Abstract:
An injector used for an internal combustion engine, wherein force acting on a valve element due to flow of fuel is reduced. The shape of either a valve element front end or a valve seat surface of a fuel injection valve is adapted such that the distance between the valve element front end and the valve seat surface which is formed by a circular conical surface is greater than in the case when the shape from a valve element circular tube surface to a spherical surface which forms a seat is connected by a circular arc. As a result, the cross-sectional area of a flow path is rapidly increased from the valve seat surface, on the outer side of the valve element, and this reduces that portion of the valve element which receives pressure due to a reduction in static pressure, reducing force acting on the valve element.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel injection valve used in internal combustion engines, in which a valve element abuts against a valve seat to thereby prevent leakage of a fuel and the valve element separates from the valve seat to perform injection. 
       BACKGROUND ART 
       [0002]    JP-B2-3737122 discloses a fuel injection valve, in which a spherical surface on a valve element side and a conical surface on a valve seat side abut against each other to thereby seal a fuel, a transition section is provided between a valve shaft and a conical section, and a sealing seat formed as a narrow spherical zone is provided between the transition section and the conical section. 
       CITATION LIST 
     [Patent Citation 1] JP-B2-3737122 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0003]    Electromagnetic type fuel injection valves are generally used for fuel injection valves that supply a fuel to internal combustion engines. Here, problems will be described taking an electromagnetic type fuel injection valve as an example. Electromagnetic type fuel injection valves are normally closed type electromagnetic valves, in which a valve element is normally pushed against a valve seat surface by a bias spring to bring about a closed state. When an electric current is introduced to a coil to generate an electromagnetic force, the valve element and the valve seat surface are caused to separate from each other to create a clearance to bring about an opened state. 
         [0004]    Here, in the opened state, when a fuel passes through a clearance between the valve element and a valve seat, an increase in velocity of flow or in pressure loss is caused and a decrease in static pressure at a tip end of the valve element is caused. Therefore, the valve element in the opened state is pushed by fuel pressure in a valve closing direction. 
         [0005]    In order to maintain the opened state against the force in the valve closing direction, it is necessary to increase an electric current introduced to a coil to increase an electromagnetic force, or to set a range of fuel pressure as used small, or to make a force, which is given by the bias spring, smaller than a predetermined value. Among these measures, there is a limit in electric power, which can be introduced to the coil, because of heat generation of the coil, attendant shortening of life, and thermal degradation of resin members. Also, because of the effect on engine combustion performance, it is not preferred that a usable range of fuel pressure be set small. 
         [0006]    Here, when a force, which is given by the bias spring, is set small, there is caused a problem that a force, which closes the valve element, becomes small to bring about a decrease in responsibility. In the course of valve closing, the force of the bias spring and a fluid force by a fuel cause the valve element to perform a valve closing motion, and when the force by the bias spring is set small so that a workable maximum fuel pressure (maximum working fuel pressure) becomes large, a small fuel pressure enables the valve element not to sufficiently receive a force required for valve closing and time required for valve closing is prolonged. That is, a valve closing delay time is prolonged. 
         [0007]    The valve closing delay time is a response delay time of a fuel injection valve related to a valve closing motion and a delay time which determines a controllable minimum injection quantity. That is, when a bias spring force is small, there is caused a problem that a valve closing delay time is prolonged and a controllable minimum injection quantity increases. 
         [0008]    Accordingly, in order to make a controllable minimum injection quantity fairly small, in other words, to shorten a valve closing delay time, it is necessary to set a bias spring force large. Here, in order that a maximum working fuel pressure does not become small, it is necessary to decrease a fluid force acting on a valve element. 
         [0009]    The invention has been thought of in view of the above and has its object to decrease a fluid force acting on a valve element. 
