Patent Application
20160348629
The present disclosure relates to a fuel injector of an internal combustion engine and, more particularly, to a pilot valve seat of the fuel injector comprised of a compacted powder metal material.
Fuel injectors include a pilot or control valve seat and a check valve ball for controlling fuel flow through the fuel injector. During operation of the fuel injector, the check ball moves from a closed position, in which the check valve ball is seated against the valve seat to inhibit fuel flow, to an open position, in which the check valve ball moves away from the valve seat to allow fuel flow. More particularly, the check valve ball is seated against the valve seat and fully in the closed position when the check valve ball is aligned along a longitudinal centerline of the valve seat.
Fuel injectors may be fluidly coupled to a high-pressure common rail such that the fuel flowing through the fuel injector is under high pressure and at a high velocity. Additionally, the length of a fuel cycle in a particular fuel injector may be approximately 1-3 microseconds. Due to the high pressure and high velocity of the fuel and the short duration of the fuel cycle, the check valve ball may move rapidly between the open and closed positions. When the check valve ball is in the open position, the ball may be moved off the longitudinal centerline of the valve seat by the fuel flow. On closing, the check valve ball may contact a conical wall of the valve seat at an off-center location away from the longitudinal centerline and may “slide” down the conical wall toward the seated position directly on the valve seat. This sliding action by the ball, the high pressure of the fuel, the high velocity of the fuel, and/or the large force exerted on the valve seat when the check valve ball returns to the closed position may lead to spalling at the valve seat. Spalling develops from cracks that occur in the sub-surface of the material comprising the valve seat which may eventually contribute to material flaking and decreased material strength at the valve seat.
In one embodiment of the present disclosure, a fuel injector comprises an injector body having an injector cavity, a valve seat, and a flow control member. The valve seat is comprised of a metallic material having a grain size of 0.05-5.0 μm. Additionally, the fuel injector comprises a nozzle valve element positioned in the injector cavity and configured to move between an open position in response to the flow control member being spaced apart from the valve seat and a closed position in response to the flow control member engaging the valve seat. Fuel is configured to flow from the fuel injector in response to the nozzle valve element being in the open position.
In another embodiment of the present disclosure, a method of manufacturing a valve seat of a fuel injector comprises providing a metallic material having a melting temperature, heating the metallic material to a liquid phase above the melting temperature, atomizing the metallic material when in the liquid phase, and forming powdered metallic particles having a diameter of less than 5.0 μm from the atomized metallic material. Additionally, the method comprises joining the powdered metallic particles to define a metallic mass and forming the valve seat from the metallic mass.
In a further embodiment of the present disclosure, a method of manufacturing a valve seat of a fuel injector comprises providing a metallic material, forming a plurality of powered particles from the metallic material, and joining the powdered particles to define a metallic mass. The metallic mass is a tool steel material having a grain size of less than 10.0 μm and comprising 1.0-2.0 wt. % carbon, 0.1-1.0 wt. % silicon, 0.1-1.0 wt. % manganese, 4.5-5.0 wt. % chromium, 3.0-4.0 wt. % molybdenum, and 3.5-4.5 wt. % vanadium. Additionally, the method comprises forming the valve seat from the metallic mass.
Advantages and features of the embodiments of this disclosure will become more apparent from the following detailed description of exemplary embodiments when viewed in conjunction with the accompanying drawings.
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Nozzle module 8 includes a nozzle element guide 24 which includes a proximal cap or end portion 26 and a control volume plug 28. A control volume 30 is formed between an end portion 32 of nozzle valve element 22 and an interior of nozzle element guide 24 when nozzle valve element 22, nozzle element guide 24, and end portion 26 are mounted in injector cavity 16.
The pressure of fuel in control volume 30 determines whether nozzle valve element 22 is in an open position or a closed position, which is further determined by injection control valve assembly 6, as is further disclosed herein. When nozzle valve element 22 is positioned in injector cavity 16, nozzle element guide 24, and more specifically, end portion 26 of nozzle element guide 24, is positioned longitudinally between nozzle valve element 22 and injection control valve assembly 6.
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Control valve member 38 is positioned in valve cavity 14 and moves reciprocally between an open position, permitting check valve ball 40 to move longitudinally to permit fuel flow through fuel delivery passage 34, and a closed position, where check valve ball 40 blocks fuel flow through fuel delivery passage 34. Actuator 42 includes a solenoid assembly 44 that includes a stator housing 46 having a first end 48 and a second end 50, a stator core 52, an annular coil assembly 54 positioned circumferentially in and around stator core 52, and an armature 56 operably connected to control valve member 38. Stator housing 46 includes a central aperture or core 58 extending through stator housing 46 from first end 48 to second end 50. Central aperture 58 includes a spring cavity 60 and is positioned to receive control valve member 38. Stator core 52 is positioned on stator housing 46, and in the exemplary embodiment, stator core 52 is secured to stator housing 46.
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To reduce spalling, exemplary valve seat body 62 is fabricated from a metallic material and, more particularly, from a tool steel formed by a powdered metallurgy process. In one embodiment, the powdered metal tool steel (“PMTS”) of valve seat body 62 is a fine-grain material generally comprising grains 80 with a grain size of less than 10 μm. For example, grains 80 of the PMTS comprising valve seat body 62 and, therefore valve seat 64, may have a grain size of 0.05-8.0 μm and, more particularly, 0.05-4.0 μm. By decreasing the grain size of the PMTS comprising valve seat body 62, the toughness, and, therefore, the fatigue strength, of the PMTS of valve seat body 62 is increased relative to other metallic materials with larger grain sizes, such as grains sizes of more than 10 μm.
