electromagnetic type fuel injection valve  1 . 
     FIG. 3A shows the plurality of injection holes  30   a  through  30   d  are respectively formed to perforate the orifice plate  10  to be directed from fuel inlets  31  to fuel outlets  32 . Additionally, the injection holes  30   a  through  30   d  are inclined in a direction so that the central axis line of the electromagnetic type fuel injection valve  1  is closest to an upstream side relative to a direction of flowing fuel of the fuel path  9  that flows through the injection holes  30   a  through  30   d . The injection holes  30   a  through  30   d  are manufactured at a predetermined inclination angle and gradually widened (tapered) from the fuel inlets  31  to the fuel outlets  32 . That is, each of the injection holes  30   a  through  30   d  is a passage that diverges or gradually widens from the fuel inlet  31  to the fuel outlet  32 . 
     Further, with reference to FIG. 4B, the respective injection holes  30   a  through  30   d  are formed to depart from a perpendicular line (central axis line)  33  orthogonal to a face of the orifice plate  10  toward a desired fuel injection direction. Shapes and sizes of the respective injection holes  30   a  through  30   d  are the same and magnitudes of θ 1 , θ 2  and θ 3 , discussed later, are equal to each other with respect to each respective injection hole. The injection holes  30   a - 30   d  are respectively formed in the same directions relative to the central axis line  33  of the orifice plate  10 . A direction of injecting fuel from the injection holes  30   a  and  30   b  and a direction of injecting fuel from the injection holes  30   c  and  30   d , are oppositely directed by 180° and the electromagnetic type fuel injection valve  1  carries out injection in two directions. 
     Now, typical angles of the injection holes  30   a - 30   d  of the orifice plate  10  will be denoted. Here, as shown by FIG. 4B, an intersection between an imaginary face including an injection hole central axis line  34  and orthogonal  33  to the orifice plate  10  will be used to identify specific angles. For instance, an injection hole inner face  35  of the orifice plate  10 , a first inclination angle formed by a first intersection  36  on a side of an obtuse angle formed by the injection hole central axis line  34  and a fuel inlet side end face  38  of the orifice plate  10 , and the central axis line  33 , is designated by notation θ 1 . A second inclination angle formed by a second intersection  37  on a side of an acute angle formed by the injection hole central axis line  34  and the fuel inlet side end face  38  of the orifice plate  10 , and the central axis line  33 , is designated by notation θ 2 . Then, there is provided a relationship of θ 1 &lt;θ 2 . That is, in each of the respective injection holes  30   a  through  30   d , the injection hole inner peripheral face  35  remote from the central axis line  33  of the orifice plate  10  relative to the injection hole central axis line  34 , is inclined to the central axis line  33  more than the injection hole inner peripheral face  35  proximate to the central axis line  33  of the orifice plate  10  relative to the injection hole central axis line  34 . 
     Further, when the first inclination angle is designated by notation θ 1 , θ 1 =15° through 45° or θ 1  is equal to or larger than 15°. Further, when notation θ 3  designates θ 2 −θ 1 , θ 3 =15° through 30° or θ 3  is equal to or larger than 15°. Further, when a plate thickness of the orifice plate  10  is designated by notation t, t=0.05 through 0.20 mm or t is equal to or larger than 0.05 mm. 
     Next, a simple explanation will be given to operation of the electromagnetic type fuel injection valve  1  according to the embodiment depicted in FIGS. 2 through 4B. 
     When electricity flows to the electromagnetic coil  4  of the electromagnetic type fuel injection valve  1  by ECU, the movable core  6  is drawn by the fixed core  5  against the force of the coil spring  16  and the nozzle needle  8  the coupling portion  25  of which is laser welded to the movable core  6 . The movable core  6  is lifted until the flange portion  26  is brought into contact with the spacer  19 . Then, the valve portion comprising the valve seat  21  of the valve body  7  and the seat portion  22  of the nozzle needle  8 , is opened. Thereby, fuel flowing into the fuel path  13  formed in the fixed core  5  of the electromagnetic type fuel injection valve  1  via the filter  57  by way of the delivery pipe after having been pressurized to a constant pressure by a fuel pump, passes from the axial hole  14  formed in the adjusting pipe  15  through a clearance at two faced portions formed at the coupling portion  25  of the nozzle needle  8 . 
     Further, fuel passes through the clearance between the cylindrical face  23  of the valve body  7  and the four faced portions formed at the sliding portion  24  of the nozzle needle  8  and reaches the fuel path  9  between the valve seat  21  of the valve body  7  and the seat portion  22  of the nozzle needle  8 . Further, fuel which passes between the valve seat  21  and the seat portion  22 , impinges on a path wall face of the orifice plate  10  inside of the fuel path  9  and flows along the path wall face of the orifice plate  10 . Further, fuel which flows from the fuel path  9  to the fuel inlets  31  of the injection holes  30   a  through  30   d , flows from inside of the fuel path  9  toward path wall faces of the injection holes  30   a  through  30   d  without producing vortices around the fuel inlets  31  of the injection holes  30   a  through  30   d  and is injected from the fuel outlets  32  of the injection holes  30   a  through  30   d  to the intake valves of the engine with appropriate timing consistent with combustion requirements. 
