Patent Publication Number: US-6908050-B2

Title: Electromagnetic fuel injection valve

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/944,597 filed Sep. 4, 2001 issued on Jan. 9, 2004 (U.S. Pat. No. 6,695,233). 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electromagnetic fuel injection valves for use in internal combustion engines. 
     BACKGROUND OF THE INVENTION 
     In conventional internal combustion engines for automobile use, an electromagnetic fuel injection valve driven by the electrical signals sent from the engine control unit is commonly used. 
     This type of fuel injection valve is constructed so that: an electromagnetic coil and a yoke are arranged around a hollow tubular type of fixed core (center core); a nozzle body containing a needle equipped with a valve body is installed at the bottom of the yoke which accommodates the electromagnetic coil, and; the needle is energized towards the valve seat by the action of the return spring. 
     Proposed an example of such a conventional electromagnetic fuel injection valve is, as disclosed in, for example, Japanese application patent laid-open publication No. Hei-10-339240 or Hei-11-132127, a single one into which a magnetic fuel connector portion, a non-magnetic intermediate pipe portion, and a magnetic valve body portion were molded by magnetizing one pipe formed of a composite magnetic material and then non-magnetizing only the intermediate portion of this pipe by use of, for example, induction heating, in order to reduce the number of parts and facilitate the assembly of the parts. 
     For this type, a cylindrical fixed core is press-fit in a fuel connector portion and a movable core with a valve body is mounted in the valve body portion. Also, an electromagnetic coil is provided on the intermediate periphery of the pipe and a yoke is provided outside the electromagnetic coil. When power is supplied to the electromagnetic coil, a magnetic circuit is formed over the area from the yoke to the fuel connector portion, the fixed core, the movable core, the valve body portion, and the yoke, and the movable core is magnetically attracted towards the fixed core. The non-magnetic portion functions as a magnetic flux short-circuiting suppressor between the fuel connector portion and the valve body portion. 
     SUMMARY OF THE INVENTION 
     In recent years, even in a gasoline engine, a fuel injection valve that directly injects a fuel into the cylinders of the internal combustion engine is placed in practical use. 
     A so-called “long nozzle type of injector” having a thin and long nozzle body at the bottom of its yoke is also proposed for the direct injection type of fuel injection valve mentioned above. When this long nozzle injector is installed on the cylinder head of an engine, if the periphery of the cylinder head is crowded with parts such as an air intake valve and an air intake pipe, only the slender nozzle body which does not take too large a space can be positioned on the cylinder head and the yoke, the connector mold, and other large-diameter valve portions can be spaced from other parts and the cylinder head to avoid interference. Therefore, this type of injector has the advantage that the flexibility of its installation is very high. 
     An object of the present invention is to supply a compact, electromagnetic fuel injection valve reduced in dimensions, especially in diameter, provided with an inexpensive and sufficient magnetic circuit, and excellent in performance, so as to make the main unit of the fuel injection valve suitable for injection schemes such as the direct intra-tubular injection scheme set forth above. 
     Another object of the present invention is to supply an electromagnetic fuel injection valve capable of suppressing the restitution of a closed valve body and preventing the occurrence of problems such as secondary fuel injection. 
     In order to accomplish the objects mentioned above, various inventions are proposed herein. The essentials of these inventions are described below. 
     An electromagnetic fuel injection valve basically having, as the major elements constituting the fuel flow channel in the axial direction of the injection valve body, 
     a fuel induction pipe, 
     a hollow tubular type of fixed core equipped with a flange at its-top end, and 
     a nozzle holder that was press-machined into a slender and tubular shape using a pipe and has an orifice plate equipped with a valve seat at the lower end of said nozzle holder, 
     is characterized in that: 
     said pipe is connected by welding to the top of the flange of the fixed core mentioned above, the upper inner surface of said nozzle holder and the outer surface of the fixed core are connected by press-fitting and welding, and one fuel flow channel assembly is thus constituted, 
     said fuel flow channel assembly contains a needle connecting a movable core to the valve body, a return spring for energizing this needle in the direction of said valve seat, and a member for adjusting the spring action of said return spring, and 
     an electromagnetic coil is provided at a peripheral position on said nozzle holder at which the nozzle holder and the fixed core are press-fit, and outside the electromagnetic coil is positioned a tubular yoke whose upper end is connected by welding to the flange of the fixed core and whose lower end is press-fit on the outer surface of the nozzle holder. 
