FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] FUEL INJECTION VALVE; MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 2 DESCRIPTION TECHNICAL FIELD [0001] The present application relates to fuel injection valves for use in fuel supply to internal combustion engines of cars and the like and, more particularly, relates to a fuel injection valve that attempts to expedite atomization in spray characteristics. BACKGROUND ART [0002] In recent years, where exhaust gas regulations on internal combustion engines of cars and the like have been strengthened, atomization of fuel spray injected from fuel injection valves has been required and various investigations on methods of attempting atomization using swirling flows have been carried out. [0003] Patent Document 1 describes a structure which includes: a plunger driven by a solenoid device; a valve seat which is arranged on the downstream side of theplunger and has an opening portion; and an injection hole plate in which a radial recess having a branch portion, an introducing portion, a cylindrical portion, and a swirling portionis formed on the upstream side and an injection hole is opened on the downstream side of the cylindrical portion, the injection hole plate being coupled to the downstream side of the valve seat to attach to the inside of a valve main body serving as a top end component of a fuel injection valve. 3 RELATED ART DOCUMENT PATENT DOCUMENT [0004] Patent Document 1: WO-A1-2017/060945 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [0005] Generally, it is preferable for the fuel injection valve,which is attached to an intake air path on the upstream side of a combustion chamber,to reduce adherence of fuel to the intake air path by being arranged close to the combustion chamber in order to more accurately control the amount of fuel entered into the combustion chamber. [0006] The fuel injection valve of the above-mentioned Patent Document 1 has a problem when the fuel injection valve is arranged close to the combustion chamber. More specifically, the valve main body serving as the top end component of the fuel injection valve has a large surface area that is exposed to a high temperature gas blown back from the combustion chamber; and accordingly, the valve main body is apt to becomehigh in temperatureand the injection hole plate or the valve seat, which is attached to the inside of the valve main body, is conducted by heat due to the high temperature from a radially end portion near the valve main body toward a central portion. 4 [0007] The injection hole plate of Patent Document 1 has a problem in that plate thickness other than theradially recessed portion formed onthe upstream side is uniform; and accordingly, the heat is easily conducted from the end portion of the injection hole plate to the vicinity of the injection hole atthe central portion, the injection hole portion becomeshigh in temperature, residual gasoline in the injection hole sticks to the inner surface of the injection hole, and deterioration of spray atomization or changes in injection flow rate are concerned. [0008] The present application discloses a technique for solving the foregoing problem and an object of the present application is to provide a fuel injection valve in which even when the fuel injection valve is arranged close to a combustion chamber, spray characteristics or flow rate characteristics are maintained in good condition by forming an injection hole plate into a shape in which an injection hole portion is difficult to have temperature rise. MEANS FOR SOLVING THE PROBLEMS [0009] A fuel injection valve disclosed in the present application is a fuel injection valve including: a valve seat having a valve seat portion and a valve seat opening portion; a valve body which is brought into contact with the valve seat portion of the valve seat to block an outflow of fuel from the valve seat opening portion and is made to separate from the valve seat portion to allow the 5 outflow of the fuel from the valve seat opening portion; and an injection hole plate which is fixed to the downstream side end surface of the valve seat and has a plurality of injection holes in which the fuel flown out from the valve seat opening portion isinjected to the outside. In the fuel injection valve,the upstream side end surface of the injection hole plate is provided with: a swirling chamber in which the injection hole is opened to be communicated to apply swirling force to fuel; and a fuel path which introduces fuel to the swirling chamber, the swirling chamber and the fuel path being constituted by a sidewall having a tapered shape enlarged toward the upstream side. Then,the downstream side end surface of the injection hole plate is provided with a concave portion in anarea including the swirling chamber and the fuel path. ADVANTAGEOUS EFFECT OF THE INVENTION [0010] According to the fuel injection valve disclosed in the present application, there can be obtained the fuel injection valve whichcan suppress temperature risein the vicinity of the injection hole, is capable of reducing fuel temperature in the swirling chamber or in the fuel path, and can maintain spray characteristics or flow rate characteristics in good condition. BRIEF DESCRIPTION OF THE DRAWINGS [0011] FIG. 1 is a sectional view showing a fuel injection valve according to Embodiment 1; 6 FIG. 2 is a sectional view (a) showing a top end portion in the fuel injection valve according to Embodiment 1 and is a sectional view (b) taken along the line A-A of the sectional view (a); FIG. 3 is an enlarged view (a) showing the upstream side end surface of an injection hole plate in a fuel injection