Patent Publication Number: US-6341592-B2

Title: Fuel injector and internal combustion engine having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of application Ser. No. 09/629,731 filed Jul. 31, 2000 now U.S. Pat.6,216,665, which is a Continuation of application Ser. No. 09/030,082 filed on Feb. 25, 1998, now U.S. Pat. No. 6,125,818 issued Oct. 3, 2000, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a fuel injector and to an internal combustion engine having a fuel injector. More particularly, the invention relates to a fuel injector capable of producing a fuel spray having a superior ignitability and a superior combustibility for use in an internal combustion engine having a fuel injector. 
     The present invention relates to a fuel injector for forming a complex fuel spray having a superior ignitability and a superior combustibility for use in an internal combustion engine. 
     An inlet pipe fuel injection device is a device which causes fuel to be injected into an inlet pipe of an internal combustion engine. In addition to an inlet pipe fuel injection device, there is also a direct fuel injection device, which operates to inject fuel directly into a combustion chamber (a cylinder) of the internal combustion engine. Such a direct fuel injection device is 5-33,739. disclosed in, for example, Japanese patent laid-open publication No. Hei 
     As disclosed in the above stated Japanese patent laid-open publication No. Hei-5 33,739, it is difficult to homogeneously mix fuel which has been injected directly into the combustion chamber with the air being drawn in the combustion chamber. Therefore, it is important to promote the atomizing of the fuel which has been injected directly into the combustion chamber. 
     To atomize the fuel, up to now, a swirling force has been imparted to the fuel which is injected from a fuel injector. As shown in the above stated Japanese patent laid-open publication No. Hei-5 33,739, a direct fuel injection device having a means for imparting a swirling force to the fuel is disclosed. 
     Herein, the direct fuel injection device disclosed in the above stated Japanese patent laid-open publication No. Hei-5 33,739, comprises an injection nozzle for injecting fuel from an injection hole, a cylindrical cover having a bottom portion constituting an air chamber at an outer side of the injection nozzle, a swirl chamber which is formed at a side of the bottom portion of the cover so as to communicate with the injection hole of the injection nozzle, and a check valve body which opens and closes the injection hole. 
     With the above stated conventional direct fuel injection device structure, the swirl chamber has an injection hole and this injection hole introduces air from a tangential direction along an inner peripheral face of the swirl chamber from the air chamber which is constituted in the cylindrical-shaped cover having the bottom portion. In accordance with the above stated air which is injected from the injection hole of the swirl chamber, the fuel injected through the injection hole of the injection nozzle will have a swirl force imparted thereto. 
     Further, the injection hole and a passage for introducing air from the air chamber into the swirl chamber are provided with a two-stage structure, namely the injection hole and the passage of the swirl chamber are provided at an upper direction and a lower direction (an axial direction of the check valve body) or an upstream side and at a downstream side of the check valve body. Each of the injection hole and the passage of the swirl chamber at the upper direction and the lower direction have the same structure. 
     However, in the above stated direct fuel injection device, the check valve is arranged at a discharge side. Further, the elements which produce the swirl force are provided at a downstream side of a metering portion of the fuel passage, rather than at an upstream side of the metering portion of the fuel passage. 
     As a result, after the fuel passes through the metering portion of the fuel passage without having a swirl force imparted thereto, the fuel is subjected to a swirl force for the first time at the downstream side of the metering portion of the fuel passage, namely the swirl force is imparted first in the swirl chamber in response to the applied air. 
     Accordingly, in the direct fuel injection device structure disclosed in the above stated Japanese patent laid-open publication No. Hei-5 33,739, there is no suggestion to impart the swirl force to the fuel using a portion of the fuel passage upstream of the metering portion of the valve body. 
     In the conventional technique employed in the above stated direct fuel injection device, the atomization of the fuel is promoted and the spray direction of the fuel and the spreading of the fuel spray have been controlled. However, as stated hereinafter, full consideration has not been given to the shape of the fuel spray, the diameter of the fuel spray and the structure of the fuel spray in which both the ignitability (a spark-in property) and the combustibility (a propagation of fire) are improved in a compatible way. 
     To attain the optimum property for the spray of fuel which is injected from the fuel injector, it is necessary to consider at least the following three characteristics. 
     First of all, the first characteristic is the fuel spray shape, and the factors for this fuel spray shape are the spreading angle and the distance or extent of travel of the fuel spray. The second characteristic is the size of a spray fuel particle, in this regard, and it is necessary to lessen the number of spray fuel particles of large size as much as possible and to improve the uniformity of the spray fuel particle size distribution. The third characteristic is the structure of the fuel spray, and, for this purpose, it is necessary to provide a suitable spatial distribution of the fuel particles to be sprayed. 
     The inventors of the present invention have studied by experimentation various analyses as to how these fuel spray characteristics relate to the combustion properties in the internal combustion engine. As a result of these studies, they have found that, in a case where the spreading angle of the spray of the fuel is large, the inertia force of the fuel spray is weak, with a result that the distance or extent of travel of the fuel spray is short, whereby it is possible to obtain stability in the combustion. Further, on the other hand, by making the spreading angle of the spray of the fuel small, the inertia force of the fuel spray is made strong, with a result that a mixture of air and fuel having a superior ignitability is produced, but it was ascertained clearly that there is a tendency for unburned gas components (HC, CO) in the fuel to increase. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a fuel injector which can inject a complex solid cone of fuel as a spray to provide a fuel spray having a superior combustibility in which the discharge amount of unburned gas components can be reduced and a fuel spray having improved ignitability can be provided for use in an internal combustion engine. 
     Another object of the present invention is to provide a fuel injector which can inject a spray in the form of complex solid cone of fuel particles to provide a fuel spray having a superior combustibility in which the discharge amount of unburned gas components can be reduced and a fuel spray having an improved ignitability can be provided for use in an internal combustion engine so as to obtain a superior ignitability of the internal combustion engine and to reduce the discharge amount of the unburned gas components in the fuel. 
     As to the spray formed as a complex solid cone of fuel particles in the fuel injector, it is desirable to form a fuel spray which comprises a first fuel spray having a large spreading angle by the inertia force thereof weak and the distance or extent of travel thereof short, and a second fuel spray having a small spreading angle by making the inertia force thereof strong. 
