Patent Application
20140232254
This invention generally relates to spark plugs and other ignition devices for internal combustion engines and, in particular, to electrode materials for spark plugs.
Spark plugs can be used to initiate combustion in internal combustion engines. Spark plugs typically ignite a gas, such as an air/fuel mixture, in an engine cylinder or combustion chamber by producing a spark across a spark gap defined between two or more electrodes. Ignition of the gas by the spark causes a combustion reaction in the engine cylinder that is responsible for the power stroke of the engine. The high temperature gradients, high electrical voltages, rapid repetition of combustion reactions, and the presence of corrosive materials in the combustion gases can create a harsh environment in which the spark plug must function. This harsh environment can contribute to erosion and corrosion of the electrodes that can negatively affect the performance of the spark plug over time, potentially leading to a misfire or some other undesirable condition.
To help control or reduce the operating temperature of the spark plug electrodes, the electrodes may include a core made of a material having a high thermal conductivity, such as copper (Cu), to help conduct heat away from a sparking end of the spark plug electrodes. The copper core may be surrounded or covered by a cladding or sheath of a material having corrosion and erosion resistant properties, such as nickel (Ni). However, traditional copper cored electrodes can sometimes experience relaxation and/or swelling issues when used in engines running periodically between full throttle and idle operation. In such operation, the electrodes experience significant temperature gradients, which in turn can create thermal stresses that can result in electrode creep, changes to the spark gap, as well as other unwanted consequences.
According to one embodiment, there is provided an electrode core material for use in a spark plug electrode. The electrode core material may comprise: a copper matrix made of a copper-based material, wherein copper is the single largest constituent of the copper matrix by weight; and a plurality of precipitates dispersed in the copper matrix, wherein the precipitates strengthen the copper matrix so that the electrode core material is a precipitate-strengthened copper alloy.
According to another embodiment, there is provided a spark plug electrode. The spark plug electrode may comprise: a core made of a precipitate-strengthened copper alloy including a copper matrix and a plurality of precipitates dispersed in the copper matrix; and a cladding surrounding the core, wherein the cladding is made of a nickel-based material where nickel is the single largest constituent of the nickel-based material by weight.
According to another embodiment, there is provided a spark plug. The spark plug may comprise: a metallic shell having an axial bore; an insulator being at least partially disposed within the axial bore of the metallic shell, the insulator having an axial bore; a center electrode being at least partially disposed within the axial bore of the insulator; and a ground electrode being attached to the metallic shell. The center electrode, the ground electrode, or both the center and ground electrodes include a cladding formed of a nickel-based material and a core comprising a copper matrix and a plurality of precipitates dispersed throughout the copper matrix.
Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
The electrode core material described herein is a thermally conductive, copper-based material that is added to a spark plug electrode in order to manage, control and/or otherwise affect the thermal characteristics of the spark plug firing end. According to one embodiment, the electrode core material possesses a thermal conductivity (e.g., greater than 250 W·m−1·K−1) that is great enough to satisfy the thermal requirements of the spark plug electrode, yet also has a strength that is great enough to resist unwanted electrode deformation and thus help avoid relaxation and/or swelling in the electrode. This electrode core material may be used in spark plugs and other ignition devices including industrial plugs, aviation igniters, glow plugs, or any other device that is used to ignite an air/fuel mixture in an engine. This includes, but is certainly not limited to, the exemplary spark plugs that are shown in the drawings and that are described below. Furthermore, it should be appreciated that the electrode core material may be used in both the center electrode and the ground electrode, or it may be used in only one of the center or ground electrodes, to cite several possibilities. Other embodiments and applications of the core material are also possible.
