Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
1999-12-29
2001-05-08
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C123S507000, C417S380000
Reexamination Certificate
active
06227174
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to internal combustion engines, and more particularly to fuel injection systems.
BACKGROUND OF THE INVENTION
Many of today's lightweight and/or high-speed engines, which are typically two-cycle engines, do not have a cam and valve overhead. When such engines are designed for fuel injection, means other than the cam must be used to actuate the injector. Addition of actuator components presents design problems, in that such components must not unduly increase the weight and cost of the engine. The actuation components must also be capable of withstanding the forces that will be exerted within the injection system due to high injection pressures and fast operation. If the actuation components require lubrication, this further increases the weight, cost, and complexity of the engine.
One alternative to a conventional cam-driven injection system is to use an injection pump mechanism external to the injector assembly. An example is a pump line nozzle injection system. However, there are limitations on where the injection pump can be mounted relative to the injector. This limitation is due to the compressibility to the fuel and the transport delay of the fuel pulse from the injection pump to the injector. This is an issue because of the high operating speed of these small engines.
Another alternative is a “unit injector”, so called because their pumping mechanism is integral to the injector assembly. An example is a cam-actuated unit injector, such as that used in on-highway diesel engines.
However, for small two cycle engines, this type of cam actuation would present the weight and lubrication problems discussed above.
SUMMARY OF THE INVENTION
One aspect of the invention is a unit injector for an internal combustion engine. A main body has a size and shape appropriate for insertion in an opening in the cylinder head. The main body further has a fuel supply port and a fuel return port and a fuel path between the fuel supply port and the fuel return port. A control valve is operable to open or close the fuel path forward of the fuel return port. A plunger extends from the main body downward into the combustion chamber. The plunger is moveable up and down within the main body in response to movement of the piston.
In one embodiment of the invention, the needle/spray assembly is inside the plunger. At least one spray aperture is at the bottom tip of the plunger. The injector needle is located above the spray apertures, and is moveable up and down within the plunger.
The fuel path before the control valve has a first void above the plunger and a second void at the tip of the needle, which become pressurized when the control valve is closed. The plunger is forced upward by the piston, which displaces fuel above the plunger and causes the injection pressure. This pressurization causes the needle to lift, opening the spray apertures.
The above-described invention solves various problems previously associated with fuel injection for lightweight high-speed engines. It permits such engines to be used with injection fuels, such as diesel, jet (i.e. JP-8, JP-6), or other heavy fuels. An example of engines with which the invention is especially useful is engines for lightweight unmanned aircraft, which are typically high-speed two-cycle engines.
An advantage of the invention is that the engine piston provides the pressure for fuel injection, via the plunger action. No pumping component other than the injector plunger and a small low-pressure primary fuel pump need be added to the injection assembly. This satisfies design criteria for injection systems that must be lightweight and compact.
The unit injector is suitable for high engine speeds. The pumping actuation provided by the plunger provides pumping mechanics in close proximity to the injection needle.
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Burrahm Robert W.
Hedrick John C.
Baker & Botts L.L.P.
Miller Carl S.
Southwest Research Institute
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