Patent Application
20190214794
The present teachings relate generally to spark plugs and, in some embodiments, to fouling-resistant insulators for spark plugs.
Spark plugs used as igniters in internal combustion engines are subject to a condition known as “fouling.” Over time, carbon and other combustion products may accumulate on the surface of an insulator tip, which is typically positioned at or near the boundary of unmixed fuel. The combustion products of a gasoline engine may include fuel additive components, such as methylcyclopentadienyl manganese tricarbonyl (MMT) and ferrocene, which are often added to gasoline (e.g., as octane enhancers or anti-knock additives). Ferrocene and MMT fuel additives are commonly used outside of North America as well as in special racing applications in order to increase fuel octane rating and prevent detonation.
During the combustion process, additives such as MMT and ferrocene will burn out and leave behind conductive deposits on the tip of a spark plug insulator. For example, MMT may leave behind manganese oxide deposits and ferrocene may leave behind iron oxide deposits. If significant amounts of these combustion products accumulate, a spark may not properly form between the center and ground electrodes. In effect, the accumulated combustion products create an electrical short circuit, such that the charge from the center electrode travels across the surface of the insulator and back to the outer metal shell.
The accumulation over time of conductive deposits on the insulator tip may eventually lead to misfiring of the spark plug, which reduces the efficiency of the combustion cycle and generates higher than normal partially burned fuel exhaust. In extreme cases, the conductive deposits may lead to pre-ignition and engine damage. Moreover, field tests indicate that the deposits from MMT and ferrocene are often fairly reactive. Thus, at combustion temperature, these deposits may react with an insulator ceramic and form different phases with alumina and glass grain boundary phases in alumina. As a result, defects (e.g., cracks) may form due to thermal mismatch and/or the thermal characteristics of the insulator (e.g., heat range) may change. Potentially, undesired heat spot may develop that in turn could lead to pre-ignition.
The scope of the present invention is defined solely by the appended claims, and is not affected to any degree by the statements within this summary.
By way of introduction, a first spark plug embodying features of the present teachings includes (a) an insulative sleeve having a central axial bore and an exterior surface, wherein a glaze coating is disposed on the exterior surface; (b) a center electrode extending through the central axial bore of the insulative sleeve and having a firing tip that extends beyond the top edge of the insulative sleeve; (c) a metal shell, wherein the insulative sleeve is positioned within and secured to the metal shell; and (d) a ground electrode supported by the metal shell and positioned in a spaced relationship relative to the center electrode so as to generate a spark gap. The glaze coating has a softening point between about 650° C. and about 1100° C., and the glaze coating includes (i) a glass material selected from the group consisting of boric acid, a borosilicate glass, a barium borate glass, a phosphorous glass, a silicate glass, and a combination thereof, and (ii) a modifier selected from the group consisting of an alkali group metal, an alkali earth group metal, aluminum, silicon, a halogen, and a combination thereof. The glaze coating is a continuous band located about 0.1 to about 5 millimeters from a top edge of the insulative sleeve. The band has a width of about 1 to about 20 mm.
A second spark plug embodying features of the present teachings includes an insulative sleeve having a glaze coating thereon, wherein the insulative sleeve has a resistance of at least 11 Gohms at 300° C. when the insulative sleeve undergoes heat treatment at a temperature of between about 700° C. and about 1000° C.
A third spark plug embodying features of the present teachings includes (a) an insulative sleeve having a glaze coating thereon; and (b) an electrode having a firing tip extending beyond the insulative sleeve. The resistance of the glaze coating at a position below the firing tip is greater than 80 Mohms at 350° C. to 400° C.
A method of making a fouling resistant spark plug embodying features of the present teachings includes: (a) providing a spark plug subassembly that includes an insulative sleeve, a center electrode, a resistor, and a terminal stud end; (b) applying a dispersion to at least a portion of an exterior surface of the insulative sleeve, the dispersion containing a glaze coating; and (c) air-drying the dispersion, thereby forming a coated spark plug assembly. The glaze coating has a softening point between about 650° C. and about 1100° C. and includes (i) a glass material selected from the group consisting of boric acid, a borosilicate glass, a barium borate glass, a phosphorous glass, a silicate glass, and a combination thereof, and (ii) a modifier selected from the group consisting of an alkali group metal, an alkali earth group metal, aluminum, silicon, a halogen, and a combination thereof. The glaze coating forms a continuous band located about 0.1 to about 5 millimeters from a top edge of the insulative sleeve, and the band has a width of about 1 to about 20 mm.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the office upon request and payment of the necessary fee.
