Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2001-05-23
2003-07-01
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S498000
Reexamination Certificate
active
06584958
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 magnetostrictive material and that 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 the efficiency of conventional diesel engines. 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 needs to 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.
Moreover, compared to low-pressure systems, higher forces are needed to open the injection valve since the valve should be strongly seated to remain sealed when the valve tip is exposed to the high pressures generated in the combustion chamber. High closing forces are also involved since the needle of a fuel injection valve for a high-pressure system should overcome the high forces generated by the exiting pressurized fuel when the needle is in the open position.
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 to open a fuel injection valve (or valves, when the engine comprises a plurality of combustion chambers). Accordingly, at typical engine operating speeds, hydraulically actuated fuel injection valves 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 gaseous fuel 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 of the hydraulic fluid between the electrical valve hardware and the needle that controls gas flow from the injector.
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 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 away from its closed/seated position to its open position.
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;
a nozzle comprising at least one nozzle orifice providing a fluid passage from the interior chamber to the combustion chamber;
(b) a valve needle formed from a ferromagnetic material and disposed within the valve housing wherein the valve needle is movable between a closed position at which a sealing end of the valve needle contacts a valve seat to fluidly seal the interior chamber from the nozzle orifice, and an open position at which the sealing end of the valve needle is spaced apart from the valve seat whereby the interior chamber is fluidly connected with the nozzle orifice;
(c) a needle biasing mechanism associated with the valve needle, the needle biasing mechanism applying a closing force to the valve needle for biasing the valve needle in the closed position; and
(d) an actuator assembly associated with the valve needle and disposed in the interior chamber, the actuator assembly comprising a magnetostrictive member actuatable to expand in length and apply an opening force to the valve needle stronger than the closing force, thereby moving the valve needle to the open position.
In a preferred injection valve, the actuator assembly is disposed within the interior chamber in an annular space surrounding at least a portion of the valve needle. The preferred needle biasing mechanism is a spring, most preferably at least one disc spring.
Locating the actuator assembly in an annular space that surrounds a portion of the valve needle is a preferred arrangement because it allows for a compact design. The actuator assembly is typically elongated and has a length that is determined by the desired lift, which in turn determines the length of the magnetostrictive member. When a magnetostrictive actuator is actuated, a magnetic field is applied to the magnetostrictive member to cause it to expand in length. Longer magnetostrictive members are able to expand by greater amounts, resulting in greater lift when used in an injection valve application.
Conventional devices with similar arrangements (that is, a solid member extending through a tubular magnetostrictive member) employ a non-ferromagnetic member to avoid interfering with the magnetic field. In the field of magnetostrictive materials, it is generally believed that employing a ferromagnetic material for the valve needle will cause leakage of magnetic flux, which may in turn compromise performance since all flux is intended to pass through the tubular magnetostrictive member and the flux paths provided by conventional poles and flux tubes. Consistent with such beliefs, conventional devices with similar arrangements have employed non-ferromagnetic materials such as, for example, austenitic stainless steel, titanium and ceramics.
Compared to ferromagnetic materials, there are a number of disadvantages of employing such non-ferromagnetic materials. For example, titanium and ceramics are generally more expensive and more difficult to machine to high tolerances, compared to ferromagnetic materials such as tool steel. In addition, non-ferromagnetic materials such as titanium and austenitic stainless steel generally can not be hardened to match the durability of ferromagnetic materials. Past approaches to solving some of these disadvantages have i
Hebbes Mike
Rahardja Irawan
Gimie Mahmoud
McAndrews Held & Malloy Ltd.
Westport Research Inc.
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