Patent Publication Number: US-6655611-B2

Title: Electromagnetic fuel injector comprising flexible element for positioning armature

Description:
TECHNICAL FIELD 
     The present invention relates to fuel injectors for delivery of fuel to the intake system of an internal combustion engine and, more particularly, to an electromagnetic fuel injector having a disk-shaped armature. 
     BACKGROUND OF THE INVENTION 
     Inclusion of a disk-shaped instead of a cylindrical armature in an electromagnetic fuel injector provides important advantages, including compactness, a substantial reduction in the mass of the armature, greatly diminished sliding friction during operation of the injector, and a consequent reduction in wear. Use of a disk-shaped armature, however, also presents some problems. During operation of the injector, the armature must be relatively precisely positioned as it contacts the valve seat in order to sufficiently prevent or control the flow of fuel to the combustion chamber. In operation, the armature is urged toward the valve seat by a return spring. The spring acts on a relatively small surface area of the armature. The return spring force is often not uniform on the surface. Uneven spring forces may tilt or tip the armature or otherwise fail to properly seat the armature on its valve seat. A conventional disk-shaped armature has a tendency to tip as it returns to its closed position, resulting in improper valve seating and undesirable fuel leakage. In the past, disk-shaped armatures have been treated with a lubricious coating to reduce friction and binding so as to encourage proper seating alignment. Coating of the armature, which requires additional processing steps, adds to the manufacturing costs of the armature. Also, in the prior art, in order to encourage proper seating alignment, disk-shaped armatures have been hinged to the mating seat. The hinged design requires precise assembly techniques which again adds to the manufacturing costs. Thus, there is a continuing need for a fuel injector comprising a disk-shaped armature that is reliably returned to a proper alignment with a valve seat during operation of the injector. Also, what is needed in the art is a reliable and inexpensive way of accomplishing this. These needs are addressed by the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an electromagnetic fuel injector having a disk-shaped armature that is biased in the closing direction by a ring-shaped flexible element and maintains a degree of lateral and rotational freedom to reliably seat itself when biased closed. The fuel injector of the present invention comprises a body having a fuel inlet and a fuel outlet and a base having a valve seat. A disk-shaped armature is disposed at the fuel outlet for controlling the flow of fuel. The armature has an upper surface and a lower surface that comprises a sealing interface with the valve seat. A flexible element comprising a ring, and at least one flexible leg projecting from the ring is in contact with the injector body and the upper surface of the armature and provides a spring bias between the body and armature upper surface. When the injector is closed, a spring bias from the return spring and the flexure act on the armature upper surface to maintain the armature in a sealing position with the valve seat, while permitting a degree of lateral and rotational freedom for the armature to be positioned flatly on the seat. When the injector is open, the return spring is compressed and the flexure is bent. With the injector open, there is an increase in spring bias between the body and armature upper surface to impel the armature to return to a sealing position with the valve seat when the solenoid is de-energized. 
     By disposing the flexures on the outer annular surface of the armature, the combined bias forces of the spring and the flexures are more stable and reliable in seating the armature than a spring only embodiment. The flexure forces provide a seating force on the outside of the armature to balance the central seating force of the return spring. With the invention, spring seating forces act on both the central surface portion of the armature and outer peripheral annular portions of the armature. Thus, the seating force is distributed across the surface of the armature and is not concentrated directly above the valve seat. By distributing the seating forces across the upper face of the armature, the invention more reliably seats the armature on the valve seat. 
     The flexures also provide radial inward forces that urge the armature to a centered position over the valve seat. As such, the flexures provide some radial restraint to resist lateral displacement of the armature during its travel from its open to its closed position on the valve seat. The invention does not require the hinges used by conventional injectors. Instead, the invention relies on the radial bias forces of the flexures to generally center the armature without connecting the armature to the valve seat. 
     An advantage of the present invention is that an inexpensive, reliable disk-shaped armature can be used in an electromagnetic fuel injector without the need for coating the armature or hinging the armature to assure proper seating. 
     Another advantage of the present invention is that some traditional, costly, precision assembly techniques need not be used to manufacture the fuel injector. 
     A further advantage of the present invention is that the disk-shaped armature is positively urged to return to a proper alignment with its valve seat during operation of the injector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are side cross-sectional views of two embodiments of the fuel injector of the present invention shown in its closed position that include a ring-shaped flexible element situated between the valve body and the armature. 
     FIG. 3 a  is an upper plan view depicting a disk-shaped armature and one embodiment of a flexible element in accordance with the present invention. 
     FIG. 3 b  is a cross-sectional view of the embodiment shown in FIG. 3 a , taken along line A—A. 
     FIG. 4 a  is an upper plan view depicting a disk-shaped armature and a further embodiment of a flexible element in accordance with the present invention. 
     FIG. 4 b  is a cross-sectional view of the embodiment shown in FIG. 4 a , taken along line B—B. 
