Connecting assembly for ignition plug in gasoline engine

Abstract: The invention aims to prevent a head of an ignition plug from being worn. A connecting assembly for an ignition plug P in a gasoline engine comprises a high tension supply terminal 11 adapted to be connected to a high tension cable C, a cylindrical ignition plug connecting terminal 12 having an outwardly extending projection 12b, a high tension supply terminal socket 13 secured to an end of the cylindrical ignition plug connecting terminal 12 and electrically contacted with the high tension supply terminal 11, and a cylindrical plug cap 14 made of a synthetic resin material for receiving the cylindrical ignition plug connecting terminal 12 therein with the outwardly extending projection 12b being embedded in an inner wall of the cap 14. The ignition plug connecting terminal 12 can be secured to the ignition plug P by embedding the outwardly extending projection 12b of the terminal 12 in the plug cap 14.

Description: This invention relates to a connecting assembly for an ignition plug in a double overhead cam shaft type gasoline engine, in which a high tension cable is connected to the ignition plug. In an overhead valve (OHV) type gasoline engine as well as a double overhead cam shaft (DOHC) type gasoline engine, an ignition plug is disposed at a deep position in the engine. Such a kind of gasoline engine is provided with a connecting assembly for the ignition plug such as the one disclosed in, for example, Japanese Utility Model Public Disclosure No. 55-168985 (1980), in order to connect a high tension cable to the ignition plug. For convenience of explanation, the above known connecting assembly for the ignition plug will be described below by referring to FIG. 11. FIG. 11 is a longitudinal sectional view of the connecting assembly 100 for the ignition plug P. The connecting assembly 100 for the ignition plug P includes an ignition plug connecting terminal 101 and a plug cap 102. The ignition plug connecting terminal 101 is attached to an end of a high tension cable C by pressing work and has a shape adapted to be mechanically mated with and electrically contacted with a terminal part Pa of the ignition plug P. Also, the ignition plug connecting terminal 101 is provided with an outwardly extending annular projection 101a on the outer periphery thereof. The plug cap 102 is made of a synthetic insulating resin material and is inserted into a plug bore 103a formed in an engine cover 103. The plug cap is also provided on the interior with a shoulder 102a which engages with the annular projection 101a of the ignition plug connecting terminal 101. The high tension cable C is inserted into the plug cap 102 through a proximal end of the cap. After a top end of the high tension cable C passed through a top end of the plug cap 102 has been pressed and connected to the ignition plug connecting terminal 101, the top end of the high tension cable C is retracted in the plug cap 102 until the annular protection 101a of the ignition plug connecting terminal engages with the shoulder 102a. On the other hand, the terminal part Pa of the ignition plug P can be inserted into the plug cap 102 through a distal end of the cap. The terminal part Pa of the ignition plug P inserted in the plug cap 102 is electrically connected to the ignition plug connecting terminal 101 supported in the plug cap 102. The plug cap 102 fixes the high tension cable C in the cap at the position where the ignition plug connecting terminal 101 contacts with the ignition plug P. The plug cap 102 is secured to the engine cover 103 through a waterresistant cap 104. In the above conventional connecting assembly 100 for the ignition plug P, the ignition plug connecting terminal 101 is held in the plug cap 102 or the ignition plug P by engaging the annular projection 101a with the shoulder 102a in the plug cap 102. However, since the ignition plug connecting terminal 101 is fixed incompletely in the plug cap 102 in the conventional connecting assembly 100, the ignition plug connecting terminal 101 and the ignition plug are vibrated at different frequencies on account of various vibrations caused during driving. Consequently, a head of the ignition plug P is subjected to a great wear. A connecting assembly for an ignition plug and in accordance with the pre-characterising portion of Claim 1 is known from EP-A-0 488 216. According to our invention, in a connecting assembly for an ignition plug in accordance with the pre-characterising portion of Claim 1, the connecting terminal and the terminal socket both comprise deep-drawn sheets of thin metal plate, and retainer rings at least partially encircling each of said connecting terminal and said socket have two retaining proturbances on an inner surface thereof, two through holes being provided in each of said connecting terminal and said socket complementary to said retaining proturbances, whereby said retaining proturbances project radially inwardly of said inner surfaces so that, when said distal ends of said plug and supply terminal are introduced into said connecting terminal and said socket respectively, said rings are urged resiliently and radially outwardly, thereby retaining said distal ends in said connector terminal and socket. This provides an assembly which is lighter, cheaper and simpler than constructions known hitherto. Also the assembly is particularly suitable for mass production. In the connecting assembly for the ignition plug in the