Spark plug and method of manufacturing the same

Abstract

A spark plug and method of manufacture in which the spark plug meets specific geometric relationships to maintain and potentially improve dielectric performance while reducing other spark plug dimensions. The spark plug includes an insulator that can withstand higher voltages while having areas of reduced cross-sectional thickness. In some embodiments, the insulator has a dielectric strength of 42 kV / mm or more, a radial thickness at the inner seal of 1.5 to 1.6 mm, inclusive, and a radial thickness at the gasket of 0.6 to 0.9 mm, inclusive.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 250,653, filed on September 30, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates generally to spark plugs, and more specifically to spark plug insulators and methods of manufacturing them. Background Technology

[0004] The electrical and mechanical requirements for spark plugs have been increasing and continue to increase. For example, some automotive specifications now require 45kV for M12 spark plugs. With further improvements in engine technology, voltage requirements are expected to increase further, while spark plug sizes are expected to decrease, for example, to M10. Therefore, there is a need for ceramic spark plug insulators that can withstand higher voltages while having a thinner cross-section. Summary of the Invention

[0005] According to one embodiment, a spark plug includes a housing having a threaded region and an axial bore. The spark plug includes an insulator having a ceramic body and an axial bore, the insulator being at least partially disposed within the axial bore of the housing, and the ceramic body being made of a ceramic material. The spark plug includes a washer at least partially disposed within the axial bore of the insulator and an internal seal at least partially disposed within the axial bore of the insulator. The spark plug includes a center electrode at least partially disposed within the axial bore of the insulator and a ground electrode configured to generate a spark gap together with the center electrode. Furthermore, or Where T IS D is the radial thickness of the insulator at the internal seal. CE It is the diameter of the central electrode, D S It is the diameter of the internal seal, D M It is the main diameter at the threaded area of ​​the outer casing, ρ TH ρ is the density of a completely dense and non-porous ceramic material, and T is the density of the ceramic material. G It is the radial thickness of the insulator at the gasket.

[0006] In some embodiments, the insulator has a dielectric strength of 42 kV / mm or greater, and the radial thickness of the insulator at the inner seal is 1.5 to 2.26 mm (including the end value).

[0007] In some embodiments, the reduction in the radial thickness of the insulator at the inner seal corresponds to a proportional increase in the thickness of the housing at the threaded region or a proportional increase in the diameter of the center electrode or the inner seal, and the proportional increase in thickness or the proportional increase in diameter is 20-30%.

[0008] In some embodiments, the radial thickness of the insulator at the internal seal is 1.5 to 1.6 mm (inclusive of the end value).

[0009] In some embodiments, the main diameter is M10, the insulator has a dielectric strength of 42 kV / mm or greater, and the radial thickness of the insulator at the gasket is 0.6 to 1.7 mm (including the end value).

[0010] In some embodiments, the reduction in the radial thickness of the insulator at the gasket corresponds to a proportional increase in the thickness of the housing at the threaded region or a proportional increase in the diameter of the center electrode or the inner electrode, and the proportional increase in thickness or the proportional increase in diameter is 20-30%.

[0011] In some embodiments, the radial thickness of the insulator at the gasket is 0.6 to 0.9 mm (inclusive of the end value).

[0012] In some embodiments, the radial thickness of the insulator at the internal seal is 1.5 to 1.6 mm (inclusive of end values), and / or the radial thickness of the insulator at the gasket is 0.6 to 0.9 mm (inclusive of end values).

[0013] In some embodiments, the ceramic body has a single-phase crystal structure with α-alumina grains.

[0014] In some embodiments, the ceramic body has a porosity of less than 1% by volume.

[0015] In some embodiments, the ceramic body has a uniform average particle size of less than 10 micrometers.

[0016] In some embodiments, the ceramic body has a uniform average particle size of less than 5 micrometers.

[0017] In some embodiments, the ceramic body comprises more than 99.8 wt% alumina.

[0018] In some embodiments, the alumina of the ceramic body is derived from alkoxide precursor alumina powder having a purity of at least 99.95 wt%.

[0019] In some embodiments, and

[0020] In some embodiments, and

[0021] In some embodiments, there is a method for manufacturing spark plugs, which includes the step of injection molding a ceramic body.

