Spark plug connector

Abstract: A high tension cable device with a series gap wherein an extraordinary discharge such as a creeping discharge which may occur along an outer face of a glass tube of a discharge tube is prevented effectively and a process of producing the same are disclosed. The high tension cable device comprises an electrically insulating tubular casing and a connecting terminal for the connection to a terminal of an ignition plug of an engine. The connecting terminal is fixedly fitted in the inside of an end portion of the casing, and a high tension cable is fitted in the other end portion of the casing. An additional function part such as a discharge tube for the formation of a series gap is mounted in the inside of the casing and coupled at an end thereof to the connecting terminal and at the other end thereof to the high tension cable, and an electrically insulating resin material is filled in a spacing in the inside of the casing.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a spark plug connector device and a process of producing the same and more particularly to a connector suitable for use with an ignition system with a series gap for an automobile engine or the like. 2. Description of the Prior Art From GB-A-1 395 139 there is known a spark plug connector having an internal spacing, housing therein a connecting terminal, a resistor and an end portion of a high tension cable. A clearance between said connecting terminal, said resistor and said high tension cable is filled with an elastomeric composition. Said spacing within said tubular casing has a triangular cross-section. Said filling material is filled into said spacing via a mouth portion of said casing opposite to said connecting terminal. Ignition systems for an automobile engine or the like are constituted such that a high voltage is applied to an ignition plug to produce a spark. As one of such ignition systems. an ignition system with a so-called series gap has been proposed wherein a discharge gap is provided in series to an ignition plug in order to prevent occurrence of smoke upon ignition and control the ignition timing accurately. Such ignition system with a series gap is disclosed, for example, in Japanese Utility Model Laid-Open No. 63-101486 and is shown in FIG. 2. Referring to FIG. 2, the ignition system shown includes an ignition plug A screwed, for example, in a cylinder head B of an engine, and a spark plug connector C removably fitted on the ignition plug A. The spark plug connector C includes a high tension cable 3 and a plug cap 6 connected to an end of the high tension cable 3. The plug cap 6 includes a connecting terminal 2 for the connection to a terminal 1 of the ignition plug A, and a cable terminal 4 coupled to the end of the high tension cable 3. The connecting terminal 2 and cable terminal 4 are disposed, for example, in a substantially tubular casing 5 in an opposing spaced relationship from each other in a longitudinal direction of the casing 5. Though not particularly shown, the casing 5 is composed of a first casing in which the connecting terminal 2 is mounted and a second casing in which the cable terminal 4 is mounted. A discharge tube 10 is mounted between the connecting terminal 2 and the cable terminal 4 in the plug cap 6, such that an outer periphery thereof closely contacts with an inner periphery of the casing 5. The discharge tube 10 includes a pair of discharge electrodes 7 and 8 sealed in a glass tube 9 in such a manner as to form a series gap S therebetween. The discharge electrodes 7 and 8 of the discharge tube 10 are fitted in and electrically connected to the connecting terminal 2 and cable terminal 4 of the casing 5, respectively. A discharge tube for use with such an ignition system with a series gap is required to have a somewhat higher starting voltage than that of an ignition plug in order to control the ignition timing accurately. However, where a discharge tube having a high starting voltage is used, a so-called creeping discharge likely occurs along an outer face of the discharge tube prior to starting of a discharge at the series gap. Accordingly, it is very difficult to miniaturize a discharge tube itself while a high starting voltage is assured, and also it is difficult to miniaturize a plug cap of a high tension cable device. Since the spark plug connector C described above is mounted on an engine, various vibrations of the engine and so forth are transmitted directly to the spark plug connector C. Where the glass tube 9 of the discharge tube 10 is fitted directly in the casing 5 of the plug cap 6 as described above, such external vibrations are transmitted directly to the discharge tube 10 and may possibly cause damage to the discharge tube 10. Further, since the discharge electrodes 7 and 8 of the discharge tube 10 and the terminals 2 and 4 in the casing 5 are respectively communicated with each other through mere fitting contact between them, there is the possibility that an instantaneous disconnection arising from incomplete contact between those members may be caused by such transmission of external vibrations to the discharge tube 10 as described above. Another spark plug connector for use with an ignition system is also known wherein a discharge tube is mounted in a plug cap such that