Patent Publication Number: US-6666389-B2

Title: Fuel injection valve

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2001-103270 filed on Apr. 2, 2001, the content of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel injection valve, in particular, a fuel injector for supplying fuel to a cylinder head or an intake manifold of a vehicle engine. 
     2. Description of Related Art 
     Conventionally, a fuel injection valve has been used for injecting and supplying fuel such as gasoline or light oil to a cylinder head of an engine. As shown in FIG. 6, the fuel injection valve  100  is provided at a lower part thereof with a housing pipe  101 , a body valve  102  and an injection hole plate  103 , as main components. 
     A valve needle  106  is inserted into an inner circumference of the housing pipe  101 , which is formed in a hollow cylinder shape. An upper end of the body valve  102  is inserted into a lower end opening of the housing pipe  101 . Circumferential surfaces of the housing pipe  101  and the body valve  102  in contact with each other are provided with a bonding portion  104  (as meshed in FIG. 6) formed by laser welding. The body valve  102  is formed in a hollow cylindrical shape. The body valve  102  is provided at an inner circumference thereof with a taper surface, whose diameter is smaller toward a lower end thereof, constituting a valve seat  105 . The injection hole plate  103  is bonded to the lower end of the valve body  102 . The injection hole plate  103 , which is formed in a cup shape, is provided at a bottom wall thereof with injection holes  107 . 
     When the valve needle  106 , which is moved up and down reciprocatingly, is seated on the valve seat  105  of the valve needle  106 , fuel is shut off. Accordingly, with respect to the valve seat  105 , higher dimensional accuracy such as roundness accuracy and lower deformation are required. 
     However, the valve seat  105  of the conventional fuel injection valve  100  tends to be largely deformed, when the body valve  102  is bonded by laser welding to the lower end of the housing pipe  101 . 
     The laser welding is performed in such a manner that, after the upper end of the body valve  102  is inserted into and comes in contact with the lower end of the housing pipe  101 , laser beam is radiated so as to draw a circle from an outer circumferential side of the housing pipe  101  to circumferential surfaces of the body valve  102  and the housing pipe  101  in contact with each other. Welding heat is generated so as to draw a circle that follows a circular movement of the laser beam. The bonding portion  104  of the body valve  102  is sequentially heated and expands from time to time when the laser beam is radiated and, then, cooled and contracts. Since the welding heat is not uniformly generated, the body valve  102  in a vicinity of the bonding portion  104  is likely to be deformed so that the deformation thereof causes a deformation of the valve seat  105 . In particular, when the deformation of the body valve  102  in a vicinity of the bonding portion  104  is not uniform circumferentially, the deformation of the valve seat  105  is more distinctive, which results in lowering a dimensional accuracy of the valve seat  105 . 
     The lower dimensional accuracy of the valve seat  105 , which is due to heat generating at the bonding portion  104 , is caused by any heat bonding such as brazing, too. 
     The lower dimensional accuracy of the valve seat  105  causes a gap between the valve needle  106  and the valve seat  105  at a valve closing time and tends to leak fuel from the gap. Accordingly, C—H chemical compounds such as CH 4 , that is, HC contents, in exhaust gas is likely to increase. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a fuel injection valve having a valve seat whose deformation due to bonding heat is smaller so that dimensional accuracy thereof is higher. 
     To achieve the above object, in a fuel injection valve having a housing pipe, a valve movable reciprocatingly and axially inside the housing pipe, and a body valve having a bottom wall constituting a valve seat with which the valve comes in contact and a side wall whose axial end is connected to a circumferential periphery of the bottom wall and whose the other axial end is fitted to and heat bonded to an end of the housing pipe, for example, by welding, the side wall is provided midway between the axial end and the other axial end thereof with a recess that is formed in advance before the body valve and the housing pipe are heat bonded to each other and serves to prevent a deformation of the side wall due to heat generated by the heat bonding from being straight transmitted to the valve seat. 
     Since the recess is provided in the side wall of the body valve, a deformation of the body valve due to heat generated by the heat bonding is partly absorbed by the recess so as not to transmit straight to the valve seat. Accordingly, the heat bonding does not lower a dimensional accuracy of the valve seat so much. 
     It is preferable that the recess is a ring shaped groove formed on an outer circumference of the side wall. The ring shaped groove serves to absorb a deformation of the body valve caused by press fitting the body valve to the housing pipe, since a bottom wall of the groove is operative like a plate spring. 
     More preferably, the ring shaped groove is located in a vicinity of a place where the body valve and the housing pipe are heat bonded to each other. In this case, a deformation area of the body valve between the ring shaped groove and the housing pipe is relatively small so that the ring shaped groove may effectively absorb the deformation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Other features and advantages of the present invention will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings: 
     FIG. 1 is a cross sectional view of a fuel injection valve according to an embodiment of the present invention; 
     FIG. 2 is a partly enlarged view of the fuel injection valve of FIG. 1; 
     FIG. 3 is a cross sectional view of a part of a fuel injection valve for FEM analysis; 
     FIG. 4 is a chart showing an axial displacement of a valve seat as a result of the FEM analysis; 
     FIG. 5 is a chart showing radial displacement of a valve seat as a result of the FEM analysis; and 
     FIG. 6 is a partly enlarged view of a conventional fuel injection valve as a prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention is described with reference to FIGS. 1 and 2. A fuel injection valve  1  according to the present embodiment is mounted in an intake manifold in a vehicle engine. The fuel injection valve  2  may be also applied to a direct injection system in which fuel is directly injected into a combustion chamber. 
     The fuel injection valve  1  is mainly composed of a housing pipe  2 , a resin mold  3 , a body valve  6  and an injection hole plate  7 . 
     The housing pipe  2  is formed in shape of a cylinder extending axially, that is, in a pipe shape, is composed of a fixed core  20 , a non-magnetic member  21  and a magnetic member  22 , which are axially arranged in order from an upper side to a down side. Each inner diameter of the non-magnetic member  21  and the magnetic member  22  is larger than an inner diameter of the fixed core  20 A so that a step  23  is formed at a boundary between the fixed core  20  and the non-magnetic member  21 . A stopper ring  28 , which has a fuel bore  280  penetrating up and down, is arranged at a lower inner circumference of the magnetic member  22 . 
     An upper end of the fixed core  20  is inserted via an O-ring  24  into a lower inner circumference of a delivery pipe (not shown). A fuel filter  25  for filtering impurity contained in the fuel supplied from the delivery pipe is arranged at an upper inner circumference of the fixed core  20 . An adjusting pipe  26  is arranged at a middle inner circumference of the fixed core  20 . 
     The non-magnetic member  21  is positioned below the fixed core  20 . A moving member  4  axially movable reciprocatingly is arranged below the step  23 , which is formed by the fixed core  20  and the non-magnetic member  21 . The moving member  4  is composed of a moving core  40  and a valve needle  41 . The valve needle  41  is composed of an insertion end  43 , a rod  44 , a shoulder  45  and a valve  46 . 
     The moving core  40 , which is formed in a hollow cylindrical shape, is slidably in contact with a guide surface  29  constituting an inner circumference of the non-magnetic member  21 . The moving core  40  is provided at an upper opening thereof with a step that retains a lower end of a spring  27 . A lower end of the adjusting pipe  26  retains an upper end of the spring  27 . That is, the spring  27  is sandwiched between the adjusting pipe  26  and the moving core  40  and biases the moving core  40  downward. 
     The insert end  43  of the valve needle  41  is inserted into and bonded to a lower opening  42  of the moving core  40 . Cross sectional shape of the lower opening  42  is circular. On the other hand, cross sectional shape of the insert end  43  is nearly rectangular. Two surfaces of the insert end  43  diagonally positioned in a long side direction of the rectangular are bonded to an inner circumference of the lower opening  42 . A gap between the circular lower opening  42  and the rectangular insert end  43  constitutes fuel passages. 
     The rod  44  extends downward from a lower end of the insert end  43 . The shoulder  45 , which is cylindrical, is positioned below the rod  44 . The stopper ring  28  is arranged above the shoulder  45 . The valve  46 , which is positioned below the shoulder  45 , is provided at a lower end thereof with a taper portion whose diameter is smaller downward. 
     The body valve  46 , which is bonded to the magnetic member  22 , is arranged around the shoulder  45  and the valve  46 . As shown in FIG. 2, the body valve  6  is formed in a hollow cylindrical shape. A bottom wall  61  of the body valve  6  has a taper portion, whose diameter is smaller downward, constituting a valve seat  60 . A cylindrical side wall  63  extends upward from a circumferential periphery of the bottom wall  61 . An upper end of the side wall  63  is press fitted into and bonded by laser welding to the inner circumference of the magnetic member  22 . A bonding portion  62  of the laser welding is formed in a ring shape. A groove  65 , whose cross sectional shape is one side opened square, is formed at a lower outer circumference of the cylindrical side wall  63  below the bonding portion  62 . The groove  65  is formed, just after the body valve  6  has been forged, by machining the outer circumference of the side wall  63 . However, the groove  65  may be formed at the same time when the body valve  6  is forged. 
     The injection hole plate  7 , which is shaped a cup, is bonded to a lower end of the body valve  6 . The injection hole plate  7  is provided at a bottom thereof with injection holes  70  communicating with a lower opening of the body valve  6 . 
     The resin mold  3  surrounds an outer circumference of the housing pipe  2 . The resin mold  3  is composed of a spool  30 , a coil  31  and a magnetic plate  32 , which are coaxially arranged in order from radially inside to outside and formed in a ring shape. Further, the resin mold  3  is provided with a connector  33  protruding radially. The connector  33  has a terminal  34  through which an electric signal is transmitted from an electric control unit (not shown) to the coil  31 . 
     An operation of the fuel injection valve  1  is described below. The fuel supplied from the delivery pipe is filtered at first by the fuel filter  25  and, then, passes through respective inner circumferences of the fixed core  20 , adjusting pipe  26  and spring  27 . Further, the fuel passes through the fuel passages between the lower opening  42  and the insert end  43  and, after passing through the fuel bore  280  of the stopper ring  28 , flows into a gap between an outer circumference of the valve  46  of the valve needle  41  and an inner circumference of the body valve  6 . 
     Upon applying the electric signal to the coil  31  through the terminal  34  for fuel injection control, a magnetic circuit, which constitutes a closed loop starting from the magnetic plate  32  and retuning thereto via the fixed core  20 , the moving core  40  and the magnetic member  22 , is produced around the coil  31 . This magnetic circuit causes a magnetic attracting force that attracts the moving core  40  toward the fixed core  20 . Accordingly, the moving core  40  is moved toward the fixed core  20  against a biasing force of the spring  27  so that the valve  46  of the valve needle  41  moves upward away from the valve seat  60 . The valve needle  41  stops at a position where the shoulder  45  comes in contact with the stopper ring  28 . When the electric signal applied to the coil  31  is shut off, the magnetic attracting force attracting the moving core  40  toward the fixed core  20  disappears so that the valve  46  of the valve needle  41  is again seated on the valve seat  60  by the biasing force of the spring  27 . 
     Next, a detail of the laser welding by which the housing pipe  2  and the body valve  6  is bonded to each other is described below. The laser beam, which is amplified by YAG laser oscillator, is radiated from the outer circumferential side of the magnetic member  22  whose inner circumference closely accommodates the body valve  6 . The laser beam is radiated to draw a circle along the outer circumference of the magnetic member  22 . Thus, the welding heat is generated so as to draw a circle as a spot to which the laser beam is radiated is moved annularly. Accordingly, the body valve  6  in a vicinity of the bonding portion  62  is deformed. However, the deformation of the body valve  6  in the vicinity of the bonding portion  62  is hardly transmitted to the valve seat  60  due to the groove  65 , which results in a less deformation of the valve seat  60 . 
     Further, the groove  65  prevents the welding heat generated at the bonding portion  62  from transferring in straight line to the valve seat  60 , since heat conductivity of an air layer existing in the groove  65  is remarkably lower than that of the body valve  6  that is made of metal such as stainless steel so that the welding heat is obliged to bypass the groove  65 . This will also to lower the deformation of the valve seat  60 . Instead of the air layer, the groove  65  may be filled with ring shaped resin foam, heat insulator, whose resiliency is lower than that of the body valve  6 . 
     Moreover, the body valve  6  is press fitted to the inner circumference of the magnetic member  22  of the housing pipe  2  so that the upper end of body valve  6  may be incidentally deformed. However, the groove  65  also serves to absorb the deformation of the upper end of the body valve due to the press fitting not to transmit straight to the valve seat  60  since a bottom wall of the groove  65  is operative like a plate spring. Accordingly, the dimensional accuracy of the valve seat  60  is not lowered so much. 
     Further, if the groove  65  is located near the bonding portion  62 , a deformation area of the upper end of the body valve  6  above the groove  65  is relatively small so that the groove  65  may effectively absorb the deformation. 
     The cross sectional shape of the groove  65  is not limited to the one side opened square but may be any shape such as a letter V having no bottom wall, unless the groove  65  is too large to maintain required strength of the body valve  6  and too small to lower the dimensional accuracy of the valve seat  60 . 
     FEM analysis and Simulation results thereof with respect to the deformation of the valve seat  60  caused by the welding are described with reference to FIGS. 3 to  5 . Both of circumferential displacement and axial displacement of points A, B, C and D in FIG. 3, that is, deformation amounts of these points, are calculated by the FEM analysis in a case that the laser beam is radiated to a single point for a purpose of brevity. The points A to D are points on a hypothetical ring  81  (shown in one dot-slash line in FIG. 3) circling along a circumference of the valve body  60 . A bonding portion  80  is the one point to which the laser beam is radiated. The point A is located on a line radially connecting between an axis of the hypothetical ring  81  and the bonding portion  80  and an angle of the point A is set circumferentially zero (0). The points B, C and D are spaced circumferentially in the hypothetical ring  81  by 90, 180 and 270 degrees from the point A, respectively. 
     In FIG. 4, the axial displacement downward in an axial direction of the hypothetical ring  81  is set to minus (−) and the axial displacement upward therein is set to plus (+). In FIG. 5, the radial displacement in a direction of expanding the radius is set to plus (+) and the radial displacement in a direction of reducing the radius is set to minus (−). 
     FIGS. 4 and 5 show only the displacements of the points A, B and C, under a comparison of the present embodiment with the conventional embodiment having no groove  65 . 
     As illustrated in FIGS. 4 and 5, each of the axial and radial displacements of the present embodiment, that is, deformation thereof, is smaller than that of the conventional embodiment.