Fuel injector with variable spray

A fuel injector is provided that creates variable spray characteristics to effectively reduce emissions, such as NOx emissions and particulate matter. The injector includes a nozzle valve element of the outwardly opening type including a fuel delivery passage and spray holes. The nozzle valve element is operable to move to a low lift position to cause fuel flowing from the spray holes to impinge on the injector body and to deflect toward the combustion chamber, and to move to a high lift position to cause fuel flowing from the spray holes to avoid impingement on injector body and flow in an obstructed manner directly into the combustion chamber. An annular chamber may be formed in the nozzle valve element adjacent the spray holes to receive fuel.

TECHNICAL FIELD

The present inventions relate generally to fuel injection systems and, more particularly, to a fuel injector and method for improved fuel spray characteristics.

BACKGROUND OF THE INVENTION

In many fuel supply systems applicable to internal combustion engines, fuel injectors are used to inject fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned to control a flow of high pressure fuel into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection, thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve element is positioned in the injector cavity and biased, for example, by a bias spring, so that when an actuation force exceeds the biasing forces acting on the element, the nozzle valve element moves to allow fuel to pass into the combustion chamber, thus marking the beginning of the injection event.

Internal combustion engine designers have increasingly come to realize that substantially improved fuel supply systems are required in order to meet the ever increasing governmental and regulatory requirements of emissions abatement and increased fuel economy. Therefore, such designers are continually searching for ways to improve control over fuel injection to help meet the economically and governmentally mandated demands for increasing fuel economy and reduced air pollution.

SUMMARY OF THE INVENTION

The inventions herein achieve the advantages described herein, and other advantages, by providing a fuel injector for injecting high pressure fuel into a combustion chamber of an internal combustion engine, comprising an injector body containing an injector cavity and including a valve seat, and a nozzle valve element positioned in said injector cavity, wherein the nozzle valve element includes a valve surface positioned adjacent the valve seat. The injector also includes a fuel delivery passage, and a plurality of spray holes fluidically connected to the fuel delivery passage. The nozzle valve element is operable to move between a closed position with the valve surface positioned in sealing abutment with the valve seat to block fuel flow from the plurality of spray holes and an open position permitting flow from the spray holes. The nozzle valve element moves outwardly away from the injector body when moving from the closed position toward the open position, wherein the open position includes a first lift position and a second lift position having a greater lift than the first lift position. At least one of the plurality of spray holes is positioned adjacent the injector body when the nozzle valve element is in the first lift position to cause fuel flowing from the at least one spray hole to impinge on the injector body and deflect toward the combustion chamber. The at least one spray hole is positioned adjacent the injector body when the nozzle valve element is in the second lift position to cause fuel flowing from the at least one spray hole to avoid impingement on the injector body. The injector also includes a nozzle valve actuator assembly adapted to move the nozzle valve element toward the open position.

The nozzle valve element may further include an annular groove formed adjacent the plurality of spray holes to receive fuel from the plurality of spray holes when the nozzle valve element is in the closed position. The fuel delivery passage may extend axially along a central longitudinal axis of the nozzle valve element. The injector body may further include a fuel supply port to receive high pressure fuel. The nozzle valve element may include a transfer passage extending transverse, and fluidically connected, to the fuel delivery passage to receive high pressure fuel from the fuel supply port. The nozzle valve actuator assembly may include a piezoelectric actuator and a drive plunger positioned axially between the piezoelectric actuator and the nozzle valve element. The nozzle valve actuator assembly may further include a hydraulic chamber to receive fuel to form a hydraulic link to transfer motion from the drive plunger to the nozzle valve element. The nozzle valve actuator assembly may further include a bias spring positioned in the hydraulic chamber to bias the nozzle valve element toward the closed position.

