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  
       [0001]     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  
       [0002]     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.  
         [0003]     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.  
         [0004]     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  
       [0005]     One embodiment of the present invention provides a nozzle for a low pressure fuel injector that enhances the atomization of the fuel delivered to a cylinder of an engine. The nozzle generally comprises a nozzle body defining a valve outlet in a longitudinal axis. A 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. A plurality of exit cavities are define in the metering plate which receive fuel from the nozzle cavity. Each exit cavity is radially spaced from the longitudinal axis an oriented along a radial axis. Each exit cavity meets the nozzle cavity at an exit orifice. Each exit cavity is oriented asymmetrically relative to the radial axis.  
         [0006]     According to more detailed aspects, each exit orifice has one or more axis of symmetry, and no axis of symmetry is aligned with the radial axis of the exit cavity. As such, the exit orifice may be triangular, trapezoidal, square, rectangular, ellipsoidal among numerous other shapes.  
         [0007]     Another embodiment of the present invention provides a nozzle for a low pressure fuel injector generally comprising 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, the nozzle cavity defined by a side wall and bottom wall. The metering plate also defines a plurality of exit cavities receiving fuel from the nozzle cavity. Each exit cavity is radially spaced from the longitudinal axis and is oriented along a radial axis. The side wall of the nozzle cavity is positioned adjacent the plurality of exit cavities and is structured to provide a tangential component to the fuel flowing into the plurality of exit cavities.  
         [0008]     According to more detailed aspects, the sidewalls comprise of a series or arcuate segments. Preferably, the curvature of the arcuate segments is asymmetric relative to the radial axis. Most preferably, the curvature of the arcuate segments has a changing slope. Thus, the sidewall has a flower-shape with pedals that are oblong. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     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:  
         [0010]      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;  
         [0011]      FIG. 2  is a plan view of the metering plate which forms a portion of the nozzle depicted in  FIG. 1 ;  
         [0012]      FIG. 3  is a cross-sectional view of another embodiment of a nozzle for a low pressure fuel injector constructed in accordance with the teachings of the present invention;  
         [0013]      FIG. 4  is plan view, partially cut-away, of another embodiment of the metering plate depicted in  FIG. 1 ;  
         [0014]      FIG. 5  is a plan view, partially cut-away, of another embodiment of the metering plate depicted in  FIG. 2 ;  
         [0015]      FIG. 6  is a plan view, partially cut-away, of another embodiment of the metering plate depicted in  FIG. 2 ; and  
         [0016]      FIG. 7  is a plan view, partially cut-away, of another embodiment of the metering plate depicted in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     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.  
         [0018]     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 .  
         [0019]     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 .  
         [0020]     The metering plate  40  has been uniquely designed to enhance the atomization of the fuel injected into the cylinder  10  of the engine, as will now be described with reference to  FIGS. 2 and 3 . As best seen in  FIG. 2 , the nozzle cavity  42  has been uniquely designed to introduce a swirl to the fuel flow through the exit orifices  52 , as shown by the rotating arrows in the figure. The plurality of exit orifices  52  can clearly be seen, each orifice aligned along a radial axis  57 . The nozzle cavity  42  generally takes a flower-shape, wherein a plurality of oblong pedals are disposed proximate each exit orifice which is radially spaced from the longitudinal axis  15  and center point  56  of the metering plate  40 . Stated another way, the sidewall  46  of the nozzle cavity  42  is comprised of a series of arcuate segments  48 . The curvature of each arcuate segments  48  is asymmetric relative to the radial axis  57  and have a changing slope. Stated another way, the sidewall  46  defines a plurality of triangularly shaped arms  49  which project radially inwardly. The arms  49  are located circumferentially between adjacent exit orifices  52  in their cavities  50 , have arcutate sidewalls, and are asymmetric between the two adjacent exit orifices  52 . Thus, the sidewall  46  has a radial position which varies circumferentially around the metering plate in a manner to introduce the tangential component to the fuel flowing through the exit orifices  52 .  
         [0021]     As best seen in  FIG. 3 , the bottom wall  44  may include annular portions  44 a in the area proximate each exit cavity  50  in exit orifice  52  which slope downwardly. By providing a downwardly sloping portion  44 a proximate each exit cavity  50 , the swirling effect to the fuel flow may be further enhanced.  
         [0022]     In accordance with another aspect of the present invention, the exit orifices  52  may be uniquely designed in order to even further enhance the atomization of the fuel flowing into the engine cylinder  10 . As shown in  FIG. 4 , an exit orifice  52   a  has been depicted as being triangular in shape. Notably, the triangular shaped orifice  52   a  has an axis of symmetry  59  which is not aligned with the radial axis  57  of the exit cavity  50 . Notably, the exit orifice  52   a  is oriented asymmetrically relative to the radial axis  57 .  
         [0023]     It will also be recognized that the exit orifice  52  can take many other shapes. By orienting the exit orifices  52  asymmetrically, a tangential component or swirl is further induced into the fuel flowing through the metering plate  40  and into the engine cylinder  10 . As shown in  FIG. 5 , the exit orifice  52   b  is square in shape, and includes four axes of symmetry  59   a ,  59   b ,  59   c  and  59   d . In this case, the axes  59   a - 59   d  are not aligned with the radial axis  57  of the exit cavity  50 .  FIG. 6  depicts the exit orifice  52   e  as taking a trapezoidal shape, wherein the axis of symmetry  59   e  is not aligned with the radial axis  57  of the exit cavity  50 .  FIG. 7  depicts an exit cavity  52   f  which is ellipsoidal or oblong in shape and defines an axis of symmetry  59   f  which is not aligned with the radial axis  57  of the exit orifice of the exit cavity  50 .  
         [0024]     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.