Abstract:
A fuel injection valve for an internal combustion engine has a tubular metal case constructed of a magnetic material in and through which a fuel is to flow. The tubular metal case has one open end. A valve seat is tightly received in the open end of the tubular metal case. The valve seat has a fuel outlet formed therein. A valve element is axially movably received in the tubular metal case. The valve element is movable between a closed position wherein a valve body of the element closes the fuel outlet and an open position wherein the valve body opens the fuel outlet. An electromagnetic actuator is disposed about the tubular metal case to actuate the valve element to move between the closed and open positions. The tubular metal case is constructed of a ferritic stainless steel containing Titanium. An end portion of the tubular metal case to which a valve seat is fixed has a wall thickness which ranges from approximately 0.1 mm to 0.9 mm.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fuel injection valves connected to an automotive internal combustion engine for injecting fuel into combustion chambers of the engine. More specifically, the present invention is concerned with the fuel injection valves of a type which is compact in size, light in weight and easy to produce. 
     2. Description of Related Art 
     Hitherto, various types of fuel injection valves are proposed and put into practical use particularly in the field of automotive internal combustion engines. Some of them are shown in Laid-open Japanese Patent Application (Tokkai) 2000-08990 and Laid-open German Patent Application (DE) 19547406A1. The fuel injection valves of these references are of a type that generally comprises a tubular metal case, a valve element axially movably received in the metal case, a solenoid coil disposed about the metal case and a plastic cover applied on both the metal case and the solenoid coil by means of injection molding technique. However, in the fuel injection valves of this type, compactness and weight reduction have been difficult due to some reasons. One reason is a difficulty with which the thickness of wall of the tubular metal case is reduced. That is, if the thickness is simply reduced, the metal case fails to have a sufficient mechanical strength bearing a marked pressure applied thereto when the injection molding is applied thereto. The other reason is a complicated shape which the tubular metal case has. In fact, the metal case is constructed to have stepped portions. Thus, the fuel injection valves of the publications tend to have a bulky and heavier construction. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a fuel injection valve which is compact in size, light in weight and easy to produce. 
     According to a first aspect of the present invention, there is provided a fuel injection valve which comprises a tubular metal case constructed of a magnetic material in and through which a fuel is to flow, the tubular metal case having one open end; a valve seat tightly received in the open end of the tubular metal case, the valve seat having a fuel outlet formed therein; a valve element axially movably received in the tubular metal case, the valve element being movable between a closed position wherein a valve body of the element closes the fuel outlet and an open position wherein the valve body opens the fuel outlet; and an electromagnetic actuator disposed about the tubular metal case to actuate the valve element to move between the closed and open positions, wherein the tubular metal case is constructed of a ferritic stainless steel containing Titanium. 
     According to a second aspect of the present invention, there is provided a fuel injection valve which comprises a tubular metal case constructed of a magnetic material in and through which a fuel is to flow, the tubular metal case including a first portion with one end, a second portion with the other end and a third portion extending between the first and third portions; a valve seat tightly received in the first portion of the metal case, the valve seat having a fuel outlet formed therein; a valve element axially movably received in the third portion of the metal case, the valve element being movable between a closed position wherein a valve body of the element closes the fuel outlet and an open position wherein the valve body opens the fuel outlet; an electromagnetic actuator disposed on and about the third portion of the metal case to actuate the valve element to move between the closed and open positions; a plastic cover applied mainly onto the second portion of the metal case through an injection molding, wherein the first portion of the metal case has a wall thickness which ranges from approximately 0.1 mm to 0.9 mm, the second portion of the metal case has a wall thickness which is greater than that of the first portion by at least approximately 0.1 mm, and the third portion of the metal case has the same wall thickness as one of the first and second portions. 
     Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinally sectional view of a fuel injection valve which is a first embodiment of the present invention; 
     FIG. 2 is a longitudinally sectional enlarged view of a nozzle part of the fuel injection valve of the first embodiment; 
     FIG. 3 is a sectional view taken along the line III—III of FIG. 1; 
     FIG. 4 is a longitudinally sectional view of a tubular metal case employed in the fuel injection valve of the first embodiment; 
     FIG. 5 is a longitudinally sectional view of a semi-finished fuel injection valve of the first embodiment; 
