Patent Application
20240136804
This disclosure generally relates to spark plugs and other ignition devices for internal combustion engines, and more particularly, to firing pads attached to spark plug electrodes.
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 causes the power stroke of the engine. The high temperatures, 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 functions. This harsh environment can contribute to erosion and corrosion of the firing pads and electrodes, which can negatively affect the performance of the spark plug over time, potentially leading to a misfire or some other undesirable condition.
To reduce erosion and corrosion of the spark plug electrodes, various types of precious metals and their alloys—such as those made from platinum and iridium—have been used. These materials, however, can be costly. Thus, spark plug manufacturers sometimes attempt to minimize the amount of precious metals used with an electrode by using such materials only at a firing tip of the electrodes where a spark jumps across a spark gap. However, minimizing the amount of material can create risks of firing pad failure, as the thinner cross-section can be more susceptible to thermal cracking.
According to one embodiment, there is provided a spark plug comprising a shell having an axial bore, an insulator disposed at least partially within the axial bore of the shell, a center electrode disposed at least partially within the axial bore of the insulator, a ground electrode configured to create a spark gap with the center electrode, and a firing pad attached to the center electrode or the ground electrode. The firing pad has a multilayer structure having a base layer and a firing layer. The base layer is a non-precious metal based material having silicon. The firing layer is a precious metal based material having yttrium in an amount of 0.1 to 0.5 wt %, inclusive.
In some embodiments, the silicon is present in an amount of 0.001 to 0.5 wt %, inclusive.
In some embodiments, the firing pad is a clad tape having a thickness that is less than or equal to 0.5 mm.
In some embodiments, a thickness of the firing layer is 0.1 to 0.25 mm, inclusive.
In some embodiments, after at least 190 hours of isothermal treatment of at least 1000° C., an extent of vertical cracking extending through the firing layer towards the base layer does not exceed 50% of a thickness of the firing layer.
In some embodiments, the extent of vertical cracking does not exceed 25% of a thickness of the firing layer.
In some embodiments, the precious metal based material of the firing layer has less than 1000 ppm silicon.
In some embodiments, the sparking surface has more yttrium oxides on grain boundaries than silicon oxides on grain boundaries.
In some embodiments, the firing layer has 0.01 to 1.75 at % silicon at the sparking surface.
In some embodiments, one or more vertical cracks of the vertical cracking do not extend to a voiding layer in the firing layer.
In some embodiments, the vertical cracking is sparking surface specific cracking.
In some embodiments, the sparking surface specific cracking is less than half of a grain size of the precious metal based material.
In some embodiments, the sparking surface specific cracking is less than 30 μm.
In some embodiments, the precious metal based material is platinum based.
In some embodiments, the non-precious metal based material is nickel based.
In accordance with another embodiment, there is provided a spark plug comprising a shell having an axial bore, an insulator disposed at least partially within the axial bore of the shell, a center electrode disposed at least partially within the axial bore of the insulator, a ground electrode configured to create a spark gap with the center electrode, and a firing pad attached to the center electrode or the ground electrode. The firing pad has a sparking surface. The firing pad is a precious metal based material having a rare earth element selected from the group of yttrium (Y), hafnium (Hf), scandium (Sc), lanthanum (La), cerium (Ce), and zirconium (Zr) in an amount of 0.1 to 1.0 wt %, inclusive. After at least 190 hours of isothermal treatment of at least 1000° C., an extent of vertical cracking does not exceed 50% of a thickness of the firing pad.
In some embodiments, the extent of vertical cracking does not exceed 25% of a thickness of the firing pad.
In some embodiments, the firing pad has a multilayer structure with a base layer and a firing layer.
Various aspects, embodiments, examples, features and alternatives set forth in the preceding paragraphs, in the claims, and/or in the following description and drawings may be taken independently or in any combination thereof. For example, features disclosed in connection with one embodiment are applicable to all embodiments in the absence of incompatibility of features.