Referring to
The center electrode 12 and/or the ground electrode 18 may include a core made from a thermally conductive material, such as the electrode core material described below, and a cladding or sheath surrounding the core. The core of the center electrode 12 and/or the ground electrode 18 is preferably designed to help conduct heat away from the firing ends of the electrodes towards cooler portions of the spark plug 10. In the embodiment shown in
Referring now to
It should be appreciated that the non-limiting spark plug embodiments described above are only examples of some of the potential uses for the electrode core material, as it may be used or employed in any firing tip, electrode, or other firing end component that is used in the ignition of an air/fuel mixture in an engine. For instance, the following components may be at least partially formed from or otherwise include the present electrode core material: a center and/or ground electrode; an electrode core that extends all the way to a firing end of a center and/or ground electrode; an electrode core that terminates or stops short of a firing end of a center and/or ground electrode; an electrode core that extends all the way to a free end of a ground electrode so that it directly contacts a spark plug shell; an electrode core that extends all the way underneath a noble metal pad or tip on a side surface of a ground electrode; an electrode core that terminates or stops short of a noble metal pad or tip on a side surface of a ground electrode; an electrode core that radially extends the entire width of a center electrode so that the core forms the outer surface of the center electrode for at least a portion thereof; or a multi-layer center and/or ground electrode where there are multiple core and/or cladding layers. These are but a few examples of the possible applications of the electrode core material, others exist as well. As used herein, the term “electrode”—whether pertaining to a center electrode, a ground electrode, a spark plug electrode, etc.—may include a base electrode member by itself, a firing tip by itself, or a combination of a base electrode member and one or more firing tips attached thereto, to cite several possibilities.
The electrode core material is a precipitate-strengthened copper alloy and may include precipitates uniformly dispersed within a copper (Cu) matrix. The precipitates and the copper (Cu) matrix have different chemical compositions and different chemical and mechanical properties. Accordingly, the precipitates and the copper (Cu) matrix each contribute a separate set of desirable attributes or characteristics to the core material. In particular, the copper (Cu) matrix provides the core material with high thermal conductivity and suitable ductility for manufacturing, while the precipitates provide the core material with creep and fatigue resistance at high temperatures by impeding dislocation motion across these precipitates, which strengthens the electrode core material.
Inclusion of the precipitates in the copper (Cu) matrix may result in the electrode core material having a thermal conductivity that is somewhat lower than the thermal conductivity of pure copper. Therefore, it is desirable to control the proportion of precipitates in the electrode core material so that the electrode core material maintains a thermal conductivity of greater than about 250 W·m−1·K−1. For example, the electrode core material preferably has a thermal conductivity of between 250 W·m−1·K−1 and 350 W·m−1·K−1, but this is not necessary or required. According to one exemplary embodiment, the precipitates may account for about 0.05-3.0 wt % of the overall electrode core material, the copper (Cu) matrix may account for about 94.5-99.94 wt % of the overall electrode core material, and impurities like Zn, Sn and Pb may account for up to about 2 wt % of the overall electrode core material.
The copper (Cu) matrix of the electrode core material may be a copper-based material including a plurality of fused copper (Cu) grains throughout which the precipitates are dispersed. The term “copper-based material,” as used herein, broadly includes any material or alloy where copper (Cu) is the single largest constituent of the material, based upon the overall weight of the material. This may include materials having greater than 50 wt % copper (Cu), as well as those having less than 50 w t% copper (Cu), so long as copper (Cu) is the single largest constituent. For example, the copper-based material may be an oxygen-free copper (OFC) alloy having a copper (Cu) content of greater than 99.95 wt %.
The precipitates in the electrode core material may constitute an incoherent phase comprising a plurality of fine particles uniformly dispersed throughout the copper (Cu) matrix. The precipitates may be referred to as “incoherent,” in that there is little or no matching between the lattice orientation of the precpitates and that of the copper (Cu) matrix. In one embodiment, the precipitates include some combination of iron (Fe), phosphorus (P), beryllium (Be), cobalt (Co), nickel (Ni) and/or silicon (Si), and form particles (e.g., particles made of iron (Fe), iron phosphoride (FeP, Fe2P and Fe3P), beryllium (Be) and nickel silicide (Ni2Si)) with mean particle diameters of less than about 2 μm. For example, the precipitates may have a mean particle diameter between 0.01 μm and 1 μm. Three different exemplary precipitate-strengthened copper alloys are disclosed below: a Cu—Fe—P alloy, a Cu—Fe—Be—Co alloy and a Cu—Ni—Si alloy.