[0022] In some embodiments, the method includes the steps of spray drying a slurry to form a granular material and pressing the granular material to form a ceramic body.

[0023] According to one embodiment, a spark plug is provided having a housing with an axial bore, wherein the housing has a main diameter of M12 at a threaded region of the housing. The spark plug includes an insulator having a ceramic body, the insulator having an axial bore and being at least partially disposed within the axial bore of the housing. The spark plug also includes an internal seal at least partially disposed within the axial bore of the insulator, a center electrode at least partially disposed within the axial bore of the insulator, and a ground electrode configured to generate a spark gap together with the center electrode. The insulator is configured to have a dielectric strength of 42 kV / mm or greater and a radial thickness of 1.5 to 1.6 mm (inclusive) at the internal seal.

[0024] According to another embodiment, a spark plug is provided having a housing with an axial bore, wherein the housing has a main diameter of M10 in a threaded region. The spark plug includes an insulator having a ceramic body, the insulator having an axial bore and being at least partially disposed within the axial bore of the housing. The spark plug also includes a washer at least partially disposed within the axial bore of the housing, a center electrode at least partially disposed within the axial bore of the insulator, and a ground electrode configured to generate a spark gap together with the center electrode. The insulator is configured to have a dielectric strength of 42 kV / mm or greater and a radial thickness of 0.6 to 0.9 mm (inclusive) at the washer.

[0025] The aspects, embodiments, examples, features, and alternatives set forth in the preceding paragraphs, claims, and / or the following description and drawings can be viewed independently or in any combination thereof. For example, features disclosed in connection with one embodiment are applicable to all embodiments in the absence of feature incompatibility. Attached Figure Description

[0026] Preferred exemplary embodiments will now be described in conjunction with the accompanying drawings, in which the same reference numerals denote the same elements, and wherein:

[0027] Figure 1 It is based on a cross-sectional view of an example spark plug;

[0028] Figure 2 yes Figure 1 A photomicrograph of the ceramic body of a spark plug insulator;

[0029] Figure 3 The diagram schematically illustrates the defects and pores in the microstructure of existing technologies;

[0030] Figure 4 It is a diagram illustrating the dielectric properties of various insulators;

[0031] Figure 5 The table shows a comparison between six exemplary prior art spark plugs (PA1-6) and eight exemplary embodiments (EX1-8) taught herein; and

[0032] Figure 6 It's a diagram. Figure 1 and 2 A flowchart illustrating an exemplary manufacturing method for an insulator and a ceramic body. Detailed Implementation

[0033] The spark plug insulators described herein comprise a high-purity alumina ceramic body that is substantially non-porous and has a dielectric strength approximately 30% higher than existing insulators. This allows the insulator to be constructed with a thinner cross-section, which is necessary for smaller spark plugs (e.g., M10 and M12), and can be used to proportionally increase the thickness of other spark plug components such as the housing, internal seals, center electrode, etc. Using conventional processing methods, the high-purity alumina material described herein can be prone to producing large (e.g., 50 to 250 micrometers) crescent-shaped voids due to poor consolidation of spray-dried particles. These crescent-shaped voids limit the dielectric and mechanical strength of the insulator. Therefore, in some embodiments, the insulator is specifically injection molded or spray-dried with specific additives and binders to enhance the microstructure of the insulator.

[0034] Figure 1 An exemplary spark plug 10 is illustrated. Spark plug 10 includes a center electrode 12, an insulator 14, a metal housing 16, and a ground electrode 18. The illustrated spark plug 10 is a J-gap spark plug having a spark gap G between the center electrode 12 and the ground electrode 18, and is advantageously suited for high-performance automotive applications. However, it should be understood that the insulator and methods described herein can be used with any type of spark plug or ignition device, including glow plugs, industrial spark plugs, aviation igniters, and / or any other device for igniting the air / fuel mixture in an engine.

[0035] The center electrode 12, which may be a single integral component or may include multiple separate components, is at least partially disposed within an axial aperture 22 extending along the axial length of the insulator 14. As shown, the axial aperture 22 includes one or more internal stepped portions 24 extending circumferentially around the inner side of the aperture and designed to receive complementary external stepped portions 20 of the center electrode 12. Figure 1In some embodiments, the axial aperture 22 includes only a single internal step or shoulder portion 24; however, the axial aperture may include additional internal step portions at different axial locations along the aperture length. An insulator 14 is at least partially disposed within an internal aperture 26 of the metal housing 16, and the internal aperture 26 extends along the length of the metal housing and is generally coaxial with the axial aperture 22. In the particular embodiment shown, the end 38 of the insulator 14 extends from and protrudes beyond the end of the internal aperture 26 of the metal housing, and the end of the center electrode 12 extends from and protrudes beyond the axial aperture 22 of the insulator. The end of the center electrode 12, together with a corresponding portion of the ground electrode 18, forms a spark gap G; this may include embodiments with or without a noble metal ignition element on the center electrode and / or the ground electrode. Figure 1 In the embodiments, both the center electrode 12 and the ground electrode 18 have precious metal ignition elements attached thereto, but the disclosed spark plug device is provided as an example only and is not required.

[0036] The insulator 14 is an elongated and generally cylindrical component made of an electrically insulating material and designed to isolate the center electrode 12 from the metal housing 16, thereby directing the high-voltage ignition pulse from the center electrode to the spark gap G. This can occur via a center lead assembly 25 comprising the center electrode 12, an internal seal 27, and terminal electrodes 28. The center lead assembly 25 is at least partially surrounded by an axial aperture 22 of the insulator 14. Various shielding thicknesses can be measured at locations along the length of the insulator 14, and the thickness herein is measured as the radial distance between the axial aperture 22 and the outer surface 23 of the insulator, as will be further detailed below. The insulator 14 includes a nose portion 30, a middle portion 32, and a terminal portion 34 along its length. The insulator 14 includes a ceramic body 35, which has a reduced thickness and increased dielectric strength compared to similar materials not manufactured according to the teachings herein. Other configurations or embodiments are, of course, possible besides those shown in the figures and may be determined at least in part by the desired application of the spark plug 10. For example, to name just a few, the insulator 14 can have a twin-cylinder design, various internal channels or grooves.

[0037] The nose-shaped portion 30 extends axially or longitudinally between the outer step 36 on the outer surface 23 of the insulator and the distal end 38 of the insulator 14 at the ignition end of the spark plug 10. The concave end of the outer step 36 forms a washer shoulder 39, which is the radially innermost portion of the outer step. The outer step 36 and the washer shoulder 39 rest on a washer 40 located between the insulator 14 and the housing 16. The outer surface 23 of the insulator 14 may include... Figure 1Other structural features, not shown, such as annular ribs, are used to limit or prevent carbon buildup and other deposits. The nose-shaped portion 30 may have a continuous and uniform taper along its axial length, or it may have sections with different tapers or no taper at all (i.e., straight sections with parallel outer surfaces). Furthermore, the extent to which the nose-shaped portion 30 extends axially or protrudes beyond the end of the metal housing 16 (sometimes referred to as a "protrusion") may be greater than or less than [the extent to which this extension extends]. Figure 1 The extent indicated. In some cases, the distal end or tip 38 of the nose portion may even retract into the insulator aperture 22, so that it does not extend beyond the metal casing at all (i.e., negative protrusion).

[0038] The middle portion 32 of the insulator extends axially between the external locking feature structure 41 and the aforementioned external step 36. Figure 1 In the specific embodiment shown, a large portion of the intermediate portion 32 is located and held within the internal aperture 26 of the metal housing 16 and serves to surround the internal seal 27. The external locking feature 41 may have an enlarged diameter shape, such that during spark plug assembly, the open end or flange 42 of the metal housing can be folded or otherwise mechanically deformed to securely hold the insulator 14 in place. The folded flange 42 also captures the annular seal 44 between the outer surface of the insulator 14 and the inner surface of the metal housing 16, thereby achieving a certain degree of sealing. In another embodiment, the annular seal 44 may be omitted, allowing the folded flange 42 to directly contact the external locking feature 41. Other intermediate portion features are, of course, also possible.

[0039] The terminal portion 34 is located at the end of the insulator 14 opposite the nose-shaped portion 30, and it extends axially between the external locking feature structure 41 and the second distal end or terminal 50. In the illustrated embodiment, the terminal portion 34 is relatively long; however, it can be shorter and / or have any number of other feature structures, such as annular ribs. During operation, the terminal portion 34 is typically located outside the combustion chamber of the engine.

[0040] The ceramic body 35 is advantageously made of a high-purity alumina material. According to one embodiment, the high-purity alumina material is greater than or equal to 99.8 wt% alumina (Al₂O₃), with the remainder being small amounts of one or more sintering aids—such as magnesium oxide (MgO), yttrium oxide (Y₂O₃), and / or zirconium oxide (ZrO₂). Other alumina-based or ceramic materials are also possible, but advantageously, the alumina powder used to manufacture the ceramic body 35 is alkoxide-derived alumina with a purity of at least 99.93 wt% alumina or more preferably at least 99.97 wt% alumina. Typically, this type of material is not very robust during manufacturing and can lead to processing defects that may limit the properties of the insulator, especially when conventional processing methods are used. However, as detailed below, the microstructure and dielectric strength can be strategically enhanced through specific manufacturing methods, thereby allowing for thinner-walled structures for the ceramic body 35.

[0041] Figure 2 This is a micrograph of the ceramic body 35, showing the microstructure 52. When made with high-purity alumina according to the manufacturing method described herein, the microstructure 52 comprises a single-phase crystal structure 54 of α-alumina grains 56 (only a portion of which is labeled for clarity). The microstructure 52 is substantially non-porous and has a density greater than 98% of its theoretical density, more preferably greater than 99% of its theoretical density. This corresponds to a porosity of less than 1% by volume. Advantageously, the α-alumina grains 56 have a uniform grain size / grain size of less than 10 micrometers, preferably less than 5 micrometers. Larger grains (as is typical of conventional processing methods using high-purity alumina) are generally unsuitable for insulators because they reduce mechanical strength and thermal shock resistance to unacceptable levels.

[0042] Figure 3 A prior art ceramic body is shown, which, despite having α-alumina grains 56, includes schematically shown defects 58 and crescent-shaped voids 60 in its microstructure 62. Conventional processing methods would produce undesirable defects 58 and voids 60 in the microstructure 62. High-purity alumina materials are particularly prone to developing large (e.g., 50 to 250 micrometers) crescent-shaped voids 60 due to poor consolidation of spray-dried particles. These crescent-shaped voids 60 limit the dielectric and mechanical strength of the ceramic body. Therefore, the manufacturing method described herein can be used to impart the necessary strength and microstructure required to create thinner-walled structures for the insulator 14.

[0043] return Figure 1 With the dielectric strength of the ceramic body 35 of the insulator 14 increased by approximately 20-30%, the thickness of each component of the spark plug 10 can be strategically adjusted. The spark plug 10 can be an M10 or M12 spark plug, such that the main diameter D of the outer shell thread at the threaded region 37... MThe sizes are 10mm or 12mm. Other sizes of spark plugs 10 can also be produced according to the teachings of this article, but the advantages of their dielectric strength make them particularly suitable for the miniaturization of spark plugs and engines (e.g., using M10 spark plugs compared to M12 spark plugs) while retaining the necessary ability to withstand various voltage limits. Although similar high-purity alumina materials have been used in the past, they typically do not perform well in smaller spark plugs and thinner-walled insulator structures.

[0044] Insulator 14 includes a strategically reduced radial thickness T at the gasket. G and the radial thickness T at the internal seal IS The thickness T at the washer G The radial extent of the ceramic body 35 is measured between the washer shoulder 39 at the starting point of the outer stepped portion 36 and the axial orifice 22 of the insulator 14. The thickness T at the internal seal... IS The radial extent of the ceramic body 35 is measured between the axial orifice 22 at the internal seal 27 and the outer surface 23 of the insulator 14 at the internal seal. Therefore, the thickness T at the gasket... G It refers to the radial insulator thickness at the gasket, while the thickness T at the internal seal is... IS This is the radial insulator thickness at the internal seal. If the internal seal 27 has a diameter variation, then the thickness T... IS Take the maximum value. Typically, insulator 14 has a thickness T. G The area at this point experiences the highest electrical stress during use, and the thickness T of the insulator at the internal seal is [missing information]. IS They are subjected to the second highest electrical stress. Therefore, controlling the thickness of these areas while maintaining the necessary dielectric strength is helpful for size reduction and spark plug performance.

[0045] In one example, spark plug 10 is an M12 spark plug with a radial thickness T at the inner seal 27. IS The thickness is 1.5 to 1.6 mm (including the end value). This is significantly less than the conventional 2.1 to 2.2 mm thickness at the internal seal 27, while maintaining or exceeding the necessary dielectric strength. Furthermore, the thickness T at the gasket or gasket shoulder 39... G The thickness is 1.0 to 1.2 mm (including the terminal value). Compared to conventional spark plugs, this reduces the thickness by approximately 30% while maintaining a dielectric strength of 42 kV / mm or higher, or more advantageously, at least 50 kV / mm to up to 70 kV / mm. In another example, spark plug 10 is an M10 spark plug with a thickness T at the internal seal 27. IS The thickness is 1.4 to 1.8 mm (inclusive). Additionally, the thickness T at 39mm on the washer shoulder... GThe thickness is 1.1 to 1.5 mm (including the end value). Compared to conventional spark plugs, this again equates to a thickness reduction of approximately 30% while maintaining a dielectric strength of 42 kV / mm or higher. This level of dielectric strength appears unattainable with similar high-purity alumina materials, especially with conventional processing methods. With the improved dielectric durability, the thickness of the spark plug insulator 14 manufactured according to the methods described herein can be reduced, thereby allowing the spark plug 10 to have an equivalent performance of 50 kV in an M10 design.

[0046] Figure 4 Figure 70 shows the dielectric properties of prior art insulators 72 and 74 compared to insulator 76 manufactured according to the teachings of this document, using ASTM D149 testing. Thirty insulators in each group were tested using a 60Hz AC voltage source. A cylindrical high-voltage electrode was positioned in the axial orifice 22 of insulator 14, and a grounding electrode sleeve (T) was positioned around the cylindrical portion of the insulator at the internal seal 27. IS The voltage gradually increases at a rate of 500 kV RMS per second until a dielectric fault occurs in the insulator. The average fault voltage in the prior art is 23.4 kV (RMS). The minimum fault voltage in the prior art is 22.0 kV (RMS). For insulator 76 tested under the same conditions, the average fault voltage is 34.0 kV (RMS), and the minimum fault voltage is 27.7 kV (RMS).

[0047] Various factors can affect the dielectric strength properties of the ceramic body 35, including the structure of the insulator 14, and electrical stress concentration due to the geometry of the electrodes and the waveform of the applied voltage. The waveform of the voltage applied in the ASTM D149 test is a continuous AC sine wave at 60 Hz. The peak voltage of the sine wave is the square root of the RMS voltage multiplied by 2 (1.414). Compared to the 23.4 kV RMS mean fault voltage from the ASTM D149 test, spark plugs using existing insulator construction and tested with an automotive ignition coil at the voltage source typically withstand 50 kV or higher. The waveform of an automotive ignition coil is a series of high-voltage pulses negative to ground. These high-voltage pulses typically occur at approximately 50 to 60 Hz, but each pulse lasts only a few milliseconds (typically less than 1 millisecond), and the pulses are separated by intervals where the applied voltage is essentially zero. Therefore, when the waveform of the voltage source is the same as that of an automotive ignition coil, approximately twice the voltage can be withstood. Therefore, spark plugs 10 manufactured according to the teachings of this paper are expected to be able to withstand voltages of 68.0 kV or higher on average. Given this improvement, the wall structure can be made thinner while maintaining the necessary strength.

[0048] Insulator 14 in seal 27 (T IS ) or washer or washer shoulder 39 (TG Having a thinner cross-section or radial thickness at this point allows for increased thickness of other components of the spark plug 10. For example, the diameter D of the internal seal 27... S This can be increased proportionally. This can reduce the current density and make the suppressor more durable under harsh engine conditions. In another example, the thickness T of the housing 16 can be increased. S Considering the torque required to install and remove spark plugs from the engine, making the M10 spark plug housing 16 too thin poses a risk of making the spark plug unsuitable. Reducing the radial thickness T of the insulator 14 at the internal seal... IS and / or the radial thickness T of insulator 14 at the gasket G Allowable shell thickness T S This is increased proportionally, which therefore facilitates the installation and / or removal of the spark plug. In yet another example, the diameter D of the center electrode 12 can be increased proportionally. CE This allows for better heat flow from the ignition tip. The various increases / decreases in these thicknesses or diameters will depend on many factors, such as, for example, the overall spark plug size and design, the amount of increase / decrease in each correspondingly adjusted component, and the type of material used.

