Patent Publication Number: US-6991188-B2

Title: Engine fuel injection valve and manufacturing method for nozzle plate used for the same injection valve

Description:
BACKGROUND OF THE INVENTION 
   a) Field of the Invention 
   The present invention relates to a fuel injection valve suitable for a fuel injection into an internal combustion engine of an automotive vehicle and a manufacturing method for a nozzle plate to be assembled into the fuel injection valve. 
   b) Description of the Related Art 
   A general fuel injection valve (normally called, fuel injector but also called fuel injection valve) used in an automotive engine includes a cylindrical valve casing having a fuel passage in its axial direction; a valve seat member having a valve seat and an injection outlet opening, the valve seat being disposed on an inner periphery of the valve casing at a tip end so as to enclose the injection outlet opening; a nozzle plate disposed at the tip of the valve casing so as to be faced against the injection outlet opening of the valve seat member and having a plurality of nozzle through-holes to inject fuel toward an external to the valve casing from the injection outlet opening; and a valve body to operatively be separated from the valve seat in response to an operation of an electromagnetic actuator installed within the fuel passage of the valve casing. 
   In such a kind of fuel injection valve as described above, the nozzle plate is formed by pressing a thin metallic plate and is attached onto the tip of the valve casing at a position so as to enclose the injection outlet opening of the valve seat member. In addition, a plurality of nozzle holes to inject fuel are penetrated through the nozzle plate. 
   A Japanese Patent Application First Publication No. Heisei 3-194163 published on Aug. 23, 1991 exemplifies a manufacturing process of the nozzle holes on the nozzle plate of the fuel injection valve. 
   A punching process is carried out for the nozzle plate using a punch so that the plurality of nozzle holes, each having a predetermined hole diameter and being inclined by a predetermined inclination angle with respect to a thickness direction of the nozzle plate and, therefore, a flow quantity of fuel and injection direction of the fuel injection valve can be determined. 
   During a valve opening of the valve body, the fuel supplied into the valve casing is injected from each nozzle hole toward an approximately intake port portion of the engine. At this time, the nozzle holes are so constructed that the fuel is injecting at a predetermined flow quantity according to their hole diameters and minute particles (granulations) of fuel can be achieved. 
   At a time of manufacturing the nozzle plate, the nozzle plate is punched in an opposite direction to the fuel injection direction of the fuel injection valve and the nozzle holes are opened on their front and rear surfaces. At this time, since one of the surface opening ends of the nozzle opening ends of fuel which is placed at outflow opening ends of fuel is an inlet side of the punch, a recess, viz., called a shear droop is formed in the vicinity to the outflow opening ends. 
   To avoid such manufacturing defects, the above-described previously proposed nozzle holes, a side surface which is placed at the outflow side of fuel from both surfaces of the nozzle plate is ground to scrape the shear droops placed in the vicinity to the nozzle holes. 
   SUMMARY OF THE INVENTION 
   An automotive vehicular engine field has demanded that since as each hole diameter of the nozzle holes becomes finer (smaller), the particles of the injected fuel becomes more minute, each nozzle hole is formed as small as possible to granulate injected fuel into minute particles and its combustibility can be improved. 
   However, even if the nozzle holes are formed to become small and a minute amount of foreign matters is slightly mixed, the nozzle holes are easier to be clogged. Hence, there is a limitation to granulate injected fuel into minute particles. In addition, the particles injected from the minute nozzle holes are high particle densities at a narrow region. Hence, the particle diameters are easy to become large with the fuel particles combined after the fuel injection. 
   Furthermore, since the particles of fuel injected from the minute nozzle holes are high particle densities at a narrow region, the particle diameters are easy to be enlarged with the combination after the fuel injection. 
   It is difficult to granulate the injected fuel sufficiently into minute particles only merely by forming the small hole diameters of nozzle holes but the nozzle holes are made to be clogged, thereby a reliability being reduced. 
   In addition, since in the previously proposed nozzle plate manufacturing method, each nozzle hole is punched in a direction opposite to the fuel injection direction using, for example, the punch, a peripheral wall of each nozzle hole becomes easy to be rough shear cross section with respect to a circulating direction of fuel. 
   However, at the opening ends at the nozzle hole inflow side of fuel which are outlet opening sides of the punch, peripheral walls of the nozzle holes provide fracture-planes of a multiple number of convex and recess cracks and defects are found at each corner of the opening ends. 
