Abstract:
An object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that is capable of preventing a high pressure fuel leak by increasing the seal surface pressure between a first body such as an injector housing, and a second body such as a nozzle body to thus permit an increase in the seal surface pressure without a change to the size of the nozzle nut or the corresponding tightening force. The present invention is directed toward the formation, over a predetermined surface area, of slightly shallow micro-recesses, in regions other than the high pressure fuel paths and the periphery of the seal surfaces, that is, at the center of the seal surface. The present invention is characterized in that slightly shallow micro-recesses are formed over a predetermined surface area of at least either one of the first seal surface of the first body and the second seal surface of the second body, avoiding the first fuel path, second fuel path, and the respective periphery of the first body and the second body.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a fuel path sealing structure for a fuel injection valve, and more particularly to a fuel path sealing structure for a fuel injection valve that injects, with predetermined timing, high pressure fuel which is supplied via an accumulator (common rail) or the like.  
         [0003]     2. Description of the Related Art  
         [0004]     A conventional fuel injection valve and the fuel path sealing structure thereof will be outlined in accordance with  FIG. 13 .  
         [0005]      FIG. 13  is a cross-sectional view of the constituent elements of a fuel injection valve  1  which comprises an injector housing  2  (first body), a nozzle body  3  (second body), a nozzle needle  4 , and a back pressure control portion  5 .  
         [0006]     Two or more first location holes  6  are formed in the injector housing  2  and an equal number of second location holes  7  are formed in the nozzle body  3 . The injector housing  2  and nozzle body  3  are aligned with one another by means of a locating pin  8  that is pushed into the first location holes  6  and the second location holes  7 , and the nozzle body  3  is attached to the tip of the injector housing  2  by means of a nozzle nut  9 , the back pressure control portion  5  being provided thereabove.  
         [0007]     Fuel from a fuel tank  10  is pressurized to a high pressure by a fuel pump  11  and accumulates in a common rail  12  (accumulator), and high pressure fuel is supplied to the fuel injection valve  1 .  
         [0008]     In other words, a first fuel path  13  is formed in the injector housing  2  and a second fuel path  14  is formed in the nozzle body  3 , and a fuel reservoir  15  is formed facing a pressure receiver  4 A of the nozzle needle  4 , such that high pressure fuel can be continually supplied to the fuel reservoir  15  from the common rail  12 .  
         [0009]     Furthermore, a fuel return line  16  is formed from the section of the back pressure control portion  5  by extending a portion of the first fuel path  13  toward the top of the figure, which permits the return of fuel to the fuel tank  10 . The fuel return line  16  forms a fuel leak path together with a spring chamber  19  (first sliding hole) and the like that will be described subsequently.  
         [0010]     The nozzle body  3  has an arbitrary number of fuel injection holes  17  formed at the tip thereof. The injection holes  17  are closed when the tip of the nozzle needle  4  is seated at the seat portion  18  that is linked with the injection holes  17 , and the injection holes  17  are opened to thus permit the injection of fuel when the nozzle needle  4  lifts from the seat portion  18 .  
         [0011]     The spring chamber  19  (first sliding hole) is formed at the center of the injector housing  2  and above the nozzle needle  4 , and provided in the spring chamber  19  are a spring seat  20 , a nozzle spring  21 , which biases the nozzle needle  4  toward the seat portion  18  in the seating direction, and a valve piston  22 , which abuts against the spring seat  20  from above.  
         [0012]     The back pressure control portion  5  controls the valve piston  22 , that is, controls the seating and lifting of the nozzle needle  4  via the spring seat  20  by controlling the back pressure on the nozzle needle  4 .  
         [0013]     The upper portion of the nozzle needle  4  is capable of sliding in a clearance seal hole  23  (second sliding hole) of the nozzle body  3 . The spring chamber  19  communicates with the low-pressure side fuel return line  16  and the nozzle body  3  separates a high-pressure side (fuel reservoir chamber  15 ) in the clearance seal hole  23  of the nozzle body  3  and the low-pressure side (spring chamber  19 ).  
         [0014]     The injector housing  2  comprises a first seal surface  24  that is at the bottom of the injector housing  2  and lies orthogonal to the longitudinal direction of the injector housing  2 . The nozzle body  3  has a second seal surface  25  at the top thereof that lies orthogonal to the longitudinal direction of the nozzle body  3 .  