     Also, an electromagnetic fuel injection valve having 
     a needle equipped with a valve body, 
     a return spring for applying a spring load to the valve seat side of said needle, 
     an electromagnetic coil, and 
     a magnetic circuit for magnetically attracting said needle in the opening direction of the valve by the excitation of said electromagnetic coil, 
     is characterized in that: 
     said needle has a movable core operating as an element of said magnetic circuit, 
     said movable core and said valve body are connected via a joint having a spring function, 
     a plate spring is built into said needle, and 
     an axially movable mass body is positioned, independently of said needle, between said return spring and said plate spring. 
    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal section of the fuel injection valve pertaining to an embodiment of the present invention. 
         FIG. 2  is a partly exploded, longitudinal section of the above-mentioned fuel injection valve. 
         FIG. 3  is a longitudinal section of the needle of the above-mentioned fuel injection valve. 
         FIG. 4  is an enlarged, sectional view of the valve body and orifice plate used in the above-mentioned embodiment. 
         FIG. 5  is a top view and A-A′ sectional view of the joint pipe used in the above-mentioned embodiment. 
         FIG. 6  is a top view and B-B′ sectional view of the orifice plate used in the above-mentioned embodiment. 
         FIG. 7  is a partly enlarged, sectional view of the movable core and fixed core used in the above-mentioned embodiment. 
         FIG. 8  is a longitudinal section of the yoke used in the above-mentioned embodiment. 
         FIG. 9  is a top view, C-C′ sectional view, and bottom view of the swirler used in the above-mentioned embodiment. 
         FIG. 10  is an exploded, diagonal view of the above-mentioned embodiment. 
         FIG. 11  is an explanatory view showing the mounting status of the fuel injection valve pertaining to the above-mentioned embodiment. 
     
    
    
     DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention are described below using drawings.  FIG. 1  shows in longitudinal section the fuel injection valve pertaining to an embodiment of the present invention.  FIGS. 2 and 3  show the fuel injection valve in partly exploded, longitudinal section.  FIG. 4  is an enlarged sectional view of the valve body and orifice plate used in the aforementioned embodiment.  FIGS. 5  to  9  show the components used in the embodiment.  FIG. 10  is an exploded diagonal view of the entire fuel injection valve. 
     First, a total outline of this embodiment is given below.  FIG. 1  exemplifies a fuel injection valve  100  that employs the so-called “top feed scheme”, in which, as shown by the arrow in the figure, when the injection valve is opened, fuel flows from the top of the valve body in its axial direction and is injected from an orifice  20  provided at the lower end of the injection valve. 
     Fuel injection valve  100  has, as the major elements constituting the fuel flow channel in the axial direction of the valve body; a fuel induction pipe  40  that was press-machined (this also applies when the other components mentioned below are press-machined during, for example, deep drawing or extrusion processes); a hollow tubular type of fixed core  1  with a flange  1   a  at its upper end, and; a nozzle holder  18  (this may also be termed a nozzle body) that was press-machined into a thin and long tubular shape using a pipe and has an orifice plate  19  equipped with a valve seat at the lower end of the nozzle holder. 
     As shown in  FIGS. 2 and 3 , fuel induction pipe  40  is provided with flanges  40   a  and  40   b  at its upper and lower ends, respectively, and flange  40   b  at the lower end is welded to the top of flange  1   a  of fixed core  1 , at the section denoted by numeral W 6 . The welding is provided in the circumferential direction of the flange, and thereby, fixed core  1  and fuel induction pipe  40  are connected before the injection valve body is assembled. 
     The upper inner surface of nozzle holder  18  and the outer surface of fixed core  1  are press-fit, and furthermore, the section denoted by numeral W 1  is welded over its entire periphery to connect nozzle holder  18  and fixed core  1 . In this way, pipe  40 , fixed core  1 , and nozzle holder  18  are connected together to form a single fuel flow channel assembly. 
