AIR ASSIST FUEL INJECTOR

Abstract: A method of air metering is providing for obtaining a desired air flow through a fuel injector (10). The fuel injector (10) comprises an air assist injector valve body (28) and an air assist back up washer (37), having two or more flow channels (76), contained within the valve body (28). The fuel injector (10) further comprises a shroud member (52) having a non-parallel surface and a flat surface, wherein the non-parallel surface abuts up against the back up washer (37) so the flat surface of the shroud member (52) combined with the flow channels in the back up washer (37) meter and/or direct the air flow.

Description: AIR ASSIST FUEL INJECTOR Field of the Invention This invention relates generally to fuel injectors of the type that are used to inject liquid fuel into the induction system of an internal combustion engine and having an atomizer that fits over the tip end of the injector to promote the atomization of the liquid fuel ejected by the fuel injector, and particularly to metering and directing the air required for an air assist fuel injector. Background of the Invention Air assist atomization of the liquid fuel ejected from the tip end of a fuel injector is a known technique that is used to promote better preparation of the combustible air/fuel mixture that is introduced into the combustion chambers of an internal combustion engine. A better mixture preparation promotes both a cleaner and a more efficient combustion process, a desirable goal from the standpoint of both exhaust emissions and fuel economy. Future engine emission requirements have driven the need to achieve better atomization of the fuel, breaking up the liquid fuel into small droplet size that would result in more thorough or efficient combustion. The improved atomization has been accomplished by a technique generally referred to as 'air assist', whereby when additional air at sonic velocity is aimed at the fuel, the impact of the air results in the air energy breaking up the liquid fuel droplets into droplets of a fine mist. This is then still aimed at the intake valve. The state of the art contains a substantial number of patents relating to air assist atomization technology. The technology recognizes the benefits that can be gained by the inclusion of special assist air passages that direct the assist air into interaction with the ejected liquid fuel. Certain air assist fuel injection systems use pressurized air, from either a pump or some other source of pressurization, as the assist air. Other systems rely on the pressure differential that exists between the atmosphere and the engine's induction system during certain conditions of engine operation. It is a common technique to mount the fuel injectors in an engine manifold or fuel rail or engine head which is constructed to include assist air passages for delivering the assist air to the individual injectors. Although several different methods of metering the air stream have been successful, one of the challenges in mass production of air assist fuel injectors remains in being able to take a production injector, and with a minimum number of design and processing changes, make it easily adaptable to an air assist application. Typically the design consists of three main parameters, which include the actual metering of the air to accomplish a known flow, a component for directing the flow, and the packaging required to contain the necessary seals to the engine. One of the past concepts utilized a cup shaped metal air shroud, containing a through hole of limited size on the bottom of the cup. The cup was attached to the injector by welds through the side of the cup, to the outer diameter of the valve body. The air flow was metered, or restricted, by the circumference of the through hole, multiplied by the height that the through hole was away from the end of the injector. The injector shroud assembly would be flowed with air, and the height of the cup from the end of the valve body would be altered, in a calibrated manner, until the air flow desired was achieved. This concept was advantageous in that the same assembly could be utilized for a range of desired air flows, to match the range of customer demands for different air calibrations. However, the disadvantages include the requirement to have a calibrations step in the assembly/manufacturing process, which results in additional process time and cost. Furthermore, the direction of the metered air flow is perpendicular to the direction of the fluid flow, which has not been shown to be advantageous for fluid targeting geometry. An alternative concept consisted of a metal shroud containing a metal air metering disc. The bottom portion of the cup sandwiched the disc to the end of the fuel injector, typically containing a special backup washer that protruded from the end of the injector. The metering area was formed by the metering disc, with at least one channel allowing air passage from the outer diameter of the shroud, to the inner, exit hole of the shroud. The air shroud/metering disc assembly was attached to the valve body typically by a staking operation, deforming the shroud into the valve body. This concept had advantages in that the assembly process did not require a calibration operation, since the flow variation was kept to a minimum by the accuracy of the manufacturing process for the metering disc. Additionally, the air metering disk design was such that split stream air assist was feasible. However, the air flow in this concept is once again perpendicular to the fluid flow. It is seen then that there exists a need for a method of air metering which allows any standard injector with a backup washer to be converted to an air assist injector, capable of air flow direction