         [0015]     The first seal surface  24  and second seal surface  25  ensure a predetermined surface pressure as a result of tightening the nozzle nut  9  using a predetermined seat tightening force. A high pressure seal surface  26  is formed between the first seal surface  24  and second seal surface  25  such that no fuel leaks to outside the fuel injection valve  1  from the first fuel path  13  and the second fuel path  14  through which high pressure fuel passes. The occurrence of a fuel leak causes problems such as that of the invasion of fuel into the engine oil, which produces a reduction in lubricity.  
         [0016]      FIG. 14  is a bottom view of the section of the injector housing  2 , and illustrates the relative positions of the first fuel path  13  and a pair of first location holes  6 .  
         [0017]     That is, as shown in the figure, the pair of first location holes  6  are formed in positions that have lateral symmetry with respect to the straight line X joining the center  19 C of the spring chamber  19  (injector housing  2 ) and the center  13 C of the first fuel path  13 .  
         [0018]     In a fuel injection valve  1  having such a constitution, the sealing is generally improved by increasing the tightening force of the nozzle nut  9  at the high pressure seal surface  26  formed by the first seal surface  24  and the second seal surface  25 .  
         [0019]     However, when the internal pressure of the first fuel path  13  and the second fuel path  14  becomes significantly high, such pressure is difficult to handle by means of a simple increase in the tightening force of the nozzle nut  9 , and even if additional improvements are made to the existing material and heat treatment and the like of the injector housing  2  and nozzle body  3 , problems arise, namely that the material strength places restrictions on the permissible surface pressure at the high pressure seal surface  26  and there is the danger of a fuel leak.  
         [0020]     More particularly, the fuel injection valve  1 , which is of a type that has a common rail  12 , is different from a conventional jerk-type fuel injection valve and has a different nozzle body. Because a rail pressure is applied from the common rail  12  to the high pressure section of the nozzle body (namely the first fuel path  13 , second fuel path  14  and fuel reservoir  15 ), there is a requirement to increase the seal surface pressure of the high pressure seal surface  26  in line with high pressure injection. Because a fuel leak from this high pressure seal surface  26  involves a fuel leak to outside the fuel injection valve  1 , a reliable seal is required.  
         [0021]     Documents relating to this kind of fuel injection valve include Japanese Patent Application Laid-Open No. H7-317631, Japanese Patent Application Laid-Open No. H8-165965, and Japanese Patent Application Laid-Open No. H9-242649.  
       SUMMARY OF THE INVENTION  
       [0022]     The present invention was conceived in view of the aforementioned problems, and has as an object to provide a fuel path sealing structure for a fuel injection valve adapted so as to reliably prevent a fuel leak by increasing the seal surface pressure between a first body such as an injector housing, and a second body such as a nozzle body.  
         [0023]     A further object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that permits an increase in the seal surface pressure without a change to the size of the nozzle nut or the corresponding tightening force.  
         [0024]     Yet another object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that makes uniform the joining surface of the seal surfaces to thereby stabilize the surface pressure distribution and increase the safety against a fuel leak by means of a reliable target surface pressure.  
         [0025]     Yet another object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that permits an increase in the seal performance of the fuel path section without affecting the fuel injection valve or engine performance.  
         [0026]     Yet another object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that is capable of preventing a leak of high pressure fuel using simple means without making any substantial changes to a conventional fuel injection valve, more particularly to the injector housing, nozzle body, and the like.  
         [0027]     Yet another object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that is capable of preventing a fuel leak by increasing the seal performance between a first body such as an injector housing and a second body such as a nozzle body.  
         [0028]     Yet another object of the present invention is to provide a fuel path sealing structure for a fuel injection valve that prevents a fuel leak and permits an increase in stability, using means other than means for increasing the seal surface pressure, that is, even if the seal surface pressure is the same and the fuel pressure is a higher pressure.  
         [0029]     That is, the present invention (the first invention) is directed toward the formation over a predetermined surface area, in the seal surface between a first body such as an injector housing and a second body such as a nozzle body, of slightly shallow micro-recesses, in regions other than the high pressure fuel path and the periphery of the seal surface, that is, at the center of the seal surface. The present invention is a fuel path sealing structure for a fuel injection valve, comprising: a first body, which is formed with a first fuel path for high pressure fuel and comprises a first seal surface that surrounds the first fuel path; and a second body, which comprises a second seal surface facing the first seal surface, and which is formed with a second fuel path that communicates with the first fuel path to enable the high pressure fuel to be supplied to injection holes for the high pressure fuel, characterized in that slightly shallow micro-recesses are formed over a predetermined surface area of at least either one of the first seal surface of the first body and the second seal surface of the second body, avoiding the first fuel path, the second fuel path, and the respective periphery of the first body and the second body.  