   No grinding off of the nozzle plate is found during the grinding process of the nozzle plate. 
   Therefore, when the fuel is injected through each nozzle hole, a stream of fuel becomes easy to be disturbed due to a rough peripheral wall of each nozzle hole and is difficult to stabilize the fuel injection. 
   These defect portions at the inflow side of the nozzle plate are not ground during the scrape process. 
   It is an object of the present invention to provide improved fuel injection valve and a manufacturing method of the fuel injection valve, particularly, the manufacturing method of its nozzle which can stably inject the fuel at the minute particle from the nozzle plate and which can improve a performance of the injection valve and its reliability. 
   These objects can be achieved by providing a fuel injection valve comprising: a substantially cylindrical valve casing in which a fuel flow passage is provided in its axial direction; a valve seat member comprising a valve seat installed within the fuel flow passage of one end of the cylindrical valve casing to enable a seating of a valve body and an injection outlet opening with a periphery of which the valve seat is enclosed, the valve body being disposed within the fuel flow passage of the valve casing to be operatively separated from the valve seat to open the fuel injection valve to inject the fuel in the fuel flow passage of the valve casing in response to an activation of an actuator; a nozzle plate faced against the injection outlet opening and on both surfaces of which openings of a plurality of nozzle holes are formed, the fuel being injected through the nozzle holes when the fuel injection valve is open; and a substantially arc-shaped chamfered portion in a substantially arc shape of cross section formed on an edge of an inner wall portion of each opening end of the corresponding nozzle hole of the nozzle plate to further expand a whole diameter of an injection stream of fuel passed through the nozzle holes. 
   The above-described object can also be achieved by providing a method of manufacturing a nozzle plate for use in a fuel injection valve, the fuel injection valve comprising: a substantially cylindrical valve casing in which a fuel flow passage is provided in its axial direction; a valve seat member comprising a valve seat installed within the fuel flow passage of one end of the cylindrical valve casing to enable a seating of a valve body and an injection outlet opening with a periphery of which the valve seat is enclosed, the valve body being disposed within the fuel flow passage of the valve casing to be operatively separated from the valve seat to open the fuel injection valve to inject the fuel in the fuel flow passage of the valve casing in response to an activation of an actuator; a nozzle plate faced against the injection outlet opening and on both surfaces of which openings of a plurality of nozzle holes are formed, the fuel being injected through the nozzle holes when the fuel injection valve is open; and a substantially arc-shaped chamfered portion in a substantially arc shape of cross section formed on an edge of an inner wall portion of each opening end of the corresponding nozzle hole of the nozzle plate to further expand a whole diameter of an injection stream of fuel passed through the nozzle holes, the manufacturing method comprising: using a punch to penetrate a plate material constituting the nozzle plate and which is mounted on a punch die; repeatedly inserting a tip of the punch into a punch hole of the die to form the plurality of nozzle holes; and circulating a fluid mixed with an abrasive through each nozzle hole to polish opening ends of the respective nozzle holes which are faced against the external of the fuel injection valve in a form of substantially arc shape of cross section with the abrasive to form the substantially arc-shaped chamfered portion on an edge of the inner wall portion of each opening end of the corresponding nozzle hole of the nozzle plate. 
   The above-described object can also be achieved by providing a method of manufacturing a nozzle plate for use in a fuel injection valve, the manufacturing method comprising: penetrating a plate material to form a plurality of nozzle holes opened to both major surfaces of the plate material; and circulating a fluid mixed with an abrasive through each nozzle hole to polish opening ends of the respective nozzle holes which are faced against the external shape of cross section with the abrasive to form the substantially arc-shaped chamfered portion on an edge of the inner wall portion of each opening end of the corresponding nozzle hole of the nozzle plate. 
   The above-described object can also be achieved by providing a method of manufacturing a nozzle plate for use in a fuel injection valve, the fuel injection valve comprising: a substantially cylindrical valve casing in which a fuel flow passage is provided in its axial direction; a valve seat member comprising a valve seat installed within the fuel flow passage of one end of the cylindrical valve casing to enable a seating of a valve body and an injection outlet opening with a periphery of which the valve seat is enclosed, the valve body being disposed within the fuel flow passage of the valve casing to be operatively separated from the valve seat to open the fuel injection valve to inject the fuel in the fuel flow passage of the valve casing in response to an activation of an actuator; and a nozzle plate faced against the injection outlet opening and on both surfaces of which openings of a plurality of nozzle holes are formed, the fuel being injected through the nozzle holes when the fuel injection valve is open, the manufacturing method comprising: using a punch to penetrate obliquely a plate material which becomes the nozzle plate and is mounted on a die toward a direction of the injection stream of fuel to provide the plurality of obliquely penetrated nozzle holes opened to both major surfaces of the plate material; and grinding the respective major surfaces of the punched plate material together with vicinities to the respective opening ends of the nozzle holes. 
