Abstract:
An upper guide system for a solenoid actuated fuel injector of an internal combustion engine includes an armature and a guide ring having a cylindrical shape and surrounding the armature and positioning the armature in a radial direction. The location of the upper guide system is substantially in the same axial location as the radial magnetic forces imposed on the armature. Features such as flutes or grooves are disposed on an outer diameter surface of the armature and/or holes through a body portion of the armature. Accordingly, the response performance of the solenoid actuated fuel injector is improved.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to fuel injection systems for internal combustion engines; more particularly, to solenoid actuated fuel injectors; and most particularly, to a ring guided armature of the injector including armature features that enable improved injector performance. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fuel injected internal combustion engines are well known. 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, resulting in better fuel economy and lower emissions. This is accomplished by the combustion of a precisely controlled charge of fuel under various operating conditions. DI is also designed to allow higher cylinder compression ratios, delivering higher performance with lower fuel consumption compared to other fuel injection systems. 
         [0003]    Generally, an electromagnetic fuel injector incorporates a solenoid armature/pintle assembly, located between the pole piece of the solenoid and a fixed valve seat. The armature/pintle assembly typically operates as a movable valve assembly and, therefore, represents the moving mass of the fuel injector. Electromagnetic fuel injectors of the pulse width type meter fuel per electric pulse at a rate of flow proportional to the width of the electric pulse. In a normally closed injector, when an injector is de-energized, its movable valve assembly is released from one stop position and accelerated by a spring towards the opposite stop position, located at the valve seat to close the valve. 
         [0004]    As the magnetic forces act radially on the armature to open the valve, the moving mass of a fuel injector must be guided in its radial direction to keep the pintle axially aligned with the seat in order for flow control across the seat to be robust and precise. Further, controlled axial alignment of the pintle helps to reduce wear between the pole piece and armature, and between the pintle and seat to provide a fuel flow rate within an established tolerance for the life of the components of the armature/pintle assembly. Thus, the guidance of the moving mass of the fuel injector is critical to function, performance, and durability of the injector. Moreover, DI injectors require a relatively high fuel pressure to operate that may be, for example, as high as about 4000 psi compared to about 60 psi required to operate a typical MPFI injector. Due to the higher operating pressure, the fuel flow of DI injectors is more sensitive to variations in the axial movement and alignment of the armature/pintle assembly than MPFI injectors. 
         [0005]    Several methods to control the alignment of the moving mass of a fuel injector are currently employed. For example, in some cases, the pintle itself is used as the guide surface. However, since the guide location is axially distanced from the location of the radial load imposed on the armature by the magnetic forces, the friction imposed on the moving mass in the area of the guide surface can be high. 
         [0006]    In other prior art guide systems, the outside diameter of the armature is used as the guide surface. While this locates the guide surface at the same axial location as the magnetic radial forces imposed on the armature, the surface area of the outside diameter of the armature that makes contact with the guide is much greater adding to the frictional losses imposed on the moving mass and contributing to a reduction in injector response time. 
         [0007]    What is needed in the art is an upper guide system for the moving mass of a solenoid actuated injector that aligns the upper guide location with the location of the radial forces imposed on the armature and that reduces the contact area at the guide point to reduce friction. 
         [0008]    It is a principal object of the present invention to provide an upper guide system of a solenoid actuated injector with a reduced surface contact area. 
       SUMMARY OF THE INVENTION 
       [0009]    Briefly described, an upper guide system for the moving mass of a solenoid-actuated injector includes a ring guided upper guide system that serves to position the armature of the solenoid in a radial direction. The location of the upper guide system is closely aligned with the radial magnetic forces acting on the armature. 
         [0010]    The ring guided upper guide system in accordance with the invention includes a guide ring having a hard surface possessing relatively good wear properties. The armature is preferably plated with a relatively hard material as well to reduce wear between the armature and guide ring. 