Glaze coating compositions for coating spark plug insulator tips and methods for making spark plugs containing glazed insulative sleeves have been discovered and are described herein. Spark plugs containing coated insulative sleeves in accordance with the present teachings may be resistant to fouling caused by the accumulation of combustion products on the insulator tip. Moreover, the misfiring of spark plugs containing coated insulative sleeves in accordance with the present teachings when used in engine-consuming fuels containing MMT and/or ferrocene additives may be prevented.
As further described below, a glaze tip coating in accordance with the present teachings may be applied to a spark plug insulator in order to prevent issues associated with MMT and ferrocene fouling. In some embodiments, the glaze coating materials are primarily applied to the nose cone portion of the spark plug insulator, which is exposed to the combustion engine chamber. In accordance with the present teachings, the softening temperature of the glaze material is selected in order to match that of the temperature of the combustion chamber, so that the glaze coating will be reactive to MMT deposits and/or ferrocene deposits but not too soft to be able to flow while the engine is running. In some embodiments, depending on the engine applications, a softening temperature of the glaze coating may be varied between about 650° C. and about 1100° C. In some embodiments, the glaze is located from about 1 to about 3 mm away from the central axial bore, so that the glaze will not adversely affect the heat range of the spark plug.
As shown in
The glaze coating 48, as described herein, may be a continuous or discontinuous coating. The glaze coating 48 may initially be continuous (e.g., no breaks or gaps visible to the naked eye) but may evolve breaks and/or gaps with use. In some embodiments, as shown in
While neither desiring to be bound by any particular theory nor intending to limit in any measure the scope of the appended claims or their equivalents, it is presently believed that the glaze coating prevents and/or reduces adhesion of MMT deposits and/or ferrocene deposits on the spark plug through a process involving diffusion. For example, MMT deposits (e.g., manganese oxides) and/or ferrocene deposits (e.g., iron oxides) may diffuse into the structure of the glass, thereby becoming part of the glass such that electrical conductivity is reduced or eliminated (e.g., electrical resistance is increased) as compared to an uncoated insulative sleeve with an equivalent amount of MMT and/or ferrocene deposits. For this reason, as described above, the softening temperature of the glaze material desirably matches the temperature of the combustion chamber, so that the glaze coating will be reactive to MMT deposits and/or ferrocene deposits but not too soft to be able to flow while the engine is running.
In accordance with the present teachings, the glaze coating may provide a surface that is more resistant to black soot discoloration and, therefore, one that is more resistant to carbon soot fouling/buildup as compared to an untreated insulative sleeve. In application, the MMT and/or ferrocene deposits may vary along the length of the spark plug. In addition, when the MMT and/or ferrocene deposits dissolve in the glaze coating, the composition and the properties of the glaze coating are thereby altered. Other challenges to solving the problem of MMT and/or ferrocene deposits include minimizing volatility of the glaze coating at the operating temperature of the spark plug coupled with having a glaze coating composition with a glass transition temperature appropriate to assist with solvation of the MMT and/or ferrocene deposits. In addition, viscosity of the glaze coating at the operating temperature of the spark plug must be adequate to prevent the glaze coating from slipping to an undesired location on the spark plug.
In some embodiments, a glaze coating for a spark plug insulator in accordance with the present teachings includes a boric acid, a borosilicate glass, a barium borate glass, a phosphorous glass, a silicate glass, or a combination thereof. The glasses may include a material selected from the group consisting of alkali group metals (e.g., alkali group metal oxides), alkali earth group metals (e.g., alkali earth group metal oxides), aluminum (e.g., alumina), silicon (e.g., silica), a halogen (e.g., chloride), and a combination thereof. In some embodiments, the coating material has a softening point between about 650° C. and about 1100° C.