In another exemplary embodiment, the invention includes a fuel injector for injecting high pressure fuel into a combustion chamber of an internal combustion engine, comprising an injector body containing an injector cavity and including a valve seat, and a nozzle valve element positioned in the injector cavity. The nozzle valve element includes a valve surface positioned adjacent the valve seat, a fuel delivery passage, and a plurality of spray holes fluidically connected to the fuel delivery passage. The nozzle valve element may be operable to move between a closed position with the valve surface positioned in sealing abutment with the valve seat to block fuel flow from the plurality of spray holes and an open position permitting flow from the spray holes. The nozzle valve element is operable to move outwardly away from the injector body when moving from the closed position toward the open position. The nozzle valve element further includes an annular groove formed adjacent the plurality of spray holes to receive fuel from the plurality of spray holes when the nozzle valve element is in the closed position. The injector further includes a nozzle valve actuator assembly adapted to move the nozzle valve element toward the open position.

These and other advantages and features of the present invention will become more apparent from the following detailed description of the preferred embodiments of the present invention when viewed in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, there is shown one embodiment of the fuel injector of the present invention indicated generally at10which includes an injector body12having a generally elongated, cylindrical shape which forms an injector cavity14. The inner portion of fuel injector body12includes a closed nozzle assembly, indicated generally at16, which includes a nozzle valve element18having injector orifices or spray holes20formed therein. Nozzle valve element18is reciprocally mounted for opening and closing the plurality of spray holes20, thereby controlling the flow of injection fuel into an engine combustion chamber (not shown).

Closed nozzle assembly16also includes a nozzle housing15including a bore17sized to form a close sliding fit with nozzle valve element18to permit reciprocal sliding movement of nozzle valve element18in bore17while creating a substantial fluid seal along the interface. Nozzle housing15includes an annular valve seat23for sealing abutment by nozzle valve element18when in the closed position. Injector body12also includes one or more additional housings, such as an actuator housing connected to nozzle housing15in any appropriate manner, such as being positioned in compressive abutting relationship using for example an outer retainer such as shown in U.S. Pat. No. 5,979,803, the entire contents of which is hereby incorporated by reference.

Fuel injector10further includes a nozzle valve actuator assembly22adapted to move nozzle valve element18toward the open position. Nozzle valve actuator assembly22includes a piezoelectric actuator24positioned in the upper portion of injector cavity14and a drive plunger26operatively connected to the inner end of piezoelectric actuator24. Piezoelectric actuator24may comprise a columnar laminated body of thin disk-shaped elements each having a piezoelectric effect. When a voltage, i.e. +150 volts, is applied to each element, the element expands along the axial direction of the column. Conversely, when a voltage of −150 volts is applied to each element, the element contracts so that the inner end of piezoelectric actuator24moves away from closed nozzle assembly16. Piezoelectric actuator24may include any type or design of piezoelectric actuator capable of actuating nozzle valve element18as described hereinbelow. The expansion/contraction of piezoelectric actuator24is directly transmitted to drive plunger26, thereby causing plunger26to reciprocate. In other embodiments, the movement of piezoelectric actuator24may be indirectly transmitted to drive plunger26using an intermediate element.

Nozzle valve actuator assembly22also includes a hydraulic chamber31formed in injector cavity14adjacent the inner end of drive plunger26. Plunger26slidably reciprocates within injector cavity14so as to expand and contract the volume of hydraulic chamber31thereby forming a hydraulic link21operatively connecting drive plunger26and nozzle valve element18. Preferably piezoelectric actuator24is directly connected to drive plunger26which in turn is directly connected to nozzle valve element18via the hydraulic link21. Therefore expansion of the piezoelectric actuator24causes movement of nozzle valve element18outwardly toward an open position, and contraction of piezoelectric actuator24causes inward movement of nozzle valve element18toward a closed position. Drive plunger26is preferably sized with a larger diameter than nozzle valve element18to provide stroke amplification, while hydraulic link21provides both wear compensation and thermal compensation by being variable in length.