         [0011]    Further, the armature in accordance with the invention includes features that reduce the area of contact of the guide system. The reduced contact area diminishes the hydraulic or viscous drag between the armature and the guide ring. Accordingly, these features improve the performance of the injector compared to injectors with prior art guide systems. 
         [0012]    In one aspect of the invention, the features having a variety of shapes and sizes are disposed on the outside diameter surface of the armature. In another aspect of the invention, other features are formed through the body of the armature to improve injector performance. A combination of these features may be incorporated in a single armature. The features incorporated in the armature in accordance with the invention for reducing the area of contact may include grooves or flutes that run in an axial direction along the outer diameter surface of the armature; the flutes may be straight or helical. The features may also be one or more circumferential grooves on the outer diameter surface of the armature. The other features to improve injector performance may include axial or radial holes formed in the armature. 
         [0013]    By including these features in the armature, separately or in combination, the suction forces between the armature and pole piece when the injector is de-energized, and/or the viscous tension between the armature and guide surfaces are reduced thereby improving injector response time. Further, through the strategic placement of these features, the magnetic flux density and the eddy current formation around the armature may be tuned. Also, by incorporating these features into the armature, a reduction in moving mass and an improvement in fuel flow past the armature can be realized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0015]      FIG. 1  is a cross-sectional view of a solenoid actuated fuel injector, in accordance with a first embodiment of the invention; 
           [0016]      FIG. 2  is a schematic diagram of the reaction forces acting on an armature pintle assembly of the solenoid actuated fuel injector, in accordance with the first embodiment of the invention; 
           [0017]      FIG. 3  is a top plan view of an armature pintle assembly of the fuel injector, in accordance with a second embodiment of the invention; and 
           [0018]      FIG. 4  is a cross-sectional view along line  4 - 4  of the armature pintle assembly of the fuel injector, in accordance with the second embodiment of the invention. 
       
    
    
       [0019]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates preferred 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 
       [0020]    Referring to  FIG. 1 , a solenoid actuated fuel injector  10  includes an upper housing  12 , a lower housing  14 , a pole piece  16  positioned between upper housing  12  and lower housing  14 , an actuator housing  18  connecting upper housing  12  with lower housing  14 , an armature/pintle assembly  20 , and a coil assembly  22  surrounding pole piece  16 . Upper housing  12 , lower housing  14 , and pole piece  16  enclose a fuel passage  24 . Pole piece  16  may be chromium plated to reduce wear caused by the pole piece being impacted by the armature/pintle assembly  20 . Fuel injector  10  may be a fuel injector for direct injection. 
         [0021]    Armature/pintle assembly  20  includes a pintle  26 , a valve  28 , such as for example a ball, and an armature  40 . Armature  40  is secured to a first end of pintle  26 , for example, by using a weld block  32 . Valve  28  is fixed at an opposite end of pintle  26 . Armature pintle assembly  20  constitutes the moving mass of fuel injector  10 . Armature/pintle assembly  20  is assembled within lower housing  14  for reciprocating movement in an axial direction along axis  30  within fuel passage  24 . A spring  34 , for biasing valve  28  toward its mating seat  36 , may be positioned in a center bore formed in pole piece  16  above armature/pintle assembly  20 . Solenoid actuated fuel injector  10  meters fuel per electric pulse that is applied to coil assembly  22  at a rate proportional to the width of the electric pulse. When injector  10  is de-energized, movable armature/pintle assembly  20  is released from a first stop position where armature  40  is in contact with pole piece  16  and is accelerated by spring  34  and the fuel pressure in passage  24  towards the opposite second stop position, located at the valve seat  36  integrated into lower housing  14 . The distance in which valve  28  travels between the first and the second stop position constitutes the stroke of fuel injector  10 . 