   The above-described object can also be achieved by providing a method of manufacturing a nozzle plate for use in a fuel injection valve, the manufacturing method comprising: using a punch to penetrate obliquely a plate material which becomes the nozzle plate and is mounted on a die toward a direction of the injection stream of fuel to provide the plurality of obliquely penetrated nozzle holes opened to both major surfaces of the plate material; and grinding the respective major surfaces of the punched plate material together with vicinities to the respective opening ends of the nozzle holes. 
   The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal cross sectional view of a fuel injection valve in a first preferred embodiment according to the present invention. 
       FIG. 2  is an expanded cross sectional view of an essential part of a tip of cylindrical valve casing shown in  FIG. 1 . 
       FIG. 3  is a plan view of a nozzle plate shown in  FIGS. 1 and 2 . 
       FIG. 4  is an expanded cross sectional view of a center portion of the nozzle plate of the fuel injection valve as viewed from an arrow-marked direction of IV—IV shown in  FIG. 3 . 
       FIG. 5  is an expanded cross sectional view of the nozzle plate shown in  FIG. 4  representing arc-shaped chamfered portion of left nozzle holes of the nozzle plate. 
       FIG. 6  is an elevation view representing an injection state in which a fuel is branched into rightward and leftward directions from the fuel injection valve shown in  FIGS. 1 through 5 . 
       FIG. 7  is a right side view of the fuel injection valve shown in  FIGS. 1 through 6  as viewed from an arrow-marked direction of VII—VII shown in  FIG. 6 . 
       FIG. 8  is a characteristic graph representing a relationship from among a dimension ratio of a radius of curvature in an arc-shaped chamfered portion to a particle diameter of injected fuel and an angle of an injection pattern. 
       FIG. 9  is an expanded cross sectional view representing a state of formation of a plate material to become the nozzle plate of the fuel injection valve in a first preferred embodiment of a manufacturing method of the nozzle plate according to the present invention. 
       FIG. 10  is an expanded cross sectional view representing a state of the plate material in which a punch is used to penetrate nozzle holes during a punching process in the plate material in the case of the second embodiment shown in  FIG. 9 . 
       FIG. 11  is an expanded cross sectional view of the state of the plate material in which the arc-shaped chamfered portion using a polish fluid in a polish process. 
       FIG. 12  is an expanded cross sectional view representing a state of the nozzle plate manufactured in a second preferred embodiment of the manufacturing method, 
       FIG. 13  is an expanded cross sectional view of a state of he plate material which is thicker than the nozzle plate during a plate material forming process in the second embodiment shown in  FIG. 12 . 
       FIG. 14  is an expanded cross sectional view representing a state of a shear droop and a defect developed during the punching in the nozzle plate in the second embodiment shown in  FIGS. 12 and 13 . 
       FIG. 15  is an expanded cross sectional view representing the state in which both surfaces of the plate material during a grinding process in the second embodiment shown in  FIGS. 12 ,  13 , and  14 . 
       FIG. 16  is an expanded cross sectional view representing the plate material whose both front and rear surfaces are ground in the second embodiment shown in  FIGS. 12 ,  13 , and  14 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention. 
     FIGS. 1 through 11  show a fuel injection valve in a first preferred embodiment according to the present invention and a manufacturing method of a nozzle plate used in the fuel injection valve. 
   A cylindrical valve casing  1  as a major body of the fuel injection valve is formed, for example, in a stepped cylindrical shape with a magnetic material such as electromagnetic stainless steel. 
   The valve casing  1  comprises: a large-diameter cylindrical envelope  1 A onto a basic end of which a resin covering is attached; a small-diameter cylindrical envelope  1 B integrally fixed at a tip of the large-diameter envelope  1 A; and a fuel passage  2  through which a valve body is inserted and which is axially disposed. 
   A cylindrical linkage member  3  fixedly attached at a basic end of the valve casing  1  is formed of the non-magnetic material and is interposed between the valve casing  1  and a fuel inflow pipe  4 . 