Closed nozzle valve assembly16is of the outwardly opening type wherein the end of nozzle valve element18moves outwardly away from the injector body12out of bore17toward an open position (FIGS. 2 and 3) and inwardly into bore17toward injector body12toward a closed position (FIG. 1) in sealing abutment with valve seat23. Nozzle valve element18includes a larger valve head portion30including a valve surface32extending annularly around head portion30and shaped to sealingly abut valve seat23when nozzle valve element18is in the closed position (FIG. 1). Nozzle valve element18further includes a fuel delivery passage34positioned to deliver high pressure fuel through element18to spray holes20. In the exemplary embodiment, fuel delivery passage34extends axially along a central longitudinal axis of nozzle valve element18terminating near the distal end of nozzle valve element18to fluidically connect with spray holes20. Spray holes20each extend from fuel delivery passage34through nozzle valve element18to an annular groove36formed in nozzle valve element18as discussed hereinbelow.

The opposite end of nozzle valve element18extends into hydraulic chamber31for receiving a drive force applied by hydraulic link21, drive plunger26, and piezoelectric actuator24of nozzle valve actuator assembly22. A bias spring25, positioned in hydraulic chamber31, acts on the outer end of nozzle valve element18to bias nozzle valve element18toward the closed position. Nozzle valve element18further includes a transverse passage38extending transversely through nozzle valve element18to fluidically connect an outer end of fuel delivery passage34with a high pressure fuel supply. Injector body12, and in the exemplary embodiment, nozzle housing15, includes a fuel supply port40positioned to communicate with bore17at one end and a high pressure fuel supply at an opposite end. Fuel supply port40connects with bore17at a point along the length of bore17such that transverse passage38is in constant communication with fuel supply port40throughout reciprocal movement of nozzle valve element18between open and closed positions. Fuel supply port40is supplied with high pressure fuel from any conventional fuel system capable of delivering a supply of fuel pressurized to a desired level for injection, i.e. such as a conventional high pressure common rail system or a system capable of cyclically delivering high pressure fuel to supply circuit52. Also, it should be noted that the inner portion of fuel injector body12is shown as only one exemplary embodiment. A practical form, and other forms, of the injector would necessarily require the inner portion of the injector body12to be formed in at least two separate pieces held together in a compressive relationship by, for example, a retainer such as disclosed in U.S. Pat. No. 4,022,166, the contents of which is hereby incorporated by reference. Specifically, it is desirable to form bore17in one injector housing structure and hydraulic chamber31in a separate structure as shown but additional injector body structures may be used.

The injector of the present inventions effectively provides variable spray characteristics to effectively reduce emissions, such as NOx emissions and particulate matter. Specifically, injector10effectively creates a first fuel spray downstream of valve seat23, i.e., into a combustion chamber of an engine, when nozzle valve element18is in a first or low lift position (FIG. 2), e.g. 0.2 mm opening, that has a hollow cone shape and/or a deep angle spray profile with very small drops of fuel and low penetration into the combustion chamber, and also effectively creates a second fuel spray comprised of unobstructed individual spray plumes with a shallow angle spray profile injected directly into the combustion chamber for deep penetration and good mixing when the nozzle valve element is in a second or high lift position (FIG. 3). With respect to the low lift position creating the hollow cone/deep angle profile, such spray characteristics may be desirable whenever fuel is introduced early in the compression stroke of an engine, such as during engine low load and idle conditions, when the cylinder (combustion chamber) pressure is relatively low which permits fuel penetration. Individual spray plumes directed into the combustion chamber, and especially individual spray plumes directly injected into the combustion chamber at a shallow angle more toward the side walls of the cylinder liner defining the combustion chamber, during an early portion of a compression stroke when cylinder pressure is low, may result in fuel impingement on the cylinder liner. By providing a hollow cone and/or directing the fuel spray from the valve seat in a more downward (vertical inFIG. 2) path at a deep angle A away from the cylinder walls, the fuel can be more effectively mixed with the combustion chamber air/gas without cylinder wall impingement thereby minimizing particulates and emissions. This low lift position or mode is especially advantageous during early pre-mixed fuel injection.

