Abstract:
A fuel injection valve device is capable of thinning a nozzle hole plate and improving fuel spray characteristics by a construction for reducing stress concentration that occurs at the weld part of the nozzle hole plate. The fuel injection valve device includes: a nozzle having a fuel passage inside and in which a valve seat is formed at an end; a needle valve for opening and closing the fuel passage by coming in contact with and separating from the valve seat; and an nozzle hole plate that is disposed at the tip of the nozzle and injects a fuel in the fuel passage at the time of opening the needle valve. The nozzle hole plate and the nozzle are fixed by welding in a state of forming an even gap between them.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fuel injection valve device for use in, for example, automobile engines and, more particularly, to a fuel injection valve device provided with a nozzle hole plate for atomization of fuel. 
   2. Description of Related Arts 
   Under the recent trend of tightening the regulations of exhaust gas, in the field of fuel injection valve device for use in automobile engines, it has been increasingly demanded to improve fuel spray characteristics. To cope with this demand, several attempts of fuel injection valve device have been proposed. In those known fuel injection valve devices, a nozzle hole plate having a plurality of nozzle holes on the downstream side of a valve member consisting of a valve disc and a valve seat is disposed so that atomized fuel is injected from every nozzle hole into each cylinder head of an engine. 
   For example, the Japanese Patent Publication (unexamined) No. 2004-169572 discloses a fuel injection valve device in which a first nozzle hole plate having vertical cylindrical holes is joined by welding on the tip (downstream side) of the valve member, and a second nozzle hole plate having an inclined cylindrical holes that are larger hole diameter than the mentioned vertical cylindrical holes and communicate with the cylindrical holes of the mentioned first nozzle hole plate is further welded in a superimposed manner on the downstream side of the mentioned first nozzle hole plate, thereby atomization of fuel being carried out. 
   The Japanese Patent Publication (unexamined) No. 2003-206828 discloses another fuel injection valve device provided with a valve seat for discharging or interrupting the fuel from the injector by engaging or disengaging with a valve seat moving up and down; and a nozzle plate (nozzle hole plate) having a plurality of orifices directly welded and fixed onto the valve seat on the downstream side; and in which the mentioned orifices are shaped into a circular corn spreading toward the downstream side; thereby atomization of fuel and improvement in quality of exhaust gas being achieved. 
   The Japanese Patent Publication (unexamined) No. 317607/1997 discloses a further fuel injection valve device in which a nozzle plate (nozzle hole plate) is cup-shaped, and a protruding face of a bottom part of this nozzle plate is welded onto a sleeve fixed to a valve member side so as to press the protruding face on the end face of an opening of the valve member, thereby it being avoided to directly fixing the nozzle hole plate to the valve member in order to suppress deflection produced on the bottom part of the mentioned nozzle plate due to fuel injection pressure. 
   SUMMARY OF THE INVENTION 
   To improve fuel spray characteristics such as atomization in the fuel injection valves, it has been conventional to adopt such means as increasing fuel pressure, thinning a nozzle hole plate or the like. In such means, however, the fuel injection valve for cylinder injection of fuel is normally high in fuel pressure (for example, 20 MPa), and therefore when thinning the nozzle hole plate, deflection of the nozzle hole plate becomes large due to application of fuel pressure. Thus, a problem exists in that stress concentration is easy to occur at a notch part between the nozzle hole plate and the weld part of the nozzle. To cope with this, it has been necessary to increase strength of the nozzle hole plate, which eventually results in a large-scaled fuel injection valve. 
