Abstract:
An injector includes a nozzle hole formation part having a nozzle_hole formation area and nozzle holes in at least one circle shape in the formation area. The formation area is divided into central and peripheral regions by a predetermined circle, the former inward from the predetermined circle and the latter in the periphery of the central region. The nozzle holes include outputting nozzle holes in the peripheral region and at least one cooling nozzle hole in the central region. Fuel through the outputting nozzle holes contributes to engine output. A smaller amount of fuel than a fuel amount through the outputting nozzle hole is injected through the cooling nozzle hole to cool the central region. A ratio of a second total fuel amount through the cooling nozzle hole to an overall total fuel amount ranges from 0.05 to 0.37.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-234543 filed on Sep. 10, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to an injector, and more particularly to an injector that injects fuel into an internal combustion engine, for example. 
         [0004]    2. Description of Related Art 
         [0005]    An injector, which injects fuel directly into a cylinder of an internal combustion engine, for example, is known as a conventional injector (see, for example, JP2000-38974A and JP10-159688A). In this kind of injector, fuel injected through a nozzle hole needs to spread in a combustion chamber of the cylinder immediately under the nozzle hole. 
         [0006]    In JP2000-38974A, at least four nozzle holes are arranged in a shape of a single annulus ring, and a spray of fuel injected through the nozzle holes is formed in a hollow conical shape as a whole. According to the above technology, an axis of the nozzle hole is inclined to be further away from a central axis of a nozzle hole plate extending in its thickness direction in a direction from a nozzle hole inlet side toward a nozzle hole outlet side. On the nozzle hole plate as a nozzle hole formation part, a nozzle hole is not arranged inward of these nozzle holes, that is, in a central region surrounded by the nozzle holes. 
         [0007]    In JP10-159688A, an inner circumference and a surrounding area of a nozzle hole on a nozzle hole plate are coated with an FAS layer made of fluoro alkyl silane (FAS). The above FAS layer has liquid repellency due to the existence of a fluoro alkyl group. 
         [0008]    In the injector according to the technology of JP2000-38974A, the nozzle hole formed in the nozzle hole plate is exposed to hot gas in the combustion chamber. Consequently, residual fuel which has remained around the nozzle hole after the fuel injection is altered into deposits (carbonaceous compound) to deposit around the nozzle hole, and thereby the nozzle hole may be blocked by the deposits. If not blocking the nozzle hole, the nozzle hole is a microscopic hole of about 100 μm because of fuel atomization. Thus, the growth of the deposits to such an extent that they enter into the nozzle hole may decrease or fluctuate fuel injection quantity as a fuel injection characteristic. For example, an adverse effect may be produced on a fuel-spray state. 
         [0009]    According to the technology of JP10-159688A, the nozzle hole plate coated with the FAS layer has action (liquid repelling action) to lift the residual fuel off the coated surface and repel it due to the existence of the fluoro alkyl group. Accordingly, adhesion of the residual fuel is limited, so that formation the deposits can be alleviated. 
         [0010]    However, in the technology of JP10-159688A, there are concerns about alteration or deterioration of the FAS layer after its prolonged exposure to a high temperature state. In the event of the alteration of the FAS layer and the like, the liquid repellency may deteriorate. 
         [0011]    The inventor devoted himself to research into a mechanism of generating the deposits and as a result, found out the following. 
         [0012]    The deposits are generated after the residual fuel produces chemical reactions other than combustion, or impure substances (e.g., carboxylate) in the residual fuel are deposited. Even though other deposits are attached to the above deposits as a core and thereby the deposits grow, bonding force between the deposits should be comparatively weak and the deposits should be easily exfoliated. Irrespective of whether the nozzle hole plate is coated in the FAS layer, the deposits grow into deposits that are firmly fixed on and difficult to exfoliate off a surface of the nozzle hole plate. 
         [0013]    Heavy elements such as phosphorus (P) and zinc (Zn) contained in an engine cleaning agent or the like, exist around the nozzle hole on the nozzle hole plate surface in the combustion chamber of the cylinder. The heavy elements such as phosphorus (P) and zinc (Zn) react with silicon dioxide (SiO2) in silane of the altered and deteriorated FAS layer, and accordingly turn into low-melting glass. Each deposit adheres on the FAS-coated surface of the plate to such a degree that it is difficult to exfoliate, due to the above low-melting glass. 
         [0014]    In the case of the nozzle hole plate without the FAS layer, on the other hand, the low-melting glass may be produced through the intervention of silicon (Si) in a silicon compound, which is used as an additive agent to engine oil for the defoaming purpose. As a result, each deposit may adhere on the surface to such a degree that it is difficult to exfoliate. 
         [0015]    Moreover, the firmly fixed deposits tend to grow in a central region on the nozzle hole plate where the nozzle hole is not arranged. In other words, irrespective of whether the nozzle hole plate is coated in the FAS layer, the deposits adhered on the plate grow when temperature of the plate surface rises (e.g., 400° C. or higher). 
         [0016]    The term low-melting glass here means amorphous glass, which is generated at about 400° C. 
       SUMMARY OF THE INVENTION 
       [0017]    The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to limit an increase of heat temperature of a nozzle hole formation part of an injector that injects fuel directly into a cylinder of an internal combustion engine. 