   A cylindrical fuel inflow pipe  4  formed with a magnetic material such as an electromagnetic stainless steel is fixed at the basic end of the valve casing  1  using the linkage member  3 . Its tip end is communicated to the fuel passage  2 . A fuel filter  5  is installed around the inner periphery of the basic end of fuel inflow pipe  4 . 
   Both fuel inflow pipe  4  and valve casing  1  are magnetically linked via a linkage core made of a magnetic metallic piece attached at outer peripheral sides. When a power supply to an electromagnetic coil  12  as will be described later is turned on, a closed magnetic path is formed among the valve casing  1 , the fuel inflow pipe  4 , the linkage core  6 , and the adsorption portion  10  as will be described later. 
   A substantially cylindrical valve seat member  7  is disposed within a small-diameter portion  1 B of the valve casing  1  with a small gap provided against the small-diameter portion  1 B. A circular injection outlet opening  7 A is formed, as typically shown in  FIG. 2 . A substantially truncated cone shaped valve seat  7 B is installed on the inner periphery of the valve seat member  7  so as to enclose the injection outlet opening  7 A. 
   A valve body  8  inserted within the fuel passage  2  of the valve casing  1 . The valve body  8  includes: as shown in  FIG. 1 , a valve axle  9  formed substantially cylindrically with a metallic plate folded; a cylindrical adsorption portion  10  fixedly attached onto the basic end of the valve axle  9 ; and a spherical valve body  11  fixedly installed at a tip of the valve axle  9  for separately landing the valve seat  7 B of the valve seat member  7 . The basic end surface of the adsorption portion  10  is faced toward the fuel inflow pipe  4  with the axial gap provided and the dimension of the gap is previously adjusted as a light quantity of the valve body  8 . A plurality of chamfered portions are formed at an outer periphery of the valve portion  11 . When the adsorption portion  10  is magnetically attracted with the electromagnetic coil  12 , the valve body  8  displaces in the axial direction thereof against a biasing force exerted by a valve spring  13 . The valve is opened with a constant light quantity form a valve closure portion at which the valve portion  11  is seated on the valve seat  7 B of the valve seat member  7  to a valve open position at which the adsorption portion  10  is contacted on the fuel inflow pipe  4 . 
   A valve spring  13  comprises a compressive spring disposed within a fuel inflow pipe  4 . The valve spring  3  is disposed between a cylindrical body  14  fixedly attached onto an upstream side of the fuel inflow pipe  4  and a basic end of the valve body  8  to bias the valve body  8  in the open direction. 
   A nozzle plate  15  is fixedly attached within the small-diameter cylindrical envelope  1 B of the valve casing  1  via a press plate  19 . The nozzle plate  15  is formed with a predetermined wall thickness t 0  between 0.05 mm and 0.25 mm, for example, and is provided with a side surface  15 A and the other side surface  15 B. 
   In addition, a nozzle plate  15  is faced against the injection outlet opening  7 A with one side surface  15 A attached onto the valve seat member  7  and exposed to an external of the valve casing  1  via an inner peripheral side of the press plate  19 . 
   The nozzle plate  15  serves to inject through nozzle holes  16 ,  16 , - - - and  17 ,  17 , - - - the fuel flowing out of the injection outlet opening  7 A of the valve seat member  7  in a state of micro particles. A multiple number of left nozzle holes  16 , m  16 , - - - are nozzle plate  15  by penetrating the nozzle plate  15  in its plate thickness direction. As viewed from  FIGS. 3 through 5 , left nozzle holes  16  are disposed at left side with respect to an Y—Y axis extended vertically along a center line  0 — 0  of, for example, the nozzle plate  15  and arranged in a double concentric circular form of right nozzle holes  17 ,  17 , - - - . 
   Each left nozzle hole  16  is, as shown in  FIG. 4 , is formed with a straight line penetrated hole having a cylindrical peripheral wall with an axial line A—A as a center. The axial line is inclined in a leftward direction by a predetermined inclination angle αA with respect to a line  0 A— 0 A parallel to a center line  0 — 0  of each left nozzle hole  15 . The predetermined inclination angle αA, e.g., corresponds to the arrangement of intake port of the engine. In addition, each left nozzle  16  has a predetermined hole diameter d of approximately 0.1 mm through 0.2 mm and a length dimension L positioned between one side surface  15 A and the other side surface  15 B of the nozzle plate  15 . 