gasoline engine in accordance with the present invention, the ignition plug connecting terminal is joined to the plug cap and movement of the ignition plug connecting terminal is limited with respect to the ignition plug. The ignition plug and the high tension cable are interconnected through the high tension supply terminal socket and the high tension supply terminal. When the plug cap is formed by a synthetic resin material with the flanges of the terminal and the socket being embedded in the inner wall of the plug cap, the resin material does not flow into the ignition plug terminal. By connecting the high tension supply terminal to the high tension supply terminal socket, the high tension cable is directly or indirectly connected to the ignition plug. FIGURE 1 is a longitudinal sectional view of an embodiment of a connecting assembly for an ignition plug in a gasoline engine in accordance with the present invention; FIGURE 2 is a flow chart illustrating an embodiment of a method for producing a connecting assembly for an ignition plug in a gasoline engine in accordance with the present invention; FIGURE 3 is a cross-sectional view of an ignition plug connecting terminal; FIGURE 4 is a plan view of a terminal body under a step of producing the terminal; FIGURE 5 is a perspective view of a terminal body under a step of producing the terminal; FIGURE 6 is a longitudinal sectional view of the terminal body illustrating a through hole; FIGURE 7 is a longitudinal sectional view of a socket body illustrating a through hole; FIGURE 8 is a longitudinal sectional view of a plug cap under a producing step; FIGURE 9 is a longitudinal sectional view of a comparative exemple of an embodiment of a connecting assembly for an ignition plug in a gasoline engine ; FIGURES 10A and 10B are perspective views of alternations of a terminal body and a socket body under a producing step; and FIGURE 11 is a longitudinal sectional view of a conventional connecting assembly for an ignition plug. Referring now to Figures 1 through 8 and 10, embodiments of a connecting assembly for an ignition plug in a gasoline engine in accordance with the present invention and a method for producing the same will be described below. Figure 1 shows a construction of a connecting assembly 10 for an ignition plug in a gasoline engine in accordance with the present invention. The connecting assembly 10 shown in Figure 1 includes a high tension supply terminal 11, an ignition plug connecting terminal 12, a high tension supply terminal socket 13, and a plug cap 14. The assembly 10 serves to connect high tension cable C to an ignition plug P secured to an engine cover (not shown). The high tension supply terminal 11 is a press fit type terminal and is attached to an end of the high tension cable C beforehand. The high tension supply terminal 11 electrically contacts with the high tension supply terminal socket 13 by being inserted into a socket body 13a of the high tension supply terminal socket 13. The ignition plug connecting terminal 12 is provided with a cylindrical terminal body 12a having no slit on the outer periphery thereof, a flange-like projection 12b integrally formed on an end of the terminal body 12a, and a C-shaped ring 12c and fitted on the terminal body 12a without any elastic deformation. The terminal part Pa of the ignition plug P is inserted into the terminal body 12a of the ignition plug connecting terminal 12. The ring 12c is provided on the interior with a projection 12ca which is embedded in the inner wall on the terminal body 12a through a through hole 12aa formed in the terminal body 12a, as shown in FIG. 3. When the terminal part Pa of the ignition plug P is inserted into the terminal body 12a, the terminal part Pa pushes the projection 12ca so that the ring 12c is widened against its elastic resistance. That is, the ignition plug connecting terminal 12 fixes the terminal part Pa of the ignition plug P inserted in the terminal body by means of the projection 12ca of the ring 12c without any elastic deformation. The high tension supply terminal socket 13 includes a cylindrical socket body 13a, a flange-like projection 13b and a ring 13c. The projection 13b is spot-welded on the projection 12b of the ignition plug connecting terminal 12, so that the high tension supply terminal socket 13 is fixed coaxially on the ignition plug connection terminal 12. The socket body 13a and projection 13b are formed integrally in the same manner as the terminal body 12a and projection 12b of the ignition plug terminal 12. Also, the ring 13c has the same shape as that of the ring 12c, is mounted on the socket body 13a, and is provided on the interior with a projection (not shown) which enters into the socket body 13a through a hole 13aa (FIG. 7) formed in the socket body 13a. As described above, the high tension supply terminal 11 is inserted into the socket body 13a. The high tension supply terminal 11 inserted into the socket body 13a pushes the projection formed on the interior of the ring 13c so that the terminal 11 widens the ring 13c against the elastic resistance of the ring. Then, the high tension supply terminal 11 is fixed on the high tension terminal socket 13 without any elastic deformation. The plug cap 14 is made of a synthetic resin material having heat resisting and insulating properties and formed into a cylindrical shape. As shown in FIG. 1, the ignition plug connecting terminal 12 and high tension supply terminal socket 13 are disposed