     In order to produce such a complex solid cone spray of fuel from a fuel injector, a fuel injector according to the present invention comprises a nozzle body having an injection hole, a valve body, and a drive means for driving the valve body in an axial direction, so that, by driving the valve body, the injection hole is opened and closed and the fuel injection is carried out. 
     In the fuel injector, at a side upstream of the injection hole, two swirl force producing means for imparting a swirl force to the fuel are arranged in the axial direction, the two swirl force producing means comprise a first swirl force producing means and a second swirl force producing means, whereby the swirl force imparted by the first swirl force producing means differs from the swirl force imparted by the second swirl force producing means, whereby a fuel injection in the form of a solid cone spray is carried out. 
     In a fuel injector according to the present invention, at a side upstream of the injection hole, two swirl force producing means for imparting a swirl force to the fuel are arranged to have a two stage form in the axial direction, the two swirl force producing means comprise an upstream side swirl force producing means and a downstream side swirl force producing means, with the upstream side swirl force producing means imparting a stronger swirl force to the fuel than the swirl force produced by the downstream side swirl force producing means, whereby a fuel injection in the form of a solid cone spray is carried out. 
     The fuel to which a strong swirl force is imparted forms a first fuel spray having a large spreading angle by weakening the inertia force and shortening the distance or extent of travel thereof. The fuel to which a weak swirl force is imparted forms a second fuel spray having the small spreading angle due to a strong inertia force. The complex solid cone fuel spray is formed by the first fuel spray and the second fuel spray. 
     In a fuel injector according to the present invention in which fuel having a swirl force imparted thereto is injected, from an injection hole, a preceding spray is injected to a central portion, and in succession to the preceding spray, another spray is injected radially to a surrounding portion of the preceding spray, whereby fuel injection having a solid cone spray is carried out. 
     In a fuel injector according to the present invention in which fuel having a swirl force imparted thereto is injected, a cross-section of the spray shape, including an axial center of the valve body of the fuel injector, produces a strong spray distributed in three directions, whereby fuel injection having a solid cone spray is carried out. 
     The fuel spray at the central portion attracts small diameter droplets, such small diameter droplets are injected continuously into the fuel at a surrounding portion of the fuel spray with a hollow shape spray and with a radial shape spray. As a result, a solid cone fuel spray structure having a superior dispersion property can be formed. 
     The fuel spray at the central portion is mainly a fuel spray made up of fuel to which is imparted a weak swirl force. The fuel spray which follows the above fuel spray and is injected with a radial shape is mainly a fuel spray made up of fuel to which is imparted a strong swirl force. 
     According to a high speed photograph of the fuel spray structure during fuel injection, it was observed that the fuel spray which is injected at the central portion reaches a remote location relative to the fuel spray which is sprayed at the surrounding portion a the radial shaped spray. A cross sectional view of the fuel spray structure will show the following characteristics. 
     Namely, in the fuel injector obtained according to the present invention, which injects fuel while imparting a swirl force to the fuel, the cross sectional view of the fuel spray structure, taken along the axial center of the fuel injection, shows a strong fuel spray extending in three directions. 
     A fuel injector according to the present invention comprises, at a side of an upstream of the injection hole, two swirl force producing means for imparting a swirl force to the fuel, which are arranged with a two stage form superimposed in the axial direction, the two swirl force producing means comprise an upstream side swirl force producing means and a downstream side swirl force producing means, and the upstream side swirl force producing means imparts a weaker swirl force to the fuel than a swirl force of the downstream side swirl force producing means, thereby a fuel injection with a solid cone spray is carried out. 
     In a fuel injector according to the present invention in which fuel is injected, while imparting a swirl force to the fuel, from an injection hole, a preceding spray is injected radially into an annular area, and in succession to the preceding spray, another spray is injected to a central portion of the annular area, thereby fuel injection with a solid cone spray is carried out. 
     A fuel injector according to the present invention comprises a nozzle body having an injection hole for injecting fuel and a seat face provided upstream of the injection hole, a valve body for opening and closing a fuel passage at the seat face of the nozzle body, at a side of an upstream of the seat face of the nozzle body, an element having a penetration hole in which the valve body extends, an axial direction fuel passage for passing fuel in an axial direction and a radial direction fuel passage communicating with the penetration hole from the axial direction passage for passing the fuel in a radial direction. 
     The radial direction fuel passage includes a first radial direction passage and a second radial passage superimposed in the axial direction, whereby an off-set amount of the first radial direction passage differs from an offset amount of the second radial direction passage, thereby fuel injection with a solid cone spray is carried out. 
     An off-set amount from an axial center of the valve body of one of the two radial direction passages, which is provided at a relatively remote position from the injection hole and communicates with the penetration hole at an upstream side thereof, is made the same or larger than an off-set amount of an opening of the other radial direction passage which is provided relatively near the injection hole, thereby fuel injection with a solid cone spray is carried out. 
     According to the above stated fuel injector, the flow direction of the fuel which passes through the radial direction passage remote from the injection hole is angled away from the axial center of the valve body as compared to the flow of the fuel which passes through the radial direction passage near to the injection hole. As a result, the fuel which has imparted the strong swirl force at the upstream side is injected continuously from the injection hole to the fuel which has imparted the weak swirl force at the downstream side. For reasons stated above, a complex solid cone fuel spray is formed. 
     A fuel injector according to the present invention comprises, an upstream of the seat face of the nozzle body, an element having a penetration hole in which the valve body extends, an axial direction fuel passage for passing fuel in an axial direction and a radial direction fuel passage communicating with the penetration hole from the axial direction fuel passage for passing the fuel in a radial direction. 
     The radial direction fuel passage includes two radial direction passages which are provided with a two stage form superimposed in the axial direction, an off-set amount from an axial center of the valve body of one of the two radial direction passages, which is provided at a position relatively remote from the injection hole in communication with the penetration hole at an upstream side thereof, is made smaller than an off-set amount of the other radial direction passage, which is provided relatively near the injection hole, thereby fuel injection with a solid cone spray is carried out. 