   A multiple number of right nozzle holes  17 ,  17 , - - - formed in substantially same manner as the left nozzle holes  16 . Each right nozzle hole  17  is disposed in more rightward direction than the Y—Y axial line of, for example, the nozzle plate  15 . Each right nozzle hole  17  is formed by penetrating the nozzle plate  15  to have the hole diameter of d. In addition, an axial line B—B of each right nozzle hole  17  is inclined by a predetermined inclination angle αB in the rightward direction of an X axis with respect to the line  0 B— 0 B parallel to the center line  0 — 0  of the nozzle plate  15 . The two predetermined inclination angles αA and αB of both of the Left and right nozzle holes serve to define branch Angles θ 1 . 
   Each right nozzle hole  17  is provided with the inflow opening end  17 A opened to one side surface  15 A of the nozzle plate  15  and with an arch-shaped chamfered portion  18  at the outflow opening end opened to the other side surface  15 B of the nozzle plate  15 . 
   Each arc-shaped chamfered portion  18  is provided on corresponding one of the respective nozzle holes  16  and  17 . Each arc-shaped chamfered portion  18  is, as shown in  FIGS. 4 and 5 , formed by chamfering the outflow side opening end of the corresponding one of nozzle boles  16  and  17  using, for example, horning, buff rolling, or grinding material or other polishing means and is extended over a whole periphery of the outflow opening end in a curved surface in an arc shape of substantially arc shape and having a predetermined radius of curvature r. 
   The arc-shaped chamfered portion  18  is progressively expanded in the outflow direction of fuel placed in the vicinity to the other side surface  15 B of the nozzle plate  15  of each nozzle hole  16  and  17 . The hole diameter of this diameter expanded portion is slightly larger than the hole diameter d of a midway portion placed in the vicinity to the other side surface  15 B of the nozzle plate  15 . 
   In addition, the radius of curvature r of the arc-shaped chamfered portion  18  is formed with a predetermined dimensional ratio with respect to the hole diameter d of the nozzle holes  16  and  17 . 
   The dimensional ratio (r/d) is previously set using an experimental data shown in  FIG. 8  as will be described later so as to fall in a range, for example, approximately 0.1 through 0.28, preferably, in a range between about 0.14 to 0.2 mm. 
   Each arc-shaped chamfered portion  18  serves to hold a predetermined flow quantity of fuel and injection direction defined according to the hole diameter d, the inclination angles of αA and αB when the fuel is injected through each nozzle hole  16  and  17  and promote the micro particles of fuel with combinations of fuel particles suppressed by slightly widening the injection pattern along the surface of each arc-shaped chamfered portion  18 . 
   On the other hand, a pressure plate  19  is formed of a substantially circular metallic plate and is welded within a small diameter cylindrical portion  1 B of the valve casing  1 . An inner peripheral portion of the pressure plate  19  is welded on a tip surface of the valve seat member  7  together with the nozzle plate  15  and valve seat member  7  are fixed within the valve casing  1 . 
   A resin covering  20  is attached so as to enclose the large-diameter cylindrical portion  1   a  of the valve casing  1 . The resin covering  20  is provided with a connector  21  as shown in  FIG. 1 . 
   A protector  22  is attached onto the small-diameter cylindrical portion  1 B of the valve casing  1  to cover the nozzle plate  15 . 
   The fuel injection valve in the preferred embodiment is so constructed as described above and its operation will be described below. 
   First, the fuel is supplied from a basic end of a fuel inflow pipe  4 . When the power is supplied to the electromagnetic coil  12  via the connector  21 , the absorption portion  10  of the valve body  8  is magnetically attracted via the valve casing  1 , the fuel inflow pipe  4 , and the linkage core  6  with the electromagnetic coil  12 . The valve body  8  is, then, opened against the valve spring  13 . The fuel within the fuel passage  2  is injected externally from, the injection outlet opening  7 A of the valve seat member  7  via the nozzle holes  16  and  17  of the nozzle plate  15 . 
   The fuel injection is carried out by branching the injected fuel into both left and right directions (X-axis direction) by branch angles αA and αB of nozzle holes  16  and  17 . These branched fuel provides a widened substantially truncated cone injection pattern having the expansion angle of θ 2  in the X-axis direction and in the Y-axis direction θ 3  in the Y-axis direction and is injected in an intake port side of the engine. 
   In this case, the injection direction is determined by circulating the injected fuel from the left nozzle holes  16 ,  16 , - - - by the length dimension L within the left nozzle holes  16  having the respective predetermined inclination angles of αA. 
