Abstract:
An object of the present, invention is to suppress the decrease in seal performance by avoiding wide-area contact between a valve face and a valve seat face which contact results from the non-circularity of the valve face and the valve seat face. In a fuel injection valve which includes: a seat member ( 102 ) having a valve seat, face ( 203 ); a valve member ( 101 ) having a valve face ( 204 ) contacted against the valve seat face ( 203 ); and valve driving means for reciprocating the valve member ( 101 ) and in which the valve driving means reciprocates the valve member ( 101 ) thus bringing the valve face ( 204 ) into contact against the valve seat face ( 203 ) for closing the valve or thus separating the valve face ( 204 ) from the valve seat face ( 203 ) for opening the valve, at least either one of the valve seat face ( 203 ) and the valve face ( 204 ) is formed with recesses ( 501, 502 ) at upstream side portion and downstream side portion with respect to a seal seat ( 202 ) where the valve face ( 204 ) and the valve seat face ( 203 ) are contacted with each other.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel injection valve, or more particularly to a fuel injection valve for directly injecting a fuel into a combustion chamber of an internal combustion engine, The fuel injection valve is provided with an actuator for operating a valve body, which includes a spherical portion at an injection-side end. The spherical portion is contacted against a valve seat face formed at a valve seat body whereby a seal seat is formed at a seat contact portion for prevention of fuel leakage. 
       BACKGROUND ART 
       [0002]    Japanese Unexamined Patent Application Publication No. H9-42114 discloses a fuel injection valve in which a valve closing body cooperates with a valve seat formed as an edge seat, the valve seat, defines the edge seat on a contact line between two faces formed at mutually different angles and directly connected with each other, and an angle α formed between the upstream face and a longitudinal axis of the valve is larger than an angle β formed between the other face and the longitudinal axis of the valve. 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Application Publication No. Hei9-42114 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    The fuel injection valve (injector) for supplying the fuel to the engine is required to reduce fuel leakage from a fuel injection hole disposed at a tip of the valve. 
         [0005]    For prevention of the fuel leakage, the fuel injection valve generally has a structure where an on-off valve thereof principally includes: a valve seat having a conical valve seat face; and a valve member having a spherical or conical valve face so arranged as to make contact with the conical face of the valve seat, and where the valve is closed or opened by bringing the valve face into or out of close contact with the valve seat face. 
         [0006]    In a closed state, the valve face is pressed against, the valve seat face by a biasing spring or the like so that a seal seat is formed by contact deformation of the valve face and the valve seat face contacted with each other. The fuel is sealed by this seal seat which shuts off the leakage of the fuel into the combustion chamber of the engine. 
         [0007]    However, the fuel injection valve of such a type has a problem that if unevenness resulting from surface roughness or non-circularity of the valve face and valve seat face is greater than deformation volume due to contact between the valve face and the valve seat face, a gap remains between the valve face and the valve seat face and hence, the fuel leaks from the remaining gap. 
         [0008]    Further, in a case where the valve face or the valve seat face having the non-circularity includes the unevenness, microscopic observation of a contact state between the valve face and the valve seat face of the valve in an open state reveals that a protrusion on the valve face and a protrusion on the valve seat face are in contact. Such a contact portion between the protrusions does not always exist within a design seat width. It is noted here that the term “design seat, width” means the contact width in a slope direction with respect to a design seat, position as the center, the contact width resulting from the deformation of the valve face and the valve seat face caused by Hertzian stress within a range of load on the valve body provided that the valve face defines idealistic sphericity and the valve seat face defines idealistic circular cone. 
         [0009]    In a case where an actual contact portion differs from the design contact position, the seal seat is formed in a state where the contact occurs at an undesigned, portion (referred to as “wide contacted state”). In the wide contacted state, the contact portion increases so as to increase the stiffness of a contact part while the seal seat is decreased in contact bearing pressure. The decreased contact bearing pressure leads to the decrease in deformation volume due to the contact between the valve face and the valve seat face. Because of the decreased volume of deformation due to the contact between the valve face and the valve seat face, the gap caused, by the surface unevenness resulting from the non-circularity of the faces cannot be closed. Hence, the valve is decreased in seal performance and the fuel leakage results. Therefore, the improvement of seal performance dictates the need for avoiding the wide-area contact. 