     FIG. 6 is a longitudinally sectional view of the semi-finished fuel injection valve that is kept set in a mold unit for being applied with a plastic cover thereon; 
     FIG. 7 is a longitudinally sectional view of the fuel injection valve of the first embodiment in a disassembled condition; 
     FIG. 8 is a view similar to FIG. 1, but showing a fuel injection valve of a second embodiment of the present invention; 
     FIG. 9 is a longitudinally sectional view of a tubular metal case employed in the fuel injection valve of the second embodiment; 
     FIG. 10 is a view similar to FIG. 2, but showing a fuel injection valve of a third embodiment of the present invention; 
     FIG. 11 is a sectional view of a metal plate that is used for producing a tubular metal case employed-in the third embodiment; 
     FIG. 12 is a sectional view showing a condition wherein the metal plate is under a first deep drawing process; 
     FIG. 13 is a view similar to FIG. 12, but showing a condition wherein the metal plate is under a second deep drawing process; 
     FIG. 14 is a longitudinally sectional view of the tubular metal case produced by being applied with a third deep drawing process after the first and second deep drawing processes; 
     FIG. 15 is a longitudinally sectional view of the fuel injection valve of the third embodiment in a disassembled condition; 
     FIG. 16 is a view similar to FIG. 4, but showing a tubular metal case employed in a fuel injection valve of a fourth embodiment of the present invention; 
     FIG. 17 is a longitudinally sectional view of a metal tube used for producing the tubular metal case employed in the fourth embodiment of the present invention; and 
     FIG. 18 is a schematic drawing showing a drawing process applied to the metal tube. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     For ease of understanding, the following explanation may include various directional terms, such as, right, left, upper, lower, rightward, etc.,. However, these terms are to be understood with respect to only the drawing or drawings on which corresponding part or portion is illustrated. Furthermore, throughout the embodiments, substantially same parts and portions are denoted by the same numerals. 
     Referring to FIGS. 1 to  7 , especially FIG. 1, there is shown a fuel injection valve of a first embodiment of the present invention, which is generally designated by numeral  100 A. 
     The fuel injection valve  100 A, like the other valves  100 B,  100 C and  100 D which will be described hereinafter, is a valve that is constructed to be practically applicable to an internal combustion engine. 
     As is seen from FIG. 1, the fuel injection valve  100 A has a valve casing unit  1  which includes a tubular metal case  2 , a tubular metal cover  12  and a plastic cover  14 . 
     The tubular metal case  2  is of a magnetic material such as a magnetic stainless steel or the like. As will be described hereinafter, the tubular metal case  2  may be constructed of a ferritic stainless steel including Titanium (Ti). For producing the metal case  2 , various techniques such as deep drawing technique, cutting technique, grinding technique and the like can be used. 
     FIG. 4 shows the detail of the tubular metal case  2  produced through such techniques. As shown in this drawing, the metal case  2  is formed with stepped portions. 
     As is seen from FIG. 1, the tubular metal case  2  comprises generally a smaller diameter lower portion (or first portion)  2 A to which an after-mentioned valve seat  5  is fixed, an intermediate portion (or third portion)  2 B which has an after-mentioned electric coil  11  disposed thereon, and a larger diameter upper portion (or second portion)  2 C which has a major portion of the plastic cover  14  disposed thereon. 
     As is seen from FIG. 4, the lower and intermediate portions  2 A and  2 B of the tubular metal case  2  have a wall thickness “a” of about 0.1 mm to 0.9 mm, preferably about 0.2 mm to 0.5 mm. The diameter of the lower portion  2 A is smaller than that of the intermediate portion  2 B. The intermediate portion  2 B is formed near the lower portion  2 A with an annular recess  2 D whose bottom wall has a thickness “t” smaller than “a”. 
     As is seen from FIG. 2, upon assembly, the annular recess  2 D is positioned to surround a given clearance “S” which is defined between mutually facing ends of after-mentioned valve element  7  and core tube  8 . Accordingly, the intermediate portion  2 B of the tubular metal case  2  has two portions, one being a valve element receiving portion  2 B 1  in which the valve element  7  is slidably received, and the other being a core tube receiving portion  2 B 2  in which the core tube  8  is tightly received. Due to provision of the annular recess  2 D, a magnetic resistance between the two portions  2 B 1  and  2 B 2  is increased, which isolates these two portions  2 B 1  and  2 B 2  magnetically. 
     The larger diameter upper portion  2 C of the tubular metal case  2  is sized larger than the intermediate portion  2 B in diameter. Furthermore, as is seen from FIGS. 1 and 2, the wall thickness “b” of the upper portion  2 C is larger than that “a” of the lower and intermediate portions  2 A and  2 B. With this increased thickness “b” of the wall, the upper portion  2 C can bear the remarkable pressure applied thereto when a molten plastic is applied thereonto under an injection molding. As is understood from the following inequality, the thickness “b” is greater than “a” by at least 0.1 mm. 
     
