Patent Application
20060097075
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 which increases the spray angle and gives better control over the direction of the spray of fuel delivery 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 has a bottom wall and a side wall, the bottom and side walls defining 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 an exit orifice. The side wall is sloping relative to the bottom wall. In particular, the slope between the side wall and the bottom wall varies circumferentially around the nozzle cavity.
According to more detailed aspects, the exit orifices and exit cavities are formed in the side wall. The bottom wall preferably includes a planar portion generally perpendicular to the longitudinal axis. Each exit cavity defines an exit axis oriented relative to the longitudinal axis and thus the orientation of the exit axes varies circumferentially around the nozzle. Stated another way, the exit axes are angled relative to the longitudinal axis, and the exit angles very circumferentially around the nozzle. Preferably, the side wall is angled relative to the bottom wall and the angle varies linearly, although it may vary non-linearly. The sloping of the side wall results in the nozzle cavity narrowing in the area proximate the exit cavities. The resulting fuel spray produced by the plurality of exit cavities is directed along an offset axis that is angled relative to the longitudinal axis.
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 bottom wall 44 has a planar portion spaced radially inwardly from the side wall 46. 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 improve the control over the direction of the fuel spray, as well as increase the angle of the fuel spray delivered to a cylinder of an engine. With reference to
The slope between the side wall 46 and the bottom wall 44 varies circumferentially around the nozzle cavity. This is best seen by viewing
It will also be recognized that the exit cavities 50 are located in the side wall 46, and more particularly the exit orifices 52 are formed in the side wall 46. Accordingly, the exit cavities 50 are each oriented along an exit axis 55, the plurality of exit axes varying circumferentially around the metering plate 40. That is, each exit cavity 50 is aligned along an exit axis 55 which is angled relative to the longitudinal axis 15. It will be recognized by those skilled in the art that the varying orientation of the exit axes 55 results in the total fuel spray produced by the plurality of exit cavities 50 to be directed along an offset axis 17 which is angled relative to the longitudinal axis 15.
The angle between the side wall 46 and bottom wall 44 preferably varies linearly, although it may vary non-linearly. Likewise, the angles of the plurality of exit axes 55 relative to the longitudinal axis varies linearly as one moves from orifice to orifice, although the variation may be non-linear. The angle of the side wall 46 and/or exit axes 55 may vary in stages, i.e. sections, or may constantly vary circumferentially around the metering plate 40.
Accordingly, it will be recognized by those skilled in art that the varying slope of the side wall 46, and the varying orientation of the exit axes 55 of the exit cavities 50, result in an offset fuel axis 17 which provides greater control and range to the resultant fuel spray delivered to the cylinder 10 of an engine. Further, 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.
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.