   When the fuel is injected externally from the left nozzle holes  16 ,  16 ,  16  - - - , an injection stream of fuel is expanded over a constant region along the surface of the arc shaped chamfered portion  18 . 
   Hence, excessive densities of the particles of fuel during the injection can be suppressed and the combinations of particles can be reduced. 
   Thus, the fuel injected from the respective left nozzle holes  16  form the injection stream along the axial line A—A and holds the micro particles state via the respective arc-shaped chamfered portion  18 . In the same manner as the injected fuel from the right nozzle holes  17 ,  17 , - - - , the injection stream is formed along the axial line B—B direction and each arc-shaped chamfered portion  18  can promote micro particles of fuel. 
   The relationship between the radius of curvature r of each arc-shaped chamfered portion will be described below with reference to the experimental data shown in  FIG. 8 . 
   First, a particle diameter of the injected fuel becomes optimized, as shown in a characteristic line  23  of  FIG. 8 , when either the radius of curvature r of the arc-shaped chamfered portion  18  or the dimension ratio (r/d) of the radius of curvature r with respect to the hole diameter of the nozzle becomes large. For example, when the dimension ratio (r/d) is in excess of about 0.1, or preferably, about 0.14, the injected fuel can sufficiently be reduced to micro particles. 
   However, the branch angle θ 1  of injection pattern and expansion angles θ 2  and θ 3  become unstable, as shown by characteristic lines  24 ,  25 , and  26  of  FIG. 8 , as the radius of curvature r of each arc shape chamfered portion  18  becomes large. That is to say, since the injection pattern of fuel is expanded along the surface of the arc shaped chamfered portion  18 , the dimension ratio (r/d) is in excess of approximately 0.2 and, at this time, the expansion angles θ 2  and θ 3  of the injection pattern are progressively increased. When the dimension ratio (r/d) is in excess of about 0.28, the expansion angles θ 2  and θ 3  are largely varied so that the branch angle θ 1  of the injection pattern receives the ill influence therefrom. 
   Hence, as described in the preferred embodiment, the dimension ratio (r/d) of the hole diameter d of the nozzle holes  16  and  17  with respect to the radius of curvature r of the arc shaped chamfered portion  18  is set to fall within the range between, for example, 0.1 and 0.28 preferably between about 0.14 and 0.2. 
   Thus, while promoting the micro particles of the injected fuel by means of arc shaped chamfered portion  18 , the injection direction of fuel and injection pattern can be held under an appropriate state. 
   Next, a manufacturing method of the nozzle plate  15  will be described below with reference to  FIGS. 9 through 11 . 
   During a plate material forming process shown in  FIG. 9 , a plate material  31  which finally becomes the nozzle plate  15  is formed by such as a press tool. 
   Next, during a punching process shown in  FIG. 10 , a plurality of through holes  32  and  33  are formed by punching the plate material  31  using a punching tool. During the punching process, a punch  35  is penetrated through the plate material  31  in such a manner that the punch  35  is directed from one side surface  31 A in the injection direction of fuel, its tip of the punch  35  invaded into the corresponding punch holes  34 A and  34 B in the fuel injection direction. Hence, a through hole  32  having opening ends  32 A and  32 B and a through hole  33  are formed in the plate material. 
   Next, during a polishing (grinding) press shown in  FIG. 11 , a fluid polish is, for example, used to cause a certain quantity of polish fluid  36  mixed with a multiple number of polish material particles (adhesive material particles) to flow in a direction reverse to the injection direction from the through holes  32  and  33  so that the outflow opening ends  32 B and  33 B are ground. Hence, the outflow opening ends in a substantially arc shape of cross section with the polish fluid  36  and, at these positions, the arc-shaped chamfered portions  18  are formed with the polish fluid  36 . 
   In this case, the radius of curvature r of the arc-shaped chamfered portion  18  can be formed to a desired value by an appropriate settings off a pressure to be applied to the polish fluid  36 , a time duration at which the polishing process is continued, and particle diameter of the abrasive material particles. Consequently, as shown in  FIG. 4 , the nozzle plate  15  on which the nozzle holes  16 ,  17 , - - - and arc-shaped chamfered portions  18  can be manufactured. 