     Next, an explanation will be given which pertains to a method of working the injection hole of the electromagnetic type fuel injection valve according to the embodiment referenced in FIGS.  1 A through FIG.  9 B. Here, FIG.  5 A through FIG. 5C are process views showing the method of forming or working the injection hole of the electromagnetic type fuel injection valve (a comparative example). 
     Here, an apparatus of working the injection hole of the orifice plate  10 , is provided with a successive feed apparatus for successively feeding a plate-like material  40  in the shape of a roll comprising a metal material such as SUS. The apparatus additionally comprises the orifice plate  10  housing an injection hole and having the plate thickness of “t” (FIG.  1 A), press dies comprising an upper die and a lower die and an upper die drive apparatus for driving the upper die (not shown). 
     Continuing with reference to FIG. 1A, the upper die of the plate dies is provided with a punch  41  a central axis line of which is inclined to a central axis line  33  which is orthogonal to the face of the plate-like material, and a punch holder  42  (also serving as a punch guide according to the invention) for reciprocally supporting the punch  41 . The punch  41  is supported in the direction of its central axis line and the lower die  43  of the press dies is provided for sandwiching and holding the plate-like member  40  between the die  43  and the punch holder  42  after the plate-like member  40  has been fed onto the end face of die  43 . Further, with reference to FIGS. 5A-5C, a front end portion of the punch  41  is formed with a tapered portion  44  constituting a diverging (tapered) shape which is the same as that of the injection hole  30  for transcribing a predetermined shape of the injection hole  30 . 
     First, in the press dies, by moving the punch  41  in its axial direction (provided with a predetermined inclination angle relative to the plate-like material  40 ) by the punch drive apparatus (punch driving means), the tapered portion  44  of the punch  41  is pressed into the plate-like material  40  fed by the successive feed apparatus. The shape of the front end portion of the punch  41  is transcribed to the plate-like material  40  (refer to FIG.  5 A). 
     Then, at a face opposed to the face of the plate-like material  40  to which the tapered portion  44  of the punch  41  is pressed, there remains a useless portion  45  of a volume of plate material which the tapered portion  44  of the punch  41  excludes. Next, the useless portion  45  is removed at a height position consistent with the surface of the plate-like material  40  (FIGS.  5 B and  5 C). This results in the formation of the injection hole  30  having a desired shape, that is, the diverging (tapered) shape in which the diameter is widened from the fuel inlet  31  to the fuel outlet  32  (FIG.  5 C). 
     According to the method of working the injection hole  30 , an inner face of the injection hole  30  is provided with a face condition which is uniform over an entire region of the inner face of the injection hole  30  without producing a broken face as in press-punching. Thereby realized is the method of working the injection hole at a low cost and with high productivity, compared to other methods, and there is achieved a dimensional accuracy or accuracy of material removal which has not been able to achieve by removal working such as electric discharge machining or press-punching. Additionally, fluid flow rates through the injection hole  30  are more accurate as a result of the material removal method. 
     Further, the plate-like material  40  is rotated on the lower die, or a pressing machine is shifted such that the injection holes are perforated by a number of punches  41 , arranged at the orifice plate  10 . By repeating the injection hole forming, the orifice plate  10  having the injection holes  30  each in the tapered shape, gradually widening from the fuel inlet  31  to the fuel outlet  32 , can be produced in a quantity to meet market needs. 
     Here, when the central axis line (injection hole central axis line  34 ) of the injection hole  30  of the electromagnetic type fuel injection valve  1  is inclined to the line orthogonal to the face of the plate-like material  40 , as shown by FIG. 6A, FIG. 6B shows that there is a possibility of breaking the punch  41  by a side force Fs (force in a direction orthogonal to the central axis line of the punch  41 ). The force Fs is produced when the front end portion of the punch  41  impinges on the plate-like material  40 , that is, in working or forming the injection hole  30 . In this case, by adopting a press die structure shown by FIGS. 1A,  1 B and  7 , the tapered inclined hole is formed to penetrate the plate-like material  40  by a single step of pressing without breaking the punch  41 . That is, the front end tapered portion  46  is inclined in such a way so that it is coincident with the punch  41  periphery and parallel to a central axis line  52  of the punch  41  to thereby constitute a shape consistent with the sliding face  47  (inner face) of the punch holder  42  (FIG.  7 ). 