         [0018]    To achieve the objective of the present invention, there is provided an injector that is configured to inject fuel into a cylinder of an internal combustion engine. The injector includes a nozzle hole formation part. The nozzle hole formation part includes a nozzle hole formation area and a plurality of nozzle holes. The nozzle hole formation area is an end surface of the nozzle hole formation part on a downstream side of the nozzle hole formation part in a fuel flow direction. The plurality of nozzle holes is formed in a shape of at least one circle in the nozzle hole formation area, and fuel is injected through the plurality of nozzle holes. The nozzle hole formation area is divided into a central region and a peripheral region by a predetermined circle that is concentric with the at least one circle, the central region being located radially inward from the predetermined circle and the peripheral region being located on an outer circumferential side of the central region. The plurality of nozzle holes includes a plurality of outputting nozzle holes formed in the peripheral region such that fuel is injected into the cylinder through the plurality of outputting nozzle holes to contribute to an output of the engine, and at least one cooling nozzle hole in the central region such that a smaller amount of fuel than an amount of fuel flowing through the outputting nozzle hole is injected through the at least one cooling nozzle hole so as to cool the central region. The plurality of outputting nozzle holes and the at least one cooling nozzle hole are configured such that a ratio of a second total amount of fuel flowing through the at least one cooling nozzle hole to an overall total fuel amount that is a sum of the second total amount and a first total amount of fuel flowing through the plurality of outputting nozzle holes is in a range of 0.05 to 0.37. 
         [0019]    To achieve the objective of the present invention, there is also provided an injector that is configured to inject fuel into a cylinder of an internal combustion engine. The injector includes a nozzle hole formation part. The nozzle hole formation part includes a nozzle hole formation area and a plurality of nozzle holes. The nozzle hole formation area is an end surface of the nozzle hole formation part on a downstream side of the nozzle hole formation part in a fuel flow direction. The plurality of nozzle holes is formed in a shape of at least one circle in the nozzle hole formation area, and fuel is injected through the plurality of nozzle holes. The nozzle hole formation area is divided into a central region and a peripheral region by a predetermined circle that is concentric with the at least one circle, the peripheral region being located radially outward from the predetermined circle and the central region being located on an inner circumferential side of the peripheral region. The plurality of nozzle holes includes a plurality of outputting nozzle holes formed in the central region such that fuel is injected into the cylinder through the plurality of outputting nozzle holes to contribute to an output of the engine, and at least one cooling nozzle hole in the peripheral region such that a smaller amount of fuel than an amount of fuel flowing through the outputting nozzle hole is injected through the at least one cooling nozzle hole so as to cool the peripheral region. The plurality of outputting nozzle holes and the at least one cooling nozzle hole are configured such that a ratio of a second total amount of fuel flowing through the at least one cooling nozzle hole to an overall total fuel amount that is a sum of the second total amount and a first total amount of fuel flowing through the plurality of outputting nozzle holes is in a range of 0.05 to 0.37. 
         [0020]    Furthermore, to achieve the objective of the present invention, there is provided an injector that is configured to inject fuel into a cylinder of an internal combustion engine. The injector includes a nozzle hole formation part. The nozzle hole formation part includes a nozzle hole formation area and a plurality of nozzle holes. The nozzle hole formation area is an end surface of the nozzle hole formation part on a downstream side of the nozzle hole formation part in a fuel flow direction. The plurality of nozzle holes is formed in a shape of at least one circle in the nozzle hole formation area, and fuel is injected through the plurality of nozzle holes. The nozzle hole formation area is divided into a central region and a peripheral region by a predetermined circle that is concentric with the at least one circle, the central region being located radially inward from the predetermined circle and the peripheral region being located on an outer circumferential side of the central region. The plurality of nozzle holes includes a plurality of outputting nozzle holes formed in the peripheral region and at least one cooling nozzle hole formed in the central region. The plurality of outputting nozzle holes and the at least one cooling nozzle hole are formed such that a spray travel of fuel injected through each of the at least one cooling nozzle hole is shorter than a spray travel of fuel injected through each of the plurality of outputting nozzle holes when the injector injects fuel. The plurality of outputting nozzle holes and the at least one cooling nozzle hole are formed to satisfy an expression of 1/10×A 1 ≦A 2 ≦½×A 1  given that A 1  is an opening area of each of the plurality of outputting nozzle holes and A 2  is an opening area of each of the at least one cooling nozzle hole. The plurality of outputting nozzle holes is formed such that a first hole axis of each of the plurality of outputting nozzle holes separates from a central axis of the nozzle hole formation part extending in a thickness direction of the nozzle hole formation part in a direction from an fuel inlet side toward an fuel outlet side of the nozzle hole formation part. The at least one cooling nozzle hole is formed such that a second hole axis of each of the at least one cooling nozzle hole approaches the central axis of the nozzle hole formation part in the direction from the fuel inlet side toward the fuel outlet side of the nozzle hole formation part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]    The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: 
           [0022]      FIG. 1  is a sectional diagram illustrating a peripheral part of a nozzle hole formation part of an injector according to a first embodiment of the invention; 