     FIG. 4 c  is an isometric view of a disk-shaped armature provided with locking depressions for receiving the legs of a flexible element in accordance with the present invention. 
     FIG. 5 a  is an upper plan view depicting a disk-shaped armature and yet a further embodiment of a flexible element in accordance with the present invention. 
     FIG. 5 b  is a cross-sectional view of the embodiment shown in FIG. 5 a , taken along line C—C. 
     FIG. 5 c  is a top view of the flexible element shown in FIG. 5 a.    
     FIG. 5 d  is a cross-sectional view of the flexible element shown in FIG. 5 c , taken along line D—D. 
     FIG. 5 e  is an isometric view of the flexible element shown in FIGS. 5 c  and  5   d.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 schematically depicts a fuel injector  100  comprising a body  101  having a fuel inlet  102  and a fuel outlet  103  and sealably connected to a base  104  that includes a valve seat  105 . Fuel injector  100  generally operates as described in U.S. Pat. No. 5,348,233, the disclosure of which is incorporated herein by reference. A disk-shaped armature  106 , which is constructed of a magnetic material, preferably stainless steel, includes an upper surface  107  and a lower surface  108  that provides a sealing interface with valve seat  105 . 
     Body  101  includes a solenoid actuator  109  and a closing spring  110 . A ring-shaped flexible element  111 , constructed of a non-magnetic material such as, for example, austenitic stainless steel, is positioned between body  101  and armature  106  and is attached to armature upper surface  107  by, for example, spot welds  112 . Flexible element  111  has an outer diameter slightly smaller then the inner diameter of a spacer ring  113  disposed between body  101  and base  104 . Solenoid actuator  109 , when energized, causes armature  106  to be urged upward and away from valve seat  105  thereby compressing return spring  110  and flexing flexible element  111 . On deactivation, return spring  110  and flexible element  111  causes armature  106  to move downward and armature lower surface  108  to seal against valve seat  105 , thereby shutting off the flow of fuel. The operation of flexible element  111  facilitates the sealing of armature  106  with valve seat  105  and permits a degree of lateral and rotational movement of armature  106 . 
     The return spring acts on the central portion of the armature. The flexure acts on the peripheral portion. The flexure force acts on the outer annular portion of the flexible element to urge the armature against the valve seat. The flexible element  111  also acts radially to urge the armature into a central position above the valve seat. Nevertheless, the flexible element  111  provides sufficient lateral flexibility to accommodate some lateral displacement of the armature and still seat the armature on the valve seat. 
     FIG. 2 depicts a further embodiment of the present invention, fuel injector  200 , comprising a body  201  having a fuel inlet  202  and a fuel outlet  203  and sealably connected to a base  204  that includes a valve seat  205 . A disk-shaped armature  206 , which is constructed of a magnetic material, preferably stainless steel, includes an upper surface  207  and a lower surface  208  that optionally includes a ball element  208   a  that seals against valve seat  205 . Body  201  includes a solenoid actuator  209  and a closing spring  210 . A ring-shaped flexible element  211 , constructed of a non-magnetic material, is clamped between body  201  and a spacer ring  212  that is disposed between body  201  and base  204 . Solenoid actuator  209 , when energized, causes armature  206  to be urged upward and away from valve seat  205  thereby compressing return spring  210  and flexing flexible element  211 . On deactivation, return spring  210  and flexible element  211  causes armature  206  to move downward and armature lower surface  208  to sealably contact valve seat  205 , thereby shutting off the flow of fuel. The operation of flexible element  211 , which facilitates the sealing of armature  206  with valve seat  205 , and permits a degree of lateral and rotational movement of armature  206 . 
     FIGS. 3 a  and  3   b  show a disk-shaped fuel injector armature  301  and a ring-shaped flexible element  302  (corresponding to flexible element  111  in FIG. 1) that includes a ring portion  309 , and three spaced, outwardly projecting flexible legs  303   a ,  303   b , and  303   c . Flexible legs are disposed between upper surface  304  of armature  301  and injector body surface  312  and in contact with injector body surface  312 . Ring portion  309  of flexible element  302  is attached to armature upper surface  304  by, for example, spot welds  305 . Armature  301  optionally comprises three spaced apart sectors  310   a ,  310   b , and  310   c , which are separated by clearance pockets  306   a ,  306   b , and  306   c . Each sector comprises recesses  313  which provide clearance for flexible element  302  to reside when the solenoid is activated and armature  301  is urged upward and away from valve seat. Armature  301  further optionally includes a centrally disposed ball element  307  surrounded by apertures  308 . 
