Pulsed air assist fuel injector

Abstract: A fuel injector (10) 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 means (20) , fuel inlet means (68), mixing chamber (38) and control means for controlling the simultaneous introduction of air and fuel into the mixing chamber. The control means 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. US-A-4 834 291 discloses a fuel injector for an internal combustion engine including a body having fuel and air inlet ports and fuel and air outlet ports located within the combustion chamber of the engine cylinder. A pair of valves open and close the air and fuel outlet ports and are sequenced so that fuel is introduced into a flow of air and the flow of air continues briefly after the fuel flow has been discontinued. Summary of the Invention According to the present invention there is provided a fuel injector for an internal combustion engine as described in claim 1. The invention will now be described by way of example with reference to the accompanying drawings. Brief Description of the Drawings 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 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, dosing 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 32 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.

Claims: A fuel injector (10) for an internal combustion engine, comprising: an air supply inlet (20); a fuel supply inlet (68); a mixing chamber (38) located at a discharge end of the fuel injector for mixing air and fuel; a control member for controlling the simultaneous introduction of air and fuel into said mixing chamber (38), the control member including: an armature/valve assembly (36) movable between valve open and closed positions to admit or prevent air and fuel flow into the mixing chamber (38), the armature/valve assembly (36) including: a fuel control valve having a hollow needle (30) defining a central air passage (60) for conveying air from a first axial end (34) of said needle (30) to a second axial end (40) of said needle (30), said hollow needle (30) being movable between valve open and closed positions to unseat or seat the second axial end (40) of the needle (30) from or against a valve seat (44) to admit or prevent fuel flow into the mixing chamber (38); an armature (26) connected with said hollow needle (30) and movable toward and away from a tubular stator (14) to simultaneously open or close the fuel and air control valves and admit or prevent fuel and air flow into the mixing chamber (38); a coil assembly (18) surrounding the tubular stator (14) for generating electromagnetic forces to magnetically attract the armature/valve assembly (36) to the stator (14) to allow air and fuel to flow into the mixing chamber (38); and biasing means (46) for biasing the armature/valve assembly (36) away from the stator (14) toward the valve closed position to prevent air and fuel from flowing into the mixing chamber (38) characterised by an air control valve head (32) mounted on the first axial end (34) of the hollow needle (30) and said valve head (32) being movable with the needle (30) between open and closed positions to unseat or seat the valve head (32) from or against an air valve seat (42) to admit or prevent air flow into the central air passage (60). A fuel injector (10) as in claim 1 wherein the air control valve is a poppet valve and the first axial end (34) of the hollow needle (30) has air holes (62) for allowing air to flow into the central air passage (60). A fuel injector (10) as in claim 1 wherein the biasing means (46) is a spring (46) acting between said air control valve head (32) and an adjustment tube (48) fixed in said air supply inlet (20). A fuel injection system comprising: an air supply (23) providing a flow of assist air; a fuel supply (67) providing a supply of fuel; and a fuel injector (10) as in any one of claims 1 to 3.

Inventors: PACE JEFF B, WARNER VERNON R, PACE, JEFF B., WARNER, VERNON R.
Applicants: SIEMENS VDO AUTOMOTIVE CORP, SIEMENS VDO AUTOMOTIVE CORPORATION
Application year: 1999
Main classification: F02M67
IPC codes: F02M67, F02M61, F02M51, F02M69