           [0023]      FIG. 2  is a plan view illustrating a nozzle hole plate as the nozzle hole formation part according to the first embodiment viewed from a downstream side in a fuel flow direction; 
           [0024]    FIG.  3 A 1  is a segmentary diagram illustrating an outputting nozzle hole in the nozzle hole formation part in  FIG. 2 ; 
           [0025]    FIG.  3 A 2  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0026]    FIG.  3 A 3  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0027]    FIG.  3 B 1  is a segmentary diagram illustrating a cooling nozzle hole in the nozzle hole formation part in  FIG. 2 ; 
           [0028]    FIG.  3 B 2  is a segmentary diagram illustrating the cooling nozzle hole; 
           [0029]    FIG.  3 B 3  is a segmentary diagram illustrating the cooling nozzle hole; 
           [0030]      FIG. 4  is a sectional diagram illustrating the nozzle hole plate in  FIG. 2 ; 
           [0031]      FIG. 5  is a sectional diagram illustrating an example of the injector according to the first embodiment; 
           [0032]      FIG. 6  is a sectional diagram illustrating an attachment position of the injector according to the first embodiment, and a spray of the valve into a combustion chamber; 
           [0033]      FIG. 7  is a graph illustrating a relationship between a ratio of a gross opening area of the cooling nozzle holes to an overall gross opening area, and heat temperature in a central region of a downstream-side end surface of the nozzle hole plate according to the first embodiment; 
           [0034]      FIG. 8  is a plan view illustrating a nozzle hole plate according to a second embodiment of the invention; 
           [0035]      FIG. 9  is a sectional diagram illustrating the nozzle hole plate in  FIG. 8 ; 
           [0036]    FIG.  10 A 1  is a segmentary diagram illustrating an outputting nozzle hole in a nozzle hole formation part in  FIG. 8 ; 
           [0037]    FIG.  10 A 2  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0038]    FIG.  10 A 3  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0039]    FIG.  10 B 1  is a segmentary diagram illustrating a cooling nozzle hole in the nozzle hole formation part in  FIG. 8 ; 
           [0040]    FIG.  10 B 2  is a segmentary diagram illustrating the cooling nozzle hole; 
           [0041]    FIG.  10 B 3  is a segmentary diagram illustrating the cooling nozzle hole; 
           [0042]      FIG. 11  is a plan view illustrating a nozzle hole plate according to a third embodiment of the invention; 
           [0043]      FIG. 12  is a sectional diagram illustrating the nozzle hole plate in  FIG. 11 ; 
           [0044]    FIG.  13 A 1  is a segmentary diagram illustrating an outputting nozzle hole in a nozzle hole formation part in  FIG. 11 ; 
           [0045]    FIG.  13 A 2  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0046]    FIG.  13 A 3  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0047]    FIG.  13 B 1  is a segmentary diagram illustrating a cooling nozzle hole in the nozzle hole formation part in  FIG. 11 ; 
           [0048]    FIG.  13 B 2  is a segmentary diagram illustrating the cooling nozzle hole; 
           [0049]    FIG.  13 B 3  is a segmentary diagram illustrating the cooling nozzle hole; 
           [0050]      FIG. 14  is a plan view illustrating a nozzle hole plate according to a fourth embodiment of the invention; 
           [0051]      FIG. 15  is a sectional diagram illustrating the nozzle hole plate in  FIG. 14 ; 
           [0052]    FIG.  16 A 1  is a segmentary diagram illustrating an outputting nozzle hole in a nozzle hole formation part in  FIG. 14 ; 
           [0053]    FIG.  16 A 2  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0054]    FIG.  16 A 3  is a segmentary diagram illustrating the outputting nozzle hole; 
           [0055]    FIG.  16 B 1  is a segmentary diagram illustrating a cooling nozzle hole in the nozzle hole formation part in  FIG. 14 ; 
           [0056]    FIG.  16 B 2  is a segmentary diagram illustrating the cooling nozzle hole; and 
           [0057]    FIG.  16 B 3  is a segmentary diagram illustrating the cooling nozzle hole. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0058]    Embodiments, in which an injector of the invention is embodied, are described below as examples with reference to drawings. 
       First Embodiment 
       [0059]    An injector  10  of a first embodiment of the invention is shown in  FIG. 5 . The injector  10  is attached to a cylinder head  102 . The injector  10  is an injector for a direct injection gasoline engine, which injects fuel directly into a combustion chamber  106  defined by an inner circumferential surface of a cylinder block  100 , an inner circumferential surface of the cylinder head  102 , and an upper end surface of a piston  104 . An injection pressure of the injector  10  is in a range of 1 MPa to 30 MPa. 
         [0060]    It is desirable that a spray of fuel injected from the injector  10  should be atomized to spread into the combustion chamber  106  in  FIG. 6 . The above spray of fuel has basically a shape of a spray  24 , which has a hollow conical shape, for example. 
         [0061]    The spray  24  may be formed by suitably setting a shape or arrangement of a nozzle hole formed on a leading-end side of the injector  10 . Shapes and arrangements of an outputting nozzle hole and a cooling nozzle hole that relate to the present invention, and fuel sprays injected through the above nozzle holes are described in greater detail hereinafter. 
         [0062]    Such a spray  24  is inclined with respect to the axis  108  such that it separates toward an end face of the piston  104  from an axis  108  of the injector  10  along a direction, in which a valve member (nozzle needle)  30  of the injector  10  in  FIG. 5  engages a valve seat  14 , as it goes in the injection direction. By suitably setting an optimal angle, at which the spray  24  is inclined with respect to the axis  108  of the injector  10  so that the spray  24  spreads into the combustion chamber  106 , adhesion of the spray  24  on an ignition plug  105 , or on the piston  104  and the inner wall surface of the cylinder block  100  that define the combustion chamber  106  in a liquid state is limited. 
         [0063]    As shown in  FIG. 5 , a valve body  12  is fixed by welding to an inner wall of a fuel-injection side-end portion of a valve housing  16 . The valve body  12  includes a conic surface  13  as its inner circumferential surface whose diameter decreases in a direction a nozzle hole plate  20  in a fuel flow direction. The conic surface  13  has the valve seat  14 , which the nozzle needle  30  as the valve member engages. 