     An internal combustion engine having a fuel injector with the features described above, according to the present invention, comprises a cylinder, a piston which reciprocates in the cylinder, an air intake means for introducing air into the cylinder, a discharge means for discharging combustion gas from the cylinder, a fuel injector for directly injecting fuel into the cylinder, a fuel supply means for supplying fuel from a fuel tank to the fuel injector, and an ignition means for igniting a mixture of air and fuel which comprises air introduced in the cylinder by the air intake means and fuel injected into the cylinder by the fuel injector, the internal combustion engine. 
     The piston of the engine has a cavity portion at an upper face thereof and the cavity portion changes the direction of the spray which is injected from the fuel injector to deflect it to the ignition means. 
     According to the internal combustion engine obtained by the present invention, as stated in above, since a complex fuel spray is formed in the cylinder, a superior ignitability is achieved in the internal combustion engine and the combustibility in the internal combustion engine can be improved, as a result of which, the discharge amount of unburned gas components of the combustion can be reduced. 
     Since the fuel is injected toward the cavity portion which is constituted on the upper face of the piston, the fuel spray having a strong inertia force which has imparted a weak swirl force collides vigorously with the cavity portion and the direction of the fuel is changed to deflect it toward the ignition device (an ignition plug). Since the fuel which is changed in direction and has a strong inertia force attracts small diameter droplets at the surrounding portion to further promote fuel dispersion, the ignitability can be improved and the combustibility in the internal combustion engine can be improved further. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a cross-sectional view showing one embodiment of an electromagnetic fuel injector according to the present invention; 
     FIG. 1B is a longitudinal cross-sectional view of a movable valve of a laminated layer fuel swirl element for use in the electromagnetic fuel injector of FIG. 1A according to the present invention; 
     FIG. 1C is a longitudinal cross-sectional view of a nozzle member, which has a valve seat angle and a fuel injection hole diameter do, for use in the electromagnetic fuel injector of FIG. 1A according to the present invention; 
     FIG. 2A is a plane view showing a laminated layer fuel swirl element for use in the electromagnetic fuel injector of FIG. 1B according to the present invention; 
     FIG. 2B is a longitudinal cross-sectional view showing the laminated layer structure swirl element of the electromagnetic fuel injector, taken along a line  2 B— 2 B in FIG. 2A, according to the present invention; 
     FIG. 2C is a plan view showing an upper plate  22 B for constituting a fuel passage of the laminated layer fuel swirl element of the electromagnetic fuel injector of FIG. 2B according to the present invention; 
     FIG. 2D is a plan view showing a middle plate  22 C for constituting a fuel passage of the laminated layer fuel swirl element of the electromagnetic fuel injector of FIG. 2B according to the present invention; 
     FIG. 2E is a plan view showing a lower plate  22 D for constituting a fuel passage of the laminated layer fuel swirl element of the electromagnetic fuel injector of FIG. 2B according to the present invention; 
     FIG. 3A is a plan view showing another example of the upper plate  34 B for constituting a fuel passage of a laminated layer fuel swirl element of an electromagnetic fuel injector according to the present invention; 
     FIG. 3B is a plan view showing another example of the lower plate  22 D′ for constituting a fuel passage of a laminated layer fuel swirl element of an electromagnetic fuel injector according to the present invention; 
     FIG. 4A is a longitudinal cross-sectional view showing a further embodiment of a laminated layer fuel swirl element of an electromagnetic system fuel injector according to the present invention; 
     FIG. 4B is a plan view showing a single plate  38 B for constituting the laminated layer fuel swirl element of the electromagnetic fuel injector of FIG. 4A according to the present invention; 
     FIG. 4C is a bottom view showing the single plate  38 B for constituting the laminated layer fuel swirl element of the electromagnetic fuel injector of FIG. 4A according to the present invention; 
     FIG. 5 is a cross-sectional view showing a further embodiment of a movable valve of a fuel swirl element of an electromagnetic fuel injector according to the present invention; 
     FIG. 6 is a longitudinal cross-sectional view showing a still further embodiment of a laminated layer fuel swirl element of an electromagnetic fuel injector according to the present invention; 
     FIG. 7A is a schematic view showing a complex fuel spray structure in which the droplet flow is mainly illustrated according to the present invention; 
     FIG. 7B is a schematic view showing a complex fuel spray structure in which the air flow is mainly according to the present invention; 
     FIG. 8 is a block diagram showing one embodiment of an internal combustion engine having a fuel injector according to the present invention; and 
     FIG. 9 is an explanatory view showing one embodiment of an essential portion of a direct injection system internal combustion engine having a fuel injector according to the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Reference will be made first of all to FIG. 9, which shows a direct fuel injection device, representing the subject matter which has been studied by the inventors of the present invention, and an internal combustion engine on which the direct fuel injection device is mounted. 
     The direct fuel injection device (hereinafter referred to as an electromagnetic fuel injector) is installed in the cylinder head of the engine with an inclination of 30°-40° degree. The injection direction of the fuel is directed toward a piston cavity (a recessed portion provided on the piston). To obtain a fuel spray having an optimum property from this kind of the electromagnetic fuel injector, it is necessary to study the following characteristics. 
     The first characteristic is the fuel spray shape. The factors for the fuel spray shape are comprised of the spreading angle and the distance or extent of travel of the fuel. The second characteristic is the size of a spray fuel particle. In this regard, it is necessary to lessen the number of fuel particles of large size as much as possible and to make fuel particle size distribution uniform. The third characteristic is the fuel spray structure. For this, it is necessary to provide a suitable spatial distribution of the fuel particles to be sprayed. 
     The inventors of the present invention have studied by experimentation how these fuel spray characteristics relate to the combustion properties in an internal combustion engine. As a result of these studies, they have found that, when the spreading angle of the fuel spray is made large, the inertia force of the fuel spray is made weak, with a result that the distance or extent of travel of the fuel is short, which is effective to obtain stability in the combustion. Further, on the other hand, when the spreading angle of the fuel spray is short, the inertia force of the fuel spray is made strong, with the result that a mixture air and fuel having a superior ignitability is produced; however, it has been ascertained clearly that, in this case, there is a tendency for unburned gas components (HC, CO) in the fuel to increase. 