     This fuel flow channel assembly contains elements such as; a needle  5  that connects a cylindrical movable core and the slender valve body (valve rod included) via the joint pipe  15  mentioned later; a return spring  7  for energizing the needle  5  in the direction of valve seat  19   a , and; a member  6  for adjusting the spring action of return spring  7  (in the present embodiment, this member is shown as a C-ring pipe whose cross section has the shape of a C-ring). 
     An electromagnetic coil  2  is provided in a position on the periphery of nozzle holder  18  at which the nozzle holder and fixed core  1  are press-fit, and a tubular yoke  4  is positioned outside the electromagnetic coil. 
     Yoke  4  is of a press-machined tubular shape (details of this shape are described later). The upper end of the yoke has a accommodation hole for electromagnetic coil  2 , and the upper fringe of this hole is connected by being welded over the entire periphery to the flange  1   a  of fixed core  1 , at the position denoted by numeral W 5 . The lower end portion  4   c  of yoke  4  is reduced in thickness, compared with electromagnetic coil storage element  4   a , and the lower end portion  4   c  is press-fit on the periphery of nozzle holder  18 . 
     This fuel injection valve  100  is constructed so that when power is supplied to electromagnetic coil  2 , a magnetic circuit is formed by yoke  4 , fixed core  1 , movable core  14 , and a portion of nozzle holder  18 , and thereby, needle  5  overcomes the action of return spring  7  and is magnetically attracted to open the valve. When the power to electromagnetic coil  2  is interrupted, needle  5  is pressed against valve seat  19   a  by the action of return spring  7 , thus closing the valve. In this embodiment, the lower edge of fixed core  1  functions as a stopper for stopping the movement of needle  5  when the valve is opened. 
     Features of the components mentioned above are set forth below. Fixed core  1  is made of magnetic stainless steel, and is press-machined and cut into a thin and long hollow cylindrical shape having a flange  1   a  at its upper end. 
     Flange  1   a  is provided with a window  1   b  for routing the terminal  29  and pin terminal  30  of electromagnetic coil  2 . Fuel induction pipe  40  is formed of a non-magnetic metal member, the bottom of which is reduced in thickness by press-machining and a C-ring pin  6  having a C-shaped cross section is press-fit on the lower inner surface of the pipe. Load adjustment of return spring  7  is accomplished by adjusting the press-fitting allowance of pin  6 . A fuel filter  31  is mounted at the upper end of fuel induction pipe  40 . 
     Although nozzle holder  18  is a magnetic material, its peripheral portion at which the lower edge of fixed core  1  is positioned (in this embodiment, the position where annular groove  18   d  is provided) is provided with non-magnetizing or weak-magnetizing processes by induction hardening (hereinafter, non-magnetizing and weak-magnetizing processes are referred to as the same). 
     The non-magnetizing process mentioned above is provided near the lower edge (magnetic attraction surface) of fixed core  1 , in other words, an area in which, at nozzle holder  4 , width (slightly greater than the annular groove width H in  FIG. 1 ) is given in a vertical direction around the position at which a perpendicular line crosses vertically to the axial line of fixed core  1 , at the lower end of the fixed core. The peripheral surface of the nozzle holder in this area is provided with an annular groove  18   d  which has a trapezoidal cross section. 
     Annular groove  18   d  mentioned above is provided to minimize, along with the non-magnetizing process mentioned above, magnetic flux leakage into the magnetic circuit formed to magnetically attract the needle  5 . That is to say, a portion of the nozzle holder  18  in this embodiment [the vicinity of the lower edge (magnetic attraction surface) of fixed core ] is non-magnetized to prevent magnetic flux leakage into the magnetic circuit near the lower edge of fixed core  1  and thus to ensure that magnetic fluxes flow intensively from fixed core  1  to movable core  14 . However, even when non-magnetization is provided, complete non-magnetization is difficult and part of the magnetic flux leaks more or less into the non-magnetized area as well. In order to minimize such leakage, the thickness of nozzle holder  18  is reduced via annular groove  18   d  to obtain higher magnetic resistance. 