         [0064]    The nozzle hole plate  20  is formed in a cylindrical shape having a bottom portion, and is held between an inner wall of a bottom portion of the valve housing  16  and an outer wall of a bottom portion of the valve body  12 . The nozzle hole plate  20  having nozzle holes  21 ,  22  that relate to the outputting nozzle hole and the cooling nozzle hole is described in greater detail hereinafter. 
         [0065]    As shown in  FIG. 5 , a cylindrical member  40  is inserted against an inner peripheral wall of an opposite side of the nozzle hole of the valve housing  16 , and is fixed by welding to the valve housing  16 . The cylindrical member  40  includes a first magnetic cylinder portion  42 , a nonmagnetic cylinder portion  44 , and a second magnetic cylinder portion  46  from the nozzle hole plate  20  side. The nonmagnetic cylinder portion  44  prevents a magnetic short circuit of the first magnetic cylinder portion  42  and the second magnetic cylinder portion  46 . 
         [0066]    A movable core  50  is formed in a cylindrical shape from a magnetic material, and is fixed by welding to an end portion  34  of the nozzle needle  30  on an opposite side of the nozzle hole. The movable core  50  reciprocates together with the nozzle needle  30 . A discharge hole  52  passing through a cylindrical wall of the movable core  50  serves as a fuel passage through which the inside and outside of the movable core  50  communicate. 
         [0067]    A fixed core  54  is formed in a cylindrical shape from a magnetic material. The fixed core  54  is inserted into the cylindrical member  40 , and is fixed by welding to the cylindrical member  40 . The fixed core  54  and the nozzle hole are located on opposite sides of the movable core  50 , and the fixed core  54  faces the movable core  50 . 
         [0068]    An adjusting pipe  56  is press-fitted into the fixed core  54 , and defines inside a fuel passage. A spring  58  engages the adjusting pipe  56  at its one end part, and engages the movable core  50  at its other end part. A load of the spring  58  applied to the movable core  50  is varied according to a degree of press fitting of the adjusting pipe  56 . The movable core  50  and the nozzle needle  30  are urged toward the valve seat  14  by urging force of the spring  58 . 
         [0069]    A coil  60  is wound around a spool  62 . A terminal  65  is insert molded in a connector  64 , and is electrically connected to the coil  60 . On energization of the coil  60 , Magnetic attraction force is generated between the movable core  50  and the fixed core  54 . The movable core  50  is attracted to a side of the fixed core  54  against the urging force of the spring  58 . 
         [0070]    A filter  70  is disposed on an upstream side of the fixed core  54  in the fuel flow direction for removing foreign substances in fuel that is supplied to an injector  10 . Fuel, which has flowed into the fixed core  54  through the filter  70 , passes through the fuel passage in the adjusting pipe  56 , a fuel passage in the movable core  50 , the discharge hole  52 , and a gap between an inner circumferential wall of the valve housing  16  and an outer circumferential wall of the nozzle needle  30  in this order. When the nozzle needle  30  disengages from the valve seat  14 , fuel passes through an opening passage formed between the nozzle needle  30  and the valve seat  14 , and is led into the nozzle holes  21 ,  22 . 
         [0071]    Next, shapes and arrangements of the nozzle hole plate  20 , and the nozzle hole (outputting nozzle hole)  21  and the nozzle hole (cooling nozzle hole)  22  that are formed in the nozzle hole plate  20  are explained below in detail with reference to  FIG. 1  to  FIG. 4 . In the following description, although a side of the injector  10  into which fuel is injected is referred to as a ‘lower’ side, and an opposite side of the above is referred to as a ‘upper’ side for the purpose of illustrating embodiments, these sides do not relate to an actual installation direction of the injector  10  in the engine. 
         [0072]    The invention is characterized in the nozzle hole plate  20  and the above nozzle holes  21 ,  22  shown in  FIG. 2  and  FIG. 4 , and particularly in shapes and arrangements of the outputting nozzle hole  21  and the cooling nozzle hole  22  formed on a lower surface, that is, a downstream side end face (end face facing the combustion chamber) of the nozzle hole plate  20 . 
         [0073]    Fuel, which is injected such that a fuel spray through the outputting nozzle hole  21  spreads in the combustion chamber  106  of a cylinder so as to contribute to engine output, is injected through the outputting nozzle hole  21 . 
         [0074]    A smaller amount of fuel than an amount of fuel flowing through the outputting nozzle hole  21 , which is a part of fuel for flowing through the fuel passage in the outputting nozzle hole  21 , is injected through the cooling nozzle hole  22 . Furthermore, unlike the fuel spray of the outputting nozzle hole  21 , the cooling nozzle hole  22  does not need to contribute to the engine output. Accordingly, the fuel spray of the cooling nozzle hole  22  does not need a penetration (fuel spray travel) that spreads in the combustion chamber  106  like the fuel spray of the outputting nozzle hole  21 . Therefore, the fuel spray of the cooling nozzle hole  22  may have a very short penetration, which is locally atomized near the cooling nozzle hole  22  (see  FIG. 4 ). 
         [0075]    As shown in  FIG. 2  viewed from a lower surface of the nozzle hole plate, the nozzle hole plate  20  has the outputting nozzle holes  21  (four outputting nozzle holes in the first embodiment) and the cooling nozzle holes  22  (four cooling nozzle holes in the first embodiment). The above nozzle holes  21 ,  22  are formed in the nozzle hole plate  20  such that an upper surface (surface facing the inside of the valve body  12  or on an upstream side in the fuel flow direction) and a lower surface (surface facing the combustion chamber  106  located outside) communicate through the nozzle holes  21 ,  22 . 