valve according to Embodiments 1 and 2 and is a sectional view (b) taken along the line B-B of the enlarged view (a); FIG. 4 is a sectional view (a) showing a top end portion in a fuel injection valve according to Embodiments 1 and 3 and is a view (b) seen from the direction of an arrow S1 on the downstream side of an injection hole plate in the fuel injection valve; FIG. 5 is a sectional view (a) showing a top end portion in a fuel injection valve according to Embodiment 4 and is a view (b) seen from the direction of an arrow S2 on the downstream side of an injection hole plate in the fuel injection valve; FIG. 6 is a sectional view (a) showing a top end portion in a fuel injection valve according to Embodiment 5 and is a view (b) seen from the direction of an arrow S3 on the downstream side of an injection hole plate in the fuel injection valve; FIG. 7 is a sectional view (a) showing a top end portion in a fuel injection valve according to Embodiment 6 and is a view (b) seen from the direction of an arrow S4 on the downstream side of an injection hole plate in the fuel injection valve; and FIG. 8 is an enlarged view (a) showing the upstream side end surface of an injection hole plate in a fuel injection valve 7 according to Embodiment 7 and is a sectional view (b) taken along the line C-C of the enlarged view (a). MODE FOR CARRYING OUT THE INVENTION [0012] Embodiment 1. FIG. 1 is a sectional view showing a fuel injection valve according to Embodiment 1. FIG. 2(a) is a sectional view showing a top end portion in the fuel injection valve according to Embodiment 1; and FIG. 2(b) is a sectional view taken along the line A-A of FIG. 2(a). [0013] Reference numeral 100 denotes the fuel injection valve. 4 denotes a solenoid device; 5 denotes a metal plate serving as a yoke portion of a magnetic circuit; 6 denotes a cylindrical core serving as a fixed core portion of the magnetic circuit; 7 denotes a coil wound around a bobbin 1 arranged on the outer circumference of the core 6; and 8 denotes a cylindrical armature serving as a movable core portion of the magnetic circuit, in which an armature upper end surface 8b is brought into contact with or removed from the lower end surface of the core 6.Then, the armature 8 has a sliding surface 8a that slides in a valve holder 11 (to be described later) and is axially slidable in the valve holder 11. 9 denotes a valve device that is composed of a valve body 10, the valve holder 11, and a valve seat 12. Incidentally, the metal plate 5 is arranged straddling the outer circumferential surface of the core 6 and the outer circumferential surface of the valve holder 11 and is fixed by welding. 8 [0014] An upstream side end portion of the valve holder 11 is press-fitted on an outer circumferential portion of the core 6 and then welded. The cylindrical armature 8 is press-fitted on an upstream side end portion of the valve body 10 and then welded; and the armature 8 and the valve body 10 are axially moved in an integrated manner. An injection hole plate 13 is coupled to the lower end surface of the valve seat 12 by welding in a welding portion 50; and the valve seat 12 and the injection hole plate 13 are of an integrated structure and are attached to the inside of a downstream side end portion of the valve holder 11. The injection hole plate 13 is provided with a plurality of injection holes 14 passing through in the plate thickness direction thereof. [0015] A ball 15 formed with a chamfered portion 15a is fixed to a downstream side end portion of the valve body 10 and the ball 15 is mounted on or removed from a valve seat portion 12a of the valve seat 12. A compression spring 16 that presses the valve body 10 in a direction pressing the ball 15 to the valve seat portion 12a of the valve seat 12 is inserted in the cylindrical core 6. Furthermore, an adjuster 2 that adjusts a load of the compression spring 16 is fixed in the cylindrical core 6. Further, a filter 3 is inserted in an upper end portion of the cylindrical core 6 which serves as an introducing portion for oil. Then, the valve holder 11, the core 6, the coil 7, and the metal plate 5 are integrally molded in a resin-made housing. A connector portion 22a is provided 9 in the resin-made housing 22 and a terminal 23 electrically connected to the coil 7 is pulled out in the connector portion 22a. [0016] The upstream side end surface of the injection hole plate 13 is provided with: a swirling chamber 18 in which the injection hole 14 isopened to be communicated to apply swirling force to fuel; and a fuel path 17 which introduces fuel to the swirling chamber 18, the swirling chamber 18 and the fuel path 17 being constituted by a sidewall 20 having a tapered shape enlarged toward the upstream side. The downstream side end surface of the injection hole plate 13 is formed with a concave portion 30 in anarea including the swirling chamber 18 and the fuel path 17. The injection hole 14 is provided in the vicinity of the center of theswirling chamber 18. The fuel path 17 is communicated with a valve seat opening portion 12b. [0017] Next, operation will be described. When an operation signal is sent to a driving circuit of the fuel injection valve 1 by a control device of an engine, current is energized to the coil 7 of the fuel injection valve 1, magnetic flux is generated in the magnetic circuit composed of the armature 8, the core 6, the housing 5, and the valve holder 11, and the armature 8 performs suction operation to the core 6 side. Then, when the valve body 10 that is an integrated structure with the armature 8 is made to separate from the valve seat portion 12a to form a gap, fuel passes through the