     The thickness of the portion of nozzle holder  18  where fixed core is press-fit, and the thickness of holder top  18   a  for accommodating movable core  14  are the greatest in the entire nozzle holder, and intermediate portion  18   b  at which the connection between movable core  14  and valve body  16  is positioned is formed into tapered form. Furthermore, holder bottom  18   c  at which the valve body at the bottom of the above-mentioned intermediate portion is located is constructed into a thin and long shape, thus forming the so-called “long nozzle type” of nozzle holder  18 . 
     In addition to annular groove  18   d  mentioned above, an annular groove  18   e  spacedly above annular groove  18   d  is provided on the periphery of holder top  18   a . The numeral W 1  at annular groove  18   e  denotes the welded section between nozzle holder  18  and fixed core  1 , and at this W 1  position, nozzle holder  18  is welded over the entire periphery of fixed core  1 . The W 1  weld serves as a seal between nozzle holder  18  and the inner surface of fixed core, thereby preventing the leakage of the fuel flowing through injection valve body  100 . 
     Also, since annular groove  18   e  is provided at weld W 1 , it is possible to weld the thin portion of nozzle holder  18  and save the thermal energy required for welding, and thereby to prevent the components of the injection valve body from suffering thermal deformation due to the welding heat. 
     On the periphery of the holder bottom (so-called the long nozzle), a groove  18   g  for installing a sealing member is provided and a sealing member  42  (for example, a Teflon seal) is mounted in the groove  18   g.    
     For this long nozzle  18   c , when the mounting density of an air intake valve  101 , an air intake/exhaust valve drive  102 , an air intake pipe, and more, is high in an injection scheme under which fuel injection valve  100  is to be installed directly on the cylinder-head  106  of an engine  105  as shown in  FIG. 11 , since the main large-size components of the injection valve can be spaced from the above-mentioned components and cylinder head  106 , the nozzle  18   c  has the advantage that the flexibility of its installation is very high. Under prior art, when fuel injection valve  100  is installed on the cylinder head of an engine, gaskets are arranged between the bottom of the large-size yoke and the cylinder head to prevent combustion gas leakage from the engine. In the present embodiment, however, since seal ring  42  provided on the periphery of the slender “long nozzle” prevents combustion gas leakage from the engine by sealing the outer surface of long nozzle  18   c  and the inner surface of its insertion hole at the cylinder head side, the combustion gas pressure-receiving area can be reduced at that seal and thus the sealing member can be constructed into a compact and simplified shape and reduced in costs. 
     An orifice plate  19  and a fuel swirler  21  (hereinafter referred to simply as the swirler) are provided at the lower end of nozzle holder  18 , and these members,  18 ,  19 , and  21 , are molded using other members. 
     Orifice plate  19  is formed using, for example, a stainless steel disc-shaped chip, in the center of which is provided an injection hole (orifice)  20 , followed by a valve seat  19   a  formed upstream. 
     Orifice plate  19  is designed so that it can be press-fit into the inner lower end  18   f  of nozzle holder  18 . 
     Swirler  21  is designed so that it can be fit into the inner lower end of nozzle holder  18 , and is formed using a sintered alloy. 
     The detailed shape of swirler  21  is shown in FIG.  9 . Its sub-figures (a), (b), and (c) are a top view, a sectional view of section C-C′, and a bottom view, respectively. 
     Swirler  21  is a chip having a shape close to an equilateral triangle, and equipped with curves in three directions, instead of vertexes. A center hole (guide)  25  for slidably guiding the front end (valve body) of needle  5  is provided in the center of the chip, and guide grooves  24  for inducting the fuel to the peripheral sides  21 ′ of the chip are formed radially and outward with an annular groove  24 ′ as its center, are provided on the surface. 
     At the bottom of swirler  21 , an annular step (flow channel)  23  is formed on its outer fringes are formed, and between annular flow channel  23  and center hole  25 , multiple (for example, six) channel grooves  26  for swirling the fuel are arranged. 
     Channel grooves  26  are formed almost tangentially from the outside diameter of swirler  21  to the inside diameter so that when the fuel is injected, swirling force is applied thereto from channel grooves  26  towards the lower end of center hole  25 . 
