Patent Application
20060097080
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 improves 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 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. The exit orifices are positioned on the sloping side wall.
According to more detailed aspects, the sidewall is sized to correspond to the diameter of the exit orifices. The sloping side wall forms the outer periphery of the nozzle cavity. The bottom wall includes a planar portion generally perpendicular to the longitudinal axis. The planar portion is located radially inwardly from the sloping sidewall. The inner section of the bottom wall and side wall occurs at a point proximate the exit orifices. The inner section points are proximate a radially inner edge of each exit orifice. The side wall may be arcuate, planar or a combination of both. An inner portion of the side wall is preferably arcuate while an outer portion of the side wall is planar. In this version, the exit orifices are preferably located within the inner portion of the side wall. Thus, the exit orifices may be arcuate in shape. Preferably, the nozzle cavity narrows in the area proximate the exit cavities.
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 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
Additionally, it will be recognized that the side wall 46 is sloping relative to the bottom wall 44. In particular, the side wall 46 includes an arcuate or radiused portion 46a and a planar or flat portion 46b. It will be recognized by those skilled in the art that the side wall 46 may be completely arcuate or completely flat, but ideally the side wall 46 is sloped relative to the bottom wall 44. The bottom wall 44 is planar and generally perpendicular to the longitudinal axis. In this manner, the nozzle cavity 42 narrows, i.e. decreases its volume in the radial outward direction towards the side wall 46.
Accordingly, the exit cavities 50 are positioned to intersect with the nozzle cavity 42 at the side wall 46. Stated another way, the exit orifices 52 which are located at this intersection are positioned on the sloping side wall 46. In this manner, fuel is rapidly accelerated through the nozzle cavity 42 to the sharp edged exit orifices 52 which enhances a turbulence and thus atomization of the fuel delivered to the engine cylinder 10.
It can be seen in
The intersection of the bottom wall 44 and the side wall 46 occurs at a point proximate the exit orifices 52. Particularly, the intersection points are proximate a radially inner edge of each exit orifice 52. As the exit orifices 52 are positioned at the arcuate sections 46a of the side wall 46, the exit orifices 52 take an arcuate shape.
Accordingly, it will be recognized that those skilled in the art that the nozzle 20 of the present invention provides a metering plate 40 which optimizes the volume of the nozzle cavity 42 in order to maximize the acceleration of the fuel flowing therethrough, as well as to provide a uniquely shaped and located exit orifice 52 leading to an exit cavity 50 which delivers fuel to the engine cylinder 10 that has been well atomized. 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.
