Abstract:
A fuel injector having a pulsed air assist atomizer to provide improved atomization and fuel spray targeting. The fuel injector provides a pulsed air supply, rather than a continuous air supply at the discharge of the fuel injector. The fuel injector includes an air inlet, a fuel inlet, mixing chamber and controller for controlling the simultaneous introduction of air and fuel into the mixing chamber. The controller controls an air jet to impact fuel flowing into the mixing chamber to atomize the fuel before discharge of the air-fuel mixture from the fuel injector.

Description:
FIELD OF THE INVENTION 
     This invention relates to air assist fuel injectors used in internal combustion engines and in particular to a fuel injector with a pulsed air assist atomizer. 
     BACKGROUND OF THE INVENTION 
     It is known in the art relating to fuel injectors to atomize the fuel injected through the nozzle of a fuel injector. In such fuel injection systems, fuel is atomized into a finely divided spray of small droplets by mixing air with the fuel upon discharge of the mixture from the fuel injector. Air assist atomization of the fuel injected from the fuel injector is used to produce a homogeneous air-fuel mixture. The homogeneity of the air-fuel mixture and gasification of fuel droplets in the combustion space affect the efficiency of the combustion process. A better mixture of air and fuel will produce both a cleaner and a more efficient combustion process. Therefore, it is desirable to obtain a fuel injector that has optimum atomization and accurate fuel spray targeting. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fuel injector which supplies pulsed air, rather than a continuous supply of air through the fuel injector. By supplying pulsed air, the atomization and fuel spray targeting are improved. The fuel injector includes air inlet means, fuel inlet means, a mixing chamber and control means for simultaneously controlling introduction of air and fuel into the mixing chamber. 
     In one embodiment, the fuel injector includes two electromagnetically actuated valves that are used to control an air jet that impacts fuel flowing into a mixing chamber. The controlled air and fuel flows provide atomization of the fuel before discharge of the air-fuel mixture from the injector. The two valves are part of an armature/valve assembly. The assembly includes an armature, air control valve head and hollow needle which forms part of a fuel control valve. The armature is connected to the hollow needle. The air control valve head is mounted on a first axial inlet end of the hollow needle. 
     In a closed position, the valve head and a second axial outlet end of the needle are seated against an air valve seat and fuel valve seat, respectively, to prevent air and fuel flow into the mixing chamber. Upon energization of an electromagnetic coil, the armature is attracted to a stator and the valve head and needle are lifted from their seats to allow air and fuel flow into the mixing chamber. As the fuel enters the mixing chamber, it is impacted by the air jet resulting in a finely atomized spray. Then the air-fuel mixture is discharged from the fuel injector through a central opening in the fuel valve seat. 
     These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with a general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a cross-sectional view of a fuel injector in accordance with the present invention; 
     FIG. 2 is an enlarged schematic view of the lower end of the fuel injector, illustrating a hollow needle in an open position allowing fuel and air to mix in a mixing chamber during discharge of the fuel injector; and 
     FIG. 3 is an enlarged schematic view of the upper end of the fuel injector, illustrating an air control valve head in an open position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, numeral  10  generally indicates a fuel injector including a pulsed air assist atomizer. The fuel injector  10  provides a pulsed air jet that impacts the fuel when fuel is being discharged from the injector  10 , and not as a continuous air supply as in conventional air assist injectors, thereby improving the atomization of the fuel. 
     With reference to FIGS. 1 and 2, the injector  10  includes a plastic cover  12 . The plastic cover  12  surrounds upper portions of a tubular stator  14  and a coil assembly housing  16 . Coil assembly  18  surrounds a lower portion of stator  14 . Stator  14  is ferromagnetic and has an air inlet  20  at a first axial end  22  of the stator  14  connected to a pressurized air supply  23 . Below the coil assembly  18  is a valve body  24  in which an armature  26  is reciprocally disposed and positioned coaxially with a second axial end  28  of the stator  14 . 