       Technical Solution 
       [0010]    In order to solve the above problems, according to the invention, a valve element or a seat member is shaped so that in a region extending from a spherical surface portion, which forms a sealing portion of the valve element, to a portion, which becomes in parallel to a cylindrical-shaped portion of the valve element, a clearance between a valve seat and the valve element is made larger than a distance between a circular arc, which connects between a terminal end of the spherical surface portion and the cylindrical-shaped portion, and a conical surface, which forms the valve seat. As a result that a fluid (fuel) increases in velocity of flow at a tip end of the valve element and dynamic pressure increases, so that static pressure decreases according to Bernoulli&#39;s theorem, or static pressure decreases due to pressure loss resulted at the tip end of the valve element, a major part of a force caused by the fuel to act on the valve element is a force due to the fact that the tip end of the valve element acts as a pressure receiving surface. Accordingly, when it is tried to decrease this force, it is necessary to decrease a fuel in velocity of flow, or to narrow a region, which is high in velocity of flow, to narrow a region for reception of the decreased static pressure. According to the invention, a region at the tip end of the valve element, which decreases in static pressure, or pressure loss to be occurred can be decreased by decreasing a region, in which a fuel is high in velocity of flow, in the vicinity of a sealing portion at the tip end of the valve element. As a result, it is possible to obtain a fuel injection valve, in which a bias spring force acting on the valve element can be increased and which is decreased in valve closing delay time and exhibits a good responsibility. 
       ADVANTAGEOUS EFFECTS 
       [0011]    According to the invention, it is possible to obtain a fuel injection valve, in which a force given by flow of a fuel acting on a valve element can be decreased and a maximum fuel pressure enabling the fuel injection valve to work can be increased, or which is made good in responsibility even at the time of low pressure by setting a bias spring force high. As a result, it is possible to obtain a fuel injection valve, in which, for example, a controllable minimum injection quantity is small and which realizes an internal combustion engine being made high in one of fuel consumption, exhaust, and output performances. 
         [0012]    Other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a cross sectional view showing a first embodiment of a fuel injection valve according to the invention. 
           [0014]      FIG. 2  is a cross sectional view showing, in enlarged scale, the neighborhood of a tip end of a valve element of the first embodiment of the fuel injection valve according to the invention. 
           [0015]      FIG. 3  is a schematic view showing a force acting on a tip end of a valve element in a conventional fuel injection valve. 
           [0016]      FIG. 4  is an enlarged view showing, in detail, a shape of the tip end of the valve element in the first embodiment of the fuel injection valve according to the invention. 
           [0017]      FIG. 5  is a graph showing a clearance between the valve element and a valve seat in the first embodiment of the fuel injection valve according to the invention. 
           [0018]      FIG. 6  is an enlarged, cross sectional view showing the neighborhood of a tip end of a valve element in a second embodiment of the fuel injection valve according to the invention. 
           [0019]      FIG. 7  is a view showing change in cross sectional area of a flow passage at the tip end of the valve element in the second embodiment of the fuel injection valve according to the invention. 
       
    
    
     EXPLANATION OF REFERENCE 
       [0000]    
       
           101 ,  301  valve element 
           102 ,  302  valve seat member 
           103  guide member 
           104  nozzle holder 
           105  valve element guide 
           106  anchor 
           107  magnetic core 
           108  coil 
           109  yoke 
           110  spring 
           111  connector 
           112  fuel supply port 
           201  injection port 
           202  spherical surface of valve element 
           203  valve seat 
           204  conical surface 
           205  cylindrical-shaped portion 
           206  sliding cylindrical surface 
           303 ˜ 306  arrow 
           601  valve element 
           602  spherical body 
           603  position of a spherical surface which becomes in parallel to a cylinder 
           604  seat conical surface 
           605  seat member 
           606  flat surface portion 
           607  shaft portion 
       
     
       DESCRIPTION OF EMBODIMENTS 
       [0046]    Embodiments of an electromagnetic type fuel injection valve according to the invention will be described hereinafter. 
       Embodiment 1 
       [0047]      FIG. 1  is a cross sectional view showing a first embodiment of an electromagnetic type fuel injection valve according to the invention. The electromagnetic type fuel injection valve shown in  FIG. 1  is an electromagnetic type fuel injection valve of in-cylinder direct injection type for gasoline engines. 
         [0048]    In  FIG. 1 , a fuel is supplied from a fuel supply port  112  to be fed to an interior of the fuel injection valve. The electromagnetic type fuel injection valve shown in  FIG. 1  is a normally closed type electromagnetically driven one and when a coil  108  is not energized, a valve element  101  is biased by a spring  110  to be pushed against a valve seat member  102 , so that a fuel is sealed. At this time, fuel pressure as supplied in the in-cylinder injection type fuel injection valve is in the range of about 2 MPa to 25 MPa. 