         [0076]    The number of the outputting nozzle holes  21  is not limited to four, and may be any number so long as there are two or more outputting nozzle holes  21 . As well, the number of the cooling nozzle holes  22  is not limited to four, and may be any number so long as there is at least one cooling nozzle hole  22 . 
         [0077]    The four outputting nozzle holes  21  are formed in the same circumference with a central axis  20   j,  which extends along a board thickness direction of the nozzle hole plate  20 , being its center. In other words, the outputting nozzle holes  21  are arranged in a shape of a single annulus ring. The outputting nozzle hole  21  has a round cross section (see FIG.  3 A 3 ) and is a straight hole (see FIG.  3 A 2 ). 
         [0078]    As well, the four cooling nozzle holes  22  are formed in the same circumference with a central axis  20   j,  which extends along a board thickness direction of the nozzle hole plate  20 , being its center. In other words, the cooling nozzle holes  22  are arranged in a shape of a single annulus ring. The cooling nozzle hole  22  has a round cross section (see FIG.  3 B 3 ) and is a straight hole (see FIG.  3 B 2 ). 
         [0079]    The cooling nozzle hole  22  is arranged between adjacent outputting nozzle holes  21 . The nozzle holes  21 ,  22  are arranged such that a second hole axis  22   j  of the cooling nozzle hole  22  and a first hole axis  21   j  of the outputting nozzle hole  21  do not cross. 
         [0080]    As shown in  FIG. 1 , the first hole axis  21   j  of the outputting nozzle hole  21  is inclined to be further away from the central axis  20   j  of the nozzle hole plate  20  in a direction from an inlet toward an outlet of the outputting nozzle hole  21 . A first angle (first inclined angle) θ 1  between the first hole axis  21   j  and the central axis  20   j  is set in a range of 5 to 60°. The first inclined angle θ 1  may be set in a range of 25 to 60°. 
         [0081]    When the first inclined angle θ 1  is smaller than 25°, fuel flowing in from an inlet side of the outputting nozzle hole  21  of the nozzle hole plate  20  does not include high turbulence energy due to a small first inclined angle θ 1 . Therefore, fuel atomization using the high turbulence energy cannot be achieved. On the other hand, although the turbulence energy is raised by making large the first inclined angle θ 1 , the outputting nozzle hole  21  is difficult to form with the first hole axis  21   j  inclined with respect to the central axis  20   j  of the nozzle hole plate  20  when the first inclined angle θ 1  is larger than 60°. 
         [0082]    As shown in  FIG. 1 , the second hole axis  22   j  of the cooling nozzle hole  22  is inclined to be closer to the central axis  20   j  of the nozzle hole plate  20  in a direction from an inlet toward an outlet of the cooling nozzle hole  22 . A second angle (second inclined angle) θ 2  between the second hole axis  22   j  and the central axis  20   j  is set in a range of 30 to 80°. The second inclined angle θ 2  may be set in a range of 30 to 80°. 
         [0083]    As shown in  FIG. 1 , the nozzle holes  21 ,  22  formed on the lower surface of the nozzle hole plate  20  are arranged such that an area (nozzle hole formation area) of the nozzle hole plate  20 , in which a fuel passage for fuel flowing through the nozzle holes  21 ,  22  is formed, is divided by the nozzle holes  21 ,  22  between a central region (region up to a radius R 1  in FIG.  3 A 1 ) inward of an area of the nozzle hole plate  20  for the outputting nozzle holes  21 , which is formed in the shape of the single annulus ring, and a peripheral region located on an outer circumferential side of the central region. 
         [0084]    As shown in  FIG. 1  and FIG.  3 A 1 , the outputting nozzle hole  21  is formed in such a peripheral region. On the other hand, as shown in  FIG. 1  and FIG.  3 B 1 , the cooling nozzle hole  22  is formed in the central region. 
         [0085]    An opening area (i.e. diameter D 2  in FIG.  3 B 3 ) of the cooling nozzle hole  22  may be smaller (D 2 &lt;D 1 ) than an opening area (i.e. diameter D 1  in FIG.  3 A 3 ) of the outputting nozzle hole  21 . 
         [0086]    Generally, atomization of fuel is further improved as a size, that is, an opening area of a nozzle hole becomes smaller. A fuel spray travel (penetration) of a fuel spray atomized in the above manner becomes short. Therefore, it is easy to keep a fuel spray that is formed on a side of the cooling nozzle hole  22  near the central region, since the penetration of the cooling nozzle hole  22  is shorter than the penetration of the outputting nozzle hole  21 . 
         [0087]    Moreover, each opening area of the cooling nozzle hole  22  and the outputting nozzle hole  21  may satisfy the following relation. That is, given that the opening area of the outputting nozzle hole  21  is A 1  and the opening area of the cooling nozzle hole  22  is A 2 , the each opening area may be set in a range of 1/10×A 1 ≦A 2 ≦½×A 1 . 
         [0088]    In the above manner, the opening area A 2  of the cooling nozzle hole  22  is set in a range of a tenth to half of the opening area A 1  of the outputting nozzle hole  21 . Accordingly, loss energy of the fuel passage, that is, pressure loss of a fuel flow in the cooling nozzle hole  22  is extremely increased as compared to pressure loss in the outputting nozzle hole  21 , and jet energy of the fuel flow in the cooling nozzle hole  22  is effectively weakened. 
