Spark plug ignition coil assembly for direct ignition system

Abstract: A spark plug and ignition coil assembly for a direct ignition system is provided. The assembly comprises a spark plug having an insulator, the insulator having a hollow upper end portion having at an outer periphery thereof a first joining section, an ignition coil, a rubber molding embedding therein the ignition coil so as to cooperate with the ignition coil to constitute an integral unit, the rubber molding having a hollow lower end portion in which the upper end portion of the insulator is fitted, the lower end portion of the rubber molding having at an inner periphery there of a second joining section joined with the first engagement section, and fastening means for fastening the first and second joining sections together. The fastening means comprises a projection provided to one of the first and second joining sections and a recess provided to the other of the first and second joining sections.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general to direct ignition systems for internal combustion engines, and more particularly to a spark plug and ignition coil assembly for direct ignition systems. 2. Description of the Related Art A direct ignition system is known in which a spark plug and an ignition coil are connected directly with each other. The direct ignition system is widely used in automotive engines for the reason that it has various advantages, for example, it is capable of eliminating spark-plug cables, reducing leakage current and interference noise, and making the ignition timing control easier. An example of a prior art spark plug and ignition coil assembly for a direct ignition system is shown in Fig. 4. A spark plug 105 has an insulator made of alumina. The insulator has a corrugated outer peripheral portion or ribs 105a for the purpose of preventing a flashover. Protruded from the upper end of the insulator is a terminal 104. An ignition coil 101 is disposed above the spark plug 105. The ignition coil 101 has an iron core 102 at the center thereof and is disposed horizontally. The spark plug 105 and the ignition coil 101 are connected with a hollow, cylindrical rubber element 106. The ignition coil 101 has a coupling sleeve 101a protruding downward. The coupling sleeve 101a is fitted in the upper side portion of the rubber element 106. The rubber element 106 is in turn fitted at the lower side portion on the corrugated outer peripheral portion 105a of the insulator. A high voltage terminal (not shown) of the ignition coil 101 and the terminal 104 of the spark plug 105 are electrically connected with a spring 103. The prior art spark plug and ignition coil assembly for direct ignition systems is encountered by the following problems. (1) Continuing use of the assembly may cause deterioration of the rubber element 106, and such deterioration may cause leakage of current. This is considered due to the fact that the rubber element 106 is simply fitted at the upper side portion on the coupling sleeve 101a of the ignition coil 101 and at the lower side portion on the insulator of the spark plug 105. (2) Since a spark plug hole formed in a cylinder head for disposition of the spark plug is about only 20 mm in diameter and its length is limited, the space for disposition of the ignition coil is so narrow that an ignition coil of a high energy type which is capable of producing a sufficiently high voltage cannot be disposed in that space. In this connection, if the terminal 104 is arranged deeper in the spark plug hole so as to attain a larger space for disposition of the ignition coil, there arises a possibility of deteriorating the flashover resistance since the insulator of the spark plug must inevitably be shorter. Another spark plug with a rubber molding is known from JP-A-60 195 374. SUMMARY OF THE INVENTION It is an object of the present invention to provide a spark plug and ignition coil assembly for a direct ignition system which can attain a sufficient space for disposition of an ignition coil without deteriorating the flashover resistance. To achieve the above object, the present invention provides a spark plug and ignition coil assembly for a direct ignition system which comprises the features according to claim 1. The spark plug having an insulator, the insulator having a hollow upper end portion having at an outer periphery thereof a first joining section, an ignition coil, a rubber molding embedding therein the ignition coil so as to cooperate with the ignition coil to constitute an integral unit, the rubber molding having a hollow lower end portion in which the upper end portion of said insulator is fitted, the lower end portion of the rubber molding having at an inner periphery thereof a second joining section joined with the first joining section, and fastening means for fastening the first and second joining sections together. The fastening means comprises a projection provided to one of the first and second joining sections and a recess provided to the other of the first and second joining sections. The upper end portion of the insulator is hollow, and the spark plug has a terminal positioned entirely inside the upper end portion of the insulator, i.e., the terminal is disposed at the bottom of the hollow upper end portion of the insulator. The spark plug and ignition coil assembly further comprises a connecting terminal electrically connecting between the terminal of the spark plug and the ignition coil, and an insulation sleeve extending away from the ignition coil and protruding partly into the upper end portion of the insulator so as to surround the connecting terminal. The connecting terminal is in the form of a needle or a compression spring. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a spark plug and ignition coil assembly for a direct ignition system according to the first embodiment of the present invention; Fig. 2 is a sectional view of a principal portion of a spark plug and ignition coil assembly for a direct ignition system according to the second embodiment of the present invention; Fig. 3 is a sectional view of a principal portion of a spark plug and ignition coil assembly for a direct ignition system according to the third embodiment of the present invention; and Fig. 4 is a sectional view of a prior art spark plug and ignition coil assembly for a direct ignition system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to Fig. 1, a spark plug and ignition coil assembly for a direct ignition system according to the first embodiment of the present invention is generally designated by 11. The spark plug and ignition coil assembly 11 includes a spark plug 20 with an insulator 21 made of ceramic containing a high percentage of alumina. The insulator 21 has a hollow upper end portion 21A with an axially recessed section 21B. The upper end portion 21A of the insulator 21 has at an outer periphery thereof a recess or a smaller diameter section 21C which constitutes part of a fastening means. In this connection, the outer periphery of the upper end portion 21A serves as a first joining section. A terminal 22 is disposed at the bottom of the recessed section 21B. In other words, the terminal 22 is disposed entirely inside the hollow upper end portion 21A of the insulator 21 or the terminal 22 is disposed so as to have an upper end positioned inside the upper end portion 21A of the insulator 21. The spark plug 20 has a ground electrode 23 and a center electrode 24. An ignition coil 12 is disposed above the spark plug 20. The ignition coil 12 has an iron core 13 at the center thereof and is disposed vertically. A rubber molding 15 embeds therein the ignition coil 12 so as to cooperate with the ignition coil 12 to constitute an integral unit. The rubber molding 15 has a hollow lower end portion 15A in which the upper end portion 21A of the insulator 21 is fitted. The hollow lower end portion 15A has at an inner periphery thereof a projection or smaller diameter section 15B. In this connection, the inner periphery of the lower end portion 15A serves as a second joining section joined with the above described first joining section, i.e., the outer periphery of the upper end portion 21A of the insulator 21. The projection 15B constitutes another part of the fastening means for fastening the first and second joining sections together, i.e., fastening the upper end portion 21A of the insulator 21 and the lower end portion 15A of the rubber molding 15 together. A connecting terminal 14 in the form of a needle is disposed at the center of the hollow lower end portion 15A of the rubber molding 15 in a way as to electrically connect between a high voltage terminal (not shown) of the ignition coil 12 and the terminal 22 of the spark plug 20 for thereby supplying a secondary voltage from the ignition coil 12 to the spark plug 20. The upper end portion 21A of the insulator 21 is fitted in the hollow lower end portion 15A of the rubber molding 15, while allowing the projection or smaller diameter inner peripheral section 15B of the rubber molding 15 to engage in the recess or smaller diameter outer peripheral section 21C of the insulator 21. By this, the ignition coil 12 and the spark plug 20 are firmly joined together. In this instance, the end of the connecting terminal 14 in the form of a needle is held assuredly in contact with the terminal 22, whereby it becomes possible to supply a high voltage produced by the ignition coil 21 to the spark plug 20 assuredly. The spark plug and ignition coil assembly 11 can produce the following effect. The ignition coil 12 is formed integral with the rubber molding 15 having the hollow lower end portion 15A, in such a manner that the core 13 is disposed vertically. The hollow lower end portion 15A of the rubber molding 15 has at the inner periphery thereof the projection 15B which is engaged in the recess 21C provided to the outer periphery of the upper end portion 21A of the insulator 21. By this, the ignition coil 12 and the spark plug 20 can be joined together with a large joining force so that leakage hardly occurs even if deterioration of the rubber molding 15 occurs to a certain extent. Further, since the connecting terminal 14 in the form of a needle protrudes into the recessed section 21A of the upper end portion of the insulator 21 to be connected to the terminal 22 disposed at the bottom of the recessed section 21B, whereby the ignition coil 12 and the spark plug 20 can be disposed nearer to each other so that a larger space than before can be attained for disposition of the ignition coil 12. By this, the ignition coil 12 can be made longer than before, thus making it possible for the ignition coil 12 to be of the higher energy type, i.e., of the type capable of storing and generating a higher energy, and making it possible to improve the ignitability of the engine. Further, the cylinder head can be made thinner, and therefore the engine can be