         [0049]      FIG. 2  is a cross sectional view showing, in enlarged scale, the neighborhood of injection ports provided at a tip end of the valve. When the fuel injection valve is in a valve closed state, the valve element  101  abuts against a valve seat  203 , which comprises a conical surface provided on the valve seat member  102 , to maintain sealing the fuel. A contact part of the valve element  101  is formed by a spherical surface  202  and contact between the valve seat  203  in the form of a conical surface and the spherical surface  202  is substantially in a linear contact state. Sealing portions, respectively, are formed on mutual contact parts of the valve element  101  and the valve seat  203 , and fuel injection ports  201  are formed on the valve seat member  102  in a manner to be positioned downstream of the sealing portions in a fuel flow direction. When in the valve closed state, a force obtained by multiplying fuel pressure by an area of a circle (a circle defined by the contact parts) having a seat diameter is acting on the valve element  101 . 
         [0050]    When the coil  108  is energized, magnetic flux is generated on a core  107 , a yoke  109 , and an anchor  106 , which constitute a magnetic circuit of the electromagnetic valve, so that magnetic attraction is generated between the core  107  and the anchor  106 , between which a clearance is present. When the magnetic attraction become larger than the force produced by the bias of the spring  110  and the fuel pressure as described above, the valve element  101  is attracted toward the core  107  by the anchor  106  to bring about a valve opened state. 
         [0051]    When put in the valve opened state, a clearance is generated between the valve seat  203  and the spherical surface  202  of the valve element and fuel injection is started. When fuel injection is started, energy given as the fuel pressure is converted into kinetic energy to reach the injection ports  201  to result in injection. 
         [0052]    The valve element  101  together with the anchor  106  is enclosed in a nozzle holder  104 . The valve element  101  is guided in two locations in a direction of driving by a guide member  103  provided on a tip end side, on which the sealing portions are formed, and a valve element guide  105  provided on a base end side, on which the anchor  106  is provided. The guide member  103  and the valve element guide  105  are provided on the nozzle holder  104  so as to guide the valve element  101  in two locations in a direction along a central axis of the valve element (a direction of valve axis). 
         [0053]      FIG. 3  is a schematic view showing a state of flow at a tip end of the fuel injection valve put in a valve opened state and a force caused by flow of fuel to act on the valve element.  FIG. 3  shows a force exerted on a valve element  301  in a conventional fuel injection valve. 
         [0054]    When the valve element  301  is displaced and the valve is put in a valve opened state, a fuel passes through a clearance between the valve element  301  and a valve seat member  302 . It is important in restricting a displacement magnitude that the clearance between the valve element  301  and the valve seat member  302  be set comparatively small. That is, in order to make the fuel injection valve good in responsibility, it is important that a displacement magnitude don&#39;t become too large. Therefore, flow of a fuel passing through a small clearance increases in velocity of flow  303 . 
         [0055]    Generally, when a fuel increases in velocity of flow, dynamic pressure (ρv 2 )/2 (ρ indicates density of fluid and v indicates velocity of flow) increases and pressure loss becomes large in proportion to dynamic pressure. When pressure loss occurs in this manner, pressure below the valve element decreases. Also, when an increase in velocity of flow causes an increase in dynamic pressure, a part being high in velocity of flow decreases in static pressure according to Bernoulli&#39;s theorem. 
         [0056]    The valve element receives a fuel pressure supplied on an upstream side thereof (for example, a position in contact with the spring  110 ) and is pushed back by fuel pressure on a downstream side thereof (that is, on the side toward the valve seat member  102 ), and a difference therebetween presents a force acting on the valve element. Accordingly, a decrease in static pressure due to conversion into kinetic energy and a decrease in static pressure due to pressure loss cause pressure indicated by arrows  305  to act as a force acting on the valve element at a tip end thereof and lowering the valve element in a valve closing direction. 
