Patent Publication Number: US-7895751-B2

Title: Variable shim for setting stroke on fuel injectors

Description:
TECHNICAL FIELD 
     The present invention relates to fuel injection systems of internal combustion engines; more particularly, to solenoid actuated fuel injectors; and most particularly, to a variable shim and valve seat assembly and to a simplified method for setting the injector valve stroke. 
     BACKGROUND OF THE INVENTION 
     Fuel injected internal combustion engines are well known. Fuel injection is a way of metering fuel into an internal combustion engine. Fuel delivery is typically through engine intake ports but is more recently directly into the cylinder through the engine head. Accordingly, fuel injection arrangements may be divided generally into multi-port fuel injection (MPFI), wherein fuel is injected into a runner of an air intake manifold ahead of a cylinder intake valve, and direct injection (DI), wherein fuel is injected directly into the combustion chamber of an engine cylinder, typically during or at the end of the compression stroke of the piston. DI is designed to allow greater control and precision of the fuel charge to the combustion chamber, providing the potential for better fuel economy and lower emissions. DI is also designed to allow higher compression ratios, providing the potential for delivering higher performance with lower fuel consumption compared to other fuel injection systems. As the industry moves more towards the fuel delivery directly into the cylinder, it is highly desirable in a modern internal combustion engine to provide high pressure fuel injectors that more precisely deliver fuel. 
     Generally, fuel injectors rely on internal valves to open a precise distance to deliver exact amounts of fuel to the engine. An electromagnetic fuel injector incorporates a solenoid armature, located between the pole piece of the solenoid and a fixed valve seat. The armature typically operates as a movable valve assembly. Electromagnetic fuel injectors are linear devices that meter fuel per electric pulse at a rate proportional to the width of the electric pulse. When an injector is energized, its movable valve assembly is lifted from one stop position against the force of a spring towards the opposite stop position. The distance between the stop positions constitutes the stroke. 
     A solenoid actuated fuel injector for automotive engines is required to operate with a small and precise stroke of its valve in order to provide a fuel flow rate within an established tolerance. The stroke of the moving mass of the fuel injector is critical to function, performance, and durability of the injector. Injectors for gasoline DI require a relatively high fuel pressure to operate. The fuel pressure may be, for example, as high as 1700 psi compared to about 60 psi required to operate a typical port fuel injection injector. Due to the higher operating pressure, the fuel flow of gasoline DI injectors is more sensitive to variations in stroke than port fuel injection injectors and, therefore, a tighter control of the stroke set is needed. Typically, a stroke tolerance of about +/−5 microns is desired for GDI injectors where a tolerance of about +/−14 microns is acceptable for port fuel injection injectors. 
     Methods for controlling the exactness of the valve opening are an ongoing design and manufacturing challenge. Current fuel injectors use a variety of methods to set and control the displacement of the valve. For example, adjusting the pole piece location is currently the most commonly used method for setting the stroke on fuel injectors. This method involves precisely pressing the pole piece to a position that gives the required valve displacement. Shortcomings of this method are the complexity of the part design, especially the achievement of the needed tolerances, and the process of accurately pressing the pole piece to the right depth without pressing too far. This approach also requires an external structure for the pole piece to slide inside thus adding more parts and cost. The sliding motion between the external structure and internal pole piece can also generate undesirable contamination in the injector. Stroke setting tolerance with this process can generally be in a +/−12 micron range. 
     Another current approach includes a threaded valve seat outer diameter and a threaded body inner diameter. By threading the outer diameter of the seat and the inner diameter of the body that the seat mates with, valve stroke is adjusted by controlling the depth that the seat is screwed into the body. This design is typically used on port injectors and functionally works satisfactory. The major shortcomings of this approach are the difficulty and cost of creating the very fine threads on the outer diameter of the small and hard seat as well as cutting threads on the inner diameter of the body. Once the correct stroke is set using this approach, the seat is typically spot welded to the body. An o-ring is usually fitted between the seat and the body to assure that no leakage occurs. Stroke setting tolerances with this process can generally be in a +/−12 micron range. 