     The above-mentioned annular step  23  is provided because it is required for the fuel to stop flowing. Also, a trilateral chamfer  21 ′ is formed on the periphery of swirler  21 . When swirler  21  is fit into the front end of nozzle holder  18 , the chamfer  21 ′ ensures the flow of the fuel at the inner surface of nozzle holder  18  and functions as a reference position during the formation of grooves such s  24  and  26 . The curved surfaces on the periphery of swirler  21  fit into the lower inner end of nozzle holder  18 . 
     When the swirler  21  is shaped into a curved form close to an almost equilateral triangle as mentioned above, there is the advantage that the chip, compared with a more-sided one, can achieve a sufficient fuel flow rate. 
     An inner surface (stepped inner surface)  18   f  with a receiving face  18   e  for mounting the swirler  21  and the orifice plate  19  is provided at the lower end (one end at the fuel injection side) of nozzle holder  18 . Swirler  21  is fit into the inner surface of the nozzle holder in such a manner that the swirler itself is accepted by the receiving face  18   e  of nozzle holder  18 , and orifice plate  19  is press-fit and welded on said inner surface so as to press swirler  21  against receiving face  18   e . Numeral W 4  denotes the welding section, at which the welding is provided over the entire periphery of orifice plate  19 . 
     In this way, swirler  21  and orifice plate  19  are mounted so that swirler  21  is held between receiving face  18   e  and orifice plate  19 . 
     In order to be pressed firmly against receiving face  18   e  located on nozzle holder  18 , the surface of swirler  21  is provided with fuel guide grooves  24 , and the fuel at the upstream side of the swirler flows into the fuel flow channel  22  on the outer surface of the swirler via the grooves  24 . 
     As shown in  FIG. 3 , the movable core  14  and valve body  16  at needle  5  are connected via a joint  15  having a spring function. Needle  5  contains a plate spring (damper plate)  50  between movable core  14  and joint  15 . 
     Also, a mass body (also referred to as a heavy bob or movable measure)  41  that can be moved in its axial direction, independently of needle  5 , is located in the area from an axial hole f, which constitutes the fuel flow channel of fixed core, to an axial hole provided in movable core  14 . Mass body  41  is positioned between return spring  7  and plate spring  50 . The spring load of return spring  7  is therefore applied to needle  5  via mass body  41  and plate spring  50 . 
     As shown in  FIGS. 2 and 3 , movable core  14  has an upper axial hole  14   a  for inducting a portion of mass body  41 , and a lower axial hole  14   b  having a thickness smaller than that of upper axial hole  14   a.    
     Joint  15  consists of a single cup-shaped pipe into which upper tubular portion  15   a  and lower tubular portion  15   c  smaller than it in terms of thickness were formed. Upper tubular portion  15   a  fits into the lower axial hole  14   b  of movable core  14  and is welded over its entire periphery to movable core  14 , at the position denoted by numeral W 2 , and thus the joint  15  and the movable core  14  are connected. 
     Plate spring  50  intervenes between the inner stepped surface  14   c , which is further located between the upper axial hole  14   a  and lower axial hole  14   b  of movable core  14 , and the upper edge of the upper tubular portion  15   a  of joint  15 . The entire upper periphery of the valve body (valve rod)  5  of the needle is welded for connection to the lower tubular portion  15   c  of joint  15 , at the position denoted by numeral W 3 . 
     Step  15   b  between the upper tubular portion  15   a  and lower tubular portion  15   c  of joint  15  functions as a plate spring. 
     As shown in  FIG. 6 , plate spring  50  is annular and its inner portion denoted by numeral  51  is a punched-through portion. A plurality of elastic pieces  50   a  are eject-formed inward via the punched-through portion, and the elastic pieces  50   a  are arranged at equal intervals in their circumferential direction. 
     The elastic pieces  50   a  of the plate spring  50  support the lower end of cylindrical movable mass body  41 . 
     In this embodiment, since plate spring  50  supports mass body (first mass body)  41  and the plate spring portion (stepped portion)  15   b  of the joint  15  supports movable core (second mass body)  14 , the mass body and the plate spring function (damper function) that supports it are of double structure. 