         [0010]    By virtue of the above-described structure, the fuel injection valve according to the patent literature  1  is adapted to avoid the wide-area contact and to achieve the improvement of seal performance. 
         [0011]    In order to avoid the wide-area contact and to improve the seal performance, however, the valve must be produced with the edge seat, positioned with very high precision. If the positioning precision of the edge seat is not high enough, the contact position between the valve body and the valve seat, deviates so that, the valve body and valve seat make the wide-area contact, which causes the decrease in seal performance. 
         [0012]    A method of quenching a member constituting the valve seat, followed by finishing the member by grinding is conceivable as a production method of the edge seat. However, it is difficult to produce the edge seat with high precision because the variations in the cutting quantities of the two conical faces and in the dimensional precision of the base material all affect, the position of the edge seat in the above production method. Furthermore, in a case where the two conical faces have poor concentricity, the circularity of the edge seat is degraded. As a result, a gap is produced between the valve body and the edge seat, resulting in the decrease in seal performance. Particularly in a case where the valve seat face is ground/finished by rotating a mounted wheel at high speed, it is difficult to form, an edge part with high precisions. Hence, well-trained workers are required for quality control, facility operation, initial setup and the like. Otherwise, expensive facilities are required. 
         [0013]    When the valve body defining the spherical surface makes contact with the edge part, contact stress between the face of the valve body and the edge part of the valve seat is larger than that of the conventional fuel injection valve. This may sometimes constitute a causative factor of wear and aging degradation. 
         [0014]    In this connection, the present, invention has an object to provide a fuel injection valve adapted to achieve a higher seal performance than a predetermined level by avoiding the wide-area contact between the valve face and the valve seat face and to be less susceptible to wear and aging degradation. 
       Solution to Problem 
       [0015]    In a fuel injection valve including: a seat member having a valve seat face; a valve member having a valve face contacted against the valve seat face; and valve driving means for reciprocating the valve member by way of a force of a spring biasing the valve member or an electromagnetic force, the valve driving means reciprocating the valve member and thus bringing the valve face into contact against the valve seat face for closing the valve, or thus separating the valve face from the valve seat face for opening the valve, the fuel injection valve has a structure wherein at least either one of the valve seat, face and the valve face is formed with recesses on upstream side portion and downstream side portion with respect to a seal seat where the valve face and the valve seat face are contacted with each other. The wide-area contact, between the valve face and the valve seat face, as a result of the effect of the surface roughness or non-circularity of the valve face and the valve seat face, is avoided by adopting such a structure. By avoiding the wide-area contact, the increase in contact, stiffness resulting from the increased contact, portions is suppressed while the decrease in contact bearing pressure on the seal seat is suppressed. Thus, the volume of contact deformation between the valve face and the valve seat face is maintained without decreasing the contact bearing pressure on the seal seat whereby the seal, performance is improved. 
         [0016]    To form the recesses at the upstream side and the downstream side with respect to the seal seat, a grinding work or cutting work is performed by using a spherical tool having a different diameter from that of the spherical valve body. By doing so, a contact position between the seat, portion of the valve seat having the conical face and the spherical, tool is uniquely determined based on a geometric relation between the spherical face and the tapered face. Therefore, the recesses can be formed with high precision. 
         [0017]    The widths of the upstream recess and the downstream recess are defined to be nearly equal to the width of linear contact between the valve face having circularity and the valve seat face having circularity whereby the increase in contact bearing pressure is suppressed, while the seal performance is improved without decreasing the aging degradation resistance or wear resistance. 