         [0057]    In the present embodiment, the valve element is formed in external shape as shown in  FIG. 4  in order to reduce a force which thus lowers the valve element in the valve closing direction.  FIG. 4  is a view showing, in further enlarged scale than  FIG. 2 , the neighborhood of the valve element. The tip end of the valve element  101  includes a cylindrical-shaped portion  205  disposed downstream of a cylindrical-shaped portion  206 , which is defined by a cylindrical-shaped surface to form a guide portion, and defined by a cylindrical-shaped surface being smaller in diameter than that of the cylindrical-shaped portion  206 , and a downstream side of the cylindrical-shaped portion  205  is contiguous to a conical surface  204 . The conical surface  204  is smoothly contiguous to the spherical surface  202 , which provides for sealing. A side downstream of the spherical surface  202  is formed to be further pointed than the spherical surface  202 . 
         [0058]    The spherical surface  202  is formed with a seat portion  202   a  which comes into contact with a seat portion  203   a  of the valve seat  203 , and in a region extending from an upstream side  202   b  to a downstream side  202   c , a spherical surface portion is formed. A center of the spherical surface portion is positioned as indicated by O. In the present embodiment, the spherical surface  202  has the same radius as that of the cylindrical-shaped portion  205 . 
         [0059]    A wide angle conical surface  203   b  having a wider angle than that of the conical surface, which defines the valve seat  203  is formed upstream of the valve seat  203 , and the wide angle conical surface  203   b  is contiguous to a conical surface, which defines the valve seat  203  inwardly (toward a valve axis) of a cylindrical-shaped surface forming the cylindrical-shaped portion  205  in a direction perpendicular to the valve axis. 
         [0060]    In the cross sectional view of  FIG. 4 , in the case where the spherical surface  202 , which forms a sealing at a tip end of the valve element, and a virtual cylindrical-shaped surface  205   a , which is in parallel to the cylindrical-shaped surface of the cylindrical-shaped portion  205  are connected together by a circular arc (a virtual spherical surface extended toward an upstream side), a line like a two-dot chain line  202   d  (a virtual spherical surface) is defined. In the present embodiment, since the conical surface  204  is provided between the cylindrical-shaped portion  205  and the spherical surface  202 , a clearance between the conical surface of the valve seat  203 , which defines a seat, and the valve element  101  becomes wide as compared with the case where a tip end configuration of the valve element  101  is defined by a profile like the two-dot chain line  202   d . A clearance between the valve element  101  and the valve seat  203  (including the wide angle conical surface  203   b ) is the shortest distance between the valve element  101  and the valve seat  203  (including the wide angle conical surface  203   b ). In the following descriptions, the valve seat  203  includes the wide angle conical surface  203   b.    
         [0061]      FIG. 5  is a graph, in which an axis of ordinates indicates a cross sectional area of a flow passage between a tip end of the valve element  101  and that conical surface, which defines the valve seat  203 , and an axis of abscissas indicates a position in a radial direction. On the axis of abscissas, a flow direction is rightward and so a side toward a central axis (valve axis) of the fuel injection valve is on the right side. 
         [0062]    When flow goes toward the central axis of the fuel injection valve, it will go in a direction, in which a radius decreases, thus showing a tendency that a cross sectional area of a flow passage decreases essentially and linearly. 
         [0063]    Description will be given along positions in the flow direction. At a position, like a position  401  shown in  FIG. 4 , being larger in a radial direction than the virtual cylindrical-shaped surface  205   a  in parallel to the cylindrical-shaped surface of the cylindrical-shaped portion  205  of the valve element, the clearance is put in a state of being extremely large as shown in a position leftwardly of a point  501  in  FIG. 5 . In contrast, in the case where the valve element is shaped by connecting the virtual cylindrical-shaped surface  205   a  and the spherical surface  202  together by the circular arc (a virtual spherical surface)  202   d , a clearance area shown by a line  505  in  FIG. 5  is provided in a position, like a point  402 , of a clearance between the valve element and the valve seat  203 . In addition, a point  403  is positioned on a line being perpendicular to the valve seat  203  and passing through the seat portion  202   a  of the spherical surface  202 . 