     And when the fuel injection valve is closed, if needle  5  collides with valve seat  19   a  by the spring action of return spring  7 , the resulting shock is absorbed by the plate spring portion  15   b  of joint  15  first and then the kinetic energy generated by the restitution of needle  5  is absorbed by the inertia of movable mass body  9  and the elastic deformation of plate spring  50  in order to prevent the restitution from actually occurring. Under the double damper structure, in particular, that is shown in this embodiment, even for the fuel injection valve of the intra-tubular injection scheme which creates significant spring load of return spring  7 , secondary injection associated with the restitution of needle  5  can be effectively prevented by sufficiently attenuating the shock energy generated when the valve body is closed. 
     An enlarged structural view of the joint  15  mentioned above is shown as FIG.  5 . Joint  15 , together with the mass body  41  mentioned above, has its interior functioning as a fuel flow channel f, and a plurality of holes  15   d  for inducting the fuel into nozzle holder  18  are arranged at stepped portion  15   d.    
     Portions of movable core  14  and valve rod  16  form a guide surface at the movable side. Also, the inner surface of the upper tubular portion  18   a  of nozzle holder  18  functions as a guide surface for slidably guiding the movable core  14 , and the inner surface of the axial hole  25  in swirler  21  functions as a guide surface for slidably guiding the valve rod  16 . Thus, the so-called “two-point support guide scheme” is constituted. 
     Yoke  4  is a press-machined, magnetic stainless steel material, and has a cylindrical coil storage element  4   a  for accommodating electromagnetic coil  2 , a tapered throttle element  4   b  located directly under the storage element, and a cylindrical yoke bottom  4   c  located directly under the tapered throttle element. 
     The upper end of the yoke has a hole, through which electromagnetic coil  2  is accommodated and is supported and positioned at the curve  4   b  of the internal boundary between coil storage element  4   a  and tapered element  4   b . The inner surface of yoke bottom  4   c  and a portion on the periphery of nozzle holder  18  are press-fit, and the annular clearance  34  surrounded by the bobbin bottom of electromagnetic coil  2 , the inner surface of tapered element  4   b , and the outer surface of nozzle holder  18 , acts as an air gap to prevent magnetic flux leakage from the needle attraction magnetic circuit formed by fixed core  1 , movable core  14 , nozzle holder  18 , and yoke  4 . 
     In this embodiment, the stroke of needle  5  is provided for at valve seat  19   a  and the lower end of fixed core  1 . 
     Since, for the above reason, the lower edge of fixed core  1  and the surface of movable core  14  collide during valve closing, the lower edge of fixed core  1  and the surface of movable core  14  are provided with hard coating (for example, chromium plating). 
     As shown in  FIG. 7 , the lower end  1   b  of fixed core  1  has a curve  1   c  functioning as a curved guide surface for press-fitting into nozzle holder  18  (curve  1   c  is an area denoted by numeral L 1  in  FIG. 7 , and in this embodiment, curve  1   c  has a curvature of about 12.5 mm). Since, in this way, the lower end  1   b  of fixed core  1  is tapered by being formed into curved guide surface  1   c , a smooth press-fit can be guaranteed, compared with the case that the lower end of the fixed core is formed into a tapered shape. That is to say, for a tapered shape, since a wide-angle edge is formed at the crossing portion between the taper line and the straight line intersecting therewith, although the press-fit section of the nozzle holder is likely to scuff at the wide-angle edge during press-fitting, this problem does not occur in the present embodiment. Although the hard coating process  60  instituted at the lower edge of fixed core  1  extends to the lower side face of fixed core  1 , the area from the lower edge of fixed core  1  to curved guide surface  1   c  (not overstepping the range of L 1 ) is provided with hard coating for sufficient wear resistance and shock resistance so as not to cause trouble with press-fitting (more specifically, so that the outside diameter of the fixed core lower edge, including the thickness of hard coating, does not exceed the outside diameter of the straight portion of the fixed core). 
     As shown in  FIG. 4 , valve body  16  of needle  5  has a front end formed into a shape consisting of a combination of a spherical surface  16   a  and a conical protrusion  16   b , and the spherical surface  16   a  and the conical protrusion  16   b  have a discontinuous portion shown as  16   c . Spherical surface  16   a  is rested on valve seat  19   a  when the valve is closed. Since the contact surface on valve seat  19   a  is formed as spherical surface  16   a , the occurrence of a clearance between the valve seat and the valve body is prevented, even when the valve body inclines. Conical protrusion  16   b  ensures smooth flow of the fuel by reducing the dead volume of orifice  20 . 