       
           b≧a+ 0.1  (1) 
       
     
     In view of the inequality (1), the thickness “b” of the wall of the larger diameter upper portion  2 C is about 0.2 mm to 1.0 mm, preferably about 0.3 mm to 0.6 mm. 
     Accordingly, as is seen from FIG. 4, the tubular metal case  2  consists of two portions, one being a thinner wall portion “A” including the lower and intermediate portions  2 A and  2 B, and the other being a thicker wall portion “B” including the upper portion  2 C. 
     Referring back to FIG. 1, within the tubular metal case  2 , there is defined a fuel passage  3  which leads to the valve seat  5  fixed in the smaller diameter lower portion  2 A of the case  2 . Furthermore, a fuel filter  4  is fixed to an upper portion of the fuel passage  3  to filter a fuel flowing through the fuel passage  3 . 
     As is best seen from FIG. 2, the valve seat  5  is shaped cylindrical and concentrically and tightly received in the lower portion  2 A of the case  2 . For the tight receiving, the valve seat  5  is welded to the lower portion  2 A. The valve seat  5  is formed with a fuel outlet  5 A which faces downward in the drawing, and a concave valve seating surface  5 B which extends around the fuel outlet  5 A. A nozzle plate  6  is secured to a bottom wall of the valve seat  5 , which is formed with a plurality of injection nozzles  6 A mated with the fuel outlet  5 A of the valve seat  5 . 
     As shown in FIG. 1, the valve element  7  is slidably received in the valve element receiving portion  2 B 1  of the tubular metal case  2 . The valve element  7  is constructed of a magnetic metal and comprises a tubular valve stem  7 A, a spherical valve body  7 B fixed to a leading end of the valve stem  7 A and hermetically contactable to the valve seating surface  5 B of the valve seat  5  and a base portion  7 C slidably received in the valve element receiving portion  2 B 1  and constituting a base of the valve stem  7 A. 
     When the valve element  7  is in a closed position, the valve body  7 B is hermetically seated on the valve seating surface  5 B by the force of an after-mentioned biasing spring  9 . Under this condition, an upper end surface faces a lower end surface of the core tube  8  keeping the given clearance “S” defined therebetween. While, when the electric coil  11  is energized to generate a magnetic field “H”, the core tube  8  magnetically attracts the valve element  7 , so that the valve element  7  is lifted up against the force of the biasing spring  9  from the valve seating surface  5 B by a distance corresponding to the given clearance “S”. With this lifting, the valve element  7  takes an open position opening the injection nozzles  6 A. 
     The core tube  8  is of a magnetic metal and press-fitted in the core tube receiving portion  2 B 2  of the tubular metal case  2 . The core tube  8  has a tubular spring holder  10  press-fitted therein. 
     The biasing spring  9  is compressed between the valve element  7  and the tubular spring holder  10 , so that valve element  7  is constantly biased downward in FIG. 2, that is, in a direction to close the injection nozzles  6 A. 
     As is best seen from FIG. 2, the electric coil  11  is arranged to put around the core tube receiving portion  2 B 2  of the tubular metal case  2 . More specifically, the electric coil  11  is a unit which is put between the metal case  2  and the metal cover  12  and comprises a bobbin  11 A of plastic disposed about the portion  2 B 2  and a coil  11 B put around the bobbin  11 A. When energized, the electric coil  11  generates a magnetic field “H” to pull and open the valve element  7  against the force of the biasing spring  9 . For feeding electric power to the coil  11 , connector pins  15 A are provided on the case  2 , as will be described in detail hereinafter. 
     The tubular metal cover  12  is of a magnetic metal and shaped cylindrical to constitute a magnetic path. As is seen from FIGS. 2 and 3, the tubular metal cover  12  comprises a larger diameter tubular portion  12 A disposed around the electric coil  11 , a smaller diameter tubular portion  12 B disposed around the valve element receiving portion  2 B 1  of the tubular metal case  2  and an annular stepped portion  12 C (see FIG. 2) extending between the larger and smaller diameter tubular portions  12 A and  12 B. 
     As is seen from FIGS. 2 and 3, within an annular space defined between the larger diameter tubular portion  12 A and the smaller diameter lower portion  2 A of the tubular metal case  2 , there is disposed a connecting metal core  13  having a generally C-shaped cross section. The core  13  is of a magnetic metal. With the metal core  13  and the annular stepped portion  12 C, the tubular metal cover  12  is magnetically connected to the metal case  2  at axially both ends of the electric coil  11 . 