         [0064]    In the present embodiment, a clearance enlarged portion is provided on a valve element portion between the cylindrical-shaped portion  205  and the spherical surface  202  to enlarge a clearance between the valve element  101  and the valve seat  203  further than the case where the valve element is shaped by connecting the virtual cylindrical-shaped surface  205   a  and the spherical surface  202  together by the circular arc (a virtual spherical surface)  202   d . For example, it is preferred that the conical surface  204  as shown in  FIG. 4  is provided. In the case where the conical surface  204  is provided, a clearance area between the valve element  101  and the valve seat  203  is larger than a clearance area indicated by  505 , like  506  in  FIG. 5 . 
         [0065]    In addition, in  FIG. 5 , a broken line  507  corresponds to a position at an end  202   b  of the spherical surface  202  and a broken line  504  corresponds to a position at an end of the wide angle conical surface  203   b . The wide angle conical surface  203   b  is provided on the left side of the broken line  504 . 
         [0066]    In the present embodiment, also by providing the wide angle conical surface  203   b , a clearance area between the valve element  101  and the valve seat  203  is larger in comparison with the case where the valve seat  203  is defined by a single conical surface. At this time, the valve element  101  may have a valve element configuration provided by connecting the virtual cylindrical-shaped surface  205   a  and the spherical surface  202  together by the circular arc (a virtual spherical surface)  202   d . Even when the wide angle conical surface  203   b  is not provided, only the conical surface  204  of the valve element  101  enables enlarging a clearance area between the valve element  101  and the valve seat  203  as described above. 
         [0067]    In case of providing the conical surface  204 , it is preferred that the spherical surface  202  be provided up to an upstream side of a position (a seated position) in contact with the valve seat  203  and the spherical surface  202  and the conical surface  204  are connected smoothly together. 
         [0068]    In this manner, by making a distance between a tip end surface of the valve element  101  and the valve seat  203  large, the cross sectional area of the flow passage between the valve element  101  and the valve seat  203  can greatly cover a wide region. That is, a clearance, as shown by the point  402  in  FIG. 4 , between the surface of the valve element  101  and the valve seat  203  can be made large as shown by a point  502  in  FIG. 5  as compared with the case where the virtual cylindrical-shaped surface  205   a  and the spherical surface  202  are connected together by the circular arc (a virtual spherical surface)  202   d . Therefore, a region being small in velocity of fuel flow can be made large. As a result of enabling enlarging a region being small in velocity of fuel flow, it is possible to achieve a decrease in pressure loss and to decrease a region being reduced in static pressure according to Bernoulli&#39;s theorem. In particular, since it is general that the tip end configuration of the valve element  101  is formed as a shape of a body of revolution, a surface outwardly of a seated position is large. Accordingly, when a decrease in static pressure is restricted outwardly of the seated position, an effect of decreasing a force acting on the valve element  101  is great. By making a valve element configuration between the spherical surface  202  and the cylindrical-shaped portion  205  as in the embodiment, it is possible to decrease a force acting on the valve element  101 . 
         [0069]    By decreasing the force acting on the valve element  101 , it is possible to decrease a force, with which the valve element  101  is closed by fuel pressure, and as a result, that range of fuel pressure, in which the fuel injection valve can operate, can be set on a high pressure side. As a result, it is possible to provide a fuel injection valve, by which a fuel further atomized due to use in high pressure is injected. Also, it is possible to provide a fuel injection valve, in which fuel pressure is wide in range of use and of which injection quantity is made large in flow rate by the use at variable fuel pressures. 
         [0070]    Alternatively, also by increasing the preset load of the spring  110 , it is possible to maintain a workable range of fuel pressure. In this manner, in the case where the preset load of the spring  110  is made large, it is possible to make a valve closing motion of a fuel injection valve quick. Since a controllable minimum injection quantity is determined by time required for the valve closing motion of a fuel injection valve, the controllable minimum injection quantity of a fuel injection valve can be decreased when the preset load of the spring  1101  is made large. As a result, it is possible to provide a fuel injection valve capable of meeting an operating condition, which needs a further small injection quantity. 
         [0071]    In addition, in the present embodiment, the cylindrical-shaped portion  205  is made a smaller cylindrical-shaped surface than the sliding guide surface  206  of the valve element in order to enlarge a region outwardly of the point  501  in  FIG. 5 , at which the cylindrical-shaped surface begins, and to reduce a region, in which a distance between the seat conical surface and the surface of the valve element  101  is reduced. While the effect of the present embodiment can be produced also in the case where the cylindrical-shaped surface of the sliding guide portion  206  and the cylindrical-shaped surface of the cylindrical-shaped portion  205  agree with each other, the cylindrical-shaped portion  205  is smaller in diameter than the sliding guide surface  206  whereby it is possible to decrease a cross sectional area affected by a decrease in static pressure. 