     Flexible element  302  is in contact with the injector body surface  312  and with upper surface  304  of armature  301  and provides a spring bias between the body and upper surface  304 . Each of the outwardly projecting legs  303   a, b, c  is located in one of clearance pockets  306   a, b, c . When the fuel injector is in a closed position, spring bias between the body and armature upper surface  304  maintains armature  301  in a sealing position with the valve seat. As armature  301  lifts under the influence of magnetic force to its open position, flexible element  302  is deflected, thereby increasing spring bias between the body surface  312  and armature upper surface  304  and urging armature  301  to return to a sealing position with the valve seat. Since there is a slight clearance between the outer diameter of flexible element  302  and the inner diameter of the spacer ring (spacer ring  113  in FIG.  1 ), armature  301  has sufficient lateral and rotational freedom both to allow its proper seating with the valve seat and minimize sliding friction during opening and closing of the injector. 
     FIGS. 4 a  and  4   b  depict a disk-shaped fuel injector armature  401  and a ring-shaped flexible element  402  (corresponding to flexible element  211  in FIG. 2) that includes a ring portion  403  and three spaced, inwardly projecting flexible legs  404   a ,  404   b , and  404   c , which are in contact with an upper surface  405  of armature  401 . Ring portion  403  of flexible element  402  is clamped between the injector body surface  408  and spacer ring  409 . Armature  401  optionally includes a centrally disposed ball element  406  surrounded by apertures  407 . 
     Flexible element  402  operates in a manner substantially similar to that describe for flexible element  302 . When the fuel injector is closed, spring bias between the body surface  408  and armature upper surface  405  maintains armature  401  in a sealing position with the valve seat, and when the injector is open, increased spring bias between the body surface  408  and armature upper surface  405  impels armature  401  to return to a sealing position with the valve seat. 
     When the fuel injector is in its closed position, the preload exerted by flexible legs  404   a, b, c  stabilizes armature  401  to control its attitude. With the injector in the open position, the deflection of legs  404   a, b, c  provides additional spring force to facilitate proper seating of armature  401 . Since flexible element  402  is not attached to armature  401 , it has sufficient freedom of lateral and rotational movement to ensure its proper positioning. 
     As depicted in FIG. 4 c , upper surface  405  of armature  401  optionally may further include locking depressions  410   a, b, c  positioned to receive flexible legs  404   a, b, c  of flexible element  402 . The width of each depression, depicted as numeral  411  in FIG. 4 c , is selected to be slightly greater than the width of corresponding flexible legs  404   a, b, c  of flexible element  402 . This allows for rotation fitting of element  402  with armature  401 . 
     In FIGS. 5 a ,  5   b ,  5   c ,  5   d  and  5   e  are shown a disk-shaped armature  501  and a ring shaped flexible element  502  that includes an annular portion  509  and three spaced, outwardly projecting flexible legs  503   a ,  503   b , and  503   c.  As depicted in FIG. 5 b , each of the flexible legs  503   a ,  503   b  and  503   c  terminate in a downwardly extending portion  505  that is (substantially orthogonal to ring portion  509  and legs  503   a ,  503   b  and  503   c.  Flexible legs  503   a ,  503   b  and  503   c  are disposed between upper surface  504  of armature  501  and injector body surface  512  and in contact with injector body surface  512 . Ring portion  509  of flexible element  502  is attached to armature upper surface  504  by, for example, spot welds (not shown). Armature  501  further optionally includes three spaced apart sectors  510   a ,  510   b  and  510   c  which are separated by clearance pockets  511   a ,  511   b  and  511   c.    
     Flexible element  502  is in contact with injector body surface  512  and with upper surface  504  of armature  501  and provides a spring bias between the body and upper surface  504 . Each of the outwardly projecting flexible legs  503   a ,  503   b  and  503   c  is located in one of clearance pockets  511   a ,  511   b  and  511   c . When the fuel injector is in a closed position, spring bias between the body and upper surface  504  maintains armature  501  in a sealing position with the valve seat. As armature  501  lifts under the influence of magnetic force to its open position, flexible element  502  is deflected, thereby increasing spring bias between body surface  512  and armature upper surface  504  and urging armature  501  to return to a sealing position with the valve seat. Since there is a slight clearance between the downward portion  505  of flexible legs  503   a ,  503   b  and  503   c , and the inner diameter of lower body portion  508 , armature  501  has sufficient lateral and rotational freedom both to allow it proper seating with the valve seat and to minimize sliding friction during opening and closing of the injector. 
     In the embodiment shown, in FIGS. 4 a ,  4   b  flexible legs  404   a ,  404   b  and  404   c  of flexible element  402  are evenly spaced and project radially inward along diametral paths. However, it is to be understood that flexible legs  404   a ,  404   b  and  404   c  may be alternately configured and positioned, such as, for example, unevenly spaced and projecting inward at angles other than along diametral paths. 
     In the embodiments shown, three flexible legs are depicted. However, it is understood that the flexible elements may be alternately configured, having any number of flexible legs more or less than three. 
     The invention has been described in detail for the purpose of illustration, but it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the following claims.