The low lift spray profile is achieved by positioning the outlets of the spray holes20relative to the injector body upstream of the valve seat23, and providing annular groove36to receive the flow from spray holes20, such that the fuel fills annular groove36between injection events when nozzle valve element18is in a closed position. As such, when nozzle valve element18moves from the closed position toward a low lift position, the fuel flows from annular groove36through the gap50formed at valve seat23circumferentially around the entire gap to form a hollow cone. Moreover, preferably, the valve seat23is formed with an angle sufficient to direct the fuel away from the cylinder walls into the cone shape at the deep angle A and more toward the centerline of the combustion chamber. As the initial volume of fuel in the annular groove36is passing out of the groove, the fuel flowing from the outlets of the spray holes20will impinge on the injector body forming bore17and/or valve seat23and be deflected/directed toward downwardly toward the combustion chamber into a deep angle hollow cone or possibly deep angle individual or overlapping plumes, depending on the extent of opening of nozzle valve element18, and the number and/or size of spray holes positioned around nozzle valve element18. In the exemplary embodiment, the entire flow of fuel from each spray hole20impinges injector body12, i.e. nozzle housing15, causing the entire flow, not a portion of the flow, to be deflected into a deep angle.

During other engine operating conditions, such as high load, when injection may occur closer to top dead center of an engine piston's movement when cylinder pressure is high, nozzle valve element18may move into a second or high lift position (FIG. 3) farther out of the bore17than the low lift position. In the high lift position, the outlets of spray holes20are positioned outward of the injector body, i.e., valve seat23, causing fuel flow from spray holes20to avoid impingement on the injector body by flowing freely in an unobstructed manner directly from the spray hole outlets into the combustion chamber. Thus the fuel spray from holes20extend as individual spray plumes into the combustion chamber at a shallow angle B to provide greater fuel penetration into the combustion chamber to achieve enhanced fuel-air mixing. The high lift position may be achieved in series immediately following the low lift position.

During operation, prior to an injection event, piezoelectric actuator24is deactuated, i.e., a voltage of −150 volts is applied, as shown inFIG. 1, allowing the bias force of bias spring25to maintain nozzle valve element18in the inward closed position with valve surface32positioned in sealing abutment against valve seat23preventing fuel injection. At predetermined time determined by, for example, an electronic control unit (ECU), not shown, the ECU sends a voltage signal to piezoelectric actuator24actuating/energizing the actuator by applying a voltage, i.e., +150 volts, to the stack of piezoelectric elements causing the stack to expand. The expansion of the piezoelectric actuator24causing outward/downward movement of drive plunger26which in turn compresses hydraulic link21which in turn applies a downward force on nozzle valve element18causing element18to move from a closed position toward an open position, i.e., a low lift and/or a high lift position. The nozzle valve element18may be controlled to define a single injection event by lifting to only the low lift position and back to the closed position under certain engine operating conditions; lifting directly to high lift position by moving through the low lift position; lifting to the low lift position, pausing at the low lift position, and then continuing movement to the high lift position; or to lift to the low lift position early in the engine cycle to form an early preinjection, closing, and then lifting again to either the low or high lift position. Movement to the respective low and high lift positions is controlled by applying different voltages across the piezoelectric elements with a lower voltage achieving the low lift position and a higher voltage achieving the high lift position. To end an injection event, the voltage to the piezoelectric elements is reversed causing the stack to contract resulting in inward movement of drive plunger26which increases the size of, and lowers the fluid pressure in, hydraulic chamber31thereby allowing bias spring25to move nozzle valve element18inwardly to the closed position.

While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto. The present invention may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the detail shown and described previously, but also includes all such changes and modifications.