[0049] Figure 5 The table illustrates a comparison between six exemplary prior art spark plugs (PA1-6) and eight exemplary embodiments (EX1-8) according to the teachings of this document. The table includes... Figure 1 Examples of various geometric dimensions are shown. As used herein, the proportional increase in thickness or diameter refers to an increase in standard-sized parts, for PA1-6 having Figure 5 The dimensions or size ranges listed are as follows: for M10, the standard thickness for the main diameter / large diameter is 1.66-1.81 mm (inclusive of end values), and for M12, it is 2.17-2.28 mm (inclusive of end values).

[0050] To achieve resistance to dielectric breakdown, the geometric factor used to design insulator 14 can be defined as either or both of the following equations 1 and 2:

[0051] (Equation 1)

[0052] (Equation 2)

[0053] The terms are defined above and, for example, in Figure 5 The table shows that T IS It is the ceramic thickness at point 27 of the inner seal, T G It is the ceramic thickness at 40mm of the washer, D. S It is the diameter of the internal seal, D. MIt is the main diameter of the thread in the threaded area 37 of the outer casing 16.

[0054] In existing spark plugs, the goal is typically to maximize these geometric factors in Equations 1 and 2 by increasing the thickness of the ceramic within the constraints of the dimensions of the housing 16, the center electrode 12, and the inner seal 27. However, spark plugs as defined herein allow for a reduction in the thickness of the ceramic insulator 14 because the ceramic has excellent resistance to dielectric breakdown. Therefore, Equations 1 and 2 can be modified to include a factor A for the ceramic, as shown in Equations 3 and 4 below, respectively:

[0055] (Equation 3)

[0056] (Equation 4)

[0057] Factor A has been found to be the density ρ of insulator 14 ceramics relative to the theoretical density ρ of fully dense, non-porous alumina. TH The function (e.g., for the high-purity alumina described herein and used for insulator 14, is 3.98 g / cm³) 3 According to one embodiment, A can be defined as follows:

[0058] (Equation 5)

[0059] Where the exponent n = 0.5.

[0060] This provides the geometric factors F1 and F2 as defined in Equations 6 and 7, respectively:

[0061] (Equation 6)

[0062] (Equation 7)

[0063] For existing spark plug technology, such as Figure 5 In PA1-6, the values ​​of these factors F1 and F2 are typically below 2, while in ceramic insulator 14 (e.g., according to the teachings of this document) Figure 5 The EX1-8 parameters allow either or both of the factors F1 and F2 to be greater than two, preferably greater than three. These geometric relationships particularly help maintain and potentially improve dielectric properties while reducing spark plug size. In some embodiments, it is desirable for both F1 and F2 to be greater than 2, and preferably greater than 3, as this results in a smaller but higher dielectric strength insulator 14. Figure 5As shown, in the examples according to the teachings of this document, the F1 of the examples (EX1-8) ranges between 2.95 and 4.9, while the F1 of the prior art insulator (PA1-6) is 1.9 or worse. For the examples (EX1-8), the F2 ranges between 2.25 and 5.67, while the F2 of the prior art insulator (PA1-6) is 1.95 or worse.

[0064] Regarding the manufacture of insulator 14 to achieve desired values ​​of F1 and / or F2 or a reduced insulator thickness region while maintaining dielectric strength, one potential method involves injection molding of a ceramic body 35. Injection molding is a final forming method, thus significantly reducing manufacturing waste, and the injection molding process helps eliminate certain processing defects associated with spray-dried powders that limit the performance of conventionally processed spark plug insulators (e.g., standard spray drying or cold isostatic pressing). For example, for injection molding, the aforementioned high-purity alumina material can be combined with a sintering aid dispersed in a thermoplastic organic medium such as wax. This is then granulated to form an injection molding raw material. The raw material is injection molded to form an insulator preform. The preform is degreased to remove the thermoplastic organic medium and then heat-treated to sinter the insulator. In some embodiments, degreasing may include water-based or solvent-based extraction methods or a toner bed. During heat treatment, the desired uniform particle size can be achieved when fired to a temperature between 1450°C and 1550°C (inclusive). During heat treatment, insulators typically shrink by about 20%. A non-porous structure can be achieved by thoroughly and carefully dispersing the precursor powder in an organic medium to prevent bubble formation and by molding to avoid introducing bubbles. Unlike pressing and turning methods, injection molding can produce non-axisymmetric insulators (e.g., bi-cylinder insulators). Furthermore, centering features are sometimes included near the gasket 40. This can be omitted in injection molding designs because tighter tolerances can be achieved.