         [0030]     The micro-recesses can be made symmetrical with respect to a straight line that passes through the center of the first and second bodies. The straight line passing through the center of the bodies may be a straight line that follows the radial direction of the bodies or a straight line in the axial direction thereof, and the symmetry may be linear symmetry or rotational symmetry.  
         [0031]     The mutual alignment of the first body and the second body can be determined by means of a locating pin that is inserted in location holes, and the micro-recesses can be afforded symmetry by forming, in the seal surfaces, an additional hole which has a diameter that corresponds to that of the location holes.  
         [0032]     The shape of the micro-recesses can be afforded symmetry with respect to at least either one of mutually orthogonal straight lines by forming the additional hole on the side opposite the fuel paths.  
         [0033]     In the fuel path sealing structure for a fuel injection valve according to the present invention (the first invention), due to the formation over a predetermined surface area, in the seal surface between a first body such as an injector housing and a second body such as a nozzle body, of slightly shallow micro-recesses, in regions other than the high pressure fuel path and the periphery of the seal surface, when the first body and the second body are brought into intimate contact with one another by means of a predetermined tightening torque, the intimate contact area is smaller than that of the prior art, and it is therefore possible to improve the seal performance by increasing the seal surface pressure even when using an equal tightening torque.  
         [0034]     If an additional hole that has a diameter equal to that of the location holes is formed and the shape of the micro-recesses can be made symmetrical with respect to mutually orthogonal straight lines, the intimate contact pressure of the joining surface can be made uniform over the whole seal surface whereby increased fuel leak stability is permitted.  
         [0035]     The present invention (the second invention) is further directed toward the formation of a fine groove (micro groove) around the high pressure oil paths (fuel paths) in the injector housing and nozzle body, and the like, and toward the secondary sealing of leaking fuel that, upon leaking from the fuel path, subsequently exhibits a pressure drop. The present invention is a fuel path sealing structure for a fuel injection valve, comprising: a first body such as an injector housing, which is formed with a first fuel path for high pressure fuel and comprises a first seal surface that surrounds the first fuel path; and a second body such as a nozzle body, which comprises a second seal surface facing the first seal surface, and which is formed with a second fuel path that communicates with the first fuel path to enable the high pressure fuel to be supplied to injection holes for the high pressure fuel, characterized in that a micro groove is formed in a position around the first fuel path or the second fuel path in at least either one of the first seal surface of the first body and the second seal surface of the second body.  
         [0036]     The micro groove can be afforded a closed circular shape.  
         [0037]     The micro groove can be afforded an open circular arc shape and can be made able to communicate with a leak path different from the fuel paths.  
         [0038]     The micro groove can be made circular and can be made able to communicate with a leak path different from the fuel paths.  
         [0039]     In addition to the injector housing and the nozzle body, and the like, the fuel path sealing structure of the present invention can be adopted for parts requiring a reliable sealing of high pressure fuel via a seal surface.  
         [0040]     In the fuel path sealing structure for a fuel injection valve according to the present invention (second invention), a fine groove (micro groove) is formed around the fuel path in a first body such as an injector housing and a second body such as a nozzle body. It is therefore possible to provide secondary sealing at the seal surfaces of leaking fuel that, upon leaking on the high pressure side, subsequently exhibits a pressure drop, such that, irrespective of whether there is any kind of increase in the seal surface pressure of the high pressure seal surface section, a fuel leak to the outside from the first fuel path and second fuel path section can be avoided and the reliability of the fuel injection valve can therefore be ensured.  