   In the case of the fuel injection valve device disclosed in the Japanese Patent Publication (unexamined) No. 2004-169572, the welding and fixation are made only at the end part of the valve member  5  and the end face of the fitting part of the second nozzle hole plate  9 . In the case of the fuel injection valve device disclosed in the Japanese Patent Publication (unexamined) No. 2003-206828, the welding and fixation are made (from underside) only at the end face of the fitting part of the nozzle plate (nozzle hole plate)  24  fitted to the end part of the valve seat  16 . Furthermore, in the case of the fuel injection valve device disclosed in the Japanese Patent Publication (unexamined) No. 317607/1997, the nozzle plate (nozzle hole plate)  61  and the sleeve  71  welded to the valve member  26  (at the weld part  91 ) are welded only at the outer circumference (at the weld part  92 ). In every foregoing art, the welding of the nozzle hole plate is made only at the end face or on the side face, and a notch part remains at the tip of the nozzle hole plate. Therefore, a stress concentration takes place at this notch part, which may result in a fatigue failure even in case of a minute deflection due to moment of the nozzle hole plate caused by high fuel pressure. Thus, there has been a limit in application of high fuel pressure or thinning the nozzle hole plate. 
   The present invention was made to solve the above-discussed problems, and has an object of providing a fuel injection valve device capable of thinning a nozzle hole plate and expanding a adjustable range of fuel spray characteristics by a construction for reducing stress concentration that occurs at the weld part of the nozzle hole plate. 
   A fuel injection valve device according to the invention includes: a nozzle having a fuel passage inside thereof and in which a valve seat is formed at an end; a needle valve for opening and closing the mentioned fuel passage by coming in contact with and separating from the mentioned valve seat; and an nozzle hole plate that is disposed at the tip of the mentioned nozzle and injects a fuel in the mentioned fuel passage at the time of opening the mentioned needle valve. The mentioned nozzle hole plate and the nozzle are fixed by welding in a state of forming an even gap between them. 
   In the fuel injection valve device of above construction according to the invention, since coefficient of stress concentration applied to a notch part at the tip of the weld part can be made small, deflection of the nozzle hole plate is suppressed and moment produced at the time of welding is made small. As a result, there is an advantage such that thickness of the nozzle hole plate can be established as small as possible even in case of high fuel pressure. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view showing an entire construction of a fuel injection valve device according to Embodiment 1 of the present invention. 
       FIG. 2  is an enlarged view showing an essential part of a tip part of the valve device of  FIG. 1 . 
       FIG. 3  is a partially enlarged view to explain a state of a valve seat and a nozzle hole plate mounted on the tip part of a nozzle member of  FIG. 2 . 
       FIG. 4  is a graphic diagram of stress produced at the tip of the weld part at the time of operating the fuel injection valve according to Embodiment 1 of the invention. 
       FIG. 5  is an enlarged view showing an essential part of a tip part of the valve device according to Embodiment 2 of the invention. 
       FIG. 6  is a partially enlarged view to explain a state of a valve seat and a nozzle hole plate mounted on the tip part of a nozzle member according to Embodiment 3 of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment 1 
   Embodiment 1 of the invention is hereinafter described with reference to the accompanying drawings.  FIG. 1  shows a longitudinal sectional view of an entire construction of a fuel injection valve device according to Embodiment 1 of the present invention, and  FIG. 2  shows an enlarged view of an essential part of a tip part of the valve device of  FIG. 1 . Referring to  FIGS. 1 and 2 , a fuel injection valve  1  mainly consists of a housing  2 , a nozzle member  3  disposed inside at the end part of this housing  2 , and a solenoid part  4  disposed inside at the intermediate part of the housing  2 . 
   The mentioned housing  2  consists of a yoke part  5  having a flange  5   a  for mounting the fuel injection valve  1  on a cylinder head  20 , and a holder  6  connected to one and of the yoke part  5 . The mentioned nozzle member  3  is shaped into a cylinder provided with steps, and consists of a nozzle  9  to which a valve seat  7  and a nozzle hole plate  8  are fixed at the tip by a later-described method; a needle valve  11  that is slidably inserted in the mentioned nozzle  9  so as to open and close a valve seat contact part  10  by moving up and down on the center axis C of the mentioned valve member  3 ; and a moving iron core  12  joined by welding to the mentioned needle valve  11  at the upper end thereof. 