     Still another approach is the selective flat shim method. The selection of a flat shim of a precise thickness to give the desired valve displacement is a long used method in high-pressure fuel injectors. The process typically involves taking interfacing component measurements, calculating the appropriate shim thickness, selecting the shim, and installing the shim into the injector during assembly. Shortcomings are that a large number of high precision shims of various thicknesses need to be on hand and ready for assembly. The mating part measurements are complex and difficult to integrate into a high volume manufacturing operation. Stroke setting tolerances with this process can generally be in a +/−5 micron range or better if disassembly and reassembly with a different shim is allowable. The shim selection method for setting the fuel injector stroke is, therefore, a very high cost process. 
     What is needed in the art is a simplified method for setting valve displacement in a fuel injector that involves fewer parts to be assembled, that involves parts that can be easily manufactured, and that can be easily integrated into a high volume manufacturing operation. It is a principal object of the present invention to provide a variable shim and valve seat assembly that enables a simplified method for setting the injector valve stroke. 
     SUMMARY OF THE INVENTION 
     Briefly described, a variable shim and valve seat assembly in accordance with the invention includes single ramped surfaces, such as a single face thread, or multiple ramped surfaces as features on the top surface of an injector valve seat and a mating shim surface. Valve stroke setting is achieved by rotating the seat relative to the injector body, thus moving the seat inward or outward depending on the direction of rotation. Once the desired valve stroke is set, the seat is welded to the injector body to achieve a leak free interface. The amount of seat displacement is dependent on the designed ramp angle, the number of ramps, and the degree of rotation. Stroke setting tolerances that can be achieved with the variable shim may be improved over known prior art methods since the seat can be axially loaded to create a significant force between the shim and seat face surface features during stroke setting and welding. Stroke setting tolerance may be in a +/−3 to 5 micron range. 
     In an alternative embodiment of the invention, the shim geometry may be included in the injector body eliminating the shim as a separate part. 
     The variable shim and seat assembly may be assembled in any injector that depends on an accurate displacement of a valve mechanism to control the delivery of fuel. The method for setting the valve displacement in a fuel injector in accordance with the invention is simple, utilizes parts that can be easily manufactured at relatively low costs, and provides for accurate setting of the injector stroke. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of a solenoid actuated fuel injector, in accordance with the invention; 
         FIG. 2   a  is an isometric view of a variable shim, in accordance with a first embodiment of the invention; 
         FIG. 2   b  is an isometric view of a valve seat, in accordance with the first embodiment of the invention; 
         FIG. 3   a  is an isometric view of a variable shim, in accordance with a second embodiment of the invention; 
         FIG. 3   b  is an isometric view of a valve seat, in accordance with the second embodiment of the invention; and 
         FIG. 4  is a cross-sectional view of a shim and seat assembly in accordance with a third embodiment of the invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates referred embodiments of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a solenoid actuated fuel injector  100  includes a cartridge assembly  110  and a solenoid assembly  120 . Fuel injector  100  may be, for example, an injector for direct injection. 
     Cartridge assembly  110  includes all moving parts and fuel containing components of injector  100 , such as an upper housing  112 , a lower housing  114 , a pole piece  116  positioned between upper housing  112  and lower housing  114 , and a valve assembly  130 . In one aspect of the invention, lower housing  114  may include a circumferential groove  138  or may be otherwise thinned out at the outer circumference for application of a continuous hermetic laser penetration weld. Upper housing  112 , lower housing  114 , and pole piece  116  enclose a fuel passage  118 . 
     Solenoid assembly  120  includes all external components of injector  100 , such as an actuator housing  122 , an electrical connector  124 , and a coil assembly  126 . Solenoid assembly  120  surrounds pole piece  116 . 