       Advantageous Effect of Invention 
       [0018]    According to the present invention, the annular recesses formed at the upstream side and the downstream side with respect to the seal seat, are effective at preventing the valve face and the valve seat face from making the wide-area contact when making contact with each other and hence, the seal performance can be improved. When the recesses are formed, the contact position between the valve body and the tool can be geometrically determined by using the spherical tool having the different diameter from that of the spherical valve body. Thus, the positioning precision can be increased without entailing cost increase. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a sectional view showing a fuel injection valve according to an embodiment of the present invention. 
           [0020]      FIG. 2  is an enlarged sectional view showing the vicinity of a tip of a valve body according to a first embodiment of the present invention. 
           [0021]      FIG. 3  is an enlarged view showing a microscopic illustration of a contact part between the valve body and a valve seat according to the first embodiment of the present invention. 
           [0022]      FIG. 4  is a sectional view showing a microscopic illustration of the vicinity of the contact part between the valve body and the valve seat, according to the first, embodiment of the present invention after generation of contact deformation of the valve body and the valve seat under load. 
           [0023]      FIG. 5  is an enlarged view showing in detail a configuration of the tip of the valve body of the fuel injection valve according to the first embodiment of the present invention. 
           [0024]      FIG. 6  is an enlarged view of the contact part between the valve body and the valve seat illustrating a case where recesses are provided at upstream side and downstream side with respect to a seat position of the fuel injection valve according to the first embodiment of the present, invention. 
           [0025]      FIG. 7  is a sectional view illustrating a method of forming the fuel injection valve according to the first embodiment of the present invention by using a spherical tool. 
           [0026]      FIG. 8  is an enlarged sectional view showing the vicinity of a tip of a valve body according to a second embodiment of the present invention. 
           [0027]      FIG. 9  is an enlarged view showing a microscopic illustration of a contact part, between the valve body and a valve seat according to the second embodiment of the present, invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    The embodiments of the present invention are described as below. 
       First Embodiment 
       [0029]      FIG. 1  is a sectional view illustrating an electromagnetic fuel injection valve as an example of the fuel injection valve according to the present invention. While the electromagnetic fuel injection valve shown in  FIG. 1  is an example of the electromagnetic fuel injection valve for use in a cylinder direction injection type gasoline engine, the present invention is also effective for an electromagnetic fuel injection valve for use in a port injection type gasoline engine and a fuel injection valve driven by a piezoelectric element or a magnetostrictor. 
         [0030]    Referring to  FIG. 1 , the fuel is supplied from a fuel supply port  112  so as to be fed into a fuel injection valve. The electromagnetic fuel injection valve shown in  FIG. 1  is a normally closed electromagnetic drive valve. When a coil  108  is not energized, a valve body  101  is biased by a spring  110  so as to be pressed against a seat member  102  having a conical face. A seal seat is formed between a valve face of the valve body  101  and a valve seat, face of the seat member  102  such as to seal the fuel. When the coil  108  shown in  FIG. 1  is energized, magnetic flux density is produced in a core  107 , yoke  109  and anchor  106  constituting a magnetic circuit of the electromagnetic valve so that a magnetic, attractive force is produced between the core  107  and the anchor  106  defining a gap therebetween. When the magnetic attractive force exceeds the combination of the biasing force of the spring  110  and the above-described fuel pressure, the valve body  101  is attracted by the anchor  106  toward the magnetic core  107 , namely toward an upstream side. The valve body  101  is brought into contact with the movable element  106  to transmit the force thereto while the valve body  102  is also displaced toward the upstream side. Hence, the valve is placed in an open state. 
         [0031]    On the other hand, when the coil  108  is de-energized, the magnetic flux produced in the magnetic core  107  vanishes while the magnetic attractive force acting on the movable element  106  also diminishes and vanishes before long. Accordingly, when the force of the biasing spring  110  acting on the valve body  101  exceeds the magnetic attractive force acting on the movable element  106 , the valve body  101  is displaced toward a downstream side. The valve body  101  comes into contact with the seat member  102  so that the valve is placed in a closed state. 