     Due to provision of the annular recess  2 D of the tubular metal case  2 , the valve element receiving portion  2 B 1  and the core tube receiving portion  2 B 2  are magnetically isolated from each other. Thus, upon energization of the electric coil  11 , a magnetic field “H” is stably produced along a magnetic path consisting of the portions  2 B 1  and  2 B 2 , the base portion  7 C of the valve element  7 , the core tube  8 , the tubular metal cover  12  and the metal core  13 , so that the core tube  8  can assuredly attract the valve element  7  to open the same. 
     As is seen from FIG. 1, the plastic cover  14  covers the upper portion of the tubular metal case  2 . For providing this plastic cover, an injection technique is used, which will be described in detail hereinafter. The plastic cover  14  comprises an upper portion covering the larger-diameter upper portion  2 C of the tubular metal case  2  and a lower portion covering the larger diameter tubular portion  12 A of the tubular metal cover  12 . The plastic cover  14  is integrally formed with the above-mentioned connector housing  15 . Connector pins  15 A are held in the connector housing  15 , which lead to the electric coil  11 . 
     When, as is seen from FIG. 6, an injection molding is practically carried out, a very high pressure of molten plastic is applied to the larger diameter upper portion  2 C of the tubular metal case  2 . Accordingly, in the first embodiment  100 A, for bearing such high pressure, the wall thickness of only the larger diameter upper portion  2 C of the case  2  is increased as compared with that of the lower and intermediate portions  2 A and  2 B. 
     In the following, operation of the fuel injection valve  100 A will be described with reference to FIGS. 1 and 2. 
     When the electric coil  11  is energized through the connector pins  15 A, a magnetic field “H” is produced as is shown in FIG. 2, causing the core tube  8  to magnetically attract the valve element  7  against the force of the biasing spring  9 . With this, the valve element  7  is released from the seating surface  5 B of the valve seat  5  opening the injection nozzles  6 A. Upon this, a given amount of fuel is injected into, for example, a combustion chamber through the injection nozzles  6 A. When energization of the electric coil  11  stops, the magnetic field “H” disappears and thus the valve element  7  is moved onto the seating surface  5 B due to the force of the biasing spring  9 . Upon this, fuel injection into the combustion chamber is stopped. 
     In the following, steps for assembling the fuel injection valve  100 A will be described with reference to the drawings. 
     First, the tubular metal case  2  as shown in FIG. 4 is produced. For this production, various techniques, such as, deep drawing technique, cutting technique, grinding technique and the like are practically used. 
     Then, as is seen from FIG. 5, the electric coil  11 , the tubular metal cover  12  and the connecting metal core  13  are put around the intermediate portion  2 B of the metal case  2  together with the connector pins  15 A, and the metal cover  12  is secured to the metal case  2  through welding. The valve seat  5  is put into the smaller diameter lower portion  2 A of the metal case  2  and welded thereto. With these steps, a so-called semi-finished assembly  16  is produced. 
     Then, the semi-finished assembly  16  is brought to an injection molding process and put into a split mold  17 , as is seen from FIG.  6 . As shown in the drawing, the mold  17  is constructed to have a cavity  17 A whose shape is matched with the finished fuel injection valve  10 A. A molten plastic is injected into the cavity  17 A at a predetermined injection pressure, and after a while, that is, when the plastic becomes cured having a certain hardness, the mold  17  is dismantled to release a product  16 ′ as shown in FIG.  7 . With this injection process, the connector housing  15 , the plastic cover  14  and an annular plastic ring  14 ′ covering the lower portion  2 A of the metal case  2  are integrally formed on the semi-finished assembly  16 . 
     As has been described hereinabove, the upper portion  2 C of the metal case  2  has a sufficiently thicker wall to bear the injection pressure, and thus, the upper portion  2 C is suppressed from undesired deformation. 
     Then, as is seen from FIG. 7, remaining parts are assembled to the product  16 ′, which are the valve element  7 , the core tube  8 , the biasing spring  9  and the spring holder  10 . 
     As has been described hereinabove, in the first embodiment  100 A of the present invention, the diameter of the intermediate portion  2 B of the case  2  about which the electric coil  11  is disposed is reduced as compared with that of the upper portion  2 C, and only the larger diameter upper portion B (see FIG. 4) or  2 C of the case  2 , to which a marked injection pressure is applied, has a larger wall thickness. That is, the lower and intermediate portions A (see FIG. 4) or  2 A and  2 B, on which the valve seat  5 , the valve element  7  and the electric coil  11  are mounted, has a thinner wall thickness. 
     Thus, a compact and light weight fuel injection valve  100 A can be easily produced. Furthermore, due to provision of the annular recess  2 D on tubular metal case  2 , the magnetic resistance between the two portions  2 B 1  and  2 B 2  (see FIG. 2) is increased and thus a magnetic isolation between the two portions is improved. 
     Referring to FIGS. 8 and 9, especially FIG. 8, there is shown a fuel injection valve of a second embodiment of the present invention, which is generally designated by numeral  100 B. 
     Since the fuel injection valve  100 B of the second embodiment is similar to the above-mentioned valve  100 A of the first embodiment, only parts or portions which are different from those of the first embodiment  100 A will be described in the following. 
     That is, as is seen from FIG. 9, a tubular metal case  22  employed in the second embodiment  100 B is different from that  2  of the first embodiment  100 A. 
     As will be understood when comparing FIGS. 9 and 4, the tubular metal case  22  of the second embodiment  100 B comprises a smaller diameter lower portion  22 A to which the valve seat  5  is to be fixed, an intermediate portion  22 B around which the electric coil  11  is to be disposed, and a larger diameter upper portion  22 C around which the major portion of the plastic cover  14  is to be disposed. 
     As shown in FIG. 9, in the second embodiment  100 B, the wall thickness of the intermediate portion  22 B is equal to that of the upper portion  22 C. The intermediate portion  22 B is formed with an annular recess  22 D whose bottom wall has a thickness “t′”. Due to provision of the annular recess  22 D, the intermediate portion  22 B is divided into a valve element receiving portion  22 B 1  and a core tube receiving portion  22 B 2 . 
     The lower portion  22 A of the tubular-metal case  22  has a wall thickness “a′” of about 0.1 mm to 0.9 mm, preferably about 0.2 mm to 0.5 mm. The intermediate portion  22 B and the upper portion  22 C of the case  22  have a wall thickness “b′” that is greater than that “a′” of the lower portion  22 A by at least 0.1 mm. That is, the tubular metal case  22  consists of two portions, one being a thinner wall portion “A′” including the lower portion  22 A, and the other being a thicker wall portion “B′” including the intermediate and upper portions  22 B and  22 C. 
     Also, in this second embodiment  100 B, the diameter of the intermediate portion  22 B of the case  22  about which the electric coil  11  is to be disposed is reduced as compared with that of the upper portion  22 C. Thus, a compact and light weight fuel injection valve  100 B can be easily produced. Due to increased wall thickness of the intermediate portion  22 B, the tubular metal case  22  is much assuredly suppressed from an undesirable deformation thereof, which would appear upon the injection molding of the valve casing unit  21 . 
     Referring to FIGS. 10 to  15 , particularly FIG. 10, there is shown a fuel injection valve of a third embodiment of the present invention, which is generally designated by numeral  100 C. 
     In the third embodiment  100 C, a tubular metal case  32  as shown in FIG. 14 is used, which is constructed of a ferritic stainless steel containing Titanium (Ti), as will be described in detail hereinafter. As shown in the drawing, in this third embodiment  100 C, the tubular metal case  32  has an even wall thickness “a” throughout the entire length thereof. Preferably, the thickness “a” is about 0.1 mm to about 0.9 mm. 
     That is, as is seen from FIG. 10, a smaller diameter lower portion  32 A to which the valve seat  5  is to be fixed, an intermediate portion  32 B which has the electric coil  11  to be disposed thereon, and a larger diameter upper portion  32 C which has the major portion of the plastic cover  14  to be disposed thereon have the even wall thickness therethroughout. As is seen from FIG. 14, a stepped portion defined between the intermediate and upper portions  32 B and  32 C is denoted by  32 C 1 , and a stepped portion defined between the lower and intermediate portions  32 A and  32 B is denoted by  32 B 1 . An annular recess formed on the intermediate portion  32 B is denoted by  32 D. Due to provision of the annular recess  32 D, the intermediate portion  32 B is divided into a valve element receiving portion  32 B 2  and a core tube receiving portion  32 B 3 . 
     In the following, the material of the tubular metal case  32  will be described in detail. 
     That is, the metal case  32  is constructed of a ferritic stainless steel containing about 0.01 to about 0.12 (preferably, 0.01 to 0.05) wt. % of Carbon, which further contains over 16 wt. % of Chromium (Cr), over 0.08 wt. % of Nickel (Ni) and about 0.2 to 0.6 wt. % of Titanium (Ti). Percentage content of Titanium (Ti) is greater than that of Carbon (C). 
     For finding out the composition of material appropriate to the tubular metal case  32 , an examination was carried out by the applicants, which will be described in the following. 
     Table-1 shows three Examples that were used as the material of the metal case  32 . For comparison, one Reference examined is also shown. 
     