Preferred example embodiments will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
The firing pads and electrodes of the present disclosure can improve the life of the spark plug by effective minimization of thermal vertical cracking. Extensive thermal vertical cracking, particularly with respect to a thinner firing pad that minimizes the use of more expensive precious metal materials, can undesirably result in firing pad failure. It was discovered that silicon dispersion from an underlying non-precious metal based material caused the thermal vertical cracking at grain boundaries in the precious metal materials, even though silicon was not present in the precious metal material at the manufacturing stage. The present embodiments selectively control the silicon dispersion in the precious metal material of the firing pad, thereby minimizing the thermal vertical cracking to an extent that is less likely to result in firing pad failure.
The firing pads and electrodes described herein can be used in spark plugs and other ignition devices including industrial plugs, aviation igniters, or any other device that is used to ignite an air/fuel mixture in an engine. This includes spark plugs used in automotive internal combustion engines, and particularly in engines equipped to provide gasoline direct injection (GDI), engines operating under lean burning strategies, engines operating under fuel efficient strategies, engines operating under reduced emission strategies, or a combination of these. The various firing pads and electrodes may provide improved ignitability, effective pad retention, and cost-effective solutions for the use of precious metal, to cite some possible improvements.
Referring to
In one example, the center electrode 12 and/or ground electrode 18 is made of a non-precious metal based material, or more particularly, a nickel (Ni) alloy material containing silicon that serves as an external or cladding portion of the body, and can include a copper (Cu) or Cu alloy material that serves as an internal core of the body. As used herein, non-precious metal based refers to a material wherein 50 wt % or more is not a precious or noble metal (e.g., nickel-based). Similarly, precious metal based refers to a material wherein 50 wt % or more is a precious or noble metal (e.g., platinum-based). Some non-limiting examples of Ni alloy materials that may be used with the center electrode 12, the ground electrode 18, or both, include an alloy composed of one or more of Ni, chromium (Cr), iron (Fe), manganese (Mn), silicon (Si), or another element; and more specific examples include materials commonly known as Inconel® 600 or 601.
In an advantageous embodiment, the non-precious metal based material used for both the center electrode 12 and the ground electrode 18 is a Ni based material containing 50 wt % or more Ni and 0.001 to 0.5 wt % Si. The Si addition in this amount helps reduce residual oxygen levels, thereby improving oxidation resistance, and control carbons in the alloy. Further, this amount of Si can enhance strength and hardness while improving corrosion resistance, which is of particular benefit in the corrosive and harsh engine environment. However, as detailed further below, Si can be a very reactive element which has a stronger tendency to diffuse into precious metal based materials unless otherwise controlled.
As shown in
With particular reference to the enlarged, schematic view in
In an advantageous embodiment, the multilayer structure 36 of the firing pad 32 is a clad tape 42 having the firing layer 40 serve as the sparking surface 34 and the base layer 38 directly interface with the electrode 12, 18. A clad tape 42 is pre-formed to structurally adhere the firing layer 40 and the base layer 38, and then individual firing pads 32 are cut from the clad tape and welded to the electrode 12, 18. The clad tape 42 further helps minimize the amount of precious metal being used, which can lower costs, while providing a broader area of precious metal available at the sparking surface 34. Additionally, as detailed below, the non-precious metal base layer 38 helps improve weldability by minimizing the difference in thermal expansion coefficients between the firing pad 32 and the electrode 12, 18.
One potential challenge with the clad tape 42 structure is the limited thickness of the firing pad 32 (TFP). While advantageous in terms of material usage, the thickness TFP of the multilayer structure 36 of the clad tape 42 is much smaller than the thickness of a standard prior art firing tip for a spark plug. In one embodiment, the thickness TFP is less than or equal to 0.5 mm, a thickness of the firing layer TFL is between about 0.1 to 0.25 mm, inclusive. In an advantageous embodiment, the thickness TFP is 0.38 mm, with a thickness of the firing layer being about 0.25 mm, and the thickness of the base layer TBL being about 0.13 mm. Given that the thickness of the firing pad TFP is less than 0.5 mm, and preferably, less than 0.4 mm, the firing pad 32 may be more susceptible to problems such as thermal vertical cracking.