     The following embodiments of a direct fuel injection device or a fuel injector, and of an internal combustion engine on which the direct fuel injection device or the fuel injector is mounted, according to the present invention are based on the above stated findings. 
     Hereinafter, one embodiment of a fuel injector according to the present invention will be explained with reference to FIGS. 1A and 1B, FIG.  2 A-FIG.  2 E and FIG.  3 B. FIG. 1A is a cross-sectional view of one embodiment of an electromagnetic fuel injector according to the present invention. Using FIG. 1A, the structure and operation of the electromagnetic fuel injector  1  will be explained. 
     FIG. 1B is a longitudinal cross-sectional view of a movable valve of a laminated layer fuel swirl element of the electromagnetic fuel injector, and FIG. 1C is a longitudinal cross-sectional view of a nozzle member which has a valve seat angle θ and a fuel injection hole diameter do for use in the electromagnetic fuel injector. 
     The electromagnetic fuel injector  1  performs an open and close operation on a seat portion in response to an ON-OFF signal having a duty factor which is controlled by a control unit to carry out an injection of fuel. A magnetic circuit for the fuel injector comprises a cylindrical yoke  3  having a bottom portion, a core  2  having a plug body portion  2   a  for closing an opening end of the yoke  3  and a column shaped portion  2   b  which extends over a central portion of the yoke  3 , and a plunger  4  which is faced to the core  2  with a gap. 
     Inside the column shaped portion  2   b  of the core  2 , a movable portion  4 A and an axial hole  4 B are provided. The movable portion  4 A comprises a plunger  4 , a rod  5 , and a ball  6 . The axial hole  4 B holds a spring member  10  serving as an elastic member, and this spring member  10  is inserted in the hole  4 B so as to press the ball  6  against a seat face  9  of an upstream side of a fuel injection hole  8  via the rod  5 . The fuel injection hole  8  is formed in a nozzle member  7  and allows fuel to pass therethrough when the ball  6  is withdrawn from the seat face  9 . 
     An upper end of the spring member  10  is in contact with a lower end of a spring adjuster  11 , which is inserted central hole  4 B of the core  2  to adjust the spring member  10  to a set load. A seal ring  12  is provided at a clearance portion which exists between an end of the column shaped portion  2   b  of the core  2  and an end of the plunger  4  of the movable portion  4 A in the yoke  3 . This seal ring  12  prevents an outflow of the fuel into the area of the coil  14  and is fixed mechanically between the column shaped portion  2   b  of the core  2  and the movable portion  4 A. 
     The coil  14  for exciting the magnetic circuit is wound on a bobbin  13 , and the outer periphery of the coil  14  is molded by a plastic member. A terminal  17  of the coil assembly body  15 , which comprises the coil  14  and the bobbin  13 , is inserted in a hole  16  which is provided in the radial portion  2   a  of the core  2 . This terminal member  17  is connected with the control unit (not shown in figure) for operation of the fuel injector. 
     At the bottom portion of the yoke  3 , a plunger receiving portion  18  for receiving the movable portion  4 A is opened, and a further plunger receiving portion  20  extends through to a tip end of the yoke  3 . The further plunger receiving portion  20  has a larger diameter than a diameter of the plunger receiving portion  18 , and further a stopper member  19  and the nozzle member  7  are mounted therein. 
     The movable portion  4 A comprises the plunger  4  made of a magnetic material, the rod  5  having one end thereof integrally formed with the plunger  4  and the ball  6  which connected to a tip end portion of the rod  5 . At a side of the plunger  4  of the rod  5 , a cavity portion  5 A having an axial fuel passage is provided for allowing the passage of the fuel axially therein. In this cavity portion  5 A, an outflow port  5 B for the fuel is provided. 
     Further, movement in the axial direction of the movable portion  4 A is guided by the contact between the outer periphery of the plunger  4 , the inner peripheral surface of the plunger receiving portion  18  and the seal ring  12 . In the vicinity of an end portion of the rod  5 , to which the ball  6  is bonded, the movable portion  4 A is guided along an inner peripheral face  23  of a laminated layer fuel swirl element  22  according to the present invention, which is inserted in a hollow interior portion of the nozzle member  7 . 
     In the nozzle member  7 , the laminated layer fuel swirl element  22  for guiding the end portion of the rod  5 , on which the ball  6  is bonded, is provided above the seat face  9  for seating the ball  6 . At a central portion of a downstream side of the seat face  9 , the fuel injection hole  8  for allowing the passage of the fuel is provided in the nozzle member  7 . The fuel injection hole  8  has a diameter do and the valve seat face  9  of the nozzle member  7  has an angle θ, as seen in FIG.  1 C. 
     Further, the stroke (a movement amount in an axial upper portion) of the movable portion  4 A is determined by the size of a gap which is formed between a receiving face  5 C of a neck portion of the rod  5  and the stopper member  19 . Further, a fuel filter  24  is provided to prevent entry of dust and foreign matter in the fuel and in the piping extending to the valve seat. 
     Now, the structure of the laminated layer structure fuel swirl element  22  of the electromagnetic fuel injector  1  according to the present invention will be explained in more detail. 
     FIG. 2A is a plane view showing one embodiment of a laminated layer fuel swirl element  22  of the electromagnetic fuel injector  1 ; FIG. 2B is a longitudinal cross-sectional view of the laminated layer structure swirl element  22  of the electromagnetic system fuel injector  1 ; and FIG. 2C is a plan view showing an upper plate  22 B for the fuel passage of the laminated layer fuel swirl element  22  of the electromagnetic fuel injector  1 . 
     FIG. 2D is a plan view showing a middle plate  22 C for the fuel passage of the laminated layer structure fuel swirl element  22  of the electromagnetic system fuel injector  1 ; FIG. 2E is a plan view showing a lower plate  22 D for the fuel passage of the laminated layer structure fuel swirl element  22  of the electromagnetic system fuel injector  1 ; and FIG. 3B is a plan view showing a modified lower plate  22 D′ for the fuel passage of a laminated layer fuel swirl element of the electromagnetic fuel injector  1 . 
