Abstract:
A nozzle for a low pressure fuel injector that improves the control and size of the spray angle, as well as enhances the atomization of the fuel delivered to a cylinder of an engine.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fuel injectors for automotive engines, and more particularly relates to fuel injector nozzles capable of atomizing fuel at relatively low pressures. 
     BACKGROUND OF THE INVENTION 
     Stringent emission standards for internal combustion engines suggest the use of advanced fuel metering techniques that provide extremely small fuel droplets. The fine atomization of the fuel not only improves emission quality of the exhaust, but also improves the cold weather start capabilities, fuel consumption and performance. Typically, optimization of the droplet sizes dependent upon the pressure of the fuel, and requires high pressure delivery at roughly 7 to 10 MPa. However, a higher fuel delivery pressure causes greater dissipation of the fuel within the cylinder, and propagates the fuel further outward away from the injector nozzle. This propagation makes it more likely that the fuel spray will condense on the walls of the cylinder and the top surface of the piston, which decreases the efficiency of the combustion and increases emissions. 
     To address these problems, a fuel injection system has been proposed which utilizes low pressure fuel, define herein as generally less than 4 MPa, while at the same time providing sufficient atomization of the fuel. One exemplary system is found in U.S. Pat. No. 6,712,037, commonly owned by the Assignee of the present invention, the disclosure of which is hereby incorporated by reference in its entirety. Generally, such low pressure fuel injectors employ sharp edges at the nozzle orifice for atomization and acceleration of the fuel. However, the relatively low pressure of the fuel and the sharp edges result in the spray being difficult to direct and reduces the range of the spray. More particularly, the spray angle or cone angle produced by the nozzle is somewhat more narrow. At the same time, additional improvement to the atomization of the low pressure fuel would only serve to increase the efficiency and operation of the engine and fuel injector. 
     Accordingly, there exists a need to provide a fuel injector having a nozzle design capable of sufficiently injecting low pressure fuel while increasing the control and size of the spray angle, as well as enhancing the atomization of the fuel. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the present invention provides a nozzle for a low pressure fuel injector which enhances the atomization of the fuel that is delivered to a cylinder of an engine. The nozzle generally comprises a nozzle body and a metering plate. The nozzle body defines a valve outlet in a longitudinal axis. The metering plate is connected to the nozzle body and is in fluid communication with the valve outlet. The metering plate defines a nozzle cavity receiving fuel from the valve outlet through an entrance orifice. The nozzle cavity is defined by a bottom wall and a side wall. The metering plate defines a plurality of exit cavities receiving fuel from the nozzle cavity. Each exit cavity is radially spaced from the longitudinal axis and oriented along a radial axis. Each exit cavity meets the nozzle cavity at an exit orifice. Each exit orifice includes an annular wall extending around the exit orifice and projecting up from the bottom wall into the nozzle cavity. 
     According to more detailed aspects, another annular wall is provided which extends around the entrance orifice and projects into the nozzle cavity. Either annular wall may follow a zig-zag line around the orifice. Either annular wall may include vertical serrations. The bottom wall in the area adjacent each exit orifice preferably includes a plurality of linear grooves. The grooves preferably extend in a direction non-aligned with the radial axis of the adjacent orifice. The annular walls may be intermittent or continuous. 
     Another embodiment of the present invention provides a nozzle for a low pressure fuel injector which delivers fuel to a cylinder of an engine. The nozzle generally comprises a nozzle body and a metering plate. The nozzle body defines a valve outlet in a longitudinal axis, while the metering plate is connected to the nozzle body and in fluid communication with the valve outlet. The metering plate defines a nozzle cavity receiving fuel from the valve outlet through an entrance orifice, the nozzle cavity defined by a bottom wall and a side wall. The metering plate defines a plurality of exit cavities receiving fuel from the nozzle cavity, each exit cavity being radially spaced from a longitudinal axis and oriented along a radial axis. Each exit cavity meets the nozzle cavity at an exit orifice. The bottom wall of the nozzle cavity in the area circumscribing each exit orifice has a plurality of linear grooves. 
     According to more detailed aspects, the grooves extend in a direction non-aligned with the radial axis of the adjacent orifice. Preferably, the grooves extend in a direction perpendicular to the radial axis of the adjacent orifice. The grooved area of the bottom wall extends completely up to the exit orifice. The grooved area may be circular, square or rectangular in shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  depicts a cross-sectional view, partially cut-away of a nozzle for a low pressure fuel injector constructed in accordance with the teachings of the present invention; 
         FIG. 2  is a plan view of an annular wall forming a portion of the nozzle depicted in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of an alternate embodiment of a metering plate forming a portion of the nozzle depicted in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view, partially cut-away, of an alternate embodiment of the metering plate forming a portion of the nozzle depicted in  FIG. 1 ; 
         FIG. 5  is a plan view, partially cut-away, of an alternate embodiment of a metering plate forming a portion of the nozzle depicted in  FIG. 1 ; and 
         FIG. 6  is cross-sectional view, partially cut-away, of the metering plate depicted in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the figures,  FIG. 1  depicts a cross-sectional of a nozzle  20  constructed in accordance with the teachings of the present invention. The nozzle  20  is formed at a lower end of a low pressure fuel injector which is used to deliver fuel to a cylinder  10  of an engine, such as an internal combustion engine of an automobile. An injector body  22  defines an internal passageway  24  having a needle  26  positioned therein. The injector body  22  defines a longitudinal axis  15 , and the internal passageway  24  extends generally parallel to the longitudinal axis  15 . A lower end of the injector body  22  defines a nozzle body  32 . It will be recognized by those skilled in the art that the injector body  22  and nozzle body  32  may be integrally formed, or alternatively the nozzle body  32  may be separately formed and attached to the distal end of the injector body  22  by welding or other well known techniques. 