     Also, the formation of the discontinuous portion mentioned above brings about the advantage that compared with the case that the conical portion and the spherical portion are made continuous, finishing by polishing can be made easy. Numeral  27  denotes a resin mold having a connector. 
     As shown in  FIG. 2 , fuel induction pipe  40  and fixed core  1  are welded beforehand. Under this state, the edge of fixed core  1  is provided with chromium plating  60 . 
     Also, orifice plate  19  is press-fit and welded at the front end of nozzle holder  18  with swirler  21  in between, preassembled needle  5  is inserted into nozzle holder  18  (after being assembled, needle  5  is provided with chromium plating  61 ), and fixed core  1  is press-fit into this nozzle holder  18 . The stroke of needle  5  is determined by the press-fitting allowance of fixed core  1 . This press-fitting allowance of fixed core  1  is detected by a sensor, and when the required press-fitting allowance is reached, the press-fitting process is completed. After this, nozzle holder  18  and fixed core  1  are welded. 
     Next, electromagnetic coil  2  is threaded onto the outer surface of fixed core  1  via a bobbin, yoke  4  is press-fit from its axial direction into the upper tubular portion  18   a  of nozzle holder  18  (the press-fitting section is the lower end  4   c  of yoke  4 ), and the upper fringe of yoke  4  is welded onto the flange  1   a  of fixed core  1 . 
     After that, the pin terminal  30  of the electromagnetic coil is bent and then provided with resin molding  27 . Mass body  41 , return spring  7 , spring adjusting member  6 , fuel filter  31 , O-ring  32 , and backup ring  33  are assembled in the final process. 
     According to the present embodiment, the following effects can be obtained: 
     (1) Fuel induction pipe  40 , fixed core  1 , and nozzle holder  18  are connected into a single unit by welding, and this unit is the fuel flow channel assembly in the present embodiment. By constituting the fuel flow channel assembly in this way, it is possible for only the fixed core  1 , which is to operate as the main magnetic circuit, to be formed into a relatively thick shape to ensure a magnetic path, and for fuel induction pipe  40  to be formed into a thin shape using a non-magnetic pipe, since this induction pipe does not function as a magnetic path. It is also possible to reduce the thickness of nozzle holder  18  and to set the elements of the fuel flow channel assembly to the appropriate specifications according to the particular needs of each. In addition, the elements of the fuel flow channel assembly can be mass-produced at low costs by press-machining each. 
     (2) Furthermore, even when nozzle holder  18  is press-fit into fixed core  1 , since yoke  4  and fixed core  1  are connected at weld W 5 , it is possible to minimize the magnetic gaps for electromagnetic valve actuation. Besides, at the magnetic path portion of fixed core  1 , the section of the nozzle holder  18  that has been press-fit and welded at the magnetic path portion of the fixed core is added to this portion, and thus, magnetic flux leakage from the magnetic circuit is minimized at the position of annular groove  18   d  by collaboration between the presence of this groove  18   d , the non-magnetizing process, and the presence of annular air gap  34 , with the result that the magnetic fluxes flow intensively between the lower end of fixed core  1  and movable core  14  and enables the magnetic attraction characteristics of the electromagnetic valve to be improved. 
     (3) Also, since both the shock during the closing of the fuel injection valve and the restitution of the valve body is effectively minimized by double damper structure, secondary injection can be prevented more effectively than before. 
     In the embodiment set forth above, although the present invention is exemplified using the fuel injection valve of the intra-tubular injection scheme, the invention can also be applied to the fuel injection valve to be located on an air intake channel. 
     As set forth above, according to the present invention, it is possible to supply a compact, electromagnetic fuel injection valve reduced in dimensions, especially in diameter, provided with an inexpensive and sufficient magnetic circuit, and excellent in performance, so as to make the main unit of the fuel injection valve suitable for injection schemes such as the direct intra-tubular injection scheme described above: