Spark plug with thermally coupled center electrode

Abstract

One example provides a spark plug including an axial centerline extending between a terminal end and a firing end, an insulator core including a center bore having a first diameter coincident with the axial centerline extending through the insulator core, an insulator nose proximate the firing end, and a counterbore coincident with the axial centerline and extending axially into the insulator nose, the counterbore having a second diameter greater than the first diameter. A center electrode includes an electrode wire disposed within the center bore and having a first end extending into the counterbore, and an electrode tip mechanically and electrically coupled to the first end of the electrode wire, a first portion of the electrode tip being within the counterbore to define an interface with the counterbore for providing a heat transfer path from the electrode tip to the insulator core.

Description

[0001] Cross-reference to related applications

[0002] This PCT application claims priority to U.S. Patent Application No. 17 / 396,149, filed August 6, 2021, entitled “SPARK PLUG WITH THERMALLY COUPLED CENTER ELECTRODE”, and U.S. Provisional Patent Application No. 63 / 062,917, filed August 7, 2020, entitled “SPARK PLUG WITH THERMALLY COUPLED CENTER ELECTRODE”. Technical Field

[0003] This disclosure relates to spark plugs having a thermally coupled center electrode. Background Technology

[0004] Spark plugs are used in the combustion chamber of a combustion system, such as in the cylinders of a vehicle's internal combustion engine, to ignite the pressurized air-fuel mixture. To extend spark plug life, harder metals (such as platinum and iridium) are increasingly being used instead of nickel-copper alloys for the spark plug electrodes. However, spark plugs made of these metals are expensive and, in some cases, may reduce engine performance compared to so-called nickel spark plugs. Summary of the Invention

[0005] A spark plug is provided, comprising an axial centerline extending between a terminal end and an ignition end, an insulating core including a center bore having a first diameter coinciding with the axial centerline extending through the insulating core, an insulating nose proximal to the ignition end, and a countersunk hole coinciding with the axial centerline and extending axially into the insulating nose, the countersunk hole having a second diameter greater than the first diameter. A center electrode includes an electrode wire disposed within the center bore and having a first end extending into the countersunk hole, and an electrode head mechanically and electrically coupled to the first end of the electrode wire, a first portion of the electrode head being located within the countersunk hole to define an interface with the countersunk hole for providing a heat transfer path from the electrode head to the insulating core. Attached Figure Description

[0006] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the embodiments. Other embodiments and many anticipated advantages of the embodiments will be readily understood as they become better understood by referring to the following detailed description. Elements of the drawings are not necessarily to scale. Similar reference numerals denote corresponding similar parts.

[0007] FIG. 1A This is a side view of an example spark plug.

[0008] FIG. 1B is an exploded view of a spark plug according to one example.

[0009] FIG. 2A is a side view of an insulating core according to one example.

[0010] FIG. 2B is a cross-sectional view of an insulating core according to one example.

[0011] FIG. 3A is a side view of a center electrode wire according to one example.

[0012] FIG. 3B is a cross-sectional view of a center electrode wire according to one example.

[0013] FIG. 4A is a side view of a center electrode tip according to one example.

[0014] FIG. 4B is a cross-sectional view of a center electrode tip according to one example.

[0015] FIG. 4C is a top view of a center electrode tip according to one example.

[0016] FIG. 4D is a side view of a center electrode tip according to one example.

[0017] FIG. 5A is a side view of a threaded sleeve of a metal shell according to one example.

[0018] FIG. 5B is a cross-sectional view of a threaded sleeve of a metal shell according to one example.

[0019] FIG. 5C is a side view of a nut of a metal shell according to one example.

[0020] FIG. 6 is a side view of a terminal electrode according to one example.

[0021] FIG. 7A is a side view of a spark plug according to one example.

[0022] FIG. 7B is a cross-sectional view of a spark plug according to one example.

[0023] FIG. 7C is an enlarged cross-sectional view of a firing end of a spark plug according to one example.

[0024] FIG. 8A is a chart showing simulated operating temperatures of a spark plug according to one example of the present disclosure.

[0025] FIG. 8B is a chart showing simulated operating heat flux for a spark plug according to one example of the disclosure.

[0026] FIG. 9A is a perspective view of a known spark plug according to one example.

[0027] FIG. 9B is a cross-sectional view of a firing end of a known spark plug according to one example.

[0028] FIG. 9C is a photograph of a firing end of a known spark plug according to one example.

[0029] FIG. 10A is a chart showing simulated operating temperature for a known spark plug according to one example.

[0030] FIG. 10B is a chart showing simulated operating heat flux for a known spark plug according to one example.

[0031] FIG. 11A is a side view of a spark plug according to one example.

[0032] FIG. 11B is an exploded view of a spark plug according to one example.

[0033] FIG. 12A is a side view of an insulating core according to one example.

[0034] FIG. 12B is a cross-sectional view of an insulating core according to one example.

[0035] FIG. 13A is a side view of a center electrode wire according to one example.

[0036] FIG. 13B is a cross-sectional view of a center electrode wire according to one example.

[0037] FIG. 14A is a side view of a center electrode tip according to one example.

[0038] FIG. 14B is a cross-sectional view of a center electrode tip according to one example.

[0039] FIG. 14C is a top view of a center electrode tip according to one example.

[0040] FIG. 15A is a side view of a metal shell according to one example.

[0041] FIG. 15B is a cross-sectional view of a metal shell according to one example.

[0042] FIG. 16 is a side view of a terminal electrode according to one example.

[0043] FIG. 17A is a side view of a spark plug according to one example.

[0044] FIG. 17B is a cross-sectional view of a spark plug according to one example.

[0045] FIG. 17C is an enlarged cross-sectional view of a firing end of a spark plug according to one example.

[0046] FIG. 18A to FIG. 18D is a simplified cross-sectional view according to one example of the disclosure, generally illustrating attachment of a center electrode wire to a center electrode tip of a spark plug. DETAILED DESCRIPTION

[0047] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific examples in which the disclosure can be practiced. It is to be understood that other examples can be utilized and structural or logical changes can be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. It is to be understood that features of the various examples described herein can be combined, in part or whole, with each other, unless specifically noted otherwise.

[0048] Spark plugs are used in combustion chambers of combustion systems to ignite pressurized air-fuel mixtures therein, such as within cylinders of a vehicle internal combustion engine. A spark plug generally includes a center electrode disposed within a generally cylindrical or tubular insulator core (e.g., ceramic), and a metal shell or housing disposed concentrically around at least a portion of an outer periphery of the insulator core, where the metal shell includes a side electrode that forms a spark gap with the center electrode at a firing end of the spark plug. When the spark plug is installed in the combustion system (e.g., threaded into a cylinder head), a portion of the firing end is disposed within the combustion chamber such that a controlled voltage applied across the center electrode and the side electrode causes a controlled spark across the spark gap to ignite the air-fuel mixture therein.

[0049] Electric fields along a surface of a charged conductor are strongest at locations having the greatest surface charge density, such as along sharp edges or at points. With this in mind, the firing end of the center electrode is typically formed with a sharp outer peripheral edge and a small diameter (so as to be point-like), where generally, the smaller the diameter, the lower the voltage required to generate a spark in the spark gap between the sharp outer peripheral edge of the center electrode and the sharp edge of the side electrode.

[0050] While there are various spark plug types available, the most common are nickel, platinum, and iridium. Nickel spark plugs use a center electrode with a copper core, around which a nickel alloy is fused, particularly at the electrode tip (e.g., 2.5 mm in diameter). While the nickel alloy has high electrical and thermal conductivity, it is a relatively soft material. Thus, under the high pressure, high temperature, and corrosive conditions within the combustion chamber, the electrode tip tends to wear relatively quickly from repeated high pressure sparking at the same point. As the electrode tip erodes, its sharp edge is lost, the spark gap widens, and thus a higher voltage is needed to initiate a spark (i.e., higher breakover voltage). Electrode tip erosion often results in spark plug fouling and reduced engine performance (e.g., engine misfire). Thus, known nickel spark plugs require relatively frequent replacement (e.g., every 20,000 miles).