         [0022]    In accordance with the present invention, fuel injector  10  further includes a guide ring  38  as part of an upper guide system for armature/pintle assembly  20 . Guide ring  38  has a cylindrical shape and surrounds armature  40 . The outer diameter of guide ring  38  is adapted to closely fit into an inner circumferential contour of lower housing  14  so as to be secured in place by the housing. The inner diameter of guide ring  38  is adapted to receive armature  40  with a minimal circumferential air gap between the armature and guide ring. Accordingly, guide ring  38  is positioned between armature  40  and lower housing  14  and, therefore, in substantially the same axial location as the radial magnetic forces acting on armature  40  when the solenoid is energized. Guide ring  38  may be assembled in a fixed position relative to lower housing  14 , for example, by welding. Armature  40  is reciprocably movable within guide ring  38  and, because of the minimal clearance between guide ring  38  and armature  40 , guide ring  38  positions armature  40  in a radial direction to thereby align the armature/pintle assembly  20  relative to the contact surfaces of pole piece  16  and seat  36 . The contact surface of guide ring  38  is hard and may be formed, for example, of a martensitic stainless steel or be chrome plated, thereby providing relatively good wear properties. The surface of the guide ring proximate the armature preferably has a smooth finish that can be achieved, for example, by grinding. To reduce wear at the interface between armature  40  and guide ring  38 , armature  40  may be plated with a relatively hard material, such as chromium or titanium nitride. Fuel in fuel passage  24  moving towards valve seat  36  lubricates the bearing area between armature  40  and guide ring  38 . While guide ring  38  has been shown and described as placed within lower housing  14 , it may be possible to assemble guide ring  38  in another part of the housing of fuel injector  10  so as to be aligned with the armature, such as, for example, actuator housing  18 . 
         [0023]    Referring to  FIG. 2 , reaction forces acting on armature pintle assembly  20  of solenoid actuated fuel injector  10  typically include a radial magnetic force  42 , a pintle-to-lower housing contact reaction force  44 , and a valve reaction force  46 . By including guide ring  38  in the assembly of fuel injector  10  and by positioning guide ring  38  to be aligned with radial magnetic force  42  as shown in  FIG. 1 , lateral movement of armature  40 , in the direction of arrow  42 , can be reduced compared to prior art fuel injector assemblies without guide ring  38 . Furthermore, including guide ring  38  in the assembly of fuel injector  10  reduces or eliminates pintle contact reaction force  44  compared to prior art fuel injector assemblies and reduces valve reaction force  46  because lateral movement of the armature is limited. 
         [0024]    Armature  40  includes features  50 , such as through holes  52  shown in  FIGS. 1 and 2  or flutes  54  on the outer diameter surface of armature  40  shown in  FIGS. 3 and 4 . Features  50  reduce the hydraulic or viscous drag imposed on the armature by the surface tension of the fuel between the pole piece and armature and the surfaces of the guide and the armature, thereby improving the response time of the injector. The features also enable tuning of the magnetic flux density and eddy current formation around the armature, and improve the passage of fuel through the injector. 
         [0025]    Features  50  located on the outside diameter surface  48  of armature  40  or in the body  49  of armature  40  may take on a number of shapes and forms. For example, features  50  located on the outside diameter surface  48  of armature  40  may include a plurality of straight flutes  54  formed substantially parallel with axis  30  (shown in  FIGS. 3 and 4 ) or helical flutes (not shown). Features  50  may also include one or more circumferential grooves (not shown) on the armature&#39;s outer diameter surface proximate the middle of armature  40 . Features  50 , as axial through holes  52  or radial through holes (not shown), may also be formed in the body of the armature. Features  50  may be evenly spaced along outer diameter surface  48  of armature  40 , as shown in  FIG. 3 , or may be unevenly spaced along outer diameter surface  48  of armature  40 . Additionally, through holes, such as holes  56  may be placed at the inner circumference of armature  40 . 
         [0026]    While the grooves and flutes, in accordance with the invention, have been described as being formed on the outside diameter surface of the armature, the grooves and flutes may also be formed on the surface of the guide proximate the armature. 
         [0027]    While the upper guide system has been described for a fuel injector for direct injection it may be applied to other solenoid actuated fuel injectors. 
         [0028]    While exemplary forms of features  50  have been described, features  50  may take on other forms. 
         [0029]    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.