Patent Application
20060097081
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.
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.
One embodiment of the present invention provides a nozzle for a low pressure fuel injector that enhances the atomization of the fuel delivered to a cylinder of an engine. The nozzle generally comprises a nozzle body defining a valve outlet in a longitudinal axis. A 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. A plurality of exit cavities are define in the metering plate which receive fuel from the nozzle cavity. Each exit cavity is radially spaced from the longitudinal axis an oriented along a radial axis. Each exit cavity meets the nozzle cavity at an exit orifice. Each exit cavity is oriented asymmetrically relative to the radial axis.
According to more detailed aspects, each exit orifice has one or more axis of symmetry, and no axis of symmetry is aligned with the radial axis of the exit cavity. As such, the exit orifice may be triangular, trapezoidal, square, rectangular, ellipsoidal among numerous other shapes.
Another embodiment of the present invention provides a nozzle for a low pressure fuel injector generally comprising a nozzle body and a metering plate. The nozzle body defines a valve outlet in 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 nozzle cavity defined by a side wall and bottom wall. The metering plate also defines a plurality of exit cavities receiving fuel from the nozzle cavity. Each exit cavity is radially spaced from the longitudinal axis and is oriented along a radial axis. The side wall of the nozzle cavity is positioned adjacent the plurality of exit cavities and is structured to provide a tangential component to the fuel flowing into the plurality of exit cavities.
According to more detailed aspects, the sidewalls comprise of a series or arcuate segments. Preferably, the curvature of the arcuate segments is asymmetric relative to the radial axis. Most preferably, the curvature of the arcuate segments has a changing slope. Thus, the sidewall has a flower-shape with pedals that are oblong.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:
Turning now to the figures,
In either case, the nozzle body 32 defines a valve seat 34 leading to a valve outlet 36. The needle 26 is translated longitudinally in and out of engagement with the valve seat 34 preferably by an electromagnetic actuator or the like. In this manner, fuel flowing through the internal passageway 24 and around the needle 26 is either permitted or prevented from flowing to the valve outlet 36 by the engagement or disengagement of the needle 26 and valve seat 34.
The nozzle 20 further includes a metering plate 40 which is attached to the nozzle body 32. It will be recognized by those skilled in the art that the metering plate 40 may be integrally formed with the nozzle body 32, or alternatively may be separately formed and attached to the nozzle body 32 by welding or other well known techniques. In either case, the metering plate 40 defines a nozzle cavity 42 receiving fuel from the valve outlet 36. The nozzle cavity 42 is generally defined by a bottom wall 44 and a side wall 46 which are formed into the metering plate 40. The metering plate 40 further defines a plurality of exit cavities 50 receiving fuel from the nozzle cavity 42. Each exit cavity 50 is radially spaced from the longitudinal axis 15 and meets the nozzle cavity 42 at an exit orifice 52.
The metering plate 40 has been uniquely designed to enhance the atomization of the fuel injected into the cylinder 10 of the engine, as will now be described with reference to
As best seen in
In accordance with another aspect of the present invention, the exit orifices 52 may be uniquely designed in order to even further enhance the atomization of the fuel flowing into the engine cylinder 10. As shown in
It will also be recognized that the exit orifice 52 can take many other shapes. By orienting the exit orifices 52 asymmetrically, a tangential component or swirl is further induced into the fuel flowing through the metering plate 40 and into the engine cylinder 10. As shown in
The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