within the plug cap while the projection 12b of the ignition plug connecting terminal 12 and projection 13b of the high tension supply terminal socket 13 are inserted into the inner wall of the plug cap 14 by insertion. The plug cap 14 is secured to the engine cover EC by the known manner. According to the above connecting assembly for the ignition plug, since the projection 12b of the ignition plug connecting terminal 12 is fixed in the plug cap 14 secured to the engine cover EC, the above mentioned vibration to be transmitted to the ignition plug P connected to the ignition plug connecting terminal 12 can be suppressed thereby reducing the wear of the head of the ignition plug P. Next, a method for producing the above connecting assembly for the ignition plug will be described by referring to FIG. 2. First, in a step S1, a terminal body 12a' and a projection 12b shown in FIG. 5 are formed integrally by drawing a stainless disc plate S shown in FIG. 4. However, the terminal body 12a' under this state has a bottom part. Another conductive metal plate may be used for the stainless plate S. Second, in a step S2, the bottom part of the terminal body 12a' is removed to form a terminal body 12. In a step S3, a through hole 12aa is formed in the terminal body 12a as shown in FIG. 6. Thus, the terminal 12a and projection 12b form an ignition plug connecting terminal 12. Next, in a step S4, a socket body 13a' having a bottom part and a projection 13b are formed integrally in the same manner as the step S1. The socket body 13a' has substantially the same external diameter as that of the terminal body 12a of the ignition plug connecting terminal 12 while the projection 13b has substantially the same internal diameter as that of the projection 12b of the ignition plug connecting terminal 12. In a step S5, the bottom part of the socket body 13a' is also removed to form a socket body 13a. In a step S6, a through hole 13aa is formed in the socket body 13a (see FIG. 7). In the step S6, the socket body 13a and projection 13b form a high tension supply terminal socket 13. In a step S7, the projection 12b of the ignition plug connecting terminal 12 is joined to the projection 13b of the high tension supply terminal socket 13 by joining means such as spot-welding. In a step S8, as shown in FIG. 3, the ring 12c is mounted on the terminal body 12a and the ring 13c is mounted on the socket body 13a in the same manner. At this time, bosses 12ca projecting from the interior of the ring 12c mates with the through hole 12aa while bosses projecting from the interior of the ring 13c mates with the through hole 13aa. In a step S9, as shown in FIG. 8, the ignition plug connecting terminal 12 and high tension supply terminal socket 13 joined with each other in the step S7 are fixed by metal molds X and Y and a molten synthetic resin material having heat resisting and insulating properties is poured into a space defined by metal molds X, Y, and Z. Thus, a plug cap 14 which embeds the projections 12b and 13b in the inner wall is formed. In a step S10, the high tension supply terminal 11 is press-fitted on an end of the high tension cable C. In a step S11, the high tension supply terminal 11 together with the high tension C are inserted into the plug cap 14 from an end of the cap and the high tension supply terminal 11 is coupled to the high tension supply terminal socket 13 fixed in the plug cap 14. The high tension cable C is fixed in the plug cap 14 with the high tension supply terminal 11 being coupled to the socket 13. In a step S12, a waterproofing cap 15 is mounted on an end of the plug cap 14 (see FIG. 1). In a step S13, the plug cap 14 is inserted into a plug bore ECa formed in the engine cover and the ignition plug connecting terminal 12 in the plug cap 14 is coupled to the terminal part Pa of the ignition plug P secured to the engine cover. The plug cap 14 is secured to the engine cover EC at the same time when the ignition plug connecting terminal 12 is coupled to the ignition plug P. Since the connecting assembly 10 which joins the high tension cable C to the ignition plug P is formed by drawings the ignition plug P is formed by drawing the ignition plug connecting terminal 12, the terminal 12 has no clearance such as a slit or a seam on the outer periphery. Accordingly, the molten resin material does not flow into the ignition plug connecting terminal 12 when the plug cap 14 is formed with the result that a part of the terminal 12 is embedded in the plug cap 14. FIG. 9 shows a comparative example of an embodiment 20 of a connecting assembly for the ignition plug in the gasoline engine. In the connecting assembly 20 shown in FIG. 9, the high tension cable C is joined through a discharge tube E to the ignition plug P. An upper electrode of the discharge tube E is connected electrically to the high tension cable C through a terminal Ea. The connecting assembly 20 includes a high tension supply terminal 21, an ignition plug connecting terminal 22, a high tension supply terminal socket 23, and a plug cap 24. The engine cover is omitted in FIG. 9. The high tension supply terminal 21 is made in a form of a spring which is connected to the other electrode of the discharge tube E. The ignition plug connecting terminal 22 includes a terminal body 22a, a projection 22b, and a ring 22c. Since the ignition plug connecting terminal 22 is the same as the ignition plug connecting terminal 12 in the former embodiment, detailed explanation thereof