         [0032]    That is the description on the basic operation of the electromagnetic fuel injection valve. The fuel injection valve is adapted to control the fuel injection quantity by controlling the energizing time of the coil  108  and thereby controlling time during which the valve body  101  is in the open state. 
         [0033]      FIG. 2  is an enlarged sectional view of the vicinity of a contact portion between the valve face at a tip of the valve body  101  and the valve seat face of the seat member  102 . When the fuel injection valve is in the closed position, a valve face  204  formed on the surface of the valve body  101  is contacted, against a valve seat face  203  defined by a conical face of the seat member  102  whereby a seal seat  202  is formed. The seal seat prevents the fuel leakage from a fuel injection hole  201  formed on the valve seat face  203  to a combustion chamber of a direct injection engine not shown. In this case, the valve face  202  of the valve body  101  is formed on a spherical surface. Hence, the seal seat  202  is defined by contact between the valve seat face  203  having the conical surface and the valve face  204  defining the spherical surface. The seal seat  202  substantially defines a linear contact. The prevention of the fuel leakage dictates the need for forming the seal seat  2   02  in a continuous annular configuration between the valve face  204  and the valve seat face  203 . When the fuel injection valve is in the closed state, the valve body  101  is subjected to a force equivalent to a product given by multiplying the fuel pressure by the area of a circle (circle defined by the contact part) having the diameter of the seal seat  202 . 
         [0034]    In this case, the pressure of the fuel supplied to the fuel injection valve for cylinder injection engine is roughly in the range of 2 MPa to 30 MPa. 
         [0035]      FIG. 3  shows a microscopic illustration of a contact state between the valve face  204  and the valve seat face  203  of a fuel injection valve to which the present invention is not applied. Referring to  FIG. 3 , because of the effect of non-circularity of the valve face  204  and the valve seat face  203 , the contact portion between the valve face  204  and the valve seat face  203  is at an undesigned contact position  301  deviated from a design seat width  302  where the valve face should essentially be seated. That is, the valve face and the valve seat face make the wide-area contact. It is noted here that the term “design seat width  302 ” means the contact width in a slope direction with respect to a design seat position  303  as the center, the contact width resulting from the deformation of the valve face  204  and the valve seat face  203  caused by Hertzian stress within a range of load on the valve body  101  provided that the valve face  204  defines idealistic sphericity and the valve seat face  203  defines idealistic circular cone. This width is normally less than 50 μm. 
         [0036]      FIG. 4  is a schematic diagram showing a microscopic illustration of a contact state between the valve seat face  204  and the valve face  203  which are deformed by press forces by the biasing spring  110 , the fuel pressure and the like. As shown in  FIG. 4 , the prevention of the fuel leakage in the wide-area contact state dictates the need for forming the seal seat  202  in the continuous annular configuration by using the press forces of the biasing spring, fuel pressure and the like to deform the protrusion at the undesigned contact position  301  into a contact face across the seat width  302  at the design seat position. Therefore, the contact stiffness is increased by a quantity equivalent to the protrusion  302  caused by the non-circularity so that the design seat portion  301  is in contact on the overall circumference thereof. This leads to the increase in load required for forming the seal seat  202  in the annular configuration. If the load for forming the seal seat  202  in the annular configuration is insufficient at this time, the gap remains between the valve face  203  and the valve seat face  2034  and the fuel leakage results. 
         [0037]    The wide-area contact must be avoided, for prevention of the fuel leakage. According to the embodiment, as shown in  FIG. 5 , an upstream recess  501  having a larger curvature radius than a spherical radius SR 3  of the valve body is formed in the valve seat face  204  at place upstream of the seat position (the position of the seal seat  202 ), while a downstream recess  502  having a smaller curvature radius than the spherical radius SR 3  of the valve body is formed in the valve seat face at place downstream from the seat position. 