The softening point of a glaze coating in accordance with the present teachings may be one of several different values or fall within one of several different ranges. For example, it is within the scope of the present teachings to select a softening point to be any one of the following values: about 650° C., 651° C., 652° C., 653° C., 654° C., 655° C., 656° C., 657° C., 658° C., 659° C., 660° C., 661° C., 662° C., 663° C., 664° C., 665° C., 666° C., 667° C., 668° C., 669° C., 670° C., 671° C., 672° C., 673° C., 674° C., 675° C., 676° C., 677° C., 678° C., 679° C., 680° C., 681° C., 682° C., 683° C., 684° C., 685° C., 686° C., 687° C., 688° C., 689° C., 690° C., 691° C., 692° C., 693° C., 694° C., 695° C., 696° C., 697° C., 698° C., 699° C., 700° C., 701° C., 702° C., 703° C., 704° C., 705° C., 706° C., 707° C., 708° C., 709° C., 710° C., 711° C., 712° C., 713° C., 714° C., 715° C., 716° C., 717° C., 718° C., 719° C., 720° C., 721° C., 722° C., 723° C., 724° C., 725° C., 726° C., 727° C., 728° C., 729° C., 730° C., 731° C., 732° C., 733° C., 734° C., 735° C., 736° C., 737° C., 738° C., 739° C., 740° C., 741° C., 742° C., 743° C., 744° C., 745° C., 746° C., 747° C., 748° C., 749° C., 750° C., 751° C., 752° C., 753° C., 754° C., 755° C., 756° C., 757° C., 758° C., 759° C., 760° C., 761° C., 762° C., 763° C., 764° C., 765° C., 766° C., 767° C., 768° C., 769° C., 770° C., 771° C., 772° C., 773° C., 774° C., 775° C., 776° C., 777° C., 778° C., 779° C., 780° C., 781° C., 782° C., 783° C., 784° C., 785° C., 786° C., 787° C., 788° C., 789° C., 790° C., 791° C., 792° C., 793° C., 794° C., 795° C., 796° C., 797° C., 798° C., 799° C., 800° C., 801° C., 802° C., 803° C., 804° C., 805° C., 806° C., 807° C., 808° C., 809° C., 810° C., 811° C., 812° C., 813° C., 814° C., 815° C., 816° C., 817° C., 818° C., 819° C., 820° C., 821° C., 822° C., 823° C., 824° C., 825° C., 826° C., 827° C., 828° C., 829° C., 830° C., 831° C., 832° C., 833° C., 834° C., 835° C., 836° C., 837° C., 838° C., 839° C., 840° C., 841° C., 842° C., 843° C., 844° C., 845° C., 846° C., 847° C., 848° C., 849° C., 850° C., 851° C., 852° C., 853° C., 854° C., 855° C., 856° C., 857° C., 858° C., 859° C., 860° C., 861° C., 862° C., 863° C., 864° C., 865° C., 866° C., 867° C., 868° C., 869° C., 870° C., 871° C., 872° C., 873° C., 874° C., 875° C., 876° C., 877° C., 878° C., 879° C., 880° C., 881° C., 882° C., 883° C., 884° C., 885° C., 886° C., 887° C., 888° C., 889° C., 890° C., 891° C., 892° C., 893° C., 894° C., 895° C., 896° C., 897° C., 898° C., 899° C., 900° C., 901° C., 902° C., 903° C., 904° C., 905° C., 906° C., 907° C., 908° C., 909° C., 910° C., 911° C., 912° C., 913° C., 914° C., 915° C., 916° C., 917° C., 918° C., 919° C., 920° C., 921° C., 922° C., 923° C., 924° C., 925° C., 926° C., 927° C., 928° C., 929° C., 930° C., 931° C., 932° C., 933° C., 934° C., 935° C., 936° C., 937° C., 938° C., 939° C., 940° C., 941° C., 942° C., 943° C., 944° C., 945° C., 946° C., 947° C., 948° C., 949° C., 950° C., 951° C., 952° C., 953° C., 954° C., 955° C., 956° C., 957° C., 958° C., 959° C., 960° C., 961° C., 962° C., 963° C., 964° C., 965° C., 966° C., 967° C., 968° C., 969° C., 970° C., 971° C., 972° C., 973° C., 974° C., 975° C., 976° C., 977° C., 978° C., 979° C., 980° C., 981° C., 982° C., 983° C., 