Patent Application
20060097082
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, provides control over the direction of the spray, and enhances 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. A rib projects into the exit cavity and separates an upstream portion and a downstream directing portion of the exit cavity. The rib defines a second exit orifice having a diameter less than the first exit orifice.
According to more detailed aspects, the second exit orifice and downstream directing portion generate a cavitating flow region. The diameter of the second exit orifice is sized relative to the diameter of the downstream directing portion to generate the cavitating flow region. The downstream directing portion has a length to diameter ratio that substantially prevents expansion of the fuel prior to delivery to the cylinder. Preferably, the downstream directing portion is cylindrical, and likewise the upstream portion is preferably cylindrical. Most preferably, the downstream directing portion has a diameter smaller than the upstream directing portion.
According to still further details, each exit cavity defines an exit axis. Each exit axis is tilted in the radial direction relative to the longitudinal axis. In this manner, the exit cavities increase the spray angle of the nozzle. The exit axis is also preferably tilted in a tangential direction relative to the longitudinal axis. In this manner, the exit cavities produce a swirl component to the fuel exiting the nozzle that enhances atomization of the fuel. A variation of the exit cavity may be employed where the upstream portion defines an upstream axis and the downstream directing portion defines a downstream axis. In this variation, the downstream axis is not aligned with the upstream axis. Accordingly, it will be seen that the unique structure of the nozzle permits an increase in the spray angle as well as better control over the direction of the spray. At the same time, the first and second exit cavities, as well as the cavitating flow region, enhance the atomization of the fuel delivered to the cylinder of the engine.
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 metering plate defines a plurality of exit cavities receiving fuel from the nozzle cavity, each exit cavity being radially spaced from the longitudinal axis. Each exit cavity has a diameter which does not increase along its length. A rib projects into the exit cavity at a point where the exit cavity and nozzle cavity meet. The rib defines an exit orifice having a diameter smaller than the largest diameter of the exit cavity.
According to more detailed aspects, the exit cavity is preferably cylindrical and has a constant diameter. The exit orifice and the exit cavity generate a cavitating flow region which enhances the atomization of the fuel. The rib preferably tapers to a sharp edge to further assist the atomization of the fuel. Each exit cavity defines an exit axis, and each exit axis may be tilted in either or both of the radial direction and the tangential direction relative to the longitudinal axis. In this manner, the spray angle of the nozzle may be increased, and a swirl component may be introduced into the fuel exiting the nozzle to enhance atomization.
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.
It can also be seen in
The rib 54 and the second exit orifice 56 also divides the exit cavity 50 into an upstream portion 58 and a downstream directing portion 60. The downstream directing portion 60 is preferably cylindrical in shape, and at least has a diameter which does not substantially increase along its length. Most preferably, the downstream directing portion 60 has a diameter that is smaller than the upstream portion 58. Further, the downstream directing portion 60 has a length to diameter ratio that substantially prevents expansion of the fuel prior to delivery to the cylinder 10. That is, when an exit cavity widens towards the cylinder 10 for directing the same, it provides relief to the fuel accelerating through nozzle cavity 42 and metering plate 40 which allows the fuel to expand as it enters the cylinder 10. In this manner, the downstream directing portion 60 will serve to prevent expansion and allow the exit cavity 50 to direct the spray of the fuel.
The structure of the exit cavity 50, and notably the rib 54 and upstream and downstream portions 58, 60, produce a cavitating flow region 62 in the area adjacent the rib 54. As such, the fuel flowing therethrough is forced to accelerate in the area adjacent this cavitating flow region 62 which enhances a turbulence of the fuel, thereby increasing atomization. The diameter of the second exit orifice 56 is preferably sized relative to the diameter of the downstream directing portion 60 to generate this cavitating flow region 62.
By directing the spray of the fuel through the downstream directing portion 60, not only can the spray be better controlled in its direction, but the spray angle of the fuel flowing through the nozzle 20 may also be increased. Specifically, the exit cavity 50 generally defines an exit axis 55. Each exit axis 55 is preferably tilted in the radial direction relative to the longitudinal axis 15 to increase the spray angle of the nozzle 20.
As best seen in
Turning now to
Turning now to
As in the prior embodiments, the exit cavity 50b preferably is oriented along an exit axis which is tilted in the radial direction and/or the tangential direction to increase the spray angle as well as produce a swirl component to the fuel exiting the nozzle 20 and entering the engine cylinder 10. In this manner, the upstream portion of the exit cavity may be eliminated, while still providing a cavitating flow region and sharp edged orifice which enhance turbulence of the fluid, while allowing control over the direction of the spray to be performed through the downstream directing cavity 60b. 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.