[0065] Another potential manufacturing method involves the specialized / special pressing of the ceramic body 35, and in Figure 6The flowchart is schematically illustrated. Method 100 differs strategically from other prior art pressing methods and helps achieve the necessary thickness and dielectric strength described herein. Method 100 includes step 102 of mixing alumina powder, one or more sintering aids, and a fluid to form a slurry. Advantageously, the alumina powder is a high-purity alumina material described herein—for example, 99.8 wt% alumina (Al₂O₃), with the balance being a small amount of one or more sintering aids (e.g., magnesium oxide (MgO), yttrium oxide (Y₂O₃), and / or zirconium oxide (ZrO₂), wherein the alumina powder is an alkoxide-derived alumina with a purity of at least 99.93 wt%, more preferably at least 99.97 wt%). The fluid may be water or any other operable medium that can be used to form a sufficient slurry.

[0066] In step 104, an organic binder is added to the slurry. The organic binder comprises a polyethylene glycol (PEG)-based material (e.g., 3-5%, including end values) and a small amount of polyvinyl alcohol (PVA) (e.g., less than 0.5%, including end values). In an advantageous embodiment, 5.0% PEG-1500 and 0.25% PVA are included as the organic binder system. PEG with a molecular weight of 1500 particularly helps to eliminate or reduce porosity in the final ceramic body 35. These specific amounts of PEG and PVA also help to reduce the formation of crescent-shaped voids during manufacturing. In one specific embodiment, the total mixture is primarily 100 kg of high-purity alumina, containing 500 ppm of sintering aids (e.g., magnesium oxide (MgO), yttrium oxide (Y2O3), and / or zirconium oxide (ZrO2), wherein the alumina powder is alkoxide-derived alumina with a purity of at least 99.93 wt%, more preferably at least 99.97 wt%). 5 kg of PEG, 0.5 kg of PVA, and approximately 35 kg of water are mixed to produce a fluid slurry. The water is removed during spray drying, resulting in 105.5 kg of granular powder containing 100 kg of alumina, 5 kg of PEG, 0.5 kg of PVA, and 500 ppm of sintering aid.

[0067] Step 106 involves spray drying the slurry to form granular material. Modifying the PEG binder in the pressing and turning manufacturing processes helps eliminate any unwanted structures that may form in the granular material during spray drying. Therefore, organic binder systems containing 3-5% PEG-1500 can help provide better spray drying results than other methods.

[0068] Step 108 involves pressing granular material into a blank, and step 110 involves shaping the blank to form a spark plug insulator preform or green blank. This can be accomplished, for example, by contour grinding of the blank obtained in step 108. Again, the PEG binder can assist during pressing step 108 and can help form an improved microstructure in the ceramic body 35.

[0069] Step 112 involves firing the insulator preform obtained in step 110. For example, high density and uniform grain size / granulation can be achieved when firing to a temperature between 1450°C and 1550°C (inclusive). The firing process can remove the binder system and produce a fully dense, virtually non-porous structure. Other post-processing steps may also be included, such as further contouring, glazing, etc.

[0070] It should be noted that the exemplary embodiments shown in the figures and described above are intended only as examples of insulators manufactured according to the processes taught herein, as these processes can be used to manufacture other insulator embodiments, including those significantly different from insulator 14. Furthermore, spark plug 10 is not limited to the illustrated embodiment and can utilize any combination of other known spark plug components, to name a few possibilities, such as terminals, internal resistors, internal seals, various gaskets, precious metal elements, etc. Moreover, insulator 14 having the thicknesses and dielectric strengths listed herein can be formed by alternative methods not specifically discussed herein.

[0071] It should be understood that the foregoing description is of one or more preferred exemplary embodiments. The invention is not limited to the specific embodiments disclosed herein, but is defined solely by the following claims. Furthermore, the statements contained in the foregoing description relate to specific embodiments and should not be construed as limiting the scope of the invention or the definitions of terms used in the claims, unless the terms or expressions are expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiments will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to fall within the scope of the appended claims.