984° C., 985° C., 986° C., 987° C., 988° C., 989° C., 990° C., 991° C., 992° C., 993° C., 994° C., 995° C., 996° C., 997° C., 998° C., 999° C., 1000° C., 1001° C., 1002° C., 1003° C., 1004° C., 1005° C., 1006° C., 1007° C., 1008° C., 1009° C., 1010° C., 1011° C., 1012° C., 1013° C., 1014° C., 1015° C., 1016° C., 1017° C., 1018° C., 1019° C., 1020° C., 1021° C., 1022° C., 1023° C., 1024° C., 1025° C., 1026° C., 1027° C., 1028° C., 1029° C., 1030° C., 1031° C., 1032° C., 1033° C., 1034° C., 1035° C., 1036° C., 1037° C., 1038° C., 1039° C., 1040° C., 1041° C., 1042° C., 1043° C., 1044° C., 1045° C., 1046° C., 1047° C., 1048° C., 1049° C., 1050° C., 1051° C., 1052° C., 1053° C., 1054° C., 1055° C., 1056° C., 1057° C., 1058° C., 1059° C., 1060° C., 1061° C., 1062° C., 1063° C., 1064° C., 1065° C., 1066° C., 1067° C., 1068° C., 1069° C., 1070° C., 1071° C., 1072° C., 1073° C., 1074° C., 1075° C., 1076° C., 1077° C., 1078° C., 1079° C., 1080° C., 1081° C., 1082° C., 1083° C., 1084° C., 1085° C., 1086° C., 1087° C., 1088° C., 1089° C., 1090° C., 1091° C., 1092° C., 1093° C., 1094° C., 1095° C., 1096° C., 1097° C., 1098° C., 1099° C., or 1100° C.
It is also within the scope of the present disclosure for the softening point of a glaze coating in accordance with the present teachings to fall within one of many different ranges. In a first set of ranges, the softening point of a glaze coating in accordance with the present teachings is in one of the following ranges: about 650° C. to 1099° C., 650° C. to 1095° C., 650° C. to 1090° C., 650° C. to 1085° C., 650° C. to 1080° C., 650° C. to 1075° C., 650° C. to 1070° C., 650° C. to 1065° C., 650° C. to 1060° C., 650° C. to 1055° C., 650° C. to 1050° C., 650° C. to 1045° C., 650° C. to 1040° C., 650° C. to 1035° C., 650° C. to 1030° C., 650° C. to 1025° C., 650° C. to 1020° C., 650° C. to 1015° C., 650° C. to 1010° C., 650° C. to 1005° C., 650° C. to 1000° C., 650° C. to 995° C., 650° C. to 990° C., 650° C. to 985° C., 650° C. to 980° C., 650° C. to 975° C., 650° C. to 970° C., 650° C. to 965° C., 650° C. to 960° C., 650° C. to 955° C., and 650° C. to 950° C. In a second set of ranges, the softening point of a glaze coating in accordance with the present teachings is in one of the following ranges: about 651° C. to 1100° C., 655° C. to 1100° C., 660° C. to 1100° C., 665° C. to 1100° C., 670° C. to 1100° C., 675° C. to 1100° C., 680° C. to 1100° C., 685° C. to 1100° C., 690° C. to 1100° C., 695° C. to 1100° C., 700° C. to 1100° C., 705° C. to 1100° C., 710° C. to 1100° C., 715° C. to 1100° C., 720° C. to 1100° C., 725° C. to 1100° C., 730° C. to 1100° C., 735° C. to 1100° C., 740° C. to 1100° C., 745° C. to 1100° C., 750° C. to 1100° C., 755° C. to 1100° C., 760° C. to 1100° C., 765° C. to 1100° C., 770° C. to 1100° C., 775° C. to 1100° C., 780° C. to 1100° C., 785° C. to 1100° C., 790° C. to 1100° C., 795° C. to 1100° C., and 800° C. to 1100° C. In a third set of ranges, the softening point of a glaze coating in accordance with the present teachings is in one of the following ranges: about 651° C. to 1099° C., 652° C. to 1090° C., 653° C. to 1080° C., 654° C. to 1070° C., 655° C. to 1060° C., 656° C. to 1050° C., 657° C. to 1040° C., 658° C. to 1030° C., 659° C. to 1020° C., 660° C. to 1010° C., and 660° C. to 1000° C.
