Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-02-10
2001-07-10
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S496000
Reexamination Certificate
active
06257203
ABSTRACT:
TECHNICAL FIELD
The present invention relates to hydraulically-actuated, electronically-controlled fuel injectors and systems therefor.
BACKGROUND OF THE INVENTION
Hydraulically-actuated, electronically-controlled fuel injectors and systems are known. Examples of such injectors and systems are shown in U.S. Pat. No. 5,460,329 to Sturman, U.S. Pat. No. 5,181,494 to Ausman et al., and U.S. Pat. No. 5,682,858 to Chen et al.
In the design alternative depicted in
FIG. 6
of Sturman, the back of the needle valve is fluidly coupled directed to the high pressure actuating fluid source. It is significant to note that this embodiment does not utilize a spring to close the needle valve. The intention of the embodiment is to eliminate the needle valve spring and to use only actuating fluid rail pressure to close the needle valve. In this embodiment, there is no means for amplifying the actuating fluid pressure acting at the back of the needle valve. The needle valve front and the needle valve back have equally sized pressurized areas. A deficiency of this design is that the needle valve may have uncontrolled opening (since there is no valve spring to maintain the needle valve in the closed condition) when combustion cylinder pressure acting on the needle valve is relatively high and when the actuating fluid common rail pressure is relatively low, for example, during engine cranking or low speed engine operation.
Chen et al. incorporates a needle valve control chamber. The fluid pressure in the control chamber is directly controlled by the injector solenoid valve. The solenoid valve exposes the chamber to either the pressure in the actuating fluid high pressure rail or to ambient pressure as a function of solenoid valve position. When the control chamber is vented to ambient, the needle valve opens by fuel pressure acting counter to the relatively small needle spring. Such an arrangement indicates that the needle opening pressure in all cases is disadvantageously at the relatively low fuel injection pressure necessary to overcome the bias of the relatively small needle valve spring. The disadvantage of this design carries across the entire engine speed and load range. When the needle valve control chamber is exposed to the actuating fluid rail pressure, the needle valve closes by the total force of the actuating fluid acting on the needle valve and the force of the needle valve spring. This needle valve closing force can be very great at high actuating fluid rail pressure. The rail pressure force is amplified by the piston in the needle valve control chamber acting on the back of the needle valve.
Typically, in the conventional prior art HEUI type injector shown in Ausman et al., needle valve operation is controlled by a fixed mechanical return spring opposed by a force generated by fuel pressure acting on the needle valve. The preload on the conventional spring is predefined. Accordingly, the needle opens and closes at fixed fuel pressures under all engine operating conditions. Selecting the return spring load involves some tradeoffs between high speed high load operability and low speed operability. If the prior art return spring load is selected based on the rated engine condition performance requirements, then, the return spring load could be too great for lower speed conditions, especially idle conditions. High valve opening pressure produces significantly greater engine operation noise, a particularly undesirable effect. At engine idle condition, with a heavy spring, the engine operation noise becomes even more pronounced. Reducing diesel engine idle noise is a critical challenge to make the diesel engine acceptable for use in family transportation vehicles, such as pickup trucks and SUV's. Reducing idle noise is a key for the diesel engine manufacturer to be able to compete in what is now a largely gasoline engine market. The low valve opening pressures of the present invention offer a significant competitive advantage.
There is a need in the industry to provide a hydraulically-actuated, electronically-controlled fuel injector and system with variable needle valve valve opening pressure. The mechanization necessary to provide such variable valve opening pressure should be designed in the most simplistic way possible in order to minimize the difficulty in constructing the injector, minimize the complexity of the injector, and in order to minimize the cost of the injector.
SUMMARY OF THE INVENTION
The injector and injector system of the present invention substantially meet the aforementioned needs of the industry. The present injector incorporates variable needle valve opening pressure at widely differing engine operation conditions. The variable needle valve opening pressure of the present invention effects needle valve opening at relatively low fuel injection pressure when the engine is at idle condition. The benefit of such opening is to favorably reduce low engine idle noise. Further, the variable needle valve opening pressure of the present invention effects a higher valve opening pressure at high engine speed in the engine load conditions. The higher valve opening pressure provides for a desirable higher average fuel injection pressure. The higher average fuel injection pressure of the present invention effects reduced engine emissions and improved vehicle driveability.
Since, as indicated above, there is a need to provide a lower valve opening pressure at low engine load conditions and a relatively higher valve opening pressure at higher engine speed and load conditions, there is a further need to find a relatively simple way to provide the desired valve opening pressures. With the fuel injection systems of the present invention, actuating fluid rail pressure has a special characteristic in that the pressure normally increases with engine speed and load. With the common rail pressure being already available to each of the injectors, the special characteristic of the rail pressure was used in the present invention to generated the desired valve opening pressures. In a preferred embodiment, the variable actuating fluid at the rail pressure is introduced at the needle valve back to effect the variable valve opening pressure. In a preferred embodiment, a piston acting on the needle valve back is utilized to amplify the effect of the actuating fluid rail pressure on the needle valve as desired.
The present invention provides for higher valve opening pressure as the desired injection pressure increases. The higher valve opening pressure attained by the present inventions allows the needle valve to delay opening at relatively higher injection pressures and closes the needle valve earlier at such relative higher injection pressures. Compared to the aforementioned lower valve opening pressure condition, the average injection pressure is much higher under the higher valve opening pressure condition. The high average injection pressure that is made possible by the higher valve opening pressure of the present invention contributes to dramatically reduce engine emissions and improve driveability under such conditions.
With the present invention, the total force on the back of the needle valve is a function of actuating fluid rail pressure (with a fixed bias provided by the needle valve return spring). The injection pressure at which the needle valve starts to open with the present invention is a linear function of actuating fluid rail pressure. This is one of the fundamental aspects of the present invention.
The present invention is a hydraulically-actuated electronically-controlled fuel injector for use with a fuel injection system having an actuating fluid high pressure common rail for conveying an actuating fluid under pressure, the pressure of the actuating fluid in the common rail being selectively variable, the fuel injection system being installed on a diesel engine, the injector having a controller valve for selectively porting the actuating fluid to an injector intensifier assembly for magnifying the pressure of the fuel to be injected, includes a needle valve for controllin
Calfa Jeffrey P.
Hernandez Gilberto
International Truck and Engine Corporation
Moulis Thomas N.
Sullivan Dennis Kelly
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