an outer periphery thereof is spaced from an inner periphery of a casing of the plug cap. A spark plug connector of the type just mentioned is shown in FIG. 3. Referring to FIG. 3, the spark plug connector also generally denoted at C is substantially similar in construction to the spark plug connector C shown in FIG. 2 except that the discharge tube 10 is fitted in the plug cap 6 with an air gap 11 left between an outer periphery of the glass tube 9 of the discharge tube 10 and an inner periphery of the casing 5. In the spark plug connector C, the discharge tube 10 is supported only at the discharge electrodes 7 and 8 thereof which have electrode terminals 7a and 8a fitted in and connected to the terminals 2 and 4 fitted in the casing 5. While the air gap 11 is shown in a somewhat exaggerated manner in FIG. 3, a similar air gap is inevitably formed more or less also between the outer periphery of the glass tube 9 of the discharge tube 10 and the inner periphery of the casing 5 of the spark plug connector C shown in FIG. 2. Where such air gap 11 exists, a creeping discharge likely occurs along the outer face of the discharge tube 10 prior to starting of discharging between the electrodes 7 and 8. Then, once such creeping discharge occurs, a required starting voltage cannot be obtained any more, and there is a problem that the ignition timing and so forth cannot be controlled precisely. It is an object of the present invention to provide a spark plug connector with a series gap, wherein an extraordinary discharge, such as a creeping discharge which may occur along an outer face an additional function part, e.g. a glass tube of a discharge tube, is prevented thus allowing the starting voltage of the discharge tube to be raised sufficiently high to assure a high reliability, and to provide a process of producing such spark plug connector. According to the present invention, this object is performed by a method as defined in claim 1 as well as by a spark plug connector as defined in claim 8. The spark plug connector according to the invention is produced by a process including the steps of preparing an electrically insulating tubular casing having a connecting terminal fixedly fitted inside an end portion thereof, the connecting terminal being provided for connection of the high tension cable device to an ignition plug, the connecting terminal having a passage hole formed therein, the connecting terminal further preferably having a check valve mechanism provided in the passage hole, which permits passage of fluid only from an end to the other end of the connecting terminal; assembling an additional function part, such as a discharge tube for the formation of a series gap, into the electrically insulating tubular casing until the additional function part is connected to the other end of the connecting terminal; preferably connecting a high tension cable to an opposite power supply side terminal portion of the additional function part; preferably fitting a head cap at the opposite end of the tubular casing, the head cap having an air discharging hole formed therein, whereby the step includes holding the casing in a vertical position such that the head cap is positioned upwardly; filling a spacing which is formed between the tubular casing, the connecting terminal and the additional function part, with an electrically insulating resin material, which preferably is thermosetting by way of the passage hole until the spacing preferably is filled up; and preferably heating the tubular casing to cause the resin material to cure. Said resin may be of the thermosetting or thermoplastic type and may be any synthetic resin only if it has the required characteristics as a component for the protection of a high tension cable device, that is, an electric insulation, a heat resisting property, an oil resistance, a flame retardancy, a sufficient mechanical strength and so forth. Such electrically insulating synthetic resin may be, for example, a polyolefine resin, a styrene-diene resin, an epoxy resin, a silicone resin or rubber, a fluorocarbon resin or rubber, an acrylic resin or rubber, a diene resin or rubber, or a polyether resin or rubber. With the spark plug connector a high tension current, supplied by way of the end portion of the high tension cable, flows through the inside of the additional function part, such as a discharge tube, to the connecting terminal for the connection to an ignition plug, and a creeping discharge or the like will not occur. Besides, the spark plug connector withstands vibrations and is reliable. Due to the electrically insulating material, a creeping discharge which tends to occur along an outer face of the sealing tube can be prevented and the starting voltage of the discharge tube can be raised sufficiently high. Consequently, the ignition timing and so forth can be controlled precisely and the improvement in performance of an engine can be attained. The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements having like functions are denoted by like reference characters all through the drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a spark plug connector showing an embodiment of the present invention: FIG. 2 is a sectional view showing a conventional spark plug connector; and FIG. 3 is a sectional view showing another conventional spark plug connector. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a spark plug connector to which the present invention is applied. The spark plug connector shown is generally denoted C and includes a high tension cable 3, which is connected at an end to a high voltage source (not shown) and at the other end to a tubular casing 5, at an end portion thereof. A connecting terminal 2 for connection at an end thereof to an ignition plug (not shown), of an ignition system (not shown), is fitted in the other end portion of the casing 5. A female terminal 12 is formed at the end of the connecting terminal 2 and held in fitting engagement with a discharge electrode terminal 13 of a discharge tube 10. A resistor 14 is connected at an end thereof to the other discharge electrode terminal 15 of the discharge tube 10, by way of an intermediate connecting terminal 16 of the both end female type. A cable terminal 4 is coupled to the end of the high tension cable 3 and fitted on and connected to the other end of the resistor 14. An electrically insulating silicone resin 17 is filled in the space which is formed between an inner face of the casing 5 and an outer face of the discharge tube and the other parts. The silicone resin 17 has a high adhesive property to a face of the casing 5 and faces of the parts accommodated in the casing 5, such as the connecting terminal 2, the discharge tube 10, the intermediate connecting terminal 16 and the resistor 14. A check valve 19 is mounted at an intermediate portion of the connecting terminal 2 in such a manner as to partition a spacing, which is formed in and extends axially through the inside of the connecting terminal 2. The electrically insulating epoxy resin 17 is filled in a spacing which is formed between inner faces of the casing 5, the head cap 18 and the outer faces the connecting terminal 2, the discharge tube 10, the intermediate connecting terminal 16, the resistor 14 and so forth in the casing 5. It is to be noted here that the electrically insulating epoxy resin 17 is formed as a single filling which surrounds and fixes those additional function parts in the casing 5. According to the present invention, the spark plug connector C shown in FIG. 1 is produced in the following manner. In particular, a discharge tube 10 is first inserted into a casing 5 having a connecting terminal 2 fitted in an end portion thereof until a discharge electrode terminal 13 of the discharge tube 10 is fitted into a female terminal 12 at an end of the connecting terminal 2. An assembly of an intermediate connecting terminal 16 of the both end female type and a resistor 14 is fitted into the other discharge electrode terminal 15 at the other end of the discharge tube 10 such that the discharge tube 10 and the resistor 14 may be coaxial with the casing 5, whereafter a cable terminal 4 of a high tension cable 3 is coupled to a terminal portion at the other of the resistor 14 and a head cap 18 is mounted onto the casing 5 to assemble the spark plug connector C. Subsequently, the assembly of the spark plug connector C is held in a vertical position such that the connecting terminal 2 may be positioned downwardly while the head cap 13 is positioned upwardly, and a thermosetting synthetic resin such as, for example, an epoxy resin. in the form of liquid is poured into the assembly of the spark plug connector C by way of a check valve 19 of the connecting terminal 2. The liquid resin is gradually filled into a hollow spacing in the casing 5 from the bottom of the assembly of the spark plug connector C until the level of the filling resin comes to at least such a degree at which the parts, including the discharge tube 10, are surrounded fully by the liquid resin. After then, the liquid resin may further be filled into a hollow spacing in the head cap 18. In order to allow air to be discharged from the spacings in the casing 5 and head cap 18, the head cap 18 has a passage hole 20 formed in an end all thereof. The liquid resin filled in the spark plug connector C in this manner is then hardened by a cross linking reaction under a suitable hardening reaction temperature condition. thereby completing the high tension cable device C. Three spark plug connector having such construction as described above were produced for the examination using discharge tubes having a starting voltage characteristic of 25 kV and three kinds of adhesive silicone resins (CY52-238. SE1885 and SE1886 produced by Toray Corporation) as electrically insulating resin materials. The spark plug connector for the examination were connected to ignition plugs each grounded at the opposite pole thereof, and a positive voltage of 30 kV was applied at a frequency of 50 Hz from the power supply side terminals of the high tension cables to effect an endurance test for 96 hours. Then, a result of the endurance test was compared with a result of a similar endurance test conducted with conventional spark plug connector wherein no electrically insulating resin material was filled. While outer faces of the discharge tubes of these spark plug connector suffered from damages due to creeping discharges, no occurrence of such creeping discharge was recognized with the spark plug connector of the present invention wherein a silicon resin was filled.