   Since, in the manufacturing method of the nozzle plate  15  in the first preferred embodiment, the arc-shaped chamfered portions  18  are disposed on the outflow opening ends, the flow quantity and injection direction can be determined according to the hole diameter. Length inclination angles αA and αB, and length dimension L of the respective nozzle holes  16  and  17 . The respective arc-shaped chamfered portions  18  can be hold the flow quantity and fuel injection direction of fuel and can expand the injection pattern at a constant range. 
   Hence, it is possible to decrease combinations of particles with the excessive densities of the injected fuel particles suppressed via the arc-shaped chamfered portions  18  so that the injected fuel can be promoted to be more granulated as the micro particles and the accurate injection of fuel toward the intake port of the engine can be made. 
   Consequently, a performance of the injection valve can be improved. 
   In this case, since the dimension ratio (r/d) of the radius of curvature r of each arc-shaped chamfered portion  18  to the hole diameter d of each nozzle hole  16  and  17  is set to fall within the above-described predetermined range, the arc-shaped chamfered portions  18  can provide an appropriate expansion of the injection pattern of fuel, can prevent an excessive expansion of the injection pattern over the wide range, and can inject stably the granulated fuel in a predetermined injection direction and in an injection pattern. 
   Since, during the polishing (grinding) process the polish tool such as the fluid polish is used, each arc-shaped chamfered portion  18  can easily be formed and the nozzle plate whose profile is stable can efficiently be manufactured. 
   Even in a case where the slid line and/or defects are formed on the peripheral walls and opening ends of the through holes  32  and  33  during the punching process, these portions can smoothly be finished with the above polishing carried out by the polish fluid  36 . Thus, these fracture portions or defects can be eliminated so as to give no influence on the fuel injection. 
   Next,  FIGS. 12 through 16  show a second preferred embodiment of the manufacturing method for the nozzle plate  15  of the fuel injection valve. 
   In the second embodiment, both surfaces of the plate material are ground in the plate thickness direction. 
   The nozzle plate  41  manufactured using the manufacturing method in the second embodiment is of, for example, the circular metallic plate, in the same manner as the nozzle plate described in the first embodiment. On the nozzle plate  42 , the plurality of left nozzle holes  42  and right nozzle holes  43  are punched. Each nozzle hole  42  and  43  is a straight penetrated hole inclined by the predetermined inclination angle with respect to the plate thickness direction. 
   Each left nozzle hole  42  is provided with inflow opening ends  42 A opened to one side surface  41 A of the nozzle plate  41  positioned at the inflow side of fuel and the outflow opening ends  42 B opened to the other side surface  41 B positioned at the outflow position of fuel. In addition, the right nozzle holes  43  are positioned with opening ends  43 A and  43 B positioned on the outflow side of fuel. The opening ends  42 A,  42 B,  43 A, and  43 B of the nozzle holes  42  and  43  are of substantially pointed edge shapes. 
   The nozzle plate  41  is provided at tip ends of the casing  1 . When the valve body  8  is opened, the fuel streamed out from the injection outlet opening  7 A of the valve seat member  7  is injected under the micro particles (granulation state) from the respective nozzle holes  42  and  43 . 
   The nozzle plate  41  to which the method of manufacturing the fuel injection valve is applicable has the above-described structure. The method of manufacturing the nozzle plate  41  will be described with reference to  FIGS. 13 through 16 . 
   First, during the plate material forming process shown in  FIG. 13 , the metallic plate is processed by a press forming so as to form a plate material  51  which becomes the nozzle plate  41 . In this case, the plate material  51  is provided with the plate thickness t 1  which is formed to become thicker than the nozzle plate  41 . 
   Next, during the punch process shown in  FIG. 14 , the punching is carried out for the plate material  51  in the substantially same manner as the punch process carried out in the first embodiment so that the plurality of penetrated holes  52  and  53  are punched. In this case, a predetermined clearance C of, for example, about 1 through 10 μm is formed as a circular gap between punch holes  54 A and  54 B of the die  54  used in the punching process and punch  55 . 
   During this process, the punch  55  is penetrated in the injection direction of fuel from the one side surface  51 A of the plate material  51  toward the other side surface  51 B. Consequently, a convexed shear droop  56  is often formed on the surrounding portion of the inflow opening ends of the through holes  52  and  53 . Defects  57  and facture-plane  58  are often formed in the proximities to the outflow opening ends. 
   During the polish process shown in  FIG. 15 , the one surface (front)  51 A of the plate material and the other (rear) surface  51 B are ground to scrap off shear droop  56 , deflects  57 , and fracture plane  58 , and so forth. 