at different angles, which have targeting benefits. Summary of the Invention This need is met by the air assist metering apparatus and method, according to the present invention. A typical injector valve body contains a backup washer; for air assist, this backup washer has a relatively thick width. The surface of the washer protrudes beyond the crimp area of the valve body, and contains a flat surface which serves to seal the air metering disc. The present invention utilizes the air assist backup washer as the air metering or air directing component. In accordance with one embodiment of the present invention, a method of air metering is provided for obtaining a desired air flow through a fuel injector. The fuel injector comprises an air assist injector valve body and an air assist backup washer, having two or more flow channels, contained within the valve body. The fuel injector further comprises a shroud member having a non-parallel surface and a flat surface, wherein the non-parallel surface abuts up against the backup washer so the flat surface of the shroud member combined with the flow channels in the backup washer meter and/or direct the air flow. It is an advantage of the present invention that it eliminates the need for an additional disk or insert to cooperate to provide the desired air flow. Consequently, the present invention provides the advantage of a higher quality air assist injector which is easier to manufacture. For a full understanding of the nature and objects of the present invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings and the appended claims. Brief Description of the Drawings In the Drawings: Fig. 1 is a prior art longitudinal view through a fuel injector containing an air assist atomizer; Fig. 2 is an enlarged view of a fuel injector outlet end, similar to that of Fig. 1 , illustrating the air assist metering concept of the present invention; Fig. 3 is a view of a backup washer of Fig 2 taken along line 3- 3; and Fig. 4 is an alternate embodiment of the backup washer of Fig 3. Description of the Preferred Embodiment Referring now to Fig. 1 , there is shown, for purposes of description only, an electrically operated fuel injector 1 0 containing an air assist atomizer 1 2. The fuel injector 1 0 has a main longitudinal axis 14 and is a top-feed type device comprising an inlet 1 6 and a nozzle 1 8 at its opposite axial ends. The passage of liquid fuel through the fuel injector between the inlet 1 6 and the nozzle 1 8 is controlled by the seating and unseating of the rounded tip end of a metal needle 20 on and from a valve seat 22 located just interior of the nozzle 1 8. The needle 20 is resiliently biased by a spring 24 to seat on the seat 22 thereby closing the passage to flow. When the valve is electrically energized by the delivery of electric energizing current to its solenoid coil 26, the needle unseats to allow fuel flow. Figs. 1 and 2 show the fuel injector closed. When the engine is operating, the pressure in the induction passage associated with the fuel injector is sub-atmospheric. Hence, a pressure difference exists across the atomizer, and this differential is effective to cause air to pass axially through the atomizer and exit at the tip end of the atomizer, associated with the injector outlet 1 8 which sprays out a fuel spray. The air that passes through the atomizer acts on the fuel spray as it is being emitted from the injector tip end to assist in the atomization of the liquid fuel entering the induction passage. The construction in the vicinity of the nozzle, or outlet end 1 8, of the fuel injector of Fig. 1 is shown in greater detail in Fig. 2, but incorporating the construction of the present invention. The fuel injector comprises a generally tubular metal valve body 28 which contains in order of assembly at the nozzle end, a metal needle guide member 30, a metal valve seat member 32, and in Fig. 1 a metal retainer member 36. Typically, the air assist injector valve body contains a special air assist backup washer 37. The upper surface 39 of the backup washer 37 protrudes beyond the crimp area of the valve body towards a thin disk orifice member 34 made of metal. In Fig. 1 , the prior art air assist atomizer comprises two parts in assembly relation with the fuel injector, one part being a shroud 52 and the other being an air metering disc or insert 54. The shroud 52, is substantially identical in both Figs. 1 and 2, possesses a general cup shape having a side wall 56 and an end wall 58. The side wall 56 has a circular cylindrical inside diameter including a shoulder 60 that divides it into a larger diameter portion 62 and a smaller diameter portion 64. The portion 64 extends from immediate contiguousness with the end wall 58 to the shoulder 60 while the portion 62 extends from the shoulder 60 to the end of the shroud 52 that is opposite the end wall 58. A portion of the valve body 28 has a nominally circular outside diameter 66 that is dimensioned to allow the portion 62 of the shroud 52 to snuggly fit onto it. However, that nominally circular outside diameter 66 is provided with one or more interruptions, such as an axial flat or slot 68, so as to thereby cooperatively define with the shroud's side wall the entrance portion of an axially extending passage means 70 for assist air to flow axially along the outside of the valve body 28 toward the nozzle 1 8. The small arrows in Fig. 2 represent assist air flow. The end wall 58 extends radially inwardly from the side wall 56 to provide an axially frusto-conically expanding aperture 72 which is coaxial with the axis 1 4 and through which fuel that has just been injected from the nozzle 1 8 passes. A raised circular annular ledge 74 is fashioned from the flat inside surface of the end wall 