[0051] Platinum and iridium spark plugs also use a copper core center electrode wire with a nickel alloy tip. However, for platinum spark plugs, the nickel alloy tip of the center electrode wire is welded to a small platinum disc (e.g., 1.1 mm in diameter). Likewise, for iridium spark plugs, an iridium "wire" (e.g., 0.4 mm in diameter) is welded to the nickel alloy tip of the center electrode wire. Platinum and iridium belong to the noble "platinum group" of metals, which is known for its hardness and its chemical non-reactivity. Because platinum and iridium are harder materials than nickel alloy, platinum and iridium spark plugs retain their edge and gap better than nickel spark plugs, and thus have a longer service life (e.g., platinum 50,000 miles, iridium 100,000 miles). Despite being more expensive, platinum and iridium spark plugs do not provide the same level of performance as conventional nickel spark plugs. However, due to the extended service life, platinum and iridium spark plugs have increased in use and replaced nickel spark plugs in many applications.

[0052] According to examples to be described in greater detail herein, the present disclosure provides a spark plug having a large center electrode tip (e.g., 8 mm in diameter) that can be formed from a non-noble metal, including the nickel alloy conventionally used for nickel spark plugs, wherein the outer peripheral edge of the large center electrode tip forms a circumferential spark gap with a circumferentially extending side electrode formed by the metal shell of the spark plug. The disclosed spark plug is less expensive than platinum and iridium spark plugs and provides improved performance (e.g., faster burn, improved torque, increased efficiency, better fuel economy) while having a similar life (e.g., 100,000 miles) as iridium spark plugs. Previous attempts have been made to develop a spark plug employing a large electrode tip comprising a non-noble metal. However, such known attempts have physically failed during operation and / or have failed to achieve those lives approaching iridium spark plugs primarily due to thermal issues. Notably, due to the high material cost, manufacturing large noble metal electrode tips (e.g., iridium and platinum) is often cost prohibitive, in fact, often prompting the use of small electrode tips.

[0053] FIG. 1A and FIG. 1B are renderings showing side and exploded views, respectively, of an exemplary spark plug 10 according to the present disclosure. The spark plug 10 includes a generally cylindrical insulator core 12 extending along an axial centerline 14 from a terminal end 16 to a firing end 18, the insulator core 12 including an insulator nose 20 at the firing end 18 and a central bore 22 extending axially therethrough. A metal shell 30 concentrically surrounds a portion of the cylindrical insulator core 12. In one example, the metal shell 30 includes a nut 32 (e.g., a hex nut) and a tubular threaded sleeve 34. The metal shell 30 functions as a bolt that is screwed into a cylinder head when the spark plug 10 is installed therein. In one example, the threaded sleeve 34 defines a side electrode 36 proximate the firing end 18, the metal shell 30 forming a conductive path from the side electrode 36 to the cylinder head when the spark plug 10 is installed therein. In one example, as shown, the side electrode 36 is a circumferentially extending peripheral electrode. Note that in most applications, the side electrode 36 functions as a ground electrode.

[0054] The spark plug 10 further includes a terminal electrode 40 and a center electrode 50 extending axially along the axial centerline 14. The terminal electrode 40 includes a terminal leg 42 extending to a terminal post 44 proximate the terminal end 16. According to the present disclosure, the spark plug 10 includes the center electrode 50, the center electrode 50 including a center electrode wire 52 and a center electrode tip 54, wherein the center electrode tip 54 is threadably connected to the center electrode wire 52. In one example, the center electrode wire 52 includes external threads 56 at a first end 57 and a lead tip 58 at an opposite second end 59, wherein the external threads 56 are threadably connected with corresponding internal threads 60 (see FIG. 4B , FIG. 7B and FIG. 7C ) in the center electrode tip 54.

[0055] With continued reference to FIG. 1A and FIG. 1B , according to one example, to assemble the spark plug 10, the center electrode wire 52 is inserted into the central bore 22 of the insulator core 12 through the terminal end 16 until the lead tip 58 engages a tapered shoulder 82 (see FIG. 2B and FIG. 7B ) within the central bore 22. The conductive glass powder 62 is disposed within the central bore 22 from the terminal end 16, followed by insertion of the terminal leg 42 of the terminal electrode 40 into the central bore 22, and the terminal leg 42 is used to compact the glass powder 62. The combination of the insulator core 12, the center electrode wire 52, and the terminal electrode 40 is then fired to a high temperature to melt the glass powder 62, wherein the melted glass powder 62 cools and solidifies to form a solid glass lock 62-1 (see FIG. 7B), which locks the terminal electrodes 40 and the center electrode 50 in place within the insulator core 12, and which serves as an electrically conductive path between the terminal electrodes 40 and the center electrode 50. In an example, the solid glass lock 62-1 provides resistance to the transmission of radio frequency interference.

[0056] The insulator core 12 is then inserted into the threaded sleeve 34, and when the nut 32 is fused (e.g., by heat treatment) with the threaded sleeve 34, the washers 64 and 66 form a seal between the inner surface of the threaded sleeve 34 and the shoulders 65 and 67 on the insulator core 12, respectively. In one example, after the nut 32 is fused with the threaded sleeve 34, the insulator nose 20 of the insulator core 12 extends axially beyond the side electrodes 36, and the threads 56 of the first end 57 of the center electrode wire 52 extend axially beyond the insulator nose 20 so as to be exposed therefrom. In one example, the center electrode tip 54 is then attached to the center electrode wire 52, such as by threading.

[0057] By attaching the center electrode tip 54 to the center electrode wire 52 after the center electrode wire 52 has been installed within the center bore 22 of the insulator core 12, the center electrode tip 54 can be sized larger than the diameter of the center bore 22. As will be described in greater detail below, the large center electrode tip provides increased linear edge length (e.g., a continuous circumferential edge), which increases the spark point diversity of the center electrode tip when forming a spark gap with a corresponding side electrode extending from a metal shell. In turn, the increased spark point diversity enables the spark plug to utilize an enlarged center electrode tip formed from a nickel alloy conventionally used for nickel spark plug electrodes, while providing improved engine performance and achieving a service life comparable to iridium spark plugs, in accordance with the present disclosure.

[0058] FIG. 2A and FIG. 2BA side view and a cross-sectional view of the insulator core 12 are shown, respectively, according to one example, and showing a central bore 22 extending through the insulator core. In one example, the central bore 22 includes a first portion 70 having a first diameter dl and a second portion 72 having a second diameter d2 that is less than the first diameter dl, and a counterbore 74 having a third diameter d3 disposed within the insulator nose 20 proximate the firing end 18 in the assembled spark plug 10, where the third diameter d3 is greater than the second diameter d2. The central bore 22 further includes a tapered shoulder region 80 proximate the terminal end 16 in the assembled spark plug 10 at an entrance of the central bore 22, a tapered shoulder region 82 at a transition from the first portion 70 of diameter dl to the second portion 72 of lesser diameter d2, and a tapered shoulder region 84 at a transition from the counterbore 74 to the second portion 72 of lesser diameter d2. The insulator nose 20 has an axial length ln, and has an end face 75 disposed concentrically about the counterbore 74. The insulator core 12 further includes a corrugated region 86 proximate the terminal end 16 in the assembled spark plug 10, the corrugated region increasing a surface distance between the terminal electrode 40 post 44 and the nut 32 of the metal shell 30 (see FIG. 1A ) to reduce arcing between the potentials.

[0059] According to one example, FIG. 3A and FIG. 3B A side view and a cross-sectional view of the center electrode wire 52 are shown, respectively. In one example, the center electrode wire 52 includes a copper core 90 with a nickel alloy 92 fused about the copper core 90, including at a first end 57 where an external thread 56 is disposed. In one example, a second end 59 includes a shoulder region 96 where the wire head 58 transitions to a smaller diameter electrode wire 52, where the shoulder region 96 is configured to engage a corresponding shoulder region 82 of the insulator core 12 (see FIG. 7B ) when installed within the central bore 22. In one example, the wire head 58 includes a recessed or gouged region 98 to receive and be filled with conductive glass powder 62 (which is subsequently melted to form a conductive glass lock 62-1, as shown in FIG. 7B As shown, the center electrode wire 52 has an electrode length le from the shoulder 96 to the first end 57, and the thread 56 has a thread length lt.

[0060] According to one example, FIG. 4A , FIG. 4B and FIG. 4CA side view, a cross-sectional view, and a top view of the center electrode tip 54 are shown, respectively. In one example, the center electrode tip 54 includes an electrode plate 100 having an upper surface 102 and an opposing lower surface 104, and a collar 106 extending from the lower surface 104, and the collar 106 includes a collar bore 107 with internal threads 60 for threaded connection with the threads 56 at the first end 57 of the electrode wire 52 (see FIG. 3A ). In one example, as shown, the electrode plate 100 is disc-shaped. However, it is noted that the electrode plate 100 is not limited to any particular shape, nor is the electrode plate 100 limited to a single plane. In examples, the electrode plate 100 can be flat, convex, concave, circular, non-circular, or any suitable shape for a given implementation of the spark plug 10.

[0061] When threaded onto the electrode wire 52, the collar 106 is within the counterbore 74 at the insulator nose 20 of the insulator core 12 such that the bottom surface 104 of the electrode plate 100 is engaged and flush with the end face 75 of the insulator nose 20 around the portion 110 of the collar 106 (see FIG. 7C ). As used herein, the term “flush” refers to being in direct contact with each other within the range of thermal expansion tolerances. In one example, the width w h of the annular portion 110 of the bottom surface 104 is the same as the width w n of the annular end face 75 of the insulator nose 20. In one example, the end face 75 of the insulator nose 20 is planar. In other examples, the end face 75 is non-planar. In examples, the end face 75 has a shape that is inverse to the shape of the portion 110 of the bottom surface 104 of the electrode plate 100 such that the portion 110 of the electrode plate 100 is flush with the end face 75 of the insulator nose 20.

[0062] In one example, as shown, the circumferential edge 114 of the electrode plate 100 slopes downwardly toward the lower surface 104 from the upper surface 102 by a head angle Θ such that the spark gap distance dgap of the spark gap 140 formed between the circumferential edge 116 of the lower surface 104 of the electrode plate 100 and the circumferentially extending side electrode 36 can vary depending on the head angle Θ (see FIG. 7B and FIG. 7C ). In one example, as shown, the electrode plate 100 has a thickness th and a diameter dh that is greater than the diameter dn of the insulator nose 20 such that the circumferential edge 116 of the lower surface 104 of the electrode plate 100 extends radially beyond the insulator nose 20 to form the spark gap 140 with the side electrode 36 (see FIG. 7A and FIG. 7B ). In other examples, the diameter dh of the electrode tip 54 can be less than the diameter dn of the insulator nose 20 but greater than the diameter d2 of the center bore 22. In one example, as FIG. 4DAs shown, the electrode plate 100 is planar (i.e., the circumferential edge 114 is not angled).

[0063] According to one example, FIG. 5A and FIG. 5B respectively show a side view and a cross-sectional view of the threaded sleeve 34, and FIG. 5C shows a side view of the nut 32 of the metal shell 30. In one example, the threaded sleeve 34 includes a collar 120 and threads 122 for threadably connecting the assembled spark plug 10 into an engine cylinder head such that the firing end 18 is disposed within the cylinder. The threaded sleeve 34 includes a bore 124 for receiving the insulator core 12, and the collar 120 for receiving and coupling (e.g., by heat staking) to the connecting portion 126 of the nut 32. In one example, the nut 32 includes a hexagonal engagement surface 128, as for a socket or wrench, to assist in installing the assembled spark plug 10 into an engine cylinder head.

[0064] As shown, the threaded sleeve 34 includes a side electrode 36 extending axially from the threaded region 122. In one example, as shown, the side electrode extends circumferentially from the threaded region 122 and is annular, with an inner diameter di formed by an inner peripheral edge 36-1, and an outer diameter do formed by an outer peripheral edge 36-2. As will be described in greater detail below (see FIG. 7C ), in one example, the outer peripheral edge of the side electrode 36 forms a spark gap 140 (see FIG. 4B ) with the outer peripheral edge of the center electrode plate 100, e.g., the circumferential edge 116 of the center electrode plate 100. While the side electrode 36 is shown as extending from and forming a continuous portion of the main body of the threaded sleeve 34, in other examples, the term “extends from” encompasses embodiments in which the side electrode 36 is an electrode that is coupled to and extends axially from the threaded sleeve 34, such as by welding.

[0065] FIG. 6 is a side view showing the terminal electrode 40 according to one example. In one example, the terminal electrode 40 includes a flange 1201 and a tapered shoulder region 1221 disposed between the terminal wire 42 and the terminal post 44, where the shoulder region 1221 engages and is within the shoulder region 80 of the insulator core 12, and the flange 1201 is for the flange 1201 to engage and be positioned flush with the end face 76 of the insulator core 12 when the terminal electrode 40 is disposed within the central bore 22 of the assembled spark plug 10 (see FIG. 2B ).

[0066] According to one example, FIG. 7A and FIG. 7B respectively show a side view and a cross-sectional view of the spark plug 10, and FIG. 7CAn enlarged cross-sectional view of the firing end 18 of the spark plug 10 is shown. As shown, the insulator nose 20 extends axially beyond the side electrode 36 of the metal shell 30 at the firing end 18, and the first end 57 of the center electrode wire 52 is disposed within the counterbore 74 of the insulator nose 20. In other examples, the insulator nose 20 does not extend axially beyond the side electrode 36.

[0067] In one example, as shown, the center electrode tip 54 is threadably connected to the outer threads 56 of the center electrode wire 52 by the inner threads 60 disposed in the collar 106, such that the bottom surface 110 of the electrode plate 100 is flush with the end face 75 of the insulator nose 20. In one example, the threads 56 / 60 forming the threaded connection between the center electrode wire 52 and the center electrode tip 54 are locking threads, which function to immobilize and secure the threaded connection to prevent the center electrode tip 54 from separating from the center electrode wire 52 during operation of the spark plug 10. Such locking threads include any suitable locking mechanism, such as cold welding (e.g., thread galling), self-locking type threads (e.g., interference threads), and, for example, a thread locking system (e.g., adhesive).

[0068] In one example, the end face 130 of the center electrode wire 52 is substantially flush with the end face 75 of the insulator nose 20. In other examples, the length of the center electrode wire 52 and the depth of the inner threads 60 of the center electrode tip 54 can vary, so long as the bottom surface 110 of the electrode plate 100 is flush with the end face 75 of the insulator nose 20. In one example, the respective shoulder regions 84 and 108 of the insulator nose 20 and the center electrode tip 54 function to position the electrode tip 54 within the counterbore 74 when threadably connected to the center electrode wire 52. In one example, as shown, expansion gaps 134 and 136 are disposed between the collar 106 of the center electrode tip 54 and the sidewall of the counterbore 74 of the insulator nose 20, and between the center electrode wire 52 and the sidewall of the center bore 22, respectively, to accommodate expansion of the center electrode wire 52 and the center electrode tip 54 due to differences in the coefficient of thermal expansion between their materials. In some examples, a thermal expansion gap can also exist between the shoulder regions 84 and 108.

[0069] In one example, as shown, the circumferentially extending lower circumferential edge 116 of the electrode plate 100 forms a continuous radial spark gap 140 having a gap distance dgap when threaded onto the electrode wire 52, and the circumferentially extending edge 36-1 defines an inner diameter di of the side electrode 36 (e.g., ground electrode). According to the present disclosure, by forming a continuous radial spark gap 140, the entire circumferential edge 116 of the electrode plate 100 forms a continuous edge that provides spark point diversity such that the electrode plate 100 does not wear or erode as quickly as known spark plugs having a single point spark gap or multiple discrete spark gaps, thereby extending the useful life of the spark plug 10. In other examples not explicitly illustrated herein, the side electrode 36 can include multiple points, each forming a separate gap with the electrode plate 100.

