Abstract:
A method of directly setting an injector lift that involves the provisioning of a valve body having an uniform internal diameter, inserting a sleeve assembly to a predetermined distance and securing the sleeve assembly. The apparatus includes a sleeve, a lower armature guide and a seat, all of which can be integral so as to facilitate the setting of the injector lift. The sleeve assembly is press-fitted and secured by known attachment techniques.

Description:
[0001]    This application claims the benefits of provisional application 60/223,981 filed 9 Aug. 2000, which is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Examples of known fuel injector use an armature assembly having an armature that reciprocates between an open position and a closed position. The distance that the armature travels is known as an injector lift height, working air gap or distance. The working air gap or distance is one of many variables that determine the amount of fuel that will be dispensed outside the fuel injector when the injector is actuated.  
           [0003]    The air gap is believed to be set by first taking a series of direct contact measurements. One direct measurement is believed to determine the distance between a contact face of a pole piece of the armature assembly and a sealing diameter of a seat. Another direct measurement is believed to determine the distance between the sealing diameter of a seat and the position of a closure member during a full open position. The difference between these two measurements determines the approximate working gap. The actual working gap is believed to be set by using a deformable ring that is inserted into a shoulder formed at one end of a valve body. The ring is subsequently crushed to the approximate working gap.  
           [0004]    The actual working gap, however, may vary between individual injectors due to variations in the direct measurement operations, the deformability of the crush ring material or the valve body. Moreover, the direct measurements oftentimes can introduce contaminants into the fuel injector, leading to the possibility of inconsistent injector performance. Additionally, the crushing operation is believed to introduce undesirable structural loading on the body of the injector. Furthermore, the use of crush ring is believed to require random samplings of the crush ring and injectors to maintain consistent injector performance. Finally, once the crush ring is installed or crushed, it is believed that no adjustment can be made unless the crush ring is extracted and replaced with a new one.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a fuel injector for use with an internal combustion engine. The fuel injector comprises a housing having a flow passage extending along a longitudinal axis between a first end and a second end; an electromagnetic actuator including a stator having an end face; an armature assembly proximate the electromagnetic actuator, the armature assembly having a surface in confronting arrangement with the end face; spring means to establish a gap between the end face and the surface; a flow metering device disposed within the flow passage proximate the second end, the flow metering device engaging the armature assembly; and a sleeve disposed along the longitudinal axis within the flow passage at a preset position, the sleeve bearing against the flow metering device to define the gap.  
           [0006]    The present invention further provides a method of setting a working gap of an armature assembly in a fuel injector. The fuel injector includes a housing including a first end and a second end extending between a longitudinal axis, a housing having a flow passage extending between the first and second ends, an electromagnetic actuator including a stator and an armature assembly, a spring disposed between the stator and the armature assembly and operable to push the armature assembly towards the second end to form a gap therein. The method comprises inserting a sleeve and a flow metering assembly within the flow passage, the flow metering assembly limiting the movement of the armature assembly towards the second end, and limiting the inserting of the flow metering assembly along the longitudinal axis toward a first end by a position of the sleeve, the position defining the magnitude of the gap between the stator and the armature assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The accompanying drawing, which is incorporated herein and constitutes part of this specification, illustrates an embodiment of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention.  
         [0008]    [0008]FIG. 1 is a cross-sectional view of the sleeve arrangement in a fuel injector. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]    Referring to FIG. 1, an enlarged partial view of a fuel injector extending between axis A-A, having a housing or valve body  200 , an armature assembly  210  and a ferromagnetic coil  220  disposed between inlet end  300 A and outlet end  300 B. The armature assembly  210  can include an armature  212 , armature tube  216  and a closure element  218 . The armature tube  216  can be integrated with the armature  212  for a two-piece armature assembly. Alternatively, the armature tube  216  can be integrated with the closure  218 . The armature assembly  210  is magnetically coupled to the electromagnetic actuator assembly  220  that includes a pole piece or a stator  214 , coil  220  and bobbin  224 . The valve body  200  is affixed to a shell  350  that is further affixed to the pole piece  214 . An elastic member  225  that can be a coil spring is disposed between the movable armature  214  and the fixed stator  214 . The elastic member  225  operates to bias the armature assembly  210  towards the outlet end  300 B of the injector, thereby forming a gap Δ between the stator  214  and the armature  212 . Although disclosed as a single spring, the elastic member  225  can include more than one coil spring for a multi-spring rate elastic member. A flow metering device or seat  244  at the outlet end  300 B of the injector engages the armature assembly  210 , and prevents the elastic member  225  from pushing the armature assembly  210  out of the valve body  200 . Where the seat  244  is located defines how far the elastic member  225  can separate the armature assembly  210  from the stator  214 . In other words, the elastic member  225  and seat  244  cooperate to define a working gap Δ between the armature  212  and the stator  214 . Finally, the location of the seat  244  also sets a spring preload on elastic member  225  that acts on the armature assembly  210  by the elastic member  225 .  
         [0010]    When the ferromagnetic coil assembly  220  is energized, magnetic flux is generated in the coil  220 , which flows to the armature assembly  210  to complete a magnetic circuit between the coil  220  and the armature assembly  210 . This causes the armature assembly  210  to move axially towards the stator  214 , against the biasing force of the elastic member  225  to close the working gap Δ. The working gap Δ, also known as an injector lift height, determines the volume of fuel to be dispensed when the injector is energized. The greater the working gap Δ, the greater the volume of fuel that can be dispensed. Thus, adjusting the working gap will also adjust the volume of fuel dispensed.  