58 in circumscription of the aperture 72. In accordance with the prior art, the air metering disk or insert 54 is disposed axially between the nozzle 1 8 and the end wall 58 and is in fact held between the annular ledge 74 and the exterior axial end face of the retainer member 36. The construction of the injector which has thus far been described is generally like that disclosed in certain commonly assigned issued patents, and therefore will not be described further at this time so that attention can be focused on the inventive features residing in the air assist atomizer 1 2 and its association with the fuel injector 1 0. The insert 54, and the complications associated therewith, are described in great detail in commonly assigned U.S. Patent No. 5, 1 74,505, for an Air Assist Atomizer for Fuel Injector, issued to J. J. Shen on December 29, 1 992, and totally incorporated herein by reference. The present invention utilizes the air assist backup washer 37 as the air metering component, eliminating the air metering disk or insert 54. The downstream end of the backup washer 37 comprises an angled surface, shaped for flow, and the inside end wall of the shroud member 52 corresponds to this shape directing the flow. The shroud member 52 and the backup washer 37 comprise matching geometries so the shroud surface abuts up against the backup washer to direct the flow. Furthermore, the flat surface of the shroud member combined with the flow channels in the backup washer meter the air flow. Air flow is indicated by arrows in Figs. 3 and 4. At least two flow channels 76 are required, as shown in Fig. 3, although more than two flow channels 76, as shown in Fig. 4, are perfectly acceptable as well. The flow channels 76 are provided in the air assist backup washer by any suitable means. For example, since a typical backup washer is stamped, the air channels could be stamped into the washer at the time of manufacture, allowing for different washers for different flows. Alternatively, the flow channels could be stamped into the washer after it is assembled into the injector. A third option would be to form the channels with a metal working option, such as a laser. Yet another embodiment could utilize a powdered metal backup washer, and the channels could be in the mold. Furthermore, in accordance with the present invention, the channels could either be perpendicular to the fluid flow, and/or at an angle, to improve fluid targeting or to use for air direction. All of these options would eliminate the need for the additional an air metering disc or insert 54 of Fig. 1 , and could further eliminate some of the orientation operation required on assembly. The air shroud 52, whether metal or plastic, abuts its concave, or angled, bottom end up against the backup washer surface. The flat surface of the shroud combined with the air channels in the backup washer meter and/or direct the flow. In addition to the previously stated advantages, the present invention results in an air assist metering concept with lower manufacturing costs and increased design flexibility. Having described the invention in detail and by reference to the preferred embodiment thereof, it will be apparent that other modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims: What is claimed is: 1 . An air-assist metering apparatus for a fuel injector comprising: an air assist injector valve body; an air assist backup washer contained within said valve body, said washer having at least two flow channels; a shroud member having an angled surface and a flat surface, said angled surface abutting up against said backup washer whereby the flat surface of said shroud member combined with said at least two flow channels in said backup washer meter a desired air flow through the injector. 2. An air-assist metering apparatus as claimed in claim 1 wherein said shroud member comprises a general cup shape having a side wall and an end wall. 3. An air-assist metering apparatus as claimed in claim 2 wherein said side wall has a circular cylindrical inside diameter. 4. An air-assist metering apparatus as claimed in claim 1 wherein said at least two flow channels are stamped into said backup washer during manufacture. 5. An air-assist metering apparatus as claimed in claim 1 wherein said at least two flow channels are stamped into said backup washer after assembly in the fuel injector. 6. An air-assist metering apparatus as claimed in claim 1 wherein said at least two flow channels are formed with a metal working option. 7. An air-assist metering apparatus as claimed in claim 1 wherein said at least two flow channels are perpendicular to fluid flow. 8. An air-assist metering apparatus as claimed in claim 1 wherein said at least two flow channels are at an angle to fluid flow. 9. An air-assist metering apparatus for a fuel injector comprising: an air assist injector valve body; an air assist backup washer contained within said valve body, said washer having at least two flow channels and defined by a first geometry; a shroud member defined by a second geometry, said second geometry of said shroud member abutting up against said first geometry of said backup washer for directing a desired air flow through the injector. 1 0. An air-assist metering apparatus as claimed in claim 9 wherein said first geometry comprises a first angled surface shaped for flow. 1 1 . An air-assist metering apparatus as claimed in claim 1 0 wherein said second geometry comprises a second angled surface corresponding to said first angled surface to direct the flow.

Inventors: BOYLAN JOHN, NALLY DEBORA E, BOYLAN, JOHN, NALLY, DEBORA, E.
Applicants: SIEMENS AUTOMOTIVE CORP LP, SIEMENS AUTOMOTIVE CORPORATION
Application year: 1998
Main classification: F02M69
IPC codes: F02M61, F02M69