         [0041]     Moreover, on account of the simple constitution, which merely involves the formation of a micro groove in the seal surface of the first body or second body, the invention can be implemented by the straightforward machining of an existing injector housing or nozzle body.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]      FIG. 1  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  30  for a fuel injection valve according to a first embodiment of the present invention (first invention);  
         [0043]      FIG. 2  is similarly a bottom view of the injector housing  2 ;  
         [0044]      FIG. 3  is an enlarged cross-sectional view of the constituent elements, of the injector housing  2  section in a fuel path sealing structure  40  for a fuel injection valve according to a second embodiment of the present invention (first invention);  
         [0045]      FIG. 4  is similarly a bottom view of the injector housing  2 ;  
         [0046]      FIG. 5  is similarly a graph showing the area of contact between the injector housing  2  and the nozzle body  3  in the fan-like regions  24 A,  24 B,  24 C and  24 D;  
         [0047]      FIG. 6  is similarly a graph that shows the flatness upon grinding of the first seal surface  24  of the injector housing  2  and of the second seal surface  25  of the nozzle body  3 , and that shows the corresponding machining amount required;  
         [0048]      FIG. 7  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  50  for a fuel injection valve according to the third embodiment of the present invention (second invention);  
         [0049]      FIG. 8  is similarly a bottom view of the injector housing  2 ;  
         [0050]      FIG. 9  is similarly a graph showing relationships between positions on the bottom of the injector housing  2  and the corresponding pressures;  
         [0051]      FIG. 10  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  60  for a fuel injection valve according to the fourth embodiment of the present invention (second invention);  
         [0052]      FIG. 11  is similarly a bottom view of the injector housing  2 ;  
         [0053]      FIG. 12  is a bottom view of the injector housing  2  in a fuel path sealing structure  70  section for a fuel injection valve according to the fifth embodiment of the present invention (second invention);  
         [0054]      FIG. 13  is a cross-sectional view of the constituent elements of a conventional fuel injection valve  1 ; and  
         [0055]      FIG. 14  is similarly a bottom view of the injector housing  2  section.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0056]     A description will be provided next of the fuel path sealing structure  30  for a fuel injection valve according to the first embodiment of the present invention (first invention), in accordance with  FIGS. 1 and 2 . However, those parts which are the same as those in  FIGS. 13 and 14  have been assigned the same reference numerals, and a detailed description thereof is thus omitted here.  
         [0057]      FIG. 1  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  30  for a fuel injection valve  1 .  FIG. 2  is similarly a bottom view of the injector housing  2 , wherein the fuel path sealing structure  30  has very shallow micro-recesses  31  formed symmetrically in a predetermined shape and area in the bottom of the injector housing  2  (the first seal surface  24 ), in regions other than the first fuel path  13 , the periphery  2 A of the injector housing  2  (that is, the periphery of the first seal surface  24  and the second seal surface  25 ), and a pair of first location holes  6 .  
         [0058]     In other words, the micro-recesses  31  lie between the periphery  2 A of the injector housing  2 , and the spring chamber  19  (first sliding hole), and the outermost portion of these recesses does not reach and avoids the first fuel path  13 , the pair of first location holes  6  and the periphery  2 A of the injector housing  2 . The micro-recesses  31  are formed around the spring chamber  19  and so as to be symmetrical with respect to the straight line X that passes through the center  19 C of the spring chamber  19  and the center  13 C of the first fuel path  13 .  
         [0059]     Furthermore, the micro-recesses  31  are constituted from the radial recesses  31 A,  31 B,  31 C and  31 D which are respectively positioned in fan-like regions  24 A,  24 B,  24 C, and  24 D divided into four by a straight line X and a straight line Y that lies orthogonal to straight line X at the center  19 C, these radial recesses  31 A,  31 B,  31 C and  31 D having substantially the same surface area and facing out ward in a radial shape from the center  19 C.  
         [0060]     Accordingly, the first seal surface  24  comprises the above-described substantially radial micro-recesses  31 , and a pressure contact seal surface  32  which excludes the micro-recesses  31  and which surrounds the micro-recesses  31  in the first seal surface  24 , wherein the first fuel path  13  and the pair of first location holes  6  are positioned as openings in the pressure contact seal surface  32 .  
         [0061]     With regard to the size of the micro-recesses  31 , these are very fine recesses whose depth is on the order of 0.013 mm, for example, which constitutes a machining minimum for end milling and the like, these micro-recesses  31  being designed in accordance with the tightening force of the nozzle nut  9  and with the fuel pressure, and so forth.  