     The laminated layer fuel swirl element  22 , as shown in FIG. 2B, comprises four pieces which include a cylindrical portion  22 A, an upper plate  22 B, a middle plate  22 C, and a lower plate  22 D. The cylindrical portion  22 A has an axial guide hole  23  for guiding the end of the movable portion  4 A. 
     Further, the upper plate  22 B, as shown in FIG. 2C, has a pair of radial direction fuel passages  25  which are off-set respectively by a value of Ls from a center axis thereof and two notch portions  26 , as well as a hole  27  at a central portion. The central hole  27  communicates with the radial direction fuel passages  25 . 
     Further, the lower plate  22 D has a pair of radial direction fuel passages  28 , which are not off-set, and a hole  29  at a central portion thereof, as shown in FIG.  2 E. The central hole  29  communicates with the radial direction fuel passages  28 . However, as shown in FIG. 3B, each of the radial direction fuel passage  28 ′ of the lower plate  22 D′ also can be formed to have an off-set amount (LS′) (more than O) smaller than the off-set amount (Ls) of the radial direction fuel passage  25  of the upper plate  22 B shown in FIG.  2 C. In other words, the off-set amount of the radial direction fuel passages in the lower plate  22  can be set to obtain a desirable fuel spray in which the range of the swirl force imparted from the radial direction fuel passages is smaller than the range of the swirl force imparted from the radial direction fuel passage  25 . Further, each of the central holes  27 ,  31 , and  29 , which are provided on each of the upper plate  22 B, the middle plate  22 C, and the lower plate  22 D, respectively, has the same diameter, or a little larger diameter, than a diameter of the guide hole  23  of the cylindrical portion  22 A. In this regard, each of the plates  22 B,  22 C, and  22 D is manufactured by punching out a very thin plate member having a disc shape, and each of the holes  27 ,  31  and  29  and each of the notch portions  26  and  30  are formed with a similar press working. 
     As stated in above, since each of the plates  22 B,  22 C, and  22 D is manufactured by a press working, the degree of design freedom of the shape of each of the plates  22 B,  22 C, and  22 D is high. For example, as to the provision of plural radial direction fuel passages, the provision of a very slim fuel passage, the provision of a complicated fuel passage having a curved line, and complicated and various shaped plates can be manufactured with a high accuracy and at a low cost. 
     The four pieces which make up the fuel swirl element  22 , including the cylindrical portion  22 A and the three plates  22 B,  22 C, and  22 D, are laminated in series as shown in FIG. 2B, and, after that, they are fixed under pressure. This laminated layer fuel swirl element  22  of the fuel injector  1  is inserted and fixed to an inner wall of the hollow portion of the nozzle member  7 , and then the axial direction passage for the fuel is formed between an outer peripheral wall of the fuel swirl element  22  and the inner wall of the hollow portion of the nozzle member  7 . 
     Further, by inserting end of the movable portion  4 A in the guide hole  23 , a fuel swirl chamber  33  is formed at an outer peripheral portion of the ball  6 . Namely, the fuel passage in which the fuel is introduced from an upper portion of the valve body is constituted, and the fuel which has passed in an axial direction through the fuel passage  32  is introduced eccentrically from an axial center by the radial direction fuel passage  24  of the upper plate  22 B. As a result, the fuel has a swirl imparted. Here, the swirl strength to be imparted (a swirl number S) is indicated by a following formula. 
     
       
         S=(angular movement amount)/(injection axial direction movement amount)×(orifice radius) =(2×do×Ls)/(n×ds 2 ×cos θ/2) 
       
     
     Where, do: fuel injection hole diameter (orifice radius) (confer, FIG. 1C) 
     Ls: radial direction passage eccentricity amount (confer, FIG. 2C) 
     n: radial direction fuel passage number 
     θ: valve seat angle (confer, FIG. 1C) 
     ds: hydraulic equivalent diameter, 
     ds is expressed using a width W and a height H of the radial direction fuel passage. (confer, FIG.  2 B and FIG.  2 C). Here, 
     
       
         ds=(2×W×H)/(W+H) 
       
     
     When, the swirl number S is made large, the atomization is promoted and a fuel spray having a large spreading angle in which the inertia force is weak is formed. 
     As understood from the above stated formula, the parameters for controlling the swirl force include the off-set amount (Ls) of the fuel passage, the number (n) of fuel passages and the hydraulic equivalent diameter (ds). Accordingly, to change the swirl force, in place of adjustment of the off-set amount (Ls) according to this embodiment of the fuel injector  1 , it is possible to change the number (n) of the fuel passages or the hydraulic equivalent diameter (ds). However, in the latter case, since a difference in pressure loss is generated in the fuel passage, the distribution of the flow amount of fuel which flows into each of the fuel passages differs. 
     As a result, it is necessary to design the fuel swirl element  22  by taking into the consideration the above stated points. On the other hand, since the off-set amount (Ls) of the fuel passage has little affect on the above stated points, it can be easily implemented. However, in a case where the design is carried out by giving full consideration to the above stated points, as to the plural stage arrangement of the radial direction fuel passages, it is possible to change the number (n) of fuel passages or the hydraulic equivalent diameter (ds). 
     Next, the operation of this embodiment of the fuel injector  1  thus constituted according to the present invention will be explained. 
     The fuel injector  1  performs an opening and closing operation of the fuel injection hole  8  by moving the ball  6  relative to the seat face  9  of the valve body of the nozzle member  7  by reciprocating downwardly the movable portion  4 A upward and downward in the axial direction in response to an electric ON-OFF signal which is supplied to the electromagnetic coil  14 , with the result that injection control of the fuel is carried out. 
     When the electric signal is supplied to the coil  14 , the core  2 , the yoke  3  and the plunger  4  form a magnetic circuit, and the plunger  4  is attracted upwardly toward the core  2 . When the plunger  4  is moved, the ball  6 , which is integrally formed with the plunger  4 , is moved, and then the ball  6  is separated from the seat face  9  of the valve body of the nozzle member  7 , so that the fuel injection hole  8  is opened. 