According to the Cu—Fe—P alloy example, the iron (Fe) and the phosphorous (P) may react to form particles of iron and iron phosphoride (FeP, Fe2P and Fe3P) that are then dispersed throughout the copper matrix. The amount of iron (Fe) in the precipitate-strengthened copper alloy may be: greater than or equal to 0.01 wt %, 0.05 wt %, 0.1 wt %, 0.5 wt %, 0.75 wt %; less than or equal to 5.0 wt %, 4.0 wt %, 3.0 wt %, or 1.5 wt %; or between 0.01-5.0 wt %, 0.05-5.0 wt %, 0.1-4.0 wt %, 0.5-3.0 wt %, or 0.75-1.5 wt %. The amount of phosphorus (P) in the precipitate-strengthened copper alloymay be: greater than or equal to 0.005 wt %, 0.01 wt %, 0.025 wt %, 0.05 wt %, 0.075 wt %; less than or equal to 0.5 wt %, 0.4 wt %, 0.3 wt %, or 0.15 wt %; or between 0.005-0.5 wt %, 0.01-0.5 wt %, 0.025-0.4 wt %, 0.05-0.3 wt %, or 0.075-0.15 wt %. According to one particular embodiment, the precipitate-strengthened copper alloycomprises iron (Fe) from about 0.01 wt % to 3.0 wt %, inclusive, phosphorus (P) from about 0.01 wt % to 0.4 wt %, inclusive, and the balance copper (Cu). Although alloys including copper, iron and phosphorous (i.e., Cu—Fe—P alloys) may be used with any suitable core configuration, as explained above, they are sometimes particularly well suited for use with longer cores like that shown in
Some preferred examples of precipitate-strengthened copper alloysthat may be used in a ground electrode, a center electrode or both, include the following materials that all have copper, iron and phosphorus (the following compositions are given in weight percentage, and the copper (Cu) constitutes the balance): Cu-(0.05-0.15)Fe-(0.025-0.04)P; Cu-(2.1-2.6)Fe-(0.015-0.15)P; Cu-0.72Fe-0.31P; and Cu-(0.8-1.2)Fe-(0.01-0.04)P.
According to the Cu-Fe-Be-Co alloy example, the precipitate-strengthened copper alloy may include copper (Cu), iron (Fe), beryllium (Be), and cobalt (Co) such that dispersed Be particles strengthen the copper matrix. For example, the precipitate-strengthened copper alloy may include about 0.2 wt % Fe, from about 0.15 wt % to about 0.5 wt % Be, inclusive, and from about 0.35 wt % to about 0.6 wt % Co, inclusive, with the balance being Cu. According to the Cu—Ni—Si alloy example, the precipitate-strengthened copper alloy uses nickel silicide (Ni2Si) particles to strengthen the copper matrix, and includes from about 2.2 wt % to about 4.2 wt % Ni, inclusive, and from about 0.25 wt % to about 1.2 wt % Si, inclusive, with the balance being Cu. Other precipitate-strengthening alloy compositions and materials are certainly possible, as the above-mentioned examples represent only some of the possibilities.
As discussed above, the electrode core material is a precipitate-strengthened copper alloy and exhibits a multi-phase microstructure, with a copper (Cu) matrix phase being distinct or distinguishable from a particulate phase.