   In this case, a grinding depth Δta of the one surface  51 A is defined in the following equation 1 using the plate thickness t 1  of, for example, the plate material  51 .
 
0.1× t   1 ≧Δ ta≧ 0  (1)
 
   An upper limit value (0.1×t 1 ) of the grinding depth is a limitation value to stabilize the injection direction of fuel by securing the length dimension of the nozzle holes  42  and  43  sufficiently. 
   On the other hand, the grinding depth Δtb of the other surface  51 B is determined according to the following equation of (2) using, for example, the plate thickness t 1  of the plate material  51  and the valve clearance C of the punch  55 .
 
0.2 ×t   1 ≧Δ ta≧ 2× C   (2)
 
   In this case, the upper limit value (0.2×t 1 ) of the grinding depth Δtb is set substantially for the same reason in the case of the grinding depth Δta. 
   The deflects  57  and facture-plane  58  are set according to the clearance C between the punch  55  and the die  54 . 
   The lower limit value (2×C) of the grinding depth Δta is set according to the clearance C. 
   Consequently, upon the completion of the grinding process, the plate thickness t 1  of the plate material  51  is ground up to the plate thickness t 2 . Hence, since the shear droop  56 , the defects  57 , and fracture-plane are scrap off, the nozzle plate  41  having the substantially pointed edge shape of the opening ends  42 A,  42 B,  43 A, and  43 B can be manufactured. 
   According to the first preferred embodiment of the manufacturing if the nozzle plate  41 , the punching process is carried out for the plate material  51  along the injection direction of fuel to provide through holes  52  and  53  and, thereafter, the one (major) surface  51 A and the other (major) surface  51 B are ground. Since, in the punching process, peripheral walls of the nozzle holes  42  and  43  can smoothly be finished with respect to the circulation direction of fuel. 
   During the grinding process, the shear droops  56 , the defects  57 , and fracture-plane  58  which are formed on both opening ends of the penetrated holes  52  and  53  can be scraped off together with a surface layer position of the plate material  51 . 
   Upon the end of the grinding, the opening ends  42 A,  42 B,  43 A, and  43 B can be formed in the pointed edge configuration. 
   Furthermore, in a case where, for example, a bowing is developed on the plate material  51  with the pressure during the pressing, both front and rear (major) surfaces of the plate material  51  can be ground in parallel to each other to compensate for the bowing. 
   Hence, only by grinding both of the one surface  51 A and the other surface  51 B, the nozzle holes  42  and  43  of the nozzle plate  41  can be formed with a high accuracy so that the nozzle plate  41  of the stable form, in other words, of no manufacturing deviation can efficiently be manufactured. 
   During the fuel injection, the granulated fuel from the nozzle holes  42  and  43  can stably be injected toward a predetermined injection direction so that a performance as the fuel injection valve can be improved. 
   In this case, a constant correlation between the inclination angle and injection pattern (injection direction) of fuel can be provided. This permits an easy setting of the inclination angles of the nozzle holes  42  and  43  which provides a desired injection pattern through a desk calculation. 
   Furthermore, during the manufacture of the nozzle plate  41  in the case of the second embodiment, in a case where a jig such as the die  54  and the punch  55  is replaced with the new one during the manufacture of the nozzle plate  41 , the edge forms of the nozzle holes  42  and  43  can be aligned irrespective of a deviation in characteristics of jigs and a yield (or productivity) of the fuel injection valve can be improved. 
   It is noted that, after the grinding process of the second embodiment manufacturing method for the nozzle plate shown in  FIG. 16 , the polishing process shown in the case of the first embodiment of the manufacturing method shown in  FIG. 11  may be added. 
   Although, in the first embodiment of the manufacturing method for the nozzle plate, the grinding fluid  36  is used to form the arc-shaped chamfered portion  18  at the outflow opening ends of the nozzle holes  16  and  17 , the present invention is not limited to this. For example, the outflow opening ends of the nozzle holes  16  and  17  may be polished with one of the various kinds of polishing tool, for example, the horning, the buff rolling for the outflow opening ends of the nozzle holes  16  and  17  to form arc-shaped chamfered portions  18 . 
   The entire contents of a Japanese Patent Application No. 2000-246893 (filed in Japan on Aug. 16, 2000) are herein incorporated by reference. Although the invention has been described above by reference to certain embodiment of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in the light of the above teachings. The scope of the invention is defined with reference to the following claims.