Abstract:
A fuel injector includes a flexural element connected to a valve armature for restricting radial movement of the armature within a fuel passage. The flexural element is flat and exerts no force on the valve when it is closed but is flexed when the valve is opened and supplements the valve spring force during closing of the valve. The flexural element also is used to set the valve stroke length equal to the element&#39;s thickness. A flat tool presses a valve ball into the armature while the ball is seated on a valve seat until the flexural element engages a seat related surface. Engagement of the tool with the flexural element fixed to the armature assures that the flexural element is in an unloaded flat position when the valve is closed and establishes the valve stroke when the valve assembly and seat are installed in the injector body

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation-in-part of copending U.S. application Ser. No. 09/551,690 filed Apr. 18, 2000, now abandoned. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to fuel injectors for use in an internal combustion engine and, more particularly, to a flexural element used for restricting radial movement of an armature within the passageway of the fuel injector.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is well known in the automotive engine art to provide solenoid actuated fuel injectors for controlling the injection of fuel into the cylinders of an internal combustion engine. Fuel injectors generally include a body having internal and external components which are assembled together to provide an internal fuel passage for fuel flow therein. An injection valve, including a magnetic armature, is actuated within the fuel passage to control fuel flow. In a plunger-type injector, the injector valve moves axially within the internal fuel passage. The inner walls of the fuel passage guide the axial movement of the injection valve such that there is minimal radial movement of the armature. Radial movement of the armature may cause sliding friction between the armature and other internal components of the injector which in turn decreases durability performance of the fuel injector. Therefore, it is desirable to provide a flexural element for restricting radial movement of the armature in an injector.  
           [0004]    In addition, the stroke length also needs to be controlled in order to achieve suitable flow tolerance for the fuel injector. Typically, this has been accomplished by making the position of the pole piece and/or the valve seat adjustable relative to the other components of the fuel injector. However a method for accurately setting the valve stroke during assembly of the injector is considered desirable.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with the present invention, a fuel injector is provided for use in an internal combustion engine. The fuel injector includes an injector body having an axially extending fuel passage for fuel flow therein, a valve seat fixed at an outlet end of the fuel passage, and an injection valve with an armature movable in the passage for controlling fuel flow. The fuel injector further includes a flexural element connected to the armature for restricting radial movement of the armature within the fuel passage. In another aspect of the invention, the flexural element is used to set the stroke length of the fuel injector. The stroke length is set during the injector assembly process by inserting an inner pole piece into the injector body so that the lower ends of inner and outer poles are coplanar. A valve assembly is then preferably assembled having a valve element, or ball, a magnetic armature and a flexural element. A flat tool presses the ball into the armature while the ball is seated on the valve seat until the flexural element seats on a surface of the valve seat or an associated spacer ring. Engagement of the tool with resilient beams of the flexural element fixed to a flat upper surface of the armature assures that the flexural element is in an unloaded flat position when the valve is closed and the armature, when installed, is spaced from the poles by the thickness of the flexural element which establishes the valve stroke.  
           [0006]    For a more complete understanding of the invention, its objects and advantages, refer to the following specification and to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a partial side sectional view of a fuel injector embodying features of the present invention;  
         [0008]    [0008]FIG. 2 is a cross-sectional view of the fuel injector which illustrates a first preferred embodiment of a flexural element in accordance with the present invention;  
         [0009]    [0009]FIG. 3 is a cross-sectional view of the fuel injector which illustrates an alternative preferred embodiment of a flexural element in accordance with the present invention;  
         [0010]    [0010]FIG. 4 is an enlarged side sectional view, taken along line  4 - 4  of FIG. 2, of the fuel injector of the present invention; and  
         [0011]    [0011]FIG. 5 is a flow chart illustrating a method for setting the stroke length during the assembly of the fuel injector in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]    An electromagnetic fuel injector  10  embodying features of the present invention is depicted in FIG. 1. The fuel injector  10  generally includes an injector body  12 , a solenoid actuator assembly  14 , a valve assembly  16  and a nozzle assembly  18 . While the following description is provided with reference to a disk type fuel injector, it is readily understood that the broader aspects of the present invention are applicable to other types of fuel injectors.  
         [0013]    In the illustrated construction, the injector body  12  is a hollow, cylindrical configuration defining a central axis  20 . The body  12  further includes an upper solenoid case portion  22  and an enlarged lower nozzle case portion  24 .  
         [0014]    The solenoid actuator assembly  14  is disposed within the enlarged upper solenoid case portion  22  of the injector body  12 . The solenoid actuator assembly  14  includes a spool-like, tubular bobbin  30  that supports a wound wire solenoid coil  32 . A magnetic pole piece  36  is slidably received in a central through bore  34  that extends coaxially through the bobbin  30 . In addition, a calibration sleeve  38  is fixed within the pole piece  36 . As will be more fully described below, energizing the solenoid coil  32  actuates the valve assembly  16 .  
         [0015]    A support casing  40  is formed as a tubular member that engages the upper solenoid case portion  22  of the injector body  12 . The support casing  40 , along with the outer surface of the pole piece  36  and the upper solenoid case portion  22  of the injector body  12 , enclose the solenoid assembly  14 . The support casing  40  also provides a lower end surface  42  for constraining an annular O-ring  44 . The O-ring  44  may extend around the upper solenoid case portion  22  of the injector body  12 . The O-ring  44  is also retained, in part, by the enlarged diameter of the lower nozzle portion  24  of the injector body  12 .  
         [0016]    The valve assembly  16  includes a valve element  50 , optionally a ball, and a disc-shaped armature  52  that extends radially within the lower nozzle portion  24  of the injector body  12 . The armature  52  is formed with outside diametral clearance so as to be freely axially movable within a spacer ring  54 , which is shown as a separate member but could be made as part of the valve seat if desired. A spherical ball positioned within the armature  52  in a cylindrical socket  56  interrupted by fuel passage cutouts  57 . The radius of the valve element  50  is selected for seating engagement with a valve seat  60 . As will be apparent to one skilled in the art, other embodiments of the valve assembly are within the scope of the present invention.  
         [0017]    The valve element  50  is normally biased into a closed position with the valve element  50  in seated engagement with the valve seat  60  by a biasing member, such as a coil spring  58 . The coil spring  58  is positioned within the pole piece  36  between the calibration sleeve  38  and the armature  52  as shown in FIG. 1. In this way, the position of the calibration sleeve  38  within the pole piece  36  adjusts the spring force exerted on the armature  52 .  
         [0018]    Within the lower nozzle portion  24  of the injector body  12 , the nozzle assembly  18  is retained therein by crimping over the outlet portions of the injector body  12 . The nozzle assembly  18  includes the valve seat  60  and a spacer ring  62 . The spacer ring  54  provides partial spacing for the armature  52  between an inwardly extending radial flange surface  64  of the lower nozzle portion  24  of the injector body  12  and a top surface of valve seat  60 . Surface  64  also forms an outer pole for engagement by the armature while the pole piece  36  forms an inner pole. The valve seat  60  provides a central discharge opening  66  to allow fuel flow through the valve seat  60 . The central discharge opening  66  is further defined as having a conical surface  68  which is engaged by the ball  50  of the valve in a closed position. An outer seal ring  70  is captured in an outer groove  72  of the valve seat  60 , thereby preventing fuel from leaking around the valve seat and bypassing the discharge opening.  
         [0019]    Furthermore, the central discharge opening  66  connects with a circular recess  74  on the underside of the valve seat  60 . A fuel spray director plate  76  is press fitted or otherwise retained in the circular recess  74  of the valve seat  60 . Fuel passing through the central discharge opening  66  is delivered to a director plate  76 , where it is distributed across a plurality of fuel directing openings  78  extending therethrough. The fuel directing openings  78  are oriented to generate a desired spray configuration in the fuel discharged from the injector.  
         [0020]    In operation, energizing of the solenoid coil  32  draws the armature  52  upward into engagement with the pole piece  36 , and outer pole  64  thereby moving the ball  50  upward from the central discharge opening  66  in the valve seat  60 . Fuel is then allowed to flow through the injector into an associated intake manifold or inlet port of an internal combustion engine (not shown). Upon de-energization of the solenoid coil  32 , the coil spring  58  biases the armature  52  back towards the valve seat  60 , thereby closing the injector.  
         [0021]    In accordance with the present invention, the armature  52  is connected with a flexural element  80  to form the valve assembly  16 . Referring to FIG. 2, the flexural element  80  is a disc-shaped member having an outer ring  81  surrounding an open center  82  into which upper portions of the armature  52  are movable when the solenoid coil is energized. At least two resilient beams  84  extend inwardly into the center  82  and then circumferentially about the center  82 . The armature  52  is coupled to the flexural element  80  at a distal end of each of the beams  84  by tack welds  86  or other suitable connector means.  
         [0022]    [0022]FIG. 3 illustrates an alternative embodiment of valve assembly  88  including a flexural element  90  wherein like numerals indicate like parts. The disc-shaped flexural element  90  includes an outer ring  91  surrounding an open center  92  into which upper portions of an armature  94  are movable when the solenoid coil is energized. At least two U-shaped resilient beams  96  extend inwardly into the center  92 . In this case, the armature  94  is coupled by tack welds  86  to the flexural element  90  at the base of each of the U-shaped beams  94 . Upper portions of the armature  96  also pass through the open center  92  to engage the poles  36 ,  64  when the coil  32  is energized. One skilled in the art will readily recognize that other configurations for a flexural element that would restrict the radial movement of the armature are within the scope of the present invention.  
         [0023]    In the prior and subsequent discussion, references to the valve assembly  16  or its components, valve element  50 , armature  52 , and flexural element  80  and its features are equally applicable to valve assembly  88  and its corresponding components and features except as otherwise indicated. The flexural element  80  is secured within the body  12  by clamping the outer ring  81  of the flexural element  90  between a top surface of the spacer ring  54  and the inner flange surface  64  of the injector body  12 . Pockets  97 ,  98 , corresponding to the geometry of the flexural elements  80 ,  90 , are located in the armatures  52 ,  96  adjacent to the location where the flexural elements  80 ,  90  are coupled to their armatures  52 ,  96 . As the armature  52 , lifts, the pockets  97 , serve as clearances for the flexural element  80 . Referring to FIG. 4, for example, an additional clearance  100  is provided between the inner pole piece  36  and the outer pole  64  to clear the portion of the flexural element  80  that is welded to the armature  52  so that the armature may move up to contact the poles  38  and  64 .  
         [0024]    In the valve closed position, the lower side of flexural element  80  lies coplanar with the top of the armature  52  and the spacer ring  62 . The flexural element thus lies flat in an unstressed condition wherein it applies no load on the valve assembly  16  in either the opening or closing direction. All the preload on the valve  16  is therefore provided by the coil spring  58  which may be accurately determined or set after assembly of the main injector components by adjustment of the calibration sleeve  38  to obtain the desired preload prior to fixing the sleeve  38  within the pole piece  36 . Having the flexural element at a neutral force position when the valve  16  is closed is desirable because the spring rate of the flexural element  80  is greater than that of the coil spring  58 , so any load applied by the element  80  when the valve is closed would affect the opening time of the valve assembly  16 , which is preferably maintained at a consistent value for all similar injectors.  
         [0025]    When the injector is energized, the armature  52  is lifted upward from the valve seat  60 . The attachment of the armature  52  to the flexural element  80  controls the trajectory of the armature  52  as it lifts up from the valve seat  60 . In particular, the radial stiffness of the cantilever beams  84  (or the U-shaped beams  94 ) are such that the flexural element  80 , allows for axial but minimal radial movement of the armature  52 . In this way, the flexural element  80  prevents the armature  52  from rubbing against the spacer ring or other internal components of the injector and thus creates a bearing with no sliding friction.  
