Low pressure fuel injector nozzle

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.

FIELD OF THE INVENTION

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

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.

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.

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

One embodiment of the present invention provides a nozzle for a low pressure fuel injector which increases the spray angle, improves control over the direction of the spray, as well as enhances the atomization of the fuel delivered to a cylinder of an engine. The nozzle generally comprises a nozzle body and a metering plate. The nozzle body defines a valve outlet and 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 metering plate defines a plurality of exit cavities receiving fuel from the nozzle cavity. Each exit cavity is radially spaced from the longitudinal axis and meets the nozzle cavity at a first exit orifice. Each exit cavity includes an upstream directing portion and a downstream portion. The intersection of the upstream directing portion and the downstream portion defines a second exit orifice. The second exit orifice has a diameter less than the smallest diameter of the upstream directing portion.

According to more detailed aspects, the upstream directing portion has a diameter which does not increase along its length in the downstream direction. Thus, the upstream directing portion may be cylindrical, conical, or generally decrease in diameter in the downstream direction. Preferably the downstream portion does increase in diameter in the downstream direction and thus forms an expanding exit cone. The upstream directing portion defines a separation zone trapping a portion of the fuel flow therein. The upstream directing portion directs fluid flow inwardly past the separation zone and towards an exit axis of the exit cavity prior to passing through the second exit orifice.

According to still further detailed aspects, each exit cavity defines an exit axis. Each exit axis may be tilted in the radial direction relative to the longitudinal axis to increase the spray angle of the nozzle. At the same time, the exit axis may be tilted in the tangential direction relative to the longitudinal axis to produce a swirl component to the fuel exiting the nozzle, thereby enhancing atomization of the fuel.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures,FIG. 1depicts a cross-sectional of a nozzle20constructed in accordance with the teachings of the present invention. The nozzle20is formed at a lower end of a low pressure fuel injector which is used to deliver fuel to a cylinder10of an engine, such as an internal combustion engine of an automobile. An injector body22defines an internal passageway24having a needle26positioned therein. The injector body22defines a longitudinal axis15, and the internal passageway24extends generally parallel to the longitudinal axis15. A lower end of the injector body22defines a nozzle body32. It will be recognized by those skilled in the art that the injector body22and nozzle body32may be integrally formed, or alternatively the nozzle body32may be separately formed and attached to the distal end of the injector body22by welding or other well known techniques.

In either case, the nozzle body32defines a valve seat34leading to a valve outlet36. The needle26is translated longitudinally in and out of engagement with the valve seat34preferably by an electromagnetic actuator or the like. In this manner, fuel flowing through the internal passageway24and around the needle26is either permitted or prevented from flowing to the valve outlet36by the engagement or disengagement of the needle26and valve seat34.

The nozzle20further includes a metering plate40which is attached to the nozzle body32. It will be recognized by those skilled in the art that the metering plate40may be integrally formed with the nozzle body32, or alternatively may be separately formed and attached to the nozzle body32by welding or other well known techniques. In either case, the metering plate40defines a nozzle cavity42receiving fuel from the valve outlet36. The nozzle cavity42is generally defined by a bottom wall44and a side wall46which are formed into the metering plate40. The metering plate40further defines a plurality of exit cavities50receiving fuel from the nozzle cavity42. Each exit cavity50is radially spaced from the longitudinal axis15and meets the nozzle cavity42at an exit orifice52.

The metering plate40has been uniquely designed to increase the spray angle, improve control over the direction of the spray, as well as to increase the atomization of the fuel flowing through the metering plate40and into the cylinder10of the engine. With reference toFIGS. 1,2and4, the exit cavity50of the metering plate includes an upstream portion58and a downstream portion60. The upstream portion preferably has a diameter which does not increase along its length in the downstream direction. Preferably, and as shown in the figure, the upstream directing portion58is cylindrical in shape. The downstream portion60however may increase in diameter and is shown as being conical in shape or flared. The intersection of the upstream directing portion58and the downstream portion60defines a second exit orifice56. The second exit orifice56is preferably sharp edged such that fuel flowing past both sharp edge orifices52,56have increased levels of turbulence which enhances the atomization of the fuel. The second exit orifice56has a diameter that is less than the smallest diameter of the upstream directing portion58. Stated another way, a shoulder54is formed at the intersection of the upstream directing portion58and the downstream portion60of the exit cavity50.

Accordingly, it will be recognized by those skilled in the art that the exit cavity50defines a separation zone62in the upstream directing portion58which traps a portion of the fuel flow against the shoulder54. In this manner, the turbulence of the fuel flowing through the exit cavity50is increased, to thereby enhance atomization of the fuel. At the same time, the constant or narrowing diameter of the upstream directing portion58prevents expansion of the fuel and thereby largely controls the direction of the fuel being spray into the cylinder10of the engine. The length to diameter ratio of the upstream directing portion58is controlled to prevent expansion of the fuel.

Accordingly, it will be recognized by those skilled in the art that the upstream directing portion58may be utilized to improve the spray angle as well as improve control over the direction of the spray of fuel entering the engine cylinder10. For example, the exit cavity50defines an exit axis55. As best seen inFIG. 2, the exit axis55is tilted radially relative to the longitudinal axis15, thereby increasing the spray angle of the nozzle20. As best seen inFIG. 4, the exit axis55is also tilted in the tangential direction relative to the longitudinal axis15. In this manner, the exit cavities50produce swirl component to the fuel exiting the nozzle20and being delivered to the engine cylinder10. Thus, by tilting the exit cavities50radially and/or tangentially, the spray angle may be increased while at the same time obtaining better control over the direction of the spray and enhancing the atomization of the fuel through the swirling component of the discharge spray.

Turning now toFIG. 3, an alternate embodiment of the nozzle and metering plate40ahas been depicted. First, it is noted that the nozzle cavity42ais annular in shape and includes an island41formed in the center thereof about the longitudinal axis15. Further, the bottom wall44aof the nozzle cavity42aslopes upwardly as it extends radially outwardly away from the longitudinal axis15. These structures reduce the volume of the nozzle cavity42ato thereby increase the pressure and acceleration of the fuel through the metering plate40.

In the embodiment ofFIG. 3, it will also be noted that the upstream directing cavity58ahas been formed in a shape which decreases in diameter in the downstream direction. That is, the upstream directing portion58ais conical. Thus the upstream directing portion58aprevents the fuel from expanding, and actually decreases the available volume to further accelerate the fuel and enhance atomization. At the same time, the second exit orifice56is still provided at the intersection of the downstream cavity60and the upstream directing cavity58a.Like the previous embodiments, the exit cavities50aare oriented along an exit axis55awhich may be tilted radially and/or tangentially relative to the longitudinal axis15in order to increase the spray angle, as well as introduce a swirl component to the spray to thereby further increase the atomization of the fuel. Thus, the structure and orientation of each exit cavity, in concert with the plurality of exit cavities, enhances the spray angle and control over the direction of the spray.