lighter. In this instance, it is to be noted the terminal 22 is disposed at the bottom of the recessed section 21B of the upper end portion 21A of the insulator 21 to be covered thereby and the insulator 21 is in turn nearly entirely covered by the rubber molding 15 which is formed integral with the ignition coil 12, while allowing the terminal 14 in the form of a needle to be similarly to be covered by the insulator 21 and the rubber molding 15, so that not only leakage between the terminal 22 and the adjacent metallic parts but leakage between the terminal 14 and the adjacent metallic parts hardly never occurs. As having been described above, in the spark plug and ignition coil assembly 11, the insulator 21 of the spark plug 20 has at the outer periphery thereof the recess 21C and the rubber molding 15 integral with the ignition coil 12 has the projection 15B engaged in the recess 21C. By this, the ignition coil 12 and the spark plug 20 are joined together with a large joining force, so leakage hardly occurs even if deterioration of the rubber molding 15 occurs to some extent. Fig. 2 shows a spark plug and ignition coil assembly according to the second embodiment of the present invention. In the figure, only a portion of the second embodiment which differs from the first embodiment of Fig. 1 is shown. In the second embodiment, the rubber molding 115 has the hollow lower end portion 115A in which the upper end portion 121A of the insulator 121 is fitted. The hollow lower end portion 115A has at an inner periphery thereof a recess or a larger diameter section 115B which constitutes part of a fastening means. The upper end portion 121A of the insulator 121 has at the outer periphery thereof a projection or a larger diameter section 121C which constitutes another part of the fastening means. The projection 121C and recess 115B are annular and have a trapezoidal cross section. The second embodiment differs from the first embodiment in that the first joining section, i.e., the outer periphery of the upper end portion 121A of the insulator 121 is provided with the projection 121C, whereas the second joining section, i.e., the inner periphery of the lower end portion 115A of the rubber molding 115 is provided with the recess 115B. Except for this, the second embodiment is substantially similar to the first embodiment and can produce substantially the same effect. Fig. 3 shows the third embodiment. In the figure, only a portion of the third embodiment which differs from the first embodiment is shown. In this second embodiment, the rubber molding 215 in which the ignition coil 12 is embedded to constitute an integral unit, has a hollow lower end portion 215A in which the upper end portion 221A of the insulator 221 is fitted. The hollow lower end portion 215A has at an inner periphery thereof a projection or a smaller diameter section 215B which constitutes part of a fastening means. On the other hand, the upper end portion 221A of the insulator 221 has at the outer periphery thereof a recess or smaller diameter section 221C which constitutes another part of the fastening means. The projection 215B and the recess 221C are annular and have a rectangular cross section. The third embodiment differs from the first embodiment in that a connecting terminal 17 in the form of a compression coil spring is used in place of the connecting terminal 14 in the form of a needle and a cylindrical insulation sleeve 18 is provided so as to surround the connecting terminal 17 in the form of a compression coil spring. The insulation sleeve 18 is disposed so as to extend away from the ignition coil 12 and protrude partly into the upper end portion 221A of the insulator 221 so as to surround the connecting terminal 17. The connecting terminal 17 in the form of a compression coil spring can contact the terminal 22 and the high voltage terminal (not shown) of the coil spring 12 with the more constant pressure as compared with the connecting terminal 14 in the form of a needle. Thus, the contact resistance is constant so it becomes possible to supply the secondary voltage produced by the ignition coil 12 to the spark plug 20 stably and assuredly. Further, since the cylindrical insulation sleeve 18 made of an insulating resinous material is provided so as to surround the connecting terminal 17, it becomes possible to make larger the resistance to leakage between the connecting terminal and other metallic parts, thus making it possible to prevent the leakage more assuredly. While the cylindrical sleeve 18 is used in combination with the connecting terminal 17 in the form of a compression spring, it can otherwise be used in combination with the connecting terminal 14 in the form of a needle. From the foregoing, it will be understood that in a spark plug and ignition coil assembly for a direct ignition system according to the present invention, a hollow upper end portion of an insulator of a spark plug has an outer periphery serving as a first joining section, a hollow lower end portion of a rubber molding which embeds therein an ignition coil so as to cooperates with the ignition coil to constitute an integral unit has an inner periphery serving as a second joining section which is joined with the first joining section, and a fastening means is provided for fastening the first and second joining sections together, so the ignition coil and the spark plug are joined together with a large joining force so that leakage hardly occurs even if deterioration