         [0089]    When the opening area A 2  is larger than a half of the opening areas A 1  of the outputting nozzle hole  21 , in the setting range of a ratio of the opening area A 2  of the cooling nozzle hole  22 , the jet energy of fuel injected through the cooling nozzle hole  22  cannot be limited to a small value. Accordingly, the spray through the cooling nozzle hole  22  may not be kept near a lower surface of the nozzle hole plate  20 . When the opening area A 2  is smaller than a tenth of the opening area A 1  of the outputting nozzle hole  21 , the jet energy is made small enough, but the cooling nozzle hole  22  is difficult to form. 
         [0090]    As shown in  FIG. 1 , the nozzle hole plate  20 , and the nozzle hole formation area, in particular, are formed in a generally plate-like shape, and furthermore, a fuel space  80  defined by a nozzle hole plate side end face  32  and a nozzle needle side end face  26  of the nozzle hole plate  20  is flattened. This is because the nozzle hole plate side end face  32  of the nozzle needle  30  is flat. 
         [0091]    Such a nozzle hole formation area of the nozzle hole plate  20  is opposed to the flat space for fuel formed on the upper surface (end face on an upstream side in the fuel flow direction) of the nozzle hole plate  20 , with the plate-shaped nozzle hole plate  20  therebetween. Moreover, the nozzle hole plate  20  is plate-shaped. Thus, heat capacity in the nozzle hole formation area is comparatively small. 
         [0092]    The nozzle hole plate  20  is constantly cooled from its upper surface side by fuel stored in the fuel passage in the valve body  12  using the comparatively small heat capacity in the nozzle hole plate, and the central region on the lower surface (end face on a downstream side in the fuel flow direction), that is, on a side of the combustion chamber, is cooled by fuel injected through the cooling nozzle hole  22 . Consequently, heat temperature of the nozzle hole plate  20  before the combustion is effectively lowered. 
         [0093]    A smaller amount of fuel than the amount of fuel flowing through the outputting nozzle hole  21  is injected in the cooling nozzle hole  22 . This means that a ratio (Qr/(Qt+Qr)) of the second total amount Qr of fuel to an overall total fuel amount (Qt+Qr) may be set in a range of 5%&lt;Qr/(Qt+Qr)×100&lt;37%, provided that a first total amount of fuel flowing through the outputting nozzle hole  21  is Qt, and a second total amount of fuel flowing through the cooling nozzle hole  22  is Qr. In other words, the ratio of the injection amount Qr of fuel injected through the cooling nozzle hole  22  is set in a range of 5 to 37% of the total injection amount (Qt+Qr) of fuel injected from the injector  10 . Accordingly, a spray of fuel injected from the outputting nozzle hole  21  is stably formed in the combustion chamber  106 , and the nozzle hole formation area is cooled down by fuel injected from the cooling nozzle hole  22 . 
         [0094]    When the ratio exceeds 37%, the jet energy of fuel injected from the outputting nozzle hole  21  is smaller than the jet energy of fuel injected from the cooling nozzle hole  22 . As a result, a shape of spray on a side of the outputting nozzle hole  21 , which should spread in the combustion chamber  106  may be disordered. This is because the disorder of the shape of spray on the side of the outputting nozzle hole  21  in the above manner has an adverse effect on the combustion. 
         [0095]    When the above ratio is smaller than 5%, a cooling effect of cooling the nozzle hole plate  20  is reduced, and accordingly, generation of deposits may not be limited. 
         [0096]    In the relation between each opening area of the cooling nozzle hole  22  and the outputting nozzle hole  21 , the opening area A 2  of the cooling nozzle hole  22  is set in a range of a tenth to half of the opening area A 1  of the outputting nozzle hole  21 . When a gross opening area GA 2  of the cooling nozzle holes  22  is small enough compared to a gross opening area GA 1  of the outputting nozzle holes  21 , for example, fuel easily flows into the outputting nozzle hole  21  whose gross opening area is larger, and as a result, the amount of fuel injected through the cooling nozzle hole  22  is set at a small amount. 
         [0097]    Thus, by suitably setting the gross opening area of the cooling nozzle holes  22 , the amount of fuel injected through the cooling nozzle hole  22  is set at a small amount, and even by this small amount of fuel, the central region on the lower surface (end face on a combustion chamber side) of the nozzle hole plate, which is not found in conventional technologies, may be cooled down. When a ratio (GA 2 /(GA 1 +GA 2 )) of the gross opening area GA 2  of the cooling nozzle holes  22  to an overall gross opening area (GA 1 +GA 2 ) is in a range of 0 to 5%, the cooling effect is small as shown in a section I in  FIG. 7 . Accordingly, the above range is not sufficient to stably limit the generation of low melting glass, which leads to fixation of the deposits. 
         [0098]      FIG. 7  illustrates the ratio (GA 1 /(GA 1 +GA 2 )) and a temperature Tp of the central part (central region)of the lower surface side of the nozzle hole plate  20 . The ratio of 0%, that is, a conventional configuration without having a cooling nozzle hole indicates that the heat temperature of the central region of the nozzle hole plate  20  is equal to or larger than 400° C. exceeding a melting point Tcg of low melting glass. When the ratio of the gross opening area GA 2  of the cooling nozzle holes  22 , which are characteristics of the first embodiment, is increased to 3% in the section I corresponding to the ratio of a range of 0 to 5%, the temperature Tp goes down to nearly 300° C. and the heat temperature of the central region greatly decreases. 