[0070] In one example, the diameter dh of the center electrode tip 54 is greater than the outer diameter dn of the insulator nose 20, but less than the inner diameter di of the side electrode 36, such that the spark gap 140 is diagonal and acute with respect to the axial centerline 14 such that the spark gap 140 is not “shadowed” by the electrode plate 100 when the spark plug 10 is disposed within a combustion chamber of an internal combustion engine. In examples, the gap distance dgap of the spark gap 140 can be varied by adjusting various structural features, such as by varying the axial length ln of the insulator nose 20, by varying the diameter dh of the center electrode tip 54, by varying the inner diameter di of the side electrode 36, by varying the apex angle Q of the circumferential edge 114 of the disc-shaped electrode plate 100, and / or by varying the thickness th of the electrode plate 100, or any combination thereof. In one example, the gap distance dgap can exceed 2.0 millimeters. In other examples, the electrode tip 54 can be disposed with respect to the side electrode 36 such that a horizontal surface gap is formed between the electrode plate 100 and the side electrode 36 (a so-called “surface gap” spark plug).

[0071] Spark plugs are configured to operate within an industry standard heat range, generally defined as between 600°C and 850°C. Spark plugs operating at temperatures above this heat range can cause the air-fuel mixture within the cylinder to ignite prematurely. If operated below this temperature range, the air-fuel mixture can not burn properly, and thus residue can build up on the spark plug (“fouling”) and cause spark production to fail or be inconsistent (“misfire”). Thus, for optimal operation, a spark plug should operate at an electrode tip temperature that is hot enough to provide self-cleaning (i.e., burn off residue), but cool enough to avoid premature ignition of the air-fuel mixture.

[0072] During engine operation, a significant amount of heat is generated within the cylinder, some of which is absorbed by the spark plug and must be dissipated by the spark plug. Because different engines generate and dissipate different amounts of heat, and are designed with different optimal operating temperatures or thermal ranges, each engine generally specifies a temperature range or thermal range within which the spark plug must operate to provide optimal engine performance. With this in mind, spark plugs are generally specified with a heat resistance rating, where such heat resistance rating indicates the ability of the spark plug to dissipate heat, and thus the temperature (or temperature range) at which the spark plug is configured to operate. So-called "hot" plugs have a configuration that draws heat away from the electrode tip more slowly, and thus have a higher operating temperature within the standard thermal range, while so-called "cold" plugs have a configuration that draws heat away from the electrode tip more quickly, and thus have a lower operating temperature within the standard thermal range. Thus, to better ensure optimal performance, engines generally specify the heat resistance rating or heat resistance rating of the spark plug to be used therewith. Using a spark plug that does not conform to the specified thermal range can result in suboptimal engine performance or even engine failure.

[0073] Spark plugs generally dissipate absorbed heat by transferring heat from the electrode tip through the center electrode wire to the insulator core, and then from the insulator core through the threaded metal shell (threaded to the cylinder head) to the engine cooling system. Generally, the thermal range of a spark plug is related to the length of the conical insulator nose of the ceramic insulator core. The longer the insulator nose, the less surface area of the ceramic insulator core is in direct contact with the metal shell to transfer heat to the engine cooling system, and the "hotter" the operating temperature of that spark plug. Conversely, the shorter the insulator nose, the more surface area of the ceramic insulator core is in direct contact with the metal shell to transfer heat to the engine cooling system, and the "colder" the operating temperature of that spark plug.

[0074] In known spark plugs, including platinum and iridium spark plugs, the center electrode tip does not exceed the diameter of the center electrode wire (i.e., does not exceed the diameter of the center bore at its narrowest point). As a result of the small electrode tip exposed surface area (the smaller the exposed surface area, the less heat absorbed by the electrode tip). Because the electrode wire of known spark plugs provides a relatively large thermal path from the electrode tip to the ceramic insulator (where the diameter of the center electrode tip does not exceed the diameter of the center electrode wire), overheating of known spark plugs is generally not an issue.

[0075] To meet industry standard heat range specifications and achieve extended expected life, the spark plug 10 according to the present disclosure dissipates a large amount of heat from the large electrode pad 100 of the center electrode tip 54 compared to known spark plugs. For example, the electrode pad 100 can be 8 millimeters in diameter, while a conventional platinum spark plug has a platinum disc that is 1.1 millimeters in diameter. As shown and described above, to be able to dissipate a large amount of heat from the electrode tip 54, the exemplary spark plug 10 of the present disclosure includes a number of unique structural features to create a large heat conducting path between the electrode tip 54 and the metal shell 30. In examples, the ability of the electrode tip 54 to quickly dissipate a large amount of heat enables the spark plug 10 to employ a large electrode pad 100 of conventional copper and nickel alloy materials (i.e., non-rare or precious metals) while providing comparable expected life and improved engine performance (e.g., faster combustion, improved torque) to known platinum and iridium spark plugs.

[0076] A first example of a unique structural feature is that the amount of surface area of the electrode pad 100 that can absorb heat that is exposed to the combustion chamber is limited by the mounting of the electrode pad 100, where a portion of the bottom surface 110 is flush with the end face 75 of the insulator nose 20. In addition to reducing the amount of exposed surface area and thus the amount of heat transferred to the electrode pad 100, the direct contact between the bottom surface 110 and the end face 75 further provides a heat path for transferring heat from the electrode pad 100 to the insulator core 12.

[0077] Another unique structural feature is the threaded connection between the center electrode tip 54 and the center electrode wire 52 via the threaded collar 106. The large circumferential surface area contact between the threaded collar 106 and the electrode wire 52 provides a large heat transfer path from the electrode pad 100 to the center electrode wire 52 and subsequently to the engine cooling system via the metal shell 30. The threaded connection enables the same or similar material to be employed by the center electrode tip 54 and the center electrode wire 52, thereby providing a continuous heat transfer path of materials having the same or similar thermal properties (e.g., thermal conductivity and coefficient of thermal expansion). The use of materials having the same or similar thermal properties also reduces the likelihood of a physical failure of the connection between the center electrode tip 54 and the center electrode wire 52, which can otherwise occur between materials having different thermal expansion properties.

[0078] Another unique structural feature is that the collar 106 is within the counterbore 74 of the insulator nose 20. Placing the collar 106 within the counterbore 74 provides a large amount of surface contact area between the center electrode tip 54 and the insulator nose 20, which creates a large heat transfer path from the center electrode tip 54 to the insulator core 12.

[0079] The above unique structural features of thermally coupling the electrode tips 54 together to the electrode wire 52 and the insulating core 12 provide a certain amount of heat transfer from the center electrode tip 54, which enables the center electrode tip 54 to use conventional copper and nickel-alloy materials. Such conventional materials have better thermal conductivity than harder, more heat-resistant materials (e.g., iridium, platinum, and other unconventional materials), thus further improving the heat dissipation capabilities of the spark plug 10.

[0080] In comparison to the known spark plug 160 (as shown in FIG. 9A to FIG. 9C the following FIG. 8A to FIG. 10B shows and describes a durability test simulation of an example spark plug similar to the spark plug shown above by the spark plug 10. FIG. 8A and FIG. 8B respectively show simulated operating temperatures and heat fluxes of, for example, the spark plug 10, while FIG. 10A and FIG. 10B respectively show simulated operating temperatures and heat fluxes of the known spark plug 160. Notably, the durability test simulation was performed using Autodesk® Fusion 360.

[0081] The durability test simulation of both the spark plug 10 and 160 used the same specified thermal model setup conditions, including operating conditions and boundary conditions. The operating conditions were modeled for a 210 HP power output at 5,000 rpm (high power, but not extreme conditions). The boundary conditions were modeled with electrodes and plug faces at 1050 °C gas temperature and htc = 750 W / m 2 K (per ID model); threads and seat fixed at 130 °C (assumed anchored to engine head temperature); plug back face (ambient temperature) of 60; and contact resistances estimated per wire to insulator, insulator to housing, and disk to insulator.

[0082] FIG. 8A is a cross-sectional view showing a map 150 of operating temperatures of the spark plug 10 according to the above durability test simulation. According to the simulation, the spark plug 10 has a maximum simulated operating temperature of 627 °C at the electrode plate 100 of the electrode tip 54, as shown at 152. The simulated operating temperature at the center electrode wire 52 is about 550 °C at 154. FIG. 8B is a cross-sectional view showing a heat flux map 156 of the spark plug 10 according to the above durability test simulation, where the simulated heat flux at the electrode plate 100 is about 3.0 W / mm 2 , as shown at 158, and at the location where the center electrode wire 52 joins with the electrode tip 54, the simulated heat flux is about 4.2 W / mm 2 , as shown at 159.

[0083] It should be noted that the maximum operating temperature of the spark plug 10 can be adjusted by increasing or decreasing the length ln of the insulating nose 20 (e.g., see FIG. 2A and FIG. 2B ) and / or by adjusting the size of the electrode plate 100 to increase / decrease the amount of surface area exposed to the combustion chamber, which increases / decreases the rate of heat transfer from the combustion heat to the electrode plate 100. In one example, as described above, the electrode plate 100 has a minimum diameter dh that is greater than the outer diameter dn of the insulating nose 20, such that the lower circumferential edge 116 of the electrode plate 100 extends from the insulating nose 20 to form the spark gap 140 with the side electrode 36. In one example, for a given arrangement (e.g., a given thickness th of the disc-shaped electrode plate 100, a given length ln of the insulating nose 20, etc.), the electrode plate 100 has a maximum diameter dh that provides a surface area exposed to the combustion chamber that results in the electrode plate 100 having a maximum operating temperature of up to an industry standard maximum spark plug temperature (e.g., 850°C), above which pre-ignition can occur.

[0084] As described above, known spark plugs that employ a large center electrode tip (e.g., greater than the diameter of the center electrode wire) have experienced physical failures and / or failed to achieve a service life approaching that of platinum and iridium spark plugs due to thermal issues (inability to dissipate heat) during operation compared to the exemplary spark plug 10 of the present disclosure. Such thermal issues can be attributed to a number of structural deficiencies.

[0085] FIG. 9A to FIG. 9C An example of a known spark plug 160 is shown that employs a large center electrode tip 162 with an electrode plate 164 having a plurality of openings or perforations 166 extending therethrough. A first structural deficiency of the known spark plug 160 is that the electrode tip 162 has a large amount of surface area exposed to the combustion heat within the combustion chamber, resulting in a high rate of heat transfer to the electrode tip. A second structural deficiency arises from the electrode plate 164 being welded to the tip 168 of the center electrode wire 170, whereby the heat transfer path from the electrode plate 164 to the center electrode wire 170 is formed only through the weld bead 169 and the tip 168, which creates a thermal bottleneck that concentrates the head in the tip 168 and limits heat transfer from the electrode tip 162. A third structural deficiency is that the electrode plate 164 and the weld material are formed of a high-temperature nickel alloy (i.e., a non-conventional copper-nickel alloy material, such as “Alloy-X”), which is not as good at thermal and electrical conductivity as conventional copper and nickel alloy materials. The use of the high-temperature nickel alloy also means that the large electrode plate 164, the weld bead 169, and the center electrode wire 170 are formed of different materials having different thermal properties (e.g., different coefficients of thermal expansion), which can lead to physical failures.

[0086] Further, in some examples, the large electrode tip of the known spark plug is spaced apart from the insulator nose, as shown by gap 172 between electrode plate 164 and insulator nose 174. Gap 172 results in an increase in surface area of electrode plate 164 exposed to the combustion chamber, as well as an increase in surface area of a portion of the end of center electrode wire 170 (fully isolated from the combustion chamber by the structure of spark plug 10 of the present disclosure). This exposure increases the rate of heat transfer to the electrode tip, and in one example, has been known to cause physical failure of the exposed portion of electrode wire 70 at the point of connection to electrode plate 164, resulting in destructive separation of electrode plate 164 from center electrode wire 170, as shown in the photograph of FIG. 9C

[0087] FIG. 10A is a cross-sectional view showing a map 180 of the operating temperatures of known spark plug 160 according to the durability test simulation described above. According to the simulation, known spark plug 160 had a maximum simulated operating temperature of 858°C at electrode plate 164 of electrode tip 162, as shown at 182. The simulated operating temperature at center electrode wire 170 at 184 was approximately 760°C. FIG. 10B is a cross-sectional view showing a heat flux map 186 of spark plug 10 according to the durability test simulation described above, where the simulated heat flux at electrode plate 100 was approximately 1.4 W / mm 2 , as shown at 188, and at the point where center electrode wire 170 joins with electrode plate 164, the simulated heat flux was approximately 8.0 W / mm 2 , as shown at 189.

[0088] FIG. 11A to FIG. 17C shows a spark plug 210 according to another example of the present disclosure. As will be described in greater detail below, in contrast to spark plug 10 shown above, center electrode wire 252 is not threaded to one another, but is attached to center electrode tip 254 by a brazing and stamping process (also referred to as “staking”; see, e.g., FIG. 18A to FIG. 18D ).

[0089] FIG. 11A and FIG. 11B ​is a rendering showing a side view and an exploded view of an exemplary spark plug 210 according to the present disclosure. The spark plug 210 includes a generally cylindrical insulator core 212 extending along an axial centerline 214 from a terminal end 216 to a firing end 218, the insulator core 212 including an insulator nose 220 at the firing end 218 and a central bore 222 extending axially through the insulator core. A metal shell 230 concentrically surrounds a portion of the cylindrical insulator core 212. In one example, the metal shell 230 includes a nut 232 (e.g., a hex nut) and a tubular threaded sleeve 234. The metal shell 230 functions as a bolt when the spark plug 210 is installed therein, being threaded into a cylinder head of an engine. In one example, the metal shell 230 defines a side electrode 236 proximate the firing end 218, the metal shell 230 forming a conductive path from the side electrode 236 to the cylinder head when the spark plug 210 is installed therein. In one example, as shown, the side electrode 236 is a circumferentially extending peripheral electrode. Note that in most applications, the side electrode 236 functions as a ground electrode.

[0090] The spark plug 210 further includes a terminal electrode 240 and a center electrode 250 extending axially along the axial centerline 214. The terminal electrode 240 includes a terminal wire 242 extending to a terminal post 244 proximate the terminal end 216. According to the example embodiment of FIG. 11A to FIG. 17C , the center electrode 250 includes a center electrode wire 252 attached to a center electrode head 254, where the center electrode head 254 is connected to the center electrode wire 252 by at least one braze joint (see, e.g., the following FIG. 18A to FIG. 18D ). In one example, as will be described in greater detail below, in addition to the braze joint, the center electrode wire 252 is further secured to the electrode head 254 by a “stake” or “swage” process, where the first end 257 is compressed to form a cap 256 within a pocket 303 of the center electrode head 254 (see, e.g., the following FIG. 14B ).

[0091] With continuing reference to FIG. 11A and FIG. 11B , according to one example, the center electrode wire 252 is inserted into the central bore 222 of the insulator core 212 via the terminal end 216 until a wire head 258 at the second end 259 engages a tapered shoulder 282 within the central bore 222 (see, e.g., the following FIG. 12B and FIG. 17B ). The insulator core 212 is inserted into the threaded sleeve 234, with a gasket 264 forming a seal between an inner surface of the threaded sleeve 234 and a shoulder 265 of the insulator core 212 (see, e.g., the following FIG. 17B). In one example, the insulating nose 220 of the insulating core 212 extends axially beyond the side electrode 236 after being inserted within the threaded sleeve 234, and the first end 257 of the center electrode wire 252 extends axially beyond the insulating nose 220 so as to be exposed therefrom. In one example, the connection of the center electrode head 254 to the center electrode wire 252 will be described in greater detail below (see FIG. 18A to FIG. 18D ), after the center electrode wire 252 and the insulating core 212 have been inserted within the threaded sleeve 234, the center electrode head 254 is connected to the center electrode wire 252.