     Valve assembly  130  includes a pintle  132  having a ball  134  attached at one end and having an armature  136  attached proximate to an opposite end. Valve assembly  130  further includes a valve seat  140  assembled within lower housing  114  at a lower end  119 . Valve seat  140  may extend beyond lower end  119  of lower housing  114 . An inner diameter of lower housing  114  is designed to receive an outer diameter of valve seat  140  such that valve seat  140  is axially and radially movable within lower housing  114 . Valve seat  140  extends axially from a top surface  142  to a bottom surface  144 . Bottom surface  144  of valve seat  140  includes a plurality of spray holes that may be opened or closed by ball  134 . Valve seat  140  may be formed, for example, by metal injection molding. Armature  136  is positioned proximate to pole piece  116 . Ball  134  is positioned within valve seat  140 . Valve assembly  130  constitutes the moving mass of fuel injector  100 . Valve assembly  130  is positioned within lower housing  114  such that reciprocating movement of valve assembly  130  is enabled. 
     Solenoid actuated fuel injector  100  is a linear devices that meters fuel per electric pulse at a rate proportional to the width of the electric pulse. When injector  100  is de-energized, reciprocating valve assembly  130  is released from a first stop position where armature  136  contacts pole piece  116  and accelerated, for example by a spring  128 , towards the opposite second stop position, located at bottom surface  144  of valve seat  140 . The displacement of valve assembly  130  between the first and the second stop position constitutes the stroke of valve assembly  130 . 
     A variable shim  150  is preferably positioned adjacent to top surface  142  of valve seat  140 . Variable shim  150  may be installed within lower housing  114  in a fixed position, for example with a light press fit, such that shim  150  may not rotate within lower housing  114 . Shim  150  and valve seat  140  include mating features  160  at an interface  154 , such as mating single ramped surfaces  156 / 146  (shown in  FIGS. 2   a  and  2   b , respectively) or mating multiple ramped surfaces  158 / 148  (shown in  FIGS. 3   a  and  3   b , respectively) that enable easy and accurate setting of the stroke of valve assembly  130  by rotation of valve seat  140  relative to variable shim  150  and, consequently, relative to lower housing  114 . Shim  150  may be formed from a material that has a relatively high hardness and is highly fuel resistant, for example stainless steel. Shim  150  may be, for example, a machined part, a cold formed stamped part, or a metal injection molded part. 
     In an alternative embodiment, mating feature  160 , such as single ramped surface  156  ( FIG. 2   a ) or multiple ramped surface  158  ( FIG. 3   a ) included in shim  210  or  310 , respectively, may be integrated in the lower housing  114  of fuel injector  100 . Mating feature  160  may be formed at an inner circumferential contour of lower housing  114 . Accordingly, shim  150  could be eliminated as separate part. In the alternative embodiment, lower housing  114  may be formed as a deep drawn part to save cost over a machined part. 
     Referring to  FIGS. 2   a  and  2   b , a variable shim  210  and a mating valve seat  220  are illustrated, respectively, in accordance with a first embodiment of the invention. Variable shim  210  includes a face  152  that is designed as a single ramped surface  156 . Valve seat  220  includes a top surface  142  that is designed as a single ramped surface  146 . Single ramped surfaces  156  and  146  of shim  210  and seat  220 , respectively, are mating surfaces. Single ramped surfaces  146  and  156  may be designed as a single face thread. Single ramped surfaces  146  and  156  may include a single helical rise/fall in 360 degrees forming a single ramp  162 . The angle of ramp  162  may be selected in accordance with a specific application. Variable shim  210  and valve seat  220  may be assembled in fuel injector  100  as shim  150  and seat  140 . 
     Referring to  FIGS. 3   a  and  3   b , a variable shim  310  and a mating valve seat  320  are illustrated, respectively, in accordance with a second embodiment of the invention. Variable shim  310  includes a face  152  that is designed as a multiple ramped surface  158 . Valve seat  320  includes a top surface that is designed as a multiple ramped surface  148 . Multiple ramped surfaces  158  and  148  of shim  310  and seat  320 , respectively, are mating surfaces. Multiple ramped surfaces  158  and  148  may be designed to include a plurality of helical rises/falls in degrees forming multiple ramps  162 . While shim  310  and seat  320  are shown each to include three ramps  162 , any other number of ramps  162  may be realized if desired for a specific application. The angle of ramps  162  may be selected in accordance with a specific application. Variable shim  310  and valve seat  320  may be assembled in fuel injector  100  as shim  150  and seat  140 . 