   The mentioned solenoid part  4  consists of a coil  13  on which copper wires are wounded; a cylindrical stationary iron core  14  mounted on the inner circumference of the mentioned coil  13 ; a rod  15  fixed to the internal part of the mentioned stationary iron core  14 ; a compression spring  16  disposed between an end of the mentioned rod  15  and an end of the needle valve  11  to urge the needle valve  11  on the valve seat  7 ; and a terminal  17  for connecting a lead wire of the coil  13  to outside via a housing part  18 . 
   Now, operations of the mentioned fuel injection valve  1  are described. When a valve opening signal from a controller (not illustrated) is inputted via the terminal  17  to the coil  13 , magnetic flux generated in the coil forms a magnetic circuit consisting of the stationary iron core  14 , moving iron core  12 , holder  6  and yoke part  5 , and generates an electromagnetic force attracting the moving iron core  13  to the side of the stationary iron core  14 . By the moving up action of the moving iron core, the needle valve  11  also moves to the side of the stationary iron core  14 , thus valve opening of the nozzle member  3  being performed. At this time, an opening area of the valve seat contact part  10  is determined by a lifting amount that is regulated by contact of the valve  11  with a stopper  19 . 
   On the other hand, when the valve opening signal is inputted from the controller, the conduction of current to the coil  13  is interrupted, and the mentioned electromagnetic attraction is vanished. Accordingly, the moving iron core  12  and the needle valve  11  are moved away from the side of the stationary iron core  14  by the urging force of the compression spring  16 , thus valve closing of the nozzle member  3  being performed. 
   Fuel injection is carried out when the tip of the needle valve  11  of the fuel injection valve  1  releases the valve seat contact part  10 . As for the sealing force of the needle valve  11 , the compression spring  16  disposed in the internal part of the mentioned stationary iron core  14  is set to a predetermined compressive force by the rod  15 . Accordingly, a sealing force is determined depending upon a compressive force of the compression spring  16  and a fluid force produced by a fuel pressure applied to the seat area of the valve seat contact part  10 . 
   In addition, the fuel injection valve  1  is mounted on the cylinder head  20  via a ring  25  of Teflon (registered trademark). This ring  25  seals combustion flame within the engine cylinder. However, a nozzle part located under the ring  25  is exposed to the flame. 
     FIG. 3  is a partially enlarged view to explain a state of mounting the valve seat  7  and nozzle hole plate  8  on the tip part of the mentioned nozzle member  3 . In the drawing, first the valve seat  7  is laid out concentrically with the nozzle hole plate  8 , and the valve seat  7  having been welded on the nozzle hole plate  8  at the outer circumference (indicated by the weld part  21 ) is press-fitted to the nozzle  9 . At this time, note that only the valve seat  7  is press-fitted, so that a step  22  is formed on the nozzle  9 , thereby an even gap g being formed on the entire circumference. Such a gap g is formed on the outer circumference of the nozzle hole plate  8  for the purpose of absorbing the eccentricity between the nozzle hole plate  8  and the valve seat  7  and, at the same time, suppressing the stress concentration on the weld part. 
   That is, the nozzle hole plate  8  and the valve seat  7  are joined at the periphery thereof through the weld part  21 . It is, however, very difficult to lay out the nozzle hole plate  8  and the valve seat  7  accurately in a perfectly concentric manner, and actually an eccentricity is somewhat produced. As a result, a slight displacement comes out at any part of the periphery. When press-fitting such eccentrically jointed member into the nozzle  9 , a strain stress toward the joint portion will be disadvantageously produced. To avoid such disadvantage, only the valve seat  7  is press-fitted, so that an even gap g is formed on the entire circumference. In addition, the gap g is set to have dimensions enabling to weld, e.g., not more than 0.2 mm in difference of diameter. By seal welding between the ends of the nozzle hole plate  8  and the nozzle  9 , the mentioned gap g is completely closed with welding beads. This portion is indicated by weld part  23 . 