[0092] With the center electrode wire 252 disposed within the center bore 222, the conductive glass powder 262 is disposed within the center bore 222 from the terminal end 216, the terminal wire 242 of the terminal electrode 240 is then inserted within the center bore 222, and the terminal wire 242 is used to compact the glass powder 262. The glass powder 262 is then fired at a high temperature so as to melt. Upon cooling, the melted glass powder 262 solidifies to form a solid glass lock 262-1 (see FIG. 17B ), which locks the terminal electrode 240 and the center electrode 250 in place within the insulating core 212, and which serves as an electrically conductive path between the terminal electrode 240 and the center electrode 250. In examples, the solid glass lock 262-1 provides a resistance that suppresses the transmission of radio frequency interference.

[0093] Similar to the description above with respect to the spark plug 10, by attaching the center electrode head 254 to the center electrode wire 252 after the center electrode wire 252 is disposed within the center bore 222 of the insulating core 212, the center electrode head 254 of the spark plug 210 can be larger in size than the diameter of the center bore 222. It should be noted that different techniques than those described herein can be employed to assemble the spark plug 210. For example, in other instances, the center electrode head 254 can be attached to the center electrode wire 252 prior to the center electrode wire 252 being inserted within the center bore 222.

[0094] As will be described in greater detail below, the large center electrode head provides an increased linear edge length (e.g., a continuous circumferential edge) that increases the spark point diversity of the center electrode head when forming a spark gap with a corresponding side electrode extending from the metal shell. In turn, the increased spark point diversity enables the spark plug to utilize an enlarged center electrode head formed from a nickel alloy conventionally used for nickel spark plug electrodes, while providing improved engine performance and achieving a service life comparable to iridium spark plugs, in accordance with the present disclosure.

[0095] FIG. 12A and FIG. 12BA side view and a cross-sectional view of the insulator core 212 are shown, respectively, according to one example, and showing a central bore 222 extending through the insulator core. In one example, the central bore 222 includes a first portion 270 having a first diameter dl and a second portion 272 having a second diameter d2 that is less than the first diameter dl, and a counterbore 274 having a third diameter d3 disposed within an insulator nose 220 proximate to the firing end 218 in the assembled spark plug 210, where the third diameter d3 is greater than the second diameter d2. The central bore 222 further includes a tapered shoulder region 280 at an entrance of the central bore 222 proximate to the terminal end 216 in the assembled spark plug 210, a tapered shoulder region 282 at a transition from the first portion 270 of diameter dl to the second portion 272 of lesser diameter d2, and a tapered shoulder region 284 at a transition from the counterbore 274 to the second portion 272 of lesser diameter d2. The insulator nose 220 has an axial length ln, and has an end face 275 disposed concentrically about the counterbore 274. The insulator core 212 further includes a corrugated region 286 proximate to the terminal end 216 in the assembled spark plug 210 that increases a surface distance between the terminal electrode 240 post 244 and the nut 232 of the metal shell 230 (see FIG. 11A ) to reduce arcing between the potentials.

[0096] According to one example, FIG. 13A and FIG. 13B top and side views of the center electrode wire 252 are shown, respectively. In one example, the center electrode wire 252 is formed using pure copper (e.g., 99.99% copper) and extends between a first end 257 and an opposite second end 259. In one example, the first end 257 includes a cap 256 that is formed by a swaging process, as described above, where the cap 256 is within a pocket 303 in the electrode tip 254 (e.g., see FIG. 14B ). In one example, the second end 259 includes a shoulder region 296 where the wire head 258 transitions to a smaller diameter electrode wire 252, where the shoulder region 296 is configured to engage a corresponding shoulder region 282 of the insulator core 212 when installed within the central bore 222 (see FIG. 17B ). In one example, the wire head 258 includes a plurality of fin-like protrusions 298 extending longitudinally therefrom that are configured to interlock and secure with the center electrode wire 252 within the conductive glass powder 262 (which is subsequently melted to form the conductive glass lock 262-1, as shown in FIG. 17B ). In one case, as shown, the wire head 258 includes a set of three fin-like protrusions 298 extending radially at 120 degrees from one another.

[0097] According to one example, FIG. 14A , FIG. 14Band FIG. 14C A side view, a cross-sectional view, and a top view of the center electrode tip 254 are shown, respectively. In one example, the center electrode tip 254 includes an electrode plate 300 having an upper surface 302 and an opposing lower surface 304, and a collar 306 extending from the lower surface 304, a bore 307 extending longitudinally through the center electrode tip 254 to receive the center electrode wire 252. In one example, as shown, the electrode plate 300 includes a pocket 303 in the upper surface 302 coaxial with the bore 307, where the pocket 303 is to receive the cap 256 of the center electrode wire 252 formed by the compression (stamping) of the first end 257 (see, e.g., FIG. 18A to FIG. 18D ). In one example, as shown, the electrode plate 300 is disc-shaped. However, it is noted that the electrode plate 300 is not limited to any particular shape, nor is the electrode plate 300 limited to a single plane. In examples, the electrode plate 300 can be flat, convex, concave, circular, non-circular, or any suitable shape for a given implementation of the spark plug 210.

[0098] When connected to the center electrode wire 252, the collar 306 is within the counterbore 274 at the insulating nose 220 of the insulating core 212 such that the bottom surface 304 of the electrode plate 300 engages and is flush with the end face 275 of the insulating nose 220 around the portion 310 of the collar 306 (see, e.g., FIG. 17C ). As used herein, the term “flush” refers to being in direct contact with each other within the range of thermal expansion tolerances. In one example, the width w h of the annular portion 310 of the bottom surface 304 is the same as the width w n of the annular end face 275 of the insulating nose 220 (see, e.g., FIG. 12B ). In one example, the end face 275 of the insulating nose 220 is planar. In other examples, the end face 275 is non-planar. In examples, the end face 275 has a shape opposite that of the portion 310 of the bottom surface 304 of the electrode plate 300 such that the portion 310 of the electrode plate 300 is flush with the end face 275 of the insulating nose 220.

[0099] In one example, as shown, the electrode plate 300 is angled downward toward the circumferential edge 314 from the upper surface 302 toward the lower surface 304 at a tip angle Q such that the spark gap distance dgap of the spark gap 340 formed between the circumferential edge 316 of the lower surface 304 of the electrode plate 300 and the circumferentially extending side electrode 236 can vary as a function of the tip angle Q (see, e.g., FIG. 7B and FIG. 7C). In one example, the electrode plate 300 can be angled in a circular or disc-like manner. In other examples, the electrode plate 300 can be angled in a stepped manner, such as by a plurality of separate angled portions (as shown) together creating the head angle Θ. In one example, as shown, the electrode plate 300 has a thickness th and a diameter dh that is greater than a diameter dn of the insulator nose 220, such that a circumferential edge 316 of the lower surface 304 of the electrode plate 300 extends radially beyond the insulator nose 220 to form a spark gap 340 (see FIG. 17C ) with the side electrode 236. In other examples, the diameter dh of the electrode head 254 can be less than the diameter dn of the insulator nose 220 but greater than the diameter d2 of the center bore 222.

[0100] According to one example, FIG. 15A and FIG. 15B respectively show a side view and a cross-sectional view of the metal shell 230. In one example, the metal shell 230 includes a threaded sleeve 234 having threads 322 to threadably connect the spark plug 210 into an engine cylinder head such that the firing end 218 is disposed within the cylinder. In one example, the nut 232 includes a hexagonal engagement surface, such as for a sleeve or wrench, to assist in installing the spark plug 210 in the engine cylinder head.

[0101] As shown, the threaded sleeve 234 includes a side electrode 236 extending axially from the threads 322. In one example, as shown, the side electrode 236 extends circumferentially from the threaded region 322 and is annular, with an inner diameter di formed by an inner peripheral edge 236-1 and an outer diameter do formed by an outer peripheral edge 236-2. As will be described in greater detail below (see FIG. 17C ), in one example, the circumferential edge of the side electrode 236 forms a spark gap 340 (see FIG. 14B ) with the circumferential edge of the center electrode plate 300, such as the circumferential edge 316 of the center electrode plate 300. While the side electrode 236 is shown as extending from and forming a continuous portion of the threaded sleeve 234, in other examples, the term “extends from” encompasses embodiments in which the side electrode 236 is an electrode that is coupled to and extends axially from the threaded sleeve 234, such as by a welded connection.