As can be seen in
The vertical cracking 44 is shown and described with respect to the prior art representations of the firing pad 32, as shown in
In the embodiment of
Extensive analysis and testing was used to show that the Si-rich grain boundaries 58 were not the result of sample preparation, and instead occurs operationally to eventually cause pad failure. With particular reference to
As shown, the amount of silicon 56 near the sparking surface 34 was 2.18 at %, whereas it is desirable to maintain the amount of silicon at the sparking surface to 0.01 to 1.75 at %, as this amount of silicon is less likely to create undesirable forms of thermal vertical cracking 44, including the sparking surface specific cracking 54. Moreover, looking at the firing layer 40 as a whole, it is advantageous to maintain the amount of diffused silicon 56 to less than 1000 ppm for each portion through the thickness TFL of the firing layer. Again, controlling the silicon diffusion to 1000 ppm or less through the thickness TFL of the firing layer 40 can help improve the structure of the firing pad 32 over time and minimize the thermal cracking 44 and the sparking surface specific cracking 54.
In one embodiment, to arrive at a structurally sound amount of vertical cracking 44 while minimizing the amount of silicon 56 oxidized near the sparking surface 34, 0.1-0.5 wt % inclusive yttrium (Y) is added to the precious metal based material of the firing layer 40.
Accordingly, the center electrode 12, the ground electrode 18, and/or the base metal layer 38 is a non-precious metal based material containing silicon to help reduce residual oxygen levels and control carbons, and the firing layer 40 of the firing pad 32 includes yttrium. With a multilayer structure 36 for the firing pad 32, the base layer 38 acts as a backing to provide strength and rigidity to a thinner precious metal firing layer 40, and is preferably made of a material that enhances initial weldability and subsequent retention to the center electrode 12/ground electrode 18. In other words, in some cases the precious metal material may be more easily attached and retained to the material of the base layer 38 than directly to the electrode body (such as in the case when manufacturing thin, multi-layered clad tapes 42). Examples of materials for the non-precious metal based material include Ni-alloys that can contain chromium (Cr), iron (Fe), aluminum (Al), manganese (Mn), Si (0.001 to 0.5 wt %, inclusive), and/or another element; and more specific examples include Inconel® 600 or 601. In a particular embodiment, the non-precious metal based material is Ni-based with Cr added in an amount from 0.01 to 25 wt % inclusive, Fe from 0.01-20 wt % inclusive, Al from 0.01-2 wt % inclusive, niobium (Nb) from 0.01-5 wt %, molybdenum (Mo) from 0.01-5 wt %, with Si up to 0.5 wt %.
For the firing layer 40, an advantageous embodiment for the precious metal based material is Pt-10Ir-(0.1-0.5)Y (in wt %). Several other precious metal based materials with a rare earth element addition could also be used, particularly with the multilayer 36 clad tape 42 implementation, where the thickness TFL of the firing layer 40 is substantially smaller than other firing pads 32. The minor addition of a rare earth element may include Y, hafnium (hf), scandium (Sc), lanthanum (La), cerium (Ce) and/or zirconium (Zr). The amount of the minor rare earth element can be added in an amount of 0.01-1 wt % inclusive. In some embodiments, one or more of these minor rare earth element additions can be added to the following precious metal materials to create the precious metal based material for the firing layer 40: (1) Pt—Ir alloy, with the Ir content being 0-49 wt %; (2) Pt-rhodium (Rh) alloy, the Rh content being 0-49 wt %; (3) Pt—Ni alloy, the Ni content being 0-49 wt %; (4) Pt-palladium (Pd) alloy, the Pd content being 0-49 wt %; (5) Pt-ruthenium (Ru) alloy, the Ru content being 0-49 wt %; (6) Ir—Rh alloy, the Rh content being 0-49 wt %; (7) Ir—Ru alloy, the Ru content being 0-49 wt %; (8) Ir—Pt alloy, the Pt content being 0-49 wt %; (9) Ir—Rh alloy, the Rh content being 0-49 wt %; or (10) Ir—Pd alloy, the Pd content being 0-49 wt %. In other embodiments, the precious metal system includes ternary alloys with the addition of the rare earth element, the ternary alloys including three major elements selected from Pt, Ir, Rh, Pd, Ru, and gold (Au).
It is to be understood that the foregoing is a description of one or more preferred example embodiments. 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. In addition, the term “and/or” is to be construed as an inclusive OR. Therefore, for example, the phrase “A, B, and/or C” is to be interpreted as covering all the following: “A”; “B”; “C”; “A and B”; “A and C”; “B and C”; and “A, B, and C.”