         [0099]    In a section II in  FIG. 7 , which corresponds to the ratio of a range of 5 to 37%, the above cooling effect is stably great, so that the generation of deposits can be effectively limited. In the section II, the heat temperature of the central region is reduced to equal to or smaller than 300° C. (Tr). 
         [0100]    A section III in  FIG. 7  corresponds to the ratio of a range of 37 to 100%. When the ratio exceeds 37%, an injection state (spray state) by the outputting nozzle hole  21  for obtaining the output is disordered. Thus, the combustion of fuel becomes worse and both fuel mileage and emission deteriorate. 
         [0101]    Additionally, the relationship between the ratio (GA 1 /(GA 1 +GA 2 )) and the central region temperature Tp of the nozzle hole plate  20  has been described in  FIG. 7 . Alternatively, the ratio (GA 1 /(GA 1 +GA 2 )) of the gross opening area GA 2  of the cooling nozzle holes  22  may be replaced with the ratio (Qr/(Qt+Qr)) of the total fuel amount Qr of the cooling nozzle holes  22 . 
         [0102]    In the first embodiment, at least two cooling nozzle holes  22  are formed in the central region. 
         [0103]    According to the above configuration, it is not an indispensable condition that the cooling nozzle hole  22  contribute to the engine output like the outputting nozzle hole  21 . Therefore, the spray of fuel injected through the cooling nozzle hole  22  may take any shape without any problem. Accordingly, two cooling nozzle holes  22 , which is a comparatively small number, are arranged in the central region, for example. Thus, even when an area of the end face of the nozzle hole plate  20  in the central region is comparatively small, the cooling nozzle hole  22  may be arranged in the central region and thereby the central region is cooled. 
         [0104]    In the first embodiment, the first hole axis  21   j  of the outputting nozzle hole  21  is inclined to be further away from the central axis  20   j  of the nozzle hole plate  20  in the direction from the inlet toward the outlet of the outputting nozzle hole  21 . Furthermore, as shown in  FIG. 1 , the second hole axis  22   j  of the cooling nozzle hole  22  is inclined to be closer to the central axis  20   j  in the direction from the inlet toward the outlet of the cooling nozzle hole  22 . 
         [0105]    Accordingly, the fuel spray through the outputting nozzle hole  21  can be formed in a shape of spray such as a hollow conical shape, which easily spreads in the combustion chamber  106 . Moreover, there is no possibility that the fuel spray on the side of the outputting nozzle hole  22  is disturbed by the fuel spray on the side of the cooling nozzle hole  22 . 
         [0106]    In addition, in the lower surface of the nozzle hole plate  20  shown in  FIG. 4 , a size of the spray injected from the cooling nozzle hole  22  is indicated by an alternate long and two short dashes line, and a size of the spray injected from the outputting nozzle hole  21  is indicated by an alternate long and short dash line. 
         [0107]    In the first embodiment described above, when fuel is injected through the outputting nozzle hole  21  formed in the peripheral region, the central region on the lower surface of the nozzle hole plate  20  is cooled by injecting fuel through the cooling nozzle hole  22  in the central region such that fuel flows in the cooling nozzle hole  22 . 
         [0108]    Moreover, because fuel injected through the cooling nozzle hole  22  does not need to contribute to the engine output, it does not need to be atomized to spread in the combustion chamber  106 . Therefore, a small amount of fuel injected from the cooling nozzle hole  22  is locally atomized near the central region. Because fuel injected through the cooling nozzle hole  22  is atomized near the end face of the central region, direct exposure of the end face to hot gas in the combustion chamber  106  is limited by fuel stagnated and evaporated near the end face. 
         [0109]    As a result, at the time of the fuel injection by the injector  10 , that is, at the time of the fuel injection through the cooling nozzle hole  22 , the central region area on the lower surface of the nozzle hole plate  20  is cooled down by fuel flowing in the cooling nozzle hole  22  as a result of the fuel injection. Furthermore, since fuel injected and atomized through the cooling nozzle hole  22  remains near the central region area, the nozzle hole plate  20  before the combustion is cooled, so that the heat temperature of the nozzle hole plate  20  is reduced. Hence, the increase of the heat temperature of the nozzle hole plate  20  is limited after the combustion. 
         [0110]    Additionally, the reason why the fuel to be injected through the cooling nozzle hole  22  has a cooling effect is that the fuel is supplied to the injector  10  from a fuel tank and its temperature is enough lower than the heat temperature of the nozzle hole formation area. 
         [0111]    Other embodiments to which the invention is applied are explained below. In the following embodiments, the same numeral as the first embodiment is used for the same configuration as or an equivalent configuration to the first embodiment, and its explanation is not repeated. 
       Second Embodiment 
       [0112]    The second embodiment is shown in  FIG. 8 . The second embodiment illustrates shapes of nozzle holes  21 ,  22  in order that a fuel spray remains immediately on a lower surface of a nozzle hole plate  20  in an efficient manner. 
         [0113]    On a lower surface of a nozzle hole plate  20  shown in  FIG. 8 , a size (alternate long and two short dashes line in  FIG. 8 ) of a spray of fuel injected through a cooling nozzle hole  22  overlaps with an occupying area, which is occupied by a spray (alternate long and short dash line in  FIG. 8 ) of fuel injected through the outputting nozzle hole  21 . 