     As shown in FIG. 8, the fuel is pressurized and adjusted through a fuel pump  80  and a fuel pump  71  and a regulator  79  for adjusting the fuel pressure. The fuel flows into an inner portion of the fuel injector  1  through the filter member  24 . And, an inner passage of the core  2  and the hollow portion  5 A, which is provided in the plunger  4 , form a passage for the fuel, through which the fuel flows downstream through the outflow port  5 B to the outer peripheral portion of the plunger  4 . 
     The fuel passes through the gap formed between the stopper member  19  and the rod  5  and through the radial direction fuel passages  25  and  26  of the fuel swirl element  22 , where the fuel is swirled and supplied to the seat portion of the nozzle member  7 . Accordingly, during the valve opening condition of the nozzle member  7 , the fuel is injected from the fuel injection hole  8  into the combustion chamber of the internal combustion engine. 
     As shown in FIG.  7 A and FIG. 7B, the injected fuel becomes a complex fuel injection spray (a comparatively solid cone fuel spray) in which a spray having a weak swirl force and a large spreading angle and a spray having a strong swirl force and a small spreading angle are mixed. Namely, the spray having the weak swirl force and the large spreading angle is generated by the upper plate  22 B, which is arranged further from the seat face  9  of the nozzle member  7  and promotes an atomization property according to the swirl force which is imparted to the fuel by the radial direction fuel passage  25 . On the other hand, the spray having the strong swirl force and the small spreading angle is generated by the lower plate  22 D, which is arranged nearer to the seat face  9  of the nozzle member  7  and imparts a weak swirl force to the fuel in comparison with the above stated swirl force and is generated in the vicinity of the axial center as a spray flow having a large velocity. The radial direction fuel passage  28  of the lower plate  22 D has an off-set amount of zero (0), but in a case where the fuel is pushed out by the strong swirl flow from the radial direction fuel passage  25  of the upper plate  22 B, a swirl force is imparted and the fuel presents a weak swirl flow. 
     The spray flow from the radial direction fuel passage  28 , which imparts a weak swirl flow to the fuel, attracts surrounding air and also attracts small diameter droplets, which produces an atomization in response to the strong swirl flow from the radial direction fuel passage  25 . As a result, a fuel spray which presents a comparatively solid cone fuel spray structure is generated. 
     FIG. 3A shows another embodiment of an upper plate  34 B of a laminated fuel swirl element for use in the fuel injector  1  according to the present invention, and this embodiment forms a modified example of the radial direction passage  25  shown in FIG. 2C of the fuel. Namely, the upper plate  34 B forms a semi-circular portion  35  in place of the notch portion shown in FIG. 2 c . In this semicircular portion  35 , an end of the radial direction fuel passage  36  is constituted. The radial direction fuel passages  36  with a central hole  37  provided in the upper plate. In this embodiment of the fuel injector  1 , the fuel is imparted fully with a swirl force and the atomization property of the fuel is promoted, so that a fuel spray having a slow velocity and a weak inertia force is generated. 
     FIG. 4A, FIG.  4 B and FIG. 4C show a further embodiment of a laminated layer fuel swirl element  38  for use in the fuel injector  1  according to the present invention, and this embodiment shows a two-piece fuel swirl element  38 . FIG. 4A shows a longitudinal cross-section view of the two-piece fuel swirl element  38 , FIG. 4B is a plan view showing a single plate  38 B for constituting a further embodiment of the laminated layer fuel swirl element  38 , and FIG. 4C is a bottom view showing the single plate  38 B for constituting the further embodiment of the laminated layer fuel swirl element  38 . 
     Namely, the two-piece fuel swirl element  38  is comprised a cylindrical portion  38 A and another cylindrical portion (a single plate)  38 B. The two parts of the fuel swirl element  38  are separate, but are joined and fixed to the inner wall  21  in the nozzle, and in the cylindrical portion  38 A a guide hole  39  for guiding the movable portion  4 A of the plunger  4  is provided. Further, at one end face forming an upper face of the other cylindrical portion (the single plate)  38 B, a pair of radial direction fuel passages  40  is provided, and the radial direction fuel passages  40  are off-set from the axial center. At the other end face forming the lower face of the cylindrical portion  38 B, a pair of radial direction fuel passages  41  is provided, but these radial direction fuel passages  41  are not off-set. 
     Further, at a central portion, a central hole  42  is provided and this central hole  42  communicates with the respective radial direction fuel passages  40  and  41 . This central hole  42  is formed to have the same diameter, or a little larger diameter, as that of the guide hole  39  which is provided in the cylindrical portion  38 A of the fuel swirl element  38 . Further, on the cylindrical portion  38 A and the other cylindrical portion (the single plate)  38 B, as shown in FIG.  4 B and FIG. 4C, a pair of cut faces  43  and  44  are provided. 
     When the cylindrical portion  38 A and the another cylindrical portion  38 B are inserted and fixed to the inner wall  21  at the central portion of the nozzle member  7 , between the two cut faces  43  and  44  and the inner wall  21  at the central portion, a space is formed which communicates with the radial direction fuel passages. 
     Since the cylindrical portion  38 B of this embodiment of the fuel injector  1  is manufactured similar to that of the first embodiment, using press working, the degree of freedom degree of design of the radial direction fuel passages  40  and  41  is comparatively high, and it is possible to manufacture the nozzle member with a high accuracy, so that the operation and effects similar to the first embodiment are obtained. 
     In the fuel swirl element of the fuel injector, it is possible for the off-set amount of a radial direction swirl fuel passage on the upstream side to be the same as the off-set amount of the radial direction swirl fuel passage on the downstream side. In this case, the swirl force which is imparted at the upstream side is weakened by the friction loss of a flow in which the fuel flows from an outlet port of the fuel swirl passage to the injection hole and is composed or joined to a strong swirl force which is imparted at the downstream side. 
     Since the swirl force at the upstream side is smaller than that of the downstream side, the following complex fuel spray is formed. Namely, after the fuel spray having a weak inertia force and a large spreading angle is produced, a fuel spray having the strong inertia force and a small spreading angle comes in the preceding fuel spray. After an arbitrarily selected time, this fuel spray has a droplet spatial distribution on a fuel spray lateral cross sectional face (at a lower portion of 50 mm from the injection hole) similar to that of the first embodiment. 