In some embodiments, a glaze coating may optionally further include an inorganic filler. The inorganic filler may be selected to have a decomposition temperature greater than or equal to about 1200° C. or, in some embodiments, greater than or equal to about 1400° C. The filler may also be chosen to have an average particle size (as determined by the longest linear dimension) of less than or equal to about 13 micrometers. Within this range, the average particle size may range from about 5 nanometers to about 10 micrometers. Representative fillers for use in accordance with the present teachings include but are not limited to silica, fumed silica, hydrophilic fumed silica, wollastonite, organoclay, natural clay, alumina, and a combination thereof.
In some embodiments, a glaze coating may be formed by applying a dispersion of the glaze coating components. Useful carriers for the dispersion include but are not limited to water, alcohol, mineral spirits, acetone, and/or the like, and a combination thereof. The dispersion may be applied to the insulative sleeve of a spark plug subassembly. In some embodiments, a spark plug subassembly includes an insulative sleeve, a center electrode, a resistor, and a terminal stud end. The dispersion may be applied by any appropriate method including but not limited to painting, dip coating, spray coating, and/or the like, and a combination thereof. Any coating applied to the center electrode may be removed by an appropriate method.
The applied dispersion may be allowed to air dry, optionally under air flow, at room temperature for at least about 15 minutes or, in some embodiments, for a period of time ranging from about 1 to about 4 hours. After air drying, the subassembly may then be treated at an elevated temperature, such as from about 650 to about 1100° C., for a period of time from about 20 minutes to about 5 hours or, in some embodiments, from about 0.5 to about 2 hours. The length of time at the elevated temperature is chosen to be sufficient to form a glaze coating.
The electrical resistivity of the insulative sleeve containing a glaze coating in accordance with the present teachings may be greater than or equal to about 1×106 ohms/mm or, in some embodiments, greater than or equal to about 1×107 ohms/mm or, in other embodiments, greater than or equal to about 2×107 ohms/mm prior to use in an engine. After use in an engine using gasoline containing MMT and/or ferrocene, the insulative sleeve including a glaze coating may, in some embodiments, have an electrical resistivity greater than or equal to about 1×106 ohms/mm.
The following examples and representative procedures illustrate features in accordance with the present teachings, and are provided solely by way of illustration. They are not intended to limit the scope of the appended claims or their equivalents.
Insulative sleeves available from Autolite were coated with a 22 weight percent dispersion in acetone of one of the six glaze coatings J1-J6 summarized in Table 2 below. Weight percent is based on the total weight of the dispersion. The glaze coating was applied as a band starting approximately 1 mm from the top edge of the insulative sleeve and continuing to the gasket seal location on the insulator. The insulative sleeves were air dried for 1 hour and then heated to 850° C. and held at that temperature for 1 hour. The insulative sleeve was then combined with the remaining elements to form a spark plug. The spark plugs were tested in an accelerated road test. The spark plugs were put into service and then tested for electrical resistivity using Fostoria Shunt Resistance Analysis. Control spark plugs having no glaze coating were also tested. The shunt resistances were measured between center electrode and metal shell of the spark plug.
When a combustion engine runs a fuel doped with MMT and/or ferrocene, deposition of the combustion byproducts may form a dense conductive layer on the surface of the spark plug insulator, as shown in
It has been found that when a glaze coating in accordance with the present teachings is used on the tip of a spark plug insulator, the above-described side firing may be effectively avoided.