of the rubber molding occurs to some extent. It will be further understood that the upper end portion of the insulator of the spark plug has a recessed section and the terminal of the spark plug is disposed at the bottom of the recessed section of the insulator, and that the ignition coil and the terminal are connected with a connecting terminal in the form a needle or a compression coil spring, thus making it possible to arrange the ignition coil and the spark plug closer to each other than before and therefore making it possible to attain a larger space for disposition of the ignition coil. By this, the ignition coil can be made longer and therefore the ignition coil can be of a larger energy type so that the ignitability of the engine can be improved. Further, the cylinder head can be thinner than before, thus making it possible to make lighter the engine. The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Claims: A spark plug and ignition coil assembly (11) for a direct ignition system comprising: a spark plug (20) having an insulator (21); said insulator (21) having a hollow upper end portion (21A; 121A; 221A) having at an outer periphery thereof a first joining section; an ignition coil (12); and a rubber molding (15) embedding therein said ignition coil (12) so as to cooperate with said ignition coil (12) to constitute an integral unit; said rubber molding (15) having a hollow lower end portion (15A; 115A; 215A)in which said upper end portion (21A; 121A; 221A) of said insulator (21) is fitted; characterized in that in an inner periphery of said lower end portion of said rubber molding a second joining section is provided connecting with that first joining section, wherein fastening means comprising a projection (15B; 121C; 215B) are provided in one of said first and second joining sections and a recess (21C; 115B; 221C) is provided in the other of said first and second joining sections for fastening said first and second joining sections together. A spark plug and ignition coil assembly according to claim 1, wherein said projection (121C) and said recess (115B) are annular and have a trapezoidal cross-section. A spark plug and ignition coil assembly according to claim 1, wherein said projection (215B) and said recess (221C) are annular and have a rectangular cross-section. A spark plug and ignition coil assembly according to claim 1, wherein said upper end portion (21A; 121A; 221A) of said insulator (21) is hollow, said spark plug (20) having a terminal (22) positioned entirely inside said upper end portion (21A; 121A; 221A) of said insulator (21). A spark plug and ignition coil assembly (11) according to claim 4, further comprising a connecting terminal (14; 17) electrically connecting between said terminal (22) of said spark plug (20) and said ignition coil (12). A spark plug and ignition coil assembly (11) according to claim 5, further comprising an insulation sleeve (18) extending away from said ignition coil (12) and protruding partly into said upper end portion (221A) of said insulator (21) so as to surround said connecting terminal (17). A spark plug and ignition coil assembly (11) according to claim 5, wherein said connecting terminal (14) is in the form of a needle. A spark plug and ignition coil assembly according to claim 5, wherein said connecting terminal (17) is in the form of a coil spring. A spark plug and ignition coil assembly (11) according to claim 1, wherein said hollow upper end portion (21A; 121A; 221A) has a larger diameter outer peripheral section (121C) and a smaller diameter outer peripheral section (21 C; 221 C); and wherein said lower end portion (15A; 115A; 215A) of said rubber molding (15) has a larger diameter inner peripheral portion (115B) and a smaller diameter inner peripheral portion (15B; 215B) which are respectively joined with said larger diameter outer peripheral section (121C) and said smaller diameter outer peripheral section (21C; 221C) of said upper end portion (21A) of said insulator (21) so that said lower end portion (15A; 115A; 215A) of said rubber molding (15) and said upper end portion (21A; 121A; 221A) of said insulator (21) are fastened together. A spark plug and ignition coil assembly (11) according to claim 9, wherein said upper end portion (21A) of said insulator (21) is hollow, said spark plug (20) having a terminal (22) which is disposed so as to have an upper end positioned inside said upper end portion (21A; 121A; 221A) of said insulator (21). A spark plug and ignition coil assembly (11) according to claim 10, further comprising a connecting terminal (14; 17) electrically connecting between said terminal (22) of said spark plug (20) and said ignition coil (12). A spark plug and ignition coil assembly (11) according to claim 11, further comprising an insulation sleeve (18) extending away from said ignition coil (12) and protruding partly into said upper end portion (221A) of said insulator (21) so as to surround said connecting terminal (17). A spark plug and ignition coil assembly according to claim 11, wherein said connecting terminal (14) is in the form of a needle. A spark plug and ignition coil assembly according to claim 11, wherein said connecting terminal (17) is in the form of a coil spring.

Inventors: YOSHIDA MITSUTAKA, YOSHIDA, MITSUTAKA, YOSHIDA, MITSUTAKA, C/O NGK SPARK PLUG CO., LTD.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD.
Application year: 1999
Main classification: F02P3
IPC codes: F02P13, H01T13, F02P3