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                 Percentage Contents (wt. %) 
               
             
          
           
               
                   
                 Example-1 
                 Exampe-2 
                 Example-3 
                 Reference 
               
               
                 Elements 
                 SUS430M2 
                 SUS430M3 
                 SUS430WD 
                 SUS430 
               
               
                   
               
             
          
           
               
                 Cr 
                 16.46 
                 17.3 
                 16.31 
                 16-18 
               
               
                 C 
                 0.03 
                 0.01 
                 0.01 
                 below 0.12 
               
               
                 Si 
                 0.39 
                 0.45 
                 0.13 
                 below 0.75 
               
               
                 Mn 
                 0.28 
                 0.22 
                 1.43 
                 below 1.00 
               
               
                 P 
                 0.022 
                 0.027 
                 0.03 
                 below 0.04 
               
               
                 S 
                 0.006 
                 0.007 
                 0.005 
                 below 0.03 
               
               
                 Ni 
                 0.12 
                 0.17 
                 0.08 
                 — 
               
               
                 Mo 
                 — 
                 0.4 
                 — 
                 — 
               
               
                 N 
                 0.009 
                 — 
                 — 
                 — 
               
               
                 Ti 
                 0.27 
                 0.55 
                 0.22 
                 — 
               
               
                 Fe 
                 Residual 
                 Residual 
                 Residual 
                 Residual 
               
               
                 Total 
                 100 
                 100 
                 100 
                 100 
               
               
                   
               
             
          
         
       
     
     Table-2 shows the performance of the three Examples and the Reference. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Example-1 
                 Example-2 
                 Example-3 
                 Reference 
               
               
                   
                 SUS430M2 
                 SUS430M3 
                 SUS430WD 
                 SUS430 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Elongation rate 
                 32 
                 32 
                 34 
                 over 22 
               
               
                 (%) 
               
               
                 Hardness (Hv) 
                 154 
                 163 
                 142 
                 below 200 
               
               
                   
               
             
          
         
       
     