   End of the mentioned weld part  23  is not a conventionally notch-shaped but is U-shaped having a certain radius of curvature, so that coefficient of stress concentration is small. Accordingly the stress produced at the end of weld part can be made small. Further, by making a radius of curvature larger, the coefficient of stress concentration can be made smaller. Furthermore, since the nozzle  9  and nozzle hole plate  8  are joined together by welding through the gap g thereby being U-shaped at the weld part, the conventionally employed equipment can be used as they are. In addition, under the conditions of different welding depth between the nozzle  9  and nozzle hole plate  8  including a case of large difference in physical properties of material between them or a case where a target welding position is extremely displaced toward the nozzle  9  side or the nozzle hole plate  8  side, any notch may be produced. Accordingly, it is desirable that the nozzle  9  and nozzle hole plate  8  are composed of the same material by adopting, for example, austenitic stainless steel, ferritic stainless steel, or martensitic stainless steel. It is also desirable that the target welding position is located between the nozzle  9  and nozzle hole plate  8 . 
   As described above, according to Embodiment 1 of the invention, the valve seat  7  and the nozzle hole plate  8  are welded at the outer circumference thereof, thereby forming stepped hole laid out so as to fit only the valve seat  7  to the nozzle  9 , and then the nozzle hole plate  8  and the nozzle  9  are welded so as to have an even gap g between them. In this manner, a weld part moderating the notch is obtained, whereby coefficient of stress concentration on the notch can be reduced. As a result, deflection of the nozzle hole plate produced at the time of applying a fuel pressure is suppressed, and moment produced at the weld part is reduced, making it possible to set the thickness of the nozzle hole plate smaller. 
     FIG. 4  shows distribution of stress produced in the weld part at the time of operating the fuel injection valve in comparison with that of the conventional valve. In the drawing, the axis of ordinates indicates weld depth in mm, and the axis of abscissas indicates developed pressure in Mpa. It is understood from this drawing that the larger the weld depth is the less the stress is. 
   Embodiment 2 
   Now referring to  FIG. 5 , Embodiment 2 of the invention is described. In this Embodiment 2, the same construction as in the foregoing Embodiment 1 is employed except that configuration of a nozzle hole plate is different. More specifically, in the nozzle hole plate  81  of this Embodiment 2, a thickness T of the outer circumference thereof is formed to be larger than a thickness t of the central part in order to suppress the moment due to fuel pressure of the nozzle hole plate. A plurality of inclined jet holes  24  is formed on this nozzle hole plate  81 . Supposing that length of a jet hole  24  is L, diameter of the jet hole  24  is D, it has been acknowledged that atomization of fuel liquid injected through the mentioned jet holes  24  is desirably controlled by appropriately setting a ratio between L and D, i.e., L/D. In addition, it is preferable that the thickness T is set to be in the range of 1.0 to 1.5 mm and the thickness t is in the range of 0.4 to 0.7 mm. 
   Generally it is preferable that L is set to be smaller in the atomization carried out by deflection of the fuel flowing through inside the jet holes  24 . When L is smaller, the time of contact between fuel and air in the jet holes  24  is shorter, and an amount of air mixed with the fuel flow becomes less enabling to perform fuel injection of high purity. Accordingly, atomization characteristics of fuel are improved by thinning the central part where the jet holes  24  are located, while the outer circumferential part being thickened, thereby securing a mechanical strength with respect to welding and the like. As a result, this Embodiment 2 provides a more preferable fuel injection control valve. 
   Embodiment 3 
   Now, referring to  FIG. 6 , Embodiment 3 of the invention is described.  FIG. 6  is an enlarged view of an essential part of a tip of a valve member  3  of a fuel injection valve  1  and corresponds to  FIG. 3  of the foregoing Embodiment 1. In this Embodiment 3, the same construction as in the foregoing Embodiment 1 is employed except that configuration of a gap  22   a  is different. That is, in the foregoing Embodiment 1, a step portion  22  is formed on the end of the nozzle in order to provide an even gap g on the entire circumference between the nozzle hole plate  8  and the nozzle. On the other hand, in this Embodiment 3, a step portion  22  is formed on the valve seat  7  and nozzle hole plate  8  side in order to provide an even gap g. As a result of such construction, since it is not necessary to apply any machining for forming the gap to the nozzle  9 , a nozzle can be configured with high accuracy.