[0102] FIG. 16 is a side view showing a terminal electrode 240 according to one example. In one example, the terminal electrode 240 includes a terminal wire 242 and a terminal post 244, and the terminal post 244 includes a flange 326 for engaging and being positioned flush with an end face 276 of the insulator core 212 when the terminal electrode 240 is disposed within the center bore 222 of the spark plug 210 (see FIG. 17B ), for example. In one example, as shown, the flange 326 is annular and has a diameter df that is greater than the diameter d2 of the center bore 222 of the spark plug 210, such that the flange 326 extends radially beyond the insulator core 212 to form a spark gap 340 (see FIG. 12B). In one example, the terminal wire 242 includes a knurled region 328 configured to interlock and secure with a terminal electrode wire 242 within the conductive glass powder 262 (which is subsequently melted to form a conductive glass lock 262-1, as shown FIG. 17B

[0103] According to one example, FIG. 17A and FIG. 17B FIGS. 23 and 24, respectively, illustrate side and cross-sectional views of the spark plug 210, and FIG. 17C FIG. 25 illustrates an enlarged cross-sectional view of the firing end 218 of the spark plug 210. As shown, the insulating nose 220 extends axially beyond the side electrode 236 of the metal shell 230 at the firing end 218, with the first end 257 of the center electrode wire 252 disposed within the counterbore 274 of the insulating nose 220. In other examples, the insulating nose 220 does not extend axially beyond the side electrode 236.

[0104] In one example, as shown, the center electrode tip 254 is attached to the center electrode wire 252 with braze material 330 disposed between the outer peripheral surface of the center electrode wire 252 and the inner surface of the bore 307 of the collar 306, such that the bottom surface 310 of the electrode plate 300 is flush with the end face 275 of the insulating nose 220. In one example, as shown, in addition to the connection formed by the braze material 330, the center electrode tip 254 is further secured to the center electrode wire 252 by a “stake” or “swage” process, in which the first end 257 of the center electrode wire 252 is compressed (swaged) to form a cap 256 within the pocket 303 of the center electrode tip 254. In other examples (not shown), the electrode tip 254 can be connected to the center electrode wire 252 via a braze connection (without the cap 256). In one example, the respective shoulder regions 284 and 308 of the insulating nose 220 and the center electrode tip 254 are used to position the electrode tip 254 within the counterbore 274 of the insulating nose 220.

[0105] In one example, as shown, when attached to the center electrode wire 252, the circumferentially extending lower circumferential edge 316 of the electrode plate 300 forms a continuous radial spark gap 340 with a gap distance dgap, and the circumferentially extending edge 236-1 defines an inner diameter di of the side electrode 236 (e.g., ground electrode). According to the present disclosure, by forming a continuous radial spark gap 340, the entire circumferential edge 316 of the electrode plate 300 forms a continuous edge that provides spark point diversity, such that the electrode plate 300 does not wear or erode as quickly as known spark plugs having a single spark gap or multiple discrete spark gaps, thereby extending the useful life of the spark plug 210. In other examples not explicitly described herein, the side electrode 236 can include multiple points, each forming a separate gap with the electrode plate 300.

[0106] ​In one example, the diameter dh of the center electrode tip 254 is greater than the outer diameter d of the insulator nose 220 n but less than the inner diameter di of the side electrode 236, such that the spark gap 340 is diagonal and acute with respect to the center axis 214, such that the spark gap 340 is not "shaded" by the electrode plate 300 when the spark plug 210 is disposed within a combustion chamber of an internal combustion engine. In examples, the gap distance dgap of the spark gap 340 can be varied by adjusting various structural features, such as by varying the axial length ln of the insulator nose 220, by varying the diameter dh of the center electrode tip 254, by varying the inner diameter di of the side electrode 236, by varying the tip angle Θ of the circumferential edge 314 of the disc-shaped electrode plate 300, and / or by varying the thickness th of the electrode plate 300, or any combination thereof. In one example, the gap distance dgap can exceed 2.0 millimeters. In other examples, the electrode tip 254 can be disposed with respect to the side electrode 236 such that a horizontal surface gap (so-called "surface gap" spark plug) is formed between the electrode plate 300 and the side electrode 236.

[0107] FIG. 18A to FIG. 18D is a simplified cross-sectional view of the firing end 218 of the spark plug 210, generally showing the attachment of the center electrode wire 252 to the center electrode tip 254. In FIG. 18A , according to one example, the center electrode tip 252 is placed on the center electrode wire 252 such that the collar 306 is in the counterbore 274 of the insulator nose 220 and the center electrode wire 252 extends through the center hole 222 of the insulator core 212 and through the hole 307 of the center electrode tip 254 and the first end 257 of the center electrode wire 252 beyond the upper surface 302. In one example, the diameter of the hole 307 is greater than the diameter of the center electrode wire 252, such that a gap 332 is formed around the circumference of the center electrode wire 252 and the counterbore 274. Referring to FIG. 18B , according to one example, a portion of the first end 257 is removed such that the remaining portion of the center electrode wire 252 extending beyond the upper surface 302 of the electrode plate 300 has a volume that matches the volume of the pocket 303 disposed circumferentially around the center electrode wire 252. Additionally, the braze material 330 is placed around the center electrode wire 252 in the pocket 303.

[0108] In FIG. 18C , in one example, the firing end 218 of the spark plug 210 is heated above the melting point of the braze material 330, such that the braze material 330 melts and is drawn by capillary action and fills the gap 332 to form a braze joint between the center electrode wire 252 and the collar 306. In FIG. 18D , the first end 257 of the electrode wire 252 is stacked ("stamped") to form a cap 256 that fills the remaining volume of the pocket 303.

[0109] AlthoughFIG. 18A to FIG. 18D The center electrode tip 254 is shown as being attached to the center electrode wire 252 by a brazing material 330 and a riveting process, but in other examples, the center electrode tip 254 can be attached to the center electrode wire 252 using brazing connections only. In one example, the center electrode 250 is formed using pure (e.g., 99.99%) copper. In one example, the center electrode tip 254 is formed using a nickel-chromium alloy. In one example, the brazing material 330 is a BCuP series brazing alloy (copper phosphorous brazing alloy). It should be noted that other suitable materials can be employed. In contrast to welding processes employed by known spark plugs 160, which result in a connection between the electrode tip and the electrode wire only through the weld bead at the tip of the electrode wire, the brazing and threading techniques described herein provide a mechanical and electrical connection between the electrode tip and the electrode wire along the length of the interface between the electrode wire and the electrode tip.

[0110] While specific examples have been illustrated and described herein, alternative and / or equivalent implementations can be substituted for the specific examples shown and described without departing from the scope of the disclosure. This application is intended to cover any alterations or variations of the specific examples discussed herein. Accordingly, the disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A spark plug, comprising: a terminal end; a firing end; an axial centerline extending between the terminal end and the firing end; an insulator core extending between the terminal end and the firing end, the insulator core comprising: a center bore having a first diameter coincident with the axial centerline extending through the insulator core; an insulator nose proximate the firing end; and a counterbore coincident with the axial centerline and extending axially into the insulator nose toward the terminal end, the counterbore having a second diameter greater than the first diameter; and a center electrode comprising: an electrode wire disposed within the center bore and having a first end extending into the counterbore; and an electrode tip electrically coupled to the first end of the electrode wire, a first portion of the electrode tip being within the counterbore to define an interface between the first portion of the electrode tip and the counterbore for providing a heat transfer path from the electrode tip to the insulator core, the electrode tip comprising: an electrode plate having a bottom surface facing the insulator nose; and the first portion of the electrode tip comprising a collar extending from the bottom surface, the collar comprising an axially extending collar bore, the collar being disposed within the counterbore, the first end of the electrode wire being disposed within the collar bore to electrically and thermally couple the first end of the electrode wire through the electrode tip.