In manufacture, the precipitate-strengthened copper alloy may be made according to a number of different metallurgical and other techniques. Skilled artisans will appreciate that the solubility of iron (Fe) and phosphorous (P) in copper (Cu) is quite low (e.g., the solubility of Fe in Cu is about 0.14 wt %). Thus, in a copper-based alloy with a saturated amount of iron (Fe) (e.g., more than 0.14 wt % Fe), the iron will likely precipitate out as a strengthening phase. Because phosphorous (P) is a fairly active element, it can react with the iron (Fe) to form an iron phosphoride phase. Thus, in the exemplary Cu—Fe—P alloys described above, it is expected that iron (Fe) and iron phosphorides (FeP, Fe2P and Fe3P) will form precipitate phases. The following process is a non-limiting example of a process that may be used to form one of the precipitate-strengthened copper alloys described herein; other methods may certainly be used instead.
To form a precipitate-strengthened copper alloy, the copper alloy may first be solution treated (e.g., at about 850° C. for approximately 1-2 hours). After solution treatment, the copper alloy may then be quenched in water, with a suitable aging treatment to follow (e.g., at about 450-550° C. for approximately 2 hours). In order to enhance the formation of the precipitates in the copper alloy, cold working techniques such as rolling and extrusion can be applied in between the solution treatment and the aging treatment steps described above. An example of a potential cold working technique involves deformation of about 20-40%, but others may be used instead. In the Cu—Fe—P alloy described above, the aforementioned steps may be used to enhance the formation of iron (Fe) and iron-phosphoride (FeP, Fe2P and Fe3P) precipitates with a regular or average particle size of about 1 μm. To form the nickel-based cladding or sheath around the electrode core material, the precipitate-strengthened copper alloy is inserted or stuffed into a tube-like cladding structure having an outer diameter of about 2 mm-5 mm and a cladding wall thickness of less than about 1.5 mm, for example. Then, in step 270, the core material and the cladding structure are extruded together to form a spark plug electrode material. If an elongated wire is desired, then the core material and the cladding structure may be cold extruded to form a fine wire having a diameter of about 1 mm to about 3 mm, inclusive, which in turn can be cut or cross-sectioned into individual pieces of a desired length. After the core material and the cladding structure have been co-extruded, any number of different post-processing techniques may be used, including welding techniques that attach one or more precious metal tips to the resulting electrodes.
The cladding structure may be made of a material having high thermal stability and corrosion resistant properties, such as nickel (Ni), iron (Fe), cobalt (Co), or an alloy thereof. Preferably, the cladding material is a nickel-based material comprising nickel (Ni) and at least one of: aluminum (Al), chromium (Cr), manganese (Mn), silicon (Si), titanium (Ti), yttrium (Y), zirconium (Zr), or mixtures thereof. The term “nickel-based material,” as used herein, broadly includes any material or alloy where nickel (Ni) is the single largest constituent of the material, based upon the overall weight of the material. This may include materials having greater than 50 wt % nickel (Ni), as well as those having less than 50 wt % nickel (Ni), so long as nickel (Ni) is the single largest constituent. Any of the following alloy systems are suitable for the cladding material: Ni—Al—Si—Y, Ni—Cr, Ni—Cr—Mn—Si, Ni—Cr—Al, Ni—Cr—Al—Mn—Si, and Ni—Cr—Mn—Si—Ti—Zr. Some preferred examples of cladding materials that may be used in a ground electrode, a center electrode or both, include the following (the following compositions are given in weight percentage, and the nickel (Ni) constitutes the balance): Ni-(1.0-1.5)A1-(1.0-1.5)Si-(0.1-0.2)Y and Ni-(1.65-1.90)Cr-(1.8-2.1)Mn-(0.35-0.55)Si-(0.2-0.4)Ti-(0.1-0.2)Zr, as well as materials that go by the trade names Inconel 600 and Inconel 601.
With reference now to
It is to be understood that the foregoing is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “for example,” “e.g.,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
This application claims the benefit of U.S. Provisional Ser. No. 61/765,246 filed on Feb. 15, 2013, the entire contents of which are incorporated herein.
| Number | Date | Country | |
|---|---|---|---|
| 61765246 | Feb 2013 | US |