         [0026]    In the open position, elastic energy is stored in the flexure element  80  and the coil spring  58 . When the injector is de-energized, the elastic energy causes the armature  52  to travel towards the valve seat  60 , thereby closing the injector and stopping the flow of fuel. Due to the high spring rate of the flexural element  80  relative to the coil spring  58 , the armature  52  closes more quickly than it otherwise would in a conventional fuel injector. Thus, the flexural element  80  also guides the trajectory of the armature  52  as it returns to the closed position.  
         [0027]    In another aspect of the present invention, the flexural element  80  is used to set the stroke length in the injector. A method for setting the stroke length during the injector assembly process is depicted in FIG. 5. The stroke length is generally set by inserting the pole piece  36  into the injector body  12  flush with the outer pole or flange surface  64 . The valve assembly  16  is then inserted into the injector body  12 , such that the flexural element  80  provides a spacing between the pole piece  36  and the armature  52 . Accordingly, this spacing sets the stroke length for the injector.  
         [0028]    More specifically, the bottom surface of the pole piece  36  is first positioned co-planar with the outer pole piece  64  of the injector. To do so, the inner pole piece  36  is fixed within the injector body  12 . The inner and outer pole pieces  36  and  64  are then simultaneously machine finished so that the bottom surfaces of the poles are coplanar. Alternatively, a flat faced tool can be used to set the pole piece position. In this case, the tool is inserted into the lower portion of the injector body and the inner pole piece  36  is firmly pressed against the nominally flat surface of the tool prior to the pole  36  piece being fixed within the injector body  12 .  
         [0029]    In another alternative, the top surface of the valve seat  60  may be used to position the pole piece  36 . The valve seat  60  is first inserted into the lower portion  24  of the injector body  12 . Next, the inner pole piece  36  is firmly pressed against the flat top surface of the valve seat  60  prior to the pole piece being fixed within the injector body  12 . The valve seat  60  can then be removed from the lower portion  24  of the injector body  12  so that the valve assembly  16  can be inserted into in the injector body  12 .  
         [0030]    Prior to inserting the valve assembly  16  into the injector body  12 , the flexural element  80  is coupled to the armature  52  of the valve assembly  16 . Preferably thereafter, the final position of the valve element or ball  50  in the armature  52  is established in any suitable manner. For example the ball may be pressed into position using a suitable fixture. However, tolerances in the components may cause unacceptable variations in the position of the armature  52 , which should have its upper surface coplanar with that of the spacer  62  when the valve element  50  is seated in the valve seat  60 .  
         [0031]    To avoid such variations, a preferable method is to first press the ball  54  into the socket  56  at a lower position in the armature  52  than desired. The valve assembly is then placed on the conical surface  68  of the actual valve seat  60  to be used in the injector  10  and the spacer  62  is placed on the valve seat. A ball setting tool with a flat lower surface surrounding the ball is then pressed down against the flat flexural element  80 , forcing the armature  52  down around the ball until the outer ring  81  of the flexural element engages the spacer ring  54 . Since the cantilever beams  84  of the flexural element  80  engage the upper surface of the armature  52 , and are in turn engaged by the ball setting tool, the armature is then spaced below the tool by the thickness of the flexural element  80 . The armature  52  is then in position so that its upper surface is coplanar with the lower surface of the flexural element  80  and the upper surface of the spacer ring  54  when the valve assembly  16  is in the valve closed position. The ball may then be fixed in the armature in the set position by laser welding or other suitable processes.  
         [0032]    The valve assembly  16  including the flexural element  80 , the spacer ring  54  and the valve seat  60  are then placed into the lower portion  24  of the injector body  12  and a portion of the outer wall is crimped over in order to retain these elements in the injector body  12 . It is envisioned that other techniques may be used to affix the valve seat  60  to the injector  12 . The coil spring  58  biases the valve element  50  against the valve seat  60  in the valve closed position so that the armature is spaced from the magnetic poles  36 ,  64  by the thickness of the flexural element  80 . Thus, the stroke of the injection valve assembly  16  for the armature to contact the poles  36 ,  64  is set equal to the thickness of the flexural element  80  by the setting of the valve ball or element  50  in the armature  52  with the flexural element  80  used as a spacer in the setting step.  
         [0033]    While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.