         [0011]    If the working gap Δ is too large, however, it is believed that the magnetic flux generated in the coil  220  may not be sufficient to allow the armature  212  to move against the elastic member  225 , thereby resulting in little or no fuel dispensed. If the working gap is too small, however, it is believed that the armature  212  will see a much stronger magnetic flux, causing the armature  212  to bounce off the stator  214  causing, it is believed, uneven fuel atomization or even droplets formation in an intake manifold. Thus, injector performance is believed to be highly dependent on the correct working gap.  
         [0012]    To initiate the process of setting the working gap Δ, a sleeve  240  is inserted in the valve body  200  to a predetermined distance Li. By virtue of the sleeve&#39;s outside diameter being substantially the same as the inside diameter of the valve body  200 , a “working” fit can be made between the sleeve  240  and the valve body  200 . “Working fit”, as used here, can include a locational clearance fit, a locational interference fit or a transitional fit. Next, the lower armature guide  242  and the seat  244  are then inserted in the valve body  200  until one of the armature guide  242  or the seat abuts the sleeve  240 .  
         [0013]    To facilitate the insertion in the valve body  200 , the valve body  200  is provided with a generally uniform internal diameter for a major portion of its length. Alternatively, the valve body  200  can also be provided with an uniform internal diameter that extends the whole length of the valve body  200 . The valve body  200  itself can also be a polygonal tube that will, of course, correspondingly require matching polygonal-shaped sleeve  240 , armature guide  242  and seat  244 .  
         [0014]    The sleeve  240  can be further secured to the valve body  200  by any one of a number of techniques including bonding, welding, tack welding and preferably laser welds. The seat  244  can be affixed by one of a number of techniques noted above. Preferably, the seat  244  can be hermetically welded to the valve body  200 .  
         [0015]    The sleeve  240  is an annulus having an outside diameter substantially equal to the internal diameter of the valve body  200 . The length of the sleeve  240  along the longitudinal axis can be at least twice the internal diameter of the valve body  200 . The annular thickness of the sleeve is preferably between 75% and 100% of the thickness of the valve body  200 . Alternatively, the thickness of the sleeve  240  can be between 5%-25% of the inside diameter of the valve body  200 . The sleeve  240  can be formed by a stamped, a casting, deep drawn or it can be formed by machining a blank. Finally, the sleeve  240  can be made of a nonmagnetic material, which is believed to reduce magnetic flux leakage from the armature assembly.  
         [0016]    The armature guide  242  and seat  244  can be integrated together into a single unit. This is believed to reduce the number of steps involved in loading the seat  244  and armature guide  242  in the valve body  200  during manufacturing of a fuel injector. Specifically, the integrated unit is of such dimensions that when the unit is inserted in the valve body  200 , the desired lift height is achieved when the seat  244  is flush with the end face  201  of the valve body  200 .  
         [0017]    Referring again to FIG. 1, the injector&#39;s working gap Δ is determined as a function of the difference between distance L2 and distance L3 with one of the datum being the sealing diameter  300  of the seat  244 . To ensure that the working gap Δ is correctly set, a tool that is similar to a bearing driver can insert the sleeve  240 . Such a tool would have a preset insertion depth Li. The distance Li at which the sleeve  240  can be inserted is determined by the sum of the thickness “T” (defined as the thickness of the seat and the armature guide  242  as measured from the sealing diameter  300  to the surface abutting the sleeve  240 ) and the distance L1 (as measured between the end face  214   a  of pole piece and the end face  201  of the valve body  200 ) minus the distance L2 (as measured between the end face of the pole piece  214   a  and the sealing diameter  300 ).  
         [0018]    In particular, to set the injector working gap or height, a valve body  200  is provided in a fuel injector. The valve body  200  has a substantially uniform internal diameter extending along the longitudinal axis A-A. An armature assembly  210  including an armature  212 , an armature tube  216  and a closure member  218  is inserted in the valve body  200 . The sleeve  240  is then inserted to a predetermined depth Li from the end face  201  of the valve body  200 . The lower armature guide  242  and the seat  244  are then inserted. The sleeve  240  is then affixed by known attachment techniques including laser welding, bonding or tack welding. The seat  244  can also be affixed in any one of the known techniques for attaching materials. Alternatively, if the sleeve  240 , the guide  242  and the seat  244  are integrated as a one-piece assembly, the assembly, i.e. the lift assembly, can be inserted in a single operation until the seat  244  is flush with the end face  201  of the valve body  200 .  
         [0019]    As can be seen above, one of the advantages of the preferred embodiment is that the working gap Δ can be changed by simply moving the sleeve  240 . This is done by calculating the insertion depth Li based on known values of L1, L2 and T. Once a new insertion depth Li is calculated, the sleeve  240  can be quickly adjusted by moving the sleeve  240  axially along the longitudinal axis A-A of the injector to the desired depth Li.  
         [0020]    Additionally, the sleeve  240  is not limited to any one type of fuel injector but can also be used with a modular type fuel injector. Similar to the fuel injector of FIG. 1, the sleeve  240  can be inserted into the modular valve body to a predetermined depth while the guide  242  and the seat  244  are also loaded into the injector.  
         [0021]    Several benefits are believed to be achieved by the use of the sleeve  240 . Costs associated with the manufacturing of the fuel injector is believed to be reduced because a shoulder for crushing the ring is no longer required to be formed on the valve body  200 . In particular, the sleeve  240  is believed to reduce the number of manufacturing operations by virtually eliminating direct contact measurements to ensure a correct lift height. Furthermore, an accurately dimensioned boss portion on the valve body  200  to ensure sufficient crushing of the crush ring is believed to be redundant and no longer required. Additionally, by using an integral unit of the sleeve, guide  242  and seat  244 , setting the lift height can be a one step operation. Finally, the use of the sleeve  240  is believed to maintain consistent working gap between individual injectors.  
         [0022]    While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the fill scope defined by the language of the following claims, and equivalents thereof.