     Referring to  FIG. 4 , a shim and seat assembly  400  in accordance with a third embodiment of the invention includes a variable shim  410  and a valve seat  420  assembled in lower housing  430  of a fuel injector (such as fuel injector  100  shown in  FIG. 1 ). Mating features  160  formed in seat  420  and shim  410  at an interface  402  may be either single ramped surfaces  146 / 156  as shown in  FIGS. 2   a  and  2   b  or multiple ramped surfaces  148 / 158  as shown in  FIGS. 3   a  and  3   b . Valve seat  420  may include recesses  422  that facilitate rotation of seat  420  relative to lower housing  430 . Contrary to  FIG. 1 , where lower housing  114  is shortened and valve seat  140  extends beyond lower end  119 , bottom surface  424  of valve seat  420  is flush with a lower end  432  of lower housing  430  except in the areas of recesses  422 . In further contrast to  FIG. 1 , lower housing  430  does not include a thinned out area at the outer circumferential contour for application of a continuous hermetic laser penetration weld. Still, a 360-degree laser penetration weld may be applied on close proximity to interface  402  of shim  410  and seat  420  by radially welding through lower housing  430  into seat  420 . 
     Referring to  FIGS. 1 through 4 , stroke setting of valve assembly  130  is achieved by rotating valve seat  140  or  420  relative to variable shim  150  or  410 , respectively. Due to the mating features  160  included in shim  150  or  410  and valve seat  140  or  420 , such as mating single ramped surfaces  156 / 146  (shown in  FIGS. 2   a  and  2   b , respectively) or mating multiple ramped surfaces  158 / 148  (shown in  FIGS. 3   a  and  3   b , respectively), valve seat  140  or  420  may be moved inward or outward of lower housing  114  or  430  depending on the direction of rotation. Accordingly, mating features  160  provide axial displacement of valve seat  140  or  420  through rotation of valve seat  140  or  420  relative to variable shim  150  or  410 , respectively. The amount of seat displacement is dependent on the ramp angle, the number of ramps, and the degree of rotation of valve seat  140  or  420  relative to lower housing  114  or  430 , respectively. 
     Once the desired valve stroke is set, valve seat  140  or  420  is fixed to lower housing  114  or  430 , respectively, for example by welding, and preferably by laser penetration welding. Preferably a continuous weld is formed for 360 degrees between valve seat  140  or  420  and lower housing  114  or  430 . Laser penetration welding has the advantage that a hermetic seal is created between valve seat  140  or  420  and lower housing  114  or  430  concurrently, eliminating the need for separate sealing features. As shown in  FIG. 1 , the lower housing may be thinned out, for example by forming groove  138 , at the location of the weld. The weld is preferably located in close proximity to the seat/shim interface  154  or  402  and as far away as possible from the position of ball  134 . During stroke setting and welding processes, an axial load may be applied to valve seat  140  or  420  creating a significant force at the interface  154  or  402  of shim  150  or  410  and valve seat  140  or  420 . Application of this load enables stroke setting within tight tolerances and prevents changes to the stroke due to the heat development during the welding process. As a result, tolerances in a range of about 3-5 microns may be achieved. 
     The displacement or stroke setting of valve assembly  130  in fuel injector  100  is done prior to the calibration of fuel injector  100 , preferably in the cartridge assembly state of the manufacture. Valve seat  140  needs to be in a fixed position relative to lower housing  114  before the spray holes included in bottom surface  144  of valve seat  140  are oriented relative to solenoid assembly  120 . 
     While variable shims  150 ,  210 ,  310 , and  410  and valve seats  140 ,  220 ,  320 , and  420  have been shown and described for assembly in direct injection fuel injector  100 , they may be useful in any type of injector that depends on an accurate displacement of a valve mechanism, such as valve assembly  130 , to control the delivery of any type of fuel. 
     By integrating mating features into the interfacing surfaces of the shim and the valve seat (such as shims  150 ,  210 ,  310 , and  410  and valve seats  140 ,  220 ,  320 , and  42 ), accurate setting of the injector valve stroke is enabled with simple parts that can be manufactured relative easily and at relatively low costs and with a simple stroke setting method. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.