Claims: A method of producing a spark plug connector having a connecting terminal (2) provided to be connected to a spark plug, said connecting terminal (2) being fixedly fitted inside an end portion of an electrically insulating tubular casing (5), said method comprising the steps of preparing said electrically insulating tubular casing (5); assembling an additional function part (10, 16, 14), such as a discharge tube (10) for the formation of a series gap, within said tubular casing (5), such that said additional function part (10, 16, 14) is connected to said connecting terminal (2); and filling a space which is formed between said tubular casing (5), the connecting terminal (2) and said additional function part (10, 16, 14) with an electrically insulating resin filling material (17) characterized by filling said electrically insulating resin filling material (17) into said space by way of a passage hole formed in said connecting terminal (2). The method according to claim 1, characterized by filling said insulating filling material (17) into said space via a check valve mechanism (19) provided in said passage hole for permitting passage of filling material (17) in only one direction. The method according to claim 1 or 2, characterized by connecting a high tension cable (3) to an opposite power supply side terminal portion (4) of said additional function part (10, 16, 14). The method according to at least one of claims 1 to 3, characterized by filling said space formed between said tubular casing (5) and said additional function part (10, 16, 14) with the resin, which is an electrically insulating thermosetting resin material (17), by way of said passage hole until said space is filled up, and heating said tubular casing (5) to cause the resin material (17) to cure. The method according to at least one of claims 1 to 4, characterized in that said electrically insulating resin material (17) is selected from thermosetting synthetic resins, which are provided in the form of liquid. The method according to at least one of claims 1 to 4, characterized by filling said space with said electrically insulating resin material (17) except at a power supply side terminal portion (4) of said additional function part (10). The method according to at least one of claims 1 to 6, characterized by fitting a head cap (18) at the opposite end of said tubular casing (5), said head cap (18) having an air discharging hole (20) formed therein, holding said casing (5) in a vertical position such that said head cap (18) is positioned upwardly. A spark plug connector having an insulating tubular casing (5) and a connecting terminal (2) which is provided to be connected with a spark plug and which is fixedly fitted in the inside of an end portion of said electrically insulating tubular casing (5), as well as an additional function part (10, 16, 14), such as a discharge tube (10) for the formation of a series gap, which is fitted inside said tubular casing (5) such that said additional function part (10, 16, 14) is connected with said connecting terminal (2) wherein a space formed between said tubular casing (5) and said additional function part (10, 16, 14) is filled with an electrically insulating filling material (17), characterized by a check valve (19) disposed intermediately in a hollow axial passage hole of said connecting terminal (2) for allowing feeding of the filling material, which is an electrically insulating resin material (17), into said casing (5) by way of said hollow axial passage hole but preventing the resin material (17) from coming out of the inside of said casing (5) by way of said hollow axial passage hole of said connecting terminal (2). A spark plug connector as claimed in claim 8, characterized in that said electrically insulating resin material (17) is filled fully in the space formed between said casing (5), a head cap (20) which is fixed at the other end of the casing, said connecting terminal (2) and the additional function part (10, 16, 14). A spark plug connector as claimed in claims 8 and 9, characterized in that said electrical insulating resin material (17) is filled in the space formed between said casing (5), said connecting terminal (2) and the additional function part (10) except at a power supply side terminal portion (4) of said additional function part (10, 16, 14) at which said additional function part (10, 16, 14) is coupled to said high tension cable (3). A spark plug connector as claimed in at least one of claims 8 to 10, characterized in that said electrically insulating resin material (17) is an adhesive silicone resin.

Inventors: WAKABAYASHI SEIICHI, YAGI KIYOSHI, WAKABAYASHI, SEIICHI, YAGI, KIYOSHI, WAKABAYASHI, SEIICHI, C/O YAZAKI PARTS CO., LTD., YAGI, KIYOSHI, C/O YAZAKI PARTS CO., LTD.
Applicants: YAZAKI CORP, YAZAKI CORPORATION
Application year: 1990
Main classification: H01T13
IPC codes: H01T13