         [0062]     In the fuel path sealing structure  30  for a fuel injection valve which is thus constituted, the first seal surface  24  of the injector housing  2  and the second seal surface  25  of the nozzle body  3  lie in intimate contact with one another to thereby form a high pressure seal surface  26  as a result of clamping the injector housing  2  and the nozzle body  3  by means of a predetermined axial tightening force imparted by the nozzle nut  9 . Of the first seal surface  24  and the second seal surface  25 , because only the section constituted by the pressure contact seal surface  32  that has a smaller surface area contacts the second seal surface  25  under pressure, the seal surface pressure is increased beyond that of the prior art, which permits an increase in the seal performance of the first fuel path  13  and second fuel path  14  section even if an equal tightening torque is applied.  
         [0063]     In addition, because the micro-recesses  31  are made symmetrical with respect to the straight line X, the balance of the seal surface pressure is made even. It is thus possible to increase the safety against fuel leak, and programmed machining by means of end milling and the like is straightforward. It is thus possible to deal with fuel leaks that accompany the high pressurization of fuel by means of a simple constitution.  
         [0064]     The micro-recesses  31  can also be made symmetrical with respect to the straight line Y in addition to the straight line X (line symmetry) and can also be made symmetrical about a straight line that is orthogonal to the straight line X and straight line Y (a straight line that passes through the center  19 C of the spring chamber  19 , that is, the center of the bodies of the injector housing  2  and the nozzle body  3 , and the like) (rotational symmetry).  
         [0065]      FIG. 3  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  40  for a fuel injection valve according to the second embodiment of the present invention (first invention).  FIG. 4  is similarly a bottom view of the injector housing  2 , wherein the fuel path sealing structure  40  has micro-recesses  41  of greater symmetry than that of the fuel path sealing structure  30  ( FIG. 2 ) which are formed in the first seal surface  24  (bottom) of the injector housing  2 , and, in addition to the pair of first location holes  6 , the fuel path sealing structure  40  is formed with an additional hole  6 A that is of the same diameter as the first location holes  6  and is formed on the opposite side of the first fuel path  13 .  
         [0066]     That is, the micro-recesses  41  are symmetrical with respect to the straight line X, and are constituted from the fan-like recesses  41 A,  41 B,  41 C, and  41 D, which have substantially the same surface area, in fan-like regions  24 A,  24 B,  24 C, and  24 D.  
         [0067]     The additional hole  6 A lies on the straight line X on the opposite side to the first fuel path  13  and is located at a midway point between the other pair of first location holes  6 .  
         [0068]     Further, the location and size of the additional hole  6 A are determined in accordance with the location, shape, and size of the micro-recesses  41 , and the corresponding fan-like recesses  41 A,  41 B,  41 C, and  41 D, and the shape of the micro-recesses  41  may be symmetrical with respect to both the straight line X and the straight line Y, and can preferably be of an arbitrary design so long as the micro-recesses  41  have a uniform surface area in the fan-like regions  24 A,  24 B,  24 C, and  24 D.  
         [0069]     Naturally, like the micro-recesses  31 , the micro-recesses  41  can also be made symmetrical with respect to the straight line Y in addition to the straight line X (line symmetry) and can also be made symmetrical about a straight line that is orthogonal to the straight line X and straight line Y (a straight line that passes through the center  19 C of the spring chamber  19 , that is, the center of the bodies of the injector housing  2  and the nozzle body  3 , and the like) (rotational symmetry).  
         [0070]     Therefore, the first seal surface  24  is constituted from the above-described substantially circular or hourglass-shaped micro-recesses  41 , and a pressure contact seal surface  42  which excludes the micro-recesses  41  and surrounds the micro-recesses  41  in the first seal surface  24 , wherein the first fuel path  13  and the additional hole  6 A are located in the pressure contact seal surface  42  and the other pair of first location holes  6  are located in the micro-recesses  41 .  
         [0071]     Like the fuel path sealing structure  30  shown in  FIGS. 1 and 2 , in the fuel path sealing structure  40  for a fuel injection valve thus constituted, the first seal surface  24  of the injector housing  2  and the second seal surface  25  of the nozzle body  3  lie in intimate contact with one another to thereby form a high pressure seal surface  26  as a result of clamping the injector housing  2  and the nozzle body  3  by means of a predetermined axial tightening force imparted by the nozzle nut  9 . Of the first seal surface  24  and the second seal surface  25 , because only the section constituted by the pressure contact seal surface  42  that has a smaller surface area contacts the second seal surface  25  under pressure, the seal surface pressure is increased beyond that of the prior art, which permits an increase in the seal performance of the first fuel path  13  and second fuel path  14  section even if an equal tightening torque is applied.  