is omitted here. The high tension supply terminal socket 23 is made in a form of a disc-like conductive metal plate such as a stainless disc plate and has the same external diameter as that of the projection 22b of the terminal 22. The plug cap 24 is substantially the same as the plug cap 14 in the former embodiment. The projection 22b of the ignition plug connecting terminal and a peripheral part of the high tension supply terminal socket 23 are embedded in the inner wall of the plug cap 24 and the ignition plug connecting terminal 22 and the socket 23 are fixed in the cap 14. The above connecting assembly 20 is produced by the substantially same routine as that shown in FIG. 2. However, the steps S4 through S6 are not necessary and the step S8 is not necessary for the high tension supply terminal socket 23. In the step S10 in this embodiment, the high tension supply terminal 21 is connected through a terminal Ea of the discharge tube E to the high tension cable C. The high tension supply terminal 21 is contacted with the high tension supply terminal socket 23 by pushing the terminal 21 as a spring onto the socket as a plate. Although the terminal bodies 12a and 22a and the projections 12b and 22b of the ignition plug connecting terminals 12 and 22 or the socket bodies 13a and the projections 13b of the high tension supply terminal socket 13 are formed by drawing the disc-like stainless plate in the above embodiment, a cylindrical body 31A (FIG. 10B) with a flange-like projection which is formed by outwardly extending an end of a cylindrical terminal member 31 (FIG. 10A) may be used for the terminal bodies 12a and 22a or the socket body 13a. In the connecting assembly for the ignition plug in the gasoline engine shown in FIG. 1 or 9, the terminal body 12a and projection 12b of the ignition plug connecting terminal 12 or the terminal body 22a and projection 22b for the ignition plug connecting terminal 22 are formed by drawing the conductive metal plate such as a stainless plate. This makes the ignition plug connecting terminal light and ultimately makes the connecting assembly per se light. Since the conductive metal plate is suitable for drawing of the ignition plug connecting terminal, it is easy to mass-produce the terminals and to reduce wastage of materials in working processes. Although the terminal bodies 12a and 22a or the socket body 13a are made in a cylindrical form in the above embodiments, they may be made in a polygonal form. Also, another electrical element except for the discharge tube may be disposed between the high tension supply terminal and the high tension cable. According to the present invention, it is possible to reduce wear of the head of the ignition plug, since the movement of the ignition plug connecting terminal with respect to the ignition piug is limited by an integral construction of the terminal and the plug cap. In addition, since the ignition plug connecting terminal is formed by the drawing work, the terminal has no clearance such as a slit or a seam on the outer periphery, thereby preventing the molten resin material from flowing into the terminal when the plug cap is formed so that the projection of the terminal is embedded in the plug cap. Accordingly, it is possible to eliminate a problem that the ignition plug connecting terminal cannot be coupled to the ignition plug on account of the resin material flown into the terminal.

Claims: A connecting assembly (10) for an ignition plug (P) for a gasoline engine wherein a high tension cable (C) is connected to said ignition plug (P), said assembly (10) comprising: a high tension supply terminal (11) electrically connected to said cable (C); an ignition plug connecting terminal (12) having a terminal flange (12b) at a first end and being adapted to receive a distal end of said ignition plug (P) at a second end; a high tension supply terminal socket (13) between said connecting terminal (12) and said supply terminal (11), said socket (13) having a socket flange (13b) at a first end and being adapted to receive a distal end of said supply terminal (11) at a second end, said terminal flange (12b) and said socket flange (13b) being in electrical contact with each other; and a substantially cylindrical, non-conducting plug cap (14) adapted to receive said connecting terminal (12) and said socket (13) with said flanges (12b, 13b) embedded therein, characterised in that the connecting terminal (12) and the terminal socket (13) both comprise deep-drawn sheets of thin metal plate, and retainer rings (12c, 13c) at least partially encircling each of said connecting terminal (12) and said socket (13) have two retaining protuberances (12ca, 13ca) on an inner surface thereof, two through holes (12aa, 13aa) being provided in each of said connecting terminal (12) and said socket (13) complementary to said retaining protuberances (12ca, 13ca), whereby said retaining protuberances (12ca, 13ca) project radially inwardly of said inner surfaces so that, when said distal ends of said plug (P) and supply terminal (11) are introduced into said connecting terminal (12) and said socket (13) respectively, said rings (12c, 13c) are urged resiliently and radially outwardly, thereby retaining said distal ends in said connector terminal (12) and socket (13).

Inventors: KOBAYASHI YOSHINAO, KOBAYASHI, YOSHINAO, Kobayashi, Yoshinao, c/o Sumitomo Wiring S. Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1993
Main classification: H01T13
IPC codes: H01T13, F02B1