     With reference to FIG. 1A, the tapered portion  46  of the punch  41  is provided with a tapered inclined shape (substantially a shape of an elliptic cone) having a first inclination angle θ 1  and a second inclination angle θ 2  relative to the central axis line  33  orthogonal to the face of the plate-like material  40 . Further, FIG. 7 shows that the punch holder  42  is formed with a support hole  47  for covering a total periphery of the punch  41  and slidably supports the punch  41  in a direction consistent with a central axis line  52  of the punch holder  42  such that the central axis line  51  of the punch  41  is inclined. Further, on an inner face of the punch holder  42 , a sliding face on which the tapered portion  46  of the punch  41  slides, is provided with the first inclination angle θ 1  relative to the central axis line  33  of the orifice plate  10  which is orthogonal to the face of the plate-like material (FIG.  1 A). Further, a discharge hole  48  capable of discharging the useless portion  45  is formed at the die  43  the upper end face of which is mounted with the plate-like material  40  in a direction conducive to a central axis line  53  of the die  43 . 
     Further, as shown by FIGS. 8A and 8B, in working the injection hole by extruding the useless (waste) portion  45  (FIG. 5B) of the volume pressed by the tapered portion  46  of the punch  41 , when clearances between the tapered portion  46  in the tapered inclined shape of the punch  41  and the upper end face of the die  43 , are designated by notations of Cr 1  and Cr 2 , the clearance Cr 1  is set to 0 through 70% of the plate thickness (t) of the plate-like material  40  and the clearance Cr 2  is set to 0 through 120% of the plate thickness (t) of the plate-like material  40 . Further, in FIG. 8B, notation B indicates a sectional shape of the punch  41  and notation C indicates a sectional shape of the die  43  (elliptical shape similar to the sectional shape of the punch  41 ). 
     According to the method of working the injection hole of the orifice plate  10  in accordance with the present invention, in working the injection hole, as shown by FIGS. 1A,  1 B,  7 ,  8 A and  8 B, there is carried out an extrusion capable of forming the injection hole  30  having the desired shape with high dimensional accuracy at the plate-like material  40  by transcribing the shape of the tapered portion  46  of the punch  41  to the plate-like material  40 . The transcribing is carried out by advancing the punch  41  in accordance with the direction of the central axis line of the punch holder  42  with the plate-like material  40  sandwiched and held between the upper end face of the die  43  and the lower end face of the punch holder  42 . The tapered portion  46  of the punch  41  is pressed to the plate-like material  40 , and the useless portion  45  (FIG. 5B) of the volume pressed and excluded by the tapered portion  46  of the punch  41  forwardly extrudes from the face of the plate-like material (FIG.  9 A). After the extrusion, the useless portion  45  is removed at a level consistent with the surface of the plate-like material  40  (FIG.  9 B). 
     When the injection hole central axis line  34  of the injection hole (FIG. 4B) is inclined relative to the orthogonal line  33  and relative to the face of the plate-like material  40 , (FIGS. 4B and 1B) a side force (Fs) is produced when the front end portion of the punch  41  impinges on the plate-like material  40 . In working the injection hole, the force Fs can be received by the sliding face (inner face) of the support hole  47  of the punch holder  42  on the side opposed to the plate-like material  40 . That is, the side force (Fs) is canceled by a reaction force (Fr) and there is no resulting bending moment to break or damage the punch  41  (FIG.  1 B). Further, with regard to a material of the punch  41 , it is preferable to use a material that is strong enough to withstand the side force (Fs) produced in working the injection hole (for example, cemented carbide). Further, with regard to a material of the punch holder  42 , it is preferable to use a material capable of withstanding the side force (Fs). Although according to the embodiment, the entire area surrounding the punch  41  is covered by the punch holder  42 , the punch holder  42  may be present only in the direction of the side force (Fs). For example, a punch holder having a partially circular arc shape is used. 
     As described above, by adopting the method of working the injection hole for forming the injection hole in the tapered shape by the single step of pressing, there is implemented a mechanism of expediting very small particle formations of sprayed fuel injected into the internal combustion engine with appropriate timing. That is, not only the working operation promoting the added value of a product having a plate  40  with injection whole  10  with a low cycle (manufacturing) time and high productivity but also a working (manufacturing) operation having high dimensional accuracy. The expense of plant and equipment investment is alleviated and a remarkable cost reduction is achieved. 
     Further, even in the case in which the injection hole central axis line  34  of the injection hole  30  of the electromagnetic type fuel injection valve  1  is inclined relative to the line orthogonal to the face of the plate-like material  40 , the side force (Fs) produced in working the injection hole with the tapered portion  46  of the punch  41 , can be opposed by the sliding face of the punch holder  42 . That is, on the side opposed to the plate-like material  40 , the side force (Fs) is canceled by the reaction force (Fr) and there is no resulting bending moment to break the tapered portion  46  of the punch  41 . Therefore, the punch  41  is not broken by the side force (Fs) produced when the tapered portion  46  of the punch  41  impinges on the plate-like material  40  in working the injection hole. 