     The armature  26  is connected with a hollow needle  30  which has an air control valve head  32  mounted on a first axial inlet end  34  of the needle  30  to form an armature/valve assembly  36 . The valve head  32  may be in the form of a poppet valve. The armature/valve assembly  36  is movable between open and closed positions to permit or prevent air and fuel flow into a mixing chamber  38  at the discharge end of the fuel injector. The valve head  32  and a second axial outlet end  40  of the needle  30  are normally urged against an air valve seat  42  and a fuel valve seat  44 , respectively, in their closed positions by a spring  46  which engages the valve head  32 . The spring  46  is compressed to desired force by an adjustment tube  48  which is pressed to an axial position within the stator  14  and defines the air inlet  20 . The air valve seat  42  forms one end of a valve tube  50  which is pressed to a mounted axial position within the stator  14 . The valve tube  50  extends from the spring  46  to the second axial end  28  of the stator  14 . 
     The needle  30  and valve head  32  are simultaneously unseated from their seats  44 ,  42  to their open positions to allow fuel and air flow in the mixing chamber  38  when the armature  26  is magnetically attracted to the stator  14  upon energization of the coil assembly  18 . The coil assembly  18  includes a plastic bobbin  52  on which an electromagnetic coil  54  is wound. Electrical terminals  56  are connected between an electrical circuit (not shown) and the coil  54  for providing energizing voltage to the coil that operates the fuel injector  10 . 
     The hollow needle  30  has a central air passage  60  extending from the first axial inlet end  34  of the needle  30  to the second axial outlet end  40  of the needle  30 . The air passage  60  conveys air from the air inlet  20  to the mixing chamber  38 . Air enters the air passage  60  through air holes  62  in the first axial end  34  of the needle  30  as shown in FIG.  3 . The diameter of the hollow needle  30  may be larger than a conventional valve needle to accommodate the air passage  60 . If a needle  30  with a larger diameter is used, a lower valve lift is required to pass the fuel thereby supplying a thinner fuel film which enhances atomization from the air jet. 
     The armature  26  is guided by an inside wall of the valve body  24  for axial reciprocation. The upper portion of the hollow needle  30  is guided within the valve tube  50 . Further, axial guidance for the needle  30  is provided by a fluid metering member  66  through which the hollow needle  30  extends. The fluid metering meter  66  is disposed within the valve body  24  upstream from the fuel valve seat  44 . 
     Fuel from a fuel supply  67  enters the fuel injector  10  through fuel inlets  68  in the valve body  24 . A filter assembly  70  is fitted to the fuel inlets  68  to filter particulate matter from the fuel entering the valve body  24  through the inlets  68 . Filtered fuel flows through the fluid metering member  66  which provides a thin fuel film to be impacted by the air jet from the second axial end  40  of the hollow needle  30  in the mixing chamber  38 . The fluid metering member  66  may be a swirl generator plate or an orifice plate. The member  66  is located upstream from the mixing chamber  38 . Also, the air-fuel mixture may be metered by a second metering member  72 , such as a thin orifice disk, located downstream from the fuel valve seat  44  at the discharge end of the fuel injector  10 . 
     In operation, fuel enters the fuel inlets  68  and passes through the filter assembly  70  into the valve body  24  and through opening  64  in the fluid metering member  66  to the fuel valve seat member  44 . When the coil  54  is not energized, the hollow needle  30  and air control valve head  32  are biased by the spring  46  into their respective closed positions and a small working gap  74  exists between the armature  26  the stator  14 . 
     Upon energizing of the coil  54 , the armature  26  is magnetically attracted to the second axial end  28  of the stator  14 , closing the working gap  74 . This movement simultaneously unseats the hollow needle  30  from the fuel valve seat  44  and lifts the air control valve head  50  from the air valve seat  42 , allowing fuel film to be impacted by an air jet in the mixing chamber  38 , resulting in a finely atomized spray. The atomized spray is discharged from the fuel injector through a central opening  76  in the fuel valve seat  44 . Upon deenergizing of the coil  54 , the spring  46  pushes the hollow needle  30  and air control valve head  32  back to their closed positions, shutting off fuel and air flow. 
     Although the invention has been described by reference to a specific embodiment, 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 embodiment, but that it have the full scope defined by the language of the following claims.