[0072] As used in this specification and claims, the terms “for example,” “e.g.,” “such as,” “like,” and “for instance,” as well as the verbs “comprising,” “having,” “including,” and their other verb forms, when used with a list of one or more components or other entries, shall be interpreted as open-ended, meaning that the list shall not be construed as excluding other, additional components or entries. Unless other terms are used in a context requiring a different interpretation, they shall be interpreted using their broadest reasonable meaning. Additionally, the term “and / or” shall be interpreted as inclusive “or.” Thus, for example, the phrase “A, B, and / or C” shall be interpreted to encompass all of the following: “A”; “B”; “C”; “A and B”; “A and C”; “B and C”; and “A, B, and C”.

Claims

1. A spark plug, comprising: A housing with a threaded area and an axial bore; An insulator having a ceramic body and an axial aperture, the insulator being at least partially disposed within the axial aperture of the housing, the ceramic body being made of ceramic material; A washer, at least partially disposed within the axial orifice of the insulator; An internal seal is provided at least partially within the axial orifice of the insulator; A central electrode is at least partially disposed within the axial orifice of the insulator; and A ground electrode configured to form a spark gap together with the central electrode. in ; or ; Where T IS D is the radial thickness of the insulator at the internal seal. CE D is the diameter of the central electrode. S D is the diameter of the internal seal. M It is the main diameter at the threaded area of ​​the outer casing, ρ TH It is the density of a completely dense and non-porous ceramic material, ρ is the density of the ceramic material, and T is the density of the ceramic material. G It is the radial thickness of the insulator at the gasket.

2. The spark plug according to claim 1, wherein, The main diameter is M12, the dielectric strength of the insulator is 42kV / mm or higher, and the radial thickness of the insulator at the internal seal is 1.5 to 2.26 mm, including the end value.

3. The spark plug according to claim 2, wherein, The reduction in the radial thickness of the insulator at the inner seal corresponds to a proportional increase in the thickness of the outer shell at the threaded region, or a proportional increase in the diameter of the central electrode or the inner seal, wherein the proportional increase in thickness or the proportional increase in diameter is 20-30%.

4. The spark plug according to claim 2, wherein, The radial thickness of the insulator at the internal seal is 1.5 to 1.6 mm, including the end value.

5. The spark plug according to claim 1, wherein, The main diameter is M10, the dielectric strength of the insulator is 42kV / mm or higher, and the radial thickness of the insulator at the washer is 0.6 to 1.7 mm, including the end value.

6. The spark plug according to claim 5, wherein, The decrease in the radial thickness of the insulator at the gasket corresponds to a proportional increase in the thickness of the housing at the threaded region, or a proportional increase in the diameter of the center electrode or the diameter of the internal seal, wherein the proportional increase in thickness or the proportional increase in diameter is 20-30%.

7. The spark plug according to claim 5, wherein, The radial thickness of the insulator at the washer is 0.6 to 0.9 mm, including the end values.

8. The spark plug according to claim 1, wherein, The radial thickness of the insulator at the internal seal is 1.5 to 1.6 mm, including the end value, and / or the radial thickness of the insulator at the gasket is 0.6 to 0.9 mm, including the end value.

9. The spark plug according to claim 1, wherein, The ceramic body has a single-phase crystal structure with α-alumina grains.

10. The spark plug according to claim 1, wherein, The ceramic body has a porosity of less than 1% by volume.

11. The spark plug according to claim 1, wherein, The ceramic body has a uniform average particle size of less than 10 micrometers.

12. The spark plug according to claim 11, wherein, The ceramic body has a uniform average particle size of less than 5 micrometers.

13. The spark plug according to claim 1, wherein, The ceramic material contains more than 99.8 wt% alumina.

14. The spark plug according to claim 13, wherein, The ceramic material is derived from alumina powder, an alkoxide precursor, having a purity of at least 99.95 wt%.

15. The spark plug according to claim 1, wherein, ; and 。 16. The spark plug according to claim 15, wherein ; and 。 17. A method of manufacturing the spark plug of claim 1, comprising the step of injection molding the ceramic body.

18. A method of manufacturing the spark plug of claim 1, comprising the steps of spray drying a slurry to form a granular material and pressing the granular material to form the ceramic body.

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