     Additionally, and with further reference to FIG. 7, the central axis line  53  of the discharge hole  48  of the die  43  is arranged in parallel with the central axis line  52  of the support hole  47  of the punch holder  42  and on the same axis line. An operator can adjust to align the punch  41  and the die  43  while visually observing the punch  41  and the die  43  and therefore, the working operation is performed with high dimensional accuracy. 
     FIG. 10 shows another embodiment of the invention and is a view showing a method of working an injection hole of an orifice plate  40 . According to the embodiment, when clearances between the tapered portion  46  of the punch  41  and the upper end face of the die  43  are designated by notations Cr 1  and Cr 2 , the clearances are set such that Cr 1 =0-20% and Cr 2 =0-20% of the plate thickness (t). By making the clearances between the tapered portion  46  of the punch  41  and the upper end face of the die  43  to be equal to or smaller than predetermined values, in extrusion, the useless portion  45  is automatically discharged from the discharge hole  48  without requiring a removing step as in the first embodiment. The removal step is not necessary because the punch  41  causes the separation of the useless portion  45  (extruded portion) extruded to a face opposite the face of the plate-like material  40  to which the tapered portion  46  of the punch  41  is pressed against. 
     FIG. 11 shows yet another embodiment of the invention and is a view showing a method of working an injection hole of an orifice plate. According to the embodiment, the central axis line  53  of the discharge hole  48  of the die  43  is arranged on a line orthogonal to the face of the plate-like material  40 . In transferring the plate-like material  40  in a successive step, there is hardly a possibility of a transfer in which the useless portion  45  shown in FIG. 9A is caught by the die  43 . Therefore, retracting the punch  41  and transferring the plate-like material  40  to the next manufacturing step is facilitated. 
     FIGS. 12A and 12B show yet another embodiment of the invention in which FIG. 12A is a view showing a fuel injection nozzle of an electromagnetic type fuel injection valve and FIG. 12B is a view showing an orifice plate viewed from a fuel inlet side. 
     According to the embodiment, the orifice plate  10  is formed with twelve (12) injection holes  30   a  through  30   l . The injection holes  30   a  through  30   d  are arranged with the fuel inlets  31  on a circular periphery on an inner peripheral side and the injection holes  30   e  through  30   l  are arranged with the fuel inlets  31  on a circular periphery on an outer peripheral side. Further, directions of injecting fuel from the injection holes  30   a ,  30   b ,  30   e    30   f ,  30   g  and  30   h  and directions of injecting fuel from the injection holes  30   c ,  30   d ,  30   i ,  30   j ,  30   k  and  30   l , are directed to be opposed to each other by 180° and two direction injection is realized. Further, in the respective injection holes  30   a  through  30   l , the relationship among θ 1 , θ 2  and θ 3  is the same as that of the first embodiment. 
     According to the embodiment, in the case of a fuel injection amount the same as that of the first embodiment, an injection amount per injection hole is reduced, because a diameter of the injection hole is reduced, thereby expediting small particle formation of the sprayed fuel. Further, the plurality of injection holes  30  can freely be arranged within a range so as not to deteriorate the effect of expediting the small particle formation of the sprayed fuel. 
     Although according to the embodiment, an explanation has been given of an example of attaching the fuel injection valve of the internal combustion engine such as the electromagnetic type fuel injection valve  1  (fuel injector) to the intake manifold of the gasoline engine, the fuel injection valve for the internal combustion engine may be attached to the combustion cylinder of the engine. The fuel injection valve may be attached to a combustion apparatus such as a water heater or an oil space heater. Further, according to the electromagnetic type fuel injection valve  1 , with a purpose of maintaining a constant small particle formation expediting function, it is preferable to set a ratio of the plate thickness t (mm) of the orifice plate  10  to the injection hole diameter (fuel inlet diameter or fuel outlet diameter) of the injection hole  30  to a specific range. 
     Although according to the embodiment, an explanation has been given applying the embodiment to the electromagnetic type fuel injection valve  1  by reciprocating the nozzle needle  8  constituting the valve member of the fuel injection nozzle in the axial direction by utilizing the electromagnetic type actuator. However, the embodiment may be applied to a fuel injection valve for reciprocating the valve member mechanically in the axial direction. For example, the invention is applicable to a fuel injection nozzle in which a valve member is opened when fuel is supplied into a valve body to reach a predetermined oil pressure. Additionally, when a fluid is intended to be injected by subjecting the fluid to small particle formation, the fluid injection nozzle according to the invention may be used as such. 
     Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore, not limited to the specific details, representative apparatus, and illustrative examples shown and described.