     In either case, the nozzle body  32  defines a valve seat  34  leading to a valve outlet  36 . The needle  26  is translated longitudinally in and out of engagement with the valve seat  34  preferably by an electromagnetic actuator or the like. In this manner, fuel flowing through the internal passageway  24  and around the needle  26  is either permitted or prevented from flowing to the valve outlet  36  by the engagement or disengagement of the needle  26  and valve seat  34 . 
     The nozzle  20  further includes a metering plate  40  which is attached to the nozzle body  32 . It will be recognized by those skilled in the art that the metering plate  40  may be integrally formed with the nozzle body  32 , or alternatively may be separately formed and attached to the nozzle body  32  by welding or other well known techniques. In either case, the metering plate  40  defines a nozzle cavity  42  receiving fuel from the valve outlet  36 . The nozzle cavity  42  is generally defined by a bottom wall  44  and a side wall  46  which are formed into the metering plate  40 . The metering plate  40  further defines a plurality of exit cavities  50  receiving fuel from the nozzle cavity  42 . Each exit cavity  50  is radially spaced from the longitudinal axis  15  and meets the nozzle cavity  42  at an exit orifice  52 . 
     As can also be seen in  FIG. 1 , the metering plate  40  includes an annular wall  56  extending around each exit orifice  52 . Similarly, the nozzle body  32  provides an annular wall  54  extending around the entrance orifice  38 . The nozzle cavity  42  meets the valve outlet  36  at an entrance orifice  38 . Accordingly, it will be seen that fuel flowing through the valve outlet  36  must flow downwardly and radially outwardly around the annular wall  54 , and then upwardly and radially outwardly around the other annular wall  56  in order to reach the exit cavity  50 . In this manner, atomization of the fuel is enhanced by adding turbulence to the fuel flowing through the metering plate  40 . It will be recognized that the annular walls  54 ,  56  can be either continuous or intermittent. 
     Turning to  FIG. 2 , another embodiment of the annular wall  56  has been depicted and denoted as  56   a . It can be seen from the figure that the annular wall  56   a  follows a zig-zag or star-shape around the perimeter of the exit orifice  52 . It will be recognized by those skilled in the art that the other annular wall  54  may also take this shape. It can also be seen that the exit orifice  52  also takes the zig-zag shape. By way of this structure, additional turbulence is added to the fuel flow through the metering plate  40  to further enhance atomization. 
     Turning now to  FIG. 3 , yet another embodiment of the annular wall  56  is shown and is denoted as  56   b . In this embodiment, the annular wall  56   b  includes vertical serrations  57 . These serrations  57  and the annular walls  56   b  further increase the turbulence of the fuel flowing through the metering plate  40 , thereby improving the atomization of the fuel. 
     Turning now to  FIG. 4 , still yet another embodiment of the metering plate  40  is shown which increases the turbulence and enhances atomization of the fuel. As shown, the bottom wall  44  of the nozzle cavity  42  includes serrations  58  formed in an area circumscribing each exit orifice  52  in exit cavity  50 . More particularly, the serrations  58  rise above the level of the bottom wall  44  of the nozzle cavity  42 . In essence, the serrations  58  form a plurality of annular walls extending around each exit orifice  52 . It can also be seen that the serrations  58  stop short of the exit orifice  52  and leave a generally planar area  59  extending around the exit orifice  52 . 
     A related embodiment is shown in  FIGS. 5 and 6 . In this embodiment, an area  60  of the bottom wall  44  adjacent each exit orifice  52  includes a plurality of linear grooves  62 . As shown in  FIG. 6 , the grooves  62  extend downwardly into the nozzle body  40 . The grooves extend in a direction not aligned with the radial axis  55  of the adjacent exit orifice  52 , and preferably is generally perpendicular to the radial axis  55 . As best seen in  FIG. 6 , the exit orifice  52  will inherently take a serrated or zig-zag shape corresponding to the grooves  62  formed into the bottom wall  44 . The grooved area may be square or rectangular in shape, or may also generally circular in shape to correspond with the shape of the exit orifice  52 . In this manner, the fuel flow will encounter the series of grooves  62  as it flows radially outward to the exit orifice  52  and exit cavity  50 , thereby increasing the turbulence thereof and promoting atomization of the fuel flowing to the engine cylinder  10 . 
     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.