Grains 80 forming the PMTS of valve seat body 62 and, therefore valve seat 64, comprise a tool steel material having a face-centered cubic crystalline microstructure. For example, the PMTS comprising valve seat body 62 and valve seat 64 is a monolithic tool steel with 1.0-2.0 wt. % carbon, 0.1-1.0 wt. % silicon, 0.1-1.0 wt. % manganese, 4.5-5.0 wt. % chromium, 3.0-4.0 wt. % molybdenum, and 3.5-4.5 wt. % vanadium. More particularly, in one embodiment, the PMTS of valve seat body 62 and valve seat 64 comprises 1.4 wt. % carbon, 0.4 wt. % silicon, 0.4 wt. % manganese, 4.7 wt. % chromium, 3.5 wt. % molybdenum, and 3.7 wt. % vanadium.
To form the PMTS of valve seat body 62 and valve seat 64, metallic materials are melted into the molten phase and the molten material is sprayed with a compressed gas to atomize the metallic material and form small-diameter metallic particles. For example, the particles may have a diameter of 5-10 μm when sprayed to form the powdered metal. The spraying process instantly cools the molten metal particles which allows for uniform distribution of the alloying elements within each of the particles. As such, the grain size of the metallic material comprising the particles remains small, for example 0.05-10.0 μm and, more particularly, 0.05-4.0 μm. In one embodiment, the grain size of the PMTS of the present disclosure is approximately 0.16 μm. Additionally, because the alloying elements are uniformly distributed within each particle, the alloying elements do not accumulate at grain boundaries 82 of the metallic material. For example, carbide matrices do not accumulate at grain boundaries 82 and, therefore, stress concentrations resulting from accumulated carbide matrices are not introduced into the metallic material. In this way, the material at grain boundaries 82 comprises the same PMTS material as grains 80 forming valve seat body 62 and valve seat 64.
After the metallic material is atomized, the particles coalesce or are joined together to form PMTS metallic bars or slugs through a solid-state welding process. Solid-state welding processes join the individual particles together to form a solid mass at temperatures below the melting temperature of the metallic material. For example, in one embodiment, the powdered metal particles may be positioned within a mold or canister and are roll welded to form the metallic slugs. Additionally, in other embodiments, the powered metal particles may be formed into the PMTS slugs through any other solid-state welding process, such as powder forging, isostatic pressing, metal injection molding, cold welding, diffusion welding, and/or friction welding.
Once formed into the metallic slugs, further processes steps may occur, such as annealing, hardening, quenching, and/or tempering. Additionally, the PMTS slugs are then machined to form valve seat body 62 and valve seat 64 of fuel injector 2.
The material comprising valve seat body 62 and valve seat 64, when formed as disclosed herein, results in a PMTS with a grain size of approximately 0.05-10.0 μm, and more particularly 0.05-4.0 μm, a hardness of 55-70 Rockwell C, and more particularly 60 Rockwell C, a density of approximately 7,500-8,000 kg/m3, and more particularly 7,700 kg/m3, at 20° C., and a modulus of elasticity of 200,000-210,000 N/mm2, and more particularly 206,000 N/mm2, at 20° C. In one embodiment, the PMTS comprising valve seat body 62 and valve seat 64 may be Vanadis® 4 Extra available from Uddeholm.
The aforementioned properties of the PMTS comprising valve seat body 62 and valve seat 64 increase the fatigue strength of valve seat 64. The fatigue strength of valve seat 64 is increased because the small grain size and uniform distribution of the alloying elements comprising the PMTS decreases the accumulation of alloying elements at grain boundaries 82. Accumulations of alloying elements at grain boundaries 82 may occur through nitriding and/or carborizing processes and can trigger the initiation of sub-surface cracks which causes spalling. However, because the formation of the PMTS of the present disclosure does not utilize a nitriding or carborizing process and, instead, uniformly distributes the alloying elements throughout the material, the number of sub-surface crack initiation sites is reduced and the fatigue strength of the PMTS is increased. In this way, the PMTS is resistant to contact fatigue from the force of check valve ball 40 closing against valve seat 64 and the force of the high-pressure and high-velocity fuel flowing through valve seat 64. More particularly, the increased fatigue strength of the PMTS comprising valve seat body 62 and valve seat 64 increases the resistance to cracks that may occur within and propagate through grains 80 within the sub-surface of valve seat body 62 and valve seat 64 due to increased plastic strain within valve seat body 62. Therefore, spalling is reduced when valve seat body 62 and valve seat 64 is comprised of the PMTS of the present disclosure.
Additionally, the increased hardness of the PMTS comprising valve seat 64 decreases the need for a coating applied to valve seat 64. Therefore, the outermost surface of check valve ball 40 is configured to directly contact the outermost surface of valve seat 64 when in the closed in positioned because no coating is added to the outermost surface of valve seat 64 and, as such, no coating is positioned intermediate the outermost surfaces of valve seat 64 and check valve ball 40. Alternatively, in other embodiments, a coating may be applied to the outermost surface of valve seat 64 and/or check valve ball 40 to increase resistance to contact fatigue at valve seat 64.
While various embodiments of the disclosure have been shown and described, it is understood that these embodiments are not limited thereto. The embodiments may be changed, modified and further applied by those skilled in the art. Therefore, these embodiments are not limited to the detail shown and described previously, but also include all such changes and modifications.
