Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2001-05-23
2003-06-10
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S498000
Reexamination Certificate
active
06575138
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to high pressure fuel injection valves or injectors for internal combustion engines, and, more specifically, to an injection valve that is directly controllable by a position actuating material (such as, for example, a piezoelectric or magnetostrictive material) and which includes a passive hydraulic link.
BACKGROUND OF THE INVENTION
Direct injection of a gaseous fuel into the combustion chamber of an internal combustion engine is desirable for several reasons. For example, direct injection allows charge stratification, eliminating throttling losses associated with homogeneous charge engines. Additionally, with direct injection late in the compression stroke, a high-compression ratio can be maintained, maintaining efficiency. Further, when the fuel that is directly injected comprises natural gas, propane, or hydrogen, the emissions of NO
x
and particulate matter (PM) are significantly reduced. The directly injected gaseous fuel can be ignited with a glow plug, with a spark plug, with pilot diesel fuel, or with any other energy source. The gaseous fuel should be injected at high pressure to overcome the combustion chamber pressure, which is high at the end of the compression stroke. Preferably, the injection pressure is high enough to promote good mixing between the injected fuel and the combustion chamber air.
Direct injection at high pressures presents several challenges. The use of high-pressure fuels for direct injection results in high fuel pressures existing within the injection valve or injector. As a result, when closed, the injection valve should typically be strongly seated to avoid leakage of the fuel into the combustion chamber between injection events. When the valve is a needle valve, the valve is seated when the sealing surfaces of the movable valve needle and the valve seat are in fluid-tight contact with each other. The valve seat is generally part of the valve housing or body. For an outward opening valve, such as a poppet valve, the valve is closed when a valve member is retracted within the valve body so that the sealing surfaces of the valve member are pressed against the valve seat to form a fluid-tight seal. A fuel injection valve with an “outward” opening configuration is defined herein as an injection valve for an internal combustion engine which employs a valve member that is movable in the direction of the engine combustion chamber to an open position and in the opposite direction to a closed position. Terms used to describe such a valve member include, for example, pintle shaft, valve stem, and valve shaft. Outward opening injection valves typically comprise a circular valve head mounted transversely on the valve member for axial motion towards and away from a mating circular valve seat associated with the valve body.
Moreover, compared to low-pressure systems, higher forces are needed to open or close the injection valve. For example, for a needle valve that employs an inwardly opening valve needle, when the needle is in the open position it may be subjected to high forces from the pressurized fuel. Conversely, with an outward opening injection valve, a high amount of force is required to keep the valve closed against the high fuel pressure within the injection valve body.
Additionally, there is only a small window of time during which the fuel can be injected. For example, at 4500 revolutions per minute (RPM), at full load, all of the fuel is preferably injected in less than 2-3 milliseconds.
Nearly all known direct fuel injection systems in internal combustion engines have been hydraulically actuated. These systems rely on a hydraulic fluid to provide the force that is needed to open an injection valve (or valves, when the engine comprises a plurality of combustion chambers). Accordingly, at typical engine operating speeds, hydraulically actuated injectors rely on rapid changes in the hydraulic fluid pressure to open and close the injection valve(s). An injection valve is typically opened by increasing the hydraulic fluid pressure and closed by reducing the hydraulic fluid pressure, such that the opening force applied to the injection valve is reduced, causing the valve to close. However, in the context of a conventional gaseous injection valve, hydraulic operation presents several drawbacks, including:
the need for additional hydraulic hardware such as a hydraulic pump, valves, and a reservoir for the hydraulic fluid;
the need for a seal to be established between the variable pressure hydraulic fluid and the high pressure gaseous fuel;
increased bulkiness of the injection valve assembly because of the additional hardware requirements; and
delayed response of the system caused by time delays associated with the dynamic flow of the hydraulic fluid, the actuation of the electronic hydraulic valve hardware and the movement of the needle that controls gas flow from the injection valve.
Moreover, the degree of controllability of the movement of the injection valve is low when the motive force is provided by a pressurized fluid rather than by a directly controllable source. In this respect, it is difficult to control lift, resulting in limited lift control capabilities when using hydraulically actuated injection valve with a double-spring configuration. Therefore, it is desirable to avoid the use of hydraulics to operate gaseous fuel injectors, particularly for high-speed engines. “Lift” in the context of injection valves is defined herein as the displacement of the valve needle or member away from its closed/seated position to its open position.
U.S. Pat. No. 5,779,149 describes an injector using a piezoelectric actuator acting on a hydraulic control valve through the intermediate of a hydraulic amplifier, which serves to amplify the movement of the actuator. The hydraulic control valve allows the main injection valve to open and close to meter the amount of fuel injected.
A problem with employing a piezoelectric or magnetostrictive actuator to operate a control valve, which in turn controls the flow of a hydraulic fluid to operate an injection valve, is that this arrangement requires the intermediate action of a hydraulic fluid. Any delays caused by the displacement of the hydraulic fluid causes delays in the actuation of the injector. Accordingly, there is a need for an injector that is directly actuated by an actuator without an intermediate active hydraulic operator generating any actuating forces. Another disadvantage of active hydraulically operated systems is that a hydraulic fluid needs to be supplied and drained from a hydraulic cylinder. When diesel fuel is the main fuel used by the engine, the diesel fuel may be used as the hydraulic fluid. However, when a gaseous fuel is the engine's main fuel, a separate hydraulic fluid system is needed to operate injectors that rely on hydraulic actuation.
SUMMARY OF THE INVENTION
An injection valve injects fuel into a combustion chamber of an internal combustion engine. The injection valve comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port; and
a valve seat for cooperating with a valve member to seal the interior chamber from the combustion chamber when the injection valve is closed;
(b) the valve member having one end disposed within the valve housing and an opposite end extendable from the valve seat toward the combustion chamber, wherein the valve member comprises a sealing surface that fluidly seals against the valve seat when the injection valve is closed and that is liftable away from the valve seat when the injection valve is open, wherein valve lift equals the distance traveled by the sealing surface away from the valve seat;
(c) a biasing mechanism associated with the valve member, the biasing mechanism applying a closing force to the valve member when the valve member is in the closed position;
(d) an actuator assembly associated with the valve member, wherein the actuator assembly may be actuated to apply an opening force to the valve member stronger tha
Hebbes Mike
Rahardja Irawan
Welch Alan B.
Gimie Mahmoud
McAndrews Held & Malloy Ltd.
Westport Research Inc.
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