         [0072]     Furthermore, because the micro-recesses  41  are made symmetrical with respect to the straight line X, and micro-recesses  41  form a nearly symmetrical shape also with respect to the straight line Y, the balance of the seal surface pressure at the first seal surface  24  is made even more even, thus permitting an increase in the safety against fuel leak, and programmed machining by means of end milling and the like is straightforward. It is thus possible to deal with fuel leaks that accompany the high pressurization of fuel by means of a simple constitution.  
         [0073]      FIG. 5  is a graph showing the area of contact between the injector housing  2  and the nozzle body  3  in the fan-like regions  24 A,  24 B,  24 C and  24 D.  FIG. 6  is similarly a graph that shows the flatness upon grinding of the first seal surface  24  of the injector housing  2  and of the second seal surface  25  of the nozzle body  3 , and that shows the corresponding amount of machining required.  
         [0074]     As shown in  FIG. 5 , when there is no additional hole  6 A (dotted line), the area of contact of the fan-like regions  24 C and  24 D is greater than that of the fan-like regions  24 A and  24 B in comparison with a case where the additional hole  6 A is present (solid line).  
         [0075]     The formation of the additional hole  6 A thus makes it possible to obtain a more uniform seal surface pressure.  
         [0076]     Also, as shown in  FIG. 6 , in comparison with a case where the additional hole  6 A is present (solid line), in the absence of the additional hole  6 A (dotted line), it is necessary to reduce the contact area by making the flatness upon grinding of the fan-like regions  24 A and  24 B lower than that of the fan-like regions  24 C and  24 D. However, when the additional hole  6 A is present (solid line), the machining amount of the seal surfaces  24  and  25  is made uniform and the mean height can be made substantially uniform.  
         [0077]     The formation of the additional hole  6 A thus makes it possible to make the machining process more uniform.  
         [0078]     The above-described micro-recesses  31  ( FIG. 2 ) and the micro-recesses  41  ( FIG. 4 ) according to the present invention can also be formed in the upper face of the nozzle body  3  (second seal surface  25 ).  
         [0079]     In addition, the micro-recesses  31  and micro-recesses  41  can be adopted not only for a product comprising a body that connects to a fuel injection nozzle such as the nozzle body  3 , but also for a part that connects interlinking high pressure fuel paths such as the first fuel path  13  and the second fuel path  14  to each other, and for a component made of a general material and subjected to general heat treatment in order to provide sealing for high pressure fuel.  
         [0080]     According to the present invention described above (the first invention), due to the formation of the micro-recesses which serve to avoid mutual contact at the center at the seal surfaces of the injector housing or the nozzle body, the seal surface pressure can be increased to thus permit greater fuel leak stability.  
         [0081]     A description will be provided next, in accordance with  FIGS. 7 through 9 , of a fuel path sealing structure  50  for a fuel injection valve according to the third embodiment of the present invention (second invention).  
         [0082]      FIG. 7  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  50  for the fuel injection valve  1 .  FIG. 8  is similarly a bottom view of the injector housing  2 , wherein the fuel path sealing structure  50  is formed, for example, with a closed circular micro groove  51  that is positioned around the first fuel path  13  in the bottom (first seal surface  24 ) of the injector housing  2  so that this micro groove  51  surrounds the first fuel path  13 .  
         [0083]     The micro groove  51  is formed between the peripheral face of the injector housing  2 , and the spring chamber  19  (first sliding hole), and the outermost portion of the micro groove  51  is located at a midway point between the peripheral face of the injector housing  2 , and the first fuel path  13 . The micro groove  51  is formed so as to ensure an equal interval from the first fuel path  13 , that is, the circumferential position of the micro groove  51  is established such that the micro groove  51  is concentric with the first fuel path  13 , such that the pressure of the high pressure fuel in the first fuel path  13  acts uniformly on the micro groove  51 .  
         [0084]     With regard to the size of the micro groove  51 , this is a very fine groove whose depth and width are on the order of 0.013 mm, for example, which constitutes a machining minimum for end milling and the like, the micro groove  51  being designed in accordance with the tightening force of the nozzle nut  9  and with the fuel pressure, and the like.  
         [0085]     In the fuel path sealing structure  50  for a fuel injection valve which is thus constituted, a leak of high pressure fuel from the first fuel path  13  and second fuel path  14  can be more reliably prevented.  