2. The spark plug of claim 1, wherein, a cross-sectional area of the electrode plate in a direction perpendicular to the axial centerline is greater than a cross-sectional area of the counterbore, and a portion of the bottom surface of the electrode tip is flush with an end surface of the insulator nose.

3. The spark plug of claim 1, wherein, the electrode plate is circular.

4. The spark plug of claim 1, the first end of the electrode wire being disposed within the collar bore and mechanically and electrically connected to the collar by a braze joint.

5. The spark plug of claim 4, wherein: the electrode plate comprises a pocket at a top surface opposite the bottom surface, the pocket being coaxial with the collar bore and having a diameter greater than a diameter of the collar bore, the collar bore extending to the pocket; and the first end of the electrode wire extends into the pocket and forms a cap in the pocket filling a volume of the pocket. a surface of the cap is coplanar with the top surface of the electrode plate.

6. The spark plug of claim 5, wherein, 7. The spark plug of claim 1, the electrode wire comprising external threads at the first end of the electrode wire, the collar comprising internal threads disposed within the collar bore to mate with the external threads to threadably connect the center electrode to the first end of the electrode wire. the threads comprise locking threads.

8. The spark plug of claim 7, wherein, the electrode wire and the electrode tip are of a same material.

9. The spark plug of claim 1, wherein, 10. A spark plug, comprising: a terminal end; a firing end; an axial centerline extending between the terminal end and the firing end; an insulator core extending between the terminal end and the firing end, the insulator core comprising: a center bore coincident with the axial centerline extending through the insulator core; and an insulator nose proximate the firing end; and a counterbore coincident with the axial centerline and extending axially into the insulator nose toward the terminal end, the counterbore having a second diameter greater than a first diameter of the center bore. a center electrode comprising: an electrode wire disposed within the center bore and having a first end proximate the insulator nose; and an electrode tip electrically coupled to the first end of the electrode wire, a portion of a bottom surface of the electrode tip flush mounted with an end surface of the insulator nose, the electrode tip comprising an electrode tip bore extending through the electrode tip and coaxial with the axial centerline, wherein the first end of the electrode wire is disposed within the electrode tip bore and is connected to the electrode tip by a braze joint.

11. The spark plug of claim 10, wherein, the electrode tip comprises: an electrode plate defining a bottom surface and having an outer periphery that extends beyond an outer periphery of the insulator nose in a direction perpendicular to the axial centerline; and a collar extending from the bottom surface, wherein the electrode tip bore extends through the electrode plate and the collar.

12. The spark plug of claim 11, wherein, the insulator nose comprises a counterbore coaxial with the axial centerline and extending toward the terminal end, and wherein the collar is disposed within the counterbore.

13. The spark plug of claim 11, wherein: the electrode plate comprises a pocket in a top surface opposite the bottom surface, the pocket coaxial with the electrode tip bore and having a diameter greater than a diameter of the electrode tip bore, the electrode tip bore extending through the collar and the electrode plate to the pocket; and the first end of the electrode wire extends into the pocket and is swaged to form a cap in the pocket that fills a volume of the pocket.

14. The spark plug of claim 13, wherein, a surface of the cap is coplanar with the top surface of the electrode plate.

15. The spark plug of claim 10, wherein, the electrode tip is threaded to the first end of the electrode wire.

16. The spark plug of claim 15, the electrode wire comprising external threads at the first end of the electrode wire, the electrode tip comprising: an electrode plate having a top surface and a bottom surface facing the insulator nose; and a collar extending axially from the bottom surface, the collar comprising internal threads that mate with the external threads.

17. The spark plug of claim 16, the insulator core comprising: a counterbore extending axially into the insulator nose toward the terminal end, the collar being within the counterbore.

18. The spark plug of claim 10, comprising: a metal shell concentrically surrounding the insulator core; and a side electrode extending from and electrically coupled to the metal shell, wherein an outer peripheral edge of the electrode tip and an outer peripheral edge of the side electrode define a spark gap.

19. A spark plug, comprising: a terminal end; a firing end; an axial centerline extending between the terminal end and the firing end; an insulator core comprising: a center bore coincident with the axial centerline extending through the insulator core; an insulator nose at the firing end; and a counterbore extending axially into the insulator nose toward the terminal end, the counterbore having a diameter greater than a diameter of the center bore. ​ ​ a side electrode defined by a metal shell concentrically surrounding the insulating core, the side electrode extending circumferentially around the firing end; and a center electrode comprising: an electrode wire disposed within the center hole and having a first end proximate the insulating nose; and an electrode head comprising: an electrode plate having a bottom surface facing the insulating nose and having a diameter greater than a diameter of the center hole; a collar extending from the bottom surface and within the counterbore and flush with an end surface of the insulating nose to define a continuous spark gap between a circumferential edge of the electrode plate and a circumferential edge of the side electrode; and a head hole coaxial with the axial centerline and extending at least partially through the electrode head, the first end of the electrode wire disposed within the head hole and mechanically and electrically connected to the electrode head.

20. The spark plug of claim 19, wherein, the insulating nose extends axially beyond the side electrode in a direction toward the firing end, and wherein the diameter of the electrode plate is greater than an outer diameter of the insulating nose to define the spark gap between a circumferential edge of the bottom surface of the electrode plate and a circumferential edge of the side electrode.

21. The spark plug of claim 20, wherein, the electrode plate has a top surface opposite the bottom surface, and wherein an outer periphery of the electrode head is angled downwardly from the top surface toward the outer peripheral electrode.

22. The spark plug of claim 20, wherein, the diameter of the electrode plate is less than an inner diameter of the side electrode to define the spark gap between a circumferential edge of the bottom surface of the electrode plate and an inner circumferential edge of the side electrode at an acute angle through the axial centerline in a direction toward the terminal end of the spark plug.

23. The spark plug of claim 19, wherein, the electrode wire and the electrode head comprise the same material.

24. The spark plug of claim 19, the first end of the electrode wire disposed within the head hole and mechanically and electrically connected to the collar by a braze joint.

25. The spark plug of claim 24, wherein: the electrode plate includes a pocket in a top surface opposite the bottom surface, the pocket coaxial with the head hole and having a diameter greater than a diameter of the head hole, the head hole extending through the collar and the electrode plate to the pocket; and the first end of the electrode wire extends into the pocket and is stamped to form a cap in and filling a volume of the pocket.

26. The spark plug of claim 25, wherein, a surface of the cap is coplanar with the top surface of the electrode plate.

27. The spark plug of claim 19, wherein, the head hole and the first end of the electrode wire are threaded, wherein the head hole is threaded to the electrode wire to mechanically and electrically connect the electrode head to the electrode wire. the insulating nose extends axially beyond the side electrode in a direction toward the firing end, and wherein the diameter of the electrode plate is greater than an outer diameter of the insulating nose to define the spark gap between a circumferential edge of the bottom surface of the electrode plate and a circumferential edge of the side electrode. the electrode plate has a top surface opposite the bottom surface, and wherein an outer periphery of the electrode head is angled downwardly from the top surface toward the outer peripheral electrode. the diameter of the electrode plate is less than an inner diameter of the side electrode to define the spark gap between a circumferential edge of the bottom surface of the electrode plate and an inner circumferential edge of the side electrode at an acute angle through the axial centerline in a direction toward the terminal end of the spark plug. the electrode wire and the electrode head comprise the same material.

24. The spark plug of claim 19, the first end of the electrode wire disposed within the head hole and mechanically and electrically connected to the collar by a braze joint.

25. The spark plug of claim 24, wherein: the electrode plate includes a pocket in a top surface opposite the bottom surface, the pocket coaxial with the head hole and having a diameter greater than a diameter of the head hole, the head hole extending through the collar and the electrode plate to the pocket; and the first end of the electrode wire extends into the pocket and is stamped to form a cap in and filling a volume of the pocket. a surface of the cap is coplanar with the top surface of the electrode plate. the head hole and the first end of the electrode wire are threaded, wherein the head hole is threaded to the electrode wire to mechanically and electrically connect the electrode head to the electrode wire.

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