     The tubular metal cases subjected to the examination were produced in the following manner, which will be described with reference to FIGS. 11,  12  and  13 . 
     As is seen from FIG. 11, four metal plates  50  of the above-mentioned ferritic stainless steel were prepared, which were Example-1, Example-2, Example-3 and Reference. 
     Each metal plate  50  was then subjected to a three-step deep drawing process which was carried out by three mold units in order. 
     First, as is seen from FIG. 12, the metal plate  50  was set in a first mold unit  52  which comprises a female die  52 A, a male die  52 B and a holder  52 C. By pushing a given portion of the metal plate  50  into a bore of the female die  52 A by the male die  52 B, the smaller diameter lower portion  32 A of the metal case  32  was drawn or produced. Then, as is seen from FIG. 12, the metal plate  50  was set in a second mold unit  54  which comprises a female die  54 A, a male die  54 B and a holder  54 C. The drawn part  32 A of the metal plate  50  was put in a bore of the female die  54 A. The bore of the female die  54 A was somewhat larger than that of the female die  52 A of the first die unit  52 . Then, the male die  54 B was pushed into the drawn part  32 A of the metal plate  50 . With this, the intermediate portion  32 B of the metal case  32 , which extends from the lower portion  32 A, was drawn or produced. Then, although not shown in the drawings, the metal plate  50  was set in a third die unit and subjected to a similar drawing process. The bore of the female die of the third mold unit was somewhat larger than that of the female die  54 A of the second mold unit  54 . With the process of the third mold unit, the larger diameter upper portion  32 C of the metal case  32  was drawn or produced. Then, the deeply drawn tubular part consisting of the three portions  32 A,  32 B and  32 C was cut away from a remaining part of the metal plate  50 . Then, the deeply drawn tubular part thus cut was subjected to cutting and shaving processes to produce a finished product, viz., the tubular metal case  32  as shown in FIG.  14 . 
     Then, the four tubular metal cases  32  thus produced were subjected to a visual inspection. No damage was found in any of the Examples-1, 2 and 3, except the Reference. 
     As is seen from FIG. 15, in an assembling process, the tubular metal case  32  is applied and equipped with the electric coil  11 , the metal cover  12 , the connecting metal core  13 , the plastic cover  14  including the connector housing  15 , the valve seat  5 , the valve element  7 , the core tube  8 , the biasing spring  9  and the spring holder  10  in the same manner as is described hereinabove. 
     In the fuel injection valve  100 C of the third embodiment, the tubular metal case  32  is constructed of a ferritic stainless steel containing Titanium (Ti). Thus, mechanical strength, corrosion resistance and productivity of the metal case  32  increased or improved. It was found that when Titanium (Ti) occupied 0.2 to 0.6 wt. % in the ferritic stainless steel and exceeded the content of Carbon (C), the deep drawing for the metal case  32  was much easily carried out. It was further found that when Carbon (C) occupied 0.01 to 0.12 wt. %, the corrosion resistance of the metal case  32  was quite improved. Furthermore, it was found that addition of over 0.3 wt. % of molybdenum (Mo) further improved the corrosion resistance of the metal case  32 . 
     Referring to FIGS. 16 to  18 , particularly FIG. 16, there is shown a tubular metal case  42  which is employed in a fuel injection valve  100 D of a fourth embodiment of the present invention. 
     In this fourth embodiment  100 D, the tubular metal case  42  is produced by rolling a metal plate  50  (see FIG. 11) to form a pipe, welding circumferentially opposed edges of the pipe and drawing given portions of the pipe to form stepped portions. A line indicated by numeral  54  in FIG. 16 is the circumferentially opposed edges to which welding has been applied. 
     That is, by taking the following steps, the metal plate  50  is shaped into a finished product, that is, the tubular metal case  42 . 
     As is seen from FIG. 17, by using a rolling machine, the metal plate  50  is shaped into a pipe  42 ′, then by using a seam welding machine, circumferentially opposed edges  54  are welded. Then, as is seen from FIG. 18, the pipe  42 ′ is applied to a drawing machine  56  which comprises a pair of rollers  58 A and  58 B and a stepped male die  60 . That is, the mail die  60  is put into the pipe  42 ′ and the pipe  42 ′ is brought into a space defined between the paired rollers  58 A and  58 B. Then, the rollers  58 A and  58 B are rotated and moved toward each other narrowing the space. With this, a stepped portion  42 B 1  is formed on-the pipe  42 ′ near the smaller diameter lower portion  42 A. By taking a similar process, another stepped portion  42 C 1  (see FIG. 16) is formed on the pipe  42 ′. 
     In the above-mentioned third and fourth embodiments  100 C and  100 D, a ferritic stainless steel containing Titanium (Ti) is used as the material of the tubular metal cases  32  and  42 . However, if desired, over 0.3 wt. % of copper (Cu), over 0.3 wt. % of niobium (Nb) or both of them may be added to the material for much increasing or improving mechanical strength and corrosion resistance of the case  32  or  42 . 
     The entire contents of Japanese Patent Applications 2001-163414 filed May 30, 2001 and 2001-165518 filed May 31, 2001 are incorporated herein by reference. 
     Although the invention has been described above with reference to the embodiments of the invention, the invention is not limited to such embodiments as described above. Various modifications and variations of such embodiments may be carried out by those skilled in the art, in light of the above description.