         [0038]    In this manner, the contact between the valve face and the valve seat face at the undesigned position resulting from the non-circularity can be inhibited by increasing the distance between the valve face  204  and the valve seat face  203  at the upstream place of the seat position and the downstream place from the seat position. Thus, the contact at the position not decided by design, as the result of the non-circularity, can be avoided. In consequence, the contact stiffness in forming the annular seal seat  202  can be reduced and the gap caused by the non-circularity can be vanished using smaller load. Hence, the fuel leakage can be prevented effectively. 
         [0039]    As shown in  FIG. 6 , a flat portion  601  is formed between the upstream recess  501  and the downstream recess  502  so as to permit the valve face  204  to make contact with the flat portion  601 . Hence, the increase in contact force between the valve face  204  and the valve seat face  203  can be suppressed. It is desirable that the width of the spherical portion  601  is larger than the width of linear contact between the valve face  204  free from the non-circularity and the valve seat face  203  free from the non-circularity. 
         [0040]    To form the recess  501  upstream of the seat position and the recess  502  downstream from the seat position, spherical tools  701  respectively having the same spherical radius SR 1 , SR 2  as that of the upstream recess  501  or the downstream recess  502  are used. The desired upstream recess  501  and downstream recess  502  can be obtained by using the spherical tools  701  respectively having the spherical radius SR 1 , SR 2 . Due to the geometric relation between the sphere and the tapered conical face, the spherical tool  701  and the valve seat face  203  make linear contact and the contact position therebetween is uniquely determined. Therefore, the recesses can be formed with high precisions. There is no relation between the order of using the spherical tool  701  having the spherical radius SR 1  and the spherical tool  701  having the spherical radius SR 2  and the resultant effect. Whichever of the upstream recess  501  and the downstream recess  502  may be first formed. Whether the angle of the valve seat face  203  is decreased or increased after the formation of the recess, the resultant effect remains the same because the geometric relation between the sphere and the tapered face is unchanged. With the increase in the difference between the radius SR 3  and the radius SR 1  or the radius SR 2 , the cutting quantity increases so that the manufacturing time and manufacturing cost increase. If the tool used for forming the upstream recess  501  has a spherical radius SR 1  that is 10 to 25% larger than the spherical radius SR 3  of the valve body and the tool used for forming the downstream recess  502  has a spherical radius SR 2  that is 10 to 25% smaller than the spherical radius SR 3  of the valve body, a desired effect can be obtained while controlling the cutting quantity for forming the recess. After cutting, the spherical tool  701  having the same spherical radius SR 3  as that of the valve body may be used for finishing by making the valve seat face  203  and the spherical tool  701  grind against each other. By doing so, the seal performance can be improved further. 
         [0041]    While the above description is principally made on the method of forming the upstream recess  501  and the downstream recess  502  by cutting, the cutting need not necessarily be used, for forming the upstream recess  501  and the downstream recess  502 . For example, a spherical grinding may be adopted. A desired effect can also be obtained by the spherical grinding work in which the protrusion at an upstream side or downstream side of the seat position where there is the potential for the wide-area contact can be smoothened by using the spherical tool  701 . This spherical grinding work requires very little cutting quantity for forming the upstream recess  501  and the downstream recess  502  and offers the desired effect, providing for the processing with super-high precision. 
         [0042]    At this time, if the tool used for forming the upstream recess  501  has a large spherical radius SR 1  that is 1 to 10% larger than the spherical radius SR 3  of the valve body and the tool used for forming the downstream recess  502  has a small spherical radius SR 2  that is 1 to 10% smaller than the spherical radius SR 3  of the valve body, a region of the order of 100 μm where there is the potential for the wide-area contact can be finished to a flat and smooth surface. Just as in the grinding work, the tool  701  having the same spherical radius SR 3  as that of the valve body is used for finishing where the valve seat face and the spherical tool are made to grind against each other, whereby the seal performance can be further improved. At this time, the pressing load on the spherical tool  701  having the spherical radius SR 3  is set to a value less than the pressing load on the spherical tool  701  having the spherical radius SR 1 , SR 2  or otherwise, the spherical grinding time for the spherical tool  701  having the spherical radius SR 3  is set to a shorter period. By doing so, the flat portion  601  can define a shorter distance from the valve face  201  than the upstream recess  501  or the downstream recess  502  does. Therefore, the effect to inhibit the wide-area contact can be further increased. 