As is evident from
In accordance with the present teachings, a glaze coating for anti-MMT and/or anti-ferrocene fouling may work in two ways. First, at elevated temperatures, the glaze coating will react with MMT and/or ferrocene deposits, and the resultant coating (e.g., solid solution) is non-conductive even at elevated temperature. Secondly, the incorporation of Mn and/or Fe in the glaze structure will in turn change the material properties of the glass solid solution. This change in properties may cause portions of the coating layer to fall off when the Mn and/or Fe concentration is very high, thus preventing further attack on the matrix material.
As described above, a glaze coating in accordance with the present teachings may include a boric acid, a borosilicate glass, a barium borate glass, a phosphorous glass, a silicate glass, or a combination thereof. The glasses may further include a material selected from the group consisting of alkali group metals (e.g., alkali group metal oxides), alkali earth group metals (e.g., alkali earth group metal oxides), aluminum (e.g., alumina), silicon (e.g., silica), halogen (e.g., chloride), and a combination thereof. United States Patent Application Publication No. 2016/0352078 A1, assigned to the assignee of the present invention, describes coatings for an insulator tip of a spark plug, and the teachings therein may be used in accordance with and to supplement the present teachings. The entire contents of U.S. Patent Application Publication No. 2016/0352078 A1 are hereby incorporated by reference, except that in the event of any inconsistent disclosure or definition from the present specification, the disclosure or definition herein shall be deemed to prevail.
Glazes containing boric acid, borosilicate glasses, barium borate glass, and phosphorous glass have been tested and shown to be effective in reducing the electrical conductivity of an MMT deposit. However, some of the glazes tested demonstrated severe devitrification properties at elevated temperature, and hence may not suitable for engine applications. Barium borate glass demonstrated excellent high temperature properties and, in some embodiments, a glaze coating in accordance with the present teachings includes barium borate glass.
Table 1 identifies two formulations of a barium borate glass in accordance with the present teachings that were tested at different conditions. In order to be used in different engine applications running at different temperature (and/or different spark plugs with different heat ranges), a high temperature glaze may be mixed with the barium borate glasses at different percentages. Table 1 shows a formulation of a high temperature glass that, in some embodiments, may be mixed with one of both of the barium borate glasses. The resultant coatings may therefore be tailored for different application temperatures.
In some embodiments, one or more mixtures of the glasses summarized in Table 1 may be used to form a glaze coating at the tip of an insulator to prevent MMT and/or ferrocene failure. The ratio of the mixture may be adjusted so that the softening point of the resultant glaze coating may be tailored to a specific engine application. Table 2 summarizes representative coating compositions and their effective temperatures with MMT deposits. The highest resistance read by the meter is 11 Gohms. Therefore, as shown by the data in Table 2, the J1 composition exhibited the best performance characteristics of the samples tested.
The left-hand side of
As shown by the data in Table 3, at room temperature, resistance was higher on the glazed part at both the “tip” and “below tip” locations. At high temperature, resistance was higher on the glazed tip at the “below tip” location. In addition, at high temperature, resistance was similar for glazed and unglazed samples at the “below tip” location due to the loss of glaze on the tip face.
In some embodiments, the resistance of the glaze coating at a position below the firing tip is greater than 300 Mohms at 350° C. to 400° C., in some embodiments greater than 400 Mohms at 350° C. to 400° C., in some embodiments greater than 500 Mohms at 350° C. to 400° C., in some embodiments greater than 600 Mohms at 350° C. to 400° C., in some embodiments greater than 700 Mohms at 350° C. to 400° C., in some embodiments greater than 800 Mohms at 350° C. to 400° C., and in some embodiments greater than 900 Mohms at 350° C. to 400° C.
It is to be understood that use of the indefinite articles “a” and “an” in reference to an element (e.g., “a glass material,” “a modifier,” etc.) does not exclude the presence, in some embodiments, of a plurality of such elements.
The foregoing detailed description and the accompanying drawings have been provided by way of explanation and illustration, and are not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.
It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding claim—whether independent or dependent—and that such new combinations are to be understood as forming a part of the present specification.