       Embodiment 2 
       [0072]      FIG. 6  is an enlarged, cross sectional view showing the neighborhood of a valve element  601  in a second embodiment of an electromagnetic type fuel injection valve according to the invention. In the second embodiment, there is provided upstream of a seat position of a seat conical surface  604  a conical surface having a larger opening angle than that of the seat conical surface  604 , or there is provided upstream of a seat position of a seat conical surface  604  a flat surface portion like a surface  606 . In this manner, that manner, in which the flat surface portion  606  is provided, is effective especially in the case where the valve element  601  is formed by a shaft portion  607  comprising a cylindrical-shaped surface and a spherical body  602 . Generally, since a spherical body is supplied as a bearing, it has the advantage of comparatively readily obtaining a spherical body of high precision and high hardness. On the other hand, since the spherical body  602  and the shaft portion  607  serving as a guide surface are joined together as by welding or the like, working after being joined involves difficulties. According to the second embodiment of the invention, there is produced an effect that by working a seat member side without working a valve element side, a clearance between the valve element and the seat conical surface is enlarged and a force acting on the valve element is reduced. 
         [0073]    In case of using the spherical body  602  for the valve element  601 , a seat member is shaped so that in a region extending to a seat position from a position  603  in parallel to the shaft portion  607 , the cross sectional area of a flow passage in a clearance between the valve element (the spherical body  602 ) and the seat conical surface  604  is enlarged as compared with the case where the position  603  and the seated position are connected together by a circular arc. 
         [0074]    The flat surface portion  606  is provided and a point of intersection of the flat surface portion  606  and the seat conical surface  604  is set inwardly of a diameter of the position  603  in parallel to a cylinder corresponding to a sphere used for the valve element  601  but outwardly of a diameter of the seat position, whereby the cross sectional area of a flow passage in a clearance between the seat conical surface  604  and the spherical body  602  is enlarged while oiltightness of the seat is ensured. 
         [0075]      FIG. 7  is an enlarged view of the neighborhood of the valve element showing change in cross sectional area of a clearance and a graph showing the relationship of the cross sectional area of a flow passage. As shown in  FIG. 7(   a ), at a point  701   a  in a fluid passage having the same diameter as that of the position  603  of the spherical body  602  in parallel to a cylinder, the cross sectional area of a flow passage is large as shown by a point  701   b  in  FIG. 7(   b ). A clearance defined between the spherical body  602  and the seat conical surface  604  assumes a curve narrowing toward an inside of a spherical surface as shown by a line  705 . 
         [0076]    In contrast, according to the present embodiment, outside a point  702   a  in a fluid passage at a point of intersection of the flat surface portion  606  and the seat conical surface  604 , a clearance between the valve element and the seat conical surface can be enlarged as shown by a line  706 . That is, the provision of the flat surface portion  606  enables making the cross sectional area of a passage large as shown by a line  706  even in a region, in which a clearance is essentially narrow as shown by the line  705 . 
         [0077]    As a result, it is possible to narrow a region, in which a large velocity of flow caused by narrowness of a fluid passage is generated, outside a seat position  703   b  (on an upstream side in a flow direction). Therefore, a decrease in static pressure and pressure loss due to an increase in dynamic pressure can be restricted and by decreasing area of influence, it is possible to decrease a force acting on the valve element  601  in the valve closing direction. 
         [0078]    While the above description has been given with respect to the embodiments, it is apparent to those skilled in the art that the invention is not limited thereto but susceptible of various changes and modifications within the spirit of the invention and the scope of the appended claims. 
       INDUSTRIAL APPLICABILITY 
       [0079]    While an in-cylinder direct injection type electromagnetic fuel injection valve for gasoline engines has been described by way of example, the invention is effective in port injection type electromagnetic fuel injection valves for gasoline engines and fuel injection valves driven by piezo elements and magnetostrictive elements.