         [0043]    A fuel injection valve achieving high seal performance while suppressing manufacturing cost increase can be offered by using a steel ball featuring high precision and high hardness as a spherical body forming the spherical tool  701 . 
       Second Embodiment 
       [0044]      FIG. 8  is an enlarged sectional view showing the vicinity of a valve body  801  according to a second embodiment of the present invention. According to the second embodiment, annular recesses  801 ,  802  or slopes are formed at upstream side and downstream side of the valve body  801  with respect to the seat position thereof. Such a method of avoiding the wide-area contact, by forming relieves on the valve body is particularly effective in a case where the valve body is produced by transferring the configuration of the valve body. Since the valve body is formed by grinding with a grinding wheel, the degree of freedom in forming the valve body  101  is comparatively high. According to this embodiment, the gap between the valve body and the conical seat face can be increased at. the upstream side and the downstream side with respect to the seat position by working the valve body but not working the valve seat. Thus is obtained the effect to prevent the fuel leakage due to the wide-area contact. In this case, the increase in contact bearing pressure as the result, of addition of the recesses  801 ,  802  is suppressed by defining a distance  803  between the upstream recess  801  and the downstream recess  802  to be larger than the width of linear contact between the valve face  204  free from the non-circularity and the valve seat face  203  free from the non-circularity. Thus, the seal performance can be improved without decreasing the aging degradation resistance or wear resistance. 
         [0045]      FIG. 9  is an enlarged view showing a microscopic illustration of a valve body  901  and a seat portion of the valve seat  102 . The wide-area contact due to the non-circularity can be avoided by providing the valve body  801  with the upstream recess  902  and the downstream recess  803 . As a result, the increase in contact stiffness due to the wide-area contact can be suppressed. Hence, the load required for forming the continuous annular seal seat for preventing the fuel leakage from the contact portion can be reduced. 
       LIST OF REFERENCE SIGNS 
       [0046]      101  . . . VALVE BODY 
         [0047]      102  . . . SEAT MEMBER 
         [0048]      103  . . . DOWNSTREAM PLUNGER ROD GUIDE 
         [0049]      104  . . . NOZZLE HOLDER 
         [0050]      105  . . . UPSTREAM PLUNGER ROD GUIDE 
         [0051]      106  . . . MOVABLE ELEMENT 
         [0052]      107  . . . MAGNETIC CORE 
         [0053]      108  . . . CORE 
         [0054]      109  . . . YOKE 
         [0055]      110  . . . SPRING 
         [0056]      111  . . . CONNECTOR 
         [0057]      112  . . . FUEL SUPPLY PORT 
         [0058]      201  . . . FUEL INJECTION HOLE 
         [0059]      202  . . . SEAL SEAT 
         [0060]      203  . . . VALVE SEAT FACE 
         [0061]      204  . . . VALVE FACE 
         [0062]      301  . . . UNDESIGNED CONTACT POSITION 
         [0063]      302  . . . DESIGN SEAT WIDTH 
         [0064]      303  . . . DESIGN SEAT POSITION 
         [0065]      401  . . . VALVE FACE DEFORMED BY PRESS FORCES 
         [0066]      501  . . . UPSTREAM RECESS 
         [0067]      502  . . . DOWNSTREAM RECESS 
         [0068]      601  . . . FLAT PORTION 
         [0069]      701  . . . SPHERICAL TOOL 
         [0070]      801  . . . UPSTREAM RECESS 
         [0071]      802  . . . DOWNSTREAM RECESS 
         [0072]      803  . . . SPHERICAL PORTION 
         [0073]      901  . . . VALVE FACE HAVING NON-CIRCULARITY