         [0114]    More specifically, the outputting nozzle hole  21  is formed to be a tapered hole (see FIG.  10 A 2 ), and its sectional shape is an ellipse (see FIG.  10 A 3 ) having a major axis D 11  in a circumferential direction of the nozzle hole plate  20 , instead of a circle. Accordingly, the size of the spray of fuel injected through the outputting nozzle hole  21  occupies comparatively widely the nozzle hole plate  20  in its circumferential direction. 
         [0115]    Thus, the spray of fuel injected from the cooling nozzle hole  22  is easily arranged on only an area, which the fuel spray of the outputting nozzle hole  21  does not occupy. In addition, the cooling nozzle hole  22  has a circular cross section (FIG.  10 B 3 ), and is a straight hole (FIG.  10 B 2 ). 
       Third Embodiment 
       [0116]    A third embodiment of the invention is shown in  FIG. 11 . The third embodiment illustrates that a direction of a second hole axis  22   j  of a cooling nozzle hole  22  and a direction of a first hole axis  21   j  of an outputting nozzle hole  21  are inclined to be further away from a central axis  20   j  of a nozzle hole plate  20  in a direction from their respective inlets toward outlets. 
         [0117]    As shown in  FIG. 12 , the outputting nozzle hole  21  and the cooling nozzle hole  22  are formed such that the first hole axis  21   j  and the second hole axis  22   j  do not cross. 
         [0118]    Since the first hole axis  21   j  and the second hole axis  22   j  do not cross in the above manner, it is possible to form a fuel spray through the outputting nozzle hole  21  into a shape that easily spreads in the combustion chamber  106 , for example, a spray having a hollow conical shape. Furthermore, the disorder of the fuel spray on a side of the outputting nozzle hole  21  by the fuel spray on a side of the cooling nozzle hole  22  is avoided. 
         [0119]    Additionally, the outputting nozzle hole  21  is formed to be a tapered hole (see FIG.  13 A 2 ), and has a circular sectional shape (FIG.  13 A 3 ). Consequently, the outputting nozzle hole  21  does not need to have an elliptical sectional shape and therefore, the outputting nozzle hole  21  is easy to form. 
       Fourth Embodiment 
       [0120]    A fourth embodiment of the invention is shown in  FIG. 14 . The fourth embodiment illustrates that a second hole axis  22   j  of a cooling nozzle hole  22  and a first hole axis  21   j  of an outputting nozzle hole  21  are inclined to be further away from a central axis  20   j  in a direction from their respective inlets toward outlets and that the cooling nozzle hole  22  is formed in a central region, and the outputting nozzle hole  21  is formed in a peripheral region. 
         [0121]    As shown in  FIG. 15 , the outputting nozzle hole  21  and the cooling nozzle hole  22  may be formed such that the first hole axis  21   j  and the second hole axis  22   j  do not cross. 
         [0122]    Accordingly, even when the outputting nozzle hole  21  is arranged in the peripheral region and the cooling nozzle hole  22  is arranged in the central region, since the first hole axis  21   j  and the second hole axis  22   j  do not cross, it is possible to form a fuel spray through the outputting nozzle hole  21  into a shape that easily spreads in the combustion chamber  106 , for example, a spray having a hollow conical shape. Furthermore, the disorder of the fuel spray on a side of the outputting nozzle hole  21  by the fuel spray on a side of the cooling nozzle hole  22  is avoided. 
         [0123]    In addition, as shown in FIG.  16 A 3  and FIG.  16 B 3 , an opening area A 2  of the cooling nozzle hole  22  may be smaller than an opening area A 1  of the outputting nozzle hole  21 . 
         [0124]    Accordingly, a penetration of the cooling nozzle hole  22  is shorter than a penetration of the outputting nozzle hole  21 , and thus the fuel spray on the side of the cooling nozzle hole  22  is easily kept near the central region. Moreover, because the penetration of the cooling nozzle hole  22  is shorter than the penetration of the outputting nozzle hole  21 , the fuel spray of the cooling nozzle hole  22  does not spread in the combustion chamber  106  like the fuel spray on the side of the outputting nozzle hole  21 . Therefore, the combustion of the fuel spray on the side of the cooling nozzle hole  22  prior to the combustion of the fuel spray on the side of the outputting nozzle hole  21  is avoided. 
         [0125]    By delaying the combustion of the fuel spray on the side of the cooling nozzle hole  22  as far as possible in the above manner, the fuel spray on the side of the cooling nozzle hole  22  remains near the central region. 
         [0126]    In the fourth embodiment described above, when fuel is injected through the outputting nozzle hole  21  formed in the peripheral region, the central region on the lower surface of the nozzle hole plate  20  is cooled by injecting fuel through the cooling nozzle hole  22  in the central region such that fuel flows in the cooling nozzle hole  22 . Furthermore, since the fuel injected from the cooling nozzle hole  22  does not need to contribute to the engine output, a small amount of fuel injected from the cooling nozzle hole  22  is locally atomized near an end face part of the central region. 
         [0127]    At the time of the fuel injection of the injector  10 , the central region on the lower surface of the nozzle hole plate  20  is cooled by fuel flowing in the cooling nozzle hole  22 , and the fuel injected and atomized from the cooling nozzle hole  22  remains near the central region. As a result, the nozzle hole plate  20  before the combustion is cooled down and thereby the heat temperature of the nozzle hole plate  20  is reduced. Hence, the increase of the heat temperature of the nozzle hole plate  20  is limited after the combustion. 
         [0128]    Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.