gap between the valve seat portion 12a and the valve body 10 from 10 the chamfered portion 15a of the ball 15 welded to a top end portion of the valve body 10 and is injected from the plurality of the injection holes 14 to an intake air path of the engine. [0018] Next, when an operation stop signal is sent to the driving circuit of the fuel injection valve 1 by the control device of the engine, the energization of current to the coil 7 is stopped, the magnetic flux in the magnetic circuit is reduced, the gap between the valve body 10 and the valve seat portion 12a becomes a closed state by the compression spring 16 that presses the valve body 10 in a valve closing direction, and the fuel injection is completed. The valve body 10 is slid on a guide portion of the inner circumferential surface of the valve holder 11 with the sliding surface 8a of the armature 8; and the armature upper end surface 8b of the armature 8 is brought into contact with the lower end surface of the core 6 in an opened valve state. [0019] In Embodiment 1, a plurality of the swirling chambers 18 by which swirling force is applied to fuel are formed by recessing the upstream side end surface of the injection hole plate 13 as shown in FIGS. 2(a) and 2(b) and FIGS. 3(a) and 3(b). The injection hole 14 is provided in the vicinity of the center of each of the swirling chambers 18. The fuel path 17 in which fuel is introduced to the swirling chamber 18 is provided corresponding to the swirling chamber 18. The fuel path 17 is communicated with the valve seat opening portion 12b. 11 [0020] Thus, the fuel flowed into the swirling chamber 18 through the fuel path 17 from the valve seat opening portion 12 flows into the injection hole 14 while generating a swirling flow. A thin liquid film along an inner wall of the injection hole 14 is formedby the swirling flow is also maintained in the inside of the injection hole 14, and atomization of the fuel is expedited by injecting the thin liquid film in a hollow-conical shape from the injection hole 14. [0021] When the fuel injection valve 1 is arranged close to a combustion chamber, the valve holder 11 serving as a top end component of the fuel injection valve 1 has a large surface area that is exposed to a high temperature gas blown back from the combustion chamber; and accordingly, the valve holder 11is apt to becomehigh in temperature. Then,its heat is conducted from an end portion of the injection hole plate 13 or an outer circumferential portion of the valve seat 12 to a central portion of the injection hole plate 13, the injection hole plate 13 and the valve seat 12 being attached to the inside of the valve holder 11;and the temperature in the vicinity of the injection hole 14 becomes high. Accordingly,residual gasoline in the injection hole 14 sticks to the inner surface of the injection hole 14 and deterioration of spray atomization or changes in injection flow rate are concerned. Furthermore, fuel in the swirling chamber 18 and in the fuel path 17 becomes high in temperature and deterioration of spray 12 atomization or changes in injection flow rate due to the generation of cavitation are concerned. [0022] Therefore, in Embodiment 1, the sidewall 20 that forms the swirling chamber 18 and the fuel path 17 is formed in the tapered shape enlarged toward the upstream side. This increases the surface area of the sidewall 20 coming in contact with fuel,in contrast with the case where the tapered shape is not provided as disclosed in Patent Document 1; and therefore, a cooling effect of the fuel is enhanced and the temperature in the vicinity of the injection hole 14 can be reduced. [0023] Further, as shown in FIGS. 4(a) and 4(b), the downstream side end surface of the injection hole plate 13 is provided with the concave portion 30 in thearea including the swirling chamber 18 and the fuel path 17 which are projected when the downstream side end surface is seen in the vertical direction from the downstream side of the injection hole plate 13 as shown byan arrow S1, and the plate thickness of the injection hole plate 13 is thinned in contrast withthe end portion of the injection hole plate 13. [0024] This can reducethe heat conduction from the end portion of the injection hole plate 13 attached to the inside of the valve holder 11 to the vicinity of the injection hole 14; and therefore, even when the fuel injection valve is arranged close to the combustion chamber, the temperature risein the vicinity of the injection hole 13 14 is suppressed and the residual gasolinecan be suppressed to stick to the inner surface of the injection hole 14. Furthermore, fuel temperature in the swirling chamber 18 or in the fuel path 17 can also be reduced; and therefore, the generation of cavitation can be suppressed and deterioration of spray atomization or changes in injection flow rate can be suppressed. [0025] Embodiment 2. FIG. 3(a) is an enlarged view showing the upstream side end surface of an injection hole plate in a fuel injection valve according to Embodiment 2; and FIG. 3(b) is a sectional view taken along the line B-B of FIG. 3(a) of Embodiment 2. [0026] It is configured such that when a fuel path 17 and an injection hole 14 are projected on a flat surface perpendicular to the center axis of a fuel injection valve 1, and if the width and the depth of a bottom portion of the fuel path 17 are represented as H and V, respectively, a tilt angle with respect to the depth direction of a sidewall 20 is represented as θ, and the distance from the center axis of the bottom portion of the fuel path 17 to the center of the injection hole 14 is represented as L, a relational equation of H/2+V·tanθ