Construction for retaining coiled spring of high-voltage terminal in engine ignition system
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a high-voltage terminal in an engine ignition system, which is directly connected with a spark plug or an ignition coil of an engine and more particularly, to a construction for retaining a coiled spring inserted into the high-voltage terminal. 
     FIG. 1 shows a known ignition system disclosed in Japanese Patent Laid-Open Publication No. 3-47475 (1991). In FIG. 1, a high-voltage terminal 2 is embedded in a high-voltage tower 1 and an electrically conductive coiled spring 5 for electrically connecting the high-voltage terminal 2 and a head terminal 4 of a spark plug 3 is inserted into a hollow of the high-voltage terminal 2. An insertion end 5a of the coiled spring 5 should be fixed to the high-voltage terminal 2 so as to prevent dropping by gravity of the coiled spring 5. To this end, an annular groove 2a is formed on a side wall of the hollow of the high-voltage terminal 2 and an outside diameter d1 of the insertion end 5a of the coiled spring 5 is so set as to be larger than an outside diameter d2 of the coiled spring 5, i.e. d1&gt;d2 as shown in detail in FIG. 2. Thus, while the insertion end 5a is being radially compressed by rotating the coiled spring 5 in its winding direction, the coiled spring 5 is inserted into the hollow of the high-voltage terminal 2 such that the insertion end 5a is brought into engagement with the groove 2a. 
     However, the known engine ignition system has such a drawback that since it is difficult to insert the large-diameter insertion end 5a of the coiled spring 5 into the hollow of the high-voltage terminal 2, efficiency for inserting the coiled spring 5 into the hollow of the high-voltage terminal 2 is poor. Furthermore, the known engine ignition system is disadvantageous in that since the force of engagement of the coiled spring 5 with the groove 2a, namely, the force for fixing the coiled spring 5 to the groove 2a of the high-voltage terminal 2 is small, the coiled spring 5 is readily disengaged from the groove 2a when pulled outwardly. 
     SUMMARY OF THE INVENTION 
     Accordingly, an essential object of the present invention is to provide a construction for retaining a coiled spring of a high-voltage terminal in an engine ignition system, in which the coiled spring can be easily inserted into a hollow of the high-voltage terminal so as to be brought into engagement with the high-voltage terminal and the coiled spring can be fixedly retained in the hollow of the high-voltage terminal so as not to be disengaged from the hollow of the high-voltage terminal. 
     In order to accomplish this object of the present invention, a construction for retaining an electrically conductive coiled spring which is inserted into a hollow of a high-voltage terminal subjected to a high voltage in an engine ignition system so as to electrically connect a head terminal of a spark plug or an ignition coil and the high-voltage terminal, according to the present invention comprises: a first stopper which is formed on a side wall of the hollow of the high-voltage terminal so as to project into the hollow and is brought into contact with an insertion end of the coiled spring so as to retain the insertion end of the coiled spring; the high-voltage terminal being formed, at locations between the first stopper and a mouth of the hollow on the side wall, with a slit and a hole; and a second stopper which radially fits around an outer surface of the side wall of the high-voltage terminal and is formed with a tongue piece and a projection; wherein the tongue piece is inserted between neighboring coil windings of the coiled spring in the hollow from the slit, while the projection is brought into engagement with the hole so as to be inserted between further neighboring coil windings of the coiled spring in the hollow. 
     In the construction for retaining the coiled spring, according to the present invention, when the insertion end of the coiled spring is inserted into the hollow of the high-voltage terminal, the insertion end of the coiled spring is brought into contact with the first stopper so as to be retained by the first stopper. During this insertion of the coiled spring into the hollow, since it is not necessary to radially compress the insertion end by rotating the coiled spring in its winding direction, the coiled spring can be inserted into the hollow smoothly. 
     Subsequently, when the second stopper fits around the outer surface of the side wall of the hollow of the high-voltage terminal so as to fit the tongue piece of the second stopper into the hollow from the slit of the high-voltage terminal, the tongue piece is inserted between neighboring coil windings of the coiled spring so as to retain the coiled spring. Therefore, even if the coiled spring is pulled outwardly from the high-voltage terminal, the coiled spring is securely retained by the tongue piece so as not to be disengaged from the hollow. 
     Meanwhile, the projection of the second stopper is brought into engagement with the holes of the high-voltage terminal so as to positively fix the second stopper to the high-voltage terminal and is inserted between neighboring coil windings of the coiled spring in the hollow. Therefore, even in the case where the coiled spring is not retained by the tongue piece for some reason or other, the coiled spring is retained by the projection so as not to be disengaged from the hollow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This object and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is a partially sectional side elevational view of a prior art engine ignition system (already referred to); 
     FIG. 2 is a fragmentary sectional view of the prior art engine ignition system of FIG. 1 (already referred to); 
     FIG. 3 is a side elevational view of an engine ignition system according to the present invention; 
     FIG. 4 is an enlarged fragmentary view of the engine ignition system of FIG. 3; 
     FIG. 5 is a sectional view taken along the line V--V in FIG. 4; 
     FIG. 6 is a sectional view of a high-voltage terminal employed in the engine ignition system of FIG. 3; 
     FIG. 7 is a side elevational view of a second stopper employed in the engine ignition system of FIG. 3; and 
     FIG. 8 is a top plan view of the second stopper of FIG. 7. 
     Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, there is shown in FIG. 3, an engine ignition system K according to one embodiment of the present invention. A cylindrical high-voltage terminal 11 made of electrically conductive material is inserted into a high-voltage tower 10 made of insulating resin. A hole 10a for receiving a head terminal 12a of a spark plug 12 is formed at a lower portion of the high-voltage tower 10. 
     As shown in FIGS. 4 to 6, the high-voltage terminal 11 has a circular hollow 11a into which a coiled spring 13 for electrically connecting the head terminal 12a of the spark plug 12 and the high-voltage terminal 11 is inserted. At an axial location spaced an identical distance from a mouth 11c of the hollow 11a, at least two first stoppers 11d are formed on a side wall 11b of the hollow 11a so as to radially project into the hollow 11a. 
     Meanwhile, at an axial location disposed between the mouth 11c and the first stoppers 11d, two circular holes 11e are formed on the side wall 11b of the hollow 11a. Furthermore, at an axial location disposed between the first stoppers 11d and the holes 11e, a slit 11f is formed on the side wall 11b of the hollow 11a. 
     As shown in FIG. 5, the holes 11e are circumferentially spaced an angle θ (≧180°) from each other about an axis a of the hollow 11a, while the slit 11f is disposed at a circumferentially central position of the angle θ. 
     On the other hand, as shown in FIGS. 7 and 8, the engine ignition system K further includes a substantially annular second stopper 14 made of elastic material. The second stopper 14 is radially fitted around an outer surface of the side wall 11b of the hollow 11a. Two radially inwardly extending projections 14a are formed on the second stopper 14 so as to be, respectively, brought into engagement with the holes 11e of the side wall 11b of the hollow 11a. The projections 14a have such a height as to radially inwardly extend into the hollow 11a when the projections 14a have been brought into engagement with the holes 11e, respectively. 
     Meanwhile, a rectangular tongue piece 14b is formed on the second stopper 14 so as to be inserted deeply into the hollow 11a from the slit 11f of the side wall 11b. 
     By the above described arrangement of the high-voltage terminal 11, the coiled spring 13 is inserted into the high-voltage terminal 11 so as to be fixed to the high-voltage terminal 11 as follows. When an insertion end 13a of the coiled spring 13 is inserted into the hollow 11a of the high-voltage terminal 11 from the mouth 11c, the insertion end 13a is brought into contact with the first stoppers 11d so as to be retained by the first stoppers 11d. During this insertion of the coiled spring 13 into the hollow 11a of the high-voltage terminal 11, since the second stopper 14 is not attached to the high-voltage terminal 11, the coiled spring 13 can be smoothly inserted into the hollow 11a of the high-voltage terminal 11. Meanwhile, in contrast with conventional high-voltage terminals, it is not necessary to radially compress the insertion end 13a by rotating the coiled spring 13 in its winding direction. 
     In this state, by depressing opposite circumferential ends of the second stopper 14 radially outwardly, the second stopper 14 is fitted around the outer surface of the side wall 11b of the hollow 11a of the high-voltage terminal 11 symmetrically with respect to the axis a of the hollow 11a. Thus, the tongue piece 14b of the second stopper 14 is fitted into the hollow 11a from the slit 11f of the side wall 11b of the hollow 11a and is inserted between neighboring coil windings of a pitch t (FIG. 6) of the coiled spring 13 in the hollow 11a so as to retain the coiled spring 13. As a result, the coiled spring 13 is securely retained by the tongue piece 14b. Therefore, even if the coiled spring 13 is pulled outwardly from the high-voltage terminal 11, the coiled spring 13 is not disengaged from the hollow 11a of the high-voltage terminal 11. 
     Meanwhile, the projections 14a of the second stopper 14 are, respectively, brought into engagement with the holes 11e of the side wall 11b of the high-voltage terminal 11 so as to elastically secure the second stopper 14 to the high-voltage terminal 11 positively. At the same time, the projections 14a project from the side wall 11b into the hollow 11a so as to be inserted between neighboring coil windings of the coiled spring 13 at a location disposed below the tongue piece 14b through one or two coil windings of the coiled spring 13. Accordingly, even in case the coiled spring 13 is not retained by the tongue piece 14b for some reason or other, the coiled spring 13 is retained in the hollow 11a by the projections 14a so as not to be disengaged from the hollow 11a. 
     As is clear from the foregoing description of the construction for retaining the coiled spring of the high-voltage terminal of the present invention, since there is no obstacle in the hollow of the high-voltage terminal at the time of insertion of the coiled spring into the hollow, the coiled spring can be inserted into the hollow quite smoothly. 
     Meanwhile, when the second stopper has been fitted around the outer surface of the side wall of the high-voltage terminal, the tongue piece is inserted between neighboring coil windings of the coiled spring in the hollow from the slit of the high-voltage terminal so as to retain the coiled spring. Therefore, even if the coiled spring is pulled outwardly from the high-voltage terminal, the coiled spring is securely retained in the hollow by the tongue piece so as not to be disengaged from the hollow. 
     Furthermore, the projections of the second stopper are brought into engagement with the holes of the high-voltage terminal so as to positively fix the second stopper to the high-voltage terminal and are inserted between neighboring coil windings of the coiled spring in the hollow of the high-voltage terminal. Therefore, even if the coiled spring is not retained by the tongue piece for some reason or other, the coiled spring is securely retained in the hollow by the projections so as not be disengaged from the hollow of the high-voltage terminal.