     Further, in a case where the off-set of the fuel swirl passage at the upstream side is smaller than that of the fuel swirl passage at the downstream side, needless to say, the above stated phenomenon becomes remarkable. 
     The structure of the internal combustion engine or the injection system suitable for the complex fuel spray produced by the fuel injector are not limited to this embodiment, but they can be constituted with the most suitable form for carrying out the embodiments of the complex fuel spray using the fuel injector according to the present invention. 
     FIG.  5  and FIG. 6 show further embodiments according to the present invention in a case where the movable valve is changed to a needle valve. FIG. 5 is a cross-sectional view of an essential portion of the nozzle portion  7  showing the surrounding portion of a needle valve  50 , and FIG. 6 is a cross-sectional view of a laminated layer fuel swirl element  51 . In these figures, the same reference numerals are used to describe the first embodiment represent the same components or elements. 
     In FIG. 6, the laminated layer swirl element  51  comprises four pieces, which include a cylindrical portion  51 A, an upper plate  51 B, a middle plate  51 C, and a lower plate  51 D, and the construction of the laminated layer swirl element  51  is similar to that of the first embodiment. The cylindrical portion  51 A has a guide hole  52  to accommodate the movable portion  4 A of the plunger  4 , the end of which is comprised of the needle valve  50 . 
     The construction of the fuel passage formed by the three plates  51 B,  51 C and  51 D is similar to that of the first embodiment. However, a central hole  53 , which communicates with the fuel passage, is formed to have a little larger diameter than the diameter of the guide hole  52 . 
     In FIG. 5, after the four pieces comprised of the cylindrical portion  51 A and the three plates  51 B,  51 C and  51 D have laminated in series similar to the first embodiment, the four piece element is inserted and fixed to the inner wall  21  of the hollow portion of the nozzle member  7 . An axial direction fuel passage  54  is formed between an outer peripheral wall of the fuel swirl element  51  and the inner wall  21  of the hollow portion of the nozzle member  7 . 
     Further, by inserting the end of the movable portion  4 A (the needle valve  50 ) into the hole  52 ,  53  in the nozzle portion, a fuel swirl chamber  55  is formed in the vicinity of the tip end of an outer peripheral portion of the needle valve  50 . Namely, the fuel which is introduced from an upper portion of the needle valve  50  and has passed through the axial direction passage  54  is introduced eccentrically through the upper plate  51 B and then has a swirl force imparted thereto, thereby producing a spray having a weak inertia force and a wide spreading angle. 
     Further, a fuel spray having a strong inertia force and a small spreading angle is generated by the lower plate  51 D, which is arranged near the upper side of the seat face  9  of the nozzle member  7 . This fuel spray is generated in the vicinity of the axial center as a fuel spray flow having a comparatively large velocity. As a result, the fuel spray in the form of a comparatively solid cone fuel spray is generated. 
     FIG.  7 A and FIG. 7B are schematic diagrams showing the fuel spray obtained by the embodiment according to the present invention, which diagrams are based on photography taken with an electric flash. FIG. 7A is a view showing a complex fuel spray structure in which the droplet flow is mainly considered according to the present invention, and FIG. 7B is a view showing a complex fuel spray structure in which air flow is mainly considered according to the present invention. 
     As stated above, until the fuel reaches the injection hole  8  of the nozzle member  7 , the fuel is separated according to the strong swirl flow from the upper portion axial direction passages and the weak swirl flow from the lower portion axial direction passages. As a result, small diameter droplets having a weak inertia force and a small velocity are generated at the outer peripheral portion of the fuel spray, and small diameter droplets (larger than the above stated outer peripheral portion droplets) having a strong inertia force and a large velocity are generated at the central portion of the fuel spray. 
     The small diameter droplets at the outer peripheral portion of the fuel spray are easily influenced by the affect of the surrounding air flow, as shown in FIG. 7B, and the small diameter droplets are divided into droplets which are directed toward the center of the fuel spray and are greatly influenced by the air flow and droplets which are directed downstream and are discharged toward the outside. 
     On the other hand, the small diameter droplets having the large velocity at the central portion of the fuel spray attract the small diameter droplets in the vicinity which are moving in the direction of the air flow. As a result, the dispersion of the droplets is promoted, so that a comparatively solid cone fuel spray structure is produced. 
     Further, as shown in FIG.  7 A and FIG. 7B, taking into consideration a cross section of the fuel spray including the axial center of the valve body, the fuel spray structure of the fuel injector according to the present invention has three strong spray components directed in the D1 direction, the D2 direction and the D3 direction. 
     In other words, the fuel spray structure has three pattern spray components, including a straight pattern fuel spray component, a left radial pattern fuel spray component and a right radial pattern fuel spray component. The straight pattern fuel spray component in the D1 direction is directed toward the lower portion, the left radial pattern fuel spray component has D2 direction component and directs for the left radial portion, and the right radial pattern fuel spray component in the D3 direction component is directed toward the right radial portion. By uniting the straight pattern fuel spray component, the left radial pattern fuel spray component and the right radial pattern fuel spray component, a comparatively solid cone fuel spray structure according to the present invention is formed. 
     From a different point of view, the above fuel spray structure according to the present invention comprises a central fuel spray structure and a peripheral fuel spray structure. The central fuel spray structure is formed by the fuel which is directed in the D1 direction and exists at the central portion of the fuel spray. On the other hand, the peripheral fuel spray structure is formed by the fuel which is directed in the D2 direction and the D3 direction. The peripheral fuel spray structure is formed around the central fuel spray structure. By uniting the central fuel spray structure and the peripheral fuel spray structure, a comparatively solid cone fuel spray structure according to the present invention is formed. 
     FIG. 8 shows the construction of an internal combustion engine, such as used in an automobile, in which one embodiment of an electromagnetic injector according to the present invention is used. In the internal combustion engine, the fuel is injected directly into a combustion chamber of the internal combustion engine. FIG. 9 shows an enlarged view of the direct fuel injection system for the internal combustion engine in which one embodiment of an electromagnetic fuel injector according to the present invention is employed. 
