Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2001-05-23
2003-05-20
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S478000
Reexamination Certificate
active
06564777
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 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.
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.
Co-owned U.S. Pat. No. 6,298,829 discloses an injection valve that can achieve the performance to inject a gaseous fuel through injection events having a duration of less than 2-3 milliseconds. A preferred embodiment of the injection valve disclosed in the '130 application comprises a tubular magnetostrictive actuator assembly with a valve needle that extends axially through the center of the actuator assembly. The actuator assembly comprises a tubular magnetostrictive member that expands in length when it is actuated by subjecting it to a magnetic field. The magnetic field is generated, for example by directing an electric current through an electric coil disposed in an annular space around the tubular magnetostrictive member.
An advantage of this arrangement is that a more compact length is achieved since the tubular actuator assembly overlaps with the valve needle. However, a concern with respect to this arrangement is that the valve needle extending through the actuator assembly may cause interference with the magnetic field and some of the magnetic flux may be drained from the magnetostrictive member and conducted through the valve needle. Accordingly, for injection valves employing such an arrangement, there is a need to ensure that the valve needle does not interfere with the operation of the actuator assembly.
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 a valve seat and at least one nozzle orifice providing a fluid passage from the interior chamber to the combustion chamber;
(b) an actuator assembly disposed within the valve housing, the actuator assembly comprising a magnetostrictive member actuatable by imposition of a magnetic field to expand in length to provide a valve opening force;
(c) a plurality of portions joined together to form a unitary valve needle disposed within the valve housing and extending through the actuator assembly, the unitary valve needle comprising:
a shaft portion formed from a non-ferromagnetic material, the shaft portion extending through the magnetostrictive actuator assembly;
a valve needle tip having sufficient durability to contact and seal the valve seat over multiple opening and closing cycles; and
a member through which the valve opening force is transferred from the tubular actuator assembly to the unitary valve needle,
wherein the unitary valve needle is movable between a closed position at which the valve needle tip contacts the valve seat to fluidly seal the interior chamber from the nozzle orifice, and an open position at which the valve needle tip is spaced apart from the valve seat whereby the interior chamber is fluidly connected with the nozzle orifice; and
(d) 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.
In a preferred injection valve, the actuator assembly and the magnetostrictive member are tubular. The valve needle tip is preferably formed from a material having through-hardness greater than that of the non-ferromagnetic material. The preferred needle biasing mechanism is a spring, most preferably at least one disc spring.
In the above-described arrangement, the actuator assembly is disposed in an annular space that surrounds a portion of the valve needle. This 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.
A disadvantage of using a non-ferromagnetic material for the present application, however, is that the valve tip is subjected to high frequency impact loads caused whenever the valve tip is seated against the valve seat. Compared to ferromagnetic materials, non-ferromagnetic materials such as titanium and austenitic stainless steel generally cannot be hardened to match the durability of ferromagnetic materials. Past approaches to solving some of these disadvantages have included coating the non-ferromagnetic material to improve its durability, but coatings are generally more suited to components that are subjected to sliding mov
Hebbes Mike
Rahardja Irawan
Gimie Mahmoud
McAndrews Held & Malloy Ltd.
Westport Research Inc.
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