         [0086]     That is,  FIG. 9  is a graph showing relationships between positions on the bottom of the injector housing  2  and the corresponding pressures. Even in the event that the fuel pressure (solid line) is larger than the seal surface pressure (dotted line) at the position P 0  on the circumference of the first fuel path  13  and there occurs a fuel leak in the peripheral direction of the first fuel path  13 , due to the drop in pressure of leaking fuel at the position P 1  on the inner circumference of the micro groove  51 , the seal surface pressure is then greater than the fuel pressure and secondary sealing is thus made possible by ensuring that the seal surface pressure at the position P 2  on the outer circumference of the micro groove  51  is greater than the fuel pressure. A fuel leak in the peripheral direction of the injector housing  2  and outside the fuel injection valve  1  can thus be prevented.  
         [0087]      FIG. 10  is an enlarged cross-sectional view of the constituent elements of the injector housing  2  section in a fuel path sealing structure  60  for a fuel injection valve according to the fourth embodiment of the present invention (second invention).  FIG. 11  is similarly a bottom view of the injector housing  2 , wherein the fuel path sealing structure  60  is formed, for example, with an open circular arc shaped micro groove  61  that is positioned around the first fuel path  13  in the bottom (first seal surface  24 ) of the injector housing  2  so that this groove  61  surrounds the first fuel path  13 . Both ends of the micro groove  61  are able to communicate with the low-pressure side spring chamber  19  (first sliding hole).  
         [0088]     The shape of the arc of the micro groove  61  is optional, and more particularly the outermost portion of the micro groove  61  is located at a midway point between the peripheral face of the injector housing  2 , and the first fuel path  13 , such that the micro groove  61  is formed so as to be symmetrical with respect to the radial direction of the injector housing  2 .  
         [0089]     Like the micro groove  51  ( FIG. 7  and  FIG. 8 ), the dimensions of the micro groove  61  are set at a depth and width that pertain to the machining minimum, for example.  
         [0090]     In a fuel path sealing structure  60  for a fuel injection valve which is thus constituted, the fuel which leaks out from the first fuel path  13  to the micro groove  61  can also be returned to the fuel tank  10  via the spring chamber  19 , which is a low-pressure side leak path, and via the fuel return line  16 .  
         [0091]     It is thus possible to prevent fuel from leaking outside the fuel injection valve  1 , that is, outside the engine, by returning leaking fuel to the fuel return line  16 , which makes it possible to prevent an offensive odor and a fire, and the like. The amount of fuel that leaks out to the fuel return line  16  is extremely small and does not affect the product performance.  
         [0092]      FIG. 12  is a bottom view of the injector housing  2  in a fuel path sealing structure  70  section for a fuel injection valve according to the fifth embodiment of the present invention (second invention), wherein the fuel path sealing structure  70  is, for example, formed with a micro groove  71  in the bottom (first seal surface  24 ) of the injector housing  2 .  
         [0093]     This micro groove  71  is constituted from the micro groove  51 , which has the same circular shape as that in the fuel path sealing structure  50 , and a linking groove  72 , which links the micro groove  51  to the spring chamber  19  (leak path).  
         [0094]     In the fuel path sealing structure  70  for a fuel injection valve thus constituted, the micro groove  71  works similarly to the micro groove  51  shown in  FIGS. 8 and 9  and is capable of discharging leaking fuel to the spring chamber  19  via the linking groove  72 .  
         [0095]     The micro groove  51  ( FIG. 8 ),  61  ( FIG. 10 ), and  71  ( FIG. 12 ) according to the present invention as described above can also be formed in the upper face (the second seal surface  25 ) of the nozzle body  3 .  
         [0096]     In addition, this micro groove  51 ,  61 ,  71  can be adopted not only for a product comprising a body that connects to a fuel injection nozzle such as the nozzle body  3 , but also for a part that connects interlinking high pressure fuel paths such as the first fuel path  13  and the second fuel path  14  to each other, and for a component made of a general material and subjected to general heat treatment in order to provide sealing for high pressure fuel.  
         [0097]     According to the present invention above (the second invention), the formation of a micro groove in the seal surface makes secondary sealing possible by causing a stepwise reduction in the fuel pressure, which makes it possible to more reliably prevent a high pressure fuel leak and to improve safety even using an equal seal surface pressure.