     In FIG. 8, a four-cylinder four cycle gasoline engine  60  is connected directly to a high pressure fuel pump  71  through a belt  72 . The high pressure fuel pump  71  pressurizes the fuel according to a cam drive, for example. In the high pressure fuel pump  71 , by moving a piston, hydraulic compression is carried out so that high pressure fuel is obtained. The high pressure fuel pump  71  has a discharge port  71   a  and a suction port  71   b . The discharge port  71   a  and a fuel gallery  75  of the engine  60  are connected by high pressure piping  73 , and an accumulator  74  is provided at a midway point of the high pressure piping  73 . To the fuel gallery  75 , a respective direct fuel injection device  1  according to the present invention is connected for each cylinder. 
     A high pressure regulator  77  is provided downstream of the fuel gallery  75 , and this high pressure regulator  77  maintains the supply pressure of the fuel to the direct fuel injection device  1  at constant level. Any superfluous fuel is introduced to a low pressure regulator  79  from the fuel gallery  73  and the high pressure regulator  77  through a lower pressure piping  78 . Next, the superfluous fuel is passed through a return piping  84 , which is connected to the lower pressure piping  79  and is returned to a fuel tank  81 . 
     Plural direct fuel injection devices  1  are provided to accommodate a number of the cylinders. A driver circuit  85  for controlling each direct fuel injection device  1  is connected to a control unit  86  of the engine  60 . The driver circuit  85  controls a supply amount etc. of the fuel to the direct fuel injection device  1  in accordance with various kinds of commands from the control unit  86  of the engine  60 . The operation of the engine  60  is controlled through the control unit  86  in accordance with the inhale air amount, the air temperature, the engine water temperature, the engine rotation number etc. 
     Next, the above stated internal combustion engine  60  thus constituted will be explained in detail with reference to FIG.  9 . 
     A piston  69  is provided to reciprocate in a cylinder  68  so as to be moved upwardly and downwardly in response to the rotation of an engine shaft (not shown in figure). A cylinder head  63  at an upper portion of the cylinder  68  forms an airtight enclosed space for the cylinder  68 . 
     To the cylinder head  63 , an air intake manifold  62  and an air discharge manifold are connected. The air intake manifold  62  leads the outside air to the cylinder  68  through an intake air amount control device  61  and the air discharge manifold leads the combustion gas which is produced by combustion in the cylinder  68  to an exhaust air device. 
     An air intake valve  64  is provided at the downstream side of the air intake manifold  62  in the cylinder head  63  and an ignition device  65  is provided at a central portion of the air intake manifold  62 . Further, an air exhaust valve  66  is provided at the opposite side of the ignition device  65  from the air intake valve  64  in the cylinder head  63 . The air intake valve  64  and the air exhaust valve  66  extend toward the combustion chamber  67  of the engine  60 . 
     Herein, the direct fuel injection device  1  according to the present invention is installed in the vicinity of a portion where the air intake manifold  62  is connected to the cylinder head  63 , and an injection of the fuel is set to be in a slightly downward direction into the combustion chamber  67 . For example, the installation angle θp of the direct fuel injection device  1  is about 30°-400° degree. The piston  69  has a cavity  69 A facing toward the fuel injection device. 
     In FIG. 9, a blank arrow shows the intake air flow and a hatched arrow shows the exhaust gas flow, respectively. The fuel of the internal combustion engine  60  is injected directly into the combustion chamber  67  by the direct fuel injection device  1  with a suitable timing relative the intake of air. An ignition signal is produced by the control unit  86  according to the driving parameters of the engine  60 . The sprayed fuel due to the injection in the combustion chamber  67  is mixed with the air which is supplied through the air intake manifold  62 . 
     At this time, a fuel spray having a large velocity at the central portion thereof is regulated in flow direction by the cavity  69 A of the piston  69 . Namely, as shown by the solid black arrow in FIG. 9, the flow direction of the fuel spray having a large velocity at the central portion thereof is directed toward the ignition device  65 . On the other hand, the small diameter droplets having a small velocity at the outer peripheral portion of the fuel spray are dispersed in the combustion chamber  67 , causing the mixture of fuel with the air to be promoted. 
     After that, the mixture of fuel and air is compressed during a compression stroke and is ignited stably by the ignition device  65 , and, accordingly, the amount of unburned gas which remains is reduced and a stable combustion of fuel in the engine  60  can be realized. 
     As stated above, due to the laminated layer fuel swirl element, at the remote side from the fuel injection hole, the fuel has a strong swirl flow imparted thereto, and, on the other hand, at the side near to the fuel injection hole, the fuel weak swirl flow imparted thereto. As a result, a fuel spray having a large velocity, which is generated at the central portion thereof, attracts small diameter droplets which are generated at the outer peripheral portion of the fuel spray, and so a fuel spray having a superior dispersion characteristic can be formed. 
     Since the fuel spray thus obtained is supplied directly into the combustion chamber of the internal combustion engine, a good ignition characteristic can be provided in the engine, and also the amount of the unburned gas components of the combustion can be reduced. 
     Further, since the laminated layer fuel swirl element can be manufactured by press punch-out working, a high accuracy in the manufacture of the laminated layer fuel swirl element can be attained, and further a low cost of manufacture of the laminated layer fuel swirl element can be attained. 
     In the various embodiments of an electromagnetic fuel injector have been described, however the means for driving the valve body is not limited to an electromagnetic type system, and, for example, a piezoelectric type system can be employed. 
     According to the present invention, by imparting different swirl forces to the fuel prior to the fuel being injected, a fuel injector is provided in which a complex fuel spray is generated. Such a complex fuel spray structure having the large wide spreading angle component produced by making the inertia force weak and by shortening the distance or extent of travel of the fuel, and small spreading angle component produced by making the inertia force strong. 
     Further, by using the above stated fuel injector in an the internal combustion engine, a good ignition characteristic can be obtained in the internal combustion engine and the amount of unburned gas components of the combustion can be reduced.